Effects of water-alcohol binary solvents on the thermochemical characteristics of L-tryptophane dissolution at 298.15 K

NASA Astrophysics Data System (ADS)

Badelin, V. G.; Smirnov, V. I.

2013-01-01

The enthalpies of L-tryptophane solution in water-methanol, water-ethanol, water-1-propanol, and water-2-propanol mixtures at alcohol concentrations of x 2 = 0-0.4 mole fractions were measured by calorimetry. The standard enthalpies of L-tryptophane solution (Δsol H ∘) and transfer (Δtr H ∘) from water to the binary solvent were calculated. The influence of the composition of the water-alcohol mixture and the structure and properties of L-tryptophane on the enthalpy characteristics of the latter was considered. The enthalpy coefficients of pair interactions ( h xy ) of L-tryptophane with alcohol molecules were calculated. The coefficients were positive and increased in the series: methanol (MeOH), ethanol (EtOH), 1-propanol (1-PrOH), and 2-propanol (2-PrOH). The solution and transfer enthalpies of L-tryptophane were compared with those of aliphatic amino acids (glycine, L-threonine, DL-alanine, L-valine, and L-phenylalanine) in similar binary solvents.

Thermodynamic Parameters of the Dissolution of 4-Hydroxy-L-Proline and L-Phenylalanine in Mixed Aqueous Solvents at 298 K

NASA Astrophysics Data System (ADS)

Smirnov, V. I.; Badelin, V. G.

2018-01-01

The enthalpies of solution of 4-hydroxy-L-proline and L-phenylalanine in binary mixed aqueous solvents containing acetonitrile (AN), 1,4-dioxane (1,4-DO), or acetone (AC) at mole fractions of 0 to 0.25 are determined at T = 298.15 K via isothermal calorimetry. The standard enthalpies of solution (Δsol H°) and transfer (Δtr H°) of 4-hydroxy-L-proline and L-phenylalanine from water to mixed aqueous solvents are calculated using the experimental calorimetric data, as are the enthalpy coefficients of paired interactions ( h xy ) between the molecules of the investigated amino acids and the organic solvents. The effects the mixed aqueous solvent composition and the structure of the organic solvent molecules have on the enthalpies of solution and transfer for the investigated amino acids are considered. The correlation between the enthalpy of solution of the amino acids and the electron-donating properties of the organic solvents in the mixed aqueous solvent systems is established.

A New Method to Determine the Half-Life for Penicillin Using Microcalorimeter

NASA Astrophysics Data System (ADS)

Li, Z. X.; Zhao, W. W.

2015-01-01

The dissolution process of penicillin in normal saline and isotonic glucose solution was reported using a microcalorimeter. Both the integral and differential heats of solution were measured. The quantitative relationships between the amount of heat released and the quantity of dissolved penicillin were established. Meanwhile, the kinetics and the half-life of the dissolution processes as well as the enthalpy of solution, the entropy of dissolution, and the free energy of dissolution were determined. The results showed that a change of the solvent from normal saline to isotonic glucose solution had little effect on the half-life of penicillin in the dissolution process, and there was no significant difference between the stabilities of penicillin in isotonic glucose solution and normal saline. Moreover, the dissolution process of penicillin in isotonic glucose solution followed the first-order kinetics. These results could provide a theoretical basis for the clinical applications of penicillin.

Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds and Ionic Liquids. Sublimation, Vaporization, and Fusion Enthalpies from 1880 to 2015. Part 2. C11-C192

NASA Astrophysics Data System (ADS)

Acree, William; Chickos, James S.

2017-03-01

The second part of this compendium concludes with a collection of phase change enthalpies of organic molecules inclusive of C11-C192 reported over the period 1880-2015. Also included are phase change enthalpies including fusion, vaporization, and sublimation enthalpies for organometallic, ionic liquids, and a few inorganic compounds. Paper I of this compendium, published separately, includes organic compounds from C1 to C10 and describes a group additivity method for evaluating solid, liquid, and gas phase heat capacities as well as temperature adjustments of phase changes. Paper II of this compendium also includes an updated version of a group additivity method for evaluating total phase change entropies which together with the fusion temperature can be useful in estimating total phase change enthalpies. Other uses include application in identifying potential substances that either form liquid or plastic crystals or exhibit additional phase changes such as undetected solid-solid transitions or behave anisotropically in the liquid state.

Solubility and dissolution thermodynamics of tetranitroglycoluril in organic solvents at 295-318 K

NASA Astrophysics Data System (ADS)

Zheng, Zhihua; Wang, Jianlong; Hu, Zhiyan; Du, Hongbin

2017-08-01

The solubility data of tetranitroglycoluril in acetone, methanol, ethanol, ethyl acetate, nitromethane and chloroform at temperatures ranging from 295-318 K were measured by gravimetric method. The solubility data of tetranitroglycoluril were fitted with Apelblat semiempirical equation. The dissolution enthalpy, entropy and Gibbs energy of tetranitroglycoluril were calculated using the Van't Hoff and Gibbs equations. The results showed that the Apelblat semiempirical equation was significantly correlated with solubility data. The dissolving process was endothermic, entropy-driven, and nonspontaneous.

Hydrogen dissolution in palladium: A resistometric study under pressure

NASA Astrophysics Data System (ADS)

Magnouche, A.; Fromageau, R.

1984-09-01

The hydrogen solubility in palladium in equilibrium with H2 gas has been measured, between room temperature and 540 °C, using a resistometric method, for pressures ranging between 0.01 and 10 MPa. In these conditions, the experimentally determined values of the solubility and of the dissolution enthalpy exhibit very close agreement with those obtained by other methods (calorimetry, volumetry, etc.), or after electrolytic charging. This good agreement demonstrates the validity of the resistometric method for determination of the solubility of hydrogen in metals.

Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2015. Part 1. C1 - C10

NASA Astrophysics Data System (ADS)

Acree, William; Chickos, James S.

2016-09-01

A compendium of phase change enthalpies published in 2010 is updated to include the period 1880-2015. Phase change enthalpies including fusion, vaporization, and sublimation enthalpies are included for organic, organometallic, and a few inorganic compounds. Part 1 of this compendium includes organic compounds from C1 to C10. Part 2 of this compendium, to be published separately, will include organic and organometallic compounds from C11 to C192. Sufficient data are presently available to permit thermodynamic cycles to be constructed as an independent means of evaluating the reliability of the data. Temperature adjustments of phase change enthalpies from the temperature of measurement to the standard reference temperature, T = 298.15 K, and a protocol for doing so are briefly discussed.

The Intramolecular Hydrogen Bond N-H···S in 2,2'-Diaminodiphenyl Disulfide: Experimental and Computational Thermochemistry.

PubMed

Ramos, Fernando; Flores, Henoc; Hernández-Pérez, Julio M; Sandoval-Lira, Jacinto; Camarillo, E Adriana

2018-01-11

The intramolecular hydrogen bond of the N-H···S type has been investigated sparingly by thermochemical and computational methods. In order to study this interaction, the standard molar enthalpies of formation in gaseous phase of diphenyl disulfide, 2,2'-diaminodiphenyl disulfide and 4,4'-diaminodiphenyl disulfide at T = 298.15 K were determined by experimental thermochemical methods and computational calculations. The experimental enthalpies of formation in gas-phase were obtained from enthalpies of formation in crystalline phase and enthalpies of sublimation. Enthalpies of formation in crystalline phase were obtained using rotatory bomb combustion calorimetry. By thermogravimetry, enthalpies of vaporization were obtained, and by combining them with enthalpies of fusion, the enthalpies of sublimation were calculated. The Gaussian-4 procedure and the atomization method were applied to obtain enthalpies of formation in gas-phase of the compounds under study. Theoretical and experimental values are in good agreement. Through natural bond orbital (NBO) analysis and a topological analysis of the electronic density, the intramolecular hydrogen bridge (N-H···S) in the 2,2'-diaminodiphenyl disulfide was confirmed. Finally, an enthalpic difference of 11.8 kJ·mol -1 between the 2,2'-diaminodiphenyl disulfide and 4,4'-diaminodiphenyl disulfide was found, which is attributed to the intramolecular N-H···S interaction.

Solubility of alkali metal halides in the ionic liquid [C4C1im][OTf].

PubMed

Kuzmina, O; Bordes, E; Schmauck, J; Hunt, P A; Hallett, J P; Welton, T

2016-06-28

The solubilities of the metal halides LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbCl, CsCl, CsI, were measured at temperatures ranging from 298.15 to 378.15 K in the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4C1im][OTf]). Li(+), Na(+) and K(+) salts with anions matching the ionic liquid have also been investigated to determine how well these cations dissolve in [C4C1im][OTf]. This study compares the influence of metal cation and halide anion on the solubility of salts within this ionic liquid. The highest solubility found was for iodide salts, and the lowest solubility for the three fluoride salts. There is no outstanding difference in the solubility of salts with matching anions in comparison to halide salts. The experimental data were correlated employing several phase equilibria models, including ideal mixtures, van't Hoff, the λh (Buchowski) equation, the modified Apelblat equation, and the non-random two-liquid model (NRTL). It was found that the van't Hoff model gave the best correlation results. On the basis of the experimental data the thermodynamic dissolution parameters (ΔH, ΔS, and ΔG) were determined for the studied systems together with computed gas phase metathesis parameters. Dissolution depends on the energy difference between enthalpies of fusion and dissolution of the solute salt. This demonstrates that overcoming the lattice energy of the solid matrix is the key to the solubility of inorganic salts in ionic liquids.

Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2015. Part 1. C{sub 1} − C{sub 10}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Acree, William; Chickos, James S.

2016-09-15

A compendium of phase change enthalpies published in 2010 is updated to include the period 1880–2015. Phase change enthalpies including fusion, vaporization, and sublimation enthalpies are included for organic, organometallic, and a few inorganic compounds. Part 1 of this compendium includes organic compounds from C{sub 1} to C{sub 10}. Part 2 of this compendium, to be published separately, will include organic and organometallic compounds from C{sub 11} to C{sub 192}. Sufficient data are presently available to permit thermodynamic cycles to be constructed as an independent means of evaluating the reliability of the data. Temperature adjustments of phase change enthalpies frommore » the temperature of measurement to the standard reference temperature, T = 298.15 K, and a protocol for doing so are briefly discussed.« less

The thermochemistry of 2,4-pentanedione revisited: observance of a nonzero enthalpy of mixing between tautomers and its effects on enthalpies of formation.

PubMed

Temprado, Manuel; Roux, Maria Victoria; Umnahanant, Patamaporn; Zhao, Hui; Chickos, James S

2005-06-30

The enthalpies of formation of pure liquid and gas-phase (Z)-4-hydroxy-3-penten-2-one and 2,4-pentanedione are examined in the light of some more recent NMR studies on the enthalpy differences between gas-phase enthalpies of the two tautomers. Correlation gas chromatography experiments are used to evaluate the vaporization enthalpies of the pure tautomers. Values of (51.2 +/- 2.2) and (50.8 +/- 0.6) kJ.mol(-1) are measured for pure 2,4-pentanedione and (Z)-4-hydroxy-3-penten-2-one, respectively. The value of (50.8 +/- 0.6) kJ.mol(-1) can be contrasted to a value of (43.2 +/- 0.2) kJ.mol(-1) calculated for pure (Z)-4-hydroxy-3-penten-2-one when the vaporization enthalpy is measured in a mixture of tautomers. The difference is attributed to an endothermic enthalpy of mixing that destabilizes the mixture relative to the pure components. Calculation of new enthalpies of formation for (Z)-4-hydroxy-3-penten-2-one and 2,4-pentanedione in both the gas, Delta(f)H degrees (m)(g) = (-378.2 +/- 1.2) and (-358.9 +/- 2.5) kJ.mol(-1), respectively, and liquid phases, Delta(f)H degrees (m)(l) = (-429.0 +/- 1.0) and (-410.1 +/- 1.2) kJ.mol(-1), respectively, results in enthalpy differences between the two tautomers both in the liquid and gas phases that are identical within experimental error, and in excellent agreement with recent gas-phase NMR studies.

Experimental formation enthalpies for intermetallic phases and other inorganic compounds

PubMed Central

Kim, George; Meschel, S. V.; Nash, Philip; Chen, Wei

2017-01-01

The standard enthalpy of formation of a compound is the energy associated with the reaction to form the compound from its component elements. The standard enthalpy of formation is a fundamental thermodynamic property that determines its phase stability, which can be coupled with other thermodynamic data to calculate phase diagrams. Calorimetry provides the only direct method by which the standard enthalpy of formation is experimentally measured. However, the measurement is often a time and energy intensive process. We present a dataset of enthalpies of formation measured by high-temperature calorimetry. The phases measured in this dataset include intermetallic compounds with transition metal and rare-earth elements, metal borides, metal carbides, and metallic silicides. These measurements were collected from over 50 years of calorimetric experiments. The dataset contains 1,276 entries on experimental enthalpy of formation values and structural information. Most of the entries are for binary compounds but ternary and quaternary compounds are being added as they become available. The dataset also contains predictions of enthalpy of formation from first-principles calculations for comparison. PMID:29064466

Radon and ammonia transects across the Cerro Prieto geothermal field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Semprini, L.; Kruger, P.

1981-01-01

Radon and ammonia transects, conducted at the Cerro Prieto geothermal field, involve measurement of concentration gradients at wells along lines of structural significance in the reservoir. Analysis of four transects showed radon concentrations ranging from 0.20 to 3.60 nCi/kg and ammonia concentrations from 17.6 to 59.3 mg/l. The data showed the lower concentrations in wells of lowest enthalpy fluid and the higher concentrations in wells of highest enthalpy fluid. Linear correlation analysis of the radon-enthalpy data indicated a strong relationship, with a marked influence by the two-phase conditions of the produced fluid. It appears that after phase separation in themore » reservoir, radon achieves radioactive equilibrium between fluid and rock, suggesting that the phase separation occurs well within the reservoir. A two-phase mixing model based on radon-enthalpy relations allows estimation of the fluid phase temperatures in the reservoir. Correlations of ammonia concentration with fluid enthalpy suggests an equilibrium partitioning model in which enrichment of ammonia correlates with higher enthalpy vapor.« less

Effect of the composition of a solution on the enthalpies of solvation of piperidine in methanol-acetonitrile and dimethylsulfoxide-acetonitrile mixed solvents

NASA Astrophysics Data System (ADS)

Kuz'mina, I. A.; Volkova, M. A.; Sitnikova, K. A.; Sharnin, V. A.

2014-01-01

Heat effects of dissolution of piperidine (ppd) are measured by calorimetry at 298.15 K over the range of composition of acetonitrile-methanol (AN-MeOH) mixed solvents. Based on the Δsol H ○(ppd)AN-MeOH values obtained using the literature data on Δsol H ○ (ppd) in acetonitrile-dimethylsulfoxide (AN-DMSO) mixed solvents and the vaporization enthalpy of ppd, the enthalpies of solvation of amine in AN-MeOH and AN-DMSO binary mixtures are calculated. A rise in the exothermicity of solvation of piperidine is observed upon the transition from AN to DMSO and MeOH, due mainly to the enhanced solvation of the amino group of ppd as a result of changes in the acid-base properties of the mixed solvent.

Surface properties, solubility and dissolution kinetics of bamboo phytoliths

NASA Astrophysics Data System (ADS)

Fraysse, Fabrice; Pokrovsky, Oleg S.; Schott, Jacques; Meunier, Jean-Dominique

2006-04-01

Although phytoliths, constituted mainly by micrometric opal, exhibit an important control on silicon cycle in superficial continental environments, their thermodynamic properties and reactivity in aqueous solution are still poorly known. In this work, we determined the solubility and dissolution rates of bamboo phytoliths collected in the Réunion Island and characterized their surface properties via electrophoretic measurements and potentiometric titrations in a wide range of pH. The solubility product of "soil" phytoliths ( pKsp0=2.74 at 25 °C) is equal to that of vitreous silica and is 17 times higher than that of quartz. Similarly, the enthalpy of phytoliths dissolution reaction (ΔHr25-80°C=10.85kJ/mol) is close to that of amorphous silica but is significantly lower than the enthalpy of quartz dissolution. Electrophoretic measurements yield isoelectric point pH IEP = 1.2 ± 0.1 and 2.5 ± 0.2 for "soil" (native) and "heated" (450 °C heating to remove organic matter) phytoliths, respectively. Surface acid-base titrations allowed generation of a 2-p K surface complexation model. Phytoliths dissolution rates, measured in mixed-flow reactors at far from equilibrium conditions at 2 ⩽ pH ⩽ 12, were found to be intermediate between those of quartz and vitreous silica. The dissolution rate dependence on pH was modeled within the concept of surface coordination theory using the equation: R=k1·{>SiOH2+}n+k2·{>SiOH0}+k3·{>SiO-}m, where {> i} stands for the concentration of the surface species present at the SiO 2-H 2O interface, ki are the rate constants of the three parallel reactions and n and m represent the order of the proton- and hydroxy-promoted reactions, respectively. It follows from the results of this study that phytoliths dissolution rates exhibit a minimum at pH ˜ 3. This can explain their good preservation in the acidic soil horizons of Réunion Island. In terms of silicon biogeochemical cycle, phytoliths represent a large buffering reservoir, which can play an important role in the regulation of silica fluxes in terrestrial aquatic environments.

Calorimetric Investigation of Thermal Stability of 304H Cu (Fe-17.7Cr-9.3Ni-2.95Cu-0.91Mn-0.58Nb-0.24Si-0.1C-0.12N-Wt Pct) Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Tripathy, Haraprasanna; Subramanian, Raju; Hajra, Raj Narayan; Rai, Arun Kumar; Rengachari, Mythili; Saibaba, Saroja; Jayakumar, Tammana

2016-12-01

The sequence of phase instabilities that take place in a Fe-17.7Cr-9.3Ni-0.58Nb-2.95Cu-0.12N (wt pct) austenitic stainless steel (304H Cu grade) as a function of temperature has been investigated using dynamic calorimetry. The results obtained from this investigation are supplemented by Thermocalc-based equilibrium and Scheil-Gulliver nonequilibrium solidification simulation. The following phase transformation sequence is found upon slow cooling from liquid: L → L + γ → L + γ + MX → γ + MX + δ → γ +MX + M23C6 → γ + MX + M23C6 + Cu. Under slow cooling, the solidification follows austenite + ferrite (AF) mode, which is in accordance with Thermocalc prediction and Scheil-Gulliver simulation. However, higher cooling rates result in skeletal δ-ferrite formation, due to increased segregation tendency of Nb and Cr to segregate to interdendritic liquid. The solidification mode is found to depend on combined Nb + Cu content. Experimental estimates of enthalpy change associated with melting and secondary phase precipitation are also obtained. In addition a semi-quantitative study on the dissolution kinetics of M23C6 type carbides has also been investigated. The standard solution treatment at 1413 K (1140 °C) is found to be adequate to dissolve both Cu and M23C6 into γ-austenite; but the complete dissolution of MX type carbonitrides occurs near the melting region.

An Examination of the Phase Transition Thermodynamics of (S)- and (RS)-Naproxen as a Basis for the Design of Enantioselective Crystallization Processes.

PubMed

Buchholz, Hannes; Emel'yanenko, Vladimir N; Lorenz, Heike; Verevkin, Sergey P

2016-05-01

A detailed experimental analysis of the phase transition thermodynamics of (S)-naproxen and (RS)-naproxen is reported. Vapor pressures were determined experimentally via the transpiration method. Sublimation enthalpies were obtained from the vapor pressures and from independent TGA measurements. Thermodynamics of fusion which have been well-studied in the literature were systematically remeasured by DSC. Both sublimation and fusion enthalpies were adjusted to one reference temperature, T = 298 K, using measured heat capacities of the solid and the melt phase by DSC. Average values from the measurements and from literature data were suggested for the sublimation and fusion enthalpies. In order to prove consistency of the proposed values the vaporization enthalpies obtained by combination of both were compared to vaporization enthalpies obtained by the group-additivity method and the correlation-gas chromatography method. The importance of reliable and precise phase transition data for thermochemical calculations such as the prediction of solid/liquid phase behaviour of chiral compounds is highlighted. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Enthalpy of Mixing in Al–Tb Liquid

DOE PAGES

Zhou, Shihuai; Tackes, Carl; Napolitano, Ralph

2017-06-21

The liquid-phase enthalpy of mixing for Al$-$Tb alloys is measured for 3, 5, 8, 10, and 20 at% Tb at selected temperatures in the range from 1364 to 1439 K. Methods include isothermal solution calorimetry and isoperibolic electromagnetic levitation drop calorimetry. Mixing enthalpy is determined relative to the unmixed pure (Al and Tb) components. The required formation enthalpy for the Al3Tb phase is computed from first-principles calculations. Finally, based on our measurements, three different semi-empirical solution models are offered for the excess free energy of the liquid, including regular, subregular, and associate model formulations. These models are also compared withmore » the Miedema model prediction of mixing enthalpy.« less

Experimental and computational investigation of the thermochemistry of the six isomers of dichloroaniline.

PubMed

Ribeiro da Silva, Manuel A V; Amaral, Luísa M P F; Gomes, José R B

2006-07-27

The standard (p(o) = 0.1 MPa) molar enthalpies of formation of 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-dichloroanilines were derived from the standard molar energies of combustion, in oxygen, to yield CO(2)(g), N(2)(g) and HCl.600H(2)O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The Calvet high-temperature vacuum sublimation technique was used to measure the enthalpies of sublimation of the six isomers. These two thermodynamic parameters yielded the standard molar enthalpies of formation of the six isomers of dichloroaniline, in the gaseous phase, at T = 298.15 K. The gas-phase enthalpies of formation were also estimated by G3MP2B3 calculations, which were further extended to the computation of gas-phase acidities, proton affinities, and ionization enthalpies.

Enthalpy of Formation of N 2 H 4 (Hydrazine) Revisited

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feller, David; Bross, David H.; Ruscic, Branko

2017-08-02

In order to address the accuracy of the long-standing experimental enthalpy of formation of gas-phase hydrazine, fully confirmed in earlier versions of Active Thermochemical Tables (ATcT), the provenance of that value is re-examined in light of new high-end calculations of the Feller-Peterson-Dixon (FPD) variety. An overly optimistic determination of the vaporization enthalpy of hydrazine, which created an unrealistically strong connection between the gas phase thermochemistry and the calorimetric results defining the thermochemistry of liquid hydrazine was identified as the probable culprit. The new enthalpy of formation of gas-phase hydrazine, based on balancing all available knowledge, was determined to be 111.57more » ± 0.47 kJ/mol at 0 K (97.41 kJ/mol at 298.15 K). Close agreement was found between the ATcT (even excluding the latest theoretical result) and FPD enthalpies.« less

Enthalpy of Formation of N2H4 (Hydrazine) Revisited.

PubMed

Feller, David; Bross, David H; Ruscic, Branko

2017-08-17

In order to address the accuracy of the long-standing experimental enthalpy of formation of gas-phase hydrazine, fully confirmed in earlier versions of Active Thermochemical Tables (ATcT), the provenance of that value is re-examined in light of new high-end calculations of the Feller-Peterson-Dixon (FPD) variety. An overly optimistic determination of the vaporization enthalpy of hydrazine, which created an unrealistically strong connection between the gas phase thermochemistry and the calorimetric results defining the thermochemistry of liquid hydrazine, was identified as the probable culprit. The new enthalpy of formation of gas-phase hydrazine, based on balancing all available knowledge, was determined to be 111.57 ± 0.47 kJ/mol at 0 K (97.42 ± 0.47 kJ/mol at 298.15 K). Close agreement was found between the ATcT (even excluding the latest theoretical result) and the FPD enthalpy.

Molecular simulation of excess isotherm and excess enthalpy change in gas-phase adsorption.

PubMed

Do, D D; Do, H D; Nicholson, D

2009-01-29

We present a new approach to calculating excess isotherm and differential enthalpy of adsorption on surfaces or in confined spaces by the Monte Carlo molecular simulation method. The approach is very general and, most importantly, is unambiguous in its application to any configuration of solid structure (crystalline, graphite layer or disordered porous glass), to any type of fluid (simple or complex molecule), and to any operating conditions (subcritical or supercritical). The behavior of the adsorbed phase is studied using the partial molar energy of the simulation box. However, to characterize adsorption for comparison with experimental data, the isotherm is best described by the excess amount, and the enthalpy of adsorption is defined as the change in the total enthalpy of the simulation box with the change in the excess amount, keeping the total number (gas + adsorbed phases) constant. The excess quantities (capacity and energy) require a choice of a reference gaseous phase, which is defined as the adsorptive gas phase occupying the accessible volume and having a density equal to the bulk gas density. The accessible volume is defined as the mean volume space accessible to the center of mass of the adsorbate under consideration. With this choice, the excess isotherm passes through a maximum but always remains positive. This is in stark contrast to the literature where helium void volume is used (which is always greater than the accessible volume) and the resulting excess can be negative. Our definition of enthalpy change is equivalent to the difference between the partial molar enthalpy of the gas phase and the partial molar enthalpy of the adsorbed phase. There is no need to assume ideal gas or negligible molar volume of the adsorbed phase as is traditionally done in the literature. We illustrate this new approach with adsorption of argon, nitrogen, and carbon dioxide under subcritical and supercritical conditions.

Predicting the enthalpies of melting and vaporization for pure components

NASA Astrophysics Data System (ADS)

Esina, Z. N.; Korchuganova, M. R.

2014-12-01

A mathematical model of the melting and vaporization enthalpies of organic components based on the theory of thermodynamic similarity is proposed. In this empirical model, the phase transition enthalpy for the homological series of n-alkanes, carboxylic acids, n-alcohols, glycols, and glycol ethers is presented as a function of the molecular mass, the number of carbon atoms in a molecule, and the normal transition temperature. The model also uses a critical or triple point temperature. It is shown that the results from predicting the melting and vaporization enthalpies enable the calculation of binary phase diagrams.

Enthalpic parameters of interaction between diglycylglycine and polyatomic alcohols in aqueous solutions

NASA Astrophysics Data System (ADS)

Mezhevoi, I. N.; Badelin, V. G.

2015-12-01

Integral enthalpies of solution Δsol H m of diglycylglycine in aqueous solutions of glycerol, ethylene glycol, and 1,2-propylene glycol are measured via solution calorimetry. The experimental data are used to calculate the standard enthalpies of solution (Δsol H°) and transfer (Δtr H°) of the tripeptide from water to aqueous solutions of polyatomic alcohols. The enthalpic pairwise coefficients h xy of interactions between the tripeptide and polyatomic alcohol molecules are calculated using the McMillan-Mayer solution theory and are found to have positive values. The findings are discussed using the theory of estimating various types of interactions in ternary systems and the effect the structural features of interacting biomolecules have on the thermochemical parameters of diglycylglycine dissolution.

Understanding cellulose dissolution: energetics of interactions of ionic liquids and cellobiose revealed by solution microcalorimetry.

PubMed

de Oliveira, Heitor Fernando Nunes; Rinaldi, Roberto

2015-05-11

In this report, the interactions between fifteen selected ionic liquids (ILs) and cellobiose (CB) are examined by high-precision solution microcalorimetry. The heat of mixing (Δmix H) of CB and ILs, or CB and IL/molecular solvent (MS) solutions, provides the first ever-published measure of the affinity of CB with ILs. Most importantly, we found that there is a very good correlation between the nature of the results found for Δmix H(CB) and the solubility behavior of cellulose. This correlation suggests that Δmix H(CB) offers a good estimate of the enthalpy of dissolution of cellulose even in solvents in which cellulose is insoluble. Therefore, the current findings open up new horizons for unravelling the intricacies of the thermodynamic factors accounting for the spontaneity of cellulose dissolution in ILs or IL/MS solutions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermodynamics of R-(+)-2-(4-Hydroxyphenoxy)propanoic Acid Dissolution in Methanol, Ethanol, and Methanol-Ethanol Mixture

NASA Astrophysics Data System (ADS)

Liu, Wei; Ma, Jinju; Yao, Xinding; Fang, Ruina; Cheng, Liang

2018-05-01

The solubilities of R-(+)-2-(4-hydroxyphenoxy)propanoic acid (D-HPPA) in methanol, ethanol and various methanol-ethanol mixtures are determined in the temperature range from 273.15 to 323.15 K at atmospheric pressure using a laser detecting system. The solubilities of D-HPPA increase with increasing mole fraction of ethanol in the methanol-ethanol mixtures. Experimental data were correlated with Buchowski-Ksiazczak λ h equation and modified Apelblat equation; the first one gives better approximation for the experimental results. The enthalpy, entropy and Gibbs free energy of D-HPPA dissolution in methanol, ethanol and methanol-ethanol mixtures were also calculated from the solubility data.

Solubility and dissolution thermodynamics of phthalic anhydride in organic solvents at 283-313 K

NASA Astrophysics Data System (ADS)

Wang, Long; Zhang, Fang; Gao, Xiaoqiang; Luo, Tingliang; Xu, Li; Liu, Guoji

2017-08-01

The solubility of phthalic anhydride was measured at 283-313 K under atmospheric pressure in ethyl acetate, n-propyl acetate, methyl acetate, acetone, 1,4-dioxane, n-hexane, n-butyl acetate, cyclohexane, and dichloromethane. The solubility of phthalic anhydride in all solvents increased with the increasing temperature. The Van't Hoff equation, modified Apelblat equation, λ h equation, and Wilson model were used to correlate the experimental solubility data. The standard dissolution enthalpy, the standard entropy, and the standard Gibbs energy were evaluated based on the Van't Hoff analysis. The experimental data and model parameters would be useful for optimizing of the separation processes involving phthalic anhydride.

Hydration of dimethyldodecylamine-N-oxide: enthalpy and entropy driven processes.

PubMed

Kocherbitov, Vitaly; Söderman, Olle

2006-07-13

Dimethyldodecylamine-N-oxide (DDAO) has only one polar atom that is able to interact with water. Still, this surfactant shows very hydrophilic properties: in mixtures with water, it forms normal liquid crystalline phases and micelles. Moreover, there is data in the literature indicating that the hydration of this surfactant is driven by enthalpy while other studies show that hydration of surfactants and lipids typically is driven by entropy. Sorption calorimetry allows resolving enthalpic and entropic contributions to the free energy of hydration at constant temperature and thus directly determines the driving forces of hydration. The results of the present sorption calorimetric study show that the hydration of liquid crystalline phases of DDAO is driven by entropy, except for the hydration of the liquid crystalline lamellar phase which is co-driven by enthalpy. The exothermic heat effect of the hydration of the lamellar phase arises from formation of strong hydrogen bonds between DDAO and water. Another issue is the driving forces of the phase transitions caused by the hydration. The sorption calorimetric results show that the transitions from the lamellar to cubic and from the cubic to the hexagonal phase are driven by enthalpy. Transitions from solid phases to the liquid crystalline lamellar phase are entropically driven, while the formation of the monohydrate from the dry surfactant is driven by enthalpy. The driving forces of the transition from the hexagonal phase to the isotropic solution are close to zero. These sorption calorimetric results are in good agreement with the analysis of the binary phase diagram based on the van der Waals differential equation. The phase diagram of the DDAO-water system determined using DSC and sorption calorimetry is presented.

Dissolution and Precipitation Behaviour during Continuous Heating of Al–Mg–Si Alloys in a Wide Range of Heating Rates

PubMed Central

Osten, Julia; Milkereit, Benjamin; Schick, Christoph; Kessler, Olaf

2015-01-01

In the present study, the dissolution and precipitation behaviour of four different aluminium alloys (EN AW-6005A, EN AW-6082, EN AW-6016, and EN AW-6181) in four different initial heat treatment conditions (T4, T6, overaged, and soft annealed) was investigated during heating in a wide dynamic range. Differential scanning calorimetry (DSC) was used to record heating curves between 20 and 600 °C. Heating rates were studied from 0.01 K/s to 5 K/s. We paid particular attention to control baseline stability, generating flat baselines and allowing accurate quantitative evaluation of the resulting DSC curves. As the heating rate increases, the individual dissolution and precipitation reactions shift to higher temperatures. The reactions during heating are significantly superimposed and partially run simultaneously. In addition, precipitation and dissolution reactions are increasingly suppressed as the heating rate increases, whereby exothermic precipitation reactions are suppressed earlier than endothermic dissolution reactions. Integrating the heating curves allowed the enthalpy levels of the different initial microstructural conditions to be quantified. Referring to time–temperature–austenitisation diagrams for steels, continuous heating dissolution diagrams for aluminium alloys were constructed to summarise the results in graphical form. These diagrams may support process optimisation in heat treatment shops.

Molecular energetics of cytosine revisited: a joint computational and experimental study.

PubMed

Gomes, José R B; Ribeiro da Silva, Maria D M C; Freitas, Vera L S; Ribeiro da Silva, Manuel A V

2007-08-02

A static bomb calorimeter has been used to measure the standard molar energy of combustion, in oxygen, at T = 298.15 K, of a commercial sample of cytosine. From this energy, the standard (p degrees = 0.1 MPa) molar enthalpy of formation in the crystalline state was derived as -(221.9 +/- 1.7) kJ.mol(-1). This value confirms one experimental value already published in the literature but differs from another literature value by 13.5 kJ.mol(-1). Using the present standard molar enthalpy of formation in the condensed phase and the enthalpy of sublimation due to Burkinshaw and Mortimer [J. Chem. Soc., Dalton Trans. 1984, 75], (155.0 +/- 3.0) kJ.mol(-1), results in a value for the gas-phase standard molar enthalpy of formation for cytosine of -66.9 kJ.mol(-1). A similar value, -65.1 kJ.mol(-1), has been estimated after G3MP2B3 calculations combined with the reaction of atomization on three different tautomers of cytosine. In agreement with experimental evidence, the hydroxy-amino tautomer is the most stable form of cytosine in the gas phase. The enthalpies of formation of the other two tautomers were also estimated as -60.7 kJ.mol(-1) and -57.2 kJ.mol(-1) for the oxo-amino and oxo-imino tautomers, respectively. The same composite approach was also used to compute other thermochemical data, which is difficult to be measured experimentally, such as C-H, N-H, and O-H bond dissociation enthalpies, gas-phase acidities, and ionization enthalpies.

A molecular dynamics study of ambient and high pressure phases of silica: structure and enthalpy variation with molar volume.

PubMed

Rajappa, Chitra; Sringeri, S Bhuvaneshwari; Subramanian, Yashonath; Gopalakrishnan, J

2014-06-28

Extensive molecular dynamics studies of 13 different silica polymorphs are reported in the isothermal-isobaric ensemble with the Parrinello-Rahman variable shape simulation cell. The van Beest-Kramer-van Santen (BKS) potential is shown to predict lattice parameters for most phases within 2%-3% accuracy, as well as the relative stabilities of different polymorphs in agreement with experiment. Enthalpies of high-density polymorphs - CaCl2-type, α-PbO2-type, and pyrite-type - for which no experimental data are available as yet, are predicted here. Further, the calculated enthalpies exhibit two distinct regimes as a function of molar volume-for low and medium-density polymorphs, it is almost independent of volume, while for high-pressure phases a steep dependence is seen. A detailed analysis indicates that the increased short-range contributions to enthalpy in the high-density phases arise not only from an increased coordination number of silicon but also shorter Si-O bond lengths. Our results indicate that amorphous phases of silica exhibit better optimization of short-range interactions than crystalline phases at the same density while the magnitude of Coulombic contributions is lower in the amorphous phase.

Enthalpies of Formation of Hydrazine and Its Derivatives.

PubMed

Dorofeeva, Olga V; Ryzhova, Oxana N; Suchkova, Taisiya A

2017-07-20

Enthalpies of formation, Δ f H 298 ° , in both the gas and condensed phase, and enthalpies of sublimation or vaporization have been estimated for hydrazine, NH 2 NH 2 , and its 36 various derivatives using quantum chemical calculations. The composite G4 method has been used along with isodesmic reaction schemes to derive a set of self-consistent high-accuracy gas-phase enthalpies of formation. To estimate the enthalpies of sublimation and vaporization with reasonable accuracy (5-20 kJ/mol), the method of molecular electrostatic potential (MEP) has been used. The value of Δ f H 298 ° (NH 2 NH 2 ,g) = 97.0 ± 3.0 kJ/mol was determined from 75 isogyric reactions involving about 50 reference species; for most of these species, the accurate Δ f H 298 ° (g) values are available in Active Thermochemical Tables (ATcT). The calculated value is in excellent agreement with the reported results of the most accurate models based on coupled cluster theory (97.3 kJ/mol, the average of six calculations). Thus, the difference between the values predicted by high-level theoretical calculations and the experimental value of Δ f H 298 ° (NH 2 NH 2 ,g) = 95.55 ± 0.19 kJ/mol recommended in the ATcT and other comprehensive reference sources is sufficiently large and requires further investigation. Different hydrazine derivatives have been also considered in this work. For some of them, both the enthalpy of formation in the condensed phase and the enthalpy of sublimation or vaporization are available; for other compounds, experimental data for only one of these properties exist. Evidence of accuracy of experimental data for the first group of compounds was provided by the agreement with theoretical Δ f H 298 ° (g) value. The unknown property for the second group of compounds was predicted using the MEP model. This paper presents a systematic comparison of experimentally determined enthalpies of formation and enthalpies of sublimation or vaporization with the results of calculations. Because of relatively large uncertainty in the estimated enthalpies of sublimation, it was not always possible to evaluate the accuracy of the experimental values; however, this model allowed us to detect large errors in the experimental data, as in the case of 5,5'-hydrazinebistetrazole. The enthalpies of formation and enthalpies of sublimation or vaporization have been predicted for the first time for ten hydrazine derivatives with no experimental data. A recommended set of self-consistent experimental and calculated gas-phase enthalpies of formation of hydrazine derivatives can be used as reference Δ f H 298 ° (g) values to predict the enthalpies of formation of various hydrazines by means of isodesmic reactions.

Experimental and computational thermochemical study and solid-phase structure of 5,5-dimethylbarbituric acid.

PubMed

Roux, María Victoria; Notario, Rafael; Foces-Foces, Concepción; Temprado, Manuel; Ros, Francisco; Emel'yanenko, Vladimir N; Verevkin, Sergey P

2010-03-18

This paper reports an experimental and computational thermochemical study on 5,5-dimethylbarbituric acid and the solid-phase structure of the compound. The value of the standard (p(o) = 0.1 MPa) molar enthalpy of formation in the gas phase at T = 298.15 K has been determined. The energy of combustion was measured by static bomb combustion calorimetry, and from the result obtained, the standard molar enthalpy of formation in the crystalline state at T = 298.15 K was calculated as -(706.4 +/- 2.2) kJ x mol(-1). The enthalpy of sublimation was determined using a transference (transpiration) method in a saturated NB(2) stream, and a value of the enthalpy of sublimation at T = 298.15 K was derived as (115.8 +/- 0.5) kJ x mol(-1). From these results a value of -(590.6 +/- 2.3) kJ x mol(-1) for the gas-phase enthalpy of formation at T = 298.15 K was determined. Theoretical calculations at the G3 level were performed, and a study on molecular and electronic structure of the compound has been carried out. Calculated enthalpies of formation are in reasonable agreement with the experimental value. 5,5-Dimethylbarbituric acid was characterized by single crystal X-ray diffraction analysis. In the crystal structure, N-H...O=C hydrogen bonds lead to the formation of ribbons connected further by weak C-H...O=C hydrogen bonds into a three-dimensional network. The molecular and supramolecular structures observed in the solid state were also investigated in the gas phase by DFT calculations.

Evaluation of a biphasic in vitro dissolution test for estimating the bioavailability of carbamazepine polymorphic forms.

PubMed

Deng, Jia; Staufenbiel, Sven; Bodmeier, Roland

2017-07-15

The purpose of this study was to discriminate three crystal forms of carbamazepine (a BCS II drug) by in vitro dissolution testing and to correlate in vitro data with published in vivo data. A biphasic dissolution system (phosphate buffer pH6.8 and octanol) was used to evaluate the dissolution of the three polymorphic forms and to compare it with conventional single phase dissolution tests performed under sink and non-sink conditions. Similar dissolution profiles of three polymorphic forms were observed in the conventional dissolution test under sink conditions. Although a difference in dissolution was seen in the single phase dissolution test under non-sink conditions as well as in the aqueous phase of the biphasic test, little relevance for in vivo data was observed. In contrast, the biphasic dissolution system could discriminate between the different polymorphic forms in the octanol phase with a ranking of form III>form I>dihydrate form. This was in agreement with the in vivo performance. The dissolved drug available for oral absorption, which was dominated by dissolution and solution-mediated phase transformation, could be reflected in the biphasic dissolution test. Moreover, a good correlation was established between in vitro dissolution in the octanol phase of the biphasic test and in vivo pharmacokinetic data (R 2 =0.99). The biphasic dissolution method is a valuable tool to discriminate between different crystal forms in the formulations of poorly soluble drugs. Copyright © 2017. Published by Elsevier B.V.

Going full circle: phase-transition thermodynamics of ionic liquids.

PubMed

Preiss, Ulrich; Verevkin, Sergey P; Koslowski, Thorsten; Krossing, Ingo

2011-05-27

We present the full enthalpic phase transition cycle for ionic liquids (ILs) as examples of non-classical salts. The cycle was closed for the lattice, solvation, dissociation, and vaporization enthalpies of 30 different ILs, relying on as much experimental data as was available. High-quality dissociation enthalpies were calculated at the G3 MP2 level. From the cycle, we could establish, for the first time, the lattice and solvation enthalpies of ILs with imidazolium ions. For vaporization, lattice, and dissociation enthalpies, we also developed new prediction methods in the course of our investigations. Here, as only single-ion values need to be calculated and the tedious optimization of an ion pair can be circumvented, the computational time is short. For the vaporization enthalpy, a very simple approach was found, using a surface term and the calculated enthalpic correction to the total gas-phase energy. For the lattice enthalpy, the most important constituent proved to be the calculated conductor-like screening model (COSMO) solvation enthalpy in the ideal electric conductor. A similar model was developed for the dissociation enthalpy. According to our assessment, the typical error of the lattice enthalpy would be 9.4 kJ mol(-1), which is less than half the deviation we get when using the (optimized) Kapustinskii equation or the recent volume-based thermodynamics (VBT) theory. In contrast, the non-optimized VBT formula gives lattice enthalpies 20 to 140 kJ mol(-1) lower than the ones we assessed in the cycle, because of the insufficient description of dispersive interactions. Our findings show that quantum-chemical calculations can greatly improve the VBT approaches, which were parameterized for simple, inorganic salts with ideally point-shaped charges. In conclusion, we suggest the term "augmented VBT", or "aVBT", to describe this kind of theoretical approach. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Energetics of zirconia stabilized by cation and nitrogen substitution

NASA Astrophysics Data System (ADS)

Molodetsky, Irina

Tetragonal and cubic zirconia are used in advanced structural ceramics, fuel cells, oxygen sensors, nuclear waste ceramics and many other applications. These zirconia phases are stabilized at room temperature (relative to monoclinic phase for pure zirconia) by cation and nitrogen substitution. This work is aimed at a better understanding of the mechanisms of stabilization of the high-temperature zirconia. phases. Experimental data are produced on the energetics of zirconia stabilized by yttria and calcia, energetics of nitrogen-oxygen substitution in zirconia and cation doped zirconia, and energetics of x-ray amorphous zirconia. obtained by low-temperature synthesis. High-temperature oxide melt solution enables direct measurement of enthalpies of formation of these refractory oxides. The enthalpy of the monoclinic to cubic phase transition of zirconia is DeltaHm-c = 12.2 +/- 1.2 kJ/mol. For cubic phases of YSZ at low yttria contents, a straight line DeltaH f,YSZ = -(52.4 +/- 3.6)x + (12.2 +/- 1.2) approximates the enthalpy of formation as a function of the yttria content, x (0. 1 < x < 0.3). Use of the quadratic fit DeltaHf,YSZ = 126.36 x 2 - 81.29 x + 12.37 (0.1 ≲ x ≲ 0.53) indicates that yttria stabilizes the cubic phase in enthalpy at low dopant content and destabilizes the cubic phase as yttria content increases. Positive entropy of mixing in YSZ and small enthalpy of long range ordering in 0.47ZrO2-0.53YO1.5, DeltaHord = -2.4 +/- 3.0 kJ/mol, indicate presence of short range ordering in YSZ. The enthalpy of formation of calcia stabilized zirconia as a function of calcia content x, is approximated as DeltaHf,c = (-91.4 +/- 3.8) x + (13.5 +/- 1.7) kJ/mol. The enthalpy of oxygen-nitrogen substitution, DeltaHO-N, in zirconium oxynitrides is a linear function of nitrogen content. DeltaH O-N ˜ -500 kJ/mol N is for Ca (Y)-Zr-N-O and Zr-N-O oxynitrides and DeltaHO-N ˜ -950 kJ/mol N is for Mg-Zr-N-O oxynitrides. X-ray amorphous zirconia is 58.6 +/- 3.3 kJ/mol less stable in enthalpy than monoclinic zirconia. The difference between the surface energies of amorphous and tetragonal zirconia phases is ˜1.19 +/- 0.05 J/m2, with a lower surface energy for the amorphous material.

A combined experimental and computational thermodynamic study of difluoronitrobenzene isomers.

PubMed

Ribeiro da Silva, Manuel A V; Monte, Manuel J S; Lobo Ferreira, Ana I M C; Oliveira, Juliana A S A; Cimas, Álvaro

2010-10-14

This work reports the experimental and computational thermochemical study performed on three difluorinated nitrobenzene isomers: 2,4-difluoronitrobenzene (2,4-DFNB), 2,5-difluoronitrobenzene (2,5-DFNB), and 3,4-difluoronitrobenzene (3,4-DFNB). The standard (p° = 0.1 MPa) molar enthalpies of formation in the liquid phase of these compounds were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. A static method was used to perform the vapor pressure study of the referred compounds allowing the construction of the phase diagrams and determination of the respective triple point coordinates, as well as the standard molar enthalpies of vaporization, sublimation, and fusion for two of the isomers (2,4-DFNB and 3,4-DFNB). For 2,5-difluoronitrobenzene, only liquid vapor pressures were measured enabling the determination of the standard molar enthalpies of vaporization. Combining the thermodynamic parameters of the compounds studied, the following standard (p° = 0.1 MPa) molar enthalpies of formation in the gaseous phase, at T = 298.15 K, were derived: Δ(f)H(m)° (2,4-DFNB, g) = -(296.3 ± 1.8) kJ · mol⁻¹, Δ(f)H(m)° (2,5-DFNB, g) = -(288.2 ± 2.1) kJ · mol⁻¹, and Δ(f)H(m)° (3,4-DFNB, g) = -(302.4 ± 2.1) kJ · mol⁻¹. Using the empirical scheme developed by Cox, several approaches were evaluated in order to identify the best method for estimating the standard molar gas phase enthalpies of formation of these compounds. The estimated values were compared to the ones obtained experimentally, and the approach providing the best comparison with experiment was used to estimate the thermodynamic behavior of the other difluorinated nitrobenzene isomers not included in this study. Additionally, the enthalpies of formation of these compounds along with the enthalpies of formation of the other isomers not studied experimentally, i.e., 2,3-DFNB, 2,6-DFNB, and 3,5-DFNB, were estimated using the composite G3MP2B3 approach together with adequate gas-phase working reactions. Furthermore, we also used this computational approach to calculate the gas-phase basicities, proton and electron affinities, and, finally, adiabatic ionization enthalpies.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortiz, E.; Kraatz, M.; Luthy, R.G.

The dissolution of naphthalene, phenanthrene, and pyrene from viscous organic phases into water was studied in continuous-flow systems for time periods ranging from several months to more than 1 year. By selecting nonaqueous phases ranging from low viscosity to semisolid, i.e., from a light lubricating oil to paraffin, the governance of mass transfer was shown to vary from water phase control to nonaqueous phase control. An advancing depleted-zone model is proposed to explain the dissolution of PAHs from a viscous organic phase wherein the formation of a depleted zone within the organic phase increases the organic phase resistance to themore » dissolution of PAHs. The experimental data suggest the formation of a depleted zone within the organic phase for systems comprising a high-viscosity oil, petrolatum (petroleum jelly), and paraffin. Organic phase resistance to naphthalene dissolution became dominant over aqueous phase resistance after flushing for several days. Such effects were not evident for low viscosity lubricating oil. The transition from aqueous-phase dissolution control to nonaqueous-phase dissolution control appears predictable, and this provides a more rational framework to assess long-term release of HOCs from viscous nonaqueous phase liquids and semisolids.« less

Predicting glass-to-glass and liquid-to-liquid phase transitions in supercooled water using classical nucleation theory

NASA Astrophysics Data System (ADS)

Tournier, Robert F.

2018-01-01

Glass-to-glass and liquid-to-liquid phase transitions are observed in bulk and confined water, with or without applied pressure. They result from the competition of two liquid phases separated by an enthalpy difference depending on temperature. The classical nucleation equation of these phases is completed by this quantity existing at all temperatures, a pressure contribution, and an enthalpy excess. This equation leads to two homogeneous nucleation temperatures in each liquid phase; the first one (Tn- below Tm) being the formation temperature of an "ordered" liquid phase and the second one corresponding to the overheating temperature (Tn+ above Tm). Thermodynamic properties, double glass transition temperatures, sharp enthalpy and volume changes are predicted in agreement with experimental results. The first-order transition line at TLL = 0.833 × Tm between fragile and strong liquids joins two critical points. Glass phase above Tg becomes "ordered" liquid phase disappearing at TLL at low pressure and at Tn+ = 1.302 × Tm at high pressure.

Calculation of Five Thermodynamic Molecular Descriptors by Means of a General Computer Algorithm Based on the Group-Additivity Method: Standard Enthalpies of Vaporization, Sublimation and Solvation, and Entropy of Fusion of Ordinary Organic Molecules and Total Phase-Change Entropy of Liquid Crystals.

PubMed

Naef, Rudolf; Acree, William E

2017-06-25

The calculation of the standard enthalpies of vaporization, sublimation and solvation of organic molecules is presented using a common computer algorithm on the basis of a group-additivity method. The same algorithm is also shown to enable the calculation of their entropy of fusion as well as the total phase-change entropy of liquid crystals. The present method is based on the complete breakdown of the molecules into their constituting atoms and their immediate neighbourhood; the respective calculations of the contribution of the atomic groups by means of the Gauss-Seidel fitting method is based on experimental data collected from literature. The feasibility of the calculations for each of the mentioned descriptors was verified by means of a 10-fold cross-validation procedure proving the good to high quality of the predicted values for the three mentioned enthalpies and for the entropy of fusion, whereas the predictive quality for the total phase-change entropy of liquid crystals was poor. The goodness of fit ( Q ²) and the standard deviation (σ) of the cross-validation calculations for the five descriptors was as follows: 0.9641 and 4.56 kJ/mol ( N = 3386 test molecules) for the enthalpy of vaporization, 0.8657 and 11.39 kJ/mol ( N = 1791) for the enthalpy of sublimation, 0.9546 and 4.34 kJ/mol ( N = 373) for the enthalpy of solvation, 0.8727 and 17.93 J/mol/K ( N = 2637) for the entropy of fusion and 0.5804 and 32.79 J/mol/K ( N = 2643) for the total phase-change entropy of liquid crystals. The large discrepancy between the results of the two closely related entropies is discussed in detail. Molecules for which both the standard enthalpies of vaporization and sublimation were calculable, enabled the estimation of their standard enthalpy of fusion by simple subtraction of the former from the latter enthalpy. For 990 of them the experimental enthalpy-of-fusion values are also known, allowing their comparison with predictions, yielding a correlation coefficient R ² of 0.6066.

Thermodynamics of the Sorption of Benzimidazoles on Octadecyl Silica Gel from Water-Methanol Eluents

NASA Astrophysics Data System (ADS)

Shafigulin, R. V.; Bulanova, A. V.

2018-02-01

The standard enthalpy and entropy component of transferring benzimidazoles from water-methanol solutions to surfaces of octadecyl silica gel are determined using reversed-phase high-performance liquid chromatography (RP HPLC). The dependences between the enthalpy and polarizability of the molecules of the studied benzimidazoles, the enthalpy and the entropy factor are studied, and the influence of the quantitative composition of the water-methanol solution on the enthalpy are studied.

Solubilization, Solution Equilibria, and Biodegradation of PAH's under Thermophilic Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Viamajala, S.; Peyton, B. M.; Richards, L. A.

Biodegradation rates of PAHs are typically low at mesophilic conditions and it is believed that the kinetics of degradation is controlled by PAH solubility and mass transfer rates. Solubility tests were performed on phenanthrene, fluorene and fluoranthene at 20 C, 40 C and 60 C and, as expected, a significant increase in the equilibrium solubility concentration and of the rate of dissolution of these polycyclic aromatic hydrocarbons (PAHs) was observed with increasing temperature. A first-order model was used to describe the PAH dissolution kinetics and the thermodynamic property changes associated with the dissolution process (enthalpy, entropy and Gibb's free energymore » of solution) were evaluated. Further, other relevant thermodynamic properties for these PAHs, including the activity coefficients at infinite dilution, Henry's law constants and octanol-water partition coefficients, were calculated in the temperature range 20-60 C. In parallel with the dissolution studies, three thermophilic Geobacilli were isolated from compost that grew on phenanthrene at 60 C and degraded the PAH more rapidly than other reported mesophiles. Our results show that while solubilization rates of PAHs are significantly enhanced at elevated temperatures, the biodegradation of PAHs under thermophilic conditions is likely mass transfer limited due to enhanced degradation rates.« less

Phase dissolution of γ-Mg17Al12 during homogenization of as-cast AZ80 Magnesium alloy and its effect on room temperature mechanical properties

NASA Astrophysics Data System (ADS)

Kulkarni, Rahul R.; Prabhu, Nityanand; Hodgson, Peter D.; Kashyap, Bhagwati P.

As-cast AZ80 Mg alloy contains α-Mg, partially divorce eutectic of α and γ (Mg17Al12), fully divorce eutectic of α and γ, and lamellar eutectic of α and γ phases. During homogenization, second phase (γ-Mg17Al12) gets dissolved can change the mechanical properties. Therefore, the aim of the present work is to bring out the kinetics of dissolution of γ phase and evaluate its effect on mechanical properties. Microstructure evolution during homogenization was investigated as a function of time for 0.5 to 100 h and at the temperatures of 400° and 439°C. In as-cast state, this material was found to contain 70% α-Mg and 30% eutectic phase. With increasing homogenization time, dissolution of lamellar eutectic occurs first which is followed by dissolution of fully divorce eutectic and partially divorce eutectic. The dissolution kinetics of γ phase was analyzed based on the decrease in its volume fraction as a function of time. The time exponent for dissolution was found to be 0.38 and the activation energy for the dissolution of γ phase was found to be 84.1 kJ/mol. This dissolution of γ phase leads to decrease in hardness and tensile strength with increase in homogenization time.

Thermodynamic and kinetic characterization of polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography.

PubMed

Howerton, Samuel B; McGuffin, Victoria L

2003-07-15

The retention of six polycyclic aromatic hydrocarbons (PAHs) was characterized by reversed-phase liquid chromatography. The PAHs were detected by laser-induced fluorescence at four points along an optically transparent capillary column. The profiles were characterized in space and time using an exponentially modified Gaussian equation. The resulting parameters were used to calculate the retention factors, as well as the concomitant changes in molar enthalpy and molar volume, for each PAH on monomeric (2.7 micromol/m2) and polymeric (5.4 micromol/m2) octadecylsilica. The changes in molar enthalpy become more exothermic as ring number increases and as annelation structure becomes less condensed. The changes in molar volume become more negative as ring number increases for the planar PAHs, but are positive for the nonplanar solutes. In addition, the rate constants, as well as the concomitant activation enthalpy and activation volume, are calculated for the first time. The kinetic data demonstrate that many of the PAHs exhibit very fast transitions between the mobile and stationary phases. The transition state is very high in energy, and the activation enthalpies and volumes become greater as ring number increases and as annelation structure becomes less condensed. The changes in thermodynamic and kinetic behavior are much more pronounced for the polymeric phase than for the monomeric phase.

Two-phase convective CO 2 dissolution in saline aquifers

DOE PAGES

Martinez, Mario J.; Hesse, Marc A.

2016-01-30

Geologic carbon storage in deep saline aquifers is a promising technology for reducing anthropogenic emissions into the atmosphere. Dissolution of injected CO 2 into resident brines is one of the primary trapping mechanisms generally considered necessary to provide long-term storage security. Given that diffusion of CO 2 in brine is woefully slow, convective dissolution, driven by a small increase in brine density with CO 2 saturation, is considered to be the primary mechanism of dissolution trapping. Previous studies of convective dissolution have typically only considered the convective process in the single-phase region below the capillary transition zone and have eithermore » ignored the overlying two-phase region where dissolution actually takes place or replaced it with a virtual region with reduced or enhanced constant permeability. Our objective is to improve estimates of the long-term dissolution flux of CO 2 into brine by including the capillary transition zone in two-phase model simulations. In the fully two-phase model, there is a capillary transition zone above the brine-saturated region over which the brine saturation decreases with increasing elevation. Our two-phase simulations show that the dissolution flux obtained by assuming a brine-saturated, single-phase porous region with a closed upper boundary is recovered in the limit of vanishing entry pressure and capillary transition zone. For typical finite entry pressures and capillary transition zone, however, convection currents penetrate into the two-phase region. As a result, this removes the mass transfer limitation of the diffusive boundary layer and enhances the convective dissolution flux of CO 2 more than 3 times above the rate assuming single-phase conditions.« less

Initial dissolution kinetics of cocrystal of carbamazepine with nicotinamide.

PubMed

Hattori, Yusuke; Sato, Maiko; Otsuka, Makoto

2015-11-01

Objectives of this study are investigating the initial dissolution kinetics of the cocrystal of carbamazepine (CBZ) with nicotinamide (NIC) and understanding its initial dissolution process. Cocrystal solids of CBZ with NIC were prepared by co-milling and solvent evaporation methods. The formation of cocrystal solid was verified via X-ray diffraction measurement. Dissolution tests of the solids were performed using an original flow cell and ultraviolet-visible spectroscopic detector. The spectra monitored in situ were analyzed to determine the dissolved compounds separately using the classical least squares regression method. The initial dissolution profiles were interpreted using simultaneous model of dissolution and phase changes. In the initial dissolution, CBZ in the cocrystal structure dissolved in water and it was suggested that CBZ reached a metastable intermediate state simultaneously with dissolution. The cocrystal solid prepared by solvent evaporation provided a higher rate constant of the phase change than that prepared by co-milling. Our results thus support the use of evaporation as the method of choice to produce ordered cocrystal structures. We suggest that CBZ forms dihydrate during the dissolution process; however, during the initial phase of dissolution, CBZ changes to a metastable intermediate phase. © 2015 Royal Pharmaceutical Society.

Thermodynamic tabulations for selected phases in the system CaO-Al2O3-SiO2-H2 at 101.325 kPa (1 atm) between 273.15 and 1800 K

USGS Publications Warehouse

Haas, John L.; Robinson, Glipin R.; Hemingway, Bruch S.

1981-01-01

The standard thermodynamic properties of phases in the lime‐alumina‐silica‐ water system between 273.15 and 1800 K at 101.325 kPa (1 atm) were evalated from published experimental data. Phases included in the compilation are boehmite, diaspore, gibbsite, kaolinite, dickite, halloysite, andalusite, kyanite, sillimanite, Ca‐Al cliniopyroxene, anorthite, gehlenite, grossular, prehnite, zoisite, margarite, wollastonite, cyclowollastonite ( = pseudowollastonite), larnite, Ca olivine, hatrurite, and rankinite. The properties include heat capacity, entropy, relative enthalpy, and the Gibbs energy function of the phases and the enthalpies, Gibbs energies, and equilibrium constants for formation both from the elements and the oxides. Tabulated values are given at 50 K intervals with the 2‐sigma confidence limit at 250 K intervals. Summaries for each phase give the temperature‐ dependent functions for heat capacity, entropy, and relative enthalpy and the experimental data used in the final evaluation.

Melting temperature and enthalpy variations of phase change materials (PCMs): a differential scanning calorimetry (DSC) analysis

NASA Astrophysics Data System (ADS)

Sun, Xiaoqin; Lee, Kyoung Ok; Medina, Mario A.; Chu, Youhong; Li, Chuanchang

2018-06-01

Differential scanning calorimetry (DSC) analysis is a standard thermal analysis technique used to determine the phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy of phase change materials (PCMs). To determine the appropriate heating rate and sample mass, various DSC measurements were carried out using two kinds of PCMs, namely N-octadecane paraffin and calcium chloride hexahydrate. The variations in phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy were observed within applicable heating rates and sample masses. It was found that the phase transition temperature range increased with increasing heating rate and sample mass; while the heat of fusion varied without any established pattern. The specific heat decreased with the increase of heating rate and sample mass. For accuracy purpose, it is recommended that for PCMs with high thermal conductivity (e.g. hydrated salt) the focus will be on heating rate rather than sample mass.

Thermally decarboxylated sodium bicarbonate: Interactions with water vapour, calorimetric study

PubMed Central

Volkova, Natalia; Hansson, Henri; Ljunggren, Lennart

2012-01-01

Isothermal titration calorimetry (ITC) was used to study interactions between water vapour and the surface of thermally converted sodium bicarbonate (NaHCO3). The decarboxylation degree of the samples was varied from 3% to 35% and the humidity range was 54–100%. The obtained enthalpy values were all exothermic and showed a positive linear correlation with decarboxylation degrees for each humidity studied. The critical humidity, 75% (RHo), was determined as the inflection point on a plot of the mean−ΔH kJ/mole Na2CO3 against RH. Humidities above the critical humidity lead to complete surface dissolution. The water uptake (m) was determined after each calorimetric experiment, complementing the enthalpy data. A mechanism of water vapour interaction with decarboxylated samples, including the formation of trona and Wegscheider’s salt on the bicarbonate surface is proposed for humidities below RHo. PMID:29403816

Ionic liquids. Combination of combustion calorimetry with high-level quantum chemical calculations for deriving vaporization enthalpies.

PubMed

Emel'yanenko, Vladimir N; Verevkin, Sergey P; Heintz, Andreas; Schick, Christoph

2008-07-10

In this work, the molar enthalpies of formation of the ionic liquids [C2MIM][NO3] and [C4MIM][NO3] were measured by means of combustion calorimetry. The molar enthalpy of fusion of [C2MIM][NO3] was measured using differential scanning calorimetry. Ab initio calculations of the enthalpy of formation in the gaseous phase have been performed for the ionic species using the G3MP2 theory. We have used a combination of traditional combustion calorimetry with modern high-level ab initio calculations in order to obtain the molar enthalpies of vaporization of a series of the ionic liquids under study.

Protonation enthalpies of metal oxides from high temperature electrophoresis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez-Santiago, V; Fedkin, Mark V.; Lvov, Serguei N.

2012-01-01

Surface protonation reactions play an important role in the behavior of mineral and colloidal systems, specifically in hydrothermal aqueous environments. However, studies addressing the reactions at the solid/liquid interface at temperatures above 100 C are scarce. In this study, newly and previously obtained high temperature electrophoresis data (up to 260 C) zeta potentials and isoelectric points for metal oxides, including SiO2, SnO2, ZrO2, TiO2, and Fe3O4, were used in thermodynamic analysis to derive the standard enthalpies of their surface protonation. Two different approaches were used for calculating the protonation enthalpy: one is based on thermodynamic description of the 1-pKa modelmore » for surface protonation, and another one on a combination of crystal chemistry and solvation theories which link the relative permittivity of the solid phase and the ratio of the Pauling bond strength and bond length to standard protonation enthalpy. From this analysis, two expressions relating the protonation enthalpy to the relative permittivity of the solid phase were obtained.« less

Protonation enthalpies of metal oxides from high temperature electrophoresis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez-Santiago, V; Fedkin, Mark V; Lvov, Serguei N.

2012-01-01

Surface protonation reactions play an important role in the behavior of mineral and colloidal systems, specifically in hydrothermal aqueous environments. However, studies addressing the reactions at the solid/liquid interface at temperatures above 100 C are scarce. In this study, newly and previously obtained high temperature electrophoresis data (up to 260 C) - zeta potentials and isoelectric points - for metal oxides, including SiO{sub 2}, SnO{sub 2}, ZrO{sub 2}, TiO{sub 2}, and Fe{sub 3}O{sub 4}, were used in thermodynamic analysis to derive the standard enthalpies of their surface protonation. Two different approaches were used for calculating the protonation enthalpy: one ismore » based on thermodynamic description of the 1-pKa model for surface protonation, and another one - on a combination of crystal chemistry and solvation theories which link the relative permittivity of the solid phase and the ratio of the Pauling bond strength and bond length to standard protonation enthalpy. From this analysis, two expressions relating the protonation enthalpy to the relative permittivity of the solid phase were obtained.« less

Phase Behavior of Ritonavir Amorphous Solid Dispersions during Hydration and Dissolution.

PubMed

Purohit, Hitesh S; Taylor, Lynne S

2017-12-01

The aim of this research was to study the interplay of solid and solution state phase transformations during the dissolution of ritonavir (RTV) amorphous solid dispersions (ASDs). RTV ASDs with polyvinylpyrrolidone (PVP), polyvinylpyrrolidone vinyl acetate (PVPVA) and hydroxypropyl methylcellulose acetate succinate (HPMCAS) were prepared at 10-50% drug loading by solvent evaporation. The miscibility of RTV ASDs was studied before and after exposure to 97% relative humidity (RH). Non-sink dissolution studies were performed on fresh and moisture-exposed ASDs. RTV and polymer release were monitored using ultraviolet-visible spectroscopy. Techniques including fluorescence spectroscopy, confocal imaging, scanning electron microscopy (SEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and nanoparticle tracking analysis (NTA) were utilized to monitor solid and the solution state phase transformations. All RTV-PVP and RTV-PVPVA ASDs underwent moisture-induced amorphous-amorphous phase separation (AAPS) on high RH storage whereas RTV-HPMCAS ASDs remained miscible. Non-sink dissolution of PVP- and PVPVA-based ASDs at low drug loadings led to rapid RTV and polymer release resulting in concentrations in excess of amorphous solubility, liquid-liquid phase separation (LLPS) and amorphous nanodroplet formation. High drug loading PVP- and PVPVA-based ASDs did not exhibit LLPS upon dissolution as a consequence of extensive AAPS in the hydrated ASD matrix. All RTV-HPMCAS ASDs led to LLPS upon dissolution. RTV ASD dissolution is governed by a competition between the dissolution rate and the rate of phase separation in the hydrated ASD matrix. LLPS was observed for ASDs where the drug release was polymer controlled and only ASDs that remained miscible during the initial phase of dissolution led to LLPS. Techniques such as fluorescence spectroscopy, confocal imaging and SEM were useful in understanding the phase behavior of ASDs upon hydration and dissolution and were helpful in elucidating the mechanism of generation of amorphous nanodroplets.

Use of glancing angle X-ray powder diffractometry to depth-profile phase transformations during dissolution of indomethacin and theophylline tablets.

PubMed

Debnath, Smita; Predecki, Paul; Suryanarayanan, Raj

2004-01-01

The purpose of this study was (i) to develop glancing angle x-ray powder diffractometry (XRD) as a method for profiling phase transformations as a function of tablet depth; and (ii) to apply this technique to (a) study indomethacin crystallization during dissolution of partially amorphous indomethacin tablets and to (b) profile anhydrate --> hydrate transformations during dissolution of theophylline tablets. The intrinsic dissolution rates of indomethacin and theophylline were determined after different pharmaceutical processing steps. Phase transformations during dissolution were evaluated by various techniques. Transformation in the bulk and on the tablet surface was characterized by conventional XRD and scanning electron microscopy, respectively. Glancing angle XRD enabled us to profile these transformations as a function of depth from the tablet surface. Pharmaceutical processing resulted in a decrease in crystallinity of both indomethacin and theophylline. When placed in contact with the dissolution medium, while indomethacin recrystallized, theophylline anhydrate rapidly converted to theophylline monohydrate. Due to intimate contact with the dissolution medium, drug transformation occurred to a greater extent at or near the tablet surface. Glancing angle XRD enabled us to depth profile the extent of phase transformations as a function of the distance from the tablet surface. The processed sample (both indomethacin and theophylline) transformed more rapidly than did the corresponding unprocessed drug. Several challenges associated with the glancing angle technique, that is, the effects of sorbed water, phase transformations during the experimental timescale, and the influence of phase transformation on penetration depth, were addressed. Increased solubility, and consequently dissolution rate, is one of the potential advantages of metastable phases. This advantage is negated if, during dissolution, the metastable to stable transformation rate > dissolution rate. Glancing angle XRD enabled us to quantify and thereby profile phase transformations as a function of compact depth. The technique has potential utility in monitoring surface reactions, both chemical decomposition and physical transformations, in pharmaceutical systems.

Calorimetric and computational study of indanones.

PubMed

Matos, M Agostinha R; Miranda, Margarida S; Monte, Manuel J S; Santos, Luís M N B F; Morais, Victor M F; Chickos, James S; Umnahanant, Patamaporn; Liebman, Joel F

2007-11-01

Condensed phase standard (p degrees = 0.1 MPa) molar enthalpies of formation for 1-indanone, 2-indanone, and 1,3-indandione were derived from the standard molar enthalpies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpies of sublimation for 1-indanone and 2-indanone, at T = 298.15 K, were measured both by correlation-gas chromatography and by Calvet microcalorimetry leading to a mean value for each compound. For 1,3-indandione, the standard molar enthalpy of sublimation was derived from the vapor pressure dependence on temperature. The following enthalpies of formation in gas phase, at T = 298.15 K, were then derived: 1-indanone, -64.0 +/- 3.8 kJ mol(-1); 2-indanone, -56.6 +/- 4.8 kJ mol(-1); 1,3-indandione, -165.0 +/- 2.6 kJ mol(-1). The vaporization and fusion enthalpies of the indanones studied are also reported. In addition, theoretical calculations using the density functional theory with the B3LYP and MPW1B95 energy functionals and the 6-311G** and cc-pVTZ basis sets have been performed for these molecules and the corresponding one-ring species to obtain the most stable geometries and to access their energetic stabilities.

Experimental and computational study on the molecular energetics of indoline and indole.

PubMed

da Silva, Manuel A V Ribeiro; Cabral, Joana I T A; Gomes, José R B

2008-11-27

Static bomb calorimetry, Calvet microcalorimetry and the Knudsen effusion technique were used to determine the standard molar enthalpy of formation in the gas phase, at T = 298.15 K, of the indole and indoline heterocyclic compounds. The values obtained were 164.3 +/- 1.3 kJ x mol(-1) and 120.0 +/- 2.9 kJ x mol(-1), respectively. Several different computational approaches and different working reactions were used to estimate the gas-phase enthalpies of formation for indole and indoline. The computational approaches support the experimental results reported. The calculations were further extended to the determination of other properties such as bond dissociation enthalpies, gas-phase acidities, proton and electron affinities and ionization energies. The agreement between theoretical and experimental data for indole is very good supporting the data calculated for indoline.

Thermochemistry and gas-phase ion energetics of 2-hydroxy-4-methoxy-benzophenone (oxybenzone).

PubMed

Lago, A F; Jimenez, P; Herrero, R; Dávalos, J Z; Abboud, J-L M

2008-04-10

We have investigated the thermochemistry and ion energetics of the oxybenzone (2-hydroxy-4-methoxy-benzophenone, C14H12O3, 1H) molecule. The following parameters have been determined for this species: gas-phase enthalpy for the of neutral molecule at 298.15K, (Delta(f)H0(m)(g) = -303.5 +/- 5.1 kJ x mol-1), the intrinsic (gas-phase) acidity (GA(1H) = 1402.1 +/- 8.4 kJ x mol-1), enthalpy of formation for the oxybenzone anion (Delta(f)H0(m)(1-,g) = -402.3 +/- 9.8 kJ x mol-1). We also have obtained the enthalpy of formation of, 4-hydroxy-4'-methoxybenzophenone (Delta(f)H0(m)(g) = -275.4 +/- 10 kJ x mol-1) and 3-methoxyphenol anion (Delta(f)H0(m)(C7H7O2-,g) = -317.7 +/- 8.7 kJ x mol-1). A reliable experimental estimation of enthalpy related to intramolecular hydrogen bonding in oxybenzone has also been obtained (30.1 +/- 6.3 kJ x mol-1) and compared with our theoretical calculations at the B3LYP/6-311++G** level of theory, by means of an isodesmic reaction scheme. In addition, heat capacities, temperature, and enthalpy of fusion have been determined for this molecule by differential scanning calorimetry.

Enthalpy of phase transitions of lactams

NASA Astrophysics Data System (ADS)

Emel'yanenko, V. N.; Verevkin, S. P.; Ralys, R. V.; Turovtsev, V. V.; Orlov, V. Yu.

2012-10-01

The transpiration method is used to measure the temperature dependences of the vapors pressures of azacyclobutan-2-one (I, CAS 930-21-2) azacyclohexan-2-one (II, CAS 675-20-7); azacyclooctan-2-one (III, CAS 673-66-5); azacyclononan-2-one (IV, CAS 935-30-8) and azacyclotridecan-2-one (V, CAS 947-04-6). Enthalpies of sublimation and vaporisation are determined. The temperatures and enthalpies of fusion of compounds (I, III-V) are found by means of differential scanning calorimetry. The dependences of the enthalpies of vaporisation of lactones, lactams, cycloalkanes, cycloalkanones on the size of a cycle are analyzed.

Beer Law Constants and Vapor Pressures of HgI2 over HgI2(s,l)

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Zhu, Shen; Ramachandran, N.; Burger, A.

2002-01-01

Optical absorption spectra of the vapor phase over HgI2(s,l) were measured at sample temperatures between 349 and 610 K for wavelengths between 200 and 600 nm. The spectra show the samples sublimed congruently into HGI2 without any observed Hg or I2 absorption spectra. The Beer's Law constants for 15 wavelengths between 200 and 440 nm were derived. From these constants the vapor pressure of HgI2, P, was found to be a function of temperature for the liquid and the solid beta-phases: ln P(atm) = -7700/T(K) + 12.462 (liquid phase) and ln P(atm) = -10150/T(K) + 17.026 (beta-phase). The expressions match the enthalpies of vaporization and sublimation of 15.30 and 20.17 kcal/mole respectively, for the liquid and the beta-phase HgI2. The difference in the enthalpies gives an enthalpy of fusion of 4.87 kcal/mole, and the intersection of the two expressions gives a melting point of 537 K.

Beer Law Constants and Vapor Pressures of HgI2 over HgI2(s,l)

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Zhu, Shen; Ramachandran, N.; Burger, A.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

The optical absorption spectra of the vapor phase over HgI2(s,l) were measured for wavelengths between 200 and 600 nm. The spectra show that the sample sublimed congruently into HgI2 with no Hg or I2 absorption spectrum observed. The Beer's Law constants for 15 wavelengths between 200 and 440 nm were determined. From these constants the vapor pressure of H912, P, was established as a function of temperatures for the liquid and the solid Beta-phases. The expressions correspond to the enthalpies of vaporization and sublimation of 15.30 and 20.17 Kcal/mole, respectively, for the liquid and the Beta-phase HgI2. The difference in the enthalpies gives an enthalpy of fusion of 4.87 Kcal/mole and the intersection of the two expressions gives a melting point of 537 K.

Highly destabilized Mg-Ti-Ni-H system investigated by density functional theory and hydrogenography

NASA Astrophysics Data System (ADS)

Broedersz, C. P.; Gremaud, R.; Dam, B.; Griessen, R.; Løvvik, O. M.

2008-01-01

Using hydrogenography, we recently mapped the thermodynamic properties of a large range of compositions in the quaternary Mg-Ti-Ni-H system. The enthalpy of hydride formation of Mg-Ni alloys is significantly altered upon Ti doping. For a small range of compositions, we find a hydrogenation enthalpy ΔH=-40kJ (molH2)-1 , which is the desired enthalpy for hydrogen storage at moderate temperature and pressure. This enthalpy value is surprising since it is significantly less negative than the ΔH of the Mg-Ni and Mg-Ti hydrides. The nanostructure of the Mg-Ti-Ni-H films hinders a direct determination of the hydride phases involved by x-ray diffraction. Using density functional theory calculations for various hydrogenation reaction paths, we establish that the destabilization of the Mg-Ni-H system by Ti doping is due to the formation of Mg2Ni and Ti-Ni intermetallics in the as-deposited state, which transform into a metastable Ti-doped Mg2NiH4 phase upon hydrogenation. The Ti-doped Mg2NiH4 phase can be considered as a heavily doped semiconductor.

Energetic study of 4(3H)-pyrimidinone: aromaticity of reactions, hydrogen bond rules, and support for an anomeric effect.

PubMed

Galvão, Tiago L P; Rocha, Inês M; Ribeiro da Silva, Maria D M C; Ribeiro da Silva, Manuel A V

2014-05-08

4(3H)-Pyrimidinone is observed in nature in equilibrium with other tautomeric forms, mimicking the tautomeric equilibrium in pyrimidine nucleobases. In this work, the enthalpy of formation in the gaseous phase of 4(3H)-pyrimidinone was derived from the combination of the enthalpy of formation in the crystalline phase, obtained by static bomb combustion calorimetry, and the enthalpy of sublimation, obtained by Knudsen effusion. The gaseous phase enthalpy of formation of 4(3H)-pyrimidinone was interpreted in terms of isodesmic reactions that consider the enthalpic effects of hydroxypyridines and pyrimidine. After comparison of the experimental and computational results, the same type of isodesmic reactions was used to study the substituent effects of the hydroxyl functional group of 2-, 4-, and 5-hydroxypyrimidines. The influence of aromaticity on the energetics of hydroxypyrimidines was evaluated using the variation of nucleus-independent chemical shifts for several reactions. The influence of intramolecular hydrogen bonds was investigated using the quantum theory of atoms in molecules and the geometric rule of Baker and Hubbard to identify hydrogen bonds. The energetic results obtained were also interpreted in terms of an in plane anomeric effect in the pyrimidine ring.

Enthalpy of formation of Fe 3Al 2Si 3O 12 (almandine) by high temperature alkali borate solution calorimetry

NASA Astrophysics Data System (ADS)

Chatillon-Colinet, C.; Kleppa, O. J.; Newton, R. C.; Perkins, D., III

1983-03-01

A high-temperature solution calorimetric method suitable for thermochemical studies of anhydrous minerals containing Fe 2+ ions has been developed. The method is based on an oxide melt solvent with 52 wt% LiBO 2 and 48 wt% NaBO 2 maintained at a temperature of 750°C. In a first application of this method the enthalpies of solution of synthetic almandine, fayalite, a mixture of fayalite plus quartz on FeSiO 3 composition, and natural quartz were measured. For the reaction: ? the enthalpy change at 1023 K is -3.82 ± 0.87 kcal, based on fayalite, quartz, corundum and almandine, and -5.96 ± 0.90 kcal based on the fayalite plus quartz mixture, corundum, and almandine. These values lead to standard molar enthalpies of formation of almandine from the oxides at 1023 K of -14.10 ± 1.22 kcal and -16.24 ± 1.74 kcal, respectively. The measured enthalpy of formation of almandine is less negative by several kilocalories than values derived from analysis of the phase equilibrium work of HSU (1968), but in closer agreement with the phase equilibrium study of O'NEILL and WOOD (1979) and similar to the phase equilibrium deduction of FROESE (1973). The agreement of the present almandine enthalpy of formation with O'NEILL and WOOD (1979) and FROESE (1973) suggests that almandine entropies at 298 K to be obtained from their studies, in the range 79-81 cal/K, are more nearly correct than the several estimates based on oxide sum and volume-entropy systematics, most of which are much lower.

Solvation of decane and benzene in mixtures of 1-octanol and N, N-dimethylformamide

NASA Astrophysics Data System (ADS)

Kustov, A. V.; Smirnova, N. L.

2016-09-01

The heats of dissolution of decane and benzene in a model system of octanol-1 (OctOH) and N, N-dimethylformamide (DMF) at 308 K are measured using a variable temperature calorimeter equipped with an isothermal shell. Standard enthalpies are determined and standard heat capacities of dissolution in the temperature range of 298-318 K are calculated using data obtained in [1, 2]. The state of hydrocarbon molecules in a binary mixture is studied in terms of the enhanced coordination model (ECM). Benzene is shown to be preferentially solvated by DMF over the range of physiological temperatures. The solvation shell of decane is found to be strongly enriched with 1-octanol. It is obvious that although both hydrocarbons are nonpolar, the presence of the aromatic π-system in benzene leads to drastic differences in their solvation in a lipid-protein medium.

Prediction of the vapor pressure and vaporization enthalpy of 1-n-alkyl-3-methylimidazolium-bis-(trifluoromethanesulfonyl) amide ionic liquids.

PubMed

Diedenhofen, Michael; Klamt, Andreas; Marsh, Kenneth; Schäfer, Ansgar

2007-09-07

The vapor pressures and vaporization enthalpies of a series of 1-n-alkyl-3-methylimidazolium-bis-(trifluoromethanesulfonyl) amide ionic liquids have been predicted with two different approaches using the COSMO-RS method and quantum chemical gas phase calculations. While the calculated enthalpies are in good agreement with the experimental data, COSMO-RS seems to underestimate the vapor pressures by roughly 0.5-4 log units dependent on the IL and approach used.

Temperature dependences of the retention indices of mono- and polyethylene glycol acetals and ethers on stationary phase DB-1 and enthalpies of their sorption from the gas phase

NASA Astrophysics Data System (ADS)

Zhabina, A. A.; Krasnykh, E. L.

2017-12-01

Gas chromatography is used to study the sorption characteristics and retention of a series of mono-, di-, and triethylene glycol ethers on nonpolar phase DB-1 in the temperature range of 70-180°C. Temperature dependences of the retention indices of the compounds are obtained and their linear character in the investigated range of temperatures is demonstrated. The enthalpies of sorption of the investigated compounds are calculated and analyzed, based on the temperature dependences of the retention factors.

How Much Binding Affinity Can be Gained by Filling a Cavity?

PubMed Central

Kawasaki, Yuko; Chufan, Eduardo E.; Lafont, Virginie; Hidaka, Koushi; Kiso, Yoshiaki; Amzel, L. Mario; Freire, Ernesto

2011-01-01

Binding affinity optimization is critical during drug development. Here we evaluate the thermodynamic consequences of filling a binding cavity with functionalities of increasing van der Waals radii (-H, -F, -Cl and CH3) that improve the geometric fit without participating in hydrogen bonding or other specific interactions. We observe a binding affinity increase of two orders of magnitude. There appears to be three phases in the process. The first phase is associated with the formation of stable van der Waals interactions. This phase is characterized by a gain in binding enthalpy and a loss in binding entropy, attributed to a loss of conformational degrees of freedom. For the specific case presented in this paper, the enthalpy gain amounts to −1.5 kcal/mol while the entropic losses amount to +0.9 kcal/mol resulting in a net 3.5-fold affinity gain. The second phase is characterized by simultaneous enthalpic and entropic gains. This phase improves the binding affinity 25-fold. The third phase represents the collapse of the trend and is triggered by the introduction of chemical functionalities larger than the binding cavity itself (CH(CH3)2). It is characterized by large enthalpy and affinity losses. The thermodynamic signatures associated with each phase provide guidelines for lead optimization. PMID:20028396

Aquitard contaminant storage and flux resulting from dense nonaqueous phase liquid source zone dissolution and remediation

EPA Science Inventory

A one-dimensional diffusion model was used to investigate the effects of dense non-aqueous phase liquid (DNAPL) source zone dissolution and remediation on the storage and release of contaminants from aquitards. Source zone dissolution was represented by a power-law source depleti...

Aluminum Target Dissolution in Support of the Pu-238 Program

DOE Office of Scientific and Technical Information (OSTI.GOV)

McFarlane, Joanna; Benker, Dennis; DePaoli, David W

2014-09-01

Selection of an aluminum alloy for target cladding affects post-irradiation target dissolution and separations. Recent tests with aluminum alloy 6061 yielded greater than expected precipitation in the caustic dissolution step, forming up to 10 wt.% solids of aluminum hydroxides and aluminosilicates. We present a study to maximize dissolution of aluminum metal alloy, along with silicon, magnesium, and copper impurities, through control of temperature, the rate of reagent addition, and incubation time. Aluminum phase transformations have been identified as a function of time and temperature, using X-ray diffraction. Solutions have been analyzed using wet chemical methods and X-ray fluorescence. These datamore » have been compared with published calculations of aluminum phase diagrams. Temperature logging during the transients has been investigated as a means to generate kinetic and mass transport data on the dissolution process. Approaches are given to enhance the dissolution of aluminum and aluminosilicate phases in caustic solution.« less

Thermodynamic Re-modeling of the Sb-Te System Using Associate and Ionic Models

NASA Astrophysics Data System (ADS)

Guo, Cuiping; Li, Changrong; Du, Zhenmin

2014-11-01

The Sb-Te system is re-modeled using the calculation of phase diagram (CALPHAD) technique. The liquid phase is modeled as (Sb, Sb2Te3, Te) using the associate model and as (Sb3+) p (Te2-,Te,Va) q using the ionic model. The solution phases rhom(Sb) and hex(Te) are described as substitutional solutions. Two compounds, delta and gamma, are treated as (Sb)0.4(Sb,Te)0.6 according to their homogeneity ranges, while the compound Sb2Te3 follows a strict stoichiometry. A set of self-consistent thermodynamic parameters is obtained. Using these thermodynamic parameters, the experimental Sb-Te phase diagram, mixing enthalpies of liquid at 911 K and 935 K, activities of Sb and Te in liquid at 911 K and 1023 K, and Gibbs energy of liquid at 911 K, is well reproduced by the calculations. And the calculated enthalpy of formation, enthalpy of fusion, and heat capacity of Sb2Te3 are also in fairly good agreement with all the available experimental data.

Determination of ideal-gas enthalpies of formation for key compounds:

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steele, W.V.; Chirico, R.D.; Nguyen, A.

1991-10-01

The results of a study aimed at improvement of group-contribution methodology for estimation of thermodynamic properties of organic and organosilicon substances are reported. Specific weaknesses where particular group-contribution terms were unknown, or estimated because of lack of experimental data, are addressed by experimental studies of enthalpies of combustion in the condensed phase, vapor-pressure measurements, and differential scanning calorimetric (d.s.c.) heat-capacity measurements. Ideal-gas enthalpies of formation of ({plus minus})-butan-2-ol, tetradecan-1-ol, hexan-1,6-diol, methacrylamide, benzoyl formic acid, naphthalene-2,6-dicarboxylic acid dimethyl ester, and tetraethylsilane are reported. A crystalline-phase enthalpy of formation at 298.15 K was determined for naphthalene-2,6-dicarboxylic acid, which decomposed at 695 Kmore » before melting. The combustion calorimetry of tetraethylsilane used the proven fluorine-additivity methodology. Critical temperature and critical density were determined for tetraethylsilane with differential scanning calorimeter and the critical pressure was derived. Group-additivity parameters useful in the application of group- contribution correlations are derived. 112 refs., 13 figs., 19 tabs.« less

Development of a biphasic dissolution test for Deferasirox dispersible tablets and its application in establishing an in vitro-in vivo correlation.

PubMed

Al Durdunji, Amal; AlKhatib, Hatim S; Al-Ghazawi, Mutasim

2016-05-01

In a biphasic dissolution medium, the integration of the in vitro dissolution of a drug in an aqueous phase and its subsequent partitioning into an organic phase is hypothesized to simulate the in vivo drug absorption. Such a methodology is expected to improve the probability of achieving a successful in vitro-in vivo correlation. Dissolution of Dispersible tablets of Deferasirox, a biopharmaceutics classification system type II compound, was studied in a biphasic dissolution medium using a flow-through dissolution apparatus coupled to a paddle apparatus. The experimental parameters associated with dissolution were optimized to discriminate between Deferasirox dispersible tablets of different formulations. The dissolution profiles obtained from this system were subsequently used to construct a level A in vitro-in vivo correlation. Copyright © 2016 Elsevier B.V. All rights reserved.

Determination of molar enthalpy of sublimation in case of orotic acid as obtained from experimental and computational data

NASA Astrophysics Data System (ADS)

Marochkin, Ilya I.; Altova, Ekaterina P.; Chilingarov, Norbert S.; Vilkova, Anna L.; Shishkov, Igor F.

2018-03-01

Saturated vapor pressure, ln(p/Pa) = (-21316 ± 511)/(T/K)+(41.64 ± 0.11), and enthalpy of sublimation of orotic acid, Δsub Hm0 (Tm) = 177 ± 4 kJ/mol, were determined by means of Knudsen effusion mass spectrometry in the temperature range of 423÷493 K. The computational approaches supported the experimental results reported. The theoretical estimation of the gas-phase enthalpy of formation for orotic acid was done with different working reactions used.

Preparation and characterization of Phase change material microcapsules by a core-shell-like emulsion polymerization method

NASA Astrophysics Data System (ADS)

Ding, Li-ming; Pei, Guang-ling

2015-07-01

Phase change material microcapsules (MicroPCMs) were synthesized by a coreshell-like emulsion polymerization method. Styrene and methylacrylic acid copolymer (PS- MAA) was used as a wall material, and paraffin was used as a core material in order to prepare spherical, high resistance and high enthalpy MicroPCMs. Scanning Electron Microscope (SEM), laser particle size analyzer, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetry (TG) and Differential Scanning Calorimeter (DSC) were employed to characterize the MicroPCMs. The results indicated that the average particle size of MicroPCMs was 42.29 μm, and the content of paraffin within microcapsules was 57.6%. The melting temperature and crystallization temperature were 30.7°C and 25.2°C.The melting enthalpy and crystallization enthalpy were -84.1 J/g and 91.3 J/g, respectively.

High-pressure hydrogen sulfide by diffusion quantum Monte Carlo.

PubMed

Azadi, Sam; Kühne, Thomas D

2017-02-28

We revisit the enthalpy-pressure phase diagram of the various products from the different proposed decompositions of H 2 S at pressures above 150 GPa by means of accurate diffusion Monte Carlo simulations. Our results entail a revision of the ground-state enthalpy-pressure phase diagram. Specifically, we find that the C2/c HS 2 structure is persistent up to 440 GPa before undergoing a phase transition into the C2/m phase. Contrary to density functional theory, our calculations suggest that the C2/m phase of HS is more stable than the I4 1 /amd HS structure over the whole pressure range from 150 to 400 GPa. More importantly, we predict that the Im-3m phase is the most likely candidate for H 3 S, which is consistent with recent experimental x-ray diffraction measurements.

Entropic Description of Gas Hydrate Ice-Liquid Equilibrium via Enhanced Sampling of Coexisting Phases

NASA Astrophysics Data System (ADS)

Małolepsza, Edyta; Kim, Jaegil; Keyes, Tom

2015-05-01

Metastable β ice holds small guest molecules in stable gas hydrates, so its solid-liquid equilibrium is of interest. However, aqueous crystal-liquid transitions are very difficult to simulate. A new molecular dynamics algorithm generates trajectories in a generalized N P T ensemble and equilibrates states of coexisting phases with a selectable enthalpy. With replicas spanning the range between β ice and liquid water, we find the statistical temperature from the enthalpy histograms and characterize the transition by the entropy, introducing a general computational procedure for first-order transitions.

Entropic description of gas hydrate ice/liquid equilibrium via enhanced sampling of coexisting phases

DOE PAGES

Malolepsza, Edyta; Kim, Jaegil; Keyes, Tom

2015-04-28

Metastable β ice holds small guest molecules in stable gas hydrates, so its solid/liquid equilibrium is of interest. However, aqueous crystal/liquid transitions are very difficult to simulate. A new MD algorithm generates trajectories in a generalized NPT ensemble and equilibrates states of coexisting phases with a selectable enthalpy. Furthermore, with replicas spanning the range between β ice and liquid water we find the statistical temperature from the enthalpy histograms and characterize the transition by the entropy, introducing a general computational procedure for first-order transitions.

Energetic studies and phase diagram of thioxanthene.

PubMed

Freitas, Vera L S; Monte, Manuel J S; Santos, Luís M N B F; Gomes, José R B; Ribeiro da Silva, Maria D M C

2009-11-19

The molecular stability of thioxanthene, a key species from which very important compounds with industrial relevance are derived, has been studied by a combination of several experimental techniques and computational approaches. The standard (p degrees = 0.1 MPa) molar enthalpy of formation of crystalline thioxanthene (117.4 +/- 4.1 kJ x mol(-1)) was determined from the experimental standard molar energy of combustion, in oxygen, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The enthalpy of sublimation was determined by a direct method, using the vacuum drop microcalorimetric technique, and also by an indirect method, using a static apparatus, where the vapor pressures at different temperatures were measured. The latter technique was used for both crystalline and undercooled liquid samples, and the phase diagram of thioxanthene near the triple point was obtained (triple point coordinates T = 402.71 K and p = 144.7 Pa). From the two methods, a mean value for the standard (p degrees = 0.1 MPa) molar enthalpy of sublimation, at T = 298.15 K (101.3 +/- 0.8 kJ x mol(-1)), was derived. From the latter value and from the enthalpy of formation of the solid, the standard (p degrees = 0.1 MPa) enthalpy of formation of gaseous thioxanthene was calculated as 218.7 +/- 4.2 kJ x mol(-1). Standard ab initio molecular orbital calculations were performed using the G3(MP2)//B3LYP composite procedure and several homodesmotic reactions in order to derive the standard molar enthalpy of formation of thioxanthene. The ab initio results are in excellent agreement with the experimental data.

The thermochemistry of cubane 50 years after its synthesis: a high-level theoretical study of cubane and its derivatives.

PubMed

Agapito, Filipe; Santos, Rui C; Borges dos Santos, Rui M; Martinho Simões, José A

2015-03-26

The gas-phase enthalpy of formation of cubane (603.4 ± 4 kJ mol(-1)) was calculated using an explicitly correlated composite method (W1-F12). The result obtained for cubane, together with the experimental value for the enthalpy of sublimation, 54.8 ± 2.0 kJ mol(-1), led to 548.6 ± 4.5 kJ mol(-1) for the solid-phase enthalpy of formation. This value is only 6.8 kJ mol(-1) higher than the 50-year-old original calorimetric result. The carbon-hydrogen bond dissociation enthalpy (C-H BDE) of cubane (438.4 ± 4 kJ mol(-1)), together with properties relevant for its experimental determination using gas-phase ion thermochemistry, namely the cubane gas-phase acidity (1704.6 ± 4 kJ mol(-1)), cubyl radical electron affinity (45.8 ± 4 kJ mol(-1)), cubane ionization energy (1435.1 ± 4 kJ mol(-1)), cubyl radical cation proton affinity (918.8 ± 4 kJ mol(-1)), cubane cation appearance energy (1099.6 ± 4 kJ mol(-1)), and cubyl ionization energy (661.2 ± 4 kJ mol(-1)), were also determined. These values were compared with those calculated for unstrained hydrocarbons (viz., methane, ethane, and isobutane). The strain energy of cubane (667.2 kJ mol(-1)) and cubyl radical (689.4 kJ mol(-1)) were independently estimated via quasihomodesmotic reactions. These values were related via a simple model to the C-H BDE in cubane. Taking into account the accuracy of the computational method, the comparison with high-precision experimental results, and the data consistency afforded by the relevant thermodynamic cycles, we claim an uncertainty better than ±4 kJ mol(-1) for the new enthalpy of formation values presented.

Moisture-Induced Amorphous Phase Separation of Amorphous Solid Dispersions: Molecular Mechanism, Microstructure, and Its Impact on Dissolution Performance.

PubMed

Chen, Huijun; Pui, Yipshu; Liu, Chengyu; Chen, Zhen; Su, Ching-Chiang; Hageman, Michael; Hussain, Munir; Haskell, Roy; Stefanski, Kevin; Foster, Kimberly; Gudmundsson, Olafur; Qian, Feng

2018-01-01

Amorphous phase separation (APS) is commonly observed in amorphous solid dispersions (ASD) when exposed to moisture. The objective of this study was to investigate: (1) the phase behavior of amorphous solid dispersions composed of a poorly water-soluble drug with extremely low crystallization propensity, BMS-817399, and PVP, following exposure to different relative humidity (RH), and (2) the impact of phase separation on the intrinsic dissolution rate of amorphous solid dispersion. Drug-polymer interaction was confirmed in ASDs at different drug loading using infrared (IR) spectroscopy and water vapor sorption analysis. It was found that the drug-polymer interaction could persist at low RH (≤75% RH) but was disrupted after exposure to high RH, with the advent of phase separation. Surface morphology and composition of 40/60 ASD at micro-/nano-scale before and after exposure to 95% RH were also compared. It was found that hydrophobic drug enriched on the surface of ASD after APS. However, for the 40/60 ASD system, the intrinsic dissolution rate of amorphous drug was hardly affected by the phase behavior of ASD, which may be partially attributed to the low crystallization tendency of amorphous BMS-817399 and enriched drug amount on the surface of ASD. Intrinsic dissolution rate of PVP decreased resulting from APS, leading to a lower concentration in the dissolution medium, but supersaturation maintenance was not anticipated to be altered after phase separation due to the limited ability of PVP to inhibit drug precipitation and prolong the supersaturation of drug in solution. This study indicated that for compounds with low crystallization propensity and high hydrophobicity, the risk of moisture-induced APS is high but such phase separation may not have profound impact on the drug dissolution performance of ASDs. Therefore, application of ASD technology on slow crystallizers could incur low risks not only in physical stability but also in dissolution performance. Copyright © 2018 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Ion migration in crystalline and amorphous HfOX

NASA Astrophysics Data System (ADS)

Schie, Marcel; Müller, Michael P.; Salinga, Martin; Waser, Rainer; De Souza, Roger A.

2017-03-01

The migration of ions in HfOx was investigated by means of large-scale, classical molecular-dynamics simulations over the temperature range 1000 ≤T /K ≤2000 . Amorphous HfOx was studied in both stoichiometric and oxygen-deficient forms (i.e., with x = 2 and x = 1.9875); oxygen-deficient cubic and monoclinic phases were also studied. The mean square displacement of oxygen ions was found to evolve linearly as a function of time for the crystalline phases, as expected, but displayed significant negative deviations from linear behavior for the amorphous phases, that is, the behavior was sub-diffusive. That oxygen-ion migration was observed for the stoichiometric amorphous phase argues strongly against applying the traditional model of vacancy-mediated migration in crystals to amorphous HfO2. In addition, cation migration, whilst not observed for the crystalline phases (as no cation defects were present), was observed for both amorphous phases. In order to obtain activation enthalpies of migration, the residence times of the migrating ions were analyzed. The analysis reveals four activation enthalpies for the two amorphous phases: 0.29 eV, 0.46 eV, and 0.66 eV (values very close to those obtained for the monoclinic structure) plus a higher enthalpy of at least 0.85 eV. In comparison, the cubic phase is characterized by a single value of 0.43 eV. Simple kinetic Monte Carlo simulations suggest that the sub-diffusive behavior arises from nanoscale confinement of the migrating ions.

Experimental and computational thermochemical study of α-alanine (DL) and β-alanine.

PubMed

da Silva, Manuel A V Ribeiro; da Silva, Maria das Dores M C Ribeiro; Santos, Ana Filipa L O M; Roux, Maria Victoria; Foces-Foces, Concepción; Notario, Rafael; Guzmán-Mejía, Ramón; Juaristi, Eusebio

2010-12-16

This paper reports an experimental and theoretical study of the gas phase standard (p° = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, of α-alanine (DL) and β-alanine. The standard (p° = 0.1 MPa) molar enthalpies of formation of crystalline α-alanine (DL) and β-alanine were calculated from the standard molar energies of combustion, in oxygen, to yield CO2(g), N2(g), and H2O(l), measured by static-bomb combustion calorimetry at T = 298.15 K. The vapor pressures of both amino acids were measured as function of temperature by the Knudsen effusion mass-loss technique. The standard molar enthalpies of sublimation at T = 298.15 K was derived from the Clausius−Clapeyron equation. The experimental values were used to calculate the standard (p° = 0.1 MPa) enthalpy of formation of α-alanine (DL) and β-alanine in the gaseous phase, Δ(f)H(m)°(g), as −426.3 ± 2.9 and −421.2 ± 1.9 kJ·mol(−1), respectively. Standard ab initio molecular orbital calculations at the G3 level were performed. Enthalpies of formation, using atomization reactions, were calculated and compared with experimental data. Detailed inspections of the molecular and electronic structures of the compounds studied were carried out.

Dissolution and Separation of Aluminum and Aluminosilicates

DOE PAGES

McFarlane, Joanna; Benker, Dennis; DePaoli, David W.; ...

2015-12-19

The selection of an aluminum alloy for target irradiation affects post-irradiation target dissolution and separations. Recent tests with aluminum alloy 6061 yielded greater than expected precipitation in the dissolver, forming up to 10 wt.% solids of aluminum hydroxides and aluminosilicates. Aluminosilicate dissolution presents challenges in a number of different areas, metals extraction from minerals, flyash treatment, and separations from aluminum alloys. We present experimental work that attempts to maximize dissolution of aluminum metal, along with silicon, magnesium, and copper impurities, through control of temperature, the rate of reagent addition, and incubation time. Aluminum phase transformations have been identified as amore » function of time and temperature, using X-ray diffraction. Solutions have been analyzed using wet chemical methods and X-ray fluorescence. Our data have been compared with published calculations of aluminum phase diagrams. Approaches are given to enhance the dissolution of aluminum and aluminosilicate phases in caustic solution.« less

Spontaneous crystalline-to-amorphous phase transformation of organic or medicinal compounds in the presence of porous media, part 2: amorphization capacity and mechanisms of interaction.

PubMed

Qian, Ken K; Suib, Steven L; Bogner, Robin H

2011-11-01

Amorphization of crystalline compounds using mesoporous media is a promising technique to improve the solubility and dissolution rate of poorly soluble compounds. The objective of this paper is to determine the capacity of amorphization and understand the mechanisms of phase transformation. Commercial grades of mesoporous silicon dioxide (SiO(2)) samples (5- to 30-nm mean pore diameters) with either constant surface area or constant pore volume were used. The amorphization capacity of naphthalene was not proportional to either the surface area or the pore volume measured using adsorption chambers. Instead, the amorphization capacity correlated with surface curvature, that is, the smaller the pore diameter and the higher the surface curvature, the greater the amorphization capacity. The change in surface chemistry due to a highly curved surface may be responsible for the enhanced amorphization capacity as well. The amorphization of crystalline compounds was facilitated through capillary condensation, with the decrease in pore volume as the direct experimental evidence. The amorphization capacity was also enhanced by the dipole-dipole or dipole-induced dipole interaction, promoted by the hydroxyl groups on the surface of SiO(2). The enthalpy of vapor-solid condensation of crystalline compounds was a useful indicator to predict the rank order of amorphization capacity. Copyright © 2011 Wiley-Liss, Inc.

The properties of clusters in the gas phase. IV - Complexes of H2O and HNOx clustering on NOx/-/

NASA Technical Reports Server (NTRS)

Lee, N.; Castleman, A. W., Jr.; Keesee, R. G.

1980-01-01

Thermodynamic quantities for the gas-phase clustering equilibria of NO2(-) and NO3(-) were determined with high-pressure mass spectrometry. A comparison of values of the free energy of hydration derived from the data shows good agreement with formerly reported values at 296 K. New data for larger NO2(-) and NO3(-) hydrates as well as NO2(-)(HNO2)n were obtained in this study. To aid in understanding the bonding and stability of the hydrates of nitrite and nitrate ions, CNDO/2 calculations were performed, and the results are discussed. A correlation between the aqueous-phase total hydration enthalpy of a single ion and its gas-phase hydration enthalpy was obtained. Atmospheric implications of the data are also briefly discussed.

Development of a discriminative biphasic in vitro dissolution test and correlation with in vivo pharmacokinetic studies for differently formulated racecadotril granules.

PubMed

Deng, Jia; Staufenbiel, Sven; Hao, Shilei; Wang, Bochu; Dashevskiy, Andriy; Bodmeier, Roland

2017-06-10

The purpose of this study was to discriminate the release behavior from three differently formulated racecadotril (BCS II) granules and to establish an in vitro-in vivo correlation. Three granule formulations of the lipophilic drug were prepared with equivalent composition but prepared with different manufacturing processes (dry granulation, wet granulation with or without binder). In vitro release of the three granules was investigated using a biphasic dissolution system (phosphate buffer pH6.8 and octanol) and compared to the conventional single phase USP II dissolution test performed under sink and non-sink conditions. In vivo studies with each granule formulation were performed in rats. Interestingly, the granule formulations exhibited pronouncedly different behavior in the different dissolution systems depending on different wetting and dissolution conditions. Single phase USP II dissolution tests lacked discrimination. In contrast, remarkable discrimination between the granule formulations was observed in the octanol phase of biphasic dissolution system with a rank order of release from granules prepared by wet granulation with binder>wet granulation without binder>dry granulation. This release order correlated well with the wettability of these granules. An excellent correlation was also established between in vitro release in the octanol phase of the biphasic test and in vivo data (R 2 =0.999). Compared to conventional dissolution methods, the biphasic method provides great potential to discriminate between only minor formulation and process changes within the same dosage form for poorly soluble drugs. Copyright © 2017 Elsevier B.V. All rights reserved.

Investigation of wood combustion in the high-enthalpy oxidizer flow

NASA Astrophysics Data System (ADS)

Reshetnikov, S. M.; Zyryanov, I. A.; Budin, A. G.; Pozolotin, A. P.

2017-01-01

The experimental data of wood combustion in the high-enthalpy oxidizer flowresearch is presented. Combustion laws of two wood species (pine and birch) in a hybrid rocket engine (HRE) are obtained. Heat flows from the flame to the condensed phase surface are defined. The prospects of the wood use in the HRE (based on thrust characteristics) are shown.

Thermodynamic evidence of flexibility in H2O and CO2 absorption of transition metal ion exchanged zeolite LTA.

PubMed

Guo, Xin; Wu, Lili; Navrotsky, Alexandra

2018-02-07

Gas absorption calorimetry has been employed to probe the intercation of water and carbon dioxide with transition metal ion (TM = Mn 2+ , Fe 2+ , Co 2+ , Cu 2+ , and Zn 2+ ) exchanged zeolite A samples. There appears to be a two-phase region, indicative of a guest-induced flexibility transition, separating hydrated zeolite A and its dehydrated form, both of which have variable water content in the single phase region. The differential enthalpy of absorption as a function of water loading directly identifies different strengths of multiple interactions along with possible binding mechanisms of Zn-A and Mn-A exhibiting the highest water absorption with most exothermic initial enthalpies of -125.28 ± 4.82 and -115.30 ± 2.56 kJ mol -1 . Zn-A and Mn-A also show moderately good capture ability for CO 2 with zero-coverage negative enthalpies of -55.59 ± 2.48 and -44.07 ± 1.53 kJ mol -1 . The thermodynamic information derived from differential enthalpy, chemical potential and differential entropy elucidated the multistage interactive behavior of small guest molecules (H 2 O/CO 2 ) and ion-exchanged frameworks.

Structure-energy relationship in barbituric acid: a calorimetric, computational, and crystallographic study.

PubMed

Roux, María Victoria; Temprado, Manuel; Notario, Rafael; Foces-Foces, Concepción; Emel'yanenko, Vladimir N; Verevkin, Sergey P

2008-08-14

This paper reports the value of the standard (p(o) = 0.1 MPa) molar enthalpy of formation in the gas phase at T = 298.15 K for barbituric acid. The enthalpies of combustion and sublimation were measured by static bomb combustion calorimetry and transference (transpiration) method in a saturated N2 stream and a gas-phase enthalpy of formation value of -(534.3 +/- 1.7) kJ x mol(-1) was determined at T = 298.15 K. G3-calculated enthalpies of formation are in very good agreement with the experimental value. The behavior of the sample as a function of the temperature was studied by differential scanning calorimetry, and a new polymorph of barbituric acid at high temperature was found. In the solid state, two anhydrous forms are known displaying two out of the six hydrogen-bonding patterns observed in the alkyl/alkenyl derivatives retrieved from the Cambridge Crystallographic Database. The stability of these motifs has been analyzed by theoretical calculations. X-ray powder diffraction technique was used to establish to which polymorphic form corresponds to the commercial sample used in this study and to characterize the new form at high temperature.

Thermophysical Characterization of MgCl₂·6H₂O, Xylitol and Erythritol as Phase Change Materials (PCM) for Latent Heat Thermal Energy Storage (LHTES).

PubMed

Höhlein, Stephan; König-Haagen, Andreas; Brüggemann, Dieter

2017-04-24

The application range of existing real scale mobile thermal storage units with phase change materials (PCM) is restricted by the low phase change temperature of 58 ∘ C for sodium acetate trihydrate, which is a commonly used storage material. Therefore, only low temperature heat sinks like swimming pools or greenhouses can be supplied. With increasing phase change temperatures, more applications like domestic heating or industrial process heat could be operated. The aim of this study is to find alternative PCM with phase change temperatures between 90 and 150 ∘ C . Temperature dependent thermophysical properties like phase change temperatures and enthalpies, densities and thermal diffusivities are measured for the technical grade purity materials xylitol (C 5 H 12 O 5 ), erythritol (C 4 H 10 O 4 ) and magnesiumchloride hexahydrate (MCHH, MgCl 2 · 6H 2 O). The sugar alcohols xylitol and erythritol indicate a large supercooling and different melting regimes. The salt hydrate MgCl 2 · 6H 2 O seems to be a suitable candidate for practical applications. It has a melting temperature of 115.1 ± 0.1 ∘ C and a phase change enthalpy of 166.9 ± 1.2 J / g with only 2.8 K supercooling at sample sizes of 100 g . The PCM is stable over 500 repeated melting and solidification cycles at differential scanning calorimeter (DSC) scale with only small changes of the melting enthalpy and temperature.

Biopharmaceutical characterisation of ciprofloxacin-metallic ion interactions: comparative study into the effect of aluminium, calcium, zinc and iron on drug solubility and dissolution.

PubMed

Stojković, Aleksandra; Tajber, Lidia; Paluch, Krzysztof J; Djurić, Zorica; Parojčić, Jelena; Corrigan, Owen I

2014-03-01

Ciprofloxacin bioavailability may be reduced when ciprofloxacin is co-administered with metallic ion containing preparations. In our previous study, physicochemical interaction between ciprofloxacin and ferrous sulphate was successfully simulated in vitro. In the present work, comparative in vitro ciprofloxacin solubility and dissolution studies were performed in the reactive media containing aluminium hydroxide, calcium carbonate or zinc sulphate. Solid phases collected from the dissolution vessel with aluminium hydroxide, calcium carbonate and zinc sulphate were investigated for their properties. The results obtained indicate that different types of adducts may form and retard ciprofloxacin solubility and dissolution. In the case of aluminium, no phase changes were observed. The solid phase generated in the presence of calcium carbonate was identified as hydrated ciprofloxacin base. Similarly to iron, a new complex consistent with Zn(SO4)2(Cl)2(ciprofloxacin)2 × nH2O stoichiometry was generated in the presence of relatively high concentrations of ciprofloxacin hydrochloride and zinc sulphate, indicating that small volume dissolution experiments can be useful for biorelevant dissolution tests.

Effects of ammonium on uranium partitioning and kaolinite mineral dissolution.

PubMed

Emerson, Hilary P; Di Pietro, Silvina; Katsenovich, Yelena; Szecsody, Jim

2017-02-01

Ammonia gas injection is a promising technique for the remediation of uranium within the vadose zone. It can be used to manipulate the pH of a system and cause co-precipitation processes that are expected to remove uranium from the aqueous phase and decrease leaching from the solid phase. The work presented in this paper explores the effects of ammonium and sodium hydroxide on the partitioning of uranium and dissolution of the kaolinite mineral in simplified synthetic groundwaters using equilibrium batch sorption and sequential extraction experiments. It shows that there is a significant increase in uranium removal in systems with divalent cations present in the aqueous phase but not in sodium chloride synthetic groundwaters. Further, the initial conditions of the aqueous phase do not affect the dissolution of kaolinite. However, the type of base treatment does have an effect on mineral dissolution. Published by Elsevier Ltd.

Use of the co-grinding method to enhance the dissolution behavior of a poorly water-soluble drug: generation of solvent-free drug-polymer solid dispersions.

PubMed

Yang, Caiqin; Xu, Xiujuan; Wang, Jing; An, Zhiqian

2012-01-01

The solid dispersion (SD) technique is the most effective method for improving the dissolution rate of poorly water-soluble drugs. In the present work, SDs of the Ca2+ channel blocker dipfluzine (DF) with polyvinylpyrrolidone K30 (PVP) and poloxamer 188 (PLXM) were prepared by the powder solid co-grinding method under a solvent-free condition. The properties of all SDs and physical mixtures were investigated by X-ray diffraction, Fourier-transform infrared, differential scanning calorimetry, scanning electron microscopy, dissolution test, and particles size determination. Eutectic compounds were produced between the DF and PLXM matrix during the co-grinding process, whereas glass suspension formed in the SDs with PVP carrier. Hydrogen bond formation was not observed between DF and carriers and DF was microcrystalline state in the PVP and PLXM matrices. The solubility of DF in different concentration of carriers at 25, 31, and 37°C was investigated; the values obtained were used to calculate the thermodynamic parameters of interaction between DF and carriers. The Gibbs free energy (ΔrGθ) values were negative, indicating the spontaneous nature of dispersing DF into the carriers. Moreover, entropy is the drive force when DF disperses into the matrix of PVP, while, enthalpy-driven dispersing encounters in the PLXM carrier. All the SDs of DF/carriers showed a considerably higher dissolution rate than pure DF and the corresponding physical mixtures. The cumulative dissolution rate at 10 min of the SD with a 1 : 3 DF/carrier ratio increased 5.1-fold for PVP and 5.5-fold for PLXM.

Enthalpy-based equation of state for highly porous materials employing modified soft sphere fluid model

NASA Astrophysics Data System (ADS)

Nayak, Bishnupriya; Menon, S. V. G.

2018-01-01

Enthalpy-based equation of state based on a modified soft sphere model for the fluid phase, which includes vaporization and ionization effects, is formulated for highly porous materials. Earlier developments and applications of enthalpy-based approach had not accounted for the fact that shocked states of materials with high porosity (e.g., porosity more than two for Cu) are in the expanded fluid region. We supplement the well known soft sphere model with a generalized Lennard-Jones formula for the zero temperature isotherm, with parameters determined from cohesive energy, specific volume and bulk modulus of the solid at normal condition. Specific heats at constant pressure, ionic and electronic enthalpy parameters and thermal excitation effects are calculated using the modified approach and used in the enthalpy-based equation of state. We also incorporate energy loss from the shock due to expansion of shocked material in calculating porous Hugoniot. Results obtained for Cu, even up to initial porosities ten, show good agreement with experimental data.

Variation in Supersaturation and Phase Behavior of Ezetimibe Amorphous Solid Dispersions upon Dissolution in Different Biorelevant Media.

PubMed

Elkhabaz, Ahmed; Sarkar, Sreya; Dinh, Janny K; Simpson, Garth J; Taylor, Lynne S

2018-01-02

The delivery of poorly water-soluble drugs using amorphous solid dispersions (ASDs) has been widely acknowledged as a promising strategy for enhancing oral bioavailability. Upon dissolution, ASDs have accelerated dissolution rates and yield supersaturated solutions leading to higher apparent solubilities. Understanding the complex phase behavior of ASDs during dissolution is crucial for developing an effective formulation. Since the absorption of a lipophilic, high permeability drug is determined primarily by the intraluminal dissolution process and the final concentration achieved, there is a need for evaluation in biorelevant dissolution media that simulate both fasting and fed gastrointestinal states. In this study, using ezetimibe as a model drug, three different ASDs were prepared using poly(acrylic acid) (PAA), polyvinylpyrrolidone (PVP), and hydroxypropyl methylcellulose acetyl succinate (HPMC-AS). Dissolution of ASDs was carried out in sodium phosphate buffer, fed-state simulated intestinal fluid (FeSSIF), and Ensure Plus to evaluate the impact of different dissolution media on release profile, supersaturation, and phase behavior. The supersaturation level and crystallization kinetics varied among the dispersions and were found to be highly dependent on the medium employed. The presence of solubilizing additives in biorelevant media greatly affected the generation and stabilization of supersaturated solutions. Second harmonic generation microscopy was found to enable the detection of crystals in all media including the highly turbid Ensure Plus system. In conclusion, it is important to evaluate the impact of complex biorelevant media on the dissolution performance of ASDs to better design supersaturating formulations for oral delivery.

Thermodynamic characteristics of protolytic equilibria of L-serine in aqueous solutions

NASA Astrophysics Data System (ADS)

Kochergina, L. A.; Volkov, A. V.; Khokhlova, E. A.; Krutova, O. N.

2011-05-01

The heat effects of the reaction of aqueous solution of L-serine with aqueous solutions of HNO3 and KOH were determined by calorimetry at temperatures of 288.15, 298.15, and 308.15 K, and ionic strength values of 0.2, 0.5, and 1.0 (background electrolyte, KNO3). Standard thermodynamic characteristics (Δr H o, Δr G o, Δr S o, Δ C {/p o}) of the acid-base reactions in aqueous solutions of L-serine were calculated. The effect of the concentration of background electrolyte and temperature on the heats of dissociation of amino acid was considered. The combustion energy of L-serine by bomb calorimetry in the medium of oxygen was determined. The standard combustion and formation enthalpies of crystalline L-serine were calculated. The heats of dissolution of crystalline L-serine in water and solutions of potassium hydroxide at 298.15 K were measured by direct calorimetry. The standard enthalpies of formation of L-serine and products of its dissociation in aqueous solution were calculated.

Characterization of two polymorphs of salmeterol xinafoate crystallized from supercritical fluids.

PubMed

Tong, H H; Shekunov, B Y; York, P; Chow, A H

2001-06-01

To characterize two polymorphs of salmeterol xinafoate (SX-I and SX-II) produced by supercritical fluid crystallization. SX-I and SX-II were crystallized as fine powders using Solution Enhanced Dispersion by Supercritical Fluids (SEDS). The two polymorphs and a reference micronized SX sample (MSX) were characterized using powder X-ray diffractometry (PXRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), aqueous solubility (and dissolution) determination at 5-40 degrees C, BET adsorption analysis, and inverse gas chromatography (IGC). Compared with SX-I, SX-II exhibited a lower enthalpy of fusion, a higher equilibrium solubility, a higher intrinsic dissolution rate, a lower enthalpy of solution (based on van't Hoff solubility plots), and a different FTIR spectrum (reflecting differences in intermolecular hydrogen bonding). Solubility ratio plot yielded a transition temperature (-99 degrees C) below the melting points of both polymorphs. MSX showed essentially the same crystal form as SX-I (confirmed by PXRD and FTIR), but a distinctly different thermal behaviour. Mild trituration of SX-I afforded a similar DSC profile to MSX while prolonged grinding of SX-I gave rise to an endotherm at -109 degrees C, corresponding to solid-solid transition of SX-I to SX-II. Surface analysis of MSX, SX-I, and SX-II by IGC revealed significant differences in surface free energy in terms of both dispersive (nonpolar) interactions and specific (polar) acid-base properties. The SEDS-processed SX-I and SX-II display high polymorphic purity and distinctly different physical and surface properties. The polymorphs are related enantiotropically with SX-I being the thermodynamically stable form at room temperature.

A unified analysis of solidification in Bridgman crystal growth

NASA Astrophysics Data System (ADS)

Lu, Ming-Fang

2012-04-01

The simulation of multiphase solidification process can be handled by combining the VOF (Volume of Fluid) transport equation, in which the continuum mechanics model is used to simulate the melt/solid interface and the conservation of mass, momentum, and energy. Because the melt phase, the solid phase, and the melt/solid interface are controlled by a single control equation; if the enthalpy model based on porosity concept represents the processing of the phase transformation range, it is possible to solve the problem of phase transformation in the same way as solving the single-phase problem. Once the energy field of enthalpy for each step in time is resolved, the position of the interface can be precisely calculated with the use of VOF equation. This type of novel VOF method can be applied to find out the conditions of vertical Bridgman crystal growing located on the earth or under microgravity.

A unified analysis of solidification in Bridgman crystal growth

NASA Astrophysics Data System (ADS)

Lu, Ming-Fang

2011-11-01

The simulation of multiphase solidification process can be handled by combining the VOF (Volume of Fluid) transport equation, in which the continuum mechanics model is used to simulate the melt/solid interface and the conservation of mass, momentum, and energy. Because the melt phase, the solid phase, and the melt/solid interface are controlled by a single control equation; if the enthalpy model based on porosity concept represents the processing of the phase transformation range, it is possible to solve the problem of phase transformation in the same way as solving the single-phase problem. Once the energy field of enthalpy for each step in time is resolved, the position of the interface can be precisely calculated with the use of VOF equation. This type of novel VOF method can be applied to find out the conditions of vertical Bridgman crystal growing located on the earth or under microgravity.

Improvement of glass-forming ability and phase separation in Cu Ti-rich

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, E S; Chang, H J; Kim, D H

2010-01-01

Present study reports improvement of glass-forming ability (GFA) and phase separation in Cu Ti-rich Cu Ti Zr Ni Si bulk metallic glasses (BMGs) by tailoring the constituent elements. The MA of metalloid element, Sn having relatively large negative enthalpy of mixing can lead to improve GFA (up to 8mm in diameter) as well as thermal stability (up toTx = 48K) by optimizing the substitution element. And the addition of elements having relatively large positive enthalpy of mixing (partial substitution of Zr or Ti with Y) can lead to the liquid state phase separation in Cu Ti Sn Zr Ni Simore » BMG, although the addition lead to drastic deterioration of the GFA.« less

Development and application of a biorelevant dissolution method using USP apparatus 4 in early phase formulation development.

PubMed

Fang, Jiang B; Robertson, Vivian K; Rawat, Archana; Flick, Tawnya; Tang, Zhe J; Cauchon, Nina S; McElvain, James S

2010-10-04

Dissolution testing is frequently used to determine the rate and extent at which a drug is released from a dosage form, and it plays many important roles throughout drug product development. However, the traditional dissolution approach often emphasizes its application in quality control testing and usually strives to obtain 100% drug release. As a result, dissolution methods are not necessarily biorelevant and meaningful application of traditional dissolution methods in the early phases of drug product development can be very limited. This article will describe the development of a biorelevant in vitro dissolution method using USP apparatus 4, biorelevant media, and real-time online UV analysis. Several case studies in the areas of formulation selection, lot-to-lot variability, and food effect will be presented to demonstrate the application of this method in early phase formulation development. This biorelevant dissolution method using USP apparatus 4 provides a valuable tool to predict certain aspects of the in vivo drug release. It can be used to facilitate the formulation development/selection for pharmacokinetic (PK) and clinical studies. It may also potentially be used to minimize the number of PK studies, and to aid in the design of more efficient PK and clinical studies.

Calorimetric Determination of Thermodynamic Stability of MAX and MXene Phases

DOE PAGES

Sharma, Geetu; Naguib, Michael; Feng, Dawei; ...

2016-11-19

MXenes are layered two dimensional materials with exciting properties useful to a wide range of energy applications. They are derived from ceramics (MAX phases) by leaching and their properties reflect their resulting complex compositions which include intercalating cations and anions and water. Their thermodynamic stability is likely linked to these functional groups but has not yet been addressed by quantitative experimental measurements. We report enthalpies of formation from the elements at 25 °C measured using high temperature oxide melt solution calorimetry for a layered Ti-Al-C MAX phase, and the corresponding Ti-C based MXene. The thermodynamic stability of the Ti 3Cmore » 2T x MXene (Tx stands for anionic surface moieties, and intercalated cations) was assessed by calculating the enthalpy of reaction of the MAX phase (ideal composition Ti 3AlC 2) to form MXene, The very exothermic enthalpy of reaction confirms the stability of MXene in an aqueous environment. The surface terminations (O, OH and F) and cations (Li) chemisorbed on the surface and intercalated in the interlayers play a major role in the thermodynamic stabilization of MXene. These findings help to understand and potentially improve properties and performance by characterizing the energetics of species binding to MXene surfaces during synthesis and in energy storage, water desalination and other applications.« less

Determination of methane concentrations in water in equilibrium with sI methane hydrate in the absence of a vapor phase by in situ Raman spectroscopy

USGS Publications Warehouse

Lu, W.; Chou, I.-Ming; Burruss, R.C.

2008-01-01

Most submarine gas hydrates are located within the two-phase equilibrium region of hydrate and interstitial water with pressures (P) ranging from 8 to 60 MPa and temperatures (T) from 275 to 293 K. However, current measurements of solubilities of methane in equilibrium with hydrate in the absence of a vapor phase are limited below 20 MPa and 283.15 K, and the differences among these data are up to 30%. When these data were extrapolated to other P-T conditions, it leads to large and poorly known uncertainties. In this study, in situ Raman spectroscopy was used to measure methane concentrations in pure water in equilibrium with sI (structure one) methane hydrate, in the absence of a vapor phase, at temperatures from 276.6 to 294.6 (??0.3) K and pressures at 10, 20, 30 and 40 (??0.4%) MPa. The relationship among concentration of methane in water in equilibrium with hydrate, in mole fraction [X(CH4)], the temperature in K, and pressure in MPa was derived as: X(CH4) = exp [11.0464 + 0.023267 P - (4886.0 + 8.0158 P)/T]. Both the standard enthalpy and entropy of hydrate dissolution at the studied T-P conditions increase slightly with increasing pressure, ranging from 41.29 to 43.29 kJ/mol and from 0.1272 to 0.1330 kJ/K ?? mol, respectively. When compared with traditional sampling and analytical methods, the advantages of our method include: (1) the use of in situ Raman signals for methane concentration measurements eliminates possible uncertainty caused by sampling and ex situ analysis, (2) it is simple and efficient, and (3) high-pressure data can be obtained safely. ?? 2007 Elsevier Ltd. All rights reserved.

Effect of Cr2O3 Pickup on Dissolution of Lime in Converter Slag

NASA Astrophysics Data System (ADS)

Yan, Wei; Chen, Weiqing; Zhao, Xiaobo; Yang, Yindong; McLean, Alex

2017-09-01

Application of low-nickel laterite ore containing chromium as charging material for ironmaking can reduce raw material costs, but result in an increase of chromium content in the hot metal and hence, Cr2O3 content in the steelmaking slag, which subsequently causes many problems related to lime dissolution for the steelmaking operation. In this work, a rotating cylinder method was employed to study the effect of Cr2O3 on lime dissolution in steelmaking slag. The lime dissolution mechanism, rate control step and affecting factors, including slag basicity, FeOx and B2O3 content, and the formation of phases at reacted layer, were discussed. It was found that mass transfer was the rate control step in slag phase, increase of Cr2O3 and slag basicity delayed lime dissolution due to the formation of high-melting temperature phases of FeO · Cr2O3 spinel and 2CaO · SiO2 at the slag/lime reacted interface. Addition of B2O3 promoted lime dissolution and suppressed formation of FeO · Cr2O3 spinel.

Thermophysical Characterization of MgCl2·6H2O, Xylitol and Erythritol as Phase Change Materials (PCM) for Latent Heat Thermal Energy Storage (LHTES)

PubMed Central

Höhlein, Stephan; König-Haagen, Andreas; Brüggemann, Dieter

2017-01-01

The application range of existing real scale mobile thermal storage units with phase change materials (PCM) is restricted by the low phase change temperature of 58 ∘C for sodium acetate trihydrate, which is a commonly used storage material. Therefore, only low temperature heat sinks like swimming pools or greenhouses can be supplied. With increasing phase change temperatures, more applications like domestic heating or industrial process heat could be operated. The aim of this study is to find alternative PCM with phase change temperatures between 90 and 150 ∘C. Temperature dependent thermophysical properties like phase change temperatures and enthalpies, densities and thermal diffusivities are measured for the technical grade purity materials xylitol (C5H12O5), erythritol (C4H10O4) and magnesiumchloride hexahydrate (MCHH, MgCl2·6H2O). The sugar alcohols xylitol and erythritol indicate a large supercooling and different melting regimes. The salt hydrate MgCl2·6H2O seems to be a suitable candidate for practical applications. It has a melting temperature of 115.1 ± 0.1 ∘C and a phase change enthalpy of 166.9 ± 1.2 J/g with only 2.8 K supercooling at sample sizes of 100 g. The PCM is stable over 500 repeated melting and solidification cycles at differential scanning calorimeter (DSC) scale with only small changes of the melting enthalpy and temperature. PMID:28772806

Thermodynamic characteristics of the interaction between nicotinic acid and phenylalanine in an aqueous buffer solution at 298 K

NASA Astrophysics Data System (ADS)

Badelin, V. G.; Tyunina, E. Yu.; Mezhevoi, I. N.; Tarasova, G. N.

2013-08-01

The interaction between L-phenylalanine and nicotinic acid is studied by solution calorimetry in an aqueous buffer solution (pH 7.35) at different ratios of the reagents. Experimental data on the enthalpy of dissolution of amino acid in the buffer solution of nicotinic acid at 298.15 K are calculated. The values of thermodynamic parameters for the complexation of L-phenylalanine with nicotinic acid are calculated. It is shown that the formation of a 1: 2 molecular complex is stabilized by the entropy factor due to the dominant role of the dehydration effect of initial reagents.

CONTAMINANT TRANSPORT RESULTING FROM MULTICOMPONENT NONAQUEOUS PHASE LIQUID POOL DISSOLUTION IN THREE-DIMENSIONAL SUBSURFACE FORMATIONS (R823579)

EPA Science Inventory

A semi-analytical method for simulating transient contaminant transport originating from the dissolution of multicomponent nonaqueous phase liquid (NAPL) pools in three-dimensional, saturated, homogeneous porous media is presented. Each dissolved component may undergo first-order...

Transformation of topologically close-packed β-W to body-centered cubic α-W: Comparison of experiments and computations.

PubMed

Barmak, Katayun; Liu, Jiaxing; Harlan, Liam; Xiao, Penghao; Duncan, Juliana; Henkelman, Graeme

2017-10-21

The enthalpy and activation energy for the transformation of the metastable form of tungsten, β-W, which has the topologically close-packed A15 structure (space group Pm3¯n), to equilibrium α-W, which is body-centered cubic (A2, space group Im3¯m), was measured using differential scanning calorimetry. The β-W films were 1 μm-thick and were prepared by sputter deposition in argon with a small amount of nitrogen. The transformation enthalpy was measured as -8.3 ± 0.4 kJ/mol (-86 ± 4 meV/atom) and the transformation activation energy as 2.2 ± 0.1 eV. The measured enthalpy was found to agree well with the difference in energies of α and β tungsten computed using density functional theory, which gave a value of -82 meV/atom for the transformation enthalpy. A calculated concerted transformation mechanism with a barrier of 0.4 eV/atom, in which all the atoms in an A15 unit cell transform into A2, was found to be inconsistent with the experimentally measured activation energy for any critical nucleus larger than two A2 unit cells. Larger calculations of eight A15 unit cells spontaneously relax to a mechanism in which part of the supercell first transforms from A15 to A2, creating a phase boundary, before the remaining A15 transforms into the A2 phase. Both calculations indicate that a nucleation and growth mechanism is favored over a concerted transformation. More consistent with the experimental activation energy was that of a calculated local transformation mechanism at the A15-A2 phase boundary, computed as 1.7 eV using molecular dynamics simulations. This calculated phase transformation mechanism involves collective rearrangements of W atoms in the disordered interface separating the A15 and A2 phases.

Capacitive Detection of Low-Enthalpy, Higher-Order Phase Transitions in Synthetic and Natural Composition Lipid Membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, Graham J.; Heberle, Frederick A.; Seinfeld, Jason S.

In-plane lipid organization and phase separation in natural membranes play key roles in regulating many cellular processes. Highly cooperative, first-order phase transitions in model membranes consisting of few lipid components are well understood and readily detectable via calorimetry, densitometry, and fluorescence. However, far less is known about natural membranes containing numerous lipid species and high concentrations of cholesterol, for which thermotropic transitions are undetectable by the above-mentioned techniques. We demonstrate that membrane capacitance is highly sensitive to low-enthalpy thermotropic transitions taking place in complex lipid membranes. Specifically, we measured the electrical capacitance as a function of temperature for droplet interfacemore » bilayer model membranes of increasing compositional complexity, namely, (a) a single lipid species, (b) domain-forming ternary mixtures, and (c) natural brain total lipid extract (bTLE). We observed that, for single-species lipid bilayers and some ternary compositions, capacitance exhibited an abrupt, temperature-dependent change that coincided with the transition detected by other techniques. In addition, capacitance measurements revealed transitions in mixed-lipid membranes that were not detected by the other techniques. Most notably, capacitance measurements of bTLE bilayers indicated a transition at ~38 °C not seen with any other method. Likewise, capacitance measurements detected transitions in some well-studied ternary mixtures that, while known to yield coexisting lipid phases, are not detected with calorimetry or densitometry. These results indicate that capacitance is exquisitely sensitive to low-enthalpy membrane transitions because of its sensitivity to changes in bilayer thickness that occur when lipids and excess solvent undergo subtle rearrangements near a phase transition. Our findings also suggest that heterogeneity confers stability to natural membranes that function near transition temperatures by preventing unwanted defects and macroscopic demixing associated with high-enthalpy transitions commonly found in simpler mixtures.« less

Capacitive Detection of Low-Enthalpy, Higher-Order Phase Transitions in Synthetic and Natural Composition Lipid Membranes

DOE PAGES

Taylor, Graham J.; Heberle, Frederick A.; Seinfeld, Jason S.; ...

2017-08-15

In-plane lipid organization and phase separation in natural membranes play key roles in regulating many cellular processes. Highly cooperative, first-order phase transitions in model membranes consisting of few lipid components are well understood and readily detectable via calorimetry, densitometry, and fluorescence. However, far less is known about natural membranes containing numerous lipid species and high concentrations of cholesterol, for which thermotropic transitions are undetectable by the above-mentioned techniques. We demonstrate that membrane capacitance is highly sensitive to low-enthalpy thermotropic transitions taking place in complex lipid membranes. Specifically, we measured the electrical capacitance as a function of temperature for droplet interfacemore » bilayer model membranes of increasing compositional complexity, namely, (a) a single lipid species, (b) domain-forming ternary mixtures, and (c) natural brain total lipid extract (bTLE). We observed that, for single-species lipid bilayers and some ternary compositions, capacitance exhibited an abrupt, temperature-dependent change that coincided with the transition detected by other techniques. In addition, capacitance measurements revealed transitions in mixed-lipid membranes that were not detected by the other techniques. Most notably, capacitance measurements of bTLE bilayers indicated a transition at ~38 °C not seen with any other method. Likewise, capacitance measurements detected transitions in some well-studied ternary mixtures that, while known to yield coexisting lipid phases, are not detected with calorimetry or densitometry. These results indicate that capacitance is exquisitely sensitive to low-enthalpy membrane transitions because of its sensitivity to changes in bilayer thickness that occur when lipids and excess solvent undergo subtle rearrangements near a phase transition. Our findings also suggest that heterogeneity confers stability to natural membranes that function near transition temperatures by preventing unwanted defects and macroscopic demixing associated with high-enthalpy transitions commonly found in simpler mixtures.« less

Understanding decomposition and encapsulation energies of structure I and II clathrate hydrates

NASA Astrophysics Data System (ADS)

Alavi, Saman; Ohmura, Ryo

2016-10-01

When compressed with water or ice under high pressure and low temperature conditions, some gases form solid gas hydrate inclusion compounds which have higher melting points than ice under those pressures. In this work, we study the balance of the guest-water and water-water interaction energies that lead to the formation of the clathrate hydrate phases. In particular, molecular dynamics simulations with accurate water potentials are used to study the energetics of the formation of structure I (sI) and II (sII) clathrate hydrates of methane, ethane, and propane. The dissociation enthalpy of the clathrate hydrate phases, the encapsulation enthalpy of methane, ethane, and propane guests in the corresponding phases, and the average bonding enthalpy of water molecules are calculated and compared with accurate calorimetric measurements and previous classical and quantum mechanical calculations, when available. The encapsulation energies of methane, ethane, and propane guests stabilize the small and large sI and sII hydrate cages, with the larger molecules giving larger encapsulation energies. The average water-water interactions are weakened in the sI and sII phases compared to ice. The relative magnitudes of the van der Waals potential energy in ice and the hydrate phases are similar, but in the ice phase, the electrostatic interactions are stronger. The stabilizing guest-water "hydrophobic" interactions compensate for the weaker water-water interactions and stabilize the hydrate phases. A number of common assumptions regarding the guest-cage water interactions are used in the van der Waals-Platteeuw statistical mechanical theory to predict the clathrate hydrate phase stability under different pressure-temperature conditions. The present calculations show that some of these assumptions may not accurately reflect the physical nature of the interactions between guest molecules and the lattice waters.

Enthalpy-based multiple-relaxation-time lattice Boltzmann method for solid-liquid phase-change heat transfer in metal foams.

PubMed

Liu, Qing; He, Ya-Ling; Li, Qing

2017-08-01

In this paper, an enthalpy-based multiple-relaxation-time (MRT) lattice Boltzmann (LB) method is developed for solid-liquid phase-change heat transfer in metal foams under the local thermal nonequilibrium (LTNE) condition. The enthalpy-based MRT-LB method consists of three different MRT-LB models: one for flow field based on the generalized non-Darcy model, and the other two for phase-change material (PCM) and metal-foam temperature fields described by the LTNE model. The moving solid-liquid phase interface is implicitly tracked through the liquid fraction, which is simultaneously obtained when the energy equations of PCM and metal foam are solved. The present method has several distinctive features. First, as compared with previous studies, the present method avoids the iteration procedure; thus it retains the inherent merits of the standard LB method and is superior to the iteration method in terms of accuracy and computational efficiency. Second, a volumetric LB scheme instead of the bounce-back scheme is employed to realize the no-slip velocity condition in the interface and solid phase regions, which is consistent with the actual situation. Last but not least, the MRT collision model is employed, and with additional degrees of freedom, it has the ability to reduce the numerical diffusion across the phase interface induced by solid-liquid phase change. Numerical tests demonstrate that the present method can serve as an accurate and efficient numerical tool for studying metal-foam enhanced solid-liquid phase-change heat transfer in latent heat storage. Finally, comparisons and discussions are made to offer useful information for practical applications of the present method.

Understanding decomposition and encapsulation energies of structure I and II clathrate hydrates.

PubMed

Alavi, Saman; Ohmura, Ryo

2016-10-21

When compressed with water or ice under high pressure and low temperature conditions, some gases form solid gas hydrate inclusion compounds which have higher melting points than ice under those pressures. In this work, we study the balance of the guest-water and water-water interaction energies that lead to the formation of the clathrate hydrate phases. In particular, molecular dynamics simulations with accurate water potentials are used to study the energetics of the formation of structure I (sI) and II (sII) clathrate hydrates of methane, ethane, and propane. The dissociation enthalpy of the clathrate hydrate phases, the encapsulation enthalpy of methane, ethane, and propane guests in the corresponding phases, and the average bonding enthalpy of water molecules are calculated and compared with accurate calorimetric measurements and previous classical and quantum mechanical calculations, when available. The encapsulation energies of methane, ethane, and propane guests stabilize the small and large sI and sII hydrate cages, with the larger molecules giving larger encapsulation energies. The average water-water interactions are weakened in the sI and sII phases compared to ice. The relative magnitudes of the van der Waals potential energy in ice and the hydrate phases are similar, but in the ice phase, the electrostatic interactions are stronger. The stabilizing guest-water "hydrophobic" interactions compensate for the weaker water-water interactions and stabilize the hydrate phases. A number of common assumptions regarding the guest-cage water interactions are used in the van der Waals-Platteeuw statistical mechanical theory to predict the clathrate hydrate phase stability under different pressure-temperature conditions. The present calculations show that some of these assumptions may not accurately reflect the physical nature of the interactions between guest molecules and the lattice waters.

Enthalpy-based multiple-relaxation-time lattice Boltzmann method for solid-liquid phase-change heat transfer in metal foams

NASA Astrophysics Data System (ADS)

Liu, Qing; He, Ya-Ling; Li, Qing

2017-08-01

In this paper, an enthalpy-based multiple-relaxation-time (MRT) lattice Boltzmann (LB) method is developed for solid-liquid phase-change heat transfer in metal foams under the local thermal nonequilibrium (LTNE) condition. The enthalpy-based MRT-LB method consists of three different MRT-LB models: one for flow field based on the generalized non-Darcy model, and the other two for phase-change material (PCM) and metal-foam temperature fields described by the LTNE model. The moving solid-liquid phase interface is implicitly tracked through the liquid fraction, which is simultaneously obtained when the energy equations of PCM and metal foam are solved. The present method has several distinctive features. First, as compared with previous studies, the present method avoids the iteration procedure; thus it retains the inherent merits of the standard LB method and is superior to the iteration method in terms of accuracy and computational efficiency. Second, a volumetric LB scheme instead of the bounce-back scheme is employed to realize the no-slip velocity condition in the interface and solid phase regions, which is consistent with the actual situation. Last but not least, the MRT collision model is employed, and with additional degrees of freedom, it has the ability to reduce the numerical diffusion across the phase interface induced by solid-liquid phase change. Numerical tests demonstrate that the present method can serve as an accurate and efficient numerical tool for studying metal-foam enhanced solid-liquid phase-change heat transfer in latent heat storage. Finally, comparisons and discussions are made to offer useful information for practical applications of the present method.

Prediction of Phase Formation in Nanoscale Sn-Ag-Cu Solder Alloy

NASA Astrophysics Data System (ADS)

Wu, Min; Lv, Bailin

2016-01-01

In a dynamic nonequilibrium process, the effective heat of formation allows the heat of formation to be calculated as a function of concentrations of the reacting atoms. In this work, we used the effective heat of formation rule to predict the formation and size of compound phases in a nanoscale Sn-Ag-Cu lead-free solder. We calculated the formation enthalpy and effective formation enthalpy of compounds in the Sn-Ag, Sn-Cu, and Ag-Cu systems by using the Miedema model and effective heat of formation. Our results show that, considering the surface effect of the nanoparticle, the effective heat of formation rule successfully predicts the phase formation and sizes of Ag3Sn and Cu6Sn5 compounds, which agrees well with experimental data.

Influence of calcium on microbial reduction of solid phase uranium(VI).

PubMed

Liu, Chongxuan; Jeon, Byong-Hun; Zachara, John M; Wang, Zheming

2007-08-15

The effect of calcium on the dissolution and microbial reduction of a representative solid phase uranyl [U(VI)], sodium boltwoodite (NaUO(2)SiO(3)OH . 1.5H(2)O), was investigated to evaluate the rate-limiting step of microbial reduction of the solid phase U(VI). Microbial reduction experiments were performed in a culture of a dissimilatory metal-reducing bacterium (DMRB), Shewanella oneidensis strain MR-1, in a bicarbonate medium with lactate as electron donor at pH 6.8 buffered with PIPES. Calcium increased the rate of Na-boltwoodite dissolution and U(VI) bioavailability by increasing its solubility through the formation of a ternary aqueous calcium-uranyl-carbonate species. The ternary species, however, decreased the rates of microbial reduction of aqueous U(VI). Laser-induced fluorescence spectroscopy (LIFS) and transmission electron microscopy (TEM) collectively revealed that microbial reduction of solid phase U(VI) was a sequentially coupled process of Na-boltwoodite dissolution, U(VI) aqueous speciation, and microbial reduction of dissolved U(VI) to U(IV) that accumulated on bacterial surfaces/periplasm. Under studied experimental conditions, the overall rate of microbial reduction of solid phase U(VI) was limited by U(VI) dissolution reactions in solutions without calcium and limited by microbial reduction in solutions with calcium. Generally, the overall rate of microbial reduction of solid phase U(VI) was determined by the coupling of solid phase U(VI) dissolution, U(VI) aqueous speciation, and microbial reduction of dissolved U(VI) that were all affected by calcium. (c) 2007 Wiley Periodicals, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Ping; Li, Yanbin; Liu, Guangliang

Cinnabar dissolution is an important factor controlling mercury (Hg) cycling. Recent studies have suggested the co-occurrence of re-adsorption of the released Hg during the course of cinnabar dissolution. However, there is a lack of feasible techniques that can quantitatively assess the amount of Hg re-adsorbed on cinnabar when investigating cinnabar dissolution. In this study, a new method, based on isotope tracing and dilution techniques, was developed to study the role of Hg re-adsorption in cinnabar dissolution. The developed method includes two key components: (1) accurate measurement of both released and spiked Hg in aqueous phase and (2) estimation of re-adsorbedmore » Hg on cinnabar surface via the reduction in spiked 202Hg 2+. By adopting the developed method, it was found that the released Hg for trials purged with oxygen could reach several hundred g L –1, while no significant cinnabar dissolution was detected under anaerobic condition. Cinnabar dissolution rate when considering Hg re-adsorption was approximately 2 times the value calculated solely with the Hg detected in the aqueous phase. Lastly, these results suggest that ignoring the Hg re-adsorption process can significantly underestimate the importance of cinnabar dissolution, highlighting the necessity of applying the developed method in future cinnabar dissolution studies.« less

Evaluating the role of re-adsorption of dissolved Hg 2+ during cinnabar dissolution using isotope tracer technique

DOE PAGES

Jiang, Ping; Li, Yanbin; Liu, Guangliang; ...

2016-06-02

Cinnabar dissolution is an important factor controlling mercury (Hg) cycling. Recent studies have suggested the co-occurrence of re-adsorption of the released Hg during the course of cinnabar dissolution. However, there is a lack of feasible techniques that can quantitatively assess the amount of Hg re-adsorbed on cinnabar when investigating cinnabar dissolution. In this study, a new method, based on isotope tracing and dilution techniques, was developed to study the role of Hg re-adsorption in cinnabar dissolution. The developed method includes two key components: (1) accurate measurement of both released and spiked Hg in aqueous phase and (2) estimation of re-adsorbedmore » Hg on cinnabar surface via the reduction in spiked 202Hg 2+. By adopting the developed method, it was found that the released Hg for trials purged with oxygen could reach several hundred g L –1, while no significant cinnabar dissolution was detected under anaerobic condition. Cinnabar dissolution rate when considering Hg re-adsorption was approximately 2 times the value calculated solely with the Hg detected in the aqueous phase. Lastly, these results suggest that ignoring the Hg re-adsorption process can significantly underestimate the importance of cinnabar dissolution, highlighting the necessity of applying the developed method in future cinnabar dissolution studies.« less

Degradation characteristics of polylactide in thermophilic anaerobic digestion with hyperthermophilic solubilization condition.

PubMed

Wang, F; Hidaka, T; Oishi, T; Osumi, S; Tsubota, J; Tsuno, H

2011-01-01

To test whether hyperthermophilic treatment promotes polylactide (PLA) dissolution and methane conversion under anaerobic digestion conditions, a single thermophilic control reactor (55 °C) and a two-phase system consisting of a hyperthermophilic reactor (80 °C) and a thermophilic reactor (55 °C) were continuously fed with a mixture of PLA and artificial kitchen garbage. In Runs 1 and 2, the PLA dissolution ratios in the two-phase system were 79.2 ± 6.5% and 85.2 ± 7.0%, respectively, higher than those of the control. Batch experimental results indicated that hyperthermophilic treatment could promote PLA dissolution to a greater degree as compared with single thermophilic treatment and that ammonia addition also had a promotional effect on PLA dissolution. In the two-phase system, after hyperthermophilic treatment, dissolved PLA was converted to methane gas under the subsequent thermophilic condition.

Shock and Rarefaction Waves in a Heterogeneous Mantle

NASA Astrophysics Data System (ADS)

Jordan, J.; Hesse, M. A.

2012-12-01

We explore the effect of heterogeneities on partial melting and melt migration during active upwelling in the Earth's mantle. We have constructed simple, explicit nonlinear models in one dimension to examine heterogeneity and its dynamic affects on porosity, temperature and the magnesium number in a partially molten, porous medium comprised of olivine. The composition of the melt and solid are defined by a closed, binary phase diagram for a simplified, two-component olivine system. The two-component solid solution is represented by a phase loop where concentrations 0 and 1 to correspond to fayalite and forsterite, respectively. For analysis, we examine an advective system with a Riemann initial condition. Chromatographic tools and theory have primarily been used to track large, rare earth elements as tracers. In our case, we employ these theoretical tools to highlight the importance of the magnesium number, enthalpy and overall heterogeneity in the dynamics of melt migration. We calculate the eigenvectors and eigenvalues in the concentration-enthalpy space in order to glean the characteristics of the waves emerging the Riemann step. Analysis on Riemann problems of this nature shows us that the composition-enthalpy waves can be represented by self-similar solutions. The eigenvalues of the composition-enthalpy system represent the characteristic wave propagation speeds of the compositions and enthalpy through the domain. Furthermore, the corresponding eigenvectors are the directions of variation, or ``pathways," in concentration-enthalpy space that the characteristic waves follow. In the two-component system, the Riemann problem yields two waves connected by an intermediate concentration-enthalpy state determined by the intersections of the integral curves of the eigenvectors emanating from both the initial and boundary states. The first wave, ``slow path," and second wave, ``fast path," follow the aformentioned pathways set by the eigenvectors. The slow path wave has a zero eigenvalue, corresponding to a wave speed of zero, which preserves a residual imprint of the initial condition. Freezing fronts textemdash those that result in a negative change in porositytextemdash feature fast path waves that travel as shocks, whereas the fast path waves of melting fronts travel as spreading, rarefaction waves.

Enthalpy-entropy compensation for the solubility of drugs in solvent mixtures: paracetamol, acetanilide, and nalidixic acid in dioxane-water.

PubMed

Bustamante, P; Romero, S; Pena, A; Escalera, B; Reillo, A

1998-12-01

In earlier work, a nonlinear enthalpy-entropy compensation was observed for the solubility of phenacetin in dioxane-water mixtures. This effect had not been earlier reported for the solubility of drugs in solvent mixtures. To gain insight into the compensation effect, the behavior of the apparent thermodynamic magnitudes for the solubility of paracetamol, acetanilide, and nalidixic acid is studied in this work. The solubility of these drugs was measured at several temperatures in dioxane-water mixtures. DSC analysis was performed on the original powders and on the solid phases after equilibration with the solvent mixture. The thermal properties of the solid phases did not show significant changes. The three drugs display a solubility maximum against the cosolvent ratio. The solubility peaks of acetanilide and nalidixic acid shift to a more polar region at the higher temperatures. Nonlinear van't Hoff plots were observed for nalidixic acid whereas acetanilide and paracetamol show linear behavior at the temperature range studied. The apparent enthalpies of solution are endothermic going through a maximum at 50% dioxane. Two different mechanisms, entropy and enthalpy, are suggested to be the driving forces that increase the solubility of the three drugs. Solubility is entropy controlled at the water-rich region (0-50% dioxane) and enthalpy controlled at the dioxane-rich region (50-100% dioxane). The enthalpy-entropy compensation analysis also suggests that two different mechanisms, dependent on cosolvent ratio, are involved in the solubility enhancement of the three drugs. The plots of deltaH versus deltaG are nonlinear, and the slope changes from positive to negative above 50% dioxane. The compensation effect for the thermodynamic magnitudes of transfer from water to the aqueous mixtures can be described by a common empirical nonlinear relationship, with the exception of paracetamol, which follows a separate linear relationship at dioxane ratios above 50%. The results corroborate earlier findings with phenacetin. The similar pattern shown by the drugs studied suggests that the nonlinear enthalpy-entropy compensation effect may be characteristic of the solubility of semipolar drugs in dioxane-water mixtures.

Microstructural stability of fine-grained fully lamellar XD TiAl alloys by step aging

NASA Astrophysics Data System (ADS)

Zhu, Hanliang; Maruyama, K.; Seo, D. Y.; Au, P.

2005-05-01

XD TiAl alloys (Ti-45 and 47Al-2Nb-2Mn+0.8 vol pct TiB2) (at. pct) were oil quenched to produce fine-grained fully lamellar (FGFL) structures, and aging treatments at different temperatures for different durations were carried out to stabilize the FGFL structures. Microstructural examinations show that the aging treatments cause phase transformation of α 2 to γ, resulting in stabilization of the lamellar structure, as indicated by a significant decrease in α 2 volume fraction. However, several degradation processes are also introduced. After aging, within lamellar colonies, the α 2 lamellae become finer due to dissolution, whereas most of the γ lamellae coarsen. The dissolution of α 2 involves longitudinal dissolution and lateral dissolution. In addition, at lamellar colony boundaries, lamellar termination migration, nucleation and growth of γ grains, and discontinuous coarsening occur. With the exception of longitudinal dissolution, all the other transformation modes are considered as degradation processes as they result in a reduction in α 2/ γ interfaces. Different phase transformation modes are present to varying degrees in the aged FGFL structures, depending on aging conditions and Al content. A multiple step aging reduces the drive force for phase transformation at high temperature by promoting phase transformation via longitudinal dissolution at low temperatures. As a result, this aging procedure effectively stabilizes the lamellar structure and suppresses other degradation processes. Therefore, the multiple step aging is suggested to be an optimal aging condition for stabilizing FGFL XD TiAl alloys.

Thermochemistry of dense hydrous magnesium silicates

NASA Technical Reports Server (NTRS)

Bose, Kunal; Burnley, Pamela; Navrotsky, Alexandra

1994-01-01

Recent experimental investigations under mantle conditions have identified a suite of dense hydrous magnesium silicate (DHMS) phases that could be conduits to transport water to at least the 660 km discontinuity via mature, relatively cold, subducting slabs. Water released from successive dehydration of these phases during subduction could be responsible for deep focus earthquakes, mantle metasomatism and a host of other physico-chemical processes central to our understanding of the earth's deep interior. In order to construct a thermodynamic data base that can delineate and predict the stability ranges for DHMS phases, reliable thermochemical and thermophysical data are required. One of the major obstacles in calorimetric studies of phases synthesized under high pressure conditions has been limitation due to the small (less than 5 mg) sample mass. Our refinement of calorimeter techniques now allow precise determination of enthalpies of solution of less than 5 mg samples of hydrous magnesium silicates. For example, high temperature solution calorimetry of natural talc (Mg(0.99) Fe(0.01)Si4O10(OH)2), periclase (MgO) and quartz (SiO2) yield enthalpies of drop solution at 1044 K to be 592.2 (2.2), 52.01 (0.12) and 45.76 (0.4) kJ/mol respectively. The corresponding enthalpy of formation from oxides at 298 K for talc is minus 5908.2 kJ/mol agreeing within 0.1 percent to literature values.

A kinetic rate model for crystalline basalt dissolution at temperature and pressure conditions relevant for geologic CO2 sequestration

NASA Astrophysics Data System (ADS)

Pollyea, R.; Rimstidt, J. D.

2016-12-01

Geologic carbon sequestration in terrestrial basalt reservoirs is predicated on permanent CO2 trapping through CO2-water-rock dissolution reactions followed by carbonate precipitation. Bench-scale experiments have shown these reaction paths to be rapid, occurring on a timescale 100 - 102 years. Moreover, recent results from the CarbFix basalt sequestration pilot project in Iceland demonstrate >95% CO2 isolation two years after a small-scale injection. In order to assess the viability of basalt sequestration worldwide (e.g., Deccan Traps, Columbia Plateau, etc.), flexible simulation tools are required that distill the dissolution reactions into a user-friendly format that is readily transmissible to existing reactive transport numerical simulators. In the present research, we combine experimental results extant in the literature for Icelandic basalt to develop kinetic rate models describing the pH-dependent dissolution of (1) basaltic glass and (2) an aggregate mineral assemblage for crystalline basalt comprising olivine, pyroxene, and plagioclase phases. In order to utilize these kinetic rate models with numerical simulation, a thermodynamic solubility model for each phase is developed for use with the reactive transport simulation code, TOUGHREACT. We use reactive transport simulation in a simple 1-D reactor to compare dissolution of the aggregate crystalline basalt phase with the traditional formulation comprising individual mineral phases for the crystalline basalt. Simulation results are in general agreement, illustrating the efficacy of this simplified approach for modeling basalt dissolution at temperature and pressure conditions typical of geologic CO2 reservoirs. Moreover, this approach may be of value to investigators seeking dissolution models for crystalline basalt in other mafic provinces.

Effects of coformers on phase transformation and release profiles of carbamazepine cocrystals in hydroxypropyl methylcellulose based matrix tablets.

PubMed

Qiu, Shi; Li, Mingzhong

2015-02-01

The aim of this study was to investigate the effects of coformers on phase transformation and release profiles of carbamazepine (CBZ) cocrystals in hydroxypropyl methylcellulose (HPMC) based matrix tablets. It has been found that selection of different coformers of saccharin (SAC) and cinnamic acid (CIN) can affect the stability of CBZ cocrystals in solution, resulting in significant differences in the apparent solubility of CBZ. The dissolution advantage of CBZ-SAC cocrystals can only be shown for a short period during dissolution because of the fast conversion to its dihydrate form (DH). HPMC can partially inhibit the crystallisation of CBZ DH during dissolution of CBZ-SAC cocrystal. However, the increased viscosity of HPMC dissolution medium reduced the dissolution rate of CBZ-SAC cocrystals. Therefore the CBZ-SAC cocrystal formulation did not show any significant advantage in CBZ release rate. In contrast the improved CBZ dissolution rate of CBZ-CIN cocrystal can be realised in both solution and formulation due to its high stability. In conclusion, exploring and understanding the mechanisms of the phase transformation of pharmaceutical cocrystals in aqueous medium for selection of lead cocrystals is the key for success of product development. Copyright © 2014 Elsevier B.V. All rights reserved.

Preparation of CMC-modified melamine resin spherical nano-phase change energy storage materials.

PubMed

Hu, Xiaofeng; Huang, Zhanhua; Zhang, Yanhua

2014-01-30

A novel carboxymethyl cellulose (CMC)-modified melamine-formaldehyde (MF) phase change capsule with excellent encapsulation was prepared by in situ polymerization. Effects of CMC on the properties of the capsules were studied by Fourier transformation infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electronic microscopy (SEM), X-ray diffractometry (XRD), and thermogravimetric analysis (TGA). The results showed that the CMC-modified capsules had an average diameter of about 50nm and good uniformity. The phase change enthalpy of the capsules was increased and the cracking ratio decreased by incorporating a suitable amount of CMC. The optimum phase change enthalpy of the nanocapsules was 83.46J/g, and their paraffin content was 63.1%. The heat resistance of the capsule shells decreased after CMC modification. In addition, the nanocapsule cracking ratio of the nanocapsules was 11.0%, which is highly attractive for their application as nano phase change materials. Copyright © 2013 Elsevier Ltd. All rights reserved.

Low concentration graphene nanoplatelets for shape stabilization and thermal transfer reinforcement of Mannitol: a phase change material for a medium-temperature thermal energy system

NASA Astrophysics Data System (ADS)

Jing, Gu; Dehong, Xia; Li, Wang; Wenqing, Ao; Zhaodong, Qi

2018-03-01

We report herein a novel series of Mannitol/GNPs (graphene nanoplatelets) composites with incremental GNPs loadings from 1 wt% to 10 wt% for further applications in medium-temperature thermal energy system. The phase change behavior and thermal conductivity of Mannitol/GNPs composite, a nanostructured PCM, have been evaluated as a function of GNPs content. Compared to the pristine Mannitol, the resultant stabilized composite with 8 wt% of GNPs displays an extremely high 1054% enhancement in thermal conductivity, and inherits 92% of phase change enthalpy of bulk Mannitol PCM (phase change material). More importantly, 92%Mannitol/GNPs composite still preserves its initial shape without any leakage even when subjected to a 400 consecutive melting/re-solidification cycles. The resulting Mannitol composites exhibit excellent chemical compatibility, large phase change enthalpy and improved thermal reliability, as compared to base PCM, which stands distinct in its class of organic with reference to the past literatures.

Towards an understanding of the molecular mechanism of solvation of drug molecules: a thermodynamic approach by crystal lattice energy, sublimation, and solubility exemplified by paracetamol, acetanilide, and phenacetin.

PubMed

Perlovich, German L; Volkova, Tatyana V; Bauer-Brandl, Annette

2006-10-01

Temperature dependencies of saturated vapor pressure for the monoclinic modification of paracetamol (acetaminophen), acetanilide, and phenacetin (acetophenetidin) were measured and thermodynamic functions of sublimation calculated (paracetamol: DeltaGsub298=60.0 kJ/mol; DeltaHsub298=117.9+/-0.7 kJ/mol; DeltaSsub298=190+/-2 J/mol.K; acetanilide: DeltaGsub298=40.5 kJ/mol; DeltaHsub298=99.8+/-0.8 kJ/mol; DeltaSsub298=197+/-2 J/mol.K; phenacetin: DeltaGsub298=52.3 kJ/mol; DeltaHsub298=121.8+/-0.7 kJ/mol; DeltaSsub298=226+/-2 J/mol.K). Analysis of packing energies based on geometry optimization of molecules in the crystal lattices using diffraction data and the program Dmol3 was carried out. Parameters analyzed were: (a) energetic contribution of van der Waals forces and hydrogen bonding to the total packing energy; (b) contributions of fragments of the molecules to the packing energy. The fraction of hydrogen bond energy in the packing energy increases as: phenacetin (17.5%)

The gaseous enthalpy of formation of the ionic liquid 1-butyl-3-methylimidazolium dicyanamide from combustion calorimetry, vapor pressure measurements, and ab initio calculations.

PubMed

Emel'yanenko, Vladimir N; Verevkin, Sergey P; Heintz, Andreas

2007-04-04

Ionic liquids are attracting growing interest as alternatives to conventional molecular solvents. Experimental values of vapor pressure, enthalpy of vaporization, and enthalpy of formation of ionic liquids are the key thermodynamic quantities, which are required for the validation and development of the molecular modeling and ab initio methods toward this new class of solvents. In this work, the molar enthalpy of formation of the liquid 1-butyl-3-methylimidazolium dicyanamide, 206.2 +/- 2.5 kJ.mol-1, was measured by means of combustion calorimetry. The molar enthalpy of vaporization of 1-butyl-3-methylimidazolium dicyanamide, 157.2 +/- 1.1 kJ.mol-1, was obtained from the temperature dependence of the vapor pressure measured using the transpiration method. The latter method has been checked with measurements of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, where data are available from the effusion technique. The first experimental determination of the gaseous enthalpy of formation of the ionic liquid 1-butyl-3-methylimidazolium dicyanamide, 363.4 +/- 2.7 kJ.mol-1, from thermochemical measurements (combustion and transpiration) is presented. Ab initio calculations of the enthalpy of formation in the gaseous phase have been performed for 1-butyl-3-methylimidazolium dicyanamide using the G3MP2 theory. Excellent agreement with experimental results has been observed. The method developed opens a new way to obtain thermodynamic properties of ionic liquids which have not been available so far.

An examination of the thermodynamics of fusion, vaporization, and sublimation of (R,S)- and (R)-flurbiprofen by correlation gas chromatography.

PubMed

Umnahanant, Patamaporn; Hasty, Darrell; Chickos, James

2012-06-01

The vaporization, fusion, and sublimation enthalpies of (R,S)- and (R)-flurbiprofen at T = 298.15 K are reported and compared with literature values when available. Correlation gas chromatography experiments were first performed to identify appropriate standards that could be used for materials containing a single fluorine substituent. Subsequent correlations resulted in a vaporization enthalpy for (R,S)-flurbiprofen and (R)-flurbiprofen, ΔH(vap) (298.15 K), of (127.5 ± 5.5) and (127.4 ± 4.7) kJ mol, respectively. Fusion enthalpies, ΔH(fus) (387 K), of (28.2 ± and, ΔH(fus) (381 K), (22.8 ± kJ mol(-1) were also measured by differential scanning calorimetry for the racemic and chiral forms of flurbiprofen. Adjusted to T = 298.15 K and combined with the vaporization enthalpy resulted in sublimation enthalpies, ΔH(sub) (298.15 K), of (155.6 ± 5.8) and (145.1 ± 5.7) kJ mol(-1) for (R,S)- and (R)-flurbiprofen, respectively. The fusion enthalpy measured for the racemic form was in excellent agreement with the literature value, while the sublimation enthalpy varies substantially from previous work. Two weak solid-solid phase transitions were also observed for (R)-flurbiprofen at T = 353.9 K (0.30 ± 0.1) and 363.2 K (0.21 ± 0.03) kJ · mol(-1). Copyright © 2012 Wiley Periodicals, Inc.

Enthalpy of formation of anisole: implications for the controversy on the O-H bond dissociation enthalpy in phenol.

PubMed

Simões, Ricardo G; Agapito, Filipe; Diogo, Hermínio P; da Piedade, Manuel E Minas

2014-11-20

Significant discrepancies in the literature data for the enthalpy of formation of gaseous anisole, ΔfHmo(PhOCH3, g), have fueled an ongoing controversy regarding the most reliable enthalpy of formation of the phenoxy radical and of the gas phase O-H bond dissociation enthalpy, DHo(PhO-H), in phenol. In the present work ΔfHmo(PhOCH3, g) was reassessed using a combination of calorimetric determinations and high-level (W2-F12) ab initio calculations. Static-bomb combustion calorimetry led to the standard molar enthalpy of formation of liquid anisole at 298.15 K, ΔfHmo(PhOCH3, l) = −(117.1 ± 1.4) kJ·mol(-1). The corresponding enthalpy of vaporization was obtained as, ΔvapHmo(PhOCH3) = 46.41 ± 0.26 kJ·mol(-1), by Calvet-drop microcalorimetry. These results give ΔfHmo(PhOCH3, g) = −(70.7 ± 1.4) kJ·mol(-1), in excellent agreement with ΔfHmo(PhOCH3, g) = −(70.8 ± 3.2) kJ·mol(-1), obtained from the W2-F12 calculations. The ΔfHmo(PhOCH3, g) here recommended leads to ΔfHmo(PhO•, g) = 55.5 ± 2.4 kJ·mol(-)1 and DH°(PhO-H) = 368.1 ± 2.6 kJ·mol(-1).

Energetics of metastudtite and implications for nuclear waste alteration

PubMed Central

Guo, Xiaofeng; Ushakov, Sergey V.; Labs, Sabrina; Curtius, Hildegard; Bosbach, Dirk; Navrotsky, Alexandra

2014-01-01

Metastudtite, (UO2)O2(H2O)2, is one of two known natural peroxide minerals, but little is established about its thermodynamic stability. In this work, its standard enthalpy of formation, −1,779.6 ± 1.9 kJ/mol, was obtained by high temperature oxide melt drop solution calorimetry. Decomposition of synthetic metastudtite was characterized by thermogravimetry and differential scanning calorimetry (DSC) with ex situ X-ray diffraction analysis. Four decomposition steps were observed in oxygen atmosphere: water loss around 220 °C associated with an endothermic heat effect accompanied by amorphization; another water loss from 400 °C to 530 °C; oxygen loss from amorphous UO3 to crystallize orthorhombic α-UO2.9; and reduction to crystalline U3O8. This detailed characterization allowed calculation of formation enthalpy from heat effects on decomposition measured by DSC and by transposed temperature drop calorimetry, and both these values agree with that from drop solution calorimetry. The data explain the irreversible transformation from studtite to metastudtite, the conditions under which metastudtite may form, and its significant role in the oxidation, corrosion, and dissolution of nuclear fuel in contact with water. PMID:25422465

Energetics of metastudtite and implications for nuclear waste alteration

DOE PAGES

Guo, Xiaofeng; Ushakov, Sergey V.; Labs, Sabrina; ...

2014-11-24

Metastudtite, (UO 2)O 2(H 2O) 2, is one of two known natural peroxide minerals, but little is established about its thermodynamic stability. In this work, its standard enthalpy of formation, $-$1,779.6 ± 1.9 kJ/mol, was obtained by high temperature oxide melt drop solution calorimetry. Decomposition of synthetic metastudtite was characterized by thermogravimetry and differential scanning calorimetry (DSC) with ex situ X-ray diffraction analysis. We observed four decomposition steps in oxygen atmosphere: water loss around 220 °C associated with an endothermic heat effect accompanied by amorphization; another water loss from 400 °C to 530 °C; oxygen loss from amorphous UO 3more » to crystallize orthorhombic α-UO 2.9; and reduction to crystalline U 3O 8. This detailed characterization allowed calculation of formation enthalpy from heat effects on decomposition measured by DSC and by transposed temperature drop calorimetry, and both these values agree with that from drop solution calorimetry. The data explain the irreversible transformation from studtite to metastudtite, the conditions under which metastudtite may form, and its significant role in the oxidation, corrosion, and dissolution of nuclear fuel in contact with water.« less

Neutral, ion gas-phase energetics and structural properties of hydroxybenzophenones.

PubMed

Dávalos, Juan Z; Guerrero, Andrés; Herrero, Rebeca; Jimenez, Pilar; Chana, Antonio; Abboud, José Luis M; Lima, Carlos F R A C; Santos, Luís M N B F; Lago, Alexsandre F

2010-04-16

We have carried out a study of the energetics, structural, and physical properties of o-, m-, and p-hydroxybenzophenone neutral molecules, C(13)H(10)O(2), and their corresponding anions. In particular, the standard enthalpies of formation in the gas phase at 298.15 K for all of these species were determined. A reliable experimental estimation of the enthalpy associated with intramolecular hydrogen bonding in chelated species was experimentally obtained. The gas-phase acidities (GA) of benzophenones, substituted phenols, and several aliphatic alcohols are compared with the corresponding aqueous acidities (pK(a)), covering a range of 278 kJ.mol(-1) in GA and 11.4 in pK(a). A computational study of the various species shed light on structural effects and further confirmed the self-consistency of the experimental results.

Compositional partitioning during the spinodal decomposition in Cu-Ni-Sn alloy

NASA Astrophysics Data System (ADS)

Basak, C. B.; Poswal, A. K.

2018-05-01

Spinodal decomposition in Cu-9.4at%Ni-3.1at%Sn alloy was elucidated with the new insight from the experimental EXAFS analysis supported by ab initio total energy calculations suggesting the strong influence of the first near-neighbour atoms. Enthalpy of mixing was calculated for all crystallographically unique first near-neighbour configurations and finally an average positive enthalpy of mixing of 1604 J/mol was obtained. Combination of ab initio results, XRD and EXAFS analysis indicate that one of the daughter phase becomes rich in Ni and Sn than the other phase; in contrary to the earlier proposition that Cu/Ni ratio remains constant in both daughter phases. It is also shown that the present thermodynamic description requires further refinement to extend the miscibility gap towards lower Ni content in Cu-Ni-Sn system.

Evaluating the role of re-adsorption of dissolved Hg(2+) during cinnabar dissolution using isotope tracer technique.

PubMed

Jiang, Ping; Li, Yanbin; Liu, Guangliang; Yang, Guidi; Lagos, Leonel; Yin, Yongguang; Gu, Baohua; Jiang, Guibin; Cai, Yong

2016-11-05

Cinnabar dissolution is an important factor controlling mercury (Hg) cycling. Recent studies have suggested the co-occurrence of re-adsorption of the released Hg during the course of cinnabar dissolution. However, there is a lack of feasible techniques that can quantitatively assess the amount of Hg re-adsorbed on cinnabar when investigating cinnabar dissolution. In this study, a new method, based on isotope tracing and dilution techniques, was developed to study the role of Hg re-adsorption in cinnabar dissolution. The developed method includes two key components: (1) accurate measurement of both released and spiked Hg in aqueous phase and (2) estimation of re-adsorbed Hg on cinnabar surface via the reduction in spiked (202)Hg(2+). By adopting the developed method, it was found that the released Hg for trials purged with oxygen could reach several hundred μgL(-1), while no significant cinnabar dissolution was detected under anaerobic condition. Cinnabar dissolution rate when considering Hg re-adsorption was approximately 2 times the value calculated solely with the Hg detected in the aqueous phase. These results suggest that ignoring the Hg re-adsorption process can significantly underestimate the importance of cinnabar dissolution, highlighting the necessity of applying the developed method in future cinnabar dissolution studies. Copyright © 2016 Elsevier B.V. All rights reserved.

Determination of some pure compound ideal-gas enthalpies of formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steele, W. V.; Chirico, R. D.; Nguyen, A.

1989-06-01

The results of a study aimed at improvement of group-additivity methodology for estimation of thermodynamic properties of organic substances are reported. Specific weaknesses where ring corrections were unknown or next-nearest-neighbor interactions were only estimated because of lack of experimental data are addressed by experimental studies of enthalpies of combustion in the condensed- phase and vapor pressure measurements. Ideal-gas enthalpies of formation are reported for acrylamide, succinimide, ..gamma..-butyrolactone, 2-pyrrolidone, 2,3-dihydrofuran, 3,4-dihydro-2H-pyran, 1,3-cyclohexadiene, 1,4-cyclohexadiene, and 1-methyl-1-phenylhydrazine. Ring corrections, group terms, and next-nearest-neighbor interaction terms useful in the application of group additivity correlations are derived. 44 refs., 2 figs., 59 tabs.

Gas-Phase Interaction of Anions with Polyisobutylenes: Collision-Induced Dissociation Study and Quantum Chemical Modeling.

PubMed

Nagy, Lajos; Kuki, Ákos; Deák, György; Purgel, Mihály; Vékony, Ádám; Zsuga, Miklós; Kéki, Sándor

2016-09-01

The gas-phase interaction of anions including fluoride, chloride, bromide, iodide, ethyl sulfate, chlorate, and nitrate with polyisobutylene (PIB) derivatives was studied using collision-induced dissociation (CID). The gas-phase adducts of anions with PIBs ([PIB + anion](-)) were generated from the electrosprayed solution of PIBs in the presence of the corresponding anions. The so-formed adducts subjected to CID showed a loss of anion at different characteristic collision energies, thus allowing the study of the strength of interaction between the anions and nonpolar PIBs having different end-groups. The values of characteristic collision energies (the energy needed to obtain 50% fragmentation) obtained by CID experiments correlated linearly with the binding enthalpies between the anion and PIB, as determined by density functional theory calculations. In the case of halide ions, the critical energies for dissociation, that is, the binding enthalpies for [PIB + anion](-) adducts, increased in the order of I(-) < Br(-) < Cl(-) < F(-). Furthermore, it was found that the binding enthalpies for the adducts formed with halide ions decreased approximately with the square radius of the halide ion, suggesting that the strength of interaction is mainly determined by the "surface" charge density of the halide ion. In addition, the characteristic collision energy versus the number of isobutylene units revealed a linear dependence.

Oxidative dissolution of silver nanoparticles: A new theoretical approach.

PubMed

Adamczyk, Zbigniew; Oćwieja, Magdalena; Mrowiec, Halina; Walas, Stanisław; Lupa, Dawid

2016-05-01

A general model of an oxidative dissolution of silver particle suspensions was developed that rigorously considers the bulk and surface solute transport. A two-step surface reaction scheme was proposed that comprises the formation of the silver oxide phase by direct oxidation and the acidic dissolution of this phase leading to silver ion release. By considering this, a complete set of equations is formulated describing oxygen and silver ion transport to and from particles' surfaces. These equations are solved in some limiting cases of nanoparticle dissolution in dilute suspensions. The obtained kinetic equations were used for the interpretation of experimental data pertinent to the dissolution kinetics of citrate-stabilized silver nanoparticles. In these kinetic measurements the role of pH and bulk suspension concentration was quantitatively evaluated by using the atomic absorption spectrometry (AAS). It was shown that the theoretical model adequately reflects the main features of the experimental results, especially the significant increase in the dissolution rate for lower pH. Also the presence of two kinetic regimes was quantitatively explained in terms of the decrease in the coverage of the fast dissolving oxide layer. The overall silver dissolution rate constants characterizing these two regimes were determined. Copyright © 2015 Elsevier Inc. All rights reserved.

DIPPR Project 871 For 1995 - Thermodynamic Properties and Ideal-Gas Enthalpies of Formation for Methyl Benzoate, Ethyl Benzoate, (R)-(+)-Limonene, Tert-Amyl Methyl Ether, Trans-Crotonaldehyde, and

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steele, W.V.

2002-07-01

Ideal-gas enthalpies of formation of methyl benzoate, ethyl benzoate, (R)-(+)-limonene, tert-amyl methyl ether, trans-crotonaldehyde, and diethylene glycol are reported. The standard energy of combustion and hence standard enthalpy of formation of each compound in the liquid phase has been measured using an oxygen rotating-bomb calorimeter without rotation. Vapor pressures were measured to a pressure limit of 270 kPa or the lower decomposition point for each of the six compounds using a twin ebulliometric apparatus. Liquid-phase densities along the saturation line were measured for each compound over a range of temperature (ambient to a maximum of 548 K). A differential scanningmore » calorimeter was used to measure two-phase (liquid + vapor) heat capacities for each compound in the temperature region ambient to the critical temperature or lower decomposition point. For methyl benzoate and tert-amyl methyl ether, critical temperatures and critical densities were determined from the DSC results and corresponding critical pressures derived from the fitting procedures. Fitting procedures were used to derive critical temperatures, critical pressures, and critical densities for each of the remaining compounds. The results of the measurements were combined to derive a series of thermophysical properties including critical temperature, critical density, critical pressure, acentric factor, enthalpies of vaporization (restricted to within {+-}50 K of the temperature region of the experimentally determined vapor pressures), and heat capacities along the saturation line. Wagner-type vapor-pressure equations were derived for each compound. All measured and derived values were compared with those obtained in a search of the literature. Recommended critical parameters are listed for each of the compounds studied. Group-additivity parameters, useful in the application of the Benson gas-phase group-contribution correlations, were derived.« less

Solution-mediated phase transformation of haloperidol mesylate in the presence of sodium lauryl sulfate.

PubMed

Greco, Kristyn; Bogner, Robin

2011-09-01

Forming a salt is a common way to increase the solubility of a poorly soluble compound. However, the solubility enhancement gained by salt formation may be lost due to solution-mediated phase transformation (SMPT) during dissolution. The SMPT of a salt can occur due to a supersaturated solution near the dissolving surface caused by pH or other solution conditions. In addition to changes in pH, surfactants are also known to affect SMPT. In this study, SMPT of a highly soluble salt, haloperidol mesylate, at pH 7 in the presence of a commonly used surfactant, sodium lauryl sulfate (SLS), was investigated. Dissolution experiments were performed using a flow-through dissolution apparatus with solutions containing various concentrations of SLS. Compacts of haloperidol mesylate were observed during dissolution in the flow-through apparatus using a stereomicroscope. Raman microscopy was used to characterize solids. The dissolution of haloperidol mesylate was significantly influenced by the addition of sodium lauryl sulfate. In conditions where SMPT was expected, the addition of SLS at low concentrations (0.1-0.2 mM) reduced the dissolution of haloperidol mesylate. In solutions containing concentrations of SLS above the critical micelle concentration (CMC) (10-15 mM), the dissolution of haloperidol mesylate increased compared to below the CMC. The solids recovered from solubility experiments of haloperidol mesylate indicated that haloperidol free base precipitated at all concentrations of SLS. Above 5 mM of SLS, Raman microscopy suggested a new form, perhaps the estolate salt. The addition of surfactant in solids that undergo solution-mediated phase transformation can add complexity to the dissolution profiles and conversion.

Dehydration kinetics and thermochemistry of selected hydrous phases, and simulated gas release pattern in carbonaceous chondrites

NASA Technical Reports Server (NTRS)

Bose, Kunal; Ganguly, J.

1992-01-01

As part of our continued program of study on the volatile bearing phases and volatile resource potential of carbonaceous chondrite, results of our experimental studies on the dehydration kinetics of talc as a function of temperature and grain size (50 to 0.5 microns), equilibrium dehydration boundary of talc to 40 kbars, calorimetric study of enthalpy of formation of both natural and synthetic talc as a function of grain size, and preliminary results on the dehydration kinetics of epsomite are reported. In addition, theoretical calculations on the gas release pattern of Murchison meteorite, which is a C2(CM) carbonaceous chondrite, were performed. The kinetic study of talc leads to a dehydration rate constant for 40-50 microns size fraction of k = (3.23 x 10(exp 4))exp(-Q/RT)/min with the activation energy Q = 376 (plus or minus 20) kJ/mole. The dehydration rate was found to increase somewhat with decreasing grain size. The enthalpy of formation of talc from elements was measured to be -5896(10) kJ/mol. There was no measurable effect of grain size on the enthalpy beyond the limits of precision of the calorimetric studies. Also the calorimetric enthalpy of both synthetic and natural talc was found to be essentially the same, within the precision of measurements, although the natural talc had a slightly larger field of stability in our phase equilibrium studies. The high pressure experimental data the dehydration equilibrium of talc (talc = enstatite + coesite + H2O) is in strong disagreement with that calculated from the available thermochemical data, which were constrained to fit the low pressure experimental results. The calculated gas release pattern of Murchison meteorite were in reasonable agreement with that determined by stepwise heating in a gas chromatograph.

Solubility of pyromorphite Pb 5(PO 4) 3Cl at 5–65°C and its experimentally determined thermodynamic parameters

DOE PAGES

Topolska, Justyna; Manecki, Maciej; Bajda, Tomasz; ...

2016-03-19

Here, the solubility of synthetic pyromorphite Pb 5(PO 4) 3Cl was determined in a series of dissolution experiments conducted at 5–65 °C and at pH = 2.0. The equilibrium was established within 4 months. The dissolution of pyromorphite was congruent at all the temperatures, and the measured solubility product log K sp,298 for the dissolution reaction: Pb 5(PO 4) 3Cl ⇌ 5Pb 2+ + 3PO 4 3- + Cl - was determined to be –79.6 ± 0.15. The equilibrium ion activity product of pyromorphite increased with temperature, indicating a positive enthalpy of the dissolution reaction in the temperature range frommore » 5 to 65 °C. The temperature dependence of the log K sp was nonlinear: log K sp = A – B/T + D log(T), where A = 478.77 ± 136.62, B = 29,378 ± 6215, and D = –185.81 ± 46.77. This allowed for calculation of ΔG° r = 454.0 ± 1.7 kJ·mol –1, ΔH° r = 101.8 ± 6.0 J·mol –1·K –1, ΔC° p,r = –1545 ± 388.9 J·mol –1·K –1, and ΔS° r = –1181 ± 382 J·mol –1·K –1 of the dissolution reaction. Using these values and the published standard state quantities for constituent ions, the values of ΔG° f = –3764.3 ± 3.5 kJ·mol –1, ΔH° f = –4108.4 ± 7.9 J·mol –1·K –1, S° f = 622 ± 382 J·mol –1·K –1, and C° pf = 402 ± 398 J·mol –1·K –1 were calculated for synthetic pyromorphite Pb 5(PO 4) 3Cl.« less

Optimization of Dissolution Compartments in a Biorelevant Dissolution Apparatus Golem v2, Supported by Multivariate Analysis.

PubMed

Stupák, Ivan; Pavloková, Sylvie; Vysloužil, Jakub; Dohnal, Jiří; Čulen, Martin

2017-11-23

Biorelevant dissolution instruments represent an important tool for pharmaceutical research and development. These instruments are designed to simulate the dissolution of drug formulations in conditions most closely mimicking the gastrointestinal tract. In this work, we focused on the optimization of dissolution compartments/vessels for an updated version of the biorelevant dissolution apparatus-Golem v2. We designed eight compartments of uniform size but different inner geometry. The dissolution performance of the compartments was tested using immediate release caffeine tablets and evaluated by standard statistical methods and principal component analysis. Based on two phases of dissolution testing (using 250 and 100 mL of dissolution medium), we selected two compartment types yielding the highest measurement reproducibility. We also confirmed a statistically ssignificant effect of agitation rate and dissolution volume on the extent of drug dissolved and measurement reproducibility.

Beyond Atomic Sizes and Hume-Rothery Rules: Understanding and Predicting High-Entropy Alloys

DOE PAGES

Troparevsky, M. Claudia; Morris, James R.; Daene, Markus; ...

2015-09-03

High-entropy alloys constitute a new class of materials that provide an excellent combination of strength, ductility, thermal stability, and oxidation resistance. Although they have attracted extensive attention due to their potential applications, little is known about why these compounds are stable or how to predict which combination of elements will form a single phase. Here, we present a review of the latest research done on these alloys focusing on the theoretical models devised during the last decade. We discuss semiempirical methods based on the Hume-Rothery rules and stability criteria based on enthalpies of mixing and size mismatch. To provide insightsmore » into the electronic and magnetic properties of high-entropy alloys, we show the results of first-principles calculations of the electronic structure of the disordered solid-solution phase based on both Korringa Kohn Rostoker coherent potential approximation and large supercell models of example face-centered cubic and body-centered cubic systems. Furthermore, we discuss in detail a model based on enthalpy considerations that can predict which elemental combinations are most likely to form a single-phase high-entropy alloy. The enthalpies are evaluated via first-principles high-throughput density functional theory calculations of the energies of formation of binary compounds, and therefore it requires no experimental or empirically derived input. Finally, the model correctly accounts for the specific combinations of metallic elements that are known to form single-phase alloys while rejecting similar combinations that have been tried and shown not to be single phase.« less

[Raman spectroscopic analysis of dissolution and phase transformation of chloropinnoite in the boric acid aqueous solution].

PubMed

Li, Xiao-Ping; Gao, Shi-Yang; Liu, Zhi-Hong; Hu, Man-Cheng; Xia, Shu-Ping

2005-01-01

Raman spectroscopy of dissolution and transformation of chloropinnoite in 4.5% (w.t.%) boric acid aqueous solution at 30 degrees C has been recorded. The Raman spectra of kinetics process have been obtained. The phase transformation product is kurnakovite (2MgO x 3B2O3 x 15H2O). The main polyborate anions and their interaction in aqueous solution have been proposed according to the Raman spectrum. Some assignments were tentatively given and the relations between the existing forms of polyborate anions and the crystallizing solid phases have been gained. A mechanisms of dissolution and crystallization reactions and the formation condition of kurnakovite in Qinghai-Tibet plateau were proposed and discussed.

Milestone report on MD potential development for uranium silicide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Jianguo; Zhang, Yongfeng; Hales, Jason Dean

2016-03-01

This report summarizes the progress on the interatomic potential development of triuranium-disilicide (U 3Si 2) for molecular dynamics (MD) simulations. The development is based on the Tersoff type potentials for single element U and Si. The Si potential is taken from the literature and a Tersoff type U potential is developed in this project. With the primary focus on the U 3Si 2 phase, some other U-Si systems such as U 3Si are also included as a test of the transferability of the potentials for binary U-Si phases. Based on the potentials for unary U and Si, two sets ofmore » parameters for the binary U-Si system are developed using the Tersoff mixing rules and the cross-term fitting, respectively. The cross-term potential is found to give better results on the enthalpy of formation, lattice constants and elastic constants than those produced by the Tersoff mixing potential, with the reference data taken from either experiments or density functional theory (DFT) calculations. In particular, the results on the formation enthalpy and lattice constants for the U 3Si 2 phase and lattice constants for the high temperature U 3Si (h-U 3Si) phase generated by the cross-term potential agree well with experimental data. Reasonable agreements are also reached on the elastic constants of U 3Si 2, on the formation enthalpy for the low temperature U 3Si (m-U 3Si) and h-U 3Si phases, and on the lattice constants of m-U 3Si phase. All these phases are predicted to be mechanically stable. The unary U potential is tested for three metallic U phases (α, β, γ). The potential is found capable to predict the cohesive energies well against experimental data for all three phases. It matches reasonably with previous experiments on the lattice constants and elastic constants of αU.« less

Integrated Approach for Understanding Impurity Adsorption on Calcite: Mechanisms for Micro-scale Surface Phenomena

NASA Astrophysics Data System (ADS)

Vinson, M. D.; Arvidson, R. S.; Luttge, A.

2004-12-01

A longstanding goal within the field of environmental geochemistry has been the development of a fundamental understanding of the kinetics that governs the interactions of solution-borne impurities with the calcite mineral surface. Recent dissolution experiments using Mg2+, Mn2+, and Sr2+ have shown distinct differences in the interaction of these three impurity ions with the calcite crystal surface. Because the dissolution of carbonate minerals in soils and sediments influences the uptake and migration of groundwater contaminants, a rigorous understanding of the basic processes that occur at the mineral-fluid interface is necessary. We have used vertical scanning interferometry (VSI) coupled with scanning probe microscopy (SPM) to examine calcite crystal dissolution in the presence of Mg2+, Mn2+, and Sr2+, all known dissolution inhibitors and possible groundwater contaminants. We have studied the kinetics of impurity-crystal interactions at a pH 8.8, and in the presence or absence of dissolved inorganic carbon. Our data show that, when individually introduced into undersaturated solutions, Mg2+ and Mn2+ are shown to activate the calcite crystal surface, resulting in enhanced etch pit nucleation rates and step density. Conversely, Sr2+ is shown to cause passivation of the calcite surface. The effect is intensified when solutions are saturated with respect to atmospheric CO2. Results indicate that aqueous CO32- (or HCO3-) may influence how aqueous metal ionic complexes interact with the crystal surface. Furthermore, the influence is differently exhibited, and passivation or activation ultimately depends on the properties of the diffusing metal ion or metal-hydroxide complex. These properties include for example, differences in hydration enthalpy, the effective ionic radius, and electron shell configuration.

A functional relation for field-scale nonaqueous phase liquid dissolution developed using a pore network model

USGS Publications Warehouse

Dillard, L.A.; Essaid, H.I.; Blunt, M.J.

2001-01-01

A pore network model with cubic chambers and rectangular tubes was used to estimate the nonaqueous phase liquid (NAPL) dissolution rate coefficient, Kdissai, and NAPL/water total specific interfacial area, ai. Kdissai was computed as a function of modified Peclet number (Pe???) for various NAPL saturations (SN) and ai during drainage and imbibition and during dissolution without displacement. The largest contributor to ai was the interfacial area in the water-filled corners of chambers and tubes containing NAPL. When Kdissai was divided by ai, the resulting curves of dissolution coefficient, Kdiss versus Pe??? suggested that an approximate value of Kdiss could be obtained as a weak function of hysteresis or SN. Spatially and temporally variable maps of Kdissai calculated using the network model were used in field-scale simulations of NAPL dissolution. These simulations were compared to simulations using a constant value of Kdissai and the empirical correlation of Powers et al. [Water Resour. Res. 30(2) (1994b) 321]. Overall, a methodology was developed for incorporating pore-scale processes into field-scale prediction of NAPL dissolution. Copyright ?? 2001 .

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stratz, S. Adam; Jones, Steven J.; Mullen, Austin D.

Newly-established adsorption enthalpy and entropy values of 12 lanthanide hexafluoroacetylacetonates, denoted Ln[hfac] 4, along with the experimental and theoretical methodology used to obtain these values, are presented for the first time. The results of this work can be used in conjunction with theoretical modeling techniques to optimize a large-scale gas-phase separation experiment using isothermal chromatography. The results to date indicate average adsorption enthalpy and entropy values of the 12 Ln[hfac] 4 complexes ranging from -33 to -139 kJ/mol K and -299 to -557 J/mol, respectively.

High-pressure transitions of diopside and wollastonite: phase equilibria and thermochemistry of CaMgSi 2O 6, CaSiO 3 and CaSi 2O 5-CaTiSiO 5 system

NASA Astrophysics Data System (ADS)

Akaogi, M.; Yano, M.; Tejima, Y.; Iijima, M.; Kojitani, H.

2004-06-01

Phase transitions of CaMgSi 2O 6 diopside and CaSiO 3 wollastonite were examined at pressures to 23 GPa and temperatures to 2000 °C, using a Kawai-type multiavil apparatus. Enthalpies of high-pressure phases in CaSiO 3 and in the CaSi 2O 5-CaTiSiO 5 system were also measured by high-temperature calorimetry. At 17-18 GPa, diopside dissociates to CaSiO 3-rich perovskite + Mg-rich (Mg,Ca)SiO 3 tetragonal garnet (Gt) above about 1400 °C. The solubilities of CaSiO 3 in garnet and MgSiO 3 in perovskite increase with temperature. At 17-18 GPa below about 1400 °C, diopside dissociates to Ca-perovskite + β-Mg 2SiO 4 + stishovite. The Mg, Si-phases coexisting with Ca-perovskite change to γ-Mg 2SiO 4 + stishovite, to ilmenite, and finally to Mg-perovskite with increasing pressure. CaSiO 3 wollastonite transforms to the walstromite structure, and further dissociates to Ca 2SiO 4 larnite + CaSi 2O 5 titanite. The latter transition occurs at 9-11 GPa with a positive Clapeyron slope. At 1600 °C, larnite + titanite transform to CaSiO 3 perovskite at 14.6±0.6 GPa, calibrated against the α-β transition pressure of Mg 2SiO 4. The enthalpies of formation of CaSiO 3 walstromite and CaSi 2O 5 titanite from the mixture of CaO and SiO 2 quartz at 298 K have been determined as -76.1±2.8, and -27.8±2.1 kJ/mol, respectively. The latter was estimated from enthalpy measurements of titanite solid solutions in the system CaSi 2O 5-CaTiSiO 5, because CaSi 2O 5 titanite transforms to a triclinic phase upon decompression. The enthalpy difference between titanite and the triclinic phase is only 1.5±4.8 kJ/mol. Using these enthalpies of formation and those of larnite and CaSiO 3 perovskite, the transition boundaries in CaSiO 3 have been calculated. The calculated boundaries for the wollastonite-walstromite-larnite + titanite transitions are consistent with the experimental determinations within the errors. The calculated boundary between larnite + titanite and Ca-perovskite has a slope of 1.3-1.8(±0.4) MPa/K, and is located at a pressure about 2 GPa higher than that determined by [Am. Mineral. 79 (1994) 1219].

Thermodynamics of Manganese Oxides at Bulk and Nanoscale: Phase Formation, Transformation, Oxidation-Reduction, and Hydration

NASA Astrophysics Data System (ADS)

Birkner, Nancy R.

Natural manganese oxides are generally formed in surficial environments that are near ambient temperature and water-rich, and may be exposed to wet-dry cycles and a variety of adsorbate species that influence dramatically their level of hydration. Manganese oxide minerals are often poorly crystalline, nanophase, and hydrous. In the near-surface environment they are involved in processes that are important to life, such as water column oxygen cycling, biomineralization, and transport of minerals/nutrients through soils and water. These processes, often involving transformations among manganese oxide polymorphs, are governed by a complex interplay between thermodynamics and kinetics. Manganese oxides are also used in technology as catalysts, and for other applications. The major goal of this dissertation is to examine the energetics of bulk and nanophase manganese oxide phases as a function of particle size, composition, and surface hydration. Careful synthesis and characterization of manganese oxide phases with different surface areas provided samples for the study of enthalpies of formation by high temperature oxide melt solution calorimetry and of the energetics of water adsorption on their surfaces. These data provide a quantitative picture of phase stability and how it changes at the nanoscale. The surface energy of the hydrous surface of Mn3O4 is 0.96 +/- 0.08 J/m2, of Mn2O3 is 1.29 +/- 0.10 J/m2, and of MnO2 is 1.64 +/- 0.10 J/m2. The surface energy of the anhydrous surface of Mn3O4 is 1.62 +/- 0.08 J/m 2, of Mn2O3 is 1.77 +/- 0.10 J/m 2, and of MnO2 is 2.05 +/- 0.10 J/m2. Supporting preliminary findings (Navrotsky et al., 2010), the spinel phase (Mn3O4) has a lower surface energy (more stabilizing) than bixbyite, while the latter has a smaller surface energy than pyrolusite. These differences significantly change the positions in oxygen fugacity---temperature space of the redox couples Mn3O4-Mn2O 3 and Mn2O3-MnO2 favoring the lower surface enthalpy phase (the spinel Mn3O4) for smaller particle size and in the presence of surface hydration. Chemisorption of water onto anhydrous nanophase Mn2O 3 surfaces promotes rapidly reversible redox phase changes at room temperature as confirmed by calorimetry, X-ray diffraction, and titration for manganese average oxidation state. Water adsorption microcalorimetry (in situ) at room temperature measured the strongly exothermic integral enthalpy of water adsorption (-103.5 kJ/mol) and monitored the energetics of the redox phase transformation. Hydration-driven redox transformation of anhydrous nanophase Mn(III) 2O3, (high surface enthalpy of anhydrous surfaces 1.77 +/- 0.10 J/m2) to Mn(II,III)3O4 (lower surface enthalpy 0.96 +/- 0.08 J/m2) occurred during the first few doses of water vapor. Surface reduction of nanoparticle bixbyite (Mn 2O3) to hausmannite (Mn3O4) occurs under conditions where no such reactions are seen or expected on grounds of bulk thermodynamics in coarse-grained materials. Layered structure manganese oxides contain alkali or alkaline earth cations and water, are generally fine-grained, and have considerable thermodynamic stability. The surface enthalpies (SE) of layered and tunnel structure complex manganese oxides are significantly lower than those of the binary manganese oxide phases. The SE for hydrous surfaces and overall manganese average oxidation state (AOS) (value in parentheses) are: cryptomelane 0.77 +/- 0.10 J/m 2 (3.78), sodium birnessite 0.69 +/- 0.13 J/m2 (3.56), potassium birnessite 0.55 +/- 0.11 J/m2 (3.52), and calcium birnessite 0.41 +/- 0.11 J/m2 (3.50). Surface enthalpies of hydrous surfaces of the calcium manganese oxide nanosheets are: deltaCa 0.39MnO2.3nH2O 0.75 +/- 0.10 J/m2 (3.89) and deltaCa0.43MnO2.3nH2O 0.57 +/- 0.12 J/m2 (3.68). The surface enthalpy of the complex manganese oxides appears to decrease with decreasing manganese average oxidation state, that is, with greater mixed valence manganese (Mn 3+/4+). Low surface energy suggests loose binding of H2O on the internal and external surfaces and may be critical to catalysis in both natural and technological settings.

Understanding SO2 Capture by Ionic Liquids.

PubMed

Mondal, Anirban; Balasubramanian, Sundaram

2016-05-19

Ionic liquids have generated interest for efficient SO2 absorption due to their low vapor pressure and versatility. In this work, a systematic investigation of the structure, thermodynamics, and dynamics of SO2 absorption by ionic liquids has been carried out through quantum chemical calculations and molecular dynamics (MD) simulations. MP2 level calculations of several ion pairs complexed with SO2 reveal its preferential interaction with the anion. Results of condensed phase MD simulations of SO2-IL mixtures manifested the essential role of both cations and anions in the solvation of SO2, where the solute is surrounded by the "cage" formed by the cations (primarily its alkyl tail) through dispersion interactions. These structural effects of gas absorption are substantiated by calculated Gibbs free energy of solvation; the dissolution is demonstrated to be enthalpy driven. The entropic loss of SO2 absorption in ionic liquids with a larger anion such as [NTf2](-) has been quantified and has been attributed to the conformational restriction of the anion imposed by its interaction with SO2. SO2 loading IL decreases its shear viscosity and enhances the electrical conductivity. This systematic study provides a molecular level understanding which can aid the design of task-specific ILs as electrolytes for efficient SO2 absorption.

Solvation enthalpies and heat capacities of n-alkanes in four polymer phases by capillary gas chromatography.

PubMed

Görgenyi, Miklós; Héberger, Károly

2005-04-01

Molar solvation enthalpy (deltasol H(o)298) and molar heat capacity changes (deltasol C(o)p) were determined by gas chromatography for the C6-C12 n-alkanes on four preferred stationary phases (100% polydimethyl siloxane, 50% diphenyl-50% dimethyl polysiloxane, 50% trifluoropropyl methylsiloxane, and polyethylene glycol) in commercial FSOT. Statistical evaluation indicated the temperature independence of deltasol C(o)p in the range 303-393 K. Deltasol H(o)298 depends linearly on the number of carbon atoms in the n-alkanes, but no linearity could be established for deltasol C(o)p of higher homologues on polar columns, which may be due to a more ordered state on the liquid phase. The homologues for which a linear temperature dependence exists demonstrated that deltasol C(o)p is related linearly to the van der Waals volume and the temperature derivative of the density of the stationary phase. The results are consistent with a simple physical explanation at the molecular level.

First-principles study of high-pressure structural phase transitions of magnesium

NASA Astrophysics Data System (ADS)

Liu, Qiuxiang; Fan, Changzeng; Zhang, Ruijun

2009-06-01

The structural phase transitions for the hcp, bcc, dhcp, and fcc of magnesium at hydrostatic pressures larger than about 200 GPa at zero temperature are studied by first-principles total energy calculations. The plane-wave basis pseudopotential method has been adopted, in which the generalized gradient approximation implanted in the CASTEP code is employed. By comparing the enthalpy differences of the hcp structure with other three structures under different pressures, it can be seen that when the pressure becomes higher than about 65, 130, and 190 GPa, the bcc, dhcp, and fcc structures become more stable relative to the hcp structure, respectively. Due to the lowest enthalpy value of the bcc structure above 65 GPa, it can be deduced that magnesium may transform to the bcc structure from the ground state hcp structure around 65 GPa, but no further phase transitions occur without additionally applying high temperature. In addition, the equation of state of magnesium is calculated, indicating that bcc structure is the softest phase.

Thermodynamic assessment of Ag–Cu–In

DOE PAGES

Muzzillo, Christopher P.; Anderson, Tim

2018-01-16

The Ag-Cu-In thermodynamic material system is of interest for brazing alloys and chalcopyrite thin-film photovoltaics. To advance these applications, Ag-Cu-In was assessed and a Calphad model was developed. Binary Ag-Cu and Cu-In parameters were taken from previous assessments, while Ag-In was re-assessed. Structure-based models were employed for ..beta..-bcc(A2)-Ag 3In, ..gamma..-Ag 9In 4, and AgIn 2 to obtain good fit to enthalpy, phase boundary, and invariant reaction data for Ag-In. Ternary Ag-Cu-In parameters were optimized to achieve excellent fit to activity, enthalpy, and extensive phase equilibrium data. Relative to the previous Ag-Cu-In assessment, fit was improved while fewer parameters were used.

Thermodynamic assessment of Ag–Cu–In

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muzzillo, Christopher P.; Anderson, Tim

The Ag-Cu-In thermodynamic material system is of interest for brazing alloys and chalcopyrite thin-film photovoltaics. To advance these applications, Ag-Cu-In was assessed and a Calphad model was developed. Binary Ag-Cu and Cu-In parameters were taken from previous assessments, while Ag-In was re-assessed. Structure-based models were employed for ..beta..-bcc(A2)-Ag 3In, ..gamma..-Ag 9In 4, and AgIn 2 to obtain good fit to enthalpy, phase boundary, and invariant reaction data for Ag-In. Ternary Ag-Cu-In parameters were optimized to achieve excellent fit to activity, enthalpy, and extensive phase equilibrium data. Relative to the previous Ag-Cu-In assessment, fit was improved while fewer parameters were used.

Influence of Calcium on Microbial Reduction of Solid Phase Uranium (VI)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chongxuan; Jeon, Byong-Hun; Zachara, John M.

2007-06-27

The effect of calcium on microbial reduction of a solid phase U(VI), sodium boltwoodite (NaUO2SiO3OH ∙1.5H2O), was evaluated in a culture of a dissimilatory metal-reducing bacterium (DMRB), Shewanella oneidensis strain MR-1. Batch experiments were performed in a non-growth bicarbonate medium with lactate as electron donor at pH 7 buffered with PIPES. Calcium increased both the rate and extent of Na-boltwoodite dissolution by increasing its solubility through the formation of a ternary aqueous calcium-uranyl-carbonate species. The ternary species, however, decreased the rates of microbial reduction of aqueous U(VI). Laser-induced fluorescence spectroscopy (LIFS) and transmission electron microscopy (TEM) revealed that microbial reductionmore » of solid phase U(VI) is a sequentially coupled process of Na-boltwoodite dissolution, U(VI) aqueous speciation, and microbial reduction of dissolved U(VI) to U(IV) that accumulated on bacterial surfaces/periplasm. The overall rates of microbial reduction of solid phase U(VI) can be described by the coupled rates of dissolution and microbial reduction that were both influenced by calcium. The results demonstrated that dissolved U(VI) concentration during microbial reduction was a complex function of solid phase U(VI) dissolution kinetics, aqueous U(VI) speciation, and microbial activity.« less

Unexpected Ground-State Structure and Mechanical Properties of Ir₂Zr Intermetallic Compound.

PubMed

Zhang, Meiguang; Cao, Rui; Zhao, Meijie; Du, Juan; Cheng, Ke

2018-01-10

Using an unbiased structure searching method, a new orthorhombic Cmmm structure consisting of ZrIr 12 polyhedron building blocks is predicted to be the thermodynamic ground-state of stoichiometric intermetallic Ir₂Zr in Ir-Zr systems. The formation enthalpy of the Cmmm structure is considerably lower than that of the previously synthesized Cu₂Mg-type phase, by ~107 meV/atom, as demonstrated by the calculation of formation enthalpy. Meanwhile, the phonon dispersion calculations further confirmed the dynamical stability of Cmmm phase under ambient conditions. The mechanical properties, including elastic stability, rigidity, and incompressibility, as well as the elastic anisotropy of Cmmm -Ir₂Zr intermetallic, have thus been fully determined. It is found that the predicted Cmmm phase exhibits nearly elastic isotropic and great resistance to shear deformations within the (100) crystal plane. Evidence of atomic bonding related to the structural stability for Ir₂Zr were manifested by calculations of the electronic structures.

Facing the challenge of predicting the standard formation enthalpies of n-butyl-phosphate species with ab initio methods

NASA Astrophysics Data System (ADS)

Saab, Mohamad; Réal, Florent; Šulka, Martin; Cantrel, Laurent; Virot, François; Vallet, Valérie

2017-06-01

Tributyl-phosphate (TBP), a ligand used in the PUREX liquid-liquid separation process of spent nuclear fuel, can form an explosive mixture in contact with nitric acid that might lead to a violent explosive thermal runaway. In the context of safety of a nuclear reprocessing plant facility, it is crucial to predict the stability of TBP at elevated temperatures. So far, only the enthalpies of formation of TBP are available in the literature with rather large uncertainties, while those of its degradation products, di-(HDBP) and mono-(H2MBP), are unknown. In this goal, we have used state-of-the art quantum chemical methods to compute the formation enthalpies and entropies of TBP and its degradation products di-(HDBP) and mono-(H2MBP) in gas and liquid phases. Comparisons of levels of quantum chemical theory revealed that there are significant effects of correlation on their electronic structures, pushing for the need of not only high level of electronic correlation treatment, namely, local coupled cluster with single and double excitation operators and perturbative treatment of triple excitations, but also extrapolations to the complete basis to produce reliable and accurate thermodynamics data. Solvation enthalpies were computed with the conductor-like screening model for real solvents [COSMO-RS], for which we observe errors not exceeding 22 kJ mol-1. We thus propose with final uncertainty of about 20 kJ mol-1 standard enthalpies of formation of TBP, HDBP, and H2MBP which amounts to -1281.7 ± 24.4, -1229.4 ± 19.6, and -1176.7 ± 14.8 kJ mol-1, respectively, in the gas phase. In the liquid phase, the predicted values are -1367.3 ± 24.4, -1348.7 ± 19.6, and -1323.8± 14.8 kJ mol-1, to which we may add about -22 kJ mol-1 error from the COSMO-RS solvent model. From these data, the complete hydrolysis of TBP is predicted as an exothermic phenomena but showing a slightly endergonic process.

Evolution of a mini-scale biphasic dissolution model: Impact of model parameters on partitioning of dissolved API and modelling of in vivo-relevant kinetics.

PubMed

Locher, Kathrin; Borghardt, Jens M; Frank, Kerstin J; Kloft, Charlotte; Wagner, Karl G

2016-08-01

Biphasic dissolution models are proposed to have good predictive power for the in vivo absorption. The aim of this study was to improve our previously introduced mini-scale dissolution model to mimic in vivo situations more realistically and to increase the robustness of the experimental model. Six dissolved APIs (BCS II) were tested applying the improved mini-scale biphasic dissolution model (miBIdi-pH-II). The influence of experimental model parameters including various excipients, API concentrations, dual paddle and its rotation speed was investigated. The kinetics in the biphasic model was described applying a one- and four-compartment pharmacokinetic (PK) model. The improved biphasic dissolution model was robust related to differing APIs and excipient concentrations. The dual paddle guaranteed homogenous mixing in both phases; the optimal rotation speed was 25 and 75rpm for the aqueous and the octanol phase, respectively. A one-compartment PK model adequately characterised the data of fully dissolved APIs. A four-compartment PK model best quantified dissolution, precipitation, and partitioning also of undissolved amounts due to realistic pH profiles. The improved dissolution model is a powerful tool for investigating the interplay between dissolution, precipitation and partitioning of various poorly soluble APIs (BCS II). In vivo-relevant PK parameters could be estimated applying respective PK models. Copyright © 2016 Elsevier B.V. All rights reserved.

In situ spectroscopic and solution analyses of the reductive dissolution of Mn02 by Fe(II)

USGS Publications Warehouse

Villinski, John E.; O'Day, Peggy A.; Corley, Timothy L.; Conklin, Martha H.

2001-01-01

The reductive dissolution of MnO2 by Fe(II) under conditions simulating acid mine drainage (pH 3, 100 mM SO42-) was investigated by utilizing a flow-through reaction cell and synchrotron X-ray absorption spectroscopy. This configuration allows collection of in situ, real-time X-ray absorption near-edge structure (XANES) spectra and bulk solution samples. Analysis of the solution chemistry suggests that the reaction mechanism changed (decreased reaction rate) as MnO2 was reduced and Fe(III) precipitated, primarily as ferrihydrite. Simultaneously, we observed an additional phase, with the local structure of jacobsite (MnFe2O4), in the Mn XANES spectra of reactants and products. The X-ray absorbance of this intermediate phase increased during the experiment, implying an increase in concentration. The presence of this phase, which probably formed as a surface coating, helps to explain the reduced rate of dissolution of manganese(IV) oxide. In natural environments affected by acid mine drainage, the formation of complex intermediate solid phases on mineral surfaces undergoing reductive dissolution may likewise influence the rate of release of metals to solution.

Cloud iron speciation: Experimental simulations

NASA Astrophysics Data System (ADS)

Sofikitis, A. M.; Colin, J. L.; Desboeufs, K. V.; Losno, R.

2003-04-01

The aim of our contribution is to identify major processes controlling iron speciation in the atmospheric aqueous phase. Fe is known to participate in a variety of redox reactions in cloud chemistry, as well as controlling free radical production in the troposphere. Iron cycling is slower than cycles with other catalytic transition metals (Cu, Mn). The residence time of each iron species is around ten minutes, this allows analytical separation and determination of each iron redox species and therefore its ratio. As the only source of trace metals in aqueous atmospheric phase is due to the solubilization of aerosols, we present here dissolution rate measurements obtained by laboratory experiments with an open flow reactor. This reactor enables us to reproduce the dissolution of a particle in aqueous atmospheric water. The dissolution rate and the speciation of iron are dependent on the mineralogy of the solid phase. Our experiments included Goethite, hematite and vermiculite, which are typical mineral constituents of dust particles. Comparisons were made with natural loess which is a blend of various crystalline and amorphous phases. We will present results of crustal origin particles dissolution experiments where kinetic parameters are determined, including iron speciation. Major functions of variation are pH and photochemistry in the aqueous weathering solution.

Column Experiments to Interpret Weathering in Columbia Hills

NASA Technical Reports Server (NTRS)

Hausrath, E. M.; Morris, R.V.; Ming, D.W.; Golden, D.C.; Galindo, C.; Sutter, B.

2009-01-01

Phosphate mobility has been postulated as an indicator of early aqueous activity on Mars. In addition, rock surfaces analyzed by the Mars Exploration Rover Spirit are consistent with the loss of a phosphate- containing mineral To interpret phosphate alteration behavior on Mars, we performed column dissolution experiments leaching the primary phases Durango fluorapatite, San Carlos olivine, and basalt glass (Stapafjell Volcano, courtesy of S. Gislason, University of Iceland) [3,4]) with acidic solutions. These phases were chosen to represent quickly dissolving phases likely present in Columbia Hills. Column dissolution experiments are closer to natural dissolution conditions than batch experiments, although they can be difficult to interpret. Acidic solutions were used because the leached layers on the surfaces of these rocks have been interpreted as resulting from acid solutions [5].

Thermal fluids for CSP systems: Alkaline nitrates/nitrites thermodynamics modelling method

NASA Astrophysics Data System (ADS)

Tizzoni, A. C.; Sau, S.; Corsaro, N.; Giaconia, A.; D'Ottavi, C.; Licoccia, S.

2016-05-01

Molten salt (MS) mixtures are used for the transport (HTF-heat transfer fluid) and storage of heat (HSM-heat storage material) in Concentration Solar Plants (CSP). In general, alkaline and earth-alkaline nitrate/nitrite mixtures are employed. Along with its upper stability temperature, the melting point (liquidus point) of a MS mixture is one of the main parameters which defines its usefulness as a HTF and HSM medium. As a result, we would like to develop a predictive model which will allow us to forecast freezing points for different MS mixture compositions; thus circumventing the need to determine experimentally the phase diagram for each MS mixture. To model ternary/quaternary phase diagram, parameters for the binary subsystems are to be determined, which is the purpose of the concerned work. In a binary system with components A and B, in phase equilibrium conditions (e.g. liquid and solid) the chemical potentials (partial molar Gibbs energy) for each component in each phase are equal. For an ideal solution it is possible to calculate the mixing (A+B) Gibbs energy:ΔG = ΔH - TΔS = RT(xAlnxA + xBlnxB) In case of non-ideal solid/liquid mixtures, such as the nitrates/nitrites compositions investigated in this work, the actual value will differ from the ideal one by an amount defined as the "mixing" (mix) Gibbs free energy. If the resulting mixtures is assumed, as indicated in the previous literature, to follow a "regular solution" model, where all the non-ideality is considered included in the enthalpy of mixing value and considering, for instance, the A component:Δ G ≡0 =(Δ HA-T Δ SA)+(ΔH¯ m i x AL-T ΔS¯ m i x AL)-(ΔH¯ m i x AS-T ΔS¯ m i x AS)where the molar partial amounts can be calculated from the total value by the Gibbs Duhem equation: (ΔH¯m i x AL=ΔHm i x-XB Ld/Δ Hm i x d XB L ) L;(ΔH¯m i x AS=ΔHm i x-XB Sd/Δ Hm i x d XB S ) S and, in general, it is possible to express the mixing enthalpy for solids and liquids as a function of the mol fraction: Δ HL m i x=XA LXB L(a1+b1XA L+c1XA LXB L),Δ HS m i x=XA SXB S(a2+b2XA S+c2XA SXB S) From the latter expressions it can be possible to modelize the phase diagram of a binary mixtures by using the a,b and c couples of parameters. To calculate those coefficients a method commonly employed in literature is to measure the mixing enthalpies, or to use one reported of the enthalpy of mixing (for instance for the liquid state) and calculate the other one using the phase diagram points. A direct ΔHmix (in solid or liquid phase) measurement can be difficult to carry out using common DSC equipment generally present in research laboratories. In fact, such determinations can be, in principle, performed, but the obtained data will be affected by large experimental errors. On the other hand, it is possible to obtain values with great precision regarding the algebraic sum of mixing enthalpies and the phase diagram trend. For this reason, only the phase diagrams are proposed to be used to calculate a, b, c parameters, and, subsequently, the total (liquid-solid algebraic sum) enthalpy of mixing will be employed to verify their validity. At this aim, a C++ code was assessed and used. Three binary mixtures were considered by combining NaNO3, KNO3 and NaNO2.

Vapour pressure and standard enthalpy of sublimation of KBF 4 by a TG based transpiration technique

NASA Astrophysics Data System (ADS)

Pankajavalli, R.; Ananthasivan, K.; Anthonysamy, S.; Vasudeva Rao, P. R.

2005-10-01

A horizontal thermobalance was adapted as a transpiration apparatus for the measurement of the vapour pressure of KBF4 (s). Attainment of equilibrium was ascertained by the invariance of the measured values of the vapour pressures over a range of flows under isothermal conditions. Measured values of the vapour pressures could be represented by the least-squares expressions: log (p/Pa) = 8.16(±0.01) - 4892(±248)/T(K)(538-560 K), log (p/Pa) = 6.85(±0.06) - 4158(±240)/T(K) (576-660 K), which correspond to the equilibria of orthorhombic and cubic KBF4 vapours, respectively. From these expressions the temperature of transformation of the orthorhombic to the cubic phase was identified to be 561 K. From the slopes of the above equations, the enthalpies of sublimation of the orthorhombic and cubic phases were found to be (93.7 ± 4.7) and (79.6 ± 4.6) kJ mol-1, respectively. These values differ by 14.1 kJ mol-1 which could be ascribed to the enthalpy of the orthorhombic to cubic phase transition of KBF4. Third-law analysis of the vapour pressure data yielded a value of (104.6 ± 1.0) kJ mol-1 for Δ Hsubo of KBF4 (s) at 298.15 K.

A FUNCTIONAL RELATION FOR FIELD-SCALE NONAQUEOUS PHASE LIQUID DISSOLUTION DEVELOPED USING A PORE NETWORK MODEL. (R825689C080)

EPA Science Inventory

Abstract

A pore network model with cubic chambers and rectangular tubes was used to estimate the nonaqueous phase liquid (NAPL) dissolution rate coefficient, K_dissa_i, and NAPL/water total specific interfacial area, a_i

A FUNCTIONAL RELATION FOR FIELD-SCALE NONAQUEOUS PHASE LIQUID DISSOLUTION DEVELOPED USING A PORE NETWORK MODEL. (R825689C079)

EPA Science Inventory

Abstract

A pore network model with cubic chambers and rectangular tubes was used to estimate the nonaqueous phase liquid (NAPL) dissolution rate coefficient, K_dissa_i, and NAPL/water total specific interfacial area, a_i

Hydration of dicalcium silicate and diffusion through neo-formed calcium-silicate-hydrates at weathered surfaces control the long-term leaching behaviour of basic oxygen furnace (BOF) steelmaking slag.

PubMed

Stewart, Douglas I; Bray, Andrew W; Udoma, Gideon; Hobson, Andrew J; Mayes, William M; Rogerson, Mike; Burke, Ian T

2018-04-01

Alkalinity generation and toxic trace metal (such as vanadium) leaching from basic oxygen furnace (BOF) steel slag particles must be properly understood and managed by pre-conditioning if beneficial reuse of slag is to be maximised. Water leaching under aerated conditions was investigated using fresh BOF slag at three different particle sizes (0.5-1.0, 2-5 and 10 × 10 × 20 mm blocks) and a 6-month pre-weathered block. There were several distinct leaching stages observed over time associated with different phases controlling the solution chemistry: (1) free-lime (CaO) dissolution (days 0-2); (2) dicalcium silicate (Ca 2 SiO 4 ) dissolution (days 2-14) and (3) Ca-Si-H and CaCO 3 formation and subsequent dissolution (days 14-73). Experiments with the smallest size fraction resulted in the highest Ca, Si and V concentrations, highlighting the role of surface area in controlling initial leaching. After ~2 weeks, the solution Ca/Si ratio (0.7-0.9) evolved to equal those found within a Ca-Si-H phase that replaced dicalcium silicate and free-lime phases in a 30- to 150-μm altered surface region. V release was a two-stage process; initially, V was released by dicalcium silicate dissolution, but V also isomorphically substituted for Si into the neo-formed Ca-Si-H in the alteration zone. Therefore, on longer timescales, the release of V to solution was primarily controlled by considerably slower Ca-Si-H dissolution rates, which decreased the rate of V release by an order of magnitude. Overall, the results indicate that the BOF slag leaching mechanism evolves from a situation initially dominated by rapid hydration and dissolution of primary dicalcium silicate/free-lime phases, to a slow diffusion limited process controlled by the solubility of secondary Ca-Si-H and CaCO 3 phases that replace and cover more reactive primary slag phases at particle surfaces.

Dissolution without disappearing: multicomponent gas exchange for CO2 bubbles in a microfluidic channel.

PubMed

Shim, Suin; Wan, Jiandi; Hilgenfeldt, Sascha; Panchal, Prathamesh D; Stone, Howard A

2014-07-21

We studied the dissolution dynamics of CO2 gas bubbles in a microfluidic channel, both experimentally and theoretically. In the experiments, spherical CO2 bubbles in a flow of a solution of sodium dodecyl sulfate (SDS) first shrink rapidly before attaining an equilibrium size. In the rapid dissolution regime, the time to obtain a new equilibrium is 30 ms regardless of SDS concentration, and the equilibrium radius achieved varies with the SDS concentration. To explain the lack of complete dissolution, we interpret the results by considering the effects of other gases (O2, N2) that are already dissolved in the aqueous phase, and we develop a multicomponent dissolution model that includes the effect of surface tension and the liquid pressure drop along the channel. Solutions of the model for a stationary gas bubble show good agreement with the experimental results, which lead to our conclusion that the equilibrium regime is obtained by gas exchange between the bubbles and liquid phase. Also, our observations from experiments and model calculations suggest that SDS molecules on the gas-liquid interface form a diffusion barrier, which controls the dissolution behaviour and the eventual equilibrium radius of the bubble.

Nonaqueous Phase Liquid Dissolution in Porous Media: Multi-Scale Effects of Multi-Component Dissolution Kinetics on Cleanup Time

DOE Office of Scientific and Technical Information (OSTI.GOV)

McNab, W; Ezzedine, S; Detwiler, R

2007-02-26

Industrial organic solvents such as trichloroethylene (TCE) and tetrachloroethylene (PCE) constitute a principal class of groundwater contaminants. Cleanup of groundwater plume source areas associated with these compounds is problematic, in part, because the compounds often exist in the subsurface as dense nonaqueous phase liquids (DNAPLs). Ganglia (or 'blobs') of DNAPL serve as persistent sources of contaminants that are difficult to locate and remediate (e.g. Fenwick and Blunt, 1998). Current understanding of the physical and chemical processes associated with dissolution of DNAPLs in the subsurface is incomplete and yet is critical for evaluating long-term behavior of contaminant migration, groundwater cleanup, andmore » the efficacy of source area cleanup technologies. As such, a goal of this project has been to contribute to this critical understanding by investigating the multi-phase, multi-component physics of DNAPL dissolution using state-of-the-art experimental and computational techniques. Through this research, we have explored efficient and accurate conceptual and numerical models for source area contaminant transport that can be used to better inform the modeling of source area contaminants, including those at the LLNL Superfund sites, to re-evaluate existing remediation technologies, and to inspire or develop new remediation strategies. The problem of DNAPL dissolution in natural porous media must be viewed in the context of several scales (Khachikian and Harmon, 2000), including the microscopic level at which capillary forces, viscous forces, and gravity/buoyancy forces are manifested at the scale of individual pores (Wilson and Conrad, 1984; Chatzis et al., 1988), the mesoscale where dissolution rates are strongly influenced by the local hydrodynamics, and the field-scale. Historically, the physico-chemical processes associated with DNAPL dissolution have been addressed through the use of lumped mass transfer coefficients which attempt to quantify the dissolution rate in response to local dissolved-phase concentrations distributed across the source area using a volume-averaging approach (Figure 1). The fundamental problem with the lumped mass transfer parameter is that its value is typically derived empirically through column-scale experiments that combine the effects of pore-scale flow, diffusion, and pore-scale geometry in a manner that does not provide a robust theoretical basis for upscaling. In our view, upscaling processes from the pore-scale to the field-scale requires new computational approaches (Held and Celia, 2001) that are directly linked to experimental studies of dissolution at the pore scale. As such, our investigation has been multi-pronged, combining theory, experiments, numerical modeling, new data analysis approaches, and a synthesis of previous studies (e.g. Glass et al, 2001; Keller et al., 2002) aimed at quantifying how the mechanisms controlling dissolution at the pore-scale control the long-term dissolution of source areas at larger scales.« less

Poly(amidoamine) dendrimers on lipid bilayers II: Effects of bilayer phase and dendrimer termination.

PubMed

Kelly, Christopher V; Leroueil, Pascale R; Orr, Bradford G; Banaszak Holl, Mark M; Andricioaei, Ioan

2008-08-07

The molecular structures and enthalpy release of poly(amidoamine) (PAMAM) dendrimers binding to 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) bilayers were explored through atomistic molecular dynamics. Three PAMAM dendrimer terminations were examined: protonated primary amine, neutral acetamide, and deprotonated carboxylic acid. Fluid and gel lipid phases were examined to extract the effects of lipid tail mobility on the binding of generation-3 dendrimers, which are directly relevant to the nanoparticle interactions involving lipid rafts, endocytosis, lipid removal, and/or membrane pores. Upon binding to gel phase lipids, dendrimers remained spherical, had a constant radius of gyration, and approximately one-quarter of the terminal groups were in close proximity to the lipids. In contrast, upon binding to fluid phase bilayers, dendrimers flattened out with a large increase in their asphericity and radii of gyration. Although over twice as many dendrimer-lipid contacts were formed on fluid versus gel phase lipids, the dendrimer-lipid interaction energy was only 20% stronger. The greatest enthalpy release upon binding was between the charged dendrimers and the lipid bilayer. However, the stronger binding to fluid versus gel phase lipids was driven by the hydrophobic interactions between the inner dendrimer and lipid tails.

Vacancies in MgO at ultrahigh pressure: About mantle rheology of super-Earths

NASA Astrophysics Data System (ADS)

Ritterbex, Sebastian; Harada, Takafumi; Tsuchiya, Taku

2018-05-01

First-principles calculations are performed to investigate vacancy formation and migration in the B2 phase of MgO. Defect energetics suggest the importance of intrinsic non-interacting vacancy pairs, even though the extrinsic vacancy concentration might govern atomic diffusion in the B2 phase of MgO. The enthalpies of ionic vacancy migration are generally found to decrease across the B1-B2 phase transition around a pressure of 500 GPa. It is shown that this enthalpy change induces a substantial increase in the rate of vacancy diffusion in MgO of almost four orders of magnitude (∼104) when the B1 phase transforms into the B2 phase with increasing pressure. If plastic deformation is controlled by vacancy diffusion, mantle viscosity is expected to decrease in relation to this enhanced diffusion rate in MgO across the B1-B2 transition in the interior of Earth-like large exoplanets. Our results of atomic relaxations near the defects suggest that diffusion controlled creep viscosity may generally decrease across high-pressure phase transitions with increasing coordination number. Plastic flow and resulting mantle convection in the interior of these super-Earths may be therefore less sluggish than previously thought.

Increasing dissolution of trospium chloride by co-crystallization with urea

NASA Astrophysics Data System (ADS)

Skořepová, Eliška; Hušák, Michal; Čejka, Jan; Zámostný, Petr; Kratochvíl, Bohumil

2014-08-01

The search for various solid forms of an active pharmaceutical ingredient (API) is an important step in drug development. Our aim was to prepare co-crystals of trospium chloride, an anticholinergic drug used for the treatment of incontinence, and to investigate if they have advantageous properties for drug formulation. Phase identification was done by powder X-ray diffraction and single-crystal X-ray diffraction. The chemical composition was verified by solution NMR and the dissolution rate of the prepared phases was studied by IDR (intrinsic dissolution rate). For further analysis of phase stability and transitions, combined thermal analysis and temperature-resolved X-ray powder diffraction were used. Urea was selected as a co-crystallization partner. Trospium chloride urea (1:1) co-crystal was prepared by a solvent evaporation. From single-crystal data, the co-crystal structure was solved in a space group P21/c and compared to previously published structures of trospium chloride. Intrinsic dissolution rate revealed that the co-crystal dissolves 32% faster than pure API. However, its low thermal and pressure stability makes it a challenging choice for the final drug formulation.

Retention behavior of neutral solutes in pressurized flow-driven capillary electrochromatography using an ODS column.

PubMed

Nakagawa, Hiroyuki; Kitagawa, Shinya; Araki, Shuki; Ohtani, Hajime

2006-02-01

Several alkyl benzenes are separated by pressurized flow-driven capillary electrochromatography using a temperature-controlled capillary column packed with octadecyl siloxane-modified silica gel, and the effect of applied voltage on the retention is investigated. The van't Hoff plot shows good linearity at the column temperature between 305 and 330 K under applications from -6 to +6 kV. The applied voltage causes a relatively large variation in the enthalpy and the entropy of transfer of the solute from the mobile phase to the stationary phase (> 20%). However, the direction of variation in the enthalpy is almost opposite to that in the entropy, both of which might compensate each other. Therefore, the retention factor is not significantly varied (< 4%) by the application of voltage.

Theoretical studies on a new furazan compound bis[4-nitramino-furazanyl-3-azoxy]azofurazan (ADNAAF).

PubMed

Zheng, Chunmei; Chu, Yuting; Xu, Liwen; Wang, Fengyun; Lei, Wu; Xia, Mingzhu; Gong, Xuedong

2016-06-01

Bis[4-nitraminofurazanyl-3-azoxy]azofurazan (ADNAAF), synthesized in our previous work [1], contains four furazan units connected to the linkage of the azo-group and azoxy-group. For further research, some theoretical characters were studied by the density functional theoretical (DFT) method. The optimized structures and the energy gaps between the HOMO and LUMO were studied at the B3LYP/6-311++G** level. The isodesmic reaction method was used for estimating the enthalpy of formation. The detonation performances were estimated with Kamlet-Jacobs equations based on the predicted density and enthalpy of formation in the solid state. ADAAF was also calculated by the same method for comparison. It was found that the nitramino group of ADNAAF can elongate the length of adjacent C-N bonds than the amino group of ADAAF. The gas-phase and solid-phase enthalpies of formation of ADNAAF are larger than those of ADAAF. The detonation performances of ADNAAF are better than ADAAF and RDX, and similar to HMX. The trigger bond of ADNAAF is the N-N bonds in the nitramino groups, and the nitramino group is more active than the amino group (-NH2).

Instability of the layered orthorhombic post-perovskite phase of SrTiO3 and other candidate orthorhombic phases under pressure

NASA Astrophysics Data System (ADS)

Bhandari, Churna; Lambrecht, Walter R. L.

2018-06-01

While the tetragonal antiferro-electrically distorted (AFD) phase with space group I 4 / mcm is well known for SrTiO3 to occur below 105 K, there are also some hints in the literature of an orthorhombic phase, either at the lower temperature or at high pressure. A previously proposed orthorhombic layered structure of SrTiO3, known as the post-perovskite or CaIrO3 structure with space group Cmcm is shown to have significantly higher energy than the cubic or tetragonal phase and to have its minimum volume at larger volume than cubic perovskite. The Cmcm structure is thus ruled out. We also study an alternative Pnma phase obtained by two octahedral rotations about different axes. This phase is found to have slightly lower energy than the I 4 / mcm phase in spite of the fact that its parent, in-phase tilted P 4 / mbm phase is not found to occur. Our calculated enthalpies of formation show that the I 4 / mcm phase occurs at slightly higher volume than the cubic phase and has a negative transition pressure relative to the cubic phase, which suggests that it does not correspond to the high-pressure tetragonal phase. The enthalpy of the Pnma phase is almost indistinguishable from the I 4 / mcm phase. Alternative ferro-electric tetragonal and orthorhombic structures previously suggested in literature are discussed.

Structure-property relationships in halogenbenzoic acids: Thermodynamics of sublimation, fusion, vaporization and solubility.

PubMed

Zherikova, Kseniya V; Svetlov, Aleksey A; Kuratieva, Natalia V; Verevkin, Sergey P

2016-10-01

Temperature dependences of vapor pressures for 2-, 3-, and 4-bromobenzoic acid, as well as for five isomeric bromo-methylbenzoic acids were studied by the transpiration method. Melting temperatures and enthalpies of fusion for all isomeric bromo-methylbenzoic acids and 4-bromobenzoic acid were measured with a DSC. The molar enthalpies of sublimation and vaporization were derived. These data together with results available in the literature were collected and checked for internal consistency using a group-additivity procedure and results from X-ray structural diffraction studies. Specific (hydrogen bonding) interactions in the liquid and in the crystal phase of halogenbenzoic acids were quantified based on experimental values of vaporization and sublimation enthalpies. Structure-property correlations of solubilities of halogenobenzoic acids with sublimation pressures and sublimation enthalpies were developed and solubilities of bromo-benzoic acids were estimated. These new results resolve much of the ambiguity in the available thermochemical and solubility data on bromobenzoic acids. The approach based on structure property correlations can be applied for the assessment of water solubility of sparingly soluble drugs. Copyright © 2016 Elsevier Ltd. All rights reserved.

Gas chemical adsorption characterization of lanthanide hexafluoroacetylacetonates

DOE PAGES

Stratz, S. Adam; Jones, Steven J.; Mullen, Austin D.; ...

2017-03-21

Newly-established adsorption enthalpy and entropy values of 12 lanthanide hexafluoroacetylacetonates, denoted Ln[hfac] 4, along with the experimental and theoretical methodology used to obtain these values, are presented for the first time. The results of this work can be used in conjunction with theoretical modeling techniques to optimize a large-scale gas-phase separation experiment using isothermal chromatography. The results to date indicate average adsorption enthalpy and entropy values of the 12 Ln[hfac] 4 complexes ranging from -33 to -139 kJ/mol K and -299 to -557 J/mol, respectively.

Reactive multiphase flow at the pore-scale: the melting of a crystalline framework during the injection of buoyant hot volatiles

NASA Astrophysics Data System (ADS)

Andrea, P.; Huber, C.; Bachmann, O.; Chopard, B.

2010-12-01

Multiphase reactive flows occur naturally in various environments in the shallow subsurface, e.g. CO2 injections in saturated reservoirs, exsolved methane flux in shallow sediments and H20-CO2 volatiles in magmatic systems. Because of their multiphase nature together with the nonlinear feedbacks between reactions (dissolution/melting or precipitation) and the flow field at the pore-scale, the study of these dynamical processes remains a great challenge. In this study we focus on the injection of buoyant hot volatiles exsolved from a magmatic intrusion underplating a crystal-rich magma (porous medium). We use some simple theoretical models and a pore-scale multiphase reactive lattice Boltzmann model to investigate how the heat carried by the volatile phase affects the evolution of the porous medium spatially and temporally. We find that when the reaction rate is relatively slow and when the injection rate of volatiles is large (high injection Capillary number), the dissolution of the porous medium can be described by a local Peclet number (ratio of advective to diffusive flux of heat/reactant in the main gas channel). When the injection rate of volatile is reduced, or when the reaction rate is large, the dynamics transition to more complex regimes, where subvertical gas channels are no longer stable and can break into disconnected gas slugs. For the case of the injection of hot volatiles in crystal-rich magmatic systems, we find that the excess enthalpy advected by buoyant volatiles penetrates the porous medium over distances ~r Pe, where r is the average radius of the volatile channel (~pore size). The transport of heat by buoyant gases through a crystal mush is therefore in most cases limited to distances < meters. Our results also suggest that buoyant volatiles can carry chemical species (Li,F, Cl) far into a mush as their corresponding local Peclet number is several orders of magnitude greater than that for heat, owing to their low diffusion coefficients.

Solvation Effect on Complexation of Alkali Metal Cations by a Calix[4]arene Ketone Derivative.

PubMed

Požar, Josip; Nikšić-Franjić, Ivana; Cvetnić, Marija; Leko, Katarina; Cindro, Nikola; Pičuljan, Katarina; Borilović, Ivana; Frkanec, Leo; Tomišić, Vladislav

2017-09-14

The medium effect on the complexation of alkali metal cations with a calix[4]arene ketone derivative (L) was systematically examined in methanol, ethanol, N-methylformamide, N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile. In all solvents the binding of Na + cation by L was rather efficient, whereas the complexation of other alkali metal cations was observed only in methanol and acetonitrile. Complexation reactions were enthalpically controlled, while ligand dissolution was endothermic in all cases. A notable influence of the solvent on NaL + complex stability could be mainly attributed to the differences in complexation entropies. The higher NaL + stability in comparison to complexes with other alkali metal cations in acetonitrile was predominantly due to a more favorable complexation enthalpy. The 1 H NMR investigations revealed a relatively low affinity of the calixarene sodium complex for inclusion of the solvent molecule in the calixarene hydrophobic cavity, with the exception of acetonitrile. Differences in complex stabilities in the explored solvents, apart from N,N-dimethylformamide and acetonitrile, could be mostly explained by taking into account solely the cation and complex solvation. A considerable solvent effect on the complexation equilibria was proven to be due to an interesting interplay between the transfer enthalpies and entropies of the reactants and the complexes formed.

Dissolution-resistance of glass-added hydroxyapatite composites

NASA Astrophysics Data System (ADS)

Seo, Dong Seok; Lee, Jong Kook

2009-04-01

Hydroxyapatite (HA) has generated a great deal of interest as a promising implant material. However, its poor mechanical properties induced by severe dissolution in biological milieu limit medical applications and lead to clinical failure. In this study, HA ceramics with 30P2O5-30CaO-40Na2O glass (1.0 wt.% and 2.5 wt.%) were prepared to improve the resistance of monophase HA. The monophase HA sintered body showed microstructural degradation due to grain boundary dissolution in buffered water. However, the dissolution-resistance of HA/glass composites was significantly improved and showed no apparent evidence of dissolution. This suggests that a less soluble glass phase should be placed at grain boundaries to protect HA from dissolution.

The influence of co-formers on the dissolution rates of co-amorphous sulfamerazine/excipient systems.

PubMed

Gniado, Katarzyna; Löbmann, Korbinian; Rades, Thomas; Erxleben, Andrea

2016-05-17

A comprehensive study on the dissolution properties of three co-amorphous sulfamerazine/excipient systems, namely sulfamerazine/deoxycholic acid, sulfamerazine/citric acid and sulfamerazine/sodium taurocholate (SMZ/DA, SMZ/CA and SMZ/NaTC; 1:1 molar ratio), is reported. While all three co-formers stabilize the amorphous state during storage, only co-amorphization with NaTC provides a dissolution advantage over crystalline SMZ and the reasons for this were analyzed. In the case of SMZ/DA extensive gelation of DA protects the amorphous phase from crystallization upon contact with buffer, but at the same time prevents the release of SMZ into solution. Disk dissolution studies showed an improved dissolution behavior of SMZ/CA compared to crystalline SMZ. However, enhanced dissolution properties were not seen in powder dissolution testing due to poor dispersibility. Co-amorphization of SMZ and NaTC resulted in a significant increase in dissolution rate, both in powder and disk dissolution studies. Copyright © 2016. Published by Elsevier B.V.

Uranium carbide dissolution in nitric solution: Sonication vs. silent conditions

NASA Astrophysics Data System (ADS)

Virot, Matthieu; Szenknect, Stéphanie; Chave, Tony; Dacheux, Nicolas; Moisy, Philippe; Nikitenko, Sergey I.

2013-10-01

The dissolution of uranium carbide (UC) in nitric acid media is considered by means of power ultrasound (sonication) or magnetic stirring. The induction period required to initiate UC dissolution was found to be dramatically shortened when sonicating a 3 M nitric solution (Ar, 20 kHz, 18 W cm-2, 20 °C). At higher acidity, magnetic stirring offers faster dissolution kinetics compared to sonication. Ultrasound-assisted UC dissolution is found to be passivated after ∼60% dissolution and remains incomplete whatever the acidity which is confirmed by ICP-AES, LECO and SEM-EDX analyses. In general, the kinetics of UC dissolution is linked to the in situ generation of nitrous acid in agreement with the general mechanism of UC dissolution; the nitrous acid formation is reported to be faster under ultrasound at low acidity due to the nitric acid sonolysis. The carbon balance shared between the gaseous, liquid, and solid phases is strongly influenced by the applied dissolution procedure and HNO3 concentration.

Effects of Bacterial Siderophore and Biofilm Synthesis on Silicate Mineral Dissolution Kinetics: Results from Experiments with Targeted Mutants

NASA Astrophysics Data System (ADS)

Van Den Berghe, M. D.; West, A. J.; Nealson, K. H.

2018-05-01

This project aims to characterize and quantify the specific microbial mechanisms and metabolic pathways responsible for silicate mineral dissolution and micronutrient acquisition directly from mineral phases.

Hidden disorder in the α '→δ transformation of Pu-1.9 at.% Ga

DOE PAGES

Jeffries, J. R.; Manley, M. E.; Wall, M. A.; ...

2012-06-06

Enthalpy and entropy are thermodynamic quantities critical to determining how and at what temperature a phase transition occurs. At a phase transition, the enthalpy and temperature-weighted entropy differences between two phases are equal (ΔH=TΔS), but there are materials where this balance has not been experimentally or theoretically realized, leading to the idea of hidden order and disorder. In a Pu-1.9 at. % Ga alloy, the δ phase is retained as a metastable state at room temperature, but at low temperatures, the δ phase yields to a mixed-phase microstructure of δ- and α'-Pu. The previously measured sources of entropy associated withmore » the α'→δ transformation fail to sum to the entropy predicted theoretically. We report an experimental measurement of the entropy of the α'→δ transformation that corroborates the theoretical prediction, and implies that only about 65% of the entropy stabilizing the δ phase is accounted for, leaving a missing entropy of about 0.5 k B/atom. Some previously proposed mechanisms for generating entropy are discussed, but none seem capable of providing the necessary disorder to stabilize the δ phase. This hidden disorder represents multiple accessible states per atom within the δ phase of Pu that may not be included in our current understanding of the properties and phase stability of δ-Pu.« less

The effect of dissolution of volcanic glass on the water chemistry in a tuffaceous aquifer, Rainier Mesa, Nevada

USGS Publications Warehouse

White, Art F.; Claassen, H.C.; Benson, Larry V.

1980-01-01

Geochemistry of ground water associated with the Tertiary tuffs within Rainier Mesa, southern Nevada, was investigated to determine the relative importance of glass dissolution in controlling water chemistry. Water samples were obtained both from interstitial pores in core sections and from free-flowing fractures. Cation com- positions showed that calcium and magnesium decreased as a function of depth in the mesa, as sodium increased. The maximum effect occurs within alteration zones containing clinoptilolite and montmorillonite, suggesting these minerals effectively remove bivalent cations from the system. Comparisons are made between compositions of ground waters found within Rainier Mesa that apparently have not reacted with secondary minerals and compositions of waters produced by experimental dissolution of vitric and crystalline tufts which comprise the principal aquifers in the area. The two tuff phases have the same bulk chemistry but produce aqueous solutions of different chemistry. Rapid parabolic dissolution of sodium and silica from, and the retention of, potassium within the vitric phase verify previous predictions concerning water compositions associated with vitric volcanic rocks. Parabolic dissolution of the crystalline phase results in solutions high in calcium and magnesium and low in silica. Extrapolation of the parabolic dissolution mechanism for the vitric tuff to long times successfully reproduces, at com- parable pH, cation ratios existing in Rainier Mesa ground water. Comparison of mass- transfer rates of the vitric and crystalline tuffs indicates that the apparent higher glass-surface to aqueous-volume ratio associated with the vitric rocks may account for dominance of the glass reaction.

Solubility of nano-zinc oxide in environmentally and biologically important matrices

PubMed Central

Reed, Robert B.; Ladner, David A.; Higgins, Christopher P.; Westerhoff, Paul; Ranville, James F.

2011-01-01

Increasing manufacture and use of engineered nanoparticles (NPs) is leading to a greater probability for release of ENPs into the environment and exposure to organisms. In particular, zinc oxide (ZnO) is toxic, although it is unclear whether this toxicity is due to the zinc oxide nanoparticles (ZnO), dissolution to Zn2+, or some combination thereof. The goal of this study was to determine the relative solubilites of both commercially available and in-house synthesized ZnO in matrices used for environmental fate and transport or biological toxicity studies. Dissolution of ZnO was observed in nanopure water (7.18– 7.40 mg/L dissolved Zn, as measured by filtration) and Roswell Park Memorial Institute medium (RPMI-1640) (~5 mg/L), but much more dissolution was observed in Dulbecco’s Modified Eagle’s Medium (DMEM), where the dissolved Zn concentration exceeded 34 mg/L. Moderately hard water exhibited low zinc solubility, likely due to precipitation of a zinc carbonate solid phase. Precipitation of a zinc-containing solid phase in RPMI also appeared to limit zinc solubility. Equilibrium conditions with respect to ZnO solubility were not apparent in these matrices, even after more than 1,000 h of dissolution. These results suggest that solution chemistry exerts a strong influence on ZnO dissolution and can result in limits on zinc solubility due to precipitation of less soluble solid phases. PMID:21994124

Order parameter free enhanced sampling of the vapor-liquid transition using the generalized replica exchange method.

PubMed

Lu, Qing; Kim, Jaegil; Straub, John E

2013-03-14

The generalized Replica Exchange Method (gREM) is extended into the isobaric-isothermal ensemble, and applied to simulate a vapor-liquid phase transition in Lennard-Jones fluids. Merging an optimally designed generalized ensemble sampling with replica exchange, gREM is particularly well suited for the effective simulation of first-order phase transitions characterized by "backbending" in the statistical temperature. While the metastable and unstable states in the vicinity of the first-order phase transition are masked by the enthalpy gap in temperature replica exchange method simulations, they are transformed into stable states through the parameterized effective sampling weights in gREM simulations, and join vapor and liquid phases with a succession of unimodal enthalpy distributions. The enhanced sampling across metastable and unstable states is achieved without the need to identify a "good" order parameter for biased sampling. We performed gREM simulations at various pressures below and near the critical pressure to examine the change in behavior of the vapor-liquid phase transition at different pressures. We observed a crossover from the first-order phase transition at low pressure, characterized by the backbending in the statistical temperature and the "kink" in the Gibbs free energy, to a continuous second-order phase transition near the critical pressure. The controlling mechanisms of nucleation and continuous phase transition are evident and the coexistence properties and phase diagram are found in agreement with literature results.

FLUID: A numerical interpolation procedure for obtaining thermodynamic and transport properties of fluids

NASA Technical Reports Server (NTRS)

Fessler, T. E.

1977-01-01

A computer program subroutine, FLUID, was developed to calculate thermodynamic and transport properties of pure fluid substances. It provides for determining the thermodynamic state from assigned values for temperature-density, pressure-density, temperature-pressure, pressure-entropy, or pressure-enthalpy. Liquid or two-phase (liquid-gas) conditions are considered as well as the gas phase. A van der Waals model is used to obtain approximate state values; these values are then corrected for real gas effects by model-correction factors obtained from tables based on experimental data. Saturation conditions, specific heat, entropy, and enthalpy data are included in the tables for each gas. Since these tables are external to the FLUID subroutine itself, FLUID can implement any gas for which a set of tables has been generated. (A setup phase is used to establish pointers dynamically to the tables for a specific gas.) Data-table preparation is described. FLUID is available in both SFTRAN and FORTRAN

The study of flow pattern and phase-change problem in die casting process

NASA Technical Reports Server (NTRS)

Wang, T. S.; Wei, H.; Chen, Y. S.; Shang, H. M.

1996-01-01

The flow pattern and solidification phenomena in die casting process have been investigated in the first phase study. The flow pattern in filling process is predicted by using a VOF (volume of fluid) method. A good agreement with experimental observation is obtained for filling the water into a die cavity with different gate geometry and with an obstacle in the cavity. An enthalpy method has been applied to solve the solidification problem. By treating the latent heat implicitly into the enthalpy instead of explicitly into the source term, the CPU time can be reduced at least 20 times. The effect of material properties on solidification fronts is tested. It concludes that the dependence of properties on temperature is significant. The influence of the natural convection over the diffusion has also been studied. The result shows that the liquid metal solidification phenomena is diffusion dominant, and the natural convection can affect the shape of the interface. In the second phase study, the filling and solidification processes will be considered simultaneously.

Observation and numerical modeling of chromospheric evaporation during the impulsive phase of a solar flare

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imada, Shinsuke, E-mail: shinimada@stelab.nagoya-u.ac.jp; Murakami, Izumi, E-mail: murakami.izumi@nifs.ac.jp; Department of Fusion Science, SOKENDAI

2015-10-15

We have studied the chromospheric evaporation flow during the impulsive phase of the flare by using the Hinode/EUV Imaging Spectrometer observation and 1D hydrodynamic numerical simulation coupled to the time-dependent ionization. The observation clearly shows that the strong redshift can be observed at the base of the flaring loop only during the impulsive phase. We performed two different numerical simulations to reproduce the strong downflows in FeXII and FeXV during the impulsive phase. By changing the thermal conduction coefficient, we carried out the numerical calculation of chromospheric evaporation in the thermal conduction dominant regime (conductivity coefficient κ{sub 0} = classical value) andmore » the enthalpy flux dominant regime (κ{sub 0} = 0.1 × classical value). The chromospheric evaporation calculation in the enthalpy flux dominant regime could reproduce the strong redshift at the base of the flare during the impulsive phase. This result might indicate that the thermal conduction can be strongly suppressed in some cases of flare. We also find that time-dependent ionization effect is important to reproduce the strong downflows in Fe XII and Fe XV.« less

Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate.

PubMed

Radha, A V; Forbes, Tori Z; Killian, Christopher E; Gilbert, P U P A; Navrotsky, Alexandra

2010-09-21

Amorphous calcium carbonate (ACC) is a metastable phase often observed during low temperature inorganic synthesis and biomineralization. ACC transforms with aging or heating into a less hydrated form, and with time crystallizes to calcite or aragonite. The energetics of transformation and crystallization of synthetic and biogenic (extracted from California purple sea urchin larval spicules, Strongylocentrotus purpuratus) ACC were studied using isothermal acid solution calorimetry and differential scanning calorimetry. Transformation and crystallization of ACC can follow an energetically downhill sequence: more metastable hydrated ACC → less metastable hydrated ACC ⇒ anhydrous ACC ∼ biogenic anhydrous ACC ⇒ vaterite → aragonite → calcite. In a given reaction sequence, not all these phases need to occur. The transformations involve a series of ordering, dehydration, and crystallization processes, each lowering the enthalpy (and free energy) of the system, with crystallization of the dehydrated amorphous material lowering the enthalpy the most. ACC is much more metastable with respect to calcite than the crystalline polymorphs vaterite or aragonite. The anhydrous ACC is less metastable than the hydrated, implying that the structural reorganization during dehydration is exothermic and irreversible. Dehydrated synthetic and anhydrous biogenic ACC are similar in enthalpy. The transformation sequence observed in biomineralization could be mainly energetically driven; the first phase deposited is hydrated ACC, which then converts to anhydrous ACC, and finally crystallizes to calcite. The initial formation of ACC may be a first step in the precipitation of calcite under a wide variety of conditions, including geological CO(2) sequestration.

Dissolution kinetics of volatile organic compound vapors in water: An integrated experimental and computational study

NASA Astrophysics Data System (ADS)

Mahmoodlu, Mojtaba G.; Pontedeiro, Elizabeth M.; Pérez Guerrero, Jesús S.; Raoof, Amir; Majid Hassanizadeh, S.; van Genuchten, Martinus Th.

2017-01-01

In this study we performed batch experiments to investigate the dissolution kinetics of trichloroethylene (TCE) and toluene vapors in water at room temperature and atmospheric pressure. The batch systems consisted of a water reservoir and a connected headspace, the latter containing a small glass cylinder filled with pure volatile organic compound (VOC). Results showed that air phase concentrations of both TCE and toluene increased relatively quickly to their maximum values and then became constant. We considered subsequent dissolution into both stirred and unstirred water reservoirs. Results of the stirred experiments showed a quick increase in the VOC concentrations with time up to their solubility limit in water. VOC vapor dissolution was found to be independent of pH. In contrast, salinity had a significant effect on the solubility of TCE and toluene vapors. VOC evaporation and vapor dissolution in the stirred water reservoirs followed first-order rate processes. Observed data could be described well using both simplified analytical solutions, which decoupled the VOC dynamics in the air and water phases, as well as using more complete coupled solutions. However, the estimated evaporation (ke) and dissolution (kd) rate constants differed by up to 70% between the coupled and uncoupled formulations. We also numerically investigated the effects of fluid withdrawal from the small water reservoir due to sampling. While decoupling the VOC air and water phase mass transfer processes produced unreliable estimates of kd, the effects of fluid withdrawal on the estimated rate constants were found to be less important. The unstirred experiments showed a much slower increase in the dissolved VOC concentrations versus time. Molecular diffusion of the VOCs within the aqueous phase became then the limiting factor for mass transfer from air to water. Fluid withdrawal during sampling likely caused some minor convection within the reservoir, which was simulated by increasing the apparent liquid diffusion coefficient.

Enthalpy and phase behavior of coal derived liquid mixtures. Technical progress report, April-June 1986

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yesavage, V.F.; Kidnay, A.J.

Enthalpy measurements for the m-cresol/tetralin binary system, and the quinoline/tertralin binary system have been completed and are included. A calibration check on the calorimeter was performed and is presented in Appendix C. Vapor liquid equilibria measurements for the quinoline/tetralin system have been completed for four isotherms; 250, 275, 300, and 325/sup 0/C. These results and a summary of progress to date for the VLE apparatus are in the appendix at the end of this report. Also, preliminary work has begun on the quinoline/m-cresol/tetralin ternary system. Correlational work has consisted of the development of mathematical expressions for fugacity and enthalpy usingmore » various combinations of mixing rules and equations of state discussed in earlier reports. Also maximum likelihood routines has been written to determine the necessary parameters for binary data obtained in this investigation.« less

The calculation of aquifer chemistry in hot-water geothermal systems

USGS Publications Warehouse

Truesdell, Alfred H.; Singers, Wendy

1974-01-01

The temperature and chemical conditions (pH, gas pressure, and ion activities) in a geothermal aquifer supplying a producing bore can be calculated from the enthalpy of the total fluid (liquid + vapor) produced and chemical analyses of water and steam separated and collected at known pressures. Alternatively, if a single water phase exists in the aquifer, the complete analysis (including gases) of a sample collected from the aquifer by a downhole sampler is sufficient to determine the aquifer chemistry without a measured value of the enthalpy. The assumptions made are that the fluid is produced from a single aquifer and is homogeneous in enthalpy and chemical composition. These calculations of aquifer chemistry involving large amounts of ancillary information and many iterations require computer methods. A computer program in PL-1 to perform these calculations is available from the National Technical Information Service as document PB-219 376.

Theoretical calculation of enthalpy of formation of multiconformational molecules: 1,2-ethanediol, propanediols, and glycerol

NASA Astrophysics Data System (ADS)

Dorofeeva, Olga V.; Suchkova, Taisiya A.

2018-04-01

The gas-phase enthalpies of formation of four molecules with high flexibility, which leads to the existence of a large number of low-energy conformers, were calculated with the G4 method to see whether the lowest energy conformer is sufficient to achieve high accuracy in the computed values. The calculated values were in good agreement with the experiment, whereas adding the correction for conformer distribution makes the agreement worse. The reason for this effect is a large anharmonicity of low-frequency torsional motions, which is ignored in the calculation of ZPVE and thermal enthalpy. It was shown that the approximate correction for anharmonicity estimated using a free rotor model is of very similar magnitude compared with the conformer correction but has the opposite sign, and thus almost fully compensates for it. Therefore, the common practice of adding only the conformer correction is not without problems.

Flow microcapillary plasma mass spectrometry-based investigation of new Al-Cr-Fe complex metallic alloy passivation.

PubMed

Ott, N; Beni, A; Ulrich, A; Ludwig, C; Schmutz, P

2014-03-01

Al-Cr-Fe complex metallic alloys are new intermetallic phases with low surface energy, low friction, and high corrosion resistance down to very low pH values (0-2). Flow microcapillary plasma mass spectrometry under potentiostatic control was used to characterize the dynamic aspect of passivation of an Al-Cr-Fe gamma phase in acidic electrolytes, allowing a better insight on the parameters inducing chemical stability at the oxyhydroxide-solution interface. In sulfuric acid pH 0, low element dissolution rates (in the µg cm(-2) range after 60 min) evidenced the passive state of the Al-Cr-Fe gamma phase with a preferential over-stoichiometric dissolution of Al and Fe cations. Longer air-aging was found to be beneficial for stabilizing the passive film. In chloride-containing electrolytes, ten times higher Al dissolution rates were detected at open-circuit potential (OCP), indicating that the spontaneously formed passive film becomes unstable. However, electrochemical polarization at low passive potentials induces electrical field generated oxide film modification, increasing chemical stability at the oxyhydroxide-solution interface. In the high potential passive region, localized attack is initiated with subsequent active metal dissolution. © 2013 Published by Elsevier B.V.

Supersaturation and crystallization: non-equilibrium dynamics of amorphous solid dispersions for oral drug delivery.

PubMed

Kawakami, Kohsaku

2017-06-01

Amorphous solid dispersions (ASDs) are one of the key formulation technologies that aid the development of poorly soluble candidates. However, their dynamic behaviors, including dissolution and crystallization processes, are still full of mystery. Further understanding of these processes should enhance their wider use. Areas covered: The first part of this review describes the current understanding of the dissolution of ASDs, where phase separation behavior is frequently involved and attempts to develop appropriate dissolution tests to achieve an in vitro-in vivo correlation are examined. The second part of this review discusses crystallization of the drug molecule with the eventual aim of establishing an accelerated testing protocol for predicting its physical stability. Expert opinion: The phase separation behavior from the supersaturated state during the dissolution test must be understood, and its relevance to the oral absorption behavior needs to be clarified. Research efforts should focus on the differences between the phase behavior in in vitro and in vivo situations. Initiation time of the crystallization was shown to be predicted only from storage and glass transition temperatures. This finding should encourage the establishment of testing protocol of the physical stability of ASDs.

Phase diagram of the Y–Y{sub 2}Se{sub 3} system, enthalpies of phase transformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreev, O.V.; Kharitontsev, V.B.; Polkovnikov, A.A., E-mail: a.a.polkovnikov@yandex.ru

A phase diagram for the Y–Y{sub 2}Se{sub 3} system has been constructed in which the YSe and Y{sub 2}Se{sub 3} phases melt congruently. The daltonide type YSe phase (ST Y{sub 0,75}Se, a=1.1393 nm, melting point=2380 K, H=2200 MPa) forms a double-sided solid solution from 49–50–53 at% Se. In the 50–53 at% Se range, the unit cell parameter increases to 1.1500 nm, the microhardness increases to 4100 MPa and electrical resistivity increases from 0.018 to 0.114 Ω m. These changes are caused by the dominating influx of newly formed structural cationic vacancies arising from the selenium anions that are surplus formore » the 1:1 Y:Se stoichiometry. The full-valence Y{sub 2}Se{sub 3} composition exists as a low-temperature modification of ε-Y{sub 2}Se{sub 3} (ST Sc{sub 2}S{sub 3}, a=1.145 nm, b=0.818 nm, c=2.438 nm, melting point=1780 K, ∆fusion enthalpy=4±0.4 J/g) and transforms into a modification of ξ-Y{sub 2}Se{sub 3} that does not undergo fixing by thermo-hardening. The eutectic melting point between the YSe and Y{sub 2}Se{sub 3} phases is 1625±5 K, with a eutectic composition that is assumed to be 57.5 at% Se and have an enthalpy of fusion of 43±4.3 J/g. The eutectic for the Y and YSe phases appears at a temperature of 1600 K and 5 at% Se. - Highlights: • Phase equilibria in the Y–Y{sub 2}Se{sub 3} system from 1000 K to melt were studies. • High-temperature polymorphic transition for Y{sub 2}Se{sub 3} were observed. • Singular points in solid solutions areas for YSe and Y{sub 2}Se{sub 3} were found.« less

The phase diagram of solid hydrogen at high pressure: A challenge for first principles calculations

NASA Astrophysics Data System (ADS)

Azadi, Sam; Foulkes, Matthew

2015-03-01

We present comprehensive results for the high-pressure phase diagram of solid hydrogen. We focus on the energetically most favorable molecular and atomic crystal structures. To obtain the ground-state static enthalpy and phase diagram, we use semi-local and hybrid density functional theory (DFT) as well as diffusion quantum Monte Carlo (DMC) methods. The closure of the band gap with increasing pressure is investigated utilizing quasi-particle many-body calculations within the GW approximation. The dynamical phase diagram is calculated by adding proton zero-point energies (ZPE) to static enthalpies. Density functional perturbation theory is employed to calculate the proton ZPE and the infra-red and Raman spectra. Our results clearly demonstrate the failure of DFT-based methods to provide an accurate static phase diagram, especially when comparing insulating and metallic phases. Our dynamical phase diagram obtained using fully many-body DMC calculations shows that the molecular-to-atomic phase transition happens at the experimentally accessible pressure of 374 GPa. We claim that going beyond mean-field schemes to obtain derivatives of the total energy and optimize crystal structures at the many-body level is crucial. This work was supported by the UK engineering and physics science research council under Grant EP/I030190/1, and made use of computing facilities provided by HECTOR, and by the Imperial College London high performance computing centre.

A numerical analysis of phase-change problems including natural convection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Y.; Faghri, A.

1990-08-01

Fixed grid solutions for phase-change problems remove the need to satisfy conditions at the phase-change front and can be easily extended to multidimensional problems. The two most important and widely used methods are enthalpy methods and temperature-based equivalent heat capacity methods. Both methods in this group have advantages and disadvantages. Enthalpy methods (Shamsundar and Sparrow, 1975; Voller and Prakash, 1987; Cao et al., 1989) are flexible and can handle phase-change problems occurring both at a single temperature and over a temperature range. The drawback of this method is that although the predicted temperature distributions and melting fronts are reasonable, themore » predicted time history of the temperature at a typical grid point may have some oscillations. The temperature-based fixed grid methods (Morgan, 1981; Hsiao and Chung, 1984) have no such time history problems and are more convenient with conjugate problems involving an adjacent wall, but have to deal with the severe nonlinearity of the governing equations when the phase-change temperature range is small. In this paper, a new temperature-based fixed-grid formulation is proposed, and the reason that the original equivalent heat capacity model is subject to such restrictions on the time step, mesh size, and the phase-change temperature range will also be discussed.« less

Crystal-liquid Fugacity Ratio as a Surrogate Parameter for Intestinal Permeability.

PubMed

Zakeri-Milani, Parvin; Fasihi, Zohreh; Akbari, Jafar; Jannatabadi, Ensieh; Barzegar-Jalali, Mohammad; Loebenberg, Raimar; Valizadeh, Hadi

We assessed the feasibility of using crystal-liquid fugacity ratio (CLFR) as an alternative parameter for intestinal permeability in the biopharmaceutical classification (BCS) of passively absorbed drugs. Dose number, fraction of dose absorbed, intestinal permeability, and intrinsic dissolution rate were used as the input parameters. CLFR was determined using thermodynamic parameters i.e., melting point, molar fusion enthalpy, and entropy of drug molecules obtained using differential scanning calorimetry. The CLFR values were in the range of 0.06-41.76 mole percent. There was a close relationship between CLFR and in vivo intestinal permeability (r > 0.8). CLFR values of greater than 2 mole percent corresponded to complete intestinal absorption. Applying CLFR versus dose number or intrinsic dissolution rate, more than 92% of tested drugs were correctly classified with respect to the reported classification system on the basis of human intestinal permeability and solubility. This investigation revealed that the CLFR might be an appropriate parameter for quantitative biopharmaceutical classification. This could be attributed to the fact that CLFR could be a measure of solubility of compounds in lipid bilayer which was found in this study to be directly proportional to the intestinal permeability of compounds. This classification enables researchers to define characteristics for intestinal absorption of all four BCS drug classes using suitable cutoff points for both intrinsic dissolution rate and crystal-liquid fugacity ratio. Therefore, it may be used as a surrogate for permeability studies. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

A fresh look at dense hydrogen under pressure. IV. Two structural models on the road from paired to monatomic hydrogen, via a possible non-crystalline phase

NASA Astrophysics Data System (ADS)

Labet, Vanessa; Hoffmann, Roald; Ashcroft, N. W.

2012-02-01

In this paper, we examine the transition from a molecular to monatomic solid in hydrogen over a wide pressure range. This is achieved by setting up two models in which a single parameter δ allows the evolution from a molecular structure to a monatomic one of high coordination. Both models are based on a cubic Bravais lattice with eight atoms in the unit cell; one belongs to space group Pabar 3, the other to space group Rbar 3m. In Pabar 3 one moves from effective 1-coordination, a molecule, to a simple cubic 6-coordinated structure but through a very special point (the golden mean is involved) of 7-coordination. In Rbar 3m, the evolution is from 1 to 4 and then to 3 to 6-coordinate. If one studies the enthalpy as a function of pressure as these two structures evolve (δ increases), one sees the expected stabilization of minima with increased coordination (moving from 1 to 6 to 7 in the Pabar 3 structure, for instance). Interestingly, at some specific pressures, there are in both structures relatively large regions of phase space where the enthalpy remains roughly the same. Although the structures studied are always higher in enthalpy than the computationally best structures for solid hydrogen - those emerging from the Pickard and Needs or McMahon and Ceperley numerical laboratories - this result is suggestive of the possibility of a microscopically non-crystalline or "soft" phase of hydrogen at elevated pressures, one in which there is a substantial range of roughly equi-enthalpic geometries available to the system. A scaling argument for potential dynamic stabilization of such a phase is presented.

Accelerated Leach Testing of Glass (ALTGLASS): II. Mineralization of hydrogels by leachate strong bases

DOE PAGES

Jantzen, Carol M.; Trivelpiece, Cory L.; Crawford, Charles L.; ...

2017-02-18

The durability of high level nuclear waste glasses must be predicted on geological time scales. Waste glass surfaces form hydrogels when in contact with water for varying test durations. As the glass hydrogels age, some exhibit an undesirable resumption of dissolution at long times while others exhibit near steady-state dissolution, that is, nonresumption of dissolution. Resumption of dissolution is associated with the formation of zeolitic phases while nonresumption of dissolution is associated with the formation of clay minerals. Hydrogels with a stoichiometry close to that of imogolite, (Al 2O 3·Si(OH) 4), with ferrihydrite (Fe 2O 3·0.5H 2O), have been shownmore » to be associated with waste glasses that resume dissolution. Aluminosilicate hydrogels with a stoichiometry of allophane-hisingerite ((Al,Fe) 2O 3·1.3-2Si(OH) 4) have been shown to be associated with waste glasses that exhibit near steady-state dissolution at long times. These phases are all amorphous and poorly crystalline and are also found on natural weathered basalt glasses. Interaction of these hydrogels with excess alkali and OH – (strong base) in the leachates, causes the Al 2O 3· nSiO 2 (where n=1-2) hydrogels to mineralize to zeolites. Excess alkali in the leachate is generated by alkali in the glass. As a result, preliminary rate-determining leach layer forming exchange reactions are hypothesized based on these findings.« less

Experimental investigation of the dissolution of fractures. From early stage instability to phase diagram

NASA Astrophysics Data System (ADS)

Osselin, Florian; Budek, Agnieszka; Cybulski, Olgierd; Kondratiuk, Pawel; Garstecki, Piotr; Szymczak, Piotr

2016-04-01

Dissolution of natural rocks is a fundamental geological process and a key part of landscape formation and weathering processes. Moreover, in current hot topics like Carbon Capture and Storage or Enhanced Oil Recovery, mastering dissolution of the host rock is fundamental for the efficiency and the security of the operation. The basic principles of dissolution are well-known and the theory of the reactive infiltration instability has been extensively studied. However, the experimental aspect has proved very challenging because of the strong dependence of the outcome with pore network, chemical composition, flow rate... In this study we are trying to tackle this issue by using a very simple and efficient device consisting of a chip of pure gypsum inserted between two polycarbonate plates and subjected to a constant flow rate of pure water. Thanks to this device, we are able to control all parameters such as flow rate, fracture aperture, roughness of the walls... but also to observe in situ the progression of the dissolution thanks to the transparency of the polycarbonate which is impossible with 3D rocks. We have been using this experimental set-up to explore and investigate all aspects of the dissolution in a fracture, such as initial instability and phase diagram of different dissolution patterns, and to compare it with theory and simulations, yielding very good agreement and interesting feedbacks on the coupling between flow and chemistry in geological media

Accelerated Leach Testing of Glass (ALTGLASS): II. Mineralization of hydrogels by leachate strong bases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jantzen, Carol M.; Trivelpiece, Cory L.; Crawford, Charles L.

The durability of high level nuclear waste glasses must be predicted on geological time scales. Waste glass surfaces form hydrogels when in contact with water for varying test durations. As the glass hydrogels age, some exhibit an undesirable resumption of dissolution at long times while others exhibit near steady-state dissolution, that is, nonresumption of dissolution. Resumption of dissolution is associated with the formation of zeolitic phases while nonresumption of dissolution is associated with the formation of clay minerals. Hydrogels with a stoichiometry close to that of imogolite, (Al 2O 3·Si(OH) 4), with ferrihydrite (Fe 2O 3·0.5H 2O), have been shownmore » to be associated with waste glasses that resume dissolution. Aluminosilicate hydrogels with a stoichiometry of allophane-hisingerite ((Al,Fe) 2O 3·1.3-2Si(OH) 4) have been shown to be associated with waste glasses that exhibit near steady-state dissolution at long times. These phases are all amorphous and poorly crystalline and are also found on natural weathered basalt glasses. Interaction of these hydrogels with excess alkali and OH – (strong base) in the leachates, causes the Al 2O 3· nSiO 2 (where n=1-2) hydrogels to mineralize to zeolites. Excess alkali in the leachate is generated by alkali in the glass. As a result, preliminary rate-determining leach layer forming exchange reactions are hypothesized based on these findings.« less

Short-time dissolution mechanisms of kaolinitic tropical soils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malengreau, N.; Sposito, Garrison

1996-03-01

Previous research on the short-time dissolution behavior of kaolinitic Oxisols suggested pH-dependent kinetics involving ligand-promoted dissolution, metal readsorption, and colloidal dispersion, with soil organic matter conjectured to play a decisive role. A novel combination of spectroscopy, lightscattering, and batch dissolution experiments, conducted at controlled pH and ionic strength over five dissolution periods ranging from 1 to 12 h, was applied to evaluate this mechanism for samples of a representative kaolinitic Oxisol; collected at both forested and cultivated field sites (leading to significant differences in organic matter content and field soil pH). The overall characteristics of the pH-dependent net release kineticsmore » of Al, Fe, and Si by the soil samples, for any dissolution period in the range investigated, were determined by the pH value at which colloid dispersion commenced, which decreased significantly as the soil organic matter content increased. Plots of log(Si/Al released) (or Si/Fe released) vs. -log [H+] ([H+] is proton concentration) were superimposable for all dissolution periods studied, rising to a plateau value above the point of zero net charge of the soils (pH 3.2). Light-scattering and X-ray diffraction data showed conclusively that this plateau represented the release of siliceous colloids containing kaolinite and X-ray amorphous material. X-ray diffraction, UV-visible diffuse reflectance spectroscopy, and electron spin resonance spectroscopy, applied to the soil samples before and after dissolution, and after conventional chemical extractions to remove Al, C, Fe, and Si, showed that kaolinite and iron oxide phases (the latter being highly Al-substituted and present in both coatings and occlusions) were essentially unaltered by dissolution, even at -log [H+] = 2, whereas substantial dissolution loss of soil quartz occurred. Diffuse reflectance spectroscopy gave strong evidence that C in these soils occurs principally in discrete solid phases, not as a reactive coating on mineral surfaces.« less

AqSo_NaCl: Computer program to calculate p-T-V-x properties in the H2O-NaCl fluid system applied to fluid inclusion research and pore fluid calculation

NASA Astrophysics Data System (ADS)

Bakker, Ronald J.

2018-06-01

The program AqSo_NaCl has been developed to calculate pressure - molar volume - temperature - composition (p-V-T-x) properties, enthalpy, and heat capacity of the binary H2O-NaCl system. The algorithms are designed in BASIC within the Xojo programming environment, and can be operated as stand-alone project with Macintosh-, Windows-, and Unix-based operating systems. A series of ten self-instructive interfaces (modules) are developed to calculate fluid inclusion properties and pore fluid properties. The modules may be used to calculate properties of pure NaCl, the halite-liquidus, the halite-vapourus, dew-point and bubble-point curves (liquid-vapour), critical point, and SLV solid-liquid-vapour curves at temperatures above 0.1 °C (with halite) and below 0.1 °C (with ice or hydrohalite). Isochores of homogeneous fluids and unmixed fluids in a closed system can be calculated and exported to a.txt file. Isochores calculated for fluid inclusions can be corrected according to the volumetric properties of quartz. Microthermometric data, i.e. dissolution temperatures and homogenization temperatures, can be used to calculated bulk fluid properties of fluid inclusions. Alternatively, in the absence of total homogenization temperature the volume fraction of the liquid phase in fluid inclusions can be used to obtain bulk properties.

Concentration gradients at the mineral-solution interface: implications for understanding dissolution mechanisms

NASA Astrophysics Data System (ADS)

Ruiz-Agudo, Encarnacion; Patiño-López, Luis David; Putnis, Christine V.; Rodriguez-Navarro, Carlos; Putnis, Andrew

2014-05-01

Dissolution is a key process in fluid-rock interactions, such as in chemical weathering, CO2 carbonation reactions, metasomatism, and metamorphism. Many multicomponent rock-forming minerals are reported to dissolve incongruently, because the elemental molar ratios, measured in the fluid during dissolution experiments, that differ from those in the solid. This frequently results in the formation of chemically and structurally altered zones at the fluid-solid interface of varying thickness that are depleted in some elements relative to the bulk mineral composition. Although the mechanisms of the formation of these altered layers is still a matter of debate (see e.g. Ruiz-Agudo et al. 2012 and Schott et al. 2012), recent AFM studies on the dissolution of two multicomponent minerals, dolomite, Ca0.5Mg0.5CO3 (Urosevic et al. 2012), and wollastonite, CaSiO3 (Ruiz-Agudo et al. 2012), provide experimental evidence showing that these layers are formed in a two-step process: (i) stoichiometric dissolution of the pristine mineral surfaces and (ii) precipitation of a secondary phase. This occurs despite the fact that the bulk solution is undersaturated with respect to such a phase. It has been suggested that after stoichiometric dissolution of the mineral, a boundary layer of fluid in contact with the surface becomes supersaturated with respect to a secondary phase that then precipitates. Here we present in situ observations of the evolution of the fluid composition at the interface during dissolution in acidic solutions (pH 1.5) of dolomite and wollastonite using real-time phase-shift interferometry. We show that immediately when the sparingly soluble dolomite or wollastonite crystals are in contact with the solution, the refractive index of the solution at the crystal surface sharply increases. A steep refractive index gradient (i.e., concentration gradient) develops as a consequence of mineral dissolution producing an interfacial fluid with a different composition to the bulk. Similar observations have been made during the replacement of KBr by KCl (Putnis et al. 2005). Thus, it seems that incongruent dissolution is essentially similar to any other mineral-fluid equilibration process: when a fluid interacts with a mineral with which it is out of equilibrium the mineral will tend to dissolve. Depending on the fluid composition, the interfacial fluid may become supersaturated with respect to a secondary phase that will eventually nucleate on the parent mineral surface. Ruiz-Agudo E., Putnis, C.V., Rodríguez-Navarro, C. and Putnis A. (2012) Geology 40, 947-950 (2012) Urosevic M., Rodríguez-Navarro C., Putnis C.V., Cardell C., Putnis A. and Ruiz Agudo, E. (2012) In Geochimica et Cosmochimica Acta 80, 1-13 Schott J., Pokrovsky O.S., Spalla O., Devreux F., Gloter A. and Mielczarski J.A. (2012) Geochimica et Cosmochimica Acta 98, 259-281 Putnis C.V., Tsukamoto K. and Nishimura Y. (2005) American Mineralogist 90, 1909-1912

Laboratory Experiments and Modeling of Pooled NAPL Dissolution in Porous Media

NASA Astrophysics Data System (ADS)

Copty, N. K.; Sarikurt, D. A.; Gokdemir, C.

2017-12-01

The dissolution of non-aqueous phase liquids (NAPLs) entrapped in porous media is commonly modeled at the continuum scale as the product of a chemical potential and an interphase mass transfer coefficient, the latter expressed in terms of Sherwood correlations that are related to flow and porous media properties. Because of the lack of precise estimates of the interface area separating the NAPL and aqueous phase, numerous studies have lumped the interfacial area into the interphase mass transfer coefficient. In this paper controlled dissolution experiments from a pooled NAPL were conducted. The immobile NAPL mass is placed at the bottom of a flow cell filled with porous media with water flowing on top. Effluent aqueous phase concentrations were measured for a wide range of aqueous phase velocities and for two types of porous media. To interpret the experimental results, a two-dimensional pore network model of the NAPL dissolution was developed. The well-defined geometry of the NAPL-water interface and the observed effluent concentrations were used to compute best-fit mass transfer coefficients and non-lumped Sherwood correlations. Comparing the concentrations predicted with the pore network model to simple previously used one-dimensional analytic solutions indicates that the analytic model which ignores the transverse dispersion can lead to over-estimation of the mass transfer coefficient. The predicted Sherwood correlations are also compared to previously published data and implications on NAPL remediation strategies are discussed.

The temporal evolution of magnesium isotope fractionation during hydromagnesite dissolution, precipitation, and at equilibrium

NASA Astrophysics Data System (ADS)

Oelkers, Eric H.; Berninger, Ulf-Niklas; Pérez-Fernàndez, Andrea; Chmeleff, Jérôme; Mavromatis, Vasileios

2018-04-01

This study provides experimental evidence of the resetting of the magnesium (Mg) isotope signatures of hydromagnesite in the presence of an aqueous fluid during its congruent dissolution, precipitation, and at equilibrium at ambient temperatures over month-long timescales. All experiments were performed in batch reactors in aqueous sodium carbonate buffer solutions having a pH from 7.8 to 9.2. The fluid phase in all experiments attained bulk chemical equilibrium within analytical uncertainty with hydromagnesite within several days, but the experiments were allowed to continue for up to 575 days. During congruent hydromagnesite dissolution, the fluid first became enriched in isotopically light Mg compared to the dissolving hydromagnesite, but this Mg isotope composition became heavier after the fluid attained chemical equilibrium with the mineral. The δ26Mg composition of the fluid was up to ∼0.35‰ heavier than the initial dissolving hydromagnesite at the end of the dissolution experiments. Hydromagnesite precipitation was provoked during one experiment by increasing the reaction temperature from 4 to 50 °C. The δ26Mg composition of the fluid increased as hydromagnesite precipitated and continued to increase after the fluid attained bulk equilibrium with this phase. These observations are consistent with the hypothesis that mineral-fluid equilibrium is dynamic (i.e. dissolution and precipitation occur at equal, non-zero rates at equilibrium). Moreover the results presented in this study confirm (1) that the transfer of material from the solid to the fluid phase may not be conservative during stoichiometric dissolution, and (2) that the isotopic compositions of carbonate minerals can evolve even when the mineral is in bulk chemical equilibrium with its coexisting fluid. This latter observation suggests that the preservation of isotopic signatures of carbonate minerals in the geological record may require a combination of the isolation of fluid-mineral system from external chemical input and/or the existence of a yet to be defined dissolution/precipitation inhibition mechanism.

Enthalpies of formation of CaAl4O7 and CaAl12O19 (hibonite) by high temperature, alkali borate solution calorimetry

NASA Technical Reports Server (NTRS)

Geiger, C. A.; Kleppa, O. J.; Grossman, L.; Mysen, B. O.; Lattimer, J. M.

1988-01-01

Enthalpies of formation were determined for two calcium aluminate phases, CaAl4O7 and CaAl12O19, using high-temperature alkali borate solution calorimetry. The aluminates were synthesized by multiple-cycle heating and grinding stoichiometric mixtures of CaCO3 and Al2O3, and the products were characteized by X-ray diffraction and SEM microbeam analysis. The data on impurities (CaAl4O7 was found to be about 89.00 percent pure by weight and the CaAl12O19 samples about 91.48 percent pure) were used to correct the heat of solution values of the synthetic products. The enthalpies of formation, at 1063 K, from oxides, were found to be equal to -(25.6 + or - 4.7) kJ/g.f.w. for CaAl4O7 and -(33.0 + or - 9.7) kJ/g.f.w. for CaAl12O19; the respective standard enthalpies of formation from elements, at 298 K, were estimated to be -4007 + or - 5.2 kJ/g.f.w. and -10,722 + or - 12 kJ/g.f.w.

Reaction paths and equilibrium end-points in solid-solution aqueous-solution systems

USGS Publications Warehouse

Glynn, P.D.; Reardon, E.J.; Plummer, Niel; Busenberg, E.

1990-01-01

Equations are presented describing equilibrium in binary solid-solution aqueous-solution (SSAS) systems after a dissolution, precipitation, or recrystallization process, as a function of the composition and relative proportion of the initial phases. Equilibrium phase diagrams incorporating the concept of stoichiometric saturation are used to interpret possible reaction paths and to demonstrate relations between stoichiometric saturation, primary saturation, and thermodynamic equilibrium states. The concept of stoichiometric saturation is found useful in interpreting and putting limits on dissolution pathways, but there currently is no basis for possible application of this concept to the prediction and/ or understanding of precipitation processes. Previously published dissolution experiments for (Ba, Sr)SO4 and (Sr, Ca)C??O3orth. solids are interpreted using equilibrium phase diagrams. These studies show that stoichiometric saturation can control, or at least influence, initial congruent dissolution pathways. The results for (Sr, Ca)CO3orth. solids reveal that stoichiometric saturation can also control the initial stages of incongruent dissolution, despite the intrinsic instability of some of the initial solids. In contrast, recrystallisation experiments in the highly soluble KCl-KBr-H2O system demonstrate equilibrium. The excess free energy of mixing calculated for K(Cl, Br) solids is closely modeled by the relation GE = ??KBr??KClRT[a0 + a1(2??KBr-1)], where a0 is 1.40 ?? 0.02, a1, is -0.08 ?? 0.03 at 25??C, and ??KBr and ??KCl are the mole fractions of KBr and KCl in the solids. The phase diagram constructed using this fit reveals an alyotropic maximum located at ??KBr = 0.676 and at a total solubility product, ???? = [K+]([Cl-] + [Br-]) = 15.35. ?? 1990.

Dissolution Kinetics of Spheroidal-Shaped Precipitates in Age-Hardenable Aluminum Alloys

NASA Astrophysics Data System (ADS)

Anjabin, Nozar; Salehi, Majid Seyed

2018-05-01

As a first attempt, a mathematical model is proposed to predict the dissolution kinetics of non-spherical secondary phase precipitates during solution heat treatment of age-hardenable aluminum alloys. The model uses general spheroidal geometry to describe the dissolution process of the alloys containing needle/disc-shaped particles with different size distributions in a finite matrix. It is found that as the aspect ratio deviates from unity, the dissolution rate is accelerated. Also, the dissolution rate of the particles in the alloy containing the particle size distribution is lower than that of mono-sized particles system. The modeling results for dissolution of θ' precipitates in an Al-Cu alloy are compared with experiments, and a good agreement was found between the modeling and the experimental results. The proposed model can be applied to different isothermal and non-isothermal annealing conditions.

Improvement of the stability of hydroxyapatite through glass ceramic reinforcement.

PubMed

Ha, Na Ra; Yang, Zheng Xun; Hwang, Kyu Hong; Kim, Tae Suk; Lee, Jong Kook

2010-05-01

Hydroxyapatite has achieved significant application in orthopedic and dental implants due to its excellent biocompatibility. Sintered hydroxyapatites showed significant dissolution, however, after their immersion in water or simulated body fluid (SBF). This grain boundary dissolution, even in pure hydroxyapatites, resulted in grain separation at the surfaces, and finally, in fracture. In this study, hydroxyapatite ceramics containing apatite-wollastonite (AW) or calcium silicate (SG) glass ceramics as additives were prepared to prevent the dissolution. AW and SG glass ceramics were added at 0-7 wt% and powder-compacted uniaxially followed by firing at moisture conditions. The glass phase was incorporated into the hydroxyapatite to act as a sintering aid, followed by crystallization, to improve the mechanical properties without reducing the biocompatibility. As seen in the results of the dissolution test, a significant amount of damage was reduced even after more than 14 days. TEM and SEM showed no decomposition of HA to the secondary phase, and the fracture toughness increased, becoming even higher than that of the commercial hydroxyapatite.

Activation characteristics of multiphase Zr-based hydrogen storage alloys for Ni/MH rechargeable batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, H.; Lee, S.M.; Lee, J.Y.

1999-10-01

AB{sub 2} type Zr-based Laves phase alloys have been studied for possible use as negative electrodes of Ni/MH batteries with high hydrogen storage capacity. However, these alloys have the serious problem of slow activation owing to the formation of surface oxide films. To overcome this problem, alloys with multiphase microstructures have been developed. These alloys become electrochemically active via the creation of micropores by the dissolution of soluble oxide components such as vanadium oxide. However, this phenomenon has been described based only on changes in the chemical composition of the oxide layer. In the present study, this phenomenon is approachedmore » with respect to interactions between the constituent phases. An electrochemical analysis of constituent phases showed that the second phase, resulting in localized Ni-rich pits on the alloy surface. The presence of microcracks at the periphery of the Ni-rich pits after 30 h exposure to KOH electrolyte implies that hydrogen is absorbed preferentially at Ni-rich pits, thereby forming a large active surface area. However, such multiphase alloys have poor cycle durability due to the persistent dissolution of components in the second phase. Through Cr substitution, the authors have developed a family of durable alloys to prevent this unwanted dissolution from the second phase.« less

First evidence for the production of OH radicals by carbonyl oxides in solution phase A DFT investigation

NASA Astrophysics Data System (ADS)

Cremer, Dieter; Kraka, Elfi; Sosa, Carlos

2001-03-01

Dimesitylketone O-oxide ( 1) rearranges in solution to yield the alcohol 2-methylhydroxy-pentamethylbenzophenone ( 5) and dimesitylketone ( 6). DFT-B3LYP/cc-pVTZ calculations reveal that H migration from an o-methyl group to the terminal O atom of the COO unit of 1 rather than the isomerization of 1 is energetically the most favorable process. Calculated activation enthalpies (gas phase: 12.8 kcal/mol; CH 3CN solution: 12.4 kcal/mol) are in excellent agreement with measured activation enthalpies (CFCl 3 solution: 13.2±0.2 kcal/mol; CH 3CN solution: 12.5±0.3 kcal/mol). The hydroperoxide formed by H migration decomposes to a OH and a benzyl radical. Recombination in the solvent cage leads to alcohol 5 while diffusion of OH out of the solvent cage yields 6.

Translational Diffusion Coefficient and Partition Coefficient of a Spin-Labeled Solute in Lecithin Bilayer Membranes

PubMed Central

Dix, James A.; Diamond, Jared M.; Kivelson, Daniel

1974-01-01

The translational diffusion coefficient and the partition coefficient of a spin-labeled solute, di-t-butyl nitroxide, in an aqueous suspension of dipalmitoyl lecithin vesicles have been studied by electron spin resonance spectroscopy. When the lecithin is cooled through its phase transition temperature near 41°C, some solute is “frozen out” of the bilayer, and the standard partial molar enthalpy and entropy of partition go more positive by a factor of 8 and 6, respectively. However, the apparent diffusion constant in the lecithin phase is only slightly smaller than that in water, both above and below the transition temperature. The fraction of bilayer volume within which solute is distributed may increase with temperature, contributing to the positive enthalpy of partition. Comparison of time constants suggests that there is a permeability barrier to this solute in the periphery of the bilayer. PMID:4360944

New phases of osmium carbide from evolutionary algorithm and ab initio computations

NASA Astrophysics Data System (ADS)

Fadda, Alessandro; Fadda, Giuseppe

2017-09-01

New crystal phases of osmium carbide are presented in this work. These results were found with the CA code, an evolutionary algorithm (EA) presented in a previous paper which takes full advantage of crystal symmetry by using an ad hoc search space and genetic operators. The new OsC2 and Os2C structures have a lower enthalpy than any known so far. Moreover, the layered pattern of OsC2 serves as a blueprint for building new crystals by adding or removing layers of carbon and/or osmium and generating many other Os  +  C structures like Os2C, OsC, OsC2 and OsC4. These again have a lower enthalpy than all the investigated structures, including those of the present work. The mechanical, vibrational and electronic properties are discussed as well.

Enhancing Entropy and Enthalpy Fluctuations to Drive Crystallization in Atomistic Simulations.

PubMed

Piaggi, Pablo M; Valsson, Omar; Parrinello, Michele

2017-07-07

Crystallization is a process of great practical relevance in which rare but crucial fluctuations lead to the formation of a solid phase starting from the liquid. As in all first order first transitions, there is an interplay between enthalpy and entropy. Based on this idea, in order to drive crystallization in molecular simulations, we introduce two collective variables, one enthalpic and the other entropic. Defined in this way, these collective variables do not prejudge the structure into which the system is going to crystallize. We show the usefulness of this approach by studying the cases of sodium and aluminum that crystallize in the bcc and fcc crystalline structures, respectively. Using these two generic collective variables, we perform variationally enhanced sampling and well tempered metadynamics simulations and find that the systems transform spontaneously and reversibly between the liquid and the solid phases.

Energetics of a uranothorite (Th 1–xU xSiO 4) solid solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Xiaofeng; Szenknect, Stephanie; Mesbah, Adel

High-temperature oxide melt solution calorimetric measurements were completed to determine the enthalpies of formation of the uranothorite, (USiO 4) x–(ThSiO 4) 1–x, solid solution. Phase-pure samples with x values of 0, 0.11, 0.21, 0.35, 0.71, and 0.84 were prepared, purified, and characterized by powder X-ray diffraction, electron probe microanalysis, thermogravimetric analysis and differential scanning calorimetry coupled with in situ mass spectrometry, and high-temperature oxide melt solution calorimetry. This work confirms the energetic metastability of coffinite, USiO 4, and U-rich intermediate silicate phases with respect to a mixture of binary oxides. Furthermore, variations in unit cell parameters and negative excess volumesmore » of mixing, coupled with strongly exothermic enthalpies of mixing in the solid solution, suggest short-range cation ordering that can stabilize intermediate compositions, especially near x = 0.5.« less

Energetics of a uranothorite (Th 1–xU xSiO 4) solid solution

DOE PAGES

Guo, Xiaofeng; Szenknect, Stephanie; Mesbah, Adel; ...

2016-10-11

High-temperature oxide melt solution calorimetric measurements were completed to determine the enthalpies of formation of the uranothorite, (USiO 4) x–(ThSiO 4) 1–x, solid solution. Phase-pure samples with x values of 0, 0.11, 0.21, 0.35, 0.71, and 0.84 were prepared, purified, and characterized by powder X-ray diffraction, electron probe microanalysis, thermogravimetric analysis and differential scanning calorimetry coupled with in situ mass spectrometry, and high-temperature oxide melt solution calorimetry. This work confirms the energetic metastability of coffinite, USiO 4, and U-rich intermediate silicate phases with respect to a mixture of binary oxides. Furthermore, variations in unit cell parameters and negative excess volumesmore » of mixing, coupled with strongly exothermic enthalpies of mixing in the solid solution, suggest short-range cation ordering that can stabilize intermediate compositions, especially near x = 0.5.« less

DESIGN CRITERIA FOR FUEL DISSOLUTION SYSTEMS AND ASSOCIATED SERVICE FACILITIES. PLANT MODIFICATIONS FOR REPROCESSING NON-PRODUCTION REACTOR FUELS. PROJECT CGC-830

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bierman, S.R.; Graf, W.A.; Kass, M.

1960-07-29

Design panameters are presented for phases of the facility to reprocess low-enrichment fuels from nonproduction reactors. Included are plant flowsheets and equipment layouts for fuel element dissolution, centrifugation, solution adjustment, and waste handling. Also included are the basic design criteria for the supporting facilities which service these phases and all other facilites located in the vicinity of the selected building (Bldg. 221-U). (J.R.D.)

Role of root exudates in dissolution of Cd containing iron oxides

NASA Astrophysics Data System (ADS)

Rosenfeld, C.; Martinez, C. E.

2011-12-01

Dissolved organic matter (DOM) in the rhizosphere contains organic acids, amino acids and more complex organic molecules that can substantially impact the solubility of soil solid phases. Plant roots and soil microorganisms contribute a large fraction of these organic compounds to DOM, potentially accelerating the transfer of solid phase elements into solution. In highly contaminated soils, heavy metals such as Cd are commonly found coprecipitated with common minerals (e.g. iron oxides). Introducing or changing vegetation on these contaminated soils may increase DOM levels in the soil pore fluids and thus enhance the biological and chemical weathering of soil minerals. Here, we investigate the role of root exudates on mineral dissolution and Cd mobility in contaminated soils. We hypothesize that plant exudates containing nitrogen and sulfur functional groups will dissolve Cd-containing mineral phases to a greater extent than exudates containing only oxygen functional groups, resulting in higher Cd concentrations in solution. Two different iron oxide mineral phases were utilized in a laboratory-scale model study system investigating the effects of low molecular weight, oxygen-, nitrogen-, and sulfur-containing organic compounds on mineral dissolution. Goethite (α-FeOOH) was synthesized in the laboratory with 0, 2.4, 5, and 100 theoretical mol% Cd, and franklinite (ZnFe2O4) was prepared with 0, 10, and 25 theoretical mol% Cd. Phase identity of all minerals was verified with X-ray diffraction (XRD). All minerals were reacted with 0.01 mM solutions containing one of four different organic ligands (oxalic acid, citric acid, histidine or cysteine) and aliquots of these solutions were sampled periodically over 40 days. Results from solution samples suggest that oxalic acid, citric acid, and histidine consistently increase mineral dissolution relative to the control (no organic compound present) while cysteine consistently inhibits dissolution relative to the control in all minerals. Increasing Cd substitution in the franklinite resulted in increased release of Fe and Zn to solution in the presence of these organic compounds, while increasing Cd substitution in the goethite generally limited Fe release to solution. In the case of cysteine, sulfur concentrations in solution decrease over time in the presence of Cd-containing minerals, indicating strong binding of the cysteine compound to the mineral surface, inhibiting Cd dissolution from the minerals. Our work indicates that amino acids present in biological soil exudates, in addition to organic acids, may have substantial impacts on iron oxide dissolution in soils, altering the availability of both bioessential (e.g., Fe and Zn) and non-essential, or potentially toxic, (e.g., Cd) elements.

Some Fundamental Experiments on Apparent Dissolution Rate of Gas Phase in the Groundwater Recovery Processes of the Geological Disposal System - 12146

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshii, Taiki; Niibori, Yuichi; Mimura, Hitoshi

The apparent dissolution rates of gas phase in the co-presence of solid phase were examined by in-room experiments in this study. The apparent dissolution rate of gas phase q (mol/m{sup 3}.s) was generally defined by q=aK{sub L}(γP{sub g}-c), where a (1/m) is specific surface area of the interface between gas and liquid phases, K{sub L} (m/s) is overall mass transfer coefficient, γ (mol/(Pa.m{sup 3})) is reciprocal number of Henry constant, P{sub g} (Pa) is partial pressure of gas phase, and c (mol/m{sup 3}) is the concentration of gas component in liquid phase. As a model gas, CO{sub 2} gas wasmore » used. For evaluating the values of K{sub L}, this study monitored pH or the migration rate of the interface between water/gas phases, using some experiments such as the packed beds and the micro channel consisting of granite chip and rubber sheet including a slit. In the results, the values of K{sub L} were distributed in the range from 5.0x10{sup -6} m/s to 5.0x10{sup -7} m/s. These values were small, in comparison with that (7.8x10{sup -4} m/s) obtained from the bubbling test where gas phase was continually injected into deionized water without solid phase. This means that the solid phase limits the local mixing of water phase near gas-liquid interfaces. (authors)« less

Dissolution of aragonite-strontianite solid solutions in nonstoichiometric Sr (HCO3)2-Ca (HCO3)2-CO2-H2O solutions

USGS Publications Warehouse

Plummer, Niel; Busenberg, E.; Glynn, P.D.; Blum, A.E.

1992-01-01

Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO2-saturated non-stoichiometric solutions of Sr(HCO3)2 and Ca(HCO3)2 at 25??C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in Ca(HCO3)2 solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In Sr(HCO3)2 solutions the reactions usually become incongruent, precipitating a Sr-rich phase before reaching stoichiometric saturation. Dissolution of mechanical mixtures of solids approaches stoichiometric saturation with respect to the least stable solid in the mixture. Surface uptake from subsaturated bulk solutions was observed in the initial minutes of dissolution. This surficial phase is 0-10 atomic layers thick in Sr(HCO3)2 solutions and 0-4 layers thick in Ca(HCO3)2 solutions, and subsequently dissolves and/or recrystallizes, usually within 6 min of reaction. The initial transient surface precipitation (recrystallization) process is followed by congruent dissolution of the original solid which proceeds to stoichiometric saturation, or until the precipitation of a more stable Sr-rich solid. The compositions of secondary precipitates do not correspond to thermodynamic equilibrium or stoichiometric saturation states. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of solid solutions on surfaces of aragonite and strontianite single crystals immersed in Sr(HCO3)2 and Ca(HCO3)2 solutions, respectively. In Sr(HCO3)2 solutions, the XPS signal from the outer ~ 60 A?? on aragonite indicates a composition of 16 mol% SrCO3 after only 2 min of contact, and 14-18 mol% SrCO3 after 3 weeks of contact. The strontianite surface averages approximately 22 mol% CaCO3 after 2 min of contact with Ca(HCO3)2 solution, and is 34-39 mol% CaCO3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer ~25 A?? (as much as 26 mol% SrCO3 on aragonite and 44 mol% CaCO3 on strontianite). The results indicate rapid formation of a solid-solution surface phase from subsaturated aqueous solutions. The surface phase continually adjusts in composition in response to changes in composition of the bulk fluid as net dissolution proceeds. Dissolution rates of the endmembers are greatly reduced in nonstoichiometric solutions relative to dissolution rates observed in stoichiometric solutions. All solids dissolve more slowly in solutions spiked with the least soluble component ((Sr(HCO3)2)) than in solutions spiked with the more soluble component (Ca(HCO3)2), an effect that becomes increasingly significant as stoichiometric saturation is approached. It is proposed that the formation of a non-stoichiometric surface reactive zone significantly decreases dissolution rates. ?? 1992.

Novel Formulations of Phase Change Materials—Epoxy Composites for Thermal Energy Storage

PubMed Central

Alvarez Feijoo, Miguel Angel

2018-01-01

This research aimed to evaluate the thermal properties of new formulations of phase change materials (PCMs)-epoxy composites, containing a thickening agent and a thermally conductive phase. The composite specimens produced consisted of composites fabricated using (a) inorganic PCMs (hydrated salts), epoxy resins and aluminum particulates or (b) organic PCM (paraffin), epoxy resins, and copper particles. Differential Scanning Calorimetry (DSC) was used to analyze the thermal behavior of the samples, while hardness measurements were used to determine changes in mechanical properties at diverse PCM and conductive phase loading values. The results indicate that the epoxy matrix can act as a container for the PCM phase without hindering the heat-absorbing behavior of the PCMs employed. Organic PCMs presented reversible phase transformations over multiple cycles, an advantage that was lacking in their inorganic counterparts. The enthalpy of the organic PCM-epoxy specimens increased linearly with the PCM content in the matrix. The use of thickening agents prevented phase segregation issues and allowed the fabrication of specimens containing up to 40% PCM, a loading significantly higher than others reported. The conductive phase seemed to improve the heat transfer and the mechanical properties of the composites when present in low percentages (<10 wt %); however, given its mass, the enthalpy detected in the composites was reduced as their loading further increased. The conductive phase combination (PCM + epoxy resin + hardener + thickening agent) presents great potential as a heat-absorbing material at the temperatures employed. PMID:29373538

Novel Formulations of Phase Change Materials-Epoxy Composites for Thermal Energy Storage.

PubMed

Arce, Maria Elena; Alvarez Feijoo, Miguel Angel; Suarez Garcia, Andres; Luhrs, Claudia C

2018-01-26

This research aimed to evaluate the thermal properties of new formulations of phase change materials (PCMs)-epoxy composites, containing a thickening agent and a thermally conductive phase. The composite specimens produced consisted of composites fabricated using (a) inorganic PCMs (hydrated salts), epoxy resins and aluminum particulates or (b) organic PCM (paraffin), epoxy resins, and copper particles. Differential Scanning Calorimetry (DSC) was used to analyze the thermal behavior of the samples, while hardness measurements were used to determine changes in mechanical properties at diverse PCM and conductive phase loading values. The results indicate that the epoxy matrix can act as a container for the PCM phase without hindering the heat-absorbing behavior of the PCMs employed. Organic PCMs presented reversible phase transformations over multiple cycles, an advantage that was lacking in their inorganic counterparts. The enthalpy of the organic PCM-epoxy specimens increased linearly with the PCM content in the matrix. The use of thickening agents prevented phase segregation issues and allowed the fabrication of specimens containing up to 40% PCM, a loading significantly higher than others reported. The conductive phase seemed to improve the heat transfer and the mechanical properties of the composites when present in low percentages (<10 wt %); however, given its mass, the enthalpy detected in the composites was reduced as their loading further increased. The conductive phase combination (PCM + epoxy resin + hardener + thickening agent) presents great potential as a heat-absorbing material at the temperatures employed.

AN EXPERIMENTAL STUDY OF COMPLETE DISSOLUTION OF A NONAQUEOUS PHASE LIQUID IN SATURATED POROUS MEDIA

EPA Science Inventory

The attenuation of gamma radiation was utilized to measure changing residual trichloroethylene (TCE) saturation in an otherwise water-saturated porous medium as clean water was flushed through the medium. A front over which dissolution actively occurred was observed. Once develop...

Probing the Production of Extreme-ultraviolet Late-phase Solar Flares Using the Model Enthalpy-based Thermal Evolution of Loops

NASA Astrophysics Data System (ADS)

Dai, Yu; Ding, Mingde

2018-04-01

Recent observations in extreme-ultraviolet (EUV) wavelengths reveal an EUV late phase in some solar flares that is characterized by a second peak in warm coronal emissions (∼3 MK) several tens of minutes to a few hours after the soft X-ray (SXR) peak. Using the model enthalpy-based thermal evolution of loops (EBTEL), we numerically probe the production of EUV late-phase solar flares. Starting from two main mechanisms of producing the EUV late phase, i.e., long-lasting cooling and secondary heating, we carry out two groups of numerical experiments to study the effects of these two processes on the emission characteristics in late-phase loops. In either of the two processes an EUV late-phase solar flare that conforms to the observational criteria can be numerically synthesized. However, the underlying hydrodynamic and thermodynamic evolutions in late-phase loops are different between the two synthetic flare cases. The late-phase peak due to a long-lasting cooling process always occurs during the radiative cooling phase, while that powered by a secondary heating is more likely to take place in the conductive cooling phase. We then propose a new method for diagnosing the two mechanisms based on the shape of EUV late-phase light curves. Moreover, from the partition of energy input, we discuss why most solar flares are not EUV late flares. Finally, by addressing some other factors that may potentially affect the loop emissions, we also discuss why the EUV late phase is mainly observed in warm coronal emissions.

Possible existence of two amorphous phases of d-mannitol related by a first-order transition

NASA Astrophysics Data System (ADS)

Zhu, Men; Wang, Jun-Qiang; Perepezko, John H.; Yu, Lian

2015-06-01

We report that the common polyalcohol d-mannitol may have two amorphous phases related by a first-order transition. Slightly above its glass transition temperature Tg (284 K), the supercooled liquid (SCL) of d-mannitol transforms to a low-energy, apparently amorphous phase with stronger hydrogen bonds. The enthalpy of this so-called Phase X is approximately halfway between those of the known amorphous and crystalline phases, a position low for glass aging and high for crystal polymorphs. Similar to the SCL, Phase X is transparent with broad X-ray diffraction and Raman scattering; upon temperature cycling, it exhibits a glass-transition-like change of heat capacity. On fast heating, Phase X transforms back to the SCL near Tg + 50 K, enabling a determination of their equilibrium temperature. The presence of d-sorbitol as a plasticizer enables observation of a first-order transition from the SCL to Phase X entirely in the liquid state (liquid-liquid transition). The transition from d-mannitol's SCL to Phase X has intriguing similarities with the formation of the glacial phase of triphenyl phosphite (TPP) and the conversion from high-density to low-density amorphous ice, both studied intensely in the context of polyamorphism. All three processes occur near Tg with substantial enthalpy decrease toward the crystalline phases; the processes in water and d-mannitol both strengthen the hydrogen bonds. In contrast to TPP, d-mannitol's Phase X forms more rapidly and can transform back to the SCL. These features make d-mannitol a valuable new model for understanding polyamorphism.

Reconstructive structural phase transitions in dense Mg

NASA Astrophysics Data System (ADS)

Yao, Yansun; Klug, Dennis D.

2012-07-01

The question raised recently about whether the high-pressure phase transitions of Mg follow a hexagonal close-packed (hcp) → body centered cubic (bcc) or hcp → double hexagonal close-packed (dhcp) → bcc sequence at room temperature is examined by the use of first principles density functional methods. Enthalpy calculations show that the bcc structure replaces the hcp structure to become the most stable structure near 48 GPa, whereas the dhcp structure is never the most stable structure in the pressure range of interest. The characterized phase-transition mechanisms indicate that the hcp → dhcp transition is also associated with a higher enthalpy barrier. At room temperature, the structural sequence hcp → bcc is therefore more energetically favorable for Mg. The same conclusion is also reached from the simulations of the phase transitions using metadynamics methods. At room temperature, the metadynamics simulations predict the onset of a hcp → bcc transition at 40 GPa and the transition becomes more prominent upon further compression. At high temperatures, the metadynamics simulations reveal a structural fluctuation among the hcp, dhcp, and bcc structures at 15 GPa. With increasing pressure, the structural evolution at high temperatures becomes more unambiguous and eventually settles to a bcc structure once sufficient pressure is applied.

Reconstructive structural phase transitions in dense Mg.

PubMed

Yao, Yansun; Klug, Dennis D

2012-07-04

The question raised recently about whether the high-pressure phase transitions of Mg follow a hexagonal close-packed (hcp) → body centered cubic (bcc) or hcp → double hexagonal close-packed (dhcp) → bcc sequence at room temperature is examined by the use of first principles density functional methods. Enthalpy calculations show that the bcc structure replaces the hcp structure to become the most stable structure near 48 GPa, whereas the dhcp structure is never the most stable structure in the pressure range of interest. The characterized phase-transition mechanisms indicate that the hcp → dhcp transition is also associated with a higher enthalpy barrier. At room temperature, the structural sequence hcp → bcc is therefore more energetically favorable for Mg. The same conclusion is also reached from the simulations of the phase transitions using metadynamics methods. At room temperature, the metadynamics simulations predict the onset of a hcp → bcc transition at 40 GPa and the transition becomes more prominent upon further compression. At high temperatures, the metadynamics simulations reveal a structural fluctuation among the hcp, dhcp, and bcc structures at 15 GPa. With increasing pressure, the structural evolution at high temperatures becomes more unambiguous and eventually settles to a bcc structure once sufficient pressure is applied.

Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal

NASA Astrophysics Data System (ADS)

Silva, Cleiton Carvalho; de Albuquerque, Victor Hugo C.; Miná, Emerson Mendonça; Moura, Elineudo P.; Tavares, João Manuel R. S.

2018-03-01

The aim of this work was to evaluate the different phases formed during solidification and after thermal aging of the as-welded 625 nickel-based alloy, as well as the influence of microstructural changes on the mechanical properties. The experiments addressed aging temperatures of 650 and 950 °C for 10, 100, and 200 hours. The samples were analyzed by electron microscopy, microanalysis, and X-ray diffraction in order to identify the secondary phases. Mechanical tests such as hardness, microhardness, and Charpy-V impact test were performed. Nondestructive ultrasonic inspection was also conducted to correlate the acquired signals with mechanical and microstructural properties. The results show that the alloy under study experienced microstructural changes when aged at 650 °C. The aging was responsible by the dissolution of the Laves phase formed during the solidification and the appearance of γ″ phase within interdendritic region and fine carbides along the solidification grain boundaries. However, when it was aged at 950 °C, the Laves phase was continuously dissolved and the excess Nb caused the precipitation of the δ-phase (Ni3Nb), which was intensified at 10 hours of aging, with subsequent dissolution for longer periods such as 200 hours. Even when subjected to significant microstructural changes, the mechanical properties, especially toughness, were not sensitive to the dissolution and/or precipitation of the secondary phases.

Dissolution mechanism of aluminum hydroxides in acid media

NASA Astrophysics Data System (ADS)

Lainer, Yu. A.; Gorichev, I. G.; Tuzhilin, A. S.; Gololobova, E. G.

2008-08-01

The effects of the concentration, temperature, and potential at the hydroxide/electrolyte interface on the aluminum hydroxide dissolution in sulfuric, hydrochloric, and perchloric acids are studied. The limiting stage of the aluminum hydroxide dissolution in the acids is found to be the transition of the complexes that form on the aluminum hydroxide surface from the solid phase into the solution. The results of the calculation of the acid-base equilibrium constants at the oxide (hydroxide)/solution interface using the experimental data on the potentiometric titration of Al2O3 and AlOOH suspensions are analyzed. A mechanism is proposed for the dissolution of aluminum hydroxides in acid media.

Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate

PubMed Central

Radha, A. V.; Forbes, Tori Z.; Killian, Christopher E.; Gilbert, P. U. P. A.; Navrotsky, Alexandra

2010-01-01

Amorphous calcium carbonate (ACC) is a metastable phase often observed during low temperature inorganic synthesis and biomineralization. ACC transforms with aging or heating into a less hydrated form, and with time crystallizes to calcite or aragonite. The energetics of transformation and crystallization of synthetic and biogenic (extracted from California purple sea urchin larval spicules, Strongylocentrotus purpuratus) ACC were studied using isothermal acid solution calorimetry and differential scanning calorimetry. Transformation and crystallization of ACC can follow an energetically downhill sequence: more metastable hydrated ACC → less metastable hydrated ACC⇒anhydrous ACC ∼ biogenic anhydrous ACC⇒vaterite → aragonite → calcite. In a given reaction sequence, not all these phases need to occur. The transformations involve a series of ordering, dehydration, and crystallization processes, each lowering the enthalpy (and free energy) of the system, with crystallization of the dehydrated amorphous material lowering the enthalpy the most. ACC is much more metastable with respect to calcite than the crystalline polymorphs vaterite or aragonite. The anhydrous ACC is less metastable than the hydrated, implying that the structural reorganization during dehydration is exothermic and irreversible. Dehydrated synthetic and anhydrous biogenic ACC are similar in enthalpy. The transformation sequence observed in biomineralization could be mainly energetically driven; the first phase deposited is hydrated ACC, which then converts to anhydrous ACC, and finally crystallizes to calcite. The initial formation of ACC may be a first step in the precipitation of calcite under a wide variety of conditions, including geological CO2 sequestration. PMID:20810918

Aripiprazole-Cyclodextrin Binary Systems for Dissolution Enhancement: Effect of Preparation Technique, Cyclodextrin Type and Molar Ratio

PubMed Central

M. Badr-Eldin, Shaimaa; A. Ahmed, Tarek; R Ismail, Hatem

2013-01-01

Objective(s): The aim of this work was to investigate the effect of the natural and the chemically modified form of cyclodextrins namely; β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) respectively on the solubility and dissolution rate of aripiprazole; an antipsychotic medication showing poor aqueous solubility. Materials and Methods: Phase solubility of aripiprazole with the studied CDs and the complexation efficiency values (CE) which reflect the solubilizing power of the CDs towards the drug was performed. Solid binary systems of aripiprazole with CDs were prepared by kneading, microwave irradiation and freeze-drying techniques at 1:1 and 1:2 (drug to CD) molar ratios. Drug-CD physical mixtures were also prepared in the same molar ratios for comparison. The dissolution of aripiprazole-binary systems was carried out to select the most appropriate CD type, molar ratio and preparation technique. Results: Phase solubility study indicated formation of higher order complexes and the complexation efficiency values was higher for HP-β-CD compared to β-CD. Drug dissolution study revealed that aripiprazole dissolution was increased upon increasing the CD molar ratio and, the freeze-drying technique was superior to the other studied methods especially when combined with the HP-β-CD. The cyclodextrin type, preparation technique and molar ratio exhibited statistically significant effect on the drug dissolution at P≤ 0.05. Conclusion: The freeze-dried system prepared at molar ratio 1:2 (drug: CD) can be considered as efficient tool for enhancing aripiprazole dissolution with the possibility of improving its bioavailability. PMID:24570827

Calorimetric study of phase transitions in nanocomposites of quantum dots and a liquid crystal

NASA Astrophysics Data System (ADS)

Kalakonda, P.; Iannacchione, G. S.

2015-06-01

The complex specific heat is measured over a wide temperature range for the liquid crystal (LC) 4-cyano-4-octylbiphenyl (8CB) and cadmium sulfate quantum dots (QDs) composites as a function of QD concentration. The thermal scans were performed under near-equilibrium conditions for all samples having QDs weight percent (φw) from 0 to 3wt% over a wide range of temperature well above and below the two transitions in pure 8CB. Isotropic (I) to nematic (N) and nematic to smectic-A (SmA) phase transitions evolve in character and their transition temperatures offset by (∼2.3 to 2.6 K) lower for all composite samples as compared to that in pure 8CB. The enthalpy change associated with I-N phase transitions shows slightly different behavior on heating and cooling and it also shows crossover behavior at lower and higher QD content. The enthalpy change associated with N-SmA phase transitions is independent of QD loading and thermal treatment. Given the homogeneous and random distribution of QD in these nanocomposites, we interpret that these results as arising that the nematic phase imposes self-assembly on QDs to form one-dimensional arrays leading to QDs and induces net local disordering effect in LC media.

Model of heterogeneous material dissolution in simulated biological fluid

NASA Astrophysics Data System (ADS)

Knyazeva, A. G.; Gutmanas, E. Y.

2015-11-01

In orthopedic research, increasing attention is being paid to bioresorbable/biodegradable implants as an alternative to permanent metallic bone healing devices. Biodegradable metal based implants possessing high strength and ductility potentially can be used in load bearing sites. Biodegradable Mg and Fe are ductile and Fe possess high strength, but Mg degrades too fast and Fe degrades too slow, Ag is a noble metal and should cause galvanic corrosion of the more active metallic iron - thus, corrosion of Fe can be increased. Nanostructuring should results in higher strength and can result in higher rate of dissolution/degradation from grain boundaries. In this work, a simple dissolution model of heterogeneous three phase nanocomposite material is considered - two phases being metal Fe and Ag and the third - nanopores. Analytical solution for the model is presented. Calculations demonstrate that the changes in the relative amount of each phase depend on mass exchange and diffusion coefficients. Theoretical results agree with preliminary experimental results.

A multiphase interfacial model for the dissolution of spent nuclear fuel

NASA Astrophysics Data System (ADS)

Jerden, James L.; Frey, Kurt; Ebert, William

2015-07-01

The Fuel Matrix Dissolution Model (FMDM) is an electrochemical reaction/diffusion model for the dissolution of spent uranium oxide fuel. The model was developed to provide radionuclide source terms for use in performance assessment calculations for various types of geologic repositories. It is based on mixed potential theory and consists of a two-phase fuel surface made up of UO2 and a noble metal bearing fission product phase in contact with groundwater. The corrosion potential at the surface of the dissolving fuel is calculated by balancing cathodic and anodic reactions occurring at the solution interfaces with UO2 and NMP surfaces. Dissolved oxygen and hydrogen peroxide generated by radiolysis of the groundwater are the major oxidizing agents that promote fuel dissolution. Several reactions occurring on noble metal alloy surfaces are electrically coupled to the UO2 and can catalyze or inhibit oxidative dissolution of the fuel. The most important of these is the oxidation of hydrogen, which counteracts the effects of oxidants (primarily H2O2 and O2). Inclusion of this reaction greatly decreases the oxidation of U(IV) and slows fuel dissolution significantly. In addition to radiolytic hydrogen, large quantities of hydrogen can be produced by the anoxic corrosion of steel structures within and near the fuel waste package. The model accurately predicts key experimental trends seen in literature data, the most important being the dramatic depression of the fuel dissolution rate by the presence of dissolved hydrogen at even relatively low concentrations (e.g., less than 1 mM). This hydrogen effect counteracts oxidation reactions and can limit fuel degradation to chemical dissolution, which results in radionuclide source term values that are four or five orders of magnitude lower than when oxidative dissolution processes are operative. This paper presents the scientific basis of the model, the approach for modeling used fuel in a disposal system, and preliminary calculations to demonstrate the application and value of the model.

Empirical model for calculating vapor-liquid equilibrium and associated phase enthalpy for the CO$sub 2$--O$sub 2$--Kr--Xe system for application to the KALC process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glass, R. W.; Gilliam, T. M.; Fowler, V. L.

An empirical model is presented for vapor-liquid equilibria and enthalpy for the CO$sub 2$-O$sub 2$ system. In the model, krypton and xenon in very low concentrations are combined with the CO$sub 2$-O$sub 2$ system, thereby representing the total system of primary interest in the High-Temperature Gas- Cooled Reactor program for removing krypton from off-gas generated during the reprocessing of spent fuel. Selected properties of the individual and combined components being considered are presented in the form of tables and empirical equations. (auth)

Enthalpies of formation of Cd–Pr intermetallic compounds and thermodynamic assessment of the Cd–Pr system

PubMed Central

Reichmann, Thomas L.; Richter, Klaus W.; Delsante, Simona; Borzone, Gabriella; Ipser, Herbert

2014-01-01

In the present study standard enthalpies of formation were measured by reaction and solution calorimetry at stoichiometric compositions of Cd2Pr, Cd3Pr, Cd58Pr13 and Cd6Pr. The corresponding values were determined to be −46.0, −38.8, −35.2 and −24.7 kJ/mol(at), respectively. These data together with thermodynamic data and phase diagram information from literature served as input data for a CALPHAD-type optimization of the Cd–Pr phase diagram. The complete composition range could be described precisely with the present models, both with respect to phase equilibria as well as to thermodynamic input data. The thermodynamic parameters of all intermetallic compounds were modelled following Neumann–Kopp rule. Temperature dependent contributions to the individual Gibbs energies were used for all compounds. Extended solid solubilities are well described for the low- and high-temperature modifications of Pr and also for the intermetallic compound CdPr. A quite good agreement with all viable data available from literature was found and is presented. PMID:25540475

Effect of Mineral Dissolution/Precipitation and CO2 Exsolution on CO2 transport in Geological Carbon Storage.

PubMed

Xu, Ruina; Li, Rong; Ma, Jin; He, Di; Jiang, Peixue

2017-09-19

Geological carbon sequestration (GCS) in deep saline aquifers is an effective means for storing carbon dioxide to address global climate change. As the time after injection increases, the safety of storage increases as the CO 2 transforms from a separate phase to CO 2 (aq) and HCO 3 - by dissolution and then to carbonates by mineral dissolution. However, subsequent depressurization could lead to dissolved CO 2 (aq) escaping from the formation water and creating a new separate phase which may reduce the GCS system safety. The mineral dissolution and the CO 2 exsolution and mineral precipitation during depressurization change the morphology, porosity, and permeability of the porous rock medium, which then affects the two-phase flow of the CO 2 and formation water. A better understanding of these effects on the CO 2 -water two-phase flow will improve predictions of the long-term CO 2 storage reliability, especially the impact of depressurization on the long-term stability. In this Account, we summarize our recent work on the effect of CO 2 exsolution and mineral dissolution/precipitation on CO 2 transport in GCS reservoirs. We place emphasis on understanding the behavior and transformation of the carbon components in the reservoir, including CO 2 (sc/g), CO 2 (aq), HCO 3 - , and carbonate minerals (calcite and dolomite), highlight their transport and mobility by coupled geochemical and two-phase flow processes, and consider the implications of these transport mechanisms on estimates of the long-term safety of GCS. We describe experimental and numerical pore- and core-scale methods used in our lab in conjunction with industrial and international partners to investigate these effects. Experimental results show how mineral dissolution affects permeability, capillary pressure, and relative permeability, which are important phenomena affecting the input parameters for reservoir flow modeling. The porosity and the absolute permeability increase when CO 2 dissolved water is continuously injected through the core. The MRI results indicate dissolution of the carbonates during the experiments since the porosity has been increased after the core-flooding experiments. The mineral dissolution changes the pore structure by enlarging the throat diameters and decreasing the pore specific surface areas, resulting in lower CO 2 /water capillary pressures and changes in the relative permeability. When the reservoir pressure decreases, the CO 2 exsolution occurs due to the reduction of solubility. The CO 2 bubbles preferentially grow toward the larger pores instead of toward the throats or the finer pores during the depressurization. After exsolution, the exsolved CO 2 phase shows low mobility due to the highly dispersed pore-scale morphology, and the well dispersed small bubbles tend to merge without interface contact driven by the Ostwald ripening mechanism. During depressurization, the dissolved carbonate could also precipitate as a result of increasing pH. There is increasing formation water flow resistance and low mobility of the CO 2 in the presence of CO 2 exsolution and carbonate precipitation. These effects produce a self-sealing mechanism that may reduce unfavorable CO 2 migration even in the presence of sudden reservoir depressurization.

High-pressure phase relations and thermodynamic properties of CaAl 4Si 2O 11 CAS phase

NASA Astrophysics Data System (ADS)

Akaogi, M.; Haraguchi, M.; Yaguchi, M.; Kojitani, H.

2009-03-01

Phase relations in CaAl4Si2O11 were examined at 12-23 GPa and 1000-1800 °C by multianvil experiments. A three-phase mixture of grossular, kyanite and corundum is stable below about 13 GPa at 1000-1800 °C. At higher pressure and at temperature below about 1200 °C, a mixture of grossular, stishovite and corundum is stable, indicating the decomposition of kyanite. Above about 1200 °C, CaAl4Si2O11 CAS phase is stable at pressure higher than about 13 GPa. The triple point is placed at 14.7 GPa and 1280 °C. The equilibrium boundary of formation of CAS phase from the mixture of grossular, kyanite and corundum has a small negative slope, and that from the mixture of grossular, stishovite and corundum has a strongly negative slope, while the decomposition boundary of kyanite has a small positive slope. Enthalpies of the transitions were measured by high-temperature drop-solution calorimetry. The enthalpy of formation of CaAl4Si2O11 CAS phase from the mixture of grossular, kyanite and corundum was 139.5 ± 15.6 kJ/mol, and that from the mixture of grossular, stishovite and corundum was 94.2 ± 15.4 kJ/mol. The transition boundaries calculated using the measured enthalpy data were consistent with those determined by the high-pressure experiments. The boundaries in this study are placed about 3 GPa higher in pressure and about 200 °C lower in temperature than those by Zhai and Ito [Zhai, S., Ito, E., 2008. Phase relations of CaAl4Si2O11 at high-pressure and high-temperature with implications for subducted continental crust into the deep mantle. Phys. Earth Planet. Inter. 167, 161-167]. Combining the thermodynamic data measured in this study with those in the literature, dissociation boundary of CAS phase into a mixture of Ca-perovskite, corundum and stishovite and that of grossular into Ca-perovskite plus corundum were calculated to further constrain the stability field of CAS phase. The result suggests that the stability of CAS phase would be limited at the bottom of transition zone and top of the lower mantle, when sediments are subducted into the deep mantle. It is also suggested that CAS phase may be stable at the depth of the upper part of the lower mantle, when partial melting of basalt occurs at the depth.

Accelerated Exploration of Multi-principal Element Alloys for Structural Applications (Postprint)

DTIC Science & Technology

2015-04-27

SS phases (BCC, HCP and FCC), three silicide phases (M5Si3, M5Si4 and M3Si3), an ordered B2 phase, and two Laves phases (C14 and C15). In total, 453...alloys containing silicide phases (M5Si3, M5Si4, and M3Si2) is probably due to very negative, often below 50 kJ/mol [51 53] enthalpies of formation of...The majority of equiatomic alloys containing two or more phases are (SSþ IM) alloys.5. BCC, HCP and FCC SS phases, three silicide phases (M5Si3, M5Si4

Dissolution of a Tetrachloroethene (PCE) pool in an Anaerobic Sand Tank Aquifer System: Bioenhancement, Ecology, and Hydrodynamics

NASA Astrophysics Data System (ADS)

Klemm, Sara; Becker, Jennifer; Seagren, Eric

2017-04-01

Dehalorespiring bacteria that reductively dechlorinate and grow on chlorinated ethenes in the aqueous phase can also achieve treatment of dense nonaqueous phase liquid (DNAPL) contaminants in the subsurface via bioenhanced dissolution, i.e., enhanced mass transfer from the DNAPL to the aqueous phase. Theoretical and experimental analyses predict that a number of interrelated physicochemical processes (e.g., advection and dispersion) and biological factors (e.g., biokinetics and competition) may influence the degree of bioenhancement. This research focused on understanding the interrelated roles that hydrodynamics and ecological interactions among dehalorespiring populations play in determining the distribution of dehalorespiring populations and the impact on bioenhanced dissolution and detoxification. The hypotheses driving this research are that: (1) ecological interactions between different dehalorespiring strains can significantly impact the dissolution rate bioenhancement and extent of dechlorination; and (2) hydrodynamics near the DNAPL pool will affect the outcome of ecological interactions and the potential for bioenhancement and detoxification. These hypotheses were evaluated via a multi-objective modeling and experimental framework focused on quantifying the impact of microbial interactions and hydrodynamics on the dissolution rate bioenhancement and plume detoxification using a model co-culture of Desulfuromonas michiganensis BB1 and Dehalococcoides mccartyi 195. The experiments were performed in a saturated intermediate-scale flow cell (1.2 m), with flow parallel to a tetrachloroethene (PCE) pool. Bioenhancement of PCE dissolution by the two dehalorespirers was evaluated using a steady-state mass balance, and initially resulted in a two- to three-fold increase in the dissolution rate, with cis-dichloroethene (cDCE) as the primary dechlorination product. Quantitative analysis of microbial population distribution and abundance using a 16S rRNA gene-based qPCR approach indicated that Dsm. michiganensis BB1 was the dominant population in the effluent. This was expected based on our previous work characterizing the PCE utilization kinetics of the two populations, and suggests that Dsm. michiganensis BB1 was the dominant population in the aquifer system and controlled PCE dissolution and its bioenhancement. This conclusion is consistent with our numerical modeling predictions for the same conditions, which suggested Dhc. mccartyi 195 had little effect on dissolution and dehalorespiration, but aided detoxification by growing on the cDCE produced by Dsm. michiganensis BB1. Subsequently, the PCE dissolution enhancement increased to six- to seven-fold relative to the abiotic dissolution rate. Quantitative analysis of population distribution and abundance in the porous media and nonreactive tracer studies suggested that microbial growth-induced bioclogging, coupled with inhibition of microbial activity near the DNAPL, resulted in increased flow immediately adjacent to the DNAPL-aqueous interface. The increased flow rate past the DNAPL could explain the observed increase in the PCE dissolution rate and is consistent with our numerical modeling of the system. The research described here is part of a larger project working to improve the fundamental understanding of the impact of hydrodynamics and ecological interactions on DNAPL dissolution rate bioenhancement and plume detoxification. These biotic data build on the baseline abiotic experiments reported in another abstract submitted to Session HS8.1.6.

Calorimetric Studies of Precipitation and Dissolution Kinetics in Aluminum Alloys 2219 and 7075

NASA Astrophysics Data System (ADS)

Papazian, John M.

1982-05-01

Differential scanning calorimetry (DSC) was used to study the kinetics of precipitation and dissolution of metastable and stable phases in aluminum alloys 2219 and 7075. A comparison of DSC scans obtained at heating rates of 1, 5, 10, and 20 K per minute showed that, during a DSC scan, the rates of precipitation of θ' and θ in 2219 and η' and η in 7075 were limited by their reaction kinetics. Likewise, the rates of dissolution of GP zones, θ' and η', were found to be dominated by kinetics. In contrast, the dissolution of θ and η was dominated by the thermodynamic equilibrium between these phases and the matrix. Analysis of the kinetically dominated reaction peaks and their dependence on heating rate and particle size showed that the GP zone dissolution reaction could best be described by a three-dimensional volume diffusion limited rate expression with an activation energy equal to that for diffusion. The rate of formation of θ' was best described by an Avrami expression with n = 1.1, indicating that nucleation was not the rate controlling step. A pronounced dependence of the θ' formation rate on prior plastic deformation was observed and ascribed to the influence of the matrix dislocation density on diffusivity.

Heat of formation of petalite, LiAlSi4O10

NASA Astrophysics Data System (ADS)

Faßhauer, D. W.; Cemič, L.

The enthalpy of formation of petalite, LiAlSi4O10, has been measured using high-temperature solution calorimetry. The measurements were carried out in a Calvet-type twin micro calorimeter at 728°C. A 2PbO.B2O3 melt was used as a solvent. Tabulated heats of formation of the components and tabulated heat capacities of the reactants and the product (Robie and Hemingway 1995) were used to calculate the standard heat of formation of petalite from the measured heats of solution. The calculations yielded a mean value of ΔfHpet298.15=-4872+/-5.4 kJ mol-1. This value may be compared to the heat of formation of ΔfHpet298.15= -4886.5+/-6.3 kJ mol-1 determined by the HF solution calorimetry by Bennington etal. (1980). Faßhauer etal. (1998) combined thermodynamic data with phase-equilibrium results to obtain best-fit thermodynamic results using the Bayes method, in order to derive an internally consistent dataset for phases in the NaAlSiO4- LiAlSiO4-Al2O3-SiO2-H2O system. They determined -4865.6+/-0.8kJmol-1 as the enthalpy of formation of petalite, a value that is appreciably closer to the enthalpy found in this work.

Friction-induced structural transformations of the carbide phase in Hadfield steel

NASA Astrophysics Data System (ADS)

Korshunov, L. G.; Sagaradze, V. V.; Chernenko, N. L.; Shabashov, V. A.

2015-08-01

Structural transformations of the carbide phase in Hadfield steel (110G13) that occur upon plastic deformation by dry sliding friction have been studied by methods of optical metallography, X-ray diffraction, and transmission electron microscopy. Deformation is shown to lead to the refinement of the particles of the carbide phase (Fe, Mn)3C to a nanosized level. The effect of the deformation-induced dissolution of (Fe, Mn)3C carbides in austenite of 110G13 (Hadfield) steel has been revealed, which manifests in the appearance of new lines belonging to austenite with an unusually large lattice parameter ( a = 0.3660-0.3680 nm) in the X-ray diffraction patterns of steel tempered to obtain a fine-lamellar carbide phase after deformation. This austenite is the result of the deformation-induced dissolution of disperse (Fe, Mn)3C particles, which leads to the local enrichment of austenite with carbon and manganese. The tempering that leads to the formation of carbide particles in 110G13 steel exerts a negative influence on the strain hardening of the steel, despite the increase in the hardness of steel upon tempering and the development of the processes of the deformation-induced dissolution of the carbide phase, which leads to the strengthening of the γ solid solution.

Reactivity of alkaline lignite fly ashes towards CO{sub 2} in water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martin Back; Michael Kuehn; Helge Stanjek

2008-06-15

The reaction kinetics between alkaline lignite fly ashes and CO{sub 2} (pCO{sub 2} = 0.01-0.03 MPa) were studied in a laboratory CO{sub 2} flow-through reactor at 25-75{sup o}C. The reaction is characterized by three phases that can be separated according to the predominating buffering systems and the rates of CO{sub 2} uptake. Phase I (pH > 12, < 30 min) is characterized by the dissolution of lime, the onset of calcite precipitation and a maximum uptake, the rate of which seems to be limited by dissolution of CO{sub 2}. Phase II (pH < 10.5, 10-60 min) is dominated by themore » carbonation reaction. CO{sub 2} uptake in phase III (pH < 8.3) is controlled by the dissolution of periclase (MgO) leading to the formation of dissolved magnesium-bicarbonate. Phase I could be significantly extended by increasing the solid-liquid ratios and temperature, respectively. At 75{sup o}C the rate of calcite precipitation was doubled leading to the neutralization of approximately 0.23 kg CO{sub 2} per kg fly ash within 4.5 h, which corresponds to nearly 90% of the total acid neutralizing capacity. 21 refs., 5 figs., 1 tab.« less

Pharmaceutical solvates, hydrates and amorphous forms: A special emphasis on cocrystals.

PubMed

Healy, Anne Marie; Worku, Zelalem Ayenew; Kumar, Dinesh; Madi, Atif M

2017-08-01

Active pharmaceutical ingredients (APIs) may exist in various solid forms, which can lead to differences in the intermolecular interactions, affecting the internal energy and enthalpy, and the degree of disorder, affecting the entropy. Differences in solid forms often lead to differences in thermodynamic parameters and physicochemical properties for example solubility, dissolution rate, stability and mechanical properties of APIs and excipients. Hence, solid forms of APIs play a vital role in drug discovery and development in the context of optimization of bioavailability, filing intellectual property rights and developing suitable manufacturing methods. In this review, the fundamental characteristics and trends observed for pharmaceutical hydrates, solvates and amorphous forms are presented, with special emphasis, due to their relative abundance, on pharmaceutical hydrates with single and two-component (i.e. cocrystal) host molecules. Copyright © 2017 Elsevier B.V. All rights reserved.

Influence of Secondary Interactions on the Structure, Sublimation Thermodynamics, and Solubility of Salicylate:4-Hydroxybenzamide Cocrystals. Combined Experimental and Theoretical Study.

PubMed

Manin, Alex N; Voronin, Alexander P; Shishkina, Anastasia V; Vener, Mikhail V; Churakov, Andrei V; Perlovich, German L

2015-08-20

Cocrystal screening of 4-hydroxybenzamide with a number of salicylates (salicylic acid, SA; 4-aminosalicylic acid, PASA; acetylsalicylic acid, ASA; and salicylsalicylic acid, SSA) was conducted to confirm the formation of two cocrystals, [SA+4-OHBZA] (1:1) and [PASA+4-OHBZA] (1:1). Their structures were determined using single-crystal X-ray diffraction, and the hydrogen-bond network topology was studied. Thermodynamic characteristics of salicylic acid cocrystal sublimation were obtained experimentally. It was proved that PASA cocrystallization with 4-OHBZA makes the drug more stable and prevents the irreversible process of decarboxylation of PASA resulting in formation of toxic 3-aminophenol. The pattern of non-covalent interactions in the cocrystals is described quantitatively using solid-state density functional theory followed by Bader analysis of the periodic electron density. It has been found that the total energy of secondary interactions between synthon atoms and the side hydroxyl group of the acid molecule in [SA+4-OHBZA] (1:1) and [PASA+4-OHBZA] (1:1) cocrystals is comparable to the energy of the primary acid-amide heterosynthon. The theoretical value of the sublimation enthalpy of [SA+4-OHBZA], 231 kJ/mol, agrees fairly well with the experimental one, 272 kJ/mol. The dissolution experiments with [SA+4-OHBZA] have proved that the relatively large cocrystal stability in relation to the stability of its components has a negative effect on the dissolution rate and equilibrium solubility. The [PASA+4-OHBZA] (1:1) cocrystal showed an enhancement of apparent solubility compared to that of the corresponding pure active pharmaceutical ingredient, while their intrinsic dissolution rates are comparable.

Precipitation of Co(2+) carbonates from aqueous solution: insights on the amorphous to crystalline transformation.

NASA Astrophysics Data System (ADS)

González-López, Jorge; Fernández-González, Ángeles; Jiménez, Amalia

2016-04-01

Cobalt is toxic metal that is present only as a trace in the Earth crust. However, Co might concentrate on specific areas due to both natural and anthropogenic factors and thus, soils and groundwater can be contaminated. It is from this perspective that we are interested in the precipitation of cobalt carbonates, since co-precipitation with minerals phases is a well-known method for metal immobilization in the environment. In particular, the carbonates are widely used due to its reactivity and natural abundance. In order to evaluate the cobalt carbonate precipitation at room temperature, a simple experimental work was carried out in this work. The precipitation occurred via reaction of two common salts: 0.05M of CoCl2 and 0.05M of Na2CO3 in aqueous solution. After reaction, the precipitated solid was kept in the remaining water at 25 oC and under constant stirring for different aging times of 5 min, 1 and 5 hours, 1, 2, 4, 7, 30 and 60 days. In addition to the aging and precipitation experiments, we carried out experiments to determine the solubility of the solids. In these experiments each precipitate was dissolved in Milli-Q water until equilibrium was reached and then the aqueous solution was analyzed regarding Co2+ and total alkalinity. Furthermore, acid solution calorimetry of the products were attained. Finally, we modeled the results using the PHREEQC code. Solid and aqueous phase identification and characterization have been extensively reported in a previous work (González-López et al., 2015). The main results of our investigation were the initial precipitation of an amorphous cobalt carbonate that evolve towards a poorly crystalline cobalt hydroxide carbonate with aging treatment. Solubility of both phases have been calculated under two different approaches: precipitation and dissolution. Values of solubility from each approach were obtained with a general error due to differences in experiment conditions, for instance, ionic strength, temperature and water content. It was surprising the low solubility product (Ksp) of the new phase Co2CO3(OH)2 in the order of 10-30 and this could explain its appearance only after 7 days of aging. On the other hand, the high solubility product of amorphous is consistent with its instantaneous precipitation at the beginning of the reaction. Solution calorimetry shows a higher value of exothermic solution enthalpy for crystalline cobalt hydroxide carbonate and hence, the solubility result are confirmed. Although geochemical models indicated that aqueous solution was supersaturated with respect both phases, the sequence of obtained phases (first amorphous and next crystalline) indicate that the evolution of the saturation index has to be dropped with respect to amorphous phase with time. These results points towards a simultaneous dissolution of the amorphous and the precipitation of crystalline phase Co2CO3(OH)2 at the first stages of the reaction. González-López, J. ; Fernández-González, Á. ; Jiménez, A. (2015) Prepublication: Crystallization of nanostructured cobalt hydroxide carbonate at ambient conditions: a key precursor of Co3O4. DOI: http://dx.doi.org/10.1180/minmag.2015.079.7.02

On carbide dissolution in an as-cast ASTM F-75 alloy.

PubMed

Caudillo, M; Herrera-Trejo, M; Castro, M R; Ramírez, E; González, C R; Juárez, J I

2002-02-01

The solution treatment of an as-cast ASTM F-75 alloy was investigated. Microstructural evolution was followed during thermal processing, in particular with regard to the content and type of carbides formed. To evidence any probable carbide transformations occurring during the heating stage, as well as to clarify their effect on the carbide dissolution kinetics, three heating rates were studied. Image analysis and scanning electron microscopy techniques were used for microstructural characterization. For the identification of precipitates, these were electrolytically extracted from the matrix and then analyzed by X-ray diffraction. It was found that the precipitates in the as-cast alloy were constituted by both a M(23)C(6) carbide and a sigma intermetallic phase. The M(23)C(6) carbide was the only phase identified in solution-treated specimens, regardless of the heating rate employed, which indicated that this carbide dissolved directly into the matrix without being transformed first into an M(6)C carbide, as reported in the literature. It was found that the kinetics of dissolution for the M(23)C(6) carbide decreased progressively during the solution treatment, and that it was sensitive to the heating rate, decreasing whenever the latter was decreased. Because the M(23)C(6) carbide was not observed to suffer a phase transformation prior to its dissolution into the matrix, the effect of the heating rate was associated to the morphological change occurred as the specimens were heated. The occurrence of the observed phases was analyzed with the aid of phase diagrams computed for the system Co-Cr-Mo-C. Copyright 2001 John Wiley & Sons, Inc. J Biomed Mater Res 59: 378-385, 2002

Non-Boussinesq Dissolution-Driven Convection in Porous Media

NASA Astrophysics Data System (ADS)

Amooie, M. A.; Soltanian, M. R.; Moortgat, J.

2017-12-01

Geological carbon dioxide (CO2) sequestration in deep saline aquifers has been increasingly recognized as a feasible technology to stabilize the atmospheric carbon concentrations and subsequently mitigate the global warming. Solubility trapping is one of the most effective storage mechanisms, which is associated initially with diffusion-driven slow dissolution of gaseous CO2 into the aqueous phase, followed by density-driven convective mixing of CO2 throughout the aquifer. The convection includes both diffusion and fast advective transport of the dissolved CO2. We study the fluid dynamics of CO2 convection in the underlying single aqueous-phase region. Two modeling approaches are employed to define the system: (i) a constant-concentration condition for CO2 in aqueous phase at the top boundary, and (ii) a sufficiently low, constant injection-rate for CO2 from top boundary. The latter allows for thermodynamically consistent evolution of the CO2 composition and the aqueous phase density against the rate at which the dissolved CO2 convects. Here we accurately model the full nonlinear phase behavior of brine-CO2 mixture in a confined domain altered by dissolution and compressibility, while relaxing the common Boussinesq approximation. We discover new flow regimes and present quantitative scaling relations for global characters of spreading, mixing, and dissolution flux in two- and three-dimensional media for the both model types. We then revisit the universal Sherwood-Rayleigh scaling that is under debate for porous media convective flows. Our findings confirm the sublinear scaling for the constant-concentration case, while reconciling the classical linear scaling for the constant-injection model problem. The results provide a detailed perspective into how the available modeling strategies affect the prediction ability for the total amount of CO2 dissolved in the long term within saline aquifers of different permeabilities.

Dissolution of methane bubbles with hydrate armoring in deep ocean conditions

NASA Astrophysics Data System (ADS)

Kovalchuk, Margarita; Socolofsky, Scott

2017-11-01

The deep ocean is a storehouse of natural gas. Methane bubble moving upwards from marine sediments may become trapped in gas hydrates. It is uncertain precisely how hydrate armoring affects dissolution, or mass transfer from the bubble to the surrounding water column. The Texas A&M Oilspill Calculator was used to simulate a series of gas bubble dissolution experiments conducted in the United States Department of Energy National Energy Technology Laboratory High Pressure Water Tunnel. Several variations of the mass transfer coefficient were calculated based on gas or hydrate phase solubility and clean or dirty bubble correlations. Results suggest the mass transfer coefficient may be most closely modeled with gas phase solubility and dirty bubble correlation equations. Further investigation of hydrate bubble dissolution behavior will refine current numeric models which aid in understanding gas flux to the atmosphere and plumes such as oil spills. Research funded in part by the Texas A&M University 2017 Undergraduate Summer Research Grant and a Grant from the Methane Gas Hydrates Program of the US DOE National Energy Technology Laboratory.

Iron dissolution kinetics of mineral dust at low pH during simulated atmospheric processing

NASA Astrophysics Data System (ADS)

Shi, Z.; Bonneville, S.; Krom, M. D.; Carslaw, K. S.; Jickells, T. D.; Baker, A. R.; Benning, L. G.

2010-11-01

We investigated the iron (Fe) dissolution kinetics of African (Tibesti) and Asian (Beijing) dust samples at acidic pH with the aim of reproducing the low pH conditions in atmospheric aerosols. The Beijing dust and three size fractions of the Tibesti dust (<20 μm: PM20; <10 μm: PM10; and <2.5 μm: PM2.5) were dissolved at pH 1, 2 and/or 3 for up to 1000 h. In the first 10 min, all dust samples underwent an extremely fast Fe solubilisation. Subsequently, the Fe dissolution proceeded at a much slower rate before reaching a stable dissolution plateau. The time-dependant Fe dissolution datasets were best described by a model comprising three acid-extractable Fe pools each dissolving according to first-order kinetics. The dissolution rate constant k of each pool was independent of the source (Saharan or Asian) and the size (PM20, PM10 or PM2.5) of the dust but highly dependent on pH. The "fast" Fe pool had a k (25 h-1 at pH=1) of a similar magnitude to "dry" ferrihydrite nanoparticles and/or poorly crystalline Fe(III) oxyhydroxide, while the "intermediate" and "slow" Fe pools had k values respectively 50-60 times and 3000-4000 times smaller than the "fast" pool. The "slow" Fe pool was likely to consist of both crystalline Fe oxide phases (i.e., goethite and/or hematite) and Fe contained in the clay minerals. The initial mass of the "fast", "intermediate" and "slow" Fe pools represented respectively about 0.5-2%, 1-3% and 15-40% of the total Fe in the dust samples. Furthermore, we showed that in systems with low dust/liquid ratios, Fe can be dissolved from all three phases, whereas at high dust/liquid ratios (e.g., in aerosols), sufficient Fe is solubilised from the "fast" phase to dominate the Fe dissolved and to suppress the dissolution of Fe from the other Fe pools. These data demonstrated that dust/liquid ratio and pH are fundamental parameters controlling Fe dissolution kinetics in the dust. In order to reduce errors in atmospheric and climate models, these fundamental controlling factors need to be included.

Pore-scale supercritical CO 2 dissolution and mass transfer under drainage conditions

DOE PAGES

Chang, Chun; Zhou, Quanlin; Oostrom, Mart; ...

2016-12-05

Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO 2 (scCO 2) and a prolonged depletion of residual scCO 2. In this paper, pore-scale scCO 2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO 2 into the sandstone-analogue pore network initially saturated by water without dissolved CO 2 (dsCO 2). During the experiments, time-lapse images of dye intensity, reflecting water pH,more » were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO 2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO 2 dissolution and phase equilibrium occurs when scCO 2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO 2 dissolution at phase interfaces and diffusion of dsCO 2 at the pore scale (10–100 µm) observed after scCO 2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO 2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. Finally, this finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO 2 at narrow pore throats.« less

Pore-scale supercritical CO 2 dissolution and mass transfer under drainage conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Chun; Zhou, Quanlin; Oostrom, Mart

Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO 2 (scCO 2) and a prolonged depletion of residual scCO 2. In this paper, pore-scale scCO 2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO 2 into the sandstone-analogue pore network initially saturated by water without dissolved CO 2 (dsCO 2). During the experiments, time-lapse images of dye intensity, reflecting water pH,more » were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO 2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO 2 dissolution and phase equilibrium occurs when scCO 2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO 2 dissolution at phase interfaces and diffusion of dsCO 2 at the pore scale (10–100 µm) observed after scCO 2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO 2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. Finally, this finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO 2 at narrow pore throats.« less

Pore-scale supercritical CO 2 dissolution and mass transfer under drainage conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Chun; Zhou, Quanlin; Oostrom, Mart

Abstract: Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO 2 (scCO 2) and a prolonged depletion of residual scCO 2. In this study, pore-scale scCO 2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO 2 into the sandstone-analogue pore network initially saturated by water without dissolved CO 2 (dsCO 2). During the experiments, time-lapse images of dye intensity, reflecting watermore » pH, were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO 2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO 2 dissolution and phase equilibrium occurs when scCO 2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO 2 dissolution at phase interfaces and diffusion of dsCO 2 at the pore scale (10-100 µm) observed after scCO 2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO 2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. This finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO 2 at narrow pore throats.« less

Physico-Chemical Properties and Phase Behaviour of Pyrrolidinium-Based Ionic Liquids

PubMed Central

Domańska, Urszula

2010-01-01

A review of the relevant literature on 1-alkyl-1-methylpyrrolidinium-based ionic liquids has been presented. The phase diagrams for the binary systems of {1-ethyl-1-methylpyrrolidinium trifluoromethanesulfonate (triflate) [EMPYR][CF3SO3] + water, or + 1-butanol} and for the binary systems of {1-propyl-1-methylpyrrolidinium trifluoromethanesulfonate (triflate) [PMPYR][CF3SO3] + water, or + an alcohol (1-butanol, 1-hexanol, 1-octanol, 1-decanol)} have been determined at atmospheric pressure using a dynamic method. The influence of alcohol chain length was discussed for the [PMPYR][CF3SO3]. A systematic decrease in the solubility was observed with an increase of the alkyl chain length of an alcohol. (Solid + liquid) phase equilibria with complete miscibility in the liquid phase region were observed for the systems involving water and alcohols. The solubility of the ionic liquid increases as the alkyl chain length on the pyrrolidinium cation increases. The correlation of the experimental data has been carried out using the Wilson, UNIQUAC and the NRTL equations. The phase diagrams reported here have been compared to the systems published earlier with the 1-alkyl-1-methylpyrrolidinium-based ionic liquids. The influence of the cation and anion on the phase behaviour has been discussed. The basic thermal properties of pure ILs, i.e., melting temperature and the enthalpy of fusion, the solid-solid phase transition temperature and enthalpy have been measured using a differential scanning microcalorimetry technique. PMID:20480044

The Influence of Alumina Properties on its Dissolution in Smelting Electrolyte

NASA Astrophysics Data System (ADS)

Bagshaw, A. N.; Welch, B. J.

The dissolution of a wide range of commercially produced aluminas in modified cryolite bath was studied on a laboratory scale. Most of the aluminas were products of conventional refineries and smelter dry scrubbing systems; a few were produced in laboratory and pilot calciners, enabling greater flexibility in the calcination process and the final properties. The mode of alumina feeding and the size of addition approximated to the point feeder situation. Alpha-alumina content, B.E.T. surface area and median particle size had little impact on dissolution behaviour. The volatiles content, expressed as L.O.I., the morphology of the original hydrate and the mode of calcination had the most influence. Discrete intermediate oxide phases were identified in all samples; delta-alumina content impacted most on dissolution. The flow properties of an alumina affected its overall dissolution.

Evidence for interfacial dissolution-precipitation during low-temperature mineral weathering

NASA Astrophysics Data System (ADS)

Ruiz-Agudo, Encarnacion; Putnis, Christine V.; Rodriguez-Navarro, Carlos; Putnis, Andrew

2013-04-01

The dissolution of most common multicomponent minerals and glasses is typically "incongruent" as shown by the nonstoichiometric release of the solid phase components. This frequently results in the formation of so-called surface leached layers. The mechanism of this process has been a recurrent subject of research and debate over the past two decades, due to its relevance to a wide range of natural and technological processes, as well as being crucial in defining rate laws for mineral reactions. Here we report experimental, in situ nanoscale observations that confirm the formation of a cation depleted layer at the mineral-solution interface during dissolution of multicomponent minerals at acidic pH. Our in situ Atomic Force Microscopy studies of the dissolution of wollastonite, CaSiO3, and dolomite, Ca0.5Mg0.5CO3, combined with compositional analysis of reaction products, provide, for the first time, clear direct experimental evidence that cation-depleted (i.e. leached) layers are formed in a tight interface-coupled two step process: stoichiometric dissolution of the pristine mineral surfaces and subsequent precipitation of a secondary phase from a supersaturated boundary layer of fluid in contact with the mineral surface. Such a mechanism presents a new paradigm that differs from the concept of preferential leaching of cations, as postulated by most currently accepted incongruent dissolution models. References Ruiz Agudo, E; Putnis, CV; Rodríguez Navarro, C and Putnis, A. (2012) Mechanism of leached layer formation during chemical weathering of silicate minerals. Geology, 40, 947-950 Urosevic, M; Rodríguez Navarro,C; Putnis, CV; Cardell, C; Putnis, A and Ruiz Agudo, E (2012) In situ nanoscale observations of the dissolution of [10-14] dolomite cleavage surfaces. Geochimica et Cosmochimica Acta, 80, 1-13

Role of valence electrons in phase transformation kinetics of thallium and its dilute alloys

NASA Technical Reports Server (NTRS)

Ahmed, R.; Ahmed, S.

1991-01-01

The kinetics of the phase transformation of thallium and its dilute alloys were investigated using XRD and calorimetry. Pure thallium exhibits a beta(bcc) to alpha(hcp) phase transformation on cooling at 508 K. With alloying additions, the crystal structure for each phase does not change, although the size of the unit cell increases. The enthalpy and the temperature of phase transformation of each alloy have been determined. The chemical free energy change associated with the phase transformation of each alloy was calculated. The valence electrons make an outstanding contribution to the chemical free energy change required for the phase change.

Possible existence of two amorphous phases of D-mannitol related by a first-order transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Men; Yu, Lian, E-mail: lian.yu@wisc.edu; Wang, Jun-Qiang

2015-06-28

We report that the common polyalcohol D-mannitol may have two amorphous phases related by a first-order transition. Slightly above its glass transition temperature T{sub g} (284 K), the supercooled liquid (SCL) of D-mannitol transforms to a low-energy, apparently amorphous phase with stronger hydrogen bonds. The enthalpy of this so-called Phase X is approximately halfway between those of the known amorphous and crystalline phases, a position low for glass aging and high for crystal polymorphs. Similar to the SCL, Phase X is transparent with broad X-ray diffraction and Raman scattering; upon temperature cycling, it exhibits a glass-transition-like change of heat capacity.more » On fast heating, Phase X transforms back to the SCL near T{sub g} + 50 K, enabling a determination of their equilibrium temperature. The presence of D-sorbitol as a plasticizer enables observation of a first-order transition from the SCL to Phase X entirely in the liquid state (liquid-liquid transition). The transition from D-mannitol’s SCL to Phase X has intriguing similarities with the formation of the glacial phase of triphenyl phosphite (TPP) and the conversion from high-density to low-density amorphous ice, both studied intensely in the context of polyamorphism. All three processes occur near T{sub g} with substantial enthalpy decrease toward the crystalline phases; the processes in water and D-mannitol both strengthen the hydrogen bonds. In contrast to TPP, D-mannitol’s Phase X forms more rapidly and can transform back to the SCL. These features make D-mannitol a valuable new model for understanding polyamorphism.« less

The long-term dissolution characteristics of a residually trapped BTX mixture in soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rixey, W.G.

1996-12-31

A mass transfer limited model is presented to describe the long-term dissolution of organic compounds from a benzene, toluene, and xylenes (BTX) mixture residually trapped in a sandy soil. The model is an extension of a previously presented equilibrium dissolution model which takes into consideration mass transfer limitations that develop later in the leaching process and is similar to that presented by Borden and Kao for modeling BTX dissolution from residually trapped gasoline. The residual nonaqueous phase liquid (NAPL) is divided into multiple regions: one region which undergoes equilibrium dissolution and additional regions in which mass transfer is progressively limited.more » Application of the model to BTX column effluent data indicates that the initial dissolution (exponential decay region) of BTX can be effectively described by equilibrium dissolution. When applied to later dissolution times (Asymptotic region) a multiple-region model is required to rationalize the data for all three components. This explanation of the observed tailing in leaching experiments form residually trapped hydrocarbons if offered as an alternative to the explanation of tailing due to rate-limited desorption from soils. 16 refs., 5 figs., 2 tabs.« less

A Binary Solid-Liquid Phase Diagram Experiment Including Determination of Purity, Enthalpy of Fusion and True Melting Point.

ERIC Educational Resources Information Center

Meyer, Edwin F.; Meyer, Joseph A.

1980-01-01

Describes an experiment as an alternative to undergraduate experiments limited to high temperature metal systems or lower temperature systems involving objectionable or unstable materials. Lists six advantages of the experiment. (Author/JN)

Cloud Chemistry of Fallout Formation

DTIC Science & Technology

1968-01-31

SILICATES ....... 19 LEACHING STUDIES ..... ............................ 26 HIGH-TEMPERATURE MASS SPECTROMETRY ............... 31 Rare-Earth Oxide ...reactions between technetium oxides ................. 39 TABLES 1 . Small Boy particle size-weight fraction description (each particle size fraction...29 9. Rare-earth oxide thermodynamics (Reaction 15) ............... 32 10. Enthalpies for gas-phase reactions

Assessment of oral bioavailability enhancing approaches for SB-247083 using flow-through cell dissolution testing as one of the screens.

PubMed

Perng, Cherng-Yih; Kearney, Albert S; Palepu, Nagesh R; Smith, Brian R; Azzarano, Leonard M

2003-01-02

SB-247083 is a potent, nonpeptidic, orally active, ETA-selective, endothelin receptor antagonist. The diacid form and three salts (monoarginine, diarginine and disodium) of SB-247083 were evaluated during the pre-clinical phase of development. The developability attributes (i.e. hygroscopicity, thermal behavior, aqueous solubility, and drug-excipient compatibility) of these compounds were evaluated. In addition to these attributes, the flow-through cell (FTC) dissolution testing (using USP Apparatus 4) was used as a screening technique to evaluate several SB-247083 formulations of the diacid and its salts. FTC dissolution testing offers two distinct advantages over the more traditional static-condition dissolution testing: (1) maintenance of sink conditions; and (2) the ability to change the dissolution medium during a dissolution run. The former advantage is especially important for poorly aqueous soluble drugs having associated dissolution-rate-limitations, and the latter advantage allows one to more closely simulate the pH gradient associated with transit through the GI tract. Based on the comparative dissolution data, three formulations were chosen for oral dosing in dogs. The reasonable correlation found between the FTC dissolution results and the oral bioavailability data demonstrate that FTC dissolution testing can be a valuable tool for aiding in salt (solid-state form) and formulation selection in the early stages of development of drug candidates.

Effects of gastric pH on oral drug absorption: In vitro assessment using a dissolution/permeation system reflecting the gastric dissolution process.

PubMed

Kataoka, Makoto; Fukahori, Miho; Ikemura, Atsumi; Kubota, Ayaka; Higashino, Haruki; Sakuma, Shinji; Yamashita, Shinji

2016-04-01

The aim of the present study was to evaluate the effects of gastric pH on the oral absorption of poorly water-soluble drugs using an in vitro system. A dissolution/permeation system (D/P system) equipped with a Caco-2 cell monolayer was used as the in vitro system to evaluate oral drug absorption, while a small vessel filled with simulated gastric fluid (SGF) was used to reflect the gastric dissolution phase. After applying drugs in their solid forms to SGF, SGF solution containing a 1/100 clinical dose of each drug was mixed with the apical solution of the D/P system, which was changed to fasted state-simulated intestinal fluid. Dissolved and permeated amounts on applied amount of drugs were then monitored for 2h. Similar experiments were performed using the same drugs, but without the gastric phase. Oral absorption with or without the gastric phase was predicted in humans based on the amount of the drug that permeated in the D/P system, assuming that the system without the gastric phase reflected human absorption with an elevated gastric pH. The dissolved amounts of basic drugs with poor water solubility, namely albendazole, dipyridamole, and ketoconazole, in the apical solution and their permeation across a Caco-2 cell monolayer were significantly enhanced when the gastric dissolution process was reflected due to the physicochemical properties of basic drugs. These amounts resulted in the prediction of higher oral absorption with normal gastric pH than with high gastric pH. On the other hand, when diclofenac sodium, the salt form of an acidic drug, was applied to the D/P system with the gastric phase, its dissolved and permeated amounts were significantly lower than those without the gastric phase. However, the oral absorption of diclofenac was predicted to be complete (96-98%) irrespective of gastric pH because the permeated amounts of diclofenac under both conditions were sufficiently high to achieve complete absorption. These estimations of the effects of gastric pH on the oral absorption of poorly water-soluble drugs were consistent with observations in humans. In conclusion, the D/P system with the gastric phase may be a useful tool for better predicting the oral absorption of poorly water-soluble basic drugs. In addition, the effects of gastric pH on the oral absorption of poorly water-soluble drugs may be evaluated by the D/P system with and without the gastric phase. Copyright © 2016 Elsevier B.V. All rights reserved.

Structural alterations in lecithin-cholesterol vesicles following interactions with monomeric and micellar bile salts: physical-chemical basis for subselection of biliary lecithin species and aggregative states of biliary lipids during bile formation.

PubMed

Cohen, D E; Angelico, M; Carey, M C

1990-01-01

Using complementary physical-chemical methods including turbidimetry, quasielastic light scattering, gel filtration, and phase analysis, we examined the interactions between dilute concentrations of the common bile salt, taurochenodeoxycholate (TCDC), and uni- and multilamellar vesicles (MLVs) composed of defined molecular species of lecithin (L) and varying contents of cholesterol (Ch). Dissolution rates of MLVs with micellar TCDC, as assessed by turbidimetry, were more rapid with vesicles composed of sn-1 palmitoyl species, typical of biliary L, compared with those composed of the more hydrophobic sn-1 stearoyl species. Incorporation of Ch retarded MLV dissolution rates in proportion to the Ch content, and only at high Ch contents were dissolution rates appreciably influenced by the sn-2 fatty acid composition of L. When MLVs contained Ch in amounts characteristic of intracellular membranes (Ch/L approximately 0.1), the dissolution rates of the individual L species by TCDC accurately predicted the steady state L composition of human bile. TCDC interacted with small unilamellar L/Ch vesicles (SUVs) at concentrations well below, as well as appreciably above, its critical micellar concentration. In accordance with the TCDC-egg yolk L-H2O phase diagram, perimicellar concentrations of TCDC interacted with SUVs to form aggregates that were approximately twice the size of the SUVs. These were consistent with the formation of a dispersed hexagonal (rod-like) phase, which co-existed with aqueous bile salt (BS) monomers and either micellar or unilamellar SUV phases. Micellar TCDC completely solubilized SUVs as mixed micelles, putatively via this transient hexagonal phase. With modest Ch-supersaturation, dissolution was followed by the reemergence of a new vesicle population that coexisted metastably with mixed micelles. With high Ch supersaturation, TCDC extracted L and Ch molecules from SUVs in different proportions to form Ch-supersaturated mixed micelles and Ch-enriched SUVs, in accordance with the metastable phase diagram. These experiments are consistent with the hypothesis that sn-1 palmitoyl L species are subselected for bile, in part, by physical-chemical interactions of intracellular BS concentrations with Ch-poor membranes and that the subsequent evolution of Ch-rich vesicles and Ch-saturated mixed micelles occurs via a transitional hexagonal (rod) phase. These liquid-crystalline states are likely to be transient in Ch-unsaturated biles, but may persist in Ch-supersaturated human biles because of their high Ch contents which retard or inhibit these phase transitions.

Enthalpy versus entropy: What drives hard-particle ordering in condensed phases?

DOE PAGES

Anthamatten, Mitchell; Ou, Jane J.; Weinfeld, Jeffrey A.; ...

2016-07-27

In support of mesoscopic-scale materials processing, spontaneous hard-particle ordering has been actively pursued for over a half-century. The generally accepted view that entropy alone can drive hard particle ordering is evaluated. Furthermore, a thermodynamic analysis of hard particle ordering was conducted and shown to agree with existing computations and experiments. Conclusions are that (i) hard particle ordering transitions between states in equilibrium are forbidden at constant volume but are allowed at constant pressure; (ii) spontaneous ordering transitions at constant pressure are driven by enthalpy, and (iii) ordering under constant volume necessarily involves a non-equilibrium initial state which has yet tomore » be rigorously defined.« less

The Molybdenum titanium Phase Diagram Evaluated from Ab initio Calculations

DTIC Science & Technology

2016-10-07

thermodynamic properties of this binary system are not well known and two conflicting descriptions of the β-phase stability have been presented in the...computational thermodynamics CALPHAD approach [13] and the Thermo-Calc software [14]. These studies led to two conflicting descriptions of the stability of...energy calculations, with an energy cutoff separating core and valence states of -6 Ry. 2.2. Thermodynamic modeling The formation enthalpy of a

Thermodynamic database for the Co-Pr system.

PubMed

Zhou, S H; Kramer, M J; Meng, F Q; McCallum, R W; Ott, R T

2016-03-01

In this article, we describe data on (1) compositions for both as-cast and heat treated specimens were summarized in Table 1; (2) the determined enthalpy of mixing of liquid phase is listed in Table 2; (3) thermodynamic database of the Co-Pr system in TDB format for the research articled entitle Chemical partitioning for the Co-Pr system: First-principles, experiments and energetic calculations to investigate the hard magnetic phase W.

Thermodynamic database for the Co-Pr system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, S. H.; Kramer, M. J.; Meng, F. Q.

2016-01-21

In this article, we describe data on (1) compositions for both as-cast and heat treated specimens were summarized in Table 1; (2) the determined enthalpy of mixing of liquid phase is listed in Table 2; (3) thermodynamic database of the Co-Pr system in TDB format for the research articled entitle Chemical partitioning for the Co-Pr system: First-principles, experiments and energetic calculations to investigate the hard magnetic phase W.

Thermodynamic database for the Co-Pr system

DOE PAGES

Zhou, S. H.; Kramer, M. J.; Meng, F. Q.; ...

2016-03-01

In this article, we describe data on (1) compositions for both as-cast and heat treated specimens were summarized in Table 1; (2) the determined enthalpy of mixing of liquid phase is listed in Table 2; (3) thermodynamic database of the Co-Pr system in TDB format for the research articled entitled ''Chemical partitioning for the Co-Pr system: First-principles, experiments and energetic calculations to investigate the hard magnetic phase W.''

Vapor pressures, thermodynamic stability, and fluorescence properties of three 2,6-alkyl naphthalenes.

PubMed

Santos, Ana Filipa L O M; Oliveira, Juliana A S A; Ribeiro da Silva, Maria D M C; Monte, Manuel J S

2016-03-01

This work reports the experimental determination of relevant thermodynamic properties and the characterization of luminescence properties of the following polycyclic aromatic hydrocarbons (PAHs): 2,6-diethylnaphthalene, 2,6-diisopropylnaphthalene and 2,6-di-tert-butylnaphthalene. The standard (p(o) = 0.1 MPa) molar enthalpies of combustion, ΔcHm(o), of the three compounds were determined using static bomb combustion calorimetry. The vapor pressures of the crystalline phase of 2,6-diisopropylnaphthalene and 2,6-di-tert-butylnaphthalene were measured at different temperatures using the Knudsen effusion method and the vapor pressures of both liquid and crystalline phases of 2,6-diethylnaphthalene were measured by means of a static method. The temperatures and the molar enthalpies of fusion of the three compounds were determined using differential scanning calorimetry. The gas-phase molar heat capacities and absolute entropies of the three 2,6-dialkylnaphthalenes studied were determined computationally. The thermodynamic stability of the compounds in both the crystalline and gaseous phases was evaluated by the determination of the Gibbs energies of formation and compared with the ones reported in the literature for 2,6-dimethylnaphthalene. From fluorescence spectroscopy measurements, the optical properties of the compounds studied and of naphthalene were evaluated in solution and in the solid state. Copyright © 2015 Elsevier Ltd. All rights reserved.

On the P 21/m and Pmmn pathways of the B1 B2 phase transition in NaCl: a quantum-mechanical study

NASA Astrophysics Data System (ADS)

Catti, Michele

2004-06-01

The monoclinic P 21/m and orthorhombic Pmmn (Watanabe et al' s-type) mechanisms of the high-pressure phase transition of NaCl between the B1 (rocksalt, Fm\\overline 3 m ) and B2 (CsCl-like, Pm\\overline 3 m ) cubic phases were investigated by ab initio DFT techniques with all-electron localized basis sets. Enthalpy profiles versus the order parameter were computed at constant pressures of 15, 26.3 (equilibrium) and 35 GPa for each pathway. The monoclinic path shows a lower activation enthalpy at the equilibrium pressure, but at different p values (hysteresis effects) the other mechanism becomes competitive. In the P 21/m case, sharp jumps of structural parameters are observed along the transformation coordinate, which can be explained by a mechanism based on discontinuous sliding of alternating pairs of (100) atomic layers. This accounts also for the predicted formation of a metastable intermediate Cmcm phase with TlI-like structure, similar to that observed experimentally at high pressure in AgCl, and the relations with the KOH structure are discussed, too. On the other hand, along the Pmmn pathway the structural parameters vary quite smoothly, indicating a continuous motion of neighbouring atomic planes within the constraint of the additional mirror symmetry.

Aluminosilicate Dissolution and Silicate Carbonation during Geologic CO2 Sequestration

NASA Astrophysics Data System (ADS)

Min, Yujia

Geologic CO2 sequestration (GCS) is considered a promising method to reduce anthropogenic CO2 emission. Assessing the supercritical CO2 (scCO2) gas or liquid phase water (g, l)-mineral interactions is critical to evaluating the viability of GCS processes. This work contributes to our understanding of geochemical reactions at CO 2-water (g, l)-mineral interfaces, by investigating the dissolution of aluminosilicates in CO2-acidified water (l). Plagioclase and biotite were chosen as model minerals in reservoir rock and caprock, respectively. To elucidate the effects of brine chemistry, first, the influences of cations in brine including Na, Ca, and K, have been investigated. In addition to the cations, the effects of abundant anions including sulfate and oxalate were also examined. Besides the reactions in aqueous phase, we also examine the carbonation of silicates in water (g)-bearing supercritical CO2 (scCO2) under conditions relevant to GCS. For the metal carbonation, in particular, the effects of particle sizes, water, temperature, and pressure on the carbonation of wollastonite were systematically examined. For understanding the cations effects in brine, the impacts of Na concentrations up to 4 M on the dissolution of plagioclase and biotite were examined. High concentrations of Na significantly inhibited plagioclase dissolution by competing adsorption with proton and suppressing proton-promoted dissolution. Ca has a similar effect to Na, and their effects did not suppress each other when Na and Ca co-existed. For biotite, the inhibition effects of Na coupled with an enhancing effect due to ion exchange reaction between Na and interlayer K, which cracked the basal surfaces of biotite. The K in aqueous phase significantly inhibited the dissolution. If the biotite is equilibrated with NaCl solutions initially, the biotite dissolved faster than the original biotite and the dissolution was inhibited by Na and K in brine. The outcomes improve our current knowledge of silicates dissolution to the high salinity conditions in subsurface environments. In addition to cations, the role of anions in geochemical reactions in subsurfaces are important. This study investigated the anion effects by studying sulfate and oxalate. Sulfate formed monodentate surface complexes with the Al sites on plagioclase surface and enhanced the dissolution. Oxalate was also found to enhance the plagioclase dissolution. Co-existing oxalate and sulfate suppressed the effects of sulfate on plagioclase dissolution. This information provides useful insights for understanding the roles of sulfate and organic compounds on the CO2 water-mineral interactions during scCO2 enhanced oil recovery. The results also aid in formulating a scientific guideline of the proper amount of SO2 co-injection with CO2. Water in GCS sites can exist in water-bearing scCO2 in addition to the aqueous phase in brine. Thus, it is important to understand the effects of water-bearing scCO2 on the carbonation of silicates. To address the gap between the nano- and micro-sized particles used in the laboratory to the large grains in field sites, we utilized wollastonite and investigated the effects of particle sizes on the wollastonite carbonation in water-bearing scCO2. The thickness of the reacted layer on the particle surfaces was found to be constant for different sized particles. The amorphous silica layer formed act as a diffusion barrier for water-bearing scCO2. In addition, the reaction extent was higher with more water, lower temperature, and higher pressure. Further, higher water saturation percentage and lower temperature can lead to the formation of more permeable amorphous silica layers. This thesis included the investigations of both liquid phase and vapor phase water that contacted with scCO2, and the effects of cations and anions on both formation and caprock minerals. The findings from this work improve our knowledge of the geochemical reactions at CO2-water-mineral interfaces, which will help us design a safer GCS operation and assess the impacts of GCS on the environmental safety and quality.

Miscibility at the immiscible liquid/liquid interface: A molecular dynamics study of thermodynamics and mechanism

NASA Astrophysics Data System (ADS)

Karnes, John J.; Benjamin, Ilan

2018-01-01

Molecular dynamics simulations are used to study the dissolution of water into an adjacent, immiscible organic liquid phase. Equilibrium thermodynamic and structural properties are calculated during the transfer of water molecule(s) across the interface using umbrella sampling. The net free energy of transfer agrees reasonably well with experimental solubility values. We find that water molecules "prefer" to transfer into the adjacent phase one-at-a-time, without co-transfer of the hydration shell, as in the case of evaporation. To study the dynamics and mechanism of transfer of water to liquid nitrobenzene, we collected over 400 independent dissolution events. Analysis of these trajectories suggests that the transfer of water is facilitated by interfacial protrusions of the water phase into the organic phase, where one water molecule at the tip of the protrusion enters the organic phase by the breakup of a single hydrogen bond.

The Relation between Vaporization Enthalpies and Viscosities: Eyring's Theory Applied to Selected Ionic Liquids.

PubMed

Bonsa, Anne-Marie; Paschek, Dietmar; Zaitsau, Dzmitry H; Emel'yanenko, Vladimir N; Verevkin, Sergey P; Ludwig, Ralf

2017-05-19

Key properties for the use of ionic liquids as electrolytes in batteries are low viscosities, low vapor pressure and high vaporization enthalpies. Whereas the measurement of transport properties is well established, the determination of vaporization enthalpies of these extremely low volatile compounds is still a challenge. At a first glance both properties seem to describe different thermophysical phenomena. However, eighty years ago Eyring suggested a theory which related viscosities and vaporization enthalpies to each other. The model is based on Eyring's theory of absolute reaction rates. Recent attempts to apply Eyring's theory to ionic liquids failed. The motivation of our study is to show that Eyring's theory works, if the assumptions specific for ionic liquids are fulfilled. For that purpose we measured the viscosities of three well selected protic ionic liquids (PILs) at different temperatures. The temperature dependences of viscosities were approximated by the Vogel-Fulcher-Tamann (VFT) relation and extrapolated to the high-temperature regime up to 600 K. Then the VFT-data could be fitted to the Eyring-model. The values of vaporization enthalpies for the three selected PILs predicted by the Eyring model have been very close to the experimental values measured by well-established techniques. We conclude that the Eyring theory can be successfully applied to the chosen set of PILs, if the assumption that ionic pairs of the viscous flow in the liquid and the ionic pairs in the gas phase are similar is fulfilled. It was also noticed that proper transfer of energies can be only derived if the viscosities and the vaporization energies are known for temperatures close to the liquid-gas transition temperature. The idea to correlate easy measurable viscosities of ionic liquids with their vaporization enthalpies opens a new way for a reliable assessment of these thermodynamic properties for a broad range of ionic liquids. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-pressure synthesis of mesoporous stishovite: potential applications in mineral physics

NASA Astrophysics Data System (ADS)

Stagno, Vincenzo; Mandal, Manik; Landskron, Kai; Fei, Yingwei

2015-06-01

Recently, we have described a successful synthesis route to obtain mesoporous quartz and its high-pressure polymorph coesite by nanocasting at high pressure using periodic mesostructured precursors, such as SBA-16 and FDU-12/carbon composite as starting materials. Periodic mesoporous high-pressure silica polymorphs are of particular interest as they combine transport properties and physical properties such as hardness that potentially enable the industrial use of these materials. In addition, synthesis of mesoporous crystalline silica phases can allow more detailed geology-related studies such as water/mineral interaction, dissolution/crystallization rate and the surface contribution to the associated thermodynamic stability (free energy and enthalpy) of the various polymorphs and their crossover. Here, we present results of synthesis of mesoporous stishovite from cubic large-pore periodic mesoporous silica LP-FDU-12/C composite as precursor with an fcc lattice. We describe the synthesis procedure using multi-anvil apparatus at 9 GPa (about 90,000 atm) and temperature of 500 °C. The synthetic mesoporous stishovite is, then, characterized by wide and small-angle X-ray diffraction, scanning/transmission electron microscopy and gas adsorption. Results show that this new material is characterized by accessible mesopores with wide pore size distribution, surface area of ~45 m2/g and volume of pores of ~0.15 cm3/g. Results from gas adsorption indicate that both porosity and permeability are retained at the high pressures of synthesis but with weak periodic order of the pores.

Continuum theory for cluster morphologies of soft colloids.

PubMed

Kosmrlj, A; Pauschenwein, G J; Kahl, G; Ziherl, P

2011-06-09

We introduce a continuum description of the thermodynamics of colloids with a core-corona architecture. In the case of thick coronas, their overlap can be treated approximately by replacing the exact one-particle density distribution by a suitably shaped step profile, which provides a convenient way of modeling the spherical, columnar, lamellar, and inverted cluster morphologies predicted by numerical simulations and the more involved theories. We use the model to study monodisperse particles with the hard-core/square-shoulder pair interaction as the simplest representatives of the core-corona class. We derive approximate analytical expressions for the enthalpies of the cluster morphologies which offer a clear insight into the mechanisms at work, and we calculate the lattice spacing and the cluster size for all morphologies of the phase sequence as well as the phase-transition pressures. By comparing the results with the exact crystalline minimum-enthalpy configurations, we show that the accuracy of the theory increases with shoulder width. We discuss possible extensions of the theory that could account for the finite-temperature effects.

Electrical neurostimulation with imbalanced waveform mitigates dissolution of platinum electrodes

PubMed Central

Kumsa, Doe; Hudak, Eric M; Montague, Fred W; Kelley, Shawn C; Untereker, Darrel F; Hahn, Benjamin P; Condit, Chris; Cholette, Martin; Lee, Hyowon; Bardot, Dawn; Takmakov, Pavel

2017-01-01

Objective Electrical neurostimulation has traditionally been limited to the use of charge-balanced waveforms. Charge-imbalanced and monophasic waveforms are not used to deliver clinical therapy, because it is believed that these stimulation paradigms may generate noxious electrochemical species that cause tissue damage. Approach In this study, we investigated the dissolution of platinum as one of such irreversible reactions over a range of charge densities up to 160 µC cm−2 with current-controlled first phase, capacitive discharge second phase waveforms of both cathodic-first and anodic-first polarity. We monitored the concentration of platinum in solution under different stimulation delivery conditions including charge-balanced, charge-imbalanced, and monophasic pulses. Main results We observed that platinum dissolution decreased during charge-imbalanced and monophasic stimulation when compared to charge-balanced waveforms. Significance This observation provides an opportunity to re-evaluate the charge-balanced waveform as the primary option for sustainable neural stimulation. PMID:27650936

First-Principles and Thermodynamic Simulation of Elastic Stress Effect on Energy of Hydrogen Dissolution in Alpha Iron

NASA Astrophysics Data System (ADS)

Rakitin, M. S.; Mirzoev, A. A.; Mirzaev, D. A.

2018-04-01

Mobile hydrogen, when dissolving in metals, redistributes due to the density gradients and elastic stresses, and enables destruction processes or phase transformations in local volumes of a solvent metal. It is rather important in solid state physics to investigate these interactions. The first-principle calculations performed in terms of the density functional theory, are used for thermodynamic simulation of the elastic stress effect on the energy of hydrogen dissolution in α-Fe crystal lattice. The paper presents investigations of the total energy of Fe-H system depending on the lattice parameter. As a result, the relation is obtained between the hydrogen dissolution energy and stress. A good agreement is shown between the existing data and simulation results. The extended equation is suggested for the chemical potential of hydrogen atom in iron within the local stress field. Two parameters affecting the hydrogen distribution are compared, namely local stress and phase transformations.

Phase transition, thermodynamics properties and IR spectrum of α- and γ-RDX: First principles and MD studies

NASA Astrophysics Data System (ADS)

Yuan, Jiaonan; Ji, Guangfu; Chen, Xiangrong; Wei, Dongqing; Zhao, Feng; Wu, Qiang

2016-01-01

In present letter, based on density functional theory plus dispersion (DFT-D) and a self-consistent charge density-functional tight-binding (SCC-DFTB) method, the structural and electronic properties are reported, and the phase transition are investigated by analyzing its thermodynamics properties and IR spectrum of RDX. The anisotropy of α- and γ-RDX were discussed at 0⿿10 GPa. By fitting the third-order Birch⿿Murnaghan equation of states, the bulk modulus and its pressure derivative of RDX were determined. The α-RDX phase is found stable at ambient condition, however, under pressures, both the values of lattice constants a, b, c and the οEvdw at around 4 GPa show abrupt changes which indicate a structural transition occurred. By analyzing the linear compressibility of a, b, c axes at 0⿿8 GPa, one clearly see that the molecules in α-RDX phase underwent rotations and translational motion to their position in the γ-RDX phase at about 4 GPa, which validates the α⿿γ phase transition. The IR spectra of α-form and γ-form RDX was calculated by analyzing the trajectory of molecules motion, which also show the phase transition from the spectra changes. Employing the quasi-harmonic Debye model, the enthalpy and specific heat were investigated at various pressures of both phases. The condition of equal enthalpies in both phases also indicates the phase transition of α-form to γ-form at around 4 GPa. The variation of specific heat with temperature approaches to the classical Dulong⿿Petit's law at high temperature, while at low-temperature it obeys the Debye's T3 law.

Predicting dense nonaqueous phase liquid dissolution using a simplified source depletion model parameterized with partitioning tracers

NASA Astrophysics Data System (ADS)

Basu, Nandita B.; Fure, Adrian D.; Jawitz, James W.

2008-07-01

Simulations of nonpartitioning and partitioning tracer tests were used to parameterize the equilibrium stream tube model (ESM) that predicts the dissolution dynamics of dense nonaqueous phase liquids (DNAPLs) as a function of the Lagrangian properties of DNAPL source zones. Lagrangian, or stream-tube-based, approaches characterize source zones with as few as two trajectory-integrated parameters, in contrast to the potentially thousands of parameters required to describe the point-by-point variability in permeability and DNAPL in traditional Eulerian modeling approaches. The spill and subsequent dissolution of DNAPLs were simulated in two-dimensional domains having different hydrologic characteristics (variance of the log conductivity field = 0.2, 1, and 3) using the multiphase flow and transport simulator UTCHEM. Nonpartitioning and partitioning tracers were used to characterize the Lagrangian properties (travel time and trajectory-integrated DNAPL content statistics) of DNAPL source zones, which were in turn shown to be sufficient for accurate prediction of source dissolution behavior using the ESM throughout the relatively broad range of hydraulic conductivity variances tested here. The results were found to be relatively insensitive to travel time variability, suggesting that dissolution could be accurately predicted even if the travel time variance was only coarsely estimated. Estimation of the ESM parameters was also demonstrated using an approximate technique based on Eulerian data in the absence of tracer data; however, determining the minimum amount of such data required remains for future work. Finally, the stream tube model was shown to be a more unique predictor of dissolution behavior than approaches based on the ganglia-to-pool model for source zone characterization.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, David L.; Schoof, Justin C.; Hobbs, Michael L.

This report presents plots of specific heat, enthalpy, entropy, and Gibbs free energy for 1439 species in the JCZS2i database. Included in this set of species are 496 condensed-phase species and 943 gas-phase species. The gas phase species contain 80 anions and 112 cations for a total of 192 ions. The JCZS2i database is used in conjunction with the TIGER thermochemical code to predict thermodynamic states from ambient conditions to high temperatures and pressures. Predictions from the TIGER code using the JCZS2i database can be used in shock physics codes where temperatures may be as high as 20,000 K andmore » ions may be present. Such high temperatures were not considered in the original JCZS database, and extrapolations made for these temperatures were unrealistic. For example, specific heat would sometimes go negative at high temperatures which fails the definition of specific heat. The JCZS2i database is a new version of the JCZS database that is being created to address these inaccuracies. The purpose of the current report is to visualize the high temperature extrapolations to insure that the specific heat, enthalpy, entropy, and Gibbs free energy predictions are reasonable up to 20,000 K.« less

Olivine-modified spinel-spinel transitions in the system Mg2SiO4-Fe2SiO4: Calorimetric measurements, thermochemical calculation, and geophysical application

NASA Astrophysics Data System (ADS)

Akaogi, Masaki; Ito, Eiji; Navrotsky, Alexandra

1989-11-01

The olivine(α)-modified spinel(β)-spinel (γ) transitions in the system Mg2SiO4-Fe2SiO4 were studied by high-temperature solution calorimetry. Enthalpies of the β-γ and a α-γ transitions in Mg2SiO4 at 975 K and of the α-γ transition in Fe2SiO4 at 298 K were measured. The γ solid solution showed a positive enthalpy of mixing. Phase relations at high pressures and high temperatures were calculated from these thermochemical data including correction for the effect of nonideality of α, β, and γ solid solutions. The calculated phase diagrams agree well with those determined experimentally by Katsura and Ito very recently. The α - (Mg0.89, Fe0.11)2SiO4 transforms to β through a region of α+β without passing through the α+γ phase field at around 400 km depth in the mantle with an interval of about 18(±5) km. Temperatures at 390 and 650 km depths are estimated to be about 1673 and 1873 K, respectively, assuming an adiabatic geotherm.

Electrochemical synthesis of a surface-porous Mg70.5Al29.5 eutectic alloy in a neutral aqueous NaCl solution

NASA Astrophysics Data System (ADS)

Yang, Feng; Li, Yong-gang; Wei, Ying-hui; Wei, Huan; Yan, Ze-ying; Hou, Li-feng

2018-03-01

A surface-porous Mg-Al eutectic alloy was fabricated at room temperature via electrochemical dealloying in a neutral, aqueous 0.6 M NaCl solution by controlling the applied potential and processing duration. Selective dissolution occurred on the alloy surface. The surface-porous formation mechanism is governed by the selective dissolution of the α-Mg phase, which leaves the Mg17Al12 phase as the porous layer framework. The pore characteristics (morphology, size, and distribution) of the dealloyed samples are inherited from the α-Mg phases of the precursor Mg70.5Al29.5 (at.%) alloy. Size control in the porous layer can be achieved by regulating the synthesis parameters.

Application of cluster-plus-glue-atom model to barrierless Cu–Ni–Ti and Cu–Ni–Ta films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xiaona, E-mail: lixiaona@dlut.edu.cn; Ding, Jianxin; Wang, Miao

To improve the thermal stability of copper and avoid its diffusion into surrounding dielectrics or interfacial reactions with them, the authors applied the cluster-plus-glue-atom model to investigate barrierless Cu–Ni–M (M = Ti or Ta) seed layers. The dissolution of the third element (Ti or Ta) in the Cu lattice with the aid of Ni significantly improved the thermal stability of the Cu seed layer. The appropriate M/Ni (M = Ti or Ta) ratio was selected to obtain a low resistivity: the resistivity was as low as 2.5 μΩ cm for the (Ti{sub 1.5/13.5}Ni{sub 12/13.5}){sub 0.3}Cu{sub 99.7} film and 2.8 μΩ cm for the (Ta{sub 1.1/13.1}Ni{sub 12/13.1}){submore » 0.4}Cu{sub 99.6} film after annealing at 500 °C for 1 h. After annealing at 500 °C for 40 h, the two films remained stable without forming a Cu{sub 3}Si compound. The authors confirmed that the range of applications of the cluster-plus-glue-atom model could be extended. Therefore, a third element M with negative enthalpies of mixing with both Cu and Ni could be selected, under the premise that the mixing enthalpy of M–Ni is more negative than that of M–Cu.« less

Thermal decomposition mechanism of 1-ethyl-3-methylimidazolium bromide ionic liquid.

PubMed

Chambreau, Steven D; Boatz, Jerry A; Vaghjiani, Ghanshyam L; Koh, Christine; Kostko, Oleg; Golan, Amir; Leone, Stephen R

2012-06-21

In order to better understand the volatilization process for ionic liquids, the vapor evolved from heating the ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIM(+)Br(-)) was analyzed via tunable vacuum ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS) and thermogravimetric analysis mass spectrometry (TGA-MS). For this ionic liquid, the experimental results indicate that vaporization takes place via the evolution of alkyl bromides and alkylimidazoles, presumably through alkyl abstraction via an S(N)2 type mechanism, and that vaporization of intact ion pairs or the formation of carbenes is negligible. Activation enthalpies for the formation of the methyl and ethyl bromides were evaluated experimentally, ΔH(‡)(CH(3)Br) = 116.1 ± 6.6 kJ/mol and ΔH(‡)(CH(3)CH(2)Br) = 122.9 ± 7.2 kJ/mol, and the results are found to be in agreement with calculated values for the S(N)2 reactions. Comparisons of product photoionization efficiency (PIE) curves with literature data are in good agreement, and ab initio thermodynamics calculations are presented as further evidence for the proposed thermal decomposition mechanism. Estimates for the enthalpy of vaporization of EMIM(+)Br(-) and, by comparison, 1-butyl-3-methylimidazolium bromide (BMIM(+)Br(-)) from molecular dynamics calculations and their gas phase enthalpies of formation obtained by G4 calculations yield estimates for the ionic liquids' enthalpies of formation in the liquid phase: ΔH(vap)(298 K) (EMIM(+)Br(-)) = 168 ± 20 kJ/mol, ΔH(f, gas)(298 K) (EMIM(+)Br(-)) = 38.4 ± 10 kJ/mol, ΔH(f, liq)(298 K) (EMIM(+)Br(-)) = -130 ± 22 kJ/mol, ΔH(f, gas)(298 K) (BMIM(+)Br(-)) = -5.6 ± 10 kJ/mol, and ΔH(f, liq)(298 K) (BMIM(+)Br(-)) = -180 ± 20 kJ/mol.

Enthalpies of formation of U-, Th-, Ce-brannerite: implications for plutonium immobilization

NASA Astrophysics Data System (ADS)

Helean, K. B.; Navrotsky, A.; Lumpkin, G. R.; Colella, M.; Lian, J.; Ewing, R. C.; Ebbinghaus, B.; Catalano, J. G.

2003-08-01

Brannerite, ideally MTi 2O 6, (M=actinides, lanthanides and Ca) occurs in titanate-based ceramics proposed for the immobilization of plutonium. Standard enthalpies of formation, Δ H0f at 298 K, for three brannerite compositions (kJ/mol): CeTi 2O 6 (-2948.8 ± 4.3), U 0.97Ti 2.03O 6 (-2977.9 ± 3.5) and ThTi 2O 6 (-3096.5 ± 4.3) were determined by high temperature oxide melt drop solution calorimetry at 975 K using 3Na 2O · 4MoO 3 solvent. The enthalpies of formation were also calculated from an oxide phase assemblage (Δ H0f-ox at 298 K): MO 2 + 2TiO 2=MTi 2O 6. Only UTi 2O 6 is energetically stable with respect to an oxide assemblage: U 0.97Ti 2.03O 6 (Δ H0f-ox=-7.7±2.8 kJ/mol). Both CeTi 2O 6 and ThTi 2O 6 are higher in enthalpy with respect to their oxide assemblages with (Δ H0f-ox=+29.4±3.6 kJ/mol) and (Δ H0f-ox=+19.4±1.6 kJ/mol) respectively. Thus, Ce- and Th-brannerite are entropy stabilized and are thermodynamically stable only at high temperature.

Adsorption of Organic Molecules to van der Waals Materials: Comparison of Fluorographene and Fluorographite with Graphene and Graphite

PubMed Central

2017-01-01

Understanding strength and nature of noncovalent binding to surfaces imposes significant challenge both for computations and experiments. We explored the adsorption of five small nonpolar organic molecules (acetone, acetonitrile, dichloromethane, ethanol, ethyl acetate) to fluorographene and fluorographite using inverse gas chromatography and theoretical calculations, providing new insights into the strength and nature of adsorption of small organic molecules on these surfaces. The measured adsorption enthalpies on fluorographite range from −7 to −13 kcal/mol and are by 1–2 kcal/mol lower than those measured on graphene/graphite, which indicates higher affinity of organic adsorbates to fluorographene than to graphene. The dispersion-corrected functionals performed well, and the nonlocal vdW DFT functionals (particularly optB86b-vdW) achieved the best agreement with the experimental data. Computations show that the adsorption enthalpies are controlled by the interaction energy, which is dominated by London dispersion forces (∼70%). The calculations also show that bonding to structural features, like edges and steps, as well as defects does not significantly increase the adsorption enthalpies, which explains a low sensitivity of measured adsorption enthalpies to coverage. The adopted Langmuir model for fitting experimental data enabled determination of adsorption entropies. The adsorption on the fluorographene/fluorographite surface resulted in an entropy loss equal to approximately 40% of the gas phase entropy. PMID:28145699

Thermodynamics and proton activities of protic ionic liquids with quantum cluster equilibrium theory

NASA Astrophysics Data System (ADS)

Ingenmey, Johannes; von Domaros, Michael; Perlt, Eva; Verevkin, Sergey P.; Kirchner, Barbara

2018-05-01

We applied the binary Quantum Cluster Equilibrium (bQCE) method to a number of alkylammonium-based protic ionic liquids in order to predict boiling points, vaporization enthalpies, and proton activities. The theory combines statistical thermodynamics of van-der-Waals-type clusters with ab initio quantum chemistry and yields the partition functions (and associated thermodynamic potentials) of binary mixtures over a wide range of thermodynamic phase points. Unlike conventional cluster approaches that are limited to the prediction of thermodynamic properties, dissociation reactions can be effortlessly included into the bQCE formalism, giving access to ionicities, as well. The method is open to quantum chemical methods at any level of theory, but combination with low-cost composite density functional theory methods and the proposed systematic approach to generate cluster sets provides a computationally inexpensive and mostly parameter-free way to predict such properties at good-to-excellent accuracy. Boiling points can be predicted within an accuracy of 50 K, reaching excellent accuracy for ethylammonium nitrate. Vaporization enthalpies are predicted within an accuracy of 20 kJ mol-1 and can be systematically interpreted on a molecular level. We present the first theoretical approach to predict proton activities in protic ionic liquids, with results fitting well into the experimentally observed correlation. Furthermore, enthalpies of vaporization were measured experimentally for some alkylammonium nitrates and an excellent linear correlation with vaporization enthalpies of their respective parent amines is observed.

Citrate, not phosphate, can dissolve calcium oxalate monohydrate crystals and detach these crystals from renal tubular cells.

PubMed

Chutipongtanate, Somchai; Chaiyarit, Sakdithep; Thongboonkerd, Visith

2012-08-15

Dissolution therapy of calcium oxalate monohydrate (COM) kidney stone disease has not yet been implemented due to a lack of well characterized COM dissolution agents. The present study therefore aimed to identify potential COM crystal dissolution compounds. COM crystals were treated with deionized water (negative control), 5 mM EDTA (positive control), 5 mM sodium citrate, or 5mM sodium phosphate. COM crystal dissolution activities of these compounds were evaluated by phase-contrast and video-assisted microscopic examinations, semi-quantitative analysis of crystal size, number and total mass, and spectrophotometric oxalate-dissolution assay. In addition, effects of these compounds on detachment of COM crystals, which adhered tightly onto renal tubular cell surface, were also investigated. The results showed that citrate, not phosphate, had a significant dissolution effect on COM crystals as demonstrated by significant reduction of crystal size (approximately 37% decrease), crystal number (approximately 53% decrease) and total crystal mass (approximately 72% decrease) compared to blank and negative controls. Spectrophotometric oxalate-dissolution assay successfully confirmed the COM crystal dissolution property of citrate. Moreover, citrate could detach up to 85% of the adherent COM crystals from renal tubular cell surface. These data indicate that citrate is better than phosphate for dissolution and detachment of COM crystals. Copyright © 2012 Elsevier B.V. All rights reserved.

Mineral dissolution and secondary precipitation on quartz sand in simulated Hanford tank solutions affecting subsurface porosity

NASA Astrophysics Data System (ADS)

Wang, Guohui; Um, Wooyong

2012-11-01

Highly alkaline nuclear waste solutions have been released from underground nuclear waste storage tanks and pipelines into the vadose zone at the US Department of Energy's Hanford Site in Washington, causing mineral dissolution and re-precipitation upon contact with subsurface sediments. High pH caustic NaNO3 solutions with and without dissolved Al were reacted with quartz sand through flow-through columns stepwise at 45, 51, and 89 °C to simulate possible reactions between leaked nuclear waste solution and primary subsurface mineral. Upon reaction, Si was released from the dissolution of quartz sand, and nitrate-cancrinite [Na8Si6Al6O24(NO3)2] precipitated on the quartz surface as a secondary mineral phase. Both steady-state dissolution and precipitation kinetics were quantified, and quartz dissolution apparent activation energy was determined. Mineral alteration through dissolution and precipitation processes results in pore volume and structure changes in the subsurface porous media. In this study, the column porosity increased up to 40.3% in the pure dissolution column when no dissolved Al was present in the leachate, whereas up to a 26.5% porosity decrease was found in columns where both dissolution and precipitation were observed because of the presence of Al in the input solution. The porosity change was also confirmed by calculation using the dissolution and precipitation rates and mineral volume changes.

Miniaturized INtrinsic DISsolution Screening (MINDISS) assay for preformulation.

PubMed

Alsenz, Jochem; Haenel, Elisabeth; Anedda, Aline; Du Castel, Pauline; Cirelli, Giorgio

2016-05-25

This study describes a novel Miniaturized INtrinsic DISsolution Screening (MINDISS) assay for measuring disk intrinsic dissolution rates (DIDR). In MINDISS, compacted mini disks of drugs (2-5mg/disk) are prepared in custom made holders with a surface area of 3mm(2). Disks are immersed, pellet side down, into 0.35ml of appropriate dissolution media per well in 96-well microtiter plates, media are stirred and disk-holders are transferred to new wells after defined periods of time. After filtration, drug concentration in dissolution media is quantified by Ultra Performance Liquid Chromatography (UPLC) and solid state property of the disk is characterized by Raman spectroscopy. MINDISS was identified as an easy-to-use tool for rapid, parallel determination of DIDR of compounds that requires only small amounts of compound and of dissolution medium. Results obtained with marketed drugs in MINDISS correlate well with large scale DIDR methods and indicate that MINDISS can be used for (1) rank-ordering of compounds by intrinsic dissolution in late phase discovery and early development, (2) comparison of polymorphic forms and salts, (3) screening and selection of appropriate dissolution media, and (4) characterization of the intestinal release behavior of compounds along the gastro intestinal tract by changing biorelevant media during experiments. Copyright © 2015 Elsevier B.V. All rights reserved.

Dissolution of steel slags in aqueous media.

PubMed

Yadav, Shashikant; Mehra, Anurag

2017-07-01

Steel slag is a major industrial waste in steel industries, and its dissolution behavior in water needs to be characterized in the larger context of its potential use as an agent for sequestering CO 2 . For this purpose, a small closed system batch reactor was used to conduct the dissolution of steel slags in an aqueous medium under various dissolution conditions. In this study, two different types of steel slags were procured from steel plants in India, having diverse structural features, mineralogical compositions, and particle sizes. The experiment was performed at different temperatures for 240 h of dissolution at atmospheric pressure. The dissolution rates of major and minor slag elements were quantified through liquid-phase elemental analysis using an inductively coupled plasma atomic emission spectroscopy at different time intervals. Advanced analytical techniques such as field emission gun-scanning electron microscope, energy-dispersive X-ray, BET, and XRD were also used to analyze mineralogical and structural changes in the slag particles. High dissolution of slags was observed irrespective of the particle size distribution, which suggests high carbonation potential. Concentrations of toxic heavy metals in the leachate were far below maximum acceptable limits. Thus, the present study investigates the dissolution behavior of different mineral ions of steel slag in aqueous media in light of its potential application in CO 2 sequestration.

Lattice model for water-solute mixtures.

PubMed

Furlan, A P; Almarza, N G; Barbosa, M C

2016-10-14

A lattice model for the study of mixtures of associating liquids is proposed. Solvent and solute are modeled by adapting the associating lattice gas (ALG) model. The nature of interaction of solute/solvent is controlled by tuning the energy interactions between the patches of ALG model. We have studied three set of parameters, resulting in, hydrophilic, inert, and hydrophobic interactions. Extensive Monte Carlo simulations were carried out, and the behavior of pure components and the excess properties of the mixtures have been studied. The pure components, water (solvent) and solute, have quite similar phase diagrams, presenting gas, low density liquid, and high density liquid phases. In the case of solute, the regions of coexistence are substantially reduced when compared with both the water and the standard ALG models. A numerical procedure has been developed in order to attain series of results at constant pressure from simulations of the lattice gas model in the grand canonical ensemble. The excess properties of the mixtures, volume and enthalpy as the function of the solute fraction, have been studied for different interaction parameters of the model. Our model is able to reproduce qualitatively well the excess volume and enthalpy for different aqueous solutions. For the hydrophilic case, we show that the model is able to reproduce the excess volume and enthalpy of mixtures of small alcohols and amines. The inert case reproduces the behavior of large alcohols such as propanol, butanol, and pentanol. For the last case (hydrophobic), the excess properties reproduce the behavior of ionic liquids in aqueous solution.

Determination of the enthalpy of vaporization and prediction of surface tension for ionic liquid 1-alkyl-3-methylimidazolium propionate [C(n)mim][Pro](n = 4, 5, 6).

PubMed

Tong, Jing; Yang, Hong-Xu; Liu, Ru-Jing; Li, Chi; Xia, Li-Xin; Yang, Jia-Zhen

2014-11-13

With the use of isothermogravimetrical analysis, the enthalpies of vaporization, Δ(g)lH(o)m(T(av)), at the average temperature, T(av) = 445.65 K, for the ionic liquids (ILs) 1-alkyl-3-methylimidazolium propionate [C(n)mim][Pro](n = 4, 5, 6) were determined. Using Verevkin's method, the difference of heat capacities between the vapor phase and the liquid phase, Δ(g)lC(p)(o)m, for [C(n)mim][Pro](n = 2, 3, 4, 5, 6), were calculated based on the statistical thermodynamics. Therefore, with the use of Δ(g)lC(p)(o)m, the values of Δ(g)lH(o)m(T(av)) were transformed into Δ(g)lH(o)m(298), 126.8, 130.3, and 136.5 for [C(n)mim][Pro](n = 4, 5, 6), respectively. In terms of the new scale of polarity for ILs, the order of the polarity of [C(n)mim][Pro](n = 2, 3, 4, 5, 6) was predicted, that is, the polarity decreases with increasing methylene. A new model of the relationship between the surface tension and the enthalpy of vaporization for aprotic ILs was put forward and used to predict the surface tension for [C(n)mim][Pro](n = 2, 3, 4, 5, 6) and others. The predicted surface tension for the ILs is in good agreement with the experimental one.

In-vitro dissolution rate and molecular docking studies of cabergoline drug with β-cyclodextrin

NASA Astrophysics Data System (ADS)

Shanmuga priya, Arumugam; Balakrishnan, Suganya bharathi; Veerakanellore, Giri Babu; Stalin, Thambusamy

2018-05-01

The physicochemical properties and dissolution profile of cabergoline drug (CAB) with β-cyclodextrin (β-CD) inclusion complex were investigated by the UV spectroscopy. The inclusion complex has used to calculate the stability constant and gives the stoichiometry molar ratio is 1:1 between CAB and β-CD. The phase solubility diagram and the aqueous solubility of CAB (60%) was found to be enhanced by β-CD. In addition, the phase solubility profile of CAB with β-CD was classified as AL-type. Binary systems of CAB with β-CD were prepared by Physical mixture, Kneading and solvent evaporation methods. The solid-state properties of the inclusion complex were characterized by Fourier transformation-infrared spectroscopy, Differential scanning calorimetry, Powder X-ray diffractometric patterns and Scanning electron microscopic techniques. Theoretically, β-CD and CAB inclusion complex obtained by molecular docking studies, it is in good correlation with the results obtained through experimental methods using the Schrödinger software program. In-vitro dissolution profiles of the inclusion complexes were carried out and obvious increase in dissolution rate was observed when compared with pure CAB drug and the complexes.

Final Report of Tank 241-C-105 Dissolution, the Phase 2 Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meznarich, Huei K.; bolling, Stacey D.; Cooke, Gary A.

2016-10-01

Three clamshell grab samples were taken from Tank 241-C-105 in October 2015 in accordance with RPP-PLAN-60011. Analytical results of those samples were issued in the report RPP-RPT-59115 by Wastren Advantage, Inc., Hanford Laboratory. Solid phase characterization results were reported separately in LAB-RPT-15-00011 and in RPP-RPT-59147. The major solid phases reported to be present were dawsonite [NaAlCO 3(OH) 2], trona [Na 3(HCO 3)(CO 3)·2H 2O], cejkaite [Na 4(UO 2)(CO 3) 3], and an unidentified organic solid, with minor amounts of gibbsite [Al(OH) 3], natrophosphate [Na 7F(PO 4) 2·19H 2O], and traces of unidentified iron-rich and manganese-rich phases. Note that the presencemore » of dawsonite, trona, and cejkaite requires a relatively low pH, likely around pH 9 to 10. One aliquot of each grab sample was provided to 222-S Laboratory Process Chemistry for dissolution studies. Phase 1 of the dissolution testing followed the approved test plan, WRPS-1404813, Rev. 3, and examined the behavior of the Tank 241-C-105 solids treated with water, 19M sodium hydroxide, 2M nitric acid, and 0.5M oxalic acid/2M nitric acid. Phase 2 of the testing was conducted in accordance with instructions from the client and emphasized treatment with 19M sodium hydroxide followed by water washing. This is the report of the Phase 2 testing.« less

Thermochemistry of amorphous and crystalline zirconium and hafnium silicates.

NASA Astrophysics Data System (ADS)

Ushakov, S.; Brown, C. E.; Navrotsky, Alexandra; Boatner, L. A.; Demkov, A. A.; Wang, C.; Nguyen, B.-Y.

2003-03-01

Calorimetric investigation of amorphous and crystalline zirconium and hafnium silicates was performed as part of a research program on thermochemistry of alternative gate dielectrics. Amorphous hafnium and zirconium silicates with varying SiO2 content were synthesized by a sol-gel process. Crystalline zirconium and hafnium silicates (zircon and hafnon) were synthesized by solid state reaction at 1450 °C from amorphous gels and grown as single crystals from flux. High temperature oxide melt solution calorimetry in lead borate (2PbO.B2O3) solvent at 800 oC was used to measure drop solution enthalpies for amorphous and crystalline zirconium and hafnium silicates and corresponding oxides. Applying appropriate thermochemical cycles, formation enthalpy of crystalline ZrSiO4 (zircon) from binary oxides (baddeleite and quartz) at 298 K was calculated as -23 +/-2 kJ/mol and enthalpy difference between amorphous and crystalline zirconium silicate (vitrification enthalpy) was found to be 61 +/-3 kJ/mol. Crystallization onset temperatures of amorphous zirconium and hafnium silicates, as measured by differential scanning calorimetry (DSC), increased with silica content. The resulting crystalline phases, as characterized by X-ray diffraction (XRD), were tetragonal HfO2 and ZrO2. Critical crystallite size for tetragonal to monoclinic transformation of HfO2 in the gel was estimated as 6 +/-2 nm from XRD data Crystallization enthalpies per mole of hafnia and zirconia in gels decrease slightly together with crystallite size with increasing silica content, for example from -22 to -15 +/-1 kJ per mol of HfO2 crystallized at 740 and 1006 °C from silicates with 10 and 70 mol Applications of thermal analyses and solution calorimetry techniques together with first-principles density functional calculations to estimate interface and surface energies are discussed.

Quantum-Theoretical Methods and Studies Relating to Properties of Materials

DTIC Science & Technology

1989-12-19

particularly sensitive to the behavior of the electron distribution close to the nuclei, which contributes only to E(l). Although the above results were...other condensed phases. So it was a useful test case to test the behavior of the theoretical computations for the gas phase relative to that in the...increasingly complicated and time- comsuming electron-correlation approximations should assure a small error in the theoret- ically computed enthalpy for a

Dissolution of spent nuclear fuel in carbonate-peroxide solution

NASA Astrophysics Data System (ADS)

Soderquist, Chuck; Hanson, Brady

2010-01-01

This study shows that spent UO2 fuel can be completely dissolved in a room temperature carbonate-peroxide solution apparently without attacking the metallic Mo-Tc-Ru-Rh-Pd fission product phase. In parallel tests, identical samples of spent nuclear fuel were dissolved in nitric acid and in an ammonium carbonate, hydrogen peroxide solution. The resulting solutions were analyzed for strontium-90, technetium-99, cesium-137, europium-154, plutonium, and americium-241. The results were identical for all analytes except technetium, where the carbonate-peroxide dissolution had only about 25% of the technetium that the nitric acid dissolution had.

A thermodynamic approach to obtain materials properties for engineering applications

NASA Technical Reports Server (NTRS)

Chang, Y. Austin

1993-01-01

With the ever increases in the capabilities of computers for numerical computations, we are on the verge of using these tools to model manufacturing processes for improving the efficiency of these processes as well as the quality of the products. One such process is casting for the production of metals. However, in order to model metal casting processes in a meaningful way it is essential to have the basic properties of these materials in their molten state, solid state as well as in the mixed state of solid and liquid. Some of the properties needed may be considered as intrinsic such as the density, heat capacity or enthalpy of freezing of a pure metal, while others are not. For instance, the enthalpy of solidification of an alloy is not a defined thermodynamic quantity. Its value depends on the micro-segregation of the phases during the course of solidification. The objective of the present study is to present a thermodynamic approach to obtain some of the intrinsic properties and combining thermodynamics with kinetic models to estimate such quantities as the enthalpy of solidification of an alloy.

Effect of Water-Table Fluctuations on Source Depletion and Dissolved-Plume Behavior of a Multi-Component Light Nonaqueous-Phase Liquid

NASA Astrophysics Data System (ADS)

Dobson, R.; Schroth, M. H.; Zeyer, J.

2006-12-01

Light nonaqueous-phase liquids (LNAPLs) such as gasoline and diesel are among the most common soil and groundwater contaminants. Dissolution and subsequent advective transport of LNAPL components can negatively impact downgradient water supplies, while biodegradation is commonly thought to be an important sink for this class of contaminants. Water-table fluctuations, either naturally occurring or intentionally induced, may affect LNAPL component transport and biodegradation in aquifers. We present a laboratory investigation of the effect of water-table fluctuations on the dissolution and biodegradation of a multi-component LNAPL in a pair of similar model aquifers, one of which was subjected to a water-table fluctuation. Water-table fluctuation resulted in LNAPL and air entrapment below the water table, an increase in the vertical extent of LNAPL contamination and an increase in the volume of water passing through the contaminated zone. Effluent concentrations of dissolved LNAPL components were higher and those of dissolved nitrate were lower in the aquifer model where a fluctuation had been induced. Thus, water table fluctuation led to enhanced LNAPL dissolution as well as enhanced biodegradation activity. The increase in biodegradation observed after fluctuation was of lesser magnitude than the increase in LNAPL dissolution, such that water-table fluctuations might be expected to result in increased exposure of downgradient receptors to dissolved LNAPL components. Conversely, the potential for free-phase LNAPL migration was reduced following a water-table fluctuation, as LNAPL entrapment by the rising water table reduced the amount of free phase LNAPL. Lateral migration of LNAPL following emplacement was observed in the model aquifer where no fluctuation occurred, but not in the model aquifer where a water-table fluctuation was induced.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Fan; Levine, Lyle E.; Allen, Andrew J.

The precipitate structure and precipitation kinetics in an Al-Cu-Mg alloy (AA2024) aged at 190 °C, 208 °C, and 226 °C have been studied using ex situ Transmission Electron Microscopy (TEM) and in situ synchrotron-based, combined ultra-small angle X-ray scattering, small angle X-ray scattering (SAXS), and wide angle X-ray scattering (WAXS) across a length scale from sub-Angstrom to several micrometers. TEM brings information concerning the nature, morphology, and size of the precipitates while SAXS and WAXS provide qualitative and quantitative information concerning the time-dependent size and volume fraction evolution of the precipitates at different stages of the precipitation sequence. Within themore » experimental time resolution, precipitation at these ageing temperatures involves dissolution of nanometer-sized small clusters and formation of the planar S phase precipitates. Using a three-parameter scattering model constructed on the basis of TEM results, we established the temperature-dependent kinetics for the cluster-dissolution and S-phase formation processes simultaneously. These two processes are shown to have different kinetic rates, with the cluster-dissolution rate approximately double the S-phase formation rate. We identified a dissolution activation energy at (149.5 ± 14.6) kJ mol-1, which translates to (1.55 ± 0.15) eV/atom, as well as an activation energy for the formation of S precipitates at (129.2 ± 5.4) kJ mol-1, i.e. (1.33 ± 0.06) eV/atom. Importantly, the SAXS/WAXS results show the absence of an intermediate Guinier-Preston Bagaryatsky 2 (GPB2)/S" phase in the samples under the experimental ageing conditions. These results are further validated by precipitation simulations that are based on Langer-Schwartz theory and a Kampmann-Wagner numerical method.« less

Development of a pore network simulation model to study nonaqueous phase liquid dissolution

USGS Publications Warehouse

Dillard, Leslie A.; Blunt, Martin J.

2000-01-01

A pore network simulation model was developed to investigate the fundamental physics of nonequilibrium nonaqueous phase liquid (NAPL) dissolution. The network model is a lattice of cubic chambers and rectangular tubes that represent pore bodies and pore throats, respectively. Experimental data obtained by Powers [1992] were used to develop and validate the model. To ensure the network model was representative of a real porous medium, the pore size distribution of the network was calibrated by matching simulated and experimental drainage and imbibition capillary pressure‐saturation curves. The predicted network residual styrene blob‐size distribution was nearly identical to the observed distribution. The network model reproduced the observed hydraulic conductivity and produced relative permeability curves that were representative of a poorly consolidated sand. Aqueous‐phase transport was represented by applying the equation for solute flux to the network tubes and solving for solute concentrations in the network chambers. Complete mixing was found to be an appropriate approximation for calculation of chamber concentrations. Mass transfer from NAPL blobs was represented using a corner diffusion model. Predicted results of solute concentration versus Peclet number and of modified Sherwood number versus Peclet number for the network model compare favorably with experimental data for the case in which NAPL blob dissolution was negligible. Predicted results of normalized effluent concentration versus pore volume for the network were similar to the experimental data for the case in which NAPL blob dissolution occurred with time.

Impact of polymers on the crystallization and phase transition kinetics of amorphous nifedipine during dissolution in aqueous media.

PubMed

Raina, Shweta A; Alonzo, David E; Zhang, Geoff G Z; Gao, Yi; Taylor, Lynne S

2014-10-06

The commercial and clinical success of amorphous solid dispersions (ASD) in overcoming the low bioavailability of poorly soluble molecules has generated momentum among pharmaceutical scientists to advance the fundamental understanding of these complex systems. A major limitation of these formulations stems from the propensity of amorphous solids to crystallize upon exposure to aqueous media. This study was specifically focused on developing analytical techniques to evaluate the impact of polymers on the crystallization behavior during dissolution, which is critical in designing effective amorphous formulations. In the study, the crystallization and polymorphic conversions of a model compound, nifedipine, were explored in the absence and presence of polyvinylpyrrolidone (PVP), hydroxypropylmethyl cellulose (HPMC), and HPMC-acetate succinate (HPMC-AS). A combination of analytical approaches including Raman spectroscopy, polarized light microscopy, and chemometric techniques such as multivariate curve resolution (MCR) were used to evaluate the kinetics of crystallization and polymorphic transitions as well as to identify the primary route of crystallization, i.e., whether crystallization took place in the dissolving solid matrix or from the supersaturated solutions generated during dissolution. Pure amorphous nifedipine, when exposed to aqueous media, was found to crystallize rapidly from the amorphous matrix, even when polymers were present in the dissolution medium. Matrix crystallization was avoided when amorphous solid dispersions were prepared, however, crystallization from the solution phase was rapid. MCR was found to be an excellent data processing technique to deconvolute the complex phase transition behavior of nifedipine.

Thermodynamics of the sorption of water-soluble vitamins in reverse-phase high performance liquid chromatography

NASA Astrophysics Data System (ADS)

Chirkin, V. A.; Karpov, S. I.; Selemenev, V. F.

2012-12-01

The thermodynamics of the sorption of certain water-soluble vitamins on a C18 reverse phase from water-acetonitrile solutions of different compositions is studied. The thermodynamic characteristics of the investigated chromatographic systems are calculated. The dependences of standard molar enthalpy and changes in entropy when the sorbate transfers from the bulk solution to the surface layer on the concentration of the organic component in the mobile phase are analyzed. The boundaries for applying the main retention models describing the sorption of the investigated compounds are discussed.

Long Chain Saturated and Unsaturated Carboxylic Acids: Filling a Large Gap of Knowledge in Their Enthalpies of Formation.

PubMed

Rogers, Donald W; Zavitsas, Andreas A

2017-01-06

Despite their abundance in nature and their importance in biology, medicine, nutrition, and in industry, gas phase enthalpies of formation of many long chain saturated and unsaturated fatty acids and of dicarboxylic acids are either unavailable or have been estimated with large uncertainties. Available experimental values for stearic acid show a spread of 68 kJ mol -1 . This work fills the knowledge gap by obtaining reliable values by quantum theoretical calculations using G4 model chemistry. Compounds with up to 20 carbon atoms are treated. The theoretical results are in excellent agreement with well established experimental values when such values exist, and they provide a large number of previously unavailable values.

A method to model latent heat for transient analysis using NASTRAN

NASA Technical Reports Server (NTRS)

Harder, R. L.

1982-01-01

A sample heat transfer analysis is demonstrated which includes the heat of fusion. The method can be used to analyze a system with nonconstant specific heat. The enthalpy is introduced as an independent degree of freedom at each node. The user input consists of a curve of temperature as a function of enthalpy, which may include a constant temperature phase change. The basic NASTRAN heat transfer capability is used to model the effects of latent heat with existing direct matrix output and nonlinear load data cards. Although some user care is required, the numerical stability of the integration is quite good when the given recommendations are followed. The theoretical equations used and the NASTRAN techniques are shown.

Determination of enthalpies of formation of energetic molecules with composite quantum chemical methods

DOE PAGES

Manaa, M. Riad; Fried, Laurence E.; Kuo, I-Feng W.

2016-02-01

We report gas-phase enthalpies of formation for the set of energetic molecules NTO, DADE, LLM-105, TNT, RDX, TATB, HMX, and PETN using the G2, G3, G4, and ccCA-PS3 quantum composite methods. Calculations for HMX and PETN hitherto represent the largest molecules attempted with these methods. G3 and G4 calculations are typically close to one another, with a larger difference found between these methods and ccCA-PS3. Furthermore there is significant uncertainty in experimental values, the mean absolute deviation between the average experimental value and calculations are 12, 6, 7, and 3 kcal/mol for G2, G3, G4, and ccCA-PS3, respectively.

COMPARISON OF SORPTION ENERGTICS FOR HYDROPHOBIC ORGANIC CHEMICALS BY SYNTHETIC AND NATURAL SORBENTS FROM METHANOL/WATER SOLVENT MIXTURES

EPA Science Inventory

Reversed-phase liquid chromatography (RPLC) was used to investigate the thermodynamics and mechanisms of hydrophobic organic chemical (HOC) retention from methanol/water solvent mixtures. The enthalpy-entropy compensation model was used to infer that the hydro- phobic sorptive me...

The topological phase diagram of cimetidine: A case of overall monotropy.

PubMed

Céolin, R; Rietveld, I B

2017-03-01

Cimetidine is a histamine H 2 -receptor antagonist used against peptic ulcers. It is known to exhibit crystalline polymorphism. Forms A and D melt within 0.35 degrees from each other and the enthalpies of fusion are similar as well. The present paper demonstrates how to construct a pressure-temperature phase diagram with only calorimetric and volumetric data available. The phase diagram provides the stability domains and the phase equilibria for the phases A, D, the liquid and the vapor. Cimetidine is overall monotropic with form D the only stable solid phase. Copyright © 2016 Académie Nationale de Pharmacie. Published by Elsevier Masson SAS. All rights reserved.

Solid/liquid phase diagram of the ammonium sulfate/glutaric acid/water system.

PubMed

Beyer, Keith D; Pearson, Christian S; Henningfield, Drew S

2013-05-02

We have studied the low temperature phase diagram and water activities of the ammonium sulfate/glutaric acid/water system using differential scanning calorimetry, infrared spectroscopy of thin films, and a new technique: differential scanning calorimetry-video microscopy. Using these techniques, we have determined that there is a temperature-dependent kinetic effect to the dissolution of glutaric acid in aqueous solution. We have mapped the solid/liquid ternary phase diagram, determined the water activities based on the freezing point depression, and determined the ice/glutaric acid phase boundary as well as the ternary eutectic composition and temperature. We have also modified our glutaric acid/water binary phase diagram previously published based on these new results. We compare our results for the ternary system to the predictions of the Extended AIM Aerosol Thermodynamics Model (E-AIM), and find good agreement for the ice melting points in the ice primary phase field of this system; however, significant differences were found with respect to phase boundaries, concentration and temperature of the ternary eutectic, and glutaric acid dissolution.

Arsenic species in weathering mine tailings and biogenic solids at the Lava Cap Mine Superfund Site, Nevada City, CA

USGS Publications Warehouse

Foster, Andrea L.; Ashley, Roger P.; Rytuba, James J.

2011-01-01

Sub- to anoxic conditions minimize dissolution of arsenopyrite at the LCMS site, but may accelerate the dissolution of As-bearing secondary iron phases such as Fe3+-oxyhydroxides and arseniosiderite, if sufficient organic matter is present to spur anaerobic microbial activity. Oxidizing, dry conditions favor the stabilization of secondary phases, while promoting oxidative breakdown of the primary sulfides. The stability of both primary and secondary As phases is likely to be at a minimum under cyclic wet-dry conditions. Biogenic iron (hydr)oxide flocs can sequester significant amounts of arsenic; this property may be useful for treatment of perpetual sources of As such as mine adit water, but the fate of As associated with natural accumulations of floc material needs to be assessed.

Boron isotope fractionation in magma via crustal carbonate dissolution

PubMed Central

Deegan, Frances M.; Troll, Valentin R.; Whitehouse, Martin J.; Jolis, Ester M.; Freda, Carmela

2016-01-01

Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to −41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle. PMID:27488228

Boron isotope fractionation in magma via crustal carbonate dissolution

NASA Astrophysics Data System (ADS)

Deegan, Frances M.; Troll, Valentin R.; Whitehouse, Martin J.; Jolis, Ester M.; Freda, Carmela

2016-08-01

Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to -41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

Boron isotope fractionation in magma via crustal carbonate dissolution.

PubMed

Deegan, Frances M; Troll, Valentin R; Whitehouse, Martin J; Jolis, Ester M; Freda, Carmela

2016-08-04

Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ(11)B values down to -41.5‰, reflecting preferential partitioning of (10)B into the assimilating melt. Loss of (11)B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports (11)B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ(11)B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

Review of high pressure phases of calcium by first-principles calculations

NASA Astrophysics Data System (ADS)

Ishikawa, T.; Nagara, H.; Suzuki, N.; Tsuchiya, J.; Tsuchiya, T.

2010-03-01

We review high pressure phases of calcium which have obtained by recent experimental and first-principles studies. In this study, we investigated the face-centered cubic (fcc) structure, the body-centered cubic (bcc) structure, the simple cubic (sc) structure, a tetragonal P43212 [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmca [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmcm [Teweldeberhan A M and Bonev S A 2008 Phys. Rev. B 78 140101(R)], an orthorhombic Pnma [Yao Y et al. 2008 Phys. Rev. B 78 054506] and a tetragonal I4/mcm(00) [Arapan S et al. 2008 Proc. Natl. Acad. Sci. USA 105 20627]. We compared the enthalpies among the structures up to 200 GPa and theoretically determined the phase diagram of calcium. The sequence of the structural transitions is fcc (0- 3.5 GPa) → bcc (3.5 - 35.7 GPa) → Cmcm (35.7- 52GPa) → P43212 (52-109 GPa) → Cmca (109-117.4GPa) → Pnma (117.4-134.6GPa) → I4/mcm(00) (134.6 GPa -). The sc phase is experimentally observed in the pressure range from 32 to 113 GPa but, in our calculation, there is no pressure region where the sc phase is the most stable. In addition, we found that the enthalpy of the hexagonal close-packed (hcp) structure is lower than that of I4/mcm(00) above 495 GPa.

Quantifying Mass Transfer Processes in Groundwater as a Function of Molecular Structure Variation for Multicomponent NAPL Sources

NASA Astrophysics Data System (ADS)

Abbott, J. B., III; Tick, G. R.; Greenberg, R. R.; Carroll, K. C.

2017-12-01

The remediation of nonaqueous liquid (NAPL) contamination sources in groundwater has been shown to be challenging and have limited success in the field. The presence of multicomponent NAPL sources further complicates the remediation due to variability of mass-transfer (dissolution) behavior as a result of compositional and molecular structure variations between the different compounds within the NAPL phase. This study investigates the effects of the contaminant of concern (COC) composition and the bulk-NAPL components molecular structure (i.e. carbon chain length, aliphatic and aromatic) on dissolution and aqueous phase concentrations in groundwater. The specific COCs tested include trichloroethene (TCE), toluene (TOL), and perfluorooctanoic acid (PFOA). Each COC was tested in a series of binary batch experiments using insoluble bulk NAPL including n-hexane (HEX), n-decane (DEC), and n-hexadecane (HEXDEC). These equilibrium batch tests were performed to understand how different carbon-chain-length (NAPL) systems affect resulting COC aqueous phase concentrations. The experiments were conducted with four different COC mole fractions mixed within the bulk-NAPL derivatives (0.1:0.9, 0.05:0.95, 0.01:0.99, 0.001:0.999). Raoult's Law was used to assess the relative ideality of the mass transfer processes for each binary equilibrium dissolution experiment. Preliminary results indicate that as mole fraction of the COC decreases (composition effects), greater deviance from dissolution ideality occurs. It was also shown that greater variation in molecular structure (i.e. greater carbon chain length of bulk-NAPL with COC and aromatic COC presence) exhibited greater dissolution nonideality via Raoult's Law analysis. For instance, TOL (aromatic structure) showed greater nonideality than TCE (aliphatic structure) in the presence of the different bulk-NAPL derivatives (i.e. of various aliphatic carbon chains lengths). The results suggest that the prediction of aqueous phase concentration, from complex multicomponent NAPL sources, is highly dependent upon both composition and molecular structure variations of COC-NAPL mixtures, and such impacts should be taken into account when designing and evaluating a remediation strategy and/or predicting COC concentrations from a source zone region.

Inverse modeling of BTEX dissolution and biodegradation at the Bemidji, MN crude-oil spill site

USGS Publications Warehouse

Essaid, H.I.; Cozzarelli, I.M.; Eganhouse, R.P.; Herkelrath, W.N.; Bekins, B.A.; Delin, G.N.

2003-01-01

The U.S. Geological Survey (USGS) solute transport and biodegradation code BIOMOC was used in conjunction with the USGS universal inverse modeling code UCODE to quantify field-scale hydrocarbon dissolution and biodegradation at the USGS Toxic Substances Hydrology Program crude-oil spill research site located near Bemidji, MN. This inverse modeling effort used the extensive historical data compiled at the Bemidji site from 1986 to 1997 and incorporated a multicomponent transport and biodegradation model. Inverse modeling was successful when coupled transport and degradation processes were incorporated into the model and a single dissolution rate coefficient was used for all BTEX components. Assuming a stationary oil body, we simulated benzene, toluene, ethylbenzene, m,p-xylene, and o-xylene (BTEX) concentrations in the oil and ground water, respectively, as well as dissolved oxygen. Dissolution from the oil phase and aerobic and anaerobic degradation processes were represented. The parameters estimated were the recharge rate, hydraulic conductivity, dissolution rate coefficient, individual first-order BTEX anaerobic degradation rates, and transverse dispersivity. Results were similar for simulations obtained using several alternative conceptual models of the hydrologic system and biodegradation processes. The dissolved BTEX concentration data were not sufficient to discriminate between these conceptual models. The calibrated simulations reproduced the general large-scale evolution of the plume, but did not reproduce the observed small-scale spatial and temporal variability in concentrations. The estimated anaerobic biodegradation rates for toluene and o-xylene were greater than the dissolution rate coefficient. However, the estimated anaerobic biodegradation rates for benzene, ethylbenzene, and m,p-xylene were less than the dissolution rate coefficient. The calibrated model was used to determine the BTEX mass balance in the oil body and groundwater plume. Dissolution from the oil body was greatest for compounds with large effective solubilities (benzene) and with large degradation rates (toluene and o-xylene). Anaerobic degradation removed 77% of the BTEX that dissolved into the water phase and aerobic degradation removed 17%. Although goodness-of-fit measures for the alternative conceptual models were not significantly different, predictions made with the models were quite variable. ?? 2003 Elsevier Science B.V. All rights reserved.

Mineral Dissolution and Secondary Precipitation on Quartz Sand in Simulated Hanford Tank Solutions Affecting Subsurface Porosity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Guohui; Um, Wooyong

2012-11-23

Highly alkaline nuclear waste solutions have been released from underground nuclear waste storage tanks and pipelines into the vadose zone at the U.S. Department of Energy’s Hanford Site in Washington, causing mineral dissolution and re-precipitation upon contact with subsurface sediments. High pH caustic NaNO3 solutions with and without dissolved Al were reacted with quartz sand through flow-through columns stepwise at 45, 51, and 89°C to simulate possible reactions between leaked nuclear waste solution and primary subsurface mineral. Upon reaction, Si was released from the dissolution of quartz sand, and nitrate-cancrinite [Na8Si6Al6O24(NO3)2] precipitated on the quartz surface as a secondary mineralmore » phase. Both steady-state dissolution and precipitation kinetics were quantified, and quartz dissolution apparent activation energy was determined. Mineral alteration through dissolution and precipitation processes results in pore volume and structure changes in the subsurface porous media. In this study, the column porosity increased up to 40.3% in the pure dissolution column when no dissolved Al was present in the leachate, whereas up to a 26.5% porosity decrease was found in columns where both dissolution and precipitation were observed because of the presence of Al in the input solution. The porosity change was also confirmed by calculation using the dissolution and precipitation rates and mineral volume changes.« less

High-pressure X-ray diffraction, Raman, and computational studies of MgCl2 up to 1 Mbar: Extensive pressure stability of the β-MgCl2 layered structure.

PubMed

Stavrou, Elissaios; Yao, Yansun; Zaug, Joseph M; Bastea, Sorin; Kalkan, Bora; Konôpková, Zuzana; Kunz, Martin

2016-08-12

Magnesium chloride (MgCl2) with the rhombohedral layered CdCl2-type structure (α-MgCl2) has been studied experimentally using synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy using a diamond-anvil cell up to 100 GPa at room temperature and theoretically using first-principles density functional calculations. The results reveal a pressure-induced second-order structural phase transition to a hexagonal layered CdI2-type structure (β-MgCl2) at 0.7 GPa: the stacking sequence of the Cl anions are altered resulting in a reduction of the c-axis length. Theoretical calculations confirm this phase transition sequence and the calculated transition pressure is in excellent agreement with the experiment. Lattice dynamics calculations also reproduce the experimental Raman spectra measured for the ambient and high-pressure phase. According to our experimental results MgCl2 remains in a 2D layered phase up to 100 GPa and further, the 6-fold coordination of Mg cations is retained. Theoretical calculations of relative enthalpy suggest that this extensive pressure stability is due to a low enthalpy of the layered structure ruling out kinetic barrier effects. This observation is unusual, as it contradicts with the general structural behavior of highly compressed AB2 compounds.

High-pressure X-ray diffraction, Raman, and computational studies of MgCl 2 up to 1 Mbar: Extensive pressure stability of the β-MgCl 2 layered structure

DOE PAGES

Stavrou, Elissaios; Yao, Yansun; Zaug, Joseph M.; ...

2016-08-12

We studied magnesium chloride (MgCl 2) with the rhombohedral layered CdCl 2-type structure (α-MgCl 2), experimentally, using synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy using a diamond-anvil cell up to 100 GPa at room temperature and theoretically using first-principles density functional calculations. Our results reveal a pressure-induced second-order structural phase transition to a hexagonal layered CdI 2-type structure (β-MgCl 2) at 0.7 GPa: the stacking sequence of the Cl anions are altered resulting in a reduction of the c-axis length. Theoretical calculations confirm this phase transition sequence and the calculated transition pressure is in excellent agreement with the experiment.more » Lattice dynamics calculations also reproduce the experimental Raman spectra measured for the ambient and high-pressure phase. According to our experimental results MgCl 2 remains in a 2D layered phase up to 100 GPa and further, the 6-fold coordination of Mg cations is retained. Theoretical calculations of relative enthalpy suggest that this extensive pressure stability is due to a low enthalpy of the layered structure ruling out kinetic barrier effects. Our observation is unusual, as it contradicts with the general structural behavior of highly compressed AB 2 compounds.« less

Characterisation, solubility and intrinsic dissolution behaviour of benzamide: dibenzyl sulfoxide cocrystal.

PubMed

Grossjohann, Christine; Eccles, Kevin S; Maguire, Anita R; Lawrence, Simon E; Tajber, Lidia; Corrigan, Owen I; Healy, Anne Marie

2012-01-17

This study examined the 1:1 cocrystal benzamide:dibenzyl sulfoxide, comprising the poorly water soluble dibenzyl sulfoxide (DBSO) and the more soluble benzamide (BA), to establish if this cocrystal shows advantages in terms of solubility and dissolution in comparison to its pure components and to a physical mixture. Solubility studies were performed by measuring DBSO solubility as a function of BA concentration, and a ternary phase diagram was constructed. Dissolution was examined through intrinsic dissolution studies. Solid-state characterisation was carried out by powder X-ray diffraction (PXRD), energy-dispersive X-ray diffraction (EDX), infra-red spectroscopy (ATR-FTIR) and thermal analysis. DBSO solubility was increased by means of complexation with BA. For the cocrystal, the solubility of both components was decreased in comparison to pure components. The cocrystal was identified as metastable and incongruently saturating. Dissolution studies revealed that dissolution of DBSO from the cocrystal was not enhanced in comparison to the pure compound or a physical mix, while BA release was retarded and followed square root of time kinetics. At the disk surface a layer of DBSO was found. The extent of complexation in solution can change the stability of the complex substantially. Incongruent solubility and dissolution behaviour of a cocrystal can result in no enhancement in the dissolution of the less soluble component and retardation of release of the more soluble component. Copyright © 2011 Elsevier B.V. All rights reserved.

Effects of alteration product precipitation on glass dissolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strachan, Denis M.; Neeway, James J.

2014-06-01

Understanding the mechanisms that control the durability of nuclear waste glass is paramount if reliable models are to be constructed so that the glass dissolution rate in a given geological repository can be calculated. Presently, it is agreed that (boro)silicate glasses dissolve in water at a rate dependent on the solution concentration of orthosilicic acid (H 4SiO 4) with higher [H 4SiO 4] leading to lower dissolution rates. Once the reaction has slowed as a result of the buildup of H 4SiO 4, another increase in the rate has been observed that corresponds to the precipitation of certain silica-bearing alterationmore » products. However, it has also been observed that the concentration of silica-bearing solution species does not significantly decrease, indicating saturation, while other glass tracer elements concentrations continue to increase, indicating that the glass is still dissolving. In this study, we have used the Geochemist’s Workbench code to investigate the relationship between glass dissolution rates and the precipitation rate of a representative zeolitic silica-bearing alteration product, analcime [Na(AlSi 2O 6)∙H 2O]. To simplify the calculations, we suppressed all alteration products except analcime, gibbsite (Al(OH) 3), and amorphous silica. The pseudo-equilibrium-constant matrix for amorphous silica was substituted for the glass pseudo-equilibrium-constant matrix because it has been shown that silicate glasses act as a silica-only solid with respect to kinetic considerations. In this article, we present the results of our calculations of the glass dissolution rate at different values for the analcime precipitation rate constant and the effects of varying the glass dissolution rate constant at a constant analcime precipitation rate constant. From the simulations we conclude, firstly, that the rate of glass dissolution is dependent on the kinetics of formation of the zeolitic phase. Therefore, the kinetics of secondary phase formation is an important parameter that should be taken into account in future glass dissolution modeling efforts. Secondly, the results indicate that, in the absence of a gel layer, the glass dissolution rate controls the rate of analcime precipitation in the long term. Finally, the meaning of these results pertinent to long-term glass durability is discussed.« less

Demonstration of Combined Zero-Valent Iron and Electrical Resistance Heating for In Situ Trichloroethene Remediation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Truex, Michael J.; Macbeth, Tamzen; Vermeul, Vincent R.

The effectiveness of in situ treatment using zero-valent iron to remediate sites with non-aqueous phase or significant sediment-associated contaminant mass can be limited by relatively low rates of mass transfer to bring contaminants in contact with the reactive media. For a field test in a trichloroethene source area, combining moderate-temperature (maximum 50oC) subsurface electrical resistance heating with in situ ZVI treatment was shown to accelerate dechlorination and dissolution rates by a factor of 4 to 6 based on organic daughter products and a factor 8-16 using a chloride concentrations. A mass-discharge-based analysis was used to evaluate reaction, dissolution, and volatilizationmore » at ambient groundwater temperature (~10oC) and as temperature was increased up to about 50oC. Increased reaction and contaminant dissolution were observed with increased temperature, but volatilization was minimal during the test because in situ reactions maintained low aqueous-phase TCE concentrations.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moeschner, Goeril; Lothenbach, Barbara; Figi, Renato

Citric acid can be used to retard the hydration of cement. Experiments were carried out to investigate the influence of citric acid on the composition of solid and liquid phases during cement hydration. Analyses of the solid phases showed that dissolution of alite and aluminate slowed down while analyses of the pore solution showed that citric acid was removed almost completely from the pore solution within the first hours of hydration. The complexation of the ions by citrate was weak, which could also be confirmed by thermodynamic calculations. Only 2% of the dissolved Ca and 0.001% of the dissolved Kmore » formed complexes with citrate during the first hours. Thus, citric acid retards cement hydration not by complex formation, but by slowing down the dissolution of the clinker grains. Thermodynamic calculations did not indicate precipitation of a crystalline citrate species. Thus, it is suggested that citrate sorbed onto the clinker surface and formed a protective layer around the clinker grains retarding their dissolution.« less

Study of thermochemical sulfate reduction mechanism using compound specific sulfur isotope analysis

USGS Publications Warehouse

Meshoulam, Alexander; Ellis, Geoffrey S.; Ahmad, Ward Said; Deev, Andrei; Sessions, Alex L.; Tang, Yongchun; Adkins, Jess F.; Liu, Jinzhong; Gilhooly, William P.; Aizenshtat, Zeev; Amrani, Alon

2016-01-01

Experiments involving sparingly soluble CaSO4 show that during the second catalytic phase of TSR the rate of sulfate reduction exceeds that of sulfate dissolution. In this case, there is no apparent isotopic fractionation between source sulfate and generated H2S, as all of the available sulfate is effectively reduced at all reaction times. When CaSO4 is replaced with fully soluble Na2SO4, sulfate dissolution is no longer rate limiting and significant S-isotopic fractionation is observed. This supports the notion that CaSO4dissolution can lead to the apparent lack of fractionation between H2S and sulfate produced by TSR in nature. The S-isotopic composition of individual OSCs record information related to geochemical reactions that cannot be discerned from the δ34S values obtained from bulk phases such as H2S, oil, and sulfate minerals, and provide important mechanistic details about the overall TSR process.

Active Thermochemical Tables: Sequential Bond Dissociation Enthalpies of Methane, Ethane, and Methanol and the Related Thermochemistry

DOE PAGES

Ruscic, Branko

2015-03-31

Active Thermochemical Tables (ATcT) thermochemistry for the sequential bond dissociations of methane, ethane, and methanol systems were obtained by analyzing and solving a very large thermochemical network (TN). Values for all possible C–H, C–C, C–O, and O–H bond dissociation enthalpies at 298.15 K (BDE 298) and bond dissociation energies at 0 K (D 0) are presented. The corresponding ATcT standard gas-phase enthalpies of formation of the resulting CH n, n = 4–0 species (methane, methyl, methylene, methylidyne, and carbon atom), C 2H n, n = 6–0 species (ethane, ethyl, ethylene, ethylidene, vinyl, ethylidyne, acetylene, vinylidene, ethynyl, and ethynylene), and COHmore » n, n = 4–0 species (methanol, hydroxymethyl, methoxy, formaldehyde, hydroxymethylene, formyl, isoformyl, and carbon monoxide) are also presented. The ATcT thermochemistry of carbon dioxide, water, hydroxyl, and carbon, oxygen, and hydrogen atoms is also included, together with the sequential BDEs of CO 2 and H 2O. The provenances of the ATcT enthalpies of formation, which are quite distributed and involve a large number of relevant determinations, are analyzed by variance decomposition and discussed in terms of principal contributions. The underlying reasons for periodic appearances of remarkably low and/or unusually high BDEs, alternating along the dissociation sequences, are analyzed and quantitatively rationalized. The present ATcT results are the most accurate thermochemical values currently available for these species.« less

Lattice potential energy and standard molar enthalpy in the formation of 1—dodecylamine hydrobromide (1-C12H25NH3·Br)(s)

NASA Astrophysics Data System (ADS)

Liu, Yu-Pu; Di, You-Ying; Dan, Wen-Yan; He, Dong-Hua; Kong, Yu-Xia; Yang, Wei-Wei

2011-02-01

This paper reports that 1-dodecylamine hydrobromide (1-C12H25NH3·Br)(s) has been synthesized using the liquid phase reaction method. The lattice potential energy of the compound 1-C12H25NH3·Br and the ionic volume and radius of the 1-C12H25NH3+ cation are obtained from the crystallographic data and other auxiliary thermodynamic data. The constant-volume energy of combustion of 1-C12H25NH3·Br(s) is measured to be ΔcUmo(1-C12H25NH3·Br, s) = -(7369.03±3.28) kJ·mol-1 by means of an RBC-II precision rotating-bomb combustion calorimeter at T = (298.15±0.001) K. The standard molar enthalpy of combustion of the compound is derived to be ΔcHmo(1-C12H25NH3·Br, s) = -(7384.52±3.28) kJ·mol-1 from the constant-volume energy of combustion. The standard molar enthalpy of formation of the compound is calculated to be ΔfHmo(1-C12H25NH3·Br, s)=-(1317.86±3.67) kJ·mol-1 from the standard molar enthalpy of combustion of the title compound and other auxiliary thermodynamic quantities through a thermochemical cycle.

Evaluation of Influence of Various Polymers on Dissolution and Phase Behavior of Carbamazepine-Succinic Acid Cocrystal in Matrix Tablets.

PubMed

Ullah, Majeed; Ullah, Hanif; Murtaza, Ghulam; Mahmood, Qaisar; Hussain, Izhar

2015-01-01

The aim of current study was to explore the influence of three commonly used polymers, that is, cellulosics and noncellulosics, for example, Methocel K4M, Kollidon VA/64, and Soluplus, on the phase disproportionation and drug release profile of carbamazepine-succinic acid (CBZ-SUC) cocrystal at varying drug to polymer ratios (1 : 1 to 1 : 0.25) in matrix tablets. The polymorphic phase disproportionation during in-depth dissolution studies of CBZ-SUC cocrystals and its crystalline properties were scrutinized by X-ray powder diffractrometry and Raman spectroscopy. The percent drug release from HPMC formulations (CSH) showed inverse relation with the concentration of polymer; that is, drug release increased with decrease in polymer concentration. On contrary, direct relation was observed between percent drug release and polymer concentrations of Kollidon VA 64/Soluplus (CSK, CSS). At similar polymer concentration, drug release from pure carbamazepine was slightly lower with HPMC formulations than that of cocrystal; however, opposite trend in release rate was observed with Kollidon VA/64 and Soluplus. The significant increase in dissolution rate of cocrystal occurred with Kollidon VA/64 and Soluplus at higher polymer concentration. Moreover, no phase change took place in Methocel and Kollidon formulations. No tablet residue was left for Soluplus formulation so the impact of polymer on cocrystal integrity cannot be predicted.

Evaluation of Influence of Various Polymers on Dissolution and Phase Behavior of Carbamazepine-Succinic Acid Cocrystal in Matrix Tablets

PubMed Central

Ullah, Majeed; Ullah, Hanif; Mahmood, Qaisar; Hussain, Izhar

2015-01-01

The aim of current study was to explore the influence of three commonly used polymers, that is, cellulosics and noncellulosics, for example, Methocel K4M, Kollidon VA/64, and Soluplus, on the phase disproportionation and drug release profile of carbamazepine-succinic acid (CBZ-SUC) cocrystal at varying drug to polymer ratios (1 : 1 to 1 : 0.25) in matrix tablets. The polymorphic phase disproportionation during in-depth dissolution studies of CBZ-SUC cocrystals and its crystalline properties were scrutinized by X-ray powder diffractrometry and Raman spectroscopy. The percent drug release from HPMC formulations (CSH) showed inverse relation with the concentration of polymer; that is, drug release increased with decrease in polymer concentration. On contrary, direct relation was observed between percent drug release and polymer concentrations of Kollidon VA 64/Soluplus (CSK, CSS). At similar polymer concentration, drug release from pure carbamazepine was slightly lower with HPMC formulations than that of cocrystal; however, opposite trend in release rate was observed with Kollidon VA/64 and Soluplus. The significant increase in dissolution rate of cocrystal occurred with Kollidon VA/64 and Soluplus at higher polymer concentration. Moreover, no phase change took place in Methocel and Kollidon formulations. No tablet residue was left for Soluplus formulation so the impact of polymer on cocrystal integrity cannot be predicted. PMID:26380301

Composite thermochemistry of gas phase U(VI)-containing molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bross, David H.; Peterson, Kirk A., E-mail: kipeters@wsu.edu

Reaction energies have been calculated for a series of reactions involving UF{sub 6}, UO{sub 3}, UO{sub 2}(OH){sub 2}, and UO{sub 2}F{sub 2} using coupled cluster singles and doubles with perturbative triples, CCSD(T), with a series of correlation consistent basis sets, including newly developed pseudopotential (PP)- and all-electron (AE) Douglas-Kroll-Hess-based sets for the U atom. The energies were calculated using a Feller-Peterson-Dixon composite approach in which CCSD(T) complete basis set (CBS) limits were combined with a series of additive contributions for spin-orbit coupling, outer-core correlation, and quantum electrodynamics effects. The calculated reaction enthalpies (both PP and AE) were combined with themore » accurately known heat of formation of UF{sub 6} to determine the enthalpies of formation of UO{sub 3}, UO{sub 2}(OH){sub 2}, and UO{sub 2}F{sub 2}. The contribution to the reaction enthalpies due to correlation of the 5s5p5d electrons of U was observed to be very slowly convergent with basis set and at the CBS limit their impact on the final enthalpies was on the order of 1 kcal/mol or less. For these closed shell molecules, spin-orbit effects contributed about 1 kcal/mol to the final enthalpies. Interestingly, the PP and AE approaches yielded quite different spin-orbit contributions (similar magnitude but opposite in sign), but the total scalar plus spin-orbit results from the two approaches agreed to within ∼1 kcal/mol of each other. The final composite heat of formation for UO{sub 2}F{sub 2} was in excellent agreement with experiment, while the two results obtained for UO{sub 3} were just outside the ±2.4 kcal/mol error bars of the currently recommended experimental value. An improved enthalpy of formation (298 K) for UO{sub 2}(OH){sub 2} is predicted from this work to be −288.7 ± 3 kcal/mol, compared to the currently accepted experimental value of −292.7 ± 6 kcal/mol.« less

Semiempirical and DFT Investigations of the Dissociation of Alkyl Halides

ERIC Educational Resources Information Center

Waas, Jack R.

2006-01-01

Enthalpy changes corresponding to the gas phase heats of dissociation of 12 organic halides were calculated using two semiempirical methods, the Hartree-Fock method, and two DFT methods. These calculated values were compared to experimental values where possible. All five methods agreed generally with the expected empirically known trends in the…

Simple interpretations of chemical transients in multi-feed, two-phase geothermal wells; Examples from Philippine Geothermal fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruaya, J.R.; Solis, R.P.; Solana, R.R.

1991-01-01

This paper reports that the main process responsible for the extreme variations in chloride concentrations in the water discharged by selected multi-feed, two-phase geothermal wells in the Philippines is steam addition brought about by fluid flashing in the formation or by a shallow and distinct steam zone. Correlation of enthalpy with chloride data over a span of seven years for well 106, Tongonan field, revealed the entry of reservoir fluid from the hotter portion of the field as the well responded to exploitation. Using a plot of discharge enthalpy versus total chloride, the deep chloride near well OP-3D which ismore » drilled at the periphery of the Bacon-Manito field, has been determined at about 8700 mg/k. This is somewhat higher than the inferred chloride level of 7000 mg/kg in the postulated main geothermal reservoir. The competing effects of returns of reinjected water and flashing in the formation on the observed chloride concentrations in the discharge water of well PN-20D, Palinpinon field, have been segregated using the technique described above.« less

Anthracene + Pyrene Solid Mixtures: Eutectic and Azeotropic Character

PubMed Central

Rice, James W.; Fu, Jinxia; Suuberg, Eric M.

2010-01-01

To better characterize the thermodynamic behavior of a binary polycyclic aromatic hydrocarbon mixture, thermochemical and vapor pressure experiments were used to examine the phase behavior of the anthracene (1) + pyrene (2) system. A solid-liquid phase diagram was mapped for the mixture. A eutectic point occurs at 404 K at x1 = 0.22. A model based on eutectic formation can be used to predict the enthalpy of fusion associated with the mixture. For mixtures that contain x1 < 0.90, the enthalpy of fusion is near that of pure pyrene. This and X-ray diffraction results indicate that mixtures of anthracene and pyrene have pyrene-like crystal structures and energetics until the composition nears that of pure anthracene. Solid-vapor equilibrium studies show that mixtures of anthracene and pyrene form solid azeotropes at x1 of 0.03 and 0.14. Additionally, mixtures at x1 = 0.99 sublime at the vapor pressure of pure anthracene, suggesting that anthracene behavior is not significantly influenced by x2 = 0.01 in the crystal structure. PMID:21116474

Physicochemical properties and solubility of alkyl-(2-hydroxyethyl)-dimethylammonium bromide.

PubMed

Domańska, Urszula; Bogel-Łukasik, Rafał

2005-06-23

Quaternary ammonium salts, which are precursors of ionic liquids, have been prepared from N,N-dimethylethanolamine as a substrate. The paper includes specific basic characterization of synthesized compounds via the following procedures: nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectra, water content, mass spectroscopy (MS) spectra, temperatures of decompositions, basic thermodynamic properties of pure ionic liquids (the melting point, enthalpy of fusion, enthalpy of solid-solid phase transition, glass transition), and the difference in the solute heat capacity between the liquid and solid at the melting temperature determined by differential scanning calorimetry (DSC). The (solid + liquid) phase equilibria of binary mixtures containing (quaternary ammonium salt + water, or + 1-octanol) has been measured by a dynamic method over wide range of temperatures, from 230 K to 560 K. These data were correlated by means of the UNIQUAC ASM and modified nonrandom two-liquid NRTL1 equations utilizing parameters derived from the (solid + liquid) equilibrium. The partition coefficient of ionic liquid in the 1-octanol/water binary system has been calculated from the solubility results. Experimental partition coefficients (log P) were negative at three temperatures.

Entropy and the driving force for the filling of carbon nanotubes with water.

PubMed

Pascal, Tod A; Goddard, William A; Jung, Yousung

2011-07-19

The spontaneous filling of hydrophobic carbon nanotubes (CNTs) by water observed both experimentally and from simulations is counterintuitive because confinement is generally expected to decrease both entropy and bonding, and remains largely unexplained. Here we report the entropy, enthalpy, and free energy extracted from molecular dynamics simulations of water confined in CNTs from 0.8 to 2.7-nm diameters. We find for all sizes that water inside the CNTs is more stable than in the bulk, but the nature of the favorable confinement of water changes dramatically with CNT diameter. Thus we find (i) an entropy (both rotational and translational) stabilized, vapor-like phase of water for small CNTs (0.8-1.0 nm), (ii) an enthalpy stabilized, ice-like phase for medium-sized CNTs (1.1-1.2 nm), and (iii) a bulk-like liquid phase for tubes larger than 1.4 nm, stabilized by the increased translational entropy as the waters sample a larger configurational space. Simulations with structureless coarse-grained water models further reveal that the observed free energies and sequence of transitions arise from the tetrahedral structure of liquid water. These results offer a broad theoretical basis for understanding water transport through CNTs and other nanostructures important in nanofluidics, nanofiltrations, and desalination.

Entropy and the driving force for the filling of carbon nanotubes with water

PubMed Central

Pascal, Tod A.; Goddard, William A.; Jung, Yousung

2011-01-01

The spontaneous filling of hydrophobic carbon nanotubes (CNTs) by water observed both experimentally and from simulations is counterintuitive because confinement is generally expected to decrease both entropy and bonding, and remains largely unexplained. Here we report the entropy, enthalpy, and free energy extracted from molecular dynamics simulations of water confined in CNTs from 0.8 to 2.7-nm diameters. We find for all sizes that water inside the CNTs is more stable than in the bulk, but the nature of the favorable confinement of water changes dramatically with CNT diameter. Thus we find (i) an entropy (both rotational and translational) stabilized, vapor-like phase of water for small CNTs (0.8–1.0 nm), (ii) an enthalpy stabilized, ice-like phase for medium-sized CNTs (1.1–1.2 nm), and (iii) a bulk-like liquid phase for tubes larger than 1.4 nm, stabilized by the increased translational entropy as the waters sample a larger configurational space. Simulations with structureless coarse-grained water models further reveal that the observed free energies and sequence of transitions arise from the tetrahedral structure of liquid water. These results offer a broad theoretical basis for understanding water transport through CNTs and other nanostructures important in nanofluidics, nanofiltrations, and desalination. PMID:21709268

Phase-field simulation of microstructure formation in technical castings - A self-consistent homoenthalpic approach to the micro-macro problem

NASA Astrophysics Data System (ADS)

Böttger, B.; Eiken, J.; Apel, M.

2009-10-01

Performing microstructure simulation of technical casting processes suffers from the strong interdependency between latent heat release due to local microstructure formation and heat diffusion on the macroscopic scale: local microstructure formation depends on the macroscopic heat fluxes and, in turn, the macroscopic temperature solution depends on the latent heat release, and therefore on the microstructure formation, in all parts of the casting. A self-consistent homoenthalpic approximation to this micro-macro problem is proposed, based on the assumption of a common enthalpy-temperature relation for the whole casting which is used for the description of latent heat production on the macroscale. This enthalpy-temperature relation is iteratively obtained by phase-field simulations on the microscale, thus taking into account the specific morphological impact on the latent heat production. This new approach is discussed and compared to other approximations for the coupling of the macroscopic heat flux to complex microstructure models. Simulations are performed for the binary alloy Al-3at%Cu, using a multiphase-field solidification model which is coupled to a thermodynamic database. Microstructure formation is simulated for several positions in a simple model plate casting, using a one-dimensional macroscopic temperature solver which can be directly coupled to the microscopic phase-field simulation tool.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Ke; De Andrade, Vincent; Feng, Zhange

The presence of impurity ions is known to significantly influence mineral surface morphology during crystal growth from aqueous solution, but knowledge on impurity ion-mineral interactions during dissolution under far-from equilibrium conditions remains limited. Here we show that calcite (CaCO 3) exhibits a rich array of dissolution features in the presence of Pb. During the initial stage, calcite exhibits non-classical surface features characterized as micro pyramids developed spontaneously in acidic Pb-bearing solutions. Subsequent pseudomorphic growth of cerussite (PbCO 3) was observed, where nucleation occurred entirely within a pore space created by dissolution at the calcite/substrate interface. Uneven growth rates yielded amore » cerussite shell made of lath- or dendritic-shaped crystals. The cerussite phase was separated from the calcite by pores of less than 200 nm under transmission X-ray microscopy, consistent with the interface-coupled dissolution-precipitation mechanism. These results show that impurity metal ions exert significant control over the microscale dissolution features found on mineral surfaces and provide new insights into interpreting and designing micro structures observed in naturally-occurring and synthetic carbonate minerals by dissolution. In addition, heterogeneous micro-environments created in transport limited reactions under pore spaces may lead to unusual growth forms during crystal nucleation and precipitation.« less

Piroxicam cocrystals with phenolic coformers: preparation, characterization, and dissolution properties.

PubMed

Emami, Shahram; Adibkia, Khosro; Barzegar-Jalali, Mohammad; Siahi-Shadbad, Mohammadreza

2018-04-04

This study explores the preparation and investigation of dissolution properties of piroxicam cocrystals. Differential scanning calorimetry (DSC) was used to determine the capability of resorcinol (RES), methylparaben (MPB), and vanillin (VAN) to form cocrystals with piroxicam (PRX). Generation of cocrystals was attempted by liquid assisted grinding and slurry methods. Cocrystals were characterized by thermal methods, powder X-ray diffraction, and Fourier-transform infrared spectroscopy. Apparent solubility, intrinsic dissolution rate (IDR), and powder dissolution profile of cocrystals were compared with anhydrous piroxicam, piroxicam monohydrate (PRXMH), and previously reported piroxicam-succinic acid cocrystal. Contact angles and particle sizes of the studied solids were also measured. Based on the DSC screening results, we prepared and characterized PRX-RES and PRX-MPB cocrystals. Interestingly, the cocrystals not only failed to improve apparent solubility and IDR of PRX but also showed lower values than PRX that were attributed to induction of phase transformation of PRX to PRXMH. In contrary, cocrystals performed better than PRX in powder dissolution studies. The higher dissolution rates of cocrystals were explained by improved wettability and reduced sizes. This study has highlighted the complexity of solid state properties of cocrystals and has provided new evidence for the in-solution stability issues of cocrystals.

Analysis of the Performance of Heat Pipes and Phase-Change Materials with Multiple Localized Heat Sources for Space Applications

DTIC Science & Technology

1989-05-01

NUMERICAL ANALYSIS OF STEFAN PROBLEMS FOR GENERALIZED MULTI- DIMENSIONAL PHASE-CHANGE STRUCTURES USING THE ENTHALPY TRANSFORMING MODEL 4.1 Summary...equation St Stefan number, cs(Tm-Tw)/H or cs(Tm-Ti)/H s circumferential distance coordinate, m, Section III s dimensionless interface position along...fluid, kg/m 3 0 viscous dissipation term in the energy eqn. (1.4), Section I; dummy variable, Section IV r dimensionless time, ta/L 2 a Stefan -Boltzmann

Investigating the structural transitions of proteins during dissolution by mass spectrometry.

PubMed

Gong, Xiaoyun; Xiong, Xingchuang; Qi, Lin; Fang, Xiang

2017-03-01

An appropriate solvent environment is essential for the implementation of biological functions of proteins. Interactions between protein residues and solvent molecules are of great importance for proteins to maintain their active structure and catalyze biochemical reactions. In this study, we investigated such interactions and studied the structural transitions of proteins during their dissolution process. Our previously developed technique, namely solvent assisted electric field induced desorption/ionization, was used for the dissolution and immediate ionization of proteins. Different solvents and proteins were involved in the investigation. According to the results, cytochrome c underwent significant unfolding during dissolution in the most commonly used NH 4 Ac buffer. The unfolding got more serious when the concentration of NH 4 Ac was further increased. Extending the dissolution time resulted in the re-folding of cytochrome c. In comparison, no unfolding was observed if cytochrome c was pre-dissolved in NH 4 Ac buffer and detected by nano-ESI. Furthermore, no unfolding was observed during the dissolution process of cytochrome c in water. Interactions between the residues of cytochrome c and the solute of NH 4 Ac might be the reason for the unfolding phenomenon. Similar unfolding phenomenon was observed on holo-myoglobin. However, the observed dissolution feature of insulin was different. No unfolding was observed on insulin during dissolution in NH 4 Ac buffers. Insulin underwent observable unfolding when water was used for dissolution. This might be due to the structural difference between different proteins. The obtained results in the present study furthered our insights into the interactions between proteins and the solvents during the phase transition of dissolution. Copyright © 2016 Elsevier B.V. All rights reserved.

Kinetics of dissolution of UO2 in nitric acid solutions: A multiparametric study of the non-catalysed reaction

NASA Astrophysics Data System (ADS)

Cordara, T.; Szenknect, S.; Claparede, L.; Podor, R.; Mesbah, A.; Lavalette, C.; Dacheux, N.

2017-12-01

UO2 pellets were prepared by densification of oxides obtained from the conversion of the oxalate precursor. Then characterized in order to perform a multiparametric study of the dissolution in nitric acid medium. In this frame, for each sample, the densification rate, the grain size and the specific surface area of the prepared pellets were determined prior to the final dissolution experiments. By varying the concentration of the nitric acid solution and temperature, three different and successive steps were identified during the dissolution. Under the less aggressive conditions considered, a first transient step corresponding to the dissolution of the most reactive phases was observed at the solid/solution interface. Then, for all the tested conditions, a steady state step was established during which the normalised dissolution rate was found to be constant. It was followed by a third step characterized by a strong and continuous increase of the normalised dissolution rate. The duration of the steady state, also called "induction period", was found to vary drastically as a function of the HNO3 concentration and temperature. However, independently of the conditions, this steady state step stopped at almost similar dissolved material weight loss and dissolved uranium concentration. During the induction period, no important evolution of the topology of the solid/liquid interface was evidenced authorizing the use of the starting reactive specific surface area to evaluate the normalised dissolution rates thus the chemical durability of the sintered pellets. From the multiparametric study of UO2 dissolution proposed, oxidation of U(IV) to U(VI) by nitrate ions at the solid/liquid interface constitutes the limiting step in the overall dissolution mechanism associated to this induction period.

NASA Astrophysics Data System (ADS)

Bechetti, Daniel H.; DuPont, John N.; deBarbadillo, John J.; Baker, Brian A.

2014-06-01

Thermodynamic and kinetic modeling were used to determine appropriate heat treatment schedules for homogenization and second phase dissolution in INCONEL® alloy 740H® (INCONEL and 740H are registered trademarks of Special Metals Corporation) fusion welds. Following these simulations, a two-step heat treatment process was applied to specimens from a single pass gas tungsten arc weld (GTAW). Scanning electron microscopy (SEM) has been used to assess the changes in the distribution of alloying elements as well as changes in the fraction of second phase particles within the fusion zone. Experimental results demonstrate that adequate homogenization of alloy 740H weld metal can be achieved by a 1373 K/4 h (1100 °C/4 h) treatment. Complete dissolution of second phase particles could not be completely achieved, even at exposure to temperatures near the alloy's solidus temperature. These results are in good agreement with thermodynamic and kinetic predictions.

Titanium α-ω phase transformation pathway and a predicted metastable structure

DOE PAGES

Zarkevich, Nickolai A.; Johnson, Duane D.

2016-01-15

A titanium is a highly utilized metal for structural lightweighting and its phases, transformation pathways (transition states), and structures have scientific and industrial importance. Using a proper solid-state nudged elastic band method employing two climbing images combined with density functional theory DFT + U methods for accurate energetics, we detail the pressure-induced α (ductile) to ω (brittle) transformation at the coexistence pressure. We also find two transition states along the minimal-enthalpy path and discover a metastable body-centered orthorhombic structure, with stable phonons, a lower density than the end-point phases, and decreasing stability with increasing pressure.

Liquid-vapor phase equilibria and the thermodynamic properties of 2-methylpropanol- n-alkyl propanoate solutions

NASA Astrophysics Data System (ADS)

Suntsov, Yu. K.; Goryunov, V. A.; Chuikov, A. M.; Meshcheryakov, A. V.

2016-08-01

The boiling points of solutions of five binary systems are measured via ebulliometry in the pressure range of 2.05-103.3 kPa. Equilibrium vapor phase compositions, the values of the excess Gibbs energies, enthalpies, and entropies of solution of these systems are calculated. Patterns in the changes of phase equilibria and thermodynamic properties of solutions are established, depending on the compositions and temperatures of the systems. Liquid-vapor equilibria in the systems are described using the equations of Wilson and the NRTL (Non-Random Two-Liquid Model).

Heat capacities and entropies of sillimanite, fibrolite, andalusite, kyanite, and quartz and the Al2SiO5 phase diagram

USGS Publications Warehouse

Hemingway, B.S.; Robie, R.A.; Evans, H.T.; Kerrick, Derrill M.

1991-01-01

Low-temperature heat capacities for sillimanite, fibrolite, and both fine-grained and coarse-grained quartz have been measured. Superambient heat capacities have been measured for four sillimanite, two andalusite, one kyanite, and two fibrolite samples. Equations are recommended for the temperature dependence of the heat capacities of kyanite, andalusite, sillimanite, and fibrolite. The heat capacity functions have been combined with thermal expansion (fibrolite and sillimanite reported here), enthalpy of solution, and phase equilibrium data in order to construct a phase diagram for the Al2SiO5 polymorphs. -from Authors

Development of media for dynamic latent heat storage for the low-temperature range. Part 1: Thermal analyses of selected salt hydrate systems

NASA Technical Reports Server (NTRS)

Kanwischer, H.; Tamme, R.

1985-01-01

Phase change temperatures and phase change enthalpies of seventeen salt hydrates, three double salts, and four eutectics were measured thermodynamically and the results reported herein. Good results were obtained, especially for congruently melting salt hydrates. Incongruently melting salt hydrates appear less suitable for heat storage applications. The influence of the second phase - water, acid and hydroxide - to the latent heat is described. From these results, basic values of the working temperatures and storage capabilities of various storage media compositions may be derived.

Gas-phase acidities of cysteine-polyalanine peptides I: A(3,4)CSH and HSCA(3,4).

PubMed

Ren, Jianhua; Tan, John P; Harper, Robert T

2009-10-15

The gas-phase acidities of four cysteine-polyalanine peptides, A(3,4)CSH and HSCA(3,4), were determined using the extended Cooks kinetic method with full entropy analysis. A triple-quadrupole mass spectrometer with an electrospray interface was employed for the experimental study. The ion activation was achieved via collision-induced dissociation (CID) experiments. The deprotonation enthalpies (Delta(acid)H) of the peptides were determined to be 332.2 +/- 2.0 kcal/mol (A(3)CSH), 325.9 +/- 2.0 kcal/mol (A(4)CSH), 319.3 +/- 3.0 kcal/mol (HSCA(3)), and 319.2 +/- 4.0 kcal/mol (HSCA(4)). The deprotonation entropies (Delta(acid)S) of the peptides were estimated based on the entropy term (Delta(DeltaS)) and the deprotonation entropies of the reference acids. By using the deprotonation enthalpies and entropies, the gas-phase acidities (Delta(acid)G) of the peptides were derived: 325.0 +/- 2.0 kcal/mol (A(3)CSH), 320.2 +/- 2.0 kcal/mol (A(4)CSH), 316.3 +/- 3.0 kcal/mol (HSCA(3)), and 315.4 +/- 4.0 kcal/mol (HSCA(4)). Conformations and energetic information of the peptides were calculated through simulated annealing (Tripos), geometry optimization (AM1), and single-point energy calculations (B3LYP/6-31+G(d)), respectively. The calculated theoretical deprotonation enthalpies (Delta(acid)H) of 334.2 kcal/mol (A(3)CSH), 327.7 kcal/mol (A(4)CSH), 320.6 kcal/mol (HSCA(3)), and 318.6 kcal/mol (HSCA(4)) are in good agreement with the experimentally determined values. Both the experimental and computational studies suggest that the two N-terminal cysteine peptides, HSCA(3,4), are significantly more acidic than the corresponding C-terminal ones, A(3,4)CSH. The high acidities of the former are likely due to the helical conformational effects for which the thiolate anion may be strongly stabilized by the interaction with the helix macrodipole.

Solubility of crystalline organic compounds in high and low molecular weight amorphous matrices above and below the glass transition by zero enthalpy extrapolation.

PubMed

Amharar, Youness; Curtin, Vincent; Gallagher, Kieran H; Healy, Anne Marie

2014-09-10

Pharmaceutical applications which require knowledge of the solubility of a crystalline compound in an amorphous matrix are abundant in the literature. Several methods that allow the determination of such data have been reported, but so far have only been applicable to amorphous polymers above the glass transition of the resulting composites. The current work presents, for the first time, a reliable method for the determination of the solubility of crystalline pharmaceutical compounds in high and low molecular weight amorphous matrices at the glass transition and at room temperature (i.e. below the glass transition temperature), respectively. The solubilities of mannitol and indomethacin in polyvinyl pyrrolidone (PVP) K15 and PVP K25, respectively were measured at different temperatures. Mixtures of undissolved crystalline solute and saturated amorphous phase were obtained by annealing at a given temperature. The solubility at this temperature was then obtained by measuring the melting enthalpy of the crystalline phase, plotting it as a function of composition and extrapolating to zero enthalpy. This new method yielded results in accordance with the predictions reported in the literature. The method was also adapted for the measurement of the solubility of crystalline low molecular weight excipients in amorphous active pharmaceutical ingredients (APIs). The solubility of mannitol, glutaric acid and adipic acid in both indomethacin and sulfadimidine was experimentally determined and successfully compared with the difference between their respective calculated Hildebrand solubility parameters. As expected from the calculations, the dicarboxylic acids exhibited a high solubility in both amorphous indomethacin and sulfadimidine, whereas mannitol was almost insoluble in the same amorphous phases at room temperature. This work constitutes the first report of the methodology for determining an experimentally measured solubility for a low molecular weight crystalline solute in a low molecular weight amorphous matrix. Copyright © 2014 Elsevier B.V. All rights reserved.

Uptake of aromatic hydrocarbon vapors (benzene and phenanthrene) at the air-water interface of micron-size water droplets.

PubMed

Raja, Suresh; Valsaraj, Kalliat T

2004-12-01

Uptake of aromatic hydrocarbon vapors (benzene and phenanthrene) by typical micrometer-sized fog-water droplets was studied using a falling droplet reactor at temperatures between 296 and 316 K. Uptake of phenanthrene vapor greater than that predicted by bulk (air-water)-phase equilibrium was observed for diameters less than 200 microm, and this was attributed to surface adsorption. The experimental values of the droplet-vapor partition constant were used to obtain the overall mass transfer coefficient and the mass accommodation coefficient for both benzene and phenanthrene. Mass transfer of phenanthrene was dependent only on gas-phase diffusion and mass accommodation at the interface. However, for benzene, the mass transfer was limited by liquid-phase diffusion and mass accommodation. A large value of the mass accommodation coefficient, alpha = (1.4 +/- 0.4) x 10(-2) was observed for the highly surface-active (hydrophobic) phenanthrene, whereas a small alpha = (9.7 +/- 1.8) x 10(-5) was observed for the less hydrophobic benzene. Critical cluster numbers ranging from 2 for benzene to 5.7 for phenanthrene were deduced using the critical cluster nucleation theory for mass accommodation. The enthalpy of mass accommodation was more negative for phenanthrene than it was for benzene. Consequently, the temperature effect was more pronounced for phenanthrene. A linear correlation was observed for the enthalpy of accommodation with the excess enthalpy of solution. A natural organic carbon surrogate (Suwannee Fulvic acid) in the water droplet increased the uptake for phenanthrene and benzene, the effect being more marked for phenanthrene. A characteristic time constant analysis showed that uptake and droplet scavenging would compete for the fog deposition of phenanthrene, whereas deposition would be unimpeded by the uptake rate for benzene vapor. For both compounds, the characteristic atmospheric reaction times were much larger and would not impact fog deposition.

Extra-thermodynamic study on surface diffusion in reversed-phase liquid chromatography using silica gels bonded with alkyl ligands of different chain lengths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miyabe, Kanji; Guiochon, Georges A

2005-06-01

Surface diffusion on adsorbents made of silica gels bonded to C{sub 1}, C{sub 4}, C{sub 8}, and C{sub 18} alkyl ligands was studied in reversed-phase liquid chromatography (RPLC) from the viewpoints of two extrathermodynamic relationships: enthalpy-entropy compensation (EEC) and linear free-energy relationship (LFER). First, the values of the surface diffusion coefficient (D{sub s}), normalized by the density of the alkyl ligands, were analyzed with the modified Arrhenius equation, following the four approaches proposed in earlier research. This showed that an actual EEC resulting from substantial physicochemical effects occurs for surface diffusion and suggested a mechanistic similarity of molecular migration bymore » surface diffusion, irrespective of the alkyl chain length. Second, a new model based on EEC was derived to explain the LFER between the logarithms of D{sub s} measured under different RPLC conditions. This showed that the changes of free energy, enthalpy, and entropy of surface diffusion are linearly correlated with the carbon number in the alkyl ligands of the bonded phases and that the contribution of the C{sub 18} ligand to the changes of the thermodynamic parameters corresponds to that of the C{sub 10} ligand. The new LFER model correlates the slope and intercept of the LFER to the compensation temperatures derived from the EEC analyses and to several parameters characterizing the molecular contributions to the changes in enthalpy and entropy. Finally, the new model was used to estimate D{sub s} under various RPLC conditions. The values of D{sub s} that were estimated from only two original experimental D{sub s} data were in agreement with corresponding experimental D{sub s} values, with relative errors of {approx}20%, irrespective of some RPLC conditions.« less

Liquid-phase growth of few-layered graphene on sapphire substrates using SiC micropowder source

NASA Astrophysics Data System (ADS)

Maruyama, Takahiro; Yamashita, Yutaka; Saida, Takahiro; Tanaka, Shin-ichiro; Naritsuka, Shigeya

2017-06-01

We demonstrated direct synthesis of graphene films consisting of a few layers (few-layered graphene) on sapphire substrates by liquid-phase growth (LPG), using liquid Ga as the melt and SiC micropowder as the source material. When the dissolution temperature was above 700 °C, almost all Si atoms of SiC diffused into the Ga melt and only carbon atoms remained at the interface beneath the liquid Ga. Above 800 °C, X-ray photoelectron spectra showed that most of the remaining carbon was graphitized. When the dissolution temperature was 1000 °C, Raman spectra showed that few-layered graphene films grew on the sapphire substrates.

Thermodynamics of Titanium-Aluminum-Oxygen Alloys Studied

NASA Technical Reports Server (NTRS)

Copland, Evan H.; Jacobson, Nathan S.

2001-01-01

Titanium-aluminum alloys are promising intermediate-temperature alloys for possible compressor applications in gas-turbine engines. These materials are based on the a2-Ti3Al + g-TiAl phases. The major issue with these materials is high oxygen solubility in a2-Ti3Al, and oxidation of unsaturated alloys generally leads to mixed non-protective TiO2+Al2O3 scales. From phase diagram studies, oxygen saturated a2-Ti3Al(O) is in equilibrium with Al2O3; however, oxygen dissolution has a detrimental effect on mechanical properties and cannot be accepted. To better understand the effect of oxygen dissolution, we examined the thermodynamics of titanium-aluminum-oxygen alloys.

Insights in the radical scavenging mechanism of syringaldehyde and generation of its anion

NASA Astrophysics Data System (ADS)

Yancheva, D.; Velcheva, E.; Glavcheva, Z.; Stamboliyska, B.; Smelcerovic, A.

2016-03-01

The ability of syringaldehyde, a naturally occurring phenolic antioxidant and medicinally important compound, to scavenge free radicals according different mechanisms was elucidated by computing the respective reaction enthalpies at DFT B3LYP/6-311++G** level. Bond dissociation enthalpy, ionization potentials and proton affinities were calculated in gas phase, benzene, water and DMSO in order to account for different environment (nonpolar lipid membranes and polar physiological liquids) where the antioxidant action in the living organism could take place and various experimental in vitro conditions. Molecular and electronic properties influencing the reactivity of syringaldehyde according to the different mechanisms were discussed in the light of the reported radical scavenging activities in crocin bleaching, oxidation potential of the first anodic peak and DPPH test. According to the calculated reaction enthalpies, in polar environment the syringaldehyde reacts preferably by sequential proton loss electron transfer which is related to the formation of a phenoxy anion. Such phenoxy anion was generated in DMSO solution and the changes in the force field, steric and electronic structure, resulting from the conversion, were described in detail based on the IR spectral data and DFT computations.

Self-Diffusion in Amorphous Silicon by Local Bond Rearrangements

NASA Astrophysics Data System (ADS)

Kirschbaum, J.; Teuber, T.; Donner, A.; Radek, M.; Bougeard, D.; Böttger, R.; Hansen, J. Lundsgaard; Larsen, A. Nylandsted; Posselt, M.; Bracht, H.

2018-06-01

Experiments on self-diffusion in amorphous silicon (Si) were performed at temperatures between 460 to 600 ° C . The amorphous structure was prepared by Si ion implantation of single crystalline Si isotope multilayers epitaxially grown on a silicon-on-insulator wafer. The Si isotope profiles before and after annealing were determined by means of secondary ion mass spectrometry. Isothermal diffusion experiments reveal that structural relaxation does not cause any significant intermixing of the isotope interfaces whereas self-diffusion is significant before the structure recrystallizes. The temperature dependence of self-diffusion is described by an Arrhenius law with an activation enthalpy Q =(2.70 ±0.11 ) eV and preexponential factor D0=(5.5-3.7+11.1)×10-2 cm2 s-1 . Remarkably, Q equals the activation enthalpy of hydrogen diffusion in amorphous Si, the migration of bond defects determining boron diffusion, and the activation enthalpy of solid phase epitaxial recrystallization reported in the literature. This close agreement provides strong evidence that self-diffusion is mediated by local bond rearrangements rather than by the migration of extended defects as suggested by Strauß et al. (Phys. Rev. Lett. 116, 025901 (2016), 10.1103/PhysRevLett.116.025901).

Solid state characterization of E2101, a novel antispastic drug.

PubMed

Kushida, Ikuo; Ashizawa, Kazuhide

2002-10-01

E2101, a novel antispastic drug, was found to exist in at least two polymorphs that were confirmed by X-ray powder diffraction (XRD). These two species are designated forms I and II. The physicochemical and thermodynamic properties of these polymorphs were characterized by variable temperature XRD, thermal analysis, hygroscopicity measurements, and dissolution studies. The transition temperature was also estimated from the solubilities determined at various temperatures. The E2101 polymorphs were anhydrous and adsorbed little moisture under high humidity conditions. The melting onsets and heats of fusion for form I were 148.1 +/- 0.2 degrees C and 38.2 +/- 1.0 kJ/mol, respectively, and for form II were 139.8 +/- 0.4 degrees C and 35.2 +/- 0.5 kJ/mol, respectively. The intrinsic dissolution rate of form II in JP 2 medium was 1.5-fold faster than that of form I, corresponding to the rank order of the aqueous solubility and the enthalpy of fusion. Accordingly, form I was thought to be thermodynamically more stable than form II and thus suitable for further development. According to the thermal analysis and variable temperature XRD results, the recrystallization of form I occurred at approximately 145 degrees C after form II melted, however, no crystal transition behavior was observed below the lower melting point. The DSC thermograms at various heating rates and van't Hoff plots from the solubility studies indicated that the polymorphic pair would be monotropic. Copyright 2002 Wiley-Liss Inc. and the American Pharmaceutical Association

Sherwood correlation for dissolution of pooled NAPL in porous media

NASA Astrophysics Data System (ADS)

Aydin Sarikurt, Derya; Gokdemir, Cagri; Copty, Nadim K.

2017-11-01

The rate of interphase mass transfer from non-aqueous phase liquids (NAPLs) entrapped in the subsurface into the surrounding mobile aqueous phase is commonly expressed in terms of Sherwood (Sh) correlations that are expressed as a function of flow and porous media properties. Because of the lack of precise methods for the estimation of the interfacial area separating the NAPL and aqueous phases, most studies have opted to use modified Sherwood expressions that lump the interfacial area into the interphase mass transfer coefficient. To date, there are only two studies in the literature that have developed non-lumped Sherwood correlations; however, these correlations have undergone limited validation. In this paper controlled dissolution experiments from pooled NAPL were conducted. The immobile NAPL mass is placed at the bottom of a flow cell filled with porous media with water flowing horizontally on top. Effluent aqueous phase concentrations were measured for a wide range of aqueous phase velocities and for two different porous media. To interpret the experimental results, a two-dimensional pore network model of the NAPL dissolution kinetics and aqueous phase transport was developed. The observed effluent concentrations were then used to compute best-fit mass transfer coefficients. Comparison of the effluent concentrations computed with the two-dimensional pore network model to those estimated with one-dimensional analytical solutions indicates that the analytical model which ignores the transport in the lateral direction can lead to under-estimation of the mass transfer coefficient. Based on system parameters and the estimated mass transfer coefficients, non-lumped Sherwood correlations were developed and compared to previously published data. The developed correlations, which are a significant improvement over currently available correlations that are associated with large uncertainties, can be incorporated into future modeling studies requiring non-lumped Sh expressions.

Influence of Coformer Stoichiometric Ratio on Pharmaceutical Cocrystal Dissolution: Three Cocrystals of Carbamazepine/4-Aminobenzoic Acid.

PubMed

Li, Zi; Matzger, Adam J

2016-03-07

Cocrystallization is a technique to optimize solid forms that shows great potential to improve the solubility of active pharmaceutical ingredients (APIs). In some systems, an API can form cocrystals in multiple stoichiometries with the same coformer. However, it remains unclear how coformer stoichiometry influences solubility. This paper investigates the pharmaceutical:coformer pair carbamazepine (CBZ)/p-aminobenzoic acid (PABA); both CBZ/PABA 1:1 and 2:1 cocrystals are known, and a novel 4:1 CBZ/PABA cocrystal is reported here. The 4:1 cocrystal is structurally characterized, and phase stability data suggest that it is a thermodynamically unstable form. Dissolution experiments show that there is no correlation between the cocrystal stoichiometry and dissolution rate in this system. On the other hand, with the relatively weak intermolecular interactions, metastable forms can be beneficial to dissolution rate, which suggests that more effort should be devoted to cocrystal production with kinetic growth methods.

The Dissolution of an Interfween Miscible Liquids

NASA Technical Reports Server (NTRS)

Vlad, D.H.; Maher, J.V.

1999-01-01

The disappearance of the surface tension of the interface of a binary mixture, measured using the dynamic surface light scattering technique, is slower for a binary mixture of higher density contrast. A comparison with a naive diffusion model, expected to provide a lower limit for the speed of dissolution in the absence of gravity shows that the interfacial surface tension disappears much slower than even by diffusion with the effect becoming much more pronounced when density contrast between the liquid phases is increased. Thus, the factor most likely to be responsible for this anomalously slow dissolution is gravity. A mechanism could be based on the competition between diffusive relaxation and sedimentation at the dissolving interface.

Anomalous behavior of cristobalite in helium under high pressure

NASA Astrophysics Data System (ADS)

Sato, Tomoko; Takada, Hiroto; Yagi, Takehiko; Gotou, Hirotada; Okada, Taku; Wakabayashi, Daisuke; Funamori, Nobumasa

2013-01-01

We have investigated the high-pressure behavior of cristobalite in helium by powder X-ray diffraction. Cristobalite transformed to a new phase at about 8 GPa. This phase is supposed to have a molar volume of about 30 % larger than cristobalite, suggesting the dissolution of helium atoms in its interstitial voids. On further compression, the new phase transformed to a different phase which showed an X-ray diffraction pattern similar to cristobalite X-I at about 21 GPa. On the other hand, when the new phase was decompressed, it transformed to another new phase at about 7 GPa, which is also supposed to have a molar volume of about 25 % larger than cristobalite. On further decompression, the second new phase transformed to cristobalite II at about 2 GPa. In contrast to cristobalite, quartz did not show anomalous behavior in helium. The behavior of cristobalite in helium was also consistent with that in other mediums up to about 8 GPa, where the volume of cristobalite became close to that of quartz. These results suggest that dissolution of helium may be controlled not only by the density (amount of voids) but also by the network structure of SiO4 tetrahedra (topology of voids).

Theoretical Insight into the Biodegradation of Solitary Oil Microdroplets Moving through a Water Column

PubMed Central

Paraskeva, Christakis A.; Kalogerakis, Nicolas; Doyle, Patrick S.

2018-01-01

In the aftermath of oil spills in the sea, clouds of droplets drift into the seawater column and are carried away by sea currents. The fate of the drifting droplets is determined by natural attenuation processes, mainly dissolution into the seawater and biodegradation by oil-degrading microbial communities. Specifically, microbes have developed three fundamental strategies for accessing and assimilating oily substrates. Depending on their affinity for the oily phase and ability to proliferate in multicellular structures, microbes might either attach to the oil surface and directly uptake compounds from the oily phase, or grow suspended in the aqueous phase consuming solubilized oil, or form three-dimensional biofilms over the oil–water interface. In this work, a compound particle model that accounts for all three microbial strategies is developed for the biodegradation of solitary oil microdroplets moving through a water column. Under a set of educated hypotheses, the hydrodynamics and solute transport problems are amenable to analytical solutions and a closed-form correlation is established for the overall dissolution rate as a function of the Thiele modulus, the Biot number and other key parameters. Moreover, two coupled ordinary differential equations are formulated for the evolution of the particle size and used to investigate the impact of the dissolution and biodegradation processes on the droplet shrinking rate. PMID:29439555

Theoretical Insight into the Biodegradation of Solitary Oil Microdroplets Moving through a Water Column.

PubMed

Kapellos, George E; Paraskeva, Christakis A; Kalogerakis, Nicolas; Doyle, Patrick S

2018-02-12

In the aftermath of oil spills in the sea, clouds of droplets drift into the seawater column and are carried away by sea currents. The fate of the drifting droplets is determined by natural attenuation processes, mainly dissolution into the seawater and biodegradation by oil-degrading microbial communities. Specifically, microbes have developed three fundamental strategies for accessing and assimilating oily substrates. Depending on their affinity for the oily phase and ability to proliferate in multicellular structures, microbes might either attach to the oil surface and directly uptake compounds from the oily phase, or grow suspended in the aqueous phase consuming solubilized oil, or form three-dimensional biofilms over the oil-water interface. In this work, a compound particle model that accounts for all three microbial strategies is developed for the biodegradation of solitary oil microdroplets moving through a water column. Under a set of educated hypotheses, the hydrodynamics and solute transport problems are amenable to analytical solutions and a closed-form correlation is established for the overall dissolution rate as a function of the Thiele modulus, the Biot number and other key parameters. Moreover, two coupled ordinary differential equations are formulated for the evolution of the particle size and used to investigate the impact of the dissolution and biodegradation processes on the droplet shrinking rate.

Urea-temperature phase diagrams capture the thermodynamics of denatured state expansion that accompany protein unfolding

PubMed Central

Tischer, Alexander; Auton, Matthew

2013-01-01

We have analyzed the thermodynamic properties of the von Willebrand factor (VWF) A3 domain using urea-induced unfolding at variable temperature and thermal unfolding at variable urea concentrations to generate a phase diagram that quantitatively describes the equilibrium between native and denatured states. From this analysis, we were able to determine consistent thermodynamic parameters with various spectroscopic and calorimetric methods that define the urea–temperature parameter plane from cold denaturation to heat denaturation. Urea and thermal denaturation are experimentally reversible and independent of the thermal scan rate indicating that all transitions are at equilibrium and the van't Hoff and calorimetric enthalpies obtained from analysis of individual thermal transitions are equivalent demonstrating two-state character. Global analysis of the urea–temperature phase diagram results in a significantly higher enthalpy of unfolding than obtained from analysis of individual thermal transitions and significant cross correlations describing the urea dependence of and that define a complex temperature dependence of the m-value. Circular dichroism (CD) spectroscopy illustrates a large increase in secondary structure content of the urea-denatured state as temperature increases and a loss of secondary structure in the thermally denatured state upon addition of urea. These structural changes in the denatured ensemble make up ∼40% of the total ellipticity change indicating a highly compact thermally denatured state. The difference between the thermodynamic parameters obtained from phase diagram analysis and those obtained from analysis of individual thermal transitions illustrates that phase diagrams capture both contributions to unfolding and denatured state expansion and by comparison are able to decipher these contributions. PMID:23813497

Freezing-Enhanced Dissolution of Iron Oxides: Effects of Inorganic Acid Anions.

PubMed

Jeong, Daun; Kim, Kitae; Min, Dae Wi; Choi, Wonyong

2015-11-03

Dissolution of iron from mineral dust particles greatly depends upon the type and amount of copresent inorganic anions. In this study, we investigated the roles of sulfate, chloride, nitrate, and perchlorate on the dissolution of maghemite and lepidocrocite in ice under both dark and UV irradiation and compared the results with those of their aqueous counterparts. After 96 h of reaction, the total dissolved iron in ice (pH 3 before freezing) was higher than that in the aqueous phase (pH 3) by 6-28 times and 10-20 times under dark and UV irradiation, respectively. Sulfuric acid was the most efficient in producing labile iron under dark condition, whereas hydrochloric acid induced the most dissolution of the total and ferrous iron in the presence of light. This ice-induced dissolution result was also confirmed with Arizona Test Dust (AZTD). In the freeze-thaw cycling test, the iron oxide samples containing chloride, nitrate, or perchlorate showed a similar extent of total dissolved iron after each cycling while the sulfate-containing sample rapidly lost its dissolution activity with repeating the cycle. This unique phenomenon observed in ice might be related to the freeze concentration of protons, iron oxides, and inorganic anions in the liquid-like ice grain boundary region. These results suggest that the ice-enhanced dissolution of iron oxides can be a potential source of bioavailable iron, and the acid anions critically influence this process.

Enhanced ferrihydrite dissolution by a unicellular, planktonic cyanobacterium: a biological contribution to particulate iron bioavailability.

PubMed

Kranzler, Chana; Kessler, Nivi; Keren, Nir; Shaked, Yeala

2016-12-01

Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places severe environmental constraints on microorganisms in aquatic environments. Cyanobacteria are a widespread group of aquatic, photosynthetic microorganisms with especially high iron requirements. While iron exists predominantly in particulate form, little is known about its bioavailability to cyanobacteria. Some cyanobacteria secrete iron solubilizing ligands called siderophores, yet many environmentally relevant strains do not have this ability. This work explores the bioavailability of amorphous synthetic Fe-oxides (ferrihydrite) to the non-siderophore producing, unicellular cyanobacterium, Synechocystis sp PCC 6803. Iron uptake assays with 55 ferrihydrite established dissolution as a critical prerequisite for iron transport. Dissolution assays with the iron binding ligand, desferrioxamine B, demonstrated that Synechocystis 6803 enhances ferrihydrite dissolution, exerting siderophore-independent biological influence on ferrihydrite bioavailability. Dissolution mechanisms were studied using a range of experimental conditions; both cell-particle physical proximity and cellular electron flow were shown to be important determinants of bio-dissolution by Synechocystis 6803. Finally, the effects of ferrihydrite stability on bio-dissolution rates and cell physiology were measured, integrating biological and chemical aspects of ferrihydrite bioavailability. Collectively, these findings demonstrate that Synechocystis 6803 actively dissolves ferrihydrite, highlighting a significant biological component to mineral phase iron bioavailability in aquatic environments. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Introduction of Differential Scanning Calorimetry in a General Chemistry Laboratory Course: Determination of Thermal Properties of Organic Hydrocarbons

ERIC Educational Resources Information Center

D'Amelia, Ronald; Franks, Thomas; Nirode, William F.

2007-01-01

In first-year general chemistry undergraduate courses, thermodynamics and thermal properties such as melting points and changes in enthalpy ([Delta]H) and entropy ([Delta]S) of phase changes are frequently discussed. Typically, classical calorimetric methods of analysis are used to determine [Delta]H of reactions. Differential scanning calorimetry…

Microstructure evolution and texture development of hot form-quench (HFQ) AZ31 twin roll cast (TRC) magnesium alloy

NASA Astrophysics Data System (ADS)

Alias, J.; Zhou, X.; Das, Sanjeev; El-Fakir, Omer; Thompson, G. E.

2017-12-01

The present study on the microstructure evolution of hot form-quench (HFQ) AZ31 twin roll cast magnesium alloy attempt to provide an understanding on the grain structure and heterogeneous intermetallic phase formation in the alloy and texture development following the HFQ process. Grain recrystallization and partial dissolution of eutectic β-Mg17Al12 phase particles were occurred during the solution heat treatment at 450°C, leaving the alloy consists of recrystallized grains and discontinuous or random β-Mg17Al12 phase particles distribution with small volume fraction. The particles act as effective nucleation sites for new grains during recrystallization and variation of recrystallization occurrence contributed to texture alteration. The partial or full β-Mg17Al12 phase dissolution following the HFQ induces void formation that act as fracture nucleation site and the corresponding texture alteration in the recrystallized grains led to poor formability in TRC alloy.

Visualising phase change in a brushite-based calcium phosphate ceramic

PubMed Central

Bannerman, A.; Williams, R. L.; Cox, S. C.; Grover, L. M.

2016-01-01

The resorption of brushite-based bone cements has been shown to be highly unpredictable, with strong dependence on a number of conditions. One of the major factors is phase transformation, with change to more stable phases such as hydroxyapatite affecting the rate of resorption. Despite its importance, the analysis of phase transformation has been largely undertaken using methods that only detect crystalline composition and give no information on the spatial distribution of the phases. In this study confocal Raman microscopy was used to map cross-sections of brushite cylinders aged in Phosphate Buffered Saline, Foetal Bovine Serum, Dulbecco’s – Minimum Essential Medium (with and without serum). Image maps showed the importance of ageing medium on the phase composition throughout the ceramic structure. When aged without serum, there was dissolution of the brushite phase concomitant to the deposition of octacalcium phosphate (OCP) around the periphery of the sample. The deposition of OCP was detectable within five days and reduced the rate of brushite dissolution from the material. The use of serum, even at a concentration of 10vol% prevented phase transformation. This paper demonstrates the value of confocal Raman microscopy in monitoring phase change in biocements; it also demonstrates the problems with assessing material degradation in non-serum containing media. PMID:27604149

Visualising phase change in a brushite-based calcium phosphate ceramic

NASA Astrophysics Data System (ADS)

Bannerman, A.; Williams, R. L.; Cox, S. C.; Grover, L. M.

2016-09-01

The resorption of brushite-based bone cements has been shown to be highly unpredictable, with strong dependence on a number of conditions. One of the major factors is phase transformation, with change to more stable phases such as hydroxyapatite affecting the rate of resorption. Despite its importance, the analysis of phase transformation has been largely undertaken using methods that only detect crystalline composition and give no information on the spatial distribution of the phases. In this study confocal Raman microscopy was used to map cross-sections of brushite cylinders aged in Phosphate Buffered Saline, Foetal Bovine Serum, Dulbecco’s - Minimum Essential Medium (with and without serum). Image maps showed the importance of ageing medium on the phase composition throughout the ceramic structure. When aged without serum, there was dissolution of the brushite phase concomitant to the deposition of octacalcium phosphate (OCP) around the periphery of the sample. The deposition of OCP was detectable within five days and reduced the rate of brushite dissolution from the material. The use of serum, even at a concentration of 10vol% prevented phase transformation. This paper demonstrates the value of confocal Raman microscopy in monitoring phase change in biocements; it also demonstrates the problems with assessing material degradation in non-serum containing media.

The analysis of magnesium oxide hydration in three-phase reaction system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Xiaojia; Guo, Lin; Chen, Chen

In order to investigate the magnesium oxide hydration process in gas–liquid–solid (three-phase) reaction system, magnesium hydroxide was prepared by magnesium oxide hydration in liquid–solid (two-phase) and three-phase reaction systems. A semi-empirical model and the classical shrinking core model were used to fit the experimental data. The fitting result shows that both models describe well the hydration process of three-phase system, while only the semi-empirical model right for the hydration process of two-phase system. The characterization of the hydration product using X-Ray diffraction (XRD) and scanning electron microscope (SEM) was performed. The XRD and SEM show hydration process in the two-phasemore » system follows common dissolution/precipitation mechanism. While in the three-phase system, the hydration process undergo MgO dissolution, Mg(OH){sub 2} precipitation, Mg(OH){sub 2} peeling off from MgO particle and leaving behind fresh MgO surface. - Graphical abstract: There was existence of a peeling-off process in the gas–liquid–solid (three-phase) MgO hydration system. - Highlights: • Magnesium oxide hydration in gas–liquid–solid system was investigated. • The experimental data in three-phase system could be fitted well by two models. • The morphology analysis suggested that there was existence of a peel-off process.« less

Dissolution and characterization of HEV NiMH batteries.

PubMed

Larsson, Kristian; Ekberg, Christian; Ødegaard-Jensen, Arvid

2013-03-01

Metal recovery is an essential part of the recycling of hybrid electric vehicle battery waste and the first step in a hydrometallurgical treatment is dissolution of the solid material. The properties of separated battery electrode materials were investigated. Focus was put on both the solid waste and then the dissolution behaviour. The cathode contains metallic nickel that remains undissolved when utilizing non-oxidizing conditions such as hydrochloric or sulphuric acid in combination with a low oxygen atmosphere. In these conditions the cathode active electrode material is fully dissolved. Not dissolving the nickel metal saves up to 37% of the acid consumption for the cathode electrode material. In the commonly used case of oxidizing conditions the nickel metal dissolves and a cobalt-rich phase remains undissolved from the cathode active material. For the anode material a complete and rapid dissolution can be achieved at mild conditions with hydrochloric, nitric or sulphuric acid. Optimal parameters for all cases of dissolution was pH 1 with a reaction time of approximately ≥ 20,000 s. Copyright © 2012 Elsevier Ltd. All rights reserved.

The effect of fission-energy Xe ion irradiation on the structural integrity and dissolution of the CeO2 matrix

NASA Astrophysics Data System (ADS)

Popel, A. J.; Le Solliec, S.; Lampronti, G. I.; Day, J.; Petrov, P. K.; Farnan, I.

2017-02-01

This work considers the effect of fission fragment damage on the structural integrity and dissolution of the CeO2 matrix in water, as a simulant for the UO2 matrix of spent nuclear fuel. For this purpose, thin films of CeO2 on Si substrates were produced and irradiated by 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate fission damage that occurs within nuclear fuels along with bulk CeO2 samples. The irradiated and unirradiated samples were characterised and a static batch dissolution experiment was conducted to study the effect of the induced irradiation damage on dissolution of the CeO2 matrix. Complex restructuring took place in the irradiated films and the irradiated samples showed an increase in the amount of dissolved cerium, as compared to the corresponding unirradiated samples. Secondary phases were also observed on the surface of the irradiated CeO2 films after the dissolution experiment.

[Study on solid dispersion of copovidone-based tanshinone II(A)].

PubMed

Jiang, Yan-Rong; Zhang, Zhen-Hai; Xia, Hai-Jiang; Jia, Xiao-Bin

2013-01-01

To apply PVP-S630 in the preparation of tanshinone II(A) (TS II(A)) solid dispersion, in order to improve its dissolution in vitro and reduce the moisture absorption of the solid dispersion. Tanshinone II(A) solid dispersion was prepared by spray drying method. Such analytical methods as SEM, DSC, XRD were used to characterize their phases and detect their dissolution, moisture absorption and stability. In the solid dispersion prepared with tanshinone II(A) and copovidone with proportion of 1:10, tanshinone II(A) was scattered on the surface of the carrier in the amorphous form, with a dissolution in vitro up to 100% at 0.5 h and a lower moisture absorption than PVP-K30 solid dispersion prepared with the same proportion. After a three-month accelerated stability test, it showed no significant change in drug dissolution and content. The solid dispersion prepared with copovidone as the carrier can significantly improve the dissolution of tanshinone II(A), with a relatively low moisture absorption and high stability, thereby having a good prospect of application.

Coupled dissolution-precipitation in natural monazite: effect of irradiation damage or fluid mediation?

NASA Astrophysics Data System (ADS)

Seydoux-Guillaume, Anne-Magali; Montel, Jean-Marc; de Parseval, Philippe; Bingen, Bernard; Janots, Emilie

2010-05-01

The LREE orthophosphate monazite is a common accessory mineral, important as a U-Th-Pb geochronometer in both metamorphic and magmatic rocks. In order to correctly interpret measured ages, it is essential to properly understand mechanisms that control them. Few studies have shown that coupled dissolution-crystallisation in the presence of a fluid phase is a mechanism incomparably more efficient that solid state diffusion to reset isotopic signature within monazite grains. It is known that dissolution-precipitation is efficiency enhanced by the presence of defects within crystals. Because of its high actinide contents (U and Th), monazite receives intense self-irradiation doses. In contrast to zircon (a silicate), monazite (a phosphate) is less sensitive to irradiation. Natural amorphous monazite has never been reported and the only proof that monazite lattice was destroyed by irradiation is shown by the presence of lattice distortion (strained lattice); this is because defect healing is more efficient than amorphization. The present study focuses on large (cm) single monazite crystals from five distinct localities in Norway, Madagascar, Srilanka, Zwaziland and Morefield. They have different chemical compositions, especially with regard to U, Th and Pb contents, and have ages ranging from ca. 500 to 1000 Ma. Nevertheless, all of them share the same petrographic features. Optical microscope and SEM images reveal variably intense fracturation. BSE imaging in the SEM indicates that monazite is composed of multiple phases: an unaltered monazite (Mnz1) + an altered monazite (Mnz2) associated with Th-rich phase (Thorium silicate or Thorium oxide) +/- Xenotime, depending on the initial composition of Mnz1. Analogous textures were already described by Seydoux-Guillaume et al. (2007) and Hetherington and Harlov (2008;). The alteration textures are always associated with radial cracks emanating from the high radioactive phase (Th-rich phase). The question addressed in the discussion is the role and the chronology of each process, i.e. irradiation vs coupled dissolution-precipitation. U-Th-Pb ages obtained by chemical dating on electron microprobe from altered and unaltered monazites show no significant differences. Therefore U-Pb dating using SIMS and LA-ICP-MS are in progress to determine precise isotopic age that would refine the alteration chronology. Finally, these results will be compared with experimental work, which are currently investigating the role of structural defects on coupled dissolution-precipitation in monazite. Hetherington and Harlov (2008). Am. Mineral., 93, 806-820. Seydoux-Guillaume et al. (2007). Eur. J. Mineral., 19, 7-14.

Iron dissolution kinetics of mineral dust at low pH during simulated atmospheric processing

NASA Astrophysics Data System (ADS)

Shi, Z.; Bonneville, S.; Krom, M. D.; Carslaw, K. S.; Jickells, T. D.; Baker, A. R.; Benning, L. G.

2011-02-01

We investigated the iron (Fe) dissolution kinetics of African (Tibesti) and Asian (Beijing) dust samples at acidic pH with the aim of reproducing the low pH conditions in atmospheric aerosols. The Beijing dust and three size fractions of the Tibesti dust (<20 μm: PM20; <10 μm: PM10; and <2.5 μm: PM2.5) were dissolved at pH 1, 2 and/or 3 for up to 1000 h. In the first 10 min, all dust samples underwent an extremely fast Fe solubilisation. Subsequently, the Fe dissolution proceeded at a much slower rate before reaching a stable dissolution plateau. The time-dependant Fe dissolution datasets were best described by a model comprising three acid-extractable Fe pools each dissolving according to first-order kinetics. The dissolution rate constant k (h-1) of each pool was independent of the source (Saharan or Asian) and the size (PM20, PM10 or PM2.5) of the dust but highly dependent on pH. The "fast" Fe pool had a k (25 h-1 at pH = 1) of a similar magnitude to "dry" ferrihydrite nanoparticles and/or poorly crystalline Fe(III) oxyhydroxide, while the "intermediate" and "slow" Fe pools had k values respectively 50-60 times and 3000-4000 times smaller than the "fast" pool. The "slow" Fe pool was likely to consist of both crystalline Fe oxide phases (i.e., goethite and/or hematite) and Fe contained in the clay minerals. The initial mass of the "fast", "intermediate" and "slow" Fe pools represented respectively about 0.5-2%, 1-3% and 15-40% of the total Fe in the dust samples. Furthermore, we showed that in systems with low dust/liquid ratios, Fe can be dissolved from all three pools, whereas at high dust/liquid ratios (e.g., in aerosols), sufficient Fe may be solubilised from the "fast" phase to dominate the Fe dissolved and to suppress the dissolution of Fe from the other Fe pools. These data demonstrated that dust/liquid ratio and pH are fundamental parameters controlling Fe dissolution kinetics in the dust. In order to reduce errors in atmospheric and climate models, these fundamental controlling factors need to be included.

Quantifying the Movement and Dissolution of Fugitive Methane in Shallow Aquifers: Visualization Experiments

NASA Astrophysics Data System (ADS)

Van De Ven, C. J. C.; Mumford, K. G.

2016-12-01

The environmental impact and potential human health implications, specifically from the contamination of groundwater sources, has sparked controversy around shale gas extraction in North America. It is clear that understanding the effects of hydraulic fracturing on shallow fresh water aquifers is of great importance, including the threat of stray gas (also referred to as fugitive methane) on groundwater quality. Faulty wells provide a preferential pathway for free gas phase (mostly methane) to migrate from deeper gas-bearing formations of natural gas to shallow aquifers, followed by its dissolution into the surrounding groundwater. An increased understanding of the fate of fugitive methane in shallow aquifers is required to assess the potential risks associated with current and future operations, as well as to better link gas migration, dissolution and the deterioration of groundwater quality. In this study, a series of laboratory experiments were performed using carbon dioxide (CO2) gas as a surrogate for methane to improve our understanding of gas dissolution in groundwater systems. Using CO2, a novel laboratory technique was developed that allows the measurement of dissolved CO2 concentrations using image analysis alongside visualization of free gas mobilization. The technique is based on the acidification of water during CO2 dissolution, which causes a colour change in an indicator dye. The colour change is recorded using a visual light transmission technique, in which digital images are used to track dissolved concentrations at high spatial (1 mm) and temporal (5 s) resolutions in a two-dimensional (25 × 25 × 1 cm3) flow cell. The experiments were completed in both homogeneous sand packs and sand packs containing layered heterogeneities to investigate the dissolution of both gas fingers and gas pools. The results demonstrate the potential of this novel technique for investigating gas dissolution, and showed significant tailing of dissolved CO2 and persistence of other gas phase components. This technique will aid in the development of conceptual models to link fugitive methane to groundwater contamination and provide detailed data required for the validation of numerical models that account for gas-water mass transfer; both of which are required for the development of sound monitoring techniques.

Electron-beam-irradiation-induced crystallization of amorphous solid phase change materials

NASA Astrophysics Data System (ADS)

Zhou, Dong; Wu, Liangcai; Wen, Lin; Ma, Liya; Zhang, Xingyao; Li, Yudong; Guo, Qi; Song, Zhitang

2018-04-01

The electron-beam-irradiation-induced crystallization of phase change materials in a nano sized area was studied by in situ transmission electron microscopy and selected area electron diffraction. Amorphous phase change materials changed to a polycrystalline state after being irradiated with a 200 kV electron beam for a long time. The results indicate that the crystallization temperature strongly depends on the difference in the heteronuclear bond enthalpy of the phase change materials. The selected area electron diffraction patterns reveal that Ge2Sb2Te5 is a nucleation-dominated material, when Si2Sb2Te3 and Ti0.5Sb2Te3 are growth-dominated materials.

The Effect of Cu:Ag Atomic Ratio on the Properties of Sputtered Cu–Ag Alloy Thin Films

PubMed Central

Hsieh, Janghsing; Hung, Shunyang

2016-01-01

Cu–Ag thin films with various atomic ratios were prepared using a co-sputtering technique, followed by rapid thermal annealing at various temperatures. The films’ structural, mechanical, and electrical properties were then characterized using X-ray diffractometry (XRD), atomic force microscopy (AFM), FESEM, nano-indentation, and TEM as functions of compositions and annealing conditions. In the as-deposited condition, the structure of these films transformed from a one-phase to a dual-phase state, and the resistivity shows a twin-peak pattern, which can be explained in part by Nordheim’s Rule and the miscibility gap of Cu–Ag alloy. After being annealed, the films’ resistivity followed the mixture rule in general, mainly due to the formation of a dual-phase structure containing Ag-rich and Cu-rich phases. The surface morphology and structure also varied as compositions and annealing conditions changed. The recrystallization of these films varied depending on Ag–Cu compositions. The annealed films composed of 40 at % to 60 at % Cu had higher hardness and lower roughness than those with other compositions. Particularly, the Cu50Ag50 film had the highest hardness after being annealed. From the dissolution testing, it was found that the Cu-ion concentration was about 40 times higher than that of Ag. The galvanic effect and over-saturated state could be the cause of the accelerated Cu dissolution and the reduced dissolution of the Ag. PMID:28774033

Rapid Dissolution of Soluble Uranyl Phases in Arid, Mine-Impacted Catchments Near Church Rock, NM

DOE Office of Scientific and Technical Information (OSTI.GOV)

deLemos, J.L.; Bostick, B.C.; Quicksall, A.N.

2009-05-14

We tested the hypothesis that runoff of uranium-bearing particles from mining waste disposal areas was a significant mechanism for redistribution of uranium in the northeastern part of the Upper Puerco River watershed (New Mexico). However, our results were not consistent with this hypothesis. Analysis of >100 sediment and suspended sediment samples collected adjacent to and downstream from uranium source areas indicated that uranium levels in the majority of the samples were not elevated above background. Samples collected within 50 m of a known waste disposal site were subjected to detailed geochemical characterization. Uranium in these samples was found to bemore » highly soluble; treatment with synthetic pore water for 24 h caused dissolution of 10-50% of total uranium in the samples. Equilibrium uranium concentrations in pore water were >4.0 mg/L and were sustained in repeated wetting events, effectively depleting soluble uranium from the solid phase. The dissolution rate of uranium appeared to be controlled by solid-phase diffusion of uranium from within uranium-bearing mineral particles. X-ray adsorption spectroscopy indicated the presence of a soluble uranyl silicate, and possibly a uranyl phosphate. These phases were exhausted in transported sediment suggesting that uranium was readily mobilized from sediments in the Upper Puerco watershed and transported in the dissolved load. These results could have significance for uranium risk assessment as well as mining waste management and cleanup efforts.« less

Rapid Dissolution of Soluble Uranyl Phases in Arid, Mine-Impacted Catchments near Church Rock, NM

PubMed Central

DELEMOS, JAMIE L.; BOSTICK, BENJAMIN C.; QUICKSALL, ANDREW N.; LANDIS, JOSHUA D.; GEORGE, CHRISTINE C.; SLAGOWSKI, NAOMI L.; ROCK, TOMMY; BRUGGE, DOUG; LEWIS, JOHNNYE; DURANT, JOHN L.

2008-01-01

We tested the hypothesis that runoff of uranium-bearing particles from mining waste disposal areas was a significant mechanism for redistribution of uranium in the northeastern part of the Upper Puerco River watershed (New Mexico). However, our results were not consistent with this hypothesis. Analysis of >100 sediment and suspended sediment samples collected adjacent to and downstream from uranium source areas indicated that uranium levels in the majority of the samples were not elevated above background. Samples collected within 50 m of a known waste disposal site were subjected to detailed geochemical characterization. Uranium in these samples was found to be highly soluble; treatment with synthetic pore water for 24 h caused dissolution of 10–50% of total uranium in the samples. Equilibrium uranium concentrations in pore water were >4.0 mg/L and were sustained in repeated wetting events, effectively depleting soluble uranium from the solid phase. The dissolution rate of uranium appeared to be controlled by solid-phase diffusion of uranium from within uranium-bearing mineral particles. X-ray adsorption spectroscopy indicated the presence of a soluble uranyl silicate, and possibly a uranyl phosphate. These phases were exhausted in transported sediment suggesting that uranium was readily mobilized from sediments in the Upper Puerco watershed and transported in the dissolved load. These results could have significance for uranium risk assessment as well as mining waste management and cleanup efforts. PMID:18589950

Microbial exudate promoted dissolution and transformation of chromium containing minerals

NASA Astrophysics Data System (ADS)

Saad, E. M.; Sun, J.; Tang, Y.

2015-12-01

Because of its utility in many industrial processes, chromium has become the second most common metal contaminant in the United States. The two most common oxidation states of chromium in nature are Cr(III), which is highly immobile, and Cr(VI), which is highly mobile and toxic. In both natural and engineered environments, the most common remediation of Cr(VI) is through reduction, which results in chromium sequestration in the low solubility mixed Cr(III)-Fe(III) (oxy)hydroxide phases. Consequently, the stability of these minerals must be examined to assess the fate of chromium in the subsurface. We examined the dissolution of mixed Cr(III)-Fe(III) (oxy)hydroxides in the presence of common microbial exudates, including the siderophore desferrioxamine B (DFOB; a common organic ligand secreted by most microbes with high affinity for ferric iron and other trivalent metal ions) and oxalate (a common organic acid produced by microbes). The solids exhibited incongruent dissolution with preferential leaching of Fe from the solid phase. Over time, this leads to a more Cr rich mineral, which is known to be more soluble than the corresponding mixed mineral phase. We are currently investigating the structure of the reacted mineral phases and soluble Cr(III) species, as well as the potential oxidation and remobilization of the soluble Cr species. Results from this study will provide insights regarding the long term transport and fate of chromium in the natural environment in the presence of microbial activities.

Rare earth elements as a fingerprint of soil components solubilization

NASA Astrophysics Data System (ADS)

Davranche, M.; Grybos, M.; Gruau, G.; Pédrot, M.; Dia, A.

2009-04-01

The retention of rare earth element (REE) in the soil profile are mainly controlled by three factors, (i) the stability of the primary REE-carrying minerals, (ii) the presence of secondary phases as clays and Fe- and Mn-oxyhydroxides and (ii) the concentration of colloidal organic matter (OM). Considering that each soil phases (mineral or organic) displays (ii) various surface properties, such as specific area, surface sites density and nature and (ii) their own REE distribution inherited from the rock weathering, their mobilization through various chemical reactions (dissolution, colloidal release….) may involve the development of various shaped REE patterns in the soil solutions. REE fractionation from the different soil phases may therefore be used to identify the response of the soil system to a particular chemical process such as reductive and/or acidic dissolution. To test this purpose, an organic-rich wetland soil sample was incubated under anaerobic condition at both pH 5 and uncontrolled pH. The REE patterns developed in the soil solution were then compared to the REE patterns obtained through either aerobic at pH 3 and 7 incubations or a chemical reduction experiment (using hydroxylamine). REE patterns in anaerobic and aerobic at pH 7 experiments exhibited the same middle rare earth element (MREE) downward concavity significant of the complexation of REE with soil OM. By contrast, under acidic condition, the REE pattern exhibited a positive Eu anomaly due to the dissolution of soil feldspar. Finally, REE pattern obtained from the chemical reducing experiment showed an intermediary flat shape corresponding to a mixing between the soil organic and mineral phases dissolution. The comparison of the various REE pattern shapes allowed to conclude that (i) biological reduction of wetland soil involved amorphous Fe(III) colloids linked to OM and, (ii) that the REE mobility was controlled by the dynamic of OM in wetland soil. They also evidence the potential of REE to be use as a tracer of the soil phases involved in the various chemical processes running in soil solutions.

Weathering profiles in soils and rocks on Earth and Mars

NASA Astrophysics Data System (ADS)

Hausrath, E.; Adcock, C. T.; Bamisile, T.; Baumeister, J. L.; Gainey, S.; Ralston, S. J.; Steiner, M.; Tu, V.

2017-12-01

Interactions of liquid water with rock, soil, or sediments can result in significant chemical and mineralogical changes with depth. These changes can include transformation from one phase to another as well as translocation, addition, and loss of material. The resulting chemical and mineralogical depth profiles can record characteristics of the interacting liquid water such as pH, temperature, duration, and abundance. We use a combined field, laboratory, and modeling approach to interpret the environmental conditions preserved in soils and rocks. We study depth profiles in terrestrial field environments; perform dissolution experiments of primary and secondary phases important in soil environments; and perform numerical modeling to quantitatively interpret weathering environments. In our field studies we have measured time-integrated basaltic mineral dissolution rates, and interpreted the impact of pH and temperature on weathering in basaltic and serpentine-containing rocks and soils. These results help us interpret fundamental processes occurring in soils on Earth and on Mars, and can also be used to inform numerical modeling and laboratory experiments. Our laboratory experiments provide fundamental kinetic data to interpret processes occurring in soils. We have measured dissolution rates of Mars-relevant phosphate minerals, clay minerals, and amorphous phases, as well as dissolution rates under specific Mars-relevant conditions such as in concentrated brines. Finally, reactive transport modeling allows a quantitative interpretation of the kinetic, thermodynamic, and transport processes occurring in soil environments. Such modeling allows the testing of conditions under longer time frames and under different conditions than might be possible under either terrestrial field or laboratory conditions. We have used modeling to examine the weathering of basalt, olivine, carbonate, phosphate, and clay minerals, and placed constraints on the duration, pH, and solution chemistry of past aqueous alteration occurring on Mars.

Increased physical stability and improved dissolution properties of itraconazole, a class II drug, by solid dispersions that combine fast- and slow-dissolving polymers.

PubMed

Six, Karel; Verreck, Geert; Peeters, Jef; Brewster, Marcus; Van Den Mooter, Guy

2004-01-01

Solid dispersions were prepared of itraconazole-Eudragit E100, itraconazole-PVPVA64, and itraconazole-Eudragit E100/PVPVA64 using a corotating twin-screw hot-stage extruder. Modulated temperature differential scanning calorimetry (MTDSC) was used to evaluate the miscibility of the extrudates, and dissolution experiments were performed in simulated gastric fluid without pepsin (SGF(sp)). Itraconazole and Eudragit E100 are miscible up to 13% w/w drug loading. From that concentration on, phase separation is observed. Pharmaceutical performance of this dispersion was satisfactory because 80% of the drug dissolved after 30 min. Extrudates of itraconazole and PVPVA64 were completely miscible but the pharmaceutical performance was low, with 45% of drug dissolved after 3 h. Combination of both polymers in different ratios, with a fixed drug loading of 40% w/w, was evaluated. MTDSC results clearly indicated a two-phase system consisting of itraconazole-Eudragit E100 and itraconazole-PVPVA64 phases. In these extrudates, no free crystalline or glassy clusters of itraconazole were observed; all itraconazole was mixed with one of both polymers. The pharmaceutical performance was tested in SGF(sp) for different polymer ratios, and Eudragit E100/PVPVA64 ratios of 50/50 and 60/40 showed significant increases in dissolution rate and level. Polymer ratios of 70/30 and 80/20, on the other hand, had a release of 85% after 30 min. Precipitation of the drug was never observed. The combination of the two polymers provides a solid dispersion with good dissolution properties and improved physical stability compared with the binary solid dispersions of itraconazole. Copyright 2004 Wiley-Liss, Inc.

Barium isotope fractionation during witherite (BaCO3) dissolution, precipitation and at equilibrium

NASA Astrophysics Data System (ADS)

Mavromatis, Vasileios; van Zuilen, Kirsten; Purgstaller, Bettina; Baldermann, Andre; Nägler, Thomas F.; Dietzel, Martin

2016-10-01

This study examines the behavior of Ba isotope fractionation between witherite and fluid during mineral dissolution, precipitation and at chemical equilibrium. Experiments were performed in batch reactors at 25 °C in 10-2 M NaCl solution where the pH was adjusted by continuous bubbling of a water saturated gas phase of CO2 or atmospheric air. During witherite dissolution no Ba isotope fractionation was observed between solid and fluid. In contrast, during witherite precipitation, caused by a pH increase, a preferential uptake of the lighter 134Ba isotopomer in the solid phase was observed. In this case, the isotope fractionation factor αwitherite-fluid is calculated to be 0.99993 ± 0.00004 (or Δ137/134Bawitherite-fluid ≈ -0.07 ± 0.04‰, 2 sd). The most interesting feature of this study, however, is that after the attainment of chemical equilibrium, the Ba isotope composition of the aqueous phase is progressively becoming lighter, indicating a continuous exchange of Ba2+ ions between witherite and fluid. Mass balance calculations indicate that the detachment of Ba from the solid is not only restricted to the outer surface layer of the solid, but affects several (∼7 unit cells) subsurface layers of the crystal. This observation comes in excellent agreement with the concept of a dynamic system at chemical equilibrium in a mineral-fluid system, denoting that the time required for the achievement of isotopic equilibrium in the witherite-fluid system is longer compared to that observed for chemical equilibrium. Overall, these results indicate that the isotopic composition of Ba bearing carbonates in natural environments may be altered due to changes in fluid composition without a net dissolution/precipitation to be observed.

Kinetic dissolution of carbonates and Mn oxides in acidic water: Measurement of in situ field rates and reactive transport modeling

USGS Publications Warehouse

Brown, J.G.; Glynn, P.D.

2003-01-01

The kinetics of carbonate and Mn oxide dissolution under acidic conditions were examined through the in situ exposure of pure phase samples to acidic ground water in Pinal Creek Basin, Arizona. The average long-term calculated in situ dissolution rates for calcite and dolomite were 1.65??10-7 and 3.64??10-10 mmol/(cm2 s), respectively, which were about 3 orders of magnitude slower than rates derived in laboratory experiments by other investigators. Application of both in situ and lab-derived calcite and dolomite dissolution rates to equilibrium reactive transport simulations of a column experiment did not improve the fit to measured outflow chemistry: at the spatial and temporal scales of the column experiment, the use of an equilibrium model adequately simulated carbonate dissolution in the column. Pyrolusite (MnO2) exposed to acidic ground water for 595 days increased slightly in weight despite thermodynamic conditions that favored dissolution. This result might be related to a recent finding by another investigator that the reductive dissolution of pyrolusite is accompanied by the precipitation of a mixed Mn-Fe oxide species. In PHREEQC reactive transport simulations, the incorporation of Mn kinetics improved the fit between observed and simulated behavior at the column and field scales, although the column-fitted rate for Mn-oxide dissolution was about 4 orders of magnitude greater than the field-fitted rate. Remaining differences between observed and simulated contaminant transport trends at the Pinal Creek site were likely related to factors other than the Mn oxide dissolution rate, such as the concentration of Fe oxide surface sites available for adsorption, the effects of competition among dissolved species for available surface sites, or reactions not included in the model.

Formulation, optimization, and evaluation of self-emulsifying drug delivery systems of nevirapine

PubMed Central

Chintalapudi, Ramprasad; Murthy, T. E. G. K.; Lakshmi, K. Rajya; Manohar, G. Ganesh

2015-01-01

Background: The aim of the present study was to formulate and optimize the self-emulsifying drug delivery systems (SEDDS) of nevirapine (NVP) by use of 22 factorial designs to enhance the oral absorption of NVP by improving its solubility, dissolution rate, and diffusion profile. SEDDS are the isotropic mixtures of oil, surfactant, co-surfactant and drug that form oil in water microemulsion when introduced into the aqueous phase under gentle agitation. Materials and Methods: Solubility of NVP in different oils, surfactants, and co-surfactants was determined for the screening of excipients. Pseudo-ternary phase diagrams were constructed by the aqueous titration method, and formulations were developed based on the optimum excipient combinations with the help of data obtained through the maximum micro emulsion region containing combinations of oil, surfactant, and co-surfactant. The formulations of SEDDS were optimized by 22 factorial designs. Results: The optimum formulation of SEDDS contains 32.5% oleic acid, 44.16% tween 20, and 11.9% polyethylene glycol 600 as oil, surfactant, and co-surfactant respectively. The SEDDS was evaluated for the following drug content, self-emulsification time, rheological properties, zeta potential, in vitro diffusion studies, thermodynamic stability studies, and in vitro dissolution studies. An increase in dissolution was achieved by SEDDS compared to pure form of NVP. Conclusion: Overall, this study suggests that the dissolution and oral bioavailability of NVP could be improved by SEDDS technology. PMID:26682191

Effects of salinity and the extent of water on supercritical CO2-induced phlogopite dissolution and secondary mineral formation.

PubMed

Shao, Hongbo; Ray, Jessica R; Jun, Young-Shin

2011-02-15

To ensure the viability of geologic CO2 sequestration (GCS), we need a holistic understanding of reactions at supercritical CO2 (scCO2)-saline water-rock interfaces and the environmental factors affecting these interactions. This research investigated the effects of salinity and the extent of water on the dissolution and surface morphological changes of phlogopite [KMg2.87Si3.07Al1.23O10(F,OH)2], a model clay mineral in potential GCS sites. Salinity enhanced the dissolution of phlogopite and affected the location, shape, size, and phase of secondary minerals. In low salinity solutions, nanoscale particles of secondary minerals formed much faster, and there were more nanoparticles than in high salinity solutions. The effect of water extent was investigated by comparing scCO2-H2O(g)-phlogopite and scCO2-H2O(l)-phlogopite interactions. Experimental results suggested that the presence of a thin water film adsorbed on the phlogopite surface caused the formation of dissolution pits and a surface coating of secondary mineral phases that could change the physical properties of rocks. These results provide new information for understanding reactions at scCO2-saline water-rock interfaces in deep saline aquifers and will help design secure and environmentally sustainable CO2 sequestration projects.

Tailoring nanoscopic confines to maximize catalytic activity of hydronium ions

NASA Astrophysics Data System (ADS)

Shi, Hui; Eckstein, Sebastian; Vjunov, Aleksei; Camaioni, Donald M.; Lercher, Johannes A.

2017-05-01

Acid catalysis by hydronium ions is ubiquitous in aqueous-phase organic reactions. Here we show that hydronium ion catalysis, exemplified by intramolecular dehydration of cyclohexanol, is markedly influenced by steric constraints, yielding turnover rates that increase by up to two orders of magnitude in tight confines relative to an aqueous solution of a Brønsted acid. The higher activities in zeolites BEA and FAU than in water are caused by more positive activation entropies that more than offset higher activation enthalpies. The higher activity in zeolite MFI with pores smaller than BEA and FAU is caused by a lower activation enthalpy in the tighter confines that more than offsets a less positive activation entropy. Molecularly sized pores significantly enhance the association between hydronium ions and alcohols in a steric environment resembling the constraints in pockets of enzymes stabilizing active sites.

Energy and enthalpy distribution functions for a few physical systems.

PubMed

Wu, K L; Wei, J H; Lai, S K; Okabe, Y

2007-08-02

The present work is devoted to extracting the energy or enthalpy distribution function of a physical system from the moments of the distribution using the maximum entropy method. This distribution theory has the salient traits that it utilizes only the experimental thermodynamic data. The calculated distribution functions provide invaluable insight into the state or phase behavior of the physical systems under study. As concrete evidence, we demonstrate the elegance of the distribution theory by studying first a test case of a two-dimensional six-state Potts model for which simulation results are available for comparison, then the biphasic behavior of the binary alloy Na-K whose excess heat capacity, experimentally observed to fall in a narrow temperature range, has yet to be clarified theoretically, and finally, the thermally induced state behavior of a collection of 16 proteins.

Hydrogen absorption properties of Mg-Ni alloys prepared by bulk mechanical alloying

NASA Astrophysics Data System (ADS)

Kuji, Toshiro

2001-04-01

The thermodynamic properties of the hydrides of Mg2-xNi (x=0-0.5) alloys produced by bulk mechanical alloying (BMA) were determined from pressure-composition (PC) isotherms for absorption over temperatures from 623 to 423 K. The vant Hoff plot for the plateau pressures of isotherms clearly indicated the existence of high and low temperature hydrides with different entropy and enthalpy for hydride formation. It was found that both the entropy and enthalpy values for the high temperature hydride were more negative than for the low temperature hydride. The phase transition temperature was 525 K for Mg2.0Ni and decreased while increasing the value of x. This allotropic transformation was well confirmed by in-situ XRD observations from RT to 673 K under hydrogen atmosphere or in vacuum.

A thermodynamic study of the gaseous thorium carbides, ThC, ThC2, ThC3, ThC4, ThC5, and ThC6

NASA Astrophysics Data System (ADS)

Gupta, Satish K.; Gingerich, Karl A.

1980-02-01

Six gaseous carbides of thorium, ThCn(n=1-6), have been identified in a Knudsen effusion mass spectrometric investigation of the vapor phase above a thorium-uranium-rhodium-graphite system at high temperatures. The partial pressures of the thorium containing species were measured as a function of temperature in the 2300-2700 °K range. Third law enthalpies for the reactions Th(g)+nC(graphite) =ThCn, n=1 to 6, and of various other homogeneous and heterogeneous reactions were evaluated. By combining the experimental enthalpies with appropriate thermodynamic data taken from literature, the following values for the atomization energies ΔH °at,298, and standard heats of formation ΔH °f,298 of thorium carbides have been derived:

A NEW TWO-PHASE FLOW AND TRANSPORT MODEL WITH INTERPHASE MASS EXCHANGE

EPA Science Inventory

The focus of this numerical investigation is on modelling the emplacement and subsequent removal, through dissolution, of a Denser-than-water Non-Aqueous Phase Liquid (DNAPL) in a saturated groundwater system. pecifically the model must address two flow and transport regimes. irs...

Production, pathways and budgets of melts in mid-ocean ridges: An enthalpy based thermo-mechanical model

NASA Astrophysics Data System (ADS)

Mandal, Nibir; Sarkar, Shamik; Baruah, Amiya; Dutta, Urmi

2018-04-01

Using an enthalpy based thermo-mechanical model we provide a theoretical evaluation of melt production beneath mid-ocean ridges (MORs), and demonstrate how the melts subsequently develop their pathways to sustain the major ridge processes. Our model employs a Darcy idealization of the two-phase (solid-melt) system, accounting enthalpy (ΔH) as a function of temperature dependent liquid fraction (ϕ). Random thermal perturbations imposed in this model set in local convection that drive melts to flow through porosity controlled pathways with a typical mushroom-like 3D structure. We present across- and along-MOR axis model profiles to show the mode of occurrence of melt-rich zones within mushy regions, connected to deeper sources by single or multiple feeders. The upwelling of melts experiences two synchronous processes: 1) solidification-accretion, and 2) eruption, retaining a large melt fraction in the framework of mantle dynamics. Using a bifurcation analysis we determine the threshold condition for melt eruption, and estimate the potential volumes of eruptible melts (∼3.7 × 106 m3/yr) and sub-crustal solidified masses (∼1-8.8 × 106 m3/yr) on an axis length of 500 km. The solidification process far dominates over the eruption process in the initial phase, but declines rapidly on a time scale (t) of 1 Myr. Consequently, the eruption rate takes over the solidification rate, but attains nearly a steady value as t > 1.5 Myr. We finally present a melt budget, where a maximum of ∼5% of the total upwelling melt volume is available for eruption, whereas ∼19% for deeper level solidification; the rest continue to participate in the sub-crustal processes.

Measuring and predicting Delta(vap)H298 values of ionic liquids.

PubMed

Deyko, Alexey; Lovelock, Kevin R J; Corfield, Jo-Anne; Taylor, Alasdair W; Gooden, Peter N; Villar-Garcia, Ignacio J; Licence, Peter; Jones, Robert G; Krasovskiy, Vladimir G; Chernikova, Elena A; Kustov, Leonid M

2009-10-14

We report the enthalpies of vaporisation (measured using temperature programmed desorption by mass spectrometry) of twelve ionic liquids (ILs), covering four imidazolium, [C(m)C(n)Im]+, five pyrrolidinium, [C(n)C(m)Pyrr]+, two pyridinium, [C(n)Py]+, and a dication, [C3(C1Im)2]2+ based IL. These cations were paired with a range of anions: [BF4]-, [FeCl4]-, [N(CN)2]-, [PF3(C2F5)3]- ([FAP]-), [(CF3SO2)2N]- ([Tf2N]-) and [SCN]-. Using these results, plus those for a further eight imidazolium based ILs published earlier (which include the anions [CF3SO3]- ([TfO]-), [PF6]- and [EtSO4]-), we show that the enthalpies of vaporisation can be decomposed into three components. The first component is the Coulombic interaction between the ions, DeltaU(Cou,R), which is a function of the IL molar volume, V(m), and a parameter R(r) which quantifies the relative change in anion-cation distance on evaporation from the liquid phase to the ion pair in the gas phase. The second and third components are the van der Waals contributions from the anion, DeltaH(vdw,A), and the cation, DeltaH(vdw,C). We derive a universal value for R(r), and individual values of DeltaH(vdw,A) and DeltaH(vdw,C) for each of the anions and cations considered in this study. Given the molar volume, it is possible to estimate the enthalpies of vaporisation of ILs composed of any combination of the ions considered here; values for fourteen ILs which have not yet been studied experimentally are given.

Pb 2+–Calcite Interactions under Far-from-Equilibrium Conditions: Formation of Micropyramids and Pseudomorphic Growth of Cerussite

DOE PAGES

Yuan, Ke; De Andrade, Vincent; Feng, Zhange; ...

2018-01-04

The presence of impurity ions is known to significantly influence mineral surface morphology during crystal growth from aqueous solution, but knowledge on impurity ion-mineral interactions during dissolution under far-from equilibrium conditions remains limited. Here we show that calcite (CaCO 3) exhibits a rich array of dissolution features in the presence of Pb. During the initial stage, calcite exhibits non-classical surface features characterized as micro pyramids developed spontaneously in acidic Pb-bearing solutions. Subsequent pseudomorphic growth of cerussite (PbCO 3) was observed, where nucleation occurred entirely within a pore space created by dissolution at the calcite/substrate interface. Uneven growth rates yielded amore » cerussite shell made of lath- or dendritic-shaped crystals. The cerussite phase was separated from the calcite by pores of less than 200 nm under transmission X-ray microscopy, consistent with the interface-coupled dissolution-precipitation mechanism. These results show that impurity metal ions exert significant control over the microscale dissolution features found on mineral surfaces and provide new insights into interpreting and designing micro structures observed in naturally-occurring and synthetic carbonate minerals by dissolution. In addition, heterogeneous micro-environments created in transport limited reactions under pore spaces may lead to unusual growth forms during crystal nucleation and precipitation.« less

Antisolvent crystallization of a cardiotonic drug in ionic liquids: Effect of mixing on the crystal properties

NASA Astrophysics Data System (ADS)

de Azevedo Jacqueline, Resende; Fabienne, Espitalier; Jean-Jacques, Letourneau; Inês, Ré Maria

2017-08-01

LASSBio-294 (3,4-methylenedioxybenzoyl-2-thienylhydrazon) is a poorly soluble drug which has been proposed to have major advantages over other cardiotonic drugs. Poorly water soluble drugs present limited bioavailability due to their low solubility and dissolution rate. An antisolvent crystallization processing can improve the dissolution rate by decreasing the crystals particle size. However, LASSBio-294 is also poorly soluble in organic solvents and this operation is limited. In order to open new perspectives to improve dissolution rate, this work has investigated LASSBio-294 in terms of its antisolvent crystallization in 1-ethyl-3-methylimidazolium methyl phosphonate [emim][CH3O(H)PO2] as solvent and water as antisolvent. Two modes of mixing are tested in stirred vessel with different pre-mixers (Roughton or T-mixers) in order to investigate the mixing effect on the crystal properties (crystalline structure, particle size distribution, residual solvent and in vitro dissolution rate). Smaller drug particles with unchanged crystalline structure were obtained. Despite the decrease of the elementary particles size, the recrystallized particles did not achieve a better dissolution profile. However, this study was able to highlight a certain number of findings such as the impact of the hydrodynamic conditions on the crystals formation and the presence of a gel phase limiting the dissolution rate.

Effect of ball milling on the physicochemical properties of atorvastatin calcium sesquihydrate: the dissolution kinetic behaviours of milled amorphous solids.

PubMed

Kobayashi, Makiko; Hattori, Yusuke; Sasaki, Tetsuo; Otsuka, Makoto

2017-01-01

The purposes of this study were to clarify the amorphization by ball milling of atorvastatin calcium sesquihydrate (AT) and to analyse the change in dissolution kinetics. The amorphous AT was prepared from crystal AT by ball milling and analysed in terms of the changes of its physicochemical properties by powder X-ray diffraction analysis (XRD), thermal analysis and infrared spectroscopy (IR). Moreover, to evaluate the usefulness of the amorphous form for pharmaceutical development, intrinsic solubility of the ground product was evaluated using a dissolution kinetic method. The XRD results indicated that crystalline AT was transformed into amorphous solids by more than 30-min milling. The thermal analysis result suggested that chemical potential of the ground AT are changed significantly by milling. The IR spectra of the AT showed the band shift from the amide group at 3406 cm -1 with an intermolecular hydrogen bond to a free amide group at 3365 cm -1 by milling. The dissolution of amorphous AT follows a dissolution kinetic model involving phase transformation. The initial dissolution rate of the ground product increased with the increase in milling time to reflect the increase in the intrinsic solubility based on the amorphous state. © 2016 Royal Pharmaceutical Society.

Lubricant-Induced Crystallization of Itraconazole From Tablets Made of Electrospun Amorphous Solid Dispersion.

PubMed

Démuth, Balázs; Farkas, Attila; Balogh, Attila; Bartosiewicz, Karolina; Kállai-Szabó, Barnabás; Bertels, Johny; Vigh, Tamás; Mensch, Jurgen; Verreck, Geert; Van Assche, Ivo; Marosi, György; Nagy, Zsombor K

2016-09-01

Investigation of downstream processing of nanofibrous amorphous solid dispersions to generate tablet formulation is in a quite early phase. Development of high speed electrospinning opened up the possibility to study tableting of electrospun solid dispersions (containing polyvinylpyrrolidone-vinyl acetate and itraconazole [ITR] in this case). This work was conducted to investigate the influence of excipients on dissolution properties and the feasibility of scaled-up rotary press tableting. The dissolution rates from tablets proved to be mainly composition dependent. Magnesium stearate acted as a nucleation promoting agent (providing an active hydrophobic environment for crystallization of ITR) hindering the total dissolution of ITR. This crystallization process proved to be temperature dependent as well. However, the extent of dissolution of more than 95% was realizable when a less hydrophobic lubricant, sodium stearyl fumarate (soluble in the medium), was applied. Magnesium stearate induced crystallization even if it was put in the dissolution medium next to proper tablets. After optimization of the composition, scaled-up tableting on a rotary press was carried out. Appropriate dissolution of ITR from tablets was maintained for 3 months at 25°C/60% relative humidity. HPLC measurements confirmed that ITR was chemically stable both in the course of downstream processing and storage. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Investigations of kinetics and mechanism of chloropinnoite in boric acid aqueous solution at 303 K by Raman spectroscopy.

PubMed

Xiaoping, Li; Shiyang, Gao; Shuping, Xia

2004-10-01

Raman spectroscopy of dissolution and transformation of chloropinnoite in 4.5% (wt.%) boric acid aqueous solution at 303 K has been recorded. The Raman spectra of kinetics process have been obtained. The phase transformation product is 2MgO.3B2O3.15H2O (kurnakovite). The main polyborate anions and their interaction in aqueous solution have been proposed according to the Raman spectrum. Some assignments were tentatively given and the relations between the existing forms of polyborate anions and the crystallizing solid phases have been gained. A mechanism of dissolution and crystallization reactions and the formation condition of kurnakovite in Qinghai-Tibet plateau were proposed and discussed.

Dissolution Kinetics of Meta-Torbernite under Circum-neutral to Alkaline Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wellman, Dawn M.; McNamara, Bruce K.; Bacon, Diana H.

2009-12-21

Autunite group minerals have been identified in contaminated sediments as the long-term controlling phase of uranium. Meta-torbernite, has been identified in subsurface environments which were subjected to co-contaminant disposal practices from past nuclear weapons and fuel operations. Under these conditions the mobility of uranium in subsurface pore waters is limited by the rate of meta-torbernite dissolution; however, there are no known investigations which report the dissolution behavior of meta-torbernite. The purpose of this investigation was to conduct a series of single-pass flow-through (SPFT) tests to 1) quantify the effect of temperature (23 - 90oC) and pH (6 -10) on meta-torbernitemore » dissolution, 2) compare the dissolution of meta-torbernite to other autunite-group minerals, and 3) evaluate the effect of aqueous phosphate on the dissolution kinetics of meta-torbernite. Results presented here illustrate meta-torbernite dissolution rates increase by ~100X over the pH interval of 6 to 10 (eta = 0.59 ± 0.07), irrespective of temperature. The power law coefficient for meta-torbernite, eta = 0.59 ± 0.07, is greater than that quantified for Ca-meta-autunite, eta = 0.42 ± 0.12. This suggests the stability of meta-torbernite is greater than that of meta-autunite, which is reflected in the predicted stability constants. The rate equation for the dissolution of meta-torbernite as a function of aqueous phosphate concentration is log rdissol (mol m-2 sec-1) = -4.7 x 10-13 + 4.1 x 10-10 [PO43-].« less

PLUTONIUM RECOVERY FROM NEUTRON-BOMBARDED URANIUM FUEL

DOEpatents

Moore, R.H.

1964-03-24

A process of recovering plutonium from fuel by dissolution in molten KAlCl/sub 4/ double salt is described. Molten lithium chloride plus stannous chloride is added to reduce plutonium tetrachloride to the trichloride, which is dissolved in a lithium chloride phase while the uranium, as the tetrachloride, is dissolved in a double-salt phase. Separation of the two phases is discussed. (AEC)

Phase Changes of Monosulfoaluminate in NaCl Aqueous Solution

DOE PAGES

Yoon, Seyoon; Ha, Juyoung; Chae, Sejung Rosie; ...

2016-05-21

Monosulfoaluminate (Ca 4Al 2(SO 4)(OH) 12∙6H 2O) plays an important role in anion binding in Portland cement by exchanging its original interlayer ions (SO 4 2- and OH -) with chloride ions. In this study, scanning transmission X-ray microscope (STXM), X-ray absorption near edge structure (XANES) spectroscopy, and X-ray diffraction (XRD) were used to investigate the phase change of monosulfoaluminate due to its interaction with chloride ions. Pure monosulfoaluminate was synthesized and its powder samples were suspended in 0, 0.1, 1, 3, and 5 M NaCl solutions for seven days. At low chloride concentrations, a partial dissolution of monosulfoaluminate formedmore » ettringite, while, with increasing chloride content, the dissolution process was suppressed. As the NaCl concentration increased, the dominant mechanism of the phase change became ion exchange, resulting in direct phase transformation from monosulfoaluminate to Kuzel’s salt or Friedel’s salt. The phase assemblages of the NaCl-reacted samples were explored using thermodynamic calculations and least-square linear combination (LC) fitting of measured XANES spectra. A comprehensive description of the phase change and its dominant mechanism are discussed.« less

Revisiting Hansen Solubility Parameters by Including Thermodynamics.

PubMed

Louwerse, Manuel J; Maldonado, Ana; Rousseau, Simon; Moreau-Masselon, Chloe; Roux, Bernard; Rothenberg, Gadi

2017-11-03

The Hansen solubility parameter approach is revisited by implementing the thermodynamics of dissolution and mixing. Hansen's pragmatic approach has earned its spurs in predicting solvents for polymer solutions, but for molecular solutes improvements are needed. By going into the details of entropy and enthalpy, several corrections are suggested that make the methodology thermodynamically sound without losing its ease of use. The most important corrections include accounting for the solvent molecules' size, the destruction of the solid's crystal structure, and the specificity of hydrogen-bonding interactions, as well as opportunities to predict the solubility at extrapolated temperatures. Testing the original and the improved methods on a large industrial dataset including solvent blends, fit qualities improved from 0.89 to 0.97 and the percentage of correct predictions rose from 54 % to 78 %. Full Matlab scripts are included in the Supporting Information, allowing readers to implement these improvements on their own datasets. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effect of excipients on the release kinetics of diclofenac sodium and papaverine hydrochloride from composed tablets.

PubMed

Kasperek, Regina; Trebacz, Hanna; Zimmer, Łukasz; Poleszak, Ewa

2014-01-01

For increased analgesic effect, new composed tablets containing diclofenac sodium (DIC) with an addition of papaverine hydrochloride (PAP) were prepared to investigate the mechanism of release of the active substances from tablets with different excipients in eight different formulations. To detect the possible interactions between active substances and excipients differential scanning calorimetry (DSC) was used. A shift of the melting point and enthalpy values of the physical mixtures of tablets components suggested a kind of interaction between components in certain formulations, however, the tabletting process was not disturbed in any of them. Kinetics of drug release from formulations was estimated by zero order, first order and Higuchi and Korsmeyer-Peppas models using results of dissolution of DIC and PAP from tablets. The study revealed that the mechanism of release of active substances was dependent on the excipients contained in tablets and the best fitted kinetics models were obtained for formulations with potentially prolonged release of DIC and PAP.

Fractionation of iron isotopes during leaching of natural particles by acidic and circumneutral leaches and development of an optimal leach for marine particulate iron isotopes

NASA Astrophysics Data System (ADS)

Revels, Brandi N.; Zhang, Ruifeng; Adkins, Jess F.; John, Seth G.

2015-10-01

Iron (Fe) is an essential nutrient for life on land and in the oceans. Iron stable isotope ratios (δ56Fe) can be used to study the biogeochemical cycling of Fe between particulate and dissolved phases in terrestrial and marine environments. We have investigated the dissolution of Fe from natural particles both to understand the mechanisms of Fe dissolution, and to choose a leach appropriate for extracting labile Fe phases of marine particles. With a goal of finding leaches which would be appropriate for studying dissolved-particle interactions in an oxic water column, three particle types were chosen including oxic seafloor sediments (MESS-3), terrestrial dust (Arizona Test Dust - A2 Fine), and ocean sediment trap material from the Cariaco basin. Four leaches were tested, including three acidic leaches similar to leaches previously applied to marine particles and sediments (25% acetic acid, 0.01 N HCl, and 0.5 N HCl) and a pH 8 oxalate-EDTA leach meant to mimic the dissolution of particles by organic complexation, as occurs in natural seawater. Each leach was applied for three different times (10 min, 2 h, 24 h) at three different temperatures (25 °C, 60 °C, 90 °C). MESS-3 was also leached under various redox conditions (0.02 M hydroxylamine hydrochloride or 0.02 M hydrogen peroxide). For all three sample types tested, we find a consistent relationship between the amount of Fe leached and leachate δ56Fe for all of the acidic leaches, and a different relationship between the amount of Fe leached and leachate δ56Fe for the oxalate-EDTA leach, suggesting that Fe was released through proton-promoted dissolution for all acidic leaches and by ligand-promoted dissolution for the oxalate-EDTA leach. Fe isotope fractionations of up to 2‰ were observed during acidic leaching of MESS-3 and Cariaco sediment trap material, but not for Arizona Test Dust, suggesting that sample composition influences fractionation, perhaps because Fe isotopes are greatly fractionated during leaching of silicates and clays but only minimally fractionated during dissolution of Fe oxyhydroxides. Two different analytical models were developed to explain the relationship between amount of Fe leached and δ56Fe, one of which assumes mixing between two Fe phases with different δ56Fe and different dissolution rates, and the other of which assumes dissolution of a single phase with a kinetic isotope effect. We apply both models to fit results from the acidic leaches of MESS-3 and find that the fit for both models is very similar, suggesting that isotope data will never be sufficient to distinguish between these two processes for natural materials. Next, we utilize our data to choose an optimal leach for application to marine particles. The oxalate-EDTA leach is well-suited to this purpose because it does not greatly fractionate Fe isotopes for a diversity of particle types over a wide variety of leaching conditions, and because it approximates the conditions by which particulate Fe dissolves in the oceans. We recommend a 2 h leach at 90 °C with 0.1 M oxalate and 0.05 M EDTA at pH 8 to measure labile ;ligand-leachable; particulate δ56Fe on natural marine materials with a range of compositions.

Optimization of binary thermodynamic and phase diagram data

NASA Astrophysics Data System (ADS)

Bale, Christopher W.; Pelton, A. D.

1983-03-01

An optimization technique based upon least squares regression is presented to permit the simultaneous analysis of diverse experimental binary thermodynamic and phase diagram data. Coefficients of polynomial expansions for the enthalpy and excess entropy of binary solutions are obtained which can subsequently be used to calculate the thermodynamic properties or the phase diagram. In an interactive computer-assisted analysis employing this technique, one can critically analyze a large number of diverse data in a binary system rapidly, in a manner which is fully self-consistent thermodynamically. Examples of applications to the Bi-Zn, Cd-Pb, PbCl2-KCl, LiCl-FeCl2, and Au-Ni binary systems are given.

Calcium with the β-tin structure at high pressure and low temperature

PubMed Central

Li, Bing; Ding, Yang; Yang, Wenge; Wang, Lin; Zou, Bo; Shu, Jinfu; Sinogeikin, Stas; Park, Changyong; Zou, Guangtian; Mao, Ho-kwang

2012-01-01

Using synchrotron high-pressure X-ray diffraction at cryogenic temperatures, we have established the phase diagram for calcium up to 110 GPa and 5–300 K. We discovered the long-sought for theoretically predicted β-tin structured calcium with I41/amd symmetry at 35 GPa in a s mall low-temperature range below 10 K, thus resolving the enigma of absence of this lowest enthalpy phase. The stability and relations among various distorted simple-cubic phases in the Ca-III region have also been examined and clarified over a wide range of high pressures and low temperatures. PMID:23012455

Detection of a new 'nematic-like' phase in liquid crystal-amphiphile mixture by differential scanning calorimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dan, Kaustabh, E-mail: kaustabhdan@gmail.com; Roy, Madhusudan, E-mail: kaustabhdan@gmail.com; Datta, Alokmay, E-mail: kaustabhdan@gmail.com

2014-04-24

Differential Scanning Calorimetry (DSC) studies on phase transitions of the pure liquid crystalline material N-4-methoxybenzylidene-4-butylaniline (MBBA) and mixtures of MBBA and the amphiphile Stearic Acid (StA) show significant changes in the behavior of mixture from pure MBBA, as regards the nematic-isotropic (N-I) transition temperature (T{sub c}) and other thermodynamic parameters like enthalpy, specific heat and activation energy with concentration of StA. In particular, the convexity of the Arrhenius plot in pure MBBA vanishes with StA concentration pointing to the formation of a new, perhaps 'nematic-like', phase in the mixtures.

Mass Transfer Limited Enhanced Bioremediation at Dnapl Source Zones: a Numerical Study

NASA Astrophysics Data System (ADS)

Kokkinaki, A.; Sleep, B. E.

2011-12-01

The success of enhanced bioremediation of dense non-aqueous phase liquids (DNAPLs) relies on accelerating contaminant mass transfer from the organic to the aqueous phase, thus enhancing the depletion of DNAPL source zones compared to natural dissolution. This is achieved by promoting biological activity that reduces the contaminant's aqueous phase concentration. Although laboratory studies have demonstrated that high reaction rates are attainable by specialized microbial cultures in DNAPL source zones, field applications of the technology report lower reaction rates and prolonged remediation times. One possible explanation for this phenomenon is that the reaction rates are limited by the rate at which the contaminant partitions from the DNAPL to the aqueous phase. In such cases, slow mass transfer to the aqueous phase reduces the bioavailability of the contaminant and consequently decreases the potential source zone depletion enhancement. In this work, the effect of rate limited mass transfer on bio-enhanced dissolution of DNAPL chlorinated ethenes is investigated through a numerical study. A multi-phase, multi-component groundwater transport model is employed to simulate DNAPL mass depletion for a range of source zone scenarios. Rate limited mass transfer is modeled by a linear driving force model, employing a thermodynamic approach for the calculation of the DNAPL - water interfacial area. Metabolic reductive dechlorination is modeled by Monod kinetics, considering microbial growth and self-inhibition. The model was utilized to identify conditions in which mass transfer, rather than reaction, is the limiting process, as indicated by the bioavailability number. In such cases, reaction is slower than expected, and further increase in the reaction rate does not enhance mass depletion. Mass transfer rate limitations were shown to affect both dechlorination and microbial growth kinetics. The complex dynamics between mass transfer, DNAPL transport and distribution, and dechlorination kinetics were reflected in a transient, spatially heterogeneous bioavailability number and dissolution enhancement. In agreement with the literature, source zone architecture largely determined the impact of mass transfer on potential dissolution enhancement, with bioavailability decreasing the most at high ganglia to pool ratios. The results of this study suggest that if mass transfer rate limitations are not considered in designing bioremediation applications at DNAPL source zones, the enhancement of DNAPL depletion and the overall effectiveness of enhanced bioremediation may be significantly overestimated.

Bioenhanced dissolution of dense non-aqueous phase of trichloroethylene as affected by iron reducing conditions: model systems and environmental samples.

PubMed

Paul, Laiby; Smolders, Erik

2015-01-01

The anaerobic biotransformation of trichloroethylene (TCE) can be affected by competing electron acceptors such as Fe (III). This study assessed the role of Fe (III) reduction on the bioenhanced dissolution of TCE dense non-aqueous phase liquid (DNAPL). Columns were set up as 1-D diffusion cells consisting of a lower DNAPL layer, a layer with an aquifer substratum and an upper water layer that is regularly refreshed. The substrata used were either inert sand or sand coated with 2-line ferrihydrite (HFO) or two environmental Fe (III) containing samples. The columns were inoculated with KB-1 and were repeatedly fed with formate. In none of the diffusion cells, vinyl chloride or ethene was detected while dissolved and extractable Fe (II) increased strongly during 60 d of incubation. The cis-DCE concentration peaked at 4.0 cm from the DNAPL (inert sand) while it was at 3.4 cm (sand+HFO), 1.7 cm and 2.5 cm (environmental samples). The TCE concentration gradients near the DNAPL indicate that the DNAPL dissolution rate was larger than that in an abiotic cell by factors 1.3 (inert sand), 1.0 (sand+HFO) and 2.2 (both environmental samples). This results show that high bioavailable Fe (III) in HFO reduces the TCE degradation by competitive Fe (III) reduction, yielding lower bioenhanced dissolution. However, Fe (III) reduction in environmental samples was not reducing TCE degradation and the dissolution factor was even larger than that of inert sand. It is speculated that physical factors, e.g. micro-niches in the environmental samples protect microorganisms from toxic concentrations of TCE. Copyright © 2014 Elsevier Ltd. All rights reserved.

DNAPL remediation with in situ chemical oxidation using potassium permanganate - Part I. Mineralogy of Mn oxide and its dissolution in organic acids

NASA Astrophysics Data System (ADS)

Li, X. David; Schwartz, Franklin W.

2004-01-01

Previous studies on in situ chemical oxidation of trichloroethylene (TCE) with potassium permanganate indicated that the solid reaction product, Mn oxide, could reduce the permeability of the porous medium and impact the success of dense non-aqueous phase liquid (DNAPL) removal. In order to address the issue of permeability reduction caused by precipitation, this study investigated the mineralogy of Mn oxides and the possibilities of removing the solid precipitates by dissolution. The solid reaction product from the oxidation of TCE by permanganate is semi-amorphous potassium-rich birnessite, which has a layered mineral structure with an interlayer spacing of 7.3 Å. The chemical formula is K 0.854Mn 1.786O 4·1.55H 2O. It has a relatively small specific surface area at 23.6±0.82 m 2/g. Its point of zero charge (pzc) was measured as 3.7±0.4. This birnessite is a relatively active species and could participate in various reactions with existing organic and inorganic matter. The dissolution kinetics of Mn oxide was evaluated in batch experiments using solutions of citric acid, oxalic acid, and ethylenediaminetetraacetic acid (EDTA). Initial dissolution rates were determined to be 0.126 mM/m 2/h for citric acid, 1.35 mM/m 2/h for oxalic acid, and 5.176 mM/m 2/h for EDTA. These rates compare with 0.0025 mM/m 2/h for nitric acid at pH=2. Organic acids dissolve Mn oxide quickly. Reaction rates increase with acid concentration, as tested with citric acid. The dissolution mechanism likely involves proton and ligand-promoted dissolution and reductive dissolution. Citric and oxalic acid can induce ligand-promoted dissolution, while EDTA can induce ligand-promoted and reductive dissolutions. At low pH, proton-promoted dissolution seems to occur with all the acids tested, but this process is not dominant. Reductive dissolution appears to be the most effective process in dissolving the solid, followed by ligand-promoted dissolution. These experiments indicate the significant potential in using these organic acids to remove precipitates formed during the oxidation reaction.

Organic carbonates: experiment and ab initio calculations for prediction of thermochemical properties.

PubMed

Verevkin, Sergey P; Emel'yanenko, Vladimir N; Kozlova, Svetlana A

2008-10-23

This work has been undertaken in order to obtain data on thermodynamic properties of organic carbonates and to revise the group-additivity values necessary for predicting their standard enthalpies of formation and enthalpies of vaporization. The standard molar enthalpies of formation of dibenzyl carbonate, tert-butyl phenyl carbonate, and diphenyl carbonate were measured using combustion calorimetry. Molar enthalpies of vaporization of these compounds were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. Molar enthalpy of sublimation of diphenyl carbonate was measured in the same way. Ab initio calculations of molar enthalpies of formation of organic carbonates have been performed using the G3MP2 method, and results are in excellent agreement with the available experiment. Then the group-contribution method has been developed to predict values of the enthalpies of formation and enthalpies of vaporization of organic carbonates.

THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED DRINKING WATER TREATMENT MEDIA 1

EPA Science Inventory

Arsenic concentrations (Total Recoverable As by EPA Method 3051, soluble, Toxicity Characteristic Leaching Procedure extractable) and solid-phase speciation (by X-ray Absorption Near-Edge Spectroscopy-XANES) were assessed as a function of depth through Fe-media beds for two comme...

THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED TREATMENT MEDIA

EPA Science Inventory

Arsenic concentrations (Total Recoverable As by EPA Method 3051) and solid-phase speciation (by X-ray Absorption Near-Edge Spectroscopy-XANES) were assessed as a function of depth through Fe-media beds for two commercially available products from pilot-scale field tests. These re...

THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED DRINKING WATER TREATMENT MEDIA - JOURNAL

EPA Science Inventory

Arsenic concentrations (Total Recoverable As by EPA Method 3051, soluble, Toxicity Characteristic Leaching Procedure extractable) and solid-phase speciation (by X-ray Absorption Near-Edge Spectroscopy-XANES) were assessed as a function of depth through Fe-media beds for two comme...

A New Thermodynamic Parameter to Predict Formation of Solid Solution or Intermetallic Phases in High Entropy Alloys (Postprint)

DTIC Science & Technology

2015-11-02

George , Relative effects of enthalpy and entropy on the phase stability of equiatomic high-entropy alloys, Acta Mater. 61 (2013) 2628e2638. [4] B... Cantor , I.T.H. Chang, P. Knight, A.J.B. Vincent, Microstructural development in equiatomic multicomponent alloys, Mater. Sci. Eng. A 375e377 (2004...an Al0.5CoCrCuFeNi high entropy alloy, In- termetallics 31 (2012) 165e172. [24] Z. Wu, H. Bei, F. Otto, G.M. Pharr, E.P. George , Recovery

DOE Office of Scientific and Technical Information (OSTI.GOV)

DeTuri, V.F.; Ervin, K.M.

Energy-resolved competitive collision-induced dissociation methods are used to measure the gas-phase acidities of a series of alcohols (methanol, ethanol, 2-propanol, and 2-methyl-2-propanol). The competitive dissociation reactions of fluoride-alcohol, [F{sup {minus}}{center{underscore}dot}HOR], alkoxide-water, [RO{sup {minus}}{center{underscore}dot}HOH], and alkoxide-methanol [RO{+-}{center{underscore}dot}HOCH{sub 3}] proton-bound complexes are studied using a guided ion beam tandem mass spectrometer. The reaction cross sections and product branching fractions to the two proton transfer channels are measured as a function of collision energy. The enthalpy difference between the two product channels is found by modeling the reaction cross sections near threshold using RRKM theory to account for the energy-dependent product branching ratiomore » and kinetic shift. From the enthalpy difference, the alcohol gas-phase acidities are determined relative to the well-known values of HF and H{sub 2}O. The measured gas-phase acidities are {Delta}{sub acid}H{sub 298}(CH{sub 3}OH) = 1599 {+-} 3 kJ/mol, {Delta}{sub acid}H{sub 298}(CH{sub 3}CH{sub 2}OH) = 1586 {+-} 5 kJ/mol, {Delta}{sub acid}H{sub 298}((CH{sub 3}){sub 2}CHOH) = 1576 {+-} 4 kJ/mol, and {Delta}{sub acid}H{sub 298}((CH{sub 3}){sub 3}COH) = 1573 {+-} 3 kJ/mol.« less

Theoretical investigation of the structural, electronic, and thermodynamic properties of CdS1-xSex alloys

NASA Astrophysics Data System (ADS)

Long, Debing; Li, Mingkai; Meng, Dongxue; Ahuja, Rajeev; He, Yunbin

2018-03-01

In this work, the structural, electronic, and thermodynamic properties of wurtzite (WZ) and zincblende (ZB) CdS1-xSex alloys are investigated using the density functional theory (DFT) and the cluster expansion method. A special quasirandom structure containing 16 atoms is constructed to calculate the band structures of random alloys. The band gaps of CdS1-xSex alloys are direct and decrease as the Se content increases. The delta self-consistent-field method is applied to correct band gaps that are underestimated by DFT. The band offsets clearly reflect the variation in valence band maxima and conduction band minima, thus providing information useful to the design of relevant quantum well structures. The positive formation enthalpies of both phases imply that CdS1-xSex is an immiscible system and tends to phase separate. The influence of lattice vibrations on the phase diagram is investigated by calculating the phonon density of states. Lattice vibration effects can reduce the critical temperature Tc and increase alloy solid solubilities. This influence is especially significant in the ZB structure. When only chemical interactions are present, the Tc values for WZ- and ZB-CdS1-xSex are 260 K and 249 K, respectively. The lattice vibration enthalpy and entropy lower the Tc to 255 K and 233 K, respectively.

Fabrication and Properties of Micro-Nanoencapsulated Phase Change Materials for Internally-Cooled Liquid Desiccant Dehumidification.

PubMed

Niu, Xiaofeng; Xu, Qing; Zhang, Yi; Zhang, Yue; Yan, Yufeng; Liu, Tao

2017-04-29

Micro-nanoencapsulated phase change materials (M-NEPCMs) are proposed to be useful in liquid desiccant dehumidification by restraining the temperature rise in the moisture-removal process and improving the dehumidification efficiency. In this paper, the n -octadecane M-NEPCMs with desirable thermal properties for internally-cooled dehumidification were fabricated by using compound emulsifiers through the in-situ polymerization method. Melamine-formaldehyde resin was used as the shell material. The effects of the mixing ratio, emulsification methods and amount of the compound emulsifiers on the morphology, size and thermal properties of the M-NEPCMs were investigated experimentally. The optimum weight mixing ratio of the compound emulsifiers is SDS (sodium dodecyl sulfate):Tween80 (polyoxyethylene sorbitan monooleate):Span80 (sorbitan monooleate) = 0.1:0.6:0.3, which achieves the best stability of the n -octadecane emulsion. When the compound emulsifiers are 10 wt. % of the core material, the melting enthalpy of M-NEPCMs reaches its maximum of 145.26 J/g of capsules, with an encapsulation efficiency of 62.88% and a mean diameter of 636 nm. The sub-cooling of the prepared M-NEPCMs is lower than 3 °C, with an acceptable thermal reliability after the thermal cycling test. A pre-emulsification prior to the addition of deionized water in the emulsification is beneficial to the morphology of the capsules, as the phase change enthalpy can be increased by 123.7%.

Calorimetry investigations of milled α-tricalcium phosphate (α-TCP) powders to determine the formation enthalpies of α-TCP and X-ray amorphous tricalcium phosphate.

PubMed

Hurle, Katrin; Neubauer, Juergen; Bohner, Marc; Doebelin, Nicola; Goetz-Neunhoeffer, Friedlinde

2015-09-01

One α-tricalcium phosphate (α-TCP) powder was either calcined at 500°C to obtain fully crystalline α-TCP or milled for different durations to obtain α-TCP powders containing various amounts of X-ray amorphous tricalcium phosphate (ATCP). These powders containing between 0 and 71wt.% ATCP and up to 2.0±0.1wt.% β-TCP as minor phase were then hydrated in 0.1M Na2HPO4 aqueous solution and the resulting heat flows were measured by isothermal calorimetry. Additionally, the evolution of the phase composition during hydration was determined by in situ XRD combined with the G-factor method, an external standard method which facilitates the indirect quantification of amorphous phases. Maximum ATCP hydration was reached after about 1h, while that of crystalline α-TCP hydration occurred between 4 and 11h, depending on the ATCP content. An enthalpy of formation of -4065±6kJ/mol (T=23°C) was calculated for ATCP (Ca3(PO4)2), while for crystalline α-TCP (α-Ca3(PO4)2) a value of -4113±6kJ/mol (T=23°C) was determined. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Vaporization of protic ionic liquids derived from organic superbases and short carboxylic acids.

PubMed

Ribeiro, Filipe M S; Lima, Carlos F R A C; Vaz, Inês C M; Rodrigues, Ana S M C; Sapei, Erlin; Melo, André; Silva, Artur M S; Santos, Luís M N B F

2017-06-28

This work presents a comprehensive evaluation of the phase behaviour and cohesive enthalpy of protic ionic liquids (PILs) composed of 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) organic superbases with short-chain length (acetic, propionic and butyric) carboxylic acids. Glass transition temperatures, T g , and enthalpies of vaporization, ΔH vap , were measured for six [BH][A] (1 : 1) PILs (B = DBN, DBU; A = MeCOO, EtCOO, nPrCOO), revealing more significant changes upon increasing the number of -CH 2 - groups in the base than in the acid. The magnitude of ΔH vap evidences that liquid PILs have a high proportion of ions, although the results also indicate that in DBN PILs the concentration of neutral species is not negligible. In the gas phase, these PILs exist as a distribution of ion pairs and isolated neutral species, with speciation being dependent on the temperature and pressure conditions - at high temperatures and low pressures the separated neutral species dominate. The higher T g and ΔH vap of the DBU PILs are explained by the stronger basicity of DBU (as supported by NMR and computational calculations), which increases the extent of proton exchange and the ionic character of the corresponding PILs, resulting in stronger intermolecular interactions in condensed phases.

A Comprehensive Study on the Electronic State of Hydrogen in α-Phase PdH(D)x-Does a Chemical Bond Between Pd and H(D) Exist?

PubMed

Dekura, Shun; Kobayashi, Hirokazu; Ikeda, Ryuichi; Maesato, Mitsuhiko; Yoshino, Haruka; Ohba, Masaaki; Ishimoto, Takayoshi; Kawaguchi, Shogo; Kubota, Yoshiki; Yoshioka, Satoru; Matsumura, Syo; Sugiyama, Takeharu; Kitagawa, Hiroshi

2018-06-12

The palladium(Pd)-hydrogen(H) system is one of the most famous hydrogen storage systems. Although there has been much research on β-phase PdH(D)x, we comprehensively investigated the nature of the interaction between Pd and H(D) in α-phase PdH(D)x (x < 0.03 at 303 K), and revealed the existence of Pd-H(D) chemical bond for the first time, by various in situ experimental techniques and first-principles theoretical calculations. The lattice expansion by H(D) dissolution in the α-phase lattice suggests the existence of interaction between Pd and H(D). The decrease of magnetic susceptibility and the increase of electrical resistivity indicate that the electronic states are changed by the H(D) dissolution in the α phase. In situ solid-state 1H and 2H NMR results and first-principles theoretical calculations revealed that a Pd-H(D) chemical bond exists in the α phase, but the bonding character of the Pd-H(D) chemical bond in the α phase is quite different from that in the β phase; the nature of the Pd-H(D) chemical bond in the α phase is a localized covalent bond whereas that in the β phase is a metallic bond. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Research of human kidney thermal properties for the purpose of cryosurgery

NASA Astrophysics Data System (ADS)

Ponomarev, D. E.; Pushkarev, A. V.

2017-11-01

Calculation of the heat transfer is required to correctly predict the results of cryosurgery, cryopreservation, etc. One of the important initial parameters are the thermophysical properties of biological tissues. In the present study, the values of the heat capacity, cryoscopic temperature and enthalpy of the phase transition of the kidney samples in vitro were obtained by differential scanning calorimetry.

Hydrogen uptake characteristics of mischmetal based alloy

NASA Astrophysics Data System (ADS)

Jain, Ankur; Jain, R. K.; Jain, I. P.

Hydrogen storage properties of Mm 39.2Ni 42.1Mn 4.9Al 1.25Co 10.2Fe 2.35 alloy have been systematically studied in the present work. An attempt is made to relate the content of hydrogen with change in resistance. It is found that the resistance of material increases with the increase in value of H/ M due to hydrogen absorption. Pressure composition (P-C-T) isotherm using water displacement method has been investigated in the temperature and pressure ranges of 308 ≤ T ≤ 338 K and 0.5 ≤ P ≤ 10 bar, respectively. The P-C isotherms show the presence of two single α and β regions one mixed α + β phase. The maximum H (wt%) was found to be around 1.53 at 308 K and around 6 bar. Since enthalpy is an index of thermochemical stability of metal hydride the thermo dynamical parameters viz., the relative partial molar enthalpy (Δ H) and relative partial molar entropy (Δ S) of dissolved hydrogen have been calculated by plotting the Van't Hoff plot. The variation of Δ H and Δ S with the hydrogen concentration confirm the phase boundaries.

New systematic methodology for incorporating dynamic heat transfer modelling in multi-phase biochemical reactors.

PubMed

Fernández-Arévalo, T; Lizarralde, I; Grau, P; Ayesa, E

2014-09-01

This paper presents a new modelling methodology for dynamically predicting the heat produced or consumed in the transformations of any biological reactor using Hess's law. Starting from a complete description of model components stoichiometry and formation enthalpies, the proposed modelling methodology has integrated successfully the simultaneous calculation of both the conventional mass balances and the enthalpy change of reaction in an expandable multi-phase matrix structure, which facilitates a detailed prediction of the main heat fluxes in the biochemical reactors. The methodology has been implemented in a plant-wide modelling methodology in order to facilitate the dynamic description of mass and heat throughout the plant. After validation with literature data, as illustrative examples of the capability of the methodology, two case studies have been described. In the first one, a predenitrification-nitrification dynamic process has been analysed, with the aim of demonstrating the easy integration of the methodology in any system. In the second case study, the simulation of a thermal model for an ATAD has shown the potential of the proposed methodology for analysing the effect of ventilation and influent characterization. Copyright © 2014 Elsevier Ltd. All rights reserved.

Interaction of phloretin and 6-ketocholestanol with DPPC-liposomes as phospholipid model membranes.

PubMed

Auner, Barbara G; O'Neill, Michael A A; Valenta, Claudia; Hadgraft, Jonathan

2005-04-27

Phloretin and 6-ketocholestanol are penetration enhancers for percutaneous delivery of certain topically applied drugs. In the present study some physicochemical experiments have been performed to elucidate the mechanism of action of phloretin and 6-ketocholestanol. The penetration enhancing effect of phloretin and 6-ketocholestanol is believed to be due to their increase of the fluidity of the intercellular lipid bilayers of the stratum corneum. Phospholipid vesicles were chosen as a simple model to represent these bilayers. The effect of phloretin and 6-ketocholestanol on phase transition temperature and enthalpy was studied using differential scanning calorimetry. Beside of that the size of liposomes was monitored when the amount of penetration enhancer in the liposome preparation was changed. Addition of increasing amounts of phloretin and 6-ketocholestanol to the bilayer resulted in lowering of phase transition temperatures and increasing the enthalpy. Additionally the size of the liposomes was increased when penetration enhancer was added. The results suggest that phloretin as well as 6-ketocholestanol would interact with stratum corneum lipids in a similar manner, both reduce the diffusional resistance of the stratum corneum to drugs with balanced hydrophilic-lipophilic characteristics.

In Vitro-In Vivo Predictive Dissolution-Permeation-Absorption Dynamics of Highly Permeable Drug Extended-Release Tablets via Drug Dissolution/Absorption Simulating System and pH Alteration.

PubMed

Li, Zi-Qiang; Tian, Shuang; Gu, Hui; Wu, Zeng-Guang; Nyagblordzro, Makafui; Feng, Guo; He, Xin

2018-05-01

Each of dissolution and permeation may be a rate-limiting factor in the absorption of oral drug delivery. But the current dissolution test rarely took into consideration of the permeation property. Drug dissolution/absorption simulating system (DDASS) valuably gave an insight into the combination of drug dissolution and permeation processes happening in human gastrointestinal tract. The simulated gastric/intestinal fluid of DDASS was improved in this study to realize the influence of dynamic pH change on the complete oral dosage form. To assess the effectiveness of DDASS, six high-permeability drugs were chosen as model drugs, including theophylline (pK a1  = 3.50, pK a2  = 8.60), diclofenac (pK a  = 4.15), isosorbide 5-mononitrate (pK a  = 7.00), sinomenine (pK a  = 7.98), alfuzosin (pK a  = 8.13), and metoprolol (pK a  = 9.70). A general elution and permeation relationship of their commercially available extended-release tablets was assessed as well as the relationship between the cumulative permeation and the apparent permeability. The correlations between DDASS elution and USP apparatus 2 (USP2) dissolution and also between DDASS permeation and beagle dog absorption were developed to estimate the predictability of DDASS. As a result, the common elution-dissolution relationship was established regardless of some variance in the characteristic behavior between DDASS and USP2 for drugs dependent on the pH for dissolution. Level A in vitro-in vivo correlation between DDASS permeation and dog absorption was developed for drugs with different pKa. The improved DDASS will be a promising tool to provide a screening method on the predictive dissolution-permeation-absorption dynamics of solid drug dosage forms in the early-phase formulation development.

Materials corrosion and protection from first principles

NASA Astrophysics Data System (ADS)

Johnson, Donald F.

Materials erode under environmental stresses such as high temperature, high pressure, and mechanical shock/stress, but erosion is often exacerbated by chemical corrosion. In this dissertation, periodic density functional theory (DFT) is employed to simulate interfacial adhesion, absorption kinetics, bulk diffusion, and other material phenomena (e.g., hydrogen-enhanced decohesion and shock-induced phase changes) with the intention of understanding corrosion and subsequent failure processes and guiding the design of new protective coatings. This work examines corrosion and/or protection of materials ( i.e., Fe, Ni, W) with important applications: structural steel, gun tubes, high-pressure oil recovery vessels, jet engine turbine blades, and fusion reactor walls. We use DFT to model the pressure-induced, bcc-to-hcp phase transformation in Fe, in which a new low energy pathway is predicted exhibiting nonadiabatic behavior coupling magnetic and structural changes. Protection of steel is addressed in two aspects: interfacial adhesion of protective coatings and assessment of corrosion resistance provided by a surface alloy. First, the current chrome-coated steel system is examined where extremely strong adhesion is predicted at the Cr/Fe interface originating in strong spin correlations. A ceramic coating, SiC, is considered as a possible replacement for Cr. Strong adhesion is predicted, especially for C-Fe interfacial bonds. To assess corrosion resistance, we model ingress of two common corrosive elements, H and C, into two Fe alloys, FeAl and Fe3Si. Adsorption and absorption thermodynamics and kinetics, as well as bulk dissolution and diffusion are calculated in order to determine whether these two alloys can inhibit uptake of H and C. Relative to pure Fe, dissolved H and C are less stable in the alloys, as the dissolution enthalpy is predicted to be more endothermic. Overall, the energy barriers and rate constants for adsorbed H/C diffusing into Fe3Si subsurface layers suggests that alloying Fe with Si can be an effective means to limit uptake of these elements into steel. Spallation of protective layers on jet engine turbine blades is a problem that arises during thermal cycling. An alternative thermal barrier coating system involving MoSi2 is considered and calculations predict strong adhesion at the MoSi2/Ni interface. The interfacial bonding structure reveals a mixture of metallic and covalent cross-interface bonds. The adhesion energy is similar across all three MoSi2 facets studied. Upon exposure to oxygen, this MoSi2 alloy will form a strongly adhered oxide scale, which in turn may strongly adhere the heat shield material (yttria-stabilized zirconia), thereby potentially extending the lifetime of the barrier coating. Lastly, the interaction of hydrogen isotopes (fusion fuel) with tungsten (a proposed fusion reactor wall material) is examined. Exothermic dissociative adsorption is predicted, along with endothermic absorption and dissolution. Surface-to-subsurface diffusion energy barriers for H incorporation into bulk W are large and the corresponding outward diffusion barriers are very small. In bulk W, deep energetic traps (trapping multiple H atoms) are predicted at vacancy defects. Thus, under high neutron fluxes that will produce vacancies in W, H are predicted to collect at these vacancies. In turn, locally high concentrations of H at such vacancies will enhance decohesion of bulk W, consistent with observed blistering under deuterium implantation. Limiting vacancy formation may be key to the survival of W as a fusion reactor wall material.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Detwiler, Russell

Fractures provide flow paths that can potentially lead to fast migration of fluids or contaminants. A number of energy-­related applications involve fluid injections that significantly perturb both the pressures and chemical composition of subsurface fluids. These perturbations can cause both mechanical deformation and chemical alteration of host rocks with potential for significant changes in permeability. In fractured rock subjected to coupled chemical and mechanical stresses, it can be difficult to predict the sign of permeability changes, let alone the magnitude. This project integrated experimental and computational studies to improve mechanistic understanding of these coupled processes and develop and test predictivemore » models and monitoring techniques. The project involved three major components: (1) study of two-­phase flow processes involving mass transfer between phases and dissolution of minerals along fracture surfaces (Detwiler et al., 2009; Detwiler, 2010); (2) study of fracture dissolution in fractures subjected to normal stresses using experimental techniques (Ameli, et al., 2013; Elkhoury et al., 2013; Elkhoury et al., 2014) and newly developed computational models (Ameli, et al., 2014); (3) evaluation of electrical resistivity tomography (ERT) as a method to detect and quantify gas leakage through a fractured caprock (Breen et al., 2012; Lochbuhler et al., 2014). The project provided support for one PhD student (Dr. Pasha Ameli; 2009-­2013) and partially supported a post-­doctoral scholar (Dr. Jean Elkhoury; 2010-­2013). In addition, the project provided supplemental funding to support collaboration with Dr. Charles Carrigan at Lawrence Livermore National Laboratory in connection with (3) and supported one MS student (Stephen Breen; 2011-­2013). Major results from each component of the project include the following: (1) Mineral dissolution in fractures occupied by two fluid phases (e.g., oil-­water or water-­CO{sub 2}) causes changes in local capillary forces and redistribution of fluids. These coupled processes enhance channel formation and the potential for development of fast flow paths through fractures. (2) Dissolution in fractures subjected to normal stress can result in behaviors ranging from development of dissolution channels and rapid permeability increases to fracture healing and significant permeability decreases. The timescales associated with advective transport of dissolved ions in the fracture, mineral dissolution rates, and diffusion within the adjacent porous matrix dictate the sign and magnitude of the resulting permeability changes. Furthermore, a high--resolution mechanistic model that couples elastic deformation of contacts and aperture-­dependent dissolution rates predicts the range of observed behaviors reasonably well. (3) ERT has potential as a tool for monitoring gas leakage in deep formations. Using probabilistic inversion methods further enhances the results by providing uncertainty estimates of inverted parameters.« less

Thermal characterization of aminium nitrate nanoparticles.

PubMed

Salo, Kent; Westerlund, Jonathan; Andersson, Patrik U; Nielsen, Claus; D'Anna, Barbara; Hallquist, Mattias

2011-10-27

Amines are widely used and originate from both anthropogenic and natural sources. Recently, there is, in addition, a raised concern about emissions of small amines formed as degradation products of the more complex amines used in CO(2) capture and storage systems. Amines are bases and can readily contribute to aerosol mass and number concentration via acid-base reactions but are also subject to gas phase oxidation forming secondary organic aerosols. To provide more insight into the atmospheric fate of the amines, this paper addresses the volatility properties of aminium nitrates suggested to be produced in the atmosphere from acid-base reactions of amines with nitric acid. The enthalpy of vaporization has been determined for the aminium nitrates of mono-, di-, trimethylamine, ethylamine, and monoethanolamine. The enthalpy of vaporization was determined from volatility measurements of laboratory generated aerosol nanoparticles using a volatility tandem differential mobility analyzer set up. The determined enthalpy of vaporization for aminium nitrates range from 54 up to 74 kJ mol(-1), and the calculated vapor pressures at 298 K are around 10(-4) Pa. These values indicate that aminium nitrates can take part in gas-to-particle partitioning at ambient conditions and have the potential to nucleate under high NO(x) conditions, e.g., in combustion plumes.

Nondisruptive Dissolution of Hyperpolarized 129 Xe into Viscous Aqueous and Organic Liquid Crystalline Environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Truxal, Ashley E.; Slack, Clancy C.; Gomes, Muller D.

2016-03-08

Studies of hyperpolarized xenon-129 in media such as liquid crystals and cell suspensions are in demand for applications ranging from biomedical imaging to materials engineering but have been hindered by the inability to bubble Xe through the desired media as a result of viscosity or perturbations caused by bubbles. This research reports on a device that can be reliably used to dissolve hp- 129 Xe into viscous aqueous and organic samples without bubbling. This method is robust, requires small sample volumes ( < 60 μL), is compatible with existing NMR hardware, and is made from readily available materials. Experiments showmore » that Xe can be introduced into viscous and aligned media without disrupting molecular order. We detected dissolved xenon in an aqueous liquid crystal that is disrupted by the shear forces of bubbling, and we observed liquid-crystal phase transitions in (MBBA). This tool allows an entirely new class of samples to be investigated by hyperpolarized-gas NMR spectroscopy. Blending into the crowd: A new device that facilitates the direct dissolution of hyperpolarized 129 Xe into viscous liquid-crystalline media is presented. 129 Xe and 2 H NMR spectra show the nondisruptive dissolution of xenon, the presence of ordered phases, and, in the case of the thermotropic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline, a nematic-isotropic phase transition.« less

Substantiation of Epitaxial Growth of Diamond Crystals on the Surface of Carbide Fe3AlC0.66 Phase Nanoparticles.

PubMed

Dzevin, Ievgenij M; Mekhed, Alexander A

2017-12-01

Samples of Fe-Al-C alloys of varying composition were synthesized under high pressures and temperatures. From X-ray analysis data, only K-phase with usual for it average parameter of elemental lattice cell, a = 0.376 nm, carbide Fe 3 C and cubic diamond reflexes were present before and after cooling to the temperature of liquid nitrogen.Calculations were made of the parameters of unit cells, the enthalpy of formation of the Fe 3 AlC, Fe 3.125 Al 0.825 C 0.5 , Fe 3.5 Al 0.5 C 0.5 , Fe 3.5 Al 0.5 C, Fe 3 Al 0.66 C 0.66 , and Fe 3 AlC 0.66 unit cells and crystallographic planes were identified on which epitaxial growth of the diamond phase was possible, using density functional theory as implemented in the WIEN2k package.The possibility of epitaxial growth of diamond crystals on Fe 3 AlC 0.66 (K-phase) nanoparticles was, therefore, demonstrated. The [200] plane was established to be the most suitable plane for diamond growth, having four carbon atoms arranged in a square and a central vacancy which can be occupied by carbon during thermal-and-pressure treatment. Distances between carbon atoms in the [200] plane differ by only 5% from distances between the carbon atoms of a diamond. The electronic structure and energetic parameters of the substrate were also investigated. It was shown that the substrate with at least four intermediate layers of K-phase exhibits signs of stability such as negative enthalpy of formation and the Fermi level falling to minimum densities of states.

Urea-temperature phase diagrams capture the thermodynamics of denatured state expansion that accompany protein unfolding.

PubMed

Tischer, Alexander; Auton, Matthew

2013-09-01

We have analyzed the thermodynamic properties of the von Willebrand factor (VWF) A3 domain using urea-induced unfolding at variable temperature and thermal unfolding at variable urea concentrations to generate a phase diagram that quantitatively describes the equilibrium between native and denatured states. From this analysis, we were able to determine consistent thermodynamic parameters with various spectroscopic and calorimetric methods that define the urea-temperature parameter plane from cold denaturation to heat denaturation. Urea and thermal denaturation are experimentally reversible and independent of the thermal scan rate indicating that all transitions are at equilibrium and the van't Hoff and calorimetric enthalpies obtained from analysis of individual thermal transitions are equivalent demonstrating two-state character. Global analysis of the urea-temperature phase diagram results in a significantly higher enthalpy of unfolding than obtained from analysis of individual thermal transitions and significant cross correlations describing the urea dependence of ΔH0 and ΔCP0 that define a complex temperature dependence of the m-value. Circular dichroism (CD) spectroscopy illustrates a large increase in secondary structure content of the urea-denatured state as temperature increases and a loss of secondary structure in the thermally denatured state upon addition of urea. These structural changes in the denatured ensemble make up ∼40% of the total ellipticity change indicating a highly compact thermally denatured state. The difference between the thermodynamic parameters obtained from phase diagram analysis and those obtained from analysis of individual thermal transitions illustrates that phase diagrams capture both contributions to unfolding and denatured state expansion and by comparison are able to decipher these contributions. © 2013 The Protein Society.

An Indirect Method for Vapor Pressure and Phase Change Enthalpy Determination by Thermogravimetry

NASA Astrophysics Data System (ADS)

Giani, Samuele; Riesen, Rudolf; Schawe, Jürgen E. K.

2018-07-01

Vapor pressure is a fundamental property of a pure substance. This property is the pressure of a compound's vapor in thermodynamic equilibrium with its condensed phase (solid or liquid). When phase equilibrium condition is met, phase coexistence of a pure substance involves a continuum interplay of vaporization or sublimation to gas and condensation back to their liquid or solid form, respectively. Thermogravimetric analysis (TGA) techniques are based on mass loss determination and are well suited for the study of such phenomena. In this work, it is shown that TGA method using a reference substance is a suitable technique for vapor pressure determination. This method is easy and fast because it involves a series of isothermal segments. In contrast to original Knudsen's approach, where the use of high vacuum is mandatory, adopting the proposed method a given experimental setup is calibrated under ambient pressure conditions. The theoretical framework of this method is based on a generalization of Langmuir equation of free evaporation: The real strength of the proposed method is the ability to determine the vapor pressure independently of the molecular mass of the vapor. A demonstration of this method has been performed using the Clausius-Clapeyron equation of state to derive the working equation. This algorithm, however, is adaptive and admits the use of other equations of state. The results of a series of experiments with organic molecules indicate that the average difference of the measured and the literature vapor pressure amounts to about 5 %. Vapor pressure determined in this study spans from few mPa up to several kPa. Once the p versus T diagram is obtained, phase transition enthalpy can additionally be calculated from the data.

Calculating the enthalpy of vaporization for ionic liquid clusters.

PubMed

Kelkar, Manish S; Maginn, Edward J

2007-08-16

Classical atomistic simulations are used to compute the enthalpy of vaporization of a series of ionic liquids composed of 1-alkyl-3-methylimidazolium cations paired with the bis(trifluoromethylsulfonyl)imide anion. The calculations show that the enthalpy of vaporization is lowest for neutral ion pairs. The enthalpy of vaporization increases by about 40 kJ/mol with the addition of each ion pair to the vaporizing cluster. Non-neutral clusters have much higher vaporization enthalpies than their neutral counterparts and thus are not expected to make up a significant fraction of volatile species. The enthalpy of vaporization increases slightly as the cation alkyl chain length increases and as temperature decreases. The calculated vaporization enthalpies are consistent with two sets of recent experimental measurements as well as with previous atomistic simulations.

Solubility prediction of naphthalene in carbon dioxide from crystal microstructure

NASA Astrophysics Data System (ADS)

Sang, Jiarong; Jin, Junsu; Mi, Jianguo

2018-03-01

Crystals dissolved in solvents are ubiquitous in both natural and artificial systems. Due to the complicated structures and asymmetric interactions between the crystal and solvent, it is difficult to interpret the dissolution mechanism and predict solubility using traditional theories and models. Here we use the classical density functional theory (DFT) to describe the crystal dissolution behavior. As an example, naphthalene dissolved in carbon dioxide (CO2) is considered within the DFT framework. The unit cell dimensions and microstructure of crystalline naphthalene are determined by minimizing the free-energy of the crystal. According to the microstructure, the solubilities of naphthalene in CO2 are predicted based on the equality of naphthalene's chemical potential in crystal and solution phases, and the interfacial structures and free-energies between different crystal planes and solution are determined to investigate the dissolution mechanism at the molecular level. The theoretical predictions are in general agreement with the available experimental data, implying that the present model is quantitatively reliable in describing crystal dissolution.

Influence of Coformer Stoichiometric Ratio on Pharmaceutical Cocrystal Dissolution: Three Cocrystals of Carbamazepine/4-Aminobenzoic Acid

PubMed Central

Li, Zi; Matzger, Adam J.

2016-01-01

Cocrystallization is a technique to optimize solid forms that shows great potential to improve the solubility of active pharmaceutical ingredients (APIs). In some systems, an API can form cocrystals in multiple stoichiometries with the same coformer. However, it remains unclear how coformer stoichiometry influences solubility. This paper investigates the pharmaceutical:coformer pair carbamazepine (CBZ)/p-aminobenzoic acid (PABA); both CBZ/PABA 1:1 and 2:1 cocrystals are known, and a novel 4:1 CBZ/PABA cocrystal is reported here. The 4:1 cocrystal is structurally characterized, and phase stability data suggest that it is a thermodynamically unstable form. Dissolution experiments show that there is no correlation between the cocrystal stoichiometry and dissolution rate in this system. On the other hand, with the relatively weak intermolecular interactions, metastable forms can be beneficial to dissolution rate, which suggests that more effort should be devoted to cocrystal production with kinetic growth methods. PMID:26837376

Formulation and Solid State Characterization of Nicotinamide-based Co-crystals of Fenofibrate

PubMed Central

Shewale, Sheetal; Shete, A. S.; Doijad, R. C.; Kadam, S. S.; Patil, V. A.; Yadav, A. V.

2015-01-01

The present investigation deals with formulation of nicotinamide-based co-crystals of fenofibrate by different methods and solid-state characterization of the prepared co-crystals. Fenofibrate and nicotinamide as a coformer in 1:1 molar ratio were used to formulate molecular complexes by kneading, solution crystallization, antisolvent addition and solvent drop grinding methods. The prepared molecular complexes were characterized by powder X-ray diffractometry, differential scanning calorimetry, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy and in vitro dissolution study. Considerable improvement in the dissolution rate of fenofibrate from optimized co-crystal formulation was due to an increased solubility that is attributed to the super saturation from the fine co-crystals is faster because of large specific surface area of small particles and prevention of phase transformation to pure fenofibrate. In vitro dissolution study showed that the formation of co-crystals improves the dissolution rate of fenofibrate. Nicotinamide forms the co-crystals with fenofibrate, theoretically and practically. PMID:26180279

Effect of the microstructure of Ti-5Mo on the anodic dissolution in H/sub 2/SO/sub 4/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Y.J.; Oriani, R.A.

1987-04-01

The effect of microstructure of the Ti-5Mo alloy on its anodic dissolution rate in sulfuric acid solution at various temperatures has been investigated. TiMo alloys exhibit a region of increased dissolution rate in the vicinity of +0.20 V (saturated calomel electrode (SCE)) in 10% H/sub 2/SO/sub 4/, the same potential region in which pure Mo exhibits a large anodic dissolution rate. Aging of Ti-5Mo at 350 C was found to lead to the formation of ..omega.. phase. Heat treatment caused larger passive currents in 10% H/sub 2/SO/sub 4/, but the critical passivation potentials and corrosion potentials were not significantly affected.more » Molybdenum was enriched in the oxide formed on aged Ti-5Mo at +0.23 V (SCE), in comparison with the Mo concentration found in the oxide on as-received Ti-5Mo.« less

Attenuation of Glass Dissolution in the Presence of Natural Additives

NASA Technical Reports Server (NTRS)

Sang, Jing C.; Barkatt, Aaron; OKeefe, John A.

1993-01-01

The study described here explored the dissolution kinetics of glasses in aqueous environments in systems which included a variety of natural crystalline solids in addition to the glass itself and the aqueous phase. The results demonstrated the possibility of a dramatic decrease in the rate of dissolution of silicate glass in the presence of certain varieties of olivine-based materials. This decrease in dissolution rate was shown to be due to the fact that these additives consist mostly of Mg-based material but also contain minor amounts of Al and Ca. The combined presence of Mg with these minor species affected the corrosion rate of the glass as a whole, including its most soluble components such as boron. The study has potentially important implications to the durability of glasses exposed to natural environments. The results may be relevant to the use of active backfill materials in burial sites for nuclear waste glasses as well as to better understanding of the environmental degradation of natural and ancient glasses.

The effects of Na on high pressure phases of CuIn(0.5)Ga(0.5)Se(2) from ab initio calculation.

PubMed

Pluengphon, P; Bovornratanaraks, T; Vannarat, S; Pinsook, U

2012-03-07

The effects of Na atoms on high pressure structural phase transitions of CuIn(0.5)Ga(0.5)Se(2) (CIGS) were studied by an ab initio method using density functional theory. At ambient pressure, CIGS is known to have chalcopyrite (I42d) structure. The high pressure phase transitions of CIGS were proposed to be the same as the order in the CuInSe(2) phase transitions which are I42d → Fm3m → Cmcm structures. By using the mixture atoms method, the Na concentration in CIGS was studied at 0.1, 1.0 and 6.25%. The positive mixing enthalpy of Na at In/Ga sites (Na(InGa)) is higher than that of Na at Cu sites (Na(Cu)). It confirmed previous studies that Na preferably substitutes on the Cu sites more than the (In, Ga) sites. From the energy-volume curves, we found that the effect of the Na substitutes is to reduce the hardness of CIGS under high pressure. The most significant effects occur at 6.25% Na. We also found that the electronic density of states of CIGS near the valence band maximum is increased noticeably in the chalcopyrite phase. The band gap is close in the cubic and orthorhombic phases. Also, the Na(Cu)-Se bond length in the chalcopyrite phase is significantly reduced at 6.25% Na, compared with the pure Cu-Se bond length. Consequently, the energy band gap in this phase is wider than in pure CIGS, and the gap increased at the rate of 31 meV GPa(-1) under pressure. The Na has a small effect on the transition pressure. The path of transformation from the cubic to orthorhombic phase was derived. The Cu-Se plane in the cubic phase displaced relatively parallel to the (In, Ga)-Se plane by 18% in order to transform to the Cmcm phase. The enthalpy barrier is 0.020 eV/atom, which is equivalent to a thermal energy of 248 K. We predicted that Fm3m and Cmcm can coexist in some pressure range.

Arsenic interactions with a fullerene-like BN cage in the vacuum and aqueous phase.

PubMed

Beheshtian, Javad; Peyghan, Ali Ahmadi; Bagheri, Zargham

2013-02-01

Adsorption of arsenic ions, As (III and V), on the surface of fullerene-like B(12)N(12) cage has been explored in vacuum and aqueous phase using density functional theory in terms of Gibbs free energies, enthalpies, geometry, and density of state analysis. It was found that these ions can be strongly chemisorbed on the surface of the cluster in both vacuum and aqueous phase, resulting in significant changes in its electronic properties so that the cluster transforms from a semi-insulator to a semiconductor. The solvent significantly affects the geometry parameters and electronic properties of the As/B(12)N(12) complexes and the interaction between components is considerably weaker in the aqueous phase than that in the vacuum.

The chemistry and isotopic composition of waters in the low-enthalpy geothermal system of Cimino-Vico Volcanic District, Italy

USGS Publications Warehouse

Battistel, Maria; Hurwitz, Shaul; Evans, William; Barbieri, Maurizio

2017-01-01

Geothermal energy exploration is based in part on interpretation of the chemistry, temperature, and discharge rate of thermal springs. Here we present the major element chemistry and the δD, δ18O, 87Sr/86Sr and δ11B isotopic ratio of groundwater from the low-enthalpy geothermal system near the city of Viterbo in the Cimino-Vico volcanic district of west-Central Italy. The geothermal system hosts many thermal springs and gas vents, but the resource is still unexploited. Water chemistry is controlled by mixing between low salinity,HCO3-rich fresh waters (<24.2°C) flowing in shallow volcanic rocks and SO4-rich thermal waters (25.3°C to 62.2°C) ascending from deep, high permeability Mesozoic limestones. The (equivalent) SO4/Cl (0.01–0.02), Na/Cl (2.82–5.83) and B/Cl ratios (0.02–0.38) of thermal waters differs from the ratios in other geothermal systems from Central Italy, probably implying a lack of hydraulic continuity across the region. The δ18O (−6.6‰ to −5.9‰) and δD (−40.60‰ to −36.30‰) isotopic composition of spring water suggest that the recharge area for the geothermal system is the summit region of Mount Cimino. The strontium isotope ratios (87Sr/86Sr) of thermal waters (0.70797–0.70805) are consistent with dissolution of the Mesozoic evaporite-carbonate units that constitute the reservoir, and the ratios of cold fresh waters mainly reflect shallow circulation through the volcanic cover and some minor admixture (<10%) of thermal water as well. The boron isotopic composition (δ11B) of fresh waters (−5.00 and 6.12‰) is similar to that of the volcanic cover, but the δ11B of thermal waters (−8.37‰ to −4.12‰) is a mismatch for the Mesozoic reservoir rocks and instead reflects dissolution of secondary boron minerals during fluid ascent through flysch units that overlie the reservoir. A slow and tortuous ascent enhances extraction of boron but also promotes conductive cooling, partially masking the heat present in the reservoir. Overall data from this study is consistent with previous studies that concluded that the geothermal system has a large energy potential.

Studies on dissolution enhancement and mathematical modeling of drug release of a poorly water-soluble drug using water-soluble carriers.

PubMed

Ahuja, Naveen; Katare, Om Prakash; Singh, Bhupinder

2007-01-01

Role of various water-soluble carriers was studied for dissolution enhancement of a poorly soluble model drug, rofecoxib, using solid dispersion approach. Diverse carriers viz. polyethylene glycols (PEG 4000 and 6000), polyglycolized fatty acid ester (Gelucire 44/14), polyvinylpyrollidone K25 (PVP), poloxamers (Lutrol F127 and F68), polyols (mannitol, sorbitol), organic acid (citric acid) and hydrotropes (urea, nicotinamide) were investigated for the purpose. Phase-solubility studies revealed AL type of curves for each carrier, indicating linear increase in drug solubility with carrier concentration. The sign and magnitude of the thermodynamic parameter, Gibbs free energy of transfer, indicated spontaneity of solubilization process. All the solid dispersions showed dissolution improvement vis-à-vis pure drug to varying degrees, with citric acid, PVP and poloxamers as the most promising carriers. Mathematical modeling of in vitro dissolution data indicated the best fitting with Korsemeyer-Peppas model and the drug release kinetics primarily as Fickian diffusion. Solid state characterization of the drug-poloxamer binary system using XRD, FTIR, DSC and SEM techniques revealed distinct loss of drug crystallinity in the formulation, ostensibly accounting for enhancement in dissolution rate.

A dissolution-precipitation mechanism is at the origin of concrete creep in moist environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pignatelli, Isabella; Kumar, Aditya; Alizadeh, Rouhollah

Long-term creep (i.e., deformation under sustained load) is a significant material response that needs to be accounted for in concrete structural design. However, the nature and origin of concrete creep remain poorly understood and controversial. Here, we propose that concrete creep at relative humidity ≥ 50%, but fixed moisture content (i.e., basic creep), arises from a dissolution-precipitation mechanism, active at nanoscale grain contacts, as has been extensively observed in a geological context, e.g., when rocks are exposed to sustained loads, in liquid-bearing environments. Based on micro-indentation and vertical scanning interferometry data and molecular dynamics simulations carried out on calcium–silicate–hydrate (C–S–H),more » the major binding phase in concrete, of different compositions, we show that creep rates are correlated with dissolution rates—an observation which suggests a dissolution-precipitation mechanism as being at the origin of concrete creep. C–S–H compositions featuring high resistance to dissolution, and, hence, creep are identified. Analyses of the atomic networks of such C–S–H compositions using topological constraint theory indicate that these compositions present limited relaxation modes on account of their optimally connected (i.e., constrained) atomic networks.« less

A dissolution-precipitation mechanism is at the origin of concrete creep in moist environments.

PubMed

Pignatelli, Isabella; Kumar, Aditya; Alizadeh, Rouhollah; Le Pape, Yann; Bauchy, Mathieu; Sant, Gaurav

2016-08-07

Long-term creep (i.e., deformation under sustained load) is a significant material response that needs to be accounted for in concrete structural design. However, the nature and origin of concrete creep remain poorly understood and controversial. Here, we propose that concrete creep at relative humidity ≥ 50%, but fixed moisture content (i.e., basic creep), arises from a dissolution-precipitation mechanism, active at nanoscale grain contacts, as has been extensively observed in a geological context, e.g., when rocks are exposed to sustained loads, in liquid-bearing environments. Based on micro-indentation and vertical scanning interferometry data and molecular dynamics simulations carried out on calcium-silicate-hydrate (C-S-H), the major binding phase in concrete, of different compositions, we show that creep rates are correlated with dissolution rates-an observation which suggests a dissolution-precipitation mechanism as being at the origin of concrete creep. C-S-H compositions featuring high resistance to dissolution, and, hence, creep are identified. Analyses of the atomic networks of such C-S-H compositions using topological constraint theory indicate that these compositions present limited relaxation modes on account of their optimally connected (i.e., constrained) atomic networks.

Effects of ranitidine (antacid), food, and formulation on the pharmacokinetics of fostamatinib: results from five phase I clinical studies.

PubMed

Flanagan, Talia; Martin, Paul; Gillen, Michael; Mathews, David; Lisbon, Eleanor; Kruusmägi, Martin

2017-02-01

Fostamatinib is an orally dosed phosphate prodrug that is cleaved by intestinal alkaline phosphatase to the active metabolite R406. Clinical studies were performed to assess the effect of food and ranitidine on exposure, to support in vitro-in vivo relationships (IVIVR) understanding and formulation transitions and to investigate absolute oral bioavailability. A series of in vitro dissolution and clinical pharmacokinetic studies were performed to support the design and introduction of a new formulation, understand the impact of changes in in vitro dissolution on in vivo performance for two fostamatinib formulations, to characterize the effects of food and ranitidine on exposure, and determine the absolute oral bioavailability. The in vivo performance of fostamatinib was generally insensitive to changes in in vitro dissolution performance, although marked slowing of the dissolution rate did impact exposures. Food and ranitidine had minor effects on R406 exposure that were not considered clinically relevant. The absolute oral bioavailability of fostamatinib was 54.6 %. The absolute oral bioavailability of fostamatinib was ~55 %. Food and ranitidine had minor effects on R406 exposure. An in vitro dissolution versus clinical performance relationship was determined that supported formulation transitions.

Dilution physics modeling: Dissolution/precipitation chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Onishi, Y.; Reid, H.C.; Trent, D.S.

This report documents progress made to date on integrating dilution/precipitation chemistry and new physical models into the TEMPEST thermal-hydraulics computer code. Implementation of dissolution/precipitation chemistry models is necessary for predicting nonhomogeneous, time-dependent, physical/chemical behavior of tank wastes with and without a variety of possible engineered remediation and mitigation activities. Such behavior includes chemical reactions, gas retention, solids resuspension, solids dissolution and generation, solids settling/rising, and convective motion of physical and chemical species. Thus this model development is important from the standpoint of predicting the consequences of various engineered activities, such as mitigation by dilution, retrieval, or pretreatment, that can affectmore » safe operations. The integration of a dissolution/precipitation chemistry module allows the various phase species concentrations to enter into the physical calculations that affect the TEMPEST hydrodynamic flow calculations. The yield strength model of non-Newtonian sludge correlates yield to a power function of solids concentration. Likewise, shear stress is concentration-dependent, and the dissolution/precipitation chemistry calculations develop the species concentration evolution that produces fluid flow resistance changes. Dilution of waste with pure water, molar concentrations of sodium hydroxide, and other chemical streams can be analyzed for the reactive species changes and hydrodynamic flow characteristics.« less

Ionic liquids: differential scanning calorimetry as a new indirect method for determination of vaporization enthalpies.

PubMed

Verevkin, Sergey P; Emel'yanenko, Vladimir N; Zaitsau, Dzmitry H; Ralys, Ricardas V; Schick, Christoph

2012-04-12

Differential scanning calorimetry (DSC) has been used to measure enthalpies of synthesis reactions of the 1-alkyl-3-methylimidazolium bromide [C(n)mim][Br] ionic liquids from 1-methylimidazole and n-alkyl bromides (with n = 4, 5, 6, 7, and 8). The optimal experimental conditions have been elaborated. Enthalpies of formation of these ionic liquids in the liquid state have been determined using the DSC results according to the Hess Law. The ideal-gas enthalpies of formation of [C(n)mim][Br] were calculated using the methods of quantum chemistry. They were used together with the DSC results to derive indirectly the enthalpies of vaporization of the ionic liquids under study. In order to validate the indirect determination, the experimental vaporization enthalpy of [C(4)mim][Br] was measured by using a quartz crystal microbalance (QCM). The combination of reaction enthalpy measurements by DSC with modern high-level first-principles calculations opens valuable indirect thermochemical options to obtain values of vaporization enthalpies of ionic liquids.

Dissolution kinetics of iron-, manganese-, and copper-containing synthetic hydroxyapatites

NASA Technical Reports Server (NTRS)

Sutter, B.; Hossner, L. R.; Ming, D. W.

2005-01-01

Micronutrient-substituted synthetic hydroxyapatite (SHA) is being evaluated by the National Aeronautics and Space Administration's (NASA) Advanced Life Support (ALS) Program for crop production on long-duration human missions to the International Space Station or for future Lunar or Martian outposts. The stirred-flow technique was utilized to characterize Ca, P, Fe, Mn, and Cu release characteristics from Fe-, Mn-, and Cu-containing SHA in deionized (DI) water, citric acid, and diethylene-triamine-pentaacetic acid (DTPA). Initially, Ca and P release rates decreased rapidly with time and were controlled by a non-SHA calcium phosphate phase(s) with low Ca/P solution molar ratios (0.91-1.51) relative to solid SHA ratios (1.56-1.64). At later times, Ca/P solution molar ratios (1.47-1.79) were near solid SHA ratios and release rates decreased slowly indicating that SHA controlled Ca and P release. Substituted SHA materials had faster dissolution rates relative to unsubstituted SHA. The initial metal release rate order was Mn >> Cu > Fe which followed metal-oxide/phosphate solubility suggesting that poorly crystalline metal-oxides/phosphates were dominating metal release. Similar metal release rates for all substituted SHA (approximately 0.01 cmol kg-1 min-1) at the end of the DTPA experiment indicated that SHA dissolution was supplying the metals into solution and that poorly crystalline metal-oxide/phosphates were not controlling metal release. Results indicate that non-SHA Ca-phosphate phases and poorly crystalline metal-oxide/phosphates will contribute Ca, P, and metals. After these phases have dissolved, substituted SHA will be the source of Ca, P, and metals for plants.

Pressure induced structural phase transition of OsB 2: First-principles calculations

NASA Astrophysics Data System (ADS)

Ren, Fengzhu; Wang, Yuanxu; Lo, V. C.

2010-04-01

Orthorhombic OsB 2 was synthesized at 1000 °C and its compressibility was measured by using the high-pressure X-ray diffraction in a Diacell diamond anvil cell from ambient pressure to 32 GPa [R.W. Cumberland, et al. (2005)]. First-principles calculations were performed to study the possibility of the phase transition of OsB 2. An analysis of the calculated enthalpy shows that orthorhombic OsB 2 can transfer to the hexagonal phase at 10.8 GPa. The calculated results with the quasi-harmonic approximation indicate that this phase transition pressure is little affected by the thermal effect. The calculated phonon band structure shows that the hexagonal P 6 3/ mmc structure (high-pressure phase) is stable for OsB 2. We expect the phase transition can be further confirmed by the experimental work.

Thermodynamic study of the gaseous thorium carbides, ThC, ThC/sub 2/, ThC/sub 3/, ThC/sub 4/, ThC/sub 5/, and ThC/sub 6/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, S.K.; Gingerich, K.A.

Six gaseous carbides of thorium, ThC/sub n/(n=1--6), have been identified in a Knudsen effusion mass spectrometric investigation of the vapor phase above a thorium--uranium--rhodium--graphite system at high temperatures. The partial pressures of the thorium containing species were measured as a function of temperature in the 2300--2700 /sup 0/K range. Third law enthalpies for the reactions Th(g)+nC(graphite) =ThC/sub n/, n=1 to 6, and of various other homogeneous and heterogeneous reactions were evaluated. By combining the experimental enthalpies with appropriate thermodynamic data taken from literature, the following values for the atomization energies ..delta..H /sup 0//sub at,298/, and standard heats of formation ..delta..H/supmore » tsdegree//sub f/,298 of thorium carbides have been derived:« less

Equation of state for shock compression of distended solids

NASA Astrophysics Data System (ADS)

Grady, Dennis; Fenton, Gregg; Vogler, Tracy

2014-05-01

Shock Hugoniot data for full-density and porous compounds of boron carbide, silicon dioxide, tantalum pentoxide, uranium dioxide and playa alluvium are investigated for the purpose of equation-of-state representation of intense shock compression. Complications of multivalued Hugoniot behavior characteristic of highly distended solids are addressed through the application of enthalpy-based equations of state of the form originally proposed by Rice and Walsh in the late 1950's. Additive measures of cold and thermal pressure intrinsic to the Mie-Gruneisen EOS framework is replaced by isobaric additive functions of the cold and thermal specific volume components in the enthalpy-based formulation. Additionally, experimental evidence reveals enhancement of shock-induced phase transformation on the Hugoniot with increasing levels of initial distension for silicon dioxide, uranium dioxide and possibly boron carbide. Methods for addressing this experimentally observed feature of the shock compression are incorporated into the EOS model.

Equation of State for Shock Compression of High Distension Solids

NASA Astrophysics Data System (ADS)

Grady, Dennis

2013-06-01

Shock Hugoniot data for full-density and porous compounds of boron carbide, silicon dioxide, tantalum pentoxide, uranium dioxide and playa alluvium are investigated for the purpose of equation-of-state representation of intense shock compression. Complications of multivalued Hugoniot behavior characteristic of highly distended solids are addressed through the application of enthalpy-based equations of state of the form originally proposed by Rice and Walsh in the late 1950's. Additivity of cold and thermal pressure intrinsic to the Mie-Gruneisen EOS framework is replaced by isobaric additive functions of the cold and thermal specific volume components in the enthalpy-based formulation. Additionally, experimental evidence supports acceleration of shock-induced phase transformation on the Hugoniot with increasing levels of initial distention for silicon dioxide, uranium dioxide and possibly boron carbide. Methods for addressing this experimentally observed facet of the shock compression are introduced into the EOS model.

Field-scale Prediction of Enhanced DNAPL Dissolution Using Partitioning Tracers and Flow Pattern Effects

NASA Astrophysics Data System (ADS)

Wang, F.; Annable, M. D.; Jawitz, J. W.

2012-12-01

The equilibrium streamtube model (EST) has demonstrated the ability to accurately predict dense nonaqueous phase liquid (DNAPL) dissolution in laboratory experiments and numerical simulations. Here the model is applied to predict DNAPL dissolution at a PCE-contaminated dry cleaner site, located in Jacksonville, Florida. The EST is an analytical solution with field-measurable input parameters. Here, measured data from a field-scale partitioning tracer test were used to parameterize the EST model and the predicted PCE dissolution was compared to measured data from an in-situ alcohol (ethanol) flood. In addition, a simulated partitioning tracer test from a calibrated spatially explicit multiphase flow model (UTCHEM) was also used to parameterize the EST analytical solution. The ethanol prediction based on both the field partitioning tracer test and the UTCHEM tracer test simulation closely matched the field data. The PCE EST prediction showed a peak shift to an earlier arrival time that was concluded to be caused by well screen interval differences between the field tracer test and alcohol flood. This observation was based on a modeling assessment of potential factors that may influence predictions by using UTCHEM simulations. The imposed injection and pumping flow pattern at this site for both the partitioning tracer test and alcohol flood was more complex than the natural gradient flow pattern (NGFP). Both the EST model and UTCHEM were also used to predict PCE dissolution under natural gradient conditions, with much simpler flow patterns than the forced-gradient double five spot of the alcohol flood. The NGFP predictions based on parameters determined from tracer tests conducted with complex flow patterns underestimated PCE concentrations and total mass removal. This suggests that the flow patterns influence aqueous dissolution and that the aqueous dissolution under the NGFP is more efficient than dissolution under complex flow patterns.

Antiferromagnetic vs. non-magnetic ε phase of solid oxygen. Periodic density functional theory studies using a localized atomic basis set and the role of exact exchange.

PubMed

Ramírez-Solís, A; Zicovich-Wilson, C M; Hernández-Lamoneda, R; Ochoa-Calle, A J

2017-01-25

The question of the non-magnetic (NM) vs. antiferromagnetic (AF) nature of the ε phase of solid oxygen is a matter of great interest and continuing debate. In particular, it has been proposed that the ε phase is actually composed of two phases, a low-pressure AF ε 1 phase and a higher pressure NM ε 0 phase [Crespo et al., Proc. Natl. Acad. Sci. U. S. A., 2014, 111, 10427]. We address this problem through periodic spin-restricted and spin-polarized Kohn-Sham density functional theory calculations at pressures from 10 to 50 GPa using calibrated GGA and hybrid exchange-correlation functionals with Gaussian atomic basis sets. The two possible configurations for the antiferromagnetic (AF1 and AF2) coupling of the 0 ≤ S ≤ 1 O 2 molecules in the (O 2 ) 4 unit cell were studied. Full enthalpy-driven geometry optimizations of the (O 2 ) 4 unit cells were done to study the pressure evolution of the enthalpy difference between the non-magnetic and both antiferromagnetic structures. We also address the evolution of structural parameters and the spin-per-molecule vs. pressure. We find that the spin-less solution becomes more stable than both AF structures above 50 GPa and, crucially, the spin-less solution yields lattice parameters in much better agreement with experimental data at all pressures than the AF structures. The optimized AF2 broken-symmetry structures lead to large errors of the a and b lattice parameters when compared with experiments. The results for the NM model are in much better agreement with the experimental data than those found for both AF models and are consistent with a completely non-magnetic (O 2 ) 4 unit cell for the low-pressure regime of the ε phase.

Subdiffusion kinetics of nanoprecipitate growth and destruction in solid solutions

NASA Astrophysics Data System (ADS)

Sibatov, R. T.; Svetukhin, V. V.

2015-06-01

Based on fractional differential generalizations of the Ham and Aaron-Kotler precipitation models, we study the kinetics of subdiffusion-limited growth and dissolution of new-phase precipitates. We obtain the time dependence of the number of impurities and dimensions of new-phase precipitates. The solutions agree with the Monte Carlo simulation results.

Nucleation, growth and evolution of calcium phosphate films on calcite.

PubMed

Naidu, Sonia; Scherer, George W

2014-12-01

Marble, a stone composed of the mineral calcite, is subject to chemically induced weathering in nature due to its relatively high dissolution rate in acid rain. To protect monuments and sculpture from corrosion, we are investigating the application of thin layers of hydroxyapatite (HAP) onto marble. The motivation for using HAP is its low dissolution rate and crystal and lattice compatibility with calcite. A mild, wet chemical synthesis route, in which diammonium hydrogen phosphate salt was reacted with marble, alone and with cationic and anionic precursors under different reaction conditions, was used to produce inorganic HAP layers on marble. Nucleation and growth on the calcite substrate was studied, as well as metastable phase evolution, using scanning electron microscopy, grazing incidence X-ray diffraction, and atomic force microscopy. Film nucleation was enhanced by surface roughness. The rate of nucleation and the growth rate of the film increased with cationic (calcium) and anionic (carbonate) precursor additions. Calcium additions also influenced phase formation, introducing a metastable phase (octacalcium phosphate) and a different phase evolution sequence. Copyright © 2014 Elsevier Inc. All rights reserved.

Analysis of minerals containing dissolved traces of the fluid phase components water and carbon dioxide

NASA Technical Reports Server (NTRS)

Freund, Friedemann

1991-01-01

Substantial progress has been made towards a better understanding of the dissolution of common gas/fluid phase components, notably H2O and CO2, in minerals. It has been shown that the dissolution mechanisms are significantly more complex than currently believed. By judiciously combining various solid state analytical techniques, convincing evidence was obtained that traces of dissolved gas/fluid phase components undergo, at least in part, a redox conversion by which they split into reduced H2 and and reduced C on one hand and oxidized oxygen, O(-), on the other. Analysis for 2 and C as well as for any organic molecules which may form during the process of co-segregation are still impeded by the omnipresent danger of extraneous contamination. However, the presence of O(-), an unusual oxidized form of oxygen, has been proven beyond a reasonable doubt. The presence of O(-) testifies to the fact that a redox reaction must have taken place in the solid state involving the dissolved traces of gas/fluid phase components. Detailed information on the techniques used and the results obtained are given.

Understanding effect of formulation and manufacturing variables on the critical quality attributes of warfarin sodium product.

PubMed

Rahman, Ziyaur; Korang-Yeboah, Maxwell; Siddiqui, Akhtar; Mohammad, Adil; Khan, Mansoor A

2015-11-10

Warfarin sodium (WS) is a narrow therapeutic index drug and its product quality should be thoroughly understood and monitored in order to avoid clinical performance issues. This study was focused on understanding the effect of manufacturing and formulation variables on WS product critical quality attributes (CQAs). Eight formulations were developed with lactose monohydrate (LM) or lactose anhydrous (LA), and were either wet granulated or directly compressed. Formulations were granulated either with ethanol, isopropyl alcohol (IPA) and IPA-water mixture (50:50). Formulations were characterized for IPA, water content, hardness, disintegration time (DT), assay, dissolution and drug physical forms (scanning electron microscopy (SEM), near infrared chemical imaging (NIR-CI), X-ray powder diffraction (XRPD) and solid state nuclear magnetic resonance (ssNMR)), and performed accelerated stability studies at 40°C/75% RH for three days. The DT and dissolution of directly compressed formulations were faster than wet granulated formulations. This was due to phase transformation of crystalline drug into its amorphous form as indicated by SEM, NIR-CI, XRPD and ssNMR data which itself act as a binder. Similarly, LM showed faster disintegration and dissolution than LA containing formulations. Stability results indicated an increase in hardness and DT, and a decrease in dissolution rate and extent. This was due to phase transformation of the drug and consolidation with particles' bonding. In conclusion, the CQAs of WS product were significantly affected by manufacturing and formulation variables. Published by Elsevier B.V.

Setting accelerated dissolution test for PLGA microspheres containing peptide, investigation of critical parameters affecting drug release rate and mechanism.

PubMed

Tomic, I; Vidis-Millward, A; Mueller-Zsigmondy, M; Cardot, J-M

2016-05-30

The objective of this study was development of accelerated in vitro release method for peptide loaded PLGA microspheres using flow-through apparatus and assessment of the effect of dissolution parameters (pH, temperature, medium composition) on drug release rate and mechanism. Accelerated release conditions were set as pH 2 and 45°C, in phosphate buffer saline (PBS) 0.02M. When the pH was changed from 2 to 4, diffusion controlled phases (burst and lag) were not affected, while release rate during erosion phase decreased two-fold due to slower ester bonds hydrolyses. Decreasing temperature from 45°C to 40°C, release rate showed three-fold deceleration without significant change in release mechanism. Effect of medium composition on drug release was tested in PBS 0.01M (200 mOsm/kg) and PBS 0.01M with glucose (380 mOsm/kg). Buffer concentration significantly affected drug release rate and mechanism due to the change in osmotic pressure, while ionic strength did not have any effect on peptide release. Furthermore, dialysis sac and sample-and-separate techniques were used, in order to evaluate significance of dissolution technique choice on the release process. After fitting obtained data to different mathematical models, flow-through method was confirmed as the most appropriate for accelerated in vitro dissolution testing for a given formulation. Copyright © 2016 Elsevier B.V. All rights reserved.

Energetics of Intermediate Temperature Solid Oxide Fuel Cell Electrolytes: Singly and Doubly doped Ceria Systems

NASA Astrophysics Data System (ADS)

Buyukkilic, Salih

Solid oxide fuel cells (SOFCs) have potential to convert chemical energy directly to electrical energy with high efficiency, with only water vapor as a by-product. However, the requirement of extremely high operating temperatures (~1000 °C) limits the use of SOFCs to only in large scale stationary applications. In order to make SOFCs a viable energy solution, enormous effort has been focused on lowering the operating temperatures below 700 °C. A low temperature operation would reduce manufacturing costs by slowing component degradation, lessening thermal mismatch problems, and sharply reducing costs of operation. In order to optimize SOFC applications, it is critical to understand the thermodynamic stabilities of electrolytes since they directly influence device stability, sustainability and performance. Rare-earth doped ceria electrolytes have emerged as promising materials for SOFC applications due to their high ionic conductivity at the intermediate temperatures (500--700 °C). However there is a fundamental lack of understanding regarding their structure, thermodynamic stability and properties. Therefore, the enthalpies of formation from constituent oxides and ionic conductivities were determined to investigate a relationship between the stability, composition, structural defects and ionic conductivity in rare earth doped ceria systems. For singly doped ceria electrolytes, we investigated the solid solution phase of bulk Ce1-xLnxO2-0.5x where Ln = Sm and Nd (0 ≤ x ≤ 0.30) and analyzed their enthalpies of formation, mixing and association, and bulk ionic conductivities while considering cation size mismatch and defect associations. It was shown that for ambient temperatures in the dilute dopant region, the positive heat of formation reaches a maximum as the system becomes increasingly less stable due to size mismatch. In concentrated region, stabilization to a certain solubility limit was observed probably due to the defect association of trivalent cations with charge-balancing oxygen vacancies. At higher temperatures near 700 °C, maximum enthalpy of formation shifts toward higher dopant concentrations, as a result of defect disordering. This concentration coincides with that of maximum ionic conductivity, extending the correlation seen previously near room temperature. It is also possible to co-dope these systems with Sm and Nd to further enhance ionic conductivity. For doubly doped ceria electrolytes, the solid solution phase of Ce1-xSm0.5xNd0.5xO2-0.5x (0 ≤ x ≤ 0.30) was investigated. It has been shown that for doubly doped ceria, the maximum enthalpy of formation occurs towards higher dopant concentration than that of singly doped counterparts, with less exothermic association enthalpies. These studies provide insight into the structure-composition-property-stability relations and aid in the rational design of the future SOFCs electrolytes.

An investigation into the mechanisms of drug release from taste-masking fatty acid microspheres.

PubMed

Qi, Sheng; Deutsch, David; Craig, Duncan Q M

2008-09-01

Fatty acid microspheres based on stearic and palmitic acids are known to form effective taste masking systems, although the mechanisms by which the drug is preferentially released in the lower gastrointestinal tract are not known. The objective of the present study was to identify the mechanisms involved, with a particular view to clarify the role of acid soap formation in the dissolution process. Microspheres were prepared by a spray chilling process. Using benzoic acid as a model drug and an alkaline dissolution medium, a faster drug release was observed in the mixed fatty acid formulation (50:50 stearic:palmitic acid (w/w)) compared to the single fatty acid component systems. Thermal and powder X-ray diffraction studies indicated a greater degree of acid soap formation for the mixed formulation in alkaline media compared to the single fatty acid systems. Particle size and porosity studies indicated a modest reduction in size for the mixed systems and an increase in porosity on immersion in the dissolution medium. It is proposed that the mixed fatty acid system form a mixed crystal system which in turn facilitates interaction with the dissolution medium, thereby leading to a greater propensity for acid soap formation which in turn forms a permeable liquid crystalline phase through which the drug may diffuse. The role of dissolution of palmitic acid into the dissolution medium is also discussed as a secondary mechanism.

Dissolution of Biogenic and Synthetic UO2 under Varied Reducing Conditions

PubMed Central

ULRICH, KAI – UWE; SINGH, ABHAS; SCHOFIELD, ELEANOR J.; BARGAR, JOHN R.; VEERAMANI, HARISH; SHARP, JONATHAN O.; LATMANI, RIZLAN BERNIER -; GIAMMAR, DANIEL E.

2008-01-01

The chemical stability of biogenic UO2, a nanoparticulate product of environmental bioremediation, may be impacted by the particles’ surface free energy, structural defects, and compositional variability in analogy to abiotic UO2+x (0 ≤ x ≤ 0.25). This study quantifies and compares intrinsic solubility and dissolution rate constants of biogenic nano-UO2 and synthetic bulk UO2.00, taking molecular-scale structure into account. Rates were determined under anoxic conditions as a function of pH and dissolved inorganic carbon in continuous-flow experiments. The dissolution rates of biogenic and synthetic UO2 solids were lowest at near neutral pH and increased with decreasing pH. Similar surface area-normalized rates of biogenic and synthetic UO2 suggest comparable reactive surface site densities. This finding is consistent with the identified structural homology of biogenic UO2 and stoichiometric UO2.00. Compared to carbonate-free anoxic conditions, dissolved inorganic carbon accelerated the dissolution rate of biogenic UO2 by 3 orders of magnitude. This phenomenon suggests continuous surface oxidation of U(IV) to U(VI), with detachment of U(VI) as the rate-determining step in dissolution. Although reducing conditions were maintained throughout the experiments, the UO2 surface can be oxidized by water and radiogenic oxidants. Even in anoxic aquifers, UO2 dissolution may be controlled by surface U(VI) rather than U(IV) phases. PMID:18754482

Improving the dissolution rate of poorly water soluble drug by solid dispersion and solid solution: pros and cons.

PubMed

Chokshi, Rina J; Zia, Hossein; Sandhu, Harpreet K; Shah, Navnit H; Malick, Waseem A

2007-01-01

The solid dispersions with poloxamer 188 (P188) and solid solutions with polyvinylpyrrolidone K30 (PVPK30) were evaluated and compared in an effort to improve aqueous solubility and bioavailability of a model hydrophobic drug. All preparations were characterized by differential scanning calorimetry, powder X-ray diffraction, intrinsic dissolution rates, and contact angle measurements. Accelerated stability studies also were conducted to determine the effects of aging on the stability of various formulations. The selected solid dispersion and solid solution formulations were further evaluated in beagle dogs for in vivo testing. Solid dispersions were characterized to show that the drug retains its crystallinity and forms a two-phase system. Solid solutions were characterized to be an amorphous monophasic system with transition of crystalline drug to amorphous state. The evaluation of the intrinsic dissolution rates of various preparations indicated that the solid solutions have higher initial dissolution rates compared with solid dispersions. However, after storage at accelerated conditions, the dissolution rates of solid solutions were lower due to partial reversion to crystalline form. The drug in solid dispersion showed better bioavailability in comparison to solid solution. Therefore, considering physical stability and in vivo study results, the solid dispersion was the most suitable choice to improve dissolution rates and hence the bioavailability of the poorly water soluble drug.

Kinetics of microbial reduction of Solid phase U(VI).

PubMed

Liu, Chongxuan; Jeon, Byong-Hun; Zachara, John M; Wang, Zheming; Dohnalkova, Alice; Fredrickson, James K

2006-10-15

Sodium boltwoodite (NaUO2SiO3OH x 1.5 H2O) was used to assess the kinetics of microbial reduction of solid-phase U(VI) by a dissimilatory metal-reducing bacterium (DMRB), Shewanella oneidensis strain MR-1. The bioreduction kinetics was studied with Na-boltwoodite in suspension or within alginate beads in a nongrowth medium with lactate as electron donor at pH 6.8 buffered with PIPES. Concentrations of U(VI)tot and cell number were varied to evaluate the coupling of U(VI) dissolution, diffusion, and microbial activity. Microscopic and spectroscopic analyses with transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and laser-induced fluorescence spectroscopy (LIFS) collectively indicated that solid-phase U(VI) was first dissolved and diffused out of grain interiors before it was reduced on bacterial surfaces and/or within the periplasm. The kinetics of solid-phase U(VI) bioreduction was well described by a coupled model of bicarbonate-promoted dissolution of Na-boltwoodite, intragrain uranyl diffusion, and Monod type bioreduction kinetics with respect to dissolved U(VI) concentration. The results demonstrated that microbial reduction of solid-phase U(VI) is controlled by coupled biological, chemical, and physical processes.

Potential for U sequestration with select minerals and sediments via base treatment.

PubMed

Emerson, Hilary P; Di Pietro, Silvina; Katsenovich, Yelena; Szecsody, Jim

2018-06-13

Temporary base treatment is a potential remediation technique for heavy metals through adsorption, precipitation, and co-precipitation with minerals. Manipulation of pH with ammonia gas injection may be especially useful for vadose zone environments as it does not require addition of liquids that would increase the flux towards groundwater. In this research, we conducted laboratory batch experiments to evaluate the changes in uranium mobility and mineral dissolution with base treatments including sodium hydroxide, ammonium hydroxide, and ammonia gas. Our data show that partitioning of uranium to the solid phase increases by several orders of magnitude following base treatment in the presence of different minerals and natural sediments from the Hanford site. The presence of dissolved calcium and carbonate play an important role in precipitation and co-precipitation of uranium at elevated pH. In addition, significant incongruent dissolution of bulk mineral phases occurs and likely leads to precipitation of secondary mineral phases. These secondary phases may remove uranium via adsorption, precipitation, and co-precipitation processes and may coat uranium phases with low solubility minerals as the pH returns to natural conditions. Copyright © 2018 Elsevier Ltd. All rights reserved.

Benzocaine polymorphism: pressure-temperature phase diagram involving forms II and III.

PubMed

Gana, Inès; Barrio, Maria; Do, Bernard; Tamarit, Josep-Lluís; Céolin, René; Rietveld, Ivo B

2013-11-18

Understanding the phase behavior of an active pharmaceutical ingredient in a drug formulation is required to avoid the occurrence of sudden phase changes resulting in decrease of bioavailability in a marketed product. Benzocaine is known to possess three crystalline polymorphs, but their stability hierarchy has so far not been determined. A topological method and direct calorimetric measurements under pressure have been used to construct the topological pressure-temperature diagram of the phase relationships between the solid phases II and III, the liquid, and the vapor phase. In the process, the transition temperature between solid phases III and II and its enthalpy change have been determined. Solid phase II, which has the highest melting point, is the more stable phase under ambient conditions in this phase diagram. Surprisingly, solid phase I has not been observed during the study, even though the scarce literature data on its thermal behavior appear to indicate that it might be the most stable one of the three solid phases. Copyright © 2013 Elsevier B.V. All rights reserved.

On the Existence of Our Metals-Based Civilization: I. Phase Space Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

D.D. Macdonald

2005-06-22

The stability of the barrier layers of bilayer passive films that form on metal and alloy surfaces, when in contact with oxidizing aqueous environments, is explored within the framework of the Point Defect Model (PDM) using phase-space analysis (PSA), in which the rate of growth of the barrier layer into the metal, (dL{sup +}/dt), and the barrier layer dissolution rate, (dL{sup -}/dt), are plotted simultaneously against the barrier layer thickness. A point of intersection of dL{sup -}/dt with dL{sup +}/dt indicates the existence of a metastable barrier layer with a steady state thickness greater than zero. If dL{sup -}/dt >more » (dL{sup +}/dt){sub L=0}, where the latter quantity is the barrier layer growth rate at zero barrier layer thickness, the barrier layer cannot exist, even as a metastable phase, as the resulting thickness would be negative. Under these conditions, the surface is depassivated and the metal may corrode at a rapid rate. Depassivation may result from a change in the oxidation state of the cation upon dissolution of the barrier layer, such that the dissolution rate becomes highly potential dependent (as in the case of transpassive dissolution of chromium-containing alloys, for example, in which the reaction Cr{sub 2}O{sub 3} + 5H{sub 2}O {yields} 2CrO{sub 4}{sup 2-} + 10H {sup +} + 6e{sup -} results in the destruction of the film), or by the action of some solution-phase species (e.g., H{sup +}, Cl{sup -}) that enhances the dissolution rate to the extent that dL{sup -}/dt > (dL{sup +}/dt){sub L=0}. The boundaries for depassivation may be plotted in potential-pH space to develop Kinetic Stability Diagrams (KSDs) as alternatives to the classical Pourbaix diagrams for describing the conditions under which metals or alloys exist in contact with an aqueous environment. The advantage of KSDs is that they provide kinetic descriptions of the state of a metal or alloy that is in much closer concert with the kinetic phenomenon of passivity and depassivation than are equilibrium thermodynamic diagrams. Thus, KSDs more accurately account for the limits of passivity in highly acidic systems, where acid depassivation occurs, and at high potentials, where transition to the transpassive state may occur in some systems. In any event, phase space analysis of the PDM permits specification of the conditions over which reactive metals will remain passive in contact with aqueous systems and hence of the conditions that must be met for the existence of our metals-based civilization.« less

Real-time monitoring of the mechanism of ibuprofen-cationic dextran crystanule formation using crystallization process informatics system (CryPRINS).

PubMed

Abioye, Amos Olusegun; Chi, George Tangyie; Simone, Elena; Nagy, Zoltan

2016-07-25

One step aqueous melt-crystallization and in situ granulation was utilized to produce ibuprofen-cationic dextran [diethylaminoethyl dextran (Ddex)] conjugate crystanules without the use of surfactants or organic solvents. This study investigates the mechanism of in situ granulation-induced crystanule formation using ibuprofen (Ibu) and Ddex. Laboratory scale batch aqueous crystallization system containing in situ monitoring probes for particle vision measurement (PVM), UV-vis measurement and focused beam reflectance measurements (FBRM) was adapted using pre-defined formulation and process parameters. Pure ibuprofen showed nucleation domain between 25 and 64°C, producing minicrystals with onset of melting at 76°C and enthalpy of fusion (ΔH) of 26.22kJ/mol. On the other hand Ibu-Ddex crystanules showed heterogeneous nucleation which produced spherical core-shell structure. PVM images suggest that internalization of ibuprofen in Ddex corona occurred during the melting phase (before nucleation) which inhibited crystal growth inside the Ddex corona. The remarkable decrease in ΔH of the crystanules from 26.22 to 11.96kJ/mol and the presence of broad overlapping DSC thermogram suggests formation of ibuprofen-Ddex complex and crystalline-amorphous transformation. However Raman and FTIR spectra did not show any significant chemical interaction between ibuprofen and Ddex. A significant increase in dissolution efficiency from 45 to 81% within 24h and reduced burst release provide evidence for potential application of crystanules in controlled drug delivery systems. It was evident that in situ granulation of ibuprofen inhibited the aqueous crystallization process. It was concluded that in situ granulation-aqueous crystallization technique is a novel unit operation with potential application in continuous pharmaceutical processing. Copyright © 2016 Elsevier B.V. All rights reserved.