Hydrothermal Synthesis of Dicalcium Silicate Based Cement

NASA Astrophysics Data System (ADS)

Dutta, N.; Chatterjee, A.

2017-06-01

It is imperative to develop low energy alternative binders considering the large amounts of energy consumed as well as carbon dioxide emissions involved in the manufacturing of ordinary Portland cement. This study is on the synthesis of a dicalcium silicate based binder using a low temperature hydrothermal route.The process consists of synthesizing an intermediate product consisting of a calcium silicate hydrate phase with a Ca:Si ratio of 2:1 and further thermal treatment to produce the β-Ca2SiO4 (C2S) phase.Effect of various synthesis parameters like water to solid ratio, dwell time and temperature on the formation of the desired calcium silicate hydrate phase is reported along with effect of heating conditions for formation of the β-C2S phase. Around 77.45% of β-C2S phase was synthesized by thermal treatment of the intermediate phase at 820°C.

Modeling Nanomechanical Behavior of Calcium-Silicate-Hydrate

DTIC Science & Technology

2012-08-01

applicability to hardened pastes of tricalcium silicate, Portland cement, and blends of Portland cement with blast-furnace slag , metakaolin, or silica...Hydrated Nanocomposites: Concrete, Bone, and Shale. J. Am. Ceram . Soc., 90(9): 2677-2692. Wu, Jianzhong. and John M. Prausnitz. 2002. Generalizations for

Crystalline phases involved in the hydration of calcium silicate-based cements: Semi-quantitative Rietveld X-ray diffraction analysis.

PubMed

Grazziotin-Soares, Renata; Nekoofar, Mohammad H; Davies, Thomas; Hübler, Roberto; Meraji, Naghmeh; Dummer, Paul M H

2017-08-30

Chemical comparisons of powder and hydrated forms of calcium silicate cements (CSCs) and calculation of alterations in tricalcium silicate (Ca 3 SiO 5 ) calcium hydroxide (Ca(OH) 2 ) are essential for understanding their hydration processes. This study aimed to evaluate and compare these changes in ProRoot MTA, Biodentine and CEM cement. Powder and hydrated forms of tooth coloured ProRoot MTA, Biodentine and CEM cement were subjected to X-ray diffraction (XRD) analysis with Rietveld refinement to semi-quantitatively identify and quantify the main phases involved in their hydration process. Data were reported descriptively. Reduction in Ca 3 SiO 5 and formation of Ca(OH) 2 were seen after the hydration of ProRoot MTA and Biodentine; however, in the case of CEM cement, no reduction of Ca 3 SiO 5 and no formation of Ca(OH) 2 were detected. The highest percentages of amorphous phases were seen in Biodentine samples. Ettringite was detected in the hydrated forms of ProRoot MTA and CEM cement but not in Biodentine. © 2017 Australian Society of Endodontology Inc.

Predictive Mechanical Characterization of Macro-Molecular Material Chemistry Structures of Cement Paste at Nano Scale - Two-phase Macro-Molecular Structures of Calcium Silicate Hydrate, Tri-Calcium Silicate, Di-Calcium Silicate and Calcium Hydroxide

NASA Astrophysics Data System (ADS)

Padilla Espinosa, Ingrid Marcela

Concrete is a hierarchical composite material with a random structure over a wide range of length scales. At submicron length scale the main component of concrete is cement paste, formed by the reaction of Portland cement clinkers and water. Cement paste acts as a binding matrix for the other components and is responsible for the strength of concrete. Cement paste microstructure contains voids, hydrated and unhydrated cement phases. The main crystalline phases of unhydrated cement are tri-calcium silicate (C3S) and di-calcium silicate (C2S), and of hydrated cement are calcium silicate hydrate (CSH) and calcium hydroxide (CH). Although efforts have been made to comprehend the chemical and physical nature of cement paste, studies at molecular level have primarily been focused on individual components. Present research focuses on the development of a method to model, at molecular level, and analysis of the two-phase combination of hydrated and unhydrated phases of cement paste as macromolecular systems. Computational molecular modeling could help in understanding the influence of the phase interactions on the material properties, and mechanical performance of cement paste. Present work also strives to create a framework for molecular level models suitable for potential better comparisons with low length scale experimental methods, in which the sizes of the samples involve the mixture of different hydrated and unhydrated crystalline phases of cement paste. Two approaches based on two-phase cement paste macromolecular structures, one involving admixed molecular phases, and the second involving cluster of two molecular phases are investigated. The mechanical properties of two-phase macromolecular systems of cement paste consisting of key hydrated phase CSH and unhydrated phases C3S or C2S, as well as CSH with the second hydrated phase CH were calculated. It was found that these cement paste two-phase macromolecular systems predicted an isotropic material behavior. Also, these systems exhibited a high bulk modulus, compared to the elastic modulus. These results are an indication and concur with the high compression strength of cement paste seen at engineering length scale. In addition, the bulk modulus of two-phase systems consisting of hydrated CSH and unhydrated C3S or C2S was found to increase with higher levels of unhydrated components. The interaction energies of two-phase cement paste molecular structures studied in the present work were calculated, showing that a higher interaction is attained when the two phases are admixed as small components instead of cluster of phases. Finally, the mechanical behavior under shear deformation was predicted by using a quasi-static deformation method and analyzed for a representative two-phase (CSH and C2S) macromolecular structure of cement paste.

Characterization of un-hydrated and hydrated BioAggregate™ and MTA Angelus™.

PubMed

Camilleri, J; Sorrentino, F; Damidot, D

2015-04-01

BioAggregate™ is a novel material introduced for use as a root-end filling material. It is tricalcium silicate-based, free of aluminium and uses tantalum oxide as radiopacifier. BioAggregate contains additives to enhance the material performance. The purpose of this research was to characterize the un-hydrated and hydrated forms of BioAggregate using a combination of techniques, verify whether the additives if present affect the properties of the set material and compare these properties to those of MTA Angelus™. Un-hydrated and hydrated BioAggregate and MTA Angelus were assessed. Un-hydrated cement was tested for chemical composition, specific surface area, mineralogy and kinetics of hydration. The set material was investigated for mineralogy, microstructure and bioactivity. Scanning electron microscopy, X-ray energy dispersive spectroscopic analysis, X-ray fluorescence spectroscopy, X-ray diffraction and isothermal calorimetry were employed. The specific surface area was investigated using a gas adsorption method with nitrogen as the probe. BioAggregate was composed of tricalcium silicate, tantalum oxide, calcium phosphate and silicon dioxide and was free of aluminium. On hydration, the tricalcium silicate produced calcium silicate hydrate and calcium hydroxide. The former was deposited around the cement grains, while the latter reacted with the silicon dioxide to form additional calcium silicate hydrate. This resulted in reduction of calcium hydroxide in the aged cement. MTA Angelus reacted in a similar fashion; however, since it contained no additives, the calcium hydroxide was still present in the aged cement. Bioactivity was demonstrated by deposition of hydroxyapatite. BioAggregate exhibited a high specific surface area. Nevertheless, the reactivity determined by isothermal calorimetry appeared to be slow compared to MTA Angelus. The tantalum oxide as opposed to bismuth oxide was inert, and tantalum was not leached in solution. BioAggregate exhibited high calcium ion release early, which was maintained over the 28-day period as opposed to MTA Angelus, which demonstrated low early calcium ion release which increased as the material aged. The mineralogical composition of BioAggregate was different to MTA Angelus. As opposed to MTA Angelus, BioAggregate did not contain aluminium and contained additives such as calcium phosphate and silicon dioxide. As a consequence, BioAggregate reacted more slowly and formation of calcium hydroxide and leaching of calcium ions in solution were not evident as the material aged. The additives in BioAggregate modify the kinetics and the end products of hydration. Although newer generation tricalcium silicate-based materials contain similar constituents to MTA, they do not undergo the same setting reactions, and thus, their clinical performance will not be comparable to that of MTA.

Hydration heat of alkali activated fine-grained ceramic

NASA Astrophysics Data System (ADS)

Jerman, Miloš; Černý, Robert

2017-07-01

Early-age hydration heat of alkali activated ceramic dust is studied as a function of silicate modulus. A mixture of sodium hydroxide and water glass is used as alkali activator. The measurements are carried out using a large-volume isothermal heat flow calorimeter which is capable of detecting even very small values of specific heat power. Experimental results show that the specific hydration heat power of alkali activated fine-ground ceramic is very low and increases with the decreasing silicate modulus of the mix.

Thermal Shock-resistant Cement

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

Sugama T.; Pyatina, T.; Gill, S.

2012-02-01

We studied the effectiveness of sodium silicate-activated Class F fly ash in improving the thermal shock resistance and in extending the onset of hydration of Secar #80 refractory cement. When the dry mix cement, consisting of Secar #80, Class F fly ash, and sodium silicate, came in contact with water, NaOH derived from the dissolution of sodium silicate preferentially reacted with Class F fly ash, rather than the #80, to dissociate silicate anions from Class F fly ash. Then, these dissociated silicate ions delayed significantly the hydration of #80 possessing a rapid setting behavior. We undertook a multiple heating -watermore » cooling quenching-cycle test to evaluate the cement’s resistance to thermal shock. In one cycle, we heated the 200 and #61616;C-autoclaved cement at 500 and #61616;C for 24 hours, and then the heated cement was rapidly immersed in water at 25 and #61616;C. This cycle was repeated five times. The phase composition of the autoclaved #80/Class F fly ash blend cements comprised four crystalline hydration products, boehmite, katoite, hydrogrossular, and hydroxysodalite, responsible for strengthening cement. After a test of 5-cycle heat-water quenching, we observed three crystalline phase-transformations in this autoclaved cement: boehmite and #61614; and #61543;-Al2O3, katoite and #61614; calcite, and hydroxysodalite and #61614; carbonated sodalite. Among those, the hydroxysodalite and #61614; carbonated sodalite transformation not only played a pivotal role in densifying the cementitious structure and in sustaining the original compressive strength developed after autoclaving, but also offered an improved resistance of the #80 cement to thermal shock. In contrast, autoclaved Class G well cement with and without Class F fly ash and quartz flour failed this cycle test, generating multiple cracks in the cement. The major reason for such impairment was the hydration of lime derived from the dehydroxylation of portlandite formed in the autoclaved cement, causing its volume to expand.« less

Hydration and leaching characteristics of cement pastes made from electroplating sludge

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

Chen, Ying-Liang; Sustainable Environment Research Center, National Cheng Kung University, No. 1, University Rd., Tainan City 70101, Taiwan; Ko, Ming-Sheng

2011-06-15

The purpose of this study was to investigate the hydration and leaching characteristics of the pastes of belite-rich cements made from electroplating sludge. The compressive strength of the pastes cured for 1, 3, 7, 28, and 90 days was determined, and the condensation of silicate anions in hydrates was examined with the {sup 29}Si nuclear magnetic resonance (NMR) technology. The leachabilities of the electroplating sludge and the hardened pastes were studied with the multiple toxicity characteristic leaching procedure (MTCLP) and the tank leaching test (NEN 7345), respectively. The results showed that the electroplating sludge continued to leach heavy metals, includingmore » nickel, copper, and zinc, and posed a serious threat to the environment. The belite-rich cement made from the electroplating sludge was abundant in hydraulic {beta}-dicalcium silicate, and it performed well with regard to compressive-strength development when properly blended with ordinary Portland cements. The blended cement containing up to 40% the belite-rich cement can still satisfy the compressive-strength requirements of ASTM standards, and the pastes cured for 90 days had comparable compressive strength to an ordinary Portland cement paste. It was also found that the later hydration reaction of the blended cements was relatively more active, and high fractions of belite-rich cement increased the chain length of silicate hydrates. In addition, by converting the sludge into belite-rich cements, the heavy metals became stable in the hardened cement pastes. This study thus indicates a viable alternative approach to dealing with heavy metal bearing wastes, and the resulting products show good compressive strength and heavy-metal stability.« less

Loss of halogens from crystallized and glassy silicic volcanic rocks

USGS Publications Warehouse

Noble, D.C.; Smith, V.C.; Peck, L.C.

1967-01-01

One hundred and sixty-four F and Cl analyses of silicic welded tuffs and lavas and glass separates are presented. Comparison of the F and Cl contents of crystallized rocks with those of nonhydrated glass and hydrated glassy rocks from the same rock units shows that most of the halogens originally present were lost on crystallization. An average of about half of the F and four-fifths of the Cl originally present was lost. Analyses of hydrated natural glasses and of glassy rocks indicate that in some cases significant amounts of halogens may be removed from or added to hydrated glass through prolonged contact with ground water. The data show that the original halogen contents of the groundmass of a silicic volcanic rock can be reliably determined only from nonhydrated glass. ?? 1967.

Hydration behaviors of calcium silicate-based biomaterials.

PubMed

Lee, Yuan-Ling; Wang, Wen-Hsi; Lin, Feng-Huie; Lin, Chun-Pin

2017-06-01

Calcium silicate (CS)-based biomaterials, such as mineral trioxide aggregate (MTA), have become the most popular and convincing material used in restorative endodontic treatments. However, the commercially available CS-based biomaterials all contain different minor additives, which may affect their hydration behaviors and material properties. The purpose of this study was to evaluate the hydration behavior of CS-based biomaterials with/without minor additives. A novel CS-based biomaterial with a simplified composition, without mineral oxides as minor additives, was produced. The characteristics of this biomaterial during hydration were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectrometry. The hydration behaviors of commercially available gray and white MTAs with mineral oxide as minor additives were also evaluated for reference. For all three test materials, the XRD analysis revealed similar diffraction patterns after hydration, but MTAs presented a significant decrease in the intensities of Bi 2 O 3 -related peaks. SEM results demonstrated similar porous microstructures with some hexagonal and facetted crystals on the outer surfaces. In addition, compared to CS with a simplified composition, the FTIR plot indicated that hydrated MTAs with mineral oxides were better for the polymerization of calcium silicate hydrate (CSH), presenting Si-O band shifting to higher wave numbers, and contained more water crystals within CSH, presenting sharper bands for O-H bending. Mineral oxides might not result in significant changes in the crystal phases or microstructures during the hydration of CS-based biomaterials, but these compounds affected the hydration behavior at the molecular level. Copyright © 2016. Published by Elsevier B.V.

Initial Estimates of Optical Constants of Mars Candidate Materials

NASA Technical Reports Server (NTRS)

Rousch, Ted L.; Brown, Adrian Jon; Bishop, Janice L.; Blake, David F.; Bristow, Thomas F.

2013-01-01

Data obtained at visible and near-infrared wavelengths by OMEGA on Mars Express and CRISM on MRO provide definitive evidence for the presence of phyllosilicates and other hydrated phases on Mars. A diverse range of both Fe/Mg-OH and Al- OH-bearing phyllosilicates were identified including the smectites, nontronite, saponite, and montmorillonite. To constrain the abundances of these phyllosilicates, spectral analyses of mixtures are needed. We report on our effort to enable the quantitative evaluation of the abundance of hydrated-hydroxylated silicates when they are contained in mixtures. We include two component mixtures of hydrated/ hydroxylated silicates with each other and with two analogs for other Martian materials; pyroxene (enstatite) and palagonitic soil (an alteration product of basaltic glass, hereafter referred to as palagonite). For the hydrated-hydroxylated silicates we include saponite and montmorillonite (Mg- and Al-rich smectites). We prepared three size separates of each end-member for study: 20-45, 63-90, and 125-150 micron.

Hydrated mineral stratigraphy of Ius Chasma, Valles Marineris

USGS Publications Warehouse

Roach, L.H.; Mustard, J.F.; Swayze, G.; Milliken, R.E.; Bishop, J.L.; Murchie, S.L.; Lichtenberg, K.

2010-01-01

New high-resolution spectral and morphologic imaging of deposits on walls and floor of Ius Chasma extend previous geomorphic mapping, and permit a new interpretation of aqueous processes that occurred during the development of Valles Marineris. We identify hydrated mineralogy based on visible-near infrared (VNIR) absorptions. We map the extents of these units with CRISM spectral data as well as morphologies in CTX and HiRISE imagery. Three cross-sections across Ius Chasma illustrate the interpreted mineral stratigraphy. Multiple episodes formed and transported hydrated minerals within Ius Chasma. Polyhydrated sulfate and kieserite are found within a closed basin at the lowest elevations in the chasma. They may have been precipitates in a closed basin or diagenetically altered after deposition. Fluvial or aeolian processes then deposited layered Fe/Mg smectite and hydrated silicate on the chasma floor, postdating the sulfates. The smectite apparently was weathered out of Noachian-age wallrock and transported to the depositional sites. The overlying hydrated silicate is interpreted to be an acid-leached phyllosilicate transformed from the underlying smectite unit, or a smectite/jarosite mixture. The finely layered smectite and massive hydrated silicate units have an erosional unconformity between them, that marks a change in surface water chemistry. Landslides transported large blocks of wallrock, some altered to contain Fe/Mg smectite, to the chasma floor. After the last episode of normal faulting and subsequent landslides, opal was transported short distances into the chasma from a few m-thick light-toned layer near the top of the wallrock, by sapping channels in Louros Valles. Alternatively, the material was transported into the chasma and then altered to opal. The superposition of different types of hydrated minerals and the different fluvial morphologies of the units containing them indicate sequential, distinct aqueous environments, characterized by alkaline, then circum-neutral, and finally very acidic surface or groundwater chemistry. ?? 2009 Elsevier Inc. All rights reserved.

Quasielastic and inelastic neutron scattering study of the hydration of monoclinic and triclinic tricalcium silicate

NASA Astrophysics Data System (ADS)

Peterson, Vanessa K.; Brown, Craig M.; Livingston, Richard A.

2006-08-01

The hydration of Mg-stabilized triclinic and monoclinic tricalcium silicate samples were studied using quasielastic neutron scattering to follow the fixation of hydrogen into the reaction products and by applying hydration models to the data. The quantity of Ca(OH) 2 produced during hydration was also determined using inelastic neutron scattering. The monoclinic form was found to be intrinsically less reactive that the triclinic form. The monoclinic form was also confirmed to produce more product than the triclinic form after 50 h, a process found to occur through a longer, rather than earlier, nucleation and growth regime. Results indicated an increase in the permeability of the hydration layer product relative to the triclinic form and the increase in the length of the nucleation and growth regime was thus attributed to an alteration in morphology or structure of the hydration layer product, extending the time for diffusion limited mechanics to be reached.

Hydration and leaching characteristics of cement pastes made from electroplating sludge.

PubMed

Chen, Ying-Liang; Ko, Ming-Sheng; Lai, Yi-Chieh; Chang, Juu-En

2011-06-01

The purpose of this study was to investigate the hydration and leaching characteristics of the pastes of belite-rich cements made from electroplating sludge. The compressive strength of the pastes cured for 1, 3, 7, 28, and 90 days was determined, and the condensation of silicate anions in hydrates was examined with the (29)Si nuclear magnetic resonance (NMR) technology. The leachabilities of the electroplating sludge and the hardened pastes were studied with the multiple toxicity characteristic leaching procedure (MTCLP) and the tank leaching test (NEN 7345), respectively. The results showed that the electroplating sludge continued to leach heavy metals, including nickel, copper, and zinc, and posed a serious threat to the environment. The belite-rich cement made from the electroplating sludge was abundant in hydraulic β-dicalcium silicate, and it performed well with regard to compressive-strength development when properly blended with ordinary Portland cements. The blended cement containing up to 40% the belite-rich cement can still satisfy the compressive-strength requirements of ASTM standards, and the pastes cured for 90 days had comparable compressive strength to an ordinary Portland cement paste. It was also found that the later hydration reaction of the blended cements was relatively more active, and high fractions of belite-rich cement increased the chain length of silicate hydrates. In addition, by converting the sludge into belite-rich cements, the heavy metals became stable in the hardened cement pastes. This study thus indicates a viable alternative approach to dealing with heavy metal bearing wastes, and the resulting products show good compressive strength and heavy-metal stability. Copyright © 2011 Elsevier Ltd. All rights reserved.

Vibrational investigation of calcium-silicate cements for endodontics in simulated body fluids

NASA Astrophysics Data System (ADS)

Taddei, Paola; Modena, Enrico; Tinti, Anna; Siboni, Francesco; Prati, Carlo; Gandolfi, Maria Giovanna

2011-05-01

Calcium-silicate MTA (Mineral Trioxide Aggregate) cements have been recently developed for oral and endodontic surgery. This study was aimed at investigating commercial (White ProRoot MTA, White and Grey MTA-Angelus) and experimental (wTC-Bi) accelerated calcium-silicate cements with regards to composition, hydration products and bioactivity upon incubation for 1-28 days at 37 °C, in Dulbecco's Phosphate Buffered Saline (DPBS). Deposits on the surface of the cements and the composition changes during incubation were investigated by micro-Raman and ATR/FT-IR spectroscopy, and pH measurements. Vibrational techniques disclosed significant differences in composition among the unhydrated cements, which significantly affected the bioactivity as well as pH, and hydration products of the cements. After one day in DPBS, all the cements were covered by a more or less homogeneous layer of B-type carbonated apatite. The experimental cement maintained a high bioactivity, only slightly lower than the other cements and appears a valid alternative to commercial cements, in view of its adequate setting time properties. The bioactivity represents an essential property to favour bone healing and makes the calcium-silicate cements the gold standard materials for root-apical endodontic surgery.

Long term mechanical properties of alkali activated slag

NASA Astrophysics Data System (ADS)

Zhu, J.; Zheng, W. Z.; Xu, Z. Z.; Leng, Y. F.; Qin, C. Z.

2018-01-01

This article reports a study on the microstructural and long-term mechanical properties of the alkali activated slag up to 180 days, and cement paste is studied as the comparison. The mechanical properties including compressive strength, flexural strength, axis tensile strength and splitting tensile strength are analyzed. The results showed that the alkali activated slag had higher compressive and tensile strength, Slag is activated by potassium silicate (K2SiO3) and sodium hydroxide (NaOH) solutions for attaining silicate modulus of 1 using 12 potassium silicate and 5.35% sodium hydroxide. The volume dosage of water is 35% and 42%. The results indicate that alkali activated slag is a kind of rapid hardening and early strength cementitious material with excellent long-term mechanical properties. Single row of holes block compressive strength, single-hole block compressive strength and standard solid brick compressive strength basically meet engineering requirements. The microstructures of alkali activated slag are studied by X-ray diffraction (XRD). The hydration products of alkali-activated slag are assured as hydrated calcium silicate and hydrated calcium aluminate.

Interaction of water vapor with silicate glass surfaces: Mass-spectrometric investigations

NASA Astrophysics Data System (ADS)

Kudriavtsev, Yu.; Asomoza-Palacio, R.; Manzanilla-Naim, L.

2017-05-01

The secondary ion mass-spectroscopy technique was used to study the results of hydration of borosilicate, aluminosilicate, and soda-lime silicate glasses in 1H2 18O water vapor containing 97% of the isotope 18O. It is shown that hydration of the surface of the soda-lime silicate glass occurs as a result of the ion-exchange reaction with alkali metals. In the case of borosilicate and aluminosilicate glasses, water molecules decompose on the glass surface, with the observed formation of hydrogenated layer in the glass being the result of a solid-state chemical reaction—presumably, with the formation of hydroxides from aluminum and boron oxides.

Why we need detailed visible-range spectral data on Kuiper belt objects?

NASA Astrophysics Data System (ADS)

Busarev, V. V.

2001-05-01

Our understanding of Kuiper belt objects (KBOs)' nature may be based on two general scenarios of their origin. First, they could result from early accretional phases of the Solar System ``in situ". Then they are probably the most primitive and unprocessed bodies among known and should be mostly icy, with a very low content of silicate component. Second, a considerable portion of them (if not a majority) might have been thrown by Jupiter and other giant planets from their zones of accumulation. If so, they could include much more silicates (possibly up to 40%). To check the suppositions we need high-resolution visible and near-infrared spectral data on Centaurs (as possible `fugitives' from the Kuiper belt) and the KBOs. Because of faintness of the objects their physicochemical properties remain still little-known. Visible-range observations of the bodies by means of a spacecraft approaching to the belt could much help in solving the problem. Visible-infrared spectrophotometric observations of the objects showed a considerable diversity among them (Jewitt D. & J. Luu, 1998, Astron. J., 115, 1667-1670). It hints at a diversity in content of their matter. Spectral features of ices could not probably dominate in the visible range spectra of silicate-bearing KBOs. Reflectance spectra of principal gases' frosts are mainly flat and featureless in the range (Wagner J. K. et al., 1987, Icarus, 69, 14-28). Besides, silicates of KBOs are probably oxidized and hydrated to a high extent. Highly hydrated main-belt C-class asteroids have absorption bands at 0.43 and 0.6-0.8 microns (up to about 5%) (Vilas F. & M. J. Gaffey, 1989, Science, 246, 790-792 and Vilas F. et al., 1993, Icarus, 102, 225-231). Similar spectral features attributed to oxidized and hydrated silicates were also found on many M- and S-asteroids (e. g., Busarev V. V., 2001, LPSC XXXII, abstract 1927). The absorption bands are interpreted as caused by electronic processes in a bulk of oxidized silicates and hydrated clay minerals including structural OH-groups. Thus, the absorption features may be considered as indicators of a presence of oxidized and/or hydrated silicates on a solid body regardless of its position in the Solar System. For these reasons we have started visible-range spectroscopic observations of Centaurs and the KBOs on Russian 6-m telescope.

Diffusion-driven D/H fractionation in silicates during hydration, dehydration and degassing

NASA Astrophysics Data System (ADS)

Roskosz, Mathieu; Laporte, Didier; Deloule, Etienne; Ingrin, Jannick; Remusat, Laurent; Depecker, Christophe; Leroux, Hugues

2017-04-01

Understanding how degassing occurs during accretion and differentiation is crucial to explain the water budget of planetary bodies. In this context, the hydrogen isotopic signature of water in mantle minerals and melts is particularly useful to trace reservoirs and their interactions. Nonetheless, little is known on the influence of mantle processes on the D/H signatures of silicates. In this study, we performed controlled hydration/dehydration experiments. We explore the possibility that diffusion-driven fractionation could affect the D/H signature of partially hydrated amorphous or molten silicates and nominally anhydrous minerals (NAMs). High purity synthetic fused silica samples were annealed at between 200 and 1000°C at 20 mbar water partial pressure for 1 to 30 days. Dehydration of initially hydrated silica was also performed at 1000°C for a few hours. A set of rhyolitic samples previously synthesized in order to study bubble nucleation during magma decompression was also analyzed. Finally a natural grossular monocrystal (Zillertaler Alps, Austria), partially dehydrated in air at 800°C for 10 hours was studied. Water content and speciation were measured both by Fourier-Transform Infra-Red and Raman spectroscopies. Isotopic analyses were performed with the IMS 1270 and 1280 ion microprobes. The silica samples, the rhyolitic glasses and the grossular monocrystal exhibit typical water concentration profiles. In all cases, water speciation does not change significantly along concentration profiles. Concerning D/H signatures, no isotopic variation is detectable across amorphous silica and rhyolitic glasses. The situation is however very different in the grossular monocrystal. A strong isotopic gradient appears correlated to the water concentration profile. Our data are interpreted in terms of diffusion mechanisms in both amorphous (and molten) silicates and NAMs. Hydration, dehydration and magma degassing are probably not able to promote large diffusion-driven fractionation of hydrogen in amorphous silicates. Conversely, the diffusion of water through the structure of NAMs affects the overall isotopic composition of dissolved water.

Interstellar dust spectra between 2.5 and 3.3 microns - A search for hydrated silicates

NASA Technical Reports Server (NTRS)

Knacke, R. F.; Mccorkle, S.; Puetter, R. C.; Erickson, E.

1985-01-01

Spectra in the 2.5-3.3 micron wavelength region of VI Cyg 12, AFGL 2205, and AFGL 2885 were obtained in a search for bound water, hydroxyl groups, and hydrated minerals in interstellar dust. No new absorption bands were found. Comparison of expected strengths of bands of serpentine and chlorite-like minerals with the data suggests that less than 25 percent and 50 percent, respectively, of the silicate in the grains is composed of these materials.

Traditional Portland cement and MgO-based cement: a promising combination?

NASA Astrophysics Data System (ADS)

Tonelli, Monica; Martini, Francesca; Calucci, Lucia; Geppi, Marco; Borsacchi, Silvia; Ridi, Francesca

2017-06-01

MgO/SiO2 cements are materials potentially very useful for radioactive waste disposal, but knowledge about their physico-chemical properties is still lacking. In this paper we investigated the hydration kinetics of cementitious formulations prepared by mixing MgO/SiO2 and Portland cement in different proportions and the structural properties of the hydrated phases formed in the first month of hydration. In particular, the hydration kinetics was investigated by measuring the free water index on pastes by means of differential scanning calorimetry, while the structural characterization was carried out by combining thermal (DTA), diffractometric (XRD), and spectroscopic (FTIR, 29Si solid state NMR) techniques. It was found that calcium silicate hydrate (C-S-H) and magnesium silicate hydrate (M-S-H) gels mainly form as separate phases, their relative amount and structural characteristics depending on the composition of the hydrated mixture. Moreover, the composition of the mixtures strongly affects the kinetics of hydration and the pH of the aqueous phase in contact with the cementitious materials. The results here reported show that suitable mixtures of Portland cement and MgO/SiO2 could be used to modify the properties of hydrated phases with potential application in the storage of nuclear waste in clayey disposal.

Removal of sulphur dioxide from flue gases

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

Ersoy-Mericboyu, A.

1999-08-01

Mixtures of Ca(OH){sub 2} and different siliceous materials such as fly ash, bentonite, silica fume, and diatomite were hydrated to produce reactive SO{sub 2} sorbents. It was observed that these sorbents showed a better reactivity toward SO{sub 2} than the Ca(OH){sub 2} itself. This behavior is closely related to the pozzolanic nature of the hydrated sorbents and to the greater surface area. The reactivity of the sorbents was strongly influenced by the source of siliceous material and the hydration conditions. The total sulphation capacities of the sorbents were determined at 338 K with a synthetic gaseous mixture containing 5,000 ppmmore » SO{sub 2} and 55% relative humidity. Depending on the chemical and physical properties of the sorbents, the SO{sub 2} captures ranged from 1.20 to 5.58 mmol SO{sub 2}/g sorbent. The amount of SO{sub 2} capture increased with the increasing surface area of the sorbent. The utilization of Ca(OH){sub 2} with SO{sub 2} improved significantly when Ca(OH){sub 2} was hydrated with siliceous materials first and later exposed to SO{sub 2}.« less

Effect of temperature on the hydration of Portland cement blended with siliceous fly ash

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

Deschner, Florian, E-mail: florian.deschner@gmail.com; Lothenbach, Barbara; Winnefeld, Frank

2013-10-15

The effect of temperature on the hydration of Portland cement pastes blended with 50 wt.% of siliceous fly ash is investigated within a temperature range of 7 to 80 °C. The elevation of temperature accelerates both the hydration of OPC and fly ash. Due to the enhanced pozzolanic reaction of the fly ash, the change of the composition of the C–S–H and the pore solution towards lower Ca and higher Al and Si concentrations is shifted towards earlier hydration times. Above 50 °C, the reaction of fly ash also contributes to the formation of siliceous hydrogarnet. At 80 °C, ettringitemore » and AFm are destabilised and the released sulphate is partially incorporated into the C–S–H. The observed changes of the phase assemblage in dependence of the temperature are confirmed by thermodynamic modelling. The increasingly heterogeneous microstructure at elevated temperatures shows an increased density of the C–S–H and a higher coarse porosity. -- Highlights: •The reaction of quartz powder at 80 °C strongly enhances the compressive strength. •Almost no strength increase of fly ash blended OPC at 80 °C was found after 2 days. •Siliceous hydrogarnet is formed upon the reaction of fly ash at high temperatures. •Temperature dependent change of the system was simulated by thermodynamic modelling. •Destabilisation of ettringite above 50 °C correlates with sulphate content of C–S–H.« less

Aqueous solubility diagrams for cementitious waste stabilization systems. 3. Mechanism of zinc immobilizaton by calcium silicate hydrate.

PubMed

Tommaseo, C E; Kersten, M

2002-07-01

Zinc oxide was added during hydration of alite (C3S) as an analogue for solidification/stabilization by cement of metal-bearing hazardous waste. Curing of samples was stopped at various intervals between 8 h and 100 d, and the reaction products were analyzed by both X-ray diffraction (XRD) and X-ray absorption spectroscopy (EXAFS at Zn, Ca, and Si K-edges). Calcium zincate hydrate (CaZn2(OH)6 x 2H2O) initially formed together with calcium silicate hydrate (CSH) vanishes from X-ray diffractograms after 14 d, and no other crystalline Zn-bearing phase could be detected thereafter. EXAFS Zn K-edge data analysis reveals that Zn(O,OH)4 tetrahedra continue to determine the first shell coordination. However, a new Zn-Si bond appears in the second coordination shell as indicated by both Zn K-edge and Si K-edge EXAFS. Together with the Ca-Zn and Ca-Ca shells derived from the Ca K-edge EXAFS spectra, a structural model for the site occupation of Zn in CSH is proposed, whereby the Zn(O,OH)4 tetrahedra are bound in layer rather than interlayer positions substituting for the silicate bridging tetrahedra and/or at terminal silicate chain sites. This structural model enables ultimately the formulation of a thermodyamic Lippmann model to predict the aqueous solubility of Zn in solid solution with a CSH phase of a Ca/Si ratio fixed to unity.

Reactive molecular simulation on the calcium silicate hydrates/polyethylene glycol composites

NASA Astrophysics Data System (ADS)

Zhou, Yang; Hou, Dongshuai; Jiang, Jinyang; She, Wei; Yu, Jiao

2017-11-01

Calcium silicate hydrates (C-S-H) may potentially exhibit extraordinary performance when modified by polymers, in which way the properties of cement-based materials can be improved from the genetic level. In this molecular dynamics simulation of the interaction between C-S-H and polyethylene glycol, apart from the H bond network connection in the interface, another chemical adsorption was observed. Calcium of C-S-H broke the Csbnd O bond of PEG and formed a new Casbnd C connection, which created a stronger link between the organic and inorganic phases.

SIMULTANEOUS CONTROL OF HG(0), SO2, AND NOX BY NOVEL OXIDIZED CALCIUM-BASED SORBENTS

EPA Science Inventory

The paper gives results of an investigation of two classes of calcium (Ca)-based sorbents (hydrated limes and silicate compounds). {NOTE: Efforts to develop multipollutant control strategies have demonstrated that adding certain oxidants to different classes of Ca-based sorbents ...

SIMULTANEOUS CONTROL OF HGO, SO2, AND NOX BY NOVEL OXIDIZED CALCIUM-BASED SORBENTS

EPA Science Inventory

The paper gives results of an investigation of two classes of calcium (Ca)-based sorbents (hydrated limes and silicate compounds). (NOTE: Efforts to develop multipollutant control strategies have demonstrated that adding certain oxidants to different classes of Ca-based sorbents...

HEALTH ASSESSMENT DOCUMENT FOR VERMICULITE

EPA Science Inventory

Vermiculite is a nonfibrous silicate mineral with multiple consumer uses that has been shown to contain various concentrations of asbestiform fibers. ermiculite is a micaceous hydrate of magnesium-iron-aluminum silicates with the ability to exfoliate or expand up to 20 times its ...

On-Going Laboratory Efforts to Quantitatively Address Clay Abundance on Mars

NASA Technical Reports Server (NTRS)

Roush, Ted L.; Bishop, Janice L.; Brown, Adrian J.; Blake, David F.; Bristow, Thomas F.

2012-01-01

Data obtained at visible and near-infrared wavelengths by OMEGA on MarsExpress and CRISM on MRO provide definitive evidence for the presence of phyllosilicates and other hydrated phases on Mars. A diverse range of both Fe/Mg-OH and Al-OH-bearing phyllosilicates were identified including the smectites, nontronite, saponite, and montmorillonite. In order to constrain the abundances of these phyllosilicates spectral analyses of mixtures are needed. We report on our on-going effort to enable the quantitative evaluation of the abundance of hydrated-hydroxylated silicates when they are contained in mixtures. We include two component mixtures of hydrated/hydroxylated silicates with each other and with two analogs for other martian materials; pyroxene (enstatite) and palagonitic soil (an alteration product of basaltic glass). For the hydrated-hydroxylated silicates we include saponite and montmorillonite (Mg- and Al- rich smectites). We prepared three size separates of each end-member for study: 20-45, 63-90, and 125-150 µm. As the second phase of our effort we used scanning electron microscopy imaging and x-ray diffraction to characterize the grain size distribution, and structural nature, respectively, of the mixtures. Visible and near-infrared reflectance spectra of the 63-90 micrometers grain size of the mixture samples are shown in Figure 1. We discuss the results of our measurements of these mixtures.

Silicate Weathering and Pervasive Authigenic Carbonate Precipitation Coupled to Methanogenesis in the Krishna-Godavari Basin, Offshore India

NASA Astrophysics Data System (ADS)

Solomon, E. A.; Spivack, A. J.; Kastner, M.; Torres, M. E.

2014-12-01

The cycling of methane in marine sediments has been actively studied for the past several decades, but less attention has been paid to the cycling of CO2 produced in methanogenic sediments. The National Gas Hydrate Program Expedition 01 cored 10 sites with the Joides Resolution drillship in the Krishna-Godavari basin, located on the southeastern margin of India. A comprehensive suite of pore water solute concentrations and isotope ratios were analyzed to investigate the distribution and concentration of gas hydrate along the margin, in situ diagenetic and metabolic reactions, fluid migration and flow pathways, and fluid and gas sources. This represents one of the most comprehensive pore water geochemical datasets collected at a continental margin to date, and provides the necessary tracers to better understand the processes and sinks controlling CO2 in margin sediments. Our results show that the CO2 produced through net microbial methanogenesis is effectively neutralized through silicate weathering throughout the sediment column drilled at each site (~100-300 m), buffering the pH of the sedimentary pore water and generating excess alkalinity through the same reaction sequence as continental silicate weathering. Most of the excess alkalinity produced through silicate weathering in the Krishna-Godavari basin is sequestered in Ca- and Fe-carbonates as a result of ubiquitous calcium release from weathering detrital silicates and Fe-reduction within the methanogenic sediments. Formation of secondary hydrous silicates (e.g. smectite) related to incongruent primary silicate dissolution acts as a significant sink for pore water Mg, K, Li, Rb, and B. The consumption of methane through anaerobic oxidation of methane, sequestration of methane in gas hydrate, and sequestration of dissolved inorganic carbon in authigenic carbonates keeps methanogenesis as a thermodynamically feasible catabolic pathway. Our results combined with previous indications of silicate weathering in anoxic sediments in the Sea of Okhotsk, suggest that silicate weathering coupled to microbial methanogenesis should be occurring in continental margins worldwide, providing a net sink of atmospheric CO2 over geologic timescales.

Studying the Hydration of a Retarded Suspension of Ground Granulated Blast-Furnace Slag after Reactivation

PubMed Central

Schneider, Nick; Stephan, Dietmar

2016-01-01

This article presents a combined use of a retarder (d-gluconic acid) and an alkaline activator (sodium hydroxide) in a binder system based on ground granulated blast-furnace slag. The properties of the retarder are extending the dormant hydration period and suppressing the generation of strength-giving phases. Different retarder concentrations between 0.25 and 1.00 wt.% regulate the intensity and the period of the retardation and also the characteristics of the strength development. The activator concentration of 30 and 50 wt.% regulates the overcoming of the dormant period and thereby the solution of the slag and hence the formation of the hydration products. The research objective is to produce a mineral binder system based on two separate liquid components. The highest concentration of retarder and activator generates the highest compressive strength and mass of hydration products—after 90 days of hydration a compressive strength of more than 50 N/mm2. The main phases are calcium silicate hydrate and hydrotalcite. Generally, the combination of retarder and activator shows a high potential in the performance increase of the hydration process. PMID:28774054

Formation of magnesium silicate hydrate (M-S-H) cement pastes using sodium hexametaphosphate

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

Zhang, Tingting; Department of Materials, Centre for Advanced Structural Ceramics, Imperial College London, South Kensington Campus, London SW7 2AZ; Department of Civil and Environmental Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ

2014-11-15

Magnesium silicate hydrate (M-S-H) gel is formed by the reaction of brucite with amorphous silica during sulphate attack in concrete and M-S-H is therefore regarded as having limited cementing properties. The aim of this work was to form M-S-H pastes, characterise the hydration reactions and assess the resulting properties. It is shown that M-S-H pastes can be prepared by reacting magnesium oxide (MgO) and silica fume (SF) at low water to solid ratio using sodium hexametaphosphate (NaHMP) as a dispersant. Characterisation of the hydration reactions by x-ray diffraction and thermogravimetric analysis shows that brucite and M-S-H gel are formed andmore » that for samples containing 60 wt.% SF and 40 wt.% MgO all of the brucites react with SF to form M-S-H gel. These M-S-H cement pastes were found to have compressive strengths in excess of 70 MPa.« less

Drying-induced atomic structural rearrangements in sodium-based calcium-alumino-silicate-hydrate gel and the mitigating effects of ZrO 2 nanoparticles

DOE PAGES

Yang, Kengran; Özçelik, V. Ongun; Garg, Nishant; ...

2018-01-01

Drying-induced nanoscopic alterations to the local atomic structure of silicate-activated slag and the mitigated effects of nano-ZrO2 are elucidated using in situ X-ray pair distribution function analysis.

Drying-induced atomic structural rearrangements in sodium-based calcium-alumino-silicate-hydrate gel and the mitigating effects of ZrO 2 nanoparticles

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

Yang, Kengran; Özçelik, V. Ongun; Garg, Nishant

Drying-induced nanoscopic alterations to the local atomic structure of silicate-activated slag and the mitigated effects of nano-ZrO2 are elucidated using in situ X-ray pair distribution function analysis.

What can meteorites tell us about comets?

NASA Technical Reports Server (NTRS)

Anders, Edward

1986-01-01

Cometary silicates, carbon, and volatiles are reviewed using data from the Halley probes, interplanetary dust particles, and cometary spectra. The origins of anhydrous Fe(2+)-bearing silicates; whether hydrated silicates, if present, were made by gaseous or liquid H2O3; sources of organic compounds: ion-molecule reactions, photochemistry, grain catalysis; sources of CO2 and of organic polymers; and interstellar molecules and grains in comets are discussed.

Imaging of drug loading distributions in individual microspheres of calcium silicate hydrate - an X-ray spectromicroscopy study

NASA Astrophysics Data System (ADS)

Guo, Xiaoxuan; Wang, Zhiqiang; Wu, Jin; Wang, Jian; Zhu, Ying-Jie; Sham, Tsun-Kong

2015-04-01

Imaging is one of the most direct and ideal ways to track drug loading distributions in drug carriers on the molecular level, which will facilitate the optimization of drug carriers and drug loading capacities. Herein, we report the mapping of an individual mesoporous calcium silicate hydrate (CSH) microsphere before and after the loading of ibuprofen (IBU) and the interactions between drug carriers and drug molecules simultaneously by scanning transmission X-ray microscopy (STXM). Nanoscaled X-ray absorption near edge structure (XANES) spectroscopy clearly indicates that IBU is bonded to calcium and silicate sites via carboxylic acid groups. More importantly, STXM has been successfully used to determine the absolute thickness of IBU, revealing its distribution in the CSH microsphere.Imaging is one of the most direct and ideal ways to track drug loading distributions in drug carriers on the molecular level, which will facilitate the optimization of drug carriers and drug loading capacities. Herein, we report the mapping of an individual mesoporous calcium silicate hydrate (CSH) microsphere before and after the loading of ibuprofen (IBU) and the interactions between drug carriers and drug molecules simultaneously by scanning transmission X-ray microscopy (STXM). Nanoscaled X-ray absorption near edge structure (XANES) spectroscopy clearly indicates that IBU is bonded to calcium and silicate sites via carboxylic acid groups. More importantly, STXM has been successfully used to determine the absolute thickness of IBU, revealing its distribution in the CSH microsphere. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07471h

Dynamical behaviors of structural, constrained and free water in calcium- and magnesium-silicate-hydrate gels

DOE PAGES

Le, Peisi; Fratini, Emiliano; Ito, Kanae; ...

2016-01-28

We present the hypothesis that the mechanical properties of cement pastes depend strongly on their porosities. In a saturated paste, the porosity links to the free water volume after hydration. Structural water, constrained water, and free water have different dynamical behavior. Hence, it should be possible to extract information on pore system by exploiting the water dynamics. With our experiments we investigated the slow dynamics of hydration water confined in calcium- and magnesium-silicate-hydrate (C-S-H and M-S-H) gels using high-resolution quasi-elastic neutron scattering (QENS) technique. C-S-H and M-S-H are the chemical binders present in calcium rich and magnesium rich cements. Wemore » measured three M-S-H samples: pure M-S-H, M-S-H with aluminum-silicate nanotubes (ASN), and M-S-H with carboxyl group functionalized ASN (ASN-COOH). A C-S-H sample with the same water content (i.e. 0.3) is also studied for comparison. We found that structural water in the gels contributes to the elastic component of the QENS spectrum, while constrained water and free water contribute the quasi-elastic component. The quantitative analysis suggests that the three components vary for different samples and indicate the variance in the system porosity, which controls the mechanical properties of cement pastes.« less

Dynamical behaviors of structural, constrained and free water in calcium- and magnesium-silicate-hydrate gels

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

Le, Peisi; Fratini, Emiliano; Ito, Kanae

We present the hypothesis that the mechanical properties of cement pastes depend strongly on their porosities. In a saturated paste, the porosity links to the free water volume after hydration. Structural water, constrained water, and free water have different dynamical behavior. Hence, it should be possible to extract information on pore system by exploiting the water dynamics. With our experiments we investigated the slow dynamics of hydration water confined in calcium- and magnesium-silicate-hydrate (C-S-H and M-S-H) gels using high-resolution quasi-elastic neutron scattering (QENS) technique. C-S-H and M-S-H are the chemical binders present in calcium rich and magnesium rich cements. Wemore » measured three M-S-H samples: pure M-S-H, M-S-H with aluminum-silicate nanotubes (ASN), and M-S-H with carboxyl group functionalized ASN (ASN-COOH). A C-S-H sample with the same water content (i.e. 0.3) is also studied for comparison. We found that structural water in the gels contributes to the elastic component of the QENS spectrum, while constrained water and free water contribute the quasi-elastic component. The quantitative analysis suggests that the three components vary for different samples and indicate the variance in the system porosity, which controls the mechanical properties of cement pastes.« less

More Evidence of the Importance of Amorphous Silicates in CM Carbonaceous Chondrites: New Observations from a Fine-Grained Rim in the CM2 Chondrite, TIL 91722

NASA Astrophysics Data System (ADS)

Brearley, A. J.; Le Guillou, C.

2015-07-01

A fine-grained rim in TIL 91722 contains abundant amorphous silicate material containing nanophase sulfides. Phyllosilicates are rare. The amorphous material has a high ferric iron content indicative of oxidation coupled with hydration.

Assessing the mineralogy and hydration of rocky cores of satellites: insights from experiments and thermodynamics

NASA Astrophysics Data System (ADS)

Reynard, B.; Neri, A.; Sotin, C.

2016-12-01

Icy satellites and similar objects likely form from a mixture of hydrated rocky material, such as the CI chondrites, and various amounts of ices. Mass-balance estimates show that hydrous silicates such as serpentine, and brucite, the simple Mg-Fe hydroxide, dominate fully hydrated mineralogy. The inferred iron content of these minerals is, however, very dependent on assumptions of iron redox state, and whether it forms sulfides or segregates into a metal core. From the determination of the moment of inertia inferred from gravity measurements at Jupiter and Saturn by the Galileo and Cassini spacecraft, Ganymede and Europa would have a differentiated iron-rich core whereas Titan and Enceladus would not. Whatever the case, iron content is generally significantly higher than that of the terrestrial ultrabasic rocks used as analogs in modeling of hydrated satellite cores. Thus, we investigated the phase relations of iron-rich ultrabasic systems based on chondritic composition by combining thermodynamic modeling and preliminary high-pressure experiments. Our starting composition model is that of CI carbonaceous chondrites. Stable mineral assemblages are calculated with the PerpleX package (Connolly, 1990), assuming excess water, and various amounts of iron in the silicate phase through varying the amount of iron sulfide (troilite) or iron oxide (magnetite). Results show stable hydrated minerals are serpentine, chlorite, brucite, Na-phlogopite and in extreme cases, talc in the 1.5-5 GPa range relevant to bodies larger than about 1000 km in radius. Dehydration temperatures are extremely sensitive to the iron content, hence on the chosen amount of iron bearing phase (troilite or magnetite), and to a lower extent on average CI composition. An experimental approach was developed to simulate hydrous alteration of CI-like material. A mixture of synthetic silicates, troilite, and organic compounds, to which excess water is added, is used. Mineralogy and composition is checked using scanning electron microscopy and Raman spectroscopy. Preliminary results at 1.5 GPa are consistent with thermodynamic calculations. Implications for rocky cores are discussed. Connolly, J. A. D. (1990). Multivariable phase diagrams : an algorithm based on generalized thermodynamics, American Journal of Science, 290, 666-718.

Calcium silicate hydrates: Solid and liquid phase composition

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

Lothenbach, Barbara, E-mail: Barbara.lothenbach@empa.ch; Nonat, André

This paper presents a review on the relationship between the composition, the structure and the solution in which calcium silicate hydrate (C–S–H) is equilibrated. The silica chain length in C–S–H increases with the silicon concentration and the calcium content in the interlayer space with the calcium concentrations. Sodium and potassium are taken up in the interlayer space, preferentially at low calcium concentrations and thus by low Ca/Si C–S–H. Aluminium uptake in C–S–H increases strongly at higher aluminium concentrations in the solution. At low Ca/Si, aluminium substitutes silica in the bridging position, at Ca/Si > 1 aluminium is bound in TAH.more » Recently developed thermodynamic models are closely related to the structure of C–S–H and tobermorite, and able to model not only the solubility and the chemical composition of the C–S–H, but also to predict the mean silica chain length and the uptake of aluminium.« less

Early Age Carbonation Heat and Products of Tricalcium Silicate Paste Subject to Carbon Dioxide Curing.

PubMed

Li, Zhen; He, Zhen; Shao, Yixin

2018-05-04

This paper presents a study on the carbonation reaction heat and products of tricalcium silicate (C₃S) paste exposed to carbon dioxide (CO₂) for rapid curing. Reaction heat was measured using a retrofitted micro-calorimeter. The highest heat flow of a C₃S paste subject to carbonation curing was 200 times higher than that by hydration, and the cumulative heat released by carbonation was three times higher. The compressive strength of a C₃S paste carbonated for 2 h and 24 h was 27.5 MPa and 62.9 MPa, respectively. The 24-h carbonation strength had exceeded the hydration strength at 28 days. The CO₂ uptake of a C₃S paste carbonated for 2 h and 24 h was 17% and 26%, respectively. The X-ray diffraction (XRD), transmission electron microscope coupled with energy dispersive spectrometer (TEM-EDS), and 29 Si magic angle spinning⁻nuclear magnetic resonance ( 29 Si MAS-NMR) results showed that the products of a carbonated C₃S paste were amorphous silica (SiO₂) and calcite crystal. There was no trace of calcium silicate hydrate (C⁻S⁻H) or other polymorphs of calcium carbonate (CaCO₃) detected.

Drying-induced atomic structural rearrangements in sodium-based calcium-alumino-silicate-hydrate gel and the mitigating effects of ZrO2 nanoparticles

NASA Astrophysics Data System (ADS)

Yang, Kengran; Özçelik, V. Ongun; Garg, Nishant; Gong, Kai; White, Claire E.

Conventional drying of colloidal materials and gels (including cement) can lead to detrimental effects due to the buildup of internal stresses as water evaporates from the nano/microscopic pores. However, the underlying nanoscopic alterations in these gel materials that are, in part, responsible for macroscopically-measured strain values, especially at low relative humidity, remain a topic of open debate in the literature. In this study, sodium-based calcium-alumino-silicate-hydrate (C-(N)-A-S-H) gel, the major binding phase of silicate-activated blast furnace slag (one type of low-CO$_2$ cement), is investigated from a drying perspective, since it is known to suffer extensively from drying-induced microcracking. By employing in situ synchrotron X-ray total scattering measurements and pair distribution function (PDF) analysis we show that the significant contributing factor to the strain development in this material at extremely low relative humidity (0%) is the local atomic structural rearrangement of the C-(N)-A-S-H gel, including collapse of interlayer spacing and slight disintegration of the gel. Moreover, analysis of the medium range (1.0 - 2.2 nm) ordering in the PDF data reveals that the PDF-derived strain values are in much closer agreement (same order of magnitude) with the macroscopically measured strain data, compared to previous results based on reciprocal space X-ray diffraction data. From a mitigation standpoint, we show that small amounts of ZrO$_2$ nanoparticles are able to actively reinforce the structure of silicate-activated slag during drying, preventing atomic level strains from developing. Mechanistically, these nanoparticles induce growth of a silica-rich gel during drying, which, via density functional theory calculations, we show is attributed to the high surface reactivity of tetragonal ZrO$_2$.

Structural characterization of magnesium silicate hydrate: towards the design of eco-sustainable cements.

PubMed

Tonelli, M; Martini, F; Calucci, L; Fratini, E; Geppi, M; Ridi, F; Borsacchi, S; Baglioni, P

2016-02-28

Magnesium-based cement is one of the most interesting eco-sustainable alternatives to standard cementitious binders. The reasons for the interest towards this material are twofold: (i) its production process, using magnesium silicates, brine or seawater, dramatically reduces CO2 emissions with respect to Portland cement production, and (ii) it is very well suited to applications in radioactive waste encapsulation. In spite of its potential, assessment of the structural properties of its binder phase (magnesium silicate hydrate or M-S-H) is far from complete, especially because of its amorphous character. In this work, a comprehensive structural characterization of M-S-H was obtained using a multi-technique approach, including a detailed solid-state NMR investigation and, in particular, for the first time, quantitative (29)Si solid-state NMR data. M-S-H was prepared through room-temperature hydration of highly reactive MgO and silica fume and was monitored for 28 days. The results clearly evidenced the presence in M-S-H of "chrysotile-like" and "talc-like" sub-nanometric domains, which are approximately in a 1 : 1 molar ratio after long-time hydration. Both these kinds of domains have a high degree of condensation, corresponding to the presence of a small amount of silanols in the tetrahedral sheets. The decisive improvement obtained in the knowledge of M-S-H structure paves the way for tailoring the macroscopic properties of eco-sustainable cements by means of a bottom-up approach.

Calcium silicate-based sealers: Assessment of physicochemical properties, porosity and hydration.

PubMed

Marciano, Marina Angélica; Duarte, Marco Antonio Hungaro; Camilleri, Josette

2016-02-01

Investigation of hydration, chemical, physical properties and porosity of experimental calcium silicate-based sealers. Experimental calcium silicate-based sealers with calcium tungstate and zirconium oxide radio-opacifiers were prepared by mixing 1g of powder to 0.3 mL of 80% distilled water and 20% propylene glycol. MTA and MTA Fillapex were used as controls. The raw materials and set sealers were characterized using a combination of scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Physical properties were analyzed according to ANSI/ADA. The pH and calcium ion release were assessed after 3, 24, 72 and 168 h. The porosity was assessed using mercury intrusion porosimetry. The analysis of hydration of prototype sealers revealed calcium hydroxide as a by-product resulting in alkaline pH and detection of calcium ion release, with high values in initial periods. The radiopacity was similar to MTA for the sealers containing high amounts of radio-opacifiers (p>0.05). Flowability was higher and film thickness was lower for resinous MTA Fillapex sealer (p<0.05). The test sealers showed water sorption and porosity similar to MTA (p>0.05). The prototype sealers presented adequate hydration, elevated pH and calcium ion release. Regarding physical properties, elevated proportions of radio-opacifiers were necessary to accomplish adequate radiopacity, enhance flowability and reduce film thickness. All the tested sealers presented water sorption and porosity similar to MTA. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Hydration kinetics and morphology of cement pastes with pozzolanic volcanic ash studied via synchrotron-based techniques

DOE PAGES

Kupwade-Patil, Kunal; Chin, Stephanie; Ilavsky, Jan; ...

2017-10-13

Here, this study investigates the early ages of hydration behavior when basaltic volcanic ash was used as a partial substitute to ordinary Portland cement using ultra-small-angle X-ray scattering and wide-angle X-ray scattering (WAXS). The mix design consisted of 10, 30 and 50% substitution of Portland cement with two different-sized volcanic ashes. The data showed that substitution of volcanic ash above 30% results in excess unreacted volcanic ash, rather than additional pozzolanic reactions along longer length scales. WAXS studies revealed that addition of finely ground volcanic ash facilitated calcium-silicate-hydrate related phases, whereas inclusion of coarser volcanic ash caused domination by calcium-aluminum-silicate-hydratemore » and unreacted MgO phases, suggesting some volcanic ash remained unreacted throughout the hydration process. Addition of more than 30% volcanic ash leads to coarser morphology along with decreased surface area and higher intensity of scattering at early-age hydration. This suggests an abrupt dissolution indicated by changes in surface area due to the retarding gel formation that can have implication on early-age setting influencing the mechanical properties of the resulting cementitious matrix. The findings from this work show that the concentration of volcanic ash influences the specific surface area and morphology of hydration products during the early age of hydration. Therefore, natural pozzolanic volcanic ashes can be a viable substitute to Portland cement by providing environmental benefits in terms of lower-carbon footprint along with long-term durability.« less

Hydration kinetics and morphology of cement pastes with pozzolanic volcanic ash studied via synchrotron-based techniques

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

Kupwade-Patil, Kunal; Chin, Stephanie; Ilavsky, Jan

Here, this study investigates the early ages of hydration behavior when basaltic volcanic ash was used as a partial substitute to ordinary Portland cement using ultra-small-angle X-ray scattering and wide-angle X-ray scattering (WAXS). The mix design consisted of 10, 30 and 50% substitution of Portland cement with two different-sized volcanic ashes. The data showed that substitution of volcanic ash above 30% results in excess unreacted volcanic ash, rather than additional pozzolanic reactions along longer length scales. WAXS studies revealed that addition of finely ground volcanic ash facilitated calcium-silicate-hydrate related phases, whereas inclusion of coarser volcanic ash caused domination by calcium-aluminum-silicate-hydratemore » and unreacted MgO phases, suggesting some volcanic ash remained unreacted throughout the hydration process. Addition of more than 30% volcanic ash leads to coarser morphology along with decreased surface area and higher intensity of scattering at early-age hydration. This suggests an abrupt dissolution indicated by changes in surface area due to the retarding gel formation that can have implication on early-age setting influencing the mechanical properties of the resulting cementitious matrix. The findings from this work show that the concentration of volcanic ash influences the specific surface area and morphology of hydration products during the early age of hydration. Therefore, natural pozzolanic volcanic ashes can be a viable substitute to Portland cement by providing environmental benefits in terms of lower-carbon footprint along with long-term durability.« less

Sealing of cracks in cement using microencapsulated sodium silicate

NASA Astrophysics Data System (ADS)

Giannaros, P.; Kanellopoulos, A.; Al-Tabbaa, A.

2016-08-01

Cement-based materials possess an inherent autogenous self-healing capability allowing them to seal, and potentially heal, microcracks. This can be improved through the addition of microencapsulated healing agents for autonomic self-healing. The fundamental principle of this self-healing mechanism is that when cracks propagate in the cementitious matrix, they rupture the dispersed capsules and their content (cargo material) is released into the crack volume. Various healing agents have been explored in the literature for their efficacy to recover mechanical and durability properties in cementitious materials. In these materials, the healing agents are most commonly encapsulated in macrocontainers (e.g. glass tubes or capsules) and placed into the material. In this work, microencapsulated sodium silicate in both liquid and solid form was added to cement specimens. Sodium silicate reacts with the calcium hydroxide in hydrated cement paste to form calcium-silicate-hydrate gel that fills cracks. The effect of microcapsule addition on rheological and mechanical properties of cement is reported. It is observed that the microcapsule addition inhibits compressive strength development in cement and this is observed through a plateau in strength between 28 and 56 days. The improvement in crack-sealing for microcapsule-containing specimens is quantified through sorptivity measurements over a 28 day healing period. After just seven days, the addition of 4% microcapsules resulted in a reduction in sorptivity of up to 45% when compared to specimens without any microcapsule addition. A qualitative description of the reaction between the cargo material and the cementitious matrix is also provided using x-ray diffraction analysis.

Early Age Carbonation Heat and Products of Tricalcium Silicate Paste Subject to Carbon Dioxide Curing

PubMed Central

Li, Zhen; He, Zhen; Shao, Yixin

2018-01-01

This paper presents a study on the carbonation reaction heat and products of tricalcium silicate (C3S) paste exposed to carbon dioxide (CO2) for rapid curing. Reaction heat was measured using a retrofitted micro-calorimeter. The highest heat flow of a C3S paste subject to carbonation curing was 200 times higher than that by hydration, and the cumulative heat released by carbonation was three times higher. The compressive strength of a C3S paste carbonated for 2 h and 24 h was 27.5 MPa and 62.9 MPa, respectively. The 24-h carbonation strength had exceeded the hydration strength at 28 days. The CO2 uptake of a C3S paste carbonated for 2 h and 24 h was 17% and 26%, respectively. The X-ray diffraction (XRD), transmission electron microscope coupled with energy dispersive spectrometer (TEM-EDS), and 29Si magic angle spinning–nuclear magnetic resonance (29Si MAS-NMR) results showed that the products of a carbonated C3S paste were amorphous silica (SiO2) and calcite crystal. There was no trace of calcium silicate hydrate (C–S–H) or other polymorphs of calcium carbonate (CaCO3) detected. PMID:29734681

An Investigation into the Properties and Microstructure of Cement Mixtures Modified with Cellulose Nanocrystal

PubMed Central

Flores, Jessica; Kamali, Mahsa; Ghahremaninezhad, Ali

2017-01-01

This paper aims to examine the effect of cellulose nanocrystals (CNC) on the hydration, transport behavior, and microstructure of cement mixtures. The addition of CNC delayed hydration at an early age but improved hydration at later ages. A small increase in the electrical resistivity of the cement mixtures with CNC was observed. Statistical nanoindentation showed a small tendency to a larger volume fraction of high density calcium-silicate-hydrate (C-S-H) and a smaller volume fraction of low-density C-S-H in the mixture with CNC. PMID:28772857

Role of Clay Minerals in Long-Distance Transport of Landslides in Valles Marineris, Mars

NASA Astrophysics Data System (ADS)

Watkins, J.; Ehlmann, B. L.; Yin, A.

2014-12-01

Long-runout (> 50 km) subaerial landslides are rare on Earth, but are common features episodically shaping Mars' Valles Marineris (VM) trough system over the past 3.5 billion years. They display two end-member morphologies: a thick-skinned inner zone, characterized by fault-bounded, rotated blocks near their source region, and a thin-skinned, exceptionally long-runout outer zone, characterized by thin sheets spreading over 10s of km across the trough floor. Four decades of studies on the latter have resulted in two main competing hypotheses to explain their long-distance transport: (1) movement of landslides over layers of trapped air or soft materials containing ice or snow, enabling basal lubrication, and (2) fluidization of landslide materials with or without the presence of water and volatiles. To address this issue, we examine the mineralogic composition of landslides across VM using Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) near-infrared spectral data analysis coupled with detailed geologic mapping and morphometric analysis of satellite images. Our survey reveals a general correlation between transport distance, significant lateral spreading, and the presence of hydrated silicates among VM landslides. Given that smectite clay absorbs water into its layered crystal structure and can reduce the friction coefficient by a factor of three v. that of dry rocks, these results suggest that hydrated silicates played a decisive role in facilitating long-runout landslide transport in VM. We propose that, concurrent with downslope failure and sliding of broken trough-wall rock, frontal landslide masses overrode and entrained hydrated-silicate-bearing trough-floor deposits, lubricating the basal sliding zones and permitting the landslide outer zones to spread laterally while moving forward over the low-friction surface. The key participation of hydrated silicates in episodic, sustained landslide activity throughout the canyon implies that clay minerals, generated by water-rock interactions in the Noachian and Hesperian (4.1- 3.3 Ga), exert a long-lasting influence on geomorphic processes that shape the surface of the planet.

The crucial effect of early-stage gelation on the mechanical properties of cement hydrates

NASA Astrophysics Data System (ADS)

Ioannidou, Katerina; Kanduč, Matej; Li, Lunna; Frenkel, Daan; Dobnikar, Jure; Del Gado, Emanuela

2016-07-01

Gelation and densification of calcium-silicate-hydrate take place during cement hydration. Both processes are crucial for the development of cement strength, and for the long-term evolution of concrete structures. However, the physicochemical environment evolves during cement formation, making it difficult to disentangle what factors are crucial for the mechanical properties. Here we use Monte Carlo and Molecular Dynamics simulations to study a coarse-grained model of cement formation, and investigate the equilibrium and arrested states. We can correlate the various structures with the time evolution of the interactions between the nano-hydrates during the preparation of cement. The novel emerging picture is that the changes of the physicochemical environment, which dictate the evolution of the effective interactions, specifically favour the early gel formation and its continuous densification. Our observations help us understand how cement attains its unique strength and may help in the rational design of the properties of cement and related materials.

Optical Constants of Mars Candidate Materials used to Model Laboratory Reflectance Spectra of Mixtures

NASA Technical Reports Server (NTRS)

Roush, Ted L.; Brown, Adrian Jon; Blake, D.; Bristow, T.

2014-01-01

Data obtained at visible and nearinfrared wavelengths by OMEGA on MarsExpress and CRISM on MRO provide definitive evidence for the presence of phyllosilicates and other hydrated phases on Mars. A diverse range of both Fe/Mg-OH and Al- OH-bearing phyllosilicates were identified including the smectites nontronite, saponite, and montmorillonite. To constrain the abundances of these phyllosilicates, spectral analyses of mixtures are needed. We report on our effort to enable the quantitative evaluation of the abundance of hydrated-hydroxylated silicates when they are contained in mixtures. Here we focus on two component mixtures of the hydrated/ hydroxylated silicates, saponite and montmorillonite (Mg- and Al-rich smectites) with each other and with two analogs for other Martian materials; pyroxene (enstatite) and palagonitic soil (an alteration product of basaltic glass, hereafter referred to as palagonite). We prepared three size separates of each end-member for study: 20-45, 63-90, and 125-150 micron. Here we focus upon mixtures of the 63-90 m size fractions.

Intrinsic differences in atomic ordering of calcium (alumino)silicate hydrates in conventional and alkali-activated cements

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

White, Claire E., E-mail: whitece@princeton.edu; Andlinger Center for Energy and the Environment, Princeton University, Princeton; Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos

2015-01-15

The atomic structures of calcium silicate hydrate (C–S–H) and calcium (–sodium) aluminosilicate hydrate (C–(N)–A–S–H) gels, and their presence in conventional and blended cement systems, have been the topic of significant debate over recent decades. Previous investigations have revealed that synthetic C–S–H gel is nanocrystalline and due to the chemical similarities between ordinary Portland cement (OPC)-based systems and low-CO{sub 2} alkali-activated slags, researchers have inferred that the atomic ordering in alkali-activated slag is the same as in OPC–slag cements. Here, X-ray total scattering is used to determine the local bonding environment and nanostructure of C(–A)–S–H gels present in hydrated tricalcium silicatemore » (C{sub 3}S), blended C{sub 3}S–slag and alkali-activated slag, revealing the large intrinsic differences in the extent of nanoscale ordering between C–S–H derived from C{sub 3}S and alkali-activated slag systems, which may have a significant influence on thermodynamic stability, and material properties at higher length scales, including long term durability of alkali-activated cements.« less

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.

A contribution to the characterization of the silicate-water interface - Part I: Implication of a new polished sample hydration technique.

PubMed

Sowoidnich, T; Gordon, L; Naber, C; Bellmann, F; Neubauer, J; Joester, D

2018-06-11

The analysis of the atomic composition of the interface between tricalcium silicate (C 3 S), the main compound of Ordinary Portland Cement, and surrounding solution is still a challenging task. At the same time, that knowledge is of profound importance for describing the basic processes during hydration. By means of Scanning Electron Microscopy (SEM) and Atom Probe Tomography (APT) we combine modern techniques in order to shed light on this topic in the present study. The results of these methods are compared with conduction calorimetry as a standard technique to study the hydration kinetics of cement. The tests were carried out on powders as well as on polished C 3 S samples. Results indicate that the progress of hydration is strongly increased when the C 3 S is used in the form of polished specimen. First C-S-H phases are detected in the powder 2.2 h after contact with water, on the polished section after 5 min. Besides SEM, the formation of C-S-H phases can be detected by APT, leading to an advantageous atomic resolution compared to EDX analysis. We propose that the use of APT will lead to deeper insights on the hydration progress and on the composition of the sensitive C-S-H phases based on these first results. Copyright © 2018 Elsevier Ltd. All rights reserved.

Mineralogical Study of Hydrated IDPs: X-Ray Diffraction and Transmission Electron Microscopy

NASA Technical Reports Server (NTRS)

Nakamura, K.; Keller, L. P.; Nakamura, T.; Noguchi, T.; Zolensky, M. E.

2004-01-01

Chondritic hydrated interplanetary dust particles (IDPs) comprise up to 50% of all IDPs collected in the stratosphere [1]. Hydrated IDPs are generally believed to be derived from asteroidal sources that have undergone aqueous alteration. However, the high C contents of hydrated IDPs (by 2 to 6X CI levels [2,3]) indicate that they are probably not derived from the same parent bodies sampled by the known chondritic meteorites. Some hydrated IDPs exhibit large deuterium enrichments [4] similar to those observed in anhydrous IDPs. Both anhydrous and hydrated IDPs contain a variety of anhydrous minerals such as silicates, sulfides, oxides, and carbonates. Controversies on hydrated IDPs still exist regarding their formation, history, and relationship to other primitive solar system materials, because of the lack of a systematic series of analysis on individual hydrated IDPs. In this study, we combine our observations of the bulk mineralogy, mineral/ organic chemistry in order to derive a more complete picture of hydrated IDPs.

Alkali-activated complex binders from class C fly ash and Ca-containing admixtures.

PubMed

Guo, Xiaolu; Shi, Huisheng; Chen, Liming; Dick, Warren A

2010-01-15

Processes that maximize utilization of industrial solid wastes are greatly needed. Sodium hydroxide and sodium silicate solution were used to create alkali-activated complex binders (AACBs) from class C fly ash (CFA) and other Ca-containing admixtures including Portland cement (PC), flue gas desulfurization gypsum (FGDG), and water treatment residual (WTR). Specimens made only from CFA (CFA100), or the same fly ash mixed with 40 wt% PC (CFA60-PC40), with 10 wt% FGDG (CFA90-FGDG10), or with 10 wt% WTR (CFA90-WTR10) had better mechanical performance compared to binders using other mix ratios. The maximum compressive strength of specimens reached 80.0 MPa. Geopolymeric gel, sodium polysilicate zeolite, and hydrated products coexist when AACB reactions occur. Ca from CFA, PC, and WTR precipitated as Ca(OH)(2), bonded in geopolymers to obtain charge balance, or reacted with dissolved silicate and aluminate species to form calcium silicate hydrate (C-S-H) gel. However, Ca from FGDG probably reacted with dissolved silicate and aluminate species to form ettringite. Utilization of CFA and Ca-containing admixtures in AACB is feasible. These binders may be widely utilized in various applications such as in building materials and for solidification/stabilization of other wastes, thus making the wastes more environmentally benign.

High calcium fly ash geopolymer stabilized lateritic soil and granulated blast furnace slag blends as a pavement base material.

PubMed

Phummiphan, Itthikorn; Horpibulsuk, Suksun; Rachan, Runglawan; Arulrajah, Arul; Shen, Shui-Long; Chindaprasirt, Prinya

2018-01-05

Granulated Blast Furnace Slag (GBFS) was used as a replacement material in marginal lateritic soil (LS) while class C Fly Ash (FA) was used as a precursor for the geopolymerization process to develop a low-carbon pavement base material at ambient temperature. Unconfined Compression Strength (UCS) tests were performed to investigate the strength development of geopolymer stabilized LS/GBFS blends. Scanning Electron Microscopy and X-ray Diffraction analysis were undertaken to examine the role of the various influencing factors on UCS development. The influencing factors studied included GBFS content, Na 2 SiO 3 :NaOH ratio (NS:NH) and curing time. The 7-day soaked UCS of FA geopolymer stabilized LS/GBFS blends at various NS:NH ratios tested was found to satisfy the specifications of the Thailand national road authorities. The GBFS replacement was found to be insignificant for the improvement of the UCS of FA geopolymer stabilized LS/GBFS blends at low NS:NH ratio of 50:50. Microstructural analysis indicated the coexistence of Calcium Silicate Hydrate (CSH) and Sodium Alumino Silicate Hydrate products in FA geopolymer stabilized LS/GBFS blends. This research enables GBFS, which is traditionally considered as a waste material, to be used as a replacement and partially reactive material in FA geopolymer pavement applications. Copyright © 2017 Elsevier B.V. All rights reserved.

Interior Models for Saturn's Moon Titan Consistent with Cassini Observations

NASA Astrophysics Data System (ADS)

Castillo-Rogez, Julie

2013-10-01

We demonstrate that a model of Titan's interior with a core dominated by hydrated silicates can explain three major geophysical constraints available for this body: the mean moment of inertia (revised values currently in the literature or being published), tidal Love number k2, both of which were inferred from Cassini radio science observations, as well as indirect estimate of the dissipation factor inferred from Titan's orbital properties. Other models in which ice has remained partially mixed with silicates as a consequence of limited early heating fail to explain the dissipation factor. A core hydrated in silicate is difficult to maintain over the long term and may be in the process of dehydrating, which may involve significant transfer of water enriched in salts from the core to the ocean and destabilize the high-pressure ice layer. We will present possible observations that could help test this model with future observations to be obtained by the Cassini Orbiter. Acknowledgements: This work has been carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Government sponsorship acknowledged.

16 CFR 1304.3 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-01-01

...) Asbestos means a group of mineral fibers composed of hydrated silicates, oxygen, hydrogen, and other... distributed for sale to or for the personal use, consumption or enjoyment of consumers in or around a...

16 CFR 1304.3 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-01-01

...) Asbestos means a group of mineral fibers composed of hydrated silicates, oxygen, hydrogen, and other... distributed for sale to or for the personal use, consumption or enjoyment of consumers in or around a...

16 CFR 1304.3 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-01-01

...) Asbestos means a group of mineral fibers composed of hydrated silicates, oxygen, hydrogen, and other... distributed for sale to or for the personal use, consumption or enjoyment of consumers in or around a...

16 CFR § 1304.3 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-01-01

...) Asbestos means a group of mineral fibers composed of hydrated silicates, oxygen, hydrogen, and other... distributed for sale to or for the personal use, consumption or enjoyment of consumers in or around a...

Effect of Hydration and Confinement on Micro-Structure of Calcium-Silicate-Hydrate Gels

NASA Astrophysics Data System (ADS)

Gadde, Harish Kumar

Calcium-silicate-hydrate(C-S-H) gel is a primary nano-crystalline phase present in hydrated Ordinary Portland Cement (OPC) responsible for its strength and creep behavior. Our reliance on cement for infrastructure is global, and there is a need to improve infrastructure life-times. A way forward is to engineer the cement with more durability and long-term strength. The main purpose of this research is to quantify the micro-structure of C-S-H to see if cement can be engineered at various length scales to improve long-term behavior by spatial arrangement. We investigate the micro-structure evolution of C-S-H in cement as a function of hydration time and confinement. Scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to quantify the material and spatial properties of C-S-H as a function of hydration time. The data obtained from these experiments was used to identify C-S-H phases in cement sample. Pair Distribution Function (PDF) analysis of HD C-S-H phase with different hydration times was done at Advanced Photon Source, Argonne National Laboratory, beamline 11-ID-B. Only nonlinear trends in the atomic ordering of C-S-H gel as a function of hydration time were observed. Solid state 29Si Nuclear Magnetic Resonance (NMR) was used to quantify the effect of confinement on two types of C-S-H: white cement C-S-H and synthetic C-S-H. NMR spectra revealed that there is no significant difference in the structure of C-S-H due to confinement when compared with unconfined C-S-H. It is also found that there is significant difference in the Si environments of these two types of C-S-H. Though it does seem possible to engineer the cement on atomic scales, all these studies reveal that engineering cement on such a scale requires a more statistically accurate understanding of intricate structure of C-S-H than is currently available.

Copper Silicate Hydrate Hollow Spheres Constructed by Nanotubes Encapsulated in Reduced Graphene Oxide as Long-Life Lithium-Ion Battery Anode.

PubMed

Wei, Xiujuan; Tang, Chunjuan; Wang, Xuanpeng; Zhou, Liang; Wei, Qiulong; Yan, Mengyu; Sheng, Jinzhi; Hu, Ping; Wang, Bolun; Mai, Liqiang

2015-12-09

Hierarchical copper silicate hydrate hollow spheres-reduced graphene oxide (RGO) composite is successfully fabricated by a facile hydrothermal method using silica as in situ sacrificing template. The electrochemical performance of the composite as lithium-ion battery anode was studied for the first time. Benefiting from the synergistic effect of the hierarchical hollow structure and conductive RGO matrix, the composite exhibits excellent long-life performance and rate capability. A capacity of 890 mAh/g is achieved after 200 cycles at 200 mA/g and a capacity of 429 mAh/g is retained after 800 cycles at 1000 mA/g. The results indicate that the strategy of combining hierarchical hollow structures with conductive RGO holds the potential in addressing the volume expansion issue of high capacity anode materials.

Retrogressive hydration of calc-silicate xenoliths in the eastern Bushveld complex: evidence for late magmatic fluid movement

NASA Astrophysics Data System (ADS)

Wallmach, T.; Hatton, C. J.; De Waal, S. A.; Gibson, R. L.

1995-11-01

Two calc-silicate xenoliths in the Upper Zone of the Bushveld complex contain mineral assemblages which permit delineation of the metamorphic path followed after incorporation of the xenoliths into the magma. Peak metamorphism in these xenoliths occurred at T=1100-1200°C and P <1.5 kbar. Retrograde metamorphism, probably coinciding with the late magmatic stage, is characterized by the breakdown of akermanite to monticellite and wollastonite at 700°C and the growth of vesuvianite from melilite. The latter implies that water-rich fluids (X CO 2 <0.2) were present and probably circulating through the cooling magmatic pile. In contrast, calc-silicate xenoliths within the lower zones of the Bushveld complex, namely in the Marginal and Critical Zones, also contain melilite, monticellite and additional periclase with only rare development of vesuvianite. This suggests that the Upper Zone cumulate pile was much 'wetter' in the late-magmatic stage than the earlier-formed Critical and Marginal Zone cumulate piles.

Models of a partially hydrated Titan interior with clathrate crust

NASA Astrophysics Data System (ADS)

Lunine, J. I.; Castillo-Rogez, J.

2012-04-01

We present an updated model of the interior evolution of Titan over time, assuming the silicate core was hydrated early in Titan's history and is dehydrating over time. The original model presented in Castillo-Rogez and Lunine (2010) was motivated by a Cassini-derived moment of inertia (Iess et al., 2010) for Titan too large to be accommodated by classical fully differentiated models in which an anhydrous silicate core was overlain by a water ice (with possible perched ocean) mantle. Our model consisted of a silicate core still in the process of dehydrating today, a situation made possible by the leaching of radiogenic potassium from the silicates into the liquid water ocean. The crust of Titan was assumed to be pure water ice I. The model was consistent with the moment of inertia of Titan, but neglected the presence of large amounts of methane in the upper crust invoked to explain methane's persistence at present and through geologic time (Tobie et al. 2006). We have updated our model with such a feature. We have also improved our modeling with a better physical model for the dehydration of antigorite and other hydrated minerals. In particular our modeling now simulates heat advection resulting from water circulation (e.g., Seipold and Schilling 2003), rather than the purely conductive heat transfer regime assumed in the first version of our model. The modeling proceeds as in Castillo-Rogez and Lunine (2010), with the thermal conductivity of the methane clathrate crust rather than that of ice I. The former is several times lower than that of the latter, and the two have rather different temperature dependences (English and Tse, 2009). The crust turns out to have essentially no bearing on the temperature of the silicate core and hence the timing of dehydration, but it profoundly affects the thickness of the high-pressure ice layer beneath the ocean. Indeed, with the insulating methane clathrate crust, there must be a liquid water ocean beneath the methane clathrate crust and in contact with the silicates beneath for most of Titan's history. Although a high-pressure ice layer is likely in place today, it is thin enough that plumes of hot water from the dehydrating core probably breach the high pressure ice layer maintaining contact between the ocean and the silicate core. Part of this work has been performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Government sponsorship acknowledged.

Densification of the interlayer spacing governs the nanomechanical properties of calcium-silicate-hydrate

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

Geng, Guoqing; Myers, Rupert J.; Qomi, Mohammad Javad Abdolhosseini

Calciuam-silicate-hydrate (C-S-H) is the principal binding phase in modern concrete. Molecular simulations imply that its nanoscale stiffness is 'defect-driven', i.e., dominated by crystallographic defects such as bridging site vacancies in its silicate chains. However, experimental validation of this result is difficult due to the hierarchically porous nature of C-S-H down to nanometers. Here in this paper, we integrate high pressure X-ray diffraction and atomistic simulations to correlate the anisotropic deformation of nanocrystalline C-S-H to its atomic-scale structure, which is changed by varying the Ca-To-Si molar ratio. Contrary to the 'defect-driven' hypothesis, we clearly observe stiffening of C-S-H with increasing Ca/Simore » in the range 0.8 ≤ Ca/Si ≤ 1.3, despite increasing numbers of vacancies in its silicate chains. The deformation of these chains along the b-Axis occurs mainly through tilting of the Si-O-Si dihedral angle rather than shortening of the Si-O bond, and consequently there is no correlation between the incompressibilities of the a-and b-Axes and the Ca/Si. On the contrary, the intrinsic stiffness of C-S-H solid is inversely correlated with the thickness of its interlayer space. This work provides direct experimental evidence to conduct more realistic modelling of C-S-H-based cementitious material.« less

Densification of the interlayer spacing governs the nanomechanical properties of calcium-silicate-hydrate

DOE PAGES

Geng, Guoqing; Myers, Rupert J.; Qomi, Mohammad Javad Abdolhosseini; ...

2017-09-08

Calciuam-silicate-hydrate (C-S-H) is the principal binding phase in modern concrete. Molecular simulations imply that its nanoscale stiffness is 'defect-driven', i.e., dominated by crystallographic defects such as bridging site vacancies in its silicate chains. However, experimental validation of this result is difficult due to the hierarchically porous nature of C-S-H down to nanometers. Here in this paper, we integrate high pressure X-ray diffraction and atomistic simulations to correlate the anisotropic deformation of nanocrystalline C-S-H to its atomic-scale structure, which is changed by varying the Ca-To-Si molar ratio. Contrary to the 'defect-driven' hypothesis, we clearly observe stiffening of C-S-H with increasing Ca/Simore » in the range 0.8 ≤ Ca/Si ≤ 1.3, despite increasing numbers of vacancies in its silicate chains. The deformation of these chains along the b-Axis occurs mainly through tilting of the Si-O-Si dihedral angle rather than shortening of the Si-O bond, and consequently there is no correlation between the incompressibilities of the a-and b-Axes and the Ca/Si. On the contrary, the intrinsic stiffness of C-S-H solid is inversely correlated with the thickness of its interlayer space. This work provides direct experimental evidence to conduct more realistic modelling of C-S-H-based cementitious material.« less

Densification of the interlayer spacing governs the nanomechanical properties of calcium-silicate-hydrate.

PubMed

Geng, Guoqing; Myers, Rupert J; Qomi, Mohammad Javad Abdolhosseini; Monteiro, Paulo J M

2017-09-08

Calciuam-silicate-hydrate (C-S-H) is the principal binding phase in modern concrete. Molecular simulations imply that its nanoscale stiffness is 'defect-driven', i.e., dominated by crystallographic defects such as bridging site vacancies in its silicate chains. However, experimental validation of this result is difficult due to the hierarchically porous nature of C-S-H down to nanometers. Here, we integrate high pressure X-ray diffraction and atomistic simulations to correlate the anisotropic deformation of nanocrystalline C-S-H to its atomic-scale structure, which is changed by varying the Ca-to-Si molar ratio. Contrary to the 'defect-driven' hypothesis, we clearly observe stiffening of C-S-H with increasing Ca/Si in the range 0.8 ≤ Ca/Si ≤ 1.3, despite increasing numbers of vacancies in its silicate chains. The deformation of these chains along the b-axis occurs mainly through tilting of the Si-O-Si dihedral angle rather than shortening of the Si-O bond, and consequently there is no correlation between the incompressibilities of the a- and b-axes and the Ca/Si. On the contrary, the intrinsic stiffness of C-S-H solid is inversely correlated with the thickness of its interlayer space. This work provides direct experimental evidence to conduct more realistic modelling of C-S-H-based cementitious material.

Interpreting the 10 micron Astronomical Silicate Feature

NASA Astrophysics Data System (ADS)

Bowey, Janet E.

1998-11-01

10micron spectra of silicate dust in the diffuse medium towards Cyg OB2 no. 12 and towards field and embedded objects in the Taurus Molecular Cloud (TMC) were obtained with CGS3 at the United Kingdom Infrared Telescope (UKIRT). Cold molecular-cloud silicates are sampled in quiescent lines of sight towards the field stars Taurus-Elias 16 and Elias 13, whilst observations of the embedded young stellar objects HL Tau, Taurus-Elias 7 (Haro6-10) and Elias 18 also include emission from heated dust. To obtain the foreground silicate absorption profiles, featureless continua are estimated using smoothed astronomical and laboratory silicate emissivities. TMC field stars and Cyg OB2 no. 12 are modelled as photospheres reddened by foreground continuum and silicate extinction. Dust emission in the non-photospheric continua of HL Tau and Elias 7 (Haro6-10) is distinguished from foreground silicate absorption using a 10micron disk model, based on the IR-submm model of T Tauri stars by Adams, Lada & Shu (1988), with terms added to represent the foreground continuum and silicate extinction. The absorption profiles of HL Tau and Elias 7 are similar to that of the field star Elias 16. Fitted temperature indices of 0.43 (HL Tau) and 0.33 (Elias 7) agree with Boss' (1996) theoretical models of the 200-300K region, but are lower than those of IR-submm disks (0.5-0.61; Mannings & Emerson 1994); the modelled 10micron emission of HL Tau is optically thin, that of Elias 7 is optically thick. A preliminary arcsecond-resolution determination of the 10micron emissivity near θ1 Ori D in the Trapezium region of Orion and a range of emission temperatures (225-310K) are derived from observations by T. L. Hayward; this Ney-Allen emissivity is 0.6micron narrower than the Trapezium emissivity obtained by Forrest et al. (1975) with a large aperture. Published interstellar grain models, elemental abundances and laboratory studies of Solar System silicates (IDPs, GEMS and meteorites), the 10micron spectra of comets, interstellar silicates, synthetic silicates and terrestrial minerals, and the effects of laboratory processing on the 10micron spectra of crystalline and amorphous silicates are reviewed to provide insight into the mineralogy of interstellar silicate dust. The wavelengths of the peaks of the 10micron silicate profiles decrease between circumstellar, diffuse medium and molecular-cloud environments, indicating (after Gürtler & Henning 1986) that the amorphous pyroxene content of initially olivine-rich interstellar dust increases with time. This is accompanied by an increase in the FWHM of the features which indicates an increase in grain size and/or an increasing fraction of chemically-varied crystalline pyroxene. Fine structure in the Cyg OB2 no. 12, Elias 16, Elias 7, HL Tau profiles indicate that hydrated layer silicates similar to terrestrial serpentines, clays and talc may be a ubiquitous component of interstellar dust. At 10microns the narrow bands of mixed crystalline pyroxenes blend, making their identification difficult. Since no fine structure is observed near 11.2microns, the fraction of crystalline olivine is small. In geology direct olivine-plus-SiO2 to pyroxene reactions occur only at high pressure within the terrestrial mantle. Therefore the fraction of amorphous pyroxene is probably increased by the hydration of Mg-rich olivine to form a serpentine-like hydrated silicate, which is subsequently annealed to form a mixture of amorphous pyroxene and olivine. Terrestrial and laboratory olivine samples are readily converted to serpentine in the presence of water, and (after extended annealing) the first crystalline band to appear is the 11.2micron olivine feature frequently observed in cometary spectra.

Producing Durable Continuously Reinforced Concrete Pavement using Glass-ceramic Coated Reinforcing Steel

DTIC Science & Technology

2010-02-01

reinforcement if the enamel is broken  Embedded cement grains hydrate if enamel is cracked to self-heal with the formation of calcium silicate hydrate Goal...Reinforced Concrete Pavement The 600% volume change in the iron to iron oxide formation put the concrete in tension and it cracks an spalls BUILDING...corrodes prematurely and delaminates the pavement  Moisture and chlorides can move through the natural porosity of concrete and the cracks in the

Nanoscale Charge-Balancing Mechanism in Alkali-Substituted Calcium-Silicate-Hydrate Gels.

PubMed

Özçelik, V Ongun; White, Claire E

2016-12-15

Alkali-activated materials and related alternative cementitious systems are sustainable technologies that have the potential to substantially lower the CO 2 emissions associated with the construction industry. However, these systems have augmented chemical compositions as compared to ordinary Portland cement (OPC), which may impact the evolution of the hydrate phases. In particular, calcium-silicate-hydrate (C-S-H) gel, the main hydrate phase in OPC, is likely to be altered at the atomic scale due to changes in the bulk chemical composition, specifically via the addition of alkalis (i.e., Na or K) and aluminum. Here, via density functional theory calculations, we reveal the presence of a charge balancing mechanism at the molecular level in C-S-H gel (as modeled using crystalline 14 Å tobermorite) when alkalis and aluminum atoms are introduced into the structure. Different structural representations are obtained depending on the level of substitution and the degree of charge balancing incorporated in the structures. The impact of these substitutional and charge balancing effects on the structures is assessed by analyzing the formation energies, local bonding environments, diffusion barriers and mechanical properties. The results of this computational study provide information on the phase stability of alkali/aluminum containing C-S-H gels, shedding light on the fundamental atomic level mechanisms that play a crucial role in these complex disordered materials.

Analysis of the Optimum Usage of Slag for the Compressive Strength of Concrete.

PubMed

Lee, Han-Seung; Wang, Xiao-Yong; Zhang, Li-Na; Koh, Kyung-Taek

2015-03-18

Ground granulated blast furnace slag is widely used as a mineral admixture to replace partial Portland cement in the concrete industry. As the amount of slag increases, the late-age compressive strength of concrete mixtures increases. However, after an optimum point, any further increase in slag does not improve the late-age compressive strength. This optimum replacement ratio of slag is a crucial factor for its efficient use in the concrete industry. This paper proposes a numerical procedure to analyze the optimum usage of slag for the compressive strength of concrete. This numerical procedure starts with a blended hydration model that simulates cement hydration, slag reaction, and interactions between cement hydration and slag reaction. The amount of calcium silicate hydrate (CSH) is calculated considering the contributions from cement hydration and slag reaction. Then, by using the CSH contents, the compressive strength of the slag-blended concrete is evaluated. Finally, based on the parameter analysis of the compressive strength development of concrete with different slag inclusions, the optimum usage of slag in concrete mixtures is determined to be approximately 40% of the total binder content. The proposed model is verified through experimental results of the compressive strength of slag-blended concrete with different water-to-binder ratios and different slag inclusions.

Analysis of the Optimum Usage of Slag for the Compressive Strength of Concrete

PubMed Central

Lee, Han-Seung; Wang, Xiao-Yong; Zhang, Li-Na; Koh, Kyung-Taek

2015-01-01

Ground granulated blast furnace slag is widely used as a mineral admixture to replace partial Portland cement in the concrete industry. As the amount of slag increases, the late-age compressive strength of concrete mixtures increases. However, after an optimum point, any further increase in slag does not improve the late-age compressive strength. This optimum replacement ratio of slag is a crucial factor for its efficient use in the concrete industry. This paper proposes a numerical procedure to analyze the optimum usage of slag for the compressive strength of concrete. This numerical procedure starts with a blended hydration model that simulates cement hydration, slag reaction, and interactions between cement hydration and slag reaction. The amount of calcium silicate hydrate (CSH) is calculated considering the contributions from cement hydration and slag reaction. Then, by using the CSH contents, the compressive strength of the slag-blended concrete is evaluated. Finally, based on the parameter analysis of the compressive strength development of concrete with different slag inclusions, the optimum usage of slag in concrete mixtures is determined to be approximately 40% of the total binder content. The proposed model is verified through experimental results of the compressive strength of slag-blended concrete with different water-to-binder ratios and different slag inclusions. PMID:28787998

Docking 90Sr radionuclide in cement: An atomistic modeling study

NASA Astrophysics Data System (ADS)

Youssef, Mostafa; Pellenq, Roland J.-M.; Yildiz, Bilge

Cementitious materials are considered to be a waste form for the ultimate disposal of radioactive materials in geological repositories. We investigated by means of atomistic simulations the encapsulation of strontium-90, an important radionuclide, in calcium-silicate-hydrate (C-S-H) and its crystalline analog, the 9 Å-tobermorite. C-S-H is the major binding phase of cement. Strontium was shown to energetically favor substituting calcium in the interlayer sites in C-S-H and 9 Å-tobermorite with the trend more pronounced in the latter. The integrity of the silicate chains in both cementitious waste forms were not affected by strontium substitution within the time span of molecular dynamics simulation. Finally, we observed a limited degradation of the mechanical properties in the strontium-containing cementitious waste form with the increasing strontium concentration. These results suggest the cement hydrate as a good candidate for immobilizing radioactive strontium.

Potential Applications of Alkali-Activated Alumino-Silicate Binders in Military Operations

DTIC Science & Technology

1985-11-01

Geopolymers for Reinforced Plastics/ Composits ," PACTEC 󈨓, Society of Plastic Engineers, Costa Mesa, CA, 1979, pp. 151-153. Davidovits, Joseph. 1983...34 Geopolymers II, Processing and Applications of Ultra-High Temperature, Inorganic Matrix Resin for Cast Composite Structures, Molds and Tools for RP/C and...alumino-silicate hydrates with an approximate composition of 3CaO - AI20 3 • 2i0 2 2120, begin to crystallize. As the gels begin to coalesce, bound water

Toward an understanding of surface layer formation, growth, and transformation at the glass-fluid interface

NASA Astrophysics Data System (ADS)

Hopf, J.; Eskelsen, J. R.; Chiu, M.; Ievlev, A. V.; Ovchinnikova, O. S.; Leonard, D.; Pierce, E. M.

2018-05-01

Silicate glass is a metastable and durable solid that has application to a number of energy and environmental challenges (e.g., microelectronics, fiber optics, and nuclear waste storage). If allowed to react with water over time silicate glass develops an altered layer at the solid-fluid interface. In this study, we used borosilicate glass (LAWB45) as a model material to develop a robust understanding of altered layer formation (i.e., amorphous hydrated surface layer and crystalline reaction products). Experiments were conducted at high surface area-to-volume ratio (∼200,000 m-1) and 90 °C in the pressurized unsaturated flow (PUF) apparatus for 1.5-years to facilitate the formation of thick altered layers and allow for the effluent solution chemistry to be monitored continuously. A variety of microscopy techniques were used to characterize reacted grains and suggest the average altered layer thickness is 13.2 ± 8.3 μm with the hydrated and clay layer representing 74.8% and 25.2% of the total altered layer, respectively. The estimate of hydrated layer thickness is within the experimental error of the value estimated from the B release rate data (∼10 ± 1 μm/yr) over the 1.5-year duration. PeakForce® quantitative nanomechanical mapping results suggest the hydrated layer has a modulus that ranges between ∼20 and 40 GPa, which is in the range of porous silica that contains from ∼20 to ∼50% porosity, yet significantly lower than dense silica (∼70-80 GPa). Scanning transmission electron microscopy (STEM) images confirm the presence of pores and an analysis of a higher resolution image provides a qualitative estimate of ≥22% porosity in the hydrated layer with variations in void volume with increasing distance from the unaltered glass. Chemical composition analyses, based on a combination of time-of-flight secondary-ion mass spectrometry (ToF-SIMS), scanning electron microscopy with X-ray energy dispersive spectroscopy (EDS), and STEM-EDS, clearly show that the altered layer is mainly composed of Al, H, Si, and O with the clay layer being enriched in Li, Zn, Fe, and Mg. The amorphous hydrated layer is enriched in Ca, H, and Zr with a minor amount of K. Furthermore, ToF-SIMS results also suggest the B profile is anti-correlated with the H profile in the hydrated layer. Our selected-area electron diffraction results suggest the structure of the hydrated layer closely resembles opal-AG (amorphous gel-like) with an average crystallite size of ∼0.7 nm which is smaller than the critical nucleus for silica nanoparticles (i.e., 1.4-3 nm). These results suggest the hydrated layer is more consistent with a polymeric gel rather than a colloidal gel and is comprised of molecular units (<1 nm in size) that result from the difficult to hydrolyze bonds, such as Sisbnd Osbnd Zr units, during the glass corrosion process. The size of individual particles or molecular units is a function of formation conditions (e.g., pH, ionic strength, nano-confinement, solute composition) in the hydrated layer.

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

Mendoza, Oscar, E-mail: oamendoz@unal.edu.co; Giraldo, Carolina; Camargo, Sergio S.

This research evaluates the effect of sodium and potassium hydroxide on the structure and nano-mechanical properties of Calcium Silicate Hydrate (C-S-H) formed from the hydration of pure alite. Monoclinic (MIII) alite was synthesized and hydrated, using water-to-alite ratios of 0.5 and 0.6 and additions of 10% NaOH and KOH by weight of alite. Based on results of X-ray diffraction, isothermal calorimetry, thermogravimetric analysis, Nuclear Magnetic Resonance and nanoindentation, two different effects of the alkaline hydroxides on the hydration reaction of alite, both at early and later ages, can be identified: (i) a differentiated hydration process, attributed to an enhancement inmore » calcium hydroxide (CH) precipitation and a stimulation of the C-S-H nuclei; and (ii) an increase in the elastic modulus of the C-S-H aggregations, attributed to an electrostatic attraction between positive charges from the alkaline cations and negative charges from the C-S-H structure.« less

Why alite stops hydrating below 80% relative humidity

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

Flatt, Robert J.; Scherer, George W., E-mail: scherer@princeton.edu; Bullard, Jeffrey W.

2011-09-15

It has been observed that the hydration of cement paste stops when the relative humidity drops below about 80%. A thermodynamic analysis shows that the capillary pressure exerted at that RH shifts the solubility of tricalcium silicate, so that it is in equilibrium with water. This is a reflection of the chemical shrinkage in this system: according to Le Chatelier's principle, since the volume of the products is less than that of the reactants, a negative (capillary) pressure opposes the reaction.

21 CFR 186.1256 - Clay (kaolin).

Code of Federal Regulations, 2012 CFR

2012-04-01

... CONSUMPTION (CONTINUED) INDIRECT FOOD SUBSTANCES AFFIRMED AS GENERALLY RECOGNIZED AS SAFE Listing of Specific...-58-7) consists of hydrated aluminum silicate. The commercial products of clay (kaolin) contain... kaolin. Kaolinite or china clay is whiter, less contaminated with extraneous minerals, and less plastic...

21 CFR 186.1256 - Clay (kaolin).

Code of Federal Regulations, 2011 CFR

2011-04-01

... CONSUMPTION (CONTINUED) INDIRECT FOOD SUBSTANCES AFFIRMED AS GENERALLY RECOGNIZED AS SAFE Listing of Specific...-58-7) consists of hydrated aluminum silicate. The commercial products of clay (kaolin) contain... kaolin. Kaolinite or china clay is whiter, less contaminated with extraneous minerals, and less plastic...

21 CFR 186.1256 - Clay (kaolin).

Code of Federal Regulations, 2013 CFR

2013-04-01

... CONSUMPTION (CONTINUED) INDIRECT FOOD SUBSTANCES AFFIRMED AS GENERALLY RECOGNIZED AS SAFE Listing of Specific...-58-7) consists of hydrated aluminum silicate. The commercial products of clay (kaolin) contain... kaolin. Kaolinite or china clay is whiter, less contaminated with extraneous minerals, and less plastic...

21 CFR 186.1256 - Clay (kaolin).

Code of Federal Regulations, 2010 CFR

2010-04-01

... CONSUMPTION (CONTINUED) INDIRECT FOOD SUBSTANCES AFFIRMED AS GENERALLY RECOGNIZED AS SAFE Listing of Specific...-58-7) consists of hydrated aluminum silicate. The commercial products of clay (kaolin) contain... kaolin. Kaolinite or china clay is whiter, less contaminated with extraneous minerals, and less plastic...

Characterization of iron-phosphate-silicate chemical garden structures.

PubMed

Barge, Laura M; Doloboff, Ivria J; White, Lauren M; Stucky, Galen D; Russell, Michael J; Kanik, Isik

2012-02-28

Chemical gardens form when ferrous chloride hydrate seed crystals are added or concentrated solutions are injected into solutions of sodium silicate and potassium phosphate. Various precipitation morphologies are observed depending on silicate and phosphate concentrations, including hollow plumes, bulbs, and tubes. The growth of precipitates is controlled by the internal osmotic pressure, fluid buoyancy, and membrane strength. Additionally, rapid bubble-led growth is observed when silicate concentrations are high. ESEM/EDX analysis confirms compositional gradients within the membranes, and voltage measurements across the membranes during growth show a final potential of around 150-200 mV, indicating that electrochemical gradients are maintained across the membranes as growth proceeds. The characterization of chemical gardens formed with iron, silicate, and phosphate, three important components of an early earth prebiotic hydrothermal system, can help us understand the properties of analogous structures that likely formed at submarine alkaline hydrothermal vents in the Hadean-structures offering themselves as the hatchery of life. © 2011 American Chemical Society

Cement hydration from hours to centuries controlled by diffusion through barrier shells of C-S-H

NASA Astrophysics Data System (ADS)

Rahimi-Aghdam, Saeed; Bažant, Zdeněk P.; Abdolhosseini Qomi, M. J.

2017-02-01

Although a few good models for cement hydration exist, they have some limitations. Some do not take into account the complete range of variation of pore relative humidity and temperature, and apply over durations limited from up a few months to up to about a year. The ones that are applicable for long durations are either computationally too intensive for use in finite element programs or predict the hydration to terminate after few months. However, recent tests of autogenous shrinkage and swelling in water imply that the hydration may continue, at decaying rate, for decades, provided that a not too low relative pore humidity (above 0.7) persists for a long time, as expected for the cores of thick concrete structural members. Therefore, and because design lifetimes of over hundred years are required for large concrete structures, a new hydration model for a hundred year lifespan and beyond is developed. The new model considers that, after the first day of hydration, the remnants of anhydrous cement grains, gradually consumed by hydration, are enveloped by contiguous, gradually thickening, spherical barrier shells of calcium-silicate hydrate (C-S-H). The hydration progress is controlled by transport of water from capillary pores through the barrier shells toward the interface with anhydrous cement. The transport is driven by a difference of humidity, defined by equivalence with the difference in chemical potential of water. Although, during the period of 4-24 h, the C-S-H forms discontinuous nano-globules around the cement grain, an equivalent barrier shell control was formulated for this period, too, for ease and effectiveness of calculation. The entire model is calibrated and validated by published test data on the evolution of hydration degree for various cement types, particle size distributions, water-cement ratios and temperatures. Computationally, this model is sufficiently effective for calculating the evolution of hydration degree (or aging) at every integration point of every finite element in a large structure.

Deciphering mineralogical changes and carbonation development during hydration and ageing of a consolidated ternary blended cement paste

PubMed Central

Grangeon, Sylvain; De Nolf, Wout; Harker, Nicholas; Boulahya, Faiza; Bourbon, Xavier

2018-01-01

To understand the main properties of cement, a ubiquitous material, a sound description of its chemistry and mineralogy, including its reactivity in aggressive environments and its mechanical properties, is vital. In particular, the porosity distribution and associated sample carbonation, both of which affect cement’s properties and durability, should be quantified accurately, and their kinetics and mechanisms of formation known both in detail and in situ. However, traditional methods of cement mineralogy analysis (e.g. chemical mapping) involve sample preparation (e.g. slicing) that can be destructive and/or expose cement to the atmosphere, leading to preparation artefacts (e.g. dehydration). In addition, the kinetics of mineralogical development during hydration, and associated porosity development, cannot be examined. To circumvent these issues, X-ray diffraction computed tomography (XRD-CT) has been used. This allowed the mineralogy of ternary blended cement composed of clinker, fly ash and blast furnace slag to be deciphered. Consistent with previous results obtained for both powdered samples and dilute systems, it was possible, using a consolidated cement paste (with a water-to-solid ratio akin to that used in civil engineering), to determine that the mineralogy consists of alite (only detected in the in situ hydration experiment), calcite, calcium silicate hydrates (C-S-H), ettringite, mullite, portlandite, and an amorphous fraction of unreacted slag and fly ash. Mineralogical evolution during the first hydration steps indicated fast ferrite reactivity. Insights were also gained into how the cement porosity evolves over time and into associated spatially and time-resolved carbonation mechanisms. It was observed that macroporosity developed in less than 30 h of hydration, with pore sizes reaching about 100–150 µm in width. Carbonation was not observed for this time scale, but was found to affect the first 100 µm of cement located around macropores in a sample cured for six months. Regarding this carbonation, the only mineral detected was calcite. PMID:29765604

Toward an Understanding of Surface Layer Formation, Growth, and Transformation at the Glass–Fluid Interface

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

Hopf, Juliane; Eskelsen, Jeremy R.; Chiu, Michelle Y.

Silicate glass is a metastable and durable solid that has application to a number of energy and environmental challenges (e.g., microelectronics, fiber optics, and nuclear waste storage). If allowed to react with water over time silicate glass develops an altered layer at the solid-fluid interface. In this study, we used borosilicate glass (LAWB45) as model material to develop a robust understanding of altered layer formation (i.e., amorphous hydrated surface layer and crystalline reaction products). Experiments were conducted at high surface area-to-volume ratio (~200,000 m-1) and 90 °C in the pressurized unsaturated flow (PUF) apparatus for 1.5-years to facilitate the formationmore » of thick altered layers and allow for the effluent solution chemistry to be monitored continuously. A variety of microscopy techniques were used to characterized reacted grains and suggest the average altered layer thickness is 13.2 ± 8.3 μm with the hydrated and clay layer representing 74.8% and 25.2% of the total altered layer, respectively. This estimate is within the experimental error of the value estimated from the B release rate data (~10 ±1 μm/yr) over the 1.5-year duration. PeakForce® quantitative nanomechanical mapping results suggest the hydrated layer has a modulus that ranges between ~20 to 40 GPa, which is in the range of porous silica that contains from ~20 to ~50% porosity, yet significantly lower than dense silica (~70 to 80 GPa). Scanning transmission electron microscopy (STEM) images confirm the presence of pores and an analysis of a higher resolution image of a region provides a qualitative estimate of ≥ 22% porosity in this layer with variations in the hydrated layer in void volume with increasing distance from the unaltered glass. Chemical composition analyses, based on a combination of time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and scanning electron microscopy with X-ray energy dispersive spectroscopy (EDS) and STEM-EDS, clearly show that the altered layer is mainly composed of Al, H, Si, and O with the clay layer being enriched in Li, Zn, Fe, and Mg. The amorphous hydrated layer is enriched in Ca, H, and Zr with a minor amount of K. Furthermore, ToF-SIMS results also suggest the B profile is anti-correlated with the H profile in the hydrated layer. Our selected-area electron diffraction results suggest the structure of the hydrated layer closely resembles opal-AG (amorphous gel-like) with an average crystallite size of ~0.7 nm which is smaller than the critical nucleus for silica nanoparticles (i.e., 1.4 to 3 nm). These results suggest the hydrated layer is more consistent with a polymeric gel rather than a colloidal gel and is comprised of molecular units (<1 nm in size) that result from the difficult to hydrolyze bonds, such as Si—O—Zr units, during the glass corrosion process. The size of individual particles or molecular units is a function of formation conditions (e.g., pH, ionic strength, nano-confinement, solute composition) in the hydrated layer.« less

Toward an Understanding of Surface Layer Formation, Growth, and Transformation at the Glass–Fluid Interface

DOE PAGES

Hopf, Juliane; Eskelsen, Jeremy R.; Chiu, Michelle Y.; ...

2018-02-01

Silicate glass is a metastable and durable solid that has application to a number of energy and environmental challenges (e.g., microelectronics, fiber optics, and nuclear waste storage). If allowed to react with water over time silicate glass develops an altered layer at the solid-fluid interface. In this study, we used borosilicate glass (LAWB45) as model material to develop a robust understanding of altered layer formation (i.e., amorphous hydrated surface layer and crystalline reaction products). Experiments were conducted at high surface area-to-volume ratio (~200,000 m-1) and 90 °C in the pressurized unsaturated flow (PUF) apparatus for 1.5-years to facilitate the formationmore » of thick altered layers and allow for the effluent solution chemistry to be monitored continuously. A variety of microscopy techniques were used to characterized reacted grains and suggest the average altered layer thickness is 13.2 ± 8.3 μm with the hydrated and clay layer representing 74.8% and 25.2% of the total altered layer, respectively. This estimate is within the experimental error of the value estimated from the B release rate data (~10 ±1 μm/yr) over the 1.5-year duration. PeakForce® quantitative nanomechanical mapping results suggest the hydrated layer has a modulus that ranges between ~20 to 40 GPa, which is in the range of porous silica that contains from ~20 to ~50% porosity, yet significantly lower than dense silica (~70 to 80 GPa). Scanning transmission electron microscopy (STEM) images confirm the presence of pores and an analysis of a higher resolution image of a region provides a qualitative estimate of ≥ 22% porosity in this layer with variations in the hydrated layer in void volume with increasing distance from the unaltered glass. Chemical composition analyses, based on a combination of time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and scanning electron microscopy with X-ray energy dispersive spectroscopy (EDS) and STEM-EDS, clearly show that the altered layer is mainly composed of Al, H, Si, and O with the clay layer being enriched in Li, Zn, Fe, and Mg. The amorphous hydrated layer is enriched in Ca, H, and Zr with a minor amount of K. Furthermore, ToF-SIMS results also suggest the B profile is anti-correlated with the H profile in the hydrated layer. Our selected-area electron diffraction results suggest the structure of the hydrated layer closely resembles opal-AG (amorphous gel-like) with an average crystallite size of ~0.7 nm which is smaller than the critical nucleus for silica nanoparticles (i.e., 1.4 to 3 nm). These results suggest the hydrated layer is more consistent with a polymeric gel rather than a colloidal gel and is comprised of molecular units (<1 nm in size) that result from the difficult to hydrolyze bonds, such as Si—O—Zr units, during the glass corrosion process. The size of individual particles or molecular units is a function of formation conditions (e.g., pH, ionic strength, nano-confinement, solute composition) in the hydrated layer.« less

Amphibole and Phlogopite Formation on the R Chondrite Parent Body: An Experimental Investigation

NASA Astrophysics Data System (ADS)

Lunning, N. G.; Waters, L. E.; McCoy, T. J.

2017-07-01

High-temperature hydrated minerals can form at the pressures and the temperatures expected for the interiors of planetesimals. Under water-saturated conditions, minimum silicate melting can initiate at temperatures as low as 870°C at 40 MPa.

A novel sol-gel-derived calcium silicate cement with short setting time for application in endodontic repair of perforations

PubMed Central

Lee, Bor-Shiunn; Lin, Hong-Ping; Chan, Jerry Chun-Chung; Wang, Wei-Chuan; Hung, Ping-Hsuan; Tsai, Yu-Hsin; Lee, Yuan-Ling

2018-01-01

Mineral trioxide aggregate (MTA) is the most frequently used repair material in endodontics, but the long setting time and reduced mechanical strength in acidic environments are major shortcomings. In this study, a novel sol-gel-derived calcium silicate cement (sCSC) was developed using an initial Ca/Si molar ratio of 3, with the most effective mixing orders of reactants and optimal HNO3 catalyst volumes. A Fourier transform infrared spectrometer, scanning electron microscope with energy-dispersive X-ray spectroscopy, and X-ray powder diffractometer were used for material characterization. The setting time, compressive strength, and microhardness of sCSC after hydration in neutral and pH 5 environments were compared with that of MTA. Results showed that sCSC demonstrated porous microstructures with a setting time of ~30 min, and the major components of sCSC were tricalcium silicate, dicalcium silicate, and calcium oxide. The optimal formula of sCSC was sn200, which exhibited significantly higher compressive strength and microhardness than MTA, irrespective of neutral or pH 5 environments. In addition, both sn200 and MTA demonstrated good biocompatibility because cell viability was similar to that of the control. These findings suggest that sn200 merits further clinical study for potential application in endodontic repair of perforations. PMID:29386894

A novel sol-gel-derived calcium silicate cement with short setting time for application in endodontic repair of perforations.

PubMed

Lee, Bor-Shiunn; Lin, Hong-Ping; Chan, Jerry Chun-Chung; Wang, Wei-Chuan; Hung, Ping-Hsuan; Tsai, Yu-Hsin; Lee, Yuan-Ling

2018-01-01

Mineral trioxide aggregate (MTA) is the most frequently used repair material in endodontics, but the long setting time and reduced mechanical strength in acidic environments are major shortcomings. In this study, a novel sol-gel-derived calcium silicate cement (sCSC) was developed using an initial Ca/Si molar ratio of 3, with the most effective mixing orders of reactants and optimal HNO 3 catalyst volumes. A Fourier transform infrared spectrometer, scanning electron microscope with energy-dispersive X-ray spectroscopy, and X-ray powder diffractometer were used for material characterization. The setting time, compressive strength, and microhardness of sCSC after hydration in neutral and pH 5 environments were compared with that of MTA. Results showed that sCSC demonstrated porous microstructures with a setting time of ~30 min, and the major components of sCSC were tricalcium silicate, dicalcium silicate, and calcium oxide. The optimal formula of sCSC was sn200, which exhibited significantly higher compressive strength and microhardness than MTA, irrespective of neutral or pH 5 environments. In addition, both sn200 and MTA demonstrated good biocompatibility because cell viability was similar to that of the control. These findings suggest that sn200 merits further clinical study for potential application in endodontic repair of perforations.

Mineral resource of the month: Vermiculite

USGS Publications Warehouse

Tanner, Arnold O.

2014-01-01

Vermiculite comprises a group of hydrated, laminar magnesium-aluminum-iron silicate minerals resembling mica. They are secondary minerals, typically altered biotite, iron-rich phlogopite or other micas or clay-like minerals that are themselves sometimes alteration products of amphibole, chlorite, olivine and pyroxene. Vermiculite deposits are associated with volcanic ultramafic rocks rich in magnesium silicate minerals, and flakes of the mineral range in color from black to shades of brown and yellow. The crystal structure of vermiculite contains water molecules, a property that is critical to its processing for common uses.

Revealing the Effect of Irradiation on Cement Hydrates: Evidence of a Topological Self-Organization.

PubMed

Krishnan, N M Anoop; Wang, Bu; Sant, Gaurav; Phillips, James C; Bauchy, Mathieu

2017-09-20

Despite the crucial role of concrete in the construction of nuclear power plants, the effects of radiation exposure (i.e., in the form of neutrons) on the calcium-silicate-hydrate (C-S-H, i.e., the glue of concrete) remain largely unknown. Using molecular dynamics simulations, we systematically investigate the effects of irradiation on the structure of C-S-H across a range of compositions. Expectedly, although C-S-H is more resistant to irradiation than typical crystalline silicates, such as quartz, we observe that radiation exposure affects C-S-H's structural order, silicate mean chain length, and the amount of molecular water that is present in the atomic network. By topological analysis, we show that these "structural effects" arise from a self-organization of the atomic network of C-S-H upon irradiation. This topological self-organization is driven by the (initial) presence of atomic eigenstress in the C-S-H network and is facilitated by the presence of water in the network. Overall, we show that C-S-H exhibits an optimal resistance to radiation damage when its atomic network is isostatic (at Ca/Si = 1.5). Such an improved understanding of the response of C-S-H to irradiation can pave the way to the design of durable concrete for radiation applications.

Total allowable concentrations of monomeric inorganic aluminum and hydrated aluminum silicates in drinking water.

PubMed

Willhite, Calvin C; Ball, Gwendolyn L; McLellan, Clifton J

2012-05-01

Maximum contaminant levels are used to control potential health hazards posed by chemicals in drinking water, but no primary national or international limits for aluminum (Al) have been adopted. Given the differences in toxicological profiles, the present evaluation derives total allowable concentrations for certain water-soluble inorganic Al compounds (including chloride, hydroxide, oxide, phosphate and sulfate) and for the hydrated Al silicates (including attapulgite, bentonite/montmorillonite, illite, kaolinite) in drinking water. The chemistry, toxicology and clinical experience with Al materials are extensive and depend upon the particular physical and chemical form. In general, the water solubility of the monomeric Al materials depends on pH and their water solubility and gastrointestinal bioavailability are much greater than that of the hydrated Al silicates. Other than Al-containing antacids and buffered aspirin, food is the primary source of Al exposure for most healthy people. Systemic uptake of Al after ingestion of the monomeric salts is somewhat greater from drinking water (0.28%) than from food (0.1%). Once absorbed, Al accumulates in bone, brain, liver and kidney, with bone as the major site for Al deposition in humans. Oral Al hydroxide is used routinely to bind phosphate salts in the gut to control hyperphosphatemia in people with compromised renal function. Signs of chronic Al toxicity in the musculoskeletal system include a vitamin D-resistant osteomalacia (deranged membranous bone formation characterized by accumulation of the osteoid matrix and reduced mineralization, reduced numbers of osteoblasts and osteoclasts, decreased lamellar and osteoid bands with elevated Al concentrations) presenting as bone pain and proximal myopathy. Aluminum-induced bone disease can progress to stress fractures of the ribs, femur, vertebrae, humerus and metatarsals. Serum Al ≥100 µg/L has a 75-88% positive predictive value for Al bone disease. Chronic Al toxicity is also manifest in the hematopoietic system as an erythropoietin-resistant microcytic hypochromic anemia. Signs of Al toxicity in the central nervous system (speech difficulty to total mutism to facial grimacing to multifacial seizures and dyspraxia) are related to Al accumulation in the brain and these symptoms can progress to frank encephalopathy. There are four groups of people at elevated risk of systemic Al intoxication after repeated ingestion of monomeric Al salts: the preterm infant, the infant with congenital uremia and children and adults with kidney disease. There is a dose-dependent increase in serum and urinary Al in people with compromised renal function, and restoration of renal function permits normal handling of systemically absorbed Al and resolution of Al bone disease. Clinical experience with 960 mg/day of Al(OH)(3) (~5 mg Al/kg-day) given by mouth over 3 months to men and women with compromised renal function found subclinical reductions in hemoglobin, hematocrit and serum ferritin. Following adult males and females with reduced kidney function found that ingestion of Al(OH)(3) at 2.85 g/day (~40 mg/kg-day Al) over 7 years increased bone Al, but failed to elicit significant bone toxicity. There was one report of DNA damage in cultured lymphocytes after high AlCl(3) exposure, but there is no evidence that ingestion of common inorganic Al compounds presents an increased carcinogenic risk or increases the risk for adverse reproductive or developmental outcomes. A number of studies of Al exposure in relation to memory in rodents have been published, but the results are inconsistent. At present, there is no evidence to substantiate the hypothesis that the pathogenesis of Alzheimer's Disease is caused by Al found in food and drinking water at the levels consumed by people living in North America and Western Europe. Attapulgite (palygorskite) has been used for decades at oral doses (recommended not to exceed two consecutive days) of 2,100 mg/day in children of 3-6 years, 4,200 mg/day in children of 6-12 years, and 9,000 mg/day in adults. Chronic ingestion of insoluble hydrated Al silicates (in kg) can result in disturbances in iron and potassium status, primarily as a result of clay binding to intestinal contents and enhanced fecal iron and zinc elimination. Sufficiently high doses of ingested Al silicates (≥50 g/day) over prolonged periods of time can elicit a deficiency anemia that can be corrected with oral Fe supplements. There is essentially no systemic Al uptake after ingestion of the hydrated Al silicates. Rats fed up to 20,000 ppm Ca montmorillonite (equivalent to 1,860 ppm total Al as the hydrated Al silicate) for 28 weeks failed to develop any adverse signs. The results of dietary Phase I and II clinical trials conducted in healthy adult volunteers over 14 days and 90 days with montmorillonite found no adverse effects after feeding up to 40 mg/kg-day as Al. Since the Al associated with ingestion of hydrated Al silicates is not absorbed into the systemic circulation, the hydrated Al silicates seldom cause medical problems unless the daily doses consumed are substantially greater than those used clinically or as dietary supplements. A no-observable-adverse-effect-level (NOAEL) of 13 mg/kg-day as total Al can be identified based on histologic osteomalacia seen in adult hemodialysis patients given Al hydroxide for up to 7 years as a phosphate binder. Following U.S. EPA methods for calculation of an oral reference dose (RfD), an intraspecies uncertainty factor of 10x was applied to that value results in a chronic oral reference dose (RfD) of 1.3 mg Al/kg-day; assuming a 70-kg adult consumes 2 L of drinking water per day and adjusting for a default 20% relative source contribution that value corresponds to a drinking water maximum concentration of 9 mg/L measured as total Al. A chronic NOAEL for montmorillonite as representative of the hydrated Al silicates was identified from the highest dietary concentration (20,000 ppm) fed in a 28-week bioassay with male and female Sprague-Dawley rats. Since young rats consume standard laboratory chow at ~23 g/day, this concentration corresponds to 56 mg Al/kg-day. Application of 3x interspecies uncertainty factor and a 3x factor to account for study duration results in a chronic oral RfD of 6 mg Al/kg-day. Of note, this RfD is 5-10 fold less than oral doses of Al silicates consumed by people who practice clay geophagy and it corresponds to a maximum drinking water concentration of 40 mg Al/L. To utilize the values derived here, the risk manager must recognize the particular product (e.g., alum) or source (e.g., groundwater, river water, clay or cement pipe) of the Al found in tap water, apply the appropriate analytical methods (atomic absorption, energy dispersive X-ray diffraction, infrared spectral analysis and/or scanning transmission electron microscopy) and compare the results to the most relevant standard. The drinking water concentrations derived here are greater than the U.S. EPA secondary maximum contaminant level (MCL) for total Al of 0.05-0.2 mg/L [40 CFR 143.3]. As such, domestic use of water with these concentrations is likely self-limiting given that its cloudy appearance will be greater than the maximum permitted (0.5-5.0 nephalometric turbidity units; 40 CFR Parts 141 and 142). Therefore, the organoleptic properties of Al materials in water determine public acceptance of potable water as contrast to any potential health hazard at the concentrations ordinarily present in municipal drinking water.

A cohesive-frictional force field (CFFF) for colloidal calcium-silicate-hydrates

NASA Astrophysics Data System (ADS)

Palkovic, Steven D.; Yip, Sidney; Büyüköztürk, Oral

2017-12-01

Calcium-silicate-hydrate (C-S-H) gel is a cohesive-frictional material that exhibits strength asymmetry in compression and tension and normal-stress dependency of the maximum shear strength. Experiments suggest the basic structural component of C-S-H is a colloidal particle with an internal layered structure. These colloids form heterogeneous assemblies with a complex pore network at the mesoscale. We propose a cohesive-frictional force field (CFFF) to describe the interactions in colloidal C-S-H materials that incorporates the strength anisotropy fundamental to the C-S-H molecular structure that has been omitted from recent mesoscale models. We parameterize the CFFF from reactive force field simulations of an internal interface that controls mechanical performance, describing the behavior of thousands of atoms through a single effective pair interaction. We apply the CFFF to study the mesoscale elastic and Mohr-Coulomb strength properties of C-S-H with varying polydispersity and packing density. Our results show that the consideration of cohesive-frictional interactions lead to an increase in stiffness, shear strength, and normal-stress dependency, while also changing the nature of local deformation processes. The CFFF and our coarse-graining approach provide an essential connection between nanoscale molecular interactions and macroscale continuum behavior for hydrated cementitious materials.

Double cross-polarization MAS NMR in the assignment of abundant-spin resonances: ¹⁹F-{²⁹Si}-¹⁹F FBCP/MAS NMR of fluoride ions incorporated in calcium silicate hydrate (C-S-H) phases.

PubMed

Tran, Thuan T; Bildsøe, Henrik; Jakobsen, Hans J; Skibsted, Jørgen

2012-08-01

A new version of the double cross-polarization MAS NMR experiment, which transfers polarization Forth and Back (FBCP) between high- and low-γ spin nuclei, is presented. The pulse sequence is demonstrated by ¹⁹F-{²⁹Si}-¹⁹F and ¹⁹F-{¹³C}-¹⁹F FBCP NMR spectra of a mixture of cuspidine (Ca₄Si₂O₇F₂) and Teflon (-CF₂-)(n). The experiment is useful for assignment of the high-γ spin resonances, as demonstrated by ¹⁹F-{²⁹Si}-¹⁹F FBCP NMR of a fluoride-containing calcium-silicate-hydrate (C-S-H) phase, where the ¹⁹F resonance from fluoride ions incorporated in the interlayer structure of the C-S-H phase is identified. Copyright © 2012 Elsevier Inc. All rights reserved.

Atom-efficient route for converting incineration ashes into heavy metal sorbents.

PubMed

Chiang, Yi Wai; Santos, Rafael M; Vanduyfhuys, Kenneth; Meesschaert, Boudewijn; Martens, Johan A

2014-01-01

Bottom ashes produced from municipal solid-waste incineration are suitable for sorbent synthesis because of their inherent composition, high alkalinity, metastable mineralogy, and residual heat. This work shows that bottom ashes can be atom-efficiently converted into valuable sorbents without the need for costly and hazardous chemicals. The ashes were hydrothermally treated in rotary autoclaves at autogenic pH conditions to promote the conversion of precursor mineral phases into zeolites and layered silicate hydrates. Two main mineral phases were formed: katoite and sodium aluminum phosphate silicate hydrate. These mineral alterations are accompanied by a tenfold increase in specific surface area and a twofold reduction in average particle size. Performance evaluation of the new sorbents for Cd(2+), Zn(2+), and Pb(2+) adsorption at pH5 indicates sorption capacities of 0.06, 0.08, and 0.22 mmol g(-1), respectively, which are similar to those of natural adsorbents and synthetic materials obtained from more demanding synthesis conditions. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mesocrystalline calcium silicate hydrate: A bioinspired route toward elastic concrete materials

PubMed Central

Picker, Andreas; Nicoleau, Luc; Burghard, Zaklina; Bill, Joachim; Zlotnikov, Igor; Labbez, Christophe; Nonat, André; Cölfen, Helmut

2017-01-01

Calcium silicate hydrate (C-S-H) is the binder in concrete, the most used synthetic material in the world. The main weakness of concrete is the lack of elasticity and poor flexural strength considerably limiting its potential, making reinforcing steel constructions necessary. Although the properties of C-S-H could be significantly improved in organic hybrids, the full potential of this approach could not be reached because of the random C-S-H nanoplatelet structure. Taking inspiration from a sea urchin spine with highly ordered nanoparticles in the biomineral mesocrystal, we report a bioinspired route toward a C-S-H mesocrystal with highly aligned C-S-H nanoplatelets interspaced with a polymeric binder. A material with a bending strength similar to nacre is obtained, outperforming all C-S-H–based materials known to date. This strategy could greatly benefit future construction processes because fracture toughness and elasticity of brittle cementitious materials can be largely enhanced on the nanoscale. PMID:29209660

A model for the biological precipitation of Precambrian iron-formation

NASA Technical Reports Server (NTRS)

Laberge, G. L.

1986-01-01

A biological model for the precipitation of Precambrian iron formations is presented. Assuming an oxygen deficient atmosphere and water column to allow sufficient Fe solubility, it is proposed that local oxidizing environments, produced biologically, led to precipitation of iron formations. It is further suggested that spheroidal structures about 30 mm in diameter, which are widespread in low grade cherty rion formations, are relict forms of the organic walled microfossil Eosphaera tylerii. The presence of these structures suggests that the organism may have had a siliceous test, which allowed sufficient rigidity for accumulation and preservation. The model involves precipitation of ferric hydrates by oxidation of iron in the photic zone by a variety of photosynthetic organisms. Silica may have formed in the frustules of silica secreting organisms, including Eosphaera tylerii. Iron formates formed, therefore, by a sediment rain of biologically produced ferric hydrates and silica and other organic material. Siderite and hematite formed diagenetically on basin floors, and subsequent metamorphism produced magnetite and iron silicates.

[Experimental surgical model of hydrocele for the use of sclerotherapy].

PubMed

Castillo Jimeno, J M; Santiago, A M; Sebastián, J L; Ruiz, J L; Pérez Unzu, A; Puras, A; Marcotegui, F

1990-10-01

Sclerosant therapy for different pathological conditions (testicular hydrocele, pneumothorax) is a little known and scantily used procedure in the clinical setting. We have developed a surgical procedure in the dog that permits reproducing adult hydrocele. This experimental model is useful for morphometric assessment of the sclerosant effects of the commonly used agents (magnesium silicate hydrate, carbolic acid, ethanolamine oleate, hydroxytetracycline chlorhydrate and quinacrine chlorhydrate). Our results show that the degree of sclerosis achieved with quinacrine and hydrotetracycline is significantly superior to that obtained with other agents.

Biological and therapeutic effects of ortho-silicic acid and some ortho-silicic acid-releasing compounds: New perspectives for therapy.

PubMed

Jurkić, Lela Munjas; Cepanec, Ivica; Pavelić, Sandra Kraljević; Pavelić, Krešimir

2013-01-08

Silicon (Si) is the most abundant element present in the Earth's crust besides oxygen. However, the exact biological roles of silicon remain unknown. Moreover, the ortho-silicic acid (H4SiO4), as a major form of bioavailable silicon for both humans and animals, has not been given adequate attention so far. Silicon has already been associated with bone mineralization, collagen synthesis, skin, hair and nails health atherosclerosis, Alzheimer disease, immune system enhancement, and with some other disorders or pharmacological effects. Beside the ortho-silicic acid and its stabilized formulations such as choline chloride-stabilized ortho-silicic acid and sodium or potassium silicates (e.g. M2SiO3; M= Na,K), the most important sources that release ortho-silicic acid as a bioavailable form of silicon are: colloidal silicic acid (hydrated silica gel), silica gel (amorphous silicon dioxide), and zeolites. Although all these compounds are characterized by substantial water insolubility, they release small, but significant, equilibrium concentration of ortho-silicic acid (H4SiO4) in contact with water and physiological fluids. Even though certain pharmacological effects of these compounds might be attributed to specific structural characteristics that result in profound adsorption and absorption properties, they all exhibit similar pharmacological profiles readily comparable to ortho-silicic acid effects. The most unusual ortho-silicic acid-releasing agents are certain types of zeolites, a class of aluminosilicates with well described ion(cation)-exchange properties. Numerous biological activities of some types of zeolites documented so far might probably be attributable to the ortho-silicic acid-releasing property. In this review, we therefore discuss biological and potential therapeutic effects of ortho-silicic acid and ortho-silicic acid -releasing silicon compounds as its major natural sources.

Ceres: Dawn visits a Warm Wet Planet

NASA Astrophysics Data System (ADS)

McCord, T. B.; Combe, J. P.

2014-12-01

Ceres likely contains considerable water, has differentiated, and formed a hydrated silicate core and water mantle. There were major dimensional, thermal and chemical changes over its history, making it more a planet than an asteroid. These factors created the present day body, which the Dawn misson will visit next March. I will summarize our current understanding of Ceres and suggest what Dawn will find. A major uncertainty is how processes, such as aqueous mineralization, impact and cratering, infall of external material, mixing, and viscous relaxation of surface features have altered the formation materials and surface, hiding Ceres' secrets. Ceres' bulk density of 2100 kg/m3, suggest major water content. Modeling of Ceres' thermodynamic evolution for different times of accretion, assuming several radioactive heating scenarios, produces results ranging from a dry Vestal-like object (earlier, hotter formation) to retention and melting of the ice and differentiation of silicates from liquid water. Mixing of liquid water and silicates leads to exothermic hydration reactions, formation of a core and a liquid mantle. Large dimensional changes are associated. A crust stays frozen but founders at times due to gravitational instability, dimensional changes and impacts. The liquid mantle freezes from top, down, but a layer of salty liquid water probably exists today near the core. Hydrated silicates from the initial differentiation would likely dehydrate near the core center due to temperature and pressure. From observations, only subdued spatial albedo and color variations are observed at UV and IR wavelengths on Ceres' surface at the scale possible from Earth (~50-100 km) and an oblate spheroid shape is found, consistent with a differentiated body. Compositional evidence includes the long known similarity of Ceres' albedo and visual-IR reflectance spectrum to those for carbonaceous chondrite meteorites. Thus, the surface is likely made of carbon-bearing, hydroxolated materials, with spectral evidence of OH and maybe H2O molecules, consistent with the results of both the evolutionary thermodynamic models and infill of carbonaceous chondrite-like materials. Two reports of OH and H2O in the exosphere, apparently originating from localized sources, suggest present day cryovolcanism.

The Relative Rates of Secondary Hydration in Basalt and Rhyolite, and the use of δD as a Paleoclimate Indicator: Implications for Paleoenvironmental and Volcanic Degassing Studies

NASA Astrophysics Data System (ADS)

Seligman, A. N.; Bindeman, I. N.

2014-12-01

The δD-H2O correlation is important for volcanic degassing and secondary hydration trends. We utilize the caibration of the TC/EA - MAT 253 continuous flow system, which permits us to analyze wt.% H2O and its δD extracted from 1-8 mg of glass with as little as 0.1 wt% H2O. Tephra that has been secondarily hydrated with meteoric water is widely used as a paleoenvironmental tool, but the rate of secondary hydration, the relative amounts of primary magmatic (degassed) and secondary meteoric water, and the retention of primary and secondary δD values are not well understood. To quantify these processes, we use a natural experiment involving dated Holocene tepha in Kamchatka and Oregon. Our research illustrates the drastic difference in hydration rates between silicic (hydrated after ~1.5 ka) and mafic tephra, which is not hydrated in the Holocene (similar to results for submarine volcanic glasses), and andesitic tephra with intermediate degrees of hydration. The 0.05-7.3 ka basaltic scoria from Klyuchevskoy volcano retains ≤0.45 wt.% primary magmatic H2O, with δD values from -99 to -121 ‰. Four other 0.05-7.6 ka basaltic tephra units from Kamchatka with <57 wt.% SiO2 all have wt.% H2O 0.21-0.84 and δD values ranging from -90 - -145 ‰. The 1.0-7.6 ka andesitic tephra have slightly higher water contents (0.9-3.0 %) and slightly lower δD values (-113 - -146 ‰). Seven 0.3-7.9 ka silicic samples with SiO2 >65 wt.% have higher (1.5 -3.4) wt.% H2O and δD values between -115 - -160 ‰. We interpret the lower δD values and higher water contents (opposite of the magmatic degassing trend) to be a characteristic of secondary hydration in regions of higher latitude such as Kamchatka and Oregon. We are also investigating 7.7 ka Mt. Mazama tephra in Oregon that are known to be fully hydrated and cover nearly 5000 km2 northeast of Crater Lake and range in elevation from ~1.3-1.9 km to understand the δD and δ18O details of the hydrated water's correspondence with local Holocene meteoric waters. In the future, we plan to use a combination of δD in mid-high latitude precipitation to delineate δD-H2O hydration trends to better understand the distinction between primary magmatic and secondary meteoric water in volcanic glass, and the exchange of hydrogen isotopes between OH- and H2Omol sites in volcanic glass.

Microstructural characterization of catalysis product of nanocement based materials: A review

NASA Astrophysics Data System (ADS)

Sutan, Norsuzailina Mohamed; Izaitul Akma Ideris, Nur; Taib, Siti Noor Linda; Lee, Delsye Teo Ching; Hassan, Alsidqi; Kudnie Sahari, Siti; Mohamad Said, Khairul Anwar; Rahman Sobuz, Habibur

2018-03-01

Cement as an essential element for cement-based products contributed to negative environmental issues due to its high energy consumption and carbon dioxide emission during its production. These issues create the need to find alternative materials as partial cement replacement where studies on the potential of utilizing silica based materials as partial cement replacement come into picture. This review highlights the effectiveness of microstructural characterization techniques that have been used in the studies that focus on characterization of calcium hydroxide (CH) and calcium silicate hydrate (C-S-H) formation during hydration process of cement-based product incorporating nano reactive silica based materials as partial cement replacement. Understanding the effect of these materials as cement replacement in cement based product focusing on the microstructural development will lead to a higher confidence in the use of industrial waste as a new non-conventional material in construction industry that can catalyse rapid and innovative advances in green technology.

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

WANG,YIFENG; XU,HUIFANG

Correctly identifying the possible alteration products and accurately predicting their occurrence in a repository-relevant environment are the key for the source-term calculation in a repository performance assessment. Uraninite in uranium deposits has long been used as a natural analog to spent fuel in a repository because of their chemical and structural similarity. In this paper, a SEM/AEM investigation has been conducted on a partially alternated uraninite sample from a uranium ore deposit of Shinkolobwe of Congo. The mineral formation sequences were identified: uraninite {yields} uranyl hydrates {yields} uranyl silicates {yields} Ca-uranyl silicates or uraninite {yields} uranyl silicates {yields} Ca-uranyl silicates.more » Reaction-path calculations were conducted for the oxidative dissolution of spent fuel in a representative Yucca Mountain groundwater. The predicted sequence is in general consistent with the SEM observations. The calculations also show that uranium carbonate minerals are unlikely to become major solubility-controlling mineral phases in a Yucca Mountain environment. Some discrepancies between model predictions and field observations are observed. Those discrepancies may result from poorly constrained thermodynamic data for uranyl silicate minerals.« less

49 CFR 173.216 - Asbestos, blue, brown or white.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 2 2013-10-01 2013-10-01 false Asbestos, blue, brown or white. 173.216 Section... Class 7 § 173.216 Asbestos, blue, brown or white. (a) Asbestos, blue, brown or white, includes each of the following hydrated mineral silicates: chrysolite, crocidolite, amosite, anthophyllite asbestos...

49 CFR 173.216 - Asbestos, blue, brown or white.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 49 Transportation 2 2010-10-01 2010-10-01 false Asbestos, blue, brown or white. 173.216 Section... Class 7 § 173.216 Asbestos, blue, brown or white. (a) Asbestos, blue, brown or white, includes each of the following hydrated mineral silicates: chrysolite, crocidolite, amosite, anthophyllite asbestos...

49 CFR 173.216 - Asbestos, blue, brown or white.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 2 2011-10-01 2011-10-01 false Asbestos, blue, brown or white. 173.216 Section... Class 7 § 173.216 Asbestos, blue, brown or white. (a) Asbestos, blue, brown or white, includes each of the following hydrated mineral silicates: chrysolite, crocidolite, amosite, anthophyllite asbestos...

49 CFR 173.216 - Asbestos, blue, brown or white.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 2 2012-10-01 2012-10-01 false Asbestos, blue, brown or white. 173.216 Section... Class 7 § 173.216 Asbestos, blue, brown or white. (a) Asbestos, blue, brown or white, includes each of the following hydrated mineral silicates: chrysolite, crocidolite, amosite, anthophyllite asbestos...

49 CFR 173.216 - Asbestos, blue, brown or white.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 2 2014-10-01 2014-10-01 false Asbestos, blue, brown or white. 173.216 Section... Class 7 § 173.216 Asbestos, blue, brown or white. (a) Asbestos, blue, brown or white, includes each of the following hydrated mineral silicates: chrysolite, crocidolite, amosite, anthophyllite asbestos...

Chitosan-coated mesoporous microspheres of calcium silicate hydrate: environmentally friendly synthesis and application as a highly efficient adsorbent for heavy metal ions.

PubMed

Zhao, Jing; Zhu, Ying-Jie; Wu, Jin; Zheng, Jian-Qiang; Zhao, Xin-Yu; Lu, Bing-Qiang; Chen, Feng

2014-03-15

Chitosan-coated calcium silicate hydrate (CSH/chitosan) mesoporous microspheres formed by self-assembly of nanosheets have been synthesized in aqueous solution under ambient conditions without using any toxic surfactant or organic solvent. The method reported herein has advantages of simplicity, low cost and being environmentally friendly. The BET specific surface area of CSH/chitosan mesoporous microspheres is measured to be as high as ~356 m(2) g(-1), which is considerably high among calcium silicate materials. The as-prepared CSH/chitosan mesoporous microspheres are promising adsorbent and exhibit a quick and highly efficient adsorption behavior toward heavy metal ions of Ni(2+), Zn(2+), Cr(3+), Pb(2+) Cu(2+) and Cd(2+) in aqueous solution. The adsorption kinetics can be well fitted by the pseudo second-order model. The maximum adsorption amounts of Ni(2+), Zn(2+), Pb(2+), Cu(2+) and Cd(2+) on CSH/chitosan mesoporous microspheres are extremely high, which are 406.6, 400, 796, 425 and 578 mg/g, respectively. The CSH/chitosan adsorbent exhibits the highest affinity for Pb(2+) ions among five heavy metal ions. The adsorption capacities of the CSH/chitosan adsorbent toward heavy metal ions are relatively high compared with those reported in the literature. Copyright © 2013 Elsevier Inc. All rights reserved.

Insights into the interfacial strengthening mechanisms of calcium-silicate-hydrate/polymer nanocomposites.

PubMed

Zhou, Yang; Hou, Dongshuai; Geng, Guoqing; Feng, Pan; Yu, Jiao; Jiang, Jinyang

2018-03-28

The mechanical properties of organic/inorganic composites can be highly dependent on the interfacial interactions. In this work, with organic polymers intercalated into the interlayer of inorganic calcium silicate hydrate (C-S-H), the primary binding phase of Portland cement, great ductility improvement is obtained for the nanocomposites. Employing reactive molecular dynamics, the simulation results indicate that strong interfacial interactions between the polymers and the substrate contribute greatly to strengthening the materials, when C-S-H/poly ethylene glycol (PEG), C-S-H/poly acrylic acid (PAA), and C-S-H/poly vinyl alcohol (PVA) were subject to uniaxial tension along different lattice directions. In the x and z direction tensile processes, the Si-OCa bonds of the C-S-H gel, which were elongated and broken to form Si-OH and Ca-OH, play a critical role in loading resistance, while the incorporation of polymers bridged the neighboring silicate sheets, and activated more the hydrolytic reactions at the interfaces to avoid strain localization, thus increasing the tensile strength and postponing the fracture. On the other hand, Si-O-Si bonds of C-S-H mainly take the load when tension was applied along the y direction. During the post-yield stage, rearrangements of silicate tetrahedra occurred to prevent rapid damage. The polymer intercalation further elongates this post-yield period by forming interfacial Si-O-C bonds, which promote rearrangements and improve the connectivity of the defective silicate morphology, significantly improving the ductility. Among the polymers, PEG exhibits the strongest interaction with C-S-H, and thus C-S-H/PEG possesses the highest ductility. We expect that the molecular-scale mechanisms interpreted here will shed new light on the stress-activated chemical interactions at the organic/inorganic interfaces, and help eliminate the brittleness of cement-based materials on a genetic level.

Models of a partially hydrated Titan interior with a clathrate crust

NASA Astrophysics Data System (ADS)

Lunine, J. I.; Castillo-Rogez, J. C.; Choukroun, M.; Sotin, C.

2012-04-01

We present a model of the interior evolution of Titan over time, assuming the silicate core was hydrated early in Titan’s history and is dehydrating over time. The original model presented in Castillo-Rogez and Lunine (2010) was motivated by a Cassini-derived moment of inertia (Iess et al., 2010) for Titan too large to be accommodated by classical fully differentiated models in which an anhydrous silicate core was overlain by a water ice (with possible perched ocean) mantle. Our model consists of a silicate core still in the process of dehydrating today, a situation made possible by the leaching of radiogenic potassium from the silicates into the perched liquid water ocean. The most recent version of our model accounts for the likely presence of large amounts of methane in the upper crust invoked to explain methane’s persistence at present and through geologic time (Tobie et al. 2006). The methane-rich crust turns out to have essentially no bearing on the temperature of the silicate core and hence the timing of dehydration, but it profoundly affects the thickness of the high-pressure ice layer beneath the ocean. Indeed, the insulating effect of the methane clathrate crust could have delayed the formation of the high-pressure layer, resulting in the interaction of liquid water with the silicate core for extended periods of time. Although a high-pressure ice layer is likely in place today, it is thin enough that plumes of hot water from the dehydrating core probably breach that layer. The implications of such a deep hydrothermal system for the later stages of the evolution of Titan’s interior and surface will be discussed. Part of this work has been performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Government sponsorship acknowledged. References: Castillo-Rogez, J., Lunine, J.: “Evolution of Titan’s rocky core constrained by Cassini observations”. GRL, Vol. 37, L20205, 2010. Iess, L., et al.: “Gravity field, shape, and moment of inertia of Titan”. Science, Vol. 327, 1367-1369. Tobie, G., et al.: “Episodic outgassing as the origin of atmospheric methane on Titan”. Nature 440: 61-64, 2006.

Computational Material Modeling of Hydrated Cement Paste Calcium Silicate Hydrate (C-S-H) Chemistry Structure - Influence of Magnesium Exchange on Mechanical Stiffness: C-S-H Jennite

DTIC Science & Technology

2015-04-27

MODELING OF C-S-H Material chemistry level modeling following the principles and techniques commonly grouped under Computational Material Science is...Henmi, C. and Kusachi, I. Monoclinic tobermorite from fuka, bitchu-cho, Okoyama Perfecture. Japan J. Min. Petr. Econ . Geol. (1989)84:374-379. [22...31] Liu, Y. et al. First principles study of the stability and mechanical properties of MC (M=Ti, V, Zr, Nb, Hf and Ta) compounds. Journal of Alloys and Compounds. (2014) 582:500-504. 10

Analysis of Mineral Assemblages Containing Unstable Hydrous Phases

NASA Astrophysics Data System (ADS)

Vaniman, D. T.; Wilson, S. A.; Bish, D. L.; Chipera, S.

2011-12-01

Minerals in many environments can be treated as durable phases that preserve a record of their formation. However many minerals, especially those with hydrogen-bonded H2O molecules as part of their structure, are ephemeral and are unlikely to survive disturbance let alone removal from their environment of formation. Minerals with exceptionally limited stability such as meridianiite (Mg-sulfate 11 hydrate), ikaite (Ca-carbonate 6 hydrate), and mirabilite (Na-sulfate 10 hydrate) are very susceptible to destabilization during analysis, and even modest changes in temperature or relative humidity can lead to change in hydration state or deliquescence. The result may be not only loss of the salt hydrate but dissolution of other salts present, precipitation of new phases, and ion exchange between the concentrated solution and otherwise unaffected phases. Exchange of H2O molecules can also occur in solid-vapor systems without any liquid involvement; moreover, recent work has shown that cation exchange between smectite and sulfate hydrates can occur without any liquid phase present other than a presumed thin film at the salt-silicate interface. Among hydrous silicates, clay minerals are susceptible to cation exchange and similar alteration can be expected for zeolites, palagonite, and possibly other hydrous silicate alteration products. Environmentally sensitive phases on Mars, such as meridianiite, may occur at higher latitudes or in the subsurface where permafrost may be present. Accurate determination of the presence and paragenesis of such minerals will be important for understanding the near-surface hydrogeology of Mars, and in situ analysis may be the only way to obtain this information. Access to the subsurface may be required, yet the act of exposure by excavation or drilling can itself lead to rapid degradation as the sample is exposed or brought to the surface for analysis. Mars is not the only body with which to be concerned, for similar concerns can be raised for sampling cold-environment deposits at the lunar poles, at the poles of Mercury, on icy satellites, and on many other bodies that may host hydrous minerals. The problem of adequate in situ analysis of such mutable assemblages extends to Earth as well, for example in the need for improved understanding of polar and permafrost regions, deep sea clathrates, cave minerals, and mine dump efflorescence. Advanced methods of in situ analysis are needed, including but not limited to contact instruments and instrumentation that can be inserted by probe or operated within a borehole that could be advanced with minimal thermal disturbance. One of the lessons of robotic analysis is that field instruments, which by necessity are less capable than laboratory equivalents, provide greatly improved interpretations if data from several different instruments can be compared.

Direct observation of void evolution during cement hydration

DOE PAGES

Moradian, Masoud; Hu, Qinang; Aboustait, Mohammed; ...

2017-09-28

This study follows the hydration of both portland cement and tricalcium silicate pastes between 30 min and 16 h of hydration. In-situ fast X-ray Computed Tomography (fCT) was used to make direct observations of the air-filled void formation in w/s of 0.40 to 0.70 with a micron resolution. The results show that over the first hour of the acceleration period the volume of air-filled voids reaches a maximum value and then decreases during the acceleration period and stays constant. The void distribution changes from a few coarse voids to a large number of smaller and more uniformly distributed voids. Thismore » behavior is suggested to be controlled by changes in the ionic strength that cause exsolution of dissolved air from the pore solution.« less

Hydration products in sulfoaluminate cements: Evaluation of amorphous phases by XRD/solid-state NMR

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

Gastaldi, D., E-mail: dgastaldi@buzziunicem.it; Paul, G., E-mail: geo.paul@uniupo.it; Marchese, L.

The hydration of four sulfoaluminate cements have been studied: three sulfoaluminate systems, having different content of sulfate and silicate, and one blend Portland-CSA-calcium sulfate binder. Hydration was followed up to 90 days by means of a combination of X-ray diffraction and solid state MAS-NMR; Differential scanning calorimetry and Scanning electron microscopy were also performed in order to help the interpretation of experimental data. High amount of amorphous phases were found in all the four systems: in low-sulfate cements, amorphous part is mainly ascribed to monosulfate and aluminium hydroxide, while strätlingite is observed if belite is present in the cement; inmore » the blend system, C-S-H contributes to the amorphous phase beyond monosulfate.« less

Direct observation of void evolution during cement hydration

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

Moradian, Masoud; Hu, Qinang; Aboustait, Mohammed

This study follows the hydration of both portland cement and tricalcium silicate pastes between 30 min and 16 h of hydration. In-situ fast X-ray Computed Tomography (fCT) was used to make direct observations of the air-filled void formation in w/s of 0.40 to 0.70 with a micron resolution. The results show that over the first hour of the acceleration period the volume of air-filled voids reaches a maximum value and then decreases during the acceleration period and stays constant. The void distribution changes from a few coarse voids to a large number of smaller and more uniformly distributed voids. Thismore » behavior is suggested to be controlled by changes in the ionic strength that cause exsolution of dissolved air from the pore solution.« less

Development and characterization of a stable adhesive bond between a poly(dimethylsiloxane) catheter material and a bacterial biofilm resistant acrylate polymer coating

PubMed Central

Tyler, Bonnie J.; Hook, Andrew; Pelster, Andreas; Williams, Paul; Alexander, Morgan; Arlinghaus, Heinrich F.

2017-01-01

Catheter associated urinary tract infections are the most common health related infections worldwide, contributing significantly to patient morbidity and mortality and increased health care costs. To reduce the incidence of these infections, new materials that resist bacterial biofilm formation are needed. A composite catheter material, consisting of bulk poly(dimethylsiloxane) (PDMS) coated with a novel bacterial biofilm resistant polyacrylate [ethylene glycol dicyclopentenyl ether acrylate (EGDPEA)-co-di(ethyleneglycol) methyl ether methacrylate (DEGMA)], has been proposed. The coated material shows excellent bacterial resistance when compared to commercial catheter materials, but delamination of the EGDPEA-co-DEGMA coatings under mechanical stress presents a challenge. In this work, the use of oxygen plasma treatment to improve the wettability and reactivity of the PDMS catheter material and improve adhesion with the EGDPEA-co-DEGMA coating has been investigated. Argon cluster three dimensional-imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used to probe the buried adhesive interface between the EGDPEA-co-DEGMA coating and the treated PDMS. ToF-SIMS analysis was performed in both dry and frozen-hydrated states, and the results were compared to mechanical tests. From the ToF-SIMS data, the authors have been able to observe the presence of PDMS, silicates, salt particles, cracks, and water at the adhesive interface. In the dry catheters, low molecular weight PDMS oligomers at the interface were associated with poor adhesion. When hydrated, the hydrophilic silicates attracted water to the interface and led to easy delamination of the coating. The best adhesion results, under hydrated conditions, were obtained using a combination of 5 min O2 plasma treatment and silane primers. Cryo-ToF-SIMS analysis of the hydrated catheter material showed that the bond between the primed PDMS catheter and the EGDPEA-co-DEGMA coating was stable in the presence of water. The resulting catheter material resisted Escherichia coli and Proteus mirabilis biofilm colonization by up to 95% compared with uncoated PDMS after 10 days of continuous bacterial exposure and had the mechanical properties necessary for use as a urinary catheter. PMID:28535686

An Atlas of extraterrestrial particles collected with NASA U-2 aircraft, 1974 - 1976

NASA Technical Reports Server (NTRS)

Brownlee, D. E.; Tomandl, D.; Blanchard, M. B.; Ferry, G. V.; Kyte, F.

1976-01-01

Extraterrestrial particles collected during U-2 flights in the stratosphere were divided into four groups: chondritic, iron-sulfur--nickel, mafic silicates, and others. The chondritic aggregates are typically composed of Fe, Mg, Si, C, S, Ca, and Ni. Detectable levels of He-4 implanted from the solar wind occur in some. Olivine, spinel, and possibly pyrrhotite and a hydrated layered-lattice silicate were identified. The chondritic ablation particles contain no sulfur and appear to have been melted. Magnetite, olivine, and pyroxene were identified. The iron-sulfur-nickel type particles resemble meteoritic iron sulfide with a small amount of nickel, and contain magnetite and troilite. The mafic silicate type particles are iron magnesium silicate grains with clumps of chondritic aggregate particles adhering to their surfaces. Olivine and possibly pyrrhotite and pyroxene were identified. Most of the iron-nickel type particles are spherules and include taenite and wustite. The other type particles include nickel-iron mounds on spheroidal glassy-like grains having chondritic-like elemental abundances.

Apatite formation on bioactive calcium-silicate cements for dentistry affects surface topography and human marrow stromal cells proliferation.

PubMed

Gandolfi, Maria Giovanna; Ciapetti, Gabriela; Taddei, Paola; Perut, Francesca; Tinti, Anna; Cardoso, Marcio Vivan; Van Meerbeek, Bart; Prati, Carlo

2010-10-01

The effect of ageing in phosphate-containing solution of bioactive calcium-silicate cements on the chemistry, morphology and topography of the surface, as well as on in vitro human marrow stromal cells viability and proliferation was investigated. A calcium-silicate cement (wTC) mainly based on dicalcium-silicate and tricalcium-silicate was prepared. Alpha-TCP was added to wTC to obtain wTC-TCP. Bismuth oxide was inserted in wTC to prepare a radiopaque cement (wTC-Bi). A commercial calcium-silicate cement (ProRoot MTA) was tested as control. Cement disks were aged in DPBS for 5 h ('fresh samples'), 14 and 28 days, and analyzed by ESEM/EDX, SEM/EDX, ATR-FTIR, micro-Raman techniques and scanning white-light interferometry. Proliferation, LDH release, ALP activity and collagen production of human marrow stromal cells (MSC) seeded for 1-28 days on the cements were evaluated. Fresh samples exposed a surface mainly composed of calcium-silicate hydrates CSH (from the hydration of belite and alite), calcium hydroxide, calcium carbonate, and ettringite. Apatite nano-spherulites rapidly precipitated on cement surfaces within 5 h. On wTC-TCP the Ca-P deposits appeared thicker than on the other cements. Aged cements showed an irregular porous calcium-phosphate (Ca-P) coating, formed by aggregated apatite spherulites with interspersed calcite crystals. All the experimental cements exerted no acute toxicity in the cell assay system and allowed cell growth. Using biochemical results, the scores were: fresh cements>aged cements for cell proliferation and ALP activity (except for wTC-Bi), whereas fresh cements

Calcium leaching behavior of cementitious materials in hydrochloric acid solution.

PubMed

Yang, Huashan; Che, Yujun; Leng, Faguang

2018-06-11

The calcium leaching behavior of cement paste and silica fume modified calcium hydroxide paste, exposed to hydrochloric acid solution, is reported in this paper. The kinetic of degradation was assessed by the changes of pH of hydrochloric acid solution with time. The changes of compressive strength of specimens in hydrochloric acid with time were tested. Hydration products of leached specimens were also analyzed by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric (TG), and atomic force microscope (AFM). Tests results show that there is a dynamic equilibrium in the supply and consumption of calcium hydroxide in hydrochloric acid solution, which govern the stability of hydration products such as calcium silicate hydrate (C-S-H). The decrease of compressive strength indicates that C-S-H are decomposed due to the lower concentration of calcium hydroxide in the pore solution than the equilibrium concentration of the hydration products. Furthermore, the hydration of unhydrated clinker delayed the decomposition of C-S-H in hydrochloric acid solution due to the increase of calcium hydroxide in pore solution of cementitious materials.

How To Use Crystallographic Information in Teaching First-Year Chemistry.

ERIC Educational Resources Information Center

Bevan, D. J. M.; And Others

1988-01-01

Emphasizes the role that crystallography plays and has played in building up the body of chemical fact. Shows how the teaching of much of this material is illuminated by reference to crystal structures and crystallochemical relationships in all areas of chemistry. Discusses close packing, silicate structures, and salt hydrates. (CW)

Water in Volcanic Glass: From Volcanic Degassing to Secondary Hydration

NASA Astrophysics Data System (ADS)

Seligman, A. N.; Bindeman, I. N.; Palandri, J. L.; Watkins, J. M.; Ross, A. M.

2015-12-01

Volcanic glass contains both primary magmatic and secondary meteoric dissolved water, which can have distinguishable hydrogen isotopic ratios. We analyzed compositionally and globally diverse volcanic glass from recent to 640 ka for their δD (‰, VSMOW) and H2Ot (wt.%) on the TC/EA MAT 253 continuous flow system. We find that rhyolite glass is hydrated faster than basaltic glass, and in the majority of glasses an increase in age and total water content leads to a decrease in δD (‰), which is opposite the trend for magmatic degassing, while a few equatorial glasses have little change in δD (‰). To better understand these results, we imaged 6 tephra clasts ranging in age and chemical composition using BSE (by FEI SEM) down to a resolution of ~1 mm. Mafic tephra have lower vesicle number densities (N/mm2 = 25-77) than silicic tephra (736) and thicker average bubble walls (0.07 mm) than silicic tephra (0.02 mm). Lengths of water diffusion were modeled by finite difference using H2Ot concentration-dependent diffusion coefficients for diffusion of water into basalt and rhyolite glass using Zhang et al. (2007) and Ni and Zhang (2008) diffusion parameterizations extrapolated to surface temperatures. Due to the 106 times slower diffusion, water only diffused ~10-5 mm into basaltic glass and ~10 mm into rhyolitic glass after 1000 years. These hydration rates match our H2Ot wt.% values for basaltic tephra, and would cause a rhyolite glass, with an average bubble wall thickness of 0.02 mm as described above, to already be fully hydrated with ~3.0-3.5 wt.% H2Ot after ~1000 years, which is similar to what we observe. Results here are our initial steps in understanding water diffusion rates at ambient temperature in basalt and rhyolite tephra, and the isotopic changes that occur during hydration, which have implications for research in physical volcanology (quantities of residual magmatic water) and paleoenvironments (low temperature hydration rates and isotopic changes of glass).

Effect of CO2 concentration on strength development and carbonation of a MgO-based binder for treating fine sediment.

PubMed

Hwang, Kyung-Yup; Kim, Jin Young; Phan, Hoang Quang Huy; Ahn, Jun-Young; Kim, Tae Yoo; Hwang, Inseong

2018-05-28

We previously described a MgO-based binder for treating fine sediment and simultaneously store CO 2 . Here, we describe a study of the physical/mechanical characteristics and carbonation reactions of the MgO-based binder used to solidify/stabilize fine sediment in atmospheres containing different CO 2 concentrations. Carbonation of the sediment treated with the MgO-based binder at the atmospheric CO 2 concentration markedly improved the compressive strength of the product. The compressive strength was 4.78 MPa after 365 days of curing, 1.3 times higher than the compressive strength of sediment treated with portland cement. This improvement was caused by the formation of carbonation products, such as hydromagnesite, nesquehonite, and lansfordite, and the constant high pH (~ 12) of the specimen, which favored the growth of hydration products such as calcium silicate hydrates and portlandite. Very low compressive strengths were found when 50 and 100% CO 2 atmospheres were used because of excessive formation of carbonation products, which occupied 78% of the specimen depth. Abundant carbonation products increased the specimen volume and decreased the pH to 10.2, slowing the growth of hydration products. The absence of brucite in specimens produced in a 100% CO 2 atmosphere indicated that MgO carbonation is favored over hydration at high CO 2 concentrations.

Trapping of water vapor from an atmosphere by condensed silicate matter formed by high-temperature pulse vaporization

NASA Technical Reports Server (NTRS)

Gerasimov, M. V.; Dikov, Yu. P.; Yakovlev, O. I.; Wlotzka, F.

1993-01-01

The origin of planetary atmospheres is thought to be the result of bombardment of a growing planet by massive planetesimals. According to some models, the accumulation of released water vapor and/or carbon dioxide can result in the formation of a dense and hot primordial atmosphere. Among source and sink processes of atmospheric water vapor the formation of hydroxides was considered mainly as rehydration of dehydrated minerals (foresterite and enstatite). From our point of view, the formation of hydroxides is not limited to rehydration. Condensation of small silicate particles in a spreading vapor cloud and their interaction with a wet atmosphere can also result in the origin of hydrated phases which have no genetic connections with initial water bearing minerals. We present results of two experiments of a simulated interaction of condensed silicate matter which originated during vaporization of dry clinopyroxene in a wet helium atmosphere.

Ceres: Evolution and Present State

NASA Astrophysics Data System (ADS)

Castillo-Rogez, J.; McCord, T.

2007-08-01

Introduction:We consider Ceres as a prototype for planetary evolution [1]. From thermal modeling by McCord and Sotin [2, 3, 4], Ceres was inferred to have differentiated into a rocky core of hydrated silicates, and an icy outer shell. Thomas et al. [5] confirmed such a model from direct observation of Ceres's shape from Hubble Space Telescope observations, and pervious occultation measurements. McCord and Sotin [4] also suggest that Ceres could have preserved a deep ocean, especially if ammonia or some other ice melting point depressant, such as salts, was incorporated during accretion. We continue to develop thermal modeling of Ceres, using increasingly sophisticated models and new observational information in order to match the observed shape. . In particular, we investigate the evolution of the core. Approach: Our models require the following initial input: initial planetesimal temperature (after [6]); composition; time of formation with respect to Calcium-Aluminum Inclusions (CAIs); and an internal heat profile after initial accretion. Modeling begins with a porous Ceres (after [7, 8]). The rock phase has the composition of an ordinary chondrite (after [9]). Short-lived radiogenic isotopes, including 26Al and 60Fe, have initial concentrations as measured by [10, 11]. Conductive thermal evolution is computed for one-dimensional models following the approach of [4] and [12]. The silicate core evolves through hydration, then dehydration and melting stages. Currently, hydrothermal cooling is not included in our algorithm. Model Results: Conditions were present for full differentiation of Ceres if accretion time t0-CAIs was less than 7 My and/or if ammonia was accreted. For times of formation t0-CAIs shorter than 2 My, the boiling point of water was reached within a few My after accretion, and may have led to major water loss.Under these conditions, hydrothermal activity was inevitable, and might still be taking place inside Ceres. Whether a deep ocean is still present within Ceres or not depends on the initial conditions, especially the presence of ammonia. The core follows very different evolutionary paths, given the range of input values. Core evolution is most strongly affected by the time of accretion, with respect to inclusion of CAIs. With the inclusion of short-lived radioisotopes, pressure and temperature conditions in the core can lead to dehydration of the silicate phase [13], and layering of the core. An outer layer consisting of hydrated silicates, and a deep core consisting of dry silicate is the result, due to the equation of state of hydrated silicates. Explosive volcanism is expected to occur [14]. Conditions can even lead to partial differentiation of a metallic core.It is these model runs, resulting in the differentiation of Ceres's core into an outer hydrated layer, dehydrated inner layer and a tiny metallic center, that also produce the observed shape. Acknowledgement: This work was supported in part by the NASA Dawn Discovery Program under contract to the Space Science Institute by the UCLA and funded by JPL/NASA. Part of this work was performed at the Jet Propulsion Laboratory - California Institute of Technology under contract to NASA. References: [1] McCord T. B. et al. 2006. Eos 87(10). [2] McCord, T. B., Sotin, C. 2003. American Astronomical Society, DPS meeting #35, #34.17; Bull. Amer. Astron. Soc. 35, 979. [3] McCord, T., Sotin, C. 2004. 35th COSPAR Scientific Assembly. Held 18 - 25 July 2004, in Paris, France., 1148. [4] McCord, T.B., C. Sotin 2005. J. Geophys. Res., 110, E05009, doi: 10.1029/2004JE002244. 1-14. [5] Thomas, P. C., et al. 2005. Nature 437, doi: 10.1038/nature03938, 224-226. [6] Mousis O. and Alibert Y. (2005) MNRAS, 358, 188-192. [7] Leliwa-Kopystynski, J., Kossacki, K. J. 1995. Planet. Space Sci. 43, 851-861. [8] Leliwa-Kopystynski, J., Kossacki, K. J. 2000. Planet. Space Sci. 48, 727-745. [9] Wasson, J. T., Kalleymen, G. W. 1988. Phil. Trans. Roy. Soc. London A 325, 535. [10] Wasserburg, G. J., Papanastassiou, D. A. 1982. in Essays in Nuclear Astrophysics, ed. C.A. Barnes, D.D. Clayton, & D.N. Schramm (New York: Cambridge Univ. Press), 77. [11] Tachibana, S., et al. 2006. Astroph. J., 639, L87-L90, doi: 10.1086/503201. [12] Castillo et al. Submitted to Icarus. [13] Ellis D. E., Wyllie P. J. 1979. Am. Miner. 64, 41-48. [14] Wilson L. et al. (1999) MPS, 34, 541-557.

Resistance of fly ash-Portland cement blends to thermal shock

DOE PAGES

Pyatina, Tatiana; Sugama, Toshifumi

2015-09-11

Thermal-shock resistance of high-content fly ash-Portland cement blends was tested in the following ways. Activated and non-activated blends with 80-90 % fly ash F (FAF) were left to set at room temperature, then hydrated for 24 hours at 85°C and 24-more hours at 300°C and tested in five thermal-shock cycles (600°C heat - 25°C water quenching). XRD, and thermal gravimetric analyses, along with calorimetric measurements and SEM-EDX tests demonstrated that the activated blends form more hydrates after 24 hours at 300°C, and achieve a higher short-term compressive strength than do non-activated ones. Sodium meta-silicate and sodaash engendered the concomitant hydrationmore » of OPC and FAF, with the formation of mixed crystalline FAF-OPC hydrates and FAF hydrates, such as garranite, analcime, and wairakite, along with the amorphous FAF hydration products. In SS-activated and non-activated blends separate OPC (tobermorite) and FAF (amorphous gel) hydrates with no mixed crystalline products formed. The compressive strength of all tested blends decreased by nearly 50% after 5 thermal-shock test cycles. These changes in the compressive strength were accompanied by a marked decrease in the intensities of XRD patterns of the crystalline hydrates after the thermalshock. As a result, there was no significant difference in the performance of the blends with different activators« less

Heterogeneous water content in the lunar interior: insights from orbital detection of water in lunar pyroclastic deposits and silicic rich domes

NASA Astrophysics Data System (ADS)

Li, S.; Milliken, R.

2015-12-01

Constraining the distribution and abundance of water (H2O and/or OH) in the lunar interior is crucial for assessing the formation and evolution of the Moon. Deriving such information from returned lunar samples is the most direct approach, but only a few regions have been sampled. Reflectance spectra for the 3μm region, remotely sensed by the Moon Mineralogy Mapper (M3), provide an alternative way to characterize lunar water at a global scale. Though such methods only probe the optical surface, hydration in some materials may result from internal processes instead of interaction with the solar wind. Constraining the volatile content of pyroclastic deposits and silicic rich domes, for example, can provide insight into volatile distribution and evolution related to magmatic processes. Thermally-corrected M3 data, constrained by Diviner temperatures and laboratory data, enable us to estimate the amount of water in these deposits. We find evidence for increased hydration signatures at nearly all large pyroclastic deposits relative to background values for surrounding terrains, suggestive of H2O-bearing magmas. Water contents for these deposits exhibit a linear correlation with the deposit range, largely consistent with lunar magma eruption models. In addition, the water content at inferred high-Ti deposits is higher than that of low-Ti pyroclastics for the same deposit range, which may reflect inherent differences in the water content or degassing history of the associated magmas. Our results also suggest that over half of the examined silicic-rich domes are very dry (no detectable water signature), which suggests either a volatile-poor source or a very different degassing history compared to pyroclastic deposits. Potential silicic-rich domes are inferred to have formed due to ascension of immiscible silicic melts in which volatiles may have been concentrated. Those silicic melts might cool slowly and allow extensive diffusion of water, whereas quenched glasses in pyroclastics may favor volatile retention. Current work is focused on the morphologic and compositional characteristics of these deposits as well as improved quantitative estimates of their water content. Latest results will be presented in the context of how these orbital observations may inform us of lunar interior processes.

Fabrication of low density ceramic material

DOEpatents

Meek, T.T.; Blake, R.D.; Sheinberg, H.

1985-01-01

A precursor mixture and a method of making a low-density ceramic structural material are disclosed. The precursor mixture includes hollow microballoons, typically made of glass, together with a cementing agent capable of being cured by microwave irradiation. A preferred cementing agent is liquid hydrated potassium silicate, which is mixed with the glass microballoons to form a slurry. Upon irradiation the potassium silicate is dehydrated to form a solid porous matrix in which the microballoons are evenly distributed. Ground glass or other filling agents may be included in the slurry to enhance the properties of the final product. Low-density structural ceramics having densities on the order of 0.1 to 0.3 are obtained.

Nanostructured calcium silicate hydrate seeds accelerate concrete hardening: a combined assessment of benefits and risks.

PubMed

Bräu, Michael; Ma-Hock, Lan; Hesse, Christoph; Nicoleau, Luc; Strauss, Volker; Treumann, Silke; Wiench, Karin; Landsiedel, Robert; Wohlleben, Wendel

2012-07-01

Nanotechnology creates new possibilities to control and improve material properties for civil infrastructure. Special focus in this area is put on Portland cement and gypsum. Together their annual production is by far larger than for any other material worldwide. Nanomodification of these materials can be done during the few hours between dissolution and hardening, especially by nucleation of the re-crystallization with suitable colloids. Here we report first results in homogeneous seeding of the precipitation of calcium silicate hydrates within a real Portland cement composition. The occupational safety during the production phase and during mixing of concrete paste is addressed in detail by in vivo testing. We perform 5-day inhalation with 21-day recovery in rats and analyze organ-specific toxicity and 71 endpoints from bronchoalveolar lavage (BALF) and blood. In BALF parameters, no test-related changes were observed, indicating the generally low toxicity of the test material. Some mild lesions were observed in larynx level. In the lungs, all animals of the 50 mg/m³ concentration group revealed a minimal to mild increase in alveolar macrophages, which recovered back to control level.

Nanoscale Charge Balancing Mechanism in Calcium-Silicate-Hydrate Gels: Novel Complex Disordered Materials from First-principles

NASA Astrophysics Data System (ADS)

Ozcelik, Ongun; White, Claire

Alkali-activated materials which have augmented chemical compositions as compared to ordinary Portland cement are sustainable technologies that have the potential to lower CO2 emissions associated with the construction industry. In particular, calcium-silicate-hydrate (C-S-H) gel is altered at the atomic scale due to changes in its chemical composition. Here, based on first-principles calculations, we predict a charge balancing mechanism at the molecular level in C-S-H gels when alkali atoms are introduced into their structure. This charge balancing process is responsible for the formation of novel structures which possess superior mechanical properties compared to their charge unbalanced counterparts. Different structural representations are obtained depending on the level of substitution and the degree of charge balancing incorporated in the structures. The impact of these charge balancing effects on the structures is assessed by analyzing their formation energies, local bonding environments, diffusion barriers and mechanical properties. These results provide information on the phase stability of alkali/aluminum containing C-S-H gels, shedding light on the fundamental mechanisms that play a crucial role in these complex disordered materials. We acknowledge funding from the Princeton Center for Complex Materials, a MRSEC supported by NSF.

Strength, leachability and microstructure characteristics of cement-based solidified plating sludge

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

Asavapisit, Suwimol; Naksrichum, Siripat; Harnwajanawong, Naraporn

2005-06-01

The solidification of the stabilized zinc-cyanide plating sludge was carried out using ordinary Portland cement (OPC) and pulverized fuel ash (PFA) as solidification binders. The plating sludge were used at the level of 0%, 10%, 20% and 30% dry weight, and PFA was used to replace OPC at 0%, 10%, 20% and 30% dry weight, respectively. Experimental results showed that a significant reduction in strength was observed when the plating sludge was added to both the OPC and OPC/PFA binders, but the negative effect was minimized when PFA was used as part substitute for OPC. SEM observation reveals that themore » deposition of the plating sludge on the surface of the clinkers and PFA could be the cause for hydration retardation. In addition, calcium zinc hydroxide hydrate complex and the unreacted di- and tricalcium silicates were the major phases in X-ray diffraction (XRD) patterns of the solidified plating waste hydrated for 28 days, although the retardation effect on hydration reactions but Cr concentration in toxicity characteristic leaching procedure (TCLP) leachates was lower than the U.S. EPA regulatory limit.« less

Variation of mineralogy and organic material during the early stages of aqueous activity recorded in Antarctic micrometeorites

NASA Astrophysics Data System (ADS)

Noguchi, T.; Yabuta, H.; Itoh, S.; Sakamoto, N.; Mitsunari, T.; Okubo, A.; Okazaki, R.; Nakamura, T.; Tachibana, S.; Terada, K.; Ebihara, M.; Imae, N.; Kimura, M.; Nagahara, H.

2017-07-01

Micrometeorites (MMs) recovered from surface snow near the Dome Fuji Station, Antarctica are almost free from terrestrial weathering and contain very primitive materials, and are suitable for investigation of the evolution and interaction of inorganic and organic materials in the early solar system. We carried out a comprehensive study on seven porous and fluffy MMs [four Chondritic porous (CP) MMs and three fluffy fine-grained (Fluffy Fg) MMs] and one fine-grained type 1 (Fg C1) MM for comparison with scanning electron microscope, transmission electron microscope, X-ray absorption near-edge structure analysis, and secondary ion mass spectrometer. They show a variety of early aqueous activities. Four out of the seven CP MMs contain glass with embedded metal and sulfide (GEMS) and enstatite whiskers/platelets and do not have hydrated minerals. Despite the same mineralogy, organic chemistry of the CP MMs shows diversity. Two of them contain considerable amounts of organic materials with high carboxyl functionality, and one of them contains nitrile (Ctbnd N) and/or nitrogen heterocyclic groups with D and 15N enrichments, suggesting formation in the molecular cloud or a very low temperature region of the outer solar system. Another two CP MMs are poorer in organic materials than the above-mentioned MMs. Organic material in one of them is richer in aromatic C than the CP MMs mentioned above, being indistinguishable from those of hydrated carbonaceous chondrites. In addition, bulk chemical compositions of GEMS in the latter organic poor CP MMs are more homogeneous and have higher Fe/(Si + Mg + Fe) ratios than those of GEMS in the former organic-rich CP MMs. Functional group of the organic materials and amorphous silicate in GEMS in the organic-poor CP MMs may have transformed in the earliest stage of aqueous alteration, which did not form hydrated minerals. Three Fluffy Fg MMs contain abundant phyllosilicates, showing a clear evidence of aqueous alteration. Phyllosilicates in thee MMs are richer in Fe than those in hydrated IDPs, typical fine-grained hydrated (Fg C1) MMs, and hydrated carbonaceous chondrites. One of the Fluffy Fg MMs contains amorphous silicate, which is richer in Fe than GEMS and contains little or no nanophase Fe metal but contains Fe sulfide. Because the chemical compositions of the amorphous silicate are within the compositional field of GEMS in CP IDPs, the amorphous silicate may be alteration products of GEMS. The entire compositional field of GEMS in the CP MMs and the amorphous silicate in the Fluffy Fg MM matches that of the previously reported total compositional range of GEMS in IDPs. One Fluffy Fg MM contains Mg-rich phyllosilicate along with Fe-rich phyllosilicate and Mg-Fe carbonate. Mg-rich phyllosilicate and Mg-Fe carbonate may have been formed through the reaction of Fe-rich phyllosilicate, Mg-rich olivine and pyroxene, and water with C-bearing chemical species. These data indicate that CP MMs and Fluffy Fg MMs recovered from Antarctic surface snow contain materials that throw a light on the earliest stages of aqueous alteration on very primitive solar system bodies. Because mineralogy and isotopic and structural features of organic materials in D10IB009 are comparable with isotopically primitive IDPs, its parent body could be comets or icy asteroids showing mass ejection (active asteroids). By contrast, organic-poor CP MMs may have experienced the earliest stage of aqueous alteration and Fluffy Fg MMs experienced weak aqueous alteration. The precursor materials of the parent bodies of Fluffy Fg MMs probably contained abundant GEMS or GEMS-like materials like CP IDPs, which is common to fine-grained matrices of very primitive carbonaceous chondrites such as CR3s. However, highly porous nature of organic-poor CP MMs and Fluffy Fg MMs suggests that parent bodies of these MMs must have been much more porous than the parent bodies of primitive carbonaceous chondrites. Given no phyllosilicate among the returned samples of 81P/Wild 2 comet, the MMs may have been derived from porous icy asteroids such as active asteroids as well as P- and D-type asteroids rather than comets.

Pseudowollastonite Carbonation Could Enable New Frontiers in Carbon Storage

NASA Astrophysics Data System (ADS)

Plattenberger, D.; Tao, Z.; Ling, F. T.; Peters, C. A.; Clarens, A. F.

2017-12-01

One of the primary challenges of CO2 mineral trapping is that precipitation reactions are reversible. A wide range of solid magnesium, iron, or calcium carbonates (such as magnesite, MgCO3) can be synthesized by reacting mineral silicates (such as olivine, Mg2SiO4) with CO2 to produce mineral carbonates. However, if CO2 remains present at high concentrations, as would be the case in many subsurface environments, the carbonate minerals could re-dissolve, making the precipitated carbonates impermanent forms of storage. In this work, we study pseudowollastonite (CaSiO3), a crystalline form of calcium silicate that is common in slags, cement, and calcium-rich volcanic formations, for its potential to produce other secondary mineral phases that may be resistant to dissolution under low pH conditions. These secondary mineral precipitation phases have morphologies and X-ray diffraction patterns that resemble both calcium silicate hydrate gels as well as crystalline calcium silicate carbonate hydrates. The combination of these phases forms a complex system that may resist acid attack while providing strength and limiting flow in the subsurface environment. High pressure and temperature column experiments carried out in our lab show that pseudowollastonite carbonation effectively lowers permeability in columns of sintered glass beads. Many of the pore throats are clogged by precipitates, as seen using micro X-ray tomography of intact columns and electron microscopy of thin sections. The spatial distribution of the products suggests that calcite forms toward the inlet of the columns where the pCO2 is highest. This forms a barrier that reduces, but does not eliminate, the availability of CO2 deeper in the porous media where the secondary phases precipitate. The existence of the calcite zone drives the reduction in permeability and the depth of this zone is self-limiting, which could have important implications for limiting leakage and unwanted migration of CO2 in some instances.

Calcium aluminates hydration in presence of amorphous SiO{sub 2} at temperatures below 90 deg. C

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

Rivas Mercury, J.M.; Turrillas, X.; Aza, A.H. de

2006-10-15

The hydration behaviour of Ca{sub 3}Al{sub 2}O{sub 6}, Ca{sub 12}Al{sub 14}O{sub 33} and CaAl{sub 2}O{sub 4} with added amorphous silica at 40, 65 and 90 deg. C has been studied for periods ranging from 1 to 31 days. In hydrated samples crystalline phases like katoite (Ca{sub 3}Al{sub 2}(SiO{sub 4}){sub 3-} {sub x} (OH){sub 4} {sub x} ) and gibbsite, Al(OH){sub 3}, were identified, likewise amorphous phases like Al(OH) {sub x} , calcium silicate hydrates, C-S-H, and calcium aluminosilicate hydrates, C-S-A-H, were identified. The stoichiometry of Ca{sub 3}Al{sub 2}(SiO{sub 4}){sub 3-} {sub x} (OH){sub 4} {sub x} (0{<=}3-x{<=}0.334), which was themore » main crystalline product, was established by Rietveld refinement of X-ray and neutron diffraction data and by transmission electron microscopy. - Graphical abstract: Katoite, Ca{sub 3}Al{sub 2}(SiO{sub 4}){sub 3-} {sub x} (OH){sub 4} {sub x} (0{<=}3-x{<=}0.334), was identified besides gibbsite, Al(OH){sub 3}, as a crystalline stable hydration products in Ca{sub 3}Al{sub 2}O{sub 6}, Ca{sub 12}Al{sub 14}O{sub 33} and CaAl{sub 2}O{sub 4} hydrated with added amorphous silica between 40 and 90 deg. C.« less

Mechanical resilience and cementitious processes in Imperial Roman architectural mortar.

PubMed

Jackson, Marie D; Landis, Eric N; Brune, Philip F; Vitti, Massimo; Chen, Heng; Li, Qinfei; Kunz, Martin; Wenk, Hans-Rudolf; Monteiro, Paulo J M; Ingraffea, Anthony R

2014-12-30

The pyroclastic aggregate concrete of Trajan's Markets (110 CE), now Museo Fori Imperiali in Rome, has absorbed energy from seismic ground shaking and long-term foundation settlement for nearly two millenia while remaining largely intact at the structural scale. The scientific basis of this exceptional service record is explored through computed tomography of fracture surfaces and synchroton X-ray microdiffraction analyses of a reproduction of the standardized hydrated lime-volcanic ash mortar that binds decimeter-sized tuff and brick aggregate in the conglomeratic concrete. The mortar reproduction gains fracture toughness over 180 d through progressive coalescence of calcium-aluminum-silicate-hydrate (C-A-S-H) cementing binder with Ca/(Si+Al) ≈ 0.8-0.9 and crystallization of strätlingite and siliceous hydrogarnet (katoite) at ≥ 90 d, after pozzolanic consumption of hydrated lime was complete. Platey strätlingite crystals toughen interfacial zones along scoria perimeters and impede macroscale propagation of crack segments. In the 1,900-y-old mortar, C-A-S-H has low Ca/(Si+Al) ≈ 0.45-0.75. Dense clusters of 2- to 30-µm strätlingite plates further reinforce interfacial zones, the weakest link of modern cement-based concrete, and the cementitious matrix. These crystals formed during long-term autogeneous reaction of dissolved calcite from lime and the alkali-rich scoriae groundmass, clay mineral (halloysite), and zeolite (phillipsite and chabazite) surface textures from the Pozzolane Rosse pyroclastic flow, erupted from the nearby Alban Hills volcano. The clast-supported conglomeratic fabric of the concrete presents further resistance to fracture propagation at the structural scale.

Investigating permeability and carbonation behavior of sustainable cements

NASA Astrophysics Data System (ADS)

White, C.; Blyth, A.; Scherer, G. W.; Morandeau, A. E.

2015-12-01

The durability of new sustainable cementitious materials is intimately linked with the ability for these materials to prevent the ingress of aggressive ions through their percolated pore networks. However, it is also important to be able to control and limit the detrimental chemical degradation mechanisms that occur to the cement binder once the ions have diffused through the pore network. Here, alkali-activated materials will be discussed, and recent research on measuring the permeability of this class of cements using the beam-bending method will be presented. It will be shown that the permeability can be controlled by tailoring the activator chemistry, and that the addition of free silica in the activator has a strong (favorable) influence on the resulting percolated pore network. Carbonation is one type of chemical degradation process that is known to severely shorten the service life of concrete, especially in environments containing elevated CO­2 levels. However, the exact atomic structural changes that occur to the main binder phase (calcium-silicate-hydrate gel) during carbonation remain largely unknown. Here, X-ray pair distribution function analysis is used to elucidate the local atomic structural changes that occur during carbonation of calcium-silicate-hydrate gel and calcium-aluminosilicate-hydrate gel (alkali-activated slag binder), where distinct differences in the extent of gel decalcification are measured according to the chemistry of the starting precursor material. The results will be discussed in the context of limiting the extent of carbonation in cementitious materials, with potential applications of alkali-activated materials in geological storage of CO2 due to their increased resistance to carbonation.

NSF-CAREER outreach at the K-6 level through Project Excite, Center for Talent Development, School of Education and Social Policy at Northwestern University

NASA Astrophysics Data System (ADS)

Jacobsen, S. D.; Cockrell, K.

2011-12-01

Many scientists can attribute their careers to some kind of impressionable exposure to experimentation and research at an early age. However, children across the country receive varying levels of exposure to professional scientists depending upon local resources and socioeconomic composition. Outreach goals under this NSF-CAREER award are predicated on the idea that children can develop a life-long interest in science and mathematics at a very early age. The PI has focused on geoscience education to local K-6 students who might not otherwise get exposure to the field at a critical stage of their intellectual development. Working with educators at Northwestern's Center for Talent Development, the PI leads Earth science modules in Project Excite, a longitudinal program that recruits minority third-grade students from local elementary schools for a six-year program involving regular visits to the Department of Earth and Planetary Sciences. The primary goal is to boost minority enrollment in advanced placement courses in science and mathematics at Evanston Township High School. Hands-on demonstration modules have been developed on Mars rovers, renewable energy, as well as rock and mineral identification. Research under this CAREER award examines the role of silicate minerals in Earth's deep water cycle from atomic to geophysical scales. Under laboratory-simulated mantle conditions of 400-700 km depth, high-pressure minerals can incorporate a remarkable amount of water into their structures, resulting in modified physical properties. Experimental studies focus on determining hydration mechanisms at the atomic scale, and understanding the influence of hydration on the behavior of Earth materials at high pressures. Results will provide geophysical indicators of mantle hydration and facilitate detection of potential deep-mantle reservoirs of water remotely using seismic waves.

Influence of man-made aluminosilicate raw materials on physical and mechanical properties of building materials.

NASA Astrophysics Data System (ADS)

Volodchenko, A. A.; Lesovik, V. S.; Stoletov, A. A.; Glagolev, E. S.; Volodchenko, A. N.; Magomedov, Z. G.

2018-03-01

It has been identified that man-made aluminosilicate raw materials represented by clay rock of varied genesis can be used as energy-efficient raw materials to obtain efficient highly-hollow non-autoclaved silicate materials. A technique of structure formation in the conditions of pressureless steam treatment has been offered. Cementing compounds of non- autoclaved silicate materials based on man-made aluminosilicate raw materials possess hydraulic properties that are conditioned by the process of further formation and recrystallization of calcium silicate hydrates, which optimizes the ratio between gellike and crystalline components and densifies the cementing compound structure, which leads to improvement of performance characteristics. Increasing the performance characteristics of the obtained products is possible by changing the molding conditions. For this reason, in order to create high-density material packaging and, as a result, to increase the strength properties of the products, it is reasonable to use higher pressure, under which raw brick is formed, which will facilitate the increase of quality of highly-hollow products.

Dentin-cement Interfacial Interaction

PubMed Central

Atmeh, A.R.; Chong, E.Z.; Richard, G.; Festy, F.; Watson, T.F.

2012-01-01

The interfacial properties of a new calcium-silicate-based coronal restorative material (Biodentine™) and a glass-ionomer cement (GIC) with dentin have been studied by confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), micro-Raman spectroscopy, and two-photon auto-fluorescence and second-harmonic-generation (SHG) imaging. Results indicate the formation of tag-like structures alongside an interfacial layer called the “mineral infiltration zone”, where the alkaline caustic effect of the calcium silicate cement’s hydration products degrades the collagenous component of the interfacial dentin. This degradation leads to the formation of a porous structure which facilitates the permeation of high concentrations of Ca2+, OH-, and CO32- ions, leading to increased mineralization in this region. Comparison of the dentin-restorative interfaces shows that there is a dentin-mineral infiltration with the Biodentine, whereas polyacrylic and tartaric acids and their salts characterize the penetration of the GIC. A new type of interfacial interaction, “the mineral infiltration zone”, is suggested for these calcium-silicate-based cements. PMID:22436906

Portland cement hydration and early setting of cement stone intended for efficient paving materials

NASA Astrophysics Data System (ADS)

Grishina, A.

2017-10-01

Due to the growth of load on automotive roads, modern transportation engineering is in need of efficient paving materials. Runways and most advanced highways require Portland cement concretes. This makes important the studies directed to improvement of binders for such concretes. In the present work some peculiarities of the process of Portland cement hydration and early setting of cement stone with barium hydrosilicate sol were examined. It was found that the admixture of said sol leads to a shift in the induction period to later times without significant change in its duration. The admixture of a modifier with nanoscale barium hydrosilicates increases the degree of hydration of the cement clinker minerals and changes the phase composition of the hydration products; in particular, the content of portlandite and tricalcium silicate decreases, while the amount of ettringite increases. Changes in the hydration processes of Portland cement and early setting of cement stone that are caused by the nanoscale barium hydrosilicates, allow to forecast positive technological effects both at the stage of manufacturing and at the stage of operation. In particular, the formwork age can be reduced, turnover of molds can be increased, formation of secondary ettringite and corrosion of the first type can be eliminated.

DNA adsorption onto glass surfaces

NASA Astrophysics Data System (ADS)

Carlson, Krista Lynn

Streaming potential measurements were performed on microspheres of silica, lime silicate (SLS) and calcium aluminate (CA) glasses containing silica and iron oxide (CASi and CAFe). The silicate based glasses exhibited acidic surfaces with isoelectric points (IEP) around a pH of 3 while the calcium aluminates displayed more basic surfaces with IEP ranging from 8--9.5. The surface of the calcium aluminate microspheres containing silica reacted with the background electrolyte, altering the measured zeta potential values and inhibiting electrolyte flow past the sample at ˜ pH 4 due to formation of a solid plug. DNA adsorption experiments were performed using the microspheres and a commercially available silicate based DNA isolation filter using a known quantity of DNA suspended in a chaotropic agent free 0.35 wt% Tris(hydroxymethyl)aminomethane (Tris) buffer solution. The microspheres and commercial filter were also used to isolate DNA from macrophage cells in the presence of chaotropic agents. UV absorbance at ˜260 nm and gel electrophoresis were used to quantify the amount and size of the DNA strands that adsorbed to the microsphere surfaces. In both experiments, the 43--106 microm CAFe microspheres adsorbed the largest quantity of DNA. However, the 43--106 microm SLS microspheres isolated more DNA from the cells than the <43 microm CAFe microspheres, indicating that microsphere size contributes to isolation ability. The UV absorbance of DNA at ˜260 nm was slightly altered due to the dissolution of the calcium aluminate glasses during the adsorption process. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) determined that calcium and aluminum ions leached from the CA and CAFe microsphere surfaces during these experiments. Circular dichroism (CD) spectroscopy showed that the leached ions had no effect on the conformation of the DNA, and therefore would not be expected to interfere in downstream applications such as DNA replication. The 0.35 wt% Tris solution completely inhibited the formation of the hydrated crystalline layer that develops when the calcium aluminate glassess are incubated in deionized water. A Tris concentration of 0.24 wt% allowed for the formation of both hexagonal and cubic hydrates, however they were severely distorted and present in low amounts such that they were undectable by XRD.

Detection of water and/or hydroxyl on asteroid (16) Psyche

USGS Publications Warehouse

Takir, Driss; Reddy, Vishnu; Sanchez, Juan A.; Shepard, Michael K.; Emery, Joshua P.

2016-01-01

In order to search for evidence of hydration on M-type asteroid (16) Psyche, we observed this object in the 3 μm spectral region using the long-wavelength cross-dispersed (LXD: 1.9–4.2 μm) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope Facility. Our observations show that Psyche exhibits a 3 μm absorption feature, attributed to water or hydroxyl. The 3 μm absorption feature is consistent with the hydration features found on the surfaces of water-rich asteroids, attributed to OH- and/or H2O-bearing phases (phyllosilicates). The detection of a 3 μm hydration absorption band on Psyche suggests that this asteroid may not be a metallic core, or it could be a metallic core that has been impacted by carbonaceous material over the past 4.5 Gyr. Our results also indicate rotational spectral variations, which we suggest reflect heterogeneity in the metal/silicate ratio on the surface of Psyche.

Detection of Water and/or Hydroxyl on Asteroid (16) Psyche

NASA Astrophysics Data System (ADS)

Takir, Driss; Reddy, Vishnu; Sanchez, Juan A.; Shepard, Michael K.; Emery, Joshua P.

2017-01-01

In order to search for evidence of hydration on M-type asteroid (16) Psyche, we observed this object in the 3 μm spectral region using the long-wavelength cross-dispersed (LXD: 1.9-4.2 μm) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope Facility. Our observations show that Psyche exhibits a 3 μm absorption feature, attributed to water or hydroxyl. The 3 μm absorption feature is consistent with the hydration features found on the surfaces of water-rich asteroids, attributed to OH- and/or H2O-bearing phases (phyllosilicates). The detection of a 3 μm hydration absorption band on Psyche suggests that this asteroid may not be a metallic core, or it could be a metallic core that has been impacted by carbonaceous material over the past 4.5 Gyr. Our results also indicate rotational spectral variations, which we suggest reflect heterogeneity in the metal/silicate ratio on the surface of Psyche.

Characterization of Impact Damage in Ultra-High Performance Concrete Using Spatially Correlated Nanoindentation/SEM/EDX

NASA Astrophysics Data System (ADS)

Moser, R. D.; Allison, P. G.; Chandler, M. Q.

2013-12-01

Little work has been done to study the fundamental material behaviors and failure mechanisms of cement-based materials including ordinary Portland cement concrete and ultra-high performance concretes (UHPCs) under high strain impact and penetration loads at lower length scales. These high strain rate loadings have many possible effects on UHPCs at the microscale and nanoscale, including alterations in the hydration state and bonding present in phases such as calcium silicate hydrate, in addition to fracture and debonding. In this work, the possible chemical and physical changes in UHPCs subjected to high strain rate impact and penetration loads were investigated using a novel technique wherein nanoindentation measurements were spatially correlated with images using scanning electron microscopy and chemical composition using energy dispersive x-ray microanalysis. Results indicate that impact degrades both the elastic modulus and indentation hardness of UHPCs, and in particular hydrated phases, with damage likely occurring due to microfracturing and debonding.

DETECTION OF WATER AND/OR HYDROXYL ON ASTEROID (16) Psyche

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

Takir, Driss; Reddy, Vishnu; Sanchez, Juan A.

In order to search for evidence of hydration on M-type asteroid (16) Psyche, we observed this object in the 3 μ m spectral region using the long-wavelength cross-dispersed (LXD: 1.9–4.2 μ m) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope Facility. Our observations show that Psyche exhibits a 3 μ m absorption feature, attributed to water or hydroxyl. The 3 μ m absorption feature is consistent with the hydration features found on the surfaces of water-rich asteroids, attributed to OH- and/or H{sub 2}O-bearing phases (phyllosilicates). The detection of a 3 μ m hydration absorption band on Psyche suggestsmore » that this asteroid may not be a metallic core, or it could be a metallic core that has been impacted by carbonaceous material over the past 4.5 Gyr. Our results also indicate rotational spectral variations, which we suggest reflect heterogeneity in the metal/silicate ratio on the surface of Psyche.« less

Mineral resource of the month: vermiculite

USGS Publications Warehouse

Potter, M.J.

2008-01-01

Vermiculite, a hydrated magnesium-aluminum-iron silicate mineral, has a range of uses that take advantage of its fire resistance, good insulating properties, high liquid absorption capacity, inertness and low density. Most applications for vermiculite use an exfoliated (heat-expanded) form of the mineral. In general, coarser grades of vermiculite are used as loose fill insulation and in horticulture. Finer grades are used in wallboard and plasters and for animal feeds and fertilizers.

Interfacial Connection Mechanisms in Calcium-Silicate-Hydrates/Polymer Nanocomposites: A Molecular Dynamics Study.

PubMed

Zhou, Yang; Hou, Dongshuai; Manzano, Hegoi; Orozco, Carlos A; Geng, Guoqing; Monteiro, Paulo J M; Liu, Jiaping

2017-11-22

Properties of organic/inorganic composites can be highly dependent on the interfacial connections. In this work, molecular dynamics, using pair-potential-based force fields, was employed to investigate the structure, dynamics, and stability of interfacial connections between calcium-silicate-hydrates (C-S-H) and organic functional groups of three different polymer species. The calculation results suggest that the affinity between C-S-H and polymers is influenced by the polarity of the functional groups and the diffusivity and aggregation tendency of the polymers. In the interfaces, the calcium counterions from C-S-H act as the coordination atoms in bridging the double-bonded oxygen atoms in the carboxyl groups (-COOH), and the Ca-O connection plays a dominant role in binding poly(acrylic acid) (PAA) due to the high bond strength defined by time-correlated function. The defective calcium-silicate chains provide significant numbers of nonbridging oxygen sites to accept H-bonds from -COOH groups. As compared with PAA, the interfacial interactions are much weaker between C-S-H and poly(vinyl alcohol) (PVA) or poly(ethylene glycol) (PEG). Predominate percentage of the -OH groups in the PVA form H-bonds with inter- and intramolecule, which results in the polymer intertwining and reduces the probability of H-bond connections between PVA and C-S-H. On the other hand, the inert functional groups (C-O-C) in poly(ethylene glycol) (PEG) make this polymer exhibit unfolded configurations and move freely with little restrictions. The interaction mechanisms interpreted in this organic-inorganic interface can give fundamental insights into the polymer modification of C-S-H and further implications to improving cement-based materials from the genetic level.

The effect of geothermal fluid composition in lime-pozzolan reactions on elastic and transport properties.

NASA Astrophysics Data System (ADS)

MacFarlane, J.; Vanorio, T.

2016-12-01

Calcium-Silicate-Hydrates (C-S-H) are a complex family of hydrates known to form within hyper-alkaline geothermal systems as well as concrete. Within both environments the formation of C-S-H can be linked to the lime-pozzolan reaction. Pozzolan's defined as a siliceous or alumino-siliceous material, which in itself possesses little or no cementing property, but in the presence of moisture chemically reacts with calcium hydroxide at ordinary temperatures to form cementitious compounds. C-S-H fibers have been discovered in a low permeability, caprock layer beneath the Campi Flegrei caldera, as well as within ancient Roman concrete made using volcanic ash and fluids from the Campi Flegrei region over 2000 years ago. By replicating the recipe for Roman concrete, fibrous minerals have been formed in laboratory experiments and imaged using a scanning electron microscope. The formation of C-S-H within concrete has been shown to depend on the mineral ions present, among other factors. Here, we report on how the geothermal fluid composition effects the elastic and transport properties of laboratory samples. Samples were made using the same volcanic ash as the Romans, called Pozzolana, slaked lime and geothermal fluid. Two geothermal fluids from the Campi Flegrei region were compared, as well as deionized water as a control. Preliminary results have shown changes in both the elastic and transport properties between sample sets made with geothermal fluid and the control. These changes are attributed to the structure of the C-S-H that forms in the lime-pozzolan reaction. Understanding how the geothermal fluid composition controls the properties of this reaction has implications for the understanding of both geothermal systems and concrete engineering.

Kinetic D/H fractionation during hydration and dehydration of silicate glasses, melts and nominally anhydrous minerals

NASA Astrophysics Data System (ADS)

Roskosz, M.; Deloule, E.; Ingrin, J.; Depecker, C.; Laporte, D.; Merkel, S.; Remusat, L.; Leroux, H.

2018-07-01

The distribution of hydrogen isotopes during diffusion-driven aqueous processes in silicate glasses, melts and crystals was investigated. Hydration/dehydration experiments were performed on silica glasses at 1000 °C and 1 bar total pressure. Dehydration triggered by decompression-driven bubble nucleation and growth was performed on rhyolitic melts at 800 °C and a few hundred MPa. Hydrogen extraction from a nominally anhydrous mineral (grossular) single crystal was carried out at 800 °C and ambient pressure. After these three series of experiments, pronounced water (sensu lato) concentration profiles were observed in all recovered samples. In the grossular single-crystal, a large spatial variation in H isotopes (δD variation > 550‰) was measured across the sample. This isotopic distribution correlates with the hydrogen extraction profile. The fit to the data suggests an extreme decoupling between hydrogen and deuterium diffusion coefficients (DH and DD respectively), akin to the decoupling expected in a dilute ideal gas (DH/DD ≈ 1.41). Conversely, no measurable spatially- and time-resolved isotopic variations were measured in silicate glasses and melts. This contrasted behavior of hydrogen isotopes likely stands in the different water speciation and solution mechanisms in the three different materials. Glasses and melts contain essentially hydroxyl and molecular water groups but the mobile species is molecular water in both cases. Protonated defects make up most of the water accommodated in grossular and other nominally anhydrous minerals (NAM). These defects are also the mobile species that diffuse against polarons. These results are crucial to accurately model the degassing behavior of terrestrial and lunar magmas and to derive the initial D/H of water trapped in fluid inclusions commonly analyzed in mantle NAMs, which suffered complex geological histories.

Aqueous alteration on main belt primitive asteroids: Results from visible spectroscopy

NASA Astrophysics Data System (ADS)

Fornasier, S.; Lantz, C.; Barucci, M. A.; Lazzarin, M.

2014-05-01

This work focuses on the study of the aqueous alteration process which acted in the main belt and produced hydrated minerals on the altered asteroids. Hydrated minerals have been found mainly on Mars surface, on main belt primitive asteroids and possibly also on few TNOs. These materials have been produced by hydration of pristine anhydrous silicates during the aqueous alteration process, that, to be active, needed the presence of liquid water under low temperature conditions (below 320 K) to chemically alter the minerals. The aqueous alteration is particularly important for unraveling the processes occurring during the earliest times of the Solar System history, as it can give information both on the asteroids thermal evolution and on the localization of water sources in the asteroid belt. To investigate this process, we present reflected light spectral observations in the visible region (0.4-0.94 μm) of 80 asteroids belonging to the primitive classes C (prevalently), G, F, B and P, following the Tholen (Tholen, D.J. [1984]. Ph.D. Dissertation, University of Arizona, Tucson). classification scheme. We find that about 65% of the C-type and all the G-type asteroids investigated reveal features suggesting the presence of hydrous materials, mainly a band centered around 0.7 μm, while we do not find evidence of hydrated materials in the other low albedo asteroids (B, F, and P) investigated. We combine the present observations with the visible spectra of asteroids available in the literature for a total of 600 primitive main belt asteroids. We analyze all these spectra in a similar way to characterize the absorption band parameters (band center, depth and width) and spectral slope, and to look for possible correlations between the aqueous alteration process and the asteroids taxonomic classes, orbital elements, heliocentric distances, albedo and sizes. Our analysis shows that the aqueous alteration sequence starts from the P-type objects, practically unaltered, and increases through the P → F → B → C → G asteroids, these last being widely aqueous altered, strengthening thus the results previously obtained by Vilas (Vilas, F. [1994]. Icarus 111, 456-467). Around 50% of the observed C-type asteroids show absorption feature in the visible range due to hydrated silicates, implying that more than ∼70% of them will have a 3 μm absorption band and thus hydrated minerals on their surfaces, based on correlations between those two absorptions (Howell, E.S. et al. [2011]. EPSC-DPS Joint Meeting 2011, vol. 6. Abstracts, 637). We find that the aqueous alteration process dominates in primitive asteroids located between 2.3 and 3.1 AU, that is at smaller heliocentric distances than previously suggested by Vilas et al. (Vilas, F., Hatch, E.C., Larson, S.M., Sawyer, S.R., Gaffey, M.J. [1993]. Icarus 102, 225-231). The percentage of hydrated asteroids is strongly correlated with their size. The aqueous alteration process is less effective for bodies smaller than 50 km, while it dominates in the 50-240 km sized primitive asteroids. No correlation is found between the aqueous alteration process and the asteroids albedo or orbital elements. Comparing the ∼0.7 μm band parameters of hydrated silicates and CM2 carbonaceous chondrites, the meteorites that have aqueous altered asteroids as parent bodies, we see that the band center of meteorites is at longer wavelengths than that of asteroids. This difference on center positions may be attributed to different minerals abundances, and to the fact that CM2 available on Earth might not be representative of the whole aqueous altered asteroids population.

Balancing strength and toughness of calcium-silicate-hydrate via random nanovoids and particle inclusions: Atomistic modeling and statistical analysis

NASA Astrophysics Data System (ADS)

Zhang, Ning; Shahsavari, Rouzbeh

2016-11-01

As the most widely used manufactured material on Earth, concrete poses serious societal and environmental concerns which call for innovative strategies to develop greener concrete with improved strength and toughness, properties that are exclusive in man-made materials. Herein, we focus on calcium silicate hydrate (C-S-H), the major binding phase of all Portland cement concretes, and study how engineering its nanovoids and portlandite particle inclusions can impart a balance of strength, toughness and stiffness. By performing an extensive +600 molecular dynamics simulations coupled with statistical analysis tools, our results provide new evidence of ductile fracture mechanisms in C-S-H - reminiscent of crystalline alloys and ductile metals - decoding the interplay between the crack growth, nanovoid/particle inclusions, and stoichiometry, which dictates the crystalline versus amorphous nature of the underlying matrix. We found that introduction of voids and portlandite particles can significantly increase toughness and ductility, specially in C-S-H with more amorphous matrices, mainly owing to competing mechanisms of crack deflection, voids coalescence, internal necking, accommodation, and geometry alteration of individual voids/particles, which together regulate toughness versus strength. Furthermore, utilizing a comprehensive global sensitivity analysis on random configuration-property relations, we show that the mean diameter of voids/particles is the most critical statistical parameter influencing the mechanical properties of C-S-H, irrespective of stoichiometry or crystalline or amorphous nature of the matrix. This study provides new fundamental insights, design guidelines, and de novo strategies to turn the brittle C-S-H into a ductile material, impacting modern engineering of strong and tough concrete infrastructures and potentially other complex brittle materials.

Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument

USGS Publications Warehouse

Mustard, J.F.; Murchie, S.L.; Pelkey, S.M.; Ehlmann, B.L.; Milliken, R.E.; Grant, J. A.; Bibring, J.-P.; Poulet, F.; Bishop, J.; Dobrea, E.N.; Roach, L.; Seelos, F.; Arvidson, R. E.; Wiseman, S.; Green, R.; Hash, C.; Humm, D.; Malaret, E.; McGovern, J.A.; Seelos, K.; Clancy, T.; Clark, R.; des Marais, D.; Izenberg, N.; Knudson, A.; Langevin, Y.; Martin, T.; McGuire, P.; Morris, Robert; Robinson, M.; Roush, T.; Smith, M.; Swayze, G.; Taylor, H.; Titus, T.; Wolff, M.

2008-01-01

Phyllosilicates, a class of hydrous mineral first definitively identified on Mars by the OMEGA (Observatoire pour la Mineralogie, L’Eau, les Glaces et l’Activitié) instrument1,2, preserve a record of the interaction of water with rocks on Mars. Global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy (Fe/Mg and Al smectite clays). This was interpreted to indicate that phyllosilicate formation occurred during the Noachian (the earliest geological era of Mars), and that the conditions necessary for phyllosilicate formation (moderate to high pH and high water activity3) were specific to surface environments during the earliest era of Mars’s history4. Here we report results from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM)4 of phyllosilicate-rich regions. We expand the diversity of phyllosilicate mineralogy with the identification of kaolinite, chlorite and illite or muscovite, and a new class of hydrated silicate (hydrated silica). We observe diverse Fe/Mg-OH phyllosilicates and find that smectites such as nontronite and saponite are the most common, but chlorites are also present in some locations. Stratigraphic relationships in the Nili Fossae region show olivine-rich materials overlying phyllosilicate-bearing units, indicating the cessation of aqueous alteration before emplacement of the olivine-bearing unit. Hundreds of detections of Fe/Mg phyllosilicate in rims, ejecta and central peaks of craters in the southern highland Noachian cratered terrain indicate excavation of altered crust from depth. We also find phyllosilicate in sedimentary deposits clearly laid by water. These results point to a rich diversity of Noachian environments conducive to habitability.

DIFFERENT ORIGINS OR DIFFERENT EVOLUTIONS? DECODING THE SPECTRAL DIVERSITY AMONG C-TYPE ASTEROIDS

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

Vernazza, P.; Marsset, M.; Groussin, O.

Anhydrous pyroxene-rich interplanetary dust particles (IDPs) have been proposed as surface analogs for about two-thirds of all C-complex asteroids. However, this suggestion appears to be inconsistent with the presence of hydrated silicates on the surfaces of some of these asteroids, including Ceres. Here, we report the presence of enstatite (pyroxene) on the surface of two C-type asteroids (Ceres and Eugenia) based on their spectral properties in the mid-infrared range. The presence of this component is particularly unexpected in the case of Ceres, because most thermal evolution models predict a surface consisting of hydrated compounds only. The most plausible scenario is that Ceres’more » surface has been partially contaminated by exogenous enstatite-rich material, possibly coming from the Beagle asteroid family. This scenario questions a similar origin for Ceres and the remaining C-types, and it possibly supports recent results obtained by the Dawn mission (NASA) that Ceres may have formed in the very outer solar system. Concerning the smaller D  ∼ 200 km C-types such as Eugenia, both their derived surface composition (enstatite and amorphous silicates) and low density (<1.5 g cm{sup −3}) suggest that these bodies accreted from the same building blocks, namely chondritic porous, pyroxene-rich IDPs and volatiles (mostly water ice), and that a significant volume fraction of these bodies has remained unaffected by hydrothermal activity likely implying a late accretion. In addition, their current heliocentric distance may best explain the presence or absence of water ice at their surfaces. Finally, we raise the possibility that CI chondrites, Tagish-Lake-like material, or hydrated IDPs may be representative samples of the cores of these bodies.« less

Different Origins or Different Evolutions? Decoding the Spectral Diversity Among C-type Asteroids

NASA Astrophysics Data System (ADS)

Vernazza, P.; Castillo-Rogez, J.; Beck, P.; Emery, J.; Brunetto, R.; Delbo, M.; Marsset, M.; Marchis, F.; Groussin, O.; Zanda, B.; Lamy, P.; Jorda, L.; Mousis, O.; Delsanti, A.; Djouadi, Z.; Dionnet, Z.; Borondics, F.; Carry, B.

2017-02-01

Anhydrous pyroxene-rich interplanetary dust particles (IDPs) have been proposed as surface analogs for about two-thirds of all C-complex asteroids. However, this suggestion appears to be inconsistent with the presence of hydrated silicates on the surfaces of some of these asteroids, including Ceres. Here, we report the presence of enstatite (pyroxene) on the surface of two C-type asteroids (Ceres and Eugenia) based on their spectral properties in the mid-infrared range. The presence of this component is particularly unexpected in the case of Ceres, because most thermal evolution models predict a surface consisting of hydrated compounds only. The most plausible scenario is that Ceres’ surface has been partially contaminated by exogenous enstatite-rich material, possibly coming from the Beagle asteroid family. This scenario questions a similar origin for Ceres and the remaining C-types, and it possibly supports recent results obtained by the Dawn mission (NASA) that Ceres may have formed in the very outer solar system. Concerning the smaller D ˜ 200 km C-types such as Eugenia, both their derived surface composition (enstatite and amorphous silicates) and low density (<1.5 g cm-3) suggest that these bodies accreted from the same building blocks, namely chondritic porous, pyroxene-rich IDPs and volatiles (mostly water ice), and that a significant volume fraction of these bodies has remained unaffected by hydrothermal activity likely implying a late accretion. In addition, their current heliocentric distance may best explain the presence or absence of water ice at their surfaces. Finally, we raise the possibility that CI chondrites, Tagish-Lake-like material, or hydrated IDPs may be representative samples of the cores of these bodies.

Design and Implementation of Alkali Activated Cement For Sustainable Development

NASA Astrophysics Data System (ADS)

Moseson, Alexander James

Herein, progress is presented on the design and implementation of technology for sustainable development in general and international development in particular. Necessarily interdisciplinary, the work draws upon the tools and techniques of Mechanical, Materials, and Civil Engineering; and History & Politics. The work was conducted along two paths, the first being the theory and methodology of sustainable development. A flexible design and dissemination framework was developed, Technology Seeding, defined as: development by the transfer and participatory adaptation of appropriate proven conceptual designs. The methodology was developed in part through two case studies which implemented, respectively, wood-turning lathes in Tanzania and upland rice planters in Thailand. The second path is the design and investigation of alkali-activated cements (AACs) for practical use. Those developed herein, for US markets, comprise ground granulated blast furnace slag, soda ash (sodium carbonate), and up to 68 wt.% granular limestone. Mixture Design of Experiment (DOE) was utilized to guide empirical and theoretical analysis of performance (e.g. compressive strength), economic & ecological aspects (e.g. cost, CO2 production, energy consumption), and chemistry (e.g. Rietveld analysis of x-ray diffractograms). Models were derived to understand the impact of mix design on performance and for optimization. Successful formulations are hydraulic and cure at room temperature, with strengths as high as 41 MPa at 3 days and 65 MPa at 28 days. Some of these formulations, compared to OPC, are competitive in performance, reduce cost by up to 40%, and reduce both CO2 production and energy consumption by up to 97%. Major chemical products include calcium silicate hydrates / calcium aluminum silicate hydrates (C-(A)-S-H), gaylussite, and calcite (both newly formed and remaining from limestone). Calcite/dolomite and C-(A)-S-H both contribute to strength. A fraction of the limestone is consumed and becomes part of the C(A)-S-H, with an average CaO/SiO2 ratio of 1.4. A six month term as a Visiting Scholar at the Indian Institute of Technology (IIT) in Mumbai, India built upon both paths. Several AACs that use local materials and techniques and pass local standards were rapidly developed, and the potential positively assessed for these AACs to be used to empower slum dwellers.

Influence of lead on stabilization/solidification by ordinary Portland cement and magnesium phosphate cement.

PubMed

Wang, Yan-Shuai; Dai, Jian-Guo; Wang, Lei; Tsang, Daniel C W; Poon, Chi Sun

2018-01-01

Inorganic binder-based stabilization/solidification (S/S) of Pb-contaminated soil is a commonly used remediation approach. This paper investigates the influences of soluble Pb species on the hydration process of two types of inorganic binders: ordinary Portland cement (OPC) and magnesium potassium phosphate cement (MKPC). The environmental leachability, compressive strength, and setting time of the cement products are assessed as the primary performance indicators. The mechanisms of Pb involved in the hydration process are analyzed through X-ray diffraction (XRD), hydration heat evolution, and thermogravimetric analyses. Results show that the presence of Pb imposes adverse impact on the compressive strength (decreased by 30.4%) and the final setting time (prolonged by 334.7%) of OPC, but it exerts much less influence on those of MKPC. The reduced strength and delayed setting are attributed to the retarded hydration reaction rate of OPC during the induction period. These results suggest that the OPC-based S/S of soluble Pb mainly depends on physical encapsulation by calcium-silicate-hydrate (CSH) gels. In contrast, in case of MKPC-based S/S process, chemical stabilization with residual phosphate (pyromorphite and lead phosphate precipitation) and physical fixation of cementitious struvite-K are the major mechanisms. Therefore, MKPC is a more efficient and chemically stable inorganic binder for the Pb S/S process. Copyright © 2017 Elsevier Ltd. All rights reserved.

Evaluation of Warm-Mix Asphalt Technologies for Use on Airfield Pavements

DTIC Science & Technology

2013-12-01

three different ways: mechanical injection of water at the plant, adding a material containing internal water, such as zeolites , and using a two...the nozzles, causing the asphalt binder to expand (Prowell and Hurley 2007). Zeolites are crystalline-hydrated aluminum silicates that are typically...sold in granular form with approximately a No. 50 mesh size and contain approximately 20% water by weight. The water is released from the zeolite

Silicification in Grasses: Variation between Different Cell Types

PubMed Central

Kumar, Santosh; Soukup, Milan; Elbaum, Rivka

2017-01-01

Plants take up silicon as mono-silicic acid, which is released to soil by the weathering of silicate minerals. Silicic acid can be taken up by plant roots passively or actively, and later it is deposited in its polymerized form as amorphous hydrated silica. Major silica depositions in grasses occur in root endodermis, leaf epidermal cells, and outer epidermal cells of inflorescence bracts. Debates are rife about the mechanism of silica deposition, and two contrasting scenarios are often proposed to explain it. According to the passive mode of silicification, silica deposition is a result of silicic acid condensation due to dehydration, such as during transpirational loss of water from the aboveground organs. In general, silicification and transpiration are positively correlated, and continued silicification is sometimes observed after cell and tissue maturity. The other mode of silicification proposes the involvement of some biological factors, and is based on observations that silicification is not necessarily coupled with transpiration. Here, we review evidence for both mechanisms of silicification, and propose that the deposition mechanism is specific to the cell type. Considering all the cell types together, our conclusion is that grass silica deposition can be divided into three modes: spontaneous cell wall silicification, directed cell wall silicification, and directed paramural silicification in silica cells. PMID:28400787

Low-δD hydration rinds in Yellowstone perlites record rapid syneruptive hydration during glacial and interglacial conditions

USGS Publications Warehouse

Bindeman, Ilya N.; Lowenstern, Jacob B.

2016-01-01

Hydration of silicic volcanic glass forms perlite, a dusky, porous form of altered glass characterized by abundant “onion-skin” fractures. The timing and temperature of perlite formation are enigmatic and could plausibly occur during eruption, during post-eruptive cooling, or much later at ambient temperatures. To learn more about the origin of natural perlite, and to fingerprint the hydration waters, we investigated perlitic glass from several synglacial and interglacial rhyolitic lavas and tuffs from the Yellowstone volcanic system. Perlitic cores are surrounded by a series of conchoidal cracks that separate 30- to 100-µm-thick slivers, likely formed in response to hydration-induced stress. H2O and D/H profiles confirm that most D/H exchange happens together with rapid H2O addition but some smoother D/H variations may suggest separate minor exchange by deuterium atom interdiffusion following hydration. The hydrated rinds (2–3 wt% H2O) transition rapidly (within 30 µm, or by 1 wt% H2O per 10 µm) to unhydrated glass cores. This is consistent with quenched “hydration fronts” where H2O diffusion coefficients are strongly dependent on H2O concentrations. The chemical, δ18O, and δD systematics of bulk glass records last equilibrium between ~110 and 60 °C without chemical exchange but with some δ18O exchange. Similarly, the δ18O of water extracted from glass by rapid heating suggests that water was added to the glass during cooling at <200 °C. Our observations support fast hydration at temperatures as low as 60 °C; prolonged exposure to high temperature of 175°–225° during water addition is less likely as the glass would lose alkalies and should alter to clays within days. A compilation of low-temperature hydration diffusion coefficients suggests ~2 orders of magnitude higher rates of diffusion at 60–110 °C temperatures, compared with values expected from extrapolation of high-temperature (>400 °C) experimental data. The thick hydration rinds in perlites, measuring hundreds of microns, preserve the original D/H values of hydrating water as a recorder of paleoclimate conditions. Measured δD values in perlitic lavas are −150 to −191 or 20–40 ‰ lower than glass hydrated by modern Yellowstone waters. This suggests that Yellowstone perlites record the low-δD signature of glacial ice. Cooling calculations, combined with the observed high water diffusion coefficients noted for 60–150 °C, suggest that if sufficient hot water or steam is available, any rhyolite flow greater than ~5 m thick can develop the observed ~250-µm hydration rinds within the expected timescale of cooling (weeks–years). As the process of hydration involves shattering of 30- to 100-µm-thick slivers to expose unhydrated rhyolite glass, the time required for hydration may be even shorter. Rapid hydration and formation of relatively thick-walled glass shards allow perlites to provide a snapshot view of the meteoric water (and thus climate) at the time of initial alteration. Perlites retain their initial hydration D/H signal better than thin-walled ash, which in contrast hydrates over many thousands of years with time-averaged precipitation.

Low-δD hydration rinds in Yellowstone perlites record rapid syneruptive hydration during glacial and interglacial conditions

NASA Astrophysics Data System (ADS)

Bindeman, Ilya N.; Lowenstern, Jacob B.

2016-11-01

Hydration of silicic volcanic glass forms perlite, a dusky, porous form of altered glass characterized by abundant "onion-skin" fractures. The timing and temperature of perlite formation are enigmatic and could plausibly occur during eruption, during post-eruptive cooling, or much later at ambient temperatures. To learn more about the origin of natural perlite, and to fingerprint the hydration waters, we investigated perlitic glass from several synglacial and interglacial rhyolitic lavas and tuffs from the Yellowstone volcanic system. Perlitic cores are surrounded by a series of conchoidal cracks that separate 30- to 100-µm-thick slivers, likely formed in response to hydration-induced stress. H2O and D/H profiles confirm that most D/H exchange happens together with rapid H2O addition but some smoother D/H variations may suggest separate minor exchange by deuterium atom interdiffusion following hydration. The hydrated rinds (2-3 wt% H2O) transition rapidly (within 30 µm, or by 1 wt% H2O per 10 µm) to unhydrated glass cores. This is consistent with quenched "hydration fronts" where H2O diffusion coefficients are strongly dependent on H2O concentrations. The chemical, δ18O, and δD systematics of bulk glass records last equilibrium between 110 and 60 °C without chemical exchange but with some δ18O exchange. Similarly, the δ18O of water extracted from glass by rapid heating suggests that water was added to the glass during cooling at <200 °C. Our observations support fast hydration at temperatures as low as 60 °C; prolonged exposure to high temperature of 175°-225° during water addition is less likely as the glass would lose alkalies and should alter to clays within days. A compilation of low-temperature hydration diffusion coefficients suggests 2 orders of magnitude higher rates of diffusion at 60-110 °C temperatures, compared with values expected from extrapolation of high-temperature (>400 °C) experimental data. The thick hydration rinds in perlites, measuring hundreds of microns, preserve the original D/H values of hydrating water as a recorder of paleoclimate conditions. Measured δD values in perlitic lavas are -150 to -191 or 20-40 ‰ lower than glass hydrated by modern Yellowstone waters. This suggests that Yellowstone perlites record the low-δD signature of glacial ice. Cooling calculations, combined with the observed high water diffusion coefficients noted for 60-150 °C, suggest that if sufficient hot water or steam is available, any rhyolite flow greater than 5 m thick can develop the observed 250-µm hydration rinds within the expected timescale of cooling (weeks-years). As the process of hydration involves shattering of 30- to 100-µm-thick slivers to expose unhydrated rhyolite glass, the time required for hydration may be even shorter. Rapid hydration and formation of relatively thick-walled glass shards allow perlites to provide a snapshot view of the meteoric water (and thus climate) at the time of initial alteration. Perlites retain their initial hydration D/H signal better than thin-walled ash, which in contrast hydrates over many thousands of years with time-averaged precipitation.

Mg-Sulfate Salts as Possible Water Reservoirs in Martian Regolith

NASA Astrophysics Data System (ADS)

Vaniman, D. T.; Bish, D. L.; Chipera, S. J.; Carey, J. W.; Feldman, W. C.

2003-12-01

Neutron spectrometer data from the Mars Odyssey orbiter provide evidence of high water-equivalent hydrogen abundance in some near-equatorial locations on Mars. In broad regions shallow (<1 m) regolith appears to have water abundances of up to ˜13 wt%. Water ice is predicted to be unstable at the present time at all depths below the surface in these equatorial regions. If present in hydrous silicate minerals such as clays or zeolites, which may contain water in abundances of ˜10-20% at Martian surface conditions, the Odyssey data require a regolith very enriched in hydrous silicates - an unlikely proposition. Viking X-ray fluorescence data and alteration assemblages in martian meteorites suggest the presence of sulfate salts in martian regolith. Viking data from excavated duricrust indicate that Mg and S are correlated and that ˜10% of an Mg-sulfate salt is a likely cementing agent. However, the range of possible Mg sulfates is large. Epsomite (7-hydrate, 51% water) and hexahydrite (6-hydrate, 47% water) are the most hydrated; both form structures of isolated SO4 tetrahedra with isolated octahedral sites consisting of Mg coordinated by six H2O molecules (epsomite has an extra H2O in addition to the six required to coordinate with Mg). Pentahydrite (5-hydrate, 43% water) has infinite chains of alternating SO4 tetrahedra and Mg octahedra, with 4/5 of the water forming apices in octahedral sites. Starkeyite (4-hydrate, 37% water) has clusters of two SO4 tetrahedra and two Mg octahedra, linked only by hydrogen bonds. The Mg-sulfate sanderite (2-hydrate, 23% water) is rare and has poorly known structure. Kieserite (1-hydrate, 13% water) is relatively common in evaporite deposits and has a framework structure of infinite tetrahedral-octahedral chains cross-linked by hydrogen bonds. The stability of Mg-sulfate hydrates under martian near-surface conditions depends on their structures; those with excess water beyond that required to form the octahedral Mg site (e.g., epsomite, pentahydrite) lose that excess readily. Experiments with epsomite and hexahydrite indicate great sensitivity to environmental conditions; epsomite is not stable at 295 K at relative humidity (RH) values less than about 55%, below which hexahydrite is the observed phase. More importantly, hexahydrite - with all water coordinated to Mg in octahedral sites - is unstable at pressures less than ˜20 mtorr. X-ray diffraction analysis of hexahydrite held at 20 mtorr for six hours shows that structural degradation is slow at 100 K but becomes obvious in 1 hour at 273 K. Thermogravimetric analysis of this amorphous solid shows that it contains ˜26% H2O (compared with 47% in crystalline hexahydrite), and its observed macroscopic expansion behavior suggests that it can reversibly hydrate and dehydrate. Although neither epsomite nor hexahydrite is likely to be stable near the surface of Mars, their amorphous derivatives or crystalline forms of the lower hydrates might be present (preliminary thermogravimetric data indicate that kieserite is likely to be stable). However, the limited rehydration of structurally degraded hexahydrite indicates that unrealistically large amounts ( ˜50%) would be required in the upper meter of regolith to account for the higher water contents ( ˜13%) suggested for some martian equatorial regions; even larger amounts of kieserite ( ˜100%) would be required. A more important role for sulfates may be in the formation of a low-permeability salt crust that could restrict dewatering of underlying soil horizons.

Interplanetary dust in the transmission electron microscope - Diverse materials from the early solar system

NASA Technical Reports Server (NTRS)

Fraundorf, P.

1981-01-01

An analytical electron microscope study of dispersed interplanetary dust aggregates collected in the earth's stratosphere shows that, in spite of their similarities, the aggregates exhibit significant differences in composition, internal morphology, and mineralogy. Of 11 chondritic particles examined, two consist mostly of a noncrystalline chondritic material with an atomic S/Fe ratio equal to or greater than 2 in places, one consists of submicron metal and reduced silicate 'microchondrules' and sulfide grains embedded in a carbonaceous matrix, and another consists of submicron magnetic-decorated unequilibrated silicate and sulfide grains with thick low-Z coatings. Although the particles are unmetamorphosed by criteria commonly applied for chondritic meteorites, the presence of reduced chemistries and the ubiquity of mafic, instead of hydrated, silicates confirm that they are not simply C1 or C2 chondrite matrix material. The observations indicate that portions of some particles have not been significantly altered by thermal or radiation processes since their assembly, and that the particles probably contain fine debris from diverse processes in the early solar system.

Fibrillar Organic Phases And Their Roles In Rigid Biological Composites

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

Arey, Bruce W.; Park, John J.; Mayer, George

2015-06-01

This study focused on determining the presence of organic phases in the siliceous components of rigid marine composites ("glass" sponge spicules), and thereby to clarify how those composites dissipate significant mechanical energy. Through the use of imaging by helium ion microscopy in the examination of the spicules, the organic phase that is present between the layers of hydrated silica was also detected within the silica cylinders of the composite, indicating the existence therein of a network, scaffolding, or other pattern that has not yet been determined. It was concluded that the presence of an interpenetrating network of some kind, andmore » tenacious fibrillar interfaces are responsible for the large energy dissipation in these siliceous composites by viscoelastic processes. This discovery means that future mechanics analyses of such composites, extending to large deformations must consider such interpenetrating phases.« less

Silica-rich deposits and hydrated minerals at Gusev Crater, Mars: Vis-NIR spectral characterization and regional mapping

USGS Publications Warehouse

Rice, M.S.; Bell, J.F.; Cloutis, E.A.; Wang, A.; Ruff, S.W.; Craig, M.A.; Bailey, D.T.; Johnson, J. R.; De Souza, P.A.; Farrand, W. H.

2010-01-01

The Mars Exploration Rover (MER) Spirit has discovered surprisingly high concentrations of amorphous silica in soil and nodular outcrops in the Inner Basin of the Columbia Hills. In Pancam multispectral observations, we find that an absorption feature at the longest Pancam wavelength (1009 nm) appears to be characteristic of these silica-rich materials; however, spectral analyses of amorphous silica suggest that the ???1009 nm spectral feature is not a direct reflection of their silica-rich nature. Based on comparisons with spectral databases, we hypothesize that the presence of H2O or OH, either free (as water ice), adsorbed or bound in a mineral structure, is responsible for the spectral feature observed by Pancam. The Gertrude Weise soil, which is nearly pure opaline silica, may have adsorbed water cold-trapped on mineral grains. The origin of the ???1009 nm Pancam feature observed in the silica-rich nodular outcrops may result from the presence of additional hydrated minerals (specific sulfates, halides, chlorides, sodium silicates, carbonates or borates). Using the ???1009 nm feature with other spectral parameters as a "hydration signature" we have mapped the occurrence of hydrated materials along the extent of Spirit's traverse across the Columbia Hills from West Spur to Home Plate (sols 155-1696). We have also mapped this hydration signature across large panoramic images to understand the regional distribution of materials that are spectrally similar to the silica-rich soil and nodular outcrops. Our results suggest that hydrated materials are common in the Columbia Hills. ?? 2009 Elsevier Inc.

Self-repairing properties of OPC clinker/natural zeolite blend in water and alkali carbonate environments at 270°C

DOE PAGES

Pyatina, Tatiana; Sugama, Toshifumi; Ronne, Arthur; ...

2018-01-01

The 10 d recoveries of the mechanical properties and crack sealing of an ordinary Portland cement (OPC) clinker/natural zeolite (ferrierite (Fer)) blend modified or unmodified with silica were tested at 270°C in water and alkali carbonate environments. The recoveries of the samples depended on their modification with silica and the curing environment, but were more than 100% after repeated damage under some test conditions. The mechanical properties and phase compositions of recovered samples were evaluated by compressive strength measurements and x-ray diffraction, differential thermogravimetric analyses, Fourier transform infrared analyses and scanning electron microscopy coupled with energy dispersive x-ray spectroscopy. Themore » sealing of 0·25 mm wide and ~2 mm deep cracks was visualised with a three-dimensional optical microscope. Fer decomposed under high-temperature alkaline conditions with the release of hydrolysates that, along with the hydrating clinker, participated in the formation of new phases contributing to strength recoveries. Here, these phases included crystalline magnesium and aluminium-containing silicates, calcium and carbonated calcium silicates and amorphous hydrates. Crack sealing was complete for the silica-modified samples and partial for unmodified ones cured in carbonate environments. The sealing was very poor for samples cured in water. Lastly, the main sealing phases included crystalline and amorphous silica, high-temperature-stable zeolites and talc mineral.« less

Further damage induced by water in micro-indentations in phosphate laser glass

NASA Astrophysics Data System (ADS)

Yu, Jiaxin; Jian, Qingyun; Yuan, Weifeng; Gu, Bin; Ji, Fang; Huang, Wen

2014-02-01

Using a microhardness tester, artificial flaws were made by micro-indentation in N31 Nd-doped phosphate laser glass. Indentation fracture toughness, KIC, was estimated as 0.45-0.53 MPa m1/2 from these indentations. The glasses with indentations were then immersed in ultrapure water to investigate further water-induced damage of these indentations. Stress-enhanced hydrolysis leads to the propagations of radial crack, lateral cracks and microcracks in the subsurface. These crack propagations therefore cause deformation in subsurface to form annular reflections regions around the indentations and further material collapse within imprints. After the residual stresses are exhausted, the leaching plays a more dominated role in glass corrosion in the further immersion. After immersion, the material structure slackens around micro-indentation, which decreases the contact stiffness and results in a lower nano-hardness. For the surface far away from flaws, water immersion presents a weak effect on the near-surface mechanical since the matrix leaching in phosphate glass restricts the formation of hydration layer. During first 20 min immersion, due to higher chemical activity and lower fracture toughness, the radial cracks show a faster propagation in phosphate glass compared with that in K9 silicate glass. For further immersion, crack healing occurs in silicate glass but not in phosphate glass. Analysis shows that the formation of hydration layer on crack walls plays an important role in crack healing in glasses.

Self-repairing properties of OPC clinker/natural zeolite blend in water and alkali carbonate environments at 270°C

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

Pyatina, Tatiana; Sugama, Toshifumi; Ronne, Arthur

The 10 d recoveries of the mechanical properties and crack sealing of an ordinary Portland cement (OPC) clinker/natural zeolite (ferrierite (Fer)) blend modified or unmodified with silica were tested at 270°C in water and alkali carbonate environments. The recoveries of the samples depended on their modification with silica and the curing environment, but were more than 100% after repeated damage under some test conditions. The mechanical properties and phase compositions of recovered samples were evaluated by compressive strength measurements and x-ray diffraction, differential thermogravimetric analyses, Fourier transform infrared analyses and scanning electron microscopy coupled with energy dispersive x-ray spectroscopy. Themore » sealing of 0·25 mm wide and ~2 mm deep cracks was visualised with a three-dimensional optical microscope. Fer decomposed under high-temperature alkaline conditions with the release of hydrolysates that, along with the hydrating clinker, participated in the formation of new phases contributing to strength recoveries. Here, these phases included crystalline magnesium and aluminium-containing silicates, calcium and carbonated calcium silicates and amorphous hydrates. Crack sealing was complete for the silica-modified samples and partial for unmodified ones cured in carbonate environments. The sealing was very poor for samples cured in water. Lastly, the main sealing phases included crystalline and amorphous silica, high-temperature-stable zeolites and talc mineral.« less

Alteration layer formation of Ca- and Zn-oxide bearing alkali borosilicate glasses for immobilisation of UK high level waste: A vapour hydration study

NASA Astrophysics Data System (ADS)

Cassingham, N. J.; Corkhill, C. L.; Stennett, M. C.; Hand, R. J.; Hyatt, N. C.

2016-10-01

The UK high level nuclear waste glass modified with CaO/ZnO was investigated using the vapour phase hydration test, performed at 200 °C, with the aim of understanding the impact of the modification on the chemical composition and microstructure of the alteration layer. Experiments were undertaken on non-modified and CaO/ZnO-modified base glass, with or without 25 wt% of simulant Magnox waste calcine. The modification resulted in a dramatic reduction in gel layer thickness and also a reduction in the reaction rate, from 3.4 ± 0.3 g m-2 d-1 without CaO/ZnO modification to 0.9 ± 0.1 g m-2 d-1 with CaO/ZnO. The precipitated phase assemblage for the CaO/ZnO-modified compositions was identified as hydrated Ca- and Zn-bearing silicate phases, which were absent from the non-modified counterpart. These results are in agreement with other recent studies showing the beneficial effects of ZnO additions on glass durability.

Influence of nano-dispersive modified additive on cement activity

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

Sazonova, Natalya, E-mail: n.a.sazonova@mail.ru; Badenikov, Artem, E-mail: rector@agta.ru; Ivanova, Elizaveta, E-mail: lisik-iva@mail.ru

2016-01-15

In the work the influence of single-walled carbon nanotubes (SWCNT) on the cement activity and the processes of structure formation of the hardened cement paste in different periods of hydration are studied. The changes in the kinetic curves of the sample strength growth modified with SWCNT in amount of 0.01 and 0.0005 % are stipulated by the results of differential scanning colorimetry, scanning electronic and ionic microscopy, X-ray-phase analysis. It was found that the nano-modified additive may increase in the axis compressive strength of the system by 1.4–6.3 fold relatively to the reference samples and may reach 179.6 MPa. It maymore » intensify the hydration process of calcium silicates as well as influence on the matrix of hardened cement paste. The studies are conducted on the structural changes in the hardened cement paste, the time periods of increase and decrease of the compressive strength of the samples, the amount of the calcium hydroxide and tobermorite-like gel as well as the degree of hydration C{sub 3}S and β-C{sub 2}S.« less

Modeling cation/anion-water interactions in functional aluminosilicate structures.

PubMed

Richards, A J; Barnes, P; Collins, D R; Christodoulos, F; Clark, S M

1995-02-01

A need for the computer simulation of hydration/dehydration processes in functional aluminosilicate structures has been noted. Full and realistic simulations of these systems can be somewhat ambitious and require the aid of interactive computer graphics to identify key structural/chemical units, both in the devising of suitable water-ion simulation potentials and in the analysis of hydrogen-bonding schemes in the subsequent simulation studies. In this article, the former is demonstrated by the assembling of a range of essential water-ion potentials. These span the range of formal charges from +4e to -2e, and are evaluated in the context of three types of structure: a porous zeolite, calcium silicate cement, and layered clay. As an example of the latter, the computer graphics output from Monte Carlo computer simulation studies of hydration/dehydration in calcium-zeolite A is presented.

Effect of phase composition of calcium silicate phosphate component on properties of brushite based composite cements

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

Sopcak, T., E-mail: tsopcak@imr.saske.sk; Medvecky, L.; Giretova, M.

The composite cement mixtures were prepared by mixing brushite (B) with, the amorphous hydrated calcium silicate phosphate (CSPH) or annealed calcium silicate phosphate (CSP composed of Si-saturated hydroxyapatite, wollastonite and silica) phases and water as liquid component. The contents of the silicate-phosphate phase in composites were 10.30 and 50 wt%. The significant effect of both the Ca/P ratio and different solubility of calcium silicate phosphate component in starting cement systems on setting time and phase composition of the final composite cements was demonstrated. The compressive strength of the set cements increased with the filler addition and the highest value (~more » 48 MPa) exhibited the 50CSP/B cement composite. The final setting times of the composite cements decreased with the CSPH addition from about 25 to 17 min in 50CSHP/B and setting time of CSP/B composites was around 30 min. The higher content of silica in cements caused the precipitation of fine hydroxyapatite particles in the form of nanoneedles or thin plates perpendicularly oriented to sample surface. The analysis of in vitro cement cytotoxicity demonstrated the strong reduction in cytotoxicity of 10CSPH/B composite with time of cultivation (a low cytotoxicity after 9 days of culture) contrary to cements with higher calcium silicate-phosphate content. These results were attributed to the different surface topography of composite substrates and possible stimulation of cell proliferation by the slow continuously release of ions from 10CSPH/B cement. - Highlights: • Ca/P ratio and solubility of calcium silicate-phosphate components affect the self-setting properties of cements. • Strong relationship between the composite in vitro cytotoxicity and surface microtopography was demonstrated. • Plate-like morphology of coarser particles allowed cells to better adhere and proliferate as compared with nanoneedles.« less

Present and future of glass-ionomers and calcium-silicate cements as bioactive materials in dentistry: Biophotonics-based interfacial analyses in health and disease

PubMed Central

Watson, Timothy F.; Atmeh, Amre R.; Sajini, Shara; Cook, Richard J.; Festy, Frederic

2014-01-01

Objective Since their introduction, calcium silicate cements have primarily found use as endodontic sealers, due to long setting times. While similar in chemistry, recent variations such as constituent proportions, purities and manufacturing processes mandate a critical understanding of service behavior differences of the new coronal restorative material variants. Of particular relevance to minimally invasive philosophies is the potential for ion supply, from initial hydration to mature set in dental cements. They may be capable of supporting repair and remineralization of dentin left after decay and cavity preparation, following the concepts of ion exchange from glass ionomers. Methods This paper reviews the underlying chemistry and interactions of glass ionomer and calcium silicate cements, with dental tissues, concentrating on dentin–restoration interface reactions. We additionally demonstrate a new optical technique, based around high resolution deep tissue, two-photon fluorescence and lifetime imaging, which allows monitoring of undisturbed cement–dentin interface samples behavior over time. Results The local bioactivity of the calcium-silicate based materials has been shown to produce mineralization within the subjacent dentin substrate, extending deep within the tissues. This suggests that the local ion-rich alkaline environment may be more favorable to mineral repair and re-construction, compared with the acidic environs of comparable glass ionomer based materials. Significance The advantages of this potential re-mineralization phenomenon for minimally invasive management of carious dentin are self-evident. There is a clear need to improve the bioactivity of restorative dental materials and these calcium silicate cement systems offer exciting possibilities in realizing this goal. PMID:24113131

Near-infrared Spectroscopy Of Outer Main Belt Asteroids

NASA Astrophysics Data System (ADS)

Takir, Driss; Emery, J.

2009-09-01

We have recently begun a spectral survey of the outer Main Belt population (3.2 AU < a < 4.6 AU), using near-infrared spectroscopy (0.8-2.5 μm). The objective of this survey is to search for signatures of H2O, organics, hydrated silicates, and/or anhydrous silicates on this group of asteroids. Studying the outer Main Belt asteroids will allow us to better understand the dynamical evolution of the Solar System and provide crucial constrains on nebular composition. Our first observing run, using the SpeX spectrograph/imager at the NASA IRTF, took place remotely form the University of Tennessee Knoxville on the nights of April 15, 16, and 17, 2009 (UT). More observing runs will be conducted this year and the beginning of next year. The initial data reduction process reveals that some of these asteroids exhibit weak and strong absorption features. We will present some of these initial spectra and results.

Post-eruptive alteration of silicic ignimbrites and lavas, Gran Canaria, Canary Islands - Strontium, neodymium, lead, and oxygen isotopic evidence

NASA Technical Reports Server (NTRS)

Cousens, Brian L.; Spera, Frank J.; Dobson, Patrick F.

1993-01-01

The isotopic composition of lavas from oceanic islands provides important information about the composition and evolution of the earth's mantle. Isotopic analyses of Miocene comenditic, pantelleritic, and trachyphonolitic ignimbrites and lavas from the Canary islands were performed. Results provide evidence for posteruptive mobility of Rb and Sr during low temperature postemplacement interaction with circulating ground water. Calculated Sr isotope ratios define a magmatic trend in the stratigraph section. 87Sr/86Sr ratios in hydrated vitrophyte and devitrified matrix separates indicate significant posteruptive interaction with meteoric water starting soon after deposition. This process extends patchily through the entire pyroclastic flow and may be ongoing. 87Sr/86Sr ratios determined by whole rock analysis of silicic rocks from oceanic islands are suspect and should not be incorporated into mantle tracer studies. Anorthoclase phenocrysts are resistant to these processes and may produce useful data.

Preliminary Results from the Viking X-ray Fluorescence Experiment: The First Sample from Chryse Planitia, Mars.

PubMed

Toulmin, P; Clark, B C; Baird, A K; Keil, K; Rose, H J

1976-10-01

Iron, calcium, aluminum, silicon, and sulfur are major elements in the first surface sample of Mars that has been analyzed by the Viking x-ray fluorescence spectrometer. Titanium is present in minor quantities. This is consistent with the sample being a mixture of fine silicate and oxide mineral grains, with a significant proportion of sulfates, possibly hydrated. Ferric oxide is regarded as the red pigmenting agent on the martian surface, but if it coats silicate grains, the coatings must be very thin (

Preliminary results from the Viking X-ray fluorescence experiment - The first sample from Chryse Planitia, Mars

NASA Technical Reports Server (NTRS)

Toulmin, P., III; Rose, H. J., Jr.; Clark, B. C.; Baird, A. K.; Keil, K.

1976-01-01

Iron, calcium, aluminum, silicon, and sulfur are major elements in the first surface sample of Mars that has been analyzed by the Viking X-ray fluorescence spectrometer. Titanium is present in minor quantities. This is consistent with the sample's being a mixture of fine silicate and oxide mineral grains, with a significant proportion of sulfates, possibly hydrated. Ferric oxide is regarded as the red pigmenting agent on the Martian surface, but if it coats silicate grains, the coatings must be very thin or discontinuous. A high abundance of Fe, relatively low abundances of Al, Rb, Sr, and Zr, and a high Ca/K ratio are distinctive features of the spectra. Preliminary determinations indicate the following abundances (as percentages by weight): Fe, 14 plus or minus 2; Ti, less than 1; S, 2 to 5; the Ca/K ratio by weight is greater than 5.

Preliminary results from the viking x-ray fluorescence experiment: The first sample from chryse planitia, Mars

USGS Publications Warehouse

Toulmin, P.; Clark, B. C.; Baird, A.K.; Keil, Klaus; Rose, H.J.

1976-01-01

Iron, calcium, aluminum, silicon, and sulfur are major elements in the first surface sample of Mars that has been analyzed by the Viking x-ray fluorescence spectrometer. Titanium is present in minor quantities. This is consistent with the sample being a mixture of fine silicate and oxide mineral grains, with a significant proportion of sulfates, possibly hydrated. Ferric oxide is regarded as the red pigmenting agent on the martian surface, but if it coats silicate grains, the coatings must be very thin (??? 2 micrometers) or discontinuous. A high abundance of Fe, relatively low abundances of Al, Rb, Sr, and Zr, and a high Ca/K ratio are distinctive features of the spectra. Preliminary determinations indicate the following abundances (as percentages by weight): Fe, 14 ?? 2; Ti < 1; S, 2 to 5; the Ca/K ratio by weight is greater than 5.

Migration Processes and Volatiles Inventory to the Inner Planets

NASA Technical Reports Server (NTRS)

Marov, M. Y.; Ipatov, S. I.

2004-01-01

Comets and asteroids colliding with the terrestrial planets can deliver volatiles and organic or prebiotic compounds to the planets, thereby depositing on the planets the fundamental building-blocks for life. The inner planets contain heavier and cosmically less abundant elements in an iron-silicate matrix than the giant planets. This can be caused by the following three mechanisms: uneven fractionation and condensation in the accretionary disk; unequal degree of degassing of the composed matter; and heterogeneous accretion. Asteroid-size bodies consisting of the last low-temperature condensates (similar to most primitive chondritic meteorites, and enriched in hydrated silicates and trapped gases) are believed to have fallen onto the inner planets during the process of the giant planets formation. The relative contribution of either endogenous (i.e. outgassing) or exogenous (i.e. asteroid/comet collisions) sources is difficult to assess, although it is constrained by the pattern of noble gas abundances in the planetary atmospheres.

The Stability of Hydrous Silicates in Earth's Lower Mantle: Experimental constraints from the System MgO-Al2O3-SiO2-H2O

NASA Astrophysics Data System (ADS)

Walter, M. J.; Thomson, A. R.; Wang, W.; Lord, O. T.; Kleppe, A. K.; Ross, J.; Kohn, S. C.

2014-12-01

Laser-heated diamond anvil cell experiments were performed at pressures from ~ 30 to 125 GPa on bulk compositions in the system MgO-Al2O3-SiO2-H2O (MASH) to constrain the stability of hydrous phases in Earth's lower mantle. Phase identification in run products by synchrotron powder diffraction reveals a consistent set of stability relations for the high-pressure, dense hydrous silicate phases D and H. Experiments show that aluminous phase D is stable to ~ 55 GPa. Aluminous phase H becomes stable at ~ 40 GPa and remains stable to higher pressures throughout the lower mantle depth range in both model peridotitic and basaltic lithologies. Preliminary FEG-probe analyses indicate that Phase H is alumina-rich at ~ 50 GPa, with only 5 to 10 wt% each of MgO and SiO2. Variations in ambient unit cell volumes show that Mg-perovskite becomes more aluminous with pressure throughout the pressure range studied, and that Phase H may become more Mg- and Si-rich with pressure. We also find that at pressures above ~ 90 GPa stishovite is replaced in Si-rich compositions by seifertite, at which point there is a corresponding increase in the Al-content of phase H. The melting curves of MASH compositions have been determined using thermal perturbations in power versus temperature curves, and are observed to be shallow with dT/dP slopes of ~ 4K/GPa. Our results show that hydrated peridotitic or basaltic compositions in the lower mantle should be partially molten at all depths along an adiabatic mantle geotherm. Aluminous Phase H will be stable in colder, hydrated subducting slabs, potentially to the core-mantle boundary. Thus, aluminous phase H is the primary vessel for transport of hydrogen to the deepest mantle, but hydrous silicate melt will be the host of hydrogen at ambient mantle temperatures.

Geotechnical and mineralogical characterisations of marine-dredged sediments before and after stabilisation to optimise their use as a road material.

PubMed

Saussaye, L; van Veen, E; Rollinson, G; Boutouil, M; Andersen, J; Coggan, J

2017-12-01

Dredging activities to extend, deepen and maintain access to harbours generate significant volumes of waste dredged material. Some ways are investigated to add value to these sediments. One solution described here is their use in road construction following treatment with hydraulic binders. This paper presents the characterisation of four sediments, in their raw state and after 90 days of curing following stabilisation treatment with lime and cement, using a combination of novel and established analytical techniques to investigate subsequent changes in mineralogy. These sediments are classified as fine, moderately to highly organic and highly plastic and their behaviour is linked to the presence of smectite clays. The main minerals found in the sediments using X-ray diffraction (XRD) and automated mineralogy are quartz, calcite, feldspars, aluminium silicates, pyrite and halite. Stabilisation was found to improve the mechanical performances of all the sediments. The formation of cementitious hydrates was not specifically detected using automated mineralogy or XRD. However, a decrease in the percentage volume of aluminium silicates and aluminium-iron silicates and an increase of the percentage volume of feldspars and carbonates was observed.

Experimental Evaluation of Sodium Silicate-Based Nanosilica against Chloride Effects in Offshore Concrete

PubMed Central

Kim, Kyoung-Min; Kim, Hak-Young; Heo, Young-Sun; Jung, Sang-Jin

2014-01-01

This study investigates the effect of a new pore filling material, named sodium silicate-based nanosilica (SS), on resisting the diffusion of the chloride ions. The proposed SS is chosen, mainly due to its smaller particle size, compared to the conventional ethyl silicate-based nanosilica. Each particle of SS is chemically treated to have the negative (−) charge on its surface. Four types of mixes with different amounts of partial replacement with fly ash and slag are prepared. Effect of water to binder ratios (0.35, 0.40, and 0.45) is also examined. Test results showed that the inclusion of SS was significantly beneficial for protecting the concrete from chloride attack. At a given strength, the SS inclusion in concrete was up to three times more effective than the control concrete without SS. It is believed that these excellent results are attributed to the small particle size and the chemical surface treatment of SS. In this study, experiments of compressive strength, hydration heat, accelerated neutralization, and sulfate erosion tests were also conducted to find the general effect of SS inclusion on the fundamental properties and durability of concrete. PMID:25574486

Experimental evaluation of sodium silicate-based nanosilica against chloride effects in offshore concrete.

PubMed

Kim, Kyoung-Min; Kim, Hak-Young; Heo, Young-Sun; Jung, Sang-Jin

2014-01-01

This study investigates the effect of a new pore filling material, named sodium silicate-based nanosilica (SS), on resisting the diffusion of the chloride ions. The proposed SS is chosen, mainly due to its smaller particle size, compared to the conventional ethyl silicate-based nanosilica. Each particle of SS is chemically treated to have the negative (-) charge on its surface. Four types of mixes with different amounts of partial replacement with fly ash and slag are prepared. Effect of water to binder ratios (0.35, 0.40, and 0.45) is also examined. Test results showed that the inclusion of SS was significantly beneficial for protecting the concrete from chloride attack. At a given strength, the SS inclusion in concrete was up to three times more effective than the control concrete without SS. It is believed that these excellent results are attributed to the small particle size and the chemical surface treatment of SS. In this study, experiments of compressive strength, hydration heat, accelerated neutralization, and sulfate erosion tests were also conducted to find the general effect of SS inclusion on the fundamental properties and durability of concrete.

Quantum Mechanical Metric for Internal Cohesion in Cement Crystals

PubMed Central

Dharmawardhana, C. C.; Misra, A.; Ching, Wai-Yim

2014-01-01

Calcium silicate hydrate (CSH) is the main binding phase of Portland cement, the single most important structural material in use worldwide. Due to the complex structure and chemistry of CSH at various length scales, the focus has progressively turned towards its atomic level comprehension. We study electronic structure and bonding of a large subset of the known CSH minerals. Our results reveal a wide range of contributions from each type of bonding, especially hydrogen bonding, which should enable critical analysis of spectroscopic measurements and construction of realistic C-S-H models. We find the total bond order density (TBOD) as the ideal overall metric for assessing crystal cohesion of these complex materials and should replace conventional measures such as Ca:Si ratio. A rarely known orthorhombic phase Suolunite is found to have higher cohesion (TBOD) in comparison to Jennite and Tobermorite, which are considered the backbone of hydrated Portland cement. PMID:25476741

Peculiarities of the processes of hydration of binding substances in the arbolite mixture

NASA Astrophysics Data System (ADS)

Innokentieva, L. S.; Egorova, A. D.; Emelianova, Z. V.

2017-09-01

Cement and sand solution is traditionally used for production of wood concrete. But it is known that impact of water-soluble substances of wood on the hardening cement is shown in the stabilizing effect. The "Cement poisons" consisting generally of the HOCH carbohydrate groups, sedimented on a surface of particles of minerals of cement 3CaO.SiO2 (three-calcic silicate) and 3CaO.Al2O3 (three-calcic aluminate) form the thinnest covers which complicate the course of processes of hydration of cement. Plaster in comparison with cement is less sensitive to extractive substances of wood therefore their combination to wood (including waste of logging and a woodworking) both coniferous and deciduous species is allowed. Composite plaster binding with hongurin as active mineral additive agent are applied at selection of composition of arbolite, at the same time dependences of their physicomechanical properties on characteristics of filler are received.

Performance Characteristics of Waste Glass Powder Substituting Portland Cement in Mortar Mixtures

NASA Astrophysics Data System (ADS)

Kara, P.; Csetényi, L. J.; Borosnyói, A.

2016-04-01

In the present work, soda-lime glass cullet (flint, amber, green) and special glass cullet (soda-alkaline earth-silicate glass coming from low pressure mercury-discharge lamp cullet and incandescent light bulb borosilicate glass waste cullet) were ground into fine powders in a laboratory planetary ball mill for 30 minutes. CEM I 42.5N Portland cement was applied in mortar mixtures, substituted with waste glass powder at levels of 20% and 30%. Characterisation and testing of waste glass powders included fineness by laser diffraction particle size analysis, specific surface area by nitrogen adsorption technique, particle density by pycnometry and chemical analysis by X-ray fluorescence spectrophotometry. Compressive strength, early age shrinkage cracking and drying shrinkage tests, heat of hydration of mortars, temperature of hydration, X-ray diffraction analysis and volume stability tests were performed to observe the influence of waste glass powder substitution for Portland cement on physical and engineering properties of mortar mixtures.

Variations in Gas and Water Pulses at an Arctic Seep: Fluid Sources and Methane Transport

NASA Astrophysics Data System (ADS)

Hong, W.-L.; Torres, M. E.; Portnov, A.; Waage, M.; Haley, B.; Lepland, A.

2018-05-01

Methane fluxes into the oceans are largely dependent on the methane phase as it migrates upward through the sediments. Here we document decoupled methane transport by gaseous and aqueous phases in Storfjordrenna (offshore Svalbard) and propose a three-stage evolution model for active seepage in the region where gas hydrates are present in the shallow subsurface. In a preactive seepage stage, solute diffusion is the primary transport mechanism for methane in the dissolved phase. Fluids containing dissolved methane have high 87Sr/86Sr ratios due to silicate weathering in the microbial methanogenesis zone. During the active seepage stage, migration of gaseous methane results in near-seafloor gas hydrate formation and vigorous seafloor gas discharge with a thermogenic fingerprint. In the postactive seepage stage, the high concentration of dissolved lithium points to the contribution of a deeper-sourced aqueous fluid, which we postulate advects upward following cessation of gas discharge.

Hydration of Concrete: The First Steps.

PubMed

Thissen, Peter; Natzeck, Carsten; Giraudo, Nicolas; Weidler, Peter; Wöll, Christof

2018-04-12

Concrete is the most important construction material used by mankind and, at the same time, one of the most complex substances known in materials science. Since this mineral compound is highly porous, a better understanding of its surface chemistry, and in particular the reaction with water, is urgently required to understand and avoid corrosion of infrastructure like buildings and bridges. We have gained insight into proton transfer from concrete upon contact with water by applying the so-called Surface Science approach to a well-defined mineral, Wollastonite. Data from IR (infrared) spectroscopy reveal that exposure of this calcium-silicate (CS) substrate to H 2 O leads to dissociation and the formation of OH-species. This proton transfer is a chemical reaction of key importance, since on the one hand it triggers the conversion of cement into concrete (a calcium-silicate-hydrate phase), but on the other hand also governs the corrosion of concrete. Interestingly, we find that no proton transfer takes place when the same surface is exposed to methanol. In order to understand this unexpected difference, the analysis of the spectroscopic data obtained was aided by a detailed, first-principles computational study employing density functional theory (DFT). The combined experimental and theoretical effort allows derivation of a consistent picture of proton transfer reactions occurring in CS and CSH phases. Implications for strategies to protect this backbone of urban infrastructure from corrosion in harsh, aqueous environments will be discussed. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sulfate content of Europa's ocean and shell: evolutionary considerations and some geological and astrobiological implications.

PubMed

McKinnon, William B; Zolensky, Michael E

2003-01-01

Recent models for the origin of Jupiter indicate that the Galilean satellites were mostly derived from largely unprocessed solar nebula solids and planetesimals. In the jovian subnebula the solids that built Europa were first heated and then cooled, but the major effect was most likely partial or total devolatilization, and less likely to have been wholesale thermochemical reprocessing of rock + metal compositions (e.g., oxidation of Fe and hydration of silicates). Ocean formation and substantial alteration of interior rock by accreted water and ice would occur during and after accretion, but none of the formation models predicts or implies accretion of sulfates. Europa's primordial ocean was most likely sulfidic. After accretion and later radiogenic and tidal heating, the primordial ocean would have interacted hydrothermally with subjacent rock. It has been hypothesized that sulfides could be converted to sulfates if sufficient hydrogen was lost to space, but pressure effects and the impermeability of serpentinite imply that extraction of sulfate from thoroughly altered Europa-rock would have been inefficient (if indeed Mg sulfates formed at all). Permissive physical limits on the extent of alteration limit the sulfate concentration of Europa's evolved ocean to 10% by weight MgSO(4) or equivalent. Later oxidation of the deep interior of Europa may have also occurred because of water released by the breakdown of hydrated silicates, ultimately yielding S magma and/or SO(2) gas. Geological and astrobiological implications are considered.

Heavily-hydrated lithic clasts in CH chondrites and the related, metal-rich chondrites Queen Alexandra Range 94411 and Hammadah al Hamra 237

NASA Astrophysics Data System (ADS)

Greshake, A.; Krot, A. N.; Meibom, A.; Weisberg, M. K.; Zolensky, M. E.; Keil, K.

2002-02-01

Fine-grained, heavily-hydrated lithic clasts in the metal-rich (CB) chondrites Queen Alexandra Range (QUE) 94411 and Hammadah al Hamra 237 and CH chondrites, such as Patuxent Range (PAT) 91546 and Allan Hills (ALH) 85085, are mineralogically similar suggesting genetic relationship between these meteorites. These clasts contain no anhydrous silicates and consist of framboidal and platelet magnetite, prismatic sulfides (pentlandite and pyrrhotite), and Fe-Mn-Mg-bearing Ca-carbonates set in a phyllosilicate-rich matrix. Two types of phyllosilicates were identified: serpentine, with basal spacing of ?0.73 nm, and saponite, with basal spacings of about 1.1-1.2 nm. Chondrules and FeNi-metal grains in CB and CH chondrites are believed to have formed at high temperature (>1300 K) by condensation in a solar nebula region that experienced complete vaporization. The absence of aqueous alteration of chondrules and metal grains in CB and CH chondrites indicates that the clasts experienced hydration in an asteroidal setting prior to incorporation into the CH and CB parent bodies. The hydrated clasts were either incorporated during regolith gardening or accreted together with chondrules and FeNi-metal grains after these high-temperature components had been transported from their hot formation region to a much colder region of the solar nebula.

An Investigation of the 3-μm Feature in M-Type Asteroids

NASA Astrophysics Data System (ADS)

Landsman, Zoe A.; Campins, H.; Hargrove, K.; Pinilla-Alonso, N.; Emery, J.; Ziffer, J.

2013-10-01

The M-type asteroids had originally been interpreted as the disrupted iron cores of differentiated bodies by spectral analogy with the NiFe meteorites. More detailed studies have since indicated a range of compositions. In particular, the presence of a 3-µm feature, diagnostic of hydration, detected in more than 35% of surveyed M-type asteroids (Jones et al. 1990, Rivkin et al. 1995, 2000) has challenged the notion that these bodies are all metallic. Spectroscopy in the 0.8 - 2.5 µm region has revealed absorption features due to mafic silicates and hydroxides or phyllosilicates (Fornasier et al. 2010, Hardersen et al. 2006, 2010, Ockert-Bell et al. 2010). Radar studies have shown that most M-types are not likely to be iron cores, but they typically have a higher metal content than average (Shepard et al. 2010). Taken together, these results paint a fairly confounding picture of the M-type asteroids. While several interpretations have been suggested, more work is needed to clarify the mineralogy of these bodies. We have started a new spectroscopic study of the M asteroids in the 2 - 4 µm region. We seek to characterize the shape, band center, and band depth of the 3-µm feature where it is present, as these measures are indicative of the type and extent of hydration present on asteroids (Lebofsky et al. 1985, Rivkin et al. 2002, Takir & Emery 2012, Volguardsen et al. 2007). With this work, we hope to shed new light on the origin of hydration on M asteroids and its context within their mineralogy and thermal evolution. In July 2013, we obtained 2 - 4 µm spectra for 69 Hesperia, 136 Austria, and 261 Prymno with the SpeX at NASA’s IRTF, and are in the process of reducing the data. We have also obtained 0.8 - 2.0 µm data for 261 Prymno using the NICS at the TNG in February 2013. We report the presence of an absorption feature near 0.9 µm in Prymno’s spectrum, indicating a partially silicate composition. Based on spectral, physical and orbital similarities to other hydrated M-types, we predict the presence of a 3-μm feature in Prymno’s 2 - 4 μm. More 2 - 4 μm observations of M-type asteroids are planned.

Present and future of glass-ionomers and calcium-silicate cements as bioactive materials in dentistry: biophotonics-based interfacial analyses in health and disease.

PubMed

Watson, Timothy F; Atmeh, Amre R; Sajini, Shara; Cook, Richard J; Festy, Frederic

2014-01-01

Since their introduction, calcium silicate cements have primarily found use as endodontic sealers, due to long setting times. While similar in chemistry, recent variations such as constituent proportions, purities and manufacturing processes mandate a critical understanding of service behavior differences of the new coronal restorative material variants. Of particular relevance to minimally invasive philosophies is the potential for ion supply, from initial hydration to mature set in dental cements. They may be capable of supporting repair and remineralization of dentin left after decay and cavity preparation, following the concepts of ion exchange from glass ionomers. This paper reviews the underlying chemistry and interactions of glass ionomer and calcium silicate cements, with dental tissues, concentrating on dentin-restoration interface reactions. We additionally demonstrate a new optical technique, based around high resolution deep tissue, two-photon fluorescence and lifetime imaging, which allows monitoring of undisturbed cement-dentin interface samples behavior over time. The local bioactivity of the calcium-silicate based materials has been shown to produce mineralization within the subjacent dentin substrate, extending deep within the tissues. This suggests that the local ion-rich alkaline environment may be more favorable to mineral repair and re-construction, compared with the acidic environs of comparable glass ionomer based materials. The advantages of this potential re-mineralization phenomenon for minimally invasive management of carious dentin are self-evident. There is a clear need to improve the bioactivity of restorative dental materials and these calcium silicate cement systems offer exciting possibilities in realizing this goal. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Fractionation products of basaltic komatiite magmas at lower crustal pressures: implications for genesis of silicic magmas in the Archean

NASA Astrophysics Data System (ADS)

Mandler, B. E.; Grove, T. L.

2015-12-01

Hypotheses for the origin of crustal silicic magmas include both partial melting of basalts and fractional crystallization of mantle-derived melts[1]. Both are recognized as important processes in modern environments. When it comes to Archean rocks, however, partial melting hypotheses dominate the literature. Tonalite-trondhjemite-granodiorite (TTG)-type silicic magmas, ubiquitous in the Archean, are widely thought to be produced by partial melting of subducted, delaminated or otherwise deeply buried hydrated basalts[2]. The potential for a fractional crystallization origin for TTG-type magmas remains largely unexplored. To rectify this asymmetry in approaches to modern vs. ancient rocks, we have performed experiments at high pressures and temperatures to closely simulate fractional crystallization of a basaltic komatiite magma in the lowermost crust. These represent the first experimental determinations of the fractionation products of komatiite-type magmas at elevated pressures. The aim is to test the possibility of a genetic link between basaltic komatiites and TTGs, which are both magmas found predominantly in Archean terranes and less so in modern environments. We will present the 12-kbar fractionation paths of both Al-depleted and Al-undepleted basaltic komatiite magmas, and discuss their implications for the relative importance of magmatic fractionation vs. partial melting in producing more evolved, silicic magmas in the Archean. [1] Annen et al., J. Petrol., 47, 505-539, 2006. [2] Moyen J-F. & Martin H., Lithos, 148, 312-336, 2012.

Tailoring the strength and porosity of rapid-hardening magnesia phosphate paste via the pre-foaming method

PubMed Central

Liu, Li-Jie; Li, Jin-Hong; Wang, Xiang; Qian, Ting-Ting; Li, Xiao-Hui

2015-01-01

High-porosity magnesia phosphate paste (HPMPP) was prepared via the pre-foaming method. In the pre-foaming method, sintering treatment was not required. The bulk density and maximum compressive strength of the HPMPP prepared according to the ratio of water to solids (W/So) of 0.32 reached 464.00 ± 5.00 Kg/m3 and 0.30 ± 0.05 MPa, respectively. The compressive strength increased with the increases in the addition amounts of sodium silicate and polypropylene fibers. The bulk density of HPMPP increased with the increase in the addition of sodium silicate and decreased with the increase in the addition of polypropylene fibers. Besides, the porosity of the magnesia phosphate paste increased from 79.85% to 81.27% and from 80.31% to 83.75% after the addition of sodium silicate and polypropylene fibers respectively. The highest porosity (83.75%) of the prepared HPMPP was realized under the addition proportion (sodium silicate: polypropylene fibers: solids = 0.06:0.0025:1). The average pore size of the prepared HPMPP is about 180 μm and the pore distribution range is relatively narrow. The hydration product (struvite) is combined with MgO particle one by one and then coated on the surface of bubbles. With the decrease of the water content, after breaking bubbles, the porous structure can be achieved. PMID:26268675

Detection of hydrated silicates in crustal outcrops in the northern plains of Mars.

PubMed

Carter, J; Poulet, F; Bibring, J-P; Murchie, S

2010-06-25

The composition of the ancient martian crust is a key ingredient in deciphering the environment and evolution of early Mars. We present an analysis of the composition of large craters in the martian northern plains based on data from spaceborne imaging spectrometers. Nine of the craters have excavated assemblages of phyllosilicates from ancient, Noachian crust buried beneath the plains' cover. The phyllosilicates are indistinguishable from those exposed in widespread locations in the southern highlands, demonstrating that liquid water once altered both hemispheres of Mars.

Dust in the Solar System - Properties and Origins

NASA Technical Reports Server (NTRS)

Messenger, Scott; Keller, Lindsay; Nakamura-Messenger, Keiko

2013-01-01

Interplanetary dust pervades the inner Solar System, giving rise to a prominent glow above the horizon at sunrise and sunset known as the zodiacal light. This dust derives from the disintegration of comets as they approach the Sun and from collisions among main-belt asteroids. The Earth accretes roughly 4x10(exp 6) kg/year of 1 - 1,000 micron dust particles as they spiral into the Sun under the influence of Poynting-Robertson drag and solar wind drag. Samples of these grains have been collected from deep sea sediments, Antarctic ice and by high-altitude aircraft and balloon flights. Interplanetary dust particles (IDPs) collected in the stratosphere have been classified by their IR spectra into olivine, pyroxene, and hydrated silicate-dominated classes. Most IDPs have bulk major and minor element abundances that are similar to carbonaceous chondrite meteorites. Hydrated silicate-rich IDPs are thought to derive from asteroids based on their mineralogy and low atmospheric entry velocities estimated from peak temperatures reached during atmospheric entry. Anhydrous IDPs are typically aggregates of 0.1 - approx. 1 micron Mg-rich olivine and pyroxene, amorphous silicates (GEMS), Fe, Nisulfides and rare spinel and oxides bound together by carbonaceous material. These IDPs are often argued to derive from comets based on compositional similarities and high atmospheric entry velocities that imply high eccentricity orbits. Infrared spectra obtained from anhydrous IDPs closely match remote IR spectra obtained from comets. The most primitive (anhydrous) IDPs appear to have escaped the parent-body thermal and aqueous alteration that has affected meteorites. These samples thus consist entirely of grains that formed in the ancient solar nebula and pre-solar interstellar and circumstellar environments. Isotopic studies of IDPs have identified silicate stardust grains that formed in the outflows of red giant and asymptotic giant branch stars and supernovae]. These stardust grains include both amorphous and crystalline silicates. The organic matter in these samples also exhibits highly anomalous H, C, and N isotopic compositions that are consistent with formation in low temperature environments at the outermost regions of the solar nebula or presolar cold molecular cloud. The scientific frontiers for these samples include working toward a better understanding of the origins of the solar system amorphous and crystalline grains in IDPs and the very challenging task of determining the chemical composition of sub-micron organic grains. Laboratory studies of ancient and present-day dust in the Solar System thus reveal in exquisite detail the chemistry, mineralogy and isotopic properties of materials that derive from a range of astrophysical environments. These studies are an important complement to astronomical observations that help to place the laboratory observations into broader context.

Modelling the leaching of Pb, Cd, As, and Cr from cementitious waste using PHREEQC.

PubMed

Halim, Cheryl E; Short, Stephen A; Scott, Jason A; Amal, Rose; Low, Gary

2005-10-17

A leaching model was developed using the United States Geological Survey public domain PHREEQC geochemical package to simulate the leaching of Pb, Cd, As, and Cr from cementitious wastes. The model utilises both kinetic terms and equilibrium thermodynamics of key compounds and provides information on leachate and precipitate speciation. The model was able to predict the leaching of Pb, Cd, As, and Cr from cement in the presence of both simple (0.1 and 0.6M acetic acid) and complex municipal landfill leachates. Heavy metal complexation by the municipal landfill leachate was accounted for by the introduction of a monoprotic organic species into the model. The model indicated Pb and As were predominantly incorporated within the calcium silicate hydrate matrix while a greater portion of Cd was seen to exist as discrete particles in the cement pores and Cr (VI) existed mostly as free CrO4(2-) ions. Precipitation was found to be the dominant mechanism controlling heavy metal solubility with carbonate and silicate species governing the solubility of Pb and carbonate, silicate and hydroxide species governing the solubility of Cd. In the presence of acetic acid, at low pH values Pb and Cd acetate complexes were predominant whereas, at high pH values, hydroxide species dominated. At high pH values, the concentration of As in the leachate was governed by the solubility of Ca3(AsO4)2 with the presence of carbonate alkalinity competing with arsenate for Ca ions. In the presence of municipal landfill leachate, Pb and Cd organic complexes dominated the heavy metal species in solution. The reduction of As and Cr in municipal landfill leachate was crucial for determining aqueous speciation, with typical municipal landfill conditions providing the reduced forms of As and Cr.

Evaluation of novel reactive MgO activated slag binder for the immobilisation of lead and zinc.

PubMed

Jin, Fei; Al-Tabbaa, Abir

2014-12-01

Although Portland cement is the most widely used binder in the stabilisation/solidification (S/S) processes, slag-based binders have gained significant attention recently due to their economic and environmental merits. In the present study, a novel binder, reactive MgO activated slag, is compared with hydrated lime activated slag in the immobilisation of lead and zinc. A series of lead or zinc-doped pastes and mortars were prepared with metal to binder ratio from 0.25% to 1%. The hydration products and microstructure were studied by X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The major hydration products were calcium silicate hydrate and hydrotalcite-like phases. The unconfined compressive strength was measured up to 160 d. Findings show that lead had a slight influence on the strength of MgO-slag paste while zinc reduced the strength significantly as its concentration increased. Leachate results using the TCLP tests revealed that the immobilisation degree was dependent on the pH and reactive MgO activated slag showed an increased pH buffering capacity, and thus improved the immobilisation efficiency compared to lime activated slag. It was proposed that zinc was mainly immobilised within the structure of the hydrotalcite-like phases or in the form of calcium zincate, while lead was primarily precipitated as the hydroxide. It is concluded, therefore, that reactive MgO activated slag can serve as clinker-free alternative binder in the S/S process. Copyright © 2014 Elsevier Ltd. All rights reserved.

Co-treatment of flotation waste, neutralization sludge, and arsenic-containing gypsum sludge from copper smelting: solidification/stabilization of arsenic and heavy metals with minimal cement clinker.

PubMed

Liu, De-Gang; Min, Xiao-Bo; Ke, Yong; Chai, Li-Yuan; Liang, Yan-Jie; Li, Yuan-Cheng; Yao, Li-Wei; Wang, Zhong-Bing

2018-03-01

Flotation waste of copper slag (FWCS), neutralization sludge (NS), and arsenic-containing gypsum sludge (GS), both of which are difficult to dispose of, are major solid wastes produced by the copper smelting. This study focused on the co-treatment of FWCS, NS, and GS for solidification/stabilization of arsenic and heavy metals with minimal cement clinker. Firstly, the preparation parameters of binder composed of FWCS, NS, and cement clinker were optimized to be FWCS dosage of 40%, NS dosage of 10%, cement clinker dosage of 50%, mill time of 1.5 h, and water-to-binder ratio of 0.25. On these conditions, the unconfined compressive strength (UCS) of the binder reached 43.24 MPa after hydration of 28 days. Then, the binder was used to solidify/stabilize the As-containing GS. When the mass ratio of binder-to-GS was 5:5, the UCS of matrix can reach 11.06 MPa after hydration of 28 days, meeting the required UCS level of MU10 brick in China. Moreover, arsenic and other heavy metals in FWCS, NS, and GS were effectively solidified or stabilized. The heavy metal concentrations in leachate were much lower than those in the limits of China standard leaching test (CSLT). Therefore, the matrices were potential to be used as bricks in some constructions. XRD analysis shows that the main hydration products of the matrix were portlandite and calcium silicate hydrate. These hydration products may play a significant role in the stabilization/solidification of arsenic and heavy metals.

Sulfide mineralization: Its role in chemical weathering of Mars

NASA Technical Reports Server (NTRS)

Burns, Roger G.

1988-01-01

Pyrrhotite-pentlandite assemblages in mafic and ultramafic igneous rocks may have contributed significantly to the chemical weathering reactions that produced degradation products in the Martian regolith. By analogy with terrestrial processes, a model is proposed whereby supergene alteration of these primary Fe-Ni sulfides on Mars has generated secondary sulfides (e.g., pyrite) below the water table and produced acidic groundwater containing high concentrations of dissolved Fe, Ni and sulfate ions. The low pH solutions also initiated weathering reactions of igneous feldspars and ferromagnesian silicates to form clay silicate and ferric oxyhydroxide phases. Near-surface oxidation and hydrolysis of ferric sulfato- and hydroxo-complex ions and sols formed gossans above the water table consisting of poorly crystalline hydrated ferric sulfates (e.g., jarosite), oxides (ferrihydrite, goethite) and silica (opal). Underlying groundwater, now permafrost, contains hydroxo sulfato complexes of Fe, Al, Mg, Ni, etc., which may be stabilized in frozen acidic solutions beneath the surface of Mars. Sublimation of permafrost may replenish colloidal ferric oxides, sulfates and phyllosilicates during dust storms on Mars.

Weathering of sulfides on Mars

NASA Technical Reports Server (NTRS)

Burns, Roger G.; Fisher, Duncan S.

1987-01-01

Pyrrhotite-pentlandite assemblages in mafic and ultramafic igneous rocks may have contributed significantly to the chemical weathering reactions that produce degradation products in the Martian regolith. By analogy and terrestrial processes, a model is proposed whereby supergene alteration of these primary Fe-Ni sulfides on Mars has generated secondary sulfides (e.g., pyrite) below the water table and produced acidic groundwater containing high concentrations of dissolved Fe, Ni, and sulfate ions. The low pH solutions also initiated weathering reactions of igneous feldspars and ferromagnesian silicates to form clay silicate and ferric oxyhydroxide phases. Near-surface oxidation and hydrolysis of ferric sulfato-and hydroxo-complex ions and sols formed gossan above the water table consisting of poorly crystalline hydrated ferric sulfates (e.g., jarosite), oxides (ferrihydrite, goethite), and silica (opal). Underlying groundwater, now permafrost contains hydroxo sulfato complexes of Fe, Al, Mg, Ni, which may be stabilized in frozen acidic solutions beneath the surface of Mars. Sublimation of permafrost may replenish colloidal ferric oxides, sulfates, and phyllosilicates during dust storms on Mars.

Thermal emission spectra of Mars (5.4-10.5 microns) - Evidence for sulfates, carbonates, and hydrates

NASA Technical Reports Server (NTRS)

Pollack, James B.; Roush, Ted; Witteborn, Fred; Bregman, Jesse; Wooden, Diane; Stoker, Carol; Toon, Owen B.

1990-01-01

Spectra of the Martian thermal emission in the 5.4-10.5 micron region are reported. Emission features at 7.8 and 9.7 microns are attributed to surface silicates, and an emission feature at 6.1 micron is attributed to a molecular water component of the surface material. An absorption band at 8.7 micron and a possible one at 9.8 microns is attributed to sulfate or bisulfate anions probably located at a distorted crystalline site, and an absorption band at 6.7 microns is attributed to carbonate or bicarbonate anions located in a distorted crystalline site. Spectral simulations indicate that the sulfate- and carbonate-bearing minerals are contained in the same particles of airborne dust as the dominant silicate minerals, that the dust optical depth is about 0.6 at a reference wavelength of 0.3 micron over the area of the observed spots, and that sulfates and carbonates constitute 10-15 percent and 1-3 percent by volume of the airborne dust, respectively.

Hydration-dependent dynamics of water in calcium-silicate-hydrate: A QENS study by global model.

PubMed

Le, Peisi; Fratini, Emiliano; Chen, Sow-Hsin

2018-02-02

In a saturated cement paste, there are three different types of water: the structural water chemically reacted with cement, the constrained water absorbed to the surface of the pores, and the free water in the center of the pores. Each type has different physicochemical state and unique relation to cement porosity. The different water types have different dynamics which can be detected using quasi-elastic neutron scattering (QENS). Since the porosity of a hardened cement paste is impacted strongly by the water to cement ratio (w/c), it should be possible to extract the hydration dependence of the pores by exploiting the dynamical parameters of the confined water. Three C-S-H samples with different water levels, 8%, 17% and 30% were measured using QENS. The measurements were carried out in the scattering vector, Q, range from 0.5 Å -1 to 1.3 Å -1 , and in the temperature interval from 230 K to 280 K. The data were analyzed using a novel global model developed for cement QENS spectra. The results show that while increasing the water content, the structural water index (SWI) decreases and the confining radius, a, increases. Both SWI and a have a linear relationship with the water content. The Arrhenius plot of the translational relaxation time shows that the constrained water dominates the non-structural water at water contents lower than 17%. The rotational activation energy is smaller for lower water content. The analysis demonstrated that our newly proposed global model is practical and useful for analyzing cement QENS data. Copyright © 2018 Elsevier B.V. All rights reserved.

Bioactive Glass-Ceramic Foam Scaffolds from ‘Inorganic Gel Casting’ and Sinter-Crystallization

PubMed Central

Molino, Giulia; Vitale Brovarone, Chiara

2018-01-01

Highly porous bioactive glass-ceramic scaffolds were effectively fabricated by an inorganic gel casting technique, based on alkali activation and gelification, followed by viscous flow sintering. Glass powders, already known to yield a bioactive sintered glass-ceramic (CEL2) were dispersed in an alkaline solution, with partial dissolution of glass powders. The obtained glass suspensions underwent progressive hardening, by curing at low temperature (40 °C), owing to the formation of a C–S–H (calcium silicate hydrate) gel. As successful direct foaming was achieved by vigorous mechanical stirring of gelified suspensions, comprising also a surfactant. The developed cellular structures were later heat-treated at 900–1000 °C, to form CEL2 glass-ceramic foams, featuring an abundant total porosity (from 60% to 80%) and well-interconnected macro- and micro-sized cells. The developed foams possessed a compressive strength from 2.5 to 5 MPa, which is in the range of human trabecular bone strength. Therefore, CEL2 glass-ceramics can be proposed for bone substitutions. PMID:29495498

Self-cementitious properties of fly ashes from CFBC boilers co-firing coal and high-sulphur petroleum coke

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

Sheng Guanghong; Li Qin; Zhai Jianping

2007-06-15

Self-cementitious properties of fly ash from circulating fluidized bed combustion boiler co-firing coal and high-sulphur petroleum coke (CPFA) were investigated. CPFA was self-cementitious which was affected by its fineness and chemical compositions, especially the contents of SO{sub 3} and free lime (f-CaO). Higher contents of SO{sub 3} and f-CaO were beneficial to self-cementitious strength; the self-cementitious strength increases with a decrease of its 45 {mu}m sieve residue. The expansive ratio of CPFA hardened paste was high because of generation of ettringite (AFt), which was influenced by its water to binder ratio (W/A), curing style and grinding of the ash. Themore » paste cured in water had the highest expansive ratio, and grinding of CPFA was beneficial to its volume stability. The hydration products of CPFA detected by X-ray diffraction (XRD) and scanning electron microscopy (SEM) were portlandite, gypsum, AFt and hydrated calcium silicate (C-S-H)« less

Microstructure of ultra high performance concrete containing lithium slag.

PubMed

He, Zhi-Hai; Du, Shi-Gui; Chen, Deng

2018-04-03

Lithium slag (LS) is discharged as a byproduct in the process of the lithium carbonate, and it is very urgent to explore an efficient way to recycle LS in order to protect the environments and save resources. Many available supplementary cementitious materials for partial replacement of cement and/or silica fume (SF) can be used to prepare ultra high performance concrete (UHPC). The effect of LS to replace SF partially by weight used as a supplementary cementitious material (0%, 5%, 10% and 15% of binder) on the compressive strengths and microstructure evolution of UHPC has experimentally been studied by multi-techniques including mercury intrusion porosimetry, scanning electron microscope and nanoindentation technique. The results show that the use of LS degrades the microstructure of UHPC at early ages, and however, the use of LS with the appropriate content improves microstructure of UHPC at later ages. The hydration products of UHPC are mainly dominated by ultra-high density calcium-silicate-hydrate (UHD C-S-H) and interfacial transition zone (ITZ) in UHPC has similar compact microstructure with the matrix. The use of LS improves the hydration degree of UHPC and increases the elastic modulus of ITZ in UHPC. LS is a promising substitute for SF for preparation UHPC. Copyright © 2018 Elsevier B.V. All rights reserved.

SEM Analysis of the Interfacial Transition Zone between Cement-Glass Powder Paste and Aggregate of Mortar under Microwave Curing

PubMed Central

Kong, Yaning; Wang, Peiming; Liu, Shuhua; Zhao, Guorong; Peng, Yu

2016-01-01

In order to investigate the effects of microwave curing on the microstructure of the interfacial transition zone of mortar prepared with a composite binder containing glass powder and to explain the mechanism of microwave curing on the improvement of compressive strength, in this study, the compressive strength of mortar under microwave curing was compared against mortar cured using (a) normal curing at 20 ± 1 °C with relative humidity (RH) > 90%; (b) steam curing at 40 °C for 10 h; and (c) steam curing at 80 °C for 4 h. The microstructure of the interfacial transition zone of mortar under the four curing regimes was analyzed by Scanning electron microscopy (SEM). The results showed that the improvement of the compressive strength of mortar under microwave curing can be attributed to the amelioration of the microstructure of the interfacial transition zone. The hydration degree of cement is accelerated by the thermal effect of microwave curing and Na+ partially dissolved from the fine glass powder to form more reticular calcium silicate hydrate, which connects the aggregate, calcium hydroxide, and non-hydrated cement and glass powder into a denser integral structure. In addition, a more stable triangular structure of calcium hydroxide contributes to the improvement of compressive strength. PMID:28773854

SEM Analysis of the Interfacial Transition Zone between Cement-Glass Powder Paste and Aggregate of Mortar under Microwave Curing.

PubMed

Kong, Yaning; Wang, Peiming; Liu, Shuhua; Zhao, Guorong; Peng, Yu

2016-08-27

In order to investigate the effects of microwave curing on the microstructure of the interfacial transition zone of mortar prepared with a composite binder containing glass powder and to explain the mechanism of microwave curing on the improvement of compressive strength, in this study, the compressive strength of mortar under microwave curing was compared against mortar cured using (a) normal curing at 20 ± 1 °C with relative humidity (RH) > 90%; (b) steam curing at 40 °C for 10 h; and (c) steam curing at 80 °C for 4 h. The microstructure of the interfacial transition zone of mortar under the four curing regimes was analyzed by Scanning electron microscopy (SEM). The results showed that the improvement of the compressive strength of mortar under microwave curing can be attributed to the amelioration of the microstructure of the interfacial transition zone. The hydration degree of cement is accelerated by the thermal effect of microwave curing and Na⁺ partially dissolved from the fine glass powder to form more reticular calcium silicate hydrate, which connects the aggregate, calcium hydroxide, and non-hydrated cement and glass powder into a denser integral structure. In addition, a more stable triangular structure of calcium hydroxide contributes to the improvement of compressive strength.

Nano-scale hydrogen-bond network improves the durability of greener cements

PubMed Central

Jacobsen, Johan; Rodrigues, Michelle Santos; Telling, Mark T. F.; Beraldo, Antonio Ludovico; Santos, Sérgio Francisco; Aldridge, Laurence P.; Bordallo, Heloisa N.

2013-01-01

More than ever before, the world's increasing need for new infrastructure demands the construction of efficient, sustainable and durable buildings, requiring minimal climate-changing gas-generation in their production. Maintenance-free “greener” building materials made from blended cements have advantages over ordinary Portland cements, as they are cheaper, generate less carbon dioxide and are more durable. The key for the improved performance of blends (which substitute fine amorphous silicates for cement) is related to their resistance to water penetration. The mechanism of this water resistance is of great environmental and economical impact but is not yet understood due to the complexity of the cement's hydration reactions. Using neutron spectroscopy, we studied a blend where cement was replaced by ash from sugar cane residuals originating from agricultural waste. Our findings demonstrate that the development of a distinctive hydrogen bond network at the nano-scale is the key to the performance of these greener materials. PMID:24036676

Behavior of Colorado Plateau uranium minerals during oxidation

USGS Publications Warehouse

Garrels, Robert Minard; Christ, C.L.

1956-01-01

Uranium occurs as U(VI) and U(IV) in minerals of the Colorado Plateau ores. The number of species containing U(VI) is large, but only two U(IV) minerals are known from the Plateau: uraninite, and oxide, and coffinite, a hydroxy-silicate. These oxidize to yield U(VI) before reacting significantly with other mineral constituents. Crystal-structure analysis has shown that U(VI) invariable occurs as uranyl ion, UO2+2. Uranyl ion may form complex carbonate or sulfate ions with resulting soluble compounds, but only in the absence of quinquevalent vanadium, arsenic, or phosphorous. In the presence of these elements in the +5 valence state, the uranyl ion is fixed in insoluble layer compounds formed by union of uranyl ion with orthovanadate, orthophosphate, or orthoarsenate. Under favorable conditions UO2+2 may react to form the relatively insoluble rutherfordine, UO2CO3, or hydrated uranyl hydroxides. These are rarely found on the Colorado Plateau as opposed to their excellent development in other uraniferous areas, a condition which is apparently related to the semiarid climate and low water table of the Plateau. Uranium may also be fixed as uranyl silicate, but little is known about minerals of this kind. In the present study emphasis has been placed on a detailing of the chemical and crystal structural changes which occur in the oxidation paragenetic sequence.

Effect of pulverized fuel ash and CO{sub 2} curing on the water resistance of magnesium oxychloride cement (MOC)

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

He, Pingping; Poon, Chi Sun, E-mail: cecspoon@polyu.edu.hk; Tsang, Daniel C.W.

This paper presents a study on the use of pulverized fuel ash (PFA) to improve the water resistance of magnesium oxychloride cement (MOC). Strength retention coefficients and volume stability were tested to evaluate the water resistance of MOC, in which the addition of PFA resulted in a remarkable improvement. The characterization of hydration products before and after water immersion was carried out using quantitative X-ray diffraction (QXRD), thermogravimetric (TG), Fourier-transformed infrared spectroscopy (FTIR) and scanning electron microscope (SEM). With the Q-XRD analysis, it was shown that the addition of PFA could result in the great increase of the amount ofmore » amorphous phase during air curing. This amorphous gel was identified as a mixture of magnesium-chloride-silicate-hydrate gel (M-Cl-S-H gel) and magnesium-chloride-hydrate gel (M-Cl-H gel) by elemental mapping scanning. It suggested that PFA could not only react with MOC to form M-Cl-S-H gel, but also change the morphology of magnesium oxychloride. The generation of insoluble M-Cl-S-H gel and M-Cl-H gel and densification of the microstructure contributed to the improvement of the water resistance of MOC. The MOC mortar expanded during air curing due to the hydration of excess MgO. Water immersion led to more expansion of MOC mortar as a result of the continuously hydration of excess MgO and the formation of Mg(OH){sub 2}. Adding PFA could increase the expansion of MOC mortar during air curing, which may because the amorphous gel could remain more water and benefit to the hydration of MgO. While, the addition of PFA could decrease the expansion of cement mortar during water immersion perhaps due to the reduction of the content of excess MgO and the insoluble amorphous-gel-layer that protect the MgO from hydration. Moreover, CO{sub 2} curing could further improve the performance of the PFA-blended MOC due to the formation of a higher content of amorphous gel.« less

Chemical and Biological Catalytic Enhancement of Weathering of Silicate Minerals and industrial wastes as a Novel Carbon Capture and Storage Technology

NASA Astrophysics Data System (ADS)

Park, A. H. A.

2014-12-01

Increasing concentration of CO2 in the atmosphere is attributed to rising consumption of fossil fuels around the world. The development of solutions to reduce CO2 emissions to the atmosphere is one of the most urgent needs of today's society. One of the most stable and long-term solutions for storing CO2 is via carbon mineralization, where minerals containing metal oxides of Ca or Mg are reacted with CO2 to produce thermodynamically stable Ca- and Mg-carbonates that are insoluble in water. Carbon mineralization can be carried out in-situ or ex-situ. In the case of in-situ mineralization, the degree of carbonation is thought to be limited by both mineral dissolution and carbonate precipitation reaction kinetics, and must be well understood to predict the ultimate fate of CO2 within geological reservoirs. While the kinetics of in-situ mineral trapping via carbonation is naturally slow, it can be enhanced at high temperature and high partial pressure of CO2. The addition of weak organic acids produced from food waste has also been shown to enhance mineral weathering kinetics. In the case of the ex-situ carbon mineralization, the role of these ligand-bearing organic acids can be further amplified for silicate mineral dissolution. Unfortunately, high mineral dissolution rates often lead to the formation of a silica-rich passivation layer on the surface of silicate minerals. Thus, the use of novel solvent mixture that allows chemically catalyzed removal of this passivation layer during enhanced Mg-leaching surface reaction has been proposed and demonstrated. Furthermore, an engineered biological catalyst, carbonic anhydrase, has been developed and evaluated to accelerate the hydration of CO2, which is another potentially rate-limiting step of the carbonation reaction. The development of these novel catalytic reaction schemes has significantly improved the overall efficiency and sustainability of in-situ and ex-situ mineral carbonation technologies and allowed direct capture and storage of CO2 from mixture gas streams eliminating the energy-intensive solvent regeneration and CO2 compression steps.

Aluminum-induced dreierketten chain cross-links increase the mechanical properties of nanocrystalline calcium aluminosilicate hydrate

NASA Astrophysics Data System (ADS)

Geng, Guoqing; Myers, Rupert J.; Li, Jiaqi; Maboudian, Roya; Carraro, Carlo; Shapiro, David A.; Monteiro, Paulo J. M.

2017-03-01

The incorporation of Al and increased curing temperature promotes the crystallization and cross-linking of calcium (alumino)silicate hydrate (C-(A-)S-H), which is the primary binding phase in most contemporary concrete materials. However, the influence of Al-induced structural changes on the mechanical properties at atomistic scale is not well understood. Herein, synchrotron radiation-based high-pressure X-ray diffraction is used to quantify the influence of dreierketten chain cross-linking on the anisotropic mechanical behavior of C-(A-)S-H. We show that the ab-planar stiffness is independent of dreierketten chain defects, e.g. vacancies in bridging tetrahedra sites and Al for Si substitution. The c-axis of non-cross-linked C-(A-)S-H is more deformable due to the softer interlayer opening but stiffens with decreased spacing and/or increased zeolitic water and Ca2+ of the interlayer. Dreierketten chain cross-links act as ‘columns’ to resist compression, thus increasing the bulk modulus of C-(A-)S-H. We provide the first experimental evidence on the influence of the Al-induced atomistic configurational change on the mechanical properties of C-(A-)S-H. Our work advances the fundamental knowledge of C-(A-)S-H on the lowest level of its hierarchical structure, and thus can impact the way that innovative C-(A-)S-H-based cementitious materials are developed using a ‘bottom-up’ approach.

Aluminum-induced dreierketten chain cross-links increase the mechanical properties of nanocrystalline calcium aluminosilicate hydrate.

PubMed

Geng, Guoqing; Myers, Rupert J; Li, Jiaqi; Maboudian, Roya; Carraro, Carlo; Shapiro, David A; Monteiro, Paulo J M

2017-03-10

The incorporation of Al and increased curing temperature promotes the crystallization and cross-linking of calcium (alumino)silicate hydrate (C-(A-)S-H), which is the primary binding phase in most contemporary concrete materials. However, the influence of Al-induced structural changes on the mechanical properties at atomistic scale is not well understood. Herein, synchrotron radiation-based high-pressure X-ray diffraction is used to quantify the influence of dreierketten chain cross-linking on the anisotropic mechanical behavior of C-(A-)S-H. We show that the ab-planar stiffness is independent of dreierketten chain defects, e.g. vacancies in bridging tetrahedra sites and Al for Si substitution. The c-axis of non-cross-linked C-(A-)S-H is more deformable due to the softer interlayer opening but stiffens with decreased spacing and/or increased zeolitic water and Ca 2+ of the interlayer. Dreierketten chain cross-links act as 'columns' to resist compression, thus increasing the bulk modulus of C-(A-)S-H. We provide the first experimental evidence on the influence of the Al-induced atomistic configurational change on the mechanical properties of C-(A-)S-H. Our work advances the fundamental knowledge of C-(A-)S-H on the lowest level of its hierarchical structure, and thus can impact the way that innovative C-(A-)S-H-based cementitious materials are developed using a 'bottom-up' approach.

Removal of atmospheric features in near infrared spectra by means of principal component analysis and target transformation on Mars: I. Method

NASA Astrophysics Data System (ADS)

Geminale, A.; Grassi, D.; Altieri, F.; Serventi, G.; Carli, C.; Carrozzo, F. G.; Sgavetti, M.; Orosei, R.; D'Aversa, E.; Bellucci, G.; Frigeri, A.

2015-06-01

The aim of this work is to extract the surface contribution in the martian visible/near-infrared spectra removing the atmospheric components by means of Principal Component Analysis (PCA) and target transformation (TT). The developed technique is suitable for separating spectral components in a data set large enough to enable an effective usage of statistical methods, in support to the more common approaches to remove the gaseous component. In this context, a key role is played by the estimation, from the spectral population, of the covariance matrix that describes the statistical correlation of the signal among different points in the spectrum. As a general rule, the covariance matrix becomes more and more meaningful increasing the size of initial population, justifying therefore the importance of sizable datasets. Data collected by imaging spectrometers, such as the OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) instrument on board the ESA mission Mars Express (MEx), are particularly suitable for this purpose since it includes in the same session of observation a large number of spectra with different content of aerosols, gases and mineralogy. The methodology presented in this work has been first validated using a simulated dataset of spectra to evaluate its accuracy. Then, it has been applied to the analysis of OMEGA sessions over Nili Fossae and Mawrth Vallis regions, which have been already widely studied because of the presence of hydrated minerals. These minerals are key components of the surface to investigate the presence of liquid water flowing on the martian surface in the Noachian period. Moreover, since a correction for the atmospheric aerosols (dust) component is also applied to these observations, the present work is able to completely remove the atmospheric contribution from the analysed spectra. Once the surface reflectance, free from atmospheric contributions, has been obtained, the Modified Gaussian Model (MGM) has been applied to spectra showing the hydrated phase. Silicates and iron-bearing hydrated minerals have been identified by means of the electronic transitions of Fe2+ between 0.8 and 1.2 μm, while at longer wavelengths the hydrated mineralogy is identified by overtones of the OH group. Surface reflectance spectra, as derived through the method discussed in this paper, clearly show a lower level of the atmospheric residuals in the 1.9 hydration band, thus resulting in a better match with the MGM deconvolution parameters found for the laboratory spectra of martian hydrated mineral analogues and allowing a deeper investigation of this spectral range.

Insights into Silicate Carbonation Processes in Water-Bearing Supercritical CO2 Fluids

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

Miller, Quin RS; Thompson, Christopher J.; Loring, John S.

2013-07-01

Long-term geologic storage of carbon dioxide (CO2) is considered an integral part to moderating CO2 concentrations in the atmosphere and subsequently minimizing effects of global climate change. Although subsurface injection of CO2 is common place in certain industries, deployment at the scale required for emission reduction is unprecedented and therefore requires a high degree of predictability. Accurately modeling geochemical processes in the subsurface requires experimental derived data for mineral reactions occurring between the CO2, water, and rocks. Most work in this area has focused on aqueous-dominated systems in which dissolved CO2 reacts to form crystalline carbonate minerals. Comparatively little laboratorymore » research has been conducted on reactions occurring between minerals in the host rock and the wet supercritical fluid phase. In this work, we studied the carbonation of wollastonite [CaSiO3] exposed to variably hydrated supercritical CO2 (scCO2) at a range of temperatures (50, 55 and 70 °C) and pressures (90,120 and 160 bar) that simulate conditions in geologic repositories. Mineral transformation reactions were followed by three novel in situ high pressure techniques, including x-ray diffraction that tracked the rate and extents of wollastonite conversion to calcite. Increased dissolved water concentrations in the supercritical CO2 resulted in increased silicate carbonation approaching ~50 wt. %. Development of thin water films on the mineral surface were directly observed with infrared spectroscopy and determined to be critical for facilitating carbonation processes. Even in extreme low water conditions, magic angle spinning nuclear magnetic resonance detected formation of Q3 [Si(OSi)3OH] and Q4 [Si(OSi)4] amorphous silica species. Unlike the thick (<10 μm) passivating silica layers observed in the fully water saturated scCO2 experiments, images obtained from a focused ion beam sectioned sample indicted these coatings were chemically wollastonite but structurally amorphous. In addition, evidence of an intermediate hydrated amorphous calcium carbonate forming under these conditions further emphasize the importance of understanding geochemical processes occurring in water bearing scCO2 fluids.« less

Self-degradable Cementitious Sealing Materials

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

Sugama, T.; Butcher, T., Lance Brothers, Bour, D.

2010-10-01

A self-degradable alkali-activated cementitious material consisting of a sodium silicate activator, slag, Class C fly ash, and sodium carboxymethyl cellulose (CMC) additive was formulated as one dry mix component, and we evaluated its potential in laboratory for use as a temporary sealing material for Enhanced Geothermal System (EGS) wells. The self-degradation of alkali-activated cementitious material (AACM) occurred, when AACM heated at temperatures of {ge}200 C came in contact with water. We interpreted the mechanism of this water-initiated self-degradation as resulting from the in-situ exothermic reactions between the reactants yielded from the dissolution of the non-reacted or partially reacted sodium silicatemore » activator and the thermal degradation of the CMC. The magnitude of self-degradation depended on the CMC content; its effective content in promoting degradation was {ge}0.7%. In contrast, no self-degradation was observed from CMC-modified Class G well cement. For 200 C-autoclaved AACMs without CMC, followed by heating at temperatures up to 300 C, they had a compressive strength ranging from 5982 to 4945 psi, which is {approx}3.5-fold higher than that of the commercial Class G well cement; the initial- and final-setting times of this AACM slurry at 85 C were {approx}60 and {approx}90 min. Two well-formed crystalline hydration phases, 1.1 nm tobermorite and calcium silicate hydrate (I), were responsible for developing this excellent high compressive strength. Although CMC is an attractive, as a degradation-promoting additive, its addition to both the AACM and the Class G well cement altered some properties of original cementitious materials; among those were an extending their setting times, an increasing their porosity, and lowering their compressive strength. Nevertheless, a 0.7% CMC-modified AACM as self-degradable cementitious material displayed the following properties before its breakdown by water; {approx}120 min initial- and {approx}180 min final-setting times at 85 C, and 1825 to 1375 psi compressive strength with 51.2 to 55.0% porosity up to 300 C.« less

The presence of carbonates on Mars: origin, terrestrial analogues and analytical tecniques ambiguity

NASA Astrophysics Data System (ADS)

Marinangeli, Lucia; Liberi, Francesca; Pompilio, Loredana; Piluso, Eugenio; Rosatelli, Gianluigi; Tranquilli, Andrea; Pepe, Monica

2013-04-01

The most common cause of carbonates formation on Earth is the chemical deposition from Ca-rich waters in sedimentary basins, mostly in shallow water. The lack of widespread exposure of carbonates on the Mars' surface in areas where geomorphological and sedimentological mapping confirms the presence of water for a long period of the Martian history, led us to look for a potential different origin of the carbonates identified on CRISM data [1, 2,3]. We suggest the presence of carbonatites on Mars and we have also investigated the capabilities of analytical tecniques for mineralogical analysis to recognise these peculiar type of rocks. Carbonatites are igneous rocks containing more than 50 percent of carbonate minerals and associated silicate minerals as olivine, pyroxene and phyllosilicates. Carbonatites are associated with alkali silicate rocks that are usually of nephelinitic or melilititic affinity. The Martian carbonates are often present in layered rocks and in association with hydrated Fe-Mg silicates (clays family) and kaolinite-group minerals at places [1]. This mineralogical association is very similar to an water-altered carbonatite. We have compared the compositional and mineralogical affinity of some carbonatite samples from different alkaline-carbonatite complexes from Uganda, Spain and Italy, with the mineralogy described for the carbonate- and phyllosolicate rich rocks on Mars, using the XRD and IR analyses. The mineral assemblage has been defined through petrographic analyses as well. It is important to stress that only with XRD analysis some minerals diagnos-tic of carbonatitic assemblage (i.e. melilite) were identified. The relationships between carbonatites and their associated silicate rocks are complex and are still not fully understood on Earth as well, however, it deserves further investigations to better explain the carbonates and silicate volcanic rocks on Mars and its crustal dynamics. References: [1] Michalski and Niles, 2010, Nature Geoscience, 751-755. [2] Helmann et al., 2008, Science, 322, 1828-1832. [3] Morris et al., 2010, Science, 329, 421-424.

Characterization and analyses of acid-extractable and leached trace elements in dental cements.

PubMed

Camilleri, J; Kralj, P; Veber, M; Sinagra, E

2012-08-01

Determination of the elemental constitution and investigation of the total and leachable arsenic, chromium and lead in Portland cement, pure tricalcium silicate, Biodentine, Bioaggregate and mineral trioxide aggregate (MTA) Angelus. The chemical composition of Portland cement, MTA Angelus, tricalcium silicate cement, Biodentine and Bioaggregate was determined using X-ray fluorescence (XRF). Measurements of arsenic, lead and chromium were taken with inductively coupled plasma-mass spectrometry (ICP-MS), following acid digestion on the hydrated material and on leachates of cements soaked in Hank's balanced salt solution (HBSS). All the cements investigated had a similar oxide composition with the main oxide being calcium and silicon oxide. Both the Portland cement and MTA Angelus had an additional aluminium oxide. The dental cements included a radiopacifying material. All the materials tested had higher acid-extractable arsenic content than the level set by ISO 9917-1 (2007) and an acceptable level of lead. Regardless these high levels of trace elements present in the materials, the leaching in HBSS was minimal for all the dental material tested in contrast to the high levels displayed by Portland cement. Dental materials based on tricalcium silicate cement and MTA Angelus release minimal quantities of trace elements when in contact with simulated body fluids. The results of acid extraction could be affected by nonspecific matrix effects by the cement. © 2012 International Endodontic Journal.

The mid-infrared transmission spectra of Antarctic ureilites

NASA Technical Reports Server (NTRS)

Sandford, Scott A.

1993-01-01

The mid-IR (4000-450/cm; 2.5-22.2 microns) transmission spectra of seven Antarctic ureilites and 10 Antarctic H-5 ordinary chondrites are presented. The ureilite spectra show a number of absorption bands, the strongest of which is a wide, complex feature centered near 1000/cm (10 microns) due to Si-O stretching vibrations in silicates. The profiles and positions of the substructure in this feature indicate that Mg-rich olivines and pyroxenes are the main silicates responsible. The relative abundances of these two minerals, as inferred from the spectra, show substantial variation from meteorite to meteorite, but generally indicate olivine is the most abundant (olivine:pyroxene = 60:40 to 95:5). Both the predominance of olivine and the variable olivine-to-pyroxene ratio are consistent with the known composition and heterogeneity of ureilites. The H-5 ordinary chondrites spanned a range of weathering classes and were used to provide a means of addressing the extent to which the ureilite spectra may have been altered by weathering processes. It was found that, while weathering of these meteorites produces some weak bands due to the formation of small amounts of carbonates and hydrates, the profile of the main silicate feature has been little affected by Antarctic exposure in the meteorites studied here. The mid-IR ureilite spectra provide an additional means of testing potential asteroidal parent bodies for the ureilites.

The Themis-Beagle families: Investigation of space-weathering processes on primitive surfaces

NASA Astrophysics Data System (ADS)

Fornasier, S.; Perna, D.; Lantz, C.; Barucci, M.

2014-07-01

In the past 20 years, enormous progress has been reached in the study of space-weathering (SW) effects on silicates and silicate asteroids. The so-called ordinary chondrite paradox, that is, lack of asteroids similar to the ordinary chondrites, which represent 80 % of meteorite falls, has been solved. These meteorites are now clearly related to S-type asteroids, as proved also by the direct measurements of the NEAR and HAYABUSA missions on the near-Earth asteroids Eros and Itokawa. Spectral differences between S-type asteroids and ordinary chondrites are caused by space-weathering effects, which produce a darkening in the albedo, a reddening of the spectra, and diminish the silicate absorption bands on the asteroids surfaces, exposed to cosmic radiation and solar wind. On the other hand, our understanding of space-weathering effects on primitive asteroids is still poor. Only few laboratory experiments have been devoted to the investigation of SW effects on dark carbonaceous chondrites and on complex organic materials. Irradiation of transparent organic materials produces firstly redder and darker materials that upon further processing turn flatter-bluish and darker (Kanuchova et al. 2012; Moroz et al. 2004). The Themis family is a natural laboratory to study primitive asteroids and space-weathering effects. The Themis family is located between 3.05 and 3.24 au, beyond the snow line, and it is composed of primitive asteroids. Themis is one of the most statistically reliable families in the asteroid belt. First discovered by Hirayama (1918), it has been identified as a family in all subsequent works, and it has 550 members as determined by Zappalà et al. (1995) and more than 4000 as determined by Nesvorny et al. (2010). The family formed probably about 2.3 Gyr ago as a result of a large-scale catastrophic disruption event of a parent asteroid 400 km in diameter colliding with a 190-km projectile (Marzari et al. 1995). Several Themis family members show absorption features associated to hydrated silicates, and, recently, water-ice and organics features have been detected on the surface of (24) Themis (Campins et al. 2010, Rivkin & Emery 2010). Hydrated silicates are produced by the aqueous-alteration process, which require low temperature (< 320 K) and the presence of liquid water in the past. The Themis family may be an important reservoir of water ice. Moreover, the main-belt comets 133P, 238P, and 176P seem to be related to the Themis family because of orbital proximities and spectral properties analogies. Within the old Themis family members, a young sub-family, Beagle, formed less than 10 Myr ago, has been identified. This sub-family has 65 members up to 2 km of diameter (Nesvorny et al. 2008). So, the Themis family is very important to shed light on the asteroid-comet continuum, to constrain the abundances of water ices in the outer part of the main belt, and to probe space-weathering effects on old Themis and young Beagle families' members. To investigate all these aspects, we carried out a spectroscopic survey in the visible and near-infrared range at the 3.6-m Italian telescope TNG (La Palma, Spain) during 6 nights in February and December 2012. We got new spectra of 8 Beagle and 22 Themis members using the DOLORES (with the LR-R and LR-B grisms) and the NICS (with the Amici prism) instruments. To look for possible coma around the targets, we also performed deep imaging in the R filter. Data are currently under analysis, and the results will be presented at the ACM meeting. None of the investigated spectra show water-ice absorption features at 1.5 and 2 microns, while few Themis members have visible absorption bands associated with hydrated silicates. The best meteoritic analogues to both Themis and Beagle members are the carbonaceous chondrites, especially CM2. The spectra of Beagle and Themis asteroids show significant differences: 'old' Themis members exhibit a wide range of spectra, including asteroids with blue/neutral and moderately red spectra (relative to the Sun), while the young Beagle members investigated are bluer and brighter than the Themis ones. These preliminary results seem to indicate that the SW effects on primitive asteroids are similar to those observed on silicate asteroids, that is, they produce reddening of the spectra and moderate darkening of the surface.

A radar survey of M- and X-class asteroids. III. Insights into their composition, hydration state, & structure

NASA Astrophysics Data System (ADS)

Shepard, Michael K.; Taylor, Patrick A.; Nolan, Michael C.; Howell, Ellen S.; Springmann, Alessondra; Giorgini, Jon D.; Warner, Brian D.; Harris, Alan W.; Stephens, Robert; Merline, William J.; Rivkin, Andrew; Benner, Lance A. M.; Coley, Dan; Clark, Beth Ellen; Ockert-Bell, Maureen; Magri, Christopher

2015-01-01

Using the S-band radar at Arecibo Observatory, we observed thirteen X/M-class asteroids; nine were previously undetected and four were re-observed, bringing the total number of Tholen X/M-class asteroids observed with radar to 29. Of these 29M-class asteroids, 13 are also W-class, defined as M-class objects that also display a 3-μm absorption feature which is often interpreted as the signature of hydrated minerals (Jones, T.D., Lebofsky, L.A., Lewis, J.S., Marley, M.S. [1990]. Icarus 88, 172-192; Rivkin, A.S., Howell, E.S., Britt, D.T., Lebofsky, L.A., Nolan, M.C., Branston, D.D. [1995]. Icarus 117, 90-100; Rivkin, A.S., Howell, E.S., Lebofsky, L.A., Clark, B.E., Britt, D.T. [2000]. Icarus 145, 351-368). Consistent with our previous work (Shepard, M.K. et al. [2008]. Icarus 195, 184-205; Shepard, M.K., Harris, A.W., Taylor, P.A., Clark, B.E., Ockert-Bell, M., Nolan, M.C., Howell, E.S., Magri, C., Giorgini, J.D., Benner, L.A.M. [2011]. Icarus 215, 547-551), we find that 38% of our sample (11 of 29) have radar albedos consistent with metal-dominated compositions. With the exception of 83 Beatrix and 572 Rebekka, the remaining objects have radar albedos significantly higher than the mean S- or C-class asteroid (Magri, C., Nolan, M.C., Ostro, S.J., Giorgini, J.D. [2007]. Icarus 186, 126-151). Seven of the eleven high-radar-albedo asteroids, or 64%, also display a 3-μm absorption feature (W-class) which is thought to be inconsistent with the formation of a metal dominated asteroid. We suggest that the hydration absorption could be a secondary feature caused by low-velocity collisions with hydrated asteroids, such as CI or CM analogs, and subsequent implantation of the hydrated minerals into the upper regolith. There is recent evidence for this process on Vesta (Reddy, V. et al. [2012]. Icarus 221, 544-559; McCord, T.B. et al. [2012]. Nature 491, 83-86; Prettyman, T.H. et al. [2012]. Science 338, 242-246; Denevi, B.W. et al. [2012]. Science 338, 246-249). Eleven members of our sample show bifurcated radar echoes at some rotation phases; eight of these are high radar albedo targets. One interpretation of a bifurcated echo is a contact binary, like 216 Kleopatra, and several of our sample are contact binary candidates. However, evidence for other targets indicates they are not contact binaries. Instead, we hypothesize that these asteroids may have large-scale variations in surface bulk density, i.e. isolated patches of metal-rich and silicate-rich regions at the near-surface, possibly the result of collisions between metal and silicate-rich asteroids.

Hydration characteristics of zirconium oxide replaced Portland cement for use as a root-end filling material.

PubMed

Camilleri, J; Cutajar, A; Mallia, B

2011-08-01

Zirconium oxide can be added to dental materials rendering them sufficiently radiopaque. It can thus be used to replace the bismuth oxide in mineral trioxide aggregate (MTA). Replacement of Portland cement with 30% zirconium oxide mixed at a water/cement ratio of 0.3 resulted in a material with adequate physical properties. This study aimed at investigating the microstructure, pH and leaching in physiological solution of Portland cement replaced zirconium oxide at either water-powder or water-cement ratios of 0.3 for use as a root-end filling material. The hydration characteristics of the materials which exhibited optimal behavior were evaluated. Portland cement replaced by zirconium oxide in varying amounts ranging from 0 to 50% in increments of 10 was prepared and divided into two sets. One set was prepared at a constant water/cement ratio while the other set at a constant water/powder ratio of 0.3. Portland cement and MTA were used as controls. The materials were analyzed under the scanning electron microscope (SEM) and the hydration products were determined. X-ray energy dispersive analysis (EDX) was used to analyze the elemental composition of the hydration products. The pH and the amount of leachate in Hank's balanced salt solution (HBSS) were evaluated. A material that had optimal properties that satisfied set criteria and could replace MTA was selected. The microstructure of the prototype material and Portland cement used as a control was assessed after 30 days using SEM and atomic ratio diagrams of Al/Ca versus Si/Ca and S/Ca versus Al/Ca were plotted. The hydration products of Portland cement replaced with 30% zirconium oxide mixed at water/cement ratio of 0.3 were calcium silicate hydrate, calcium hydroxide and minimal amounts of ettringite and monosulphate. The calcium hydroxide leached in HBSS solution resulted in an increase in the pH value. The zirconium oxide acted as inert filler and exhibited no reaction with the hydration by-products of Portland cement. A prototype dental material composed of Portland cement replaced with 30% zirconium oxide as radiopacifier leached calcium ions on hydration which reacted with phosphates present in simulated tissue fluids. This resulted in bioactive cement that could prospectively be used as a root-end filling material. The zirconium oxide acted as inert filler and did not participate in the hydration reaction of the Portland cement. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Carbon Mineralization Using Phosphate and Silicate Ions

NASA Astrophysics Data System (ADS)

Gokturk, H.

2013-12-01

Carbon dioxide (CO2) reduction from combustion of fossil fuels has become an urgent concern for the society due to marked increase in weather related natural disasters and other negative consequences of global warming. CO2 is a highly stable molecule which does not readily interact with other neutral molecules. However it is more responsive to ions due to charge versus quadrupole interaction [1-2]. Ions can be created by dissolving a salt in water and then aerosolizing the solution. This approach gives CO2 molecules a chance to interact with the hydrated salt ions over the large surface area of the aerosol. Ion containing aerosols exist in nature, an example being sea spray particles generated by breaking waves. Such particles contain singly and doubly charged salt ions including Na+, Cl-, Mg++ and SO4--. Depending on the proximity of CO2 to the ion, interaction energy can be significantly higher than the thermal energy of the aerosol. For example, an interaction energy of 0.6 eV is obtained with the sulfate (SO4--) ion when CO2 is the nearest neighbor [2]. In this research interaction between CO2 and ions which carry higher charges are investigated. The molecules selected for the study are triply charged phosphate (PO4---) ions and quadruply charged silicate (SiO4----) ions. Examples of salts which contain such molecules are potassium phosphate (K3PO4) and sodium orthosilicate (Na4SiO4). The research has been carried out with first principle quantum mechanical calculations using the Density Functional Theory method with B3LYP functional and Pople type basis sets augmented with polarization and diffuse functions. Atomic models consist of the selected ions surrounded by water and CO2 molecules. Similar to the results obtained with singly and doubly charged ions [1-2], phosphate and silicate ions attract CO2 molecules. Energy of interaction between the ion and CO2 is 1.6 eV for the phosphate ion and 3.3 eV for the silicate ion. Hence one can expect that the selected ions would enhance the absorption of CO2 into the aerosol even more than the singly or doubly charged ions. Ion containing aerosols also help to catalyze reactions between water and CO2. Hydrated phosphate and silicate ions tend to attract hydrogen atoms from neighboring water molecules to reduce the charged state. When there is CO2 in the vicinity of the ion, the remainder of the water molecule which loses the hydrogen(s) reacts with CO2 to form carbonates. (PO4---) + H2O + CO2 -> (HPO3--) + (HCO3-) (SiO4----) + H2O + CO2 -> (HSiO4---) + (HCO3-) (SiO4----) + H2O + CO2 -> (H2SiO4--) + (CO3--) In conclusion, highly charged phosphate and silicate ions dissolved in water and aerosolized into small droplets can facilitate both the capture and the mineralization of CO2. This method would be especially effective in a CO2 rich environment such as the exhaust gas of a combustion process. [1] H. Gokturk, "Geoengineering with Charged Droplets," AGU Fall Meeting, San Francisco 2011 [2] H. Gokturk, "Atomistic Simulation of Sea Spray Particles," AGU Fall Meeting, San Francisco 2012

Polymeric microcapsules with switchable mechanical properties for self-healing concrete: synthesis, characterisation and proof of concept

NASA Astrophysics Data System (ADS)

Kanellopoulos, A.; Giannaros, P.; Palmer, D.; Kerr, A.; Al-Tabbaa, A.

2017-04-01

Microcapsules, with sodium silicate solution as core, were produced using complex coacervation in a double, oil-in-water-in oil, emulsion system. The shell material was a gelatin-acacia gum crosslinked coacervate and the produced microcapsules had diameters ranging from 300 to 700 μm. The shell material designed with switchable mechanical properties. When it is hydrated exhibits soft and ‘rubbery’ behaviour and, when dried, transitions to a stiff and ‘glassy’ material. The microcapsules survived drying and rehydrating cycles and preserved their structural integrity when exposed to highly alkaline solutions that mimic the pH environment of concrete. Microscopy revealed that the shell thickness of the microcapsules varies across their perimeter from 5 to 20 μm. Thermal analysis showed that the produced microcapsules were very stable up to 190 °C. Proof of concept investigation has demonstrated that the microcapsules successfully survive and function when exposed to a cement-based matrix. Observations showed that the microcapsules survive mixing with cement and rupture successfully upon crack formation releasing the encapsulated sodium silicate solution.

Bioactive Glass-Ceramic Scaffolds from Novel ‘Inorganic Gel Casting’ and Sinter-Crystallization

PubMed Central

Elsayed, Hamada; Rincón Romero, Acacio; Ferroni, Letizia; Gardin, Chiara; Zavan, Barbara; Bernardo, Enrico

2017-01-01

Highly porous wollastonite-diopside glass-ceramics have been successfully obtained by a new gel-casting technique. The gelation of an aqueous slurry of glass powders was not achieved according to the polymerization of an organic monomer, but as the result of alkali activation. The alkali activation of a Ca-Mg silicate glass (with a composition close to 50 mol % wollastonite—50 mol % diopside, with minor amounts of Na2O and P2O5) allowed for the obtainment of well-dispersed concentrated suspensions, undergoing progressive hardening by curing at low temperature (40 °C), owing to the formation of a C–S–H (calcium silicate hydrate) gel. An extensive direct foaming was achieved by vigorous mechanical stirring of partially gelified suspensions, comprising also a surfactant. The open-celled structure resulting from mechanical foaming could be ‘frozen’ by the subsequent sintering treatment, at 900–1000 °C, causing substantial crystallization. A total porosity exceeding 80%, comprising both well-interconnected macro-pores and micro-pores on cell walls, was accompanied by an excellent compressive strength, even above 5 MPa. PMID:28772531

Titan's Methane Cycle is Closed

NASA Astrophysics Data System (ADS)

Hofgartner, J. D.; Lunine, J. I.

2013-12-01

Doppler tracking of the Cassini spacecraft determined a polar moment of inertia for Titan of 0.34 (Iess et al., 2010, Science, 327, 1367). Assuming hydrostatic equilibrium, one interpretation is that Titan's silicate core is partially hydrated (Castillo-Rogez and Lunine, 2010, Geophys. Res. Lett., 37, L20205). These authors point out that for the core to have avoided complete thermal dehydration to the present day, at least 30% of the potassium content of Titan must have leached into an overlying water ocean by the end of the core overturn. We calculate that for probable ammonia compositions of Titan's ocean (compositions with greater than 1% ammonia by weight), that this amount of potassium leaching is achievable via the substitution of ammonium for potassium during the hydration epoch. Formation of a hydrous core early in Titan's history by serpentinization results in the loss of one hydrogen molecule for every hydrating water molecule. We calculate that complete serpentinization of Titan's core corresponds to the release of more than enough hydrogen to reconstitute all of the methane atoms photolyzed throughout Titan's history. Insertion of molecular hydrogen by double occupancy into crustal clathrates provides a storage medium and an opportunity for ethane to be converted back to methane slowly over time--potentially completing a cycle that extends the lifetime of methane in Titan's surface atmosphere system by factors of several to an order of magnitude over the photochemically-calculated lifetime.

Properties of Chemically Combusted Calcium Carbide Residue and Its Influence on Cement Properties.

PubMed

Sun, Hongfang; Li, Zishanshan; Bai, Jing; Memon, Shazim Ali; Dong, Biqin; Fang, Yuan; Xu, Weiting; Xing, Feng

2015-02-13

Calcium carbide residue (CCR) is a waste by-product from acetylene gas production. The main component of CCR is Ca(OH)₂, which can react with siliceous materials through pozzolanic reactions, resulting in a product similar to those obtained from the cement hydration process. Thus, it is possible to use CCR as a substitute for Portland cement in concrete. In this research, we synthesized CCR and silica fume through a chemical combustion technique to produce a new reactive cementitious powder (RCP). The properties of paste and mortar in fresh and hardened states (setting time, shrinkage, and compressive strength) with 5% cement replacement by RCP were evaluated. The hydration of RCP and OPC (Ordinary Portland Cement) pastes was also examined through SEM (scanning electron microscope). Test results showed that in comparison to control OPC mix, the hydration products for the RCP mix took longer to formulate. The initial and final setting times were prolonged, while the drying shrinkage was significantly reduced. The compressive strength at the age of 45 days for RCP mortar mix was found to be higher than that of OPC mortar and OPC mortar with silica fume mix by 10% and 8%, respectively. Therefore, the synthesized RCP was proved to be a sustainable active cementitious powder for the strength enhanced of building materials, which will result in the diversion of significant quantities of this by-product from landfills.

The Effects of Air-Cooled Blast Furnace Slag (ACBFS) Aggregate on the Chemistry of Pore Solution and the Interfacial Transition Zone

NASA Astrophysics Data System (ADS)

Panchmatia, Parth

Numerous laboratory and field studies have demonstrated that concrete incorporating air cooled blast furnace slag (ACBFS) aggregate showed a higher degree of infilling of voids with ettringite as opposed to concrete prepared using naturally mined carbonate aggregates when exposed to similar environmental conditions. This observation prompted some to link the deterioration observed in the ACBFS aggregate concrete structures to the compromised freeze-thaw resistance due to infilling of air voids. Concerns about the release of sulfur from ACBFS aggregate into the pore solution of concrete had been presented as the reason for the observed ettringite deposits in the air voids. However, literature quantifying the influence of ACBFS aggregate on the chemistry of the pore solution of concrete is absent. Therefore, the main purpose of this research was to quantify the effects of ACBFS aggregate on the chemistry of the pore solution of mortars incorporating them. Coarse and crushed ACBFS aggregates were submerged in artificial pore solutions (APSs) representing pore solutions of 3-day, 7-day, and 28-day hydrated plain, binary, and ternary paste systems. The change in the chemistry of these artificial pore solutions was recorded to quantify the chemical contribution of ACBFS aggregate to the pore solution of concrete. It was observed that the sulfate concentration of all APSs increased once they were in contact with either coarse or crushed ACBFS aggregate. After 28 days of contact, the increase in sulfate concentration of the APSs ranged from 4.85 - 12.23 mmol/L and 14.21 - 16.87 mmol/L for contact with coarse and crushed ACBFS aggregate, respectively. More than 40% of the total sulfate that was released by the ACBFS aggregate occurred during the first 72 hours (3 days) of its contact with the APSs. There was little or no difference in the amount of sulfate released from ACBFS aggregate in the different types of APSs. In other words, the type of binder solution from which pore solution was extracted had no effect on the amount of sulfate that was released when it was in contact with ACBFS aggregate. The relatively quick release of sulfur from ACBFS aggregate into the APSs prompted investigation of the chemical composition of the pore solution of mortar (at early stages of hydration) incorporating ACBFS aggregate. The chemical composition of the pore solutions obtained from mortars prepared using ACBFS aggregate and plain and binary paste matrices was compared those of mortars prepared using Ottawa sand and plain and binary paste matrices. After 7 days of hydration, the sulfur (S) concentration of the pore solution extracted from mortars prepared using ACBFS aggregate was 3.4 - 5.6 times greater than that obtained from corresponding mortars (i.e. mortars with the same paste matrix) prepared using Ottawa sand. Binary mortars containing fly ash (FA) showed the lowest S content after 7 days of hydration amongst all mortars prepared using ACBFS aggregate. On the other hand, binary mortars prepared using slag cement (SC) and ACBFS aggregate had the highest S concentration after 7 days of hydration. These effects on the S concentration in the pore solutions can be explained by the difference in the chemical makeup of the binders, and not because of different rate of release of S from ACBFS into the pore solution. In addition, TGA analysis of 7-day hydrated mortars revealed that the ettringite, monosulfate, and calcium hydroxide content was lower in mortars prepared using ACBFS aggregate as opposed to those prepared using Ottawa sand. This could be because of the low degree of hydration in mortars with ACBFS aggregate because of the high sulfate concentration in its pore solution. The properties of the interfacial transition zone (ITZ), i.e. the zone in the vicinity of the aggregate surface, depends on the property of the aggregate such as its porosity and texture. Therefore, it is expected that the properties of ITZ around the ACBFS particle, which is porous and proven to contribute sulfate, be different from the ITZ around the naturally mined siliceous aggregate. Image analysis conducted on backscattered images obtained using scanning electron microscope revealed that the ITZ of naturally mined siliceous aggregate was more porous compared to the ITZ of ACBFS aggregate. In addition, calcium hydroxide deposits were more frequent and larger in size in the ITZ around siliceous sand than in the case of the ITZ around the ACBFS aggregate.

Stabilization of azadirachtin A in neem formulations: effect of some solid carriers, neem oil, and stabilizers.

PubMed

Kumar, J; Parmar, B S

1999-04-01

Formulation of azadirachtin A on attapulgite, kaolinite, fuller's earth, hydrated calcium silicate, and fly ash revealed that it degraded to the tune of 70-95% on different solid carriers as compared to 56% in neem oil, during the 14 day heat storage studies at 54 +/- 1 degrees C in the laboratory. The degradation was reduced by 26-60% on different carriers by employing either anthraquinone or epichlorohydrin as stabilizer. Pyrogallol and hydroquinone enhanced the degradation. The cation exchange capacity and surface area of the carriers revealed a significant negative correlation with t(1/2) of azadirachtin A.

Investigation into the stabilization/solidification performance of Portland cement through cement clinker phases.

PubMed

Qiao, X C; Poon, C S; Cheeseman, C R

2007-01-10

This research studied the influence of individual heavy metal on the hydration reactions of major cement clinker phases in order to investigate the performance of cement based stabilization/solidification (S/S) system. Tricalcium silicate (C3S) and tricalcium aluminate (C3A) had been mixed with individual heavy metal hydroxide including Zn(OH)2, Pb(OH)2 and Cu(OH)2, respectively. The influences of these heavy metal hydroxides on the hydration of C3S and C3A have been characterized by X-ray diffraction (XRD) and differential scanning calorimetry-thermogravimetry (DSC-TG). A mixture of Zn(OH)2, Pb(OH)2 and Cu(OH)2 was blended with Portland cement (PC) and evaluated through compressive strength and dynamic leach test. XRD and DSC-TG data show that all the heavy metal hydroxides (Zn(OH)2, Pb(OH)2 and Cu(OH)2) have detrimental effects on the hydration of C3A, but only Zn(OH)2 does to the C3S at early curing ages which can completely inhibit the hydration of C3S due to the formation of CaO(Zn(OH)2).2H2O. Cu6Al2O8CO(3).12H2O, Pb2Al4O4(CO3)(4).7H2O and Zn6Al2O8CO(3).12H2O are formed in all the samples containing C3A in the presence of metal hydroxides. After adding CaSO4 into C3A, the detrimental effect of heavy metals increases due to the coating effect of both calcium aluminate sulphates and heavy metal aluminate carbonates. The influence of heavy metal hydroxide on the hydration of C3S and C3A can be used to predict the S/S performance of Portland cement.

Recycling of porcelain tile polishing residue in portland cement: hydration efficiency.

PubMed

Pelisser, Fernando; Steiner, Luiz Renato; Bernardin, Adriano Michael

2012-02-21

Ceramic tiles are widely used by the construction industry, and the manufacturing process of ceramic tiles generates as a major residue mud derived from the polishing step. This residue is too impure to be reused in the ceramic process and is usually discarded as waste in landfills. But the analysis of the particle size and concentration of silica of this residue shows a potential use in the manufacture of building materials based on portland cement. Tests were conducted on cement pastes and mortars using the addition of 10% and 20% (mass) of the residue. The results of compressive strength in mortars made up to 56 days showed a significant increase in compressive strength greater than 50%. The result of thermogravimetry shows that portlandite is consumed by the cement formed by the silica present in the residue in order to form calcium silicate hydrate and featuring a pozzolanic reaction. This effect improves the performance of cement, contributes to research and application of supplementary cementitious materials, and optimizes the use of portland cement, reducing the environmental impacts of carbon dioxide emissions from its production.

Effect of the crystal chemistry on the hydration mechanism of swelling micas

NASA Astrophysics Data System (ADS)

Pavón, Esperanza; Alba, María D.; Castro, Miguel A.; Cota, A.; Osuna, Francisco J.; Pazos, M. Carolina

2017-11-01

Swelling and dehydration under minor changes in temperature and water vapor pressure is an important property that clays and clay minerals exhibit. In particular, their interlayer space, the solid-water interface and the layers' collapse and re-expansion have received much attention because it affects to the dynamical properties of interlayer cations and thus the transfer and fate of water and pollutants. In this contribution, the dehydration and rehydration mechanism of a swelling high-charge mica family is examined by in situ X-ray Diffraction. The effect of the aluminosilicate layer charge and the physicochemical properties of the interlayer cations on these processes are analyzed. The results showed that the dehydration temperature and the number of steps involved in this process are related to the layer charge of the silicate and the physicochemical properties of the interlayer cations. Moreover, the ability to adsorb water molecules in a confined space with high electric field by the interlayer cations does not only depend on their hydration enthalpy but also on the electrostatic parameters of these cations.

Mineralogical, Spectral, and Compositional Changes During Heating of Hydrous Carbonaceous Chondrites

NASA Technical Reports Server (NTRS)

Nakamura, T.; Matsuoka, M.; Yamashita, S.; Sato, Y.; Mogi, K.; Enokido, Y.; Nakata, A.; Okumura, S.; Furukawa, Y.; Zolensky, M.

2017-01-01

Hydrous carbonaceous chondrites experienced hydration and subsequent dehydration by heating, which resulted in a variety of mineralogical and spectral features [e. g., 1-6]. The degree of heating is classified according to heating stage (HS) II to IV based on mineralogy of phyllosilicates [2], because they change, with elevating temperature, to poorly crystal-line phases and subsequently to aggregates of small secondary anhydrous silicates of mainly olivine. Heating of hydrous carbonaceous chondrites also causes spectral changes and volatile loss [3-6]. Experimental heating of Murchison CM chondrite showed flattening of whole visible-near infrared spectra, especially weakening of the 3µm band strength [1, 4, 7]. In order to understand mineralogical, spectral, and compositional changes during heating of hydrous carbonaceous chondrites, we have carried out systematic investigation of mineralogy, reflectance spectra, and volatile composition of hydrated and dehydrated carbonaceous chondrites as well as experimentally-heated hydrous carbonaceous chondrites. In addition, we investigated reflectance spectra of tochilinite that is a major phase of CM chondrites and has a low dehydration temperature (250degC).

Leaching and mechanical behaviour of concrete manufactured with recycled aggregates.

PubMed

Sani, D; Moriconi, G; Fava, G; Corinaldesi, V

2005-01-01

The reuse of debris from building demolition is of increasing public interest because it decreases the volume of material to be disposed to landfill. This research is focused on the evaluation of the possibility of reusing recycled aggregate from construction or demolition waste (C&D) as a substitute for natural aggregate in concrete production. In most applications, cement based materials are used for building construction due to their cost effectiveness and performance; however their impact on the surrounding environment should be monitored. The interstitial pore fluid in contact with hydrated cementitious materials is characterized by persistent alkaline pH values buffered by the presence of hydrate calcium silicate, portlandite and alkaline ions. An experimental plan was carried out to investigate concrete structural properties in relation to alkali release in aqueous solution. Results indicate that the presence of recycled aggregate increases the leachability of unreactive ions (Na, K, Cl), while for calcium the substitution resulted in a lower net leaching. In spite of the lower mechanical resistance (40% less), such a waste concrete may be suggested as more environmentally sustainable.

Lunar and Planetary Science XXXV: Weird Martian Minerals: Complex Mars Surface Processes

NASA Technical Reports Server (NTRS)

2004-01-01

The session "Complex Mars Surface" included the following reports:A Reappraisal of Adsorbed Superoxide Ion as the Cause Behind the Reactivity of the Martian Soils; Sub-Surface Deposits of Hydrous Silicates or Hydrated Magnesium Sulfates as Hydrogen Reservoirs near the Martian Equator: Plausible or Not?; Thermal and Evolved Gas Analysis of Smectites: The Search for Water on Mars; Aqueous Alteration Pathways for K, Th, and U on Mars; Temperature Dependence of the Moessbauer Fraction in Mars-Analog Minerals; Acid-Sulfate Vapor Reactions with Basaltic Tephra: An Analog for Martian Surface Processes; Iron Oxide Weathering in Sulfuric Acid: Implications for Mars; P/Fe as an Aquamarker for Mars; Stable Isotope Composition of Carbonates Formed in Low-Temperature Terrestrial Environments as Martian Analogs; Can the Phosphate Sorption and Occlusion Properties Help to Elucidate the Genesis of Specular Hematite on the Mars Surface?; Sulfate Salts, Regolith Interactions, and Water Storage in Equatorial Martian Regolith; Potential Pathways to Maghemite in Mars Soils: The Key Role of Phosphate; and Mineralogy, Abundance, and Hydration State of Sulfates and Chlorides at the Mars Pathfinder Landing Site.

The Origin of Organic Matter in the Solar System: Evidence from Interplanetary Dust Particles

NASA Technical Reports Server (NTRS)

Flynn, G. J.; Keller, L. P.; Jacobsen, C.; Wirick, S.

2001-01-01

The origin of the organic matter in interplanetary materials has not been established. A variety of mechanisms have been proposed, with two extreme cases being a Fisher-Tropsch type process operating in the gas phase of the solar nebula or a Miller-Urey type process, which requires interaction with an aqueous fluid, presumably occurring on an asteroid. In the Fisher-Tropsch case, we might expect similar organic matter in hydrated and anhydrous interplanetary materials. However, aqueous alteration is required in the case of the Miller-Urey process, and we would expect to see organic matter preferentially in interplanetary materials that exhibit evidence of aqueous activity, such as the presence of hydrated silicates. The types and abundance of organic matter in meteorites have been used as an indicator of the origin of organic matter in the Solar System. Indigenous complex organic matter, including amino acids, has been found in hydrated carbonaceous chondrite meteorites, such as Murchison. Much lower amounts of complex organic matter, possibly only terrestrial contamination, have been found in anhydrous carbonaceous chondrite meteorites, such as Allende, that contain most of their carbon in elemental form. These results seem to favor production of the bulk of the organic matter in the Solar System by aqueous processing on parent bodies such as asteroids, a Miller-Urey process. However, the hydrated carbonaceous chondrite meteorites have approximately solar abundances of the moderately volatile elements, while all anhydrous carbonaceous chondrite meteorites have significantly lower contents of these moderately volatile elements. Two mechanisms, incomplete condensation or evaporation, both of which involve processing at approx. 1200 C, have been suggested to explain the lower content of the moderately volatile elements in all anhydrous meteorites. Additional information is contained in the original extended abstract.

Aqueous alteration on main-belt asteroids

NASA Astrophysics Data System (ADS)

Fornasier, S.; Lantz, C.; Barucci, M.; Lazzarin, M.

2014-07-01

The study of aqueous alteration is particularly important for unraveling the processes occurring during the earliest times in Solar System history, as it can give information both on the thermal processes and on the localization of water sources in the asteroid belt, and for the associated astrobiological implications. The aqueous alteration process produces the low temperature (< 320 K) chemical alteration of materials by liquid water which acts as a solvent and produces materials like phyllosilicates, sulphates, oxides, carbonates, and hydroxides. This means that liquid water was present in the primordial asteroids, produced by the melting of water ice by heating sources, very probably by ^{26}Al decay. Hydrated minerals have been found mainly on Mars surface, on primitive main-belt asteroids (C, G, B, F, and P-type, following the classification scheme by Tholen, 1984) and possibly also on few transneptunian objects. Reflectance spectroscopy of aqueous altered asteroids shows absorption features in the 0.6-0.9 and 2.5-3.5-micron regions, which are diagnostic of, or associated with, hydrated minerals. In this work, we investigate the aqueous alteration process on a large sample of 600 visible spectra of C-complex asteroids available in the literature. We analyzed all these spectra in a similar way to characterize the absorption-band parameters (band center, depth, and width) and spectral slope, and to look for possible correlations between the aqueous alteration process and the asteroids taxonomic classes, orbital elements, heliocentric distances, albedo, and sizes. We find that 4.6 % of P, 7.7 % of F, 9.8 % of B, 50.5 % of C, and 100 % of the G-type asteroids have absorption bands in the visible region due to hydrated silicates. Our analysis shows that the aqueous alteration sequence starts from the P-type objects, practically unaltered, and increases through the P → F → B → C → G asteroids, these last being widely aqueously altered, strengthening thus the results previously obtained by Vilas (1994). We confirm the strong correlation between the 0.7-μm band and the 3-μ m band, the deepest feature associated with hydrated minerals, as 95 % of the asteroids showing the 0.7-μ m band have also the 3-μ m feature. 45 % of the asteroids belonging to the C-complex (the F, B, C, and G classes) have signatures of aqueously altered materials in the visible range. It must be noted that this percentage represents a lower limit in the number of hydrated asteroids, simply because the 3-μ m band, the main absorption feature produced by hydrated silicates, may be present in the spectra of primitive asteroids when no bands are detected in the visible range. All this considered, we estimate that 70 % of the C-complex asteroids might have the 3-μ m signature in the IR range and thus were affected by the aqueous alteration process in the past. We find that the aqueous alteration process dominates in primitive asteroids located between 2.3 and 3.1 au, that is, at smaller heliocentric distances than previously suggested by Vilas et al. (1993). The percentage of hydrated asteroids is strongly correlated with their size (Fornasier et al. 2014). The aqueous alteration process is less effective for bodies smaller than 50 km, while it dominates in the 50-240-km sized primitive asteroids. No correlation is found between the aqueous alteration process and the asteroid albedo or orbital elements. Aqueously altered asteroids are the plausible parent bodies of CM2 meteorites. Nevertheless, we see a systematic difference in the 0.7-μ m band center position, the CM2 meteorites having a band centered at longer wavelengths (0.71-0.75 μ m) compared to that of hydrated asteroids. Moreover, the hydrated asteroids are more clustered in spectral slope and band depth than the CM meteorites. All these spectral differences may be attributed to different mineral abundances (CM2 meteorites being more serpentine rich than the asteroids), and/or to grain-size effects, or simply to the fact the CM2 collected on the Earth might not be representative of the whole population of aqueously altered asteroids.

Aluminum-induced dreierketten chain cross-links increase the mechanical properties of nanocrystalline calcium aluminosilicate hydrate

DOE PAGES

Geng, Guoqing; Myers, Rupert J.; Li, Jiaqi; ...

2017-03-10

The incorporation of Al and increased curing temperature promotes the crystallization and cross-linking of calcium (alumino)silicate hydrate (C-(A-)S-H), which is the primary binding phase in most contemporary concrete materials. However, the influence of Al-induced structural changes on the mechanical properties at atomistic scale is not well understood. Herein, synchrotron radiation-based high-pressure X-ray diffraction is used to quantify the influence of dreierketten chain cross-linking on the anisotropic mechanical behavior of C-(A-)S-H. We show that the ab-planar stiffness is independent of dreierketten chain defects, e.g. vacancies in bridging tetrahedra sites and Al for Si substitution. The c-axis of non-cross-linked C-(A-)S-H is moremore » deformable due to the softer interlayer opening but stiffens with decreased spacing and/or increased zeolitic water and Ca 2+ of the interlayer. Dreierketten chain cross-links act as ‘columns’ to resist compression, thus increasing the bulk modulus of C-(A-)S-H. We provide the first experimental evidence on the influence of the Al-induced atomistic configurational change on the mechanical properties of C-(A-)S-H. Our work advances the fundamental knowledge of C-(A-)S-H on the lowest level of its hierarchical structure, and thus can impact the way that innovative C-(A-)S-H-based cementitious materials are developed using a ‘bottom-up’ approach.« less

Aluminum-induced dreierketten chain cross-links increase the mechanical properties of nanocrystalline calcium aluminosilicate hydrate

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

Geng, Guoqing; Myers, Rupert J.; Li, Jiaqi

The incorporation of Al and increased curing temperature promotes the crystallization and cross-linking of calcium (alumino)silicate hydrate (C-(A-)S-H), which is the primary binding phase in most contemporary concrete materials. However, the influence of Al-induced structural changes on the mechanical properties at atomistic scale is not well understood. Herein, synchrotron radiation-based high-pressure X-ray diffraction is used to quantify the influence of dreierketten chain cross-linking on the anisotropic mechanical behavior of C-(A-)S-H. We show that the ab-planar stiffness is independent of dreierketten chain defects, e.g. vacancies in bridging tetrahedra sites and Al for Si substitution. The c-axis of non-cross-linked C-(A-)S-H is moremore » deformable due to the softer interlayer opening but stiffens with decreased spacing and/or increased zeolitic water and Ca 2+ of the interlayer. Dreierketten chain cross-links act as ‘columns’ to resist compression, thus increasing the bulk modulus of C-(A-)S-H. We provide the first experimental evidence on the influence of the Al-induced atomistic configurational change on the mechanical properties of C-(A-)S-H. Our work advances the fundamental knowledge of C-(A-)S-H on the lowest level of its hierarchical structure, and thus can impact the way that innovative C-(A-)S-H-based cementitious materials are developed using a ‘bottom-up’ approach.« less

CM and CO chondrites: A common parent body or asteroidal neighbors? Insights from chondrule silicates

NASA Astrophysics Data System (ADS)

Schrader, Devin L.; Davidson, Jemma

2017-10-01

By investigating the petrology and chemical composition of type II (FeO-rich) chondrules in the Mighei-like carbonaceous (CM) chondrites we constrain their thermal histories and relationship to the Ornans-like carbonaceous (CO) chondrites. We identified FeO-rich relict grains in type II chondrules by their Fe/Mn ratios; their presence indicates chondrule recycling among type II chondrules. The majority of relict grains in type II chondrules are FeO-poor olivine grains. Consistent with previous studies, chemical similarities between CM and CO chondrite chondrules indicate that they had similar formation conditions and that their parent bodies probably formed in a common region within the protoplanetary disk. However, important differences such as mean chondrule size and the lower abundance of FeO-poor relicts in CM chondrite type II chondrules than in CO chondrites suggest CM and CO chondrules did not form together and they likely originate from distinct parent asteroids. Despite being aqueously altered, many CM chondrites contain pre-accretionary anhydrous minerals (i.e., olivine) that are among the least thermally metamorphosed materials in chondrites according to the Cr2O3 content of their ferroan olivine. The presence of these minimally altered pre-accretionary chondrule silicates suggests that samples to be returned from aqueously altered asteroids by the Hayabusa2 and OSIRIS-REx asteroid sample return missions, even highly hydrated, may contain silicates that can provide information about the pre-accretionary histories and conditions of asteroids Ryugu and Bennu, respectively.

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

Cantrill, E.R.; Ray, A.; Stevens, M.G.

The interfacial bond between fiber and matrix is one of the most important factors influencing fiber-reinforced composites. This is particularly apparent in cellulose wood pulp reinforced cement/quartz composites cured by autoclaving under saturated steam at 180 C. Scanning electron microscopy (SEM) studies have shown that there is little modification of the surface of the hydrated calcium silicate matrix immediately adjacent to the cellulose fiber surface, provided the cellulose fiber is relatively free from lignin, hemicelluloses, or chemicals from the pulping process. Coutts & Campbell (1979) in their investigation of water cured cement composites, applied several commercial coupling agents to cellulosemore » fibres and established that two of these agents significantly increased the strength of the interfacial bond. In this paper, the surface of cellulose fibres was modified by sodium silicate, CTBN [carboxy terminated butadiene nitrile] and ATBN [amino terminated butadiene nitrile] in order to enhance the interfacial bond, and also to increase the resistance of the cellulose to oxidation, alkaline or thermal degradation, and algal attack. Algal attack can occur as the calcium silicate matrix is neutralized by atmospheric carbonation, especially in external wall board applications of the sheet composite. In addition, suitable coatings will protect the cellulose fiber from degradation arising from the presence of elevated temperature and alkaline solutions during the autoclaving process. Cellulose reinforced composites with substandard strengths, due to inhibited autoclave reactions, cannot be reautoclaved as the resultant material is too brittle due, in part, to the degradation of the cellulose fiber.« less

Physico-chemical characterization of mortars as a tool in studying specific hydraulic components: application to the study of ancient Naxos aqueduct

NASA Astrophysics Data System (ADS)

Maravelaki-Kalaitzaki, P.; Galanos, A.; Doganis, I.; Kallithrakas-Kontos, N.

2011-07-01

Mortars and plasters from the ancient aqueduct on the island of Naxos, Greece, were studied with regard to mineralogical and chemical composition, grain size distribution, raw materials and hydraulic properties, in order to assess their characteristics and design compatible repair mortars. The authentic materials contained lime, crushed-brick, siliceous and calcitic aggregates, in different proportions according to mortar type. Crushed-bricks fired at low temperatures and lightweight volcanic aggregates contained amorphous phases, which upon reaction with lime yielded hydraulic components capable of protecting the construction from the continuous presence of water. Hydraulic calcium silicate/aluminate hydrates, the proportions and the perfect packing of the raw materials, along with the diligent application justify the longevity and durability of the studied samples. The hydraulic properties of samples were pointed out through (a) the well-established CO2/H2O ratio derived from the thermogravimetric analysis and (b) by introducing two powerful indices issued from the chemical analysis, namely CaOhydr and soluble SiO2 hydr. These indices improved the clustering of hydraulic mortars and provided better correlation between mortars, plasters and their binders. By comparing grain size distribution and hydraulicity indices it was possible to distinguish among the construction phases. Based on this study, repair mortars were formulated by hydraulic lime, siliceous sand, calcareous and crushed-brick aggregates, with the optimal water content, ensuring optimum workability and compatible appearance with the authentic ones.

Analytical pyrolysis and stable isotope analyses reveal past environmental changes in coralloid speleothems from Easter Island (Chile).

PubMed

Miller, Ana Z; De la Rosa, José M; Jiménez-Morillo, Nicasio T; Pereira, Manuel F C; González-Pérez, José A; Calaforra, José M; Saiz-Jimenez, Cesareo

2016-08-26

This study comprises an innovative approach based on the combination of chromatography (analytical pyrolysis and pyrolysis compound-specific isotope analysis (Py-CSIA)), light stable isotopes, microscopy and mineralogy analyses to characterize the internal layering of coralloid speleothems from the Ana Heva lava tube in Easter Island (Chile). This multidisciplinary proxy showed that the speleothems consist of banded siliceous materials of low crystallinity with different mineralogical compositions and a significant contribution of organic carbon. Opal-A constitutes the outermost grey layer of the coralloids, whereas calcite and amorphous Mg hydrate silicate are the major components of the inner whitish and honey-brown layers, respectively. The differences found in the mineralogical, elemental, molecular and isotopic composition of these distinct coloured layers are related to environmental changes during speleothem development. Stable isotopes and analytical pyrolysis suggested alterations in the water regime, pointing to wetter conditions during the formation of the Ca-rich layer and a possible increase in the amount of water dripping into the cave. The trend observed for δ(15)N values suggested an increase in the average temperature over time, which is consistent with the so-called climate warming during the Holocene. The pyrolysis compound-specific isotope analysis of each speleothem layer showed a similar trend with the bulk δ(13)C values pointing to the appropriateness of direct Py-CSIA in paleoenvironmental studies. The δ(13)C values for n-alkanes reinforced the occurrence of a drastic environmental change, indicating that the outermost Opal layer was developed under drier and more arid environmental conditions. Copyright © 2016 Elsevier B.V. All rights reserved.

Lime as an Anti-Plasticizer for Self-Compacting Clay Concrete

PubMed Central

Landrou, Gnanli; Brumaud, Coralie; Winnefeld, Frank; Flatt, Robert J.; Habert, Guillaume

2016-01-01

This paper focuses on the modification of clay properties with inorganic additives to deflocculate and flocculate inorganic soil for the development of a material that would be as easy to use as the current concrete products, but with a much lower environmental impact. Considering that the rheological behaviour of clays is controlled by their surface charge, we first introduce potential determining ions to deflocculate the clay particles and to reduce the yield stress of the earth material. Their efficiency is characterized using zeta potential measurements and rheological tests. We then achieve the flocculation of clay particles by using natural minerals that slowly dissolve in the interstitial liquid and ultimately precipitate calcium silicate hydrate (C–S–H). The precipitation products are identified by X-ray diffraction and the consequences of this delayed precipitation are followed by oscillatory rheometric measurements. Finally, it is suggested that in this process, C–S–H precipitation is not used as a binding vector but as an anti-plasticizer that removes the inorganic dispersant additives. PMID:28773453

Lime as an Anti-Plasticizer for Self-Compacting Clay Concrete.

PubMed

Landrou, Gnanli; Brumaud, Coralie; Winnefeld, Frank; Flatt, Robert J; Habert, Guillaume

2016-04-29

This paper focuses on the modification of clay properties with inorganic additives to deflocculate and flocculate inorganic soil for the development of a material that would be as easy to use as the current concrete products, but with a much lower environmental impact. Considering that the rheological behaviour of clays is controlled by their surface charge, we first introduce potential determining ions to deflocculate the clay particles and to reduce the yield stress of the earth material. Their efficiency is characterized using zeta potential measurements and rheological tests. We then achieve the flocculation of clay particles by using natural minerals that slowly dissolve in the interstitial liquid and ultimately precipitate calcium silicate hydrate (C-S-H). The precipitation products are identified by X-ray diffraction and the consequences of this delayed precipitation are followed by oscillatory rheometric measurements. Finally, it is suggested that in this process, C-S-H precipitation is not used as a binding vector but as an anti-plasticizer that removes the inorganic dispersant additives.

Phenolic Modified Ceramic Coating on Biodegradable Mg Alloy: The Improved Corrosion Resistance and Osteoblast-Like Cell Activity.

PubMed

Lee, Hung-Pang; Lin, Da-Jun; Yeh, Ming-Long

2017-06-25

Magnesium alloys have great potential for developing orthopedic implants due to their biodegradability and mechanical properties, but the rapid corrosion rate of the currently-available alloys limits their clinical applications. To increase the corrosion resistance of the substrate, a protective ceramic coating is constructed by a micro-arc oxidation (MAO) process on ZK60 magnesium alloy. The porous ceramic coating is mainly composed of magnesium oxide and magnesium silicate, and the results from cell cultures show it can stimulate osteoblastic cell growth and proliferation. Moreover, gallic acid, a phenolic compound, was successfully introduced onto the MAO coating by grafting on hydrated oxide and chelating with magnesium ions. The gallic acid and rough surface of MAO altered the cell attachment behavior, making it difficult for fibroblasts to adhere to the MAO coating. The viability tests showed that gallic acid could suppress fibroblast growth and stimulate osteoblastic cell proliferation. Overall, the porous MAO coating combined with gallic acid offered a novel strategy for increasing osteocompatibility.

Phenolic Modified Ceramic Coating on Biodegradable Mg Alloy: The Improved Corrosion Resistance and Osteoblast-Like Cell Activity

PubMed Central

Lee, Hung-Pang; Lin, Da-Jun; Yeh, Ming-Long

2017-01-01

Magnesium alloys have great potential for developing orthopedic implants due to their biodegradability and mechanical properties, but the rapid corrosion rate of the currently-available alloys limits their clinical applications. To increase the corrosion resistance of the substrate, a protective ceramic coating is constructed by a micro-arc oxidation (MAO) process on ZK60 magnesium alloy. The porous ceramic coating is mainly composed of magnesium oxide and magnesium silicate, and the results from cell cultures show it can stimulate osteoblastic cell growth and proliferation. Moreover, gallic acid, a phenolic compound, was successfully introduced onto the MAO coating by grafting on hydrated oxide and chelating with magnesium ions. The gallic acid and rough surface of MAO altered the cell attachment behavior, making it difficult for fibroblasts to adhere to the MAO coating. The viability tests showed that gallic acid could suppress fibroblast growth and stimulate osteoblastic cell proliferation. Overall, the porous MAO coating combined with gallic acid offered a novel strategy for increasing osteocompatibility. PMID:28773055

Development of hydrate risk quantification in oil and gas production

NASA Astrophysics Data System (ADS)

Chaudhari, Piyush N.

Subsea flowlines that transport hydrocarbons from wellhead to the processing facility face issues from solid deposits such as hydrates, waxes, asphaltenes, etc. The solid deposits not only affect the production but also pose a safety concern; thus, flow assurance is significantly important in designing and operating subsea oil and gas production. In most subsea oil and gas operations, gas hydrates form at high pressure and low temperature conditions, causing the risk of plugging flowlines, with a undesirable impact on production. Over the years, the oil and gas industry has shifted their perspective from hydrate avoidance to hydrate management given several parameters such as production facility, production chemistry, economic and environmental concerns. Thus, understanding the level of hydrate risk associated with subsea flowlines is an important in developing efficient hydrate management techniques. In the past, hydrate formation models were developed for various flow-systems (e.g., oil dominated, water dominated, and gas dominated) present in the oil and gas production. The objective of this research is to extend the application of the present hydrate prediction models for assessing the hydrate risk associated with subsea flowlines that are prone to hydrate formation. It involves a novel approach for developing quantitative hydrate risk models based on the conceptual models built from the qualitative knowledge obtained from experimental studies. A comprehensive hydrate risk model, that ranks the hydrate risk associated with the subsea production system as a function of time, hydrates, and several other parameters, which account for inertial, viscous, interfacial forces acting on the flow-system, is developed for oil dominated and condensate systems. The hydrate plugging risk for water dominated systems is successfully modeled using The Colorado School of Mines Hydrate Flow Assurance Tool (CSMHyFAST). It is found that CSMHyFAST can be used as a screening tool in order to reduce the parametric study that may require a long duration of time using The Colorado School of Mines Hydrate Kinetic Model (CSMHyK). The evolution of the hydrate plugging risk along flowline-riser systems is modeled for steady state and transient operations considering the effect of several critical parameters such as oil-hydrate slip, duration of shut-in, and water droplet size on a subsea tieback system. This research presents a novel platform for quantification of the hydrate plugging risk, which in-turn will play an important role in improving and optimizing current hydrate management strategies. The predictive strength of the hydrate risk quantification and hydrate prediction models will have a significant impact on flow assurance engineering and design with respect to building safe and efficient hydrate management techniques for future deep-water developments.

MTA and F-doped MTA cements used as sealers with warm gutta-percha. Long-term study of sealing ability.

PubMed

Gandolfi, M G; Prati, C

2010-10-01

To evaluate the long-term sealing ability (up to 6 months) of two experimental calcium silicate MTA cements used as root canal sealers in association with warm gutta-percha. Calcium silicate (MTA) and calcium-fluoro-silicate powders were prepared. Sodium fluoride was included in FMTA (Fluoride-doped Mineral Trioxide Aggregate) as an expansive and retardant agent. Single-rooted teeth were instrumented with NiTi rotary instruments, filled with warm gutta-percha in association with one of the experimental sealers or with AH Plus as a control (n = 20 for each sealer) and stored at 37 °C. Sealing was assessed at 24, 48 h, 1, 2 weeks and 1, 3, 6 months by a fluid filtration method. Scanning electron microscopy with energy dispersive analysis (SEM/EDX) was used to study the dentine/sealer interface of roots stored for 6 months and the surface of cement disks stored for 24 h. All sealers revealed a statistically significant reduction (P < 0.05) in fluid filtration after the first 2 weeks. No statistically significant differences were observed between FMTA and AH Plus at all analysis times. At short times (24, 48-h), no statistically significant differences were found between the experimental cements and AH Plus. At long-term evaluations (1, 3, 6 months), FMTA and AH Plus sealed significantly better (P < 0.05) than MTA. FMTA was associated with lower fluid filtration rates, and the seal was stable from 48 h to 6 months, thus proving the most effective material. Scanning electron microscopy with energy dispersive analysis of root sections filled with calcium silicate sealers revealed the formation of a blend layer of gutta-percha and cement consequent to the warm gutta-percha condensation technique. Scanning electron microscopy with energy dispersive analysis of 24-h-stored disks identified a Ca-rich coating on the outer surface consisting of globular particles (calcium hydroxide and calcium carbonate), and a deeper internal Ca- and Si-rich region consisting of needle-like ettringite crystals and round formations of calcium silicate hydrate gel. Fluoride-doped MTA demonstrated stable sealing during a period of up to 6 months and significantly better than conventional calcium silicate MTA cements and comparable to AH Plus. The study supports the suitability of calcium silicate MTA cements as sealers in association with warm gutta-percha for root filling. © 2010 International Endodontic Journal.

Effect of Material Ion Exchanges on the Mechanical Stiffness Properties and Shear Deformation of Hydrated Cement Material Chemistry Structure C-S-H Jennite -- A Computational Modeling Study

NASA Astrophysics Data System (ADS)

Adebiyi, Babatunde Mattew

Material properties and performance are governed by material molecular chemistry structures and molecular level interactions. Methods to understand relationships between the material properties and performance and their correlation to the molecular level chemistry and morphology, and thus find ways of manipulating and adjusting matters at the atomistic level in order to improve material performance, are required. A computational material modeling methodology is investigated and demonstrated for a key cement hydrated component material chemistry structure of Calcium-Silicate-Hydrate (C-S-H) Jennite in this work. The effect of material ion exchanges on the mechanical stiffness properties and shear deformation behavior of hydrated cement material chemistry structure of Calcium Silicate Hydrate (C-S-H) Jennite was studied. Calcium ions were replaced with Magnesium ions in Jennite structure of the C-S-H gel. Different level of substitution of the ions was used. The traditional Jennite structure was obtained from the American Mineralogist Crystal Structure Database and super cells of the structures were created using a Molecular Dynamics Analyzer and Visualizer Material Studio. Molecular dynamics parameters used in the modeling analysis were determined by carrying out initial dynamic studies. 64 unit cell of C-S-H Jennite was used in material modeling analysis studies based on convergence results obtained from the elastic modulus and total energies. NVT forcite dynamics using COMPASS force field based on 200 ps dynamics time was used to determine mechanical modulus of the traditional C-S-H gel and the Magnesium ion modified structures. NVT Discover dynamics using COMPASS forcefield was used in the material modeling studies to investigate the influence of ionic exchange on the shear deformation of the associated material chemistry structures. A prior established quasi-static deformation method to emulate shear deformation of C-S-H material chemistry structure that is based on a triclinic crystal structure was used, by deforming the triclinic crystal structure at 0.2 degree per time step for 75 steps of deformation. It was observed that there is a decrease in the total energies of the systems as the percentage of magnesium ion increases in the C-S-H Jennite molecular structure systems. Investigation of effect of ion exchange on the elastic modulus shows that the elastic stiffness modulus tends to decrease as the amount of Mg in the systems increases, using either COMPASS or universal force field. On the other hand, shear moduli obtained after deforming the structures computed from the stress-strain curve obtained from material modeling increases as the amount of Mg increases in the system. The present investigations also showed that ultimate shear stress obtained from predicted shear stress---strain also increases with amount of Mg in the chemistry structure. Present study clearly demonstrates that computational material modeling following molecular dynamics analysis methodology is an effective way to predict and understand the effective material chemistry and additive changes on the stiffness and deformation characteristics in cementitious materials, and the results suggest that this method can be extended to other materials.

Presolar silicates in the matrix and fine-grained rims around chondrules in primitive CO3.0 chondrites: Evidence for pre-accretionary aqueous alteration of the rims in the solar nebula

NASA Astrophysics Data System (ADS)

Haenecour, Pierre; Floss, Christine; Zega, Thomas J.; Croat, Thomas K.; Wang, Alian; Jolliff, Bradley L.; Carpenter, Paul

2018-01-01

To investigate the origin of fine-grained rims around chondrules (FGRs), we compared presolar grain abundances, elemental compositions and mineralogies in fine-grained interstitial matrix material and individual FGRs in the primitive CO3.0 chondrites Allan Hills A77307, LaPaz Icefield 031117 and Dominion Range 08006. The observation of similar overall O-anomalous (∼155 ppm) and C-anomalous grain abundances (∼40 ppm) in all three CO3.0 chondrites suggests that they all accreted from a nebular reservoir with similar presolar grain abundances. The presence of presolar silicate grains in FGRs combined with the observation of similar estimated porosity between interstitial matrix regions and FGRs in LAP 031117 and ALHA77307, as well as the identification of a composite FGR (a small rimmed chondrule within a larger chondrule rim) in ALHA77307, all provide evidence for a formation of FGRs by accretion of dust grains onto freely-floating chondrules in the solar nebula before their aggregation into their parent body asteroids. Our study also shows systematically lower abundances of presolar silicate grains in the FGRs than in the matrix regions of CO3 chondrites, while the abundances of SiC grains are the same in all areas, within errors. This trend differs from CR2 chondrites in which the presolar silicate abundances are higher in the FGRs than in the matrix, but similar to each other within 2σ errors. This observation combined with the identification of localized (micrometer-scaled) aqueous alteration in a FGR of LAP 031117 suggests that the lower abundance of presolar silicates in FGRs reflects pre-accretionary aqueous alteration of the fine-grained material in the FGRs. This pre-accretionary alteration could be due to either hydration and heating of freely floating rimmed chondrules in icy regions of the solar nebula or melted water ice associated with 26Al-related heating inside precursor planetesimals, followed by aggregation of FGRs into the CO chondrite parent-body.

The Origin of Chondrites: Metal-Silicate Separation Experiments Under Microgravity Conditions, Experiment 2

NASA Technical Reports Server (NTRS)

Moore, S. R.; Franzen, M.; Benoit, P. H.; Sears, D. W. G.; Holley, A.; Myers, M.; Godsey, R.; Czlapinski, J.

2003-01-01

Chondrites are categorized into different groups by several properties, including the metal-to-silicate ratio. Various processes have been suggested to produce distinct metal/silicate ratios, some based on sorting in the early solar nebular and others occurring after accretion on the parent body. Huang et al. suggested that a weak gravitational field accompanied by degassing, could result in metal/silicate separation on parent bodies. We suggest that asteroids were volatile-rich, at least early in their histories. Spectroscopic evidence from asteroid surfaces indicates that one-third of all asteroids maybe rich in clays and hydrated minerals, similar to carbonaceous chondrites. Internal and/or external heating could have caused volatiles to evaporate and pass through a surface dust layer. Spacecraft images of asteroids show they have a thick regoliths. Housen, and Asphaug and Nolan proposed that even a 10 km diameter asteroid could potentially have a significant regolith. Grain size and grain density sorting could occur in the unconsolidated layer by the process known as fluidization. This process occurs when an upward stream of gas is passed through a bed of particles which are lifted against a gravitational force. Fluidization is commonly used commercially to sort particulates. This type of behavior is based upon the bed, as a whole, and differs from aerodynamic sorting. Two sets of reduced gravity experiments were conducted during parabolic flights aboard NASA's KC-135 aircraft. The first experiment employed 310 tubes of 2.5 cm diameter, containing mixtures of sand and metal grains. A gas source was used to fluidize the mixture at reduced gravity conditions and mixtures were analyzed after the flight. However, this experiment did not allow a description of the fluidization as a function of gravity. A second experiment was conducted on the KC-135 aircraft in the summer of 2001, consisting of two Plexiglas cylinders containing a metal/silicate mixture, and video cameras to record the experiment on tape. Here we summarize this experiment and discusses the implications for metalsilicate separation on asteroid bodies.

Green remediation and recycling of contaminated sediment by waste-incorporated stabilization/solidification.

PubMed

Wang, Lei; Tsang, Daniel C W; Poon, Chi-Sun

2015-03-01

Navigational/environmental dredging of contaminated sediment conventionally requires contained marine disposal and continuous monitoring. This study proposed a green remediation approach to treat and recycle the contaminated sediment by means of stabilization/solidification enhanced by the addition of selected solid wastes. With an increasing amount of contaminated sediment (20-70%), the 28-d compressive strength of sediment blocks decreased from greater than 10MPa to slightly above 1MPa. For augmenting the cement hydration, coal fly ash was more effective than lime and ground seashells, especially at low sediment content. The microscopic and spectroscopic analyses showed varying amounts of hydration products (primarily calcium hydroxide and calcium silicate hydrate) in the presence of coal fly ash, signifying the influence of pozzolanic reaction. To facilitate the waste utilization, cullet from beverage glass bottles and bottom ashes from coal combustion and waste incineration were found suitable to substitute coarse aggregate at 33% replacement ratio, beyond which the compressive strength decreased accordingly. The mercury intrusion porosimetry analysis indicated that the increase in the total pore area and average pore diameter were linearly correlated with the decrease of compressive strength due to waste replacement. All the sediment blocks complied with the acceptance criteria for reuse in terms of metal leachability. These results suggest that, with an appropriate mixture design, contaminated sediment and waste materials are useful resources for producing non-load-bearing masonry units or fill materials for construction uses. Copyright © 2014 Elsevier Ltd. All rights reserved.

Infrared and Raman spectroscopic studies of structural variations in minerals from Apollo 11, 12, 14 and 15 samples, volume 3

NASA Technical Reports Server (NTRS)

Estep, P. A.; Kovach, J. J.; Waldstein, P.; Karr, C., Jr.

1972-01-01

Infrared and Raman vibrational spectroscopic data, yielding direct information on molecular structure, were obtained for single grains ( 150 microns) of minerals, basalts, and glasses isolated from Apollo 11, 12, 14, and 15 rock and dust samples, and for grains in Apollo 14 polished butt samples. From the vibrational data, specification substitutions were determined for the predominant silicate minerals of plagioclase, pyroxene, and olivine. Unique spectral variations for grains of K-feldspar, orthopyroxene, pyroxenoid, and ilmenite were observed to exceed the ranges of terrestrial samples, and these variations may be correlatable with formation histories. Alpha-quartz was isolated as pure single grains, in granitic grains composited with sanidine, and in unique grains that were intimately mixed with varying amounts of glass. Accessory minerals of chromite and ulvospinel were isolated as pure grains and structurally characterized from their distinctive infrared spectra. Fundamental vibrations of the SiO4 tetrahedra in silicate minerals were used to classify bulk compositions in dust sieved fractions, basalt grains and glass particles, and to compare modal characteristics for maria, highland and rille samples. No hydrated minerals were found in any of the samples studied, indicating anhydrous formation conditions.

Utilization of Mineral Wools as Alkali-Activated Material Precursor

PubMed Central

Yliniemi, Juho; Kinnunen, Paivo; Karinkanta, Pasi; Illikainen, Mirja

2016-01-01

Mineral wools are the most common insulation materials in buildings worldwide. However, mineral wool waste is often considered unrecyclable because of its fibrous nature and low density. In this paper, rock wool (RW) and glass wool (GW) were studied as alkali-activated material precursors without any additional co-binders. Both mineral wools were pulverized by a vibratory disc mill in order to remove the fibrous nature of the material. The pulverized mineral wools were then alkali-activated with a sodium aluminate solution. Compressive strengths of up to 30.0 MPa and 48.7 MPa were measured for RW and GW, respectively, with high flexural strengths measured for both (20.1 MPa for RW and 13.2 MPa for GW). The resulting alkali-activated matrix was a composite-type in which partly-dissolved fibers were dispersed. In addition to the amorphous material, sodium aluminate silicate hydroxide hydrate and magnesium aluminum hydroxide carbonate phases were identified in the alkali-activated RW samples. The only crystalline phase in the GW samples was sodium aluminum silicate. The results of this study show that mineral wool is a very promising raw material for alkali activation. PMID:28773435

β-Dicalcium silicate-based cement: synthesis, characterization and in vitro bioactivity and biocompatibility studies.

PubMed

Correa, Daniel; Almirall, Amisel; García-Carrodeguas, Raúl; dos Santos, Luis Alberto; De Aza, Antonio H; Parra, Juan; Delgado, José Ángel

2014-10-01

β-dicalcium silicate (β-Ca₂ SiO₄, β-C₂ S) is one of the main constituents in Portland cement clinker and many refractory materials, itself is a hydraulic cement that reacts with water or aqueous solution at room/body temperature to form a hydrated phase (C-S-H), which provides mechanical strength to the end product. In the present investigation, β-C₂ S was synthesized by sol-gel process and it was used as powder to cement preparation, named CSiC. In vitro bioactivity and biocompatibility studies were assessed by soaking the cement samples in simulated body fluid solutions and human osteoblast cell cultures for various time periods, respectively. The results showed that the sol-gel process is an available synthesis method in order to obtain a pure powder of β-C₂ S at relatively low temperatures without chemical stabilizers. A bone-like apatite layer covered the material surface after soaking in SBF and its compressive strength (CSiC cement) was comparable with that of the human trabecular bone. The extracts of this cement were not cytotoxic and the cell growth and relative cell viability were comparable to negative control. © 2013 Wiley Periodicals, Inc.

Methane hydrates in nature - Current knowledge and challenges

USGS Publications Warehouse

Collett, Timothy S.

2014-01-01

Recognizing the importance of methane hydrate research and the need for a coordinated effort, the United States Congress enacted the Methane Hydrate Research and Development Act of 2000. At the same time, the Ministry of International Trade and Industry in Japan launched a research program to develop plans for a methane hydrate exploratory drilling project in the Nankai Trough. India, China, the Republic of Korea, and other nations also have established large methane hydrate research and development programs. Government-funded scientific research drilling expeditions and production test studies have provided a wealth of information on the occurrence of methane hydrates in nature. Numerous studies have shown that the amount of gas stored as methane hydrates in the world may exceed the volume of known organic carbon sources. However, methane hydrates represent both a scientific and technical challenge, and much remains to be learned about their characteristics and occurrence in nature. Methane hydrate research in recent years has mostly focused on: (1) documenting the geologic parameters that control the occurrence and stability of methane hydrates in nature, (2) assessing the volume of natural gas stored within various methane hydrate accumulations, (3) analyzing the production response and characteristics of methane hydrates, (4) identifying and predicting natural and induced environmental and climate impacts of natural methane hydrates, (5) analyzing the methane hydrate role as a geohazard, (6) establishing the means to detect and characterize methane hydrate accumulations using geologic and geophysical data, and (7) establishing the thermodynamic phase equilibrium properties of methane hydrates as a function of temperature, pressure, and gas composition. The U.S. Department of Energy (DOE) and the Consortium for Ocean Leadership (COL) combined their efforts in 2012 to assess the contributions that scientific drilling has made and could continue to make to advance our understanding of methane hydrates in nature. COL assembled a Methane Hydrate Project Science Team with members from academia, industry, and government. This Science Team worked with COL and DOE to develop and host the Methane Hydrate Community Workshop, which surveyed a substantial cross section of the methane hydrate research community for input on the most important research developments in our understanding of methane hydrates in nature and their potential role as an energy resource, a geohazard, and/or as an agent of global climate change. Our understanding of how methane hydrates occur in nature is still growing and evolving, and it is known with certainty that field, laboratory, and modeling studies have contributed greatly to our understanding of hydrates in nature and will continue to be a critical source of the information needed to advance our understanding of methane hydrates.

Applications for special-purpose minerals at a lunar base

NASA Technical Reports Server (NTRS)

Ming, Douglas W.

1992-01-01

Maintaining a colony on the Moon will require the use of lunar resources to reduce the number of launches necessary to transport goods from the Earth. It may be possible to alter lunar materials to produce minerals or other materials that can be used for applications in life support systems at a lunar base. For example, mild hydrothermal alteration of lunar basaltic glasses can produce special-purpose minerals (e.g., zeolites, smectites, and tobermorites) that in turn may be used in life support, construction, waste renovation, and chemical processes. Zeolites, smectites, and tobermorites have a number of potential applications at a lunar base. Zeolites are hydrated aluminosilicates of alkali and alkaline earth cations that possess infinite, three-dimensional crystal structures. They are further characterized by an ability to hydrate and dehydrate reversibly and to exchange some of their constituent cations, both without major change of structure. Based on their unique absorption, cation exchange, molecular sieving, and catalytic properties, zeolites may be used as a solid support medium for the growth of plants, as an adsorption medium for separation of various gases (e.g., N2 from O2), as catalysts, as molecular sieves, and as a cation exchanger in sewage-effluent treatment, in radioactive waste disposal, and in pollution control. Smectites are crystalline, hydrated 2:1 layered aluminosilicates that also have the ability to exchange some of their constituent cations. Like zeolites, smectites may be used as an adsorption medium for waste renovation, as adsorption sites for important essential plant growth cations in solid support plant growth mediums (i.e., 'soils'), as cation exchangers, and in other important application. Tobermorites are cystalline, hydrated single-chained layered silicates that have cation-exchange and selectivity properties between those of smectites and most zeolites. Tobermorites may be used as a cement in building lunar base structures, as catalysts, as media for nuclear and hazardous waste disposal, as exchange media for waste-water treatment, and in other potential applications. Special-purpose minerals synthesized at a lunar base may also have important applications at a space station and for other planetary missions. New technologies will be required at a lunar base to develop life support systems that are self-sufficient, and the use of special-purpose minerals may help achieve this self-sufficiency.

IN SITU INFRARED MEASUREMENTS OF FREE-FLYING SILICATE DURING CONDENSATION IN THE LABORATORY

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

Ishizuka, Shinnosuke; Kimura, Yuki; Sakon, Itsuki

2015-04-20

We developed a new experimental system for infrared (IR) measurements on free-flying nucleating nanoparticles in situ and applied it to studies on silicate particles. We monitored the condensation of magnesium-bearing silicate nanoparticles from thermally evaporated magnesium and silicon monoxide vapor under an atmosphere of oxygen and argon. The IR spectrum of newly condensed particles showed a spectral feature for non-crystalline magnesium-bearing silicate that is remarkably consistent with the IR spectrum of astronomically observed non-crystalline silicate around oxygen-rich evolved stars. The silicate crystallized at <500 K and eventually developed a high crystallinity. Because of the size effects of nanoparticles, the silicatemore » would be expected to be like a liquid at least during the initial stages of nucleation and growth. Our experimental results therefore suggest decreasing the possible formation temperature of crystalline silicates in dust formation environments with relatively higher pressure.« less

Transformation of meta-stable calcium silicate hydrates to tobermorite: reaction kinetics and molecular structure from XRD and NMR spectroscopy

PubMed Central

2009-01-01

Understanding the integrity of well-bore systems that are lined with Portland-based cements is critical to the successful storage of sequestered CO2 in gas and oil reservoirs. As a first step, we investigate reaction rates and mechanistic pathways for cement mineral growth in the absence of CO2 by coupling water chemistry with XRD and NMR spectroscopic data. We find that semi-crystalline calcium (alumino-)silicate hydrate (Al-CSH) forms as a precursor solid to the cement mineral tobermorite. Rate constants for tobermorite growth were found to be k = 0.6 (± 0.1) × 10-5 s-1 for a solution:solid of 10:1 and 1.6 (± 0.8) × 10-4 s-1 for a solution:solid of 5:1 (batch mode; T = 150°C). This data indicates that reaction rates for tobermorite growth are faster when the solution volume is reduced by half, suggesting that rates are dependent on solution saturation and that the Gibbs free energy is the reaction driver. However, calculated solution saturation indexes for Al-CSH and tobermorite differ by less than one log unit, which is within the measured uncertainty. Based on this data, we consider both heterogeneous nucleation as the thermodynamic driver and internal restructuring as possible mechanistic pathways for growth. We also use NMR spectroscopy to characterize the site symmetry and bonding environment of Al and Si in a reacted tobermorite sample. We find two [4]Al coordination structures at δiso = 59.9 ppm and 66.3 ppm with quadrupolar product parameters (PQ) of 0.21 MHz and 0.10 MHz (± 0.08) from 27Al 3Q-MAS NMR and speculate on the Al occupancy of framework sites by probing the protonation environment of Al metal centers using 27Al{1H}CP-MAS NMR. PMID:19144195

Dynamic behaviors of water contained in calcium-silicate-hydrate gel at different temperatures studied by quasi-elastic neutron scattering spectroscopy

NASA Astrophysics Data System (ADS)

Yi, Zhou; Deng, Pei-Na; Zhang, Li-Li; Li, Hua

2016-10-01

The dynamic behaviors of water contained in calcium-silicate-hydrate (C-S-H) gel with different water content values from 10% to 30% (by weight), are studied by using an empirical diffusion model (EDM) to analyze the experimental data of quasi-elastic neutron scattering (QENS) spectra at measured temperatures ranging from 230 K to 280 K. In the study, the experimental QENS spectra with the whole Q-range are considered. Several important parameters including the bound/immobile water elastic coefficient A, the bound water index BWI, the Lorentzian with a half-width at half-maximum (HWHM) Γ 1(Q) and Γ 2(Q), the self-diffusion coefficients D t1 and D t2 of water molecules, the average residence times τ 01 and τ 02, and the proton mean squared displacement (MSD) are obtained. The results show that the QENS spectra can be fitted very well not only for small Q (≤ 1 Å-1) but also for large Q. The bound/immobile water fraction in a C-S-H gel sample can be shown by the fitted BWI. The distinction between bound/immobile and mobile water, which includes confined water and ultra-confined water, can be seen by the fitted MSD. All the MSD tend to be the smallest value below 0.25 Å2 (the MSD of bound/immobile water) as the Q increases to 1.9 Å-1, no matter what the temperature and water content are. Furthermore, by the abrupt changes of the fitted values of D t1, τ 01, and Γ 1(Q), a crossover temperature at 250 K, namely the liquid-to-crystal-like transition temperature, can be identified for confined water in large gel pores (LGPs) and/or small gel pores (SGPs) contained in the C-S-H gel sample with 30% water content.