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1

Crystal lattice tilting in prismatic calcite.  

PubMed

We analyzed the calcitic prismatic layers in Atrina rigida (Ar), Haliotis iris (Hi), Haliotis laevigata (HL), Haliotis rufescens (Hrf), Mytilus californianus (Mc), Pinctada fucata (Pf), Pinctada margaritifera (Pm) shells, and the aragonitic prismatic layer in the Nautilus pompilius (Np) shell. Dramatic structural differences were observed across species, with 100-?m wide single-crystalline prisms in Hi, HL and Hrf, 1-?m wide needle-shaped calcite prisms in Mc, 1-?m wide spherulitic aragonite prisms in Np, 20-?m wide single-crystalline calcite prisms in Ar, and 20-?m wide polycrystalline calcite prisms in Pf and Pm. The calcite prisms in Pf and Pm are subdivided into sub-prismatic domains of orientations, and within each of these domains the calcite crystal lattice tilts gradually over long distances, on the order of 100 ?m, with an angle spread of crystal orientation of 10-20°. Furthermore, prisms in Pf and Pm are harder than in any other calcite prisms analyzed, their nanoparticles are smaller, and the angle spread is strongly correlated with hardness in all shells that form calcitic prismatic layers. One can hypothesize a causal relationship of these correlated parameters: greater angle spread may confer greater hardness and resistance to wear, thus providing Pf and Pm with a structural advantage in their environment. This is the first structure-property relationship thus far hypothesized in mollusk shell prisms. PMID:23806677

Olson, Ian C; Metzler, Rebecca A; Tamura, Nobumichi; Kunz, Martin; Killian, Christopher E; Gilbert, Pupa U P A

2013-08-01

2

Crystal growth of calcite from calcium bicarbonate solutions at constant PCO2 and 25??C: a test of a calcite dissolution model  

USGS Publications Warehouse

A highly reproducible seeded growth technique was used to study calcite crystallization from calcium bicarbonate solutions at 25??C and fixed carbon dioxide partial pressures between 0.03 and 0.3 atm. The results are not consistent with empirical crystallization models that have successfully described calcite growth at low PCO2 (< 10-3 atm). Good agreement was found between observed crystallization rates and those calculated from the calcite dissolution rate law and mechanism proposed by Plummer et al. (1978). ?? 1981.

Reddy, M. M.; Plummer, L. N.; Busenberg, E.

1981-01-01

3

Visualization of acoustic cavitation effects on suspended calcite crystals.  

PubMed

The acoustic cavitation (42,080 Hz, 7.1 W cm(-2) or 17 W) effects on suspended calcite crystals, sized between 5 and 50 ?m, have been visualized for the first time using high speed photography. High speed recordings with a duration of 1 s containing up to 300,000 frames per second, revealed the effect of cluster and streamer cavitation on several calcite crystals. Cavitation clusters, evolved from cavitation inception and collapse, caused attrition, disruption of aggregates and deagglomeration, whereas streamer cavitation was observed to cause deagglomeration only. Cavitation on the surface gave the crystals momentum. However, it is shown that breakage of accelerated crystals by interparticle collisions is unrealistic because of their small sizes and low velocities. Crystals that were accelerated by bubble expansion, subsequently experienced a deceleration much stronger than expected from drag forces, upon bubble collapse. Experiments with pre-dried crystals seemed to support the current theory on bubble nucleation through the presence of pre-existing gas pockets. However, experiments with fully wetted crystals also showed the nucleation of bubbles on the crystal surface. Although microjet impingement on the crystal surface could not be directly visualized with high speed photography, scanning electron microscopy (SEM) analysis of irradiated calcite seeds showed deep circular indentations. It was suggested that these indentations might be caused by shockwave induced jet impingement. Furthermore, the appearance of voluminous fragments with large planes of fracture indicated that acoustic cavitation can also cause the breakage of single crystal structures. PMID:20579928

Wagterveld, R M; Boels, L; Mayer, M J; Witkamp, G J

2011-01-01

4

Calcite mesocrystals: "morphing" crystals by a polyelectrolyte.  

PubMed

Crystallization of calcite from different concentrated calcium chloride solutions by the CO(2) vapor diffusion technique in the presence of polystyrenesulfonate (PSS) yields defined assemblies of nanoparticles with unusual morphology. From the typical calcite rhombohedra, the morphology can be systematically varied via rounded edges and truncated triangles to concavely bent lens-like shapes. Although these "crystals" are apparently well facetted as observed in light microscopy, electron microscopy analysis and BET isotherms reveal that the structures are highly porous and are composed of almost perfectly three-dimensionally aligned calcite nanocrystals, scaffolded to the final, partly curved structures. The formation of all mesostructures is discussed within the framework of a polymer-mediated structure-formation process, in which the polymer is acting in four different ways. The present model case also provides evidence for the importance of nonclassical mesoscopic processes in polymer-controlled crystallization in general. PMID:16800016

Wang, Tongxin; Antonietti, Markus; Cölfen, Helmut

2006-07-24

5

Hydroxyapatite synthesis from biogenic calcite single crystals into phosphate solutions at ambient conditions  

NASA Astrophysics Data System (ADS)

Hydroxyapatite is one of the most important bone substitute biomaterials. Here, it has been successfully overgrown on biogenic seed crystals at ambient conditions. Single crystals of calcite from Atrina rigida, Paracentrotus lividus and Heterocentrotus mammillatus have been soaked in phosphate solution with different concentrations and pHs for 2 months. X-ray powder diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy have been used to characterize soaking precipitates. The results show that the conversion of calcite to hydroxyapatite occurs to an extent which depends on composition and morphology of seed crystals, and starting concentration and pH of phosphate solutions. In the same experimental conditions, synthetic calcite single crystals did not convert to hydroxyapatite. The morphological observations suggest for hydroxyapatite formation, a mechanism that involves a superficial dissolution of calcite and a subsequently overgrowth of hydroxyapatite. Moreover, the final architectural assembly of the hydroxyapatite crystals resembles the shape of the starting biogenic seed crystals.

Marchegiani, Francesca; Cibej, Eleonora; Vergni, Patrizia; Tosi, Giovanna; Fermani, Simona; Falini, Giuseppe

2009-08-01

6

Dependence of calcite growth rate and Sr partitioning on solution stoichiometry: Non-Kossel crystal growth  

Microsoft Academic Search

Seeded calcite growth experiments were conducted at fixed pH (10.2) and two degrees of supersaturation (?=5, 16), while varying the Ca2+ to CO32- solution ratio over several orders of magnitude. The calcite growth rate and the incorporation of Sr in the growing crystals strongly depended on the solution stoichiometry. At a constant degree of supersaturation, the growth rate was highest

G. Nehrke; G.-J. Reichart; P. Van Cappellen; C. Meile; J. Bijma

2007-01-01

7

Calcite Crystal Growth Rate Inhibition by Polycarboxylic Acids  

Microsoft Academic Search

Calcite crystal growth rates measured in the presence of several polycarboxyclic acids show that tetrahydrofurantetracarboxylic acid (THFTCA) and cyclopentanetetracarboxylic acid (CPTCA) are effective growth rate inhibitors at low solution concentrations (0.01 to 1 mg\\/L). In contrast, linear polycarbocylic acids (citric acid and tricarballylic acid) had no inhibiting effect on calcite growth rates at concentrations up to 10 mg\\/L. Calcite crystal

Michael M. Reddy; Anthony R. Hoch

2001-01-01

8

Calcite microneedle arrays produced by inorganic ion-assisted anisotropic dissolution of bulk calcite crystal.  

PubMed

Besides studies on the mineralization process, research on the demineralization of minerals provides another way to understand the crystallization mechanism of biominerals and fabricate crystals with complicated morphologies. The formation of ordered arrays of c-axis-oriented calcite microneedles with a tri-symmetric structure and lengths of more than 20??m was realized on a large scale for the first time through anisotropic dissolution of calcite substrates in undersaturated aqueous solution in the presence of ammonium salts. The lengths and the aspect ratios of the calcite microneedles can be tuned by simply changing the concentrations of the ammonium salts and the dissolution time. The shape of the transverse cross sections of the calcite microneedles obtained in the presence of NH4 Cl and NH4 Ac is almost regularly triangular. The tri-symmetric transverse cross-section geometry of the calcite microneedles could be attributed to the tri-symmetric feature of rhombohedral calcite atomic structures, the synergetic interactions between electrostatic interaction of ammonium ions and dangling surface carbonate groups, and the ion incorporation of halide ions. PMID:24644237

Long, Xia; Meng, Ruijie; Wu, Weike; Ma, Yurong; Yang, Dong; Qi, Limin

2014-04-01

9

Calcite crystal growth rate inhibition by polycarboxylic acids  

USGS Publications Warehouse

Calcite crystal growth rates measured in the presence of several polycarboxyclic acids show that tetrahydrofurantetracarboxylic acid (THFTCA) and cyclopentanetetracarboxylic acid (CPTCA) are effective growth rate inhibitors at low solution concentrations (0.01 to 1 mg/L). In contrast, linear polycarbocylic acids (citric acid and tricarballylic acid) had no inhibiting effect on calcite growth rates at concentrations up to 10 mg/L. Calcite crystal growth rate inhibition by cyclic polycarboxyclic acids appears to involve blockage of crystal growth sites on the mineral surface by several carboxylate groups. Growth morphology varied for growth in the absence and in the presence of both THFTCA and CPTCA. More effective growth rate reduction by CPTCA relative to THFTCA suggests that inhibitor carboxylate stereochemical orientation controls calcite surface interaction with carboxylate inhibitors. ?? 20O1 Academic Press.

Reddy, M. M.; Hoch, A. R.

2001-01-01

10

Molecular Expressions: Optical Microscopy Primer - Birefringence in Calcite Crystals  

NSDL National Science Digital Library

This item is an interactive Java simulation for students of introductory physics or optics relating to birefringence. It features a virtual calcite crystal superimposed over the word "Birefringence". Due to the refractive properties of this type of crystal, the letters appear as a ghosted double image. The user can rotate the crystal and the polarizer to alter the transmission axis. This item is part of a larger collection of materials on introductory optics developed by the National High Magnetic Field Laboratory.

Davidson, Michael; Parry-Hill, Matthew J.; Murphy, Douglas B.; Spring, Kenneth R.; Long, John

2008-08-23

11

Electrical conduction and polarization of calcite single crystals  

NASA Astrophysics Data System (ADS)

The electrical conductivity and polarization properties of calcite single crystals with three orientations, namely, a (00.1) plane perpendicular to the crystallographic c axis (10.0) plane parallel to the crystallographic c axis, and a (10.4) cleavage plane, were studied by both complex impedance and thermally stimulated depolarization current (TSDC) measurements. Conductivities for (00.1)-, (10.0)-, and (10.4)-oriented single calcite crystals at 400-600 °C were 1.16 × 10-7 - 1.05 × 10-5, 7.40 × 10-8 - 4.27 × 10-6, and 4.27 × 10-7 - 2.86 × 10-5 ?-1 m-1, respectively, and the activation energies for conduction were 112, 103, and 101 kJ mol-1, respectively. The TSDC spectra verified the electrical polarizability of calcite crystals. The activation energy for depolarization, estimated from TSDC spectra, of the (00.1)-, (10.0)-, and (10.4)-oriented calcite substrates were 112, 119, and 114 kJ mol-1, respectively. Considering the correlation between the processes of conduction and electric polarization, we proposed the mechanisms of conduction and polarization in calcite on the assumption of oxide ion transport.

Wada, Norio; Horiuchi, Naohiro; Wang, Wei; Hiyama, Tetsuo; Nakamura, Miho; Nagai, Akiko; Yamashita, Kimihiro

2012-10-01

12

Simulations of calcite crystallization on self-assembled monolayers.  

PubMed

This paper presents simulations of calcium carbonate ordering in contact with self-assembled monolayers. The calculations use potential-based molecular dynamics to model the crystallization of calcium carbonate to calcite expressing both the (00.1) and (01.2) surfaces. The effect of monolayer properties: ionization; epitaxial matching; charge density; and headgroup orientation on the crystallization process are examined in detail. The results demonstrate that highly charged surfaces are vital to stimulate ordering and crystallization. Template directed crystallization requires charge epitaxy between both the crystal surface and the monolayer. The orientation of the headgroup appears to make no contribution to the selection of the crystal surface. PMID:18672912

Freeman, Colin L; Harding, John H; Duffy, Dorothy M

2008-09-01

13

A mechanistic model for calcite crystal growth using surface speciation  

NASA Astrophysics Data System (ADS)

A new mechanistic model for the crystal growth kinetics of calcite is presented, accounting for the presence of various surface complexes. Calcite crystal growth rates were determined with the constant composition method at ? c (calcite supersaturation) values of 1.5-9.8. In general the rate increases with ? c, but variations in CO 2 partial pressures and the (CO 32-)/(Ca 2+) ratio also have a major effect on the crystal growth rate. These effects are eliminated by assuming that calcite crystal growth proceeds through three reversible reactions, in which CaCO 30(aq) and Ca 2+(aq) are incorporated at specific surface complexes. The model derived rates closely follow the experimental rates over the entire experimental range ( r = 0.996, n = 23). The obtained rate constants indicate that CaCO 30(aq) is ?20 times more reactive than Ca 2+(aq) at the calcite-water interface. This agrees with the fact that dehydration of metal ions precedes crystal growth and, in analogy with other metal-ligand complexes, the CO 32- ligand will increase the rate of water exchange of Ca. This model is a modified version of a rhodochrosite crystal growth model (Sternbeck, 1997) which allows for the comparison of reaction mechanisms and rate constants. The rate constants for incorporation of CaCO 30(aq) at the mineral surface are 55 to 270 times higher than for MnCO 30(aq). This difference can not likely be explained by the water exchange rates, but may be due to the fact that ligand exchange mechanisms for Ca and Mn differ.

Nilsson, Ö.; Sternbeck, J.

1999-01-01

14

Crystallographic orientation inhomogeneity and crystal splitting in biogenic calcite.  

PubMed

The calcitic prismatic units forming the outer shell of the bivalve Pinctada margaritifera have been analysed using scanning electron microscopy-electron back-scatter diffraction, transmission electron microscopy and atomic force microscopy. In the initial stages of growth, the individual prismatic units are single crystals. Their crystalline orientation is not consistent but rather changes gradually during growth. The gradients in crystallographic orientation occur mainly in a direction parallel to the long axis of the prism, i.e. perpendicular to the shell surface and do not show preferential tilting along any of the calcite lattice axes. At a certain growth stage, gradients begin to spread and diverge, implying that the prismatic units split into several crystalline domains. In this way, a branched crystal, in which the ends of the branches are independent crystalline domains, is formed. At the nanometre scale, the material is composed of slightly misoriented domains, which are separated by planes approximately perpendicular to the c-axis. Orientational gradients and splitting processes are described in biocrystals for the first time and are undoubtedly related to the high content of intracrystalline organic molecules, although the way in which these act to induce the observed crystalline patterns is a matter of future research. PMID:23804442

Checa, Antonio G; Bonarski, Jan T; Willinger, Marc G; Faryna, Marek; Berent, Katarzyna; Kania, Bogusz; González-Segura, Alicia; Pina, Carlos M; Pospiech, Jan; Morawiec, Adam

2013-09-01

15

Growth modification of seeded calcite using carboxylic acids: atomistic simulations.  

PubMed

Molecular dynamics simulations were used to investigate possible explanations for experimentally observed differences in the growth modification of calcite particles by two organic additives, polyacrylic acid (PAA) and polyaspartic acid (p-ASP). The more rigid backbone of p-ASP was found to inhibit the formation of stable complexes with counter-ions in solution, resulting in a higher availability of p-ASP compared to PAA for surface adsorption. Furthermore the presence of nitrogen on the p-ASP backbone yields favorable electrostatic interactions with the surface, resulting in negative adsorption energies, in an upright (brush conformation). This leads to a more rapid binding and longer residence times at calcite surfaces compared to PAA, which adsorbed in a flat (pancake) configuration with positive adsorption energies. The PAA adsorption occurring despite this positive energy difference can be attributed to the disruption of the ordered water layer seen in the simulations and hence a significant entropic contribution to the adsorption free energy. These findings help explain the stronger inhibiting effect on calcite growth observed by p-ASP compared to PAA and can be used as guidelines in the design of additives leading to even more marked growth modifying effects. PMID:20304410

Aschauer, Ulrich; Spagnoli, Dino; Bowen, Paul; Parker, Stephen C

2010-06-01

16

Nanoripples formation in calcite and indium phosphide (InP) single crystals  

Microsoft Academic Search

In this project we studied the formation of nanoripples in calcite and InP single crystals by continuous scanning using the nanoindenter in the ambient environment and by Argon ion irradiation under ultra high vacuum conditions, respectively. Formation of tip induced nanowear ripples is studied on a freshly cleaved calcite single crystal as a function of scanning frequency and contact load

Ramakrishna Gunda

2007-01-01

17

Struvite and calcite crystallization induced by cellular membranes of Myxococcus xanthus  

NASA Astrophysics Data System (ADS)

In this work we have proved that struvite and calcite crystals can be obtained in the presence of the cellular membrane fraction of Myxococcus xanthus, when appropriate supersaturated solutions are used. Probably, the negative charged points of the external side of the cellular structures could reduce the metastability field of struvite and calcite, acting as heterogeneous nuclei of crystallization.

González-Muñoz, Ma Teresa; Omar, Nabil Ben; Martínez-Cañamero, Magdalena; Rodríguez-Gallego, Manuel; Galindo, Alberto López; Arias, JoséMa

1996-06-01

18

Geobacillus thermoglucosidasius Endospores Function as Nuclei for the Formation of Single Calcite Crystals  

PubMed Central

Geobacillus thermoglucosidasius colonies were placed on an agar hydrogel containing acetate, calcium ions, and magnesium ions, resulting in the formation of single calcite crystals (calcites) within and peripheral to the plating area or parent colony. Microscopic observation of purified calcites placed on the surface of soybean casein digest (SCD) nutrient medium revealed interior crevices from which bacterial colonies originated. Calcites formed on the gel contained [1-13C]- and [2-13C]acetate, demonstrating that G. thermoglucosidasius utilizes carbon derived from acetate for calcite formation. During calcite formation, vegetative cells swam away from the parent colony in the hydrogel. Hard-agar hydrogel inhibited the formation of calcites peripheral to the parent colony. The calcite dissolved completely in 1 M HCl, with production of bubbles, and the remaining endospore-like particles were easily stained with Brilliant green dye. The presence of DNA and protein in calcites was demonstrated by electrophoresis. We propose that endospores initiate the nucleation of calcites. Endospores of G. thermoglucosidasius remain alive and encapsulated in calcites.

Murai, Rie

2013-01-01

19

An assessment of calcite crystal growth mechanisms based on crystal size distributions  

USGS Publications Warehouse

Calcite crystal growth experiments were undertaken to test a recently proposed model that relates crystal growth mechanisms to the shapes of crystal size distributions (CSDs). According to this approach, CSDs for minerals have three basic shapes: (1) asymptotic, which is related to a crystal growth mechanism having constant-rate nucleation accompanied by surface-controlled growth; (2) lognormal, which results from decaying-rate nucleation accompanied by surface-controlled growth; and (3) a theoretical, universal, steady-state curve attributed to Ostwald ripening. In addition, there is a fourth crystal growth mechanism that does not have a specific CSD shape, but which preserves the relative shapes of previously formed CSDs. This mechanism is attributed to supply-controlled growth. All three shapes were produced experimentally in the calcite growth experiments by modifying nucleation conditions and solution concentrations. The asymptotic CSD formed when additional reactants were added stepwise to the surface of solutions that were supersaturated with respect to calcite (initial ? = 20, where ? = 1 represents saturation), thereby leading to the continuous nucleation and growth of calcite crystals. Lognormal CSDs resulted when reactants were added continuously below the solution surface, via a submerged tube, to similarly supersaturated solutions (initial ? = 22 to 41), thereby leading to a single nucleation event followed by surface-controlled growth. The Ostwald CSD resulted when concentrated reactants were rapidly mixed, leading initially to high levels of supersaturation (? >100), and to the formation and subsequent dissolution of very small nuclei, thereby yielding CSDs having small crystal size variances. The three CSD shapes likely were produced early in the crystallization process, in the nanometer crystal size range, and preserved during subsequent growth. Preservation of the relative shapes of the CSDs indicates that a supply-controlled growth mechanism was established and maintained during the constant-composition experiments. CSDs having shapes intermediate between lognormal and Ostwald also were generated by varying the initial levels of supersaturation (initial ? = 28.2 to 69.2) in rapidly mixed solutions. Lognormal CSDs were observed for natural calcite crystals that are found in septarian concretions occurring in southeastern Colorado. Based on the model described above, these CSDs indicate initial growth by surface control, followed by supply-controlled growth. Thus, CSDs may be used to deduce crystal growth mechanisms from which geologic conditions early in the growth history of a mineral can be inferred. Conversely, CSD shape can be predicted during industrial crystallization by applying the appropriate conditions for a particular growth mechanism.

Kile, D. E.; Eberl, D. D.; Hoch, A. R.; Reddy, M. M.

2000-01-01

20

An artificial biomineral formed by incorporation of copolymer micelles in calcite crystals.  

PubMed

Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass those of their synthetic counterparts. A key feature of these materials, which sets them apart from synthetic crystals, is their nanocomposite structure, which derives from intimate association of organic molecules with the mineral host. We here demonstrate the production of artificial biominerals where single crystals of calcite occlude a remarkable 13 wt% of 20 nm anionic diblock copolymer micelles, which act as 'pseudo-proteins'. The synthetic crystals exhibit analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite. Further, the micelles are specifically adsorbed on {104} faces and undergo a change in shape on incorporation within the crystal lattice. This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of occlusion of biomacromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure. PMID:21892179

Kim, Yi-Yeoun; Ganesan, Kathirvel; Yang, Pengcheng; Kulak, Alexander N; Borukhin, Shirly; Pechook, Sasha; Ribeiro, Luis; Kröger, Roland; Eichhorn, Stephen J; Armes, Steven P; Pokroy, Boaz; Meldrum, Fiona C

2011-11-01

21

An artificial biomineral formed by incorporation of copolymer micelles in calcite crystals  

NASA Astrophysics Data System (ADS)

Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass those of their synthetic counterparts. A key feature of these materials, which sets them apart from synthetic crystals, is their nanocomposite structure, which derives from intimate association of organic molecules with the mineral host. We here demonstrate the production of artificial biominerals where single crystals of calcite occlude a remarkable 13?wt% of 20?nm anionic diblock copolymer micelles, which act as ‘pseudo-proteins’. The synthetic crystals exhibit analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite. Further, the micelles are specifically adsorbed on {104} faces and undergo a change in shape on incorporation within the crystal lattice. This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of occlusion of biomacromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure.

Kim, Yi-Yeoun; Ganesan, Kathirvel; Yang, Pengcheng; Kulak, Alexander N.; Borukhin, Shirly; Pechook, Sasha; Ribeiro, Luis; Kröger, Roland; Eichhorn, Stephen J.; Armes, Steven P.; Pokroy, Boaz; Meldrum, Fiona C.

2011-11-01

22

Eggshell matrix protein mimics: designer peptides to induce the nucleation of calcite crystal aggregates in solution.  

PubMed

Ansocalcin is a novel goose eggshell matrix protein with 132 amino acid residues, which induces the formation of polycrystalline calcite aggregates in in vitro crystallization experiments. The central region of ansocalcin is characterized by the presence of multiplets of charged amino acids. To investigate the specific role of charged amino acid multiplets in the crystal nucleation, three short peptides REWD-16, REWDP-17 (containing charged doublets), and RADA-16 (alternating charged residues) were synthesized and characterized. The aggregation of these peptides in solution was investigated using circular dichroism, intrinsic tryptophan fluorescence, and dynamic light scattering experiments. The peptides REWD-16 and REWDP-17 induced the polycrystalline calcite crystal aggregates, whereas RADA-16 did not induce significant changes in calcite crystal morphology or aggregate formation in in vitro crystallization experiments. The lattice and morphology of the calcite crystals were characterized using X-ray diffraction and scanning electron microscope. The results discussed in this paper reveal the importance of multiplets of charged amino acid residues toward the nucleation of polycrystalline calcite crystal aggregates in solution. PMID:12959601

Ajikumar, Parayil Kumaran; Lakshminarayanan, Rajamani; Ong, Boon Tee; Valiyaveettil, Suresh; Kini, R Manjunatha

2003-01-01

23

Capillarity creates single-crystal calcite nanowires from amorphous calcium carbonate.  

PubMed

Single-crystal calcite nanowires are formed by crystallization of morphologically equivalent amorphous calcium carbonate (ACC) particles within the pores of track etch membranes. The polyaspartic acid stabilized ACC is drawn into the membrane pores by capillary action, and the single-crystal nature of the nanowires is attributed to the limited contact of the intramembrane ACC particle with the bulk solution. The reaction environment then supports transformation to a single-crystal product. PMID:22069168

Kim, Yi-Yeoun; Hetherington, Nicola B J; Noel, Elizabeth H; Kröger, Roland; Charnock, John M; Christenson, Hugo K; Meldrum, Fiona C

2011-12-23

24

Calcite crystal growth inhibition by humic substances with emphasis on hydrophobic acids from the Florida Everglades  

Microsoft Academic Search

The crystallization of calcium carbonate minerals plays an integral role in the water chemistry of terrestrial ecosystems. Humic substances, which are ubiquitous in natural waters, have been shown to reduce or inhibit calcite crystal growth in experiments. The purpose of this study is to quantify and understand the kinetic effects of hydrophobic organic acids isolated from the Florida Everglades and

A. R. Hoch; M. M. Reddy; G. R. Aiken

2000-01-01

25

The thermodynamics and kinetics of calcite crystallization: Baseline for understanding biomineral formation  

NASA Astrophysics Data System (ADS)

Calcite is the most abundant bio-mineral that forms in the nearly ubiquitous presence of aspartic acid-rich organic matrices. This study investigated the interactions of aspartic acid (Asp) with calcite surfaces and the kinetic and thermodynamic effect of Asp on calcite crystallization. The interactions of Asp with calcite {101¯4} faces were examined through dissolution experiments using in situ Fluid Cell AFM and ex situ optical methods. A change in etch pit morphologies on {101¯4} faces after the introduction of Asp suggests that the Asp-calcite crystal face interactions are direction-specific. The effect of Asp on calcite crystallization was examined by characterizing growth spirals in Asp-free and Asp-bearing solutions. In the absence of Asp, measured critical step length scaled linearly with 1/sigma where sigma is the supersaturation. This linear relationship confirmed the Gibbs-Thomson prediction and yielded the step edge free energy for calcite crystallization. After the introduction of Asp, a change in the morphology of growing spirals and a reduction of step edge free energies were observed. These findings demonstrate the possible energetic controls of Asp during calcite biomineralization. Complex kinetic behavior was observed for step advancement in each direction in the absence and presence of Asp. The non-linear dependence of step velocity upon supersaturation was attributed to impurity effect and the kinetic coefficients of step advancement were obtained in Asp-free solutions based upon the models of impurity impact. A comparison of the kinetic data in Asp-free and Asp-bearing solutions suggests that Asp is not a growth inhibitor for calcite crystallization. Rate expressions for spiral growth based upon surface processes and the theories of crystal growth were derived and compared with those based upon chemical affinities of precipitation reactions. An analysis of the relationship between the two types of rate laws demonstrated that affinity-based rate equations only approximate spiral growth under special conditions: growth proceeds by single soured, single spirals at near equilibrium supersaturations. This suggests that, in general, it is not appropriate to deduce growth mechanisms from macroscopic kinetic measurements.

Teng, Hui Henry

26

The interaction of magnesium with calcite during crystal growth at 25-90°C and one atmosphere  

Microsoft Academic Search

Calcite crystals were grown in a closed system by recrystallization of synthetic and natural aragonite crystals, in the presence of various CaCl 2 -MgCl 2 solutions with and without NaCl. The distribution of Mg 2+ between calcite and solution at the entire temperature range is heterogeneous, closely following the ( and , 1925) distribution law. Mg 2+ C is strongly

Amitai Katz

1973-01-01

27

Dispersion-equation coefficients for the refractive index and birefringence of calcite and quartz crystals  

Microsoft Academic Search

The refractive index, birefringence and their dispersions are analyzed accurately in a physically meaningful model of a dispersion equation having only five coefficients for the calcite and quartz crystals. This dispersion equation is based on the average electronic absorption gap in the UV region and the effective lattice resonance absorption gap in the IR region. The five coefficients of the

Gorachand Ghosh

1999-01-01

28

Atomic layer wear of single-crystal calcite in aqueous solution using scanning force microscopy  

Microsoft Academic Search

Scanning force microscopy (SFM) is employed to study nm-scale wear of single-crystal calcite in an aqueous solution. When the SFM tip is drawn back and forth in a linear fashion across the edge of a preexisting single atomic layer etch pit, dissolution is strongly enhanced at the point where the tip crosses the step. The wear rate as a function

Nam-Seok Park; Myoung-Won Kim; S. C. Langford; J. T. Dickinson

1996-01-01

29

Heterogeneous deformation resulting from stress gradients in calcite single crystals  

Microsoft Academic Search

The stress gradient calculated from an isotropic elastic approximation does not directly reflect the distribution of permanent deformation in a crystal of the same shape under the same conditions. However, with additional crystallographic constraints, it serves to predict locations where twinning and slip are first activated in a stressed crystal. In this study, thick-walled hollow cylinders were cored from single

Annemarie Meike

1988-01-01

30

Swift heavy ion irradiation induced phase transformation in calcite single crystals  

NASA Astrophysics Data System (ADS)

Ion irradiation induced phase transformation in calcite single crystals have been studied by means of Raman and infrared spectroscopy using 120 MeV Au 9+ ions. The observed bands have been assigned according to group theory analysis. For higher fluence of 5×10 12 ion/cm 2, an extra peak on either side of the 713 cm -1 peak and an increase in the intensity of 1085 cm -1 peak were observed in Raman studies. FTIR spectra exhibit extra absorption bands at 674, 1589 cm -1 and enhancement in bands at 2340 and 2374 cm -1 was observed. This might be due to the phase transformation from calcite to vaterite. The damage cross section ( ?) for all the Raman and FTIR active modes was determined. The increase of FWHM, shift in peak positions and appearance of new peaks indicated that calcite phase is converted into vaterite.

Nagabhushana, H.; Nagabhushana, B. M.; Lakshminarasappa, B. N.; Singh, Fouran; Chakradhar, R. P. S.

2009-11-01

31

Trigonal dendritic calcite crystals forming from hot spring waters at Waikite, North Island, New Zealand  

SciTech Connect

Amorphous silica and calcite form the deposits in the vent and on the discharge apron of Waikite Spring 100 (WS-100), which is located in the Waikite Geothermal area on North Island, New Zealand. These precipitates formed from spring water that has a temperature of >90 C and a pH of 8.1--8.8. The opaline silica is restricted to areas around the vent where cooling and evaporation of the spring water triggered precipitation. The calcite deposits in the spring vent and on the discharge apron are formed of large (up to 15 cm long) asymmetrical dendrite crystals that are characterized by multiple levels of branching. Branches grew preferentially from the downflow side of their parent branch. All branches have a trigonal transverse cross section except in areas where competition for growth space induced merger of neighboring crystals. The primary branches of the dendrite crystals are (sub)perpendicular to the substrate even in areas where the discharge apron slopes at a high angle (up to 80{degree}). On the steeper parts of the discharge apron, the plate-like primary branches form the floors of the small terrace pools whereas their distal edges form the rims of the pools. Growth of these dendrite crystals is attributed to abiotic processes. High levels of saturation with respect to calcite were caused by rapid CO{sub 2} degassing of the sheets of spring water that flowed down the steep discharge apron. Calcite crystals with different crystal morphologies characterize other springs near this spring. The variation in crystal morphologies from spring to spring is attributed to different levels of saturation that are related to the initial PCO{sub 2} of the spring water upon discharge and the rate of CO{sub 2} degassing at each spring.

Jones, B.; Renault, R.W.; Rosen, M.R.

2000-05-01

32

In situ study of boron partitioning between calcite and fluid at different crystal growth rates  

NASA Astrophysics Data System (ADS)

The boron isotopic and chemical content of carbonates (expressed as ?11B and B/Ca ratios) have been proposed as proxies for seawater carbonate system parameters. Thermodynamic and kinetic effects on ?11B and B partitioning are not yet fully constrained, underscoring the importance of exploring possible effects of growth rate on boron incorporation in synthetic calcium carbonate minerals, which is the focus of this study. Secondary Ion Mass Spectrometry (SIMS) measurements of B/Ca and ?11B were performed on single crystal of calcite synthesized by diffusion of CO2 under controlled conditions from a solution of NH4Cl-CaCl2 doped with boron. Growth rates of calcite (V, nm/s) within crystals grown isothermally at 24.6 °C were monitored by sequentially spiking calcite-precipitating fluids with rare earth element (REE) dopants. The REE were analyzed with SIMS at spots that match those locations where B/Ca and ?11B ratios were measured. Values for the boron Nernst partition coefficient, defined as DB = B(calcite)/B(fluid), increase from 0.5 (pHNBS = 8.15) to 0.9 (pH = 8.00) with values of V increasing from 0.04 to 0.13 nm/s. For ?11B behavior, it was not possible to draw conclusive results due to the analytical error (2.2‰; 2?). pH effects on DB during calcite precipitation, associated with an increase in pH from 8.00 to 8.15, appear to be masked by the competing effects of changing V. We conclude that over the range of growth rates and other conditions investigated in this study, growth rate effects on B partitioning need to be accounted for when using B/Ca ratios in biogenic calcite as a proxy for seawater carbonate system parameters.

Gabitov, Rinat I.; Rollion-Bard, Claire; Tripati, Aradhna; Sadekov, Aleksey

2014-07-01

33

Effects of chitosan on the alignment, morphology and shape of calcite crystals nucleating under Langmuir monolayers  

NASA Astrophysics Data System (ADS)

The mechanisms governing selective CaCO3 crystal nucleation in living organisms remain unclear. For example, nacreous layers from the inner surfaces of shells are built as brick-and-mortar complexes of plate-like aragonite single crystals and organic layers. Unstable [001] surfaces of calcite columns in prismatic layers are also stabilized by organic molecules. Biogenic calcite crystals show different morphologies compared to geological calcite minerals. Langmuir monolayers are used as structured templates in simulated biomineralization from CaCO3 supersaturated subphases. But pure or mixed Langmuir monolayers do not mimic the nucleation sites of aspartic-rich proteins found within real biominerals. It has previously been shown that there is organic-inorganic lattice relaxation in the cases of BaF2 and hydrocerussite (2PbCO3·Pb(OH) 2) nucleation under fatty (carboxylate) acid with preferred orientation of crystals, but no lattice match is observed during CaCO3 crystallization under fatty acid Langmuir monolayers. Overall, geometric influences such as structural match between the interfacial lattices and the interactions between monolayer headgroups and aqueous ions do not guarantee any well-defined orientation of CaCO3 crystallization. CaCO3 mineralization on self-assembled monolayers on metal and alloy substrates have achieved higher degrees of orientations, even though molecules in Langmuir monolayers are better ordered than in self-assembled monolayers. Until now, Langmuir monolayer experiments have emphasized only the function of the acidic proteins. To better mimic the real organic template, it is important to include the hydrophobic and polyelectrolyte characteristics of real organic templates in shells. The organic matrix in actual shells contains hydrophobic silk fibroin (which is hydrophobic) and polyelectrolytes. Some acidic proteins reside on the surface of silk fibroins. There is also semi-crystalline beta-chitin structure whose function has not been fully understood. To better simulate the biological system, chitosan was added to the aqueous subphase. The crystallization processes were monitored using in-situ Grazing incidence X-ray diffraction (GID). Scanning electron microscopy (SEM) was used to perform morphological studies on grown crystals. Dissolved chitosan causes distinct concentration-dependent changes in orientation, shape and morphology of the calcite crystals nucleating under acid and sulfate monolayers. Our results suggest that polyelectrolytes may play essential roles in controlling the growth of biogenic calcite crystals.

Kim, Kyungil

34

Seeded Single Crystal Silicon Carbide Growth and Resulting Crystals.  

National Technical Information Service (NTIS)

A method is disclosed for producing a high quality bulk single crystal of silicon carbide in a seeded growth system and in the absence of a solid silicon carbide source, by reducing the separation between a silicon carbide seed crystal and a seed holder u...

D. P. Malta H. M. Hobgood J. R. Jenny M. Brady S. G. Mueller

2005-01-01

35

Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite  

NASA Astrophysics Data System (ADS)

Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation.

Benzerara, Karim; Menguy, Nicolas; Guyot, François; Dominici, Christian; Gillet, Philippe

2003-06-01

36

Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite.  

PubMed

Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation. PMID:12792020

Benzerara, Karim; Menguy, Nicolas; Guyot, Francois; Dominici, Christian; Gillet, Philippe

2003-06-24

37

Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite  

PubMed Central

Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation.

Benzerara, Karim; Menguy, Nicolas; Guyot, Francois; Dominici, Christian; Gillet, Philippe

2003-01-01

38

Correlation between Anisotropy and Lattice Distortions in Single Crystal Calcite Nanowires Grown in Confinement.  

PubMed

Growing nanostructures in confinement allows for the control of their shape, size and structure, as required in many technological applications. We investigated the crystal structure and morphology of calcite nanowires, precipitated in the pores of track-etch membranes, by employing transmission electron microscopy and selected area electron diffraction (SAED). The data showed that the nanowires show no preferred growth orientation and that the crystallographic orientation rotated along the length of the nanowire, with lattice rotation angles of several degrees per micrometer. Finite element calculations indicated that the rotation is caused by the anisotropic crystallographic nature of the calcite mineral, the nanoscale diameter of the wires and the confined space provided by the membrane pore. This phenomenon should also be observed in other single crystal nanowires made from anisotropic materials, which could offer the potential of generating nanostructures with tailored optical, electronic and mechanical properties. PMID:24644031

Verch, Andreas; Côté, Alexander S; Darkins, Robert; Kim, Yi-Yeoun; van de Locht, Renée; Meldrum, Fiona C; Duffy, Dorothy M; Kröger, Roland

2014-07-01

39

Spin-Lattice Relaxation-Time Measurements of Trivalent Iron in Single-Crystal Calcite  

Microsoft Academic Search

The spin-lattice relaxation time for the M=-12-->12 transition of trivalent iron in single-crystal calcite has been measured at X band by pulse recovery from 1.4 to 45 K and by spectral line broadening from 40 to 195 K. The resulting transition-probability data are well described by the sum of a direct-process term and a Raman-process term, the latter having a

S. A. Marshall; S. V. Nistor; R. A. Serway

1972-01-01

40

Shaping calcite crystals by means of comb polyelectrolytes having neutral hydrophilic teeth.  

PubMed

Comb polyelectrolytes (CPs) having neutral hydrophilic teeth, similar to double hydrophilic block copolymers, are a powerful tool to modify the chemical-physical properties of inorganic crystalline materials. One of their main applications is in concrete technology, where they work as superplasticizers, particle-dispersing agents. Here, CPs, having the same poly(acrylic acid) (PAA) backbone chain and differing in the grafting with methoxy poly(ethylene glycol) chains (MPEG) of two molecular weights, were used to investigate the influence of tooth chains in polymer aggregation and in control on morphology and aggregation of calcite particles. These polymers aggregate, forming interpolymer hydrogen bonds between carboxylic groups and ether oxygen functionalities. The presence of calcium ions in solution further enhances aggregation. Crystallization experiments of calcite in the presence of CPs show that the specificity of interactions between polymers and crystal planes and control on aggregation and size of particles is a function of the content and chain length of the MPEG in the PAA backbone. These parameters limit and can make specific the electrostatic interactions with ionic crystalline planes. Moreover, the mechanism of crystallization, classical or nonclassical, is addressed by the CP structure and concentration. These findings have implications in the understanding of the complex chemical processes associated to concrete superplasticizers action and in the study of the biomineralization processes, where biological comb polyelectrolytes, the acidic glycoproteins, govern formation of calcitic structures. PMID:23320460

Malferrari, Danilo; Fermani, Simona; Galletti, Paola; Goisis, Marco; Tagliavini, Emilio; Falini, Giuseppe

2013-02-12

41

Morphological tranformation of calcite crystal growth by prismatic "acidic" polypeptide sequences.  

SciTech Connect

Many of the interesting mechanical and materials properties of the mollusk shell are thought to stem from the prismatic calcite crystal assemblies within this composite structure. It is now evident that proteins play a major role in the formation of these assemblies. Recently, a superfamily of 7 conserved prismatic layer-specific mollusk shell proteins, Asprich, were sequenced, and the 42 AA C-terminal sequence region of this protein superfamily was found to introduce surface voids or porosities on calcite crystals in vitro. Using AFM imaging techniques, we further investigate the effect that this 42 AA domain (Fragment-2) and its constituent subdomains, DEAD-17 and Acidic-2, have on the morphology and growth kinetics of calcite dislocation hillocks. We find that Fragment-2 adsorbs on terrace surfaces and pins acute steps, accelerates then decelerates the growth of obtuse steps, forms clusters and voids on terrace surfaces, and transforms calcite hillock morphology from a rhombohedral form to a rounded one. These results mirror yet are distinct from some of the earlier findings obtained for nacreous polypeptides. The subdomains Acidic-2 and DEAD-17 were found to accelerate then decelerate obtuse steps and induce oval rather than rounded hillock morphologies. Unlike DEAD-17, Acidic-2 does form clusters on terrace surfaces and exhibits stronger obtuse velocity inhibition effects than either DEAD-17 or Fragment-2. Interestingly, a 1:1 mixture of both subdomains induces an irregular polygonal morphology to hillocks, and exhibits the highest degree of acute step pinning and obtuse step velocity inhibition. This suggests that there is some interplay between subdomains within an intra (Fragment-2) or intermolecular (1:1 mixture) context, and sequence interplay phenomena may be employed by biomineralization proteins to exert net effects on crystal growth and morphology.

Kim, I; Giocondi, J L; Orme, C A; Collino, J; Evans, J S

2007-02-13

42

Morphogenetic control of calcite crystal growth in sulfonic acid based hydrogels.  

PubMed

In this paper the mineralization of CaCO(3) in various hydrogel matrices is presented. Sulfonic acid based hydrogels were prepared by introduction of sulfonate-containing monomers into a polyacrylamide network. The sulfonate content of polyacrylamide-co-vinylsulfonate and polyacrylamide-co-allylsulfonate decreases during elution of the copolymers in demineralized water, indicating insufficient linking of the sulfonate-bearing monomers within the hydrogel. In contrast to this, acrylamidomethylpropanesulfonate (AMPS) effectively copolymerizes with acrylamide (AAm) monomers. To study the influence of spatial arrangement of ionic functional groups within hydrogel networks on the mineralization of CaCO(3), AMPS copolymers with different degrees of AMPS cross-linking were synthesized. For the mineralization experiments the copolymers were placed into a double-diffusion arrangement. Calcite as the thermodynamically stable modification of CaCO(3) was obtained with a particular morphology. The pseudocubic habitus resembles aggregates obtained by mineralization in pure polyacrylamide. However, closer examination of the aggregates by scanning electron microscopy (SEM) shows that the crystal growth in the AMPS copolymers is different from that observed in polyacrylamide. Whereas the morphology of the calcite aggregates could be fine-tuned by using copolymers with different sulfonate content, the spatial distribution of the ionic functional groups alters the course of crystallization. Calcium ions are locally accumulated due to the heterogeneous distribution of functional sulfonate groups within the copolymer network. Thereby the nucleation of calcite is triggered, resulting in enhanced mineralization. PMID:12645020

Grassmann, Olaf; Löbmann, Peer

2003-03-17

43

Development of artificial seed crystal for crystallization of calcium phosphate.  

PubMed

An artifical seed crystal material consisting of calcium silicate hydrate (5CaO x 6SiO2 x 5H2O : tobermorite crystals) applicable for phosphorus removal by crystallization was developed. Card-house shaped tobermorite crystals were developed on the seed material where orthophosphate crystallized as a calcium phosphate. The seed material can be manufactured by mixing siliceous and calcareous raw materials, pelletizing and subsequent autoclaving. Laboratory experiments were conducted to apply the new developed seed crystal material in the phosphorus recovery from sludge sidestreams of a wastewater treatment plant. In this crystallization process, the performance the carbon dioxide degassingprocess usually carried out when applying crystallization was not necessary, the hydroxyapatite was able to crystallize at a pH of 8.0 to 8.5 without precipitation of calcium carbonates. In the treatment of a sidestream with orthophosphate concentrations of 50 mgl(-1) and COD concentrations between 200 to 400 mgl(-1), phosphorus removal efficiencies ranging from 75 to 85% were observed. The seed crystal material was collected after the laboratory experiments and the chemical estimation and the germination test for agricultural reuse were performed. As a result, it was shown that the hydroxyapatite precipitated on the seed material had a 100% fusibility to soil and had characteristics to be a good nutrient source as a fertilizer for plants. PMID:11804345

Moriyama, K; Kojima, T; Minawa, Y; Matsumoto, S; Nakamachi, K

2001-11-01

44

In vitro effects of recombinant Otoconin 90 upon calcite crystal growth. Significance of tertiary structure  

PubMed Central

Otoconia are biomineral particles of microscopic size essential for perception of gravity and maintenance of balance. Millions of older Americans are affected in their mobility, quality of life and in their health by progressive demineralization of otoconia. Currently, no effective means to prevent or counteract this process are available. Because of prohibitive anatomical and biological constraints, otoconial research is lagging far behind other systems such as bone and teeth. We have overcome these obstacles by generating otoconial matrix proteins by recombinant techniques. In the present study, we evaluated the effects of recombinant Otoconin 90 (OC90), the principal soluble matrix protein upon calcite crystal growth patterns in vitro. Our findings highlight multiple effects, including facilitation of nucleation, and inhibition of crystal growth in a concentration-dependent manner. Moreover, OC90 induces morphologic changes characteristic of native otoconia. OC90 is considerably less acidic than the prototypical invertebrate CaCO3 –associated protein, but is nevertheless an effective modulator of calcite crystal growth. Based on homology modeling of the sPLA2-like domains of OC90, we propose that the lower density of acidic residues of the primary sequence is compensated by formation of major anionic surface clusters upon folding into tertiary conformation.

Lu, Wenfu; Zhou, Dan; Freeman, John J.; Thalmann, Isolde; Ornitz, David M.; Thalmann, Ruediger

2010-01-01

45

Dispersion-equation coefficients for the refractive index and birefringence of calcite and quartz crystals  

NASA Astrophysics Data System (ADS)

The refractive index, birefringence and their dispersions are analyzed accurately in a physically meaningful model of a dispersion equation having only five coefficients for the calcite and quartz crystals. This dispersion equation is based on the average electronic absorption gap in the UV region and the effective lattice resonance absorption gap in the IR region. The five coefficients of the dispersion equation are different for each fundamental parameters. The dispersion equation for the birefringence leads to represent a standardized equation describing the birefringence of all optical materials.

Ghosh, Gorachand

1999-05-01

46

In vitro calcite crystal morphology is modulated by otoconial proteins otolin-1 and otoconin-90.  

PubMed

Otoconia are formed embryonically and are instrumental in detecting linear acceleration and gravity. Degeneration and fragmentation of otoconia in elderly patients leads to imbalance resulting in higher frequency of falls that are positively correlated with the incidence of bone fractures and death. In this work we investigate the roles otoconial proteins Otolin-1 and Otoconin 90 (OC90) perform in the formation of otoconia. We demonstrate by rotary shadowing and atomic force microscopy (AFM) experiments that Otolin-1 forms homomeric protein complexes and self-assembled networks supporting the hypothesis that Otolin-1 serves as a scaffold protein of otoconia. Our calcium carbonate crystal growth data demonstrate that Otolin-1 and OC90 modulate in vitro calcite crystal morphology but neither protein is sufficient to produce the shape of otoconia. Coadministration of these proteins produces synergistic effects on crystal morphology that contribute to morphology resembling otoconia. PMID:24748133

Moreland, K Trent; Hong, Mina; Lu, Wenfu; Rowley, Christopher W; Ornitz, David M; De Yoreo, James J; Thalmann, Ruediger

2014-01-01

47

In Vitro Calcite Crystal Morphology Is Modulated by Otoconial Proteins Otolin-1 and Otoconin-90  

PubMed Central

Otoconia are formed embryonically and are instrumental in detecting linear acceleration and gravity. Degeneration and fragmentation of otoconia in elderly patients leads to imbalance resulting in higher frequency of falls that are positively correlated with the incidence of bone fractures and death. In this work we investigate the roles otoconial proteins Otolin-1 and Otoconin 90 (OC90) perform in the formation of otoconia. We demonstrate by rotary shadowing and atomic force microscopy (AFM) experiments that Otolin-1 forms homomeric protein complexes and self-assembled networks supporting the hypothesis that Otolin-1 serves as a scaffold protein of otoconia. Our calcium carbonate crystal growth data demonstrate that Otolin-1 and OC90 modulate in vitro calcite crystal morphology but neither protein is sufficient to produce the shape of otoconia. Coadministration of these proteins produces synergistic effects on crystal morphology that contribute to morphology resembling otoconia.

Moreland, K. Trent; Hong, Mina; Lu, Wenfu; Rowley, Christopher W.; Ornitz, David M.; De Yoreo, James J.; Thalmann, Ruediger

2014-01-01

48

Cyclic development of large, complex, calcite dendrite crystals in the Clinton travertine, Interior British Columbia, Canada  

NASA Astrophysics Data System (ADS)

Bands of large (up to 4 cm long) three-dimensional crystallographic dendrites form the terrace fronts in an old travertine mound exposed near Clinton, British Columbia. The dendrites, with their long axes perpendicular to the terrace front, are characterized by numerous levels of branching. Each branch is formed of multitudes of skeletal rhombs, four- and six(?)-sided bipyramidal crystals, or prismatic hexagonal crystals that are precisely aligned along crystallographic precepts. Although individual branches are formed of one type of subcrystal, neighbouring branches may be formed of different subcrystal types. Highly supersaturated waters that were generated by rapid CO 2 degassing of the spring water during its turbulent flow over the steep terrace fronts probably drove dendrite precipitation. The presence of growth lines indicates that growth was episodic. Type I growth lines probably formed annually in response to seasonal climate changes whereas Type II growth lines, which formed less frequently, may reflect changes in the flow velocity and/or flow patterns of the spring waters. Early diagenetic modification of the dendrites involved crystal face enlargement, cements formed of trigonal prisms or needle-fiber crystals, microbial infestation that mediated substrate dissolution, and/or deposition of detrital calcite crystals that formed in the water column. Much of the diagenetic modification may have taken place during the periods when the dendrites had temporarily stopped growing. The dendrites in the Clinton travertine are an excellent example of complex, episodic calcite crystal growth that was extensively modified by early diagenetic processes in a surface environment. The same spring waters from which the dendrites were precipitated mediated much of the early diagenesis.

Jones, Brian; Renaut, Robin W.

2008-01-01

49

Optical measurements to determine the thickness of calcite crystals and the mass of thin carbonate particles such as coccoliths.  

PubMed

We describe a procedure for measuring the thickness and mass of calcite particles that works for most calcite particles <4.5-?m thick. The calcite particles are observed in cross-polarized light, which enables the light transmitted through the calcite particles to be correlated with their thickness. Three polarizing planes are used to minimize the darkening of crystals at some orientations (black cross). This allows direct measurement of the thickness without recourse to a transfer function. This procedure has been used recently to determine the degree of calcification of coccoliths, which provides an indicator of ocean acidification. It takes only a few minutes per sample, and it is an improvement over the former protocol, which did not allow measurement of the thickness and mass of particles thicker than 1.5 ?m. PMID:24556786

Beaufort, Luc; Barbarin, Nicolas; Gally, Yves

2014-03-01

50

Vertical Bridgman growth of sapphire-Seed crystal shapes and seeding characteristics  

NASA Astrophysics Data System (ADS)

The growth of sapphire by the traditional vertical Bridgman (VB) method was studied by using various shapes of seed crystals and tungsten (W) crucibles shaped to match the seeds. Approximately 2-in. diameter, c-axis sapphire single crystals were reproducibly grown from three kinds of seed: thin, tapered and full diameter. Factors relating seed type to single-crystal growth are discussed, including the reproducibility of seeding processes, and the generation and elimination of low-angle grain boundaries (LAGBs). What was learned facilitated the subsequent growth of large-diameter, 3-, 4- and 6-in., c-axis single-crystal sapphires from full-diameter seeds.

Hoshikawa, K.; Osada, J.; Saitou, Y.; Ohba, E.; Miyagawa, C.; Kobayashi, T.; Yanagisawa, J.; Shinozuka, M.; Kanno, K.

2014-06-01

51

Device for isolation of seed crystals during processing of solution  

DOEpatents

A device is described for isolation of seed crystals during processing of solutions. The device enables a seed crystal to be introduced into the solution without exposing the solution to contaminants or to sources of drying and cooling. The device constitutes a seed protector which allows the seed to be present in the growth solution during filtration and overheating operations while at the same time preventing the seed from being dissolved by the under saturated solution. When the solution processing has been completed and the solution cooled to near the saturation point, the seed protector is opened, exposing the seed to the solution and allowing growth to begin. 3 figs.

Montgomery, K.E.; Zaitseva, N.P.; Deyoreo, J.J.; Vital, R.L.

1999-05-18

52

Sr, Cd, Mn and Co distribution coefficients in calcite as a function of calcite precipitation rate  

NASA Astrophysics Data System (ADS)

Distribution coefficients, as a function of precipitation rate, were determined for the metals Sr 2+, Co 2+, Mn 2+ and Cd 2+in calcite. A pH-stat was used to maintain a constant degree of-saturation, and hence precipitation rate, during each coprecipitation run. The precipitation rate was proportional to the degree of supersaturation and the mass of seed crystal introduced. Distribution coefficients (?) as a function of rate were determined using radioactive isotopes for solutions with saturations ? = 1 to ? = 5.5. Strontium distribution coefficients increased with increasing precipitation rate, while Co, Mn and Cd distribution coefficients decreased with increasing precipitation rate. The following rate expressions (at 25°C) were derived: log?Sr = 0.249 log R -1.57 log?Mn = -0.266 log R + 1.35 log?Co = -0.173 log R + 0.68 log?Cd = -0.194 log R + 1.46 where R is the observed precipitation rate in nmoles CaCO 3 per mg seed crystal per min. In separate experiments the uptake of radioactive isotopes was monitored during the recrystallization of calcite seed crystals. Rates of recrystallization were from 100 to 10, 000 times slower than the pH-stat experiments, but yielded distribution coefficients consistent with the above rate expressions. Using gross estimates of biogenic crystal growth rates, aragonite to calcite transformation rates, and the above Sr rate expression, biogenic calcite and diagenetic calcite Sr contents are estimated. These experiments indicate that in addition to solution composition, precipitation rate is a significant factor influencing the trace metal content of naturally occurring calcite.

Lorens, Robert B.

1981-04-01

53

Calcite growth kinetics: Modeling the effect of solution stoichiometry  

NASA Astrophysics Data System (ADS)

Until recently the influence of solution stoichiometry on calcite crystal growth kinetics has attracted little attention, despite the fact that in most aqueous environments calcite precipitates from non-stoichiometric solution. In order to account for the dependence of the calcite crystal growth rate on the cation to anion ratio in solution, we extend the growth model for binary symmetrical electrolyte crystals of Zhang and Nancollas (1998) by combining it with the surface complexation model for the chemical structure of the calcite-aqueous solution interface of Wolthers et al. (2008). To maintain crystal stoichiometry, the rate of attachment of calcium ions to step edges is assumed to equal the rate of attachment of carbonate plus bicarbonate ions. The model parameters are optimized by fitting the model to the step velocities obtained previously by atomic force microscopy (AFM, Teng et al., 2000; Stack and Grantham, 2010). A variable surface roughness factor is introduced in order to reconcile the new process-based growth model with bulk precipitation rates measured in seeded calcite growth experiments. For practical applications, we further present empirical parabolic rate equations fitted to bulk growth rates of calcite in common background electrolytes and in artificial seawater-type solutions. Both the process-based and empirical growth rate equations agree with measured calcite growth rates over broad ranges of ionic strength, pH, solution stoichiometry and degree of supersaturation.

Wolthers, Mariëtte; Nehrke, Gernot; Gustafsson, Jon Petter; Van Cappellen, Philippe

2012-01-01

54

Device for isolation of seed crystals during processing of solution  

DOEpatents

A device for isolation of see crystals during processing of solutions. The device enables a seed crystal to be introduced into the solution without exposing the solution to contaminants or to sources of drying and cooling. The device constitutes a seed protector which allows the seed to be present in the growth solution during filtration and overheating operations while at the same time preventing the seed from being dissolved by the under saturated solution. When the solution processing has been completed and the solution cooled to near the saturation point, the seed protector is opened, exposing the seed to the solution and allowing growth to begin.

Montgomery, Kenneth E. (Tracy, CA); Zaitseva, Natalia P. (Livermore, CA); Deyoreo, James J. (Livermore, CA); Vital, Russell L. (Tracy, CA)

1999-01-01

55

Crystallizing short-read assemblies around seeds  

PubMed Central

Background New short-read sequencing technologies produce enormous volumes of 25–30 base paired-end reads. The resulting reads have vastly different characteristics than produced by Sanger sequencing, and require different approaches than the previous generation of sequence assemblers. In this paper, we present a short-read de novo assembler particularly targeted at the new ABI SOLiD sequencing technology. Results This paper presents what we believe to be the first de novo sequence assembly results on real data from the emerging SOLiD platform, introduced by Applied Biosystems. Our assembler SHORTY augments short-paired reads using a trivially small number (5 – 10) of seeds of length 300 – 500 bp. These seeds enable us to produce significant assemblies using short-read coverage no more than 100×, which can be obtained in a single run of these high-capacity sequencers. SHORTY exploits two ideas which we believe to be of interest to the short-read assembly community: (1) using single seed reads to crystallize assemblies, and (2) estimating intercontig distances accurately from multiple spanning paired-end reads. Conclusion We demonstrate effective assemblies (N50 contig sizes ~40 kb) of three different bacterial species using simulated SOLiD data. Sequencing artifacts limit our performance on real data, however our results on this data are substantially better than those achieved by competing assemblers.

Hossain, Mohammad Sajjad; Azimi, Navid; Skiena, Steven

2009-01-01

56

Controls on the precipitation of barite (BaSO 4) crystals in calcite travertine at Twitya Spring, a warm sulphur spring in Canada's Northwest Territories  

NASA Astrophysics Data System (ADS)

Twitya Spring discharges warm (24 °C), anoxic, sulphide-, calcium- (65 ppm) and barium- (? 0.78 ppm) rich spring water to a steep flow path that is inhabited by streamer and mat-forming microbes ( Thiothrix, Beggiatoa, Oscillatoria, Spirulina, diatoms, rod shaped bacteria). Oxidation and CO 2 degassing drive precipitation of elemental sulphur, barite, opaline silica, and calcite. A mound of travertine at the base of the flow path, dominantly composed of bedded barium-enriched crystallographic and noncrystallographic dendritic calcite crystals and calcite cements, hosts three types of barite crystals: type 1 (T1) intergrown tabular crystals that formed in solution, type 2 (T2) tabular and rhombic crystals that nucleated on calcite, and type 3 (T3) subhedral and anhedral microcrystals that nucleated on microbial cell surfaces and in microbial extracellular polymeric substances. The formation and distribution of T1, T2, and T3 barite in the Twitya Spring flow path are controlled by physiochemical gradients, calcite precipitation rates, and adsorption of barium to microbial biomass, all of which vary seasonally and episodically at Twitya Spring. The complex physiochemical and biological controls on barite formation at Twitya Spring both suggest that the classification of biogenic or inorganic sedimentary barite on the basis of crystal size and morphology may be oversimplified. There is also the potential that primary and authigenic barite crystals hosted in carbonates may yield information about the microbial ecology and ambient physiochemistry of their depositional environments.

Bonny, Sandy M.; Jones, Brian

2008-01-01

57

High surface area calcite  

NASA Astrophysics Data System (ADS)

Calcite (CaCO3) is important in many fields—in nature, because it is a component of aquifers, oil reservoirs and prospective CO2 storage sites, and in industry, where it is used in products as diverse as paper, toothpaste, paint, plastic and aspirin. It is difficult to obtain high purity calcite with a high surface area but such material is necessary for industrial applications and for fundamental calcite research. Commercial powder is nearly always contaminated with growth inhibitors such as sugars, citrate or pectin and most laboratory synthesis methods deliver large precipitates, often containing vaterite or aragonite. To address this problem, we (i) adapted the method of carbonating a Ca(OH)2 slurry with CO2 gas to develop the first simple, cheap, safe and reproducible procedure using common laboratory equipment, to obtain calcite that reproducibly had a surface area of 14-17 m2/g and (ii) conducted a thorough characterization of the product. Scanning electron microscopy (SEM) revealed nanometer scale, rhombohedral crystals. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) confirmed highly crystalline, pure calcite that more closely resembles the dimensions of the biogenic calcite produced by algae in coccoliths than other methods for synthesizing calcite. We suggest that this calcite is useful when purity and high surface area are important.

Schultz, L. N.; Andersson, M. P.; Dalby, K. N.; Müter, D.; Okhrimenko, D. V.; Fordsmand, H.; Stipp, S. L. S.

2013-05-01

58

Calcite growth-rate inhibition by fulvic acids isolated from Big Soda Lake, Nevada, USA, The Suwannee River, Georgia, USA and by polycarboxylic acids  

USGS Publications Warehouse

Calcite crystallization rates are characterized using a constant solution composition at 25°C, pH=8.5, and calcite supersaturation (?) of 4.5 in the absence and presence of fulvic acids isolated from Big Soda Lake, Nevada (BSLFA), and a fulvic acid from the Suwannee River, Georgia (SRFA). Rates are also measured in the presence and absence of low-molar mass, aliphatic-alicyclic polycarboxylic acids (PCA). BSLFA inhibits calcite crystal-growth rates with increasing BSLFA concentration, suggesting that BSLFA adsorbs at growth sites on the calcite crystal surface. Calcite growth morphology in the presence of BSLFA differed from growth in its absence, supporting an adsorption mechanism of calcite-growth inhibition by BSLFA. Calcite growth-rate inhibition by BSLFA is consistent with a model indicating that polycarboxylic acid molecules present in BSLFA adsorb at growth sites on the calcite crystal surface. In contrast to published results for an unfractionated SRFA, there is dramatic calcite growth inhibition (at a concentration of 1 mg/L) by a SRFA fraction eluted by pH 5 solution from XAD-8 resin, indicating that calcite growth-rate inhibition is related to specific SRFA component fractions. A cyclic PCA, 1, 2, 3, 4, 5, 6-cyclohexane hexacarboxylic acid (CHXHCA) is a strong calcite growth-rate inhibitor at concentrations less than 0.1 mg/L. Two other cyclic PCAs, 1, 1 cyclopentanedicarboxylic acid (CPDCA) and 1, 1 cyclobutanedicarboxylic acid (CBDCA) with the carboxylic acid groups attached to the same ring carbon atom, have no effect on calcite growth rates up to concentrations of 10 mg/L. Organic matter ad-sorbed from the air onto the seed crystals has no effect on the measured calcite crystal-growth rates.

Reddy, Michael M.; Leenheer, Jerry

2011-01-01

59

Variations in the Sr/Ca, ?44Ca and ?18O composition of calcite as a function of solution chemistry and crystal growth rate  

NASA Astrophysics Data System (ADS)

The trace element and isotopic composition of calcite can be used to probe the temperatures and rates of mineral formation as well as the degree of post-mineralization alteration. The accuracy with which these effects can be interpreted is limited by our ability to distinguish signatures arising from equilibrium partitioning versus kinetic or mass transport effects. Our focus in this work is on mass transport effects in aqueous environments, and specifically, the growth rate-dependence of trace element and isotopic incorporation into calcite. This requires experiments in which the degree of supersaturation, or the solution chemistry, is held constant and the rate of crystal growth can be determined. In our experiments, N2+CO2 gas mixture is bubbled through a beaker containing 1300 mL of solution (30 mM CaCl2 + 5 mM NH4Cl + 0.1 mM SrCl2). The degree of supersaturation with respect to calcite is controlled by the pCO2 of the gas mixture, which is constantly replenished from a gas source. As CO2 from the gas dissolves into solution, calcite crystals grow on the beaker walls and the pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. During an experiment we control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate. At the same time we monitor the total alkalinity, the pCO2 of the gas outflow, the gas outflow rate, and the amount of NaOH added. The rate of calcite precipitation can be determined in three ways: (1) the change in total alkalinity due to Ca2+ removal, mass balance of C in the system, and (3) post-run measurement of [Ca2+] in aliquots of solution taken during an experiment. We present results from experiments where growth rates are estimated to range from 0.5 to 16 mmol/m2/hr. Our experiments thus far have yielded calcite crystals that are out of calcium and oxygen isotopic equilibrium with the parent solution. Crystals are enriched in the light isotope of Ca by 0.4 to 1.8‰. The light isotope enrichment increases with growth rate and is correlated with Sr/Ca in calcite. These results are in excellent agreement with the results of Tang et al. (2008) for crystals grown at 25°C and suggest that mass discrimination is controlled by mass transport kinetics at the mineral-solution interface. Oxygen isotopes are more complicated because of the addition of CO2 to the bulk solution. For crystals grown from our stock solution, the O composition is highly variable and not correlated with growth rate. We attribute this to relatively slow kinetics of O isotope exchange between gaseous or dissolved CO2 and water. For crystals grown in the presence of 0.01 grams of bovine carbonic anhydrase (CA), an enzyme which catalyzes the interconversion of CO2 and H2O to bicarbonate and protons, the O isotope composition of calcite appears to be independent of growth rate. Hence addition of CA to solution might offer a means of determining the equilibrium fractionation factor for oxygen isotopes in carbonate minerals. We will present results from additional experiments that test how CA and other organic molecules in solution affect the growth rate and mass discrimination during mineral precipitation.

Watkins, J. M.; DePaolo, D. J.; Ryerson, F. J.

2012-12-01

60

Crystallization in nano-confinement seeded by a nanocrystal-A molecular dynamics study  

NASA Astrophysics Data System (ADS)

Seeded crystallization and solidification in nanoscale confinement volumes have become an important and complex topic. Due to the complexity and limitations in observing nanoscale crystallization, computer simulation can provide valuable details for supporting and interpreting experimental observations. In this article, seeded crystallization from nano-confined liquid, as represented by the crystallization of a suspended gold nano-droplet seeded by a pre-existing gold nanocrystal seed, was investigated using molecular dynamics simulations in canonical (NVT) ensemble. We found that the crystallization temperature depends on nano-confinement volume, crystal orientation, and seed size as explained by classical two-sphere model and Gibbs-Thomson effect.

Pan, Heng; Grigoropoulos, Costas

2014-03-01

61

Growth of silicon carbide crystals on a seed while pulling silicon crystals from a melt  

NASA Technical Reports Server (NTRS)

A saturated solution of silicon and an element such as carbon having a segregation coefficient less than unity is formed by placing a solid piece of carbon in a body of molten silicon having a temperature differential decreasing toward the surface. A silicon carbide seed crystal is disposed on a holder beneath the surface of the molten silicon. As a rod or ribbon of silicon is slowly pulled from the melt, a supersaturated solution of carbon in silicon is formed in the vicinity of the seed crystal. Excess carbon is emitted from the solution in the form of silicon carbide which crystallizes on the seed crystal held in the cool region of the melt.

Ciszek, T. F.; Schwuttke, G. H. (inventor)

1979-01-01

62

Elastic constants of calcite  

USGS Publications Warehouse

The recent measurements of the elastic constants of calcite by Reddy and Subrahmanyam (1960) disagree with the values obtained independently by Voigt (1910) and Bhimasenachar (1945). The present authors, using an ultrasonic pulse technique at 3 Mc and 25??C, determined the elastic constants of calcite using the exact equations governing the wave velocities in the single crystal. The results are C11=13.7, C33=8.11, C44=3.50, C12=4.82, C13=5.68, and C14=-2.00, in units of 1011 dyncm2. Independent checks of several of the elastic constants were made employing other directions and polarizations of the wave velocities. With the exception of C13, these values substantially agree with the data of Voigt and Bhimasenachar. ?? 1962 The American Institute of Physics.

Peselnick, L.; Robie, R. A.

1962-01-01

63

Crystallization of struvite from metastable region with different types of seed crystal  

NASA Astrophysics Data System (ADS)

The main feature of this paper was to recognize struvite crystallization in the metastable region of supersaturation. Thermodynamic equilibria of struvite were simulated to identify the minimum struvite solubility limit, thereafter validated by existing thermodynamic modelling packages such as PHREEQC and the derived data from existing struvite solubility curve. Using laser light scattering detection, spontaneous nucleation was identified by the slow increase of pH in a supersaturated solution of struvite. The crystallization experiment, conducted close to the saturation region in metastable zone, initiated struvite growth. The conducted experiment showed that mother crystal (struvite) was more effective as seeds for struvite crystallization.

Ali, Imtiaj; Schneider, Phil Andrew

2005-05-01

64

Why calcite can be stronger than quartz  

NASA Astrophysics Data System (ADS)

In the Neves area (Eastern Alps), calcite forms asymmetric centimeter-scale single-crystal porphyroclasts in quartz mylonites developed during hydrous amphibolite facies metamorphism at ˜550°C. Under these conditions, coarse calcite was clearly stronger than the surrounding polycrystalline, dynamically recrystallized, quartz matrix. Experimental results indicate that coarse calcite is less strain rate sensitive than wet quartzite, consistent with an inversion in strength on extrapolation to natural strain rates. For this to occur, wet quartzite must be weak, flowing at differential stress of <10 MPa. The lack of high-temperature twins (showing bulging or recrystallization) in calcite clasts is consistent with such low stresses during shear zone development under near peak metamorphic conditions. The maximum effective viscosity ratio of coarse calcite to quartzite for these conditions is probably not large (<10). However, numerical modeling shows that ratios of around 2 are sufficient to maintain near rigid calcite clast behavior for power law rheology with stress exponents appropriate to quartz (n ˜ 3-4) and coarse calcite (n ? 6). The inversion in relative strength reflects the difference in influence of water on the crystal plastic flow of calcite and quartz: water has a dramatic effect for quartz but little or no effect for calcite. Quartz-rich rocks under hydrous amphibolite facies conditions in the middle to lower crust are therefore relatively weak (in fact, weaker than coarse calcite) and flow at much lower stresses than dry quartz-rich rocks at similar crustal levels.

Mancktelow, Neil S.; Pennacchioni, Giorgio

2010-01-01

65

Why calcite can be stronger than quartz  

Microsoft Academic Search

In the Neves area (Eastern Alps), calcite forms asymmetric centimeter-scale single-crystal porphyroclasts in quartz mylonites developed during hydrous amphibolite facies metamorphism at ?550°C. Under these conditions, coarse calcite was clearly stronger than the surrounding polycrystalline, dynamically recrystallized, quartz matrix. Experimental results indicate that coarse calcite is less strain rate sensitive than wet quartzite, consistent with an inversion in strength on

Neil S. Mancktelow; Giorgio Pennacchioni

2010-01-01

66

The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution  

PubMed Central

The sea urchin tooth is a remarkable grinding tool. Even though the tooth is composed almost entirely of calcite, it is used to grind holes into a rocky substrate itself often composed of calcite. Here, we use 3 complementary high-resolution tools to probe aspects of the structure of the grinding tip: X-ray photoelectron emission spectromicroscopy (X-PEEM), X-ray microdiffraction, and NanoSIMS. We confirm that the needles and plates are aligned and show here that even the high Mg polycrystalline matrix constituents are aligned with the other 2 structural elements when imaged at 20-nm resolution. Furthermore, we show that the entire tooth is composed of 2 cooriented polycrystalline blocks that differ in their orientations by only a few degrees. A unique feature of the grinding tip is that the structural elements from each coaligned block interdigitate. This interdigitation may influence the fracture process by creating a corrugated grinding surface. We also show that the overall Mg content of the tooth structural elements increases toward the grinding tip. This probably contributes to the increasing hardness of the tooth from the periphery to the tip. Clearly the formation of the tooth, and the tooth tip in particular, is amazingly well controlled. The improved understanding of these structural features could lead to the design of better mechanical grinding and cutting tools.

Ma, Yurong; Aichmayer, Barbara; Paris, Oskar; Fratzl, Peter; Meibom, Anders; Metzler, Rebecca A.; Politi, Yael; Addadi, Lia; Gilbert, P. U. P. A.; Weiner, Steve

2009-01-01

67

Critical issues in single crystal growth of PMN-PT by seeded polycrystal conversion  

Microsoft Academic Search

Pb(Mg13\\/Nb23\\/)O3-35mol%PbTiO3 [PMN-35PT] single crystals have been produced via the Seeded Polycrystal Conversion process by embedding a seed crystal in a polycrystalline ceramic matrix, and inducing the single crystal boundary to migrate at the expense of the smaller matrix grains. Maintaining single crystal growth until full conversion of the polycrystal can only be achieved with an improved fundamental understanding of the

H. M. Chan; M. P. Harmer; E. P. Gorzkowski; P. T. King; A. M. Scotch; D. J. Rockosi

2002-01-01

68

The role of silicate surfaces on calcite precipitation kinetics  

NASA Astrophysics Data System (ADS)

The aim of this study is to illuminate how calcite precipitation depends on the identity and structure of the growth substrate. Calcite was precipitated at 25 °C from supersaturated aqueous solutions in the presence of seeds of either calcite or one of six silicate materials: augite, enstatite, labradorite, olivine, basaltic glass and peridotite rock. Calcite saturation was achieved by mixing a CaCl2-rich aqueous solution with a NaHCO3-Na2CO3 aqueous buffer in mixed-flow reactors containing 0.5-2 g of mineral, rock, or glass seeds. This led to an inlet fluid calcite saturation index of 0.6 and a pH equal to 9.1. Although the inlet fluid composition, flow rate, and temperature were identical for all experiments, the onset of calcite precipitation depended on the identity of the seeds present in the reactor. Calcite precipitated instantaneously and at a constant rate in the presence of calcite grains. Calcite precipitated relatively rapidly on labradorite, olivine, enstatite, and peridotite (mainly composed of Mg-olivine) surfaces, but more slowly on augite and basaltic glass. Calcite precipitation rates, however, became independent of substrate identity and mass over time, and all rates approach 10-9.68 ± 0.08 mol/s for ?10 day long experiments and 10-9.21 ± 0.2 mol/s for ?70 day long experiments. Scanning Electron Microscope images showed olivine, enstatite and peridotite surfaces to be covered extensively with calcite coatings at the end of the experiments. Less calcite was found on labradorite and augite, and the least on basaltic glass. In all cases, calcite precipitation occurs on the mineral, rock or glass surfaces. Calcite precipitation on these surfaces, however, negligibly affects the dissolution rates of the silicate grains. These results support ultramafic and basalt carbonation as a long-term carbon storage strategy, as calcite readily precipitates on the surfaces of minerals contained in these rocks without inhibiting their dissolution.

Stockmann, Gabrielle J.; Wolff-Boenisch, Domenik; Bovet, Nicolas; Gislason, Sigurdur R.; Oelkers, Eric H.

2014-06-01

69

Calcite precipitation induced by polyurethane-immobilized Bacillus pasteurii  

Microsoft Academic Search

Polyurethane (PU) foam was used to immobilize the whole cell of Bacillus pasteurii. The immobilized cells exhibited the rates of calcite precipitation and ammonia production as high as those of the free cells. Scanning electron micrographs identified the cells embedded in calcite crystals throughout PU matrices. Calcite in PU showed little effect on the elastic modulus and tensile strength of

Sookie S. Bang; Johnna K. Galinat; V. Ramakrishnan

2001-01-01

70

Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals  

DOEpatents

A method of fabricating bulk YBa.sub.2 Cu.sub.3 O.sub.x where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa.sub.2 Cu.sub.3 O.sub.x are heated in the presence of a Nd.sub.1+x Ba.sub.2-x Cu.sub.3 O.sub.y seed crystal to a temperature sufficient to form a liquid phase in the YBa.sub.2 Cu.sub.3 O.sub.x while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa.sub.2 Cu.sub.3 O.sub.x material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material.

Todt, Volker (Lemont, IL); Miller, Dean J. (Darien, IL); Shi, Donglu (Oak Park, OH); Sengupta, Suvankar (Columbus, OH)

1998-01-01

71

Fracture-aperture alteration induced by calcite precipitation  

NASA Astrophysics Data System (ADS)

Mineral precipitation significantly alters the transport properties of fractured rock. Chemical solubility gradients that favor precipitation induce mineral growth, which decreases the local aperture and alters preferential flow paths. Understanding the resulting development of spatial heterogeneities is necessary to predict the evolution of transport properties in the subsurface. We present experimental results that quantify the relationship between mineral precipitation and aperture alteration in a transparent analog fracture, 7.62cm x 7.62cm, with a uniform aperture of ~200 ?m. Prior to flow experiments, a pump circulated a super-saturated calcite solution over the bottom glass, coating the glass surface with calcite. This method of seeding resulted in clusters of calcite crystals with large reactive surface area and provided micro-scale variability in the aperture field. A continuous flow syringe pump injected a reactive fluid into the fracture at 0.5 ml/min. The fluid was a mixture of sodium bicarbonate (NaHCO3, 0.02M) and calcium chloride (CaCl2 0.0004M) with a saturation index, ?, of 8.51 with respect to calcite. A strobed LED panel backlit the fracture and a high-resolution CCD camera monitored changes in transmitted light intensity. Light transmission techniques provided a quantitative measurement of fracture aperture over the flow field. Results from these preliminary experiments showed growth near the inlet of the fracture, with decreasing precipitation rates in the flow direction. Over a period of two weeks, the fracture aperture decreased by 17% within the first 4mm of the inlet. Newly precipitated calcite bridged individual crystal clusters and smoothed the reacting surface. This observation is an interesting contradiction to the expectation of surface roughening induced by mineral growth. Additionally, the aperture decreased uniformly across the width of the fracture due to the initial aperture distribution. Future experiments of precipitation within variable-aperture fields will investigate the dependency of growth patterns on heterogeneous aperture distributions. (a) Aperture strain (?b/bi) after 14 days. Precipitation is concentrated near the inlet and decreases in the flow direction. (b) Width-averaged profiles of the initial and final aperture field show changes in aperture and smoothing that results from calcite precipitation between the initial discrete crystals.

Jones, T.; Detwiler, R. L.

2013-12-01

72

Zinc isotope fractionation during adsorption on calcite  

NASA Astrophysics Data System (ADS)

Zinc is an important element as a nutrient in the marine biosphere. However, our understanding of its biogeochemical cycling in the oceans is relatively limited. The Zn stable isotope system holds the promise of providing novel insights, since published Zn isotopic values for various natural samples reveal significant fractionations in the marine environment. Surface seawater, basalts, shales, deep-sea clay sediments, sediment trap material, bulk plankton and zooplankton samples, and eolian dust fall within a tight range (?66/64Zn from -0.1 to 0.5‰), but modern ferromanganese crusts (?66/64Zn from 0.5 to 1.2‰), as well as carbonates (?66/64Zn from 0.3 to 1.4‰), are notably enriched in heavy Zn isotopes [1-4]. In this study we seek to constrain the mechanism by which carbonates are enriched in heavier isotopes. In particular, we have conducted experiments to quantify isotope fractionation during adsorption of Zn onto the surfaces of calcite crystals that are in equilibrium with solution. The adsorption experiments were carried out in a series of small-volume batch reactions in a clean laboratory environment, using high-purity reagents and calcite seed crystals. The calcite was equilibrated with the solution prior to addition of Zn at atmospheric CO2 pressure (i.e., in air) for 5 days until a stable pH of 8.3 was reached. Later, a small aliquot of dissolved ZnCl2 was added such that the solution remained undersaturated with respect to hydrozincite. Experimental duration varied among the replicates from 6 to 144 hours, and then all solids and solutions were separated by filtration, purified by ion exchange chromatography, and analyzed by MC-ICP-MS. Zn adsorbed on calcite is isotopically heavier than in the co-existing solutions, with ?68/66Zncalcite-solution of approximately 0.3‰. The variation of ?68/66Zncalcite-solution beyond 24 hours is insignificant, so we infer that isotopic equilibrium is reached by this time. Previous work strongly suggests that a difference in coordination number between dissolved Zn and adsorbed Zn is drives the observed fractionation. Elzinga and Reeder[5] determined using EXAFS (Extended X-ray Absorption Fine Structure) that Zn adsorbed to calcite surfaces is tetrahedrally coordinated, sharing three oxygens with the calcite surface. Meanwhile density functional theory calculations[6] predicted that tetrahedral Zn-O species should be heavier than octahedral Zn-O species. Thus we infer that equilibrium between octahedrally coordinated, dissolved Zn and tetrahedrally coordinated, adsorbed Zn is the mechanism of fractionation in our experiments. Our further studies will determine whether the isotopically heavy pool of adsorbed Zn becomes the Zn incorporated within carbonates; if so, then we are closer to understanding the mechanism by which carbonate rocks in nature are enriched in heavier isotopes of zinc. [1] Bermin et al., 2006, Chem. Geol. 226, 280. [2] Maréchal et al., 2000, Geochem. Geophys. Geosyst. 1, 1999GC-000029. [3] Dong et al., 2013, Talanta 114, 103-109. [4] Pichat et al., 2003, Earth Planet. Sci. Lett. 210, 167-178. [5] Elzinga and Reeder, 2002, Geochim. Cosmochim. Acta 66, 3943-3954. [6] Schauble, 2003, EOS, Trans. AGU, Fall Meet. Suppl. 84(46), B12B-0781.

Dong, S.; Wasylenki, L. E.

2013-12-01

73

Phosphate removal and recovery through crystallization of hydroxyapatite using xonotlite as seed crystal.  

PubMed

Xonotlite was synthesized and tested for phosphate removal and recovery from synthetic solution in a batch mode. The effects of pH, initial calcium concentration, bicarbonate concentration on phosphate removal through crystallization were examined. The morphology and X-ray diffraction (XRD) pattern of xonotlite before and after crystallization confirmed the formation of crystalline hydroxyapatite. The results indicated that the crystallization product had a very high P content (> 10%), which is comparable to phosphate rock at the dosage of 50-200 mg xonotlite per liter, with a maximum P content of 16.7%. The kinetics of phosphate removal followed the second-order reaction equation. The phosphate removal ability increased with increasing pH. The precipitation of calcium phosphate took place when pH was higher than 7.2, whereas the crystallization occurred at pH 6.0. A high calcium concentration could promote the removal of phosphate via crystallization, while a high bicarbonate concentration also enhanced phosphate removal, through that the pH was increased and thus induced the precipitation process. When xonotlite was used to remove phosphate from wastewater, the removal efficiency could reach 91.3% after 24 h reaction, with removal capacity 137 mg/g. The results indicated that xonotlite might be used as an effective crystal seed for the removal and recovery of phosphate from aqueous solution. PMID:20108657

Chen, Xuechu; Kong, Hainan; Wu, Deyi; Wang, Xinze; Lin, Yongyong

2009-01-01

74

Growth of Cadmium-Zinc Telluride Crystals by Controlled Seeding Contactless Physical Vapor Transport  

NASA Technical Reports Server (NTRS)

Bulk crystals of cadmium-zinc telluride, 23 mm in diameter and up to 45 grams in weight were grown. Controlled seed formation procedure was used to limit the number of grains in the crystal. Most uniform distribution of ZnTe in the crystals was obtained using excess (Cd + Zn) pressure in the ampoule.

Palosz, W.; Grasza, K.; Gillies, D.; Jerman, G.

1996-01-01

75

Selectively Nucleated Lateral Crystallization of Lead Zirconate Titanate Thin Films Using Titanium Island Seed Layer  

Microsoft Academic Search

We have investigated the selectively nucleated lateral crystallization (SNLC) of lead zirconate titanate (PZT) thin film using a titanium seed. The titanium island seed layer was formed on Pt(200 nm)\\/SiO2(500 nm)\\/Si by radio frequency magnetron sputtering and lift-off process at room temperature. Selectively nucleated lateral crystallization happened at 570°C and a rectangular array of PZT single grains was formed after

JONG-IN YUN; NAM-KYU SONG; SEUNG-KI JOO

2004-01-01

76

Crystallization kinetics of palm stearin in blends with sesame seed oil  

Microsoft Academic Search

This study investigates the crystallization kinetics of palm stearin (PS), a palm oil fraction, in blends with sesame seed\\u000a oil. The results indicate that the crystallization behavior of PS in sesame oil is mainly associated with the crystallization\\u000a of tripalmitin. Therefore, crystallization of blends of 26, 42, 60, and 80% (wt\\/vol) PS in sesame oil was described by equations\\u000a developed

J. F. Toro-Vazquez; M. Briceño-Montelongo; E. Dibildox-Alvarado; M. Charó-Alonso; J. Reyes-Hernández

2000-01-01

77

Why calcite can be stronger than quartz  

NASA Astrophysics Data System (ADS)

Calcite and quartz are two of the most common minerals in the continental crust and it is therefore not surprising that these minerals have been extensively studied since the very beginning of laboratory rock mechanics experiments. Extending such laboratory data to geological deformation rates around 10-14 s-1 requires an extrapolation of more than 7 orders of magnitude, with correspondingly large uncertainties. Extrapolation is based on the assumption that flow parameters are constant with changing conditions and that parameters not included in the flow law have a negligible influence on the creep properties. The validity of this extrapolation can only be tested, at least semi-quantitatively, by comparison with naturally deformed rocks. Observations generally indicate that quartz is significantly stronger than calcite in natural rocks, with quartz forming porphyroclasts in calcite marble mylonites, or with quartzite layers being folded or boudinaged within a weaker calcite marble matrix. However, in the Neves area (Tauern Window, Eastern Alps), shearing of Alpine coarse grained quartz-calcite veins under hydrous amphibolite facies conditions (ca. 550Ë? C) produced quartz mylonites containing asymmetric cm-scale single crystal calcite porphyroclasts. Under these conditions, coarse calcite is clearly stronger than the surrounding polycrystalline, dynamically recrystallized, quartz matrix. The important parameter controlling this difference in observed natural behaviour is the grain size of the calcite. Although there is considerable variation, uncertainty and even contradiction in the published experimental results, we show that extrapolation of laboratory creep data on calcite single crystals and coarse marbles, together with the corresponding data for wet quartzites, is indeed consistent with these natural observations. Extrapolation indicates an inversion in the relative strength of coarse calcite and quartz at a strain rate around 10-11 s-1, corresponding to a differential flow stress of ca. 50 MPa. At lower strain rates and stresses, wet quartz should be weaker than coarse calcite crystals. Field evidence (flow of quartz-rich layers even for orientations with very low resolved shear stress) and the preserved microstructure (lack of recrystallized or bulged twins in the calcite porphyroclasts) in the Neves area are also consistent with flow stresses of less than ca. 50 MPa. These low values during deformation under water-rich amphibolite facies conditions are in marked contrast to the much higher differential stresses reported for the flow (and fracture) of quartz-rich rocks under dry conditions in the middle to lower crust.

Mancktelow, N. S.; Pennacchioni, G.

2009-04-01

78

Unidirectional seeded single crystal growth from solution of benzophenone  

Microsoft Academic Search

A novel crystal growth method has been established for the growth of single crystal with selective orientation at room temperature. Using volatile solvent, the saturated solution containing the material to be crystallized was taken in an ampoule and allowed to crystallize by slow solvent evaporation assisted with a ring heater. The orientation of the growing crystal was imposed by means

K. Sankaranarayanan; P. Ramasamy

2005-01-01

79

Truncated tetrahedron seed crystals initiating stereoaligned growth of FeSi nanowires.  

PubMed

We have synthesized epitaxially grown freestanding FeSi nanowires (NWs) on an m-Al(2)O(3) substrate by using a catalyst-free chemical vapor transport method. FeSi NW growth is initiated from FeSi nanocrystals, formed on a substrate in a characteristic shape with a specific orientation. Cross-section TEM analysis of seed crystals reveals the crystallographic structure and hidden geometry of the seeds. Close correlation of geometrical shapes and orientations of the observed nanocrystals with those of as-grown NWs indicates that directional growth of NWs is initiated from the epitaxially formed seed crystals. The diameter of NWs can be controlled by adjusting the composition of Si in a Si/C mixture. The epitaxial growth method for FeSi NWs via seed crystals could be employed to heteroepitaxial growth of other compound NWs. PMID:22966939

Kim, Si-in; Yoon, Hana; Seo, Kwanyong; Yoo, Youngdong; Lee, Sungyul; Kim, Bongsoo

2012-10-23

80

Ammonothermal growth of high-quality GaN crystals on HVPE template seeds  

NASA Astrophysics Data System (ADS)

High quality GaN crystals have been successfully grown by the ammonothermal method in alkaline ammonia solutions using hydride vapor phase epitaxy (HVPE) seeds. The grown crystals, over 1 mm thick, are clear and possess excellent structural and optical properties. The crystalline structure of the as-grown bulk GaN is as good as, or better than the HVPE seeds as measured by high resolution X-ray rocking curves with 100 arcsec of full width at half maximum (FWHM) on (0 0 2) and 90 arcsec on (1 0 2) diffractions. The crystal quality is improved through a process of careful seed selection and controlled heating during nucleation, so that the ammonothermal growth replicates the seed crystals on both the nitrogen and gallium faces. The results are confirmed by low temperature photoluminescence spectra resolving donor-bound and free excitons as well as multiple phonon replicas, and further by room temperature cathodoluminescence indicating reduced yellow-band emission. Successful growth of high quality GaN crystals on HVPE seeds will facilitate the scale-up to large area growth by use of large area GaN HVPE templates as seeds.

Wang, Buguo; Bliss, David; Suscavage, Michael; Swider, Stacy; Lancto, Robert; Lynch, Candace; Weyburne, David; Li, Ti; Ponce, Fernando A.

2011-03-01

81

Protein-induced, previously unidentified twin form of calcite  

PubMed Central

Using single-crystal x-ray diffraction, we found a formerly unknown twin form in calcite crystals grown from solution to which a mollusc shell-derived 17-kDa protein, Caspartin, was added. This intracrystalline protein was extracted from the calcitic prisms of the Pinna nobilis shells. The observed twin form is characterized by the twinning plane of the (108)-type, which is in addition to the known four twin laws of calcite identified during 150 years of investigations. The established twin forms in calcite have twinning planes of the (001)-, (012)-, (104)-, and (018)-types. Our discovery provides additional evidence on the crucial role of biological macromolecules in biomineralization.

Pokroy, B.; Kapon, M.; Marin, F.; Adir, N.; Zolotoyabko, E.

2007-01-01

82

A finite element analysis of the seeding process for crystal growth by the Horizontal Bridgeman method. [SOLID6  

SciTech Connect

A Front Tracking finite element code was used to study movements of the solid-liquid interface which occur during the seeding process of semiconductor crystal growth. The analysis focused on improving control of the interface through use of seed crystal ''blankets.'' Thermal properties of the blanket materials ranged from isotropic to strongly anisotropic. Results showed that a seed blanket can be effective in control of both the interface position and shape during the seeding process.

Smidebush, M.

1985-09-01

83

Twin crystals of calcium oxalate in the seed coat of the kidney bean  

Microsoft Academic Search

Summary Examination of the seed coat of the kidney beanPhaseolus vulgaris L. (var. Kentucky Wonder) in the mature dry condition revealed a layer of cells in which almost every component cell contains a calcium oxalate crystal. These crystals were isolated and studied by light and scanning electron microscopy, and we determined with powder X-ray diffraction that the crystalline substance is

H. J. Arnott; M. A. Webb

1983-01-01

84

Characterization of Semi-Insulating CdTe Crystals Grown by Horizontal Seeded Physical Vapor Transport  

NASA Technical Reports Server (NTRS)

CdTe crystals were grown by horizontal seeded physical vapor transport technique in uncoated and boron nitride coated fused silica ampoules with the source materials near the congruent sublimation condition. The grown crystals were characterized by current-voltage measurements, low temperature photoluminescence spectroscopy, near IR transmission optical microscopy, spark source mass spectroscopy and chemical etching. The measured resistivities of the crystals were in the high-10(exp 8) ohm-cm range. Although the crystal grown in the boron nitride coating was contaminated with boron from the photoluminescence measurements, the coating yielded a single crystal with no inclusions or precipitates.

Chattopadhyay, K.; Feth, S.; Chen, H.; Burger, A.; Su, Ching-Hua

1998-01-01

85

Alternate deposition of oriented calcite and amino acid layer on calcite substrates.  

PubMed

Material synthesis inspired by novel nacre architecture and mechanism is popular and has attracted more and more attention. In this paper, iso-oriented calcite tablets/layers and amino acid layers were formed alternately on calcite wafers. It is interesting that the neonatal calcite tablets/layers have the same crystal orientation with their inorganic substrates through amino acid layers. It is quite possible that the amino acid layers in this study could transfer crystal orientation from formed inorganic layers to neighboring neonatal layers due to their fixed and appropriate structures, which may imply the process of nacre formation, and the role of aligned organic matrix sheets in nacre. Moreover, it could provide a new way to produce oriented calcite tablets/layers. PMID:18841888

Qiao, Li; Feng, Qingling; Li, Zhuo; Lu, Shanshan

2008-10-30

86

Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals  

DOEpatents

A method of fabricating bulk YBa{sub 2}Cu{sub 3}O{sub x} where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa{sub 2}Cu{sub 3}O{sub x} are heated in the presence of a Nd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub y} seed crystal to a temperature sufficient to form a liquid phase in the YBa{sub 2}Cu{sub 3}O{sub x} while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa{sub 2}Cu{sub 3}O{sub x} material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material. 7 figs.

Todt, V.; Miller, D.J.; Shi, D.; Sengupta, S.

1998-07-07

87

Inhibition of Seeded Growth of Enamel Apatite Crystals by Amelogenin and Enamelin Proteins in vitro  

Microsoft Academic Search

The effect of enamel matrix proteins on the seeded growth of enamel apatite crystals was studied in stable supersaturated solutions at pH 7.4 and 37°C. Of the two major protein classes in the enamel matrix, the enamelins were considerably more effective than the amelogenins in retarding seeded growth. However, the amelogenin species that did show significant inhibitory activity are those

Y. Doi; E. D. Eanes; H. Shimokawa; J. D. Termine

1984-01-01

88

MFI zeolite nanosponges possessing uniform mesopores generated by bulk crystal seeding in the hierarchical surfactant-directed synthesis.  

PubMed

The synthesis of a mesoporous material with uniform mesopore diameters and crystalline MFI zeolite walls has been achieved, simply by seeding the multiammonium surfactant-directed synthesis with bulk zeolite crystals. The bulk seeds disappeared in the final product. As a result of seeding, the mesoporous zeolites could be generated rapidly even at high Al content. PMID:24633468

Jo, Changbum; Cho, Kanghee; Kim, Jaeheon; Ryoo, Ryong

2014-03-25

89

Dislocation Creep in Magnesium Calcite  

Microsoft Academic Search

To investigate the effect of dissolved Mg on plastic deformation of calcite, we performed triaxial deformation experiments on synthetic calcite with varying amount of Mg content. Mixtures of powders of calcite and dolomite were isostatically hot pressed (HIP) at 850° C and 300 MPa confining pressure for different intervals (2 to 20hrs) resulting in homogeneous aggregates of high-magnesium calcite; Mg

L. Xu; X. Xiao; B. J. Evans

2003-01-01

90

Development of a versatile high temperature top seeded solution growth unit for growing cesium lithium borate crystals  

Microsoft Academic Search

The design and fabrication of a state of the art high temperature top seeded solution growth (HTTSSG) unit with seed and crucible rotation options is discussed. Crystals from solid solutions of high viscosity could be grown using the setup. The fabricated setup is used to grow high optical quality single crystals of cesium lithium borate with dimensions 50×40×40 mm3 for

Babu Reddy J N; Suja Elizabeth; H. L. Bhat; A. K. Karnal

2009-01-01

91

Tensile-Strained Single-Crystal Si Film on Insulator by Epitaxially Seeded and Laser-Induced Lateral Crystallization  

NASA Astrophysics Data System (ADS)

Tensile-strained single-crystal silicon films on insulator islands have been grown from Si wafer substrates by a process combining selective epitaxial growth (SEG) and pulsed laser crystallization. An amorphous Si film on an insulator island is completely melted by a single excimer laser pulse, leading to the solidification of the molten Si seeded from epitaxially grown single-crystal Si regions. Analyses of the resulting microstructures reveal that the laterally crystallized film is single-crystalline. A tensile strain of up to 8.8× 10-3 within the crystallized region was measured by Raman spectroscopy. The tensile-strained Si film has potential applications in high-performance devices for three-dimensionally stacked integrated circuits.

Cho, Hans S.; Xianyu, Wenxu; Zhang, Xiaoxin; Yin, Huaxiang; Noguchi, Takashi

2006-10-01

92

Biogenic and synthetic high magnesium calcite - a review.  

PubMed

Systematic studies on the Mg distributions, the crystal orientations, the formation mechanisms and the mechanical properties of biogenic high-Mg calcites in different marine organisms were summarized in detail in this review. The high-Mg calcites in the hard tissues of marine organisms mentioned generally own a few common features as follows. Firstly, the Mg distribution is not uniform in most of the minerals. Secondly, high-Mg calcite biominerals are usually composed of nanoparticles that own almost the same crystallographic orientations and thus they behave like single crystals or mesocrystals. Thirdly, the formation of thermodynamically unstable high-Mg calcites in marine organisms under mild conditions is affected by three key factors, that is, the formation of amorphous calcium (magnesium) carbonate precursor, the control of polymorph via biomolecules and the high Mg/Ca ratios in modern sea. Lastly, the existence of Mg ions in the Mg-containing calcite may improve the mechanical properties of biogenic minerals. Furthermore, the key progress in the synthesis of high-Mg calcites in the laboratory based on the formation mechanisms of the biogenic high-Mg calcites was reviewed. Many researchers have realized the synthesis of high-Mg calcites in the laboratory under ambient conditions with the help of intermediate amorphous phase, mixed solvents, organic/inorganic surfaces and soluble additives. Studies on the structural analysis and formation mechanisms of thermodynamically unstable biogenic high-Mg calcite minerals may shed light on the preparation of functional materials with enhanced mechanical properties. PMID:24291472

Long, Xia; Ma, Yurong; Qi, Limin

2014-01-01

93

TEM study of Pt-C replicas of calcite overgrowths precipitated from electrolyte solutions  

NASA Astrophysics Data System (ADS)

The surface microtopography of synthetic magnesian calcite overgrowths on calcite powders was imaged on Pt-C replicas by transmission electron microscopy. The overgrowths were precipitated at room temperature under steady-state conditions from seawater-like solutions, in the presence and absence of Mg 2+, SO 42- and PO 43- ions, and over a range of saturation states. Overgrowths produced from the Mg-free electrolyte show smooth coverage of the substrate with a few hillocks suggestive of spiral growth. Electrolytes containing Mg consistently produced patchy overgrowths on the {1014} faces of the seed crystals and differential inhibition of growth at their corners and edges. The patchy over-growths consist of flat-topped islands whose morphology is consistent with two-dimensional surface nucleation rather than spiral growth. The density of islands, their rounding, and their degree of coalescence increased with the saturation state of the precipitating solution. The effect of SO 42- on the surface topography was imperceptible. Soluble reactive phosphate (SRP), on the other hand, clearly inhibited growth and dissolution along specific crystallographic directions. The development of irregular surfaces along specific edges and corners of the seed crystals shows that foreign ions promote the development of complex crystal morphology even at high saturation states.

Paquette, Jeanne; Vali, Hojatollah; Mucci, Alfonso

1996-12-01

94

A comparative appraisal of adsorption of citrate on whewellite seed crystals  

NASA Astrophysics Data System (ADS)

Adsorption of citrate by whewellite was examined with three different techniques: solution depletion, seeded crystal growth inhibition, and microelectrophoresis (zeta potential). Comparison of the results from the three techniques indicates that at the concentrations giving 50% coverage or 50% inhibition, there was reasonable agreement if the adsorbate was assumed to be trivalent citrate.

Curreri, P. A.; Onoda, G.; Finlayson, B.

1981-05-01

95

Crystal structure control in Au-free self-seeded InSb wire growth.  

PubMed

In this work we demonstrate experimentally the dependence of InSb crystal structure on the ratio of Sb to In atoms at the growth front. Epitaxial InSb wires are grown by a self-seeded particle assisted growth technique on several different III-V substrates. Detailed investigations of growth parameters and post-growth energy dispersive x-ray spectroscopy indicate that the seed particles initially consist of In and incorporate up to 20 at.% Sb during growth. By applying this technique we demonstrate the formation of zinc-blende, 4H and wurtzite structure in the InSb wires (identified by transmission electron microscopy and synchrotron x-ray diffraction), and correlate this sequential change in crystal structure to the increasing Sb/In ratio at the particle-wire interface. The low ionicity of InSb and the large diameter of the wire structures studied in this work are entirely outside the parameters for which polytype formation is predicted by current models of particle seeded wire growth, suggesting that the V/III ratio at the interface determines crystal structure in a manner well beyond current understanding. These results therefore provide important insight into the relationship between the particle composition and the crystal structure, and demonstrate the potential to selectively tune the crystal structure in other III-V compound materials as well. PMID:21346304

Mandl, Bernhard; Dick, Kimberly A; Kriegner, Dominik; Keplinger, Mario; Bauer, Günther; Stangl, Julian; Deppert, Knut

2011-04-01

96

The coordination of Mg in foraminiferal calcite  

NASA Astrophysics Data System (ADS)

The Mg/Ca ratio of foraminiferal calcite is a widely accepted and applied empirical proxy for ocean temperature. The analysis of foraminifera preserved in ocean sediments has been instrumental in developing our understanding of global climate, but the mechanisms behind the proxy are largely unknown. Analogies have been drawn to the inorganic precipitation of calcite, where the endothermic substitution of Mg for Ca is favoured at higher temperatures. However, evidence suggests that foraminiferal Mg incorporation may be more complex: foraminiferal magnesium is highly heterogeneous at the sub-micron scale, and high Mg areas coincide with elevated concentrations of organic molecules, Na, S and other trace elements. Fundamentally, the incorporation mode of Mg in foraminifera is unknown. Here we show that Mg is uniformly substituted for Ca within the calcite mineral lattice. The consistency of Mg-specific X-ray spectra gathered from nano-scale regions across the shell ('test') reveals that the coordination of Mg is uniform. The similarity of these spectra to that produced by dolomite shows that Mg is present in an octahedral coordination, ideally substituted for Ca in a calcite crystal structure. This demonstrates that Mg is heterogeneous in concentration, but not in structure. The degree of this uniformity implies the action of a continuous Mg incorporation mechanism, and therefore calcification mechanism, across these compositional bands in foraminifera. This constitutes a fundamental step towards a mechanistic understanding of foraminiferal calcification processes and the incorporation of calcite-bound palaeoenvironment proxies, such as Mg.

Branson, Oscar; Redfern, Simon A. T.; Tyliszczak, Tolek; Sadekov, Aleksey; Langer, Gerald; Kimoto, Katsunori; Elderfield, Henry

2013-12-01

97

Lattice Dynamics of Calcite  

Microsoft Academic Search

The phonon dispersion relations for the lowest-ten external branches, and for wave vectors along the optic axis, ahve been measured in calcite, CaCO3, at room temperature, by means of inelastic-neutron-scattering techniques. The results are shown to be consistent with a simple shell model containing ten adjustable parameters.

E. R. Cowley; A. K. Pant

1973-01-01

98

Optical, structural, thermal and dielectric spectroscopy characterizations of seeded melt grown 2-hydroxy biphenyl single crystal.  

PubMed

Organic single crystal of 2-hydroxy biphenyl (2-HB) was grown by top seeded melt growth method. Scanning electron microscopy studies has been carried out on the surface of the grown crystals to investigate the nature of growth and defects. The crystalline perfection and lattice parameters of 2-HB has been determined by single crystal XRD analysis and it belongs to orthorhombic crystal system with space group Fdd2. The functional groups and molecular associations were confirmed by FT-IR. The optical characteristics such as cut-off and transmittance were carried out using UV-Vis-NIR spectra. Absence of absorption in the region between 320 and 1100nm makes the grown crystal desirable to optical applications. Thermal stability of grown crystals was characterized by thermogravimetric (TGA), differential thermal analysis (DTA) and differential scanning calorimetric (DSC) analyses. Broadband dielectric studies reveals that dielectric constant of grown crystal is low. The resistivity of grown crystal was studied by impedance analysis. The second harmonic generation intensity of 3.8mJ was studied. The grown crystal belongs to soft material studied by hardness test. PMID:24792201

Sadhasivam, S; Rajesh, Narayana Perumal

2014-09-15

99

Fractal Statistics of Modeled Zoning Patterns in Calcite  

NASA Astrophysics Data System (ADS)

In recent years, the phenomenon of oscillatory zoning has been established in more than 70 rock-forming and accessory minerals having been formed in different geological media [Shore & Fowler, 1996]. Observations of oscillatory zoning in solution-grown calcite crystals are reported by Reeder et al. [1990]. In these calcites periodic zonal variations in Mn2+ content were not correlated with changes in any bulk solution parameters, and it was interpreted that the oscillatory behavior developed autonomously. Wang and Merino [1992] describe a dynamic model for calcite grown from an aqueous solution containing growth-inhibiting cations such as Mn2+. This model, based on a feedback involving H+ accumulation, surface adsorption, and calcite growth inhibition is able to autonomously produce oscillatory changes of Ca2+ and H2CO3 concentrations adjacent to a calcite growth surface without large-scale changes in bulk water chemistry.

Bryksina, Natalia; Halden, Norman; Mejia, Sergio

100

Novel Fabrication Method for Transparent Conducting Oxide Films Utilizing Solid-Phase Crystallized Seed Layers  

NASA Astrophysics Data System (ADS)

High quality ZnO:Al (AZO) films have been obtained by our novel fabrication method utilizing solid-phase crystallized (SPC) seed layers. The crystal grain size of AZO films with seed layers is 5 times larger than that of conventional films, which is due to the low nuclei density of seed layers. As a result, the resistivity of AZO films of 18 nm in total film thickness is drastically reduced from 40×10-4 ? cm for the conventional films to 5×10-4 ? cm for our films. No differences in transparency hve been observed between AZO films with and without seed layers and their optical transmittance is higher than 80% in a wide wavelength range of 400-2500 nm. These results reveal that our method is very promising for fabrication of transparent conducting oxide films. Our method opens up a new avenue for oxide fabrications of nm thick films with excellent crystallinity, because it can be easily extended to other oxides whose amorphous phase is difficult to obtain.

Itagaki, Naho; Kuwahara, Kazunari; Nakahara, Kenta

2011-12-01

101

Effects of mixing, seeding, material of baffles and final temperature on solution crystallization of l-glutamic acid in an oscillatory baffled crystallizer  

Microsoft Academic Search

In this paper, we report the effects of mixing intensity, seeding, composition of baffle material and final temperature on meta-stable zone width (MSZW) and crystal polymorph in solution crystallization of an industrially important compound, l-glutamic acid, in an oscillatory baffled crystallizer (OBC). The results show that the MSZW decreases with increasing of mixing; meta-stable ? crystals are transformed into stable

Xiongwei Ni; Anting Liao

2010-01-01

102

Improving the diffraction of full-length human selenomethionyl metavinculin crystals by streak-seeding  

PubMed Central

Metavinculin is an alternatively spliced isoform of vinculin that has a 68-residue insert in its tail domain (1134 total residues) and is exclusively expressed in cardiac and smooth muscle tissue, where it plays important roles in myocyte adhesion complexes. Mutations in the metavinculin-specific insert are associated with dilated cardiomyopathy (DCM) in man. Crystals of a DCM-associated mutant of full-length selenomethionine-labeled metavinculin grown by hanging-drop vapor diffusion diffracted poorly and were highly sensitive to radiation, preventing the collection of a complete X-ray diffraction data set at the highest possible resolution. Streak-seeding markedly improved the stability, crystal-growth rate and diffraction quality of DCM-associated mutant metavinculin crystals, allowing complete data collection to 3.9?Å resolution. These crystals belonged to space group P43212, with two molecules in the asymmetric unit and unit-cell parameters a = b = 170, c = 211?Å, ? = ? = ? = 90°.

Rangarajan, Erumbi S.; Izard, Tina

2010-01-01

103

Seeded Physical Vapor Transport of Cadmium-Zinc Telluride Crystals: Growth and Characterization  

NASA Technical Reports Server (NTRS)

Crystals of Cd(1-x)Zn(x)Te with x = 0.2 and 40 g in weight were grown on monocrystalline cadmium-zinc telluride seeds by closed-ampoule physical vapor transport with or without excess (Cd + Zn) in the vapor phase. Two post-growth cool-down rates were used. The crystals were characterized using low temperature photoluminescence, atomic force microscopy, chemical etching, X-ray diffraction and electrical measurements. No formation of a second, ZnTe-rich phase was observed.

Palosz, W.; George, M. A.; Collins, E. E.; Chen, K.-T.; Zhang, Y.; Burger, A.

1997-01-01

104

Native crystal structure of a nitric oxide-releasing lectin from the seeds of Canavalia maritima  

Microsoft Academic Search

Here, we report the crystallographic study of a lectin from Canavalia maritima seeds (ConM) and its relaxant activity on vascular smooth muscle, to provide new insights into the understanding of structure\\/function relationships of this class of proteins. ConM was crystallized and its structure determined by standard molecular replacement techniques. The amino acid residues, previously suggested incorrectly by manual sequencing, have

Carlos Alberto de Almeida Gadelha; Frederico Bruno Mendes Batista Moreno; Tatiane Santi-Gadelha; João Batista Cajazeiras; Bruno Anderson Matias da Rocha; Ana Maria Sampaio Assreuy; Mário Rogério Lima Mota; Nilson Vieira Pinto; Ana Vaneska Passos Meireles; Júlio César Borges; Beatriz Tupinamba Freitas; Fernanda Canduri; Emmanuel Prata Souza; Plínio Delatorre; David Neil Criddle; Walter Filgueira de Azevedo; Benildo Sousa Cavada

2005-01-01

105

Seed crystals with improved properties for melt processing superconductors for practical applications  

DOEpatents

A method of fabricating bulk superconducting material is disclosed including RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} comprising heating compressed powder oxides and/or carbonates of R and Ba and Cu present in mole ratios to form RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} in physical contact with an oxide single crystal seed to a temperature sufficient to form a liquid phase in the RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} while maintaining the single crystal seed solid to grow the superconducting material and thereafter cooling to provide a material including RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}. R is a rare earth or Y or La and the single crystal seed has a lattice mismatch with RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} of less than about 2% at the growth temperature. The starting material may be such that the final product contains a minor amount of R{sub 2}BaCuO{sub 5}.

Veal, B.W.; Paulikas, A.; Balachandran, U.; Zhong, W.

1997-03-18

106

Seed crystals with improved properties for melt processing superconductors for practical applications  

DOEpatents

A method of fabricating bulk superconducting material including RBa.sub.2 Cu.sub.3 O.sub.7-.delta. comprising heating compressed powder oxides and/or carbonates of R and Ba and Cu present in mole ratios to form RBa.sub.2 Cu.sub.3 O.sub.7-.delta. in physical contact with an oxide single crystal seed to a temperature sufficient to form a liquid phase in the RBa.sub.2 Cu.sub.3 O.sub.7-.delta. while maintaining the single crystal seed solid to grow the superconducting material and thereafter cooling to provide a material including RBa.sub.2 Cu.sub.3 O.sub.7-.delta.. R is a rare earth or Y or La and the single crystal seed has a lattice mismatch with RBa.sub.2 Cu.sub.3 O.sub.7-.delta. of less than about 2% at the growth temperature. The starting material may be such that the final product contains a minor amount of R.sub.2 BaCuO.sub.5.

Veal, Boyd W. (Downers Grove, IL); Paulikas, Arvydas (Downers Grove, IL); Balachandran, Uthamalingam (Hinsdale, IL); Zhong, Wei (Chicago, IL)

1997-01-01

107

Transformation of echinoid Mg calcite skeletons by heating  

NASA Astrophysics Data System (ADS)

Interambularcral plates of echinoid Heterocentrotus trigonarius, composed of Mg calcite 1 (?14 mol% MgCO 3), were heated in three timed series of experiments at 300°C. Dried plate fragments and fragments with added water were heated separately in pressurized bombs. X-ray powder diffractometry, unit cell dimensions, and phase compositions are used to monitor reaction progress. After 10 h heating in the bombs dolomite (43.5 mol% MgCO 3) and Mg calcite appear (4-7 mol% MgCO 3); by 20 h all Mg calcite 1 is consumed, and at 120 h dolomite composition has evolved to ?47 mol% MgCO 3 and calcite to ?2 mol% MgCO 3. Whole plates heated at 300°C in an open muffle furnace develop dolomite (?42 mol% MgCO 3) and Mg calcite 2 (?6 mol% MgCO 3) after 10 h and remain compositionally invariant throughout subsequent heating to 620 h. Limited skeletal water catalyzes the early reaction but escapes from the open furnace and consequently reaction ceases after ?10 h. The experimentally produced dolomite has relative Mg-Ca ordering of 75% to 79%. The stabilization of echinoid Mg calcite by heating at 300°C to a mixture of dolomite and calcite occurs through a dissolution/precipitation reaction. The alteration fabric produced within the stereom consists of irregularly shaped, branched dolomite crystals > 5 ?m homoaxially set in a calcite 2 (bomb) or Mg calcite 2 (furnace) matrix. Round and tubular pores 1 to 5 ?m are randomly distributed throughout this fabric. The stereom pore system remains intact during furnace heating but is destroyed during heating in bombs. The texture of experimentally stabilized echinoid skeletons is different from that of fossil echinoderms that are composed of microrhomic dolomite homoaxially set in a single calcite crystal.

Dickson, J. A. D.

2001-02-01

108

Structure of KTiOPO{sub 4} single crystals grown by the top-seeded solution and spontaneous flux crystallization methods  

SciTech Connect

This paper reports on the results of precision X-ray structural investigations of KTiOPO{sub 4} single crystals grown by one method (crystallization from a solution in the melt) in two variants (the spontaneous formation of crystallization centers or top-seeded solution growth during slow cooling of saturated solution melts). It is shown that spontaneous flux crystallization leads to the formation of a larger number of defects. Potassium atoms are found to be disordered. The splitting of the K1 and K2 potassium positions is equal to 0.347(4) and 0.279(3) A, respectively, for the crystals grown by the top-seeded solution method and 0.308(5) and 0.321(4) A, respectively, for the crystals grown through the spontaneous flux crystallization.

Novikova, N. E., E-mail: natnov@ns.crys.ras.ru; Verin, I. A.; Sorokina, N. I.; Alekseeva, O. A. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Voronkova, V. I. [Moscow State University (Russian Federation); Tseitlin, M. [Ariel University Center of Samaria (Israel); Roth, M. [Hebrew University of Jerusalem, Faculty of Science (Israel)

2008-11-15

109

Controlling mechano- and seeding-triggered single-crystal-to-single-crystal phase transition: molecular domino with a disconnection of aurophilic bonds.  

PubMed

Green and blue polymorphs: A single-crystal-to-single-crystal (SCSC) phase transition of phenyl(3,5-dimethylphenyl isocyanide)gold(I) was triggered by mechanical picking or solid seeding and propagated spontaneously with a domino-like mechanism. As a result, one phase with intense green emission was transformed to another phase with weaker blue emission. PMID:24281880

Seki, Tomohiro; Sakurada, Kenta; Ito, Hajime

2013-12-01

110

The steam reforming of phenol over natural calcite materials  

Microsoft Academic Search

Five natural calcite materials of different geographical origin were studied towards the steam reforming of phenol reaction and the activity results obtained were correlated with some of their physico-chemical properties. It was found that the specific catalytic activity (?mol\\/(m2s)) of the calcite material following calcination at 850°C was not correlated with the BET area and the primary crystal size of

Domna A. Constantinou; Angelos M. Efstathiou

2009-01-01

111

Growth of AlN bulk crystals on SiC seeds: Chemical analysis and crystal properties  

NASA Astrophysics Data System (ADS)

AlN single crystals are grown by physical vapor transport (PVT) in sintered TaC crucibles in the presence of SiC, i.e. by seeding on 6H-SiC or by adding SiC to the AlN source material. Different growth conditions, i.e. growth temperatures T=1900-2050 °C and off-orientation angles in respect to [0001] ?=0-42°, are applied in order to investigate to which extent the incorporation of Si and/or C can be controlled during the PVT growth. Chemical analysis is performed by energy-dispersive X-ray analysis (EDX), secondary ion mass spectrometry (SIMS), and Rutherford backscattering spectroscopy (RBS). The grown crystals are significantly contaminated with Si and C in the range of several atomic percents, but they do not represent pseudo-binary AlN-SiC solid solutions. Samples cut from these crystals are probed by Raman micro-spectroscopy, optical absorption, cathodoluminescence (CL), and near band-gap photoluminescence (PL) in order to evaluate the crystal properties. All crystals exhibit phonon bands at the positions of AlN phonon energies, and a low-temperature band-gap exceeding 5.8 eV, which is only slightly lower than the band-gap of pure AlN. On the other hand, the samples show very different optical properties below the band-gap, including coloration. As the changes in optical properties do not correlate to chemical analysis, we suggest that self-compensation of silicon and carbon as well as formation of intrinsic defects lead to a complex compensation scenario in the samples. The grown crystals are thus to be considered as highly compensated, Si/C co-doped AlN.

Bickermann, Matthias; Filip, Octavian; Epelbaum, Boris M.; Heimann, Paul; Feneberg, Martin; Neuschl, Benjamin; Thonke, Klaus; Wedler, Elke; Winnacker, Albrecht

2012-01-01

112

Vapor-Phase Growth of Bulk Crystals of Cadmium Telluride and Cadmium Zinc Telluride on Gallium Arsenide Seeds  

NASA Astrophysics Data System (ADS)

The growth of large-area bulk crystals of cadmium telluride and cadmium zinc telluride has been demonstrated using the combination of a novel physical vapor transport growth system and heteroepitaxial seeding on GaAs wafers. X-ray diffraction studies show the resulting material to be of extremely high quality despite the large lattice mismatch between the seed and the grown crystal. This process should provide a reliable growth route for large-area large-volume single-crystal boules of cadmium telluride and cadmium zinc telluride.

Mullins, J. T.; Cantwell, B. J.; Basu, A.; Jiang, Q.; Choubey, A.; Brinkman, A. W.; Tanner, B. K.

2008-09-01

113

Calcite epitaxy on Au and Ag (1 1 1)  

Microsoft Academic Search

Crystallization control is an intensely studied field. This study concerns synthesis of epitaxial calcite on Au and Ag substrate without the use of any template. The crystals were analyzed in situ by micro-Raman spectroscopy and ex situ by Scanning Electron Microscopy (SEM) and Electron Backscattering Diffraction (EBSD). Undersaturated solution containing only calcium and hydrogen carbonate is used. Electrochemically induced dissolved

Hassiba Teghidet; Marie Claude Bernard; Stephan Borensztajn; Lila Chaal; Suzanne Joiret; Boualem Saidani

2011-01-01

114

Seeded growth of AlN bulk crystals in m- and c-orientation  

NASA Astrophysics Data System (ADS)

Seeded growth of AlN boules was achieved on m-(1 0 1¯ 0) and c-(0 0 0 1¯) orientations by physical vapor transport (PVT). The single crystalline m- and c-plane seeds were cut from freestanding AlN single crystals. AlN boules 12 mm in diameter and 7 mm in height were grown at source temperatures around 2280 °C in N 2 atmosphere at 500 Torr of total pressure. Under identical process conditions, the m- and c-plane boules exhibited the same growth rates, 150-170 ?m/h, and similar expansion angles, 22-27°, which indicated that the growth was controlled by the thermal profile inside the crucible rather than by crystallographic differences. X-ray rocking curve analysis and Raman spectroscopy confirmed that both m- and c-plane grown crystals possessed high crystalline quality. The dislocation density in both crystals was non-uniform and in the range 10 2-10 5 cm -2, as characterized by X-ray topography.

Lu, P.; Collazo, R.; Dalmau, R. F.; Durkaya, G.; Dietz, N.; Raghothamachar, B.; Dudley, M.; Sitar, Z.

2009-12-01

115

Primary magmatic calcite reveals origin from crustal carbonate  

NASA Astrophysics Data System (ADS)

We have investigated lava flows representative of the whole eruptive history of the Colli Albani ultrapotassic volcanic district (Central Italy). One of the most intriguing features concerning some of these lava flows is the occurrence of primary, magmatic calcite in the groundmass. The primary, magmatic nature of calcite has been inferred by microtextural investigations showing that it typically occurs i) interstitially, associated with clinopyroxene, nepheline and phlogopite, ii) in spherical ocelli, associated with nepheline, fluorite and tangentially arranged clinopyroxene, and iii) in corona-like reaction zones around K-feldspar xenocrysts. These microtextural features distinctly indicate that calcite crystallized from a carbonate melt in a partially molten groundmass, implying that the temperature of the system was above the solidus of the hosted lava flow (> 850 °C). Geochemical features of calcite crystals (i.e., stable isotope values and trace element patterns) corroborate their primary nature and give insights into the origin of the parental carbonate melt. The trace element patterns testify to a high-temperature crystallization process (not hydrothermal) involving a carbonate melt coexisting with a silicate melt. The high ?18O (around 27‰ SMOW) and wide ?13C (? 18 to + 5‰ PDB) values measured in the calcites preclude a mantle origin, but are consistent with an origin in the crust. In this framework, the crystallization of calcite can be linked to the interaction between magmas and carbonate-bearing wall rocks and, in particular, to the entrapment of solid and/or molten carbonate in the silicate magma. The stability of carbonate melt at low pressure and the consequent crystallization of calcite in the lava flow groundmass are ensured by the documented, high activity of fluorine in the studied system and by the limited ability of silicate and carbonate melts to mix at syn-eruptive time scales.

Gozzi, Fernando; Gaeta, Mario; Freda, Carmela; Mollo, Silvio; Di Rocco, Tommaso; Marra, Fabrizio; Dallai, Luigi; Pack, Andreas

2014-03-01

116

Growth of Bulk InBO 3 Crystals  

Microsoft Academic Search

Conditions are optimized for top-seeded solution growth of bulk indium orthoborate, InBO3?, crystals using the Na2O–BaO–B2O3 flux system. InBO3 has a hexagonal unit cell and is isostructural with calcite; a= 4.812 Å, c = 15.47 Å, microhardness of 11 ± 0.70 GPa. InBO3 crystals are essentially insoluble in common organic and inorganic solvents.

N. G. Kononova; A. E. Kokh; T. B. Bekker; P. P. Fedorov; E. A. Tkachenko

2004-01-01

117

Growth of high-quality ZnO single crystals by seeded CVT using the newly designed ampoule  

NASA Astrophysics Data System (ADS)

The high-quality ZnO single crystals were grown by seeded chemical vapor transport (CVT) in a newly designed ampoule using carbon as a transport agent. The well-faceted crystal of about 5×5×5 mm 3 can be grown reproducibly. Secondary ion mass spectroscopy (SIMS) analysis, X-ray rocking curve (XRC) and photoluminescence (PL) measurements demonstrate that the grown single crystal is of high purity and high crystallinity.

Hong, Sang-Hwui; Mikami, Makoto; Mimura, Kouji; Uchikoshi, Masahito; Yasuo, Akihiko; Abe, Seishi; Masumoto, Katashi; Isshiki, Minoru

2009-07-01

118

Effect of pH on calcite growth at constant a/a ratio and supersaturation  

NASA Astrophysics Data System (ADS)

In situ Atomic Force Microscopy (AFM) was used to study the growth of calcite at a constant supersaturation ( ? = 6.5) and solution stoichiometry (a/a=1) in the pH range 7.5-12. The calcite growth rate decreased with increasing pH in the studied range. The results can be successfully explained by the surface complexation model for calcite growth and by considering the effect of OH - ions on solute hydration. At pH below 8.5, growth occurs mainly by CaCO 30 incorporation at >CaHCO 30 surface sites. CaCO 30 should be more easily incorporated than free Ca 2+ ions, as water exchange is usually faster if water molecules in the ion hydration shells are substituted by other ligands, as in CaCO 30. However, at pH above 9, Ca 2+ incorporation at >CaHCO 30 sites also contributes to calcite growth as a result of the increased frequency of water exchange in calcium hydration shells due to the presence of strongly hydrated OH -. This also leads to an increase in the solid-liquid interfacial tension at high pH, which seems to reduce the nucleation rate and increase the average size of crystals precipitated in macroscopic, non-seeded experiments. The reduction of calcite growth rate is a consequence of decreasing surface concentration of active growth sites (i.e., >CaHCO 30) with increasing pH under our experimental conditions. Changes in two-dimensional island morphology were observed at high pH (12), possibly due to the stabilization of polar scalenohedral faces by the presence of OH - ions. This work may help to improve our understanding of the effects of carbonate-solution reactions resulting from potential changes in the pH of the oceans and surface waters in response to variations in atmospheric CO 2, as well as in understanding calcite precipitation in highly alkaline environments both natural (e.g., alkali lakes) and artificial (e.g., cement carbonation).

Ruiz-Agudo, E.; Putnis, C. V.; Rodriguez-Navarro, C.; Putnis, A.

2011-01-01

119

Calcite/barium fluoride ultraviolet polarizing prism  

NASA Astrophysics Data System (ADS)

A calcite/barium fluoride polarizing prism gives improved ultraviolet transmittance compared with a calcite/calcite ultraviolet polarizing prism. Beam spatial distortion is transmitted because of variations in absorption (and path length) in the calcite half of the calcite/barium fluoride prism.

Wu, Fuquan; Li, Guohua; Huang, Jiayin; Yu, Dehong

1995-07-01

120

Calcite epitaxy on Au and Ag (1 1 1)  

NASA Astrophysics Data System (ADS)

Crystallization control is an intensely studied field. This study concerns synthesis of epitaxial calcite on Au and Ag substrate without the use of any template. The crystals were analyzed in situ by micro-Raman spectroscopy and ex situ by Scanning Electron Microscopy (SEM) and Electron Backscattering Diffraction (EBSD). Undersaturated solution containing only calcium and hydrogen carbonate is used. Electrochemically induced dissolved oxygen reduction on the metal electrode was used to increase the pH of the solution in the vicinity of the metallic surface, leading to calcium carbonate formation. The calcite crystals so obtained were uniform in size and orientation and presented a (0 0 1) face parallel to the Au or Ag (1 1 1) surface. In order to verify the selectivity of those surfaces, calcium carbonate was also crystallized on copper (1 1 1) adlayers electrodeposited on gold (1 1 1) film. The epitaxial calcite appeared only on Au or Ag substrate when various rhombohedra could be evidenced on the copper modified surface. From these results, an epitaxial relationship has been suggested where hexagonal symmetry of the (0 0 1) calcite plane was in a R30° ?3×?3 arrangement on the Au (1 1 1) surface. This led to a mismatch for lattice parameters below 0.5%. Moreover the cathodic shift of potential needed to form epitaxial calcite on silver was an indirect proof that the first plane in contact with gold was a calcium one.

Teghidet, Hassiba; Bernard, Marie Claude; Borensztajn, Stephan; Chaal, Lila; Joiret, Suzanne; Saidani, Boualem

2011-09-01

121

Tunable ring laser with internal injection seeding and an optically-driven photonic crystal reflector.  

PubMed

Continuous tuning over a 1.6 THz region in the near-infrared (842.5-848.6 nm) has been achieved with a hybrid ring/external cavity laser having a single, optically-driven grating reflector and gain provided by an injection-seeded semiconductor amplifier. Driven at 532 nm and incorporating a photonic crystal with an azobenzene overlayer, the reflector has a peak reflectivity of ~80% and tunes at the rate of 0.024 nm per mW of incident green power. In a departure from conventional ring or external cavity lasers, the frequency selectivity for this system is provided by the passband of the tunable photonic crystal reflector and line narrowing in a high gain amplifier. Sub - 0.1 nm linewidths and amplifier extraction efficiencies above 97% are observed with the reflector tuned to 842.5 nm. PMID:22714491

Zheng, Jie; Ge, Chun; Wagner, Clark J; Lu, Meng; Cunningham, Brian T; Hewitt, J Darby; Eden, J Gary

2012-06-18

122

Characterization of physicochemical and thermal properties and crystallization behavior of krabok (Irvingia Malayana ) and rambutan seed fats.  

PubMed

Fatty acid composition, physicochemical and thermal properties and crystallization behavior of fats extracted from the seeds of krabok (Irvingia Malayana) and rambutan (Nephelium lappaceum L.) trees grown in Thailand were studied and compared with cocoa butter (CB). The krabok seed fat, KSF, consisted of 46.9% lauric and 40.3% myristic acids. It exhibited the highest saponification value and slip melting point but the lowest iodine values. The three fats displayed different crystallization behavior at 25°C. KSF crystallized into a mixture of ?' and pseudo-?' structures with a one-step crystallization curve and high solid fat content (SFC). The fat showed simple DSC crystallization and melting thermograms with one distinct peak. The rambutan seed fat, RSF, consisted of 42.5% arachidic and 33.1% oleic acids. Its crystallization behavior was more similar to CB than KSF, displaying a two-step crystallization curve with SFC lower than that of KSF. RSF solidified into a mixture of ?' and pseudo-?' before transforming to ? after 24 h. The large spherulitic microstructures were observed in both KSF and RSF. According to these results, the Thai KSF and RSF exhibited physicochemical, thermal characteristics and crystallization behavior that could be suitable for specific applications in several areas of the food, cosmetic and pharmaceutical industries. PMID:23196867

Sonwai, Sopark; Ponprachanuvut, Punnee

2012-01-01

123

Unusual calcite stromatolites and pisoids from a landfill leachate collection system  

NASA Astrophysics Data System (ADS)

Low-magnesium calcite stromatolites and pisoids were found to have precipitated within the leachate collection system piping of a Palm Beach County, Florida, landfill. The stromatolites and pisoids formed in an aphotic and anoxic environment that was at times greatly supersaturated with calcite. The stromatolites are composed of branching cylindrical bundles of concentrically laminated radial fibrous crystals. The pisoids consist of concentric layers of radial fibrous and microcrystalline calcite. Bacteria, likely sulfate reducing, appear to have acted as catalysts for calcite crystal nucleation, and thus the formation of the stromatolites and pisoids. The leachate system stromatolites provide a recent example of stromatolites that formed largely by cement precipitation. By acting as catalysts for calcite nucleation, bacteria may cause more rapid cementation than would have occurred under purely abiotic conditions. Rapid calcite precipitation catalyzed by bacteria has interfered with the operation of the Palm Beach County landfill leachate collection by obstructing pipes and may be an unrecognized problem at other landfill sites.

Maliva, Robert G.; Missimer, Thomas M.; Leo, Kevin C.; Statom, Richard A.; Dupraz, Christophe; Lynn, Matthew; Dickson, J. A. D.

2000-10-01

124

Improving the diffraction of full-length human selenomethionyl metavinculin crystals by streak-seeding.  

PubMed

Metavinculin is an alternatively spliced isoform of vinculin that has a 68-residue insert in its tail domain (1134 total residues) and is exclusively expressed in cardiac and smooth muscle tissue, where it plays important roles in myocyte adhesion complexes. Mutations in the metavinculin-specific insert are associated with dilated cardiomyopathy (DCM) in man. Crystals of a DCM-associated mutant of full-length selenomethionine-labeled metavinculin grown by hanging-drop vapor diffusion diffracted poorly and were highly sensitive to radiation, preventing the collection of a complete X-ray diffraction data set at the highest possible resolution. Streak-seeding markedly improved the stability, crystal-growth rate and diffraction quality of DCM-associated mutant metavinculin crystals, allowing complete data collection to 3.9?Å resolution. These crystals belonged to space group P4(3)2(1)2, with two molecules in the asymmetric unit and unit-cell parameters a=b=170, c=211?Å, ?=?=?=90°. PMID:21139209

Rangarajan, Erumbi S; Izard, Tina

2010-12-01

125

Chemistry and petrography of calcite in the KTB pilot borehole, Bavarian Oberpfalz, Germany  

USGS Publications Warehouse

The KTB pilot borehole in northeast Bavaria, Germany, penetrates 4000 m of gneiss, amphibolite, and subordinate calc-silicate, lamprophyre and metagabbro. There are three types of calcite in the drilled section: 1) metamorphic calcite in calc-silicate and marble; 2) crack-filling calcite in all lithologies; and 3) replacement calcite in altered minerals. Crack-filling and replacement calcite postdate metamorphic calcite. Multiple calcite generations in individual cracks suggest that different generations of water repeatedly flowed through the same cracks. Crack-filling mineral assemblages that include calcite originally formed at temperatures of 150-350??C. Presently, crack-filling calcite is in chemical and isotopic equilibrium with saline to brackish water in the borehole at temperatures of ???120??C. The saline to brackish water contains a significant proportion of meteoric water. Re-equilibration of crack-filling calcite to lower temperatures means that calcite chemistry tells us little about water-rock interactions in the crystal section of temperatures higher than ~120??C. -from Author

Komor, S. C.

1995-01-01

126

Anisotropic lattice distortions in biogenic calcite induced by intra-crystalline organic molecules  

Microsoft Academic Search

We have performed precise structural measurements on five different calcitic seashells by high-resolution X-ray powder diffraction on a synchrotron beam line and by laboratory single crystal X-ray diffraction. The unit cell parameters a and c of biogenic calcite were found to be systematically larger than those measured in the non-biogenic calcite. The maximum lattice distortion (about 2·10?3) was detected along

Boaz Pokroy; Andrew N. Fitch; Frederic Marin; Moshe Kapon; Noam Adir; Emil Zolotoyabko

2006-01-01

127

EPR theoretical study of local lattice structure on Mn 2+ ion doped in calcite and differences between single crystal and fresh water snail, Pila globosa  

NASA Astrophysics Data System (ADS)

By diagonalizing the complete energy matrices for a d5 configuration ion in a trigonal ligand-field and considering the second-order, fourth-order EPR parameters D and ( a - F) simultaneously, the substitution position of Mn 2+ ion in the CaCO 3:Mn 2+ system has been studied by analyzing the optical absorption and EPR spectra of single crystal and the ostracum layer of operculum of fresh water snail Pila globosa. The results show that in the single crystal there is an obvious compressed distortion ? R = -0.158 Å and ? ? = 0.70°, and the distortion in P. globosa is ? R = -0.107 Å and ? ? = -0.34° ˜ -0.23°. Meanwhile the EPR parameters 10 4( a - F) = 7.02-7.29 cm -1 and 10 4a = 6.35 cm -1 are predicted in P. globosa.

Fu, Cheng-Guo; Kuang, Xiao-Yu; Wang, Hui; Yang, Xiong; Tan, Xiao-Ming

2006-06-01

128

EPR theoretical study of local lattice structure on Mn 2+ ion doped in calcite and differences between single crystal and fresh water snail, Pila globosa  

Microsoft Academic Search

By diagonalizing the complete energy matrices for a d5 configuration ion in a trigonal ligand-field and considering the second-order, fourth-order EPR parameters D and (a?F) simultaneously, the substitution position of Mn2+ ion in the CaCO3:Mn2+ system has been studied by analyzing the optical absorption and EPR spectra of single crystal and the ostracum layer of operculum of fresh water snail

Cheng-Guo Fu; Xiao-Yu Kuang; Hui Wang; Xiong Yang; Xiao-Ming Tan

2006-01-01

129

The influence of P CO 2 on the partitioning of magnesium in calcite overgrowths precipitated from artificial seawater at 25° and 1 atm total pressure  

NASA Astrophysics Data System (ADS)

The influence of carbon dioxide partial pressure (P CO 2) on the composition of magnesian calcite overgrowths precipitated from artificial seawater at 25 °C on synthetic, rhombohedral calcite seeds was investigated using a chemo-stat precipitation technique. Powder X-ray diffraction (XRD) analyses of the overgrowths indicate that the amount of MgCO 3 incorporated during the precipitation is independent of the p co 2 over four orders of magnitude (10 -0.5 to 10 -4.6 atm). The magnesium content of the overgrowths estimated from mass balance calculations of the carbonate alkalinity of the reacting solutions (? Ac) and flame atomic absorption spectrophotometric (AA) analyses of the reacted solids yield similar results. Values determined by the latter method are compromised by calculation errors arising from gas phase disequilibrium when the alkalinity is computed from the steady state pH and P CO 2, of the gas phase. The concentration of sodium in the overgrowths, however, appears to correlate with variations in P CO 2. The lack of correlation between magnesium partitioning in calcite overgrowths and P CO 2 observed in this study contrasts with results obtained by previous investigators but does not preclude that the composition of calcite cements could be affected by variations in growth mechanism induced by changes in solution variables or the nature of the substrate. Based on the results of this study and recent laboratory and field observations, we propose that a change in growth mechanism and differential partitioning of magnesium on nonequivalent faces of a growing calcite crystal in seawater could explain some of the compositional variability of modern, marine calcite cements. In view of these latter considerations, we feel that it is premature to speculate on conditions that led to cyclic secular variations in the composition and mineralogy of marine carbonate cements precipitated during the Phanerozoic.

Hartley, George; Mucci, Alfonso

1996-01-01

130

Capillary-Seeding Crystallization and Preliminary Crystallographic Analysis of a Solvent-Tolerant Elastase from Pseudomonas aeruginosa Strain K  

PubMed Central

Seeding is a versatile method for optimizing crystal growth. Coupling this technique with capillary counter diffusion crystallization enhances the size and diffraction quality of the crystals. In this article, crystals for organic solvent-tolerant recombinant elastase strain K were successfully produced through microseeding with capillary counter-diffusion crystallization. This technique improved the nucleation success rate with a low protein concentration (3.00 mg/mL). The crystal was grown in 1 M ammonium phosphate monobasic and 0.1 M sodium citrate tribasic dihydrate pH 5.6. The optimized crystal size was 1 × 0.1 × 0.05 mm3. Elastase strain K successfully diffracted up to 1.39 Å at SPring-8, Japan, using synchrotron radiation for preliminary data diffraction analysis. The space group was determined to be monoclinic space group P1211 with unit cell parameters of a = 38.99 ?, b = 90.173 Å and c = 40.60 Å.

Ali, Mohd Shukuri Mohamad; Said, Zatty Syamimi @ Adura Mat; Raja Abd Rahman, Raja Noor Zaliha; Thean Chor, Adam Leow; Basri, Mahiran; Salleh, Abu Bakar

2013-01-01

131

Magnetic susceptibility as a tool to study deformed calcite with variable impurity content  

Microsoft Academic Search

A set of calcite mylonites were systematically sampled along the basal shear zone of the Morcles Nappe, located in the southwestern Swiss Alps, to investigate the relationship among crystallographic preferred orientation (CPO), chemistry, and anisotropy of magnetic susceptibility (AMS). Second-phase minerals are ?10 vol % of the rock. The substitution of trace impurities for Ca in the calcite crystal lattice,

Bjarne S. G. Almqvist; Marco Herwegh; Volkmar Schmidt; Thomas Pettke; Ann M. Hirt

2010-01-01

132

Controlled growth of vertically aligned ZnO nanowires with different crystal orientation of the ZnO seed layer.  

PubMed

A novel synthesis and growth method achieving vertically aligned zinc oxide (ZnO) nanowires on a silicon dioxide (SiO(2)) coated silicon (Si) substrate is demonstrated. The growth direction of the ZnO nanowires is determined by the crystal structure of the ZnO seed layer, which is formed by the oxidation of a DC-sputtered Zn film. The [002] crystal direction of the seed layer is dominant under optimized thickness of the Zn film and thermal treatment. Vertically aligned ZnO nanowires on SiO(2) coated Si substrate are realized from the appropriately thick oxidized Zn seed layer by a vapor-solid growth mechanism by catalyst-free thermal chemical vapor deposition (CVD). These experimental results raise the possibility of using the nanowires as functional blocks for high-density integration systems and/or photonic applications. PMID:21825796

Cha, S N; Song, B G; Jang, J E; Jung, J E; Han, I T; Ha, J H; Hong, J P; Kang, D J; Kim, J M

2008-06-11

133

X-Ray Characterization of Structural Defects in Seeded and Self-Seeded ZnSe Crystal Grown by PVT in Horizontal and Vertical Configurations  

NASA Technical Reports Server (NTRS)

As part of a pre-flight ground based investigation of crystal growth of II-VI compound semiconductors, a number of ZnSe boules have been grown by physical vapor transport (PVT) at Marshall Space Flight Center. Boules were grown in both horizontal and vertical configurations and seeded and self-seeded growth techniques were employed. As-grown and/or cleaved boules were examined by a combination of synchrotron white beam x-ray topography (SWBXT) and high resolution triple axis diffraction (HRTXD) to characterized the structural defects and correlate them with the growth conditions. Horizontal grown boules tend to grow away from the ampoule wall (contactless growth) and generally exhibit large (110) facets parallel to the gravity vector. Vertical grown boules grew to the full diameter of the ampoule and exhibited no faceting. X-ray topography combined with back reflection x-ray diffraction revealed the presence of lamellar twins (180 deg type about the [111] axis) in horizontal grown boules while vertically grown boules contain a few large grains, some of which are twinned. X-ray topographs and reciprocal space maps recorded from the boules show the better crystal quality of horizontal grown boules. The relationship between crystal quality and gravity vector is investigated. Further, an attempt is made to extend the Hurle theory of twin nucleation in Czochralski grown crystals to explain the twinning mechanisms in horizontal grown boules.

Raghothamachar, B.; Dudley, M.; Su, C.-H.; Volz, H. M.; Matyi, R.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

134

Cyanobacterial Calcite Precipitation - Laboratory Study on Different Spatial Scales  

NASA Astrophysics Data System (ADS)

Lacustrine calcite precipitation with sedimentation rates up to 1 mm per year can result in large carbonate deposits. Varved lake sediments high in calcite content are now intensively studied as high-resolution continental archives for environmental change. Especially in oligotrophic hardwater lakes, eukaryotic and prokaryotic picoplankton was found to be important in the overall process of calcite precipitation. Rates and mechanisms of bacteria-surface mediated precipitation reactions, however, remain poorly understood. For interpreting geochemical and isotopic information stored in sediments, it is essential to know the carbonate precipitation mechanisms and the governing environmental factors. Thus, laboratory experiments with picoplankton under controlled conditions were combined with electron and atomic force microscopy in order to obtain insights into the details of the calcite precipitation mechanisms of cyanobacteria. This study aimed at evaluating the potential of such laboratory studies and investigating the influence of environmental parameters as a first step. Under carefully controlled chemical and physical conditions, precipitation of calcite was induced by adding cultures of picocyanobacteria to supersaturated solutions of CaCO3 at different CaCl2/NaHCO3 ratios. The cell suspensions were purged with an artificial atmosphere at constant CO2 concentration. Abiotic solutions were used as reference systems. Chemical conditions such as pH, calcium and carbonate concentrations were continuously monitored by ion selective electrodes. The influence of supersaturation in the range of ? = 2 - 20 on biogenic precipitation was quantified at different ratios of calcium (0.7 - 48 mM) /carbonate (6 ? M - 35 ? M). In a series of bulk experiments it was possible to detect critical values of supersaturation for the onset of precipitation both with and without cells, both in the range of ? = 5 - 10. The morphology of the precipitates was analyzed by scanning electron microscopy. Both, initial crystals (<500 nm) and larger grown crystals (>10 ? m) showed rhombohedral and hexagonal-prism shapes characteristic for calcite. Ultrathin-sections ( ˜100nm) of the cyanobacteria cells and the attached calcite crystals were prepared by Focused Ion Beam. This technique allowed us to preserve the cell wall - crystal interface as intact as possible in order to perform Transmission Electron Microscopy (TEM) analysis of the sections. Using TEM-Electron Energy Loss Spectroscopy, carbon bonds in both calcite crystals and cyanobacteria cells were detected and identified. The carbon absorption spectra are significantly different to discriminate the organic and inorganic carbon. Thus, the absorption peaks are the fingerprints of the analyzed material and can be used to analyze the transition zone between the cell and the particle.

Obst, M.; Mavrocordatos, D.; Gasser, P.; Dittrich, M.

2003-12-01

135

Gamma-linolenic acid enrichment from Borago officinalis and Echium fastuosum seed oils and fatty acids by low temperature crystallization.  

PubMed

Solvent winterization of seed oil and free fatty acids (FFAs) was employed to obtain gamma-linolenic acid (GLA; 18:3omega6) concentrates from seed oils of two Boraginaceae species, Echium fastuosum and Borago officinalis. Different solutions of seed oils and FFAs from these two oils at 10%, 20% and 40% (w/w) were crystallized at 4 degrees C, -24 degrees C and -70 degrees C, respectively, using hexane, acetone, diethyl ether, isobutanol and ethanol as solvents. Best results were obtained for B. officinalis FFAs in hexane, reaching a maximum GLA concentration of 58.8% in the liquid fraction (LF). In E. fastuosum, the highest GLA concentration (39.9%) was also achieved with FFAs in hexane. PMID:16233632

López-Martínez, Juan Carlos; Campra-Madrid, Pablo; Guil-Guerrero, José Luis

2004-01-01

136

Sea urchin tooth mineralization: Calcite present early in the aboral plumula  

PubMed Central

In both vertebrate bone, containing carbonated hydroxyapatite as the mineral phase, and in invertebrate hard tissue comprised of calcium carbonate, a popular view is that the mineral phase develops from a long-lived amorphous precursor which later transforms into crystal form. Important questions linked to this popular view are: When and where is the crystallized material formed, and is amorphous solid added subsequently to the crystalline substrate? Sea urchin teeth, in which the earliest mineral forms within isolated compartments, in a time and position dependent manner, allow direct investigation of the timing of crystallization of the calcite primary plates. Living teeth of the sea urchin Lytechinus variegatus, in their native coelomic fluid, were examined by high-energy synchrotron x-ray diffraction. The diffraction data show that calcite is present in the most aboral portions of the plumula, representing the very earliest stages of mineralization, and that this calcite has the same crystal orientation as in the more mature adoral portions of the same tooth. Raman spectroscopy of the aboral plumula confirms the initial primary plate mineral material is calcite and does not detect amorphous calcium carbonate; in the more mature adoral incisal flange, it does detect a broader calcite peak, consistent with two or more magnesium compositions. We hypothesize that some portion of each syncytial membrane in the plumula provides the information for nucleation of identically oriented calcite crystals that subsequently develop to form the complex geometry of the single crystal sea urchin tooth.

Stock, Stuart R.; Veis, Arthur; Xiao, Xianghui; Almer, Jonathan D.; Dorvee, Jason R.

2012-01-01

137

An approach for phosphate removal with quartz sand, ceramsite, blast furnace slag and steel slag as seed crystal.  

PubMed

The phosphate removal abilities and crystallization performance of quartz sand, ceramsite, blast furnace slag and steel slag were investigated. The residual phosphate concentrations in the reaction solutions were not changed by addition of the ceramsite, quartz sand and blast furnace slag. The steel slag could provide alkalinity and Ca(2+) to the reaction solution due to its hydration activity, and performed a better phosphate removal performance than the other three. Under the conditions of Ca/P 2.0, pH 8.5 and 10 mg P/L, the phosphate crystallization occurred during 12 h. The quartz sand and ceramsite did not improve the phosphate crystallization, but steel slag was an effective seed crystal. The phosphate concentration decreased drastically after 12 h after addition of steel slag, and near complete removal was achieved after 48 h. The XRD analysis showed that the main crystallization products were hydroxyapatite (HAP) and the crystallinity increased with the reaction time. Phosphate was successfully recovered from low phosphate concentration wastewater using steel slag as seed material. PMID:22378001

Qiu, Liping; Wang, Guangwei; Zhang, Shoubin; Yang, Zhongxi; Li, Yanbo

2012-01-01

138

Characterization of Al2O3 coatings oxidized from Al with different proportion of seed crystals at a lower temperature  

NASA Astrophysics Data System (ADS)

Al layer with ?-Al2O3 seed crystals was prepared on the surface of 316L stainless steel (SS) by a double cathodes discharge technique, in which the mixed targets of pure Al doped with different proportions of ?-Al2O3 were used. Then, Al2O3 coatings were obtained after plasma oxidization at 580 °C. The phase composition, microstructure and morphology of the coatings were studied respectively by means of glancing-angle (1°) X-ray diffractometry (GAXRD) and scanning electron microscopy (SEM). Furthermore, the bonding force and corrosion resistance of the coatings were measured. The results indicated that ?-Al2O3 nucleated and grew surrounding the seed crystals as the Volmer-Weber Mode. The Al2O3 coating was compact, performing a good corrosion resistance and metallurgical bonding. The inducing effects of ?-Al2O3 with different fractions were discussed. ?-Al2O3 (5.5 wt.%) was distributed in the Al layer when the target possessing 10% ?-Al2O3 was used. After plasma oxidation, 65.54 wt.% ?-Al2O3 was obtained which was 10.34% more than that obtained by the oxidation of pure Al at the same condition. However, the inducing effects became weak with the further increment of content of ?-Al2O3 seed crystals.

Wang, Chen; Lin, Yuebin; He, Fei; Luo, Xinyi; Tao, Jie

2013-10-01

139

Urinary stone formation: Efficacy of seed extract of Ensete superbum (Roxb.) Cheesman on growth inhibition of calcium hydrogen phosphate dihydrate crystals  

NASA Astrophysics Data System (ADS)

The effect of aqueous seed extract of Ensete superbum (Roxb.) Cheesman on in vitro crystallization and growth patterns of calcium hydrogen phosphate dihydrate (CaHPO4·2H2O, CHPD) crystals was studied using single diffusion gel growth technique. Reduction in growth of CHPD crystals was noticed with increasing concentrations of seed extract. The morphology of CHPD or brushite crystals was studied by microscopy. The structural changes of the treated crystals were assessed by SEM, FT-IR, XRD and TGA/DTA analysis. It is expected that this multidisciplinary approach for in vitro crystallization and characterization of CHPD crystals will provide a better explanation to develop novel strategies for prevention of urinary stones.

Diana, K. J.; George, K. V.

2013-01-01

140

Thermodynamic Aspects of the Vaterite-Calcite Phase Transition  

Microsoft Academic Search

Although vaterite is the least stable anhydrous calcium carbonate polymorph, it is formed as a metastable phase in some normal\\u000a and pathological biomineralisation processes. In this work, thermodynamic aspects of the vaterite-calcite phase transition\\u000a were comprehensively studied. Vaterite samples were prepared by different methods and characterised for the composition, crystal\\u000a structure, specific surface and grain size. All products were identified

G. Wolf; E. Königsberger; H. G. Schmidt; L.-C. Königsberger; H. Gamsjäger

2000-01-01

141

Interaction of uranyl with calcite in the presence of EDTA.  

PubMed

Adsorption of uranyl at the surface of calcite was investigated by using batch sorption experiments and synchrotron X-ray standing wave (XSW) measurements. Aqueous solutions containing 236U(VI) (4.5 x 10(-7) to 1.0 x 10(-4) M) and EDTA (5.0 x 10(-7) to 1.1 x 10(-4) M) were reacted for 90 s to 60 min with freshly cleaved calcite (104) surfaces and calcite powders. Surface exchange coefficients, sorption kinetics, and influence of powder surface area/solution volume (SA/V) ratio were investigated by alpha-counting of 236U. Powder sorption results at SA/V = 870 cm2/mL fit a Freundlich isotherm [log [U]surface (in monolayers) = log K + n log [U]aq (in moles/L)], where K = 1.9+/-0.5 and n = 0.9+/-0.1, consistent with uptake of U(VI) by a specific surface reaction where the availability of sorption sites is nonlimiting in the U concentration range measured. Measured U(VI) coverages along this isotherm, based on the calcite (104) surface Ca site density, ranged from 0.04% to 5.4% of a monolayer. Steady state surface coverages were obtained within 90 s. Sorption of U(VI) on calcite (104) single-crystal cleavage surfaces using identical solutions yielded higher coverages, because of increased step density induced by dissolution at the relatively low SA/V ratio (approximately 1) of these measurements. The crystallographic location of the sorbed U(VI) was examined with the synchrotron XSW technique. Measurements were performed at the Advanced Photon Source on fresh calcite (104) cleavage surfaces reacted for 90 s with U(VI) solutions. Coherent fractions for sorbed U ranged from 0.14 to 0.62, and the mean value of the U coherent position was 0.84+/-0.02. This position was independent of dissolved U(VI) concentration and corresponds to a distance between the U atom and the calcite (104) plane of 2.55+/-0.06 A. These results are consistent with U(VI) adsorption atthe calcite surface as an inner-sphere uranyl-carbonate surface complex bonded with the outer oxygen atom(s) of a single surface carbonate group. Steric considerations allow this observed U(VI) surface complex to occur both at step sites ((441)_ and (481)_) and on terrace areas adjacent to Ca vacancies. PMID:15506202

Rihs, Sophie; Sturchio, Neil C; Orlandini, Kent; Cheng, Likwan; Teng, Henry; Fenter, Paul; Bedzyk, Michael J

2004-10-01

142

Bioremediation of Cd by microbially induced calcite precipitation.  

PubMed

Contamination by Cd is a significant environmental problem. Therefore, we examined Cd removal from an environmental perspective. Ureolysis-driven calcium carbonate precipitation has been proposed for use in geotechnical engineering for soil remediation applications. In this study, 55 calcite-forming bacterial strains were newly isolated from various environments. Biomineralization of Cd by calcite-forming bacteria was investigated in laboratory-scale experiments. A simple method was developed to determine the effectiveness of microbially induced calcite precipitation (MICP). Using this method, we determined the effectiveness of biomineralization for retarding the flow of crystal violet through a 25-mL column. When the selected bacteria were analyzed using an inductively coupled plasma optical emission spectrometer, high removal rates (99.95%) of Cd were observed following incubation for 48 h. Samples of solids that formed in the reaction vessels were examined using a scanning electron microscope. The CdCO3 compounds primarily showed a spherical shape. The results of this study demonstrate that MICP-based sequestration of soluble heavy metals via coprecipitation with calcite may be useful for toxic heavy metal bioremediation. PMID:24458656

Kang, Chang-Ho; Han, Sang-Hyun; Shin, Yujin; Oh, Soo Ji; So, Jae-Seong

2014-03-01

143

An Interpretation of the Mechanisms of Ice-Crystal Formation Operative in the Lake Almanor Cloud-Seeding Program.  

NASA Astrophysics Data System (ADS)

In a 1984 85 winter cloud-seeding program at Lake Almanor, California, indium sesquioxide (In2O3) aerosol particle generators were collocated with silver iodide (AgI) aerosol particle generators as a source of inert tracer aerosol. The In2O3 aerosol served as an indicator of the amount of AgI aerosol scavenged. Based on the aerosol emission rates, if AgI aerosol was only captured by scavenging processes, and played no part in forming ice crystals and snowfall, the silver to indium ratio (Ag:In) in the analyzed snow would be 0.8.Analysis of snow samples from the target area produced frequent Ag[ratio]In ratio values in excess of 1.1. In the snowfall at the closest sampling sites to the aerosol generator the high ratios of Ag[ratio]In cannot be explained by the contact-freezing ice formation mechanism. A mechanism with a much faster rate than possible by contact freezing is necessary to produce the high Ag[ratio]In ratios that were observed. Part of the AgI seeding aerosol functioned rapidly to produce ice crystals by a forced condensation-freezing mechanism immediately after generation, and those ice crystals contributed to the snowfall at those sites closest to the generator.

Chai, Steven K.; Finnegan, William G.; Pitter, Richard L.

1993-11-01

144

Microstructural control of calcite via incorporation of intracrystalline organic molecules in shells  

NASA Astrophysics Data System (ADS)

It is widely accepted that organic substances regulate or influence the structure of biominerals, but its direct evidences are not plenty. Here we show that the crystallographic microstructures in biotic calcites arise from incorporated intracrystalline organic molecules (IOMs), through a comparison between biotic calcites in shells and synthetic ones with the IOMs extracted from the shells. Although the prismatic layers of a pearl oyster (Pinctada fucata) and a pen shell (Atrina pectinata) morphologically resemble each other, the crystallographic features of constituent calcites are considerably different; in Pinctada, the IOMs are distributed inhomogeneously to form small-angle grain boundaries and associated crystal defects, whereas in Atrina, the IOMs are distributed almost homogeneously and defects are rare in the calcite crystals. We conducted in vitro calcite syntheses in the presence of the IOMs in EDTA-soluble extracts from the prisms. The IOMs in the extracts from Pinctada and Atrina were incorporated into synthetic calcites in a different manner, exhibiting defect-rich/free features as observed in the natural shells. With regard to amino acid compositions of the IOMs, the extract from Atrina has a higher proportion of acidic amino acids than that from Pinctada, implying that acidic proteins do not correlate directly to their affinity for calcium carbonate crystals.

Okumura, Taiga; Suzuki, Michio; Nagasawa, Hiromichi; Kogure, Toshihiro

2013-10-01

145

Purification, crystallization and preliminary crystallographic studies of a Kunitz-type proteinase inhibitor from tamarind (Tamarindus indica) seeds.  

PubMed

A Kunitz-type proteinase inhibitor has been purified from tamarind (Tamarindus indica) seeds. SDS-PAGE analysis of a purified sample showed a homogeneous band corresponding to a molecular weight of 21 kDa. The protein was identified as a Kunitz-type proteinase inhibitor based on N-terminal amino-acid sequence analysis. It was crystallized by the vapour-diffusion method using PEG 6000. The crystals belonged to the orthorhombic space group C222(1), with unit-cell parameters a = 37.2, b = 77.1, c = 129.1 A. Diffraction data were collected to a resolution of 2.7 A. Preliminary crystallographic analysis indicated the presence of one proteinase inhibitor molecule in the asymmetric unit, with a solvent content of 44%. PMID:19574654

Patil, Dipak N; Chaudhry, Anshul; Sharma, Ashwani K; Tomar, Shailly; Kumar, Pravindra

2009-07-01

146

Thermodynamics of magnesian calcite solid-solutions at 25??C and 1 atm total pressure  

USGS Publications Warehouse

The stability of magnesian calcites was reexamined, and new results are presented for 28 natural inorganic, 12 biogenic, and 32 synthetic magnesian calcites. The magnesian calcite solid-solutions were separated into two groups on the basis of differences in stoichiometric solubility and other physical and chemical properties. Group I consists of solids of mainly metamorphic and hydrothermal origin, synthetic calcites prepared at high temperatures and pressures, and synthetic solids prepared at low temperature and very low calcite supersaturations (??calcite ??? 1.5) from artificial sea water or NaClMgCl2CaCl2 solutions. Group I solids are essentially binary s of CaCO2 and MgCO2, and are thought to be relatively free of structural defects. Group II solid-solutions are of either biogenic origin or are synthetic magnesian calcites and protodolomites (0-20 and ??? 45 mole percent MgCO3) prepared at high calcite supersaturations (??calcite??? 3) from NaClNa2SO4MgCl2CaCl2 or NaClMgCl2CaCl2 solutions. Group II solid-solutions are treated as massively defective solids. The defects include substitution foreign ions (Na+ and SO42-) in the magnesian calcite lattice (point defects) and dislocations (~2 ?? 109 cm-2). Within each group, the excess free energy of mixing, GE, is described by the mixing model ge = X(1- x)[A0 + A1(2x - 1)], where x is the mole fraction of the end-member Ca0.5Mg0.5CO3 in the solid-solution. The values of A0 and A1 for Group I and II solids were evaluated at 25??C. The equilibrium constants of all the solids are closely described by the equation ln Kx = x(1-x) RT[A0 + A1(2x- 1)]+ (1 - x) ln [KC(1- x)]+ x ln (KDx), where KC and KD are the equilibrium constants of calcite and Ca0.5Mg0.5CO3. Group I magnesian calcites were modeled as sub-regular solid-solutions between calcite and dolomite, and between calcite and "disordered dolomite". Both models yield almost identical equilibrium constants for these magnesian calcites. The Group II magnesian calcites were modeled as sub-regular solid-solutions between defective calcite and protodolomite. Group I and II solid-solutions differ significantly in stability. The rate of crystal growth and the chemical composition of the aqueous solutions from which the solids were formed are the main factors controlling stoichiometric solubility of the magnesian calcites and the density of crystal defects. The literature on the occurrence and behavior of magnesian calcites in sea water and other aqueous solutions is also examined. ?? 1989.

Busenberg, E.; Niel, Plummer, L.

1989-01-01

147

Alternative origins for nannobacteria-like objects in calcite  

NASA Astrophysics Data System (ADS)

More than 40 calcite-precipitation experiments were performed under sterile conditions in order to investigate the origins of 25 300 nm spherical-, rod-, and ovoid-shaped objects that have been widely interpreted as evidence of nanometer-scale life (i.e., nannobacteria). Individual experiments included the addition of soluble organic compounds, common species of eubacteria, or phage-induced eubacterial lysates. These experiments indicate that many of the nanometer-scale objects have inorganic or nonnannobacterial origins. In the precipitation experiments, calcite formed euhedral crystals 50 800 nm in diameter and smaller (<50 nm) anhedral or rounded particles or protocrystals. The small anhedral or rounded solids resembled nannobacteria. The relative amount of anhedral or rounded calcite was greatest in experiments with a dissolved organic component. These controlled experiments are in accord with observations that rounded nanometer-scale objects are more common in minerals formed in organic-rich environments. Bacterial fragments occur as rounded to irregularly shaped particles that included cell-wall fragments, expulsed cytoplasm, and relict capsules that also closely resembled nannobacteria. Acid etching of the large euhedral crystals produced in the precipitation experiments also resulted in the formation of nanometer-scale features that resembled nannobacteria in natural carbonates. The shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching. Much caution is advisable in interpreting the origin of rounded features <50 nm.

Kirkland, Brenda L.; Lynch, F. Leo; Rahnis, Michael A.; Folk, Robert L.; Molineux, Ian J.; McLean, Robert J. C.

1999-04-01

148

Secondary nucleation of magnesium sulphate from single seed crystal by fluid shear in agitated supersaturated aqueous solution  

NASA Astrophysics Data System (ADS)

Distributions of the waiting time, the time required for a first nucleation at a constant degree of supercooling, and supercooling temperatures (or the maximum undercoolings) were measured for the fluid shear secondary nucleation from a single seed crystal (0.014-0.018 g) suspended by a fine nylon thread (0.1 mm in diameter) in an agitated supersaturated solution. These data are analysed by a stochastic model (random nucleation model) which deals with the nucleation as a random process. The waiting time is distributed exponentially. From the distribution, the nucleation probability B, a probability of nucleation per unit time and per seed crystal, was determined at undercooling of 3.0-7.0°C for the solution saturated at 40.0°C. The average supercooling temperature predicted by the model using B thus determined is in good agreement with the values measured at cooling rates of 3.35 × 10 -3, 6.75 × 10 -3 and 1.33 × 10 -2°C/s. The model explains reasonably well the cooling rate dependence of the supercooling temperature.

Kubota, Noriaki; Kubota, Kuokan

1986-07-01

149

Design of a diamond-crystal monochromator for the LCLS hard x-ray self-seeding project  

NASA Astrophysics Data System (ADS)

As the result of collaborations between the Advanced Photon Source (APS), Argonne National Laboratory, and the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory, we have designed and constructed a diamond crystal monochromator for the LCLS hard x-ray self-seeding project. The novel monochromator is ultrahigh-vacuum compatible to meet the LCLS linear accelerator vacuum environmental requirement. A special graphite holder was designed for strain-free mount of the 110-?m thin synthetic diamond crystal plate provided by Technological Institute for Super-hard and Novel Carbon Materials of Russia (TISNCM). An in-vacuum multi-axis precision positioning mechanism is designed to manipulate the thin-film diamond holder with resolutions and stabilities required by the hard x-ray self-seeding physics. Optical encoders, limit switches, and hardware stops are established in the mechanism to ensure system reliability and to meet the accelerator personal and equipment safety interlock requirements. Molybdenum shields are installed in the monochromator to protect the encoders and associated electronics from radiation damage. Mechanical specifications, designs, and preliminary test results of the diamond monochromator are presented in this paper.

Shu, D.; Shvyd'ko, Y.; Amann, J.; Emma, P.; Stoupin, S.; Quintana, J.

2013-03-01

150

Optimizing seeded casting of mono-like silicon crystals through numerical simulation  

NASA Astrophysics Data System (ADS)

Recently, silicon ingots produced by typical multicrystalline casting systems but having monocrystalline features are entering the photovoltaic market. In order to look into the particular properties of this novel method, the normal silicon casting process is numerically simulated, and compared to an optimized mono-like casting process, based on the use of oriented monocrystalline silicon seeds. The seeding process was optimized by reducing the time spent in the melt in order to reduce the back diffusion of harmful non-feedstock metal impurities such as iron, reducing the thermomechanical stress to avoid dislocation multiplication, and decreasing the overall interface curvature. Additionally, the growth conditions in the zone just above the seeds were fine-tuned to increase the production of vacancy point defects, in the hope of achieving "vacancy passivation" of harmful interstitial iron by moving it to substitutional position.

Black, Andrés; Medina, Juan; Piñeiro, Axa; Dieguez, Ernesto

2012-08-01

151

(U-Th)/He dating and He diffusion in calcite from veins and breccia  

NASA Astrophysics Data System (ADS)

Knowledge of He retention in crystalline calcite is mandatory to estimate the possibility of (U-Th)/He dating of calcite. To this aim, fault-filling calcite crystals from the Eocene/Oligocene Gondrecourt graben, Paris Basin, Eastern France, have been sampled, based on their relatively old, Eocene-Oligocene, precipitation age and cold thermal history (<40°C since precipitation). The samples were sorted into three main tectonic and morphological groups, including successively (1) micro-fracture calcites, (2) breccia and associated geodic calcites, and (3) vein and associated geodic calcites. (U-Th)/He dating of 63 calcite fragments yields ages dispersed from 0.2×0.02 to 35.8×2.7 Ma, as well as two older dates of 117×10 and 205×28 Ma (1s). These He ages correlate to grain chemistry, such as to Sr and ?REE concentrations or (La/Yb)N ratios, and these correlations probably reflect the evolution of parent fluid. Only the oldest He ages are in agreement with the He-retentive character of calcite as determined by Copeland et al. (2007), and these ages were obtained for the most recently precipitated crystals. To better understand the large He-age scatter and why calcites precipitated earlier show younger ages, He diffusion experiments have been conducted on 10 Gondrecourt calcite fragments from 3 samples with He ages of 0.2 to 6 Ma. In addition, a crystallographic investigation by X-Ray Diffraction (XRD) performed on similar samples reveals that the crystal structure evolves with increasing temperature, showing with micro-cracks and cleavage opening. These XRD results indicate that, in fault-filling calcite, He retention is controlled by multiple diffusion domains (MDD, Lovera et al., 1991) with various sizes, and therefore, evolves through time with strong consequences on (U-Th)/He age. We thus interpret the Gondrecourt calcite (U-Th)/He age scatter of older samples as a consequence of cleavage opening due to a succession of calcite crystallization phases related to the deformation history. Finally, we propose that the crystallization age of a calcite crystal with a known thermal history can nevertheless be retrieved by the (U-Th)/He method provided the He diffusion pattern can be measured by careful step-heating degassing analysis. Copeland, P., Watson, E.B., Urizar, S.C., Patterson, D., Lapen, T.J., 2007. Alpha thermochronology of carbonates. Geochim. Cosmochim. Acta, 71: 4488-4511. Cros, A. Gautheron, C., Pagel, M., Berthet, P., Tassan-Got, L., Douville, E., Pinna-Jamme, R., Sarda, P., submitted GCA, He behavior in calcite filling viewed by (U-Th)/He dating, He diffusion and crystallographic studies. Lovera, O.M., Richter, F.M., Harrison, T.M., 1991. Diffusion domains determined by 39Ar released during step heating. Journal of Geophysical Research, 96: 2057-2069.

Gautheron, C.; Cros, A.; Pagel, M.; Berthet, P.; Tassan-Got, L.; Douville, E.; Pinna-Jamme, R.; Sarda, P.

2013-12-01

152

In-situ observation of ettringite crystals  

NASA Astrophysics Data System (ADS)

In-situ observation of growing ettringite crystals in solution has been carried out and the morphology change of ettringite has been investigated under various conditions. In particular, the acceleration behavior of ettringite growth in the presence of calcite, the cause of which is not yet understood, is examined. Spherulite with calcite in its core is formed first followed by the generation of acicular crystals. Compared with the in-situ observation result of crystal growth in a solution with no calcite, the effect of added calcite can be explained as a decrease in the activation energy of nucleation for ettringite around calcite.

Komatsu, Ryuichi; Mizukoshi, Norihiro; Makida, Koji; Tsukamoto, Katsuo

2009-01-01

153

Etch Pits on Calcite Cleavage Faces  

Microsoft Academic Search

THIS communication describes some of the effects observed on calcite cleavage faces after etching with dilute acid. Puchegger1 has reported etch pits which formed a rib-like pattern on either side of scratch marks made on calcite. More striking features are described here.

H. Watts

1959-01-01

154

Barium recovery by crystallization in a fluidized-bed reactor: effects of pH, Ba/P molar ratio and seed.  

PubMed

The effects of process conditions, including upward velocity inside the column, the amount of added seed and seed size, the pH value of the precipitant or the phosphate stream and the Ba/P molar ratio in a fluidized-bed reactor (FBR) were studied with a view to producing BaHPO? crystals of significant size and maximize the removal of barium. XRD were used to identify the products that were collected from the FBR. Experimental results show that an upward velocity of 48 cmmin(-1) produced the largest BaHPO? crystals with a size of around 0.84-1.0mm. The addition of seed crystals has no effect on barium removal. The use of a seed of a size in the ranges unseeded<0.149-0.29 mm<0.149 mm<0.29-0.42 mm produced increasing amounts of increasingly large crystals. The largest BaHPO? crystals were obtained at pH 8.4-8.8 with a Ba/P molar ratio of 1.0. In the homogeneous and heterogeneous processes, around 98% of barium was removed at pH 8.4-8.6 and [Ba]/[P]=1.0. The XRD results show that a significant amount of barium phosphate (Ba?(PO?)?) was obtained at pH 11. The compounds BaHPO? and BaO were present at a pH of below 10. PMID:24462085

Su, Chia-Chi; Reano, Resmond L; Dalida, Maria Lourdes P; Lu, Ming-Chun

2014-06-01

155

Solution composition-dependence of the Ca isotope composition of inorganic calcite  

NASA Astrophysics Data System (ADS)

Laboratory experiments have shown that the Ca isotope composition of calcite precipitated from aqueous solution may be sensitive to solution chemistry, temperature, and solution pH. Generally, inorganic calcite precipitation experiments yield calcite crystals that are enriched in the light isotope of Ca relative to the parent solution. Previous studies by Lemarchand et al. (2004) and Tang et al. (2008) showed that the Ca isotope composition (?44Ca) of calcite varies systematically with precipitation rate (R). The studies, however, obtained the opposite relationship between ?44Ca and R despite precipitating calcite at comparable pH, temperature, and Ca2+ as well as CO32- ion concentrations. There is evidence that Ca isotope variability in calcite reflects a mass dependence on reaction rate coefficients, but it is unknown if the mass dependence varies with solution chemistry. A potentially important difference between the studies is that Lemarchand et al. (2004) used parent solutions with higher ionic strength (0.85 versus 0.035). The purpose of this study is to determine the solution composition dependence, if any, on Ca isotope incorporation during calcite growth from aqueous solutions. For our experiments, a beaker containing 300 mL of CaCl2+NH4Cl solution was placed in a container filled with 1 atm of an N2+CO2 gas mixture. The degree of supersaturation with respect to calcite was controlled by the pCO2 of the gas, which was constantly replenished. As CO2 dissolved into solution, calcite crystals grew on the beaker walls. The pH of the solution was maintained by an autotitrator with NaOH as the titrant. Calcite precipitation rates are typically expressed in mmol/m2/hr, but this is difficult to quantify as the reactive surface area of the crystals is not controlled. Relative growth rates are determined by weighing the amount of calcite precipitated over the course of an entire experiment on a fixed surface area. This provides a first estimate of R and we are investigating methods for improving this aspect of the results. Experiments have yielded calcite crystals enriched in the light isotope of Ca relative to the parent solution by 0.4‰ to 1.6‰. Growth rates are estimated to range from 0.01 to 131 mmol/m2/hr, overlapping with the rates from Lemarchand et al. (2004) and Tang et al. (2008). In experiments where we use a solution with high ionic strength (0.7), we find that ?44Ca in calcite increases with increasing precipitation rate. This is in agreement with the findings of Lemarchand et al. (2004), although Ca isotopes are more fractionated in our experiments. We are exploring if a solution with lower ionic strength reproduces the results of Tang et al. (2008), in which ?44Ca in calcite decreased with increasing precipitation rate. Our hypothesis is that solution chemistry may play an important role in calcium isotope incorporation in calcite and we will present results using different parent solution compositions that explore this relationship. The ultimate goal is to understand the molecular scale controls on isotope separation at the mineral surface during crystal growth.

Gonzales, M. S.; Watkins, J. M.; Depaolo, D. J.

2010-12-01

156

Growth kinetics in seeded cooling crystallization of 3-nitro-1,2,4-triazol-5-one in water– N-methylpyrrolidone  

Microsoft Academic Search

Growth kinetics in spherulitic crystallization of explosives 3-nitro-1,2,4-triazol-5-one (NTO) in water–N-methylpyrrolidone (NMP) are explored by seeded cooling crystallization. The effects of supersaturation, temperature and solvent composition were investigated. The orders of the growth for NTO spherulites with respect to supersaturation were found to be 3.62, 2.67 and 2.04, and the activation energies for formation of NTO spherulites were determined as

Kwang-Joo Kim; Kap-Mo Kim

2002-01-01

157

Seed crystals and catalyzed epitaxy of single-walled carbon nanotubes  

NASA Astrophysics Data System (ADS)

This thesis demonstrates the continued growth of single-walled carbon nanotubes (SWNTs) from seeded SWNTs in a way analogous to epitaxy or cloning; that is, the SWNTs grow as a seamless extension to the existing seeded SWNTs and have the same diameter and chirality as those of the SWNT seeds. The experiments were carried out in three key steps, including: (1) preparing a macroscopic array of open-ended SWNTs; (2) reductively docking transition metals as a catalyst to the nanometer-sized open ends; and then (3) heating the whole up to 700--850°C in the presence of a carbon feedstock such as ethanol or ethylene. The resulting SWNT ropes inherit the diameters and chirality from the seeded SWNTs, as indicated by the closely matched frequencies of Raman radial breathing modes before and after the growth. As a control, only sparse nanotubes grew from closed-ended SWNTs, ruling out spontaneous nucleation as a dominating mechanism in our experiments. This experiment proved for the first time the growth of SWNTs can be separated from the nucleation step. The ability to separate the typically inefficient nucleation step from the growth of SWNTs and to restart the growth opens the possibility of amplifying SWNTs with only the desired (n, m). The success in the continued growth was enabled with the creation of macroscopic arrays of open-ended SWNTs from a neat SWNT fiber. A variety of techniques including cryo-microtoming and surface etching chemistry have been developed to produce a macroscopic (˜1200mum2), aligned, and clean---largely free of amorphous carbon, oxides, and metal residuals---SWNT substrate with open-ended SWNTs aligned along the fiber axis. Alternatively, the fiber was milled perpendicular to the fiber axis with a gallium focused ion beam to produce a planar, free-standing, ultra-thin, "bed-of-nails" SWNT membrane---a single layer of parallel SWNTs densely packed and aligned along the normal of the membrane.

Wang, Yuhuang

158

In-Situ Partial Pressure Measurements and Visual Observation during Crystal Growth of ZnSe by Seeded Physical Vapor Transport  

NASA Technical Reports Server (NTRS)

An in-situ monitoring furnace was constructed with side windows to perform partial pressure measurements by optical absorption and visual observation of the growing crystal. A fused silica -rowth ampoule with a 4.5 cm long square tube between the source and the seed was prepared for the optical absorption measurements. A ZnSe crystal was grown by the seeded physical vapor transport (PVT) technique in the horizontal configuration. The growth temperature was 1120 C and the furnace translation rate was 3nmVday. Partial pressures of Se2, P(sub Se2), at three locations along the length of the growth ampoule were measured at 90 min intervals during the growth process. The measured P (sub Se2) were in the range of 2.0 to 6.5 x 10(exp -3) atm. The P(sub Se2) results indicated that the partial pressure profile was inconsistent with the results of the one-dimensional diffusion mass transport model and that the source composition shifted toward Se-rich during the run, i.e. the grown crystal was more Zn-rich than the source. The visual observation showed that the seed crystal first etched back, with greater thermal etching occurring along the edges of the seed crystal. Once the growth started, the crystal crew in a predominately contactless mode and facets were evident during growth. The crystal did not grow symmetrically which is believed to be due to the unintentional asymmetry of the radial thermal profile in the furnace.

Su, Ching-Hua; Feth, Shari; Lehoczky, Sandor L.

1999-01-01

159

Simulating Succinate-Promoted Dissolution at Calcite {104} Steps  

NASA Astrophysics Data System (ADS)

Organic molecules of a wide range of molecular weights from small organic acids, amino-acids, acidic peptides and acidic proteins to humic and fulvic acids play a key role in modulating nucleation, crystal growth and dissolution of calcium carbonate polymorphs. In general, these acidic molecules inhibit calcite growth and, promote dissolution preferentially along specific crystallographic directions, in the process, regulating crystal shape and size, and even whether a metastable polymorph (e.g., vaterite or aragonite) is nucleated first. For example, chiral faces of calcite are selected by chiral amino-acids and the unusual {hk0} faces are expressed in the presence of amino-acids [Orme et al., 2001], and unusual heptagonal dissolution etch-pit are seen in the presence of succinate compared to the normal rhombohedral pits in water alone [Teng et al., 2006]. Thus, the presence of unusual crystal morphologies may indicate organic-mediated growth, thus serving as a biosignature. We have conducted the Molecular Dynamics (MD) simulations using the Consistent Valence Force Field (CVFF) as implemented in the FORCITE© module of the Materials Studio © software package (Accelrys, Inc. TM) to model the adsorption of succinate, a dicarboxylic acid, and charge- balancing Na+ ions on dry and hydrated steps in different directions on the {104} cleavage face of calcite [Mkhonto and Sahai, in prep.]. At the site of succinate adsorption, we find elongation of the interatomic distances (Ca-OCO3,i) between surface Ca2+ cation and the oxygen of the underlying inorganic CO32- anion the first surface layer of calcite, compared to the corresponding distances in the presence of water alone, suggesting greater ease of surface Ca2+ detachment. This result is consistent with the empirically observed increase in overall dissolution rate with succinate [Teng et al., 2006]. Furthermore, succinate adsorption lowers the step energies, which explains the appearance of steps in the unsusual [42-1] and [010] directions in the presence of succinate as observed by Atomic Force Microscopy [Teng et al., 2006]. Finally, the calculated succinate adsorption energies at hydrated steps decreases in the sequence [-441] > [42-1] > [010], which also corresponds to the sequence of steps opening at dissolution etch-pits in the presence of succinate [Teng et al., 2006]. Our study provides a strong example of the utility of MD simulations in exploring organic-mediated mineral crystal dissolution (and growth) mechanisms, resulting in unusual morphologies, that may serve as biosignatures on Earth, and potentially on Mars and other worlds.

Mkhonto, D.; Sahai, N.

2008-12-01

160

Crystallization and preliminary X-ray studies of a galactose-specific lectin from the seeds of bitter gourd (Momordica charantia).  

PubMed

A galactose-specific lectin from the seeds of bitter gourd (Momordica charantia) is a four-chain type II ribosome-inactivating protein (RIP) resulting from covalent association through a disulfide bridge between two identical copies of a two-chain unit. The available structural information on such four-chain RIPs is meagre. The bitter gourd lectin was therefore crystallized for structural investigation and the crystals have been characterized. It is anticipated that the structure of the orthorhombic crystals will be analysed using molecular replacement by taking advantage of its sequence, and presumably structural, homology to normal two-chain type II RIPs. PMID:20823520

Chandran, Thyageshwar; Sharma, Alok; Vijayan, M

2010-09-01

161

The potential for phosphorus pollution remediation by calcite precipitation in UK freshwaters  

NASA Astrophysics Data System (ADS)

This paper examines the potential for calcium carbonate to reduce phosphate pollution in freshwaters by co-precipitation, a process known as a "self cleansing mechanism". Calcium carbonate saturation levels and phosphate concentrations (SRP - soluble reactive phosphate) across the major eastern UK river basins are examined to test for solubility controls. The study shows that calcite saturation varies for each catchment as a function of flow and biological activity rather than by direct regulation by SRP. Indeed, there is no evidence, for any of the rivers studied, that calcite solubility controls hold. However, for groundwater and groundwater-fed springs in the Chalk of the Thames basin, calcite saturation is observed with associated low SRP levels. A self-cleansing mechanism may well be operative within the Chalk due to two factors. Firstly, there is a high potential for nucleation on the calcite micro-crystals in the aquifer. Secondly, there are within aquifer reactions that remove the calcite nucleating inhibitors (SRP and dissolved organic carbon, DOC) to levels lower than those occurring within the rivers do. These inhibitors enter the catchment at very high concentrations in association with agricultural pollution (fertilizer application and animal slurry) and household contamination (e.g. sewage sources from septic tanks). Under low flow conditions, when the saturation index for calcite is at its highest, so too is the concentration of the nucleation inhibitor SRP. Companion work shows that calcite precipitation can occur at the water-sediment interface of the river and this may involve SRP removal. The data, as a whole, define an apparent bound for calcite solubility control where in the presence of nucleating centres, SRP must be less than 4 mM-P l-1 and DOC must be less than 150 mM-C l-1: a condition that does not seem to pertain within most UK rivers.

Neal, Colin

162

Sorption of phosphate onto calcite; results from batch experiments and surface complexation modeling  

NASA Astrophysics Data System (ADS)

The adsorption of phosphate onto calcite was studied in a series of batch experiments. To avoid the precipitation of phosphate-containing minerals the experiments were conducted using a short reaction time (3 h) and low concentrations of phosphate (?50 ?M). Sorption of phosphate on calcite was studied in 11 different calcite-equilibrated solutions that varied in pH, P, ionic strength and activity of Ca 2+, CO32- and HCO3-. Our results show strong sorption of phosphate onto calcite. The kinetics of phosphate sorption onto calcite are fast; adsorption is complete within 2-3 h while desorption is complete in less than 0.5 h. The reversibility of the sorption process indicates that phosphate is not incorporated into the calcite crystal lattice under our experimental conditions. Precipitation of phosphate-containing phases does not seem to take place in systems with ?50 ?M total phosphate, in spite of a high degree of super-saturation with respect to hydroxyapatite (SI HAP ? 7.83). The amount of phosphate adsorbed varied with the solution composition, in particular, adsorption increases as the CO32- activity decreases (at constant pH) and as pH increases (at constant CO32- activity). The primary effect of ionic strength on phosphate sorption onto calcite is its influence on the activity of the different aqueous phosphate species. The experimental results were modeled satisfactorily using the constant capacitance model with >CaPO 4Ca 0 and either >CaHPO 4Ca + or > CaHPO4- as the adsorbed surface species. Generally the model captures the variation in phosphate adsorption onto calcite as a function of solution composition, though it was necessary to include two types of sorption sites (strong and weak) in the model to reproduce the convex shape of the sorption isotherms.

Ugilt Sø, Helle; Postma, Dieke; Jakobsen, Rasmus; Larsen, Flemming

2011-05-01

163

Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes?  

NASA Astrophysics Data System (ADS)

Calcitic nanofibres are ubiquitous habits of secondary calcium carbonate (CaCO3) accumulations observed in calcareous vadose environments. Despite their widespread occurrence, the origin of these nanofeatures remains enigmatic. Three possible mechanisms fuel the debate: (i) purely physicochemical processes, (ii) mineralization of rod-shaped bacteria, and (iii) crystal precipitation on organic templates. Nanofibres can be either mineral (calcitic) or organic in nature. They are very often observed in association with needle fibre calcite (NFC), another typical secondary CaCO3 habit in terrestrial environments. This association has contributed to some confusion between both habits, however they are truly two distinct calcitic features and their recurrent association is likely to be an important fact to help understanding the origin of nanofibres. In this paper the different hypotheses that currently exist to explain the origin of calcitic nanofibres are critically reviewed. In addition to this, a new hypothesis for the origin of nanofibres is proposed based on the fact that current knowledge attributes a fungal origin to NFC. As this feature and nanofibres are recurrently observed together, a possible fungal origin for nanofibres which are associated with NFC is investigated. Sequential enzymatic digestion of the fungal cell wall of selected fungal species demonstrates that the fungal cell wall can be a source of organic nanofibres. The obtained organic nanofibres show a striking morphological resemblance when compared to their natural counterparts, emphasizing a fungal origin for part of the organic nanofibres observed in association with NFC. It is further hypothesized that these organic nanofibres may act as templates for calcite nucleation in a biologically influenced mineralization process, generating calcitic nanofibres. This highlights the possible involvement of fungi in CaCO3 biomineralization processes, a role still poorly documented. Moreover, on a global scale, the organomineralization of organic nanofibres into calcitic nanofibres might be an overlooked process deserving more attention to specify its impact on the biogeochemical cycles of both Ca and C.

Bindschedler, S.; Cailleau, G.; Braissant, O.; Millière, L.; Job, D.; Verrecchia, E. P.

2014-05-01

164

Sodium polyacrylate mediated dispersion of calcite  

Microsoft Academic Search

The stabilising action of sodium polyacrylate (NaPA) on colloidal dispersions of calcite has been investigated through measurement\\u000a of viscosity, electrophoretic mobility and solution ion concentration. The dose of NaPA was in the range 0 to 28 mg per g\\u000a of calcite and the dispersions were prepared at a solids content of 70% (by weight). The ionic strength of the dispersions

K. R. Rogan; A. C. Bentham; G. W. A. Beard; I. A. George; D. R. Skuse

165

Spectroscopic characterization of natural calcite minerals  

Microsoft Academic Search

The FT-IR, FT-Raman, NMR spectral data of ten different limestone samples have been compared. FT-IR and FT-Raman spectral data show that calcium carbonate in limestone, principally in the form of calcite, as identified by its main absorption bands at 1426, 1092, 876 and 712cm?1. The sharp diffractions at the d-spacings, 3.0348, 1.9166 and 1.8796 confirm the presence of calcite structure

S. Gunasekaran; G. Anbalagan

2007-01-01

166

Do organic ligands affect calcite dissolution rates?  

NASA Astrophysics Data System (ADS)

Steady state Iceland-spar calcite dissolution rates were measured at 25 °C in aqueous solutions containing 0.1 M NaCl and up to 0.05 M dissolved bicarbonate at pH from 7.9 to 9.1 in the presence of 13 distinct dissolved organic ligands in mixed-flow reactors. The organic ligands considered in this study include those most likely to be present in either (1) aquifers at the conditions pertinent to CO 2 sequestration or (2) soil/early diagenetic environments: acetate, phthalate, citrate, EDTA 4-, succinate, D-glucosaminate, L-glutamate, D-gluconate, 2,4-dihydroxybenzoate, 3,4-dihydroxybenzoate, fumarate, malonate, and gallate. Results show that the presence of <0.05 mol/kg of these organic anions changes calcite dissolution rates by less than a factor of 2.5 with the exception of citrate and EDTA 4-. The presence of 0.05 mol/kg citrate and EDTA 4- increases calcite dissolution rates by as much as a factor of 35 and 500, respectively, compared to rates in organic anion-free solutions. Further calcite dissolution experiments were performed in the presence of organic polymers similar to bacterial exudates, cell exopolysaccharides, and analogs of microbial cell envelopes: alginate, lichen extract, humic acid, pectin, and gum xanthan. In no case did the presence of <100 ppm of these organics change calcite dissolution rates by more than a factor of 2.5. Results obtained in this study suggest that the presence of aqueous organic anions negligibly affects calcite forward dissolution rates in most natural environments. Some effect on calcite reactivity may be observed, however, by the presence of organic anions if they change substantially the chemical affinity of the fluid with respect to calcite.

Oelkers, Eric H.; Golubev, Sergey V.; Pokrovsky, Oleg S.; Bénézeth, Pascale

2011-04-01

167

Coprecipitation of Chromate with Calcite: Batch Experiments and X-ray Absorption Spectroscopy  

SciTech Connect

Batch experiments, combined with in situ spectroscopic methods, are used to examine the coprecipitation of Cr(VI) with calcite, including partitioning behavior, site-specific distribution of Cr on the surface of calcite single crystals, and local coordination of Cr(VI) in the calcite structure. It is found that the concentration of Cr incorporated in calcite increases with increasing Cr concentration in solution. The calculated apparent partition coefficient, K{sub d}*, is highest at low Cr solution concentration, and decreases to a constant value with increasing Cr solution concentration. DIC images of the (1 0 {bar 1} 4) surface of calcite single crystals grown in the presence of CrO{sub 4}{sup 2-}exhibit well-defined growth hillocks composed of two pairs of symmetrically nonequivalent vicinal faces, denoted as + and -, which reflect the orientation of structurally nonequivalent growth steps. Micro-XRF mapping of the Cr distribution over a growth hillock shows preferential incorporation of Cr into the -- steps, which is considered to result from differences in surface structure geometry. XANES spectra confirm that incorporated Cr is hexavalent, and no reduction of Cr(VI) in the X-ray beam was observed up to 2 days at room temperature. EXAFS fit results show the incorporated Cr(VI) has the expected first shell of 4 O at {approx}1.64 {+-} 0.01 {angstrom}, consistent with CrO{sub 4}{sup 2-}. Best fit results show that the second shell is split with {approx}2.5 Ca at {approx}3.33 {+-} 0.05 and {approx}2.2 Ca at 3.55 {+-} 0.05 {angstrom}, which confirms the incorporation of chromate into calcite. Consideration of possible local coordination indicates that significant distortion or disruption is required to accommodate CrO{sub 4}{sup 2-}in the calcite structure.

Tang,Y.; Elzinga, E.; Lee, Y.; Reeder, R.

2007-01-01

168

Trace concentration - Huge impact: Nitrate in the calcite/Eu(III) system  

NASA Astrophysics Data System (ADS)

The interactions of trivalent lanthanides and actinides with secondary mineral phases such as calcite is of high importance for the safety assessment of deep geological repositories for high level nuclear waste (HLW). Due to similar ionic radii, calcium-bearing mineral phases are suitable host minerals for Ln(III) and An(III) ions. Especially calcite has been proven to retain these metal ions effectively by both surface complexation and bulk incorporation. Since anionic ligands (e.g., nitrate) are omnipresent in the geological environment and due to their coordinating properties, their influence on retentive processes should not be underestimated. Nitrate is a common contaminant in most HLW forms as a result of using nitric acid in fuel reprocessing. It is also formed by microbial activity under aerobic conditions. In this study, atomic force microscopy investigations revealed a major influence of nitrate upon the surface of calcite crystals. NaNO3 causes serious modifications even in trace amounts (<10-7 M) and forms a soft surface layer of low crystallinity on top of the calcite crystal. Time-resolved laser fluorescence spectroscopy of Eu(III) showed that, within this layer, Eu(III) ions are incorporated, while losing most of their hydration shell. The results show that solid solution modelling for actinides in calcite must take into account the presence of nitrate in pore and ground waters.

Hofmann, Sascha; Voïtchovsky, Kislon; Schmidt, Moritz; Stumpf, Thorsten

2014-01-01

169

Hydrothermal replacement of calcite by Mg-carbonates  

NASA Astrophysics Data System (ADS)

The transport of heat and mass through the Earth's crust is coupled to mineral reactions and the exchange of isotopes and elements between different phases. Carbonate minerals are a major constituent of the Earth's crust and play an important role in different physical, chemical and even biological processes. In this experimental study, the element exchange reaction between calcite (CaCO3) and a Mg-rich fluid phase is investigated under hydrothermal conditions. Single crystals of calcite (2x2x2 mm) react with 1 ml of a 1 M MgCl2 solution at 200° C in a Teflon-lined steel autoclave for different times between one day and four weeks. The reaction leads to the formation of a porous reaction front and the pseudomorphic replacement of calcite by dolomite [CaMg(CO3)2] and magnesite (MgCO3). Scanning electron microscopy revealed that the reaction rim consists of small Mg-carbonate rhombs closely attached to each other, suggesting that the replacement reaction takes place by a dissolution-precipitation mechanism. Typically, the observed reaction front can be divided into two different domains. The outer part of the reaction rim, i.e. from the mineral surface in contact to the fluid inwards, consists of magnesite, whereas the inner part of the rim surrounding the unreacted calcite core consists of Ca-rich dolomite. The formation of a porous microstructure that varies in different parts of the reaction rim is a direct result of the large molar volume change induced by the replacement of calcite by magnesite and dolomite. The developing porosity therefore creates fluid pathways that promote the progress of the reaction front towards the unreacted core of the single crystal. Compositional profiles measured perpendicular to the mineral surface across the reactions rims using electron microprobe (EMPA) further revealed a compositional gradient within the reaction rim with regard to the structure-forming elements Mg and Ca. Here, the amount of Mg incorporated in both product phases increases with increasing distance from the unreacted calcite core, countered by a decrease of Ca incorporated. Both the coexistence of two different product phases and the distinct compositional gradient within the forming reaction rim are unequivocal signs of a chemical zonation of Ca and Mg in the fluid phase which mediates the element exchange between the reaction interface and the bulk solution. Atomic adsorption spectroscopy revealed that the Ca/Mg ratio in the reacted fluid increases as a function of time, reflecting the progressive exchange of Mg and Ca between the fluid and the solid phase. The time-dependence of the evolving Ca/Mg ratio can be fitted with a square root of time relation that indicates a transport controlled reaction. We interpret the hydrothermal replacement of calcite to operate via a dissolution/re-precipitation mechanism, whereas the reaction progress is controlled by the transport of the structure forming elements through the developing reaction rim.

Jonas, Laura; Mueller, Thomas; Dohmen, Ralf

2014-05-01

170

Sea Urchin Spine Calcite Forms via a Transient Amorphous Calcium Carbonate Phase  

Microsoft Academic Search

The skeletons of adult echinoderms comprise large single crystals of calcite with smooth convoluted fenestrated morphologies, raising many questions about how they form. By using water etching, infrared spectroscopy, electron diffraction, and environmental scanning electron microscopy, we show that sea urchin spine regeneration proceeds via the initial deposition of amorphous calcium carbonate. Because most echinoderms produce the same type of

Yael Politi; Talmon Arad; Eugenia Klein; Steve Weiner; Lia Addadi

2004-01-01

171

Structure and interactions of calcite spherulites with ?-chitin in the brown shrimp ( Penaeus aztecus) shell  

Microsoft Academic Search

White spots form in the brown shrimp (Penaeus aztecus, Decapoda) shell during frozen storage. The mineral formed consists of calcite incorporated into an amorphous ?-chitin matrix. We studied mechanisms of interaction of amorphous ?-chitin macromolecules with hkl crystal planes to form highly ordered structures, as well as the role of specific sites in the biopolymer, which can be related to

A. Heredia; M. Aguilar-Franco; C. Magaña; C. Flores; C. Piña; R. Velázquez; T. E. Schäffer; L. Bucio; V. A. Basiuk

2007-01-01

172

Precipitation of calcite induced by Synechocystis sp. PCC6803.  

PubMed

Calcite with laminate structure was successfully prepared by culturing Synechocystis sp. PCC6803 with different concentrations of calcium chloride (CaCl?) in BG11 media. S. PCC6803 was examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser confocal scanning microscope (LCSM) and energy dispersive spectroscopy (EDS). The effects of Ca²? concentrations and pH values on calcification were investigated and the micro morphs of the CaCO? crystals were observed by means of SEM. These results showed that CaCO? crystals could be more easily formed with increasing the concentration of CaCl? in S. PCC6803 culture solution. S. PCC6803 could largely bind calcium ions, most of which were present in extracellular polymeric substances and on the cell wall. Inside the cells there were a lot of circular areas rich in calcium ions without the crystallization of calcium. Some cells produced a thicker gelatinous sheath outside of the translucent organic thin layer. And the cells inside also produced major changes that the original chloroplasts were almost transformed into starch grains whose sizes were from 0.5 to 1 ?m with relatively uniform in sizes. At the same time the cell sizes significantly reduced to only about 8-9 ?m almost changing to half of its original diameters. The calcite crystals with a highly preferred orientation induced by S. PCC6803 were observed with X-ray diffraction (XRD). A critical implication was that S. PCC6803 could induce bio-calcification and then mediate the further growth of CaCO? crystals in the biological system. PMID:23543209

Han, Zuozhen; Yan, Huaxiao; Zhou, Shixue; Zhao, Hui; Zhang, Yan; Zhang, Ningning; Yao, Chuankai; Zhao, Lin; Han, Chunyan

2013-10-01

173

Effects of temperature and transport conditions on calcite growth in the presence of Mg 2+: Implications for paleothermometry  

Microsoft Academic Search

This study links direct measurement of Mg-calcite growth kinetics with high-spatial-resolution analysis of Mg contents in experimental crystals, with particular attention to the effects of temperature on growth rate and reactant transport conditions on Mg distribution. In contrast to previous experiments on Mg partitioning into calcite, here the layer-growth mechanism was observed in situ and step speeds precisely measured with

Laura E. Wasylenki; Patricia M. Dove; James J. De Yoreo

2005-01-01

174

Interatomic potentials for CaCO 3 polymorphs (calcite and aragonite), fitted to elastic and vibrational data  

Microsoft Academic Search

Calcite and aragonite have been modeled using rigid-ion, two-body Born-type potentials, supplemented by O-C-O angular terms inside the CO3 groups. A shell model has also been developed for calcite. Atomic charges, repulsive parameters and force constants have been optimized to reproduce the equilibrium crystal structures, the elastic constants and the Raman and infrared vibrational frequencies. The rigid-ion potential RIM (atomic

A. Pavese; M. Catti; G. D. Price; R. A. Jackson

1992-01-01

175

Interatomic potentials for CaCO3 polymorphs (calcite and aragonite), fitted to elastic and vibrational data  

Microsoft Academic Search

Calcite and aragonite have been modeled using rigid-ion, two-body Born-type potentials, supplemented by O-C-O angular terms inside the CO3 groups. A shell model has also been developed for calcite. Atomic charges, repulsive parameters and force constants have been optimized to reproduce the equilibrium crystal structures, the elastic constants and the Raman and infrared vibrational frequencies. The rigid-ion potential RIM (atomic

A. Pavese; M. Catti; G. D. Price; R. A. Jackson

1992-01-01

176

Dissolution kinetics of calcite, dolomite and magnesite at 25 °C and 0 to 50 atm pCO 2  

Microsoft Academic Search

Dissolution rates of calcite, dolomite and magnesite were measured at 25 °C and pH from 3 to 4 as a function of salinity (0.001 M?[NaCl]?1 M) and partial pressure of CO2 (10?3.5?pCO2?55 atm). Experiments on calcite and dolomite crystal planes dissolution were performed in a batch reactor under controlled hydrodynamic conditions using the rotating disk technique. Dissolution experiments using mixed-flow

Oleg S. Pokrovsky; Sergey V. Golubev; Jacques Schott

2005-01-01

177

Upscaling Calcite Growth Rates From the Mesoscale to the Macroscale  

SciTech Connect

Quantitative prediction of mineral reaction rates in the subsurface remains a daunting task partly because a key parameter for macroscopic models, the reactive site density, is poorly constrained. Here we report atomic force microscopy (AFM) measurements on the calcite surface of monomolecular step densities, treated as equivalent to the reactive site density, as a function of aqueous calcium-to-carbonate ratio and saturation index. Data for the obtuse step orientation are combined with existing step velocity measurements to generate a model that predicts overall macroscopic calcite growth rates. The model is quantitatively consistent with several published macroscopic rates under a range of alkaline solution conditions, particularly for two of the most comprehensive data sets without the need for additional fit parameters. The model reproduces peak growth rates and its functional form is simple enough to be incorporated into reactive transport or other macroscopic models designed for predictions in porous media. However, it currently cannot model equilibrium, pH effects, and may overestimate rates at high aqueous calcium-to-carbonate ratios. The discrepancies in rates at high calcium-to-carbonate ratios may be due to differences in pre-treatment, such as exposing the seed material to SI 1.0 to generate/develop growth hillocks, or other factors.

Bracco, Jacquelyn N [ORNL; Stack, Andrew G [ORNL; Steefel, Carl I [Lawrence Berkeley National Laboratory (LBNL)

2013-01-01

178

4He behavior in calcite filling viewed by (U-Th)/He dating, 4He diffusion and crystallographic studies  

NASA Astrophysics Data System (ADS)

Fault-filling calcite crystals sampled from the Eocene/Oligocene Gondrecourt graben, Paris Basin, Eastern France, have been studied in order to test the potentiality of calcite (U-Th)/He dating, based on recognized He retention behavior in crystal lattice at surface temperature (Copeland et al., 2007). The samples have been selected because of their relatively old Eocene to Oligocene precipitation age and cold thermal history (<40 °C since precipitation). They were sorted into three main tectonic and morphological groups in order of precipitation, including (1) micro-fracture calcites, (2) breccia and associated geodic calcites, and (3) vein and associated geodic calcites. (U-Th)/He dating of 63 calcite fragments yields ages dispersed from 0.2 ± 0.02 to 35.8 ± 2.7 Ma, as well as two older dates of 117 ± 10 and 205 ± 28 Ma (1?). These He ages correlate with grain chemistry, such as Sr, ?REE concentrations or (La/Yb)N ratios, likely reflecting parent fluid evolution. Only the oldest He ages, which correspond to the most recently precipitated crystals, have preserved the total 4He budget since precipitation. To better understand both the age dispersion and why calcites precipitated earlier show younger ages, 4He diffusion experiments have been conducted on 10 Gondrecourt calcite fragments from 3 samples with He ages of ˜0.2-6 Ma. Additionally, a crystallographic investigation by X-ray diffraction (XRD) performed on similar samples reveals that crystal structure evolves with increasing temperature, beginning with micro-cracks and cleavage opening. These XRD results shed light on the (U-Th)/He data, indicating that, in fault-filling calcite, He retention is controlled by multiple diffusion domains (MDD) with various sizes, and therefore, evolves through time with strong consequences on (U-Th)/He age. We thus interpret the Gondrecourt calcite (U-Th)/He age scatter as a consequence of the production of defects due to successive calcite crystallization phases associated with the deformation history.

Cros, Alexandre; Gautheron, Cécile; Pagel, Maurice; Berthet, Patrick; Tassan-Got, Laurent; Douville, Eric; Pinna-Jamme, Rosella; Sarda, Philippe

2014-01-01

179

Cocrystallization of Co(II) with calcite: Implications for the mobility of cobalt in aqueous environments  

Microsoft Academic Search

Two different experimental processes (precipitation and crystallization in silica gel) have been carried out to investigate the degree of non-ideality and the crystallization behavior of the calcite–sphaerocobaltite solid solution from aqueous solutions. Solid phases of different compositions were precipitated at 25 °C by mixing a Na2CO3 aqueous solution with solutions with different ratios of CaCl2 and CoCl2. The precipitates were characterized

Dionisis Katsikopoulos; Ángeles Fernández-González; Angel Carmelo Prieto; Manuel Prieto

2008-01-01

180

Hydro-gel environment and solution additives modify calcite growth mechanism to an accretion process of amorphous nanospheres  

NASA Astrophysics Data System (ADS)

Various biominerals form via the transformation of a transient amorphous precursor phase into a mature crystalline phase. The mature biominerals usually exhibit morphology reminiscent of aggregated nanoparticles. Although these observations suggest an accretion-based growth process consisting on nanoparticles, the key factors that control the accretion process are unknown. We investigated the transformation of solid amorphous calcium carbonate (ACC) into calcite. When plant cystoliths, a biogenic stable ACC phase, are transformed into calcite in vitro by immersion in water, calcite crystals grow in two distinct steps (Gal et al., Angewandte Chemie, 2013). First, rhombohedral crystals grow that show flat facets as expected from ion-by-ion growth. These crystals then grow by the aggregation and crystallization of the original ACC nanospheres leading to a surface morphology dominated by aggregated spheres. The transformation process occurs within an organic hydro-gel that originates from inside the cystoliths. We tested the importance of the gel phase to the transformation process by transforming synthetic ACC into calcite inside various gels. In all the investigated systems: in gelatin, agarose, and pectin gels, calcite crystals grew that showed the nanosphere aggregation morphology. In additional experiments we demonstrated that also other additives, such as phosphate ions and biogenic macromolecules, that slow down ACC dissolution and calcite precipitation from ions can induce the accretion process dominance (see figure attached). These experiments show that although in solution the dominant process is dissolution to ions of the ACC and crystal growth by ion-by-ion mechanism, the presence of an additive that slows the ion-mediated processes makes the ACC nanospheres stable long enough to interact with the crystal surface. As a result, the metastable ACC nanospheres undergo secondary nucleation on the crystal surface without dissolving. These experiments highlight two factors that may underlie many biomineralization processes in nature: the first formed amorphous mineral phase can transform to a crystalline phase without dissolving if the solution properties of the environment are altered by an additive. And, accretion-based crystal-growth may become dominant when the amorphous precursor is abundant and the competing ion-based process is slowed down. SEM images of: (A) calcite crystal that grew from the transformation of ACC in DDW by ion-by-ion growth mechanism; (B) calcite crystal that grew from the transformation of ACC in 10mM phosphate solution by nanosphere accretion mechanism. Scale bars are 100 nm.

Gal, A.; Kahil, K.; Habraken, W.; Gur, D.; Fratzl, P.; Addadi, L.; Weiner, S.

2013-12-01

181

Project Explorer: Get Away Special #007. [alloy solidification, seed germination, crystal growth, and radio transmission of payload data  

NASA Technical Reports Server (NTRS)

Tentatively scheduled to fly on STS-17 (41G), this get away special aims to demonstrate amateur radio transmissions to global ground stations in the English language. Experiments No. 1, 2, and 3 use the micro-gravity of space flight to study the solidification of lead-antimony and aluminum-copper alloys, the germination of radish seeds, and the growth of potassium-tetracyanoplatinate hydrate crystals in an aqueous solution. Flight results are to be compared with Earth-based data. Experiment No. 4 (the Marshall Amateur Radio Club Experiment - MARCE) features radio transmissions and also provides timing for the start of all other experiments. A microprocessor obtains real-time data from all experiments as well as temperature and pressure measurements within the GAS canister. These data are to be transmitted on previously announced amateur radio frequencies after they are converted into the English language by a digitalker for general reception. The support structure for the G #007 experiments consists of two primary plates and four bumper assemblies.

Henderson, A. J., Jr.

1984-01-01

182

The role of citrate and phthalate during Co(II) coprecipitation with calcite  

NASA Astrophysics Data System (ADS)

The influence of citrate and phthalate on Co coprecipitation with calcite was investigated using a combination of batch experiments, Fourier-transform infra-red (FT-IR) spectroscopy, and thermogravimetric analysis (TGA) over a wide range of precipitation rates. Steady-state growth conditions (at constant [Ca], [Co], DIC, and pH) were generally achieved within 3-5 h, after which Co(II) partitioning into calcite was evaluated. Only minor differences are observed in the partition coefficient ( Kd) trends with and without citrate and phthalate as a function of calcite precipitation rate except at very low rates. Slight inhibition of calcite growth is observed in the presence of citrate or phthalate, which can be attributed to adsorption at surface sites. TGA curves for samples coprecipitated with citrate show a significant mass loss between 375 and 550 °C, whereas the weight-loss curves for the Co-phthalate coprecipitates are indistinguishable from those of the organic-free Co coprecipitates. This indicates that citrate is incorporated into calcite during calcite crystallization, whereas phthalate is excluded. FT-IR spectra for the sample with citrate show a broad absorption in the range 3700-3100 cm -1, which is attributable to water molecules coordinated to citrate coprecipitated with calcite. The preferential incorporation of citrate over phthalate likely reflects differences in both aqueous speciation and conformation of the carboxylate groups. This new finding may provide new insight to the factors that control the behavior of macromolecules and their incorporation into the structure of calcium carbonate during biomineralization.

Lee, Young J.; Reeder, Richard J.

2006-05-01

183

Stable isotopes in pedogenic calcite: Can the positive linear covariant trends be used to quantify paleo-evaporation rates?  

NASA Astrophysics Data System (ADS)

Paleoclimatological models suggest enhanced evaporation rates in subtropical regions during greenhouse- world conditions. Laboratory evaporation experiments show that calcites precipitated from variably saturated solutions yield a positive linear covariant trend (PLCT) in ?18O vs ?13C values. This investigation experimentally quantifies calcite PLCT so that ?13C of subtropical paleosol calcretes may be used as a regional proxy of paleo-evaporation rates. A series of powdered CaCO3 samples with ?18O and ?13C values of -19.6‰ and -37.2‰ VPDB respectively were dissolved in deionized water in a pressure sealed container; it also contained separate vials of calcite reacted with HCl to generate a range of pCO2 environments, thus simulating a soil atmosphere. The variable pCO2 conditions simulate expected soil atmosphere pCO2 conditions in a calcrete horizon during alternative phases of calcite dissolution and precipitation. After 24 hrs, the solutions were placed in an open beaker in an incubator at 36°C and allowed to evaporate. Aliquots of 100 ?L were removed at 24 hr intervals and the time of calcite crystal nucleation was also noted. Water analyses yielded ?18O enrichments ranging from an initial value of -4.8‰ VSMOW to a range of +10.0‰ to +14.8‰ VSMOW after an evaporation period of 75 hrs. The most enriched water values were attained from the solutions formed under lower pCO2 conditions (more enriched calcite ?18O, ?13C). The array of calcite ?18O vs ?13C values fall upon a PLCT that projects from a theoretical meteoric calcite line (MCL) calculated from the incubation temperature and deionized water ?18O and ?13C values. The precipitated calcite ?18O values range from the MCL value of -8.8‰ VPDB to +0.5‰ VPDB. The higher pCO2 waters precipitated calcite very early during evaporation, and thus the ?18O and ?13C calcite values are slightly enriched relative to the theoretical MCL. The lower pCO2 conditions precipitated calcite late in the evaporation of the fluids, and thus yield more enriched calcite ?18O and ?13C values. Ongoing experiments under warmer and cooler evaporation temperatures will aid in the development of a quantitative model for paleo-evaporation rates from paleosol calcretes.

Gröcke, D.; Ufnar, D.; Beddows, P. A.

2007-12-01

184

Interaction of europium and nickel with calcite studied by Rutherford Backscattering Spectrometry and Time-Resolved Laser Fluorescence Spectroscopy  

NASA Astrophysics Data System (ADS)

This study aims at elucidating the mechanisms regulating the interaction of Eu and Ni with calcite (CaCO3). Calcite powders or single crystals (some mm sized) were put into contact with Eu or Ni solutions at concentrations ranging from 10-3 to 10-5 mol L-1 for Eu and 10-3 mol L-1 for Ni. The sorption durations ranged from 1 week to 1 month. Rutherford Backscattering Spectrometry (RBS) well adapted to discriminate incorporation processes such as: (i) adsorption or co precipitation at the mineral surfaces or, (ii) incorporation into the mineral structure (through diffusion for instance), has been carried out. Moreover, using the fluorescence properties of europium, the results have been compared to those obtained by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) on calcite powders. For the single crystals, complementary SEM observations of the mineral surfaces at low voltage were also performed. Results showed that Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation and (ii) incorporation at depth greater than 160 nm after 1 month of sorption. Ni was found to accumulate at the surface of calcite without incorporation.

Sabau, A.; Pipon, Y.; Toulhoat, N.; Lomenech, C.; Jordan, N.; Moncoffre, N.; Barkleit, A.; Marmier, N.; Brendler, V.; Surblé, S.; Giffaut, E.

2014-08-01

185

Selective adsorption of l- and d-amino acids on calcite: Implications for biochemical homochirality  

PubMed Central

The emergence of biochemical homochirality was a key step in the origin of life, yet prebiotic mechanisms for chiral separation are not well constrained. Here we demonstrate a geochemically plausible scenario for chiral separation of amino acids by adsorption on mineral surfaces. Crystals of the common rock-forming mineral calcite (CaCO3), when immersed in a racemic aspartic acid solution, display significant adsorption and chiral selectivity of d- and l-enantiomers on pairs of mirror-related crystal-growth surfaces. This selective adsorption is greater on crystals with terraced surface textures, which indicates that d- and l-aspartic acid concentrate along step-like linear growth features. Thus, selective adsorption of linear arrays of d- and l-amino acids on calcite, with subsequent condensation polymerization, represents a plausible geochemical mechanism for the production of homochiral polypeptides on the prebiotic Earth.

Hazen, Robert M.; Filley, Timothy R.; Goodfriend, Glenn A.

2001-01-01

186

Transformation mechanism of amorphous calcium carbonate into calcite in the sea urchin larval spicule  

PubMed Central

Sea urchin larval spicules transform amorphous calcium carbonate (ACC) into calcite single crystals. The mechanism of transformation is enigmatic: the transforming spicule displays both amorphous and crystalline properties, with no defined crystallization front. Here, we use X-ray photoelectron emission spectromicroscopy with probing size of 40–200 nm. We resolve 3 distinct mineral phases: An initial short-lived, presumably hydrated ACC phase, followed by an intermediate transient form of ACC, and finally the biogenic crystalline calcite phase. The amorphous and crystalline phases are juxtaposed, often appearing in adjacent sites at a scale of tens of nanometers. We propose that the amorphous-crystal transformation propagates in a tortuous path through preexisting 40- to 100-nm amorphous units, via a secondary nucleation mechanism.

Politi, Yael; Metzler, Rebecca A.; Abrecht, Mike; Gilbert, Benjamin; Wilt, Fred H.; Sagi, Irit; Addadi, Lia; Weiner, Steve; Gilbert, P. U. P. A.

2008-01-01

187

Crystal Growth and Characterization of (Bi0.5Na0.5)TiO3--BaTiO3 Single Crystals Obtained by a Top-Seeded Solution Growth Method under High-Pressure Oxygen Atmosphere  

NASA Astrophysics Data System (ADS)

A single crystal of ferroelectric 0.88(Bi,Na)TiO3--0.12BaTiO3 (BNT--BT) solid solution with tetragonal P4mm structure was grown by a top-seeded solution growth (TSSG) method at a high oxygen pressure (PO\\scale70%2) of 0.9 MPa. The crystals exhibited a large remanent polarization (Pr) of 54 ?C/cm2, which leads to a spontaneous polarization estimated to be 54 ?C/cm2. The large Pr compared with that of crystals grown at PO\\scale70%2 = 0.1 MPa is suggested to originate from a low oxygen vacancy concentration. The high-PO\\scale70%2 TSSG method is demonstrated to be effective for obtaining large-sized, high-quality BNT--BT crystals.

Onozuka, Hiroaki; Kitanaka, Yuuki; Noguchi, Yuji; Miyayama, Masaru

2011-09-01

188

Strain rate dependent calcite microfabric evolution at natural conditions  

NASA Astrophysics Data System (ADS)

Crystal plastic deformational behaviour of calcite has been the focus of many experimental studies. Different strain rates, pressure and temperature conditions have been addressed to investigate a wide range of deformation regimes. However, a direct comparison with natural fault rocks remains difficult because of extreme differences between experimental and natural strain rates. A flanking structure developed in almost pure calcite marble on Syros (Cyclades, Greece). Due to rotation of a planar feature (crack) a heterogeneous strain field in the surrounding area occurred resulting in different strain domains and the formation of the flanking structure. Assuming that deformation was active continuously during the development of the flanking structure, the different strain domains correspond to different strain-rate domains. The outcrop thus represents the final state of a natural experiment and gives us a great opportunity to get natural constraints on strain rate dependent deformation behaviour of calcite. Comparing the microfabrics in the 1 to 2.5 cm thick shear zone and the surrounding host rocks, which formed under the same metamorphic conditions but with different strain rates, is the central focus of this study. Due to the extreme variation in strain and strain rate, different microstructures and textures can be observed corresponding to different deformation mechanisms. With increasing strain rate we observe a change in dominant deformation mechanism from dislocation glide to dislocation creep and finally diffusion creep. Additionally, a change from subgrain rotation to bulging recrystallization can be observed in the dislocation creep regime. Crystallographic preferred orientations (CPO) and the grade of intracrystalline deformation were measured on a FEI Quanta 3D FEG instrument equipped with an EDAX Digiview IV EBSD camera. At all strain rates clear CPOs developed leading to the assumption that calcite preferentially deforms within the dislocation creep field. However, we can also find clear evidence for grain size sensitive deformation mechanisms at smaller grain sizes (3.6 ?m) consistent with experimental observations and determined flaw laws. The results of this study are compared with experimental data, closing the gap between experimental and natural geological strain rates.

Rogowitz, Anna; Grasemann, Bernhard; Huet, Benjamin; Habler, Gerlinde

2014-05-01

189

Effect of hydraulic retention time and seed material on phosphorus recovery and crystal size from urine in an air-agitated reactor.  

PubMed

Phosphorus (P) recovery from urine is affected by various parameters. This study evaluates the effects of hydraulic retention time (HRT) and seed material on P recovery and crystal size in an air-agitated reactor. Results show that ortho-phosphate removal and struvite recovery efficiencies were 96.3% and 89.5%, and 97.1% and 93.0%, after five runs of HRTs of 1 and 2 h, respectively. Low loss of crystals from effluent urine solutions indicates high struvite recovery efficiency and is correlated with the structure and design of the reactor. The average particle size decreased from 40.0 to 31.7 ?m as the HRT increased from 1 to 2 h. The two types of seed materials (zeolite and molecular sieve) did not affect the ortho-phosphate removal efficiency but affected the struvite crystal size. In particular, multi-stage addition of zeolites increased the average crystal size from 33.7 to 57.0 ?m. PMID:24718337

Liu, Xiaoning; Hu, Zhengyi; Wang, Jinzhi; Wen, Guoqi

2014-01-01

190

Inhibition of calcite precipitation by natural organic material: Kinetics, mechanism, and thermodynamics  

USGS Publications Warehouse

The inhibition of calcite precipitation by natural organic material (NOM) in solutions seeded with calcite was investigated using a pH-stat system. Experiments were carried out using three NOMs with different physical/chemical properties. For each of the materials, inhibition was found to be more effective at lower carbonate/calcium ratios and lower pH values. The reduction in the precipitation rate could be explained by a Langmuir adsorption model using a conditional equilibrium constant. By identification of the type of site on the NOM molecules that is involved in the adsorption reaction, the "conditional" equilibrium constants obtained at different solution compositions converged to a single "nonconditional" value. The thermodynamic data determined at 25??C and 1 atm suggest that the interaction between NOM molecules and the calcite surface is chemisorptive in nature and that adsorption is an endothermic reaction driven by the entropy change. The greatest degree of inhibition was observed for the NOM with the highest molecular weight and aromatic carbon content. For a given type of NOM, the degree of inhibition of calcite precipitation was dictated by the balance between the enthalpy change and the entropy change of the adsorption reaction. ?? 2005 American Chemical Society.

Lin, Y. -P.; Singer, P. C.; Aiken, G. R.

2005-01-01

191

Fabrication of size-tunable TiO2 tubes using rod-shaped calcite templates.  

PubMed

Titania tubes with tunable wall thickness were produced by the sol-gel reaction of titanium(IV) n-butoxide in the presence of rod-shaped calcite particles that act as templates. A shell of amorphous titania was deposited around the calcite particles by sol-gel synthesis. The titania was crystallized to the anatase or rutile phase by sintering at different temperatures, and then acid etching was used to remove the calcite core, leaving hollow titania tubes. The influences of several parameters on the final particle formation were investigated, including calcite templates, surfactant, the method of adding reagents, and catalyst. The average width of the prepared titania tubes ranges from nearly 100 nm to 1 microm, with wall thickness ranging from approximately 70 to 300 nm. A possible growth mechanism of the titania tubes is presented. The ability to control titania tube size and crystal structure is important for photocatalysis, photovoltaics, and other applications. The fabrication approach presented is applicable to form tubes of other oxide materials by sol-gel synthesis. PMID:17718582

Liu, Dongxia; Yates, Matthew Z

2007-09-25

192

The ionic conductivity in high-pressure polymorphs of calcite  

Microsoft Academic Search

Ionic conductivity of polycrystalline calcite containing varying amounts of PO43-ions was measured in the pressure range of 1–6 GPa and at room temperature. Electrical conductivity increased with pressure corresponding to the phase transition of calcite I to calcite II. The conductivity in calcite III decreased exponentially with pressure. Calculated activation volumes of the conductivity varied with PO43-content in the range

M. Ishikawa; A. Sawaoka; M. Ichikuni

1982-01-01

193

Cd sup 2+ uptake by calcite, solid-state diffusion, and the formation of solid-solution: Interface processes observed with near-surface sensitive techniques (XPS, LEED, and AES)  

Microsoft Academic Search

X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES) allowed direct observations of structure and bonding environments at the calcite surface. Pure calcite crystals were cleaved from precleaned Iceland spar and were briefly exposed to aqueous solutions containing various concentrations of Cd{sup 2+}, COâ²⁻, ClOâ⁻, and\\/or Cl⁻. LEED results demonstrate that the calcite surface is atomically

S. L. Stipp; M. F. Jr. Hochella; G. A. Parks; J. O. Leckie

1992-01-01

194

Biologically induced calcite and its isotopic composition in Lake Ontario  

Microsoft Academic Search

We studied water, sediment trap, and core samples from eastern Lake Ontario to reconstruct the factors controlling the biologically induced production and sedimentation of calcite during so-called whiting events. Calcite accumulation and its isotopic composition are controlled by a complex set of interrelated factors, including temperature, primary productivity, and the abundance of pica-cyanobacteria during the stratified period. Calcite precipitation is

David A. Hodell; Claire L. Schelske; Gary L. Fahnenstiel; Lisa L. Robbins

1998-01-01

195

Orientation and Mg Incorporation of Calcite Grown on Functionalized Self-Assembled Monolayers:  A Synchrotron X-ray Study  

Microsoft Academic Search

Calcite crystals were nucleated from MgCl2\\/CaCl2 solutions onto functionalized self-assembled monolayers adsorbed onto E-beam evaporated Au films. Synchrotron X-ray scattering studies of the crystals reveal new information about preferred orientation and Mg incorporation. The Au (111) axis is distributed within 2.6° of the film surface normal, but the oriented crystals may be tilted up to 6° away from this axis.

Seo-Young Kwak; Elaine DiMasi; Yong-Jin Han; Joanna Aizenberg; Ivan Kuzmenko

2005-01-01

196

Shock-induced effects in calcite from Cactus Crater  

NASA Technical Reports Server (NTRS)

The paper discusses shock metamorphism of calcite from coralline limestone samples retrieved from a borehole drilled into rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll. The metamorphism was detected and quantified using electron spin resonance (ESR); the ESR spectra of Mn(+) present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. It is suggested that the decrease in hyperfine peak splitting reflects a decrease in crystal field splitting, and therefore, small increases on cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models suggested by the ESR results are a depiction of a steady decay of the shock wave, and a delineation of a breccia lens with a breccia-bedrock interface at 20 plus or minus 5 m.

Vizgirda, J.; Ahrens, T. J.; Tsay, F.-D.

1980-01-01

197

Paired gill slits in a fossil with a calcite skeleton.  

PubMed

The chordates, hemichordates (such as acorn worms) and echinoderms (such as starfish) comprise the group Deuterostomia, well established as monophyletic. Among extant deuterostomes, a skeleton in which each plate has the crystallographic structure of a single crystal of calcite is characteristic of echinoderms and is always associated with radial symmetry and never with gill slits. Among fossils, however, such a skeleton sometimes occurs without radial symmetry. This is true of Jaekelocarpus oklahomensis, from the Upper Carboniferous of Oklahoma, USA, which, being externally almost bilaterally symmetrical, is traditionally placed in the group Mitrata (Ordovician to Carboniferous periods, 530-280 million years ago), by contrast with the bizarrely asymmetrical Cornuta (Cambrian to Ordovician periods, 540 to 440 million years ago). Using computer X-ray microtomography, we describe the anatomy of Jaekelocarpus in greater detail than formerly possible, reveal evidence of paired gill slits internally and interpret its functional anatomy. On this basis we suggest its phylogenetic position within the deuterostomes. PMID:12075349

Dominguez, Patrício; Jacobson, Antone G; Jefferies, Richard P S

2002-06-20

198

Understanding control of calcitic biomineralization-proteomics to the rescue.  

PubMed

The avian eggshell is one of the fastest calcifying processes known and represents a unique model for studying biomineralization. Eggshell strength is a crucial economic trait for table egg production, and ensures that a safe egg reaches the consumer kitchen. However, a common toolkit for eggshell mineralization has not yet been defined. In this issue, label-free MS-based protein quantification technology has been used by Sun et al. (Proteomics 2013, 13, 3523-3536) to detect differences in protein abundance between eggshell matrix from strong and weak eggs and between the corresponding uterine fluids bathing strong and weak eggs. Proteins associated with the formation of strong eggshells are identified, which are now candidates for further investigations to define the regulatory relationship between specific eggshell matrix proteins and calcite crystal texture. PMID:24307661

Hincke, Maxwell T

2013-12-01

199

in situ Calcite Precipitation for Contaminant Immobilization  

SciTech Connect

in situ Calcite Precipitation for Contaminant Immobilization Yoshiko Fujita (Yoshiko.fujita@inl.gov) (Idaho National Laboratory, Idaho Falls, Idaho, USA) Robert W. Smith (University of Idaho-Idaho Falls, Idaho Falls, Idaho, USA) Subsurface radionuclide and trace metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of DOE’s greatest challenges for long-term stewardship. One promising stabilization mechanism for divalent trace ions, such as the short-lived radionuclide strontium-90, is co-precipitation in calcite. Calcite, a common mineral in the arid western U.S., can form solid solutions with trace metals. The rate of trace metal incorporation is susceptible to manipulation using either abiotic or biotic means. We have previously demonstrated that increasing the calcite precipitation rate by stimulating the activity of urea hydrolyzing microorganisms can result in significantly enhanced Sr uptake. Urea hydrolysis causes the acceleration of calcium carbonate precipitation (and trace metal co-precipitation) by increasing pH and alkalinity, and also by liberating the reactive cations from the aquifer matrix via exchange reactions involving the ammonium ion derived from urea: H2NCONH2 + 3H2O ? 2NH4+ + HCO3- + OH- urea hydrolysis >X:2Ca + 2NH4+ ? 2>X:NH4 + Ca2+ ion exchange Ca2+ + HCO3- + OH- ? CaCO3(s) + H2O calcite precipitation where >X: is a cation exchange site on the aquifer matrix. This contaminant immobilization approach has several attractive features. Urea hydrolysis is catalyzed by the urease enzyme, which is produced by many indigenous subsurface microorganisms. Addition of foreign microbes is unnecessary. In turn the involvement of the native microbes and the consequent in situ generation of reactive components in the aqueous phase (e.g., carbonate and Ca or Sr) can allow dissemination of the reaction over a larger volume and/or farther away from an amendment injection point, as compared to direct addition of the reactants at a well (which can lead to clogging). A final particularly attractive characteristic of this approach is its long-term sustainability; the remediation scheme is geared toward environments that are already saturated with respect to calcite, and in such systems the bulk of any newly precipitated calcite will remain stable once engineered manipulations cease. This means that the co-precipitated contaminants will be effectively sequestered over the long term. We are currently conducting integrated field, laboratory, and computational research to evaluate a) the relationships between urea hydrolysis rate, calcite precipitation rate, and trace metal partitioning under environmentally relevant conditions; and b) the coupling between flow/flux manipulations and calcite precipitate distribution and metal uptake. We are also assessing the application of geophysical and molecular biological tools to monitor the relevant chemical and physical processes. The primary emphasis is on field-scale processes, with the laboratory and modeling activities designed specifically to support the field studies. Field experiments are being conducted in perched water (vadose zone) at the Vadose Zone Research Park (VZRP) at the Idaho National Laboratory; the VZRP provides an uncontaminated setting that is an analog of the 90Sr-contaminated vadose zone at the Idaho Nuclear Technology and Engineering Center. A summary of results to date will be presented.

Yoshiko Fujita; Robert W. Smith

2009-08-01

200

Fluid inclusion studies of calcite veins from Yucca Mountain, Nevada, Tuffs: Environment of formation  

SciTech Connect

Calcite vein and vug fillings at four depths (130-314m), all above the present water table in USW G-1 bore hole at Yucca Mountain, Nevada, contain primary fluid inclusions with variable vapor/liquid raitos: Most of these inclusions are either full of liquid or full of vapor. The liquid-filled inclusions show that most of the host calcite crystallized from fluids at <100{degrees}C. The vapor-filled inclusions provide evidence that a separate vapor phase was present in the fluid during crystallization. Studies of these vapor-filled inclusions on the microscope crushing stage were interpreted in an earlier paper as indicating trapping of an air-water-CO{sub 2} vapor phase at ``<100{degrees}C``. Our new studies reveal the additional presence of major methane in the vapor-filled inclusion, indicating even lower temperatures of trapping, perhaps at near-surface temperatures. They also show that the host calcite crystals grew from a flowing film of water on the walls of fractures open to the atmosphere, the vapor-filled inclusions representing bubbles that exsolved from this film onto the crystal surface.

Roedder, E. [Harvard Univ., Cambridge, MA (United States); Whelan, J.F. [Geological Survey, Denver, CO (United States); Vaniman, D.T. [Los Alamos National Lab., NM (United States)

1994-12-31

201

Calcium-43 NMR studies of polymorphic transition of calcite to aragonite.  

PubMed

Phase transformation between calcite and aragonite is an important issue in biomineralization. To shed more light on the mechanism of this process at the molecular level, we employ solid-state (43)Ca NMR to study the phase transformation from calcite to aragonite as regulated by magnesium ions, with (43)Ca enrichment at a level of 6%. Using the gas diffusion approach, the phase of Mg-calcite is formed initially and the system subsequently transforms to aragonite as the reaction time proceeds. Our (43)Ca solid-state NMR data support the dissolution-recrystallization mechanism for the calcite to aragonite transition. We find that the (43)Ca NMR parameters of Mg-calcite are very similar to those of pure calcite. Under the high-resolution condition provided by magic-angle spinning at 4 kHz, we can monitor the variation of the (43)Ca NMR parameters of the aragonite signals for the samples obtained at different reaction times. Our data suggest that in the presence of a significant amount of Mg(2+) ions, aragonite is the most stable polymorph of calcium carbonate. The initial precipitated crystallites of aragonite have spine-like morphology, for which the (43)Ca spin-lattice relaxation data indicate that the ions in the lattice have considerable motional dynamics. As the crystallinity of aragonite improves further, the (43)Ca T(1) parameter of the aragonite phase changes considerably and becomes very similar to that obtained for pure aragonite. For the first time, the difference in crystal morphologies and crystallinity of the aragonite phase has been traced down to the subtle difference in the motional dynamics at the molecular level. PMID:23163540

Huang, Yu-Chieh; Mou, Yun; Tsai, Tim Wen-Tin; Wu, Yu-Ju; Lee, Hsin-Kuan; Huang, Shing-Jong; Chan, Jerry C C

2012-12-13

202

Calcite growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic calcite formation  

USGS Publications Warehouse

Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing calcite supersaturation (?c). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic calcite modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. Calcite growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic calcite, was measured separately and in combination under identical, highly reproducible experimental conditions. Calcite growth rates (pH=8.5 and ?c=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10?4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a calcite growth-rate inhibitor as FA. Calcite growth rate in the presence of both FA (0.5 mg/L) and Mg (10?4 M) is reduced to 5% of the control rate. Mg inhibits calcite growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits calcite growth rates by binding multiple carboxylate groups on the calcite surface. FA and Mg together have an increased affinity for the calcite growth sites reducing calcite growth rates.

Michael M Reddy

2012-01-01

203

Calcite growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic calcite formation  

NASA Astrophysics Data System (ADS)

Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing calcite supersaturation (?c). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic calcite modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. Calcite growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic calcite, was measured separately and in combination under identical, highly reproducible experimental conditions. Calcite growth rates (pH=8.5 and ?c=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10-4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a calcite growth-rate inhibitor as FA. Calcite growth rate in the presence of both FA (0.5 mg/L) and Mg (10-4 M) is reduced to 5% of the control rate. Mg inhibits calcite growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits calcite growth rates by binding multiple carboxylate groups on the calcite surface. FA and Mg together have an increased affinity for the calcite growth sites reducing calcite growth rates.

Reddy, Michael M.

2012-08-01

204

Bio-inspired formation of functional calcite/metal oxide nanoparticle composites  

NASA Astrophysics Data System (ADS)

Biominerals are invariably composite materials, where occlusion of organic macromolecules within single crystals can significantly modify their properties. In this article, we take inspiration from this biogenic strategy to generate composite crystals in which magnetite (Fe3O4) and zincite (ZnO) nanoparticles are embedded within a calcite single crystal host, thereby endowing it with new magnetic or optical properties. While growth of crystals in the presence of small molecules, macromolecules and particles can lead to their occlusion within the crystal host, this approach requires particles with specific surface chemistries. Overcoming this limitation, we here precipitate crystals within a nanoparticle-functionalised xyloglucan gel, where gels can also be incorporated within single crystals, according to their rigidity. This method is independent of the nanoparticle surface chemistry and as the gel maintains its overall structure when occluded within the crystal, the nanoparticles are maintained throughout the crystal, preventing, for example, their movement and accumulation at the crystal surface during crystal growth. This methodology is expected to be quite general, and could be used to endow a wide range of crystals with new functionalities.Biominerals are invariably composite materials, where occlusion of organic macromolecules within single crystals can significantly modify their properties. In this article, we take inspiration from this biogenic strategy to generate composite crystals in which magnetite (Fe3O4) and zincite (ZnO) nanoparticles are embedded within a calcite single crystal host, thereby endowing it with new magnetic or optical properties. While growth of crystals in the presence of small molecules, macromolecules and particles can lead to their occlusion within the crystal host, this approach requires particles with specific surface chemistries. Overcoming this limitation, we here precipitate crystals within a nanoparticle-functionalised xyloglucan gel, where gels can also be incorporated within single crystals, according to their rigidity. This method is independent of the nanoparticle surface chemistry and as the gel maintains its overall structure when occluded within the crystal, the nanoparticles are maintained throughout the crystal, preventing, for example, their movement and accumulation at the crystal surface during crystal growth. This methodology is expected to be quite general, and could be used to endow a wide range of crystals with new functionalities. Electronic supplementary information (ESI) available: Further analysis of products. See DOI: 10.1039/c3nr05081e

Kim, Yi-Yeoun; Schenk, Anna S.; Walsh, Dominic; Kulak, Alexander N.; Cespedes, Oscar; Meldrum, Fiona C.

2013-12-01

205

Sorption of divalent metals on calcite  

Microsoft Academic Search

The sorption of seven divalent metals (Ba, Sr, Cd, Mn, Zn, Co, and Ni) was measured on calcite over a large initial metal (Me) concentration range in constant ionic strength (I = 0.1), equilibrium CaCOâ(s)-CaCOâ(aq) suspensions that varied in pH. At higher initial Me concentrations (10⁻⁵ to 10⁻⁴ mol\\/L) geochemical calculations indicated that the equilibrium solutions were saturated with discrete

J. M. Zachara; C. E. Cowan; C. T. Resch

1991-01-01

206

Preparation and formation mechanism of wood-block-like calcite particles  

SciTech Connect

Pure calcite crystal with different morphologies such as wood-block and spherical aggregates were prepared by a precipitation reaction in the presence of citric acid. The as-prepared products were characterized with scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that citric acid obviously influenced the formation of precipitates and the morphology of final products. The formation mechanism of wood-block-like particles was proposed according to theoretical deduction and the proposed growth mode. - Graphical abstract: Pure calcite crystal with different morphologies such as wood-block and spherical aggregates were prepared by a simple precipitation reaction in the presence of citric acid and the formation mechanism was proposed.

Guo Hua [State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China); Yu Jiaguo [State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China)]. E-mail: jiaguoyu@yahoo.com; Cheng Bei [State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China)

2006-08-15

207

Biogenic calcite granules--are brachiopods different?  

PubMed

Brachiopods are still one of the least studied groups of organisms in terms of biomineralization despite recent studies indicating the presence of highly complex biomineral structures, particularly in taxa with calcitic shells. Here, we analyze the nanostructure of calcite biominerals, fibers and semi-nacre tablets, in brachiopod shells by high-resolution scanning electron microscopy (SEM) and atomic force microscopy (AFM). We demonstrate that basic mechanisms of carbonate biomineralization are not uniform within the phylum, with semi-nacre tablets composed of spherical aggregates with sub-rounded granules and fibers composed of large, triangular or rod-like particles composed of small sub-rounded granules (40-60 nm). Additionally, proteinaceous envelopes surrounding calcite fibers have been shown for the first time to have a dual function: providing a micro-environment in which granules are produced and acting as the organic template for particle orientation as fiber components. In summary, these new findings in brachiopod shells reveal a complex and distinctive style of biomineralization among carbonate-producing organisms. PMID:23026148

Pérez-Huerta, Alberto; Dauphin, Yannicke; Cusack, Maggie

2013-01-01

208

Comparison of solidification/stabilization effects of calcite between Australian and South Korean cements  

SciTech Connect

The differences in the effect of calcite on the strength and stability of Pb-rich wastes solidified and stabilized using Australian and South Korean ordinary Portland cements are examined in this study. Pb-rich waste stabilized using Australian OPC has been shown to possess both substantially higher unconfined compressive strength and lead immobilization ability than South Korean OPC as a result of its higher C{sub 3}S content and the associated enhanced degree of precipitation of lead on the surfaces of silicate phases present. Calcite addition is observed to have an accelerating effect on the OPC-induced solidification/stabilization of Pb-rich wastes as gauged by the unconfined compressive strength and leachability of the solids formed. This effect is observed to be far more dramatic for South Korean OPC than for Australian OPC. Using scanning electron microscopy, waste stabilized with cement and calcite was observed to develop significantly greater proportions of hydrated crystals than wastes stabilized with cement alone. The results of X-ray diffraction studies have shown that the presence of calcite in South Korean OPC results in greater acceleration in the formation of portlandite than is the case for Australian OPC.

Lee, Dongjin [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Waite, T. David [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia)]. E-mail: d.waite@unsw.edu.au; Swarbrick, Gareth [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Lee, Sookoo [School of Environmental Engineering, Seoul National University of Technology, Nowon-Gu, Seoul, 139-743 (Korea, Republic of)

2005-11-15

209

Binding of ethanol on calcite: the role of the OH bond and its relevance to biomineralization.  

PubMed

The interaction of OH-containing compounds with calcite, CaCO(3), such as is required for the processes that control biomineralization, has been investigated in a low-water solution. We used ethanol (EtOH) as a simple, model, OH-containing organic compound, and observed the strength of its adsorption on calcite relative to OH from water and the consequences of the differences in interaction on crystal growth and dissolution. A combination of atomic force microscopy (AFM) and molecular dynamics (MD) simulations showed that EtOH attachment on calcite is stronger than HOH binding and that the first adsorbed layer of ethanol is highly ordered. The strong ordering of the ethanol molecules has important implications for mineral growth and dissolution because it produces a hydrophobic layer. Ethanol ordering is disturbed along steps and at defect sites, providing a bridge from the bulk solution to the surface. The strong influence of calcite in structuring ethanol extends further into the liquid than expected from electrical double-layer theory. This suggests that in fluids where water activity is low, such as in biological systems optimized for biomineralization, organic molecules can control ion transport to and from the mineral surface, confining it to specific locations, thus providing the organism with control for biomineral morphology. PMID:20812690

Sand, K K; Yang, M; Makovicky, E; Cooke, D J; Hassenkam, T; Bechgaard, K; Stipp, S L S

2010-10-01

210

Kinetics and mechanisms of cadmium carbonate heteroepitaxial growth at the calcite (10 1bar 4) surface  

NASA Astrophysics Data System (ADS)

Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at calcite-water interfaces was investigated by exposing calcite (10 1bar 4) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the calcite substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and calcite shows perfect, dislocation-free epitaxy.

Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien

2014-06-01

211

Solubility and surface spectroscopy of zinc precipitates on calcite  

NASA Astrophysics Data System (ADS)

The Sorption and precipitation of Zn was investigated in equilibrium calcite (CaCO 3(s)) suspensions at Zn concentrations that approached and exceeded the solubility of known zinc carbonate solids. Surface-enhanced precipitation was not observed and CaCO 3(s) did not nucleate Zn solids when the aqueous ion activity product (IAP) was below the equilibrium IAP of the least soluble, kinetically viable Zn phase. The CaCO 3(s) surface was not requisite for Zn precipitation. When CaCO 3(s) was present the precipitate formed a surface coating or discrete Zn particles bound to the surface. X-ray photoelectron spectroscopy, X-ray diffraction, and energy dispersive X-ray spectrometry of both Zn-treated CaCO 3(s) and isolated Zn particles implied, but did not confirm, that the precipitate was hydrozincite [ Zn5( OH) 6( CO3) 2( S) ] or its hydrated form. Zinc-treated calcite maintained Zn concentrations that agreed with the solubility of a synthetic hydrozincite measured by Schindler et al. (1969). Direct measurements showed that the equilibrium solubility of the precipitate exceeded that of a natural hydrozincite ( log IAP = a 5Zn2+a 2CO 2-3 /a 6H+ = 6.41 ± 0.51 ) and was less than a natural smithsonite ( logIAP = aZn2+aCO2-3 = -10.53 ± 0.10). It is suggested that a poorly ordered form of hydrozincite that regulates Zn activities at higher levels than well-crystallized natural varieties readily precipitates in CaCO 3(aq)/CaCO 3(s) systems. The environmental significance of this phase is unknown.

Zachara, J. M.; Kittrick, J. A.; Dake, L. S.; Harsh, J. B.

1989-01-01

212

New Shocked Calcite and Fe Grains from Noerdlingen Ries Impact Crater  

NASA Astrophysics Data System (ADS)

Shocked minerals with simple chemical composition of silica, carbon or iron material reveal high-pressure phase during compression process [1]. As calcite mineral shows high-pressure phase of aragonite it should have the "shocked phase" formed from high-pressure phase mixed with quenched materials of gas-melt reaction [2,3,4]. The main purposes of this paper are (1) to discuss new shocked materials of calcite found in the Noerdlingen Ries impact crater. Germany and artificial impact phases. and (2) to show new findings of fine Fe-grains and anomalous plagioclase in suevite. Single grains of anomalous calcite for X-ray analysis were selected from limestone with wormy or bubble-included texture in Buschelberg Ries impact crater (sample R8) [3 4]. Powdered and single grain samples of anomalous calcites show low X-ray intensity and high Bragg angle shift. compared with standard calcite of Akiyoshi limestone as listed in Table 1 [2.3.4]. The unit-cell dimensions of the single grain measured with the four-axes X-ray diffractometer in Yamaguchi University were determined by the least square calculation from the "highest X-ray intensity peak" of each crystal plane which is the same data of the powdered X-ray diffraction sample as an average structure . Both powdered and single grain data reveal high density of 2.76 g/cm^3 (between aragonite of density: rho=2.8g/cm^3, and normal calcite: rho=2.71g/cm^3) of the calcite cell which is the same characters of shocked phases of quartz or graphite [1,2,3,4] (Table 1). Anomalous calcite contains minor amount of Si Fe Ti, though major cation is Ca of 99.4% in cation content. These foreign elements are mixed with during the formation in vapor plume [5]. Table 1, showing the x-ray density and unit-cell parameters of anomalous shocked calcite with high density from Ries and artificial impact craters, appears here in the hard copy. Two types of shocked calcites are found in artificial impact experiments of railgun of the ISAS. Japan. (a) Shocked calcite formed on oxidation condition (near the rim of vapor plume of impact [7]). (b)Shocked calcite formed on reduction condition (interior of vapor plume of impact [7]). The shocked calcites of the Buschelberg (R8) inside the crater are correspondent to shocked calcite with reduction state. which suggests recrystallization inside the crater. The detailed experiments of the R8 samples are checked on yellow (Fe-rich) colored sample of R8Yl and white colored sample (R8W). From the X-ray diffraction data of Bragg angle shift, the R8W1 is more close to reduction state during impact. The shocked calcites under oxidation state are formed as non-stoichiometric compound (and high density) after gas of C02 formation mainly near rim of vapor plume, which is the same data of artificial impact experiments of oxidation condition (i.e. sample No. LSRGl). The shocked calcite under reduction state are formed relatively as normal calcite (with normal or a little high density) and carbon after formation of gaseous materials of CO, 02 and Ca. Thus cabon source from target rock of limestone [2,3,4] can be explained as reduction formation of impact, as listed in Table 2. Table 2, showing, the formation process of shocked calcite materials by shock impact, appears here in the hard copy. References [1] Miura Y.(l991): Shock Waves, 1, 135-141. ?2] Miura Y. (1994): Proc. ISAS Lunar & Planet. Sci. (ISAS, Japan), 27, 204-207. [3] Miura Y. et al. (1995): Shock Waves, Japan, 613-624. [4] Miura Y. and Okanoto M. (19995): Antarctic Meteorites (NIP?), 20, 169-171. ?1989): Tma;l(-.t. r?r;lt.?rin? ?rhrfnr? llniv?r?i?v Pr? )A? 7?;

Miura, Y.

1995-09-01

213

Reaction mechanism for the replacement of calcite by dolomite and siderite: implications for geochemistry, microstructure and porosity evolution during hydrothermal mineralisation  

NASA Astrophysics Data System (ADS)

Carbonate reactions are common in mineral deposits due to CO2-rich mineralising fluids. This study presents the first in-depth, integrated analysis of microstructure and microchemistry of fluid-mediated carbonate reaction textures at hydrothermal conditions. In doing so, we describe the mechanisms by which carbonate phases replace one another, and the implications for the evolution of geochemistry, rock microstructures and porosity. The sample from the 1.95 Moz Junction gold deposit, Western Australia, contains calcite derived from carbonation of a metamorphic amphibole—plagioclase assemblage that has further altered to siderite and dolomite. The calcite is porous and contains iron-rich calcite blebs interpreted to have resulted from fluid-mediated replacement of compositionally heterogeneous amphiboles. The siderite is polycrystalline but nucleates topotactically on the calcite. As a result, the boundaries between adjacent grains are low-angle boundaries (<10°), which are geometrically similar to those formed by crystal-plastic deformation and recovery. Growth zoning within individual siderite grains shows that the low-angle boundaries are growth features and not due to deformation. Low-angle boundaries develop due to the propagation of defects at grain faces and zone boundaries and by impingement of grains that nucleated with small misorientations relative to each other during grain growth. The cores of siderite grains are aligned with the twin planes in the parent calcite crystal showing that the reactant Fe entered the crystal along the twin boundaries. Dolomite grains, many of which appear to in-fill space generated by the siderite replacement, also show alignment of cores along the calcite twin planes, suggesting that they did not grow into space but replaced the calcite. Where dolomite is seen directly replacing calcite, it nucleates on the Fe-rich calcite due to the increased compatibility of the Fe-bearing calcite lattice relative to the pure calcite. Both reactions are interpreted as fluid-mediated replacement reactions which use the crystallography and elemental chemistry of the calcite. Experiments of fluid-mediated replacement reactions show that they proceed much faster than diffusion-based reactions. This is important when considering the rates of reactions relative to fluid flow in mineralising systems.

Pearce, Mark A.; Timms, Nicholas E.; Hough, Robert M.; Cleverley, James S.

2013-10-01

214

Removal of organic magnesium in coccolithophore calcite  

NASA Astrophysics Data System (ADS)

Coccolithophore calcite refers to the plates of calcium carbonate (CaCO3) produced by the calcifying phytoplankton, coccolithophores. The empirical study of the elemental composition has a great potential in the development of paleoproxies. However, the difficulties to separate coccolithophore carbonates from organic phases hamper the investigation of coccoliths magnesium to calcium ratios (Mg/Ca) in biogeochemical studies. Magnesium (Mg) is found in organic molecules in the cells at concentrations up to 400 times higher than in inorganically precipitated calcite in present-day seawater. The aim of this study was to optimize a reliable procedure for organic Mg removal from coccolithophore samples to ensure reproducibility in measurements of inorganic Mg in calcite. Two baseline methods comprising organic matter oxidations with (1) bleach and (2) hydrogen peroxide (H2O2) were tested on synthetic pellets, prepared by mixing reagent grade CaCO3 with organic matter from the non-calcifying marine algae Chlorella autotrophica and measured with an ICP-AES (inductively coupled plasma-atomic emission spectrometer). Our results show that treatments with a reductive solution [using hydroxylamine-hydrochloride (NH2OH·HCl + NH4OH)] followed by three consecutive oxidations (using H2O2) yielded the best cleaning efficiencies, removing >99% of organic Mg in 24 h. P/Ca and Fe/Ca were used as indicators for organic contamination in the treated material. The optimized protocol was tested in dried coccolithophore pellets from batch cultures of Emiliania huxleyi, Calcidiscus leptoporus and Gephyrocapsa oceanica. Mg/Ca of treated coccolithophores were 0.151 ± 0.018, 0.220 ± 0.040, and 0.064 ± 0.023 mmol/mol, respectively. Comparison with Mg/Ca literature coccolith values, suggests a tight dependence on modern seawater Mg/Ca, which changes as a consequence of different seawater origins (<10%). The reliable determination of Mg/Ca and Sr/Ca, and the low levels of organic contamination (Fe/Ca and P/Ca) make this protocol applicable to field and laboratory studies of trace elemental composition in coccolithophore calcite.

Blanco-Ameijeiras, S.; Lebrato, M.; Stoll, H. M.; Iglesias-Rodriguez, M. D.; Méndez-Vicente, A.; Sett, S.; Müller, M. N.; Oschlies, A.; Schulz, K. G.

2012-07-01

215

Uranyl Incorporation in Organic-Bearing Soil Calcite  

Microsoft Academic Search

Phosphor imaging and fission track maps reveal a close correlation between uranium and organic-rich calcite that lines roots in an ancient caliche soil. Concordant U-Pb ages show that this uranium has not been mobilized since the soil calcite formed 298 ñ 1 Ma ago. Luminescence spectroscopic analysis of the organic-rich calcite demonstrates that uranium is present in the oxidized state.

E. Rasbury; C. Tait; R. J. Donohoe

2003-01-01

216

Cloud Condensation Nucleus Activity of calcite and calcite coated with model humic and fulvic acids  

NASA Astrophysics Data System (ADS)

Many recent studies have shown that organics can alter the water adsorption and cloud condensation nuclei (CCN) activity of common deliquescent species in the Earth's atmosphere. However, very little is known about the effect of organics on water adsorption and CCN activity of common inactive cloud nuclei, such as mineral aerosol. As many studies have shown that a large fraction of unidentified organic material in aerosol particles is composed of polycarboxylic acids resembling humic substances, the presence of these large molecular weight Humic-Like Substances (HULIS) may also alter the water adsorption and CCN activity of mineral aerosol. Thus, we have measured the water adsorption and CCN activity of model humic and fulvic acids. Additionally, the water adsorption and CCN activity of mineral aerosol particles coated with humic and fulvic acids have been studied. We find that humic and fulvic acids show continual multilayer water adsorption as the relative humidity is raised. Additionally, we find that calcite particles mixed with humic and fulvic acids take up more water by mass, by a factor of two, compared to the uncoated calcite particles at approximately 70% RH. CCN measurements also indicate that internally mixed calcite-humic or fulvic acid aerosols are more CCN active than the otherwise inactive, uncoated calcite particles. Our results suggest that mineral aerosol particles coated with high molecular weight organic materials will take up more water and become more efficient CCN in the Earth's atmosphere than single-component mineral aerosol.

Hatch, C. D.; Gierlus, K. M.; Schuttlefield, J. D.; Grassian, V. H.

2007-12-01

217

Impact of trace metals on the water structure at the calcite surface  

NASA Astrophysics Data System (ADS)

Carbonate minerals play an important role in regulating the chemistry of aquatic environments, including the oceans, aquifers, hydrothermal systems, soils and sediments. Through mineral surface processes such as dissolution, precipitation and sorption, carbonate minerals affect the biogeochemical cycles of not only the constituent elements of carbonates, such as Ca, Mg, Fe and C, but also H, P and trace elements. Surface charging of the calcite mineral-water interface, and its reactivity towards foreign ions can be quantified using a surface structural model that includes, among others, the water structure at the interface (i.e. hydrogen bridging) [1,2] in accordance with the CD-MUSIC formalism [3]. Here we will show the impact of foreign metals such as Mg and Sr on the water structure around different surface sites present in etch pits and on growth terraces at the calcite (10-14) surface. We have performed Molecular Dynamics simulations of metal-doped calcite surfaces, using different interatomic water potentials. Results show that the local environment around the structurally distinct sites differs depending on metal presence, suggesting that metal substitutions in calcite affect its reactivity. The information obtained in this study will help in improving existing macroscopic surface model for the reactivity of calcite [2] and give more general insight in mineral surface reactivity in relation to crystal composition. [1] Wolthers, Charlet, & Van Cappellen (2008). Am. J. Sci., 308, 905-941. [2] Wolthers, Di Tommaso, Du, & de Leeuw (2012). Phys. Chem. Chem. Phys. 14, 15145-15157. [3] Hiemstra and Van Riemsdijk (1996) J. Colloid Interf. Sci. 179, 488-508.

Wolthers, Mariette; Di Tommaso, Devis; De Leeuw, Nora

2014-05-01

218

Spin Hamiltonian parameters and local structures for Co2+ ions in calcite-type trigonal carbonates MCO3 (M=Co, Cd and Ca)  

Microsoft Academic Search

From the perturbation formulas based on the cluster approach for 3d7 ion in trigonal octahedral sites of crystals, the spin Hamiltonian parameters (g factors g||, g? and hyperfine structure constants A||, A?) for Co2+ in calcite-type MCO3 (M=Co, Cd, Ca) crystals are calculated. In the calculations, for CoCO3 crystal, the structural data of pure crystal are used, whereas for the

Zheng Wen-Chen; Wu Shao-Yi; Dong Hui-Ning; Tang Sheng

2004-01-01

219

Spin Hamiltonian parameters and local structures for Co 2+ ions in calcite-type trigonal carbonates MCO 3 (M=Co, Cd and Ca)  

Microsoft Academic Search

From the perturbation formulas based on the cluster approach for 3d7 ion in trigonal octahedral sites of crystals, the spin Hamiltonian parameters (g factors g?, g? and hyperfine structure constants A?, A?) for Co2+ in calcite-type MCO3 (M=Co, Cd, Ca) crystals are calculated. In the calculations, for CoCO3 crystal, the structural data of pure crystal are used, whereas for the

Zheng Wen-Chen; Wu Shao-Yi; Dong Hui-Ning; Tang Sheng

2004-01-01

220

First-principles calculations of structural, electronic, optical and elastic properties of magnesite MgCO 3 and calcite CaCO 3  

Microsoft Academic Search

Detailed ab initio calculations of the structural, electronic, optical and elastic properties of two crystals – magnesite (MgCO3) and calcite (CaCO3) – are reported in the present paper. Both compounds are important natural minerals, playing an important role in the carbon dioxide cycling. The optimized crystal structures, band gaps, density of states diagrams, elastic constants, optical absorption spectra and refractive

M. G. Brik

2011-01-01

221

First-principles calculations of structural, electronic, optical and elastic properties of magnesite MgCO3 and calcite CaCO3  

Microsoft Academic Search

Detailed ab initio calculations of the structural, electronic, optical and elastic properties of two crystals - magnesite (MgCO3) and calcite (CaCO3) - are reported in the present paper. Both compounds are important natural minerals, playing an important role in the carbon dioxide cycling. The optimized crystal structures, band gaps, density of states diagrams, elastic constants, optical absorption spectra and refractive

M. G. Brik

2011-01-01

222

Aqueous cadmium uptake by calcite: a stirred flow-through reactor study  

NASA Astrophysics Data System (ADS)

Uptake of cadmium ions from solution by a natural Mg-containing calcite was investigated in stirred flow-through reactor experiments. Input NaCl solutions were pre-equilibrated with calcite (pH 8.0) or not (pH 6.0), prior to being spiked with CdCl 2. For water residence times in the reactor less than 0.5 h, irreversible uptake of Cd by diffusion into the bulk crystal had a minor effect on the measured cadmium breakthrough curves, hence allowing us to quantify "fast" Cd 2+ adsorption. At equal aqueous activities of Cd 2+, adsorption was systematically lower for the pre-equilibrated input solutions. The effect of variable solution composition on Cd 2+ adsorption was reproduced by a Ca 2+-Cd 2+ cation exchange model and by a surface complexation model for the calcite-aqueous solution interface. For the range of experimental conditions tested, the latter model predicted binding of aqueous Ca 2+ and Cd 2+ to the same population of carbonate surface sites. Under these circumstances, both adsorption models were equivalent. Desorption released 80 to 100% of sorbed cadmium, confirming that fast uptake of Cd 2+ was mainly due to binding at surface sites. Slow, irreversible cadmium uptake by the solid phase was measured in flow-through reactor experiments with water residence times exceeding 0.7 h. The process exhibited first-order kinetics with respect to the concentration of adsorbed Cd 2+, with a linear rate constant at 25°C of 0.03 h -1. Assuming that diffusion into the calcite lattice was the mechanism of slow uptake, a Cd 2+ solid-state diffusion coefficient of 8.5×10 -21 cm 2 s -1 was calculated. Adsorbed Cd 2+ had a pronounced effect on the dissolution kinetics of calcite. At maximum Cd 2+ surface coverage (˜10 -5 mol m -2), the calcite dissolution rate was 75% slower than measured under initially cadmium-free conditions. Upon desorption of cadmium, the dissolution rate increased again but remained below its initial value. Thus, the calcite surface structure and reactivity retained a memory of the adsorbed Cd 2+ cations after their removal.

Martin-Garin, A.; Van Cappellen, P.; Charlet, L.

2003-08-01

223

Spectroscopic characterization of natural calcite minerals  

NASA Astrophysics Data System (ADS)

The FT-IR, FT-Raman, NMR spectral data of ten different limestone samples have been compared. FT-IR and FT-Raman spectral data show that calcium carbonate in limestone, principally in the form of calcite, as identified by its main absorption bands at 1426, 1092, 876 and 712 cm -1. The sharp diffractions at the d-spacings, 3.0348, 1.9166 and 1.8796 confirm the presence of calcite structure and the calculated lattice parameters are: a = 4.9781 Å, c = 17.1188 Å. The range of 13C chemical shifts for different limestone samples is very small, varying from 198.38 to 198.42 ppm. The observed chemical shifts are consistent with the identical C-O bonding in different limestone samples. 27Al MAS NMR spectra of the samples exhibit a central line at 1 ppm and another line at 60 ppm corresponding to octahedral and tetrahedral Al ions, respectively. The five component resonances were observed in 29Si MAS NMR spectrum of limestone and these resonances were assigned to Si (4 Al), Si (3 Al), Si (2 Al), Si (1 Al) and Si (0 Al) from low field to high field.

Gunasekaran, S.; Anbalagan, G.

2007-11-01

224

Basal slip and texture development in calcite: new results from torsion experiments  

SciTech Connect

The deformation behavior of calcite has been of longstanding interest. Through experiments on single crystals, deformation mechanisms were established such as mechanical twinning on e = {l_brace}{bar 1}018{r_brace} <40{bar 4}1> in the positive sense and slip on r = {l_brace}10{bar 1}4{r_brace} <20{bar 2}{bar 1}> and f = {l_brace}{bar 1}012{r_brace} <0{bar 2}2{bar 1}> both in the negative sense. More recently it was observed that at higher temperatures f{l_brace}{bar 1}012{r_brace} <10{bar 1}1> slip in both senses becomes active and, based on slip line analysis, it was suggested that e(0001) <11{bar 2}0> slip may occur. So far there had been no direct evidence for basal slip, which is the dominant system in dolomite. With new torsion experiments on calcite single crystals at 900 K and transmission electron microscopy, this study identifies (0001) <11{bar 2}0> slip unambiguously by direct imaging of dislocations and diffraction contrast analysis. Including this slip system in polycrystal plasticity simulations, enigmatic texture patterns observed in compression and torsion of calcite rocks at high temperature can now be explained, resolving a long-standing puzzle.

Barber, D. J.; Wenk, H.-R.; Gomez-Barreiro, J.; Rybacki, E.; Dresen, G. (UCB); (Essex); (GFZ)

2008-06-09

225

The Coordination of Mg in Foraminiferal Calcite  

NASA Astrophysics Data System (ADS)

The Mg/Ca ratio in calcite shells ('tests') of foraminifera is an empirical ocean temperature proxy widely used to interpret palaeoclimates. We explore the distribution and local environment of Mg in foram tests using STXM and NEXAFS spectroscopy to test the fundamental assumptions behind the proxy, and shed light on the mechanisms underpinning this vital oceanographic tool. Throughout the development of the Mg/Ca proxy, it has been assumed that Mg in foraminifera tests substitutes directly into the calcite lattice (1). This assumption is based on XRD analyses of various high-Mg biogenic carbonates, where Mg concentrations are manifest in the shifted position of diffraction peaks (2, 3). The extrapolation of this trend to foraminiferal calcite links the proxy to inorganic precipitation experiments, and provides a theoretical mechanistic framework to understand the link between Mg/Ca and temperature: the substitution of Mg is endothermic, and favoured at higher temperatures. However, the concentration of Mg in most foraminifera (0-10 mmol/mol Mg/Ca) is below the detection limit of XRD methods, and the analogy to inorganic systems has not been explicitly tested. Electron microprobe (4-6), LA-ICP-MS (7) and high-resolution nanoSIMS mapping (Sadekov, unpub.) of foraminifera tests have revealed the presence of high 'trace element' bands running in plane with the test surface, enriched in Mg, Sr, S, organic molecules and other trace elements. This emphasises a key question highlighted by Dodd (1) when the proxy was still in its infancy: how is Mg incorporated into mineral skeletons? By direct substitution into the calcite lattice, interstitially in a separate distinct mineral phase, or associated with organic compounds? We address this fundamental question using scanning transmission X-ray microscopy (STXM) and X-ray absorption spectroscopy at ALS beamline 11.0.2 to examine the distribution and local atomic environment of Mg in two contrasting species of foraminifera. Our data conclusively demonstrate that the Mg in the high- and low-trace element bands in the two different species is incorporated in the same mode. Foraminiferal Mg K-edge spectra are most similar to that of dolomite, where Ca and Mg are interchangeable and both present in octahedral sites. This indicates that Mg directly substitutes for Ca in the calcite test, validating the assumptions underlying the use of the Mg/Ca proxy. The uniformity of Mg environment also sheds light on the drivers of Mg heterogeneity, suggesting that Mg banding is driven by fluctuations in medium chemistry, rather than any change in Mg incorporation mechanism. The ultimate cause of Mg heterogeneity remains an open question, however. 1. J. R. Dodd, J Paleontology, 1313-1329 (1967). 2. K. E. Chave, J Geol 62, 266-283 (1954). 3. J. Titschack, F. Goetz-Neunhoeffer, J. Neubauer, Am Min 96, 1028 (2011). 4. J. Lipps, P. Ribbe, J Paleontology 41, 492-496 (1967). 5. A. Y. Sadekov, S. M. Eggins, P. de Deckker, G3 6, Q12P06 (2005). 6. J. Erez, Rev Min Geochem 54, 115 (2003). 7. A. Y. Sadekov, S. M. Eggins, G. P. Klinkhammer, Y. Rosenthal, Earth Planet Sc Lett 292, 312-324 (2010).

Branson, O.; Redfern, S. A.; Tyliszczak, T.; Sadekov, A.; Langer, G.; Elderfield, H.

2012-12-01

226

Effects of temperature and transport conditions on calcite growth in the presence of Mg 2+: Implications for paleothermometry  

NASA Astrophysics Data System (ADS)

This study links direct measurement of Mg-calcite growth kinetics with high-spatial-resolution analysis of Mg contents in experimental crystals, with particular attention to the effects of temperature on growth rate and reactant transport conditions on Mg distribution. In contrast to previous experiments on Mg partitioning into calcite, here the layer-growth mechanism was observed in situ and step speeds precisely measured with fluid cell atomic force microscopy over a range of temperatures, degrees of supersaturation, and solution Mg concentrations. Data collected from 15° to 30°C yield an activation energy for calcite precipitation of 33 kJ/mol for solutions with [Mg] = 5 × 10 -5 molal. Electron microprobe analyses of large hillocks grown at corresponding conditions demonstrate that Mg has a strong preference for incorporation at negative (acute) step edges, rather than at positive (obtuse) edges when growth rate is limited by surface reactions. This preference is reversed when growth is instead limited by diffusion of reactants through a boundary layer at the mineral-solution interface. These findings show that temperature is not the only strong control on the extent of Mg incorporation and distribution in calcite; transport conditions during mineral growth may also be a first-order factor governing the compositions of natural calcite samples.

Wasylenki, Laura E.; Dove, Patricia M.; De Yoreo, James J.

2005-09-01

227

Dissolution dynamics of the calcite-water interface observed in situ by glancing-incidence X-ray scattering  

SciTech Connect

Glancing-incidence X-ray scattering measurements made at the National Synchrotron Light Source were used to investigate dissolution dynamics in situ at the calcite-water interface. The relation between calcite saturation state and roughness of the calcite (1014) cleavage surface as a function of time was examined during pH titrations of an initially calcite-saturated solution. Systematic variations in roughness were observed as a function of saturation state as pH was titrated to values below that of calcite saturation. Different steady-state values of roughness were evident at fixed values of {Delta}G{sub r}, and these were correlated with the extent of undersaturation. A significant increase in roughness begins to occur with increasing undersaturation at a {Delta}G{sub r} value of approximately {minus}2.0 kcal/mol. The dissolution rate corresponding to this increase is about 1.5 x 10{sup 7} mmol/cm {center_dot} sec. This increase in roughness is attributed to a transition in the principal rate-determining dissolution mechanism, and is consistent with both powder-reaction studies of dissolution kinetics and single-crystal dissolution studies by atomic force microscopy. These data indicate some important potential applications of GIXS in the study of mineral-water interface geochemistry.

Sturchio, N.C.; Chiarello, R.P.

1995-06-02

228

Colloidal stability of calcite dispersion treated with sodium polyacrylate  

Microsoft Academic Search

The stabilising action of sodium polyacrylate on colloidal dispersions of calcite has been investigated through measurement of viscosity, ion concentration and electrophoretic mobility. The dose of sodium polyacrylate was in the range 0 to 28 mg per g of calcite and the dispersions were prepared at a sodids content of 70% (by weight). The ionic strength of the dispersions, ca.

K. R. Rogan; A. C. Bentham; I. A. George; D. R. Skuse

1994-01-01

229

Nanofiber calcite in Asian dust and its atmospheric roles  

Microsoft Academic Search

Calcite is the most important mineral in Asian dust, and it reacts with atmospheric gases during its long-range transport. Mineralogical and chemical analyses of Asian dust and source soils showed two types of calcite that differ greatly in morphology and origin: (i) micron-sized irregular particles derived from the erosion of bedrock, and (ii) nanosized fibers that were chemically precipitated in

Gi Young Jeong; Youngsin Chun

2006-01-01

230

The kinetics of microstructural evolution during deformation of calcite  

Microsoft Academic Search

There is a strong coupling between the microstructure and the strength of rocks that is thought to play a key role in the evolution of shear zones and in our ability to interpret the mechanics of natural deformation processes. To investigate the microstructural evolution of calcite-rich rocks, we have performed a series of hydrostatic and deformation experiments on synthetic calcite

Nicholas Austin; Brian Evans

2009-01-01

231

Seed-mediated synthesis of single-crystal gold nanospheres with controlled diameters in the range 5-30 nm and their self-assembly upon dilution.  

PubMed

Single-crystal gold nanospheres with controlled diameters in the range 5-30 nm were synthesized by using a facile approach that was based on successive seed-mediated growth. The key to the success of this synthesis was the use of hexadecyltrimethylammonium chloride (CTAC) as a capping agent and a large excess of ascorbic acid as a reductant to ensure fast reduction and, thus, single crystallinity and a spherical shape of the resultant nanoparticles. The diameters of the gold nanospheres could be readily controlled by varying the amount of seeds that were introduced into the reaction system. The gold nanospheres could be produced with uniform diameters of up to 30 nm; thus, their localized surface plasmon resonance properties could be directly compared with the results that were obtained from theoretical calculations. Interestingly, we also found that these gold nanospheres self-assembled into dimers, larger aggregates, and wavy nanowires when they were collected by centrifugation, dispersed in deionized water, and then diluted to different volumes with deionized water. PMID:23362050

Zheng, Yiqun; Ma, Yanyun; Zeng, Jie; Zhong, Xiaolan; Jin, Mingshang; Li, Zhi-Yuan; Xia, Younan

2013-04-01

232

Characterization and In-Situ Monitoring of ZnSe Crystal Growth by Seeded PVT for Microgravity Applications  

NASA Technical Reports Server (NTRS)

Crystal growth from the vapor phase continues to play a significant role in the production of II-VI semiconductor compounds (ZnO, ZnTe, CdTe, etc.) and SiC. As compared to melt growth methods (where available) the advantages are: (1) lower growth temperature(s); (2) reduction in defect concentration; (3) additional purification; and (4) enhanced crystal perfection. A powerful tool in determining the mechanism of PVT is microgravity. Under normal gravity conditions the transport mechanism is a superposition of diffusive and convective fluxes. Microgravity offers the possibility of studying the transport properties without the influence of convective effects. Research on the crystal growth of ZnSe by PVT (P.I.: Su of NASA/MSFC) will help to clarify the effects of convection on crystal growth. A crystal growth furnace with in-situ and real time optical monitoring capabilities was constructed and used to monitor the vapor composition and growing crystal surface morphology during the PVT growth of ZnSe. Using photoluminescence and SIMS, ex-situ, the incorporation of point defects (Zn vacancy) and impurities was found to be correlated to the gravity vector due to the influence of the convective flow. A summary of the results to date will be presented.

Feth, Shari T.

2001-01-01

233

The ionic conductivity in high-pressure polymorphs of calcite  

NASA Astrophysics Data System (ADS)

Ionic conductivity of polycrystalline calcite containing varying amounts of PO{4/3-}ions was measured in the pressure range of 1 6 GPa and at room temperature. Electrical conductivity increased with pressure corresponding to the phase transition of calcite I to calcite II. The conductivity in calcite III decreased exponentially with pressure. Calculated activation volumes of the conductivity varied with PO{4/3-}content in the range of 0.94 5.34 cm3/mol. This variation corresponded to the lattice parameter change of calcite I due to PO{4/3-}incorporation and indicated the contribution of CO{3/2-}-vacancies associated with PO{4/3-}ions to the conductivity.

Ishikawa, M.; Sawaoka, A.; Ichikuni, M.

1982-11-01

234

Selectively increasing of polyunsaturated (18:2) and monounsaturated (18:1) fatty acids in Jatropha curcas seed oil by crystallization using D-optimal design  

PubMed Central

Background This study was done to obtain concentrated polyunsaturated fatty acid (PUFA) linoleic acid (LA; 18:2) and monounsaturated fatty acid (MUFA) oleic acid (OA; 18:1) from Jatropha curcas seed oil by urea complexation. Urea complexation is a method used by researchers to separate fatty acids (FAs) based on their molecular structure. Effects the ratio of urea-to-FAs, crystallization temperature and crystallization time on the final products of urea complexation were examined. D-optimal Design was employed to study the significance of these factors and the optimum conditions for the technique were predicted and verified. Results Optimum conditions of the experiment to obtain maximum concentration of LA were predicted at urea-to-FAs ratio (w/w) of 5:1, crystallization temperature of ?10°C and 24 h of crystallization time. Under these conditions, the final non-urea complex fraction (NUCF) was predicted to contain 92.81% of LA with the NUCF yield of 7.8%. The highest percentage of OA (56.01%) was observed for samples treated with 3:1 urea-to-FAs ratio (w/w) at 10°C for 16 h. The lowest percentage of LA (8.13%) was incorporated into urea complex fraction (UCF) with 1:1 urea-to-FAs ratio (w/w) at 10°C for 8 h. Conclusions The separation of PUFA (LA) and MUFA (OA) described here. Experimental variables should be carefully controlled in order to recover a maximum content of PUFA and MUFA of interest with reasonable yield% with a desirable purity of fatty acid of interest.

2012-01-01

235

Ion microprobe study of oxygen isotopic compositions of structurally nonequivalent growth surfaces on synthetic calcite  

SciTech Connect

A synthetic calcite crystal that exhibits surface-structure-controlled, differential incorporation of a trace element was examined by ion microprobe to determine whether the controls causing differential element incorporation have a corresponding influence on incorporation of oxygen isotopes. In contrast both to the behavior of trace elements and to several previous studies claiming surface structural control on isotopic fractionation, the synthetic calcite fails to show any such surface effect. These ion probe experiments also represent the first isotopic analyses of symmetrically nonequivalent vicinal faces that compose the flanks of growth spirals. Hence we establish that structurally nonequivalent growth steps, which also differ in growth step velocity, and occurring on a single crystal face, show no measurable difference in fractionation during low-temperature solution growth. Although our findings for a synthetic crystal differ from other reports for natural crystals that were based on different techniques and larger sample size, our results are consistent with the view that surface-site preferences during growth are not significantly sensitive to the slight mass and vibrational differences among light stable isotopes. 28 refs., 4 figs., 1 tab.

Reeder, R.J. [Univ. of New York, Stony Brook, NY (United States)] [Univ. of New York, Stony Brook, NY (United States); Valley, J.W. [Univ. of Wisconsin, Madison, WI (United States)] [Univ. of Wisconsin, Madison, WI (United States); Graham, C.M. [Univ. of Edinburgh (United Kingdom)] [Univ. of Edinburgh (United Kingdom); Eiler, J.M. [California Institute of Technology, Pasadena, CA (United States)] [California Institute of Technology, Pasadena, CA (United States)

1997-12-01

236

The influence of impurities on the growth rate of calcite  

NASA Astrophysics Data System (ADS)

The effects of 34 different additives on the growth rate of calcite were investigated. An initial growth rate of about one crystal monolayer (3 × 10 -8 cm) per minute was adjusted at a constant supersaturation which was maintained by a control circuit. Then the impurity was added step by step and the reduction of the growth rate was measured. The impurity concentration necessary to reduce the initial growth rate by a certain percentage increased in the order Fe 2+, ATP, P 3O 5-10, P 2O 4-7, (PO 3) 6-6, Zn 2+, ADP, Ce 3+, Pb 2+, carbamyl phosphate, Fe 3+, PO 3-4, Co 2+, Mn 2+, Be 2+, ?-glycerophosphate, Ni 2+, Cd 2+, "Tris", phenylphosphate, chondroitine sulphate, Ba 2+, citrate, AMP, Sr 2+, tricarballylate, taurine, SO 2-4, Mg 2+ by 4 orders of magnitude. The most effective additives halved the initial growth rate in concentrations of 2 × 10 -8 mol/1. For Fe 2+ the halving concentration was nearly proportional to the initial rate. The mechanism of inhibition by adsorption of the impurities at growth sites (kinks) is discussed.

Meyer, H. J.

1984-05-01

237

Nano-structured calcite produced by micro-organisms in ancient and modern loess in Chinese Loess Plateau  

NASA Astrophysics Data System (ADS)

The results from transmission electron microscopy (TEM) and field emission gun scanning microscopy (FEG-SEM) investigation show that there are calcite nano-fibers (CNFs) formed during pedogenic process. The CNFs are widely distributed in the loess and red clay samples of Caoxian, Luochuan, Lingtai, Lantian, and Xifeng profiles as well as the samples of modern surface loess soils in Chinese Loess Plateau. Diameters of all the NFCs are about 40 nm, the length of the CNFs ranges from tens nanometer to several micrometers. Elongation direction of NFCs is unusual near parallel (105)* or (115)*. Crystals of NFCs arrange as bird net like and lattice-like frameworks. X-ray EDS spectra show the weak peaks of magnesium, phosphorous, and sulfur. Our investigation indicates that CNFs are in pore space of loess and paleosol and made up most of carbonate except for caliche nodular layers. Concentration of NFCs in the loess layers are significantly higher than those of paleosol layers because of leaching of carbonate in the paleosol forming environment (warn and wet paleoclimate). The "nanobacteria-like CNFs are well crystalline calcite single crystals with smoothes surfaces. The morphologies of CNFs are very unusual and different from the calcite single crystals observed in most geological environments. The CNFs are directly related to microbial activities in both ancient and modern loess. It is proposed that the intervention of organic compounds derived from microbial activities control the formation of the calcite nano-fibers. Both morphology and bulk composition of CNFs indicate that the formation of the CNFs involves bio-organics derived from microorganisms in loess deposit environment. Formation conditions of the calcite nano-fibers may information about paleoclimate, paleo-environment and paleoecology. So, the discovery of CNFs in loess-paloesol sequences can provide a new route for reconstruct paleoclimate by oxygen and carbon isotope from the CNFs.

Xu, H.; Chen, T.; Lu, H.; Wang, X.

2005-12-01

238

Organic Surfaces Promote Calcite Nucleation Through Biomolecule-Specific Reductions in Interfacial Free Energy  

NASA Astrophysics Data System (ADS)

Sites of biogenic calcification are comprised of complex macromolecular assemblages that are implicated in regulating the onset of mineralization. Classical nucleation theory predicts that the organic templates provided by these proteins and polysaccharides significantly affect nucleation rate by modulating interfacial free energy, which determines the thermodynamic barrier to nucleation. Recent evidence suggests that calcium carbonate (CaCO3) formation often involves pre-nucleation clusters and transient precursor phases, which raises the question of how biomolecular controls on crystallization are related to emerging concepts in non-classical mineralization. While previous studies qualitatively demonstrate that the chemical functionalities of biomolecules influence the nucleating mineral phase and morphology, a mechanistic understanding of their control over nucleation kinetics and thermodynamics is not well established. Here we test the hypothesis that specific chemical functional groups regulate the kinetics and thermodynamics of CaCO3 formation by using self-assembled monolayers (SAMs) as substrates for calcite nucleation. We measured nucleation rates on substrates with different termini (-COOH, -PO4, and -SH) and alkanethiol chain lengths (16-C and 11-C) at a variety of chemical driving forces, both above and below the reported solubility of amorphous calcium carbonate (ACC). Using classical nucleation theory to interpret the kinetic data, we calculated calcite-substrate interfacial energies and estimated substrate-specific effects on the thermodynamic barrier to nucleation. Calcite - substrate interaction forces were quantified with independent dynamic force spectroscopy (DFS) measurements. The nucleation rate measurements show that organic templates reduce the thermodynamic barrier to calcite nucleation compared to homogeneous nucleation through reductions in interfacial free energy. These free energies are correlated with independent DFS measurements of calcite-substrate interaction force by a systematic relationship that is general to chemistry and chain length. Calcite nucleation in these systems is accurately described with classical models of nucleation. The findings demonstrate a physical basis for how organic surfaces reduce the thermodynamic barrier to nucleation and show that precursor phases and pre-nucleation clusters are not required for template-directed mineralization.

Hamm, L. M.; Han, N.; Giuffre, A. J.; De Yoreo, J.; Dove, P. M.

2012-12-01

239

Strontium, nickel, cadmium, and lead substitution into calcite, studied by density functional theory.  

PubMed

We have used density functional theory to predict the ion exchange energies for divalent cations Ni(2+), Sr(2+), Cd(2+), and Pb(2+) into a calcite {10.4} surface in equilibrium with water. Exchange energies were calculated for substitution into the topmost surface layer, at the mineral-fluid interface, and into the second layer of the solid. This information can be used as an indicator for cation substitution in the bulk phase, such as for the uptake of toxic metals from the environment and the growth of secondary phases. In both the surface and in the second layer, Ni(2+), Cd(2+), and Pb(2+) substitute exothermically and Sr(2+) substitutes endothermically. Our results agree with published experimental data that demonstrate trace metal coprecipitation with calcite as a sink for Ni(2+), Cd(2+), and Pb(2+), whereas Sr(2+) has a distribution constant significantly smaller than 1. Ni(2+) substitution is favored at the mineral-fluid interface compared with bulk substitution, which also agrees with experimental data. Our results predict that Ni(2+), Cd(2+), and Pb(2+) form a stable solid solution with calcite. Successful prediction of the experimental results gives us confidence in our ability to predict the divalent cation preference for surfaces rather than for sites within the bulk crystal structure, which cannot be directly derived from experiment. PMID:24823264

Andersson, M P; Sakuma, H; Stipp, S L S

2014-06-01

240

Strontium incorporation into calcite generated by bacterial ureolysis  

NASA Astrophysics Data System (ADS)

Strontium incorporation into calcite generated by bacterial ureolysis was investigated as part of an assessment of a proposed remediation approach for 90Sr contamination in groundwater. Urea hydrolysis produces ammonium and carbonate and elevates pH, resulting in the promotion of calcium carbonate precipitation. Urea hydrolysis by the bacterium Bacillus pasteurii in a medium designed to mimic the chemistry of the Snake River Plain Aquifer in Idaho resulted in a pH rise from 7.5 to 9.1. Measured average distribution coefficients (D EX) for Sr in the calcite produced by ureolysis (0.5) were up to an order of magnitude higher than values reported in the literature for natural and synthetic calcites (0.02-0.4). They were also higher than values for calcite produced abiotically by ammonium carbonate addition (0.3). The precipitation of calcite in these experiments was verified by X-ray diffraction. Time-of-flight secondary ion mass spectrometry (ToF SIMS) depth profiling (up to 350 nm) suggested that the Sr was not merely sorbed on the surface, but was present at depth within the particles. X-ray absorption near edge spectra showed that Sr was present in the calcite samples as a solid solution. The extent of Sr incorporation appeared to be driven primarily by the overall rate of calcite precipitation, where faster precipitation was associated with greater Sr uptake into the solid. The presence of bacterial surfaces as potential nucleation sites in the ammonium carbonate precipitation treatment did not enhance overall precipitation or the Sr distribution coefficient. Because bacterial ureolysis can generate high rates of calcite precipitation, the application of this approach is promising for remediation of 90Sr contamination in environments where calcite is stable over the long term.

Fujita, Yoshiko; Redden, George D.; Ingram, Jani C.; Cortez, Marnie M.; Ferris, F. Grant; Smith, Robert W.

2004-08-01

241

The coprecipitation of Sr into calcite precipitates induced by bacterial ureolysis in artificial groundwater: Temperature and kinetic dependence  

NASA Astrophysics Data System (ADS)

A suite of experiments was performed to investigate the partitioning of Sr 2+ (to mimic the radionuclide 90Sr) between calcite and artificial groundwater in response to the hydrolysis of urea (ureolysis) by Bacillus pasteurii under simulated in situ aquifer conditions. Experiments were performed at 10, 15, and 20°C over 7 days in microcosms inoculated with B. pasteurii ATCC 11859, containing an artificial groundwater and urea (AGW) or an AGW including a Sr contaminant treatment. During the experiments, the concentration of ammonium generated by bacterial ureolysis increased asymptotically, and derived rate constants ( k urea) that were between 13 and 10 times greater at 20°C than at 15 and 10°C. Calcite precipitation was initiated after similar amounts of urea had been hydrolyzed (˜ 4.0 mmol L -1) and a similar critical saturation state (mean S critical = 53, variation = 20%) had been reached, independent of temperature and Sr treatment. Because of the positive relationship between the rate of ureolysis and temperature, precipitation began by the end of day 1 at 20°C, and between days 1 and 2 at 15 and 10°C. The rate of calcite precipitation increased with, and was fundamentally controlled by calcite saturation state ( S), irrespective of temperature. The presence of Sr slightly slowed calcite precipitation rates at equivalent values of S, which may reflect the screening of active nucleation and crystal growth sites by Sr. Homogeneous partitioning coefficients (D Sr) exhibited a positive association with calcite precipitation rates, but were greater at higher experimental temperatures at equivalent precipitation rates (20°C mean = 0.46; 15°C mean = 0.24; 10°C mean = 0.29).

Mitchell, Andrew C.; Ferris, F. Grant

2005-09-01

242

Formation of a ternary neptunyl(V) biscarbonato inner-sphere sorption complex inhibits calcite growth rate.  

PubMed

Neptunyl, Np(V)O(2)(+), along with the other actinyl ions U(VI)O(2)(2+) and Pu(V,VI)O(2)((+,2+)), is considered to be highly mobile in the geosphere, while interaction with mineral surfaces (inner- or outer-sphere adsorption, ion-exchange, and coprecipitation/structural incorporation) may retard its migration. Detailed information about the exact interaction mechanisms including the structure and stoichiometry of the adsorption complexes is crucial to predict the retention behavior in diverse geochemical environments. Here, we investigated the structure of the neptunyl adsorption complex at the calcite-water interface at pH 8.3 in equilibrium with air by means of low-temperature (15K) EXAFS spectroscopy at the Np-L(III) edge. The coordination environment of neptunyl consists of two axial oxygen atoms at 1.87(±0.01)Å, and an equatorial oxygen shell of six atoms at 2.51(±0.01)Å. Two oxygen backscatterers at 3.50(±0.04)Å along with calcium backscatterers at 3.95(±0.03)Å suggest that neptunyl is linked to the calcite surface through two monodentate bonds towards carbonate groups of the calcite surface. Two additional carbon backscatterers at 2.94(±0.02)Å are attributed to two carbonate ions in bidentate coordination. This structural environment is conclusively interpreted as a ternary surface complex, where a neptunyl biscarbonato complex sorbs through two monodentate carbonate bonds to steps at the calcite (104) face, while the two bidentately coordinated carbonate groups point away from the surface. This structural information is further supported by Mixed Flow Reactor (MFR) experiments. They show a significant decrease of the calcite growth rate in the presence of neptunyl(V), in line with blockage of the most active crystal growth sites, step and kink sites, by adsorption of neptunyl. Formation of this sorption complex constitutes an important retention mechanism for neptunyl in calcite-rich environments. PMID:21429616

Heberling, Frank; Scheinost, Andreas C; Bosbach, Dirk

2011-06-01

243

crystal  

NASA Astrophysics Data System (ADS)

A Nd3+:Na2La4(WO4)7 crystal with dimensions of ? 17 × 30 mm3 was grown by the Czochralski method. The thermal expansion coefficients of Nd3+:Na2La4(WO4)7 crystal are 1.32 × 10-5 K-1 along c-axis and 1.23 × 10-5 K-1 along a-axis, respectively. The spectroscopic characteristics of Nd3+:Na2La4(WO4)7 crystal were investigated. The Judd-Ofelt theory was applied to calculate the spectral parameters. The absorption cross sections at 805 nm are 2.17 × 10-20 cm2 with a full width at half maximum (FWHM) of 15 nm for ?-polarization, and 2.29 × 10-20 cm2 with a FWHM of 14 nm for ?-polarization. The emission cross sections are 3.19 × 10-20 cm2 for ?-polarization and 2.67 × 10-20 cm2 for ?-polarization at 1,064 nm. The fluorescence quantum efficiency is 67 %. The quasi-cw laser of Nd3+:Na2La4(WO4)7 crystal was performed. The maximum output power is 80 mW. The slope efficiency is 7.12 %. The results suggest Nd3+:Na2La4(WO4)7 crystal as a promising laser crystal fit for laser diode pumping.

Yu, Yi; Huang, Yisheng; Zhang, Lizhen; Lin, Zhoubin; Sun, Shijia; Wang, Guofu

2014-07-01

244

Dynamic and topographic observation of calcite dissolution using enhanced in-situ phase-shift interferometry  

NASA Astrophysics Data System (ADS)

The dissolution rate of calcite in water with and without flow was measured using enhanced phase-shift interferometry (PSI). This technique uses a white light source instead of laser light to shorten the coherent wave-length providing quick and precise measurements of mineral dissolution and growth over relatively short time scales (several tens of minutes). Phase shift interferometry is non-invasive technique that allows surface observation at the molecular level in water as well as direct, simultaneous measurement of step velocity and the behavior of crystal surfaces during dissolution. The theoretical PSI resolution in the vertical direction in water is 0.78 nm; however the practical detection limit of the calcite dissolution experiments was 4.2 nm due to the effects of external and internal inferences such as apparatus drift, air drag, etc. The calcite dissolution rate at zero water flow was estimated from the retreat velocity as 0.0494 nm/s, which corresponds to flux rate of 1.33E-10 mol/cm2/s. This is around the lower limit of previously published data obtained mainly by powder experiments. The dissolution rates for different vicinal slopes of the surface were also measured. These rates were well-correlated with the vicinal slopes in accordance with BCF theory indicating that there is a mutual interaction between neighboring growth/dissolution steps via diffusion, consistent with previously published AFM measurements. The effect of topographical features on the microscopic dissolution behavior was clearly observed during the PSI measurements. The dissolution velocity at the isolated step in pure water was obtained as 2.8 nm/s by fitting the experimental data. Thus, it is possible to examine and determine global calcite dissolution rates using the topographical measurements determined from PSI experiments.

Ueta, Shinzo; Satoh, Hisao; Nishimura, Yoshihiro; Ueda, Akira; Tsukamoto, Katsuo

2013-01-01

245

An oxygen isotope study of illite and calcite in three Appalachian Paleozoic vertic paleosols  

SciTech Connect

The oxygen isotope compositions of pedogenic calcite and illite in three Paleozoic vertic red bed paleosols record a complex history of pedogenic and diagenetic processes. The paleosols are preserved in the upper Mississippian (Chesterian) Mauch Chunk (Pennsylvania), Hinton (West Virginia), and Pennington (Tennessee) Formations in the Appalachian Basin and were buried to 7--8 km (230--260 C), 3--4 km (100--145 C), and 1.5--3 km (70--100 C), respectively. The submicron-size clay fractions of the paleosols are presently composed of R3-ordered illite/smectite (I/S), inferred from K-Ar dates and soil morphology to have been authigenically produced by the reaction of smectite to illite. Oxygen isotope fractionations, calculated pore-fluid compositions, and K-Ar dates were used to constrain the conditions and timing of I/S and pedogenic calcite (re)crystallization in each of the paleosols. The data were interpreted in light of three possible end-member environments for formation and recrystallization: (1) the pedogenic environment; (2) the burial diagenetic environment; and (3) a burial environment dominated by hot, tectonically driven fluid. The {delta}{sup 18}O values of pedogenic calcite and authigenic I/S in vertic red bed paleosols generally reflect recrystallization and exchange during burial diagenesis and are thus not suitable for interpretation of paleoenvironment or paleoclimate. The involvement of orogenic fluids during burial cannot be ruled out, but it is not required by any of the paleosols. In the coastal-margin Pennington Formation paleosol, I/S formation may have been initiated in the pedogenic environment in response to cyclical wetting and drying of the soil clay matrix. Continued smectite transformation and coarsening and ordering of I/S during a long period of shallow burial led to its isotopic reequilibration with pore fluids at slightly elevated temperature, but oxygen isotope compositions of pedogenic calcite in the paleosol are preserved.

Mora, C.I.; Sheldon, B.T.; Driese, S.G. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Geological Sciences; Elliott, W.C. [Georgia State Univ., Atlanta, GA (United States). Dept. of Geology

1998-05-01

246

Crystal growth of micropipe free 4H–SiC on 4H–SiC { 0 3 3 ¯ 8 } seed and high-purity semi-insulating 6H–SiC  

Microsoft Academic Search

Micropipe free c-plane 4H–SiC wafers were achieved by sublimation growth on the 4H–SiC {033¯8} seed. 4H–SiC {033¯8} seeds were obtained by inclining the c-plane to ?011¯0? at 54.7°. A transmission X-ray topograph of the micropipe free c-plane wafer revealed that there were no macroscopic defects with lattice displacements. Crystal growth of undoped (vanadium-free) semi-insulating 6H–SiC was carried out by our

Hiromu Shiomi; Hiroyuki Kinoshita; Tomoaki Furusho; Toshihiko Hayashi; Michio Tajima; Eiko Higashi

2006-01-01

247

Complete subsite mapping of a "loopful" GH19 chitinase from rye seeds based on its crystal structure.  

PubMed

Crystallographic analysis of a mutated form of "loopful" GH19 chitinase from rye seeds a double mutant RSC-c, in which Glu67 and Trp72 are mutated to glutamine and alanine, respectively, (RSC-c-E67Q/W72A) in complex with chitin tetrasaccharide (GlcNAc)? revealed that the entire substrate-binding cleft was completely occupied with the sugar residues of two (GlcNAc)? molecules. One (GlcNAc)? molecule bound to subsites -4 to -1, while the other bound to subsites +1 to +4. Comparisons of the main chain conformation between liganded RSC-c-E67Q/W72A and unliganded wild type RSC-c suggested domain motion essential for catalysis. This is the first report on the complete subsite mapping of GH19 chitinase. PMID:23871710

Ohnuma, Takayuki; Umemoto, Naoyuki; Kondo, Kaori; Numata, Tomoyuki; Fukamizo, Tamo

2013-08-19

248

Benefits of a dual sagittal crystal transducer for ultrasound imaging during I-125 seed implantation for permanent prostate brachytherapy  

PubMed Central

Purpose To investigate whether a longer sagittal view and less movement using a dual sagittal crystal probe (DSCP) for trans rectal ultra sound (TRUS) allow for more accurate online-planning in I-125 permanent implant brachytherapy of the prostate, compared to a single sagittal crystal probe (SSCP). Material and methods Between March 2008 and March 2010, 50 patients with prostate cancer were consecutively included in the study. The first 25 of these patients had both their pre- and online-planning based on a single sagittal crystal probe (SSCP). The treatment-plans of the other 25 patients were based on a DSCP TRUS. Three weeks after implantation a post-planning was made based on CT. TRUS online and CT post-plan dose-volume histogram (DVH) parameters, D90 and V100, were compared for both groups. Also, the post-plan DVH parameters of SSCP were compared to DSCP. The possible factors that might influence the post-plan D90 and V100 were analysed using Analysis of Variance (ANOVA). Results SSCP and DSCP online mean D90 and V100 were significantly larger than post-plan mean D90 and V100 (P < 0.01). The post-plan mean D90 and mean V100 were both non-significantly larger for SSCP based post-plans compared to DSCP based post plans (P = 0.76 and P = 0.68). ANOVA showed significant impact of prostate volume on the post-plan D90 and V100. Conclusions The advantages of the dual sagittal crystal probe did not lead to more accurate online planning by investigating DVH-parameters. The only factor found to have influence on the DVH-parameters was the prostate volume.

Pieters, Bradley; Koedooder, Kees; Lucas, Cees; Koning, Caro

2012-01-01

249

Subaerial meteoric calcitization and lithification of high-magnesian calcite muds, Belize  

SciTech Connect

Holocene ({lt}1000-1500 yrs old) high-magnesian calcite-dominated muddy sediments (1 m thick) on subaerially exposed cays in northern Belize are in the process of being converted to low-magnesian calcite micrite. Mineralogic stabilization and attendant lithification result from interaction of the sediments with meteoric fluids believed to be derived from seasonal upward discharge through subjacent Pleistocene limestones. The initial marine-derived sediments, composed of {gt}85% HMC (and minor skeletal aragonite), consist of mud and associated soritid and miliolid foraminifera both with MgCO{sub 3} content of 11-15 mol%, and isotopic compositions of -1.0 to -2.5{per thousand} PDB (O), 0 to +1.5{per thousand} PDB (C). With depth, lithified LMC crusts appear in the section, and the Mg concentration of the sediments and associated crusts decreases rapidly to 3 mol% or less, with a corresponding isotopic depletion to values approaching -7.0{per thousand} (O) and -5.8{per thousand} (C). Concomitantly there is progressive dissolution of skeletal aragonite in the sediments, reduction of porosity due to cementation by LMC, and in the muds, a decrease in Sr and increase in Mn contents. The resultant petrofabric of these lithified LMC deposits, derived from the alteration of HMC-dominated muds, is characterized by micrite with patches of pore-filling micritic and microsparitic LMC cements. Such a fabric is similar to and can be confused easily with calcitized aragonite-dominated precursor muds, except for the relative rarity in the samples examined of aragonite relicts in component microspar and/or pseudospar.

Mazzullo, S.J.; Bischoff, W.D. (Wichita State Univ., KS (United States))

1991-03-01

250

Formation of calcite thin films by cooperation of polyacrylic acid and self-generating electric field due to aligned dipoles of polarized substrates.  

PubMed

We demonstrated the formation of calcite thin films on positively and negatively charged surfaces of a hydroxyapatite (HAp) electret coexisting with polyacrylic acid (PAA) and self-generating surface electric fields due to HAp electrets with electrically aligned dipoles. The cooperation of PAA and the self-generating surface electric field due to the electrets favored the formation of calcite thin films and acted remarkably on the negatively charged surface. Calcite thin films, 4-10 microm thick, with a shell-like microstructure were produced on the negatively charged surfaces with a small amount of PAA. In contrast, under other reaction conditions, calcite thin films with a fan-like structure in the cross section formed on the polarized substrates, and their thickness ranged from 2 to 7 microm. The films were composed of hemispheric- or flat island-shaped aggregates that were made of the calcite crystals that elongated along the c-axis. The morphology of the PAA-Ca(2+) complex assembly, which adsorbed onto the polarized HAp substrates, was controlled by the balance of the spatial charge distribution in its structure and the properties of the self-generating surface electric field, which led to the different morphologies of the calcite thin films. We proposed that the formation mechanism of the films formed coexisting with PAA and the self-generating electric fields. PMID:19062036

Wada, Norio; Nakamura, Miho; Tanaka, Yumi; Kanamura, Kiyoshi; Yamashita, Kimihiro

2009-02-15

251

Trace metal distribution and isotope variations in low-temperature calcite and groundwater in granitoid fractures down to 1 km depth  

NASA Astrophysics Data System (ADS)

Studies of low-temperature fracture calcite in Proterozoic or Archaean crystalline rocks are very limited, mainly because this calcite usually is, first, not very abundant and second, very fine-grained or forms rims on older (and much more abundant) hydrothermal calcite and is thus difficult to distinguish. Knowledge of chemical characteristics and the correlation with groundwater chemistry is thus scarce for low-temperature calcite in these settings, and consequently, knowledge of the recent palaeohydrogeological history is limited. Boreholes drilled with triple-tube technique in the upper 1 km of the Palaeoproterozoic crystalline crust at Laxemar, SE Sweden, have enabled preservation of fragile and potentially recently formed fracture minerals. Earlier investigations of these boreholes have resulted in an extensive set of groundwater chemistry data from various depths, and in detailed knowledge of the fracture mineral assemblages (ranging from 1.8 Ga to present). This has made it possible to identify and sample low-temperature, potentially recently formed, calcite from water-flowing fractures for which representative groundwater chemical data exists. This, in turn, provides an opportunity to detailed comparisons of fracture calcite (age span in the order of million years, with possibility of post-glacial contributes) and groundwater (age in the order of decades to more than a million year depending on depth) in terms of both isotopic and geochemical properties, giving input to the understanding of groundwater history, partition coefficients derived in laboratory experiment, and reliability of calcite geochemistry in terms of representing the actual source fluid composition. In this study, the focus is on trace elements (Fe, Mg, Mn and Sr), stable isotopes and Sr isotopes and, for the groundwater data set, also aquatic speciation with Visual MINTEQ. An optimised step-by-step sample specific analytical procedure was used for the collection of calcite coatings. The methods used depended on the crystal homogeneity (one or several calcite generations), discerned by detailed SEM-investigations (back-scatter and cathodo-luminescence). 87Sr/86Sr ratios as well as ?18O signatures in calcite are in the range expected for the precipitates from present-day groundwater, or older groundwater with similar composition (except in sections with a considerable portion of glacial water, where calcite definitely is older than the latest glaciation). Stable carbon isotopes in calcite generally show values typically associated with HCO3- originating from soil organic matter but at intermediate depth frequently with HCO3- originating from in situ microbial anaerobic oxidation of methane (highly depleted ?13C). For one of the studied metals - manganese - there was a strong correlation between the sampled calcite coatings and hypothetical calcite predicted by applying laboratory-based partition coefficients (literature data) on groundwater chemistry for sections corresponding to those where the calcites were sampled. This points to temporal and spatial stability in groundwater Mn/Ca ratios over millions of years, or even more, and show that it is possible to assess, based on laboratory-derived data on Mn partitioning, past groundwater Mn-composition from fracture calcites. For other metals - Fe, Sr, and Mg - which are expected to interact with co-precipitating minerals to a higher degree than Mn, the correlations between measured and predicted calcite were weaker for various reasons.

Drake, Henrik; Tullborg, Eva-Lena; Hogmalm, K. Johan; Åström, Mats E.

2012-05-01

252

crystal  

NASA Astrophysics Data System (ADS)

The polarized absorption, emission spectra and decay time measurements of Pr3+-doped CaYAlO4 single crystal have been performed at room temperature. Based on the Judd-Ofelt theory, the spectroscopic parameters , radiative transition probabilities, radiative lifetimes and branching ratios were obtained. The stimulated emission cross-section, fluorescence lifetimes and the quantum efficiency of the promising laser transition were also calculated and compared with other reported crystals. The results show that Pr3+:CaYAlO4 is a promising candidate for visible solid-state laser emission.

Lv, Shaozhen; Wang, Yan; Zhu, Zhaojie; You, Zhenyu; Li, Jianfu; Gao, Shufang; Wang, Hongyan; Tu, Chaoyang

2014-07-01

253

Mechanical twinning in calcite considered with the concept of ferroelasticity  

Microsoft Academic Search

The mechanical twinning of calcite is compared with ferroelastic behavior. For calcite a paraelastic prototype phase does\\u000a not exist, therefore a virtual prototype is defined with cubic m3m symmetry. Using this condition the strain tensors of all\\u000a domain states of mechanical twinning are calculated. With the use of the strain tensors, application of Sapriel's strain compatibility\\u000a law gives the crystallographic

S. Bueble; W. W. Schmahl

1999-01-01

254

The effect of dissolved magnesium on diffusion creep in calcite  

Microsoft Academic Search

We experimentally tested a series of synthetic calcite marbles with varying amounts of dissolved magnesium in a standard triaxial deformation machine at 300 MPa confining pressure, temperatures between 700 and 850°C, stresses between 2 and 100 MPa, and strain rates between 10?7 and 10?3 s?1. The samples were fabricated by hot isostatic pressing of a mixture of calcite and dolomite

Marco Herwegh; Xiaohui Xiao; Brian Evans

2003-01-01

255

Estimation of vorticity from fibrous calcite veins, central Maine, USA  

Microsoft Academic Search

An estimate for the vorticity of a mid-Paleozoic deformation was made using deformed and\\/or rotated calcite veins as natural vorticity and shear-strain gauges in a northern part of the U.S. Appalachians. The spatial distribution of extended, shortened, and shortened-then-extended elongate fibrous calcite veins in limestone layers were used to construct a Mohr circle for the position gradient tensor H, from

H. A. Short; S. E. Johnson

2006-01-01

256

Relative Shock Effects in Mixed Powders of Calcite, Gypsum, and Quartz: A Calibration Scheme from Shock Experiments  

NASA Technical Reports Server (NTRS)

The shock behavior of calcite and gypsum is important in understanding the Cretaceous/Tertiary event and other terrestrial impacts that contain evaporite sediments in their targets. Most interest focuses on issues of devolatilization to quantify the production of CO2 or SO2 to better understand their role in generating a temporary atmosphere and its effects on climate and biota [e.g., papers in 1,2,3,4]. Devolatilization of carbonate is also important because the dispersion and fragmentation of ejecta is strongly controlled by the expansion of large volumes of gas during the impact process as well [5,6]. Shock recovery experiments for calcite yield seemingly conflicting results: early experimental devolatilization studies [7,8,9] suggested that calcite was substantially outgassed at 30 GPa (> 50%). However, the recent petrographic work of [10,11,12] presented evidence that essentially intact calcite is recovered from 60 GPa experiments. [13] reported results of shock experiments on anhydrite, gypsum, and mixtures of those phases with silica. Their observations indicate little or no devolatilization of anhydrite shocked to 42 GPa and that the fraction of sulfur, by mass, that degassed is approx.10(exp -2) of theoretical prediction. In another (preliminary) report of shock experiments on calcite, anhydrite, and gypsum, [14] observe calcite recrystallization when shock loaded at 61 GPa, only intensive plastic deformation in anhydrite shock loaded at 63 GPa, and gypsum converted to anhydrite when shock loaded at 56 GPa. [15] shock loaded anhydrite and quartz to a peak pressure of 60 GPa. All of the quartz grains were trans-formed to glass and the platy anhydrite grains were completely pseudomorphed by small crystallized anhydrite grains. However, no evidence of interaction between the two phases could be observed and they suggest that recrystallization of anhydrite grains is the result of a solid state transformation. [16] reanalyzed the calcite and anhydrite shock wave experiments of [17] using improved equations of state of porous materials and vaporized products. They determined the pressures for incipient and complete vaporization to be 32.5 and 122 GPa for anhydrite and 17.8 and 54.1 GPa for calcite, respectively, a factor of 2 to 3 lower than reported earlier by [17].

Bell, Mary S.

2009-01-01

257

Low latitude (12°N) climate signatures preserved in the stable isotope composition of soil phyllosilicate and calcite, northwestern Ethiopia, Africa  

NASA Astrophysics Data System (ADS)

The mineralogical, chemical, oxygen and hydrogen-isotope composition of the <0.2?m size fraction of phyllosilicates and coexisting calcite are presented from four modern soil profiles developed upon fluvial terraces of the Shinfa River (lowlands of northwestern Ethiopia). The <0.2?m size fraction of most soils is dominated by smectite, with varying amounts of kaolinite. Mineralogical and chemical data were used to calculate oxygen and hydrogen fractionation factors for each phyllosilicate mixture. These fractionation factors were used in conjunction with measured ?18O and ?D values to calculate phyllosilicate crystallization temperatures as well as the oxygen isotope composition of soil water from which the phyllosilicates formed. Measured ?18OV-SMOW and ?DV-SMOW values of the phyllosilicates range from 22.1‰ to 26.7‰, and -42‰ to -35‰, respectively and correspond to a range of crystallization temperatures from 25 ± 3°C to 33 ± 3°C. Equilibrium soil water ?18O values range from -1.9‰ to +2.0‰. The average ?18OV-SMOW values of coexisting soil calcite range from 28.3‰ to 29.9‰. Estimates of soil water ?18O values from the phyllosilicates in conjunction with calcite ?18O values correspond to calcite crystallization temperatures that range from 25 to 32°C, likely indicating chemical equilibrium between these two soil minerals. Shinfa River water ?18OV-SMOW are highly variable, as a result of extreme seasonality and evaporation, ranging from approximately -2‰ during the rainy season. to +20‰ during the dry season. Comparison of calculated soil water ?18O values with Shinfa River water ?18O values suggest that pedogenic phyllosilicates and calcite preserve a record of the oxygen isotopic composition of local meteoric waters that fall during the wet, summer months (June-September). The local variations in calculated temperatures of phyllosilicate and calcite crystallization among terraces appear to correlate with extent of canopy cover at each sight. Specifically, the lowest calculated temperature of 25°C is associated with an open woodland environment with ~20-30% canopy cover, while the highest calculated temperatures (i.e., 30 to 33°C) are associated with actively cultivated sights that have little, or no, canopy cover. These results emphasize the point that chemical equilibrium may exist between soil minerals, but they need not preserve isotopic information about mean annual conditions.

Rosenau, N. A.; Tabor, N. J.; Myers, T. S.; Kappelman, J.

2012-12-01

258

X-ray crystal structure determination and refinement at 1.9 A resolution of isolectin I from the seeds of Lathyrus ochrus.  

PubMed

Orthorhombic crystals of isolectin I (LOLI) from the seeds of Lathyrus ochrus were first obtained during the STS 29 space shuttle mission. Subsequently, isostructural crystals were also obtained in the laboratory. They belong to the space group P2(1)2(1)2, with cell dimensions a = 135.84 A, b = 63.12 A and c = 54.54 A with one functional entity, a dimer, in the asymmetric unit (Vm = 2.2 A3/Da). The three-dimensional structure of LOLI, which was solved by the molecular replacement method using a 3 A resolution model of pea lectin, has subsequently been refined by using crystallographic data between 8.0 A and 1.9 A resolution, coupled to molecular dynamics and energy minimization techniques. The conventional R-factor is 0.185 for Fo greater than 1 sigma(Fo). The final model includes 220 well-defined water molecules and has root-mean-square deviations from ideal bond distances and angles of 0.004 A and 3 degrees, respectively. Only slight conformation differences have been found between the two alpha beta monomers. The molecular structure of LOLI, the first to be determined from the genus Lathyrus, is very similar to those of concanavalin A, pea lectin and favin. Differences are confined to the loop regions and beta-chain termini. Comparison of equivalent C alpha atom positions between our final model and the pea lectin structure shows slight differences in the association of the two monomers, which are probably due to the different environments in the crystals. The root-mean-square deviation between C alpha atoms of LOLI and pea lectin is 0.40 A. The metal binding sites are very similar in pea lectin, concanavalin A and LOLI. The sugar-binding sites of LOLI are occupied by four well-ordered water molecules each. The cleavage site for one of the monomers is specially well defined in the final electron density map: the amino group of Glul (alpha) seems to form a salt bridge with the carboxylate group of the terminal Asn181 (beta). A detailed analysis of the difference in crystal packing contacts between pea lectin and LOLI shows that, as might be expected, several of the intermolecular interactions are mediated by residues that correspond to substitutions in the LOLI amino acid sequence. PMID:2380988

Bourne, Y; Abergel, C; Cambillau, C; Frey, M; Rougé, P; Fontecilla-Camps, J C

1990-07-20

259

The differnces between bond lengths in biogenic and geologocal calcite.  

SciTech Connect

We used high-resolution neutron powder diffraction to accurately measure the atomic positions and bond lengths in biogenic and geological calcite. A special procedure for data analysis was developed in order to take into account the considerable amounts of magnesium present in all the investigated samples. As a result, in biogenic calcite we found some atomic bonds to have significantly different lengths as compared to those in geological calcite, after the contribution of magnesium is accounted for. The maximum effect (elongation up to 0.7%) was found for the C-O bonds. We also analyzed changes in frequencies and spectral widths of normal vibrations of carbonate groups in biogenic calcite (as compared to geological calcite) measured by Raman and Fourier transform IR techniques. Surprisingly, the frequency shifts after subtracting the magnesium contribution are close to zero. At the same time, substantial spectral broadening (up to 1.2%) in biogenic calcite as compared to geological samples was detected. Possible explanations for the experimental findings are discussed.

Zlotoyabko, E.; Caspi, E. N.; Fieramosca, J. S.; Von Dreele, R. B.; Marin, F.; Mor, G.; Politi, Y.; Addadi, L.; Weiner, S. (X-Ray Science Division); ( PNS); (Technion-Israel Inst. of Tech.); (Nuclear Research Centre); (Univ. de Bourgogne); (Weizmann Inst. of Science)

2010-01-01

260

Viscosity and its relationship to crystallization in a binary system of saturated triacylglycerides and sesame seed oil  

Microsoft Academic Search

This paper describes the relationship of viscosity with the crystallization process in a binary system formed by sasame oil\\u000a and different concentrations of tripalmitin (TP) and tristerian (TS) (0.0, 0.032, 0.098, 0.18, 0.26, 0.344 g\\/dL). The behavior\\u000a of the reduced viscosity (?red) indicated that TP and TS affected the native bilayer lamellar organization of sesame oil triacylglycerides. The behaviour\\u000a of

Jorge F. Toro-Vazquez; Alberto Gallegos-Infante

1996-01-01

261

Stable isotope `vital effects' in coccolith calcite  

NASA Astrophysics Data System (ADS)

Uncertainties about the origin of the many disequilibrium or 'vital effects' in a variety of calcifying organisms, and whether these effects are constant or variable, have hampered paleoceanographic application of carbon and oxygen isotopic ratios. Unraveling the source of these effects will improve paleoceanographic applications and may provide new information on changes in cell physiology and ecology. Culture of eight species of coccolithophorids, a dominant marine phytoplankton group, reveals a 5‰ array of disequilibrium or 'vital effects' in both the carbon and oxygen isotopic composition of coccolith calcite. In moderate light and nutrient-replete cultures, oxygen isotopic fractionation and carbon isotopic fractionation correlates directly with cell division rates and correlates inversely with cell size across a range of species. However, when growth rates of a single species are increased or decreased by higher or lower light levels, ? 18O is relatively invariant. Likewise, growth rate variations as a function of temperature do not influence coccolith ? 18O; the slope of the ? 18O vs. temperature relation in cultures of both Gephyrocapsa oceanica and Helicosphaera carteri is the same as for abiogenic carbonates. This suggests a constant, species-specific isotopic fractionation which does not vary with cell physiology. The constancy of vital effects suggests that coccolith stable isotopes will provide reliable phase for paleoceanographic reconstruction of temperature and seawater chemistry, as long as monospecific fractions are analyzed or changes in nannofossil assemblages are accounted for with species-specific correction factors. We suspect that the cell size, and its constraints on the rate of CO 2 diffusion relative to C fixation, may be the first order influence on coccolith stable isotope vital effects. A quantitative model of this process may provide important constraints on mechanisms of carbon acquisition of coccolithophorids in both modern and extinct species.

Ziveri, P.; Stoll, H.; Probert, I.; Klaas, C.; Geisen, M.; Ganssen, G.; Young, J.

2003-05-01

262

Microencapsulation studies on aminophylline involving spherical crystallization, spheronization and drug loading on to non-pareil seeds.  

PubMed

Aminophylline was formulated as small spherical cores for subsequent coating in an attempt to develop a competitor microencapsulated product to the commercial available sustained-release tablet, Phyllocontin. Optimum spherical crystallization conditions yielded cores of loosely adhering crystals of active, with highly irregular surface morphology and poor mechanical strength during pan coating. Aqueous spheronization yielded satisfactory cores in high yield when microcrystalline cellulose and liquid paraffin were used. However, application of large amounts of controlled-release coatings based on Eudragit RL and RS failed to produce a product with retarded drug dissolution comparable to the commercial product. Drug loaded non-pareils were easily formed, but required application of about 20 per cent Eudragit RL/RS coating to achieve adequate prolonged-release properties. Application of 10 per cent hydrogenated castor oil/ethylcellulose based coating gave acceptable in vitro release only if the microcapsules formed were tableted and annealed. All products investigated rapidly discoloured during storage and none were considered to represent a realistic alternative to tableting technology for the production of a sustained-release oral dosage form of aminophylline. PMID:8138875

Boles, M G; Deasy, P B; Donnellan, M F

1994-01-01

263

Interatomic potentials for CaCO3 polymorphs (calcite and aragonite), fitted to elastic and vibrational data  

NASA Astrophysics Data System (ADS)

Calcite and aragonite have been modeled using rigid-ion, two-body Born-type potentials, supplemented by O-C-O angular terms inside the CO3 groups. A shell model has also been developed for calcite. Atomic charges, repulsive parameters and force constants have been optimized to reproduce the equilibrium crystal structures, the elastic constants and the Raman and infrared vibrational frequencies. The rigid-ion potential RIM (atomic charges: z O= -0.995 e, z C = 0.985 e, z Ca = 2.0 e) fitted to calcite properties is able to account for those of aragonite as well. Experimental unit-cell edges, elastic constants, internal and lattice frequencies are reproduced with average relative errors of 2.1, 5.5, 2.4, 15.1% for calcite and of 0.2, 19.4, 2.5, 11.8% for aragonite, respectively. The RIM potential is suitable for thermodynamic and phase diagram simulations in the CaCO3 system, and is discussed and compared to other potentials.

Pavese, A.; Catti, M.; Price, G. D.; Jackson, R. A.

1992-08-01

264

Homoepitaxial single crystal diamond grown on natural diamond seeds (type IIa) with boron-implanted layer demonstrating the highest mobility of 1150 cm 2\\/V s at 300 K for ion-implanted diamond  

Microsoft Academic Search

The homoepitaxial single crystal diamond growth by microwave plasma assisted CVD at high microwave power density 200W\\/cm3 in a 2.45GHz MPACVD reactor using natural diamond seeds (type IIa) was investigated. The semiconductor CVD diamond of p-type was obtained by doping technique of ion implantation. Boron ions were implanted at the acceleration energy of 80keV with two cases of dose: 5·1014

A. K. Ratnikova; M. P. Dukhnovsky; Yu. Yu. Fedorov; V. E. Zemlyakov; A. B. Muchnikov; A. L. Vikharev; A. M. Gorbachev; D. B. Radishev; A. A. Altukhov; A. V. Mitenkin

2011-01-01

265

Evaluation of defects generation in crystalline silicon ingot grown by cast technique with seed crystal for solar cells  

PubMed Central

Although crystalline silicon is widely used as substrate material for solar cell, many defects occur during crystal growth. In this study, the generation of crystalline defects in silicon substrates was evaluated. The distributions of small-angle grain boundaries were observed in substrates sliced parallel to the growth direction. Many precipitates consisting of light elemental impurities and small-angle grain boundaries were confirmed to propagate. The precipitates mainly consisted of Si, C, and N atoms. The small-angle grain boundaries were distributed after the precipitation density increased. Then, precipitates appeared at the small-angle grain boundaries. We consider that the origin of the small-angle grain boundaries was lattice mismatch and/or strain caused by the high-density precipitation.

Tachibana, Tomihisa; Sameshima, Takashi; Kojima, Takuto; Arafune, Koji; Kakimoto, Koichi; Miyamura, Yoshiji; Harada, Hirofumi; Sekiguchi, Takashi; Ohshita, Yoshio; Ogura, Atsushi

2012-01-01

266

Epitaxial high saturation magnetization FeN thin films on Fe(001) seeded GaAs(001) single crystal wafer using facing target sputterings  

SciTech Connect

It was demonstrated that Fe-N martensite ({alpha}') films were grown epitaxially on Fe(001) seeded GaAs(001) single crystal wafer by using a facing target sputtering method. X-ray diffraction pattern implies an increasing c lattice constant as the N concentration increases in the films. Partially ordered Fe{sub 16}N{sub 2} films were synthesized after in situ post-annealing the as-sputtered samples with pure Fe{sub 8}N phase. Multiple characterization techniques including XRD, XRR, TEM, and AES were used to determine the sample structure. The saturation magnetization of films with pure Fe{sub 8}N phase measured by VSM was evaluated in the range of 2.0-2.2 T. The post annealed films show systematic and dramatic increase on the saturation magnetization, which possess an average value of 2.6 T. These observations support the existence of giant saturation magnetization in {alpha}''-Fe{sub 16}N{sub 2} phase that is consistent with a recent proposed cluster-atom model and the first principles calculation [N. Ji, X. Q. Liu, and J. P. Wang, New J. Phys. 12 063032 (2010)].

Ji Nian; Wu Yiming; Wang Jianping [Center for Micromagnetics and Information Technologies (MINT) and Department of Electrical and Computer Engineering, University of Minnesota, 200 Union St SE, 4-174 EE/CSci, Minneapolis, Minnesota 55455 (United States)

2011-04-01

267

Crystal structure of an essential enzyme in seed starch degradation: barley limit dextrinase in complex with cyclodextrins.  

PubMed

Barley limit dextrinase [Hordeum vulgare limit dextrinase (HvLD)] catalyzes the hydrolysis of ?-1,6 glucosidic linkages in limit dextrins. This activity plays a role in starch degradation during germination and presumably in starch biosynthesis during grain filling. The crystal structures of HvLD in complex with the competitive inhibitors ?-cyclodextrin (CD) and ?-CD are solved and refined to 2.5 Å and 2.1 Å, respectively, and are the first structures of a limit dextrinase. HvLD belongs to glycoside hydrolase 13 family and is composed of four domains: an immunoglobulin-like N-terminal eight-stranded ?-sandwich domain, a six-stranded ?-sandwich domain belonging to the carbohydrate binding module 48 family, a catalytic (?/?)(8)-like barrel domain that lacks ?-helix 5, and a C-terminal eight-stranded ?-sandwich domain of unknown function. The CDs are bound at the active site occupying carbohydrate binding subsites +1 and +2. A glycerol and three water molecules mimic a glucose residue at subsite -1, thereby identifying residues involved in catalysis. The bulky Met440, a unique residue at its position among ?-1,6 acting enzymes, obstructs subsite -4. The steric hindrance observed is proposed to affect substrate specificity and to cause a low activity of HvLD towards amylopectin. An extended loop (Asp513-Asn520) between ?5 and ?6 of the catalytic domain also seems to influence substrate specificity and to give HvLD a higher affinity for ?-CD than pullulanases. The crystal structures additionally provide new insight into cation sites and the concerted action of the battery of hydrolytic enzymes in starch degradation. PMID:20863834

Vester-Christensen, Malene Bech; Abou Hachem, Maher; Svensson, Birte; Henriksen, Anette

2010-11-12

268

Self-consistent ion-by-ion growth model for kinetic isotopic fractionation during calcite precipitation  

NASA Astrophysics Data System (ADS)

Microscopic mechanisms operating at the mineral-aqueous interface control rates of growth and dissolution, isotope fractionation and trace element partitioning during crystal growth. Despite the importance of characterizing surface kinetic controls on isotopic partitioning, no self-consistent microscopic theory has yet been presented which can simultaneously model both mineral growth rate and isotopic composition. Using a kinetic theory for AB or di-ionic crystal growth, we derive a model to predict precipitation rate and isotope fractionation as a function of growth solution oversaturation and solution stoichiometry and apply the theory to calcium isotope fractionation during calcite precipitation. Our model assimilates the current understanding of surface controlled isotope fractionation with kinetic theories of ion-by-ion mineral growth to predict isotopic partitioning during the growth of ionic crystals. This approach accounts for the effect of solution composition on microscopic mineral surface structure and composition, providing numerous testable hypotheses for growth of sparingly soluble AB crystals such as calcite, namely: Both oversaturation and solution stoichiometry control growth rate and partitioning of isotopes during precipitation; for growth driven primarily by step propagation, distinct expressions describe dislocation- and 2D nucleation-driven growth rates, while the expression for isotope fractionation is the same for both mechanisms; mineral precipitation occurring via the formation of an amorphous precursor will generate isotope effects that are not compatible with ion-by-ion growth theory and may therefore be excluded from comparison; and, the absolute kinetic limit of isotope fractionation may not be accessible at high oversaturation due to the formation of amorphous precursors. Using calcite as a model system, we derive expressions for growth rate and isotopic fractionation as a function of oversaturation and Ca:CO32- in solution. Increasing oversaturation increases mineral growth rate and drives isotope partitioning towards the kinetic limit, while increasing the concentration of Ca relative to CO32- at a given oversaturation tends to drive crystal growth towards isotopic equilibrium. These competing effects attenuate the magnitude of isotope fractionations observable in terrestrial environments.

Nielsen, Laura C.; DePaolo, Donald J.; De Yoreo, James J.

2012-06-01

269

Uranyl Incorporation in Organic-Bearing Soil Calcite  

NASA Astrophysics Data System (ADS)

Phosphor imaging and fission track maps reveal a close correlation between uranium and organic-rich calcite that lines roots in an ancient caliche soil. Concordant U-Pb ages show that this uranium has not been mobilized since the soil calcite formed 298 ñ 1 Ma ago. Luminescence spectroscopic analysis of the organic-rich calcite demonstrates that uranium is present in the oxidized state. More or less comparable luminescence spectra were collected using a CW lamp at room temperature and at liquid nitrogen (LN2) temperature. Spectra for inorganic U species are generally greatly enhanced at liquid nitrogen temperatures over room temperature and thus the similarity may suggest that the U is bound to organic matter. UV-excitation Raman spectroscopy of the calcite samples reveals a vibrational signature that is, in addition to the calcite peaks, essentially identical to that of sodium humate, acquired under similar conditions and consistent with those reported previously for humate substances. Since these spectra are dominated by the carbon backbone structure, the persistence of a carbon backbone structure is noted, but persistence of the ligating functional groups cannot be proven directly. We suggest that this sample records a snapshot of the process of uranium complexation with organic acids in natural systems. In our model organic acids with active functional groups that complex uranyl are sorbed onto the calcite surface and then incorporated as humate into the mineral with further calcite precipitation. Further, the uranyl complex is preserved through near-surface reducing conditions and temperatures to the conditions associated with 2700 meters burial depths. These combined observations suggest that the encapsulating calcite not only prevents reduction of uranium in the surface environment, but also inhibits the breakdown of the humate with burial. Due to the long time scale of immobilization of uranium, evidenced by the age of the calcite, this study has profound implications for understanding sampling for U-series and U-Pb dating of carbonates as well as for developing strategies for nuclear waste management. This study also has implications for any other deposits where uranium is associated with organic matter.

Rasbury, E.; Tait, C.; Donohoe, R. J.

2003-12-01

270

Uptake of dissolved Cd by biogenic and abiogenic aragonite: a comparison with sorption onto calcite  

NASA Astrophysics Data System (ADS)

The uptake of Cd 2+ by aragonite and calcite is investigated by combining macroscopic measurements with some qualitative sorption experiments performed in a hydrogel medium. Both biogenic and abiogenic aragonites were studied in order to evaluate the process on materials with different textures. Assuming that sorption occurs by surface precipitation of metal-bearing solids, the gel produces a drastic decrease in the nucleation density, which allows for the precipitation of crystallites that are large enough to be analysed by scanning electron microscopy and characterized by glancing-incidence X-ray techniques. The macroscopic study reveals that aragonite is a powerful sorbent for cadmium in aqueous environments. Microscopic observations indicate that cadmium is sorbed onto aragonite by surface precipitation of (Cd, Ca)CO 3 solid solutions with a calcite-type structure. The precipitating individuals grow randomly oriented on the surface to reach sizes in the micrometre range. As a consequence, the concentration of cadmium in the aqueous solution decreases dramatically to values controlled by the low solubility of the cadmium-rich end member. This mechanism involves simultaneous dissolution-crystallization and is the same for both abiogenic and biogenic aragonites, the only difference being a result of the higher specific surface area of the biogenic starting material. Long-term uptake of cadmium by calcite occurs through a similar dissolution-crystallization mechanism, the final outcome being virtually the same, that is, surface precipitation of (Cd,Ca)CO 3 solid solutions. In this case, however, substrate and precipitate are isostructural and the process occurs by oriented overgrowth of thin lamellar crystallites, which spread to quickly cover the surface by a layer a few nanometers thick. This epitaxial layer armors the substrate from further dissolution, so that the process stops when only a small amount of cadmium has been removed from the fluid. As a result, the "sorption capacity" of calcite is considerably lower than that of aragonite. The study illustrates reaction pathways and "partial" equilibrium endpoints in surface-precipitation processes involving solid solutions.

Prieto, Manuel; Cubillas, Pablo; Fernández-Gonzalez, Ángeles

2003-10-01

271

The Thermodynamics Of Calcite Nucleation On Organic Surfaces: Classical Vs. Non-Classical Pathways  

NASA Astrophysics Data System (ADS)

Nucleation in the natural world often occurs at organic surfaces. During biomineralization, living organisms use macromolecular matrices to direct nucleation of a variety of inorganic materials by controlling the timing, polymorphism, morphology, and crystallographic orientation of mineral nuclei. In geochemical settings, mineral surfaces, which are often covered with organic layers or biofilms, surround the volume within which nucleation occurs. Despite the importance of nucleation phenomena in these natural settings, our understanding of the reaction dynamics and energetics of the process is limited. Issues such as the role of pre-nucleation clusters, formation of amorphous precursors, and polymorph selection during the initial stages of nucleation, as well as the structural relationships between the organic matrix and the emerging nucleus are poorly understood. Using self-assembled monolayers (SAMs) of alkanethiols as simple models for macromolecular matrices and organic films, we address the gaps in our understanding by employing a suite of in situ methods to investigate CaCO3 nucleation. From optical measurements of calcite nucleation rates on alkanethiol SAMs, we find that for two carboxyl-terminated alkanethiol SAMs with odd (mercaptoundecanoic acid) and even (mercaptohexadecanoic acid) carbon chains, the rate exhibits the supersaturation dependence expected from classical theory and the effective interfacial energy is reduced from about 109 mJ/m2 in bulk solution to 81 mJ/m2 and 72 mJ/m2, respectively. Theoretical analysis shows that the corresponding free energy barrier is reduced from 105kT for homogeneous nucleation in bulk solution to 27KT and 19kT, respectively. The results demonstrate that calcite nucleation on these carboxyl SAMs is described well in purely classical terms through a reduction in the thermodynamic barrier due to decreased interfacial free energy. In addition, although amorphous particles form prior to crystal nucleation on hydroxyl SAMs and during crystal nucleation on carboxyl SAMs — even well below the accepted bulk solubility limit for amorphous calcium carbonate (ACC) — they do not grow and are not precursors to the crystalline phase. Instead, calcite nucleates independently. These results call into question the emerging view of calcite nucleation as a non-classical process. Finally we show how questions concerning formation pathways and energetic controls of templated nucleation can be investigated with in situ transmission electron microscopy (TEM) at nanometer scale and video rates. This capability is enabled by the combination of a custom designed TEM stage and fluid cell. Significantly, the design of the cell and holder ensures temperature and electrochemical control over the reaction environment, allowing for direct investigation of nucleation dynamics.

Nielsen, M.; Hu, Q.; Hamm, L. M.; Lee, J. R.; Becker, U.; Dove, P. M.; De Yoreo, J.

2012-12-01

272

Nuclear anomalies in the buccal cells of calcite factory workers  

PubMed Central

The micronucleus (MN) assay on exfoliated buccal cells is a useful and minimally invasive method for monitoring genetic damage in humans. To determine the genotoxic effects of calcite dust that forms during processing, MN assay was carried out in exfoliated buccal cells of 50 (25 smokers and 25 non-smokers) calcite factory workers and 50 (25 smokers and 25 non-smokers) age- and sex-matched control subjects. Frequencies of nuclear abnormalities (NA) other than micronuclei, such as binucleates, karyorrhexis, karyolysis and ‘broken eggs', were also evaluated. Micronuclei and the other aforementioned anomalies were analysed by two way analysis of covariance. The linear correlations between the types of micronucleus and nuclear abnormalities were determined by Spearman's Rho. There was a positive correlation between micronuclei and other types of nuclear abnormalities in accordance with the Spearman's Rho test. Results showed statistically significant difference between calcite fabric workers and control groups. MN and NA frequencies in calcite fabric workers were significantly higher than those in control groups (p < 0.05). The results of this study indicate that calcite fabric workers are under risk of significant cytogenetic damage.

2010-01-01

273

A Raman spectroscopic comparison of calcite and dolomite.  

PubMed

Raman spectroscopy was used to characterize and differentiate the two minerals calcite and dolomite and the bands related to the mineral structure. The (CO3)(2-) group is characterized by four prominent Raman vibrational modes: (a) the symmetric stretching, (b) the asymmetric deformation, (c) asymmetric stretching and (d) symmetric deformation. These vibrational modes of the calcite and dolomite were observed at 1440, 1088, 715 and 278 cm(-1). The significant differences between the minerals calcite and dolomite are observed by Raman spectroscopy. Calcite shows the typical bands observed at 1361, 1047, 715 and 157 cm(-1), and the special bands at 1393, 1098, 1069, 1019, 299, 258 and 176 cm(-1) for dolomite are observed. The difference is explained on the basis of the structure variation of the two minerals. Calcite has a trigonal structure with two molecules per unit cell, and dolomite has a hexagonal structure. This is more likely to cause the splitting and distorting of the carbonate groups. Another cause for the difference is the cation substituting for Mg in the dolomite mineral. PMID:23988531

Sun, Junmin; Wu, Zeguang; Cheng, Hongfei; Zhang, Zhanjun; Frost, Ray L

2014-01-01

274

Surface kinetic model for isotopic and trace element fractionation during precipitation of calcite from aqueous solution  

SciTech Connect

A surface reaction kinetic model is developed for predicting Ca isotope fractionation and metal/Ca ratios of calcite as a function of rate of precipitation from aqueous solution. The model is based on the requirements for dynamic equilibrium; i.e. proximity to equilibrium conditions is determined by the ratio of the net precipitation rate (R{sub p}) to the gross forward precipitation rate (R{sub f}), for conditions where ionic transport to the growing crystal surface is not rate-limiting. The value of R{sub p} has been experimentally measured under varying conditions, but the magnitude of R{sub f} is not generally known, and may depend on several factors. It is posited that, for systems with no trace constituents that alter the surface chemistry, R{sub f} can be estimated from the bulk far-from-equilibrium dissolution rate of calcite (R{sub b} or k{sub b}), since at equilibrium R{sub f} = R{sub b}, and R{sub p} = 0. Hence it can be inferred that R{sub f} {approx} R{sub p} + R{sub b}. The dissolution rate of pure calcite is measureable and is known to be a function of temperature and pH. At given temperature and pH, equilibrium precipitation is approached when R{sub p} (= R{sub f} - R{sub b}) << R{sub b}. For precipitation rates high enough that R{sub p} >> R{sub b}, both isotopic and trace element partitioning are controlled by the kinetics of ion attachment to the mineral surface, which tend to favor more rapid incorporation of the light isotopes of Ca and discriminate weakly between trace metals and Ca. With varying precipitation rate, a transition region between equilibrium and kinetic control occurs near R{sub p} {approx} R{sub b} for Ca isotopic fractionation. According to this model, Ca isotopic data can be used to estimate R{sub f} for calcite precipitation. Mechanistic models for calcite precipitation indicate that the molecular exchange rate is not constant at constant T and pH, but rather is dependent also on solution saturation state and hence R{sub p}. Allowing R{sub b} to vary as R{sub p}{sup 1/2}, consistent with available precipitation rate studies, produces a better fit to some trace element and isotopic data than a model where R{sub b} is constant. This model can account for most of the experimental data in the literature on the dependence of {sup 44}Ca/{sup 40}Ca and metal/Ca fractionation in calcite as a function of precipitation rate and temperature, and also accounts for {sup 18}O/{sup 16}O variations with some assumptions. The apparent temperature dependence of Ca isotope fractionation in calcite may stem from the dependence of R{sub b} on temperature; there should be analogous pH dependence at pH < 6. The proposed model may be valuable for predicting the behavior of isotopic and trace element fractionation for a range of elements of interest in low-temperature aqueous geochemistry. The theory presented is based on measureable thermo-kinetic parameters in contrast to models that equire hyper-fast diffusivity in near-surface layers of the solid.

DePaolo, D.

2010-10-15

275

Clumped isotope paleothermometry of marine calcite cements from the Late Ordovician Kullsberg and Boda Limestones, Sweden  

NASA Astrophysics Data System (ADS)

18O/16O ratios (?18O) in well-preserved marine carbonates provide a critical archive of information about ancient climates and seawater chemistry, but this proxy suffers from a fundamental limitation. Because ?18O reflects a temperature-dependent equilibrium fractionation between the measured mineral and the water with which it equilibrated, neither the temperature nor the isotopic composition of this water (?18Owater) can be determined directly from ?18O of carbonate without independent knowledge of one of the controlling variables. Lack of such knowledge has been the major factor preventing resolution of a long-running debate over the interpretation of secular trends in ?18O. Clumped isotope paleothermometry is a recently developed thermodynamic proxy that permits independent determination of carbonate crystallization temperature and can place unique constraints on ?18Owater. Most clumped isotope analyses have focused on calcitic fossils, but marine calcite cements are common in carbonate-rich successions and provide a complementary archive that may shed light on both primary temperature trends and their diagenetic alteration. We examined the clumped isotope systematics of samples from the Late Ordovician Kullsberg and Boda Limestones of central Sweden. These units have never been substantially buried but may have affected by the nearby Siljan impact of Late Devonian age. Both were deposited at tropical to low subtropical latitudes and contain large micritic buildups rich in "stromatactis" voids containing multiple cement generations. Previous work (Tobin and Walker, 1996) characterized the Kullsberg cements and posited that translucent fibrous calcites record unaltered to slightly altered marine signatures and turbid fibrous calcites record variable alteration by restricted marine fluids, with subsequent generations of equant calcite recording meteoric and/or burial fluids. Translucent and turbid fibrous calcite in the Kullsberg exhibit narrow ?18O ranges (-2.2 to -4.5‰ VPDB) but significant variations in temperature (31° to 51°C), implying partially closed system diagenetic behavior. Many samples capture physical mixtures of relatively primary phases with 18O-depleted, high temperature meteoric or burial phases (mean ?18O = -8.1 ± 0.7‰ VPDB, mean temp. = 58 ± 3° C). Boda cements record generally higher temperatures, consistent with other evidence suggesting that the Boda has experienced more diagenetic alteration. Consequently, we interpret the lowest-temperature Kullsberg samples as most likely to record a primary marine signature. Samples yielding temperatures <35°C exhibit ?18Owater values from 0.94 to -0.14‰ VSMOW. Minimum ?18Owater values inferred from these sampled are indistinguishable from those inferred from well preserved calcitic fossils from the contemporaneous Decorah Formation of the U.S. midcontinent that record lighter ?18O values and higher temperatures. This suggests that both least-altered Kullsberg cements and Decorah Formation fossils were sampling isotopically similar seawater in the 0 to -1‰ VSMOW range but precipitated at different temperatures, an observation consistent with their relative latitudinal positions.

Finnegan, S.; Eiler, J. M.; Fischer, W. W.

2012-12-01

276

The Raman spectrum of CaCO3 polymorphs calcite and aragonite: A combined experimental and computational study  

NASA Astrophysics Data System (ADS)

Powder and single crystal Raman spectra of the two most common phases of calcium carbonate are calculated with ab initio techniques (using a "hybrid" functional and a Gaussian-type basis set) and measured both at 80 K and room temperature. Frequencies of the Raman modes are in very good agreement between calculations and experiments: the mean absolute deviation at 80 K is 4 and 8 cm-1 for calcite and aragonite, respectively. As regards intensities, the agreement is in general good, although the computed values overestimate the measured ones in many cases. The combined analysis permits to identify almost all the fundamental experimental Raman peaks of the two compounds, with the exception of either modes with zero computed intensity or modes overlapping with more intense peaks. Additional peaks have been identified in both calcite and aragonite, which have been assigned to 18O satellite modes or overtones. The agreement between the computed and measured spectra is quite satisfactory; in particular, simulation permits to clearly distinguish between calcite and aragonite in the case of powder spectra, and among different polarization directions of each compound in the case of single crystal spectra.

De La Pierre, Marco; Carteret, Cédric; Maschio, Lorenzo; André, Erwan; Orlando, Roberto; Dovesi, Roberto

2014-04-01

277

The Raman spectrum of CaCO3 polymorphs calcite and aragonite: a combined experimental and computational study.  

PubMed

Powder and single crystal Raman spectra of the two most common phases of calcium carbonate are calculated with ab initio techniques (using a "hybrid" functional and a Gaussian-type basis set) and measured both at 80 K and room temperature. Frequencies of the Raman modes are in very good agreement between calculations and experiments: the mean absolute deviation at 80 K is 4 and 8 cm(-1) for calcite and aragonite, respectively. As regards intensities, the agreement is in general good, although the computed values overestimate the measured ones in many cases. The combined analysis permits to identify almost all the fundamental experimental Raman peaks of the two compounds, with the exception of either modes with zero computed intensity or modes overlapping with more intense peaks. Additional peaks have been identified in both calcite and aragonite, which have been assigned to (18)O satellite modes or overtones. The agreement between the computed and measured spectra is quite satisfactory; in particular, simulation permits to clearly distinguish between calcite and aragonite in the case of powder spectra, and among different polarization directions of each compound in the case of single crystal spectra. PMID:24784289

De La Pierre, Marco; Carteret, Cédric; Maschio, Lorenzo; André, Erwan; Orlando, Roberto; Dovesi, Roberto

2014-04-28

278

Hydration layer structures on calcite facets and their roles in selective adsorptions of biomolecules: A molecular dynamics study  

NASA Astrophysics Data System (ADS)

The selective adsorptions of biomolecules onto crystal faces are the key issues in the studies of biomineralization. Frequently, the adsorption processes are understood by using the direct binding model between organic compounds and inorganic crystals during the molecular dynamic studies. However, water molecules near crystals always exhibit intense ordering and preferential orientation to form structured hydration layer. By using the adsorption of poly acrylic acid oligomer, acrylic acid (AA) dimer, onto calcite as an example, we demonstrate that the induced hydration layers contribute significant effects on the organic-inorganic interactions. In particular, on calcite (104) plane, two carboxyl groups of AA dimer both interact with the crystal but the molecule has to compete with water due to the well-structured hydration layer. On (110) plane, although only one carboxyl group of AA dimer interacts with this surface, the water layer is relatively loose so that the molecule can easily replace water. With a consideration of the hydration layer, our free energy analysis indicates that AA dimer has a stronger interaction with (110) face than with (104) face, which is consistent with the experimental observations. The study follows that the attachment of organic additive onto inorganic crystal facet is greatly mediated by near-surface hydration layers, and therefore, the critical role of structured water layers must be taken into account in the understanding of biomineralization interfaces.

Zhu, Beibei; Xu, Xurong; Tang, Ruikang

2013-12-01

279

Spectroscopic study of phase transitions in natural calcite mineral  

NASA Astrophysics Data System (ADS)

The process and the formation of new minerals upon heating the carbonate rocks containing clay minerals, together with calcite are determined with thermal analysis, X-ray diffraction, infrared and Raman spectroscopy. The calcite-calcium oxide phase transition sequence was followed up to 947 °C in naturally occurring limestone samples. The spectral variations of the internal modes of the carbonate trigonal ( ?1, ?2, ?3 and ?4) were used to probe the structural phase transitions. The calcium oxide phase (which on reaction with atmospheric water forms portlandite) with an onset temperature of around 950 °C was also characterized by the appearance of the infrared mode around 450 cm -1. The minerals, which were formed upon heating the calcite, were calcium oxide and wollastonite.

Gunasekaran, S.; Anbalagan, G.

2008-04-01

280

Novel TEM approaches to imaging of microstructures in carbonates: Clues to growth mechanisms in calcite and dolomite  

SciTech Connect

Relating microstructures imaged by transmission electron microscopy (TEM) to specific growth mechanisms requires imaging of both the surface microtopography on crystal faces and its corresponding microstructure in the bulk crystal. Pt-C replicas of as-grown surfaces are ideally suited to this task, as they provide a high-resolution, nearly three-dimensional image of surface topography that can be correlated with microstructures visible in sections at high angle to the as-grown surface. Ultramicrotomy enables the preparation of ultrathin sections more quickly than conventional ion-thinning and can be used to investigate chemical heterogeneities by analytical electron microscopy (AEM). The authors evaluate the potential of both techniques for the study of microstructures in calcite and dolomite. (1) TEM images were obtained from Pt-C replicas of synthetic calcite. The as-grown (10{bar 1}4) face of a Mg/Mn-doped crystal growth showed growth hillocks aligned along preferred orientations. In Pb/Mn/Sr-doped calcite, sections at high angle to as-grown faces showed a uniform microstructure in {l{underscore}brace}10{bar 1}4{r{underscore}brace} sectors. The {l{underscore}brace}01{bar 1}2{r{underscore}brace} sectors contained concentric zones that alternated from striated to uniform microstructures, suggesting periodic variations in growth rate and possibly in the growth mechanism. An oscillatory-zoned Mn-doped calcite showed fine-scale banding (30--150 mm) and periodic roughening of (10{bar 1}4) surfaces that suggest repetitive transitions between growth mechanisms.(2) In sedimentary dolomites, Pt-C replicas of surfaces cleaved parallel to a (10{bar 1}4) face showed a hillocky topography or smooth (10{bar 1}4) surfaces modified by non-equivalent facets. Surfaces produced by cleavage at high angle to a (10{bar 1}4) face exposed sectors with fine-scale banding crosscut by sharp boundaries, suggestive of closely spaced growth hillocks intercalated with non-equivalent subsectors. Ultrathin sections prepared by microtomy showed some disruption of the crystal structure but, in some dolomite samples, domains with distinctive microstructures similar in scale and shape to those seen in the Pt-C replica were identified. (3) The growth microstructures in {l{underscore}brace}10{bar 1}4{r{underscore}brace} sectors of dolomite present striking similarities to the larger scale compositional zoning patterns produced by growth spirals in calcite doped with trace elements. At this stage, Pt-C replicas and ultramicrotomy can distinguish among dolomites that are petrographically very similar.

Paquette, J.; Vali, H.; Mountjoy, E.

1999-12-01

281

Modelling excess surface energy in dry and wetted calcite systems  

Microsoft Academic Search

We have combined the calcite force field of Hwang et al. (J. Phys. Chem. B 105:4,122–4,127, 2001) with the F3C water model\\u000a and a hybrid Lennard-Jones\\/van der Waals 3-site potential for CO2 to investigate the $${\\\\left({10\\\\overline14}\\\\right)}$$ and $${\\\\left( {10\\\\overline10}\\\\right)}$$ cleaving surfaces of calcite under dry and wetted conditions. The wetting fluid included both pure water and water–carbon\\u000a dioxide mixture. Excess surface

Bjørn Kvamme; Tatyana Kuznetsova; Daniel Uppstad

2009-01-01

282

Polysaccharide chemistry regulates kinetics of calcite nucleation through competition of interfacial energies  

PubMed Central

Calcified skeletons are produced within complex assemblages of proteins and polysaccharides whose roles in mineralization are not well understood. Here we quantify the kinetics of calcite nucleation onto a suite of high-purity polysaccharide (PS) substrates under controlled conditions. The energy barriers to nucleation are PS-specific by a systematic relationship to PS charge density and substrate structure that is rooted in minimization of the competing substrate–crystal and substrate–liquid interfacial energies. Chitosan presents a low-energy barrier to nucleation because its near-neutral charge favors formation of a substrate–crystal interface, thus reducing substrate interactions with water. Progressively higher barriers are measured for negatively charged alginates and heparin that favor contact with the solution over the formation of new substrate–crystal interfaces. The findings support a directing role for PS in biomineral formation and demonstrate that substrate–crystal interactions are one end-member in a larger continuum of competing forces that regulate heterogeneous crystal nucleation.

Hamm, Laura M.; Han, Nizhou; De Yoreo, James J.; Dove, Patricia M.

2013-01-01

283

Polysaccharide chemistry regulates kinetics of calcite nucleation through competition of interfacial energies.  

PubMed

Calcified skeletons are produced within complex assemblages of proteins and polysaccharides whose roles in mineralization are not well understood. Here we quantify the kinetics of calcite nucleation onto a suite of high-purity polysaccharide (PS) substrates under controlled conditions. The energy barriers to nucleation are PS-specific by a systematic relationship to PS charge density and substrate structure that is rooted in minimization of the competing substrate-crystal and substrate-liquid interfacial energies. Chitosan presents a low-energy barrier to nucleation because its near-neutral charge favors formation of a substrate-crystal interface, thus reducing substrate interactions with water. Progressively higher barriers are measured for negatively charged alginates and heparin that favor contact with the solution over the formation of new substrate-crystal interfaces. The findings support a directing role for PS in biomineral formation and demonstrate that substrate-crystal interactions are one end-member in a larger continuum of competing forces that regulate heterogeneous crystal nucleation. PMID:23690577

Giuffre, Anthony J; Hamm, Laura M; Han, Nizhou; De Yoreo, James J; Dove, Patricia M

2013-06-01

284

High strain deformation of calcite-anhydrite aggregates  

NASA Astrophysics Data System (ADS)

Localization of deformation in nature occurs dominantly in polyphase rocks. However, high strain experimental deformation studies have up to now mainly been performed on monophase materials. In order to study the process of localization as well as the interaction between different phases during deformation, a calcite-anhydrite aggregate was deformed in torsion to large amounts of shear strain. Calcite and anhydrite do not chemically react and have similar strengths at the deformation conditions performed in this study. However, the deformation behaviour of the two phases is strikingly different with increasing strain. The synthetic calcite-anhydrite aggregates were produced from reagent powders by HIP-ping (Bruhn et al., 1999). Torsion experiments were performed on fine-grained (5-8 micrometers) calcite-anhydrite samples with volume proportions of 30/70, 50/50 and 70/30 and on the pure end-member samples (100% calcite and 100% anhydrite). The experiments were performed at 600 °C, 300 MPa confining pressure and a constant shear strain rate of 1.10-3 s-1. A maximum shear strain of 12.5 was reached. With progressive deformation the samples deformed more and more inhomogeneously. On a bulk sample scale progressive localization of the deformation was observed. This is in contrast to previous experiments in torsion performed on monophase materials (including calcite and anhydrite) where deformation always remained very homogeneous. The rheological data showed that the pure anhydrite was the strongest material and calcite the weakest. However after a shear strain of 1, the anhydrite end-member weakened dramatically until similar stresses were reached at high shear strains of 3 as for the pure calcite end-member. The calcite-anhydrite mixtures had strengths in between those of the end-members and showed a weakening behaviour between the end-members. Microstructural analysis of SEM backscatter electron images of the two phase samples show that in the localized zones preferred alignments of both phases are present. Very thin layers (about 5 micrometer thick, roughly one grain) of calcite and anhydrite alternate with each other. By contrast, in the non-localized parts of the sample the two phases are still homogeneously mixed as in the starting material. The alignment of single phases causes localization of deformation in this two-phase aggregate, because the laminar microstructure corresponds to the minimum strength (lower bound) configuration in simple shear. These results suggest that the presence of two or more phases may play an important role in localization in nature. Reference: Bruhn, D.F., Olgaard, D.L., Dell'Angelo, L.N., 1999. Evidence for enhanced deformation in two-phase rocks: Experiments on the rheology of calcite-anhydrite aggregates. Journal of Geophysical Research B104, 707-724.

Barnhoorn, A.; Bystricky, M.; Kunze, K.; Burlini, L.

2003-04-01

285

crystals  

NASA Astrophysics Data System (ADS)

A novel combined interferometric-mask method for the formation of micro- and nanometric scale three-dimensional (3D) rotational symmetry quasi-crystalline refractive lattice structures in photorefractive materials is demonstrated experimentally. The method is based on micrometric scale spatial modulation of the light by amplitude mask in the radial directions and along the azimuthal angle and the use of counter-propagating beam geometry building up Gaussian standing wave, which defines the light modulation in the axial direction with half-wavelength periodicity. 3D intensity pattern can be represented as numerous mask-generated 2D quasi-periodic structures located in each anti-node of the standing wave. The formed 3D intensity distributions of the optical beams can be imparted into the photorefractive medium thus creating the micro- and sub-micrometric scale 3D refractive index volume lattices. The used optical scheme allows also the formation of 2D lattices by removing the back-reflecting mirror. 2D and 3D refractive lattices were recorded with the use of 532 nm laser beam and rotational symmetry mask in doped lithium niobate crystals and were tested by the probe beam far-field diffraction pattern imaging and direct observation by phase microscope. The formed rotational symmetry 3D refractive structures have the periods of 20-60 ?m in the radial directions, 60 ?m along the azimuthal angle and half-wavelength 266 nm in the axial direction.

Badalyan, A.; Hovsepyan, R.; Mantashyan, P.; Mekhitaryan, V.; Drampyan, R.

2014-07-01

286

Seed Dispersal  

NSDL National Science Digital Library

In this outdoor activity and bingo-like game, learners explore why and how seeds spread far from the plants that produce them. To understand natural adaptions that let seeds and fruit be dispersed, learners make modifications to dried beans and peas so they could be dispersed by natural forces like water, air, or an animal moving from one place to another. In the "Seed-Go" Game, learners match ways that seeds are dispersed, to fill rows on the game board.

Science, Lawrence H.

1979-01-01

287

Seed Size  

NSDL National Science Digital Library

In this activity, learners collect, arrange, and draw various seeds from smallest to biggest. They also estimate how many of the smallest would fit into the biggest. In addition, learners predict how many seeds they would find inside an apple or lemon, and cut open these fruits to check their prediction against the real seed count. The Did You Know section describes the biggest and smallest seeds on Earth.

Science, Lawrence H.

2007-01-01

288

Interaction of ethanol and water with the {1014} surface of calcite.  

PubMed

Molecular dynamics simulations have been used to model the interaction between ethanol, water, and the {1014} surface of calcite. Our results demonstrate that a single ethanol molecule is able to form two interactions with the mineral surface (both Ca-O and O-H), resulting in a highly ordered, stable adsorption layer. In contrast, a single water molecule can only form one or other of these interactions and is thus less well bound, resulting in a more unstable adsorption layer. Consequently, when competitive adsorption is considered, ethanol dominates the adsorption layer that forms even when the starting configuration consists of a complete monolayer of water at the surface. The computational results are in good agreement with the results from atomic force microscopy experiments where it is observed that a layer of ethanol remains attached to the calcite surface, decreasing its ability to interact with water and for growth at the {1014} surface to occur. This observation, and its corresponding molecular explanation, may give some insight into the ability to control crystal form using mixtures of different organic solvents. PMID:20795691

Cooke, D J; Gray, R J; Sand, K K; Stipp, S L S; Elliott, J A

2010-09-21

289

Field test of a calcite dissolution rate law: Fort's Funnel Cave, Mammoth Cave National Park  

SciTech Connect

The laboratory-derived calcite dissolution rate law of Plummer et al. (1978) is the most widely used and mechanistically detailed expression currently available for predicting dissolution rates as a function of water chemistry. Such rate expressions are of great use in understanding timescales associated with limestone karst development. Little work has gone into the field testing of the rate law under natural conditions. This work measured dissolution rates by a crystal weight loss experiment in Buffalo Creek within Fort's funnel Cave, which lies within a pristine, forested catchment of Mammoth Cave National Park. Continuous water chemistry sampling over the same period allowed a time-integrated prediction of the dissolution based on the Plummer et al. (1978) expression. Results indicate that the rate law overpredicted dissolution by a factor of about ten. This concurs with earlier laboratory work suggesting that the law tends to overpredict rates in solutions close to equilibrium with respect to calcite, as were the waters within this part of the groundwater flow system.

Slunder, J.S. (EMPE Inc., Nashville, TN (United States)); Groves, C.G. (Western Kentucky Univ., Bowling Green, KY (United States). Center for Cave and Karst Studies)

1994-03-01

290

Crystal growth of micropipe free 4H-SiC on 4H-SiC {0 3 3¯ 8} seed and high-purity semi-insulating 6H-SiC  

NASA Astrophysics Data System (ADS)

Micropipe free c-plane 4H-SiC wafers were achieved by sublimation growth on the 4H-SiC {0 3 3¯ 8} seed. 4H-SiC {0 3 3¯ 8} seeds were obtained by inclining the c-plane to <0 1 1¯ 0> at 54.7°. A transmission X-ray topograph of the micropipe free c-plane wafer revealed that there were no macroscopic defects with lattice displacements. Crystal growth of undoped (vanadium-free) semi-insulating 6H-SiC was carried out by our sublimation system. In order to achieve high resistivity, high-purity SiC source and controlled instruments were used for the reduction of nitrogen, boron and metal impurity backgrounds. Hence high-purity and high-resistivity 6H-SiC 2 and 3 in in diameter were developed for high-frequency power transistors.

Shiomi, Hiromu; Kinoshita, Hiroyuki; Furusho, Tomoaki; Hayashi, Toshihiko; Tajima, Michio; Higashi, Eiko

2006-07-01

291

Experimentelle Bildung von Forsterit und Calcit aus Tremolit und Dolomit  

Microsoft Academic Search

The equilibrium temperature for the reaction: 1 tremolite + 11 dolomite 8 forsterite + 13 Calcit + 9 CO 2 + 1 H 2 O was experimentally determined as a function of the CO 2 -content of the CO 2 -H 2 O fluid phase for the total pressures of 500 and 1000 bars. The results are plotted as two

Paul Metz

1967-01-01

292

Utricular otoconia of some amphibians have calcitic morphology  

NASA Technical Reports Server (NTRS)

This report concerns the morphological features of otoconia removed from the inner ear of four amphibian species. Results from scanning electron microscopic examination are compared based on the site of origin. These results show that utricular otoconia have a mineral structure that mimics calcite, rather than the widely accepted idea that they are mineralized by calcium carbonate of the aragonite polymorph.

Pote, K. G.; Ross, M. D.

1993-01-01

293

Orientational order-disorder phase transition in calcite  

Microsoft Academic Search

We have performed inelastic neutron scattering experiments on calcite in the ordered phase, focusing on a zone boundary F-point that shows X-ray diffuse scattering. At this position we have observed an incipient soft mode along with a column of inelastic scattering ranging in energy between the soft mode energy and zero energy. The intensity of this scattering varies dramatically with

M. Hagen; M. T. Dove; M. J. Harris; U. Steigenberger; B. M. Powell

1992-01-01

294

Using neutron diffraction to investigate mechanical twinning in calcite  

Microsoft Academic Search

Mechanical twinning in calcite provides one of the most widely used methods for inferring the orientation and magnitude of the stresses and strains that are responsible for natural rock deformation, and yet the strong sensitivity of twinning activity to microstructural variables such as grain size and lattice preferred orientation remains poorly characterized. This reflects the fact that whole sample behaviour,

P. F. Schofield; S. J. Covey-Crump

2010-01-01

295

Reconstructing Cambro-Ordovician Seawater Composition using Clumped Isotope Paleothermometry on Calcitic and Phosphatic Brachiopods  

NASA Astrophysics Data System (ADS)

A secular increase in ?18O values of marine fossils through early Phanerozoic time raises questions about the evolution of climate and the water cycle. This pattern suggests two end-member hypotheses 1) surface temperatures during early Paleozoic time were very warm, in excess of 40°C (tropical MAT), or 2) the isotopic composition of seawater increased by up to 7-8‰. It has been difficult to evaluate these hypotheses because the ?18O composition of fossils depends on both temperature and the ?18O of water. Furthermore, primary isotopic signatures can be overprinted by diagenetic processes that modify geological materials. This too could explain the decrease in ?18O values of marine fossils with age. Carbonate clumped isotope thermometry can constrain this problem by providing an independent measure of crystallization temperature and, when paired with classical ?18O paleothermometry, can determine the isotopic composition of the fluid the mineral last equilibrated with. Combined with traditional tools, this method has the potential to untangle primary isotopic signatures from diagenetic signals. We measured the isotopic ordering of CO3 groups (?47) substituted into the phosphate lattice of phosphatic brachiopods in Cambrian strata. Phosphatic fossils are generally less soluble than carbonates in surface and diagenetic environments, and so are hypothesized to provide a more robust record of primary growth conditions. They also provide an archive prior to the rise of thick shelled calcitic fossils during the Ordovician Radiation. Additionally, measurements of the ?18O of the CO3 groups can be compared with the ?18O of PO4 groups to test whether their mutual fractionation is consistent with primary growth and the apparent temperature recorded by carbonate clumped isotope measurements. We are constructing a phosphatic brachiopod calibration for carbonate clumped isotope thermometry, and ?47 values of CO2 extracted from modern phosphatic brachiopods suggest they faithfully record seawater temperatures following a calibration similar to the canonical calcite clumped isotope thermometer. Samples from Japan yield a temperature of 23±1.5°C (1 SD) and ?18O water composition of 0.2±0.5‰ VSMOW (calculated assuming CO3 groups have fractionations with respect to water equal to that of calcite). Nine samples of calcitic brachiopods from the 455 Ma Ordovician Decorah Formation yield a mean temperature of 36±3°C and a ?18Owater composition of -0.7±1‰ VSMOW, excluding three brachiopods with temperatures in the low 40s. Four measurements of well-preserved phosphatic brachiopods from the 500 Ma Eau Claire Formation yield a mean temperature of 34±3°C and a ?18Owater composition of -3.3±1‰ VSMOW. The ?18O measurements of PO4 groups from the brachiopods suggest similar water compositions based on equilibrium precipitation at 34°C (Pucéat et al., 2010). These results constrain the climate and potential variation in ?18O of seawater during the early Paleozoic, suggesting that shallow tropical marine environments were somewhat warmer than today, but less so than some predicted (e.g. Trotter et al., 2008). Future measurements of phosphatic brachiopods from the Decorah Formation and modern phosphatic and calcitic brachiopods from a range of environments will provide a direct comparison of the calcitic and phosphatic record.

Bergmann, K.; Robles, M.; Finnegan, S.; Hughes, N. C.; Eiler, J. M.; Fischer, W. W.

2012-12-01

296

AFM-Study on Calcite Nucleation by Cyanobacteria  

NASA Astrophysics Data System (ADS)

Prokaryotic picoplankton plays an important role in lacustrine calcite precipitation, especially in oligotrophic lakes. The mechanisms of cyanobacteria-surface mediated precipitation reactions, however, remain poorly understood. For interpreting geochemical and isotopic information stored in sediments, it is essential to know the carbonate precipitation mechanisms and microscopical details of nucleation on the cell surface. A microscopy study was designed, based on previous results of cyanobacterial calcite precipitation. In order to investigate the nucleation of calcite on the cell surface under controlled conditions, experiments with Synechococcus (PCC 7942) were performed in a flow-through design of an atomic force microscope (AFM). The AFM was operated in `Tapping Mode' providing information on the topography and additionally on physicochemical properties by mapping the phase shift of the oscillating cantilever. For these experiments cells were immobilized on glass slides. As the basic requirement, growth experiments were performed in order to ensure that the fixed cells were alive. To our knowledge one of the first times the successive steps of a cyanobacterial cell division were observed by AFM. The growth of cell agglomerates was monitored over a period of 6 days. AFM images finally reveal the formation of a cyanobacterial biofilm on the glass surface. These observations were supported by the results obtained by epifluorescence microscopy. In a second step, calcite nucleation experiments were performed. Under carefully controlled physical and chemical conditions, nucleation of calcite was enhanced by flushing the fluid cell of the AFM with supersaturated solutions of CaCO3 (CaCl2 and NaHCO3). These solutions were 7 and 10 times supersaturated. As the result of the addition of the CaCO3-solution, changes of the microtopography and physicochemical properties of the cell surface were observed. In our study in-situ-AFM was shown to be powerful tool investigating mechanisms of biomineralization and nucleation under controlled natural conditions.

Obst, M.; Kuehn, H.; Dittrich, M.

2004-12-01

297

Calcite solubility in supercritical CO 2?H 2O fluids  

NASA Astrophysics Data System (ADS)

An extraction-quench apparatus was used to measure calcite solubilities in supercritical CO 2?H 2O mixtures. Experiments were conducted at 1 kbar and 2 kbar, between 240°C and 620°C and from XCO 2 = .02 toXCO 2 = .15 in order to determine the solubility behavior as a function of pressure, temperature and CO 2 content. The results indicate that calcite solubilities under these conditions behave similarly to previously investigated calcite solubilities at lower pressures and temperatures (SHARP and Kennedy, 1965). At constant XCO 2, the solubility increases with increasing pressure, but it decreases with increasing temperature. When the temperature and pressure are constant, the calcite solubility rises with increasing XCO 2 to a maximum value at XCO 2 between 0.02 and 0.05. For higher CO 2 contents, up to XCO 2 = .15, the calcite solubility decreases, probably due to the decrease of H 2O activities to values significantly below unity. The solubility behavior can be successfully modeled by making the assumption that Ca ++ is the dominant calcium species and that the carbon-bearing species are CO 2(aq) and HCO -3. Since for these dilute H 2O?CO 2 fluids, all activity coefficients can be assumed to not differ significantly from unity, ionization constants for the reaction H 2O + CO 2(aq) H + + HCO -3 can be calculated at 1 and 2 kbar between 250°C and 550°C. These calculated values are in good agreement with the low temperature determinations of the ionization constants for this reaction determined by Read (1975). Values of the molal Gibbs free energy of CO 2(aq) obtained in our study exhibit a much greater positive departure from ideality than those calculated with the modified Redlich-Kwong equations of either Flowers (1979) or Kerrick and Jacobs (1981) for dilute CO 2 aqueous solutions.

Fein, Jeremy B.; Walther, John V.

1987-06-01

298

Molecular ordering of ethanol at the calcite surface.  

PubMed

To produce biominerals, such as shells, bones, and teeth, living beings create organic compounds that control the growth of the solid phase. Investigating the atomic scale behavior of individual functional groups at the mineral-fluid interface provides fundamental information that is useful for constructing accurate predictive models for natural systems. Previous investigations of the activity of coccolith-associated polysaccharides (CAP) on calcite, using atomic force microscopy (AFM) [Henriksen, K., Young, J. R., Bown, P. R., and Stipp, S. L. S. Palentology 2004, 43 (Part 3), 725-743] and molecular dynamics (MD) modeling [Yang, M., Stipp, S. L. S., and Harding, J. H. Cryst. Growth Des. 2008, 8 (11), 4066-4074], have suggested that OH functional groups control polysaccharide attachment. The purpose of this work was to characterize, using X-ray reflectivity (XR) combined with molecular dynamics (MD) simulations, the structuring on calcite of a layer of the simplest carbon chain molecule that contains an OH group, ethanol (CH(3)-CH(2)-OH). We found evidence that EtOH forms a highly ordered structure at the calcite surface, where the first layer molecules bond with calcite. The ethanol molecules stand up perpendicularly at the interface or nearly so. As a consequence, the fatty, CH(3) ends form a new surface, about 6 Å from the termination of the bulk calcite, and beyond that, there is a thin gap where ethanol density is low. Following is a more disordered layer that is two to three ethanol molecules thick, about 14 Å, where density more resembles that of bulk liquid ethanol. The good agreement between theory and experiment gives confidence that a theoretical approach can offer information about behavior in more complex systems. PMID:22060260

Pasarín, I S; Yang, M; Bovet, N; Glyvradal, M; Nielsen, M M; Bohr, J; Feidenhans'l, R; Stipp, S L S

2012-02-01

299

Molecular models of a hydrated calcite mineral surface  

NASA Astrophysics Data System (ADS)

Hydrated mineral surfaces play an important role in many processes in biological, geological, and industrial applications. An energy force field was developed for molecular mechanics and molecular dynamics simulations of hydrated carbonate minerals and was applied to investigate the behavior of water on the (101¯4) calcite surface. The force field is a significant development for large-scale molecular simulations of these systems, and provides good agreement with experimental and previous modeling results. Simulations indicate that water molecules are significantly ordered near the calcite surface. The predominant surface configuration (75-80%) results from coordination of a water molecule with a single calcium cation-carbonate anion pair, while the less common situation involves water coordination with two ion pairs. Surface restructuring and variation in coordination in the water layers results in distinct distances for water oxygens above the calcite surface—a two-component first monolayer (2.3 and 3.0 Å) and a secondary monolayer (5.0 Å). The different coordinations also alter lateral displacement, hydrogen bonding, and surface-normal orientation of the water molecules. The ordering of water molecules and the formation of a unique hydrogen bonding network at the calcite surface influence the physical properties of the interfacial water. Surface exchange of water molecules is observed by molecular dynamics simulation to occur at a rate of one exchange per 10 ps. Diffusion coefficients derived from mean square displacement analysis of atomic trajectories indicate a dependence of water transport based on the distance of the water molecules from the calcite surface.

Perry, Thomas D.; Cygan, Randall T.; Mitchell, Ralph

2007-12-01

300

Calcite genesis in the Upper Freeport coal bed as indicated by stable isotope geochemistry  

Microsoft Academic Search

The grinding and sizing in float-sink testing of the Upper Freeport coal bed physically separates calcite of different origins. The different origins are distinguished by different isotopic compositions. The isotopic compositions of calcite indicates at least two, possibly three, stages of calcite formation in the Upper Freeport coal bed. Calcite samples obtained from cleat, and isolated from 8x100 mesh-1.8 specific

F. T. Dulong; E. C. Spiker; C. B. Cecil; R. W. Stanton

1985-01-01

301

Water adsorption and cloud condensation nuclei activity of calcite and calcite coated with model humic and fulvic acids  

NASA Astrophysics Data System (ADS)

Recent studies have shown that organics can alter the water adsorption and cloud condensation nuclei (CCN) activity of common deliquescent species in the Earth's atmosphere. However, very little is known about the effect of organics on water adsorption and CCN activity of insoluble nuclei, such as mineral dust aerosol. A large fraction of unidentified organic material in aerosol particles is composed of poly-acidic compounds resembling humic substances. The presence of these humic-like substances (HULIS) can alter the water adsorption and CCN activity of mineral dust aerosol. We have measured the CCN activity of model humic and fulvic acids and of mineral dust particles coated with these substances in the laboratory. We find that coatings of humic and fulvic acids on calcite particles significantly increases water adsorption compared to uncoated particles. CCN measurements indicate that humic- or fulvic acid-coated calcite particles are more CCN active than uncoated calcite particles. Additionally, thicker coatings of humic or fulvic acids appear to result in more efficient CCN activity. Thus, mineral dust particles coated with high molecular weight organic materials will take up more water and become more efficient CCN in the atmosphere than uncoated mineral dust particles, potentially altering the effect of mineral dust on the Earth's climate. In addition to the experimental results, we have explored a newly modified Köhler theory for predicting the CCN activity of insoluble, wettable particles based on multi layer water adsorption measurements of calcite.

Hatch, Courtney D.; Gierlus, Kelly M.; Schuttlefield, Jennifer D.; Grassian, Vicki H.

302

Caspartin and calprismin, two proteins of the shell calcitic prisms of the Mediterranean fan mussel Pinna nobilis.  

PubMed

We used the combination of preparative electrophoresis and immunological detection to isolate two new proteins from the shell calcitic prisms of Pinna nobilis, the Mediterranean fan mussel. The amino acid composition of these proteins was determined. Both proteins are soluble, intracrystalline, and acidic. The 38-kDa protein is glycosylated; the 17-kDa one is not. Ala, Asx, Thr, and Pro represent the dominant residues of the 38-kDa protein, named calprismin. An N-terminal sequence was obtained from calprismin. This sequence, which comprises a pattern of 4 cysteine residues, is not related to any known protein. The second protein, named caspartin, exhibits an unusual amino acid composition, since Asx constitutes by far the main amino acid residue. Preliminary sequencing surprisingly suggests that the first 75 N-terminal residues are all Asp. Caspartin self-aggregates spontaneously into multimers. In vitro tests show that it inhibits the precipitation of calcium carbonate. Furthermore, it strongly interferes with the growth of calcite crystals. A polyclonal antiserum raised against caspartin was used to localize this protein in the shell by immunogold. The immunolocalization demonstrates that caspartin is distributed within the prisms and makes a continuous film at the interface between the prisms and the surrounding insoluble sheets. Our finding emphasizes the prominent role of aspartic acid-rich proteins for the building of calcitic prisms among molluscs. PMID:15994301

Marin, Frédéric; Amons, Reinout; Guichard, Nathalie; Stigter, Martin; Hecker, Arnaud; Luquet, Gilles; Layrolle, Pierre; Alcaraz, Gérard; Riondet, Christophe; Westbroek, Peter

2005-10-01

303

Stability of basalt+anhydrite+calcite at HP-HT: implications for Venus, the Earth and Mars  

NASA Astrophysics Data System (ADS)

“Canali” observed at Venus’ surface by Magellan are evidence for very long melt flows, but their composition and origin remain uncertain. The hypothesis of water-rich flow is not reasonable regarding Venus’ surface temperature. The length of these channels could not be explained by a silicate melt composition but more likely, by a carbonate-sulfate melt which has a much lower viscosity (Kargel et al 1994). One hypothesis is that calcite CaCO3 and anhydrite CaSO4 - which are alteration products of basalts - melted during meteorite impacts. A famous example recorded on the Earth (Chicxulub) produced melt and gas rich in carbon and sulfur. Calcite and sulfate evaporites are also present on Mars surface, associated with basalts. An impact on these materials may release C- and S-rich melt or fluid. Another type of planetary phenomenon (affecting only the Earth) might provoke a high pressure destabilization of basalt+anhydrite+calcite. Very high contents of C and S are measured in some Earth’s magmas, either dissolved or in the form of crystals (Luhr 2008). As shown by the high H content and high fO2 of primary igneous anhydrite-bearing lavas, the high S content in their source may be explained by the subduction of an anhydrite-bearing oceanic crust, either directly (by melting followed by eruption) or indirectly (by release of S-rich melt or fluid that metasomatize the mantle). Calcite is a major product of oceanic sedimentation and alteration of the crust. Therefore, sulfate- and calcite-rich material may be subducted to high pressures and high temperatures (HP-HT) and release S- and C-rich melts or fluids which could influence the composition of subduction zone lavas or gases. Both phenomena - meteorite impact and subduction - imply HP-HT conditions - although the P-T-time paths are different. Some HP experimental/theoretical studies have been performed on basalt/eclogite, calcite and anhydrite separately or on a combination of two. In this study we performed piston-cylinder experiments at 1 GPa between 950 and 1700°C using a mixture of 70wt% tholeiitic basalt + 15wt% anhydrite + 15wt% calcite. Up to ~1440°C, an ultracalcic (CaO>13.5 wt%; CaO/Al2O3>1 wt%) picrobasaltic (SiO2~40-45 wt%; Na2O+K2O<2 wt%) melt containing up to 5 wt% SO3 and up to 5.3 wt% CO2+H2O (calculated by difference) is present in equilibrium with clinopyroxene, anhydrite, spinel-chromite, a CAS-phase and a gas composed mainly of CO and an aliphatic thiol (CH2)4SH. Hydrogen was incorporated either by contact between the starting material and air or by diffusion through the capsule during the experiments. The S content in the gas increases with temperature and run duration, implying that gases with various C/S ratios might be released during an impact or at subduction zones, depending on the P-T-t path and on the H content. Above ~1440°C, a Ca-rich carbonate-sulfate melt forms (in equilibrium with the picrobasaltic melt) which contains a few percents of Na and K. Such melt is not expected to form at Earth’s subduction temperatures. If it forms by meteorite impact, it might crystallize too fast to explain long flows like Venus’ canali. A different basalt/anhydrite/calcite ratio might, however, decrease its formation temperature.

Martin, A. M.; Righter, K.; Treiman, A. H.

2010-12-01

304

Stability of Basalt plus Anhydrite plus Calcite at HP-HT: Implications for Venus, the Earth and Mars  

NASA Technical Reports Server (NTRS)

"Canali" observed at Venus surface by Magellan are evidence for very long melt flows, but their composition and origin remain uncertain. The hypothesis of water-rich flow is not reasonable regarding the temperature at Venus surface. The length of these channels could not be explained by a silicate melt composition but more likely, by a carbonate-sulfate melt which has a much lower viscosity (Kargel et al 1994). One hypothesis is that calcite CaCO3 and anhydrite CaSO4 which are alteration products of basalts melted during meteorite impacts. A famous example recorded on the Earth (Chicxulub) produced melt and gas rich in carbon and sulfur. Calcite and sulfate evaporites are also present on Mars surface, associated with basalts. An impact on these materials might release C- and S-rich melt or fluid. Another type of planetary phenomenon (affecting only the Earth) might provoke a high pressure destabilization of basalt+anhydrite+calcite. Very high contents of C and S are measured in some Earth s magmas, either dissolved or in the form of crystals (Luhr 2008). As shown by the high H content and high fO2 of primary igneous anhydrite-bearing lavas, the high S content in their source may be explained by subduction of an anhydrite-bearing oceanic crust, either directly (by melting followed by eruption) or indirectly (by release of S-rich melt or fluid that metasomatize the mantle) . Calcite is a major product of oceanic sedimentation and alteration of the crust. Therefore, sulfate- and calcite-rich material may be subducted to high pressures and high temperatures (HP-HT) and release S- and C-rich melts or fluids which could influence the composition of subduction zone lavas or gases. Both phenomena - meteorite impact and subduction - imply HP-HT conditions - although the P-T-time paths are different. Some HP experimental/theoretical studies have been performed on basalt/eclogite, calcite and anhydrite separately or on a combination of two. In this study we performed piston-cylinder experiments at 1 GPa between 950 and 1700 C using a mixture of 70wt% tholeiitic basalt + 15wt% anhydrite + 15wt% calcite. Up to 1440 C, an ultracalcic (CaO>13.5 wt%; CaO/Al2O3>1 wt%) picrobasaltic (SiO240-45 wt%; Na2O+K2O<2 wt%) melt containing up to 5 wt% SO3 and up to 5.3 wt% CO2+H2O (calculated by difference) is present in equilibrium with clinopyroxene, anhydrite, spinel-chromite, a CAS-phase and a gas composed mainly of CO and an aliphatic thiol (CH2)4SH. Hydrogen was incorporated either by contact between the starting material and air or by diffusion through the capsule during the experiments. The S content in the gas increases with temperature and run duration, implying that gases with various C/S ratios might be released during an impact or at subduction zones, depending on the P-T-t path and on the H content. Above approx.1440 C, a Ca-rich carbonate-sulfate melt forms (in equilibrium with the picrobasaltic melt) which contains a few percents of Na and K. Such melt is not expected to form at Earth s subduction temperatures. If it forms by meteorite impact, it might crystallize too fast to explain long flows like Venus canali. A different basalt/anhydrite/calcite ratio might, however, decrease its formation temperature.

Martin, A. M.; Righter, K.; Treiman, A. H.

2010-01-01

305

Surface morphology study of basic ammonothermal GaN grown on non-polar GaN seed crystals of varying surface orientations from m-plane to a-plane  

NASA Astrophysics Data System (ADS)

GaN crystals were grown on hydride vapor phase epitaxy (HVPE) GaN seed crystals with non-polar surface orientations varying between on-axis m-plane and a-plane using the basic ammonothermal method. Three different surface morphology regimes were observed with the surface features including mounds, slate-like morphologies, and pyramidal 'spikes' composed of (0001) and non-polar microfacets. A macroscopic off-orientation of the non-steady-state surface and newly appearing steady-state growth surfaces towards [0001¯] by approximately 1° was observed with geometric constraints suggesting an off-orientation of the observed {10-10} microfacets towards [0001¯] by approximately 1° or greater.

Pimputkar, S.; Kawabata, S.; Speck, J. S.; Nakamura, S.

2013-04-01

306

Arsenic-bearing calcite in natural travertines: evidence from sequential extraction, ?XAS, and ?XRF.  

PubMed

Recent studies demonstrated that synthetic calcite may host considerable amounts of arsenic (As). In this paper, the concentration of As in natural calcite was determined using two novel, specifically designed, sequential extraction procedures. In addition, the oxidation state of As and its distribution between calcite and coexisting Fe-oxyhydroxides was unravelled by ?XRF elemental mapping and As K-edge ?XAS spectroscopy. Our results conclusively demonstrate that arsenic can be found in natural calcite up to 2 orders of magnitude over the normal crustal As abundances. Because of the large diffusion of calcite in the environment, this phase may exert an important control on As geochemistry, mobility, and bioavailability. PMID:23738848

Costagliola, Pilario; Bardelli, Fabrizio; Benvenuti, Marco; Di Benedetto, Francesco; Lattanzi, Pierfranco; Romanelli, Maurizio; Paolieri, Mario; Rimondi, Valentina; Vaggelli, Gloria

2013-06-18

307

Traveling Seeds  

NSDL National Science Digital Library

In this activity, learners make three different "seed" types and determine which design flies the farthest. Learners wad a piece of paper, wad a piece of tape, and make a paper helicopter to represent plant seeds. Learners measure and record the distance each seed travels. Use this activity to help learners practice measuring and recording data. This activity guide contains sample questions to ask, literary connections, extensions, and alignment to local and national standards.

Houston, Children'S M.

2014-03-10

308

Microbially-Mediated Subsurface Calcite Precipitation for Removal of Hazardous Divalent Cations  

SciTech Connect

We are investigating microbially-mediated acceleration of calcite precipitation and co-precipitation of hazardous divalent cations (e.g., 90Sr) in calcite saturated subsurface systems. In theory, the addition of urea to an aquifer or vadose zone and its subsequent hydrolysis by indigenous microbes will cause an increase in alkalinity, pH and calcite precipitation. Lab studies indicated the ability of various bacteria to precipitate calcite through urea hydrolysis and that incorporation of strontium in biogenically-formed calcite is greater than in abiotically formed calcite. Results from a field experiment in a pristine location in the Snake River Plain aquifer involving the phased addition of molasses and then urea showed increases in total cell numbers, rate of urea hydrolysis and calcite formation during the study. The combined diagnostic approaches of microbiology, molecular ecology and analytical chemistry demonstrate the feasibility of this biogeochemical manipulation for subsurface remediation at arid Western DOE sites such as Hanford and INEEL.

Colwell, Frederick S.; Smith, R.W.; Ferris, F. Gratn; Ingram, Jani C.; Reysenbach, A.-L.; Fujita, Yoshiko; Tyler, T.L.; Taylor, J.L.; Banta, A.; Delwiche, M.E.; McLing, T.; Cortez, Marnie, M.; Watwood, M.E.

2003-03-27

309

Kinetics of dry grinding of industrial minerals: calcite and barite  

Microsoft Academic Search

This paper presents the kinetics study of dry ball milling of calcite and barite minerals. The experimental mill used was a laboratory size of 209 mm diameter, 175 mm length, providing a total mill volume of 6001 cm3, with a total mass of 5.6 kg of steel balls of 46, 26 and 12.8 mm diameter, so as to occupy 20%

E Teke; M Yekeler; U Ulusoy; M Canbazoglu

2002-01-01

310

Oxygen Isotope Fractionation between Coexisting Calcite and Dolomite.  

PubMed

The oxygen isotopic composition of calcite from carbonate rocks of the lower unit of the Flagstaff formation (Paleocene) exposed along the western margin of the Wasatch Plateau, Utah, is about 7 per mil lower than that of coexisting dolomite, suggesting that isotopic equilibration of these two minerals can occur at relatively low temperatures. Unlike recent isotopic evidence presented by Degens and Epstein, the data do not preclude a primary chemical origin for the dolomite. PMID:17802014

Weber, J N

1964-09-18

311

Cosmogenic Chlorine36 Production in Calcite by Muons  

Microsoft Academic Search

At depths below a few metres, 36Cl production in calcite is initiated almost entirely by cosmic ray muons. The principal reactions are (1) direct negative muon capture by Ca; 40Ca(??,?)36Cl, and (2) capture by 35Cl of secondary neutrons produced in muon capture and muon-induced photodisintegration reactions. We have determined rates for 36Cl and neutron production due to muon capture in

J. O. H. Stone; J. M. Evans; L. K. Fifield; G. L. Allan; R. G. Cresswell

1998-01-01

312

Spin-lattice coupling of Mn2+ ions in calcite  

Microsoft Academic Search

It is found theoretically that the spin-lattice coupling constant GA1 is proportional to the axial zero-field splitting parameter D for a 6S-state ion in D3d symmetry. A study of the ratio GA\\/sup \\/\\/1D provides an effective way of deciding the relative importance of the various mechanisms which contribute to the zero-field splitting. For Mn2+ in calcite (CaCO3) the spin-orbit coupling

Yu Wan-Lun; Zhao Min-Guang

1987-01-01

313

Arsenite sorption and co-precipitation with calcite  

Microsoft Academic Search

Sorption of As(III) by calcite was investigated as a function of As(III) concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log [As(OH)3 degrees \\/ Assat] plot is S-shaped and has been modelled on an extended version of the surface precipitation model. At low concentrations, As(OH)3 degrees is adsorbed by complexation to surface Ca surface sites, as

Gabriela Roman-Ross; Gabriel Cuello; Xavier Turrillas; Alejandro Fernandez-Martinez; Laurent Charlet

2008-01-01

314

Arsenite sorption and co-precipitation with calcite  

Microsoft Academic Search

Sorption of As(III) by calcite was investigated as a function of As(III) concentration, time and pH. The sorption isotherm, i.e. the log ?As(III) vs. log [As(OH)3°\\/Assat] plot is S-shaped and has been modelled on an extended version of the surface precipitation model [Farley, K.J., Dzombak, D.A., Morel, F.F.M., 1985. A surface precipitation model for the sorption of cations on metal

G. Román-Ross; Gabriel Cuello; Xavier Turrillas; A. Fernández-Martínez; Laurent Charlet

2006-01-01

315

Fast diffusion along mobile grain boundaries in calcite  

Microsoft Academic Search

Experimental measurements of grain boundary diffusion are usually conducted on static boundaries, despite the fact that grain\\u000a boundaries deep in the Earth are frequently mobile. In order to explore the possible effect of boundary mobility on grain\\u000a boundary diffusion rates we have measured the uptake of 44Ca from a layer of 44Ca-enriched calcite powder during the static recrystallization of a

Andrew McCaig; Stephen J. Covey-Crump; Walid Ben Ismaïl; Geoffrey E. Lloyd

2007-01-01

316

Texture effects on megahertz dielectric properties of calcite rock samples  

Microsoft Academic Search

Dielectric measurements have been made from 0.5 to 1300 MHz on Whitestone, a quarried calcite rock, saturated with salty water. Whitestone shows a large increase in dielectric permittivity (dispersion) at the low end of this frequency range. When the conductivity of the water is varied, the dielectric permittivity of Whitestone is found to scale as water conductivity\\/frequency, i.e., as the

W. E. Kenyon

1984-01-01

317

Arsenic uptake by natural calcite: An XAS study  

NASA Astrophysics Data System (ADS)

As-bearing travertine rocks from Tuscany (Italy), where previous studies suggested the existence of a CO 32- ? AsO 33- substitution in the calcite lattice, were investigated with X-ray Absorption Spectroscopy (XAS) at the As K-edge (11,867 eV). In two of the studied samples, XANES indicates that As is in the 5+ oxidation state only, and EXAFS analysis reveals a local environment typical of arsenate species. For these samples, the lack of detectable second shell signals suggests a poorly ordered environment, possibly corresponding to an adsorption onto oxide and/or silicate phases. On the other hand, in the third sample XANES reveals a mixed As oxidation state (III and V). This sample also presents evident next nearest neighbor coordination shells, attributed to As-Ca and As-As contributions. The occurrence of next neighbor shells is evidence that part of As is incorporated in an ordered lattice. Furthermore, the local structure revealed by EXAFS is compatible with As incorporation in the calcite phase, as further supported by DFT simulations. The observation of next neighbors shells only in the As(III)-rich sample suggests the substitution of the arsenite group in place of the carbonate one (CO 32- ? AsO 33-). The conclusion of this work is that uptake of As by calcite is in general less favored than adsorption onto iron oxhydroxides, but could become environmentally important wherever the latter phenomenon is hindered.

Bardelli, F.; Benvenuti, M.; Costagliola, P.; Di Benedetto, F.; Lattanzi, P.; Meneghini, C.; Romanelli, M.; Valenzano, L.

2011-06-01

318

Calcite deposition at Miravalles geothermal field, Costa Rica  

SciTech Connect

The calcite deposition problem at Miravalles has been studied since it was observed in the first three wells drilled on the slopes of the Miravalles Volcano. Long-term tests have been carried out to study reservoir characteristics. The change in the production behavior of the wells with the restriction imposed by the deposited calcite has been studied trying to evaluate and quantify the scaling problem. Work is being done on predictions of the deposition rate, location and distribution of the deposited mineral inside the wells. This work was compared with real data obtained from caliper logs of the wells before and after production. The feasibility of the first 55 MW power plant has been demonstrated. It was considered that the solution for the calcite problem is the reaming during discharge of the wells trying at the same time to minimize the cleaning interventions with a new well design. It is believed, due to the thermodynamics and chemical characteristics of the extracted fluids, that it is possible to find a non-deposition zone which will permit the drilling of wells without a scaling problem.

Vaca, L.; Alvarado, A.; Corrales, R. (Instituto Costarricense de Electricidad, San Jose (Costa Rica))

1989-01-01

319

Earthworm-produced calcite granules: A new terrestrial palaeothermometer?  

NASA Astrophysics Data System (ADS)

In this paper we show for the first time that calcite granules, produced by the earthworm Lumbricus terrestris, and commonly recorded at sites of archaeological interest, accurately reflect temperature and soil water ?18O values. Earthworms were cultivated in an orthogonal combination of two different (granule-free) soils moistened by three types of mineral water and kept at three temperatures (10, 16 and 20 °C) for an acclimatisation period of three weeks followed by transfer to identical treatments and cultivation for a further four weeks. Earthworm-secreted calcite granules were collected from the second set of soils. ?18O values were determined on individual calcite granules (?18Oc) and the soil solution (?18Ow). The ?18Oc values reflect soil solution ?18Ow values and temperature, but are consistently enriched by 1.51 (± 0.12)‰ in comparison to equilibrium in synthetic carbonates. The data fit the equation 1000 ln ? = [20.21 ± 0.92] (103 T-1) - [38.58 ± 3.18] (R2 = 0.95; n = 96; p < 0.0005). As the granules are abundant in modern soils, buried soils and archaeological contexts, and can be dated using U-Th disequilibria, the developed palaeotemperature relationship has enormous potential for application to Holocene and Pleistocene time intervals.

Versteegh, Emma A. A.; Black, Stuart; Canti, Matthew G.; Hodson, Mark E.

2013-12-01

320

18 O values, 87 Sr \\/ 86 Sr and Sr\\/Mg ratios of Late Devonian abiotic marine calcite: Implications for the composition of ancient seawater  

Microsoft Academic Search

Late Devonian (Frasnian) abiotic marine calcite has been microsampled and analyzed for 87 Sr \\/ 86 Sr ratios, 18 O and 13 C values, and minor element concentrations. Portions of marine cement crystals from the Alberta and Canning Basins have escaped diagenetic alteration and preserve original marine 18 O values (-4.8%. ± 0.5, PDB), 13 C values (+2.0 to +3.0%.,

Scott J. Carpenter; K. C. Lohmann; Peter Holden; Lynn M. Walter; Ted J. Huston; Alex N. Halliday

1991-01-01

321

Sign and magnitude of spin Hamiltonian parameters for Mn2+ impurities in calcite. A multi- and low-frequency EPR study  

Microsoft Academic Search

L-, S-, and X-band powder EPR spectra and an L-band single-crystal spectrum of Mn impurities in calcite were analysed by the fitting of full spectral traces to a theoretical model. This analysis gives as parameters the traditional spin Hamiltonian parameters reflecting the three-fold symmetry of the cation lattice site as well as parameters determining the band shape and width of

Stergios Piligkos; Ib Laursen; Axel Morgenstjerne; Høgni Weihe

2007-01-01

322

Origin of gem corundum in calcite marble: The Revelstoke occurrence in the Canadian Cordillera of British Columbia  

NASA Astrophysics Data System (ADS)

The calcite marble-hosted gem corundum (ruby, sapphire) occurrence near Revelstoke, British Columbia, Canada, occurs in the Monashee Complex of the Omineca Belt of the Canadian Cordillera. Corundum occurs in thin, folded and stretched layers with green muscovite + Ba-bearing K-feldspar + anorthite (An0.85-1) ± phlogopite ± Na-poor scapolite. Other silicate layers within the marble are composed of: (1) diopside + tremolite ± quartz and (2) garnet (Alm0.7-0.5Grs0.2-0.4) + Na-rich scapolite + diopside + tremolite + Na,K-amphiboles. Non-silicate layers in the marble are either magnetite- or graphite-bearing. Predominantly pink (locally red or purple) opaque to transparent corundum crystals have elevated Cr2O3 (? 0.21 wt.%) and variable amounts of TiO2; rare blue rims on the corundum crystals contain higher amounts of TiO2 (? 0.53 wt.%) and Fe2O3 (? 0.07 wt.%). The associated micas have elevated Cr, V, Ti, and Ba contents. Petrography of the silicate layers show that corundum formed from muscovite at the peak of metamorphism (~ 650-700 °C at 8.5-9 kbar). Because the marble is almost pure calcite (dolomite is very rare), the corundum was preserved because it did not react with dolomite to spinel + calcite during decompression. The scapolite-bearing assemblages formed during or after decompression of the rock at ~ 650 °C and 4-6 kbar. Gem-quality corundum crystals formed especially on borders of the mica-feldspar layers in an assemblage with calcite. Whole rock geochemistry data show that the corundum-bearing silicate (mica-feldspar) layers formed by mechanical mixing of carbonate with the host gneiss protolith; the bulk composition of the silicate layers was modified by Si and Fe depletion during prograde metamorphism. High element mobility is supported by the homogenization of ?18O and ?13C values in carbonates and silicates for the marble and silicate layers. The silicate layers and the gneiss contain elevated contents of Cr and V due to the volcanoclastic component of their protolith.

Dzikowski, Tashia J.; Cempírek, Jan; Groat, Lee A.; Dipple, Gregory M.; Giuliani, Gaston

2014-06-01

323

Temperature Dependence of the Structural Parameters in the Transformation of Aragonite to Calcite, as Determined from In Situ Synchrotron Powder X-ray-Diffratction Data  

SciTech Connect

The temperature dependency of the crystal structure and the polymorphic transition of CaCO{sub 3} from aragonite to calcite were studied using Rietveld structure refinement and high-temperature in situ synchrotron powder X-ray-diffraction data at ambient pressure, P. The orthorhombic metastable aragonite at room P, space group Pmcn, transforms to trigonal calcite, space group R{bar 3}c, at about T{sub c} = 468 C. This transformation occurs rapidly; it starts at about 420 C and is completed by 500 C, an 80 C interval that took about 10 minutes using a heating rate of 8 C/min. Structurally, from aragonite to calcite, the distribution of the Ca atom changes from approximately hexagonal to cubic close-packing. A 5.76% discontinuous increase in volume accompanies the reconstructive first-order transition. Besides the change in coordination of the Ca atom from nine to six from aragonite to calcite, the CO{sub 3} groups change by a 30{sup o} rotation across the transition.

Antao, Sytle M.; Hassan, Ishmael (Calgary); (West Indies)

2011-09-06

324

Interrogating coccolith calcite: paleoceanographic proxy data from nannofractions, foraminifera and single coccolith specimens  

NASA Astrophysics Data System (ADS)

Nannofossils are the calcareous cell-wall coverings of oceanic phytoplankton and the most abundant but smallest routinely studied fossil group. Small size (typically <8 microns and <400 pg of calcite per lith) has limited their use as geochemical proxies because it is difficult to separate them by mechanical picking or using centrifuge or filtration techniques. However, the <63µm fraction of marine sediments is often implied to represent the bulk nannofossil signal in geochemical studies, but actually represents a spectrum of oceanic carbonate, from parts of larger organisms (potentially benthic, nektonic and planktonic) to micarb (of unknown, possibly non-biological, origin), consequently obfuscating the true nannofossil signal. Additionally, it is known that certain nannofossil taxa are more responsive to paleoenvironmental change than others, and so a bulk nannofossil signal is potentially misleading. Consequently, there has been a strong incentive to develop techniques that overcome these difficulties, as coccoliths represent a potentially invaluable and inexhaustible geochemical archive of paleoenvironmental information. Most importantly, coccoliths are hugely abundant in marine sediments deposited above the calcite compensation depth (billions of specimens per gram) and their chemical composition is resistant to the modifying effects of diagenesis since they are relatively non-porous structures formed from a small number of solid calcite crystals. Here we compare a range of paleoceanographic geochemical proxies (element ratios, stable isotopes) measured from (a) bulk sediment, single foraminifers and sieved near-monotaxic nannofossil fractions using wet chemistry and (b) single coccolith specimens using an ion microprobe SIMS. The data come from the PETM interval of ODP Leg 207 Site 1259 (Demerara Rise, western equatorial Atlantic) and enable comparisons between paleontological, assemblage-based productivity proxies and geochemical proxies based on nannofraction samples and single-species/single-nannofossil specimens. The latter technique is particularly informative, with low Mg and very low B values demonstrating that coccolithophores exert a far greater selectivity on incorporation of trace elements during calcification compared with, for example, foraminifera. Sr values, however, reveal clear and distinct taxon-specific ranges that are consistent with paleoecological interpretations inferred by other means (e.g. regarding eutrophs vs. oligotrophs). The lack of significant change in the Sr values into and through the PETM, despite major nannofossil assemblage shifts and inferred paleoenvironmental change, suggests that production of nannoplankton was not greatly affected at this site. However, Sr measured in nannofraction samples and bulk showed distinctly different trends that require explanation.

Bown, P. R.; Lees, J. A.; Young, J.; Robinson, S. A.; MacLeod, K. G.; Grocke, D. R.; Schmidt, D. N.; Hinton, R.

2009-12-01

325

Simulating the Dissolution and Precipitation of Calcite in Soils using a Soil Hydrological Model  

NASA Astrophysics Data System (ADS)

The spatial distributions of calcite rich horizons within dryland soils are commonly used as proxies for ancient precipitation regimes. As water percolates through a soil, it dissolves minerals, such as calcite, transporting the soluble minerals downward. As soil water is removed by evaporation or root water uptake the water solution may become supersaturated resulting in precipitation of calcite at a new depth. Greater amounts of annual precipitation are thought to result in deeper leaching, yielding deeper calcite horizons. However, other variables such as temperature, root water uptake, soil CO2 concentrations, and soil hydraulic parameters may also influence the solubility and precipitation depth of calcite, confounding otherwise simple relationships between calcite distribution and precipitation. There have been multiple empirical calibrations of depth to Bk (a subsoil horizon rich in calcite) as a proxy for mean annual precipitation (MAP), some of which are soil-order specific. However, it is difficult to constrain all variables using natural soils because the appropriate soil sequences do not always exist. To help quantify the factors controlling the distribution of calcite in soils, we simulated calcite movement using the soil hydrologic model HYDRUS. This approach builds on previous modeling efforts and incorporates several advancements, including a more accurate representation of soil water flow and CO2 transport. We used an irrigation pattern consisting of 2 days of precipitation followed by 8 days of evaporation applied to the surface of a sandy loam soil column 1 meter in depth. This irrigation pattern was repeated during 8, 50, 200, and 500 year simulations with MAP of 73 cm/year. Simulated Bk horizon depth increased with run time and began to stabilize at 500 years. Simulated calcite concentration profiles qualitatively match the commonly observed calcite distribution pattern in dryland soils; after the 500 year simulation, calcite was progressively leached from the upper third of the column and accumulated at a horizon 35 cm below the soil surface. This simulation considered soil evaporative flux as the sole sink for soil moisture. The spatial distribution of simulated calcite accumulation is also related to evaporation rate; larger evaporation rates result in thinner, more concentrated calcite horizons because less moisture is available to leach calcite deeper into the column. Increased simulation run time and the addition of root water uptake, root attributed CO2 production, calcite dust influx at the surface, and the use of measured meteorological variables as boundary conditions will increase the accuracy of the model. Once validated against natural soils, we will use the model to determine the relative importance of multiple variables on calcite accumulation and dissolution.

Meyer, N. A.; Breecker, D. O.

2011-12-01

326

Calcite production by coccolithophores in the south east Pacific Ocean  

NASA Astrophysics Data System (ADS)

BIOSOPE cruise covered an oceanographic transect through the centre of the South Pacific Gyre (SPG) from the Marquesas archipelago to the Peru-Chile upwelling (PCU). Water samples from 6 depths in the euphotic zone were collected at 20 stations. The concentrations of suspended calcite particles, coccolithophores cells and detached coccoliths were estimated together with size and weight using an automatic polarizing microscope, a digital camera, and a collection of softwares performing morphometry and pattern recognition. Some of these softwares are new and described here for the first time. The coccolithophores standing stocks were usually low and reached maxima west of the PCU. The coccoliths of Emiliania huxleyi, Gephyrocapsa spp. and Crenalithus spp. (Order Isochrysidales) represented more than 30% of all the suspended calcite particles detected in the size range 0.1 46 ?m (22% of PIC in term of calcite weight). These species grew preferentially in the Chlorophyll maximum zone. In the SPG their maximum cell concentrations were recorded between depth of 150 and 200 m, which is unusually deep for these taxa. The weight of coccoliths and coccospheres were correlated to their size. Large and heavy coccoliths and coccospheres were found in regions with relatively high fertility in the Marquises Island and in the PCU. Small and light coccoliths and coccospheres were found west of the PCU. This distribution is strongly related to ocean chemistry in particular to alkalinity and to carbonate ions concentration. The biotic (coccolithophores production) influence on calcification is mainly driven at the local scale (depth) whereas the abiotic (carbonate chemistry) plays its most important role at the regional (horizontal) level. Here 94% of the variability of coccolith and coccosphere weight can be explained by a change in 7 environmental variables.

Beaufort, L.; Couapel, M.; Buchet, N.; Claustre, H.; Goyet, C.

2008-08-01

327

Principles of Calcite Dissolution in Human and Artificial Otoconia  

PubMed Central

Human otoconia provide mechanical stimuli to deflect hair cells of the vestibular sensory epithelium for purposes of detecting linear acceleration and head tilts. During lifetime, the volume and number of otoconia are gradually reduced. In a process of degeneration morphological changes occur. Structural changes in human otoconia are assumed to cause vertigo and balance disorders such as benign paroxysmal positional vertigo (BPPV). The aim of this study was to investigate the main principles of morphological changes in human otoconia in dissolution experiments by exposure to hydrochloric acid, EDTA, demineralized water and completely purified water respectively. For comparison reasons artificial (biomimetic) otoconia (calcite gelatin nanocomposits) and natural calcite were used. Morphological changes were detected in time steps by the use of environmental scanning electron microscopy (ESEM). Under in vitro conditions three main dissolution mechanisms were identified as causing characteristic morphological changes of the specimen under consideration: pH drops in the acidic range, complex formation with calcium ions and changes of ion concentrations in the vicinity of otoconia. Shifts in pH cause a more uniform reduction of otoconia size (isotropic dissolution) whereas complexation reactions and changes of the ionic concentrations within the surrounding medium bring about preferred attacks at specific areas (anisotropic dissolution) of human and artificial otoconia. Owing to successive reduction of material, all the dissolution mechanisms finally produce fragments and remnants of otoconia. It can be assumed that the organic component of otoconia is not significantly attacked under the given conditions. Artificial otoconia serve as a suitable model system mimicking chemical attacks on biogenic specimens. The underlying principles of calcite dissolution under in vitro conditions may play a role in otoconia degeneration processes such as BPPV.

Walther, Leif Erik; Blodow, Alexander; Buder, Jana; Kniep, Rudiger

2014-01-01

328

Passivation of the calcite surface with phenylmalonate and benzylmalonate ions.  

PubMed

We explored the affinity of calcite to adsorbed organic molecules as an approach to the conservation of cultural heritage built of marble and limestone. The utilization of phenylmalonic and benzylmalonic acids provided a hydrophobic adsorptive interface, adequate to prevent processes of aqueous weathering. Samples of marble powder (polycrystalline calcite) were impregnated with solutions of phenylmalonic and benzylmalonic acid at three concentrations (5 x 10(-2), 5 x 10(-3), and 5 x 10(-4) M) and different pH values (6.00, 7.00, and 8.00). The surface charge of the calcite suspensions was determined by potentiometric measurements under equilibrium conditions at room temperature in aqueous solution of the dicarboxylic acids, in order to understand the influence of the electrokinetic potential in the surface association. The adsorbed amounts were determined by calculation of the thermodynamic equilibria of solutions. The presence of the organic interface on the mineral surface was corroborated by Raman spectroscopy and small-angle X-ray scattering (SAXS). The results indicate effective adsorption of both dicarboxylic acids as a function of the concentration and pH, and several other conditions that favors coulombic interaction, an absence of electrophoretic mobility or surface electroneutrality related to the solid surface potentials. The coverage of pores by dicarboxylic adsorbate modified the geometrical pore shape and the pore size distribution, filling all the pores of larger than 80 A diameter, giving as a result a mesoporous structure. This change in the surface morphology by organic adsorbates constitutes a modification in the diffusional processes of the environment on the mineral surface. PMID:15848404

Salinas-Nolasco, Manlio F; Méndez-Vivar, Juan; Lara, Víctor H; Bosch, Pedro

2005-06-01

329

Evidence for an organic origin of pedogenic calcitic nanofibres  

NASA Astrophysics Data System (ADS)

Calcium carbonate nanofibres are found in numerous terrestrial environments, often associated with needle fibre calcite. This study attempts to mimic the natural system and generate comparable crystalline structures. A comparison of natural and synthesized nanofibre structures, using HRTEM as well as electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), has demonstrated that this type of nanocrystal can result from precipitation on organic templates, most likely cellulose nanofibres. This study emphasizes the fundamental role of organic templates in the precipitation of calcium carbonate in vadose environments, even at the nanoscale.

Cailleau, Guillaume; Dadras, Massoud; Abolhassani-Dadras, Sousan; Braissant, Olivier; Verrecchia, Eric P.

2009-04-01

330

Calcite dissolution: an in situ study in the Panama Basin  

SciTech Connect

The results of an in situ study of calcite dissolution in the Panama Basin indicate that the rate of dissolution in the water column increases suddenly below a water depth of about 2800 meters. This coincides with the depth at which the calcium carbonate content of surface sediments begins to decrease rapidly or the sedimentary lysocline. Since this level of increased dissolution both in the water column and on the sea floor does not appear to be related to the transition from supersaturation to undersaturation with respect to carbonate, there may be a kinetic origin for the lysocline in this region.

Thunell, R.C. (Univ. of South Carolina, Columbia); Keir, R.S.; Honjo, S.

1981-05-08

331

The ubiquitous nature of accessory calcite in granitoid rocks: Implications for weathering, solute evolution, and petrogenesis  

USGS Publications Warehouse

Calcite is frequently cited as a source of excess Ca, Sr and alkalinity in solutes discharging from silicate terrains yet, no previous effort has been made to assess systematically the overall abundance, composition and petrogenesis of accessory calcite in granitoid rocks. This study addresses this issue by analyzing a worldwide distribution of more than 100 granitoid rocks. Calcite is found to be universally present in a concentration range between 0.028 to 18.8 g kg-1 (mean = 2.52 g kg-1). Calcite occurrences include small to large isolated anhedral grains, fracture and cavity infillings, and sericitized cores of plagioclase. No correlation exists between the amount of calcite present and major rock oxide compositions, including CaO. Ion microprobe analyses of in situ calcite grains indicate relatively low Sr (120 to 660 ppm), negligible Rb and 87Sr/86Sr ratios equal to or higher than those of coexisting plagioclase. Solutes, including Ca and alkalinity produced by batch leaching of the granitoid rocks (5% CO2 in DI water for 75 d at 25??C), are dominated by the dissolution of calcite relative to silicate minerals. The correlation of these parameters with higher calcite concentrations decreases as leachates approach thermodynamic saturation. In longer term column experiments (1.5 yr), reactive calcite becomes exhausted, solute Ca and Sr become controlled by feldspar dissolution and 87Sr/ 86Sr by biotite oxidation. Some accessory calcite in granitoid rocks is related to intrusion into carbonate wall rock or produced by later hydrothermal alteration. However, the ubiquitous occurrence of calcite also suggests formation during late stage (subsolidus) magmatic processes. This conclusion is supported by petrographic observations and 87Sr/86Sr analyses. A review of thermodynamic data indicates that at moderate pressures and reasonable CO2 fugacities, calcite is a stable phase at temperatures of 400 to 700??C. Copyright ?? 2005 Elsevier Ltd.

White, A. F.; Schulz, M. S.; Lowenstern, J. B.; Vivit, D. V.; Bullen, T. D.

2005-01-01

332

Effects of magnesium ions on near-equilibrium calcite dissolution: Step kinetics and morphology  

Microsoft Academic Search

Dissolution kinetics at the aqueous solution-calcite (101¯4) interface at 50 °C were investigated using in situ atomic force microscopy (AFM) to reveal the influence of magnesium concentration and solution saturation state on calcite dissolution kinetics and surface morphology. Under near-equilibrium conditions, dissolved Mg2+ displayed negligible inhibitory effects on calcite dissolution even at concentrations of 10-4molal(m). Upon the introduction of 10-3mMg2+,

Man Xu; Steven R. Higgins

2011-01-01

333

Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C  

Microsoft Academic Search

Uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone, analytical grade calcite, and superpure calcite. The tests were performed at 28°C-150°C, effective stresses of 20-47 MPa, and a pore pressure of 20 MPa, using presaturated CaCO3 solution as the pore fluid. Sample grain sizes ranged from 12 to 86 mum. The aim was to

Xiangmin Zhang; Christopher J. Spiers; Colin J. Peach

2010-01-01

334

Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C  

Microsoft Academic Search

Uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone, analytical grade calcite, and superpure calcite. The tests were performed at 28°C–150°C, effective stresses of 20–47 MPa, and a pore pressure of 20 MPa, using presaturated CaCO3 solution as the pore fluid. Sample grain sizes ranged from 12 to 86 ?m. The aim was to

Xiangmin Zhang; Christopher J. Spiers; Colin J. Peach

2010-01-01

335

Water release patterns of heated speleothem calcite and hydrogen isotope composition of fluid inclusions  

Microsoft Academic Search

Speleothem fluid inclusions are a potential paleo-precipitation proxy to reconstruct past rainwater isotopic composition (?18O, ?D). To get a better insight in the extraction of inclusion water from heated speleothem calcite, we monitored the water released from crushed and uncrushed speleothem calcite, heated to 900 °C at a rate of 300 °C\\/h, with a quadrupole mass spectrometer. Crushed calcite released water in

Sophie Verheyden; Dominique Genty; Olivier Cattani; Martin R. van Breukelen

2008-01-01

336

Diagenesis of calcite cement in Frio Formation sandstones and its relationship to formation water chemistry  

SciTech Connect

Calcite cement is one of the most volumetrically important diagenetic minerals formed during burial of Frio Formation sandstones from the Corpus Christi area of Texas. Syndepositional calcite is restricted to shore-zone sandstones, whereas later, post-quartz-over-growth, burial-diagenetic calcite is present in both shore-zone and shelf sandstones. The {delta}{sup 18}O of burial-diagenetic calcite becomes depleted with depth. Chemical and textural evidence favors partial dissolution and reprecipitation (recrystallization) with consequent isotopic resetting as being responsible for the change in calcite {delta}{sup 18}O with progressive burial. The change in calcite {sup 87}Sr/{sup 86}Sr with depth also supports progressive recrystallization of calcite. There is a strong relationship between the {sup 87}Sr/{sup 86}Sr and trace element composition of calcite and formation water from individual growth-fault blocks. Significant differences in strontium isotopic and trace element composition exist between adjacent fault blocks, implying that each fault block has behaved as a chemically separate system since the time of calcite precipitation.

Lynch, F.L.; Land, L.S. [Univ. of Texas, Austin, TX (United States). Dept. of Geological Sciences

1996-05-01

337

Growth rate anisotropy and absorption studies on ?-BaB 2O 4 single crystals grown by the top-seeded solution growth technique  

NASA Astrophysics Data System (ADS)

Beta barium borate (?-BaB 2O 4; BBO) single crystals have been grown from Na 2O flux by the TSSG technique and the observed growth rate anisotropy is reported. The symmetrical conoscopic interference pattern on the c-cut plate confirmed strain-free and optical homogeneity of the crystals. The observed growth habits of as-grown crystals are explained using crystal growth theories. The relative growth rate along different crystallographic directions of BBO can be described by R[100] = R[010] > R[001]. The absorption measurements show a nearly 9 nm shift in fundamental absorption edges in X and Z cut samples. Band gap energies measured were 6.45 and 6.2 eV along the X and Z directions, respectively. The absorption spectra near the fundamental absorption edges (AE) follow Urbach's rule.

Bhatt, Rajeev; Ganesamoorthy, S.; Bhaumik, Indranil; Karnal, A. K.; Wadhawan, V. K.

2007-03-01

338

Efficient direct frequency conversion of a non-resonant injection-seeded laser diode using a periodically-poled KTP waveguide crystal  

Microsoft Academic Search

Summary form only given. There is considerable interest in compact lasers that operate in the blue spectral region. A blue laser source combining a diode laser with a waveguided nonlinear crystal represents such a compact source which is also stable, self-contained and has a low overall cost. By using a picosecond-pulse diode laser with a periodically-poled KTP waveguide crystal a

D. J. L. Birkin; E. U. Rafailov; W. Sibbett; P. Battle; T. Fry

2001-01-01

339

Bioengineering single crystal growth.  

PubMed

Biomineralization is a "bottom-up" synthesis process that results in the formation of inorganic/organic nanocomposites with unrivaled control over structure, superior mechanical properties, adaptive response, and the capability of self-repair. While de novo design of such highly optimized materials may still be out of reach, engineering of the biosynthetic machinery may offer an alternative route to design advanced materials. Herein, we present an approach using micro-contact-printed lectins for patterning sea urchin embryo primary mesenchyme cells (PMCs) in vitro. We demonstrate not only that PMCs cultured on these substrates show attachment to wheat germ agglutinin and concanavalin A patterns but, more importantly, that the deposition and elongation of calcite spicules occurs cooperatively by multiple cells and in alignment with the printed pattern. This allows us to control the placement and orientation of smooth, cylindrical calcite single crystals where the crystallographic c-direction is parallel to the cylinder axis and the underlying line pattern. PMID:21265521

Wu, Ching-Hsuan; Park, Alexander; Joester, Derk

2011-02-16

340

Environmental controls on the Emiliania huxleyi calcite mass  

NASA Astrophysics Data System (ADS)

Although ocean acidification is expected to impact (bio)calcification by decreasing the seawater carbonate ion concentration, [CO32-], there exists evidence of non-uniform response of marine calcifying plankton to low seawater [CO32-]. This raises questions on the role of environmental factors other than acidification and on the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including temperature, nutrient (nitrate and phosphate) availability, and seawater carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi, the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying well above the modern lysocline. The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of phosphorus and temperature in determining coccolith mass by affecting primary calcification and possibly driving the E. huxleyi morphotype distribution. This evidence does not necessarily argue against the potentially important role of the rapidly changing seawater carbonate chemistry in the future, when unabated fossil fuel burning will likely perturb ocean chemistry beyond a critical point. Rather our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high CO2 world and improve interpretation of paleorecords.

Horigome, M. T.; Ziveri, P.; Grelaud, M.; Baumann, K.-H.; Marino, G.; Mortyn, P. G.

2013-06-01

341

Isotopic analysis for degradation diagnosis of calcite matrix in mortar.  

PubMed

Mortar that was used in building as well as in conservation and restoration works of wall paintings have been analysed isotopically (delta(13)C and delta(18)O) in order to evaluate the setting environments and secondary processes, to distinguish the structural components used and to determine the exact causes that incurred the degradation phenomena. The material undergoes weathering and decay on a large proportion of its surface and in depth, due to the infiltration of water through the structural blocks. Mineralogical analysis indicated signs of sulphation and dissolution/recrystallisation processes taking place on the material, whereas stable isotopes provided information relative to the origin of the CO(2) and water during calcite formation and degradation processes. Isotopic change of the initial delta(13)C and delta(18)O in carbonate matrix was caused by alteration of the primary source of CO(2) and H(2)O in mortar over time, particularly by recrystallisation of calcite with porewater, evaporated or re-condensed water, and CO(2) from various sources of atmospheric and biogenic origin. Human influence (surface treatment) and biological growth (e.g. fungus) are major exogenic processes which may alter delta(18)O and delta(13)C in lime mortar. PMID:19784637

Dotsika, E; Psomiadis, D; Poutoukis, D; Raco, B; Gamaletsos, P

2009-12-01

342

Nyerereite from calcite carbonatite at the Kerimasi Volcano, Northern Tanzania  

NASA Astrophysics Data System (ADS)

The extinct Quaternary Kerimasi volcano located in the southern part of the Gregory Rift, northern Tanzania, contains both intrusive and extrusive calciocarbonatites. One carbonate mineral with a high content of Na and Ca has been found in a sample of volcanic carbonatite, which is probably a cumulate rock. On the basis of Raman spectroscopy and SEM/EDS, this mineral was identified as nyerereite, ideally Na2Ca(CO3)2. It occurs as solid inclusions up to 300 × 200 ?m in size in magnetite and contains (wt. %) 25.4-27.4 Na2O, 26.0-26.8 CaO, 1.6-1.9 K2O, 0.6-1.8 FeO, 0.3-0.6 SrO, <0.4 BaO, 1.4-2.3 SO3, and 0.6-0.9 P2O5. The average mineral formula is (Na1.84K0.08)?1.92(Ca1.00Fe0.03Sr0.01)?1.04[(CO3)1.91(SO4)0.05(PO4)0.02]?1.98. A few inclusions in magnetite also contain calcite, which is considered here to be a late-stage, subsolidus mineral. The occurrence of nyerereite in carbonatite supports Hay's (1983) idea that some of the extrusive carbonatites at the Kerimasi volcano were originally alkaline rich and contained both calcite and nyerereite as primary minerals.

Zaitsev, A. N.

2010-12-01

343

Environmental controls on the Emiliania huxleyi calcite mass  

NASA Astrophysics Data System (ADS)

Although ocean acidification is expected to impact (bio) calcification by decreasing the seawater carbonate ion concentration, [CO32-], there is evidence of nonuniform response of marine calcifying plankton to low seawater [CO32-]. This raises questions about the role of environmental factors other than acidification and about the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including seawater temperature, nutrient (nitrate and phosphate) availability, and carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi, the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying above the modern lysocline (with the exception of eight samples that are located at or below the lysocline). The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of seawater nutrient availability (phosphate and nitrate) and carbonate chemistry (pH and pCO2) in determining coccolith mass by affecting primary calcification and/or the geographic distribution of E. huxleyi morphotypes. Our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high-CO2 world and improve interpretation of paleorecords.

Horigome, M. T.; Ziveri, P.; Grelaud, M.; Baumann, K.-H.; Marino, G.; Mortyn, P. G.

2014-04-01

344

Porosity and hydric behavior of typical calcite microfabrics in stalagmites  

NASA Astrophysics Data System (ADS)

Petrophysical techniques commonly used for material characterization are applied for the first time to speleothem samples to investigate the porosity and hydric behavior of calcite stalagmites used in paleoclimatology. These techniques allow the determination of the stalagmites' potential to undergo diagenetic transformations when substantial changes in drip waters occur in the cave environment. The petrophysical techniques include water absorption under vacuum and by capillarity, nuclear magnetic resonance, environmental scanning electron microscopy, and mercury intrusion porosimetry. The studied samples comprise five common calcite microfabrics, which have markedly different porosities and hydric behaviors and, as a consequence, different sensibilities to diagenetic processes related to the influx of water. The experiments show that stalagmites can behave as complex, small-scale hydrological systems and that the circulation of water through them by complex nets of interconnected pores might be common. As the circulation of water favors diagenetic transformations that involve geochemical and isotopic changes, the characterization of flow patterns is key for outlining areas that are susceptible to such modifications, which is critical to paleoclimatic studies that are based on speleothems because geochemical and stable isotopic data are used as paleoenvironmental proxies and absolute ages are obtained by using radioactive isotope ratios. These potential modifications also have obvious implications for studies based on fluid inclusions in speleothems. The integrated methodology, which uses primarily non-destructive techniques, shows a high potential for characterization of any type of speleothem and other continental carbonates such as tufas or sinters.

Muñoz-García, M. B.; López-Arce, P.; Fernández-Valle, M. E.; Martín-Chivelet, J.; Fort, R.

2012-07-01

345

Calcite (1 0 4)-water interface structure, revisited  

NASA Astrophysics Data System (ADS)

The structure of the calcite (1 0 4)-water interface is reassessed using a new set of high-precision specular X-ray reflectivity measurements. In situ measurements of the specular reflectivity signal to a vertical structural resolution of 0.45 Å are used to define the interfacial structure, including vertical displacement patterns of the Ca and CO3 groups as well as the nature of interfacial water. These new data show two organized interfacial water layers, consistent with previous results, and distortion of the interfacial calcite structure to a depth of four to six unit cells, at least two deeper than previously reported. These results are in reasonable agreement with recent computational studies, at least in terms of the locations of the first and second water layers. The difference between the interfacial structure derived from previous X-ray reflectivity results and that presented here emphasizes the need for high-precision measurements to provide a robust understanding of the interfacial structures of reactive minerals in aqueous environments.

Fenter, P.; Sturchio, N. C.

2012-11-01

346

Many Seeds: Estimating Hidden Seeds  

NSDL National Science Digital Library

In this activity, learners will estimate how many seeds are in a fruit or vegetable, then count to find out. The result: mix estimation with healthy eating. Vary the level of difficulty by using different foods: for younger learners, choose something with up to about 15 seeds inside (e.g. apples, snow peas); for a medium level of difficulty, try melon slices or cucumbers; for more challenge, use pomegranates or mini-pumpkins. Available as a web page or downloadable pdf.

Terc

2010-01-01

347

String stabilized ribbon growth a method for seeding same  

DOEpatents

This invention is a method of initiating or seeding the growth of a crystalline or polycrystalline ribbon by the String Stabilized Ribbon Growth Method. The method for seeding the crystal growth comprises contacting a melt surface with a seed and two strings used in edge stabilization. The wetted strings attach to the wetted seed as a result of the freezing of the liquid melt. Upon drawing the seed, which is attached to the strings, away from the melt surface a melt liquid meniscus, a seed junction, and a growth interface forms. Further pulling of the attached seed causes a crystal ribbon to grow at the growth interface. The boundaries of the growing ribbon are: at the top the seed junction, at the bottom the freezing boundary of the melt liquid meniscus, and at the edges frozen-in strings.

Sachs, Emanuel M. (39 Harding Ave., Belmont, MA 02178)

1987-08-25

348

Using Clumped Isotopes To Help Understand Isotopic Sector Zoning In Calcite  

NASA Astrophysics Data System (ADS)

Debated among scientists for decades, observations of compositional differences between different crystallographic faces within a same growth zone -called sector zoning- represents a major challenge for geochemistry, and in particular for isotope geochemistry. Nowadays, convincing evidence for the existence of sector zoning has been reported in the literature. However, no consensus on the mechanisms triggering sector zoning has been reached. Understanding how and why sector zoning occurs is essential because the presence of sector zoning could skew the isotopic characterization of a carbonate mineral depending on the area being sampled. This would result in an ambiguous interpretation of the data. The emphasis of this study, which is part of the Qatar Carbonates and Carbon Research Center (QCCSRC), is thus placed on deciphering different processes leading to isotopic sector zoning in calcite, with the help of a new tool: the clumped isotopes (i.e. isotopologues). Large calcite crystals with clearly visible growth zones have been collected from fracture infills in Oman. The minerals growth zones and sectors are recognized via cathodoluminescence microscopy, and the trace element content of the different zones in several sectors is estimated via electron microprobe. These different sectors are then sampled by a micro-drill following single growth zones and analyzed for their oxygen and carbon isotopic compositions. The approach highlighted above allows for the recognition of the presence of sector zoning, but does not constrain the type of mechanism(s) possibly affecting isotopic fractionation. To gain further insight, we turn to clumped isotopes (multiply substituted isotopologues) which are molecules with distinct chemical and physical properties. This should theoretically lead to distinctive fractionations. Clumped isotopes have been used recently to measure the temperature of precipitation of carbonate minerals. If each of the crystalline phases of a given crystal were precipitated under thermodynamic equilibrium, one would expect a constant clumped isotope value between sectors. We intend to use clumped isotopes as a discriminative geochemical tool to check if any differences in the ?47 values between sectors exist. If this is the case, isotopologues could provide new insights on sector zoning and would give an extra-dimension to the quest of the different factors resulting in these type of isotopic zonations. Combining compositional, stable isotopes and clumped isotopes information could ultimately permit to reveal the secrets of sector zoning.

Jourdan, A.; John, C. M.; Inchenko, A.; Davis, S.

2010-12-01

349

Relationship between surface structure, growth mechanism, and trace element incorporation in calcite  

NASA Astrophysics Data System (ADS)

Crystal growth and coprecipitation experiments demonstrate the manner in which surface structure and, in turn, crystal structure influence growth mechanism and trace element incorporation in calcite. Dominant {10 overline14} faces grow by the spiral mechanism, producing asymmetric polygonized growth hillocks comprised of two pairs of nonequivalent vicinal faces. Trace elements Mg, Mn, and Sr are differentially incorporated into structurally distinct growth steps that comprise the nonequivalent vicinal faces. The resulting trace element distributions represent intrasectoral zoning patterns and are found to be consistent with face symmetry. Lateral spreading rates are also different for nonequivalent growth steps at a given degree of supersaturation, and the rate anisotropy is dependent on the Ca 2+:CO 32- ratio in the growth solution. A rounding transition associated with changes in kink site density occurs preferentially on only one pair of equivalent growth steps, further demonstrating the importance of step-specific kinetics and affinities on {10 overline14} faces. Growth on other forms, including {01 overline12}, {11 overline20}, and {0001}, does not result in differential partitioning of trace elements and intrasectoral zoning, which is consistent with each of their surface symmetries and allowed growth mechanisms. However, sectoral zoning of Mg, Mn, and Sr occurs between these nonequivalent sectors, as well as {10 overline14}. We present a model detailing the geometry and coordination of elementary kink sites to explain both the differential incorporation and the rate anisotropy between nonequivalent growth steps on individual {10 overline14} faces. The model, constrained by face symmetry, accounts for affinities of different trace elements among four structurally distinct kink sites at which incorporation is preferred. The model also explains the observed differences in growth step velocity, as well as the in situ observations of growth step velocities by atomic force microscopy. Trace element incorporation on the dominant {10 overline14} faces of calcite is controlled by the detailed structure of the interface, which varies spatially on a face, as well as with external conditions. Consequently, our observed trace element distributions violate equilibrium partitioning, and it is likely that many trace element distributions in natural carbonates also may not reflect equilibrium.

Paquette, Jeanne; Reeder, Richard J.

1995-02-01

350

Nonclassical crystallization: mesocrystals and morphology change of CaCO3 crystals in the presence of a polyelectrolyte additive.  

PubMed

Crystallization of calcite from differently concentrated calcium chloride solutions by the CO2 gas diffusion technique in the presence of polystyrene sulfonate yields crystal superstructures with unusual morphology. From the typical calcite rhombohedra as a starting situation, the morphology can be systematically varied via rounded edges and truncated triangles to finally concavely bended lens-like superstructures. Although these "crystals" are apparently well-faceted in light microscopy, electron microscopy analysis and BET reveal that the structures are highly porous and are composed of almost perfectly 3D-aligned calcite nanocrystals scaffolded to the final, partly nicely curved superstructures. At high supersaturations, superstructures with changed symmetry indicative of dipolar interaction potentials between the building blocks are found. The present model case also gives evidence for the importance of nonclassical, mesoscopic processes in crystallization in general. PMID:15755119

Wang, Tongxin; Cölfen, Helmut; Antonietti, Markus

2005-03-16

351

Thermal Expansion and Crystal Structure  

Microsoft Academic Search

In this investigation, the coefficients of thermal expansion of a number of crystals belonging to two structure types rutile and calcite have been studied by the x-ray method with a view to correlating thermal expansion with crystal structure. The crystals studied are MgF2, ZnF2, NiF2, MnF2, CoF2, FeF2, SnO2, PbO2, TiO2 (rutile), CrO2 and RuO2 belonging to the rutile type

K. V. Krishna Rao

1974-01-01

352

Reconciling disparate views of template-directed nucleation through measurement of calcite nucleation kinetics and binding energies  

PubMed Central

The physical basis for how macromolecules regulate the onset of mineral formation in calcifying tissues is not well established. A popular conceptual model assumes the organic matrix provides a stereochemical match during cooperative organization of solute ions. In contrast, another uses simple binding assays to identify good promoters of nucleation. Here, we reconcile these two views and provide a mechanistic explanation for template-directed nucleation by correlating heterogeneous nucleation barriers with crystal–substrate-binding free energies. We first measure the kinetics of calcite nucleation onto model substrates that present different functional group chemistries (carboxyl, thiol, phosphate, and hydroxyl) and conformations (C11 and C16 chain lengths). We find rates are substrate-specific and obey predictions of classical nucleation theory at supersaturations that extend above the solubility of amorphous calcium carbonate. Analysis of the kinetic data shows the thermodynamic barrier to nucleation is reduced by minimizing the interfacial free energy of the system, ?. We then use dynamic force spectroscopy to independently measure calcite–substrate-binding free energies, ?Gb. Moreover, we show that within the classical theory of nucleation, ? and ?Gb should be linearly related. The results bear out this prediction and demonstrate that low-energy barriers to nucleation correlate with strong crystal–substrate binding. This relationship is general to all functional group chemistries and conformations. These findings provide a physical model that reconciles the long-standing concept of templated nucleation through stereochemical matching with the conventional wisdom that good binders are good nucleators. The alternative perspectives become internally consistent when viewed through the lens of crystal–substrate binding.

Hamm, Laura M.; Giuffre, Anthony J.; Han, Nizhou; Tao, Jinhui; Wang, Debin; De Yoreo, James J.; Dove, Patricia M.

2014-01-01

353

Seed Catalogues  

NSDL National Science Digital Library

The Smithsonian Institutions Libraries Web site currently features a unique collection of seed and nursery catalogs dating from 1830 to the present. Online visitors may view a portion of the exhibit, which offers a look at "the history of the seed and agricultural implement business in the United States, as well as provides a history of botany and plant research such as the introduction of plant varieties into the US." Although this site does include much material, gardeners and anyone else with a horticultural bent should enjoy a casual browse through the online exhibit.

354

A calcite permeable reactive barrier for the remediation of Fluoride from spent potliner (SPL) contaminated groundwater  

Microsoft Academic Search

The use of calcite (CaCO3) as a substrate for a permeable reactive barrier (PRB) for removing fluoride from contaminated groundwater is proposed and is illustrated by application to groundwater contaminated by spent potliner leachate (SPL), a waste derived from the aluminium smelting process. The paper focuses on two issues in the implementation of calcite permeable reactive barriers for remediating fluoride

Brett D. Turner; Philip J. Binning; Scott W. Sloan

2008-01-01

355

Effect of Mg on the Grain Growth and Dislocation Creep of Calcite  

Microsoft Academic Search

We tested the effect of variations in the amount of the solute impurity (Mg) on grain growth and strength of calcite aggregate. Synthetic marbles were produced by hot isostatic pressing mixtures of powders of calcite and dolomite at 850° C and 300 MPa confining pressure for different intervals (2 to 30 hrs). The HIP treatment resulted in homogeneous aggregates of

L. Xu

2004-01-01

356

Effect of Solute Impurity of Mg on the Microstructure of Calcite  

Microsoft Academic Search

We produced synthetic marbles by hot isostatic pressing (HIPing) mixtures of calcite and dolomite powders for different intervals (2 to 30 hrs) at 850°C and 300 MPa confining pressure. The HIP treatment resulted in macroscopically homogeneous calcite aggregates with Mg content ranging from 0.5 to 17 mol%. We performed creep tests on samples after HIP at differential stresses from ~

L. Xu; B. J. Evans; J. Renner

2006-01-01

357

The role of disseminated calcite in the chemical weathering of granitoid rocks  

Microsoft Academic Search

Accessory calcite, present at concentrations between 300 and 3000 mg kg?1, occurs in fresh granitoid rocks sampled from the Merced watershed in Yosemite National Park, CA, USA; Loch Vale in Rocky Mountain National Park CO USA; the Panola watershed, GA USA; and the Rio Icacos, Puerto Rico. Calcite occurs as fillings in microfractures, as disseminated grains within the silicate matrix,

Art F White; T HOMAS D. BULLEN; DAVISON V. VIVIT; MARJORIE S. SCHULZ; DAVID W. CLOW

1999-01-01

358

[Research on Raman spectra of calcite phase transition at high pressure].  

PubMed

The present research studied the process of phase transition from calcite-I to calcite-III under the condition of high hydrostatic pressure using hydrothermal diamond anvil cell and Raman spectrum technique. The hydrothermal diamond anvil cell is the most useful instrument to observe sample in-situation under high temperature and high pressure. The authors can get effective results from this instrument and pursue further research. The method of Raman spectra is the most useful measure tool and it can detect the material according to the spectrum. The result shows that three characteristic Raman peaks of calcite-I move to high-position with adding pressure. Water media in system becomes frozen at the pressure of 1103 MPa, and there is no change in the structure of calcite-I. The abrupt change of characteristic Raman peaks of calcite-I happens when the system pressure reaches 1752 MPa, and changed characteristic Raman peaks explain that calcite-I changes to calcite-III. There are two types of calcite-III, and type A happens in the system because of the effect of hydrostatic pressure. The characteristic Raman peak in different areas of minerals shows that the degree of phase transition becomes larger from inner part to edge part. The research also shows the advantage of hydrothermal diamond anvil cell and Raman spectrum for qualitative analysis of mineral structure using in-situ technique. PMID:22007398

Wang, Shi-Xia; Zheng, Hai-Fei

2011-08-01

359

Interactions between calcite precipitation (natural and artificial) and phosphorus cycle in the hardwater lake  

Microsoft Academic Search

The influence of calcite precipitation on the phosphorus cycle in stratified hardwater lake was studied before and during experiments with a new restoration technique. Surveys of the chemical composition of water column and monitoring of settling particles of Lake Luzin (North–East) showed that calcite precipitation occurs each year over 2–3 periods during spring and summer. The change of the phosphorus

Maria Dittrich; Rainer Koschel

2002-01-01

360

Waves and rays in uniaxial birefringent crystals  

NASA Astrophysics Data System (ADS)

In this paper, we present a more elaborate and complete way of the formalism that we have developed in successive steps for ray tracing through uniaxial birefringent media in view of the optical design. With the obtained formulas we analyze in detail what we see through a cleavage calcite crystal.

Simon, Maria C.; Gottschalk, Karin V.

2007-10-01

361

International Seed Saving Institute: Basic Seed Saving  

NSDL National Science Digital Library

This straightforward site from the International Seed Saving Institute on Basic Seed Saving will be of use to any growers interested in learning how to save seeds from season to season. The site provides links "to specific seed saving instructions for 27 common vegetables" including many favorites like corn, carrots, broccoli, and lettuce. The site also links to a glossary of seed saving terms and a six-step Seed Saving Tutorial.

362

Age constraints on fluid inclusions in calcite at Yucca Mountain  

SciTech Connect

The {sup 207}Pb/{sup 235}U ages for 14 subsamples of opal or chalcedony layers younger than calcite formed at elevated temperature range between 1.88 {+-} 0.05 and 9.7 {+-} 1.5 Ma with most values older than 6-8 Ma. These data indicate that fluids with elevated temperatures have not been present in the unsaturated zone at Yucca Mountain since about 1.9 Ma and most likely since 6-8 Ma. Discordant U-Pb isotope data for chalcedony subsamples representing the massive silica stage in the formation of the coatings are interpreted using a model of the diffusive loss of U decay products. The model gives an age estimate for the time of chalcedony formation around 10-11 Ma, which overlaps ages of clay minerals formed in tuffs below the water table at Yucca Mountain during the Timber Mountain thermal event.

Neymark, Leonid A.; Amelin, Yuri V.; Paces, James B.; Peterman, Zell E.; Whelan, Joseph F.

2001-04-29

363

Critical occlusion via biofilm induced calcite precipitation in porous media  

NASA Astrophysics Data System (ADS)

A model for biofilm induced calcite precipitation with pressure driven flow is presented at the scale of a single pore within a porous medium. The system, an extension of previous work (Zhang and Klapper 2010 Water Sci. Technol. 61 2957–64, Zhang and Klapper 2011 Int. J. Non-Linear Mech. 46 657–66), is based on a mixture model including biomaterial, mineral, and water with dissolved components. Computational results suggest the possibility of critical occlusion in the sense that there is a distinguished trans-pore pressure head such that for pressure drops below this level, pore clogging occurs relatively quickly while for pressure drops above, clogging occurs after much longer times if at all. Beyond its relevance to engineered biofilm applications, this phenomenon is suggestive of the subtleties of embedding simple biofilm models in larger media.

Zhang, Tianyu; Klapper, Isaac

2014-05-01

364

In situ study of the R{bar 3}c-R{bar 3}m orientational disorder in calcite.  

SciTech Connect

The temperature dependences of the crystal structure and intensities of the (113) and (211) reflections in calcite, CaCO{sub 3}, were studied using Rietveld structure refinements based on synchrotron powder X-ray diffraction data. Calcite transforms from R{bar 3}c to R{bar 3}m at about T{sub c} = 1240 K. A CO{sub 3} group occupies, statistically, two positions with equal frequency in the disordered R{bar 3}m phase, but with unequal frequency in the partially ordered R{bar 3}c phase. One position for the CO{sub 3} group is rotated by 180{sup o} with respect to the other. The unequal occupancy of the two orientations in the partially ordered R{bar 3}c phase is obtained directly from the occupancy factor, x, for the O1 site and gives rise to the order parameter, S = 2x - 1. The a cell parameter shows a negative thermal expansion at low T, followed by a plateau region at higher T, then a steeper contraction towards T{sub c}, where the CO{sub 3} groups disorder in a rapid process. Using a modified Bragg-Williams model, fits were obtained for the order parameter S, and for the intensities of the (113) and (211) reflections.

Antao, S. M.; Hassan, I.; Mulder, W. H.; Lee, P. L.; Toby, B. H.; X-Ray Science Division; Univ. of West Indies

2009-01-01

365

The quantitative determination of calcite associated with the carbonate-bearing apatites  

USGS Publications Warehouse

The CO2 combined as calcite in carbonate-bearing apatites as been distinguished from that combined as carbonate-apatite, or present in some form other than calcite, by use of X-ray powder patterns, differential thermal analyses, and differential solubility tests. These methods were applied to several pure apatite minerals, to one fossil bone, and to a group of phosphorites from the Phosphoria formation of Permian age from Trail Canyon and the Conda mine, Idaho, and the Laketown district, Utah. With the exceptions of pure fluorapatite, pure carbonate-flueorapatite, and one phosphorite from Trail Canyon, these substances contain varying amounts of calcite, but in all the samples an appreciable part of the carbonite content is not present as calcite. The results of solubility tests, in which the particle size of sample and the length of solution time were varied, imply that the carbonate content is not due to shielded calcite entrapped along an internal network of surfaces.

Silverman, Sol R.; Fuyat, Ruth K.; Weiser, Jeanne D.

1951-01-01

366

Injection seeding. I. Theory  

Microsoft Academic Search

Injection seeding has proven to be a practical method of controlling the spectral output of a laser in an efficient and reliable manner. To achieve satisfactory injection seeding performance, a sufficiently large seed must be employed. To characterize the required seed, an injection seeding theory is developed here which establishes two interrelated concepts, threshold for injection seeding and spectral purity

Norman P. Barnes; James C. Barnes

1993-01-01

367

Big Seed  

NSDL National Science Digital Library

This iOS app helps develop spatial reasoning and strategic thinking. Users reflect seed squares (horizontally, vertically and diagonally) to grow larger pieces that eventually cover the given design space without spilling over. A graduated set of difficulty levels makes the game accessible to a wide range of ages.

2012-12-06

368

Seed Bargains  

NSDL National Science Digital Library

Children as well as adults are usually intrigued by the ideas of bargains. More seeds for less money is often enough to convince them to buy a larger, cheaper package. In this case, the children are savvy enough to question the value of either package. On

Konicek-Moran, Richard

2008-04-01

369

Silicon Crystal Pulling  

NSDL National Science Digital Library

This Quicktime animation shows the first step in the silicon wafer manufacturing process. Under 15 seconds in length, the animation shows the melting of polysilicon and the addition of minute amounts of electrically active elements to form the "seed" of the silicon crystal. The crystal is then extracted from the crystal-growing equipment.The next animation in this sequence about Silicon Ingot Rod Grinding can be seen here.

2009-10-23

370

The Intrinsically Disordered C-RING Biomineralization Protein, AP7, Creates Protein Phases That Introduce Nanopatterning and Nanoporosities into Mineral Crystals.  

PubMed

We report an interesting process whereby the formation of nanoparticle assemblies on and nanoporosities within calcite crystals is directed by an intrinsically disordered C-RING mollusk shell nacre protein, AP7. Under mineralization conditions, AP7 forms protein phases that direct the nucleation of ordered calcite nanoparticles via a repetitive protein phase deposition process onto calcite crystals. These organized nanoparticles are separated by gaps or spaces that become incorporated into the forming bulk crystal as nanoporosities. This is an unusual example of organized nanoparticle biosynthesis and mineral modification directed by a C-RING protein phase. PMID:24977921

Chang, Eric P; Russ, Jennie A; Verch, Andreas; Kröger, Roland; Estroff, Lara A; Evans, John Spencer

2014-07-15

371

? 18O values, 87Sr /86Sr and Sr/Mg ratios of Late Devonian abiotic marine calcite: Implications for the composition of ancient seawater  

NASA Astrophysics Data System (ADS)

Late Devonian (Frasnian) abiotic marine calcite has been microsampled and analyzed for 87Sr /86Sr ratios, ? 18O and ? 13C values, and minor element concentrations. Portions of marine cement crystals from the Alberta and Canning Basins have escaped diagenetic alteration and preserve original marine ? 18O values (-4.8%. ± 0.5, PDB), ? 13C values (+2.0 to +3.0%., PDB), 87Sr /86Sr ratios (0.70805 ± 3), and Sr/Mg weight ratios (0.04 to 0.05). Marine 87Sr /86Sr ratios are globally consistent and can be correlated within the Alberta Basin, and among the Alberta, Canning, and Williston Basins. Correlation of isotopic and chemical data strengthen the conclusion that marine cements from the Leduc Formation preserve original marine ? 18O values which are 3 to 4%. lower than those of modern marine cements. These low ? 18O values are best explained by precipitation from 18O-depleted seawater and not by elevated seawater temperature or diagenetic alteration. For comparison with Devonian data, analogous data were collected from Holocene Mg-calcite and aragonite marine cements from Enewetak Atoll, Marshall Islands. Mg-calcite and aragonite marine cements are in isotopic equilibrium with ambient seawater, and Mg-calcite cements are homogeneous with respect to Sr and Mg contents. Empirically derived homogeneous distribution coefficients for Mg and Sr in modern, abiotic Mg-calcite from Enewetak Atoll are 0.034 and 0.15, respectively. An equation describing the dependence of DSr on Mg content was based on a compilation of Sr and Mg data from Holocene abiotic marine calcite ( DSr = 3.52 × 10 -6 (ppm Mg) + 6.20 × 10 -3). Unlike that derived from experimental data, this Sr-Mg relation is consistent over a range of 4 to 20 mol% MgCO 3 and may represent precipitation phenomena which are minimally controlled by kinetic effects. Comparison of Sr and Mg contents of analogous Devonian and Holocene marine cements suggests that the Mg/Ca ratio of Late Devonian seawater was significantly lower and that the Sr/Ca ratio was significantly higher than that of modern seawater.

Carpenter, Scott J.; Lohmann, K. C.; Holden, Peter; Walter, Lynn M.; Huston, Ted J.; Halliday, Alex N.

1991-07-01

372

Stable calcium isotope composition of a pedogenic carbonate in forested ecosystem: the case of the needle fibre calcite (NFC).  

NASA Astrophysics Data System (ADS)

Calcium (Ca), carbon (C) and oxygen (O) are important elements in terrestrial environment, as their biogeochemical cycles are directly related to the storage of atmospheric carbon. Nevertheless, contrarily to C and O, Ca isotope composition has been only poorly studied in the terrestrial carbonates. Needle Fibre Calcite (NFC) is one of the most common pedogenic carbonates, unless its origin is still under debate. Recent studies explain its formation by precipitation inside fungal hyphae. Due to this possible biogenic origin, NFC can be considered as a potential bridge between the biochemistry (precipitation inside organic structure) and geochemistry (pedogenic carbonate related to soil conditions) of the Ca. Thus, the study of the Ca isotope composition of NFC seem to be of first interest in order to shed light on the behaviour of Ca in terrestrial environment, especially when precipitation of secondary carbonates is involved. The sampling site is situated in the Swiss Jura Mountains and has been chosen due to a previous complete study of the C and O isotope composition of NFC in relation to the ecosystem, which represent a good precondition for the understanding of the NFC Ca isotope signatures in this context. In this study, the implication of the fungi in the origin of NFC is investigated, by comparing the Ca isotope composition of NFC and a purely physicochemical calcite cement (LCC), both precipitated in the same environment. The ?44Ca signature of NFC and LCC crystals were used to determine possible differences of the precipitation rate during their formation. NFC and LCC have similar ?18O composition and are supposed to precipitate at the same temperature (Milliere et al., 2011a). Thus the study of Ca isotope composition of NFC seems to demonstrate that the elongated shape of the calcite needle can be explained by different precipitation processes than the rhombohedric calcite crystals precipitated in the same environment; and more precisely, the specific shape of NFC could be ascribed to a growth related to fungal organic molecules or potentially inside fungal hyphae. Three microscopic morphologies of NFC, previously defined (Milliere et al., 2011a), have been also examined in order to trace the evolution of the NFC inside the soil porosity. The Ca isotope composition of the simple needles, which are supposed to be the original form of NFC are the less fractionated compared to the soil solution, whereas the Ca isotope composition of the two other microscopic morphologies, namely the simple needle with nanofibres and the simple needle with overgrowths, are more fractionated, like the LCC, indicating potentially the influence of biogenic processes in the formation of the simple needles. Milliere L, Hasinger O, Bindschedler S, Cailleau G, Spangenberg JE, Verrecchia EP. 2011a. Stable carbon and oxygen isotopic signatures of pedogenic needle fibre calcite. Geoderma 161, 74-87.

Milliere, Laure; Verrecchia, Eric; Gussone, Nikolaus

2014-05-01

373

Orientation with a Viking sun-compass, a shadow-stick, and two calcite sunstones under various weather conditions.  

PubMed

It is widely accepted that Vikings used sun-compasses to derive true directions from the cast shadow of a gnomon. It has been hypothesized that when a cast shadow was not formed, Viking navigators relied on crude skylight polarimetry with the aid of dichroic or birefringent crystals, called "sunstones." We demonstrate here that a simple tool, that we call "shadow-stick," could have allowed orientation by a sun-compass with satisfying accuracy when shadows were not formed, but the sun position could have reliably been estimated. In field tests, we performed orientation trials with a set composed of a sun-compass, two calcite sunstones, and a shadow-stick. We show here that such a set could have been an effective orientation tool for Vikings only when clear, blue patches of the sky were visible. PMID:24085076

Bernáth, Balázs; Blahó, Miklós; Egri, Adám; Barta, András; Kriska, György; Horváth, Gábor

2013-09-01

374

Heteroepitaxial growth of a manganese carbonate secondary nano-phase on the (1 0 1¯ 4) surface of calcite in solution  

NASA Astrophysics Data System (ADS)

Heteroepitaxy of a manganese carbonate phase with nano-meter dimensions on the (1 0 1¯ 4) surface of calcite (CaCO 3) using an AFM has been observed in solution during dissolution of calcite when the ion activity product of Mn 2+ and CO 32- nears the solubility limit of MnCO 3. Growth rate observations at different Mn concentrations, coupled with X-ray photoelectron spectroscopy and electron paramagnetic resonance measurements, suggest that the resulting phase is Mn 0.5Ca 0.5CO 3. These islands, while growing many microns in length along the [2 2¯ 1] direction, have a uniform width in the range of 120-240 nm and a uniform height of approximately 2.7 nm, corresponding to nine atomic layers. The islands cease growing when they encounter step edges and have been observed to dissolve when undercut by a growing etch pit. Comparison of the crystal lattices of calcite and Mn 0.5Ca 0.5CO 3 indicates that [2 2¯ 1] is the direction of preferred growth. A glued-wetting-layer model with a condition of constant surface chemical potential has been used to model the observed cross section of the heteroepitaxial layer. Although not all the required parameters are accurately known, the model accurately depicts the measured profiles of the islands.

Lea, A. S.; Hurt, T. T.; El-Azab, A.; Amonette, J. E.; Baer, D. R.

2003-02-01

375

Design considerations for a Johann X-ray crystal spectrometer using double reflection in a single crystal to obtain spatially resolved information about a hot plasma seeded with highly charged ions  

Microsoft Academic Search

Enhanced confinement regimes with steep gradients of density profiles and the need to place rotation velocity profiles call for maximum spatial resolution in the tokamak plasma. It is proposed to achieve such a resolution by using X-ray spectroscopy with double reflections in single crystals.

B. S. Fraenkel; Z. H. Kalman; M. Bitter; J. Rice; A. Ince-Cushman

2005-01-01

376

Effect of Second-phase Particles on Static Adjustment of Calcite Grain Boundaries in Carbonate Mylonites  

NASA Astrophysics Data System (ADS)

Static adjustment of grain boundaries during the waning stage of deformation with sustained heat (e.g. at the end of an orogeny) has not been studied much, although it is important for the interpretation of microstructural status during the main stage of deformation. We report here that static adjustment of calcite grain boundaries is dependent on second-phase particles in carbonate mylonites from the Geounri Shear Zone in the Taebaeksan Basin of South Korea. The carbonate mylonites consist of relic (porphyroclastic) calcites (120-400 ?m) and dynamically recrystallized calcites (30-35 ?m) with second-phase particles (15-20 ?m) of quartz and phyllosilicates. Both calcite grains contain mechanical twins and the twins are wider (10-20 ?m thick) in the relic calcites than in the dynamically recrystallized ones (1-3 ?m thick). In the layers of carbonate mylonite with less than 3% of second phases, grain boundaries of calcites are straight with triple junctions. In contrast, calcite grain boundaries are lobate to wavy in the layers with more than 3% of second phases, suggesting dynamic grain boundary migration. Calcite grains in both layers show a strong lattice preferred orientation indicating dominant slip system of basal with minor one of rhomb . We interpret that the foam texture of calcite in the mylonite layers with less than 3% of second phases was produced during the waning stage of the main deformation with a sustained heat since both syntectonic and posttectonic chloritoid porphyroblasts occur in adjacent phyllonite layers in the shear zone. 3% volume fraction of second-phase particles might be a critical value above which deformation microstructures of the main phase were ‘frozen’ without static adjustment in our carbonate mylonites.

Ree, J.; Lee, S.; Jung, H.

2010-12-01

377

Direct visualization of single ions in the Stern layer of calcite.  

PubMed

Calcite is among the most abundant minerals on earth and plays a central role in many environmental and geochemical processes. Here we used amplitude modulation atomic force microscopy (AFM) operated in a particular regime to visualize single ions close to the (1014) surface of calcite in solution. The results were acquired at equilibrium, in aqueous solution containing different concentrations of NaCl, RbCl, and CaCl(2). The AFM images provide a direct and atomic-level picture of the different cations adsorbed preferentially at certain locations of the calcite-water interface. Highly ordered water layers at the calcite surface prevent the hydrated ions from directly interacting with calcite due to the energy penalty incurred by the necessary restructuring of the ions' solvation shells. Controlled removal of the adsorbed ions from the interface by the AFM tip provides indications about the stability of the adsorption site. The AFM results show the familiar "row pairing" of the carbonate oxygen atoms, with the adsorbed monovalent cations located adjacent to the most prominent oxygen atoms. The location of adsorbed cations near the surface appears better defined for monovalent ions than for Ca(2+), consistent with the idea that Ca(2+) ions remain further away from the surface of calcite due to their larger hydration shell. The precise distance between the different hydrated ions and the surface of calcite is quantified using MD simulation. The preferential adsorption sites found by MD as well as the ion residence times close to the surface support the AFM findings, with Na(+) ions dwelling substantially longer and closer to the calcite surface than Ca(2+). The results also bring new insights into the problem of the Stern and electrostatic double layer at the surface of calcite, showing that parameters such as the thickness of the Stern layer can be highly ion dependent. PMID:23339738

Ricci, Maria; Spijker, Peter; Stellacci, Francesco; Molinari, Jean-Francois; Voïtchovsky, Kislon

2013-02-19

378

Activators of photoluminescence in calcite: evidence from high-resolution, laser-excited luminescence spectroscopy  

USGS Publications Warehouse

Laser-excited luminescence spectroscopy of a red-algal, biogenic calcite and a synthetic Mn-calcite can make the distinction between organic and trace-element activators of photoluminescence. Organic-activated photoluminescence in biogenic calcite is characterized by significant peak shifts and increasing intensity with shorter-wavelength excitation and by significant decreases in intensity after heating to ??? 400??C. In contrast, Mn-activated photoluminescence shows no peak shift, greatest intensity under green excitation and limited changes after heating. Examination of samples with a high-sensitivity spectrometer using several wavelengths of exciting light is necessary for identification of photoluminescence activators. ?? 1990.

Pedone, V. A.; Cercone, K. R.; Burruss, R. C.

1990-01-01

379

Non-Markovian behavior of ultrafast coherent ionization dynamics in a crystal exposed to a seeded free-electron-laser pulse  

NASA Astrophysics Data System (ADS)

We investigate the ionization dynamics of a crystal structure driven by ultrafast coherent x-ray pulses of moderate to high intensities for excitations where dipole-allowed, single-photon ionization dominates. Using a simple model of the crystal, we demonstrate that quantum coherences may already play an important role at moderate pulse intensities, leading to qualitatively novel features which cannot be described by rate equations. In particular, the ionization may exhibit a minimum as a function of the pulse duration, where the ionization drops to almost zero, although during the pulse a noticeable fraction of the electrons is promoted to unbound states. For higher intensities, the qualitative deviations between the coherent quantum-mechanical treatment and the rate description is even more pronounced. In particular, due to the presence of quantum-mechanical coherences, the full theory predicts, even for the single-photon transitions to a continuum of free-electron states, a Rabi-type behavior similar to what is known for two-level systems.

Brand, A.; Kaiser, B.; Vagov, A.; Axt, V. M.; Pietsch, U.

2014-06-01

380

Influence of geometry upon crack healing rate in calcite  

NASA Astrophysics Data System (ADS)

Crack healing experiments were conducted at 780°, 815°, and 850° C in dry carbon dioxide over periods of 0.5 to 1320 h on small penny-shaped cracks of known geometry in Stahl calcite. As observed by previous investigators, healing initiates with the formation of tubes around the leading edge of the crack, followed by the pinching off of spherical bubbles from these tubes. Pillars and peninsular structures formed and grew at cleavage steps and other surface irregularities, greatly accelerating the healing process in some cracks. The crack tip regression distance at constant temperature follows a simple power law in time; although, with the exception of one crack at 850° C, the time exponent systematically decreases from 0.59 at 780° C to 0.15 and 0.07 at 815° and 850° C, respectively. Only the largest exponent is consistent with existing theory: the two smaller time exponents are, as yet, unexplained. Healing rates are strongly inversely dependent upon crack aperture, in qualitative agreement with theory. For example, cracks with maximum apertures of less than 60 nm (6×10-8 m) healed completely in 0.5 to 25 h at 850° C; while fatter cracks, with maximum apertures of about 700 nm, showed very little healing after up to 1320 h at the same temperature. At 780° C, the functional dependence of healing rate upon crack aperture was consistent with several aspects of the present model.

Hickman, Stephen H.; Evans, Brian

1987-10-01

381

Seed Treatment. Bulletin 760.  

ERIC Educational Resources Information Center

This manual gives a definition of seed treatment, the types of seeds normally treated, diseases and insects commonly associated with seeds, fungicides and insecticides used, types of equipment used for seed treatment, and information on labeling and coloring of treated seed, pesticide carriers, binders, stickers, and safety precautions. (BB)

Lowery, Harvey C.

382

Top seeded growth and joining of bulk YBCO.  

SciTech Connect

We report (i) systematic studies of the growth rate for melt textured YBCO, (ii) top seeding growth techniques to determine the minimum seed size, and (iii) joining techniques for melt textured YBCO, enabling the fabrication of large single domain structures of arbitrary shape. Seeded growth of YBCO occurs in a narrow temperature window about 20 C below the peritectic decomposition temperature. Successful top seeding depends on the size of the NdBCO seed crystal. Small seeds are eventually dissolved in the melt before nucleation occurs, while large seeds regularly produce single domain monoliths. Joining techniques based on seeding of low melting point Tm123/Y211 filler material by neighboring YBCO are described. Magneto-optical images of the YBCO/TmBCO/YBCO assembly show no detectable penetration of magnetic field at the joints.

Zheng, H.; Veal, B. W.; Paulikas, A.; Nikolova, R.; Welp, U.; Claus, H.; Crabtree, G. W.

1999-10-26

383

Indirectly seeded optical parametric generation in PPLN  

NASA Astrophysics Data System (ADS)

We show that pulsed quasi-phase matched optical parametric generation can be indirectly seeded with a weak cw beam with a wavelength different from that of either the signal or the idler waves. This is accomplished by first mixing the cw seed beam with the pulsed pump beam in a periodically poled lithuim niobate (PPLN) crystal to produce a weak signal beam which is then further amplified in the same crystal. The crystal has two regions with different domain structure periodicities. In the first region the periodicity is chosen to create a beam at 1561.5 nm, resulting from mixing a 15 mW, 632.8 nm beam and an intense, 7 ns 1064 nm pulse