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1

Growth of calcite seeds in a magnetized environment  

NASA Astrophysics Data System (ADS)

Using the constant-composition technique, the growth rates of calcite seeds in a simulated cooling-water environment, i.e., at a temperature higher than room temperature and in the presence of impurity, were measured in a stirred-tank crystallizer under the influence of a magnetic field. When the impurity was absent, the magnetic field would gradually reduce the growth rate of calcite seeds and would have varying impact on the time needed for the seeds to stop growing for different levels of supersaturation, temperature, and pH. In the presence of impurities, including Sr2+ and Fe2+ in the concentration range between 0 and 2.0 ppm, the growth experiments were conducted at two temperatures, i.e., 25 °C and 35 °C. In the presence of Sr2+ the calcite seeds grew steadily after a premagnetization time of 20 h, which was long enough to completely stop the growth of calcite seeds in the absence of impurities. On the other hand, the effect of Fe2+ on calcite growth rate in the presence of magnetic field was rather complicated; either reduced or enhanced rate has been observed. The magnetic field indeed inhibited or stopped the growth of calcite seed for some instances.

Tai, Clifford Y.; Chang, Meng-Chun; Liu, Chong-Chang; Wang, Steven S.-S.

2014-03-01

2

Nanostructured Calcite Single Crystals with Gyroid Morphologies  

E-print Network

Nanostructured Calcite Single Crystals with Gyroid Morphologies By Alexander S. Finnemore, Maik R of which has a complex, sponge-like structure, and yet is a single crystal of calcite.[2] In contrast calcite crystals. Biologically controlled mineralization depends on the interplay between a number

Steiner, Ullrich

3

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

4

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

5

Pressure effect on magnesian calcite coating calcite and synthetic magnesian calcite seeds added to seawater in a closed system  

NASA Astrophysics Data System (ADS)

When pure crystalline calcite seeds are added to supersaturated seawater, precipitation results in a coating which with time equilibrates at atmospheric pressure with seawater and corresponds to a calcite containing probably only 2 or 3% of MgCO 3 (mole fraction). If synthetic crystalline magnesian calcite is added, the surface layer equilibrates not only with respect to seawater but also in relation with the crystalline sites initiating precipitation. Adding Mg 0.03Ca 0.97CO 3 results in a coating with a solubility close to that of calcite. This confirms that the surface coating on pure calcite seeds contains about 2 or 3% MgCO 3 ( K' sp = 10-6.30). The surface layer precipitated on a synthetic Mg 0.08Ca 0.92CO 3 equilibrates finally with a carbonate more soluble than calcite ( K' sp = 10-5.94) corresponding to the seeds composition. Experiments at 1000 kg cm t-2 imply that when magnesian calcites are precipitated at the surface of calcite or magnesian calcite seeds, the precipitate must be hydrated, otherwise pressure accelerated recrystallization or rearrangement with loss of Mg would thermodynamically be impossible. By changing the pressure of a seawater sample originally saturated with a solid carbonate phase, changes in pH result from the effect of pressure on the dissociation constants of carbonic acid and boric acid causing either undersaturation or supersaturation with respect to the solid. By changing pressure we can show whether precipitation, dissolution and recrystallization are reversible processes if pH is taken as criteria of reversibility.

Koch, B.; Disteche, A.

1984-03-01

6

Radiation damage in diopside and calcite crystals from uranothorianite inclusions.  

E-print Network

Radiation damage in diopside and calcite crystals from uranothorianite inclusions. ANNE of UTh grains surrounded by both aluminous diopside (Cpx) and calcite (Cc1) crystals. Optical microscope) a wide "reaction zone" at the Cpx/UTh interface, composed of "secondary calcite" (Cc2) with low

Paris-Sud XI, Université de

7

The crystal structure of calcite III Joseph R. Smyth  

E-print Network

The crystal structure of calcite III Joseph R. Smyth Department of Geological Sciences, University of Technology, Pasadena, CA. Abstract. The crystal structure of calcite III has been deduced from existing high of the calcite I structure. The structure is monoclinic with space group C2 and a Z of 6. There are two Ca

Smyth, Joseph R.

8

Brittlestar-Inspired Microlens Arrays Made of Calcite Single Crystals.  

PubMed

Unique concave microlens arrays (MLAs) made of calcite single crystals with tunable crystal orientations can be readily fabricated by template-assisted epitaxial growth in solution without additives under ambient conditions. While the non-birefringent calcite (001) MLA showed excellent imaging performance like brittlestar's microlens arrays, the birefringent calcite (104) MLA exhibited remarkable polarization-dependent optical properties. PMID:25366272

Ye, Xiaozhou; Zhang, Fei; Ma, Yurong; Qi, Limin

2014-11-01

9

Seeds to crystals  

Microsoft Academic Search

Seeding has been critical for obtaining diffraction-quality crystals for many structures. In this article, applications and recommendations for seeding are presented based on examples from our laboratory and other groups. The implementation of seeding in high-throughput crystallization, robotics, and other emerging technologies is also discussed.

Terese Bergfors

2003-01-01

10

Ultrasonic reactivation of phosphonate poisoned calcite during crystal growth.  

PubMed

The effect of ultrasonic irradiation (42,150 Hz, 17 W dm(-3)/7.1 W cm(-2)) on the growth of calcite in the presence of the inhibitor nitrilotris(methylene phosphonic acid) (NTMP) was investigated at constant composition conditions. In seeded growth experiments, it was found that the inhibiting effect of NTMP on crystal growth could be seriously mitigated under influence of ultrasonic irradiation. An approximately twofold increase in volumetric growth rate was achieved during ultrasonic irradiation, and recovery of the growth rate following inhibition was strongly enhanced compared to growth experiments without ultrasonic irradiation. The results could be explained in part by the physical effect of ultrasound that causes breakage and attrition of poisoned crystals, which resulted in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that there is also a chemical effect of ultrasound that plays an important role. Several breakdown products were identified, which showed that ultrasound caused the progressive loss of phosphonate groups from NTMP, probably by means of physicochemically generated free radicals and/or pyrolysis in the hot bubble-bulk interface. PMID:21463963

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

2011-09-01

11

Laser seeding for biomolecular crystallization  

Microsoft Academic Search

Crystal seeding, which permits the decoupling of crystal nucleation and growth, is a potentially powerful tool for biomolecular crystallization. However, its usefulness is severely limited by the inability of current techniques to manipulate single seeds and it is often considered as a last resort in protein crystal growth trials. Remarkably, current practice relies on the cumbersome technique of entraining seed

Peter A Bancel; Victoria B Cajipe; Francis Rodier; Jean Witz

1998-01-01

12

Synthesis of Calcite Single Crystals with Porous Surface by Templating of Polymer Latex Particles  

E-print Network

Synthesis of Calcite Single Crystals with Porous Surface by Templating of Polymer Latex Particles in solution. After template removal, well-defined, calcite single crystals exhibiting a rhombohedral morphology and uniform surface pores are obtained. The surface pore size of the calcite single crystals can

Qi, Limin

13

Tip-Induced Calcite Single Crystal Nanowear Ramakrishna Gunda, and Alex A. Volinsky  

E-print Network

Tip-Induced Calcite Single Crystal Nanowear Ramakrishna Gunda, and Alex A. Volinsky Department Wear behavior of freshly cleaved single crystal calcite (CaCO3) was investigated by continuous scanning of effects. The wear regime is due to abrasive wear. Single crystal calcite hardness of 2.8±0.3 GPa

Volinsky, Alex A.

14

Selenium incorporation into calcite and its effect on crystal growth: An atomic force microscopy study  

E-print Network

Selenium incorporation into calcite and its effect on crystal growth: An atomic force microscopy December 2012 Available online 7 January 2013 Editor: J. Fein Keywords: Calcite Atomic force microscopy Crystal growth Selenium The atomic processes leading to calcite growth are still debated. The presence

Montes-Hernandez, German

15

Calcite crystal growth orientation: implications for trace metal uptake into coccoliths  

E-print Network

Calcite crystal growth orientation: implications for trace metal uptake into coccoliths V. E. PAYNE, OX1 3PR, UK ABSTRACT Inorganic calcite precipitation experiments were conducted to determine whether inducing specific orientations of calcite crystal growth can cause the enrichment of cations larger than Ca

Benning, Liane G.

16

Author's personal copy Selenium incorporation into calcite and its effect on crystal growth: An atomic force  

E-print Network

Author's personal copy Selenium incorporation into calcite and its effect on crystal growth December 2012 Accepted 29 December 2012 Available online 7 January 2013 Editor: J. Fein Keywords: Calcite Atomic force microscopy Crystal growth Selenium The atomic processes leading to calcite growth are still

17

Tetrahedral calcite crystals facilitate self-assembly at the air-water interface S. M. Hashmi  

E-print Network

Tetrahedral calcite crystals facilitate self-assembly at the air-water interface S. M. Hashmi; published 26 October 2005 Calcite crystals often nucleate and grow in solutions of calcium carbonate out of aqueous solution is known to form fractal aggregates of micron-sized rhombohedral calcite

18

The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite.  

E-print Network

The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to calcite, via calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate

Benning, Liane G.

19

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

Microsoft Academic Search

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

Kyungil Kim

2008-01-01

20

Crystallographic orientation inhomogeneity and crystal splitting in biogenic calcite  

PubMed Central

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

2013-01-01

21

Evaluation of strengthening mechanisms in calcite single crystals from mollusk shells.  

PubMed

Biogenic single-crystal calcite is often reported to be harder and tougher than geologic calcite in the form of Iceland spar. However, the mechanistic origins of the superior mechanical properties of the biogenic materials are still debated. We investigate the hardness and modulus of biogenic calcite from the prismatic layer of the mollusk Atrina rigida compared with a pure geologic calcite, Iceland spar. On the {001} face, biogenic calcite is found to be 50-70% harder than geologic calcite. This range is due to the fact that changes in azimuthal angle of the indenter tip lead to a hardness variation of ?20% in A. rigida but only ?7% in Iceland spar. The higher hardness and increased anisotropy of biogenic calcite could be accounted for by hardening mechanisms based on hindered dislocation motion rather than crack deflection. PMID:23036948

Kunitake, Miki E; Mangano, Lauren M; Peloquin, John M; Baker, Shefford P; Estroff, Lara A

2013-02-01

22

Well-defined star-shaped calcite crystals formed in agarose gels Dong Yang, Limin Qi* and Jiming Ma  

E-print Network

Well-defined star-shaped calcite crystals formed in agarose gels Dong Yang, Limin Qi* and Jiming Ma April 2003 Single crystals of calcite exhibiting a morphology of well- defined 8-armed stars, which evolved from original rhombo- hedral calcite crystals with their 8 points extending radially into eight

Qi, Limin

23

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. PMID:23455343

Murai, Rie

2013-01-01

24

Effects of Chitosan on the Morphology and Alignment of Calcite Crystals Nucleating Under Langmuir Monolayers  

SciTech Connect

The growth of calcium carbonate crystals under Langmuir monolayers was investigated in the presence of chitosan, a soluble derivative of chitin added to the subphase to better simulate the polyelectrolyte-containing in vivo environment. Chitosan causes distinct concentration-dependent changes in the 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, K.; Uysal, A; Kewalramani, S; Stripe, B; Dutta, P

2009-01-01

25

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

SciTech Connect

The growth of calcium carbonate crystals under Langmuir monolayers was investigated in the presence of chitosan, a soluble derivative of chitin added to the subphase to better simulate the polyelectrolyte-containing in vivo environment. Chitosan causes distinct concentration-dependent changes in the 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; Uysal, Ahmet; Kewalramani, Sumit; Stripe, Benjamin; Dutta, Pulak; (NWU); (BNL)

2009-04-22

26

Supporting Information Figure S1. Calcite crystals nucleated and grown on Kevlar threads in the absence of any  

E-print Network

1 Supporting Information Figure S1. Calcite crystals nucleated and grown on Kevlar threads in the absence of any peptides or proteins. We define this as the negative control synthetic calcite. Please and SEM imaging techniques. Figure S2. Calcite crystals nucleated and grown on Kevlar threads

Coppersmith, Susan N.

27

Initial formation of calcite crystals in the thin prismatic layer with the periostracum of Pinctada fucata.  

PubMed

Although the formation mechanism of calcite crystals in the prismatic layer has been studied well in many previous works, the initial state of calcite formation has not been observed in detail using electron microscopes. In this study, we report that the soft prismatic layer with transparent color (the thin prismatic layer) in the tip of the fresh shell of Pinctada fucata was picked up to observe the early calcification phase. A scanning electron microscope (SEM) image showed that the growth tip of the thin prismatic layer was covered by the periostracum, which was also where the initial formation of calcite crystals began. A cross-section containing the thin calcite crystals in the thin prismatic layer with the periostracum was made using a focused ion beam (FIB) system. In a transmission electron microscope (TEM) observation, the thin calcite crystal (thickness is about 1?m) on the periostracum was found to be a single crystal with the c-axis oriented perpendicular to the shell surface. On the other hand, many aggregated small particles consisting of bassanite crystals were observed in the periostracum suggesting the possibility that not only organic sulfate but also inorganic sulfates exist in the prismatic layer. These discoveries in the early calcification phase of the thin prismatic layer may help to clarify the mechanism of regulating the nucleation and orientation of the calcite crystal in the shell. PMID:23176816

Suzuki, Michio; Nakayama, Seiji; Nagasawa, Hiromichi; Kogure, Toshihiro

2013-02-01

28

Direct Observation of the Transition from Calcite to Aragonite Growth as Induced by Abalone Shell Proteins  

E-print Network

Direct Observation of the Transition from Calcite to Aragonite Growth as Induced by Abalone Shell are known to cause the nucleation and growth of aragonite on calcite seed crystals in supersaturated with calcite crystals did not observe this transition because no information about the crystal polymorph

Fygenson, Deborah Kuchnir

29

Interactions of sea-urchin skeleton macromolecules with growing calcite crystals- a study of intracrystalline proteins  

Microsoft Academic Search

The exoskeletons of sea urchins are composed of magnesiumbearing calcite. Individual test plates and spines behave as single crystals in polarized light or when examined by X-ray diffraction1-3. They do not, however, cleave like inorganic calcite crystals along the {104} hexagonal cleavage planes, but have conchoidal fracture surfaces reminiscent of amorphous glass. Discussion of this paradox revolves around whether the

A. Herman; L. Addadi; S. Weiner

1988-01-01

30

Control of macromolecule distribution within synthetic and biogenic single calcite crystals  

SciTech Connect

The ability of organisms to exercise control over crystal growth is wonderfully exemplified by skeleton formation in echinoderms. A sea urchin spine is a unique composite of a single crystal of calcite and glycoproteins intercalated inside the crystal during its growth. Here we performed a detailed morphological and high-resolution synchrotron X-ray diffraction study of the textures of synthetic and biogenic calcite crystals. We show that the intracrystalline macromolecules from sea urchin spines, when allowed to interact with growing calcite crystals in vitro, selectively reduce the coherence lengths and degrees of alignment of the perfect domains in specific crystallographic directions. These directions also correspond to the newly-developed stable faces. In contrast, the defect distribution of young sea urchin spines composed entirely of spongy stereomic structure is much more isotropic. In mature spines containing secondarily filled-in wedges of calcite, the degree of anisotropy is intermediate between that of the synthetic crystals and the young spines. The macromolecules extracted from young and mature spines are, however, very similar. These observations demonstrate the inherent capability of occluded matrix macromolecules to finely differentiate between crystal planes by stereochemical recognition processes. 20 refs., 5 figs., 2 tabs.

Aizenberg, J.; Weiner, S.; Addadi, L. [Weizmann Inst. of Science, Rehovot (Israel)] [Weizmann Inst. of Science, Rehovot (Israel); Hanson, J.; Koetzle, T.F. [Brookhaven National Lab., Upton, NY (United States)] [Brookhaven National Lab., Upton, NY (United States)

1997-02-05

31

E.S.R. OF CO3-3-Li+ CENTRE IN IRRADIATED SYNTHETIC SINGLE CRYSTAL CALCITE  

E-print Network

427 E.S.R. OF CO3-3-Li+ CENTRE IN IRRADIATED SYNTHETIC SINGLE CRYSTAL CALCITE G. BACQUET, J. DUGAS décembre 1974, accepté le 9 janvier 1975) Résumé. 2014 Dans des monocristaux de calcite synthétique in synthetic single crystal calcite X-irradiated at 20 °C. From the g values it is deduced that this spectrum

Boyer, Edmond

32

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

33

SEMI-BATCH CRYSTALLIZATION OF GYPSUM FROM CALCITE AND SULFURIC ACID  

E-print Network

SEMI-BATCH CRYSTALLIZATION OF GYPSUM FROM CALCITE AND SULFURIC ACID F. Bard, D. Garcia , G. Févotte or reusing some compounds they contain in other production processes. The latter is of great interest, both- scale installation modeling the neutralization of a sulphuric acid solution by injection of a diluted

Paris-Sud XI, Université de

34

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

E-print Network

The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal, 2009 (received for review October 13, 2008) The sea urchin tooth is a remarkable grinding tool. Even in the field of biomin- eralization is the ability of the sea urchin tooth to grind down limestone, because

Gilbert, Pupa Gelsomina De Stasio

35

Observation of an Organic-Inorganic Lattice Match during Biomimetic Growth of (001)-Oriented Calcite Crystals under Floating Sulfate Monolayers  

SciTech Connect

Macromolecular layers rich in amino acids and with some sulfated polysaccharides appear to control oriented calcite growth in living organisms. Calcite crystals nucleating under floating acid monolayers have been found to be unoriented on average. We have now observed directly, using in situ grazing incidence X-ray diffraction, that there is a 1:1 match between the monolayer unit cell and the unit cell of the (001) plane of calcite. Thus, sulfate head groups appear to act as templates for the growth of (001)-oriented calcite crystals, which is the orientation commonly found in biominerals.

Kewalramani, S.; Kim, K; Stripe, B; Evmenenko, G; Dommett, G; Dutta, P

2008-01-01

36

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

37

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

38

Morphology of calcite crystals in clast coatings from four soils in the Mojave desert region  

NASA Technical Reports Server (NTRS)

Pedogenic calcite-crystal coatings on clasts were examined in four soils along an altitudinal gradient on Kyle Canyon alluvium in southern Nevada. Clast coatings were studied rather than matrix carbonate to avoid the effects of soil matrix on crystallization. Six crystal sizes and shapes were recognized and distinguished. Equant micrite was the dominant crystal form with similar abundance at all elevations. The distributions of five categories of spar and microspar appear to be influenced by altitudinally induced changes in effective moisture. In the drier, lower elevation soils, crystals were equant or parallel prismatic with irregular, interlocking boundaries while in the more moist, higher elevation soils they were randomly oriented, euhedral, prismatic, and fibrous. There was little support for the supposition that Mg(+2) substitution or increased (Mg + Ca)/HCO3 ratios in the precipitating solution produced crystal elongation.

Chadwick, Oliver A.; Sowers, Janet M.; Amundson, Ronald G.

1989-01-01

39

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

40

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

41

Crystallization of seed globulins from legumes.  

PubMed

Seeds contain large quantities of proteins and are therefore main food sources. In the last century, protein extracts of legume seeds were dialysed against distilled water and in some cases small crystals of pure protein appeared. However, those crystals were generally of poor quality with respect to X-ray diffraction. Recently, the crystallization of some of them was improved and the structures of two 7S globulins, phaseolin from Phaseolus vulgaris and canavalin from Canavalia ensiformis, have been determined at 3.0 and 2.6 A resolution, respectively. Efforts to improve the quality of the phaseolin crystals resulted in three new crystal forms which will be discussed in this paper. The only high-resolution X-ray analysis of a seed globulin from legumes is that of narbonin, a 2S protein from Vicia narbonensis. The crystal structure at 1.8 A shows a very compact packing in layers of molecules. The intermolecular contacts include salt bridges and hydrophobic clusters that might facilitate both the aggregation of the molecules and their crystallization. Because the seed globulins appear in large quantities in the protein bodies of the seeds, efficient packing of the molecules similar to the crystal packing can be assumed. PMID:15299427

Hennig, M; Schlesier, B

1994-07-01

42

Precipitation of different calcite crystal morphologies in the presence of sodium stearate.  

PubMed

The influence of sodium stearate (NaSt) on the precipitation of calcium carbonate during the semicontinuous process of slaked lime carbonation was studied in the systems in which process parameters, like concentration of total dissolved calcium, temperature, CO(2) flow rate and initial addition rate of slaked lime, were controlled. It was found that calcite was the only calcium carbonate polymorph that appeared under the investigated experimental conditions, while FT-IR spectroscopy and thermogravimetric analysis of samples confirmed the presence of stearate on the surface of precipitated calcium carbonate (PCC). Specific surface area of PCC increased with increasing stearate content: the highest value, s = 52.8 m(2) g(-1), was obtained at t = 20 degrees C, c(tot) = 17.0 mmol dm(-3) and the stearate content of m(NaSt)/m(CaO) = 0.03. It was also found that hydrophobic calcite crystals in the form of rhombohedral and scalenohedral morphology can be produced at m(NaSt)/m(CaO) > 0.01. The exception is the case of nanosized PCC production, when much higher concentration of NaSt is needed, m(NaSt)/m(CaO) = 0.22. Minimal amount of stearate necessary to build up the monolayer and corresponding cross sectional area of one stearate molecule were estimated for the obtained calcite morphologies. PMID:18848702

Ukrainczyk, Marko; Kontrec, Jasminka; Kralj, Damir

2009-01-01

43

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. PMID:24748133

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

2014-01-01

44

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

45

Simulation of organic monolayers as templates for the nucleation of calcite crystals.  

PubMed

Living organisms can control the size, shape, and structure of minerals. Attempts to reproduce this biological control in the laboratory often use Langmuir monolayers of long-chain carboxylic acids. We use large-scale molecular dynamics simulations to calculate the interfacial energies of calcite crystals grown on stearic (octadecanoic) acid monolayers. In light of these simulations we discuss the argument that the orientation of the growing mineral is controlled by the organic substrate acting as a template which the mineral must fit in order to grow. PMID:15323512

Duffy, Dorothy M; Harding, John H

2004-08-31

46

A Chemical Model for the Cooperation of Sulfates and Carboxylates in Calcite Crystal Nucleation: Relevance to Biomineralization  

Microsoft Academic Search

Acidic matrix macromolecules involved in regulation of biological crystal growth often contain aspartic acid-rich domains and covalently bound sulfated polysaccharides. We propose that sulfates and beta -sheet structured carboxylates cooperate in oriented calcite crystal nucleation. The sulfates concentrate calcium, creating the supersaturation necessary for nucleation on the structured carboxylate domains. An artificial model, composed of sulfonated polystyrene surfaces and adsorbed

L. Addadi; J. Moradian; E. Shay; N. G. Maroudas; S. Weiner

1987-01-01

47

Formation of star-shaped calcite crystals with Mg{sup 2+} inorganic mineralizer without organic template  

SciTech Connect

Star-shaped calcite crystals with 3-bar m symmetry were obtained in the mixed solvent of ethanol and H{sub 2}O (4:1vol%) using Mg{sup 2+} as grow mineralizer without any organic template under the solvothermal condition. The crystals branched to the six directions perpendicular to the c-axis. In the process, Mg{sup 2+} takes an important influence on such novel morphology via entering the crystal lattice of calcite to absorb the special plane and change the general growth habit. The aqueous solvent is favorable to form aragonite, while the presence of alcohol promotes the formation of calcite, the thermodynamically stable phase. The products were characterized by the techniques of XRD, SEM, SAED, IR and ICP. The formation process was also primarily studied.

Zhu Liying [School of Chemical and Materials Engineering, Southern Yangtze University, Wuxi, Jiangsu 214036 (China); Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026 (China); Zhao Qingrui [Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026 (China); Zheng Xiuwen [Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026 (China); Xie Yi [School of Chemical and Materials Engineering, Southern Yangtze University, Wuxi, Jiangsu 214036 (China) and Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026 (China)]. E-mail: yxielab@ustc.edu.cn

2006-04-15

48

Modification of calcite crystal growth by abalone shell proteins: an atomic force microscope study.  

PubMed Central

A family of soluble proteins from the shell of Haliotis rufescens was introduced over a growing calcite crystal being scanned in situ by an atomic force microscope (AFM). Atomic step edges on the crystal surface were altered in shape and speed of growth by the proteins. Proteins attached nonuniformly to the surface, indicating different interactions with crystallographically different step edges. The observed changes were consistent with the habit modification induced by this family of proteins, as previously observed by optical microscopy. To facilitate further studies in this area, AFM techniques and certain AFM imaging artifacts are discussed in detail. Images FIGURE 1 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 8 FIGURE 9 PMID:9138588

Walters, D A; Smith, B L; Belcher, A M; Paloczi, G T; Stucky, G D; Morse, D E; Hansma, P K

1997-01-01

49

Microrobotic Streak Seeding For Protein Crystal Growth CUCS04104  

E-print Network

Microrobotic Streak Seeding For Protein Crystal Growth CUCS­041­04 Atanas Georgiev 1 Peter Allen 1 crystallographers streak seeding it is used entice certain protein crystals grow. Our system features a of custom this paper known crystallographers streak seeding a technique where small nuclei (or micro­crystals

50

PHYSICAL REVIEW E 87, 012305 (2013) Crystallization on prestructured seeds  

E-print Network

PHYSICAL REVIEW E 87, 012305 (2013) Crystallization on prestructured seeds Swetlana Jungblut, the pres- ence of impurities can strongly enhance crystallization of undercooled fluids [1]. Such seeded spheres will induce crystallization [4,5]. We showed, for seeds of the same size, that the structure

Dellago, Christoph

51

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

52

Temperature-Controlled Support for a Seed Crystal  

NASA Technical Reports Server (NTRS)

A rodlike structure called a sting has been proposed for supporting a seed crystal at center of a body of saturated fluid and for controlling temperature/time profile of seed for experiments on crystal growth. Seed crystal is cooled or heated by thermoelectric modules while surrounding sheath remains at solution temperature. Heat is withdrawn to cooling fins by heat pipe, which replaces solid copper rod in a previous design.

Reeve, J. L.

1982-01-01

53

Ab initio study of single-crystalline and polycrystalline elastic properties of Mg-substituted calcite crystals.  

PubMed

We employ ab initio calculations and investigate the single-crystalline elastic properties of (Ca,Mg)CO3 crystals covering the whole range of concentrations from pure calcite CaCO3 to pure magnesite MgCO3. Studying different distributions of Ca and Mg atoms within 30-atom supercells, our theoretical results show that the energetically most favorable configurations are characterized by elastic constants that nearly monotonously increase with the Mg content. Based on the first principles-derived single-crystalline elastic anisotropy, the integral elastic response of (Ca,Mg)CO3 polycrystals is determined employing a mean-field self-consistent homogenization method. As in case of single-crystalline elastic properties, the computed polycrystalline elastic parameters sensitively depend on the chemical composition and show a significant stiffening impact of Mg atoms on calcite crystals in agreement with the experimental findings. Our analysis also shows that it is not advantageous to use a higher-scale two-phase mix of stoichiometric calcite and magnesite instead of substituting Ca atoms by Mg ones on the atomic scale. Such two-phase composites are not significantly thermodynamically favorable and do not provide any strong additional stiffening effect. PMID:23507262

Zhu, L-F; Friák, M; Lymperakis, L; Titrian, H; Aydin, U; Janus, A M; Fabritius, H-O; Ziegler, A; Nikolov, S; Hemzalová, P; Raabe, D; Neugebauer, J

2013-04-01

54

Direct synthesis of high-silica mordenite using seed crystals  

Microsoft Academic Search

The direct hydrothermal synthesis of high-silica mordenite (MOR) zeolite in the presence of tetraethylammonium hydroxide using various seed crystals was investigated. When seed crystals with the Si\\/Al ratio of 15 synthesized without NaF were employed, the highly crystalline MOR zeolite with the Si\\/Al ratio of approximately 30 and the crystal length of ?8?m was successfully prepared.

Baowang Lu; Tomohiro Tsuda; Yasunori Oumi; Keiji Itabashi; Tsuneji Sano

2004-01-01

55

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

56

Realisation of four-wave mixing phase matching for frequency components at intracavity stimulated Raman scattering in a calcite crystal  

SciTech Connect

The possibilities of implementing four-wave mixing (FWM) phase matching at stimulated Raman scattering (SRS) in a birefringent SRS-active crystal placed in a cavity with highly reflecting mirrors have been theoretically and experimentally investigated. Phase-matching angles providing conditions for five types of phase matching are determined for a calcite crystal. These types are characterised by different combinations of polarisation directions for the interacting waves and ensure FWM generation of either an anti-Stokes wave or the second Stokes SRS component. In agreement with the calculation results, low-threshold generation of the second Stokes SRS component with a wavelength 0.602 {mu}m was observed at angles of incidence on a calcite crystal of 4.8 Degree-Sign and 18.2 Degree-Sign , under SRS pumping at a wavelength of 0.532 {mu}m. This generation is due to the FWM coupling of the first and second Stokes SRS components with the SRS-pump wave. (nonlinear optical phenomena)

Smetanin, Sergei N; Fedin, Aleksandr V; Shurygin, Anton S

2013-06-30

57

Stochastic Nonlinear Observers for Industrial Seeded Batch Crystallization Processes  

E-print Network

Stochastic Nonlinear Observers for Industrial Seeded Batch Crystallization Processes Ali Mesbah1-mail address: ali.mesbah@tudelft.nl Keywords: Batch crystallization, Real-time control, Stochastic process is produced in crystalline form. Batch crystallization is a key separation and purification unit

Van den Hof, Paul

58

Precise tailoring of the crystal size distribution by controlled growth and continuous seeding from impinging jet crystallizers  

E-print Network

Precise tailoring of the crystal size distribution by controlled growth and continuous seeding from by combining controlled seeding by impinging jet crystallization with a batch crystallizer operating by any process equipment that can continuously provide crystal seeds, typically through the application

Braatz, Richard D.

59

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

60

Evolution and the Calcite Eye Lens  

E-print Network

Calcite is a uniaxial, birefringent crystal, which in its optically transparent form, has been used for animal eye lenses, the trilobite being one such animal. Because of the calcite birefringence there is a difficulty in using calcite as a lens. When the propagation direction of incoming light is not exactly on the c-axis, the mages blur. In this paper, calcite blurring is evaluated, and the non-blurring by a crystallin eye lens is compared to a calcite one.

Williams, Vernon L

2013-01-01

61

Evolution and the Calcite Eye Lens  

E-print Network

Calcite is a uniaxial, birefringent crystal, which in its optically transparent form, has been used for animal eye lenses, the trilobite being one such animal. Because of the calcite birefringence there is a difficulty in using calcite as a lens. When the propagation direction of incoming light is not exactly on the c-axis, the mages blur. In this paper, calcite blurring is evaluated, and the non-blurring by a crystallin eye lens is compared to a calcite one.

Vernon L. Williams

2013-04-03

62

Towards achieving a flattop crystal size distribution by continuous seeding and controlled growth  

E-print Network

Towards achieving a flattop crystal size distribution by continuous seeding and controlled growth a b s t r a c t A semi-continuous crystallizer configuration that combines continuous seeding using distribution is limited in industrial batch crystallizations, in which seed crystals are added near the start

Braatz, Richard D.

63

Uranyl incorporation in natural calcite.  

SciTech Connect

The occurrence of trace amounts of uranyl in natural calcite has posed a long-standing problem in crystal chemistry because of speculation that the size and shape of the uranyl ion may preclude its incorporation in a stable lattice position in calcite. This also defines an important environmental problem because of its bearing on the transport and sequestration of uranyl released from nuclear facilities and uranium mining operations. Calcite is a nearly ubiquitous mineral in soils and groundwater aquifers. X-ray absorption spectroscopy and X-ray fluorescence microprobe studies of uranium in relatively U-rich {approx}13700-year-old calcite from a speleothem in northernmost Italy indicate substitution of uranyl for a calcium and two adjacent carbonate ions in calcite. These new data imply that uranyl has a stable lattice position in natural calcite, indicating that it may be reliably sequestered in calcite over long time scales.

Kelly, S. D.; Newville, M. G.; Cheng, L.; Kemner, K. M.; Sutton, S. R.; Fenter, P.; Sturchio, N. C.; Spotl, C.; Environmental Research; Univ. of Chicago; Univ. of Illiois at Chicago; Univ. of Innsbruck

2003-01-01

64

Seeded Growth of AlN Crystals on Non-Polar Seeds Via Physical Vapor Transport  

SciTech Connect

Seeded growth of AlN single crystals was demonstrated in an induction-heated, high-temperature reactor via a physical vapor transport (PVT) process. AlN seeds were prepared from a self-seeded boule containing large single-crystalline grains. Seeded growth was interrupted several times in order to refill the AlN powder source, and a dedicated process scheme was used to ensure epitaxial growth on the seed surface, after prior exposure to air. The growth temperatures were in the range of 2200-2300 C, and the reactor pressure was in the range of 500-900 torr of UHP-grade nitrogen during each growth run. Under these growth conditions, a seed (10 mm diameter) expanded at an angle of 45{sup o}, and a larger single crystal up to 18 mm in diameter was obtained. The as-grown surface had three facets, of which facet (1120) was smooth and featureless while the other two, (4150) and (2570), showed serrated morphologies. The double-crystal x-ray rocking curve and glow discharge mass spectroscopy analysis confirmed that the grown crystal was of high crystalline quality with low impurity incorporation.

Zhuang,D.; Herro, Z.; Schlesser, R.; Ragothamachar, B.; Dudley, M.; Sitar, Z.

2006-01-01

65

Preparation of acicular strontium barium potassium niobate seed crystals  

Microsoft Academic Search

Acicular strontium barium potassium niobate seed crystals with approximate composition Sr0.36Ba0.51K0.31Nb2O6 can be synthesized from SrCO3, BaCO3 and Nb2O5 in molten salt. When KCl is used as molten salt, unfortunately, the synthesized seed crystals have asymmetric diameter and aspect ratio distribution due to the evaporation of KCl flux. While K2SO4 is used as molten salt, highly anisotropic Sr0.36Ba0.51K0.31Nb2O6 particles and

Li-Hui Zhu; Qing-Wei Huang; Hui Gu

2004-01-01

66

Kinetic and thermodynamic factors controlling the distribution of SO32- and Na+ in calcites and selected aragonites  

USGS Publications Warehouse

Significant amounts of SO42-, Na+, and OH- are incorporated in marine biogenic calcites. Biogenic high Mg-calcites average about 1 mole percent SO42-. Aragonites and most biogenic low Mg-calcites contain significant amounts of Na+, but very low concentrations of SO42-. The SO42- content of non-biogenic calcites and aragonites investigated was below 100 ppm. The presence of Na+ and SO42- increases the unit cell size of calcites. The solid-solutions show a solubility minimum at about 0.5 mole percent SO42- beyond which the solubility rapidly increases. The solubility product of calcites containing 3 mole percent SO42- is the same as that of aragonite. Na+ appears to have very little effect on the solubility product of calcites. The amounts of Na+ and SO42- incorporated in calcites vary as a function of the rate of crystal growth. The variation of the distribution coefficient (D) of SO42- in calcite at 25.0??C and 0.50 molal NaCl is described by the equation D = k0 + k1R where k0 and k1 are constants equal to 6.16 ?? 10-6 and 3.941 ?? 10-6, respectively, and R is the rate of crystal growth of calcite in mg??min-1??g-1 of seed. The data on Na+ are consistent with the hypothesis that a significant amount of Na+ occupies interstitial positions in the calcite structure. The distribution of Na+ follows a Freundlich isotherm and not the Berthelot-Nernst distribution law. The numerical value of the Na+ distribution coefficient in calcite is probably dependent on the number of defects in the calcite structure. The Na+ contents of calcites are not very accurate indicators of environmental salinities. ?? 1985.

Busenberg, E.; Niel, Plummer L.

1985-01-01

67

Production of Calcite (Calcium Carbonate) Crystals by Soil Bacteria is a General Phenomenon  

Microsoft Academic Search

CERTAIN bacteria form crystals from the solutes in their aqueous environment, and some authors have associated this activity with the extensive deposits of CaCO3 in such places as the Grand Bahama, in spite of the belief that physicochemical effects, such as rapid changes in pH, salinity and temperature, are responsible1-4. Drew5 isolated a denitrifying bacterium able to form CaCO3 crystals

E. Boquet; A. Boronat; A. Ramos-Cormenzana

1973-01-01

68

Heterogeneous nucleation and growth of calcium carbonate on calcite and quartz  

Microsoft Academic Search

The precipitation of calcium carbonate as a binding salt for the consolidation of loose sand formations is a promising approach. The heterogeneous nucleation and growth of calcite were investigated in supersaturated solutions. The ionic activities in the solutions tested were selected so that they included both supersaturations in which crystal growth took place only following the introduction of seed particles

Maria G. Lioliou; Christakis A. Paraskeva; Petros G. Koutsoukos; Alkiviades C. Payatakes

2007-01-01

69

Puzzling calcite-III dimorphism: crystallography, high-pressure behavior, and pathway of single-crystal transitions  

NASA Astrophysics Data System (ADS)

High-pressure phase transformations between the polymorphic forms I, II, III, and IIIb of CaCO3 were investigated by analytical in situ high-pressure high-temperature experiments on oriented single-crystal samples. All experiments at non-ambient conditions were carried out by means of Raman scattering, X-ray, and synchrotron diffraction techniques using diamond-anvil cells in the pressure range up to 6.5 GPa. The composite-gasket resistive heating technique was applied for all high-pressure investigations at temperatures up to 550 K. High-pressure Raman spectra reveal distinguishable characteristic spectral differences located in the wave number range of external modes with the occurrence of band splitting and shoulders due to subtle symmetry changes. Constraints from in situ observations suggest a stability field of CaCO3-IIIb at relatively low temperatures adjacent to the calcite-II field. Isothermal compression of calcite provides the sequence from I to II, IIIb, and finally, III, with all transformations showing volume discontinuities. Re-transformation at decreasing pressure from III oversteps the stability field of IIIb and demonstrates the pathway of pressure changes to determine the transition sequence. Clausius-Clapeyron slopes of the phase boundary lines were determined as: ? P/? T = -2.79 ± 0.28 × 10-3 GPa K-1 (I-II); +1.87 ± 0.31 × 10-3 GPa K-1 (II/III); +4.01 ± 0.5 × 10-3 GPa K-1 (II/IIIb); -33.9 ± 0.4 × 10-3 GPa K-1 (IIIb/III). The triple point between phases II, IIIb, and III was determined by intersection and is located at 2.01(7) GPa/338(5) K. The pathway of transition from I over II to IIIb can be interpreted by displacement with small shear involved (by 2.9° on I/II and by 8.2° on II/IIIb). The former triad of calcite-I corresponds to the [20-1] direction in the P21/ c unit cell of phase II and to [101] in the pseudomonoclinic C setting of phase IIIb. Crystal structure investigations of triclinic CaCO3-III at non-ambient pressure-temperature conditions confirm the reported structure, and the small changes associated with the variation in P and T explain the broad stability of this structure with respect to variations in P and T. PVT equation of state parameters was determined from experimental data points in the range of 2.20-6.50 GPa at 298-405 K providing = 87.5(5.1) GPa, ( ?K T/ ?T) P = -0.21(0.23) GPa K-1, ? 0 = 0.8(21.4) × 10-5 K-1, and ? 1 = 1.0(3.7) × 10-7 K-1 using a second-order Birch-Murnaghan equation of state formalism.

Pippinger, T.; Miletich, R.; Merlini, M.; Lotti, P.; Schouwink, P.; Yagi, T.; Crichton, W. A.; Hanfland, M.

2015-01-01

70

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

71

Modification of calcite crystal morphology by designed phosphopeptides and primary structures and substrate specifities of the cysteine proteases mexicain and chymomexicain  

Microsoft Academic Search

In order to better understand the mechanism of biomineralization, we have undertaken to synthesize polypeptide model compounds of well-defined structure that can interact with specific faces of calcite and alter its crystal morphology. These peptides were designed based on the structure of alpha-helical winter flounder antifreeze polypeptide HPLC-6. In these peptides, from one to three of the threonine residues in

Zhirui Lian

1999-01-01

72

BACTERIALLY-INDUCED DISSOLUTION OF CALCITE  

E-print Network

BACTERIALLY-INDUCED DISSOLUTION OF CALCITE: THE ROLE OF BACTERIA IN LIMESTONE WEATHERING Fatimah The interaction between microorganisms and the calcite mineral surface in aqueous solutions, under earth surface and metabolism increase the dissolution rates of calcite crystals and alter their surfaces in solution. A natural

73

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

74

Carbon nanotube seeded silicon crystal growth  

NASA Astrophysics Data System (ADS)

Crystal growth of liquid silicon on the heterogeneous surfaces of carbon nanotubes (CNTs) is simulated. Silicon atoms are concentrated to form perfect coaxial cylindrical configurations around CNT cores. The heredity effect makes silicon imprint cylindrical shapes of CNTs during the solidification. The CNTs have a great influence on the stacking sequence of silicon atoms. Growth competition between CNT cores is clearly observed, which results in defects at the shared interface. The internal potential field around CNTs is responsible for growth competition and the heredity effect.

Li, Y. F.; Li, H.; Sun, F. W.; Zhang, X. Q.; Liew, K. M.

2011-07-01

75

Isolation and thermal characterization of high-melting seed crystals formed during cocoa butter solidification  

Microsoft Academic Search

Seed crystals which formed during early stages of cocoa butter solidification have been isolated and determined to have extremely\\u000a high melting points. The melting points of the seed crystals generally exceeded 60C, in contrast to cocoa butter, which melts\\u000a between 30–35C. In addition, the melting point of the seed crystals decreased as a function of crystal growth time. Evidence\\u000a suggests

Thomas R. Davis; Paul S. Dimick

1989-01-01

76

Phospholipid composition of lipid seed crystal isolates from ivory coast cocoa butter  

Microsoft Academic Search

Seed crystals isolated from Ivory Coast cocoa butter were shown to differ in chemical and thermal characteristics from solidified\\u000a Ivory Coast butter. Higher concentrations of complex lipids in the seed crystals have led to speculation on the role these\\u000a polar molecules play in lipid crystallization events. Phospholipids separated from lipid seed crystal isolates were twelve-fold\\u000a more concentrated than the original

Doris H. Arruda; Paul S. Dimick

1991-01-01

77

The Crystallization of Fluorapatite in the Presence of Hydroxyapatite Seeds and of Hydroxyapatite in the Presence of Fluorapatite Seeds  

Microsoft Academic Search

The kinetics of growth of crystals induced by hydroxyapatite (HAP) seed crystals in supersaturated solutions of fluorapatite and of fluorapatite (FAP) seed crystals in supersaturated solutions of hydroxyapatite have been studied using the constant composition method. The reactions were investigated at relative supersaturations ranging from ?FAP= 0.99 to 12.0 at pH 6.5 and for HAP, ?HAP= 3.6 to 12.6 at

Yue Liu; G. Sethuraman; Wenju Wu; G. H. Nancollas; M. Grynpas

1997-01-01

78

MASSIVE CELLULAR DISRUPTION OCCURS DURING EARLY IMBIBITION OF CUPHEA SEEDS CONTAINING CRYSTALLIZED TRIACYLGLYCEROLS  

Technology Transfer Automated Retrieval System (TEKTRAN)

The transition from anhydrobiotic to hydrated state occurs during early imbibition of seeds and is lethal if lipid reserves in seeds are crystalline. Lipids are crystallized by low temperatures used during seed storage. Here, we examine the nature of cellular damage observed in seeds of Cuphea wrig...

79

Influence of Bacillus subtilis Cell Walls and EDTA on Calcite  

E-print Network

Influence of Bacillus subtilis Cell Walls and EDTA on Calcite Dissolution Rates and Crystal Surface features on the calcite {101h4} surface. The calcite dissolution rates are compared at equivalent for by a decrease of the saturation state of the solution with respect to calcite resulting from bonding

Long, Bernard

80

Lipid composition of high-melting seed crystals formed during cocoa butter solidification  

Microsoft Academic Search

High-melting seed crystals which form during the early stages of cocoa butter solidification possess a lipid composition different\\u000a than the cocoa butter from which the seed crystals were grown. Significantly large quantities of glycolipids, 11.1%, and phospholipids,\\u000a 6.6–8.1%, were found in the high-melting seed crystals along with a dramatic decrease in the simple lipid class. The fatty\\u000a acids comprising the

Thomas R. Davis; Paul S. Dimick

1989-01-01

81

Stray grain formation in the seed region of single-crystal turbine blades  

Microsoft Academic Search

Seed crystals are frequently used to provide an off-axial ?001? crystallographic orientation to investment cast single-crystal,\\u000a nickel-based superalloy turbine blades. However, stray grain defects can form during the melt-back of the seed crystal, requiring\\u000a the use of a helical grain selector between the seed and the blade to remove them. Using meso-scale numerical simulations,\\u000a the formation mechanisms of these stray

X. L. Yang; P. D. Lee; N. D’Souza

2005-01-01

82

CRYSTALLIZATION DURING VOLUME REDUCTION OF SOLUTIONS WITH A COMPOSITION CORRESPONDING TO THAT IN THE COLLECTING DUCT. THE INFLUENCE OF HYDROXYAPATITE SEED CRYSTALS AND URINARY MACROMOLECULES  

Microsoft Academic Search

To examine the effect of hydroxyapatite (HAP) seed crystals and urinary macromolecules on the crystallization under conditions similar to those in the collecting duct (CD), we evaporated 100 ml samples of salt solutions with an ion- composition assumed to correspond to that in the CD without and with HAP seed crystals. The crystallization in seeded solutions was assessed both with

Inge Højgaard; Anne-Marie Fornander; Mari-Anne Nilsson; Hans Göran Tiselius

83

Seeded crystal growth of pseudobinary systems with large liquidus-solidus separation  

NASA Technical Reports Server (NTRS)

The design and execution of seeded melt growth involving concentrated alloys is strongly dependent on the crystal-melt interface temperature and its change during seeding and growth. Thermodynamic instabilities during the seeding process can be controlled by the choice of the seed and melt composition and by the axial temperature gradient of the growth apparatus. These basic factors controlling seeded melt growth of concentrated alloys are of major importance for planning space experiments.

Bourret, E. D.; Witt, A. F.

1983-01-01

84

& Microarrays Calcite Microneedle Arrays Produced by Inorganic Ion-Assisted  

E-print Network

& Microarrays Calcite Microneedle Arrays Produced by Inorganic Ion-Assisted Anisotropic Dissolution of Bulk Calcite Crystal Xia Long,[a] Ruijie Meng,[b] Weike Wu,[c] Yurong Ma,*[a] Dong Yang,[b] and Limin and fabricate crystals with complicated morphologies. The formation of ordered arrays of c-axis-oriented calcite

Qi, Limin

85

Experimental calcite dissolution under stress: Evolution of grain contact microstructure during  

E-print Network

Experimental calcite dissolution under stress: Evolution of grain contact microstructure during calcite dissolution under stress. The obtained results enabled identification of the relative importance that pressure solution of calcite crystals at the grain scale occurred by two different mechanisms. Diffusion

86

Microrobotic Streak Seeding For Protein Crystal Growth CUCS-041-04  

E-print Network

Microrobotic Streak Seeding For Protein Crystal Growth CUCS-041-04 Atanas Georgiev1 , Peter K Abstract We present a microrobotic system for protein crystal micromanipulation tasks. The focus in this paper is on the task known by crystallographers as streak seeding ­ it is used to entice certain protein

87

Modification of calcite crystal morphology by designed phosphopeptides and primary structures and substrate specifities of the cysteine proteases mexicain and chymomexicain  

NASA Astrophysics Data System (ADS)

In order to better understand the mechanism of biomineralization, we have undertaken to synthesize polypeptide model compounds of well-defined structure that can interact with specific faces of calcite and alter its crystal morphology. These peptides were designed based on the structure of alpha-helical winter flounder antifreeze polypeptide HPLC-6. In these peptides, from one to three of the threonine residues in HPLC-6 were substituted by phosphoserine or phosphotyrosine. CD spectra show that all the peptides have virtually the same alpha-helicity, i.e., about 90% at 4°C and 50% at 25°C. However, only peptides which contain at least two phosphate groups spaced 16.8-A apart can modify the crystal morphology of the calcite. The newly developed surface has been tentatively identified as the (001) basal face. Molecular modeling indicates that the spacing of phosphate groups allows for a good match with crystal lattice ions on the (001) plane. Another peptide, CBP-3D, in which the three threonine residues in HPLC-6 were substituted by aspartic acids, appears to bind only to {104} rhombohedral faces of calcite. These experiments suggest that conformation and orientation of the binding ligands in the peptide are important factors governing the mutual recognition of crystal surface and proteins. The complete amino acid sequences of the cysteine proteases mexicain and chymomexicain, isolated from the latex of the plant Pileus mexicanus , were determined by Edman degradation of proteolytic fragments. Mexicain and chymomexicain show-high sequence homology to the papain family of cysteine protease. Mexicain and chymomexicain are monomeric polypeptides, with molecular masses of 23,762 Da and 23,694 Da, respectively, and both contain three deduced disulfide bonds. The proteolytic substrate specificities of mexicain and chymomexicain were studied by digesting a series of synthetic peptides and analyzing the fragments by mass spectrometry. The two proteases showed virtually the same substrate specificity, having a rather broad specificity, but with some preference for Val, Thr, Phe, Tyr and Leu at the P2 position. However, they do not appear to cleave peptide bonds where P2 is Lys, Arg or Ile. Their computated 3-dimensional structures were found to be nearly identical to papain and related proteins by homology modeling.

Lian, Zhirui

88

Development of a reusable protein seed crystal processed by chemical cross-linking  

Microsoft Academic Search

A reusable protein seed crystal processed by chemical cross-linking is developed. The process used to achieve cross-linking with glutaraldehyde is described. The lattice constants of the resulting crystals were analyzed using X-ray diffraction, and the characteristics of the seed crystals were investigated using an optical microscope and an atomic-force microscope. The results showed that the lattice constants of the crystalline

Yoshikazu Iimura; Izumi Yoshizaki; Long Rong; Satoshi Adachi; Shinichi Yoda; Hiroshi Komatsu

2005-01-01

89

Ammonothermal growth of GaN on a self-nucleated GaN seed crystal  

NASA Astrophysics Data System (ADS)

We performed ammonothermal synthesis of a self-nucleated GaN seed and grew crystalline GaN on the seed in the presence of an NH4F-based mineralizer. Our results suggest that spontaneously nucleated, high-quality GaN crystals can be obtained by recrystallization of polycrystalline hydride vapor phase epitaxy (HVPE) GaN under acidic ammonothermal conditions. We achieved average growth speeds of up to 410 and 465 ?m/day on the c- and m-directions, respectively, after four consecutive crystal growths of GaN on a self-nucleated seed. GaN crystals grown on an HVPE seed and on a self-nucleated seed had comparable crystal quality, judged from room-temperature photoluminescence measurements.

Bao, Quanxi; Saito, Makoto; Hazu, Kouji; Kagamitani, Yuji; Kurimoto, Kouhei; Tomida, Daisuke; Qiao, Kun; Ishiguro, Tohru; Yokoyama, Chiaki; Chichibu, Shigefusa F.

2014-10-01

90

Seeded infiltration and growth of single-domain Gd–Ba–Cu–O bulk superconductors using a generic seed crystal  

Microsoft Academic Search

We report the seeded infiltration and growth (IG) of Gd–Ba–Cu–O (GdBCO) bulk superconductors for varying molten Ba–Cu–O liquid compositions using an Mg-doped Nd–Ba–Cu–O (Mg-NdBCO) melt-textured seed crystal developed recently at the IRC. All the samples were grown in the form of single grains, although the size of the grain was observed to decrease for an increasingly Ba-rich initial composition. The

K Iida; N H Babu; Y Shi; D A Cardwell

2006-01-01

91

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

92

Crystallization during volume reduction of solutions with a composition corresponding to that in the collecting duct: the influence of hydroxyapatite seed crystals and urinary macromolecules  

Microsoft Academic Search

To examine the effect of hydroxyapatite (HAP) seed crystals and urinary macromolecules on the crystallization under conditions\\u000a similar to those in the collecting duct, we evaporated 100?ml samples of salt solutions with an ion composition assumed to\\u000a correspond to that in the collecting duct without and with HAP seed crystals. The crystallization in seeded solutions was\\u000a assessed both with and

Inge Højgaard; Anne-Marie Fornander; Mari-Anne Nilsson; Hans-Göran Tiselius

1999-01-01

93

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

94

Modeling the calcite Lysocline  

Microsoft Academic Search

A numerical model of calcite dissolution in contact with sediment pore water is used to predict the depth and shape of the calcite lysocline in the deep sea. Model results are compared with lysocline data from 13 regions in the Atlantic, Pacific, and Indian Oceans. The model lysocline shape is sensitive to the calcite dissolution rate constant, the calcite, organic

David Archer

1991-01-01

95

Segregation during directional melting and its implications on seeded crystal growth: A theoretical analysis  

NASA Technical Reports Server (NTRS)

Directional melting of binary systems, as encountered during seeding in melt growth, is analyzed for concurrent compositional changes at the crystal-melt interface. It is shown that steady state conditions cannot normally be reached during seeding and that the growth interface temperature at the initial stages of seeded growth is a function of backmelt conditions. The theoretical treatment is numerically applied to Hg1-xCdXTe and Ga-doped Ge.

Bourret, E. D.; Favier, J. J.; Witt, A. F.

1982-01-01

96

Ammonothermal Growth of GaN on an over-1-inch Seed Crystal  

Microsoft Academic Search

GaN was grown on a 3× 4 cm2 oval-shaped GaN seed crystal by the ammonothermal method. About 15-mum-thick GaN films were uniformly grown on each side of the seed. The Ga-polar surface was filled with pits whereas the N-polar surface was featureless. The photoluminescence (PL) characterization also indicated qualitatively uniform optical properties on each side of the crystal. The PL

Tadao Hashimoto; Kenji Fujito; Makoto Saito; James S. Speck; Shuji Nakamura

2005-01-01

97

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

98

Differentiating between anthropogenic calcite in plaster, ash and natural calcite using infrared spectroscopy: implications in archaeology  

Microsoft Academic Search

Infrared spectroscopy provides information not only on the type of calcium carbonate polymorph, but also on the extent of atomic order. In calcite, three major infrared absorption peaks are identified: ?3, ?2, and ?4. It was shown that the ratio between ?2 and ?4 bands reflects the order of the calcite crystal structure. In this paper we analyse this ratio

Vikki Chu; Lior Regev; Steve Weiner; Elisabetta Boaretto

2008-01-01

99

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

100

Journal of Crystal Growth 310 (2008) 29462953 Textural properties of synthetic nano-calcite produced by hydrothermal  

E-print Network

carbonation of calcium hydroxide (Ca(OH)2) at high pressure of CO2 (initial PCO2 ¼ 55 bar) and moderate kg/m3 h) and high purity of product (about 96%). However, the various initial physicochemicalJournal of Crystal Growth 310 (2008) 2946­2953 Textural properties of synthetic nano

Montes-Hernandez, German

101

The effect of osteopontin immobilized collagen granules in the seed crystal method  

Microsoft Academic Search

Osteopontin (OPN) is a urinary protein which inhibits calcium oxalate (CaOx) crystal growth in the seed crystal system. The aim of this study was to evaluate the effects of OPN immobilized on collagen granules (CG) for CaOx crystal growth and aggregation in this system. OPN-immobilized CG showed a 30% decrease in inhibitory activity compared with non-OPN-immobilized CG. Scanning electron microscopy

T. Umekawa; M. Iguchi; T. Kurita

2001-01-01

102

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

103

Defect formation in 4H-SiC single crystal grown on the prismatic seeds  

NASA Astrophysics Data System (ADS)

The defect structure of 4H silicon carbide single crystals grown by PVT method on three prismatic seeds (10-10), (11-20) and (8.3.-11.0) is considered. The only defects existing in the grown ingots are stacking faults and basal plane dislocations. The type of stacking fault is studied. The dependence of stacking fault morphology on the seed orientation is analyzed.

Fadeev, A. Yu; Lebedev, A. O.; Tairov, Yu M.

2014-12-01

104

In-situ growth of calcite at Devils Hole, Nevada: Comparison of field and laboratory rates to a 500,000 year record of near-equilibrium calcite growth  

USGS Publications Warehouse

Calcite grew continuously for 500,000 years on the submerged walls of an open fault plane (Devils Hole) in southern Nevada, U.S.A. at rates of 0.3 to 1.3 mm/ka, but ceased growing approximately 60,000 years ago, even though the fault plane remained open and was continuously submerged. The maximum initial in-situ growth rate on pre-weighed crystals of Iceland spar placed in Devils Hole (calcite saturation index, SI, is 0.16 to 0.21 at 33.7??C) for growth periods of 0.75 to 4.5 years was 0.22 mm/ka. Calcite growth on seed crystals slowed or ceased following initial contact with Devils Hole groundwater. Growth rates measured in synthetic Ca-HCO3 solutions at 34??C, CO2 partial pressures of 0.101, 0.0156 (similar to Devils Hole groundwater) and 0.00102 atm, and SI values of 0.2 to 1.9 were nearly independent of P(CO)(2), decreased with decreasing saturation state, and extrapolated through the historical Devils Hole rate. The results show that calcite growth rate is highly sensitive to saturation state near equilibrium. A calcite crystal retrieved from Devils Hole, and used without further treatment of its surface, grew in synthetic Devils Hole groundwater when the saturation index was raised nearly 10-fold that of Devils Hole water, but the rate was only 1/4 that of fresh laboratory crystals that had not contacted Devils Hole water. Apparently, inhibiting processes that halted calcite growth in Devils Hole 60,000 years ago continue today.

Plummer, L.N.; Busenberg, E.; Riggs, A.C.

2000-01-01

105

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

2014-04-25

106

UBC Social Ecological Economic Development Studies (SEEDS) Student Report Carla Turner, Crystal Chan, Sherry Xu, Tania Leon  

E-print Network

UBC Social Ecological Economic Development Studies (SEEDS) Student Report Carla Turner, Crystal, 2014 1011 1619 University of British Columbia Disclaimer: "UBC SEEDS provides students or the SEEDS Coordinator about the current status of the subject matter of a project/report". #12;UBC Food

107

Characterization of semi-insulating CdTe crystals grown by horizontal seeded physical vapor transport  

NASA Astrophysics Data System (ADS)

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 8 ? cm range. The photoluminescence spectra of the crystal grown in the boron nitride coated ampoule showed similar features previously observed in the CdTe crystals doped with group III elements. Although the crystal was contaminated with boron, the boron nitride coating of the growth ampoule has yielded a single crystal with no inclusions or precipitates.

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

1998-07-01

108

Crystal Structure of a 16 kDa Double-headed Bowman-Birk Trypsin Inhibitor from Barley Seeds at  

E-print Network

Crystal Structure of a 16 kDa Double-headed Bowman- Birk Trypsin Inhibitor from Barley Seeds at 1 The Bowman-Birk trypsin inhibitor from barley seeds (BBBI) consists of 125 amino acid residues with two inhibitory loops. Its crystal structure in the free state has been determined by the multiwavelength

Suh, Se Won

109

Crystal structure of a pro-inflammatory lectin from the seeds of Dioclea wilsonii Standl  

Microsoft Academic Search

The crystal structure and pro-inflammatory property of a lectin from the seeds of Dioclea wilsonii (DwL) were analyzed to gain a better understanding of structure\\/function relationships of Diocleinae lectins. Following crystallization and structural determination by standard molecular replacement techniques, DwL was found to be a tetramer based on PISA analysis, and composed by two metal-binding sites per monomer and loops

Thaiz Batista Azevedo Rangel; Bruno Anderson Matias Rocha; Gustavo Arruda Bezerra; Ana Maria Sampaio Assreuy; Alana de Freitas Pires; Antonia Sâmia Fernandes do Nascimento; Maria Julia Barbosa Bezerra; Kyria Santiago do Nascimento; Celso Shiniti Nagano; Alexandre Holanda Sampaio; Karl Gruber; Plínio Delatorre; Patrícia Machado Bueno Fernandes; Benildo Sousa Cavada

110

A novel crystal growth technique from the melt: Levitation-Assisted Self-Seeding Crystal Growth Method  

NASA Astrophysics Data System (ADS)

A novel melt crystal growth technique was developed and applied for growing bulk In2O3 single crystals. In this new method the In2O3 starting material inside an inductively heated metal crucible is subjected to a controlled decomposition in such a way that a certain amount of free metallic indium forms. As a result, the electromagnetic field from an RF coil couples also to the In2O3 starting material, in addition to the metal crucible, which facilitates the melting. Liquid In2O3 has good electrical conductivity so that eddy currents are induced in the melt close to the crucible wall. This in turn induces a counter magnetic field that ultimately leads to levitation of a portion of the molten In2O3. The amount of the levitated material depends on the mutual RF coil-crucible position, their configurations as well as other components of a growth furnace. A consequence of the partial levitation of In2O3 melt is the formation of a liquid neck between the levitated and the quiescent melt portions. This neck is crucial as it acts as a seed during the crystallization process. The neck can be further shaped by controlled overheating or soaking. By cooling down, two single crystals are formed on the opposite sides of the seed. We named this new crystal growth technique “Levitation-Assisted Self-Seeding Crystal Growth Method”. It is in principle applicable to any oxides whose melts are electrically conductive. Thanks to this method we have successfully grown truly bulk In2O3 single crystals from the melt for the first time worldwide.

Galazka, Zbigniew; Uecker, Reinhard; Fornari, Roberto

2014-02-01

111

Microrobotic Streak Seeding For Protein Crystal Atanas Georgiev1, Peter K. Allen1, Ting Song2, Andrew Laine2, William Edstrom3, John Hunt3  

E-print Network

Microrobotic Streak Seeding For Protein Crystal Growth Atanas Georgiev1, Peter K. Allen1, Ting Song to crystallographers as streak seeding ­ it is used to entice certain protein crystals to grow. Our system features the throughput in crystal production. The focus here is on the task known by crystallographers as streak seeding

Georgiev, Atanas

112

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

113

Top-seeded solution growth of CLBO crystals  

NASA Astrophysics Data System (ADS)

CsLiB6O10 (CLBO) is a highly promising nonlinear optical material. However, its application is limited due to the difficulties in producing optically uniform CLBO crystals. High viscosity of Cs2O-Li2O-B2O3 melt retards both natural and forced convection in the melt. With the goal to improve the heat and mass transfer in the melt, the study of crystallization in the Cs2O-Li2O- B2O3-MoO3 system was carried out. The CLBO crystals 60 X 40 X 20 mm in size grown using LiCsMoO4 as a solvent were found to be free of cracks, bubbles, and inclusions. Nonlinear optical parameters and physical properties of those crystals turned out to be similar to those reported before. Mohs' hardness is 5.5, transparency window ranges from 0.18 to 2.7 micrometers , nonlinear coefficient is 1 pm/V, angular and spectral bandwidth of synchronism are 0.5 mrad-m and 0.1 nm-cm. The walk-off angle is 2 degree(s) at 0.53 micrometers . The nonlinear optical elements for the 4th harmonic of Nd:YAG laser were fabricated and tested.

Pylneva, Ninel A.; Kononova, Nadegda G.; Yurkin, Alexander M.; Kokh, Alexandr E.; Bazarova, Gibzema G.; Danilov, Victor I.; Lisova, Irina A.; Tsirkina, Natalia L.

1999-05-01

114

Pulse-compression down to 20 fs using a photonic crystal fiber seeded by a diode-pumped  

E-print Network

Pulse-compression down to 20 fs using a photonic crystal fiber seeded by a diode-pumped Yb-dispersion photonic crystal fiber in order to optimize the pulse duration and pulse shape. 20.3-fs pulses centered at 1070 nm have been produced using a diode-pumped system based on Yb:SYS crystal. The limitations

Paris-Sud XI, Université de

115

Diffusion of Ca and Mg in Calcite  

SciTech Connect

The self-diffusion of Ca and the tracer diffusion of Mg in calcite have been experimentally measured using isotopic tracers of {sup 25}Mg and {sup 44}Ca. Natural single crystals of calcite were coated with a thermally-sputtered oxide thin film and then annealed in a CO{sub 2} gas at one atmosphere total pressure and temperatures from 550 to 800 C. Diffusion coefficient values were derived from the depth profiles obtained by ion microprobe analysis. The resultant activation energies for Mg tracer diffusion and Ca self-diffusion are respectively: E{sub a}(Mg) = 284 {+-} 74 kJ/mol and E{sub a}(Ca) = 271 {+-} 80 kJ/mol. For the temperature ranges in these experiments, the diffusion of Mg is faster than Ca. The results are generally consistent in magnitude with divalent cation diffusion rates obtained in previous studies and provide a means of interpreting the thermal histories of carbonate minerals, the mechanism of dolomitization, and other diffusion-controlled processes. The results indicate that cation diffusion in calcite is relatively slow and cations are the rate-limiting diffusing species for the deformation of calcite and carbonate rocks. Application of the calcite-dolomite geothermometer to metamorphic assemblages will be constrained by cation diffusion and cooling rates. The direct measurement of Mg tracer diffusion in calcite indicates that dolomitization is unlikely to be accomplished by Mg diffusion in the solid state but by a recrystallization process.

Cygan, R.T.; Fisler, D.K.

1999-02-10

116

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

NASA Astrophysics Data System (ADS)

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 1100 nm 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 3.8 mJ was studied. The grown crystal belongs to soft material studied by hardness test.

Sadhasivam, S.; Rajesh, Narayana Perumal

2014-09-01

117

Molecular Structure of Calcite  

NSDL National Science Digital Library

Calcite is an essential mineral in limestone and marble which are used in the building, steel, chemical, and glass industries. It is found in abundance on the earth. Calcite was first produced in translucent ("Iceland Spar") form in the seventeenth century for optical uses. In 1928, William Nicol used it for Polaroid Sunglasses in an effort to deflect the sunlight. Today, calcite has a large number of uses: optical and crystallography research; as a component of animal feed, antacids, statues, and dough strengthener; in the production of paper and photography; and to make mortar, cement, concrete and asphalt.

2002-08-14

118

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

Microsoft Academic Search

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

Xuechu CHEN; Hainan KONG; Deyi WU; Xinze WANG; Yongyong LIN

2009-01-01

119

Structural investigation of the seeding process for physical vapor transport growth of 4H-SiC single crystals  

NASA Astrophysics Data System (ADS)

Structural investigation of the seeding process for the physical vapor transport (PVT) growth of 4H-SiC single crystals was conducted by high-resolution x-ray diffraction (HRXRD) and synchrotron x-ray topography. Characteristic lattice plane bending behavior was observed in the near-seed regions of the grown crystals. The bending of the (112¯0) lattice plane was localized near the seed/grown crystal interface, and the (0001) basal plane bent convexly in the growth direction near the interface, indicative of the insertion of extra-half planes pointing toward the growth direction during the seeding process for PVT growth. This study discusses a possible mechanism for the observed lattice plane bending and sheds light on defect formation processes during the PVT growth of 4H-SiC single crystals.

Ohtani, Noboru; Ohshige, Chikashi; Katsuno, Masakazu; Fujimoto, Tatsuo; Sato, Shinya; Tsuge, Hiroshi; Ohashi, Wataru; Yano, Takayuki; Matsuhata, Hirofumi; Kitabatake, Makoto

2014-01-01

120

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

121

Isolation, purification, crystallization and preliminary crystallographic studies of chitinase from tamarind (Tamarindus indica) seeds  

PubMed Central

A protein with chitinase activity has been isolated and purified from tamarind (Tamarindus indica) seeds. N-terminal amino-acid sequence analysis of this protein confirmed it to be an ?34?kDa endochitinase which belongs to the acidic class III chitinase family. The protein was crystallized by the vapour-diffusion method using PEG 4000. The crystals belonged to the tetragonal space group P41, with two molecules per asymmetric unit. Diffraction data were collected to a resolution of 2.6?Å. PMID:19342775

Patil, Dipak N.; Datta, Manali; Chaudhary, Anshul; Tomar, Shailly; Kumar Sharma, Ashwani; Kumar, Pravindra

2009-01-01

122

Research paper Nanostructured calcite precipitated under hydrothermal conditions in the presence  

E-print Network

Research paper Nanostructured calcite precipitated under hydrothermal conditions in the presence-L-cystine Crystallographic incorporation into calcite Selenium Selenium is an important trace metalloid, whose global cycle associated with carbonate phases, with Se being gener- ally incorporated as an impurity in calcite crystals

123

PRIMARY CALCITE Cfluid << Csolid ~  

E-print Network

to foraminfer nannofossil ooze nannofossil chalk to foraminfer nannofossil chalk nannofossil chalk to foraminfer nannofossil chalk Determinng the fractionation factor between Ca in calcite and Ca in solu- tion is important

Fantle, Matthew

124

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

SciTech Connect

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

125

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

126

The Temperature Dependence of Calcite Growth Rates: An Essential Step Toward Robust Biogenic Carbonate Paleothermometry  

NASA Astrophysics Data System (ADS)

The critical need for paleoclimate proxies independent of ocean salinity and polar ice volume has directed much attention to biogenic carbonate minerals as hosts of chemical records of formation temperatures. The minor and trace element signatures in these carbonates are complex products of inorganic and biological, or \\`{}vital,\\'{} controls. In order to interpret these records accurately and unambiguously, it is essential to deconvolve the thermodynamic, kinetic, and biological influences on minor and trace element incorporation in calcite, particularly over the range of temperatures relevant to natural waters. Toward this end, we present well-characterized, in situ, molecular scale measurements of calcite growth rates as a function of temperature. This work yields precise information about the thermodynamic and kinetic effects of temperature on calcite precipitation, which is critical for eventual assessment of the biological processes that also contribute to the relationships between biomineral compositions and conditions of formation. We used fluid cell atomic force microscopy (AFM) to observe the flow of monomolecular steps on calcite growth hillocks. This technique enables direct, microscopic measurement of growth rates of individual, 3.1Å steps on calcite seed crystals. Near-equilibrium growth solutions with supersaturation values (ln [aCa2+ x aCO32-/Ksp]) ranging from 0.9-1.7 were cooled or heated with a Peltier device and pumped continuously through the fluid cell chamber at 20°C or 30°C for each experiment. Temperature was monitored at the exit port of the fluid cell and remained within 1.5°C of the target temperature. Experimental results and preliminary geochemical modeling show that, although the degree of supersaturation changes little as a function of temperature, both obtuse (positive) and acute (negative) angle steps migrate nearly twice as quickly at 30°C as at 20°C, suggesting that the kinetic effects of changing temperature dominate over thermodynamic effects within the range of conditions studied thus far. Further work will span the range of temperatures relevant to natural waters and will define precisely the relationships between temperature, supersaturation, and crystal growth rates. This study represents an important step toward development of robust and accurate paleothermometric techniques based on biogenic calcite. Once we have established inorganic baseline information about calcite growth as a function of temperature, we will continue with measurement of the extent and distribution of impurity incorporation with temperature variation. This in turn will set the stage for comparison with biogenic samples to precisely constrain information about paleoclimates and global cycling of carbon.

Wasylenki, L. E.; Dove, P. M.; de Yoreo, J. J.

2002-12-01

127

Demonstration of Single-Crystal Self-Seeded Two-Color X-Ray Free-Electron Lasers  

NASA Astrophysics Data System (ADS)

A scheme for generating two simultaneous hard-x-ray free-electron laser pulses with a controllable difference in photon energy is described and then demonstrated using the self-seeding setup at the Linac Coherent Light Source (LCLS). The scheme takes advantage of the existing LCLS equipment, which allows two independent rotations of the self-seeding diamond crystal. The two degrees of freedom are used to select two nearby crystal reflections, causing two wavelengths to be present in the forward transmitted seeding x-ray pulse. The free-electron laser system must support amplification at both desired wavelengths.

Lutman, A. A.; Decker, F.-J.; Arthur, J.; Chollet, M.; Feng, Y.; Hastings, J.; Huang, Z.; Lemke, H.; Nuhn, H.-D.; Marinelli, A.; Turner, J. L.; Wakatsuki, S.; Welch, J.; Zhu, D.

2014-12-01

128

Demonstration of single-crystal self-seeded two-color x-ray free-electron lasers.  

PubMed

A scheme for generating two simultaneous hard-x-ray free-electron laser pulses with a controllable difference in photon energy is described and then demonstrated using the self-seeding setup at the Linac Coherent Light Source (LCLS). The scheme takes advantage of the existing LCLS equipment, which allows two independent rotations of the self-seeding diamond crystal. The two degrees of freedom are used to select two nearby crystal reflections, causing two wavelengths to be present in the forward transmitted seeding x-ray pulse. The free-electron laser system must support amplification at both desired wavelengths. PMID:25554887

Lutman, A A; Decker, F-J; Arthur, J; Chollet, M; Feng, Y; Hastings, J; Huang, Z; Lemke, H; Nuhn, H-D; Marinelli, A; Turner, J L; Wakatsuki, S; Welch, J; Zhu, D

2014-12-19

129

Seeded growth in a soft lined crucible: Application to phosphorus doped optical germanium single crystals  

NASA Astrophysics Data System (ADS)

Phosphorus doped (n-type) germanium crystals have been grown by a seeded vertical gradient freeze method using a graphite crucible lined with soft graphite felt. The axial dopant distribution has been determined using the electrical resistivity and Hall effect measurements and found to deviate significantly from the normal freezing behaviour. This indicates that mixing in the melt is reduced due to the low temperature gradients in the growth system. As a result an EPD of 5 X 10 2 to 10 3 cm -2 on the (111) surface was found, which is almost by an order of magnitude lower than that of large diameter CZ pulled crystals. The homogeneity of the refractive index at 10.6 ?m and the optical imaging quality (estimated from the dispersion of the Modulation Transfer Function) have been found comparable to the best CZ crystals. Further improvement of the growth method and its use for other materials is also suggested.

Azoulay, M.; Gafni, G.; Roth, M.

1986-12-01

130

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

131

Seeded growth of AlN bulk crystals in m-and c-orientation , R. Collazo a,, R.F. Dalmau b  

E-print Network

Seeded growth of AlN bulk crystals in m- and c-orientation P. Lu a , R. Collazo a,Ã?, R.F. Dalmau b). The single crystalline m- and c-plane seeds were cut from freestanding AlN single crystals. AlN boules 12 mm-ray topography A2. Growth from vapor A2. Seeded vapor growth B1. Nitrides a b s t r a c t Seeded growth of Al

Dietz, Nikolaus

132

Extracellular matrix protein in calcified endoskeleton: a potential additive for crystal growth and design  

NASA Astrophysics Data System (ADS)

In this study, we demonstrate a key function of extracellular matrix proteins (ECMPs) on seed crystals, which are isolated from calcified endoskeletons of soft coral and contain only CaCO 3 without any living cells. This is the first report that an ECMP protein extracted from a marine organism could potentially influence in modifying the surface of a substrate for designing materials via crystallization. We previously studied with the ECMPs from a different type of soft coral ( Sinularia polydactyla) without introducing any seed crystals in the process , which showed different results. Thus, crystallization on the seed in the presence of ECMPs of present species is an important first step toward linking function to individual proteins from soft coral. For understanding this interesting phenomenon, in vitro crystallization was initiated in a supersaturated solution on seed particles of calcite (1 0 4) with and without ECMPs. No change in the crystal growth shape occurred without ECMPs present during the crystallization process. However, with ECMPs, the morphology and phase of the crystals in the crystallization process changed dramatically. Upon completion of crystallization with ECMPs, an attractive crystal morphology was found. Scanning electron microscopy (SEM) was utilized to observe the crystal morphologies on the seeds surface. The mineral phases of crystals nucleated by ECMPs on the seeds surface were examined by Raman spectroscopy. Although 50 mM Mg 2+ is influential in making aragonite in the crystallization process, the ECMPs significantly made calcite crystals even when 50 mM Mg 2+ was present in the process. Crystallization with the ECMP additive seems to be a technically attractive strategy to generate assembled micro crystals that could be used in crystals growth and design in the Pharmaceutical and biotechnology industries.

Azizur Rahman, M.; Fujimura, Hiroyuki; Shinjo, Ryuichi; Oomori, Tamotsu

2011-06-01

133

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

134

Sorption and desorption of arsenate and arsenite on calcite  

NASA Astrophysics Data System (ADS)

The adsorption and desorption of arsenate (As(V)) and arsenite (As(III)) on calcite was investigated in a series of batch experiments in calcite-equilibrated solutions. The solutions covered a broad range of pH, alkalinity, calcium concentration and ionic strength. The initial arsenic concentrations were kept low (<33 ?M) to avoid surface precipitation. The results show that little or no arsenite sorbs on calcite within 24 h at an initial As concentration of 0.67 ?M. In contrast, arsenate sorbs readily and quickly on calcite. Likewise, desorption of arsenate from calcite is fast and complete within hours, indicating that arsenate is not readily incorporated into the calcite crystal lattice. The degree of arsenate sorption depends on the solution chemistry. Sorption increases with decreasing alkalinity, indicating a competition for sorption sites between arsenate and (bi)carbonate. pH also affects the sorption behavior, likely in response to changes in arsenate speciation or protonation/deprotonation of the adsorbing arsenate ion. Finally, sorption is influenced by the ionic strength, possibly due to electrostatic effects. The sorption of arsenate on calcite was modeled successfully using a surface complexation model comprising strong and weak sites. In the model, the adsorbing arsenate species were HAsO4- and CaHAsO40. The model was able to correctly predict the adsorption of arsenate in the wide range of calcite-equilibrated solutions used in the batch experiments and to describe the non-linear shape of the sorption isotherms. Extrapolation of the experimental results to calcite bearing aquifers suggests a large variability in the mobility of arsenic. Under reduced conditions, arsenite, which does not sorb on calcite, will dominate and, hence, As will be highly mobile. In contrast, when conditions are oxidizing, arsenate is the predominant species and, because arsenate adsorbs strongly on calcite, As mobility will be significantly retarded. The estimated retardation factors for arsenate in carbonate aquifers range from 25 to 200.

Sø, Helle U.; Postma, Dieke; Jakobsen, Rasmus; Larsen, Flemming

2008-12-01

135

Seed Crystals.  

ERIC Educational Resources Information Center

Grapples with the issues that face writers who take seriously both their artistic and social responsibilities. Addresses the widespread denigration of social awareness that goes along with labeling something as "PC" (politically correct). (SR)

Rosen, Michael J.

1995-01-01

136

4, 961991, 2007 foraminiferal calcite  

E-print Network

BGD 4, 961­991, 2007 Copper in foraminiferal calcite L. J. de Nooijer et al. Title Page Abstract in foraminiferal calcite: results from culturing experiments L. J. de Nooijer, G. J. Reichart, A. Due Copper in foraminiferal calcite L. J. de Nooijer et al. Title Page Abstract Introduction Conclusions

Paris-Sud XI, Université de

137

Single-contact pressure solution creep on calcite monocrystals  

E-print Network

Pressure solution creep rates and interface structures have been measured by two methods on calcite single crystals. In the first kind of experiments, calcite monocrystals were indented at 40 degrees C for six weeks using ceramic indenters under stresses in the 50-200 MPa range in a saturated solution of calcite and in a calcite-saturated aqueous solution of NH4Cl. The deformation (depth of the hole below the indenter) is measured ex-situ at the end of the experiment. In the second type of experiment, calcite monocrystals were indented by spherical glass indenters for 200 hours under stresses in the 0-100 MPa range at room temperature in a saturated aqueous solution of calcite. The displacement of the indenter was continuously recorded using a specially constructed differential dilatometer. The experiments conducted in a calcite-saturated aqueous solution of NH4Cl show an enhanced indentation rate owing to the fairly high solubility of calcite in this solution. In contrast, the experiments conducted in a calc...

Zubtsov, Sergei; Gratier, Jean-Pierre; Dysthe, Dag; Traskine, Vladimir

2005-01-01

138

Influence of temperature on the composition of magnesian calcite overgrowths precipitated from seawater  

Microsoft Academic Search

A constant disequilibrium technique was used to determine the composition of magnesian calcite overgrowths precipitated on pure calcite seeds from artificial seawater at 5, 25 and 40°C. The amount of magnesium incorporated in the overgrowths at a given temperature is independent of the precipitation rate over a wide range of saturation states and is believed to correspond to a composition

Alfonso Mucci

1987-01-01

139

Crystal structure of Korean pine (Pinus koraiensis) 7S seed storage protein with copper ligands.  

PubMed

The prevalence of food allergy has increased in recent years, and Korean pine vicilin is a potential food allergen. We have previously reported the crystallization of Korean pine vicilin purified from raw pine nut. Here we report the isolation of vicilin mRNA and the crystal structure of Korean pine vicilin at 2.40 Å resolution. The overall structure of pine nut vicilin is similar to the structures of other 7S seed storage proteins and consists of an N-terminal domain and a C-terminal domain. Each assumes a cupin fold, and they are symmetrically related about a pseudodyad axis. Three vicilin molecules form a doughnut-shaped trimer through head-to-tail association. Structure characterization of Korean pine nut vicilin unexpectedly showed that, in its native trimeric state, the vicilin has three copper ligands. Sequence alignments suggested that the copper-coordinating residues were conserved in winter squash, sesame, tomato, and several tree nuts, while they were not conserved in a number of legumes, including peanut and soybean. Additional studies are needed to assess whether the copper-coordinating property of vicilins has a biological function in the relevant plants. The nutritional value of this copper-coordinating protein in tree nuts and other edible seeds may be worth further investigations. PMID:24328105

Jin, Tengchuan; Wang, Yang; Chen, Yu-Wei; Fu, Tong-Jen; Kothary, Mahendra H; McHugh, Tara H; Zhang, Yuzhu

2014-01-01

140

Interaction of alcohols with the calcite surface.  

PubMed

A clearer understanding of calcite interactions with organic molecules would contribute to a range of fields including harnessing the secrets of biomineralisation where organisms produce hard parts, increasing oil production from spent reservoirs, remediating contaminated soils and drinking water aquifers and improving manufacturing methods for industrial products such as pigments, soft abrasives, building materials and optical devices. Biomineralisation by some species of blue green algae produces beautifully elaborate platelets of calcite where the individual crystals are of nanometer scale. Controlling their growth requires complex polysaccharides. Polysaccharide activity depends on the functionality of OH groups, so to simplify the system in order to get closer to a molecular level understanding, we investigated the interaction of OH from a suite of alcohols with clean, freshly cleaved calcite surfaces. X-ray photoelectron spectroscopy (XPS) provided binding energies and revealed the extent of surface coverage. Molecular dynamics (MD) simulations supplemented with information about molecule ordering, orientation and packing density. The results show that all alcohols studied bond with the calcite surface through the OH group, with their carbon chains sticking away in a standing-up orientation. Alcohol molecules are closely packed and form a well-ordered monolayer on the surface. PMID:25533590

Bovet, N; Yang, M; Javadi, M S; Stipp, S L S

2015-02-01

141

Precipitation of ordered dolomite via simultaneous dissolution of1 calcite and magnesite: New experimental insights into an old2  

E-print Network

1 Precipitation of ordered dolomite via simultaneous dissolution of1 calcite and magnesite: New that ordered dolomite can be precipitated via24 simultaneous dissolution of calcite and magnesite under; High-carbonate alkalinity; Magnesite; Calcite; Crystal growth;46 Hydrothermal systems.47 48 insu

Paris-Sud XI, Université de

142

Stable (H, O, C) and noble-gas (He and Ar) isotopic compositions from calcite and fluorite in the Speewah Dome, Kimberley Region, Western Australia: implications for the conditions of crystallization and evidence for the influence of crustal-mantle fluid mixing  

NASA Astrophysics Data System (ADS)

In this study, the C-O-isotopic data from calcite at Yungul and Wilmott (Speewah. Western-Australia) are integrated with microthermometry, H2O-, CO2-content and H-He-Ar-isotopic data from fluid inclusions in genetically related calcite and fluorite to map the origin and crystallization paths of the fluids. In addition to the hydrogen isotopic compositions of fluid inclusions in fluorite, oxygen isotopic compositions were also determined by cavity ring-down spectroscopy. The geochemical data suggest mixing of a CO2-dominated mantle fluid and a H2O-domintated crustal brine. The fluid produced by this mixing is characterized by radiogenic (crustal-like) 3He/4He ratios, crustal-like ?D values, relatively high salinity (19 - 24wt.% NaCl eq.), moderate homogenization temperatures (150 - 450 °C) and mantle-like CO2/3He ratios. Moreover, the large isotopic and elemental variations found in calcite indicate that its formation was accompanied by an extensive degassing (open system) leading to a decrease in ?D and an increase in the CO2/3He values relative to the starting fluid composition. This degassing is consistent with the fluidal- and breccia-like texture of calcite observed in the field. In contrast, the fluorite which has coarse-grained banded to vughy textures formed in a passive aqueous system. Apparently the fluid that formed the fluorite has the same origin as the calcite, but the higher water content and the more radiogenic 3He/4He ratios reflect a greater involvement of crustal fluids. The historical description of the calcite-fluorite system in the Speewah area as "carbonatite" is now considered inappropriate because there is no evidence that crystallization is dominated by magmatic processes.

Czuppon, Gy; Ramsay, R. R.; Özgenc, I.; Demény, A.; Gwalani, L. G.; Rogers, K.; Eves, A.; Papp, L.; Palcsu, L.; Berkesi, M.; Downes, P. J.

2014-12-01

143

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

144

1 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com Brittlestar-Inspired Microlens Arrays Made of Calcite  

E-print Network

-Inspired Microlens Arrays Made of Calcite Single Crystals Xiaozhou Ye, Fei Zhang, Yurong Ma, and Limin Qi] As a typical linearly birefringent crystal, calcite has been widely used for control and charac- terization of the polarization states of light,[14,24,25] but the controllable fabrication of MLAs built from calcite single

Qi, Limin

145

Dislocation characterization in crystals of potash alum grown by seeded solution growth under conditions of low supersaturation  

NASA Astrophysics Data System (ADS)

An analysis has been carried out of the genesis and character of growth dislocations present in all growth sectors of single crystals of potash alum. The crystals, grown from seeded solutions by the temperature lowering method under conditions of low supersaturation, presented the well-developed forms: {111} dominant, {100} and {110}. Growth dislocations formed predominately during refacetting of the edges and corners of the seed, rounded during preparation and insertion into the supersaturated solution. From here they become refracted into the {111} sectors which proved to be the most defective. Smaller numbers of dislocations form at the {111}, {100} and {110} seed interfaces and propagate in these sectors. In crystals of inferior quality, a number of inclusions were found predominantly in the fast growing {100} sectors which become the source of additional dislocations. Dislocations present in the original seed did not propagate across the interface into the developing crystal. Dislocations of all characters were observed. The principal Burgers vectors were found to be <100>, <110> and <111>.

Bhat, H. L.; Risti?, R. I.; Sherwood, J. N.; Shripathi, T.

1992-08-01

146

Sulfated Macromolecules as Templates for Calcite Nucleation and Growth  

NASA Astrophysics Data System (ADS)

Mineralization of egg and seashells is controlled by an intimate association of inorganic materials with organic macromolecules. Among them, particular polyanionic sulfated macromolecules referred to as proteoglycans have been described to be involved in the calcification of these biominerals. The sulfated moieties of the proteoglycans are part of polymer chains constituted of building-blocks of disaccharide units, referred to as sulfated glycosaminoglycans (GAGs), which are covalently attached to a protein core. By using a sitting drop crystallization assay under controlled conditions of time, pH and reactants concentration, we have tested several sulfated and non-sulfated GAGs (i.e.: dermatan and keratan sulfate, hyaluronic acid and heparin), differing in their sulfonate and carboxylate degree and pattern, in their ability to modify calcium carbonate crystal morphology as observed under scanning electron microscopy. Without the addition of GAGs, regular \\{104\\} rhombohedral calcite crystals were obtained. When hyaluronic acid (HA), a non-sulfated but carboxylated GAG, was added, 20 mm long piles of unmodified calcite crystals were observed. When desulfated dermatan, which is an epimeric form of HA but shorter polymer, having their carboxylate groups in an inverted configuration, was added, isolated rhombohedral \\{104\\} calcite crystals showing rounded corners with planes oriented parallel to the c axis were observed. When dermatan sulfated was added, isolated calcite crystals exhibit a columnar morphology as a \\{hk0\\} cylinder with three \\{104\\} faces forming a cap at both ends. Heparin activity depends on the fraction added. Fast-moving heparin fraction (FM), is an undersulfated, low-molecular-weight heterogeneous polymer, while slow-moving heparin fraction (SM) is an high-molecular-weight homogeneous polymer rich in trisulfated-disaccharide units. When FM was added, isolated calcite crystals displayed rhombohedrical \\{104\\} faces but flat corners of \\{111\\} faces. The addition of the hypersulfated heparin SM induce the formation of large rosette-like aggregated calcite crystals, where the majority of the \\{104\\} faces appeared not to be lost, although aggregation is done by different kind of faces. It is concluded that, the variation of the sulfate and carboxylate content and configuration drastically changed the morphology of the calcite crystals. The production of calcite particles with defined morphologies could be interesting for the design of novel materials with desirable shape- and texture-depending properties. Granted by FONDAP 11980002.

David, M.; Passalacqua, K.; Neira, A. C.; Fernandez, M. S.

2003-12-01

147

Oxygen isotope fractionation in synthetic magnesian calcite  

NASA Astrophysics Data System (ADS)

Mg-bearing calcite was precipitated at 25°C in closed system free-drift experiments from solutions containing NaHCO 3, CaCl 2 and MgCl 2. The chemical and isotope composition of the solution and precipitate were investigated during time course experiments of 24-h duration. Monohydrocalcite and calcite precipitated early in the experiments (<8 h), while Mg-calcite was the predominant precipitate (>95%) thereafter. Solid collected at the end of the experiments displayed compositional zoning from pure calcite in crystal cores to up to 23 mol% MgCO 3 in the rims. Smaller excursions in Mg were superimposed on this chemical record, which is characteristic of oscillatory zoning observed in synthetic and natural solid-solution carbonates of differing solubility. Magnesium also altered the predominant morphology of crystals over time from the {104} to {100} and {110} growth forms. The oxygen isotope fractionation factor for the magnesian-calcite-water system (as 10 3ln? Mg-cl-H 2O ) displayed a strong dependence on the mol% MgCO 3 in the solid phase, but quantification of the relationship was difficult due to the heterogeneous nature of the precipitate. Considering only the Mg-content and ? 18O values for the bulk solid, 10 3ln? Mg-cl-H 2O increased at a rate of 0.17 ± 0.02 per mol% MgCO 3; this value is a factor of three higher than the single previous estimate (Tarutani T., Clayton R.N., and Mayeda T. K. (1969) The effect of polymorphims and magnesium substitution on oxygen isotope fractionation between calcium carbonate and water. Geochim. Cosmochim. Acta 33, 987-996). Nevertheless, extrapolation of our relationship to the pure calcite end member yielded a value of 27.9 ± 0.02, which is similar in magnitude to published values for the calcite-water system. Although no kinetic effect was observed on 10 3ln? Mg-cl-H 2O for precipitation rates that ranged from 10 3.21 to 10 4.60 ?mol · m -2 · h -1, it was impossible to disentangle the potential effect(s) of precipitation rate and Mg-content on 10 3ln? Mg-cl-H 2O due to the heterogeneous nature of the solid. The results of this study suggest that paleotemperatures inferred from the ? 18O values of high magnesian calcite (>10 mol% MgCO 3) may be significantly underestimated. Also, the results underscore the need for additional experiments to accurately characterize the effect of Mg coprecipitation on the isotope systematics of calcite from a chemically homogeneous precipitate or a heterogeneous material that is analyzed at the scale of chemical and isotopic zonation.

Jiménez-López, Concepción; Romanek, Christopher S.; Huertas, F. Javier; Ohmoto, Hiroshi; Caballero, Emilia

2004-08-01

148

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

149

Amorphous Calcium Carbonate Transforms into Calcite during Sea Urchin Larval Spicule Growth  

Microsoft Academic Search

Sea urchin larvae form an endoskeleton composed of a pair of spicules. For more than a century it has been stated that each spicule comprises a single crystal of the CaCO3 mineral, calcite. We show that an additional mineral phase, amorphous calcium carbonate, is present in the sea urchin larval spicule, and that this inherently unstable mineral transforms into calcite

Elia Beniash; Joanna Aizenberg; Lia Addadi; Stephen Weiner

1997-01-01

150

Dynamic crystallization of cocoa butter. I. characterization of simple lipids in rapid- and slow-nucleating cocoa butters and their seed crystals  

Microsoft Academic Search

Six cocoa butters with different crystallization induction times and their seed crystals were analyzed for simple lipid composition.\\u000a The rapid-nucleating cocoa butter samples had higher concentrations of 1-palmitoyl-2-oleoyl-3-stearoylglycerol and 1,3-stearoyl-2-oleoylglycerol\\u000a (SOS), and lower concentrations of the diunsaturated triacylglycerols, 1-palmitoyl-2,3-oleoylglycerol and 1-stearoyl-2,3-oleoylglycerol,\\u000a as well as higher stearic acid concentrations within their diacylglycerol fractions when compared to the slow-nucleating samples.\\u000a At the

Siree Chaiseri; Paul S. Dimick

1995-01-01

151

Properties of GdBCO bulk superconductors melt-processed in air using a Mg-doped Nd–Ba–Cu–O generic seed crystal  

Microsoft Academic Search

A Mg-doped Nd–Ba–Cu–O (NdBCO) generic seed crystal has been developed recently for the fabrication of any type of rare earth (RE) based (RE)-Ba–Cu–O single grain bulk superconductor. The new generic seed significantly simplifies the top seeded melt growth (TSMG) process for light RE based (Nd, Sm, Gd or mixed rare earth elements) bulk superconductors in particular. In this paper we

Y Shi; N Hari Babu; K Iida; D A Cardwell

2007-01-01

152

Improvement in microstructure and crystal alignment of ZnO films grown by metalorganic chemical vapor deposition using a seed layer  

Microsoft Academic Search

An epitaxially aligned ZnO nano-seed layer was used to improve the microstructure and crystal alignment in metalorganic chemical vapor deposited ZnO films on Al2O3 (0 0 0 1) substrates. Comparative investigations were performed on the properties of the ZnO films grown with and without the seed layer. The ZnO film grown directly on the substrate without applying the seed layer

Jae Young Park; Dong Ju Lee; Byung-Teak Lee; Jong Ha Moon; Sang Sub Kim

2005-01-01

153

Improvement in microstructure and crystal alignment of ZnO films grown by metalorganic chemical vapor deposition using a seed layer  

Microsoft Academic Search

An epitaxially aligned ZnO nano-seed layer was used to improve the microstructure and crystal alignment in metalorganic chemical vapor deposited ZnO films on Al2O3 (0001) substrates. Comparative investigations were performed on the properties of the ZnO films grown with and without the seed layer. The ZnO film grown directly on the substrate without applying the seed layer shows an irregular,

Jae Young Park; Dong Ju Lee; Byung-Teak Lee; Jong Ha Moon; Sang Sub Kim

2005-01-01

154

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

155

Development of a generic seed crystal for the fabrication of large grain (RE)–Ba–Cu–O bulk superconductors  

Microsoft Academic Search

The critical current density, Jc, irreversibility field, Birr, and magnetic field trapping ability of (LRE)–Ba–Cu–O bulk superconductors, where LRE is a light rare earth element such as Nd, Sm, Eu and Gd, are generally superior to those of the more common melt-processed Y–Ba–Cu–O (YBCO). The lack of availability of a suitable seed crystal to grow large, single grain (LRE)–Ba–Cu–O superconductors

Y Shi; N Hari Babu; D A Cardwell

2005-01-01

156

Indiana is well known for its limestone, but did you know that limestone is made primarily of the mineral calcite (CaCO3)?  

E-print Network

of the mineral calcite (CaCO3)? Most people think of limestone as a nondescript, mostly gray rock, but the mineral calcite can have many different forms and colors. The minerals in limestone usually are tiny and not easily seen with the naked eye. When calcite forms visible crystals, they are often six-sided (hexagonal

Polly, David

157

Characterization of boron incorporation and speciation in calcite and aragonite from co-precipitation experiments under controlled pH, temperature and precipitation rate  

NASA Astrophysics Data System (ADS)

About 20 years ago, the boron isotopic composition of marine carbonates was proposed as a proxy of ancient seawater pH. Since that time, a large body of studies has used boron isotopes in carbonates to reconstruct seawater paleo-pH and atmospheric paleo-CO2 concentration. To date, however, no systematic investigation of the physicochemical parameters that control boron incorporation in calcite and aragonite (pH, temperature, precipitation rate, etc.) has been performed. To fill this gap, we have experimentally investigated the inorganic co-precipitation of boron with calcite and aragonite at 5 and 25 °C in the presence and absence of seed crystals and over the pHNBS range 7.4 < pH < 9.5 in 0.1 or 0.2 M NaCl solutions. The boron partition coefficient, DB, between CaCO3 and the fluid is defined as: DB = {(XB/XCO3)CaCO3}/([B]/[CO32-])fluid} with Xi and [i] standing for the mole fraction and molality of the ith species in the solid and fluid, respectively. DB measured in this study are very small (DB ? 10-3 and ? 10-4 for aragonite and calcite, respectively) and exhibit a strong dependence on the solution pH and the calcium carbonate precipitation rate. High field 11B MAS NMR analyses of the precipitated carbonates show that boron in aragonite is mostly in the form of tetragonal B (? 85%[IV]B) but that both trigonal and tetragonal B are present in calcite. A significant amount of tetragonal boron in calcite may be in non-lattice (defect) sites, in addition to the structural site. The relative abundance of [III]B and [IV]B in calcite is independent of the parent solution pH but appears to decrease with increasing precipitation rate. The change in boron coordination during its incorporation in calcite and its distribution in, at least, two different sites strongly suggest that the mechanisms controlling B incorporation in this mineral are more complex than for aragonite. It follows that calcite-based calibrations may be less reliable than aragonite calibrations for ocean paleo-pH reconstructions.

Mavromatis, Vasileios; Montouillout, Valérie; Noireaux, Johanna; Gaillardet, Jérôme; Schott, Jacques

2015-02-01

158

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. PMID:23989606

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

159

Comparative Study of Nanoscale Surface Structures of Calcite Microcrystals Using FE-SEM, AFM, and TEM  

E-print Network

and millimeter-size cleavage fragments were imaged by three different microscopic techniques: field individual cleavage or flat surface at a time. Key words: atomic force microscopy, calcite crystal growth, Pt

Long, Bernard

160

X-ray interfacial crystallography of water on calcite  

Microsoft Academic Search

The atomic structure of the calcite-water interface has been found using in-situ x-ray interfacial crystallography. This technique determines structure by fitting parameters of an atomic-scale model of the interface to rods of scattering in reciprocal space, called crystal truncation rods (CTRs), that originate from the abrupt change in structure at a crystal surface. Seven allowed and two crystallographically forbidden CTRs

Marc Phillip Geissbuhler

2000-01-01

161

Investigations on the growth of LiB 3O 5 crystal by top-seeded solution growth technique  

NASA Astrophysics Data System (ADS)

Single crystal growth of LiB3O5 (LBO) by top-seeded solution growth technique has been investigated using a boron oxide-rich solution. The X-ray diffraction measurements and differential thermal analysis performed on different samples have revealed the strong dependence of crystal quality on phase purity of the starting charge used for growth and the thermal treatment of the solution. In the case of LiB3O5 charge synthesized by the solid-state sintering method, Li2B4O7 and Li2B8O13 impurity phases are found to be present in significant amount. The results show that the presence of Li2B4O7 in the solution promotes the growth of polycrystalline LBO by providing uncontrolled sites for crystallization.

Sabharwal, S. C.; Tiwari, Babita; Sangeeta

2004-03-01

162

High Birefringence Isothiocyanato Tolane Liquid Crystals Sebastian GAUZA, Haiying WANG, Chien-Hui WEN, Shin-Tson WU, Alexander J. SEED1  

E-print Network

High Birefringence Isothiocyanato Tolane Liquid Crystals Sebastian GAUZA, Haiying WANG, Chien-Hui WEN, Shin-Tson WU, Alexander J. SEED1 and Roman DABROWSKI2 School of Optics/CREOL, University: High birefringence, isothiocyanato tolanes, liquid crystals, polarizability 1. Introduction High

Wu, Shin-Tson

163

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. PMID:22940703

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

2012-01-01

164

Effect of pH on boron coprecipitation by calcite: Further evidence for nonequilibrium partitioning of trace elements  

NASA Astrophysics Data System (ADS)

The influence of pH and concentration on boron coprecipitation by calcite were evaluated under near-equilibrium conditions at 25°C. Calcite was precipitated by adding a metastable polymorph (vaterite or aragonite) to a solution of known boron concentration. This method maintains a nearly constant solution composition during the slow conversion of the metastable polymorph to calcite. Boron uptake in calcite was found to be strongly pH-dependent, increasing two orders of magnitude from pH 8.5 to pH 10.5. Boron incorporation into calcites precipitated from vaterite-saturated solutions was five times greater than in calcites precipitated from aragonite-saturated solutions. Ostensibly, these results suggest that the calcite precipitation rates were not low enough to attain equilibrium partitioning of boron into calcite. However, scanning electron micrograph analyses showed that the prevalent crystal forms of calcite generated from aragonite and those generated from vaterite were distinctly different. The different quantities of boron incorporated into these calcites may reflect different crystal growth mechanisms, consistent with face-dependent, nonequilibrium partitioning of trace elements in calcite. At a constant pH of 9.0, boron uptake increased from less than 15 to over 290 mg/kg CaCO 3 as the solution boron concentration was increased from 5 to 100 mg/kg. Our results agree with those of other investigators, despite differences in solution composition, and calcite precipitation techniques used. The agreement between the studies may be because the crystal growth morphology of the calcite was rhombohedral in both cases.

Hobbs, M. Y.; Reardon, E. J.

1999-04-01

165

Enhancing mechanical properties of calcite by Mg substitutions: An ab initio study  

NASA Astrophysics Data System (ADS)

Arthropoda representing a majority of all known animal species are protected by an exoskeleton formed by their cuticle. The cuticle represents a hierarchically structured multifunctional bio-composite based on chitin and proteins. Some groups like Crustacea reinforce the load-bearing parts of their cuticle with calcite. As the calcite sometimes contains Mg it was speculated that Mg may have a stiffening impact on the mechanical properties of the cuticle. We present a theoretical parameter-free quantum-mechanical study of thermodynamic, structural and elastic properties of Mg-substituted calcite. Our results show that substituting Ca by Mg causes an almost linear decrease in the crystal volume with Mg concentration and of substituted crystals. As a consequence the calcite crystals become stiffer giving rise e.g. to substantially increased bulk moduli.

Elstnerova, Pavlina; Friak, Martin; Hickel, Tilmann; Fabritius, Helge Otto; Lymperakis, Liverios; Petrov, Michal; Raabe, Dierk; Neugebauer, Joerg; Nikolov, Svetoslav; Zigler, Andreas; Hild, Sabine

2011-03-01

166

Synthesis of layer-structured ferroelectric Bi 3NbTiO 9 plate-like seed crystals  

Microsoft Academic Search

Pure bismuth layer-structured ferroelectric Bi3NbTiO9 plate-like seed crystals are synthesized by molten-salt method in NaCl–KCl flux using Bi3NbTiO9 precursor from precipitation. Single phase Bi3NbTiO9 powder is obtained in NaCl–KCl flux at 700 °C for only 0.5 h, which is 200 °C lower than the formation temperature of pure Bi3NbTiO9 Aurivillius phase without chloride salts. The Bi3NbTiO9 platelet synthesized at 900

Ping-Hua Xiang; Yoshiaki Kinemuchi; Koji Watari

2005-01-01

167

Chiral solutes can seed the formation of enantiomorphic domains in a twist-bend nematic liquid crystal.  

PubMed

The twist-bend nematic, an enantiomorphic liquid-crystalline phase, exhibited by the structurally symmetric liquid-crystal dimer CB7CB is induced to form a single domain of uniform handedness, in the bulk, by the addition of the dopant chiral solute (S)-1-phenylethanol. Addition of a nonracemic (or scalemic) mixture of both R and S enantiomers of this solute produced equal volumes of P and M chiral domains for the twist-bend nematic phase. This seeding of the domains in an enantiomorphic nematic conglomerate is revealed using deuterium NMR spectroscopy. PMID:23679359

Emsley, James W; Lesot, Philippe; Luckhurst, Geoffrey R; Meddour, Abdelkrim; Merlet, Denis

2013-04-01

168

Experimental Study of Sr Partitioning into Calcite at Various Linear Growth Rates and Temperatures: Preliminary Results.  

NASA Astrophysics Data System (ADS)

The surface of a crystal in equilibrium with surrounding fluid can have a composition that differs from the bulk crystal. If growth rate of the crystal exceeds a minimum value at which partitioning-equilibrium can be maintained, then the crystal surface composition may be "captured" by the newly-formed lattice. The degree of this entrapment increases with increasing crystal growth rate. Non-equlibrium partitioning of Sr into calcite probably occurs by this entrapment mechanism. Sr and calcite are geochemically significant in understanding the thermal history of the ocean because the substitution of Sr for Ca in calcite is temperature dependent. To improve our understanding of the partitioning of Sr into calcite, we conducted two different types of experiment: 1) calcite growth from Sr-bearing solution with analysis of the crystal cross-section by electron microprobe (bulk crystal-liquid runs); and 2) treatment of calcite cleavage surfaces with Sr-bearing solutions and examination of the top few nm surface layer by X-ray photoelectron spectroscopy (surface-liquid runs). In the series of bulk-liquid experiments crystals were grown by three different procedures: 1) precipitation on glass slide (pre-coated with calcite), where a steady flow of CaCl2 - SrCl2 and Na2CO3 solutions were mixed just before passage through a tube and allowed to drip onto a slide ("cave"-type experiments, ionic strength I=0.01); 2) growth from a CaCl2 - NH4Cl - SrCl2 solution by diffusion of CO2 from an ammonium carbonate source ("drift" experiments, I=0.52); 3) coarsening of small calcite crystals in the CaCO3-SrCO3-NaCl-H2O system at 800-950° C and 0.5-1 kb in a cold seal apparatus. The growth rate of individual crystals was determined by periodic monitoring of crystal size with time or roughly by comparison of final size with duration of the experiment. Surface-liquid experiments were performed by treatment of cleavage surfaces of natural calcite fragments in a Sr(ClO4)2 solution for 1 minute. After treatment the remaining solution was blown out by a stream of nitrogen to preclude the precipitation of Sr phase. We observed that the precipitated calcite crystals can be very different in size even if the runs have the same input rate of calcite components. The cave-type and cold-seal runs yielded 15-40 ? m calcites, but in the drift experiments crystal size varied between 60 ? m and 1 mm. Electron microprobe analysis across the large crystals show that the concentration of Sr is higher in the center and decreases toward the edge. This is probably due to the cube-root dependence of radial growth on the volume change of the growing crystals. Like previous workers who measured bulk uptake of Sr as a function of precipitation rate, we observed that increased growth rate (V, nm/s) enhances Sr uptake into the crystal, raising Kdbulk/liquid=(Sr/Ca)bulk/(Sr/Ca)liquid. Kdbulk/liquid = 0.03 to 0.06 when log(V)=-1.1 to -0.6 at 25° C in the cave-type runs (I=0.01). At higher ionic strength (I=0.52) and T=55° C, Kdbulk/liquid=0.11 to 0.15 when log(V)=-0.6 to 0.4 in the drift experiments. XPS analysis of surface-liquid experiments yielded higher Kdsurface/liquid=(Sr/Ca)surface/(Sr/Ca)liquid values compared with Kdbulk/liquid. This combined evidence supports the idea that Sr is enriched at the calcite surface relative to the bulk crystal during crystal growth.

Gabitov, R. I.; Watson, B. E.

2004-05-01

169

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

PubMed Central

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 C2221, with unit-cell parameters a = 37.2, b = 77.1, c = 129.1?Å. Diffraction data were collected to a resolution of 2.7?Å. 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.; Preeti; Chaudhry, Anshul; Sharma, Ashwani K.; Tomar, ­Shailly; Kumar, Pravindra

2009-01-01

170

Combustion synthesis of rod-like ?-SiAlON seed crystals  

Microsoft Academic Search

Rod-like single-phase crystals of Y-?-SiAlON were synthesized by combustion of Si, Al, ?-Si3N4, SiO2 and Y2O3 powders. SEM observation of crystals, separated by chemical etching (HNO3\\/HF=2:1) followed by ultrasonic agitation in ethanol showed rod-like crystals, assigned to almost pure and well crystallized ?-SiAlON.

Renli Fu; Kexin Chen; Xin Xu; José M. F. Ferreira

2004-01-01

171

Carbon13 fractionation between aragonite and calcite  

Microsoft Academic Search

Aragonite and calcite were precipitated from bicarbonate solutions by slow removal of carbon dioxide at 25°C. Carbon isotope fractionation factors (expressed as 1000 ln ) are: calcite-bicarbonate ion 0.9 ± 0.2; aragonite-bicarbonate ion 2.7 ± 0.2; aragonite-calcite 1.8 ± 0.2. Theoretical calculation of the aragonite-calcite fractionation gives 0.9.

Michael Rubinson; Robert N. Clayton

1969-01-01

172

Is calcite (1014) a chiral surface? Open Questions Is Calcite (1014) a Chiral Surface?  

E-print Network

Is calcite (1014) a chiral surface? Open Questions Is Calcite (1014) a Chiral Surface? Philipp of the most stable calcite (1014) surface is achiral due to a glide plane symmetry,[14] the existence properties of the calcite (1014) surface, unambigu- ously concluding that the bulk-truncated surface

Kühnle, Angelika

173

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

174

5, 123, 2008 Calcite dissolution by  

E-print Network

BGD 5, 1­23, 2008 Calcite dissolution by microzooplankton and copepod grazing A. N. Antia et al of coccolithophorid calcite by microzooplankton and copepod grazing A. N. Antia 1 , K. Suffrian 1 , L. Holste 2 , M. N (aantia@ifm-geomar.de) 1 #12;BGD 5, 1­23, 2008 Calcite dissolution by microzooplankton and copepod grazing

Paris-Sud XI, Université de

175

Infiltration growth of Mg-doped Nd-Ba-Cu-O seed crystals for the fabrication of large grain RE-Ba-Cu-O bulk superconductors  

NASA Astrophysics Data System (ADS)

By employing the infiltration growth (IG) technique, Mg-doped Nd-Ba-Cu-O (NdBCO) seed crystals were successfully prepared through 1 wt% MgO addition both to a Nd4Ba2Cu2O10 (Nd-422) precursor powder and to a liquid source with the composition Nd2O3:CuO:BaCuO2 = 1:6:10. Differential thermal analysis (DTA) results showed that the decomposition temperature of the processed Mg-doped NdBCO crystals increased by about 20?°C compared with the general, Mg-free NdBCO seeds, thus they can be used as generic seed crystals to induce the growth of any RE-Ba-Cu-O (REBCO) single grain. This result is consistent with that observed in melt growth (MG) processed Mg-doped NdBCO crystals. Finally, highly c-axis oriented Gd-Ba-Cu-O (GdBCO) and Y-Ba-Cu-O (YBCO) large grains were successfully grown using the produced seed crystals.

Li, Guo-Zheng; Li, De-Jun; Deng, Xiang-Yun; Deng, Jian-Hua; Yang, Wan-Min

2013-05-01

176

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

177

Integrated Approach for Understanding Impurity Adsorption on Calcite: Mechanisms for Microscale Surface Phenomena  

Microsoft Academic Search

A longstanding goal within the field of environmental geochemistry has been the development of a fundamental understanding of the kinetics that governs the interactions of solution-borne impurities with the calcite mineral surface. Recent dissolution experiments using Mg2+, Mn2+, and Sr2+ have shown distinct differences in the interaction of these three impurity ions with the calcite crystal surface. Because the dissolution

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

2004-01-01

178

Magnesium stable isotope fractionation in marine biogenic calcite and aragonite  

NASA Astrophysics Data System (ADS)

This survey of magnesium stable isotope compositions in marine biogenic aragonite and calcite includes samples from corals, sclerosponges, benthic porcelaneous and planktonic perforate foraminifera, coccolith oozes, red algae, and an echinoid and brachiopod test. The analyses were carried out using MC-ICP-MS with an external repeatability of ±0.22‰ (2SD for ? 26Mg; n = 37), obtained from a coral reference sample (JCp-1). Magnesium isotope fractionation in calcitic corals and sclerosponges agrees with published data for calcitic speleothems with an average ? 26Mg calcite-seawater = -2.6 ± 0.3‰ that appears to be weakly related to temperature. With one exception ( Vaceletia spp.), aragonitic corals and sclerosponges also display uniform Mg isotope fractionations relative to seawater with ? 26Mg biogenic aragonite-seawater = -0.9 ± 0.2. Magnesium isotopes in high-Mg calcites from red algae, echinoids and perhaps some porcelaneous foraminifera as well as in all low-Mg calcites (perforate foraminifera, coccoliths and brachiopods) display significant biological influences. For planktonic foraminifera, the Mg isotope data is consistent with the fixation of Mg by organic material under equilibrium conditions, but appears to be inconsistent with Mg removal from vacuoles. Our preferred model, however, suggests that planktonic foraminifera synthesize biomolecules that increase the energetic barrier for Mg incorporation. In this model, the need to remove large quantities of Mg from vacuole solutions is avoided. For the high-Mg calcites from echinoids, the precipitation of amorphous calcium carbonate may be responsible for their weaker Mg isotope fractionation. Disregarding superimposed biological effects, it appears that cation light isotope enrichments in CaCO 3 principally result from a chemical kinetic isotope effect, related to the incorporation of cations at kink sites. In this model, the systematics of cation isotope fractionations in CaCO 3 relate to the activation energy required for cation incorporation, which probably reflects the dehydration of the cation and the crystal surface and bond formation at the incorporation site. This kinetic incorporation model predicts (i) no intrinsic dependence on growth rate, unless significant back reaction upon slow growth reduces the isotope fractionation towards that characteristic for equilibrium isotope partitioning (this may be observed for Ca isotopes in calcites), (ii) a small decrease of isotope fractionation with increasing temperature that may be amplified if higher temperatures promote back reaction and (iii) a sensitivity to changes in the activation barrier caused by additives such as anions or biomolecules or by the initial formation of amorphous CaCO 3.

Wombacher, F.; Eisenhauer, A.; Böhm, F.; Gussone, N.; Regenberg, M.; Dullo, W.-Chr.; Rüggeberg, A.

2011-10-01

179

The Effect of Preincubation of Seed Crystals of Uric Acid and Monosodium Urate with Undiluted Human Urine to Induce Precipitation of Calcium Oxalate in Vitro: Implications for Urinary  

E-print Network

Background: Previous studies demonstrated that crystals of uric acid (UA) and sodium urate (NaU) can induce the precipitation of calcium oxalate (CaOx) from its inorganic metastable solutions, but similar effects have not been unequivocally shown to occur in urine. The aim of this investigation was to determine whether preincubation of these seeds with urine alter their ability to induce deposition of CaOx from solution and thus provide a possible explanation for discrepancy of results obtained from aqueous inorganic solutions and undiluted urine. Materials and Methods: The effects of commercial seed crystals of UA, NaU and CaOx (6 mg/100 ml) on CaOx crystallization were compared in a solution with the same crystals that had been preincubated for 3 hours with healthy

Stone Formation; Phulwinder K. Grover; Rosemary L. Ryall

2002-01-01

180

Nickel and manganese interaction with calcite  

SciTech Connect

Many divalent metal cations sorb to calcite surfaces and incorporate into calcite to varying degrees. Since calcite may sorb trace elements in the environment, the factors controlling metal-calcite interactions are critical to understanding element cycling. The interaction of divalent metal cations with calcite can be critical to toxic metal immobilization, nutrient cycling, interpretation of past redox conditions, tracing fluid flow, for example. Sorption of Ni and Mn on calcite surfaces was studied by Zachara et al.. At any particular pH, the sorption of Mn on calcite was greater than Ni. This was attributed in part to the similarity of divalent Mn and Ca with respect to ion size. Although direct spectroscopic evidence was not available, sorption/desorption results suggested that Mn quickly forms a surface precipitate or solid solution while Ni forms a hydrated surface complex that may incorporate into calcite much more slowly via recrystallization. Because Mn(II) ionic radius is similar to that of Ca(II) (0.80 versus 1.0{angstrom}), and because MnCO{sub 3} has a structure similar to calcite, it is likely that Mn can substitute directly for Ca in the calcite structure. The ionic radius of Ni(II) is significantly smaller (0.69{angstrom}) and Ni(OH){sub 2} precipitation is likely to be favored in most systems. For Ni, direct substitution for Ca is less likely or may require more significant calcite lattice deformation.

Doner, H; Zavarin, M

1999-08-09

181

JOURNAL DE PHYSIQUE Colloque C 3, supplment au no 7-8, Tome 27, juillet-aot 1966, page C 3-137 DISLOCATIONS DE MACLE DANS LA CALCITE  

E-print Network

-137 DISLOCATIONS DE MACLE DANS LA CALCITE INTERFÃ?RENCESENTRE LES CHAMPS D'ONDES CRÃ?Ã?S A LA TRAVERSÃ?ED'UNE LAMELLE cristaux de calcite contenant des lamellesen position de macle :mouvement des dislocationsdemacle sousl by X-Ray topography twin lamellae in calcite crystals:move- ment of twinning dislocations under thermal

Paris-Sud XI, Université de

182

Relationship between surface structure, growth mechanism, and trace element incorporation in calcite  

Microsoft Academic Search

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 {1014} 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

Jeanne Paquette; Richard J. Reeder

1995-01-01

183

Calcite precipitation by marine bacteria  

Microsoft Academic Search

Calcite precipitation occurs when trimethylamino?N?oxide and medium are added to surface waters collected above Lodestone and Keeper Reefs of the Great Barrier Reef. The calcium content of the water was initially 430 ppm. After 30 days incubation at 28 °C, the pH had risen and only 90 ppm of calcium remained in solution. The precipitate was analyzed by X?ray diffraction

Richard Y. Morita

1980-01-01

184

High power single frequency 780nm laser source generated from frequency doubling of a seeded fiber amplifier in a cascade of PPLN crystals.  

PubMed

We report on the generation of over 900 mW of tunable cw light at 780 nm by single pass frequency doubling of a high power fiber amplifier in a cascade of two periodically poled Lithium Niobate (PPLN) crystals. Over 500 mW is generated in the first crystal. In the limit of low pump power, we observe an efficiency of 4.6 mW/W2-cm for a single crystal, and 5.6 mW/W2-cm for a combination of two crystals, with an enhancement of the doubling efficiency observed with two crystals due to the presence of second harmonic light from the first crystal acting as a seed for the second. We have frequency locked this laser source relative to a rubidium D2 hyperfine line and demonstrated its utility in a sophisticated laser cooling apparatus. PMID:19466050

Thompson, R; Tu, M; Aveline, D; Lundblad, N; Maleki, L

2003-07-14

185

crystals  

NASA Astrophysics Data System (ADS)

We present the crystal growth, optical spectroscopy, and room temperature continuous-wave (CW) laser operation of monoclinic Ho:KLu(WO4)2 crystals. Macro defect-free crystals of several dopant concentrations were grown by top-seeded solution growth slow-cooling method. The evolution of unit cell parameters with holmium doping level and temperature was studied using X-ray powder diffraction. The spectroscopic properties were characterized in terms of room- and low-temperature optical absorption and photoluminescence. From low-temperature optical absorption measurements, the energy of the Stark levels was determined. Calculation of the emission and gain cross sections is presented. CW laser action was realized for 3 and 5 at. % Ho-doped KLu(WO4)2 by in-band pumping using a Tm:KLu(WO4)2 pump laser. A maximum output power of 507 mW with a slope efficiency of ~38 % with respect to the incident power was achieved at 2,080 nm with the Ho:KLu(WO4)2 laser.

Jambunathan, V.; Mateos, X.; Pujol, M. C.; Carvajal, J. J.; Zaldo, C.; Griebner, U.; Petrov, V.; Aguiló, M.; Díaz, F.

2014-08-01

186

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

187

Biaxially-Textured Photovoltaic Film Crystal Silicon on Ion Beam Assisted Deposition CaF2 Seed Layers on Glass  

SciTech Connect

We grow biaxially textured heteroepitaxial crystal silicon (c-Si) films on display glass as a low-cost photovoltaic material. We first fabricate textured CaF{sub 2} seed layers using ion-beam assisted deposition, then coat the CaF{sub 2} with a thin, evaporated epitaxial Ge buffer and finally deposit heteroepitaxial silicon on the Ge. The silicon is grown by hot-wire chemical vapor deposition, a high-rate, scalable epitaxy technology. Electron and X-ray diffraction confirm the biaxial texture of the CaF{sub 2} and epitaxial growth of the subsequent layers. Transmission electron microscopy reveals columnar silicon grains about 500 nm across. We fabricate a proof-of-concept epitaxial film c-Si solar cell with an open circuit voltage of 375 mV that is limited by minority carrier lifetime.

Groves, J. R.; Li, J. B.; Clemens, B. M.; LaSalvia, V.; Hasoon, F.; Branz, H. M.; Teplin, C. W.

2012-05-01

188

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

189

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

PubMed Central

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.

2010-01-01

190

Seeded growth from flux and neutron study of La 1? x Ba x MnO 3 (0.2< x<0.5) single crystals  

Microsoft Academic Search

The flux technique for growing large crystals of La1?xBaxMnO3(0.2seed is discussed. Based on up to 40wt% solubility of the solute, good rheological properties of corresponding flux melts, and desirable Ba substitution, the 25–40mol%B2O3\\/45–60mol%BaO\\/15–30mol%BaF2 range of solvents has been selected to grow crystals up to 1.5cm3 in volume. The best crystals have been grown under constant or a

S. N. Barilo; G. L. Bychkov; L. A. Kurnevich; S. V. Shiryaev; L. A. Kurochkin; J. W. Lynn; L. Vasiliu-Doloc

2000-01-01

191

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

192

Crystallization and preliminary X-ray diffraction analysis of a plant ribonuclease from the seeds of the bitter gourd Momordica charantia.  

PubMed

Single crystals of ribonuclease Mc, a new class of plant ribonuclease from the seeds of the bitter gourd, were obtained from solutions of polyethylene glycol 8000 by the hanging-drop vapour diffusion method. The crystals belong to the orthorhombic space group P2(1)2(1)2(1) with cell dimensions a = 67.28 A, b = 75.21 A, c = 38.54 A. The assumption of one monomer per asymmetric unit gives rise to a Vm value of 2.29 A3/Da. The crystals diffract beyond 2.0 A resolution and are suitable for high resolution X-ray structure analysis. PMID:1474592

De, A; Funatsu, G

1992-12-20

193

Controls of carbonate mineralogy and solid-solution of Mg in calcite: evidence from spelean systems  

SciTech Connect

Precipitation of carbonate minerals in spelean systems occurs under a wide range of fluid chemistry, Mg-Ca ratios, alkalinities, pH and temperatures; thus, spelean systems provide ideal settings to determine factors controlling the mineralogy of precipitated carbonates and solid-solution of Mg in calcite. Cave waters and actively-precipitating carbonate speleothems were collected from Carlsbad Caverns National Park, New Mexico and the Mammoth-Flint Cave System, Kentucky. Carbonate mineralogy of precipitated phases was determined by x-ray diffraction, and major and minor element composition of waters and accompanying minerals were determined by Atomic Absorption Spectrophotometry. Results demonstrate that at a constant CO3 concentration the precipitation threshold for calcite to aragonite is controlled dominantly by the Mg/Ca ratio of the ambient fluid. Aragonite precipitation is favored by high Mg/Ca ratios. Conversely, with increasing CO3 concentration at constant fluid Mg/Ca ratios, calcite is preferentially precipitated. Solid-solution of Mg in calcite is positively correlated with both increased Mg/Ca ratios and CO3 concentrations. These data suggest that Mg contents of calcite can not be defined solely in terms of a homogeneous distribution coefficient. Rather, Mg concentrations can be also be affected by the CO3 concentration and degree of calcite saturation, suggesting that the rate of crystal growth also plays and important role in Mg solid-solution in calcites.

Gonzalez, L.A.; Lohmann, K.C.

1985-01-01

194

Shock-induced devolatilization of calcite  

NASA Technical Reports Server (NTRS)

Experimental measurements of the release adiabats by Vizgirda (1981) indicate that substantial vaporization takes place upon release from shock pressures of 37 GPa for calcite and 14 GPa for aragonite. The present investigation includes the first controlled partial vaporization experiments on calcite. The experiments were conducted to test the predictions of the release adiabat experiments. The quantities of the gaseous species produced from shocked calcite and their carbon and oxygen isotopic compositions were determined, and the shock-induced effect on the Mn(2+) electron spin resonance spectrum in the shock-recovered calcite was observed. On the basis of the obtained results, it is concluded that shock stresses at the 17-18 GPa level give rise to volatilization of 0.03-0.3 (mole) percent of calcite to CO2 and CO. The devolatilization of calcite occurs at low pressure at significantly lower entropy densities than predicted on the basis of thermodynamic continuum models.

Boslough, M. B.; Ahrens, T. J.; Vizgirda, J.; Becker, R. H.; Epstein, S.

1982-01-01

195

Preparation of Bulk AlN Seeds by Spontaneous Nucleation of Freestanding Crystals  

NASA Astrophysics Data System (ADS)

Freestanding AlN single crystals are grown in a RF-heated furnace by physical vapor transport (PVT). Three different growth regimes with growth temperatures between 2080-2200°C result in different crystal habits and very high structural quality. The Rocking curves show FWHM < 21 arcsec in the 0002 and 10bar 10 Reflection on the as-grown facets. Isometric AlN crystals with sizes up to 10 × 10 × 12mm3 show a zonar structure consisting of a yellowish core area which is grown on the N-polar (000bar 1) facet and a nearly colorless edge region grown on prismatic {10bar 10} facets. In the two growth zones nearly the same C concentrations but different amounts of O and Si are measured by secondary ion mass spectrometry (SIMS). The yellowish core area show a very low defect density (EPD <= 100 cm-2) and a higher deep UV transparency compared to the edge region.

Hartmann, Carsten; Wollweber, Juergen; Dittmar, Andrea; Irmscher, Klaus; Kwasniewski, Albert; Langhans, Frank; Neugut, Tom; Bickermann, Matthias

2013-08-01

196

Crystallization and preliminary X-ray diffraction analysis of the lectin from Canavalia boliviana Piper seeds  

PubMed Central

Plant lectins are the most studied group of carbohydrate-binding proteins. Despite the high similarity between the members of the Diocleinae subtribe (Leguminosae) group, they present differing biological activities. Canavalia boliviana lectin (Cbol) was purified using a Sephadex G-50 column and crystallized in the presence of X-Man by hanging-drop vapour diffusion at 293?K. After optimization, crystals suitable for diffraction were obtained under the condition 0.1?M HEPES pH 7.5 and 3.0?M sodium formate. The crystal belonged to the monoclinic space group C2, with unit-cell parameters a = 126.70, b = 66.64, c = 64.99?Å, ? = 90.0, ? = 120.8, ? = 90.0°. Assuming the presence of a dimer in the asymmetric unit, the solvent content was estimated to be about 46%. A complete data set was collected at 1.5?Å resolution. PMID:19255467

Moura, Tales Rocha; Bezerra, Gustavo Arruda; Bezerra, Maria Julia Barbosa; Teixera, Cícero Silvano; Bezerra, Eduardo Henrique Salviano; Benevides, Raquel Guimarães; da Rocha, Bruno Anderson Matias; de Souza, Luiz Augusto Gomes; Delatorre, Plínio; Nagano, Celso Shiniti; Cavada, Benildo Sousa

2009-01-01

197

Geochemical controls on a calcite precipitating spring  

Microsoft Academic Search

A small spring fed stream was found to precipitate calcite by mainly inorganic processes and in a nonuniform manner. The spring water originated by rainwater falling in a 0.8 km2 basin, infiltrating, and dissolving calcite and dolomite followed by dissolution of gypsum or anhydrite. The Ca2+\\/Mg2+ indicates that calcite is probably precipitated in the subsurface from a supersaturated solution. This

Roger L. Jacobson; Eberhard Usdowski

1975-01-01

198

Crystal structure and chitin oligosaccharide-binding mode of a 'loopful' family GH19 chitinase from rye, Secale cereale, seeds.  

PubMed

The substrate-binding mode of a 26-kDa GH19 chitinase from rye, Secale cereale, seeds (RSC-c) was investigated by crystallography, site-directed mutagenesis and NMR spectroscopy. The crystal structure of RSC-c in a complex with an N-acetylglucosamine tetramer, (GlcNAc)(4) , was successfully solved, and revealed the binding mode of the tetramer to be an aglycon-binding site, subsites +1, +2, +3, and +4. These are the first crystallographic data showing the oligosaccharide-binding mode of a family GH19 chitinase. From HPLC analysis of the enzymatic reaction products, mutation of Trp72 to alanine was found to affect the product distribution obtained from the substrate, p-nitrophenyl penta-N-acetyl-?-chitopentaoside. Mutational experiments confirmed the crystallographic finding that the Trp72 side chain interacts with the +4 moiety of the bound substrate. To further confirm the crystallographic data, binding experiments were also conducted in solution using NMR spectroscopy. Several signals in the (1) H-(15) N HSQC spectrum of the stable isotope-labeled RSC-c were affected upon addition of (GlcNAc)(4) . Signal assignments revealed that most signals responsive to the addition of (GlcNAc)(4) are derived from amino acids located at the surface of the aglycon-binding site. The binding mode deduced from NMR binding experiments in solution was consistent with that from the crystal structure. PMID:22831795

Ohnuma, Takayuki; Numata, Tomoyuki; Osawa, Takuo; Inanaga, Hideko; Okazaki, Yoko; Shinya, Shoko; Kondo, Kaori; Fukuda, Tatsuya; Fukamizo, Tamo

2012-10-01

199

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

200

Atomistic Simulations of Corrosion Inhibitors Adsorbed on Calcite Surfaces I. Force field Parameters for Calcite  

E-print Network

ARTICLES Atomistic Simulations of Corrosion Inhibitors Adsorbed on Calcite Surfaces I. Force field Parameters for Calcite Sungu Hwang, Mario Blanco, and William A. Goddard III* Materials and Process, 2001 We report a new force field for calcite suitable to study scale formation and squeeze treatments

Goddard III, William A.

201

GaN single crystals grown on HVPE seeds in alkaline supercritical ammonia  

Microsoft Academic Search

Ammonothermal growth (synthesis in supercritical (sc) ammonia fluid) has the promise of producing large low defect gallium nitride crystals through the application of techniques\\u000a similar to those used in hydrothermal growth. Retrograde solubility of GaN greater than 5% by weight using group I amides\\u000a as mineralizers is demonstrated in high nickel content autoclaves at pressures of one to three kilobars

M. Callahan; B.-G. Wang; K. Rakes; D. Bliss; L. Bouthillette; M. Suscavage; S.-Q. Wang

2006-01-01

202

Step dynamics and spiral growth on calcite  

Microsoft Academic Search

The authors present novel in situ observations of the dynamics of monomolecular growth steps on calcite. Steps do not interact at separations of [approximately]10 nm and above, indicating that surface diffusion does not control calcite growth. Instead, steps advance by material addition from solution onto step sites or a narrow adjacent zone. Step nucleation is primarily at growth spirals, and

A. J. Gratz; P. E. Hillner; P. K. Hansma

1993-01-01

203

HEMATITE AND CALCITE COATINGS ON FOSSIL VERTEBRATES  

Microsoft Academic Search

Hematite coatings are common on vertebrate fossils from Paleocene\\/Eocene paleosol deposits in the Bighorn Basin, Wyoming. In general, hematite coatings are found only on fossils and are limited to soils exhibiting hydromorphic features and moderate maturity. Pet- rographic and isotopic evidence suggests that hematite and micritic calcite formed at nearly the same time in a pedogenic environment, whereas sparry calcite

HUIMING BAO; PAUL L. KOCH; ROBERT P. HEPPLE

204

Structural Characterization of Lateral-grown 6H-SiC am-plane Seed Crystals by Hot Wall CVD Epitaxy  

NASA Technical Reports Server (NTRS)

The performance of commercially available silicon carbide (SiC) power devices is limited due to inherently high density of screw dislocations (SD), which are necessary for maintaining polytype during boule growth and commercially viable growth rates. The NASA Glenn Research Center (GRC) has recently proposed a new bulk growth process based on axial fiber growth (parallel to the c-axis) followed by lateral expansion (perpendicular to the c-axis) for producing multi-faceted m-plane SiC boules that can potentially produce wafers with as few as one SD per wafer. In order to implement this novel growth technique, the lateral homoepitaxial growth expansion of a SiC fiber without introducing a significant number of additional defects is critical. Lateral expansion is being investigated by hot wall chemical vapor deposition (HWCVD) growth of 6H-SiC am-plane seed crystals (0.8mm x 0.5mm x 15mm) designed to replicate axially grown SiC single crystal fibers. The post-growth crystals exhibit hexagonal morphology with approximately 1500 m (1.5 mm) of total lateral expansion. Preliminary analysis by synchrotron white beam x-ray topography (SWBXT) confirms that the growth was homoepitaxial, matching the polytype of the respective underlying region of the seed crystal. Axial and transverse sections from the as grown crystal samples were characterized in detail by a combination of SWBXT, transmission electron microscopy (TEM) and Raman spectroscopy to map defect types and distribution. X-ray diffraction analysis indicates the seed crystal contained stacking disorders and this appears to have been reproduced in the lateral growth sections. Analysis of the relative intensity for folded transverse acoustic (FTA) and optical (FTO) modes on the Raman spectra indicate the existence of stacking faults. Further, the density of stacking faults is higher in the seed than in the grown crystal. Bundles of dislocations are observed propagating from the seed in m-axis lateral directions. Contrast extinction analysis of these dislocation lines reveals they are edge type basal plane dislocations that track the growth direction. Polytype phase transition and stacking faults were observed by high-resolution TEM (HRTEM), in agreement with SWBXT and Raman scattering.

Goue, Ouloide Yannick; Raghothamachar, Balaji; Dudley, Michael; Trunek, Andrew J.; Neudeck, Philip G.; Woodworth, Andrew A.; Spry, David J.

2014-01-01

205

Intercalation of sea urchin proteins in calcite: Study of a crystalline composite material  

SciTech Connect

Sea urchin skeletal elements are composed of single crystals of calcite. Unlike their synthetic counterparts, these crystals do not have well-developed cleavage and are consequently much more resistant to fracture. This phenomenon is due in part to the presence of acidic glycoproteins occluded within the crystals. By means of x-ray diffraction with synchrotron radiation, it is shown that the presence of the protein in synthetic calcite only slightly decreases the coherence length but significantly increases the angular spread of perfect domains of the crystals. In biogenic calcite, the coherence length is 1/3 to 1/4 as much as that in synthetic calcite and the angular spread is 20 to 50 times as wide. It is proposed that the presence of macromolecules concentrated at mosaic boundaries that are oblique to cleavage planes is responsible for the change in fracture properties. These results may be important in the material sciences, because of the unusual nature of this material, namely, a composite based on the controlled intercalation of macromolecules inside single-crystal lattices. 20 refs., 3 figs.

Berman, A.; Addadi, L.; Leiserowitz, L.; Weiner, S. (Weizmann Institute of Science, Rehovot (Israel)); Kvick, A.; Nelson, M. (Brookhaven National Laboratory, Upton, NY (USA))

1990-11-02

206

Nucleation, growth and evolution of calcium phosphate films on calcite.  

PubMed

Marble, a stone composed of the mineral calcite, is subject to chemically induced weathering in nature due to its relatively high dissolution rate in acid rain. To protect monuments and sculpture from corrosion, we are investigating the application of thin layers of hydroxyapatite (HAP) onto marble. The motivation for using HAP is its low dissolution rate and crystal and lattice compatibility with calcite. A mild, wet chemical synthesis route, in which diammonium hydrogen phosphate salt was reacted with marble, alone and with cationic and anionic precursors under different reaction conditions, was used to produce inorganic HAP layers on marble. Nucleation and growth on the calcite substrate was studied, as well as metastable phase evolution, using scanning electron microscopy, grazing incidence X-ray diffraction, and atomic force microscopy. Film nucleation was enhanced by surface roughness. The rate of nucleation and the growth rate of the film increased with cationic (calcium) and anionic (carbonate) precursor additions. Calcium additions also influenced phase formation, introducing a metastable phase (octacalcium phosphate) and a different phase evolution sequence. PMID:25233226

Naidu, Sonia; Scherer, George W

2014-12-01

207

Ultra-high-speed lateral solid phase crystallization of GeSn on insulator combined with Sn-melting-induced seeding  

NASA Astrophysics Data System (ADS)

To produce high-performance devices on flexible plastic substrates, it is essential to form Ge-based group IV semiconductors on insulating substrates at low temperatures (?250 °C). We have developed a technique for solid phase crystallization of amorphous GeSn (?220 °C) enhanced by Sn doping, and combined with a seeding technique induced by Sn melting (˜250 °C). This combination produces lateral crystallization of amorphous GeSn from seed arrays with no incubation time. As a result, extremely high growth velocities at 220 °C, depending on Sn concentration, e.g., 0.13 ?m/h (14% Sn) and 1100 ?m/h (23% Sn), are achieved. These velocities are 104-108 times higher than that of pure Ge. This technique enables growth of crystalline GeSn island arrays (diameters: 50-150 ?m) at low temperatures (?250 °C) at controlled positions on insulating substrates.

Chikita, H.; Matsumura, R.; Kai, Y.; Sadoh, T.; Miyao, M.

2014-11-01

208

Effects of added cBN seed crystals on the reaction sintering of cBN accompanied by a conversion from h-BN to cBN  

Microsoft Academic Search

Reaction sintering behaviour of c-BN which is accompanied by a conversion from h-BN to c-BN was investigated under high pressure (7 GPa) and temperature (1700°C) conditions for 30 to 60min. A high conversion yield of c-BN in the sintered compact was attained by adding fine-grained c-BN seed crystals (particle size 0.5 to 8µm) to h-BN powder in the presence of

Hideaki Itoh; Tsuneaki Matsudaira; Katsuya Inoue; Shigeharu Naka

1990-01-01

209

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

210

Crystal structure of a ribonuclease from the seeds of bitter gourd (Momordica charantia) at 1.75 A resolution.  

PubMed

The ribonuclease MC1 (RNase MC1) from seeds of bitter gourd (Momordica charantia) consists of 190 amino acid residues with four disulfide bridges and belongs to the RNase T(2) family, including fungal RNases typified by RNase Rh from Rhizopus niveus and RNase T(2) from Aspergillus oryzae. The crystal structure of RNase MC1 has been determined at 1.75 A resolution with an R-factor of 19.7% using the single isomorphous replacement method. RNase MC1 structurally belongs to the (alpha+beta) class of proteins, having ten helices (six alpha-helices and four 3(10)-helices) and eight beta-strands. When the structures of RNase MC1 and RNase Rh are superposed, the close agreement between the alpha-carbon positions for the total structure is obvious: the root mean square deviations calculated only for structurally related 151 alpha-carbon atoms of RNase MC1 and RNase Rh molecules was 1.76 A. Furthermore, the conformation of the catalytic residues His-46, Glu-105, and His-109 in RNase Rh can be easily superposed with that of the possible catalytic residues His-34, Glu-84, and His-88 in RNase MC1. This observation strongly indicates that RNase MC1 from a plant origin catalyzes RNA degradation in a similar manner as fungal RNases. PMID:10446375

Nakagawa, A; Tanaka, I; Sakai, R; Nakashima, T; Funatsu, G; Kimura, M

1999-08-17

211

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 manuscript 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 at present-day. Moreover, on a global scale, the organomineralization of organic nanofibres into calcitic nanofibres might have a great, however overlooked, impact on the biogeochemical cycles of both Ca and C.

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

2014-01-01

212

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

213

Preliminary Results of Bacteria Distribution in Chinese Loess and Their Control on the Calcite Formation  

NASA Astrophysics Data System (ADS)

Continuous loess-paleosol sequences on the Chinese Loess Plateau are viewed as one of best continental archives of paleoclimatic and paleoenvironmental changes of the Late Cenozoic era. Carbonate, mainly calcite, commonly occurs throughout the entire sequence; though some are detrital, most are in-situ pedogenic. TEM studies have shown various morphologies of calcites in Chinese loess, especially nano-rod calcite widely occurring in loess and paleosols which are biogenic. In this study, we collected fresh and undisturbed loess and paleosol samples and successfully separated dominant microbial communities. These microbes are mainly bacteria, especially Bacillus anthracis, and a few fungi. The amount of bacteria decreases sharply with the depth. Then we added the bacteria into the near saturated solution of CaCl2 and Na2CO3. It is interesting that the original calcite crystals formed under abiotic conditions changed from quadrilateral face to pentagonal or hexagonal and the crystal size enlarged almost twice. SEM and AFM observations display bacteria control on the growth of calcite, which cause the lighter carbon isotopic ratios.

Chen, Y.; Lian, B.; Hu, Q.; Teng, H. H.; Wu, T.; Ji, J.; Chen, J.

2005-12-01

214

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

215

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

216

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

217

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

218

Acceleration of calcite kinetics by abalone nacre proteins  

SciTech Connect

The fascinating shapes and hierarchical designs of biomineralized structures have long been an inspiration to materials scientists because of the potential they suggest for biomolecular control over synthesis of crystalline materials. One prevailing view is that mineral-associated macromolecules are responsible for initiating and stabilizing non-equilibrium crystal polymorphs and morphologies through interactions between anionic moieties and cations in solution or at mineral surfaces. Indeed, numerous studies have demonstrated that bio-organic additives can dramatically alter crystal shapes and growth-rates in vitro. However, previous molecular-scale studies revealing mechanisms of growth modification focused on small molecules such as amino acids or peptides and always observed growth inhibition. In contrast, studies using full proteins were non-quantitative and underlying sources of growth modification were ill-defined. Here we investigate interactions between proteins isolated from abalone shell nacre and growing surfaces of calcite. We find that these proteins significantly accelerate the molecular-scale kinetics and, though much larger than atomic steps, alter growth morphology through step-specific interactions that lower their free energies. We propose that these proteins act as surfactants to promote ion attachment at calcite surfaces.

Fu, G; Qiu, S R; Orme, C A; Morse, D E; De Yoreo, J J

2005-06-09

219

Nickel adsorption on chalk and calcite.  

PubMed

Nickel uptake from solution by two types of chalk and calcite was investigated in batch sorption studies. The goal was to understand the difference in sorption behavior between synthetic and biogenic calcite. Experiments at atmospheric partial pressure of CO2, in solutions equilibrated with calcite and chalk and pH ranging from 7.7 to 8.8, explored the influence of initial concentration and the amount and type of sorbent on Ni uptake. Adsorption increases with increased surface area and pH. A surface complexation model describes the data well. Stability constants for the Ni surface complex are log KNi=-1.12 on calcite and log KNi=-0.43 and -0.50 on the two chalk samples. The study confirms that synthetic calcite and chalk both take up nickel, but Ni binds more strongly on the biogenic calcite than on inorganically precipitated, synthetic powder, because of the presence of trace amounts of polysaccharides and clay nanoparticles on the chalk surface. PMID:25300061

Belova, D A; Lakshtanov, L Z; Carneiro, J F; Stipp, S L S

2014-12-01

220

Nickel adsorption on chalk and calcite  

NASA Astrophysics Data System (ADS)

Nickel uptake from solution by two types of chalk and calcite was investigated in batch sorption studies. The goal was to understand the difference in sorption behavior between synthetic and biogenic calcite. Experiments at atmospheric partial pressure of CO2, in solutions equilibrated with calcite and chalk and pH ranging from 7.7 to 8.8, explored the influence of initial concentration and the amount and type of sorbent on Ni uptake. Adsorption increases with increased surface area and pH. A surface complexation model describes the data well. Stability constants for the Ni surface complex are log KNi = - 1.12 on calcite and log KNi = - 0.43 and - 0.50 on the two chalk samples. The study confirms that synthetic calcite and chalk both take up nickel, but Ni binds more strongly on the biogenic calcite than on inorganically precipitated, synthetic powder, because of the presence of trace amounts of polysaccharides and clay nanoparticles on the chalk surface.

Belova, D. A.; Lakshtanov, L. Z.; Carneiro, J. F.; Stipp, S. L. S.

2014-12-01

221

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

222

Experimental Design and Inferential Modeling in Pharmaceutical Crystallization  

E-print Network

. Braatz. 160 January 2001 et al., 19991, the ratio of the nucleated crystal mass to seed crystal massExperimental Design and Inferential Modeling in Pharmaceutical Crystallization Timokleia seed type, seed amount, temperature, solvent ratio, addition time, and agitation intensity

Braatz, Richard D.

223

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

224

Crystals  

NSDL National Science Digital Library

In this earth science/math/art activity, learners use simple ingredients to grow crystals and examine the repeating geometric shapes and patterns. Learners compare the growth of crystals from four types of crystal-starters (table salt, Borax, sand, and Epsom salt) to see which starter grows the most crystals in 14 days. Learners report their results online and find out what other learners discovered. Afterward, learners can use the crystals they grew to create works of art.

Science, Lawrence H.

2009-01-01

225

Low-magnesium calcite produced by coralline algae in seawater of Late Cretaceous composition.  

PubMed

Shifts in the MgCa ratio of seawater driven by changes in midocean ridge spreading rates have produced oscillations in the mineralogy of nonskeletal carbonate precipitates from seawater on time scales of 10(8) years. Since Cambrian time, skeletal mineralogies of anatomically simple organisms functioning as major reef builders or producers of shallow marine limestones have generally corresponded in mineral composition to nonskeletal precipitates. Here we report on experiments showing that the ambient MgCa ratio actually governs the skeletal mineralogy of some simple organisms. In modern seas, coralline algae produce skeletons of high-Mg calcite (>4 mol % MgCO(3)). We grew three species of these algae in artificial seawaters having three different MgCa ratios. All of the species incorporated amounts of Mg into their skeletons in proportion to the ambient MgCa ratio, mimicking the pattern for nonskeletal precipitation. Thus, the algae calcified as if they were simply inducing precipitation from seawater through their consumption of CO(2) for photosynthesis; presumably organic templates specify the calcite crystal structure of their skeletons. In artificial seawater with the low MgCa ratio of Late Cretaceous seas, the algae in our experiments produced low-Mg calcite (<4 mol % MgCO(3)), the carbonate mineral formed by nonskeletal precipitation in those ancient seas. Our results suggest that many taxa that produce high-Mg calcite today produced low-Mg calcite in Late Cretaceous seas. PMID:12399549

Stanley, Steven M; Ries, Justin B; Hardie, Lawrence A

2002-11-26

226

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. PMID:11331767

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

2001-01-01

227

Selective adsorption of L- and D-amino acids on calcite: Implications for biochemical homochirality  

NASA Technical Reports Server (NTRS)

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 (CaCO(3)), 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, R. M.; Filley, T. R.; Goodfriend, G. A.

2001-01-01

228

Effect of seed crystal and composition of solution on the formation of TiO 2 thin film from aqueous solution  

Microsoft Academic Search

TiO2 thin film can be formed from aqueous solution at ordinary temperature and ordinary pressure by using hydrolysis reaction of titanium fluoro-complex. In this study, effect of seed crystal and composition of solution on the formation of TiO2 thin film was investigated. The amount of deposited TiO2 increased with increasing both (NH4)2TiF6 and B2O3 concentrations. Crystallinity of TiO2 increased with

Naoshi Ozawa; Yoichiro Kumazawa; Takeshi Yao

2002-01-01

229

Experimental and theoretical study of red-shifted solitonic resonant radiation in photonic crystal fibers and generation of radiation seeded Raman solitons  

E-print Network

The red shifted solitonic resonant radiation is a fascinating phase matching phenomenon that occurs when an optical pulse, launched in the normal dispersion regime of photonic crystal fiber, radiates across the zero dispersion wavelength. The formation of such phase-matched radiation is independent of the generation of any optical soliton and mainly governed by the leading edge of input pump which forms a shock front. The radiation is generated at the anomalous dispersion regime and found to be confined both in time and frequency domain. We experimentally investigate the formation of such radiations in photonic crystal fibers with detailed theoretical analysis. Our theoretical predictions corroborate well with experimental results. Further we extend our study for long length fiber and investigate the interplay between red-shifted solitonic resonant radiation and intrapulse Raman scattering (IPRS). It is observed that series of radiation-seeded Raman solitons are generated in anomalous dispersion regime.

Bose, Surajit; Chattopadhyay, Rik; Pal, Mrinmay; Bhadra, Shyamal K

2015-01-01

230

Structure and reactivity of the calcite-water interface.  

PubMed

The zetapotential of calcite in contact with aqueous solutions of varying composition is determined for pre-equilibrated suspensions by means of electrophoretic measurements and for non-equilibrium solutions by means of streaming potential measurements. Carbonate and calcium are identified as charge determining ions. Studies of the equilibrium solutions show a shift of isoelectric point with changing CO(2) partial pressure. Changes in pH have only a weak effect in non-equilibrium solutions. The surface structure of (104)-faces of single crystal calcite in contact to solutions corresponding to those of the zetapotential investigations is determined from surface diffraction measurements. The results reveal no direct indication of calcium or carbonate inner-sphere surface species. The surface ions are found to relax only slightly from their bulk positions; the most significant relaxation is a ?4° tilt of the surface carbonate ions towards the surface. Two ordered layers of water molecules are identified, the first at 2.35±0.05Å above surface calcium ions and the second layer at 3.24±0.06Å above the surface associated with surface carbonate ions. A Basic-Stern surface complexation model is developed to model observed zetapotentials, while only considering outer-sphere complexes of ions other than protons and hydroxide. The Basic-Stern SCM successfully reproduces the zetapotential data and gives reasonable values for the inner Helmholtz capacitance, which are in line with the Stern layer thickness estimated from surface diffraction results. PMID:21087772

Heberling, Frank; Trainor, Thomas P; Lützenkirchen, Johannes; Eng, Peter; Denecke, Melissa A; Bosbach, Dirk

2011-02-15

231

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

232

Compositional variation in Si-rich SiGe single crystals grown by multi-component zone melting method using Si seed and source crystals  

Microsoft Academic Search

The effect of the supply of depleted Si solute elements on the compositional variation in the Si-rich SiGe bulk crystals was studied using the method which was used to grow Ge-rich SiGe single crystals with a uniform composition. By selecting the proper pulling rate, we can obtain Si-rich Si1?xGex bulk crystals with uniform composition of x=0.1 without using the supply

Kazuo Nakajima; Toshihiro Kusunoki; Yukinaga Azuma; Noritaka Usami; Kozo Fujiwara; Toru Ujihara; Gen Sazaki; Toetsu Shishido

2002-01-01

233

Crystallization and preliminary X-ray studies of two serine proteinase inhibitors, BGIA and BGIT, from the seeds of bitter gourd.  

PubMed

Two serine proteinase inhibitors from seeds of the bitter gourd, BGIA (bitter gourd inhibitor against acidic amino acid-specific proteinase of Streptomyces griseus) and BGIT (bitter gourd trypsin inhibitor), were crystallized for X-ray structure determination. Crystals of BGIA belong to the monoclinic space group C2 with cell dimensions of a = 54.0 A, b = 23.7 A, c = 47.9 A, and beta = 105.4 degrees, and diffracted X-ray up to 1.5 A resolution. Crystals of BGIT belong to the triclinic space group P1 with cell dimensions of a = 22.8 A, b = 23.5 A, c = 28.4 A, alpha = 93.1 degrees, beta = 99.6 degrees, and gamma = 101.0 degrees, giving X-ray diffraction of over 1.2 A resolution. Intensity data of BGIA and BGIT crystals were collected using synchrotron radiation up to 1.7 and 1.4 A, respectively. PMID:9417986

Kondo, H; Nakanose, J; Nakagawa, A; Tanaka, I; Kimura, M; Funatsu, G

1997-11-01

234

Optimal control of crystallization of alpha-lactose monohydrate  

E-print Network

are temperature, feed rate, and the choice of an appropriate crystal seed. I. INTRODUCTION Crystallization - water - evap. feed 6 hydration -nucl. -mono crystal seed -mono crystal - product seed 6 ? attr are feed rate in semi-batch mode, temperature of envelope, and the distribution of the crystal seed. Based

Noll, Dominikus

235

Colouring crystals with inorganic nanoparticles.  

PubMed

A simple, one-pot method is presented whereby gold nanoparticles coated with a zwitterionic diblock copolymer are incorporated within single crystals of calcite. This may provide a versatile alternative to dyeing crystal with organic molecules and could be extended to create a series of new nanocomposite crystals with novel properties. PMID:24202647

Kulak, Alexander N; Yang, Pengcheng; Kim, Yi-Yeoun; Armes, Steven P; Meldrum, Fiona C

2014-01-01

236

Cyclic Cratonic Carbonates and Phanerozoic Calcite Seas.  

ERIC Educational Resources Information Center

Discusses causes of cyclicity in cratonic carbonate sequences and evidence for and potential significance of postulated primary calcite sediment components in past Paleozoic seas, outlining problems, focusing on models explaining existing data, and identifying background. Future sedimentary geologists will need to address these and related areas…

Wilkinson, Bruce H.

1982-01-01

237

The calcite-aragonite transition, reinvestigated  

Microsoft Academic Search

The calcite-aragonite equilibrium has been investigated between 200 and 600° C both in a carefully calibrated hydrothermal apparatus and in a piston-cylinder device of high precision. The equilibrium pressure is 5 kb at 180° C, 7 kb at 300° C, 9 kb at 400° C, and 11 kb at 480° C.

W. Johannes; D. Puhan

1971-01-01

238

Calcite Precipitation and Trace Metal Partitioning in Groundwater and the Vadose Zone: Remediation of Strontium-90 and Other Divalent Metals and Radionuclides in Arid Western Environments  

SciTech Connect

Radionuclide and metal contaminants are present in the vadose zone and groundwater throughout the U.S. Department of Energy (DOE) weapons complex. Demonstrating in situ immobilization of these contaminants in vadose zones or groundwater plumes is a cost-effective remediation strategy. However, the implementation of in situ remediation requires definition of the mechanism that controls sequestration of the contaminants. One such mechanism for metals and radionuclides is co-precipitation of these elements in authigenic calcite and calcite overgrowths. Calcite, a common mineral in many aquifers and vadose zones in the arid western U.S., can incorporate divalent metals such as strontium, cadmium, lead, and cobalt into its crystal structure by the formation of solid solutions. The rate at which trace metals are incorporated into calcite is a function of calcite precipitation kinetics, adsorption interactions between the calcite surface and the trace metal in solution, solid solution properties of the trace metal in calcite, and also the surfaces upon which the calcite is precipitating. A fundamental understanding of the coupling of calcite precipitation and trace metal partitioning and how this may occur in aquifers and vadose environments is lacking. The focus of the research proposed here is to investigate the facilitated partitioning of metal and radionuclides by their coprecipitation with calcium carbonate. Our specific research objectives include: (1) Elucidating the mechanisms and rates of microbially facilitated calcite precipitation and divalent cation adsorption/co-precipitation occurring in a natural aquifer as a result of the introduction of urea. (2) Assessing the effects of spatial variability in aquifer host rock and the associated hydro/biogeochemical processes on calcite precipitation rates and mineral phases within an aquifer.

Smith, Robert W.; Colwell, F. ''Rick'' S.; Ingram, Jani C.; Ferris, F. Grant; Reysenbach, Anna-Louise

2001-08-09

239

Calcite Precipitation and Trace Metal Partitioning in Groundwater and the Vadose Zone: Remediation of Strontium-90 and Other Divalent Metals and Radionuclides in Arid Western Environments  

SciTech Connect

Radionuclide and metal contaminants are present in the vadose zone and groundwater throughout the U.S. Department of Energy (DOE) weapons complex. Demonstrating in situ immobilization of these contaminants in vadose zones or groundwater plumes is a cost-effective remediation strategy. However, the implementation of in situ remediation requires definition of the mechanism that controls sequestration of the contaminants. One such mechanism for metals and radionuclides is co-precipitation of these elements in authigenic calcite and calcite overgrowths. Calcite, a common mineral in many aquifers and vadose zones in the arid western U.S., can incorporate divalent metals such as strontium, cadmium, lead, and cobalt into its crystal structure by the formation of solid solutions. The rate at which trace metals are incorporated into calcite is a function of calcite precipitation kinetics, adsorption interactions between the calcite surface and the trace metal in solution, solid solution properties of the trace metal in calcite, and also the surfaces upon which the calcite is precipitating. A fundamental understanding of the coupling of calcite precipitation and trace metal partitioning and how this may occur in aquifers and vadose environments is lacking. The focus of the research proposed here is to investigate the facilitated partitioning of metal and radionuclides by their coprecipitation with calcium carbonate. Our specific research objectives include: (1) Elucidating the mechanisms and rates of microbially facilitated calcite precipitation and divalent cation adsorption/co-precipitation occurring in a natural aquifer and vadose zone perched water body as a result of the introduction of urea. (2) Assessing the effects of spatial variability in aquifer host rock and the associated hydro/biogeochemical processes on calcite precipitation rates and mineral phases within an aquifer and a vadose zone perched water body.

Smith, Robert W.; Colwell, F. ''Rick'' S.; Ingram, Jani C.; Ferris, F. Grant; Reysenbach, Anna-Louise

2000-07-19

240

Structural evolution of calcite at high temperatures: Phase V unveiled  

PubMed Central

The calcite form of calcium carbonate CaCO3 undergoes a reversible phase transition between Rc and Rm at ~1240?K under a CO2 atmosphere of ~0.4?MPa. The joint probability density function obtained from the single-crystal X-ray diffraction data revealed that the oxygen triangles of the CO3 group in the high temperature form (Phase V) do not sit still at specified positions in the space group Rm, but migrate along the undulated circular orbital about carbon. The present study also shows how the room temperature form (Phase I) develops into Phase V through an intermediate form (Phase IV) in the temperature range between ~985?K and ~1240?K. PMID:24084871

Ishizawa, Nobuo; Setoguchi, Hayato; Yanagisawa, Kazumichi

2013-01-01

241

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

242

Authigenic low-Mg calcite in Lake Turkana, Kenya  

NASA Astrophysics Data System (ADS)

Lake Turkana is an important modern analog to ancient rift environments in east Africa and elsewhere. Carbonate is second in abundance after the detrital silicate fraction of the sediments in the lake. It consists of ostracod tests and a silt-sized micrite. Scanning electron microscopy and X-ray diffraction analysis revealed the micrite to be euhedral crystals of low-Mg calcite about 10 microns in length. Carbon isotope values of the micrite indicate that it forms in the upper water column rather than in the sediments after burial. The oxygen isotope analyses indicate that the micrite could be at isotopic equilibrium with the modern lake waters at temperatures of 36°C. This suggests that the micrite forms either in the surface waters of the open lake or in isolated shallow bays, and is then transported to the deep lake.

Halfman, John D.; Johnson, Thomas C.; Showers, William J.; Lister, Guy S.

243

Single-contact pressure solution creep on calcite monocrystals  

E-print Network

1 Single-contact pressure solution creep on calcite monocrystals Sergey Zubtsov1,2 , François Corresponding author: François Renard Abbreviated title: Pressure solution on calcite monocrystals hal-00202090: Pressure solution creep rates and interface structures have been measured by two methods on calcite single

Paris-Sud XI, Université de

244

Surface-Potential Heterogeneity of Reacted Calcite and Rhodochrosite  

E-print Network

Surface-Potential Heterogeneity of Reacted Calcite and Rhodochrosite C H O N G Z H E N G N A , T R, nanostructures on the (101h4) surfaces of calcite and rhodochrosite are characterized by their surface potentials using Kelvin probe force microscopy. Water- induced nanostructures on calcite have a topographic height

245

Sequestration of Selenium on Calcite Surfaces Revealed by Nanoscale Imaging  

E-print Network

Sequestration of Selenium on Calcite Surfaces Revealed by Nanoscale Imaging Christine V. Putnis, ISTerre, BP 53, F-38041 Grenoble, France *S Supporting Information ABSTRACT: Calcite, a widespread natural and for human health. In the form of selenite (Se(IV) ), selenium can be incorporated into calcite during growth

246

Synthesis of a Se0 /calcite composite using hydrothermal1  

E-print Network

1 Synthesis of a Se0 /calcite composite using hydrothermal1 carbonation of Ca(OH)2 coupled )/calcite composite. Under O2-poor conditions, the composite was mainly characterized6 by red spherical selenium nanoparticles "non crystalline elemental selenium" (calcite matrix

Paris-Sud XI, Université de

247

Temperature limits for preservation of primary calcite clumped isotope paleotemperatures  

E-print Network

Temperature limits for preservation of primary calcite clumped isotope paleotemperatures Gregory A in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe

Grossman, Ethan L.

248

Trace elements in calcite from carbonatite of the Bear Lodge deposit, northeast Wyoming: evidence of hydrothermal alteration?  

NASA Astrophysics Data System (ADS)

The Bear Lodge Mountains of northeast Wyoming is the locality of a carbonatite-hosted rare earth element deposit. The carbonatite is emplaced as subvertical, northwest trending dikes primarily situated within three diatreme structures. Carbonatite dikes located outside the northern boundary of the Bull Hill diatreme—northwest Bull Hill—are narrower, trend north-south, and have lower ore grades. Characterization of carbonatite dikes from northwest Bull Hill reveals several calcite textures. These textures include: fine-grained, anhedral, inclusion free calcite frequently displaying 120 degree contacts; coarser-grained, consertal to serrated, equant to elongate, inclusion rich calcite; and coarser-grained, euhedral, rhombic calcite. The fine-grained calcite was first theorized to be related to chill margins except it was found to be mottled with coarser-grained calcite throughout the samples and/or proximal to hexagonal pseudomorphs. Rare earth mineralization in the Bear Lodge deposit is primarily secondary rare earth element carbonate mineral aggregates in hexagonal pseudomorphs after a primary rare earth mineral. The differing calcite textures could be a result of hydrothermal alteration and/or fluid driven recrystallization associated with the production of hexagonal pseudomorphs. Calcite from carbonatite samples of varying texture and mineralogy were analyzed using LA-ICPMS. The majority of samples contain calcite with two or more chondrite normalized rare earth element patterns: 1) A majority of coarser-grained calcite—rhombic and consertal—have log-linear, steep (La/YbCN= 500 to 4000) to moderate (La/YbCN=7 to 37), negative patterns from La (values 1000 to 4000 times chondrites) to Lu (values 2 to 30 times chondrites). 2) Several coarse-grained calcite and finer-grained, consertal calcite in samples containing abundant hexagonal pseudomorphs have relatively flat patterns with slight undulations at the middle rare earth elements. Rare earth element values range from 20 to 300 times chondrites. 3) A majority of fine-grained, anhedral calcite proximal and distal to hexagonal pseudomorphs have convex up, "humped", chondrite normalized rare earth element patterns with a positive slope (La/GdCN= 0.01 to 0.36) from La to Sm or Gd and a steeper negative slope from Sm or Gd to Tm which flattens from Tm to Lu. The slope from the middle rare earth elements to Lu parallels the trends of observed linear patterns. Linear, negative chondrite normalized rare earth element trends have been ascribed to calcite crystallizing as the main phase in a light rare earth element-rich carbonatite. The relatively flat chondrite normalized rare earth element patterns could relate to cumulate processes or late-stage calcite crystallization after a rare earth element enriched phase/phases. Hydrothermal processes or co-crystallization of a light rare earth element bearing phase could explain the "humped" chondrite normalized rare earth element patterns with light rare earth element depletion while a seemingly "magmatic" trend from middle to heavy rare earth elements is maintained.

Olinger, D.

2012-12-01

249

Biosorption of divalent Pb, Cd and Zn on aragonite and calcite mollusk shells.  

PubMed

The potential of using mollusk shell powder in aragonite (razor clam shells, RCS) and calcite phase (oyster shells, OS) to remove Pb(2+), Cd(2+) and Zn(2+) from contaminated water was investigated. Both biogenic sorbents displayed very high sorption capacities for the three metals except for Cd on OS. XRD, SEM and XPS results demonstrated that surface precipitation leading to crystal growth took place during sorption. Calcite OS displayed a remarkably higher sorption capacity to Pb than aragonite RCS, while the opposite was observed for Cd. However, both sorbents displayed similar sorption capacities to Zn. These could be due to the different extent of matching in crystal lattice between the metal bearing precipitate and the substrates. The initial pH of the solution, sorbent's dosage and grain size affected the removal efficiency of the heavy meals significantly, while the organic matter in mollusk shells affected the removal efficiency to a lesser extent. PMID:21550150

Du, Yang; Lian, Fei; Zhu, Lingyan

2011-07-01

250

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

251

Passive kimberlite intrusion into actively dilating dyke-fracture arrays: evidence from fibrous calcite veins and extensional fracture cleavage  

NASA Astrophysics Data System (ADS)

Calcite veins are invariably associated with en-echelon kimberlite dyke-fracture arrays. A detailed microstructural study of veining indicates four vein types. Type I stretched or ataxial veins are defined by high aspect ratio calcite fibers that are crystallographically continuous with calcite of the kimberlite matrix wall rock, by elongated phenocrystic phlogopite with sharp crystal terminations centered on contacts between adjacent calcite fibers and by phenocrystic phlogopite that grows or extends across these veins. Type I vein mineralogy indicates syn-dilational crystallization of vein minerals in local tensional areas within the kimberlite. Vein Types II (stretched to syntaxial elongate-blocky) and III (antitaxial) indicate late crystallization vein mineral growth during subsequent or repeated dilation. Calcite fibers in Type I to Type III veins are orthogonal to the contacts of their host dykes regardless of the orientation of vein margins. Type IV calcite veins, with blocky or mosaic/polycrystalline textures, are attributed to minor post-intrusion extension, which was potentially accompanied by repeated kimberlite intrusion within a given dyke array. Syn-crystallization/syn-intrusion Type I veins and an ubiquitous dyke-parallel fracture cleavage, in a zone up to 4 m on either side of dyke contacts, suggest that en-echelon kimberlite dyke-fracture arrays occupied the approximate center of zones of active dilation within the brittle carapace of the upper crust. Type II and III veins indicate that extension or dilation continued, independently of an occupying kimberlite fluid phase, after initial intrusion. Arrested mobile hydrofracturing, under low differential stress within the upper brittle or seismic carapace of the continental crust, followed by repeated dilation of the dyke-fracture system, is proposed as a mechanism for producing the features observed in this study. The conditions constrained in this study indicate passive dyke intrusion into dilating fracture arrays during crustal extension.

Basson, I. J.; Viola, G.

2004-09-01

252

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

SciTech Connect

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 degrees of the film surface normal, but the oriented crystals may be tilted up to 6 degrees away from this axis. For low Mg{sup 2+} content, SO{sub 3}--functionalized films nucleated primarily near the (106) calcite face, odd-chain-length carboxylic acid terminated alkanethiol films nucleated near the (012) face, and even-chain-length carboxylic acid terminated alkanethiol films nucleated near the (113) face. [Mg{sup 2+}]/[Ca{sup 2+}] concentration ratios (n) of 2 and greater defeated this preferred orientation and created a powder texture. Diffraction patterns within the layer plane from the coarse calcite powders indicated a shift to higher 2 accompanied by peak broadening with increasing n. For 0.5 < n < 3.5, a double set of calcite peaks is observed, showing that two distinct Mg calcite phases form: one of comparatively lower Mg content, derived from the templated crystals, and a Mg-rich phase derived from amorphous precursor particles. According to the refinement of lattice parameters, Mg incorporation of up to 18 mol % occurs for n = 4, independent of film functionality. We discuss the differences between the differently functionalized monolayers and also introduce the hypothesis that two separate routes to Mg calcite formation occur in this system.

Kwak,S.; DiMasi, E.; Han, Y.; Aizenberg, J.; Kuzmenko, I.

2005-01-01

253

Shock Compression of Crustal Rocks: Data for Quartz, Calcite, and Plagioclase Rocks  

Microsoft Academic Search

ttugoniot data in the 4- to 250-kb stress range were obtained for quartzite and novaculite, sandstones of varying porosity, single-crystal calcite, marble, porous and non- porous limestone, several plagioclases of varying composition, and a basalt. Conventional plane-wave, in-contact explosive assemblies were used; the shock state was computed from measured shock velocities; particle velocities are inferred from either specimen or driver

Thomas J. Ahrens; V. G. Gregson

1964-01-01

254

Textural properties of synthetic nano-calcite produced by hydrothermal carbonation of calcium hydroxide  

NASA Astrophysics Data System (ADS)

The hydrothermal carbonation of calcium hydroxide (Ca(OH) 2) at high pressure of CO 2 (initial P=55 bar) and moderate to high temperature (30 and 90 °C) was used to synthesize fine particles of calcite. This method allows a high carbonation efficiency (about 95% of Ca(OH) 2-CaCO 3 conversion), a significant production rate (48 kg/m 3 h) and high purity of product (about 96%). However, the various initial physicochemical conditions have a strong influence on the crystal size and surface area of the synthesized calcite crystals. The present study is focused on the estimation of the textural properties of synthesized calcite (morphology, specific surface area, average particle size, particle size distribution and particle size evolution with reaction time), using Rietveld refinements of X-ray diffraction (XRD) spectra, Brunauer-Emmett-Teller (BET) measurements, and scanning electron microscope (SEM) and transmission electron microscope (TEM) observations. This study demonstrate that the pressure, the temperature and the dissolved quantity of CO 2 have a significant effect on the average particle size, specific surface area, initial rate of precipitation, and on the morphology of calcium carbonate crystals. In contrast, these PT x conditions used herein have an insignificant effect on the carbonation efficiency of Ca(OH) 2. Finally, the results presented here demonstrate that nano-calcite crystals with high specific surface area ( SBET=6-10 m 2/g) can be produced, with a high potential for industrial applications such as adsorbents and/or filler in papermaking industry.

Montes-Hernandez, G.; Fernández-Martínez, A.; Charlet, L.; Tisserand, D.; Renard, F.

2008-05-01

255

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

256

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.

Reddy, Michael M.

2012-01-01

257

Arsenate Uptake by Calcite: Macroscopic and Spectroscopic Characterization of Adsorption and Incorporation Mechanisms  

SciTech Connect

Batch uptake experiments and X-ray element mapping and spectroscopic techniques were used to investigate As(V) (arsenate) uptake mechanisms by calcite, including adsorption and coprecipitation. Batch sorption experiments in calcite-equilibrated suspensions (pH 8.3; PCO{sub 2} = 10{sup -3.5} atm) reveal rapid initial sorption to calcite, with sorption rate gradually decreasing with time as available sorption sites decrease. An As(V)-calcite sorption isotherm determined after 24 h equilibration exhibits Langmuir-like behavior up to As concentrations of 300 {mu}M. Maximum distribution coefficient values (K{sub d}), derived from a best fit to a Langmuir model, are {approx}190 L kg{sup -1}. Calcite single crystals grown in the presence of As(V) show well-developed rhombohedral morphology with characteristic growth hillocks on (10{bar 1}4) surfaces at low As(V) concentrations ({<=}5 {mu}M), but habit modification is evident at As(V) concentrations {>=}30 {mu}M in the form of macrostep development preferentially on the - vicinal surfaces of growth hillocks. Micro-X-ray fluorescence element mapping of (10{bar 1}4) surfaces shows preferential incorporation of As in the - vicinal faces relative to + vicinals. EXAFS fit results for both adsorption and coprecipitation samples confirm that As occurs in the 5+ oxidation state in tetrahedral coordination with oxygen, i.e., as arsenate. For adsorption samples, As(V) forms inner-sphere surface complexes via corner-sharing with Ca octahedra. As(V) coprecipitated with calcite substitutes in carbonate sites but with As off-centered, as indicated by two Ca shells, and with likely disruption of local structure. The results indicate that As(V) interacts strongly with the calcite surface, similar to often-cited analog phosphate, and uptake can occur via both adsorption and coprecipitation reactions. Therefore, calcite may be effective for partial removal of dissolved arsenate from aquatic and soil systems.

Alexandratos,V.; Elzinga, E.; Reeder, R.

2007-01-01

258

Kinetics and Mechanisms of Cadmium Carbonate Heteroepitaxial Growth at the Calcite (101¯4) Surface  

SciTech Connect

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 (10-14) 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 N.

2014-06-01

259

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

260

Physical and stable-isotope evidence for formation of secondary calcite and silica in the unsaturated zone, Yucca Mountain, Nevada  

USGS Publications Warehouse

Calcite and silica form coatings on fracture footwalls and cavity floors in the welded tuffs at Yucca Mountain, the potential site of a high-level radioactive waste repository. These secondary mineral deposits are heterogeneously distributed in the unsaturated zone (UZ) with fewer than 10% of possible depositional sites mineralized. The paragenetic sequence, compiled from deposits throughout the UZ, consists of an early-stage assemblage of calcite??fluorite??zeolites that is frequently capped by chalcedony??quartz. Intermediate- and late-stage deposits consist largely of calcite, commonly with opal on buried growth layers or outermost crystal faces of the calcite. Coatings on steep-dipping fractures usually are thin (??? 3 mm) with low-relief outer surfaces whereas shallow-dipping fractures and lithophysal cavities typically contain thicker, more coarsely crystalline deposits characterized by unusual thin, tabular calcite blades up to several cms in length. These blades may be capped with knobby or corniced overgrowths of late-stage calcite intergrown with opal. The observed textures in the fracture and cavity deposits are consistent with deposition from films of water fingering down fracture footwalls or drawn up faces of growing crystals by surface tension and evaporated at the crystal tips. Fluid inclusion studies have shown that most early-stage and some intermediate-stage calcite formed at temperatures of 35 to 85??C. Calcite deposition during the past several million years appears to have been at temperatures < 30??C. The elevated temperatures indicated by the fluid inclusions are consistent with temperatures estimated from calcite ??18O values. Although others have interpreted the elevated temperatures as evidence of hydrothermal activity and flooding of the tuffs of the potential repository, the authors conclude that the temperatures and fluid-inclusion assemblages are consistent with deposition in a UZ environment that experienced prolonged heat input from gradual cooling of nearby plutons. The physical restriction of the deposits (and, therefore, fluid flow) to fracture footwalls and cavity floors and the heterogeneous and limited distribution of the deposits provides compelling evidence that they do not reflect flooding of the thick UZ at Yucca Mountain. The textures and isotopic and chemical compositions of these mineral deposits are consistent with deposition in a UZ setting from meteoric waters percolating downward along fracture flow paths.

Whelan, J.F.; Paces, J.B.; Peterman, Z.E.

2002-01-01

261

Preparation and characterization of silicalite-1 membranes prepared by secondary growth of seeds with different crystal sizes  

Microsoft Academic Search

MFI-type zeolite particles of 0.1–1?m in diameter were prepared by adjusting tetra-n-propylammonium hydroxide (TPAOH) and water contents in synthesis mixtures. Using those particles as seeds, MFI-type zeolite membranes were prepared on the surface of a porous mullite tube by secondary growth. The membranes were formed as polycrystalline zeolite layers on and inside the porous support, and the membranes were composed

Y. Hasegawa; T. Ikeda; T. Nagase; Y. Kiyozumi; T. Hanaoka; F. Mizukami

2006-01-01

262

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

263

Biological control of crystal texture: A widespread strategy for adapting crystal properties to function  

SciTech Connect

Textures of calcite crystals from a variety of mineralized tissues belong to organisms from four phyla were examined with high-resolution synchrotron x-ray radiation. Significant differences in coherence length and angular spread were observed between taxonomic groups. Crystals from polycrystalline skeletal ensembles were more perfect than those that function as single-crystal elements. Different anistropic effects on crystal texture were observed for sea urchin and mollusk calcite crystals, whereas none was found for the foraminifer, Patellina, and the control calcite crystals. These results show that the manipulation of crystal texture in different organisms is under biological control and that crystal textures in some tissues are adapted to function. A better understanding of this apparently widespread biological phenomenon may provide new insights for improving synthetic crystal-containing materials. 18 refs., 3 figs., 1 tab.

Berman, A.; Leiserowitz, L.; Weiner, S.; Addadi, L. (Weizmann Inst. of Science, Rehovot (Israel)); Hanson, J.; Koetzle, T.F. (Brookhaven National Lab., Upton, NY (United States))

1993-02-05

264

Optimal control of crystallization of alpha-lactose monohydrate  

E-print Network

quality. Control inputs are temperature, feed rate, and the choice of an appropriate crystal seed. 1 - evap. feed 6 hydration - nucl. -mono crystal seed -mono crystal - product seed 6 ? attr. growth rate in semi-batch mode, temperature of envelope, and the distribution of the crystal seed. Based

Paris-Sud XI, Université de

265

Optimal control of crystallization of alpha-lactose monohydrate  

E-print Network

on product quality. Control inputs are temperature, feed rate, and the choice of an appropriate crystal seed seed -mono crystal - product seed 6 ? attr. growth ? feed ? feed Figure 1: Solvated crystallization, and the distribution of the crystal seed. Based on mathematical modeling the process is optimized in order to maximize

Paris-Sud XI, Université de

266

Dissolution and Resolidification of ... Seed during Top Seeded Melt Texturing of ...  

E-print Network

INTRODUCTION Top-seeded melt growth [1]-[2] has been widely used to prepare well-oriented large single-domained YBa 2 Cu 3 O 7-y (Y123) crystal [1]-[10]. SmBa 2 Cu 3 O 7-y (Sm123), NdBa 2 Cu 3 O 7y (Nd123) single crystals, or their 211 excessive forms whose melting points are higher than that of a Y123 phase, are generally used as seed materials to provide the artificial growth site. The seed crystals are, in general, placed on the top of the samples, and then the seeded samples are meltprocessed at temperatures below the melting points of the seed crystals. Under conditions of restricted nucleation, Y123 crystal grows at the seed with the same orientation as that of the seed. In principle, the seed materials should not melt during the processing, because maximum processing temperature is lower than their melting points. But th

Young A. Jee; Gye-won Hong; Chan-joong Kim

267

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

268

Tuning calcite morphology and growth acceleration by a rational design of highly stable protein-mimetics  

SciTech Connect

In nature, proteins play a significant role in biomineral formation. One of the ultimate goals of bioinspired materials science is to develop highly stable synthetic molecules that mimic the function of these natural proteins by controlling crystal formation. Here, we demonstrate that both the morphology and the degree of acceleration or inhibition observed during growth of calcite in the presence of peptoids can be rationally tuned by balancing the electrostatic interactions (EI) and hydrophobic interactions (HI), with HI playing the dominant role. While either strong EI or HI inhibit growth and suppress (104) face expression, correlations between peptoid-crystal binding energies and observed changes in calcite growth indicate moderate EI allow peptoids to weakly adsorb while moderate HI cause disruption of surface-adsorbed water layers, leading to growth acceleration with retained expression of (104) faces. This study provides fundamental principles for designing peptoids as crystallization promoters, and offers a straightforward screening method based on macroscopic crystal morphology. Because peptoids are sequence-specific, highly stable, and easily synthesized, peptoid-enhanced crystallization offers a broad range of potential applications.

Chen, Chunlong; Qi, Jiahui; Tao, Jinhui; Zuckermann, Ronald; De Yoreo, James J.

2014-09-05

269

Tuning calcite morphology and growth acceleration by a rational design of highly stable protein-mimetics  

NASA Astrophysics Data System (ADS)

In nature, proteins play a significant role in biomineral formation. One of the ultimate goals of bioinspired materials science is to develop highly stable synthetic molecules that mimic the function of these natural proteins by controlling crystal formation. Here, we demonstrate that both the morphology and the degree of acceleration or inhibition observed during growth of calcite in the presence of peptoids can be rationally tuned by balancing the electrostatic and hydrophobic interactions, with hydrophobic interactions playing the dominant role. While either strong electrostatic or hydrophobic interactions inhibit growth and reduces expression of the {104} faces, correlations between peptoid-crystal binding energies and observed changes in calcite growth indicate moderate electrostatic interactions allow peptoids to weakly adsorb while moderate hydrophobic interactions cause disruption of surface-adsorbed water layers, leading to growth acceleration with retained expression of the {104} faces. This study provides fundamental principles for designing peptoids as crystallization promoters, and offers a straightforward screening method based on macroscopic crystal morphology. Because peptoids are sequence-specific, highly stable, and easily synthesized, peptoid-enhanced crystallization offers a broad range of potential applications.

Chen, Chun-Long; Qi, Jiahui; Tao, Jinhui; Zuckermann, Ronald N.; Deyoreo, James J.

2014-09-01

270

Tuning calcite morphology and growth acceleration by a rational design of highly stable protein-mimetics.  

PubMed

In nature, proteins play a significant role in biomineral formation. One of the ultimate goals of bioinspired materials science is to develop highly stable synthetic molecules that mimic the function of these natural proteins by controlling crystal formation. Here, we demonstrate that both the morphology and the degree of acceleration or inhibition observed during growth of calcite in the presence of peptoids can be rationally tuned by balancing the electrostatic and hydrophobic interactions, with hydrophobic interactions playing the dominant role. While either strong electrostatic or hydrophobic interactions inhibit growth and reduces expression of the {104} faces, correlations between peptoid-crystal binding energies and observed changes in calcite growth indicate moderate electrostatic interactions allow peptoids to weakly adsorb while moderate hydrophobic interactions cause disruption of surface-adsorbed water layers, leading to growth acceleration with retained expression of the {104} faces. This study provides fundamental principles for designing peptoids as crystallization promoters, and offers a straightforward screening method based on macroscopic crystal morphology. Because peptoids are sequence-specific, highly stable, and easily synthesized, peptoid-enhanced crystallization offers a broad range of potential applications. PMID:25189418

Chen, Chun-Long; Qi, Jiahui; Tao, Jinhui; Zuckermann, Ronald N; DeYoreo, James J

2014-01-01

271

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

272

Textural properties of synthetic nano-calcite produced by hydrothermal carbonation of calcium hydroxide  

E-print Network

The hydrothermal carbonation of calcium hydroxide (Ca(OH)2) at high pressure of CO2 (initial PCO2 1/4 55 bar) and moderate to high temperature (30 and 90 1C) was used to synthesize fine particles of calcite. This method allows a high carbonation efficiency (about 95% of Ca(OH)2-CaCO3 conversion), a significant production rate (48 kg/m3 h) and high purity of product (about 96%). However, the various initial physicochemical conditions have a strong influence on the crystal size and surface area of the synthesized calcite crystals. The present study is focused on the estimation of the textural properties of synthesized calcite (morphology, specific surface area, average particle size, particle size distribution and particle size evolution with reaction time), using Rietveld refinements of X-ray diffraction (XRD) spectra, Brunauer-Emmett-Teller (BET) measurements, and scanning electron microscope (SEM) and transmission electron microscope (TEM) observations. This study demonstrate that the pressure, the temperatu...

Montes-Hernandez, German; Charlet, L; Tisserand, Delphine; Renard, F

2008-01-01

273

Magnesium content of calcite in carapaces of benthic armine Ostracoda  

E-print Network

- skeletal magnesium calcite is known to occur in deep-sea and intra-reef environments (Friedman, Amiel, & Schneidermann, 1974), synthesis of inorganic magnesium calcite in the laboratory has not been achieved except by using solutions with salt... magnesium for their assumed phylogenetic level, including ostracodes, decapods, and echinoderms. Moberly (1968) used an electron microprobe to study calcite of coral- line algae and bivalves from temperate localities where there is seasonal temperature...

Cadot, H. M.; Kaesler, R. L.

1977-07-22

274

The influence of temperature, pH, and growth rate on the ?18O composition of inorganically precipitated calcite  

NASA Astrophysics Data System (ADS)

The oxygen isotope composition of carbonate minerals varies with temperature as well as other environmental variables. For carbonates that precipitate slowly, under conditions that approach thermodynamic equilibrium, the temperature-dependence of 18O uptake is the dominant signal and the measured 18O content can be used as a paleotemperature proxy. In the more common case where carbonate minerals grow in a regime where they are not in isotopic equilibrium with their host solution, their oxygen isotope compositions are a convolution of multiple environmental variables. Here we present results from calcite growth experiments demonstrating the occurrence of large (>2‰) non-equilibrium oxygen isotope effects under conditions relevant to biogenic calcite growth and many natural inorganic systems. We show that these non-equilibrium effects vary systematically with pH and crystal growth rate. An isotopic ion-by-ion crystal growth model quantifies the competing roles of temperature, pH, and growth rate, and provides a general description of calcite-water oxygen isotope fractionation under non-equilibrium conditions. The crystal growth model results show that (1) there are both equilibrium and kinetic contributions to calcite oxygen isotopes at biogenic growth rates, (2) calcite does not directly inherit the oxygen isotope composition of DIC even at fast growth rates, (3) there is a kinetically controlled variation of about 1‰ per pH unit between pH=7.7 and 9.3 at constant growth rate for inorganic calcite as well as biogenic calcite, and (4) extreme light isotope enrichments in calcite in alkaline environments are likely due to disequilibrium among DIC species in aqueous solution. The model can be extended to 13C uptake into carbonates as well as clumped isotopes but additional data are needed to constrain the kinetic fractionation factors for carbon isotopes. The experimental and model results constitute an important step in separating the relative influence of inorganic and biologic processes on isotopic fractionation and may aid the development of new paleoproxies based on non-equilibrium effects.

Watkins, James M.; Hunt, Jonathan D.; Ryerson, Frederick J.; DePaolo, Donald J.

2014-10-01

275

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

276

A Reacidification Model for Acidified Lakes Neutralized With Calcite  

NASA Astrophysics Data System (ADS)

In lake liming operations in Sweden, acidified lakes are reclaimed by neutralization with calcite powder. The amount added is intended to neutralize the water column as well as to delay the reacidification. The reacidification of limed lakes is dependent on the dilution of the dissolved calcium carbonate with time and, for a limited period of time, the dissolution of calcite from the lake sediments. Calcite on the lake bottom will, in addition to being covered by sedimentation, become inactivated by precipitates of humus and clay minerals clogging the calcite surfaces. A model has been developed to calculate the reacidification of a limed lake which includes the following mechanisms: (1) the dissolution of calcite and a subsequent neutralization of acid water, (2) owing to the increase inpH value, occurrence of precipitation of humus and dissolved metals onto the calcite surface and inhibition of the dissolution of calcite (3) reversible sorbtion of calcium from the water column by sediments not covered with calcite, and (4) diffusive transport through a boundary bottom layer to the water column. In a first approach the lake was modeled as a continuously stirred tank. The equations were derived from a mass balance and the dissolution kinetics for calcite to describe the long-term development ofpH, alkalinity, and calcium concentration in the lake. The differential equations describing the mechanisms were solved with the help of a computer code. The model accurately describes the reacidification and the mass balances observed in several limed lakes.

Sverdrup, Harald; Warfvinge, Per

1985-09-01

277

Effects of Spatial Heterogeneity on Calcite Dissolution Rates.  

E-print Network

??The prediction of carbonate reservoirs behavior, including rock and fluid interactions, is challenging due to their complex mineralogy, porosity, and permeability heterogeneities. Calcite dissolution, one… (more)

Skocik, Mariya

2014-01-01

278

Bent crystal spectrometer for both frequency and wavenumber resolved x-ray scattering at a seeded free-electron laser  

NASA Astrophysics Data System (ADS)

We present a cylindrically curved GaAs x-ray spectrometer with energy resolution ?E/E = 1.1 × 10-4 and wave-number resolution of ?k/k = 3 × 10-3, allowing plasmon scattering at the resolution limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It spans scattering wavenumbers of 3.6 to 5.2/Å in 100 separate bins, with only 0.34% wavenumber blurring. The dispersion of 0.418 eV/13.5 ?m agrees with predictions within 1.3%. The reflection homogeneity over the entire wavenumber range was measured and used to normalize the amplitude of scattering spectra. The proposed spectrometer is superior to a mosaic highly annealed pyrolytic graphite spectrometer when the energy resolution needs to be comparable to the LCLS seeded bandwidth of 1 eV and a significant range of wavenumbers must be covered in one exposure.

Zastrau, Ulf; Fletcher, Luke B.; Förster, Eckhart; Galtier, Eric Ch.; Gamboa, Eliseo; Glenzer, Siegfried H.; Heimann, Philipp; Marschner, Heike; Nagler, Bob; Schropp, Andreas; Wehrhan, Ortrud; Lee, Hae Ja

2014-09-01

279

Bent crystal spectrometer for both frequency and wavenumber resolved x-ray scattering at a seeded free-electron laser  

E-print Network

We present a cylindrically curved GaAs x-ray spectrometer with energy resolution $\\Delta E/E = 1.1\\cdot 10^{-4}$ and wave-number resolution of $\\Delta k/k = 3\\cdot 10^{-3}$, allowing plasmon scattering at the resolution limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It spans scattering wavenumbers of 3.6 to $5.2/$\\AA\\ in 100 separate bins, with only 0.34\\% wavenumber blurring. The dispersion of 0.418~eV/$13.5\\,\\mu$m agrees with predictions within 1.3\\%. The reflection homogeneity over the entire wavenumber range was measured and used to normalize the amplitude of scattering spectra. The proposed spectrometer is superior to a mosaic HAPG spectrometer when the energy resolution needs to be comparable to the LCLS seeded bandwidth of 1~eV and a significant range of wavenumbers must be covered in one exposure.

Zastrau, Ulf; Foerster, Eckhart; Galtier, Eric Ch; Gamboa, Eliseo; Glenzer, Siegfried H; Heimann, Philipp; Marschner, Heike; Nagler, Bob; Schropp, Andreas; Wehrhan, Ortrud; Lee, Hae Ja

2014-01-01

280

The coordination of Mg in foraminiferal calcite. Supplementary Material Branson et al, 2013.  

E-print Network

The coordination of Mg in foraminiferal calcite. Supplementary Material Branson et. al., 2013 to assess the coordination of Mg in foraminiferal calcite. We calcite, and the efficacy of the fitting algorithm used to assess

Cambridge, University of

281

Oxygen isotope fractionation in quartz, albite, anorthite and calcite  

Microsoft Academic Search

Laboratory measurements of equilibrium oxygen isotope fractionation in quartz, albite, anorthite, and calcite have been carried out by anhydrous exchange between silicates and calcite at temperatures of 600°C and above. Exchange in these systems is as rapid as exchange between silicates and water. In this paper results are compared with published theoretical estimates as well as data derived from hydrothermal

Robert N. Clayton; Julian R. Goldsmith; Toshiko K. Mayeda

1989-01-01

282

Lead and cadmium immobilization on calcitic limestone materials  

Microsoft Academic Search

Calcite minerals are used as an alternative low-cost retention material for metal removal in aquatic systems. The pollutant retention process occurring on the surface of these minerals has not been studied in sufficient detail particularly as regards the influence of surface characteristics of calcite-containing soil. To tackle the above, batch equilibrium sorption tests of three sampled limestone solids with different

G. Rangel-Porras; J. B. García-Magno; M. P. González-Muñoz

2010-01-01

283

Calcite deposition at Miravalles geothermal field, Costa Rica  

Microsoft Academic Search

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

L. Vaca; A. Alvarado; R. Corrales

1989-01-01

284

Discovery of a Cretaceous Scleractinian Coral with a Calcitic Skeleton  

Microsoft Academic Search

It has been generally thought that scleractinian corals form purely aragonitic skeletons. We show that a well- preserved fossil coral, Coelosmilia sp. from the Upper Cretaceous (ca. 70 Ma), has preserved skeletal structural features identical to those observed in present day scleractinians. However, the skeleton of Coelosmilia sp. is entirely calcitic. Its fine-scale structure and chemistry indicate that the calcite

J. Stolarski; A. Meibom; R. Przenioslo; M. Mazur

2007-01-01

285

Dissolution of coccolithophorid calcite by microzooplankton and copepod grazing  

NASA Astrophysics Data System (ADS)

Independent of the ongoing acidification of surface seawater, the majority of the calcium carbonate produced in the pelagial is dissolved by natural processes above the lysocline. We investigate to what extent grazing and passage of coccolithophorids through the guts of copepods and the food vacuoles of microzooplankton contribute to calcite dissolution. In laboratory experiments where the coccolithophorid Emiliania huxleyi was fed to the rotifer Brachionus plicatilis, the heterotrophic flagellate Oxyrrhis marina and the copepod Acartia tonsa, calcite dissolution rates of 45-55%, 37-53% and 5-22% of ingested calcite were found. We ascribe higher loss rates in microzooplankton food vacuoles as compared to copepod guts to the strongly acidic digestion and the individual packaging of algal cells. In further experiments, specific rates of calcification and calcite dissolution were also measured in natural populations during the PeECE III mesocosm study under differing ambient pCO2 concentrations. Microzooplankton grazing accounted for between 27 and 70% of the dynamic calcite stock being lost per day, with no measurable effect of CO2 treatment. These measured calcite dissolution rates indicate that dissolution of calcite in the guts of microzooplankton and copepods can account for the calcite losses calculated for the global ocean using budget and model estimates.

Antia, A. N.; Suffrian, K.; Holste, L.; Müller, M. N.; Nejstgaard, J. C.; Simonelli, P.; Carotenuto, Y.; Putzeys, S.

2008-01-01

286

An AFM study of calcite dissolution in concentrated electrolyte solutions  

Microsoft Academic Search

Calcite-solution interactions are of a paramount importance in a range of processes such as the removal of heavy metals, carbon dioxide sequestration, landscape modeling, weathering of building stone and biomineralization. Water in contact with minerals often carries significant amounts of solutes; additionally, their concentration may vary due to evaporation and condensation. It is well known that calcite dissolution is affected

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

2009-01-01

287

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

288

Effect of fluid salinity on subcritical crack propagation in calcite  

NASA Astrophysics Data System (ADS)

The slow propagation of cracks, also called subcritical crack growth, is a mechanism of fracturing responsible for a ductile deformation of rocks under crustal conditions. In the present study, the double-torsion technique was used to measure the effect of fluid chemistry on the slow propagation of cracks in calcite single crystals at room temperature. Time-lapse images and measurements of force and load-point displacement allowed accurate characterization of crack velocities in a range of 10- 8 to 10- 4 m/s. Velocity curves as a function of energy-release rates were obtained for different fluid compositions, varying NH4Cl and NaCl concentrations. Our results show the presence of a threshold in fluid composition, separating two regimes: weakening conditions where the crack propagation is favored, and strengthening conditions where crack propagation slows down. We suggest that electrostatic surface forces that modify the repulsion forces between the two surfaces of the crack may be responsible for this behavior.

Rostom, Fatma; Røyne, Anja; Dysthe, Dag Kristian; Renard, François

2013-01-01

289

AAS, XRPD, SEM\\/EDS, and FTIR characterization of Zn 2+ retention by calcite, calcite–kaolinite, and calcite–clinoptilolite minerals  

Microsoft Academic Search

In this study, the sorption behavior of Zn2+ on calcite, kaolinite, and clinoptilolite, in addition to mixtures of calcite with kaolinite and clinoptilolite, was investigated at various loadings and mixture compositions using atomic absorption spectroscopy, scanning electron microscopy\\/energy dispersive X-ray spectroscopy, X-ray powder diffraction, and Fourier transform infrared techniques. According to the obtained results, within the experimental operating conditions, the

T. Shahwan; B. Zünbül; Ö. Tunuso?lu; A. E. Ero?lu

2005-01-01

290

Strain rate dependent calcite microfabric evolution - An experiment carried out by nature  

NASA Astrophysics Data System (ADS)

A flanking structure developed along a secondary shear zone in calcite marbles, on Syros (Cyclades, Greece), provides a natural laboratory for directly studying the effects of strain rate variations on calcite deformation at identical pressure and temperature conditions. The presence and rotation of a fracture during progressive deformation caused extreme variations in finite strain and strain rate, forming a localized ductile shear zone that shows different microstructures and textures. Textures and the degree of intracrystalline deformation were measured by electron backscattered diffraction. Marbles from the host rocks and the shear zone, which deformed at various strain rates, display crystal-preferred orientation, suggesting that the calcite preferentially deformed by intracrystalline-plastic deformation. Increasing strain rate results in a switch from subgrain rotation to bulging recrystallization in the dislocation-creep regime. With increasing strain rate, we observe in fine-grained (3 ?m) ultramylonitic zones a change in deformation regime from grain-size insensitive to grain-size sensitive. Paleowattmeter and the paleopiezometer suggest strain rates for the localized shear zone around 10-10 s-1 and for the marble host rock around 10-12 s-1. We conclude that varying natural strain rates can have a first-order effect on the microstructures and textures that developed under the same metamorphic conditions.

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

2014-12-01

291

Kinetics of Lactose Crystallization  

Microsoft Academic Search

The effects of certain variables on a-lac- tose crystallization were examined. The tem- perature for optimum crystallization rate varied with the initial supersaturation. Crystallization rate was not directly pro- portional to seed crystal surface area, probably because of false graining or be- cause mutarotation has a limiting effect on rate as surface area is increased. When the position of the

W. C. Twieg; T. A. Nickerson

1968-01-01

292

Calcitization and silicification of evaporites in Guadalupian back-reef carbonates of the Delaware basin, west Texas and New Mexico  

SciTech Connect

Outcrop of the Seven Rivers, Yates, and Tansill formations contain numerous examples of evaporites that have been replaced by both quartz and calcite. The original evaporites consisted of discrete horizons, scattered nodules, enterolithic layers, and individual crystal laths of gypsum and/or anhydrite within a predominantly dolomitic matrix. Based on field and petrographic observations, evaporite replacement proceeded from the exterior to the interior of the nodules. The earliest replacement was by euhedral, black megaquartz containing abundant hydrocarbon inclusions. Calcite replacement followed silicification and consists of coarse, equant, blocky spar. Isotopic analyses of these calcites form two distinct groups: the first group ranges from -10.9 to -20.1{per thousand} (average -16.4{per thousand}) {delta}{sup 13}C and -6.4 to -13.8{per thousand} (average -10.9{per thousand}) {delta}{sup 18}O; the second group ranges from +1.4 to 5.8{per thousand} (average -2.4{per thousand}) {delta}{sup 13}C and -6.2 to 14.1{per thousand} (average -9.2{per thousand}) {delta}{sup 18}O. Evaporite silicification was coeval with hydrocarbon migration as indicated by the inclusion data. Calcitization, however, was associated with mid-Tertiary block faulting that uplifted the area causing deep groundwater circulation. The isotopically very light calcites resulted from the mixing of meteoric fluids and hydrocarbon-rich pore fluids, probably during early uplift while these strata were still at significant depth. The calcites with heavier isotopic values were produced somewhat later by meteoric fluids that had little or no contact with hydrocarbons. Evaporite diagenesis in the Delaware basin is an ongoing process that started during hydrocarbon migration, continued over millions of years, and has the potential to significantly change the porosity of these units.

Ulmer, D.S.; Scholle, P.A. (Southern Methodist Univ., Dallas, TX (United States))

1991-03-01

293

Calcite Biomineralization by Bacterial Isolates from the Recently Discovered Pristine Karstic Herrenberg Cave  

PubMed Central

Karstic caves represent one of the most important subterranean carbon storages on Earth and provide windows into the subsurface. The recent discovery of the Herrenberg Cave, Germany, gave us the opportunity to investigate the diversity and potential role of bacteria in carbonate mineral formation. Calcite was the only mineral observed by Raman spectroscopy to precipitate as stalactites from seepage water. Bacterial cells were found on the surface and interior of stalactites by confocal laser scanning microscopy. Proteobacteria dominated the microbial communities inhabiting stalactites, representing more than 70% of total 16S rRNA gene clones. Proteobacteria formed 22 to 34% of the detected communities in fluvial sediments, and a large fraction of these bacteria were also metabolically active. A total of 9 isolates, belonging to the genera Arthrobacter, Flavobacterium, Pseudomonas, Rhodococcus, Serratia, and Stenotrophomonas, grew on alkaline carbonate-precipitating medium. Two cultures with the most intense precipitate formation, Arthrobacter sulfonivorans and Rhodococcus globerulus, grew as aggregates, produced extracellular polymeric substances (EPS), and formed mixtures of calcite, vaterite, and monohydrocalcite. R. globerulus formed idiomorphous crystals with rhombohedral morphology, whereas A. sulfonivorans formed xenomorphous globular crystals, evidence for taxon-specific crystal morphologies. The results of this study highlighted the importance of combining various techniques in order to understand the geomicrobiology of karstic caves, but further studies are needed to determine whether the mineralogical biosignatures found in nutrient-rich media can also be found in oligotrophic caves. PMID:22179248

Rusznyák, Anna; Akob, Denise M.; Nietzsche, Sándor; Eusterhues, Karin; Totsche, Kai Uwe; Neu, Thomas R.; Frosch, Torsten; Popp, Jürgen; Keiner, Robert; Geletneky, Jörn; Katzschmann, Lutz; Schulze, Ernst-Detlef

2012-01-01

294

Quantifying Surface Kinetic Fractionations for Isotopes and Trace Elements in Calcite Precipitated from Aqueous Solution  

NASA Astrophysics Data System (ADS)

The isotopic ratios and trace element concentrations in calcite and other carbonate minerals form the basis for several paleoenvironmental indicators that are relied upon to reconstruct past Earth climates and ocean processes. Most of these carbonate minerals form at low temperatures (0 to 30C) and consequently are unlikely to have precipitated from aqueous solutions at equilibrium. The non-equilibrium nature of the precipitation process is well illustrated by the experimentally demonstrated precipitation rate-dependence of parameters such as the Ca and O isotopic composition, and the Sr, Mg, and Mn concentrations of calcite. We have been focused on understanding how to predict the magnitude and controls on these kinetic effects using a general transition-state theory approach, as well as models of ion-by-ion growth, molecular dynamics simulations of the desolvation step required for addition of cations to a mineral surface, and further experiments that involve carefully controlled solution compositions and crystal growth rates. Although models have been proposed that invoke diffusion as the primary control on the non-equilibrium aspects of calcite precipitation, it is relatively easy to show that diffusion is not likely to be the primary controlling process. We have focused on understanding the kinetic effects operating at and near the mineral surface, which are undeniably present and important, and appear to be of the correct magnitude and direction to account for observations in both laboratory and natural calcites. The approach we are using is also applicable to higher temperature aqueous precipitation. There are indications from Ca isotopes that similar surface kinetic effects occur at temperatures of 300 to 400C. Kinetic isotope and trace element effects are critically dependent on molecular exchange rates between the mineral surface and the aqueous solution, and the ratio of these rates to the net crystal growth rate. The challenge is to predict and/or measure these rates, which are dependent in a complex fashion on solution saturation state, cation/anion ratios, ionic strength, and other aspects of solution composition. In effect, trace elements and isotopes can provide a measure of these rates, and the derived rates from available experimental data are broadly compatible with measured calcite dissolution and precipitation rates and their dependence on solution composition. Overall, it appears possible to develop a comprehensive framework for understanding kinetic trace element and isotopic fractionation effects during precipitation of minerals from aqueous solution, and to constrain the important controlling parameters using a combination of experiments and simulations.

DePaolo, D. J.; Nielsen, L. C.; Hofmann, A. E.; DeYoreo, J.; Gagnon, A. C.; Watkins, J. M.; Ryerson, F. J.; Brown, S. T.

2011-12-01

295

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

296

TRIACYLGLYCEROL PHASE AND SEED STORAGE BEHAVIOR  

Technology Transfer Automated Retrieval System (TEKTRAN)

Anecdotal stories have long suggested that oil-rich seeds store poorly; however, laboratory studies show that lipid content does not correlate with seed quality. Recently, we found that the tendency of triacylglycerols (TAG) to crystallize during storage of Cuphea seeds has a profound effect on see...

297

Crystallization Pathways in Biomineralization  

NASA Astrophysics Data System (ADS)

A crystallization pathway describes the movement of ions from their source to the final product. Cells are intimately involved in biological crystallization pathways. In many pathways the cells utilize a unique strategy: They temporarily concentrate ions in intracellular membrane-bound vesicles in the form of a highly disordered solid phase. This phase is then transported to the final mineralization site, where it is destabilized and crystallizes. We present four case studies, each of which demonstrates specific aspects of biological crystallization pathways: seawater uptake by foraminifera, calcite spicule formation by sea urchin larvae, goethite formation in the teeth of limpets, and guanine crystal formation in fish skin and spider cuticles. Three representative crystallization pathways are described, and aspects of the different stages of crystallization are discussed. An in-depth understanding of these complex processes can lead to new ideas for synthetic crystallization processes of interest to materials science.

Weiner, Steve; Addadi, Lia

2011-08-01

298

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

299

High-pressure deformation of calcite marble and its transformation to aragonite under non-hydrostatic conditions  

USGS Publications Warehouse

We conducted deformation experiments on Carrara marble in the aragonite and calcite stability fields to observe the synkinematic transformation of calcite to aragonite, and to identify any relationships between transformation and deformation or sample strength. Deformation-induced microstructures in calcite crystals varied most significantly with temperature, ranging from limited slip and twinning at 400??C, limited recrystallization at 500??C, widespread recrystallization at 600 and 700??C, to grain growth at 800-900??C. Variations in confining pressure from 0.3 to 2.0 GPa have no apparent effect on calcite deformation microstructures. Aragonite grew in 10-6-10-7 s-1strain rate tests conducted for 18-524 h at confining pressures of 1.7-2.0 GPa and temperatures of 500-600??C. As in our previously reported hydrostatic experiments on this same transformation, the aragonite nucleated on calcite grain boundaries. The extent of transformation varied from a few percent conversion near pistons at 400??C, 2.0 GPa and 10-4 s-1 strain rate in a 0.8 h long experiment, to 98% transformation in a 21-day test at a strain rate of 10-7 s-7, a temperature of 600??C and a pressure of 2.0 GPa. At 500??C, porphyroblastic 100-200 ??m aragonite crystals grew at a rate faster than 8 ?? 10-1m s-1. At 600??C, the growth of aragonite neoblasts was slower, ???6 ?? 10-1 m s -1, and formed 'glove-and-finger' cellularprecipitation-like textures identical to those observed in hydrostatic experiments. The transformation to aragonite is not accompanied by a shear instability or anisotropic aragonite growth, consistent with its relatively small volume change and latent heat in comparison with compounds that do display those features. ?? 1993.

Hacker, B.R.; Kirby, S.H.

1993-01-01

300

Uranyl incorporation into calcite and aragonite: XAFS and luminescence studies  

SciTech Connect

X-ray absorption, luminescence, and Raman spectroscopic studies of U(VI)-containing calcite and aragonite show that the UO{sub 2}{sup 2+} ion, the dominant and mobile form of dissolved uranium in near-surface waters, has a disordered and apparently less stable coordination environment when incorporated into calcite in comparison to aragonite, both common polymorphs of CaCO{sub 3}. Their findings suggest that calcite, a widely distributed authigenic mineral in soils and near-surface sediments and a principal weathering product of concrete-based containment structures, is not likely to be a suitable host for the long-term sequestration of U(VI). The more stable coordination provided by aragonite suggests that its long-term retention should be favored in this phase, until it inverts to calcite. Consequently, future remobilization of U(VI) coprecipitated with calcium carbonate minerals should not be ruled out in assessments of contaminated sites. Their observation of a similar equatorial coordination of UO{sub 2}{sup 2+} in aragonite and the dominant aqueous species [UO{sub 2}(CO{sub 3}){sub 3}{sup 4{minus}}] but a different coordination in calcite indicates that a change in UO{sub 2}{sup 2+} coordination is required for its incorporation into calcite. This may explain the observed preferential uptake of U(VI) by aragonite relative to calcite.

Reeder, R.J.; Nugent, M.; Lamble, G.M.; Tait, C.D.; Morris, D.E.

2000-02-15

301

Strontium Incorporation into Calcite Generated by Bacterial Ureolysis  

SciTech Connect

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 (DEX) 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.

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

2004-08-01

302

Vertical Distribution of Calcite at Yucca Mountain, Nevada, as an Indicator of Flow Through a Thick Unsaturated Zone  

SciTech Connect

Meteoric water percolating through 500 to 700 m of hydrologically unsaturated felsic tuffs provides a mechanism for release and transport of radionuclides from a potential high-level radioactive waste repository at Yucca Mountain, Nevada. Modern flow through the unsaturated zone (UZ) is low (probably <20 mm/year) and has not been observed directly. However, calcite formed from water percolating through fracture and lithophysal cavities over the last 12.8 million years provides, in part, a time-integrated record of UZ flow. Calcite concentration profiles were determined in dry-drilled boreholes USW WT-24 and USW SD-6 by acidifying samples of powdered rock cuttings collected over 5-foot intervals and measuring the evolved CO{sub 2} using gas chromatography. Resulting CO{sub 2}-derived calcite concentrations ranged from 30,800 to less than 20 ppm. Aliquots of the same powders also were analyzed for Ca, Ti, and Zr by energy-dispersive X-ray fluorescence. Concentrations of Ti and Zr in the crystal-poor, high-silica rhyolite parts of the Topopah Spring Tuff are uniform (standard deviations of 3 to 4%); however, Ca scatters widely (standard deviations of 21 and 32%). Concentrations of Ca are positively correlated to CO{sub 2}-derived calcite concentrations and regressions for samples of the two major rhyolitic tuffs yielded r{sup 2} values >0.9, CO{sub 2}-intercept Ca concentrations in the range of values determined on fresh rock samples, and slopes equivalent to addition of stoichiometric calcite. Therefore, combined CO{sub 2} and Ca data provide a means of determining the amount of secondary calcite added to the rock mass from percolating water. The vertical distribution of calcite is related to lithostratigraphy with the largest concentrations in the welded hydrogeologic unit of the Tiva Canyon Tuff near the land surface and progressively smaller values with depth into the underlying nonwelded units. Large values also may be present in the upper parts of the underlying welded hydrogeologic unit of the Topopah Spring Tuff, but generally decrease in the deeper parts of the unit. The spatial distribution of calcite is complex and likely is related, in part, to spatial variations in the amount of water and vapor transported through the thick UZ.

J.B. Paces; Z.E. Peterman

2001-07-20

303

Paleoclimatic and paleohydrologic records from secondary calcite: Yucca Mountain, Nevada  

SciTech Connect

Stable isotope analyses of calcite and opal, fluid inclusion formation conditions and gas compositions, Sr isotope ratios, and REE compositions all support formation of secondary calcite in the unsaturated zone of Yucca Mountain from infiltration of surface-derived (and soil zone buffered) waters of meteoric origin. Detailed sampling of growth-banding preserved by the secondary calcite should provide a record of past variations in the stable isotope chemistry of these infiltrating waters, and, hence, of precipitation at Yucca Mountain, i.e., a proxy of past climate at Yucca Mountain. The precision of this record depends on how well it can be dated. The distribution and texture of secondary calcite occurrences, if mapped in careful detail from existing bore hole samples and underground workings (as exposures become accessible), could provide a time/space map of fracture and fault unsaturated-zone ground water flow-paths during past wetter climates which might prevail in the future with change in climate.

Whelan, J.F.; Stuckless, J.S.; Moscati, R.J. [Geological Survey, Denver, CO (United States); Vaniman, D.T. [Los Alamos National Lab., NM (United States)

1994-12-31

304

O of cellulose organic fraction combined with 18 O of calcite and 18  

E-print Network

1 18 O of cellulose organic fraction combined with 18 O of calcite and 18 O of diatoms in lake of authigenic calcite and 18 O of diatoms (if available). The results of 18 O of authigenic calcite, diatom and cellulose are presented in Fig.3. Fig. 3. Oxygen isotopic composition of authigenic calcite, diatom

Edwards, Thomas W.D.

305

Biogenic and synthetic high magnesium calcite A review q Xia Long, Yurong Ma  

E-print Network

Review Biogenic and synthetic high magnesium calcite ­ A review q Xia Long, Yurong Ma , Limin Qi e i n f o Article history: Available online 26 November 2013 Keywords: High-Mg calcite Biominerals-Mg calcites in different marine organisms were summarized in detail in this review. The high-Mg calcites

Qi, Limin

306

Spectroscopic study of phase transitions in natural calcite mineral  

Microsoft Academic Search

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

S. Gunasekaran; G. Anbalagan

2008-01-01

307

A Cretaceous Scleractinian Coral with a Calcitic Skeleton  

Microsoft Academic Search

It has been generally thought that scleractinian corals form purely aragonitic skeletons. We show that a well-preserved fossil coral, Coelosmilia sp. from the Upper Cretaceous (about 70 million years ago), has preserved skeletal structural features identical to those observed in present-day scleractinians. However, the skeleton of Coelosmilia sp. is entirely calcitic. Its fine-scale structure and chemistry indicate that the calcite

Jaroslaw Stolarski; Anders Meibom; Radoslaw Przenioslo; Maciej Mazur

2007-01-01

308

Precipitation of Calcite by Indigenous Microorganisms to Strengthen Liquefiable Soils  

Microsoft Academic Search

Enrichments for indigenous microorganisms capable of hydrolyzing urea in the presence of CaCl2 were performed on potentially liquefiable saturated soils in both the laboratory and in situ. Following enrichment, treatment of soils with nutrients, CaCl2 and urea resulted in significant in situ precipitation of calcite, even at depth, by indigenous microorganisms. The biomineralized soils showed properties that indicate calcite precipitation

Malcolm B. Burbank; Thomas J. Weaver; Tonia L. Green; Barbara C. Williams; Ronald L. Crawford

2011-01-01

309

Biomimetic synthesis of monodisperse rosette-like calcite mesocrystals regulated by carboxymethyl cellulose and the proposed mechanism?:? An unconventional rhombohedra-stacking route  

Microsoft Academic Search

Carboxymethyl cellulose (CMC) is systematically investigated for the first time in regulating the CaCO3 crystallization using a biomimetic gas-diffusion method. Monodisperse rosette-like calcite spherules in uniform size with their surfaces composed of rhombohedral subunits were synthesized in certain conditions. According to time-resolved experiment, the evolution of the crystal morphology was traced and the possible route in which rosette-like spherules form

Wei Li; Peiyi Wu

2009-01-01

310

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

311

Incorporation of Pb at the calcite (104)-water interface.  

PubMed

Lead (Pb) is a common environmental pollutant, and its transport in surface waters and groundwater is controlled in part by sorption and precipitation reactions at mineral surfaces. Using in situ specular and resonant anomalous X-ray reflectivity measurements, we investigated the interaction of the calcite (104) surface with a dilute Pb- and EDTA-bearing solution that is slightly undersaturated with respect to calcite. The X-ray results reveal Pb coherently substituting for Ca in the near-surface layers of strained calcite with Pb/(Pb + Ca) atom fractions as high as 0.28 in the outermost layer. The larger ionic radius of Pb(2+) relative to Ca(2+) is accommodated in calcite by vertical displacements of Pb relative to the Ca site. In situ atomic force microscopy images obtained during the reaction suggest that Pb incorporation below the surface occurs after initial dissolution followed by regrowth of a strained epitaxial Pb-rich calcite solid-solution at the calcite (104)-water interface. This process could produce a widespread host phase for Pb in groundwater aquifers and soil pore fluids. PMID:25007415

Callagon, Erika; Fenter, Paul; Nagy, Kathryn L; Sturchio, Neil C

2014-08-19

312

Heat-Exchanger Method of Crystal Growth  

NASA Technical Reports Server (NTRS)

Large crystals of silicon are grown from melt, in either vacuum or pressurized atmosphere, without moving crucible, furnace, or anything else. Seed crystal is mounted on helium-cooled heat exchanger, which prevents seed from melting when furnace melts rest of silicon material in crucible; heat exchanger draws off heat from melt so that a solid ingot grows outward from seed in a regular crystal structure. Bottom of crucible is insulated so that heat exchanger cools only seed.

Khattak, C. P.; Schmid, F.

1982-01-01

313

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

314

Infrared spectroscopic investigations of the calcite-rhodochrosite and parts of the calcite-magnesite mineral series  

Microsoft Academic Search

The infrared spectroscopic measurements of synthetic and natural carbonate samples show that significant frequency shifts in the v2 and v4 vibrational bands of the carbonate ion group occur in the calcite-rhodochrosite and calcite-magnesite mineral series as a function of the chemical composition. These shifts are due to cationic substitution, reflecting the different ionic raddii and masses of the end-members. A

M. E. Böttcher; P.-L. Gehlken; E. Usdowski

1992-01-01

315

Seeding Rangeland  

E-print Network

Most Texas rangeland produces below its potential. Improving rangeland requires brush control and/or seeding to restore production to the site's potential. This publication is a guide to seeding rangelands, and discusses when, where, how, and what...

Welch, Tommy G.; Hafercamp, Marshall R.

2001-01-04

316

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

317

The Raman spectrum of CaCO{sub 3} polymorphs calcite and aragonite: A combined experimental and computational study  

SciTech Connect

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{sup ?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 {sup 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.

De La Pierre, Marco, E-mail: cedric.carteret@univ-lorraine.fr, E-mail: marco.delapierre@unito.it; Maschio, Lorenzo; Orlando, Roberto; Dovesi, Roberto [Dipartimento di Chimica, Università di Torino and NIS (Nanostructured Interfaces and Surfaces) Centre of Excellence, Via P. Giuria 7, 10125 Torino (Italy)] [Dipartimento di Chimica, Università di Torino and NIS (Nanostructured Interfaces and Surfaces) Centre of Excellence, Via P. Giuria 7, 10125 Torino (Italy); Carteret, Cédric, E-mail: cedric.carteret@univ-lorraine.fr, E-mail: marco.delapierre@unito.it; André, Erwan [Laboratoire de Chimie Physique et Microbiologie pour l’Environnement (LCPME), UMR 7564, Université de Lorraine-CNRS, 405 rue de Vandoeuvre, 54601 Villers-lès-Nancy (France)] [Laboratoire de Chimie Physique et Microbiologie pour l’Environnement (LCPME), UMR 7564, Université de Lorraine-CNRS, 405 rue de Vandoeuvre, 54601 Villers-lès-Nancy (France)

2014-04-28

318

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

319

Seed proteomics  

Technology Transfer Automated Retrieval System (TEKTRAN)

Seeds comprise a protective covering, a small embryonic plant, and a nutrient-storage organ. Seeds are protein-rich, and have been the subject of many mass spectrometry-based analyses. Seed storage proteins (SSP), which are transient depots for reduced nitrogen, have been studied for decades by cel...

320

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

NASA Astrophysics Data System (ADS)

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 ( Rp) to the gross forward precipitation rate ( Rf), for conditions where ionic transport to the growing crystal surface is not rate-limiting. The value of Rp has been experimentally measured under varying conditions, but the magnitude of Rf 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, Rf can be estimated from the bulk far-from-equilibrium dissolution rate of calcite ( Rb or kb), since at equilibrium Rf = Rb, and Rp = 0. Hence it can be inferred that Rf ? Rp + Rb. 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 Rp (= Rf - Rb) ? Rb. For precipitation rates high enough that Rp ? Rb, 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 Rp ? Rb for Ca isotopic fractionation. According to this model, Ca isotopic data can be used to estimate Rf 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 Rp. Allowing Rb to vary as Rp1/2, consistent with available precipitation rate studies, produces a better fit to some trace element and isotopic data than a model where Rb is constant. This model can account for most of the experimental data in the literature on the dependence of 44Ca/ 40Ca and metal/Ca fractionation in calcite as a function of precipitation rate and temperature, and also accounts for 18O/ 16O variations with some assumptions. The apparent temperature dependence of Ca isotope fractionation in calcite may stem from the dependence of Rb 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 require hyper-fast diffusivity in near-surface layers of the solid.

DePaolo, Donald J.

2011-02-01

321

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

322

The inhibition of calcium carbonate crystal growth by the cysteine-rich Mdm2 peptide  

Microsoft Academic Search

The crystal growth of calcite, the most stable calcium carbonate polymorph, in the presence of the cysteine-rich Mdm2 peptide (containing 48 amino acids in the ring finger configuration), has been investigated by the constant composition technique. Crystallization took place exclusively on well-characterized calcite crystals in solutions supersaturated only with respect to this calcium carbonate salt. The kinetic results indicated a

E. Dalas; A. Chalias; D. Gatos; K. Barlos

2006-01-01

323

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

324

Extension of self-seeding scheme with single crystal monochromator to lower energy < 5 keV as a way to generate multi-TW scale pulses at the European XFEL  

E-print Network

We propose a use of the self-seeding scheme with single crystal monochromator to produce high power, fully-coherent pulses for applications at a dedicated bio-imaging beamline at the European X-ray FEL in the photon energy range between 3.5 keV and 5 keV. We exploit the C(111) Bragg reflection (pi-polarization) in diamond crystals with a thickness of 0.1 mm, and we show that, by tapering the 40 cells of the SASE3 type undulator the FEL power can reach up to 2 TW in the entire photon energy range. The present design assumes the use of a nominal electron bunch with charge 0.1 nC at nominal electron beam energy 17.5 GeV. The main application of the scheme proposed in this work is for single shot imaging of individual protein molecules.

Geloni, Gianluca; Saldin, Evgeni

2012-01-01

325

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. PMID:23690577

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

2013-01-01

326

On the formation and functions of high and very high magnesium calcites in the continuously growing teeth of the echinoderm Lytechinus variegatus: development of crystallinity and protein involvement.  

PubMed

Sea urchin teeth grow continuously and develop a complex mineralized structure consisting of spatially separate but crystallographically aligned first stage calcitic elements of high Mg content (5-15 mol% mineral). These become cemented together by epitaxially oriented second stage very high Mg calcite (30-40 mol% mineral). In the tooth plumula, ingressing preodontoblasts create layered cellular syncytia. Mineral deposits develop within membrane-bound compartments between cellular syncytial layers. We seek to understand how this complex tooth architecture is developed, how individual crystalline calcitic elements become crystallographically aligned, and how their Mg composition is regulated. Synchrotron microbeam X-ray scattering was performed on live, freshly dissected teeth. We observed that the initial diffracting crystals lie within independent syncytial spaces in the plumula. These diffraction patterns match those of mature tooth calcite. Thus, the spatially separate crystallites grow with the same crystallographic orientation seen in the mature tooth. Mineral-related proteins from regions with differing Mg contents were isolated, sequenced, and characterized. A tooth cDNA library was constructed, and selected matrix-related proteins were cloned. Antibodies were prepared and used for immunolocaliztion. Matrix-related proteins are acidic, phosphorylated, and associated with the syncytial membranes. Time-of-flight secondary ion mass spectroscopy of various crystal elements shows unique amino acid, Mg, and Ca ion distributions. High and very high Mg calcites differ in Asp content. Matrix-related proteins are phosphorylated. Very high Mg calcite is associated with Asp-rich protein, and it is restricted to the second stage mineral. Thus, the composition at each part of the tooth is related to architecture and function. PMID:21555859

Veis, Arthur; Stock, Stuart R; Alvares, Keith; Lux, Elizabeth

2011-01-01

327

Crystallization phenomena of magnesium ammonium phosphate (MAP) in a fluidized-bed-type crystallizer  

Microsoft Academic Search

In this study, experiments using a fluidized crystallizer with added seed, were performed, to observe the crystal growth and nucleation phenomena of MAP, by changing the degree of supersaturation. The average growth rate of suspended seed crystals correlated relatively well with the degree of supersaturation to obtain the quantitative correlation equation. Also the average crystal growth rate was in good

Izumi Hirasawa; Shogo Kaneko; Yuuji Kanai; Shingo Hosoya; Kumiko Okuyama; Takashi Kamahara

2002-01-01

328

Designer Seeds  

NSDL National Science Digital Library

In this activity students examine a variety of seeds, describe them, and determine how they are dispersed. Students investigate seed dispersal mechanisms. Students, working in pairs, create and test a wind dispersed seed that they have designed themselves. Students are limited to using a single piece of white paper, one lima bean to represent a seed, tape and scissors. Seeds are tested by dropping them in front of a window fan and recording the distance they travel. Repeat trials are conducted, averages calculated, and class data recorded. Students examine the features of successful seeds and redesign their seed to try to increase the distance it can be carried by wind. Results are analyzed and comparisons made to natural phenomena.

BEGIN:VCARD VERSION:2.1 FN:Frank Taylor N:Taylor;Frank ORG:Radford High School REV:2005-04-09 END:VCARD

1995-06-30

329

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. PMID:21637497

2010-01-01

330

Specific effects of background electrolytes on the kinetics of step propagation during calcite growth  

NASA Astrophysics Data System (ADS)

The mechanisms by which background electrolytes modify the kinetics of non-equivalent step propagation during calcite growth were investigated using Atomic Force Microscopy (AFM), at constant driving force and solution stoichiometry. Our results suggest that the acute step spreading rate is controlled by kink-site nucleation and, ultimately, by the dehydration of surface sites, while the velocity of obtuse step advancement is mainly determined by hydration of calcium ions in solution. According to our results, kink nucleation at acute steps could be promoted by carbonate-assisted calcium attachment. The different sensitivity of obtuse and acute step propagation kinetics to cation and surface hydration could be the origin of the reversed geometries of calcite growth hillocks (i.e., rate of obtuse step spreading < rate of acute step spreading) observed in concentrated (ionic strength, IS = 0.1) KCl and CsCl solutions. At low IS (0.02), ion-specific effects seem to be mainly associated with changes in the solvation environment of calcium ions in solution. With increasing electrolyte concentration, the stabilization of surface water by weakly paired salts appears to become increasingly important in determining step spreading rate. At high ionic strength (IS = 0.1), overall calcite growth rates increased with increasing hydration of calcium in solution (i.e., decreasing ion pairing of background electrolytes for sodium-bearing salts) and with decreasing hydration of the carbonate surface site (i.e., increasing ion pairing for chloride-bearing salts). Changes in growth hillock morphology were observed in the presence of Li +, F - and SO42-, and can be interpreted as the result of the stabilization of polar surfaces due to increased ion hydration. These results increase our ability to predict crystal reactivity in natural fluids which contain significant amounts of solutes.

Ruiz-Agudo, Encarnación; Putnis, Christine V.; Wang, Lijun; Putnis, Andrew

2011-07-01

331

Uranium and thorium isotope concentrations in foraminiferal calcite  

NASA Astrophysics Data System (ADS)

Uranium and thorium isotope activities were measured by isotope dilution alpha spectrometry in four late Pleistocene and Holocene foraminiferal calcite samples. Sample cleaning methods were utilized to separate calcite tests from contaminating clay and surface oxide coatings. The maximum concentration of lattice bound uranium is 0.023 ppm (10 × 10 -9 moles U/mole Ca), consistent with the lowest reported value, 0.025 ppm [1]. 230Th/ 234U activity ratios in samples cleaned as described above are much greater than one, indicating that the cleaning methods used do not effectively remove 230Th from the surfaces of the calcite. The upper limit for lattice bound 232Th is 0.039 ppm (17 × 10 -9 moles Th/mole Ca).

Delaney, Margaret Lois; Boyle, Edward A.

1983-02-01

332

Microbially Induced Calcite Precipitation for Subsurface Immobilization of Contaminants  

NASA Astrophysics Data System (ADS)

Subsurface radionuclide and metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of the greatest challenges for long-term stewardship. One promising stabilization mechanism for divalent trace ions, such as the short-lived radionuclide 90Sr, is co-precipitation in calcite. We have found that calcite precipitation and co-precipitation of Sr can be accelerated by the activity of urea hydrolyzing microorganisms, that higher calcite precipitation rates can result in increased Sr partitioning, and that nutrient additions can stimulate ureolytic activity. To extend our understanding of microbially induced calcite precipitation (MICP) in an aquifer setting a continuous recirculation field experiment evaluating MICP was conducted at the Integrated Field Research Challenge (IFRC) site located at Rifle, CO. In this experiment, groundwater extracted from an onsite well was amended with urea (total mass of 42.5 kg) and molasses (a carbon and electron donor) and re-injected into a well approximately 4 meters up-gradient for a period of 12 days followed by 10 months of groundwater sampling and monitoring. Crosshole radar and electrical tomographic data were collected prior, during, and after the MICP treatment. The urea and molasses treatment resulted in an enhanced population of sediment associated urea hydrolyzing organisms as evidenced by increases in the number of ureC gene copies, increases in 14C urea hydrolysis rates, and long-term observations of ammonium (a urea hydrolysis product) in the injection, extraction and down gradient monitoring wells. Permeability changes and increases in the calcite saturation indexes in the well field suggest that mineral precipitation has occurred; ongoing analysis of field samples seeks to confirm this. Changes in dielectric constant and electrical conductivity were used to interpret the spatiotemporal distribution of the injectate and subsequent calcite precipitation. Modeling activities are underway to define field-scale urea hydrolysis rates.

Smith, R. W.; Fujita, Y.; Ginn, T. R.; Hubbard, S. S.; Dafflon, B.; Delwiche, M.; Gebrehiwet, T.; Henriksen, J. R.; Peterson, J.; Taylor, J. L.

2011-12-01

333

Discovery of a Cretaceous Scleractinian Coral with a Calcitic Skeleton  

NASA Astrophysics Data System (ADS)

It has been generally thought that scleractinian corals form purely aragonitic skeletons. We show that a well- preserved fossil coral, Coelosmilia sp. from the Upper Cretaceous (ca. 70 Ma), has preserved skeletal structural features identical to those observed in present day scleractinians. However, the skeleton of Coelosmilia sp. is entirely calcitic. Its fine-scale structure and chemistry indicate that the calcite is primary and did not from via diagenetic alteration of aragonite. This result implies that corals, like other groups of marine, calcium carbonate- producing organisms, can form skeletons of different carbonate polymorphs. Implications for coral biomineralization and evolution will be discussed.

Stolarski, J.; Meibom, A.; Przenioslo, R.; Mazur, M.

2007-12-01

334

A Cretaceous scleractinian coral with a calcitic skeleton.  

PubMed

It has been generally thought that scleractinian corals form purely aragonitic skeletons. We show that a well-preserved fossil coral, Coelosmilia sp. from the Upper Cretaceous (about 70 million years ago), has preserved skeletal structural features identical to those observed in present-day scleractinians. However, the skeleton of Coelosmilia sp. is entirely calcitic. Its fine-scale structure and chemistry indicate that the calcite is primary and did not form from the diagenetic alteration of aragonite. This result implies that corals, like other groups of marine, calcium carbonate-producing organisms, can form skeletons of different carbonate polymorphs. PMID:17916731

Stolarski, Jaroslaw; Meibom, Anders; Przenioslo, Radoslaw; Mazur, Maciej

2007-10-01

335

Comparative Study of Nanoscale Surface Structures of Calcite Microcrystals Using FE-SEM, AFM, and TEM  

NASA Astrophysics Data System (ADS)

The bulk morphology and surface features that developed upon precipitation on micrometer-size calcite powders and millimeter-size cleavage fragments were imaged by three different microscopic techniques: field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) of Pt-C replicas, and atomic force microscopy (AFM). Each technique can resolve some nanoscale surface features, but they offer different ranges of magnification and dimensional resolutions. Because sample preparation and imaging is not constrained by crystal orientation, FE-SEM and TEM of Pt-C replicas are best suited to image the overall morphology of microcrystals. However, owing to the decoration effect of Pt-C on the crystal faces, TEM of Pt-C replicas is superior at resolving nanoscale surface structures, including the development of new faces and the different microtopography among nonequivalent faces in microcrystals, which cannot be revealed by FE-SEM. In conjunction with SEM, Pt-C replica provides the evidence that crystals grow in diverse and face-specific modes. The TEM imaging of Pt-C replicas has nanoscale resolution comparable to AFM. AFM yielded quantitative information (e.g., crystallographic orientation and height of steps) of microtopographic features. In contrast to Pt-C replicas and SEM providing three-dimensional images of the crystals, AFM can only image one individual cleavage or flat surface at a time.

Chien, Yung-Ching; Mucci, Alfonso; Paquette, Jeanne; Sears, S. Kelly; Vali, Hojatollah

2006-07-01

336

Origin of authigenic calcite and aragonite in pelagic sediments of the Mendeleev Ridge (Arctic Ocean) and their paleoceanographicimplications  

NASA Astrophysics Data System (ADS)

Carbonate minerals were discovered from the giant box core (PS72/410-1) of the pelagic sediments recovered from the Canadian Arctic across the central Mendeleev Ridge (Station location= Lat. 80°30.37"N, Long. 175°44.38"W) during the Arctic cruise by Polarstern in 2008. The core was 39 cm long and was collected from the water depth of 1802 meters. The sediments show various colours from grey to brown as previously reported in other Arctic pelagic sediments. The sediments include planktonic foraminifers together with carbonate minerals. The contents of planktonic foraminifers and carbonate minerals vary with core depth, however these carbonate minerals are present through the whole sequence except for a few centimetres. After wet sieving, coarse fractions were texturally examined with binocular microscope and SEM, and stable isotope and trace element contents were obtained. Mineralogy of carbonate minerals were determined using crystal shapes and qualitative Sr contents by EDAX together with trace element analysis. The carbonates are composed of high Mg-calcite, low Mg-calcite and aragonite. Aragonite crystals show (1) radiating fibrous texture, (2) randomly oriented fibrous texture, (3) spherulitic fibrous texture, and (4) bladed texture, and calcite crystals show (1) foliated texture, (2) randomly bladed texture, (3) spherulitic fibrous texture, and (4) equant texture. Various crystal shapes of aragonite and calcite together with clear growth shapes of the crystals suggest that they are inorganic in origin. Highly enriched carbon isotope compositions (?13C = 0 ~ +5‰ vs. PDB) strongly indicate that they formed in methanogenic zone below sediment/water interface by the reaction between anoxic pore fluids and host sediments induced by methanogenic bacteria. However, a wide range of oxygen isotope values (?18O = -5 ~ +5‰ vs. PDB) may indicate that porewater has been changed due to reaction between residual seawater and volcanic sediments. Four types of stable isotope compositions are recognized and they imply complicated evolution of early diagenetic pore waters. Because the core sediments are not organic-rich, the presence of the authigenic carbonates may be related to paleoceanograhic conditions of the Arctic Ocean which resulted in anoxic pore water conditions just a few centimetres below the sediment/water interface. Trace elemental compositions show clear divisions at the boundary of ca. 10 cm in core depth. Carbonates found shallower than this depth show higher Mg, Mn, Fe and Sr compositions which may imply paleoenvironmental changes with time.

Woo, K. S.; Ji, H. S.; Nam, S.; Stein, R. H.; Mackensen, A.; Matthiessen, J. J.

2013-12-01

337

Production of Calcite by the Green Alga Halimeda in Artificial Cretaceous Seawater  

NASA Astrophysics Data System (ADS)

The codiacean green alga Halimeda contributes 20-30% of the carbonate sediment in lagoonal areas adjacent to modern Caribbean and Indo-Pacific coral reefs. This alga is syncytial, lacking cell membranes, so that an individual thallus functions as a giant, multinucleate cell. The thallus grows as branching chains of segments interconnected by tubular filaments. A segment is formed in a single day and then filled with calcium carbonate over several days. Aragonite crystals grow within segments in the form of needles, but in some regions of a segment these are subsequently dissolved and their calcium carbonate is reprecipitated as microgranular aragonite. Some of the needles grow in a spherulitic pattern similar to that of inorganic aragonite precipitates. It has been debated whether Halimeda employs organic templates to secrete the aragonite polymorph of calcium carbonate or simply induces precipitation by taking up carbon dioxide for photosynthesis. We have found that Halimeda incrassata segments grown in seawater of modern ionic composition (Mg/Ca molar ratio = 5.2) actually contain an average of about 8% high-Mg calcite (mean 16 mol % Mg substituting for Ca). As the Mg/Ca ratio of ambient seawater is stepped down, calcite constitutes an increasing percentage of the calcium carbonate produced, and, as we have found for numerous other kinds of organisms, the Mg content of the calcite declines. For segments grown in seawater with the imputed Cretaceous Mg/Ca molar ratio of 1.5, calcite constituted, on average, 46% of the calcium carbonate (maximum, 67%) and contained about 6 mol% Mg. Experiments show that in artificial seawaters having different Mg/Ca molar ratios but otherwise having the ionic strength and chemical composition of modern seawater, aragonite can precipitate inorganically when the Mg/Ca molar ratio is above 2. The fact that Halimeda produces slightly more aragonite than calcite when the ambient Mg/Ca molar ratio is 1.5 indicates that it does exert a degree of biological control over its calcium carbonate production, but that the control is incomplete. Our growth experiments showed that there is a correlation between rate of production of carbonate and rate of production of organic matter by Halimeda, apparently because, as has been previously demonstrated, this alga's photosynthesis is enhanced by the carbon dioxide produced by its calcification. Productivity was highest in seawater of modern composition. Experiments in which either the ambient Mg/Ca ratio or the absolute concentration of Ca was held constant while the other was varied showed that an increase in either one led to a higher rate of production of both organic matter and calcium carbonate. Nonetheless, rates of production were higher in imputed Cretaceous seawater (Mg/Ca molar ratio = 1.5) than in imputed Oligocene seawater (Mg/Ca molar ratio = 2.5), presumably because in the Oligocene treatment, both of the minerals produced (high-Mg calcite and aragonite) were favored by the ambient Mg/Ca ratio, whereas in the Cretaceous treatment, 56% of the calcium carbonate was aragonite, which was not favored by the ambient Mg/Ca ratio.

Stanley, S. M.; Ries, J. B.

2006-12-01

338

Microbes Caught in the Act: Disentangling the Role of Biofilms in the Formation of Low Mg Calcite Ooids in a Freshwater Lake  

NASA Astrophysics Data System (ADS)

Biofilms and molds of cyanobacteria infilling depressions within the outermost cortex of ooids have been previously described in recent ooidal sands of Lake Geneva (Switzerland). Detailed sedimentological and mineralogical analyses of these ooids further indicated a low-Mg calcite composition of their cortex. Observed ooidal morphological features called for a fundamental role of biofilms triggering carbonate precipitation. A detailed microbiological study was much needed, however, in order to decipher the relative role of organic versus purely physicochemical processes during ooid formation. An experimental device consisting of frosted microscope slides was set at 2.50 m water depth in western Lake Geneva. These slides provide an attractive substrate for the microorganisms involved in low-Mg calcite precipitation allowing the in-situ harvesting of biofilms on a regular basis during more than three years. The inspection of the frosted slides showed the development of biofilms on their surface containing coccoid and filamentous cyanobacteria, heterotrophic bacteria and diatom frustules. Microscopical observations under natural light and autoflorescence show a close association between freshly low Mg-calcite precipitates and biofilms containing at least five species of filamentous and coccoid cyanobacteria. Carbonate precipitation peaks at early spring and late summer, and low Mg calcite crystals are always in close association with mostly cyanobacteria filaments (e.g., Tolipothrix, Oscillatoria). Ultra high-resolution elemental analyses performed immediately after recovering the samples confirmed the microscopical observations. Further SEM inspection of the samples revealed a clear seasonal pattern of carbonate precipitation identifying low Mg- calcite with crystal shapes varying from poorly to not crystallized compact aggregates; subautomorph to automorph rhomboedric crystals; and snowy cluster in which particles are very little or not crystallized. Liquid and solid cultures were further developed in the laboratory from the harvested biofilms allowing the determination of the microbial community using a PCR-DGGE approach. Two different primers were used to target all bacteria, and cyanobacteria and diatoms (341F-GC/907RM and 359F-GC/781 (a+b), respectively). Initial results indicate a similar microbial diversity between the sampled natural biofilms and those from BG11 enriched cultures. These data will allow us to design further laboratory experiments on low-Mg calcite precipitation including changes in pH, temperature and light intensity that mimic the natural biological and physicochemical cycle of the modern lake water throughout the year. Hence, this first dataset illustrates the significance of the in situ experiment to validate previous observations. Combined with the ongoing microbial cultures under laboratory-controlled conditions the outcome of our investigations will bring new light behind the role of biofilms in freshwater ooids formation.

Plee, K.; Ariztegui, D.; Sahan, E.; Martini, R.; Davaud, E.

2006-12-01

339

Aragonite and Calcite as Constituents of Adult Oyster Shells.  

PubMed

Adult oyster shells are composed mainly of calcite, but there are five small areas of aragonite: the resilium, the two pads at which the adductor muscle is inserted, and the two pads at which Quenstedt's muscles are inserted. Quenstedt's muscles are proposed as a name for the small modified, one-time pedal muscles of unknown function, discovered by Quenstedt. PMID:17834841

Stenzel, H B

1963-10-11

340

A data-driven model of the global calcite lysocline  

Microsoft Academic Search

Gridded maps of sediment calcium carbonate (calcite) concentration and overlying water saturation state [Archer, 1996] are combined with maps of benthic oxygen fluxes and sediment accumulation rates from Jahnke [1996] and Cweink [1986] to drive a diagenetic model of calcium carbonate preservation in deep-sea sediments. The only model input for which we cannot draw a detailed map is the rain

David Archer

1996-01-01

341

Control of Aragonite or Calcite Polymorphism by Mollusk Shell Macromolecules  

Microsoft Academic Search

Many mineralizing organisms selectively form either calcite or aragonite, two polymorphs of calcium carbonate with very similar crystalline structures. Understanding how these organisms achieve this control has represented a major challenge in the field of biomineralization. Macromolecules extracted from the aragonitic shell layers of some mollusks induced aragonite formation in vitro when preadsorbed on a substrate of beta-chitin and silk

Giuseppe Falini; Shira Albeck; Steve Weiner; Lia Addadi

1996-01-01

342

Molecular models of a hydrated calcite mineral surface  

Microsoft Academic Search

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

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

2007-01-01

343

Use of coupled passivants and consolidants on calcite mineral surfaces  

Microsoft Academic Search

Deterioration of monuments, buildings, and works of art constructed of carbonate-based stone potentially can be arrested by applying a combination of chemical passivants and consolidants that prevent hydrolytic attack and mechanical weakening. The authors used molecular modeling and laboratory synthesis to develop an improved passivating agent for the calcite mineral surface based on binding strength and molecular packing density. The

K. L. Nagy; R. T. Cygan; C. J. Brinker; C. S. Ashley; C. S. Scotto

1997-01-01

344

Copper incorporation in foraminiferal calcite: results from culturing experiments  

NASA Astrophysics Data System (ADS)

A partition coefficient for copper (DCu) in foraminiferal calcite has been determined by culturing individuals of two benthic species under controlled laboratory conditions. The partition coefficient of a trace element (TE) is an emperically determined relation between the TE/Ca ratio in seawater and the TE/Ca ratio in foraminiferal calcite and has been established for many divalent cations. Despite its potential to act as a tracer of human-induced, heavy metal pollution, data is not yet available for copper. Since partition coefficients are usually a function of multiple factors (seawater temperature, pH, salinity, metabolic activity of the organism, etc.), we chose to analyze calcite from specimens cultured under controlled laboratory conditions. They were subjected to different concentrations of Cu2+ (0.1-20 µmol/l) and constant temperature (10 and 20°C), seawater salinity and pH. We monitored the growth of new calcite in specimens of the temperate, shallow-water foraminifer Ammonia tepida and in the tropical, symbiont-bearing Heterostegina depressa. Newly formed chambers were analyzed for Cu/Ca ratios by laser ablation-ICP-MS. The estimated partition coefficient (0.1-0.4) was constant to within experimental error over a large range of (Cu/Ca)seawater ratios and was remarkably similar for both species. Neither did the presence or absence of symbionts affect the DCu, nor did we find a significant effect of temperature or salinity on Cu-uptake.

de Nooijer, L. J.; Reichart, G. J.; Dueñas-Bohórquez, A.; Wolthers, M.; Ernst, S. R.; Mason, P. R. D.; van der Zwaan, G. J.

2007-07-01

345

Copper incorporation in foraminiferal calcite: results from culturing experiments  

NASA Astrophysics Data System (ADS)

A partition coefficient for copper (DCu) in foraminiferal calcite has been determined by culturing individuals of two benthic species under controlled laboratory conditions. The partition coefficient of a trace element (TE) is an emperically determined relation between the TE/Ca ratio in seawater and the TE/Ca ratio in foraminiferal calcite and has been established for many divalent cations. Despite its potential to act as a tracer of human-induced, heavy metal pollution, data is not yet available for copper. Since partition coefficients are usually a function of multiple factors (seawater temperature, pH, salinity, metabolic activity of the organism, etc.), we chose to analyze calcite from specimens cultured under controlled laboratory conditions. They were subjected to different concentrations of Cu2+ (0.1-20 µmol/l) and constant temperature (10 and 20°C), seawater salinity and pH. We monitored the growth of new calcite in specimens of the temperate, shallow-water foraminifer Ammonia tepida and in the tropical, symbiont-bearing Heterostegina depressa. Newly formed chambers were analyzed for Cu/Ca ratios by laser ablation-ICP-MS. The calculated partition coefficient (0.1-0.4) was constant to within experimetnal error over a large range of (Cu/Ca)seawater ratios and was remarkably similar for both species. Neither did the presence or absence of symbionts affect the DCu, nor did we find a significant effect of temperature or salinity on Cu-uptake.

de Nooijer, L. J.; Reichart, G. J.; Dueñas-Bohórquez, A.; Wolthers, M.; Ernst, S. R.; Mason, P. R. D.; van der Zwaan, G. J.

2007-04-01

346

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

347

Atomistic Simulation of the Free Energies of Dissolution of Ions from Flat and Stepped Calcite Surfaces  

SciTech Connect

Molecular dynamics simulations were used to describe the interaction of calcite flat and stepped surfaces with water. The calculations show that the disruptions of the water density caused by the presence of monoatomic steps extend further in the direction normal to the surface than in the direction normal to the step edge. When vacancies were introduced the disruption of the water density was dependant on both the type of vacancy and step. By performing a series of molecular dynamics simulations we were able to obtain free energy profiles of the dissolution of ions from flat and stepped surfaces. These results show that the type of surface that the ion is being dissolved from has a profound affect on the free energy of dissolution. In addition, our calculations suggest that the relationship between the overall free energy of dissolution and the number of crystal bonds to be broken is not linear, as normally assumed in dissolution models such as solid-on-solid model.

Spagnoli, Dino; Kerisit, Sebastien N.; Parker, Stephen C.

2006-08-15

348

Modelling of the thermal dependence of structural and elastic properties of calcite, CaCO3  

NASA Astrophysics Data System (ADS)

A computational method, based on the quasiharmonic approximation, has been computer-coded to calculate the temperature dependence of elastic constants and structural features of crystals. The model is applied to calcite, CaCO3; an interatomic potential based on a C-O Morse function and Ca-O and O-O Borntype interactions, including a shell model for O, has been used. Equilibrations in the range 300 800 K reproduce the experimental unit-cell edges and bond lengths within 1%. The simulated thermal expansion coefficients are 22.3 (//c) and 2.6 (? c), against 25.5 and-3.7×10-6K-1 experimental values, respectively. The thermal coefficients of elastic constants tend to be underestimated; for the bulk modulus, -2.3 against-3.7×10-4K-1 is obtained.

Pavese, A.; Catti, M.; Parker, S. C.; Wall, A.

1996-03-01

349

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

350

SUPPORTING INFORMATION Surface-Potential Heterogeneity of Reacted Calcite and Rhodochrosite  

E-print Network

S1 SUPPORTING INFORMATION Surface-Potential Heterogeneity of Reacted Calcite and Rhodochrosite histograms of steps and terraces for calcite and rhodochrosite surfaces of Figure 1. Figure S4: Topography for data shown in Figure 3 Sample Dependent Variable Probability (> F-Test Value)* h(nano) 2.6Ã?10-4 calcite

351

The solubility of fish-produced high magnesium calcite in seawater Ryan J. Woosley,1  

E-print Network

The solubility of fish-produced high magnesium calcite in seawater Ryan J. Woosley,1 Frank J calcite as part of the physiological mechanisms responsible for maintaining salt and water balance 0.09) is approximately two times higher than aragonite and similar to the high magnesium calcite

Grosell, Martin

352

Arsenite sorption and co-precipitation with calcite G. Romn-Ross1#  

E-print Network

1 Arsenite sorption and co-precipitation with calcite G. Román-Ross1# , G. J. Cuello2 , X Girona, Spain. E-mail: gabriela.roman@udg.es Keywords: calcite, arsenite, adsorption, coprecipitation hal : 10.1016/j.chemgeo.2006.04.007 #12;2 Abstract Sorption of As(III) by calcite was investigated

Paris-Sud XI, Université de

353

Estimation of surface precipitation constants for sorption of divalent metals onto hydrous ferric oxide and calcite  

E-print Network

oxide and calcite Chen Zhu * Department of Geology and Planetary Science, University of Pittsburgh for modeling surface precipitation of divalent metals, M2+ , onto hydrous ferric oxide and calcite were+ . D 2002 Elsevier Science B.V. All rights reserved. Keywords: Surface adsorption; Iron oxide; Calcite

Polly, David

354

Phosphoric acid fractionation factors for calcite and aragonite between 25 and 75 C: Revisited  

E-print Network

Phosphoric acid fractionation factors for calcite and aragonite between 25 and 75 °C: Revisited-determine the phosphoric acid fractionation factor for calcite and aragonite in order to improve the accuracy and limit the uncertainty of this very important quantity. The 18 O/16 O ratio of 100% of the oxygen in calcite

Long, Bernard

355

Inter-relations entre aiguilles de calcite et hyphes Gabriel CALLOT, Andr GUYON Daniel MOUSAIN  

E-print Network

Inter-relations entre aiguilles de calcite et hyphes mycéliens Gabriel CALLOT, André GUYON Daniel'intérieur des hyphes de Basidiomycètes. Ces concentrations minérales s'identifient aux aiguilles de calcite, mycorhizes. SUMMARY Relation between calcite needles and fungal hyphae in the soil. Study of soil

Paris-Sud XI, Université de

356

In situ AFM study of the dissolution and recrystallization behaviour of polished and stressed calcite surfaces  

E-print Network

calcite surfaces J. Bisschop a,*, D.K. Dysthe a , C.V. Putnis b , B. Jamtveit a a Physics of Geological in revised form 12 December 2005 Abstract We investigated the dissolution behaviour of polished calcite to study the effects of applied surface stress and crystallographic orientation on calcite dissolution

Dysthe, Dag Kristian

357

Molecular Self-Assembly of Enantiopure Heptahelicene-2-Carboxylic Acid on Calcite (1014)  

E-print Network

Molecular Self-Assembly of Enantiopure Heptahelicene-2-Carboxylic Acid on Calcite (1014)-heptahelicene-2-carboxylic acid ((M)-[7]HCA) on the calcite (1014) cleavage plane under ultrahigh vacuum along the calcite [0110] direction. Here, we investigate the enantiopure (M)- [7]HCA compound, resulting

Kühnle, Angelika

358

Cite this: CrystEngComm, 2013, 15, Calcite formation by hydrothermal carbonation of  

E-print Network

Cite this: CrystEngComm, 2013, 15, 3392 Calcite formation by hydrothermal carbonation-Hernandezb and C. Noguera*cd The present study complements experimental results of calcite nanoparticle formation calcite particles ­ are considered. The simulation is performed with the help of the NANOKIN code

Montes-Hernandez, German

359

Strong kinetic effects on Sr/Ca ratios in the calcitic bivalve Pecten maximus  

E-print Network

G22048 Strong kinetic effects on Sr/Ca ratios in the calcitic bivalve Pecten maximus Anne Lorrain Although Sr/Ca ratios in abiogenic calcite are strongly controlled by precipitation rates, such a kinetic effect has never been demonstrated in calcitic bivalve shells. Therefore, we report 1 hal-00452403

Brest, Université de

360

Measurement of c-axis angular orientation in calcite (CaCO3) nanocrystals using  

E-print Network

Measurement of c-axis angular orientation in calcite (CaCO3) nanocrystals using X-ray absorption are demonstrated here on geologic calcite (CaCO3) and used to investigate the prismatic layer of a mollusk shell, Pinctada fucata. These XANES-PEEM data reveal multiply oriented nanocrystals within calcite prisms

Coppersmith, Susan N.

361

Peptide Controls on Calcite Mineralization: Polyaspartate Chain Length Affects Growth Kinetics and Acts as a Stereochemical  

E-print Network

Peptide Controls on Calcite Mineralization: Polyaspartate Chain Length Affects Growth Kinetics interactions with step edges. Here, we show that the morphology and growth kinetics of calcite are modified suggest a process by which small fluctuations in primary structure in proteins can control calcite shape

Dove, Patricia M.

362

Atomistic simulations of calcite nanoparticles and their interaction David J. Cooke and James A. Elliotta  

E-print Network

Atomistic simulations of calcite nanoparticles and their interaction with water David J. Cooke 12 September 2007 Molecular dynamics MD simulations have been used to study the stability of calcite, an understand- ing of the chemical and physical properties of calcium car- bonate polymorphs, especially calcite

Elliott, James

363

ELSEVIER Tectonophysics 305 (1999) 275286 SevierLaramide deformation of the continental interior from calcite  

E-print Network

from calcite twinning analysis, west-central North America John P. Craddock a,L , Ben A. van der Pluijm by mechanically twinned calcite. Shortening directions are generally parallel to the Sevier thrust as 2000 km into the plate interior. The inferred calcite twinning differential stress magnitudes generally

364

Atomic-Scale Study of Calcite Nucleation in Calcium Oxide Rmy Besson*  

E-print Network

Atomic-Scale Study of Calcite Nucleation in Calcium Oxide Rémy Besson* Groupe de MétallurgieO, by considering insertion of CO2 within the subsurface, in configurations characteristic of calcite surface a mechanism for calcite nucleation, as well as a plausible explanation for the degradation of performances

Paris-Sud XI, Université de

365

Temperature Dependence of1 Oxygen Isotope Fractionation in Coccolith Calcite:2  

E-print Network

Temperature Dependence of1 Oxygen Isotope Fractionation in Coccolith Calcite:2 A Culture and Core temperature dependence of 18 O fractionation in biogenic calcite was first established in the 1950s and26 the objective of the present study is to re-evaluate this temperature dependence in coccolith calcite27

Paris-Sud XI, Université de

366

hal-00194999,version1-8Dec2007 Arsenic uptake by gypsum and calcite  

E-print Network

hal-00194999,version1-8Dec2007 Arsenic uptake by gypsum and calcite: Modeling and probing studies performed on As-doped gypsum (CaSO4 2H2O) and calcite (CaCO3), using neutron (D20-ILL) and x- ray As gets into the bulk of gypsum and calcite structures or is simply adsorbed on the surface. Different

Paris-Sud XI, Université de

367

Fluids in the Crust Redox effects on calcite-portlandite-fluid equilibria at forearc conditions: Carbon  

E-print Network

Fluids in the Crust Redox effects on calcite-portlandite-fluid equilibria at forearc conditions: Carbon mobility, methanogenesis, and reduction melting of calcite Codi lazar*,1,2 , Chi zhang1,3 , Craig­10 kbar). Experimental calcite solubility was constant at O2 values from quartz-fayalite-magnetite (QFM

Manning, Craig

368

Effect of Celestite-Calcite Mineralogy on Their Separation by Attrition Scrubbing  

Microsoft Academic Search

Celestite ore is one of the principle economic resources of strantium element. Naturally, it contains some impurities, with the main one being the calcite mineral. In this article, the separation of celestite from calcite was conducted using attrition scrubbing based on the difference in the hardness between the two minerals. Due to the friability of calcite, it was expected to

Ayman A. El-Midany; Ali Q. Selim; Suzan S. Ibrahim

2011-01-01

369

Molecular Dynamics of Structure Formation in Silicon Crystal Nucleation Process Shigeo MARUYAMA and Kazunori TESHIMA  

E-print Network

simulations using Tersoff 3 potential. Amorphous or liquid silicon clusters with a crystal seed in the center are kept at certain temperature. Depending on the seed crystal size, either growth or decay of crystal atoms + r () r + 1.0 Seed atoms Fig. 1 Crystal nucleation from amorphous Si or liquid Si. 0.5 1.0 1.5 2

Maruyama, Shigeo

370

Bed-parallel calcite veins in the core of Wills Mountain anticline: Implications for deformation conditions and fluid flow during the Alleghanian orogeny  

Microsoft Academic Search

Thick, bed-parallel to sub-bed-parallel calcite veins are found in Upper Ordovician Trenton and Black River Group limestones exposed in the core of Wills Mountain anticline, Pendleton County, West Virginia. The veins range in thickness from less than 5 centimeters to over 2 meters, and contain individual crystals up to 20 centimeters across. The veins have a 1 to 3 mete

M. A. Evans; D. A. Battles

1994-01-01

371

Fluid mediated transformation of aragonitic cuttlebone to calcite  

NASA Astrophysics Data System (ADS)

The aragonite to calcite transition has been studied extensively over the years because of its wide spectra of applications and of its significant geochemical interest. While studies of kinetics (e.g. Topor et al., 1981), thermodynamics (e.g. Wolf et al., 1996) and behavior of ions such as Sr and Mg (e.g. Yoshioka et al., 1986) have been made there are still unanswered questions regarding this reaction especially in the cases where the effects of fluid composition are considered. It is well known that when heated in air, aragonite transforms by a solid state reaction to calcite. The aragonite cuttlebone of the sepia officinalis that was used for our experiments undergoes a phase transition at ~370-390Ë? C, measured by in situ heating experiments in a Philips X'pert X-ray powder diffractometer equipped with a HTK 1200 High temperature oven. Successive X-ray scans were taken at isothermal temperatures at 200C intervals. A similar temperature range was found by Vongsavat et al. 2006, who studied this transition in Acropora corals. It is possible however to promote this transition at considerably lower temperatures by means of a fluid mediated reaction where the replacement takes place by a dissolution-precipitation mechanism (Putnis & Putnis, 2007). We have successfully carried out hydrothermal experiments where cuttlebone has been converted to calcite at 200Ë? C. Using the PhreeqC program we calculated the required composition of a solution that would be undersaturated with respect to aragonite and saturated with respect to calcite leading to dissolution of the aragonite and to a consequent precipitation of the new calcite phase, similar to the experiments described in an earlier study (Perdikouri et al, 2008). This reaction is not pseudomorphic and results in the destruction of the morphology, presumably due to the molar volume increase. A total transformation of the cuttlebone produced a fine calcite powder. The cuttlebone exhibits a unique microstructure, made up of interconnected chambers. The aragonite grown during biomineralization of the cuttlebone is interlaced with a β-chitin organic phase that provides the framework for the morphology that is observed. Experiments carried out with the same constant conditions but for different periods of time have revealed the evolution of the transformation to calcite. At shorter reaction times the product was made up of calcite powder and of well preserved aragonite septa, as was confirmed by powder X-ray diffraction. In other words, the vertical pillars appear to react at faster rates than the horizontal septa. It has been reported by Florek et al. 2008 that the septa contain higher quantities of β-chitin. The aim of this study is the investigation of these observations and the determination of the effect of the organic component on the kinetics of the aragonite to calcite transformation. Florek M., Fornal E., Gómez-Romero P., Zieba E., Paszkowicz W., Lekki J.,Nowak J., Kuczumow A. Materials Science and Engineering C, In Press (2008) Perdikouri C., Kasioptas A., Putnis C.V., Putnis A. Mineralogical Magazine 72, 111-114 (2008) Putnis A., Putnis C.V. Solid State Chemistry 180, 1783-1786 (2007) Topor N. D., Tolokonnikova L. I., Kadenatsi B. M. Journal of Thermal Analysis 20, 169-174 (1981) Vongsavat V., Winotai P., Meejoo S. Nuclear Instruments and Methods in Physics Research B 243, 167-173 (2006) Wolf G., Lerchner J., Schmidt H., Gamsjäger H., Königsberger E., Schmidt P. Journal of Thermal Analysis 46, 353-359 (1996) Yoshioka S., Ohde S., Kitano Y., Kanamori N. Marine Chemistry 18, 35-48 (1986)

Perdikouri, C.; Kasioptas, A.; Putnis, A.

2009-04-01

372

Physical behavior of purified and crude wax obtained from Sunflower ( Helianthus annuus ) seed oil refineries and seed hulls  

Microsoft Academic Search

The sunflower seed waxes obtained from two sources (i) seed hull as astandard and (ii) crude wax from oil refineries were studied for theircrystallization, melting characteristics and morphology of crystals. Theresults of differential scanning calorimetry of wax obtained from seed hullsshowed the melting temperature range of 13.18 °C with the onsetat 62.32 °C, for purified wax, compared to the melting

T. C. Sindhu Kanya; K. Udaya Sankar; M. C. Shamnathaka Sastry

2003-01-01

373

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

374

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

375

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

376

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

377

U(VI) behaviour in hyperalkaline calcite systems  

NASA Astrophysics Data System (ADS)

The behaviour of U(VI) in hyperalkaline fluid/calcite systems was studied over a range of U(VI) concentrations (5.27 × 10-5 ?M to 42.0 ?M) and in two high pH systems, young and old synthetic cement leachate in batch sorption experiments. These systems were selected to be representative of young- (pH 13.3) and old-stage (pH 10.5) leachate evolution within a cementitious geological disposal facility. Batch sorption experiments, modelling, extended X-ray absorption fine structure spectroscopy, electron microscopy, small angle X-ray scattering and luminescence spectroscopy were used to define the speciation of U(VI) across the systems of study. At the lowest concentrations (5.27 × 10-5 ?M 232U(VI)) significant U removal was observed for both old and young cement leachates, and this was successfully modelled using a first order kinetic adsorption modelling approach. At higher concentrations (>4.20 ?M) in the young cement leachate, U(VI) showed no interaction with the calcite surface over an 18 month period. Small angle X-ray scattering techniques indicated that at high U concentrations (42.0 ?M) and after 18 months, the U(VI) was present in a colloidal form which had little interaction with the calcite surface and consisted of both primary and aggregated particles with a radius of 7.6 ± 1.1 and 217 ± 24 Å, respectively. In the old cement leachate, luminescence spectroscopy identified two surface binding sites for U(VI) on calcite: in the system with 0.21 ?M U(VI), a liebigite-like Ca2UO2(CO3)3 surface complex was identified; at higher U(VI) concentrations (0.42 ?M), a second binding site of undetermined coordination was identified. At elevated U(VI) concentrations (>2.10 ?M) in old cement leachate, both geochemical data and luminescence spectroscopy suggested that surface mediated precipitation was controlling U(VI) behaviour. A focused ion beam mill was used to create a section across the U(VI) precipitate-calcite interface. Transmission electron microscope images of the section revealed that the calcite surface was coated with a nano crystalline, U containing phase. Selected area electron diffraction images of the U precipitate which was formed at a U(VI) concentration of 4.20 ?M were consistent with the formation of calcium uranate. XAS spectroscopy at higher concentrations (?21.0 ?M) suggested the formation of a second U(VI) phase, possibly a uranyl oxyhydroxide phase. These results indicated that in the young cement leachate, U(VI) did not react with the calcite surface unless U(VI) concentrations were very low (5.27 × 10-5 ?M). At higher concentrations, speciation calculations suggested that U(VI) was significantly oversaturated and experimental observations confirmed it existed in a colloidal form that interacted with the mineral surface only weakly. In the old cement leachate systems at low concentrations batch sorption and luminescence data suggested that U(VI) removal was being driven by a surface complexation mechanism. However, at higher concentrations, spectroscopic methods suggest a combination of both surface complexation and surface mediated precipitation was responsible for the observed removal. Overall, U(VI) behaviour in hyperalkaline calcite systems is distinct from that at circumneutral pH conditions: at high pH and anything but low U(VI) concentrations, a surface mediated precipitation mechanism occurs; this is in contrast to circumneutral pH conditions where U(VI) surface complexation reactions tend to dominate.

Smith, Kurt F.; Bryan, Nicholas D.; Swinburne, Adam N.; Bots, Pieter; Shaw, Samuel; Natrajan, Louise S.; Mosselmans, J. Frederick W.; Livens, Francis R.; Morris, Katherine

2015-01-01

378

Seed proteomics.  

PubMed

Seeds comprise a protective covering, a small embryonic plant, and a nutrient-storage organ. Seeds are protein-rich, and have been the subject of many mass spectrometry-based analyses. Seed storage proteins (SSP), which are transient depots for reduced nitrogen, have been studied for decades by cell biologists, and many of the complicated aspects of their processing, assembly, and compartmentation are now well understood. Unfortunately, the abundance and complexity of the SSP requires that they be avoided or removed prior to gel-based analysis of non-SSP. While much of the extant data from MS-based proteomic analysis of seeds is descriptive, it has nevertheless provided a preliminary metabolic picture explaining much of their biology. Contemporary studies are moving more toward analysis of protein interactions and posttranslational modifications, and functions of metabolic networks. Many aspects of the biology of seeds make then an attractive platform for heterologous protein expression. Herein we present a broad review of the results from the proteomic studies of seeds, and speculate on a potential future research directions. PMID:21172463

Miernyk, Ján A; Hajduch, Martin

2011-04-01

379

DOI: 10.1002/adma.200600368 Growth of CdSe Quantum Rods and Multipods Seeded  

E-print Network

. This method uses metallic nano- particles as seeds to promote anisotropic crystal growth.[17] The metallic seed particles melt, precursor atoms dissolve in them, and crystal growth occurs at the metalDOI: 10.1002/adma.200600368 Growth of CdSe Quantum Rods and Multipods Seeded by Noble

Swihart, Mark T.

380

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

381

Relating Mechanical Behavior and Microstructural Observations in Calcite Fault Gouge  

NASA Astrophysics Data System (ADS)

Many important earthquakes, magnitude 5-7, nucleate and/or propagate through carbonate-dominated lithologies. Additionally, the presence of precipitated calcite in (cement) and near (vein fill) faults indicates that the mechanical behavior of carbonate-dominated material likely plays an important role in shallow- and mid-crustal faulting. We report on laboratory experiments designed to explore the mechanical behavior of calcite and relate that behavior to post experiment microstructural observations. We sheared powdered gouge of Carrara Marble, >98% CaCO3, at constant normal stresses between 1 and 50 MPa under saturated conditions at room temperature. We performed velocity-stepping tests, 0.1-1000 ?m/s, to evaluate frictional stability, and slide-hold-slide tests, 1-10,000 seconds, to measure the amount of frictional healing. Small subsets of experiments were performed under different environmental conditions and shearing velocities to better elucidate physicochemical processes and their role in the mechanical behavior of calcite fault gouge. All experimental samples were collected for SEM analysis. We find that the frictional healing rate is 7X higher under saturated conditions than under nominally dry conditions. We also observe a divergence between the rates of creep relaxation (increasing) and frictional healing (decreasing) as shear velocity is increased from 1 to 3000 ?m/s. Our highest healing rates are observed at our lowest normal stresses. We observe a frictional strength of ? = 0.64, consistent with previous data under similar conditions. Furthermore, although we observe velocity-weakening frictional behavior in both the saturated and dry cases, rate- and-state friction parameters are distinctly different for each case. Our combined observations of rapid healing and of velocity-weakening frictional behavior indicate that faults where calcite-dominated gouge is present are likely to be seismic and have the ability to regain their strength quickly. Furthermore, our mechanical results highlight the important role of fluids in the evolution of frictional strength and thus fault behavior.

Carpenter, B. M.; Di Stefano, G.; Viti, C.; Collettini, C.

2013-12-01

382

A re-evaluation of aragonite versus calcite seas  

Microsoft Academic Search

Some workers have argued that the mineralogy of ancient carbonates may have been different from that of modern sediments,\\u000a with calcite being considered the dominant mineral during the Ordovician, Devonian-mid Carboniferous, and Jurassic-Cretaceous\\u000a to Early\\/Middle Cenozoic (e.g. Sandberg 1983; Wilkinson and Algeo 1989). Variation in carbonate mineralogy has been related\\u000a to the position of global sea level (emergent or submergent

Mohammad H. Adabi

2004-01-01

383

In situ study on ?11B and B/Ca in synthetic aragonite and calcite: the effect of growth rate and temperature  

NASA Astrophysics Data System (ADS)

Boron isotopic and chemical content of carbonates (expressed as ?11B and B) is being developed as seawater pH and CO32- proxy. However, thermodynamic and kinetic effects on ?11B and B are not well understood. It underscores the importance of exploring possible effects of temperature and growth rate on ?11B and B fractionation in synthetic calcium carbonate minerals, which is the focus of this study. In situ Secondary Ion Mass Spectrometry (SIMS) analyses of ?11B were conducted in the aragonite spherulites precipitated from seawater at 50°C, 65°C and 75°C. Here spherulite centers represent the onset of crystallization with the rates that are significantly higher than those of the later grown fibres [1,2]. Boron isotopic composition reflects these two morphologically distinct domains: ?11B (centers) are lower than ?11B (fibres) by up to one order of magnitude. This observation is consistent with ?11B difference between coral early mineralization zone and fibrous aragonite [3]. Also, our preliminary results suggest averaged ?11B (centers+fibres) increases with temperature within the range of 55 to 75°C. SIMS measurements of B/Ca were performed on single crystals of calcites synthesized from laboratory prepared solution of NH4Cl-CaCl2 doped with boron by diffusion of CO2. Growth rates of calcite (V) within crystals grown isothermally (T=2, 15, 20, 22 and 25°C) were monitored by sequentially spiking calcite-precipitating fluids with rare earth element (REE) dopants. The REE were analyzed with SIMS at spots matching those where B/Ca were determined. REE patterns reveal concentric domains of calcite growth. The growth rate of calcite generally decreases with time - i.e., crystal rims advanced at slower rates than cores. Fluids were sampled periodically for B, Ca, dissolved inorganic carbon, and pH. Boron Nernst partition coefficient DB=B(calcite)/B(fluid) increases from 0.38 (pH=8.11±0.04) to 0.68 (pH=8.03±0.03) with increasing V from 0.039 to 0.12 nm/s at 25°C. Also, DB potentially decreases with increasing of temperature at the range of 20 to 25°C. We anticipate presenting DB for the full studied temperature range. The depletion of 11B in the centers of aragonite spherulite relative to its fibres suggests the reverse relationship of ?11B with aragonite growth rate. Our results in synthetic calcite suggest both temperature and especially growth rate should be accounted while using boron as pH or CO32- recorder in biogenic calcite. pH effect was masked by V while pH increased from 8 to 8.15 during calcite precipitation at 25°C. [1] Gabitov et al. (2008) Geochim. Cosmochim. Acta, 73, 4166-4179. [2] Holcomb et al. (2009) Geochim. Cosmochim. Acta, 72, 4058-4068. [3] Blamart et al. (2007) G-cubed, Q12001, doi:10.1029/2007GC001686.

Gabitov, R. I.; Rollion-Bard, C.; Sadekov, A.

2011-12-01

384

Arsenite sorption and co-precipitation with calcite  

E-print Network

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 previously described by the X-ray standing wave technique. The inflexion point of the isotherm, where As(OH)3 degrees is limited by the amount of surface sites (ST), yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this value, the amount of sorbed arsenic increases linearly with solution concentration, up to the saturation of arsenic with respect to the precipitation of CaHAsO3(s). The solid solutions formed in this concentration range were examined by X-ray and neutron diffraction. The doped calcite lattice parameters increase with arsenic content while c/a ratio remains constant. Our results made on bulk calcite on...

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

2008-01-01

385

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

386

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

387

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

388

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

389

Titania single crystals with a curved surface  

NASA Astrophysics Data System (ADS)

Owing to its scientific and technological importance, crystallization as a ubiquitous phenomenon has been widely studied over centuries. Well-developed single crystals are generally enclosed by regular flat facets spontaneously to form polyhedral morphologies because of the well-known self-confinement principle for crystal growth. However, in nature, complex single crystalline calcitic skeleton of biological organisms generally has a curved external surface formed by specific interactions between organic moieties and biocompatible minerals. Here we show a new class of crystal surface of TiO2, which is enclosed by quasi continuous high-index microfacets and thus has a unique truncated biconic morphology. Such single crystals may open a new direction for crystal growth study since, in principle, crystal growth rates of all facets between two normal {101} and {011} crystal surfaces are almost identical. In other words, the facet with continuous Miller index can exist because of the continuous curvature on the crystal surface.

Yang, Shuang; Yang, Bing Xing; Wu, Long; Li, Yu Hang; Liu, Porun; Zhao, Huijun; Yu, Yan Yan; Gong, Xue Qing; Yang, Hua Gui

2014-11-01

390

Microstructural and compositional study of a bulk Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-PbTiO{sub 3} single crystal grown from a BaTiO{sub 3} seed  

SciTech Connect

The microstructure, composition and homogeneity of a Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-PbTiO{sub 3} (PMNT) single crystal were studied using a combination of electron-microprobe techniques: scanning electron microscopy, orientation analysis and quantitative X-ray microanalysis. A PMNT single crystal was grown from a polycrystalline PMNT matrix using a BaTiO{sub 3} single crystal as a seed. The PMNT crystal retained the same crystallographic orientation as the seed with no interdiffusion at the interface. The average chemical composition, determined with optimized quantitative wavelength-dispersive X-ray microanalysis, was Pb(Mg{sub 1/3}Nb{sub 2/3}){sub 1-X}Ti {sub X}O{sub 3} where x = 0.33. A statistical evaluation of the data using the analysis of variance showed that the achieved experimental uncertainty was below {+-} 1% relative. The compositional homogeneity of the crystal was verified on the micrometer-scale; however on the macro-scale slight fluctuations of the Mg, Nb and Ti concentrations were observed across the crystal. The measured variations from the average composition were {+-} 2.3% relative for Ti, {+-} 1.3% for Nb and {+-} 1.4% for Mg. In contrast, the Pb concentration was found to be uniform on both the micro- and macro-scale, showing a variation below {+-} 0.5% relative.

Samardzija, Zoran [Institite 'Jozef Stefan', Jamova 39, SI-1000 Ljubljana (Slovenia)]. E-mail: zoran.samardzija@ijs.si; Jeon, Jae-Ho [Korea Institute of Machinery and Materials, 66 Sangnam-Dong, Changwon (Korea, Republic of); Ceh, Miran [Institite 'Jozef Stefan', Jamova 39, SI-1000 Ljubljana (Slovenia)

2007-06-15

391

Watermelon Seed Germination  

E-print Network

Watermelon Seed Germination Purdue University Cooperative Extension Service BP-62 Seed Germination of the necessary genetic material or chromosomes. These seed, known as triploid, have special germination requirements. This bulletin addresses triploid watermelon seed germination and transplant production. First

392

Aragonite–calcite–vaterite: A temperature influenced sequential polymorphic transformation of CaCO{sub 3} in the presence of DTPA  

SciTech Connect

Highlights: ? Crystallization of CaCO{sub 3} between 60 and 230 °C in the presence of DTPA. ? Formation of exclusive and individual polymorphs at different temperatures. ? Violation of second law of thermodynamics/Ostwald rule of stages has been observed. - Abstract: Calcium carbonate was precipitated from calcium chloride using sodium carbonate in the presence of diethylenetriaminepentaacetic acid (DTPA) between 60 and 230 °C. The samples were characterized by FTIR, Raman, XRD and SEM techniques. CaCO{sub 3} with different crystal morphologies such as spherolite/datura pod, dumbbell, peanut, were obtained depending on the experimental conditions. The results showed that pure aragonite, calcite and vaterite were formed at low, moderate and high temperatures respectively. A binary mixture of calcite and vaterite was resulted between 150 and 200 °C. The data suggested an unusual conversion of stable calcite to meta stable vaterite at higher temperature in presence of DTPA. The study revealed a novel methodology for the exclusive/individual preparation of different crystalline polymorphs of CaCO{sub 3}. Formation of pure vaterite above 200 °C divulged the possibility of DTPA as a potential scale inhibitor and boiler sludge conditioner at elevated temperatures.

Gopi, Shanmukhaprasad [Department of Chemistry, Annamalai University, Annamalainagar 608002, Tamilnadu (India); Subramanian, V.K., E-mail: drvksau@gmail.com [Department of Chemistry, Annamalai University, Annamalainagar 608002, Tamilnadu (India); Palanisamy, K. [Department of Chemistry, Annamalai University, Annamalainagar 608002, Tamilnadu (India)

2013-05-15

393

Redistribution of Snowfall across a Mountain Range by Artificial Seeding: A Case Study  

Microsoft Academic Search

Clouds over the western slopes of the Cascade Mountains were artificially seeded to reduce the riming and fall speeds of snow crystals and to divert snowfall across the crest. Aircraft observations showed that the clouds were glaciated by the seeding. The crystal habits and the degrees of riming of snow crystals reaching the target area were modified. Snowfall rates decreased

Peter V. Hobbs; L. F. Radke

1973-01-01

394

Hydrodynamic control of inorganic calcite precipitation in Huanglong Ravine, China: Field measurements and theoretical prediction of deposition rates  

NASA Astrophysics Data System (ADS)

Hydrochemical and hydrodynamical investigations are presented to explain tufa deposition rates along the flow path of the Huanglong Ravine, located in northwestern Sichuan province, China, on an altitude of about 3400 m asl. Due to outgassing of CO 2 the mainly spring-fed stream exhibits, along a valley of 3.5 km, calcite precipitation rates up to a few mm/year. We have carried out in situ experiments to measure calcite deposition rates at rimstone dams, inside of pools and in the stream-bed. Simultaneously, the downstream evolution of water chemistry was investigated at nine locations with respect to Ca 2+, Mg 2+, Na +, Cl -, SO 42-, and alkalinity. Temperature, pH, and conductivity were measured in situ, while total hardness, Ca T, and alkalinity have been determined immediately after sampling, performing standard titration methods. The water turned out to be of an almost pure Ca?Mg?HCO 3 type. The degassing of CO 2 causes high supersaturation with respect to calcite and due to calcite precipitation the Ca 2+ concentration decreases from 6·10 -3 mole/1 upstream down to 2.5·10 -3 mole/1 at the lower course. Small rectangular shaped tablets of pure marble were mounted under different flow regimes, i.e., at the dam sites with fast water flow as well as inside pools with still water. After the substrate samples had stayed in the water for a period of a few days, the deposition rates were measured by weight increase, up to several tens of milligrams. Although there were no differences in hydrochemistry, deposition rates in fast flowing water were higher by as much as a factor of four compared to still water, indicating a strong influence of hydrodynamics. While upstream rates amounted up to 5 mm/year, lower rates of about 1 mm/year were observed downstream. Inspection of the marble substrate surfaces by EDAX and SEM (scanning electron microscope) revealed authigeneously grown calcite crystals of about 10 ?m. Their shape and habit are indicative of a chemically controlled inorganic origin. By applying a mass transfer model for calcite precipitation taking into account the reaction rates at the surface given by Plummer et al. (1978), slow conversion of CO 2 into H + and HCO 3- , and diffusional mass transport across a diffusion boundary layer, we have calculated the deposition rates from the hydrochemistry of the corresponding locations. The calculated rates agree within a factor of two with the experimental results. Our findings confirm former conclusions with respect to fast flow conditions: reasonable rates of calcite precipitation can be estimated in reducing the PWP-rate calculated from the chemical composition of the water by a factor of about ten, thus correcting for the influence of the diffusion boundary layer.

Zaihua, Liu; Svensson, U.; Dreybrodt, W.; Daoxian, Yuan; Buhmann, D.

1995-08-01

395

Preliminary Results of Bacteria Distribution in Chinese Loess and Their Control on the Calcite Formation  

Microsoft Academic Search

Continuous loess-paleosol sequences on the Chinese Loess Plateau are viewed as one of best continental archives of paleoclimatic and paleoenvironmental changes of the Late Cenozoic era. Carbonate, mainly calcite, commonly occurs throughout the entire sequence; though some are detrital, most are in-situ pedogenic. TEM studies have shown various morphologies of calcites in Chinese loess, especially nano-rod calcite widely occurring in

Y. Chen; B. Lian; Q. Hu; H. H. Teng; T. Wu; J. Ji; J. Chen

2005-01-01

396

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

397

EFFETS RAMAN STIMULS DANS LA CALCITE Par G. BISSON et G. MAYER.  

E-print Network

97. EFFETS RAMAN STIMUL�S DANS LA CALCITE Par G. BISSON et G. MAYER. Département de Recherches Nous décrivons des expériences conçues pour vérifier dans la calcite la théorie des effets Raman been designed to check in calcite the theory of first order stimulated Raman effects. For the Stokes

Paris-Sud XI, Université de

398

Les calcites de Fontainebleau : une cl pour dater la silicification des grs ?  

E-print Network

0 Les calcites de Fontainebleau : une clé pour dater la silicification des grès ? Sortie géologique du 25 novembre 2012 état des lieux 238 ans après la première publication relative aux calcites de-00762302,version1-6Dec2012 #12;1 Les calcites de Fontainebleau : une clé pour dater la silicification des

Paris-Sud XI, Université de

399

Influence of Calcite and Dissolved Calcium on Uranium(VI) Sorption to a Hanford Subsurface Sediment  

Microsoft Academic Search

The influence of calcite and dissolved calcium on U(VI) adsorption was investigated using a calcite-containing sandy silt\\/clay sediment from the U. S. Department of Energy Hanford site. U(VI) adsorption to sediment, treated sediment, and sediment size fractions was studied in solutions that both had and had not been preequilibrated with calcite, at initial [U(VI)] - 10-7-10-5 mol\\/L and final pH

Wenming Dong; William P. Ball; Chongxuan Liu; Zheming Wang; Alan T. Stone; Jing Bai; John M. Zachara

2005-01-01

400

Scleractinian corals produce calcite, and grow more slowly, in artificial Cretaceous seawater  

Microsoft Academic Search

The mineralogies of most biotic and abiotic carbonates have alternated in synchroneity between the calcite (hexagonal) and aragonite (orthorhombic) polymorphs of CaCO3 throughout the Phanerozoic Eon. These intervals of calcite and aragonite production, or calcite seas and aragonite seas, are thought to be caused primarily by secular variation in the molar magnesium\\/calcium ratio of seawater (mMg\\/Ca > 2 = aragonite

Justin B. Ries; Steven M. Stanley; Lawrence A. Hardie

2006-01-01

401

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

402

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. PMID:25048115

Walther, Leif Erik; Blödow, Alexander; Buder, Jana; Kniep, Rüdiger

2014-01-01

403

The sensitized luminescence of manganese-activated calcite  

USGS Publications Warehouse

Synthetic manganese-activated calcites are shown to be practically inert to ultraviolet excitation in the range 2000-3500A, while they are luminescent under cathode-ray excitation. The incorporation of small amounts of an auxiliary impurity along with the manganese produces the strong response to ultraviolet radiation hitherto ascribed to CaCO3:Mn itself. Three such impurities have been studied: lead, thallium, and cerium. The first two induce excitation in the neighborhood of the mercury resonance line, while the cerium introduces a response principally to longer wave ultraviolet. The strong response to 2537A excitation shown by some natural calcites is likewise found to be due to the presence of lead along with the manganese, rather than to the manganese alone. The data do not warrant ascribing the longer wave-length ultraviolet-excited luminescence of all natural calcites to the action of an auxiliary impurity. The essential identity of the cathode-ray excited luminescence spectra of CaCO 3:Mn, CaCO3: (Pb+Mn), CaCO3:(Tl+Mn), and CaCO3:(Ce+Mn) with the 2537A-excited spectra of the latter three is evidence that the luminescent center in all cases is the manganese ion or the MnO6 group. It is shown that a "cascade" mechanism for the action of the auxiliary impurities, lead, thallium, and cerium, is incorrect; and that the phenomenon must be considered as a case of sensitized luminescence. Owing to the nature of cathode-ray excitation, the manganese activator can be excited by this agent even in the absence of a second impurity. For optical excitation, however, an absorption band for the ultraviolet must be established by building into the CaCO3:Mn a second impurity or "sensitizer.".

Schulman, J.H.; Evans, L.W.; Ginther, R.J.; Murata, K.J.

1947-01-01

404

Big Seed  

NSDL National Science Digital Library

This free 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

405

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

406

Molecular tectonics: from crystals to crystals of crystals.  

PubMed

The in situ combination of M(II) cations (Co, Ni, Cu or Zn) with 2,4,6-pyridinetricarboxylic acid as a ligand, a bisamidinium dication as a H-bond donor tecton and NaOH leads to the formation of anionic metal complexes ML2(2-) and their interconnection into isomorphous 3D H-bonded networks displaying different colours which were used as preformed seed crystals for the formation of crystals of crystals by 3D epitaxial growth. PMID:24154609

Marinescu, Gabriela; Ferlay, Sylvie; Kyritsakas, Nathalie; Hosseini, Mir Wais

2013-12-11

407

A generalised chemical precipitation modelling approach in wastewater treatment applied to calcite.  

PubMed

Process simulation models used across the wastewater industry have inherent limitations due to over-simplistic descriptions of important physico-chemical reactions, especially for mineral solids precipitation. As part of the efforts towards a larger Generalized Physicochemical Modelling Framework, the present study aims to identify a broadly applicable precipitation modelling approach. The study uses two experimental platforms applied to calcite precipitating from synthetic aqueous solutions to identify and validate the model approach. Firstly, dynamic pH titration tests are performed to define the baseline model approach. Constant Composition Method (CCM) experiments are then used to examine influence of environmental factors on the baseline approach. Results show that the baseline model should include precipitation kinetics (not be quasi-equilibrium), should include a 1st order effect of the mineral particulate state (Xcryst) and, for calcite, have a 2nd order dependency (exponent n = 2.05 ± 0.29) on thermodynamic supersaturation (?). Parameter analysis indicated that the model was more tolerant to a fast kinetic coefficient (kcryst) and so, in general, it is recommended that a large kcryst value be nominally selected where insufficient process data is available. Zero seed (self nucleating) conditions were effectively represented by including arbitrarily small amounts of mineral phase in the initial conditions. Both of these aspects are important for wastewater modelling, where knowledge of kinetic coefficients is usually not available, and it is typically uncertain which precipitates are actually present. The CCM experiments confirmed the baseline model, particularly the dependency on supersaturation. Temperature was also identified as an influential factor that should be corrected for via an Arrhenius-style correction of kcryst. The influence of magnesium (a common and representative added impurity) on kcryst was found to be significant but was considered an optional correction because of a lesser influence as compared to that of temperature. Other variables such as ionic strength and pH were adequately captured by the quasi-equilibrium description of the aqueous-phase and no further kinetic corrections were required. The baseline model is readily expandable to include other precipitation reactions. For simple representations, large values for kcryst with n = 2 (or n = 2 or 3 for other minerals, as appropriate) should be selected without corrections to kcryst. Where accuracy is required (e.g., in mechanistic studies), machine estimation of kcryst should be performed with robust process data and kcryst should at least be corrected for temperature. PMID:25462741

Kazadi Mbamba, Christian; Batstone, Damien J; Flores-Alsina, Xavier; Tait, Stephan

2014-10-15

408

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. PMID:24434555

Hamm, Laura M.; Giuffre, Anthony J.; Han, Nizhou; Tao, Jinhui; Wang, Debin; De Yoreo, James J.; Dove, Patricia M.

2014-01-01

409

Crystallization of single phase (K, Na)clinoptilolite  

Microsoft Academic Search

A single phase (K, Na)-clinoptilolite was hydrothermally crystallized without seed crystals from a reactant mixture of (K, Na)-aluminosilicate gel slurry through homogeneous mixing at 150 °C for 144 h. Compositions of the reactant mixtures and reaction temperatures to obtain the clinoptilolite were restricted within narrow limits in the case of syntheses without seed crystals, while the compositions and temperatures were

Shigeo Satokawa; Keiji Itabashi

1997-01-01

410

Cd 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)  

NASA Astrophysics Data System (ADS)

Cadmium uptake by calcite from aqueous solution was studied using techniques sensitive to the near-surface: X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). These techniques allowed direct observations of structure and bonding environments at the calcite surface. The results indicate that the main processes involved in cadmium uptake by calcite are adsorption and solid-state diffusion into the crystal, which leads eventually to the formation of solid-solution. Pure calcite crystals were cleaved from precleaned Iceland spar and were briefly exposed to aqueous solutions containing various concentrations of Cd 2+, CO 32-, ClO 4-, and/or Cl -. Some Cd 2+ was radiolabelled. LEED results demonstrate that the calcite surface is atomically ordered, even after hydration and cadmium uptake. ?-scintillation data from crystals exposed briefly to solutions of 109Cd 2+ indicate that surface uptake ranged from the equivalent of about 1 to 4 monolayers. XPS analyses in the first 2 hours after exposure detected Cd within the top 30 Å, but crystals stored in air or in ultra-high vacuum showed a decrease in Cd surface concentration with time such that after two days, Cd was barely detectable in the near-surface region. In other experiments, LEED verified the crystallinity of otavite (CdCO 3) grown epitaxially over the {101} cleavage faces of calcite, and XPS showed almost no Ca in the near-surface on scans taken immediately after precipitation; but after storage for a month in ultrahigh vacuum, binding energy shifts and the presence of a Ca peak strongly suggested the development of solid-solution by diffusion through the solid. No Cd enrichment was observed at sites of surface defects using AES, indicating that solid-state diffusion into the mineral surface was not accomplished simply by migration along microfractures alone. This work suggests that solid-state diffusion may play a role in the rate and extent of uptake of certain trace metals from solution and probably leads to the formation of solid-solution in calcite and other carbonate minerals. It also suggests that the process of diffusion into the solid mineral host should be considered in hydrogeochemical models that intend to simulate and predict trace-metal mobility in carbonate terrains.

Stipp, Susan L.; Hochella, Michael F., Jr.; Parks, George A.; Leckie, James O.

1992-05-01

411

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

412

Crystal structures of the ribonuclease MC1 from bitter gourd seeds, complexed with 2'-UMP or 3'-UMP, reveal structural basis for uridine specificity.  

PubMed

Ribonuclease MC1 (RNase MC1) isolated from seeds of bitter gourd (Momordica charantia) consists of 190 amino acids and is characterized by a preferential cleavage at the 5'-side of uridine. This uridine specificity distinguishes RNase MC1 from other enzymes belonging to the RNase T2 family. The three-dimensional structures of RNase MC1, in a complex with either 2'-UMP or 3'-UMP, were determined at 1.48 and 1.77 A resolutions, respectively. The side chains of Gln9 and Asn71 interact with O4 and N3, respectively, of the uracil base by hydrogen bondings. In addition, the uracil base is sandwiched by the hydrophobic side chains of Leu73 and Phe80. Compared with these amino acid residues and corresponding residues in RNases in the RNase T2 family, Gln9 and Phe80 are highly conserved in the RNases in T2 family, while Asn71 and Leu73 in RNase MC1 are variant in sequences. It is thus likely that interactions of the side chains of Asn71 and Leu73 with the uracil base are responsible for the absolute uridine specificity of RNase MC1. Site-directed mutagenesis experiments showed that replacement of Asn by Thr decreased both the catalytic efficiency and the binding affinity by 2.3- and 7.0-fold, respectively, and substitution of Leu73 for Ala predominantly decreased the binding affinity by 14. 5-fold, compared with findings in case of wild-type RNase MC1. It is thus demonstrated that Asn71 and Leu73 play an essential role in uridine preference for RNase MC1. PMID:10964705

Suzuki, A; Yao, M; Tanaka, I; Numata, T; Kikukawa, S; Yamasaki, N; Kimura, M

2000-08-28

413

Dielectric and optical behaviors in relaxor ferroelectric Pb(In1/2Nb1/2)1KxTixO3 crystal  

E-print Network

%) single crystal grown by the modified Bridgman method with Pb(Mg1/3Nb2/3)0.71Ti0.29O3 (PMNT29%) seed29% seed crystal, exhibits higher piezoelectric constant d33 (O2000 pC/N) and electromechanical PINT35% (starting composition) single crystal grown with PMNT33% seed crystal, also shows high

414

Structure and stability of NH complexes in single-crystal ZnO S. J. Jokela and M. D. McCluskeya  

E-print Network

into single-crystal ZnO, using seeded chemical vapor transport in an ammonia ambient. An infrared IR reversed. In the present experiments, a seed crystal was placed at the deposition end. Seed crystals wereStructure and stability of N­H complexes in single-crystal ZnO S. J. Jokela and M. D. Mc

McCluskey, Matthew

415

SEMI-BATCH PRECIPITATION OF CALCIUM SULFATE DIHYDRATE FROM CALCITE AND SULFURIC ACID  

E-print Network

SEMI-BATCH PRECIPITATION OF CALCIUM SULFATE DIHYDRATE FROM CALCITE AND SULFURIC ACID Frédéric BARD1 a calcite suspension to a sulfuric acid solution from industrial waste. The morphology of the precipitated, sulfuric acid, industrial waste. 1. INTRODUCTION Gypsum is a mineral compound of first importance

Paris-Sud XI, Université de

416

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

417

Assessing the potential for using biogenic calcites as dosemeters for luminescence dating  

Microsoft Academic Search

Calcium carbonate emits an intense thermoluminescence (TL) signal and previous work has explored the potential of using this signal to date both inorganic carbonates such as limestones and stalagmites and biogenic calcite produced by marine organisms. Luminescence analysis of biogenic calcites directly dates the secretion of the mineral by the organism and is therefore not reliant upon exposure of the

G. A. T. Duller; K. E. H. Penkman; A. G. Wintle

2009-01-01

418

Research paper Uranium loss and aragoniteecalcite age discordance in a calcitized aragonite  

E-print Network

Research paper Uranium loss and aragoniteecalcite age discordance in a calcitized aragonite Aragonite Recrystallization Uranium series dating Laser ablation MC-ICPMS a b s t r a c t We analyzed uranium-series concentrations and isotopic ratios in a mixed aragonite and calcite stalagmite from

Asmerom, Yemane

419

Uranium in foraminiferal calcite as a recorder of seawater uranium concentrations  

Microsoft Academic Search

The authors present results of an investigation of uranium\\/calcium ratios in cleaned foraminiferal calcite as a recorder of seawater uranium concentrations. For accurate reconstruction of past seawater uranium content, shell calcite must incorporate uranium in proportion to seawater concentration and must preserve its original uranium composition over time. Laboratory culture experiments with live benthic (Amphistegina lobifera) and live planktonic (Globigerinell

A. D. Russell; S. Emerson; B. K. Nelson; J. Erez; D. W. Lea

1994-01-01

420

Development of a high-efficiency phosphorus recovery method using a fluidized-bed crystallized phosphorus removal system  

Microsoft Academic Search

The authors have been engaged in the research and development concerning the recovery of MAP (Magnesium Ammonium Phosphate) using a fluidized-bed crystallized phosphorus removal system. In the reactor of the fluidized-bed crystallized phosphorus removal system, seed crystals (of MAP) are fluidized previously and new MAP crystals are produced on the seed crystal surfaces. Conventionally, the reactor consisted of one reaction

K. Shimamura; T. Tanaka; Y. Miura; H. Ishikawa

421

Isotopic composition of a calcite-cemented layer in the Lower Jurassic Bridport Sands, southern England: Implications for formation of laterally extensive calcite-cemented layers  

SciTech Connect

[delta][sup 18]O[sub PDB] and [delta][sup 13]C[sub PDB] values have been measured on 107 calcite cement samples from a laterally extensive (> 3 km) and continuous calcite-cemented layer 0.5 m thick in the coastal exposures of the Lower Jurassic shallow-marine Bridport Sands in Dorset, southern England. The samples were taken from a two-dimensional grid with 10-cm horizontal and vertical spacing between samples and along individual vertical lines across the calcite-cemented layer, [delta][sup 18]O[sub PDB] values vary between [minus]4.8% and [minus]9.2% and decrease radially outwards from points with lateral spacings on the order of 0.5-1 m in the middle of the calcite-cemented layer. The [delta][sup 18]O[sub PDB] values therefore indicate that the calcite-cemented layer was formed by merging of concretions. All [delta][sup 13]C[sub PDB] values measured are in the narrow range [minus]2.2% to [minus]0.5%, which suggests that the dominant source of calcite cement in the layer was biogenic carbonate.

Bjoerkum, P.A. (Statoil, Stavanger (Norway)); Walderhaug, O. (Rogaland Research, Stavanger (Norway))

1993-07-01

422

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.

423

Seed Treatment. Manual 92.  

ERIC Educational Resources Information Center

This training manual provides information needed to meet minimum EPA standards for certification as a commercial applicator of pesticides in the seed treatment category. The text discusses pests commonly associated with seeds; seed treatment pesticides; labels; chemicals and seed treatment equipment; requirements of federal and state seed laws;…

Missouri Univ., Columbia. Agricultural Experiment Station.

424

Re-evaluating boron speciation in biogenic calcite and aragonite using 11B MAS NMR  

NASA Astrophysics Data System (ADS)

Understanding the partitioning of aqueous boron species into marine carbonates is critical for constraining the boron isotope system for use as a marine pH proxy. Previous studies have assumed that boron was incorporated into carbonate through the preferential uptake of tetrahedral borate B(OH) 4-. In this study we revisit this assumption through a detailed solid state 11B magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopic study of boron speciation in biogenic and hydrothermal carbonates. Our new results contrast with those of the only previous NMR study of carbonates insofar as we observe both trigonal and tetrahedral coordinated boron in almost equal abundances in our biogenic calcite and aragonite samples. In addition, we observe no strict dependency of boron coordination on carbonate crystal structure. These NMR observations coupled with our earlier re-evaluation of the magnitude of boron isotope fractionation between aqueous species suggest that controls on boron isotope composition in marine carbonates, and hence the pH proxy, are more complex that previously suggested.

Klochko, Kateryna; Cody, George D.; Tossell, John A.; Dera, Przemyslaw; Kaufman, Alan J.

2009-04-01

425

Influence of calcite on uranium(VI) reactive transport in the groundwater–river mixing zone  

SciTech Connect

Calcite is an important mineral that can affect uranyl reactive transport in subsurface sediments. This study investigated the distribution of calcite and its influence on uranyl adsorption and reactive transport in the groundwater-river mixing zone at US Hanford 300A, Washington State. Simulations using a 2D reactive transport model under field-relevant hydrogeochemical conditions revealed a complex distribution of calcite concentration as a result of dynamic groundwater-river interactions. The calcite concentration distribution in turn affected the spatial and temporal changes in aqueous carbonate, calcium, and pH, which subsequently influenced U(VI) mobility and discharge rates into the river. The results implied that calcite distribution and its concentration dynamics is an important consideration for field characterization, monitoring, and reactive transport prediction.

Ma, Rui; Liu, Chongxuan; Greskowiak, Janek; Prommer, Henning; Zachara, John M.; Zheng, Chunmiao

2014-01-23

426

Toward Molecular Nanowires Self-Assembled on an Insulating Substrate: Heptahelicene-2-carboxylic acid on Calcite (101j4)  

E-print Network

acid on Calcite (101j4) Philipp Rahe,,§ Markus Nimmrich,,§ Andreas Greuling, Jens Schu¨tte, Irena G) cleavage plane of calcite. The molecule used is racemic heptahelicene-2-carboxylic acid, which forms

Kühnle, Angelika

427

Production, oxygen respiration rates, and sinking velocity of copepod fecal pellets: Direct measurements of ballasting by opal and calcite  

E-print Network

measurements of ballasting by opal and calcite Helle Ploug1 Alfred Wegener Institute for Polar and Marine independent on diet (range: 0.08­ 0.21 d21). Because of ballasting of opal and calcite, sinking velocities

Matthews, Adrian

428

Scleractinian corals produce calcite, and grow more slowly, in artificial Cretaceous seawater  

NASA Astrophysics Data System (ADS)

The mineralogies of most biotic and abiotic carbonates have alternated in synchroneity between the calcite (hexagonal) and aragonite (orthorhombic) polymorphs of CaCO3 throughout the Phanerozoic Eon. These intervals of calcite and aragonite production, or calcite seas and aragonite seas, are thought to be caused primarily by secular variation in the molar magnesium/calcium ratio of seawater (mMg/Ca > 2 = aragonite + high-Mg calcite; mMg/Ca < 2 = low-Mg calcite), a ratio that has oscillated between 1.0 and 5.2 throughout the Phanerozoic. In laboratory experiments, we show that three species of scleractinian corals, which produce aragonite in modern seawater and which have flourished as important reef builders primarily during aragonite seas of the past, began producing calcite in artificial seawater with an ambient mMg/Ca ratio below that of modern seawater (5.2). The corals produced progressively higher percentages of calcite and calcified at lower rates with further reduction of the ambient mMg/Ca ratio. In artificial seawater of imputed Late Cretaceous composition (mMg/Ca = 1.0), which favors the precipitation of the calcite polymorph, scleractinian corals produced skeletons containing >30% low-Mg calcite (skeletal mMg/Ca < 0.04). These results indicate that the skeletal mineral used by scleractinian corals is partially determined by seawater chemistry. Furthermore, slow calcification rates, resulting from the production of largely aragonitic skeletons in chemically unfavorable seawater (mMg/Ca < 2), probably contributed to the scleractinians' diminished reef-building role in the calcite seas of Late Cretaceous and early Cenozoic time.

Ries, Justin B.; Stanley, Steven M.; Hardie, Lawrence A.

2006-07-01

429

Growing YAG and GGG Optical Quality Crystals Erick Bodett, Dr. Kelvin Lynn, Joshah Jennings, Drew Haven  

E-print Network

the ingredients for a particular type of crystal in a crucible to its melting point, then dipping a seed crystal in the melt and pulling it out slowly. As the seed crystal is pulled, the melt cools into the desiredGrowing YAG and GGG Optical Quality Crystals Erick Bodett, Dr. Kelvin Lynn, Joshah Jennings, Drew

Collins, Gary S.

430

Calcite orientations and composition ranges within teeth across Echinoidea.  

PubMed

Sea urchin's teeth from four families of order Echinoida and from orders Temnopleuroida, Arbacioida and Cidaroida were studied with synchrotron X-ray diffraction. The high and very high Mg calcite phases of the teeth, i.e. the first and second stage mineral constituents, respectively, have the same crystallographic orientations. The co-orientation of first and second stage mineral, which the authors attribute to epitaxy, extends across the phylogenic width of the extant regular sea urchins and demonstrates that this is a primitive character of this group. The range of compositions ?x for the two phases of Ca1-xMgxCO3 is about 0.20 or greater and is consistent with a common biomineralization process. PMID:25158180

Stock, Stuart R; Ignatiev, Konstantin; Lee, Peter L; Almer, Jonathan D

2014-08-01

431

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

432

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

433

Implications of solution chemistry effects: Direction-specific restraints on the step kinetics of calcite growth  

NASA Astrophysics Data System (ADS)

Classical crystallization models successfully depict the dependence of growth kinetics on thermodynamic driving force but cannot predict the roles of solution chemistry. Yet, it has become increasingly clear that crystal growth rate at fixed supersaturations depends on pH, ionic strength, and the relative abundance of cations and anions in the parent solutions. We conducted experiments to isolate the effect of individual solution-chemistry parameters on calcite step growth kinetics. Our results revealed a distinct correlation between step velocity and pH in acute and obtuse directions and a simultaneous trend change at pH ?9.5. Step speeds varied with solution stoichiometry, and each direction reached its maximal rate at a different [Ca]/[CO32-] value. In addition, the solution cation/anion at which maximal step speed occurred appeared to be pH dependent as well. Limited effect of ionic strength on step growth was observed in the obtuse direction at low background electrolyte concentrations, but no obvious change was found for growth at the acute side. We proposed a growth model based upon independent incorporation of cations and anions and interpreted these observations as: (1) solute constituents enter kinks through direct solution diffusion at obtuse steps but surface diffusion at acute steps; (2) growth is limited by Ca2+ dehydration at the obtuse side, but by surface adsorption and reorientation and rearrangement of CO32- in the acute direction; and (3) background electrolyte (NaCl in our study) competes with solutes for surface sites at more easily accessible kinks.

Hong, Mina; Teng, H. Henry

2014-09-01

434

Total immersion crystal growth  

NASA Technical Reports Server (NTRS)

Crystals of wide band gap materials are produced by positioning a holder receiving a seed crystal at the interface between a body of molten wide band gap material and an overlying layer of temperature-controlled, encapsulating liquid. The temperature of the layer decreases from the crystallization temperature of the crystal at the interface with the melt to a substantially lower temperature at which formation of crystal defects does not occur, suitably a temperature of 200 to 600 C. After initiation of crystal growth, the leading edge of the crystal is pulled through the layer until the leading edge of the crystal enters the ambient gas headspace which may also be temperature controlled. The length of the column of liquid encapsulant may exceed the length of the crystal such that the leading edge and trailing edge of the crystal are both simultaneously with the column of the crystal. The crystal can be pulled vertically by means of a pulling-rotation assembly or horizontally by means of a low-angle withdrawal mechanism.

Morrison, Andrew D. (inventor)

1987-01-01

435

Distinguishing Phosphate Structural Defects From Inclusions in Calcite and Aragonite by NMR Spectroscopy (Invited)  

NASA Astrophysics Data System (ADS)

Variations in the concentration of minor and trace elements are being studied extensively for potential use as proxies to infer environmental conditions at the time of mineral deposition. Such proxies rely fundamentally on a relationship between the activities in the solution and in the solid that would seem to be simple only in the case that the species substitutes into the mineral structure. Other incorporation mechanisms are possible, including inclusions (both mineral and fluid) and occlusion of surface adsorbate complexes, that might be sensitive to other factors, such as crystallization kinetics, and difficult to distinguish analytically. For example, it is known from mineral adsorption studies that surface precipitates can be nanoscopic, and might not be apparent at resolutions typical of microchemical analysis. Techniques by which a structural relationship between the substituting element and the host mineral structure are needed to provide a sound basis for geochemical proxies. NMR spectroscopy offers methods for probing such spatial relationship. We are using solid-state NMR spectroscopy to investigate phosphate incorporation in calcium carbonate minerals, including calcite speleothems and coral skeletal aragonite, at concentrations of the order 100 ?g P g -1. In 31P NMR spectra of most samples, narrow peaks arising from crystalline inclusions can be resolved, including apatite in coral aragonite and an unidentified phase in calcite. All samples studied yield also a broad 31P signal, centered near chemical shifts of +3 to +4 ppm, that could be assigned to phosphate defects in the host mineral and from which the fraction of P occurring in the carbonate mineral structure can be determined. To test this assignment we applied rotational-echo double-resonance (REDOR) NMR techniques that probe the molecular-scale proximity of carbonate groups to the phosphate responsible for the broad 31P peak. This method measures dipole-dipole coupling between 31P of phosphate and carbonate carbon, which varies with the inverse-cube of the internuclear distance. 31P{13C} REDOR NMR results for synthetic phosphate/(13C)-aragonite coprecipitates show that the broad peak is closely associated with carbonate, exhibiting a 31P-13C dipolar coupling qualitatively consistent with phosphate occupying an anion structural site (i.e., 6 C at 0.32 nm). 31P-detected 1H NMR spectra, which contain signal only from H located near P, show that structural water molecules help accommodate phosphate in the structure. Similar methods can be applied to other elements of potential paleo-proxy interest having NMR-active isotopes, including B, Mg, and Cd.

Phillips, B. L.; Mason, H. E.

2010-12-01

436

Project EARTH-13-RR1: A Sea Change: Resolving the most recent Calcite-Aragonite Sea transition  

E-print Network

Project EARTH-13-RR1: A Sea Change: Resolving the most recent Calcite-Aragonite Sea transition of `sea change': changes in the major-ion composition of the ocean and termed `calcite' and `aragonite. The aim of this project is therefore to investigate the most recent transition from `calcite

Henderson, Gideon

437

True Atomic-Resolution Imaging of (10j14) Calcite in Aqueous Solution by Frequency Modulation Atomic Force Microscopy  

E-print Network

True Atomic-Resolution Imaging of (10j14) Calcite in Aqueous Solution by Frequency ModulationVed October 16, 2008. ReVised Manuscript ReceiVed January 2, 2009 Calcite (CaCO3) is one of the most abundant stable cleavage plane of calcite under liquid conditions using frequency modulation atomic force

Kühnle, Angelika

438

Porous, Biphasic CaCO3-Calcium Phosphate Biomedical Cement Scaffolds from Calcite (CaCO3) Powder  

E-print Network

Porous, Biphasic CaCO3-Calcium Phosphate Biomedical Cement Scaffolds from Calcite (CaCO3) Powder A. Cuneyt Tas* Department of Biomedical Engineering, Yeditepe University, Istanbul 34755, Turkey Calcite (CaH 3.2 by adding NaOH, to form biphasic, micro-, and macroporous calcite-apatitic calcium phosphate (Ap

Tas, A. Cuneyt

439

PII S0016-7037(02)00888-8 EXAFS study of rare-earth element coordination in calcite  

E-print Network

PII S0016-7037(02)00888-8 EXAFS study of rare-earth element coordination in calcite E. J. ELZINGA,1 , Sm3 , Dy3 , Yb3 ) coprecipitated with calcite in minor concentrations from room-temperature aqueous are longer than the Ca-O distance in calcite and longer than what is consistent with ionic radii sums

Peale, Robert E.

440

Sr isotopes and pore fluid chemistry in carbonate sediment of the Ontong Java Plateau: Calcite recrystallization rates and evidence  

E-print Network

Sr isotopes and pore fluid chemistry in carbonate sediment of the Ontong Java Plateau: Calcite of calcite recrystallization at ODP Site 807A on the Ontong Java Plateau, an 800-meter thick section in an accumulating section. The deduced calcite recrystallization rate is 2% per million years (%/Myr) near the top

Fantle, Matthew