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Sample records for amorphous calcium carbonate

  1. Biologically formed amorphous calcium carbonate.

    PubMed

    Weiner, Steve; Levi-Kalisman, Yael; Raz, Sefi; Addadi, Lia

    2003-01-01

    Many organisms from a wide variety of taxa produce amorphous calcium carbonate (ACC), despite the fact that it is inherently unstable and relatively soluble in its pure state. These properties also make it difficult to detect and characterize ACC. Raman spectroscopy is a particularly useful method for investigating ACC because the sample can be examined wet, and extended X-ray absorption fine structure (EXAFS) analysis can provide detailed information on the short-range order. Other methods for characterizing ACC include infrared spectroscopy, thermogravimetric analysis and differential thermal analysis (TGA and DTA), transmission electron microscopy (TEM), and electron and X-ray diffraction. Because of the difficulties involved, we suspect that ACC is far more widely distributed than is presently known, and a comparison of EXAFS spectra shows that different biogenic ACC phases have different short-range order structures. We also suspect that ACC fulfils many different functions, including as a transient precursor phase during the formation of crystalline calcium carbonate.

  2. Apatite Formation from Amorphous Calcium Phosphate and Mixed Amorphous Calcium Phosphate/Amorphous Calcium Carbonate.

    PubMed

    Ibsen, Casper J S; Chernyshov, Dmitry; Birkedal, Henrik

    2016-08-22

    Crystallization from amorphous phases is an emerging pathway for making advanced materials. Biology has made use of amorphous precursor phases for eons and used them to produce structures with remarkable properties. Herein, we show how the design of the amorphous phase greatly influences the nanocrystals formed therefrom. We investigate the transformation of mixed amorphous calcium phosphate/amorphous calcium carbonate phases into bone-like nanocrystalline apatite using in situ synchrotron X-ray diffraction and IR spectroscopy. The speciation of phosphate was controlled by pH to favor HPO4 (2-) . In a carbonate free system, the reaction produces anisotropic apatite crystallites with large aspect ratios. The first formed crystallites are highly calcium deficient and hydrogen phosphate rich, consistent with thin octacalcium phosphate (OCP)-like needles. During growth, the crystallites become increasingly stoichiometric, which indicates that the crystallites grow through addition of near-stoichiometric apatite to the OCP-like initial crystals through a process that involves either crystallite fusion/aggregation or Ostwald ripening. The mixed amorphous phases were found to be more stable against phase transformations, hence, the crystallization was inhibited. The resulting crystallites were smaller and less anisotropic. This is rationalized by the idea that a local phosphate-depletion zone formed around the growing crystal until it was surrounded by amorphous calcium carbonate, which stopped the crystallization. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Is Mg-stabilized amorphous calcium carbonate a homogeneous mixture of amorphous magnesium carbonate and amorphous calcium carbonate?

    PubMed

    Yang, Sheng-Yu; Chang, Hsun-Hui; Lin, Cang-Jie; Huang, Shing-Jong; Chan, Jerry C C

    2016-10-04

    We find two types of carbonate ions in Mg stabilized amorphous calcium carbonate (Mg-ACC), whose short-range orders are identical to those of ACC and amorphous magnesium carbonate (AMC). Mg-ACC comprises a homogeneous mixture of the nano-clusters of ACC and AMC. Their relative amount varies systematically at different pH.

  4. Phase transitions in biogenic amorphous calcium carbonate

    NASA Astrophysics Data System (ADS)

    Gong, Yutao

    Geological calcium carbonate exists in both crystalline phases and amorphous phases. Compared with crystalline calcium carbonate, such as calcite, aragonite and vaterite, the amorphous calcium carbonate (ACC) is unstable. Unlike geological calcium carbonate crystals, crystalline sea urchin spicules (99.9 wt % calcium carbonate and 0.1 wt % proteins) do not present facets. To explain this property, crystal formation via amorphous precursors was proposed in theory. And previous research reported experimental evidence of ACC on the surface of forming sea urchin spicules. By using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), we studied cross-sections of fresh sea urchin spicules at different stages (36h, 48h and 72h after fertilization) and observed the transition sequence of three mineral phases: hydrated ACC → dehydrated ACC → biogenic calcite. In addition, we unexpectedly found hydrated ACC nanoparticles that are surrounded by biogenic calcite. This observation indicates the dehydration from hydrated ACC to dehydrated ACC is inhibited, resulting in stabilization of hydrated ACC nanoparticles. We thought that the dehydration was inhibited by protein matrix components occluded within the biomineral, and we designed an in vitro assay to test the hypothesis. By utilizing XANES-PEEM, we found that SM50, the most abundant occluded matrix protein in sea urchin spicules, has the function to stabilize hydrated ACC in vitro.

  5. Phase transitions in biogenic amorphous calcium carbonate

    PubMed Central

    Gong, Yutao U. T.; Killian, Christopher E.; Olson, Ian C.; Appathurai, Narayana P.; Amasino, Audra L.; Martin, Michael C.; Holt, Liam J.; Wilt, Fred H.; Gilbert, P. U. P. A.

    2012-01-01

    Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amorphous calcium carbonate (ACC·H2O) → dehydrated amorphous calcium carbonate (ACC) → calcite. Unexpectedly, we find ACC·H2O-rich nanoparticles that persist after the surrounding mineral has dehydrated and crystallized. Protein matrix components occluded within the mineral must inhibit ACC·H2O dehydration. We devised an in vitro, also using XANES-PEEM, assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC·H2O in vitro. PMID:22492931

  6. Structural Characteristics of Synthetic Amorphous Calcium Carbonate

    SciTech Connect

    Michel, F. Marc; MacDonald, Jason; Feng, Jian; Phillips, Brian L.; Ehm, Lars; Tarabrella, Cathy; Parise, John B.; Reeder, Richard J.

    2008-08-06

    Amorphous calcium carbonate (ACC) is an important phase involved in calcification by a wide variety of invertebrate organisms and is of technological interest in the development of functional materials. Despite widespread scientific interest in this phase a full characterization of structure is lacking. This is mainly due to its metastability and difficulties in evaluating structure using conventional structure determination methods. Here we present new findings from the application of two techniques, pair distribution function analysis and nuclear magnetic resonance spectroscopy, which provide new insight to structural aspects of synthetic ACC. Several important results have emerged from this study of ACC formed in vitro using two common preparation methods: (1) ACC exhibits no structural coherence over distances > 15 {angstrom} and is truly amorphous; (2) most of the hydrogen in ACC is present as structural H{sub 2}O, about half of which undergoes restricted motion on the millisecond time scale near room temperature; (3) the short- and intermediate-range structure of ACC shows no distinct match to any known structure in the calcium carbonate system; and (4) most of the carbonate in ACC is monodentate making it distinctly different from monohydrocalcite. Although the structure of synthetic ACC is still not fully understood, the results presented provide an important baseline for future experiments evaluating biogenic ACC and samples containing certain additives that may play a role in stabilization of ACC, crystallization kinetics, and final polymorph selection.

  7. Amorphous calcium carbonate particles form coral skeletons.

    PubMed

    Mass, Tali; Giuffre, Anthony J; Sun, Chang-Yu; Stifler, Cayla A; Frazier, Matthew J; Neder, Maayan; Tamura, Nobumichi; Stan, Camelia V; Marcus, Matthew A; Gilbert, Pupa U P A

    2017-08-28

    Do corals form their skeletons by precipitation from solution or by attachment of amorphous precursor particles as observed in other minerals and biominerals? The classical model assumes precipitation in contrast with observed "vital effects," that is, deviations from elemental and isotopic compositions at thermodynamic equilibrium. Here, we show direct spectromicroscopy evidence in Stylophora pistillata corals that two amorphous precursors exist, one hydrated and one anhydrous amorphous calcium carbonate (ACC); that these are formed in the tissue as 400-nm particles; and that they attach to the surface of coral skeletons, remain amorphous for hours, and finally, crystallize into aragonite (CaCO3). We show in both coral and synthetic aragonite spherulites that crystal growth by attachment of ACC particles is more than 100 times faster than ion-by-ion growth from solution. Fast growth provides a distinct physiological advantage to corals in the rigors of the reef, a crowded and fiercely competitive ecosystem. Corals are affected by warming-induced bleaching and postmortem dissolution, but the finding here that ACC particles are formed inside tissue may make coral skeleton formation less susceptible to ocean acidification than previously assumed. If this is how other corals form their skeletons, perhaps this is how a few corals survived past CO2 increases, such as the Paleocene-Eocene Thermal Maximum that occurred 56 Mya.

  8. Amorphous calcium carbonate particles form coral skeletons

    PubMed Central

    Mass, Tali; Giuffre, Anthony J.; Sun, Chang-Yu; Stifler, Cayla A.; Frazier, Matthew J.; Neder, Maayan; Tamura, Nobumichi; Stan, Camelia V.; Marcus, Matthew A.

    2017-01-01

    Do corals form their skeletons by precipitation from solution or by attachment of amorphous precursor particles as observed in other minerals and biominerals? The classical model assumes precipitation in contrast with observed “vital effects,” that is, deviations from elemental and isotopic compositions at thermodynamic equilibrium. Here, we show direct spectromicroscopy evidence in Stylophora pistillata corals that two amorphous precursors exist, one hydrated and one anhydrous amorphous calcium carbonate (ACC); that these are formed in the tissue as 400-nm particles; and that they attach to the surface of coral skeletons, remain amorphous for hours, and finally, crystallize into aragonite (CaCO3). We show in both coral and synthetic aragonite spherulites that crystal growth by attachment of ACC particles is more than 100 times faster than ion-by-ion growth from solution. Fast growth provides a distinct physiological advantage to corals in the rigors of the reef, a crowded and fiercely competitive ecosystem. Corals are affected by warming-induced bleaching and postmortem dissolution, but the finding here that ACC particles are formed inside tissue may make coral skeleton formation less susceptible to ocean acidification than previously assumed. If this is how other corals form their skeletons, perhaps this is how a few corals survived past CO2 increases, such as the Paleocene–Eocene Thermal Maximum that occurred 56 Mya. PMID:28847944

  9. Amorphous calcium carbonate particles form coral skeletons

    NASA Astrophysics Data System (ADS)

    Mass, Tali; Giuffre, Anthony J.; Sun, Chang-Yu; Stifler, Cayla A.; Frazier, Matthew J.; Neder, Maayan; Tamura, Nobumichi; Stan, Camelia V.; Marcus, Matthew A.; Gilbert, Pupa U. P. A.

    2017-09-01

    Do corals form their skeletons by precipitation from solution or by attachment of amorphous precursor particles as observed in other minerals and biominerals? The classical model assumes precipitation in contrast with observed “vital effects,” that is, deviations from elemental and isotopic compositions at thermodynamic equilibrium. Here, we show direct spectromicroscopy evidence in Stylophora pistillata corals that two amorphous precursors exist, one hydrated and one anhydrous amorphous calcium carbonate (ACC); that these are formed in the tissue as 400-nm particles; and that they attach to the surface of coral skeletons, remain amorphous for hours, and finally, crystallize into aragonite (CaCO3). We show in both coral and synthetic aragonite spherulites that crystal growth by attachment of ACC particles is more than 100 times faster than ion-by-ion growth from solution. Fast growth provides a distinct physiological advantage to corals in the rigors of the reef, a crowded and fiercely competitive ecosystem. Corals are affected by warming-induced bleaching and postmortem dissolution, but the finding here that ACC particles are formed inside tissue may make coral skeleton formation less susceptible to ocean acidification than previously assumed. If this is how other corals form their skeletons, perhaps this is how a few corals survived past CO2 increases, such as the Paleocene–Eocene Thermal Maximum that occurred 56 Mya.

  10. Disordered amorphous calcium carbonate from direct precipitation

    SciTech Connect

    Farhadi Khouzani, Masoud; Chevrier, Daniel M.; Güttlein, Patricia; Hauser, Karin; Zhang, Peng; Hedin, Niklas; Gebauer, Denis

    2015-06-01

    Amorphous calcium carbonate (ACC) is known to play a prominent role in biomineralization. Different studies on the structure of biogenic ACCs have illustrated that they can have distinct short-range orders. However, the origin of so-called proto-structures in synthetic and additive-free ACCs is not well understood. In the current work, ACC has been synthesised in iso-propanolic media by direct precipitation from ionic precursors, and analysed utilising a range of different techniques. The data suggest that this additive-free type of ACC does not resemble clear proto-structural motifs relating to any crystalline polymorph. This can be explained by the undefined pH value in iso-propanolic media, and the virtually instantaneous precipitation. Altogether, this work suggests that aqueous systems and pathways involving pre-nucleation clusters are required for the generation of clear proto-structural features in ACC. Experiments on the ACC-to-crystalline transformation in solution with and without ethanol highlight that polymorph selection is under kinetic control, while the presence of ethanol can control dissolution re-crystallisation pathways.

  11. Disordered amorphous calcium carbonate from direct precipitation

    DOE PAGES

    Farhadi Khouzani, Masoud; Chevrier, Daniel M.; Güttlein, Patricia; ...

    2015-06-01

    Amorphous calcium carbonate (ACC) is known to play a prominent role in biomineralization. Different studies on the structure of biogenic ACCs have illustrated that they can have distinct short-range orders. However, the origin of so-called proto-structures in synthetic and additive-free ACCs is not well understood. In the current work, ACC has been synthesised in iso-propanolic media by direct precipitation from ionic precursors, and analysed utilising a range of different techniques. The data suggest that this additive-free type of ACC does not resemble clear proto-structural motifs relating to any crystalline polymorph. This can be explained by the undefined pH value inmore » iso-propanolic media, and the virtually instantaneous precipitation. Altogether, this work suggests that aqueous systems and pathways involving pre-nucleation clusters are required for the generation of clear proto-structural features in ACC. Experiments on the ACC-to-crystalline transformation in solution with and without ethanol highlight that polymorph selection is under kinetic control, while the presence of ethanol can control dissolution re-crystallisation pathways.« less

  12. Calcium carbonate polyamorphism and its role in biomineralization: how many amorphous calcium carbonates are there?

    PubMed

    Cartwright, Julyan H E; Checa, Antonio G; Gale, Julian D; Gebauer, Denis; Sainz-Díaz, C Ignacio

    2012-11-26

    Although the polymorphism of calcium carbonate is well known, and its polymorphs--calcite, aragonite, and vaterite--have been highly studied in the context of biomineralization, polyamorphism is a much more recently discovered phenomenon, and the existence of more than one amorphous phase of calcium carbonate in biominerals has only very recently been understood. Here we summarize what is known about polyamorphism in calcium carbonate as well as what is understood about the role of amorphous calcium carbonate in biominerals. We show that consideration of the amorphous forms of calcium carbonate within the physical notion of polyamorphism leads to new insights when it comes to the mechanisms by which polymorphic structures can evolve in the first place. This not only has implications for our understanding of biomineralization, but also of the means by which crystallization may be controlled in medical, pharmaceutical, and industrial contexts. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Amorphous Calcium Carbonate Based-Microparticles for Peptide Pulmonary Delivery.

    PubMed

    Tewes, Frederic; Gobbo, Oliviero L; Ehrhardt, Carsten; Healy, Anne Marie

    2016-01-20

    Amorphous calcium carbonate (ACC) is known to interact with proteins, for example, in biogenic ACC, to form stable amorphous phases. The control of amorphous/crystalline and inorganic/organic ratios in inhalable calcium carbonate microparticles may enable particle properties to be adapted to suit the requirements of dry powders for pulmonary delivery by oral inhalation. For example, an amorphous phase can immobilize and stabilize polypeptides in their native structure and amorphous and crystalline phases have different mechanical properties. Therefore, inhalable composite microparticles made of inorganic (i.e., calcium carbonate and calcium formate) and organic (i.e., hyaluronan (HA)) amorphous and crystalline phases were investigated for peptide and protein pulmonary aerosol delivery. The crystalline/amorphous ratio and polymorphic form of the inorganic component was altered by changing the microparticle drying rate and by changing the ammonium carbonate and HA initial concentration. The bioactivity of the model peptide, salmon calcitonin (sCT), coprocessed with alpha-1-antitrypsin (AAT), a model protein with peptidase inhibitor activity, was maintained during processing and the microparticles had excellent aerodynamic properties, making them suitable for pulmonary aerosol delivery. The bioavailability of sCT after aerosol delivery as sCT and AAT-loaded composite microparticles to rats was 4-times higher than that of sCT solution.

  14. Bivalves build their shells from amorphous calcium carbonate

    NASA Astrophysics Data System (ADS)

    Jacob, D. E.; Wirth, R.; Soldati, A. L.; Wehrmeister, U.

    2012-04-01

    One of the most common shell structures in the bivalve class is the prism and nacre structure. It is widely distributed amongst both freshwater and marine species and gives cultured pearls their sought-after lustre. In freshwater bivalves, both shell structures (prism and nacre) consist of aragonite. Formation of the shell form an amorphous precursor phase is a wide-spread strategy in biomineralization and presents a number of advantages for the organisms in the handling of the CaCO3 material. While there is already evidence that larval shells of some mollusk species use amorphous calcium carbonate (ACC) as a transient precursor phase for aragonite, the use of this strategy by adult animals was only speculated upon. We present results from in-situ geochemistry, Raman spectroscopy and focused-ion beam assisted TEM on three species from two different bivalve families that show that remnants of ACC can be found in shells from adult species. We show that the amorphous phase is not randomly distributed, but is systematically found in a narrow zone at the interface between periostracum and prism layer. This zone is the area where spherulitic CaCO3- structures protrude from the inner periostracum to form the initial prisms. These observations are in accordance with our earlier results on equivalent structures in freshwater cultured pearls (Jacob et al., 2008) and show that the original building material for the prisms is amorphous calcium carbonate, secreted in vesicles at the inner periostracum layer. Quantitative temperature calibrations for paleoclimate applications using bivalve shells are based on the Mg-Ca exchange between inorganic aragonite (or calcite) and water. These calibrations, thus, do not take into account the biomineral crystallization path via an amorphous calcium carbonate precursor and are therefore likely to introduce a bias (a so-called vital effect) which currently is not accounted for. Jacob et al. (2008) Geochim. Cosmochim. Acta 72, 5401-5415

  15. Amorphous Calcium Carbonate in Biomineralization: Stable and Precursor Phases

    NASA Astrophysics Data System (ADS)

    Weiner, S.

    2003-12-01

    The biological formation of the crystalline polymorphs of calcium carbonate, aragonite and calcite, is widespread. The less stable polymorphs, vaterite and monohydrocalcite are also formed by some organisms. Surprisingly, the highly unstable phase, amorphous calcium carbonate (ACC), is formed by a variety of organisms from different phyla. Most of these are stable at least within the lifetime of the organism. The stable forms all have a stoichiometry of CaCO3.H2O. Despite the fact that they do not diffract X-rays. Studies of their short range order by EXAFS, reveal species specific variations in the number and distances of atoms that surround the calcium ion. Proteins extracted from stable biogenic ACC are able to stabilize the phase in vitro. ACC has also been identified as a transient precursor phase during the formation of the calcitic larval spicule of the sea urchin and the formation of the larval shell of a bivalve. The transient form has little or no water associated with the CaCO3. Preliminary EXAFS data suggest that the short range order of the sea urchin spicule transient ACC resembles calcite. Proteins extracted from these spicules are able to stabilize ACC provided Mg is present in the solution. As the mollusks and the echinoderms are on two different branches of the animal phylogenetic tree, it is conceivable that the strategy of using ACC as a precursor phase at least for larval mineralization may be widespread. It has yet to be shown that it is used by adults of either phylum. The manner in which organisms precipitate, stabilize and destabilize if necessary, this highly metastable phase of calcium carbonate presents many fascinating and enigmatic questions, whose solutions could well contribute to a better understanding of basic processes in biomineralization. For more details and references, see Addadi, L., Raz, S. and Weiner, S. (2003). Taking advantage of disorder: Amorphous calcium carbonate and its roles in biomineralization. Adv. Mat.15, 959-970.

  16. Dehydration-induced amorphous phases of calcium carbonate.

    PubMed

    Saharay, Moumita; Yazaydin, A Ozgur; Kirkpatrick, R James

    2013-03-28

    Amorphous calcium carbonate (ACC) is a critical transient phase in the inorganic precipitation of CaCO3 and in biomineralization. The calcium carbonate crystallization pathway is thought to involve dehydration of more hydrated ACC to less hydrated ACC followed by the formation of anhydrous ACC. We present here computational studies of the transition of a hydrated ACC with a H2O/CaCO3 ratio of 1.0 to anhydrous ACC. During dehydration, ACC undergoes reorganization to a more ordered structure with a significant increase in density. The computed density of anhydrous ACC is similar to that of calcite, the stable crystalline phase. Compared to the crystalline CaCO3 phases, calcite, vaterite, and aragonite, the computed local structure of anhydrous ACC is most-similar to those of calcite and vaterite, but the overall structure is not well described by either. The strong hydrogen bond interaction between the carbonate ions and water molecules plays a crucial role in stabilizing the less hydrated ACC compositions compared to the more hydrated ones, leading to a progressively increasing hydration energy with decreasing water content.

  17. Increased calcium absorption from synthetic stable amorphous calcium carbonate: Double-blind randomized crossover clinical trial in post-menopausal women

    USDA-ARS?s Scientific Manuscript database

    Calcium supplementation is a widely recognized strategy for achieving adequate calcium intake. We designed this blinded, randomized, crossover interventional trial to compare the bioavailability of a new stable synthetic amorphous calcium carbonate (ACC) with that of crystalline calcium carbonate (C...

  18. Freeze-drying yields stable and pure amorphous calcium carbonate (ACC).

    PubMed

    Ihli, Johannes; Kulak, Alexander N; Meldrum, Fiona C

    2013-04-18

    A simple synthetic method is presented for the precipitation of high purity, dry amorphous calcium carbonate (ACC) based on freeze-drying saturated, counter ion free CaCO3 solutions, where the ACC produced shows an extended atmospheric stability. Translation of the methodology to amorphous calcium phosphate demonstrates the generality of the approach.

  19. Calcium Isotope Signature of Amorphous Calcium Carbonate: A Probe of Crystallization Pathway? (Invited)

    NASA Astrophysics Data System (ADS)

    Gagnon, A. C.; Depaolo, D. J.; Deyoreo, J. J.

    2010-12-01

    Stable isotope fractionation is sensitive to the energy landscape of nucleation and growth. Thus isotope ratios represent a promising tool to understand the chemical mechanisms controlling precipitation in geological systems. To realize this potential we must (1) determine the isotopic fractionation associated with different growth pathways, (2) use these isotopic constraints to test nucleation or growth mechanism, and (3) compare these signatures to natural isotopic variability. The first two goals can be explored by laboratory precipitation under controlled conditions. Through inorganic synthesis of amorphous calcium carbonate (ACC), we quantify the impact of an important amorphous precursor phase on calcium isotope ratios. Synthetic ACC was first characterized spectroscopically, then calcium isotope analysis was conducted using a double-spike method on a thermal ionization mass spectrometer. Experiments spanning a range of oversaturations and temperatures show that ACC is consistently less fractionated than CaCO3 precipitated as crystalline calcite. These data suggest the rate-limiting step that controls calcium incorporation is different between ACC and direct precipitation of calcite. Furthermore, different isotopic signatures between ACC and calcite appear to represent a useful proxy for crystallization pathway. To further explore this possibility, we plan to measure the calcium isotope composition of several biominerals where an ACC precursor phase has been identified. It is hoped that our investigation will lead to both improved identification of the ACC pathway and a better understanding of the general rules that control CaCO3 crystal growth and composition.

  20. Pressure-Induced Polyamorphism and Formation of 'Aragonitic' Amorphous Calcium Carbonate

    SciTech Connect

    Fernandez-Martinez, Alejandro; Kalkan, Bora; Clark, Simon M.; Waychunas, Glenn A.

    2013-09-23

    Amorphous calcium carbonate (ACC) undergoes a reversible amorphous–amorphous phase transition at 10 GPa, adopting an aragonite-like local order. This result suggests a mechanism by which Mg2+—a cation with smaller ionic radius than Ca2+—modifies the local order of ACC to an aragonite-like order by helping to decrease the molar volume of the amorphous phase.

  1. Aragonite nanorods in calcium carbonate/polymer hybrids formed through self-organization processes from amorphous calcium carbonate solution.

    PubMed

    Kajiyama, Satoshi; Nishimura, Tatsuya; Sakamoto, Takeshi; Kato, Takashi

    2014-04-24

    Nanostructured inorganic/polymer hybrid thin films comprising aragonite nanorods derived from aqueous suspensions of amorphous calcium carbonate (ACC) are prepared. For the formation of calcium carbonate (CaCO₃)/polymer hybrids, spincoated and annealed films of poly(vinyl alcohol) (PVA) that function as polymer matrices are soaked in aqueous colloidal solutions dispersing ACC stabilized by poly(acrylic acid) (PAA). In the initial stage, calcite thin films form on the surface. Subsequently, aragonite crystals start to form inside the PVA matrix that contains PVA crystallites which induce aragonite nucleation. Nanostructured hybrids composed of calcite thin films consisting of nanoparticles and assembled aragonite nanorods are formed in the matrices of PVA.

  2. Synthesis of novel amorphous calcium carbonate by sono atomization for reactive mixing.

    PubMed

    Kojima, Yoshiyuki; Kanai, Makoto; Nishimiya, Nobuyuki

    2012-03-01

    Droplets of several micrometers in size can be formed in aqueous solution by atomization under ultrasonic irradiation at 2 MHz. This phenomenon, known as atomization, is capable of forming fine droplets for use as a reaction field. This synthetic method is called SARM (sono atomization for reactive mixing). This paper reports on the synthesis of a novel amorphous calcium carbonate formed by SARM. The amorphous calcium carbonate, obtained at a solution concentration of 0.8 mol/dm(3), had a specific surface area of 65 m(2)/g and a composition of CaCO(3)•0.5H(2)O as determined using thermogravimetric/differential thermal analysis (TG-DTA). Because the ACC had a lower hydrate composition than conventional amorphous calcium carbonate (ACC), the ACC synthesized in this paper was very stable at room temperature. Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.

  3. In vitro synthesis and stabilization of amorphous calcium carbonate (ACC) nanoparticles within liposomes

    SciTech Connect

    Tester, Chantel C.; Brock, Ryan E.; Wu, Ching-Hsuan; Krejci, Minna R.; Weigand, Steven; Joester, Derk

    2012-02-07

    We show that amorphous calcium carbonate (ACC) can be synthesized in phospholipid bilayer vesicles (liposomes). Liposome-encapsulated ACC nanoparticles are stable against aggregation, do not crystallize for at least 20 h, and are ideally suited to investigate the influence of lipid chemistry, particle size, and soluble additives on ACC in situ.

  4. A solvothermal method for synthesizing monolayer protected amorphous calcium carbonate clusters.

    PubMed

    Sun, Shengtong; Gebauer, Denis; Cölfen, Helmut

    2016-05-19

    A solvothermal method was developed for synthesizing organic monolayer protected amorphous calcium carbonate clusters using 10,12-pentacosadiynoic acid as ligand, ethanol as solvent and NaHCO3 decomposition as CO2 source, which can be extended to synthesize other monolayer protected mineral clusters.

  5. Amorphous calcium carbonate controls avian eggshell mineralization: A new paradigm for understanding rapid eggshell calcification.

    PubMed

    Rodríguez-Navarro, Alejandro B; Marie, Pauline; Nys, Yves; Hincke, Maxwell T; Gautron, Joel

    2015-06-01

    Avian eggshell mineralization is the fastest biogenic calcification process known in nature. How this is achieved while producing a highly crystalline material composed of large calcite columnar single crystals remains largely unknown. Here we report that eggshell mineral originates from the accumulation of flat disk-shaped amorphous calcium carbonate (ACC) particles on specific organic sites on the eggshell membrane, which are rich in proteins and sulfated proteoglycans. These structures known as mammillary cores promote the nucleation and stabilization of a amorphous calcium carbonate with calcitic short range order which predetermine the calcite composition of the mature eggshell. The amorphous nature of the precursor phase was confirmed by the diffuse scattering of X-rays and electrons. The nascent calcitic short-range order of this transient mineral phase was revealed by infrared spectroscopy and HRTEM. The ACC mineral deposited around the mammillary core sites progressively transforms directly into calcite crystals without the occurrence of any intermediate phase. Ionic speciation data suggest that the uterine fluid is equilibrated with amorphous calcium carbonate, throughout the duration of eggshell mineralization process, supporting that this mineral phase is constantly forming at the shell mineralization front. On the other hand, the transient amorphous calcium carbonate mineral deposits, as well as the calcite crystals into which they are converted, form by the ordered aggregation of nanoparticles that support the rapid mineralization of the eggshell. The results of this study alter our current understanding of avian eggshell calcification and provide new insights into the genesis and formation of calcium carbonate biominerals in vertebrates. Copyright © 2015 Elsevier Inc. All rights reserved.

  6. Nanoporous Structure and Medium-Range Order in Synthetic Amorphous Calcium Carbonate

    SciTech Connect

    Goodwin, Andrew L.; Michel, F. Marc; Phillips, Brian L.; Keen, David A.; Dove, Martin T.; Reeder, Richard J.

    2010-12-03

    We adopt a reverse Monte Carlo refinement approach, using experimental X-ray total scattering data, to develop a structure model for synthetic, hydrated amorphous calcium carbonate (ACC). The ACC is revealed to consist of a porous calcium-rich framework that supports interconnected channels containing water and carbonate molecules. The existence of a previously unrecognized nanometer-scale channel network suggests mechanisms of how additives can be accommodated within the structure and provide temporary stabilization, as well as influence the crystallization process. Moreover, while lacking long-range order, the calcium-rich framework in the ACC contains similar Ca packing density to that present in calcite, aragonite, and vaterite, yielding clues of how the amorphous material converts into the different crystalline forms. Our results provide a new starting point for advancing our understanding of biomineralization as well as the development of biomimetic approaches to next-generation materials synthesis.

  7. On the structure of amorphous calcium carbonate--a detailed study by solid-state NMR spectroscopy.

    PubMed

    Nebel, Holger; Neumann, Markus; Mayer, Christian; Epple, Matthias

    2008-09-01

    The calcium carbonate phases calcite, aragonite, vaterite, monohydrocalcite (calcium carbonate monohydrate), and ikaite (calcium carbonate hexahydrate) were studied by solid-state NMR spectroscopy ( (1)H and (13)C). Further model compounds were sodium hydrogencarbonate, potassium hydrogencarbonate, and calcium hydroxide. With the help of these data, the structure of synthetically prepared additive-free amorphous calcium carbonate (ACC) was analyzed. ACC contains molecular water (as H 2O), a small amount of mobile hydroxide, and no hydrogencarbonate. This supports the concept of ACC as a transient precursor in the formation of calcium carbonate biominerals.

  8. Solid-State Transformation of Amorphous Calcium Carbonate to Aragonite Captured by CryoTEM.

    PubMed

    Walker, Jessica M; Marzec, Bartosz; Nudelman, Fabio

    2017-07-25

    Early-stage reaction mechanisms for aragonite-promoting systems are relatively unknown compared to the more thermodynamically stable calcium carbonate polymorph, calcite. Using cryoTEM and SEM, the early reaction stages taking place during aragonite formation were identified in a highly supersaturated solution using an alcohol-water solvent, and an overall particle attachment growth mechanism was described for the system. In vitro evidence is provided for the solid-state transformation of amorphous calcium carbonate to aragonite, demonstrating the co-existence of both amorphous and crystalline material within the same aragonite needle. This supports non-classical formation of aragonite within both a synthetic and biological context. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. A transparent hybrid of nanocrystalline cellulose and amorphous calcium carbonate nanoparticles

    NASA Astrophysics Data System (ADS)

    Gebauer, Denis; Oliynyk, Vitaliy; Salajkova, Michaela; Sort, Jordi; Zhou, Qi; Bergström, Lennart; Salazar-Alvarez, German

    2011-09-01

    Nanocellulose hybrids are promising candidates for biodegradable multifunctional materials. Hybrids of nanocrystalline cellulose (NCC) and amorphous calcium carbonate (ACC) nanoparticles were obtained through a facile chemical approach over a wide range of compositions. Controlling the interactions between NCC and ACC results in hard, transparent structures with tunable composition, homogeneity and anisotropy.Nanocellulose hybrids are promising candidates for biodegradable multifunctional materials. Hybrids of nanocrystalline cellulose (NCC) and amorphous calcium carbonate (ACC) nanoparticles were obtained through a facile chemical approach over a wide range of compositions. Controlling the interactions between NCC and ACC results in hard, transparent structures with tunable composition, homogeneity and anisotropy. Electronic supplementary information (ESI) available: Additional experimental procedures and results. See DOI: 10.1039/c1nr10681c

  10. Self-assembly of amorphous calcium carbonate microlens arrays.

    PubMed

    Lee, Kyubock; Wagermaier, Wolfgang; Masic, Admir; Kommareddy, Krishna P; Bennet, Mathieu; Manjubala, Inderchand; Lee, Seung-Woo; Park, Seung B; Cölfen, Helmut; Fratzl, Peter

    2012-03-06

    Biological materials are often based on simple constituents and grown by the principle of self-assembly under ambient conditions. In particular, biomineralization approaches exploit efficient pathways of inorganic material synthesis. There is still a large gap between the complexity of natural systems and the practical utilization of bioinspired formation mechanisms. Here we describe a simple self-assembly route leading to a CaCO(3) microlens array, somewhat reminiscent of the brittlestars' microlenses, with uniform size and focal length, by using a minimum number of components and equipment at ambient conditions. The formation mechanism of the amorphous CaCO(3) microlens arrays was elucidated by confocal Raman spectroscopic imaging to be a two-step growth process mediated by the organic surfactant. CaCO(3) microlens arrays are easy to fabricate, biocompatible and functional in amorphous or more stable crystalline forms. This shows that advanced optical materials can be generated by a simple mineral precipitation.

  11. Microwave hydrothermal transformation of amorphous calcium carbonate nanospheres and application in protein adsorption.

    PubMed

    Qi, Chao; Zhu, Ying-Jie; Chen, Feng

    2014-03-26

    Calcium carbonate and calcium phosphate are the main components of biominerals. Among all of the forms of biominerals, amorphous calcium carbonate (ACC) and amorphous calcium phosphate (ACP) are the most important forms because they play a pivotal role in the process of biomineralization and are the precursors to the crystalline polymorphs. In this work, we first synthesized ACC in vitro using adenosine 5'-triphosphate disodium salt (ATP) as the stabilizer and investigated the transformation of the ACC under microwave hydrothermal conditions, and ACC/ACP composite nanospheres and carbonated hydroxyapatite (CHA) nanospheres were successfully prepared. In this novel strategy, ATP has two main functions: it serves as the stabilizer for ACC and the phosphorus source for ACP and CHA. Most importantly, the morphology and the size of the ACC precursor can be well-preserved after microwave heating, so it provides a new method for the preparation of calcium phosphate nanostructured materials using phosphorus-containing biomolecule-stabilized ACC as the precursor. Furthermore, the as-prepared ACC/ACP composite nanospheres have excellent biocompatibility and high protein adsorption capacity, indicating that they are promising for applications in biomedical fields such as drug delivery and protein adsorption.

  12. Amorphous calcium carbonate transforms into calcite during sea urchin larval spicule growth

    PubMed Central

    Beniash, E.; Aizenberg, J.; Addadi, L.; Weiner, S.

    1997-01-01

    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 with time. This observation significantly changes our concepts of mineral formation in this well-studied organism.

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

    PubMed

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

    2011-12-23

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

  14. Increased calcium absorption from synthetic stable amorphous calcium carbonate: double-blind randomized crossover clinical trial in postmenopausal women.

    PubMed

    Vaisman, Nachum; Shaltiel, Galit; Daniely, Michal; Meiron, Oren E; Shechter, Assaf; Abrams, Steven A; Niv, Eva; Shapira, Yami; Sagi, Amir

    2014-10-01

    Calcium supplementation is a widely recognized strategy for achieving adequate calcium intake. We designed this blinded, randomized, crossover interventional trial to compare the bioavailability of a new stable synthetic amorphous calcium carbonate (ACC) with that of crystalline calcium carbonate (CCC) using the dual stable isotope technique. The study was conducted in the Unit of Clinical Nutrition, Tel Aviv Sourasky Medical Center, Israel. The study population included 15 early postmenopausal women aged 54.9 ± 2.8 (mean ± SD) years with no history of major medical illness or metabolic bone disorder, excess calcium intake, or vitamin D deficiency. Standardized breakfast was followed by randomly provided CCC or ACC capsules containing 192 mg elemental calcium labeled with 44Ca at intervals of at least 3 weeks. After swallowing the capsules, intravenous CaCl2 labeled with 42Ca on was administered on each occasion. Fractional calcium absorption (FCA) of ACC and CCC was calculated from the 24-hour urine collection following calcium administration. The results indicated that FCA of ACC was doubled (± 0.96 SD) on average compared to that of CCC (p < 0.02). The higher absorption of the synthetic stable ACC may serve as a more efficacious way of calcium supplementation. © 2014 American Society for Bone and Mineral Research.

  15. Amorphous and crystalline calcium carbonate distribution in the tergite cuticle of moulting Porcellio scaber (Isopoda, Crustacea).

    PubMed

    Neues, Frank; Hild, Sabine; Epple, Matthias; Marti, Othmar; Ziegler, Andreas

    2011-07-01

    The main mineral components of the isopod cuticle consists of crystalline magnesium calcite and amorphous calcium carbonate. During moulting isopods moult first the posterior and then the anterior half of the body. In terrestrial species calcium carbonate is subject to resorption, storage and recycling in order to retain significant fractions of the mineral during the moulting cycle. We used synchrotron X-ray powder diffraction, elemental analysis and Raman spectroscopy to quantify the ACC/calcite ratio, the mineral phase distribution and the composition within the anterior and posterior tergite cuticle during eight different stages of the moulting cycle of Porcellio scaber. The results show that most of the amorphous calcium carbonate (ACC) is resorbed from the cuticle, whereas calcite remains in the old cuticle and is shed during moulting. During premoult resorption of ACC from the posterior cuticle is accompanied by an increase within the anterior tergites, and mineralization of the new posterior cuticle by resorption of mineral from the anterior cuticle. This suggests that one reason for using ACC in cuticle mineralization is to facilitate resorption and recycling of cuticular calcium carbonate. Furthermore we show that ACC precedes the formation of calcite in distal layers of the tergite cuticle.

  16. Controlled synthesis of crystalline calcium carbonate aggregates with unusual morphologies involving the phase transformation from amorphous calcium carbonate

    SciTech Connect

    Tang Hua; Yu Jiaguo Zhao Xiufeng

    2009-04-02

    Peanut-shaped CaCO{sub 3} aggregates, featured of two dandelion-like heads built up from rod-like subunits, have been synthesized via a facile precipitation reaction between Na{sub 2}CO{sub 3} and CaCl{sub 2} at ambient temperature in the presence of magnesium ions and ethanol solvent. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The results show that a high magnesium concentration and ethanol solvent are necessary for the formation of the unusual peanut-like aggregates. In addition, a multistep phase transformation process from amorphous calcium carbonate (ACC) to a mixture of ACC and calcite and ultimately to calcite and aragonite was observed in the formation process of the unusual structures. A possible mechanism for the formation of the unusual peanut-shape aggregates has been proposed and discussed.

  17. Calcium Carbonate Storage in Amorphous Form and Its Template-Induced Crystallization

    SciTech Connect

    Han, T Y; Aizenberg, J

    2007-08-31

    Calcium carbonate crystallization in organisms often occurs through the transformation from the amorphous precursor. It is believed that the amorphous phase could be temporarily stabilized and stored, until its templated transition to the crystalline form is induced. Here we develop a bio-inspired crystallization strategy that is based on the above mechanism. Amorphous calcium carbonate (ACC) spherulitic particles are formed and stabilized on a self-assembled monolayer (SAM) of hydroxy-terminated alkanethiols on Au surface. The ACC is stored as a reservoir for ions and is induced to crystallize on command by introducing a secondary surface that is functionalized with carboxylic acid-terminated SAM. This secondary surface acts as a template for oriented and patterned nucleation. Various oriented crystalline arrays and micropatterned films are formed. We also show that the ACC phase can be doped with foreign ions (e.g. Mg) and organic molecules (e.g. dyes) and that these dopants later function as growth modifiers of calcite crystals and become incorporated into the crystals during the transformation process of ACC to calcite. We believe that our strategy opens the way of using a stabilized amorphous phase as a versatile reservoir system that can be converted in a highly controlled fashion to a crystalline form upon contacting the nucleating template.

  18. Amorphous Calcium Carbonate Precipitation by Cellular Biomineralization in Mantle Cell Cultures of Pinctada fucata

    PubMed Central

    Xiang, Liang; Kong, Wei; Su, Jingtan; Liang, Jian; Zhang, Guiyou; Xie, Liping; Zhang, Rongqing

    2014-01-01

    The growth of molluscan shell crystals is generally thought to be initiated from the extrapallial fluid by matrix proteins, however, the cellular mechanisms of shell formation pathway remain unknown. Here, we first report amorphous calcium carbonate (ACC) precipitation by cellular biomineralization in primary mantle cell cultures of Pinctada fucata. Through real-time PCR and western blot analyses, we demonstrate that mantle cells retain the ability to synthesize and secrete ACCBP, Pif80 and nacrein in vitro. In addition, the cells also maintained high levels of alkaline phosphatase and carbonic anhydrase activity, enzymes responsible for shell formation. On the basis of polarized light microscopy and scanning electron microscopy, we observed intracellular crystals production by mantle cells in vitro. Fourier transform infrared spectroscopy and X-ray diffraction analyses revealed the crystals to be ACC, and de novo biomineralization was confirmed by following the incorporation of Sr into calcium carbonate. Our results demonstrate the ability of mantle cells to perform fundamental biomineralization processes via amorphous calcium carbonate, and these cells may be directly involved in pearl oyster shell formation. PMID:25405357

  19. Amorphous calcium carbonate precipitation by cellular biomineralization in mantle cell cultures of Pinctada fucata.

    PubMed

    Xiang, Liang; Kong, Wei; Su, Jing-Tan; Su, Jingtan; Liang, Jian; Zhang, Gui-You; Zhang, Guiyou; Xie, Li-Ping; Xie, Liping; Zhang, Rong-Qing; Zhang, Rongqing

    2014-01-01

    The growth of molluscan shell crystals is generally thought to be initiated from the extrapallial fluid by matrix proteins, however, the cellular mechanisms of shell formation pathway remain unknown. Here, we first report amorphous calcium carbonate (ACC) precipitation by cellular biomineralization in primary mantle cell cultures of Pinctada fucata. Through real-time PCR and western blot analyses, we demonstrate that mantle cells retain the ability to synthesize and secrete ACCBP, Pif80 and nacrein in vitro. In addition, the cells also maintained high levels of alkaline phosphatase and carbonic anhydrase activity, enzymes responsible for shell formation. On the basis of polarized light microscopy and scanning electron microscopy, we observed intracellular crystals production by mantle cells in vitro. Fourier transform infrared spectroscopy and X-ray diffraction analyses revealed the crystals to be ACC, and de novo biomineralization was confirmed by following the incorporation of Sr into calcium carbonate. Our results demonstrate the ability of mantle cells to perform fundamental biomineralization processes via amorphous calcium carbonate, and these cells may be directly involved in pearl oyster shell formation.

  20. Synthesis and structure of synthetically pure and deuterated amorphous (basic) calcium carbonates

    SciTech Connect

    Wang, Hsiu-Wen; Daemen, Luke L.; Cheshire, Michael C.; Kidder, Michelle K.; Stack, Andrew G.; Allard, Lawrence F.; Neuefeind, Jörg; Olds, Daniel; Liu, Jue; Page, Katharine

    2017-01-01

    It is generally believed that H2O and OH- are the key species stabilizing and controlling amorphous calcium carbonate “polyamorph” forms, and may in turn control the ultimate crystallization products during synthesis and in natural systems. Yet, the locations and hydrogen-bonding network of these species in ACC have never been measured directly using neutron diffraction. We report a synthesis route that overcomes the existing challenges with respect to yield quantities and deuteration, both of which are critically necessary for high quality neutron studies.

  1. Synthesis and structure of synthetically pure and deuterated amorphous (basic) calcium carbonates

    DOE PAGES

    Wang, Hsiu-Wen; Daemen, Luke L.; Cheshire, Michael C.; ...

    2017-02-17

    It is generally believed that H2O and OH- are the key species stabilizing and controlling amorphous calcium carbonate “polyamorph” forms, and may in turn control the ultimate crystallization products during synthesis and in natural systems. Yet, the locations and hydrogen-bonding network of these species in ACC have never been measured directly using neutron diffraction. In this paper, we report a synthesis route that overcomes the existing challenges with respect to yield quantities and deuteration, both of which are critically necessary for high quality neutron studies.

  2. ATP-stabilized amorphous calcium carbonate nanospheres and their application in protein adsorption.

    PubMed

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

    2014-05-28

    Calcium carbonate is a common substance found in rocks worldwide, and is the main biomineral formed in shells of marine organisms and snails, pearls and eggshells. Amorphous calcium carbonate (ACC) is the least stable polymorph of calcium carbonate, which is so unstable under normal conditions that it is difficult to be prepared in vitro because it rapidly crystallizes to form one of the more stable polymorphs in aqueous solution. Herein, we report the successful synthesis of highly stable ACC nanospheres in vitro using adenosine 5'-triphosphate disodium salt (ATP) as a stabilizer. The effect of ATP on the stability of ACC nanospheres is investigated. Our experiments show that ATP plays an unique role in the stabilization of ACC nanospheres in aqueous solution. Moreover, the as-prepared ACC nanospheres are highly stable in phosphate buffered saline for a relatively long period of time (12 days) even under relatively high concentrations of calcium and phosphate ions. The cytotoxicity tests show that the as-prepared highly stable ACC nanospheres have excellent biocompatibility. The highly stable ACC nanospheres have high protein adsorption capacity, implying that they are promising for applications in biomedical fields such as drug delivery and protein adsorption. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Investigating the Role of Carbonate Ion Concentration on the Magnesium Content of Amorphous Calcium Carbonate

    NASA Astrophysics Data System (ADS)

    Blue, C.; Dove, P. M.; Han, N.

    2011-12-01

    The fields of biomineralization and carbonate geochemistry are undergoing a paradigm shift with the realization that the formation of calcite with diverse compositions and textures can be understood within the framework of multiple pathways to mineralization. Many organisms do not form their skeletons via the classical step-growth process, but instead mineralization occurs through a mesocrystal pathway that begins with the formation of amorphous calcium carbonate (ACC), which subsequently transforms to calcite. Little is known about factors that regulate this type of calcification because the last 50 years of research have focused almost entirely on step-growth processes. In particular, new findings indicate that the chemical signatures and properties of calcites that form via an amorphous pathway are significantly different. Variable temperature has been shown to influence the amount of magnesium that is incorporated into ACC, but the effect of alkalinity has not been constrained. Here, a flow-through method was developed to produce ACC within a geochemically relevant pH range and with a constant supersaturation, and to determine the effect of carbonate ion concentration on magnesium uptake. The experimental approach uses a high precision syringe pump to prepare ACC under specified and constant chemical conditions. This study used two syringes that contained: 1) 100 ml of MgCl2?6H2O and CaCl2?2H2O such that the Mg/Ca ratio is fixed at 5:1 (modern seawater), and 2) 100 ml of 60mM - 400mM NaHCO3. The initial sodium bicarbonate solutions were buffered to a pH of 9.75 using NaOH, and upon mixing with the 5:1 Mg/Ca solution the resulting pH range was 9.2 - 9.7. All experiments were performed at temperatures between 21.5 and 23 degrees Celsius. Solution and solids were collected on 0.20 micron filter paper with a vacuum pump running continuously. Experiments were typically conducted for an hour and a half and all samples were rinsed with distilled deionized water before

  4. Transformation of amorphous calcium carbonate to rod-like single crystal calcite via "copying" collagen template.

    PubMed

    Xue, Zhonghui; Hu, Binbin; Dai, Shuxi; Du, Zuliang

    2015-10-01

    Collagen Langmuir films were prepared by spreading the solution of collagen over deionized water, CaCl2 solution and Ca(HCO3)2 solution. Resultant collagen Langmuir monolayers were then compressed to a lateral pressure of 10 mN/m and held there for different duration, allowing the crystallization of CaCO3. The effect of crystallization time on the phase composition and microstructure of CaCO3 was investigated. It was found that amorphous calcium carbonate (ACC) was obtained at a crystallization time of 6 h. The amorphous CaCO3 was transformed to rod-like single crystal calcite crystals at an extended crystallization time of 12 h and 24 h, via "copying" the symmetry and dimensionalities of collagen fibers. Resultant calcite crystallites were well oriented along the longitudinal axis of collagen fibers. The ordered surface structure of collagen fibers and electrostatic interactions played key roles in tuning the oriented nucleation and growth of the calcite crystallites. The mineralized collagen possessing both desired mechanical properties of collagen fiber and good biocompatibility of calcium carbonate may be assembled into an ideal biomaterial for bone implants.

  5. Properties of amorphous calcium carbonate and the template action of vaterite spheres.

    PubMed

    Shen, Qiang; Wei, Hao; Zhou, Yong; Huang, Yaping; Yang, Hengrui; Wang, Dujin; Xu, Duanfu

    2006-02-23

    The fast mixing of aqueous solutions of calcium chloride and sodium carbonate could immediately result in amorphous calcium carbonate (ACC). Under vigorous stirring, the formed ACC in the precipitation system will dissolve first and, then, transform within minutes to produce crystalline forms of vaterite and calcite. After that, the solution-mediated mechanism dominates the transformation of the thermodynamically unstable vaterite into the thermodynamically stable calcite. Although ACC is the least stable form of the six anhydrous phases of calcium carbonate (CaCO(3)), it could be, however, produced and stabilized by a variety of organisms. To better understand the formation-transformation mechanism of ACC and vaterite into calcite, ex-situ methods (i.e., scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction spectroscopy) were used to characterize the formation-transformation process of ACC and vaterite in aqueous systems without organic additives, showing that ACC sampled at different conditions has different properties (i.e., lifetime, morphology, and spectrum characterization). It is also very interesting to capture the obviously polycrystalline particles of CaCO(3) during the transformation process from vaterite to calcite, which suggests the formation mechanism for the calcite superstructure with multidimensional morphology.

  6. Two modes of transformation of amorphous calcium carbonate films in air.

    PubMed

    Xu, Xurong; Han, Joong Tark; Kim, Do Hwan; Cho, Kilwon

    2006-02-16

    Large-area amorphous calcium carbonate (ACC) films in air are shown to be transformed into crystalline calcium carbonate (CaCO(3)) films via two modes-dissolution-recrystallization and solid-solid phase transition-depending on the relative humidity of the air and the temperature. Moisture in the air promotes the transformation of ACC into crystalline forms via a dissolution-recrystallization process. Increasing the humidity increases the rate of ACC crystallization and gives rise to films with numerous large pores. As the temperature is increased, the effect of moisture in the air is reduced and solid-solid transition by thermal activation becomes the dominant transformation mechanism. At 100 and 120 degrees C, ACC films are transformed into predominantly (110) oriented crystalline films. Collectively, the results show that calcium carbonate films with different morphologies, crystal phases, and structures can be obtained by controlling the humidity and temperature. This ability to control the transformation of ACC should assist in clarifying the role of ACC in the biomineralization of CaCO(3) and should open new avenues for preparing CaCO(3) films with oriented and fine structure.

  7. Distinct Short-Range Order Is Inherent to Small Amorphous Calcium Carbonate Clusters (<2 nm)

    SciTech Connect

    Sun, Shengtong; Chevrier, Daniel M.; Zhang, Peng; Gebauer, Denis; Cölfen, Helmut

    2016-09-09

    Amorphous intermediate phases are vital precursors in the crystallization of many biogenic minerals. While inherent short-range orders have been found in amorphous calcium carbonates (ACCs) relating to different crystalline forms, it has never been clarified experimentally whether such orders already exist in very small clusters less than 2 nm in size. Here, we studied the stability and structure of 10,12-pentacosadiynoic acid (PCDA) protected ACC clusters with a core size of ca. 1.4 nm consisting of only seven CaCO3 units. Ligand concentration and structure are shown to be key factors in stabilizing the ACC clusters. More importantly, even in such small CaCO3 entities, a proto-calcite short-range order can be identified but with a relatively high degree of disorder that arises from the very small size of the CaCO3 core. Our findings support the notion of a structural link between prenucleation clusters, amorphous intermediates, and final crystalline polymorphs, which appears central to the understanding of polymorph selection.

  8. Coupled dissolution-precipitation as a mechanism for amorphous-to-crystalline calcium carbonate phase transition

    NASA Astrophysics Data System (ADS)

    Rodriguez-Navarro, Carlos Manuel; Kudłacz, Krzysztof; Ruiz-Agudo, Encarnacion

    2014-05-01

    Growing evidence shows that several calcium carbonate biominerals form via an amorphous precursor phase. Such a biomineralization strategy could also be applicable for the biomimetic synthesis of novel functional materials. A crucial step in this process is the transformation of amorphous calcium carbonate (ACC) into calcite. However, controversy exists as to what is the actual mechanism of this transformation: Is it a solid-solid (solid state) or a dissolution/precipitation mechanism? Determining the transition mechanism is critical for example in interpreting the formation of oriented crystalline structures in biominerals (e.g., echinoderm spicles). We studied calcium carbonate precipitation and phase transitions according to the overall reaction Ca(OH)2 + CO2 = CaCO3+ H2O. Mineral phase transformations during this reaction were studied using transmission electron microscopy (TEM). Our TEM analysis showed that two different types of ACC are sequentially formed during this reaction. Type I ACC shows no well-defined short-range order, while Type II ACC shows a short-range order corresponding to calcite. Following e-beam irradiation, Type I ACC particles transform into randomly oriented CaO nanocrystals, while irradiation of Type II ACC leads to the formation of pseudomorphs made up of perfectly oriented aggregates of calcite nanocrystals. Moreover, calcite crystals formed in solution or in air (85 % relative humidity) after Type II ACC are also pseudomorphs made up of porous aggregates of preferentially oriented calcite nanocrystals. Our results give experimental evidence showing that the ACC to calcite transformation under relevant biomineralization conditions (low T and P), also applicable in the biomimetic synthesis of calcite, is a pseudomorphic dissolution-precipitation process. This mechanism involves the tightly interface-coupled dissolution of the precursor amorphous phase (with the crystalline phase protostructure) and concomitant deposition of the

  9. Preparation and characterization of novel biphasic calcium phosphate powders (alpha-TCP/HA) derived from carbonated amorphous calcium phosphates.

    PubMed

    Li, Yanbao; Kong, Fanzhi; Weng, Wenjian

    2009-05-01

    Novel biphasic calcium phosphate (BCP) powders composed of alpha-tricalcium phosphate (alpha-TCP) and hydroxyapatite (HA) were prepared by thermal decomposition of carbonated amorphous calcium phosphates (CACP). At first, the CACP precipitates were synthesized by adding ammonium carbonate in the presence of poly(ethylene glycol) at pH 10 with an initial Ca/P molar ratio of 1.60 at 5 degrees C. The Ca/P molar ratios of the CACP precursors are between 1.50 and 1.67 investigated by ICP. Then BCP (alpha-TCP/HA) powders were obtained after heating the CACP precursors at relatively low temperature (800 degrees C) for 3 h. alpha-TCP/HA powders were characterized by X-ray diffractometry, Fourier transform infrared spectra, transmission electron microscopy/scanning electron microscopy, and sedimentation experiment. The results show that alpha-TCP and HA phases form in one powder, alpha-TCP/HA powders are sphere with the diameter of 300 nm to less than 100 nm varied with their chemical compositions and the ratio of alpha-TCP and HA in the powders can be adjusted by the adding amount of carbonates. The possible formation process of biphasic alpha-TCP/HA powders was proposed.

  10. Biogenic Fish-gut Calcium Carbonate is a Stable Amorphous Phase in the Gilt-head Seabream, Sparus aurata

    PubMed Central

    Foran, Elizabeth; Weiner, Steve; Fine, Maoz

    2013-01-01

    The main source of calcium carbonate (CaCO3) in the ocean comes from the shells of calcifying planktonic organisms, but substantial amounts of CaCO3 are also produced in fish intestines. The precipitation of CaCO3 assists fish in intestinal water absorption and aids in whole body Ca2+ homeostasis. Here we report that the product formed in the intestinal lumen of the gilt-head seabream, Sparus aurata, is an amorphous calcium carbonate (ACC) phase. With FTIR spectroscopy and SEM imaging, our study shows that the fish-derived carbonates from S. aurata are maintained as a stable amorphous phase throughout the intestinal tract. Moreover, intestinal deposits contained up to 54 mol% Mg2+, the highest concentration yet reported in biogenic ACC. Mg is most likely responsible for stabilizing this inherently unstable mineral. The fish carbonates also displayed initial rapid dissolution when exposed to seawater, exhibiting a significant increase in carbonate concentration. PMID:23609008

  11. Biomineralisation by earthworms - an investigation into the stability and distribution of amorphous calcium carbonate.

    PubMed

    Hodson, Mark E; Benning, Liane G; Demarchi, Bea; Penkman, Kirsty E H; Rodriguez-Blanco, Juan D; Schofield, Paul F; Versteegh, Emma A A

    Many biominerals form from amorphous calcium carbonate (ACC), but this phase is highly unstable when synthesised in its pure form inorganically. Several species of earthworm secrete calcium carbonate granules which contain highly stable ACC. We analysed the milky fluid from which granules form and solid granules for amino acid (by liquid chromatography) and functional group (by Fourier transform infrared (FTIR) spectroscopy) compositions. Granule elemental composition was determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and electron microprobe analysis (EMPA). Mass of ACC present in solid granules was quantified using FTIR and compared to granule elemental and amino acid compositions. Bulk analysis of granules was of powdered bulk material. Spatially resolved analysis was of thin sections of granules using synchrotron-based μ-FTIR and EMPA electron microprobe analysis. The milky fluid from which granules form is amino acid-rich (≤ 136 ± 3 nmol mg(-1) (n = 3; ± std dev) per individual amino acid); the CaCO3 phase present is ACC. Even four years after production, granules contain ACC. No correlation exists between mass of ACC present and granule elemental composition. Granule amino acid concentrations correlate well with ACC content (r ≥ 0.7, p ≤ 0.05) consistent with a role for amino acids (or the proteins they make up) in ACC stabilisation. Intra-granule variation in ACC (RSD = 16%) and amino acid concentration (RSD = 22-35%) was high for granules produced by the same earthworm. Maps of ACC distribution produced using synchrotron-based μ-FTIR mapping of granule thin sections and the relative intensity of the ν2: ν4 peak ratio, cluster analysis and component regression using ACC and calcite standards showed similar spatial distributions of likely ACC-rich and calcite-rich areas. We could not identify organic peaks in the μ-FTIR spectra and thus could not determine whether ACC-rich domains also had relatively high amino

  12. Transformation and Crystallization Energetics of Synthetic and Biogenic Amorphous Calcium Carbonate

    SciTech Connect

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

    2010-01-01

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

  13. Formation of amorphous calcium carbonate in caves and its implications for speleothem research

    PubMed Central

    Demény, Attila; Németh, Péter; Czuppon, György; Leél-Őssy, Szabolcs; Szabó, Máté; Judik, Katalin; Németh, Tibor; Stieber, József

    2016-01-01

    Speleothem deposits are among the most valuable continental formations in paleoclimate research, as they can be dated using absolute dating methods, and they also provide valuable climate proxies. However, alteration processes such as post-depositional mineralogical transformations can significantly influence the paleoclimatic application of their geochemical data. An innovative sampling and measurement protocol combined with scanning and transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy is presented, demonstrating that carbonate precipitating from drip water in caves at ~10 °C contains amorphous calcium carbonate (ACC) that later transforms to nanocrystalline calcite. Stable oxygen isotope fractionations among calcite, ACC and water were also determined, proving that ACC is 18O-depleted (by >2.4 ± 0.8‰) relative to calcite. This, in turn, has serious consequences for speleothem-based fluid inclusion research as closed system transformation of ACC to calcite may induce a negative oxygen isotope shift in fluid inclusion water, resulting in deterioration of the original compositions. ACC formation increases the speleothems’ sensitivity to alteration as its interaction with external solutions may result in the partial loss of original proxy signals. Mineralogical analysis of freshly precipitating carbonate at the studied speleothem site is suggested in order to determine the potential influence of ACC formation. PMID:28004767

  14. Formation of amorphous calcium carbonate in caves and its implications for speleothem research

    NASA Astrophysics Data System (ADS)

    Demény, Attila; Németh, Péter; Czuppon, György; Leél-Őssy, Szabolcs; Szabó, Máté; Judik, Katalin; Németh, Tibor; Stieber, József

    2016-12-01

    Speleothem deposits are among the most valuable continental formations in paleoclimate research, as they can be dated using absolute dating methods, and they also provide valuable climate proxies. However, alteration processes such as post-depositional mineralogical transformations can significantly influence the paleoclimatic application of their geochemical data. An innovative sampling and measurement protocol combined with scanning and transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy is presented, demonstrating that carbonate precipitating from drip water in caves at ~10 °C contains amorphous calcium carbonate (ACC) that later transforms to nanocrystalline calcite. Stable oxygen isotope fractionations among calcite, ACC and water were also determined, proving that ACC is 18O-depleted (by >2.4 ± 0.8‰) relative to calcite. This, in turn, has serious consequences for speleothem-based fluid inclusion research as closed system transformation of ACC to calcite may induce a negative oxygen isotope shift in fluid inclusion water, resulting in deterioration of the original compositions. ACC formation increases the speleothems’ sensitivity to alteration as its interaction with external solutions may result in the partial loss of original proxy signals. Mineralogical analysis of freshly precipitating carbonate at the studied speleothem site is suggested in order to determine the potential influence of ACC formation.

  15. A mixed flow reactor method to synthesize amorphous calcium carbonate under controlled chemical conditions.

    PubMed

    Blue, Christina R; Rimstidt, J Donald; Dove, Patricia M

    2013-01-01

    This study describes a new procedure to synthesize amorphous calcium carbonate (ACC) from well-characterized solutions that maintain a constant supersaturation. The method uses a mixed flow reactor to prepare ACC in significant quantities with consistent compositions. The experimental design utilizes a high-precision solution pump that enables the reactant solution to continuously flow through the reactor under constant mixing and allows the precipitation of ACC to reach steady state. As a proof of concept, we produced ACC with controlled Mg contents by regulating the Mg/Ca ratio of the input solution and the carbonate concentration and pH. Our findings show that the Mg/Ca ratio of the reactant solution is the primary control for the Mg content in ACC, as shown in previous studies, but ACC composition is further regulated by the carbonate concentration and pH of the reactant solution. The method offers promise for quantitative studies of ACC composition and properties and for investigating the role of this phase as a reactive precursor to biogenic minerals.

  16. Stabilization and transformation of amorphous calcium carbonate: structural and kinetic studies

    NASA Astrophysics Data System (ADS)

    Schmidt, Millicent Promise

    Amorphous calcium carbonate (ACC) is a common transient precursor in the formation of more stable crystalline calcium carbonate minerals, most notably calcite, vaterite, and aragonite. Formation of ACC from calcium carbonate rich aqueous solution rather than direct crystallization of crystalline polymorphs by organisms provides several advantages: control of morphology, grain size, orientation, hardness, and other bulk properties as well as reduction of energy costs during growth cycles. Despite decades of study, stabilization and transformation mechanisms of synthetic and biogenic ACC remain unclear. In particular, the roles of H2O and inorganic phosphate in ACC structure and transformation, and the variables affecting transformation kinetics and polymorph selection are understudied. In this research, we addressed structure and kinetic behavior of ACC through four complementary investigations: two studies focus on synthetic ACC stabilization and two focus on synthetic and biogenic ACC transformation behavior in solution at ambient temperatures. We explored ACC stabilization via compositional and thermal analyses, X-ray scattering, X-ray absorption spectroscopy, and nuclear magnetic resonance spectroscopy. Transformation experiments used a novel method of in situ structural analysis that provided quantitative kinetic and structural data and allowed us to visualize the ACC transformation pathway. Results revealed the complexity of H2O structure in ACC samples synthesized from three methods, indicating that the distinct hydrous populations produced define ACC behavior. Transformation kinetics and polymorph selection were strongly affected by the hydration state and type of synthetic ACC reacted. In situ transformation experiments also showed differences in kinetic behavior due to reaction medium. The structural role of hydrous components was again evident in in situ transformation experiments for ACC from a biogenic lobster gastrolith (LG) reacted with water. LG

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

    PubMed Central

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

    2010-01-01

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

  18. A carbonate controlled-addition method for amorphous calcium carbonate spheres stabilized by poly(acrylic acid)s.

    PubMed

    Huang, Shu-Chen; Naka, Kensuke; Chujo, Yoshiki

    2007-11-20

    Stable amorphous calcium carbonate (ACC) composite particle with a size-controlled monodispersed sphere was obtained by a new simple carbonate controlled-addition method by using poly(acrylic acid) (PAA) (Mw = 5000), in which an aqueous ammonium carbonate solution was added into an aqueous solution of PAA and CaCl2 with a different time period. The obtained ACC composite products consist of about 50 wt % of ACC, 30 wt % of PAA, and H2O. Average particle sizes of the ACC spheres increased from (1.8 +/- 0.4) x 102 to (5.5 +/- 1.2) x 102 nm with an increase of the complexation time of the PAA-CaCl2 solution from 3 min to 24 h, respectively. The ACC formed from the complexation time for 3 min was stable for 10 days with gentle stirring as well as 3 months under a quiescent condition in the aqueous solution. Moreover, the ACC was also stable at 400 degrees C. Stability of the amorphous phase decreased with an increase of the complexation time of the PAA-CaCl2 solution. No ACC was obtained when the lower molar mass PAAs (Mw = 1200 and 2100) were used. In the higher molar mass case (Mw = 25 000), a mixture of the amorphous phase and vaterite and calcite crystalline product was produced. The present results demonstrate that the interaction and the reaction kinetics of the PAA-Ca2+-H2O complex play an important role in the mineralization of CaCO3.

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

    PubMed

    Rodriguez-Blanco, Juan Diego; Shaw, Samuel; Benning, Liane G

    2011-01-01

    The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range of environmentally relevant temperatures (7.5-25 °C) using synchrotron-based in situ time-resolved Energy Dispersive X-ray Diffraction (ED-XRD) in conjunction with high-resolution electron microscopy, ex situ X-ray diffraction and infrared spectroscopy. The crystallization process occurs in two stages; firstly, the particles of ACC rapidly dehydrate and crystallize to form individual particles of vaterite; secondly, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate controlled by the surface area of calcite. The second stage of the reaction is approximately 10 times slower than the first. Activation energies of calcite nucleation and crystallization are 73±10 and 66±2 kJ mol(-1), respectively. A model to calculate the degree of calcite crystallization from ACC at environmentally relevant temperatures (7.5-40 °C) is also presented.

  20. Impact of sodium polyacrylate on the amorphous calcium carbonate formation from supersaturated solution.

    PubMed

    Liu, J; Pancera, S; Boyko, V; Gummel, J; Nayuk, R; Huber, K

    2012-02-21

    A detailed in situ scattering study has been carried out on the formation of amorphous calcium carbonate (ACC) particles modulated by the presence of small amounts of sodium polyacrylate chains. The work is aiming at an insight into the modulation of ACC formation by means of two polyacrylate samples differing in their molecular weight by a factor of 50. The ACC formation process was initiated by an in situ generation of CO(3)(2-) ions via hydrolysis of 10 mM dimethylcarbonate in the presence of 10 mM CaCl(2). Analysis of the formation process by means of time-resolved small-angle X-ray and light scattering in the absence of any additives provided evidence for a monomer addition mechanism for the growth of ACC particles. ACC formation under these conditions sets in after a lag-period of some 350 s. In the presence of sodium polyacrylate chains, calcium polyacrylate aggregates are formed during the lag-period, succeeded by a modulated ACC growth in a second step. The presence of anionic polyacrylate chains changed the shape of the growing particles toward loose and less homogeneous entities. In the case of low amounts (1.5-7.5 mg/L) of the long chain additive with 97 kDa, the size of the aggregates is comparable to the size of the successively formed hybrid particles. No variation of the lag-period has been observed in this case. Use of the short chain additive with 2 kDa enabled increase of the additive concentration up to 100 mg/L and resulted in a significant increase of the lag-period. This fact, together with the finding that the resulting hybrid particles remained stable in the latter case, identified short chain sodium polyacrylates as more efficient modulators than long chain polyacrylates.

  1. Calcium Carbonate

    MedlinePlus

    Calcium carbonate is a dietary supplement used when the amount of calcium taken in the diet is not ... for healthy bones, muscles, nervous system, and heart. Calcium carbonate also is used as an antacid to relieve ...

  2. Carboxylated molecules regulate magnesium content of amorphous calcium carbonates during calcification

    PubMed Central

    Wang, Dongbo; Wallace, Adam F.; De Yoreo, James J.; Dove, Patricia M.

    2009-01-01

    With the realization that many calcified skeletons form by processes involving a precursor phase of amorphous calcium carbonate (ACC), a new paradigm for mineralization is emerging. There is evidence the Mg content in biogenic ACC is regulated by carboxylated (acidic) proteins and other macromolecules, but the physical basis for such a process is unknown. We test the hypothesis that ACC compositions express a systematic relationship to the chemistry of carboxyl-rich biomolecules. A series of inorganic control experiments were conducted to establish the dependence of Mg/Ca ratios in ACC on solution composition. We then determined the influence of a suite of simple carboxylated organic acids on Mg content. Molecules with a strong affinity for binding Ca compared with Mg promote the formation of Mg-enriched ACC that is compositionally equivalent to high-magnesium calcites and dolomite. Measurements show Mg/Ca ratios are controlled by a predictable dependence upon the binding properties of the organic molecules. The trend appears rooted in the conformation and electrostatic potential topology of each molecule, but dynamic factors also may be involved. The dependence suggests a physical basis for reports that specific sequences of calcifying proteins are critical to modulating mineralization. Insights from this study may provide a plausible explanation for why some biogenic carbonates and carbonaceous cements often contain higher Mg signatures than those that are possible by classical crystal growth processes. The findings reiterate the controls of microenvironment on mineralization and suggest an origin of compositional offsets, or vital effects, long recognized by the paleoclimate community. PMID:19955417

  3. Spatial distribution of calcite and amorphous calcium carbonate in the cuticle of the terrestrial crustaceans Porcellio scaber and Armadillidium vulgare.

    PubMed

    Hild, Sabine; Marti, Othmar; Ziegler, Andreas

    2008-07-01

    The crustacean cuticle is an interesting model to study the properties of mineralized bio-composites. The cuticle consists of an organic matrix composed of chitin-protein fibres associated with various amounts of crystalline and amorphous calcium carbonate. It is thought that in isopods the relative amounts of these mineral polymorphs depend on its function and the habitat of the animal. In addition to the composition, the distribution of the various components should affect the properties of the cuticle. However, the spatial distribution of calcium carbonate polymorphs within the crustacean cuticle is unknown. Therefore, we analyzed the mineralized cuticles of the terrestrial isopods Armadillidium vulgare and Porcellio scaber using scanning electron-microscopy, electron probe microanalysis and confocal mu-Raman spectroscopic imaging. We show for the first time that the mineral phases are arranged in distinct layers. Calcite is restricted to the outer layer of the cuticle that corresponds to the exocuticle. Amorphous calcium carbonate is located within the endocuticle that lies below the exocuticle. Within both layers mineral is arranged in rows of granules with diameters of about 20 nm. The results suggest functional implications of mineral distribution that accord to the moulting and escape behaviour of the animals.

  4. Biogenic fish-gut calcium carbonate is a stable amorphous phase in the gilt-head seabream, Sparus aurata.

    PubMed

    Foran, Elizabeth; Weiner, Steve; Fine, Maoz

    2013-01-01

    The main source of calcium carbonate (CaCO₃) in the ocean comes from the shells of calcifying planktonic organisms, but substantial amounts of CaCO₃ are also produced in fish intestines. The precipitation of CaCO₃ assists fish in intestinal water absorption and aids in whole body Ca²⁺ homeostasis. Here we report that the product formed in the intestinal lumen of the gilt-head seabream, Sparus aurata, is an amorphous calcium carbonate (ACC) phase. With FTIR spectroscopy and SEM imaging, our study shows that the fish-derived carbonates from S. aurata are maintained as a stable amorphous phase throughout the intestinal tract. Moreover, intestinal deposits contained up to 54 mol% Mg²⁺, the highest concentration yet reported in biogenic ACC. Mg is most likely responsible for stabilizing this inherently unstable mineral. The fish carbonates also displayed initial rapid dissolution when exposed to seawater, exhibiting a significant increase in carbonate concentration.

  5. Calcium Carbonate.

    PubMed

    Al Omari, M M H; Rashid, I S; Qinna, N A; Jaber, A M; Badwan, A A

    2016-01-01

    Calcium carbonate is a chemical compound with the formula CaCO3 formed by three main elements: carbon, oxygen, and calcium. It is a common substance found in rocks in all parts of the world (most notably as limestone), and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. CaCO3 exists in different polymorphs, each with specific stability that depends on a diversity of variables. © 2016 Elsevier Inc. All rights reserved.

  6. Structure and Transformation of Amorphous Calcium Carbonate: A Solid-State 43Ca NMR and Computational Molecular Dynamics Investigation

    SciTech Connect

    Singer, Jared W.; Yazaydin, A. O.; Kirkpatrick, Robert J.; Bowers, Geoffrey M.

    2012-05-22

    Amorphous calcium carbonate (ACC) is a metastable precursor to crystalline CaCO{sub 3} phases that precipitates by aggregation of ion pairs and prenucleation clusters. We use {sup 43}Ca solid-state NMR spectroscopy to probe the local structure and transformation of ACC synthesized from seawater-like solutions with and without Mg{sup 2+} and computational molecular dynamics (MD) simulations to provide more detailed molecular-scale understanding of the ACC structure. The {sup 43}Ca NMR spectra of ACC collected immediately after synthesis consist of broad, featureless resonances with Gaussian line shapes (FWHH = 27.6 {+-} 1 ppm) that do not depend on Mg{sup 2+} or H{sub 2}O content. A correlation between {sup 43}Ca isotropic chemical shifts and mean Ca-O bond distances for crystalline hydrous and anhydrous calcium carbonate phases indicates indistinguishable maximum mean Ca-O bond lengths of {approx}2.45 {angstrom} for all our samples. This value is near the upper end of the published Ca-O bond distance range for biogenic and synthetic ACCs obtained by Ca-X-ray absorption spectroscopy. It is slightly smaller than the values from the structural model of Mgfree ACC by Goodwin et al. obtained from reverse Monte Carlo (RMC) modeling of X-ray scattering data and our own computational molecular dynamics (MD) simulation based on this model. An MD simulation starting with the atomic positions of the Goodwin et al. RMC model using the force field of Raiteri and Gale shows significant structural reorganization during the simulation and that the interconnected carbonate/water-rich channels in the Goodwin et al. model shrink in size over the 2 ns simulation time. The distribution of polyhedrally averaged Ca-O bond distances from the MD simulation is in good agreement with the {sup 43}Ca NMR peak shape, suggesting that local structural disorder dominates the experimental line width of ACC.

  7. Control of Polymorph Selection in Amorphous Calcium Carbonate Crystallization by Poly(Aspartic Acid): Two Different Mechanisms.

    PubMed

    Zou, Zhaoyong; Bertinetti, Luca; Politi, Yael; Fratzl, Peter; Habraken, Wouter J E M

    2017-06-01

    Poly(aspartic acid) (pAsp) is known to stabilize amorphous calcium carbonate (ACC) and affect its crystallization pathways. However, little is known about the mechanisms behind these phenomena. Here it is shown that ACC is stabilized by pAsp molecules in the solution rather than by the amount of pAsp incorporated into the ACC bulk, and that the effect of pAsp on the polymorph selection is entirely different at low and high concentration of pAsp. At low concentrations, pAsp is more effective in inhibiting the nucleation and growth of vaterite than calcite. At high concentrations, when calcite formation is prevented, the crystallization of vaterite proceeds via a pseudomorphic transformation of ACC nanospheres, where vaterite nucleates on the surface of ACC nanospheres and grows by a local transformation of the bulk ACC phase. These results shed some light on the function of pAsp during an ACC-mediated biomineralization process and provide an explanation for the presence of metastable vaterite at conditions where calcite is thermodynamically favored. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Chemical and physical controls on the transformation of amorphous calcium carbonate into crystalline CaCO3 polymorphs

    NASA Astrophysics Data System (ADS)

    Blue, C. R.; Giuffre, A.; Mergelsberg, S.; Han, N.; De Yoreo, J. J.; Dove, P. M.

    2017-01-01

    Calcite and other crystalline polymorphs of CaCO3 can form by pathways involving amorphous calcium carbonate (ACC). Apparent inconsistencies in the literature indicate the relationships between ACC composition, local conditions, and the subsequent crystalline polymorphs are not yet established. This experimental study quantifies the control of solution composition on the transformation of ACC into crystalline polymorphs in the presence of magnesium. Using a mixed flow reactor to control solution chemistry, ACC was synthesized with variable Mg contents by tuning input pH, Mg/Ca, and total carbonate concentration. ACC products were allowed to transform within the output suspension under stirred or quiescent conditions while characterizing the evolving solutions and solids. As the ACC transforms into a crystalline phase, the solutions record a polymorph-specific evolution of pH and Mg/Ca. The data provide a quantitative framework for predicting the initial polymorph that forms from ACC based upon the solution aMg2+/aCa2+ and aCO32-/aCa2+ and stirring versus quiescent conditions. This model reconciles discrepancies among previous studies that report on the nature of the polymorphs produced from ACC and supports the previous claim that monohydrocalcite may be an important, but overlooked, transient phase on the way to forming some aragonite and calcite deposits. By this construct, organic additives and extreme pH are not required to tune the composition and nature of the polymorph that forms. Our measurements show that the Mg content of ACC is recorded in the resulting calcite with a ≈1:1 dependence. By correlating composition of these calcite products with the Mgtot/Catot of the initial solutions, we find a ≈3:1 dependence that is approximately linear and general to whether calcite is formed via an ACC pathway or by the classical step-propagation process. Comparisons to calcite grown in synthetic seawater show a ≈1:1 dependence. The relationships suggest that the

  9. Hydrogels from Amorphous Calcium Carbonate and Polyacrylic Acid: Bio-Inspired Materials for "Mineral Plastics".

    PubMed

    Sun, Shengtong; Mao, Li-Bo; Lei, Zhouyue; Yu, Shu-Hong; Cölfen, Helmut

    2016-09-19

    Given increasing environmental issues due to the large usage of non-biodegradable plastics based on petroleum, new plastic materials, which are economic, environmentally friendly, and recyclable are in high demand. One feasible strategy is the bio-inspired synthesis of mineral-based hybrid materials. Herein we report a facile route for an amorphous CaCO3 (ACC)-based hydrogel consisting of very small ACC nanoparticles physically cross-linked by poly(acrylic acid). The hydrogel is shapeable, stretchable, and self-healable. Upon drying, the hydrogel forms free-standing, rigid, and transparent objects with remarkable mechanical performance. By swelling in water, the material can completely recover the initial hydrogel state. As a matrix, thermochromism can also be easily introduced. The present hybrid hydrogel may represent a new class of plastic materials, the "mineral plastics". © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Amorphous calcium (ortho)phosphates.

    PubMed

    Dorozhkin, Sergey V

    2010-12-01

    Amorphous calcium phosphates (ACPs) represent a unique class of biomedically relevant calcium orthophosphate salts, having variable chemical but essentially identical glass-like physical properties, in which there is neither translational nor orientational long-range ordering of the atomic positions. Normally, ACPs are the first solid phases, precipitated after a rapid mixing of aqueous solutions containing ions of Ca(2+) and PO₄³⁻; however, other production techniques are known. Interestingly, ACPs prepared by wet-chemical techniques were found to have a relatively constant chemical composition over a relatively wide range of preparation conditions, which suggests the presence of a well-defined local structural unit, presumably with the structure of Ca₉(PO₄)₆ - so-called Posner cluster. However, the presence of similar clusters in ACPs produced by other techniques remains uncertain. All ACPs are thermodynamically unstable compounds and, unless stored in dry conditions or doped by stabilizers, spontaneously tend to transform to crystalline calcium orthophosphates, mainly to calcium apatites. This solution instability of ACPs and their easy transformation to crystalline phases are of a great biological relevance. Specifically, the initiating role ACPs play in matrix vesicle biomineralization raises the importance of ACPs from a mere laboratory curiosity to that of a key intermediate in skeletal calcification. In addition, due to significant chemical and structural similarities with calcified mammalian tissues, as well as excellent biocompatibility and bioresorbability, all types of ACPs are very promising candidates for the manufacture of artificial bone grafts. This review summarizes the current knowledge on the occurrence, preparation, composition, structure, major properties and biomedical applications of ACPs. To assist readers in looking for the specific details on ACPs, a great number of references have been collected and systematized. Copyright

  11. Phosphate-water interplay tunes amorphous calcium carbonate metastability: spontaneous phase separation and crystallization vs stabilization viewed by solid state NMR.

    PubMed

    Kababya, Shifi; Gal, Assaf; Kahil, Keren; Weiner, Steve; Addadi, Lia; Schmidt, Asher

    2015-01-21

    Organisms tune the metastability of amorphous calcium carbonates (ACC), often by incorporation of additives such as phosphate ions and water molecules, to serve diverse functions, such as modulating the availability of calcium reserves or constructing complex skeletal scaffolds. Although the effect of additive distribution on ACC was noted for several biogenic and synthetic systems, the molecular mechanisms by which additives govern ACC stability are not well understood. By precipitating ACC in the presence of different PO4(3-) concentrations and regulating the initial water content, we identify conditions yielding either kinetically locked or spontaneously transforming coprecipitates. Solid state NMR, supported by FTIR, XRD, and electron microscopy, define the interactions of phosphate and water within the initial amorphous matrix, showing that initially the coprecipitates are homogeneous molecular dispersions of structural water and phosphate in ACC, and a small fraction of P-rich phases. Monitoring the transformations of the homogeneous phase shows that PO4(3-) and waters are extracted first, and they phase separate, leading to solid-solid transformation of ACC to calcite; small part of ACC forms vaterite that subsequently converts to calcite. The simultaneous water-PO4(3-) extraction is the key for the subsequent water-mediated accumulation and crystallization of hydroxyapatite (HAp) and carbonated hydroxyapatite. The thermodynamic driving force for the transformations is calcite crystallization, yet it is gated by specific combinations of water-phosphate levels in the initial amorphous coprecipitates. The molecular details of the spontaneously transforming ACC and of the stabilized ACC modulated by phosphate and water at ambient conditions, provide insight into biogenic and biomimetic pathways.

  12. Time-resolved evolution of short- and long-range order during the transformation of amorphous calcium carbonate to calcite in the sea urchin embryo

    NASA Astrophysics Data System (ADS)

    Tester, Chantel; Wu, Ching-Hsuan; Krejci, Minna; Mueller, Laura; Park, Alex; Lai, Barry; Chen, Si; Sun, Chengjun; Balasubramanian, Mahaling; Joester, Derk

    2013-03-01

    The biological use of amorphous mineral precursors is thought to be directly related to the ability to create single crystalline, yet composite materials with complex shapes that are beyond our synthetic capabilities. Despite considerable effort in recent years, it has not been possible to capture the mechanistic detail of the disorder-to-order transformation that is a key element of this process. This is largely due to lack of sensitivity, lack of temporal and spatial resolution, and artifacts of sample preparation. To overcome these challenges we use strontium as a probe for X-ray absorption spectroscopy (XAS). In pulse-chase experiments, sea urchin embryos incorporate Sr2 + from Sr-enriched seawater into small volumes of the developing endoskeleton. During the chase, the transformation of the newly deposited amorphous mineral is characterized by Sr-K α XAS of cryo-frozen whole embryos. We find that the initial mineral has short-range order resembling hydrated amorphous calcium carbonate. Within 3h, the short-range order of calcite is adopted, with long-range order developing over the next 20h. Pulse-chase experiments combined with heavy element labeling can be used in numerous mineralizing systems to study phase transformations during biological crystal growth.

  13. Amorphous carbon for photovoltaics

    NASA Astrophysics Data System (ADS)

    Risplendi, Francesca; Grossman, Jeffrey C.

    2015-03-01

    All-carbon solar cells have attracted attention as candidates for innovative photovoltaic devices. Carbon-based materials such as graphene, carbon nanotubes (CNT) and amorphous carbon (aC) have the potential to present physical properties comparable to those of silicon-based materials with advantages such as low cost and higher thermal stability.In particular a-C structures are promising systems in which both sp2 and sp3 hybridization coordination are present in different proportions depending on the specific density, providing the possibility of tuning their optoelectronic properties and achieving comparable sunlight absorption to aSi. In this work we employ density functional theory to design suitable device architectures, such as bulk heterojunctions (BHJ) or pn junctions, consisting of a-C as the active layer material.Regarding BHJ, we study interfaces between aC and C nanostructures (such as CNT and fullerene) to relate their optoelectronic properties to the stoichiometry of aC. We demonstrate that the energy alignment between the a-C mobility edges and the occupied and unoccupied states of the CNT or C60 can be widely tuned by varying the aC density to obtain a type II interface.To employ aC in pn junctions we analyze the p- and n-type doping of a-C focusingon an evaluation of the Fermi level and work function dependence on doping.Our results highlight promising features of aC as the active layer material of thin-film solar cells.

  14. Influence of Magnesium Content on the Local Structure of Amorphous Calcium Carbonate (ACC): Real Time Determination by In Situ PDF Analysis

    NASA Astrophysics Data System (ADS)

    Mergelsberg, S. T.; Ulrich, R. N.; Michel, F. M.; Dove, P. M.

    2016-12-01

    Calcium carbonate minerals are an essential component in the exoskeletons of crustaceans and mollusks. The onset of exoskeleton mineralization includes the precipitation of amorphous calcium carbonate (ACC) as a reactive intermediate that later transforms to produce diverse structures. Despite the importance of ACC as a critical phase during skeleton formation, the chemical and physical properties are not well characterized at conditions that approximate biological environments. Of particular interest are the solubility of ACC, the short-range structure at the time of formation, and the evolution of ACC structure to final products. Recent advances showing the widespread occurrence of multistep pathways to mineralization in biological and geological settings (De Yoreo et al., 2015) underline the importance of understanding amorphous intermediates. Using quantitative laboratory techniques developed by our research group (Blue et al., 2013; Blue and Dove, 2015; Blue et al., in press), this experimental study quantifies the solubility of ACC in parallel with the physical characterization of the corresponding structure. We measured ACC solubility at specific time points during the precipitation and during its subsequent evolution under the mild pH conditions that approximate biological and environmental conditions. In parallel experiments, structural data were collected from in situ pair distribution function (PDF) analyses were conducted to follow the evolution of individual samples from initial precipitation to final product. The measurements are leading to a quantitative solubility function for ACC with variable Mg contents and an x-ray based understanding of ACC structure in the same particles. We are also finding temporal changes in the short-range order of ACC after precipitation and this order is dependent upon Mg content. Moreover, the data show Mg distribution through the ACC particles is dependent upon total alkalinity. Insights from this study hold promise

  15. Biomimetic mineralization of CaCO3 on a phospholipid monolayer: from an amorphous calcium carbonate precursor to calcite via vaterite.

    PubMed

    Xiao, Junwu; Wang, Zhining; Tang, Yecang; Yang, Shihe

    2010-04-06

    A phospholipid monolayer, approximately half the bilayer structure of a biological membrane, can be regarded as an ideal model for investigating biomineralization on biological membranes. In this work on the biomimetic mineralization of CaCO(3) under a phospholipid monolayer, we show the initial heterogeneous nucleation of amorphous calcium carbonate precursor (ACC) nanoparticles at the air-water interface, their subsequent transformation into the metastable vaterite phase instead of the most thermodynamically stable calcite phase, and the ultimate phase transformation to calcite. Furthermore, the spontaneity of the transformation from vaterite to calcite was found to be closely related to the surface tension; high surface pressure could inhibit the process, highlighting the determinant of surface energy. To understand better the mechanisms for ACC formation and the transformation from ACC to vaterite and to calcite, in situ Brewster angle microscopy (BAM), ex situ scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction analysis were employed. This work has clarified the crystallization process of calcium carbonate under phospholipid monolayers and therefore may further our understanding of the biomineralization processes induced by cellular membranes.

  16. Investigating the Basis of Biogenic Calcium Carbonate Formation from an Amorphous Precursor: Nature of the Transformation to Calcite on Hydroxyl Functionalized Surfaces

    NASA Astrophysics Data System (ADS)

    Wang, D.; Lee, J. R.; Talley, C. E.; Murphy, K. E.; Han, T. Y.; Deyoreo, J. J.; Dove, P. M.

    2006-12-01

    Calcium carbonate biominerals are particularly significant because of their direct role in regulating the global carbon cycle, as well as their ubiquitous occurrence across earth environments. Biogenic carbonates are further distinguished by their broad phlyogenetic distribution; hence it has been suggested that unrelated eukaryotes must have used similar biochemical strategies to control mineralization. Recent studies have shown that an amorphous calcium carbonate (ACC) phase potentially plays a key role in the initial formation of carbonate minerals and in "shaping" them into complex morphologies widely seen in biominerals. Echinoderms, mollusks, and possibly many other organisms use ACC as a precursor phase that is first nucleated in cellularly controlled environments such as vesicles and subsequently transforms into a fully crystalline material. Recent studies on sea urchin embryos have shown that during transformation ACC develops short range that resembles calcite before fully crystallizing and serve as inspiration for our studies in synthetic systems. Self-assembled monolayers (SAM) on gold and silver have been used as simple model systems that approximate biological surfaces. Many studies have shown that thiol monolayers with hydroxyl termination stabilize a transitory ACC film that with prolonged exposure to aqueous solution transforms into calcite nucleated on {104} faces. Using Near Edge X-ray Absorption Fine Structure (NEXAFS) we studied SAM/mineral interactions with well ordered mercaptophenol monolayers showed that when these films are first exposed to calcium carbonate solutions, they become disordered and remain so after subsequent deposition of an ACC over-layer. Yet calcite nucleates and grows from the surface bound ACC with predominantly {104} orientation, which suggests a dynamic structural relationship between the SAMs and the mineral phase. While the monolayer/mineral phase interaction has been characterized, the mechanism for nucleating

  17. Allotropic composition of amorphous carbon

    SciTech Connect

    Yastrebov, S. G. Ivanov-Omskii, V. I.

    2007-08-15

    Using the concept of an inhomogeneous broadening of spectral lines of the basic oscillators responsible for forming the spectrum, the experimental dependences of the dispersion of the imaginary part of permittivity are analyzed for amorphous carbon. It turned out that four types of oscillators contribute to this dependence. The first three types represent the electron transitions from the energy-spectrum ground state for {pi} and {sigma} electrons of amorphous carbon to an excited state. The fourth type is related to the absorption of electromagnetic radiation by free charge carriers. The absolute values of squared plasma frequencies of oscillators are estimated, and, using them, the relative fraction of sp{sup 2}-bonded atoms forming the amorphous-carbon skeleton is calculated. This estimate agrees closely with the theoretical predictions for amorphous carbon of the same density as the material under study. The dependence of the relative fraction of sp{sup 2}-bonded atoms contained in amorphous hydrogenised carbon on annealing temperature is determined. The developed method is also applied to the analysis of the normalized curve for the light extinction in the interstellar medium. The contribution to the extinction of two varieties of interstellar matter is detected.

  18. TRANSIENT AMORPHOUS CALCIUM PHOSPHATE IN FORMING ENAMEL

    PubMed Central

    Beniash, Elia; Metzler, Rebecca A.; Lam, Raymond S.K.; Gilbert, P.U.P.A.

    2009-01-01

    Enamel, the hardest tissue in the body, begins as a three-dimensional network of nanometer size mineral particles, suspended in a protein gel. This mineral network serves as a template for mature enamel formation. To further understand the mechanisms of enamel formation we characterized the forming enamel mineral at an early secretory stage using x-ray absorption near-edge structure (XANES) spectromicroscopy, transmission electron microscopy (TEM), FTIR microspectroscopy and polarized light microscopy. We show that the newly formed enamel mineral is amorphous calcium phosphate (ACP), which eventually transforms into apatitic crystals. Interestingly, the size, shape and spatial organization of these amorphous mineral particles and older crystals are essentially the same, indicating that the mineral morphology and organization in enamel is determined prior to its crystallization. Mineralization via transient amorphous phases has been previously reported in chiton teeth, mollusk shells, echinoderm spicules and spines, and recent reports strongly suggest the presence transient amorphous mineral in forming vertebrate bones. The present finding of transient ACP in murine tooth enamel suggests that this strategy might be universal. PMID:19217943

  19. A comparison of amorphous calcium carbonate crystallization in aqueous solutions of MgCl2 and MgSO4: implications for paleo-ocean chemistry

    NASA Astrophysics Data System (ADS)

    Han, Mei; Zhao, Yanyang; Zhao, Hui; Han, Zuozhen; Yan, Huaxiao; Sun, Bin; Meng, Ruirui; Zhuang, Dingxiang; Li, Dan; Liu, Binwei

    2017-07-01

    Based on the terminology of "aragonite seas" and "calcite seas", whether different Mg sources could affect the mineralogy of carbonate sediments at the same Mg/Ca ratio was explored, which was expected to provide a qualitative assessment of the chemistry of the paleo-ocean. In this work, amorphous calcium carbonate (ACC) was prepared by direct precipitation in anhydrous ethanol and used as a precursor to study crystallization processes in MgSO4 and MgCl2 solutions having different concentrations at 60 °C (reaction times 240 and 2880 min). Based on the morphology of the aragonite crystals, as well as mineral saturation indices and kinetic analysis of geochemical processes, it was found that these crystals formed with a spherulitic texture in 4 steps. First, ACC crystallized into columnar Mg calcite by nearly oriented attachment. Second, the Mg calcite changed from columnar shapes into smooth dumbbell forms. Third, the Mg calcite transformed into rough dumbbell or cauliflower-shaped aragonite forms by local dissolution and precipitation. Finally, the aragonite transformed further into spherulitic radial and irregular aggregate forms. The increase in Ca2+ in the MgSO4 solutions compared with the MgCl2 solutions indicates the fast dissolution and slow precipitation of ACC in the former solutions. The phase transition was more complete in the 0.005 M MgCl2 solution, whereas Mg calcite crystallized from the 0.005 M MgSO4 solution, indicating that Mg calcite could be formed more easily in an MgSO4 solution. Based on these findings, aragonite and Mg calcite relative to ACC could be used to provide a qualitative assessment of the chemistry of the paleo-ocean. Therefore, calcite seas relative to high-Mg calcite could reflect a low concentration MgSO4 paleo-ocean, while aragonite seas could be related to an MgCl2 or high concentration of MgSO4 paleo-ocean.

  20. 21 CFR 184.1191 - Calcium carbonate.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... soda process”; (2) By precipitation of calcium carbonate from calcium hydroxide in the “Carbonation process”; or (3) By precipitation of calcium carbonate from calcium chloride in the “Calcium...

  1. 21 CFR 184.1191 - Calcium carbonate.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... soda process”; (2) By precipitation of calcium carbonate from calcium hydroxide in the “Carbonation process”; or (3) By precipitation of calcium carbonate from calcium chloride in the “Calcium...

  2. 21 CFR 184.1191 - Calcium carbonate.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... soda process”; (2) By precipitation of calcium carbonate from calcium hydroxide in the “Carbonation process”; or (3) By precipitation of calcium carbonate from calcium chloride in the “Calcium...

  3. 21 CFR 184.1191 - Calcium carbonate.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... soda process”; (2) By precipitation of calcium carbonate from calcium hydroxide in the “Carbonation process”; or (3) By precipitation of calcium carbonate from calcium chloride in the “Calcium...

  4. Amorphous Carbon-Boron Nitride Nanotube Hybrids

    NASA Technical Reports Server (NTRS)

    Kim, Jae Woo (Inventor); Siochi, Emilie J. (Inventor); Wise, Kristopher E. (Inventor); Lin, Yi (Inventor); Connell, John (Inventor)

    2016-01-01

    A method for joining or repairing boron nitride nanotubes (BNNTs). In joining BNNTs, the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures. In repairing BNNTs, the damaged site of the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures at the damage site.

  5. High resolution electron microscopy study of amorphous calcium phosphate

    NASA Astrophysics Data System (ADS)

    Brès, E. F.; Moebus, G.; Kleebe, H.-J.; Pourroy, G.; Werkmann, J.; Ehret, G.

    1993-03-01

    "Amorphous" calcium phosphate (ACP) from human tooth enamel and different synthetic materials has been analysed by high resolution electron microscopy (HREM). All the materials studied showed, in addition to a "truly" amorphous phase, other calcium phosphate phases such as poorly crystalline hydroxyapatite (OHAP), well crystallized OHAP and poorly crystalline CaO type phase. Such structural heterogeneities have not been observed before in ACP, and are only possible to be detected by HREM as this is the only technique able to analyse nanometre size materials in the real space.

  6. Impregnating Coal With Calcium Carbonate

    NASA Technical Reports Server (NTRS)

    Sharma, Pramod K.; Voecks, Gerald E.; Gavalas, George R.

    1991-01-01

    Relatively inexpensive process proposed for impregnating coal with calcium carbonate to increase rates of gasification and combustion of coal and to reduce emission of sulfur by trapping sulfur in calcium sulfide. Process involves aqueous-phase reactions between carbon dioxide (contained within pore network of coal) and calcium acetate. Coal impregnated with CO2 by exposing it to CO2 at high pressure.

  7. Calcium carbonate phase transformations during the carbonation reaction of calcium heavy alkylbenzene sulfonate overbased nanodetergents preparation.

    PubMed

    Chen, Zhaocong; Xiao, Shan; Chen, Feng; Chen, Dongzhong; Fang, Jianglin; Zhao, Min

    2011-07-01

    The preparation and application of overbased nanodetergents with excess alkaline calcium carbonate is a good example of nanotechnology in practice. The phase transformation of calcium carbonate is of extensive concern since CaCO(3) serves both as an important industrial filling material and as the most abundant biomineral in nature. Industrially valuable overbased nanodetergents have been prepared based on calcium salts of heavy alkylbenzene sulfonate by a one-step process under ambient pressure, the carbonation reaction has been monitored by the instantaneous temperature changes and total base number (TBN). A number of analytical techniques such as TGA, DLS, SLS, TEM, FTIR, and XRD have been utilized to explore the carbonation reaction process and phase transformation mechanism of calcium carbonate. An enhanced understanding on the phase transformation of calcium carbonate involved in calcium sulfonate nanodetergents has been achieved and it has been unambiguously demonstrated that amorphous calcium carbonate (ACC) transforms into the vaterite polymorph rather than calcite, which would be of crucial importance for the preparation and quality control of lubricant additives and greases. Our results also show that a certain amount of residual Ca(OH)(2) prevents the phase transformation from ACC to crystalline polymorphs. Moreover, a vaterite nanodetergent has been prepared for the first time with low viscosity, high base number, and uniform particle size, nevertheless a notable improvement on its thermal stability is required for potential applications. Copyright © 2011 Elsevier Inc. All rights reserved.

  8. Structural modeling of amorphous conducting carbon film

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Somnath; Pati, Swapan K.; Subramanyam, S. V.

    1998-04-01

    Amorphous conducting carbon films are prepared using plasma assisted polymerization process. SEM and TEM shows random aggregate of globular clusters of micron size inside the samples. Electrical measurements indicate a near metallic nature. A tendency of saturation of resistivity at low temperature is observed. From spectroscopic analysis we find some unusual features. Based on these observations a structural model of this carbon is proposed.

  9. Thermally induced evolution of hydrogenated amorphous carbon

    NASA Astrophysics Data System (ADS)

    Mangolini, Filippo; Rose, Franck; Hilbert, James; Carpick, Robert W.

    2013-10-01

    The thermally induced structural evolution of hydrogenated amorphous carbon (a-C:H) films was investigated in situ by X-ray photoelectron spectroscopy for annealing temperatures up to 500 °C. A model for the conversion of sp3- to sp2-hybridized carbon in a-C:H vs. temperature and time was developed and applied to determine the ranges of activation energies for the thermally activated processes occurring. The energies are consistent with ordering and clustering of sp2 carbon, scission of sp3 carbon-hydrogen bonds and formation of sp2 carbon, and direct transformation of sp3- to sp2-hybridized carbon.

  10. Mechanisms of mineral membrane fouling growth modulated by pulsed modes of current during electrodialysis: evidences of water splitting implications in the appearance of the amorphous phases of magnesium hydroxide and calcium carbonate.

    PubMed

    Cifuentes-Araya, Nicolás; Astudillo-Castro, Carolina; Bazinet, Laurent

    2014-07-15

    Experiments revealed the fouling nature evolutions along different electrodialysis (ED) trials, and how it disappears when current pulsation acts repetitively on the interfaces of ion-exchange membranes (IEMs). Fouling was totally controlled on the diluate side of cation-exchange membrane (CEM) by the repetitive pulsation frequency of the higher on-duty ratios applied. They created steady water splitting proton-barriers that neutralized OH(-) leakage through the membrane, decreasing the interfacial pH, and fouling of the concentrate side. The anion-exchange membrane (AEM) on the diluate side was similarly protected, but it was fouled once water splitting OH(-) generation became either intense enough or excessively weak. Interestingly, amorphous magnesium hydroxide (AMH) stemmed on the CEM-diluate side from brucite under intense water splitting OH(-) generation, and/or strong OH(-) leakage electromigration through the membrane. Water dissociation and overlimiting current regimes triggered drastic water molecule removal from crystal lattices through an accelerated cascade water splitting reaction. Also, amorphous calcium carbonate (ACC) appeared on CEM under intense water splitting reaction, and disappeared once intense OH(-) leakage was allowed by the water splitting proton-barrier dissipation. Our findings have implications for membrane fouling control, as well as for the understanding of the growth behavior of CaCO3 and Mg(OH)2 species on electromembrane interfaces. Copyright © 2014 Elsevier Inc. All rights reserved.

  11. Atomic structure of intracellular amorphous calcium phosphate deposits.

    PubMed Central

    Betts, F; Blumenthal, N C; Posner, A S; Becker, G L; Lehninger, A L

    1975-01-01

    The radial distribution function calculated from x-ray diffraction of mineralized cytoplasmic structures isolated from the hepatopancreas of the blue crab (Callinectes sapidus) is very similar to that previously found for synthetic amorphous calcium phosphate. Both types of mineral apparently have only short-range atomic order, represented as a neutral ion cluster of about 10 A in longest dimension, whose probable composition is expressed by the formula Ca9(PO4)6. The minor differences observed are attributed to the presence in the biological mineral of significant amounts of Mg-2+ and ATP. Synthetic amorphous calcium phosphate in contact with a solution containing an amount of ATP equivalent to that of the biological mineral failed to undergo conversion to the thermodynamically more stable hydroxyapatite. The amorphous calcium phosphate of the cytoplasmic mineral granules is similarly stable, and does not undergo conversion to hydroxyapatite, presumably owing to the presence of ATP and Mg-2+, known in inhibitors of the conversion process. The physiological implications of mineral deposits consisting of stabilized calcium phosphate ion clusters are discussed. PMID:1056015

  12. Atomic structure of intracellular amorphous calcium phosphate deposits.

    PubMed

    Betts, F; Blumenthal, N C; Posner, A S; Becker, G L; Lehninger, A L

    1975-06-01

    The radial distribution function calculated from x-ray diffraction of mineralized cytoplasmic structures isolated from the hepatopancreas of the blue crab (Callinectes sapidus) is very similar to that previously found for synthetic amorphous calcium phosphate. Both types of mineral apparently have only short-range atomic order, represented as a neutral ion cluster of about 10 A in longest dimension, whose probable composition is expressed by the formula Ca9(PO4)6. The minor differences observed are attributed to the presence in the biological mineral of significant amounts of Mg-2+ and ATP. Synthetic amorphous calcium phosphate in contact with a solution containing an amount of ATP equivalent to that of the biological mineral failed to undergo conversion to the thermodynamically more stable hydroxyapatite. The amorphous calcium phosphate of the cytoplasmic mineral granules is similarly stable, and does not undergo conversion to hydroxyapatite, presumably owing to the presence of ATP and Mg-2+, known in inhibitors of the conversion process. The physiological implications of mineral deposits consisting of stabilized calcium phosphate ion clusters are discussed.

  13. Stable prenucleation calcium carbonate clusters.

    PubMed

    Gebauer, Denis; Völkel, Antje; Cölfen, Helmut

    2008-12-19

    Calcium carbonate forms scales, geological deposits, biominerals, and ocean sediments. Huge amounts of carbon dioxide are retained as carbonate ions, and calcium ions represent a major contribution to water hardness. Despite its relevance, little is known about the precipitation mechanism of calcium carbonate, and specified complex crystal structures challenge the classical view on nucleation considering the formation of metastable ion clusters. We demonstrate that dissolved calcium carbonate in fact contains stable prenucleation ion clusters forming even in undersaturated solution. The cluster formation can be characterized by means of equilibrium thermodynamics, applying a multiple-binding model, which allows for structural preformation. Stable clusters are the relevant species in calcium carbonate nucleation. Such mechanisms may also be important for the crystallization of other minerals.

  14. Continuous synthesis of amorphous carbonated apatites.

    PubMed

    Tadic, D; Peters, F; Epple, M

    2002-06-01

    Amorphous carbonated hydroxyapatite was prepared by rapid mixing of aqueous solutions of a continuous computer-controlled reactor. The variation of the carbonate content in the solid product is possible by adjustment of the ratios of phosphate to carbonate in the initial solution. The principal reaction parameters (temperature, pH, stirrer speed, solution composition and supersaturation) are controlled and monitored. By controlling these processing parameters, a non-stoichiometric hydroxyapatite with fine-tuned crystallinity, morphology, and carbonate content can be reproducibly prepared. The higher solubility under the conditions of osteoclastic resorption was tested in vitro at constant pH (4.4).

  15. Infrared emission from hydrogenated amorphous carbon and amorphous carbon grains in the interstellar medium

    NASA Technical Reports Server (NTRS)

    Duley, W. W.; Jones, A. P.; Taylor, S. D.; Williams, D. A.

    1993-01-01

    The correlations deduced by Boulanger et al. (1990) from IRAS maps of the Chamaeleon, Taurus and Ursa Major molecular cloud complexes are interpreted in terms of the evolutionary hydrogenated amorphous carbon model of interstellar dust. In particular, regions of relatively strong 12-micron emission may be regions where recently accreted carbon is being converted by ambient UV to small PAHs in situ. Regions of weak 12-micron emission are probably quiescent regions where carbon has been annealed to amorphous carbon. Observational consequences of these inferences are briefly described.

  16. Amorphous silica-like carbon dioxide

    NASA Astrophysics Data System (ADS)

    Santoro, Mario; Gorelli, Federico A.; Bini, Roberto; Ruocco, Giancarlo; Scandolo, Sandro; Crichton, Wilson A.

    2006-06-01

    Among the group IV elements, only carbon forms stable double bonds with oxygen at ambient conditions. At variance with silica and germania, the non-molecular single-bonded crystalline form of carbon dioxide, phase V, only exists at high pressure. The amorphous forms of silica (a-SiO2) and germania (a-GeO2) are well known at ambient conditions; however, the amorphous, non-molecular form of CO2 has so far been described only as a result of first-principles simulations. Here we report the synthesis of an amorphous, silica-like form of carbon dioxide, a-CO2, which we call `a-carbonia'. The compression of the molecular phase III of CO2 between 40 and 48GPa at room temperature initiated the transformation to the non-molecular amorphous phase. Infrared spectra measured at temperatures up to 680K show the progressive formation of C-O single bonds and the simultaneous disappearance of all molecular signatures. Furthermore, state-of-the-art Raman and synchrotron X-ray diffraction measurements on temperature-quenched samples confirm the amorphous character of the material. Comparison with vibrational and diffraction data for a-SiO2 and a-GeO2, as well as with the structure factor calculated for the a-CO2 sample obtained by first-principles molecular dynamics, shows that a-CO2 is structurally homologous to the other group IV dioxide glasses. We therefore conclude that the class of archetypal network-forming disordered systems, including a-SiO2, a-GeO2 and water, must be extended to include a-CO2.

  17. Hydrolytic conversion of amorphous calcium phosphate into apatite accompanied by sustained calcium and orthophosphate ions release.

    PubMed

    Niu, Xufeng; Chen, Siqian; Tian, Feng; Wang, Lizhen; Feng, Qingling; Fan, Yubo

    2017-01-01

    The aim of this study is to investigate the calcium and orthophosphate ions release during the transformation of amorphous calcium phosphate (ACP) to hydroxyapatite (HA) in aqueous solution. The ACP is prepared by a wet chemical method and further immersed in the distilled water for various time points till 14d. The release of calcium and orthophosphate ions is measured with calcium and phosphate colorimetric assay kits, respectively. The transition of ACP towards HA is detected by x-ray diffraction (XRD), transmission electron microscopy (TEM), and fourier transform infrared spectroscopy (FTIR). The results indicate that the morphological conversion of ACP to HA occurs within the first 9h, whereas the calcium and orthophosphate ions releases last for over 7d. Such sustained calcium and orthophosphate ions release is very useful for ACP as a candidate material for hard tissue regeneration. Copyright © 2016 Elsevier B.V. All rights reserved.

  18. Intracellular amorphous carbonates uncover a new biomineralization process in eukaryotes.

    PubMed

    Martignier, A; Pacton, M; Filella, M; Jaquet, J-M; Barja, F; Pollok, K; Langenhorst, F; Lavigne, S; Guagliardo, P; Kilburn, M R; Thomas, C; Martini, R; Ariztegui, D

    2017-03-01

    Until now, descriptions of intracellular biomineralization of amorphous inclusions involving alkaline-earth metal (AEM) carbonates other than calcium have been confined exclusively to cyanobacteria (Couradeau et al., 2012). Here, we report the first evidence of the presence of intracellular amorphous granules of AEM carbonates (calcium, strontium, and barium) in unicellular eukaryotes. These inclusions, which we have named micropearls, show concentric and oscillatory zoning on a nanometric scale. They are widespread in certain eukaryote phytoplankters of Lake Geneva (Switzerland) and represent a previously unknown type of non-skeletal biomineralization, revealing an unexpected pathway in the geochemical cycle of AEMs. We have identified Tetraselmis cf. cordiformis (Chlorophyta, Prasinophyceae) as being responsible for the formation of one micropearl type containing strontium ([Ca,Sr]CO3 ), which we also found in a cultured strain of Tetraselmis cordiformis. A different flagellated eukaryotic cell forms barium-rich micropearls [(Ca,Ba)CO3 ]. The strontium and barium concentrations of both micropearl types are extremely high compared with the undersaturated water of Lake Geneva (the Ba/Ca ratio of the micropearls is up to 800,000 times higher than in the water). This can only be explained by a high biological pre-concentration of these elements. The particular characteristics of the micropearls, along with the presence of organic sulfur-containing compounds-associated with and surrounding the micropearls-strongly suggest the existence of a yet-unreported intracellular biomineralization pathway in eukaryotic micro-organisms. © 2016 John Wiley & Sons Ltd.

  19. Nanostructural characterization of amorphous diamondlike carbon films

    SciTech Connect

    SIEGAL,MICHAEL P.; TALLANT,DAVID R.; MARTINEZ-MIRANDA,L.J.; BARBOUR,J. CHARLES; SIMPSON,REGINA L.; OVERMYER,DONALD L.

    2000-01-27

    Nanostructural characterization of amorphous diamondlike carbon (a-C) films grown on silicon using pulsed-laser deposition (PLD) is correlated to both growth energetic and film thickness. Raman spectroscopy and x-ray reflectivity probe both the topological nature of 3- and 4-fold coordinated carbon atom bonding and the topographical clustering of their distributions within a given film. In general, increasing the energetic of PLD growth results in films becoming more ``diamondlike'', i.e. increasing mass density and decreasing optical absorbance. However, these same properties decrease appreciably with thickness. The topology of carbon atom bonding is different for material near the substrate interface compared to material within the bulk portion of an a-C film. A simple model balancing the energy of residual stress and the free energies of resulting carbon topologies is proposed to provide an explanation of the evolution of topographical bonding clusters in a growing a-C film.

  20. Extracting Crystal Chemistry from Amorphous Carbon Structures.

    PubMed

    Deringer, Volker L; Csányi, Gábor; Proserpio, Davide M

    2017-03-08

    Carbon allotropes have been explored intensively by ab initio crystal structure prediction, but such methods are limited by the large computational cost of the underlying density functional theory (DFT). Here we show that a novel class of machine-learning-based interatomic potentials can be used for random structure searching and readily predicts several hitherto unknown carbon allotropes. Remarkably, our model draws structural information from liquid and amorphous carbon exclusively, and so does not have any prior knowledge of crystalline phases: it therefore demonstrates true transferability, which is a crucial prerequisite for applications in chemistry. The method is orders of magnitude faster than DFT and can, in principle, be coupled with any algorithm for structure prediction. Machine-learning models therefore seem promising to enable large-scale structure searches in the future.

  1. A new precipitation pathway for calcium sulfate dihydrate (gypsum) via amorphous and hemihydrate intermediates.

    PubMed

    Wang, Yun-Wei; Kim, Yi-Yeoun; Christenson, Hugo K; Meldrum, Fiona C

    2012-01-14

    This work investigates the early stages of precipitation of calcium sulfate from aqueous solution at room temperature and shows for the first time that amorphous calcium sulfate (ACS) and calcium sulfate hemihydrate are sequentially precipitated prior to calcium sulfate dihydrate (gypsum). This journal is © The Royal Society of Chemistry 2012

  2. Calcium phosphate scaffold from biogenic calcium carbonate by fast ambient condition reactions

    NASA Astrophysics Data System (ADS)

    Dutta, Abhishek; Fermani, Simona; Arjun Tekalur, Srinivasan; Vanderberg, Abigail; Falini, Giuseppe

    2011-12-01

    Calcium phosphate biogenic materials are biocompatible and promote bioactivity and osteoconductivity, which implies their natural affinity and tendency to bond directly to bones subsequently replacing the host bone after implantation owing to its biodegradability. Calcium hydrogen phosphate dihydrate, CaHPO 4·2H 2O, is known to be a nucleation precursor, in aqueous solutions, for apatitic calcium phosphates and, hence, a potential starting material for bone substitutes. Numerous approaches, via hydrothermal and ambient synthetic routes, have been used to produce calcium phosphate from biogenic calcium carbonate, taking advantage of the peculiar architecture and composition of the latter. In this article, the lamellar region of the cuttlefish bone ( Sepia officinalis) was used as a framework for the organized deposition of calcium phosphate crystals, at ambient conditions via a fast procedure involving an amorphous calcium carbonate intermediate, and ending with a conversion to calcium phosphate and a fixation procedure, thereby resulting in direct conversion of biogenic calcium carbonate into calcium phosphates at ambient conditions from the scale of months to hours.

  3. Chemical elimination of amorphous carbon on amorphous carbon nanotubes and its electrochemical performance

    NASA Astrophysics Data System (ADS)

    He, Xiaojun; Jiang, Li; Fan, Chuangang; Lei, Jiangwei; Zheng, Mingdong

    2007-04-01

    Chemical elimination of amorphous carbon on amorphous carbon nanotubes (ACNTs) was for the first time investigated by different treatment processes. Electrochemical performance of the modified ACNTs/carbon paste electrode (ACNTs/CPE) was measured by cyclic voltammetry. Field emission scanning and transmission electron microscope (STEM) observation reveals that the diameter of ACNTs is in the range of 60-100 nm. The amorphous nature of ACNTs was proved by the result of Raman analysis. FT-IR spectra showed that it might be one of the low-cost ways to eliminate amorphous carbon on the surface of ACNTs to treat ACNTs with HNO 3 in microwave oven. Further oxidation in air would lead to the decrease of electron transfer rate on the ACNTs/CPE because OH groups on the wall of ACNTs were partly eliminated by oxidation in air. The results of cyclic voltammetry showed that ACNTs/CPE treated with HNO 3 in microwave oven has optimal peak in relation to the highest redox peak current.

  4. Amorphous calcium phosphate and its application in dentistry

    PubMed Central

    2011-01-01

    Amorphous Calcium Phosphate (ACP) is an essential mineral phase formed in mineralized tissues and the first commercial product as artificial hydroxyapatite. ACP is unique among all forms of calcium phosphates in that it lacks long-range, periodic atomic scale order of crystalline calcium phosphates. The X-ray diffraction pattern is broad and diffuse with a maximum at 25 degree 2 theta, and no other different features compared with well-crystallized hydroxyapatite. Under electron microscopy, its morphological form is shown as small spheroidal particles in the scale of tenths nanometer. In aqueous media, ACP is easily transformed into crystalline phases such as octacalcium phosphate and apatite due to the growing of microcrystalline. It has been demonstrated that ACP has better osteoconductivity and biodegradability than tricalcium phosphate and hydroxyapatite in vivo. Moreover, it can increase alkaline phosphatase activities of mesoblasts, enhance cell proliferation and promote cell adhesion. The unique role of ACP during the formation of mineralized tissues makes it a promising candidate material for tissue repair and regeneration. ACP may also be a potential remineralizing agent in dental applications. Recently developed ACP-filled bioactive composites are believed to be effective anti-demineralizing/remineralizing agents for the preservation and repair of tooth structures. This review provides an overview of the development, structure, chemical composition, morphological characterization, phase transformation and biomedical application of ACP in dentistry. PMID:21740535

  5. Amorphous calcium phosphate and its application in dentistry.

    PubMed

    Zhao, Jie; Liu, Yu; Sun, Wei-Bin; Zhang, Hai

    2011-07-08

    Amorphous Calcium Phosphate (ACP) is an essential mineral phase formed in mineralized tissues and the first commercial product as artificial hydroxyapatite. ACP is unique among all forms of calcium phosphates in that it lacks long-range, periodic atomic scale order of crystalline calcium phosphates. The X-ray diffraction pattern is broad and diffuse with a maximum at 25 degree 2 theta, and no other different features compared with well-crystallized hydroxyapatite. Under electron microscopy, its morphological form is shown as small spheroidal particles in the scale of tenths nanometer. In aqueous media, ACP is easily transformed into crystalline phases such as octacalcium phosphate and apatite due to the growing of microcrystalline. It has been demonstrated that ACP has better osteoconductivity and biodegradability than tricalcium phosphate and hydroxyapatite in vivo. Moreover, it can increase alkaline phosphatase activities of mesoblasts, enhance cell proliferation and promote cell adhesion. The unique role of ACP during the formation of mineralized tissues makes it a promising candidate material for tissue repair and regeneration. ACP may also be a potential remineralizing agent in dental applications. Recently developed ACP-filled bioactive composites are believed to be effective anti-demineralizing/remineralizing agents for the preservation and repair of tooth structures. This review provides an overview of the development, structure, chemical composition, morphological characterization, phase transformation and biomedical application of ACP in dentistry.

  6. Amorphous silicon-carbon alloys and amorphous carbon from direct methane and ethylene activation by ECR

    SciTech Connect

    Conde, J.P.; Chu, V.; Giorgis, F.; Pirri, C.F.; Arekat, S.

    1997-07-01

    Hydrogenated amorphous silicon-carbon alloys are prepared using electron-cyclotron resonance (ECR) plasma-enhanced chemical vapor deposition. Hydrogen is introduced into the source resonance cavity as an excitation gas. Silane is introduced in the main chamber in the vicinity of the plasma stream, whereas the carbon source gases, methane or ethylene, are introduced either with the silane or with the hydrogen as excitation gases. The effect of the type of carbon-source gas, excitation gas mixture and silane-to-carbon source gas flow ratio on the deposition rate, bandgap, subgap density of states, spin density and hydrogen evolution are studied.

  7. Gravimetric Determination of Calcium as Calcium Carbonate Hydrate.

    ERIC Educational Resources Information Center

    Henrickson, Charles H.; Robinson, Paul R.

    1979-01-01

    The gravimetric determination of calcium as calcium carbonate is described. This experiment is suitable for undergraduate quantitative analysis laboratories. It is less expensive than determination of chloride as silver chloride. (BB)

  8. Gravimetric Determination of Calcium as Calcium Carbonate Hydrate.

    ERIC Educational Resources Information Center

    Henrickson, Charles H.; Robinson, Paul R.

    1979-01-01

    The gravimetric determination of calcium as calcium carbonate is described. This experiment is suitable for undergraduate quantitative analysis laboratories. It is less expensive than determination of chloride as silver chloride. (BB)

  9. 21 CFR 184.1191 - Calcium carbonate.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... three common methods of manufacture: (1) As a byproduct in the “Lime soda process”; (2) By precipitation of calcium carbonate from calcium hydroxide in the “Carbonation process”; or (3) By precipitation...

  10. Gold nanoparticles promote amorphous carbon to be ammonia gas sensor

    NASA Astrophysics Data System (ADS)

    Hsu, Hua-Shu; Ju, Shin-Pon; Sun, Shih-Jye; Chou, Hsiung; Chia, C. H.

    2016-05-01

    As gold-nanoparticles-embedded in amorphous carbon films the sp 3 carbon orbits near the interface will be partially transferred to sp 2. The Raman spectrum measurements as well as the molecular-dynamics simulations used the second reactive empirical bond order (REBO) potential simulating the interatomic force between carbon atoms both confirm the orbital transformations. The amorphous carbon films are initially inert to gases, while the films embedded with gold nanoparticles exhibit the increase of resistance in ammonia atmosphere. Namely, gold-nanoparticles-embedded amorphous carbon films become the candidate for ammonia gas sensor materials.

  11. Characterization of calcium carbonate/chitosan composites

    SciTech Connect

    Gonsalves, K.E.; Zhang, S.

    1995-12-31

    The crystal growth of calcium carbonate on a chitosan substrate was achieved using a supersaturated calcium carbonate solution, by using various additives, polyacrylic acid (PAA). Polyacrylic acid modified the chitosan-film surface and promoted the nucleation of calcium carbonate crystals.

  12. 21 CFR 73.1070 - Calcium carbonate.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 1 2014-04-01 2014-04-01 false Calcium carbonate. 73.1070 Section 73.1070 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1070 Calcium carbonate. (a) Identity. (1) The color additive calcium carbonate is a fine, white, synthetically prepared powder consisting essentially of...

  13. 21 CFR 73.1070 - Calcium carbonate.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 1 2011-04-01 2011-04-01 false Calcium carbonate. 73.1070 Section 73.1070 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1070 Calcium carbonate. (a) Identity. (1) The color additive calcium carbonate is a fine, white, synthetically prepared powder consisting essentially of...

  14. 21 CFR 73.1070 - Calcium carbonate.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 1 2012-04-01 2012-04-01 false Calcium carbonate. 73.1070 Section 73.1070 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1070 Calcium carbonate. (a) Identity. (1) The color additive calcium carbonate is a fine, white, synthetically prepared powder consisting essentially of...

  15. 21 CFR 582.5191 - Calcium carbonate.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 6 2014-04-01 2014-04-01 false Calcium carbonate. 582.5191 Section 582.5191 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Supplements 1 § 582.5191 Calcium carbonate. (a) Product. Calcium carbonate. (b) Conditions of use. This...

  16. 21 CFR 73.1070 - Calcium carbonate.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Calcium carbonate. 73.1070 Section 73.1070 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1070 Calcium carbonate. (a) Identity. (1) The color additive calcium carbonate is a fine, white, synthetically prepared powder consisting essentially of...

  17. 21 CFR 582.1191 - Calcium carbonate.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 6 2013-04-01 2013-04-01 false Calcium carbonate. 582.1191 Section 582.1191 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Additives § 582.1191 Calcium carbonate. (a) Product. Calcium carbonate. (b) Conditions of use. This...

  18. 21 CFR 582.1191 - Calcium carbonate.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 6 2012-04-01 2012-04-01 false Calcium carbonate. 582.1191 Section 582.1191 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Additives § 582.1191 Calcium carbonate. (a) Product. Calcium carbonate. (b) Conditions of use. This...

  19. 21 CFR 73.1070 - Calcium carbonate.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 1 2013-04-01 2013-04-01 false Calcium carbonate. 73.1070 Section 73.1070 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1070 Calcium carbonate. (a) Identity. (1) The color additive calcium carbonate is a fine, white, synthetically prepared powder consisting essentially of...

  20. 21 CFR 582.5191 - Calcium carbonate.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 6 2013-04-01 2013-04-01 false Calcium carbonate. 582.5191 Section 582.5191 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Supplements 1 § 582.5191 Calcium carbonate. (a) Product. Calcium carbonate. (b) Conditions of use. This...

  1. 21 CFR 582.1191 - Calcium carbonate.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 6 2014-04-01 2014-04-01 false Calcium carbonate. 582.1191 Section 582.1191 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Additives § 582.1191 Calcium carbonate. (a) Product. Calcium carbonate. (b) Conditions of use. This...

  2. 21 CFR 582.1191 - Calcium carbonate.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 6 2011-04-01 2011-04-01 false Calcium carbonate. 582.1191 Section 582.1191 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Additives § 582.1191 Calcium carbonate. (a) Product. Calcium carbonate. (b) Conditions of use. This...

  3. 21 CFR 582.5191 - Calcium carbonate.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 6 2012-04-01 2012-04-01 false Calcium carbonate. 582.5191 Section 582.5191 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Supplements 1 § 582.5191 Calcium carbonate. (a) Product. Calcium carbonate. (b) Conditions of use. This...

  4. 21 CFR 582.1191 - Calcium carbonate.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Calcium carbonate. 582.1191 Section 582.1191 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Additives § 582.1191 Calcium carbonate. (a) Product. Calcium carbonate. (b) Conditions of use. This...

  5. 21 CFR 582.5191 - Calcium carbonate.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 6 2011-04-01 2011-04-01 false Calcium carbonate. 582.5191 Section 582.5191 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Supplements 1 § 582.5191 Calcium carbonate. (a) Product. Calcium carbonate. (b) Conditions of use. This...

  6. 21 CFR 582.5191 - Calcium carbonate.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Calcium carbonate. 582.5191 Section 582.5191 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL... Supplements 1 § 582.5191 Calcium carbonate. (a) Product. Calcium carbonate. (b) Conditions of use. This...

  7. Coaxial carbon plasma gun deposition of amorphous carbon films

    NASA Technical Reports Server (NTRS)

    Sater, D. M.; Gulino, D. A.; Rutledge, S. K.

    1984-01-01

    A unique plasma gun employing coaxial carbon electrodes was used in an attempt to deposit thin films of amorphous diamond-like carbon. A number of different structural, compositional, and electrical characterization techniques were used to characterize these films. These included scanning electron microscopy, scanning transmission electron microscopy, X ray diffraction and absorption, spectrographic analysis, energy dispersive spectroscopy, and selected area electron diffraction. Optical absorption and electrical resistivity measurements were also performed. The films were determined to be primarily amorphous, with poor adhesion to fused silica substrates. Many inclusions of particulates were found to be present as well. Analysis of these particulates revealed the presence of trace impurities, such as Fe and Cu, which were also found in the graphite electrode material. The electrodes were the source of these impurities. No evidence of diamond-like crystallite structure was found in any of the film samples. Details of the apparatus, experimental procedure, and film characteristics are presented.

  8. Amorphous titania/carbon composite electrode materials

    DOEpatents

    Vaughey, John T.; Jansen, Andrew; Joyce, Christopher D.

    2017-05-09

    An isolated salt comprising a compound of formula (H.sub.2X)(TiO(Y).sub.2) or a hydrate thereof, wherein X is 1,4-diazabicyclo[2.2.2]octane (DABCO), and Y is oxalate anion (C.sub.2O.sub.4.sup.-2), when heated in an oxygen-containing atmosphere at a temperature in the range of at least about 275.degree. C. to less than about 400.degree. C., decomposes to form an amorphous titania/carbon composite material comprising about 40 to about 50 percent by weight titania and about 50 to about 60 percent by weight of a carbonaceous material coating the titania. Heating the composite material at a temperature of about 400 to 500.degree. C. crystallizes the titania component to anatase. The titania materials of the invention are useful as components of the cathode or anode of a lithium or lithium ion electrochemical cell.

  9. Free energy and structure of calcium carbonate nanoparticles during early stages of crystallization

    NASA Astrophysics Data System (ADS)

    Quigley, D.; Rodger, P. M.

    2008-06-01

    We introduce a metadynamics based scheme for computing the free energy of nanoparticles as a function of their crystalline order. The method is applied to small nanoparticles of the biomineral calcium carbonate to determine the preferred structure during early stages of crystal growth. For particles 2 nm in diameter, we establish a large energetic preference for amorphous particle morphologies. Particles with partial crystalline order consistent with vaterite are also observed with substantially lower probability. The absence of the stable calcite phase and stability of the amorphous state support recent conjectures that calcite formation starts via the deposition of amorphous calcium carbonate.

  10. Unveiling descriptors for predicting the bulk modulus of amorphous carbon

    NASA Astrophysics Data System (ADS)

    Takahashi, Keisuke; Tanaka, Yuzuru

    2017-02-01

    Descriptors for the bulk modulus of amorphous carbon are investigated through the implementation of data mining where data sets are prepared using first-principles calculations. Data mining reveals that the number of bonds in each C atom and the density of amorphous carbon are found to be descriptors representing the bulk modulus. Support vector regression (SVR) within machine learning is implemented and descriptors are trained where trained SVR is able to predict the bulk modulus of amorphous carbon. An inverse problem, starting from the bulk modulus towards structural information of amorphous carbon, is performed and structural information of amorphous carbon is successfully predicted from the desired bulk modulus. Thus, treating several physics factors in multidimensional space allows for the prediction of physical phenomena. In addition, the reported approach proposes that "big data" can be generated from a small data set using machine learning if descriptors are well defined. This would greatly change how amorphous carbon would be treated and help accelerate further development of amorphous carbon materials.

  11. Novel low Wigner energy amorphous carbon-carbon composite

    NASA Astrophysics Data System (ADS)

    Dasgupta, Kinshuk; Prakash, Jyoti; Tripathi, B. M.

    2014-02-01

    A novel amorphous carbon-carbon composite has been developed using carbon black dispersed in carbonized phenolic resin matrix in order to avoid Wigner energy problem associated with graphite. The as prepared sample showed a density of 1320 kg m-3. This has been further densified by resin impregnation and chemical vapour infiltration. The effect of processing parameters on final density (1517 kg m-3) has been investigated. This composite possesses the compressive strength of 65 Mpa, coefficient of thermal expansion of 3 × 10-6 K-1 and the specific heat of 1.2 J g-1 K-1. This novel composite was subjected to 145 MeV Ne+6 heavy ion irradiation at different doses. The highest dose was kept at 3 × 10-4 dpa. The stored energy in the composite was found to be 212 J g-1 at the highest dose of irradiation, which is much below than that of graphite. The composite remained amorphous after irradiation as confirmed by X-ray diffraction.

  12. Degree of vinyl conversion in experimental amorphous calcium phosphate composites

    NASA Astrophysics Data System (ADS)

    Tarle, Z.; Knežević, A.; Matošević, D.; Škrtić, D.; Ristić, M.; Prskalo, K.; Musić, S.

    2009-04-01

    An experimental dental composite, based on amorphous calcium phosphate (ACP) with the potential to arrest caries development and regenerate mineral-deficient tooth structures has recently been developed. The aim of this study was to assess the degree of vinyl conversion (DVC) attained in experimental composites based on zirconia-modified ACP. Photo-activated resins were based on ethoxylated bisphenol A dimethacrylate (EBPADMA) [ETHM series with varying EBPADMA/triethylene glycol dimethacrylate (TEGDMA) molar ratios assigned 0.5-ETHM I, 0.85-ETHM II and 1.35-ETHM III], or 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenyl]-propane (Bis-GMA) [BTHZ series]. To asses a possible effect of filler particle size on DVC, composites containing 60 mass % resin and 40 mass % of either milled ACP (mACP; median diameter d m = 0.9 μm) or coarse ACP (cACP; d m = 6.0 μm) were prepared, and irradiated with LED curing unit for 40 s. The DVC was calculated as the % change in the ratio of the integrated peak areas between the aliphatic and aromatic absorption bands determined by Fourier transform infrared spectroscopy (FTIR). The highest DVCs values were attained in mACP-BTHZ, cACP-BTHZ and mACP-ETHM III formulations. DVC of tested ACP composites (on average (76.76 ± 4.43)%) compares well with or exceeds DVCs values reported for the majority of commercial materials.

  13. Nanocomposite containing amorphous calcium phosphate nanoparticles for caries inhibition

    PubMed Central

    Xu, Hockin H. K.; Moreau, Jennifer L.; Sun, Limin; Chow, Laurence C.

    2011-01-01

    Objectives The main challenges facing composite restorations are secondary caries and bulk fracture. The objectives of this study were to synthesize novel nanoparticles of amorphous calcium phosphate (NACP), develop NACP nanocomposite with calcium (Ca) and phosphate (PO4) ion release to combat caries, and investigate the effects of NACP filler level and glass co-filler reinforcement on composite properties. Methods NACP (diameter = 116 nm) were synthesized via a spray-drying technique for the first time. Since the local plaque pH in the oral cavity can decrease to 5 or 4, photo-activated composites were tested with immersion in solutions of pH 7, 5.5, and 4. Composite mechanical properties as well as Ca and PO4 ion release were measured vs. pH and filler level. Results Increasing the NACP filler level increased the ion release. At 28 d and pH 4, the Ca release was (4.66 ± 0.05) mmol/L at 20% NACP, much higher than (0.33 ± 0.08) at 10% NACP (p < 0.05). Decreasing the pH increased the ion release. At 20% NACP, the PO4 release at 28 d was (1.84 ± 0.12) mmol/L at pH 4, higher than (0.59 ± 0.08) at pH 5.5, and (0.12 ± 0.01) at pH 7 (p < 0.05). However, pH had little effect on composite mechanical properties. Flexural strength at 15% NACP was (96 ± 13) MPa at pH 4, similar to (89 ± 13) MPa at pH 5.5, and (89 ± 19) MPa at pH 7 (p > 0.1). The new NACP nanocomposites had strengths that were 2-fold those of previous calcium phosphate composites and resin-modified glass ionomer control. Significance NACP composites were developed for the first time. Their strengths matched or exceeded a commercial composite with little ion release, and were 2-fold those of previous Ca-PO4 composites. The nanocomposite was “smart” as it greatly increased the ion release at a cariogenic pH 4, when these ions would be most needed to inhibit caries. Hence, the new NACP composite may be promising for stress-bearing and caries-inhibiting restorations. PMID:21514655

  14. Nanocomposite containing amorphous calcium phosphate nanoparticles for caries inhibition.

    PubMed

    Xu, Hockin H K; Moreau, Jennifer L; Sun, Limin; Chow, Laurence C

    2011-08-01

    The main challenges facing composite restorations are secondary caries and bulk fracture. The objectives of this study were to synthesize novel nanoparticles of amorphous calcium phosphate (NACP), develop NACP nanocomposite with calcium (Ca) and phosphate (PO(4)) ion release to combat caries, and investigate the effects of NACP filler level and glass co-filler reinforcement on composite properties. NACP (diameter=116 nm) were synthesized via a spray-drying technique for the first time. Since the local plaque pH in the oral cavity can decrease to 5 or 4, photo-activated composites were tested with immersion in solutions of pH 7, 5.5, and 4. Composite mechanical properties as well as Ca and PO(4) ion release were measured vs. pH and filler level. Increasing the NACP filler level increased the ion release. At 28 d and pH 4, the Ca release was (4.66±0.05)mmol/L at 20% NACP, much higher than (0.33±0.08) at 10% NACP (p<0.05). Decreasing the pH increased the ion release. At 20% NACP, the PO(4) release at 28 d was (1.84±0.12)mmol/L at pH 4, higher than (0.59±0.08) at pH 5.5, and (0.12±0.01) at pH 7 (p<0.05). However, pH had little effect on composite mechanical properties. Flexural strength at 15% NACP was (96±13)MPa at pH 4, similar to (89±13)MPa at pH 5.5, and (89±19)MPa at pH 7 (p>0.1). The new NACP nanocomposites had strengths that were 2-fold those of previous calcium phosphate composites and resin-modified glass ionomer control. NACP composites were developed for the first time. Their strengths matched or exceeded a commercial composite with little ion release, and were 2-fold those of previous Ca-PO(4) composites. The nanocomposite was "smart" as it greatly increased the ion release at a cariogenic pH 4, when these ions would be most needed to inhibit caries. Hence, the new NACP composite may be promising for stress-bearing and caries-inhibiting restorations. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  15. The effect of amorphous calcium phosphate on protein protection against thermal denaturation.

    PubMed

    Yang, Yuling; Wang, Guangchuan; Zhu, Genxing; Xu, Xurong; Pan, Haihua; Tang, Ruikang

    2015-05-21

    The hybrid nanoparticles of amorphous calcium phosphate (ACP)-catalase (CAT) developed by in situ biomineralization can create a stable semi-aqueous nanoscale environment for entrapped proteins against thermal denaturation. This finding indicates the importance of an amorphous mineral phase in the preservation of organic macromolecules.

  16. Preparation, characterization and in vivo evaluation of amorphous atorvastatin calcium nanoparticles using supercritical antisolvent (SAS) process.

    PubMed

    Kim, Min-Soo; Jin, Shun-Ji; Kim, Jeong-Soo; Park, Hee Jun; Song, Ha-Seung; Neubert, Reinhard H H; Hwang, Sung-Joo

    2008-06-01

    In this work, amorphous atorvastatin calcium nanoparticles were successfully prepared using the supercritical antisolvent (SAS) process. The effect of process variables on particle size and distribution of atorvastatin calcium during particle formation was investigated. Solid state characterization, solubility, intrinsic dissolution, powder dissolution studies and pharmacokinetic study in rats were performed. Spherical particles with mean particle size ranging between 152 and 863 nm were obtained by varying process parameters such as precipitation vessel pressure and temperature, drug solution concentration and feed rate ratio of CO2/drug solution. XRD, TGA, FT-IR, FT-Raman, NMR and HPLC analysis indicated that atorvastatin calcium existed as anhydrous amorphous form and no degradation occurred after SAS process. When compared with crystalline form (unprocessed drug), amorphous atorvastatin calcium nanoparticles were of better performance in solubility and intrinsic dissolution rate, resulting in higher solubility and faster dissolution rate. In addition, intrinsic dissolution rate showed a good correlation with the solubility. The dissolution rates of amorphous atorvastatin calcium nanoparticles were highly increased in comparison with unprocessed drug by the enhancement of intrinsic dissolution rate and the reduction of particle size resulting in an increased specific surface area. The absorption of atorvastatin calcium after oral administration of amorphous atorvastatin calcium nanoparticles to rats was markedly increased.

  17. Binding of calcium and carbonate to polyacrylates.

    PubMed

    Tribello, Gareth A; Liew, CheeChin; Parrinello, Michele

    2009-05-21

    Polyacrylate molecules can be used to slow the growth of calcium carbonate. However, little is known about the mechanism by which the molecules impede the growth rate. A recent computational study (Bulo et al. Macromolecules 2007, 40, 3437) used metadynamics to investigate the binding of calcium to polyacrylate chains and has thrown some light on the coiling and precipitation of these polymers. We extend these simulations to examine the binding of calcium and carbonate to polyacrylate chains. We show that calcium complexed with both carbonate and polyacrylate is a very stable species. The free energies of calcium-carbonate-polyacrylate complexes, with different polymer configurations, are calculated, and differences in the free energy of the binding of carbonate are shown to be due to differences in the amount of steric hindrance about the calcium, which prevents the approach of the carbonate ion.

  18. Spinning up the polymorphs of calcium carbonate

    PubMed Central

    Boulos, Ramiz A.; Zhang, Fei; Tjandra, Edwin S.; Martin, Adam D.; Spagnoli, Dino; Raston, Colin L.

    2014-01-01

    Controlling the growth of the polymorphs of calcium carbonate is important in understanding the changing environmental conditions in the oceans. Aragonite is the main polymorph in the inner shells of marine organisms, and can be readily converted to calcite, which is the most stable polymorph of calcium carbonate. Both of these polymorphs are significantly more stable than vaterite, which is the other naturally occurring polymorph of calcium carbonate, and this is reflected in its limited distribution in nature. We have investigated the effect of high shear forces on the phase behaviour of calcium carbonate using a vortex fluidic device (VFD), with experimental parameters varied to explore calcium carbonate mineralisation. Variation of tilt angle, rotation speed and temperature allow for control over the size, shape and phase of the resulting calcium carbonate. PMID:24448077

  19. Optical properties of amorphous hydrogenated carbon films

    NASA Astrophysics Data System (ADS)

    Chen, Jing Qiu

    Carbon can be formed either as fully crystalline structures, such as diamond, graphite, and fullerene (C60). or as mostly amorphous structures, like amorphous hydrogenated carbon (a-C:H). A study was made of a-C:H films which had been deposited by plasma enhanced chemical vapor deposition (PECVD) using CH4, H2 and Ar (or N2 for doping) gas mixtures. Each film exhibits unique physical, optical and electronic properties dependent upon the specific deposition parameters. The study is intended to extend our understanding of the properties of a-C:H films. Samples prepared by James Johnson, similar to those used in his previous studies (using mainly 4 separate sets of deposition parameters), were evaluated along with other samples which were unique to this study. Film preparation parameters were varied to allow an examination of the effects induced through the variation of deposition power level, partial substitution of nitrogen for methane in the deposition process gasses and post-deposition thermal annealing. The film optical properties were evaluated using combination of non-destructive test methods, including Raman scattering, photoluminescence (PL), optical absorption and photoluminescence excitation (PLE) spectroscopies. Different PL responses at low temperature (6 K) were recorded for doped and/or annealed samples deriving from the main set of samples. Two new features at 564 and 637 nm of nitrogen doped films replaced the 597 and 703 nm of undoped films. For the first time, three Raman phonon peaks were observed in a nitrogen doped and annealed film. Additional FTIR data indicated that the third Raman phonon peak was associated with CH2 and CH3 bonding structures. The Raman scattering data contributed to an improved understanding of the two-phase (sp2, sp3) model developed by Robertson. Optical absorption measurements could only be obtained for the films deposited on fused quartz. All other measurements were made on films deposited on silicon, which is opaque in

  20. Non-aqueous formation of the calcium carbonate polymorph vaterite: astrophysical implications

    NASA Astrophysics Data System (ADS)

    Day, S. J.; Thompson, S. P.; Parker, J. E.; Evans, A.

    2013-05-01

    Aims: We study the formation of calcium carbonate, through the solid-gas interaction of amorphous Ca-silicate with gaseous CO2, at elevated pressures, and link this to the possible presence of calcium carbonate in a number of circumstellar and planetary environments. Methods: We use in-situ synchrotron X-ray powder diffraction to obtain detailed structural data pertaining to the formation of the crystalline calcium carbonate phase vaterite and its evolution with temperature. Results: We found that the metastable calcium carbonate phase vaterite was formed alongside calcite, at elevated CO2 pressure, at room temperature and subsequently remained stable over a large range of temperature and pressure. Conclusions: We report the formation of the calcium carbonate mineral vaterite whilst attempting to simulate carbonate dust grain formation in astrophysical environments. This suggests that vaterite could be a mineral component of carbonate dust and also presents a possible method of formation for vaterite and its polymorphs on planetary surfaces.

  1. Light transmittance and polymerization kinetics of amorphous calcium phosphate composites.

    PubMed

    Par, Matej; Marovic, Danijela; Skenderovic, Hrvoje; Gamulin, Ozren; Klaric, Eva; Tarle, Zrinka

    2017-05-01

    This study investigated light transmittance and polymerization kinetics of experimental remineralizing composite materials based on amorphous calcium phosphate (ACP), reinforced with inert fillers. Light-curable composites were composed of Bis-EMA-TEGDMA-HEMA resin and ACP, barium glass, and silica fillers. Additionally, a commercial composite Tetric EvoCeram was used as a reference. Light transmittance was recorded in real-time during curing, and transmittance curves were used to assess polymerization kinetics. To obtain additional information on polymerization kinetics, temperature rise was monitored in real-time during curing and degree of conversion was measured immediately and 24 h post-cure. Light transmittance values of 2-mm thick samples of uncured ACP composites (2.3-2.9 %) were significantly lower than those of the commercial composite (3.8 %). The ACP composites presented a considerable transmittance rise during curing, resulting in post-cure transmittance values similar to or higher than those of the commercial composite (5.5-7.9 vs. 5.4 %). The initial part of light transmittance curves of experimental composites showed a linear rise that lasted for 7-20 s. Linear fitting was performed to obtain a function whose slope was assessed as a measure of polymerization rate. Comparison of transmittance and temperature curves showed that the linear transmittance rise lasted throughout the most part of the pre-vitrification period. The linear rise of light transmittance during curing has not been reported in previous studies and may indicate a unique kinetic behavior, characterized by a long period of nearly constant polymerization rate. The observed kinetic behavior may result in slower development of polymerization shrinkage stress but also inferior mechanical properties.

  2. Impedance changes during setting of amorphous calcium phosphate composites.

    PubMed

    Par, Matej; Šantić, Ana; Gamulin, Ozren; Marovic, Danijela; Moguš-Milanković, Andrea; Tarle, Zrinka

    2016-11-01

    To investigate the electrical properties of experimental light-curable composite materials based on amorphous calcium phosphate (ACP) with the admixture of silanized barium glass and silica fillers. Short-term setting was investigated by impedance measurements at a frequency of 1kHz, while for the long-term setting the impedance spectra were measured consecutively over a frequency range of 0.05Hz to 1MHz for 24h. The analysis of electrical resistivity changes during curing allowed the extraction of relevant kinetic parameters. The impedance results were correlated to the degree of conversion assessed by Raman spectroscopy, water content determined by gravimetry, light transmittance measured by CCD spectrometer and microstructural features observed by scanning electron microscopy. ACP-based composites have shown higher immediate degree of conversion and less post-cure polymerization than the control composites, but lower polymerization rate. The polymerization rate assessed by impedance measurements correlated well with the light transmittance. The differences in the electrical conductivity values observed among the materials were correlated to the amount of water introduced into composites by the ACP filler. High correlation was found between the degree of conversion and electrical resistivity. Equivalent circuit modeling revealed two electrical contributions for the ACP-based composites and a single contribution for the control composites. The impedance spectroscopy has proven a valuable method for gaining insight into various features of ACP-based composites. Better understanding of the properties of ACP-based composites should further the development of these promising bioactive materials. Copyright © 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  3. Multi-Functions of Carbonated Calcium Deficient Hydroxyapatite (CDHA)

    NASA Astrophysics Data System (ADS)

    Zhou, Huan

    Natural bone is a complex composite mainly constituted of inorganic minerals and organic collagen molecules. Calcium phosphate (CaP) based materials have been proposed as the predominant bone substitute for bone tissue engineering applications due to their chemical similarity to bone mineral. Amorphous carbonated calcium deficient hydroxyapatite (CDHA) is an important compound among CaP materials because of the amorphous crystallite structure. The presence of extra ions in its lattice structure not only influences cell attachment and proliferation of osteoblasts, but also helps in bone metabolism. Biomimetic coating approach is the most widely used approach to produce CDHA coatings to implant. It is a process using simulated body fluid (SBF) to deposit bone-like CDHA coating to various material surfaces. The CDHA formation mechanism, SBF compositions and reacting conditions of biomimetic coating have already been sufficiently studied and compared in the past 20 years. It is an attempt in this thesis to explore new applications of SBF in biomedical research, focusing on different biomaterial applications: 1) based on the low temperature reaction condition of SBF, bisphosphonate incorporated CDHA coatings were deposited onto Ti6Al4V surface for the treatment of osteoporosis; 2) amorphous calcium phosphate nanospheres with extra elements in the lattice structure were prepared by a novel microwave assisted approach, providing a new potential of CaP materials production; 3) CDHA particles formed in SBF can be used as great fillers with biopolymers for preparing biocomposites for biomedical applications; 4) based on the high activity of CDHA amorphous structure and the stabilization ability of ethanol, yttrium and europium doped calcium phosphates were prepared using CDHA as a sacrificing template. In the end, future work based on these observations in the thesis is addressed, including areas of drug delivery, biocomposite fabrication and preparation of functionalized

  4. Induced calcium carbonate precipitation using Bacillus species.

    PubMed

    Seifan, Mostafa; Samani, Ali Khajeh; Berenjian, Aydin

    2016-12-01

    Microbially induced calcium carbonate precipitation is an emerging process for the production of self-healing concrete. This study was aimed to investigate the effects and optimum conditions on calcium carbonate biosynthesis. Bacillus licheniformis, Bacillus sphaericus, yeast extract, urea, calcium chloride and aeration were found to be the most significant factors affecting the biomineralization of calcium carbonate. It was noticed that the morphology of microbial calcium carbonate was mainly affected by the genera of bacteria (cell surface properties), the viscosity of the media and the type of electron acceptors (Ca(2+)). The maximum calcium carbonate concentration of 33.78 g/L was achieved at the optimum conditions This value is the highest concentration reported in the literature.

  5. Amorphization of Silicon Carbide by Carbon Displacement

    SciTech Connect

    Devanathan, Ram; Gao, Fei; Weber, William J.

    2004-05-10

    We have used molecular dynamics simulations to examine the possibility of amorphizing silicon carbide (SiC) by exclusively displacing C atoms. At a defect generation corresponding to 0.2 displacements per atom, the enthalpy surpasses the level of melt-quenched SiC, the density decreases by about 15%, and the radial distribution function shows a lack of long-range order. Prior to amorphization, the surviving defects are mainly C Frenkel pairs (67%), but Si Frenkel pairs (18%) and anti-site defects (15%) are also present. The results indicate that SiC can be amorphized by C sublattice displacements. Chemical short-range disorder, arising mainly from interstitial production, plays a significant role in the amorphization.

  6. Solid state characterization of commercial crystalline and amorphous atorvastatin calcium samples.

    PubMed

    Shete, Ganesh; Puri, Vibha; Kumar, Lokesh; Bansal, Arvind K

    2010-06-01

    Atorvastatin calcium (ATC), an anti-lipid BCS class II drug, is marketed in crystalline and amorphous solid forms. The objective of this study was to perform solid state characterization of commercial crystalline and amorphous ATC drug samples available in the Indian market. Six samples each of crystalline and amorphous ATC were characterized using X-ray powder diffractometry (XRPD), differential scanning calorimetry (DSC), thermogravimetric analysis, Karl Fisher titrimetry, microscopy (hot stage microscopy, scanning electron microscopy), contact angle, and intrinsic dissolution rate (IDR). All crystalline ATC samples were found to be stable form I, however one sample possessed polymorphic impurity, evidenced in XRPD and DSC analysis. Amongst the amorphous ATC samples, XRPD demonstrated five samples to be amorphous 'form 27', while, one matched amorphous 'form 23'. Thermal behavior of amorphous ATC samples was compared to amorphous ATC generated by melt quenching in DSC. ATC was found to be an excellent glass former with T(g)/T(m) of 0.95. Residual crystallinity was detected in two of the amorphous samples by complementary use of conventional and modulated DSC techniques. The wettability and IDR of all amorphous samples was found to be higher than the crystalline samples. In conclusion, commercial ATC samples exhibited diverse solid state behavior that can impact the performance and stability of the dosage forms.

  7. Carbonated calcium phosphates are suitable pH-stabilising fillers for biodegradable polyesters.

    PubMed

    Schiller, Carsten; Epple, Matthias

    2003-05-01

    Carbonated amorphous calcium phosphates were prepared with different carbonate content. Their ability to neutralise acidity was probed by time-resolved titration experiments with lactic acid, the monomer that results from degradation of polylactide. The results show that although calcium phosphate as such can reduce acidity, their buffering range lies at a pH of about 4, i.e. outside the physiological range. This is not related to the rate of dissolution. Carbonated calcium phosphates as well as calcium carbonate (calcite) alone are able to keep the pH around 7.4. Consequently, carbonated calcium phosphates are suitable basic filler materials as they are able to compensate acidity, and to buffer within the physiological pH-range.

  8. Fracture of Carbon Nanotube - Amorphous Carbon Composites: Molecular Modeling

    NASA Technical Reports Server (NTRS)

    Jensen, Benjamin D.; Wise, Kristopher E.; Odegard, Gregory M.

    2015-01-01

    Carbon nanotubes (CNTs) are promising candidates for use as reinforcements in next generation structural composite materials because of their extremely high specific stiffness and strength. They cannot, however, be viewed as simple replacements for carbon fibers because there are key differences between these materials in areas such as handling, processing, and matrix design. It is impossible to know for certain that CNT composites will represent a significant advance over carbon fiber composites before these various factors have been optimized, which is an extremely costly and time intensive process. This work attempts to place an upper bound on CNT composite mechanical properties by performing molecular dynamics simulations on idealized model systems with a reactive forcefield that permits modeling of both elastic deformations and fracture. Amorphous carbon (AC) was chosen for the matrix material in this work because of its structural simplicity and physical compatibility with the CNT fillers. It is also much stiffer and stronger than typical engineering polymer matrices. Three different arrangements of CNTs in the simulation cell have been investigated: a single-wall nanotube (SWNT) array, a multi-wall nanotube (MWNT) array, and a SWNT bundle system. The SWNT and MWNT array systems are clearly idealizations, but the SWNT bundle system is a step closer to real systems in which individual tubes aggregate into large assemblies. The effect of chemical crosslinking on composite properties is modeled by adding bonds between the CNTs and AC. The balance between weakening the CNTs and improving fiber-matrix load transfer is explored by systematically varying the extent of crosslinking. It is, of course, impossible to capture the full range of deformation and fracture processes that occur in real materials with even the largest atomistic molecular dynamics simulations. With this limitation in mind, the simulation results reported here provide a plausible upper limit on

  9. Angular magnetoresistance in semiconducting undoped amorphous carbon thin films

    SciTech Connect

    Sagar, Rizwan Ur Rehman; Saleemi, Awais Siddique; Zhang, Xiaozhong

    2015-05-07

    Thin films of undoped amorphous carbon thin film were fabricated by using Chemical Vapor Deposition and their structure was investigated by using High Resolution Transmission Electron Microscopy and Raman Spectroscopy. Angular magnetoresistance (MR) has been observed for the first time in these undoped amorphous carbon thin films in temperature range of 2 ∼ 40 K. The maximum magnitude of angular MR was in the range of 9.5% ∼ 1.5% in 2 ∼ 40 K. The origin of this angular MR was also discussed.

  10. Thermally reduced graphenes exhibiting a close relationship to amorphous carbon

    NASA Astrophysics Data System (ADS)

    An Wong, Colin Hong; Ambrosi, Adriano; Pumera, Martin

    2012-07-01

    Graphene is an important material for sensing and energy storage applications. Since the vast majority of sensing and energy storage chemical and electrochemical systems require bulk quantities of graphene, thermally reduced graphene oxide (TRGO) is commonly employed instead of pristine graphene. The sp2 planar structure of TRGO is heavily damaged, consisting of a very short sp2 crystallite size of nanometre length and with areas of sp3 hybridized carbon. Such a structure of TRGO is reminiscent of the key characteristic of the structure of amorphous carbon, which is defined as a material without long-range crystalline order consisting of both sp2 and sp3 hybridized carbons. Herein, we describe the characterization of TRGO, its parent graphite material and carbon black (a form of amorphous carbon) via transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry experiments. We used the data obtained as well as consideration of practical factors to perform a comparative assessment of the relative electrochemical performances of TRGO against amorphous carbon. We found out that TRGO and amorphous carbon exhibit almost identical characteristics in terms of density of defects in the sp2 lattice and a similar crystallite size as determined by Raman spectroscopy. These two materials also exhibit similar amounts of oxygen containing groups as determined by XPS and nearly indistinguishable cyclic voltammetric response providing almost identical heterogeneous electron transfer constants. This leads us to conclude that for some sensing and energy storage electrochemical applications, the use of amorphous carbon might be a much more economical solution than the one requiring digestion of highly crystalline graphite with strong oxidants to graphite oxide and then thermally exfoliating it to thermally reduced graphene oxide.

  11. Mapping residual organics and carbonate at grain boundaries and the amorphous interphase in mouse incisor enamel

    PubMed Central

    Gordon, Lyle M.; Joester, Derk

    2015-01-01

    Dental enamel has evolved to resist the most grueling conditions of mechanical stress, fatigue, and wear. Adding insult to injury, it is exposed to the frequently corrosive environment of the oral cavity. While its hierarchical structure is unrivaled in its mechanical resilience, heterogeneity in the distribution of magnesium ions and the presence of Mg-substituted amorphous calcium phosphate (Mg-ACP) as an intergranular phase have recently been shown to increase the susceptibility of mouse enamel to acid attack. Herein we investigate the distribution of two important constituents of enamel, residual organic matter and inorganic carbonate. We find that organics, carbonate, and possibly water show distinct distribution patterns in the mouse enamel crystallites, at simple grain boundaries, and in the amorphous interphase at multiple grain boundaries. This has implications for the resistance to acid corrosion, mechanical properties, and the mechanism by which enamel crystals grow during amelogenesis. PMID:25852562

  12. Novel technique for phosphorus recovery from aqueous solutions using amorphous calcium silicate hydrates (A-CSHs).

    PubMed

    Okano, Kenji; Uemoto, Masahide; Kagami, Jumpei; Miura, Keiichi; Aketo, Tsuyoshi; Toda, Masaya; Honda, Kohsuke; Ohtake, Hisao

    2013-05-01

    A novel technique for phosphorus (P) recovery from aqueous solutions was developed using amorphous calcium silicate hydrates (A-CSHs). A-CSHs, which have a high Ca/Si molar ratio of 2.0 or greater, could be synthesized using unlimitedly available, inexpensive materials such as siliceous shale and calcium hydroxide. A-CSHs showed high performance for P recovery from an anaerobic sludge digestion liquor (ASDL) and the synthetic model liquor (s-ASDL) containing 89 mg PO4-P/L. After 20 min mixing, 1.5 g/L A-CSHs could remove approximately 69 and 73% PO4-P from ASDL and s-ASDL, respectively. By contrast, autoclaved lightweight concrete particles, which contained crystalline calcium silicate hydrates as a principal component, removed only 10 and 6% PO4-P from ASDL and s-ASDL, respectively, under the same experimental conditions. When A-CSHs were washed with deionized water to remove free Ca(OH)2, P removability was significantly improved (up to 82%) despite the reduction in the amount of Ca(2+) released. Unlike in the case of Ca(OH)2, no significant carbonate inhibition was observed with P removal by A-CSHs. Moreover, P removed by A-CSHs showed better settleability, filterability, and dewaterability than P precipitated with conventional CaCl2 and Ca(OH)2. The present study demonstrated that A-CSHs have great potential as a novel, beneficial material for P recovery and recycling.

  13. A shear localization mechanism for lubricity of amorphous carbon materials

    PubMed Central

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-01

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials. PMID:24412998

  14. A shear localization mechanism for lubricity of amorphous carbon materials

    NASA Astrophysics Data System (ADS)

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-01

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials.

  15. A shear localization mechanism for lubricity of amorphous carbon materials.

    PubMed

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-13

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials.

  16. Protein-Mediated Precipitation of Calcium Carbonate

    PubMed Central

    Polowczyk, Izabela; Bastrzyk, Anna; Fiedot, Marta

    2016-01-01

    Calcium carbonate is an important component in exoskeletons of many organisms. The synthesis of calcium carbonate was performed by mixing dimethyl carbonate and an aqueous solution of calcium chloride dihydrate. The precipitation product was characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) measurements. In addition, the turbidity of the reaction solution was acquired to monitor the kinetics of the calcium carbonate structure’s growth in the investigated system. In this study, samples of CaCO3 particles obtained with individual proteins, such as ovalbumin, lysozyme, and a mixture of the proteins, were characterized and compared with a control sample, i.e., synthesized without proteins. The obtained data indicated that the addition of ovalbumin to the reaction changed the morphology of crystals from rhombohedral to ‘stack-like’ structures. Lysozyme, however, did not affect the morphology of calcium carbonate, yet the presence of the protein mixture led to the creation of more complex composites in which the calcium carbonate crystals were constructed in protein matrices formed by the ovalbumin-lysozyme interaction. It was also observed that in the protein mixture, ovalbumin has a major influence on the CaCO3 formation through a strong interaction with calcium ions, which leads to the coalescence and creation of a steric barrier reducing particle growth. The authors proposed a mechanism of calcium carbonate grain growth in the presence of both proteins, taking into account the interaction of calcium ions with the protein. PMID:28774065

  17. Transformation of Amorphous Calcium Phosphate to Crystalline Dahllite in the Radular Teeth of Chitons

    NASA Astrophysics Data System (ADS)

    Lowenstam, H. A.; Weiner, S.

    1985-01-01

    A comparison of infrared spectra from individual teeth along the radula of a chiton (Polyplacophora, Mollusca) shows that the first-formed calcium phosphate mineral is amorphous. Over a period of weeks the mineral transforms to dahllite. The c axes of the dahllite crystals are aligned approximately perpendicular to the tooth surface.

  18. Deposition of superhard amorphous carbon films by pulsed arc sources

    SciTech Connect

    Scheibe, H.J.; Schultrich, B.; Ziegele, H.; Siemroth, P.

    1996-12-31

    Hydrogen-free amorphous carbon films with hardness comparable to crystalline superhard materials have been deposited by special Pulsed arc techniques. By the combination of very high hardness, low adhesion and high smoothness, these films show superior behaviour in wear and glide applications. The influence of plasma and deposition conditions on these film properties and the choice of optimum conditions are discussed.

  19. Machine learning based interatomic potential for amorphous carbon

    NASA Astrophysics Data System (ADS)

    Deringer, Volker L.; Csányi, Gábor

    2017-03-01

    We introduce a Gaussian approximation potential (GAP) for atomistic simulations of liquid and amorphous elemental carbon. Based on a machine learning representation of the density-functional theory (DFT) potential-energy surface, such interatomic potentials enable materials simulations with close-to DFT accuracy but at much lower computational cost. We first determine the maximum accuracy that any finite-range potential can achieve in carbon structures; then, using a hierarchical set of two-, three-, and many-body structural descriptors, we construct a GAP model that can indeed reach the target accuracy. The potential yields accurate energetic and structural properties over a wide range of densities; it also correctly captures the structure of the liquid phases, at variance with a state-of-the-art empirical potential. Exemplary applications of the GAP model to surfaces of "diamondlike" tetrahedral amorphous carbon (ta -C) are presented, including an estimate of the amorphous material's surface energy and simulations of high-temperature surface reconstructions ("graphitization"). The presented interatomic potential appears to be promising for realistic and accurate simulations of nanoscale amorphous carbon structures.

  20. Obtaining and Characterization of Polyolefin-Filled Calcium Carbonate Composites Modified with Stearic Acid

    NASA Astrophysics Data System (ADS)

    Croitoru, C.; Pascu, A.; Roata, I. C.; Stanciu, E. M.

    2017-06-01

    In order to obtain high performance calcium carbonate-reinforced HDPE and PP composites, the dispersibility and compatibility of the inorganic phase in the polymer has been achieved through surface treatment of the amorphous calcium carbonate filler with stearic acid. The surface coating of the inorganic phase has been proved by XRD and FTIR spectroscopy, through forming of an intermediate layer of calcium stearate which acts as a surfactant, efficient in providing an optimum compatibility with the dominatingly hydrophobic polymer matrix, as determined from the structural information obtained through samples cross-sections analysing.

  1. Hard, amorphous carbon deposited from a fullerene discharge

    SciTech Connect

    Maiken, E.B.; Taborek, P.

    1995-12-31

    Hard, amorphous carbon films were deposited from an ion source using fullerite as carbon feedstock. For fixed ion energies, the film resistivities decreased exponentially with substrate temperature, suggesting activated growth of a conductive phase. Resistivity at 300 K ranged from 10{sup -3} to 10{sup 4} {Omega}m. E{sub -4} optical gaps of conductive films ranged from 0.1 to 1.1 eV.

  2. Amorphous diamond: a high-pressure superhard carbon allotrope.

    PubMed

    Lin, Yu; Zhang, Li; Mao, Ho-kwang; Chow, Paul; Xiao, Yuming; Baldini, Maria; Shu, Jinfu; Mao, Wendy L

    2011-10-21

    Compressing glassy carbon above 40 GPa, we have observed a new carbon allotrope with a fully sp(3)-bonded amorphous structure and diamondlike strength. Synchrotron x-ray Raman spectroscopy revealed a continuous pressure-induced sp(2)-to-sp(3) bonding change, while x-ray diffraction confirmed the perseverance of noncrystallinity. The transition was reversible upon releasing pressure. Used as an indenter, the glassy carbon ball demonstrated exceptional strength by reaching 130 GPa with a confining pressure of 60 GPa. Such an extremely large stress difference of >70 GPa has never been observed in any material besides diamond, indicating the high hardness of this high-pressure carbon allotrope.

  3. Amorphous diamond: A high-pressure superhard carbon allotrope

    SciTech Connect

    Lin, Yu; Zhang, Li; Mao, Ho Kwang; Chow, Paul; Xiao, Yuming; Baldini, Maria; Shu, Jinfu; Mao, Wendy L.

    2011-01-01

    Compressing glassy carbon above 40 GPa, we have observed a new carbon allotrope with a fully sp³-bonded amorphous structure and diamondlike strength. Synchrotron x-ray Raman spectroscopy revealed a continuous pressure-induced sp²-to-sp³ bonding change, while x-ray diffraction confirmed the perseverance of noncrystallinity. The transition was reversible upon releasing pressure. Used as an indenter, the glassy carbon ball demonstrated exceptional strength by reaching 130 GPa with a confining pressure of 60 GPa. Such an extremely large stress difference of >70 GPa has never been observed in any material besides diamond, indicating the high hardness of this high-pressure carbon allotrope.

  4. Elemental calcium intake associated with calcium acetate/calcium carbonate in the treatment of hyperphosphatemia

    PubMed Central

    Wilson, Rosamund J; Copley, J Brian

    2017-01-01

    Background Calcium-based and non-calcium-based phosphate binders have similar efficacy in the treatment of hyperphosphatemia; however, calcium-based binders may be associated with hypercalcemia, vascular calcification, and adynamic bone disease. Scope A post hoc analysis was carried out of data from a 16-week, Phase IV study of patients with end-stage renal disease (ESRD) who switched to lanthanum carbonate monotherapy from baseline calcium acetate/calcium carbonate monotherapy. Of the intent-to-treat population (N=2520), 752 patients with recorded dose data for calcium acetate (n=551)/calcium carbonate (n=201) at baseline and lanthanum carbonate at week 16 were studied. Elemental calcium intake, serum phosphate, corrected serum calcium, and serum intact parathyroid hormone levels were analyzed. Findings Of the 551 patients with calcium acetate dose data, 271 (49.2%) had an elemental calcium intake of at least 1.5 g/day at baseline, and 142 (25.8%) had an intake of at least 2.0 g/day. Mean (95% confidence interval [CI]) serum phosphate levels were 6.1 (5.89, 6.21) mg/dL at baseline and 6.2 (6.04, 6.38) mg/dL at 16 weeks; mean (95% CI) corrected serum calcium levels were 9.3 (9.16, 9.44) mg/dL and 9.2 (9.06, 9.34) mg/dL, respectively. Of the 201 patients with calcium carbonate dose data, 117 (58.2%) had an elemental calcium intake of at least 1.5 g/day, and 76 (37.8%) had an intake of at least 2.0 g/day. Mean (95% CI) serum phosphate levels were 5.8 (5.52, 6.06) mg/dL at baseline and 5.8 (5.53, 6.05) mg/dL at week 16; mean (95% CI) corrected serum calcium levels were 9.7 (9.15, 10.25) mg/dL and 9.2 (9.06, 9.34) mg/dL, respectively. Conclusion Calcium acetate/calcium carbonate phosphate binders, taken to control serum phosphate levels, may result in high levels of elemental calcium intake. This may lead to complications related to calcium balance. PMID:28182142

  5. Elemental calcium intake associated with calcium acetate/calcium carbonate in the treatment of hyperphosphatemia.

    PubMed

    Wilson, Rosamund J; Copley, J Brian

    2017-01-01

    Calcium-based and non-calcium-based phosphate binders have similar efficacy in the treatment of hyperphosphatemia; however, calcium-based binders may be associated with hypercalcemia, vascular calcification, and adynamic bone disease. A post hoc analysis was carried out of data from a 16-week, Phase IV study of patients with end-stage renal disease (ESRD) who switched to lanthanum carbonate monotherapy from baseline calcium acetate/calcium carbonate monotherapy. Of the intent-to-treat population (N=2520), 752 patients with recorded dose data for calcium acetate (n=551)/calcium carbonate (n=201) at baseline and lanthanum carbonate at week 16 were studied. Elemental calcium intake, serum phosphate, corrected serum calcium, and serum intact parathyroid hormone levels were analyzed. Of the 551 patients with calcium acetate dose data, 271 (49.2%) had an elemental calcium intake of at least 1.5 g/day at baseline, and 142 (25.8%) had an intake of at least 2.0 g/day. Mean (95% confidence interval [CI]) serum phosphate levels were 6.1 (5.89, 6.21) mg/dL at baseline and 6.2 (6.04, 6.38) mg/dL at 16 weeks; mean (95% CI) corrected serum calcium levels were 9.3 (9.16, 9.44) mg/dL and 9.2 (9.06, 9.34) mg/dL, respectively. Of the 201 patients with calcium carbonate dose data, 117 (58.2%) had an elemental calcium intake of at least 1.5 g/day, and 76 (37.8%) had an intake of at least 2.0 g/day. Mean (95% CI) serum phosphate levels were 5.8 (5.52, 6.06) mg/dL at baseline and 5.8 (5.53, 6.05) mg/dL at week 16; mean (95% CI) corrected serum calcium levels were 9.7 (9.15, 10.25) mg/dL and 9.2 (9.06, 9.34) mg/dL, respectively. Calcium acetate/calcium carbonate phosphate binders, taken to control serum phosphate levels, may result in high levels of elemental calcium intake. This may lead to complications related to calcium balance.

  6. Laser-induced exfoliation of amorphous carbon layer on an individual multiwall carbon nanotube

    NASA Astrophysics Data System (ADS)

    Singh, G.; Rice, P.; Hurst, K. E.; Lehman, J. H.; Mahajan, R. L.

    2007-07-01

    Pulsed laser treatment of an individual multiwall carbon nanotube induced selective exfoliation of the amorphous carbon contamination layer. The multiwall carbon nanotube (MWCNT) was exposed to a 248nm excimer laser. After the treatment, transmission electron microscopy images show that the amorphous layer has expanded and separated from the crystalline MWCNT walls. This interesting observation has implications for laser cleaning and possible thinning of MWCNTs to reduce the radial dimensions.

  7. Calcium, carbonic anhydrase and gastric acid secretion.

    PubMed

    Puscas, I; Coltau, M; Baican, M; Domuta, G; Hecht, A

    2001-01-01

    Previous data concerning the action of calcium (Ca) on gastric acid secretion (GAS) indicated that calcium ions increase GAS elicited by gastrin released through a vagal mechanism, and also by a direct effect on parietal cells. Our research showed that the stimulating effect of calcium on gastric acid secretion can be antagonized by verapamil administration, which reduces gastric acid secretion . In the present study we followed the effect induced by administration of calcium and Ca-chelating agents (disodium EDTA) on gastric acid secretion and on carbonic anhydrase (CA) activity. We selected two groups of healthy volunteers: Group I (n=21) received a single i.v. dose of CaCl2 (15 mg/kg b.w.), whereas Group II (n=22) received a single i.v. dose of disodium EDTA (5 mg/kg b.w.). We determined blood calcium before and after treatment, gastric acid secretion at 2 hours. erythrocyte CA II activity, and CA IV activity in membrane parietal cells, which were isolated from gastric mucosa obtained by endoscopic biopsy. Assessment of carbonic anhydrase activity was achieved by the stopped-flow method. In Group I calcium administration increased blood calcium, HCl output, CA II and CA IV activity as compared to initial values. In Group II, disodium EDTA reduced blood calcium, HCl output, CA II and CA IV activity as compared to initial values. The results demonstrated that increased blood calcium and GAS values after calcium administration correlated with the increase of erythrocyte CA II and parietal cell CA IV activity, while disodium EDTA induced a reversed process. Our results also show that cytosolic CA II and membrane CA IV values are sensitive to calcium changes and they directly depend on these levels. Our data suggest that intra- and extracellular pH changes induced by carbonic anhydrase might account for the modulation of the physiological and pathological secretory processes in the organism.

  8. Microstructure and mechanical properties of nanocomposite amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Tay, B. K.; Sun, C. Q.; Lau, S. P.

    2002-07-01

    Nanocomposite amorphous carbon films such as a-C:Al, a-C:Ti, and a-C:Si have been prepared using a filtered cathodic vacuum arc technique. The films were characterized using x-ray photoelectron spectroscopy (XPS), atomic force microscopy, surface profilometry, a nanoindenter, and Raman spectrometry. It was found that metal contents in the films deviate from the target depending on the constituent element, which is attributed to the effect of dynamic balance deposition. XPS results revealed the presence of a carbide phase in a-C:Ti and a-C:Si but not in a-C:Al nanocomposite carbon films. Incorporating metal into amorphous carbon films significantly reduces the compressive stress but maintains the relative high hardness and Young's modulus. copyright 2002 American Vacuum Society.

  9. Microwave Switching in Amorphous-Carbon Quantum Wells

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Somnath; Gomez Rojas, Luis; Silva, S. Ravi. P.

    2007-03-01

    Demonstration of long phase coherence length showing resonant tunnelling and fast switching in amorphous carbon quantum well structures has recently been established [1]. Here we show a bias controlled reversible switching of the complex impedance by transmitting a microwave signal up to 110GHz through amorphous carbon resonant tunnel diodes. By employing a coplanar waveguide technique and through the analysis of the return loss (S11) microwave enhanced mobility greater than 30cm^2(Vs)-1 in the delocalized regime of (filamentary) conduction in these devices is demonstrated. Also a switching behaviour at about 85GHz can also be observed. We suggest a new model for the microscopic origin of the increased mobility and show routes to achieve longer coherence lengths. In addition microwave conductance of carbon quantum wells parallel to their plane and across a channel length larger than 100 nm determines the momentum scattering time of electrons in carbon. These results exhibit a potential for pure amorphous carbon-based fast memory devices. [1] S. Bhattacharyya, S.J. Henley, E. Mendoza, L. Gomez Rojas, J. Allam and S.R.P. Silva, Nature Mater. 5, 19 (2006).

  10. Constraints on Biogenic Emplacement of Crystalline Calcium Carbonate and Dolomite

    NASA Astrophysics Data System (ADS)

    Colas, B.; Clark, S. M.; Jacob, D. E.

    2015-12-01

    Amorphous calcium carbonate (ACC) is a biogenic precursor of calcium carbonates forming shells and skeletons of marine organisms, which are key components of the whole marine environment. Understanding carbonate formation is an essential prerequisite to quantify the effect climate change and pollution have on marine population. Water is a critical component of the structure of ACC and the key component controlling the stability of the amorphous state. Addition of small amounts of magnesium (1-5% of the calcium content) is known to promote the stability of ACC presumably through stabilization of the hydrogen bonding network. Understanding the hydrogen bonding network in ACC is fundamental to understand the stability of ACC. Our approach is to use Monte-Carlo simulations constrained by X-ray and neutron scattering data to determine hydrogen bonding networks in ACC as a function of magnesium doping. We have already successfully developed a synthesis protocol to make ACC, and have collected X-ray data, which is suitable for determining Ca, Mg and O correlations, and have collected neutron data, which gives information on the hydrogen/deuterium (as the interaction of X-rays with hydrogen is too low for us to be able to constrain hydrogen atom positions with only X-rays). The X-ray and neutron data are used to constrain reverse Monte-Carlo modelling of the ACC structure using the Empirical Potential Structure Refinement program, in order to yield a complete structural model for ACC including water molecule positions. We will present details of our sample synthesis and characterization methods, X-ray and neutron scattering data, and reverse Monte-Carlo simulations results, together with a discussion of the role of hydrogen bonding in ACC stability.

  11. Calcination of calcium carbonate and blend therefor

    SciTech Connect

    Mallow, W.A.; Dziuk, J.J. Jr.

    1989-05-09

    This patent describes a method for the accelerated calcination of a calcium carbonate material. It comprises: heating the calcium carbonate material to a temperature and for a time sufficient to calcine the material to the degree desired while in the presence of a fused salt catalyst consisting of particles having a size above or below that of the calcium carbonate material; the catalyst comprising at least one fused salt having the formula M{sub 2}CO{sub 3}. CaCO{sub 3}-CaO-H{sub 2}O{sub {ital x}}, wherein M is an alkali metal selected from sodium or potassium and x is 0 to 1 and the salt is formed by fusing M{sub 2}CO{sub 3} and CaCO{sub 3} in a molar ratio of about 1:2 to 2:1 when the alkali metal is sodium and about 1:1 to 2:1 when the alkali metal is potassium. This patent also describes a blend adapted to be heated to form CaO. It comprises: a calcium carbonate material and a catalyst consisting of particles having a size above or below that of the calcium carbonate material; the catalyst comprising at least one fused salt having the formula M{sub 2}CO{sub 3}-CaCO{sub 3}CaO-H{sub 2}O{sub {ital x}}.

  12. Calcination of calcium carbonate and blend therefor

    SciTech Connect

    Mallow, William A.; Dziuk, Jr., Jerome J.

    1989-01-01

    A method for calcination of a calcium carbonate material comprising heating the calcium carbonate material to a temperature and for a time sufficient to calcine the material to the degree desired while in the presence of a catalyst; said catalyst comprising at least one fused salt having the formula MCO.sub.3.CaCO.sub.3.CaO.H.sub.2 O.sub.x, wherein M is an alkali metal and x is 0 to 1 and formed by fusing MCO.sub.3 and CaCO.sub.3 in a molar ratio of about 1:2 to 2:1, and a blend adapted to be heated to CaO comprising a calcium carbonate material and at least one such fused salt.

  13. Carbonated beverages and urinary calcium excretion.

    PubMed

    Heaney, R P; Rafferty, K

    2001-09-01

    Intake of carbonated beverages has been associated with increased fracture risk in observational studies. The usual explanation given is that one or more of the beverage constituents increase urinary calcium. We assessed the short-term effects on urinary calcium excretion of carbonated beverages of various compositions. An incomplete random block design was used to study 20-40-y-old women who customarily consumed > or =680 mL carbonated beverages daily. Four carbonated beverages were tested: 2 with caffeine and 2 without. Two contained phosphoric acid as the acidulant and 2 contained citric acid. The study included one neutral control (water) and one positive control (skim or chocolate milk). Serving size was 567 mL for the carbonated beverages and water and 340 mL for the milks. Beverages were consumed with a light breakfast after an overnight fast; no other foods were ingested until urine collection was complete. pH, titratable and total acidity, sodium, creatinine, and calcium were measured in 2-h (morning) fasting and 5-h postbeverage urine specimens. Relative to water, urinary calcium rose significantly only with the milks and the 2 caffeine-containing beverages. The excess calciuria was approximately 0.25 mmol, about the same as previously reported for caffeine alone. Phosphoric acid without caffeine produced no excess calciuria; nor did it augment the calciuria of caffeine. The excess calciuria associated with consumption of carbonated beverages is confined to caffeinated beverages. Acidulant type has no acute effect. Because the caffeine effect is known to be compensated for by reduced calciuria later in the day, we conclude that the net effect of carbonated beverage constituents on calcium economy is negligible. The skeletal effects of carbonated beverage consumption are likely due primarily to milk displacement.

  14. A template route to the preparation of mesoporous amorphous calcium silicate with high in vitro bone-forming bioactivity.

    PubMed

    Li, Xia; Shi, Jianlin; Zhu, Yufang; Shen, Weihua; Li, Hua; Liang, Jian; Gao, Jianhua

    2007-11-01

    The mesoporous amorphous calcium silicate (MACS) was first synthesized using mesoporous silica SBA-15 as both the template and silicon source, and Ca(NO(3))(2) as the calcium source. The MACS shows a well-defined mesoporous structure with high specific surface area. In vitro bioactivity studies of the MACS were carried out by soaking it in simulated body fluid (SBF) solutions for 4 h up to 5 days. Owing to the high specific surface area and pore volume, the MACS had a significantly enhanced bone-forming bioactivity compared with the conventional amorphous CaSiO(3). The MACS did develop a carbonate-containing hydroxyapatite (HCA) layer on the surface after being immersed in SBF for 4 h with near-spherical agglomerated hydroxyapatite (HA) nanoparticles. At longer soaking times, the number of agglomerated HA particles increased and the surface structure of the samples became more compact. Such MACS could be useful in developing new biomaterials and may have potential use in implanting and drug delivery for tissue regeneration.

  15. An in vitro comparison of casein phosphopeptide-amorphous calcium phosphate paste, casein phosphopeptide-amorphous calcium phosphate paste with fluoride and casein phosphopeptide-amorphous calcium phosphate varnish on the inhibition of demineralization and promotion of remineralization of enamel.

    PubMed

    Thakkar, Prachi Jayesh; Badakar, Chandrashekhar M; Hugar, Shivayogi M; Hallikerimath, Seema; Patel, Punit M; Shah, Parin

    2017-01-01

    This study aims to determine and compare the extent of inhibition of demineralization and promotion of remineralization of permanent molar enamel with and without application of three remineralizing agents. Forty extracted permanent molars were randomly divided into two groups 1 and 2, longitudinally sectioned into four and divided into subgroups A, B, C, and D. The sections were coated with nail varnish leaving a window of 3 mm × 3 mm. All sections of Group 1 were treated with their respective subgroup-specific agent: Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) paste for subgroup A, CPP-amorphous calcium phosphate fluoride (ACPF) paste for subgroup B, CPP-ACPF varnish for subgroup C and subgroup D served as a control. The sections were then subjected to demineralization for 12 days following which lesional depth was measured under the stereomicroscope. All the sections of Group 2 were subjected to demineralization for 12 days, examined for lesional depth, then treated with their respective subgroup specific agents and immersed in artificial saliva for 7 days. The sections were then examined again under the stereomicroscope to measure the lesional depth. CPP-ACPF varnish caused significant inhibition of demineralization. All three agents showed significant remineralization of previously demineralized lesions. However, CPP-ACPF varnish showed the greatest remineralization, followed by CPP-ACPF paste and then CPP-ACP paste. This study shows that CPP-ACPF varnish is effective in preventing demineralization as well as promoting remineralization of enamel. Thus, it can be used as an effective preventive measure for pediatric patients where compliance with the use of tooth mousse may be questionable.

  16. Calcium Carbonate Precipitation by Ureolytic Subsurface Bacteria

    SciTech Connect

    Fujita, Y.; Colwell, Frederick Scott; Smith, Robert William; Ferris, F. G.; Lawson, R. L.

    2000-10-01

    Coprecipitation in carbonate minerals offers a means of slowing the transport of divalent radionuclides and contaminant metals (e.g.,90Sr2+, UO2+, Co2+) in the subsurface. It may be possible to accelerate this process by stimulating the native microbial community to generate chemical conditions favoring carbonate precipitation. In a preliminary evaluation of this approach, we investigated the ability of ureolytic subsurface bacteria to produce alkaline conditions conducive to calcium carbonate precipitation. Groundwater samples from the Eastern Snake River Plain (ESRP) aquifer in Idaho were screened for urea-hydrolyzing microorganisms; three isolates were selected for further evaluation. Analysis of 16S rRNA gene sequences indicated that two of the ESRP isolates were of the genus Pseudomonas , and the other was a Variovorax sp. The specific urease activities of the ESRP isolates appeared to be similar to each other but less than that of Bacillus pasteurii , a known urease-positive organism. However, calcium carbonate was rapidly precipitated in all cultures that were supplied with urea and calcium, and X-ray diffraction analyses indicated that calcite was always the predominant carbonate polymorph produced. The correspondence between measured calcium concentrations and equilibrium predictions suggested that the rate of calcite precipitation was directly linked to the rate of urea hydrolysis. These results are promising with respect to the potential utility of this approach for in situ remediation and indicate that further evaluation of this approach under conditions more closely simulating environmental conditions is warranted.

  17. Raman spectra of amorphous carbon films deposited by SWP

    NASA Astrophysics Data System (ADS)

    Xu, Junqi; Liu, Weiguo; Hang, Lingxia; Su, Junhong; Fan, Huiqing

    2010-10-01

    Amorphous carbon film is one of the most important anti-reflection protective films coated on infrared optical components. In this paper, hydrogen-free amorphous carbon films were deposited by new type surface-wave-sustained plasma (SWP) source with a graphite target at various experiment parameters. The laser Raman spectroscopy at wavelength of 514 nm was used to investigate the structure and bonding of these carbon films. The results showed consanguineous correlations between the intensity ratio ID/IG and the experiment parameters such as microwave power, target voltage and gas pressure applied to the SWP source. Raman spectra proved the structure of these carbon films prepared by SWP technique is typical diamond-like carbon (DLC). The analysis on G peak position and intensity ratio ID/IG indicated that Raman shifts moves to low wavenumber and ID/IG decreases with the increasing of microwave power from 150 W to 330 W. These results means the formation of sp3 bond prefers higher microwave power. DLC films prepared at target voltage of -200 V have higher sp3 content than that of -350 V, moreover, an increase of gas pressure during experiments yields higher sp3 content at the microwave power below 270 W, whereas the change of sp3 content is slight with the various conditions when microwave power exceeds 270 W.

  18. Amorphous Diamond: A High-Pressure Superhard Carbon Allotrope

    SciTech Connect

    Lin, Yu; Zhang, Li; Mao, Ho-kwang; Chow, Paul; Xiao, Yuming; Baldini, Maria; Shu, Jinfu; Mao, Wendy L.

    2011-12-09

    Compressing glassy carbon above 40 GPa, we have observed a new carbon allotrope with a fully sp{sup 3}-bonded amorphous structure and diamondlike strength. Synchrotron x-ray Raman spectroscopy revealed a continuous pressure-induced sp{sup 2}-to-sp{sup 3} bonding change, while x-ray diffraction confirmed the perseverance of noncrystallinity. The transition was reversible upon releasing pressure. Used as an indenter, the glassy carbon ball demonstrated exceptional strength by reaching 130 GPa with a confining pressure of 60 GPa. Such an extremely large stress difference of >70 GPa has never been observed in any material besides diamond, indicating the high hardness of this high-pressure carbon allotrope.

  19. Bonding topologies in diamondlike amorphous-carbon films

    SciTech Connect

    SIEGAL,MICHAEL P.; PROVENCIO,PAULA P.; TALLANT,DAVID R.; SIMPSON,REGINA L.; KLEINSORGE,B.; MILNE,W.I.

    2000-01-27

    The carbon ion energy used during filtered cathodic vacuum arc deposition determines the bonding topologies of amorphous-carbon (a-C) films. Regions of relatively low density occur near the substrate/film and film/surface interfaces and their thicknesses increase with increasing deposition energy. The ion subplantation growth results in mass density gradients in the bulk portion of a-C in the growth direction; density decreases with distance from the substrate for films grown using ion energies < 60 eV and increases for films grown using ion energies > 160 eV. Films grown between these energies are the most diamondlike with relatively uniform bulk density and the highest optical transparencies. Bonding topologies evolve with increasing growth energy consistent with the propagation of subplanted carbon ions inducing a partial transformation of 4-fold to 3-fold coordinated carbon atoms.

  20. Chemical modification of sputtered amorphous-carbon surfaces

    NASA Astrophysics Data System (ADS)

    Leezenberg, Pieter B.; Johnston, William H.; Tyndall, George W.

    2001-03-01

    Methods to chemically passivate the surfaces of amorphous-carbon films (a-C) produced by dc magnetron sputtering were studied. The chemical composition of carbon surfaces produced via sputtering are dependent upon the environment to which the carbon is exposed immediately following deposition. When the sputtered film is vented to ambient conditions, free radicals produced at the surface during the deposition process are quenched by reaction with oxygen and/or water to form an oxidized, hydrophilic surface. If the sputtered carbon film is, however, exposed to a reactive gas prior to venting to ambient, the chemical nature of the resulting surface can be modified substantially. Specifically, a less highly oxidized and much more hydrophobic carbon surface is produced when the surface free radicals are quenched via either an addition reaction (demonstrated with a fluorinated olefin) or a hydrogen abstraction reaction (demonstrated with two alkyl amines). Chemical modification of amorphous-carbon films can also be accomplished by performing the sputtering in a reactive plasma formed from mixtures of argon with molecular hydrogen, amines, and perfluorocarbons. The elemental composition of these films, and the relative reactivity of the surfaces formed, were investigated via x-ray photoelectron spectroscopy and contact-angle goniometry, respectively. In the case of sputtering with a mixture of argon and hydrogen, increasing the hydrogen flow results in an increase in the amount of hydrogen incorporated into the carbon film and a decrease in the surface free energy. Sputtering in diethylamine produces an amorphous-carbon film into which nitrogen is incorporated. The free energies of the a-C:N surfaces produced in this process are similar to those of the a-C:H films. Sputtering in a fluorocarbon vapor results in the incorporation of fluorine into the film structure and the formation of very low free-energy surfaces. Increasing the concentration of the fluorocarbon in the

  1. Egg-white-mediated crystallization of calcium carbonate

    NASA Astrophysics Data System (ADS)

    Zheng, Liang; Hu, Yanli; Ma, Yongjun; Zhou, Yong; Nie, Fude; Liu, Xun; Pei, Chonghua

    2012-12-01

    In this paper, shape-controlled crystallization and self-assembly of CaCO3 hierarchical architectures has been successfully synthesized via the gas diffusion method in egg white solution. Stepwise growth and assembly of CaCO3 nanoparticles has been observed from transition of an amorphous CaCO3 to the crystallization and stabilization of platelet-like nanoparticles and eventually, the wool sphere-like CaCO3 hierarchical architectures assembling of nanoparticles. The proteins binding on nanoparticle surfaces proved to regulate the growth of nanoparticles and subsequent assembly into hierarchical superstructures via electrostatic and dipole interactions. The samples were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and nano mechanical Tester. The measured average elastic modulus and the hardness of calcium carbonate hybrid materials were 5.32 GPa and 0.1886 GPa by the nano-indenter test, respectively.

  2. Anhydrous Amorphous Calcium Oxalate Nanoparticles from Ionic Liquids: Stable Crystallization Intermediates in the Formation of Whewellite.

    PubMed

    Gehl, Aaron; Dietzsch, Michael; Mondeshki, Mihail; Bach, Sven; Häger, Tobias; Panthöfer, Martin; Barton, Bastian; Kolb, Ute; Tremel, Wolfgang

    2015-12-07

    The mechanisms by which amorphous intermediates transform into crystalline materials are not well understood. To test the viability and the limits of the classical crystallization, new model systems for crystallization are needed. With a view to elucidating the formation of an amorphous precursor and its subsequent crystallization, the crystallization of calcium oxalate, a biomineral widely occurring in plants, is investigated. Amorphous calcium oxalate (ACO) precipitated from an aqueous solution is described as a hydrated metastable phase, as often observed during low-temperature inorganic synthesis and biomineralization. In the presence of water, ACO rapidly transforms into hydrated whewellite (monohydrate, CaC2 O4 ⋅H2 O, COM). The problem of fast crystallization kinetics is circumvented by synthesizing anhydrous ACO from a pure ionic liquid (IL-ACO) for the first time. IL-ACO is stable in the absence of water at ambient temperature. It is obtained as well-defined, non-agglomerated particles with diameters of 15-20 nm. When exposed to water, it crystallizes to give (hydrated) COM through a dissolution/recrystallization mechanism. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Nonenzymatic Transformation of Amorphous CaCO3 into Calcium Phosphate Mineral after Exposure to Sodium Phosphate in Vitro: Implications for in Vivo Hydroxyapatite Bone Formation.

    PubMed

    Müller, Werner E G; Neufurth, Meik; Huang, Jian; Wang, Kui; Feng, Qingling; Schröder, Heinz C; Diehl-Seifert, Bärbel; Muñoz-Espí, Rafael; Wang, Xiaohong

    2015-06-15

    Studies indicate that mammalian bone formation is initiated at calcium carbonate bioseeds, a process that is driven enzymatically by carbonic anhydrase (CA). We show that amorphous calcium carbonate (ACC) and bicarbonate (HCO3 (-) ) cause induction of expression of the CA in human osteogenic SaOS-2 cells. The mineral deposits formed on the surface of the cells are rich in C, Ca and P. FTIR analysis revealed that ACC, vaterite, and aragonite, after exposure to phosphate, undergo transformation into calcium phosphate. This exchange was not seen for calcite. The changes to ACC, vaterite, and aragonite depended on the concentration of phosphate. The rate of incorporation of phosphate into ACC, vaterite, and aragonite, is significantly accelerated in the presence of a peptide rich in aspartic acid and glutamic acid. We propose that the initial CaCO3 bioseed formation is driven by CA, and that the subsequent conversion to calcium phosphate/calcium hydroxyapatite (exchange of carbonate by phosphate) is a non-enzymatic exchange process. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Preparation and Characterization of Calcium Carbonate Nanoparticles

    NASA Astrophysics Data System (ADS)

    Hassim, Aqilah; Rachmawati, Heni

    2010-10-01

    Taking calcium supplements can reduce the risk of developing osteoporosis, but they are not readily absorbed in the gastrointestinal tract. Nanotechnology is expected to resolve this problem. In this study, we prepared and characterized calcium carbonate nanoparticle to improve the solubility by using bottom-up method. The experiment was done by titrating calcium chloride with sodium carbonate with the addition of polyvinylpyrrolidone (PVP) as stabilizer, using ultra-turrax. Various concentrations of calcium chloride and sodium carbonate as well as various speed of stirring were used to prepare the calcium carbonate nanoparticles. Evaluations studied were including particle size, polydispersity index (PI) and zeta potential with particle analyzer, surface morphology with scanning electron microscope, and saturated solubility. In addition, to test the ability of PVP to prevent particles growth, short stability study was performed by storing nano CaCO3 suspension at room temperature for 2 weeks. Results show that using 8000 rpm speed of stirring, the particle size tends to be bigger with the range of 500-600 nm (PI between 0.2-0.4) whereas with stirring speed of 4000 rpm, the particle size tends to be smaller with 300-400 nm (PI between 0.2-0.4). Stirring speed of 6000 rpm produced particle size within the range of 400-500 nm (PI between 0.2-0.4). SEM photograph shows that particles are monodisperse confirming that particles were physically stable without any agglomeration within 2 weeks storage. Taken together, nano CaCO3 is successfully prepared by bottom-up method and PVP is a good stabilizer to prevent the particle growth.

  5. Platelet adhesion on phosphorus-incorporated tetrahedral amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Liu, Aiping; Zhu, Jiaqi; Liu, Meng; Dai, Zhifei; Han, Xiao; Han, Jiecai

    2008-11-01

    The haemocompatibility of phosphorus-incorporated tetrahedral amorphous carbon (ta-C:P) films, synthesized by filtered cathodic vacuum arc technique with PH 3 as the dopant source, was assessed by in vitro platelet adhesion tests. Results based on scanning electron microscopy and contact angle measurements reveal that phosphorus incorporation improves the wettability and blood compatibility of ta-C film. Our studies may provide a novel approach for the design and synthesis of doped ta-C films to repel platelet adhesion and reduce thrombosis risk.

  6. Ammonia sensitivity of amorphous carbon film/silicon heterojunctions

    SciTech Connect

    Gao Xili; Xue Qingzhong; Hao Lanzhong; Zheng Qingbin; Li Qun

    2007-09-17

    The amorphous carbon film/n-Si (a-C/Si) junctions have been fabricated by magnetron sputtering. The results show that these junctions have good rectifying properties and high ammonia (NH{sub 3}) gas sensitivity. For a given reverse bias voltage, the resistance of the junction can increase by 100 times rapidly when exposed to NH{sub 3} gas. This phenomenon may be attributed to the change of the space charge width of the junction, which is caused by the adsorption of NH{sub 3} gas molecules. This study shows that these a-C/Si junctions have potential application as NH{sub 3} gas detect sensors.

  7. Cathodic deposition of amorphous alloys of silicon, carbon, and fluorine

    SciTech Connect

    Lee, C.H.; Kroger, F.A.

    1982-05-01

    Amorphous silicon containing fluorine and carbon, pure and doped with boron or phosphorus, was deposited cathodically from solutions of K/sub 2/SiF/sub 6/ in acetone with HF. The conditions for optimum deposition were determined, and the deposits were characterized by electron microprobe x-ray emission, electrical conductivity, and infrared absorption. Doping with phosphorus causes a change from p- to n-type semiconductor behavior, with a maximum of resistivity >10/sup 13/ /OMEGA/ cm at the compensation point. 48 refs.

  8. Physicochemical characterization of atorvastatin calcium/ezetimibe amorphous nano-solid dispersions prepared by electrospraying method.

    PubMed

    Jahangiri, Azin; Barzegar-Jalali, Mohammad; Javadzadeh, Yousef; Hamishehkar, Hamed; Adibkia, Khosro

    2016-07-13

    In the present study, electrospraying was applied as a novel method for the fabrication of amorphous nano-solid dispersions (N-SDs) of atorvastatin calcium (ATV), ezetimibe (EZT), and ATV/EZT combination as poorly water-soluble drugs. N-SDs were prepared using polyvinylpyrrolidone K30 as an amorphous carrier in 1:1 and 1:5 drug to polymer ratios and the total solid (including drug and polymer) concentrations of 10 and 20% (w/v). The prepared formulations were further investigated for their morphological, physicochemical, and dissolution properties. Scanning electron microscopy studies indicated that the morphology and diameter of the electrosprayed samples (ESs) were influenced by the solution concentration and drug:polymer ratio, so that an increase in the solution concentration resulted in fiber formation while an increase in the polymer ratio led to enhancement of the particle diameter. Differential scanning calorimetry and X-ray powder diffraction studies together with in vitro dissolution test revealed that the ESs were present in an amorphous form with improved dissolution properties. Infrared spectroscopic studies showed hydrogen-bonding interaction between the drug and polymer in ESs. Since the electrospraying method benefits from the both amorphization and nanosizing effect, this novel approach seems to be an efficient method for the fabrication of N-SDs of poorly water-soluble drugs.

  9. The formation and transformation mechanism of calcium carbonate in water

    SciTech Connect

    Ogino, Takeshi; Suzuki, Toshio; Sawada, Kiyoshi )

    1987-10-01

    High supersaturated solutions of Ca{sup 2+} and CO{sub 3}{sup 2{minus}} ions rapidly precipitate amorphous calcium carbonate, ACC, the logarithmic thermodynamic solubility product of which is about {minus}6.0 at 25{degree}C. The ACC initially formed is transformed to a mixture of several crystalline calcium carbonate polymorphs within several minutes. The transformed polymorphs are vaterite and calcite at low temperature (14 to 30{degree}C), and aragonite and calcite at high temperature (60 to 80{degree}C). At intermediate temperatures (40 to 50{degree}C) the formation of all three polymorphs was observed. Metastable polymorphs are gradually transformed to the stable form, calcite. It takes about 200 min at 25{degree}C and 370 min at 30{degree}C for the complete transformation of vaterite to calcite, and 100-1300 min for that of aragonite to calcite at 60-80{degree}C. At 50{degree}C, vaterite is predominantly transformed at first to aragonite within 60 min, and then the aragonite is transformed to calcite in about 900 min. The results of the change in the ion activity product of the solution and the abundances of the polymorphs strongly suggest that the polymorphic transformation of vaterite and aragonite to calcite takes place through dissolution of the metastable phase and growth of the stable phase, calcite. The rate-determining step of the transformation is the growth of calcite. The relative abundance of vaterite becomes higher at 25{degree}C with increasing concentrations of calcium and carbonate ions in the supersaturated solution. When the ion activity product of the initial supersaturated solution is lower than the solubility product of ACC at 25{degree}c, only vaterite directly precipitates after some induction period. The vaterite crystals formed are free of calcite seeds and the vaterite saturated solutions are stable for several days.

  10. In-situ observation of the transformation of amorphous calcium phosphate to crystalline hydroxyapatite

    NASA Astrophysics Data System (ADS)

    Stammeier, Jessica; Hippler, Dorothee; Mavromatis, Vasileios; Sacher, Stephan; Dietzel, Martin

    2016-04-01

    Amorphous calcium phosphate (Ca3(PO4)2*nH2O; ACP) is often a precursor phase of the mineral (hydroxy-) apatite (Ca5(PO4)3(OH)) that can be formed in natural settings during both authigenic and biogenic mineral formation. Particularly, in the biomineralization process of fish tissue, ACP has shown to be an important transient phase. In solution ACP rapidly transforms into the crystalline phase. The transformation rate highly depends on the physico-chemical conditions of the solution: Ca & P availability, pH and temperature. In natural settings Ca can be provided by different sources: from (1) seawater, (2) porewater, or (3) diagenetically-altered carbonates, whereas local supersaturation of P can be induced by microbial activity. In this study, we performed phosphate precipitation experiments in order to monitor the transformation process of the ACP to crystalline hydroxyapatite (HAP) using in-situ Raman spectroscopy. During the experiments the temperature was kept constant at 20.0 ± 0.01 ° C and pH at 9 ± 0.1. 50 ml of 0.3 CaCl 2H2O was titrated at a rate of 5 ml/min to an equal volume of 0.2 M Na2HPO4. The pH was kept constant by titration of 1 M NaOH. During the experiment samples were taken from the solution and instantly filtered. The obtained solid samples were lyophilized and analyzed with XRD, ATR and SEM. The respective solution samples were analyzed using ion chromatography and ICP OES, coupling the spectroscopic data with detailed solution chemistry data. We observed transformation of ACP to HAP to occur within 14 hours, illustrated in a clear peak shift in Raman spectra from 950 cm-1 to 960 cm-1. The obtained results are discussed in the aspects of distribution of major elements during the formation of phosphates and/or the diagenetic alteration of carbonates to phosphates in geologic settings. Financial support by DFG-FG 736 and NAWI Graz is kindly acknowledged.

  11. Two competitive nucleation mechanisms of calcium carbonate biomineralization in response to surface functionality in low calcium ion concentration solution

    PubMed Central

    Deng, Hua; Wang, Shuo; Wang, Xiumei; Du, Chang; Shen, Xingcan; Wang, Yingjun; Cui, Fuzhai

    2015-01-01

    Four self-assembled monolayer surfaces terminated with –COOH, –OH, –NH2 and –CH3 functional groups are used to direct the biomineralization processes of calcium carbonate (CaCO3) in low Ca2+ concentration, and the mechanism of nucleation and initial crystallization within 12 h was further explored. On −COOH surface, nucleation occurs mainly via ion aggregation mechanism while prenucleation ions clusters may be also involved. On −OH and −NH2 surfaces, however, nucleation forms via calcium carbonate clusters, which aggregate in solution and then are adsorbed onto surfaces following with nucleation of amorphous calcium carbonate (ACC). Furthermore, strongly negative-charged −COOH surface facilitates the direct formation of calcites, and the −OH and −NH2 surfaces determine the formation of vaterites with preferred crystalline orientations. Neither ACC nor crystalline CaCO3 is observed on −CH3 surface. Our findings present a valuable model to understand the CaCO3 biomineralization pathway in natural system where functional groups composition plays a determining role during calcium carbonate crystallization. PMID:26814639

  12. Transparent, superhard amorphous carbon phase from compressing glassy carbon

    NASA Astrophysics Data System (ADS)

    Yao, Mingguang; Xiao, Junping; Fan, Xianhong; Liu, Ran; Liu, Bingbing

    2014-01-01

    Raman spectroscopy has been used to study the transformations of glassy carbon (GC) under high pressure. A GC sphere has been observed to transform into a transparent carbon phase above 33 GPa. The transformation is associated with a change in bonding character of carbon from sp2 to sp3 hybridization and an increase in hardness. The yield strength of the GC sphere reaches a value of 120 GPa at a confining pressure of 62 GPa, which is comparable to that of diamond at ambient conditions. The stress induced by the pressure medium is important for the observed transformations of GC under pressure.

  13. The effect of high calcium milk and casein phosphopeptide-amorphous calcium phosphate on enamel erosion caused by cholinated water.

    PubMed

    Vongsawan, Kadkao; Surarit, Rudee; Rirattanapong, Praphasri

    2010-11-01

    The aim of this study was to determine the effectiveness of high calcium milk and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on enamel erosion caused by chlorinated water. Thirty-six bovine enamel samples without wear or caries 3x4 mm in size were placed in acrylic blocks. All specimens were randomly allocated into 3 groups (n=12/group): CPP-ACP in the form of paste, Anlene concentrated milk and a control (no treatment). All specimens were soaked in chlorinated water (pH =5.0) at room temperature for 72 hours following by soaking in artificial saliva for 30 minutes. Then, microhardness was determined using a microhardness tester. Data were analyzed using a one-way ANOVA and paired t-test. The microhardness value change in the control group was significantly higher than the other groups. No significant differences were seen between the 2 study groups. High calcium milk and CPP-ACP enhanced remineralization of enamel erosion caused by chlorinated water.

  14. Calcium carbonate crystal growth beneath Langmuir monolayers of acidic β-hairpin peptides.

    PubMed

    Gong, Haofei; Yang, Yi; Pluntke, Manuela; Marti, Othmar; Majer, Zsuzsa; Sewald, Norbert; Volkmer, Dirk

    2014-11-28

    Four amphiphilic peptides with designed hairpin structure were synthesized and their monolayers were employed as model systems to study biologically inspired calcium carbonate crystallization. Langmuir monolayers of hairpin peptides were investigated by surface pressure area isotherms, surface potential isotherms, Brewster angle microscopy (BAM), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. A β-hairpin conformation was found for all peptides at the air-water interface although their packing arrangements seem to be different. Crystallization of calcium carbonate under these peptide monolayers was investigated at different surface pressures and growth times both by in situ optical microscopy, BAM and ex situ investigations such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). An amorphous calcium carbonate precursor was found at the initial crystallization stage. The crystallization process occurred in three stages. It starts from the nucleation of amorphous particles being a kinetically controlled process. Crystal nuclei subsequently aggregate to large particles and vaterite crystals start to form inside the amorphous layer, with the monolayer fluidity exerting an important role. The third process includes the re-crystallization of vaterite to calcite, which is thermodynamically controlled by monolayer structural factors including the monolayer flexibility and packing arrangement of the polar headgroups. Thus, the kinetic factors, monolayer fluidity and flexibility as well as structure factors govern the crystal morphology and polymorph distribution simultaneously and synergistically.

  15. A safer disposal of hazardous phosphate coating sludge by formation of an amorphous calcium phosphate matrix.

    PubMed

    Navarro-Blasco, I; Duran, A; Pérez-Nicolás, M; Fernández, J M; Sirera, R; Alvarez, J I

    2015-08-15

    Phosphate coating hazardous wastes originated from the automotive industry were efficiently encapsulated by an acid-base reaction between phosphates present in the sludge and calcium aluminate cement, yielding very inert and stable monolithic blocks of amorphous calcium phosphate (ACP). Two different compositions of industrial sludge were characterized and loaded in ratios ranging from 10 to 50 wt.%. Setting times and compressive strengths were recorded to establish the feasibility of this method to achieve a good handling and a safe landfilling of these samples. Short solidification periods were found and leaching tests showed an excellent retention for toxic metals (Zn, Ni, Cu, Cr and Mn) and for organic matter. Retentions over 99.9% for Zn and Mn were observed even for loadings as high as 50 wt.% of the wastes. The formation of ACP phase of low porosity and high stability accounted for the effective immobilization of the hazardous components of the wastes.

  16. Arrangement techniques of proteins and cells using amorphous calcium phosphate nanofiber scaffolds

    NASA Astrophysics Data System (ADS)

    Nonoyama, Takayuki; Kinoshita, Takatoshi; Higuchi, Masahiro; Nagata, Kenji; Tanaka, Masayoshi; Kamada, Mari; Sato, Kimiyasu; Kato, Katsuya

    2012-12-01

    We demonstrate arrangement techniques of proteins and cells using an amorphous calcium phosphate (ACP) nanofiber scaffold. It is well known that protein andosteoblastic cell are preferably adsorbed onto ACP surface. The ACP nanofiber scaffold was prepared by calcium phosphate mineralization on a polypeptide monolayer-coated mica substrate, and ACP nanofibers were oriented unidirectionaly. In a protein system, the ACP nanofiber scaffold was soaked in a fluorescein isothiocyanate conjugated immunoglobulin G (IgG-FITC) aqueous solution. From fluorescence microscopic measurement, the adsorbed IgG-FITC was highly confined and arranged on the ACP nanofiber. In a cell system, a mouse osteoblast-like cell (MC3T3-E1) behavior on the ACP nanofiber scaffold was observed. The cell was elongated unidirectionaly, and its cytoskeletal shape showed high aspect ratio. These results are clearly different from an ACP bulk template or bare mica substrate, and the arrangement technique enable to fabricate a fine-tuned biomaterial template.

  17. Proton and deuteron nuclear magnetic resonance studies of amorphous hydrogenated silicon, carbon, and carbon alloys

    NASA Astrophysics Data System (ADS)

    Kernan, Mary Jane Wurth

    Despite the profound influence of semiconductors and the changes they have produced, many fundamental questions remain unanswered. We have used proton and deuteron nuclear magnetic resonance (NMR) to explore the role of hydrogens in amorphous silicon and amorphous carbon and carbon alloy films. In the carbon films, dipolar filtering techniques reveal a two-component shifted lineshape in the proton NMR spectra and deuteron magnetic resonance (DMR) data demonstrate a feedstock gas dependence in the film deposition process. In these measurements, DMR is used to examine the effect of hydrogen on the photovoltaic properties of amorphous silicon thin films. We have measured the effects of photoillumination on amorphous silicon, particularly with respect to the process of metastable defect formation (the Staebler-Wronski effect). The creation and passivation of dangling silicon bonds is observed and quantified. We report large-scale light-induced atomic rearrangements which produce shifts and broadenings of the DMR lineshapes. The deuterium NMR lineshape component most affected by atomic rearrangements is a broad central feature which is shown to be molecular in origin. This spectral feature includes hydrogens trapped and immobile on surfaces created by strains and dislocations in the material. Narrowing of the lineshape at elevated temperatures indicates motion with a small activation energy. The substantial population represented by this feature is shown to account for at least 15% of the total hydrogens in high-quality amorphous silicon samples.

  18. Stress Writing Textured Graphite Conducting Wires/Patterns in Insulating Amorphous Carbon Matrix as Interconnects.

    PubMed

    Wang, Ding-Shiang; Chang, Shou-Yi; Chen, Tai-Sheng; Chou, Tung-Huan; Huang, Yi-Ching; Wu, Jin-Bao; Leu, Ming-Sheng; Lai, Hong-Jen

    2017-08-29

    This study reports a mechanical stress-based technique that involves scratching or imprinting to write textured graphite conducting wires/patterns in an insulating amorphous carbon matrix for potential use as interconnects in future carbonaceous circuits. With low-energy post-annealing below the temperature that is required for the thermal graphitization of amorphous carbon, the amorphous carbon phase only in the mechanically stressed regions transforms into a well aligned crystalline graphite structure with a low electrical resistivity of 420 μΩ-cm, while the surrounding amorphous carbon matrix remains insulating. Micro-Raman spectra with obvious graphitic peaks and high-resolution transmission electron microscopic observations of clear graphitic lattice verified the localized phase transformation of amorphous carbon into textured graphite exactly in the stressed regions. The stress-induced reconstruction of carbon bonds to generate oriented graphitic nuclei is believed to assist in the pseudo-self-formation of textured graphite during low-temperature post annealing.

  19. Creation and formation mechanism of new carbon phases constructed by amorphous carbon

    NASA Astrophysics Data System (ADS)

    Yao, Mingguang; Cui, Wen; Liu, Bingbing

    Our recent effort is focusing on the creation of new hard/superhard carbon phases constructed by disordered carbons or amorphous carbon clusters under high pressure. We showed that the pressure-induced amorphous hard carbon clusters from collapsed fullerenes can be used as building blocks (BBs) for constructing novel carbon structures. This new strategy has been verified by compressing a series of intercalated fullerides, pre-designed by selecting various dopants with special features. We demonstrate that the boundaries of the amorphous BBs are mediated by intercalated dopants and several new superhard materials have been prepared. We also found that the dopant-mediated BBs can be arranged in either ordered or disordered structures, both of which can be hard enough to indent the diamond anvils. The hardening mechanisms of the new phases have also been discussed. For the glassy carbon (GC) constructructed by disordered fullerene-like nanosized fragments, we also found that these disordered fragments can bond and the compressed GC transformed into a transparent superhard phase. Such pressure-induced transformation has been discovered to be driven by a novel mechanism (unpublished). By understanding the mechanisms we can clarify the controversial results on glassy carbon reported recently. The authors would like to thank the financial support from the National Natural Science Foundation of China (No. 11474121, 51320105007).

  20. The synergic role of collagen and citrate in stabilizing amorphous calcium phosphate precursors with platy morphology.

    PubMed

    Delgado-López, José Manuel; Bertolotti, Federica; Lyngsø, Jeppe; Pedersen, Jan Skov; Cervellino, Antonio; Masciocchi, Norberto; Guagliardi, Antonietta

    2017-02-01

    Bioinspired in vitro collagen mineralization experiments have been performed in the presence of citrate and the combined role of the two bone organic matrix components in controlling mineral formation was investigated for the first time. Mineralized and non-mineralized collagen fibrils have been in depth characterized by combining small- and wide-angle X-ray scattering (SAXS/WAXS) techniques with Atomic Force Microscopy (AFM) imaging. A synergic effect of collagen and citrate in driving the formation of long-term stable amorphous calcium phosphate (ACP) nanoparticles with platy morphology was found. AFM images on mineralized collagen fibrils revealed that some of the ACP nanoparticles were deposited on the intramolecular nanoscopic holes of collagen fibrils. Citrate is an important component of the bone organic matrix but its specific role in bone mineralization is presently unclear. In this work, bioinspired in vitro collagen mineralization experiments in the presence of citrate have been carried out and the combined role of collagen and citrate in controlling mineral formation has been addressed for the first time. Through X-ray scattering and Atomic Force Microscopy characterizations on mineralized and non-mineralized collagen fibrils, we have found that citrate in synergy with collagen stabilizes an amorphous calcium phosphate (ACP) phase with platy morphology over one week and controls its deposition on collagen fibrils. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  1. Structural analysis of amorphous carbon films by spectroscopic ellipsometry, RBS/ERDA, and NEXAFS

    NASA Astrophysics Data System (ADS)

    Zhou, XiaoLong; Suzuki, Tsuneo; Nakajima, Hideki; Komatsu, Keiji; Kanda, Kazuhiro; Ito, Haruhiko; Saitoh, Hidetoshi

    2017-05-01

    The structural analysis of amorphous carbon films is not only the premise of their unique properties applied in the industrial fields but also the indispensable element on their classification. In this letter, we refurbished the classification of amorphous carbon films based on the optical constants in terms of the refractive index (n) and the extinction coefficient (k). In the selected photon energy range, we defined the maximum of n (En-max) and k at a value more than 10-4 (Ek) to explore the relationship between different classification schemes for amorphous carbon films deposited by different techniques. We found that Ek and En-max of the deposited amorphous carbon films have an exponential relationship with the hydrogen contents. Thus, the spectroscopic ellipsometry analysis can also be used as one of the effective methods for the structural evaluation of the amorphous carbon films.

  2. Structure-property relations in amorphous carbon for photovoltaics

    SciTech Connect

    Risplendi, Francesca; Cicero, Giancarlo; Bernardi, Marco; Grossman, Jeffrey C.

    2014-07-28

    Carbon is emerging as a material with great potential for photovoltaics (PV). However, the amorphous form (a-C) has not been studied in detail as a PV material, even though it holds similarities with amorphous Silicon (a-Si) that is widely employed in efficient solar cells. In this work, we correlate the structure, bonding, stoichiometry, and hydrogen content of a-C with properties linked to PV performance such as the electronic structure and optical absorption. We employ first-principles molecular dynamics and density functional theory calculations to generate and analyze a set of a-C structures with a range of densities and hydrogen concentrations. We demonstrate that optical and electronic properties of interest in PV can be widely tuned by varying the density and hydrogen content. For example, sunlight absorption in a-C films can significantly exceed that of a same thickness of a-Si for a range of densities and H contents in a-C. Our results highlight promising features of a-C as the active layer material of thin-film solar cells.

  3. A facile magnesium-containing calcium carbonate biomaterial as potential bone graft.

    PubMed

    He, Fupo; Zhang, Jing; Tian, Xiumei; Wu, Shanghua; Chen, Xiaoming

    2015-12-01

    The calcium carbonate is the main composition of coral which has been widely used as bone graft in clinic. Herein, we readily prepared novel magnesium-containing calcium carbonate biomaterials (MCCs) under the low-temperature conditions based on the dissolution-recrystallization reaction between unstable amorphous calcium carbonate (ACC) and metastable vaterite-type calcium carbonate with water involved. The content of magnesium in MCCs was tailored by adjusting the proportion of ACC starting material that was prepared using magnesium as stabilizer. The phase composition of MCCs with various amounts of magnesium was composed of one, two or three kinds of calcium carbonates (calcite, aragonite, and/or magnesian calcite). The different MCCs differed in topography. The in vitro degradation of MCCs accelerated with increasing amount of introduced magnesium. The MCCs with a certain amount of magnesium not only acquired higher compressive strength, but also promoted in vitro cell proliferation and osteogenic differentiation. Taken together, the facile MCCs shed light on their potential as bone graft. Copyright © 2015 Elsevier B.V. All rights reserved.

  4. Synthesis, characterization, and in-vitro cytocompatibility of amorphous β-tri-calcium magnesium phosphate ceramics.

    PubMed

    Singh, Satish S; Roy, Abhijit; Lee, Boeun; Banerjee, Ipsita; Kumta, Prashant N

    2016-10-01

    Biphasic mixtures of crystalline β-tricalcium magnesium phosphate (β-TCMP) and an amorphous calcium magnesium phosphate have been synthesized and reported to support enhanced hMSC differentiation in comparison to β-tricalcium phosphate (β-TCP) due to the release of increased amounts of bioactive ions. In the current study, completely amorphous β-TCMP has been synthesized which is capable of releasing increased amounts of Mg(2+) and PO4(3-) ions, rather than a biphasic mixture as earlier reported. The amorphous phase formed was observed to crystallize between temperatures of 400-600°C. The scaffolds prepared with amorphous β-TCMP were capable of supporting enhanced hMSC proliferation and differentiation in comparison to commercially available β-TCP. However, a similar gene expression of mature osteoblast markers, OCN and COL-1, in comparison to biphasic β-TCMP was observed. To further study the role of Mg(2+) and PO4(3-) ions in regulating hMSC osteogenic differentiation, the capability of hMSCs to mineralize in growth media supplemented with Mg(2+) and PO4(3-) ions was studied. Interestingly, 5mM PO4(3-) supported mineralization while the addition of 5mM Mg(2+) to 5mM PO4(3-) inhibited mineralization. It was therefore concluded that the release of Ca(2+) ions from β-TCMP scaffolds also plays a role in regulating osteogenic differentiation on these scaffolds and it is noted that further work is required to more accurately determine the exact role of Mg(2+) in regulating hMSC osteogenic differentiation. Copyright © 2016 Elsevier B.V. All rights reserved.

  5. Presence of Amorphous Carbon Nanoparticles in Food Caramels

    NASA Astrophysics Data System (ADS)

    Palashuddin, Sk; Jaiswal, Amit; Paul, Anumita; Ghosh, Siddhartha Sankar; Chattopadhyay, Arun

    2012-04-01

    We report the finding of the presence of carbon nanoparticles (CNPs) in different carbohydrate based food caramels, viz. bread, jaggery, sugar caramel, corn flakes and biscuits, where the preparation involves heating of the starting material. The CNPs were amorphous in nature; the particles were spherical having sizes in the range of 4-30 nm, depending upon the source of extraction. The results also indicated that particles formed at higher temperature were smaller than those formed at lower temperature. Excitation tuneable photoluminescence was observed for all the samples with quantum yield (QY) 1.2, 0.55 and 0.63%, for CNPs from bread, jaggery and sugar caramels respectively. The present discovery suggests potential usefulness of CNPs for various biological applications, as the sources of extraction are regular food items, some of which have been consumed by humans for centuries, and thus they can be considered as safe.

  6. Presence of Amorphous Carbon Nanoparticles in Food Caramels

    PubMed Central

    Sk, Md Palashuddin; Jaiswal, Amit; Paul, Anumita; Ghosh, Siddhartha Sankar; Chattopadhyay, Arun

    2012-01-01

    We report the finding of the presence of carbon nanoparticles (CNPs) in different carbohydrate based food caramels, viz. bread, jaggery, sugar caramel, corn flakes and biscuits, where the preparation involves heating of the starting material. The CNPs were amorphous in nature; the particles were spherical having sizes in the range of 4–30 nm, depending upon the source of extraction. The results also indicated that particles formed at higher temperature were smaller than those formed at lower temperature. Excitation tuneable photoluminescence was observed for all the samples with quantum yield (QY) 1.2, 0.55 and 0.63%, for CNPs from bread, jaggery and sugar caramels respectively. The present discovery suggests potential usefulness of CNPs for various biological applications, as the sources of extraction are regular food items, some of which have been consumed by humans for centuries, and thus they can be considered as safe. PMID:22540029

  7. Structural and electronic properties of a tetrahedral amorphous carbon surface

    NASA Astrophysics Data System (ADS)

    Dong, Jianjun; Drabold, D. A.

    1997-03-01

    We present ab initio studies of a model of tetrahedral amorphous carbon (ta-C) surface. Our methodology is LDA (with Harris functional and local basis) molecular dynamics simulations. The surface is modeled by a 216 atom slab supercell. Several candidate slabs are constructed by starting with the DTW model (B.R. Djordjevic, M.F. Thorpe and F. Wooten, Phys. Rev. B 52) 5685 (1995) and applying various simulated heating/quenching cycles. We analyze the structural and electronic properties of the surface , with special attention forcused on the electronic signatures of surface structural defects. Preliminary results indicate that the surface layer significantly graphitizes, and many surface gap states are present in the electronic density of states.

  8. Adsorption ability comparison of plasma proteins on amorphous carbon surface

    NASA Astrophysics Data System (ADS)

    Takeda, Aoi; Akasaka, Hiroki; Ohshio, Shigeo; Toda, Ikumi; Nakano, Masayuki; Saitoh, Hidetoshi

    2012-11-01

    To understand why amorphous carbon (a-C:H) film shows antithrombogenicity, an adsorption ability of plasma proteins on a-C:H surface was investigated. Protein adsorption is the initial process of clot formation. The protein adsorption ability on a-C:H film surface was compared by the detection using the surface plasmon resonance (SPR) phenomenon to estimate the protein adsorption. The protein adsorption abilities of a fibrinogen (Fib) and a human γ-globulin (HGG) were estimated by the SPR method using a multilayer structure of a-C:H/Au/Cr/glass. Although the adsorption of HGG for a-C:H was saturated at 32 μM in HGG concentration, the adsorption of Fib was not saturated under the detection limit of this method. These results indicated that the adsorption ability to the a-C:H film surface of Fib was higher than HGG.

  9. Amorphous carbon buffer layers for separating free gallium nitride films

    NASA Astrophysics Data System (ADS)

    Altakhov, A. S.; Gorbunov, R. I.; Kasharina, L. A.; Latyshev, F. E.; Tarala, V. A.; Shreter, Yu. G.

    2016-11-01

    The possibility of using amorphous diamond-like carbon (DLC) films for self-separation of gallium nitride (GaN) layers grown by hydride vapor-phase epitaxy has been analyzed. DLC films have been synthesized by plasma-enhanced chemical vapor deposition under low pressure on sapphire (Al2O3) substrates with a (0001) crystallographic orientation. The samples have been studied by the methods of Raman scattering and X-ray diffraction analysis. It is shown that thin DLC films affect only slightly the processes of nucleation and growth of gallium nitride films. Notably, the strength of the "GaN film-Al2O3" substrate interface decreases, which facilitates separation of the GaN layers.

  10. Heat treatment of cathodic arc deposited amorphous hard carbon films

    SciTech Connect

    Anders, S.; Ager, J.W. III; Brown, I.G.

    1997-02-01

    Amorphous hard carbon films of varying sp{sup 2}/sp{sup 3} fractions have been deposited on Si using filtered cathodic are deposition with pulsed biasing. The films were heat treated in air up to 550 C. Raman investigation and nanoindentation were performed to study the modification of the films caused by the heat treatment. It was found that films containing a high sp{sup 3} fraction sustain their hardness for temperatures at least up to 400 C, their structure for temperatures up to 500 C, and show a low thickness loss during heat treatment. Films containing at low sp{sup 3} fraction graphitize during the heat treatment, show changes in structure and hardness, and a considerable thickness loss.

  11. Properties of nitrogen-doped amorphous hydrogenated carbon films

    SciTech Connect

    Amir, O.; Kalish, R. )

    1991-11-01

    Nitrogen-containing hydrogenated amorphous carbon (a-C:H(N)) films are grown from a dc plasma of a N{sub 2}+C{sub 6}H{sub 6} gas mixture. By varying the N{sub 2} fraction in this mixture films with different amounts of N are produced. The actual amount of nitrogen in the {ital a}-C:H(N) films is determined by nuclear reaction analysis and by Auger electron spectroscopy profiling. The nitrogen concentration in the films grows exponentially with nitrogen content in the gas mixture reaching concentrations as high as 10 at.% for the films grown from a N{sub 2}-rich gas mixture (N{sub 2}/(N{sub 2}+C{sub 6}H{sub 6})=0.75). The electrical and structural properties of the N{sub 2}-doped films are studied by performing electrical conductivity, thermopower (TP), optical absorption, and electron-paramagnetic resonance measurements. Films with low ({lt}1 at.%) nitrogen content exhibit fairly high resistivities, have an optical gap of 1 eV, are rich with dangling bonds (5{times}10{sup 20} cm{sup {minus}3}) and their thermopower is positive and in the mV/K regime, indicating conductivity in the valence band tail. However, with increased N doping, the resistivity decreases and the optical band gap shrinks and reached zero for the highest doped film. The TPs for films containing more than 1 at.% are in the {mu}V/K range, indicating hopping conductivity around the Fermi level. The results of all measurements are consistent with the model of Robertson for the electrical structure of amorphous hydrogenated carbon and for the proposed doping mechanism in this material.

  12. Oxidation of fluorinated amorphous carbon (a-CF(x)) films.

    PubMed

    Yun, Yang; Broitman, Esteban; Gellman, Andrew J

    2010-01-19

    Amorphous fluorinated carbon (a-CF(x)) films have a variety of potential technological applications. In most such applications these films are exposed to air and undergo partial surface oxidation. X-ray photoemission spectroscopy has been used to study the oxidation of fresh a-CF(x) films deposited by magnetron sputtering. The oxygen sticking coefficient measured by exposure to low pressures (<10(-3) Torr) of oxygen at room temperature is on the order of S approximately 10(-6), indicating that the surfaces of these films are relatively inert to oxidation when compared with most metals. The X-ray photoemission spectra indicate that the initial stages of oxygen exposure (<10(7) langmuirs) result in the preferential oxidation of the carbon atoms with zero or one fluorine atom, perhaps because these carbon atoms are more likely to be found in configurations with unsaturated double bonds and radicals than carbon atoms with two or three fluorine atoms. Exposure of the a-CF(x) film to atmospheric pressures of air (effective exposure of 10(12) langmuirs to O(2)) results in lower levels of oxygen uptake than the low pressure exposures (<10(7) langmuirs). It is suggested that this is the result of oxidative etching of the most reactive carbon atoms, leaving a relatively inert surface. Finally, low pressure exposures to air result in the adsorption of both nitrogen and oxygen onto the surface. Some of the nitrogen adsorbed on the surface at low pressures is in a reversibly adsorbed state in the sense that subsequent exposure to low pressures of O(2) results in the displacement of nitrogen by oxygen. Similarly, when an a-CF(x) film oxidized in pure O(2) is exposed to low pressures of air, some of the adsorbed oxygen is displaced by nitrogen. It is suggested that these forms of nitrogen and oxygen are bound to free radical sites in the film.

  13. Research Update: Direct conversion of amorphous carbon into diamond at ambient pressures and temperatures in air

    SciTech Connect

    Narayan, Jagdish Bhaumik, Anagh

    2015-10-01

    We report on fundamental discovery of conversion of amorphous carbon into diamond by irradiating amorphous carbon films with nanosecond lasers at room-temperature in air at atmospheric pressure. We can create diamond in the form of nanodiamond (size range <100 nm) and microdiamond (>100 nm). Nanosecond laser pulses are used to melt amorphous diamondlike carbon and create a highly undercooled state, from which various forms of diamond can be formed upon cooling. The quenching from the super undercooled state results in nucleation of nanodiamond. It is found that microdiamonds grow out of highly undercooled state of carbon, with nanodiamond acting as seed crystals.

  14. Polymorphs calcium carbonate on temperature reaction

    SciTech Connect

    Chong, Kai-Yin; Chia, Chin-Hua; Zakaria, Sarani

    2014-09-03

    Calcium carbonate (CaCO{sub 3}) has three different crystal polymorphs, which are calcite, aragonite and vaterite. In this study, effect of reaction temperature on polymorphs and crystallite structure of CaCO{sub 3} was investigated. X-ray powder diffraction (XRD), fourier transform infrared (FTIR), and variable pressure scanning electron microscope (VPSEM) were used to characterize the obtained CaCO{sub 3} particles. The obtained results showed that CaCO{sub 3} with different crystal and particle structures can be formed by controlling the temperature during the synthesis process.

  15. Clonorcis sinensis eggs are associated with calcium carbonate gallbladder stones.

    PubMed

    Qiao, Tie; Ma, Rui-hong; Luo, Zhen-liang; Yang, Liu-qing; Luo, Xiao-bing; Zheng, Pei-ming

    2014-10-01

    Calcium carbonate gallbladder stones were easily neglected because they were previously reported as a rare stone type in adults. The aim of this study was to investigate the relationship between calcium carbonate stones and Clonorchis sinensis infection. A total of 598 gallbladder stones were studied. The stone types were identified by FTIR spectroscopy. The C. sinensis eggs and DNA were detected by microscopic examination and real-time fluorescent PCR respectively. And then, some egg-positive stones were randomly selected for further SEM examination. Corresponding clinical characteristics of patients with different types of stones were also statistically analyzed. The detection rate of C. sinensis eggs in calcium carbonate stone, pigment stone, mixed stone and cholesterol stone types, as well as other stone types was 60%, 44%, 36%, 6% and 30%, respectively, which was highest in calcium carbonate stone yet lowest in cholesterol stone. A total of 182 stones were egg-positive, 67 (37%) of which were calcium carbonate stones. The C. sinensis eggs were found adherent to calcium carbonate crystals by both light microscopy and scanning electron microscopy. Patients with calcium carbonate stones were mainly male between the ages of 30 and 60, the CO2 combining power of patients with calcium carbonate stones were higher than those with cholesterol stones. Calcium carbonate gallbladder stones are not rare, the formation of which may be associated with C. sinensis infection. Copyright © 2014 Elsevier B.V. All rights reserved.

  16. Calcium content of different compositions of gallstones and pathogenesis of calcium carbonate gallstones.

    PubMed

    Yu, Ji-Kuen; Pan, Huichin; Huang, Shing-Moo; Huang, Nan-Lan; Yao, Chung-Chin; Hsiao, Kuang-Ming; Wu, Chew-Wun

    2013-01-01

    Our aim was to investigate the calcium content of different gallstone compositions and the pathogenic mechanisms of calcium carbonate gallstones. Between August 2001 and July 2007, gallstones from 481 patients, including 68 calcium carbonate gallstones, were analyzed for total calcium content. Gallbladder bile samples from 33 cases and six controls were analyzed for pH, carbonate anion level, free-ionized calcium concentration and saturation index for calcium carbonate. Total calcium content averaged 75.6 %, 11.8 %, and 4.2 % for calcium carbonate, calcium bilirubinate and cholesterol gallstones. In 29.4 % of patients, chronic and/or intermittent cystic duct obstructions were caused by polypoid lesions in the neck region and 70.6 % were caused by stones. A total of 82 % of patients had chronic low-grade inflammation of the gallbladder wall and 18.0 % had acute inflammatory exacerbations. In the bile, we found the mean pH, mean carbonate anion, free-ionized calcium concentrations, and mean saturation index for calcium carbonate to be elevated in comparison to controls. From our study, we found chronic and/or intermittent cystic duct obstructions and low-grade GB wall inflammation lead to GB epithelium hydrogen secretion dysfunction. Increased calcium ion efflux into the GB lumen combined with increased carbonate anion presence increases SI_CaCO(3) from 1 to 22.4. Thus, in an alkaline milieu with pH 7.8, calcium carbonate begins to aggregate and precipitate. Copyright © 2012. Published by Elsevier B.V.

  17. Preparation and fluorescence property of red-emitting Eu{sup 3+}-activated amorphous calcium silicate phosphor

    SciTech Connect

    Kojima, Yoshiyuki; Kamei, Shinnosuke; Nishimiya, Nobuyuki

    2010-02-15

    This paper describes the energy efficient synthesis of a red-emitting Eu{sup 3+}-activated amorphous calcium silicate phosphor produced by heating a Eu{sup 3+}-activated calcium silicate hydrate phosphor. Concentration quenching of the Eu{sup 3+}-activated calcium silicate hydrate phosphor was not observed and the emission intensity did not decrease up to a Eu/(Ca+Eu) atomic ratio of 0.46. Heating of the Eu{sup 3+}-activated calcium silicate hydrate (Eu/(Ca+Eu) atomic ratio = 0.32) phosphor produced an amorphous Eu{sup 3+}-activated calcium silicate phosphor, which had a maximum emission intensity at 870 {sup o}C and emitted in the red under near-ultraviolet irradiation (395 nm). The emission intensity of the Eu{sup 3+}-activated amorphous calcium silicate phosphor was about half that of a commercial BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor, and shows great potential for application in white light-emitting diodes.

  18. Physicochemical properties and oral bioavailability of amorphous atorvastatin hemi-calcium using spray-drying and SAS process.

    PubMed

    Kim, Jeong-Soo; Kim, Min-Soo; Park, Hee Jun; Jin, Shun-Ji; Lee, Sibeum; Hwang, Sung-Joo

    2008-07-09

    The objective of the study was to prepare amorphous atorvastatin hemi-calcium using spray-drying and supercritical antisolvent (SAS) process and evaluate its physicochemical properties and oral bioavailability. Atorvastatin hemi-calcium trihydrate was transformed to anhydrous amorphous form by spray-drying and SAS process. With the SAS process, the mean particle size and the specific surface area of amorphous atorvastatin were drastically changed to 68.7+/-15.8nm, 120.35+/-1.40m2/g and 95.7+/-12.2nm, 79.78+/-0.93m2/g from an acetone solution and a tetrahydrofuran solution, respectively and appeared to be associated with better performance in apparent solubility, dissolution and pharmacokinetic studies, compared with unprocessed crystalline atorvastatin. Oral AUC0-8h values in SD rats for crystalline and amorphous atorvastatin were as follow: 1121.4+/-212.0ngh/mL for crystalline atorvastatin, 3249.5+/-406.4ngh/mL and 3016.1+/-200.3ngh/mL for amorphous atorvastatin from an acetone solution and a tetrahydrofuran solution with SAS process, 2227.8+/-274.5 and 2099.9+/-339.2ngh/mL for amorphous atorvastatin from acetone and tetrahydrofuran with spray-drying. The AUCs of all amorphous atorvastatin significantly increased (P<0.05) compared with crystalline atorvastatin, suggesting that the enhanced bioavailability was attributed to amorphous nature and particle size reduction. In addition, the SAS process exhibits better bioavailability than spray-drying because of particle size reduction with narrow particle size distribution. It was concluded that physicochemical properties and bioavailability of crystalline atorvastatin could be improved by physical modification such as particle size reduction and generation of amorphous state using spray-drying and SAS process. Further, SAS process was a powerful methodology for improving the physicochemical properties and bioavailability of atorvastatin.

  19. Sputtering deposition and characterization of ultrathin amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Lu, Wei

    1999-11-01

    This dissertation focuses on experimental investigations of ultrathin, ultrasmooth amorphous carbon (a-C) films deposited on Si(100) substrates by radio frequency (RF) sputtering and characterization of the nanomechanical and nanotribological properties and thermal stability of the films. Ultrathin a-C films of thickness 5--100 nm and typical root-mean-square roughness of 0.15--1 nm were deposited on ultrasmooth Si(100) substrates using pure argon as the sputtering gas. A low-pressure RF argon discharge model was used to analyze the plasma parameters in the film growth environment. These plasma parameters correlate the deposition conditions with the film growth processes. Atomic force microscopy (AFM) and surface force microscopy (SFM) were used to characterize the nanomechanical and nanotribological properties of the a-C films. X-ray photoelectron spectroscopy (XPS) was used to investigate the compositions and microstructures of the films. Sputter-etching measurements of the a-C films by energetic argon ion bombardment were used to study the surface binding energy of carbon atoms in a-C films deposited under different conditions. The dependence of film properties on deposition conditions was studied, and relations between nanomechanical and nanotribological properties were discussed in terms of a modified deformation index. The deformation and nanotribology mechanisms of the a-C films were compared with those of other films, such as TiC and Cr films (both 100 nm thick), and bulk Si(100). Reactive RF sputtering of nitrogenated amorphous carbon (a-CNx) films was investigated by introducing nitrogen into the a-C films during film growth by using an argon-nitrogen gas mixture as the sputtering gas. The alloying effect of nitrogen on the film growth and properties, such as hardness and surface energy, was studied and interpreted in terms of the changes in the plasma environment induced due to differences in the composition of the sputtering gas mixture. The thermal

  20. Scuffing performance of amorphous carbon during dry-sliding contact.

    SciTech Connect

    Alzoubi, M. F.; Ajayi, O. O.; Woodford, J. B.; Erdemir, A.; Fenske, G. R.; Energy Technology

    2001-10-01

    Scuffing is a major problem that limits the life and reliability of sliding tribo-components. When scuffing occurs, friction force rises sharply and is accompanied by an increase in noise and vibration; severe wear and plastic deformation also occur on the damaged surface. Attempts have been made over the years to combat scuffing by enhancing the surface properties of the machine elements, and by methods involving lubricant formulation and coating application. In this study, the authors evaluated the scuffing performance of an amorphous, near-frictionless carbon (NFC) coating that provides super-low friction under dry sliding conditions. The test configuration used a ball-on-flat contact in reciprocating sliding. The coating was deposited on HI3 steel. An uncoated 52100 steel ball was tested against various coated flats in room air. Compared to uncoated surfaces, the carbon coating increased the scuffing resistance of the sliding surfaces by two orders of magnitude. Microscopic analysis shows that scuffing occurred on coaled surfaces only if the coating had been completely removed. It appears that depending on coating type, the authors observed that coating failure occurs before scuffing failure by one of two distinct mechanisms: the coating failed in a brittle manner and by spoiling, or by gradual wear.

  1. Calcium and Oxygen Isotopic Composition of Calcium Carbonates

    NASA Astrophysics Data System (ADS)

    Niedermayr, Andrea; Eisenhauer, Anton; Böhm, Florian; Kisakürek, Basak; Balzer, Isabelle; Immenhauser, Adrian; Jürgen Köhler, Stephan; Dietzel, Martin

    2016-04-01

    Different isotopic systems are influenced in multiple ways corresponding to the crystal structure, dehydration, deprotonation, adsorption, desorption, isotope exchange and diffusion processes. In this study we investigated the structural and kinetic effects on fractionation of stable Ca- and O-isotopes during CaCO3 precipitation. Calcite, aragonite and vaterite were precipitated using the CO2 diffusion technique[1]at a constant pH of 8.3, but various temperatures (6, 10, 25 and 40° C) and precipitation rates R (101.5 to 105 μmol h-1 m-2). The calcium isotopic fractionation between solution and vaterite is lower (Δ44/40Ca= -0.10 to -0.55 ‰) compared to calcite (-0.69 to -2.04 ‰) and aragonite (-0.91 to -1.55 ‰). In contrast the fractionation of oxygen isotopes is highest for vaterite (32.1 ‰), followed by aragonite (29.2 ‰) and calcite (27.6 ‰) at 25° C and equilibrium. The enrichment of 18O vs. 16O in all polymorphs decreases with increasing precipitation rate by around -0.7 ‰ per log(R). The calcium isotopic fractionation between calcite/ vaterite and aqueous Ca2+ increases with increasing precipitation rate by ˜0.45 ‰ per log(R) and ˜0.1 ‰ per log(R) at 25° C and 40° C, respectively. In contrast the fractionation of Ca-isotopes between aragonite and aqueous Ca2+ decreases with increasing precipitation rates. The large enrichment of 18O vs. 16O isotopes in carbonates is related to the strong bond of oxygen to the small and highly charged C4+-ion. In contrast equilibrium isotopic fractionation between solution and calcite or vaterite is nearly zero as the Ca-O bond length is similar for calcite, vaterite and the hydrated Ca. Aragonite incorporates preferentially the lighter 40Ca isotope as it has very large Ca-O bonds in comparison to the hydrated Ca. At the crystal surface the lighter 40Ca isotopes are preferentially incorporated as dehydration and diffusion of lighter isotopes are faster. Consequently, the surface becomes enriched in 40

  2. Calcium and calcium isotope changes during carbon cycle perturbations at the end-Permian

    NASA Astrophysics Data System (ADS)

    Komar, N.; Zeebe, R. E.

    2016-01-01

    Negative carbon and calcium isotope excursions, as well as climate shifts, took place during the most severe mass extinction event in Earth's history, the end-Permian (˜252 Ma). Investigating the connection between carbon and calcium cycles during transient carbon cycle perturbation events, such as the end-Permian, may help resolve the intricacies between the coupled calcium-carbon cycles, as well as provide a tool for constraining the causes of mass extinction. Here we identify the deficiencies of a simplified calcium model employed in several previous studies, and we demonstrate the importance of a fully coupled carbon cycle model when investigating the dynamics of carbon and calcium cycling. Simulations with a modified version of the Long-term Ocean-atmosphere-Sediment CArbon cycle Reservoir model, which includes a fully coupled carbon-calcium cycle, indicate that increased weathering rates and ocean acidification (potentially caused by Siberian Trap volcanism) are not capable of producing trends observed in the record, as previously claimed. Our model results suggest that combined effects of carbon input via Siberian Trap volcanism (12,000 Pg C), the cessation of biological carbon export, and variable calcium isotope fractionation (due to a change in the seawater carbonate ion concentration) represents a more plausible scenario. This scenario successfully reconciles δ13C and δ44Ca trends observed in the sediment record, as well as the proposed warming of >6°C.

  3. Polymerization shrinkage and stress development in amorphous calcium phosphate/urethane dimethacrylate polymeric composites

    PubMed Central

    Antonucci, J.M.; Regnault, W. F.; Skrtic, D.

    2010-01-01

    This study explores how substituting a new high molecular mass oligomeric poly(ethylene glycol) extended urethane dimethacrylate (PEG-U) for 2-hydroxyethyl methacrylate (HEMA) in photo-activated urethane dimethacrylate (UDMA) resins affects degree of vinyl conversion (DC), polymerization shrinkage (PS), stress development (PSSD) and biaxial flexure strength (BFS) of their amorphous calcium phosphate (ACP) composites. The composites were prepared from four types of resins (UDMA, PEG-U, UDMA/HEMA and UDMA/PEG-U) and zirconia-hybridized ACP. Introducing PEG-U improved DC while not adversely affecting PS, PSSD and the BFS of composites. This improvement in DC is attributed to the long, more flexible structure between the vinyl groups of PEG-U and its higher molecular mass compared to poly(HEMA). The results imply that PEG-U has the potential to serve as an alternative to HEMA in dental and other biomedical applications. PMID:20169007

  4. Microstructure of amorphous aluminum hydroxide in belite-calcium sulfoaluminate cement

    SciTech Connect

    Song, Fei; Yu, Zhenglei; Yang, Fengling; Lu, Yinong Liu, Yunfei

    2015-05-15

    Belite-calcium sulfoaluminate (BCSA) cement is a promising low-CO{sub 2} alternative to ordinary Portland cement. Herein, aluminum hydroxide (AH{sub 3}), the main amorphous hydration product of BCSA cement, was investigated in detail. The microstructure of AH{sub 3} with various quantities of gypsum was investigated via scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The AH{sub 3} with various morphologies were observed and confirmed in the resulting pastes. Particular attention was paid to the fact that AH{sub 3} always contained a small amount of Ca according to the results of EDS analysis. The AH{sub 3} was then characterized via high resolution transmission electron microscopy (HRTEM). The results of HRTEM indicated that Ca arose from nanosized tricalcium aluminate hexahydrate which existed in the AH{sub 3}.

  5. ILLUMINATING THE ROLE OF AGGLOMERATES ON CRITICAL PHYSICOCHEMICAL PROPERTIES OF AMORPHOUS CALCIUM PHOSPHATE COMPOSITES

    PubMed Central

    O’Donnell, J.N.R.; Antonucci, J.M.; Skrtic, D.

    2009-01-01

    Water sorption (WS), mechanical strength, and ion release of polymeric composites formulated with 40 % as-made or milled amorphous calcium phosphate (ACP) are compared after 1, 2 and 3 months of aqueous exposure. Ethoxylated bisphenol A dimethacrylate, triethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate and methacryloxyethyl phthalate comprised the resin. The WS (mass %) peaked at 3 months. WS of as-made ACP composites was significantly higher than WS of milled ACP composites and copolymers. Both composite groups experienced decreases in biaxial flexural strength (BFS) with water aging, with milled ACP composites retaining a significantly higher BFS throughout immersion. Ion release was moderately reduced in milled ACP composites, though they remained superior to as-made ACP composites due to significantly lower WS and higher BFS after prolonged aqueous exposure. PMID:19774100

  6. Determination of the Effects of Magnesium on the Structural Order of Amorphous Calcium Phosphate

    NASA Astrophysics Data System (ADS)

    Hoeher, A.; Michel, F. M.; Rakovan, J. F.; Borkiewicz, O.; Klysubun, W.

    2016-12-01

    Determining the pathways and mechanisms of calcium phosphate formation is important for understanding bone mineralization and advancing potential biological applications such as coatings on internal prosthetics. Studies show that amorphous calcium phosphate (ACP) is a precursor phase in the low temperature crystallization of hydroxylapatite, the primary mineral component found in bone and teeth of most modern vertebrates. ACP has been shown to have a structural order out to about 1 nm. Our recent extended x-ray absorption fine structure (EXAFS) spectroscopy analysis of synthetic ACP showed that the local structure of calcium in ACP differed from that in hydroxylapatite. Phosphorus EXAFS, however, indicated that the local structure in ACP is similar to hydroxylapatite (i.e., tetrahedrally coordinated with oxygen). EXAFS results were limited to only the first and second nearest neighbors in these samples, so the intermediate range order in ACP is yet unexplored. Furthermore, it remains unclear how ACP structure varies as a function of initial solution chemistry, how common impurities such as Mg are incorporated, and what role they play in determining the structural and physical characteristics of the final crystalline solid. We are using synchrotron x-ray total scattering for pair distribution function (PDF) analysis to investigate the influence of initial solution chemistry and Mg content on the structure of ACP. Magnesium is commonly used to stabilize the amorphous nature of the material, preventing crystallization. Ex situ samples synthesized at pH 10, with Ca:Mg ratios of 2:1, and freeze-dried are structurally similar to hydroxylapatite. Samples synthesized in identical conditions without Mg are structurally similar to another calcium phosphate mineral, brushite. In situ PDF measurements done at similar conditions in a custom mixed-flow reactor reveal that the short range order of ACP after 10 minutes of reacting is structurally different from ACP formed ex situ

  7. In Situ Electrical Study on Primary Hydrogen Spillover from Nanocatalysts to Amorphous Carbon Support

    SciTech Connect

    Lin, C.; Yang, Z.; Xu, T.; Zhao, Y.

    2008-01-01

    Primary hydrogen spillover has been studied using a unique electrical method. We observed that at ambient temperature, when a discontinuous nanogranular Pd film is on the top of an amorphous carbon film, the electrical conductance of the carbon film decreases in pressurized hydrogen. In comparison, in the absence of this Pd layer, the conductance of the carbon film remains unchanged in pressurized hydrogen. The observed decrease in the current in the Pd/carbon structure is ascribed to the hydrogenation of the dangling carbon bonds and sp{sup 2}-sp{sup 3} transition in the amorphous carbon by the primary spillover hydrogen atoms from Pd nanoclusters.

  8. Fullerene nanostructure-induced excellent mechanical properties in hydrogenated amorphous carbon

    NASA Astrophysics Data System (ADS)

    Wang, Qi; Wang, Chengbing; Wang, Zhou; Zhang, Junyan; He, Deyan

    2007-10-01

    Hydrogenated amorphous carbon films were deposited by dc-pulse plasma chemical vapor deposition. The structure of as-prepared films, characterized by transmission electron microscopy, Raman spectra, and x-ray photoelectron spectra, is considered as nanocomposite thin films with C60 and fullerene crystalline nanoparticles embedded in amorphous sp2 and sp3 carbon matrices. The high hardness and high elastic recovery of as-prepared films are attributed to the unique structure that C60 and fullerene nanocrystalline grains (soft) dispersed in amorphous carbon phase (hard) to form a network structure, which restrains the dislocation migration, assists the stress relaxation, and hence, enhances the mechanical properties of the films.

  9. Gas desorption during friction of amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Rusanov, A.; Fontaine, J.; Martin, J.-M.; Mogne, T. L.; Nevshupa, R.

    2008-03-01

    Gas desorption induced by friction of solids, i.e. tribodesorption, is one of the numerous physical and chemical phenomena, which arise during friction as result of thermal and structural activation of material in a friction zone. Tribodesorption of carbon oxides, hydrocarbons, and water vapours may lead to significant deterioration of ultra high vacuum conditions in modern technological equipment in electronic, optoelectronic industries. Therefore, knowledge of tribodesorption is crucial for the performance and lifetime of vacuum tribosystems. Diamond-like carbon (DLC) coatings are interesting materials for vacuum tribological systems due to their high wear resistance and low friction. Highly hydrogenated amorphous carbon (a-C:H) films are known to exhibit extremely low friction coefficient under high vacuum or inert environment, known as 'superlubricity' or 'superlow friction'. However, the superlow friction period is not always stable and then tends to spontaneous transition to high friction. It is supposed that hydrogen supply from the bulk to the surface is crucial for establishing and maintaining superlow friction. Thus, tribodesorption can serve also as a new technique to determine the role of gases in superlow friction mechanisms. Desorption of various a-C:H films, deposited by PECVD, ion-beam deposition and deposition using diode system, has been studied by means of ultra-high vacuum tribometer equipped with a mass spectrometer. It was found that in superlow friction period desorption rate was below the detection limit in the 0-85 mass range. However, transition from superlow friction to high friction was accompanied by desorption of various gases, mainly of H2 and CH4. During friction transition, surfaces were heavily damaged. In experiments with DLC films with low hydrogen content tribodesorption was significant during the whole experiment, while low friction was not observed. From estimation of maximum surface temperature during sliding contact it was

  10. Calcium and calcium isotope changes during carbon cycle perturbations at the end-Permian

    NASA Astrophysics Data System (ADS)

    Komar, Nemanja; Zeebe, Richard

    2016-04-01

    Negative carbon and calcium isotope excursions, as well as climate shifts, took place during the most severe mass extinction event in Earth's history, the end-Permian (˜252 Ma). Investigating the connection between carbon and calcium cycles during transient carbon cycle perturbation events, such as the end-Permian, may help resolve the intricacies between the coupled calcium-carbon cycles, as well as provide a tool for constraining the causes of mass extinction. Here, we identify the deficiencies of a simplified calcium model employed in several previous studies and we demonstrate the importance of a fully coupled carbon-cycle model when investigating the dynamics of carbon and calcium cycling. Simulations with a modified version of the LOSCAR model, which includes a fully coupled carbon-calcium cycle, indicate that increased weathering rates and ocean acidification (potentially caused by Siberian Trap volcanism) are not capable of producing trends observed in the record, as previously claimed. Our model results suggest that combined effects of carbon input via Siberian Trap volcanism (12,000 Pg C), the cessation of biological carbon export, and variable calcium isotope fractionation (due to a change in the seawater carbonate ion concentration) represents a more plausible scenario. This scenario successfully reconciles δ13C and δ44Ca trends observed in the sediment record, as well as the proposed warming of >6oC.

  11. Effect of glycoursodeoxycholate on precipitation of calcium carbonate.

    PubMed

    Marteau, C; Portugal, H; Pauli, A M; Gerolami, A

    1985-01-01

    The potential role of bile salts in preventing calcium carbonate precipitation was investigated by studying their interaction of Ca2+ and their inhibitory effects on calcium carbonate formation. Glycochenodeoxycholate micelles bound more calcium than did glycocholate. At bile salt concentrations exceeding 12.5 mM, glycoursodeoxycholate bound calcium as well as glycochenodexycholate did. Similar results for calcium binding were observed in mixed micelles of bile salts and lecithin. In bicarbonate (25 or 50 mM) and CaCl2 (10 mM) solutions, calcium carbonate formation was inhibited by the bile salts. Glycoursodeoxycholate and glycochenodeoxycholate (25 mM) prevented calcium carbonate formation which was delayed by glycocholate. This effect is not due to differences between both series of bile salts for calcium binding since glycoursodeoxycholate or glycochenodeoxycholate (25 mM) more efficiently prevented calcium carbonate precipitation than did 35 mM glycocholate in spite of the same Ca2+ binding. These results suggest that some bile salts may have a specific role in preventing calcium precipitation in bile. The mechanism is unknown. The physical properties of glycoursodeoxycholate and glycochenodeoxycholate do not support a role for CaCO3 precipitation in gallstone calcification during litholytic therapy.

  12. Amorphous calcium phosphate/urethane methacrylate resin composites. I. Physicochemical characterization.

    PubMed

    Regnault, William F; Icenogle, Tonya B; Antonucci, Joseph M; Skrtic, Drago

    2008-02-01

    Urethane dimethacrylate (UDMA), an oligomeric poly(ethylene glycol) extended UDMA (PEG-U) and a blend of UDMA/PEG-U were chosen as model systems for introducing both hydrophobic and hydrophilic segments and a range of compliances in their derived polymers. Experimental composites based on these three resins with amorphous calcium phosphate (ACP) as the filler phase were polymerized and evaluated for mechanical strength and ion release profiles in different aqueous media. Strength of all composites decreased upon immersion in saline (pH = 7.4). Both polymer matrix composition and the pH of the liquid environment strongly affected the ion release kinetics. In saline, the UDMA/PEG-U composite showed a sustained release for at least 350 h. The initially high ion release of the PEG-U composites decreased after 72 h, seemingly due to the mineral re-deposition at the composite surface. Internal conversion from ACP to poorly crystallized apatite could be observed by X-ray diffraction. In various lactic acid (LA) environments (initial pH = 5.1) ion release kinetics was much more complex. In LA medium without thymol and/or carboxymethylcellulose, as a result of unfavorable changes in the internal calcium/phosphate ion stoichiometry, the ion release rate greatly increased but without observable conversion of ACP to apatite.

  13. Amorphous calcium phosphate/urethane methacrylate resin composites. I. Physicochemical characterization

    PubMed Central

    Regnault, W.F.; Icenogle, T.B.; Antonucci, J.M.; Skrtic, D.

    2008-01-01

    Urethane dimethacrylate (UDMA), an oligomeric poly(ethylene glycol) extended UDMA (PEG-U) and a blend of UDMA/PEG-U were chosen as model systems for introducing both hydrophobic and hydrophilic segments and a range of compliances in their derived polymers. Experimental composites based on these three resins with amorphous calcium phosphate (ACP) as the filler phase were polymerized and evaluated for mechanical strength and ion release profiles in different aqueous media. Strength of all composites decreased upon immersion in saline (pH = 7.4). Both polymer matrix composition and the pH of the liquid environment strongly affected the ion release kinetics. In saline, the UDMA/PEG-U composite showed a sustained release for at least 350 h. The initially high ion release of the PEG-U composites decreased after 72 h, seemingly due to the mineral re-deposition at the composite surface. Internal conversion from ACP to poorly crystallized apatite could be observed by X-ray diffraction. In various lactic acid (LA) environments (initial pH = 5.1) ion release kinetics was much more complex. In LA medium without thymol and/or carboxymethylcellulose, as a result of unfavorable changes in the internal calcium/phosphate ion stoichiometry, the ion release rate greatly increased but without observable conversion of ACP to apatite. PMID:17619969

  14. Amorphous Calcium Phosphate-Based Bioactive Polymeric Composites for Mineralized Tissue Regeneration

    PubMed Central

    Skrtic, D.; Antonucci, J. M.; Eanes, E. D.

    2003-01-01

    Amorphous calcium phosphate (ACP), a postulated precursor in the formation of biological hydroxyapatite, has been evaluated as a filler phase in bioactive polymeric composites that utilize dental monomers to form the matrix phase on polymerization. In addition to excellent biocompatibility, these composites provided sustained release of calcium and phosphate ions into simulated saliva milieus. In an effort to enhance the physicochemical and mechanical properties and extend the utility of remineralizing ACP composites to a greater variety of dental applications, we have focused on: a) hybridizing ACP by introducing silica and/or zirconia, b) assessing the efficacy of potential coupling agents, c) investigating the effects of chemical structure and compositional variation of the resin matrices on the mechanical strength and ion-releasing properties of the composites, and d) improving the intrinsic adhesiveness of composites by using bifunctional monomers with an affinity for tooth structure in resin formulations. Si- and Zr-modified ACPs along with several monomer systems are found useful in formulating composites with improved mechanical and remineralizing properties. Structure-property studies have proven helpful in advancing our understanding of the remineralizing behavior of these bioactive composites. It is expected that this knowledge base will direct future research and lead to clinically valuable products, especially therapeutic materials appropriate for the healing or even regeneration of defective teeth and bone structures. PMID:27413603

  15. In Vitro Properties of Orthodontic Adhesives with Fluoride or Amorphous Calcium Phosphate

    PubMed Central

    Chow, Clara Ka Wai; Wu, Christine D.; Evans, Carla A.

    2011-01-01

    This in vitro study evaluated the efficacy of orthodontic adhesives with fluoride or amorphous calcium phosphate (ACP) in reducing bacterial adhesion and enamel demineralization. Forty human premolars each sectioned buccolingually into three parts were bracketed with control resin (Transbond XT) or adhesives containing ACP (Aegis Ortho) or fluoride (QuickCure). Artificial lesions induced by pH cycling were examined by X-ray photoelectron spectrophotometry (XPS) and polarized light microscopy (PLM). After 28 days, Aegis Ortho demonstrated the lowest calcium and phosphorous content by XPS analysis. After 42 days, reductions in lesion depth areas were 23.6% for Quick Cure and 20.3% for Aegis Ortho (P < 0.05). In the presence of 1% sucrose, adhesion of Streptococcus mutans to Aegis Ortho and Quick Cure was reduced by 41.8% and 37.7% (P < 0.05) as compared to Transbond XT. Composites containing ACP or fluoride reduced bacterial adherence and lesion formation as compared to a composite without ACP or fluoride. PMID:21912546

  16. In vitro evaluation of enamel remineralisation by a casein phosphopeptide-amorphous calcium phosphate paste.

    PubMed

    Willershausen, Brita; Schulz-Dobrick, Burkhard; Gleissner, Christiane

    2009-01-01

    The aim of this preliminary in vitro study was to evaluate the effect of a casein phosphopeptide and amorphous calcium phosphate (CPP-ACP) paste on untreated enamel surfaces that had previously been exposed to an erosive challenge. Over a period of 6 h, enamel samples from five fully erupted, caries-free molars were incubated with apple juice and later covered with CPP-ACP paste for 15 min. Enamel samples incubated with physiological sodium chloride solution or with apple juice alone served as controls. The quantitative elementary analysis for calcium and phosphorus in various depths ranging from 5 to 50 microm was performed using an electron-probe microanalyser. Exposure to apple juice resulted in a loss of minerals down to a depth of 30 microm with a mean loss of 13% at 5 microm and 6% at 10 microm. After treatment with CPP-ACP paste, the mineral loss decreased to a mean of 9% at 5 microm and remained at 5% at a depth of 10 microm (not a statistically significant difference). At a depth of 20 microm, no further mineral loss was recorded. This study demonstrated that there is a slight gain in the mineral contents after the application of a CPP-ACP paste, mainly in the upper enamel layer. Within the limitations of this in vitro study, the application of CPP-ACP paste may enhance the remineralisation after an erosive challenge and thus offer some protection for patients who are at risk for erosion.

  17. Evaluation of thin amorphous calcium phosphate coatings on titanium dental implants deposited using magnetron sputtering.

    PubMed

    Yokota, Sou; Nishiwaki, Naruhiko; Ueda, Kyosuke; Narushima, Takayuki; Kawamura, Hiroshi; Takahashi, Tetsu

    2014-06-01

    Calcium phosphate is used for dental material because of its biocompatibility and osteoconductivity. Amorphous calcium phosphate (ACP) coatings deposited by magnetron sputtering can control their thickness and absorbability. This study aimed to evaluate and characterize ACP coatings deposited via magnetron sputtering. It was hypothesized that ACP coatings would enhance bone formation and be absorbed rapidly in vivo. ACP coatings that are 0.5 μm in thickness were deposited via magnetron sputtering on dental implants. Uncoated implants served as controls. The effect of the ACP coatings in vivo was investigated in New Zealand white rabbit. To evaluate the effect of the ACP coatings on the bone response of the implants, the removal torque, implant stability quotient, and histomorphometric analysis were performed on the implants at 1, 2, and 4 weeks after implantation. Results of the x-ray diffraction analyses confirmed the deposition of ACP coatings. Images from the scanning electron microscopy revealed that the coatings were dense, uniform, and 0.5 μm in thickness and that they were absorbed completely. Mechanical stability and bone formation in the case of the ACP-coated implants were higher than those of control. These results suggest that implants coated with thin ACP layers improve implant fixation and accelerate bone response.

  18. Thermal decomposition of fullerene nanowhiskers protected by amorphous carbon mask

    PubMed Central

    Guo, Hongxuan; Wang, Chengxiang; Miyazawa, Kun’ichi; Wang, Hongxin; Masuda, Hideki; Fujita, Daisuke

    2016-01-01

    Fullerene nanostructures are well known for their unique morphology, physical and mechanical properties. The thermal stability of fullerene nanostructures, such as their sublimation at high temperature is also very important for studying their structures and applications. In this work, We observed fullerene nanowhiskers (FNWs) in situ with scanning helium ion microscopy (HIM) at elevated temperatures. The FNWs exhibited different stabilities with different thermal histories during the observation. The pristine FNWs were decomposed at the temperatures higher than 300 °C in a vacuum environment. Other FNWs were protected from decomposition with an amorphous carbon (aC) film deposited on the surface. Based on high spacial resolution, aC film with periodic structure was deposited by helium ion beam induced deposition (IBID) on the surface of FNWs. Annealed at the high temperature, the fullerene molecules were selectively sublimated from the FNWs. The periodic structure was formed on the surface of FNWs and observed by HIM. Monte Carlo simulation and Raman characterization proved that the morphology of the FNWs was changed by helium IBID at high temperature. This work provides a new method of fabricating artificial structure on the surface of FNWs with periodic aC film as a mask. PMID:27991498

  19. Electromagnetic Wave Absorbing Properties of Amorphous Carbon Nanotubes

    PubMed Central

    Zhao, Tingkai; Hou, Cuilin; Zhang, Hongyan; Zhu, Ruoxing; She, Shengfei; Wang, Jungao; Li, Tiehu; Liu, Zhifu; Wei, Bingqing

    2014-01-01

    Amorphous carbon nanotubes (ACNTs) with diameters in the range of 7–50 nm were used as absorber materials for electromagnetic waves. The electromagnetic wave absorbing composite films were prepared by a dip-coating method using a uniform mixture of rare earth lanthanum nitrate doped ACNTs and polyvinyl chloride (PVC). The microstructures of ACNTs and ACNT/PVC composites were characterized using transmission electron microscope and X-ray diffraction, and their electromagnetic wave absorbing properties were measured using a vector-network analyzer. The experimental results indicated that the electromagnetic wave absorbing properties of ACNTs are superior to multi-walled CNTs, and greatly improved by doping 6 wt% lanthanum nitrate. The reflection loss (R) value of a lanthanum nitrate doped ACNT/PVC composite was −25.02 dB at 14.44 GHz, and the frequency bandwidth corresponding to the reflector loss at −10 dB was up to 5.8 GHz within the frequency range of 2–18 GHz. PMID:25007783

  20. Electromagnetic Wave Absorbing Properties of Amorphous Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Zhao, Tingkai; Hou, Cuilin; Zhang, Hongyan; Zhu, Ruoxing; She, Shengfei; Wang, Jungao; Li, Tiehu; Liu, Zhifu; Wei, Bingqing

    2014-07-01

    Amorphous carbon nanotubes (ACNTs) with diameters in the range of 7-50 nm were used as absorber materials for electromagnetic waves. The electromagnetic wave absorbing composite films were prepared by a dip-coating method using a uniform mixture of rare earth lanthanum nitrate doped ACNTs and polyvinyl chloride (PVC). The microstructures of ACNTs and ACNT/PVC composites were characterized using transmission electron microscope and X-ray diffraction, and their electromagnetic wave absorbing properties were measured using a vector-network analyzer. The experimental results indicated that the electromagnetic wave absorbing properties of ACNTs are superior to multi-walled CNTs, and greatly improved by doping 6 wt% lanthanum nitrate. The reflection loss (R) value of a lanthanum nitrate doped ACNT/PVC composite was -25.02 dB at 14.44 GHz, and the frequency bandwidth corresponding to the reflector loss at -10 dB was up to 5.8 GHz within the frequency range of 2-18 GHz.

  1. Wake potential of swift ion in amorphous carbon target

    NASA Astrophysics Data System (ADS)

    Al-Bahnam, Nabil janan; Ahmad, Khalid A.; Aboo Al-Numan, Abdullah Ibrahim

    2017-02-01

    The wake potential and wake phenomena for swift proton in an amorphous carbon target were studied by utilising various dielectric function formalisms, including the Drude dielectric function, the Drude-Lorentz dielectric function and quantum dielectric function. The Drude model results exhibited a damped oscillatory behaviour in the longitudinal direction behind the projectile; the pattern of these oscillations decreases exponentially in the transverse direction. In addition, the wake potential extends slightly ahead of the projectile which also depends on the proton coordinate and velocity. The effect of electron binding on the wake potential, characterised by the ratio ωp2 / ω02 = 10 to 0.1, has been studied alongside the Drude-Lorentz dielectric function and quantum dielectric function formalisms; the results evidently show that the wake potential dip depth decreases with more oscillations when the electron density ratio ωp2 / ω02 decreases from 10 to 0.1. One of the primary objectives of the present work is to construct a reasonably realistic procedure for simulating the response of target to swift ions by combining an expression for the induced wake potential along with several important dielectric function models; the aim of this research is to reduce computational complexity without sacrificing accuracy. This is regarded as being an efficient strategy in that it creates suitable computer simulation procedures which are relevant to actual solids. After comparing this method with other models, the main differences and similarities have been noted while the end results have proved encouraging.

  2. Laser induced crystallization of hydrogenated amorphous silicon-carbon alloys

    NASA Astrophysics Data System (ADS)

    Summonte, C.; Rizzoli, R.; Servidori, M.; Milita, S.; Nicoletti, S.; Bianconi, M.; Desalvo, A.; Iencinella, D.

    2004-10-01

    Laser induced crystallization of hydrogenated amorphous silicon carbon alloy (a-Si1-xCx:H) films has been investigated by means of synchrotron x-ray diffraction. The a-Si1-xCx:H films were deposited on (100) silicon wafers by very high frequency plasma enhanced chemical vapor deposition at 100MHz in hydrogen diluted silane-methane gas mixtures. The substrate was kept at 250°C or 350°C and the stoichiometry was changed from x =0.20 to 0.63. The structural characterization of the as-grown films has been carried out by Rutherford backscattering (hydrogen concentration) and infrared spectroscopy (film ordering). The films were irradiated by a KrF excimer laser (248nm ) with varying energy density and number of pulses. After irradiation, the formation of SiC crystallites has been revealed by synchrotron x-ray diffraction. Besides SiC nanocrystals, the formation of crystalline Si and graphite is observed for under- (x <0.50) and over-stoichiometric (x>0.50) samples, respectively. The essential role played by hydrogen concentration and hydrogen bonding configuration in determining the melting threshold and the consequent SiC grain formation is highlighted.

  3. Thermal decomposition of fullerene nanowhiskers protected by amorphous carbon mask

    NASA Astrophysics Data System (ADS)

    Guo, Hongxuan; Wang, Chengxiang; Miyazawa, Kun’Ichi; Wang, Hongxin; Masuda, Hideki; Fujita, Daisuke

    2016-12-01

    Fullerene nanostructures are well known for their unique morphology, physical and mechanical properties. The thermal stability of fullerene nanostructures, such as their sublimation at high temperature is also very important for studying their structures and applications. In this work, We observed fullerene nanowhiskers (FNWs) in situ with scanning helium ion microscopy (HIM) at elevated temperatures. The FNWs exhibited different stabilities with different thermal histories during the observation. The pristine FNWs were decomposed at the temperatures higher than 300 °C in a vacuum environment. Other FNWs were protected from decomposition with an amorphous carbon (aC) film deposited on the surface. Based on high spacial resolution, aC film with periodic structure was deposited by helium ion beam induced deposition (IBID) on the surface of FNWs. Annealed at the high temperature, the fullerene molecules were selectively sublimated from the FNWs. The periodic structure was formed on the surface of FNWs and observed by HIM. Monte Carlo simulation and Raman characterization proved that the morphology of the FNWs was changed by helium IBID at high temperature. This work provides a new method of fabricating artificial structure on the surface of FNWs with periodic aC film as a mask.

  4. Electromagnetic wave absorbing properties of amorphous carbon nanotubes.

    PubMed

    Zhao, Tingkai; Hou, Cuilin; Zhang, Hongyan; Zhu, Ruoxing; She, Shengfei; Wang, Jungao; Li, Tiehu; Liu, Zhifu; Wei, Bingqing

    2014-07-10

    Amorphous carbon nanotubes (ACNTs) with diameters in the range of 7-50 nm were used as absorber materials for electromagnetic waves. The electromagnetic wave absorbing composite films were prepared by a dip-coating method using a uniform mixture of rare earth lanthanum nitrate doped ACNTs and polyvinyl chloride (PVC). The microstructures of ACNTs and ACNT/PVC composites were characterized using transmission electron microscope and X-ray diffraction, and their electromagnetic wave absorbing properties were measured using a vector-network analyzer. The experimental results indicated that the electromagnetic wave absorbing properties of ACNTs are superior to multi-walled CNTs, and greatly improved by doping 6 wt% lanthanum nitrate. The reflection loss (R) value of a lanthanum nitrate doped ACNT/PVC composite was -25.02 dB at 14.44 GHz, and the frequency bandwidth corresponding to the reflector loss at -10 dB was up to 5.8 GHz within the frequency range of 2-18 GHz.

  5. Controlled epitaxial graphene growth within removable amorphous carbon corrals

    SciTech Connect

    Palmer, James; Hu, Yike; Hankinson, John; Guo, Zelei; Heer, Walt A. de; Kunc, Jan; Berger, Claire

    2014-07-14

    We address the question of control of the silicon carbide (SiC) steps and terraces under epitaxial graphene on SiC and demonstrate amorphous carbon (aC) corrals as an ideal method to pin SiC surface steps. aC is compatible with graphene growth, structurally stable at high temperatures, and can be removed after graphene growth. For this, aC is first evaporated and patterned on SiC, then annealed in the graphene growth furnace. There at temperatures above 1200 °C, mobile SiC steps accumulate at the aC corral that provide effective step flow barriers. Aligned step free regions are thereby formed for subsequent graphene growth at temperatures above 1330 °C. Atomic force microscopy imaging supports the formation of step-free terraces on SiC with the step morphology aligned to the aC corrals. Raman spectroscopy indicates the presence of good graphene sheets on the step-free terraces.

  6. Non-catalytic synthesis of diamond from amorphous carbon at high static pressure

    NASA Astrophysics Data System (ADS)

    Higashi, K.; Onodera, A.

    1986-05-01

    Amorphous carbon prepared from furfuryl alcohol resin was studied under static high pressure above 10 GPa without planned addition of catalyst. Diamond can be formed at temperatures lower than required for the catalytic process.

  7. Effect of amorphous calcium phosphate and silver nanocomposites on dental plaque microcosm biofilms

    PubMed Central

    Cheng, Lei; Weir, Michael D.; Xu, Hockin H. K.; Antonucci, Joseph M.; Lin, Nancy J.; Lin-Gibson, Sheng; Xu, Sarah M.; Zhou, Xuedong

    2012-01-01

    A dental composite containing amorphous calcium phosphate nanoparticles (NACP) was developed that released calcium (Ca) and phosphate (PO4) ions and possessed acid-neutralization capability. There has been little study on incorporation of antibacterial agents into calcium phosphate composites. The objective of this study was to investigate the effect of silver nanoparticle (NAg) mass fraction in NACP nanocomposite on mechanical properties and dental plaque microcosm biofilm for the first time. NACP nanoparticles of 116 nm were synthesized via a spray-drying technique. NAg nanoparticles were synthesized using Ag 2-ethylhexanoate and 2-(tert-butylamino)ethyl methacrylate, yielding NAg of particle size of 2.7 nm that were well-dispersed in the resin. Five NACP nanocomposites were fabricated with NAg mass fractions of 0, 0.028, 0.042, 0.088, and 0.175%, respectively. Mechanical properties of NACP nanocomposites containing 0–0.042% of NAg matched those of a commercial composite without antibacterial activity. Live/dead assay of dental plaque microcosm biofilms showed complete coverage with live bacteria on commercial composite. However, there were increasingly more dead bacteria with higher NAg content in the NACP nanocomposite. Colony-forming unit (CFU) counts for total microorganisms, total Streptococci, and mutans Streptococci for NACP nanocomposite with 0.042% NAg were about 1/4 those of commercial composite. Lactic acid production on NACP nanocomposite with 0.042% NAg was 1/3 that on commercial composite. In conclusion, novel NACP–NAg nanocomposites were developed which possessed good mechanical properties and potent antibacterial properties, with substantially reduced biofilm viability and lactic acid production. Hence, the NACP–NAg nanocomposites are promising for dental restorations with remineralizing and antibacterial capabilities. PMID:22566464

  8. Antibacterial amorphous calcium phosphate nanocomposites with a quaternary ammonium dimethacrylate and silver nanoparticles

    PubMed Central

    Cheng, Lei; Weir, Michael D.; Xu, Hockin H. K.; Antonucci, Joseph M.; Kraigsley, Alison M.; Lin, Nancy J.; Lin-Gibson, Sheng; Zhou, Xuedong

    2012-01-01

    Objectives Calcium and phosphate ion-releasing resin composites are promising for remineralization. However, there has been no report on incorporating antibacterial agents to these composites. The objective of this study was to develop antibacterial and mechanically-strong nanocomposites incorporating a quaternary ammonium dimethacrylate (QADM), nanoparticles of silver (NAg), and nanoparticles of amorphous calcium phosphate (NACP). Methods The QADM, bis(2-methacryloyloxyethyl) dimethylammonium bromide (ionic dimethacrylate-1), was synthesized from 2-(N,N-dimethylamino)ethyl methacrylate and 2-bromoethyl methacrylate. Ng was synthesized by dissolving Ag 2-ethylhexanoate salt in 2-(tertbutylamino)ethyl methacrylate. Mechanical properties were measured in three-point flexure with bars of 2×2×25 mm (n = 6). Composite disks (diameter = 9 mm, thickness = 2 mm) were inoculated with Streptococcus mutans. The metabolic activity and lactic acid production of biofilms were measured (n = 6). Two commercial composites were used as controls. Results Flexural strength and elastic modulus of NACP+QADM, NACP+NAg, and NACP+QADM+NAg matched those of commercial composites with no antibacterial property (p > 0.1). The NACP+QADM+NAg composite decreased the titer counts of adherent S. mutans biofilms by an order of magnitude, compared to the commercial composites (p < 0.05). The metabolic activity and lactic acid production of biofilms on NACP+QADM+NAg composite were much less than those on commercial composites (p < 0.05). Combining QADM and NAg rendered the nanocomposite more strongly antibacterial than either agent alone (p < 0.05). Significance QADM and NAg were incorporated into calcium phosphate composite for the first time. NACP+QADM+NAg was strongly-antibacterial and greatly reduced the titer counts, metabolic activity, and acid production of S. mutans biofilms, while possessing mechanical properties similar to commercial composites. These nanocomposites are promising to have

  9. Elucidating the Effect of Biomolecule Structure on Calcium Carbonate Crystal Formation

    NASA Astrophysics Data System (ADS)

    Kulbok, K. E.; Duckworth, O.

    2011-12-01

    , as well as the effect of biomolecule structure on calcium carbonate crystals. Preliminary XRD and SEM analyses have shown vaterite, calcite, and amorphous CaCO3 to be the primary morphologies present. This analysis indicates a lack of stability for crystals grown quickly at elevated CO2 concentrations. The rate of precipitation of calcium carbonate solids and the subsequent decrease in free calcium concentration has been shown to be largely a function of pH.

  10. Calcium carbonate suppresses haem toxicity markers without calcium phosphate side effects on colon carcinogenesis

    PubMed Central

    Allam, Ossama; Bahuaud, Diane; Taché, Sylviane; Naud, Nathalie; Corpet, Denis E; Pierre, Fabrice H F

    2011-01-01

    Red meat intake is associated with increased risk of colorectal cancer. We have previously shown that haemin, haemoglobin and red meat promote carcinogen-induced preneoplastic lesions, aberrant crypt foci, in the colon of rats. We have also shown that dietary calcium phosphate inhibits haemin-induced promotion, and normalizes faecal lipoperoxides and cytotoxicity. Unexpectedly, high-calcium phosphate control diet-fed rats had more preneoplastic lesions in the colon than low-calcium control diet-fed rats. The present study was designed to find a calcium supplementation with no adverse effect, by testing several doses and types of calcium salts. One in vitro study and two short-term studies in rats identified calcium carbonate as the most effective calcium salt to bind haem in vitro and to decrease faecal biomarkers previously associated with increased carcinogenesis: faecal water cytotoxicity, thiobarbituric acid reactive substances. A long term carcinogenesis study in dimethylhydrazine-injected rats demonstrated that a diet containing 100 μmol/g calcium carbonate did not promote aberrant crypt foci, in contrast with previously tested calcium phosphate diet. The results suggest that calcium carbonate, and not calcium phosphate, should be used to reduce haem-associated colorectal cancer risk in meat-eaters. They support the concept that the nature of the associated anion to a protective metal ion is important for chemoprevention. PMID:21134327

  11. Direct /TEM/ observation of the catalytic oxidation of amorphous carbon by Pd particles

    NASA Technical Reports Server (NTRS)

    Moorhead, R. D.; Poppa, H.; Heinemann, K.

    1980-01-01

    The catalytic oxidation of amorphous carbon substrates by Pd particles is observed by in situ transmission electron microscopy. Various modes of selective attack of the carbon substrate in the immediate neighborhood of Pd particles are observed, which can be correlated with different degrees of particle mobility. Using amorphous substrates we have been able to demonstrate that the particle-substrate interaction is influenced by the structure of the particle. This has not previously been noted.

  12. [Study on solid dispersion of precipitated calcium carbonate-based oleanolic acid].

    PubMed

    Yan, Hong-mei; Zhang, Zhen-hai; Jia, Xiao-bin; Jiang, Yan-rong; Sun, E

    2015-05-01

    Oleanolic acid-precipitated calcium carbonate solid dispersion was prepared by using solvent evaporation method. The microscopic structure and physicochemical properties of solid dispersion were analyzed using differential scanning calorimetry and scanning electron microscopy (SEM). And its in vitro release also was investigated. The properties of the precipitated calcium carbonate was studied which was as a carrier of oleanolic acid solid dispersion. Differential scanning calorimetry analysis suggested that oleanolic acid may be present in solid dispersion as amorphous substance. The in vitro release determination results of oleanolic acid-precipitated calcium carbonate (1: 5) solid dispersion showed accumulated dissolution rate of.oleanolic acid was up to 90% at 45 min. Accelerating experiment showed that content and in vitro dissolution of oleanolic acid solid dispersion did not change after storing over 6 months. The results indicated that in vitro dissolution of oleanolic acid was improved greatly by the solid dispersion with precipitated calcium carbonate as a carrier. The solid dispersion is a stabilizing system which has actual applied value.

  13. Oral calcium carbonate affects calcium but not phosphorus balance in stage 3–4 chronic kidney disease

    PubMed Central

    Hill, Kathleen M.; Martin, Berdine R.; Wastney, Meryl; McCabe, George P.; Moe, Sharon M.; Weaver, Connie M.; Peacock, Munro

    2014-01-01

    Chronic kidney disease (CKD) patients are given calcium carbonate to bind dietary phosphorus and reduce phosphorus retention, and to prevent negative calcium balance. Data are limited on calcium and phosphorus balance in CKD to support this. The aim of this study was to determine calcium and phosphorus balance and calcium kinetics with and without calcium carbonate in CKD patients. Eight stage 3/4 CKD patients, eGFR 36 mL/min, participated in two 3-week balances in a randomized placebo-controlled cross-over study of calcium carbonate (1500 mg/d calcium). Calcium and phosphorus balance were determined on a controlled diet. Oral and intravenous 45calcium with blood sampling and urine and fecal collections were used for calcium kinetics. Fasting blood and urine were collected at baseline and end of each week of each balance period for biochemical analyses. Results showed that patients were in neutral calcium and phosphorus balance while on placebo. Calcium carbonate produced positive calcium balance, did not affect phosphorus balance, and produced only a modest reduction in urine phosphorus excretion compared with placebo. Calcium kinetics demonstrated positive net bone balance but less than overall calcium balance suggesting tissue deposition. Fasting biochemistries of calcium and phosphate homeostasis were unaffected by calcium carbonate. If they can be extrapolated to effects of chronic therapy, these data caution against the use of calcium carbonate as a phosphate binder. PMID:23254903

  14. Laser annealing study of PECVD deposited hydrogenated amorphous silicon carbon alloy films

    NASA Astrophysics Data System (ADS)

    Coscia, U.; Ambrosone, G.; Gesuele, F.; Grossi, V.; Parisi, V.; Schutzmann, S.; Basa, D. K.

    2007-12-01

    The influence of carbon content on the crystallization process has been investigated for the excimer laser annealed hydrogenated amorphous silicon carbon alloy films deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) technique, using silane methane gas mixture diluted in helium, as well as for the hydrogenated microcrystalline silicon carbon alloy films prepared by PECVD from silane methane gas mixture highly diluted in hydrogen, for comparison. The study demonstrates clearly that the increase in the carbon content prevents the crystallization process in the hydrogen diluted samples while the crystallization process is enhanced in the laser annealing of amorphous samples because of the increase in the absorbed laser energy density that occurs for the amorphous films with the higher carbon content. This, in turn, facilitates the crystallization for the laser annealed samples with higher carbon content, resulting in the formation of SiC crystallites along with Si crystallites.

  15. Calcium carbonate and calcium sulfate in Martian meteorite EETA79001

    NASA Technical Reports Server (NTRS)

    Gooding, J. L.; Wentworth, S. J.

    1987-01-01

    Chips of glassy Lithology C of EETA79001 were studied by scanning electron microscopy and energy dispersive X-ray spectroscopy to determine the mineralogy and petrogenesis of the glass that was shown by others to contain trapped Mars-like gases. Calcium carbonite was identified as massive to acicular crystals for which Ca, C, and O were the major elements. Calcium sulfate was identified as prismatic-acicular crystals with Ca and S as the major elements.

  16. Effect of ball milling on the physicochemical properties of atorvastatin calcium sesquihydrate: the dissolution kinetic behaviours of milled amorphous solids.

    PubMed

    Kobayashi, Makiko; Hattori, Yusuke; Sasaki, Tetsuo; Otsuka, Makoto

    2017-01-01

    The purposes of this study were to clarify the amorphization by ball milling of atorvastatin calcium sesquihydrate (AT) and to analyse the change in dissolution kinetics. The amorphous AT was prepared from crystal AT by ball milling and analysed in terms of the changes of its physicochemical properties by powder X-ray diffraction analysis (XRD), thermal analysis and infrared spectroscopy (IR). Moreover, to evaluate the usefulness of the amorphous form for pharmaceutical development, intrinsic solubility of the ground product was evaluated using a dissolution kinetic method. The XRD results indicated that crystalline AT was transformed into amorphous solids by more than 30-min milling. The thermal analysis result suggested that chemical potential of the ground AT are changed significantly by milling. The IR spectra of the AT showed the band shift from the amide group at 3406 cm(-1) with an intermolecular hydrogen bond to a free amide group at 3365 cm(-1) by milling. The dissolution of amorphous AT follows a dissolution kinetic model involving phase transformation. The initial dissolution rate of the ground product increased with the increase in milling time to reflect the increase in the intrinsic solubility based on the amorphous state. © 2016 Royal Pharmaceutical Society.

  17. Influence of calcium sources on microbially induced calcium carbonate precipitation by Bacillus sp. CR2.

    PubMed

    Achal, Varenyam; Pan, Xiangliang

    2014-05-01

    Stimulation of microbially induced calcium carbonate precipitation (MICCP) is likely to be influenced by calcium sources. In order to study such influences, we performed MICCP using Bacillus sp. CR2 in nutrient broth containing urea, supplemented with different calcium sources (calcium chloride, calcium oxide, calcium acetate and calcium nitrate). The experiment lasted 7 days, during which bacterial growth, urease activity, calcite production and pH were measured. Our results showed that calcium chloride is the better calcium source for MICCP process, since it provides higher urease activity and more calcite production. The influences of calcium sources on MICCP were further studied using Fourier transform-infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. These analyses confirmed that the precipitate formed was CaCO3 and composed of predominantly calcite crystals with a little amount of aragonite and vaterite crystals. The maximum yield of calcite precipitation was achievable with calcium chloride followed by calcium nitrate as a calcium source. The results of present study may be applicable to media preparation during efficient MICCP process.

  18. Casein Phosphopeptide-Amorphous Calcium Phosphate and Shear Bond Strength of Adhesives to Primary Teeth Enamel

    PubMed Central

    Farokh Gisovar, Elham; Hedayati, Nassim; Shadman, Niloofar; Shafiee, Leila

    2015-01-01

    Background: CPP-ACP (Phosphopeptide-Amorphous Calcium Phosphate) has an important role in caries prevention in pediatric patients. This study was done, because of the great use of CPP-ACP and the need for restoration for teeth treated with CPP-ACP as well as the importance of shear bond strength of adhesives in the success of restorations. Objectives: This study aimed to evaluate the effect of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on shear bond strength of dental adhesives to enamel of primary teeth molars. Materials and Methods: This in vitro study was conducted on 180 extracted primary molars. They were randomly divided into 6 groups and each group was divided into 2 subgroups (treated with CPP-ACP and untreated). In subgroups with CPP-ACP, enamel was treated with CPP-ACP paste 1 h/d for 5 days. Types of adhesives that were evaluated in this study were Tetric N-Bond, AdheSE, AdheSE One F, single Bond 2, SE Bond, and Adper Prompt L-Pop. Shear bond strength was tested with a universal testing machine and mode of failure was evaluated under stereomicroscope. Data were analyzed by T test, 2-way analysis of variance (ANOVA), Tukey and Fisher exact test using SPSS18. P < 0.05 was considered as significance level. Results: Shear bond strengths of different adhesive systems to enamel of primary teeth treated and untreated with CPP-ACP showed no significant difference (P > 0.05). Mode of failure in all groups regardless of CPP-ACP administration was mainly adhesive type. Our results indicated that CPP-ACP did not affect shear bond strength of studied adhesives to primary teeth enamel. Conclusions: To have a successful and durable composite restoration, having a high strength bonding is essential. Considering the wide use of CPP-ACP in preventing tooth decay and the role of adhesive shear bond strength (SBS) in success of composite restoration, we conducted the present study to evaluate the effect of CPP-ACP on the SBS of adhesives to primary teeth

  19. Casein phosphopeptide-amorphous calcium phosphate and shear bond strength of adhesives to primary teeth enamel.

    PubMed

    Farokh Gisovar, Elham; Hedayati, Nassim; Shadman, Niloofar; Shafiee, Leila

    2015-02-01

    CPP-ACP (Phosphopeptide-Amorphous Calcium Phosphate) has an important role in caries prevention in pediatric patients. This study was done, because of the great use of CPP-ACP and the need for restoration for teeth treated with CPP-ACP as well as the importance of shear bond strength of adhesives in the success of restorations. This study aimed to evaluate the effect of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on shear bond strength of dental adhesives to enamel of primary teeth molars. This in vitro study was conducted on 180 extracted primary molars. They were randomly divided into 6 groups and each group was divided into 2 subgroups (treated with CPP-ACP and untreated). In subgroups with CPP-ACP, enamel was treated with CPP-ACP paste 1 h/d for 5 days. Types of adhesives that were evaluated in this study were Tetric N-Bond, AdheSE, AdheSE One F, single Bond 2, SE Bond, and Adper Prompt L-Pop. Shear bond strength was tested with a universal testing machine and mode of failure was evaluated under stereomicroscope. Data were analyzed by T test, 2-way analysis of variance (ANOVA), Tukey and Fisher exact test using SPSS18. P < 0.05 was considered as significance level. Shear bond strengths of different adhesive systems to enamel of primary teeth treated and untreated with CPP-ACP showed no significant difference (P > 0.05). Mode of failure in all groups regardless of CPP-ACP administration was mainly adhesive type. Our results indicated that CPP-ACP did not affect shear bond strength of studied adhesives to primary teeth enamel. To have a successful and durable composite restoration, having a high strength bonding is essential. Considering the wide use of CPP-ACP in preventing tooth decay and the role of adhesive shear bond strength (SBS) in success of composite restoration, we conducted the present study to evaluate the effect of CPP-ACP on the SBS of adhesives to primary teeth enamel.

  20. VUV-visible measurements on different samples of amorphous carbon

    NASA Technical Reports Server (NTRS)

    Blanco, A.; Borghesi, A.; Bussoletti, E.; Colangeli, Luigi; Fonti, Sergio; Gumlich, H. E.; Jung, CH.; Orofino, Vincenso; Schwehm, G.

    1989-01-01

    Among various candidate materials for interstellar dust, amorphous carbon (AC) is playing an increasingly important role (Greenstein, 1981; Hecht et al., 1984; Jura, 1983, 1986). Furthermore, recent in situ measurements have clearly shown the presence of carbonaceous grains in the coma of comet Halley (Kissel et al., 1986). Laboratory investigations on AC grains may be very useful to better interpret observations and to support theoretical elaborations. Recently, the authors started an international research program which also includes UV extinction analyses on AC samples, by using synchrotron light. Preliminary results obtained in a first shift of measurements, last June, are given. At the present stage of the data analysis, the authors can only draw some preliminary considerations. A wide band falling at around 240 nm is detected in all the analyzed samples. It intensity seems to decrease with increasing the dust collecting distance. A peak at 150 nm decreases in intensity with increasing the collecting distance. The band seems absent in the samples characterized by a larger amount of dust. A feature at about 200 nm is detected in some samples. At the moment the authors tend to attribute it to the transmission properties of the LiF substrates at the wavelength and/or to some problems in the experimental setup. It is unclear if a hump at 120 nm is real or due to instrumental effects. The profile of the spectra does not show substantial changes when the samples are cooled down to about 100 K. The present results appear to be in general agreement with previous findings, but their analysis is in progress and the interpretation is still on the way.

  1. Radiation damages to amorphous-carbon optical coatings

    NASA Astrophysics Data System (ADS)

    Juha, L.; Bittner, M.; De Grazia, M.; Feldhaus, J.; Gaudin, J.; Guizard, S.; Jacobi, S.; Kozlova, M.; Krasa, J.; Krzywinski, J.; Merdji, H.; Michaelsen, C.; Mocek, T.; Nietubyc, R.; Jurek, M.; Polan, J.; Prag, A. R.; Rus, B.; Sobierajski, R.; Steeg-Keitel, B.; Stoermer, M.; Stupka, M.; Vorlicek, V.; Wiesmann, J.; Wild, J.

    2005-08-01

    The multi-mJ, 21-nm soft-x-ray laser at the PALS facility was focused on the surface of amorphous carbon (a-C) coating, developed for heavily loaded XUV/x-ray optical elements. AFM (Atomic Force Microscopy) images show 3-micrometer expansion of the irradiated material. Raman spectra, measured with an Ar+ laser microbeam in both irradiated and unirradiated areas, confirm a high degree of graphitization in the irradiated layer. In addition to this highfluence (~ 1 J/cm2), single-shot experiment, it was necessary to carry out an experiment to investigate consequences of prolonged XUV irradiation at relatively low fluence. High-order harmonic (HH) beam generated at the LUCA facility in CEA/Saclay Research Center was used as a source of short-wavelength radiation delivering high-energy photons on the surface at a low single-shot fluence but with high-average power. a-C irradiated at a low fluence, i.e., < 0.1 mJ/cm2 by many HH shots exhibits an expansion for several nanometers. Although it is less dramatic change of surface morphology than that due to single-hot x-ray-laser exposure even the observed nanometer-sized changes caused by the HH beam on a-C surface could influence reflectivity of a grazing incidence optical element. These results seem to be important for estimating damages to the surfaces of highly irradiated optical elements developed for guiding and focusing the ultraintense XUV/x-ray beams provided by new generation sources (i.e., VUV FEL and XFEL in Hamburg; LCLS in Stanford) because, up to now, only melting and vaporization, but not graphitization, have been taken into account.

  2. Risk factors for calcium carbonate urolithiasis in goats.

    PubMed

    Nwaokorie, Eugene E; Osborne, Carl A; Lulich, Jody P; Fletcher, Thomas F; Ulrich, Lisa K; Koehler, Lori A; Buettner, Michelle T

    2015-08-01

    To identify demographic or signalment factors associated with calcium carbonate urolith formation in goats. Retrospective case series and case-control study. 354 goats with calcium carbonate uroliths (case animals) and 16,366 goats without urinary tract disease (control animals). Medical records of the Minnesota Urolith Center were reviewed to identify case goats for which samples were submitted between January 1, 1984, and December 31, 2012. Control goats evaluated at US veterinary teaching hospitals in the same time period were identified by searching Veterinary Medical Database records. Age, breed, sex, reproductive status, geographic location, season, and anatomic location of collected uroliths were analyzed to identify risk or protective factors associated with calcium carbonate urolithiasis. Nigerian dwarf goats had higher odds of developing calcium carbonate uroliths than did Pygmy goats (reference group). Several breeds had lower odds of this finding, compared with Pygmy goats; odds were lowest for mixed, Anglo-Nubian, and Toggenburg breeds. Breeds of African origin (Pygmy, Nigerian Dwarf, and Boer) comprised 146 of 275 (53%) case goats with data available. Goats of African descent had a higher risk of developing calcium carbonate uroliths than did goats of non-African descent (reference group). Males and neutered goats had higher odds of calcium carbonate urolithiasis, compared with females and sexually intact goats, respectively. Age category, geographic location, and season were associated with detection of calcium carbonate uroliths. Goats with calcium carbonate uroliths were typically neutered males, > 1 year of age, and of African descent. This study identified factors associated with calcium carbonate urolithiasis in goats; however, these associations do not allow conclusions regarding cause-and-effect relationships.

  3. Effect of Calcium Carbonate on Bioavailability of Orally Administered Gemifloxacin

    PubMed Central

    Pletz, M. W.; Petzold, P.; Allen, A.; Burkhardt, O.; Lode, H.

    2003-01-01

    We investigated the effect of calcium carbonate on the oral bioavailability of gemifloxacin. Gemifloxacin was administered alone, 2 h before, simultaneously, or 2 h after calcium carbonate in 16 volunteers. Data for 320 mg of gemifloxacin alone were as follows: maximum concentration of drug in serum (Cmax),13 μg/ml; half-life, 7.33 h; and area under the concentration-time curve from 0 h to infinity (AUC∞), 6.79 μg · h/ml. Only simultaneous coadministration of calcium carbonate reduced Cmax (−17%) and AUC∞ (−21%) significantly. PMID:12821462

  4. Physico-chemical studies of amorphous carbon nanotubes synthesized at low temperature

    SciTech Connect

    Tan, Kim Han; Ahmad, Roslina; Leo, Bey Fen; Yew, Ming Chian; Ang, Bee Chin; Johan, Mohd Rafie

    2012-08-15

    Highlights: ► Amorphous carbon nanotubes are successfully produced via a simple method at low temperature. ► Nanotubes in straight morphologies with open ends. ► Acid treatment increases the extent of amorphous for nanotubes. ► Amorphous nanotubes exhibit phenomena of π plasmon absorbance and possess higher bandgap. -- Abstract: This work provides better understanding on the nature of amorphous carbon nanotubes, which are synthesized via a simple chemical route. Amorphous carbon nanotubes (α-CNTs) are successfully synthesized by heating a mixture of ferrocene and ammonium chloride at temperature as low as 200 °C and are treated with hydrochloric acid. Transmission and field emission scanning electron microscopy techniques are performed to examine the morphology and dimension of the samples. X-ray diffraction tests confirm the amorphous structure of the nanotubes. The Fourier transform infrared spectroscopy and Raman studies indicate that the treated α-CNTs consist of many defective walls and are more amorphous compared with the untreated α-CNTs. Ultraviolet–visible absorption studies reveal that the untreated and treated α-CNTs exhibit plasmon absorbance with high bandgaps of 4 eV and 4.35 eV, respectively.

  5. Evidence for calcium carbonate at the Mars Phoenix landing site.

    PubMed

    Boynton, W V; Ming, D W; Kounaves, S P; Young, S M M; Arvidson, R E; Hecht, M H; Hoffman, J; Niles, P B; Hamara, D K; Quinn, R C; Smith, P H; Sutter, B; Catling, D C; Morris, R V

    2009-07-03

    Carbonates are generally products of aqueous processes and may hold important clues about the history of liquid water on the surface of Mars. Calcium carbonate (approximately 3 to 5 weight percent) has been identified in the soils around the Phoenix landing site by scanning calorimetry showing an endothermic transition beginning around 725 degrees C accompanied by evolution of carbon dioxide and by the ability of the soil to buffer pH against acid addition. Based on empirical kinetics, the amount of calcium carbonate is most consistent with formation in the past by the interaction of atmospheric carbon dioxide with liquid water films on particle surfaces.

  6. Novel dental adhesives containing nanoparticles of silver and amorphous calcium phosphate

    PubMed Central

    Melo, Mary Anne S.; Cheng, Lei; Zhang, Ke; Weir, Michael D.; Rodrigues, Lidiany K. A.; Xu, Hockin H. K.

    2012-01-01

    Objectives Secondary caries is the main reason for restoration failure, and replacement of the failed restorations accounts for 50–70% of all restorations. Antibacterial adhesives could inhibit residual bacteria in tooth cavity and invading bacteria along the margins. Calcium (Ca) and phosphate (P) ion release could remineralize the lesions. The objectives of this study were to incorporate nanoparticles of silver (NAg) and nanoparticles of amorphous calcium phosphate (NACP) into adhesive for the first time, and to investigate the effects on dentin bond strength and plaque microcosm biofilms. Methods Scotchbond Multi-Purpose adhesive was used as control. NAg were added into primer and adhesive at 0.1% by mass. NACP were mixed into adhesive at 10%, 20%, 30% and 40%. Microcosm biofilms were grown on disks with primer covering the adhesive on a composite. Biofilm metabolic activity, colony-forming units (CFU) and lactic acid were measured. Results Human dentin shear bond strengths (n=10) ranged from 26 to 34 MPa; adding NAg and NACP into adhesive did not decrease the bond strength (p > 0.1). SEM examination revealed resin tags from well-filled dentinal tubules. Numerous NACP infiltrated into the dentinal tubules. While NACP had little antibacterial effect, NAg in bonding agents greatly reduced the biofilm viability and metabolic activity, compared to the control (p < 0.05). CFU for total microorganisms, total streptococci, and mutans streptococci on bonding agents with NAg were an order of magnitude less than those of the control. Lactic acid production by biofilms for groups containing NAg was 1/4 of that of the control. Significance Dental plaque microcosm biofilm viability and acid production were greatly reduced on bonding agents containing NAg and NACP, without compromising dentin bond strength. The novel method of incorporating dual agents (remineralizing agent NACP and antibacterial agent NAg) may have wide applicability to other dental bonding systems. PMID

  7. Structure-Composition-Property Relationships in Polymeric Amorphous Calcium Phosphate-Based Dental Composites†

    PubMed Central

    O’Donnell, Justin N.R.; Schumacher, Gary E.; Antonucci, Joseph M.; Skrtic, Drago

    2009-01-01

    Our studies of amorphous calcium phosphate (ACP)-based materials over the last decade have yielded bioactive polymeric composites capable of protecting teeth from demineralization or even regenerating lost tooth mineral. The anti-cariogenic/re-mineralizing potential of these ACP composites originates from their propensity, when exposed to the oral environment, to release in a sustained manner sufficient levels of mineral-forming calcium and phosphate ions to promote formation of stable apatitic tooth mineral. However, the less than optimal ACP filler/resin matrix cohesion, excessive polymerization shrinkage and water sorption of these experimental materials can adversely affect their physicochemical and mechanical properties, and, ultimately, limit their lifespan. This study demonstrates the effects of chemical structure and composition of the methacrylate monomers used to form the matrix phase of composites on degree of vinyl conversion (DVC) and water sorption of both copolymers and composites and the release of mineral ions from the composites. Modification of ACP surface via introducing cations and/or polymers ab initio during filler synthesis failed to yield mechanically improved composites. However, moderate improvement in composite’s mechanical stability without compromising its remineralization potential was achieved by silanization and/or milling of ACP filler. Using ethoxylated bisphenol A dimethacrylate or urethane dimethacrylate as base monomers and adding moderate amounts of hydrophilic 2-hydroxyethyl methacrylate or its isomer ethyl-α-hydroxymethacrylate appears to be a promising route to maximize the remineralizing ability of the filler while maintaining high DVC. Exploration of the structure/composition/property relationships of ACP fillers and polymer matrices is complex but essential for achieving a better understanding of the fundamental mechanisms that govern dissolution/re-precipitation of bioactive ACP fillers, and, ultimately, the

  8. Calcium carbonate does not affect nilotinib pharmacokinetics in healthy volunteers.

    PubMed

    Tawbi, Hussein A; Tran, An L; Christner, Susan M; Lin, Yan; Johnson, Matthew; Mowrey, Emily; Appleman, Leonard R; Stoller, Ronald; Miller, Brian M; Egorin, Merrill J; Beumer, Jan H

    2013-11-01

    Gastric upset is a common side effect of nilotinib therapy, and calcium carbonate is frequently used concomitantly, either as antacid or as calcium supplementation. With the increasing number of oral agents in cancer therapy, oral drug-drug interactions are becoming more relevant. Nilotinib has already been shown to be absorbed to a much lesser extent when co-administered with proton pump inhibitors. Because exposure to sub-therapeutic concentrations of anticancer drugs such as nilotinib may result in selection of resistant clones and ultimately relapse, we studied the effect of a calcium carbonate supplement (Tums Ultra 1000®) on nilotinib pharmacokinetics. Calcium carbonate may be co-administered with nilotinib without significantly affecting the pharmacokinetics of nilotinib and potentially impacting efficacy. Nilotinib is a second-generation oral tyrosine kinase inhibitor with superior efficacy compared with imatinib mesylate in the treatment for chronic phase chronic myelogenous leukemia. Calcium carbonate is commonly used as a source of calcium supplementation or as antacid to ameliorate the gastrointestinal side effects associated with nilotinib, which could have unknown effects on nilotinib absorption. The purpose of this study was to provide information on the effect of calcium carbonate on the PK of nilotinib in healthy volunteers. Healthy subjects were enrolled in a two-period, open-label, single-institution, randomized, cross-over, fixed-schedule study. In one period, each subject received 400 mg of nilotinib p.o. In the other period, 4,000 mg of calcium carbonate (4 X Tums Ultra 1000®) was administered p.o. 15 min prior to the nilotinib dose. Plasma samples were collected at specified timepoints, concentrations of nilotinib were quantitated by LC-MS, and data were analyzed non-compartmentally. Eleven subjects were evaluable. Calcium supplementation did not significantly affect nilotinib pharmacokinetic parameters including area under the plasma

  9. Amorphous manganese-calcium oxides as a possible evolutionary origin for the CaMn₄ cluster in photosystem II.

    PubMed

    Najafpour, Mohammad Mahdi

    2011-06-01

    In this paper a few calcium-manganese oxides and calcium-manganese minerals are studied as catalysts for water oxidation. The natural mineral marokite is also studied as a catalyst for water oxidation for the first time. Marokite is made up of edge-sharing Mn(3+) in a distorted octahedral environment and eight-coordinate Ca(2+) centered polyhedral layers. The structure is similar to recent models of the oxygen evolving complex in photosystem II. Thus, the oxygen evolving complex in photosystem II does not have an unusual structure and could be synthesized hydrothermally. Also in this paper, oxygen evolution is studied with marokite (CaMn₂O₄), pyrolusite (MnO₂) and compared with hollandite (Ba(0.2)Ca(0.15)K(0.3)Mn(6.9)Al(0.2)Si(0.3)O(16)), hausmannite (Mn₃O₄), Mn₂O₃.H₂O, Ca Mn₃O₆.H₂O, CaMn₄O₈.H₂O, CaMn₂O₄.H₂O and synthetic marokite (CaMn₂O₄). I propose that the origin of the oxygen evolving complex in photosystem II resulted from absorption of calcium and manganese ions that were precipitated together in the archean oceans by protocyanobacteria because of changing pH from ~5 to ~8-10. As reported in this paper, amorphous calcium-manganese oxides with different ratios of manganese and calcium are effective catalysts for water oxidation. The bond types and lengths of the calcium and manganese ions in the calcium-manganese oxides are directly comparable to those in the OEC. This primitive structure of these amorphous calcium-manganese compounds could be changed and modified by environmental groups (amino acids) to form the oxygen evolving complex in photosystem II.

  10. SECONDARY HYPERPARATHYROIDISM AFTER BARIATRIC SURGERY: TREATMENT IS WITH CALCIUM CARBONATE OR CALCIUM CITRATE?

    PubMed Central

    BARETTA, Giorgio Alfredo Pedroso; CAMBI, Maria Paula Carlini; RODRIGUES, Arieli Luz; MENDES, Silvana Aparecida

    2015-01-01

    Background : Bariatric surgery, especially Roux-en-Y gastric bypass, can cause serious nutritional complications arising from poor absorption of essential nutrients. Secondary hyperparathyroidism is one such complications that leads to increased parathyroid hormone levels due to a decrease in calcium and vitamin D, which may compromise bone health. Aim : To compare calcium carbonate and calcium citrate in the treatment of secondary hyperparathyroidism. Method : Patients were selected on the basis of their abnormal biochemical test and treatment was randomly done with citrate or calcium carbonate. Results : After 60 days of supplementation, biochemical tests were repeated, showing improvement in both groups. Conclusion : Supplementation with calcium (citrate or carbonate) and vitamin D is recommended after surgery for prevention of secondary hyperparathyroidism. PMID:26537273

  11. SECONDARY HYPERPARATHYROIDISM AFTER BARIATRIC SURGERY: TREATMENT IS WITH CALCIUM CARBONATE OR CALCIUM CITRATE?

    PubMed

    Baretta, Giorgio Alfredo Pedroso; Cambi, Maria Paula Carlini; Rodrigues, Arieli Luz; Mendes, Silvana Aparecida

    2015-01-01

    Bariatric surgery, especially Roux-en-Y gastric bypass, can cause serious nutritional complications arising from poor absorption of essential nutrients. Secondary hyperparathyroidism is one such complications that leads to increased parathyroid hormone levels due to a decrease in calcium and vitamin D, which may compromise bone health. To compare calcium carbonate and calcium citrate in the treatment of secondary hyperparathyroidism. Patients were selected on the basis of their abnormal biochemical test and treatment was randomly done with citrate or calcium carbonate. After 60 days of supplementation, biochemical tests were repeated, showing improvement in both groups. Supplementation with calcium (citrate or carbonate) and vitamin D is recommended after surgery for prevention of secondary hyperparathyroidism.

  12. Single walled carbon nanotube network—Tetrahedral amorphous carbon composite film

    SciTech Connect

    Iyer, Ajai Liu, Xuwen; Koskinen, Jari; Kaskela, Antti; Kauppinen, Esko I.; Johansson, Leena-Sisko

    2015-06-14

    Single walled carbon nanotube network (SWCNTN) was coated by tetrahedral amorphous carbon (ta-C) using a pulsed Filtered Cathodic Vacuum Arc system to form a SWCNTN—ta-C composite film. The effects of SWCNTN areal coverage density and ta-C coating thickness on the composite film properties were investigated. X-Ray photoelectron spectroscopy measurements prove the presence of high quality sp{sup 3} bonded ta-C coating on the SWCNTN. Raman spectroscopy suggests that the single wall carbon nanotubes (SWCNTs) forming the network survived encapsulation in the ta-C coating. Nano-mechanical testing suggests that the ta-C coated SWCNTN has superior wear performance compared to uncoated SWCNTN.

  13. The effect of brushing with nano calcium carbonate and calcium carbonate toothpaste on the surface roughness of nano-ionomer

    NASA Astrophysics Data System (ADS)

    Anisja, D. H.; Indrani, D. J.; Herda, E.

    2017-08-01

    Nanotechnology developments in dentistry have resulted in the development of nano-ionomer, a new restorative material. The surface roughness of restorative materials can increase bacteria adhesion and lead to poor oral hygiene. Abrasive agents in toothpaste can alter tooth and restorative material surfaces. The aim of this study is to identify the effect of brushing with nano calcium carbonate, and calcium carbonate toothpaste on surface roughness of nano-ionomer. Eighteen nano-ionomer specimens were brushed with Aquabidest (doubledistilled water), nano calcium carbonate and calcium carbonate toothpaste. Brushing lasted 30 minutes, and the roughness value (Ra) was measured after each 10 minute segment using a surface roughness tester. The data was analyzed using repeated ANOVA and one-way ANOVA test. The value of nano-ionomer surface roughness increased significantly (p<0.05) after 20 minutes of brushing with the nano calcium carbonate toothpaste. Brushing with calcium carbonate toothpaste leaves nano-ionomer surfaces more rugged than brushing with nano calcium carbonate toothpaste.

  14. Calcium carbonate does not affect imatinib pharmacokinetics in healthy volunteers.

    PubMed

    Tawbi, Hussein; Christner, Susan M; Lin, Yan; Johnson, Matthew; Mowrey, Emily T; Cherrin, Craig; Chu, Edward; Lee, James J; Puhalla, Shannon; Stoller, Ronald; Appleman, Leonard R; Miller, Brian M; Beumer, Jan H

    2014-01-01

    Imatinib mesylate (Gleevec(®)/Glivec(®)) has revolutionized the treatment of chronic myeloid leukemias and gastrointestinal stromal tumors, and there is evidence for an exposure response relationship. Calcium carbonate is increasingly used as a calcium supplement and in the setting of gastric upset associated with imatinib therapy. Calcium carbonate could conceivably elevate gastric pH and complex imatinib, thereby influencing imatinib absorption and exposure. We aimed to evaluate whether use of calcium carbonate has a significant effect on imatinib pharmacokinetics. Eleven healthy subjects were enrolled in a 2-period, open-label, single-institution, randomized crossover, fixed-schedule study. In one period, each subject received 400 mg of imatinib p.o. In the other period, 4,000 mg calcium carbonate (Tums Ultra(®)) was administered p.o. 15 min before 400 mg of imatinib. Plasma concentrations of imatinib and its active N-desmethyl metabolite CGP74588 were assayed by LC-MS; data were analyzed non-compartmentally and compared after log transformation. Calcium carbonate administration did not significantly affect the imatinib area under the plasma concentration versus time curve (AUC) (41.2 μg/mL h alone vs. 40.8 μg/mL h with calcium carbonate, P = 0.99), maximum plasma concentration (C(max)) (2.35 μg/mL alone vs. 2.39 μg/mL with calcium carbonate, P = 0.89). Our results indicate that the use of calcium carbonate does not significantly affect imatinib pharmacokinetics.

  15. Urea hydrolysis and calcium carbonate reaction fronts

    NASA Astrophysics Data System (ADS)

    Fox, D. T.; Redden, G. D.; Henriksen, J.; Fujita, Y.; Guo, L.; Huang, H.

    2010-12-01

    The mobility of toxic or radioactive metal contaminants in subsurface environments can be reduced by the formation of mineral precipitates that form co-precipitates with the contaminants or that isolate them from the mobile fluid phase. An engineering challenge is to control the spatial distribution of precipitation reactions with respect to: 1) the location of a contaminant, and 2) where reactants are introduced into the subsurface. One strategy being explored for immobilizing contaminants, such as Sr-90, involves stimulating mineral precipitation by forming carbonate ions and hydroxide via the in situ, microbially mediated hydrolysis of urea. A series of column experiments have been conducted to explore how the construction or design of such an in situ reactant production strategy can affect the temporal and spatial distribution of calcium carbonate precipitation, and how the distribution is coupled to changes in permeability. The columns were constructed with silica gel as the porous media. An interval midway through the column contained an adsorbed urease enzyme in order to simulate a biologically active zone. A series of influent solutions were injected to characterize hydraulic properties of the column (e.g., bromide tracer), profiles of chemical conditions and reaction products as the enzyme catalyzes urea hydrolysis (e.g., pH, ammonia, urea), and changes that occur due to CaCO3 precipitation with the introduction of a calcium+urea solutions. In one experiment, hydraulic conductivity was reduced as precipitate accumulated in a layer within the column that had a higher fraction of fine grained silica gel. Subsequent reduction of permeability and flow (for a constant head condition) resulted in displacement of the hydrolysis and precipitation reaction profiles upstream. In another experiment, which lacked the physical heterogeneity (fine grained layer), the precipitation reaction did not result in loss of permeability or flow velocity and the reaction profile

  16. Behaviour of calcium carbonate in sea water

    USGS Publications Warehouse

    Cloud, P.E.

    1962-01-01

    Anomalies in the behaviour of calcium carbonate in natural solutions diminish when considered in context. Best values found by traditional oceanographie methods for the apparent solubility product constant K'CaCO3 in sea water at atmospheric pressure are consistent mineralogically-at 36 parts per thousand salinity and T-25??C, K'aragonlte is estimated as 1.12 ?? 10-6 and K'calcite as 0.61 ?? 10-6. At 30??C the corresponding values are 0.98 ?? 10-6 for aragonite and 0.53 ?? 10-6 for calcite. Because the K' computations do not compensate for ionic activity, however, they cannot give thermodynamically satisfactory results. It is of interest, therefore, that approximate methods and information now available permit the estimation from the same basic data of an activity product constant KCaCO3 close to that found in solutions to which Debye-Hu??ckel theory applies. Such methods indicate approximate Karagonite 7.8 ?? 10-9 for surface sea water at 29??C; Kcalcite would be proportionately lower. Field data and experimental results indicate that the mineralogy of precipitated CaCO3 depends primarily on degree of supersaturation, thus also on kinetic or biologic factors that facilitate or inhibit a high degree of supersaturation. The shallow, generally hypersaline bank waters west of Andros Island yield aragonitic sediments with O18 O16 ratios that imply precipitation mainly during the warmer months, when the combination of a high rate of evaporation, increasing salinity (and ionic strength), maximal temperatures and photosynthetic removal of CO2 result in high apparent supersaturation. The usual precipitate from solutions of low ionic strength is calcite, except where the aragonite level of supersaturation is reached as a result of diffusion phenomena (e.g. dripstones), gradual and marked evaporation, or biologic intervention. Published data also suggest the possibility of distinct chemical milieus for crystallographic variations in skeletal calcium carbonate. It appears

  17. Peculiarities in thermal evolution of precipitated amorphous calcium phosphates with an initial Ca/P ratio of 1:1.

    PubMed

    Zyman, Zoltan; Epple, Matthias; Goncharenko, Anton; Rokhmistrov, Dmytro; Prymak, Oleg; Loza, Kateryna

    2017-03-01

    Thermal evolution of amorphous calcium phosphate (ACP) powder from a fast nitrate synthesis with a Ca/P ratio of 1:1 were studied in the range of 20-980 °C. The powder consisted of amorphous dicalcium phosphate anhydrate (CaHPO4) after heating to 200 °C. CaHPO4 gradually condensed to amorphous calcium pyrophosphate Ca2P2O7 (CPP) between 200 to 620 °C. Amorphous CPP crystallized at 620-740 °C to a metastable polymorph α'-CPP of the high-temperature phase α-CPP and β-CPP. The α'-CPP/ β-CPP phase ratio reached a maximum at 800 °C (60 wt% α'-CPP/40 wt% β-CPP), and α'-CPP gradually transformed to β-CPP at a higher temperature. Some β-TCP occurred at 900 °C, so that a three-phasic mixture was obtained in the powder heated to 980 °C. The occurrence of metastable α'-CPP is attributed to Ostwald's step rule, and a mechanism for β-TCP formation is proposed. The advantages of prospective biomaterials from these powders are discussed.

  18. Effect of lanthanum carbonate vs. calcium carbonate on serum calcium in hemodialysis patients: a crossover study.

    PubMed

    Toida, Tatsunori; Fukudome, Keiichi; Fujimoto, Shouichi; Yamada, Kazuhiro; Sato, Yuji; Chiyotanda, Susumu; Kitamura, Kazuo

    2012-09-01

    Lanthanum carbonate (LC) is a non-calcium-containing phosphate binder and shows a comparable effect with other phosphate binders on hyperphosphatemia in dialysis patients. LC also contributes to a reduced oral calcium load compared with calcium carbonate (CaC) treatment. However, no crossover studies which compare the influence on serum calcium level between treatments with LC and CaC in hemodialysis (HD) patients have been carried out. After washout for 2 weeks, 50 patients on HD were randomized (1 : 1) to receive LC or CaC for 3 months. Thereafter, patients underwent a second 2-week washout period and were switched to the alternative binder for the next 3 months. Mineral and bone metabolism markers were measured with the changes of vitamin D doses. The serum phosphate level showed a similar decrease from baseline to 3 months in both groups. During the study periods, hypercalcemia was observed only in patients taking CaC. The dose of vitamin D analogue was increased more frequently in the patients of the LC group compared with LC group. The iPTH level showed a significant decrease in the CaC group, but not in the LC group. Serum levels of BAP, TRAP5b, and ALP were significantly elevated in the LC group, whereas the FGF-23 level showed a significant decrease. LC effectively reduced the serum phosphate level (like CaC) and allowed the vitamin D analogue dosage to be increased without hypercalcemia in HD patients. LC is one of the useful phosphate binders without hypercalcemia. (UMIN-CTR registration number: UMIN000002331).

  19. Atomic-scale compositional mapping reveals Mg-rich amorphous calcium phosphate in human dental enamel

    PubMed Central

    La Fontaine, Alexandre; Zavgorodniy, Alexander; Liu, Howgwei; Zheng, Rongkun; Swain, Michael; Cairney, Julie

    2016-01-01

    Human dental enamel, the hardest tissue in the body, plays a vital role in protecting teeth from wear as a result of daily grinding and chewing as well as from chemical attack. It is well established that the mechanical strength and fatigue resistance of dental enamel are derived from its hierarchical structure, which consists of periodically arranged bundles of hydroxyapatite (HAP) nanowires. However, we do not yet have a full understanding of the in vivo HAP crystallization process that leads to this structure. Mg2+ ions, which are present in many biological systems, regulate HAP crystallization by stabilizing its precursor, amorphous calcium phosphate (ACP), but their atomic-scale distribution within HAP is unknown. We use atom probe tomography to provide the first direct observations of an intergranular Mg-rich ACP phase between the HAP nanowires in mature human dental enamel. We also observe Mg-rich elongated precipitates and pockets of organic material among the HAP nanowires. These observations support the postclassical theory of amelogenesis (that is, enamel formation) and suggest that decay occurs via dissolution of the intergranular phase. This information is also useful for the development of more accurate models to describe the mechanical behavior of teeth. PMID:27617291

  20. Atomic-scale compositional mapping reveals Mg-rich amorphous calcium phosphate in human dental enamel.

    PubMed

    La Fontaine, Alexandre; Zavgorodniy, Alexander; Liu, Howgwei; Zheng, Rongkun; Swain, Michael; Cairney, Julie

    2016-09-01

    Human dental enamel, the hardest tissue in the body, plays a vital role in protecting teeth from wear as a result of daily grinding and chewing as well as from chemical attack. It is well established that the mechanical strength and fatigue resistance of dental enamel are derived from its hierarchical structure, which consists of periodically arranged bundles of hydroxyapatite (HAP) nanowires. However, we do not yet have a full understanding of the in vivo HAP crystallization process that leads to this structure. Mg(2+) ions, which are present in many biological systems, regulate HAP crystallization by stabilizing its precursor, amorphous calcium phosphate (ACP), but their atomic-scale distribution within HAP is unknown. We use atom probe tomography to provide the first direct observations of an intergranular Mg-rich ACP phase between the HAP nanowires in mature human dental enamel. We also observe Mg-rich elongated precipitates and pockets of organic material among the HAP nanowires. These observations support the postclassical theory of amelogenesis (that is, enamel formation) and suggest that decay occurs via dissolution of the intergranular phase. This information is also useful for the development of more accurate models to describe the mechanical behavior of teeth.

  1. The role of Carboxydothermus hydrogenoformans in the conversion of calcium phosphate from amorphous to crystalline state.

    PubMed

    Haddad, Mathieu; Vali, Hojatollah; Paquette, Jeanne; Guiot, Serge R

    2014-01-01

    Two previously unknown modes of biomineralization observed in the presence of Carboxydothermus hydrogenoformans are presented. Following the addition of NaHCO3 and the formation of an amorphous calcium phosphate precipitate in a DSMZ medium inoculated with C. hydrogenoformans, two distinct crystalline solids were recovered after 15 and 30 days of incubation. The first of these solids occurred as micrometric clusters of blocky, angular crystals, which were associated with bacterial biofilm. The second solid occurred as 30-50 nm nanorods that were found scattered among the organic products of bacterial lysis. The biphasic mixture of solids was clearly dominated by the first phase. The X-ray diffractometry (XRD) peaks and Fourier transform infrared spectroscopy (FTIR) spectrum of this biphasic material consistently showed features characteristic of Mg-whitlockite. No organic content or protein could be identified by dissolving the solids. In both cases, the mode of biomineralization appears to be biologically induced rather than biologically controlled. Since Mg is known to be a strong inhibitor of the nucleation and growth of CaP, C. hydrogenoformans may act by providing sites that chelate Mg or form complexes with it, thus decreasing its activity as nucleation and crystal growth inhibitor. The synthesis of whitlockite and nano-HAP-like material by C. hydrogenoformans demonstrates the versatility of this organism also known for its ability to perform the water-gas shift reaction, and may have applications in bacterially mediated synthesis of CaP materials, as an environmentally friendly alternative process.

  2. Axially aligned organic fibers and amorphous calcium phosphate form the claws of a terrestrial isopod (Crustacea).

    PubMed

    Vittori, Miloš; Srot, Vesna; Žagar, Kristina; Bussmann, Birgit; van Aken, Peter A; Čeh, Miran; Štrus, Jasna

    2016-08-01

    Skeletal elements that are exposed to heavy mechanical loads may provide important insights into the evolutionary solutions to mechanical challenges. We analyzed the microscopic architecture of dactylus claws in the woodlice Porcellio scaber and correlated these observations with analyses of the claws' mineral composition with energy dispersive X-ray spectrometry (EDX), electron energy loss spectroscopy (EELS) and selected area electron diffraction (SAED). Extraordinarily, amorphous calcium phosphate is the predominant mineral in the claw endocuticle. Unlike the strongly calcified exocuticle of the dactylus base, the claw exocuticle is devoid of mineral and is highly brominated. The architecture of the dactylus claw cuticle is drastically different from that of other parts of the exoskeleton. In contrast to the quasi-isotropic structure with chitin-protein fibers oriented in multiple directions, characteristic of the arthropod exoskeleton, the chitin-protein fibers and mineral components in the endocuticle of P. scaber claws are exclusively axially oriented. Taken together, these characteristics suggest that the claw cuticle is highly structurally anisotropic and fracture resistant and can be explained as adaptations to predominant axial loading of the thin, elongated claws. The nanoscale architecture of the isopod claw may inspire technological solutions in the design of durable machine elements subjected to heavy loading and wear.

  3. Analysis of anticaries potential of pit and fissures sealants containing amorphous calcium phosphate using synchrotron microtomography.

    PubMed

    Delben, A C B; Cannon, M; Vieira, A E M; Basso, M D; Danelon, M; Santo, M R E; Stock, S R; Xiao, X; De Carlo, F

    2015-01-01

    The aim of this study was to analyze the anticaries potential of pit and fissure sealants containing amorphous calcium phosphate (ACP) by synchrotron microtomography. Bovine enamel blocks (4×4 mm; n=50) were selected through surface hardness (Knoop) analysis. Slabs were obtained through cross-sections taken 1 mm from the border of the enamel. Five indentations, spaced 100 μm apart, were made 300 μm from the border. Ten specimens were prepared for each tested material (Ultraseal XT plus TM, Aegis, Embrace, Vitremer and Experimental Sealant). The materials were randomly attached to the sectioned surfaces of the enamel blocks and fixed with sticky wax. The specimens were submitted to pH cycling. After that, the surface hardness (SH1) was determined, and the blocks were submitted to synchrotron microcomputed tomography analysis to calculate the mineral concentration (ΔgHAp cm(-3)) at different areas of the enamel. The comparison between the SH1 and ΔgHAp cm(-3) showed a correlation for all groups (r=0.840; p<0.001). The fluoride groups presented positive values of ΔgHAp cm(-3), indicating a mineral gain that was observed mainly in the outer part of the enamel. The ACP showed mineral loss in the outer enamel compared with fluoride groups, although it inhibited the demineralization in the deeper areas of enamel. The combination of two remineralizing agents (fluoride and ACP) was highly effective in preventing demineralization.

  4. The Role of Carboxydothermus hydrogenoformans in the Conversion of Calcium Phosphate from Amorphous to Crystalline State

    PubMed Central

    Haddad, Mathieu; Vali, Hojatollah; Paquette, Jeanne; Guiot, Serge R.

    2014-01-01

    Two previously unknown modes of biomineralization observed in the presence of Carboxydothermus hydrogenoformans are presented. Following the addition of NaHCO3 and the formation of an amorphous calcium phosphate precipitate in a DSMZ medium inoculated with C. hydrogenoformans, two distinct crystalline solids were recovered after 15 and 30 days of incubation. The first of these solids occurred as micrometric clusters of blocky, angular crystals, which were associated with bacterial biofilm. The second solid occurred as 30–50 nm nanorods that were found scattered among the organic products of bacterial lysis. The biphasic mixture of solids was clearly dominated by the first phase. The X-ray diffractometry (XRD) peaks and Fourier transform infrared spectroscopy (FTIR) spectrum of this biphasic material consistently showed features characteristic of Mg-whitlockite. No organic content or protein could be identified by dissolving the solids. In both cases, the mode of biomineralization appears to be biologically induced rather than biologically controlled. Since Mg is known to be a strong inhibitor of the nucleation and growth of CaP, C. hydrogenoformans may act by providing sites that chelate Mg or form complexes with it, thus decreasing its activity as nucleation and crystal growth inhibitor. The synthesis of whitlockite and nano-HAP-like material by C. hydrogenoformans demonstrates the versatility of this organism also known for its ability to perform the water-gas shift reaction, and may have applications in bacterially mediated synthesis of CaP materials, as an environmentally friendly alternative process. PMID:24586811

  5. Ion beam deposition of amorphous carbon films with diamond like properties

    NASA Technical Reports Server (NTRS)

    Angus, John C.; Mirtich, Michael J.; Wintucky, Edwin G.

    1982-01-01

    Carbon films were deposited on silicon, quartz, and potassium bromide substrates from an ion beam. Growth rates were approximately 0.3 micron/hour. The films were featureless and amorphous and contained only carbon and hydrogen in significant amounts. The density and carbon/hydrogen ratio indicate the film is a hydrogen deficient polymer. One possible structure, consistent with the data, is a random network of methylene linkages and tetrahedrally coordinated carbon atoms.

  6. Nanoparticle tracers in calcium carbonate porous media

    NASA Astrophysics Data System (ADS)

    Li, Yan Vivian; Cathles, Lawrence M.; Archer, Lynden A.

    2014-08-01

    Tracers are perhaps the most direct way of diagnosing subsurface fluid flow pathways for ground water decontamination and for natural gas and oil production. Nanoparticle tracers could be particularly effective because they do not diffuse away from the fractures or channels where flow occurs and thus take much less time to travel between two points. In combination with a chemical tracer they can measure the degree of flow concentration. A prerequisite for tracer applications is that the particles are not retained in the porous media as the result of aggregation or sticking to mineral surfaces. By screening eight nanoparticles (3-100 nm in diameter) for retention when passed through calcium carbonate packed laboratory columns in artificial oil field brine solutions of variable ionic strength we show that the nanoparticles with the least retention are 3 nm in diameter, nearly uncharged, and decorated with highly hydrophilic polymeric ligands. The details of these column experiments and the tri-modal distribution of zeta potential of the calcite sand particles in the brine used in our tests suggests that parts of the calcite surface have positive zeta potential and the retention of negatively charged nanoparticles occurs at these sites. Only neutral nanoparticles are immune to at least some retention.

  7. Seeded Growth Route to Noble Calcium Carbonate Nanocrystal.

    PubMed

    Islam, Aminul; Teo, Siow Hwa; Rahman, M Aminur; Taufiq-Yap, Yun Hin

    2015-01-01

    A solution-phase route has been considered as the most promising route to synthesize noble nanostructures. A majority of their synthesis approaches of calcium carbonate (CaCO3) are based on either using fungi or the CO2 bubbling methods. Here, we approached the preparation of nano-precipitated calcium carbonate single crystal from salmacis sphaeroides in the presence of zwitterionic or cationic biosurfactants without external source of CO2. The calcium carbonate crystals were rhombohedron structure and regularly shaped with side dimension ranging from 33-41 nm. The high degree of morphological control of CaCO3 nanocrystals suggested that surfactants are capable of strongly interacting with the CaCO3 surface and control the nucleation and growth direction of calcium carbonate nanocrystals. Finally, the mechanism of formation of nanocrystals in light of proposed routes was also discussed.

  8. Seeded Growth Route to Noble Calcium Carbonate Nanocrystal

    PubMed Central

    Islam, Aminul; Teo, Siow Hwa; Rahman, M. Aminur; Taufiq-Yap, Yun Hin

    2015-01-01

    A solution-phase route has been considered as the most promising route to synthesize noble nanostructures. A majority of their synthesis approaches of calcium carbonate (CaCO3) are based on either using fungi or the CO2 bubbling methods. Here, we approached the preparation of nano-precipitated calcium carbonate single crystal from salmacis sphaeroides in the presence of zwitterionic or cationic biosurfactants without external source of CO2. The calcium carbonate crystals were rhombohedron structure and regularly shaped with side dimension ranging from 33–41 nm. The high degree of morphological control of CaCO3 nanocrystals suggested that surfactants are capable of strongly interacting with the CaCO3 surface and control the nucleation and growth direction of calcium carbonate nanocrystals. Finally, the mechanism of formation of nanocrystals in light of proposed routes was also discussed. PMID:26700479

  9. Hen eggwhite-mediated stack crystallization of calcium carbonate

    NASA Astrophysics Data System (ADS)

    Hu, Yanli; Ma, Yongjun; Zhou, Yong; Nie, Fude; Duan, Xiaohui; Pei, Chonghua

    2010-03-01

    In this paper, the stack-like crystallization of calcium carbonate in the presence of hen eggwhite under direct drying and vacuum freeze drying was investigated, and marked morphological changes in the calcium carbonate particles were observed depending on the reaction condition used. Scanning electron microscopy (SEM), Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Transmission electron microscopy (TEM), and Nano Mechanical Tester were employed to characterize the samples. Results indicate that gelling eggwhite-mediated the formation of the "stack-like" layered calcium carbonate aggregates composed of considerable nanosheets under direct drying while only rhombohedra calcite crystal (1 0 4) was formed without any additives. An analogous structure to the brick-and-mortar arrangement was attainted by vacuum freeze drying. The average elastic modulus and the hardness of "stack-like" calcium carbonate hybrid material were assessed 0.9952 and 0.0415 GPa with Nano-indenter test, respectively.

  10. Effect of amorphous phases during the hydraulic conversion of α-TCP into calcium-deficient hydroxyapatite.

    PubMed

    Hurle, Katrin; Neubauer, Juergen; Bohner, Marc; Doebelin, Nicola; Goetz-Neunhoeffer, Friedlinde

    2014-09-01

    Powders of α-tricalcium phosphate (α-TCP), which readily react with water to form calcium-deficient hydroxyapatite (CDHA), are frequently used in bone cements. As, for clinical applications, it is important to adjust the setting reaction of the cements to a reasonable reaction time, exact knowledge of the hydration mechanism is essential. It is known that prolonged milling results in partial amorphization of α-TCP powders and that dissolution of the amorphous phase significantly accelerates the hydration, but it is not clear yet when the amorphous phase reacts in comparison to the crystalline α-TCP. Therefore the aim of this study was to investigate the development of quantitative phase content of α-TCP samples during hydration. For this purpose, three α-TCP powders, containing 0, 16 and 71wt.% of amorphous phase (ATCP), were mixed with either deionized water or a 0.1M Na2HPO4 aqueous solution. The crystalline evolution of the paste was assessed quantitatively during the first 48h of hydration at 23°C by G-factor quantification. The present investigations demonstrate that ATCP reacted earlier than crystalline α-TCP. The results also suggest the formation of an X-ray amorphous phase during the hydraulic conversion formation of α-TCP into CDHA.

  11. Large-deformation and high-strength amorphous porous carbon nanospheres

    PubMed Central

    Yang, Weizhu; Mao, Shimin; Yang, Jia; Shang, Tao; Song, Hongguang; Mabon, James; Swiech, Wacek; Vance, John R.; Yue, Zhufeng; Dillon, Shen J.; Xu, Hangxun; Xu, Baoxing

    2016-01-01

    Carbon is one of the most important materials extensively used in industry and our daily life. Crystalline carbon materials such as carbon nanotubes and graphene possess ultrahigh strength and toughness. In contrast, amorphous carbon is known to be very brittle and can sustain little compressive deformation. Inspired by biological shells and honeycomb-like cellular structures in nature, we introduce a class of hybrid structural designs and demonstrate that amorphous porous carbon nanospheres with a thin outer shell can simultaneously achieve high strength and sustain large deformation. The amorphous carbon nanospheres were synthesized via a low-cost, scalable and structure-controllable ultrasonic spray pyrolysis approach using energetic carbon precursors. In situ compression experiments on individual nanospheres show that the amorphous carbon nanospheres with an optimized structure can sustain beyond 50% compressive strain. Both experiments and finite element analyses reveal that the buckling deformation of the outer spherical shell dominates the improvement of strength while the collapse of inner nanoscale pores driven by twisting, rotation, buckling and bending of pore walls contributes to the large deformation. PMID:27072412

  12. Properties of Amorphous Carbon Microspheres Synthesised by Palm Oil-CVD Method

    SciTech Connect

    Zobir, S. A. M.; Zainal, Z.; Sarijo, S. H.; Rusop, M.

    2011-03-30

    Amorphous carbon microspheres were synthesized using a dual-furnace chemical vapour deposition method at 800-1000 deg. C. Palm oil-based cooking oil (PO) and zinc nitrate solution was used as a carbon source and catalyst precursor, respectively with PO to zinc nitrate ratio of 30:20 (v/v) and a silicon wafer as the sample target. Regular microsphere shape of the amorphous carbons was obtained and a uniform microsphere structure improved as the carbonization temperature increased from 800 to 1000 deg. C. At 800 deg. C, no regular microspheres were formed but more uniform structure is observed at 900 deg. C. Generally the microspheres size is uniform when the heating temperature was increased to 1000 deg. C, but the presence of mixed sizes can still be observed. X-ray diffraction patterns show the presence of oxide of carbon, ZnO phase together with Zn oxalate phase. Raman spectra show two broad peaks characteristic to amorphous carbon at 1344 and 1582 cm{sup -1} for the D and G bands, respectively. These bands become more prominent as the preparation temperature increased from 800 to 1000 deg. C. This is in agreement with the formation of amorphous carbon microspheres as shown by the FESEM study and other Zn-based phases as a result of the oxidation process of the palm oil as the carbon source and the zinc nitrate as the catalyst precursor, respectively.

  13. Large-deformation and high-strength amorphous porous carbon nanospheres

    NASA Astrophysics Data System (ADS)

    Yang, Weizhu; Mao, Shimin; Yang, Jia; Shang, Tao; Song, Hongguang; Mabon, James; Swiech, Wacek; Vance, John R.; Yue, Zhufeng; Dillon, Shen J.; Xu, Hangxun; Xu, Baoxing

    2016-04-01

    Carbon is one of the most important materials extensively used in industry and our daily life. Crystalline carbon materials such as carbon nanotubes and graphene possess ultrahigh strength and toughness. In contrast, amorphous carbon is known to be very brittle and can sustain little compressive deformation. Inspired by biological shells and honeycomb-like cellular structures in nature, we introduce a class of hybrid structural designs and demonstrate that amorphous porous carbon nanospheres with a thin outer shell can simultaneously achieve high strength and sustain large deformation. The amorphous carbon nanospheres were synthesized via a low-cost, scalable and structure-controllable ultrasonic spray pyrolysis approach using energetic carbon precursors. In situ compression experiments on individual nanospheres show that the amorphous carbon nanospheres with an optimized structure can sustain beyond 50% compressive strain. Both experiments and finite element analyses reveal that the buckling deformation of the outer spherical shell dominates the improvement of strength while the collapse of inner nanoscale pores driven by twisting, rotation, buckling and bending of pore walls contributes to the large deformation.

  14. Large-deformation and high-strength amorphous porous carbon nanospheres.

    PubMed

    Yang, Weizhu; Mao, Shimin; Yang, Jia; Shang, Tao; Song, Hongguang; Mabon, James; Swiech, Wacek; Vance, John R; Yue, Zhufeng; Dillon, Shen J; Xu, Hangxun; Xu, Baoxing

    2016-04-13

    Carbon is one of the most important materials extensively used in industry and our daily life. Crystalline carbon materials such as carbon nanotubes and graphene possess ultrahigh strength and toughness. In contrast, amorphous carbon is known to be very brittle and can sustain little compressive deformation. Inspired by biological shells and honeycomb-like cellular structures in nature, we introduce a class of hybrid structural designs and demonstrate that amorphous porous carbon nanospheres with a thin outer shell can simultaneously achieve high strength and sustain large deformation. The amorphous carbon nanospheres were synthesized via a low-cost, scalable and structure-controllable ultrasonic spray pyrolysis approach using energetic carbon precursors. In situ compression experiments on individual nanospheres show that the amorphous carbon nanospheres with an optimized structure can sustain beyond 50% compressive strain. Both experiments and finite element analyses reveal that the buckling deformation of the outer spherical shell dominates the improvement of strength while the collapse of inner nanoscale pores driven by twisting, rotation, buckling and bending of pore walls contributes to the large deformation.

  15. Properties of Amorphous Carbon Microspheres Synthesised by Palm Oil-CVD Method

    NASA Astrophysics Data System (ADS)

    Zobir, S. A. M.; Zainal, Z.; Sarijo, S. H.; Rusop, M.

    2011-03-01

    Amorphous carbon microspheres were synthesized using a dual-furnace chemical vapour deposition method at 800-1000° C. Palm oil-based cooking oil (PO) and zinc nitrate solution was used as a carbon source and catalyst precursor, respectively with PO to zinc nitrate ratio of 30:20 (v/v) and a silicon wafer as the sample target. Regular microsphere shape of the amorphous carbons was obtained and a uniform microsphere structure improved as the carbonization temperature increased from 800 to 1000° C. At 800° C, no regular microspheres were formed but more uniform structure is observed at 900° C. Generally the microspheres size is uniform when the heating temperature was increased to 1000° C, but the presence of mixed sizes can still be observed. X-ray diffraction patterns show the presence of oxide of carbon, ZnO phase together with Zn oxalate phase. Raman spectra show two broad peaks characteristic to amorphous carbon at 1344 and 1582 cm-1 for the D and G bands, respectively. These bands become more prominent as the preparation temperature increased from 800 to 1000° C. This is in agreement with the formation of amorphous carbon microspheres as shown by the FESEM study and other Zn-based phases as a result of the oxidation process of the palm oil as the carbon source and the zinc nitrate as the catalyst precursor, respectively.

  16. The Optical Properties of Hydrogenated Amorphous Carbon Films

    NASA Astrophysics Data System (ADS)

    Furton, D. G.; Witt, A. N.

    1993-01-01

    We present the initial results of a laboratory study of hydrogenated amorphous carbon (HAC) thin films. We produce a quantitative summary of the optical and physical properties of a consistent set of HAC films processed in various ways and use these results to gain insight into the formation and evolution of dust grains in the interstellar medium. HAC thin films were deposited on NaCl coated substrates in a plasma-enhanced chemical-vapor deposition (PECVD) chamber, removed from the substrates, and characterized and processed in a variety of ways. Raman, photoluminescence (PL), transmission, and absorption spectroscopy were used to characterize these films in the visible. Infrared absorption and PL spectroscopy were used to analyze these films in the 1-20 micron region. Electron energy-loss spectroscopy (EELS) was used to calculate the index of refraction in the UV and the sp(2}/sp({3)) bonding ratio, and combustion analysis was used to determine the C/H ratio. Each member of a set of identically grown films was characterized as described above, processed to various extents, then characterized again. Some of the films were thermally annealed in vacuum over a range of temperatures and durations, while others were exposed to intense UV radiation. Our initial results are summarized as follows: The H-concentration, PL efficiency, band-gap, and transmission in the visible decrease with the extent of thermal or UV annealing. Thermally induced changes occur rapidly and long-term annealing at lower temperatures does not produce the same effects as higher temperature annealing. The films are essentially graphitized when annealed at temperatures higher than about 400(deg) C and they are completely obliterated when exposed to very intense UV radiation. We have also developed a thermal effusion oven to test to what extent HAC films can be ``rehydrogenated'' by exposure to neutral atomic hydrogen. These experiments are nearly complete and the results will be included if possible

  17. Calcium and calcium magnesium carbonate specimens submitted as urinary tract stones.

    PubMed

    Gault, M H; Chafe, L; Longerich, L; Mason, R A

    1993-02-01

    Of 8,129 specimens submitted as urinary stones from 6,095 patients, 67 from 15 patients were predominantly calcium carbonate or calcium magnesium carbonate (dolomite) by infrared analysis. Detailed study of 1 man and 4 women who submitted 3 or more such specimens showed that all were of aragonite calcium carbonate crystal form in 2 women and all calcite in the man. All 3 patients had a long history of nephrolithiasis preceding submission of calcium carbonate stones. There was frequent and often painful spontaneous passage of many small stones. Medullary sponge kidney was reported in 2 patients. Specimens submitted by the other 2 women included dolomite and quartz artifacts. Of the other 10 patients 4 had calcite and 1 had aragonite (possibly true stones). Five patients had artifacts with dolomite in 3 and mixed specimens in 2. True calcium carbonate kidney stones and calcium carbonate artifacts may be difficult to distinguish, and dolomite and quartz artifacts may require x-ray diffraction for clear-cut diagnosis.

  18. Highly conductive carbon black supported amorphous molybdenum disulfide for efficient hydrogen evolution reaction

    NASA Astrophysics Data System (ADS)

    Cao, Pengfei; Peng, Jing; Li, Jiuqiang; Zhai, Maolin

    2017-04-01

    Molybdenum disulfide (MoS2) is a promising electrocatalyst for hydrogen evolution reaction (HER), however, the catalytic activity of reported MoS2-based materials towards HER still can't satisfy the requirement of practical application. Herein, highly conductive carbon black (CB) supported amorphous MoS2 nanocomposite is synthesized by a facile one-pot hydrothermal process. XRD and TEM analysis proves the amorphous morphology of MoS2. XPS further confirms both hexagonal and orthorhombic S ligands exist in the amorphous MoS2. Compared with crystalline MoS2, amorphous MoS2/CB shows an onset overpotential of 78 mV and current density of 470 mA cm-2 at the overpotential of 200 mV, which is even 50% higher than that of the commercial 20% Pt/C catalyst. Furthermore, a fairly stable performance can be achieved even after 5000 CV cycles. The outstanding HER activity and stability of the amorphous MoS2/CB nanocomposite can be attributed to these advantages: (1) amorphous structure offers more active sites in MoS2; (2) highly conductive CB reduces the charge transfer resistance (RCT); (3) relative hydrophilic CB can largely reduce the resistance between catalyst/electrolyte interface and allows rapid mass transport; (4) electron penetration effect between amorphous MoS2 and CB increases the intrinsic activity of amorphous MoS2 by two orders of magnitude.

  19. Calcium carbonate mineralization: X-ray microdiffraction probing of the interface of an evaporating drop on a superhydrophobic surface.

    PubMed

    Accardo, Angelo; Burghammer, Manfred; Di Cola, Emanuela; Reynolds, Michael; Di Fabrizio, Enzo; Riekel, Christian

    2011-07-05

    The liquid/air interface of calcium bicarbonate solution drops was probed by synchrotron radiation microbeam scattering. The drops were deposited on a nanopatterned superhydrophobic poly(methyl methacrylate) surface and raster-scanned during evaporation by small-angle and wide-angle X-ray scattering. The appearance of about 200-nm-size calcite crystallites at the interface could be spatially resolved at the onset of crystallization. Diffuse scattering from the interface is attributed to a dense nanoscale amorphous calcium carbonate phase. Calcite was found to be the major phase in the solid residue with vaterite as minor phase.

  20. Effect of casein phosphopeptide-amorphous calcium phosphate added to acidic beverages on enamel erosion in vitro.

    PubMed

    Manton, D J; Cai, F; Yuan, Y; Walker, G D; Cochrane, N J; Reynolds, C; Brearley-Messer, L J; Reynolds, E C

    2010-09-01

    To investigate, in vitro, the effect on enamel erosion of the addition of 0.2% w/v casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) to four commercially-available soft drinks, two of which were carbonated. Enamel specimens (n=27) were sectioned from sound extracted human third molar teeth and polished to a mirror finish. Exposed enamel windows of 1 mm2 were created by painting the surface with acid-resistant nail varnish. Four citric flavoured soft drinks (pH range 2.2 to 2.4) and distilled deionized water (DDW) were tested. Each drink was tested with and without 0.2% CPP-ACP w/v. The specimens were placed into 50 mL of solution at 37 °C for 30 minutes, rinsed and varnish removed. The samples were profiled with a white light profilometer and erosive depths recorded. All soft drinks tested caused enamel erosion but adding 0.2% w/v CPP-ACP significantly reduced (p<.05) erosive depth in all test solutions in comparison with the solutions without CPP-ACP. The erosive depths for all solutions with 0.2% CPP-ACP did not differ significantly from those of DDW. Adding CPP-ACP at 0.2% w/v significantly decreased the erosivity of all four soft drinks. The erosivity of the soft drinks with 0.2% CPP-ACP added did not differ significantly from that of distilled water.

  1. Oral calcium carbonate affects calcium but not phosphorus balance in stage 3-4 chronic kidney disease.

    PubMed

    Hill, Kathleen M; Martin, Berdine R; Wastney, Meryl E; McCabe, George P; Moe, Sharon M; Weaver, Connie M; Peacock, Munro

    2013-05-01

    Patients with chronic kidney disease (CKD) are given calcium carbonate to bind dietary phosphorus, reduce phosphorus retention, and prevent negative calcium balance; however, data are limited on calcium and phosphorus balance during CKD to support this. Here, we studied eight patients with stage 3 or 4 CKD (mean estimated glomerular filtration rate 36 ml/min) who received a controlled diet with or without a calcium carbonate supplement (1500 mg/day calcium) during two 3-week balance periods in a randomized placebo-controlled cross-over design. All feces and urine were collected during weeks 2 and 3 of each balance period and fasting blood, and urine was collected at baseline and at the end of each week. Calcium kinetics were determined using oral and intravenous (45)calcium. Patients were found to be in neutral calcium and phosphorus balance while on the placebo. Calcium carbonate supplementation produced positive calcium balance, did not affect phosphorus balance, and produced only a modest reduction in urine phosphorus excretion compared with placebo. Calcium kinetics demonstrated positive net bone balance but less than overall calcium balance, suggesting soft-tissue deposition. Fasting blood and urine biochemistries of calcium and phosphate homeostasis were unaffected by calcium carbonate. Thus, the positive calcium balance produced by calcium carbonate treatment within 3 weeks cautions against its use as a phosphate binder in patients with stage 3 or 4 CKD, if these findings can be extrapolated to long-term therapy.

  2. Calcium acetate versus calcium carbonate as phosphorus binders in patients on chronic haemodialysis: a controlled study.

    PubMed

    Ring, T; Nielsen, C; Andersen, S P; Behrens, J K; Sodemann, B; Kornerup, H J

    1993-01-01

    The first reported double-blind cross-over comparison between the phosphorus binders calcium carbonate and calcium acetate was undertaken in 15 stable patients on chronic maintenance haemodialysis. Detailed registration of diet and analysis of the protein catabolic rate suggested an unchanged phosphorus intake during the study. It was found that predialytic serum phosphate concentration was significantly decreased by 0.11 mmol/l (0.34 mg/dl) (P = 0.021, 95% confidence limits 0.02-0.21 mmol/l; 0.06-0.65 mg/dl) during calcium acetate treatment. The calcium phosphate product was insignificantly decreased during treatment with calcium acetate whereas we could not exclude the possibility that calcium concentration had increased.

  3. Antibacterial activity and ion release of bonding agent containing amorphous calcium phosphate nanoparticles

    PubMed Central

    Chen, Chen; Weir, Michael D.; Cheng, Lei; Lin, Nancy; Lin-Gibson, Sheng; Chow, Laurence C.; Zhou, Xuedong; Xu, Hockin H. K.

    2015-01-01

    Objectives Recurrent caries at the margins is a primary reason for restoration failure. The objectives of this study were to develop bonding agent with the double benefits of antibacterial and remineralizing capabilities, to investigate the effects of NACP filler level and solution pH on Ca and P ion release from adhesive, and to examine the antibacterial and dentin bond properties. Methods Nanoparticles of amorphous calcium phosphate (NACP) and a quaternary ammonium monomer (dimethylaminododecyl methacrylate, DMADDM) were synthesized. Scotchbond Multi-Purpose (SBMP) primer and adhesive served as control. DMADDM was incorporated into primer and adhesive at 5% by mass. NACP was incorporated into adhesive at filler mass fractions of 10%, 20%, 30% and 40%. A dental plaque microcosm biofilm model was used to test the antibacterial bonding agents. Calcium (Ca) and phosphate (P) ion releases from the cured adhesive samples were measured vs. filler level and solution pH of 7, 5.5 and 4. Results Adding 5% DMADDM and 10–40% NACP into bonding agent, and water-aging for 28 days, did not affect dentin bond strength, compared to SBMP control at 1 day (p > 0.1). Adding DMADDM into bonding agent substantially decreased the biofilm metabolic activity and lactic acid production. Total microorganisms, total streptococci, and mutans streptococci were greatly reduced for bonding agents containing DMADDM. Increasing NACP filler level from 10% to 40% in adhesive increased the Ca and P ion release by an order of magnitude. Decreasing solution pH from 7 to 4 increased the ion release from adhesive by 6–10 folds. Significance Bonding agents containing antibacterial DMADDM and remineralizer NACP were formulated to have Ca and P ion release, which increased with NACP filler level from 10% to 40% in adhesive. NACP adhesive was “smart” and dramatically increased the ion release at cariogenic pH 4, when these ions would be most-needed to inhibit caries. Therefore, bonding agent

  4. Theoretical investigation of magnetic properties in interfaces of magnetic nanoparticles and amorphous carbons

    NASA Astrophysics Data System (ADS)

    Sun, Shih-Jye; Hsu, Hua-Shu; Ovchinnikov, Sergei; Chen, Guan-Long

    2017-06-01

    Based on the experimental finding of the exchange bias in amorphous carbon samples with embedded Co nanoparticles and on the graphited character of the amorphous carbon interface confirmed by molecular dynamics simulations we have proposed the interface of graphited carbon to be antiferromagnetic. A theoretical model, which comprises the Kondo interactions in the interfaces of Co nanoparticles and the induced antiferromagnetic interactions in the graphited carbons, is employed to evaluate the ferromagnetism of the interfaces of Co nanoparticles. We have shown that the ferromagnetism of interfaces of Co nanoparticles will be enhanced by the increase of antiferromagnetic interaction as well as the increase of electron density in the graphited carbons. In particular, we found that the antiferromagnetic interactions in graphited carbons will change the spin-wave excitation in interfaces of Co nanoparticles from the quasiacoustic mode to the quasioptical one.

  5. Attaching molecules to chlorinated and brominated amorphous carbon substrates via Grignard reactions

    PubMed Central

    Lockett, Matthew R.; Smith, Lloyd M.

    2009-01-01

    Amorphous carbon thin films are an attractive material as they provide a chemically robust surface that has been utilized in biomolecule array, biosensor, and bioelectronic applications. These thin films are particularly versatile as they are deposited at room temperature making them readily integrated with other materials and devices. Here we present an alternative means of functionalizing carbon substrates based on Grignard chemistry. First, the amorphous carbon substrates are halogenated with a solution-based, radical-initiated halogenation reaction using PX5 (X = Br or Cl). Next, the halogenated surfaces are modified via the formation of a carbon-carbon bond between the surface and the Grignard reagents employed. An alkyl-, perfluoroalkyl-, and a poly(ethylene glycol)-Grignard reagent were chosen to show the utility of this reaction scheme in functionalizing carbon surfaces to withstand oxidation and provide a hydrophobic and/or biocompatible substrate. PMID:19708232

  6. Characterization of cytolytic neutrophil activation in vitro by amorphous hydrated calcium phosphate as a model of biomaterial inflammation.

    PubMed

    Edwards, Felicity C; Taheri, Amir; Dann, Sophie C; Dye, Julian F

    2011-03-01

    Calcium ions are utilized in biomolecular biomaterial design for osteomimetic scaffolds and as divalent cross-linking agents, typically for gelation of alginates, stabilisation of protein structure (e.g., fibrinogen) and enzyme activation (e.g., thrombin). Biological interactions with defined calcium phosphates (e.g., hydroxyapatite) are exploited for osteogenesis, although crystalline calcium phosphates (e.g., calcium pyrophosphate) stimulate inflammation. We found that the calcium concentration used in the manufacture of prototype dermal scaffolds made from fibrin/alginate composite was related to the inflammatory infiltration during in vivo integration. In investigating a cause for this inflammatory response, we have identified and characterized a cytolytic inflammatory effect of amorphous calcium phosphate (CaP) formed in physiological solutions, relevant to biomaterial biocompatibility. Isolated human neutrophils (Nφ) were incubated in phosphate-buffered saline with CaCl(2) ranging 2.5-20 mM total calcium. Nφ activation was assessed by morphology and integrin-β2 (CD18a) expression. Mediator release (Nφ-elastase, IL-8, and TNFα) was measured from both Nφ and whole blood cultures plus CaCl(2). CaP exposure increased CD18a expression over 1 h (maximal at 10 mM calcium/ phosphate) with concurrent phagocytosis, cytolysis, and Nφ-elastase release. CaCl(2) induced expression of IL-8 and TNFα in whole blood cultures. These results suggest that CaP formed from the resorption of calcium-containing biomaterials could induce inflammation and accelerate biomaterial degradation, driving further CaP release. This demonstrates a novel mechanism for biomaterial-induced inflammation. The in vitro system described could aid preclinical evaluation of novel biomaterial inflammatory potential. Copyright © 2011 Wiley Periodicals, Inc.

  7. Protective potential of casein phosphopeptide amorphous calcium phosphate containing paste on enamel surfaces.

    PubMed

    Somasundaram, Padmini; Vimala, N; Mandke, Lalita Gauri

    2013-03-01

    Dental caries remains the most common dental disease facing mankind. Prevention of initiation and interruption in progression of early lesions are the desirable modes of caries management. There is a scope for agents, which may be used to enhance anti - caries activity. This need has redirected research to develop novel preventive agents that can act as an adjunct to fluoride or independent of it. Casein Phosphopeptide - Amorphous Calcium Phosphate (CPP-ACP) is one such agent that has been proposed to have anti cariogenic properties. The purpose of this in vitro study was to evaluate the effect of paste containing CPP-ACP, MI Paste, on enamel remineralization. This study consisted of 30 samples embedded in orthodontic resin with either the buccal or lingual surface exposed. The samples were assigned to either a CPP-ACP containing paste; Fluoridated toothpaste; or a control group. The groups were then subjected to cycling in a demineralizing solution and a remineralizing solution. Groups II and III received prior application of MI paste and Fluoridated toothpaste respectively followed by cycling in a demineralizing solution and a remineralizing solution. Following 14 days of cycling, the samples were sectioned and examined using confocal microscopy. The lesion depth, were evaluated. Image Proplus software was used to analyze the images. The values were statistically evaluated using one - way ANOVA and Scheffe's Test. Within the limitations of the study it was concluded that enamel surfaces treated with the CPP-ACP paste exhibited the least lesion depths followed by the enamel surfaces treated with the fluoridated tooth paste and control group respectively.

  8. Protective potential of casein phosphopeptide amorphous calcium phosphate containing paste on enamel surfaces

    PubMed Central

    Somasundaram, Padmini; Vimala, N; Mandke, Lalita Gauri

    2013-01-01

    Background: Dental caries remains the most common dental disease facing mankind. Prevention of initiation and interruption in progression of early lesions are the desirable modes of caries management. There is a scope for agents, which may be used to enhance anti - caries activity. This need has redirected research to develop novel preventive agents that can act as an adjunct to fluoride or independent of it. Casein Phosphopeptide – Amorphous Calcium Phosphate (CPP-ACP) is one such agent that has been proposed to have anti cariogenic properties. Aim: The purpose of this in vitro study was to evaluate the effect of paste containing CPP-ACP, MI Paste, on enamel remineralization. Materials and Methods: This study consisted of 30 samples embedded in orthodontic resin with either the buccal or lingual surface exposed. The samples were assigned to either a CPP-ACP containing paste; Fluoridated toothpaste; or a control group. The groups were then subjected to cycling in a demineralizing solution and a remineralizing solution. Groups II and III received prior application of MI paste and Fluoridated toothpaste respectively followed by cycling in a demineralizing solution and a remineralizing solution. Following 14 days of cycling, the samples were sectioned and examined using confocal microscopy. The lesion depth, were evaluated. Statistical Analysis: Image Proplus software was used to analyze the images. The values were statistically evaluated using one – way ANOVA and Scheffe's Test. Results and Conclusion: Within the limitations of the study it was concluded that enamel surfaces treated with the CPP-ACP paste exhibited the least lesion depths followed by the enamel surfaces treated with the fluoridated tooth paste and control group respectively. PMID:23716969

  9. AMORPHOUS CALCIUM PHOSPHATE COMPOSITES AND THEIR EFFECT ON COMPOSITE-ADHESIVE-DENTIN BONDING

    PubMed Central

    Antonucci, J.M.; O’Donnell, J.N.R.; Schumacher, G.E.; Skrtic, D.

    2009-01-01

    This study evaluates the bond strength and related properties of photo-polymerizable, remineralizing amorphous calcium phosphate (ACP) polymeric composite-adhesive systems to dentin after various periods of aqueous aging at 37 °C. An experimental ACP base and lining composite was made from a photo-activated resin comprising 2,2-bis[p-(2’-hydroxy-3’-methacryloxypropoxy)phenyl]propane (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA) and zirconyl dimethacrylate (ZrDMA); designated BTHZ. An experimental orthodontic composite was formulated from a photo-activated resin comprising ethoxylated bisphenol A dimethacrylate (EBPADMA), TEGDMA, HEMA and methacryloxyethyl phthalate (MEP); designated ETHM. In both composite series three fillers were compared: 1) freshly precipitated zirconium-modified ACP freshly precipitated (as-prepared Zr-ACP), 2) milled Zr-ACP and 3) an ion-leachable fluoride glass. In addition to the shear bond strength (SBS), work to fracture and failure modes of the orthodontic composites were determined. The SBS of the base and lining ACP composites appeared unaffected by filler type or immersion time. In the orthodontic ACP composite series, milled ACP composites showed initial mechanical advantages over as-prepared ACP composites, and produced higher incidence of a failure mode consistent with stronger adhesion. After six months of aqueous exposure, 80 % of specimens failed at the dentin-primer interface, with a 42 % overall reduction in bond strength. BTHZ and ETHM based ACP composites are potentially effective anti-demineralizing-remineralizing agents with possible clinical utility as protective base-liners and orthodontic cements, respectively. The analysis of the bond strength and failure modalities suggests that milled ACP composites may offer greater potential in clinical applications. PMID:19696914

  10. ADHESION OF AMORPHOUS CALCIUM PHOSPHATE COMPOSITES BONDED TO DENTIN: A STUDY IN FAILURE MODALITY

    PubMed Central

    O’Donnell, J.N.R.; Schumacher, G.E.; Antonucci, J.M.; Skrtic, D.

    2009-01-01

    Aims As a bioactive filler capable of remineralizing tooth structures, the main disadvantage of as-made amorphous calcium phosphate (am-ACP) are its large agglomerates. The objective of this study was to mill ACP, and compare the adhesive strength to dentin, work to fracture, and failure modes of both groups to glass-filled composites and one commercial compomer after 24 h, 1 week, 1, 3 and 6 months of exposure to simulated saliva solution (SLS). Flat dentin surfaces were acid-etched, primed, and photopolymerized. Composites were applied, photo-cured, and debonded in shear. The resin used in each composite was identical: ethoxylated bisphenol A dimethacrylate, triethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate and methacryloxyethyl phthalate. Fillers consisted of am-ACP and milled ACP (m-ACP), and a strontium-containing glass (Sr-glass) at respective mass fractions of (40, 60, and 75) %. Findings 90 % of the fracture surfaces in this study showed adhesive failure, with most of these occurring at the dentin/primer interface. 52 % of failures after 24 h immersion occurred at the primer/composite interface. After six months of SLS exposure, 80 % of specimens failed at the dentin/primer interface, with a 42 % overall reduction in bond strength. Conclusions Milled ACP composites showed initial mechanical advantages over am-ACP composites and the compomer, and produced a higher incidence of a failure mode consistent with stronger adhesion. Evidence is provided which suggests that milled ACP composites may offer enhanced potential in clinical bonding applications. PMID:19107798

  11. In vitro remineralization of enamel by polymeric amorphous calcium phosphate composite: Quantitative micro-radiographic study

    PubMed Central

    Langhorst, S.E.; O'Donnell, J.N.R.; Skrtic, D.

    2009-01-01

    Objective: This study explores the efficacy of an experimental orthodontic amorphous calcium phosphate (ACP) composite to remineralize in vitro subsurface enamel lesions microradiographically similar to those seen in early caries. Methods: Lesions were artificially created in extracted human molars. Single tooth sections a minimum of 120 μm thick were cut and individually placed in holders exposing only the carious enamel surface. The exposed surfaces were either left untreated (control) or coated with a 1 mm thick layer of the experimental ACP composite (mass fraction 40 % zirconiahybridized ACP and 60 % photo-activated resin), or a commercial fluoride-releasing orthodontic cement. The composite-coated sections were then photo-cured and microradiographic images were taken of all three groups of specimens before the treatment. Specimens were then cyclically immersed in demineralizing and remineralizing solutions for one month at 37 °C to simulate the pH changes occurring in the oral environment. Microradiographs of all specimens were taken before and after treatment. Results: Quantitative digital image analysis of matched areas from the contact microradiographs taken before and after treatment indicated higher mineral recovery with ACP composites compared to the commercial orthodontic F-releasing cement (14.4 % vs. 4.3 %, respectively), while the control specimens showed an average of 55.4 % further demineralization. Significance: Experimental ACP composite efficiently established mineral ion transfer throughout the body of the lesions and restored the mineral lost due to acid attack. It can be considered a useful adjuvant for the control of caries in orthodontic applications. PMID:19215975

  12. Casein phosphopeptide-amorphous calcium phosphate remineralization of primary teeth early enamel lesions.

    PubMed

    Zhou, Chunhua; Zhang, Dongliang; Bai, Yuxing; Li, Song

    2014-01-01

    Early childhood caries (ECC) is a serious problem that progresses rapidly and often goes untreated. Current traumatic treatments may be replaced by safe and effective remineralization at very early stages. The aim of this in vitro study was to evaluate the remineralization effects of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) paste on enamel lesions by assessing ultrastructure, nanomechanical properties, and compound and elemental analysis. Enamel specimens from 6-year-old children were divided into groups: (1) native enamel; (2) water as negative control; (3) 500ppm NaF as positive control; and (4-7) CPP-ACP paste for 4, 8, 12, and 24h, as test groups. Ultrastructure and roughness were observed by atomic force microscopy (AFM); nanohardness and elastic modulus were measured by nanoindentation; compound and crystal size of enamel surface patterns were investigated by X-ray diffractometer (XRD). An electron microprobe (EPMA) was used for element analysis. Data were analyzed using one-way ANOVA. The CPP-ACP paste repaired the microstructure of enamel, including prism and interprism, through significantly increased hydroxyapatite crystal size (12.06±0.21nm) and Ca/P molar ratios (1.637±0.096) as compared with NaF (8.56±0.13nm crystal size and 1.397±0.086 Ca/P, p<0.01). Both CPP-ACP and NaF decrease roughness, and increase the nanohardness and elastic modulus, with no significant differences between the materials. The CPP-ACP paste is more suitable for children than NaF, due to advantages for remineralization. The AFM, nanoindentation, EPMA, and XRD are very helpful methods for further understanding of microscale and nanoscale remineralization mechanisms. Copyright © 2013 Elsevier Ltd. All rights reserved.

  13. Twelve-month bracket failure rate with amorphous calcium phosphate bonding system.

    PubMed

    Hammad, Shaza M; El Banna, Mai S; Elsaka, Shaymaa E

    2013-10-01

    The aim of the study was to compare the survival rate of orthodontic brackets over a 12-month period using amorphous calcium phosphate (ACP) bonding system with a conventional adhesive (CA). In 30 patients with a mean age of 15 years 7 months, one operator bonded 138 brackets with a split-mouth design, using a resin-based CA and ACP-containing adhesive. The survival rate of the brackets was estimated by Kaplan-Meier analysis. Bracket survival distributions with respect to bonding procedure, dental arch, type of tooth (incisor, canine, and premolar), and patients' gender were compared using the log-rank test. The bond failure interface was determined using the Adhesive Remnant Index (ARI). The bond failure rates of the CA and ACP-containing adhesive were 2.67 and 3.8 per cent, respectively. There was no significant difference between the failure rates of ACP and CA-bonded systems (P > 0.05). Survival rates did not show significant differences between the upper and lower dental arches (P > 0.05). Lower survival rates were found for canine and premolar teeth than incisors (P < 0.05). Bond failure rates were higher for males than females (P < 0.05). There was a significant difference for ARI scores between the adhesive materials (P = 0.028); more of the ACP-based adhesive was left on the tooth at debond. ACP-containing adhesive can be effectively used to bond orthodontic brackets and can serve as a practicable alternative to the conventional bonding adhesives.

  14. Preferential refilling and planarization of grooves with amorphous carbon by using gas cluster ion beam irradiations

    SciTech Connect

    Naito, K.; Toyoda, N.; Yamada, I.

    2011-01-07

    Surface planarization is important for fabrication of patterned media. One of the methods is smoothing of the patterned surface after deposition of refilling materials. However it requires two process steps. In this study, we studied planarization of patterned media by formation of refilling films with gas cluster ion beam (GCIB) assisted deposition to reduce the process step. Hard amorphous carbon films were deposited on line-and-space pattern (100 nm pitch, 20 nm in depth) by using Ar-GCIB assisted deposition. From the atomic force microscope and the cross-sectional transmission electron microscope observations, the line-and-space patterns were refilled with amorphous carbon films with Ar-GCIB assisted deposition and smooth surface was obtained. The thickness of the amorphous carbon film required for surface planarization was 32 nm, which was very small compared to the initial peak to valley (20 nm). By using this method, sputtering process for planarization can be omitted.

  15. Planarization of amorphous carbon films on patterned substrates using gas cluster ion beams

    SciTech Connect

    Toyoda, Noriaki; Yamada, Isao; Nagato, Keisuke; Nakao, Masayuki; Hamaguchi, Tetsuya; Tani, Hiroshi; Sakane, Yasuo

    2009-04-01

    Surface planarization and modification of a patterned surface were demonstrated using gas cluster ion beam (GCIB). Grooves with 100-400 nm intervals were formed on amorphous carbon films using focused ion beams to study the special frequency dependence of the planarization. Also, line and space patterns were fabricated on Si substrates, and amorphous carbons were deposited as a model structure of discrete track media. Subsequently, surface planarization using Ar-GCIB was carried out. After GCIB irradiations, all of the grooves were completely removed, and a flat surface was realized. And it showed that GCIB irradiation planarized grooves without huge thickness loss. From the power spectrum density of an atomic force microscope, GCIB preferentially removed grooves with small intervals. It was found from energy dispersive x-ray spectroscopy that surface planarization without severe damage in the amorphous carbon and magnetic layers was carried out with GCIB.

  16. Removal of free carbon and crystal structure change of amorphous silica fume by calcination

    NASA Astrophysics Data System (ADS)

    Tie, Shengnian; Zhang, Shaohong

    2017-07-01

    The calcination process was used to remove free carbon and to change the structure of amorphous microsilica powder. The results show that the carbon content in amorphous silica powder strongly depends on the calcination temperature. When the calcination temperature is higher than 900∘C, the free carbon content, SiO2 content and weight loss of microsilica powder tend to be stable, with values of 0.05%, 83.8% and 4.8%, respectively. The crystalline structure, particle size and morphology start changing at a calcination temperature of 850∘C. When the calcination temperature is higher than 900∘C, the amorphous microsilica powder is fully crystallized. The morphology of the silica fume kept its original spherical shape under 850∘C, while above 850∘C the microsilica powder recrystallizes. These results provide a basis for chemical removal of metal impurities in the preparation of high-purity silica powder.

  17. Raman spectroscopic study of the phase transition of amorphous to crystalline beta-carbonic acid.

    PubMed

    Kohl, Ingrid; Winkel, Katrin; Bauer, Marion; Liedl, Klaus R; Loerting, Thomas; Mayer, Erwin

    2009-01-01

    What's the matter? The laboratory Raman spectra for carbonic acid (H(2)CO(3)), both for the beta-polymorph and its amorphous state, are required to detect carbonic acid on the surface of the pole caps of Mars in 2009, when the Mars Microbeam Raman Spectrometer lands on the planet. The picture shows a martian crater with ice of unknown composition, possibly containing carbonic acid (image adapted from DLR, with permission from ESA, DLR, and FU Berlin--G. Neukum).

  18. Formation of hollow bone-like morphology of calcium carbonate on surfactant/polymer templates

    NASA Astrophysics Data System (ADS)

    Mantilaka, M. M. M. G. P. G.; Pitawala, H. M. T. G. A.; Rajapakse, R. M. G.; Karunaratne, D. G. G. P.; Upul Wijayantha, K. G.

    2014-04-01

    Novel hollow, bone-like structures of Precipitated Calcium Carbonate (PCC) are fabricated, for the first time, starting from naturally occurring dolomite. The hollow, bone-like structures are prepared by precipitating calcium carbonate on self-assembled poly(acrylic acid)/cetyltrimethylammonium chloride (PAA/CTAC) template. Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Field Emission Scanning Electron Microscopic (FE-SEM) studies reveal that the bone-like structure is composed of Amorphous Calcium Carbonate (ACC) nanoparticles in the center and calcite nanoparticles at the edges. Bone-like PCC particles are in particle length of 2-3 μm and particle width of 1 μm. The internal hollow structures of bone-like particles are observed from TEM images. As identified by FE-SEM images, the bone-like structure has been formed through the crystal growth of initially formed ACC nanoparticles. The ACC particles are stabilized in the center while the calcite crystals have been grown from the ACC toward the edges of the structure to form a bone-like morphology. We also propose a possible mechanism for the formation of hollow bone-like PCC in this study. The fabricated hollow, bone-like PCC has potential applications in the preparation of release systems such as drugs, cosmetics and pigments.

  19. In vitro cytocompatibility assessment of amorphous carbon structures using neuroblastoma and Schwann cells.

    PubMed

    Jain, Shilpee; Sharma, Ashutosh; Basu, Bikramjit

    2013-05-01

    The development of scaffolds for neural tissue engineering application requires an understanding of cell adhesion, proliferation, and migration of neuronal cells. Considering the potential application of carbon as scaffold materials and the lack of understanding of compatibility of amorphous carbon with neuronal cells, the carbon-based materials in the forms of carbon films and continuous electrospun carbon nanofibers having average diameter of ~200 nm are being investigated with or without ultraviolet (UV) and oxy-plasma (OP) treatments for cytocompatibility property using mouse Neuroblastoma (N2a) and rat Schwann cells (RT4-D6P2T). The use of Raman spectroscopy in combination with Fourier transform infrared (FTIR) and X-ray diffraction establishes the amorphous nature and surface-bonding characteristics of the studied carbon materials. Although both UV and OP treatments make carbon surfaces more hydrophilic, the cell viability of N2a cells is statistically more significant on OP treated fibers/films compared to UV fiber/film substrates after 4 days in culture. The electrospun carbon fibrous substrate provides the physical guidance to the cultured Schwann cells. Overall, the experimental results of this study demonstrate that the electrospun amorphous carbon nanofibrous scaffolds can be used as a suitable biomaterial substrate for supporting cell adhesion and proliferation of neuronal cells in the context of their applications as artificial nerve implants.

  20. Growth Mechanism for Low Temperature PVD Graphene Synthesis on Copper Using Amorphous Carbon

    PubMed Central

    Narula, Udit; Tan, Cher Ming; Lai, Chao Sung

    2017-01-01

    Growth mechanism for synthesizing PVD based Graphene using Amorphous Carbon, catalyzed by Copper is investigated in this work. Different experiments with respect to Amorphous Carbon film thickness, annealing time and temperature are performed for the investigation. Copper film stress and its effect on hydrogen diffusion through the film grain boundaries are found to be the key factors for the growth mechanism, and supported by our Finite Element Modeling. Low temperature growth of Graphene is achieved and the proposed growth mechanism is found to remain valid at low temperatures. PMID:28276475

  1. Growth Mechanism for Low Temperature PVD Graphene Synthesis on Copper Using Amorphous Carbon

    NASA Astrophysics Data System (ADS)

    Narula, Udit; Tan, Cher Ming; Lai, Chao Sung

    2017-03-01

    Growth mechanism for synthesizing PVD based Graphene using Amorphous Carbon, catalyzed by Copper is investigated in this work. Different experiments with respect to Amorphous Carbon film thickness, annealing time and temperature are performed for the investigation. Copper film stress and its effect on hydrogen diffusion through the film grain boundaries are found to be the key factors for the growth mechanism, and supported by our Finite Element Modeling. Low temperature growth of Graphene is achieved and the proposed growth mechanism is found to remain valid at low temperatures.

  2. Intrinsically disordered mollusk shell prismatic protein that modulates calcium carbonate crystal growth.

    PubMed

    Ndao, Moise; Keene, Ellen; Amos, Fairland F; Rewari, Gita; Ponce, Christopher B; Estroff, Lara; Evans, John Spencer

    2010-10-11

    The formation of calcite prism architecture in the prismatic layer of the mollusk shell involves the participation of a number of different proteins. One protein family, Asprich, has been identified as a participant in amorphous calcium carbonate stabilization and calcite architecture in the prismatic layer of the mollusk, Atrina rigida . However, the functional role(s) of this protein family are not fully understood due to the fact that insufficient quantities of these proteins are available for experimentation. To overcome this problem, we employed stepwise solid-phase synthesis to recreate one of the 10 members of the Asprich family, the 61 AA single chain protein, Asprich "3". We find that the Asprich "3" protein inhibits the formation of rhombohedral calcite crystals and induces the formation of round calcium carbonate deposits in vitro that contain calcite and amorphous calcium carbonate (ACC). This mineralization behavior does not occur under control conditions, and the formation of ACC and calcite is similar to that reported for the recombinant form of the Asprich "g" protein. Circular dichroism studies reveal that Asprich "3" is an intrinsically disordered protein, predominantly random coil (66%), with 20-30% β-strand content, a small percentage of β-turn, and little if any α-helical content. This protein is not extrinsically stabilized by Ca(II) ions but can be stabilized by 2,2,2-trifluoroethanol to form a structure consisting of turn-like and random coil characteristics. This finding suggests that Asprich "3" may require other extrinsic interactions (i.e., with mineral or ionic clusters or other macromolecules) to achieve folding. In conclusion, Asprich "3" possesses in vitro functional and structural qualities that are similar to other reported for other Asprich protein sequences.

  3. Formation and structure of amorphous carbon char from polymer materials

    NASA Astrophysics Data System (ADS)

    Lawson, John W.; Srivastava, Deepak

    2008-04-01

    Amorphous carbonaceous char produced from burning polymer solids has insulating properties that make it valuable in thermal protection and fire-retardant systems. A pyrolytic molecular dynamics simulation method is devised to study the transformation of the local microstructure from virgin polymer to a dense, disordered char. Release of polymer hydrogen is found to be critical to allow the system to collapse into a highly coordinated char structure. Mechanisms of the char formation process and the morphology of the resulting structures are elucidated.

  4. Survival in end stage renal disease: calcium carbonate vs. sevelamer.

    PubMed

    Borzecki, A M; Lee, A; Wang, S W; Brenner, L; Kazis, L E

    2007-12-01

    There is concern regarding long-term excess calcium intake in end-stage renal disease populations. Because calcium carbonate is an over-the-counter (OTC) medication, few studies have been able to track its use. The Veterans Health Administration (VA) tracks national pharmacy data for both OTC and prescription drugs. We thus compared survival in incident dialysis patients on sevelamer and calcium carbonate phosphate binders. This was a retrospective cohort study of veterans initiating haemodialysis using existing VA databases. Patients were divided into calcium only (n = 769) and sevelamer only (n = 608) groups, then followed for up to 2 years until FY03 end. Survival was modelled using Cox regression adjusting for age, gender, race, marital status, service-connected disability, region, diabetes, hypertension and Charlson index. Stability of findings was examined using propensity score analysis. Sevelamer only vs. calcium only subjects were younger (respective mean ages 59.6 and 63.0, P < 0.001) with fewer comorbidities (Charlson index 3.8 and 4.5, P < 0.001). By study end, 24% of sevelamer and 30% of calcium subjects had died. Comparing sevelamer to calcium, the unadjusted hazard ratio for death was 0.62 (95% CI 0.50-0.76); the adjusted hazard ratio was 0.67 (CI 0.54-0.84). Propensity score analysis revealed similar results, with a hazard ratio of 0.65 (CI 0.54-0.80). In a national incident dialysis cohort, sevelamer treatment was associated with improved survival compared with calcium carbonate. Further research should investigate whether the worse survival with calcium is a long-term consequence of increased calcium accumulation.

  5. Biomineralization of calcium carbonates and their engineered applications: a review

    PubMed Central

    Dhami, Navdeep K.; Reddy, M. Sudhakara; Mukherjee, Abhijit

    2013-01-01

    Microbially induced calcium carbonate precipitation (MICCP) is a naturally occurring biological process in which microbes produce inorganic materials as part of their basic metabolic activities. This technology has been widely explored and promising with potential in various technical applications. In the present review, the detailed mechanism of production of calcium carbonate biominerals by ureolytic bacteria has been discussed along with role of bacteria and the sectors where these biominerals are being used. The applications of bacterially produced carbonate biominerals for improving the durability of buildings, remediation of environment (water and soil), sequestration of atmospheric CO2 filler material in rubbers and plastics etc. are discussed. The study also sheds light on benefits of bacterial biominerals over traditional agents and also the issues that lie in the path of successful commercialization of the technology of microbially induced calcium carbonate precipitation from lab to field scale. PMID:24194735

  6. [Does carbonate originate from carbonate-calcium crystal component of the human urinary calculus?].

    PubMed

    Yuzawa, Masayuki; Nakano, Kazuhiko; Kumamaru, Takatoshi; Nukui, Akinori; Ikeda, Hitoshi; Suzuki, Kazumi; Kobayashi, Minoru; Sugaya, Yasuhiro; Morita, Tatsuo

    2008-09-01

    It gives important information in selecting the appropriate treatment for urolithiasis to confirm the component of urinary calculus. Presently component analysis of the urinary calculus is generally performed by infrared spectroscopy which is employed by companies providing laboratory testing services in Japan. The infrared spectroscopy determines the molecular components from the absorption spectra in consequence of atomic vibrations. It has the drawback that an accurate crystal structure cannot be analyzed compared with the X-ray diffraction method which analyzes the crystal constituent based on the diffraction of X-rays on crystal lattice. The components of the urinary calculus including carbonate are carbonate apatite and calcium carbonate such as calcite. Although the latter is reported to be very rare component in human urinary calculus, the results by infrared spectroscopy often show that calcium carbonate is included in calculus. The infrared spectroscopy can confirm the existence of carbonate but cannot determine whether carbonate is originated from carbonate apatite or calcium carbonate. Thus, it is not clear whether calcium carbonate is included in human urinary calculus component in Japan. In this study, we examined human urinary calculus including carbonate by use of X-ray structural analysis in order to elucidate the origin of carbonate in human urinary calculus. We examined 17 human calculi which were reported to contain calcium carbonate by infrared spectroscopy performed in the clinical laboratory. Fifteen calculi were obtained from urinary tract, and two were from gall bladder. The stones were analyzed by X-ray powder method after crushed finely. The reports from the clinical laboratory showed that all urinary culculi consisted of calcium carbonate and calcium phosphate, while the gallstones consisted of calcium carbonate. But the components of all urinary calculi were revealed to be carbonate apatite by X-ray diffraction. The components of

  7. Calcium Acetate or Calcium Carbonate for Hyperphosphatemia of Hemodialysis Patients: A Meta-Analysis

    PubMed Central

    Zhang, Han; Yang, Bo; Mao, Zhiguo

    2015-01-01

    Background High levels of serum phosphorus both at baseline and during follow-up are associated with increased mortality in dialysis patients, and administration of phosphate binders was independently associated with improved survival among hemodialysis population. Calcium-based phosphate binders are the most commonly used phosphate binders in developing countries for their relatively low costs. Objectives To compare the efficacy and safety between calcium carbonate and calcium acetate in the treatment of hyperphosphatemia in hemodialysis patients. Methods PubMed, EMBASE, Cochrane Library, Google scholar and Chinese databases (Wanfang, Weipu, National Knowledge Infrastructure of China) were searched for relevant studies published before March 2014. Reference lists of nephrology textbooks and review articles were checked. A meta-analysis of randomized controlled trials (RCTs) and quasi-RCTs that assessed the effects and adverse events of calcium acetate and calcium carbonate in adult patients with MHD was performed using Review Manager 5.0. Results A total of ten studies (625 participants) were included in this meta-analysis. There was insufficient data in all-cause mortality and cardiovascular events for meta-analysis. Compared with calcium carbonate group, the serum phosphorus was significantly lower in calcium acetate group after4 weeks’ administration (MD -0.15 mmol/L, 95% CI -0.28 to -0.01) and after 8 weeks’ administration (MD -0.25 mmol/L, 95% CI -0.40 to -0.11). There was no difference in serum calcium levels or the incidence of hypercalcemia between two groups at 4 weeks and 8 weeks. No statistical difference was found in parathyroid hormone (PTH) levels or serum calcium by phosphorus (Ca x P) product. There was significantly higher risk of intolerance with calcium acetate treatment (RR 3.46, 95% CI 1.48 to 8.26). Conclusions For hyperphosphatemia treatment, calcium acetate showed better efficacy and with a higher incidence of intolerance compared with

  8. Calcium acetate or calcium carbonate for hyperphosphatemia of hemodialysis patients: a meta-analysis.

    PubMed

    Wang, Yong; Xie, Guoqiang; Huang, Yuanhang; Zhang, Han; Yang, Bo; Mao, Zhiguo

    2015-01-01

    High levels of serum phosphorus both at baseline and during follow-up are associated with increased mortality in dialysis patients, and administration of phosphate binders was independently associated with improved survival among hemodialysis population. Calcium-based phosphate binders are the most commonly used phosphate binders in developing countries for their relatively low costs. To compare the efficacy and safety between calcium carbonate and calcium acetate in the treatment of hyperphosphatemia in hemodialysis patients. PubMed, EMBASE, Cochrane Library, Google scholar and Chinese databases (Wanfang, Weipu, National Knowledge Infrastructure of China) were searched for relevant studies published before March 2014. Reference lists of nephrology textbooks and review articles were checked. A meta-analysis of randomized controlled trials (RCTs) and quasi-RCTs that assessed the effects and adverse events of calcium acetate and calcium carbonate in adult patients with MHD was performed using Review Manager 5.0. A total of ten studies (625 participants) were included in this meta-analysis. There was insufficient data in all-cause mortality and cardiovascular events for meta-analysis. Compared with calcium carbonate group, the serum phosphorus was significantly lower in calcium acetate group after4 weeks' administration (MD -0.15 mmol/L, 95% CI -0.28 to -0.01) and after 8 weeks' administration (MD -0.25 mmol/L, 95% CI -0.40 to -0.11). There was no difference in serum calcium levels or the incidence of hypercalcemia between two groups at 4 weeks and 8 weeks. No statistical difference was found in parathyroid hormone (PTH) levels or serum calcium by phosphorus (Ca x P) product. There was significantly higher risk of intolerance with calcium acetate treatment (RR 3.46, 95% CI 1.48 to 8.26). For hyperphosphatemia treatment, calcium acetate showed better efficacy and with a higher incidence of intolerance compared with calcium carbonate. There are insufficient data to

  9. Ultrasound influence upon calcium carbonate precipitation on bacterial cellulose membranes.

    PubMed

    Stoica-Guzun, Anicuta; Stroescu, Marta; Jinga, Sorin; Jipa, Iuliana; Dobre, Tanase; Dobre, Loredana

    2012-07-01

    The effect of ultrasonic irradiation (40 kHz) on the calcium carbonate deposition on bacterial cellulose membranes was investigated using calcium chloride (CaCl(2)) and sodium carbonate (Na(2)CO(3)) as starting reactants. The composite materials containing bacterial cellulose-calcium carbonate were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The polymorphs of calcium carbonate that were deposited on bacterial cellulose membranes in the presence or in the absence of ultrasonic irradiation were calcite and vaterite. The morphology of the obtained crystals was influenced by the concentration of starting solutions and by the presence of ultrasonic irradiation. In the presence of ultrasonic irradiation the obtained crystals were bigger and in a larger variety of shapes than in the absence of ultrasounds: from cubes of calcite to spherical and flower-like vaterite particles. Bacterial cellulose could be a good matrix for obtaining different types of calcium carbonate crystals. Copyright © 2011 Elsevier B.V. All rights reserved.

  10. Incorporation of Chromate into Calcium Carbonate Structure during Coprecipitation

    SciTech Connect

    Hua, Bin; Deng, Baolin; Thornton, Edward C.; Yang, J.; Amonette, James E.

    2006-09-08

    To assess treatment technologies and establish regulatory framework for chromate-contaminated site remediation, it is imperative to know the exact chromium speciation in soil matrices. In an earlier study, Thornton and Amonette (1999) reported that some chromate in the bulk particles was not accessible to gaseous reductants or solution-phase extractants, based on XANES studies. We hypothesized that part of this non-extractable chromate may reside in the structure of minerals such as calcium carbonate. To test this hypothesis, a number of calcium carbonate precipitates were prepared in the presence of various concentrations of chromate during the precipitation, which could coprecipitate chromate, or by adding chromate after the precipitation was completed. Hydrochloric acid was used to dissolve calcium carbonate and therefore extract the coprecipitated and surface attached chromate. The results showed that the coprecipitated chromate was non-extractable by hot alkaline solution or phosphate buffer, but could be solubilized by HCl in proportional to the amount of calcium carbonate dissolved. The X-ray diffraction experiments revealed that the coprecipitation of chromate with calcium carbonate had an influence on its crystal structure: the higher the chromate concentration, the greater the ratio of vaterite to calcite.

  11. Availability of calcium from skim milk, calcium sulfate and calcium carbonate for bone mineralization in pigs.

    PubMed

    Pointillart, A; Coxam, V; Sève, B; Colin, C; Lacroix, C H; Guéguen, L

    2000-01-01

    Dairy products provide abundant, accessible calcium for humans, while some calcium sulfate-rich mineral waters could provide appreciable amounts of calcium. But there is little evidence that this calcium is as available as milk calcium for making bone. The availability of calcium was studied by monitoring bone parameters in 2-month-old pigs fed restricted amounts of calcium (70% RDA) for 2.5 months. The 3 main (> or = 50% Ca intake) Ca sources were either CaCO3 or CaSO4 or skim milk powder (29% of the diet). The bones of the pigs fed the "milk" diet had higher (P < 0.01) ash contents, breaking strength and density (DEXA) than those of the two others groups, in which the bone values were similar. Thus, the calcium provided by a diet containing milk appears to ensure better bone mineralization than do calcium salts included in a non-milk diet. The calcium restriction may have enhanced some milk properties to stimulate calcium absorption in these young, rapidly growing pigs.

  12. Acute effects of calcium carbonate, calcium citrate and potassium citrate on markers of calcium and bone metabolism in young women.

    PubMed

    Karp, Heini J; Ketola, Maarit E; Lamberg-Allardt, Christel J E

    2009-11-01

    Both K and Ca supplementation may have beneficial effects on bone through separate mechanisms. K in the form of citrate or bicarbonate affects bone by neutralising the acid load caused by a high protein intake or a low intake of alkalising foods, i.e. fruits and vegetables. Ca is known to decrease serum parathyroid hormone (S-PTH) concentration and bone resorption. We compared the effects of calcium carbonate, calcium citrate and potassium citrate on markers of Ca and bone metabolism in young women. Twelve healthy women aged 22-30 years were randomised into four controlled 24 h study sessions, each subject serving as her own control. At the beginning of each session, subjects received a single dose of calcium carbonate, calcium citrate, potassium citrate or a placebo in randomised order. The diet during each session was identical, containing 300 mg Ca. Both the calcium carbonate and calcium citrate supplement contained 1000 mg Ca; the potassium citrate supplement contained 2250 mg K. Markers of Ca and bone metabolism were followed. Potassium citrate decreased the bone resorption marker (N-terminal telopeptide of type I collagen) and increased Ca retention relative to the control session. Both Ca supplements decreased S-PTH concentration. Ca supplements also decreased bone resorption relative to the control session, but this was significant only for calcium carbonate. No differences in bone formation marker (bone-specific alkaline phosphatase) were seen among the study sessions. The results suggest that potassium citrate has a positive effect on the resorption marker despite low Ca intake. Both Ca supplements were absorbed well and decreased S-PTH efficiently.

  13. Formation and structure of amorphous carbon char from polymer materials

    NASA Astrophysics Data System (ADS)

    Lawson, John; Srivastava, Deepak

    2008-03-01

    Amorphous carbonaceous char produced from burning polymer solids has insulating properties that makes it valuable for aerospace thermal protection systems as well as for fire retardants. A pyrolytic molecular dynamics simulation method is devised to study the transformation of the local microstructure from virgin polymer to a dense, disordered char. Release of polymer hydrogen is found to be critical to allow the system to collapse into a highly coordinated structure. Mechanisms of the char formation process and the morphology of the resulting structure are elucidated.

  14. Automatic photometric titrations of calcium and magnesium in carbonate rocks

    USGS Publications Warehouse

    Shapiro, L.; Brannock, W.W.

    1955-01-01

    Rapid nonsubjective methods have been developed for the determination of calcium and magnesium in carbonate rocks. From a single solution of the sample, calcium is titrated directly, and magnesium is titrated after a rapid removal of R2O3 and precipitation of calcium as the tungstate. A concentrated and a dilute solution of disodium ethylenediamine tetraacetate are used as titrants. The concentrated solution is added almost to the end point, then the weak solution is added in an automatic titrator to determine the end point precisely.

  15. Catalytic properties of composite amorphous carbon-platinum layers in fuel cells

    SciTech Connect

    Nechitailov, A. A. Zvonareva, T. K.; Remenyuk, A. D.; Tolmachev, V. A.; Goryachev, D. N.; El'tsina, O. S.; Belyakov, L. V.; Sreseli, O. M.

    2008-10-15

    Catalytic properties of composite amorphous carbon-platinum layers produced by magnetron cosputtering have been studied. The layers were characterized by electron microscopy, IR spectroscopy, ellipsometry, gravimetry, and spectrophotometric chemical analysis. The catalytic activity of the layers was studied in an air-hydrogen fuel cell by measuring its load and power characteristics.

  16. Low-Temperature Synthesis of Hierarchical Amorphous Basic Nickel Carbonate Particles for Water Oxidation Catalysis.

    PubMed

    Yang, Yisu; Liang, Fengli; Li, Mengran; Rufford, Thomas E; Zhou, Wei; Zhu, Zhonghua

    2015-07-08

    Amorphous nickel carbonate particles are catalysts for the oxygen evolution reaction (OER), which plays a critical role in the electrochemical splitting of water. The amorphous nickel carbonate particles can be prepared at a temperature as low as 60 °C by an evaporation-induced precipitation (EIP) method. The products feature hierarchical pore structures. The mass-normalized activity of the catalysts, measured at an overpotential of 0.35 V, was 55.1 A g(-1) , with a Tafel slope of only 60 mV dec(-1) . This catalytic activity is superior to the performance of crystalline NiOx particles and β-Ni(OH)2 particles, and compares favorably to state-of-the-art RuO2 catalysts. The activity of the amorphous nickel carbonate is remarkably stable during a 10 000 s chronoamperometry test. Further optimization of synthesis parameters reveals that the amorphous structure can be tuned by adjusting the H2 O/Ni ratio in the precursor mixture. These results suggest the potential application of easily prepared hierarchical basic nickel carbonate particles as cheap and robust OER catalysts with high activity.

  17. Design of Amorphous Manganese Oxide@Multiwalled Carbon Nanotube Fiber for Robust Solid-State Supercapacitor.

    PubMed

    Shi, Peipei; Li, Li; Hua, Li; Qian, Qianqian; Wang, Pengfei; Zhou, Jinyuan; Sun, Gengzhi; Huang, Wei

    2017-01-24

    Solid-state fiber-based supercapacitors have been considered promising energy storage devices for wearable electronics due to their lightweight and amenability to be woven into textiles. Efforts have been made to fabricate a high performance fiber electrode by depositing pseudocapacitive materials on the outer surface of carbonaceous fiber, for example, crystalline manganese oxide/multiwalled carbon nanotubes (MnO2/MWCNTs). However, a key challenge remaining is to achieve high specific capacitance and energy density without compromising the high rate capability and cycling stability. In addition, amorphous MnO2 is actually preferred due to its disordered structure and has been proven to exhibit superior electrochemical performance over the crystalline one. Herein, by incorporating amorphous MnO2 onto a well-aligned MWCNT sheet followed by twisting, we design an amorphous MnO2@MWCNT fiber, in which amorphous MnO2 nanoparticles are distributed in MWCNT fiber uniformly. The proposed structure gives the amorphous MnO2@MWCNT fiber good mechanical reliability, high electrical conductivity, and fast ion-diffusion. Solid-state supercapacitor based on amorphous MnO2@MWCNT fibers exhibits improved energy density, superior rate capability, exceptional cycling stability, and excellent flexibility. This study provides a strategy to design a high performance fiber electrode with microstructure control for wearable energy storage devices.

  18. Sustained delivery of calcium and orthophosphate ions from amorphous calcium phosphate and poly(L-lactic acid)-based electrospinning nanofibrous scaffold

    PubMed Central

    Niu, Xufeng; Liu, Zhongning; Tian, Feng; Chen, Siqian; Lei, Lei; Jiang, Ting; Feng, Qingling; Fan, Yubo

    2017-01-01

    The purpose of this study is to investigate electrospinning poly(L-lactic acid) (PLLA) nanofibrous scaffold with different contents of amorphous calcium phosphate (ACP), which is suitable for using in bone regeneration through sustained release of calcium and orthophosphate ions. Three groups of nanofibrous scaffolds, ACP-free PLLA, ACP-5 wt%/PLLA and ACP-10 wt%/PLLA, are developed and characterized by scanning electron microscopy and gel permeation chromatography. Calcium and phosphate colorimetric assay kits are used to test ions released from scaffold during hydrolytic degradation. The results show ACP-5 wt%/PLLA and ACP-10 wt%/PLLA scaffolds have relatively high degradation rates than ACP-free PLLA group. The bioactivity evaluation further reveals that ACP-5 wt%/PLLA scaffold presents more biocompatible feature with pre-osteoblast cells and significant osteogenesis ability of calvarial bone defect. Due to the facile preparation method, sustained calcium and orthophosphate release behavior, and excellent osteogenesis capacity, the presented ACP/PLLA nanofibrous scaffold has potential applications in bone tissue engineering. PMID:28361908

  19. A Chemical Template for Synthesis of Molecular Sheets of Calcium Carbonate

    NASA Astrophysics Data System (ADS)

    Rianasari, Ina; Benyettou, Farah; Sharma, Sudhir Kumar; Blanton, Thomas; Kirmizialtin, Serdal; Jagannathan, Ramesh

    2016-05-01

    Inspired by the discovery of graphene and its unique properties, we focused our research to develop a scheme to create nacre like lamellar structures of molecular sheets of CaCO3 interleaved with an organic material, namely carbon. We developed a facile, chemical template technique, using a formulation of poly(acrylic) acid (PAA) and calcium acetate to create lamellar stacks of single crystal sheets of CaCO3, with a nominal thickness of 17 Å, the same as a unit-cell dimension for calcite (c–axis = 17.062 Å), interleaved with amorphous carbon with a nominal thickness of 8 Å. The strong binding affinity between carboxylate anions and calcium cations in the formulation was used as a molecular template to guide CaCO3 crystallization. Computational modeling of the FTIR spectra showed good agreement with experimental data and confirmed that calcium ions are bridged between polymer chains, resulting in a net-like polymer structure. The process readily lends itself to explore the feasibility of creating molecular sheets of other important inorganic materials and potentially find applications in many fields such as super capacitors and “low k di-electric” systems.

  20. A Chemical Template for Synthesis of Molecular Sheets of Calcium Carbonate

    PubMed Central

    Rianasari, Ina; Benyettou, Farah; Sharma, Sudhir Kumar; Blanton, Thomas; Kirmizialtin, Serdal; Jagannathan, Ramesh

    2016-01-01

    Inspired by the discovery of graphene and its unique properties, we focused our research to develop a scheme to create nacre like lamellar structures of molecular sheets of CaCO3 interleaved with an organic material, namely carbon. We developed a facile, chemical template technique, using a formulation of poly(acrylic) acid (PAA) and calcium acetate to create lamellar stacks of single crystal sheets of CaCO3, with a nominal thickness of 17 Å, the same as a unit-cell dimension for calcite (c–axis = 17.062 Å), interleaved with amorphous carbon with a nominal thickness of 8 Å. The strong binding affinity between carboxylate anions and calcium cations in the formulation was used as a molecular template to guide CaCO3 crystallization. Computational modeling of the FTIR spectra showed good agreement with experimental data and confirmed that calcium ions are bridged between polymer chains, resulting in a net-like polymer structure. The process readily lends itself to explore the feasibility of creating molecular sheets of other important inorganic materials and potentially find applications in many fields such as super capacitors and “low k di-electric” systems. PMID:27145699

  1. Template confined synthesis of amorphous carbon nanotubes and its confocal Raman microscopy

    SciTech Connect

    Maity, Supratim; Roychowdhury, Tuhin; Chattopadhyay, Kalyan Kumar

    2014-04-24

    Amorphous carbon nanotubes (aCNTs) were synthesized by AAO (anodic aluminum oxide) template at a temperature 500 °C in nitrogen atmosphere using the citric acid as a carbon source without the help of any catalyst particles. Morphological analysis of the as prepared samples was carried out by field emission scanning electron microscopy (FESEM). Confocal Raman imaging has been studied and an attempt has been made to find out the graphitic (sp{sup 2}) and disordered phase of the CNTs.

  2. Molecular dynamics simulation of benzene in graphite and amorphous carbon slit pores.

    PubMed

    Fomin, Yu D

    2013-11-15

    It is well known that confining a liquid into a pore strongly alters the liquid behavior. Investigations of the effect of confinement are of great importance for many scientific and technological applications. Here, we present a study of the behavior of benzene confined in carbon slit pores. Two types of pores are considered-graphite and amorphous carbon ones. We show that the effect of different pore structure is of crucial importance for the benzene behavior. Copyright © 2013 Wiley Periodicals, Inc.

  3. Electron beam-induced nanopatterning of multilayer graphene and amorphous carbon films with metal layers

    SciTech Connect

    Rodriguez-Manzo, Julio A.; Banhart, Florian

    2011-05-02

    Thin Co and Ni lamellae grow under electron irradiation of metal crystals supported on multilayer graphene or amorphous carbon films. The lateral growth of a lamella from a source crystal is achieved by directing an electron beam to the periphery of the metal crystal and moving the beam over the surrounding carbon. Patterns of linear, branched, or ringlike metal lamellae can be created. The patterning is carried out in situ in a transmission electron microscope, allowing simultaneous structuring and imaging. The process is driven by the metal-carbon interaction at a beam-activated carbon surface.

  4. Reaction of Calcium Silicates with Carbon Dioxide and Water

    DTIC Science & Technology

    1979-09-26

    for Ca3SiO5 to 22.9 kcal/mole for CaSiO3 . The reaction products were calcium carbonate (CaCO3) and a calcium silicate hydrate of variable...Ca3SiO5, beta-Ca2SiO4, and gamma-Ca2SiO4 if free water is present. Aragonite forms in the absence of free H2O and in the carbonation of CaSiO3 . The

  5. Distribution of calcium carbonate in desert soils: A model

    SciTech Connect

    Mayer, L.; McFadden, L.D.; Harden, J.W.

    1988-04-01

    A model that describes the distribution of calcium carbonate in desert soils as a function of dust flux, time, climate, and other soil-forming factors shows which factors most strongly influence the accumulation of carbonate and can be used to evaluate carbonate-based soil age estimates or paleoclimatic reconstructions. Models for late Holocene soils have produced carbonate distributions that are very similar to those of well-dated soils in New Mexico and southern California. These results suggest that (1) present climate is a fair representation of late Holocene climate, (2) carbonate dust flux can be approximated by its Holocene rate, and (3) changes in climate and/or dust flux at the end of the Pleistocene effected profound and complex changes in soil carbonate distributions. Both higher carbonate dust flux and greater effective precipitation are required during the latest Pleistocene-early Holocene to explain carbonate distributions in latest Pleistocene soils. 21 refs., 4 figs., 1 tab.

  6. Effects of Atomic-Scale Structure on the Fracture Properties of Amorphous Carbon - Carbon Nanotube Composites

    NASA Technical Reports Server (NTRS)

    Jensen, Benjamin D.; Wise, Kristopher E.; Odegard, Gregory M.

    2015-01-01

    The fracture of carbon materials is a complex process, the understanding of which is critical to the development of next generation high performance materials. While quantum mechanical (QM) calculations are the most accurate way to model fracture, the fracture behavior of many carbon-based composite engineering materials, such as carbon nanotube (CNT) composites, is a multi-scale process that occurs on time and length scales beyond the practical limitations of QM methods. The Reax Force Field (ReaxFF) is capable of predicting mechanical properties involving strong deformation, bond breaking and bond formation in the classical molecular dynamics framework. This has been achieved by adding to the potential energy function a bond-order term that varies continuously with distance. The use of an empirical bond order potential, such as ReaxFF, enables the simulation of failure in molecular systems that are several orders of magnitude larger than would be possible in QM techniques. In this work, the fracture behavior of an amorphous carbon (AC) matrix reinforced with CNTs was modeled using molecular dynamics with the ReaxFF reactive forcefield. Care was taken to select the appropriate simulation parameters, which can be different from those required when using traditional fixed-bond force fields. The effect of CNT arrangement was investigated with three systems: a single-wall nanotube (SWNT) array, a multi-wall nanotube (MWNT) array, and a SWNT bundle system. For each arrangement, covalent bonds are added between the CNTs and AC, with crosslink fractions ranging from 0-25% of the interfacial CNT atoms. The SWNT and MWNT array systems represent ideal cases with evenly spaced CNTs; the SWNT bundle system represents a more realistic case because, in practice, van der Waals interactions lead to the agglomeration of CNTs into bundles. The simulation results will serve as guidance in setting experimental processing conditions to optimize the mechanical properties of CNT

  7. In situ X-ray pair distribution function analysis of accelerated carbonation of a synthetic calcium-silicate-hydrate gel

    SciTech Connect

    Morandeau, Antoine E.; White, Claire E.

    2015-04-21

    Calcium–silicate–hydrate (C–S–H) gel is the main binder component in hydrated ordinary Portland cement (OPC) paste, and is known to play a crucial role in the carbonation of cementitious materials, especially for more sustainable alternatives containing supplementary cementitious materials. However, the exact atomic structural changes that occur during carbonation of C–S–H gel remain unknown. Here, we investigate the local atomic structural changes that occur during carbonation of a synthetic calcium–silicate–hydrate gel exposed to pure CO₂ vapour, using in situ X-ray total scattering measurements and subsequent pair distribution function (PDF) analysis. By analysing both the reciprocal and real-space scattering data as the C–S–H carbonation reaction progresses, all phases present during the reaction (crystalline and non-crystalline) have been identified and quantified, with the results revealing the emergence of several polymorphs of crystalline calcium carbonate (vaterite and calcite) in addition to the decalcified C–S–H gel. Furthermore, the results point toward residual calcium being present in the amorphous decalcified gel, potentially in the form of an amorphous calcium carbonate phase. As a result of the quantification process, the reaction kinetics for the evolution of the individual phases have been obtained, revealing new information on the rate of growth/dissolution for each phase associated with C–S–H gel carbonation. Moreover, the investigation reveals that the use of real space diffraction data in the form of PDFs enables more accurate determination of the phases that develop during complex reaction processes such as C–S–H gel carbonation in comparison to the conventional reciprocal space Rietveld analysis approach.

  8. Evaluation of the remineralization potential of amorphous calcium phosphate and fluoride containing pit and fissure sealants using scanning electron microscopy.

    PubMed

    Choudhary, Prashant; Tandon, Shobha; Ganesh, M; Mehra, Anshul

    2012-01-01

    To evaluate the remineralization potential of Amorphous Calcium Phosphate (ACP) and Fluoride containing pit and Fissure Sealants using Scanning Electron Microscopy. Thirty maxillary first premolars were divided into three groups of ten each and were randomly selected for ACP containing (Aegis- Opaque White, Bosworth Co. Ltd.), Fluoride containing (Teethmate F1 Natural Clear, Kuraray Co. Ltd.), resin based (Concise- Opaque White, 3M ESPE Co. Ltd.) pit and fissure sealant applications. The Concise group served as a control. The teeth weresubjected to the pH-cycling regimen for a period of two weeks. After two weeks, the teeth were sectioned bucco-lingually into 4mm sections and were observed under Scanning Electron Microscope at 50X, 250X, 500X, 1000X and 1500X magnifications. The qualitative changes at the tooth surface and sealant interface were examined and presence of white zone at the interface was considered positive for remineralization. Both ACP containing (Aegis) and Fluoride containing (Teethmate F1) group showed white zone at the tooth surface-sealant interface. The resin based group (Concise) showed regular interface between the sealant and the tooth structure, but no clear cut white zone was observed. Both, Aegis and Teethmate F1 have the potential to remineralize. Release of Amorphous Calcium Phosphate molecules in Aegis group and formation of Fluoroapetite in Teethmate F1 group, were probably responsible for the remineralization.

  9. Core-shell amorphous silicon-carbon nanoparticles for high performance anodes in lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Sourice, Julien; Bordes, Arnaud; Boulineau, Adrien; Alper, John P.; Franger, Sylvain; Quinsac, Axelle; Habert, Aurélie; Leconte, Yann; De Vito, Eric; Porcher, Willy; Reynaud, Cécile; Herlin-Boime, Nathalie; Haon, Cédric

    2016-10-01

    Core-shell silicon-carbon nanoparticles are attractive candidates as active material to increase the capacity of Li-ion batteries while mitigating the detrimental effects of volume expansion upon lithiation. However crystalline silicon suffers from amorphization upon the first charge/discharge cycle and improved stability is expected in starting with amorphous silicon. Here we report the synthesis, in a single-step process, of amorphous silicon nanoparticles coated with a carbon shell (a-Si@C), via a two-stage laser pyrolysis where decomposition of silane and ethylene are conducted in two successive reaction zones. Control of experimental conditions mitigates silicon core crystallization as well as formation of silicon carbide. Auger electron spectroscopy and scanning transmission electron microscopy show a carbon shell about 1 nm in thickness, which prevents detrimental oxidation of the a-Si cores. Cyclic voltammetry demonstrates that the core-shell composite reaches its maximal lithiation during the first sweep, thanks to its amorphous core. After 500 charge/discharge cycles, it retains a capacity of 1250 mAh.g-1 at a C/5 rate and 800 mAh.g-1 at 2C, with an outstanding coulombic efficiency of 99.95%. Moreover, post-mortem observations show an electrode volume expansion of less than 20% and preservation of the nanostructuration.

  10. Drug loading into porous calcium carbonate microparticles by solvent evaporation.

    PubMed

    Preisig, Daniel; Haid, David; Varum, Felipe J O; Bravo, Roberto; Alles, Rainer; Huwyler, Jörg; Puchkov, Maxim

    2014-08-01

    Drug loading into porous carriers may improve drug release of poorly water-soluble drugs. However, the widely used impregnation method based on adsorption lacks reproducibility and efficiency for certain compounds. The aim of this study was to evaluate a drug-loading method based on solvent evaporation and crystallization, and to investigate the underlying drug-loading mechanisms. Functionalized calcium carbonate (FCC) microparticles and four drugs with different solubility and permeability properties were selected as model substances to investigate drug loading. Ibuprofen, nifedipine, losartan potassium, and metronidazole benzoate were dissolved in acetone or methanol. After dispersion of FCC, the solvent was removed under reduced pressure. For each model drug, a series of drug loads were produced ranging from 25% to 50% (w/w) in steps of 5% (w/w). Loading efficiency was qualitatively analyzed by scanning electron microscopy (SEM) using the presence of agglomerates and drug crystals as indicators of poor loading efficiency. The particles were further characterized by mercury porosimetry, specific surface area measurements, differential scanning calorimetry, and USP2 dissolution. Drug concentration was determined by HPLC. FCC-drug mixtures containing equivalent drug fractions but without specific loading strategy served as reference samples. SEM analysis revealed high efficiency of pore filling up to a drug load of 40% (w/w). Above this, agglomerates and separate crystals were significantly increased, indicating that the maximum capacity of drug loading was reached. Intraparticle porosity and specific surface area were decreased after drug loading because of pore filling and crystallization on the pore surface. HPLC quantification of drugs taken up by FCC showed only minor drug loss. Dissolution rate of FCC loaded with metronidazole benzoate and nifedipine was faster than the corresponding FCC-drug mixtures, mainly due to surface enlargement, because only small

  11. CALCIUM CARBONATE DISSOLUTION RATE IN LIMESTONE CONTACTORS

    EPA Science Inventory

    The rate of carbonate mineral dissolution from limestone was studied using a rotating disk apparatus and samples of limestone of varied composition. The purpose of this study was to determine the effect of limestone composition on the kinetics of carbonate mineral dissolution. Th...

  12. CALCIUM CARBONATE DISSOLUTION RATE IN LIMESTONE CONTACTORS

    EPA Science Inventory

    The rate of carbonate mineral dissolution from limestone was studied using a rotating disk apparatus and samples of limestone of varied composition. The purpose of this study was to determine the effect of limestone composition on the kinetics of carbonate mineral dissolution. Th...

  13. Precipitation of calcium carbonate from a calcium acetate and ammonium carbamate batch system

    NASA Astrophysics Data System (ADS)

    Prah, J.; Maček, J.; Dražič, G.

    2011-06-01

    In this paper, we report a novel approach for preparing precipitated calcium carbonate using solutions of ammonium carbamate and calcium acetate as the sources of calcium and carbon dioxide, respectively. Two different concentrations of the starting solutions at three different temperatures (15, 25 and 50 °C) were used for the reaction. The influence of temperature and concentration on the polymorphism and the resulting morphology of calcium carbonate are discussed. The most important parameter for controlling a particular crystal structure and precipitate morphology were the concentrations of the initial solutions. When initial solutions with lower concentrations were used, the crystal form of the precipitate changed with time. Regardless the different polymorphism at different temperatures, after one day only the calcite form was detected in all samples, regardless of at which temperature the samples were prepared. At higher concentrations, pure vaterite or a mixture of vaterite and calcite were present at the beginning of the experiment. After one day, pure vaterite was found in the samples that were prepared at 15 and 25 °C. If calcium carbonate precipitated at 50 °C, the XRD results showed a mixture of calcite and vaterite regardless of the time at which the sample was taken. The morphology of calcium carbonate particles prepared at various conditions changed from calcite cubes to spherical particles of vaterite and aragonite needles. When a low starting concentration was used, the morphology at the initial stage was strongly affected by the temperature at which the experiments were conducted. However, after one day only, cubes were present in all cases at low initial concentrations. In contrast, at high concentrations spherical particles precipitated at all three temperatures at the beginning of the reaction. Spherical particles were made up from smaller particles. Over time, the size of the particles was diminishing due to their disintegration into

  14. The IR emission features - Emission from PAH molecules and amorphous carbon particles

    NASA Technical Reports Server (NTRS)

    Allamandola, L. J.; Tielens, A. G. G. M.; Barker, J. R.

    1987-01-01

    Techniques for the assessment of the importance of the various forms of PAHs, and recent infrared observations concerning the PAH problem, are considered. Spectroscopic data suggest that the observed interstellar spectrum is due to both free molecule-sized PAHs producing the narrow features, and amorphous carbon particles contributing to the broad underlying components. Explanations for the multicomponent emission spectrum are discussed. A model of the emission mechanism for the example of chrysene is presented, and an exact treatment of the IR fluorescence from highly vibrationally excited large molecules shows that species containing 20-30 carbon atoms are responsible for the narrow features, although the spectra more closely resemble those of amorphous carbon particles. It is suggested that future emphasis should be placed on the spatial characteristics of the component spectra.

  15. The IR emission features - Emission from PAH molecules and amorphous carbon particles

    NASA Technical Reports Server (NTRS)

    Allamandola, L. J.; Tielens, A. G. G. M.; Barker, J. R.

    1987-01-01

    Given the current understanding of polycyclic aromatic hydrocarbons (PAHs), the spectroscopic data suggest that are at least two components which contribute to the interstellar emission spectrum: (1) free molecule-sized PAHs producing the narrow features and (2) amorphous carbon particles (which are primarily composed of an irregular 'lattice' of PAHs) contributing to the broad underlying components. An exact treatment of the IR fluorescence from highly vibrationally excited large molecules demonstrates that species containing between 20 and 30 carbon atoms are responsible for the narrow features, although the spectra match more closely with the spectra of amorphous carbon particles. It is concluded that, since little is known about the spectroscopic properties of free PAHs and PAH clusters, much laboratory work is required along with an observational program focusing on the spatial characteristics of the spectra.

  16. The role of amorphous precursors in the crystallization of La and Nd carbonates

    NASA Astrophysics Data System (ADS)

    Vallina, Beatriz; Rodriguez-Blanco, Juan Diego; Brown, Andrew P.; Blanco, Jesus A.; Benning, Liane G.

    2015-07-01

    Crystalline La and Nd carbonates can be formed from poorly-ordered nanoparticulate precursors, termed amorphous lanthanum carbonate (ALC) and amorphous neodymium carbonate (ANC). When reacted in air or in aqueous solutions these precursors show highly variable lifetimes and crystallization pathways. We have characterized these precursors and the crystallization pathways and products with solid-state, spectroscopic and microscopic techniques to explain the differences in crystallization mechanisms between the La and Nd systems. ALC and ANC consist of highly hydrated, 10-20 nm spherical nanoparticles with a general formula of REE2(CO3)3.5H2O (REE = La, Nd). The stabilities differ by ~2 orders of magnitude, with ANC being far more stable than ALC. This difference is due to the Nd3+ ion having a far higher hydration energy compared to the La3+ ion. This, together with temperature and reaction times, leads to clear differences not only in the kinetics and mechanisms of crystallization of the amorphous precursor La- and Nd-carbonate phases but also in the resulting crystallite sizes and morphologies of the end products. All crystalline La and Nd carbonates developed spherulitic morphologies when crystallization occurred from hydrous phases in solution at temperatures above 60 °C (La system) and 95 °C (Nd system). We suggest that spherulitic growth occurs due to a rapid breakdown of the amorphous precursors and a concurrent rapid increase in supersaturation levels in the aqueous solution. The kinetic data show that the crystallization pathway for both La and Nd carbonate systems is dependent on the reaction temperature and the ionic potential of the REE3+ ion.Crystalline La and Nd carbonates can be formed from poorly-ordered nanoparticulate precursors, termed amorphous lanthanum carbonate (ALC) and amorphous neodymium carbonate (ANC). When reacted in air or in aqueous solutions these precursors show highly variable lifetimes and crystallization pathways. We have

  17. The IR emission features - Emission from PAH molecules and amorphous carbon particles

    NASA Technical Reports Server (NTRS)

    Allamandola, L. J.; Tielens, A. G. G. M.; Barker, J. R.

    1987-01-01

    Techniques for the assessment of the importance of the various forms of PAHs, and recent infrared observations concerning the PAH problem, are considered. Spectroscopic data suggest that the observed interstellar spectrum is due to both free molecule-sized PAHs producing the narrow features, and amorphous carbon particles contributing to the broad underlying components. Explanations for the multicomponent emission spectrum are discussed. A model of the emission mechanism for the example of chrysene is presented, and an exact treatment of the IR fluorescence from highly vibrationally excited large molecules shows that species containing 20-30 carbon atoms are responsible for the narrow features, although the spectra more closely resemble those of amorphous carbon particles. It is suggested that future emphasis should be placed on the spatial characteristics of the component spectra.

  18. The IR emission features - Emission from PAH molecules and amorphous carbon particles

    NASA Technical Reports Server (NTRS)

    Allamandola, L. J.; Tielens, A. G. G. M.; Barker, J. R.

    1987-01-01

    Given the current understanding of polycyclic aromatic hydrocarbons (PAHs), the spectroscopic data suggest that are at least two components which contribute to the interstellar emission spectrum: (1) free molecule-sized PAHs producing the narrow features and (2) amorphous carbon particles (which are primarily composed of an irregular 'lattice' of PAHs) contributing to the broad underlying components. An exact treatment of the IR fluorescence from highly vibrationally excited large molecules demonstrates that species containing between 20 and 30 carbon atoms are responsible for the narrow features, although the spectra match more closely with the spectra of amorphous carbon particles. It is concluded that, since little is known about the spectroscopic properties of free PAHs and PAH clusters, much laboratory work is required along with an observational program focusing on the spatial characteristics of the spectra.

  19. Application of amorphous carbon based materials as antireflective coatings on crystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    da Silva, D. S.; Côrtes, A. D. S.; Oliveira, M. H.; Motta, E. F.; Viana, G. A.; Mei, P. R.; Marques, F. C.

    2011-08-01

    We report on the investigation of the potential application of different forms of amorphous carbon (a-C and a-C:H) as an antireflective coating for crystalline silicon solar cells. Polymeric-like carbon (PLC) and hydrogenated diamond-like carbon films were deposited by plasma enhanced chemical vapor deposition. Tetrahedral amorphous carbon (ta-C) was deposited by the filtered cathodic vacuum arc technique. Those three different amorphous carbon structures were individually applied as single antireflective coatings on conventional (polished and texturized) p-n junction crystalline silicon solar cells. Due to their optical properties, good results were also obtained for double-layer antireflective coatings based on PLC or ta-C films combined with different materials. The results are compared with a conventional tin dioxide (SnO2) single-layer antireflective coating and zinc sulfide/magnesium fluoride (ZnS/MgF2) double-layer antireflective coatings. An increase of 23.7% in the short-circuit current density, Jsc, was obtained using PLC as an antireflective coating and 31.7% was achieved using a double-layer of PLC with a layer of magnesium fluoride (MgF2). An additional increase of 10.8% was obtained in texturized silicon, representing a total increase (texturization + double-layer) of about 40% in the short-circuit current density. The potential use of these materials are critically addressed considering their refractive index, optical bandgap, absorption coefficient, hardness, chemical inertness, and mechanical stability.

  20. The role of amorphous precursors in the crystallization of La and Nd carbonates.

    PubMed

    Vallina, Beatriz; Rodriguez-Blanco, Juan Diego; Brown, Andrew P; Blanco, Jesus A; Benning, Liane G

    2015-07-28

    Crystalline La and Nd carbonates can be formed from poorly-ordered nanoparticulate precursors, termed amorphous lanthanum carbonate (ALC) and amorphous neodymium carbonate (ANC). When reacted in air or in aqueous solutions these precursors show highly variable lifetimes and crystallization pathways. We have characterized these precursors and the crystallization pathways and products with solid-state, spectroscopic and microscopic techniques to explain the differences in crystallization mechanisms between the La and Nd systems. ALC and ANC consist of highly hydrated, 10-20 nm spherical nanoparticles with a general formula of REE2(CO3)3·5H2O (REE = La, Nd). The stabilities differ by ∼2 orders of magnitude, with ANC being far more stable than ALC. This difference is due to the Nd(3+) ion having a far higher hydration energy compared to the La(3+) ion. This, together with temperature and reaction times, leads to clear differences not only in the kinetics and mechanisms of crystallization of the amorphous precursor La- and Nd-carbonate phases but also in the resulting crystallite sizes and morphologies of the end products. All crystalline La and Nd carbonates developed spherulitic morphologies when crystallization occurred from hydrous phases in solution at temperatures above 60 °C (La system) and 95 °C (Nd system). We suggest that spherulitic growth occurs due to a rapid breakdown of the amorphous precursors and a concurrent rapid increase in supersaturation levels in the aqueous solution. The kinetic data show that the crystallization pathway for both La and Nd carbonate systems is dependent on the reaction temperature and the ionic potential of the REE(3+) ion.

  1. Thermosensitive polymer controlled morphogenesis and phase discrimination of calcium carbonate.

    PubMed

    Jiang, Jun; Tauer, Klaus; Qiu, Yun-Hao; Zhong, Ya-Xu; Gao, Min-Rui; Antonietti, Markus; Yu, Shu-Hong

    2017-06-13

    Homogeneous aragonite flowers with controlled surface structures can be synthesized by using a thermosensitive polymer, i.e. poly (ethylene glycol)-poly(N-isopropyl acrylamide)-poly(acrylamido methyl propane sulfonate) (PEG-PNIPAM-PAMPS), as a crystal growth modifier in the mineralization of calcium carbonate.

  2. Calcium carbonate polymorph control using droplet-based microfluidics

    PubMed Central

    Yashina, Alexandra; Meldrum, Fiona; deMello, Andrew

    2012-01-01

    Calcium carbonate (CaCO3) is one of the most abundant minerals and of high importance in many areas of science including global CO2 exchange, industrial water treatment energy storage, and the formation of shells and skeletons. Industrially, calcium carbonate is also used in the production of cement, glasses, paints, plastics, rubbers, ceramics, and steel, as well as being a key material in oil refining and iron ore purification. CaCO3 displays a complex polymorphic behaviour which, despite numerous experiments, remains poorly characterised. In this paper, we report the use of a segmented-flow microfluidic reactor for the controlled precipitation of calcium carbonate and compare the resulting crystal properties with those obtained using both continuous flow microfluidic reactors and conventional bulk methods. Through combination of equal volumes of equimolar aqueous solutions of calcium chloride and sodium carbonate on the picoliter scale, it was possible to achieve excellent definition of both crystal size and size distribution. Furthermore, highly reproducible control over crystal polymorph could be realised, such that pure calcite, pure vaterite, or a mixture of calcite and vaterite could be precipitated depending on the reaction conditions and droplet-volumes employed. In contrast, the crystals precipitated in the continuous flow and bulk systems comprised of a mixture of calcite and vaterite and exhibited a broad distribution of sizes for all reaction conditions investigated. PMID:22655005

  3. Calcium carbonate polymorph control using droplet-based microfluidics.

    PubMed

    Yashina, Alexandra; Meldrum, Fiona; Demello, Andrew

    2012-06-01

    Calcium carbonate (CaCO(3)) is one of the most abundant minerals and of high importance in many areas of science including global CO(2) exchange, industrial water treatment energy storage, and the formation of shells and skeletons. Industrially, calcium carbonate is also used in the production of cement, glasses, paints, plastics, rubbers, ceramics, and steel, as well as being a key material in oil refining and iron ore purification. CaCO(3) displays a complex polymorphic behaviour which, despite numerous experiments, remains poorly characterised. In this paper, we report the use of a segmented-flow microfluidic reactor for the controlled precipitation of calcium carbonate and compare the resulting crystal properties with those obtained using both continuous flow microfluidic reactors and conventional bulk methods. Through combination of equal volumes of equimolar aqueous solutions of calcium chloride and sodium carbonate on the picoliter scale, it was possible to achieve excellent definition of both crystal size and size distribution. Furthermore, highly reproducible control over crystal polymorph could be realised, such that pure calcite, pure vaterite, or a mixture of calcite and vaterite could be precipitated depending on the reaction conditions and droplet-volumes employed. In contrast, the crystals precipitated in the continuous flow and bulk systems comprised of a mixture of calcite and vaterite and exhibited a broad distribution of sizes for all reaction conditions investigated.

  4. Micro and colloidal stickie pacification with precipitated calcium carbonate

    Treesearch

    John H. Klungness; Roland L. Gleisner; Marguerite S. Sykes

    2002-01-01

    Colloidal stickies that build up in mill process water during pulping are problematic and difficult to remove. We examined precipitated calcium carbonate (PCC) as a means to ameliorate process water stickies. The effectiveness of PCC added directly into a slurry of deinked pulp was compared with in situ precipitation of PCC by the fiber loading method. We found that...

  5. Micro and colloidal stickie pacification with precipitated calcium carbonate

    Treesearch

    John H. Klungness; Roland L. Gleisner; Marguerite Sykes

    2004-01-01

    The colloidal stickies which build up in mill process water during pulping are problematic and difficult to remove. The USDA Forestry Service examined precipitated calcium carbonate (PCC) as a means to ameliorate process water stickies, comparing: i) the effectiveness of PCC added directly into a slurry of deinked pulp with ii) in situ precipitation of PCC by the fibre...

  6. Osteoblast response to nanocrystalline calcium hydroxyapatite depends on carbonate content.

    PubMed

    Adams, Brandy R; Mostafa, Amany; Schwartz, Zvi; Boyan, Barbara D

    2014-09-01

    Normal bone mineral is a carbonated-apatite, but there are limited data on the effect of mineral containing carbonate on cell response. We characterized surface chemical compositions of three experimental carbonated hydroxyapatite (CO3(2-) HA) substrates and investigated their effect on osteoblast differentiation. Carbonate was incorporated into the hydroxyapatite powders while phosphate and hydroxyl groups were shown to be reduced by analyzing the chemical composition of the substrate surfaces. CO3(2-) HA powders with increasing carbonate concentrations designated as C1 (3.88%), C2 (4.85%), and C3 (5.82%) were molded, pressed, and fired into 14 mm discs. We observed that calcium phosphate ratios increased monotonically with increasing carbonate content, whereas differentiation of MG63 cells decreased. CO3(2-) HA surfaces also affected factor production. Addition of carbonate caused a 70% reduction in osteoprotegerin (OPG) compared to cultures on pure HA, but the effect of carbonate was not dose-dependent. Low carbonate content reduced VEGF-A by 80%, but higher levels of carbonate reversed this effect in a concentration dependent manner, with the C3 VEFG-A levels approximately twice that of C1 levels. These observations collectively indicate that bone cells are sensitive to carbonate content in bone mineral and the effects of carbonate substitution vary with the outcome being measured. Overall, this study provides a preliminary understanding of how carbonate substitution within hydroxyapatite modulates cellular behavior. © 2013 Wiley Periodicals, Inc.

  7. From atoms to minerals: how calcium carbonates form and why we should care.

    NASA Astrophysics Data System (ADS)

    Diego Rodriguez-Blanco, Juan

    2017-04-01

    Calcium carbonate minerals are ubiquitous on Earth where they play a key role in many marine and terrestrial biomineralization processes, controlling the evolution of past and future ocean chemistry and a large part of the global carbon cycle. However, the mechanisms by which biominerals form and transform are not well understood because these processes frequently involve the formation of poorly-ordered and crystalline metastable phases (e.g., amorphous calcium carbonate, vaterite, monohydrocalcite). Furthermore, the degree of ordering, hydration and particle size of these phases and their crystallisation pathways are largely controlled by their origin and conditions of formation. These include a number of factors like temperature, pH, and concentration of foreign ions in solution (e.g., Mg2+, Sr2+, SO42-, organics, etc.). Over the last few years, new experimental and characterization approaches have been developed, combining classical characterization techniques with synchrotron-based methods that allow in situ and real-time monitoring of the reactions (e.g., time-resolved synchrotron-based scattering and diffraction, pair distribution function). These techniques have provided very useful data to attain the mechanisms and quantify the kinetics of crystallization in abiotic systems. I will present a series of results obtained from synchrotron- and lab-based experiments that shed light on the mechanisms of formation of a number of biominerals (e.g., vaterite, calcite, aragonite, monohydrocalcite, dolomite). These results provide a detailed understanding of how calcium carbonate phases form during biomineralization processes, the effects of seawater ions and organics during the formation and transformation of biominerals, and the implications for past and future ocean chemistry, CO2 capture and storage and industrial mineral synthesis.

  8. Reactive Infiltration of Silicon Melt Through Microporous Amorphous Carbon Preforms

    NASA Technical Reports Server (NTRS)

    Sangsuwan, P.; Tewari, S. N.; Gatica, J. E.; Singh, M.; Dickerson, R.

    1999-01-01

    The kinetics of unidirectional capillary infiltration of silicon melt into microporous carbon preforms have been investigated as a function of the pore morphology and melt temperature. The infiltrated specimens showed alternating bands of dark and bright regions, which corresponded to the unreacted free carbon and free silicon regions, respectively. The decrease in the infiltration front velocity for increasing infiltration distances, is in qualitative agreement with the closed-form solution of capillarity driven fluid flow through constant cross section cylindrical pores. However, drastic changes in the thermal response and infiltration front morphologies were observed for minute differences in the preforms microstructure. This suggests the need for a dynamic percolation model that would account for the exothermic nature of the silicon-carbon chemical reaction and the associated pore closing phenomenon.

  9. Calcium carbonate crystallization in the α-chitin matrix of the shell of pink shrimp, Pandalus borealis, during frozen storage

    NASA Astrophysics Data System (ADS)

    Mikkelsen, A.; Engelsen, S. B.; Hansen, H. C. B.; Larsen, O.; Skibsted, L. H.

    1997-05-01

    Calcium carbonate precipitates in the shell of pink shrimp, Pandalus borealis, during frozen storage (investigated for temperatures above - 30°C), and as a result white spots appear in the shell. During continued frozen storage the white spots grow in size and eventually cover the entire, originally transparent, shell. Material isolated from shrimp shells was dried and subjected to infrared and Raman spectroscopy, X-ray diffraction, electron microscopy and EDX analyses. It was found that the white spots were composed of crystalline calcium carbonate in the two crystal forms of calcite and vaterite, and of amorphous α-chitin. It is proposed that α-chitin plays an important role in the crystallization process of white spots, as an integral part of the white spots. It is shown that the relative w/w-concentrations of α-chitin and calcium carbonate in white spots were constant (0.34 : 0.66), and it did not depend on chemical treatments comparable to those in use by the fishing industry for production of raw and frozen shrimps. However, the ratio of the polymorphic forms of calcium carbonate varied.

  10. Amorphous hollow carbon spheres synthesized using radio frequency plasma-enhanced chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Yang, G. M.; Xu, Q.; Tian, H. W.; Wang, X.; Zheng, W. T.

    2008-10-01

    We report a method to synthesize amorphous hollow carbon spheres, with diameters ranging from 100 to 800 nm, which are dispersed among bent graphitized carbon nanotubes using radio frequency plasma-enhanced chemical vapour deposition in mixed CH4/H2 gases. The products are characterized by techniques including scanning electron microscopy, energy-dispersive x-ray spectroscopy, Raman spectroscopy and transmission electron microscopy. It is found that MgO and Ni nanoparticles together with hydrogen play important roles in the formation of the spheres. A possible formation mechanism for the carbon composites has been proposed.

  11. 40 CFR 415.300 - Applicability; description of the calcium carbonate production subcategory.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... resulting from the production of calcium carbonate by the milk of lime process and by the recovery process... calcium carbonate production subcategory. 415.300 Section 415.300 Protection of Environment ENVIRONMENTAL... SOURCE CATEGORY Calcium Carbonate Production Subcategory § 415.300 Applicability; description of...

  12. 40 CFR 415.300 - Applicability; description of the calcium carbonate production subcategory.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... calcium carbonate production subcategory. 415.300 Section 415.300 Protection of Environment ENVIRONMENTAL... SOURCE CATEGORY Calcium Carbonate Production Subcategory § 415.300 Applicability; description of the calcium carbonate production subcategory. The provisions of this subpart are applicable to discharges...

  13. 40 CFR 415.300 - Applicability; description of the calcium carbonate production subcategory.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... calcium carbonate production subcategory. 415.300 Section 415.300 Protection of Environment ENVIRONMENTAL... SOURCE CATEGORY Calcium Carbonate Production Subcategory § 415.300 Applicability; description of the calcium carbonate production subcategory. The provisions of this subpart are applicable to discharges...

  14. 40 CFR 415.300 - Applicability; description of the calcium carbonate production subcategory.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... calcium carbonate production subcategory. 415.300 Section 415.300 Protection of Environment ENVIRONMENTAL... SOURCE CATEGORY Calcium Carbonate Production Subcategory § 415.300 Applicability; description of the calcium carbonate production subcategory. The provisions of this subpart are applicable to discharges...

  15. 40 CFR 415.300 - Applicability; description of the calcium carbonate production subcategory.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... calcium carbonate production subcategory. 415.300 Section 415.300 Protection of Environment ENVIRONMENTAL... SOURCE CATEGORY Calcium Carbonate Production Subcategory § 415.300 Applicability; description of the calcium carbonate production subcategory. The provisions of this subpart are applicable to discharges...

  16. Wear Performance of Calcium Carbonate-Containing Knee Spacers.

    PubMed

    Mueller, Ulrike; Reinders, Joern; Smith-Romanski, Sydney; Kretzer, Jan Philippe

    2017-07-15

    Articulating spacers should be wear-resistant and load-bearing to avoid prolonged immobilization of the patient and to reduce morbidity. However, due to the articulation of both components, a release of cement wear particles is to be expected. The aim of this study was to investigate the wear performance of a new spacer cement that contains calcium carbonate as a radio-opaque substance, in comparison to an established barium sulphate-containing spacer material, and also to characterize the amount, morphology, and size distributions of the released cement particles in detail. Force-controlled simulation was carried out on an AMTI knee simulator. The test parameters were in accordance with the standard ISO 14243-1 with a 50% reduced axial force. Tests were run for 500,000 cycles at a frequency of 1 Hz. For wear analysis, photographic documentation of the wear scars, gravimetric wear measurements and wear particle analysis were performed. The barium sulphate spacer material showed a total articular wear of 375.53 ± 161.22 mg. For the calcium carbonate-containing cement, reduced articular wear of 136.32 ± 37.58 mg was determined. Isolated cement wear particles of the barium sulphate-containing cement had a diameter of 0.429 ± 0.224 μm and were significantly larger compared to the calcium carbonate-containing cement (0.380 ± 0.216 μm, p = 0.02). The calcium carbonate-containing cement showed better wear performance in terms of gravimetric wear and particle release. Thus, calcium carbonate seems to be a promising material as a radio-opaque substrate in cement spacers.

  17. Study of electrochemical performance of amorphous carbon-coated graphite for Li-ion battery

    NASA Astrophysics Data System (ADS)

    Rohman, Fadli; Azizah, Umi; Prihandoko, Bambang

    2017-03-01

    Electrochemical performance of graphite coated by amorphous carbon as anode material in the Li-ion battery has been studied with citric acid (labelled CA) as a carbon source with different composition. Citric acid as the amorphous carbon source was mixed with graphite in the ethanol solvent at 80°C using magnetic stirrer with the compositions CA: graphite 2:1, 1:1 and 1:3, respectively. The mixture of graphite and CA were dried at 350°C for 5 hours under Ar atmosphere to evaporate the solvent. This dried mixture was then sintered at 600°C under Ar atmosphere to form amorphous carbon layer on the surface of graphite. The crystal structure and morphology of the particles were characterized using XRD, SEM and TEM, respectively. Electrochemical properties of the samples have been evaluated by cyclic voltammetry and charge-discharge test using WBCS 3000. Cyclic voltammogram showed the working potential and redox reaction peak of the sample. Charge-discharge data was obtained to determine the specific capacity of the sample at 0.1C - 2C.

  18. Molecular dynamics modeling of microstructure evolution during growth of amorphous carbon films

    SciTech Connect

    Glosli, J.N.; Belak, J.; Philpott, M.R.

    1996-01-08

    Amorphous carbon films approximately 20 nm thick are used throughout the computer industry as protective coatings on magnetic storage disks. As storage densities increase, the role of the overcoat becomes increasingly important because of smaller spacings between the recording head and the spinning disk. Furthermore, future-generation disks call for an overcoat thickness of 5 nm or less. These small length scales and the high speed of the spinning disk (10-30 m/s) suggest that a molecular dynamics (MD) model might provide useful insight into friction and wear mechanisms when the head and disk make contact. One of the necessary inputs required to carry out such an MD model is a specification of the position of all the atoms in the simulation, i.e. a detailed model of the material microstructure. Such a detailed understanding of the microstructure of amorphous carbon overcoats does not presently exist. Neutron and electron diffraction studies demonstrate that the material is amorphous. Previous classical MD simulations yield pair distribution functions in qualitative agreement with the diffraction studies, but they all differ in detail. More recent, quantum-mechanical tight-binding MD (TBMD) studies give a better description of the interatomic interactions and the chemical hybridization (sp{sup 2}-graphite-like versus sp{sup 3}-diamond-like). However, these studies are presently limited to rather small system sizes and rapid quench rates. In this paper we present molecular dynamics simulations of the growth of amorphous carbon films deposited onto a diamond substrate using a bond-order potential model. This classical potential mimics the quantum mechanics allowing carbon to form strong chemical bonds with a variety of hybridizations. It was found that the system formed unphysical bonding configurations without an added torsional energy between sp{sup 2} hybridized carbon atoms. This torsional energy was included for all results presented here. 18 refs., 3 figs.

  19. Dissolution and storage stability of nanostructured calcium carbonates and phosphates for nutrition

    NASA Astrophysics Data System (ADS)

    Posavec, Lidija; Knijnenburg, Jesper T. N.; Hilty, Florentine M.; Krumeich, Frank; Pratsinis, Sotiris E.; Zimmermann, Michael B.

    2016-10-01

    Rapid calcium (Ca) dissolution from nanostructured Ca phosphate and carbonate (CaCO3) powders may allow them to be absorbed in much higher fraction in humans. Nanosized Ca phosphate and CaCO3 made by flame-assisted spray pyrolysis were characterized by nitrogen adsorption, X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy. As-prepared nanopowders contained both CaCO3 and CaO, but storing them under ambient conditions over 130 days resulted in a complete transformation into CaCO3, with an increase in both crystal and particle sizes. The small particle size could be stabilized against such aging by cation (Mg, Zn, Sr) and anion (P) doping, with P and Mg being most effective. Calcium phosphate nanopowders made at Ca:P ≤ 1.5 were XRD amorphous and contained γ-Ca2P2O7 with increasing hydroxyapatite content at higher Ca:P. Aging of powders with Ca:P = 1.0 and 1.5 for over 500 days gradually increased particle size (but less than for CaCO3) without a change in phase composition or crystallinity. In 0.01 M H3PO4 calcium phosphate nanopowders dissolved ≈4 times more Ca than micronsized compounds and about twice more Ca than CaCO3 nanopowders, confirming that nanosizing and/or amorphous structuring sharply increases Ca powder dissolution. Because higher Ca solubility in vitro generally leads to greater absorption in vivo, these novel FASP-made Ca nanostructured compounds may prove useful for nutrition applications, including supplementation and/or food fortification.

  20. Linking crystal structure with temperature-sensitive vibrational modes in calcium carbonate minerals.

    PubMed

    Xu, Ben; Poduska, Kristin M

    2014-09-07

    We demonstrate a correlation between how an IR-active vibrational mode responds to temperature changes and how it responds to crystallinity differences. Infrared (IR) spectroscopy was used to track changes in carbonate-related vibrational modes in three different CaCO3 polymorphs (calcite, aragonite, and vaterite) and CaMg(CO3)2 (dolomite) during heating. Of the three characteristic IR-active carbonate modes, the in-plane bending mode (ν4) shows the most pronounced changes with heating in polymorphs that have planar carbonate arrangements (calcite, aragonite, and dolomite). In contrast, this mode is virtually unchanged in vaterite, which has a canted arrangement of carbonate units. We correlate these trends with recent studies that identified the ν4 mode as most susceptible to changes related to crystallinity differences in calcite and amorphous calcium carbonate. Thus, our results suggest that studies of packing arrangements could provide a generalizable approach to identify the most diagnostic vibrational modes for tracking either temperature-dependent or crystallinity-related effects in IR-active solids.

  1. Tuning calcium carbonate growth through physical confinement and templating with amyloid-like polypeptide aggregates

    NASA Astrophysics Data System (ADS)

    Colaco, Martin Francis

    The creation of useful composite materials requires precise control of the interface between the components in order to tune the overall shape and material properties. Despite the current research into nanotechnology, our ability to create materials with nanoscale precision is nascent. However, nature has a paradigm for the creation of finely structured composites under mild conditions called biomineralization. Through control of protein template assembly, solution conditions, and physical confinement, organisms are able to create useful optical and structural materials, such as bones, teeth, and mollusk shells. The objective of this thesis is to elucidate the importance of these various controls in synthetic systems to further our ability to create nanostructured materials. We begin by examining the formation of self-assembled monolayers (SAMs) of organosilanes on silica oxides. The formation of functionalized surfaces can help control the mineralization of amorphous or crystalline calcium carbonate. Long-chained organosilanes organize on surfaces to form dense, solid-like films, with the terminal groups determining the hydrophobicity and stereochemistry of the film. Our work has shown that uniform hydrophobic and hydrophilic films can be formed by using cleaned silica over glass or mica and through a vapor phase reaction over a liquid one. Additionally, we showed that mixed SAMs with phase-separated domains could be created through the selection of organosilanes and reaction conditions. We have built on these functionalized surfaces through the use of microfabrication and a gas permeable polymer to create three-dimensionally confined microcrystallizers. Other researchers have shown that one-dimensional confinement with a multi-functional surface (patterned with a small nucleating ordered region in a disordered SAM) can stabilize the creation of an amorphous calcium carbonate film before a single, large, micropatterned crystal is grown. Our work has determined

  2. Direct Observation of Completely Processed Calcium Carbonate Dust Particles

    SciTech Connect

    Laskin, Alexander; Iedema, Martin J.; Ichkovich, Aviad; Graber, Ellen R.; Taraniuk, Ilya; Rudich, Yinon

    2005-05-27

    This study presents, for the first time, field evidence of complete, irreversible processing of solid calcium carbonate (calcite)-containing particles and quantitative formation of liquid calcium nitrate particles apparently as a result of heterogeneous reaction of calcium carbonate-containing mineral dust particles with gaseous nitric acid. Formation of nitrates from individual calcite and sea salt particles was followed as a function of time in aerosol samples collected at Shoresh, Israel. Morphology and compositional changes of individual particles were observed using conventional scanning electron microscopy with energy dispersive analysis of X-rays (SEM/EDX) and computer controlled SEM/EDX. Environmental scanning electron microscopy (ESEM) was utilized to determine and demonstrate the hygroscopic behavior of calcium nitrate particles found in some of the samples. Calcium nitrate particles are exceptionally hygroscopic and deliquesce even at very low relative humidity (RH) of 9 -11% which is lower than typical atmospheric environments. Transformation of non-hygroscopic dry mineral dust particles into hygroscopic wet aerosol may have substantial impacts on light scattering properties, the ability to modify clouds and heterogeneous chemistry.

  3. Bioinspired synthesis of calcium carbonate hollow spheres with a nacre-type laminated microstructure.

    PubMed

    Dong, Wenyong; Cheng, Haixing; Yao, Yuan; Zhou, Yongfeng; Tong, Gangsheng; Yan, Deyue; Lai, Yijian; Li, Wei

    2011-01-04

    In this Article, we combine the characters of hyperbranched polymers and the concept of double-hydrophilic block copolymer (DHBC) to design a 3D crystal growth modifier, HPG-COOH. The novel modifier can efficiently control the crystallization of CaCO(3) from amorphous nanoparticles to vaterite hollow spheres by a nonclassical crystallization process. The obtained vaterite hollow spheres have a special puffy dandelion-like appearance; that is, the shell of the hollow spheres is constructed by platelet-like vaterite mesocrystals, perpendicular to the globe surface. The cross-section of the wall of a vaterite hollow sphere is similar to that of nacres in microstructure, in which platelet-like calcium carbonate mesocrystals pile up with one another. These results reveal the topology effect of the crystal growth modifier on biomineralization and the essential role of the nonclassical crystallization for constructing hierarchical microstructures.

  4. Deposition of calcium carbonate films by a polymer-induced liquid-precursor (PILP) process

    NASA Astrophysics Data System (ADS)

    Gower, Laurie B.; Odom, Damian J.

    2000-03-01

    A polypeptide additive has been used to transform the solution crystallization of calcium carbonate to a solidification process of a liquid-phase mineral precursor. In situ observations reveal that polyaspartate induces liquid-liquid phase separation of droplets of a mineral precursor. The droplets deposit on the substrate and coalesce to form a coating, which then solidifies into calcitic tablets and films. Transition bars form during the amorphous to crystalline transition, leading to sectorization of calcite tablets, and the defect textures and crystal morphologies are atypical of solution grown crystals. The formation of nonequilibrium crystal morphologies using an acidic polypeptide may have implications in the field of biomineralization, and the environmentally friendly aspects of this polymer-induced liquid-precursor (PILP) process may offer new techniques for aqueous-based processing of ceramic films, coatings, and particulates.

  5. Accelerated carbonation of Friedel's salt in calcium aluminate cement paste

    SciTech Connect

    Goni, S.; Guerrero, A

    2003-01-01

    The stability of Friedel's salt with respect to carbonation has been studied in calcium aluminate cement (CAC) pastes containing NaCl (3% of Cl{sup -} by weight of cement). Carbonation was carried out on a powdered sample in flowing 5% CO{sub 2} gas at 65% relative humidity to accelerate the process. At an intermediate carbonation step, a part of the sample was washed and dried up to 10 cycles to simulate a dynamic leaching attack. The two processes were followed by means of X-ray diffraction (XRD), pH and Cl{sup -} analyses in the simulated pore solution.

  6. Calcium supplements

    MedlinePlus

    ... TYPES OF CALCIUM SUPPLEMENTS Forms of calcium include: Calcium carbonate: Over-the-counter (OTC) antacid products, such as Tums and Rolaids, contain calcium carbonate. These sources of calcium do not cost much. ...

  7. In Situ Mechanical Property Measurements of Amorphous Carbon-Boron Nitride Nanotube Nanostructures

    NASA Technical Reports Server (NTRS)

    Kim, Jae-Woo; Lin, Yi; Nunez, Jennifer Carpena; Siochi, Emilie J.; Wise, Kristopher E.; Connell, John W.; Smith, Michael W.

    2011-01-01

    To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation. We demonstrate multiple in situ tensile, compressive, and lap shear tests with a-C/BNNT hybrid nanostructures. The tensile strength of the a-C/BNNT hybrid nanostructure is 5.29 GPa with about 90 vol% of a-C. The tensile strength and strain of the end-to-end joint structure with a-C welding is 0.8 GPa and 5.2% whereas the lap shear strength of the side-by-side joint structure with a-C is 0.25 GPa.

  8. Structural Models of Amorphous Carbon and its Surfaces by Tight-Binding Molecular Dynamics

    SciTech Connect

    Haerle, R.; Baldereschi, A.; Galli, G.

    1999-10-26

    We use liner-scaling tight-binding molecular dynamics to generate three structural models of bulk amorphous carbon with different atomic density. Amorphous carbon surfaces are then obtained by imposing tensile strain on these computer generated networks until fracture occurs. Our results show that for a given density, the formation energy of surfaces obtained with different tensile strains differ by only a few 10{sup -1} eV/atom and their structural properties are qualitatively similar. The presence of sp sites at the surface is observed at all densities, but with different values of the concentration. The surface thicknesses obtained in our simulations agree with experimental data. Furthermore we find that surface roughness increases with the amount of graphitic component in the bulk sample. The same trends of the macroscopic properties are obtained when using a two-center tight-binding Hamiltonian, an environmental dependent one, and first principles calculations.

  9. Carbon nanotube-amorphous silicon hybrid solar cell with improved conversion efficiency.

    PubMed

    Funde, Adinath M; Nasibulin, Albert G; Syed, Hashmi Gufran; Anisimov, Anton S; Tsapenko, Alexey; Lund, Peter; Santos, J D; Torres, I; Gandía, J J; Cárabe, J; Rozenberg, A D; Levitsky, Igor A

    2016-05-06

    We report a hybrid solar cell based on single walled carbon nanotubes (SWNTs) interfaced with amorphous silicon (a-Si). The high quality carbon nanotube network was dry transferred onto intrinsic a-Si forming Schottky junction for metallic SWNT bundles and heterojunctions for semiconducting SWNT bundles. The nanotube chemical doping and a-Si surface treatment minimized the hysteresis effect in current-voltage characteristics allowing an increase in the conversion efficiency to 1.5% under an air mass 1.5 solar spectrum simulator. We demonstrated that the thin SWNT film is able to replace a simultaneously p-doped a-Si layer and transparent conductive electrode in conventional amorphous silicon thin film photovoltaics.

  10. The structure and evolution of hydrogenated amorphous carbon grains and mantles in the interstellar medium

    NASA Astrophysics Data System (ADS)

    Jones, A. P.; Duley, W. W.; Williams, D. A.

    1990-12-01

    Hydrogenated amorphous carbons (HACs) have been proposed as the major constituent of interstellar dust. The HAC model can account successfully for observed properties of interstellar dust, and has great predictive power. A review is presented of relevant laboratory data on amorphous carbon, known to exist in three major phases: graphitic, diamondlike, and polymeric. These data indicate the probable nature of HAC in the interstellar medium. The properties of the HAC dust model, the deposition of HAC in the interstellar medium, and its evolution as interstellar conditions change are summarized. The properties of laboratory HAC in its various forms account successfully for observed interstellar extinction and for variations in extinction, for infrared emission features, and for extended red emission seen in reflection nebulae. A full evolutionary sequence that links the various HAC modifications found in different interstellar environments is proposed. It is concluded that the interstellar dust is an active component of the interstellar medium, responsive to its environment.

  11. In Situ Mechanical Property Measurements of Amorphous Carbon-Boron Nitride Nanotube Nanostructures

    NASA Technical Reports Server (NTRS)

    Kim, Jae-Woo; Lin, Yi; Nunez, Jennifer Carpena; Siochi, Emilie J.; Wise, Kristopher E.; Connell, John W.; Smith, Michael W.

    2011-01-01

    To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation. We demonstrate multiple in situ tensile, compressive, and lap shear tests with a-C/BNNT hybrid nanostructures. The tensile strength of the a-C/BNNT hybrid nanostructure is 5.29 GPa with about 90 vol% of a-C. The tensile strength and strain of the end-to-end joint structure with a-C welding is 0.8 GPa and 5.2% whereas the lap shear strength of the side-by-side joint structure with a-C is 0.25 GPa.

  12. A near-wearless and extremely long lifetime amorphous carbon film under high vacuum

    PubMed Central

    Wang, Liping; Zhang, Renhui; Jansson, Ulf; Nedfors, Nils

    2015-01-01

    Prolonging wear life of amorphous carbon films under vacuum was an enormous challenge. In this work, we firstly reported that amorphous carbon film as a lubricant layer containing hydrogen, oxygen, fluorine and silicon (a-C:H:O:F:Si) exhibited low friction (~0.1), ultra-low wear rate (9.0 × 10–13 mm3 N–1 mm–1) and ultra-long wear life (>2 × 106 cycles) under high vacuum. We systematically examined microstructure and composition of transfer film for understanding of the underlying frictional mechanism, which suggested that the extraordinarily excellent tribological properties were attributed to the thermodynamically and structurally stable FeF2 nanocrystallites corroborated using first-principles calculations, which were induced by the tribochemical reaction. PMID:26059254

  13. An atomistic study of growth mode and microstructure evolution of amorphous carbon films by different incident carbon atoms

    NASA Astrophysics Data System (ADS)

    Xue, Chen; Zhou, Jianqiu

    2014-09-01

    In this paper, molecular dynamics (MD) simulation has been performed to describe the growth and interfacial microstructure of amorphous carbon films. We focus on the film growth mode and surface morphology for diverse deposition process parameters mainly including incident energy and incident angle. To explore the relationship between the motion of deposition atoms and amorphous films growth, a series of snapshots for each deposition process has been taken for comparison. The snapshots show that the films growth modes are diverse at different incident parameters. In the next step, surface morphology, atom distribution along film growth direction and internal structure including vacancy defects evolution during deposition process are analyzed. The results reveal that incident energy on the horizontal plane dominates the surface roughness, and incident energy on the vertical plane dominates the compactness of the film. We conclude that a suitable incident parameter is not only beneficial to prepare amorphous films with compact and smooth or bump-like surface which will meet different needs, but also can avoid formation of defects during deposition. The simulation results are expected to provide useful guidance for improving amorphous carbon films quality.

  14. Photo-oxidation of polymer-like amorphous hydrogenated carbon under visible light illumination

    DOE PAGES

    Baxamusa, Salmaan; Laurence, Ted; Worthington, Matthew; ...

    2015-11-10

    Amorphous hydrogenated carbon (a-C:H), a polymer-like network typically synthesized by plasma chemical vapor deposition, has long been understood to exhibit optical absorption of visible light (λ > 400 nm). In this report we explain that this absorption is accompanied by rapid photo-oxidation (within minutes) that behaves in most respects like classic polymer photo-oxidation with the exception that it occurs under visible light illumination rather than ultraviolet illumination.

  15. Vacuum ultraviolet of hydrogenated amorphous carbons. II. Small hydrocarbons production in Photon Dominated Regions

    NASA Astrophysics Data System (ADS)

    Alata, I.; Jallat, A.; Gavilan, L.; Chabot, M.; Cruz-Diaz, G. A.; Munoz Caro, G. M.; Béroff, K.; Dartois, E.

    2015-12-01

    Context. Hydrogenated amorphous carbons (a-C:H) are a major component of the carbonaceous solids present in the interstellar medium. The production and existence of these grains is connected in particular with the balance between their photolysis, radiolysis, and hydrogenation. During grain processing, H2 and other small organic molecules, radicals, and fragments are released into the gas phase. Aims: We perform photolytic experiments on laboratory produced interstellar a-C:H analogues to monitor and quantify the release of species and compare to relevant observations in the interstellar medium. Methods: Hydrogenated amorphous carbon analogues at low temperature are exposed to ultraviolet (UV) photons, under ultra-high vacuum conditions. The species produced are monitored using mass spectrometry and post irradiation temperature-programmed desorption. Additional experiments are performed using deuterated analogues and the species produced are unambiguously separated from background contributions. We implement the laboratory measured yields for the released species in a time dependent model to investigate the effect of the UV photon irradiation of hydrogenated amorphous carbons in a photon dominated region, and estimate the associated time scale. Results: The UV photolysis of hydrogenated amorphous carbons leads to the production of H2 molecules and small hydrocarbons. The model shows that the photolytic evolution of a-C:Hs in photon dominated regions, such as the Horsehead Nebula, can raise the abundance of carbonaceous molecules by several orders of magnitude at intermediate visual extinctions, i.e., after the C+ maximum and before the dense cloud conditions prevail where models generally show a minimum abundance for such carbonaceous species. The injection time peak ranges from a thousand to ten thousand years in the models, considering only the destruction of such grains and no re-hydrogenation. This time scale is consistent with the estimated advection front of

  16. Photo-oxidation of polymer-like amorphous hydrogenated carbon under visible light illumination

    SciTech Connect

    Baxamusa, Salmaan; Laurence, Ted; Worthington, Matthew; Ehrmann, Paul

    2015-11-10

    Amorphous hydrogenated carbon (a-C:H), a polymer-like network typically synthesized by plasma chemical vapor deposition, has long been understood to exhibit optical absorption of visible light (λ > 400 nm). In this report we explain that this absorption is accompanied by rapid photo-oxidation (within minutes) that behaves in most respects like classic polymer photo-oxidation with the exception that it occurs under visible light illumination rather than ultraviolet illumination.

  17. Vacuum ultraviolet photolysis of hydrogenated amorphous carbons . I. Interstellar H2 and CH4 formation rates

    NASA Astrophysics Data System (ADS)

    Alata, I.; Cruz-Diaz, G. A.; Muñoz Caro, G. M.; Dartois, E.

    2014-09-01

    Context. The interstellar hydrogenated amorphous carbons (HAC or a-C:H) observed in the diffuse medium are expected to disappear in a few million years, according to the destruction time scale from laboratory measurements. The existence of a-C:H results from the equilibrium between photodesorption, radiolysis, hydrogenation and resilience of the carbonaceous network. During this processing, many species are therefore injected into the gas phase, in particular H2, but also small organic molecules, radicals or fragments. Aims: We perform experiments on interstellar a-C:H analogs to quantify the release of these species in the interstellar medium. Methods: The vacuum ultraviolet (VUV) photolysis of interstellar hydrogenated amorphous carbon analogs was performed at low (10 K) to ambient temperature, coupled to mass-spectrometry detection and temperature-programed desorption. Using deuterium isotopic substitution, the species produced were unambiguously separated from background contributions. Results: The VUV photolysis of hydrogenated amorphous carbons leads to the efficient production of H2 molecules, but also to small hydrocarbons. Conclusions: These species are formed predominantly in the bulk of the a-C:H analog carbonaceous network, in addition to the surface formation. Compared with species made by the recombination of H atoms and physisorbed on surfaces, they diffuse out at higher temperatures. In addition to the efficient production rate, it provides a significant formation route in environments where the short residence time scale for H atoms inhibits H2 formation on the surface, such as PDRs. The photolytic bulk production of H2 with carbonaceous hydrogenated amorphous carbon dust grains can provide a very large portion of the contribution to the H2 molecule formation. These dust grains also release small hydrocarbons (such as CH4) into the diffuse interstellar medium, which contribute to the formation of small carbonaceous radicals after being dissociated

  18. Methotrexate intercalated calcium carbonate nanostructures: Synthesis, phase transformation and bioassay study.

    PubMed

    Dai, Chao-Fan; Wang, Wei-Yuan; Wang, Lin; Zhou, Lei; Li, Shu-Ping; Li, Xiao-Dong

    2016-12-01

    The formation and stabilization of amorphous calcium carbonate (ACC) is an active area of research owing to the presence of stable ACC in various biogenic minerals. In this paper, the synthesis of calcium carbonate (CaCO3) under the participation of methotrexate (MTX) via a facile gas diffusion route was reported. The results indicated that the addition of MTX can result in the phase transformation of CaCO3, and then two kinds of hybrids, i.e., MTX-vaterite and stable MTX-ACC came into being. Interestingly, the functional agent MTX served as both the target anticancer drug loaded and effective complexation agents to modify and control the morphology of final samples. The examination of MTX-ACC biodegradation process revealed that the collapse of MTX-ACC nanoparticles was due to the synergistic effect of drug release and the phase transformation. Finally, our study also proved that MTX-ACC exhibited the most excellent suppressing function on the viability of cancer cells, especially after long-time duration. Copyright © 2016. Published by Elsevier B.V.

  19. The effect of Argon ion irradiation on the thickness and structure of ultrathin amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Xie, J.; Komvopoulos, K.

    2016-03-01

    Carbon films synthesized by plasma-enhanced chemical vapor deposition (PECVD) and filtered cathodic vacuum arc (FCVA) exhibit a layered structure consisting of a bottom (interface) and a top (surface) layer rich in sp2 atomic carbon bonding and a middle (bulk) layer of much higher sp3 content. Because of significant differences in the composition, structure, and thickness of these layers, decreasing the film thickness may negatively affect its properties. In this study, transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) were used to examine the effect of Ar+ ion irradiation on the structure and thickness of ultrathin films of hydrogenated amorphous carbon (a-C:H) and hydrogen-free amorphous carbon (a-C) deposited by PECVD and FCVA, respectively. The TEM and EELS results show that 2-min ion irradiation decreases the film thickness without markedly changing the film structure and composition, whereas 4-min ion irradiation results in significant film thinning and a moderate decrease of the sp3 content of the bulk layer. This study demonstrates that Ar+ ion irradiation is an effective post-deposition process for reducing the thickness and tuning the structure of ultrathin carbon films. This capability has direct implications in the synthesis of ultrathin protective carbon overcoats for extremely high-density magnetic recording applications.

  20. The effect of Argon ion irradiation on the thickness and structure of ultrathin amorphous carbon films

    SciTech Connect

    Xie, J.; Komvopoulos, K.

    2016-03-07

    Carbon films synthesized by plasma-enhanced chemical vapor deposition (PECVD) and filtered cathodic vacuum arc (FCVA) exhibit a layered structure consisting of a bottom (interface) and a top (surface) layer rich in sp{sup 2} atomic carbon bonding and a middle (bulk) layer of much higher sp{sup 3} content. Because of significant differences in the composition, structure, and thickness of these layers, decreasing the film thickness may negatively affect its properties. In this study, transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) were used to examine the effect of Ar{sup +} ion irradiation on the structure and thickness of ultrathin films of hydrogenated amorphous carbon (a-C:H) and hydrogen-free amorphous carbon (a-C) deposited by PECVD and FCVA, respectively. The TEM and EELS results show that 2-min ion irradiation decreases the film thickness without markedly changing the film structure and composition, whereas 4-min ion irradiation results in significant film thinning and a moderate decrease of the sp{sup 3} content of the bulk layer. This study demonstrates that Ar{sup +} ion irradiation is an effective post-deposition process for reducing the thickness and tuning the structure of ultrathin carbon films. This capability has direct implications in the synthesis of ultrathin protective carbon overcoats for extremely high-density magnetic recording applications.

  1. Yolk @ cage-Shell Hollow Mesoporous Monodispersion Nanospheres of Amorphous Calcium Phosphate for Drug Delivery with High Loading Capacity

    NASA Astrophysics Data System (ADS)

    Huang, Suping; Li, Chunxia; Xiao, Qi

    2017-04-01

    In this paper, yolk-shell hollow nanospheres of amorphous calcium phosphate (ACP) are prepared, and its loading capacity is investigated by comparing with that of solid-shell hollow structure ACP and cage-shell hollow structure ACP. Results show that the products are yolk @ cage-shell of ACP with large shell's pores size (15-40 nm) and large cavity volume. Adsorption results show that the loading capacity of yolk @ cage-shell hollow spherical ACP is very high, which is more than twice that of hollow ACP and 1.5 times of cage-like ACP. The main reasons are that the big shell's pore size contributes the large molecular doxorubicin hydrochloride (DOX · HCl) to enter the inner of hollow spheres easier, and the yolk-shell structure provides larger interior space and more adsorption sites for loading drugs.

  2. Yolk @ cage-Shell Hollow Mesoporous Monodispersion Nanospheres of Amorphous Calcium Phosphate for Drug Delivery with High Loading Capacity.

    PubMed

    Huang, Suping; Li, Chunxia; Xiao, Qi

    2017-12-01

    In this paper, yolk-shell hollow nanospheres of amorphous calcium phosphate (ACP) are prepared, and its loading capacity is investigated by comparing with that of solid-shell hollow structure ACP and cage-shell hollow structure ACP. Results show that the products are yolk @ cage-shell of ACP with large shell's pores size (15-40 nm) and large cavity volume. Adsorption results show that the loading capacity of yolk @ cage-shell hollow spherical ACP is very high, which is more than twice that of hollow ACP and 1.5 times of cage-like ACP. The main reasons are that the big shell's pore size contributes the large molecular doxorubicin hydrochloride (DOX · HCl) to enter the inner of hollow spheres easier, and the yolk-shell structure provides larger interior space and more adsorption sites for loading drugs.

  3. Ultraviolet Spectral Changes in Amorphous Carbon Grains Induced by Ion Irradiation

    NASA Astrophysics Data System (ADS)

    Mennella, V.; Baratta, G. A.; Colangeli, L.; Palumbo, P.; Rotundi, A.; Bussoletti, E.; Strazzulla, G.

    1997-05-01

    Small carbon grains, processed by UV radiation and cosmic rays, have been proposed as carriers of the 217.5 nm bump present in the interstellar extinction curves (Hecht 1986; Sorrell 1990). In this paper, we present the results of an experiment aimed at simulating, in a first approximation, the cosmic-ray irradiation active in space. We have studied the effects induced by 3 keV He+ ions on the UV spectrum of small cosmic analog carbon grains. Two different kinds of grains have been analyzed. They were produced by vapor condensation in hydrogen and argon quenching atmospheres. Spectrophotometric measurements have been carried out on grains as they were produced and after ion irradiation in the spectral range 0.19-2 μm. Relevant UV spectral changes are observed after ion irradiation: while the UV absorption band shifts from 203 to 215 nm in hydrogenated amorphous carbon grains, an opposite trend is observed for the samples produced in the argon atmosphere. In this case the UV band moves from 240 to 218 nm. These spectral changes are well correlated with the optical gap variations and are therefore interpreted in terms of grain microstructure changes induced by the interactions with ions. At the highest ion fluence considered, the two carbons tend to have a similar microstructure, as testified by the UV peak position and optical gap values because of a saturation effect of the two competitive processes, amorphization and graphitization, which occur in carbon samples during ion irradiation (Compagnini & Calcagno 1996). The results of the present experiment suggest that hydrogenated amorphous carbon grains cannot be transformed into graphite grains by cosmic-ray irradiation. Moreover, the efficiency of ion irradiation in destroying well-ordered aromatic structures poses the problem of the survival itself of polycrystalline or pure graphite particles in the interstellar medium.

  4. Structural and dynamical studies of acid-mediated conversion in amorphous-calcium-phosphate based dental composites

    SciTech Connect

    Zhang, Fan; Allen, Andrew J.; Levine, Lyle E.; Vaudin, Mark D.; Skrtic, Drago; Antonucci, Joseph M.; Hoffman, Kathleen M.; Giuseppetti, Anthony A.; Ilavsky, Jan

    2014-07-28

    Our objective was to investigate the complex structural and dynamical conversion process of the amorphous-calcium-phosphate (ACP)-to-apatite transition in ACP based dental composite materials. Composite disks were prepared using zirconia hybridized ACP fillers (0.4 mass fraction) and photo-activated Bis-GMA/TEGDMA resin (0.6 mass fraction). We performed an investigation of the solution-mediated ACP-to-apatite conversion mechanism in controlled acidic aqueous environment with in situ ultra-small angle X-ray scattering based coherent X-ray photon correlation spectroscopy and ex situ X-ray diffraction, as well as other complementary techniques. We established that the ACP-to-apatite conversion in ACP composites is a two-step process, owing to the sensitivity to local structural changes provided by coherent X-rays. Initially, ACP undergoes a local microstructural rearrangement without losing its amorphous character. We established the catalytic role of the acid and found the time scale of this rearrangement strongly depends on the pH of the solution, which agrees with previous findings about ACP without the polymer matrix being present. In the second step, ACP is converted to an apatitic form with the crystallinity of the formed crystallites being poor. Separately, we also confirmed that in the regular Zr-modified ACP the rate of ACP conversion to hydroxyapatite is slowed significantly compared to unmodified ACP, which is beneficial for targeted slow release of functional calcium and phosphate ions from dental composite materials. Significantly, for the first time, we were able to follow the complete solution-mediated transition process from ACP to apatite in this class of dental composites in a controlled aqueous environment. A two-step process, suggested previously, was conclusively identified.

  5. Structural and dynamical studies of acid-mediated conversion in amorphous-calcium-phosphate based dental composites.

    PubMed

    Zhang, Fan; Allen, Andrew J; Levine, Lyle E; Vaudin, Mark D; Skrtic, Drago; Antonucci, Joseph M; Hoffman, Kathleen M; Giuseppetti, Anthony A; Ilavsky, Jan

    2014-10-01

    To investigate the complex structural and dynamical conversion process of the amorphous-calcium-phosphate (ACP)-to-apatite transition in ACP based dental composite materials. Composite disks were prepared using zirconia hybridized ACP fillers (0.4 mass fraction) and photo-activated Bis-GMA/TEGDMA resin (0.6 mass fraction). We performed an investigation of the solution-mediated ACP-to-apatite conversion mechanism in controlled acidic aqueous environment with in situ ultra-small angle X-ray scattering based coherent X-ray photon correlation spectroscopy and ex situ X-ray diffraction, as well as other complementary techniques. We established that the ACP-to-apatite conversion in ACP composites is a two-step process, owing to the sensitivity to local structural changes provided by coherent X-rays. Initially, ACP undergoes a local microstructural rearrangement without losing its amorphous character. We established the catalytic role of the acid and found the time scale of this rearrangement strongly depends on the pH of the solution, which agrees with previous findings about ACP without the polymer matrix being present. In the second step, ACP is converted to an apatitic form with the crystallinity of the formed crystallites being poor. Separately, we also confirmed that in the regular Zr-modified ACP the rate of ACP conversion to hydroxyapatite is slowed significantly compared to unmodified ACP, which is beneficial for targeted slow release of functional calcium and phosphate ions from dental composite materials. For the first time, we were able to follow the complete solution-mediated transition process from ACP to apatite in this class of dental composites in a controlled aqueous environment. A two-step process, suggested previously, was conclusively identified. Copyright © 2014 Academy of Dental Materials. All rights reserved.

  6. Structural and dynamical studies of acid-mediated conversion in amorphous-calcium-phosphate based dental composites

    DOE PAGES

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

    2014-07-28

    Our objective was to investigate the complex structural and dynamical conversion process of the amorphous-calcium-phosphate (ACP)-to-apatite transition in ACP based dental composite materials. Composite disks were prepared using zirconia hybridized ACP fillers (0.4 mass fraction) and photo-activated Bis-GMA/TEGDMA resin (0.6 mass fraction). We performed an investigation of the solution-mediated ACP-to-apatite conversion mechanism in controlled acidic aqueous environment with in situ ultra-small angle X-ray scattering based coherent X-ray photon correlation spectroscopy and ex situ X-ray diffraction, as well as other complementary techniques. We established that the ACP-to-apatite conversion in ACP composites is a two-step process, owing to the sensitivity to localmore » structural changes provided by coherent X-rays. Initially, ACP undergoes a local microstructural rearrangement without losing its amorphous character. We established the catalytic role of the acid and found the time scale of this rearrangement strongly depends on the pH of the solution, which agrees with previous findings about ACP without the polymer matrix being present. In the second step, ACP is converted to an apatitic form with the crystallinity of the formed crystallites being poor. Separately, we also confirmed that in the regular Zr-modified ACP the rate of ACP conversion to hydroxyapatite is slowed significantly compared to unmodified ACP, which is beneficial for targeted slow release of functional calcium and phosphate ions from dental composite materials. Significantly, for the first time, we were able to follow the complete solution-mediated transition process from ACP to apatite in this class of dental composites in a controlled aqueous environment. A two-step process, suggested previously, was conclusively identified.« less

  7. Plasma-deposited amorphous hydrogenated carbon films and their tribological properties

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Pouch, John J.; Alterovitz, Samuel A.

    1989-01-01

    Recent work on the properties of diamondlike carbon films and their dependence on preparation conditions are reviewed. The results of the study indicate that plasma deposition enables one to deposit a variety of amorphous hydrogenated carbon (a-C:H ) films exhibiting more diamondlike behavior to more graphitic behavior. The plasma-deposited a-C:H can be effectively used as hard, wear-resistant, and protective lubricating films on ceramic materials such as Si(sub 3)N(sub 4) under a variety of environmental conditions such as moist air, dry nitrogrn, and vacuum.

  8. Synthesis and optical enhancement of amorphous carbon nanotubes/silver nanohybrids via chemical route at low temperature.

    PubMed

    Han, Tan Kim; Fen, Leo Bey; Nee, Ng Meng; Johan, Mohd Rafie

    2014-01-01

    We report the synthesis of amorphous carbon nanotubes/silver (αCNTs/Ag) nanohybrids via simple chemical route without additional reactant and surfactant at low temperature. Field emission scanning microscope (FESEM) and transmission electron microscope (TEM) confirmed formation of CNTs. X-ray diffraction (XRD) pattern confirmed the amorphous phase of carbon and the formation of Ag nanoparticles crystalline phase. Raman spectra revealed the amorphous nature of α CNTs. UV-visible spectroscopy showed enhancement of optical properties of α CNTs/Ag nanohybrids.

  9. Enamel-like apatite crown covering amorphous mineral in a crayfish mandible

    PubMed Central

    Bentov, Shmuel; Zaslansky, Paul; Al-Sawalmih, Ali; Masic, Admir; Fratzl, Peter; Sagi, Amir; Berman, Amir; Aichmayer, Barbara

    2012-01-01

    Carbonated hydroxyapatite is the mineral found in vertebrate bones and teeth, whereas invertebrates utilize calcium carbonate in their mineralized organs. In particular, stable amorphous calcium carbonate is found in many crustaceans. Here we report on an unusual, crystalline enamel-like apatite layer found in the mandibles of the arthropod Cherax quadricarinatus (freshwater crayfish). Despite their very different thermodynamic stabilities, amorphous calcium carbonate, amorphous calcium phosphate, calcite and fluorapatite coexist in well-defined functional layers in close proximity within the mandible. The softer amorphous minerals are found primarily in the bulk of the mandible whereas apatite, the harder and less soluble mineral, forms a wear-resistant, enamel-like coating of the molar tooth. Our findings suggest a unique case of convergent evolution, where similar functional challenges of mastication led to independent developments of structurally and mechanically similar, apatite-based layers in the teeth of genetically remote phyla: vertebrates and crustaceans. PMID:22588301

  10. Hardness and modulus properties in ion-beam-modified amorphous carbon: Temperature and dose rate dependences

    SciTech Connect

    Lee, D.; Lee, H.; Park, B.

    1997-08-01

    Ion implantation into amorphous carbon has been initiated to investigate the possibility of superhard carbon-nitride formation. Studies of implantation-temperature effects by 100 keV N{sup +} or 80 keV C{sup +} ions at 50 {mu}A show a narrow temperature window at approximately {minus}100{degree}C for the optimum surface hardness and elastic modulus (measured by nanoindentation), both values much higher than those for the unimplanted amorphous carbon. No distinguishable properties are found between nitrogen and self (carbon) implantations. At a dose rate of 5 {mu}A, however, the optimum hardness and modulus are found at a lower implantation temperature, with a broader temperature window. The enhanced strengths are well correlated with the asymmetric diffuse peak at around 1500cm{sup {minus}1} in Raman spectroscopy, and the increased ratio of sp{sup 3}- over sp{sup 2}- bonded carbon sites observed by electron energy loss spectroscopy. {copyright} {ital 1997 Materials Research Society.}

  11. Effect of some organic solvent-water mixtures composition on precipitated calcium carbonate in carbonation process

    NASA Astrophysics Data System (ADS)

    Konopacka-Łyskawa, Donata; Kościelska, Barbara; Karczewski, Jakub

    2015-05-01

    Precipitated calcium carbonate particles were obtained during carbonation of calcium hydroxide slurry with carbon dioxide. Aqueous solutions of isopropyl alcohol, n-butanol and glycerol were used as solvents. Concentration of organic additives in the reactive mixture was from 0% to 20% (vol). Precipitation process were performed in a stirred tank reactor equipped with gas distributor. Multimodal courses of particles size distribution were determined for produced CaCO3 particles. Calcium carbonate as calcite was precipitated in all experiments. The mean Sauter diameter of CaCO3 particles decreased when the concentration of all used organic additives increased. The amount of small particle fraction in the product increased with the increasing concentration of organic solvents. Similar physical properties of used liquid phase resulted in the similar characteristics of obtained particles.

  12. Polymorph-selective crystallization of calcium carbonate inspired by biomineralization

    NASA Astrophysics Data System (ADS)

    Kim, Il Won

    This dissertation primarily examines bioinspired mineralization, focusing on the polymorph-selective crystallization of calcium carbonate. (1) The effect of epitaxy on the polymorphic control of calcium carbonate was studied with aragonite-type inorganic substrates. The critical epitaxial mismatch for aragonite growth, when conditions disfavor aragonite, seems to be less than 7.1%. Larger epitaxial strain appeared to prohibit aragonite formation even though the substrates had the same crystal structure. The epitaxy required for aragonite nucleation seems to be more precise than that often suggested for biological systems. (2) Polymers of different aqueous-solution properties were tested to observe the effect on the crystallization of calcium carbonate. Near exclusive formation of aragonite was attained through the inhibition of more stable calcite with poly(vinyl alcohol). The contributing characteristics of poly(vinyl alcohol) seemed to be its ability to hydrogen bond and its tendency to adsorb non-specifically onto solid surfaces. Similar inhibition activity is suggested for various biomacromolecules involved in biogenic aragonite formation of mollusks, with the biomacromolecules acting in the same way as poly(vinyl alcohol). (3) Polymer surfaces imprinted by aragonite-type crystals (strontium carbonate) were studied as substrates for the crystallization of calcium carbonate. Only calcite formed under vaterite-, aragonite-, and calcite-favorable conditions. This result seemed to arise from the nature of functional groups, rather than from the molecular structure of the imprint. Interaction between the functional groups and calcium carbonate is suggested to have enhanced the crystallization rate, resulting in the rapid formation of the thermodynamically stable calcite irrespective of the bulk crystallization conditions. (4) A catechol-based monomer was synthesized in the course of developing a dental adhesive, which mimics the functionalities of mussel adhesive

  13. Supplemental Information: Phototransformation-Induced Aggregation of Functionalized Single-Walled Carbon Nanotubes: the Importance of Amorphous Carbon

    EPA Pesticide Factsheets

    Additional information about the carboxylated SWCNT calibration curve, AFM images, EDS results, solar simulator light and UVB lamp spectra, TEM image ofparent carboxylated SWCNTs, XPS spectra of the dark control P3 sample and the irradiated P3 sample, and a table summarizing the kinetic parameters (PDF)This dataset is associated with the following publication:Hou, W., C. He, Y. Wang, D. Wang, and R. Zepp. Phototransformation-Induced Aggregation of Functionalized Single-Walled Carbon Nanotubes: The Importance of Amorphous Carbon. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, USA, 50(7): 3494–3502, (2016).

  14. Importance of unburned coal carbon, black carbon, and amorphous organic carbon to phenanthrene sorption in sediments.

    PubMed

    Cornelissen, Gerard; Gustafsson, Orjan

    2005-02-01

    The aim of this paper was to estimate the contribution to total phenanthrene sorption from unburned coal and black carbon (BC; soot and charcoal) in sediment. We determined sorption isotherms for five Argonne Premium Coal standards over a wide concentration interval (0.01-10 000 ng/L). The coals showed strong and nonlinear sorption (carbon-normalized K(F) = 5.41-5.96; nF = 0.68-0.82). Coal sorption appeared to become more nonlinear with increasing coal maturity. The coal's specific surface area appeared to influence K(F). On the basis of the current coal sorption observations combined with earlier petrographic analyses and BC sorption experiments, we calculated for one particular sediment that coal, BC, and "other" OC were all important to PHE sorption in the environmentally relevant nanogram per liter range. This indicates that it is important to consider strong sorption to coal in the risk assessment of coal-impacted geosorbents (e.g., river beds) where coal is mined/shipped and manufactured gas plant sites.

  15. HRTEM low dose: the unfold of the morphed graphene, from amorphous carbon to morphed graphenes.

    PubMed

    Calderon, H A; Okonkwo, A; Estrada-Guel, I; Hadjiev, V G; Alvarez-Ramírez, F; Robles Hernández, F C

    We present experimental evidence under low-dose conditions transmission electron microscopy for the unfolding of the evolving changes in carbon soot during mechanical milling. The milled soot shows evolving changes as a function of the milling severity or time. Those changes are responsible for the transformation from amorphous carbon to graphenes, graphitic carbon, and highly ordered structures such as morphed graphenes, namely Rh6 and Rh6-II. The morphed graphenes are corrugated layers of carbon with cross-linked covalently nature and sp(2)- or sp(3)-type allotropes. Electron microscopy and numerical simulations are excellent complementary tools to identify those phases. Furthermore, the TEAM 05 microscope is an outstanding tool to resolve the microstructure and prevent any damage to the sample. Other characterization techniques such as XRD, Raman, and XPS fade to convey a true identification of those phases because the samples are usually blends or mixes of the mentioned phases.

  16. The ir emission features: Emission from PAH (Polycyclic Aromatic Hydrocarbons) molecules and amorphous carbon particles

    SciTech Connect

    Allamandola, L.J.; Tielens, A.G.G.M.; Barker, J.R.

    1986-01-01

    PAHs can have several forms in the interstellar medium. To assess the importance of each requires the availability of a collection of high quality, complete mid-ir interstellar emission spectra, a collection of laboratory spectra of PAH samples prepared under realistic conditions and a firm understanding of the microscopic emission mechanism. Given what we currently know about PAHs, the spectroscopic data suggests that there are at least two components which contribute to the interstellar emission spectrum: free molecule sized PAHs producing the narrow features and amorphous carbon particles (which are primarily made up of an irregular ''lattice'' of PAHs) contributing to the broad underlying components. An exact treatment of the ir fluorescence from highly vibrationally excited large molecules shows that species containing between 20 and 30 carbon atoms are responsible for the narrow features, although the spectra match more closely with the spectra of amorphous carbon particles. Since little is known about the spectroscopic properties of free PAHs and PAH clusters, much laboratory work is called for in conjunction with an observational program which focuses on the spatial characteristics of the spectra. In this way the distribution and evolution of carbon from molecule to particle can be traced. 38 refs., 9 figs.

  17. Vertical electric field stimulation of neural cells on porous amorphous carbon electrodes

    NASA Astrophysics Data System (ADS)

    Jain, Shilpee; Sharma, Ashutosh; Basu, Bikramjit

    2014-03-01

    We demonstrate the efficacy of amorphous macroporous carbon substrates as electrodes to stimulate neuronal cell proliferation in presence of external electric field. The electric field was applied perpendicular to carbon electrode, while growing mouse neuroblastoma (N2a) cells in vitro. The placement of the second electrode outside of the cell culture medium allows the investigation of cell response to electric field without the concurrent complexities of submerged electrodes such as potentially toxic electrode reactions, electro-kinetic flows and charge transfer (electrical current) in the cell medium. The macroporous carbon electrodes are uniquely characterized by a higher specific charge storage capacity (0.2 mC/cm2) and low impedance (3.3 k Ω at 1 kHz). When a uniform or a gradient electric field was applied perpendicular to the amorphous carbon substrate, it was found that the N2a cell viability and neurite length were higher at low electric field strengths (<= 2.5 V/cm) compared to that measured without an applied field (0 V/cm). Overall, the results of the present study unambiguously establish the uniform/gradient vertical electric field based culture protocol to stimulate neurite outgrowth and viability of nerve cells.

  18. Thermally induced transformations of amorphous carbon nanostructures fabricated by electron beam induced deposition.

    PubMed

    Kulkarni, Dhaval D; Rykaczewski, Konrad; Singamaneni, Srikanth; Kim, Songkil; Fedorov, Andrei G; Tsukruk, Vladimir V

    2011-03-01

    We studied the thermally induced phase transformations of electron-beam-induced deposited (EBID) amorphous carbon nanostructures by correlating the changes in its morphology with internal microstructure by using combined atomic force microscopy (AFM) and high resolution confocal Raman microscopy. These carbon deposits can be used to create heterogeneous junctions in electronic devices commonly known as carbon-metal interconnects. We compared two basic shapes of EBID deposits: dots/pillars with widths from 50 to 600 nm and heights from 50 to 500 nm and lines with variable heights from 10 to 150 nm but having a constant length of 6 μm. We observed that during thermal annealing, the nanoscale amorphous deposits go through multistage transformation including dehydration and stress-relaxation around 150 °C, dehydrogenation within 150-300 °C, followed by graphitization (>350 °C) and formation of nanocrystalline, highly densified graphitic deposits around 450 °C. The later stage of transformation occurs well below commonly observed graphitization for bulk carbon (600-800 °C). It was observed that the shape of the deposits contribute significantly to the phase transformations. We suggested that this difference is controlled by different contributions from interfacial footprints area. Moreover, the rate of graphitization was different for deposits of different shapes with the lines showing a much stronger dependence of its structure on the density than the dots.

  19. Effect of amorphous carbon layers on the growth of diamond in dual-frequency plasma

    NASA Astrophysics Data System (ADS)

    Reinke, P.; Klemberg-Sapieha, J. E.; Martinu, L.

    1994-11-01

    In the present work we study the growth of diamond in a dual-mode microwave/radio frequency plasma. We investigate the effect of the thickness of predeposited hydrogenated amorphous carbon (a-C:H) films and of ion bombardment of the nucleation process and on the crystal quality. The deposits are characterized by x-ray photoelectron spectroscopy (XPS) and by scanning electron microscopy. The XPS spectra of the C(1s) carbon peak and of the plasmon features confirm the presence of an amorphous, carbonaceous phase and of silicon carbide on the surface. Radio frequency biasing during the initial stage of diamond growth leads to a lower crystal quality, but to a higher nucleation density N(sub D). Without biasing, good quality, predominantly (100) oriented diamond crystals are obtained on a Si(100) surface. The N(sub D) values are found to increase with the thickness of the predeposited a-C:H layer. Evolution of the nucleus size distributions indicates that the a-C:H film contributes to the carbon supply, enhancing the nucleation efficiency and shortening the incubation time of seed crystals. Before a continuous layer is formed, the growth of crystals is determined by the interaction with the gas phase as well as by the amount of carbon available on the surface.

  20. Silicon and aluminum doping effects on the microstructure and properties of polymeric amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoqiang; Hao, Junying; Xie, Yuntao

    2016-08-01

    Polymeric amorphous carbon films were prepared by radio frequency (R.F. 13.56 MHz) magnetron sputtering deposition. The microstructure evolution of the deposited polymeric films induced by silicon (Si) and aluminum(Al) doping were scrutinized through infrared spectroscopy, multi-wavelength Raman spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The comparative results show that Si doping can enhance polymerization and Al doping results in an increase in the ordered carbon clusters. Si and Al co-doping into polymeric films leads to the formation of an unusual dual nanostructure consisting of cross-linked polymer-like hydrocarbon chains and fullerene-like carbon clusters. The super-high elasticity and super-low friction coefficients (<0.002) under a high vacuum were obtained through Si and Al co-doping into the films. Unconventionally, the co-doped polymeric films exhibited a superior wear resistance even though they were very soft. The relationship between the microstructure and properties of the polymeric amorphous carbon films with different elements doping are also discussed in detail.

  1. Using Calcium Isotopic Composition of Calcium Carbonate Veins to Assess the Roles of Vein Formation and Seafloor Alteration in Regulation of the Carbon Cycle

    NASA Astrophysics Data System (ADS)

    Chen, F.; Coggon, R. M.; Teagle, D. A. H.; Turchyn, A. V.

    2016-12-01

    Calcium carbonate vein formation in the oceanic crust has been proposed as a climate-sensitive feedback mechanism that regulates the carbon cycle on million-year timescales. The suggestion has been that higher pCO2 levels may drive changes in ocean temperature and pH that increase seafloor alteration, releasing more calcium from oceanic basalt. This results in more removal of carbon from Earth's surface through calcium carbonate formation, which includes calcium carbonate vein formation in oceanic crust. The importance of this feedback mechanism remains enigmatic. Measurements of the δ44Ca of calcium carbonate veins in the oceanic crust may constrain the sources of calcium and timing of vein formation. Seawater and basalt are the only sources present shortly after crustal formation, whereas other sources, such as anhydrite dissolution and sedimentary carbonates become available when the crust ages, at which point carbonate veins may form far from the ridge axis. We report the calcium isotopic composition of 65 calcium carbonate veins, ranging from 108 to 1.2 million years old, in hydrothermally altered basalt from the Mid-Atlantic and Juan de Fuca ridges. We also present 43 δ44Ca measurements of 5.9 million year old basalts and dikes from the Costa Rica Rift that have undergone hydrothermal alteration over a range of conditions in upper crust. The δ44Ca of the calcium carbonate veins ranges from -1.59 to 1.01‰ (versus Bulk Silicate Earth), whereas the δ44Ca of altered basalts ranges from -0.18 to 0.28‰. Depth and temperature of formation seem to be major influences on calcium carbonate vein δ44Ca, with veins formed at cool, shallower depths having higher δ44Ca, closer to seawater. In contrast, we note no temporal variation in δ44Ca of calcium carbonate veins when comparing samples from older and younger crust. The majority of veins (54 out of 65) have δ44Ca between that of seawater and basalt, which implies that they may have formed quite soon after

  2. On diamond, graphitic and amorphous carbons in primitive extraterrestrial solar system materials

    NASA Technical Reports Server (NTRS)

    Rietmeijer, Frans J. M.

    1990-01-01

    Carbon is among the most abundant elements in the universe and carbon chemistry in meteorites and comets is an important key to understanding many Solar System and interstellar processes. Yet, the mineralogical properties and interrelations between various structural forms of elemental carbon remain ambiguous. Crystalline elemental carbons include rhombohedral graphite, hexagonal graphite, cubic diamond, hexagonal diamond (i.e., lonsdaleite or carbon-2H) and chaoite. Elemental carbon also occurs as amorphous carbon and poorly graphitized (or turbostratic) carbon but of all the forms of elemental carbon only graphite is stable under physical conditions that prevail in small Solar System bodies and in the interstellar medium. The recent discovery of cubic diamond in carbonaceous chondrites and hexagonal diamond in chondritic interplanetary dust particles (IDPs) have created a renewed interest in the crystalline elemental carbons that were not formed by shock processes on a parent body. Another technique, Raman spectroscopy, confirms a widespread occurrence of disordered graphite in the Allende carbonaceous chondrite and in chondritic IDPs. Elemental carbons have also been identified by their characteristic K-edge features in electron energy loss spectra (EELS). However, the spectroscopic data do not necessarily coincide with those obtained by selected area electron diffraction (SAED). In order to interpret these data in terms of rational crystalline structures, it may be useful to consider the principles underlying electron diffraction and spectroscopic analyses. Electron diffraction depends on electron scattering, on the type of atom and the distance between atoms in a crystal lattice. Spectroscopic data are a function of the type of atom and the energy of bonds between atoms. Also, SAED is a bulk sampling technique when compared to techniques such as Raman spectroscopy or EELS. Thus, it appears that combined analyses provide contradictory results and that amorphous

  3. On diamond, graphitic and amorphous carbons in primitive extraterrestrial solar system materials

    NASA Technical Reports Server (NTRS)

    Rietmeijer, Frans J. M.

    1990-01-01

    Carbon is among the most abundant elements in the universe and carbon chemistry in meteorites and comets is an important key to understanding many Solar System and interstellar processes. Yet, the mineralogical properties and interrelations between various structural forms of elemental carbon remain ambiguous. Crystalline elemental carbons include rhombohedral graphite, hexagonal graphite, cubic diamond, hexagonal diamond (i.e., lonsdaleite or carbon-2H) and chaoite. Elemental carbon also occurs as amorphous carbon and poorly graphitized (or turbostratic) carbon but of all the forms of elemental carbon only graphite is stable under physical conditions that prevail in small Solar System bodies and in the interstellar medium. The recent discovery of cubic diamond in carbonaceous chondrites and hexagonal diamond in chondritic interplanetary dust particles (IDPs) have created a renewed interest in the crystalline elemental carbons that were not formed by shock processes on a parent body. Another technique, Raman spectroscopy, confirms a widespread occurrence of disordered graphite in the Allende carbonaceous chondrite and in chondritic IDPs. Elemental carbons have also been identified by their characteristic K-edge features in electron energy loss spectra (EELS). However, the spectroscopic data do not necessarily coincide with those obtained by selected area electron diffraction (SAED). In order to interpret these data in terms of rational crystalline structures, it may be useful to consider the principles underlying electron diffraction and spectroscopic analyses. Electron diffraction depends on electron scattering, on the type of atom and the distance between atoms in a crystal lattice. Spectroscopic data are a function of the type of atom and the energy of bonds between atoms. Also, SAED is a bulk sampling technique when compared to techniques such as Raman spectroscopy or EELS. Thus, it appears that combined analyses provide contradictory results and that amorphous

  4. Calcium carbonate nucleation driven by ion binding in a biomimetic matrix revealed by in situ electron microscopy.

    PubMed

    Smeets, Paul J M; Cho, Kang Rae; Kempen, Ralph G E; Sommerdijk, Nico A J M; De Yoreo, James J

    2015-04-01

    The characteristic shapes, structures and properties of biominerals arise from their interplay with a macromolecular matrix. The developing mineral interacts with acidic macromolecules, which are either dissolved in the crystallization medium or associated with insoluble matrix polymers, that affect growth habits and phase selection or completely inhibit precipitation in solution. Yet little is known about the role of matrix-immobilized acidic macromolecules in directing mineralization. Here, by using in situ liquid-phase electron microscopy to visualize the nucleation and growth of CaCO3 in a matrix of polystyrene sulphonate (PSS), we show that the binding of calcium ions to form Ca-PSS globules is a key step in the formation of metastable amorphous calcium carbonate (ACC), an important precursor phase in many biomineralization systems. Our findings demonstrate that ion binding can play a significant role in directing nucleation, independently of any control over the free-energy barrier to nucleation.

  5. A study of the formation of amorphous calcium phosphate and hydroxyapatite on melt quenched Bioglass using surface sensitive shallow angle X-ray diffraction.

    PubMed

    Martin, R A; Twyman, H; Qiu, D; Knowles, J C; Newport, R J

    2009-04-01

    Melt quenched silicate glasses containing calcium, phosphorous and alkali metals have the ability to promote bone regeneration and to fuse to living bone. These glasses, including 45S5 Bioglass((R)) [(CaO)(26.9)(Na(2)O)(24.4)(SiO(2))(46.1)(P(2)O(5))(2.6)], are routinely used as clinical implants. Consequently there have been numerous studies on the structure of these glasses using conventional diffraction techniques. These studies have provided important information on the atomic structure of Bioglass((R)) but are of course intrinsically limited in the sense that they probe the bulk material and cannot be as sensitive to thin layers of near-surface dissolution/growth. The present study therefore uses surface sensitive shallow angle X-ray diffraction to study the formation of amorphous calcium phosphate and hydroxyapatite on Bioglass((R)) samples, pre-reacted in simulated body fluid (SBF). Unreacted Bioglass((R)) is dominated by a broad amorphous feature around 2.2 A(-1) which is characteristic of sodium calcium silicate glass. After reacting Bioglass((R)) in SBF a second broad amorphous feature evolves ~1.6 A(-1) which is attributed to amorphous calcium phosphate. This feature is evident for samples after only 4 h reacting in SBF and by 8 h the amorphous feature becomes comparable in magnitude to the background signal of the bulk Bioglass((R)). Bragg peaks characteristic of hydroxyapatite form after 1-3 days of reacting in SBF.

  6. Geometrically structured implants for cranial reconstruction made of biodegradable polyesters and calcium phosphate/calcium carbonate.

    PubMed

    Schiller, Carsten; Rasche, Christian; Wehmöller, Michael; Beckmann, Felix; Eufinger, Harald; Epple, Matthias; Weihe, Stephan

    2004-01-01

    The aim of this study was the development of a processing pathway for manufacturing of biodegradable skull implants with individual geometry. The implants on the basis of polylactide and calcium phosphate/calcium carbonate were prepared by a combination of hot pressing and gas foaming. On the inside, the implant consists of a macroporous and faster degradable material (poly(D,L-lactide)+CaCO3) to allow the ingrowth of bone cells. The pore size is in the range of 200-400 microm. On the outside, the implant consists of a compact and slower biodegradable material (poly(L-lactide) and calcium phosphate) to ensure mechanical stability and protection. To overcome problems like inflammatory reactions caused by acidic degradation products of polylactide, the polyester was combined with basic filling materials (calcium salts). The filler neutralises the lactic acid produced during polymer degradation and increases the bioactivity of the material. The stabilised pH was demonstrated by long-term in vitro pH studies. Over a time period of 250 d in demineralised water, the pH was in the physiological range. The in vitro biocompatibility was shown by cell cultures with human osteoblasts. A good proliferation of the cells was observed over the whole test period of 4 weeks.

  7. Carbonate-containing apatite (CAP) synthesis under moderate conditions starting from calcium carbonate and orthophosphoric acid.

    PubMed

    Pham Minh, Doan; Tran, Ngoc Dung; Nzihou, Ange; Sharrock, Patrick

    2013-07-01

    The synthesis of carbonate-containing apatite (CAP) from calcium carbonate and orthophosphoric acid under moderate conditions was investigated. In all cases, complete precipitation of orthophosphate species was observed. The reaction temperature influenced strongly the decomposition of calcium carbonate and therefore the composition of formed products. The reaction temperature of 80 °C was found to be effective for the complete decomposition of calcium carbonate particles after 48 h of reaction. Infra-red spectroscopy (IR), nuclear magnetic resonance (NMR), thermogravimetry/mass spectroscopy (TG-MS) coupling, and X-ray diffraction (XRD) characterizations allowed the identification of the composition of formed products. By increasing the reaction temperature from 20 °C to 80 °C, the content of A-type CAP increased and that of B-type CAP decreased, according to the favorable effect of temperature on the formation of A-type CAP. The total amount of carbonate content incorporated in CAP's structure, which was determined by TG-MS analysis, increased with the reaction temperature and reached up to 4.1% at 80 °C. At this temperature, the solid product was mainly composed of apatitic components and showed the typical flat-needle-like structure of CAP particles obtained in hydrothermal conditions. These results show an interesting one-step synthesis of CAP from calcium carbonate and orthophosphoric acid as low cost but high purity starting materials. Copyright © 2013 Elsevier B.V. All rights reserved.

  8. Absorption of inorganic halides produced from Freon 12 by calcium carbonate containing iron(III) oxide

    SciTech Connect

    Imamura, Seiichiro; Matsuba, Yoichi; Yamada, Etsu; Takai, Kenji; Utani, Kazunori

    1997-09-01

    Inorganic halides produced by the catalytic decomposition of Freon 12 were fixed by calcium carbonate, which is the main component of limestone. Iron(III) oxide, which is present as a contaminant in limestone, promoted the absorption of the halides by calcium carbonate at low temperatures. The supposed action of iron(III) oxide was to first react with inorganic halides, forming iron halides, and, then, transfer them to calcium carbonate to replace carbonate ion in a catalytic way. Thus, calcium carbonate containing iron oxides (limestone) can be used as an effective absorbent for the inorganic halogens produced during the decomposition of Freons.

  9. Magnesium and calcium in carbonate bedrock and groundwaters, Peninsular Malaysia

    NASA Astrophysics Data System (ADS)

    Crowther, J.

    Groundwaters draining Kuala Lumpur Limestone, Kinta Limestone and limestones of the Setul Formation were monitored over a 1 yr period. The closeness of the mean Mg:Ca + Mg ratios of the groundwaters (12.8%) and bedrock (13.3%) indicates calcium and magnesium dissolution to be broadly congruent. Ratios < 2.5and> 35% are much less common in groundwaters than in bedrock because of: (i) heterogeneity in bedrock mineralogy within groundwater catchments; (ii) differential solubilities of calcium and magnesium in calcites, high magnesium calcites and dolomites; and (iii) preferential precipitation of calcium in secondary carbonate deposits. In groundwaters with variable discharges, Mg:Ca + Mg correlates negatively with discharge, as calcium deposition per unit volume of water diminishes at higher flows. Use of groundwater survey data to locate areas of dolomitization and make specific inferences about the mineralogy of limestone formations is discussed, and estimates of net chemical denudation rates (range, 56.6-70.9m 3/km 2/yr) are presented.

  10. In situ electron microscopy studies of calcium carbonate precipitation from aqueous solution with and without organic additives.

    PubMed

    Verch, Andreas; Morrison, Ian E G; Locht, Renee van de; Kröger, Roland

    2013-08-01

    For the understanding of mineral formation processes from solution it is important to obtain a deeper insight into the dynamics of crystal growth. In this study we applied for this purpose a novel atmospheric scanning electron microscope that allows the investigation of CaCO3 particle formation in solution under atmospheric conditions with a resolution of approximately 10nm. Furthermore it permits the in situ observation of the dynamics of crystal evolution. With this tool the precipitation of CaCO3 was studied in the absence and presence of additives, namely poly(acrylic acid) and poly(styrene sulfonate-co-maleic acid) which are known to influence the crystal growth rate and morphology. We determined particle growth rates and investigated the formation and dissolution dynamics of an observed transient phase, believed to be amorphous calcium carbonate. This technique also enabled us to study the depletion zones, areas of lower intensity due to reduced ion concentrations. Ion flux rates were obtained from the depletion zone width, which amounted to several μm assuming the formation and dissolution dynamics of amorphous calcium carbonate being the rate determining process. This assumption was confirmed since the obtained fluxes were found to be in good agreement with fluxes derived from the experimentally observed crystal growth rates. Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.

  11. Effect of calcium on adsorption capacity of powdered activated carbon.

    PubMed

    Li, Gang; Shang, Junteng; Wang, Ying; Li, Yansheng; Gao, Hong

    2013-12-01

    We investigated the effect of calcium ion on the adsorption of humic acid (HA) (as a target pollutant) by powered activated carbon. The HA adsorption isotherms at different pH and kinetics of two different solutions including HA alone and HA doped Ca(2+), were performed. It was showed that the adsorption capacity of powdered activated carbon (PAC) for HA was markedly enhanced when Ca(2+) was doped into HA. Also, HA and Ca(2+) taken as nitrate were tested on the uptake of each other respectively and it was showed that the adsorbed amounts of both of them were significantly promoted when HA and calcium co-existed. Furthermore, the adsorbed amount of HA slightly decreased with the increasing of Ca(2+) concentration, whereas the amount of calcium increased with the increasing of HA concentration, but all above the amounts without addition. Finally, the change of pH before and after adsorption process is studied. In the two different solutions including HA alone and HA doped Ca(2+), pH had a small rise, but the extent of pH of later solution was bigger.

  12. Photovoltaic characteristics of Pd doped amorphous carbon film/SiO{sub 2}/Si

    SciTech Connect

    Ma Ming; Xue Qingzhong; Chen Huijuan; Zhou Xiaoyan; Xia Dan; Lv Cheng; Xie Jie

    2010-08-09

    The Pd doped amorphous carbon (a-C:Pd) films were deposited on n-Si substrates with or without a native SiO{sub 2} layer using magnetron sputtering. The photovoltaic characteristics of the a-C:Pd/SiO{sub 2}/Si and a-C:Pd/Si junctions were studied. It is found that under light illumination of 15 mW/cm{sup 2} at room temperature, the a-C:Pd/SiO{sub 2}/Si solar cell fabricated at 350 deg. C has a high power conversion efficiency of 4.7%, which is much better than the a-C/Si junctions reported before. The enhanced conversion efficiency is ascribed to the Pd doping and the increase in sp{sup 2}-bonded carbon clusters in the carbon film caused by the high temperature deposition.

  13. Proteomic analysis of a rare urinary stone composed of calcium carbonate and calcium oxalate dihydrate: a case report.

    PubMed

    Kaneko, Kiyoko; Matsuta, Yosuke; Moriyama, Manabu; Yasuda, Makoto; Chishima, Noriharu; Yamaoka, Noriko; Fukuuchi, Tomoko; Miyazawa, Katsuhito; Suzuki, Koji

    2014-03-01

    The objective of the present study was to investigate the matrix protein of a rare urinary stone that contained calcium carbonate. A urinary stone was extracted from a 34-year-old male patient with metabolic alkalosis. After X-ray diffractometry and infrared analysis of the stone, proteomic analysis was carried out. The resulting mass spectra were evaluated with protein search software, and matrix proteins were identified. X-ray diffraction and infrared analysis confirmed that the stone contained calcium carbonate and calcium oxalate dihydrate. Of the identified 53 proteins, 24 have not been previously reported from calcium oxalate- or calcium phosphate-containing stones. The protease inhibitors and several proteins related to cell adhesion or the cytoskeleton were identified for the first time. We analyzed in detail a rare urinary stone composed of calcium carbonate and calcium oxalate dihydrate. Considering the formation of a calcium carbonate stone, the new identified proteins should play an important role on the urolithiasis process in alkaline condition. © 2013 The Japanese Urological Association.

  14. Fractional absorption of active absorbable algal calcium (AAACa) and calcium carbonate measured by a dual stable-isotope method

    USDA-ARS?s Scientific Manuscript database

    With the use of stable isotopes, this study aimed to compare the bioavailability of active absorbable algal calcium (AAACa), obtained from oyster shell powder heated to a high temperature, with an additional heated seaweed component (Heated Algal Ingredient, HAI), with that of calcium carbonate. In ...

  15. Effects of heating time on the growth and behavior of amorphous carbon nanostructures from ferrocene

    NASA Astrophysics Data System (ADS)

    Rafiqul Islam, Md; Rashid, A. K. M. B.; Ferdous, Md; Shafiul Azam, Md

    2017-05-01

    Heating time is one of the crucial factors in various methods employed for the synthesis of carbon nanostructures (CNSs) from ferrocene. However, the effects of heating time on the growth and morphology of the nanostructured materials has not been well explored yet, particularly for amorphous carbon. Herein, we investigate how the variation of heating time impacts the growth of CNSs by carrying out the reaction between ferrocene and ammonium chloride in a solvent free condition at 250 °C. Several different forms of carbon nanostructures yielded from this reaction at 25 min (CNS-25), 30 min (CNS-30), 35 min (CNS-35) and 40 min (CNS-40) were analyzed by means of field emission scanning electron microscopy (FESEM) coupled with energy-dispersive x-ray (EDX), Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy. The final product CNS-40 was washed several times with concentrated hydrochloric acid solution to remove the impurities and then characterized by the means of similar techniques. FTIR spectra of all the nanostructures confirmed the presence of several functional groups such as C  =  C, C-O and -OH etc, which are common in carbonaceous nanostructures. However, the FESEM images obtained are significantly different and suggest a gradual growth of the carbon nanostructures ending up with long carbon nanotubes after 40 min. No absorption peak in the visible region of the UV-Vis spectra of the final product confirms the amorphous nature, which is also supported by XRD of the synthesized nanotube. Moreover, a noteworthy redshift in the UV-Vis peaks reflecting a huge increase in length and diameter of the nanostructures indicates the maximum longitudinal growth of the carbon nanotubes occurs during 35 min to 40 min.

  16. Comparison of the Absorption of Calcium Carbonate and Calcium Citrate after Roux-en-Y Gastric Bypass

    PubMed Central

    Tondapu, P.; Provost, D.; Adams-Huet, B.; Sims, T.; Chang, C.; Sakhaee, K.

    2015-01-01

    Introduction Roux-en-Y gastric bypass (RYGB) restricts food intake. Consequently, patients consume less calcium. In addition, food no longer passes through the duodenum, the main site of calcium absorption. Therefore, calcium absorption is significantly impaired. The goal of this study is to compare two common calcium supplements in gastric bypass patients. Method Nineteen patients were enrolled in a randomized, double-blinded, crossover study comparing the absorption of calcium from calcium carbonate and calcium citrate salts. Serum and urine calcium levels were assessed for peak values (Cmax) and cumulative calcium increment (area under the curve [AUC]). Serum PTH was assessed for minimum values (PTHmin) and cumulative PTH decrement (AUC). Statistical analysis was performed using a repeated analysis of variance model. Results Eighteen subjects completed the study. Calcium citrate resulted in a significantly higher serum Cmax (9.4+0.4 mg/dl vs. 9.2+0.3 mg/dl, p=0.02) and serum AUC (55+2 mg/dl vs. 54+2 mg/dl, p=0.02). Calcium citrate resulted in a significantly lower PTHmin (24+11 pg/ml vs. 30+13 pg/ml, p=0.01) and a higher AUC (−32+51 pg/ml vs. −3+56 pg/ml, p=0.04). There was a non-significant trend for higher urinary AUC in the calcium citrate group (76.13+36.39 mg/6 h vs. 66.04+40.82, p=0.17). Conclusion Calcium citrate has superior bioavailability than calcium carbonate in RYGB patients. PMID:19437082

  17. Enhancement of photovoltaic effects and photoconductivity observed in Co-doped amorphous carbon/silicon heterostructures

    SciTech Connect

    Jiang, Y. C.; Gao, J.

    2016-08-22

    Co-doped amorphous carbon (Co-C)/silicon heterostructures were fabricated by growing Co-C films on n-type Si substrates using pulsed laser deposition. A photovoltaic effect (PVE) has been observed at room temperature. Open-circuit voltage V{sub oc} = 320 mV and short-circuit current density J{sub sc }= 5.62 mA/cm{sup 2} were measured under illumination of 532-nm light with the power of 100 mW/cm{sup 2}. In contrast, undoped amorphous carbon/Si heterostructures revealed no significant PVE. Based on the PVE and photoconductivity (PC) investigated at different temperatures, it was found that the energy conversion efficiency increased with increasing the temperature and reached the maximum at room temperature, while the photoconductivity showed a reverse temperature dependence. The observed competition between PVE and PC was correlated with the way to distribute absorbed photons. The possible mechanism, explaining the enhanced PVE and PC in the Co-C/Si heterostructures, might be attributed to light absorption enhanced by localized surface plasmons in Co nanoparticles embedded in the carbon matrix.

  18. Raman Spectroscopy Characterization of amorphous carbon coatings for computer hard disks

    SciTech Connect

    Ager III, Joel W.

    1998-05-07

    Amorphous carbon films are used as protective coatings on magnetic media to protect the magnetic layer from wear and abrasion caused by the read/write head during hard disk drive start-up and operation. A key requirement in increasing the storage capacity and reliability of hard-disk drives is improving the performance of these coatings. This cooperative agreement used optical characterization techniques developed at LBNL to study thin-film hard disk media produced by Seagate Technology, major US hard drive manufacturer. The chief scientific goal was relating quantitatively the results of the optical characterization to the underlying chemical structure of the overcoat. In a collaboration with Seagate, LBNL, and Cambridge University, optical and electron-based characterization were used to evaluate the chemical structure of overcoats. The sp3 fraction of the sputtered amorphous carbon films was measured quantitatively for the first time and related to the optical spectroscopy results. This work and other selected aspects of the research performed under the agreement were presented at technical meetings and published in the open literature. The chief technical goal was designing manufacturing processes for the protective carbon overcoat for use in new generations of Seagate disk drives. To this end, joint research carried out under this agreement enabled Seagate to speed development of new coatings which are currently being used in the production of disk media in Seagate's disk-media manufacturing plants in Fremont, CA.

  19. Resonant tunnelling assisted electrical switching in amorphous-carbon multilayer-superlattice structures

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Somnath; Silva, S. R. P.

    2007-03-01

    Negative differential resistance (NDR) in an amorphous carbon (a-C) double barrier resonant tunnel diode (DB-RTD) with an estimated cut-off frequency well into the gigahertz regime is reported [1]. Presently we extend this work in carbon multi-layer superlattice structures by showing room temperature resonant tunnelling and establish a high value of the phase coherence length of ˜10 nm for low-dimensional amorphous materials. By applying a high bias, these structures are modified with reversible current switching of up to four orders of magnitude with a NDR signature and multiple peaks representative of resonant tunnelling in the ON state. In addition to the formation of filamentary channels by applying high bias, all these features are also explained using concepts based on tunnelling through the interface of the carbon layers, quantum-dot heterostructures and the presence of a confined two dimensional electron gas. This switching behavior and its tunability have been tested by applying a microwave signal up to 100 GHz which suggest the potential for novel high-speed memory devices. [1] S. Bhattacharyya, S.J. Henley, E. Mendoza, L.G-Rojas, J. Allam and S.R.P. Silva, Nature Mater. 5, 19 (2006).

  20. Structural properties of nitrogenated amorphous carbon films: Influence of deposition temperature and radiofrequency discharge power

    SciTech Connect

    Lazar, G.; Bouchet-Fabre, B.; Zellama, K.; Clin, M.; Ballutaud, D.; Godet, C.

    2008-10-01

    The structural properties of nitrogenated amorphous carbon deposited by radiofrequency magnetron sputtering of graphite in pure N{sub 2} plasma are investigated as a function of the substrate temperature and radiofrequency discharge power. The film composition is derived from x-ray photoemission spectroscopy, nuclear reaction analysis and elastic recoil detection measurements and the film microstructure is discussed using infrared, Raman, x-ray photoemission and near edge x-ray absorption fine structure spectroscopic results. At low deposition temperature and low radiofrequency power, the films are soft, porous, and easily contaminated with water vapor and other atmospheric components. The concentration of nitrogen in the films is very large for low deposition temperatures ({approx}33.6 at. % N at 150 deg. C) but decreases strongly when the synthesis temperature increases ({approx}15 at. % N at 450 deg. C). With increasing deposition temperature and discharge power values, the main observed effects in amorphous carbon nitride alloys are a loss of nitrogen atoms, a smaller hydrogen and oxygen contamination related to the film densification, an increased order of the aromatic sp{sup 2} phase, and a strong change in the nitrogen distribution within the carbon matrix. Structural changes are well correlated with modifications of the optical and transport properties.

  1. Extinction due to amorphous carbon grains in red quasars from the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Czerny, B.; Li, J.; Loska, Z.; Szczerba, R.

    2004-03-01

    We construct a quasar extinction curve based on the blue and red composite quasar spectra of Richards et al. prepared from the Sloan Digital Sky Survey. This extinction curve does not show any traces of the 2200-Å feature characteristic of the interstellar medium, and this indicates that graphite grains are likely to be absent close to quasar nuclei. The extinction is best modelled by an AC sample of amorphous carbon grains, assuming a standard distribution of grain sizes (p= 3.5) but slightly larger minimum grain size (amin= 0.016 μm) and lower maximum grain size (amin= 0.12 μm) than the respective canonical values for the interstellar medium. The dust composition is thus similar to that of the dust in carbon reach asymptotic giant branch stars. Since graphite grains form from amorphous carbon exposed to strong ultraviolet irradiation, the results indicate that the dust forms either surprisingly far from the active nucleus or in a wind that leaves the nucleus quickly enough to avoid crystallization into graphite.

  2. The healing effect of stearic acid applied on amorphous carbon film with dispersed nanodiamonds

    NASA Astrophysics Data System (ADS)

    Yamazaki, T.; Shoji, K.; Ikeshoji, T.-T.; Suzumura, A.

    2012-08-01

    Diamond-like carbon (DLC) films have been shown to improve the friction and wear properties of applications with severe loads. Hydrogenated amorphous carbon films (a-C:H), a type of DLC film, were coated onto 440C stainless steel disk surfaces. The plasma enhanced chemical vapour deposition method was used as a coating process, and nanodiamond (ND) particles were dispersed into the film during the deposition process. Stearic acid was expected to affect the lubricating properties of the film because of its reported effectiveness on diamond surfaces. A lubricated reciprocal sliding friction test with 10,000 cycles confirmed that stearic acid improved the friction and wear properties of the ND dispersed a-C:H film. Furthermore, film wear caused by a sliding test without stearic acid could be healed by sliding with stearic acid as long as the level of critical damage was not reached. Raman spectra for the worn tracks revealed the healing effect of the stearic acid on the film because the spectra for the worn tracks after 10,000 cycles were identical to those of the control film, which was not worn. In contrast, the spectra for the worn tracks or debris showed a broad D band peak and no G peak, which was consistent with disordered amorphous carbon.

  3. Precipitation of calcium carbonate and calcium phosphate under diffusion controlled mixing

    SciTech Connect

    Tsigabu Gebrehiwet; James R. Henriksen; Luanjing Guo; Don T. Fox; Hai Huang; Lee Tu; Yoshiko Fujita; Robert W. Smith; George Redden

    2014-07-01

    Multi-component mineral precipitation in porous, subsurface environments is challenging to simulate or engineer when in situ reactant mixing is controlled by diffusion. In contrast to well-mixed systems, the conditions that favor mineral precipitation in porous media are distributed along chemical gradients, which evolve spatially due to concurrent mineral precipitation and modification of solute transport in the media. The resulting physical and chemical characteristics of a mixing/precipitation zone are a consequence of coupling between transport and chemical processes, and the distinctive properties of individual chemical systems. We examined the spatial distribution of precipitates formed in “double diffusion” columns for two chemical systems, calcium carbonate and calcium phosphate. Polyacrylamide hydrogel was used as a low permeability, high porosity medium to maximize diffusive mixing and minimize pressure- and density-driven flow between reactant solutions. In the calcium phosphate system, multiple, visually dense and narrow bands of precipitates were observed that were reminiscent of previously reported Liesegang patterns. In the calcium carbonate system, wider precipitation zones characterized by more sparse distributions of precipitates and a more open channel structure were observed. In both cases, formation of precipitates inhibited, but did not necessarily eliminate, continued transport and mixing of the reactants. A reactive transport model with fully implicit coupling between diffusion, chemical speciation and precipitation kinetics, but where explicit details of nucleation processes were neglected, was able to qualitatively simulate properties of the precipitation zones. The results help to illustrate how changes in the physical properties of a precipitation zone depend on coupling between diffusion-controlled reactant mixing and chemistry-specific details of precipitation kinetics.

  4. The anti-caries efficacy of calcium carbonate-based fluoride toothpastes.

    PubMed

    Lynch, R J M; ten Cate, J M

    2005-01-01

    To summarise clinical support for the anti-caries efficacy of fluoride toothpastes containing sodium monofluorophosphate (SMFP) and to discuss the possible means by which the abrasive particles in calcium carbonate-based SMFP toothpastes might complement and/or enhance fluoride efficacy. The anti-caries efficacy of fluoride has been proven beyond any reasonable doubt, and the efficacy of SMFP, when incorporated into a variety of compatible toothpaste formulations, has been established in numerous clinical trials. Calcium carbonate-based toothpastes may also influence caries by effecting an increase in plaque calcium levels; an inverse relationship between plaque calcium and caries is well-established. It has also been reported that plaque fluoride levels are dependent on plaque calcium levels. Hence elevated plaque calcium resulting from the use of calcium carbonate-based toothpastes has the potential to elevate plaque fluoride, itself linked to reduced caries experience. It has been shown that calcium carbonate particles are retained by plaque and this may also influence caries by neutralising harmful plaque acids and concurrently liberating calcium. Fluoride delivered from calcium carbonate-based SMFP toothpastes is an effective means of reducing caries. Further, calcium carbonate may confer additional benefits through elevation of oral calcium levels and neutralisation of plaque-acids.

  5. A near-frictionless and extremely elastic hydrogenated amorphous carbon film with self-assembled dual nanostructure.

    PubMed

    Liu, Xiaoqiang; Yang, Jun; Hao, Junying; Zheng, Jianyun; Gong, Qiuyu; Liu, Weimin

    2012-09-04

    A highly crosslinking network combined with a fullerene-like structure is disclosed in a hydrogenated amorphous carbon film. The very soft carbon film exhibits super-low friction and excellent wear resistance even under a Hertzian contact pressure comparable to its hardness under vacuum, which is an extraordinary tribological behavior in the filed of solid lubrication films or coatings.

  6. Formation of a crystalline phase in amorphous hydrogenated carbon-germanium films by electron beam irradiation

    SciTech Connect

    Tyczkowski, J.; Pietrzyk, B.; Mazurczyk, R.; Polanski, K.; Balcerski, J.; Delamar, M.

    1997-11-01

    The influence of electron beam irradiation on morphology of plasma deposited amorphous hydrogenated carbon-germanium films produced from tetramethylgermanium in a three-electrode af reactor has been studied. It has been found that the insulating films are insensitive to this treatment, whereas a crystalline phase occurs in the semiconducting films. Although the molar content of germanium in these films amounts only to about 0.2, the crystalline phase is composed of pure germanium nanocrystals which contain about 70{percent} of the whole amount of germanium existing in the films. The nanocrystals are agglomerated in globules of 50{endash}500 nm in diameter. {copyright} {ital 1997 American Institute of Physics.}

  7. Subsurface defect of amorphous carbon film imaged by near field acoustic microscopy

    NASA Astrophysics Data System (ADS)

    Zeng, J. T.; Zhao, K. Y.; Zeng, H. R.; Song, H. Z.; Zheng, L. Y.; Li, G. R.; Yin, Q. R.

    2008-05-01

    Amorphous carbon films were examined by low frequency scanning-probe acoustic microscopy (LF-SPAM). Local elastic properties as well as topography were imaged in the acoustic mode. Two kinds of subsurface defects were revealed by the LF-SPAM method. The influence of the subsurface defects on the elastic properties was also discussed. The ability to image subsurface defects was dependent on the scan area and the scan speed. Our results showed that the low frequency scanning-probe acoustic microscopy is a useful method for imaging subsurface defects with high resolution.

  8. Strength and tribology of bulk and electroformed nickel amorphized by implantation of titanium and carbon

    SciTech Connect

    Myers, S.M.; Knapp, J.A.; Follstaedt, D.M.; Dugger, M.T.; Christenson, T.R.

    1997-10-01

    Dual ion implantation of titanium and carbon was shown to produce an amorphous layer of exceptional strength within annealed bulk Ni and electroformed Ni and Ni{sub 80}Fe{sub 20} materials used in micro-electromechanical systems. The intrinsic elastic and plastic mechanical properties of the implanted region were quantified using nanoindentation testing in conjunction with finite-element modeling, and the results were interpreted in the light of microstructures observed by electron microscopy. The implantation treatment was found to produce substantial reductions in unlubricated friction and wear.

  9. Stereocomplexed poly(limonene carbonate): a unique example of the cocrystallization of amorphous enantiomeric polymers.

    PubMed

    Auriemma, Finizia; De Rosa, Claudio; Di Caprio, Maria Rosaria; Di Girolamo, Rocco; Ellis, W Chadwick; Coates, Geoffrey W

    2015-01-19

    We report the cocrystallization of the regio- and stereoregular chiral copolymer poly(limonene carbonate). To the best of our knowledge, this marks the first example of an amorphous, enantiomerically pure polymer that becomes crystalline upon stereocomplexation with its complementary enantiomer. By analyzing X-ray powder diffraction data, we propose a packing model in which sheets of enantiopure chains interdigitate with layers of the opposite enantiomer, forming a "steric zipper". © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Nacre-like calcium carbonate controlled by ionic liquid/graphene oxide composite template.

    PubMed

    Yao, Chengli; Xie, Anjian; Shen, Yuhua; Zhu, Jinmiao; Li, Hongying

    2015-06-01

    Nacre-like calcium carbonate nanostructures have been mediated by an ionic liquid (IL)-graphene oxide (GO) composite template. The resultant crystals were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray powder diffractometry (XRD). The results showed that either 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) or graphene oxide can act as a soft template for calcium carbonate formation with unusual morphologies. Based on the time-dependent morphology changes of calcium carbonate particles, it is concluded that nacre-like calcium carbonate nanostructures can be formed gradually utilizing [BMIM]BF4/GO composite template. During the process of calcium carbonate formation, [BMIM]BF4 acted not only as solvents but also as morphology templates for the fabrication of calcium carbonate materials with nacre-like morphology. Based on the observations, the possible mechanisms were also discussed. Copyright © 2015 Elsevier B.V. All rights reserved.

  11. Transglutaminase-induced crosslinking of gelatin-calcium carbonate composite films.

    PubMed

    Wang, Yuemeng; Liu, Anjun; Ye, Ran; Wang, Wenhang; Li, Xin

    2015-01-01

    The effects of transglutaminase (TGase) on the rheological profiles and interactions of gelatin-calcium carbonate solutions were studied. In addition, mechanical properties, water vapour permeability and microstructures of gelatin-calcium carbonate films were also investigated and compared. Fluorescence data suggested that the interaction of TGase and gelation-calcium carbonate belonged to a static quenching mechanism, and merely one binding site between TGase and gelatin-calcium carbonate was identified. Moreover, differential scanning calorimetry (DSC), the mechanical properties and the water vapour permeability studies revealed that TGase favoured the strong intramolecular polymerisation of the peptides in gelatin. The microstructures of the surfaces and cross sections in gelatin-calcium carbonate films were shown by scanning electron microscope (SEM) micrographs. The results of the fourier transform infrared spectroscopy (FTIR) indicated that TGase caused conformational changes in the proteins films. Therefore, TGase successfully facilitated the formation of gelatin-calcium carbonate composite films. Copyright © 2014 Elsevier Ltd. All rights reserved.

  12. Calcium isotope evidence for suppression of carbonate dissolution in carbonate-bearing organic-rich sediments

    NASA Astrophysics Data System (ADS)

    Turchyn, Alexandra V.; DePaolo, Donald J.

    2011-11-01

    Pore fluid calcium isotope, calcium concentration and strontium concentration data are used to measure the rates of diagenetic dissolution and precipitation of calcite in deep-sea sediments containing abundant clay and organic material. This type of study of deep-sea sediment diagenesis provides unique information about the ultra-slow chemical reactions that occur in natural marine sediments that affect global geochemical cycles and the preservation of paleo-environmental information in carbonate fossils. For this study, calcium isotope ratios (δ 44/40Ca) of pore fluid calcium from Ocean Drilling Program (ODP) Sites 984 (North Atlantic) and 1082 (off the coast of West Africa) were measured to augment available pore fluid measurements of calcium and strontium concentration. Both study sites have high sedimentation rates and support quantitative sulfate reduction, methanogenesis and anaerobic methane oxidation. The pattern of change of δ 44/40Ca of pore fluid calcium versus depth at Sites 984 and 1082 differs markedly from that of previously studied deep-sea Sites like 590B and 807, which are composed of nearly pure carbonate sediment. In the 984 and 1082 pore fluids, δ 44/40Ca remains elevated near seawater values deep in the sediments, rather than shifting rapidly toward the δ 44/40Ca of carbonate solids. This observation indicates that the rate of calcite dissolution is far lower than at previously studied carbonate-rich sites. The data are fit using a numerical model, as well as more approximate analytical models, to estimate the rates of carbonate dissolution and precipitation and the relationship of these rates to the abundance of clay and organic material. Our models give mutually consistent results and indicate that calcite dissolution rates at Sites 984 and 1082 are roughly two orders of magnitude lower than at previously studied carbonate-rich sites, and the rate correlates with the abundance of clay. Our calculated rates are conservative for these

  13. Oxygen spectroscopy and polarization-dependent imaging contrast (PIC)-mapping of calcium carbonate minerals and biominerals.

    PubMed

    DeVol, Ross T; Metzler, Rebecca A; Kabalah-Amitai, Lee; Pokroy, Boaz; Politi, Yael; Gal, Assaf; Addadi, Lia; Weiner, Steve; Fernandez-Martinez, Alejandro; Demichelis, Raffaella; Gale, Julian D; Ihli, Johannes; Meldrum, Fiona C; Blonsky, Adam Z; Killian, Christopher E; Salling, C B; Young, Anthony T; Marcus, Matthew A; Scholl, Andreas; Doran, Andrew; Jenkins, Catherine; Bechtel, Hans A; Gilbert, Pupa U P A

    2014-07-17

    X-ray absorption near-edge structure (XANES) spectroscopy and spectromicroscopy have been extensively used to characterize biominerals. Using either Ca or C spectra, unique information has been obtained regarding amorphous biominerals and nanocrystal orientations. Building on these results, we demonstrate that recording XANES spectra of calcium carbonate at the oxygen K-edge enables polarization-dependent imaging contrast (PIC) mapping with unprecedented contrast, signal-to-noise ratio, and magnification. O and Ca spectra are presented for six calcium carbonate minerals: aragonite, calcite, vaterite, monohydrocalcite, and both hydrated and anhydrous amorphous calcium carbonate. The crystalline minerals reveal excellent agreement of the extent and direction of polarization dependences in simulated and experimental XANES spectra due to X-ray linear dichroism. This effect is particularly strong for aragonite, calcite, and vaterite. In natural biominerals, oxygen PIC-mapping generated high-magnification maps of unprecedented clarity from nacre and prismatic structures and their interface in Mytilus californianus shells. These maps revealed blocky aragonite crystals at the nacre-prismatic boundary and the narrowest calcite needle-prisms. In the tunic spicules of Herdmania momus, O PIC-mapping revealed the size and arrangement of some of the largest vaterite single crystals known. O spectroscopy therefore enables the simultaneous measurement of chemical and orientational information in CaCO3 biominerals and is thus a powerful means for analyzing these and other complex materials. As described here, PIC-mapping and spectroscopy at the O K-edge are methods for gathering valuable data that can be carried out using spectromicroscopy beamlines at most synchrotrons without the expense of additional equipment.

  14. Alginate hydrogel-mediated crystallization of calcium carbonate

    SciTech Connect

    Ma, Yufei; Feng, Qingling

    2011-05-15

    We documented a specific method for combining calcium ions and alginate molecules slowly and continuously in the mineralization system for the purpose of understanding the mediating function of alginate on the crystallization of calcium carbonate. The alginate was involved in the nucleation and the growth process of CaCO{sub 3}. The crystal size, morphology and roughness of crystal surface were significantly influenced by the type of the alginate, which could be accounted for by the length of the G blocks in alginate. A combination of Fourier transform infrared spectroscopy and thermogravimetric analysis showed that there were the chemical interactions between the alginate and the mineral phase. This strategic approach revealed the biologically controlled CaCO{sub 3} mineralization within calcium alginate hydrogels via the selective nucleation and the confined crystallization of CaCO{sub 3}. The results presented here could contribute to the understanding of the mineralization process in hydrogel systems. -- Graphical abstract: Schematic illustration of the growth of calcite aggregates with different morphologies obtained from (a) Low G alginate gels and (b) High G alginate gels. Display Omitted highlights: > We use a specific method for combining calcium ions and alginate molecules slowly and continuously in the mineralization system to understand the mediating function of alginate on the crystallization of CaCO{sub 3} crystals. > The crystal size, morphology and crystal surface roughness are influenced by the length of G blocks in alginate. There are chemical interactions between the alginate and the mineral phase. > We propose a potential mechanism of CaCO{sub 3} crystallization within High G and Low G calcium alginate hydrogel.

  15. Crystallization of Calcium Carbonate in a Large Scale Field Study

    NASA Astrophysics Data System (ADS)

    Ueckert, Martina; Wismeth, Carina; Baumann, Thomas

    2017-04-01

    The long term efficiency of geothermal facilities and aquifer thermal energy storage in the carbonaceous Malm aquifer in the Bavarian Molasse Basin is seriously affected by precipitations of carbonates. This is mainly caused by pressure and temperature changes leading to oversaturation during production. Crystallization starts with polymorphic nuclei of calcium carbonate and is often described as diffusion-reaction controlled. Here, calcite crystallization is favoured by high concentration gradients while aragonite crystallization is occurring at high reaction rates. The factors affecting the crystallization processes have been described for simplified, well controlled laboratory experiments, the knowledge about the behaviour in more complex natural systems is still limited. The crystallization process of the polymorphic forms of calcium carbonate were investigated during a heat storage test at our test site in the eastern part of the Bavarian Molasse Basin. Complementary laboratory experiments in an autoclave were run. Both, field and laboratory experiments were conducted with carbonaceous tap water. Within the laboratory experiments additionally ultra pure water was used. To avoid precipitations of the tap water, a calculated amount of {CO_2} was added prior to heating the water from 45 - 110°C (laboratory) resp. 65 - 110°C (field). A total water volume of 0.5 L (laboratory) resp. 1 L (field) was immediately sampled and filtrated through 10 - 0.1

  16. Epitaxial relationships between calcium carbonate and inorganic substrates.

    PubMed

    Yang, Taewook; Jho, Jae Young; Kim, Il Won

    2014-09-15

    The polymorph-selective crystallization of calcium carbonate has been studied in terms of epitaxial relationship between the inorganic substrates and the aragonite/calcite polymorphs with implication in bioinspired mineralization. EpiCalc software was employed to assess the previously published experimental results on two different groups of inorganic substrates: aragonitic carbonate crystals (SrCO3, PbCO3, and BaCO3) and a hexagonal crystal family (α-Al2O3, α-SiO2, and LiNbO3). The maximum size of the overlayer (aragonite or calcite) was calculated for each substrate based on a threshold value of the dimensionless potential to estimate the relative nucleation preference of the polymorphs of calcium carbonate. The results were in good agreement with previous experimental observations, although stereochemical effects between the overlayer and substrate should be separately considered when existed. In assessing the polymorph-selective nucleation, the current method appeared to provide a better tool than the oversimplified mismatch parameters without invoking time-consuming molecular simulation.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Cobalt is toxic metal that is present only as a trace in the Earth crust. However, Co might concentrate on specific areas due to both natural and anthropogenic factors and thus, soils and groundwater can be contaminated. It is from this perspective that we are interested in the precipitation of cobalt carbonates, since co-precipitation with minerals phases is a well-known method for metal immobilization in the environment. In particular, the carbonates are widely used due to its reactivity and natural abundance. In order to evaluate the cobalt carbonate precipitation at room temperature, a simple experimental work was carried out in this work. The precipitation occurred via reaction of two common salts: 0.05M of CoCl2 and 0.05M of Na2CO3 in aqueous solution. After reaction, the precipitated solid was kept in the remaining water at 25 oC and under constant stirring for different aging times of 5 min, 1 and 5 hours, 1, 2, 4, 7, 30 and 60 days. In addition to the aging and precipitation experiments, we carried out experiments to determine the solubility of the solids. In these experiments each precipitate was dissolved in Milli-Q water until equilibrium was reached and then the aqueous solution was analyzed regarding Co2+ and total alkalinity. Furthermore, acid solution calorimetry of the products were attained. Finally, we modeled the results using the PHREEQC code. Solid and aqueous phase identification and characterization have been extensively reported in a previous work (González-López et al., 2015). The main results of our investigation were the initial precipitation of an amorphous cobalt carbonate that evolve towards a poorly crystalline cobalt hydroxide carbonate with aging treatment. Solubility of both phases have been calculated under two different approaches: precipitation and dissolution. Values of solubility from each approach were obtained with a general error due to differences in experiment conditions, for instance, ionic strength, temperature and

  18. Morphology Change of Calcium Carbonate in the Presence of Two-Dimensional DNA Lattices

    PubMed Central

    Lukeman, Philip S.; Stevenson, Mary L.; Seeman, Nadrian C.

    2012-01-01

    Two-dimensional DNA lattices are grown under conditions that also are suitable for the magnesium-free growth of three-dimensional calcium carbonate crystals. These lattices are used to template morphology changes in calcium carbonate. The effects of DNA lattices, sub-assemblies, duplexes, single strands, dinucleotides, and mononucleotides on calcium carbonate morphology are studied. A ”rotated” morphology of calcite is found to predominate when a critical concentration of any polynucleotide is reached in the templating solution. PMID:24511280

  19. Vertical electric field stimulated neural cell functionality on porous amorphous carbon electrodes.

    PubMed

    Jain, Shilpee; Sharma, Ashutosh; Basu, Bikramjit

    2013-12-01

    We demonstrate the efficacy of amorphous macroporous carbon substrates as electrodes to support neuronal cell proliferation and differentiation in electric field mediated culture conditions. The electric field was applied perpendicular to carbon substrate electrode, while growing mouse neuroblastoma (N2a) cells in vitro. The placement of the second electrode outside of the cell culture medium allows the investigation of cell response to electric field without the concurrent complexities of submerged electrodes such as potentially toxic electrode reactions, electro-kinetic flows and charge transfer (electrical current) in the cell medium. The macroporous carbon electrodes are uniquely characterized by a higher specific charge storage capacity (0.2 mC/cm(2)) and low impedance (3.3 kΩ at 1 kHz). The optimal window of electric field stimulation for better cell viability and neurite outgrowth is established. When a uniform or a gradient electric field was applied perpendicular to the amorphous carbon substrate, it was found that the N2a cell viability and neurite length were higher at low electric field strengths (≤ 2.5 V/cm) compared to that measured without an applied field (0 V/cm). While the cell viability was assessed by two complementary biochemical assays (MTT and LDH), the differentiation was studied by indirect immunostaining. Overall, the results of the present study unambiguously establish the uniform/gradient vertical electric field based culture protocol to either enhance or to restrict neurite outgrowth respectively at lower or higher field strengths, when neuroblastoma cells are cultured on porous glassy carbon electrodes having a desired combination of electrochemical properties.

  20. Crystallized nano-sized alpha-tricalcium phosphate from amorphous calcium phosphate: microstructure, cementation and cell response.

    PubMed

    Vecbiskena, Linda; Gross, Karlis Agris; Riekstina, Una; Yang, Thomas Chung-Kuang

    2015-04-17

    New insight on the conversion of amorphous calcium phosphate (ACP) to nano-sized alpha tricalcium phosphate (α-TCP) provides a faster pathway to calcium phosphate bone cements. In this work, synthesized ACP powders were treated with either water or ethanol, dried, crystallized between 700 and 800 °C, and then cooled at different cooling rates. Particle size was measured in a scanning electron microscope, but crystallite size calculated by Rietveld analysis. Phase composition and bonding in the crystallized powder was assessed by x-ray diffraction and Fourier-transform infrared spectroscopy. Results showed that 50 nm sized α-TCP formed after crystallization of lyophilized powders. Water treated ACP retained an unstable state that may allow ordering to nanoapatite, and further transition to β-TCP after crystallization and subsequent decomposition. Powders treated with ethanol, favoured the formation of pure α-TCP. Faster cooling limited the growth of β-TCP. Both the initial contact with water and the cooling rate after crystallization dictated β-TCP formation. Nano-sized α-TCP reacted faster with water to an apatite bone cement than conventionally prepared α-TCP. Water treated and freeze-dried powders showed faster apatite cement formation compared to ethanol treated powders. Good biocompatibility was found in pure α-TCP nanoparticles made from ethanol treatment and with a larger crystallite size. This is the first report of pure α-TCP nanoparticles with a reactivity that has not required additional milling to cause cementation.

  1. Magnesium substitution in the structure of orthopedic nanoparticles: A comparison between amorphous magnesium phosphates, calcium magnesium phosphates, and hydroxyapatites.

    PubMed

    Nabiyouni, Maryam; Ren, Yufu; Bhaduri, Sarit B

    2015-01-01

    As biocompatible materials, magnesium phosphates have received a lot of attention for orthopedic applications. During the last decade multiple studies have shown advantages for magnesium phosphate such as lack of cytotoxicity, biocompatibility, strong mechanical properties, and high biodegradability. The present study investigates the role of Mg(+2) and Ca(+2) ions in the structure of magnesium phosphate and calcium phosphate nanoparticles. To directly compare the effect of Mg(+2) and Ca(+2) ions on structure of nanoparticles and their biological behavior, three groups of nanoparticles including amorphous magnesium phosphates (AMPs) which release Mg(+2), calcium magnesium phosphates (CMPs) which release Mg(+2) and Ca(+2), and hydroxyapatites (HAs) which release Ca(+2) were studied. SEM, TEM, XRD, and FTIR were used to evaluate the morphology, crystallinity, and chemical properties of the particles. AMP particles were homogeneous nanospheres, whereas CMPs were combinations of heterogeneous nanorods and nanospheres, and HAs which contained heterogeneous nanosphere particles. Cell compatibility was monitored in all groups to determine the cytotoxicity effect of particles on studied MC3T3-E1 preosteoblasts. AMPs showed significantly higher attachment rate than the HAs after 1 day and both AMPs and CMPs showed significantly higher proliferation rate when compared to HAs after 7days. Gene expression level of osteoblastic markers ALP, COL I, OCN, OPN, RUNX2 were monitored and they were normalized to GAPDH housekeeping gene. Beta actin expression level was monitored as the second housekeeping gene to confirm the accuracy of results. In general, AMPs and CMPs showed higher expression level of osteoblastic genes after 7 days which can further confirm the stimulating role of Mg(+2) and Ca(+2) ions in increasing the proliferation rate, differentiation, and mineralization of MC3T3-E1 preosteoblasts. Copyright © 2015 Elsevier B.V. All rights reserved.

  2. Computational Evaluation of Amorphous Carbon Coating for Durable Silicon Anodes for Lithium-Ion Batteries.

    PubMed

    Hwang, Jeongwoon; Ihm, Jisoon; Lee, Kwang-Ryeol; Kim, Seungchul

    2015-10-13

    We investigate the structural, mechanical, and electronic properties of graphite-like amorphous carbon coating on bulky silicon to examine whether it can improve the durability of the silicon anodes of lithium-ion batteries using molecular dynamics simulations and ab-initio electronic structure calculations. Structural models of carbon coating are constructed using molecular dynamics simulations of atomic carbon deposition with low incident energies (1-16 eV). As the incident energy decreases, the ratio of sp² carbons increases, that of sp³ decreases, and the carbon films become more porous. The films prepared with very low incident energy contain lithium-ion conducting channels. Also, those films are electrically conductive to supplement the poor conductivity of silicon and can restore their structure after large deformation to accommodate the volume change during the operations. As a result of this study, we suggest that graphite-like porous carbon coating on silicon will extend the lifetime of the silicon anodes of lithium-ion batteries.

  3. Study on nitrogenated amorphous carbon films prepared by unbalanced magnetron sputtering

    SciTech Connect

    Shi, J.R.

    2006-02-01

    Nitrogenated amorphous carbon (a-CN{sub x}) films were prepared by unbalanced magnetron sputtering (UBMS) at different N{sub 2}/Ar gas flow rate ratios and different bias voltages. The films were characterized using x-ray photoelectron spectroscopy, Raman scattering, nanoindenter, atomic force microscopy nanoscratch, and contact angle measurement. It was found that a negative bias of 150 V is the optimal condition for the formation of sp{sup 3} bonded carbon atoms. As the N{sub 2}/Ar flow rate ratio changes from 0 to 0.47, the nitrogen to carbon ratio in deposited films increases from 0 to 0.22, and the sp{sup 3} fraction of carbon atoms decreases from 0.51 to 0.28. The pure carbon film has the highest sp{sup 3} faction of carbon atoms and therefore the highest hardness and the lowest scratching depth. Comparing to the films prepared by conventional magnetron sputtering, all the a-CN{sub x} films prepared by UBMS show a lower scratching depth. The a-CN{sub x} films have a hydrophilic characteristic with a surface free energy from 56.6 to 65.6 mN/m and a predominant polar component.

  4. Computational Evaluation of Amorphous Carbon Coating for Durable Silicon Anodes for Lithium-Ion Batteries

    PubMed Central

    Hwang, Jeongwoon; Ihm, Jisoon; Lee, Kwang-Ryeol; Kim, Seungchul

    2015-01-01

    We investigate the structural, mechanical, and electronic properties of graphite-like amorphous carbon coating on bulky silicon to examine whether it can improve the durability of the silicon anodes of lithium-ion batteries using molecular dynamics simulations and ab-initio electronic structure calculations. Structural models of carbon coating are constructed using molecular dynamics simulations of atomic carbon deposition with low incident energies (1–16 eV). As the incident energy decreases, the ratio of sp2 carbons increases, that of sp3 decreases, and the carbon films become more porous. The films prepared with very low incident energy contain lithium-ion conducting channels. Also, those films are electrically conductive to supplement the poor conductivity of silicon and can restore their structure after large deformation to accommodate the volume change during the operations. As a result of this study, we suggest that graphite-like porous carbon coating on silicon will extend the lifetime of the silicon anodes of lithium-ion batteries. PMID:28347087

  5. Calcium Carbonate Produced by Coccolithophorid Algae in Long Term, Carbon Dioxide Sequestration

    SciTech Connect

    V.J. Fabry

    2007-06-30

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO2 through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids - single-celled, marine algae that are the major global producers of calcium carbonate - to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  6. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V.J. Fabry

    2004-04-26

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids single-celled, marine algae that are the major global producers of calcium carbonate to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  7. Calcium Carbonate Production by Coccolithophorid Algae in Long Term, Carbon Dioxide Sequestration

    SciTech Connect

    V.J. Fabry

    2005-04-29

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  8. CALCIUM CARBONATE PRODUCTION BY COCCOLITHAPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V. J.Fabry

    2004-01-30

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  9. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V.J. Fabry, Ph.D.

    2003-04-15

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  10. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V.J. Fabry, Ph.D.

    2001-12-15

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  11. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V.J. Fabry, Ph.D.

    2002-04-05

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  12. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V.J. Fabry

    2001-07-01

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids single-celled, marine algae that are the major global producers of calcium carbonate to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  13. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V.J. Fabry, Ph.D.

    2001-09-10

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  14. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V.J. Fabry, Ph.D.

    2002-07-09

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  15. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V. J. Fabry

    2005-01-24

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids ? single-celled, marine algae that are the major global producers of calcium carbonate ? to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  16. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V. J. Fabry

    2003-10-30

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds or bioreactors to abate CO{sub 2} emissions from power plants.

  17. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V.J. Fabry, Ph.D.

    2002-09-30

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  18. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V.J. Fabry, Ph.D.

    2002-12-15

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  19. CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

    SciTech Connect

    V.J. Fabry, Ph.D.

    2003-07-15

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  20. Calcium Carbonate Production by Coccolithophorid Alge in Long Term Carbon Dioxide Sequestration

    SciTech Connect

    V. J. Fabry

    2006-09-30

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the growth conditions that will result in the maximum amount of CO{sub 2} sequestration through coccolithophorid calcite production and to evaluate the costs/benefits of using coccolithophorid cultivation ponds to abate CO{sub 2} emissions from power plants.

  1. Calcium Carbonate Production by Coccolithophorid Algae in Long Term, Carbon Dioxide Sequestration

    SciTech Connect

    V. J. Fabry

    2006-06-30

    Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried out immediately and the amount of carbon sequestered as CaCO{sub 3} could be readily quantified. The significant advantages of this approach warrant its serious investigation. The major goals of the proposed research are to identify the