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1.
The effect of sodium alginate in supersaturated solutions of calcium carbonate was investigated under plethostatic conditions. The rates of crystal growth measured in the presence of sodium alginate at concentrations as low as 0.83 × 10-7mol dm-3 were drastically reduced. Kinetic analysis according to a Langmuir-type adsorption isotherm led to the calculation of an affinity constant K
aff = 999.8 × 10-4mol dm-3. The apparent order found from kinetic data was 3.0±0.2 suggesting a surface nucleation mechanism. 相似文献
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Calcium carbonate has been found to precipitate into tablets which were self-aligned with respect to each other on limestone aggregates in Portland cement-based materials. A surface layer of water and reaction in 100% relative humidity air environments were critical for alignment of precipitates. The organization of the calcium carbonate precipitates resembled the cross-section of nacre, but without an organic phase. Possible implications for organized material synthesis, as well as biomineralization, are discussed. © 1998 Kluwer Academic Publishers 相似文献
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Yoong Lee Yeong Min Hahm Shigeki Matsuya Masaharu Nakagawa Kunio Ishikawa 《Journal of Materials Science》2007,42(14):5728-5735
Calcium carbonate is one of the bioceramics and has been used clinically as a bone substitute in dental and orthopedic surgery.
Introduction of macropores into the bioceramics is highly recommended because those pores enable tissue ingrowth and accelerated
osteointegration. We tried to prepare calcium carbonate body with macropores through the new carbonation method of calcium
hydroxide/sodium chloride composite. Sodium chloride acted as a water-soluble porogen in developing macropores in calcium
carbonate body and was removed completely by washing with distilled water after carbonation. We investigated effects of sodium
chloride content and molding pressure on the porosity and the mechanical strength of the calcium carbonate body. Through this
study, it was found that the porosity of body increased with the sodium chloride content in composite and was hardly affected
by molding pressure. On the other hand, the mechanical strength was increased with the molding pressure and reduced with the
porosity. In addition, the increase in content of sodium chloride caused the enlargement of hole size as well as the enhancement
of extent of interconnection among pores through hole. Especially, the calcium carbonate body with over 90% porosity could
be prepared when 90 wt.% sodium chloride was used under 10 MPa molding pressure. Its average pore and hole size were 177 and
80 μm, respectively. 相似文献
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The effect of acetaminophen, a well known analgesic and fever-reducing medicine, on the calcium carbonate crystal growth was
investigated under plethostatic conditions. The calcification rates measured was reduced by 9.1–63.2% in the presence of acetaminophen.
Kinetic analysis according to a Langmuir-type adsorption isotherm lead to the calculation of an affinity constant K
aff = 8.33 × 102 dm3 mol−1. The apparent order found from kinetic data was two suggesting a surface diffusion controlled spiral growth mechanism. 相似文献
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The process of calcium carbonate biomineralization in the solution containing collagen and magnesium ions was studied in this paper. The results were characterized by using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect rules were obtained by the cooperation of collagen and magnesium ions in different concentration. The experiment results showed that in the presence of both collagen and magnesium ions, aragonite and vaterite were precipitated at low Mg/Ca ion concentration ratio, while only aragonite with regular spherical morphology was precipitated at high Mg/Ca ion concentration ratio. It indicated that collagen has a promotional effect on magnesium ions in controlling the polymorph of calcium carbonate crystal. A much wider range of calcium carbonate morphologies was observed in the presence of both collagen and magnesium ions. The experiments suggested that collagen acts in combination with magnesium ions to inhibit calcite crystal growth, while favoring the formation of aragonite crystals. 相似文献
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Kinetics of crystallization of calcium molybdate from unstirred molten solutions of lithium chloride of low to medium supersaturation
in platinum crucibles by the process of continuous cooling at 5° C hr−1 from temperaturesT
0=700 and 750°C are investigated. The crystal size measured by optical microscopy for different crystallization periods reveals
that both crystal length and width generally increase with cooling period. The degree of crystallizationα
t,also increases with cooling period, attaining a maximum of 0·90. The diffusion rate constants,K
Dlat 700 and 750°C are 0·0776 and 0·1138 respectively. The effect of variation of the crystallization temperature on the crystal
size and their number is also studied. 相似文献
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《Materials Letters》2001,47(4-5):267-270
The acceleration effects of polarized lead zirconate titanium (Pb(Ti,Zr)O3, PZT) on the crystallization of calcium phosphate were demonstrated when PZT plates were immersed in saturated solutions of hydroxyapatite (HA, Ca10(PO4)6(OH)2). Moreover, it is indicated that polarization also had influences on the orientation of the deposited crystals because crystalline layers of OCP (Ca8H2(PO4)6·5H2O) were found on the negatively charged surfaces of PZT. 相似文献
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The kinetics of calcite (CaCO3) crystallization on calcite seed crystals in the presence of taurine was investigated by the constant composition method.
The presence of taurine (4× 10− 5− 4× 10−4M) in the supersaturated solutions lead to calcite crystals with a characteristic discontinuous planes of growth and poor
habit, as compared to the hombohedral morphology of the seed crystals. The acceleration effect of taurine on the crystal growth
rate was 17–96%. The apparent order of the crystal growth was found to be 2.0± 0.2 typical for a surface diffusion-controlled
spiral growth processes. 相似文献
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The effect of sodium alginate on the crystal growth of hydroxyapatite (HAP) was investigated at sustained supersaturation by the constant composition technique. Sodium alginate was found to inhibit HAP crystal growth at low concentrations and reduced the crystal growth rates by 42–86% for inhibitor concentrations of 2.1 × 10− 7–12.6 × 10− 7 mol/l. The inhibition effect on the crystal growth rate may be explained possibly through adsorption onto the active growth sites. A detailed kinetics analysis suggested a Langmuir-type adsorption of the alginate on HAP surface and a value of 1.63 × 107 l/mol was obtained for the affinity constant of sodium alginate for the surface of HAP. The apparent order for the crystallization reaction was determined to be approximately 2, thus suggesting a surface diffusion controlled spiral growth mechanism. 相似文献
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L. F. Koroleva 《Inorganic Materials》2010,46(4):405-411
The formation of nanocrystalline calcium carbonate phosphates doped with Fe2+, Mg2, Zn2+, K+, Si4+, and Mn2+ has been studied by X-ray diffraction, IR spectroscopy, differential thermal analysis, and energy dispersive X-ray fluorescence
analysis. The results indicate that the synthesis involves the formation of hydroxy carbonate complexes from the three calcium
carbonate polymorphs (calcite, vaterite, and aragonite) in a solution of ammonium chloride and ammonium carbonate, followed
by reaction with orthophosphoric acid. This ensures the preparation of a bioactive material based on chlorophosphates, octacalcium
hydrogen phosphate, and calcium chloride hydroxide phosphates containing cation vacancies. Particle-size analysis data show
that the materials contain nanoparticles down to 10 nm in size. Heat treatment of the doped calcium carbonate phosphates produces
calcium hydroxyapatite containing cation vacancies, which can be used as a bioactive ceramic. 相似文献
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The formation of nano-sized crystals of gadolinium carbonate via reaction crystallization was studied in a semi-batch crystallizer using gadolinium chloride and ammonium hydrogen carbonate as the reactants. The gadolinium carbonate crystals were formed by the aggregation of primary particles sized about 5 nm. Thereby, the crystallization parameters acting directly on the aggregation of the primary particles, such as the reactant concentrations, non-stoichiometry of the reactants, solution pH, acoustic energy, and agitation speed, were mechanistically investigated. As such, increasing the reactant concentrations enhanced the crystal size due to higher nucleation of the primary particles for the aggregation. Non-stoichiometric reactant concentrations resulted in a significant reduction of the crystal size, due to the adsorption of the excess species on the primary particles. Similarly, the surface charge of the primary particles depended on the solution pH. Thus, the crystal size was reduced when the pH deviated from the neutral point. The acoustic cavitation of the ultrasound was much more effective than the turbulent fluid motion of the agitation in inhibiting the primary particle aggregation. Thus, the crystal size was remarkably reduced, even at a low acoustic energy of 6 watts. 相似文献
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Dey A Bomans PH Müller FA Will J Frederik PM de With G Sommerdijk NA 《Nature materials》2010,9(12):1010-1014
Unravelling the processes of calcium phosphate formation is important in our understanding of both bone and tooth formation, and also of pathological mineralization, for example in cardiovascular disease. Serum is a metastable solution from which calcium phosphate precipitates in the presence of calcifiable templates such as collagen, elastin and cell debris. A pathological deficiency of inhibitors leads to the uncontrolled deposition of calcium phosphate. In bone and teeth the formation of apatite crystals is preceded by an amorphous calcium phosphate (ACP) precursor phase. ACP formation is thought to proceed through prenucleation clusters--stable clusters that are present in solution already before nucleation--as was recently demonstrated for CaCO(3) (refs 15,16). However, the role of such nanometre-sized clusters as building blocks for ACP has been debated for many years. Here we demonstrate that the surface-induced formation of apatite from simulated body fluid starts with the aggregation of prenucleation clusters leading to the nucleation of ACP before the development of oriented apatite crystals. 相似文献
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G. S. Deshmukh S. U. Pathak D. R. Peshwe J. D. Ekhe 《Bulletin of Materials Science》2010,33(3):277-284
PBT/CaCO3 composites were prepared in a single screw extruder with particle content varying from 0–30% by weight. The influence of
surface treatment of the particles, with and without stearic acid (SA), on the mechanical, thermal and structural properties
was studied. The experiments included tensile tests, impact tests, differential scanning calorimetry (DSC), scanning electron
microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The composite systems containing SA
coated CaCO3 were found to exhibit better mechanical properties as compared to composite systems containing uncoated CaCO3, with the S3 system (20% of SA coated CaCO3) exhibiting best combination of mechanical properties. Thermal study revealed that particle type and content had no influence
on the melting temperature but the crystallization temperature, % crystallinity and thermal stability increased on increasing
the CaCO3 content in PBT matrix. Morphological observation indicated that in PBT composites containing SA coated CaCO3, the coupling agent favours a better polymer filler interaction rendering inorganic polymer interface compatible, which is
also evident from better mechanical and thermal properties. 相似文献
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用间歇碳化法制备了针状纳米CaCO3,对它们的形成机理进行了分析,实现了对针状CaCO3的粒度控制.通过对反应物Ca(OH)2浓度、反应温度、添加剂等操作条件对产品粒径和形态的影响考察,发现添加剂的加入时间是影响结晶习性和碳酸钙粉体形状的决定性因素.制得了平均粒径40~50nm、长径比约为10的针状纳米碳酸钙粉体. 相似文献
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间歇鼓泡碳化法生产超细碳酸钙的碳化过程是一个四相浆态反应过程。本文在双膜理论基础上 ,提出用“四膜模型”的观点来探讨碳化各阶段的动力学区域和碳化机理 ;探讨了包裹返碱现象发生的规律和碳化过程的化学理论基础。 相似文献