A novel nanotube of composite of calcium carbonate and calcium sulfate

Nanotube-shaped precursor which is composed of layered structured sodium dodecylsulfate (SDS) calcium carbonate were obtained by titration of an aqueous solution of Na₂CO₃ into an aqueous solution containing CaCl₂ and SDS at 333-335 K. A unit of the repetition of the precursor was about 4 nm. Nanotube-shaped composite which is composed of CaCO₃ and CaSO₄ of 100-200 nm in diameter and 0.5-2 µm in length was obtained from nanotube-shaped precursor composed of layers of CaCO₃ and SDS by calcinations at 673 K in air. The precursor sheet composed of CaCO₃ layers on which SDS molecules attached to both side seemed to curl up and form a pipe.     

超细碳酸钙的碳化机理探讨

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。     

Preparation and characterization of novel diatomite/ground calcium carbonate composite humidity control material

Three kinds of novel diatomite/ground calcium carbonate composite humidity control materials were prepared with different calcination temperatures using diatomite and ground calcium carbonate (GCC) as raw materials. The microstructure and morphology properties of samples were studied by nitrogen gas adsorption, mercury intrusion porosimetry (MIP) and fractal dimensions on the basis of gas adsorption isotherms with FHH methods. Fourier transform infrared spectroscope (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the mineral composition and surface properties. Furthermore, X-ray diffraction (XRD), thermo-gravimetry and differential scanning calorimetry (TG-DSC) were used to analyze the formation mechanism of composite material. It was indicated that DG750 showed the better moisture adsorption performance. The 72 h moisture adsorbed amount of DG750 reached 11.66%, 8.81% and 8.00% at 98%RH, 85%RH and 75%RH, respectively, which improved about 0.46, 0.54 and 0.53-fold as those of diatomite. The hydrophilic calcium silicate, calcium oxide and calcium hydroxide were formed in the DG750 during the calcinations process. As compared with the raw materials, the content of mesoporous component increases in the DG750, which is in favor of capillary condensation and improving moisture adsorption ability.     

Manufacturing of Al/SiCp composite foams using calcium carbonate as foaming agent

Abstract

The aluminium composite foams reinforced by different volume fractions of SiC particles were manufactured with the direct foaming route of melt using different contents of CaCO₃ foaming agent. The density of produced foams changed from 0·43 to 0·76 g cm^?3. The microstructural features and compressive properties of the Al/SiC_p composite foams were investigated. Compressive stress–strain curve of Al/SiC_p composite foams is not smooth and exhibits some serrations. At the same relative density of composite foams, the plateau stress of the composite foams increases with increasing volume fraction of SiCp and decreasing weight percentage of CaCO₃. The relation between plateau stress, relative density, weight percentage of CaCO₃ and SiCp volume fraction of Al/SiCp composite foams with a given particle size was investigated.     

纳米CaCO3复合涂料研究进展

简述了纳米CaCO3在涂料中应用的意义,详细综述了纳米CaCO3在PVC防石击涂料、聚氨酯涂料、造纸涂料、建筑涂料、防腐涂料以及丙烯酸涂料中应用的研究现状,并对如何加快纳米CaCO3在涂料中的应用提出了建议.     

Fabrication of porous low crystalline calcite block by carbonation of calcium hydroxide compact

Calcium carbonate (CaCO₃) has been widely used as a bone substitute material because of its excellent tissue response and good resorbability. In this experimental study, we propose a new method obtaining porous CaCO₃ monolith for an artificial bone substitute. In the method, calcium hydroxide compacts were exposed to carbon dioxide saturated with water vapor at room temperature. Carbonation completed within 3 days and calcite was the only product. The mechanical strength of CaCO₃ monolith increased with carbonation period and molding pressure. Development of mechanical strength proceeded through two steps; the first rapid increase by bonding with calcite layer formed at the surface of calcium hydroxide particles and the latter increase by the full conversion of calcium hydroxide to calcite. The latter process was thought to be controlled by the diffusion of CO₂ through micropores in the surface calcite layer. Porosity of calcite blocks thus prepared had 36.8–48.1% depending on molding pressure between 1 MPa and 5 MPa. We concluded that the present method may be useful for the preparation of bone substitutes or the preparation of source material for bone substitutes since this method succeeded in fabricating a low-crystalline, and thus a highly reactive, porous calcite block.     

Synthesis of nano-sized ceria powders by two-emulsion method using sodium hydroxide

In the present study, nano-sized ceria powders were prepared by the two-emulsion method in the presence of aqueous sodium hydroxide. The effect of the ceria precursor concentration and the addition of an aqueous sodium hydroxide on the crystallite size, the size distribution and the morphology of the synthesized powders were investigated. The precipitates were obtained by mixing two water-in-oil emulsions with kerosene containing cerium nitrate aqueous solution and sodium hydroxide aqueous solution. The synthesized ceria powders were characterized by XRD and TEM. The synthesized ceria powders had nearly spherical shape and a uniform crystallite size in a range of 10 to 20 nm depending on the concentration of precursor solution and an addition amount of mineralizer.     

Phase and morphology evolution of calcium carbonate precipitated by carbonation of hydrated lime

Phase and morphology evolution of CaCO₃ precipitated during carbonation of lime pastes via the reaction Ca(OH)₂ + CO₂ → CaCO₃ + H₂O has been investigated under different conditions (pCO₂ ≈ 10^−3.5 atm at 60 % RH and 93 % RH; pCO₂ = 1 atm at 93 % RH) using XRD, FTIR, TGA, and SEM. Simulations of the pore solution chemistry for different stages and conditions of carbonation were performed using the PHREEQC code to investigate the evolution of the chemistry of the system. Results indicate initial precipitation of amorphous calcium carbonate (ACC) which in turn transforms into scalenohedral calcite under excess Ca²⁺ ions. Because of their polar character, { 21[`3]4 } left{ {21bar{3}4} right} scalenohedral faces (type S) interact more strongly with excess Ca<sup>2+</sup> than non-polar { 10[`1]4 } left{ {10bar{1}4} right} rhombohedral faces (type F), an effect that ultimately favors the stabilization of { 21[`3]4 } left{ {21bar{3}4} right} faces. Following the full consumption of Ca<sup>2+</sup> ions and further dissolution of CO<sub>2</sub> leading to a pH drop of the pore solution, { 21[`3]4 } left{ {21bar{3}4} right} scalenohedra are subjected to dissolution. This eventually results in re-precipitation of { 10[`1]4 } left{ {10bar{1}4} right} rhombohedra at close-to-neutral pH. This crystallization sequence progresses through the carbonated depth with a strong dependence on the degree of exposure to CO₂, which is controlled by the carbonated pore structure governing the diffusion of CO₂. Both the carbonation process and the scalenohedral-to-rhombohedral transformation are kinetically favored under high RH and high pCO₂. Supersaturation plays a critical role on the nucleation density and size of CaCO₃ crystals. These results have important implications in understanding the behavior of ancient and modern lime mortars for applications in architectural heritage conservation.     

The crystallization of calcium carbonate on sodium cholate

Recent studies in the bibliography showed that calcium carbonate was the major constituent (77.8%) in gall stones, and the polymorph calcite was at 62.5% of the cases examined. The kinetics of crystallization of calcite on sodium cholate has been studied using the constant composition technique. Analysis of the initial rates as a function of the solution supersaturation, according to the classical nucleation theory, yielded a value of 33 mJ m^-2 for the surface energy of the growing phase and a five-ion cluster, forming the critical nucleus. The apparent order for the calcite crystallization was found to be 4.5±0.7 indicative of a surface nucleation mechanism. The formation of calcite may be initiated through the interaction of Ca²⁺ ions with the negative end of the C=0 bond of the sodium cholate molecule.     

氢氧化钙的固碳功能性研究-CO2浓度与碳化时间的影响

矿物固碳是降低大气中CO2浓度的有效方法之一,但是目前大量的研究集中于提高矿物固碳效率,而忽略了碳化产物的二次利用问题。本文采用氢氧化钙固碳,研究了CO2浓度和碳化时间对碳化速率以及碳化产物强度的影响。研究发现,在相同CO2浓度下,氢氧化钙碳化速率随碳化时间的延长而逐渐提高;随着CO2浓度的增加,氢氧化钙的碳化速度不断增大;随碳化时间的延长,碳化产物的强度不断提高,但是当碳化时间超过24 h后,碳化产物的强度明显下降。高浓度CO2环境对氢氧化钙碳化产物的强度发展不利,随CO2浓度的增加碳化产物的强度逐渐降低。通过SEM、EDS和XRD分析发现,随着碳化时间的延长,氢氧化钙表面形成方解石型碳酸钙层,阻碍了碳化进程;当碳化时间达到28 d时,由于碳酸钙层的胀裂,碳化产物的强度出现明显下降。     

Direct observation of the carbonation process on the surface of calcium hydroxide crystals in hardened cement paste using an Atomic Force Microscope

The surface carbonation process of calcium hydroxide crystals in samples of hardened Portland cement paste has been investigated at the nanometer scale with the aid of an Atomic Force Microscope (AFM). The AFM, encapsulated in a glove-box, was operated in contact mode at ambient temperature. Successive real-time measurements were performed in (i) a pure non-reacting N₂ atmosphere, (ii) a N₂ + H₂O, (iii) a N₂ + CO₂ and finally (iv) in a N₂ + CO₂ + H₂O atmosphere, respectively. In the N₂ + H₂O atmosphere, until 30–40% relative humidity, a minor change as surface smoothing with an occurring instability was detected. In the N₂ + CO₂ atmosphere, no change was detected, except for some very small grains becoming after two days even a little bit smaller. However, in the N₂ + CO₂ + H₂O atmosphere, i.e., in a simultaneous CO₂ + H₂O environment, with a stepwise increase of the relative humidity until 26%–30%, on the surface of the calcium hydroxide crystals several small scattered spots were found. These spots were weakly linked to the surface and could be pushed away with the scanning tip. Under constant conditions (temperature, humidity- and CO₂-content), the small spots start to grow, and after a long-term exposition of the crystals to the ambient humid air, develop a specific spherular structure. The latter is interpreted to be calcium carbonate, a result of the surface carbonation process of the initial calcium hydroxide crystals.     

Formation of macropores in calcium phosphate cement implants

A calcium phosphate cement (CPC) was shown to harden at ambient temperatures and form hydroxyapatite as the only end-product. Animal study results showed that CPC resorbed slowly and was replaced by new bone. For some clinical applications, it would be desirable to have macropores built into the CPC implant to obtain a more rapid resorption and concomitant osseointegration of the implant. The present study investigated the feasibility of a new method for producing macropores in CPC. Sucrose granules, NaHCO₃, and Na₂HPO₄ were sieved to obtain particle sizes in the range of 125 m to 250 m. The following mixtures of CPC powder (an equimolar mixture of tetracalcium phosphate, Ca₄(PO_{4 2}O, and dicalcium phosphate anhydrous, CaHPO₄) and one of the above additive granules were prepared: control–no additive; mixture A–0.25 mass fraction of sucrose; mixture B–0.25 mass fraction of NaHCO₃; mixture C–0.25 mass fraction of Na₂HPO₄, and mixture D–0.33 mass fraction of Na₂HPO₄. Cement samples were prepared by mixing 0.3 g of the above mixtures with 0.075 ml of the cement liquid (1 mol/l Na₂HPO₄). After hardening, the specimens were placed in water for 20 h at about 60 °C to completely dissolve the additive crystals. Well-formed macropores in the shapes of the entrapped crystals were observed by scanning electron microscope (SEM). The macroporosities (mean±standard deviation; n = 6) expressed as volume fraction in % were 0, 18.9 ± 1.7, 26.9 ± 1.6, 38.3 ± 4.4 and 50.3 ± 2.7 for the control, A, B, C and D, respectively. The diametral tensile strengths (mean±standard deviation; n = 3) expressed in MPa were 10.1 ± 0.7, 3.7 ± 0.3, 2.4 ± 0.2, 1.5 ± 0.5 and 0.4 ± 0.1, respectively, for the five groups. The results showed that macropores can readily be formed in CPC implants with the use of water-soluble crystals. The mechanical strength of CPC decreased with increasing macroporosity. © 2001 Kluwer Academic Publishers     

卤水-氨法制备纤维状碱式氯化镁

以MgCl2·H2O和NH3·H2O为原料，采用直接沉淀法合成纤维状碱式氯化镁。考察了各种因素对产物理化性能的影响，获得了最佳的工艺条件。利用XRD、SEM及化学分析方法对产品进行了表征。     

Development of a novel calcium phosphate cement composed mainly of calcium sodium phosphate with high osteoconductivity

Two novel calcium phosphate cements (CPC) have been developed using calcium sodium phosphate (CSP) as the main ingredient. The first of these cements, labeled CAC, contained CSP, α-tricalcium phosphate (TCP), and anhydrous citric acid, whereas the second, labeled CABC, contained CSP, α-TCP, β-TCP, and anhydrous citric acid. Biopex^®-R (PENTAX, Tokyo, Japan), which is a commercially available CPC (Com-CPC), and OSferion^® (Olympus Terumo Biomaterials Corp., Tokyo, Japan), which is a commercially available porous β-TCP, were used as reference controls for analysis. In vitro analysis showed that CABC set in 5.7 ± 0.3 min at 22 °C and had a compressive strength of 86.0 ± 9.7 MPa after 5 days. Furthermore, this material had a compressive strength of 26.7 ± 3.7 MPa after 2 h in physiologic saline. CAC showed a statistically significantly lower compressive strength in the presence of physiologic saline and statistically significantly longer setting times than those of CABC. CABC and CAC exhibited apatite-forming abilities in simulated body fluid that were faster than that of Com-CPC. Samples of the materials were implanted into the femoral condyles of rabbits for in vivo analysis, and subsequent histological examinations revealed that CABC exhibited superior osteoconductivity and equivalent bioresorbability compared with Com-CPC, as well as superior osteoconductivity and bioresorbability compared with CAC. CABC could therefore be used as an alternative bone substitute material.     

Synthesizing a composite material of amorphous calcium carbonate and aspartic acid

A composite material of amorphous calcium carbonate and aspartic acid (Asp) was synthesized using a highly concentrated solution of calcium aspartate: a new approach. A transparent and amorphous solid with approximately 1 mm thickness was obtained. UV-vis transmittance spectrum of the composite shows no characteristic absorption in visible region. A Raman spectrum of the composite revealed a peak assigned to the symmetric stretching of carbonate ion. This study demonstrated that amorphous calcium carbonate could be stabilized using not only organic artificial macromolecules but also using Asp, a small biomolecule. This result is expected to engender development of new biomimetic materials.     

The effect of sodium alginate on the crystal growth of calcium carbonate

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.     

新型可降解硫酸钙/聚酰胺复合材料的制备和表征

以6-氨基己酸（6-aminohexanoic acid,N6）和丁内酰胺（又名α-吡咯烷酮,α-pyrrolidone,α-P）为原料,通过6-氨基己酸熔融缩聚使丁内酰胺开环制备了一系列新型聚酰胺,优化选取6-氨基己酸与丁内酰胺摩尔比为7∶3的聚合物作为基体与硫酸钙（CS）复合,制备了新型可降解硫酸钙/聚酰胺复合材料。通过乌氏粘度计、万能力学实验机、红外光谱（IR）、差示扫描量热分析（DSC）、X射线衍射（XRD）和X光电子能谱（XPS）对其特性黏数、抗压强度及组成与结构进行了表征,并研究了复合材料在磷酸缓冲溶液（PBS）的体外降解性能。结果表明产物为具有酰胺键结构的聚合物,6-氨基己酸与丁内酰胺摩尔比为7∶3时聚合物既能最大程度地引入丁内酰胺又具有较好的力学性能。复合材料无机相与有机相之间存在化学键作用。体外降解实验表明本文合成的聚酰胺是可降解的;相比于聚合物,硫酸钙/聚酰胺复合材料具有更快的降解速率;随着硫酸钙含量的增加,复合材料的失重率增加;在降解过程中降解液pH值维持在6.6～7.4之间。由于复合材料既具备有机组分良好的力学性能又具备硫酸钙良好的生物相容性和降解性能,所以该硫酸钙/聚酰胺复合材料可望在骨修复领域得到运用。     

Morphology and polymorphic phase changes of calcium carbonate micro/nanocrystals using fruit extracts

This study reveals the morphology and polymorphic phase changes of calcium carbonate crystals into a mixture of calcite and aragonite micro/nanocrystals of interesting morphology at room temperature by a simple reaction with fruit extracts of Tamarindus indica and Emblica officinalis respectively by mixing CaCO3 solutions with their corresponding extracts. The control experiments were carried out to establish the plausible role of tartaric acid from Tamarindus indica and ascorbic acid from Emblica officinalis in this regard. The quantitative determination of CaCO3 phases was done based on the use of intensities obtained from corresponding XRD spectrum. The molar % of aragonite was found to be more in case of TA and AA rather than TI and EO respectively, however the calcite was observed to be the predominant phase in all four reactions. Interestingly, the TI changes the rhombohedral morphology of calcite to elongated rods, whereas EO induces a great polymorphic phase change.