Kinetics of Hydroxyapatite Formation at Low Temperature

The influence of temperature on the kinetics of formation of calcium-deficient hydroxyapatite by an acid-base reaction has been determined. Calcium-deficient hydroxyapatite is compositionally similar to bone apatite. Reactants used in this study were tetracalcium phosphate, a calcium phosphate more basic than hydroxyapatite, and dicalcium phosphate, which is more acidic than hydroxyapatite. The kinetics of hydroxyapatite formation are initially controlled by the surface areas of the reactants; however, eventually the rate of hydroxyapatite formation becomes diffusionally controlled. The origin of diffusion control appears to be associated with the epitaxial formation of hydroxyapatite on the surface of the dicalcium phosphate reactant. The microstructure of hydroxyapatite formed at 5°, 15°, and 25°C were generally similar and are characterized by the formation of a porous acicular product which covers the surfaces of the reactants. The microstructure of the hydroxyapatite formed at 38°C was distinct from this and exhibited a pseudomorphic relationship with the dicalcium phosphate reactant. Seeding with hydroxyapatite accelerated the initial reaction but did not appear to have major long-term effects on the fractional degree of reaction or on microstructural development. Reaction was also accelerated in a neutral salt solution of high ionic strength.     

聚碳硅烷低温制备碳化硅泡沫陶瓷

采用具有连通气孔的聚氨酯海绵浸渍聚碳硅烷（polycarbosilane,PCS）、碳化硅微粉与四氢呋喃配制的浆料,挂浆素坯经热氧化不熔化处理后,在惰性气氛中于1 000℃热解制备碳化硅泡沫陶瓷。研究了固相含量和PCS含量对碳化硅泡沫陶瓷微观结构、体积密度、线收缩率和抗弯强度的影响,结果表明：固相含量为43.1%～69...     

Properties of Acetylated Wood Prepared at Low Temperature in the Presence of Catalysts

Abstract

In the presence of catalysts such as sodium acetate, zinc chloride, magnesium perchlorate, and magnesium chloride hexahydrate, acetylation of wood at 75°C was investigated. The results showed that it was possible to endow wood with high dimensional stability at low temperature by a catalyzed acetylation method. In particular, the magnesium chloride–catalyzed acetylation of wood showed very little or no effect on the color change or mechanical property of wood, as contrasted to those of the zinc chloride or magnesium perchlorate–catalyzed treatment, which showed a great effect. In addition, the concentrations of catalysts proved to have an effect on weight percent gain.     

低温下水盐体系相平衡研究进展

盐湖无机盐资源作为我国的战略性资源,其有效开发利用都离不开水盐体系相图的理论指导。近年对于水盐体系相平衡的研究主要集中在常温、高温条件下的研究,而对于低温条件下的研究相对较少。归纳总结了国内外对低温下水盐体系相平衡的研究进展,并指出低温下水盐体系研究过程中存在的问题和今后的发展趋势。     

Elasticity and Anelasticity of Uranium Oxides at Room Temperature: II, Hyperstoichiometric Oxides

The Young's modulus and internal friction of hyperstoichiometric uranium oxide at room temperature were determined by a sonic technique. Young's modulus decreased, whereas internal friction increased, with increasing O/U ratios. These effects are attributed to the precipitation of U₄O₉. A complete microstructural characterization is needed.     

Fe-Nb Oxides: Phase Relations at 1180°C

Subsolidus phase relations of the oxides in the system Fe–Nb–O were experimentally determined at 1180°C, 1 atm total pressure, and variable partial pressures of oxygen. Niobium pentoxide reacts readily with either ferrous or ferric oxide at subsolidus temperatures and the following ternary compounds were synthesized: Fe₄Nb₂O₉, FeNbO₄, and FeNb₂O₆. It is shown that the rutile structure of NbO₂ will take Fe-Nb₂O₆ into solid solution and that the spinel structure of Fe₃O₄ will incorporate up to 7 at.% Nb.     

低温制备Fe-TiO2及其可见光催化性能研究

采用大量水体系溶胶-凝胶方法在低温下制备了掺杂铁的二氧化钛纳米材料(Fe-TiO2),通过XRD、XPS、SEM、UV-Vis对样品进行了结构、形貌以及光化学方面的表征,研究了铁掺杂浓度对样品结构和性能的影响。结果表明,低温下合成的样品主要以锐钛矿型存在,结合有少量板钛矿型。掺杂1%的Fe-TiO2具有最大的吸收带红移,在室内具有最好的对甲基橙光催化性能。主要认为铁的掺杂抑制了电子和空穴的复合并且增强了其在可见光区的吸收。     

Mn-Ta Oxides: Phase Relations at 1200°C

Subsolidus phase relations among oxides in the system Mn–Ta–O were experimentally determined by the quenching method. The conditions during the heating period were 1200°C, 1 atm total pressure, and various partial pressures of oxygen between 10^–17 atm and 1 atm. At the limits of this range, the stable assemblages at f -= 10^–17 atm are: MnO, Mn₆Ta₂O₁₁, Mn₄-Ta₂O₉, Mn_1.4 TaO_3.9, MnTa₂O₆, and β-Ta₂O₅; at p _o2= 1 atm they are: Mn₃O₄, Mn_1.4TaO_4.2, MnTa₂O₆, and β-Ta₂O₅. There are five univariant assemblages of three solid phases plus vapor in the phase diagram.     

Fe-Ta Oxides: Phase Relations at 1200°C

Subsolidus phase relations of the oxides in the system Fe-Ta-O were experimentally determined at 1200°C, 1 atm total pressure, and variable partial pressures of oxygen. Tantalum pentoxide reacts readily with either ferrous or ferric oxide at subsolidus temperatures and the following ternary compounds have been synthesized: Fe₄Ta₂0₉, Fe₃Ta₂O_8-1, FeTaO₄, FeTa₂O₆, solid solutions between the latter two compounds, and tantalian magnetites. The compositions of solid solutions between FeTaO₄ and FeTa₂O₆ were very sensitive to variation of oxygen pressure. This sensitivity explains the oxidation behavior of tapiolite. The incorporation into magnetite of up to 7 at.% Ta was demonstrated, with a resulting increase in the size of the unit cell and decrease in magnetic permeability.     

Crystallization of Fine, Chemically Prepared Lead Lanthanum Zirconate Titanate Powders at Low Temperature

Fine, homogeneous lead lanthanum zirconate titanate (PLZT) powder prepared by the hydrolysis of an aqueous nitrate solution with ammonia gas exhibits high reactivity when calcined. The minimum temperature for crystal formation in PLZT is 400°C. The kinetics of crystallization between 400° and 600°C are studied isothermally by XRD. The isothermal crystallization process is best fitted to a first-order equation derived for a random, nucleation-controlled system on a large number of small particles with an activation energy of 297 kJ/mol. Characterization of the powder by XRD line-broadening and BET surface-area examination in the range 400° to 500°C shows a microstructure consisting of ∼20-nm subunits agglomerated into ∼60-nm particles. Each subunit evidently generates a single nucleus, which grows within that subunit.     

Factors in Phase Formation in the Heterogeneous Chain Oxidation of Dichlorosilane at Low Pressures

Dichlorosilane oxidation, a heterogeneous branching-chain reaction, is considered in terms of unsteady-state nucleation theory taking into account the condensation growth of nuclei, and the following observations are interpreted: the crossover between the homogeneous and heterogeneous phase formation; the dependence of the amount of aerosol on the initial temperature, pressure, and admixture concentration; and the kinetics of phase formation and of the disappearance of the original substance. Introducing an inhibitor is found to reduce the mean size of aerosol particles. This result is in qualitative agreement with experimental data. It is found that it is because of the growing equilibrium vapor pressure of the new phase that the amount of aerosol formed decreases with increasing initial temperature, including when an active admixture is present. The reactivity of the silicon dioxide aerosol obtained in the presence of Freon-12 varies reversibly. The role of surface diffusion and surface nucleation in the deposition of thin films is discussed.     

Effect of Mn Dispersion on Gas Phase Ozone Decomposition at Room Temperature Using Natural Manganese Oxides

In this study, various analyses were performed to evaluate the ozone removal characteristics using natural manganese ore (NMO) at room temperature. NMO exists primarily in the form of MnO₂, and the specific forms of manganese oxide are formed as the calcination temperature increases. The activity tests, XRD, BET, and XPS analyses confirmed that the dispersion of manganese site exposed to the surface was a critical factor for ozone removal using NMO. To evaluate the actual application of NMO as a catalyst for ozone decomposition, NMO was also made as a form of monolith; as a result, the catalyst showed an excellent conversion rate (over 80%) even at space velocity 30,000 h^?1.     

低温油相合成金钯纳米粒子及其催化性能研究

采用低温油相法合成了不同金钯量比的双金属纳米催化剂,对其形貌和电催化性能进行了分析。透射电镜表征结果显示,金钯的量比对催化剂的分散性和纳米颗粒的尺寸有一定的影响。当金钯等量比时,分散性最好、纳米颗粒的粒径最小。而电化学测试表明,当金钯等量比时,高分散、小尺寸的金钯纳米催化剂更易于裸露有效活性位点,从而对甲酸和乙醇显示出较高的催化活性和稳定性。     

Simultaneous Heat and Momentum Transfer in Two-Phase Systems at Low Pressure and High Temperature: Vapor Phase

The heat and momentum transfer in a liquid-vapor two-phase film system at high temperature and low pressure is studied by the example of the removal of highly volatile fractions from high-boiling liquids in film evaporators. The temperature and velocity distributions in the vapor phase are determined.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 3, 2005, pp. 251–258.Original Russian Text Copyright © 2005 by Babak.     

Invar Like Behavior of the Cr2AlC MAX Phase at Low Temperature

The structure of Cr₂AlC has been studied using neutron scattering experiments performed in a temperature range running from room temperature down to 1.8 K. It is shown that the unit cell volume does not vary significantly below 80 K. This anomalous behavior, correlated with the existence of a weak ferromagnetic ordering revealed from superconducting quantum interference device experiments, is similar to that characteristic of Invar alloys. Just above the Curie temperature T_C ~ 73 ± 5 K, the Cr₂AlC undergoes significant distortions of the octahedron and triangular prisms units. Above 100 K, Cr₂AlC follows an usual thermal expansion.     

低温低压液相催化制甲醇,甲酸甲酯

甲醇是大宗化工产品,甲酸甲酯(MF)是新一代C_1化工产品的基础中间体之一。本文介绍以合成气为原料,低温低压液相催化联产甲醇和MF的新工艺,该工艺反应温度低,利用浆态床反应器。与ICI公司的通用合成甲醇工艺及甲醇羰化法制造甲酸甲酯工艺相比,均显示了操作条件温和、成本低等优点,在国际上亦处于领先地位,这一新工艺的开发将会提升我国有关产品的国际竞争能力。     

低温制备二氧化钛纳米晶及其光催化性能研究

采用溶胶凝胶法在低温(40℃)制备TiO2纳米晶体。采用XRD、红外(IR)、透射电镜(TEM)以及DRS等技术对样品进行表征。结果显示,样品的平均粒径不到10nm,粒径分布比较均匀、具有良好的结晶度。以罗丹明B的光催化降解为目标反应,测试样品的光催化性能。结果显示样品在紫外光照射下,120min罗丹明B的降解率为95%,显示出样品具有较高的光催化活性。     

Climb-Dissociated Dislocations in Monazite at Low Temperature

Three types of climb-dissociated partial dislocations were observed by high-resolution transmission electron microscopy in monazite (LaPO₄) that was indented at room temperature. Two types were found on twin boundaries, and a third in the lattice. Formation mechanisms are discussed. Glide of climb-dissociated partial dislocations that is allowed by stacking fault migration is considered.     

BxO: Phases Present at High Pressure and Temperature

Boron suboxide compounds are of interest because of their low densities coupled with high hardness. In the present study, we have attempted to determine the nature of the B _x O phases that occur in the field defined by pressures of zero to 1.5 GPa, temperature between 1200° and 1700°C, and the compositional range 2/3 x 24. Amorphous boron powder and boric acid B₂O₃ were the starting reactants for all the runs. The processing of the specimens was carried out in a controlled atmosphere furnace, a hot-pressing assembly, and in a piston—cylinder high-pressure apparatus within quasi-hydrostatic and inductively heated cell assemblies. After processing at elevated temperature and pressure, for compositions over the range 2/3 x 6, B₂O₃ (identical to the hexagonal starting material) and B₆O ( R 3¯ m ) were the dominant phases present. For the compositions 6 x 24, B₆O and rhombohedral B were the primary phases identified. In general, the hardness of the processed composites was dominated by the occurrence of B₆O (approximately equivalent to B₄C). However, there is some suggestion of particularly high values of hardness on a very localized scale in specimens near the B₂₂O composition.     

低温甲醇洗相平衡模型和气液平衡计算(1)——相平衡模型

以实验和文献数据为基础建立了能描述低温甲醇洗工艺中Ｈ２、Ｎ２、ＣＯ２、Ｈ２Ｓ和ＣＨ３ＯＨ气液相平衡的模型；用修改的ＲＫ方程，并考虑量子气体Ｈ２存在的影响，处理气相的非理想性；用Ｗｉｌｓｏｎ方程处理液相的非理想性，获得满意结果。