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研究了碱性溶液中苯丙酮酸盐的结晶过程。在分析苯丙酮酸钠盐在碱性溶液中溶解度的基础上,通过对中和用酸的选择、加酸过程和搅拌速度的控制,以及结晶时间的选择,得到了优化的结晶工艺。苯丙酮酸钠盐的结晶收率达到91.7%,纯度达到98.5%。 相似文献
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磁场影响溶液结晶过程研究进展 总被引:1,自引:0,他引:1
论述了磁场对溶液结晶过程影响的研究进展情况,指出磁场不仅可以化溶液结晶过程,刺激结晶成核,提高结晶生长速率,控制晶体粒径的分布,也可抑制溶液的结晶,降低结晶生长速率。针对不同的工程目的,选择合理的磁处理参数显得尤为重要。并提出磁场技术目前存在的问题和展望。 相似文献
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利用单轴声悬浮装置观察了毫米大小的无机盐水溶液悬浮液滴蒸发和结晶的动态过程,为认识伴随均匀成核和结晶过程的溶液液滴形态变化规律提供了一个理想的环境.通过对NH4Cl溶液液滴广泛的实验观察发现,开始结晶后通常先在液滴表面的局部形成外壳,局部外壳发展到完全成壳经过3种可能的生长历程,即局部外壳向液滴内的生长,沿液滴表面的扩展,以及从局部外壳上个别点向外的枝状物或晶须生长.多数溶质液滴都经历与NH4Cl液滴相同的过程演化到完全成壳,但完全成壳后的形态变化却各不相同.初步考察了溶质性质与形态变化的关系,以及二元混合溶液液滴的形态变化规律,并定性地讨论分析了声场存在对于观察结果代表性可能的影响. 相似文献
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结晶是一种重要的分离和纯化手段。在医药、食品、材料制备等领域中众多产品都是以晶体的形式存在。热力学是结晶过程研究的理论基础,目标体系的热力学性质对结晶方式(降温结晶、蒸发结晶和溶析结晶等)的选择有重要影响,而热力学平衡关系则决定了结晶收率的极限以及不同条件下各种晶型的稳定性,因此热力学的相关研究对于结晶过程的优化和放大设计有重要的指导意义。归纳了不同结晶体系的固液平衡数据测量方法,介绍了NRTL方程、e-NRTL方程、MSE模型等热力学模型在无机盐以及药物结晶过程中的相平衡计算和预测实例,分析了过饱和度、介稳区以及相图在结晶过程优化方面的作用,此外还总结了过程分析技术在溶液结晶领域的应用现状,展望了结晶领域未来的发展前景。 相似文献
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The batch cooling crystallization initiated from spontaneous nucleation for aqueous solution of potas- sium nitrate was studied.The concentration and transmittance data were acquired on line throughout the operation. Based on solute mass transfer in both liquid and solid phases,a kinetic model was deduced by assuming that the late period of primary nucleation resembles the initial period of the secondary nucleation.Nucleation and crystal growth stages were identified.Kinetic parameters were estimated piecewise from online experimental data and compared with those in literature.The estimated kinetic parameters for stages without apparent primary nucleation agreed well with those in literature.Further,a simulated concentration curve was also drawn from the estimated kinetic parameters and it matched well with that in experiment. 相似文献
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Humin Cheng Jiming Ma Zhenguo Zhao Di Qiang Yongxiang Li Xi Yao 《Journal of the American Ceramic Society》1992,75(5):1123-1128
A pure, acicular lead titanate (PbTiO3 ) fine powder with a white color has been prepared by hydrothermal synthesis. It is a new phase of PbTiO3 with I 4 symmetry, cell parameters of a = 12.358 Å and b = 14.541 Å, and a density of 6.80 g.cm−3 . The influences of pH (12.5 to 14.4), Pb/Ti ratio (1.0 to 1.6) in the feedstock, reaction temperature (130° to 230°C), time (0.25 to 4 h), starting materials, and additives on the formation of acicular PbTiO3 under hydrothermal conditions have been investigated. The acicular PbTiO3 with I 4 symmetry, referred to as the PX phase, can be converted to the perovskite-type (PE phase) of PbTiO3 at about 605°C while its acicular morphology is essentially unchanged. The preferable conditions for preparing pure acicular PX-phase PbTiO3 are that the pH is 13.0 to 14.0, Pb/Ti ratio is >1.3, reaction temperature is 170° to 200°C, time is 0.5 to 1.0 h, titanium butoxide (Ti[O(CH2 )3 CH3 ]4 ) is the starting material, and poly(vinyl alcohol) is an additive. The acicular grain of the PX phase is usually less than 100 nm in diameter and more than 1000 nm in length. 相似文献
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Preparation of Strontium Titanate Thin Film on Titanium Metal Substrate by Hydrothermal-Electrochemical Method 总被引:1,自引:0,他引:1
Seung Eul Yoo Motoo Hayashi Nobuo Ishizawa Masahiro Yoshimura 《Journal of the American Ceramic Society》1990,73(8):2561-2563
Polycrystalline SrTiO3 thin films have been prepared on Timetal substrates by the hydrothermal-electrochemical method. The films were prepared at temperatures ranging from 100° to 200°C and under saturated vapor pressures in electrolytic solutions of 1 N to 5 N Sr(OH)2 . A galvanostat was used to apply a direct current of 5 to 25 mA/cm2 . The films had smooth and homogeneous surfaces without any visible pores or defects. The dielectric constant of the films was approximately 129 assuming 25 nm for film thickness. 相似文献
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研究以钛酸丁酯和氯化锶为原料,采用溶胶-沉淀法合成纳米钛酸锶(SrTiO3),通过对产物X射线衍射分析,可知NaOH浓度对产物结构具有较大影响;研究不同淀粉添加量与纳米SrTiO3粒度分布之规律,通过改变淀粉配量可有效地控制纳米SrTiO3粒度分布;通过透射电子显微镜和扫描电子显微镜对产品形态和结构进行表征,所得纳米SrTiO3形态比较规则,多数呈球形颗粒,单分散性好,粒径分布为30~80nm。讨论溶胶一沉淀法制备纳米SrTiO3的反应过程,阐明淀粉对纳米SrTiO3粒度调控作用。 相似文献
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钛酸锶粉体的制备及催化降解孔雀石绿废水 总被引:1,自引:0,他引:1
采用沉淀法制备钛酸锶粉体,通过XRD、SEM对产物进行表征。研究钛酸锶粉体对孔雀石绿废水的催化活性。对比了无钛酸锶的同样条件下,超声辅助双氧水降解孔雀石绿的效果。探讨了钛酸锶催化剂的投加量、时间等对催化效果的影响。结果表明,钛酸锶用量为0.1g,氧化剂双氧水滴加0.5mL,100mL浓度为30mg/L的孔雀石绿废水超声10min降解率可达97.8%。超声辅助钛酸锶-H2O2体系催化降解孔雀石绿废水效果好。对降解三苯甲烷类染料废水有一定实用参考意义。 相似文献
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Grain-Boundary Chemistry of Barium Titanate and Strontium Titanate: I, High-Temperature Equilibrium Space Charge 总被引:2,自引:0,他引:2
Direct observations using scanning transmission electron microscopy (STEM) of the grain-boundary chemistry of selectively doped SrTiO3 and BaTiO3 show the predominant solute segregation in both systems to be that of acceptors (negative effective charge). Appreciable donor segregation is not observed even at lattice concentrations as high as 10 mol%. Donor and acceptor codoped materials show segregation of the acceptor only. The results are consistent with a grain-boundary space-charge distribution consisting of a positive boundary and negative space charge. All grain boundaries examined also show an excess of Ti relative to the A-site cations, suggesting that the positive boundary charge is at least partially accommodated by an excess of Ti ions. The sign and magnitude of the electrostatic potential appear to be remarkably insensitive to changes in lattice defect structure with solute doping. Grain-boundary chemistry appears dominated by space-charge segregation, in contrast with the predictions of recent atomistic simulations which neglect the space-charge potential. 相似文献
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Two series of experiments were done to investigate the effect of dislocations on grain growth in SrTiO3 . In the first series, we observed the growth behavior of a single-crystal plate toward a TiO2 -excess SrTiO3 powder compact, containing different dislocation densities on two equivalent {100} surfaces. The surface with a higher dislocation density exhibited faster growth, showing interface mobility enhancement by dislocation. In the second series, a polycrystalline SrTiO3 sample which had been plastically deformed by hot pressing was embedded in a TiO2 -excess SrTiO3 powder compact, and its growth behavior toward the powder compact was compared with that of a sample without hot pressing. As with a single crystal, the grains with the higher dislocation density in the plastically deformed sample grew faster. In addition, some grains in the plastically deformed sample showed the characteristic of abnormal grain growth. The transmission electron microscopy (TEM) observations on a sintered TiO2 -excess SrTiO3 showed that the abnormally large grains contained many dislocations while the fine matrix grains contained practically no dislocations. This result suggests that the uneven distribution of dislocations between grains is possibly one of the causes of the abnormal grain growth in polycrystalline SrTiO3 . 相似文献
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Dieter Brunner Shahram Taeri-Baghbadrani Wilfried Sigle Manfred Rühle 《Journal of the American Ceramic Society》2001,84(5):1161-1163
Oxides such as SrTiO3 are expected to fail via brittle fracture at low temperatures. Surprisingly, in the present study, SrTiO3 single crystals could be plastically deformed in compression in two temperature ranges: from 78 K to ∼1050 K and from 1500 K to 1800 K. SrTiO3 was brittle at temperatures between these two ranges (∼1050–1500 K). This phenomenon of a ductile–brittle–ductile transition, together with microstructural investigations, suggests that the role of dislocations in the plasticity of ceramics must be reconsidered. 相似文献