反应结晶过程中晶粒沉降速度模型研究

反应结晶过程是盐化工生产的一个重要环节。以硫酸钾的生产为例，从流体力学角度，通过建立沉降速度模型，研究晶体颗粒在液体中的沉降速度和阻力系数，探讨反应结晶过程中晶粒的沉降性能与终端沉降速度。研究结果表明：硫酸钾颗粒沉降速度与直径成正比。所建模型能较好地反映实际条件下的情况，为该工序的工艺设计与正常运行提供理论依据和技术支撑。     

磁场影响溶液结晶过程研究进展

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。     

溶液结晶热力学与过程分析研究进展

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。     

溶液自发结晶过程动力学参数研究

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.     

反应结晶过程中二水硫酸钙晶粒性能

设计了CaHPO₄·2H₂O-H₂SO₄-H₃PO₄-H₂O体系结晶温度、液相SO₄^2-含量、液相P₂O₅含量、搅拌速率和结晶时间的五因素四水平正交实验,通过测量晶体平均粒径优化出平均粒径最大的工艺参数:结晶温度80℃、液相SO₄^2-含量50g·L^-1、液相P₂O₅含量260g·L^-1、搅拌速率50r·min^-1和结晶时间2h。在该工艺参数下进行结晶过程研究,通过分析液相SO₄^2-浓度和P₂O₅浓度,XRD、SEM、EDS和激光粒度分析仪表征晶体,研究发现:0~40min为反应阶段,平均粒径减小;40min之后结晶过程遵从Ostwald递变法则,从CaSO₄·0.5H₂O过渡到CaSO₄·2H₂O,平均粒径几乎不变。     

间歇结晶过程的分析

本文概要地介绍了用于研究在间歇悬浮结晶器中的结晶动力学和晶体粒度分布（CSD）的实验技术和数据分析的新进展,讨论了包括最大CSD的特征化、累积CSD方法、热响应技术、最大允许成长速率在内的几个简单而有用的方法。     

水热法制备纳米钛酸锶的研究

用SrCl2·6H2O和KOH制取Sr(OH)2,再滴加TiCl4水溶液,在水相条件下,加热至95—98℃进行反应,然后过滤、洗涤、干燥,即可制得纳米钛酸锶,粒径在10—20nm,粉体形貌呈球形。开辟了一条制备纳米钛酸锶的新途径,为电子陶瓷制备提供了优良的原料。     

溶液结晶研究进展

本文综述了近期溶液结晶的研究进展及其在工业生产中的应用实例。     

结晶过程中溶液溶解度的在线检测

溶解度和过饱和度是溶液结晶动力学的重要参数。建立了溶解度在线测量的实验装置 ,以KNO3-H2 O为模型体系 ,得到了结晶过程的实时溶解度和过饱和度 ,为结晶动力学的研究奠定了基础     

水热法制备的陶瓷粉体晶粒粒度

系统地报道了水热法制备各种化合物晶粒变化及与水热反在条件的关系，通过选择不同形式的前驱适度调度控化合物晶为闰的粒度。改变水热反应条件，可制得同种化合物的异构体，由于同质异构体的结晶习性不同，使所制得的晶粒形态生粒度有很大的差异。     

Hydrothermal Synthesis of Acicular Lead Titanate Fine Powders

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)₃CH₃]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.     

Preparation of Strontium Titanate Thin Film on Titanium Metal Substrate by Hydrothermal-Electrochemical Method

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.     

钛酸锶钡结构与制备工艺研究进展

钛酸锶钡[(Ba,Sr)TiO3,SBT]是1种重要的电子陶瓷材料,具有高介电常数、低漏电流、高热释电系数,高的介电可调等特性,广泛用于动态随机存储器、热释电探测器、介质移相器等电子元件的制备。综述了钛酸锶钡[(Ba,Sr)TiO3,SBT]的结构和制备工艺研究进展,评述了制备工艺和掺杂等对钛酸锶钡的结构和性能的影响,并指出了钛酸锶钡尚待解决的问题。     

以淀粉为分散剂控制合成纳米钛酸锶研究

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。     

钛酸锶粉体的制备及催化降解孔雀石绿废水

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。     

一步水热法制备钛酸锂材料

采用一步水热法制备钛酸锂材料,并对制备的钛酸锂的性能进行研究。该方法与传统的水热合成法相比,具有制备工艺周期缩短,无其它试剂使用,减少环境污染等优点。结果表明,该方法制备的钛酸锂材料,在0.1 C倍率下的首次放电比容量为163 mAh·g^-1,首次效率为100%;XRD分析表明,其晶型结构与标准的钛酸锂图谱一致;SEM表征显示其颗粒形貌规则、分布均匀;循环伏安法测试表明,其具有良好的充放电可逆性能。     

Grain-Boundary Chemistry of Barium Titanate and Strontium Titanate: I, High-Temperature Equilibrium Space Charge

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.     

Effect of Dislocations on Grain Growth in Strontium Titanate

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.     

Surprising Results of a Study on the Plasticity in Strontium Titanate

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.     

制备工艺对钛酸钴纳米粉体结晶性能和显微结构的影响

采用水热法,以TiCl3、Co（CH3COO）2·4H2O为原料制备了纳米钛酸钴（CoTiO3）粉体。用X射线衍射、激光Raman光谱、扫描电子显微镜、透射电子显微镜分析了水热温度、前驱体溶液pH值、水热时问对CoTiO3晶相、生长取向和显微结构的影响。结果显示：升高水热温度至280℃有利于CoTiO3结晶性能的提高,...