Transient Crystal Size Distribution in DTB and FC Crystallizers

This work deals with the transient analysis of crystal size distribution (CSD) for imperfectly mixed draft tube baffled (DTB) and forced circulation (FC) crystallizers. The DTB and FC crystallizers are described by the Compartmental and Mixed models respectively. Monte Carlo (MC) scheme has been employed for simulation purposes. The simulation results have been compared with the available experimental data of BENNETT and VAN BUREN for continuous urea crystallizers.     

Design of Continuous Mixed-Suspension Crystallizers

Several different basic types of continuous mixed suspension crystallizer are described and some fundamental design equations developed. Worked examples are given to indicate applications to problems of industrial interest.     

Analysis of Transient Crystal Size Distribution in a Continuous Sodium Chloride Crystallizer

This work deals with the transient analysis of crystal size distribution (CSD) in a continuous sodium chloride crystallizer. The crystallization is assumed to take place under diffusion controlled conditions and the crystal growth models reported by Sen Gupta and Dutta elsewhere have been used. Monte Carlo (MC) scheme has been employed for simulation purposes. The simulation results have been compared with the available experimental data at steady state.     

Influence of Various Parameters on Crystal Size Distribution from the Cascade of two Perfectly Mixed Tanks

The influence of properties of crystallizing substance and operation parameters of simplest, two-stage cascade of mixed tanks on crystal size distribution was examined. The mathematical model of cascade was formulated to this end. The relations found enabled to decide which parameters influence the CSD. Computations were performed then with the purpose to compare the CSD from cascade and CSD from single crystallizer with the same mean retention time as in cascade and with identical input values. These computations were performed for arbitrarily chosen, but met in practice values of physico-chemical constants of crystallizing substance and parameters of crystallizers performance. It was found that for a given set of input values optimal conditions of cascade performance could be found.     

Monte Carlo Simulation of Transient Crystal Size Distribution in a Continuous Crystallizer Using the ASL Model

A Monte Carlo simulation scheme is proposed for transient crystal size distribution in a continuous crystallizer to account for size-dependent growth rate. Crystal growth rates are described by Abegg , Stevens and Larson (ASL) model. The proposed model is used to predict the transient and steady state crystal size distribution from potassium carbonate crystallizer. The agreement between theory and available data confirms the validity of the model.     

Main Factors Influencing the Crystal Size Distribution from a Batch Cooling Crystallizer

An experimental investigation was carried out with a view to characterizing the influence of some typical operating factors on the size distribution of the crystal product obtained from a batch cooling crystallization. Reference was made to K₂SO₄ crystallizing from aqueous solutions, a system for which some data are available in the literature making possible some interesting comparisons. The obtained results indicate that a consistent improvement of the product size distribution can be achieved by limiting the stirring rate, by the use fo seeding, and by the presence of a draft-tube, in that order; little in-fluence seems to have the cooling medium temperature. Quite important is also the cooling policy adopted and in this sense a linear cooling curve lead to the best product quality.     

The Effect of Volume Shape Factor on the Crystal Size Distribution of Fragments due to Attrition

The effect of volume shape factor on crystal size distribution (CSD) is usually ignored to simplify the analysis of population balance equation. In the present work, the CSD of fragments generated from a mechanically stirred crystallizer as the result of attrition mechanism has been reported when the volume shape factor conforms to normal distribution. The physical model of GAHN and MERSMANN which relates the attrition resistance of a crystalline substances to its mechanical properties has been employed. The simulation of fragment size distribution was performed by Monte Carlo (MC) technique. The results are compared with those reported by GAHN and MERSMANN.     

不同表面活性剂对合成介孔氧化镁晶体性质的影响

采用液相法,以Mg(NO3)2·6H2O为镁源,NH3·H2O为沉淀剂,研究了不同表面活性剂对介孔MgO晶体性质的影响.采用XRD、FT-IR、SEM、BET和CO2-TPD等手段对介孔MgO晶相组成、骨架结构、微观形貌、孔结构及表面化学性质进行了分析表征.研究结果表明,不同表面活性剂对介孔MgO晶体物化性质影响较大.以非离子型PEG-2000为表面活性剂制得产品表面碱强度和碱总量均大于以阴离子型SDS、阳离子型CTAB制得的产品.以非离子型PEG-2000为表面活性剂制备得到的介孔MgO同时具有弱碱、中强碱特征,碱总量为0.192 mmol·g-1,比表面积、孔容和平均孔径分别为145.42 m2·g-1、0.67 cm3·g-1和18.56 nm.     

Size Distribution Analysis of Needle-Shaped Crystals

Two methods of measurement of the crystal size distribution of needle-shaped carystals are compared: direct measurement of a number of crystals on a microphotograph, which is rather tedious and time consuming, and the photosedimetric method which is quicker, easy to perform but not so suitable for not isometric crystals. A methods is described that brings results of both of these methods into agreement. The method has been verified on strongly anisometric particles of calcium sulphate.     

低压环境中外加氩气流对激光沉积纳米硅晶粒尺寸及分布的影响

采用脉冲激光沉积(PLD)技术,在烧蚀点正上方0.35 cm、距靶0.7 cm处引入Ar气流,保持环境气压0.3 Pa,烧蚀高阻抗单晶硅(Si)靶.在烧蚀点正下方0.35 cm,距靶0.5 cm、0.7 cm、1.4 cm、2.1 cm、2.8 cm、3.0 cm和3.5cm处水平放置衬底来收集纳米Si晶粒.利用原子力显微镜(AFM)、X射线衍射(XRD)、Raman散射对样品表面形貌和微观结构进行分析表征.结果表明:在引入气流前后,纳米Si晶粒的尺寸均随着与靶距离的增加而逐渐减小;在同一位置,引入气流比不引入气流晶粒尺寸小,面密度大;在3.0～3.5 cm处,不引入气流时的样品不再有纳米Si晶粒,而引入气流的还存在纳米Si晶粒.     

Influence of pH on the Crystal Size Distribution of Mg(OH)2 Prepared by the Hydration of MgO

The effect of pH and temperature of aqueous solution on hydration of MgO in a batch laboratory reactor was investigated. The experiments were carried out at the temperatures of 120 and 140 °C, pH of cool solution was changed from 10 to 13. It was found that even a small amount of added base substance influences remarkably the size of Mg(OH)₂ crystals. Increasing of pH of aqueous environment of causes the decrease of the size of crystals. The increase of the temperature increase dimensions (L₅₀) of crystals. This effect is more important at higher alkalinity of the solution.     

HVPE生长室气流分布模拟及GaCl载气流量对GaN单晶生长的影响

采用计算流体力学软件Fluent对HVPE反应室进行了数值模拟,研究了GaCl载气流量对HVPE反应室气流分布的影响,发现GaCl载气流量是影响GaCl和NH3在衬底上均匀分布的重要因素.采用HVPE方法在不同GaCl载气流量下生长GaN单晶,研究了GaCl载气流量对GaN单晶质量的影响,得到了与模拟一致的结果.     

KDP晶体缺陷对生长应力分布的影响

本文采用有限元法分析了不同尺寸、形状的晶体缺陷对大口径KDP晶体生长应力分布的影响.结果表明,晶体中的缺陷导致了晶体内部应力集中,且应力集中程度与缺陷尺寸、晶体生长尺寸呈反向变化,而最大主应力与缺陷尺寸、晶体生长尺寸呈正向变化.当缺陷含有棱边或尖角时,应力集中程度和最大主应力值都明显增加.由于KDP晶体易脆性开裂,随着最大主应力值的增大,开裂机率也增大.     

大尺寸单晶金刚石制备的研究进展

单晶金刚石在电学,光学方面有着良好的应用前景,已经成为金刚石领域的研究焦点之一.本文论述了大尺寸单晶金刚石的制备方法、生长条件、研究现状以及存在的缺陷,概述了制备单晶金刚石过程中出现的问题并针对部分问题提出改善措施.     

泡生法制备大尺寸蓝宝石单晶体

蓝宝石单晶作为光学材料在紫外、可见和红外波段有宽的透射带及高的透射率,与许多其它光学窗口材料相比,有更好的机械性能和物理性能,如高硬度、高拉伸强度、抗冲刷性、热导性、机械稳定性和显著的抗热冲击性能等。这些光学与机械性质的组合使蓝宝石材料被用于一系列高科技的光电应用中。刚玉单晶生长的高纯净、大尺寸化一直是科研工作者的研究方向。     

大尺寸高质量GaSb单晶研究

采用垂直布里奇曼法(VB法)生长2英寸GaSb单晶,分析了GaSb多晶产生的原因,即GaSb原料与覆盖剂中残留水分发生化学反应生成氧化镓残渣,残渣吸附在坩埚内壁导致GaSb多晶形成.通过增加覆盖剂除水工艺,成功生长出2英寸高质量GaSb单晶.此外,研究了单晶内部位错分布特点,结果显示GaSb晶体具有较低的位错密度,EPD≤500 cm-2;同时,对晶体进行XRD摇摆曲线测试,其FWHM值为27 arcsec,表明晶体质量较高;此外,对晶体进行了电学性能测试,结果显示制备的GaSb晶体呈P型导电,晶体迁移率为610 cm2/V·s,载流子浓度达到了1.68×1017cm-3.     

KDP晶体杂质对生长及出槽应力分布的影响

KDP晶体中的杂质易导致其开裂.本文采用有限元法分析了不同属性、尺寸、形状的晶体杂质对大尺寸KDP晶体生长及出槽应力分布的影响.结果表明,不同属性的杂质对晶体生长应力和出槽应力分布具有不同程度的影响.杂质附近的生长应力与杂质的弹性模量呈正向变化;杂质附近的出槽应力与杂质和晶体的热膨胀系数之差呈正向变化;杂质的尺寸越大,形状越尖锐,杂质附近的生长应力和出槽应力均增大.     

泡生法生长蓝宝石晶体中的气泡分布

气泡是蓝宝石晶体中的主要缺陷之一.本文中研究了采用泡生法生长蓝宝石晶体中气泡的俘获机理以及在晶体中的分布情况.研究结果表明气泡的分布与温场的结构相关,气泡产生的直接原因是结晶前沿较快的晶体生长速度.晶体中的气泡可以通过对生长速率的适当调整予以消除.     

大尺寸长波红外非线性晶体CdSe生长及应用

利用压力辅助法合成批量、高纯CdSe多晶原料,进行籽晶定向高压布里奇曼法生长,制备出φ(50 ～ 55) mm×(80 ～ 100) mm高品质单晶棒,加工出多相位匹配角度、多规格尺寸(6 ～8)2×(40 ～50) mm3晶体元件.元件在2.1 μm、2.6 μm、10.8 μm等多波段o、e偏振光测试下,吸收系数分别≤0.02 cm-1、≤0.02 cm-1、≤0.01 cm-1,通过光参量振荡实验,元件在10.1～10.8 μm波段实现1.05W长波红外激光输出.