氟化钙单晶炉温场的计算机模拟及改进

对氟化钙晶体生长炉的顶部保温、加热器和下保温装置进行了改进研究.结合数值模拟,对改进前后晶体的轴向温度梯度、径向温度梯度和固液界面附近温度分布进行了对比分析.模拟结果表明,改进了顶部保温后增加了晶体炉内的辐射传热,有效降低了温度梯度,减小了晶体内热应力从而避免了晶体开裂;对加热器和底部保温进行改进后,减少了坩埚底部的热损失,相同温度时降低了加热功率.     

泡生法生长蓝宝石晶体中固液界面形状的数值模拟研究

在泡生法蓝宝石单晶生长中,固液界面形状对晶体生长质量影响极大.本文针对泡生法蓝宝石晶体生长进行数值模拟,研究了晶体半透明性、放肩角、底部钼屏保温层厚度、加热器侧部和底部功率分配比等对固液界面形状的影响.模拟结果发现:不考虑蓝宝石晶体的半透明性,则固液界面凹向熔体生长,反之则固液界面凸向熔体生长;放肩角增大、底部钼屏保温层增厚,都造成固液界面凸度减小;加热器侧部与底部的功率比增大,则固液界面凸度增大.实际的固液界面形状取决于多种参数的综合作用.     

晶体对热辐射的吸收对晶体生长的影响

本文综述了晶体对熔体热辐射吸收对晶体生长的影响,包括对热腔热耗散的影响;对晶体生长温度时间特性的影响;对液流形态和固液界面形状的影响;对晶体界面反转的影响;对晶体中温度分布和应力分布的影响.     

泡生法蓝宝石单晶不同生长阶段的数值模拟研究

针对泡生法蓝宝石单晶生长的不同生长阶段的温场、流场和固液界面形状进行数值模拟研究.并分析了加热器相对坩埚的轴向位置和不同生长速率对蓝宝石单晶生长的影响.结果表明:在蓝宝石单晶生长中,在靠近坩埚壁面和固液界面的熔体内,等温线密,温度梯度较大;在靠近坩埚底部的熔体内,等温线稀疏,温度梯度较小.随着晶体高度的增加,熔体对流由放肩阶段的两个涡胞变成等径阶段的一个涡胞,熔体平均温度有小幅度下降;加热器相对坩埚的轴向位置对晶体生长炉内温场和固液界面形状影响很大,随着加热器位置上移,晶体内平均温度升高,温度梯度减小;熔体内平均温度降低,温度梯度增大.同时固液界面凸度增大.随着晶体生长速率增大,固液界面凸度增大,界面更加凸向熔体.     

改进热交换法生长蓝宝石晶体的气泡研究

采用改进的热交换法生长的蓝宝石晶体,气泡是其主要缺陷之一.本文采用数值模拟研究了晶体生长过程中氦气流量对坩埚内温场、固液界面形状的影响.并结合晶体生长实验结果,分析了在实际的晶体生长过程中,氦气流量的线性增加对晶体内气泡的尺寸、形态和分布的影响.     

液面位置对φ300mm硅单晶固液界面形状影响的数值计算

数值模拟技术已经成为分析和优化工业化晶体生长工艺必不可少的工具.本文利用有限元分析软件计算了φ300 mm直拉硅单晶生长过程中,不同液面位置时的晶体固液界面形状,模拟计算考虑了热传导、辐射、气流等物理现象,分析了晶体长度和液面位置对晶体生长界面形状的影响,得出了随着晶体长度的增加固液界面的凸度会增大的规律.     

液面位置对Ф300mm硅单晶固液界面形状影响的数值计算

数值模拟技术已经成为分析和优化工业化晶体生长工艺必不可少的工具。本文利用有限元分析软件计算了Ф300mm直拉硅单晶生长过程中,不同液面位置时的晶体固液界面形状,模拟计算考虑了热传导、辐射、气流等物理现象,分析了晶体长度和液面位置对晶体生长界面形状的影响,得出了随着晶体长度的增加固液界面的凸度会增大的规律。     

热屏间距对泡生法蓝宝石单晶生长影响研究

太空、军事和科研等高科技领域的持续发展极大促进了对蓝宝石晶体的需求,泡生法是蓝宝石晶体的主要制造方法之一;热场结构对所得蓝宝石晶体的质量具有重要影响.本文对采用泡生法工艺制造蓝宝石单晶过程中,具有内置7层氧化锆外置8层钼金属的新型热屏结构间距进行研究.通过数值模拟考察热屏间距对单晶炉功率、固-液界面形状和晶体热应力的影响确定了合理的热场结构;并与试验生产结果进行对比验证.结果表明:热屏间距增大使得单晶炉功率明显提升,并引起固-液界面凸度增大;而蓝宝石晶体热应力出现减小.综合考察三个影响因素的影响,最后确定热屏间距为5 mm时单晶炉能耗较低,可用于制造高质量的蓝宝石晶体.     

热交换法蓝宝石晶体生长的数值模拟研究

针对热交换法蓝宝石晶体各生长阶段的温场、流场和热应力进行数值模拟研究,并讨论了上部保温层结构、热交换器内管高度对晶体生长的影响.结果表明:长晶初期,固液界面呈椭球形;等径阶段,固液界面平坦,晶体与坩埚壁不接触;长晶后期,中心轴向晶体生长速率增加,晶体中心首先冒出熔体液面.随晶体高度增加,熔体对流由初期的两个涡胞变为等径阶段的一个涡胞,最大对流速度量级为10-3 m/s.晶体中最大热应力分布在晶体底部,热应力分布呈W型.增加炉体上部保温层,长晶后期固液界面变得平坦;降低热交换器内管高度,有利于降低晶体底部热应力.     

旋转对Cz法硅晶生长过程中热输运和熔体流动影响的数值模拟

建立了一个120 kg单晶炉的二维轴对称全局模型,分别对无旋转、加入晶体旋转、加入坩埚旋转、同时加入晶体旋转和坩埚旋转的四种工况展开了数值模拟研究.得到了晶体旋转及坩埚旋转对晶体生长过程的拉晶功率、炉内温度分布和熔体流动的影响;得到了不同晶体长度下拉晶炉内的温度分布以及熔体流动的变化规律.结果显示,加入晶体旋转对晶体生长过程的拉晶功率、温度分布和熔体流动的影响小于坩埚旋转的影响;随着晶体长度的增加,晶体旋转及坩埚旋转对温度分布和熔体流动的影响不断减小.因此在单晶炉设计和优化过程中应考虑整个晶体生长过程.     

Modelling of mechanism of agglomeration of KCl crystallization

The article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

Velocities of Disappearance and Lifetime of Faces of Growing Crystals

The formulae for absolute R_disap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity R_A/R_critA of the vanishing face A with respect to the critical growth velocity R_critA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in R_A/R_critA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.