电光晶体硒酸氢铷(RHSe)的生长动力学

本文采用动态循环观察法测量了RHSe晶体在水溶液中不同过饱和度下主要显露晶面的生长速率.结果表明,RHSe晶体主要显露晶面的生长机制是多二维成核生长机制,在饱和点为38.00℃的溶液中,RHSe晶体的{111}和{101}晶面的临界过饱和度分别为1.01;和1.16;.实验过程中还发现,当过饱和度大于1.76;时,晶体生长速率太快而出现宏观缺陷,因而在生长RHSe单晶时,过饱和度应控制在1.76;以下.     

过饱和度对KDP晶体生长与光学性能的影响研究

在不同过饱和度的溶液中生长了KDP晶体,对生长晶体的透过率,光散射和激光损伤阈值进行了表征.研究了不同过饱和度对KDP晶体生长及光学性能的影响.实验表明:KDP晶体可以在高过饱和度(σ＞3;)溶液中实现快速生长,生长速度可大于10 mm/d;但随着溶液过饱和度的增加,KDP晶体生长溶液的稳定性降低,晶体容易出现包藏、开裂和添晶等缺陷,晶体的光学性能也随之降低.     

Fe3+对KDP晶体生长影响的研究

金属离子对KDP晶体的影响是多方面的.本文采用不同的过饱和度,在不同的Fe3+掺杂浓度的生长溶液中生长KDP晶体,定量地研究了Fe3+对KDP晶体生长的影响.实验发现,无论是在高过饱和度还是在低过饱和度下生长KDP晶体,在一定的浓度范围内,Fe3+的掺入既可以增加生长溶液的稳定性,又可以有效抑制晶体柱面的扩展,而且晶体基本不楔化,同时,对晶体光学性能的影响也不大.     

溶剂对有机非线性光学晶体NPAN生长习性的影响

本文测定了有机晶体N-(4-硝基苯)-N-甲基-2-氨基乙腈(简称NPAN)在某些醇和酮有机溶剂中的溶解度,研究了NPAN在这些有机溶剂中的溶液热力学性质、溶质与溶剂的相互作用以及溶剂对NPAN结晶习性的影响.根据界面熵因子α值,预测了NPAN晶体在不同溶剂中低指数晶面的晶体生长机制.选择丁酮为生长溶剂,进行单晶生长实验.在35～25℃温度区间内,用溶液降温法在较高过饱和度下成功地培养出尺寸为37×7.0×7.0 mm3的棱柱状透明单晶,所得晶体的外形与预测的结果相吻合.     

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.     

KDP晶体中包裹体形成机制的探讨

本文介绍了包裹体对KDP晶体质量的影响,并从两个方面探讨了KDP晶体生长过程中包裹体的形成机制.通过分析KDP晶体表面原子结构研究了不同杂质的吸附情况以及杂质对生长台阶的阻碍作用,通过分析晶体生长过程中流体动力学和质量输运条件的变化研究了旋转晶体的流体切应力和表面过饱和度,结果表明吸附杂质对生长台阶的阻碍和表面过饱和度的不均匀造成了生长台阶的弯曲和宏观台阶的形成,导致生长台阶形貌的不稳定是包裹体形成的重要原因.     

负离子配位多面体生长基元的理论模型与晶粒形貌

本文介绍了一种新的形貌判定准则--配位多面体生长习性法则.首先在负离子配位多面体生长基元模型的基础上建立了晶体的生长机理模型和界面模型,在此基础上提出了晶体形貌判定法则.即晶体的各晶面的生长速度与其结构中的配位多面体在界面上显露的元素种类有关.显露配位多面体顶点的晶面生长速度快,显露面的晶面生长速度慢,显露棱的晶面生长速度介于两者之间.此外,晶体的各晶面的生长速度还与配位多面体在界面上显露的元素数目有关.显露配位多面体元素数目多的晶面生长速度快.根据此法则成功地解释了γ-AlO(OH)晶体和极性晶体ZnO,SiO2的形貌特征.最后,本文还提出了两种晶体形貌的调制方法,即添加剂调制法和过饱和度调制法.成功地调制了ZnO晶体的形貌.     

旋转半径对KDP晶体生长过程影响的数值模拟研究

相比传统KDP晶体同心旋转的生长方式,本文利用数值模拟的方法,针对不同旋转半径和不同籽晶摆放方式对KDP晶体生长过程中溶液流动和物质输运的影响进行研究,以寻找提高晶体表面过饱和度及其均匀性的方法.计算结果表明:随着旋转半径从0 cm增大到3 cm,晶面时均过饱和度整体也逐渐增大,柱面平均均方差逐渐减小,锥面平均均方差先增大后减小;当晶体摆放方式采用棱边迎流时,晶体表面时均过饱和度相比柱面迎流略有下降,但其平均均方差最小,有利于减少包裹体的产生.     

晶体生长机制和生长动力学的蒙特卡罗模拟研究

采用动力学蒙特卡罗方法,对在完整光滑界面上低过饱和度溶液中的晶体生长机制和动态过程进行计算机模拟,得到了晶体生长速率与溶液过饱和度之间的关系以及晶体生长的表面形态.对以二维成核为主要生长机制的动力学生长规律进行分析,发现了二维成核生长的生长死区以及单核生长转变为多核生长时的过饱和度临界值,讨论了热粗糙度、表面扩散、台阶平均高度以及表面尺寸对晶体平均生长速率的影响.     

祖母绿晶体水热生长习性研究

本文研究了在水热条件下祖母绿晶体的生长习性,指出了祖母绿晶面的发育顺序,并用负离子配位多面体生长基元理论进行了解释,根据对晶体的不同用途结合晶体生长习性采用不同的籽晶切型,生长出了符合特殊形态要求的祖母绿晶体.     

Wachstum von Graphitkristallen in kohlenstoffhaltigen Eisenschmelzen bei höheren Überschreitungen

The rates of growth for the basic and the prismatic faces of graphite crystals are calculated in dependence of the supersaturation on the assumption that the faces at high supersaturations grow by twodimensional nucleation from an iron-carbon melt. Near the thermodynamic equilibrium prismatic faces grow more quickly than basic faces. At high supersaturations the ratio of the growth rate is reversed. The results are suitable to explain the different kinds of graphite crystals in cast iron.     

一水甲酸锂单晶生长和(110)面边界层的全息研究

本文合成一水甲酸锂原料,选择适宜生长条件,用水溶液法培育出完美一水甲酸锂单晶(LFM).利用全息相衬干涉显微术对(110)面边界层特性进行实时观测和研究.实验表明,在自然对流情况下,边界层内折射率梯度分布函数Δn(x)和浓度分布函数Cx(x)为指数形式;另外,体过饱和度与晶面过饱和度之间呈指数关系.     

On the theory of two-dimensional nucleation on a structureless substrate. Effect of supersaturation

The work of formation of two-dimensional nuclei of the (100), (110), and (111) faces of crystal with simple cubic lattice on a structureless substrate was calculated. The simplification of the equilibrium form with increasing supersaturation was taken into consideration. At low supersaturations the formation of nuclei of the (100) face alone is possible. With increasing supersaturation the appearance of two-dimensional nuclei of the other two faces becomes possible. The probability of their formation increases but never exceeds the probability of the formation of two-dimensional nuclei of the (100) face. There exists a limiting supersaturation above which the work of formation of two-dimensional nuclei of the three kinds of faces becomes equal to zero.     

Polyhedral stability ‐ on the growth of flat crystal faces on small molecule and protein crystals

The old standing problem of face morphology is discussed. A special emphasis is put on the macroscopically flat faces, appearing on small molecule crystals mostly during calm growth, under low supersaturations. As distinct, protein crystals are growing with macroscopically flat faces even under surprisingly high supersaturations. Explanations of these facts are suggested by considering the surface micro‐profile of crystal faces which growth is driven by screw dislocations. It is shown that, due to kinetic reasons, the tips of the growth hillocks and the valley between them have to be levelled to some extent (at least on a quasi‐atomic scale) under low enough supersaturations. The amplitude of the surface roughness has to be suppressed also due to the surface energy gain, especially under quasi‐equilibrium. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A stability diagram for crystal growth from the vapor – a review

Stability of the solid‐vapor interface is investigated. Surface roughening and evolution of flat faces at the growth interface is considered in terms of relation between gradient of temperature in the crystal and gradient of concentration in the vapor. Stability diagram is proposed, based on experimental data. The diagram summarizes the various forms and structures, which can be obtained using a typical system for growth from the vapor. The critical lines for constitutional supersaturation and appearance of low and high index faces were plotted. This attempt to the problem of stability of the growth interface differs from the former investigations mainly in looking for dependence between temperature field and concentration field rather than between more absolute parameters like temperature and supersaturation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

一水甲酸锂晶体生长动力学和生长机理的研究

本文实时测定了312.16K时一水甲酸锂晶体(LFM)(010)和(021)面的生长速率。根据Bennema修正的用于水溶液晶体生长的BCF表面扩散模型,计算了晶体生长过程的激活能以及动力学系数。结果表明LFM晶体生长主要是表面扩散控制的螺位错生长机制。     

On the Formation of Dislocation Hollow Cores on Cleaved {100} Faces of L-Arginine Phosphate Monohydrate Single Crystals

Thermodynamic conditions and energy considerations for the formation of hollow cores at the emergence points of monolayer cleavage steps associated with screw dislocations on the cleaved {100} faces of LAP single crystals are discussed. Analysis of the formation of hollow cores and the change of the curvature of steps in the vicinity of their origins reveals that dislocations responsible for the origin of hollow cores have stress fields due to trapped mother liquor of different supersaturations. The results also show that (1) the radius of a hollow core is inversely proportional to the one-third power of the interface supersaturation while the volume of hollow corés increases exponentially with their radius, and that (2) the strain energy associated with a dislocation is responsible for the formation of an equilibrium hollow core of a particular depth at the origins of cleavage steps associated with dislocations.     

On the kinetic of crystallization of zinc oxalate (II). Determination of the specific surface energy at the crystal solution interface by kinetic studies

An apparatus based on turbidimetry was constructed for studying the kinetics of crystallization of sparingly soluble salts. The kinetics of crystallization of zinc oxalate was investigated at various supersaturations and pHs of the medium. The specific surface energy at the crystal-solution interface was determined from the induction periods of the S-shaped curves by means of the classical theory of nucleation. The calculations were made using the slope of the logarithmic dependence of I or τ, respectively, on supersaturation (equations 1 and 2) and the critical supersaturation which was also determined on the basis of kinetic data. Various values of σ were found for the different supersaturations. Different values for this quantity were also obtained when supersaturation was presented by the concentration ratio (S = C/C₀) or by the ratio of the product of the two ions concentrations in the supersaturated solution to that in the saturated one (S = ab/L_p). These σ values were lower than those obtained using the critical supersaturations at the two different solution pHs. For the present it is impossible to give a definite explanation of the results obtained. The experiments for determining the specific surface energy at the crystal-solution interface will be continued.     

Various Growth Shapes of Na2S2O3 5H2O Crystals

The relation between the growth shapes and supersaturations and/or supercoolings was investigated in the Na₂S₂O₃ 5H₂O crystals: (i) The growth shapes changed from a hexagonal prismatic crystal, aggregate of platy crystals and to a spherulite with an increase of supersaturations and/or supercooloings. (ii) The deposition rate suddenly increased at a certain supersaturation and/or supercooling, where the growth shape changed from the hexagonal prism to the aggregate of platy crystals. (iii) The deposition rates of spherulites become higher with increasing the solute concentrations. (iv) The formation process of the spherulites were in situ observed by the Schlieren and/or Mach‐zehnder interferometer methods.     

Growth morphology of potassium bichromate crystals from aqueous solutions

The results of a systematic study of growth morphology of potassium bichromate single crystals on seeds and by self-nucleation at different temperatures and supersaturations are presented. The observed growth morphology is analysed in the light of theoretical predictions. An increase in both growth temperature and supersaturation leads to a symmetrical morphology, and the transition from asymmetrical to symmetrical morphology is monotonous. The predicted sequence of morphological importance agrees only in the case of crystals grown at low temperatures and supersaturations.