The Study of KCSH Crystals Grown from Aqueous Solutions by Accelerated Technique

Crystallography Reports - Potassium cobalt sulfate hexahydrate (K2Co(SO4)2 · 6H2O, KCSH) crystals have been grown at a supersaturation σ in the range of 2–8.1%. The optimal...     

Study of the Growth Morphology of Ammonium Oxalate Monohydrate Crystals Obtained from Aqueous Solutions

The experimental results of the growth morphology of ammonium oxalate monohydrate [(NH₄)₂C₂O₄ · H₂O; AO] single crystals obtained from aqueous solutions at 30 and 40 °C and supersaturation up to 9% are presented. The observations are compared with the theoretical morphology predicted by PBC analysis and Braivais-Donnay-Harker law.     

An Experimental Study of the Recrystallization of Potash Alum Suspension in a Double Crystallizer

Experimental results of the development in time particle size distribution pertataining to a KAl(SO₄)₂ · 12 H₂O suspension being recrystallized at 25 °C in a laboratory double crystallizer are presented. The technique used represents a suitable means for studying the dependence of the intensity of recrystallization on experimental conditions, particularly on the frequency and amplitude of the temperature cycling, to which the suspension is exposed in the apparatus.     

Influence of Enhanced Gravitation on the Growth of Ammonium Oxalate Monohydrate Crystals from Aqueous Solutions

The growth behaviour of ammonium oxalate monohydrate crystals on seeds from aqueous solutions under terrestrial and enhanced gravity conditions has been investigated. It was found that all types of faces on the crystals revealed growth layers on them. The faces of the crystals obtained under both terrestrial and enhanced gravity conditions on seeds hung on nylon threads show cracks, trapped inclusions and macrospirals, while the faces of the crystals grown on seeds in fixed holders under enhanced gravity conditions are devoid of cracks, inclusions and macrospirals.     

Batch Precipitation of Calcium Sulphate

Results of the experiments with batch neutralisation of sulphuric acid with milk of lime have been used for calculation of the nucleation and growth rates and of the product crystal sizes of the calcium sulphate dihydrate. The procedure is based on the experimental values of calcium concentration in solution measured at various time intervals.     

Precipitation of Alkaline-earth Metal Hydroxoberyllate,Hydroxoaluminates and Allied Salts from Aqueous Solution: Ionic Equilibria,Crystalline Phases and Precipitation Mechanisms

The precipitations of alkaline-earth metal hydroxoberyllates and zincates, hydroxochromates (III), ferrates (III), aluminates and gallates, hydroxotitanates, zirconates and stannates (IV) and hydroxoantimonates (V) from different aqueous solutions are surveyed. The relevant ionic equilibria (hydroxoanion formation, precipitation of hydroxosalts, amphoteric metal hydroxides and alkaline-earth metal hydroxides) that may influence these precipitations are examined. The crystalline phases precipitated from different systems are tabulated and precipitation mechanisms are analysed.     

Effect of Supersaturation and Temperature on the Growth Morphology of Ammonium Oxalate Monohydrate Crystals Obtained from Aqueous Solutions

The experimental results of a study of the effect of supersaturation and temperature on the growth morphology of ammonium oxalate monohydrate [(NH₄)₂C₂O₄H₂O; AO] single crystals obtained from aqueous solutions at 30 and 40 °C and supersaturation up to 9% are presented. The observations are analysed in terms of theoretical morphology, growth models and attachment energy for growth units in steps of growing faces.     

Precipitation Rate of Calcium Sulphate Crystals

Results of experiments with continuous neutralisation of sulphuric acid with milk of lime have been used for the calculation of the nucleation and growth rates of calcium sulphate dihydrate. The treatment is based on experimental values of the mass of deposited crystals and of the supersaturation measured for varying experimental conditions. The data so obtained are compared with values published in the literature.     

The Effect of Nonelectrolyte Additives with Hydrophilic and Hydrophobic Hydration on the Growth of KDP Crystals from Aqueous Solutions

Crystallography Reports - The effect of nonelectrolyte additives with hydrophilic and hydrophobic hydration on the growth of potassium dihydrogen phosphate (KH2PO) crystals in the kinetic mode at...     

Structures of Complex Crystals of Alkylammonium Salts with Aromatic Molecules

Abstract

The complex crystal structures of dodecyltrimethylammonium chloride (DTAC) with catechol and hydroquinone were analysed by an X-ray diffraction method. Both complexes have isomorphous layered structures. The guest molecules locate between the interdigitated host molecules. Crystal structures are stabilized by mainly hydrogen bonds including water molecules. A cross-section balance between hydrophilic and hydrophobic parts is important for an energetically stable packing. DTAC can form the crystalline complexes with catechol and hydroquinone by both crystallizing from the solution and mixing host and guest powders in a mortar. In addition, DTAC can also make a complex with resorcinol. Powder diffraction pattern indicates that this complex has similar layered structure with complexes of DTAC / catechol and DTAC / hydroquinone. However, it is unstable in atmospheric condition.     

The Growth of KDP Crystals and its Mechanism by Splicing Misoriented in Aqueous Solution

The growing characteristics of splicing misoriented KDP seeds of both bulk and thin pieces were investigated. The chemical etching method was used to determine the prismatic and Z-plate surfaces of the crystals grown by splicing bulk KDP seeds. The X-ray Lang topography method was employed to measure original thin platy crystals grown by splicing thin pieces of KDP seeds. From the results it can be concluded that when the misorientation of two seeds on the Z-axis direction was about 1.5°, the crystal was grown successfully if the secondary capping was controlled properly. In comparison with the growth of splicing “parallel” seeds, the misorientation of both seeds increases such that the secondary capping becomes difficult, the sub-grain boundary stretches longer, the stress field around the secondary cap enlarges and the crystals grown crack easily.     

移动加热器法生长碲锌镉晶体的组分输运与界面形貌研究

移动加热器法(THM)生长碲锌镉晶体时,界面稳定性对晶体生长的质量有很大影响。本文基于多物理场有限元仿真软件Comsol建立了THM生长碲锌镉晶体的数值模拟模型,讨论了Te边界层与组分过冷区之间的关系,对不同生长阶段的物理场、Te边界层与组分过冷区进行仿真研究,最后讨论了微重力对物理场分布的影响,并对比了微重力与正常重力下的生长界面形貌。模拟结果表明,Te边界层与组分过冷区的分布趋势是一致的,在不同生长阶段,流场中次生涡旋的位置会发生移动,从而导致生长界面的形貌随着生长的进行发生变化,同时微重力条件下形成的生长界面形貌最有利于单晶生长。因此,在晶体生长的中前期,对次生涡旋位置的控制和对组分过冷的削弱,是THM生长高质量晶体的有效方案。     

Growth from Solutions and Surface Properties of Anthracene Crystals

Crystallography Reports - The influence of different solvents on the growth of anthracene crystals from solutions and on their morphological quality has been investigated. The dependence of the...     

The Catalysed and Uncatalysed Nucleation of Gypsum Crystals from Aqueous Solution

Gypsum (Calcium Sulphate Dihydrate) has been precipitated by mixing aqueous solutions of calcium chloride, sodium sulphate and sodium chloride at 25°C. In the absence of solid gypsum, classical nucleation theory predicts rates reasonably well only at the expense of some adjustable parameters like surface energy term. This has been attributed to the difficulties associated with the application of equilibrium thermodynamics to a process of kinetic origin. The presence of solid matter acts as a catalyst and decreases the induction period. In this case, the habit as well as the quantity of gypsum added greatly influences the induction period. Possible reasons for this have been given.     

一些溶液法生长的晶体非平衡枝状形貌及其对称性分类

本文基于一些简单的溶液法晶体生长实验及观察,对非平衡枝状晶体形貌进行了对称性探讨,并提出一种依据晶体的对称性对非平衡形貌进行分类的方案,即:形貌具各向异性且完全受晶体本身的对称性控制,称枝晶;形貌总体具各向同性但局部具各向异性,这种局部各向异性与晶体本身的对称不完全一样,但与晶体本身对称有关,称枝蔓晶;形貌具各向同性,不受晶体本身的对称控制,称密枝(或球粒晶).这一分类方案对进一步认清非平衡枝状形貌的本质特征、规范一些形貌术语有重要意义.     

Synthesis of Submicron Silicalite‐1 Crystals from Clear Solutions

Discrete and monodisperse submicron crystals of silicalite‐1 with a mean size of 0.3 μ m were synthesized from clear crystallization solutions. The effects of silica content, alkalinity of batch and the nature of silica source on the product yield, crystal morphology and particle size distribution were investigated. The crystal shape was sphere‐like or hexagonal twinned disks when silicic acid was the silica source. Change of silica source to sodium silicate solution leads to the formation of rounded‐edged‐hexahedron crystals. Silica content of batch does not influence crystal morphology. Alkalinity of clear crystallization solution has a strong effect both on the particle size distribution and yield of product. Increase of alkalinity caused bimodal particle size distribution and decrease of yield.     

常压混合碱液条件下ZnO单晶生长习性的研究

采用常压混合碱液法,以NaOH、LiOH和H2O的混合碱液作助熔剂,重复生长了无色透明的六方片状、六方柱状和带六方双锥的完整单晶.经X射线衍射确认所生长的晶体均为六方纤锌矿型ZnO.实验表明,生长体系中NaOH与LiOH的物质的量比及ZnO的物质的量分数都对晶体的形貌有明显影响.NaOH与LiOH物质的量比为10:1、ZnO物质的量分数为0.077时,获得ZnO晶体的尺寸、透明度为最佳.     

Precipitation of Alkaline-Earth Metal Silicate Hydrates from Aqueous Solution: Ionic Equilibria,Crystalline Phases and Precipitation Mechanisms

The precipitations of magnesium, calcium, strontium, barium and zinc silicate hydrates from aqueous solutions and suspensions at ambient temperature to 200 °C are surveyed. The relevant ionic equilibria (silicate and polysilicate anion formation, hydroxocation formation, alkaline-earth metal silicate hydrate and hydroxide precipitation from supersaturated solution) that may influence these precipitations are examined. - The microcrystalline and crystalline phases precipitated in systems of different cation/silicate compositions and temperatures are tabulated. Precipitation mechanisms are analysed.