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.     

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.     

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.     

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.     

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.     

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.     

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。     

Dynamic Scattering and Material Flow in a Nematic Liquid Crystal

Results are presented which show how defects in a nematic liquid crystal can be used to investigate material flow when external electric fields are applied. These results include measurements of the size of flow cells, which were created between the electrodes by an electric field. The electrodes, which were made of transparent conductive coated glass, were placed in a vertical position so that flow cells could be observed from the top while dynamic scattering was observed when viewing normal to the electrodes.     

Crystal Growth in Gel: Nuclei and Precipitation Distribution in Gel

The investigation of the gel structure and properties influence upon the crystallization processes have been carried out and are reported in this paper. The gel acidity and nucleation centers distribution are chosen as the parameters describing this process. The analytical approximations for the nucleation and precipitation density along the gel column are proposed. It has been shown that in the view of the parameters chosen it is impossible separately to determine the gel structure and proton concentration effects on crystallization processes.     

Studies of Morphology and Size of Calcium Carbonate Crystals Nucleating on Surfaces of Various Materials

Crystallography Reports - The effects of material surface characteristics on the morphology and size of calcium carbonate crystals nucleating under cold wall pipe flow conditions were studied. We...     

Conformational Behavior of N1-(Diphenylphosphoryl)acetyl-N4-phenyl-thiosemicarbazide in Various Crystal Environments

Crystallography Reports - Three crystal modifications of phenyl-substituted diphenylphosphoryl thiosemicarbazide (compound (1) and two its solvates with dimethyl sulfoxide (2, 3)) have been...     

大尺寸优质声光晶体TeO2的生长

采用坩埚下降法生长了二氧化碲(TeO2)声光晶体,从原料角度分析了散射、云雾状云层等缺陷的形成,研究了晶体开裂和晶体结构的关系,从而确定了晶体生长最佳工艺条件为生长速率<0.6mm/h,固液界面的温度梯度约为45°C/cm,沿<110>方向生长可减少开裂.获得了尺寸大于55×55×120mm3的优质TeO2晶体,并测试了晶体的性能.     

KRS-5 Crystal Growth in Various Ambient Gases and Polycrystalline Fiber Preparation by an Extrusion Method

KRS-5 single crystals have been grown in three kinds of ambient gases: air, Ar, and Ar + I². The scattering centers in crystals were inspected and the metal impurities and oxygen content of the crystals were analysed. The polycrystalline fibers with 0.5–1 mm in diameter have been prepared by an extrusion method. The stability and attenuation of the fiber are discussed.     

Study of the Concentration Distribution of SiC Vapour in the Crystal Growth Zone

In the present work the gas dynamics in the growth zone of SiC crystals is investigated. It is shown that the propagation of SiC vapour from the growth cavity walls towards the lids is effected by diffusion. On this basis the calculation of the concentration distribution of SiC vapour (n), the equilibrium vapour concentration (n_s), and the supersaturation $ \left({\alpha {\rm = }\frac{{n - n_{\rm s} }}{{n_{\rm s} }} \cdot {\rm 100\%}} \right) $ in the crystal growth zone at different radial and axial temperature gradients is carried out by solving the Laplace equation in cylindrical coordinates for a stationary case corresponding to the conditions of crystal growth. The received results are compared with the available experimental data which gives a possibility for explaining some of the observed peculiarities during SiC crystal growth from the vapour phase by the sublimation method.     

Study of Formation,Phase Behavior,and Microdroplet Size of a Polyurethane-based Polymer-dispersed Liquid Crystal

Using calorimetry and scanning electron microscopy, we have investigated the formation process and phase behavior of a polyurethane-based polymer-dispersed liquid crystal system. We have measured the kinetics and energetics of the cure process during which liquid crystal microdroplets form by phase separation from the matrix as it cross-links. The greatest degree of cure occurs for samples cured at 375 K. For a given cure temperature, the heat of cure decreases more or less linearly with increasing liquid crystal concentration due to a dilution effect. The time constant for the cure process decreases rapidly with increasing temperature but is much less sensitive to liquid crystal content.

Samples cured below 375 K are apparently not fully phase separated, but subsequent treatment at higher temperatures evidently increases the degree of cure. The highest nematic-isotropic transition temperatures were achieved for liquid crystal concentrations above 40 volume percent. The nematic isotropic transition enthalpy, ΔH_NI, is a measure of the amount of liquid crystal contained in the microdroplets. A model has been developed which explains the linear increase of ΔH_NI with increasing liquid crystal concentration.

Optimum microdroplet formation occurs at 375 K, but only for liquid crystal concentrations below about 53 volume percent. At higher concentrations a reversed phase (“polymer ball”) morphology is seen. For the lower concentrations droplet size increases linearly with LC content. Droplet number density decreases with increasing droplet size in rough agreement with a simple model.