Analysis Of Crystallization Process Research Articles

Entropic analysis of a batch-crystallization process

The analysis of crystallization processes considering an entropic perspective is the primary purpose of this paper. Although the modeling of crystallization processes is well established in the literature, the entropic representation of these processes still needs to be studied. The modeling considering the second law of thermodynamics was investigated, which resulted in a model that represents the entropy production rate of a batch-crystallization process. The results indicate that the entropy production of the batch cooling crystallization is related to the variability of the crystal size distribution. The model of the entropy production rate could be used as a restriction criterion for multi-objective optimization of the cooling temperature profile of a batch crystallizer to improve the quality of the crystal size distribution of the final product.

Functioned carbon nanotube templated hierarchical Silicate-1 synthesis: On the existence of super-micropore

In present study, the functioned carbon nanotube was used as secondary template for hierarchical Silicate-1 synthesis. Special attentions were paid to the existence of super-micropore (1–2 nm) and additional hysteresis loop between 0.1 and 0.2 in nitrogen adsorption isotherms of the synthesized samples. The main findings of present study are: (1) Silicate-1 with additional mesoporosity can be synthesized with functioned carbon nanotube as secondary template through impregnation or direct hydrothermal synthesis method. The functional group in carbon nanotube doesn't influence the crystallization process with impregnation method but have large influence in direct hydrothermal synthesis method; (2) With typical subsequently impregnation method, no hysteresis loop between 0.1 and 0.2 was found in the nitrogen adsorption isotherms of samples. And the single wall carbon nanotube penetrated the zeolite crystal as a bundle other than separate nanotube with size range in 1–2 nm, (3) In zeolite samples synthesized with direct hydrothermal method, additional hysteresis loop was found in several samples. However, SEM and crystallization process analysis indicated that the hysteresis loop was more likely due to the large crystal size other than the existence of any real pores.

Crystallization in glass-forming liquids: Effects of fragility and glass transition temperature

The relevance of the concepts of fragility, m, of the liquid and of the reduced glass transition temperature, Tg/Tm (Tg: glass-transition temperature, Tm: melting or liquidus temperature) for the understanding of crystal nucleation and growth in glass-forming liquids is explored. Based on the analysis of crystallization processes in glass-forming melts, it is shown that classical fragility can be relevant for the understanding of the crystallization behavior only if several severe conditions are fulfilled that are rarely met. By this reason, a new definition of liquid fragility is introduced. This new definition does not involve the commonly utilized temperature ratio Tg/T (T: actual temperature). Instead, we employ the reduced variable Tm/T and do not restrict the computation of m to the glass transition temperature, Tg, as in the standard approach. Moreover, we specify the fragility index by computing it for the temperature appropriate for the particular kinetic process being analyzed. With this modified definition of fragility applied to both the diffusion coefficient controlling crystallization and viscosity, fragility becomes one of the main factors determining the temperatures and magnitudes of the maxima of nucleation, growth, and overall crystallization rates. In addition, the origin of the previously reported correlations between reduced glass transition temperatures and intensity of crystallization processes is specified.

The Temperature Control of the Preheating Tank in the Procedure of Chloroacetic Acid’s Crystallization

Based on detailed analysis of crystal process in Chloroacetic Acid (MCA)’s production, a certain control method is exert on it. In order to overcome the time delay ,large inertia, time-varying ,a fuzzy Smith intelligent method is proposed.Simulation results show that this method apparently is superior to the general PID control and Smith control.

Kinetics of Crystallization of Co-Based Multi-Component Amorphous Alloy

Abstract Crystallization is a thermally activated process in non-crystalline and amorphous solids. The kinetics of the solid state phase transformations can be studied using thermal analysis techniques such as differential scanning calorimetry (DSC). For the kinetic analysis of the crystallization process under non-isothermal conditions, the choice of a reliable method is very important. The methods for the analysis of non-isothermal data are, in general, derived by extending the formalism developed for isothermal conditions. Most methods for the kinetic analysis of crystallization processes rely on the isokinetic hypothesis to separate the kinetics of the transformation from its dependence on temperature. It is assumed that the transformation rate can be described by a differential equation separable in α (transformed fraction) and T (temperature), i.e., for continuous heating regime, (dα/dT)=(1/β)k(T)f(α), where β is the heating rate, k(T) is the rate constant, and f(α) is the kinetic function (reaction model). The crystallization kinetics of glassy Co66Si16B12Fe4Mo2 have been studied with DSC and analyzed using non-isothermal theoretical expressions. The Avrami exponent, (n), frequency factor, (A), and activation energy, (E), of crystallization are evaluated using Matusita and Sakka (MS) and modified Kissinger equations. Besides, isoconversional kinetic analysis has been applied to DSC data for the determination of these different kinetic parameters. The isoconversional methods calculate Eα values at progressive degrees of conversion, α, without modelistic assumptions, and hence, this approach takes care of the variation of kinetic parameters with the fraction crystallized. The activation energy has been determined using both linear integral and differential isoconversional methods and also by the non-linear isoconversional method suggested by Vyazovkin and Wight. These methods are found to give consistent results for E. Furthermore, a comparison has been made among various kinetic parameters obtained using different approaches to investigate the relative applicability and usefulness of the proposed methods.

CW Argon-ion Laser Crystallization of a-Si:H Thin Films

ABSTRACTThin a-Si:H films, with a thickness of 1 µm, with different hydrogen concentrations, prepared by hot wire deposition were crystallized by 514.5 nm cw Ar ion laser radiation, with a power density between 150 and 270 kW/cm2. The crystallization was continuously monitored by Raman spectroscopy for exposures up to hours. The analysis of crystallization process using Johnson-Mehl phenomenological equations showed an apparent crystallization energy of around 0.5 eV and low dimensional crystal growth. The mean value of the crystal size decreases with increasing irradiation energy and initial hydrogen content and varies between 3 and 6 nm.

Integrated System for Design and Analysis of Separation Processes with Electrolyte Systems

A thermodynamic insights based algorithm for integrated design and analysis of crystallization processes with electrolyte systems is presented. This algorithm consists of a thermodynamic calculation part, a process design/analysis part and a process simulation part, which are integrated through a calculation engine. The main feature of the algorithm is the use of thermodynamic insights, not only to identify and generate the feasible process alternatives, but also to obtain good initial estimates for the process simulation part, and for visualization of process synthesis/design. The main steps of the integrated system are illustrated through two case studies where one represents an industrial crystallization process.

Integrated system for design and analysis of industrial processes with electrolyte system

An algorithm for design and analysis of crystallization processes with electrolyte systems is presented. This algorithm consists of a thermodynamic part, a synthesis part and a design part. The three parts are integrated through a simulation engine. The main features of the algorithm is the use of thermodynamic insights not only to generate process alternatives but also to obtain good initial estimates for the simulation engine and for visualization of process synthesis/design. The main steps of the algorithm are highlighted through a case study involving an industrial crystallization process.

The numerical micro/macro model of solidification process

Copyright (c) 1997 Elsevier Science S.A. All rights reserved. In the paper the problems connected with numerical modelling of the solidification and cooling processes in a system casting-mould are discussed. The task is treated as a boundary-initial problem in which the crystallization process (in micro scale) is taken into account, in other words the component describing a capacity of internal heat sources in adequate energy equation results from the analysis of crystallization process on a microscopic level. The mathematical model of crystallization process was constructed on a basis of the theory given by Kolmogorov. The number of nuclei and also their temporary dimensions (i.e. crystallization model) result from the local values of undercooling below the equilibrium temperature [1,2,3. Such approach is widely knownn− but the numerical procedures worked out by the authors make possible to follow the vicissitudes of successive grains generations and it is a new element in mathematical modelling of crystallization process. Numerical solution of the boundary-initial problem discussed has been obtained on the basis of the Boundary Element Method. It is well known that this method assures a relatively good approximation of geometrical and boundary conditions. In the case of solidification process modelling this advantage is very essential because of the great values of temperature gradients near the casting-mould contact surface. As an example the tasks concerning the aluminium plate solidifying in the typical sand moulds will be presented, at the same time it is possible (in a simple way) to widen the algorithm in the direction ofn2D or 3Dnproblems and more complex materials (e.g. binary alloys).

Mössbauer analysis of crystallization processes in iron-soda-lime-silicate glasses

57Fe Mossbauer spectroscopy was used to observe the crystallization process in glasses with composition denoted by [0.50SiO2, 0.45Na2O, 0.05CaO]100-x(Fe2O3)x with x equal to 4, 10 and 16 mol%. It is shown that Mossbauer spectroscopy is a very suitable technique for detecting and checking the very early stages of crystallite formation in amorphous materials. The crystallization process was observed and qualitatively analysed by means of classical volume nucleation theory.

Crystallization of some amorphous metallic alloys studied by Mössbauer spectroscopy

The present work provides an analysis of crystallization processes in amorphous metallic alloys Fe80Si4Cr1.0B14 and Fe67Co18B14Si1. Crystallization of the first sample started at the temperature of 648 K. The fully crystalline state was observed after annealing at 748 K. We identified four sextets. One corresponds to crystalline Fe2B and the three others to FeSi solid solution with 10 at .% of Si. Crystallization of Fe67Co18B14Si1 started at the temperature of 623 K. We identified two crystalline phases. The first may have its origin as (Fe1−xCox)3B, the second one may correspond to a Fe−Co solid solution with a different Co content.