Determination of nucleation parameters and the solid liquid interfacial energy of the KCl‐ethanol‐water system

The kinetic parameters of homogeneous nucleation of KCl in different ethanol‐water solvent mixtures were determined at 25°C from the experimental measurements of the width of the metastable zone at different cooling rates. The ethanol mass ratio in the ethanol water solvent mixture was varied from 0‐0.9 and the metastable zone width for each solvent mixture was measured under the cooling rates of 10, 20 and 30 K/h. The influence of ethanol ratio on the activity coefficient was calculated. It was found that increasing the ethanol ratio in the solvent mixture leads to an increase in the mean molal activity coefficient. The experimental results obtained showed that the increase in the ethanol ratio in the solvent widens the metastable zone for the crystallization of KCl. Also it has inferred from the calculations based on the classical nucleation theory that increasing of the ethanol ratio in the solvent mixture resulted in an increase of the nucleation rate order, increase of the critical size of nuclei and increase of the solid liquid interfacial energy. It has been found that the solid liquid interfacial energy can be good correlated with inversely proportionality to the solubility. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of nucleation kinetics of potassium tetraborate tetrahydrate

In this study, the metastable zone width of potassium tetraborate tetrahydrate was determined for four different temperatures and cooling rates. The induction period of potassium tetraborate tetrahydrate in aqueous solution was examined according to polythermal method by using visual observation. The induction period, which changes inversely proportional to the nucleation rate has been used to determine the interfacial tension between the potassium tetraborate tetrahydrate and aqueous solution. By using interfacial tension, the nucleation parameters such as Gibbs free energy change for the formation of critical nucleus, ΔG*, free energy of formation, ΔG, radius of critical nucleus, r and number of molecules in the critical nucleus, i* has been calculated. The effect of Li⁺ and Ca²⁺ impurities on metastable zone width has been studied. The metastable zone width of aqueous solution of potassium tetraborate tetrahydrate decreases with increasing impurity concentrations. The equilibrium saturation concentration change is high in the presence of Ca²⁺ ions while it is low in the presence of Li⁺ ions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigations on the nucleation kinetics of bis glycine sodium nitrate

The nucleation parameters such as, energy per unit volume, radius of critical nucleus, critical free energy barrier, number of molecules in the critical nucleus and nucleation rate have been evaluated for bis glycine sodium nitrate single crystals. The interfacial energy of the solution at various temperatures has been estimated from existing solubility data. The metastable zone width and induction period measurements have been carried out experimentally.     

Metastable zone width for secondary nucleation and secondary nucleation inside the metastable zone

This study presents an evaluation of a new method, called zero growth activation free energy, used to determine the metastable zone width for the secondary nucleation case. It predicts the metastable zone width with a maximum error of 5‐10%. Estimation of the metastable zone width for different isothermal crystallization conditions can be modeled according to a chosen reference set of growth experiments carried out in the volume diffusion regime at different initial supersaturations, using seed crystals of a certain characteristic size. Moreover, the activation free energy of the secondary nucleation was estimated. The role of the enthalpy of immersion in the formation of secondary nucleation events inside the metastable zone was pointed out, as well as its effect in causing extra‐fast growth rate. Furthermore, sucrose crystal surface free energy was estimated. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Scale Formation on Cooling Surfaces in Crystallizers

Using a simple apparatus the effect of various parameters on encrustations formation was studied. Critical temperature difference and critical time of scaling were introduced as variables characterizing the tendency of the system to form encrustations. These parameters are linked with the metastable zone width of the system.     

Crystallization Kinetics of Sodium Perborate

Some basic physicochemical properties of aqueous sodium perborate solutions, essential in designing an effective control, were measured. The kinetics of primary nucleation was determined by the measurement of the metastable zone width. The differential method was applied for the determination of the crystal growth rate equation. It was found that the solubility and the nucleation rate constants are in very good agreement with the literature data whereas the parameters of the growth rate equation show an influence of the experimental conditions.     

L-精氨酸掺杂下ZTS溶液的稳定性研究

研究了L-精氨酸掺杂下硫脲硫酸锌(ZTS)溶液中的成核过程,测量了在不同掺杂浓度下ZTS溶液的亚稳区和诱导期.结果表明:随掺杂浓度的增加,溶液的亚稳区变宽,诱导期增大;根据经典成核理论计算了晶体的成核热、动力学参数,分析了溶液稳定性与掺杂浓度的关系,即随着L-精氨酸掺杂浓度的增加,溶液的稳定性得到明显提高.利用化学腐蚀法对ZTS晶体(100)面进行了腐蚀,并用光学显微镜对腐蚀面进行观察,得到了清晰的位错蚀坑.当L-精氨酸掺杂浓度为1.5mol;时,ZTS晶体(100)面位错蚀坑密度最小,适合高光学质量晶体的生长.     

Determination of nucleation kinetics of lovastatin in acetone solution

The metastable zone widths of lovastatin in acetone solution were determined at different temperatures, cooling rates and initial concentrations by polythermal method. It decreases with the increase of temperature and initial concentration, increases with the increase of cooling rate. The induction periods of lovastatin in acetone solution were also investigated as a function of supersaturation ratios. The crystal‐liquid interfacial tension, thus the fundermental nucleation parameters including Gibbs free energy change for the formation of critical nucleus, radius of critical nucleus and number of molecules in the critical nucleus have been gotten based on the classical homogeneous nucleation theory. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solubility and metastable zone width of DL‐tartaric acid in aqueous solution

Solubility and metastable zone width (MSZW) of DL‐tartaric acid (DL‐TA) in aqueous solution have been determined. Solubility of DL‐TA was measured in the temperature range from 0 to 50 °C at atmospheric pressure by means of the conventional polythermal method using Turbidity Monitoring Technique, which was verified by a gravimetric method. The dissolution enthalpy and entropy of DL‐TA were then calculated from the solubility data using van't Hoff equation. Two approaches was used to estimate the nucleation kinetics from the measured metastable zone width data, the self‐consistent approach and the approach based on 3D nucleation. In addition, the metastable zone width slightly decreases with increasing agitation rate and was independent of working volume.     

Metastable regions of aqueous solutions of inorganic soluble salts

Based on the nucleation conception of metastable zones in aqueous solutions of soluble salts and employing the thermodynamics, a relation was derived correlating the metastable zone width with physico-chemical characteristics of the substance. The derived relation holds well for values, obtained when using an identical experimental method. The mean size of a “critical” salt nucleus corresponding to the method used was calculated from the correlation line. It is demonstrated that the relation can be used for those sets of data, which were obtained at approximately the same degree of mechanical stressing and solution purity.     

Treatment of data on metastable zone width leading to nucleation characteristics and measurements in the system potassium dichromate-water

Measurements of the width of metastable zone can be used for characterisation of the kinetics of nucleation. Methods of treatment these data discussed in literature are summarised, re-examined and arranged in order to enable smoothing of experimental data and simultaneous calculation of the values of certain characteristic nucleation parameters. An example (potassium dichromate in aqueous solution) shows that the values obtained in this way are within usual limits given in the literature. The results indicate that in unseeded solutions the nucleation was probably heterogeneous one, whereas in presence of a fixed seed an adsorbed layer mechanism of secondary nucleation followed by a fluid shear action seems to explain the results.     

Crystallization of copper sulphate

Results of the studies of copper sulphate pentahydrate batch crystallization in the temperature range from 70 down to 30 °C are presented. In some of the experiments, free sulphuric acid has been added. The metastable zone width, nucleation and growth kinetic parameters, as well as the system kinetic constant were determined and compared with the data published in the literature.     

Determination of Nucleation Parameters of YBCO from High Temperature Solution

The growth kinetics of YBCO single crystal from high temperature solution of YBCO-BaO/CuO solute-solvent system has been studied. Based on regular solution model and classical nucleation theory the thermodynamical data investigated for the system are used to determine the nucleation parameters: interfacial energy, metastable zone-width (supercooling temperature), free energy change, critical nucleation radius etc. which leads to the understanding of the nucleation phenomena of YBCO.     

Determination of metastable zone width for combined anti-solvent/cooling crystallization

The metastable zone width (MSZW), induction time and primary nucleation kinetics have been measured and estimated for simultaneous anti-solvent and cooling crystallization of paracetamol in iso-propanol/water solution. ATR-FTIR spectroscopy and laser back-scattering are used to measure the solute concentration and primary nucleation event, respectively. Response surface analysis was applied to find the contribution of the crystallization mechanism on the MSZW and obtain a statistical model for quick estimation of the MSZW. Two theoretical approaches for the estimation of nucleation rate kinetic parameters from experimental data are presented. The methods are obtained by modifying the classical Nyvlt's correlation for simultaneous cooling/anti-solvent crystallizations. The nucleation order n for primary nucleation was deduced from the slope of a linear plot of log(MSZW) vs. log(cooling and anti-solvent rates). The induction time was also estimated by changing the classical methods for combined cooling and anti-solvent crystallization.     

Influence of the pH-Value on the Metastable Zone Width of Potassium Sulphate

Aqueous solution of the potassium sulphate with addition of sulphuric acid or potassium hydroxide has been chosen for the metastable zone width measurements in order to check how the solution structure affects the nucleation. Hydration analysis of corresponding sub-systems indicated involved structure changes. The solubility of K₂SO₄ increases with addition of H₂SO₄ and decreases with addition of KOH. The hydration analysis has shown that low acid concentrations have an inexpressive effect on the structure of solution. Much distinct effect exhibit low concentrations of the hydroxide. The metastable zone width decreases with increasing the value of pH. This decrease is less perceptible in the acidic region but more distinct in the alkaline region. The same holds for the critical nucleus size L* and the specific surface energy σ*. The behaviour quoted above supports the conception that the pH affects the solution structure and that the latter has a significant effect on the nucleation.     

On the interpretation of metastable zone width in anti‐solvent crystallization

Considering nonlinear dependence of solute concentration on anti‐solvent–solvent composition a modified Nývlt‐like equation based on traditional power‐law relation between nucleation rate and developing supersaturation and a new equation based on the classical theory of three‐dimension nucleation are proposed to explain the dependence of anti‐solvent addition rate on metastable zone width defined as excessive anti‐solvent composition in anti‐solvent crystallization. The experimental data on the metastable zone width in anti‐solvent crystallization of benzoic acid are analyzed and discussed from the standpoint of these equations. It is found that the new approach based on the classical nucleation theory provides better insight into the processes involved in anti‐solvent crystallization. Analysis of the experimental results on anti‐solvent crystallization of benzoic acid [D. O'Grady, M. Barret, E. Casey, and B. Glennon, Trans. IChemE A 85 , 945, (2007)] revealed that: (1) the value of metastable zone width for a solvent–anti‐solvent system is determined by the solute–solvent and solute–anti‐solvent interactions, (2) the dependence of the metastable zone width on stirring is associated with the enthalpy of mixing, and (3) the new approach predicts a threshold anti‐solvent addition rate associated with the setting up of an equilibrium between solvent and anti‐solvent and a maximum anti‐solvent addition rate connected with the induction period t_ind for the onset of crystallization. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

γ-氨基丁酸晶体成核动力学、晶体生长及热力学性质研究

本文研究了γ-氨基丁酸的热力学及成核动力学性质.对γ-氨酪酸晶体的热力学性质进行研究,γ-氨基丁酸的差示扫描量热研究表明:γ-氨基丁酸的熔点为190.6 ℃,熔化焓为-343.4 J/g.测定了不同温度下γ-氨基丁酸在水中的溶解度及不同过饱和度下的诱导期.结果表明:γ-氨基丁酸的诱导期随着过饱和度的增加而降低.通过经典成核理论计算了固-液表面张力、成核自由能和临界成核半径.     

Investigations on the Nucleation Thermodynamics of RbTiOXO4 (X = P or As) Crystals Grown from High Temperature Solution

The nucleation thermodynamics of RbTiOXO₄ (where X = P or As) family crystals crystallizing from high temperature solution using the phosphate and tungstate solvents have been studied. Using the regular solution model and classical nucleation theory the nucleation thermodynamical parameters like interfacial energy, chemical potential, free energy change, critical energy barrier and radius of critical nucleus have been calculated which leads to better understanding of the nucleation process. Comparative study has also been made to investigate the metastable zone width of the above family crystals grown from different fluxes.     

Nucleation, growth and characterization of L-tartaric acid—nicotinamide NLO crystals

The solubility, metastable zone width and nucleation parameters of organic nonlinear optical material L-tartaric acid–nicotinamide (LTN) have been determined. The crystals of LTN are grown by the slow cooling method. The grown crystals are morphologically interpreted. The crystalline powder of the grown crystals has been examined by X-ray diffraction and thermogravimetric analysis. The different modes of vibrations present in the crystal are identified by the Fourier infrared spectroscopy analysis. The powder SHG efficiency of LTN is comparable with that of KDP.     

Nucleation and polymorphism explored via an easy-to-use microfluidic tool

We present an easy-to-use microfluidic set-up, easily transferable to the laboratory and determine an accurate method for metastable zone width measurement. We clearly define a zone in the phase diagram where nucleation is mononuclear. We nucleate a single crystal of metastable phase, which turns out to be stable. This approach holds promise for the control and the study of crystallization processes.