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)     

On the dependence of interfacial tension on the size of two-dimensional nucleation

Among the assumptions in the derivation of the classical nucleation equations has been important that of the independence of the interfacial tension on the critical size of the two-dimensional nucleus. The one layer adsorption model based on Bragg-Williams approximation with empty sites has been used to investigate the dependence of interfacial tension on the number of molecules in the square shaped critical nucleus. Using the Gibbs adsorption at constant temperature for a two-component system, the number of molecules in the critical nucleus is exactly calculated in terms of the supersaturation, the interfacial tension and the interaction energies between the adsorbed molecules. The correction for the free energy of formation of critical two-dimensional nucleus due to the new term associated with the dependence of the interfacial tension on cluster size is derived. Assuming the correction term for the free energy is negligibly small, the expression for the variation of interfacial tension of an embryo from that of a plane surface is established. It is found that the deviation is significant for small clusters and decreases with increase in the size of thejnucleus.     

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 nucleation,thermodynamical parameters and growth of Benzimidazole crystals from low temperature solution

Metastable zonewidth and induction period measurements of Benzimidazole (BMZ) are presented. The nucleation parameters such as interfacial tension, radius of the critical nucleus and critical free energy change have been calculated for the solution grown Benzimidazole (BMZ) single crystals at different supersaturation ratios. The grown BMZ crystals were characterized by the differential scanning calorimetric studies for analysis of thermal properties. The dielectric behaviour of the crystal was studied at different temperature and frequency. The laser damage threshold studies show that BMZ crystal has higher laser damage threshold. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nucleation Studies in Supersaturated Triglycine Sulphate Solutions

Rates of nucleation of supersaturated aqueous solutions of Triglycine sulphate are measured by the induction period over the temperature range 30–50 °C. The effects of temperature and supersaturation on the induction period are reported. The interfacial tension, energy of formation and radius of the critical nuclei of the crystal are calculated in accordance with classical nucleation theory. Nucleation rate increases with increase in supersaturation and temperature, while interfacial tension decreases with increase in temperature.     

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.     

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.     

Nucleation kinetics of the formation of low dimensional calcium sulfate dihydrate crystals in isopropyl alcohol medium

Calcium sulfate dihydrate, constituted as uniform crystals of low dimensions, is a potential biomaterial for clinical applications like bone graft substitution and drug delivery. In this work, isopropyl alcohol has been used as a solvent to obtain low dimensional calcium sulfate dihydrate crystals from calcium nitrate ‐ sulfuric acid system. Reactants in 0.5 molar concentration at ambient conditions generated uniform rod‐shaped crystals of length 3–5 µm. Analysis using X‐ray Diffractometry and Fourier Transform Infrared Spectrometry showed the material to be well crystallized, phase‐pure calcium sulfate dihydrate. The nucleation kinetics has been studied by observing the induction time of phase formation in solutions of millimolar concentrations through turbidimetry at 300 K. The data have been analysed using classical nucleation theory to deduce parameters like interfacial tension (or surface free energy), nucleation rate and critical radius. The surface free energy obtained (5.6 mJ/m²) is comparatively lower than that reported for aqueous precipitation, which could be attributed to the presence of isopropyl alcohol. On escalating the supersaturation ratio, the nucleation rate drastically increased and the critical radius decreased exponentially. Particles formed at supersaturation 1.39 showed a monomodal distribution centered at 8.2 nm in Dynamic Light Scattering analysis. Comparable particle sizes were obtained in Transmission Electron Microscopy.     

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.     

Supersaturation Dependence of Induction Period for Three-Dimensional Nucleation of Substances from Aqueous Solutions Revisited

The available experimental data on the supersaturation dependence of induction period for the nucleation of some compounds crystallizing from solutions are analysed from the standpoint of the classical nucleation theory and the mononuclear and polynuclear models in order to obtain values of interfacial tension and pre-exponential factor for homogeneous and heterogeneous nucleation. It was found that the contributions of homogeneous and heterogeneous nucleations to the experimental data can be separated by assuming that the nucleation rates due to the two nucleations are additive and that the polynuclear model in combination with the separated contribution of homogeneous nucleation to the induction period gives a satisfactory agreement between theoretical estimates and experimental values of the interfacial tension and the pre-exponential factor.     

Investigations on nucleation kinetics,growth and characterization of sulphanilic acid single crystals

Nucleation parameters such as radius of critical nucleus, critical free energy change and interfacial tension were evaluated for Sulphanilic acid (SAA) single crystals. Metastable zone width and induction period values were determined to optimize the growth parameters. The interfacial tension values estimated using the experimentally determined induction period is found to be comparable with theoretical values. SAA crystals were grown with the optimized growth parameters. The formation of SAA crystals was confirmed by powder X‐ray diffraction and FT‐IR studies. The density measurements were carried out by both theoretical and experimental methods. The NLO behaviour of SAA crystals was tested by Kurtz‐ Perry technique. The mechanical hardness was studied by Vickers Microhardness tester. The UV‐Vis spectral analysis was carried out on the SAA crystals to study the optical properties. The laser damage threshold values of the SAA crystals are found to be 7.6 and 6.6 GW/cm² for single and multiple shots, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nucleation kinetics and growth aspects of semi organic non‐linear optical bis thiourea cadmium acetate single crystals

Nucleation parameters such as metastable zone width, induction period and interfacial energy have been determined for the aqueous solution growth of bis thiourea cadmium acetate (BTCA) single crystals. Solubility of BTCA has been determined for various temperatures. Metastable zone width and induction period values have been estimated in order to optimize the growth parameters. The interfacial tension values derived from experimentally determined induction period are found to be comparable with theoretical values. Bulk crystals of BTCA have been grown using the optimized growth parameters. The grown crystals have been subjected to structural, optical and mechanical property studies. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

The mechanism of the formation of enantiotropic polymorphs of carisbamate in solution crystallization

The nucleation kinetics, as a function of supersaturation level, was studied for carisbamate, a polymorphic crystalline compound, in methanol, ethanol, 2-propanol and water. The induction times in nucleation kinetics varied markedly with respect to relative supersaturation in the range 1.3–2.3. At the same relative supersaturation, the induction time for carisbamate in methanol is the shortest, increasing in order from ethanol, 2-propanol, and then water. The interfacial tensions γ between carisbamate and methanol, ethanol, 2-propanol, and water were estimated from their induction times based on nucleation theory and were found to be about 3.6, 4.1, 4.5, and 5.7 mJ/m², respectively. These values were of same order of magnitude as those obtained from solubility data. The equation that displays the influence of interfacial tension, supersaturation and temperature on crystallization kinetics was derived, and found to be consistent with experimental observations. The mechanism of enantiotropic polymorphism for carisbamate in the solvents is illustrated. Using interfacial tension values determined for single solvents, the polymorphic form resulting from crystallization in mixed and pure solvent systems could be predicted with good accuracy.     

Salting-out precipitation of potassium dihydrogen phosphate (KDP). I. Precipitation mechanism

The precipitation of KDP produced by salting-out with aqueous solutions with different contents of ethanol, 1-propanol and 2-propanol have been studied at 30°C. Induction periods were determined as function of the solution initial supersaturation by a visual procedure. From the experimental results it was possible to conclude that the formation of the new solid phase is controlled by primary nucleation followed by normal growth. The interfacial surface tension of KDP in different solvents was also obtained.     

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.     

Influence of a polyacrylate antiscalant on gypsum nucleation and growth

Calcium sulphate dihydrate (gypsum) crystallization was studied under conditions, of supersaturation and temperature, simulating a brackish water desalination unit using solar energy. The effect of an commercial sodium salt of poly(acrylic acid), based compound known as RPI, on homogeneous nucleation and growth of gypsum was also examined. Gypsum was precipitated by mixing aqueous CaCl₂ and Na₂SO₄ solutions. It was found that, with increasing temperature or supersaturation, the induction time decreases and the growth rate increases. By using classical nucleation theory, the interfacial tension and the nucleation rate values were estimated. It was shown that the interfacial tension is temperature dependent. The addition of increasing quantities of RPI, in the same conditions of temperature and supersaturation, prolongs the induction time, decreases the nucleation rate and increases the interfacial tension. The addition mode of RPI (in calcium or in sulphate solution) was found as an important parameter in controlling the inhibition process of gypsum crystallization. XRD and SEM analysis showed that RPI antiscalant strongly affected the texture and the morphology of the deposit gypsum. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of the Curvature Dependence of Interfacial Energy on Homogeneous Nucleation Kinetics

Influence of the curvature dependence of surface tension on nucleation rate and cluster distribution function is studied. When the curvature dependence of the interfacial energy of a cluster, σ, is taken into account the number of monomers decreases, in contrast to the case when σ = const. Decrease of monomers caused the decrease of nucleation rate.     

Curvature- and temperature-dependent interfacial tension in classical nucleation theory

Curvature- and temperature-dependent interfacial tension is introduced in classical nucleation theory (CT-CNT). In this case, the nucleation rate depends on temperature, T, viscosity, η, the reduced surface tension, , the difference between the chemical functions of the liquid and solid phase, Δμ, and unlike with the common classical nucleation theory (CNT), also on the derivative of this function, ∂Δμ/∂T. Because of this latter dependency, the nucleation rate is highly sensitive to Δμ and no approximation formula can be used for this function. Kauzmann's catastrophe can be introduced artificially by approximation formulas that are commonly used in CNT. The latter theory is not sensitive to this problem.     

Determination of the solid liquid interfacial energy and thereby the critical nucleus size of paracetamol in different solvents

The effect of the type of solvent on the solid liquid interfacial energy was determined by performing induction time measurements of paracetamol in methanol, 1‐propanol, acetone and water at a constant supersaturation temperature of 30 °C and different levels of supersaturation (a/a*) ranging from 1.03 to 1.24. At equal supersaturation level and temperature the induction time increases with decreasing solubility whereas the solid liquid interfacial energy decreases with increasing solubility. The interfacial energy has a minimum value of 1.45 mJ/m² in the solvent where paracetamol has a maximum solubility (methanol) whereas it has its maximum value of 2.91 mJ/m² in the solvent with minimum solubility. The interfacial energy is a function of the solubility has been established. The critical radius for homogeneous nucleation was found to be minimum in the solvent of highest solubility. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)