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.     

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)     

Thermodynamics of Crystal Nucleation in an External Electric Field

The influence of electric field on crystal nucleation in a saturated solution has been studied both theoretically and experimentally. The classical equations for nucleation have been used to determine the free energy of formation, critical radius of the cluster and the concentration of the critical nuclei. The theory shows that an externally applied electric field can modify the free energy of formation of a crystalline cluster in its aqueous solution. The impact of the field will be stronger on large molecules. Two experimental set ups have been designed to study the nucleation of crystals in saturated aqueous solutions, in the presence of electric fields. Experiments conducted using a metal coordination compound bis‐ thiourea zinc chloride show that electric fields of strength around 10⁵ V/m would increase its nucleation.     

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.     

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 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)     

Decisive role of Au layer on the oriented growth of ZnO nanorod arrays via a simple aqueous solution method

Vertically aligned arrays of ZnO nanorod were synthesized on the Au/SiO₂/Si(1 0 0) substrate by a simple aqueous solution growth process, without pre-prepared ZnO seed layer. For comparison, glass and SiO₂/Si were also used as substrates, and the results show that the Au layer plays a decisive role in orienting the growth of the ZnO nanorod. The effects of other growth parameters, including Zn²⁺ concentration and growth time, on morphology, density, and orientation of the ZnO nanostructure were also studied and with longer reaction time, a new structure namely ZnO nanotip was obtained. Moreover, the growth mechanism of ZnO nanorod arrays grown on the Au/SiO₂/Si substrate was proposed.     

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,growth, solubility and dielectric studies of L‐proline cadmium chloride monohydrate semi organic nonlinear optical single crystal

Nucleation parameters such as solubility, induction period, interfacial energy and metastable zone width have been investigated for the aqueous solution growth of a semi‐organic nonlinear optical (NLO) material of L‐Proline cadmium chloride monohydrate (L‐PCCM) single crystal. Metastable zone width and induction period values were determined experimentally in order to optimize the growth parameters. The grown crystals are transparent (dimensions: 16 x 8 x 5 mm³) and characterized by powder X‐Ray Diffraction and dielectric studies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In situ time-resolved X-ray diffraction study of octacalcium phosphate transformations under physiological conditions

The present study is focused on the in vitro investigation of octacalcium phosphate (OCP) transformations when mixed with physiological solution (aqueous isotonic 0.9% NaCl) by the energy dispersive X-ray diffraction technique. This technique allowed in situ monitoring of the processes taking place in this system in real time. It was demonstrated that when OCP is mixed with physiological solution, it undergoes two simultaneous processes: (1) amorphous-into-crystalline OCP transformation (37%), and OCP average grain size growth from 22 up to 35 nm; (2) partial phase transformation of OCP (33%) into hydroxyapatite (HA), and HA average grain growth up to 5 nm. Both processes take place simultaneously with the same characteristic time (2.90±0.25) h.     

Seeded batch crystallization of ammonium aluminum sulfate from aqueous solution

Seed crystals of ammonium aluminum sulfate ((NH₄)Al(SO₄)₂··12H₂O) were grown in aqueous solution by cooling. The temperature of a crystallizer was lowered with no control by circulating cooling water through the jacket. It fell in an exponential manner. The effects of seed amount and size on the product crystal size distribution were examined. The product crystals obtained were of narrow and uni-modal size distribution with suppressed secondary nucleation if seed crystals were loaded more than a critical value. The critical value was determined and well compared with previously reported values for other material systems. This crystallization technique does not need any prior knowledge of the kinetics of crystal growth and nucleation. It is simple and robust, and can be easily applied to an existing crystallizer without installing any additional control systems.     

Spontaneous crystallization of potassium chloride from aqueous and aqueous‐ethanol solutions Part 1: Kinetics and mechanism of the crystallization process

Kinetics of spontaneous crystallization of potassium chloride from aqueous and aqueous‐ethanol solutions were studied. During the crystallization of the salt the electrical conductance and optical transmission of the supersaturated solutions were measured automatically. For monitoring of the total surface of growing potassium chloride crystals at the crystallization the turbidimetric method was used. The growth rate and activation energy of the crystals were determined. The crystal growth rate was proportional to supersaturation. When the volume fraction of ethanol in the solution increased from 0 to 25.76%, the activation energy of the growth process did not change and was about 60 kJ·mol^‐1. Aggregation of the crystals was found. The aggregation kinetics of the crystals may be described approximately by the famous Smoluchowski equation for coagulation of colloidal particles. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical prediction of bulk glass forming ability (BGFA) of Ti-Cu based multicomponent alloys

The bulk glass forming ability (BGFA) of Ti-Cu based multicomponent alloys has been evaluated via theoretical modeling and computer simulation studies based on a combination of electronic theory of alloys in the pseudopotential approximation and the statistical thermodynamical theory of liquid alloys. The magnitude of atomic ordering energies, calculated by means of the electronic theory of alloys in the pseudopotential approximation, was subsequently used for calculation of the key thermodynamic parameters such as enthalpy, entropy and Gibbs free energy of mixing, viscosity, and critical cooling rate of the binary Ti-Cu and ternary Ti-Cu-X alloys. The potential alloying elements (X) can be divided in two groups defined by their effect on the variation of the negative heat of mixing and their influence on the critical cooling rate. Most of the predicted candidate alloying elements from either X_I (Al, Si, Ag) or X_II (Co, Ni, Fe, Sn, Be) and/or both groups have already been used successfully for the fabrication of new Ti-Cu based bulk metallic glasses. It was also shown that the critical cooling rate appears to be a more important parameter rather than the change in the negative heat of mixing for the prediction of candidate alloying elements improving BGFA.     

LPE growth rate calculations

The expressions for LPE growth rate calculations are developed on the basis of the steadystate growth model assuming the nucleation at the second interface and in the volume of the solution. The solution layer thickness can be calculated at which the LPE growth rate reaches maximum for any solution cooling rate. The interface and volume nucleation parameters, critical supersaturation and supercooling of the solution have been determined from experimental GaP LPE data within temperature range 800 – 1030°C. Calculated growth rates fit very closely with experimental rates of GaP LPE growth.     

Characterization of α and γ polymorphs of glycine crystallized from water‐ammonia solution

Crystallization of metastable α and stable γ polymorphs of glycine was carried out from aqueous solution in the presence of ammonia. Pure aqueous solution and solution with lower concentration of ammonia yield α nucleation and solution with a critical concentration of ammonia yield γ nucleation. Variation in the solubility of glycine in double distilled water and pH of the resulting solution due to the ammonia incorporation was studied in a range of temperatures. The induction period for the α and γ nucleation in the solution was determined and its variation due to the ammonia incorporation was also studied. Single crystals of both the polymorphs were grown by slow evaporation method. Effect of ammonia concentration and the resultant pH of the solution on the nucleation, growth and morphology of the grown polymorphs were investigated. The unidirectional growth of the γ polymorph along the polar axis was revealed. X‐ray powder diffraction method was employed to distinguish both the polymorphs structurally. Their thermal stability above room temperature was studied by differential scanning calorimetry which revealed that the as‐grown γ polymorph transforms to α at 179.6 °C while the as‐grown α retains its phase until melting. The optical transmittance of the grown γ polymorph was studied in the UV‐Vis‐Near IR region. The second harmonic generation (SHG) efficiency of the grown γ polymorph was studied with a Nd:YAG laser source and is about 6.8% higher than that of the inorganic standard KDP. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of a newly synthesized organic nonlinear optical crystal: Urea ninhydrin monohydrate

Urea ninhydrin monohydrate (UNM) was synthesized and grown for the first time from aqueous solution employing the slow evaporation method. Single crystal structure was determined by X-ray diffraction data and it reveals that the crystal belongs to centrosymmetric with space group of P2₁/c. The grown crystals were characterized by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and UV–vis–NIR spectroscopy. Preliminary Z-scan measurement indicates that nonlinear refractive index of this crystal is −4.1×10⁻⁸ cm²/W. The etching study was performed to assess the growth pattern of the crystal. Dielectric response of the crystal was analyzed for different frequencies and temperatures.     

Investigations on the Nucleation Kinetics of L-Arginine Phosphate single crystals

The nucleation parameters, such as radius of the critical nucleus and critical free energy change have been evaluated for LAP single crystals. The interfacial tension determined by conducting the induction period measurements has been used for the evaluation of nucleation parameters. The determined interfacial tension is found to be comparable with theoretical literature values.     

Growth and characterization of succinic acid single crystals

Single crystals of ferroelectric succinic acid were grown from aqueous solution by low temperature solution growth technique. The cell parameters and space group are found using powder X‐ray diffraction analysis. The presence of the functional groups has been estimated qualitatively by FTIR analysis. The UV‐Visible spectrum shows the cut‐off wavelength at 240 nm. The thermal stability of the crystal was studied by TG/DTA. The dielectric constant of the crystal studied as a function of frequency shows the pyroelectric property. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)