Crystallization of calcium sulfate dihydrate at different supersaturation ratios and different free sulfate concentrations

Free Sulfate is a major parameter affecting gypsum crystallization during phosphoric acid production. Gypsum crystal size, shape and filtration rate are significantly affected by the concentration of free sulfate. It is, therefore, important to evaluate the effectiveness of different sulfate levels from 1.5% to 3.5% on induction time and gypsum morphology. The crystallization of gypsum was carried out under simulated conditions of phosphoric acid production by the dihydrate process. Calcium hydrogen phosphate and sulfuric acid were mixed with dilute phosphoric acid at 80 °C, and the turbidity of the reaction mixture was measured at different time periods to calculate the induction time of gypsum crystals formation. With increasing free sulfate concentration, the induction time was significantly decreased. Chemical processing of Central and South Florida phosphate concentrates under different concentrations of free sulfate from 1.5% to 5.5% was carried out. The change on crystal size distribution and filtration rate were traced with free sulfate concentrations. The results show that, filtration rate of phosphogypsum was correlated to the mean diameter of crystals. In addition, induction time and co‐crystallized (lattice) P₂O₅ % in gypsum are decreased with increasing free sulfate content from 1.5% to 3.5%. Morphology of formed gypsum crystals at different sulfate contents and different supersaturation ratios are investigated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of the phase diagram for the crystallization of L‐asparaginase II by a turbidity technique ‐ part II. ‐MPD and crystallography studies‐

The phase diagram for the crystallization of L‐asparaginase II including the metastable zone width (MZW), in the presence of PEG₆₀₀₀ and ethanol, respectively, has been studied by an online turbidity technique out of the crystallization in solution (see part I of this work 1 ). Here this paper describes a further investigation on constructing a phase diagram including MZW for the crystallization of L‐asparaginase II with a different precipitant agent of 2‐methyl‐2, 4‐pentandiol (MPD). Along with the phase diagram, the single crystal X‐ray data were successfully collected at 100K from a crystal formed in the presence of 26% (v/v) MPD. The crystals indicate an orthorhombic form and belong to the space group of P2₁2₁2₁ with the unit cell parameters a = 93.9, b = 125.77, c = 151.75Å. The crystal diffracted up to a resolution of 2.88 Å.     

Synthesis,characterization and thermal analysis of ursolic acid solid forms

This study performed a solid‐state characterization of ursolic acid (UA) crystalline forms, a poorly water‐soluble triterpene with anticancer activity. Two new polymorphs (form I, II), two new solvates (propanol and isopropanol solvates), and a known ethanol solvate were determined and elucidated using a combination of multi‐techniques, including X‐ray single crystal and powder diffraction, Fourier transform infrared spectroscopy (FT‐IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A colorless single crystal of UA was grown from a propanol solution, and its crystalline structure was determined through X‐ray single crystal diffraction. It was determined that the propanol solvate was crystallized in the orthorhombic space group P2₁2₁2₁ with unit‐cell parameters a = 7.17200 (8) Å, b = 12.24100 (16) Å, c = 33.8950 (4) Å and Z = 4. The ethanol solvate and propanol solvate were isomorphous crystals. The results of the thermal analysis demonstrate that form I is a meta‐stable form, while form II is a stable form that is monotropically related.     

Crystal structures of salicylideneguanylhydrazinium chloride and its copper(II) and cobalt(III) chloride complexes

The crystal structures of salicylideneguanylhydrazinium chloride hydrate hemiethanol solvate (I), salicylideneguanylhydrazinium trichloroaquacuprate(II) (II), and bis(salicylideneguanylhydrazino)cobalt(III) chloride trihydrate (III) are determined using X-ray diffraction. The structures of compounds I, II, and III are solved by direct methods and refined using the least-squares procedure in the anisotropic approximation for the non-hydrogen atoms to the final factors R = 0.0597, 0.0212, and 0.0283, respectively. In the structure of compound I, the monoprotonated molecules and chlorine ions linked by hydrogen bonds form layers aligned parallel to the (010) plane. In the structure of compound II, the salicylaldehyde guanylhydrazone cations and polymer chains consisting of trichloroaquacuprate(II) anions are joined by an extended three-dimensional network of hydrogen bonds. In the structure of compound III, the [Co(LH)₂]⁺ cations, chloride ions, and molecules of crystallization water are linked together by a similar network.     

Hydrogen in Cu?Ti and Ni?Ti Metallic Glasses

The hydrogen solubility and its effect on the crystallization of Cu Ti and Ni Ti glasses were studied by differential scanning calorimetry, thermogravimetry, and X-ray diffraction. Dependence of the crystallization products of the hydrogenated Ti-based alloys on the hydrogen content was found. Whereas in Cu-Ti alloys hydrogenation leads to drastic decreasing in the thermal stability due to phase separation in the amorphous state and to formation of microcrystalline structure during crystallization, in Ni Ti system hydrogen produces hydrides with Ni as well with Ti, which after heat treatment decompose, and finally the same crystalline phases as in unhydrogenated alloy are formed. The isothermal crystallization kinetics of the maximum hydrogenated Cu₅₀Ti₅₀ amorphous alloy was also investigated to obtain additional information about this transformation leading to nano-crystalline material.     

Behavior of LiOH·H2O crystals obtained by evaporation and by drowning out

In the present work, the behavior of crystals derived from two different crystallization methods applied in a concentrated aqueous lithium salt solution was studied. The LiOH·H₂O crystals obtained by a simple evaporation (Crystal I) differed in terms of morphology and solubility from those precipitated from lithium hydroxide solutions by addition of ethanol as a co‐solvent (Crystal II). Solubility of Crystal II at different temperatures (15 to 35°C) and mass ratios of ethanol to water (0 to 0.1) was determined. Polymorphic like behavior of these crystals was evidenced from X‐ray diffraction patterns. Measurement of density, refractive index, absolute viscosity and electrical conductivity of saturated solutions are reported. A thermodynamic analysis in terms of the Chen model for the calculation of activity coefficients, indicate that the polymorphic system in water and in water + ethanol (ethanol/water ratio 0.1) is enantiotropic. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal Structure of 2‐methyl cinnamanilide and 2‐methoxy cinnamanilide

The crystal structures of two cinnamanilide derivatives 2‐methyl cinnamanilide (C₁₆ H₁₅ N O – compound I) and 2‐methoxy cinnamanilide (C₁₆ H₁₅ N O₂ – compound II) are reported. In both crystal structures, the cinnamamide group is almost planar. The inter‐planar angle between the two phenyl rings are 71.6(1)° for compound I and 7.5(1)° for compound II. The N‐H…O and C‐H…O type of hydrogen bond interactions between the amide group and the carbonyl group stabilizes the molecular packing as chains in the crystal lattice.     

Effect of CuCl2 on hydrothermal crystallization of calcium sulfate whiskers prepared from FGD gypsum

Using purified flue‐gas desulfurization (FGD) gypsum as raw material, effects of CuCl₂ on crystal morphology, phase structure, aspect ratio and crystallization of hydrothermal products prepared via hydrothermal crystallization in H₂SO₄‐H₂O solutions were investigated. The results show that dosage of CuCl₂ has a significant effect on the morphology, aspect ratio and crystallization of calcium sulfate whiskers (CSWs), but no effect on their phase transformation . At a dosage of 15 g CuCl₂/kg FGD gypsum, the produced calcium sulfate whiskers had diameters ranging from 1 to 3 μm with average aspect ratio greater than 200 . Transmission electron diffraction patterns and highly magnified surface morphology of CSWs were found different from those of self‐assembly crystals. Compared to self‐assembly crystals, the produced CSWs showed a single crystal structure and their surface was very smooth.     

Effects of the addition of SiC on the crystallization of Al84Ni8Co4Y3Zr1 (at.%) amorphous ribbons

Amorphous alloys present exceptional values of mechanical strength but lack any significant plasticity at room temperature. Deformation of amorphous alloys occurs in shear transformation zones that connect to form shear bands, which are easier to deform than the surrounding matrix, thus facilitating further deformation in the same location of the specimen. However, the presence of particles dispersed in the amorphous matrix can modify such strain softening behavior, resulting in real plastic deformation before fracture. Also, depending on the type of particles and how they are introduced, they can modify the crystallization behavior of the amorphous matrix by acting as heterogeneous nucleation sites. In this context, this paper reports on the effects of the addition of SiC particles on the crystallization of Al₈₄Ni₈Co₄Y₃Zr₁ amorphous ribbons. Pre-alloyed ingots with and without added SiC particles were melt-quenched into amorphous ribbons by the single-roller melt-spinning technique and then selectively and partially crystallized at the first and second crystallization temperatures, as determined by differential scanning calorimetry. Primary crystallization of nanometric-sized fcc-Al crystals was found to occur in both ribbons (with and without added SiC), confirming that crystallization reactions were not altered by the ceramic particles. Aluminum carbide (Al₄C₃) crystals resulting from high-temperature liquid metal/SiC reactions were observed as coatings on the SiC particles and as isolated particles dispersed in the amorphous solid matrix. In both cases, the Al₄C₃ particles also did not change the crystallization behavior of the amorphous Al₈₄Ni₈Co₄Y₃Zr₁ matrix, since no heterogeneous nucleation of fcc-Al crystals was observed.     

Synthesis,crystal structure and characterization of new transition metal compounds of bromophenols: Bis(2,4,6‐tribromophenolato) di(N‐methylimidazole)M(II) (M=Co,Cu)

Bis(2,4,6‐tribromophenolato)di(N‐methyl imidazole)M(II), where M stands for cobalt and copper metals, was synthesized via reaction of the corresponding metal sulphate and 2,4,6‐tribromophenolate in aqueous media in the presence of N‐methyl imidazole and sodium hydroxide. Although various crystallization procedures were applied only cobalt complex was obtained as single crystals. The Co(II) ion has a distorted octahedral enviroment involving two O atoms and two N atoms of the Bis(2,4,6‐tribromophenolato)di(N‐methyl imidazole) ligand. Powder x‐ray diffraction pattern of copper compound was used for cooper complex. For characterizations of complexes carbon, hydrogen and nitrogen elemental analysis, FTIR and UV spectroscopy, DSC thermal analysis and magnetic susceptibility measurements at room temperature were performed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Controlled deposition and transformation of amorphous calcium carbonate thin films

Controlled synthesis of amorphous calcium carbonate (ACC) films was realized by using the multiple templates, which are composed of a self‐assembled film (SAF, insoluble Poly (ε‐caprolactone) film) and a soluble modifier (poly allylamine), as modifiers. The formation of self‐assembled film was analyzed by monitoring the morphologies using atomic force microscopy. Even more noteworthy, using anhydrous ethanol as media, the ACC‐to‐vaterite‐to‐calcite transformation was also investigated, and the obtained products were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. The results demonstrated that organic solvent has profound influence on transformation of amorphous calcium carbonate thin films. In the air of anhydrous ethanol, the controlled synthesis of calcium carbonate films with different morphologies, such as planar films with a few sporadic particles, symmetric rhombohedral crystals, novel crystals with symmetrical terraced convexity formation of calcite, was obtained by the fine‐tuning of induction time. It provides a new and simple method to prepare polymorphic CaCO₃ crystal films from the ACC films by controlling the crystallization process (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of amorphous AgI studied by optical absorption of excitons

Exciton absorption spectra are reported for AgI measured during crystallization from the amorphous state. No well-defined absorption band could be observed in the disordered structure obtained by evaporating AgI onto a substrate at 80 K. An absorption band began to appear as the films were annealed to successively higher temperatures. The position of the absorption peak indicates that the crystallization of disordered AgI into a stable zinc blende structure occurs only after passing through an unstable wurtzite form which more closely resembles the amorphous structure. The activation energy for the initial crystallization process was found to be 2.0 × 10^?2 eV.     

Crystallization behaviour of an amorphous Ti50Be40Zr10 alloy

The crystallization behaviour of an amorphous Ti₅₀Be₄₀Zr₁₀ alloy during a continuous heating mode from room temperature to 973 K and isothermal annealing at temperatures above the glass transition temperature is examined by differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS) measurement and large-angle X-ray diffractometry (LAXD). DSC indicated two well-defined exothermic peaks, a slight shoulder at the higher temperature side of the second peak and a small heat evolution at higher temperature. The Kissinger plot for the first and the second peak gives a straight line, from which the apparent activation energy is estimated to be 269 and 413 kJ/mol respectively; the enthalpies for the first and second crystallization process are 1.04 kJ/mol and 4.39 kJ/mol for a heating rate of 20 K/min. The SAXS intensities increase sharply after annealing at about 673 K (corresponding to the first peak in the DSC curves); the scattering is due to the formation of fine-scale crystalline Ti particles by the LAXD. The size of the particles does not change significantly while the number of scattering particles increases, indicating that the reaction is almost nucleation controlled and the growth is very limited. Another crystalline phase would appear in addition to the Ti particles on annealing at temperatures above about 753 K (corresponding to the second peak in the DSC curves), where the SAXS intensities decrease compared with those for only the first-stage of crystallization. The crystalline phase might be a metastable cubic phase with the lattice parameter a₀?0.2994 nm.The sequence in the crystallization of the initial non-crystalline material is amorphous → microcrystalline (MS I) → crystalline (MS II; S III), although the structure of crystalline phase in the final stage (S III) was not identified. It is also likely that cold-rolling does not have a perceptible effect on the crystallization behaviour of the present amorphous alloy.     

Structure and magnetic properties of bulk amorphous Fe60Co10Ni10Zr7B13 alloy formed by mechanical synthesis and hot pressing

Formation and magnetic properties of the bulk amorphous Fe₆₀Co₁₀Ni₁₀Zr₇B₁₃ alloy are described. The amorphous powder was prepared by high-energy ball milling of the amorphous ribbon and then was pressed under high pressure and temperature to obtain a bulk alloy in the form of a disc 5 mm in diameter and 2.5 mm thick. The compacted discs are fully amorphous as confirmed by X-ray diffraction and Mössbauer spectroscopy measurements. Differential scanning calorimetry curve recorded for the amorphous ribbon shows two exothermal peaks related to two stages of crystallization. Similar thermal behavior is observed for the powder samples. Hysteresis loops obtained for the amorphous ribbon, as-milled and compacted powders reveal their soft magnetic properties.     

Crystal and molecular structures of selected oxidative nitration products of aminopyrazine and 2-amino-3-hydroxypyridine

2,3,5,6-Tetraoxopiperazine (I), ammonium 2,3,5,6-tetraoxo-4-nitropyridinate crystal hydrate (II), co-crystallized dimethylammonium 2,3,5,6-tetraoxo-4-nitropyridinate and dimethylammonium chloride (III), and ammonium 2,6-dioxo-3,5-dinitropyridinate (IV) were isolated in the crystalline state and studied by X-ray diffraction. All heterocycles are planar and nonaromatic. They consist of two conjugated moieties linked together by C-C single bonds. The short C...O contacts (2.841–3.048 Å), which link the molecules to form zigzag two-dimensional chains, make a considerable contribution to the formation of the crystal structure of I, whereas hydrogen bonds that form three-dimensional networks play the most important role in the formation of the crystals of II–IV.     

Detection of the II–I Etiracetam solvent-mediated polymorphic transformation through the online monitoring of the suspension apparent viscosity

Although going to complex techniques can be useful at some stage of process development of crystallization processes, the goal of this article is to show that process control can also be achieved with relatively simple measurements, depending of course on what type of control is needed. Focusing on the Etiracetam crystallization process, this work demonstrates the potential of the online monitoring of the power dissipated in the suspension, a property that can be directly related to the suspension apparent viscosity for the detection of the solvent-mediated polymorphic transformation from form II to form I. Even if the work presented in this paper focused on a specific crystallization process, this easy-to-use method seems promising for the control of other crystallization processes exhibiting solvent-mediated polymorphic transformations with similar characteristics: (i) significant difference in the PSD of the crystals of the stable and the metastable forms, (ii) solid volumetric fraction in the suspension higher than 40% and (iii) absence of phenomena (breaking, attrition, agglomeration, secondary nucleation, etc.) interfering with the polymorphic transformation and affecting the PSD of the crystals.     

Crystallization of mefenamic acid and polymorphs

The crystallization of Mefenamic Acid, (MA), which has a prevalent usage in drug formulation, was investigated. MA is a high‐dose, anti‐inflammatory, analgesic agent used for pain in menstrual disorders. Some negative properties of MA are a high hydrophobicity and propensity to stick to surfaces, which cause great problems during granulation and tabletting. To facilitate tabletability, enhance dissolution rates, and develop a stable and reproducible dosage form, investigation of the physicochemical properties of mefenamic acid is necessary. Pharmaceutical drugs are commonly crystalline materials and are therefore subject to polymorphism. Polymorphism, the ability of a substance to exist in more than one crystalline form, is a significant phenomenon in the field of chemical engineering sciences, including pharmaceutical development. Establishing the polymorphic behaviour of a drug molecule early in development minimizes the number of unsuitable candidates developed and reduces the risk of encountering issues later which may have a major financial and time impact. Mefenamic acid crystals were recrystallized from five different solvents of N, N‐dimethylformamide (DMF), acetone, N, N‐dimethylacetamide (DMA), Dimethylsulfoxide (DMS) and Ethyl Acetate (EA). In order to characterize the Mefenamic Acid crystal structure and the polymorphic forms of the crystals obtained by recrystallization, the scanning electron microscopy (SEM), Raman diffractometry and X‐ray pattern were used. From the industrial crystallization point of view, the crystal size distribution (CSD), the crystal shape, the polymorphic form and the crystallization steps are important factors that affect the quality and bioavailability of a drug. For the determination of crystal size distribution of MA, The Focused Beam Reflectance Measurement (FBRM) technique was practiced and CSD profiles were obtained. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Variation of crystallization mechanisms in flash-lamp-irradiated amorphous silicon films

Flash lamp annealing (FLA) can form polycrystalline silicon (poly-Si) films with various microstructures depending on the thickness of precursor amorphous Si (a-Si) films due to the variation of crystallization mechanisms. Intermittent explosive crystallization (EC) takes place in precursor a-Si films thicker than approximately 2 μm, and the periodicity of microstructure formed resulting from the intermittent EC is independent of the thickness of a-Si films if their thickness is 2 μm or greater. In addition to the intermittent EC, continuous EC and homogeneous solid-phase crystallization (SPC) also occur in thinner films. These crystallization mechanisms are governed by the ignition of EC at Si film edges and the homogeneous heating of interior a-Si. The results obtained in this study could be applied to control the microstructures of flash-lamp-crystallized poly-Si films.     

Photo-enhanced crystallization by laser irradiation and thermal annealing in amorphous GeSe2

The laser irradiated crystallization process in amorphous GeSe₂ was studied by Raman scattering to discriminate between thermal and photo-induced contributions. Amorphous GeSe₂ crystallizes into a low-temperature (LT) form, LT-GeSe₂, and a high-temperature (HT) form, HT-GeSe₂. An amorphous sample was annealed at various temperatures and times in an electric furnace with and without laser irradiation. The laser power was adjusted to about 20 mW having a 0.4 mm spot size to determine the photo-induced effect. The difference between the thermal and laser irradiated crystallization process was discussed by considering the activation energy of crystallization. The activation energy due to laser irradiation above the band-gap energy was found to be smaller than that for the pure thermal crystallization process. We present a model for the photo-enhanced effect in which the lone-pair electrons of Se atoms are excited by the photons and the bond switching or atomic rearrangement occurs when the electrons relax through an electron–phonon interaction.     

Kinetics of non-isothermal crystallization and glass transition phenomena in Ga10Se87Pb3 and Ga10Se84Pb6 chalcogenide glasses by DSC

The crystallization process affects solid properties through the crystal structure and morphology established during the transition process. An important aspect of the crystallization process is its kinetics, both from the fundamental point of view of amorphous material as well as the modeling and phase transition. In the present research work, non-isothermal crystallization data in the form of heat flow vs. temperature curves has been studied by using some well known models for amorphous Ga₁₀Se₈₇Pb₃ and Ga₁₀Se₈₄Pb₆ chalcogenide glasses, prepared by the melt quenching technique. The glass transition phenomena and crystallization of these glasses have been studied by using non-isothermal differential scanning calorimetery (DSC) measurements at constant heating rates of 5, 10, 15, 20, 25 and 30 K/min. The glass transition temperature (T_g), crystallization temperature (T_c), and melting temperature (T_m) were determined from DSC thermograms. The dependence of T_g and T_c on the heating rate was used to determine different crystallization parameters such as the order parameter (n), the glass transition energy (ΔE_g) and the crystallization activation energy (ΔE_c). The results of crystallization were discussed on the basis of different models such as Kissinger's approach and the modification for non-isothermal crystallization in addition to Johnson, Mehl, Ozawa and Avrami.