Crystallization and Characterization of Orthorhombic β‐MgSO4 · 7H2O

In solution, the growth rate and the crystal habit are influenced by a number of factors such as supersaturation, temperature, pH of the solution, cooling rate, agitation, viscosity, initial state of the seed crystal and the presence of impurities. The crystallization of orthorhombic β‐MgSO₄ · 7H₂O, from low temperature aqueous solution by slow cooling process was studied. The metastable zone width, the induction periods (τ) for different supersaturations and the effect of pH on the growth rate of the crystals were investigated. The increase of pH yielded bigger crystals. The structural, optical, thermal and mechanical properties of β‐MgSO₄ · 7H₂O have been studied using FT‐IR, X‐ray diffraction, TGA‐DTG and micro hardness analyses.     

Electrical Conductivity and Thermal Dehydration Studies of Mixed Single Crystals of BaCu(C2O4)2 · 6 H2O,Ba1–xCuxC2O4 · 4 H2O and Ba1–2x(NH4)2xC2O4 · 4 H2O

The measurement of electrical conductivity for the investigation of the number of water molecules present in the mixed crystals of barium copper oxalate and barium ammonium oxalate lattice have been carried out in the temperature range 30 to 450 °C. The dehydration temperature and the number of water molecules removed out of the structure at a particular temperature is estimated from the sharp increase in conductivity at these points. The almost steep increase of conductivity is attributed to the increase in the number of mobile charge carriers H⁺ and OH^– ions generated from the escaping water molecules. The study of electrical conductivity in association with the thermal behaviour has been used to understand the mechanism of conduction.     

Effect of Ca on HoPO4·nH2O (n = 1 and 2) crystallization from phosphoric acid solution

Ca‐substituted holmium phosphate, isomorphic with tetragonal form of HoPO₄·H₂O was synthesized by crystallization from boiling phosphoric acid (2 M H₃PO₄) solution containing 0.02M of Ho and 0–0.2 M of Ca. Calcium concentration, higher than 0.2 M Ca in solution resulted in biphasic solid crystallization: tetragonal HoPO₄·H₂O and orthorhombic HoPO₄·2H₂O. Ca incorporation in the solid according to substitution mechanism: Ca²⁺ + H⁺ ↔ Ho³⁺ was limited to ∼3 wt.% and was coupled with simultaneous incorporation of HPO₄²⁻. Ca for Ho substitution caused an expansion of the tetragonal unit cell of HoPO₄·H₂O, resulted from differences in the ionic radii (r_Ca > r_Ho). Effects of thermal treatment at 900 °C were as follows: (i) the orthorhombic admixture of HoPO₄·2H₂O re‐crystallized into tetragonal anhydrous HoPO₄, (ii) Ca–at first dissolved in crystal structure of HoPO₄·H₂O was expelled from it during re‐crystallization to form Ca(PO₃)₂, and that was associated with a contraction of the unit cell; a ‐ and c‐ axes went down to the level of Ca‐free anhydrous tetragonal form of HoPO₄. (iii) HPO₄²⁻ present in the solids as prepared underwent condensation according to reaction 2HPO₄²⁻ → P₂O₇⁴⁻ + H₂O. Scanning electron micrographs revealed significant changes in size and morphology of the crystals ranging from spherical globules of HoPO₄·H₂O formed in Ca‐free H₃PO₄ with increasing diameter in the presence of lower Ca concentration to rod‐like crystals organized in bundles resembling the “scheaf of wheat”, while crystallized from phosphoric acid solution with higher than 0.2 M Ca.     

Crystal Structure Study of Co(II) Complexes with 2,2′-(1,4-Ethylenedioxyl) Dibenzoic Acid-[Co · L · (H2O)3]n · nH2O· 0.2 nH2O

The structure ofS the title complex [Co. L. (H₂O)₃]_n. nH₂O. 0.2 nH₂O has been established by single crystal X-ray diffraction. Crystals of the complex are monoclinic, space group C2/c with cell constants α = 45.29(4), b=10.631(6), c = 8.015(6) Å, β = 90.65(8)°, Z = 8, D_c = 1.489 g. cm⁻³ The structure was solved and refined to R =0.0478 (wR = 0.0577). In the chain structure, Co(II) ions are hexacoordinated by 0 atoms in an octahedral arrangement. CoO₆ octahedra share corners (bridged) through O atoms of water, with each L^2--ligand binding two adjacent Co atoms.     

Crystallization kinetics of MgSO4 · 7 H2O in presence of tenside

The effect of sodium dodecyl sulfate (SDS) on crystallization kinetics and crystal habit of MgSO₄ · 7 H₂O from aqueous solutions at 25 °C was investigated in batch experiments. It highly depends on the supersaturation level. Both increasing supersaturation and rising concentration of the tenside promote the production of needle-like crystals but the influence of the driving force is much more pronounced. SDS increases the crystallization rate and the linear crystal growth rate in length direction of the crystals. To a high degree it also influences properties of the crystallizing solution such as surface tension and viscosity.     

The Setting Behaviour of α‐ and β‐CaSO4 · 0,5 H2O as a Function of Crystal Structure and Morphology

Calcium sulphate subhydrates (CaSO₄ · x H₂O, 0 < x ≤ 0.8) have a honeycomb‐shaped channel structure. The symmetry is either trigonal or a slight deviation thereof. Due to insufficient diffraction data and the high pseudosymmetry of the structure, it is not possible at this point to determine with certainty the specific arrangement of the water molecules in the channels. When the Fourier transformation method is used to calculate the growth form of the hemihydrate (x = 0.5), the calculated crystal form corresponds to the observed form only when the trigonal structural symmetry is largely retained. During dehydration of gypsum or, conversely, during the setting process of hemihydrate, heteroepitaxial growths of hemihydrate are observed on gypsum, or gypsum is grown heteroepitaxially on hemihydrate. The (100) faces of the hemihydrate and (010) of gypsum for the most part run parallel. Using diffraction and spectroscopic methods, it can be shown that a structural difference exists between α‐ and β‐hemihydrates, and that this difference probably accounts for the different setting behaviours. It is in this context that the presence of oxonium ions, particularly in β‐hemihydrate, found in NMR experiments is of interest. Textural studies indicated that the arrangement of gypsum crystals found in hardened gypsum is determined by the hemihydrate.     

Single crystal growth of La2(SO4)3 · 9 D2O

Single crystals of La₂(SO₄)₃ · 9 D₂O were grown from saturated D₂O solutions. According to X-ray diffraction measurements, the crystals have a hexagonal structure with unit cell parameters a = 10.996 Å and c = 8.077 Å (space group C–P6₃/m). Several physical properties were also determined (density, refractive indices, dielectric constants, specific heat, coefficient of linear expansion, microhardness).     

The Thermal Decomposition of Polyhalite K2SO4 · MgSO4 · 2 CaSO4 · 2 H2O

The thermal decomposition of polyhalite (K₂SO₄ · MgSO₄ · 2 CaSO₄ · 2H₂O) was investigated by DSC/TG and X-ray powder diffraction. The decomposition of the polyhalite starts at 285 °C in releasing the crystal water within one step. Simultaneously the decomposition of the polyhalite into anhydrite and two solid solutions of the compositions K₂SO₄ · 1.76 MgSO₄ · 0.24 CaSO₄ and K₂SO₄ · 0.64 MgSO₄ · 1.36 CaSO₄ is taking place. The mechanism of decomposition runs through K₂SO₄ · MgSO₄ CaSO₄. This phase reacts immediately to the solid solutions, mentioned above.     

Crystallization features of YBa2Cu3O7‐δ in the Y2BaCuO5‐BaCuO2‐CuO and Y2Cu2O5‐BaCuO2 systems

Based on the data of X‐ray phase and microstructure analysis, the sample composition was optimized in order to provide maximum size of the textured macrograins of YBa₂Cu₃O_7‐δ and of the crystallites in the Y₂BaCuO₅‐BaCuO₂‐CuO, Y₂Cu₂O₅‐BaCuO₂ systems. The growth rate has been studied and the YBa₂Cu₃O_7‐δ growth activation energy has been calculated for the samples of Y₂BaCuO₅+3BaCuO₂+2.3CuO, Y₂BaCuO₅+3BaCuO₂+0.6CuO, and Y₂Cu₂O₅+3.5BaCuO₂ compounds in the temperature range of 1240‐1270K for the case of use of the Y₂Cu₂O₅ and Y₂BaCuO₅ precursors with an average grain diameter of 10 μm and 1mm. A crystallization mechanism of YBa₂Cu₃O_7‐δ in the Y₂BaCuO₅‐BaCuO₂‐CuO and Y₂Cu₂O₅‐BaCuO₂ systems in the case of different sizes of Y₂BaCuO₅ and Y₂Cu₂O₅ precursor grains was proposed and validated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization kinetics of MgSO4 · 7 H2O at higher ranges of the driving force

By means of batch crystallization technique the crystallization kinetics of MgSO₄ · 7 H₂O at 25 °C at higher ranges of the supersaturation from pure aqueous solutions was investigated. It was observed that the growth rate highly depends on the habit of crystals and on their ratio of length to width, respectively. This ratio is a function of the initial supersaturation of each crystal.     

Unidirectional growth of α‐NiSO4·6H2O crystal by Sankaranarayanan–Ramasamy (SR) method

Large cylindrical [001] direction α‐nickel sulphate hexahydrate crystal with 20 mm diameter and 140 mm length was grown from an aqueous solution by uniaxially solution‐crystallization method of Sankaranarayanan–Ramasamy (SR). The grown crystal was examined by X‐ray diffraction, UV‐Vis‐NIR spectroscopy and TGA/DTA analysis methods.     

On the (MgxNi1–x)SeO4 · 6 H2O and (MgxCu1–x)SeO4 · 5 H2O mixed crystal formation

Mixed crystals (Mg_xNi_1–x)SeO₄ · 6 H₂O and (Mg_xCu_1–x)SeO₄ · 5 H₂O have been prepared studying the solubility in the MgSeO₄–NiSeO₄–H₂O and MgSeO₄–CuSeO₄–H_2O systems at 25 °C. It has been shown that the monoclinic structure of MgSeO₄ · 6 H₂O is unstable and undergoes a change into tetragonal structure due to the included nickel ions (about 4 at %). The lattice parameters of (Mg_{xNi 1–x})SeO₄ 6 H₂O have been calculated. It has been established that the magnesium ions incorporate isodimorphously in the crystal structure of CuSeO₄ · 5 H₂O which could be an indication of the existence of MgSeO₄ · 5 H₂O isostructural with the triclinic CuSeO₄ 5 H₂O. The distribution coefficients of the salt components between the liquid and solid phases have been calculated.     

Solubility of YBa2Cu3O7−δ and Nd1+xBa2−xCu3O7±δ in the BaO/CuO flux

The knowledge of the phase relations and solubilities in the Y–Ba–Cu–O and Nd–Ba–Cu–O systems are of fundamental importance for crystal growth and liquid-phase epitaxy of YBa₂Cu₃O_7−δ (YBCO) and Nd_1+xBa_2−xCu₃O_7±δ (NdBCO). The determination of the solubility curve of YBCO and NdBCO in a BaO/CuO flux containing 31 mol% BaO was done by observation of the formation and dissolution of crystals on the surface of the high-temperature solution. The heat of the solution of YBCO at 1000°C was found to be 34.7 kcal/mol, and for NdBCO at 1060°C, it was found to be 28.1 kcal/mol. The determination of the solubility curves requires special care, and the problems of the time-dependent shift of the solution composition due to the corrosion of the crucible is discussed. The scatter of the solubility data published by different authors could be due to the use of solutions with different Ba : Cu ratios, different determination methods, i.e. different crystallization mechanisms, different crucibles and starting chemicals.     

Some characteristic features of formation of composite material based on KDP single crystal with incorporated Al2O3·nH2O nanoparticles

Composite material based on KDP (KH₂PO₄) crystal matrix with incorporated aluminum oxyhydroxide Al₂O₃·nH₂O nanoparticles is obtained and peculiarities of the formation of KDP:Al₂O₃·nH₂O composite structure are studied by selective etching, optical and scanning electron microscopy. Influence of the nanoparticles on the formation of defect subsystem is analyzed. The obtained material is shown to have a zonal structure with a period independent of the concentration of nanoparticles. By means of FTIR‐spectroscopy, interaction of nanoparticles with KH₂PO₄ solution is studied. A model of the capture of nanoparticles by the {100} KDP crystal face is proposed.     

Characterisation of the Six-coordinated Octahedral Site in Cd(C4H2O4) · 2H2O Crystals

Optical absorption spectra of Co(II) and Ni(II) doped cadmium maleate dihydrate (CMDH) are recorded at room temperature and liquid nitrogen temperature. The UV–VIS–NIR spectra are characteristic of the transition metal ions in solids. The results and analyses of the spectra indicate near octahedral site symmetry for cobalt ion and trigonally distorted octahedral site symmetry for nickel ion. The following crystal field parameters are derived. The IR spectra are characteristic of the host lattice CMDH.     

Electronic Structure of [Cu(C7H4NO3S)2(H2O)4] · 2H2O Crystal

The electronic absorption spectrum and ESR spectrum of the crystal of the title compound [Cu(C₇H₄NO₃S)₂(H₂O)₄] · 2 H₂O, are measured. The experimental results are discussed quantitatively by using the ligand field theory and the radial wave function of non-free Cu(II). The electronic structure of the compound is in agreement with its crystal structure.