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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. 相似文献
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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. 相似文献
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R. Kijkowska D. Malina A. Sobczak‐Kupiec Z. Wzorek R. Orlicki 《Crystal Research and Technology》2012,47(7):804-809
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 (rCa > rHo). 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. 相似文献
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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, Dc = 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 L2--ligand binding two adjacent Co atoms. 相似文献
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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. 相似文献
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S. Follner A. Wolter A. Preusser S. Indris C. Silber H. Follner 《Crystal Research and Technology》2002,37(10):1075-1087
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. 相似文献
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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). 相似文献
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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. 相似文献
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N. A. Kalanda L. I. Gurskii A. M. Saad V. M. Truhan T. V. Haliakevich 《Crystal Research and Technology》2008,43(6):599-605
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 YBa2Cu3O7‐δ and of the crystallites in the Y2BaCuO5‐BaCuO2‐CuO, Y2Cu2O5‐BaCuO2 systems. The growth rate has been studied and the YBa2Cu3O7‐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 YBa2Cu3O7‐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) 相似文献
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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. 相似文献
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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. 相似文献
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Mixed crystals (MgxNi1–x)SeO4 · 6 H2O and (MgxCu1–x)SeO4 · 5 H2O have been prepared studying the solubility in the MgSeO4–NiSeO4–H2O and MgSeO4–CuSeO4–H2O 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 (MgxNi 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. 相似文献
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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 YBa2Cu3O7−δ (YBCO) and Nd1+xBa2−xCu3O7±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. 相似文献
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I. M. Pritula A. V. Kosinova M. I. Kolybaeva O. N. Bezkrovnaya V. V. Grebenev A. E. Voloshin D. A. Vorontsov D. S. Sofronov O. M. Vovk V. N. Baumer 《Crystal Research and Technology》2014,49(5):345-352
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. 相似文献
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R. V. S. S. N. Ravikumar S. N. Reddy S. N. Rao B. J. Reddy Y. P. Reddy 《Crystal Research and Technology》1995,30(8):1121-1126
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. 相似文献
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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. 相似文献