CRYSTALLIZATION OF ZINC SULPHATE SINGLE CRYSTALS AND ITS STRUCTURAL, THERMAL AND OPTICAL CHARACTERIZATION J.K. SAHA AND J. PODDER* Department of Physics, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh ABSTRACT Zinc sulphate (ZnSO4.7H 2O), an inorganic material has been crystallized by an isothermal evaporation method. ZnSO 4.7H2O is highly soluble in water and the solubility is found to be increased almost linearly with the increase of temperature. At room temperature around 34C, the solubility was found to be 92.41 gm/50 ml. The FT-IR spectroscopy was performed on pure zinc sulphate crystals to identify the presence of functional groups. The grown crystals have been subjected to powder X-ray diffraction to determine the unit cell dimensions and the crystal structure. The lattice parameters are found to be, a = 9.9810 Å, b = 7.2500 Å and c = 24.2800 Å, respectively. The values were in good agreement with those of the reported values. The TGA and DTA study revealed that the grown crystals have good thermal stability. The UV-vis spectrum showed that the material has wide optical transparency in the Ultra-violet region.
Key words: Isothermal evaporation, Crystatization, Zine sulphate, Structural characterization INTRODUCTION Zinc Sulphate Heptahydrate (ZSHH) possesses wide range of applications in the field of telecommunication, solar systems for solar energy storage, coagulation bath for rayon and optical information storage devices. The search for new frequency conversion materials over the past decade has led to the discovery of many organic materials with high nonlinear susceptibilities. However, their often inadequate transparency, poor optical quality, and lack of robustness, low laser damage threshold and inability to grow into large size have impeded the use of single crystal in various devices. Recent interest is centered on inorganic crystals because pure inorganic materials typically have excellent mechanical and thermal properties. Crystallization of heptahydrate sulphate material such as zinc vitriol (ZnSO4.7H2O) of high purity has become an important field of research for both academic and industrial applications in various areas like medical, agricultural and chemical industry (Ema et al.1998, Ikeya et al. 2000). The pure zinc sulphate crystals were grown at low temperature from aqueous solutions (Kasatkin 2002, Ramalingom et al. 2001, Sgualdino et al. 1987, Tomas et al. 1969.) The zinc vitriol is included in a group of heptahydrate sulphate with the general formula RSO4.7H2O (R = Zn, Mg, Ni) (Dana and Ford 1985). ZnSO4.7H2O belongs to a *
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SAHA AND PODDER
family of inorganic non linear optical crystal (Dhumane et al. 1998, Hussani et al. 2008). Zinc vitriol is used to supply zinc in fertilizers, in making lithopone; in electrolyte for zinc plating; as a mordant in dyeing, as a preservative for skins and leather and in medicine as an astringent and emetic. ZnSO4.7H2O crystallizes in the orthorhombic structure. During industrial crystallization, the size and shape of the crystal plays an important factor, since the undesirable habits such as plate like or needle like causes the problems of separating, washing or drying (Cano et al. 2001). The physical properties such as packing density, agglomeration and re-dissolution mainly depend on the shape of the crystal. The main objective of the research was to study the growth mechanism of pure ZnSO 4.7H2O and its different physical properties. Here the synthesis, solubility, structural, optical, and thermal properties of ZnSO 4.7H2O have been reported. MATERIALS AND METHODS Analar grade zinc sulphate heptahydrate and doubled distilled water were used in the crystallization process. In the first stage a mother solution of 2000 ml was prepared using recrystallized salt of ZnSO4.7H2O and stirred well with a magnetic stirrer...