• P Mohan Rao

      Articles written in Bulletin of Materials Science

    • Growth of single crystals of some complex salts in silica gels

      M S Joshi P Mohan Rao A V Antony

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      Single crystals of ammonium nickel sulphate, potassium nickel sulphate, ammonium alum and potassium alum are grown in sodium-metasilicate gels. The method of gel preparation and growth procedure are described. Both single diffusion and double diffusion methods are used. Studies on nucleation and characterisation of crystals are also reported. Crystals grown are illustrated.

    • Periodic crystallization of barium oxalate in silica hydrogel

      S M Dharma Prakash P Mohan Rao

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      The experimental conditions for obtaining periodic crystallization of barium oxalate in silica hydrogel are investigated. The Liesegang rings formed by the reaction of oxalic acid and barium chloride are studied. The dependence of velocity constant and the spacing coefficient on pH, concentrations of inner and outer electrolytes and temperature have also been studied and a possible mechanism for the behaviour is suggested. The deviations from Isemura’s general observations are interpreted by considering the microcrystals constituting the rings and the irreversibility of inner and outer electrolytes.

    • Studies on etching of gel-grown barium oxalate dihydrate crystals

      S M Dharmaprakash P Mohan Rao

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      Etch pits produced by selective etchants such as 1 M HCl, 1 M HNO3, 4 M BaCl2, 4 M NH4Cl and 4 M NH4Cl-1 M HCl solutions on the as-grown {110} faces of barium oxalate dihydrate crystals are illustrated and explained. The kinetics of etching is studied. From Arrhenius plots, the activation energy of etching and the pre-exponential factor are computed. An empirical equation governing the kinetics has been suggested.

    • Thermal properties of barium-cadmium oxalate crystals

      S M Dharmaprakash P Mohan Rao

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      The kinetics and thermodynamics of the thermal dehydration of crystalline powders of BaC2O4·2H2O, CdC2O4·3H2O and Ba1−xCdxC2O4·2·5H2O have been studied by means of thermogravimetry, as a function of temperature. The dynamic dehydration kinetics are also examined using DTA, recorded simultaneously with TG as a function of temperature. The validity of the estimated mechanism and kinetic parameters is briefly discussed. From DTA study it is concluded that all dehydration peaks are endothermic and the decomposition peaks of barium oxalate to barium carbonate, cadmium oxalate to cadmium oxide and barium cadmium oxalate to barium carbonate and cadmium oxide are exothermic.

    • Physico-chemical characterization of BaHPO4 crystals

      K C Hebbar S M Dharmaprakash P Mohan Rao

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      Characterization of the gel-grown barium hydrogen phosphate (BHP) crystals was performed by utilizing the techniques of chemical analysis, X-ray diffraction, infrared and thermal behaviour. The results show that BHP crystals had chemical composition BaHPO4 at room temperature. TG and DTA studies revealed the BHP crystals to be anhydrous at room temperature and decomposed at temperatures above 370°C and the decomposition was an endothermic process. Magnetic susceptibility measurements indicate the material to be diamagnetic.

    • Growth and characterization of barium copper oxalate single crystals in gels

      Kasthuri V Bangera P Mohan Rao

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      Barium copper oxalate was grown in silica hydrogel at ambient temperature. The effect of various parameters like gel pH, gel density, gel aging and concentrations of reactants on the growth of these crystals was studied. The crystals grown were characterized by chemical analysis, X-ray powder diffractometry, infrared spectroscopy, thermogravimetric and differential thermal analysis. The results of these observations are described and discussed.

    • Surface topographical studies of prism faces of barium copper oxalate single crystals

      Kasthuri V Bangera P Mohan Rao

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      The present paper reports observations made on microstructures of gel-grown barium copper oxalate crystals. Growth spirals, growth layers, liquid inclusions and growth of microcrystallites are described and discussed in relation to the mechanism and conditions of crystal growth.

    • Studies on impurity incorporation in cadmium oxalate crystals grown by gel method

      N Jagannatha P Mohan Rao

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      Aspects of gel growth of cadmium oxalate single crystals doped with monovalent (Li+, Na+, K+ and NH4+) and divalent (Ca2+, Co2+, Ni2+ and Zn2+) cation impurities are discussed. The growth experiments were carried out by single diffusion method. In this paper the effect of composition of the supernatant solution is considered. Rigorous characterization involves determination of composition of cations by employing atomic absorption spectrophotometer and of anions by titration method. The Pauling radius, hydration energy and distribution coefficient of the cations are tabulated and the results are described and discussed.

    • Effect of heavy-ion irradiation on dielectric constant and electrical conductivity of doped and undoped nonlinear substance

      K Somashekhara Udupa P Mohan Rao Sriramana Aithal A P Bhat D K Avasthi

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      Implantations were carried out on gel-grown potassium dihydrogen orthophosphate (KDP) and those doped with magnesium oxide (MgO) single crystals using 100 MeV Ag+ heavy-ion beam of 15 UD 16 MV pelletron accelerator. To conduct a comparative study, measurements were carried out in the temperature range 243 K-403 K at frequencies ranging from 1 kHz-1 MHz on irradiated and nonirradiated nonlinear samples. It was observed that the mechanism of dielectric behaviour varied with frequency, temperature and ion irradiation. Further, implantation produced erratic variation in the conductivity both in the intrinsic and extrinsic regions, and also in the dielectric behaviour of the substance. The property of sensitive dependence on initial conditions, namely, chaos had set in after ion irradiation. However, the doping effect had not completely terminated the above transition, leading to chaos in the nonlinear medium.

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