• Volume 2, Issue 1

      January 1980,   pages  1-82

    • Fine particle physics and technology; some results

      M S Multani N G Nanadikar V R Palkar A K Pansare A Gurjar R Vijayaraghavan

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      The new techniques of fine particle synthesis are shown to lead to better ceramic materials such as yttrium iron garnet (YIG) and ferroelectric lead zirconate titanate (PZT). The densities are greater than 99% of the theoretical density and the grain size can be easily controlled from 2 microns upwards. For YIG this means higher values of the nonlinear spin-wave excitation thresholdhc. For PZT the result is higher values of the tensor componentd33 and poling voltage. It is also shown that the fine particle systems and the fine-grain microstructure lead to interesting physics results. For PZT the lowering of the peak dielectric constant, the increasing transition temperatures and the decreasing values ofd33 with decreasing grain size can be understood in terms of the changing low-frequency cut-off of the soft lattice vibration mode. Another interesting result is that for 2000 Å size particles of α-Fe2O3 the anisotropy constant is found to be 1·38 × 102 ergs/cm3 from Mössbauer measurements.

    • Production and characterisation of amorphous alloys at varanasi

      P Ramachandrarao S Ranganathan T R Anantharaman

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      Amorphous alloys, more commonly referred to as metallic glasses, represent a striking advance in inorganic materials technology of recent times. While the probable atomic arrangements in noncrystalline alloys have aroused scientific curiosity, their unusual mechanical strength, attractive magnetic properties and remarkable corrosion resistance have excited technological interest. This report describes the progress of research at Varanasi on the following aspects: adaptation, innovation and development of techniques for rapid solidification, study and refinement of structural models, calculation of thermodynamic quantities, evaluation of strength and corrosion resistance and studies of glass to crystal transition.

    • Nucleation and growth of potassium dihydrogen phosphate crystals in silica gels

      M S Joshi A V Antony

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      Kinetic studies on nucleation and growth of potassium dihydrogen phosphate crystals in silica gels show that the rate-determining process for the growth of these crystals in silica gels is diffusion. Morphology, microhardness and perfection of gel grown crystals are also reported.

    • Studies on a wear-resistant cast iron

      N Ranganathan Malur N Srinivasan N Raman

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      The possibility of developing a good wear-resistant cast iron with manganese and chromium as alloying elements in white cast iron was explored. The results indicate that it is possible, but the composition of the alloy in respect of manganese and chromium should be controlled within close limits to achieve the desired objective.

    • Microhardness studies in ammonium halide crystals

      K J Pratap V Hari Babu

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      Microhardness studies of NH4Cl (pure and doped), NH4Br and alkali halide crystals are presented. The hardness of ammonium halides is found to be less as compared to alkali halide crystals. Doping NH4Cl crystals with copper (Cu2+) is found to increase the hardness enormously and the results obtained with various concentrations of copper are presented. The results have been analysed and the various factors contributing to the increase in hardness at lower loads have been discussed.

    • X-ray study of the air-oxidiseda-Ga2Se3 and Ga2Te3 powders

      A K Mukherjee U Dhawan K D Kundra S Z Ali

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      X-ray studies of the stoichiometrically prepareda-Ga2Se3 and Ga2Te3 are reported after various stages of air-oxidation in the temperature ranges 250 to 825° C and 250 to 650° C respectively. Diffractometric powder data of Ga2Te3 are also reported over the complete 2ϑ range with remarkable difference in the relative intensities of the (444) and (642) reflections. Ina-Ga2Se3 the oxidation proceeds by formation of the most stable phase, beta-gallium sesquioxide, complete oxidation occurring at 650° C. For Ga2Te3 a mixture of Ga2TeO6 and TeO2 is obtained as the intermediate oxidation products in the range 500 to 600° C, while at 450° C some extra lines which could be indexed on the super-lattice cell of Ga2Te3, along with Te and unchanged Ga2Te3 lines, are observed. Oxidation at the higher temperature of 650° C led to the disappearance of TeO2 lines leaving Ga2TeO6 as the final well-crystallised phase.

    • Dielectric properties of Bi4(GeO4)3 and Bi4(SiO4)3

      Lalitha Sirdeshmukh Y R Reddy

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      Dielectric constant, dielectric loss and conductivity of Bi4(GeO4)3 and Bi4(SiO4)3 single crystals have been measured as a function of frequency and in the temperature range from liquid nitrogen temperature to 400° C. The values of the static dielectric constant at room temperature are 16·4 and 13·7 for Bi4(GeO4)3 and Bi4(SiO4)3 respectively. The plots of log (σ) against reciprocal temperature at different frequencies of these crystals merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0·95 eV and 1·2 eV for Bi4(GeO4)3 and Bi4(SiO4)3 respectively.

    • Phase transformation studies on pure and doped strontium carbonate

      C Rama Mohan Rao P N Mehrotra

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      The orthorhombic-hexagonal transformation of strontium carbonate is a reversible reconstructive transformation. Cationic impurities like K+, Ca2+, Ba2+, Cd2+, Y3+, La3+, Nd3+, Sm3+, Gd3+, Dy3+, Ho3+, Bi3+, Zr4+ doped in pure strontium carbonate affect the kinetics and energetics of the transformation.

    • Surface structures on second order prism faces of synthetic quartz crystals

      M S Joshi K B Saraf A V Antony

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      Surface structure studies on various {1120} (second order prism) faces of synthetic quartz crystals are reported. Horizontal striations and polygonal growth pyramids are predominant on these faces. Growth layers modified by the presence of guest microcrystals attached to the host second order prism faces are illustrated and explained. It is shown that microcrystals and impurities influence growth and development of second order prism faces of synthetic quartz crystals. Mechanism of growth of these faces is assessed in the light of the observed surface structures.

    • DC electrical conductivity of CoSiF6·6H2O and (NH4)2SO4

      S S Mitra S K Ghorai S K Dutta Roy

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      D.C. electrical conductivity of single crystals of (NH4)2SO4 and CoSiF6·6H2O have shown conductivity jump near their respective structural transition temperature. Activation energy of (NH4)2SO4 has been found to be consistent with the earlier data. However, CoSiF6·6H2O has given prolonged aging effect due to dipolar relaxation and formation of space charge polarisation.σtrue andPmax have been measured.Pmax has shown a negative maximum at the transition point. Activation energy of ZnSiF6·6H2O has been found to be comparable with CoSiF6·6H2O.

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