• Volume 5, Issue 5

      December 1983,   pages  381-468

    • Crystal growth of barium molybdate by flux evaporation

      S K Arora G S Trivikrama Rao

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      Single crystals of BaMoO4 have been grown by isothermal evaporation of lithium chloride at 700°C. The morphology and mechanism of growth of the crystals have been discussed. The quality of the crystal has been assessed by selective etching.

    • Crystal growth and electrical properties of CaSO4:Dy single crystals

      S H Jagdale S H Pawar

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      Single crystals of CaSO4:Dy, with and without charge compensator were grown by the solution growth technique. Electrical conductivity was studied at room temperature for diverse concentrations of Dysprosium and showed that it increases upto 0.2 wt % of Dy, beyond which saturation sets in. Electrical conductivity was studied in the region 400 to 700°K and the migration energies estimated for various dopant concentrations. The variation of electrical conductivity and migration energy with diverse dopent concentration is explained on the basis of the theory of defects. The thermoelectric power measurements reveal that the crystals grown are ofP type.

    • Growth mechanism of Herring-Bone and Hour-glass synthetic gypsum

      D Jayakumar K S Raju

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      Synthetic gypsum crystals are grown from sodium meta silicate gel when 1M calcium chloride solution diffuses into the gel imbedded with 1M amonium sulphate solution. Acicular-shaped crystals of Herring-Bone structure are observed. When methanol was added to the gel medium, tabular crystals revealing Hour-glass structure are rarely observed. In the presence of methanol the silicate particles are inhibited from being incorporated into the crystals as a result of pushing and incorporating mechanisms. Inclusion of silicate particles in traces gives rise to Hour-glass pattern. The implications are discussed.

    • ZnS:Sm and ZnS:Cu, Sm electroluminescent phosphors

      R C Maheshwari R K Tripathi

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      Electroluminescent ZnS: Sm and ZnS: Cu, Sm phosphors have been prepared and their electroluminescent (el) characteristics have been studied. The time-averagedel brightness follows the Alfrey-Taylor relation over a wide range of frequencies. The constants of this relation have been determined. Theel emission shows one main and one auxiliary peak during each half cycle of the applied voltage. Variation of current with applied voltage has also been investigated.

    • Electrical properties of CdSxSe1−x single crystals

      D Raja Reddy B K Reddy P J Reddy

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      Electrical conductivity and Hall effect were studied on vapour phase grown CdSxSe1−x single crystals in the entire range of composition in the temperature range 90–300 K. The conductivities of the as-grown crystals varied significantly. High conducting samples were obtained by annealing either in vacuum or in cadmium vapour. Hall mobilities, carrier concentration and donor activation energies were calculated. No definite variation in mobility with composition was observed. Donor activation energy showed an increasing trend with increase of CdS content.

    • Electrical conductivity, crystallinity and glass transition in vulcanised rubber

      N P Daw R C Bhuniya

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      Temperature variation of electrical conductivity has been measured for rubber vulcanised with different concentrations of sulphur. Change of amorphous character with sulphur concentration has also been measured from the amorphous halo of the Debye-Scherrer x-ray photographs of the samples. The conductivity of vulcanised rubber in glassy state shows a slow and gradual increase; but during glass transition it increases suddenly to a high value which again exhibits gradual increase in high elastic state. X-ray studies show that with increase of sulphur, the amorphous region decreases due to formation of cross-links by the chain units. The decrease of conductivity with increase of sulphur is then due to decrease of amorphous region. The fast decrease of conductivity with sulphur at low concentration in the high elastic state indicates high rate of formation of cross-links at such concentration.

    • Effect of zinc composition on properties on PEC cells based on sprayed Cd1−xZnxS films

      M D Uplane S H Pawar

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      Polycrystalline Cd1−xZnxS films were prepared by spray pyrolysis technique, both on conducting and non-conducting glasses. These films were used as photoanodes in photoelectrochemical cells. The optical and electrical properties of these cells are studied and the effect of zinc composition on these properties is revealed.

    • Time measurement technique for internal friction studies with a torsion pendulum

      C N Rao M K Asundi

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      A new technique for measuring internal friction by the free decay method using time measurements with a torsion pendulum is described. It has been applied for the automation of measurements with a Kê type pendulum. The method enables rapid and precise measurement of internal friction. Results of the grain boundary peak for aluminum are presented for illustration.

    • Microhardness and interatomic binding in some cubic crystals

      K Kishan Rao D B Sirdeshmukh

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      Vicker’s microhardness measurements have been carried out on single crystals of CaF2, SrF2, BaF2, CdF2, PbF2, EuF2, ThO2, NaClO3, NaBrO3, Bi4 (GeO4)3, Bi4(SiO4)3, Bi12GeO20 and Bi12SiO20. The hardness values are discussedvis-a-vis the interatomic binding in these crystals. While most of the fluorite-type crystals are highly ionic, covalency is indicated in the bismuth compounds studied.

    • Microhardness studies of SnI2 and SnI4 single crystals

      C C Desai J L Rai

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      The variation in the microhardness of tin-di-iodide (SnI2) and tin-tetra-iodide (SnI4) crystals has been determined using Vicker’s microhardness indentor. It is observed that the microhardness of the crystals depends on the applied load and is independent of the duration of loading. Vickers Hardness Numerals (vhn) for SnI2 is found to be greater than that of SnI4 crystals. Mayer’s equation and implications have been discussed.

    • Changes in texture and grain size in hot rolled magnesium and effect on yield strength

      G Sambasiva Rao Y V R K Prasad

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      Variations in the grain size and basal texture in magnesium hot-rolled in the temperature range 570–770 K have been studied and compared with those observed in specimens hot-rolled at 570 K and annealed at different temperatures in the range 570–770 K. In specimens hot-rolled temperatures higher than 670 K, a rapid increase in grain size and a weakening in basal texture have been observed. The yield stress of the specimen is lower than that predicted by the Hall-Petch relation and this result is interpreted in terms of the reduced basal texture. The dependence of yield stress on grain size in magnesium hot-rolled at different temperatures lower than 670 K matches with that observed in specimens annealed at different temperatures.

    • Stroboscopic studies of the elastic behaviour of some Indian timbers

      M A Kareem D B Sirdeshmukh

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      The dynamic Young’s modulus has been determined for eleven Indian timbers using an electronic flash lamp stroboscope to measure the frequency of vibration of the timber bars. A linear relationship is observed between Young’s modulus and the density of the timbers.

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