• C C Desai

      Articles written in Bulletin of Materials Science

    • SEM-studies of tin-iodide whiskers

      C C Desai J L Rai

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      Optical and scanning electron microscopic observations have been made of tin-iodide whiskers crystals grown by the gel-method. Most of the whiskers have been found to be of two types: (i) hollow and (ii) solid whiskers. The observations indicate that the formation of hollow whiskers is possible with or without the presence of impurities. By using electron micro probe, the overgrowth of tin-tetra iodide crystals on tin-iodide whisker crystals have been identified. A growth mechanism for tin-iodide whiskers have been suggested. The implications are discussed.

    • X-ray topographic analysis of dislocation line defectsin calcium fluoride crystals

      C C Desai

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      One-to-one correspondence of dislocation etch pits have been established on the matched cleavage faces and on the opposite sides of thin flakes of calcium fluoride crystals. By selecting 022 and 022 reflections and MoKα1 radiation, stereopair projection x-rays topographs were studied and critically compared with optical micrographs. The dislocation etch pits and dislocation out crop images show a close resemblance. The orientation of the Burgers vectors of the dislocation lines has been identified and these lines lie parallel to the <110> directions. The growth history of the stratigraphical pattern has been studied using x-ray topographic technique.

    • 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.

    • Morphological aspects of some symmetrical ammonium hydrogen tartrate crystals grown by silica gel technique

      C C Desai A N Hanchinal

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      Ammonium hydrogen tartrate single crystals have been prepared by the reaction of NH4Cl and tartaric acid in silica gel. The morphology of some as-grown symmetrical crystals has been studied by optical microscopy. The growth morphology studies indicate that the grown crystals are needle-shaped, orthorhombic disphenoidal and tetrahedral disphenoidal. The growth mechanism has been assessed.

    • Magnetic susceptibility measurements of LHP and LNP crystals

      C C Desai M S V Ramana

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      Ferroelectric single crystals such as lead hydrogen phosphate (LHP) and dihydrated lead nitrate phosphate (LNP) have been derived from the diffusion of lead nitrate into the set gel containing orthophosphoric acid. By employing Faraday’s Gouy balance technique, the magnetic susceptibilities of LHP and LNP have been determined. It has been observed that (i) the gram and molar susceptibilities are independent of magnetic field, (ii)χM of LNP materials are greater than that of LHP materials and (iii) the positive values of magnetic susceptibilities suggest that LHP and LNP are paramagnetic materials.

    • Measurements of the microhardness and compression testing of ferroelectric lead nitrate phosphate single crystals

      C C Desai M S V Ramana

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      Ferroelectric crystals of lead nitrate phosphate (LNP) have been grown employing the controlled reaction between lead nitrate and orthophosphoric acid. The microhardness of LNP crystals has been determined. The effect of annealing and quenching on the mechanical properties of these crystals has been studied.

    • Electrolytic growth and properties of single crystals of ammonium hydrogen tartrate

      C C Desai

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      The growth of orthorhombic disphenoidal and long needle habit single crystals of ammonium hydrogen tartrate (AHT) in silica gels under the influence of an externally applied uniform field is described. The properties resulting from different growth parameters are reported. Variation in the electrical conductivities of AHT is illustrated. Two distinct electrical conductivity processes are reported. The polarization effect contributing to the dielectric constants is studied. The mechanism of dielectric behaviour which is different in lower and higher temperature ranges is discussed.

    • Controlled nucleation and growth kinetics of lead nitrate phosphate in silica hydrogel and characterization of grown crystals

      C C Desai M S V Ramana

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      Lead nitrate phosphate (LNP) single crystals were grown in silica hydrogel at an ambient temperature employing various nucleation control methods. The effect of concentration of feed solution, gel density, gel pH, ageing of gels and temperature on reduction of nucleation centres is reported. Kinetic studies of the nucleation and growth of LNP crystals and dentrites were studied. The crystals are characterized by X-ray diffraction, density measurements, magnetic susceptibility, mechanical strength measurements and dissolution behaviour.

    • Synthesis, characterization and properties of ferroelectric rubidium hydrogen tartrate single crystals

      C C Desai A H Patel

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      Rubidium hydrogen tartrate single crystals were grown in silica hydrogel. Controlled reaction was employed between tartaric acid and rubidium chloride solutions by slow diffusion process in the gel medium. Colourless transparent crystals were grown at room temperature. The average density of crystals measured pyknometrically was 2·263 g cm−3. Thermal stability of the materials was studied. Chemical etching was employed to determine the perfection of these crystals.

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