• Volume 5, Issue 1

      March 1983,   pages  1-83

    • Manganous-zinc ferrites synthesized out of MnO

      C E Deshpande P P Bakare M N Sankarshana Murthy

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      Manganous-zinc ferrites are best prepared directly from MnO and can be conveniently pressed with non-volatilizable binders such as polyvinyl alcohol which however can be burnt out without oxidizing the Mn2+ in the ferrite by sintering in a static atmosphere generated by the thermal dissociation of active ferric oxide pellets placed out of contact with the ferrite in the closed sintering unit. Such a process eliminates cracks and rejections in the sintered pieces besides giving very satisfactory and reproducible results.

    • Growth and characterization of hydrothermally-grown zeolite crystals

      M S Joshi B T Bhoskar

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      Studies on hydrothermal synthesis of zeolite crystals, in Na2O-Al2O3-SiO2-H2O system, are reported. Experimental procedure and growth parameters are briefly described. Cube-like and rod-like crystals (called VSZ-1 and VSZ-2) are illustrated. It is established that VSZ-1 crystals are metastable, while VSZ-2 crystals are stable. Crystallanity of these two samples is established. Observations and results of characterization of these two varieties by TEM, SEM, electron microprobe and infrared methods are described, illustrated and interpreted. The role of Si/Al ratio is explained.

    • Glass formation region and electrical conductivity in the system B2O3-Li2O-Li3PO4

      B Basu H S Maiti A Paul

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      Glass formation region was determined for the B2O3-Li2O-Li3PO4 system. Under the present experimental conditions, binary lithium borate glasses could be formed containing a maximum of 27 mol% Li2O. However, this could be increased to 36 mol% in the ternary system. Electrical conductivity was measured at temperatures ranging from room temperature to 350°C. The temperature dependence of the electrical conductivity of these glasses follows Arrhenius equation. The conductivity increased with increasingly alkali content. Maximum conductivity of the order of 10−4 ohm−1 cm−1 was obtained with the glass containing about 36 mol% Li2O at 250°C. Activation energy for conduction also varied with total Li2O content.

    • Effect of flux content on thermoluminescence yield of BaS phosphors

      R P Rao D R Rao

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      BaS phosphors doped with impurities like Cu and Bi were prepared by using NaCl as flux. Thermoluminescence of these samples prepared with different quantities of flux has been studied by exciting them at room temperature with x-rays. The amount of flux for a good thermoluminescence yield has been estimated between 25 to 30% by weight depending upon the type of phosphor.

    • Development of zinc oxide varistors

      H S Kalsi B K Das

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      Grain growth kinetics of ZnO ceramics containing 6% additives of Bi2O3, CoO and MnO in equal molar ratios has been studied in the temperature range 1000 to 1350°C. It has been observed that the grain growth data fits theD2=kt law and the activation energy computed from the rate constants is 65 kcal/mol.

    • Linear electrooptic effect in doped KDP crystals

      KBR Varma K V Ramanaiah K Veerabhadra Rao

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      The dispersion of half wave voltages with wave length and temperature of potassium dihydrogen ortho phosphate (KDP) crystals with additives and dopants like borax, nickel phosphate, manganese phosphate, sodium dihydrogen orthophosphate and potassium arsenate were determined. The refractive index for all the above crystals were found by the modified Rayleigh’s refractometer method. The linear electrooptic coefficients were calculated at various wavelengths of light. The variation of half wave voltage was also studied as a function of concentration of the dopant.

    • Use of gold/palladium surface replicas for high kV (30),sem examination of low Z materials

      R M Pradhan

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      A procedure for making high fidelity gold/palladium surface replicas of various low atomic number (Z) materials for SEM examination has been developed. The procedure facilitates simultaneous replication of a number of SEM specimens. These replicas provide improved image quality, elimination of charging and beam penetration artifacts and microtopographical information, often not available by direct SEM examination of low Z materials at 30 kV.

    • Electron microscopic studies on the effect of Sn addition on the ageing characteristics of Al-0.7% Mg2Si alloy

      Gouthama Kishore

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      The effect of trace addition of Sn on the ageing characteristics of Al-0.7% Mg2Si has been studied by hardness measurements and transmission electron microscopy. The changes observed in the microstructural features have been explained on the basis of the strong interaction existing between Sn atoms and quenched-in vacancies. At ageing temperatures below 200°C Sn addition brings about a ratardation in the kinetics of G.P. zone growth whereas at higher ageing temperatures, it aided the precipitate nucleation and growth. The hardness data agree well with the deductions based on observations made on the thin foils.

    • Stress relaxation in ferroelectric materials

      V C S Prasad

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      Stress relaxation takes place in BaTiO3 type ferroelectric materials due to the motion of non 180° domain boundaries, which are the twin boundaries. The nature of stress relaxation taking place due to plastic deformation in crystalline solids and that due to twin boundaries in ferro electric materials is discussed. The usefulness of the stress relaxation data for the study of domain wall motions in this type of ferroelectrics is pointed out.

    • Microhardness of rhombohedral crystals: Calcite and sodium nitrate

      J R Pandya L J Bhagia A J Shah

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      The variation of hardness of rhombohedral single crystals of calcite and sodium nitrate with quenching temperature is studied. Vickers and Knoop hardness numbers are determined from the indentations produced on freshly-cleaved crystal surfaces for various loads. The variation of hardness number with quenching temperature can be represented byHTqk=constant where the exponentk is less than unity and its sign determines the nature of material.

    • Announcements

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