• Volume 8, Issue 5

      December 1986,   pages  543-595

    • A simple hydrothermal cell for synthesis at moderate temperatures and pressures

      J A K Tareen B Basavalingu M A Shankara Ali Reza Fazeli

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      A simple hydrothermal cell without threaded parts has been developed for routine synthesis of materials at moderate temperatures (upto 500°C) and pressures (upto 5 kb). The sealing of the fluid pressure in the cell has been achieved with a cone-seat arrangement, but the sealing pressure has been through a hydraulic ram instead of a threaded cap. Experience showed that this cell is more convenient for rapid and routine experimentation.

    • Characterization and thermal behaviour of lanthanum tartrate crystals grown from silica gels

      P N Kotru N K Gupta K K Raina M L Koul

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      Results obtained on characterization of lanthanum tartrate crystals, grown by the gel method, using chemical analysis, x-ray and electron diffraction, infra-red and mass spectroscopy are reported. The thermal behaviour is studied using DTA, TGA and DTG. The decomposition pattern is reported to be typical of a hydrated metal tartrate. Kinetic parameters like order of reaction, frequency factor and activation energy are evaluated. Contracting cylinder kinetic model is found to be the best fit for the decomposition processes involved. Magnetic susceptibility measurements indicate the material to be diamagnetic.

    • Glass ceramics containing ferroelectric phases

      Om Parkash Devendra Kumar Lakshman Pandey

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      Glass ceramics prepared by controlled crystallization of glasses produce fine dispersion of crystallites in a glassy matrix. Glasses containing a mjor portion of constituents of a ferroelectric phase produce crystallites of ferroelectric phase in glass through a suitable heat treatment. The amount of network former in the initial glass has a profound influence on its crystallization behaviour and microstructure of the resulting ferroelectric glass ceramics. The value of dielectric constant and the nature of ferroelectric to paraelectric transition depend on the crystallite size and volume fraction of the ferroelectric phase. These glass ceramics are transparent for crystallite size less than 0·1µm and exhibit large quadratic-electro-optic effect.

    • Magnetic hysteresis and crystallization studies on metallic glass alloy Fe67Co18B14Si1

      A M Varaprasad C Radhakrishnamurthy

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      Magnetic hysteresis studies were carried out on Metglas 2605 Co(Fe67Co18B14Si1) samples, cut parallel and perpendicular to the ribbon axis and annealed at different temperatures. The samples annealed at 450°C for 2 hr show a coercive force of 8·75 Oe and 0·60 Oe in the parallel and perpendicular directions respectively. Electron probe micro analysis studies revealed the onset of primary crystallization at 400°C and a gradual displacement of B and Si from the lattice as the annealing temperature was increased to 450°C. The observed large coercive force is due to an increase in anisotropy resulting from an intergrowth pattern of the type FexCo1 −x, 0·3<x<1·0, including boron containing phases such as (FeCo)B, (FeCo)2B, (FeCo)3B, developed by the displacement of and Si from the original amorphous lattice.

    • Influence of eutectic addition on the electrical conductivity of Li2O:B2O3 system

      V K Deshpande K Singh

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      Addition of three eutectics, Li2SO4:Li2CO3, 3Li2O·Nb2O5:LiNbO3 and AgI:Ag2SO4 has been tried in the Li2O:B2O3 glass system. The electrical conductivity increases with the addition of eutectic. The amount of lithium fraction and the melting point of the eutectic govern the conductivity.

    • Optical black coatings for space applications

      K Ramaseshan M Viswanathan G K M Thutupalli

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      The durability properties of PTX-205 optical black coatings deposited on metallic and non-metallic substrates are studied. The coatings are stable against adverse environmental requirements for space applications. Typically, coatings with 8–11 µ thickness are opaque and have an average reflectance loss (<5%) in the spectral range of 200–1500 nm. The absorption to emission ratio is 1·01.

    • Dislocation density in electrolytically-coloured KCl crystals

      N L Bhole B T Deshmukh

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      Dislocation densities have been investigated in potassium chloride crystals, electrolytically coloured in the temperature range of 550–710°C. The results show an increase in the dislocation density with coloration temperature upto 650°C and decrease thereafter. This is attributed to the movement of dislocations and interactions between them during electrolytic coloration of the crystals.

    • A low-temperature attachment for a four-circle neutron diffractometer

      A Sequeira Sandhya Bhakay-Tamhane S R Sawant

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      A single-stage closed-cycle helium gas cryogenerator, capable of cooling between 77 K and 300 K, has been installed on the 4-circle neutron diffractometer at CIRUS. The cryo-tip assembly has been incorporated directly on the ϕ-circle of the full-circle crystal orienter in place of the goniometer head used in room temperature experiments. The salient features of this low-temperature attachment and its performance are discussed.

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