• D Chakravorty

      Articles written in Bulletin of Materials Science

    • Glass fibre research at indian institute of technology, kanpur

      D Chakravorty

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      Research and development on glass fibres was started at the Indian Institute of Technology (IIT), Kanpur, about three years ago. The two main directions in which efforts have been concentrated are (i) development of indigenous technology for producing glass fibres, (ii) development of new glass compositions for drawing fibres having novel physical properties. In this note, we briefly describe the activities of this group and some of the salient results obtained so far.

    • Optical properties of bismuth granules in a glass matrix

      G C Das R Das D Chakravorty

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      Optical absorption characteristics for ultra-fine bismuth particles having dimensions around 10 nm and dispersed in both silicate and vanadium phosphate glass matrices have been investigated in the wavelength range 300 to 700 nm. Bismuth particles in vanadium phosphate matrix show an absorption peak around 440 nm whereas in silicate glass matrix they give two peaks in the ranges 500 to 530 nm and 420 to 430 nm respectively. The peak positions in all the glass-bismuth metal systems are predicted in fair agreement with experiment by Maxwell-Garnett (mg), as extended by Polder and van Santen (mg-pvs) and Bruggeman (br) effective medium theories. It is observed, however, thatmg-pvs andbr models give the best fit to experimental data over the entire wavelength range studied.

    • Glass-metal particulate composites

      D Chakravorty

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      Oxide glasses containing ultrafine metal particles have interesting physical properties and have been widely used in practical systems. The various preparational techniques developed so far for making these materials are discussed. Electrical conduction in these composites is controlled by electron tunnelling between the metal islands. At high electric fields certain glasses containing bismuth granules show a memory switching effect. The latter has been explained by a particle stretching model. Optical absorption characteristics of these composites can be explained on the basis of various effective medium theories developed so far for inhomogeneous materials. Glasses containing ferromagnetic metal grains show a superparamagnetic behaviour with a transition temperature below 300 K. Improvement in the mechanical properties of glasses can be achieved by incorporating metal particles of suitable characteristics within them. In this paper the present state of understanding of all these properties is reviewed.

    • Synthesis and properties of manganese-doped barium titanate

      L M Arunachalam D Chakravorty E C Subbarao

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      An oxalate route for the production of BaTiO3 has been modified to incorporate Mn (upto 2%) as a dopant and the reaction sequence has been studied. The resulting Mn-doped BaTiO3 exhibits a dielectric constant with an increasing insensitivity to temperature and applied a.c. field as the Mn content is increased. These samples possess a high electrical resistivity even after treatment in hydrogen at 1100°C and are therefore suitable as dielectric for multilayer capacitors with base metal electrodes.

    • Cluster effects on optical properties of glass-metal nanocomposites

      G C Das D Chakravorty

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      Optical absorption characteristics in a glass-metal nanocomposite system involving bismuth metal have been analysed using effective medium theories with a model incorporating single strand chains andfcc clusters of metallic bismuth particles. The computed values show fair agreement with experimental data.

    • Foreword

      P Rama Rao K J Rao D Chakravorty H S Maiti

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    • Nanocomposites

      D Chakravorty

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      Nanocrystalline metals having sizes of the order of a few nanometres dispersed in an oxide glass matrix have been discussed in this review. The various physical and chemical routes developed so far for synthesizing such materials have been described. The different physical properties, especially optical, electrical and magnetic behaviour of these nanocomposites have been delineated. The physical mechanisms which give rise to these characteristics are discussed.

    • Synthesis of aluminium matrix composites containing nanocrystalline oxide phases

      S K Pradhan A Datta A Chatterjee M De D Chakravorty

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      Using nanocrystalline particles of mullite and zirconia respectively with diameters in the range 20–30 nm prepared by a sol-gel route, aluminium metal-matrix composites have been synthesized. A hot pressing technique has been used with temperatures varying from 450–610°C. The vickers hardness values for the composites are found to be substantially higher than that of pure aluminium. An order of magnitude increase in hardness is achieved when Al5Mo phase is grown in the composite.

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