• Volume 12, Issue 5

      December 1989,   pages  449-505

    • 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.

    • Zirconia-mullite ceramics by reaction-sintering

      B L Mitra N C Biswas P S Aggarwal

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      Zirconia-mullite composites were prepared byin situ reaction between zircon and alumina. Stabilizers like yttria and magnesium carbonate were used. Almost vitrified bodies were obtained by sintering at 1465–1535°C. Flexural strength increased on annealing at 1040°C.

    • Studies on dielectric hysteresis of ferroelectric potassium vanadate and lithium vanadate doped with Gd2O3

      A P Kashid V V Patil S H Chavan

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      The dielectric hysteresis property of undoped and Gd2O3-doped potassium vanadate and lithium vanadate has been investigated in the temperature range covering their transition points. The hysteresis loop method has been used for coercive field measurements. The coercive field of Gd2O3-doped KVO3 and LiVO3 increases for 0·025, 0·05, and 0·1 mol %, however, it decreases for 0·5, 1 and 3 mol % of Gd2O3. It was found that the Curie temperatures of KVO3 and LiVO3 remain the same for various concentrations of Gd2O3.

    • Thermal properties of barium-cadmium oxalate crystals

      S M Dharmaprakash P Mohan Rao

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      The kinetics and thermodynamics of the thermal dehydration of crystalline powders of BaC2O4·2H2O, CdC2O4·3H2O and Ba1−xCdxC2O4·2·5H2O have been studied by means of thermogravimetry, as a function of temperature. The dynamic dehydration kinetics are also examined using DTA, recorded simultaneously with TG as a function of temperature. The validity of the estimated mechanism and kinetic parameters is briefly discussed. From DTA study it is concluded that all dehydration peaks are endothermic and the decomposition peaks of barium oxalate to barium carbonate, cadmium oxalate to cadmium oxide and barium cadmium oxalate to barium carbonate and cadmium oxide are exothermic.

    • Nature and reactivity of silica available in rice husk and its ashes

      G Rama Rao A R K Sastry P K Rohatgi

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      Scanning electron microscopy, reactivity and surface area measurements of rice husk and its ashes reveal the gradual formation of amorphous silica during ashing. The reactivity of the silica thus formed is found to be at its maximum for ashing temperatures between 400 and 600°C and hold-time from 6 to 12 h. The reactivity of the ash is found to decrease with increasing temperature (⩾ 600°C) and hold-time.

    • Evaluation of the reactivity of titanium with mould materials during casting

      R L Saha T K Nandy R D K Misra K T Jacob

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      A methodology for evaluating the reactivity of titanium with mould materials during casting has been developed. Microhardness profiles and analysis of oxygen contamination have provided an index for evaluation of the reactivity of titanium. Microhardness profile delineates two distinct regions, one of which is characterised by a low value of hardness which is invariant with distance. The reaction products are uniformly distributed in the metal in this region. The second is characterised by a sharp decrease in microhardness with distance from the metal-mould interface. It represents a diffusion zone for solutes that dissolve into titanium from the mould. The qualitative profiles for contaminants determined by scanning electron probe microanalyser and secondary ion mass spectroscopy in the as-cast titanium were found to be similar to that of microhardness, implying that microhardness can be considered as an index of the contamination resulting from metal-mould reaction.

    • Effect of different reinforcements on composite-strengthening in aluminium

      A K Kuruvilla V V Bhanuprasad K S Prasad Y R Mahajan

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      In the development of metal-matrix composites, reinforcements of aluminium and its alloys with ceramic materials has been pursued with keen interest for quite sometime now. However, a systematic comparison of the effect of different reinforcements in powder-processed aluminium and its alloys is not freely available in the published literature. This study examines the influence of SiC, TiC, TiB2 and B4C on the modulus and strength of pure aluminium. B4C appears slightly superior as a reinforcement when comparing the effect of SiC, TiC, B4C and TiB2 on specific modulus and specific strength values of composites. However, TiC appears to be a more effective reinforcement, yielding the best modulus and strength values among those considered in this study. The differences in thermal expansion characteristics between aluminium and the reinforcements do not seem to explain this observation. The other advantage of TiC is that it is economically a more viable candidate as compared to B4C and TiB2 for reinforcing aluminium alloys. It is suggested that the superior effect of TiC as a reinforcement is probably related to the high integrity of the bond at the Al-TiC interface.

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