• J Mukerji

      Articles written in Bulletin of Materials Science

    • Synthesis of boron nitride

      A K Basu J Mukerji

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      The authors examine the boric oxide—ammonia route with special stress on the yield and composition of the intermediate addition compound (BN)x(B2O3)y(NH3)z. It has been concluded that B2O3 and NH3 present in the addition compound formed between 350°C and 900°C cannot be further reacted to convert the B2O3 into BN and the BN yield remains at around 66%. A formula (BN)12·7(B2O3)7·5NH3 has been suggested for the addition compound.

    • Preparation and characterization of silicon nitride-silicon carbide composites

      N Kishan Reddy J Mukerji

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      Silicon nitride-silicon carbide (Si3N4-SiC) composites were prepared by varying the percentage of silicon nitride at temperatures of 1350 to 1450°C. The mechanical and thermal properties of these composites were determined. The modulus of rupture of the composites increases with increase of temperature whereas the thermal expansion decreases. Composites with 10% and 50% Si3N4 have modulus of rupture of 49 and 86 MPa at 1400°C and thermal expansion coefficients (25°–1000°C) of 4·4 × 10−6 and 3·2 × 10−6°C−1 respectively.

    • Properties of reaction bonded silicon nitride obtained from slip cast preforms

      J Rakshit J Mukerji

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      Fabrication of silicon preforms of high green density (>1·2 g/cm3) by slip casting of silicon (in aqueous medium) has been studied. The nitridation product consists of 59–85% α-Si3N4, 7–22%β-Si3N4 and 7–23% Si2N2O phase. The amounts of un-nitrided silicon were negligible. The microstructure is either granular or consists of needle-like grains (α-Si3N4) and whiskers deposited in the large pores. MOR values of the specimens are almost constant up to 1000°C or 1400°C or show slight increase up to 1000°C or 1200°C. In some cases a little dip around 1200°C, then a sharp increase in MOR up to 1400°C was observed.Kic values are almost constant up to 1000°C, and thereafter increase sharply.

      Pore size distribution, existence of Si2N2O phase and oxidation of RBSN at high temperatures have been considered for the explanation of the observed behaviour.

    • Oxidation kinetics of reaction-sintered silicon carbide

      O P Chakrabarti J Mukerji

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      The oxidation kinetics of reaction-sintered silicon carbide has been studied over the temperature range 1200° to 1350°C. The material has a bulk density of 3·00 g/cm3 and the unreacted Si content is 22·5% (v/v). The activation energy for oxidation is 28·75 ± 2·61 kcal/mol. It is proposed that the diffusion of oxygen through the growing oxide film is the rate-controlling process.

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