Synthesis and characterization of silicon nitride powders.

Carbothermal reduction-nitridation of silica-carbon mixture is known to yield silicon nitride powders with high alpha phase content. The reactions involved are complex and the mechanisms for reduction -nitridation are far from clear. In the present investigation an attempt is made to carbothermally reduce-nitride intimate mixtures of silica and carbon obtained from both aqueous as well as organo sol-gel route. The nitridation process was conducted at different temperatures and with different molar ratios of the starting acid and base catalysed gels. The kinetics of the process were investigated using isothermal thermogravimetry and the powders obtained were characterised by XRD, SEM and IR spectroscopy. The acid catalysed gels exhibited dense intimate mixtures while the base catalysed gets exhibited loose composites of high surface area. On nitridation, the latter had yielded powders of higher surface area as compared to those obtained from the former. The rate constants for nitridation-reaction were much higher for base catalysed gels as compared to acid catalysed gels. More Info

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