SOME FACTORS INFLUENCING THE FORMATION OF REACTION-BONDED SILICON-NITRIDE

Several salient factors influencing the formation of reaction-bonded silicon nitride (RBSN) compacts have been studied. These include the effects of mullite and alumina furnace tubes typically employed during ''high-purity'' nitridation studies, pre-sintering of green silicon compacts, free powder versus compact nitridation, and the influence of metal/metal oxide additions. The latter studies have provided experimental evidence for enhancement due to dissociated nitrogen, and suggest that (1 ) beta-Si3N4 formation does not necessarily require a liquid phase, (2) atomic nitrogen stimulates beta-phase formation, and (3) the liquid phase provides an efficient source for volatile silicon, promoting alpha-Si3N4. These conclusions are consistent with accepted mechanisms for the formation of the two phases.