NONAQUEOUS PROCESSING OF SILICON FOR REACTION-BONDED SILICON-NITRIDE

Ethanolic silicon suspensions, with and without a polyethoxylated amin e of low molecular weight, were studied by rheological, adsorption, el ectrophoretic, and sedimentation methods. Pellets were pressure-cast a nd nitrided to form reaction-bonded silicon nitride. Density and bindi ng strength in the green state relate well to rheological behavior and other collodial aspects of the suspensions used, particularly the add itive's role and distribution. Density and degree of nitridation in th e final state are not importantly affected by the additive's use. Its greatest benefit is to modify the binding strength in the green state. The mode by which this small molecule affects the processing of silic on consists of adsorption, combined with an increased electrostatic in terparticle repulsion which increases the suspension viscosity and tha t of undried pellets. Although the improved binding strength is accomp anied by decreased green and nitrided densities, high degrees of conve rsion to silicon nitride are still achieved.