Nonaqueous Processing of Silicon for Reaction-Bonded Silicon Nitride

Ethanolic silicon suspensions, with and without a polyethoxylated amine of low molecular weight, were studied by rheological, adsorption, electrophoretic, and sedimentation methods. Pellets were pressure-cast and nitrided to form reaction-bonded silicon nitride. Density and binding strength in the green state relate well to rheological behavior and other collodial aspects of the suspensions used, particularly the additive’s role and distribution. Density and degree of nitridation in the 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 silicon consists of adsorption, combined with an increased electrostatic interparticle repulsion which increases the suspension viscosity and that of undried pellets. Although the improved binding strength is accompanied by decreased green and nitrided densities, high degrees of conversion to silicon nitride are still achieved.