AQUEOUS PROCESSING OF SINTERED REACTION-BONDED SILICON-NITRIDE .1. DISPERSION PROPERTIES OF SILICON POWDER

An aqueous-based system (Si-Al2O3-Y2O3-Fe2O3) for processing sintered reaction-bonded silicon nitride (SRBSN) was investigated with an empha sis on chemical control of suspension component interactions. Chemical stability and dispersion properties of a commercial silicon powder we re characterized using electroacoustic, adsorption isotherm, and rheol ogical measurements. The interactions of silicon with nitriding agent, sintering aids, dispersants, and binder were considered. The effects of pH, electrolyte, aging, particle size, and solids loading were exam ined. The suspension properties of the silicon powder were influenced by the native oxide film and powder treatment history. The silicon-oxi de composite particles exhibit dispersion behavior similar to silica, characterized by a negative surface potential above pH 2. A method to improve the dispersion and homogeneity of suspension components based on the use of quaternary amine dispersants is proposed.