EFFECTS OF SOXHLET EXTRACTION ON THE SURFACE OXIDE LAYER OF SILICON-NITRIDE POWDERS

An aqueous soxhlet extraction procedure was used to surface-clean five commercial silicon nitride powders. The solid-solution interface properties were characterized before and after extraction by electrokinetic sonic amplitude measurements. The isoelectric point (pH(iep)) was found to increase significantly for some powders after treatment. The powder surface was analyzed using X-ray photoelectron spectroscopy and X-ray induced Auger electron spectroscopy before and after extraction. The surface oxygen content and oxide layer thickness decrease after treatment. A linear correlation was found between oxide thickness and pH(iep), which yields a pristine pH(iep) of about 9.7 for the unoxidized Si3N4 particle.