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 prop erties were characterized before and after extraction by electrokineti c sonic amplitude measurements. The isoelectric point (pH(iep)) was fo und to increase significantly for some powders after treatment. The po wder 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 tr eatment. 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.