CHANGES IN SURFACE CHARACTERISTICS OF SILICON-NITRIDE PREPARED FOR EXTRUSION

The preparation step for extrusion (with binders) of Si3N4 powder, as well as the extrusion process itself; modify the original properties o f the powder so that its recovery and subsequent rework are not possib le. X-ray photoelectron spectroscopy (XPS), X-ray diffraction, infra-r ed spectroscopy, potentiometric titrations and zeta potential determin ations have been used to identify the surface modifications in Si3N4 d ue to addition of binders, and to examine powders after elimination of the binders by extraction with organic solvents and heat treatment. T he original Si3N4 with binders showed a shift in zeta potential and po int of zero charge (PZC) to lower pH, indicating the adsorption of org anic compounds on the Si3N4 surface at this step. The appearance of on e O-ls peak at 532.3 eV in the XPS spectrum showed the presence of Si2 N2O. After extraction with organic solvents the PZC value was close to that of the Si3N4 + binders (pH = 3.2), indicating incomplete removal of organics; this was confirmed by XPS determination (C-ls intensity data) and chemical analysis. The presence of Si2N2O was not modified a s shown by XPS and the value of the isoelectric point. Heat treatment removes the organics completely but produces an oxidation of Si3N4 to SiO2 as evidenced by a shift in the binding energy of the O-ls, photop eak to 534.0 eV. (C) 1996 Elsevier Science Limited.