Abstract
The preparation step for extrusion (with binders) of Si 3N 4 powder, as well as the extrusion process itself, modify the original properties of the powder so that its recovery and subsequent rework are not possible. X-ray photoelectron spectroscopy (XPS), X-ray diffraction, infra-red spectroscopy, potentiometric titrations and zeta potential determinations have been used to identify the surface modifications in Si 3N 4 due to addition of binders, and to examine powders after elimination of the binders by extraction with organic solvents and heat treatment. The original Si 3N 4 with binders showed a shift in zeta potential and point of zero charge (PZC) to lower pH, indicating the adsorption of organic compounds on the Si 3N 4 surface at this step. The appearance of one O ls peak at 532.3 eV in the XPS spectrum showed the presence of Si 2N 2O. After extraction with organic solvents the PZC value was close to that of the Si 3N 4 + 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 Si 2N 2O was not modified as shown by XPS and the value of the isoelectric point. Heat treatment removes the organics completely but produces an oxidation of Si 3N 4 to SiO 2 as evidenced by a shift in the binding energy of the O ls photopeak to 534.0 eV.
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