Rmt. Sanchez et al., CHANGES IN SURFACE CHARACTERISTICS OF SILICON-NITRIDE PREPARED FOR EXTRUSION, Journal of the European Ceramic Society, 16(10), 1996, pp. 1127-1132
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.