Abstract
A chemical adsorption method in a Si3N4 slurry that contained a nitrate solution was studied during ball milling, with particular interest in increasing the oxide layer in the Si3N4 powder and improving the distribution homogeneity of the sintering additives. The nitrate salts Al(NO3)3·9H2O and Y(NO3)3·6H2O were selected as sintering additives. The following characterization techniques were used: oxygen–nitrogen analysis, X‐ray photoelectron spectroscopy, high‐resolution electron microscopy (coupled with energy‐dispersive X‐ray spectroscopy), and X‐ray imaging (using wavelength‐dispersive X‐ray spectroscopy). The thickness of the amorphous layer and the oxygen content of the Si3N4 powder were greater for samples that were milled with nitrate additives, which were heat‐treated at 600°C, than those of powders that were milled with oxide additives. The chemical composition of the oxygen‐containing layer—that is, the amorphous layer that formed and/or changed on the Si3N4 surface—was similar to Si2N2O in heat‐treated Si3N4 powder with nitrate additives, whereas the composition of heat‐treated Si3N4 powder with oxide additives was similar to SiO2. Furthermore, a homogeneous distribution of the additives was achieved via the incorporation of aluminum and yttrium into the amorphous layer on the Si3N4 surface. The metal ratio (Y:Al) of the adsorbates was somewhat higher than that of the additives.
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