Surface Modification of Silicon Nitride Powder with Aluminum

Surface modification of Si 3 N 4 with alumina was tried. It was achieved by simply mixing Si 3 N 4 powder with an alumina sol up to ∼2 wt% as alumina in an aqueous medium, dried, and followed by calcination at 400°C for 1 h. A TEM micrograph showed a coating layer of ∼15 nm thickness. The isoelectric point of the modified Si 3 N 4 powder with porous alumina was at pH 7.8, which is different from 5.8 and 8.6 for Si 3 N 4 and amorphous alumina, respectively.