Dispersion of concentrated aqueous Si3N4-Y2O3-Al2O3 slips with tetramethylammonium hydroxide

The influence of pH and sintering aid powders on the viscosity and on the a mount of tetramethylammonium ions adsorbed of 35Vol% aqueous Si3N4 slips we re determined. The as-received Si3N4 powder was used. A mixture of 6 wt% Y2 O3 and 4wt% Al2O3 was used as sintering aid. Aqueous slips were prepared at different pH values in a range of 9.7 to 12.3 in an attrition mill. Tetram ethylammonium hydroxide was used to adjust the pH. The viscosity of Si3N4 s lips increased with increasing pH at the pH range studied. The sintering ai d powders had a positive effect on the dispersion of the Si3N4 powder at pH higher than 10.3 since a greater degree of dispersion could be obtained. T he lowest viscosity value (30 mPa.s) could be achieved from Si3N4/sintering aid slips at pH 10.5. (C) 1998 Elsevier Science Limited and Techna S.r.l. All rights reserved.