Homogeneous Mixing of Si3N4 with Sintering Additives by Coprecipitation Method

,; ,

J. Korean Ceram. Soc. > Volume 30(10); 1993 > Article

Journal of the Korean Ceramic Society 1993;30(10): 829.

질화규소의 소결첨가제의 공침법에 의한 균일혼합

김지순

울산대학교 재료공학과

Homogeneous Mixing of Si3N4 with Sintering Additives by Coprecipitation Method

ABSTRACT

Chemically and geometrically homogeneous mixing of Si3N4 powders with sintering additives(YAG, 3Y2O3$.$5Al2O3) was attempted via coprecipitation method. X-ray dot maps for the additive elements(Al and Y) showed that the additives are evenly distributed in the powder mixture prepared by coprecipitation method(CP). TEM observation of the coprecipittion-treated Si3N4 powders revealed that they are covered with extremely fine crystallites of additive. The shift in isoelectric point(IEP) of Si3N4 powders from pH 6.7 to pH 7.9 after coprecipitation mixing gave another evidence for coating of Si3N4 powders with YAG additives. SIMS analysis for composition on the surface and in the matrix of mixed powders showed that the YAG additives are highly enriched on the surface of coprecipitation-treated Si3N4 powders. Especially when a small amount of additive was used, the effect of homogeneous additive distribution on densification was preceptible: After pressureless-sintering of powder compacts containing 5 mol% YAG at 1800$^{circ}C$ for 0.5h, a sintered density of 96.5% theoretical was obtained from the specimens prepared bycoprecipitation in comparison with 93.8% from the mechanically-mixed one.