Grinding of Agglomerate AlN Powder by Wet Milling

Fine AlN powder doped with Y2O3 and CaO as sintering additives was ground by a ball mill, a planetary ball mill and a super-fine grinding mill in order to obtain fine homogenous powder for low-temperature sintering. The size reduction and the sinterability of ground powders at 1500oC for 6 h were investigated. The size and shape of the agglomeration showed no significant change after the ball mill and planetary mill processes, resulting in poor densification. On the contrary, AlN particles with size of 50~100 nm was pulverized and dispersed by a super-fine grinding mill with very small ZrO2 beads as a mill media. The microstructures of the specimen exhibited equiaxed and homogenous grains with size of 0.3~0.4 μm. Pores in the specimens were eliminated. The thermal conductivity was 70W/mK, which is better than that of Al2O3 ceramics (~20W/mK).