Aluminum nitride sintering aids

Aluminum nitride powder synthesized by high-temperature routes can be sintered to a density of more than 97% of the theoretical density by adding calcium or yttrium compounds as sintering aids [52-54]. Therefore, new processing routes to aluminum nitride predominantly aim at powders with lower quantities of cationic impurities. In addition, the formation of aluminum nitride coatings [55-58] or fibers [59] has become subject of extensive research. 

Well known sintering aids in category (1) are alkali-earth oxides or rare-earth oxides such as Y2O3 (17,18) and CaO (19,20). These can be added not only as oxide but also as nonoxide compounds such as halide, nitride, carbide, nitrite, or carbonate. Some of the transition elements such as NiO and Ti02 can be classified as category (2) additives. Rare earth or alkali-earth oxide additive reacts with aluminum oxide of AIN powder (i.e. oxide layer of AIN powder) to form aluminate liquid at a high temperature Eq. (4) and promotes liquid-phase sintering of AIN powder. 

---