Effective sintering aids for low-temperature sintering of AlN ceramics

A disappearing sintering aid was used to promote densification during the i nitial and middle stages of sintering and to be removed in gaseous form fro m the specimens during the final stage of sintering. From thermodynamic con sideration such as assessment of Gibbs free energy change of formation of A l2O3 compounds including metal-oxide and evaluation of the vapor pressure o f metal-oxide, Li2O is expected to become a disappearing sintering aid for AlN sintering. Doping with Li2O resulted in densification of AlN ceramics w ith Y2O3 and CaO additives by sintering at a firing temperature of 1600 deg rees C. The amount of Li2O in the specimens decreased by volatilization at temperatures higher than 1300 degrees C, and its amount was at a level of s everal ppm after firing at 1600 degrees C for 6 h. Low-temperature densific ation of AlN specimens by addition of Li2O also caused the improvement of t hermal conductivity and mechanical strength of sintered specimens. Present results indicate that a Li2O addition is effective for ALN sintering. Furth ermore, LiYO2 was also used as a new sintering aid instead of Li2O and Y2O3 , and the results of thermal conductivity and mechanical strength are shown .