Abstract:
The main objective of this study is to investigate the sintering behaviors of silicon nitride ceramic added with alkaline earth oxide (i.e. magnesia, calcia, strontia, and baria) co-doped with yttria and silica. The alpha silicon nitride powder was used by a composition of 81.24 mol% with 9.53 mol% of alkaline earth oxide, 2.84 mol% of yttria, and 6.39 mol% of silica and mixed by ball milling. The mixed powders were pressed. The single-step sintering was conducted by sintered at 1650°C, 1750°C and 1850°C for 2 h under 1 or 10 atm of nitrogen gas with/without packing powder to get high density. The two-step sintering was then applied by sintered samples at 1650°C or 1750°C, and the temperature was then raised up to 1950°C for 8 h under 10 atm to remove some glassy phases. The sintered samples added with alkaline earth oxides at difference temperature showed difference properties between each other. The adding of magnesia and calcia have the same thermal conductivity as about 80-85 W/mK after two-step sintering. The resulting materials show high relative density as 98%, thermal conductivity of 85 W/mK, and mechanical strength of 834 MPa when added with calcia. On the other hands, the samples added with strontia and baria show lower mechanical strength and thermal conductivity.