Effect of ultrafine (AlN/Al) and Y₂O₃ powder addition on sintering characteristics and thermal diffusivity of AlN

Ultrafine powder AlN/Al with an average size of 300 nm was synthesized by an arc-plasma method. This powder was added up to 20 mass% into two kinds of commercial AlN powders prepared by direct nitridation of Al and carbothermal reaction of Al₂O₃. The samples were sintered at a temperature range from 1973 to 2123 K in a flow of N₂ gas with the help of sintering aid Y₂O₃ and their density and thermal conductivity were measured at 300 K. The ultrafine powder AlN/Al has a noticeable effect to reduce the sintering temperature and enhance the thermal diffusivity of the two kinds of AlN powders. This effect is more significant in the direct nitrided powder than that in the reduced powder. The sintered AlN compact with high density and high thermal diffusivity can be obtained at temperature lower than 2123 K with the aid of the ultrafine powder AlN/Al. Mechanism of this effect can be elucidated by the fact that the ultrafine powder AlN/Al has a large specific surface area and react easily with Y₂O₃ at low temperature where the commercial AlN powders can not. The effect of the ultrafine powder AlN/Al changes with the sintering temperature and Y₂O₃ content and the good effect of the ultrafine powder AlN/Al is observed when the sintering temperature is lower than 2123 K and Y₂O₃ is less than 8 mass%.