Preparation and evaluation of sinterable silicon nitride powder by imide decomposition method

A chemical synthesis process for producing high-quality Si[sub 3]N[sub 4] powder was developed by applying an imide decomposition method and well-controlled heat-treatment to the crystallization process. Si[sub 3]N[sub 4] powder produced by this process had superior characteristics, such as high purity, fine particle, high [alpha]-content, and good sinterability. Highly dense Si[sub 3]N[sub 4] ceramics were fabricated by both high-pressure hot-pressing of Si[sub 3]N[sub 4] without additives and pressureless sintering of oxide-doped Si[sub 3]N[sub 4], and their excellent mechanical properties were demonstrated. [alpha]/[beta]-SiAlON ceramics were fabricated by sintering the mixture of [alpha]-Si[sub 3]N[sub 4] and Ln-[alpha]-SiAlON powders (where Ln = Y and lanthanide elements), and the thermomechanical properties of SiAlON-based ceramics were much improved by selecting Tm or Yb as the lanthanide elements.