RAPID PROCESS FOR MANUFACTURING ALUMINUM NITRIDE POWDER

A rapid, direct nitridation process for the manufacture of sinterable aluminum nitride (AlN) powder was developed at the pilot scale. Atomized aluminum metal and nitrogen gas were heated and reacted rapidly to synthesize AlN while they passed through the reaction zone of a transport flow reactor. The heated walls of the reactor simultaneously initiated the reaction and removed the generated heat to control the exotherm. Several variations of the process were required to achieve high conversion and reduce wall deposition of the product. The fine AlN powder produced did not require a postreaction grinding step to reduce particle size. However, a secondary heat treatment, following a mild milling step to expose fresh surface, was necessary to ensure complete conversion of the aluminum. In some instances, a final air classification step to remove large particles was necessary to promote densification by pressureless sintering. The AlN powder produced was pressureless sintered with 3 wt% yttria to fabricate fully dense parts which exhibited high thermal conductivity. The powder was shown to be less sinterable than commercially available carbothermally produced powders.