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. Atomiz ed aluminum metal and nitrogen gas were heated and reacted rapidly to synthesize AlN while they passed through the reaction zone of a transp ort flow reactor. The heated walls of the reactor simultaneously initi ated the reaction and removed the generated heat to control the exothe rm. Several variations of the process were required to achieve high co nversion and reduce wall deposition of the product. The fine AlN powde r produced did not require a postreaction grinding step to reduce part icle size. However, a secondary heat treatment, following a mild milli ng step to expose fresh surface, was necessary to ensure complete conv ersion 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 si ntered with 3 wt% yttria to fabricate fully dense parts which exhibite d high thermal conductivity. The powder was shown to be less sinterabl e than commercially available carbothermally produced powders.