Aluminum nitride (AlN) powders were produced in an aerosol flow reactor by direct nitridation of aluminum vapor with ammonia and nitrogen in flowing argon. In the presence of excess NH3, pure AlN powders were obtained from 1400 to 1873 K. These powders had higher specific surface areas than commercially available AlN powders. The effects of reactor temperature and gas flow rate on AlN purity, yield, and grain and crystallite size were investigated. The BET grain diameter of AlN increased as the process temperature increased, indicating sintering controlled particle formation and growth. Both the crystallite size and the BET grain size of pure AlN powders slightly decreased as ammonia flow rate was increased. Increasing temperature and flow rate increased the AlN yield.