AlN powders produced via three major industrial processes, i.e., chemical vapor deposition (CVD) from triethyl aluminum, carbothermal reduction and nitridation of alumina, and direct nitridation of aluminum, are analyzed by using diffuse reflectance infrared Fourier transform spectroscopy with in situ heating in vacuum up to 700 degrees C. Powders from the CVD and direct nitridation processes showed OHs over tetrahedrally coordinated Al ions (Al-IV) above 250 degrees C, indicating a boehmite (AlOOH)-like surface oxide structure on the surfaces of original powders, while the powder from the carbothermal process did not present an apparent Al-IV-OH band, implying a theta-Al2O3-like surface oxide structure. The bands at 2245 and 2120 cm(-1) appearing above 200 degrees C, which were not identified previously, might be assigned to cyanato and cyano groups, respectively.