The silation of gamma-Al2O3 with hexamethyldisilazane (HMDS) has been examined over the temperature range 150-450 degrees C. The products and sequence of the reactions at the alumina surface have been determined, and a mechanism is proposed. At all temperatures and feed rates of HMDS the initial gaseous product is methane. The molar ratio of methane formed to HMDS consumed increases with increasing temperature. As the reaction progresses, hexamethyldisiloxane (HMDSO), ammonia, and nitrogen are formed. The quantity of each of these products decreases with increasing temperature. The proportion of Si and N irreversibly bound to the alumina surface from HMDS consumed increases with increasing temperature. The reaction of HMDS with alumina is sequential. Initially, HMDS reacts with surface sites to generate pendant -O-SiMe3 and -NH-SiMe3 moieties. At temperatures over 300 degrees C the predominant subsequent reaction is elimination of methane by reaction of the pendant silyl groups with acidic surface hydroxyls. At lower temperatures reactions between silyl groups to form HMDSO, protonation of amino groups to form ammonia, and redox reactions to form elemental nitrogen predominate over methane elimination.