ON THE INTERACTION OF CRO2CL2 VAPOR WITH THE SURFACE OF GAMMA-AL2O3 AND THE FORMATION OF A CHROMIUM-OXIDE COVERING

Samples of gamma -Al//2O//3 containing different amounts of residual hydroxyl groups were obtained by thermal treatment. The possibility of interaction of the surface hydroxyl groups of gamma -Al//2O//3 with chromyl chloride vapor was studied by IR spectroscopy. The hydrogen chloride evolved as a result of the reaction interacts with both strained Al-O-Al bridges and the surface OH groups. Different types of OH groups show different reactivities with respect to the interaction with CrO//2Cl//2. Bands at 3780 and 3700 cm** minus **1 are due to OH groups which have a much higher reactivity than the OH groups responsible for bands at 3744 and 3733 cm** minus **1. Not all of the OH groups participate in the surface reaction. Decrease in their surface density results in increase in the reactivity. Modification of the gamma -Al//2O//3 surface is achieved by reaction cycles consisting of treatment with CrO//2Cl//2 vapor and hydrolysis of the compounds obtained by water vapor.