Many organic acids, such as benzoic acid, salicylic acid, o-or p- phthalic acid and tartaric acid, can disperse spontaneously onto the surface of γ-Al~2O~3 in a monolayer state. The critical dispersion temperature depends on the number and polarity of the polar groups in the molecule. The structure of benzoic acid-γ-Al~2O~3 system has been characterized by XRD, Raman, FT-IR, UV-vis and TG. The results show that benzoic acid can disperse onto the surface of γ-Al~2O~3 very readily, even at room temperature. After dispersion, the H-bond association structure among benzoic acid molecules collapses and the carboxyl groups react with the surface hydroxyl groups of γ-Al~2O~3 to form a salt-like structure on the surface. There is not any direct interaction between the benzene ring of benzoic acid molecule and the surface of γ-Al~2O~3. The dispersion threshold determined by XRD is 1.1 mmol benzoic acid/100m^2 γ-Al~2O~3, which is very close to the utmost monolayer dispersion capacity 1.2mmol/100m^2 calculated according to a model that the benzene ring in benzoic acid molecule is perpendicular to the surface of γ-Al~2O~3.

Key words: ALUMINIUM OXIDE, BENZENECARBOXYLIC ACID, SALICYLIC ACID, BENZENEDICARBOXYLIC ACID, TARTARIC ACID, X-RAY DIFFRACTION ANALYSIS, FOURIER TRANSFORM, INFRARED SPECTROPHOTOMETRY