Reactivity of clean and oxidized aluminum surfaces towards sulphur compounds

Abstract

The interaction of H2S, CS2 and SO2 with clean and oxidized Al films has been investigated in the temperature range –78 to 200°C. Dissociative adsorption of H2S on Al films at –78°C was accompanied by H2 evolution, while CS2 uptake at this temperature was mainly molecular and reversible. With SO2, extensive adsorption and incorporation was possible at –78°C. The completion of the surface layer with each gas at temperatures –78°C was followed by a tarnishing reaction for which both the energy of activation and the pre-exponential factor were determined.The metal film of Al had a large and stable area after sintering at 70°C for 20 min; the roughness factor was usually 7.0. Oxygen adsorption on the film at 30°C caused some further reduction in area, but the roughness factor did not fall below 5.0 even when the film was saturated with oxygen at 30°C under an oxygen pressure of 5 N m–2. The presence of an oxide layer on the Al film decreased its tendency for subsequent adsorption of the sulphur compounds at all temperatures in the range –78 to 200°C. The uptake of CS2 by oxidized Al films above 50°C was extremely slow but accompanied by CO evolution.The pre-exponential factor for the reaction of each gas increased as the energy of activation increased and a compensation effect was assumed to operate in the tarnishing reactions by sulphur compounds on both clean and oxidized Al surfaces.