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.