DETECTION OF ELEMENTAL SULFUR ON GALENA OXIDIZED IN ACIDIC SOLUTION

Galena (PbS) oxidation on potentiostatically treated specimens in acet ate buffer was investigated by atomic force microscopy (AFM) and by X- ray photoelectron spectroscopy (XPS), Elemental sulphur was detected a s an oxidation product by XPS. To minimize the evaporation of elementa l sulphur during the XPS experiments in ultra high vacuum, sample cool ing was required before the evacuation was started. Decreasing the pre ssure to 1 torr for 5 min, before the sample was cooled, removed the e lemental sulphur almost completely from the surface, In addition, when an electrochemically oxidized sample was exposed to air at ambient pr essure for about 3 h, the relative intensity of the S2p component of e lemental sulphur was observed to decrease to about half of the value a chieved by instant cooling and measuring, AFM images showed elemental sulphur to be present on galena surface as local accumulations rather than as a uniform layer, The sulphur formation is highly localized, bu t does not seem to occur preferentially at steps, (C) 1997 Elsevier Sc ience B.V.