Detection of elemental sulphur on galena oxidized in acidic solution

Galena (PbS) oxidation on potentiostatically treated specimens in acetate buffer was investigated by atomic force microscopy (AFM) and by X-ray photoelectron spectroscopy (XPS), Elemental sulphur was detected as an oxidation product by XPS. To minimize the evaporation of elemental sulphur during the XPS experiments in ultra high vacuum, sample cooling was required before the evacuation was started. Decreasing the pressure to 1 torr for 5 min, before the sample was cooled, removed the elemental sulphur almost completely from the surface, In addition, when an electrochemically oxidized sample was exposed to air at ambient pressure for about 3 h, the relative intensity of the S2p component of elemental sulphur was observed to decrease to about half of the value achieved 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, but does not seem to occur preferentially at steps, (C) 1997 Elsevier Science B.V