27 research outputs found
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
X-ray induced surface modification of aluminovanadate oxide
Aluminovanadate oxide, ââVâAlâOââ, has been studied by X-ray photoelectron spectroscopy (XPS) with the emphasis to reveal chemical modifications as a function of the X-irradiation time. Considerable damage was found for VâAlâO and less so for vanadium pentoxide, V2O5, and sapphire, a-Al2O3, both serving as reference samples. Modifications in VâAlâO were seen even at low radiation doses. Absolute and relative shifts in binding energies along with changes of peak intensities and widths demonstrate that an appreciable amount of V5+ is reduced to lower oxidation states. X-ray induced chemical modifications extend at least to the depth sampled by the V3p electrons. It is suggested that the damage is caused by electron-hole pair generation and Auger decay. AlâOâH in VâAlâO is also affected by X-rays. This causes O2 and water desorption as followed by mass spectrometry of the residual gas.info:eu-repo/semantics/publishe