Stoichiometric vanadium oxides studied by XPS

Recovery of vanadium oxide from steelmaking slag is of great interest for Swedish steel producers and the technique for assessing the oxidation state of vanadium is crucial in the optimization of vanadium recovery. There is a large spread in the reported values of published V2p3/2 binding energy values for various oxidation states of vanadium. Therefore, an extensive analysis of vanadium oxide standards was performed aimed at obtaining reliable data and improved methods for the preparation of representative oxide standards. Powdered oxide standards of V2O5, VO2, V2O3, and VO, with purity better than 99%, were chosen. In their as-received state, all of the standards are covered by a thin layer of vanadium pentoxide that does not allow accurate evaluation of X-ray photoelectron spectroscopy spectra for vanadium oxides at lower oxidation states. Therefore, different methods for obtaining a representative surface for vanadium oxide standards were tested. The experimental results show high sensitivity of vanadium oxide standards to argon ion etching. Hence, a method to obtain a representative surface of standards by special heat treatment is proposed. Such approach was developed using a preparation chamber (furnace) attached to an X-ray photoelectron spectroscopy instrument. The annealing was performed in a vacuum at defined temperatures from 400 to 900?degrees C for 424 h; the annealing parameters were selected based on thermodynamic equilibrium data for vanadium oxides. Experimental fitting parameters (peak position E and full width of half maximum of the peak) for vanadium V2p3/2 and oxygen O1s peaks are thus obtained for stoichiometric vanadium oxides. Copyright (c) 2011 John Wiley & Sons, Ltd.