Stoichiometric Vanadium Oxides Studied by XPS

Artikel i vetenskaplig tidskrift, 2012

Recovery of vanadium oxide from the steelmaking slag is of great interest for Swedish steel producers and technique for assessing the oxidation state of vanadium is crucial in optimization of the vanadium recovery. There is a large spread in the reported values of the published V2p3/2 binding energy values for various oxidation states of vanadium. Therefore extensive analysis of vanadium oxide standards was performed aiming to obtain reliable data as well as improved methods for preparation of representative oxide standards. Powdered oxide standards of V2O5, VO2, V2O3 and VO of purity better than 99% were chosen. In as-received state all of the standards are covered by a thin layer of vanadium pentoxide that does not allow accurate evaluation of XPS spectra for vanadium oxides in lower oxidation states. Therefore different methods for obtaining of 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 representative surface chemical compositions of standards by special heat-treatment is proposed. Such approach was developed using preparation chamber (furnace) attached to the XPS instrument. The annealing was performed in vacuum at defined temperatures from 400 to 900ºC for 4-24 hours; 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 FWHM) for vanadium V2p3/2 and oxygen O1s peaks are thus obtained for stoichiometric vanadium oxides.