Characterization of plasma-sprayed titanias by X-ray photoelectron spectroscopy and electron spin resonance spectroscopy

Abstract

Several plasma-sprayed titania coatings were characterized by the methods of X-ray photoelectron spectroscopy (XPS), electron spin resonance spectroscopy and X-ray diffraction (XRD). The main component of all the sprayed titanias was identified as a rutile phase and small amounts of secondary phases were detected in titanias II and III (sprayed using ArH 2 and ArHe gas mixture respectively). An electron spin resonance was observed near g = 1.9 in titanias II and II By comparison with XRD and secondary ion mass spectrometry results, the resonance originates from Ti 3+ ions in the secondary phases and it is suggested that the secondary phases are somewhat reduced and not very crystalline. Furthermore, from the linewidths and the g values of the resonances at room temperature and 77 K it is deduced that the Ti 3+ ions are in octahedral environments and that the short-range environment round the Ti 3+ ions in titania II is less symmetrical than that in titania III. XPS analysis indicates that titanium ions near the surface of titania sprayed on carbon are tetravalent but a reduction of the rutile phase was observed on Ar + ion sputtering.