Studying the surface reaction between NiO and Al₂O₃ via total reflection EXAFS (ReflEXAFS)

The reaction between NiO and (0001)- and ()-oriented Al₂O₃ single crystals has been investigated on model experimental systems by using the ReflEXAFS technique. Depth-sensitive information is obtained by collecting data above and below the critical angle for total reflection. A systematic protocol for data analysis, based on the recently developed CARD code, was implemented, and a detailed description of the reactive systems was obtained. In particular, for ()-oriented Al₂O₃, the reaction with NiO is almost complete after heating for 6 h at 1273 K, and an almost uniform layer of spinel is found below a mixed (NiO + spinel) layer at the very upmost part of the sample. In the case of the (0001)-oriented Al₂O₃, for the same temperature and heating time, the reaction shows a lower advancement degree and a residual fraction of at least 30% NiO is detected in the ReflEXAFS spectra.