Studying the surface reaction between NiO and Al2O3via total reflection EXAFS (ReflEXAFS)

The reaction between NiO and (0001)- and (1 1102)-orientedAl2O3single 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 developedCARDcode, was implemented, and
a detailed description of the reactive systems was obtained. In particular, for
(1
1102)-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.