EVIDENCE FROM DR SPECTRA AND TPR ON THE OXIDIC FORMS OCCURRING IN NIO-AL2O3 SYSTEMS

The UV/Vis diffuse reflectance (DR) spectra of NiO-Al2O3 systems obtai ned by mechanical mixing of oxides followed by calcination between 350 and 1400 degrees C are used for a detailed discussion and the reactua lisation of an earlier band assignment. From temperature-programmed re duction (TPR) curves, a percent distribution of the total nickel conte nt among various oxidic species, identified by hydrogen consumption pe aks, was estimated. An attempt was made to estimate the fraction of oc tahedral Ni2+ ions in the spinel forms from the same TPR data. The res ults were correlated with XRD data and magnetisation measurements on t he reduced samples.