The influence of two dopants: Li2O and Cr2O3 on the dissolution of NiO has been investigated using dilute sulfuric acid solutions at 60 °C. The dissolution rate is decreased by chromium additions of up to 1.0 mol pct Cr2O3, but the addition of 1 mol pct Li2O dramatically increases the dissolution rate. The results are interpreted in terms of the modification of the defect structure of NiO (p-type semiconductor with metal vacancies) by the dopants. It is proposed that Li+ doping increases the surface concentration of Ni3+ and that subsequent strong Ni3+-S O4 2- interaction enhances NiO dissolution. The NiO-S O4 2- surface interaction is confirmed with electrophoretic mobility measurements. A similar, though less pronounced, trend is observed when perchloric acid is used instead of sulfuric acid as the dissolution reagent. The difference in the behavior of the acids is attributed to differences in their affinities for the oxide surface.
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