Kinetics of growth and lateral spreading of a spinel layer around NiO particles on Al 2O 3 substrate

Abstract

The kinetics of thickening and lateral spreading of a thin layer of NiAl 2O 4 spinel around individual NiO particles, located on single crystalline Al 2O 3 substrate, have been analyzed theoretically and studied experimentally by SEM and AFM in the temperature range 1000–1100 °C. It was assumed that, due to small thickness of the forming layer, the kinetics of thickening is limited by the reaction rate at the spinel–substrate interface, whereas the lateral propagation of the layer is controlled by surface diffusion of NiO molecules. The reaction rate control at the spreading front of the growing compound layer was also taken into account. By comparison the rates of lateral spreading with relations derived, the diffusion coefficients of NiO on the NiAl 2O 4 spinel surface and the surface diffusion activation energy have been estimated.