Mechanism of low temperature decomposition of NiO single crystals

The decomposition of NiO single crystal was investigated under dissociative conditions in the temperature interval between 330 and 850 °C in the absence of reducing gas species. An unusually fast and constant decomposition rate was measured at the lowest temperatures, coupled with an unusual largely porous microstructure of the metallic product layer. This anomalous high reaction rate was interpreted on the basis of a decomposition mechanism implying the dissociative vaporization of the oxide followed by the condensation of the metal. The proposed mechanism is supported by the microstructure of the product and of the reacting interface. The complex dependence of reaction rate from temperature was shown to be related to a collapse of the porous product to form a compact metal layer at higher temperatures due to sintering.