Kinetic dissociation of nickel titanate and nickel tungstate in oxygen potential gradients

Abstract

Nickel titanate (NiTiO) and nickel tungstate (NiWO) were exposed to oxygen potential gradients at 1400 and 1100° C, and they were found to dissociate into their constituent oxides, namely, NiO and TiO, and WO and NiO, respectively. This is consistent with the non-equilibrium phenomenon of kinetic decomposition. In the case of nickel titanate, at the low-oxygen-potential side, TiO was formed as sharp needle-like structures within the titanate matrix, while at the high-oxygen-potential side, NiO was formed. In contrast, NiO was formed at the lower-oxygen-potential side in the case of nickel tungstate, while WO volatized off from the high-oxygen-potential side. This indicated that W diffuses faster than Ni in tungstates. In both cases, there were significant macroscopic shifts of the oxide with respect to the original position, established with Pt markers, towards the high-oxygen-potential side