Water-vapour uptake and electrical conduction in chromia

Abstract

Chromia was prepared by heating in air, at 200 °C for 5 h, the thermal decomposition product of CrO₃. The rate of the adsorption of water on the oxide was followed gravimetrically. An equation of the Elovich type was obtained dq/dt=k′p^0.6 exp (–α′q/RT_p^0.5) where k′ and α′ are constants, q is the amount of adsorbed water and p is the pressure. The dependence of the electrical conduction of chromia on increasing water-vapour adsorption can be explained in terms of two different mechanisms: a decreasing semiconduction mechanism of a p-type conductor and an increasing protonic conduction mechanism.