The isotopic exchange of oxygen-18 with the oxygen of niobium (V) oxide

The kinetics of the exchange of gas-phase oxygen-18 with the oxygen of niobium(V) oxide has been studied in a staticcirculation'' apparatus. Both the surface and bulk oxygen in the oxide possess low mobility and exhibit energetically uniform behaviour. From the experimental data for the specific rates of exchange, at 620 to 700 deg C, an activation energy of 61 kcal x mole/ sup -1/ was calculated. The reaction order was 0.6 in the oxygen pressure range 5 to 30 torr. Kinetic data are interpreted. Relationships between the low oxygen mobility in a transition metal oxide and the degree of covalency of the metal/oxygen bond are discussed. (GE)