Kinetics of oxide film formation on zirconium in molten NaN03-KN03 eutectic

Abstract EN

Kinetics of oxide growth on Zr was studied under open circuit and polarization conditions at different temperatures by potential measurements.

Under open circuit conditions a thin insulating oxide film is formed following a iogerithmic law of growth, then the formation of a much less insulating film occurs.

Under polarization the effeciency of oxide formation was found to decrease with increasing temperature or current density on the expense of the other anodic processes, especially the melt oxidation (O2 evolution).

The latter process occurs even through the early stage of ploarization causes the failure of growth of the insulating oxide and predominates at last.

Doping of the insulating oxide by the evolved oxygen gas and other anodic products reduces the resistance and the electric field strength across the film and hence the ionic migration ceases.

The doping process manifests itself as a peak in the potential-time curve at high current densities.

Such peak is explained in terms of change in the film conductivity via doping of the oxide by the evolved O2 gas and other anodic products.