Investigation of mechanisms of corrosion due to diffusion of impurities by direct current glow discharge mass spectrometry depth profiling

Abstract

A glow discharge mass spectrometer was used to study the incorporation of impurities, such as lithium, boron and zinc, in ZrO2 layers grown on Zircaloy samples by two different techniques: (1) through heat treatment in an autoclave, under thermodynamic conditions and in a chemical environment similar to the primary cooling system used in pressurised water nuclear reactors (PWR), and (2) by reactive sputter deposition on aluminium and silicon substrates. The results obtained show a lithium intake in the oxide layer and confirmed the beneficial effect of the addition of boron to the corrosive environment by the decrease of the oxide layer thickness by a factor of 4, although not being incorporated in the oxide structure. The influence of zinc, used in boiling water reactors (BWR), on the corrosion behaviour could not be identified but its presence in the oxide network was clearly determined. The need for the application of the secondary cathode technique for the determination of the depth profile of insulating ZrO2 layers, as an alternative to the use of radiofrequency powered glow discharge techniques, is established.