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

A glow discharge mass spectrometer was used to study the incorporation of i mpurities, such as lithium, boron and zinc, in ZrO2 layers grown on Zircalo y samples by two different techniques: (1) through heat treatment in an aut oclave, under thermodynamic conditions and in a chemical environment simila r to the primary cooling system used in pressurised water nuclear reactors (PWR), and (2) by reactive sputter deposition on aluminium and silicon subs trates. The results obtained show a lithium intake in the oxide layer and c onfirmed the beneficial effect of the addition of boron to the corrosive en vironment by the decrease of the oxide layer thickness by a factor of 4, al though not being incorporated in the oxide structure. The influence of zinc , used in boiling water reactors (BWR), on the corrosion behaviour could no t be identified but its presence in the oxide network was clearly determine d. The need for the application of the secondary cathode technique for the determination of the depth profile of insulating ZrO2 layers, as an alterna tive to the use of radiofrequency powered glow discharge techniques, is est ablished.