Behaviour of oxide films in boric acid - lithium hydroxide solutions

This chapter presents a combined approach for studying oxide scales formed on stainless steels surface in exposure to 300° C water containing boric acid and lithium hydroxide in an autoclave. The in-situ electrochemical impedance spectra (EIS) are obtained to relate the behavior of the oxide layer to the electrochemical processes taking place during the exposure. The ex-situ analysis by XPS is performed to determine a depth profile of the composition of the oxide layer. Additionally, a point defect computer model is used to simulate the oxide layer behavior in respect to the charge transfer through the interfaces. The first EIS results shows that the high frequency part of the Nyquist diagram confirms formation of an oxide layer, however the data are too spread to be interpreted in terms of thickness and composition. Complementary, XPS profiles provides well defined composition depth profiles, possible to be quantified both in depth and composition (molecular speciation) within some inherent limits. Preliminary results of the Point Defect Model (PDM) simulation reveal the typical charge distribution in ID case for a bicarrier monoxide.