The nature of the passive film on cathodically modified stainless steels

This paper discusses the effect of additions of platinum group metals (PGMs) on the composition of the passive surface layer formed on stainless steels in reducing acid media. It has been shown that there is an accumulation of these noble metals on the surface of the alloy during the period of active dissolution. The morphology and factors influencing this accumulation of PGMs on the surface are discussed. It was also found that there are differences between passive films formed spontaneously and those formed under potentiostatic control. An interesting fact emerging from the investigations is that different PGMs form different types of oxides on the passivated surfaces. Areas for possible future research are mentioned.