The use of x-ray absorption spectroscopic techniques to study the influence of alloying elements on passive films

X-ray absorption spectroscopic techniques can be used to investigate the structure, composition, and electronic properties of in situ and ex-situ passive films on metal surfaces. Earlier EXAFS (extended x-ray absorption fine structure) studies on the effect of Cr on the structure of the passive film on iron indicated that the addition of Cr produces a less crystalline film than that which forms on pure iron. EXAFS by means of surface reflection (reflEXAFS) enables the study of surface films directly on bulk alloy surfaces. ReflEXAFS has been applied to a study of the films on rapidly solidified Mg alloys, in which it was also found that the more protective films have a less well ordered structure. In addition, the electronic properties of passive layers on FeCr alloys have been studied by means of reflEXAFS in which the NEXAFS (near edge x-ray absorption fine structure) was used to examine the effect of Cr and Cl− (introduced to initiate breakdown) on ex-situ passive films.