The correlation of XPS analysis with electrochemical history in aqueous corrosion

Abstract

The response of the surface composition of aluminium brass to electrochemical polarization is sea water has been studied by XPS in an attempt to elucidate the behaviour of condenser tube surfaces in marine environments. Individual specimens were polarized at 100 mV intervals between +100 and −1200 mV (SHE) for a charge transfer of 500 mA s. The rather complex spectra were normalised using Jorgenson's factors to permit meaningful discussion of the surface chemistry. In addition an ion etching was used to remove the high surface coverage of carbon molecules picked up from solution. The validity of each of these techniques, necessary for examination of samples removed from the aqueous phase, is discussed. In the present case they permit the observation of a strong correlation between the Mg ++/Cl − ratio and the surface potential. The movement of the ratio gives a nice demonstration of cathodic basicity and anodic acidity in accord with electrochemical concepts. This result may be of practical use in ascertaining whether corrosion pits on industrial plant are still active.