Electrochemical and X-ray photoelectron spectroscopy investigation into anodic behaviour of electroless Ni–9·5 wt-%P in acidic chloride environment

Abstract

This paper reports on the anodic behaviour of as plated (X-ray amorphous) and heat treated (crystalline) high P electroless Ni-P deposits investigated by potentiodynamic and potentiostatic methods in acidic aqueous chloride solutions. Potentiodynamic measurements show an active-passive behaviour for both structures. The valence of P dissolution was assessed by the weight loss v. charge technique; dissolution valences do not correlate clearly with potentiodynamic behaviour. This can nevertheless be clearly interpreted in terms of ex situ X-ray photoelectron spectroscopy analyses of attacked layer composition; the layers formed at lower anodic potential within the passive range consist of NiO, the ones obtained at high anodic polarisation contain phosphate. Differences in anodic behaviour of as plated and heat treated specimens can be explained in terms of the defectiveness of protective NiO layers as a function of grain boundaries emerging at the surface.