Microstructural investigations of pure nickel exposed to KCl induced high temperature corrosion

Oxidation of 99?99% pure nickel was studied with and without 0?10 mg cm22 KCl(s) in an environment containing 5 vol.-%O2, 40 vol.-%H2O and 55 vol.-%N2 at 600uC for up to 168 h. Oxide microstructure was investigated by X-ray diffraction (XRD), focused ion beam (FIB), broad ion beam (BIB) and SEM/EDX. Oxidised nickel shows an approximately parabolic oxide growth rate. The oxide scale is dense with some pores at the oxide/metal interface. Adding small amounts of KCl does not result in a faster corrosion rate of nickel. However, the surface morphology changes and small oxide crusts were observed in the vicinity of former KCl particles. This is proposed to be the result of a NiCl2–KCl eutectic on top of the oxide scale formed above 514uC. The oxide scale formed in the presence of KCl contains more and differently distributed voids than the scale formed without KCl.