Segregation of phosphorus at the metal/scale interface during oxidation of Ni and Ni–20Cr

The segregation of phosphorus at the metal/scale interface formed upon oxidation of Ni and Ni–20Cr at high temperatures was studied. Auger electron spectroscopy with high spatial resolution was used in combination with thermogravimetric measurements. The chemistry of the interface was related to its microstructure. The effects of oxidation procedure and surface preparation on the composition and microstructure of the interface were considered. The incorporation of phosphorus in an oxidized state into the NiO scale formed at 700°C and 1000°C was revealed. The oxidation rate at 1000°C is retarded by segregated phosphorus. The segregation of phosphorus at the metal/scale interface formed upon oxidation of Ni–20Cr alloy at high temperatures was observed for oxidation at low and at atmospheric oxygen pressures. Phosphorus and sulphur segregated at the interface retard the oxidation rate at the initial stage of oxidation at 1000°C and at atmospheric oxygen pressures.