Annealed pure Al oxidized in air at various temperatures, 20, 430 and 480°C, was investigated by positron angular correlation experiments. It was found that the intensity of the low-momentum component (parabola portion) increased dramatically for the sample oxidized at 480°C as compared with those oxidized at 430 or 20°C. The results were explained as due to the interaction of a positron with anhydrous γ-Al2O3 which was formed at an oxidation temperature of ~ 480°C but not at 430°C or less. It was concluded that it is possible to use the positron method as a means of NDE to evaluate the types of oxide states formed on Al.
Physics Letters. Section A: General, Atomic and Solid State Physics 88(9), pp.479-482