It was noted that the diffusion of O in sapphire was accelerated, by heating in a 28GHz microwave furnace, as compared with the results of heating in a conventional furnace. Tracer diffusion experiments were carried out by using 18O. Monocrystalline wafers with a (10▪2) rhombohedral planar orientation were used as the substrate. Concentration depth profiling was performed by means of proton activation analysis, using a 5MeV Van de Graaff accelerator. It was found that the diffusion of 18O was greatly enhanced by microwave heating, as compared with conventional heating, at temperatures ranging from 1500 to 18000C. The apparent activation energy for 18O bulk diffusion was estimated to be equal to 390kJ/mol during microwave heating, and to 650kJ/mol during conventional heating.

M.A.Janney, H.D.Kimrey, W.R.Allen, J.O.Kiggans: Journal of Materials Science, 1997, 32[6], 1347-55