ENHANCED DIFFUSION IN SAPPHIRE DURING MICROWAVE-HEATING

The diffusion of oxygen in sapphire was accelerated by heating in a 28 GHz microwave furnace as compared with heating in a conventional furn ace. Tracer diffusion experiments were conducted using O-18. Single cr ystal sapphire wafers with a (<10(1)over bar 2>) rhombohedral planar o rientation were used as the substrate. Concentration depth profiling w as done by proton activation analysis using a 5 MeV Van de Graaff acce lerator. The diffusion of O-18 was greatly enhanced by microwave heati ng as compared with conventional heating in the 1500-1800 degrees C ra nge. The apparent activation energy for O-18 bulk diffusion was determ ined to be 390 kJ mol(-1) with microwave heating and 650 kJ mol(-1) wi th conventional heating.