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.