Argon diffusivities and solubilities in single gem-quality crystals of corundum were determined from experiments conducted under 0.5 to ~6000bar Ar pressures at 425 to 1200C. The Arrhenius relationship was:

D (m2/s) = 1.2 x 10-20exp[-33(kJ/mol)/RT]

The activation energy was probably an apparent one which was a combination of the effects of the lattice diffusion of Ar atoms, with trapping in point-defect vacancies. There were no discernible differences in Ar diffusion in different crystallographic directions, and the diffusivity did not vary as a function of the intrinsic oxygen fugacity of the experimental vessel.

J.B.Thomas, D.J.Cherniak, E.B.Watson: Chemical Geology, 2008, 253[1-2], 1-22