The exchange of zinc vapor with crystals of zinc oxide was measured between 900 and 1025C. The ZnO crystals, incorporating radioactive 65Zn, were prepared by the reaction of zinc vapor and atmospheric oxygen. A sample of the crystals was weighed into a small quartz bucket suspended in a cylindrical quartz vessel. After addition of enough pure zinc to give the requisite vapor pressure, the vessel was evacuated and sealed. The ZnO sample contained about 1000 acicular crystals, with a mean diameter of 0.01mm and a selected narrow distribution of diameters. At different times the bucket was withdrawn, and the residual radioactivity of the ZnO was determined. Except for the initial stages, the exchange reaction appeared to be controlled by the diffusion of Zn in ZnO. The diffusion coefficient D was calculated at 1atm zinc pressure to be

D(cm2/s) = 4.8 x 100exp[-73.0(kcal/mol)/RT]

Variation of zinc pressure from 0.2 to 2.0atm showed that D varied as Pzn0.65, suggesting that the diffusing species was the singly dissociated interstitial zinc ion, Zni+. These results were consistent with observations on the rate of solution of zinc in zinc oxide, if D = fiDi where fi was the concentration of interstitial zinc and Di was its mobility, but the possibility that the exchange rate was not diffusion controlled could not be rigorously excluded.

Diffusion and Exchange of Zinc in Crystalline Zinc Oxide. Secco, E.A., Moore, W.J.: The Journal of Chemical Physics, 1957, 26[4], 942-8