Surface-diffusion studies on UO₂ and MgO

Abstract

An optical interferometric technique has been used to study the growth of grain boundary grooves and the decay of surface scratches on UO₂ and MgO at temperatures in the range 1100 to 1700° C. The results were interpreted using equations derived by W. W. Mullins and it was found that surface-diffusion was the predominant material transport process for both oxides under the experimental conditions used. Surface-diffusion coefficients and activation energies were calculated, and gave the following equations for the variation of the mass transfer surface-diffusion coefficientD _s with temperature.

$$\begin{gathered} UO_{2.005, } {\text{ }}D_s = 1.3 x 10^8 exp^{ - 11000 \pm 15000} /RT[1200{\text{ to }}1{\text{400}}^\circ {\text{ C]}} \hfill \\ MgO, D_s = 8 x 10^4 exp^{ - 88500 \pm 15000} /RT[1200{\text{ to }}15{\text{00}}^\circ {\text{ C]}} \hfill \\ \end{gathered}$$

It was found that for UO₂ the rate of grooving increased markedly as the oxygen content of the oxide increased.