High-temperature gas release in krypton bombarded platinum due to the formation and motion of bubbles

Abstract

To get information on the role played by bubbles in inert-gas diffusion, gas-release measurements in krypton-bombarded platinum have been correlated with transmission electron microscopy. Release components having temperatures of roughly ambient 500° C, 500–850° C, and > 850° C are shown to occur in specimens bombarded at each of the energies 0.5, 3 and 9 keV. The parallel microscope work reveals that the dislocation loops formed in the bombardment are stable at the temperatures of the first release component, though begin annealing in approximate coincidence with the second component. At higher temperatures (650–700° C), spots resembling bubbles and normally free of dislocations and grain boundaries appear at all three energies. That the spots are really bubbles is implied both by the presence of up to 25 % of the original gas at high temperatures and by the qualitative similarity of their depth distribution to that of the gas. The bubbles can be made to move and escape by pulse-heating or by using a heating stage. It is concluded that the high-temperature release component is consistent with bubble motion by the surface-diffusion mechanism of Greenwood and Speight. That is, the predicted temperatures for bubble release as a function of bubble diameter overlap those observed for the gas release. An incidental result of the work is that the value 66 ± 6 kcal/mole is obtained for the activation enthalpy for Kr-Pt. This value is believed to be applicable only at high gas concentrations.