DIFFUSION IN METALS AT ULTRA-HIGH PRESSURES.
BRIGHAM YOUNG UNIV PROVO UTAH DEPT OF PHYSICS
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Silver wires 3 mil in diameter have been quenched from temperatures between 500 and 1000 C to room temperatures for pressures up to 30 kbar. Upon quenching, an increase in room temperature resistance was measured, but 90 of this increase was permanent and remained even after high temperature anneals. The increase in resistance could therefore not be correlated directly with vacancy formation. Because of the uncertainty in explaining the results it was not possible to obtain meaningful activation energies or volumes from the measurements. The diffusion of silver into lead has been investigated using radioactive tracer techniques in a temperature range within 200 C of the melting point of lead for six pressures between zero and 40 kbar. The activation energy was found to increase from 15.2 to 21.9 .3 kcalmole as the pressure increased from atmospheric to 39.2 kbar. The activation volume for pressures below 11.9 kbar ranged from .54 .06 to .48 .05 atomic volumes as the temperature decreased from 769 to 556 K. Above 11.9 kbar the activation volume was nearly constant at .38 .03 atomic volumes over the same temperature interval. As a result of the large decrease in the activation volume that occurs between zero and 11.9 kbar it is suggested that the diffusion process for silver into lead changes from a composite of interstitial plus vacancy to an interstitial mechanism. Author