Effect of Pressure on Self-Diffusion in Lead

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Abstract
Data are presented for the self-diffusion of lead as a function of temperature from 174° to 322° and for pressures from 1–8000 atmos. The decrease in the self-diffusion coefficient with pressure follows a relationship of the form (dlnD)/dζ=−(1/RT0)(Q0−ΔVactdTm/dP),where ζ = Tm/T, T0 and Q0 are the normal melting point and the zero pressure activation energy, respectively, and ΔVact is the activation volume. To first order the derivative is constant, deviations arising at high pressure because of the pressure dependence of dTm/dP. Several relationships are derived from thermodynamic considerations of the activated state, and are shown to be valid experimentally: (1) ΔHact = bRTm, with b = 20.7, and (2) ΔHact = ΔHm·(ΔVact/ΔVm), where ΔHm and ΔVm are the latent heat and volume change on fusion, respectively.

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