Enhanced diffusion of Au in γ-Fe by vacancies induced under elevated hydrogen pressure Original Research Article

The diffusion coefficients of Au, DAu*, in γ-Fe in the temperature range from 1263 to 1653 K at 0.1 MPa Ar and from 1207 to 1351 K at 3–5 GPa H2 have been determined by relating the interdiffusion coefficients in single-phase Fe/Fe–Au couples with the Darken–Manning relation. The value of DAu* in γ-Fe at 5 GPa H2 is 2–3 times larger than that at 0.1 MPa Ar. The temperature dependence of DAu* in γ-Fe at 0.1 MPa Ar and at 5 GPa H2 can be expressed as DAu*=8.1−2.3+3.2×10−5exp{−(290±4) kJ mol−1/RT} m2 s−1 and DAu*=1.4×10−3exp(−310 kJ mol−1/RT) m2 s−1, respectively. The value of the activation energy at 5 GPa H2 is 20 kJ mol−1 larger than that at 0.1 MPa Ar, whereas the value of the pre-exponential factor at 5 GPa H2 is 17 times larger than that at 0.1 MPa Ar. Therefore, the enhancement of the diffusion at 5 GPa H2 is attributed to a high value of activation entropy.