Determining the self-diffusion coefficient of iron under mantle conditions
thesisposted on 28.03.2022, 13:03 by Morgan Stewart
Diffusion is one of the key processes that allows material to move around, it is a controlling factor both of planetary formation and of deformation. This study focuses on self - diffusion of fcc phase iron . Here a laser heated diamond anvil cells were used to generate the high pressures and temperatures, simulating mantle conditions. Iron self - diffusion was measured at 43.6 GPa at both 2100 K and 2000 K, giving diffusion coefficient measurements of 1.46x10 - 14 m 2 /s - 1 at 2100 K and 9.92x10 - 14 m 2 /s - 1 at 2000 K. These diffusion coefficients were then plotted along with existing data at lower pressures against three different diffusion models, to see whether the models include reasonable assumptions and are accurate at predicting the diffusion of iron at high temperatures. All three of the models consistently underestimated the diffusion coefficient at higher pressures by at least two orders of magnitude . One of the models was recalculated using new values for activation volume (1.43 cm 3 /mol) and activation energy (431 kJ/mol), the model now reliably predicts the diffusion coefficient of iron at high pressures.