My Research: "The Diffusion of Volatiles in Earth's Mantle: Is it all about Grain Boundaries?"
Abstract: There are two mechanisms by which diffusion can occur in Earth's deep interior: 1) Through mineral lattices; lattice diffusion or 2) Along the boundaries between grains; grain boundary diffusion. To date very little work has been conducted on grain boundary diffusion of volatiles under mantle conditions. Here we use a novel experimental design to determine grain boundary diffusion rates, initially looking at hydrogen. Data will be used to determine the mobility of hydrogen in the mantle and constrain the important influence it has on bulk mantle properties.
Description: We investigate grain boundary diffusion using a piston cylinder apparatus which enables us to subject our experimental capsules to temperatures and pressures characteristic of the upper mantle. Our current experiments looking at grain boundary diffusion of volatiles in the mantle are conducted at temperatures of between 600C and 1600C and at a pressure of 3GPa. Durations are varied as the relationship between diffusion rate and temperature is exponential - to date durations of between 20 minutes and 3 days have been used. Following the experimental run the capsules are retrieved, cut in half, polished and mounted in indium. They are then examined on the Scanning Electron Microscope (SEM) for integrity and to create a map of grains within the capsule. Volatile contents are then measured by Secondary Ion Mass Spectrometry (SIMS) (to be conducted in September 2011).
The data obtained from these experiments will be used to determine the relative importance of grain boundary diffusion as compared to lattice diffusion and will form a significant part of my thesis.
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