Home Research CV

Diffusion of hydrogen in nominally anhydrous minerals (NAMs)

Small amounts of hydrogen (sometimes called water or hydroxyl) in deep-earth minerals such as olivine and clinopyroxene can significantly affect the melting temperature of rocks and therefore the movement of lithospheric plates and occurrence of, for instance, volcanic eruptions. Understanding how hydrogen behaves in these minerals will help to explain these phenomena and perhaps even provide a clock to measure the ascent rate of magma in volcanoes.

diopside viewed down c axis

The whole-block method

Paper now in press at American Mineralogist
Preprint available to MSA members

I developed a way to measure hydrogen diffusivity in NAMs by FTIR without cutting the sample. This "whole-block" method has several advantages over previously established approaches. For instance, because my approach is nondestructive, I can perform multiple experiments using the same sample (e.g., a time series or reversal). I can also estimate diffusivities in three orthogonal directions from the same sample.

Movie 1, Movie 2, Movie 3
(mp4; may require plugin)

Site-specific hydrogen diffusion in clinopyroxene

AGU abstract

PDF of poster

The FTIR spectra of most nominally anhydrous minerals reveal multiple peaks that correspond to different sites in which hydrogen is incorporated. I am working toward establishing diffusivities for each of these sites in clinopyroxenes such as diopside and augite. This effort if complicated by the non-diffusion-related redistribution of these peaks upon heating.

FTIR spectra show changes in hydrogen site distribution

Ti-in-zircon geothermometry

Paper in Journal of European Mineralogy

The concentration of titanium in zircon can give a rough estimate of the temperature at which a rock last reached thermodynamic equilibrium. I used computational techniques to show that the pressure correction for this geothermometer is likely on the order of 100°C/GPa, and it may not be useful at all for systems that have experienced pressures above ~3.5 GPa (a depth of ~110 km).

Actinide-bearing zircon-structured solid solutions

Paper in American Mineralogist

The mineral zircon is very common in the natural world and has been considered for long-term disposal of actinides such as plutonium. I used computational techniques to calculate thermodynamic properties of seven related systems, including phase diagrams and ordering schemes. ZrSiO4 and HfSiO4 form a nearly ideal solid solution, but the miscibility of (Zr,Th)SiO4, (Zr,U)SiO4 (Zr,Pu)SiO4,(Zr,Ce)SiO4, (Hf,Pu)SiO4, and (U,Th)SiO4 was limited to no more than 12 mole % of the substituting cation.

UO2 oxidation in the presence of corroding steel

Paper in Journal of Nuclear Materials

Solid uranium dioxide (UO2) is chemically similar to nuclear fuel. When UO2 corrodes in air and water, the U is oxidized to form the highly mobile ion UO22+. My experiments indicated that surrounding the UO2 with corroding steel may significantly slow the corrosion process.