Oxygen self-diffusion in rutile was studied in synthetic and natural samples over the temperature range 750 to 1000C and the pressure range 0.1 to 1000MPa using an 18O-enriched source. Most experiments investigated the dependence of D upon temperature, water pressure, crystallographic direction, and experiment duration. A few experiments investigated the dependence of D upon fO2 and confining pressure. The uptake profiles of 18O in experimental products were measured by nuclear reaction analysis using the reaction 18O(p,α)15N. Two mechanisms were responsible for O diffusion in rutile, and one was faster than the other by about an order of magnitude. The O that diffused via the faster mechanism was described by:

D||c(m2/s) = 4.7 x 10-7exp[-258(kJ/mol)/RT]

Diffusion via the slower mechanism was described by:

D||c(m2/s) = 5.9 x 10-5exp[-330(kJ/mol)/RT]

The presence or absence of water during reduction affected the diffusion behavior. When water was absent during rutile growth and/or subsequent reduction, only the faster mechanism operated, and when water was present during growth or reduction, both mechanisms operated simultaneously, though the contribution from the slow mechanism dominated that of the fast mechanism. Because few geological environments were dry, the slower law was generally preferable for modelling O diffusion in rutile in nature. Comparison with other studies of rutile suggested that the migration of O vacancies was the mechanism responsible for the faster diffusion law whereas migration of Ti interstitials was responsible for the slower diffusion law. Oxygen diffusion in rutile, was slower perpendicular to the c-axis, than parallel to that axis, by about half an order of magnitude. There was no perceptible effect of confining pressure upon D below 100MPa, or between 600 and 1000MPa. However, between 100 and 600MPa, D decreased by nearly an order of magnitude.

Oxygen Diffusion in Rutile from 750 to 1000°C and 0.1 to 1000. Moore, D.K.: American Mineralogist, 1998, 83[7-8], 700-11