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| Titel |
Diffusion in natural ilmenite |
| VerfasserIn |
Iona Stenhouse, Hugh O'Neill, Gordon Lister |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250031879
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| Zusammenfassung |
| Diffusion rates in natural ilmenite of composition Fe0.842+ Fe0.163+Mn0.07Mg0.01Ti 0.92O3
from the Vishnevye Mountains (Urals, Russia) have been measured at 1000Ë C. Experiments
were carried out in a one atmosphere furnace with oxygen fugacity controlled by flow
of a CO-CO2 gas mixture, over a period of four hours. The diffusant source was
a synthetic ilmenite (FeTiO3) powder doped with trace amounts of Mg, Co, Ni,
Zr, Hf, V, Nb, Ta, Al, Cr, Ga and Y. Since, the natural ilmenite crystal contained
Mn it was also possible to study diffusion of Mn from the ilmenite crystal. The
experiments were analysed using the electron microprobe and scanning laser ablation
ICP-MS. Diffusion profiles were measured for Al, Mg, Mn, Co, Ni, Ga, and Y.
Diffusion of Cr, Hf, Zr, V, Nb and Ta was too slow to allow diffusion profiles to be
accurately measured for the times and temperatures studied so far. The preliminary
results show that diffusion in ilmenite is fast, with the diffusivity determined in
this study on the order of 10-13 to 10-16 m2s-1. For comparison, Chakraborty
(1997) found interdiffusion of Fe and Mg in olivine at 1000Ë C on the order of
10-17 to 10-18m2s-1 and Dieckmann (1998) found diffusivity of Fe, Mg, Co in
magnetite at 1200Ë C to be on the order of 10-13 to 10-14 m2s-1. The order in
which the diffusivity of the elements decreases is Mn > Co > Mg -¥ Ni > Al -¥ Y
-¥ Ga, that is to say that Mn diffuses the fastest and Ga the slowest. Overall, this
study intends to determine diffusion parameters such as frequency factor, activation
energy and activation volume as a function of temperature and oxygen fugacity. This
research is taking place in the context of a larger study focusing on the use of the
garnet-ilmenite system as a geospeedometer. Examination of the consequences of
simultaneous diffusion of multiple elements is a necessity if we are to develop an
understanding of the crystal-chemical controls on diffusion (cf Spandler & O’Neill, in
press).
Chakraborty, S. (1997). Rates and mechanisms of Fe-Mg interdiffusion in olivine at 980Ë
C -1300Ë C. Journal of geophysical research 102 (B6) p.12317-12331.
Dieckmann, R. (1998). Point defects and transport in non-stoichiometric oxides:
solved and unsolved problems. Journal of Physics and Chemistry of Solids 59 (4) p.
507-525.
Spandler, C., O’Neill, H. St. C. (in press). Diffusion and partition coefficients of
minor and trace elements in San Carlos olivine at 1300Ë C with some geochemical
implications. Contributions to Mineralogy and Petrology doi: 10.1007/s00410-009-0456-8. |
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