| Autor: |
Ursula Eicke, Ursula Köhler, Matthias Rosenhauer, Heinz Büttner, Knut Roselieb |
| Rok vydání: |
1996 |
| Předmět: |
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| Zdroj: |
Chemical Geology. 128:207-216 |
| ISSN: |
0009-2541 |
| Popis: |
The pressure dependence of the diffusivity of Ar and Kr in a jadeite melt was investigated experimentally. Sorption studies on spheres (∼ 1.6–3.4 mm in diameter) were performed in an internally heated pressure vessel at 800°C and pressures between 200 and 6000 bar. Run times ranged from 24 to 240 hr. Sorbed noble gases were analysed by gas chromatography. From a comparison of a partially saturated sphere and a saturated powder, the diffusivity is calculated. Results indicate decreasing diffusivity of Ar and Kr with increasing pressure. Least-squares fitting of an Arrhenian type equation D = D 0 exp (− PV RT ) to the data yields activation volumes of 11.4 ± 1.3 cm 3 /mol (log D 0 = −9.14 ± 0.02; D 0 in cm 2 /s) and 17.3 ± 4.3 cm 3 /mol (log D 0 = −10.81 ± 0.07; D 0 in cm 2 /s) for Ar and Kr, respectively. Both values are close to the atomic volume. A comparison with diffusivities of charged species in jadeite melts shows that Si 4+ , Al 3+ and O 2− diffusivities increase with increasing pressure while MD simulation predicts decreasing diffusivity of Na + . From the activation volumes of Ar and Kr an average jump distance of 1.77 nm can be estimated. For Na + , Ar and Kr a linear relationship between activation volume and activation energy is observed. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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