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| Titel |
Viscosity of carbonate-rich melts under different oxygen fugacity conditions |
| VerfasserIn |
Danilo Di Genova, Kai-Uwe Hess, Corrado Cimarelli, Donald B. Dingwell |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109435
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| Publikation (Nr.) |
 EGU/EGU2015-9343.pdf |
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| Zusammenfassung |
| Viscosity is a fundamental property of many materials and its changes affects the fluid
dynamics of natural system as well as industrial processes.
The mobility of carbonatitic melts, which are carbonate-rich and very fluid melts, has
attracted renewed interest in both earth science and industry. In fact, these melts are
considered the main transport agent of carbon from the mantle to the crust and may be
intimately linked to the generation of kimberlites.
At the same time lithium, potassium and sodium carbonate are used as electrolytes in
molten carbonate fuel cells which operate at high temperatures (~650Ë C) for the production
of electricity without CO2 emissions.
Accurate measurement of the transport property (i.e. viscosity) of carbonatitic melts is a
priority in order to understand the carbonatite mobility and reaction rates. Additionally,
obtaining accurate viscosity measurements of such low viscosity melts is however an
experimental challenge due to volatility, very low torques and chemical melt instability in the
viscometer.
To overcome these limitations we have customized a Modular Compact Rheometer (MCR
502 from Anton Paar) ad hoc equipped with 2 narrow gap concentric-cylinder geometries of
steel and Pt-Au. The rheometer is characterized by an air-bearing-supported synchronous
motor with torque ranging between 0.01 μNm and 230 mNm (resolution of 0.1 nNm),
achieving very low viscosity measurements in the order of mPa s, temperatures up to 1000Ë
C and shear rates ranging between 1 and 100 sec-1. These experimental conditions
well match the temperature-viscosity-shear rate window relevant for carbonate
melts.
Here we present the calibration of the rheometer and the results of a rheological
characterization study on a series of very low viscous synthetic and natural carbonatitic melts
at different oxygen fugacity (air and CO2 saturated atmosphere).
Viscosity measurements on carbonate melts have been performed in the temperature
range between ~650 and 1000Ë C. Measured values range between ~2 and 20 mPa sec. The
results point out that the viscosity of synthetic samples is inversely related to the
cations radius, being Li2CO3 melt the more viscous. Viscosity measurements on
natural samples (carbonatitic lava from Lengai volcano, Tanzania), reveal a higher
viscosity (~1000 mPa s) and a dramatic higher activation energy than the synthetic
samples.
Our results have been compared with literature data in order to determine the effect of
chemical composition and oxygen fugacity conditions on the liquid viscosity of carbonatitic
melts. |
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