 |
| Titel |
A new X-radiography based method for measuring thermal diffusivity at high pressures |
| VerfasserIn |
Simon Hunt, Don Weidner, Li Li, Richard McCormack, David Dobson |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041972
|
|
|
|
|
|
| Zusammenfassung |
| We have developed a new variation of the Ångstrom method for measuring thermal
diffusivity at high pressures by using X-radiography. We have measured the thermal
diffusivity of a number of upper-mantle and transition-zone phases and our data are in
agreement with previous measurements.
The Ångstrom method for measuring thermal diffusivity at high pressure uses a stationary
thermal wave which is induced in the sample by varying the power sinusoidally
in the surrounding cylindrical furnace. The thermal diffusivity (κ) is determined
from the phase lag, Φ0 - ΦR, and amplitude difference, θ0-θR, of the thermal
wave between points at the axis of the sample and radius, R (e.g. Khedari et al.,
1995).
Our method differs from previous multi-anvil implementations of the Ångstrom
method in that instead of using thermocouples to monitor the temperature variation
we use thin strips of metal foil, which are placed at discrete intervals along the
sample length and imaged X-radiographically. The metal strips monitor the thermal
expansion of a slice across the sample in response to the sinusoidal temperature
profile. This represents an improvement over previous methods since (i) the change in
temperature is averaged along the sample length, (ii) we measure the phase of the
thermal wave at all radii and (iii) since the expansion of the sample is observed
as a proxy for the change in temperature there are no problems associated with
contact thermal resistance at the thermocouples. Furthermore, this development does
away with the need to prepare long cylinders of weakly metastable phases with a
thermocouple inserted precisely down the middle; a process which is technically extremely
difficult.
To date we have measured the thermal diffusivity of NaCl, olivine, majorite and a number
of other upper-mantle and transition-zone phases. The measurements we have made are all in
agreement with previously published data. The simplifications to the technique inherent in
this X-radiographic technique will allow us to measure the thermal diffusivity of
lower-mantle phases. |
|
|
|
|
|
|