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Thermal Conductivity of Materials under Conditions of Planetary Interiors
Uppsala University, Disciplinary Domain of Science and Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The presented thesis focuses on study of transport and thermoelastic properties of materials under conditions of planetary interiors by means of high-pressure experimental tools and finite element modeling, and their role in the dynamics and states of cores of terrestrial planets.

Experiments in laser-heated diamond anvil cell (LHDAC) in combination with numerical simulations of heat transfer in DAC are shown to yield information on thermal conductivity of a pressurized sample. The novel technique consists of one-sided laser heating and double-sided temperature measurements and utilizes a precise determination of several parameters in course of the experiment, including the sample geometry, laser beam power distribution, and optical properties of employed materials. The pressure-temperature conditions at the probed portion of the sample are, however, not uniform. To address this problem, thermal pressure in the laser-heated diamond anvil cell and anisotropic thermal conductivity originating from the texture development upon uniaxial compression have been studied by means of numerical simulations.

The method for determination of thermal conductivity is applied to iron at pressures up to 70 GPa and temperatures of 2000 K, meeting the Earth’s lower mantle conditions and covering Mercury’s entire core. The obtained results are extrapolated to the conditions of the Earth’s core-mantle boundary using a theoretical model of the density dependence of thermal conductivity of metals and published values on Grüneisen parameter and bulk modulus. After considering the effect of minor core elements, the obtained value at these conditions supports case for the downward revision of the thermal conductivity in the core.

From the point of view of core dynamics and energy budget, the lower thermal conductivity implies more favorable conditions to drive the dynamo. Similar scenario applies for Mercury where, for high values of thermal conductivity, heat flux conducted along the iron-core adiabat exceeds the actual heat flux through the core-mantle boundary. This leads to a negative rate of entropy production in the core that makes it impossible to sustain the dynamo process presumably responsible for the observed magnetic field of Mercury.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 81 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 815
Keyword [en]
iron, high pressures-high temperatures, thermal conductivity, diamond anvil cell, laser-heating, planetary cores
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-150396ISBN: 978-91-554-8047-9OAI: oai:DiVA.org:uu-150396DiVA: diva2:407194
Public defence
2011-05-13, Axel Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2011-04-20 Created: 2011-03-29 Last updated: 2011-05-05Bibliographically approved
List of papers
1. Thermal conductivity of hcp iron at high pressure and temperature
Open this publication in new window or tab >>Thermal conductivity of hcp iron at high pressure and temperature
2011 (English)In: High Pressure Research, ISSN 0895-7959, Vol. 31, no 1, 228-236 p.Article in journal (Refereed) Published
Abstract [en]

Results of steady-state heat transfer experiments on iron in laser-heated diamond anvil cell, combined with numerical simulation using finite-element method are reported. Thermal boundary conditions, dimensions of sample assemblage, heating-laser beam characteristics and relevant optical properties have been well defined in the course of experiments. The thermal conductivity of the polycrystalline hexagonal-iron foil has been determined up to pressure 70GPa and temperature 2000K. At these conditions, the conductivity value of 32 ± 7W/mK was found. Sources of errors arising from uncertainties in input parameters and applied experimental procedures are discussed. Considering results of earlier preferred-orientation studies in diamond anvil cell, an averaging effect of polycrystalline texture on the intrinsic anisotropy is assumed. The obtained conductivity is interpreted as an effective value, falling in between the upper and lower bounds on the average conductivity of a random aggregate of uniaxial crystals.

Keyword
iron, laser heated diamond anvil cell, thermal conductivity
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-139222 (URN)10.1080/08957959.2010.545059 (DOI)000288660500042 ()
Available from: 2010-12-22 Created: 2010-12-22 Last updated: 2011-05-05Bibliographically approved
2. Thermal pressure and displacements in the laser heated diamond anvil cell
Open this publication in new window or tab >>Thermal pressure and displacements in the laser heated diamond anvil cell
(English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550Article in journal (Other academic) Submitted
Identifiers
urn:nbn:se:uu:diva-151947 (URN)
Available from: 2011-04-20 Created: 2011-04-20 Last updated: 2011-05-05
3. Determination of thermal conductivity of materials in laser-heated DAC
Open this publication in new window or tab >>Determination of thermal conductivity of materials in laser-heated DAC
2009 (English)Conference paper (Refereed)
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-142418 (URN)
Conference
SMEC, Study of Matter at Extreme Conditions, March 28 - April 2, 2009, Miami
Available from: 2011-01-13 Created: 2011-01-13 Last updated: 2011-10-07Bibliographically approved
4. Thermal conductivity in the Earth’s core
Open this publication in new window or tab >>Thermal conductivity in the Earth’s core
(English)In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395Article in journal (Other academic) Submitted
Identifiers
urn:nbn:se:uu:diva-151948 (URN)
Available from: 2011-04-20 Created: 2011-04-20 Last updated: 2011-05-05
5. On the thermal state and dynamo in the core of Mercury
Open this publication in new window or tab >>On the thermal state and dynamo in the core of Mercury
(English)In: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643Article in journal (Other academic) Submitted
Identifiers
urn:nbn:se:uu:diva-151950 (URN)
Available from: 2011-04-20 Created: 2011-04-20 Last updated: 2011-05-05

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