Thermal conductivity of materials in planetary interiors belongs to key parameters controlling thermal evolution and dynamics of planets. Yet it is insufficiently constrained, in particular under the deep mantle and core conditions. For example, thermal conductivity of iron alloy in the Earth’s core has been recently revised by a factor of two . Laser-heated diamond anvil cell technique offers, in principle, possibility for the experimental determination of thermal conductivity at extreme conditions, provided that the boundary conditions of sample assemblage are precisely characterized and controlled. Indeed, feasibility of such studies has been demonstrated in a number of heat-transfer simulations in DAC utilizing finite element method [e.g. 2], as well as in a recent pioneering study on the transient heat propagation facilitated by a pulsed laser heating .We will present results of steady-state heat transfer experiments combined with numerical simulations (COMSOL) on the high pressure thermal conductivity of iron in LHDAC, carried out in the HP laboratory as well as at the APS. We assess the effects of uncertainties and trade-offs between various parameters on the determination of conductivity. For the explored case of a thin foil of iron embedded in MgO, the key parameters, which have to be measured with a high precision and accuracy include radial temperature gradients on both sides of the foil, power distribution profile in the laser beam, and exact 3D geometry of the sample assemblage, including the pressure medium and adjacent gasket. Determination of the amount of absorbed laser power, especially at high temperatures, represents a challenge. State-of-the-art measurements will have to address also the effects of spatially varying thermal stress during a laser heating, and of the extrinsic anisotropy in thermal conductivity induced by preferred-orientation effects and a large uniaxial stress component. Diffusion, chemical reaction, and oxidation at the sample - pressure medium interface may result in the creation of a thin but potentially significant thermal barrier affecting the heat flow. We will discuss these issues and outline possibilities for a solution.
 F. D. Stacey, D. E. Loper, Phys. Earth Planet. Int. 2007, 161, 13. B. Kiefer, T. S. Duffy, J. Appl. Phys. 2005, 97, 114902. P. Beck, A. F. Goncharov, V. V. Struzhkin, B. Militzer, H. K. Mao, R. J. Hemley, Appl. Phys. Lett. 2007, 91, 181914.
2009. 117- p.
XLVIIth EHPRG Conference, Paris, 6-11 Sept. 2009