Electrical resistivity measurement of pure iron in the multi-anvil press: discussions on different techniques.
Abstract
The thermal evolution of the core of the terrestrial planets is associated with their metallic (e.g. Fe and Fe-Ni) core's thermal properties, especially on the thermal conductivity. Generally, both direct and indirect approaches are used to value the core's thermal conductivity. Former includes transient heating (TH) laser technique and ultrafast time-domain thermoreflectance (TDTR). The latter indirect approach is electrical resistivity measurement. For the pure iron's thermal conductivity at high pressure and high temperature conditions, it is still in the debate from different studies. Except for using DAC (diamond-anvil cell) as a pressure producer, the multi-anvil press is also widely used in measuring iron's resistivity. Four-point technique and four-probe van der Pauw method are two basic methods. Although the resistivity of pure iron has been measured and verified using multi-anvil press by different groups, there are some disagreements on their results. To obtain accurate thermal conductivity values for the core, precise electrical resistivity value is needed.
We conducted a series of experiments to measure the pure iron's resistivity in the multi-anvil press using two techniques mentioned above. The results at the pressure of 5 GPa show that the four-point technique may lead to 7-10% error on the final calculated resistivity while the four-probe van der Pauw technique could reduce error to <5%. At higher pressure conditions (>20 GPa), the measured resistivity for iron using the van der Pauw technique still has excellent small errors. Moreover, these two techniques result in different slopes for resistivity against temperatures ((∂ρ/∂T)P) of fcc-iron at 5 GPa . We find that the pure iron's resistivity may increase about 11% onset of melting at 5 GPa. Above all, the four-probe van der Pauw technique has more advantages than the four-point technique to be used in multi-anvil press or DAC for measuring iron's and metal's resistivity.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMMR0210005Y
- Keywords:
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- 3939 Physical thermodynamics;
- MINERAL PHYSICS;
- 3672 Planetary mineralogy and petrology;
- MINERALOGY AND PETROLOGY;
- 5134 Thermal properties;
- PHYSICAL PROPERTIES OF ROCKS;
- 5460 Physical properties of materials;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS