[SIT22-P19] High P-T electrical resistivity measurements on iron in an internally-heated diamond anvil cell
キーワード：惑星コア、電気伝導度、鉄、高圧力実験、内部抵抗加熱
Dipole magnetic field of the Earth is generated by self-sustained dynamo action for geological timescales. Secular cooling of the Earth’s core induces growth of the solid inner core that contributes additional buoyant source for the core convection. The electrical and thermal conductivities of core are two key parameters needed to determine the fundamental timescale for heat diffusion and generation and sustainability of magnetic field in the Earth’s core.
A laser-heated diamond anvil cell (LHDAC) technique is commonly used for measurement of physical properties of deep Earth materials at high pressure (P) and temperature (T) conditions. However, the laser heating produces large temperature gradient in the heated area and is difficult to maintain stable heating. Direct measurements of the electrical and thermal conductivities of iron (Fe) in a LHDAC have been reported (Konôpková et al., 2016; Ohta et al., 2016). The reported electrical conductivity at 135 GPa and 3700 K corresponding to the Earth’s core-mantle boundary (CMB) condition (Ohta et al., 2016) is 3~4 times higher than the one estimated from thermal conductivity measurements (Konôpková et al., 2016). It is possible that a large temperature gradient in their Fe samples due to laser heating caused the discrepancy between the two studies.
Here we employed an internally-heated diamond anvil cell (IHDAC) technique to measure electrical resistivity (inverse of conductivity) of Fe at high P-T conditions. The experiments were carried out at 50 and 70 GPa and up to ~2500 K. We found this heating method could achieve much lower temperature gradient in the sample than the laser heating. Our results show that the electrical resistivity of Fe at high P-T conditions is slightly higher than the value reported by Ohta et al. (2016). Our estimates of Fe conductivity at high P-T would give the new constraints on the transport properties of the Earth's core.
References
Ohta, K., Y. Kuwayama, K. Hirose, K. Shimizu, and Y. Ohishi (2016), Experimental determination of the electrical resistivity of iron at Earth’s core conditions, Nature, 534, 95–98, doi:10.1038/nature17957.
Konôpková, Z., R. McWilliams, N. Gómez-Pérez, and A. Goncharov (2016), Direct measurement of thermal conductivity in solid iron at planetary core conditions, Nature, 534, 99–101, doi:10.1038/nature18009.
A laser-heated diamond anvil cell (LHDAC) technique is commonly used for measurement of physical properties of deep Earth materials at high pressure (P) and temperature (T) conditions. However, the laser heating produces large temperature gradient in the heated area and is difficult to maintain stable heating. Direct measurements of the electrical and thermal conductivities of iron (Fe) in a LHDAC have been reported (Konôpková et al., 2016; Ohta et al., 2016). The reported electrical conductivity at 135 GPa and 3700 K corresponding to the Earth’s core-mantle boundary (CMB) condition (Ohta et al., 2016) is 3~4 times higher than the one estimated from thermal conductivity measurements (Konôpková et al., 2016). It is possible that a large temperature gradient in their Fe samples due to laser heating caused the discrepancy between the two studies.
Here we employed an internally-heated diamond anvil cell (IHDAC) technique to measure electrical resistivity (inverse of conductivity) of Fe at high P-T conditions. The experiments were carried out at 50 and 70 GPa and up to ~2500 K. We found this heating method could achieve much lower temperature gradient in the sample than the laser heating. Our results show that the electrical resistivity of Fe at high P-T conditions is slightly higher than the value reported by Ohta et al. (2016). Our estimates of Fe conductivity at high P-T would give the new constraints on the transport properties of the Earth's core.
References
Ohta, K., Y. Kuwayama, K. Hirose, K. Shimizu, and Y. Ohishi (2016), Experimental determination of the electrical resistivity of iron at Earth’s core conditions, Nature, 534, 95–98, doi:10.1038/nature17957.
Konôpková, Z., R. McWilliams, N. Gómez-Pérez, and A. Goncharov (2016), Direct measurement of thermal conductivity in solid iron at planetary core conditions, Nature, 534, 99–101, doi:10.1038/nature18009.