Evaluating self-diffusion coefficient of iron under high pressure by a combination of resistive-heated diamond anvil cell and secondary ion mass spectrometry
Abstract
Self-diffusion of Earth's inner core material controls viscosity of the inner core, which is a fundamental parameter to interpret its dynamics and evolution. Since Earth's inner core is composed of iron alloy and under extremely high-pressure conditions, it is important to evaluate pressure effects on self-diffusion coefficient of iron. There have been several previous studies using piston cylinder, multi-anvil press or laser-heated diamond anvil cell (LHDAC) to evaluate iron-nickel inter-diffusion at high pressure as a proxy of iron self-diffusion. However, actual self-diffusion coefficient of iron under high pressure conditions have never been studied experimentally. We conducted a preliminary self-diffusion experiment of 57Fe-rich and 56Fe-rich foils in contact under pressure condition of 30 GPa, and observed diffusion profile after the experiment by Secondary Ion Mass Spectrometry (SIMS) analysis. We employed internal resistive-heated diamond anvil cell (DAC) to generate high temperature and pressure condition, which provides stable heating and less temperature gradient compare to LHDAC and also allows higher pressure condition compare to the piston cylinder and the multi-anvil press.
A diffusion couple composed of 56Fe-rich and 57Fe-rich foils was loaded into resistive-heated DAC and subsequently heated by increasing voltage supply through the sample. Target temperature of 1840 K was achieved in 10 seconds and maintained for 130 seconds under 30 GPa. Pressure and temperature was estimated by Raman spectrometry of diamond anvil and Planck's radiation from hot spot respectively. After heating, we recovered a thin cross section across the center of the hot spot. The thin cross section was further mounted on a silicon wafer for the SIMS analysis. From the SIMS image analysis, we can get diffusion profile across the boundary between 56Fe-rich and 57Fe-rich foils. We are currently estimating quantitative validity of the diffusion profile from SIMS analysis. We are also preparing diffusion experiments at higher pressure to precisely evaluate pressure effects on self-diffusion coefficient of iron.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR24A..08P
- Keywords:
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- 3909 Elasticity and anelasticity;
- MINERAL PHYSICS;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 5139 Transport properties;
- PHYSICAL PROPERTIES OF ROCKS;
- 8124 Earth's interior: composition and state;
- TECTONOPHYSICS