2:00 PM - 2:25 PM
[SCG58-02] High-speed in-situ stress-strain measurements of enstatite using high-energy and high-flux X-rays
★Invited Papers
Keywords:High pressure, High-speed time-resolution, In-situ measurement, Enstatite, Rheology
Orthoenstatite is a major mineral in the Earth's upper mantle, second only to olivine, and its rheological properties are crucial for understanding mantle dynamics. However, due to its phase transition to protoenstatite under low-pressure and high-temperature conditions, there has been limited research on its rheological properties. Then, in this study, we determine the flow law of Enstatite by using high-speed in-situ stress-strain measurements with a portable deformation-type large volume press and a high-flux 100 keV pink beam at SPring-8 BL15XU.
A flat panel detector and CMOS camera with a GaGG scintillator were used for 2D-XRD and X-ray radiography measurements, respectively, to observe stress and strain. The experimental conditions were approximately 3 GPa and 1000–1250°C, with displacement rates of 1–12 µm/min. A rotating slit capable of switching X-ray sizes at up to 144 Hz was used to measure stress-strain simultaneously at 1–4 Hz. The obtained stress and strain rates were 0.1–1.5 GPa and 8.8×10-6–2.6×10-4/s, respectively. In this study, the ability to measure stress and strain in sub-seconds allows for the rapid confirmation of the achievement of steady-state creep, which meant that the sample deform at constant stress and strain rate conditions. As a result, the stress-strain relationship for steady-state creep under various stress and temperature conditions was determined in a single experiment. This enabled a more precise determination of the enstatite flow law compared to previous studies.
Fitting these results to the flow law equation, the stress exponent (n) was found to be 1.0±0.1, and the activation energy (E) was 176±24 kJ/mol. Based on the stress exponent, diffusion creep would be the dominant deformation mechanism in this study. At high stress condition, stress exponent becomes larger. This means dislocation creep become dominant at high stress condition. Zhang et al. (2017) on diffusion creep under high-pressure, hydrous conditions also show activation energies around 200 kJ/mol. Our results are consistent with previous study. This suggest the influence of water on the activation energy of the flow law of enstatite is minimal.
A flat panel detector and CMOS camera with a GaGG scintillator were used for 2D-XRD and X-ray radiography measurements, respectively, to observe stress and strain. The experimental conditions were approximately 3 GPa and 1000–1250°C, with displacement rates of 1–12 µm/min. A rotating slit capable of switching X-ray sizes at up to 144 Hz was used to measure stress-strain simultaneously at 1–4 Hz. The obtained stress and strain rates were 0.1–1.5 GPa and 8.8×10-6–2.6×10-4/s, respectively. In this study, the ability to measure stress and strain in sub-seconds allows for the rapid confirmation of the achievement of steady-state creep, which meant that the sample deform at constant stress and strain rate conditions. As a result, the stress-strain relationship for steady-state creep under various stress and temperature conditions was determined in a single experiment. This enabled a more precise determination of the enstatite flow law compared to previous studies.
Fitting these results to the flow law equation, the stress exponent (n) was found to be 1.0±0.1, and the activation energy (E) was 176±24 kJ/mol. Based on the stress exponent, diffusion creep would be the dominant deformation mechanism in this study. At high stress condition, stress exponent becomes larger. This means dislocation creep become dominant at high stress condition. Zhang et al. (2017) on diffusion creep under high-pressure, hydrous conditions also show activation energies around 200 kJ/mol. Our results are consistent with previous study. This suggest the influence of water on the activation energy of the flow law of enstatite is minimal.