Exploring hydrogen behavior in metallic iron from high-pressure and high-temperature experiments and its applications for the Earth's core

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K04051
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Japan Synchrotron Radiation Research Institute
• Principal Investigator: Hirao Naohisa 公益財団法人高輝度光科学研究センター, 回折・散乱推進室, 主幹研究員 (70374915)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 地球中心核 / 水素 / 高温高圧 / 放射光 / X線回折 / 相平衡関係 / メスバウアー分光

Outline of Final Research Achievements

In this study, in order to constrain the chemical composition of the Earth's core which is still one of the important and unsolved problems in geoscience, high-pressure and high-temperature experiments were carried out on hydrogen in the Earth's core which may be a key to solve the light element problem. As a result of studying the phase stability of iron hydride, an alloy of hydrogen and metallic iron which is the main component of the Earth's core, we found the different high-pressure phases between hydrogen-rich and hydrogen-poor systems under the extreme conditions of 80-90 GPa and 1500 K. In the presence of hydrogen-rich regions and depleted regions in the Earth's core and/or the core-mantle boundary, the large density difference between two iron hydrides may cause sedimentation and float in the Earth's core, which may greatly affect the Earth's core dynamics.

Free Research Field

地球深部科学

Academic Significance and Societal Importance of the Research Achievements

地球核の化学組成は未解明問題の一つであり，水素はその鍵といえる．全地球深部の内部構造やダイナミクス，進化史を解明する上で，地球核にどのくらい水素が存在するのか，密度はどのくらいかという点は，重要な制約条件となる．本研究から，水素に富む領域と枯渇する領域で，地球核の主成分である鉄に固溶する水素量が異なり，その大きな密度差により地球核内で化学的沈降・浮遊が生じる可能性を示唆する重要な成果が得られた．
地磁気は人間社会活動と大きく関係している．地磁気の発生場である地球核の物質科学的解明，特に水素が果たす役割は，その発生メカニズムの解明や地磁気の変遷を理解する上でも重要である．