Determination of hydrogen partitioning between metal and silicate by in situ synchrotron X-ray observation under high pressure and micro-area analysis

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K13635
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Ehime University
• Principal Investigator: Kuwahara Hideharu 愛媛大学, 地球深部ダイナミクス研究センター, 助教 (50505394)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 核 / マントル / 水素 / 分配

Outline of Final Research Achievements

The purpose of this study is to constrain the distribution of hydrogen between the core and mantle during planetary differentiation. Since in-situ observation experiments using synchrotron radiation, which were originally planned, were not successful, we decided to analyze quenched experimental samples.
The high-pressure experiments were carried out at 2 GPa and 1923 K. The samples were encapsulated in boron nitride or SiO2 capsules. The starting sample consisted of a mixture of iron and oxide powders with Mg(OH)2 as a hydrogen source. The capsule was sealed in a platinum tube to prevent water loss from the capsule during the experiment.
The amount of water in the quenched silicate glass of the recovered sample was 0.13~0.24 mass% for the starting sample containing 0.25 mass% water and 0.53 mass% for the starting sample containing 0.5 mass% water, suggesting that most of the hydrogen was partitioned to the silicate under the experimental conditions.

Free Research Field

固体地球科学

Academic Significance and Societal Importance of the Research Achievements

地球の海は地球質量の0.023%しかなく、これに対して惑星材料物質と考えられている始原天体は数質量%の水を含んでいると推定されている。地球の海と始原天体における水量の不一致の解決策として水素に富む金属核の存在が指摘されてきたが、この仮説を検証するためには惑星形成過程において水素が核に取り込まれた可能性について明らかにしなければいけなかった。
本研究課題で得られた成果は惑星がまだ小さかった場合の核形成過程において、圧力や温度の低い初期段階では水素は核ではなく、マントルに分配されることを示唆するものである。今後より、高温高圧下での実験により地球核が水素の貯蔵層となりうるのか検証することが望まれる。