日時 ： ２００８年６月１３日（金）17：00〜
場所 ： 愛媛大学理学部講義棟1F101室
要 旨
Sulfur is believed to be an alloying light element in iron-rich planetary cores such as those of the Earth and Mars 1, 2. Recent studies have suggested that Mars, like the Earth, could have a liquid metallic outer core together with a solid inner core 3. Hence, it is important to investigate the evolution of the Fe-FeS phase diagram and of the structural properties of the liquid Fe-FeS alloys in respect to pressure, temperature and sulphur content.
A new cell assembly has been developed to heat samples to more than 1300 K at 17 GPa using the Paris Edinburgh Press4. This allows us to conduct detailed structural investigations of the Fe-FeS eutectic liquid by in situ X-ray diffraction5 . Analysis of these data highlights an increase of the liquid compacity with increasing pressure. We also show that the eutectic liquid structure is closer to that of FeSi, explaining the closure of the miscibility gap in the Fe-S-Si system 6. The evolution of the Fe-FeS eutectic liquid structure at high pressure could have significant effect on extrapolated wave speed of metallic Fe-FeS alloy at core pressures7.
We have used a double-sided laser-heated diamond-anvil cell 8 to study the Fe-FeS phase diagram up to 65 GPa and 2500 K9. We used laser heated diamond anvil cell coupled with synchrotron radiation and confirm a S-solubility below 4 at% (2.3 %wt) up to 65 GPa. The eutectic temperatures present a uniform increase, with a rate of ~15K/GPa, up to 65 GPa and 2200 K. Finally, we present new constraints on the phase diagram evolution to very high pressures which provide unambiguous evidence for an upper limit of 4-8%wt for the inner core S-content. Therefore, sulphur is not favoured to be the major light element in the Earth's core.
問い合わせ先：土屋 卓久 TEL （089）927-8198
E-mail takut@sci.ehime-u.ac.jp
