[S-IT18] Planetary cores: Structure, formation, and evolution

[SIT18-12] Wetting property of Fe-S melt in solid iron: Implication to core crystallization in planetesimals

Daisuke Yumitori¹, *Hidenori Terasaki¹, Takashi Yoshino², Satoru Urakawa¹ (1.Faculty of Science, Okayama University, 2.Institute of Planetary Materials, Okayama University)

Keywords:Dihedral angle, Core, percolation, planetesimal

Wetting property of iron-alloy melts in solid iron-alloys controls whether the melt can percolate through solid iron-alloys or the melt is trapped in solid grain boundaries during core crystallization. Thus, it is closely related to differentiation process between liquid and solid core and efficiency of solid core growth. In this study, we measured dihedral angle between Fe-S melt and solid Fe at 1 GPa and discuss the differentiation process of the planetesimal core.

High pressure experiments were performed at 1 GPa and 1323 K, just above eutectic temperature of the Fe-FeS system, using piston cylinder apparatus at Institute for Planetary Materials. Starting material was composed of a powder mixture of Fe and FeS with Fe-2wt%S composition to obtain small melt fraction and was enclosed into MgO, BN, or Al₂O₃ capsule. Duration time of the experiment ranged from 15 min to 12 hours. Textural observation and chemical analysis of the recovered samples were carried out using SEM-EDS.

Based on the back-scattered electron images, Fe-S melt can be distinguished from solid Fe by a quench texture composed of Fe-FeS mixture, and interconnected networks of Fe-S melt were observed in solid Fe grains regardless of the capsule materials. Measured dihedral angle between Fe-S melt and solid Fe ranges 30-43^o, which is much lower than percolation threshold of 60^o. Therefore, the Fe-S melt can percolate through solid Fe, suggesting that segregation of Fe-S melt from solid Fe proceeds efficiently during core crystallization in planetesimals.