2:45 PM - 3:00 PM
[SIT18-05] The Fe-Fe2P and Ni-Ni2P phase diagrams at 6 GPa
Keywords:iron phosphide, nickel phosphide, high-pressure experiment, planetary core , meteorite
The Fe-Fe2P system has two stable phosphide compounds: Fe3P and Fe2P. The Fe-Fe3P eutectic is established at 1075 oC and 16 mol% P. The Fe3P compound melts incongruently at 1250 oC to produce Fe2P and liquid containing 23 mol% P. The Fe2P compound melts congruently at 1575 oC. In whole studied temperature range, metallic iron dissolved measurable amounts of P suggesting an existence of limited solid solutions of P in Fe. The maximum P content in Fe, 4.2-5.2 mol%, is established at 1100-1200 oC. X-ray diffraction study indicates that Fe2P corresponds to barringerite structure, whereas Fe3P corresponds to schreibersite. Thus, quenched phases at 6 GPa do not corresponds to high-pressure polymorphs, such as (Fe,Ni)2P allabogdanite (Britvin et al., 2002), which was synthesized previously at 8 GPa (Dera et al., 2008).
The Ni-Ni2P system has three stable phosphide compounds: Ni3P, Ni3-xP, where x = 0.4-0.7 and Ni2P. The Ni-Ni3P eutectic locates at 975 oC and 20 mol% P. The Ni3-xP solid solution field narrows to the Ni2.3P composition as temperature increases to 1175 oC, where Ni2.3P melts incongruently to Ni2P and liquid containing 29 mol% P. The Ni2P compound melts congruently at 1250 oC. Ni also forms limited solid solutions with P. Similarly to Fe-P system, Ni2P and Ni3P compounds corresponds to barringerite and nickelphosphide crystal structures at 6 GPa. The intermediate compound Ni3-xP has variable composition, which may correspond to Ni5P2 or Ni12P5 observed at 1 atm.
The work is supported by Russian Science Foundation (No 17-17-01177).
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