Low temperature phase equilibria in the Fe-Ni and Fe-Ni-P systems: application to the thermal history of metallic phases in meteorites |
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| Authors: | AD Romig JI Goldstein |
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| Institution: | Sandia National Laboratories, Albuquerque, NM 87185, U.S.A.;Lehigh University, Bethlehem, PA 18015, U.S.A. |
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| Abstract: | The solubility limits of the α (kamacite) and γ (taenite) phases in the Fe-Ni and Fe-Ni-P phase diagrams have been measured at low temperatures, 700-300°C. The predicted retrograde solubility below 500°C was demonstrated experimentally for the first time in the Fe-Ni system. The minimum solubility of Ni in γ at the boundary increases with decreasing temperature to as much as 54 wt% at 300°C. The addition of P increases the maximum solubility of Ni in α by as much as 1.6 wt% and decreases the minimum solubility of Ni in γ by as much as 7 wt% at 300°C.The solubility limits of kamacite and taenite were also obtained from heat-treated samples of the Grant and Cape York iron meteorites. The data indicate that in iron meteorites minor and trace elements other than P do not significantly shift the Ni solubility limits of the Fe-Ni and Fe-Ni-P phase diagrams. The measured phase diagrams can be used to explain the Agrell effect and the differences in maximum Ni content of taenite among irons and chondrites. The formation of plessite and the influence of the measured solubility limits on the cooling rate simulation method are also considered. |
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