P-V-Tmeasurements of Fe3C to 117 GPa and 2100 K: Implications for stability of Fe3C phase at core conditions

Abstract

This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Phase Relations of Earth’s Core-Forming Materials

“…On the other hand, Mashino et al [156] reported the Fe 3 C phase as a liquidus phase in their melting experiments in the Fe-C system to 203 GPa, but placed the possible occurrence of reaction (R2) at 255 GPa from chemical and textural analyses of recovered samples (Figure 29b). McGuire et al [169] made thermodynamic calculations on the P-T locations of reaction (R2) using their newly established EoS for Fe 3 C. The reaction is located at 87 GPa and 300 K and 251 GPa and 3000 K and its boundary is consistent with the results of both Tateno et al [23] and Mashino et al [156] (Figure 29b).…”

“…The figure is from [156]. Takahashi et al [167]; McGuire et al [169]). The solid red line shows reaction Fe 3 C = Fe 7 C 3 +Fe calculated in [169].…”

“…An invariant point occurs on the reaction boundary (R2) where Fe, Fe 3 C, Fe 7 C 3 , and liquid are stable, which places constraints on the liquidus temperature of a C-rich outer core [166,169]. From the invariant point, melting reactions originate: Fe 3 C = Fe 7 C 3 + liquid, Fe + Fe 3 C = liquid, and Fe + Fe 7 C 3 = liquid (Figure 29c).…”

“…From the invariant point, melting reactions originate: Fe 3 C = Fe 7 C 3 + liquid, Fe + Fe 3 C = liquid, and Fe + Fe 7 C 3 = liquid (Figure 29c). Two possible P-T locations for the invariant point were predicted from existing experimental data combined with reaction (R2) determined in [169] (Figure 29c): 360 GPa and 5500 K based on XRD studies [23,167] and 275 GPa and 3500 K based on a texture analysis-based study [156]. If the XRD-based model is the case, Fe 3 C is stable over the outer core pressure conditions and the Fe-Fe 3 C subsystem may be relevant for an outer core composition near the eutectic point.…”

“…(R2) determined in [169] (Figure 29c): 360 GPa and 5500 K based on XRD studies [23,167] and 275 GPa and 3500 K based on a texture analysis-based study [156]. If the XRD-based model is the case, Fe3C is stable over the outer core pressure conditions and the Fe-Fe3C subsystem may be relevant for an outer core composition near the eutectic point.…”