Thermal Transport Properties of Fe-Ni Metals, Meteorites, and Melts vs. Composition, Structure, Temperature, and Pressure

To provide accurate transport properties of planetary alloys, we measure thermal diffusivity (D) within ±2%–3% from room temperature (T) to ~1600 K of three nearly pure Fe metals, two Ni metals, nine iron meteorites, two Fe-Ni alloys, and several melts using laser flash analysis. Fifteen additional meteorites and alloys define D298 across the Fe-Ni binary. Chemical and structural characteristics agree with literature values. Single-crystal and polycrystalline Fe have nearly the same D(T). Fe, Ni, and three alloys splat quenched from melt have D298 up to 2.8× larger than annealed material, despite micro-cracking. Octahedrites have higher D298 than their exsolved bcc and fcc phases and display Curie transitions for both phases. High T, fcc phases with <50 wt% Ni have D(T) similar to that of fcc-Fe, and molten meteorites have D(T) close to that of molten Fe. The dependencies of meteorite D on T, Ni content, crystal structure, and texture suggest that material strength is important to heat diffusion, and that homogeneity over micro- and macroscopic scales mitigates grain-boundary resistance. Available data on density (ρ) and heat capacity (cP) are used to calculate thermal conductivity K from DρcP within ±5% for meteorites at 298 K, at high T, and of melts. Pressure dependencies of K and D calculated from thermodynamic identities are mechanism independent and more reliable than recent measurements and calculations. High K at high T and P promotes rapid cooling of Fe-Ni alloys from melt, suggesting that thermal histories of some ataxites with unusually high K diverge from that of the slowly cooled majority and that Earth’s core likely has K > 380 Wm−1K−1.