An equation of state for liquid iron and implications for the Earth's core
Abstract
An equation of state is presented for liquid iron based on published ultrasonic, thermal expansion, and enthalpy data at 1 bar and on pulseheating and shock wave compression and sound speed data up to 10 Mbar. The equation of state parameters, centered at 1 bar and 1811 K (the normal melting point of iron), are density, ρ_{0}=7019 kg/m^{3}, isentropic bulk modulus, K_{S0}=109.7 GPa, and the first and secondpressure derivatives of K_{S}, K^{'}_{S0}=4.66 and K^{`}_{S0}=0.043 GPa^{1}. A parameterization of the Grüneisen parameter γ as a function of density ρ and specific internal energy E is γ=γ_{0}+γ'(ρ/ρ_{0})`(EE_{0}) where γ_{0}=1.735, γ'=0.130 kg/MJ, n=1.87, and E_{0} is the internal energy of the liquid at 1 bar and 1811 K. The model gives the temperature dependence of γ at constant volume as (∂γ/∂T)_{V}_{1 bar,1811K}=8.4×10^{5}K^{1}. The constant volume specific heat of liquid Fe at core conditions is 4.04.5 R. The model gives excellent agreement with measured temperatures of Fe under shock compression. Compression with a preliminary reference Earth model indicates that the light component of the core does not significantly affect the magnitude of the isentropic bulk modulus of liquid Fe but does decrease its pressure derivative by ~10%. Pure liquid Fe is 36% more dense than the inner core, supporting the presence of several percent of light elements in the inner core.
 Publication:

Journal of Geophysical Research
 Pub Date:
 March 1994
 DOI:
 10.1029/93JB03158
 Bibcode:
 1994JGR....99.4273A
 Keywords:

 Earth Core;
 Equations Of State;
 Geophysical Fluids;
 Geophysics;
 Iron;
 Liquid Metals;
 Compressing;
 Enthalpy;
 Internal Energy;
 Parameterization;
 Shock Waves;
 Solid Phases;
 Specific Heat;
 Temperature Dependence;
 Thermal Expansion;
 Ultrasonics;
 Geophysics;
 Mineral Physics: Equations of state;
 Mineral Physics: Highpressure behavior;
 Mineral Physics: Physical thermodynamics;
 Tectonophysics: Core processes