The K₂CO₃ fusion curve revisited: New experiments at pressures up to 12 GPa

Abstract

The melting temperatures of K₂CO₃ were experimentally determined to be 1220 ± 20 °C (4.0 ± 0.5 GPa), 1290 ± 10 °C (9.0 ± 0.5 GPa), and 1313 ± 10 °C (11.5 ± 0.5 GPa) in a 2000 ton split–sphere apparatus and 1195 ± 15 °C (5.0 ± 0.5 GPa) in a 1000 ton uniaxial split–cylinder apparatus. The fusion curves of K₂CO₃ were calculated up to ~ 12.0 GPa for various K₀′ (pressure dependence of bulk modulus) values of the liquid, according to the thermodynamic properties for crystalline and liquid K₂CO₃. On the basis of these experimental results and fusion curves of K₂CO₃, the K₀′ for liquid K₂CO₃ is constrained to be ~ 14.4 ± 1.1 at pressures lower than 5.0 GPa in a third–order Birch–Murnaghan equation of state (EOS). However, the results at pressures above 9.0 GPa deviate from this trend, which suggests a possible phase transformation in either the crystalline or liquid phase of K₂CO₃ between 5.0 and 9.0 GPa. Determination of liquid K₀′ allows the density of K₂CO₃ liquid to be calculated to high pressure. In comparison with other common carbonates, K₂CO₃ is shown to have the lowest melting temperature.