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.