The K_2CO_3 fusion curve revisited: New experiments at pressures up to 12 GPa

摘要

The melting temperatures of K_2CO_3 were experimentally determined to be 1220 ± 20 ℃ (4.0 ± 0.5 GPa), 1290 ± 10 ℃ (9.0 ± 0.5 GPa), and 1313 ± 10 ℃ (11.5 ± 0.5 GPa) in a 2000 ton split-sphere apparatus and 1195 ± 15 ℃ (5.0 ± 0.5 GPa) in a 1000 ton uniaxial split-cylinder apparatus. The fusion curves of K_2CO_3 were calculated up to ~ 12.0 GPa for various K_o' (pressure dependence of bulk modulus) values of the liquid, according to the thermodynamic properties for crystalline and liquid K_2CO_3. On the basis of these experimental results and fusion curves of K_2CO_3, the K_0' for liquid K_2CO_3 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 K_2CO_3 between 5.0 and 9.0 GPa. Determination of liquid K_0' allows the density of K_2CO_3 liquid to be calculated to high pressure. In comparison with other common carbonates, K_2CO_3 is shown to have the lowest melting temperature.