HEATS OF MIXING OF SILICATE LIQUID IN THE SYSTEMS DIOPSIDE-ANORTHITE-AKERMANITE, DIOPSIDE-ANORTHITE-FORSTERITE, AND DIOPSIDE-SILICA

Abstract

Fusion enthalpies were measured by differential scanning calorimetry (DSC) for mineral mix-tures of eutectic composition in the systems anorthite-diopside (An42Di58, wt%), anorthite-akermanite (An46Ak54), akermanite-diopside (Ak42Di58), diopside-silica (Di84Qt16), and anorthite-diopside-forsterite (Di49Fo7.5An43.5), along with akermanite. Heats of mixing of silicate liquid in those systems were calculated based on the DSC data. The liquids of Di49Fo7.5An43.5, An42Di58, An46Ak54, and Ak42Di58 have negative excess enthalpies of 4 to 10 (± 5) kJ/mol, whereas the Di84Qt16 liquid has positive excess enthalpy of 5.0(± 1.7) kJ/mol. Those values are consistent with the heats of mixing estimated by thermodynamic analyses of phase equilibria of the above systems. The results suggest that the differential scanning calorimetry is useful and sufficiently accurate for direct calorimetric measure-ment of small endothermic or exothermic heat of mixing in silicate liquid.