New density measurements on carbonate liquids and the partial molar volume of the CaCO 3 component

Abstract

Density measurements on nine liquids in the CaCO 3 –Li 2 CO 3 –Na 2 CO 3 –K 2 CO 3 quaternary system were performed at 1 bar between 555 and 969 °C using the double-bob Archimedean method. Our density data on the end-member alkali carbonate liquids are in excellent agreement with the NIST standards compiled by Janz (1992). The results were fitted to a volume equation that is linear in composition and temperature; this model recovers the measured volumes within experimental error (±0.18% on average, with a maximum residual of ±0.50%). Our results indicate that the density of the CaCO 3 component in natrocarbonate liquids is 2.502 (±0.014) g/cm 3 at 800 °C and 1 bar, which is within the range of silicate melts; its coefficient of thermal expansion is 1.8 (±0.5)×10 −4 K −1 at 800 °C. Although the volumes of carbonate liquids mix linearly with respect to carbonate components, they do not mix linearly with silicate liquids. Our data are used with those in the literature to estimate the value of in alkaline silicate magmas (≥20 cm 3 /mol at 1400 °C and 20 kbar), where CO 2 is dissolved as carbonate in close association with Ca. Our volume measurements are combined with sound speed data in the literature to derive the compressibility of the end-member liquids Li 2 CO 3 , Na 2 CO 3 , and K 2 CO 3 . These results are combined with calorimetric data to calculate the fusion curves for Li 2 CO 3 , Na 2 CO 3 , and K 2 CO 3 to 5 kbar; the calculations are in excellent agreement with experimental determinations of the respective melting reactions.