Accurate measurements of thermal conductivity and thermal diffusivity of molten carbonates
Xing Zhang, Hendro Wicaksono, Seiji Fujiwara, Motoo Fujii
Thermal conductivity and thermal diffusivity of molten carbonates (Li2CO3 / K2CO3, Li2CO3 / Na2CO3, and Li2CO3 / Na2CO3/K2CO3) were measured by the transient short-hot-wire method in the temperature range from 530 to 670 °C. Two types of probes were examined. One was a platinum short-hot-wire probe coated with a thin film of alumina (Al2O3) to prevent current leakage and corrosion. The other was a bare gold short-hot-wire probe. In the case of the platinum probe, the quality of the coating deteriorates gradually during the measurements on molten carbonates because of their high corrosiveness. The deterioration of the quality of coating leads to relatively large errors in the measured thermal conductivity and thermal diffusivity, of around 9% and 50%, respectively. In the case of the bare gold probe, corrosion due to electrochemical reaction can be neglected, and the effect of current leakage into the molten carbonates can be estimated. This allows the temperature dependence of electric resistivity to be calibrated accurately and compared with existing data. By using such a gold probe without coating on the hot-wire surface, the thermal conductivity and thermal diffusivity of molten carbonates can be measured within errors of 3% and 12%, respectively. The gold probe can be used repeatedly without any reduction of quality.