Improving the thermal properties of ternary carbonates for concentrating solar power through simple chemical modifications by adding sodium hydroxide and nitrate

In order to meet the requirements of high temperature solar thermal power generation better, the melting point of mixed carbonates should be further reduced. Starting with ternary carbonates, we modified their composition ratios and added NaNO3 or NaOH as additives. Their new melting points, initial crystallization points, decomposition temperatures, specific heats and thermal stabilities were analyzed. While the melting points of the mixed nitrate/carbonate salts were maintained at 394.7 °C, the melting points of the mixed hydroxide/carbonate salts were reduced to 323.2 °C. Also the initial crystallization temperature of the mixed hydroxide/carbonate salts was dependent on their composition. Among the hydroxide-mixed molten salts, there are six samples with lower initial crystallization temperature. The decomposition temperature of the selected six samples was nearly 800 °C. Their specific heats were fitted with the quadratic polynomial of the temperature and their thermal stability was shown by the excellent repeatability of five heating curves. Only the very first heating curves showed that the initial measured value of a melting point was higher than all the later values of the molten salts due to starting with the powder. Furthermore, possible issues that arise with the addition of NaOH are discussed.