Li2CO3-Na2CO3-K2CO3 molten salt mixtures are potentially suitable for high temperature thermal energy storage in the concentrating solar power. We investigated the LiNaK carbonate salt with hydroxides of lithium (LiOH), potassium (KOH), or calcium (Ca(OH)(2)) by using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). From the repeated heating DSC curves, lower melting points with excellent reproducibility were found when 10 wt% LiOH or KOH was added into 40 wt%Li2CO3-20 wt%Na2CO3-40 wt%K2CO3. Based on the characterization of XRD patterns, the molten eutectic mixtures consisted of LiKCO3, LiNaCO3, and residual Li2CO3 when the ternary carbonate salt was heated at the temperature above the melting point and cooled rapidly. In the system of LiNaK carbonate salt with additives of LiOH or KOH, more LiKCO3 and LiNaCO3 with lower melting point can be formed by substitution reaction. Thus, optimal molar ratio for the mixed molten salts with low melting point could be quickly obtained by studying the composition of the resulting eutectic mixtures. (C) 2015 Elsevier B.V. All rights reserved.