Phase transitions and energy storage properties of some compositions in the (1-x)Li2SO4-xNa2SO4 system

In the binary system (1-x)Li2SO4-xNa(2)SO(4), the solid-solid phase transitions and energy storage properties of Li2SO4, Na2SO4, the binary compound LiNaSO4 and two eutectoids (E-1: 0.726Li(2)SO(4)-0.274Na(2)SO(4); E-2: 0.03Li(2)SO(4)-0.97Na(2)SO(4)) were investigated by X-ray diffraction and differential scanning calorimetry. Li2SO4 has a solid-solid phase transition at 578 degrees C with the transition enthalpy 252 J g(-1). The binary compound LiNaSO4 gives a slightly lower enthalpy value, 214 J g(-1) and its transition temperature is clearly reduced to 514 degrees C. The transition enthalpy of the eutectoid E-1 is maintained to 177 J g(-1) and its transition temperature is further reduced to 474 degrees C. Li2SO4, LiNaSO4 and the eutectoid E-1 are applicable phase transition materials because of their large transition enthalpies. The enthalpies of Na2SO4 and the eutectoid E-2 are not very high (similar to 45 J g(-1)), but their transition temperatures are quite low (similar to 250 degrees C); thus their transition properties may be applied at such low temperatures.