Structured Na2SO4 components and thermal properties of the Li2SO4-Na2SO4 system

The salts analysed are Li2SO4 and Na2SO4, what is relevant is the Li2SO4-Na2SO4 system which is suitable for thermal energy storage due to a solid-solid phase transition that takes place at temperatures comprised between 475°C and 578°C. The temperature of the phase transition is related to the molar composition of the system. By thermally treating tablets with different ratio of Na2SO4 and Li2SO4 it was possible to assess the accuracy of the phase diagram and to detect the reason of the change in colour of the tablets when treated at temperatures above 500°C. Additive manufacturing, specifically direct ink writing, was used to produce Na2SO4 components in order to detect the mechanical properties of different geometries with different percentages of porosity. The aforementioned technique is used to obtain 3D structures with customizable geometries that in this case were designed in order to allow volume changes that occur during the phase transitions. In order to extrude the salt an ink made of Na2SO4, Ehtanol and Polyvinylpyrrolidone was produced.