Thermodynamic assessment of binary solid-state thermal storage materials

Polyalcohols are potential thermal energy storage materials that exhibit energetic solid-state phase transformations, and usually referred to as 'Plastic Crystals'. The adjustment of solid-state phase transition temperatures is of significance to practical applications; phase diagram are useful for this purpose. We have established binary phase diagrams of 2-amino-2-methyl-1,3-propanediol (AMPL)-neopentylglycol (NPG), pentaerythritol (PE)-AMPL,tris(hydroxymethyl)aminomethane (TRIS)-NPG systems. In this work, we present results of our thermodynamic assessments of these organic binary systems. The CALPHAD approach using Thermo-Calc software was utilized for this purpose. It is interesting to note that two high temperature plastic phases co-exist in all three binaries considered here. Thermal energies are predominantly stored in these cubic γ or γ′ plastic phases in molecular librations (O-H⋯O bonds) and lattice vibrations. The calculated phase diagrams are in close agreement with the experimental phase diagrams.