Three–step method to determine the eutectic composition of binary and ternary mixtures: Tested on two novel eutectic phase change materials based on salt hydrates

A three-step method to determine the eutectic composition of a binary or ternary mixture is introduced. The method consists in creating a temperature–composition diagram, validating the predicted eutectic composition via differential scanning calorimetry and subsequent T-History measurements. To test the three-step method, we use two novel eutectic phase change materials based on Zn ( NO 3 ) 2 · 6 H 2 O and NH 4 NO 3 respectively Mn ( NO 3 ) 2 · 6 H 2 O and NH 4 NO 3 with equilibrium liquidus temperatures of 12.4 and 3.9 ∘ C respectively with corresponding melting enthalpies of 135 J g - 1 (237 J cm - 3 ) respectively 133 J g - 1 (225 J cm - 3 ). We find eutectic compositions of 75/25 mass% for Zn ( NO 3 ) 2 · 6 H 2 O and NH 4 NO 3 and 73/27 mass% for Mn ( NO 3 ) 2 · 6 H 2 O and NH 4 NO 3 . Considering a temperature range of 15 K around the phase change, a maximum storage capacity of about 172 J g - 1 (302 J cm - 3 ) respectively 162 J g - 1 (274 J cm - 3 ) was determined for Zn ( NO 3 ) 2 · 6 H 2 O and NH 4 NO 3 respectively Mn ( NO 3 ) 2 · 6 H 2 O and NH 4 NO 3 .