Determination of the eutectic concentration between Mn.sub.2·6H.sub.2O and NaNO.sub.3 using the DSC peak sharpness method

While inorganic eutectic phase change materials (PCM) present the advantage of a high volumetric melting enthalpy and a high thermal stability under repeated heating/cooling cycles, there is a lack of known materials in the temperature range of 20-24 °C, interesting for building applications. The DSC peak sharpness method is employed to determine the eutectic concentration between Mn(NO.sub.3).sub.2·6H.sub.2O and NaNO.sub.3, which is 96.5 mass% Mn(NO.sub.3).sub.2·6H.sub.2O and 3.5 mass% NaNO.sub.3. Thereby, the DSC peak sharpness method is demonstrated to yield the same result independently of the two chosen heating/cooling rates of 0.5 and 2 K min.sup.-1. The eutectic PCM has an onset temperature of 22.1 °C and a melting enthalpy of (126 ± 6) J g.sup.-1. Even though the same eutectic concentration is obtained for both heating/cooling rates, the heating/cooling rate of 0.5 K min.sup.-1 reveals that the melting peak of Mn(NO.sub.3).sub.2·6H.sub.2O is composed of two overlapping melting peaks. The second melting peak supposedly corresponds to the eutectic between Mn(NO.sub.3).sub.2·6H.sub.2O and Mn(NO.sub.3).sub.2·4H.sub.2O, which melts at a slightly lower temperature than Mn(NO.sub.3).sub.2·6H.sub.2O (difference of -0.6 °C). This assumption is in accordance with the water content of the purchased Mn(NO.sub.3).sub.2·6H.sub.2O measured via Karl Fischer titration being (0.66 ± 0.2) mass% too low.