In particular nitrate and nitrites and their mixtures promise to be suitable PCMs, if requirements such as handling and steel compatibility are taken into account. Table 2 shows that the number of nitrates and their mixtures, suggested in literature is limited. Hence, the aim of this work it to identify from literature and by own measurements potential binary mixtures of nitrites and nitrates. Table 3 summarizes relevant properties of selected alkali nitrates and alkali metal nitrites which were considered in this work. Due to their hygroscopic behavior, handling of the alkaline-earth nitrates Ca(NO3)2 and Mg(NO3)2 is difficult. Hence, these nitrates were excluded.

In this work, a comprehensive literature survey regarding the minimum melting temperature of the 21 binary alkali nitrate/nitrite systems was carried out [4,34-44]. Table 4 summarizes the result of this survey. Except for a few binary systems, melting enthalpy data of these systems are not known. Also, as can be seen some temperatures could not be identified (Table 4). Hence, additional experiments were carried out with particular reference to temperatures around 170°C,
since this temperature is not covered by known systems. The methods and results of the experiments are described in the next section.