Enthalpy and temperature of the phase change solid–liquid – An analysis of data of compounds employing entropy

• One-thousand hundred and twenty materials were analysed plotting hm per atom as a function of sm/R per atom.
• Two effects not included in the common melting model lead to high melting entropy.
• The first one is a change of bond type between the solid and the liquid phase.
• The second one is a change of the particle structure, meaning a chemical reaction.
• Latent heat storage by phase change solid–liquid can include a chemical reaction.

Latent heat storage with materials undergoing a phase change solid–liquid is gaining increasing interest due to its potential for applications in energy systems. The demand for optimized storage materials has led to an intensification of materials research in recent years. The research focuses mainly on developing materials with high storage density, and related to this the question what the theoretical limit is. For both it is necessary to understand what affects the melting enthalpy and melting temperature on the atomic and molecular level. In this paper, 1120 different materials (elements and simple chemical compounds) have been analysed to find out what affects the melting enthalpy, entropy, and temperature on the atomic and molecular level. The analysis has been performed plotting data of hm per atom as a function of sm/R per atom. While loosening the inter-particle bonds is a necessity for the change of phase from solid to liquid, several other effects have been identified. The most important ones are a change of bond type between the solid and the liquid phase, and a change of the particle structure, which is equal to a chemical reaction. The latter shows that latent heat storage employing a phase change solid–liquid can include a chemical reaction.

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