Organic acids are phase change materials (PCMs), which store and release energy in phase transitions. Like conventional salt hydrate PCMs, carboxylic acids have energy storage applications because of their low melting points and comparable enthalpies of fusion (~120 J/g). Eight binary combinations of nine consecutive straight-chain acids (decanoic - octadecanoic) were analyzed using differential scanning calorimetry (TA DSC250, PE DSC7), and the data used to create phase diagrams and compare enthalpies of fusion. Consecutive systems showed single DSC peaks at all compositions, and exhibited low-melting, azeotrope-like behavior. The narrow two-phase regions were approximated with lines derived from the Equal Gibbs equation. Further analysis using the contact method under polarizing light microscopy suggested that consecutive systems formed solid solutions. These consecutive systems have one effective fusion transition at all compositions, and thus are particularly suited to practical, outdoor thermal energy storage; melting points can be tailored to different climates and seasons based on composition.

Organic materials for thermal energy storage: Binary mixtures of consecutive straight-chain carboxylic acids form low-melting solid solutions

2019 Spring National Meeting

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