A eutectic mixture of galactitol and mannitol as a phase change material for latent heat storage

Abstract

Abstract The thermophysical properties of mixtures of galactitol and mannitol were examined via differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) analysis. The aforementioned sugars were found to form a eutectic mixture at a 30:70 molar ratio of galactitol and manntitol, and displayed a melting point of 153 C while maintaining a high latent heat of fusion (ΔH<inf>fus</inf> = 292 J g-1). The XRD data revealed that the eutectic mixture contained the α, β, and δ forms of mannitol with the δ form being the major component. By varying the temperature ramp rates utilized in the DSC measurements from 0.5 C min-1 to 20 C min-1, the heat of crystallization as well as the crystallization temperature increased (c.f., ΔH<inf>crys</inf>: 64 J g-1 → 197 J g-1; T<inf>c</inf>: 68 C → 105 C). In addition, the temperature and the enthalpy of crystallization were also improved by up to 34% through the addition of small quantities (up to 0.5 wt%) of nucleating agents, such as graphite powder or silver iodide. After 100 heating/cooling cycles under an atmosphere of nitrogen, the heat of fusion of the eutectic mixture decreased by only 4% with no change in the melting point, and the mixture appeared to be chemically stable according to a Fourier transform infrared (FT-IR) spectroscopic analysis. Collectively, these data indicate that the eutectic mixture exhibits excellent cyclic stability under ambient atmospheres and offers potential for use in thermal energy storage applications. © Elsevier Ltd