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

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 degrees C while maintaining a high latent heat of fusion (Delta H-fus = 292 J g(-1)). The XRD data revealed that the eutectic mixture contained the alpha, beta, and delta forms of mannitol with the delta form being the major component. By varying the temperature ramp rates utilized in the DSC measurements from 0.5 degrees C min(-1) to 20 degrees C min(-1), the heat of crystallization as well as the crystallization temperature increased (c.f., Delta H-crys: 64 J g(-1) -> 197 J g(-1); T-c: 68 degrees C -> 105 degrees 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. (C) 2015 Elsevier Ltd. All rights reserved