Interfacial modification regulation in CaCl2·6H2O/Expanded Perlite/Nano-γ-Al2O3 composite form-stable phase change materials for building thermal storage

Abstract

To address the issues of high supercooling, phase separation, leakage, and low thermal conductivity in calcium chloride hexahydrate (CCH, CaCl₂·6H₂O), a novel expanded perlite (EP)/ CaCl₂·6H₂O /Nano-γ-Al₂O₃ composite form-stable hydrated salt phase change material with favorable thermal performance and stability was developed. In this study, nano-γ-Al₂O₃ and SrCl₂·6H₂O were introduced as composite nucleating agents to reduce the supercooling effect and enhance thermal conductivity. Additionally, expanded perlite was modified through KOH etching and hydrophilic surface interface modulation. The PCM was confined within the EP pores using vacuum adsorption and polymer encapsulation methods. Leakage experiments were conducted to assess the impact of various modifier dosages on the properties of the FSPCM. The results demonstrated that the composite nucleating agents (1.5 wt% nano-γ-Al₂O₃ and 0.5 wt% SrCl₂·6H₂O) almost eliminated supercooling and enhanced liquid thermal conductivity by 78.3 %. The triple-interface regulation methods—including hydrophilic adsorption in micropores, a hydrophobic outer surface, and polymer coating—significantly improved PCM adsorption and thermal stability while minimizing leakage. After modification, the mass fraction of CCH increased from 45 wt% to 80 wt%. The prepared FSPCM exhibited a phase transition temperature of 27.17 °C and a latent heat of 138.22 J/g. Its thermal conductivity reached 0.315 W/(m·K), representing a 39.4 % improvement compared to unmodified EP/CCH. Even after 1000 thermal cycles, the latent heat of FSPCM remained at 121.72 J/g, with only an 11.94 % reduction. This novel FSPCM exhibits excellent heat storage capacity, stability, and non-flammability, making it highly promising for applications in building energy storage.