Preparation of stearic acid/modified expanded vermiculite composite phase change material with simultaneously enhanced thermal conductivity and latent heat

• Expanded vermiculite loaded with titanium dioxide and treated with nitric acid (aEVT) was used for absorbing stearic acid (SA) by vacuum impregnation method.
• The latent heats of SA/aEVT were 146.8 J/g at the melting temperature of 65.9 °C and 141.7 J/g at the freezing temperature of 63.4 °C.
• The thermal conductivity of SA/aEVT was 0.58 W/mK.
• The latent heat and thermal conductivity of SA/aEVT were both higher than those of SA/EV and SA/aEV.
• The SA/aEVT composite PCM has good thermal and chemical stabilities.

A novel stearic acid/modified expanded vermiculite composite phase change material (PCM) was prepared in this study. Titanium dioxide-loaded expanded vermiculite was treated with nitric acid (aEVT) and then used as stearic acid (SA) supporting matrix. The thermal conductivity and latent heats of the SA/aEVT composite PCM were enhanced simultaneously compared with those of SA/expanded vermiculite (EV) and SA/expanded vermiculite with acid treatment (aEV) composite PCMs. The thermal conductivity of SA/aEVT was 0.58 W/mK, which was 11.4% and 20.3% higher than those of SA/EV and SA/aEV, respectively. The latent heats of SA/aEVT were 146.8 J/g at the melting temperature of 65.9 °C and 141.7 J/g at the freezing temperature of 63.4 °C, which were also higher than those of SA/EV and SA/aEV. The results of the thermal cycling test and Fourier transform infrared spectroscopy (FT-IR) indicated that the SA/aEVT composite PCM was thermally stable and chemically inert. Thus, the prepared SA/aEVT is a promising composite PCM for latent heat storage systems.

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