Abstract

Recently, sol–gel techniques for synthesize inorganic shape-stabilized phase change materials (SS-PCMs) were proposed to successfully improve thermal properties and to accomplish real applications for latent thermal energy storage (TES). In this work, the use of sol–gel process was deeply investigated to develop inorganic SS-PCM, using tetraethyl orthosilicate (TEOS) as monomer and Na₂SO₄^.10H₂O as phase change material (PCM). In addition, the influence of pH (acid and basic hydrolysis) and PCM content in the physic and thermal properties of achieved materials were analyzed. Stabilized materials were characterized by infrared spectroscopy, X-ray diffraction, scanning electronic microscopy, scanning differential calorimetry, and thermogravimetry. The characterization results established that direct sol–gel method via acid hydrolysis showed potential to develop inorganic SS-PCMs. However, results indicate that the Na₂SO₄^.10H₂O loses water molecules during synthesis, resulting in the anhydrous compound Na₂SO₄-SiO₂; therefore, materials were proposed for high temperature TES applications. Melting point of 880–886 °C and enthalpy of fusion of 23–100 kJ kg⁻¹ were obtained for materials with 20–60 wt.% of PCM content. The new obtained SS-PCMs have enhanced thermal properties, compared with anhydrous Na₂SO₄: latent storage range R_L among 0.1–3.0 °C and thermal cycle stability, for high TES. In addition, direct sol–gel technique was compared with vacuum impregnation method, employing SiO₂ as support material. Impregnation procedures were not successfully achieved in this work to stabilize the PCM, which prove the superior significance of direct sol–gel method.

中文翻译：

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无机形状稳定相变材料的合成路线设计。直接溶胶-凝胶工艺与真空浸渍法

摘要

最近，提出了用于合成无机形状稳定相变材料（SS-PCM）的溶胶-凝胶技术，以成功地改善热性能并实现潜在的热能存储（TES）的实际应用。在这项工作中，以原硅酸四乙酯（TEOS）为单体和Na ₂ SO ₄为原料，对溶胶-凝胶法开发无机SS-PCM进行了深入研究^。10小时₂O作为相变材料（PCM）。此外，分析了pH（酸和碱性水解）和PCM含量对所得材料的物理和热性能的影响。稳定的材料通过红外光谱，X射线衍射，扫描电子显微镜，差示扫描量热法和热重分析法进行表征。表征结果表明，通过酸水解的直接溶胶-凝胶法显示出开发无机SS-PCM的潜力。但是，结果表明是Na ₂ SO ₄ ^。10H ₂ O在合成过程中会损失水分子，从而生成无水化合物Na ₂ SO ₄ -SiO ₂; 因此，提出了用于高温TES应用的材料。对于PCM含量为20-60 wt。％的材料，熔点为880-886°C，熔融焓为23-100 kJ kg ^-1。与无水Na ₂ SO ₄相比，新获得的SS-PCM具有增强的热性能：对于高TES，潜在存储范围R _L在0.1-3.0°C之间，并且热循环稳定性高。此外，将直接溶胶-凝胶技术与采用SiO ₂作为载体材料的真空浸渍法进行了比较。在这项工作中未能成功完成浸渍程序以稳定PCM，这证明了直接溶胶-凝胶法的优越性。