Thermal storage performance of shape stabilized phase change materials with high thermal conductivity derived from ZIF-67 etched via tannic acid
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摘要: 为解决有机固-液相变材料(PCMs)导热系数低和相变易泄漏的难题,利用丹宁酸刻蚀ZIF-67制备碳基骨架作为支撑体(HX-C),硬脂酸(SA)为相变芯材,采用真空熔融吸附法构筑导热增强型定形相变材料(SA/HX-C)。为评估其储热能力,对热稳定性、储热性能、导热系数、定形能力及光热转换能力进行研究。同时,借助氮气等温吸附-脱附、傅里叶红外光谱、X-射线衍射和扫描电子显微镜进行表征。结果表明:丹宁酸刻蚀ZIF-67可实现对其碳化衍生物的扩孔作用,提高SA/HX-C的定形能力。所制备的SA/HX-C具有良好的储热性能、导热能力及光热转换性能。其中,刻蚀时间为6 min的复合相变材料(SA/H6-C)的储热效率可达80.84%,光热转化效率高达76.29%,导热系数(0.461 W/(m·K))相比于SA提高了156.11%。SA/H6-C在相变过程中无任何形貌变化和泄漏,重复循环储/放热100次后仍然具有良好的储热能力。Abstract: To solve the defects of low thermal conductivity and leakage of organic solid-liquid phase change materials (PCMs), ZIF-67 was etched by tannin acid to obtain the carbon-based supports (HX-C), stearic acid (SA) was the phase change material and then used to prepare the enhanced thermal conductivity PCMs (SA/HX-C) via vacuum melting adsorption method. In detail, thermal stability, heat storage property, thermal conductivity, shape stability and photo-thermal conversion were investigated to evaluate the thermal storage performance. Meanwhile, characterizations of nitrogen isothermal adsorption-desorption, FTIR, XRD and SEM were conducted. Results revealed that tannic acid can expand the pore size of carbonized ZIF-67 derivatives, thus enhancing the shape stability. The obtained SA/HX-C own favorable heat storage property, thermal conductivity, and photo-thermal conversion. Among them, etching time of 6 min for PCMs (SA/H6-C) exhibits high thermal storage efficiency of 80.84% and photo-thermal conversion of 76.29%. Thermal conductivity is strengthened to 0.461 W/(m·K), which is 156.11% higher than that of SA. No leakage and shape change are observed for SA/H6-C during phase transition, it still shows good thermal storage performance even after recycling 100 times.
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Key words:
- phase change thermal storage /
- shape stability /
- ZIF-67 /
- photo-thermal conversion /
- stearic acid
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表 1 SA/HX-C制备参数
Table 1. Preparation parameters of SA/HX-C
Precursor Etching time/min Support Carbonization temperature/℃ Composite PCM SA mass fraction/wt% ZIF-67 0 H0-C 700 SA/H0-C 60 ZIF-H3 3 H3-C SA/H3-C ZIF-H4 4 H4-C SA/H4-C ZIF-H6 6 H6-C SA/H6-C ZIF-H8 8 H8-C SA/H8-C ZIF-H10 10 H10-C SA/H10-C Notes: PCM—Phase change material; SA—Stearic acid. 表 2 HX-C的比表面积、孔容和平均孔径
Table 2. Surface area, pore volume and average pore diameter of HX-C
Sample Surface area/(m2·g−1) Pore volume/(cm3·g−1) Average pore diameter/nm H0-C 357.63 0.240 2.63 H3-C 259.74 0.337 6.02 H4-C 247.11 0.381 7.43 H6-C 249.13 0.386 7.46 H8-C 238.53 0.432 9.43 H10-C 267.30 0.498 9.69 表 3 SA和SA/HX-C的热性能
Table 3. Thermal properties of SA and SA/HX-C
Sample Tm/Tf /℃ ΔHm/ΔHf/(J·g−1) ΔT/℃ λ/(W·(m·K)−1) SA 68.53/65.01 220.28/221.48 3.52 0.180 SA/H0-C 67.72/67.12 109.52/110.48 0.60 0.452 SA/H3-C 67.53/66.70 106.80/101.43 0.77 0.453 SA/H4-C 67.53/66.84 109.34/103.21 0.69 0.457 SA/H6-C 67.38/66.70 109.93/104.35 0.68 0.461 SA/H8-C 67.25/66.55 109.09/100.27 0.70 0.456 SA/H10-C 67.17/66.32 109.67/99.80 0.75 0.458 Notes: Tm, Tf and ΔT—Melting temperature, solidification temperature and supercooling; ΔHm and ΔHf—Latent heat of melting and latent heat of solidification; λ—Thermal conductivity. 表 4 SA/H6-C循环储/放热100次前后的热性能
Table 4. Thermal properties of SA/H6-C before and after 100 cycles of storage/exhaust heat
Cycle time Tm/Tf/℃ ΔHm/ΔHf/(J·g−1) ΔT/℃ Before the cycle 67.38/66.70 109.93/104.35 0.68 After 100 cycles 67.39/66.71 109.25/103.72 0.68 -
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