自工業革命以來，大量的溫室氣體導致全球暖化的狀況日益嚴重，為了減少製冷設備所消耗的能源，可利用輻射冷卻來降低溫度。輻射冷卻系統為一種被動的冷卻方式，在不須消耗能源以及不排放溫室氣體的情況下，可透過由大氣窗口區域（波長 8 至 13 μm）向外太空散發熱輻射達到冷卻效果。二氧化矽粉末在大氣窗口內具有優秀的發射能力，聚甲基丙烯酸甲酯做為黏著劑於紅外光譜下吸收率低，二氧化鈦粉末於太陽輻射下具高反射率，因此本實驗將結合此三種材料製備輻射冷卻塗層。
本研究將分為三個部分：首先，將利用不同粒徑（0.4、1.0、2.1、3.7以及 6.8 微米) 之商用二氧化矽製備於輻射冷卻塗層(SiO2-PMMA coating)，同時探討粒徑對於塗層冷卻能力的影響；接著，利用不同前驅物濃度與製備方式合成不同粒徑大小之二氧化矽。前驅物濃度分別為0.3、0.6 和 0.9 M，而製備方法包含噴霧熱裂解法(Spray pyrolysis, SP)與噴霧乾燥法(Spray drying, SD)，並進行粉體以及塗層的分析；最後，以三種不同製備順序添加二氧化鈦於塗層中，以增強塗層的相對反射率，提高降溫效果。其中，將以 X 光繞射分析儀、氮氣吸/脫附分析儀、掃描式電子顯微鏡、傅立葉轉換紅外線光譜儀、紫外光/可見光/近紅外光譜儀及日曬溫度量測分別分析相組成、比表面積、表面形貌、紅外光發射光譜、漫反射光
譜以及塗層的冷卻效果。
實驗結果顯示不同粒徑之商粉以 0.4 微米商粉二氧化矽所製備的塗層具有最佳的降溫效果，最大溫差可達約 7.8 °C。另外，以噴霧熱裂解法合成的 0.7 μm 二氧化矽粉末製備的冷卻塗層，在相同環境下與商粉相比，可達到更佳的熱輻射發射能力以及冷卻效果。此外，以(PMMA-TiO2)- SiO2塗層的製備順序添加二氧化鈦於塗層中，可有效增強塗層之太陽反射率，並達到更佳的降溫效果。

Since the industrial revolution, a large amount of greenhouse gas has caused global warming to become more and more serious. In order to reduce the energy consumption of cooling equipment, radiative cooling phenomenon was used to decrease the nvironmental temperature. Radiative cooling is a passive cooling technology, which achieves ooling by emitting heat radiation to outer space from the atmospheric window region (8~13 μm wavelength) without consuming energy and releasing greenhouse gases. SiO2 has xcellent emission ability in the atmospheric window, PMMA as the binder has low absorptivity in the infrared spectrum, and TiO2 has high reflectivity under solar radiation. Thus, in this experiment, these three materials will be combined to prepare the radiative cooling coating.
In this study, the experiment was divided into three parts: First, this study prepared the SiO2-PMMA coatings using commercial SiO2 powders including various particle sizes (0.4, 1.0, 2.1, 3.7, and 6.8 μm) and discussed the effect of SiO2 particle size on the cooling performance of the coatings; next, this study synthesized SiO2 with various particle sizes by various precursor concentrations 0.3, 0.6 and 0.9 M) and preparation methods (spray pyrolysis and spray drying). Also, the cooling performance of the powders and coatings was analysed; finally, TiO2 was added to the coating in three various preparation sequences for enhancing the relative reflectivity of the coating and improving the cooling effects. Phase composition, surface area, surface morphology, particle distribution, emissive spectrum, solar reflectance spectrum, and cooling performance of the coatings were studied using X-ray diffraction, nitrogen adsorption/desorption isotherm (BET), scanning electron
microscopy, Fourier transform infrared spectroscopy, UV-Vis-NIR spectroscopy, and temperature measurements.
The experimental results showed that among the commercial SiO2 powders with various particle sizes, the coating prepared with 0.4 μm commercial SiO2 particles has the best cooling performance, and the maximum temperature difference reached about 7.8 °C. In addition, compared with commercial powder in the same environment, the SiO2-PMMA coating prepared by 0.7 μm SiO2 particles synthesized by spray pyrolysis method can achieve better heat radiation emission ability and cooling effect. Moreover, adding TiO2 to the coating in the preparation sequence of (PMMA-TiO2)-SiO2 coating effectively enhanced the solar reflectance of the coating and achieve better cooling effect.

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