Thermal Performance and Interfacial Aspects of Kaolinite- Based Stearic Acid Composite in the Presence of Nitric Acid

摘要

The effect of nitric acid on the thermal performance of stearic acid/kaolinite (SA/Kaol) composite phase change materials (PCMs) was studied. SA/Kaol was subjected to HNO3 manipu- lations at different acidity conditions. The results indicated that inferior thermal properties were detected at the acid-treated composites with pH < 2. The latent heat value of SA/Kaol-0.5 demonstrated an obvious reduction of about 30% compared with that of SA/Kaol, and its supercooling extent could reach as many as 11.2°C while that of SA/Kaol was only 1.4°C. Based on interfacial reaction analysis, the reduced crystallinity of SA should be attributed to the confinement effect originated from acid molecular clusters, while the supercooling behavior was caused by external ions. These ions could hinder SA molecules from adsorbing to the surface of crystal nucleus and thus delay the solidification process. As a result of segregation effect, the latent heat value of acid-treated samples was deteriorated but the supercooling extent was relieved during thermal cycles. This work was the first that reported the effect of nitrogen oxides on PCMs. We believe that the results could play an enlightening role in the stability study of thermal property during PCMs practical applications.