Unveiling real-time crystallization with nucleators and thickeners for zinc nitrate hexahydrate as a phase change material
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AbstractThe primary challenge of salt hydrates as phase change materials (PCMs) is their high degree of supercooling (TSup). Past studies have attempted to alleviate TSupby incorporating nucleators possessing similar lattice structure, without a thorough analysis of the nucleator/PCM interactions. This work presents a novel inoperando study to visually observe the crystallization process of zinc nitrate hexahydrate (ZNH) in realtime using suitable nucleators and a thickener. We have introduced a new dataset where zinc acetate dihydrate (ZnAc.2H) has been employed as an additive to ZNH for thermal energy storage (TES). According to our inoperando study, ZnAc.2H underwent hydrolysis in molten ZNH to precipitate needlelike ZnO particles, which acted as nucleators for the PCM. In the absence of a thickener, the crystal propagation of ZNH exhibited a preferential directional tendency, whereas incorporation of thickener made the phase change process uniform along all directions. Selfhydrolysis of ZnAc.2H generated excess water which caused the undesirable effect of broadening the endothermic peak. The addition of carboxymethyl cellulose (CMC) thickener could restrict the activity of excess water and reduce the broadening of the endothermic peak. Differential scanning calorimetry (DSC) revealed that 5wt% ZnAc.2H additive and 2wt% CMC thickener added to ZNH can considerably improve the TES properties of ZNH PCM (HFusion125.9Jg1, TSup3.0C, melting point [M.P.] 29.0C). Our inoperando studies can unveil realtime phase change behaviors to better design PCM systems with desired characteristics.
