The anti-supercooling effect of surface-modified nano-scaled SiO2 in hydrated salts phase transition system

Phase change characteristics of hydrate salt were analyzed for a system consisting of three types of SiO2 nano-particles doped phase change materials (PCMs). By using the three nano-particles of Aerosol SiO2, RNS-A SiO2 and Liquid phase SiO2, the surface effect of the interaction between nano-particles and hydrate salts was investigated. The time-temperature curves and Differential Scanning Calorimeter (DSC) testing results showed that Aerosol SiO2 had the most effective and stable performance as the nucleators for hydrate salts. The analysis of FT-IR showed that there were strong characteristic hydroxyl bonds on the surface of Aerosol SiO2. And the designed hydroxyl controllable silica gel system could prove the effect of hydroxyl bonds on suppressing supercooling of hydrate salts. It was concluded that supercooling of hydrate salts could be easily suppressed by the nano-additives with high specific surface area and strong polar hydroxyls in the surface. The ion-exchange attraction between hydroxyls and hydrate salts might mainly result in the supersaturation of hydrate salts in the interface of nano-particles. And then the supercooling of hydrate salts could be suppressed. The theoretical analysing model based on interionic attraction is a novel approach for investigating the nucleation of hydrate salts. And this result might provide a potential low-cost approach for the applications of nano-additivs in building energy storage and coolant.