Encapsulation of Sodium Acetate Trihydrate and Stearic Acid for Thermal Energy Storage

Cores(< 1 mm diameter) of organic stearic acid(SA) and inorganic sodium acetate trihydrate(SAT) as phase change material(PCM) with a melting point in the range of 50-60 o C were manufactured. Single-layer coating was performed for SA cores with poly urethane(PU), poly methyl methacrylate(PMMA), and silicon, respectively, while tertiary-layer coating was performed for SAT cores with PMMA and Wax. In case of SAT, gelatin as thickener and sodium pyrophosphate decahydrate(Na4P2O7 10H2O) as nucleator were added to prevent the phase separation and the supercooling respectively. Coated PCMs were analyzed by optical microscopy, scanning electron microscopy(SEM), thermogravimetry(TG), and differ- ential scanning calorimetry(DSC) to investigate their morphology, coating thickness, thermal stability. As a result, we obtaine d the ball-shaped PCM cores with the uniform coating thickness of 10-20 μm, constant latent heat of 50-60 cal/g and 35 cal/g in case of SAT and SA respectively. But 10 o C of supercooling was observed for SAT after 12th cycle of thaw-freezing test, while no supercooling was observed for the SA coated with PU. Thermal stability of the coating polymers used in SA decreased in the order of PU, PMMA and silicon.