Green chemistry solutions for sol–gel micro-encapsulation of phase change materials for high-temperature thermal energy storage

NaNO 3 has been selected as phase change material (PCM) due to its convenient melting and crystallization temperatures for thermal energy storage (TES) in solar plants or recovering of waste heat in industrial processes. However, incorporation of PCMs and NaNO 3 in particular requires its protection (i.e. encapsulation) into containers or support materials to avoid incompatibility or chemical reaction with the media where incorporated (i.e. corrosion in metal storage tanks). As a novelty, in this study, microencapsulation of an inorganic salt has been carried out also using an inorganic compound (SiO 2 ) instead of the conventional polymeric shells used for organic microencapsulations and not suitable for high temperature applications (i.e. 300–500 °C). Thus, NaNO 3 has been microencapsulated by sol–gel technology using SiO 2 as shell material. Feasibility of the microparticles synthetized has been demonstrated by different experimental techniques in terms of TES capacity and thermal stability as well as durability through thermal cycles. The effectiveness of microencapsulated NaNO 3 as TES material depends on the core:shell ratio used for the synthesis and on the maximum temperature supported by NaNO 3 during use.