Review

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

¹ INESCOP, Centre for Technology and Innovation, Elda-Alicante, Spain
² National R&D Institute for Nonferrous and Rare Metals, 102 Biruintei Blvd, Pantelimon, Ilfov, Romania

^* e-mail: rpiticescu@imnr.ro

Received: 15 November 2017
Accepted: 18 January 2018

Abstract

NaNO₃ 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 NaNO₃ 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 (SiO₂) instead of the conventional polymeric shells used for organic microencapsulations and not suitable for high temperature applications (i.e. 300–500 °C). Thus, NaNO₃ has been microencapsulated by sol–gel technology using SiO₂ 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 NaNO₃ as TES material depends on the core:shell ratio used for the synthesis and on the maximum temperature supported by NaNO₃ during use.