Calorimetric examination of suitability of calcium, cobalt and nickel nitrate hydrates for thermal energy storage
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Calorimetric examination of suitability of calcium, cobalt and nickel nitrate hydrates for thermal energy storage Pavla Honcová1 · Galina Sádovská1,2 · Lukas Binder1 · Petr Koštál1 · Daniel Honc3 Received: 1 September 2019 / Accepted: 9 February 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Selected nitrate hydrates were characterized using X-ray diffraction, helium pycnometer, Calvet-type calorimeter and simultaneous thermogravimetry coupled with differential scanning calorimeter. Melting and crystallization of all studied nitrate hydrates were observed by differential scanning calorimeter, and the supercooling (difference between melting temperature and crystallization temperature) was found to be more than 80, 14 and 37 °C for calcium nitrate tetrahydrate, cobalt and nickel nitrate hexahydrates, respectively. Those salts were mixed with selected nucleating agents to suppress supercooling and then tested under repeating of heating–cooling cycles. Calcium nitrate tetrahydrate showed reversible liquid–solid process with addition of CaO, Ca(OH)2, BaO, Ba(OH)2·8H2O, graphite and graphene, but the supercooling remains too high, and the enthalpy change significantly decreased. In the case of cobalt nitrate hexahydrate, the CaO, Ba(OH)2·8H2O and graphite are the most effective nucleating agent in amount of 1 mass%. The supercooling of nickel nitrate hexahydrate was effectively reduced by addition of CaO, Sr(OH)2 and graphite. The cobalt and nickel nitrates were tested with combination of two nucleating agents (1:1). The best results were obtained for composites with addition of 1 mass% of nucleating agent mixture consisting of both graphite and Ba(OH)2·8H2O for cobalt nitrate hexahydrate, and CaO with Mg(OH)2 for nickel nitrate hexahydrate. Keywords Calcium nitrate tetrahydrate · Cobalt nitrate hexahydrate · Nickel nitrate hexahydrate · Dehydration · Phasechange materials · DSC · Nucleating agent · Supercooling
Introduction Inorganic salt hydrates are intensively studied for their ability to store/release quite a high amount of heat during their phase-change, i.e. melting and crystallization, occurred in low and medium temperature ranges [1–3]. The main advantage of this kind of material is a small volume change associated with solid–liquid phase change, high amount of heat, good thermal conductivity and lower cost. However, * Pavla Honcová [email protected] 1
Faculty of Chemical Technology, University of Pardubice, Doubravice 41, 53210 Pardubice, Czech Republic
2
J. Heyrovský Institute of Physical Chemistry, Academy of Science of the Czech Republic, Dolejskova 3, 182 23 Praha 8, Czech Republic
3
Faculty of Electrical Engineering and Informatics, University of Pardubice, Cs. Legii Sq. 565, 53002 Pardubice, Czech Republic
there are also disadvantages as an occurrence of supercooling (temperature of melting during charging is higher than temperature of crystallization during discharging), phase separation and corrosion of metal containers/capsules [4–7]. When the phase-change materials (P
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