Corrosion evaluation and prevention of reactor materials to contain thermochemical material for thermal energy storage

Thermochemical materials (TCM) can be used for seasonal heat storage, storing high amounts of thermal energy coming from the sun in summer and releasing it in winter, when heating for houses is needed. One promising TCM for building comfort applications is the Na2S/water pair due to its high energy density and appropriate reaction temperature that can be achieved by a solar collector. Nonetheless, Na2S reacts with oxygen and is corrosive to metals, especially with those used to build up heat exchangers or reactors that contain the TCM. Therefore, corrosion tests in a self-developed experimental setup under vacuum conditions, 13 mbar, between Na2S⋅9H2O/5H2O and two reactor metals - copper and stainless steel 316 - have been performed. Since copper is corroded and is highly used for thermochemical reactors, two promising coatings, Halar and electroless nickel, have been applied. Furthermore, aluminium has also been tested coated with these coatings. Halar is a potential candidate to protect both copper and aluminium heat exchangers/reactor that may contain Na2S/H2O pair for thermochemical energy storage. Stainless steel 316 is also corrosion resistant to the selected TCM.