In-situ neutron imaging study of NH₃ absorption and desorption in SrCl₂ within a heat storage prototype reactor

Strontium chloride octaammine Sr(NH₃)₈Cl₂ offers high volumetric and gravimetric NH₃ densities and can store and release heat upon exo-/endothermal absorption and desorption of NH₃. Thus, it is a promising material for thermochemical heat storage (THS) applications. In the present work, in-situ neutron imaging was applied to analyze spatio-temporal development of Sr(NH₃)₈Cl₂ powder in a thermochemical heat storage prototype reactor during NH₃ absorption and desorption processes. The powder was embedded in a stainless steel honeycomb for the efficient heat transfer during the NH₃ desorption process. 2D radiography images were obtained during NH₃ ab-/desorption cycles at selected temperatures. The swelling and formation of the porous structure in SrCl₂ is monitored during the first cycles. A powder bed expansion of up to 10% upon NH₃ absorption was observed. Neutron tomography experiment were also performed to acquire 3D information which revealed the deformation of the honeycomb. This neutron imaging experiment brought crucial information for optimizing the design of efficient and safe THS systems.