Experimental evaluation of barium bromide-ammonia equilibrium lines

• A new method, the Fast Temperature Ramp, is presented for identifying the onset of multi-transition ammonia-salt reactions. • The positions of NH3-BaBr 2 equilibrium lines are identified for the first time using both temperature jump and TGA methods. • New ∆H and ∆S values are presented, showing that BaBr 2 may be considered as a pseudo single-transition salt in future work. • BaBr 2 is identified as a viable salt for use in heat pumping, thermal transformation and thermal storage applications. This work has experimentally evaluated the position of thermochemical equilibrium lines of barium bromide (BaBr 2 ) reacting with ammonia (NH 3 ). BaBr 2 samples, contained in discs of Expanded Natural Graphite, were placed in an experimental Large Temperature Jump rig and a new methodology, termed the Fast Temperature Ramp, was used to reveal adsorption and desorption reactions. Reaction onset points were plotted to generate equilibrium lines and calculate reaction enthalpies and entropies. Significant hysteresis between adsorption and desorption reactions was found, with the degree of hysteresis increasing as the salt becomes more deammoniated. The hysteresis effect was greatest for BaBr 2 (2–1) and BaBr 2 (1–0) reactions and also increased at higher pressures, exceeding 20 °C at 900 kPa for BaBr 2 (1–0). Adsorption reactions were found to occur over a very small temperature range, giving rise to a single transition ‘zone’ less than 20 °C wide. TGA experiments confirmed the position of equilibrium lines, although they were not successful in differentiating between two of the four ammoniated states. The close position of all equilibrium lines gives rise to a temperature ‘zone’ encompassing all four reactions, and in future work it may be advantageous to consider BaBr 2 as a pseudo single-transition salt instead.