Heat-storage mixture of sodium halogenides and chromates

A three-component system of sodium chlorides, bromides, and chromates was studied with differential thermal, differential scanning calorimetric methods of physicochemical analysis. The ratio of the components in the invariant composition, which crystallizes at $555^{\circ}$C with a specific enthalpy of melting of $92.9$ J/g, has been established. It was noted that the solid phase contains a polymorphic transformation $\rm Na_2\rm CrO_4$ at $423^{\circ}$C with a specific enthalpy of $42.6$ J/g. The developed composition can be used as a working fluid in devices that accumulate thermal energy in a temperature range of $300$ to $600^{\circ}$C. A three-dimensional model was constructed for the phase complex systems $\rm Na^+||\rm Cl^-$, $\rm Br^-$, $\rm CrO^{2-}_4$ and the identified mono- and invariant phase reactions. The spatial model of the system makes it possible to analyze the phase complex of the system and to construct arbitrarily selected isothermal and polythermal sections.