On the Enthalpy of Formation and Enthalpy of Sublimation of Dihydroxylammonium 5,5′‐bitetrazole‐1,1′‐dioxide (TKX‐50)

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The thermodynamic characterization of dihydroxylammonium 5,5′‐bitetrazole‐1,1′‐dioxide (TKX‐50) was reinvestigated. Although TKX‐50 is one of the most promising new‐generation energetic materials, contradictory reports are found in the literature with regard to its solid enthalpy of formation. The standard ( p o =10 5 Pa) molar enthalpy of formation of crystalline TKX‐50, (175.3±1.9) kJ ⋅ mol −1 , was determined experimentally based on the measured standard massic energy of combustion, determined through static‐bomb combustion calorimetry. Additionally, the standard molar enthalpy of sublimation of TKX‐50, at T =298.15 K, (165.0±2.4) kJ ⋅ mol −1 , was derived from vapor pressure measurements determined by a Knudsen mass‐loss effusion technique. Finally, different approaches were used in attempts to calculate the standard enthalpy of formation of TKX‐50 in the solid state. A critical overview and assessment of the data on the enthalpy of formation of TKX‐50 is also presented.