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

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 degrees=10(5) Pa) molar enthalpy of formation of crystalline TKX-50, (175.3 +/- 1.9) kJ center dot 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 center dot 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.