New insights into the thermal behavior and stability of ammonium bifluoride: non-isothermal thermokinetic analysis

In this research, the thermal behavior of NH4HF2 was studied by non-isothermal thermogravimetric analysis between 298 and 600 K in a nitrogen atmosphere. The thermal analysis indicated that the gasification of this material begins in the solid state from 343 K, approximately, and continues after the melting point (398 K) in the liquid state. The Friedman's isoconversional method and combined kinetic analysis were used to evaluate the thermokinetic characteristics of the gasification of this compound in solid and liquid states. The results show that both processes follow an F0 model with $$Ea_{{{\text{Sol}}}}$$  = 71.3 kJ mol−1 and $$\ln \left( {A_{{{\text{Sol}}}} /s^{ - 1} } \right)$$  = 12.8, and $$Ea_{{{\text{Liq}}}}$$  = 66.6 kJ mol−1 and $$\ln \left( {A_{{{\text{Liq}}}} /s^{ - 1} } \right)$$  = 11.5. The kinetic triplets were corroborated by reconstructing the original experimental curves and predicting curves obtained under experimental conditions different from those used in the study. The F0 model indicates that the processes are dominated by sublimation/vaporization. The released gases were condensed and characterized, suggesting the formation of a new species, the “NH4HF2 gas.”