Kinetics of Bu-NENA Evaporation from Bu-NENA/NC Propellant Determined by Isothermal Thermogravimetry

Bu-NENA (N-butyl-N-nitratoethyl nitramine) base propellants have versatile qualities, such as, higher energy, reduced sensitivity, and enhanced mechanical properties. The evaporation of Bu-NENA, which takes place in the propellant grains in the course of time, can reduce the physical properties of the propellants, weaken the propellant grains, cause the propellants to crack at stress-concentrated points, and finally result in unfavorable increases or fluctuations of the burning rate and poor performance of the rocket motor. In this study, the evaporation of Bu-NENA from a double base propellant was investigated using isothermal thermogravimetry. The results showed that the entire process of Bu-NENA evaporation complied with the power law of evaporation rate with time. The values of kinetic parameters of Bu-NENA evaporation were calculated: E_vap=67.68 kJ mol⁻¹ and A_vap=1.57×10⁵ s⁻¹. In comparison, the values of NG (nitroglycerin) evaporation were determined: E_vap=69.68 kJ mol⁻¹ and A_vap=1.33×10⁶ s⁻¹. The value of the activation energy of Bu-NENA evaporation was close to that of NG, but the pre-exponential factors differed by an order of magnitude. The evaporation of Bu-NENA followed zero-order kinetics at the early stage, and the enthalpy of Bu-NENA evaporation was calculated to be 69.75 kJ mol⁻¹ according to Langmuir and Clausius-Clapeyron equations.