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

Abstract

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: Evap=67.68 kJ mol−1 and Avap=1.57×105 s−1. In comparison, the values of NG (nitroglycerin) evaporation were determined: Evap=69.68 kJ mol−1 and Avap=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.

A Facile Way to Prolong Service Life of Double Base Propellant

“…It is visible from Figure 3 that the DB propellant shows two stages of mass loss which correspond to the evaporation and decomposition [29] of NG (120–170 °C) and the decomposition of NC (170–230 °C), respectively. No significant difference was determined for PTFE-DB propellant in the process of NC and NG decomposition.…”

“…The obtained sample mass vs. time curve were converted to the conversion (α) vs. time according to Equation (1) [29]:sans-serifα=mt−m0mf−m0, where m 0 is the initial sample mass, m f is the final sample mass (NG completely evaporated), and m t is the instantaneous sample mass.…”

“…Since evaporation readily is intrinsic property of NG molecule, using other energetic plasticizers to dissolve NC may obtain desired volatility. For this reason, we have introduced N-butyl-N-nitratoethyl nitramine (Bu-NENA) to DB propellant and studied its evaporation characteristics [29]. It showed much lower volatilization rate for Bu-NENA/NC propellant than that of NG/NC propellant as we expected.…”

A molecular dynamics study of plasticiser migration in nitrocellulose binders

“…The EC added to each mixture was 1% by weight of the total binder ingredients. 7,37 Both of the binder mixture configurations were built using the program Packmol. A tolerance of 2.5 Å between the molecules was applied.…”

Mechanical Properties of HTPE/Bu-NENA Binder and the Kinetics of Bu-NENA Evaporation

“…In previous reports, Tompa et al [20] found that the size and shape of a propellant both directly affect the rate of evaporation. Zhao et al [21], using isothermal thermogravimetry (TG), calculated that the enthalpy of Bu-NENA evaporation from an NC/Bu-NENA propellant was 69.75 kJ/mol. The evaporation of Bu-NENA follows a zeroorder reaction model at a very early stage of evaporation, while the power law of the evaporation rate changes with time.…”