Thermal degradation and activation energies of two insensitive propellants: an experimental study

International audienceLow vulnerability gun propellants are energetics materials designed to resist unintended ignition stimuli. The present work aims to determine activation energies (Ea) for two Low-Vulnerability Ammunition (LOVA) propellants. The first propellant is made of 84% of 1,3,5-Trinitro-1,3,5-triazinane, usually called hexogen (RDX) and around 16% of hydroxyl-terminated polybutadiene (HTPB) as binder. The second one is a nitrocellulose (NC) based propellant (98%) which also contains diphenylamine (2%). These propellants are commercial products and were provided by ArianeGroup. Both have a cylindrical shape with or without several perforations but here only a few milligrams of each samples is used. Combustion properties of these two propellants were already studied and results recently published. The present experimental study focuses on two thermal degradation methods which are the Thermogravimetric Analysis (TGA) and the Differential Scanning Calorimetry (DSC). This study is complementary to the previous works on combustion behavior. Data obtained with such thermal analysis techniques provide important results concerning thermal behavior of propellants. These results are useful to study ignition and combustion, but also storage (aging). For each propellant DSC and TGA experiments were performed using several heating rates (β = 0.1-0.3-0.5-0.8-1.0 K.min-1) and different surrounding gases (nitrogen N2, argon Ar). Heating rates must be lower than 1 K.min-1 to obtain kinetics parameters because this kind of materials presents a thermal runaway behavior (and in this case temperature is not controlled). The figure 1 presents results plotted as mass variation and heat flow against temperature for the RDX based propellant by a heating rate of 1 K.min-1 and under argon atmosphere. Post treatment of raw data is performed using the thermokinetics software Advanced Kinetics Technology Solutions (AKTS). The output is Ea for each propellant. Comparison is made between DSC and TGA results and between both propellants. These specific thermal analyses will provide data for simulation codes and help to predict ignition behavior of propellants. Figure 1: TGA (red) and DSC (blue) signals for a RDX based propellant under argon atmosphere (β =1.0 K.min-1)