INVESTIGATION ON THE PYROLYSIS PRODUCTS OF LOW VULNERABILITY PROPELLANTS BASED ON RDX

Low vulnerability gun propellants are energetic materials specifically designed to resist unintended initiation stimuli and aim at replacing the usual nitrocellulose (NC) based ones. As a result, low vulnerability gun propellants are more difficult to ignite than conventional propellants. In order to achieve efficient ignition, it is essential to study the preliminary pyrolysis and combustion of these propellants. Due to the strong coupling that exists between pyrolysis and combustion, it is necessary to provide a fine analysis of chemical reactions that drives the entire process. The present work focuses on the analysis of the pyrolysis products of three propellants which belong to the family of Low Vulnerability Ammunition (LOVA). The propellants consist of hexogen (RDX) and nitrocellulose. Three different ratios of NC were studied. The weight percentages of RDX/NC are of 95-5, 90-10 and 85-15. The energetic materials studied in this work are not commercial ones but are produced at the French-German Research Institute of Saint-Louis (ISL). The pyrolysis of these energetic materials is studied with two different experiments. On the one hand propellant’s pyrolysis is obtained by means of a laser diode. To determine the gaseous species produced during the pyrolysis, a mass spectrometer is linked to the analysis chamber of a cylindrical closed reactor. This in-situ analysis provides information about the pyrolysis species evolution. By varying the duration of energy deposition and the initial pressure in the reactor, it is possible to maintain a pyrolysis at the pellet surface without initiating a flame. Two different atmospheres are tested, nitrogen and argon. Emitted gases are analyzed and their amounts are compared according to surrounding gas and initial pressure. On the other hand, the pyrolysis of these propellants is investigated with a flash pyrolysis device linked to a gas chromatograph coupled to a mass spectrometer (Py-GC-MS). The propellant sample is heated at 8 000 °C.sec-1 and the pyrolysis products are analyzed thanks to the GC-MS. Results are given for different maximum temperatures. Obtained results with the two setups are confronted and compared to the few available literature data. The experimental data collected should serve in the future to have a better understanding of the chemical reactions driving the combustion process of these LOVA propellants.