Kinetic data on the thermal decomposition of RDX in the processing solvents cyclohexanone and gamma-butyrolactone determined with ARC and heat flow microcalorimetry

To improve its crystalline quality RDX is processed in suitable solvents; among them are cyclohexanone and gamma-butyrolactone. In spite of its relatively high thermal stability RDX can decompose to a certain extend during processing. Several qualities of RDX were investigated: so-called insensitive RDX (I-RDX) from Eurenco SA, Sorgues, France and so-called reduced sensitivity RDX (RS-RDX) from Chemring Nobel AS, Saetre, Norway. In addition, both types were used in a coarse (class 1) and a fine (class 5) particle size. Adiabatic selfheating was determined by ARC (Accelerating Rate Calorimetry) on solutions of RDX with concentrations between 6 mass-% and 10 mass-% in the two solvents using 1 inch titanium ARC bombs. The instrument was the ES-ARCTM from THT Inc. Bletchley, UK. It was operated in the so-called ‘heat-wait-search’ mode to register the decomposition exotherm reached by pseudo-adiabatic selfheating. The temperature range of detected decomposition is between 130°C and 230°C. The amount of RDX in the solutions was used-up during the selfheating course and the full decomposition curve was established. The curves show an initial faster increase in self-heat rate. Mostly this is indicative for chemical species, which accelerate decomposition. Such features can be caused autocatalytically. The curves were described with reaction kinetic models and Arrhenius parameters have been obtained. Heat generation rates were obtained by isothermal heat flow microcalorimetry (HFMC) using TAMTM III and a modified TAMTM II instruments from TA Instruments. Measurement temperatures were 80°C, 90°C, 100°C, 110°C, 120°C and 130°C, using 4ml stainless steel ampoules with glass inserts. The data were evaluated by differential iso-conversional description (Fried-man analysis) using AKTS software (AKTS AG, Technopôle 1, 3960 Siders, CH), providing the Arrhenius parameters as function of conversion.