DEFLAGRATION-DETONATION EXPERIMENTS OF SENSITIZED MIXTURES OF AMMONIUM OR UREA NITRATES AND AN ENERGETIC THERMOPLASTIC ELASTOMER

摘要

Ammonium nitrate (NH_4NO_3) is the base component of a known family of explosives, gas generators and pyrotechnic composite mixtures. Urea nitrate ((NH_2)2.COHNO_3) is a recent used nitrate in deflagration and detonation studies motivated, most of them, by forensic research works. The existence of CO, in the molecule of urea nitrate, changes its contribution of this nitrate in reaction propagation. To increase energetic level of mixture, an Energetic Thermoplastic Elastomer (ETPE) has been used as binder. It has been prepared from commercial available GAP and Poly-BAMO via chain elongation with difunctional isocyanates. In this case it was used an ETPE of GAP content of 65.3 % (with 29.6 %, of Poly-BAMO and 5.1 % of 1,4-Phenylenediisocyanate). The prediction of decomposition products of reactants and of the combustion and detonation characteristics of this energetic mixture, ammonium nitrate or urea nitrate mixed with ETPE, has been done using THOR code. They have an equivalence ratio from 0.8 to 2.0, using AN, and from 1.2 to 2.2, using UN. Detonation properties were also evaluated, using an HL equation of state and adapted equations for condensed species. All the tested experimental mixtures were done using original twin screws mixing system that allows the direct injection of the mixture inside the test confinement. Deflagration of tested mixtures, were reviewed and discussed. Obtained results present low flame velocity propagation in cigar burning tests, at atmospheric pressure, and flame temperatures from 650 to 1000 °C. Detonation sensibility tests were performed, initially, using commercial detonator initiation and printed aluminum witness plates. A new configuration, based in a circular box (were reactant mixtures were enclosed in a aluminium tube of 4 mm height and 50 mm diameter), having peripheral shock initiation generated from a peripheral PETN detonating cord, was presented. This configuration was tested and show, clearly, the non-detonation behaviour of the mixtures, originating not only the expected printed figures in the witness plates, but also the compaction of the energetic sample after the inducted shock.