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Thermal Degradation Behaviour and Kinetics of aged TNT-based Melt Cast Composition B

Singh Arjun, Sharma Tirupati Chander, Singh Vasundhara, Mukherjee Niladri

Central European Journal of Energetic Materials

2019

Vol. 16, no. 3

360--379

In the present paper, three kinds of aged and freshly prepared 2,4,6-trinitrotoluene (TNT) based Composition B stockpiled, for a period of 20 and 32 years, were investigated for the effect of natural ageing on their thermal degradation behaviour and kinetic parameters. The properties investigated indicated that there was no significant change in the thermal stability of the samples aged under natural environmental conditions. The kinetic parameters were studied by means of the Kissinger method using the peak temperature at maximum reaction rate from DSC data, and the isoconversional Kissinger-Akahira-Sunnose (KAS) and ASTM E689 methods from TGA data. The apparent activation energies calculated by the Kissinger method were 173.8 kJ·mol–1 for fresh, 170.4 kJ·mol–1 for 20 y old and 187.1 kJ·mol–1 for 32 y old Composition B, respectively. The values calculated by the KAS method were found to be in the range 77.2-235.8 kJ·mol–1 for fresh Composition B, 75.7-224.0 kJ·mol–1 for 20 y old and 70.4-196.0 kJ·mol–1 for 30 y old Composition B, respectively. The activation energies obtained from the KAS methods are in good agreement and consistent with the isoconversional ASTM E689 kinetic method. The thermodynamic parameters, such the Gibbs free energy of activation (ΔG#), activation enthalpy (ΔH#) and activation entropy (ΔS#) for the formation of activated complexes were also studied and are discussed.

Design and operation of a small scale set back force simulator and its use in investigation into composition B fillings subjected to hot gun scenarios

Cartwright M., Delany P.

Central European Journal of Energetic Materials

2009

Vol. 6, nr 1

103-117

Ammunition fired from large calibre gun chambers may experience accelerations in the regions of 150,000 m s-2 and as a result are subjected to considerable force during the process of set back. During firing some of the energy may be transferred to the filling and any defects present in the shell filling can lead to local hotspots which may result in premature ignition of the warhead. A potential source of defects is the application of excessive heat to the ammunition either by storage in a hot environment or accidentally by leaving the ammunition in a hot gun scenario in the chamber of the gun. A hot gun scenario can be defined as arising after 50 rounds or more have been fired in a four hour period. In this scenario the filling may easily exceed the qualification temperature with two possible accidents occurring. Cook-off of the filling can result in spontaneous firing of the round or, when correctly initiated, the round may premature in the gun barrel both of which may have catastrophic results. Currently there is no standard test to evaluate the behaviour of composition B (60% RDX: 40% TNT) filled ammunition subjected to a hot gun scenario. Because of its low melting point 80 °C the liquid TNT can separate from the RDX increasing its sensitivity and increasing the probability of an in bore premature when fired. This paper describes the design and operation of a small scale simulator for set back forces and its use to investigate the conditions under which composition B fillings, subjected to a hot gun scenario, could initiate. Samples of composition B were subjected to thermal treatments to mimic hot gun conditions and then subjected to simulated set back conditions and the level of impact energy required for initiation determined. This was compared with the level for untreated samples and a possible evaluation of current hot gun procedures undertaken. The indications are that the process can be cost effective in simulating set back induced premature ignitions.