Characterization of solid residue formation in LX-17 exposed to abnormal thermal environments

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Concerns surround whether insensitive (or any) energetic materials are more dangerous to handle when exposed to abnormal thermal environments. This study characterizes the residual material remaining after LX‐17 (92.5 % 1,3,5‐triamino 2,4,6‐trinitro benzene (TATB) and 7.5 % Kel‐F) is exposed to various thermal environments in a sealed small‐scale vessel cook‐off test reactor (heated at 0.1 to 100 °C/min until the reactor opened at 3000 psi (20.7 MPa)). Previous work has shown no additional sensitivity of these residues as evaluated by small‐scale safety analysis, but characterization on the molecular scale indicates the TATB is transformed to more reactive compounds as well as the residue could be precursors to toxic gases. The solids and chars were characterized by various analytical methods. Heat‐flow measurements indicated exothermic release is due to a mixture of residual TATB and related decomposition products (which may be more energetic). The N/C and O/N ratios indicated a material much more degraded than TATB. Primarily, the solids were a network of amorphous C inter‐dispersed with N and O. Types of bonding include C−C, C−N, N−H, N−C, N=C, N≡C, C−O=, and −OH. Solvent extracts of the solids showed TATB decomposition intermediates benzo‐furazans and benzo‐furoxans, substituted TATB (mono‐nitroso, hydroxyl, and chlorinated) along with several unidentified smaller molecules. These results indicate thermal treatment produces an amorphous carbon residue with heteroatoms incorporated through differing functionality, varying depending upon the thermal severity of exposure. These structures also could further decompose producing toxic light gases (such as cyanide).

Section: Resultsmentioning

confidence: 82%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

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LX‐17 Thermal Decomposition‐Characterization of Solid Residues from Cook‐Off in a Small‐Scale Vessel Under Confinement

Reynolds

Muetterties

Nelson

et al. 2021

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Experimental Investigation of the Thermal Decomposition Pathways and Kinetics of TATB by Isotopic Substitution

Köroğlu

Crowhurst

Kahl

et al. 2021

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Real-time measurements of the product gases arising from the thermal decomposition of triamino-trinitro benzene (TATB), its deuterated analogue, and plastically bonded TATB (LX-17) are presented in this study. Gas-phase decomposition products are identified by IR absorption spectroscopy. The frequency shifts in rovibrational spectra due to isotopic substitution and the change in rate of formation of decomposition products due to the kinetic-isotope-effect (KIE) help elucidate the decomposition pathways. The formation of H 2 O precedes other molecules (e. g., HCN, HNCO) during decomposition. After the concentrations of HCN and HNCO molecules reach a peak, their amounts gradually decrease. The concentrations of the other decomposition products (e. g., NH 3 and CO 2 ) rapidly rise after an induction period, which is attributed to the presence of autocatalytic reactions. The trends of chemical evo-lution are similar for all the samples, but their kinetic behaviors are different. This indicates the rates of consistent pathways are changed during thermal decomposition. The kinetics of deuterated TATB decomposition is slower than that of unsubstituted TATB due to the KIE (k H /k D~1 .41). The rate of LX-17 decomposition is slightly lower than unsubstituted TATB (k TATB /k LX-17~1 .15). The KIE is more pronounced during the early stage of decomposition, which is attributed to the first steps of TATB decomposition involving water formation (i. e., H vs D transfer). The KIE slows down the formation of all gases, including those lacking hydrogen (e. g., CO 2 ). These results suggest the TATB thermal decomposition mechanism might involve a series of pathways rather than a set of independent and parallel reactions.

Cookoff of Powdered and Pressed Explosives Using a Micromechanics Pressurization Model

Hobbs

Brown

Kaneshige

et al. 2021

Cookoff experiments of powdered and pressed TATB‐based plastic bonded explosives (PBXs) have been modeled using a pressure‐dependent universal cookoff model (UCM) in combination with a micromechanics pressurization (MMP) model described in a companion paper. The MMP model is based on the accumulation of decomposition gases at nucleation sites that load the surrounding TATB crystals and binder. This is the first cookoff model to use an analytical mechanics solution for compressibility and thermal expansion to describe internal pressurization caused by both temperature and decomposition occurring within closed‐pore explosives. This approach produces more accurate predictions of ignition time and pressurization within high‐density explosives than simple equation‐of‐state models. The current paper gives details of the reaction chemistry, model parameters, predicted uncertainty, and validation using experiments from multiple laboratories with errors less than 6 %. The UCM/MMP model framework gives more accurate thermal ignition predictions for high density explosives that are initially impermeable to decomposition gases.