One Dimensional Time To Explosion Research Articles

An Integrated Experimental and Modeling Approach for Assessing High-Temperature Decomposition Kinetics of Explosives.

We present a new integrated experimental and modeling effort that assesses the intrinsic sensitivity of energetic materials based on their reaction rates. The High Explosive Initiation Time (HEIT) experiment has been developed to provide a rapid assessment of the high-temperature reaction kinetics for the chemical decomposition of explosive materials. This effort is supported theoretically by quantum molecular dynamics (QMD) simulations that depict how different explosives can have vastly different adiabatic induction times at the same temperature. In this work, the ranking of explosive initiation properties between the HEIT experiment and QMD simulations is identical for six different energetic materials, even though they contain a variety of functional groups. We have also determined that the Arrhenius kinetics obtained by QMD simulations for homogeneous explosions connect remarkably well with those obtained from much longer duration one-dimensional time-to-explosion (ODTX) measurements. Kinetic Monte Carlo simulations have been developed to model the coupled heat transport and chemistry of the HEIT experiment to explicitly connect the experimental results with the Arrhenius rates for homogeneous explosions. These results confirm that ignition in the HEIT experiment is heterogeneous, where reactions start at the needle wall and propagate inward at a rate controlled by the thermal diffusivity and energy release. Overall, this work provides the first cohesive experimental and first-principles modeling effort to assess reaction kinetics of explosive chemical decomposition in the subshock regime and will be useful in predictive models needed for safety assessments.

TATB thermal decomposition: An improved kinetic model for explosive safety analysis

AbstractWe investigate and model the cook‐off behavior of 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) to understand the response of explosive systems in abnormal thermal environments. Decomposition has been explored via conventional ODTX (one‐dimensional time‐to‐explosion), PODTX (ODTX with pressure‐measurement), PyGC‐MS (pyrolysis gas chromatography mass spectrometry), TGA (thermo‐gravimetric analysis), DSC (differential scanning calorimetry), and IR (infrared spectroscopy) experiments under isothermal and ramped temperature profiles. The data were used to fit rate parameters for proposed reaction schemes in a MATLAB thermo‐chemical computational model. These parameterizations were carried out utilizing a genetic algorithm optimization method on LLNL's high‐performance computing clusters, which enabled significant parallelization. These results include a multi‐step reaction decomposition model, identification of likely autocatalytic gas‐phase species, accurate high‐temperature sensitization, and prediction of confined system pressurization. This model will be scalable to several applications involving TATB‐based explosives, like LX‐17, including thermal safety models of full‐scale systems.

Vented and sealed cookoff of powdered and pressed ε-CL-20

ABSTRACT We have completed a series of vented and sealed cookoff experiments of the ε-polymorph of CL-20 in our Sandia Instrumented Thermal Ignition (SITI) apparatus using both powder and pressed pellets at nominal densities of 313 ± 8 kg/m3 and 1030 ± 4 kg/m3, respectively. The boundary temperature of our aluminum confinement cylinder was ramped in 10 minutes from room temperature to a prescribed set-point temperature ranging between 448 nd 468 K and held at the set-point temperature until ignition. A universal cookoff model (UCM) has been calibrated using the ε-CL-20 SITI data to predict pressurization and thermal ignition of ε-CL-20. The ignition model was validated by using one-dimensional time-to-explosion (ODTX) ignition data from a different laboratory. We found that a thirtyfold increase in the reaction rates due to liquefaction at 520 K could explain the high temperature ODTX cookoff data. The model gives a plausible explanation of why melting is important in fast cookoff events involving CL-20. Our model also gives support to 520 K as the liquefaction point of CL-20, which has different values in the literature.

Study of thermal sensitivity and thermal explosion violence of energetic materials in the LLNL ODTX system

Incidents caused by fire and combat operations can heat energetic materials that may lead to thermal explosion and result in structural damage and casualty. Some explosives may thermally explode at fairly low temperatures (< 100 °C) and the violence from thermal explosion may cause significant damage. Thus it is important to understand the response of energetic materials to thermal insults. The One Dimensional Time to Explosion (ODTX) system at the Lawrence Livermore National Laboratory has been used for decades to measure times to explosion, threshold thermal explosion temperature, and determine kinetic parameters of energetic materials. Samples of different configurations (pressed part, powder, paste, and liquid) can be tested in the system. The ODTX testing can also provide useful data for assessing the thermal explosion violence of energetic materials. Recent ODTX experimental data are reported in the paper.

Friction-induced ignition modeling of energetic materials

The heat released during the external frictional motion is a factor responsible for initiating energetic materials under all types of mechanical stimuli including impact, drop, or penetration. We model the friction-induced ignition of cyclotrimethylenetrinitramine (RDX), cyclotetramethylene-tetranitramine (HMX), and ammonium-perchlorate/ hydroxylterminated-polybutadiene (AP/HTPB) propellant using the BAM friction apparatus and one-dimensional time to explosion (ODTX) apparatus whose results are used to validate the friction ignition mechanism and the deflagration kinetics of energetic materials, respectively. A procedure to obtain the time-to-ignition for each energetic sample due to friction is outlined.

An LX-10 Kinetic Model Calibrated Using Simulations of Multiple Small-Scale Thermal Safety Tests

A new chemical kinetic model for the beta-delta transition and decomposition of LX-10 (95% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, 5% Viton A binder) is presented here. This model implements aspects of previous kinetic models but calibrates the model parameters to data sets of three experiments: differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and one-dimensional time to explosion (ODTX). The calibration procedure contains three stages: one stage uses open-pan DSC and TGA to develop a base reaction for formation of heavy gases, a second stage features closed-pan DSC to ascertain the autocatalytic behavior of reactant gases attacking the solid explosive, and a final stage adjusts the rate for the breakdown of heavy reactant gases using ODTX experimental data. The resultant model presents a large improvement in the agreement between simulated DSC and TGA results and their respective experiments while maintaining the same level of agreement with ODTX, scaled thermal explosion, and laser heating explosion times when compared to previous models.

Effects of Endothermic Binders on Times to Explosion of HMX- and TATB-Based Plastic Bonded Explosives

Plastic-bonded explosives (PBXs) based on octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) or 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) formulated with the endothermic binders Estane, Viton, or Kel-F exhibit longer times to thermal explosion than do pure HMX and TATB in the one-dimensional time to explosion (ODTX) and in other thermal experiments. Previous chemical kinetic thermal decomposition models for HMX- and TATB- based PBXs assumed that the binders decomposed independently of and at lower temperatures than the explosives. Recent chemical decomposition rate measurements showed that Estane, Viton, and Kel-F are more thermally stable than HMX and TATB. Thus, the longer thermal explosion times for these PBXs are most likely due to endothermic decompositions of the binders by reactions with the gaseous decomposition products of HMX and TATB. New PBX chemical decomposition models are developed using the global HMX and TATB models, measured binder kinetics, and cross-reactions between gaseous explosive products and binders. These new models accurately predict ODTX time to explosion and other experimental data.

The Decomposition of some RDX and HMX Based Materials in the One Dimensional Time to Explosion Apparatus. Part 2. Estimating the Violence of the Cook‐Off Event

AbstractVarious methods of assessment have been applied to the One Dimensional Time to Explosion (ODTX) apparatus and experiments with the aim of allowing an estimate of the comparative violence of the explosion event to be made. Non‐mechanical methods used were a simple visual inspection, measuring the increase in the void volume of the anvils following an explosion and measuring the velocity of the sound produced by the explosion over 1 metre. Mechanical methods used included monitoring piezo‐electric devices inserted in the frame of the machine and measuring the rotational velocity of a rotating bar placed on the top of the anvils after it had been displaced by the shock wave. This last method, which resembles original Hopkinson Bar experiments, seemed the easiest to apply and analyse, giving relative rankings of violence and the possibility of the calculation of a “detonation” pressure.

The Decomposition of some RDX and HMX Based Materials in the One‐Dimensional Time to Explosion Apparatus. Part 1. Time to Explosion and Apparent Activation Energy

AbstractA One‐Dimensional Time to Explosion (ODTX) apparatus has been used to study the times to explosion of a number of compositions based on RDX and HMX over a range of contact temperatures. The times to explosion at any given temperature tend to increase from RDX to HMX and with the proportion of HMX in the composition. Thermal ignition theory has been applied to time to explosion data to calculate kinetic parameters. The apparent activation energy for all of the compositions lay between 127 kJ mol−1 and 146 kJ mol−1. There were big differences in the pre‐exponential factor and this controlled the time to explosion rather than the activation energy for the process.

Sensitivity of 2,6-Diamino-3,5-Dinitropyrazine-1-Oxide

ABSTRACT The thermal and shock sensitivities of plastic bonded explosive formations based on 2,6-diamino-3,5-dinitropyrazine-1-oxide (commonly called LLM-105 for Lawrence Livermore Molecule #105) are reported. The One-Dimensional Time to Explosion (ODTX) apparatus was used to generate times to thermal explosion at various initial temperatures. A four-reaction chemical decomposition model was developed to calculate the time to thermal explosion versus inverse temperature curve. Three embedded manganin pressure gauge experiments were fired at different initial pressures to measure the pressure buildup and the distance required for transition to detonation. An Ignition and Growth reactive model was calibrated to this shock initiation data. LLM-105 exhibited thermal and shock sensitivities intermediate between those of triaminotrinitrobenzene (TATB) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX).

Thermal decomposition models for HMX-based plastic bonded explosives

Global multistep chemical kinetic models for the thermal decomposition of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX)-based plastic bonded explosives (PBXs) using endothermic or exothermic binders are developed for calculation of the times to thermal explosion as functions of heating rate and geometry in the Chemical TOPAZ heat-transfer computer code. The decomposition mechanisms of the binder materials are treated separately from that of HMX, and the chemical reactions of each constituent are assumed to occur independently. Experimental data and theoretical predictions of the thermal properties, decomposition pathways, and chemical kinetic reaction rate constants are used to develop reaction sequences for each of the components present in the PBX at various weight percentages. The measured times to thermal explosion at various initial temperatures in a new One-Dimensional Time-to-Explosion (ODTX) apparatus are compared to the Chemical TOPAZ predictions. Two series of pristine HMX spheres formulated with coarse and fine particles are tested for the first time in an ODTX apparatus. The pure HMX data clearly show that the presence of an endothermic binder in a PBX increases the times to thermal explosion, while the presence of an exothermic binder decreases the times to explosion. The magnitudes of these changes in explosion time depend upon the chemical stabilities and heats of reaction of these binders. A four-step decomposition model is developed for HMX, which includes the β to δ solid-phase transition as the first endothermic reaction. This model accurately reproduces the pure HMX curves. Decomposition models for the various binder components are then used with the HMX model to accurately reproduce the ODTX time-to-explosion curves. Comparisons are also made to times to thermal explosion obtained in various experiments involving aged PBXs, ramped temperature rate increases, unconfined explosives, and a larger size, cylindrical geometry called the scaled thermal explosion experiment.

Thermal Decomposition of Pentaerythritol Tetranitrate

AbstractA chemical kinetic model for the thermal decomposition of the solid high explosive pentaerythritol tetranitrate (PETN) is developed for prediction of times to thermal explosion using the Chemical TOPAZ heat transfer computer code. The model is based on times to thermal explosion measured in a new One Dimensional Time to Explosion (ODTX) apparatus. ODTX experiments are reported for pure PETN and for Semtex 1A. The pure PETN results are accurately modeled using a four reaction decomposition process in which an autocatalytic process produces intermediate reaction product gases, which subsequently react in a second order gas phase process to produce the final reaction products. Semtex 1A exhibits longer times to explosion than PETN at low temperatures, indicating that its endothermic binder decomposition absorbs heat produced by PETN decomposition. This binder reaction is modeled as a first order endothermic process. Three experiments on 5.08 cm diameter unconfined cylinders of PETN ramp heated to explosion at different rates are reported. The PETN model accurately predicts the thermocouple records and explosion times for these unconfined experiments in which only intermediate gaseous products can form.

Critical Conditions for Impact- and Shock-Induced Hot Spots in Solid Explosives

Chemical kinetic thermal decomposition models of pressed solid high explosives containing octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and triaminotrinitrobenzene (TATB), which accurately calculate the times to explosion at various initial temperatures measured in the one-dimensional time to explosion (ODTX) test, are extended to higher temperatures to predict the critical temperatures, times to explosion, and dimensions of the impact- and shock-induced hot spots that are known to control the ignition of exothermic reaction in solid explosives. The effects of hot spot geometry and surrounding temperature on the critical hot spot conditions are investigated. Since hot spot temperatures and dimensions cannot be measured experimentally, these estimated temperatures, sizes, and times required for exothermic chemical reaction provide a means to evaluate proposed physical mechanisms of hot spot formation in accident scenarios involving impact (friction and shear) and shock compression of solid explosives.