The problem of accidental initiation of detonation in granular material has been the initial focus of the Los Alamos explosives safety program. Preexisting models of deflagration-to-detonation transition (DDT) in granular explosives, especially the Baer & Nunziato (BN) model, have been examined. The main focus of this paper is the reaction rate model. Comparison with experiments are made using the BN rate model. Many features are replicated by the simulations. However, some qualitative features, such as inert plug formation in DDT tube-test experiments and other trends, are not produced in the simulations. By modifying the reaction rate model we show inert plug formation that more closely replicates the qualitative features of experimental observations. Additional improvements to the rate modeling are suggested.

A simplified method for determining the reactive rate parameters for the ignition and growth model is presented. This simplified ignition and growth (SIG) method consists of only two adjustable parameters, the ignition (I) and growth (G) rate constants. The parameters are determined by iterating these variables in DYNA2D hydrocode simulations of the failure diameter and the gap test sensitivity until the experimental values are reproduced. Examples of four widely different explosives were evaluated using the SIG model. The observed embedded gauge stress-time profiles for these explosives are compared to those calculated by the SIG equation and the results are described.

The central issue determining initiation response of explosive crystals to shock or impact is the generation of the energy necessary to cause molecular dissociation. This controls the initial rate of release of chemical energy. Here, the energy dissipated in the crystals as they undergo plastic deformation due to shock or impact is taken to be the source of the energy required to achieve initiation. This determines initiation sensitivity to shock or impact. Several problems are discussed including initiation of detonation and the von Neumann pressure spike structure of a detonation wave.

Experimental measurements of material effects induced by the passage of sharp shock fronts require techniques which provide high temporal resolution and high spatial resolution. Since typical shock velocities are a few microns per nanosecond, sub-nanosecond probing requires sub-micron spatial resolution. In our experiments, the required temporal resolution is furnished using picosecond laser generated shock waves and picosecond spectroscopy. The spatial resolution is furnished by engineering nanometer scale structures into our shock target arrays. In one technique, absorption transients in the spectrum of a thin layer of molecules, termed an optical nanogauge, are investigated. Shock-induced molecular energy transfer processes are observed in condensed matter for the first time. In a second technique, sub-micron particles of an energetic material are shocked and probed using ps coherent Raman spectroscopy. This probing technique permits the instantaneous measurement of the temperature, pressure and composition of an energetic material under dynamic shock loading.

Molecular processes associated with shock induced chemical decomposition of a mixture of nitromethane with ethylenediamine (0.1 wt%)are examined using time-resolved, Raman scattering. When shocked by stepwise loading to 14.2 GPa pressure, changes in the nitromethane vibrational modes and the spectral background characterize the onset of reaction. The CN stretch mode softens and disappears even as the NO2 and CH3 stretch modes, though modified, retain their identities. The shape and intensity of the spectral background also shows changes characteristic of reaction. Changes in the background, which are observed even at lower peak pressures of 11.4 GPa, are assigned to luminescence from reaction intermediates. The implications of these results to various molecular models of sensitization are discussed.

Time resolved vibrational spectroscopy with picosecond tunable mid-infrared pulses is used to measure the rates and investigate the detailed mechanisms of multiphonon up-pumping and vibrational cooling in a condensed high explosive, nitromethane. Both processes occur on the ˜100 ps time scale under ambient conditions. The mechanisms involve sequential climbing or descending the ladder of molecular vibrations. Efficient intermolecular vibrational energy transfer from various molecules to the symmetric stretching excitation of NO2 is observed. The implications of these measurements for understanding shock initiation to detonation and the sensitivities of energetic materials to shock initiation are discussed briefly.

The initial step of chemical reaction initiated by laser-generated shock waves has been observed in glycidyl azide polymer (GAP) in condensed phase. Shocks are generated by pulsed laser vaporization of thin aluminum films and launched into adjacent films of GAP at 77 K. Comparison of FIIR spectra obtained before and after shock passage shows that initial reaction involves elimination of molecular nitrogen from the azide functional groups of the polymer. The shock arrival time has been measured by a velocity interferometer as a function of thickness of GAP and laser fluence. The shock pressure has been calculated by using a universal liquid state Hugoniot. A simple model is proposed to calculate shock velocity and pressure as a function of laser fluence. The results are in agreement with experimental data.

We have developed a technique in which the decomposition of energetic materials can be initiated under high pressure conditions which resemble the pressures reached in the non-ideal detonation process. A gem anvil cell is cooled to cryogenic temperatures, 50 K, and remains in thermal contact with the cooling element throughout the experiment. Following initiation, the reaction products are rapidly cooled and quenched on the microsecond time scale and detected using FTIR spectroscopy. In the present study, binary mixtures of boron with energetic materials containing (CHNOF) and lacking fluorine (CHNO) are compared. The differences in the reaction products suggest that the presence of the fluorine substituent leads to a complete combustion of boron to B2O3. In the decomposition of binary mixtures lacking the fluorine substituent, the boron in appears to be unchanged following the reaction of the oxidizer. The observed products are compared to predict the affect of fluorine on the formation of boron combustion products in the two environments.

The initial step of the thermal decomposition of NTO (5-nitro-2,4-dihydro-3H-1,2,4- triazol-3-one) is determined by pulsed infrared laser pyrolysis of thin films. Rapid heating of the film and quenching to 77 K allows one to trap the initial decomposition products in the condensed phase and analyze them using transmission Fourier-transform infrared spectroscopy. The initial decomposition product is CO2; NO2 and HONO are not observed. We propose a new mechanism for NTO decomposition in which CO2 is formed.

The study of the deflagration or detonation reactions of energetic materials is challenging due to the high pressure, high temperature, and time domain under which the reactions occur. Experimental measurements, are presented that demonstrate the ability to continuously monitor the global reaction times and reaction sequences associated with chemical reactions under these conditions. Time resolved absorption spectroscopy is used in conjunction with a high pressure gem anvil cell to probe the real-time chemical processes during pulsed-heating. Samples are initiated by a rapid thermal jump induced by absorption of a single laser pulse. Time resolved absorption spectroscopy of 3,6 trinitroethylamine tetrazine reaction is demonstrated by the real time measurement of the decrease in the ϕ-ϕ* absorption at 110 ns temporal resolution during laser heating at pressures up to 3.5 Gpa

The detonation of underwater explosives is a complex problem involving a temporally dependent heterogeneous reaction regime of oxidizer reactions and high pressure metal combustion. For simplicity, underwater explosions may be described as a two stage reaction process. First, the oxidizing material detonates to produce species under extreme conditions of temperature (up to 5000 K) and pressure (up to 10 GPa). The chemical energy produced from this reaction is transferred to the bulk water as three forms of work: (I) shock, (2) heat, and (3) initial bubble formation. Second, the species produced by the oxidizer detonation form a high pressure and high temperature reactive fluid that surrounds the solid particles. The solid particles are primarily consumed while the pressure is decreasing from 10 GPa to 0.1 GPa at a reaction temperature in excess of 3200 K. The secondary reaction of the solid particles produces a lower energy shock and a pressure response that reinforces the initial energy delivered to the bulk water medium. The ability to tailor this late energy release between shock and bubble formation is dependent on the reaction time and chemistry of the solid particle under extreme conditions. We present a series of single-shot time resolved emission experiments that probe the reaction of aluminum particles under extreme conditions. The temporal behavior of the observed species is used to gain insight into the chemical reaction mechanism that leads to the formation of A1203 during underwater detonations.

We have studied shock-induced changes in homogeneous high explosives including nitromethane, tetranitromethane, and single crystals of pentaerythritol tetranitrate (PETN) by using fast time-resolved emission and Raman spectroscopy at a two-stage light-gas gun. The results reveal three distinct steps during which the homogeneous explosives chemically evolve to final detonation products. These are i) the initiation of shock compressed high explosives after an induction period, ii) thermal explosion of shock-compressed and/or reacting materials, and iii) a decay to a steady-state representing a transition to the detonation of uncompressed high explosives. Based on a gray-body approximation, we have obtained the CJ temperatures: 3800 K for nitromethane, 2950 K for tetranitromethane, and 4100 K for PETN. We compare the data with various thermochemical equilibrium calculations. In this paper we will also show a preliminary result of single-shot time-resolved Raman spectroscopy applied to shock-compressed nitromethane.

The possibility of producing underwater unconfined explosions with the use of propylcarborane as a fuel and water as an oxidant was demonstrated experimentally. The specific TNT equivalent of the energy release in the explosion reaction between propylcarborane and water was found to be 1.5 times higher than conventional explosives. A possibility of organizing the combustion of initially unmixed propylcarborane and water was experimentally proven as well

A new reactive flow model for highly non-ideal explosives and propellants is presented. These compostions, which contain large amounts of metal, upon explosion have reaction kinetics that are characteristic of both fast detonation and slow metal combustion chemistry. A reaction model for these systems was incorporated into the two-dimensional, finite element, Lagrangian hydrodynamic code, DYNA2D. A description of how to determine the model parameters is given.

A Debye-Gruneisen equation of state for hematite (Fe2O3) was developed for use in studying the high pressure solid state reaction Al + Fe2O3 → Fe + A12O3. A simple, single Curie temperature Curie-Weiss ferromagnetic term was used to account for the complex antiferromagnetic contributions to the entropy and specific heat. In the absence of information on the variation of Curie temperature with pressure, it is taken to be constant, so that the antiferromagnetism makes no contribution to the pressure-volume equation of state.

Theroretical calculation of detonation and deflagration properties of pyrotechnic mixtures have been performed including report charges and display charges. Calculation were performed with the KHT (Kihara-Hikta-Tanaka) code[l]. KHT results are compared with a modified version of the TIGER code[2] which allows calculation with 900 gaseous and 600 condensed product species at high pressure. Detonation properties computed by KHT and BKWS (Becker-Kistiakowskii-Wilson) give favorable agreement with experimental results of detonation velocity measurements. Hydrodynamic computation by one dimensional Lagrangian hydrodynamic code using the isentrope given by KHT constant volume explosion, indicated that experimental results for blast wave measurement for 30kg and 50kg of report charge were an incomplete reaction. Underwater detonation experiments with explosive charge of 25g, however, indicates a more energetic nature than the KHT prediction. This scale effect indicates complicated slow reactions and a number of condensed phase deflagration products of powder mixtures such as aluminum or titanium with oxidizers such as potassium perchlorate or nitrate salts as suggested by Hobbs et al[3].

Ultrafine diamond dust and the metastable fullerenes C60 and B24N36 offer new pathways of energy release which are unattainable in conventional energetic materials. Theoretical and experimental studies indicate that the high bare-surface strain energies of these small particles are released in rapid (< 1 μsec) phase changes. For diamond, C60 and B24N36, strain energies of 1000, 1210 and 1245 cal/g, respectively, may be released during transition to graphite, diamond and hexagonal BN under pressures exceeding 100 kbar. It is shown that the behavior of these nanoscale particles under high shocks may be traced to their intrinsic five-fold and icosahedral symmetry, which leads to an incompatibility of global and local driving forces for space filling under high compression. From a correlation function analysis, it is shown that shear can induce long range correlations of fluctuations which arise from geometrical frustration, thereby reducing the activation energy for phase change. For the first time, critical stresses and symmetry rules are determined for such phase changes in aggregates of nanoscale particles.

The detonation of explosives typically creates 100's of kbar pressures and 1000's K temperatures. These pressures and temperatures last for only a fraction of a microsecond as the products expand. Nucleation and growth of crystalline materials can occur under these conditions. Recovery of these materials is difficult but can occur in some circumstances. This paper describes the detonation synthesis facility, recovery of nano-size diamond, and plans to synthesize other nano-size materials by modifying the chemical composition of explosive compounds. The characterization of nano-size diamonds by transmission electron microscopy and electron diffraction, X-ray diffraction and Raman spectroscopy will also be reported.

This paper discusses experimental results from an effort conducted to discern the basic mechanism of reactions in porous metal/metal compositions under rapid plastic flow conditions. Small-scale impact tests were performed on various intermetallic mixtures: 3CuO + 2AI, Fe2O3 + 2AI, Ni + Al, and 5Ti + 3Si. The addition of polytetrafluoroethylene (Teflon) to the metal/metal mixtures has been demonstrated to affect the extent of the reactions. Real-time emissivity and species evolution measurements of the reacting materials were used to discern the chemical reactions occurring under rapid plastic flow conditions.