We have made time-of-flight mass-spectroscopic observations of 85/15 wt % water/glycine solutions and of crystalline alpha-glycine subjected to strong shock loading. The shockwaves were produced by placing the materials in contact with detonating solid explosives. In the solution observations, we have done experiments with glycine molecules composed of ordinary isotopes and with molecules labeled with (13)C, (15)N, and D atoms. The primary reason for conducting this research was to examine whether glycine molecules can survive exposure to strong shock loading, e.g., as might occur in the entry of a meteor into the earth's atmosphere. Our results show that glycine molecules can withstand the rigors of shock environments that generate pressure and temperature up to 180 kbar and 3200 K. Glycine in a 85 H(2)O/15 glycine wt % solution (i.e., one molecule of glycine to ca. 24 H(2)O molecules) exists primarily in its zwitterionic form. In both the solution and crystal experiments, we observed zwitterionic dimers, trimers, and, possibly, tetramers, after the materials were shocked. This implies that the solvating water molecules in the solution experiments must reside on the exterior of groups of solvated glycine molecules. We report quantum-chemical calculations, using density functional theory, that predict that two glycine zwitterions are bound together by ca. 15.72 kcal when immersed in an Onsager model of water. Our observations allow us to place lower-bound estimates on the lifetime of glycine zwitterions under our conditions. We have examined our data to determine whether dipeptide formation has occurred and found no evidence that it has. Compressible fluid-mechanical calculations were performed to estimate the pressures, temperatures, and the time scales present in the experiments.

We have observed, via time-of-flight mass spectrometry, 13 chemical species more massive than CS2 produced by shocking liquid CS2 to very high pressure/temperature. The stoichiometry of three of these species is uniquely determined from the 12CS2 experiments; these species are C2S2, C3S2, and C4S2. The stoichiometry of the other 10 structures cannot be uniquely determined from 12CS2 experiments. However, by redoing the experiments using isotopically labeled CS2 (i.e., 13CS2), we determined the stoichiometry of nine of the remaining structures. The nine structures are Sn (n = 3-8) and CS3, C2S5, and C4S6. A structure with mass 297.1 amu was also observed in the 12CS2 experiments but was not detected in the 13CS2 experiments. This structure must be C6S7, C14S4, or C22S; given the low carbon content of the other observed carbon species, it is probably C6S7. The shockwaves to which the CS2 molecules were subjected were produced by the detonation of high mass-density solid explosives. The explosives used were either a plastic bonded form of cyclotetramethlylene tetranitramine or pure hexanitrostilbene. Numerical compressible fluid-mechanical simulations were done to estimate the pressures, temperatures, and time scales of the processes that occurred in the shocked CS2. The results obtained in the present experiments are related to earlier work on CS2's chemical reactivity that used both shockwave methods and static techniques to produce very high pressure.

Polydimethylsiloxane (PDMS) is a common silicone polymer. Understanding its decomposition product distribution is required for calculating its equation of state under shock conditions. We have detonated small samples of HMX explosive in contact with the polymer in a high vacuum chamber and used a time-of-flight mass spectrometer to analyze the chemical products of PDMS decomposition. We have used the computer code CTH to model the time history of pressure and temperature in the sample. The time scale of a few nanoseconds in these experiments generates products that are significantly different than the equilibrium products observed in thermal pyrolysis experiments. The mass spectrum under shock conditions predominately shows monomers to heptamers of dimethylsiloxane, and the n-mers minus methyl groups. We have compared spectra of high molecular weight liquid PDMS, crosslinked solid PDMS, and silica filled solid PDMS.

The detonation properties of liquid nitromethane [CH3NO2] are probably the most thoroughly studied of any condensed-phase explosive. Because it is homogeneous (i.e., lacks hot-spot phenomena), it provides a window into the underlying chemical processes induced by a passing shock or detonation wave-such information is submerged in the complex fluid mechanics when heterogeneous explosives are detonated. In this paper, we provide experimental data and data analysis of the effect that deuterating nitromethane's methyl group has on some aspects of the processes that occur in the detonating liquid material. In the experimental part of this study, we report diameter-effect curves (i. e., inverse charge internal radius vs steady detonation speed) for pure CH3NO2 and pure CD3NO2 confined in right-circular cylinders of C-260 brass. Large differences in the infinite-medium (i. e., plane wave) detonation speed and in the failure diameter of the two materials are observed. Interpretations of the observations based on physical and chemical theory are given. The observed large decrease in deuterated nitromethane's infinite-medium detonation speed, relative to the protonated material, is interpreted in terms of the Zeldovitch, von Neumann, and Doering theory of steady-state detonation. We also estimate the relative size of the steady plane-wave reaction-zone length of the two materials. We interpret the observed increases in NM's failure diameter and its steady one-dimensional chemical-reaction-zone length due to deuteration in terms of the quantity of NM aci ion present. The new results are placed in the context of earlier work on detonating liquid nitromethane.

We examine the effect of the addition of small amounts of the organic base diethylenetriamine [NH2(CH2CH2)NH(CH2CH2)NH2] on the chemical reaction-zone length (CRZ) of detonating liquid nitromethane (CH3NO2). This is done by making accurate measurements of the detonating materials’ diameter-effect curves (i.e., detonation speed versus lateral charge size) as a function of the amount of chemical sensitizer added. Detonation speed experiments were performed with additions of the organic base in amounts between 0.00 and 0.25wt%. Reductions in the CRZ of as much as 25% were produced by base addition. Most of the reduction in length is produced by very small amounts of base addition—i.e., ca. 0.05wt% of base or less (i.e., 1 molecule of the base per 3300 nitromethane molecules or less). Measured detonation speeds are given for five compositions of nitromethane and base as a function of charge internal diameter. Absolute CRZs are estimated using a value of liquid nitromethane’s CRZ obtained by other means. Earlier work has determined a relationship between the failure diameter of sensitized nitromethane compositions and the amount of base addition. Here we have found a relationship between relative CRZ and the amount of base addition. By eliminating the base parameterization, we give a phenomenological relationship between the failure diameter of such materials and their steady one-dimensional CRZs.

Numerous workers have suggested that the “A” parameter in the relation D(R)=D(∞)[1−A/R] is a measure of the steady-state one-dimensional chemical-reaction-zone length of a detonating explosive. This equation relates the steady-state detonation speed in an explosive material to the lateral dimension of the (usually cylindrical) charge [e.g., the cylinder’s radius (R)]. D(∞) is the detonation speed at infinite lateral charge size. The argument for A being the chemical-reaction-zone length is purely a dimensional one. We show that this supposed relation between A and an explosive’s steady one-dimensional chemical-reaction-zone length is untrue—because the A value is different for the same explosive fired in two types of confinement. However, we give experimental evidence that the ratio of the A values for closely related pairs of explosives, fired in the same confinement material, is a measure of the two explosive’s relative chemical-reaction-zone length. This is done by firing two closely related nitromethane-based explosives in two different types of confinement. We apply this positive result to examining the relative chemical-reaction-zone lengths of other closely related explosive pairs. In all cases, the A ratios agreed with intuition based on experimental results.

Isopropyl nitrate (IPN) is a liquid explosive of rather low energy. We have measured the sound speed and used it in the universal liquid Hugoniot to produce an estimated Hugoniot for this material. Gas-gun-driven, multiple-magnetic-gauge measurements were made to measure a Hugoniot state at 6 GPa; it was in good agreement with the prediction. Two similar experiments were conducted at higher pressure inputs to study the shock-to-detonation transition in IPN; the high inputs required for initiation necessitated the use of a two-stage gun. One experiment with an input of 9.0 GPa into the IPN produced a run to detonation of about 3 mm and the in-situ particle velocity profiles showed the expected homogeneous initiation behavior of a growing wave behind the shock front that overtakes the front and decays to a steady detonation. The reactive wave in the shocked IPN appears to have achieved a steady superdetonation in both of the initiation experiments. This is the first time a steady superdetonation has been measured with in-situ gauges.

It has long been known that there are fundamental differences between homogeneous and heterogeneous high explosives. The shock initiation behavior of these materials was first described in the literature by Campbell et al, in 1961. Chaiken was also involved in describing this process for liquid nitromethane. Since then, there have been a number of studies which have added considerable incite into the shock initiation/detonation behavior of these materials. We only give a few references here (Refs. 4 - 11) and these should be considered representative; e.g. they do not represent an exhaustive list of references available. Many of these studies were done on homogeneous explosives, most often nitromethane (NM) and include particle velocity gauge measurements, optical temperature measurements, VISAR measurements, as well as streak camera measurements of interfaces. In some cases NM was heterogenized by gelling and adding silica particles. Homogeneous materials are typically liquids or single crystals in which there are a minimal number of physical imperfections (e.g. bubbles or voids) that can cause perturbations in the input shock and the flow behind it. Homogeneous materials viewed with macroscopic probes characteristic of detonation physics experiments appear uniform. Heterogeneous explosives are generally all other types; these are usually pressed, cast,more » machined, or extruded into the shapes or parts desired. These materials contain imperfections of a variety of types that cause fluid-mechanical irregularities (called hot spots) when a shock or detonation wave passes over them. Such hot spots cause associated space/time fluctuations in the thermodynamic fields (e.g., the pressure or temperature fields) in the material. These thermodynamic variations affect the local chemical-heat-release rate - they produce an average heat-release rate that is a combination of chemistry and mechanics. Hot spots could be the result of voids, shock interactions, jetting, shock impedance mismatches, etc. Shock initiation of homogeneous explosives is due to a thermal explosion that occurs in the material shocked the longest. This reaction produces a reactive wave that grows behind the front and eventually overtakes the front. The reactive wave may grow into what is called a superdetonation before it overtakes the initial shock and settles down to a steady detonation. The shock initiation process in heterogeneous explosives differs a great deal because the hot spots cause early chemical reaction as soon as the shock passing over a region creates them. This causes reactive growth both in and behind the shock front. This leads to a relatively smooth growth of the initiating shock to a detonation, in contrast to the abrupt changes that occur in the homogeneous case. These differences are apparent in both the in-situ reaction wave profiles and the acceleration of the shock front.« less

We report experimental observations of a chemically bound dimer of 2,4,6-trinitrotoluene (TNT) produced by high-pressure shock waves. The experimental observations were made with a time-of-flight (TOF) mass spectrometer within which it is possible to produce strong shock waves by detonating condensed-phase explosives. The dimer is thought to arise from a Diels−Alder (DA) cross-linking of two TNT molecules. It is noteworthy that DA reactions are strongly pressure enhanced. We found that under some shock conditions a significant fraction of the TNT molecules are dimerized. The dimerization reaction, which is endothermic, may play a role in the shock insensitivity of TNT. Ancillary experiments in which TNT was evaporated and expanded through a nozzle into the mass spectrometer are also reported. It was possible in these experiments to produce a weakly bound TNT dimer in which the binding forces are those characteristic of a crystal. We show that this type of dimer has a different fragmentation pattern caused...

We report the measured failure diameter and a detonation speed for the liquid explosive mixture 90.5/9.5 wt % H2O2/H2O confined in thick seamless 304 stainless steel tubing and Fired at ca. 30 degrees C. The detonation speed datum and knowledge of the diameter effect curves of other liquid explosives are used to estimate the infinite-medium (i.e., planewave) detonation speed of this material. Ambient condition sound speed measurements and the universal liquid Hugoniot form are used to obtain the unreacted Hugoniot of the 90.5/9.5 wt % H2O2/H2O mixture. This Hugoniot and the Rayleigh line obtained From the estimated infinite-medium detonation wave speed are used to predict the von Neumann spike pressure of the material. Estimates of the fully reacted (i.e., products) Hugoniot, the Chapman-Jouguet (CJ) detonation pressure, and CJ detonation speed for other H2O2/H2O mixtures are obtained using the CHEETAH equilibrium thermochemical code. Predictions of the infinite-medium detonation speed and the von Neumann spike and CJ pressures of 85.0/15.0, 90.0/10.0, 92.5/7.5, 95.0/5.0, 7.5/2.5, and 100.0/0.0 wt % H2O2/H2O mixtures are also obtained. A general analytical expression is given for the primary shock Hugoniot of any H2O2/H2O mixture at 22.6 degrees C.

Archival front curvature data from two studies of nitromethane detonating in Pyrex tubes are re-read from the original films to obtain detonation wave shapes. Each data set is fit with an analytic form, for which the fitting parameters are tabulated. The wavefront fits are also plotted in normal velocity-curvature (D-n[kappa]) space in which, according to the simplest detonation shock dynamics model, they should follow a common curve. All D-n[kappa] curves do overlay for sufficiently small curvatures, but diverge at larger curvatures. A single best D-n[kappa] function is obtained by a global optimization scheme that considers both the diameter effect curve and each shock shape. The effect of a concentration chi of diethylenetriamine sensitizer is estimated by scaling this calibration function for pure nitromethane kin a manner consistent with sensitized rate stick data, giving a calibration surface D-n[kappa, chi].

Bromonitromethane (CH2BrNO2)(BrNM) is chemically similar to nitromethane (NM), with one hydrogen atom replaced by bromine. It is a liquid explosive with an initial density of 2.009 g/cm3. We have shown its sensitivity to shock to be similar to neat NM. Its von Neumann spike pressure is calculated to be nearly twice that of NM while the CJ pressure appears to be only slightly higher than NM. The sound speed of BrNM was measured to be 1.16 km/s and was used in the Universal Liquid Hugoniot (1). Shock Hugoniot measurements were shown to be consistent with this prediction. In addition, we report the results of failure diameter measurements, and the diameter effect curve in brass confinement. Detonation wave profiles obtained using VISARs that record the interface particle velocity between detonating BrNM and a poly(methyl methacrylate) window are also reported.

Liquid nitromethane (CH3NO2—NM) is an important explosive material because of its chemical and physical simplicity. It has proved useful in studies of the chemistry and physics of initiation and detonation. We have experimentally investigated some of the effects on its properties due to replacing one of its hydrogen atoms with bromine (BrNM) and all its hydrogen atoms with deuterium (DNM). French workers have found that the failure diameter of DNM in glass is more than double that of NM. We report critical diameters and diameter effect curves for NM, BrNM, and DNM confined in brass. In addition, detonation wave profiles were obtained by use of VISAR techniques. We recorded interface particle velocity profiles between the detonating liquids and polymethyl methacrylate (PMMA) windows. DNM has a larger critical diameter in brass than either NM or BrNM. DNM’s diameter-effect curve lies below that of NM and above that of BrNM.