Joel R. Carney

Time-resolved optical measurements of the post-detonation combustion of aluminized explosives

The dynamic observation and characterization of light emission following the detonation and subsequent combustion of an aluminized explosive is described. The temporal, spatial, and spectral specificity of the light emission are achieved using a combination of optical diagnostics. Aluminum and aluminum monoxide emission peaks are monitored as a function of time and space using streak camera based spectroscopy in a number of light collection configurations. Peak areas of selected aluminum containing species are tracked as a function of time to ascertain the relative kinetics (growth and decay of emitting species) during the energetic event. At the chosen streak camera sensitivity, aluminum emission is observed for 10μs following the detonation of a confined 20g charge of PBXN-113, while aluminum monoxide emission persists longer than 20μs. A broadband optical emission gauge, shock velocity gauge, and fast digital framing camera are used as supplemental optical diagnostics. In-line, collimated detection is ...

Water temperature and concentration measurements within the expanding blast wave of a high explosive

We present an application of absorption spectroscopy to directly measure temperature and concentration histories of water vapor within the expansion of a high explosive detonation. While the approach of absorption spectroscopy is well established, the combination of a fast, near-infrared array, broadband light source, and rigid gauge allow the first application of time-resolved absorption measurements in an explosive environment. The instrument is demonstrated using pentaerythritol tetranitrate with a sampling rate of 20 kHz for 20 ms following detonation. Absorption by water vapor is measured between 1335 and 1380 nm. Water temperatures are determined by fitting experimental transmission spectra to a simulated database. Water mole fractions are deduced following the temperature assignment. The sources of uncertainty and their impact on the results are discussed. These measurements will aid the development of chemical-specific reaction models and the predictive capability in technical fields including combustion and detonation science.

Time-resolved measurements of near infrared emission spectra from explosions: Pure pentaerythritol tetranitrate and its mixtures containing silver and aluminum particles

Measurements of chemical transients and thermodynamic conditions are difficult to obtain yet fundamentally important in understanding the behavior of explosives. We have constructed a fast near infrared (NIR) spectrometer and have made temporally and spectrally-resolved emission measurements during postdetonation combustion of pure pentaerythritol tetranitrate (PETN) charges and PETN charges doped with 10 wt % microparticles composed of silver (Ag) and aluminum (Al). We have observed postdetonation PETN emission spectra between 750 and 1500 nm at rates up to 46 992 spectra/s. The instrument captures the highly structured spectra immediately following breakout as well as the longer-lived broadband NIR emission signals from hot particles. The early spectra reveal spectral signatures related to PETN and the reacting constituents of the particles. The later spectra provide a means to infer the gray-body temperature history of the particles.

Atmospheric Effects on the Combustion of Detonating Aluminized Explosives

The detonation and subsequent combustion of aluminized explosive formulations depend heavily on the oxidation reactions of aluminum. Fuel‐rich formulations require oxygen from an external source (nominally an oxygen‐containing atmosphere or detonation products) to burn the fuel to completion. Dynamic spectroscopic measurements are made for an aluminized explosive (PBXIH‐135) to investigate the effect of changing atmospheres on the combustion properties of aluminum. The explosive formulation is tested under normal atmospheric conditions and in an atmosphere of nitrogen. Light emission (from 350–550 nm) from the explosive event is collected in a spectrometer and dispersed temporally in a streak camera. Aluminum emission (centered at 396 nm) is commonly observed in each atmosphere although the emission persists longer in nitrogen. Aluminum nitride (AlN) is observed as an intermediate in the oxidation of aluminum when oxygen is removed from the atmosphere. New, nitrogen‐containing species (near 387 and 418 nm...

Laser dispersion and ignition of metal fuel particles

The development of a laser-shock technique for dispersing Al metal fuel particles at velocities approaching those expected in a detonating explosive is discussed. The technique is described in detail by quantifying how air drag affects the temporal variation of the velocity of the dispersed particle plume. The effect of particle size is incorporated by examining various poly-dispersed commercial Al powders at different dispersion velocities (390-630 m/s). The technique is finally tested within a preliminary study of particle ignition delay and burn time, where the effect of velocity is highlighted for different particle sizes. It was found that plume velocity exhibits a modified exponential temporal profile, where smaller particles are more susceptible to air drag than larger ones. Moreover, larger particles exhibit longer ignition delays and burn times than smaller ones. The velocity of a particle was found to significantly affect its ignition delay, burn time, and combustion temperature, especially for particles in the diffusion-controlled regime. Shorter ignition delays and burn times and lower temperatures were observed at higher particle velocities. The utility of this technique as a combustion screening test for future, novel fuels is discussed.

Preparation and characterization of functionalized aluminum nanoparticles

Aluminum nanocomposite materials have been prepared by treating commercially available aluminum powders with long-chain perfluorinated carboxylic acids. The acid coated aluminum qualitatively shows enhanced burning compared to the same aluminum powder that was not treated with the acid. This preparation method will allow for the large scale production of air-stable, passivated aluminum nanoparticles. Aluminum nanocomposite materials with size ranges less than 500 nm have been prepared with various surface passivation/functionalization schemes that mitigate aluminum oxide effects and reduce the fuel-oxidizer distance to the molecular level. These materials have been characterized to understand the changes in particle size and morphology that occur with different preparation schemes. TGA, XPS and IR results are presented.

Irreversible phase transitions in doped metal oxides for use as temperature sensors in explosions

The temperature of post-detonation fireballs produced by advanced energetic formulations is commonly determined using optical methods such as pyrometry and spectral line fitting. These methods are noninvasive and provide an average temperature predominantly from the surface of the fireball. However, for many applications the ability to probe the internal temperature as well as temperature gradients within the fireball is highly desirable. One such method that has shown promise in providing this information is seeding micron to nano-sized temperature sensors into the fireball which can be collected post-detonation and analyzed to determine a temperature profile. In this work, disordered rare-earth-doped metal oxide nanoparticles were synthesized and subjected to various types of heat treatment, including furnace heating, T-Jump (fast pyroprobe), and explosive heating. The heat treatment leads to irreversible phase transitions which are monitored by optically active rare-earth dopants. Eu3+ in particularly ...

Time-Resolved Optical Measurements of Detonation and Combustion Products

A first attempt at measuring the species evolution in the opaque post‐detonation combustion product environment of a fuel‐rich explosive using time‐resolved absorption spectroscopy is presented. The time‐resolved concentration of these species is helpful in identifying the rate and location of the extra energy released in the post‐detonation phase due to the aluminum combustion, thus shedding light on the factors affecting the overall efficiency of air and internal‐blast explosions. The methodology and results of time‐resolved absorption spectroscopy are compared to previous emission spectroscopy investigations. The experimental arrangement and preliminary results of time‐resolved absorption spectroscopy based on atomic aluminum in the post detonation environment of aluminized pressed PETN charges are presented. An assessment of the experimental approach and its usefulness in future detonation experiments is discussed.

Thermal history sensing inside high-explosive environments using thermoluminescent microparticles

Thermoluminescent LiF:Mg,Ti (TLD-100) microparticle sensors are demonstrated to record the thermal history of the region near a detonated high explosive. Microparticles were gamma-irradiated to fill their charge-carrier traps and then exposed to the detonation of 20 g of a plastic bonded explosive formulation containing HMX and Al particles at a test distance of approximately 22 cm from the center of the detonation. The thermal history was reconstructed by measuring the thermoluminescent signature of the traps and matching it to appropriate models. The trap populations derived from luminescence measurements and modeling indicate that the particles experienced a maximum temperature of 240 °C, then cooled to 1 °C above ambient temperature within 0.4 seconds. The resulting glow curve intensity is calculated to match the observed post-detonation signal to 3% averaged over the comparison values used for reconstruction.

EXPERIMENTAL INVESTIGATIONS OF MULTIPHASE EXPLOSIONS

The addition of solid fuel particles to explosive formulations generally reduces the detonation velocity, but can enhance the blast performance if prompt combustion of the particles occurs in the detonation products and surrounding air early enough to support the shock. The degree to which fuel particles burn heavily depends on their dispersal throughout the explosion field and access to oxidizers. To distinguish the factors affecting the dispersal of fuel particles from those controlling their combustion, we began by analyzing the dispersal of equivalent mock inert particles. Solid glass spheres embedded in detonating small explosive charges were tracked using high‐speed digital shadowgraphy. Two different particle sizes, 3 and 30 μm, and different mass fractions in the explosive compositions were considered. Shadowgraphs and pressure measurements were compared to the predictions of a newly developed multiphase numerical model. Reactive aluminum particles in the range of 1 to 120 μm in diameter were also analyzed. During the first 50 μs of the expansion, the general trend for both reactive and inert particles is for the smaller particles to expand near or beyond the leading shock wave to a greater extent than the larger particles. Expansion beyond the initial shock from the detonation is presumed to occur when particles agglomerate. The results are consistent with the predictions of the numerical models, highlighting the role of simple factors such as particle size and density in the early time expansion and mixing of fuels for enhanced blast applications.