Nanoscale composite energetics (also known as metastable intermolecular composites) represent an exciting new class of energetic materials. thermites are examples these The nanoscale studied consist a metal and oxide with particle sizes in the 30-200 nm range. They have potential for use wide range applications. modes combustion reaction behavior materials not yet well understood. This investigation considers four different nanoaluminum/metal-oxide composites. same aluminum was used each...

Combustion velocities were experimentally determined for nanocomposite thermite powders composed of aluminum (Al) fuel and molybdenum trioxide (MoO3) oxidizer under well-confined conditions. Pressures also measured to provide detailed information about the reaction mechanism. Samples three different particle sizes (44, 80, 121nm) analyzed determine influence size on combustion velocity. Bulk powder density was varied from approximately 5% 10% theoretical maximum (TMD). The ranged 600...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe relationship between complex stability constants and rates of cation transport through liquid membranes by macrocyclic carriersJ. D. Lamb, J. Christensen, L. Oscarson, B. Nielsen, W. Asay, R. M. IzattCite this: Am. Chem. Soc. 1980, 102, 22, 6820–6824Publication Date (Print):October 15, 1980Publication History Published online1 May 2002Published inissue 15 October...

An unexpected mechanism for fast oxidation of Al nanoparticles covered by a thin oxide shell (OS) is proposed. The volume change due to melting induces pressures 0.1–4GPa and causes spallation the OS. A subsequent unloading wave creates high tensile resulting in dispersion liquid clusters, which not limited diffusion (in contrast traditional mechanisms). Physical parameters controlling this process are determined. Methods promote melt mechanism, consequently, improve efficiency energetic...

Abstract : Microscale combustion is of interest in small-volume energy-demanding systems, such as power supplies, actuation, ignition, and propulsion. Energetic materials can have high burning rates that make these advantageous, especially for microscale applications which the rate energy release important or air not available an oxidizer. In this study we examine mixtures nanoscale aluminum with molybdenum trioxide channels. Nanoscale composites very are much higher than typical materials....

An unexpected mechanism for fast reaction of Al nanoparticles covered by a thin oxide shell during heating is proposed and justified theoretically experimentally. For nanoparticles, the melting occurs before fracture. The volume change due to induces pressures 1–2 GPa causes dynamic spallation shell. unbalanced pressure between core exposed surface creates an unloading wave with high tensile resulting in dispersion atomic scale liquid clusters. These clusters fly at velocity their not...

In this and the accompanying paper [L. Smilowitz et al., J. Chem. Phys. 117, 3789, 2002] we present a theoretical treatment experimental study, respectively, of β–δ solid state phase transition in organic nitramine molecule octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The is thermodynamically first order with measured latent heat, occurs via nucleation growth, exhibits thermally activated rate transformation. We construct two kinetic model system consisting equilibrium terms β or...

A new phenomenon is theoretically predicted, namely, that solid-solid transformation with a relatively large strain can occur through virtual melting along the interface at temperatures significantly (more than 100 K) below temperature. The energy of elastic stresses, induced by strain, increases driving force for and reduces Immediately after melting, stresses relax unstable melt solidifies. Fast solidification in thin layer leads to nanoscale cracking, which does not affect thermodynamics...

Abstract Metastable Intermolecular Composite (MIC) materials are comprised of a mixture oxidizer and fuel with particle sizes in the nanometer range. They subclass known as thermites. The mechanism responsible for propagation reaction loose compacts is not well understood. We have conducted series experiments using high‐speed photography pressure transducers an attempt to identify dominant mechanism. studied aluminum molybdenum trioxide. Of four possible candidates (radiation, convection,...

Abstract The heterogeneous interaction between nitromethane (NM), particles of nanoscale aluminum (38 and 80 nm diameter), fumed silica is examined in terms the deflagration detonation characteristics. Burning rates are quantified as functions pressure using an optical vessel up to 14.2 MPa, while structure characterized failure diameter. Nitromethane gelled (CAB‐O‐SIL ® ), well by nanoaluminum themselves. Use with slightly increases burning compared use larger diameter Al particles; however...

In this paper we present second harmonic generation (SHG) experiments designed to confirm the mechanism and quantify transformation kinetics of β–δ solid state phase transition in organic nitramine molecule octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The β adopts a centrosymmetric crystallographic configuration (P21/c) while δ noncentrosymmetric one (P61(P65)). As expected, results very poor SHG intensity from phase, is efficient, rivaling KH2PO4 absolute efficiency. thus...

We demonstrate the use of optical second harmonic generation (SHG) to identify $\ensuremath{\beta}\ensuremath{-}\ensuremath{\delta}$ phase transition in polycrystalline HMX. This has been implicated thermal decomposition HMX for over 30 years. measure an order magnitude difference SHG cross section from $\ensuremath{\beta}$ and $\ensuremath{\delta}$ phases this intensity observe during ${\mathrm{CO}}_{2}$ laser irradiation. is first known situ measurement a such energetic material dynamic...

We theoretically predict a new phenomenon, namely, that solid-solid phase transformation (PT) with large strain can occur via internal stress-induced virtual melting along the interface at temperatures significantly (more than 100 K) below temperature. show energy of elastic stresses, induced by strain, increases driving force for and reduces Immediately after melting, stresses relax unstable melt solidifies. Fast solidification in thin layer leads to nanoscale cracking which does not affect...

A current issue important to high explosive safety is deflagration-to-detonation transitions (DDTs) in accident scenarios. In order better understand the reactive mechanisms involved DDT and begin approach fast ignition heating rates seen DDT, high-irradiance ( h 800W/cm 2 ) CO laser experiments were performed on common explosives octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Reported data include time as a function of irradiance, energy,...

Abstract Time‐resolved emission experiments on deflagrating metastable interstitial composites of nano‐aluminum and nano‐molybdenum trioxide were performed. Early in the experiment (before disassembly sample) temperature obtained by fitting to a Planckian gray body appears accurate better than ±100 K (at 3200 K). Spectral features due Al AlO species observed top an apparent thermal background. The intensity was change with ratio Al/MoO 3 , larger intensities associated faster wave...

The beta-to-delta phase transition in HMX has been implicated as the primary reason behind increased sensitivity of explosive it is heated. Both physical and chemical changes accompany transition, but no study conclusively shown which specific change, or set changes, responsible. We present evidence that shows mechanical differences, themselves, do not result to shock compression HMX.

Abstract Near-exit measurements of NO, HCN, NH;1 and coal burnout an: reported for a highmoisture,subbituminous pulverized fired with air in laboratory combustor. Test variableswere moisture level, stoichiometric ratio swirl number the secondary inlet stream.Data arc also undried wherein gas-char samples were obtained from throughoutthe Concentrations major gas species, clcmcn tal composition char, gasmixture fraction N-pollutant concentrations are reported. Effects on burnoutwere negligible...

The particle size distribution and morphology of HMX (cyclotetramethylene-tetranitramine) in the plastic-bonded explosive, PBX 9501 (95% 5% polymeric binder, by weight), are important to understanding micromechanical behavior this material. This paper shows that "as-received" powder, as measured light scattering, is not preserved through processing operations formulation into molding powder subsequent consolidation hydrostatic pressing. Morphological features such cracking twinning examined...

The thermal cook–off response of energetic materials (ignition resulting from direct, bulk heating) is important a safety point view, but also challenges our understanding these materials. Explosives are not designed to be cooked off, and, especially in the case slow cook–off, by time material ignites it substantially different, both chemically and physically, its original state. In attempting model such process numerically, has generally been assumed that combustion proceeds, an ignition...