Carbon aerogels with tailored pore sizes were prepared by using a combination of sol-gel processing, supercritical CO2 extraction and pyrolysis. Ruthenium particles were incorporated via impregnation of organometallic precursors using supercritical CO2, followed by in situ thermal reduction. TEM studies reveal that the carbon aerogels are characterized by a continuous pore structure and that the ruthenium particles are highly dispersed with a narrow size distribution. It is found that under certain circumstances the carbon aerogels undergo a structural transition under the electron beam, in which the original tortuous aerogel network transforms into onion-like structures.

Flame propagation in Al/MoO3 thermites is measured as a function of bulk density and initial sample temperature. The composites are composed of nano-scale reactant particles mixed and pressure molded to between 49 and 73% of the theoretical maximum density. A relationship between cylindrical die pressure and final pellet density is derived. Experiments are also performed by initially pre-heating samples to a uniform temperature ranging from 20 to 200 °C. Ignition sensitivity was determined by measuring the ignition delay time and temperature using a 50-W CO2 laser and thermocouples, respectively. Combustion wave speeds were measured using high-speed imaging diagnostics. Results allow comparison of combustion behaviors associated with nano- vs. micron-scale particle composites. The nano-scale particle composites are extremely sensitive to ignition, especially when initially preheated. Combustion wave speeds for the compressed nano-composites were found to double when compared to the micron-scale composites.

Volatile organic compounds (“VOCs”) are widely used in industrial process, transportation fuels, and households. It is inevitable that some VOCs will escape into the atmosphere. Emission of VOCs will cause three major problems, including (1) increased exposure level of the population to know carcinogenic compounds such as benzene and carbon tetrachloride, (2) increased ozone concentration in the atmosphere at ground level, and (3) stratospheric depletion of the ozone layer, which alters global climate and increases exposure to UV radiation. Reducing the concentrations of VOCs will greatly improve air quality. A common method for VOC removal is catalytic decomposition. Most works have only focus on reducing VOC concentrations down to a few parts per million (ppm). Very little research has been conducted on reducing the VOCs down to parts per billion (ppb) levels, or less. This paper reports the decomposition of VOCs using a unique class of nanofibrous bird's-nest superstructure material. This open-inter-woven nanofibrous superstructure provides superb host for catalytic reactions and permits relatively easy flow of the gas stream through the structure. The nanofibrous MnO2 is highly effective in destroy more than 50 VOCs on USEPA's top priority list toxic VOCs to ppb level or less at a 200 − 350°C temperature.

The thermodynamically complete equation of state P=P(ρ,T) for a intermetallic mixture of nickel and aluminum is obtained via first principle calculations for pressures up to 300GPa and temperatures up to 1000K. The calculations for the static-lattice EOS are carried out in the framework of the density functional theory (DFT), using generalized gradient approximations and ultrasoft psuedopotentials. The phonon modes are calculated by using the density functional perturbation theory (DFPT). First, the EOS for each species is obtained based on ab initio prediction of the electron ground state and thermal excitations. Then, the mixture theories are utilized to obtain the EOS for the mixture. Two mixture theories are proposed, which correspond to the two limiting cases. The nature of the real mixture is intermediate to those of the two idealized mixtures and hence can be modeled as a weighted combination of the two cases. The Comparisons of the EOS for nickel and aluminum obtained from existing shock Hugoniot data show good agreement with the theoretical results.

Carbon nanotubes-based materials appeal for explosive emission, in forming cathode plasma, of interest for high-power microwave tubes. Cs intercalation has demonstrated a significant reduction of the work function of carbon nanotubes, thus improving field emission properties. An understanding of the detailed adsorption effects is important because the current saturation is attributed, in part, to adsorption mechanisms. In this paper, we report a density functional theory study of the effects of Cs on field emission of single-wall carbon nanotubes (SWCNTs), as an example of an approach to be taken for a fundamental understanding of such properties.

The amount of energy storage and its release in controllable pathways are two of the fundamental requirements of a high-energy material. The novel chemistry brought about by large surface-to-volume ratio of nanomaterials provides an attractive way to design and synthesize materials that optimize these two requirements. First principles calculations based on density functional theory and generalized gradient approximation have been used to study the potential of AlxLiyOz and Al(MnO4)x clusters as candidates for high-energetic materials. The equilibrium geometries and total energies of these clusters and their fragments are obtained to study the energy stored in these clusters and its release along various pathways. Interesting results include the substantial increase in binding energy by either adding an Al to MnO4 or adding a MnO4 to Al(MnO4)x unit indicating that Al(MnO4)3 may be a potential candidate for energetic materials as well as super-oxidizers. Similar calculations also show that during the combustion of Al addition of small amounts of Li to Al nano-powder helps to reduce the amount of non-combustible Al.

After a brief review of the history of mechanochemistry, and of the theoretical principles of chemical reactivity, four examples are described of reactions that demonstrate the importance of elastic shear strains compared with hydrostatic compressive strains (volume changes). Techniques for separating shear strains from volume changes, and for isolating elastic strains from plastic deformation are described. The latter (isolation) is achieved simply by localizing a strained region making it too small for dislocation nucleation. Shear strain acts by reducing the chemical hardness (activation energy) of a reactant. The four examples are: (1) “hammer chemistry” in which physisorped methane is struck by argon atoms with enough kinetic energy to cause chemisorption; (2) enhanced oxidation of silicon at stressed crack tips; (3) selective dissolution of crystals at screw dislocations; and (4) increased rates of catalyzed reactions when surface acoustic waves are passed through the catalyst.

Multiscale modeling using an embedded cluster approach is presented and applied to study the structure and properties of molecular crystals. We discuss the results of hydrostatic compression modeling of 1,1-diamino-2,2-dinitroethylene obtained with the embedded cluster model and the Hartree-Fock method and compare these with the full periodic crystal structure calculations. Details of the electronic structure of the perfect, highly compressed material are discussed. The results demonstrate the applicability of the embedded cluster model. We show that the band gap of the perfect material is not sensitive to hydrostatic compression, but some changes induced by the pressure take place in the valence band.

The objective of this work is to try to create new behaviors of energetic materials by using sol-gel processing and freeze drying to incorporate the energetic material into the fuel matrix at the nano particle size scale. Hydrazinium diperchlorate ([N2H6][ClO4]2) and resorcinol-formaldehyde were chosen in one example, and CL-20 and nitrocellulose were chosen in another. High solids loadings were achieved by the cryogel method. Characterization was carried out by elemental analysis, SEM, TEM, AFM, T-jump/FTIR spectroscopy, DSC, and drop-weight impact testing. The nanoscale formulations do indeed exhibit several different behaviors, such as enhanced burning characteristics and unusual morphologies, and appear to be a promising direction to pursue.

Ferroxane nanoparticles are precursors to iron oxide ceramic porous membranes. The ferroxane-derived ceramics have an average pore size of 24 nm and a surface area of 80 m2/g. Previous work has shown that these membranes have a molecular weight cut off of 180,000 dalton and their permeability is comparable to commercially available membranes. The ferroxane nanoparticles were reacted with manganese acetyl acetonate and then applied to the fabrication of mixed metal oxides. The nanoparticles were dried to form a ceramic chip. Upon sintering, asymmetric mixed metal oxide ceramic membranes were obtained. The materials were characterized by EXAFS, EDAX imaging and IDX mapping. EXAFS showed that the atomic environment of the iron and dopant material was different from those in the initial compounds, thus confirming that the reaction took place. The concentration of dopant metal was between 7% and 10%, with uniform concentration throughout the material.

Results from research aimed towards the understanding of the effect that ultrafine aluminium powder has on the explosive performance of underwater explosives are presented. A series of aluminised explosive compositions using a commercially available nanometric aluminium powder (Alex) have been prepared and quantified underwater. The results have been compared with the corresponding compositions using conventional aluminium powders. An enhancement in explosive properties can be seen. The effect is not universal but can be related to the reaction zone length, and time, of the base explosive being sufficiently long for the oxidation of the aluminium, with its substantial energy release, to take place in or close to the reaction zone.

Nano-sized energetic metals and boron particles (with dimensions less than 100 nanometers) possess desirable combustion characteristics such as high heats of combustion and fast energy release rates. Because of their capability to enhance performance, various metals have been introduced in solid propellant formulations, gel propellants, and solid fuels. There are many advantages of incorporating nano-sized materials into fuels and propellants, such as: 1) shortened ignition delay; 2) shortened burn times, resulting in more complete combustion in volume-limited propulsion systems; 3) enhanced heat-transfer rates from higher specific surface area; 4) greater flexibility in designing new energetic fuel/propellants with desirable physical properties; 5) nano-particles can act as a gelling agent to replace inert or low-energy gellants; 6) nano-sized particles can also be dispersed into high-temperature zone for direct oxidation reaction and rapid energy release, and 7) enhanced propulsive performance with increased density impulse. In view of these advantages, numerous techniques have been developed for synthesizing nano-particles of different sizes and shapes. To reduce any possible hazards associated with the handling of nano-sized particles as well as unwanted particle oxidation, various passivation procedures have been developed. Some of these coating materials could enhance the ignition and combustion behavior, others could increase the compatibility of the particles with the surrounding material. Many researchers have been actively engaged in the characterization of the ignition and combustion behavior of nano-sized particles as well as the assessment of performance enhancement of propellants and fuels containing energetic nano-particles. For example, solid fuels could contain a significant percentage of nano-sized particles to increase the mass-burning rate in hybrid rocket motors, the regression rate of solid propellants can be increased by several times when nano-sized particles are incorporated into the formulation. Specifically, hybrid motor data showed that the addition of 13% energetic aluminum powders can increase the linear regression rate of solid HTPB-based fuel by 123% in comparison to the non-aluminized HTPB fuel at a moderate gaseous oxidizer mass flow rate. Strand burner studies of two identical solid propellant formulations (one with 18% regular aluminum powder and the other with 9% aluminum replaced by Alex® powder) showed that nano-sized particles can increase the linear burning rate of solid propellants by 100%. In addition to solid fuels and propellants, spray combustion of bipropellants has been conducted using gel propellants impregnated with nano-sized boron particles as the fuel in a rocket engine. High combustion efficiencies were obtained from burning nano-sized boron particles contained in a non-toxic liquid-fuel spray. Materials characterization such as chemical analyses to determine the active aluminum content, density measurements, and imaging using an electron microscope have been performed on both neat nano-sized particles and mixtures containing the energetic materials. In general, using energetic nano-sized particles as a new design parameter, propulsion performance of future propellants and fuels can be greatly enhanced.

Molecular dynamics (MD) simulations of shock-induced deformations in diamond were performed using a reactive bond order (REBO) potential. A splitting of shock wave structure into elastic and crystal deformation fronts was observed in the [110] and [111] crystallographic directions above piston velocity thresholds of up ≈ 1.8 and 2.5 km/s, respectively. The crystal lattice response in a split two-wave regime consists of the relative movement of {111} planes in the diamond crystal and has different structural character for [110] and [111] shock waves. The strain produced by a [110] shock wave occurs only along one of the transverse crystalline directions, whereas in the [111] case crystal deformation involves the movement of the atoms in both transverse directions. To gain insight into the atomistic mechanisms of orientational dependence of shock compression of crystals, we have investigated in detail the constitutive stress-strain relationships under static uniaxial compression. The REBO potential gives a reasonably good description of stresses and energetics under moderate uniaxial compressions corresponding to an elastic shock wave regime. However, under compressions higher than 10% ([110] case) and 20% ([111] case) the REBO potential shows deficiencies in the quantitative description of stress response that might affect the MD picture of shock wave deformations in diamond.

Surface passivation of unpassivated Al nanoparticles has been realized using self assembled monolayers (SAMs). Nanoscale Al particles were prepared in solution by catalytic decomposition of H3Al•NMe3 or H3Al•N(Me)Pyr by Ti(OiPr)4 and coated in situ using a perfluoroalkyl carboxylic acid SAM. Because the Al particles are prepared using wet chemistry techniques and coated in solution, they are free of oxygen passivation. This SAM coating passivates the aluminum and seems to prevent the oxidation of the particles in air and renders the composite material, to some extent, soluble in polar organic solvents such as diethyl ether. Characterization data including SEM, TEM, TGA, and ATR-FTIR of prepared materials is presented.

Ni/Al nanostructured multilayer foils were machined with femtosecond pulse-length laser irradiation at various fluences. Scanning electron microscopy, back-scattered electron detection, and atomic force microscopy were used to characterize the resulting laser modified regions. We show that material removal at the micron scale is possible with no ignition of a self-propagation reaction emanating from the irradiated areas, a danger minimized by the fact that the extremely short time duration of the pulse produces negligible heat dissipation into the multilayer system. Nevertheless, initial AFM and BSE results give indication that multilayers may be intermixing and reacting locally in areas smaller than the laser beam diameter, though the exact ignition mechanism is still to be determined.

Highly metastable, nano-scale energetic materials were prepared by Arrested Reactive Milling (ARM). When reactive milling is carried out with materials systems suitable for Self-Propagating High Temperature Synthesis (SHS), reaction between the components occurs spontaneously and violently after a certain period of milling. In this research, metastable nanocom-posites with high energy density, were prepared by arresting the milling process prior to the spontaneous reaction. Products thus obtained are powders with particle sizes in the 10–50 μm range. Individual particles are intimate mixtures of reactive components, comparable to Metast-able Intermolecular Composites (MIC), with near theoretical maximum density. The time of arrest determines the degree of grain refinement and therefore the sensitivity to mechanical, electrical, or thermal initiation. Particle sizes of the product powders can be adjusted by appropriate choice of milling parameters. This paper describes the application of ARM to the material systems Al-Fe2O3 and Al-MoO3. After empirical determination of optimum milling parameters, the reactive composites are structurally characterized by electron microscopy and x-ray diffraction. First results of combustion tests are presented.

A picosecond laser flash-heating technique is combined with ultrafast spectroscopic probe diagnostics to investigate the fundamental mechanisms of nanoenergetic material performance. The systems studied include Al nanoparticle aggregates in nitrocellulose (NC) oxidizer, size-selected Al nanoparticles in NC and in Teflon oxidizers, and nanoparticle thermites consisting of 30 nm Al and nanometric MoO3. The time-dependence of reactions between Al and the oxidizer on the picosecond to nanosecond time scales are studied using coherent anti-Stokes Raman scattering (CARS) to monitor oxidizer consumption. The time-dependence of energy release is measured using fast optical spectroscopy. The space-dependence of chemical reaction propagation over 100 to 1500 nm distances is studied using the average distance between nanoparticles as a ruler. The distance of reaction propagation from a flash-heated Al nanoparticle increases linearly with energy, which is explained by a hydrodynamic model.

Novel properties associated with nanostructured materials, including nanoenergetic materials, have attracted a great deal of interest recently. Metastable Intermolecular Composite (MIC) materials are comprised of a mixture of oxidizer and fuel with particle sizes in the nanometer range. They can have high energy densities and exhibit combustion velocities above 1 km/s. These properties make them very attractive in a number of applications, including lead-free primers and igniters. However characterizing these materials is challenging, and the mechanism responsible for the propagation of reaction in loose compacts is not well understood. In this paper I will present an overview of efforts at Los Alamos to characterize and better understand the reaction mechanisms of these advanced energetic materials. We also have continuing efforts to make new MIC materials. Two applications are illustrated for MIC materials.

Combustion synthesis, or Self-propagating High- temperature Synthesis (SHS), is currently being used by the Center for Commercial Applications of Combustion in Space (CCACS) at the Colorado School of Mines to produce advanced porous materials for several important applications. These materials include ceramic, inter- metallic, and metal- matrix composites that can be used for orthopedic implants, heat exchanger and damping systems and micro-and macro-filter applications. Functionally graded materials, both in porosity and composition, can be produced using a range of combustion synthesis reactions systems. There are multiple factors that contribute to the final SHS product, e.g. reactant stoichiometry, initial relative density and pre-heat. The synthesis of nickel-titanium (NiTi) intermetallic compounds and composites is of considerable interest due to the ability to create a porous, shape memory and super-elastic alloy with high corrosion resistance. The synthesis effects of adding a carbon reactant so as to modify the reaction products and reaction exothermicity have been studied through the use of two different reaction stoichiometries involving elemental nickel, titanium and carbon. This paper outlines the synthesis of NiTi intermetallic composites based on the following SHS chemical reaction:

The effect of the carbon reactant and the initial sample green density on the apparent porosity, bulk density, pore size and pore distribution of the final materials has been studied and is presented within this paper. A NiTi- TiC intermetallic ceramic composite has been synthesized that is functionally graded in both composition and porosity: the latter grading being due to buoyancy and gas evolution effects. Proposed kinetic mechanisms that drive this synthesis process and control the graded structure are discussed in detail.

Single wall carbon nanotubes (SWNTs) with diameters below 1 nm prepared by chemical vapor deposition (CVD), and with diameters of 1.3 nm and higher prepared by laser ablation and carbon-arc techniques, were electrochemically functionalized with hydrogen and nitro groups, and chemically derivatized with 4-nitroaniline. Hydrogen adsorption on SWNTs was carried out in the presence or absence of electrodeposited catalytic nanoparticles of magnesium. SWNTs deposited on Teflon-coated membranes by vacuum filtration and lifted off as free-standing nanopaper, were used as the electrodes for electrochemical functionalization reactions. Hydrogen uptake on the nanotubes was characterized by micro-Raman spectroscopy, thermogravimetry and thermopower measurements. Electrochemically-induced functionalization with −NO2 groups on metallic, laser-synthesized SWNTs was clearly detected by Raman spectroscopy. Chemical functionalization was achieved on CVD-produced SWNTs by acidification to form −COOH groups followed by reaction with thionyl chloride and then with 4-nitroaniline. Photoacoustic effects that are likely to be precursors of photo-induced initiation of energetic reactions, were observed to occur at varying laser intensities for these materials in experiments using a pulsed Nd-YAG laser emitting at 532 nm.