We present the first quantitative assessment of combustion dynamics of on-chip porous silicon (PS) energetic material using sulfur and nitrate-based oxidizers with potential for improved moisture stability and/or minimized environmental impact compared to sodium perchlorate (NaClO4). Material properties of the PS films were characterized using gas adsorption porosimetry, and profilometry to calculate specific surface area, porosity and etch depth. The PS/sulfur energetic composite was formed using three pore loading techniques, where the combustion speeds ranged from 2.9 – 290 m/s. The nitrate-based oxidizers were solution-deposited using different compatible solvents, and depending on the metal-nitrate yielded combustion speeds of 3.1 – 21 m/s. Additionally, the combustion enthalpies from bomb calorimetry experiments are reported for the alternative PS/oxidizer systems in both nitrogen and oxygen environments.

Oxidation behavior of aggregated aluminum nanoparticles (Al-NPs), specifically the combustion propagation, is studied, when only part of the aggregated Al-NPs is heated to 1100 K and the rest of the system is kept at 300 K. Here, multi-million atoms molecular dynamics (MD) simulation reveals the sintering/coalescence phenomena for the different diameters (D = 26, 36 and 46 nm) aggregated systems. Various consuming rates of core aluminum are investigated for different layers and different diameters aggregated systems. The formation of Al2O3 fragments outside the shell (the largest covalently bonded aluminum-oxide cluster) structure is confirmed from AlO and AlO2 intermediates. The smaller size of Al-NPs results in faster trend of transition from Al-rich to O-rich for most outside small clusters. However, more core aluminum reacts with shell oxygen leads to faster decreasing of the ratio of O/Al in the shell fragment for larger Al-NPs system.

The present study explores the burning of microscale porous silicon channels with sodium perchlorate. These on-chip porous silicon energetics were embedded in crystalline silicon, and therefore surrounded on three sides by an efficient thermal conductor. For slow burning systems, this presents complications as heat loss to the crystalline silicon substrate can result in inconsistent burning or flame extinction. We investigated <100 μm wide porous silicon strips, sparsely filled with sodium perchlorate (NaClO4), to probe the limits of on-chip combustion. Four different etch times were attempted to decrease the dimensions of the porous silicon strips. The smallest size achieved was 12 x 64 µm, and despite the small dimensions, demonstrated the same flame speed as the larger porous silicon strips of 6-7 m/s. We predict that unreacted porous silicon acts as a thermal insulator to aid combustion for slow burning porous silicon channels, and SEM images provide evidence to support this. We also investigated the small scale combustion of a rapidly burning sample (∼1200 m/s). Despite the rapid flame speed, the propagation followed a designed, winding flame path. The use of these small scale porous silicon samples could significantly reduce the energetic material footprint for future microscale applications.

Recent research has demonstrated that ternary aluminum-boron-iodine (Al-B-I2) materials prepared by mechanical milling are effective in generating biocidal combustion products. Such reactive materials are of interest for the munitions aimed to defeat stockpiles of biological weapons. In this research, ternary Mg∙B∙I2 composites were synthesized using two-stage milling. The first stage consisted of a binary B∙I2 powder prepared by mechanical milling, followed by addition of magnesium for iodine stabilization. Specific compositions for each ternary material were varied. Stability of the samples was assessed by their heating in argon at a constant rate using Thermo Gravimetric Analysis (TGA) and observing weight loss. Oxidation of the prepared powders was also studied by TGA. Ternary Mg∙B∙I2 composite powders prepared by two-stage milling were more stable than any of the previously prepared iodine-bearing materials with the same concentration of iodine (20 wt %). Particle size distributions were measured using low-angle laser light scattering. Powders were ignited using in an air-acetylene flame and in a constant volume explosion apparatus. Particle burn times and temperatures were measured optically. Substantially longer burn times and lower temperatures were observed for the prepared materials compared to the reference pure Mg powder.

Contributions of electronic (or ligand) and geometric (or ensemble) effects on the AuM bimetallic nano-catalyst were elucidated by using a simple aerobic oxidation of 1-phenylethanol to acetophenone on the basis of difference in the ionization energy values (Ei) between Au and M elements. The poly(N-vinylpyrrolidone) (PVP)-protected Au60M40 bimetallic NPs (M = Ag, Cu, Pd, Pt and Ir) were prepared with a polyol reduction method, and stabilized onto the solid base hydrotalcite support affording the Au60M40-PVP/HT catalysts. The yields for acetophenone were observed as the following order; Au60Pd40-PVP/HT (>99%) >> Au60Ag40-PVP/HT (17.4%) > Au60Cu40-PVP/HT (13.8%) > Au60Pt40-PVP/HT (7.1%) > Au60Ir40-PVP/HT (5.5%), at 343 K for 6 h. Differences in the Ei between Au and M (EiAu-EiM) indicted that the yields over the Ag, Cu, Pt, and Ir incorporated Au catalysts were well-understood on the ligand effects theory, though geometric factors such as differences in nanostructure around Au atom in Au60M40 NPs on HT should be further considered as other contributed factors. The significant activity on Au60Pd40-PVP/HT was studied in terms of the electron density of Pd atoms. It was observed that the Pd 4d density was varied by the amount of Au loading. According to these observations combined with our previous studies, we suggest that the advantages in AuPd bimetallic catalyst are not only in the ligand effect serving negatively-charged Au but also the ensemble effect of neighbor Pd, and they synergistically contribute to the novel activity for aerobic alcohol oxidation over AuPd catalyst.

We have demonstrated the synthesis of highly reactive boron nanomaterials by alkali metal reduction of BCl3 under sonication, followed by annealing. Unlike ordinary boron powders, these materials combust completely and release close to their theoretical energy content (based on elemental analysis) in polymer protected bomb calorimetry experiments. We have scaled up the synthesis using a commercial (Columbia International CIT-UHiPR-U1000V600) ultrasonic hi-pressure reactor. The synthesis reactions exhibit a scale problem, where they yield diminishes considerably on scale up, probably a result of alkali metals becoming trapped inside a mass of salts and rendered unable to react. We measured the combustion properties of the materials by bomb calorimetry, and thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), and report elemental analyses on selected samples.

Because of the high energy density, easy ignition, and good storability, mechanically alloyed Al·Mg powder has the potential to improve the performance characteristics of various energetic and gas-generating materials. Here, the use of this powder in combustible mixtures for generation of oxygen and hydrogen is explored. The mixtures for oxygen generation consisted of sodium chlorate, nanoscale cobalt oxide catalyst, and Al·Mg powder, while those for hydrogen generation included water, polyacrylamide as a gellant, and Al·Mg powder. To increase hydrogen yield, ammonia borane (NH3BH3) was also added to Al·Mg − water mixtures. Combustion experiments were conducted in an argon environment, using laser ignition. The thermal wave propagation over the oxygen-generating mixtures was studied using infrared video recording. It has been shown that mechanically alloyed Al·Mg material is a promising alternative to currently used iron because significantly smaller amounts of this additive are needed for a steady propagation of the combustion wave. The hydrogen generation experiments have shown that mixtures of mechanically alloyed Al·Mg powder with 10−60 wt% gelled water are combustible, with the front velocities exceeding the values obtained for the mixtures of water with nanoscale Al. Hydrogen yield was measured using mass-spectrometry. In the mixtures that included ammonia borane, D2O was used instead of H2O. Measurements of H2, D2, and HD concentrations in the product gas provided insight into the reaction mechanisms. The isotopic tests have shown that AB participates in two parallel processes − thermolysis and hydrolysis, thus increasing hydrogen yield.

Nano-sized metallic powders have advantages as fuels including faster, more complete combustion than micron-sized metal powder particles; however, the unpassivated nanoparticles of some metals of interest, such as Al, are pyrophoric and highly reactive, making them difficult to handle. Additionally, metal-hydrides are of great potential interest for a significant gravimetric energy increase without a penalty in the volumetric energy content, as the inclusion of hydrogen in the metallic matrix does not significantly decrease overall density of the material. Reactive metal amorphous powders produced by the sonochemical decomposition and dehydrogenation of an in situ-produced mixed borohydride-tetrahydroaluminate of titanium and containing hydrogen are examined in the current work and show exceptional air-stability and higher energy content than nano-Al. An aerosolized powder burner is used to investigate the combustion behavior of these powders mixed with gaseous fuels to quantify the energy density and reaction rate as compared to commercial aluminum powders in an effort to benchmark the performance of the sonochemically generated amorphous Ti-Al-B powder fuels.

Reactive nanocomposite powders with compositions 2Al∙3CuO, 2.35Al∙Bi2O3, 2Al∙Fe2O3, and 2Al∙MoO3 were prepared by arrested reactive milling, placed in monolayers on a conductive substrate and ignited by an electro-static discharge (ESD) or spark in air, argon, and vacuum. The ESD was produced by discharging a 2000 pF capacitor charged to a voltage varied from 5 to 20 kV. Emission from ignited particles was monitored using a photomultiplier equipped with an interference filter. Experimental variables included particle sizes, milling time used to prepare composite particles, surrounding environment, and starting ESD voltage. All materials ignited in all environments, producing individual burning particles that were ejected from the substrate. The spark duration varied from 1 to 5 µs; the duration of the produced emission pulse was in the range of 80 – 250 µs for all materials studied. The longest emission duration was observed for the nanocomposite thermite using MoO3 as an oxidizer. The reaction rates of the ESD-initiated powders were defined primarily by the scale of mixing of and reactive interface area between the fuel and oxidizer in composite materials rather than by the external particle surface or particle dimensions. In vacuum, particles were heated by ESD while remaining on the substrate until they began generating gas combustion products. In air and argon, particles initially pre-heated by ESD were lifted and accelerated to ca. 100 m/s by the generated shock wave; the airborne particles continued self-heating due to heterogeneous redox reactions.

The present work deals with the production and characterization of metal and bimetallic nanopowders.

The electric explosion wire method for production of metal nanopowders is presented. The method enables to produce both metal and bimetallic nanoparticles (BMNP) with controlled content of metals within one particle. An alternative method to obtain bimetallic nanoparticles is also suggested using a spontaneous electrochemical process from salt solutions. BMNP for both Al-Cu and Al-Ni have been prepared and studied.

The oxidation, ignition and thermal reactivity of the BMNP of Al-Cu and Al-Ni in a simultaneous thermogravimetric (TG) and differential scanning calorimetry (DSC) experiments have been carried out. The microstructure has been characterized with a scanning electron microscope (SEM) and transmission electron microscope (TEM). The phase compositions of the reaction products have been investigated with X-ray diffraction.

By comparing the peak temperature of the first exothermic reaction in DSC and the phase transition temperatures in the respective binary systems, it has been found that for Al-Cu BMNP the melting of an alloy played a pivotal role for the early ignition reaction. The comparison of the reactivity of BMNP with that of aluminum nanoparticles has shown a greater reactivity of BMNP Al-Cu and Al-Ni.