Metal particle combustion and nanotechnology (original) (raw)

Effect of surface coatings on aluminum fuel particles toward nanocomposite combustion

Surface and Coatings Technology, 2013

Flame front velocity (FFV) of three energetic material composites was measured in order to understand the effects of surface functionalization on aluminum reactivity. Composites were prepared using molybdenum trioxide (MoO 3 ) and aluminum (Al) fuel particles with and without surface functionalization. The surface functionalization consisted of a 5-nm-thick layer (35% by weight) of perfluorotetradecanoic acid (PFTD) bonded to the Al 2 O 3 surface of the Al particles. The first composite consisted of Al functionalized with PFTD and MoO 3 , the second consisted of Al with MoO 3 and added PFTD particles to the same weight percentage as in the Al functionalized PFTD, and the third composite consisted of Al with MoO 3 . The results showed a dramatic increase in FFV from 100 to 500 m/s resulting from the surface functionalization. The results of the experiments show that the surface functionalized Al composite (Al-PFTD/MoO 3 ) has a reaction rate 2× than that of the simple Al/MoO 3 and 3.5× than that of the Al/MoO 3 /PFTD composite.

Ignition Catalyzed by Unsupported Metal Nanoparticles

Energy & Fuels, 2011

The short residence times available in supersonic combustion require some pre-reaction under mixing-controlledrich conditions and/or methods to lower the reaction temperature for auto-ignition. Adding catalysts could be such an option to achieve this objective. Catalytic ignition of toluene over the surfaces of in situ-generated free metal (Fe and Ni) nanoparticles was investigated experimentally in an aerosol reactor. The metal nanoparticles (Fe and Ni) were generated by decomposition of the corresponding metal carbonyls. Gas-phase (aerosol) size distributions along with transmission electron microscopy used to characterize the morphology of catalyst particles at different temperatures are presented. The effluent gas product and the fuel ignition temperature were determined by mass spectrometry. In comparison to non-catalytic homogeneous ignition, the addition of metal nanoparticles can lower the ignition temperature by as much as 150°C under rich conditions but had little effect under lean conditions. Iron was found to be a more active catalyst than nickel. Inspection of the catalyst product indicated that sintering was occurring at relatively low temperatures presumably as a result of the exothermic reaction on the particle surface. Turnover frequency as high as 80 s À1 was achieved, implying a greater catalyst efficiency than commonly found for substrate-stabilized catalysts.

Nano Aluminum Energetics: The Effect of Synthesis Method on Morphology and Combustion Performance

Propellants, Explosives, Pyrotechnics, 2011

Nanoscale aluminum based energetic composites were prepared using polytetrafluoroethylene (PTFE) as an oxidizer, and optimized according to the maximum experimentally observed flame propagation rate in an instrumented burn tube. Optimization of the aluminum-based composites was performed using nanometric aluminum from two manufacturers, Argonide Corporation and Novacentrix, and the combustion results represent the first direct comparison of these two materials in a burn tube configuration. Argonide aluminum was found to consist of many fused spheres of nano aluminum mixed with some larger micron sized particles. Novacentrix aluminum consisted of spherical particles with a closer particle size distribution. The propagation rate optimized wt.-% aluminum powder values were 50 and 44.5 for Novacentrix and Argonide, respectively. At the optimized conditions, the time to steady propagation for both Argonide and Novacentrix were similar, however the startup time for the Novacentrix based mixtures was more sensitive to changes in the mixture ratio. The presence of micron sized aluminum and lower surface area, but higher active content in the Argonide mixtures resulted in lower propagation rates, pressurization rates and peak pressures but higher total impulse values. It was found that peak pressure is not the sole determining factor in propagation rate, but the highest pressurization rates correlate with propagation rate.

Experimental studies on the burning of coated and uncoated micro and nano-sized aluminium particles

Aerospace Science and Technology, 2007

Two different approaches are used in this work to reduce the burning times of aluminium particles with the ultimate goal to improve the performances of solid propellants. One method is to coat the micro-sized particles by nickel, and the second is to decrease the particle sizes to nano-metric scales.A thin coating of Ni on the surface of Al particles can prevent their agglomeration and at the same time facilitates their ignition, thus increasing the efficiency of aluminized propellants. In this work, ignition and burning of single Ni-coated Al particles are investigated using an electrodynamic levitation setup and laser heating of the particles. The levitation experiments are used to measure the particle ignition delay time and burning time at different Ni contents in the particles.Decreasing the size of Al particles increases their specific surface, and hence decreases the burning time of the same mass of particles. In this investigation, a cloud of Al nano-particles formed in a combustion tube is ignited by an electric spark. The cloud experiments are used to measure comparative flame front propagation velocities for different Al particle sizes with and without organic coating.The results and their analysis show that both methods reduce the Al burning time. Ni coating reduces significantly the ignition time of micro-sized Al particles and hence the total burning time compared to non-coated particles. Nano-sized particle clouds burn faster than micro-sized Al particle clouds.Deux approches sont étudiées pour diminuer le temps de combustion des particules d'aluminium dans le but d'améliorer les performances des propergols solides. Il s'agit d'une part d'enrober les particules de tailles micrométriques dans une fine couche de nickel, et d'autre part, d'utiliser des particules d'aluminium de taille nanométrique.Une mince couche de nickel couvrant les particules d'Al permet d'empêcher leur agglomération et facilite leur allumage. Dans ce travail, l'allumage et la combustion des particules isolées d'Al enrobées dans du Nickel sont étudiés à l'aide du lévitateur électrodynamique du LCSR équipé d'un dispositif d'allumage par laser. Ce dispositif permet de déterminer les temps d'allumage et de combustion des particules en fonction de la composition du milieu gazeux environnant, la pression et le contenu en Nickel de la particule. Les expériences sont conduites notamment dans de l'air et le CO2 jusqu'à 40 bars et des pourcentages en Nickel de la particule de 0 à 15% en masse.Diminuer la taille des particules à des échelles nanométriques augmente leur surface spécifique et par conséquent diminue le temps de combustion d'une même masse d'Al. Dans cette étude, un nuage de nano particules d'Al est formé dans un tube de combustion et allumé par des électrodes. Ces expériences permettent de déterminer les vitesses comparatives de propagation du front de flamme en fonction de la taille des particules et de la nature de leur enrobage (alumine ou des matériaux organiques).Les résultats préliminaires et leurs analyses montrent que les deux méthodes permetent de réduire d'une façon significative les temps de combustion des particules de'aluminium.

Pyrophoricity of nano-sized aluminum particles

Journal of Nanoparticle Research, 2012

The temperature histories are calculated for spherical nano-sized aluminum particles with no protective oxide shell inserted in air at 300 K. In calculations, initial particle temperatures varied and the minimum initial temperature leading to the particle ignition was determined. The particle, initially without any oxide coating, was assumed to react adiabatically forming a monomolecular oxide coverage; the following oxidation was assumed to be governed by the Cabrera-Mott reaction mechanism. Convection and radiation heat losses were considered. Convection was accounted for using a transition regime heat transfer model by Fuchs. Aluminum particles with diameters less than about 68 nm are predicted to be pyrophoric, e.g., ignite without appreciable initial pre-heating.

Effect of nano-aluminium in plateau-burning and catalyzed composite solid propellant combustion

Combustion and …, 2009

Nano-aluminium particles of 50nmsize,producedatthislaboratory,areaddedtocompositesolidpropellantsbasedonammoniumperchlorateandhydroxyl−terminatedpoly−butadienebinderthatexhibitplateauburningratetrendsandthoseincludingburningratecatalysts.Thenano−aluminizedpropellantburningratesarecomparedwithcorrespondingmicro−aluminizedandnon−aluminizedonesinthe1−12MPapressurerange.Themid−pressureextinctionofthematrixescontainingthefine−sizedammoniumperchlorateparticlesinthepropellantalongwiththebinderisinvestigatedinallthecasestounderstandthemechanismofplateau−burning.Further,thevariationsinaluminiumcontent,thealuminiumsize(withinnano−andmicro−ranges),bimodalcombinationofnano−andmicro−aluminiumareconsidered.Ferricoxideandtitaniumdioxidearetheburningratecatalystsconsidered.Largescaleaccumulationofaluminiumisobservednotonlyinmicro−aluminizedmatrixes,butalsoinnano−aluminizedonesasclustersof1−5lmsize.Sincealuminiumisaddedattheexpenseofthecoarseammoniumperchlorateparticlestopreservethetotal−solidsloadinginthepresentformulations,additionofmicroaluminiumdecreasestheburningrate;whereas,nano−aluminizedpropellantsexhibit50 nm size, produced at this laboratory, are added to composite solid propellants based on ammonium perchlorate and hydroxyl-terminated poly-butadiene binder that exhibit plateau burning rate trends and those including burning rate catalysts. The nano-aluminized propellant burning rates are compared with corresponding micro-aluminized and non-aluminized ones in the 1-12 MPa pressure range. The mid-pressure extinction of the matrixes containing the fine-sized ammonium perchlorate particles in the propellant along with the binder is investigated in all the cases to understand the mechanism of plateau-burning. Further, the variations in aluminium content, the aluminium size (within nano-and micro-ranges), bimodal combination of nano-and micro-aluminium are considered. Ferric oxide and titanium dioxide are the burning rate catalysts considered. Large scale accumulation of aluminium is observed not only in micro-aluminized matrixes, but also in nano-aluminized ones as clusters of 1-5 lm size. Since aluminium is added at the expense of the coarse ammonium perchlorate particles to preserve the total-solids loading in the present formulations, addition of microaluminium decreases the burning rate; whereas, nano-aluminized propellants exhibit 50nmsize,producedatthislaboratory,areaddedtocompositesolidpropellantsbasedonammoniumperchlorateandhydroxyl−terminatedpoly−butadienebinderthatexhibitplateauburningratetrendsandthoseincludingburningratecatalysts.Thenano−aluminizedpropellantburningratesarecomparedwithcorrespondingmicro−aluminizedandnon−aluminizedonesinthe1−12MPapressurerange.Themid−pressureextinctionofthematrixescontainingthefine−sizedammoniumperchlorateparticlesinthepropellantalongwiththebinderisinvestigatedinallthecasestounderstandthemechanismofplateau−burning.Further,thevariationsinaluminiumcontent,thealuminiumsize(withinnano−andmicro−ranges),bimodalcombinationofnano−andmicro−aluminiumareconsidered.Ferricoxideandtitaniumdioxidearetheburningratecatalystsconsidered.Largescaleaccumulationofaluminiumisobservednotonlyinmicro−aluminizedmatrixes,butalsoinnano−aluminizedonesasclustersof1−5lmsize.Sincealuminiumisaddedattheexpenseofthecoarseammoniumperchlorateparticlestopreservethetotal−solidsloadinginthepresentformulations,additionofmicroaluminiumdecreasestheburningrate;whereas,nano−aluminizedpropellantsexhibit80-100% increase in the burning rate under most conditions. The near-complete combustion of nano-aluminium close to the burning surface of the propellant provides heat feedback that controls the burning rate. Midpressure extinctions of matrixes and plateau burning rates of propellants are washed out when nano-aluminium is progressively added beyond 50% in bimodal aluminium blends, but low pressure-exponents are observed in the nano-aluminized propellant burning rates at elevated pressures. Adjusting the plasticizer content in the binder alters the pressure range of plateau burning rates in non-aluminized propellants. Catalysts increase the burning rate by 50−10050-100% in non-aluminized and micro-aluminized propellants, but in nano-aluminized propellants, the lm-sized catalyst does not affect the burning rate significantly; whereas, the nanometre size catalysts increases the burning rate merely by 50−1005-15%.

Comparison of engineered nanocoatings on the combustion of aluminum and copper oxide nanothermites

Surface and Coatings Technology, 2013

Water-repellent nano-coatings for submerged combustion of nano-energetic composite materials were developed. These coatings may have applications for oceanic power generation, underwater ordnance, propulsion, metal cutting, and torch technologies. Nano-coatings were deposited on thermite pellets by a vapor-phase technique. Two types of deposition techniques studied were chemical vapor deposition (CVD) and atomic layer deposition (ALD). A total of six types of nano-coatings were applied on the thermite pellets. Various process parameters to produce the coatings were explored. Characterization of the nano-coatings was carried out using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and contact angle goniometry. Submerged combustion tests of the nano-coated thermite pellets were performed as a function of submerged time. The pellets were submerged in de-ionized water for 3, 5, and 10 days. The energy released by the thermite reaction was analyzed and compared to other types of nano-coated pellets. Initial results of a fluorocarbon self-assembled monolayer (FSAM) coating were compared with an ALD coating composed of Al 2 O 3 . Results show that with increasing submerged time, there was a decrease in the ratio of bubble energy to total energy of combustion (K c =K bubble /K combustion ) for all coatings tested. The initial bubble energy of the pellets coated with FSAM and ALD with Al 2 O 3 was 133.3 and 142.2 (KJ/Kg), respectively. After submersion for 10 days, the bubble energy reduced to 10.4 and 15.6 (KJ/Kg), respectively. The value of K c for the FSAM coating decreased by a factor of 12.8 whereas the ALD with Al 2 O 3 coating decreased by a factor of 9.1. The hydrophobic coating is critical for energy generation because without it, the pellets do not ignite, resulting in 100% loss of energy.

Formation of metal oxide nanoparticles in combustion of titanium and aluminum droplets

Combustion, Explosion, and Shock Waves, 2006

A study was performed of the formation of metal oxide nanoparticles during combustion of aluminum and titanium drops which moved in air at a velocity of up to 3 m/sec. The source of the burning particles was a pyrotechnic mixture which contained an oxidizer, a binder, and metal particles of size 4-350 µm. Transmission electron microscopic studies showed that the combustion products were 1-10 µm aggregates of fractal structure consisting of primary particles (spherules) of Al 2 O 3 /TiO 2 5-150 nm in diameter. The Brownian diffusion of the aggregates and their motion in electric and gravitational fields were observed using videomicroscopic recording. The charge distribution of TiO 2 aggregates and the equivalent radius of Brownian mobility were determined. In Al combustion, the zone of nanoparticle formation is separated from the particle surface by a distance approximately equal to the particle radius, and in Ti combustion, this zone is located directly near the surface. Coagulation of the oxide aerosol in the track of a burning particle leads to aerogelation with the formation of huge aggregates. Analytical expressions for approximate calculation of the parameters of the oxide particles and zones of their formation are proposed.