Nano-aluminum Particles Research Articles

Experimental Study on Microstructural Changes of Nanoaluminum Particles during the Slow Heating Process in Vacuum and Aerobic Environments

Experimental Study on Microstructural Changes of Nanoaluminum Particles during the Slow Heating Process in Vacuum and Aerobic Environments

Mechanical properties of epoxy composites filled with multi-walled carbon nanotube, Nanoaluminum particles and glass fibers at elevated temperatures

The present work investigates the mechanical properties of a composite material composed of multi-walled carbon nanotubes (MWCNTs), nano-aluminum powder (NAP), and glass fibers (GF) for five different compositions. The study further investigated how MWCNTs contribute to maintaining the mechanical properties of nanocomposites when exposed to elevated temperatures, up to 180 °C. The evaluation of impact strength revealed that the nanocomposite, composed of 2 % MWCNTs, 15 % NAP, and 10 % GF, demonstrated the greatest impact strength. At room temperature, the composite containing 2 % MWCNTs, 5 % NAP, and 20 % GF exhibited the highest ultimate tensile strength (UTS). Conversely, at elevated temperatures reaching up to 180 °C, the highest UTS was observed in the composition with 2 % MWCNTs, 10 % NAP, and 15 % GF. The hardness of the nanocomposite was influenced by its composition; at room temperature, the maximum hardness was observed in the mixture containing 2 % MWCNTs, 20 % NAP, and 5 % GF. In contrast, at elevated temperatures, the composition with 2 % MWCNTs, 5 % NAP, and 20 % GF exhibited the highest hardness. Overall, the study found that incorporating GF and NAP improved the mechanical properties of the composite. These results indicate that the composite's performance could be further optimized for specific applications through the addition of filler materials.

Tailorable piezoelectric and flexoelectric output of a polymer-particle composite

Materials with different combinations of piezoelectric and flexoelectric properties offer multifunctionality and versatility in terms of modes of operation in sensing, actuation, and energy harvesting. We explore a microscopic mechanism for tailoring the macroscopic quasi-static mechanoelectrical output of polymer-particle composites by taking advantage of heterogeneity-induced enhancement of the stress fields and strain gradient fields. The idea focuses on using microscopic inclusions, such as embedded particles and voids, to manipulate the activation and relative contributions of the piezoelectric and flexoelectric effects under different modes of mechanical excitation, such as uniaxial compression and flexural bending. The material system studied is a composite of poly(vinylidene fluoride-co-trifluoroethylene [P(VDF-TrFE)] polymer and nanoaluminum (nAl) particles, or P(VDF-TrFE)/nAl. This system is interesting because P(VDF-TrFE) exhibits both piezoelectric and flexoelectric behaviors and nAl particles have significantly higher elastic stiffness than the polymer. A range of piezoelectric and flexoelectric properties of P(VDF-TrFE) and the stiffness of the particles are considered. Significant microstructural effects are found to enable tailoring of the mechanoelectrical response through microstructure variation. The responses of the composite are quantified using the effective piezoelectric constant (d33,effo) and the effective flexoelectric coefficient (μTR,effo). It is found that the effective macroscopic piezoelectric and flexoelectric behaviors can be changed either independently or simultaneously through different combinations of microstructure attribute changes. The mechanism revealed points out avenues for developing materials with tunable mechanoelectrical behaviors and multifunctionality.

The Effect of Organic Matter from Sewage Sludge as an Interfacial Layer on the Surface of Nano-Al and Fluoride.

Due to its high reactivity, the nano aluminum particle (n-Al) has attracted more attention in energetic materials but is easily oxidized during processing. In order to realize sewage sludge (SS) resource and n-Al coating, the organic matter was extracted from SS, using the deep eutectic solvent method due to its strong dissolving capacity, and then the organic matter was pretreated by ball milling, which was used as an interfacial layer between n-Al and fluoride. It was found that organic matter was successfully extracted from SS. The main organic matter is proteins. The ball milling method can effectively destroy the secondary structure of proteins to release more active functional groups. During the pretreatment, the Maillard reaction broke the proteins structure to form more active low molecular weight compounds. It was confirmed that n-Al can be coated by PBSP under mild conditions to form a uniform core-shell structure. PFOA can effectively coat the n-Al@PBSP to form n-Al@PBSP/PFOA, which can enhance the combustion of n-Al. The gas phase flame temperature can notably improve to 2892 K. The reaction mechanism between n-Al and coating was analyzed. The results could help SS treatment and provide new insights for n-Al coating and SS-based organic matter recovery and utilization.

Construction of hollow heterogeneous microspheres containing energy storage fibers by electric spray to promote combustion of nano aluminum

To solve the problem of nano-aluminum (nAl) powder easy agglomeration and improve its thermal reaction, nAl was combined with adhesive (Viton A, F2602) and oxidizer (Ammonium perchlorate, AP) forming microspheres by electrostatic spray method. The morphology and structure were analyzed by SEM, EDS and XPS. The results showed that the microspheres (diameter≈Φ10–15 μm) were hollow structures formed by winding of fluoropolymer fibers, while AP and nano aluminum particles were embedded on the fibers. By controlling the electric spray process, the well-dispersed AP and nAl nanocrystals were assembled on the fiber. Thermal analysis indicated that the gas phase products decomposed by AP were absorbed by porous microspheres, and part of the heat was stored in polymer fibers, thus promoting the breakdown of the alumina shell and accelerating the pre-ignition reaction. The combustion and laser ignition experiments proved hollow heterogeneous microspheres have excellent thermodynamic properties. The assembled microspheres not only solved the problem of poor rheology caused by the agglomeration of nAl, but also improved the insufficient combustion of nAl and the condensation of products.

Synthesis, Analysis, and Characterization of Aluminum Nanoparticles Coated with 2,2,4-Trimethylpentane

In this study, to solve the problem of low activity of aluminum nanoparticles in combustion, aluminum nanoparticles were coated with 2,2,4-trimethylpentane (C8H18-Al), enabling the deactivation of aluminum nanoparticles to be effectively inhibited. The morphological characteristics, particle size distribution, chemical state, and thermal properties of C8H18-Al were characterized via SEM, TEM, DLS, XPS, and TG-DSC. The stability and energy performance of C8H18-Al were studied based on the national standard test method. The results showed that C8H18-Al had a typical shell–core structure with a smooth surface and good sphericity. The particle size was normally distributed, and the content of active aluminum nanoparticles was high (85.45%), with good thermal stability and a fast energy release rate (about four times that of ordinary nano aluminum particles). The results demonstrated that an in situ C8H18 coating is beneficial for the preparation of structurally stable aluminum nanoparticle composites with good performance.

Dielectric breakdown driven by flexoelectric and piezoelectric charge generation as hotspot ignition mechanism in aluminized fluoropolymer films

Using multiphysics simulations and experiments, we demonstrate that dielectric breakdown due to electric charge accumulation can lead to sufficient hotspot development leading to the initiation of chemical reactions in P(VDF-TrFE)/nAl films comprising a poly(vinylidene fluoride-co-trifluoroethylene) binder and nano-aluminum particles. The electric field (E-field) development in the material is driven by the flexoelectric and piezoelectric responses of the polymer binder to mechanical loading. A two-step sequential multi-timescale and multi-physics framework for explicit microscale computational simulations of experiments is developed and used. First, the mechanically driven E-field development is analyzed using a fully coupled mechanical–electrostatic model over the microsecond timescale. Subsequently, the transient dielectric breakdown process is analyzed using a thermal–electrodynamic model over the nanosecond timescale. The temperature field resulting from the breakdown is analyzed to establish the hotspot conditions for the onset of self-sustained chemical reactions. The results demonstrate that temperatures well above the ignition temperatures can be generated. Both experiments and analyses show that flexoelectricity plays a primary role and piezoelectricity plays a secondary role. In particular, the time to ignition and the time to pre-ignition reactions of poled films (possessing both piezoelectricity and flexoelectricity) are ∼10% shorter than those of unpoled films (possessing only flexoelectricity).

Peptide Assembly of Al/CuO Nanothermite for Enhanced Reactivity of Nanoaluminum Particles.

Biological self-assembly procedures, which are generally carried out in an aqueous solution, have been found to be the most promising method for directing the fabrication of diverse nanothermites, including Al/CuO nanothermite. However, the aqueous environment in which Al nanoparticles self-assemble has an impact on their stability. We show that using a peptide to self-assemble Al or CuO nanoparticles considerably improves their durability in phosphate buffer aqueous solution, with Al and CuO nanoparticles remaining intact in aqueous solution for over 2 weeks with minimal changes in the structure. When peptide-assembled Al/CuO nanothermite was compared with a physically mixed sample in phosphate buffer for 30 min, the energy release of the former was higher by 26%. Furthermore, the energy release of peptide-assembled Al/CuO nanocomposite in phosphate buffer showed a 6% reduction by Day 7, while that of the peptide-assembled Al/CuO nanocomposite in ultrapure water was reduced by 75%. Taken together, our study provides an easy method for keeping the thermal activity of Al/CuO nanothermite assembled in aqueous solution.

EFFECT OF PIEZOELECTRICITY ON THE REACTIVITY OF NANOALUMINUM P(VDF-TrFE) ENERGETIC COMPOSITES

In this study, the effect of piezoelectricity on the sensitivity to ignition by laser radiation of 10% wt nanoaluminum/poly(vinylidene fluoride-trifluoroethylene) [nAl/P(VDF-TrFE)] composite films was investigated. Nanoaluminum particles were dispersed in P(VDF-TrFE) copolymer solution and cast into ~ 45 μm thick films. Ignition samples across which an electric field of 25 kV/mm could be applied were created by sputter coating gold electrodes on opposing sides of the film. Electrodes were coated on one side with a layer of carbon paint to absorb laser radiation. Samples were tested under four conditions: unmodified, unpoled with an applied electric field, poled without an electric field, and poled with an electric field. Results from this study indicate that both the application of an electric field and the activation of the piezoelectric properties of PVDF sensitize the composite as measured by a decrease in a mean time to ignition, with piezoelectricity activation sensitizing the composite to a greater degree than only an applied electric field.

Numerical study on the characteristics of a nano-aluminum dust-air jet flame

Nano-sized aluminum dust is quite attractive in the application scenarios with limited residence time. This study simulated an aluminum nanoparticle-air jet flame in a burner that was proposed to characterize the mixing and burning properties of dust and air in a classical ramjet configuration. The model considers the flow of gas phase by employing three-dimensional multicomponent Navier-Stokes equations, and the aluminum particles via the Lagrange approach. A combustion sub-model was developed to characterize the heat convection, radiation and combustion processes of nano-sized aluminum particles. Thereafter, the model was validated by comparing with experimental results of dust jet flow and aluminum particle combustion. With the present model, the characteristics of flow field, and variations of particle temperature, heat release and statuses etc. were examined in detail, by which the mixing zone and flame structure were defined. The results showed that the nano-aluminum particles in the inner mixing layer were firstly ignited by the hot co-flow air and burned, and these particles in the core jet region were ignited downstream. Once the aluminum particles were ignited, they burned out promptly in this burner. The effects of particle size were evaluated, and the results show that the lengths of mixing layer and reaction zone, as well as the width of reaction zone reduce with decreasing particle size, whereas the width of mixing layer stays the same.

Thermally active nano-aluminum particles with improved flowability prepared by adsorbing multi-component layer

The flowability of nano-aluminum (nAl) particles is poorly characterized or tailored but must be improved for their manufacturing or application of interest. In this work, a strategy was proposed to improve the fluidity of nAl particles and increase the active aluminum content of nAl particles to be higher than that of naturally passivated nAl with similar size by 14%. The main method was introducing the non-cohesive layers with high absorption ability to slow down the oxidizing gas diffusion on the nAl surface at room temperature. The gasses released by the adsorption layer combustion could inhibit the sintering of the produced nAl particles and thereby enhance the reaction efficiency at high temperatures, thus endowing nAl with thermal activity. Characterization and experimental results indicated that the multi-component adsorption layers were composed of amorphous carbon, thin oxide layer, and solvent molecules, which improved the flowability by weakening the cohesion between nAl particles. As a result, the produced nAl particles with improved flowability were evenly dispersed in the nAl/oxidizer mixture. This characteristic was conducive to the mass transfer and energy diffusion on the nAl surface during initial ignition and reaction propagation.

Photoflash and laser ignition of full density nano-aluminum PVDF films

Laser or flash excitation is an attractive ignition option for many energetic systems because of increased safety and control. Commonly used electrical ignition systems are more likely to cause accidental ignition due to stray currents. Upgrading to laser or flash ignition mitigates this problem as well as allowing the ignition at multiple sites more easily for improved control of the energy release. Carbon nanotubes and nanoscale aluminum have been shown to be flash ignitable in loose powders or very porous low-density materials; however, these previous low-density formulations may not be as useful in practical energetic systems. In this study, nano aluminum particles are combined with a polyvinylidene fluoride binder/oxidizer in order to create a full-density photosensitive material. Using a low energy broadband flash source and an Nd:YAG laser at 1064 and 532 nm, films of nano aluminum and polyvinylidene fluoride were successfully ignited experimentally and ignition response was quantified. Solids loading was found to be the dominating factor controlling minimum ignition energies, with the lowest energies observed at 20 to 25 wt.% nAl. Simulations of the wave and particle interactions were modeled with COMSOL Multiphysics® for both the flash and laser-induced heating. The results show that optimal energy absorption occurs at nAl particle fractions of 20–25 wt.%, consistent with the experimental observation. Additionally, the results show the effect of plasmonic resonant enhancement of the heating, specifically at lower wavelengths near 250 nm.

Enhancing the stability and combustion of a nanofluid fuel with polydopamine-coated aluminum nanoparticles

In this experimental study, we examine the stability and combustion of a new nanofluid fuel created by mixing kerosene and nano-aluminum (n-Al) particles coated with polydopamine (PDA). Focus is placed on examining the effect of the PDA coating time, and hence the PDA film thickness, with the aid of a proposed heat transfer mechanism for the combustion of [email protected]/kerosene droplets. The results indicate that [email protected](1 h)/kerosene (i.e. a PDA coating time of one hour), which remains stable for seven hours, exhibits better stability than all the other samples, but that the stability worsens as the PDA coating time increases. The ignition character of n-Al/kerosene nanofluid droplets is not quite sensitive to PDA layer. The combustion processes of n-Al/kerosene and [email protected]/kerosene are remarkably similar, consisting of four distinct stages: ignition, classic combustion, vapor flame extinguishing, and Al droplet combustion. The burning intensity of n-Al agglomerates coated with PDA is stronger than that without PDA, with more black smoke generated and more n-Al particles expelled near the end of the n-Al burning stage. The combustion rates of kerosene droplets containing 5% [email protected](1 h) and 5% [email protected](2 h) are higher than other samples. The intensity of the emission spectra for the [email protected](2 h) agglomerates is the highest among all the samples. Taken together, these results indicate that, compared with uncoated n-Al/kerosene and other PDA-coated nanofluid fuels, [email protected](2 h)/kerosene exhibits superior ignition and combustion characteristics, opening new possibilities for tailoring Al-based nanofluid fuels.

A numerical investigation on heterogeneous combustion of aluminum nanoparticle clouds

This study investigated the heterogeneous combustion of nano-sized aluminum dust clouds. A numerical model was developed to capture the combustion properties of aluminum nanoparticle clouds by employing multiphase flow approach and combustion model of nano-aluminum particle. The simulation framework adopts an accurate modeling of heat convection in the transition and free-molecular regimes besides considering inter-particle radiation and surface reaction. The numerical model was validated by comparison against predicted/experimental results. The flame structure of nano-aluminum dust-air mixture has been demonstrated, whose flame thickness is thinner than their micron-sized counterparts. The ignition front propagation speed increases with raising equivalence ratio in the lean mixture and almost maintains a constant under fuel-rich conditions; and it raises with decreasing particle size and increasing oxygen concentration. The oxygen content plays a significant role on flame behaviors than the particle concentration and size. The flame temperature and feedback of heat from reaction zone to preheat zone plays a crucial role in ignition front propagating process.

The thermal decomposition behavior of the TNT‐RDX‐Al explosive by molecular kinetic simulation

AbstractThe TNT‐RDX‐Al Explosive is an aluminum‐containing mixed explosive often used in civil and military equipment, but the decomposition mechanism has not been theoretically studied. In this paper, the reaction force field containing C/H/O/N/Al parameters was used to simulate the thermal decomposition of the TNT‐RDX‐Al Explosive by reaction kinetics simulation. And the results were compared with the thermal decomposition behaviors of the binary systems TNT/AlO RDX/AlO and TNT/RDX. The partially passivated nano‐aluminum particles were constructed and then mixed with TNT supercell, RDX supercell, and the constructed TNT/RDX supercell. The obtained mixed systems were then heated to a high temperature, where the explosive was completely decomposed. The decomposition process of the TNT‐RDX‐Al Explosive can be divided into several stages: the adsorption of aluminum atoms on TNT molecules and RDX molecules, the diffusion of O atoms into nano aluminum particles, the decomposition of TNT molecules and RDX molecules, the diffusion of C, H, N atoms into the nano aluminum particles, the Al atoms in the center of the aluminum sphere diffuse outward, and the final stage is the formation of the final product. The results show that the aluminum nanoparticles in the ternary system are easier to diffuse and spreads more widely. The addition of RDX molecules advances the time to complete decomposition of TNT molecules, and promotes the time when TNT molecules is completely decomposed to be closer to the time when RDX molecules is completely decomposed.

An investigation on the dust explosion of micron and nano scale aluminium particles

A series of dust explosion were conducted to compare the flame structure between nano and micron aluminium dusts. Two-color pyrometer technique is applied to have qualitative observation of flame development. Measurement of temperature indicates that explosion in micron aluminium dust clouds start in a single spot at 3000 K, in contrast, explosion in nano aluminium dust clouds start when hot powder accumulated to a certain amount at lower temperature of 2600 K. For micron aluminium dust clouds, flame at leading edge has the highest temperature and propagates in all directions. On the other hand, flame in nano aluminium dust clouds propagate only upward with the hottest part left behind at the downside. As flame propagates, the temperature at top edge gradually decreases from 2600 K to finally 2000 K, but temperature at bottom edge maintains in 3000 K with no significant displacement. The unevenness of flame structure is considered as the consequence of different particle densities, which suggests that the reaction of nano aluminium particles stays in molten state, meanwhile, the high surface area also leads to unignorable heat loss.

Combustion characteristics of oxygenated slurry droplets of nano-Al/EtOH and nano-Al/TPGME blends

In this study, two oxygenated slurry fuels were prepared by blending nano-aluminum (Al) particles (5 wt%) with ethanol (EtOH) and tripropylene glycol monomethyl ether (TPGME), respectively. The prepared oxygenated slurries were suspended as droplets on a thermocouple wire, and a laser ignition testing system was used for investigating their combustion characteristics. Snapshots of the combustion process showed that a slurry droplet of nano-Al/EtOH suffered three continuous stages, namely, an ignition delay stage, a droplet combustion stage, and a core combustion stage. In contrast, a slurry droplet of nano-Al/TPGME suffered only the first two stages during its combustion; however, an additional microexplosion phenomenon was also observed. During the droplet combustion stage, nano-Al/EtOH blend displayed higher average burning rate, but lower droplet surface temperature than nano-Al/TPGME blend. Emission spectra indicated the formation of gas-phase intermediate products, namely, Al, AlO, AlO2, and Al2O, via nano-Al oxidation during the combustion of both types of oxygenated slurry fuels. Nano-Al/EtOH and nano-Al/TPGME blends displayed higher emission spectral intensity of AlO and AlO2, respectively. The normalized ignition delay time of nano-Al/EtOH droplets was 41.3% longer than that of nano-Al/TPGME droplets. However, the normalized total combustion time of nano-Al/EtOH droplets was 26.4% shorter than that of nano-Al/TPGME droplets.

Initial oxidation of nano-aluminum particles by H2O/H2O2: Molecular dynamics simulation

Molecular dynamics simulations on the reactions of nano-aluminum, water with different proportions of hydrogen peroxide were performed by ReaxFF. The reaction rate of the system increases by 27% as the molar ratio of H2O2 increases from 0 to 30%. The reaction paths in each period are elucidated by the change of the numbers of reactants and products. The reaction absorbs heat and releases isolated H atoms in the initial stage through pathways Al + 3H2O → Al(OH)3 + 3H and 3Al + 2H2O → 2AlO + AlH3 + H. Subsequently, H2O2 decomposes and releases O2 through 2H2O2 → 2H2O + O2 as the temperature rises to 350 K. And these O2 are rapidly involved in the formation of Al2O3, corresponding to the process 4AlO + O2 → 2Al2O3 and 2Al(OH)3 + 2AlH3 + 3O2 → 2Al2O3 + 6H2O. In the final stage, H2 molecules generated in accordance with the pathways of Al(OH)3 + AlH3 → Al2O3 + 3H2 and 2AlH3 + 3H2O → Al2O3 + 6H2. Particularly, the production of H2 decreases by 28.2%, 49.8% and 68.6%, as the molar ratio of H2O2 increases from 0 to 10%, 20% and 30%, respectively. Meanwhile, the reaction of Al/H2O/H2O2 releases much more energy (271.40–440.53 kJ/mol) than that of Al/H2O (180.67 kJ/mol). Moreover, the ignition temperature decreases with the increase of H2O2 concentration, but is proportional to the heating rate of ignition. When the molar ratio of H2O2 increases from 0 to 30%, the adiabatic flame temperature of the mixture increases linearly from 2400 K to 3000 K according to the adiabatic simulation.

Characterization of the influence of aluminum particle size on the temperature of composite-propellant flames using CO absorption and AlO emission spectroscopy

Understanding the temperature of aluminized, composite-propellant flames is critical to achieving robust rocket motor designs and developing accurate, predictive models for propellant combustion. This work presents measurements of (1) the temperature of CO (within the flame bath gas) and (2) the temperature of AlO (located primarily within regions surrounding the burning aluminum particles) within aluminized, composite-propellant flames as a function of height above the burning propellant surface. Three aluminized, ammonium-perchlorate (AP), hydroxyl-terminated polybutadiene (HTPB) composite propellants with varying aluminum particle size (nominally 31 μm, 4.5 μm, or 80 nm) and one non-aluminized AP-HTPB propellant were studied while burning in air at 1 atm. A wavelength-modulation-spectroscopy technique was utilized to measure CO temperature and mole fraction via mid-infrared wavelengths and a conventional AlO emission-spectroscopy technique was utilized to measure the temperature of AlO. The bath-gas temperature varied significantly between propellants, particularly within 2 cm of the burning surface. The propellant with the smallest particles (nano-scale aluminum) had the highest average temperatures and far less variation with measurement location. At all measurement locations, the average bath-gas temperature increased as the initial particle size of aluminum in the propellant decreased, likely due to increased aluminum combustion. The results support arguments that larger aluminum particles can act as a heat sink near the propellant surface and require more time and space to ignite and burn completely. On a time-averaged basis, the temperatures measured from AlO and CO agreed within uncertainty at near 2650 K in the nano-aluminum propellant flame, however, AlO temperatures often exceeded CO temperatures by ≈ 250 to 800 K in the micron-aluminum propellant flames. This result suggests that in the flames studied here, and on a time-averaged basis, the micron-aluminum particles burn in the diffusion-controlled combustion regime, whereas the nano-aluminum particles burn within or very close to the kinetically controlled combustion regime.

Energy release prediction and structure characterization of nano aluminum powder in situ coated by polyethylene glycol

In order to solve decreasing of reactivity of nano aluminum powder due to the alumina shell on the surface, used polyethylene glycol (PEG) as a coating material to obtain in situ PEG on nano aluminum particles with electrical explosion wires method. Based on the minimum free energy principle and BKW equation, the combustion and explosion performance of the coated sample is estimated. SEM and TEM to observe sample’s morphology and then used dynamic light scattering (DLS) nano-particle size analyzer to characterize sample’s particle size distribution. The chemical states of surface elements were analyzed by X-ray photoelectron spectroscopy. The thermal behavior of three samples were characterized by simultaneous thermal analyzer. The combustion heat, pressure-time curve, active Al content and vacuum stability was measured according to national standards. The results show that the coated sample was nearly sphere and particles were deduced multi-core structure. The active Al content reached 71.17% which is 12.53% higher than raw nano-Al particles. It was proved that PEG relieves oxidation of nano-Al, and the coating is stable. The coated samples can release energy more rapidly compared to micro-Al. The PVA in situ coated nano-Al particles has high active Al content and reactivity. Its application in energetic materials has good prospects.