Micron-sized Aluminum Particles Research Articles

Exploring the combustion mechanism of single micron-sized aluminum particles with a numerical model

In this work, we explore the combustion mechanism of single micron-sized aluminum particles using a numerical model. The Burcat database and Catoire mechanism is considered as the thermodynamic data and the kinetic mechanism for our numerical model of aluminum combustion. Two independent experiments, including particle temperature profiles, ignition delay and burning time, are selected to evaluate the performance of the numerical model. The model shows great agreement for all considered properties. A parametric study is further conducted to identify the effect of involved physical parameters on the combustion process. The diffusion coefficient (D) of oxidizers and the activation energy of surface kinetics (Esurf) and evaporation coefficient (α) of aluminum impact the particle temperature the most. Burning time is most sensitive to the activation energy of surface kinetics (Esurf). The optical measurement in a solid propellant combustion indicates that the contact angle of the oxide cap on Al particle is between 10° and 20°. It is found that the selection of contact angle of the oxide cap significantly impacts the prediction of combustion time and residual of active aluminum. The current work highlights the importance of physical properties on the prediction of Al combustion, suggesting that more detailed evaluation from experiments and theory is encouraged.

Study on laser ignition and combustion characteristics of micron-sized aluminum and Al-Mg alloys particles

In response to the problems of easy sintering and long ignition delay time of micron aluminum in the combustion of aluminum-containing propellants, choose the way to add magnesium to metal aluminum to construct an alloy system, through boiling, micro-explosions are generated during the ignition and combustion process to weaken the sintering behavior and shorten the ignition delay time of aluminum. Selecting aluminum and Al-Mg alloy powder fuel with a particle diameter of about 10 μm as the research object, a set of individual-particle fuel laser ignition and microscopic high-speed imaging experimental devices was built that can observe the whole process of ignition and combustion of micron-sized fuel. Thermal analysis was used to detect and characterize the thermal decomposition process of micron-sized aluminum and Al-Mg alloy powders; combined with the results of scanning electron microscopy, the difference in ignition performance of micron-sized individual particle aluminum and Al-Mg alloys was studied. Experiments have found that, compared with aluminum, the initial oxidation temperature of Al-Mg alloys is lower and the combustion is more complete. However, the effect of adding magnesium to aluminum is only reflected before 900 °C. The ignition and combustion images and flame propagation laws of micron-sized single-particle aluminum and Al-Mg alloys were obtained. It was found that adding magnesium shortened the ignition delay time, and the combustion produced less residual.

Predictive model for the ignition and combustion behaviors of micron-sized aluminum particles in a water vapor environment

Predictive model for the ignition and combustion behaviors of micron-sized aluminum particles in a water vapor environment

Study on the oxidation mechanism of micron- and nano-sized aluminum powders influenced by alumina shell

Thermal behaviors for aluminum particles at oxidative atmosphere gradually heating system were discussed. Heating micron- and nano-sized aluminum powders from room temperature to 1400℃ using thermal analysis method. The results showed that the reaction process for micron-sized aluminum particles can be divided into four stages which include the phase change of oxidized shell, increasing thickness of alumina shell, main broken shell oxidizing process and the phase change of alumina shell in high temperature. Thermal analysis for micro aluminum particles was carried out with shell thickness adjustments via ambient manual means. It turned out that the oxide layer thickness would have full limitation effects on the slow oxidation for micro aluminum particles with shell structure when it was increased above twice of the original thickness. The limitation effects of oxide shell thickness on the heating processes in gradually heating system were proposed. Humidity environment can make the thickness of alumina increase in a certain range when the particles are in nano-scale. Complete oxidation processes were observed but an increase of the oxidation temperature was identified.

Fabrication of alumina ceramic membrane supports using LCD 3D printing and titania nanoparticle doping

The integration of 3D printing technology into the production of ceramic membranes has garnered significant interest. Nonetheless, challenges persist in fabricating macroporous supports with both high porosity and strength through 3D printing. In this study, titania nanoparticles were introduced to facilitate the fusion of alumina nanoparticles. This freed the pores occupied by alumina nanoparticles and enhanced the connections between micron-sized alumina particles. Consequently, both the permeability and strength of the ceramic membrane supports were improved. The impact of ceramic slurry composition on photocuring performance, sintering processes, and the addition of titania nanoparticles on the microstructure and properties of the porous ceramic membrane support were investigated. The optimized membrane support featured a pore size of approximately 1.36 µm, achieving a porosity of 42.4% and a pure water permeance of 3700 L·m−2·h−1·bar−1. These findings provide a fundamental groundwork for subsequent endeavors in the development of high-performance ceramic membranes.

Numerical study on flame propagation of nano- and micron-sized aluminum dust combustion in air

A code was developed for numerical simulations of both nano- and micron-sized aluminum dust combustion in air. This code incorporates a combustion model that provides a comprehensive framework for modeling the burning of an aluminum particle under a transition regime, enabling accurate modeling of aluminum dust combustion across a wide range of particle sizes. The pseudo-transient approach was employed to solve the steady multiphase governing equations of aluminum dust combustion. The predicted variation trend of burning velocity with varying dust concentration exhibits good agreement with experimental measurements for both nano- and micron-sized aluminum dust combustion. Analyses exploring the effects of dust concentration, oxygen volume fraction and thermophoretic force on aluminum dust combustion were conducted. Simulation results indicate that introducing thermophoretic force in micron-sized aluminum dust combustion further enhances burning velocities and increases flame thicknesses compared to nano-sized aluminum dust combustion, primarily attributed to reduced gas entrainment of micron-sized aluminum particles.

NUMERICAL SIMULATION OF THE INTERACTION OF HETEROGENEOUS DETONATION WITH THE POROUS INSERT OF DIFFERENT GEOMETRY

Numerical simulation of interaction of heterogeneous detonation with a porous insert was carried out. The mathematical model for porous inserts assumed that the porous zone was a continuous medium in the form of a grid of stationary cylinders. Main regimes and critical conditions of detonation attenuation in porous zones were obtained for micron-sized aluminum particles. Main features of the flow field in the channel were described. It was found that for micron particles in the empty space, a planar detonation wave formed. Main patterns for micron-sized combustible particles and inert porous zone were found. The critical height of the empty space without porous inserts was determined. The critical height of the empty space did not depend on the amount of open areas in the porous zone. The critical height did not depend on the width of the channel. For micron-sized particles, a physical explanation for the existence of planar detonation based on the values of thermal relaxation times is proposed.

Improving ignition and combustion performance of Al@Ni in CMDB Propellants: Effect of nickel coating

Micron-sized aluminum particles tend to melt into agglomerates, leading to incomplete combustion, two-phase flow losses, and energy decrease of propellants. The higher ignition performance of core–shell Al@Ni makes it a promising candidate fuel with high combustion efficiency. However, little work has been done to study the combustion of Al@Ni in propellants. Here, we report a first attempt to investigate the combustion mechanism of core–shell Al@Ni in the double-based propellant containing high energy explosive HMX, and evaluate its potential as a fuel. Nickel in Al@Ni is determined to play a critical role during its intrinsic combustion and the combustion in propellants. In the condensed phase, the presence of Ni enhances the oxidation process by forming a porous oxide layer on the aluminum surface that promotes oxygen diffusion. Subsequently the phase transition and expansion of Ni break down this oxide layer, leading to the earlier ignition on the burning surface. Upon Al melting, the alloying of Ni and Al accelerates the volume expansion and surface tension reduction of the fuel, giving rise to vigorous melt-dispersion combustion and enhanced energy release. Enhanced thermal feedback and thermal decomposition exotherm combined to increase the burning rate of propellant. The resulting higher flame temperature allows the evaporation of small aluminum droplets into vapor to form smoke oxide productions, further reducing the size distribution of the condensed combustion products (CCPs). This study demonstrates the potential of Al@Ni as an effective fuel for double-based propellants, and provides the insight into its combustion mechanism in HMX-CMDB propellants, which is believed to be important for the development of novel aluminum-based fuels for solid propellants.

Influence of micron-sized aluminum particles on micro-explosion and combustion characteristics of ethanol-biodiesel droplets under co-heat flow

• The characteristics of droplets doped with micron-sized particles were studied. • Increasing the particle size will promote the micro-explosion phenomenon. • The droplet heating time will vary due to changes in particle content. • The particle content of the optimal micro-explosion intensity is about 20%. As a high-energy metal fuel, aluminum powder particles (AP) have long been used as fuel propellants and combustion-supporting additives in explosives to meet the design requirements of a new generation of high-energy–density fuels. In this experiment, the micro-explosion and combustion characteristics of ethanol-biodiesel mixed droplets with different aluminum powder particle contents and particle sizes were studied under high temperature and pure oxygen environment. In order to better control the experimental variables, a more accurate single-droplet suspension method was adopted in this experiment. The entire evaporation and combustion process of the mixed fuel was completely recorded and analyzed by using high-speed photography technology, binarization imaging technology and droplet optimization algorithms. The experimental results show that when the content of aluminum powder particles remains unchanged, increasing the particle size of aluminum powder in the mixed droplets will promote the micro-explosion phenomenon. When the particle size of the aluminum powder contained in the mixed fuel is different, the increase of the particle content will have a completely different effect on the heating time of the droplet. When the particle size of aluminum powder particles is small, the combustion duration of the mixed droplets increases with the increase of aluminum powder content, while the opposite results are shown when the aluminum powder particles are larger. Increasing the amount of aluminum powder also extends the full life of the droplets. In addition, this study introduces the microburst intensity (MI), which provides a new idea and method for laterally comparing the microburst phenomena of fuel droplets with different initial diameters. For mixed fuel containing micron-sized aluminum particles, the particle content that produces the best micro-explosion intensity is about 20%.

Ignition and combustion of a dense powder jet of micron-sized aluminum particles in hot gas

Aiming at the potential implementation of aluminum as a primary fuel in powder-fueled ramjets or engines, this work seeks to investigate the ignition and combustion characteristics of a dense gas-suspended jet of micron-sized aluminum particles in a hot flow with controlled temperature and compositions. Aluminum particles with a mean diameter of 40 µm are aerosolized using a custom-made feeder and carried into the burner by a nitrogen stream. The powder jet with a particle density of up to 1–3 kg/m3 can be ignited and burned violently at a surrounding gas temperature as low as 1500 K. The lowered ignition temperature of the powder jet can be attributed to a cooperative mechanism resulting in fast reactions. Meanwhile, the ignition delay time decreases from ∼25 to ∼5 ms when the surrounding temperature increases from 1500 to 2200 K. The burning powder jet generates strong luminance and AlO emission signals detected by a spectrometer. Particle image velocimetry (PIV) and camera pyrometry are used to derive the two-dimensional velocity and average projected temperature distribution, respectively. Furthermore, a high-speed camera with a microscopic lens captures the transition from dispersed combustion to group combustion that forms a large-scale flame column wrapping the entire powder jet. The aluminum oxide produced in the columnar flame forms a large number of nanosized smoke particles in the condensation region. Finally, a numerical model considering the collective effect of the powder jet is developed to predict the particle temperature history during the ignition stage, which shows good agreement with the temperature profiles derived from camera pyrometry and PIV techniques.

27Al Solid-State Magic-Angle Spinning NMR Studies of Aluminum Powder Particle Surfaces Treated with a Methyltriethoxysilane Coupling Agent under Acidic Conditions

We report on the reaction between methyltriethoxysilane (MTES) and micrometer-sized aluminum particles, facilitated by HCl. This reaction ultimately produces silane-coated aluminum particles. Using 27Al magic-angle spinning solid-state nuclear magnetic resonance, we find that aluminum powder starts with a mixture of tetrahedrally, pentahedrally, and octahedrally coordinated aluminum, with the pentahedral species dominating. In the presence of HCl, however, the aluminum undergoes a restructuring, so that octahedrally coordinated aluminum is the dominant species. Using diffuse reflectance infrared spectroscopy to confirm the deposition of silane, we find that this restructuring of the aluminum in the presence of HCl is both a sufficient and necessary condition for the deposition of the silane.

On Modeling the Combustion of a Single Micron-Sized Aluminum Particle with the Effect of Oxide Cap.

The formation of oxide cap, which results from the condensation of gaseous aluminum oxide, makes a non-negligible impact on the combustion process of micron-sized aluminum particles, but its growth and effect are still unknown. Also, the transition of combustion modes during the combustion process, which affects the growth rate of the oxide cap, needs to be explored. Therefore, a detailed combustion model of a single micron-sized aluminum particle is developed to predict the transition of combustion modes and the effect of the oxide cap. This combustion model consists of a vapor-phase kinetic model and a particle model coupled by the Strang splitting algorithm. The predicted ignition delay and combustion times are compared with experimental data to validate the combustion model. Three combustion modes including vapor-phase, transitional, and surface combustions are considered in this combustion model. We find that the two modes coexist for particles between 100 and 200 μm when the ambient temperature and pressure are 2500 K and 1 atm, respectively. A higher ambient temperature extends the transition of combustion mode toward smaller sizes. An oxide cap model considering surface free energy is proposed to study the growth and effect of the oxide cap on the combustion process of micron-sized aluminum particles. We find that the formation of oxide cap limits the evaporation rate of aluminum directly due to the reduced active surface area. The oxide cap stabilizes the evolution of particle temperature and determines the burning time. The predicted burning time is reduced by a factor of 2 at least considering the growth of oxide cap.

Experimental Study of Combustion Characteristics of Micron-Sized Aluminum Particles and Liquid Water

Experiments have been performed to explore the combustion behaviors of spherical micron-sized aluminum (Al) particles and liquid water for Al particle sizes in the range of . The ignition of quasi-homogeneous Al/water mixtures was successfully implemented by employing a novel ignition method, and self-sustained flame propagation was obtained in the mixtures over a broad range of fuel-equivalence ratio . The burning rates, flammability limits, and thermal structure of the propagating flame were determined. The combustion products were also analyzed. For the particle sizes considered, the burning rates were found to first increase and then decrease as increased, with the maximum values occurring at and substantially lower than nano- mixtures. The dependence of the burning rate on particle size follows a power law, , indicating that the reaction process of and water is kinetically controlled. Base on the experimental observations, a simplified flame propagation model was developed to provide insight into the effects of particle size and equivalence ratio. Combustion product analyses revealed that Al residues increased as was further increased from 0.7, and the combustion efficiency of aluminum decreased accordingly.

Temperature measurements and high-speed photography of micron-sized aluminum particles burning in methane flat-flame exhaust

This work seeks to investigate the ignition and burning of micron-sized aluminum particles using nonintrusive temperature measurements and high-speed photography. First, the detected emission spectra were used to deduce the particle temperature according to Planck’s laws, and the emissivity dependence on the wavelength was determined. Second, the ratio pyrometer method using a Nikon digital camera was developed to specify the two-dimensional temperature profile. These two methods were preliminarily validated through a B-type thermocouple of known temperature. Further, aluminum particles with controlled sizes of approximately 45 and 125 µm were injected as a well-dispersed stream or discrete single particles, respectively, into the hydrocarbon combustion exhaust with controlled gas temperature and compositions. The temperature evolutions of 45 µm aluminum particles derived from the camera pyrometer are in reasonable agreement with the numerical results predicted by a previously developed model. Regarding 125 µm particles, the temperature contour shows a sharp temperature increase and flame expansion during ignition. It can be attributed to the transition from surface reaction to more vigorous combustion in the vapor phase, which was visualized by a high-speed camera equipped with a long-distance microscopic lens. In this work, the camera pyrometer has demonstrated the capability of measuring the average projected particle temperature and characterizing the combustion process of micron-sized aluminum particles, with promising simplicity and economy.

Experimental study on the collision behaviors of micron-sized aluminum droplets with solid wall in high temperature burned gas

The collision and deposition behaviors of aluminum/alumina droplets on a solid wall play a crucial role in improving the engine performance of a solid rocket motor (SRM). This study employed a high temperature oxy-methane flame and a solid wall to simulate the environment of SRM. Micron-sized aluminum particles were axially added into the flame and they were melted and ignited before collision with the wall. The velocities of the particles were varied by adjusting the flow rates of gaseous reactant and the collision angle was adjusted by arranging the solid wall layout. The dynamic deforming process of micron-sized droplets colliding on a hot wall was observed by high speed photography. And thousands of droplets were tracked to examine the deposition probability on the hot wall. The results show that the collision velocity, angle and particle size codetermine the post-collision behaviors, which typically include rebound, deposition and splashing. The heat transfer between the droplet and wall plays an important role in the deposition process. By further considering the component of the condensed droplet, the dimensionless parameter of normal Weber number has been proposed to quantify the deposition rate. And an empirical formula has been obtained by employing the Weber number and collision angle.

Detonation flows in aluminium particle gas suspensions, inhomogeneous in concentrations

A physical and mathematical model of the reduced kinetics is presented describing heterogeneous detonation in suspensions non-uniform in particle concentration. The model is based on the heterogeneous media approaches, semi-empirical laws of ignition and combustion, and data on the dependence of the detonation velocity on particle concentration. Formation of suboxides and incomplete combustion of aluminum are taken into account integrally. The dependence of the heat release of chemical reactions and the fraction of unburnt particles on the initial composition is determined from the solution of the stationary problem of the structure of the detonation wave. In the calculations of unsteady detonation flows, it is supposed to solve an additional equation for the spatial distribution of initial concentrations. The problems of initiation and development of cellular detonation in flat channels in suspensions of micron-sized aluminum particles are studied. Dependences of the cell size on particle concentration in uniform suspensions are determined. The flow patterns of cellular structures, the forms of the leading front, and the propagation velocities in channels with longitudinal or transversal gradients of particle concentration are analyzed.

Effects of the Particle Size and Gas Environment on Afterburning Reactions and Explosion Performance of Aluminized HMX-Based Explosives

In this paper, confined explosions of HMX-based aluminized explosives in a spherical chamber are studied. The effects of aluminum particles on the afterburning reaction and explosive performance are obtained by changing the size of the particles and the gas environment. The results show that the concentration of oxygen in air is not sufficient to support complete combustion of aluminum particles. The estimated oxidation rate of aluminum particles is 87–93%, and it tends to decrease with increasing particle size. Part of aluminum particles oxidize with detonation products, and the reaction can last for hundreds of microseconds. However, the degree of oxidation between the large-sized aluminum particles and detonation products is small. A new method is used to estimate the initial energy of detonation by observing the time difference between sensing the initial light and the pressure wave. This method leads to a conclusion that some of the aluminum particles are oxidized during detonation and provide additional energy to the primary blast wave. Small micron-sized aluminum particles in the range of 48.9 nm to 46.7 $$\mu$$ m extend the duration of the fireball.

The Simulation of Different Combustion Stages of Micron-sized Aluminum Particles

In this study, a quasi-steady combustion model of an aluminum particle is established, which is more accurate to simulate the physical combustion process. Detailed gas-phase reaction mechanism and surface reaction mechanism are considered. Moreover, the particle temperature is not constant in this work, which is calculated in different combustion stages. The judgement standard of each combustion stage is from observational data in the experiment and the simulation results of combustion durations of each stage, and distribution of ambient temperature and gas-phase species profiles are in good agreement with experimental results. The calculation results show that in the first stage, burning rate of the particle is the fastest, and in the second stage, particle temperature can drop to more than 100 K below the boiling point for the large particles, which is slightly below the boiling point for small ones. As the combustion stage changes, Da number is going to keep going down, which will lead to the transition of combustion method from diffusion-limited control to kinetic-limited control for an aluminum particle.

Particle surface effects on the spall strength of particle-reinforced polymer matrix composites

Prior research has observed that the presence of secondary phases in metal alloys influence the failure behaviour of the bulk material, a response which varies based on secondary phase morphology and adhesion to the matrix material. Particle-reinforced polymer composites offer a material system in which variations in adhesion between the sub-phase and polymer matrix can be manipulated with relative ease. In the present study, we investigate the influence of both the particle morphology and matrix-particle interface adhesion on the spall strength of particle-reinforced polymer composites. Adhesion control was achieved using a adhesion-impeding silane treatment of the surface of micron-sized alumina particles. The composites were characterized based on their dynamic tensile (spall) failure strengths. The results showed that while particle morphology effects were minimal, the loss of surface adhesion resulted in a drastic reduction in spall strength. Fractography performed on the fracture surface of the recovered samples showed evidence of poor wetting in the silane-treated composites, confirming the role of particle adhesion in moderating this failure mode.

Fracture toughness of alumina filler filled glass fabric reinforced epoxy composites

Micron sized alumina particles (≤10 µm) are incorporated between the plies of a conventional glass fabric reinforced epoxy (GE) composite to improve the fracture toughness ( K IC ). The influence of the alumina filler content (0, 7.5, and 10 wt%) on K IC are investigated. These composites are prepared by hand layup assisted by the vacuum bagging method. The prepared composites are evaluated for K IC at room temperature, elevated temperature (100 °C) and at cryogenic temperature (−15 °C). The K IC test was conducted utilizing single notched edge bend specimen under mode I according to ASTM D5045 standard. The test results indicated that K IC of GE is improved by addition of alumina particles. Furthermore, these composites maintained higher K IC at −15 °C and decreased significantly at elevated temperature. The maximum K IC is recorded at particle loading of 10 wt% GE hybrid composite.