Micron-sized Aluminum Powder Research Articles

Experimental investigation on synergistic slow oxidation and rapid combustion of micron-sized iron and aluminum powders for energy storage application

The investigation into the individual application of iron and aluminum as carbon-free fuel sources has been extensively explored and holds significant promise. However, there remains a gap in understanding synergistic effects achievable through the blending of these two fuels, as well as a need for comparative analyses between the slow oxidation and rapid combustion processes of these fuels to complement each other. This research proposes blending micron aluminum and iron powders to analyze their slow oxidation and rapid combustion features under diverse atmospheric conditions and heating rates, using thermogravimetric methods, kinetic calculations, and in-flow experiments. The research blending micron iron and aluminum powders to analyze their slow oxidation and rapid combustion features under diverse atmospheric conditions and heating rates, using thermogravimetric methods, kinetic calculations, and in-flow experiments. The findings reveal that the combination of aluminum and iron powders promotes oxidation, resulting in increased weight gain and heat flux rate compared to individual metals. Moreover, the triggering temperature rises from 545 to 652 °C with an increase in aluminum powder content. As heating rates increase, characteristic parameters T1, T2, and Hpeak2, rise for both fuels. However, aluminum powder tends to decrease Ti, while iron powder slightly increases it due to differences in oxide layers. The slow oxidation of aluminum and iron powders conforms to different models, yielding distinct oxidation patterns. The apparent activation energy of aluminum decreases from 258.4 to 238.7 kJ·mol−1 with rising heating rates, while that of iron exhibits a lower increase and remains lower than aluminum providing insights into combustion initiation conditions. Combustion initiation is contingent upon the concentration of metal powder and oxygen, with both aluminum and iron powders combustion being enhanced and subsequently attenuated with increasing excess air ratio. However, due to differing reactivity and surface passivation layers, the excess air ratio required for aluminum powder combustion (1.2–2.4) exceeds that of iron powder (1.3–1.7). The research elucidates the mechanisms underlying the slow oxidation of iron and aluminum fuels, delineates suitable combustion conditions, and furnishes new empirical and theoretical underpinnings for the oxidation characteristics of mixed iron-aluminum fuels, thereby advancing metal-fueled energy storage technologies.

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.

Ignition and combustion characteristics of aluminum-based fluorine-containing composite powder

To improve the combustion characteristics of micron-sized aluminum (Al) powder, a composite powder was prepared by doping a small amount (15 wt%) of magnesium fluoride (MgF2), polytetrafluoroethylene (PTFE), and fluorinated graphite (FG) into the aluminum powder through solution dispersion method. The physical phase composition, micro morphology, thermal reactivity, and combustion performance of the composite powders were also characterized. The findings suggest that the promoting effect of the three fluorides on aluminum combustion can be ranked in the following descending order: FG > PTFE > MgF2. The fluorides can to erode the Al2O3 shell layer directly, thus creating cracks and reaction pathways for the Al core enclosed within the shell. Moreover, the gasification of AlF3 within the combustion products can escape from the surface of Al particles and promote the oxidation combustion of the exposed aluminum, which enhances the diffusion reaction on the active aluminum surface.

Thermal enhancement of the oxidation layer of micron-sized aluminum powder and its anti-oxidation performance

Micron-sized aluminum powder, with its typical core-shell structure, exhibits oxidation behavior upon slow heating in an oxidative atmosphere that is related to the particle size of the aluminum powder. A particle size-dependent thermal response mechanism for micron-sized aluminum powder is established: a "shell-breaking eruption" thermal response mechanism. The oxide layer is thermally enhanced, and the anti-oxidation reaction behavior mechanism of the enhanced samples is studied. Aluminum powder samples, heated slowly to specific temperatures to obtain changes in the oxide layer structure, are analyzed using a thermal analyzer to compare the slow heating response behavior of aluminum powder before and after the oxidation layer changes. It was found that after thermal enhancement of the aluminum powder oxidation layer, which changed from amorphous to γ-phase and whose thickness increased to twice the original thickness, the slow oxidation process of micron-sized aluminum powder was inhibited, and the aluminum powder was completely deactivated in the slow heating response.

Reaction mechanism of micron-sized aluminum powders in O2 and CO2 gradually heated environment

The behavior of aluminum powders in specific oxidized environment is different from each other obviously. Thermal behaviors of micron-sized aluminum powders in different oxygenated and gradually heating environments were discussed in order to find out the oxidation mechanism. Particular attention is paid to the reaction mechanism of oxygen and carbon dioxide atmosphere. Thermogravimetric analysis and related characterization methods are used and the results demonstrated that under the certain condition, reaction process of micron-sized aluminum powders can be divided into four stages. General routes for the oxidation of micron-sized aluminum in general heating system are the same, however, itis different among the extent of reaction at the third stage in different kinds of oxidizing gas atmospheres. Gas phased products were detected during the main reaction stage under carbon dioxide by combining thermal analysis and mass spectrometry which contributes to the rupture of alumina shell and further reaction of micron-sized aluminum powders. Consequently, rapider and more complete reaction process was achieved. The increasing thickness of original alumina shell can restrict the reaction rate of aluminum powders harder at the same time.

Unusual Size Effect in Ion and Charge Transport in Micron‐Sized Particulate Aluminum Anodes of Lithium‐Ion Batteries

Aluminum is a promising anode material for lithium-ion batteries owing to its high theoretical capacity, excellent conductivity, and natural abundance. An anomalous size effect was observed for micron-sized aluminum powder electrodes in this work. Experimental and theoretical investigations reveal that the insulating oxide surface layer is the underlying cause, which leads to poor electrical conductivity and limited capacity utilization when the particle is too small. Additionally, poor electrolyte wettability also accounts for the hindered reaction kinetics due to the weak polarity feature of the oxide layer. Surface grafting of polar amino groups was demonstrated to be an effective strategy to improve electrolyte wettability. The present work revealed the critical limitations and underlying mechanisms for the aluminum anode, which is crucial for its practical application. Our results are also valuable for other metallic anodes with similar issues.

Oxidation Mechanism of Core-Shell Structured Al@PVDF Powders Synthesized by Solvent/Non-Solvent Method.

Micron-sized aluminum (Al) powders are extensively added to energy-containing materials to enhance the overall reactivity of the materials. However, low oxidation efficiency and energy release limit the practical application of Al powders. Polyvinylidene fluoride (PVDF), the most common fluoropolymer, can easily react with Al to form aluminum fluoride (AlF3), thus promoting the oxidation of Al powders. In this paper, core-shell structured Al@PVDF powders were synthesized by solvent/non-solvent method. Thermal analysis results show that the weight and exothermic enthalpy of Al@PVDF powders are 166.10% and 11,976 J/g, which are superior to pure Al powders (140.06%, 6560 J/g). A detailed description of the oxidation mechanisms involved is provided. Furthermore, constant volume pressure results indicate that Al@PVDF powders have outstanding pressure output ability in the environment of 3 MPa oxygen. The study provides a valuable reference for the application of Al powders in energetic materials.

Ignition sensitivity and explosion behaviors of micron-sized aluminum powder: Comparison between flake aluminum powder and spherical aluminum powder

The addition of aluminum powder can increase the energy of the combustion system. The spherical aluminum powder can be flaked by the ball milling technology, which can remove the oxide layer on the particle surface and improve the reaction activity. However, the ignition sensitivity and thermal behavior of flake aluminum powder should arouse extensive attention. In this paper, experimental measurements and statistical analysis are carried out for the ignition characteristics and explosion mechanism of micron-sized flake and spherical aluminum powder. Because the oxide layer is an important component in the oxidation process of aluminum powder, a theoretical model to calculate its equivalent thickness and fracture conditions is proposed. Moreover, the surface effect has a significant impact on intensifying the explosion hazard. For micron-sized aluminum powder, the relationship between ignition temperature and particle size is as follows: Ti∝d320.2. The maximum rise rate of explosion pressure for flake aluminum powder is 4.19 times than that for large spherical aluminum powder. Furthermore, the MEC results corresponding to the ignition probability are obtained by using the Logistic regression model. Present work recommends that the safety design should be based on the MEC prediction result of p = 0.5.

Sodium fluoroaluminate promoting the combustion of micron-sized aluminum powder with different particle sizes in carbon dioxide

To improve the ignition and combustion performance of micron-sized aluminum powder (m-Al) in CO2, a self-made pipe furnace experimental platform was established to study the effects of sodium fluoroaluminate (Na3AlF6) on the ignition delay times, combustion processes, combustion efficiencies, and combustion products of 1–2, 5, and 30 μm aluminum (m-Al1, m-Al5, and m-Al30) powders in CO2 at 1000 °C. The combustion phenomenon was recorded by a high speed camera. The ignition delay time was obtained by post-processing the sequential images. m-Al containing Na3AlF6 has a lower initial reaction temperature and a shorter ignition delay time than those of m-Al without Na3AlF6 addition. The effect of Na3AlF6 content on the ignition delay time is different for m-Al with different sizes. The ignition delay times for m-Al1 and m-Al5 increase with increasing the Na3AlF6 content, while the corresponding values of m-Al30 first increase and then decrease. The combustion products were subjected to the analyses of morphology, composition, and combustion efficiency. The oxidation shell of Al is fluorinated by Na3AlF6, thereby promoting its ignition and burning. The combustion efficiency of m-Al is significantly enhanced, especially for m-Al30. The effect mechanism of Na3AlF6 on the ignition and combustion of m-Al in CO2 was discussed.

Experiment on the flammability variation of micron-sized aluminum powder depending on combustion environment for burning of aluminum-diluted oxygen

Experimental research was conducted to study the combustion characteristics of clouds composed of micrometer-sized aluminum particles with an oxidizer blend of oxygen and superheated steam. Both ignition and combustion of an aluminum particle are difficult because it is enveloped by an oxide layer that has a high melting point (above 2300 K). To overcome the problem, we induced a particular shape of the combustor that can keep a stable flame of aluminum dust clouds at a lower feeding-rate. The combustion characteristics were examined using a system applied combustor involving a variety of parameters affecting the burning of the dust clouds. Based on these attempts, the aluminum dust clouds had an upper flammability limit above the equivalence ratio (Ф) 1.9 for oxygen diluted by air. Varying the lower limit of flammability, we found, crucially, that the feeding-rate and velocity of the particles are more effective than the equivalence ratio or combustor length. Furthermore, we could confirm the changing of the lower limit from 0.3 to 0.26 because the steam was additionally fed in the combustion of aluminum-oxygen.

Comparison on Laser Ignition and Combustion Characteristics of Nano- and Micron-Sized Aluminum

ABSTRACT This paper presents a comparative study on the laser-induced ignition and combustion characteristics between nanometer-sized aluminum (nano-Al) and micron-sized aluminum (micro-Al) powder stacks. Six different sizes of Al powders (56.0 nm, 74.4 nm, 93.4 nm for nano-Al and 2.9 μm, 6.1 μm, 10.8 μm for micro-Al) were selected to conduct ignition and combustion experiments, at the same operation conditions in the static air flow with atmospheric temperature and pressure and 55% relative humidity. The results demonstrated that ignition delay time of nano-Al is much lower than that of micro-Al. The size of nano-Al has a weak effect on ignition delay time. Whereas, the size of micro-Al has an exponential effect on ignition delay time. The combustion of nano-Al is more intense and the self-maintenance performance is better than micro-Al. Finally, a comparative model on the ignition and combustion difference between nano-Al and micro-Al was built, which comprehensively considers the influences of particle core size, oxide shell thickness and porosity. This study will be helpful to recognize the difference of ignition and combustion characteristics between nano-Al and micro-Al and promote the application in solid rockets.

Influence of the Amount of Fe2O3Modifier on the Oxidation Rate of ASD-4 Micron-Sized Powder

The effect of the modification of ASD-4 micron-sized aluminum powder by iron oxide on its oxidation in air was investigated. The metal particle surface was modified by coating with a gel based on Fe(OH)(HCOO)2 and ethylene glycol monomethyl ether, CH3OC2H4OH, with subsequent heat treatment in air. It was found that the presence of iron oxide generally had a positive effect on the oxidation dynamics of ASD-4 powder under heating in air. The oxidation rate of modified powders increases with increasing content of iron oxide in them. X-ray diffraction analysis using a synchrotron radiation source under heating to 1000°C showed the presence of only the basic phases of $$\gamma$$ -Al2O3and $$\alpha$$ -Al2O3, $$\gamma$$ -Fe2O3, and $$\alpha$$ -Fe2O3in the samples, and other iron oxides or intermetallic compounds were not detected. At a mass concentration of 10% Fe, an earlier appearance of the $$\alpha$$ -Al2O3phase was observed and the exothermic heat release peak was shifted to lower temperatures (893°C) compared to the unmodified ASD-4 powder (1045°C).

Minimum ignition temperatures and explosion characteristics of micron-sized aluminium powder

To forestall, control, and mitigate the detrimental effects of aluminium dust, a 20-L near-spherical dust explosion experimental system and an HY16429 type dust-cloud ignition temperature test device were employed to explore the explosion characteristics of micron-sized aluminium powder under different ignition energies, dust particle sizes, and dust cloud concentration (Cdust) values; the minimum ignition temperature (MIT) values of aluminium powder under different dust particle sizes and Cdust were also examined. Flame images at different times were photographed by a high-speed camera. Results revealed that under similar dust-cloud concentrations and with dust particle size increasing from 42.89 to 141.70 μm, the MIT of aluminium powder increased. Under various Cdust values, the MIT of aluminium dust clouds attained peak value when concentrations enhanced. Furthermore, the increase of ignition energy contributed to the increase of the explosion pressure (Pex) and the rate of explosion pressure rise [(dP/dt)ex]. When dust particle size was augmented gradually, the Pex and (dP/dt)ex attenuated. Decreasing particle size lowered both the most violent explosion concentration and explosive limits.

Combustion of Aluminum and Boron Agglomerates Free Falling in Air. I. Experimental Approach

This paper presents a review of studies of the combustion of composite propellants containing a combined fuel based on aluminum and boron. A method for studying the combustion of large particles of the combined Al + B fuel in air is described. Burning agglomerated Al/B particles 300–700 μm in diameter were obtained by ignition of miniature pieces of a composition containing 32% binder and 68% micron-sized aluminum and boron powders in the ratio Al/B = 81/19 placed in a burning metal-free sample. Agglomerates formed by the merger of many small particles burned in free fall in air. Procedures are described that were used to process video records of the combustion process and study condensed combustion products (combustion residues of agglomerates) in order to determine the burning time and analyze the transformation of the combined fuel into oxide.

Enhancing ignition and combustion characteristics of micron-sized aluminum powder in steam by adding sodium fluoride

Micron-sized aluminum powder exhibits difficulties in ignition and burnout in steam. To overcome these problems, we added various sodium fluoride contents to micron-sized aluminum powder in steam at 800, 900, and 1000 °C to assess their effects on ignition and combustion performances. The ignition delay times, ignition temperatures, and combustion characteristics of all samples were measured primarily using two high-temperature tube resistance electric furnace systems. The experiments showed that adding sodium fluoride to micron-sized aluminum powder decreases its ignition delay time and temperature. Moreover, the ignition delay time and temperature of aluminum powder with addition of sodium fluoride decreases considerably when the temperature increases. For this study, the components and morphology of solid combustion products were obtained using X-ray diffraction and scanning electron microscopy. The combustion efficiency was measured volumetrically using a specially designed apparatus. The obtained combustion efficiency was found to increase with the amount of sodium fluoride added and increase in the temperature. The relationship among the parameters related to combustion characteristics and product characterization was examined in detail to reveal the combustion mechanism.

Thermal Reaction Characteristics of Nano/Micron-Sized Aluminum Mixtures in Carbon Dioxide

Thermal reaction characteristics of nano/micron-sized aluminum mixtures in a carbon dioxide atmosphere were investigated by thermogravimetry that aimed to examine the interactions between nanosized aluminum powder and micron-sized aluminum powder. Thermal reaction characteristics of nano/micron-sized aluminum mixtures at different ratios were studied. The synergistic effect mechanism was discussed by comparing experiment result and theoretical calculation. The morphologies and compositions of products were obtained by scanning electron microscopy and X-ray diffraction technologies. Results indicated that there were three weight gain stages for nano/micron-sized aluminum mixtures at different ratios. Although the temperature range of synergistic effect of nano/micron-sized aluminum mixtures with various ratios had somewhat differences, there was a significant synergistic effect from about 900 to 1040°C. The products analyses indicated that the products morphologies of nano/micron-sized aluminum particles showed molten and stuck together, and products contained aluminum and α-Al2O3.

Study of Ignition of High-Energy Materials with Boron and Aluminum and Titanium Diborides

This paper describes the ignition of high-energy materials (HEMs) on the basis of ammonium perchlorate and ammonium nitrate and an energetic binder, containing the powders of Al (base composition), B, AlB2, AlB12, and TiB2, upon initiation of the process by a CO2 laser in the heat flux density range of 90–200 W/cm2. The ignition delay time and surface temperature of the reaction layer during the heating and ignition of HEMs in air are determined. It is obtained that the complete replacement of a micron-sized aluminum powder by amorphous boron in the composition of HEMs significantly reduces the ignition delay time of the sample (by 2.2–2.8 times) with the same heat flux density, and this occurs due to the high chemical activity of and difference between the mechanisms of oxidation of boron particles. The use of aluminum diboride in HEMs reduces the ignition delay time by 1.7–2.2 times in comparison with the base composition. The ignition delay time of the HEM sample with titanium diboride decreases slightly (by 10–25%) relative to the ignition delay time of the base composition.

Utilization of Mechanically Activated Aluminum in Hybrid Rockets

Polytetrafluoroethylene is known to enhance the reactivity of aluminum. The enhancement in the reactivity is produced by mechanically activating the aluminum using polytetrafluoroethylene. In this study, mechanically activated aluminum powder is used along with paraffin wax as the fuel grain for a hybrid propellant. Here, gaseous oxygen is used as oxidizer. To achieve an optimum composition for the best specific impulse, the aluminum fraction in the composition is restricted to 50% of the base fuel composition along with 50% wax/ethylene vinyl acetate (combination of wax and ethylene vinyl acetate, in a ratio of ). The polytetrafluoroethylene in mechanically activated aluminum powder is added at the expense of wax/ethylene vinyl acetate in the fuel composition. When compared with the composition having pyral aluminum powder (which has flake like particles of very high specific surface area), mechanically activated powder increases the fuel regression rate by at an oxidizer mass flux of -s. It is also observed that the combustion efficiency of the hybrid motor is 59% with the use of mechanically activated aluminum powder in comparison to 39% obtained with micron-sized aluminum powder.

Experimental Study and Numerical Investigation of the Phenomena Occurring During Long Duration Cold Spray Deposition

Low Pressure Cold Spray process is a relatively new additive technique allowing to create high quality metallic coatings, through the high velocity spraying of particles, on both metallic and non-metallic substrates. The adhesion mechanism of the particles is, to date, not fully understood and the phenomena occurring during long depositions (which are the more interesting for industrial processes) are not known and studied in details. Aiming to fulfill this lack of knowledge, the phenomena occurring during long deposition were studied through both careful experimental evaluations and numerical approach. Particular attention was paid at the working conditions of the De Laval nozzle system which accelerates the particles, a computational fluid dynamics model focusing on both geometrical features and spray behavior was proposed. Micron-sized aluminum powders and compressed air as carrier gas were used in this experimentation, numerical simulations are performed to predict the gas flow regime. It has been found that the deposition efficiency tends to decrease due to the critical phenomena occur into the spray nozzle during long time depositions. The sprayed particles tend to stick to the walls of the nozzle and, moreover, shock waves occur inside the nozzle further promoting the particles stick phenomena, making the system inefficient.

Oxidation mechanism of micron-sized aluminum particles in Al-CO2 gradually heating system

Micron-sized aluminum powders were heated in carbon dioxide atmosphere through differential scanning calorimetry (DSC) method in this work. Aluminum powders were oxidized into four distinct stages from room temperature to 1500°C. Stage I, amorphous alumina shell turns to γ-Al2O3 phase from room temperature to 620°C. Stage II, accompany with the aluminum core melting, alumina shell becomes thicker and fragile at the temperature around 667°C which is the melting point of aluminum. Stage III, in the temperature range of 690-1150°C, alumina shell was broken partially because of the inside pressure. Liquid aluminum spurts out through the weak point which becomes cracks on the surface just like volcano eruption and then oxidized by CO2 while the temperature increased from 700°C to 900°C. Stage IV, alumina changes to stable α-Al2O3. From what was presented above, a mechanism of micron-sized aluminum particle oxidation in CO2 under gradually increasing temperature condition was proposed as “eruption model”.