Alumina Particle Size Research Articles

Effect of aluminum and ammonium perchlorate particle sizes on the condensed combustion products characteristics of aluminized NEPE propellants

Aluminum (Al) is usually added to solid propellants to improve the combustion performance, however the condensed combustion products (CCPs) especially the large agglomerates generated from aluminum combustion can reduce the specific impulse of the engine, and result in two-phase loss, residue accumulation and throat liner ablation. Al and ammonium perchlorate (AP), as important components of NEPE propellants, can affect the formation process of the CCPs of aluminized NEPE propellants. To clarify the effect of Al and AP particle sizes on the properties of the CCPs of aluminized NEPE propellants, a constant-pressure quench vessel was adopted to collect the combustion products of four different formulations of NEPE propellants. It was found that the condensed combustion products are mainly divided into aluminum agglomerates and oxide particles, the diameter of the aluminum agglomerates of these four different formulations of NEPE propellants at 7 MPa was smaller than that in 3 MPa, and the shells of the aluminum agglomerates were smoother and the spherical shape was more perfect. X-ray diffraction analysis of the CCPs of the four NEPE propellants under 3 MPa revealed the presence of both Al and Al2O3. With the increase of the particle size of Al and AP, the oxidation degree of aluminum particles decreases. The particle size of the CCPs of the four different formulations of NEPE propellants under 1 and 3 MPa was analyzed by using a laser particle size analyzer, it is found that the increase of AP particle size is helpful to reduce the size of condensate combustion products. Based on the classical pocket theory, establishing a new agglomeration size prediction model, which can be used to predict the agglomeration size on the burning surface. Compared with the empirical model, the new agglomeration size prediction model is in good agreement with the experimental results.

Solvent Effects on Particle Size of Alumina Produced by Corrosion and Sol-Gel Method

Solvent Effects on Particle Size of Alumina Produced by Corrosion and Sol-Gel Method

New experimental method for the simultaneous determination of concentration and size profiles of condensed combustion products around a burning aluminum droplet

When an aluminum particle burns in the diffusive regime, a cloud of nanometric particles of its primary oxide, alumina, is formed around the droplet. Characterizing this oxide smoke surrounding a burning aluminum droplet is essential. The original contribution of this paper is to introduce an experimental approach that allows for simultaneous size and concentration measurement of the particles composing the oxide smoke. This paper employs an electrodynamic levitator to facilitate the self-sustained combustion of an isolated aluminum particle, with a radius of 35μm, in atmospheric air. This levitation apparatus is paired with an optical setup that allows for a multi-spectral light extinction method. This technique is specifically designed to measure the size and concentration of alumina particles below the micrometric scale, which is scarcely documented in existing literature. Consequently, spatially resolved concentration and size profiles of the nanometric alumina particles are measured and compared to simulated data from the literature. The radii of alumina particles in the cloud are found to evolve closely around 80 nm. Volume fractions are evaluated from 2.8⋅10−4 near the particle surface to 3⋅10−5 further in the cloud. Therefore, significant concentrations of alumina particles are revealed during the short (15 to 20 ms) combustion process at distances of the order of magnitude of a few initial particle diameters. Such characterization could then lead to a better assessment of the interaction distance among aluminum particles as they burn collectively.Novelty and significance statementThis article introduces the first experimentally determined profiles of alumina concentration and size distribution surrounding a single burning aluminum droplet. The uniqueness of our experimental setup lies in its ability to study of the most fundamental case of the autonomous combustion of a single levitating particle, without any convective effects. A new non-intrusive method specifically designed provides unprecedented results in the field of metallic particle combustion. Data provided in the paper are crucial as they serve as the first reference case for future simulation and experiments. The results introduced in this paper highlight the inability of current simulation methods to accurately account for nucleation and condensation processes, and emphasize the need for a non-invasive characterization method.

Effects of aluminum particle size on metal acceleration for CL-20-based aluminized explosives

The addition of aluminum (Al) powder to CL-20 significantly enhances the overall energy of mixed explosives. Nonetheless, the metal acceleration ability of explosion after Al addition shows unpredictable behavior due to the unclear reaction characteristics of Al in CL-20 detonation products. This study utilizes a plate push test employing CL-20-based aluminized explosives to acquire the reaction degree formulation for Al powder with varying particle sizes in a CL-20 detonation environment. Moreover, it elucidates the reaction mechanism of microsized Al particles during the initial phase of afterburning. Additionally, this reaction formulation enhances the equation of state (EOS) for CL-20-based aluminized explosives. Subsequently, the new EOS is implemented in LS-DYNA to simulate the metal flyer acceleration process. Consequently, the impact of Al particle size on the metal acceleration capability of aluminized CL-20 is examined. The results indicate that for CL-20-based aluminized explosives with 15 % Al content, an optimal Al particle size of 34.12 μm exists when the particle size exceeds 10 μm. This optimum increases the speed of the driving metal plate by 7.4 % compared to CL-20/LiF explosives.

Understanding the explosion risk presented by ammonium nitrate and aluminium home-made explosives detonated as surface charges in hexahedral main charge containers

Ammonium nitrate and aluminium (AN–Al) has been used as a typical homemade explosive (HME) by non-state actors since the turn of the century. Despite the regulation applied to ammonium nitrate above 16% nitrogen content and an aluminium particle size below 200 µm, their use has been widespread in Afghanistan, Columbia, Iraq, Syria and Yemen. Containers used to utilise AN–Al as a man-portable improvised explosive device (IED) are typically hexahedral in shape, not the spherical or hemispherical geometries used to theorise risk mitigation. This is particularly important in post-blast investigation where explosives of a non-ideal nature are often used in non-spherical containers.Given the breadth of HME available to criminals, the explosion performance of forty hexahedral containers filled with AN–Al of unknown manufacture is examined. Performance of the AN–Al is determined through the surface detonation of these containers on alluvial soil, with apparent crater volume compared to theoretical calculations for spherical charges of TNT detonated in that same medium. A conversion factor for hexahedral main charges to spherical charges is then established to achieve more accurate predictions of the explosion risk using Kingery-Bulmash and Bowen curves. The paper provides worked examples for practical application and a methodology by which predictions of charge mass in other mediums such as asphalt can be determined.

Enhancing Lithium‐Ion Battery Performance with Alumina‐Coated Separators: Exploring the Potential of Different Alumina Particle Sizes, Coating Techniques, and Calendering

AbstractA range of techniques for the coating of high purity alumina (HPA) on porous polypropylene battery separators has been investigated. A slurry was prepared by dispersion of the alumina powder in acetone solvent and poly (vinylidene fluoride‐co‐hexafluoropropylene) (PVdF‐HFP) as the binder to obtain an excellent adhesion to the membrane. Doctor blade, spin coating, and electro‐spin coating techniques were utilized to coat a thin layer of HPA on the separator that was followed up with a calendering step to improve compactness, decrease thickness and enhance adhesion. Furthermore, the effect of HPA particle size, distribution, and the use of a calendering step on coating thickness, compactness, and electrochemical performance were investigated using three HPA sources. The doctor blade technique was found to give the most uniform coating with the best mechanical properties and high‐temperature resistance. The coated separators were incorporated into lithium‐ion coin cells to evaluate the rate capability and long‐term cycling performance.

The liquid-phase hydrogenation of TMCB for preparation of CBDO by fluorine-modified Ruthenium-Stannum bimetallic catalysts

A series of Ruthenium-Stannum bimetallic catalysts were prepared using the isovolumetric impregnation method and investigated for the liquid-phase hydrogenation of 2,2,4,4-tetramethyl-1,3-cyclobutanedione to its corresponding 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The effects of the reaction temperature and pressure, fluorine-modified alumina, reaction solvent, and catalyst particle size on the catalytic performance were discussed. The optimum reaction conditions were obtained with a temperature of 80 ℃, a hydrogen pressure of 4.0 MPa, and a reaction solvent of tetrahydrofuran. In addition, characterization techniques, such as BET, XRD, TEM, NH3-TPD, and Py-IR, showed that the active component nanoparticles were effectively introduced into the alumina carriers, and the alumina was modified by a low concentration of NH4F solution (0.05 mol/L), which ensured that the complete conversion of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was obtained while maintaining a selectivity of over 95 % for the 2,2,4,4-tetramethyl-1,3-cyclobutanediol.

Investigation of aluminum particle ignition dynamics in various propellant environments

The ignition delay of aluminum particles can be profoundly influenced by the agglomeration and combustion characteristics of solid propellants. In this experimental study, the ignition of individual aluminum particles in nitrate ester plasticized polyether (NEPE) and hydroxyl‑terminated polybutadiene (HTPB) propellant atmospheres was examined using laser ignition tests and high-speed photography. Focus was directed at the effects of the atmospheric composition, pressure, and aluminum particle size (500, 800 and 1000 µm). It was observed that the non-homogeneous reaction heat generation and convective heat exchange rates during particle ignition could be increased by increasing the CO2 content or ambient temperature, resulting in a shorter ignition delay time. This explains why aluminum particles tended to burn more efficiently in nitrate ester plasticized polyether than in hydroxyl‑terminated polybutadiene. In addition, it was found that the ignition delay time decreased with increasing pressure and was inversely proportional to the particle size squared. An ignition model for aluminum particle ignition in a multi-component atmosphere was developed and validated to describe the temperature change and energy transfer during ignition. The calculated ignition delay times were found to be within 5% of the experimental values. The model also showed that increasing the ambient temperature was more effective than increasing the CO2 content at enhancing ignition, and that CO2 was more effective than O2, which was itself more effective than H2O. Overall, this study provides useful insight into the ignition characteristics of aluminum particles in different propellant environments. The results could be used to develop more effective propellant formulations, optimize combustion processes, and improve safety in the handling and use of aluminum-based propellants.

Preparation and performance of alumina/epoxy-siloxane composites: A comparative study on thermal- and photo-curing process

Although epoxy-based composites that consist of inorganic fillers and matrixes are widely used in “conventional” electronic packaging applications due to their excellent insulation and robust properties, they limit their uses in “advanced electronic packaging” which requires enhanced thermal conductivity. However, conventional thermal curing methods for fabrication of epoxy-based composites do not fulfill sufficient thermal conductivity. Herein, we apply photo-induced curing strategy for fabricating alumina-incorporated epoxy-siloxane composites that consist of sol-gel derived siloxane matrix and bimodal sized alumina particles as a thermally conductive filler. We investigate how curing mechanism (thermal- or UV-curing) and varying the ratios of the alumina particles of two different sizes affect the various physical properties. It is found that photo-curing process makes greatly enhanced thermal conductivity, low thermal expansion, and high mechanical robustness compared to thermally-cured composites. As the results, we can achieve significantly enhanced thermal conductivity (>11 W/m K) with high thermal stability and mechanical robustness.

Influence of particle size and aggregates on translucent alumina ceramics fabricated by gelcasting

Three types of alumina powders and a polymer electrolyte Isobam system were used to fabricate translucent alumina ceramics via gelcasting, and each powder had the highest attainable solid loading. The effects of alumina particle size on slurry dispersion, microstructures and properties of green bodies and ceramics were investigated. All of the high-solid loading slurries contained strong aggregates, which could bridge with each other to form weak agglomerates. The smaller the initial particle size was, the more the contained particle number per aggregate. In addition, the smaller the aggregate size was, the lower the sintering activation energy of the ceramic and, finally, the higher the relative density. The initial particle size of the powder may not be the critical factor determining ceramic sintering, but the aggregate size and effective volume fraction of the aggregates may be the critical factors. Finally, the in-line transmittance of the ceramic with a higher density reached 22% at a wavelength of 650 nm and a thickness of 0.8 mm.

Сравнительный анализ структуры и свойств керамик на основе оксида алюминия, полученных методами свободного и электроимпульсного плазменного спекания

The effect of the initial size of alumina particles on the density, microstructure, hardness, and fracture toughness of ceramics obtained by conventional and spark plasma sintering (SPS) has been studied. We studied ceramics obtained from commercial Al2O3 powders with an initial particle size of 40 – 50 nm, 0.2 mm, and 1 mm, and domestic fine powders with an initial particle size of 0.2 – 3 mm, and Al2O3 + 0.25 vol. % MgO and Al2O3 + 10 vol. % ZrO2. It is shown that the density of alumina ceramics nonmonotonically depends on the initial size of Al2O3 powder particles. It has been established that an increase in the grain size leads to a nonmonotonic change in the hardness of alumina ceramics. It has been established that the addition of 0.25 vol. % MgO accelerates the sintering of alumina. The addition of 10 vol. % ZrO2 makes it possible to provide an optimal combination of hardness and fracture toughness. It is shown that fine-grained ceramics obtained by the SPS method have a higher hardness. It has been suggested that SPS of submicron alumina powders with an amorphous layer on the surface, additionally stabilized by zirconia particles, is promising for further increasing the hardness of alumina ceramics.

Cut/puncture resistance and mechanisms of protective composite textiles reinforced with inorganic powder

This study presents a soft-rigid unified structure (SRUS) textile composed of an inorganic powder (IP) reinforced epoxy resin block (EIPB) array and a soft textile substrate via a pattern-controllable integrated molding method. The influence of IP content and alumina particle size on the cut and puncture resistance of the resulting SRUS textile was systematically investigated. Furthermore, the anti-puncture and anti-cutting mechanisms of the SRUS textile were comprehensively evaluated based on the analysis of damage morphology and process. The experimental results demonstrated a significant enhancement in the puncture and cut resistance of the SRUS textile upon the incorporation of IP. Moreover, the cut/puncture resistance of the SRUS textile increased with an increase in IP content and the size of Al2O3, and the optimal cut/puncture resistance was observed at 60 mesh-50 wt.%. Additionally, the anti-puncture mechanism of the SRUS textile was attributed to the presence of hard passivation at the EIPB, as well as friction self-locking at the gaps. The anti-cutting mechanism was ascribed to the reverse cutting action exerted by the hard particles on the blade, preventing further penetration. Overall, these findings provide valuable insights into the underlying mechanisms that contribute to its enhanced protective performance.

Effect of Surface Textures and Fabrication Methods on Shear Bond Strength Between Titanium Framework and Auto-Polymerizing Acrylic Repair Resin.

The aim of the study was to evaluate the effect of airborne particle abrasion (using different sizes of alumina particles) on the shear bond strength (SBS) between cast and milled titanium metal frameworks and auto-polymerizing acrylic repair resin. Forty flat cylindrical titanium disks were divided into two main divisions: cast and milled titanium. The two divisions were further subdivided into four groups based on metal surface treatment. Three particle sizes of aluminum oxide air abrasive powders (50µm, 110µm, and 250µm) were used for metal surface treatment by airborne particle abrasion. One group was the control group with no surface treatment. Auto-polymerizing acrylic repair resin was applied to all titanium disks. The specimens were subjected to SBS testing using a universal testing machine (Instron Corporation, Norwood, Massachusetts, United States). Surface evaluation was performed using a scanning electron microscope. One-way ANOVA was used for statistical analysis. The results showed a significant increase in SBS after airborne particle abrasion of both milled and cast titanium groups (p<0.001). The SBS was directly proportional to the size of the aluminum oxide particles. The milled titanium group showed higher SBS values than the cast group when the surface was not treated with alumina particles (p < 0.001) and when the surface was treated with the smaller particle sizes of 50 µm, whereas the cast group demonstrated higher SBS values than the milled group (p < 0.01) when the particle size was increased to 110 µm and 250 µm. It could be concluded that SBS between titanium metal frameworks and auto-polymerizing repair acrylic resin was directly related to the size of the alumina airborne particle abrasives. The fabrication method of the titanium frameworkalso influenced the SBS as the untreated milled frameworks demonstrated favorable SBS values compared to the untreated cast frameworks.

Effect of the alumina micro-particle sizes on the thermal conductivity and dynamic mechanical property of epoxy resin.

Epoxy thermal conductive adhesives with high thermal conductivity and dynamic mechanical properties are important thermally conductive materials for fabricating highly integrated electronic devices. In this paper, micro-Al2O3 is used as a thermally conductive filler for the epoxy resin composite and investigated the effect of micron-sized alumina particle size on the thermal conductivity and dynamic mechanical property of epoxy resin by the transient planar hot plate method and DMA (Dynamic mechanical analysis). The experimental results show that with the same amount of alumina filling, the thermal conductivity and Tg (glass transition temperature) of epoxy/Al2O3 composite material decrease with the increase of alumina particle size. The maximum thermal conductivity of the composite material is 0.679 (W/mK), while the energy storage modulus of epoxy/Al2O3 composite material increases with the increase of alumina particle size, and the maximum energy storage modulus of the composite material is 160MPa. Compared with pure epoxy resin, the thermal conductivity and energy storage modulus have increased by 2.7 and 3.2 times, respectively. The epoxy/Al2O3 composite was applied to the COB (Chips On Board) type LED package, and the substrate temperature of the LED dropped to the lowest after 1.5 hours of operation using EP-A5 composite, and the temperature was stabilized at 38.2°C, indicating that the addition of 5-micron alumina composite has the best heat dissipation in the COB type LED package. These results are critical for the implementation of particulate-filled polymer composites in practical applications because relaxed material specifications and handling procedures can be incorporated in production environments to improve efficiency.

The Influence of Alumina Airborne-Particle Abrasion on the Properties of Zirconia-Based Dental Ceramics (3Y-TZP)

The objective of this study was to assess the effect of airborne-particle abrasion with alumina particles of various sizes (50 μm, 110 μm, 250 μm) on the surface properties of 3Y-TZP (3 mol% yttria-stabilized tetragonal zirconia polycrystals). The analysis comprised the Vickers hardness test (HV1kp), a surface roughness evaluation (Ra, Rq, Rz, Rsk, Rsm, Rt, Vo, profile displays), and SEM–EDS microanalysis (scanning electron microscopy–energy-dispersive X-ray spectroscopy). Any statistical relationships were assessed using the Kruskal–Wallis one-way analysis-of-variance-by-rank test (p = 0.05). While airborne-particle abrasion with 50 µm alumina significantly increases the Vickers hardness of 3Y-TZP (1678.8 HV1kp), 110 μm and 250 μm alumina particles do not appear to have any such effect. The surface roughness of 3Y-TZP increases with the size of the alumina particles (Ra, Rq, Rz, Rt, Vo: vertical plane and retention volume assessment); a higher Rsm (horizontal plane assessment) was noted for specimens air-abraded with 250 µm alumina particles; air abrasion with 50 μm alumina particles yielded a symmetrical surface roughness profile (Rsk). The major topographic pattern of the surface of 3Y-TZP is altered by alumina airborne-particle abrasion, with larger alumina particles causing more severe changes. Aluminum traces on the 3Y-TZP surface are observed. The shape of the alumina particles is irregular, with rough edges; the size of the alumina particles plays a significant role in the air abrasion of zirconia-based dental ceramics, affecting their morphology and properties.

Effect of spherical alumina crystalline phase content and particle size distribution polydispersity on the properties of silicone rubber composites

High loading of thermally conductive fillers for enhancing thermal conductivity (TC) conflicts with proper rheological viscosity in excellent thermal interface materials (TIMs), which remains a significant challenge. The physical properties (crystalline phase, particle size and distribution, etc.) of thermally conductive filler are the base of the high load in the polymer. In this paper, the α-phase content of spherical aluminum (S–Al2O3) increases after calcination, leading to the viscosity of composites increasing sharply but was only slightly improved for the TC. The polydispersity of the S–Al2O3 particle size distribution was regulated to fill the silicone rubber under the premise of controlling the same average particle size, crystalline phase content and filling amount. Results indicated the viscosity of the sample with a polydispersity value of 0.74 was 41.21 Pa s at a shear rate of 10 s−1 at 66 vol%, which was 87.7% lower than that of the sample with a polydispersity value of 0.48. And the viscosity difference became more prominent with the increasing filling amount. However, the difference in TC between several groups of samples with different polydispersity is insignificant at 60–67 vol%, which provides practical, theoretical guidance for achieving controllable viscosity and developing low-viscosity TIMs in the processing process.

Aluminum precipitation on oxygen-deficient alumina in laser alumina reduction

Alumina reduction by thermal decomposition using CW laser ablation is being studied to obtain aluminum and oxygen on the lunar surface without the use of reducing agents such as carbon or hydrogen. When an alumina rod is heated by a laser beyond the ablation temperature, oxygen-deficient alumina (Al2O2.4-2.8) and aluminum microparticles are generated on the laser-irradiated surface. For this study, rods made of oxygen-deficient alumina were ablated to obtain more aluminum than normal alumina ablation. Results show that approximately 1.7 times as much aluminum was precipitated as that obtained from normal alumina ablation. The average particle size of the precipitated aluminum particles was found using SEM image analyses to be about 1.6 times larger than that of normal alumina.

The Influence of Alumina Airborne-Particle Abrasion with Various Sizes of Alumina Particles on the Phase Transformation and Fracture Resistance of Zirconia-Based Dental Ceramics.

The surface of zirconia-based dental ceramic restorations require preparation prior to adhesive cementation. The purpose of this study was to assess the influence of airborne-particle abrasion with different sizes of alumina particles (50 μm, 110 μm, or 250 μm) on the mechanical strength of zirconia-based ceramics' frameworks and on the extent of phase transformations. A fracture resistance test was performed. The central surface of the frameworks was subjected to a load [N]. The identification and quantitative determination of the crystalline phase present in the zirconia specimens was assessed using X-ray diffraction. The Kruskal-Wallis one-way analysis of variance was used to establish significance (α = 0.05). The fracture resistance of zirconia-based frameworks significantly increases with an increase in the size of alumina particles used for air abrasion: 715.5 N for 250 μm alumina particles, 661.1 N for 110 μm, 608.7 N for 50 μm and the lowest for the untreated specimens (364.2 N). The X-ray diffraction analysis showed an increase in the monoclinic phase content after air abrasion: 50 μm alumina particles-26%, 110 μm-40%, 250 μm-56%, and no treatment-none. Air abrasion of the zirconia-based dental ceramics' surface with alumina particles increases the fracture resistance of zirconia copings and the monoclinic phase volume. This increase is strongly related to the alumina particle size.

Preparation and properties of porous mullite-based ceramics fabricated by solid state reaction

In this study, the effect of the alumina particle size on the formation of mullite using a silica gel powder and micro- and nano-scale Al2O3 powders as raw materials was investigated. The optimized Al2O3 source was then reacted with the silica gel to prepare porous mullite-based ceramics. The results revealed that the highly reactive nano-Al2O3 powder could form mullite at a relatively low firing temperature. Therefore, the nano-Al2O3 powder was used to prepare porous mullite-based ceramics by firing at 1600 °C, 1650 °C and 1700 °C. The pore size of the prepared porous mullite-based ceramics ranges from tens to hundreds of micrometres, with the apparent porosity being 42.8–58.0%. Further, the mullite content in the samples increased with increasing firing temperature, and a higher firing temperature promoted sintering, resulting in improved strength of the sample. After calcination at 1700 °C, the mullite content in the sample reached 81.8%, and the sample showed excellent thermal shock resistance. The strengths of the samples before and after thermal shock were found to be 23.6 and 15.58 MPa, with the residual strength ratio being 66%.

Incorporating fluoropolymer-coated micron-sized aluminum with enhanced reactivity into aluminized explosives to improve their detonation performance

Micro-sized aluminum (m-Al) has been widely applied in explosives as fuel additives. Unfortunately, m-Al displays long ignition delay and insufficient combustion, making it fail to fully release its energy in aluminized explosives. In this work, fluoropolymer-coated m-Al composites were prepared using the solvent evaporation method. Then, the surface state of the m-Al composites was determined based on scanning electron microscopy (SEM) images, and their thermal behavior was investigated through thermogravimetric analysis (TGA) at a temperature range of 30–1200 ​°C. Moreover, the reactivity and combustion kinetics of aluminum were explored using laser ignition experiments. To evaluate the metal acceleration ability and detonation performance of CL-20-based explosives containing fluoropolymer-coated m-Al composites, the disc acceleration experiment (DAX) was specially designed taking into account the influence of aluminum particle size. The results of this study show that fluoropolymers were uniformly distributed on the surface of m-Al, and most of the as-prepared particles were microspheres without apparent agglomeration. The presence of fluoropolymers is beneficial to the oxidation of aluminum particles. The explosive sample containing fluoropolymer-coated aluminum composites exhibited shortened ignition delay and an increase in the burning speed from 3.3 ​mm·s−1 to 7.9 ​mm·s−1 compared to the sample with uncoated Al. Most especially, its specific kinetic energy increased from 8.45 ​kJ·g−1 to 9.29 ​kJ·g−1, its detonation velocity increased from 7.75 ​km·s−1 to 7.82 ​km·s−1, and its detonation pressure increased from 25.57 ​GPa to 30.89 ​GPa.