Al Microparticles Research Articles

Ultrastable Aluminum Nanoparticles with Enhanced Combustion Performance Enabled by a Polydopamine/Polyethyleneimine Nanocoating.

In national defense, aluminum nanoparticles (Al NPs) have better combustion performance than Al microparticles but are easily oxidized during processing, especially in oxidative liquids. Although some protective coatings have been reported, it is still challenging to obtain Al NPs stable in oxidative liquids (e.g., hot liquids) without scarifying combustion performance. Here, we report ultrastable Al NPs with enhanced combustion performance enabled by the crosslinked polydopamine/polyethyleneimine (PDA/PEI) nanocoating merely ∼15 nm in thickness and ∼0.24 wt % in mass. The Al@PDA/PEI NPs are fabricated by one-step rapid graft copolymerization of dopamine and PEI on Al NPs at room temperature. The formation mechanism of the nanocoating is discussed including reactions between dopamine and PEI and interactions of the nanocoating with Al NPs. The Al@PDA/PEI NPs show excellent stability in hot water, and the mechanism is interpreted by molecular dynamics simulation. The PDA/PEI nanocoating can also enhance the combustion heat and burning rate of Al NPs.

High-temperature resistant interconnection using Ni nanoparticles and Al microparticles paste sintered in an atmosphere

Next-generation power devices using wide bandgap semiconductors, such as SiC, are expected to operate at higher temperatures than conventional Si power devices, and their operating temperatures are expected to exceed 250 °C. We developed a novel high-temperature resistant interconnection technology for die-bonding of SiC power devices using Ni nanoparticles and Al microparticles composite paste. The bond strength of the Al-metallized Si chip to Ni-plated direct bonded copper substrate was evaluated using shear tests. The initial shear strength of samples from pressureless sintering at 350 °C for 15 min in the air exceeded 30 MPa. Furthermore, no significant degradation was observed in a high-temperature storage test at 250 °C for 1000 h.

Enhancing the ignitability of the Al–TiO2–B2O3 powder mixture through intensive vibratory ball milling (C:P12)

Alumina-TiB2 is a hard ceramic composite with applications in aviation, aerospace and wear resistant tools. It can be manufactured in-situ through a highly exothermic aluminothermic self-sustaining reaction from the starting materials of Al, TiO2 and B2O3. In this paper, the effect of vibration ball milling on the particle size reduction and the reactivity enhancement of the Al–TiO2–B2O3 powder mixture is examined by XRD, SEM, EDS, DTA and particle analysis techniques. Measures for combating the stoichiometric inconsistencies deriving from the tendency of B2O3 to absorb atmospheric water, giving boric acid H3BO3, are implemented. Characterisation of the milled samples display Al microparticles with d(0.9) below 64 μm, coated with nano-particles of TiO2 and B2O3, with particle sizes up to 600 nm. Differential thermal analysis reveals that ignition is feasible for all of the milled mixtures, unlike the un-milled one. It also presents that extensive milling results in a reduction in the ignition temperature of the reactant mixture to 925 °C for the 5 h-30Hz milled sample, from the previous 982 °C recorded for the 1 h–20Hz milled sample. The in-situ synthesised Al2O3–TiB2 matrix deriving from the 5 h-30Hz milled sample, gives less of the unwanted Al5BO9 phase and improved skeletal and bulk densities, by 0.15 g/cc and 0.1 g/cc respectively, compared to the respective composite deriving from un-milled reactants powder mixture.

Development of Thermal Barrier Coating Systems from Al Microparticles—Part II: Characterisation of Mechanical and Thermal Transport Properties

In this study, the mechanical resistance and the thermal insulation potential of novel thermal barrier coatings (TBCs) made of a foam of hollow alumina particles are assessed through scratch testing, micro-indentation and thermal diffusivity measurements using laser-flash. The thermal diffusivity of the foam coatings ranges between 0.6 × 10−7 and 5 × 10−7 m2·s−1 and is thus comparable with the thermal insulation potential of the standard plasma-sprayed (PS) and electron beam–physical vapour-deposited (EB-PVD) TBCs made of yttria-stabilised zirconia (YSZ). The coatings annealed in more oxidative atmospheres exhibit greater mechanical resistance due to the thickening of the alumina shells and the increased sintering of the foam. However, when the oxidation is poorly tailored, the adhesion of the foam to the substrate decreases due to the presence of unwanted oxide that grows at the substrate/coating interface.

Al-Microcapsules with a Self-Sacrificial Oxidation Method for High-Temperature Thermal Energy Storage.

Traditional high-temperature energy utilization systems employ conventional solid sensible heat storage (SHS) for energy storage. Latent heat storage (LHS) serves as a surrogate for energy storage as opposed to the SHS system due to the presence of phase-change materials (PCMs). In this paper, we report the production and characterization of Al microencapsulated PCM (MEPCM) through a simple one-step self-sacrificial oxidation fabrication process, where the core–shell type microencapsulated with Al microsphere (mean diameter 35 μm, melting temperature 669 °C) acted as the core (PCM) and Al2O3 as the shell. During the oxidation process, the surface layer of the Al microparticle was sacrificed to form a stable Al2O3 shell, which was only about 50 nm thick presented by means of a focused ion beam (FIB). In terms of the analyses of FIB and X-ray photoelectron spectroscopy (XPS), it is apparent that Al2O3 is successfully formed on the surface of Al microparticles, which can keep a stable solid shell structure during solid–liquid phase transitions. The latent heat of MEPCM was 310.4 kJ/kg, and the melting temperature was 668 °C. Thus, the one-step self-sacrificial heat-oxidation technique can lead to better commercialization and environmental friendliness of next-generation LHS-based high-temperature thermal energy storage materials.

High-temperature Resistant Interconnections Formed by Ni Nanoparticles/Al Micro-particles Composite Paste for SiC Power Device Application

Sintering bonding using metal nanoparticles is considered a promising die-attach technique for high-temperature operating power devices, such as SiC. However, the thermal stress produced by the difference in coefficient of thermal expansion (CTE) between the chip and substrate, often affects the reliability of this technique. To address this limitation, we analyzed a sintering bonding using Ni nanoparticles and Al microparticles composite paste. The results revealed that the Al microparticles significantly reduced the voids and cracks in the bonding layer formed by Ni nanoparticles paste. Three chips with different sizes were bonded to Cu substrates, and the bonding strength was measured. The result revealed that the bonding strengths in the samples were higher than those of the samples bonded using conventional metal nanoparticles. In addition, the fracture observation after the shear test revealed that the Al particles suffered plastic deformation. Furthermore, the high-temperature storage test at 250°C confirmed the long-term bonding reliability.

Nanoscale‐Sculptured Al Microparticles as Universal Hierarchical Adhesion Promoters

The adhesion between two non-stick polymers can be significantly increased through hierarchical mechanical interlocking by using a low amount of nanoscale-sculptured Al microparticles with hook-like structures at the polymer interface. The approach demonstrated by Rainer Adelung and co-workers in article number 2100296 has the potential to be used as an environmentally friendly universal adhesion promoter for nonstick polymers and can be easily applied at an industrial scale.

Is laser space propulsion practical?: review.

In this paper, we review practical limitations to laser space propulsion that have been discussed in the literature. These are as follows: (1) thermal coupling to the propelled payload, which might melt it; (2) a decrease in mechanical coupling with number of pulses, which has been observed in some cases; and (3) destruction of solar panels in debris removal proposals that might create more debris rather than less. Previously, lack of data prevented definite assessments. Now, new data on multipulse vacuum laser impulse coupling coefficient Cm on several materials at 1064 nm, at 1030 nm, and at 532 nm are available. We are now able to compare the results for single and multiple pulses on materials that have been considered for laser ablation space propulsion (LASP), or that are likely space debris constituents, and decide whether LASP is a practical idea. Laser space propulsion and debris removal concepts depend on thousands or hundreds of thousands of repetitive pulses. Repetitive pulse mechanical coupling as well as thermal coupling (which can melt the target rather than propel it) are both important considerations. Materials studied were 6061T6 aluminum, carbon-doped polyoxymethylene (POM), undoped POM, a yellow POM copolymer, and a mixture of Al and POM microparticles combined and pressed, containing a 50%/50% mixture of the two materials by mass. We address 6 and 70 ps pulses because of the availability of data at these pulse durations. We also briefly consider continuous wave (CW) laser propulsion. Finally, we consider a recent paper concerning solar panel destruction from a positive perspective.

Nanoscale‐Sculptured Al Microparticles as Universal Hierarchical Adhesion Promoters

A combination of properties (e.g., biocompatibility, abrasion resistance, chemical inertness, etc.) from different polymers is desirable in many applications such as in medical and marine fields. However, joining nonstick polymers is still challenging. Herein, a facile and environmentally friendly approach is demonstrated to improve the adhesion between nonstick polymers through mechanical interlocking using a low amount of nanoscale‐sculptured Al microparticles. The hook‐like structures for mechanical interlocking are created on Al microparticles by nanoscale sculpturing, that is, a wet chemical etching process. By the incorporation of nanoscale‐sculptured Al microparticles at a polydimethylsiloxane (PDMS)/polythiourethane (PTU) interface serving as just one demonstrator example, the peeling strength of PDMS from PTU is 30 times higher compared with that without Al microparticles and 4 times higher than that with untreated Al microparticles, respectively. The significant increase in adhesion can be attributed to the penetration of both polymers into the hook‐like structures of nanoscale‐sculptured Al microparticles, forming a tight and strong hierarchical mechanical interlocking.

Enhanced thermal- and impact-initiated reactions of PTFE/Al energetic materials through ultrasonic-assisted core-shell construction

A facile and economical approach was developed for the large-scale production of powdered core-shell structured PTFE/Al (CS-PA) energetic materials through ultrasonic-assisted mixing. The low-cost micrometer-sized PTFE and Al particles were used as starting materials. Under high-power ultrasonic waves, the PTFE powder was dispersed into nano-to sub-micrometer-sized particles and then encapsulated the Al microparticles to form the core-shell structure. The heat of combustion, burning rate, and pressurization rate of the powdered CS-PA were measured. The thermal-initiated reaction behavior was further evaluated using thermogravimetry-differential scanning calorimetry. Subsequently, the bulk CS-PA with a uniform microstructure was obtained via cold isostatic pressing of the powdered CS-PA followed by vacuum sintering. For the bulk CS-PA, the quasi-static compression behavior was characterized, and the impact-initiated reaction processes were conducted using the Split Hopkinson Pressure Bar (SHPB) and evaluated by a high-speed camera. Compared to physically mixed PTFE/Al materials, the powdered and bulk CS-PA demonstrated enhanced thermal- and impact-initiated reaction characteristics respectively, proving the effectiveness of our approach for constructing core-shell structures.

Sustainable atmospheric fog water generator through superhydrophobic electrospun nanocomposite fibers of recycled expanded polystyrene foams

In recent years, the production of disposable plastic products is increasing day by day and resulting in global growing concern that it poses to the environment. Microorganisms hardly resolve these types of plastic wastes; therefore, recycling the value-added materials is very important. Recycling and reusing plastic wastes to produce superhydrophobic nanofibers for atmospheric clean water production could be a partial solution to address the environmental issues. Herein, superhydrophobic-hydrophilic nanocomposites fibers were fabricated using recycled expanded polystyrene (REPS) as inspired by the fog-harvesting capability of Stenocara beetles in the Namib Desert. The REPS were electrospun with various proportions of titanium dioxide (TiO2) nanoparticles and aluminum (Al) microparticles. The fiber morphology, surface hydrophobicity, thermal properties, and fog water-harvesting performance of the nanocomposite fibers were studied. The as-prepared nanocomposites fibers with a 10% inclusion of combined micro-and nanoparticles exhibit superhydrophobic properties with a water contact angle of 157° and daily water productivity of more than 1.35 liter/m2 of nanocomposites. The expenses of materials to produce such nanocomposites needed to supply the minimum daily water consumption for a two-member household (6 liters) are only US$2.67. These nanocomposites are inexpensive, reusable, do not require additional energy consumption, and are particularly suitable for producing clean water in arid areas. This study offers a new technology for the mass production of clean water through nanotechnology at a relatively low cost.

Corrosion performance of slurry aluminide coatings in molten NaCl–KCl

The corrosion performance of water-based slurry aluminide coatings elaborated on iron- and nickel-based materials is investigated in molten chlorides as candidate heat transfer fluids (HTF) for thermal energy storage (TES) in third generation concentrated solar power (CSP) plants. This work presents a screening of four different materials (ferritic-martensitic P91 steel, austenitic stainless steel 316L, Inconel 600 and high-purity nickel) to investigate the influence of the alloying elements (e.g. Fe, Cr, Ni contents) on the microstructure and corrosion performance of slurry aluminide coatings. Individual metallic samples were diffusion-coated with slurries containing Al microparticles and subsequently exposed to molten NaCl–KCl at 700 °C for 100 h under argon. The experimental observations indicate that the performance of the aluminide coatings is governed by the precipitation of secondary phases within the B2 aluminide matrix rather than its intrinsic Al concentration (where B2 refers to either FeAl, (Fe,Ni)Al or NiAl intermetallic compounds). Of those, Fe-rich aluminide coatings were found to be more resistant to molten chlorides than Ni-rich ones. This is attributed to the greater solubility of Cr in iron aluminides than in nickel aluminides, preventing the precipitation of Cr-rich intermetallic compounds and/or Cr-rich carbides within the B2 matrix. Cr-rich phases were selectively dissolved upon exposure leaving the coating matrix with void channels. According to residual coating thickness measurements, the following ranking with increasing corrosion resistance can be given for Al-slurry coated materials: Inconel 600 < high-purity nickel < austenitic stainless steel 316L < ferritic-martensitic P91 steel.

Influence of rheology and activation energy on the structure of protective coatings formed from CMC suspensions with Al powder

Influence of the temperature and rotation speed of the viscometer spindle on the rheological properties of CMC-based suspensions with aluminum powder is considered. It is shown that suspensions belong to pseudoplastic systems. It is established that, with an increase in the activation energy of viscous flow in CMC-based suspensions, the intensity of intermolecular interactions between polymer macromolecules and oxide shells of Al microparticles increases. Using infrared and scanning microscopy, the structure and morphological features of coatings formed from suspensions are studied. It is revealed that the structure hardening of composite coatings occurs due to hydrogen bonds available for interaction in the OH groups of an aqueous solution of CMC.

Synthesis and Characterisation of Acrylic Resin-Al Powder Composites Suitable for Additive Manufacturing.

Stereolithography is an additive manufacturing technology commonly used to build either prototypes or final parts. Nevertheless, the manufacture of structural parts has been ruled out owing to the poor mechanical properties of conventional UV-curable resins. Moreover, the inventory of available commercial resins is still limited and they exhibit low thermal and electrical conductivity values. In this work, some composite materials were designed using Al microparticles dispersed within an SLA commercial resin matrix. These composites overcame the difficulties caused by the light scattering effect during the photopolymerisation process in the SLA technology. Dispersion of the filler was characterised by means of SEM/EDX and AFM. The composites exhibited improved thermal and mechanical behaviour in comparison with the pristine resin. The simplicity of the synthesis method used to prepare the composites provides a convenient starting point to explore new ways of designing composites for SLA with improved mechanical and functional properties.

Recycling of polymer laminated aluminum packaging (PLAP) materials into carbonaceous metallic microparticles

This research describes the recycling of laminated metal packaging into multiple products by utilizing three different techniques. PLAP materials have been thermally disengaged at 550 °C for 20 min in an argon gas created inert atmosphere to recycle into solid Al and graphitic carbon. In a different route, in the presence of gaseous N2 at 600 °C for 1h, the PLAP materials are degraded into bio-oil. A new technique to produce powdered materials from the ductile metal (Al) has been introduced in this study. In this technique, recycled Al and C from the first route at 550 °C, undergoes mechanical milling at cryogenic temperature (−196 °C) created by liquid N2. The translatory high energy ball milling process varied for 2, 4, 6, and 8 cycles (time: 17, 29, 41, and 53 min respectively). As the milling process is extensively high impact loaded at a very low temperature, the foil-like Al recycled from the packaging waste transforms into smaller particles within a very short time (20 min). Upon further milling (41 min), the microparticles (particle size below 100 μm) of Al can be observed. The microparticles received from the cryo-mill are characterized to investigate the particle size, morphology, crystallographic structure, thermal behavior, chemical state, and dispersibility in different liquid media. Flake shaped, and micro-sized carbonaceous Al microparticles are contamination-free and thermally stable and can be useful in the fields of additive manufacturing.

Microstructural characterization of NiAl–Al2O3 composite materials obtained by in situ aluminothermic reduction of NiO for potential coating applications

Aluminothermic reactions between Al microparticles and preoxidized Ni particles were carried out to fabricate mixed compounds of NixAly containing in situ generated Al2O3. The mixed composites were obtained by applying a thermal treatment to either a mixture of NiO and Al powders or to a stacking of powders. The effects of the particle size, thickness of oxide, heating ramp and temperature on the microstructure of the NiAl–Al2O3 coating are discussed. The results indicate that Ni3Al forms first during the synthesis, followed by NiAl and Al3Ni2 while Al3Ni forms on cooling. Moreover, the alumina was observed to form a continuous network surrounding NixAly intermetallic compounds. It derives that these composites have a potential to form self-healing coatings.

Effects of Size and Prestressing of Aluminum Particles on the Oxidation of Levitated exo-Tetrahydrodicyclopentadiene Droplets.

Addition of high-energy-density materials such as aluminum (Al) microparticles or nanoparticles to liquid propellants potentially improves performance of the fuel. We report on the effects of untreated, prestressed, and superquenched aluminum particles with diameters of 100 nm, 250 nm, 500 nm, 1.6 μm, and 8.8 μm on the combustion of JP-10 droplets acoustically levitated in an oxygen-argon atmosphere. Ignition was initiated by a carbon dioxide laser, and the resulting oxidation processes were traced by Raman, Fourier-transform infrared (FTIR), and ultraviolet-visible (UV-vis) spectroscopies together with high-speed optical and IR thermal-imaging cameras. The UV-vis emission spectra reveal that the key reactive radical intermediates hydroxyl (OH), methylidyne (CH), dicarbon (C2), aluminum monoxide (AlO), and aluminum monohydride (AlH) were formed in addition to atomic aluminum (Al) and the final oxidation products of JP-10, namely, water (H2O) and carbon dioxide (CO2). The Al particles facilitated ignition of the JP-10 droplets and produced higher temperatures in the combustion process of up to typically 2600 K. The effect of the Al particles on the ignition and maximum flame temperatures increased as the diameters reduced. The different stress treatments did not produce observable changes for the ignition or combustion of the droplets, which indicates that the liquid propellant was not significantly affected by manipulating the mechanical properties of the fuel particle additive. The initiation and enhancement of the combustion were a consequence of forming highly reactive atomic oxygen (O) and aluminum monoxide (AlO) radicals in the reaction of aluminum atoms with molecular oxygen in the gas phase. These radicals initiate the degradation of JP-10 via atomic hydrogen abstraction forming the hydroxyl (OH) and aluminum hydroxide (AlOH) radicals in reactions which are mainly exothermic by up to 68 kJ mol-1. In contrast, hydrogen abstractions from JP-10 by molecular oxygen or atomic aluminum are strongly endothermic by up to 236 kJ mol-1, thus making these reactions less competitive. The generation of C10H15 hydrocarbon radicals from the JP-10 initiates successive oxidations and chain reactions with molecular oxygen leading eventually to carbon dioxide and water. These combined experimental results provide insight into how aluminum particles facilitate the oxidation and reaction mechanisms of JP-10 droplets.

Genotoxicity of Aluminum and Aluminum Oxide Nanomaterials in Rats Following Oral Exposure.

Due to several gaps remaining in the toxicological evaluation of nanomaterials (NMs), consumers and public health agencies have shown increasing concern for human health protection. In addition to aluminum (Al) microparticles, Al-containing nanomaterials (Al NMs) have been applied by food industry as additives and contact materials. Due to the limited amount of literature on the toxicity of Al NMs, this study aimed to evaluate the in vivo genotoxic potential of Al0 and Al2O3 NMs after acute oral exposure. Male Sprague-Dawley rats were administered three successive gavages at 6, 12.5 and 25 mg/kg bw. A comparison with AlCl3 was done in order to assess the potential effect of dissolution into Al ions. Both DNA strand breaks and oxidative DNA damage were investigated in six organs/tissues (duodenum, liver, kidney, spleen, blood and bone marrow) with the alkaline and the Fpg-modified comet assays. Concomitantly, chromosomal damage was investigated in bone marrow and colon with the micronucleus assay. The comet assay only showed DNA damage with Al2O3 NMs in bone marrow (BM), while AlCl3 induced slight but non-significant oxidative DNA damage in blood. No increase of chromosomal mutations was observed after treatment with the two Al MNs either in the BM or in the colons of rats.

Core-shell microparticles formed by the metal-organic framework CIM-80(Al) (Silica@CIM-80(Al)) as sorbent material in miniaturized dispersive solid-phase extraction

Core-shell SiO2@CIM-80(Al) microspheres were synthesized, characterized, and used as novel sorbent in a dispersive miniaturized solid-phase extraction (D-μSPE) method for the determination of fourteen polycyclic aromatic hydrocarbons (PAHs) in wastewaters by ultra-high performance liquid chromatography coupled to a fluorescence detector (UHPLC-FD). A Doehlert experimental design permitted to optimize the main parameters affecting the microextraction procedure, intending the obtaining of a simple approach. Optimized extraction conditions include 13 mg of SiO2@CIM-80(Al) microparticles (~2 mg CIM-80(Al)), 2.5 min of extraction time, 0.125 mL of acetonitrile (ACN) as desorption solvent and 0.5 min of desorption time. The entire method showed adequate analytical performance with limits of detection down to 5 ng L−1, and inter-day precision lower than 14.1% for a concentration level of 0.5 μg L−1. The extraction capability of SiO2@CIM-80(Al) microspheres was compared to that obtained with commercially available silica microspheres and the neat MOF CIM-80(Al), demonstrating the advantages of the use of MOF core-shell sorbents in D-μSPE.

Development of thermal barrier coating systems from Al microparticles. Part I: Influence of processing conditions on the mechanisms of formation

This work presents the mechanisms of formation on pure nickel of full thermal barrier coating systems (aluminide coating, thermally grown oxide and thermal barrier top coating) from micro-sized Al particles dispersed in a slurry annealed in different atmospheres (Ar, synthetic air, water vapour and mixtures thereof). The simultaneous formation of nickel aluminides and of a thermal barrier made of sintered hollow alumina spheres involved self-propagating high-temperature synthesis in all conditions. However, the microstructures and adherence of the top coatings changed markedly with either a diffusion step (700°C-2 h) or a complete heat treatment (700°C-2 h + 1100°C-2 h) depending on the atmosphere. Whereas fast consumption of Al occurred in Ar to form the nickel aluminides, synthetic air and water vapour fostered the peripheral oxidation of Al micro-sized particles that impeded the release of Al and its diffusion towards the substrate. This resulted in heterogeneous diffusion layers but thicker top coatings with better sintering and thicker alumina shells.