Search Results (7)

The synthesis of oxide nanopowders through ultrasonic spray pyrolysis (USP) represents a sustainable method for producing high-purity, spherical particles tailored for advanced material applications. Recent developments in USP synthesis leverage the continuous transport of aerosols from an ultrasonic generator to a high-temperature furnace, with nanopowders collected efficiently using an electrostatic precipitator. This study explored the use of USP for titanium oxysulfate and aluminum nitrate solutions derived from the aluminum industry, focusing on resource recovery and waste reduction. Titanium oxysulfate was synthesized by leaching slag, generated during the reduction of red mud, with sulfuric acid under oxidizing, high-pressure conditions. After purification, the titanium oxysulfate solution was processed using USP in a hydrogen reduction atmosphere to yield spherical titanium dioxide (TiO₂) nanopowders. The hydrogen atmosphere enabled precise control over the nanoparticles’ morphology and crystallinity, enhancing their suitability for use in applications such as photocatalysis, pigments, and advanced coatings. In parallel, both synthetic and laboratory solutions of aluminum nitrate [Al(NO₃)₃] were prepared. The laboratory solution was prepared by leaching aluminum hydroxide oxide (AlOOH) with hydrochloric acid to form aluminum chloride (AlCl₃), followed by a conversion to aluminum nitrate through the addition of nitric acid. The resulting aluminum nitrate solution was subjected to USP, producing highly uniform, spherical alumina (Al₂O₃) nanopowders with a narrow size distribution. The resulting nanopowders, characterized by their controlled properties and potential applicability, represent an advancement in oxide powder synthesis and resource-efficient manufacturing techniques. Full article

Aluminum nanoparticles (Al NPs) are interesting for energetic and plasmonic applications due to their enhanced size-dependent properties. Passivating the surface of these particles is necessary to avoid forming a native oxide layer, which can degrade energetic and optical characteristics. This work utilized a radiofrequency (RF)-driven capacitively coupled argon/hydrogen plasma to form surface-modified Al NPs from aluminum trichloride (AlCl₃) vapor and 5% silane in argon (dilute SiH₄). Varying the power and dilute SiH₄ flow rate in the afterglow of the plasma led to the formation of varying nanoparticle morphologies: Al–SiO₂ core–shell, Si–Al₂O₃ core–shell, and Al–Si Janus particles. Scanning transmission electron microscopy with a high-angle annular dark-field detector (STEM-HAADF) and energy-dispersive X-ray spectroscopy (EDS) were employed for characterization. The surfaces of the nanoparticles and sample composition were characterized and found to be sensitive to changes in RF power input and dilute SiH₄ flow rate. This work demonstrates a tunable range of Al–SiO₂ core–shell nanoparticles where the Al-to-Si ratio could be varied by changing the plasma parameters. Thermal analysis measurements performed on plasma-synthesized Al, crystalline Si, and Al–SiO₂ samples are compared to those from a commercially available 80 nm Al nanopowder. Core–shell particles exhibit an increase in oxidation temperature from 535 °C for Al to 585 °C for Al–SiO₂. This all-gas-phase synthesis approach offers a simple preparation method to produce high-purity heterostructured Al NPs. Full article

The microstructures and structures of modified Al₂O₃/IF-WS₂ coatings prepared on aluminum substrates are studied. Amorphous Al₂O₃ oxide coatings are obtained on EN AW 5251 aluminum alloy using the electrooxidation process. The quality of the IF-WS₂ nanopowder is of great importance in the process of its introduction into the nanopores of the Al₂O₃ oxide coating. Commercial nanopowder tends to agglomerate, and without appropriate pretreatment, it is difficult to introduce it into the nanopores of the coating. To improve the degree of fragmentation of the IF-WS₂ nanopowder, an experiment was carried out to distribute the nanopowder in the presence of strong ultrasounds, and new conditions for introducing the powder into the nanopores were used. A two-level design of experiment (DOE) was used. The SEM examination made it possible to conclude that Method A contributed to a more even distribution of nanoparticles in the microstructure of Al₂O₃ coatings. GIXD analyses showed the presence of WO₃ derived from the IF-WS₂ modifier next to crystal structures derived from aluminum and WS₂. Modification of coatings using Method A resulted in surfaces with lower contact angles measured with polar liquids and higher surface free energy compared to Method B. Full article

In the present study, a comprehensive parametric analysis was carried out using the electrical discharge machining of Ti6Al4V, using pulse-on time, current, and pulse-off time as input factors with output measures of surface roughness and material removal rate. The present study also used two different nanopowders, namely alumina and nano-graphene, to analyze their effect on output measures and surface defects. All the experimental runs were performed using Taguchi’s array at three levels. Analysis of variance was employed to study the statistical significance. Empirical relations were generated through Minitab. The regression model term was observed to be significant for both the output responses, which suggested that the generated regressions were adequate. Among the input factors, pulse-off time and current were found to have a vital role in the change in material removal rate, while pulse-on time was observed as a vital input parameter. For surface quality, pulse-on time and pulse-off time were recognized to be influential parameters, while current was observed to be an insignificant factor. Teaching–learning-based optimization was used for the optimization of output responses. The influence of alumina and nano-graphene powder was investigated at optimal process parameters. The machining performance was significantly improved by using both powder-mixed electrical discharge machining as compared to the conventional method. Due to the higher conductivity of nano-graphene powder, it showed a larger improvement as compared to alumina powder. Lastly, scanning electron microscopy was operated to investigate the impact of alumina and graphene powder on surface morphology. The machined surface obtained for the conventional process depicted more surface defects than the powder-mixed process, which is key in aeronautical applications. Full article

The development of novel methods for industrial production of metal-matrix composites with improved properties is extremely important. An aluminum matrix reinforced by “in situ” α-Al₂O₃ nanoparticles was fabricated via direct chemical reaction between molten aluminum and rutile TiO₂ nanopowder under the layer of molten salts at 700–800 °C in air atmosphere. Morphology, size, and distribution of the in situ particles, as well as the microstructure and mechanical properties of the composites were investigated by XRD, SEM, Raman spectra, and hardness and tensile tests. Synthesized aluminum–alumina composites with Al₂O₃ concentration up to 19 wt.% had a characteristic metallic luster, their surfaces were smooth without any cracks and porosity. The obtained results indicate that the “in situ” particles were mainly cube-shaped on the nanometer scale and uniform matrix distribution. The concentration of Al₂O₃ nanoparticles depended on the exposure time and initial precursor concentration, rather than on the synthesis temperature. The influence of the structure of the studied materials on their ultimate strength, yield strength, and plasticity under static loads was established. It is shown that under static uniaxial tension, the cast aluminum composites containing aluminum oxide nanoparticles demonstrated significantly increased tensile strength, yield strength, and ductility. The microhardness and tensile strength of the composite material were by 20–30% higher than those of the metallic aluminum. The related elongation increased three times after the addition of nano-α Al₂O₃ into the aluminum matrix. Composite materials of the Al-Al₂O₃ system could be easily rolled into thin and ductile foils and wires. They could be re-melted for the repeated application. Full article

Thermites or composite energetic materials are mixtures made of fuel and oxidizer particles at micron-scale. Thermite reactions are characterized by high adiabatic flame temperatures (>1000 °C) and high heats of reaction (>kJ/cm³), sometimes combined with gas generation. These properties strongly depend on the chemical nature of the couple of components implemented. The present work focuses on the use of indium (III) oxide nanoparticles as oxidizer in the elaboration of nanothermites. Mixed with an aluminum nanopowder, heat of reaction of the resulting Al/In₂O₃ energetic nanocomposite was calculated and its reactive performance (sensitivity thresholds regarding different stimuli (impact, friction, and electrostatic discharge) and combustion velocity examined. The Al/In₂O₃ nanothermite, whose heat of reaction was determined of about 11.75 kJ/cm³, was defined as insensitive and moderately sensitive to impact and friction stimuli and extreme sensitive to spark with values >100 N, 324 N, and 0.31 mJ, respectively. The spark sensitivity was decreased by increasing In₂O₃ oxidizer (27.71 mJ). The combustion speed in confined geometries experiments was established near 500 m/s. The nature of the oxidizer implemented herein within a thermite formulation is reported for the first time. Full article

This article focuses on the development of nanoalumina-based cement mortars for overlay applications in concrete floors. It focuses on the effect of applying aluminum oxide (Al₂O₃) nanopowder to the cement mortar used to make the overlay, on the adhesion of this overlay to concrete substrate and on its functional properties. It was claimed that the addition of 0.5% of Al₂O₃ nanopowder has a positive effect on the adhesion of the cement mortar used to make the overlay to the substrate made of concrete. The prior studies performed using scanning electron microscopy (SEM) confirmed that the reason for the improvement in adhesion is the fact that cement mortar used to make the overlay with the addition of 0.5% of Al₂O₃ nanopowder is less porous than the reference mortar within the interphase. The article concurs that the most favorable results, in terms of lower abrasion resistance and higher subsurface tensile strength of the cement mortar used to make the overlay, are mainly brought about by adding 0.5% of Al₂O₃ nanopowder. Full article