Submicron Size Research Articles

Influence of the neck length of urease-powered flask-like colloidal motors on their kinematic behavior.

Enzyme-powered synthetic colloidal motors hold promising potential for in vivo medical applications because of their unique features such as self-propulsion, sub-micrometer size, fuel bioavailability, and structural and functional versatility. However, the key parameters influencing the propulsion efficiency of enzyme-powered colloidal motors still remain unclear. Here, we report the effect of the neck length of urease-powered pentosan flask-like colloidal motors on their kinematic behavior resembling the role of bacterial flagella. The sub-micrometer-sized and streamlined pentosan flask-like colloidal motors with variable neck lengths are synthesized through a facile interfacial dynamic assembly and polymerization strategy. The urease molecules are loaded through vacuum infusion technology and thus the urease-triggered catalytic reaction can propel the pentosan flask-like colloidal motors to move autonomously in the urea solution. The self-propelled speed of these pentosan flask-like colloidal motors significantly increases with the elongating neck lengths. The mechanism of the relationship between the neck length and self-propelled motion is that a longer neck can provide a larger self-propelled force due to the larger force area and stabilize the rotation because of the increased rotational friction. This research can provide guidance for the design of biomedical colloidal motors.

Performance of construction and demolition waste as recycled aggregates in concrete – review

This article presents a structured and comprehensive review of the existing literature on physical, chemical, microstructure, and durability properties of recycled aggregate concrete (RAC). The engineering properties of concrete made from such recycled aggregates are critically analysed by focusing mainly on the fresh and hardened states along with several characterisation techniques such as scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetry/differential thermal analysis. Also, creep, shrinkage, microstructure and durability of RAC were evaluated critically. In addition, improvement techniques in its microstructure are also explored with efficient mixing approaches for the development of geopolymer RAC. Furthermore, techniques to enhance the mechanical characteristics and long-term performance of recycled aggregate are distilled and divided into three categories: (1) lowering the porosity of recycled aggregate, (2) lowering the layer of old mortar on the surface of recycled aggregate, and (3) enhancing the property without changing the recycled aggregate. It is evident from the thorough examination that recycled aggregates can be used in concrete up to a certain amount. For the creation of sustainable and high-performance concrete, it is also necessary to incorporate mineral admixtures of micron, sub-micron, and nano size to address the drawbacks of recycled aggregates.

Preparation, morphology, antiradical and biological activity of quercetin-containing nanoparticles of zein and their submicron aggregates

Nanoparticles of corn prolamine protein zein (NPQ) containing 0.005–0.26 g/g quercetin (Q) were prepared by desolvation of a 25–30 mg/mL ethanol protein solution containing the encapsulated compound with an aqueous polystyrene sulfonate. The size of zein nanoparticles and their aggregates was characterized by dynamic light scattering and atomic force microscopy; the quercetin content – by the Folin-Ciocalteu assay. While the quercetin/zein ratio in solution is less than 0.08 g/g, the polyphenol is quantitatively included in the nanoparticles, and their hydrodynamic diameter is 60–75 nm. As the quercetin/zein ratio rises to 0.20 g/g, the average particle diameter increases to 150 nm. In concentrated dispersions, aggregates with a diameter of 500–600 nm are formed. The kinetics of quercetin release from NPQ with different mass fractions of Q in distilled water and solutions simulating the environment of the stomach and intestines at 37 °C were studied.Zein nanoparticles exhibit weak activity in the reaction with ABTS cation-radicals. Quercetin encapsulated in the zein matrix generally retains the antiradical activity characteristic of the free flavonoid, however, the rate of decolorization of ABTS cation-radicals decreases due to the prolonged release of quercetin from NPQ. The cytoprotective properties of quercetin in zein nanoparticles are significantly reduced and manifest themselves only in partial preservation of the integrity of cell membranes and a decrease in the release of lactate dehydrogenase from UV-C irradiated HaCaT cells. In contrast to free quercetin, the introduction of Q in zein nanoparticles or their submicron aggregates increases the number of metabolically dead UV-C-irradiated HaCaT cells, enhancing the cytotoxic effect of UV radiation. Empty zein aggregates of submicron size have a similar effect.

In-vehicle air quality in public buses during real-world trips in Kathmandu Valley, Nepal

Urban air quality shows notable variability across various microenvironments. Transport-related microenvironments often have one of the highest air pollution levels, where commuters have significant exposure to air pollutants. In Kathmandu Valley (KV), Nepal, passengers’ exposure to air pollutants in such microenvironments remain a poorly understood issue. In this study, we analyzed cabin air quality and ventilation rates in public buses operated in KV. In-cabin and in-route ambient air pollution levels were monitored during real-world bus operations in 32 trips on a test route selected in the core city area. A CO2 mass balance model was applied to estimate cabin ventilation rates. The mean in-cabin and outdoor PM2.5 concentrations were 95.9 ± 40.4 (mean ± standard deviation) and 94.7 ± 32.4 μg/m3, respectively. Likewise, mean in-cabin and outdoor PM1 concentrations were 72.5 ± 31.3 and 69.7 ± 25.3 μg/m3, respectively, with mean PM1 to PM2.5 ratio >0.75, indicating that a majority of particle mass was in the sub-micron size range, which is often more health-hazardous. We estimated passengers’ inhalation dose for PM2.5 and PM1 as 5.65 ± 2.32 and 4.27 ± 1.79 μg/km, respectively. Among various factors considered, traffic hour significantly affected both in-cabin and ambient particulate matter concentrations. The trip-average in-cabin CO2 concentration ranged from 513 to 1230 ppm, whereas cabin ventilation rates ranged from 8.0 to 72.4 L/s/person. Ventilation levels in a majority of bus trips were inadequate, especially considering the recommended thresholds to reduce the transmission risk of airborne diseases. Setting standards for ventilation and air conditioning systems in public buses is crucial to ensure thermal comfort, protect bus commuters from the harmful impacts of air pollution, and to improve public transport services in KV.

Electrochemical Reactions of Graphite Fluoride Electrodes in Ionic Liquids

Li-graphite fluoride (CF x ) primary batteries show the highest energy density (2180 Wh kg− 1) among commercialized Li primary batteries, long life storage, and wide operating temperature range, and are the power sources for medical equipment, stand-alone devices, remote keyless systems, and space crafts. Recently, Li-CF x cells could be used as secondary batteries1 and are attracting attention as next-generation storage batteries with high energy density. Current problems of conventional Li-CF x batteries are safety issues due to using flammable organic electrolytes and short cycle life originated from oxidative decomposition of organic solvents while using as secondary batteries. In this study, we focused on the application of ionic liquids which shows nonvolatile, nonflammable, and wide electrochemical potential window. However, there had been no previous reports of Li-CF x battery operation using ionic liquids.In Li-CF x primary batteries with organic electrolytes, solvent and Li+ co-intercalate into CF x layer to form an intermediate product and that decomposes to LiF and amorphous carbon (intermediate mechanism).2 Because of the strong interaction between organic solvent and Li+, the solvated Li+ can diffuse into the bulk of the CF x . The slow desolvation within the CF x layer contributes to the small and dispersed crystallization of LiF, and CF x can react completely.3 In the case of ionic liquids, however, Li+ and CF x may react directly due to the lack of solvent, resulting in localized crystallization of LiF, inhibiting subsequent Li+ intercalation and preventing CF from reacting completely.Therefore, in this study, we focused on shortening the diffusion distance of Li+ and made the CF x particles finer to submicron size and the electrochemical reaction of CF x with Li+ ions were successfully carried out completely in ionic liquids. In this presentation, we will report the fundamentals on the electrochemical reactions of CF x electrodes in ionic liquids, including how the components of ionic liquids influence on the electrode potential of CF x . The realization of Li-CF x batteries using ionic liquids will expand the range of applications with batteries at the environments (undersea, subterranean, and outer space) where conventional batteries have been difficult to be used. Y. Ito, et al., Chem. Mater., 34, 19, 8711, (2022).H. Touhara, et al., Solid State Ionics, 14, 163 (1984).J. Wang, J. Mater. Chem. A, 8, 6105 (2020).

In-situ thermite combustion of micro magnesium fuel and lunar regolith simulant nanoparticles

Significant heat generation will be required for humans and equipment to the lunar night. In this work, we investigate the use of a sustainable in-situ thermite material as a fuel to provide the thermal energy required to keep components in working conditions. Magnesium is used as a reactive metal fuel, with lunar regolith simulant ball milled to sub-micron sizes as a solid oxidizer producing exothermic reactions. Enhanced combustion is achieved by controlling particle size and composition of the thermite mixture. Simulant particles ranging from hundreds of nanometers to tens of microns in diameter are tested, as well as the magnesium fuel compositions of 20% to 40% by weight. Small pellets of 3 mm in diameter and 3 mm in height are ignited by laser in both air and vacuum to quantify the combustion properties in different environments. High speed video, infrared camera and pyrometry techniques are taken to quantify the sample combustion properties. These pellets demonstrate the burning rates between 2.3 and 5.9 mm/s and temperatures ranging from 1100 to 1480 °C in vacuum and in air conditions, respectively. The samples composed of 20% magnesium and 80% regolith simulant release around 400 J/g, and sustain elevated temperatures for 15 s after combustion, making them suitable for in-situ lunar heating. Novel 2D temperature mapping allows greater understanding of the simulant thermite combustion. Based on the results, we discuss the design considerations that would need to be made in the creation of an in-situ metal fuel heating lunar system.

Assessment of Sub-micrometer-Sized Particles with Practical Activities in an Underground Coal Mine

This assessment was designed to explore and characterize the airborne particles, especially for the sub-micrometer sizes, in an underground coal mine. Airborne particles present in the breathing zone were evaluated by using both (1) direct reading real-time instruments (RTIs) to measure real-time particle number concentrations in the workplaces and (2) gravimetric samplers to collect airborne particles to obtain mass concentrations and conduct further characterizations. Airborne coal mine particles were collected via three samplers: inhalable particle sampler (37 mm cassette with polyvinyl chloride (PVC) filter), respirable dust cyclone (10 mm nylon cyclone with 37 mm Zefon cassette and PVC filter), and a Tsai diffusion sampler (TDS). The TDS, a newly designed sampler, is for collecting particles in the nanometer and respirable size range with a polycarbonate filter and grid. The morphology and compositions of collected particles on the filters were characterized using electron microscopy (EM). RTIs reading showed that the belt entry had a greatly nine-times higher total particle number concentration in average (~ 34,700 particles/cm3) than those measured at both the underground entry and office building (~ 4630 particles/cm3). The belt entry exhibited not only the highest total particle number concentration, but it also had different particle size fractions, particularly in the submicron and smaller sizes. A high level of submicron and nanoparticles was found in the belt conveyor drift area (with concentrations ranging from 0.54 to 1.55 mg/m3 among three samplers). The data support that small particles less than 300 nm are present in the underground coal mine associated with dust generated from practical mining activities. The chemical composition of the air particles has been detected in the presence of Ca, Cu, Si, Al, Fe, and Co which were all found to be harmful to miners when inhaled.

Emitted droplets and aerosols and their transmission when drying hands under an air-jet dryer

When drying hands with a high-speed air jet dryer, the jet impingement on hands can quickly atomize the remnant water on the hand skins into droplets and aerosols. Emission of droplets and liquid aerosols, their spatial transport and the possible inhaling exposure to the hand dryer user remain unclear. This investigation measured the jet flows from a downward air jet dryer, by the particle image velocimetry (PIV), the helium bubble trajectory analysis, and an ultrasonic anemometer. Emission of the droplets when turning over the hands, the droplet spatial motion, and their deposition on human body were photographed by a high speed camera. Concentrations of the liquid aerosols were monitored and the total emitted aerosol numbers and size spectrum were analyzed. The possible inhalation exposure to the emitted liquid aerosols was examined. It is found that number of droplets in size of 0.1 to 0.6 mm can deposit on the mouth and nose and the surrounding face. A typical hand drying process may emit approximately 105 liquid aerosols, of which 93 % are in the submicron size. A hand dryer user may inhale thousands of the emitted liquid aerosols if drying hands without wearing face mask.

Preparation and optimization of La0.6Sr0.4Fe1-yCoyO3-δ cathodes for intermediate temperature solid oxide fuel cells

It is shown in this work that a synthetic route based on the auto-combustion of an ethylene glycol-metal nitrate polymerized gel precursor can be efficiently used to easily produce a range of La0.6Sr0.4Fe1-yCoyO3-δ nanopowders at moderate temperatures. We have been able to determine on air-sintered samples the effect of sintering temperature on the microstructure. At sintering temperatures as low as 1100 to1200 °C, grains are well defined with a uniform round spherical morphology and have a homogeneous sub-micrometer size distribution showing a highly densified microstructure. The electronic conductivity and thermal expansion coefficients (TEC) of sintered LSFC samples have been determined according to the variation of Fe/Co composition. Both measures clearly increase with the Co content. These materials also must exhibit chemical stability with electrolytes, most commonly used for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this way, the material as obtained is optimized in terms of chemical homogeneity and good stoichiometric control, microstructural characteristics of sintered samples, and finally the adequate Cobalt content to avoid high TEC mismatch with other components of the SOFC. This is a crucial issue as it causes an important thermo¬mechanical stress; promote extensive microcraking and significant performance degradation. Finally, these cathodes must exhibit acceptable electrochemical parameters for use in IT-SOFC.

Innovative use of lipid mesophase dispersions for bisphenol A sequestration in water

HypothesisMesophase dispersions are promising colloids for removing micropollutants from water. We hypothesized that the complex internal nanostructure and tunable lipid/water interface amounts play a crucial role in absorbed quantities. Modifications in interfacial organization within the particles while trapping the micropollutant is assumed. ExperimentsWe formulated stable monolinolein-based dispersions with four types of mesophases (bicontinuous and micellar cubic, hexagonal, and fluid isotropic L2) by varying dodecane contents. The absorption of bisphenol A by these dispersions from water was monitored using molecular spectroscopy. At equilibrium, absorbed quantities by mesophase dispersions were compared to unstructured dodecane/water miniemulsions for two bisphenol concentrations. Structural changes during bisphenol incorporation were identified using small-angle X-ray scattering. FindingsLipid mesophase particles of submicron size showed greater bisphenol incorporation than dodecane/water miniemulsions, with cubosomes being most effective ones, absorbing twice as much as unstructured emulsions. Higher absorption levels are observed for more complex nanostructures with increased lipid/dodecane ratios. The incorporation of bisphenol affected the curvature of internal interfaces, potentially causing phase transitions and indicating that bisphenol settles at interfaces. Similar absorption levels in identical mesophases suggest a strong correlation between nano-structure and absorbed quantities.

The emission and physicochemical properties of airborne microplastics and nanoplastics generated during the mechanical recycling of plastic via shredding

This study examined the emission and physicochemical properties of microplastics and nanoplastics (MPs/NPs) generated during shredding, which is regularly used in mechanical recycling. Waste and new polyethylene terephthalate, polypropylene, and high-density polyethylene were investigated herein for a total of six categories. The concentration and size distribution of particles were measured using two spectrometer instruments, and morphology and elemental composition of emitted particles were analyzed with microscopy and spectroscopy. This study found that number concentrations in both submicron and micron sizes of respirable particles were 3–2910× higher during periods of shredding than pre-shredding background concentrations. Maximum concentrations of particles within 10–420 nm, across all six categories, ranged from 22,000- to 1,300,000-particles/cm3 during shredding, compared to average background levels of 700 particles/cm3. Maximum concentrations of particles within 0.3 to 10 μm, across all six categories, ranged from 24- to 2000-particles/cm3 during shredding, compared to average background levels of 2 particles/cm3. Waste plastics consistently generated higher emissions than their new counterparts, which is attributed to the labels, adhesives, and increased additives incorporated into the waste plastic. Morphology varied drastically between particles and an elemental composition analysis found that the samples consisted primarily of C and O, representing the polymer material, as well as Na, Mg, Al, Si, Cu, Cl, K, Ca, Ti, Fe, Rb, and Br representing additives, label, and other contaminates. The shredding of plastic has the potential to expose workers to elevated concentrations of airborne MPs/NPs, especially those between 10 and 100 nm.

Sol-gel synthesis, structure and adsorption properties of LiMgxMn(2-x)O4 (0 ≤ x ≤ 0.7) Oxides

Lithium manganese оxides with a spinel structure LiMgxMn(2–x)O4, doped with Mg2+ ions in the range 0 ≤ x ≤ 0.7, were obtained by sol-gel synthesis. Phase composition and morphology of obtained оxides were studied by using X-ray phase analysis and scanning electron microscopy. It is shown, that in the studied range 0 ≤ x ≤ 0.7 Mg-doped lithium manganese оxides saved the structure of the original cubic spinel LiMn2O4, while an increase in parameter a was observed from 8.175 to 8.309 Å and average crystallite size practically unchanged (30–36 nm). Samples of the initial LiMn2O4 and Mg-doped spinels were represented by prismatic particles of submicron (0.1–0.2 µm) and micron (1.0–3.0 µm) sizes, respectively. The effect of the adsorbent dose (0.05–0.3 g/l) and pH (3.0–13.0) of the solution on the adsorption efficiency was studied. The adsorption isotherms of the LiMg0.3Mn1.7O4 samples were described by the Langmuir monomolecular adsorption equation. An increase in the temperature of the model solution from 25 to 45°C was accompanied by an increase in the maximum adsorption of the LiMg0.3Mn1.7O4 samples from 10.50 to 10.98 mmol/g, which indicates the endothermic nature of the adsorption process. The kinetics of adsorption was well described by a pseudo-second order equation, which indicates the occurrence of chemical interaction during the adsorption process.

Micron-scale imaging using bulk ultrasonics

An extraordinary resolution down to 50 microns is demonstrated for the first time for bulk ultrasonics, using novel micro-fabricated metamaterial lenses. The development and performance of the silicon-based Fabry–Perot type metalenses with an array of 10 micrometre square holes are discussed. Challenges in wave reception are addressed by a custom-developed micro-focal laser with a sub-micron spot size and an innovative experimental set-up together with physics based signal processing. The results provide a pathway for material diagnostics at greater depths with high resolution using micro-metalens-enhanced ultrasound as an alternative to expensive and radiation prone electromagnetic techniques.

Chemical synthesis, structural and magnetic properties of Al-doped neodymium orthoferrite

Crystalline and single phase of Al doped orthoferrite with stoichiometry NdFe1-xAlxO3 was synthesized by a hydrothermal method. The effect of Al doping on the structure features was investigated by powder X-ray diffraction (PXRD) technique. In this sense, Rietveld refinement was applied in refining the PXRD data. Scanning electron microscopy (SEM) was used to characterize the morphology. And from image analyses show a sub-micron particle size distributions for all samples. Using hydrothermal synthesis method, a micro-sized particle distribution is reached. Measurement of magnetic hysteresis loops showed that the highest coercivity (Hc) obtained was 5.2 kOe for the sample with x=2. Compared to previous results using sol-gel synthesis, the hydrothermal method used in this study showed improved magnetization properties.

Submicron-scale Au-decorated TiO2 mesoporous spheres for enhanced photon harvesting in DSSCs through near-field enhancement, light scattering, and dye loading

Light harvesting materials are crucial for capturing the sunlight in a device such as a solar cell for better efficiency. In this study, we developed high surface area, submicron-sized TiO2 spheres (MTS) incorporated with anisotropic Au nanoparticles (Au_MTS) to create highly light-absorbing photoanodes for enhanced dye-sensitized solar cell (DSSC) efficiency. The high surface area of MTS (∼125 m2/g) allows for increased dye-loading, while their submicron size (150–300 nm) provides superior light-scattering capabilities for significantly enhancing the photoanode’s light absorption. Furthermore, incorporating of anisotropic Au nanoparticles enables broadband surface plasmon resonance (SPR) coupling, synergistically boosting photon harvesting in the Au_MTS photoanodes. The interconnected tiny TiO2 nanoparticle network in MTS supports charge carrier generation and transport, providing ample sites for dye adsorption and efficient electron pathways. Au_MTS with varying amounts of Au nanoparticles synthesized by a greener microwave-assisted synthesis method and DSSC devices were fabricated and compared with devices made from pristine MTS and P25 nanoparticles. The optimal Au_MTS device, containing ∼1.3 wt% Au nanoparticles, achieved a maximum power conversion efficiency (PCE) of ∼7.7%, representing improvements of ∼40% and ∼60% over pristine MTS (PCE of ∼5.2%) and P25 nanoparticles (PCE of ∼4.71%), respectively. Overall, this work demonstrates the effectiveness of plasmonic mesoporous photoanodes in enhancing DSSC performance through improved photo response, light scattering, and dye loading.

Sol-Gel Derived Alumina Particles for the Reinforcement of Copper Films on Brass Substrates.

The aim of this study is to provide tailored alumina particles suitable for reinforcing the metal matrix film. The sol-gel method was chosen to prepare particles of submicron size and to control crystal structure by calcination. In this study, copper-based metal matrix composite (MMC) films are developed on brass substrates with different electrodeposition times and alumina concentrations. Scanning electron microscopy (FE-SEM) with energy-dispersive spectroscopy (EDS), TEM, and X-ray diffraction (XRD) were used to characterize the reinforcing phase. The MMC Cu-Al2O3 films were synthesized electrochemically using the co-electrodeposition method. Microstructural and topographical analyses of pure (alumina-free) Cu films and the Cu films with incorporated Al2O3 particles were performed using FE-SEM/EDS and AFM, respectively. Hardness and adhesion resistance were investigated using the Vickers microindentation test and evaluated by applying the Chen-Gao (C-G) mathematical model. The sessile drop method was used for measuring contact angles for water. The microhardness and adhesion of the MMC Cu-Al2O3 films are improved when Al2O3 is added. The concentration of alumina particles in the electrolyte correlates with an increase in absolute film hardness in the way that 1.0 wt.% of alumina in electrolytes results in a 9.96% increase compared to the pure copper film, and the improvement is maximal in the film obtained from electrolytes containing 3.0 wt.% alumina giving the film 2.128 GPa, a 134% hardness value of that of the pure copper film. The surface roughness of the MMC film increased from 2.8 to 6.9 times compared to the Cu film without particles. The decrease in the water contact angle of Cu films with incorporated alumina particles relative to the pure Cu films was from 84.94° to 58.78°.

Stearic Acid as Polymerization Medium, Dopant and Hydrophobizer: Chemical Oxidative Polymerization of Pyrrole.

In recent years, fatty acids have garnered significant attention as a natural phase-change material and a hydrophobizer due to their biocompatibility and biodegradability. In this study, the utilization of fatty acid is proposed as a polymerization medium for the first time. As a specific reaction, chemical oxidative polymerizations of pyrrole is conducted using ferric chloride as an oxidant in a stearic acid medium. The polymerizations resulted in the production of micrometer-sized polypyrrole (PPy) grains, which are aggregates of atypical primary particles with submicrometer size. The PPy grains are doped with stearic acid, suggesting that the stearic acid functioned as a dopant and a hydrophobizing agent as well as a polymerization medium. The dried PPy grains can adsorb at the air-water interface and function as a liquid marble stabilizer with light-to-heat photothermal properties. The liquid marble can move on a planar air-water interface by Marangoni flow induced by NIR laser light irradiation.

Evaluation of the electrochemical response of aromatic peptides for biodetection of dopamine

Biologically inspired aromatic peptide-based materials are gaining increasing interest as novel charge transport materials for bioelectronics due to their remarkable electrical response and inherent biocompatibility. In this work, the electrochemical response of ten aromatic amino acids and eleven aromatic peptides has been evaluated to assess the potential of incorporating peptides into electrochemical sensors not as biorecognition elements but as biocompatible electronic materials. While the electrochemical response of amino acids is null in all cases, the hexapeptide of phenylalanine (Phe) capped with eight polyethylene glycol units at the N-terminus and, especially, the cyclic dipeptide formed by two dehydro-phenylalanine residues (cyclo(ΔPhe2)), which organize in fibrillary self-assembled structures of nano- and submicrometric size, respectively, are the most electroactive peptides. Electrodes to electrochemically detect the oxidation of dopamine have been prepared using a plasma-activated polyethylene terephthalate glycol substrate covered with a poly(3,4-ethylenedioxythiophene) layer and a peptide coating deposited at the surface. The highest analytical sensitivity and the lowest limits of detection and quantifications have been obtained for the electrode coated with cyclo(ΔPhe2), which shows much better results than that without peptide. These results, on the one hand, confirm the significant role of electron transport through π-stacking interactions in the electrochemical response of peptides and, on the other hand, demonstrate that peptides can be directly used as electronic materials rather than as simple recognition elements in electrochemical biosensors.

STUDY OF THE STRUCTURAL AND ELECTROMAGNETIC CHARACTERISTICS OF FERROMAGNETIC-DIAMAGNETIC COMPOSITES OBTAINED BY THE METHOD OF MODIFIED CHEMICAL CO PRECIPITATION

The microwave electromagnetic properties of ferromagnetic-paramagnetic and ferromagnetic-diamagnetic composites can be changed by varying the concentration of diamagnetic (paramagnetic) and ferromagnetic components. To implement the task of introducing such composites into production, research is required to find effective and simple synthesis technologies that make it possible to vary the content of components with different magnetic characteristics. This work demonstrates a simple method for the synthesis of ferromagnetic ((NiZn)Fe2 O4 )- diamagnetic (ZnO) composites by modified chemical deposition followed by annealing. Also, a comprehensive study of the structural and electromagnetic characteristics of experimental samples was carried out. Using the powder X-ray diffraction method, it was revealed that the phase composition of the final samples is represented exclusively by diamagnetic and ferromagnetic phases. Using scanning electron microscopy, it was found that after thermal annealing the powders have submicron sizes with an average size of 100–137 nm. Using vibration magnetometry, magnetic hysteresis loops were measured, the analysis of which showed that an increase in the concentration of the diamagnetic phase leads to an increase in the coercive force of the composites. The measured microwave spectra of complex magnetic permeability show that by changing the ratio between the ferromagnetic and paramagnetic phases, it is possible to realize a frequency shift of natural ferromagnetic resonance. Also, through the calculation of the reflection coefficient on a metal plate, it is shown that the resulting composites can be used as the basis for new radio-absorbing materials. In addition, the synthesized powders can also be used to create microwave devices and microwave antennas.

Novel Fe-rich hypo-eutectic high entropy alloy developed for laser powder bed fusion in the Al-Co-Cr-Fe-Ni-Zr system

A novel heat resistant Fe-rich hypo-eutectic high entropy alloy (HEA) was manufactured using laser powder bed fusion (LPBF). The prealloyed Al1/4Co2Cr2Fe6Ni3/2Zr powder was characterized and processed using different preheating temperatures (650°C, 700°C and 800°C). The as-built microstructure showed dissimilar morphologies throughout the melt pool, with eutectic grains of ultra fine lamella spacing (λ≈25 nm) inside the core regions, and coarser dendritic and globulitic growth patterns at the interlayer boundaries (ILBs). An annealing treatment at 1000°C for 6 h yielded a homogenous composite microstructure of a Fe-rich matrix with ∼40 % of fine dispersed Zr-rich intermetallic (IM) phases of submicron size. Synchrotron high energy x-ray diffraction (HEXRD) revealed M2Zr Laves (M = Co, Fe, Ni) as the main IM for the as-built condition and the additional growth of M23Zr6 upon annealing. Further HEXRD in-situ high temperature tests examined the lattice parameter evolution and coefficient of thermal expansion (CTE) up to 1100°C. The mechanical performance of the as-built and annealed condition was evaluated through hardness and compression testing at room temperature (RT). Additional compression testing from RT to 1000°C were conducted on the annealed condition to assess the high temperature strength and give comparison to other high temperature materials like Ni-based superalloys.