Spherical Metal Research Articles

РАЗРАБОТКА ЛИТЕЙНОЙ ТЕХНОЛОГИИ ПОЛУЧЕНИЯ ПОРИСТОГО КОМПОЗИЦИОННОГО МАТЕРИАЛА НА ОСНОВЕ АЛЮМИНИЯ

The work is devoted to the development of technology for obtaining composite material based on aluminium alloy with a given morphology of pores by using hollow metal spheres as pore formers. In the course of work the following researches have been carried out: selection of material-former of hollow metal spheres forming the structure and physical and mechanical properties of porous aluminum; study of influence of binder type on uniformity of conductive coating on the surface of form-former; study of influence of electrolysis modes on continuity of metal coating on the surface of conductive layer of formformer; production of porous aluminum by foundry technology. It is shown that the use of hollow metallized spheres as a pore former allowed to reduce the density of the AK12 alloy prototype by 40%.

An experimental study on quenching of metallic spheres in seawater

Motivated by quenching of melt droplets and debris particles in seawater during a hypothetical severe accident of light water reactors (LWRs), the quenching process of stainless-steel spheres in a seawater pool was investigated in the present study. The polished spheres were pre-heated up to 1000℃ in an induction furnace with inserted atmosphere, and then immersed into the subcooled water pool in a chamber made of transparent quartz. A thermocouple was embedded in the center of the sphere to measure the history of the sphere’s temperature, while a high-speed camera was employed to record the quenching process and vapor film dynamics. Quantitative data, e.g. film thickness and oscillation, of the vapor film evolution during the quenching process were obtained through an image processing program developed on the MATLAB platform.The experimental results indicated that the quenching rate was higher in seawater than in deionized water, and the vapor film collapsed at a temperature higher than the Leidenfrost temperature in deionized water. The trend appeared more significant with increasing subcooling of water. The comparison of the quenched spheres suggested the surface of the sphere in seawater achieved higher degree of discoloration and roughening than that in deionized water, probably due to the additives of salt which change water properties. The image processing and analysis revealed that the vapor film had different thickness profile along the upper and lower hemispheres, and the averaged film thickness was smaller in seawater than in de-ionized water during the stage of stable film boiling. The vapor film was thinning and oscillating with time, and its fluctuations appeared different frequencies and amplitudes at the upper and lower locations, which may explain the mechanism of the earlier collapse of vapor film in the quenching process of a high-temperature sphere in seawater.

Anderson localization of electromagnetic waves in three dimensions

Anderson localization is a halt of diffusive wave propagation in disordered systems. Despite extensive studies over the past 40 years, Anderson localization of light in three dimensions has remained elusive, leading to the question of its very existence. Recent advances have enabled finite-difference time-domain calculations to be sped up by orders of magnitude, allowing us to conduct brute-force numerical simulations of light transport in fully disordered three-dimensional systems with unprecedented dimension and refractive index difference. We show numerically three-dimensional localization of vector electromagnetic waves in random aggregates of overlapping metallic spheres, in sharp contrast to the absence of localization for dielectric spheres with a refractive index up to 10 in air. Our work opens a wide range of avenues in both fundamental research related to Anderson localization and potential applications using three-dimensional localized light. Whether Anderson localization of light can be achieved in three dimensions has remained an open question. Numerical calculations now show that it is possible with a random arrangement of metallic spheres, but not with dielectric ones.

Abrasion resistance of metakaolin-based geopolymers through accelerated testing and natural wear

Construction and building materials are subject to abrasion wear in a variety of routine applications. The objective of this paper was to investigate the abrasion resistance of metakaolin-based geopolymer concretes. A geopolymer mixture with only metakaolin as precursor material and another mixture with the replacement of 10% of metakaolin by rice husk ash were investigated. Three accelerated abrasion tests were performed. The inorganic abrasion test studies the wear caused by the imposition of sand on the concrete surface. The hydraulic abrasion test wears the concrete surface with metallic spheres in an aquatic environment. The deep abrasion test measures abrasion through wear on a stainless-steel cylinder using silicon carbide. A natural validation step through the exposure of slabs in a natural environment was created to confirm the performance of the geopolymers. The abrasion resistance of geopolymers was the same or better than the abrasion resistance shown in the literature for Portland cement concrete. This behavior is related to the great adhesion of the geopolymer matrix with the aggregates. The performance was validated in the natural exposure of geopolymer concrete slabs to low vehicle traffic.

Potentials of Ultrasonically Atomized Cored Wires for Powder Metallurgy and Additive Manufacturing

Abstract Powder production for additive manufacturing is currently mainly done by inert gas atomization. A new process is the production of low-oxygen and highly spherical metal powders by ultrasonic atomization from a wire or rod feedstock. As a crucible-free process and because of an electric arc as an energy source, even materials with a high liquidus temperature up to 1800 °C can be processed. A limitation of this technique can be found in the continuous processing of high-strength materials, like martensitic hardenable tool steels, from a stiff wired feedstock because of the limited feed ability. This paper investigates the possibility of processing high-strength steel powder using cored wire as the starting material for the ultrasonic atomization process to circumvent the feeding problem of high-strength materials. Thereby, two carbon martensitic hardenable hot work tool steels with a carbon content of 0.12 wt. % and 0.4 wt. % are considered as reference materials. After the atomization process with varying parameters, powders are characterized concerning their morphology, chemical composition, phases formed, and related powder properties. In addition to flowability, the bulk density are also determined. Based on these results, a conclusion will finally be given on the suitability of ultrasonically atomized powders for additive manufacturing and fast sintering techniques.

In situ growth of porous organic framework on iron wire for microextraction of polycyclic aromatic hydrocarbons

In this work, a novel spherical metal organic framework (MOF) was first in situ grown on the surface of iron wire (IW), in which IW served as the substrate and metal source for MOF (type NH2-MIL88) growth without adding additional metal salts in the process, while spherical NH2-MIL88 provided more active sites for further construction of multifunctional composites. Subsequently, a covalent organic framework (COF) was covalently bonded to the surface of the NH2-MIL88 to obtain the IW@NH2-MIL88@COF fibers, which were used for headspace solid-phase microextraction (HS-SPME) of polycyclic aromatic hydrocarbons (PAHs) in milk samples prior to determination by gas chromatography-flame ionization detection (GC-FID). Compared with the fiber prepared by physical coating, the IW@NH2-MIL88@COF fiber prepared by in situ growth and covalent bonding exhibits better stability and possesses more uniform layer. The extraction mechanism of the IW@NH2-MIL88@COF fiber for PAHs was discussed, which mainly owed to π-π interactions and hydrophobic interactions. After optimization of the primary extraction conditions, the SPME-GC-FID method was established for five PAHs with a wide linear range (1–200 ng mL−1), good linearity coefficient (0.9935–0.9987) and low detection limits (0.017–0.028 ng mL−1). The relative recoveries for PAHs detection in milk samples ranged from 64.69 to 113.97%. This work not only provides new ideas for the in situ growth of other types of MOF, but also provides new methods for the construction of multifunctional composites.

Metal atoms adsorbed Ga2O3 monolayer: As a potential application in optoelectronic devices

Density functional theory based on first principles has been used to analyze the electronic, magnetic, work function, and optical absorption characteristics of metal atoms adsorbed Ga2O3 monolayer structures. The outcomes demonstrate that the Pt–Ga2O3 and Zn–Ga2O3 systems remain nonmagnetic semiconductor characteristics, while the Ag–Ga2O3, K–Ga2O3, Li–Ga2O3 and Na–Ga2O3 systems exhibit nonmagnetic metal behaviors. Meanwhile, the Al–Ga2O3, Cr–Ga2O3, Fe–Ga2O3 and Ni–Ga2O3 systems reveal magnetic metal behaviors, and the Au–Ga2O3, Bi–Ga2O3, Ge–Ga2O3 and Sn–Ga2O3 systems show magnetic semiconductor characteristics. Whereas the Co–Ga2O3 system emerges magnetic semimetal behavior. Furthermore, the work function of Ga2O3 adsorbed by metals are reduced. Importantly, after the adsorption of metal atoms, the optical absorption of Ga2O3 systems has been improved to varying degrees in the visible and infrared regions, and many absorption peaks have appeared, indicating that the introduction of metal atoms can improve the optical absorption of the Ga2O3 systems in both visible and near-infrared regions. Moreover, spherical metal nanoparticles placed on top of Ga2O3 nanosheets can excite localized surface plasmon resonance, which will greatly enhance the absorption properties of the structure. Therefore, the above results suggest that the metal atoms adsorbed Ga2O3 systems will be useful for the fabrication of spintronics, field emission devices and solar photovoltaic devices.

Estimation of Thickness and Radius of Hollow Metallic Spheres With a Simplified Forward Model

The measurement of metallic spherical objects in various industrial applications has a significant role in guaranteeing safety and product quality, which can be realized by the eddy-current testing technique without contact. In this study, for the measurement of thickness and radius of non-magnetic spherical shells, the original analytical model is simplified according to the asymptotic forms of the modified spherical Bessel functions. The simplified model contains only elementary functions, and can therefore accelerates the sphere property estimation by employing the optimization approach based on the Newton-Raphson method. In numerical simulation and experimental study, the proposed method can provide accurate spherical shell radii with less computational time compared with the original analytical model.

The difference in microwave loss mechanism between nano- and micron-sized Ag particles

Separated E/H-field heating in microwave cavities enables us to examine the microwave loss mechanisms. We prepared mixtures of SiO2 particles (having almost no microwave loss) and Ag particles with micrometer- and nano-sizes. Their average impedance and dielectric constants were measured. Electric conductivity exhibited percolation behavior at a specific threshold of Ag fraction. When the mixtures were heated in the separated fields, H-field heating was dominant in all the fraction ranges for the micrometer-sized Ag mixture. However, E-field heating was dominant below the percolation threshold for the nano-sized Ag mixture, and above the threshold, the H-field became dominant. This change in heating rates indicates the change in the energy loss mechanism. According to the size dependence of the induction current loss in a metallic sphere, the loss becomes less effective below the size of skin depth, namely, in the nano-size region. The permittivity of nano-sized Ag particles was estimated by an approximated Lindhard’s equation, which was input into the Maxwell–Garnett mixing model for predicting the effective complex permittivity of the mixture. It was possible to interpret the measured permittivity dependence on the Ag fraction.

On Monitoring Position of a Charged Particle Moving near a Metal Sphere by Means of Diffraction Radiation

On Monitoring Position of a Charged Particle Moving near a Metal Sphere by Means of Diffraction Radiation

A New Quarter Concave Cylinder Linked Dihedral Reflector for Fully Polarimetric Calibration of Wideband Nonreciprocal Radar Systems

Traditionally, fully polarimetric calibration of a nonreciprocal radar system requires measurements of at least two passive calibrators, such as a dihedral corner reflector plus a metal plate or sphere. Interchanging measurements of multiple calibrators results in not only higher complexity but also degraded uncertainty. In this work, a new polarimetric passive calibrator is proposed, which is designed as quarter concave cylinder linked dihedral (QCCLD). The backscattering of a single QCCLD contains both depolarizing and nondepolarizing components when rotating along the radar line of sight (LOS). This unique characteristic makes it an excellent polarimetric calibrator, which allows fully polarimetric calibration of a nonreciprocal radar system by measuring just a single QCCLD. The theoretical polarimetric scattering matrix (PSM) is derived based on physical optics (PO). Using complex exponential (CE) model-based parametric representation, a novel polarimetric calibration procedure is developed to suppress undesirable scattering components, which degrade the calibration accuracy. Experimental calibration results are presented with the polarization isolation improvement of more than 15 dB over 6–18 GHz frequency band, demonstrating the usefulness of the proposed QCCLD calibrator for fully polarimetric calibration of a wideband nonreciprocal radar system.

High-speed etching of gallium nitride substrate using hydrogen-contained atmospheric-pressure plasma

Atmospheric-pressure plasma etching of a gallium nitride (GaN) substrate using hydrogen radicals instead of chlorine radicals was investigated toward the backside thinning of GaN vertical power devices to reduce on-resistance. As a basic experiment, a pipe-shaped electrode was placed facing the GaN substrate to generate atmospheric-pressure plasma of a gas mixture of helium and hydrogen and high-speed etching of approximately 4 μm min−1 was achieved. Although many spherical Ga metal particles were observed on the surface after processing, the addition of oxygen gas was found to be able to suppress them.

Proliferation resistance of light water reactor versus pebble bed reactor

Intrinsic proliferation resistance (PR) against the weaponization of U and Pu in used nuclear fuel discharged from a 500 MWt pebble bed reactor (PBR) and an integral pressurized water reactor (iPWR) was assessed. Four inherent characteristics (spontaneous fission neutron emission, heat load, radiation exposure, and Rossi-α) of U and Pu in the used fuel were the basis for the PR evaluation. These four characteristics for a significant quantity of U (75 kg of 235U) and Pu (8 kg) metallic sphere made from used fuel were quantified by performing reactor neutronics simulations. The intrinsic PR values for PBR used fuel were found to be lower compared to the iPWR for all the cases analyzed due to the higher quantity and better quality of nuclear material. Online refueling with an effective safeguards approach and a better choice of PBR fuel composition are needed to increase the PR of its used fuel.

Ammonium Ion Batteries: Material, Electrochemistry and Strategy.

Ammonium-ion batteries (AIBs) have recently attracted increasing attention in the field of aqueous batteries owing to their high safety and fast diffusion kinetics. The NH4 + storage mechanism is quite different from that of spherical metal ions (e.g. Li+ , Na+ , K+ , Mg2+ , and Zn2+ ) because of the formation of hydrogen bonds between NH4 + and host materials. Although many materials have been proposed as electrode materials for AIBs, their performances hardly meet the requirement of future electrochemical energy storage devices. It is thus urgent to design and exploit advanced materials for AIBs. This review highlights the state-of-the-art research on AIBs. The insights into the basic configuration, operating mechanism and recent progress of electrode materials and corresponding electrolytes for AIBs have been comprehensively outlined. The electrode materials are classified and compared according to different NH4 + storage behaviour in the structure. The challenges, design strategies and perspectives are also discussed for the future development of AIBs.

Ammonium Ion Batteries: Material, Electrochemistry and Strategy

AbstractAmmonium‐ion batteries (AIBs) have recently attracted increasing attention in the field of aqueous batteries owing to their high safety and fast diffusion kinetics. The NH4+storage mechanism is quite different from that of spherical metal ions (e.g. Li+, Na+, K+, Mg2+, and Zn2+) because of the formation of hydrogen bonds between NH4+and host materials. Although many materials have been proposed as electrode materials for AIBs, their performances hardly meet the requirement of future electrochemical energy storage devices. It is thus urgent to design and exploit advanced materials for AIBs. This review highlights the state‐of‐the‐art research on AIBs. The insights into the basic configuration, operating mechanism and recent progress of electrode materials and corresponding electrolytes for AIBs have been comprehensively outlined. The electrode materials are classified and compared according to different NH4+storage behaviour in the structure. The challenges, design strategies and perspectives are also discussed for the future development of AIBs.

Effect of Electrode Induction Melting Gas Atomization on Powder Quality: Satellite Formation Mechanism and Pressure

Electrode induction melting gas atomization (EIGA) is a wildly applied method for preparing ultra-clean and spherical metal powders, which is a completely crucible-free melting and atomization process. Based on several experiments, we found that although the sphericity of metal powders prepared by EIGA was higher than that of other atomization methods, there were still some satellite powders. To understand the formation mechanism of the satellite, a computational fluid dynamics (CFD) approach FLUENT and a discrete particle model (DPM) were developed to simulate the gas atomization process, and several EIGA experiments with different argon pressures (2.5-4.0 MPa) were designed. A numerical simulation of the gas-flow field verified the formation trajectory of satellites, and the Hall flow rate of the powder produced under different pressures was 13.3, 13.8, 15.6, and 16.8, which were consistent with the prediction of the numerical simulation. This study provides theoretical support for understanding the satellite formation mechanism and improving powder sphericity in the EIGA process.

Research on vibration characteristics of the longitudinal-radial composite piezoelectric ultrasonic transducer

The transducer with high power capacity and extensive radiating area is required in some industrial processes like ultrasonic sonochemistry, ultrasonic cleaning and ultrasonic defoaming and so on. In order to achieve the desired effects, the longitudinal-radial composite piezoelectric ultrasonic transducer is proposed in this paper. The transducer is composed of a longitudinal sandwich piezoelectric transducer, a stepped ultrasonic horn and a metal sphere. The longitudinal vibrations of the sandwich piezoelectric transducer and the stepped ultrasonic horn excite the radial vibration of the metal sphere so that the longitudinal-radial coupled vibration of the transducer is achieved. The equivalent circuits for a sphere in radial vibration and for the entire system in longitudinal-radial coupled vibration have been developed. To validate the proposed equivalent circuits, the vibration characteristics of the transducer are investigated using the equivalent circuit method, numerical method, and experiment. The resonance frequencies obtained from the equivalent circuit method, numerical method and experiment are 29992 Hz, 29990 Hz and 30590 Hz, respectively, and the simulated and experimental results indicate that the frequencies correspond to the designed longitudinal-radial coupled resonance mode of the transducer. The measured frequency and displacement distribution showed good agreement with the analytical and numerical calculation results.

Analytical results for enhancement factor (EF) of surface enhanced Raman spectroscopy (SERS) for two metallic spheres and nano-shells

Interactions between symmetric two metallic spheres and an electromagnetic (EM) field polarized in the symmetric axis are described. Spherical symmetries of the present systems are exploited by the use of bi-spherical coordinates. Boundary conditions are applied, which assume a very large negative value for the dielectric constant of special metals. The EM field in small gaps (in hotspots) is amplified by many orders of magnitude relative to the external field. Analytical results for the maximal enhancement factor in surface enhanced Raman spectroscopy for two metallic spheres and two nano-shells are obtained as a function of various parameters. The calculations are based on potentials derived by using an electrostatic model, which is valid for very small particles.

On the Moving Charged Particle’s Position Monitoring Using Its Diffraction Radiation on the Metal Sphere

On the Moving Charged Particle’s Position Monitoring Using Its Diffraction Radiation on the Metal Sphere

CT scan trajectory calibration based on projected metal spheres: When and how should errors from elliptical distortion be corrected?

The majority of geometry calibration procedures for industrial X-ray Computed Tomography (CT) are based on determining projected sphere centres in X-ray projections. The centres are typically derived from the elliptical contours that arise for cone beam setups. However, the ellipse centre is not identical with the projected sphere centre. A correction method (also known as Deng correction) exists, but is only used in some instances in literature. To this extent, it is an open question for which cases the correction leads to a significant improvement. For specific cases, it can even lead to larger errors. In this contribution, we therefore analyse the parameter range for which the correction is suitable. This is done by means of a simulation parameter study. Additionally, we propose an adapted correction formula that can be used for 3D scan trajectory calibration where the source-detector-distance is known. It is further proposed to keep the ellipse orientation in the ellipse fitting routine fixed. The results from simulation are selectively compared with experimental findings. Overall, the adapted correction leads to superior results compared with the original Deng correction. Whether a correction leads to an improvement at all strongly depends on the ratio between the axial source-object-distance and the sphere radius and on the position of the projected sphere centre on the detector. A theoretically derived decision criterion was largely confirmed. The presented results therefore can give a guidance for potential users who want to decide whether a correction is advantageous for a given sphere radius and CT system geometry.