Spherical Metal Research Articles

Front Cover: H‐Bonded Counterion‐Directed Catalysis: Enantioselective Gold(I)‐Catalyzed Addition to 2‐Alkynyl Enones as a Case Study (Eur. J. Org. Chem. 42/2022)

The Front Cover illustrates the ability of the squaramide group to remove a chiral anionic ligand from Au(I) by H-bonding interactions, by analogy with a magnet that attracts a metallic sphere. H-bonded counterion-directed catalysis was used to perform an enantioselective tandem cycloisomerization-nucleophile addition to 2-alkynyl enones. More information can be found in the Research Article by A. M. Echavarren, A. Franchino et al.

Generalized response spectrum analysis based computational morphogenesis for metal gridshells with buckling-restrained braces subjected to seismic loading

Structural morphogenesis is widely used as a parametric tool to find an optimal structural shape of shell structures for a prescribed objective function and a given design load. However, the current optimization methods are limited to finding a geometry under only a specific static load like the dead load or an equivalent static seismic load for predefined geometrical shapes, and so can not be applied to free-form gridshells. This poses a challenge to achieving an efficient free-form shell structure in high seismic hazard areas. This paper aims to resolve this by presenting a computational morphogenesis method to obtain form-found shell structures by considering the dynamic seismic loads and the response reduction effects of seismic energy-dissipating devices using generalized response spectrum analysis. The method was applied to optimize the buckling-restrained brace layouts on target spherical metal gridshell structures with different diameter-to-height ratios. The resulting form-found structures had an efficient roof geometry, along with an efficient damper layout (to prevent member buckling and the dropout of finishing materials). Dampers were found to be more efficient if placed in the (relatively heavy) supporting structure instead of the roof, and a flattened but locally bulged roof shape proved to be the most efficient in mitigating the seismic response. The generalized response spectrum analysis significantly reduced the computation time while evaluating the displacement response with sufficient practical accuracy, although it slightly underestimates the acceleration response if compared to the conventional nonlinear response history analysis results.

Extinction by plasmonic nanoparticles in dispersive and dissipative media.

Extinction of small metallic spheres has been well understood through the classical Mie theory when the host medium is dispersive and transparent. However, the role of host dissipation on the particulate extinction remains a competition between the enhancing and reducing effects on the localized surface plasmonic resonance (LSPR). Here, using a generalized Mie theory, we elaborate on the specific influence mechanisms of host dissipation on the extinction efficiency factors of a plasmonic nanosphere. To this end, we isolate the dissipative effects by comparing the dispersive and dissipative host with its dissipationless counterpart. As a result, we identify the damping effects of host dissipation on the LSPR including the resonance widening and amplitude reducing. The resonance positions are shifted by host dissipation, which cannot be predicted by the classical Fröhlich condition. Finally, we demonstrate that a wideband extinction enhancement due to host dissipation can be realized away from the positions of the LSPR.

Characterization of the Native Oxide Shell of Copper Metal Powder Spherical Particles.

The native oxide layer that forms on copper (Cu) metal spherical particle surfaces under ambient handling conditions has been shown to have a significant effect on sintering behavior during microwave heating in a previous study, where an abnormal expansion was observed and characterized during sintering of Cu compacts using reducing gases. Because microwave (MW) heating is selective and depends greatly on the dielectric properties of the materials, this thin oxide layer will absorb MW energy easily and can consequently be heated drastically starting from room temperature until the reduction process occurs. In the current study, this oxide ceramic layer was qualitatively and quantitatively characterized using the carrier gas hot extraction (CGHE) method, Auger electron spectroscopy (AES), and a dual-beam focused ion beam (FIB)/scanning electron microscope (SEM) system that combines both FIB and SEM in one single instrument. Two different commercial gas-atomized spherical Cu metal powders with different particle sizes were investigated, where the average oxygen content of the powders was found to be around 0.575 wt% using the CGHE technique. Furthermore, AES spectra along with depth profile measurements were used to qualitatively characterize this oxide layer, with only a rough quantitative thickness approximation due to method limitations and the electron beam reduction effect. For the dual-beam FIB-SEM system, a platinum (Pt) coating was first deposited on the Cu particle surfaces prior to any characterization in order to protect and to preserve the oxide layer from any possible beam-induced reduction. Subsequently, the Pt-coated Cu particles were then cross-sectioned in the middle in situ using an FIB beam, where SEM micrographs of the resulted fresh sections were characterized at a 36° angle stage tilt with four different detector modes. Quantitative thickness characterization of this native oxide layer was successfully achieved using the adapted dual-beam FIB-SEM setup with more accuracy. Overall, the native Cu oxide layer was found to be inhomogeneous over the particles, and its thickness was strongly dependent on particle size. The thickness ranged from around 22–67 nm for Cu powder with a 10 µm average particle size (APS) and around 850–1050 nm for one with less than 149 µm.

A Model for Multiple Metal Spheres in Oscillating Magnetic Fields Using Displaced Dipoles

In this article, we derive a magnetic dipole model for two identical, electrically conducting, and permeable spheres that are exposed to an oscillating homogeneous magnetic field. Our model predicts both amplitude and phase of the induced field outside the spheres. The description is provided for parallel and transverse excitation relative to the axis through the sphere centers. This geometric decomposition allows the application of arbitrary excitation field directions. Our approach is based on one dipole per sphere. The origins of these secondary dipole fields are proposed to be found at positions slightly displaced from the sphere centers to consider the mutual interaction. This displacement and the resulting phase of the dipole moments strongly depend on the distance between the spheres as well as on complex-valued first and second order response factors, which contain material properties and the oscillation frequency. We demonstrate the usefulness of our displaced dipole model in terms of efficiency and accuracy compared to other computationally simple approaches.

Numerical Investigation of Negative Corona Discharge From Protrusion on Parallel Plane Electrodes in Air Insulation

Compared to a spherical metal particle motion within gas insulation, a wire-type particle could have a standing position on the ground electrode. In this work, a numerical investigation and validation from the experimental data of corona discharge from a small protrusion in air insulation within a uniform field under a dc voltage are performed. Three drift-diffusion models and Poisson equations are employed and solved using a finite element method to investigate negative corona discharge phenomena. The results show that the current characteristic with different applied voltages is within good agreement with the experimental results. A typical pulse train and the total number of charged species are also presented. Furthermore, the spatial distribution of charged species, the electric field distribution, and the ionization rate are explained. The effect of physical geometries of the particle on negative corona discharge characteristics is also investigated. It is found that the variation of the particle length, diameter, and tip radius is influencing the pulse characteristics.

Experimental investigation of WEDM process parameters on properties of bronze particles using the Taguchi method

Electrical discharge erosion in liquid media is a simple, effective technique to generate multi-scale metallic particles. An experimental investigation was conducted to determine the main machining parameters which contribute to particle size (PS) and size distribution (SD) in WEDM of bronze. Five factors, including three-level built-in processing patterns, wire speed and dielectric medium, are selected as control parameters using an orthogonal array L16(45) Taguchi method, PS and SD of produced powders are the measure of quality. The goal is to obtain micron-scale spherical metal powder with uniform particle size. Results show that cutting-section pattern is the most significant factor, and the electrolyte is the least. The PS and SD performance of the optimized powders is significantly improved by using Taguchi method. Spherical bronze powder with particle size of d10 11.05 μm, d50 31.13 μm and d90 67.48 μm are prepared using the optimized WEDM process parameter, which is A3–B4–C3–D1–E1 including dielectric medium water, cutting class 4, cutting division 3, cutting Sect. 1 and wire speed 200 μm/s. The research confirms that WEDM can be used to produce micron-scale metallic powders, providing cheap and high-quality metallic powders for the metal additive manufacturing industry.

Lewis acid-assisted reduction of nitrite to nitric and nitrous oxides via the elusive nitrite radical dianion.

Reduction of nitrite anions (NO2-) to nitric oxide (NO), nitrous oxide (N2O) and ultimately dinitrogen (N2) takes place in a variety of environments, including in the soil as part of the biogeochemical nitrogen cycle and in acidified nuclear waste. Nitrite reduction typically takes place within the coordination sphere of a redox-active transition metal. Here we show that Lewis acid coordination can substantially modify the reduction potential of this polyoxoanion to allow for its reduction under non-aqueous conditions (-0.74 V versus NHE). Detailed characterization confirms the formation of the borane-capped radical nitrite dianion (NO22-), which features a N(II) oxidation state. Protonation of the nitrite dianion results in the facile loss of nitric oxide (NO), whereas its reaction with NO results in disproportionation to nitrous oxide (N2O) and nitrite (NO2-). This system connects three redox levels in the global nitrogen cycle and provides fundamental insights into the conversion of NO2- to NO.

Comprehensive Characterization of an Ellipsoidal Cylinder Calibrator for Radar Cross Section Measurement

Currently, a set of scaled squat circular cylinders (SCCs) have been widely used for co-polarimetric radar cross section (RCS) calibration in various test ranges where low RCS metal pylons are used. The major drawback of a circular cylinder (CC) is its high sensitivity to elevation angle, as well as the frequency-dispersive theoretical RCS. In this work, we propose a new RCS calibrator, the metal ellipsoidal cylinder (EC), whose RCS characteristics are similar to a metal sphere, while it can be mounted on a metal pylon with little electromagnetic (EM) interactions as a CC does. A high-frequency RCS expression is derived using geometrical optics (GO) for the new calibrator. The scattering mechanisms are analyzed to establish the accurate parametric representation of the theoretical RCS. Based on surface current analysis and numerical calculation, the calibrator-pylon interaction (CPI), the angular sensitivity, and the bistatic RCS characteristics are discussed, enabling the calibration uncertainty evaluation for applying the proposed calibrator in the ground-plane range (GPR). Numerical and experimental results of a manufactured squat EC (SEC) are presented to demonstrate the excellent performance of the proposed EC calibrator for co-polarimetric RCS calibration.

Augmented Reality Experiment with a Van de Graaff Generator

The Van de Graaff (VDG) generator is ubiquitous in the physics laboratory, but the high-voltage discharges that emanate from it can cause user discomfort or damage to nearby electronics during experimentation. In this work, an augmented reality (AR) tool is developed to help students conduct the experiment safely. More specifically, it allows them to observe and investigate the discharge characteristics as a function of distance between the charged metallic sphere of the VDG generator and the spherical wand. The tool is shown to work well, and the feedback from students on its use was positive.

Non-contact heating efficiency of flowing liquid effected by different susceptors in high-frequency induction heating system

Abstract The skin effect causes about 86% of the energy to be concentrated in the narrow surface layer during the induction heating process, which leads to the uneven temperature distribution during the treatment of flowing liquid by induction heating technology. The concentration of heat caused by the skin effect can be avoided by dispersing the induced heating metal structure in the treated fluid, but in most cases, this will lead to a decrease in heating efficiency. Therefore, the purpose of this study is to compare and design the susceptor structures that can avoid the heating concentration problem caused by the skin effect and have higher efficiency. Hence, in this research four kinds of susceptor structures that are the metal sphere, sheet metal, static mixer, and metal pipe were studied. The results show that the combination of metal sphere susceptor and sheet metal susceptor can result in higher heating efficiency than the metal sphere susceptor alone. Ferromagnetic stainless steel with lower relative permeability is more suitable for making sheet metal susceptor than paramagnetic stainless steel. Adding internal components to the metal pipe susceptor will not change its heating efficiency. The heating efficiency of metal sphere type susceptor, sheet metal susceptor, and static mixer susceptor can be up to 58%, 64%, and 67%, respectively. When 430 metal pipe heater is used, the highest heating efficiency can be obtained, and the highest heating efficiency is 80%.

High-speed astigmatic dual-beam interferometric particle imaging for direct depth displacement and velocity measurement of metal droplet

High-speed astigmatic dual-beam interferometric particle imaging (HADIPI) is adopted to simultaneously measure the three-dimensional (3D) position, velocity and size of spherical metal droplets. We propose to infer the depth displacement of the droplet directly from the angle shift of the interference fringe. Angular cross power spectral density is used to detect the angular shifts of the interference fringe. The depth displacements and velocities can be further obtained from the obtained angular shifts. Proof-of-concept experiments are conducted on micron-sized gallium droplets, demonstrating that the 3D trajectories of the droplets can be accurately obtained, with depth displacement accuracy of tens of microns, improving accuracy in depth position measurement compared to the traditional Lagrangian framework. Different from traditional imaging methods, HADIPI can directly display the 3D movement of droplets, including in the depth direction. In the combustion measurements of the solid rocket motor, the motion state of metal droplets can be precisely determined, demonstrating the feasibility and practicality.

Research on electromagnetic characteristics of metal spheres with variable parameter defects based on COMSOL finite element method

In order to study the influence of defect geometric parameters (width, thickness) on the electromagnetic characteristics of the space around the defect in the process of eddy current testing of metal spheres, based on the principle of eddy current testing, a metal sphere detection model with different defect parameters was established by COMSOL software for simulation. The distribution of the magnetic field around the defect under different parameters is analyzed with the help of the butterfly diagram composed of the radial magnetic induction intensity and the axial magnetic induction intensity. The results show that: When the width of the corrosion defect is different, the butterfly diagram will change differently. When the width is small, the butterfly diagram basically does not change. When the width reaches a certain value, the butterfly diagram begins to change significantly. The intersection of the graph and the initial butterfly graph is defined as the influence node, and the width of the defect can be quantitatively analyzed according to the sequence of the influence nodes. The influence of the thickness of the corrosion defect on the magnetic field on the surface of the sphere is different under different defect widths. The larger the thickness of the corrosion defect, the greater the influence on the magnetic field near the center of the defect, and the deeper the depression of the butterfly diagram.

Local control of optical absorption properties of glass using precipitation of gold nanoparticles via gold sphere movement driven by laser

Glass embedded with metal nanoparticles is a promising material necessary for optical devices because of its absorption properties associated with the surface plasmon resonance (SPR) of metal nanoparticles. We demonstrated that continuous-wave laser illumination of the metal sphere in glass migrates the metal sphere and dopes the migration trajectory. In this study, we have attempted to locally control the absorption properties of borosilicate glass via gold nanoparticle precipitation using gold sphere migration. The gold sphere was moved in the glass via laser illumination, and the gold nanoparticles were precipitated in the movement trajectory. The trajectory was colored in red and purple gradations because of the SPR of gold nanoparticles. The particle size of the precipitated gold nanoparticles and the absorption peak wavelength increased with increasing velocity of the gold sphere. The absorption properties of the trajectory depend on the velocity of the gold sphere migration, which enabled local control of the absorption properties of the glass.

Optical properties of single metallic nanorods: An analytical model

It is well known that the optical properties of spherical metal particles can be described with the Rayleigh approximation or the rigorous Mie theory. However, for the single metallic nanorods, a theory well capturing the fundamental resonance and scattering features is still absent. In this study, an analytical model is developed for the metallic nanorod, considering the longitudinally non-uniform conduction current and surface charges. With the circuit parameters deduced from the kinetic and electromagnetic energy of the nanorod, a formula, which agrees well with the simulations, has been suggested for the resonance wavelength of the fundamental longitudinal mode. Moreover, by introducing the radiative resistance to the circuit theory, the dipole moment, the extinction spectrum, and the near-field enhancement of the nanorod have been derived analytically and confirmed numerically. The results are important for understanding the optical properties of the metallic nanorods and provide a guideline for designing the light scattering and absorption.

Energy-absorbing properties of thin-walled square tubes filled with hollow spheres

The smooth thin shell structure has exhibited significant advantages in light weight and high energy absorption and been widely applied in transportation, aerospace fields. This study proposed the thin-walled square tube filled with hollow aluminum metal spheres (TST-HS) to improve the crashworthiness. In this structure, hollow aluminum spheres were filled into thin-walled square tubes in different stacking modes, such as simple cubic (SC), body-centered cubic(BCC), and face-centered cubic (FCC). A series of quasi-static compression experiments and numerical simulations were conducted to investigate the deformation mechanism and crashworthiness of TST-HS. The results indicated that filled hollow spheres lead to the change in the deformation mode and an increase in the number of plastic hinges of TST-HS. The mean load of TST-HS was increased by 68.98% and 15.6%, respectively, compared to the square tubes and the foam-filled tube of same mass. Parametric studies show that the wall thickness, size and stacking modes of the hollow spheres have major impacts on the crashworthiness of the TST-HS. Energy analysis reveals the contribution of the interaction between hollow sphere and square tube to the total energy absorption of TST-HS.

Surface Charging Affecting Metal Particle Lifting Behaviors Around Epoxy Spacer of HVDC GIL/GIS

In this article, the mechanisms of surface charging and surface modification of epoxy spacer affecting the lifting voltage and the motion trajectory of spherical metal particles in a downsized dc gas insulated transmission line (GIL) are investigated by simulations and experiments. Results show that the lifting voltage can be predicted with much accuracy by calculating the electric field distribution under the capacitive condition. Prestressing leads to a 27% decrease of lifting voltage, which is traceable to that surface charging making a major contribution to the enhancement of electric field force. Direct fluorination is proven as an effective modification method to improve the insulation performance of epoxy spacer again. The lifting inclination is significantly inhibited after treatment because of less surface charge accumulation and more rationalized electric field distribution. The trajectory simulation results indicate that more serious surface charging can activate more metal particles to lift up and drive them to more collisions. The lifting probability and velocity of metal particles around the epoxy spacer are markedly decreased by fluorination, which is a promising treatment for dc GIL/gas insulated switchgear (GIS) application.

Buckling of a tilted line of confined hard spheres

ABSTRACT A linear chain of hard spheres confined in a transverse harmonic potential is unstable and buckles, if tilted beyond some critical angle. We examine this symmetry breaking using a computational model that was previously applied to buckling under compression. Results are presented in a bifurcation diagram (in terms of energy as a function of tilt), including both stable and unstable equilibrium states. The key results are consistent with experiments using metal spheres resting in a cylinder.

Raman Enhancement Factor (EF) Calculations for Hot Spots at Two Metallic Spheres

Raman Enhancement Factor (EF) Calculations for Hot Spots at Two Metallic Spheres

Calibration of D3R Weather Radar Using UAV-Hosted Target

The accuracy of weather radar-measured products, such as reflectivity, plays a crucial factor in obtaining good quality, derived remote sensing products, such as hydrometeor classification. A slight mismatch of a few decibels in reflectivity may cause the hydrometeor classification to deviate from the actual truth. In order to obtain accurate remote-sensing measurements, calibration of weather radars should be carried out at regular intervals of time. The dual-frequency, dual-polarization, Doppler radar (D3R) is a well-established tool for measuring light rain and snow. There are various methods which are used for the calibration of weather radars, such as suspending a metallic sphere from a weather balloon or using corner reflectors on top of a tower or structure. In this work, we have shown the potential of using a UAV to suspend a calibration sphere, which is then used for calibrating the D3R radar. In this work, the advantages along with the practical aspects to be considered for calibration using UAV are discussed in detail. From the calibration results, it was observed that an offset of 2.2 dB was present in the Ku H-Pol reflectivity, Ku V-Pol was well calibrated and offsets within 2 dB were observed in the Ka H-Pol and V-Pol reflectivities.