Search

The preparation and storage of aluminum nanoparticles pose significant challenges due to their high chemical reactivity. This paper proposes a one-step method for the production of carbon-coated aluminum nanoparticles using an argon protective arc in a liquid nitrogen environment. The emission spectra of the arc validate that the method proposed in this paper can effectively mitigate the adverse impact of impurity gases such as oxygen and water on the product without the need for expensive vacuum equipment. The obtained nanoparticles underwent characterization through high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman analysis, thermogravimetric analysis, and dynamic light scattering. The characterization results demonstrate the successful synthesis of carbon-coated aluminum nanoparticles with nitrogen-doped fullerene shells. With an increase in arc current, the nanoparticles exhibit a corresponding enlargement in diameter, accompanied by a broader distribution. The characterization of the electrode erosion suggests that the aluminum droplet ejection plays a more important role in the nanoparticle generation process as the arc current increases. Optimized strategies are proposed to increase the percentage of successfully-formed carbon-coated aluminum nanoparticles. • One-step preparation of carbon-coated aluminum nanoparticles. • Arc discharge in liquid environment without vacuum and sealing equipment. • Core-shell structure: Al core wrapped in N-doped fullerenes. • The arc current impacts electrode erosion pattern and product characteristics. [ABSTRACT FROM AUTHOR]

Abstract: To change the structures and yields of carbon nano-products, transverse magnetic field (TMF) was introduced to arc discharge in liquid (de-ionized water, liquid nitrogen). Direct current was used to sustain the arc discharge between two graphite electrodes and cobalt powder was filled in drilled anodes as catalyst sometimes. Scanning electron microscopy and high-resolution transmission electron microscopy were used to investigate the nano-products. Some novel carbon nano-structures were obtained with the effect of TMF. For arc discharge in water, curled multi-walled carbon nanotubes and nano-structures with few layers were found in cathode depositions and floating products, respectively. For arc discharge in liquid nitrogen, twists of single-walled carbon nanotubes appeared in cathode depositions and the yields of spherical nano-particles in floating products increased. [Copyright &y& Elsevier]

Abstract: Based on two-temperature magnetic hydrodynamic (MHD) model, the influence of saddle-shaped distributed axial magnetic field (AMF, linearly increases along radial position) and bell-shaped distributed AMF (linearly decreases along radial position) on plasma loss and heat flux density to anode in subsonic high-current vacuum arc (HCVA) is simulated and analyzed. According to the simulation results, the saddle-shaped AMF can more effectively inhibit plasma loss from arc column than that of bell-shaped AMF. Comparisons between simulation results and experimental results further verify the correctness of model and simulation. [Copyright &y& Elsevier]

Abstract: A magnetic field parallel to the carbon arc in water was used to increase the directionality of moving carbon particles and generate carbon nano-materials. The products were analyzed and compared with those obtained without a magnetic field. The study shows that the purity and quality of multi-walled carbon nanotubes in the cathode deposition formed by an arc in water with a magnetic field were both improved, and cylinder-like carbon structures were also found in the deposition. The influence of the magnetic field on the formation of the products was analyzed. [Copyright &y& Elsevier]

Due to the peculiar magnetic properties and the ability to function in cell-level biological interaction, superparamagnetic nanoparticles (SMNP) have been being the attractive carrier for gene delivery. The superparamagnetic nanoparticles with surface-bound gene vector can be attracted to the surface of cells by the Kelvin force provided by external magnetic field. In this article, the influence of the oscillating magnetic field on the characteristics of magnetofection is studied in terms of the magnetophoretic velocity. The magnetic field of a cylindrical permanent magnet is calculated by equivalent current source (ECS) method, and the Kelvin force is derived by using the effective moment method. The results show that the static magnetic field accelerates the sedimentation of the particles, and drives the particles inward towards the axis of the magnet. Based on the investigation of the magnetophoretic velocity of the particle under horizontally oscillating magnetic field, an oscillating velocity within the amplitude of the magnet oscillation is observed. Furthermore, simulation results indicate that the oscillating amplitude plays an important role in regulating the active region, where the particles may present oscillating motion. The analysis of the magnetophoretic velocity gives us an insight into the physical mechanism of the magnetofection. It's also helpful to the optimal design of the magnetofection system. [ABSTRACT FROM AUTHOR]

Highlights • Closed-form magnetic moment and magnetic force analysis. • The influence of magnetic dipole interaction force on the self-assembly of MNPs. • 3D self-assembly process of MNPs. Abstract The self-assembly of magnetic core-shell nanoparticles in the presence of a magnetic template, which consists of an array of soft-magnetic elements embedded in non-magnetic substrate, is analyzed by using discrete element method. An external bias magnetic field is used to magnetize the soft-magnetic elements to saturate state. The high-gradient field produced by elements combined with biased uniform magnetic field provides a flexible way to control the behavior of particles. An equivalent source method is adopted to obtain the closed-form magnetic field analysis, which not only improves the calculation efficiency but also enables accurate prediction of the Kelvin force. In the presence of magnetic field, the behavior of the magnetic nanoparticles is dependent on the magnetic and hydrodynamic forces. Therefore, the assembled structures of magnetic nanoparticles are firstly investigated without considering the magnetic dipole interaction force, in which an unordered nanostructure is formed. As a contrast, the self-assembly of particles is also simulated by taking all forces into account. In this case, the magnetic nanoparticles assemble into an ordered 3D structure, which presents a hexagonal close packed structure. A comparison between the results of the mentioned two cases denotes that the magnetic dipole interaction force plays an important role in controlling the self-assembly of magnetic nanoparticles. [ABSTRACT FROM AUTHOR]

Highlights • The dye-tracing and concentration-measuring experiments provide a means of observing the behavior of particle and fluid. • A closed-form magnetic field analysis is performed to obtain an accurate prediction of magnetic force. • Three-dimensional distribution of particle concentration is investigated by using Fluent, Ansys. • A comparison between the uncoupled model and coupled model is provided. • A comparison between experimental and numerical results is provided. Abstract Dye-tracing and concentration-measuring experiments are carried out to investigate the magnetophoresis of magnetic nanoparticles (MNP) in the presence of an external cylindrical permanent magnet. The magnetophoresis of MNP, inducing an obvious forced-convective flowing of the carrier fluid, which can be observed by visualizing flowing of carrier fluid, results in a temporal and spatial variation of particle concentration. Moreover, in order to get insight into the physical mechanisms of magnetophoresis of MNP, a coupled particle-fluid analysis, in which the non-linear drift-diffusion differential equation is incorporated into the Navier-Stokes equation, is adopted to discuss the influence of particle-fluid interaction on the variation of particle concentration and the kinetics of carrier fluid. It is worth noting that the equivalent current source (ECS) method is adopted to obtain a closed-form field analysis, which provides exactly prediction of the Kelvin force and enables magnetophoretic analysis more efficient. In dye-tracing experiments, an obvious vortex can be observed as the methylene blue moves with the convection of carrier fluid. Furthermore, this phenomenon is also predicted by using the coupled particle-fluid model. A comparison between the experimental and numerical results shows that the hydrodynamic interactions between MNP and carrier fluid plays an important role in inducing forced-convective flowing of carrier fluid and enhancing the magnetophoresis of MNP. Furthermore, these results also denote that the coupled particle-fluid model provides a more efficient and accurate method in investigating the magnetophoresis of MNP. [ABSTRACT FROM AUTHOR]

The quench protection switch (QPS) is very important for ensuring the safety of the magnet coils of a superconducting Tokamak. The main function of a QPS is to protect the magnet as the coil quench occurs. Besides, a QPS has to withstand almost all of the coil current of some tens of kA flowing through it in the normal operation condition. This task is undertaken by the by-pass switch (BPS), which is an indispensable component of a QPS, no matter what principle the QPS is based on. Therefore, the study of the temperature rise is very important for optimal design of a BPS. In this paper, a scheme of a high-current BPS is proposed. The steady temperature rise of the BPS is simulated in the condition of natural convection with the approach of Computational Fluid Dynamics (CFD). Furthermore, the influence of the space between each individual switch unit is investigated. Simulation results indicate that there exists an appropriate space, beyond which the mutual influence of adjacent contacts can be accepted. This space can be regarded as a reference in designing a BPS with the trade-off between the dimension of the BPS (and the QPS) and its current-carrying capacity. [ABSTRACT FROM AUTHOR]

In this study, the mechanism of the photoresist (PR) etching by means of a kHz AC atmospheric pressure plasma jet (APPJ) is investigated. The scanning electron (SEM) and the polarizing microscope are used to perform the surface analysis, and the mechanical profilometry is applied to diagnose the etch rate. The results show that granulated structure with numerous microparticles appears at the substrate surface after APPJ treatment, and the etch rate in the etch center is the fastest and gradually slows down to the edge of etch region. In addition, the pin-ring electrode APPJ has the highest etch rate at but easy to damage the Si wafer, the double-ring APPJ is the most stable but requires long time to achieve the ideal etch result, and the etch rate and the etch result of the multi-electrode APPJ fall in between. Ar APPJ had much higher PR etch rate and more irregular etch trace than He APPJ. It is speculated that Ar APPJ is more energetic and effective in transferring reactive species to the PR surface. It is also observed that the effective etch area initially increases and then decreases as plasma jet outlet to the PR surface distance increases. [ABSTRACT FROM AUTHOR]

• The combination of Ω- and straight-shaped obstacles enhance the mixing performance. • Well mixing is achieved as the obstacles are in contact with the walls of Tesla chambers. • Increasing the radius of Ω-shaped obstacles can improve the performance of micromixer. • The hexagonal chambers are better than triangle and Tesla chambers. An efficient fluid mixing performance is achieved by a Tesla/hexagon-shaped passive micromixer in a wide range of Reynolds numbers with short mixing length (4.2 mm/1.15 mm from the origin). The passive micromixers are composed of Tesla/hexagonal chambers and Ω-shaped obstacles or combined with straight-shaped obstacles that induce the generation of vortex, contraction and expansion process, the changes of the flow direction, and even the split and recombination of streams. The mixing process of two fluids (water and ferrofluid) is numerically investigated using computational fluid dynamics. For the Tesla-shaped micromixer embedded with Ω-shaped obstacles, a sufficient mixing is obtained as the obstacles are in contact with the internal walls of Tesla chambers. In the hexagon-shaped micromixer, the combination of straight- and omega-shaped obstacles greatly enhance the performance of micromixer in particular at moderate flow rate (1< Re <10). Moreover, reasonable increasing the curvature radius of the omega-shaped obstacles can further improve its mixing performance. The designed passive micromixers were also fabricated, tested and compared with the numerical results through the soft-lithography processes, and the good agreement between the experimental and numerical results identifies our predictions. The good performance of the designed micromixers provides a new direction in designing micromixer with high-throughput and short mixing length. [Display omitted] [ABSTRACT FROM AUTHOR]

• A hybrid magnetic field produced by microwires and Halbach magnets is proposed to enhance the mixing between ferrofluid and water. • We numerically and experimentally analyze the effects of the arrangement and the number of microwires on the mixing efficiency. • By adjusting the direction and the magnetite of uniform magnetic field, we receive optimal mixing efficiency 99.06%. With the development in biomedical and biotechnological areas, novel and efficient microfluidic devices integrated with sufficient and rapid mixing function have been attracting enormous scientific attention as versatile and robust platform for low cost and non-contact biological analysis and diagnose. Here, we design and fabricate a magnetic micromixer integrated with special designed microwires, a Y-shaped microchannel and uniform magnetic field for realizing rapid mixing between ferrofluid and deionized water. A comprehensive analysis on the dynamic behavior of ferrofluid is performed by using 3D Eulerian-Eulerian model. Good consistency between experiment and numerical results demonstrates that the enhanced mixing in the presence of longitudinally arranged microwires is due to the introduction of eddies, whose impacts are strengthened with the increase of the number of microwires (n w). However, increasing n w requires a long microchannel and long time to complete mixing. In order to further improve the mixing performance of our micromixer, a horizontally arranged microwire combined with a particular uniform magnetic field is proposed to provide enough magnetic force for enhancing the mixing of ferrofluid and deionized water, receiving optimal mixing efficiency 99.06%. The flexible tunability of external uniform magnetic field enables desired performance of our designed system. [ABSTRACT FROM AUTHOR]