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Microwave Processing of Materials and Applications

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: closed (20 July 2023) | Viewed by 12727

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Dr. Kirill Rybakov

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Guest Editor

Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia
Interests: microwave–materials interactions; electromagnetic and multiphysics modeling; microwave processing of materials

Special Issue Information

Dear Colleagues,

Microwave processing of materials has attracted significant research interest in recent decades. The capability of rapid, volumetric, energy-efficient heating inherent in this technique offers a basis for the development of promising applications. On the other hand, the interaction of microwave electromagnetic field with materials gives rise to a rich variety of effects that can be of fundamental importance for physics, chemistry, and materials science.

For this Special Issue, papers are invited in all fields related to microwave processing of materials, including but not limited to:

- Microwave interactions with materials;

- Microwave sintering of ceramics, composite materials, and powder metals;

- Microwave processing of polymers;

- Microwave chemistry;

- Hybrid and energy-intensive microwave processes;

- Microwave equipment, temperature measurement, and process control;

- Microwave processing applications;

- Dielectric and magnetic properties of the materials undergoing microwave processing;

- Multiphysics modeling and numerical simulation of microwave processing.

Dr. Kirill Rybakov
Guest Editor

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Keywords

Microwave processing of materials
Microwave heating
Microwave sintering
Microwave chemistry
Microwave processing applications
Microwave processing equipment and process control
Microwave dielectric properties

Published Papers (6 papers)

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Research

14 pages, 6499 KiB

Open AccessArticle

Sequential Solidification of Metal Powder by a Scanning Microwave Applicator

by Yoav Shoshani, Tal Weinstein, Zahava Barkay and Eli Jerby

Materials 2023, 16(3), 1136; https://doi.org/10.3390/ma16031136 - 28 Jan 2023

Viewed by 1238

Abstract

This study examines the fundamental feasibility of sequential metal-powder solidification by localized microwave-heating (LMH) provided by a scanning, all-solid-state microwave applicator. This continuous process is considered for the additive manufacturing (AM) and 3D printing (3DP) applications of metal parts. In previous studies, we employed LMH for the incremental solidification of small batches of metal powder in a stepwise vertical manner. Here, we study a continuous lateral LMH process, layer by layer, in a fashion similar to laser scanning in powder beds, as performed in common laser-based AM systems. LMH solidification at scanning rates of ~1 mm³/s is obtained in bronze powder using ~0.25-kW microwave power. The effect is studied here by LMH scanning in one lateral dimension (~20-mm long) in layers, each of ~1–4 mm thickness and ~2–4 mm width (mechanically confined). Imperfect solid bars of ~

20 \times 4 \times 5

mm³ are obtained with rough surfaces. Their joining in an L shape is also demonstrated. The experimental solidified products are tested, and their hardness and density properties are found to be comparable to laser-based AM products. The capabilities and limitations of the LMH scanning concept for metal-powder solidification are evaluated. The potential feasibility of a solid-state LMH–AM technology is discussed. Full article

(This article belongs to the Special Issue Microwave Processing of Materials and Applications)

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16 pages, 26344 KiB

Open AccessArticle

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

by Morsi M. Mahmoud

Materials 2022, 15(20), 7236; https://doi.org/10.3390/ma15207236 - 17 Oct 2022

Cited by 4 | Viewed by 1633

Abstract

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. Full article

(This article belongs to the Special Issue Microwave Processing of Materials and Applications)

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14 pages, 3519 KiB

Open AccessArticle

Antenna Characteristics of Helical Coil with 2.45 GHz Semiconductor Microwave for Microwave-Enhanced Laser-Induced Breakdown Spectroscopy (MW-LIBS)

by Yuji Ikeda, Yoshihiko Hirata, Joey Kim Soriano and Ikuo Wakaida

Materials 2022, 15(8), 2851; https://doi.org/10.3390/ma15082851 - 13 Apr 2022

Cited by 19 | Viewed by 2214

Abstract

A copper helical coil antenna was developed, characterized, and optimized for 2.45 GHz operations supplied by a microwave semiconductor oscillator. The application field of interest is laser-induced breakdown spectroscopy enhanced by microwave. Simulations using the Ansys HFSS demonstrate the superior localized E-field strength of the helical coil antenna, compared with other antenna-type structures. Simulation results show that E-field strength at the tip of the antenna has a logarithmic trend for increasing the coil pitch. The optimum pitch is 5 mm for a coil diameter of 6.5 mm upon consideration of the system compactness. Despite the antenna’s open-circuit end, the presence of target samples does not interfere with the E-field and H-field distribution of the antenna and the surrounding environment. Applications in microwave-enhanced laser-induced breakdown spectroscopy (MWLIBS) confirm the importance of the antenna reflector. The electric field strength was over 100 times higher than the previous capacitor-like antenna. The antenna configuration angle was then experimentally optimized for maximum enhancement effects in the spectrochemical analysis of Al₂O₃. The antenna angle of 60° from the laser beam propagation achieved maximum enhancement in the emission signal of Al I. Full article

(This article belongs to the Special Issue Microwave Processing of Materials and Applications)

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15 pages, 10183 KiB

Open AccessArticle

Development of 2.45 GHz Semiconductor Microwave System for Combustion Ignition Enhancement and Failure Analysis

by Yuji Ikeda

Materials 2022, 15(6), 2042; https://doi.org/10.3390/ma15062042 - 10 Mar 2022

Cited by 10 | Viewed by 2809

Abstract

We developed a semiconductor microwave system to improve the ignition process in a combustion system. Under atmospheric pressure conditions, large plasma was successfully ignited by a 2.45 GHz microwave, and it is characterized in comparison with standard spark plug ignition and laser ignition. The size of the microwave power source was also effectively reduced with the minimal size (100 × 60 mm²) that could fit in the palm of a hand. We then prototyped a microwave plug with a diameter of 4 mm, which is smaller than the standard spark plugs for passenger cars. The design and electric field strength are discussed in detail. Combustion experiments were conducted using a motorcycle engine and an actual light vehicle, and significant fuel efficiency improvement was experimentally obtained. We investigated the wear of the plug caused by continuous operation, and efficiently improved the endurance by swinging the resonance frequency between 2.4 and 2.5 GHz. In a passenger car engine experiment using a flat panel igniter, significant fuel efficiency improvement was confirmed. Further failure analysis revealed that the ceramic was severely damaged by a large current surge. Full article

(This article belongs to the Special Issue Microwave Processing of Materials and Applications)

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9 pages, 2493 KiB

Open AccessArticle

Behaviour of Microwave-Heated Al₄SiC₄ at 2.45 GHz

by Takashi Fujii, Akio Oshita and Keiichiro Kashimura

Materials 2021, 14(17), 4878; https://doi.org/10.3390/ma14174878 - 27 Aug 2021

Cited by 3 | Viewed by 1643

Abstract

The ongoing development of high-temperature processes with the use of microwaves requires new microwave absorbers that are useful at these temperatures. In this study, we propose Al₄SiC₄ powders as important and efficient microwave absorbers. We investigated both the behavioural microwave heating and electrical permittivity characteristics of Al₄SiC₄ powders with various particle sizes at 2.45 GHz. The TE₁₀₃ single-mode cavity indicated that Al₄SiC₄ powder samples yielded different heating behaviours and dielectric constants for each particle size compared with SiC. By microwave heating ∅50 mm × 5 mm disks of Al₄SiC₄ and SiC, we demonstrate that for specific sizes, Al₄SiC₄ can be heated at a higher temperature than SiC. Finally, the results of the two-dimensional two-colour thermometer show that an energy concentration appears at the interface of the microwave-heated Al₄SiC₄. These phenomena, which are inconsistent in individual physical property values, can be explained without contradicting microwave heating physics. Full article

(This article belongs to the Special Issue Microwave Processing of Materials and Applications)

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12 pages, 1956 KiB

Open AccessEditor’s ChoiceArticle

Green Microwave-Assisted Synthesis of CoFeRu-Based Electrocatalyst for the Oxygen Reduction Reaction

by Antonia Sandoval, Edgar Borja, Lorena Magallón and Javier Su

Materials 2021, 14(7), 1662; https://doi.org/10.3390/ma14071662 - 28 Mar 2021

Cited by 1 | Viewed by 2063

Abstract

A simple and rapid synthesis of a CoFeRu-based electrocatalyst by a microwave-assisted method (using water as the microwave absorbing solvent) is reported in this work. Agglomerates with different sizes and shapes are observed by scanning electron microscopy technique. The energy dispersive X-ray spectroscopy shows a low atomic percentage of Co and similar atomic percentage of Fe and Ru. However, the X-ray diffraction exhibits only the presence of metallic Ru and Fe₂O₃ (hematite) phases. The oxygen reduction without and with 2 mol L⁻¹ methanol is studied using the rotating disk electrode technique. The electrochemical kinetic parameters obtained are compared to a similar electrocatalyst reported in the literature, which was synthesized using a mixture of an organic solvent with DI water as the microwave absorbing solvent. An improvement on the activity of the electrocatalyst synthesized is observed, where high Tafel slopes are not observed. The electrocatalyst also showed tolerance to the presence of methanol during the oxygen reduction reaction. Full article

(This article belongs to the Special Issue Microwave Processing of Materials and Applications)

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