Special Issue "Conventional and Microwave Sintering Techniques in Materials"

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

Deadline for manuscript submissions: closed (30 September 2019).

Special Issue Editor

Prof. Dinesh Agrawal
E-Mail Website
Guest Editor
Engineering Science and Mechanics, Pennsylvania State University, USA
Interests: microwave processing of ceramics; composites; metals; etc., low thermal expansion materials; ceramic processing; rad-waste management
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue of Materials is focused on the sintering of materials involving conventional and microwave heating methods. In the last couple of decades, microwave heating has emerged as a well-recognized method for the sintering of a variety of materials, including ceramics, composites, metals, semiconductors, and advanced ceramics. The theories to explain the sintering mechanism(s) during microwave heating are still under discussion and have not been fully explained. Papers involving comparisons between conventional and microwave methods are welcome. Microwave heating takes place as a result of the interaction of an electromagnetic field with matter through various inherent properties of the material under study. Microwave sintering of metallic materials is a rather new area of research. Papers involving these aspects are most welcome. The spark plasma sintering method and other methods involving electromagnetic fields are also rapid sintering methods of specific materials. Papers based on these methods are also welcome for this Special Issue.

Prof. Dinesh Agrawal
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Keywords

  • microwave energy
  • sintering methods
  • ceramics
  • metal powders
  • electromagnetic field
  • Spark Plasma Sintering
  • Dielectric loss mechanism
  • Composites

Published Papers (5 papers)

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Research

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Open AccessFeature PaperArticle
Microwave Sintering of Alumina at 915 MHz: Modeling, Process Control, and Microstructure Distribution
Materials 2019, 12(16), 2544; https://doi.org/10.3390/ma12162544 - 09 Aug 2019
Abstract
Microwave energy can be advantageously used for materials processing as it provides high heating rates and homogeneous temperature field distribution. These features are partly due to the large microwave penetration depth into dielectric materials which is, at room temperature, a few centimeters in [...] Read more.
Microwave energy can be advantageously used for materials processing as it provides high heating rates and homogeneous temperature field distribution. These features are partly due to the large microwave penetration depth into dielectric materials which is, at room temperature, a few centimeters in most dielectric materials. However, up to now, this technology is not widely spread for high-temperature material processing applications (>1200 °C), because its reproducibly and ability to sinter large size samples (>30 cm3) still needs to be improved. In this context, this paper describes both an empirically designed 915 MHz single-mode cavity made from SiC susceptors and refractory thermal insulation, and the 3D modeling of the process in order to improve our understanding of it. Different susceptors geometries and coupling slit position were numerically tested in order to better understand how these parameters impact the field homogeneity and the process stability. It was found that positioning the largest surface of the susceptors parallel to the electrical field allows a very uniform and hybrid heating of the material, while avoiding plasma or thermal instabilities. This was correlated to the 3D modeling results. Finally, thanks to a fully-automatized system this apparatus was used to sinter large size (~30 cm3) low-loss dielectric alumina samples. The sintered materials were subsequently characterized in terms of density, grain size distribution, and homogeneity. The reproducibility was also discussed, demonstrating the process efficiency and reliability. Full article
(This article belongs to the Special Issue Conventional and Microwave Sintering Techniques in Materials)
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Open AccessArticle
Microwave Sintering of SiAlON Ceramics with TiN Addition
Materials 2019, 12(8), 1345; https://doi.org/10.3390/ma12081345 - 25 Apr 2019
Cited by 1
Abstract
α-β SiAlON/TiN composites with nominal composition of α:β = 25:75 were fabricated by microwave sintering. The effect of titanium nitride addition on the phases, microstructure, microwave absorption ability and mechanical properties (Vickers hardness and fracture toughness) of the SiAlON-based composites were studied. Finite [...] Read more.
α-β SiAlON/TiN composites with nominal composition of α:β = 25:75 were fabricated by microwave sintering. The effect of titanium nitride addition on the phases, microstructure, microwave absorption ability and mechanical properties (Vickers hardness and fracture toughness) of the SiAlON-based composites were studied. Finite Difference Time Domain (FDTD) software was used for the numerical simulation in order to assess the most suitable experimental setup. Sintering trials were performed in a single mode microwave furnace operating at 2.45 GHz and a power output of 660 W, for a reaction time of 30 min. SiC blocks were used as a susceptor to accelerate the microwave processing by hybrid heating, with reduced heat losses from the surface of the material of the α-β SiAlON/TiN composites. The optimum comprehensive mechanical properties, corresponding to a relative density of 96%, Vickers hardness of 12.98 ± 1.81 GPa and Vickers indentation fracture toughness of 5.52 ± 0.71 MPa.m1/2 were obtained at 850 °C when the content of TiN was 5 wt.%. Full article
(This article belongs to the Special Issue Conventional and Microwave Sintering Techniques in Materials)
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Open AccessArticle
Effect of Microwave Sintering on the Properties of 0.95(Ca0.88Sr0.12)TiO3–0.05(Bi0.5Na0.5)TiO3 Ceramics
Materials 2019, 12(5), 803; https://doi.org/10.3390/ma12050803 - 08 Mar 2019
Cited by 2
Abstract
Perovskite ceramics are a common microwave dielectric material, but the development and application of this material has been limited by the high, positive resonance frequency temperature coefficient and sintering temperature. Therefore, adjusting the temperature coefficient of the resonance frequency and reducing the sintering [...] Read more.
Perovskite ceramics are a common microwave dielectric material, but the development and application of this material has been limited by the high, positive resonance frequency temperature coefficient and sintering temperature. Therefore, adjusting the temperature coefficient of the resonance frequency and reducing the sintering temperature have become important research directions. In this work, 0.95(Ca0.88Sr0.12)TiO3–0.05(Bi0.5Na0.5)TiO3 ceramics (referred to as 0.95CST-0.05BNT) were prepared by standard solid-state reaction and microwave sintering. Microwave sintering greatly shortened the sintering period and holding time. Moreover, the 0.95CST–0.05BNT ceramics showed more uniform grain size distribution, and microwave sintering reduced energy consumption in the experiment. Therefore, the temperature coefficient of the resonance frequency of MWS ceramics was reduced by 119 × 10−6 /℃. All of the ceramics, which were sintered at 1300 °C for 40 minutes, showed optimal microwave dielectric properties: εr = 187.6, Q × f = 8958 GHz, and τf = +520 × 10−6 /°C. Full article
(This article belongs to the Special Issue Conventional and Microwave Sintering Techniques in Materials)
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Open AccessArticle
An On-Line System for High Temperature Dielectric Property Measurement of Microwave-Assisted Sintering Materials
Materials 2019, 12(4), 665; https://doi.org/10.3390/ma12040665 - 22 Feb 2019
Cited by 1
Abstract
Microwave-assisted sintering materials have been proven to deliver improvements in the mechanical and physicochemical properties of the materials, compared with conventional sintering methods. Accurate values of dielectric properties of materials under high temperatures are essential for microwave-assisted sintering. In view of this, this [...] Read more.
Microwave-assisted sintering materials have been proven to deliver improvements in the mechanical and physicochemical properties of the materials, compared with conventional sintering methods. Accurate values of dielectric properties of materials under high temperatures are essential for microwave-assisted sintering. In view of this, this paper, proposes an on-line system to measure the high temperature dielectric properties of materials under microwave processing at a frequency of 2450 MHz. A custom-designed ridge waveguide is utilized, where samples are heated and measured simultaneously. An artificial neural network (ANN) trained with the corresponding simulation data is integrated into this system to reverse the permittivity of the measured materials. This whole system is tested at room temperature with different materials. Accuracies of measuring dielectric property with an error lower than 9% with respect to theoretical data have been achieved even for high loss media. The functionality of the dielectric measurement system has also been demonstrated by heating and measuring Macor and Duran ceramic glass samples up to 800 °C. All the preliminary experiments prove the feasibility of this system. It provides another method for dielectric property measurement and improves the understanding of the mechanism between microwave and media under high temperatures, which is helpful for optimizing the microwave-assisted sintering of materials. Full article
(This article belongs to the Special Issue Conventional and Microwave Sintering Techniques in Materials)
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Review

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Open AccessFeature PaperReview
Application of the Microwave Technique in Continuous Flow Processing of Organophosphorus Chemical Reactions
Materials 2019, 12(5), 788; https://doi.org/10.3390/ma12050788 - 07 Mar 2019
Abstract
The microwave (MW) technique is an efficient tool in the realization of organic reactions, as well as in the analytical field and in the food industry. The continuous flow approach is of special interest as a promising way to scale-up MW-assisted syntheses. Besides [...] Read more.
The microwave (MW) technique is an efficient tool in the realization of organic reactions, as well as in the analytical field and in the food industry. The continuous flow approach is of special interest as a promising way to scale-up MW-assisted syntheses. Besides summarizing the batch precedents, this review focuses on the utilization of the MW technique in the continuous-flow realization of organophosphorus transformations. The advantages of the continuous flow technique against the batch accomplishment are also shown. A few materials chemistry-related applications are also mentioned. Full article
(This article belongs to the Special Issue Conventional and Microwave Sintering Techniques in Materials)
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