• Journal of the Chinese Ceramic Society
  • Vol. 53, Issue 3, 700 (2025)
LIU Bingyan1, YIN Hongfeng1,*, TANG Yun1, REN Xiaohu1..., XIN Yalou1,2, LIU Yuchi1 and YUAN Hudie1|Show fewer author(s)
Author Affiliations
  • 1College of Materials Science and Engineering, Xi’an University of Architecture &Technology, Xi'an 710055, China
  • 2State Key Laboratory of Refractory Materials and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China
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    DOI: 10.14062/j.issn.0454-5648.20240530 Cite this Article
    LIU Bingyan, YIN Hongfeng, TANG Yun, REN Xiaohu, XIN Yalou, LIU Yuchi, YUAN Hudie. Progress on High-Temperature Wave-Transmitting Materials in Microwave Sintering[J]. Journal of the Chinese Ceramic Society, 2025, 53(3): 700 Copy Citation Text show less

    Abstract

    Industrial operations lead to energy consumption and environmental pollution with the economy development. In developed countries, the thermal efficiency of ceramic kilns in ceramic industry reaches over 50%, while in China it is only about 28%. Combined with the pollution reduction and carbon reduction in recent years, the gradual development of industrial kilns towards green and intelligent direction becomes an inevitable trend in the context of dual carbon. As is well known, microwave energy can reduce energy consumption and greenhouse gas emissions in drying processes. Microwave sintering technology is also regarded as a ‘new generation sintering technology of the 21st century‘. This technology is an efficient and environmentally friendly method used in metallurgy, powder and ceramics preparation due to its advantages such as volumetric heating, selective heating, time-saving and high efficiency. Compared with conventional sintering methods, a coupling effect between microwaves and materials is utilized in microwave sintering process, thereby producing dielectric loss, converting microwave energy into thermal energy. The microwave sintering furnace mainly involves microwave generator, waveguide tube and sintering chamber. In the operation, the microwave generated by the microwave generator is transmitted through a wave guide, thus entering the sintering chamber after passing through multiple layers of insulation, interacting with the material in the crucible, generating dielectric loss inside the material and converting microwave energy into thermal energy. For this purpose, some imperative requirements put forward for the selection of furnace lining materials. In addition to conventional fire resistance, the lining material used for microwave sintering furnaces also has good wave transmission properties. However, the existing research on transparent materials mostly focus on aircraft radome, and there is still a lack of systematic introduction on wave-transparent materials used in microwave sintering furnaces.This review briefly introduces the working principle of microwave sintering technology and the wave transmission mechanism of materials, and summarizes several common types of high-temperature wave transmitting materials like ceramic firebrick, ceramic fiberboard, ceramic aerogel. Among them, ceramic aerogels have typically nano-pores of up to 90%, which can reduce the dielectric constant of the material significantly. Ceramic fiberboard has a low density and thermal conductivity. However, the application of these two materials is limited due to their lower operating temperatures. Ceramic firebrick with its superior mechanical properties and high-temperature stability shows a broad application prospect in fused silica, alumina, silicate and phosphate ceramics, and these materials with porous structures are more widely used because of the lower dielectric constant of air. Some influencing factors on the dielectric properties of materials are described. Combination with the mechanical properties and dielectric properties of materials, the performance of each ceramic is analyzed, and the advantages and disadvantages of different high-temperature wave transmitting materials are given. Among them, aluminum silicate ceramic shows a promising application prospect in the lining materials for microwave furnace. However, the comprehensive properties of the material in the industrial microwave frequency range still need to be further investigated.Summary and prospectsAlthough the favourable dielectric property of ceramic aerogel and fiberboard is proved in the selection of lining materials for microwave sintering, some problems of operating temperature still remain in the practical application. For ceramic firebrick, compared with nitride ceramics (i.e., Si3N4、SiAlON and Si2N2O), some porous oxides ceramics (i.e., fused quartz, alumina, silicate and hosphate ceramics) become a research hotspot because of the lower cost and better antioxidant properties. All the materials show some advantages in mechanical properties and dielectric properties. For instance, fused quartz with relatively stable dielectric properties has a lower operating temperature. Alumina ceramics have a higher operating temperature, but their thermal shock resistance needs to be improved and its dielectric properties have a temperature dependence. Mulite ceramics have excellent characteristics such as high melting point (i.e., 1830 ℃), low thermal expansion coefficient (i.e., 4.5×10-6 K-1), and low thermal conductivity, which can be used in air at 1750 ℃ without high temperature oxidation. In addition, mulite ceramics also have the superior dielectric properties (i.e., ε is about 3-6, tanδ is about 10-3). Some refractory materials with mullite as a main component are commonly used as lining materials in conventional high-temperature furnace. Furthermore, according to the existing studies, the increase of porosity can effectively reduce the dielectric constant of materials, and has a negative impact on the mechanical properties of materials. In this case, mullite ceramics are easy to form grains with acicular morphology during sintering, which is beneficial to maintaining high mechanical properties of the material at a high porosity. However, some challenges still remain in the scientific researches and practical application, such as some related studies on the dielectric properties at high temperatures are limited at <1200 ℃, but it is far from enough for the lining materials of microwave kiln, in which the working temperature can often reach 1700 ℃. The change of the transmittance of materials at higher temperatures is still of great research value. Also, it is necessary to optimize the dielectric constant test system at high temperatures. Finally, some novel material systems of oxides ceramic in a largescale need to be further explored for the microwave sintering application. Meanwhile, exploring the relevance between microstructure and properties and further accelerating the upgrading and application of ceramic based wave-transmitted materials in microwave sintering technology become some research hotspots, which can reduce the pollution and carbon emissions caused by the use of industrial kilns and lay a foundation for the realization of ’carbon neutrality’.
    LIU Bingyan, YIN Hongfeng, TANG Yun, REN Xiaohu, XIN Yalou, LIU Yuchi, YUAN Hudie. Progress on High-Temperature Wave-Transmitting Materials in Microwave Sintering[J]. Journal of the Chinese Ceramic Society, 2025, 53(3): 700
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