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.