microwave sintering

Microwave sintering is a method of densification achieved by coupling the special band of microwave with the basic fine structure of the material to generate heat. The dielectric loss of the material in the electromagnetic field heats the material as a whole to the sintering temperature. Microwave is a high-frequency electromagnetic wave with a frequency range of 0.3-300GHz, but the frequencies used in microwave sintering technology are mainly in the 915MHz and 2.45GHz bands. Microwave sintering is a new ceramic research method developed since the 1960s. The fundamental difference between microwave, sintering, and conventional sintering is that conventional sintering uses the heating element around the sample to heat, while microwave sintering uses the sample itself to absorb microwave and generate heat. According to the basic theory of microwave sintering, the heat energy is caused by the loss of the medium inside the material, so it is a volume heating effect. Compared with conventional sintering, it has the following characteristics: short sintering time, low sintering temperature, reducing the activation energy of Dry media reaction, making its grains refined, uniform structure, improving the mechanical properties of sintered samples, and reducing high temperature environmental pollution. However, the detailed mechanism of microwave sintering and the repeatability of microwave sintering process are still key issues for the further development of this new technology. At present, microwave sintering technology has been widely used for experimental research on various ceramic composite materials

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Technical characteristics of microwave sintering:

① Direct coupling between microwave and material leads to overall heating. Due to the volume heating effect of microwaves, zero gradient uniform heating of large areas in the material can be achieved, reducing the internal thermal stress of the material, thereby reducing the tendency for cracking and deformation. Meanwhile, due to the direct absorption of microwave energy by materials and its conversion into thermal energy, the energy utilization rate is extremely high, saving more than 80% energy compared to conventional sintering.

② Microwave sintering has a fast heating rate and short sintering time. After the temperature of certain materials exceeds the critical temperature, their loss factor rapidly increases, resulting in extremely fast temperature rise. In addition, the presence of microwaves reduces the activation energy, accelerates the sintering process of the material, and shortens the sintering time. Short time sintering makes it difficult for grains to grow, resulting in a uniform fine-grained microstructure with few internal voids and a rounder pore shape than traditional sintering, resulting in better ductility and toughness. At the same time, the sintering temperature also decreases to varying degrees.

③ Safe and pollution-free. The rapid sintering characteristics of microwave sintering greatly reduce the amount of gas used as the sintering atmosphere during the sintering process, which not only reduces costs but also reduces the emissions of waste gas and heat during the sintering process.

④ Capable of achieving spatial selective sintering. For multiphase mixed materials, due to the different dielectric losses of different materials, the generated dissipation power and thermal effects are also different. This can be used to selectively sinter composite materials, research new material products, and obtain better material properties.

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