As the name implies, microwave selective heating means that microwave can only heat some materials but not some materials. Therefore, the materials can be divided into four categories according to their properties:

1、 Reflective materials, generally conductor materials such as metal iron blocks, graphite presswork, etc., can reflect microwave and cannot be microwave heating ；

2、 Transmitting materials, such as quartz, polytetrafluoroethylene and other materials, can not or are difficult to be heated by microwave because the microwave is penetrated by the reflective part on the surface of such materials and is rarely absorbed;

3、 Microwave absorbing materials, which have good microwave absorption capacity and high dielectric loss, can convert electromagnetic energy in microwave into heat energy.

4、 Heterogeneous materials are one of the research hotspots in recent years. stay Microwave metallurgy In the field of material synthesis, the objects of microwave heating are mostly two-phase or multiphase heterogeneous materials, and its mechanism is very complex. Such materials are characterized by the local field enhancement effect under microwave irradiation, which can cause discharge and generate ultraviolet light to promote photocatalysis, which is a new mechanism of microwave assisted catalysis.

It is worth mentioning that when a class of conductor materials such as iron, copper and graphite are processed into powder state, they have very good microwave absorption ability and can rapidly rise to hundreds of degrees Celsius or even 1000 degrees Celsius in a short time. Therefore, whether the material can be heated by microwave is related to the characteristics of the material itself, as well as the physical state of the material.