The research results indicate that microwave radiation promotes densification, grain growth, and accelerates chemical reactions. Because in sintering, microwaves are not only used as a heating energy source, but the sintering process itself is also an activation sintering process. By analyzing the phenomenon of microwave promoted structure, the apparent activation energy Ea during the sintering process of high-purity A1203 was determined, and it was found that microwave sintering. Ea is 170kj/mol, while in conventional resistance heating sintering, Ea-575kj/mol， It can be inferred that microwaves promote atomic diffusion. The diffusion process of A203 single crystal was further measured using the 180 tracer method, which also proved that the diffusion coefficient under microwave heating conditions was higher than that under conventional heating.
Microwave high-temperature sintering equipmentThe experimental results indicate that microwave fields have the effect of enhancing ion conductivity. It is believed that high-frequency electric fields can promote the migration of charged vacancies on the surface of grains, resulting in plastic deformation similar to diffusion creep, thereby promoting sintering.
Several advantages of microwave high-temperature sintering equipment must be mentioned:
cleanliness and hygiene
When processing and drying food, drugs, etc., microwave heating and biological effects can quickly kill insects and sterilize at lower temperatures, and can maximize the preservation of nutrients and original color. Therefore, microwave heating has been widely used in the food industry.
Selective heating
Materials with different properties have different absorption losses for microwaves, and they have the characteristic of selective heating, which is beneficial for the drying process. Because water molecules have a large absorption loss for microwaves, the parts with high moisture content absorb more microwave power than those with lower moisture content, resulting in a faster drying rate. But some substances have a negative temperature coefficient. The higher the temperature, the greater the er and tgs, and the better the absorption, causing positive feedback and a sharp rise in temperature in this part. When microwave heating these materials, it is necessary to pay attention to the reasonable development of processing technology.
uniform heating
When using external heating method for heating, in order to increase the heating speed, it is necessary to raise the external temperature and increase the temperature difference gradient. However, this can easily lead to the phenomenon of external coke generation. When microwave heating, regardless of its shape, the microwave can penetrate uniformly and generate heat, thus greatly improving uniformity.
Energy-efficient
Different materials have different absorption rates for microwaves, and substances containing moisture are prone to absorbing microwave energy. Glass, ceramics, polypropylene, polyethylene, fluoroplastics, and other materials rarely absorb microwaves, while metals reflect them. These substances cannot be heated by microwaves. When microwave heating is used, the material to be reheated is usually placed in a heating chamber made of metal. The heating chamber is a closed cavity for electromagnetic waves, which cannot leak out and can only be absorbed by the heated object. The air and corresponding containers in the heating chamber are not heated, so the thermal efficiency is high. At the same time, the ambient temperature in the workplace will not increase as a result, and the production environment will be significantly improved.
easy to control
The control of microwave power is adjusted by switches and knobs, which are both on and off, without thermal inertia, and the power is continuously adjustable.
Fast heating speed
Conventional heating methods, such as flames, hot air, electric heating, steam, etc., utilize heat conduction, convection, and radiation to first transfer heat to the surface of the object being heated, and then gradually increase the center temperature through heat conduction (commonly known as external heating). It requires a certain amount of heat conduction time to reach the desired temperature in the central area, and even longer for objects with poor thermal conductivity. Microwave heating is an internal heating method, where electromagnetic energy directly acts on the molecules of the medium to convert them into heat, and transmission heats both the inside and outside of the medium simultaneously, without the need for heat conduction. Therefore, uniform heating can be achieved in a short period of time.