Sintering technology of alumina ceramics

The technical method of densifying granular ceramic blank and forming solid material is called sintering. Sintering is a method to remove the cavities between particles in the green body, remove a small amount of gas and impurity organic matter, and make the particles grow up and combine with each other to form new substances.

Electric furnace is the most widely used heating equipment in sintering. In addition to normal pressure sintering, that is, pressureless sintering, there are also hot pressing sintering and hot isostatic pressing sintering. Although continuous hot pressing sintering improves the output, the cost of equipment and mould is too high, and the length of product is limited due to axial heating. Hot isostatic pressing sintering uses high temperature and high pressure gas as pressure transmission medium, which has the advantage of uniform heating in all directions and is very suitable for sintered products with complex shapes. Because of the uniform structure, the material properties are improved by 30 ~ 50% compared with those of cold pressing sintering. Compared with general hot pressing sintering, it is increased by 10- 15%. Therefore, some high value-added alumina ceramic products or special parts needed by national defense and military industry, such as ceramic bearings, mirrors, nuclear fuel, gun barrels, etc., are sintered by hot isostatic pressing.

In addition, microwave sintering, arc plasma sintering and self-propagating sintering technology are also under development and research. In order to strengthen alumina ceramics and significantly improve its mechanical strength, a new strengthening process of alumina ceramics was introduced abroad. This method is novel and simple. The technical means adopted is to coat a silicon compound film on the surface of alumina ceramics by electron beam vacuum coating, sputtering vacuum coating or chemical vapor deposition, and heat at 1200℃ ~ 1580℃ to toughen alumina ceramics.

The mechanical strength of reinforced alumina ceramics can be greatly improved on the original basis, and ultra-high strength alumina ceramics can be obtained.