Sintering technology of alumina ceramics
The technical method of densifying the granular ceramic body and forming a solid material is called sintering. The method of sintering is to remove the void between the particles in the body of the billet, remove a small amount of gas and impurity organic matter, and make the particles grow and combine with each other to form new substances.
The heating device used for firing is the most widely used electric furnace. In addition to normal pressure sintering, there are also hot pressing sintering and hot isostatic pressing sintering. Although continuous hot pressing sintering increases the output, the equipment and mold costs are too high, and the length of the product is limited due to axial heating. Hot isostatic pressing sintering uses high temperature and high pressure gas as the pressure transfer medium, has the advantage of uniform heating in all directions, and is suitable for sintering of complex shaped products. Due to the uniform structure, the properties of the material are 30 ~ 50% higher than that of cold pressing sintering. 10-15% higher than the general hot pressing sintering. Therefore, some high value-added alumina ceramic products or special parts needed for national defense, such as ceramic bearings, mirrors, nuclear fuel and gun barrels and other products, the field uses hot isostatic pressing sintering method.
In addition, microwave sintering method, arc plasma sintering method and self-propagating sintering technology are also being developed.
Finishing and packaging processes
Some alumina ceramic materials need to be finished after sintering. Products that can be used as artificial bones require a high surface finish, such as a mirror, to increase lubricity. Due to the high hardness of alumina ceramic materials, it is necessary to use harder grinding and polishing brick materials for finishing. Such as SIC, B4C or diamond. It is usually used from coarse to fine abrasive grinding step by step, the final surface polishing. Generally can be used < 1μm micron Al203 powder or diamond paste for grinding and polishing. In addition, laser processing and ultrasonic processing grinding and polishing methods can also be used.
Alumina ceramic strengthening process
In order to strengthen alumina ceramics and significantly improve their mechanical strength, a new alumina ceramics strengthening process has been developed abroad. The technology is novel and simple, and the technical means taken is to plate a layer of silicon compound film on the surface of alumina ceramics by electron ray vacuum coating, sputtering vacuum coating or chemical vapor evaporation method, and heat treatment at 1200℃ ~ 1580℃ to toughen the alumina ceramics.
The mechanical strength of the strengthened alumina ceramics can be greatly increased on the original basis, and the alumina ceramics with ultra-high strength can be obtained.
