What is the common firing technology of alumina ceramics?

What is the common firing technology of alumina ceramics?

The technology of densification of granular ceramic body and formation of solid material is called sintering. Sintering is a method to remove the voids between the particles in the green body, remove a small amount of gas and impurity organic matter, and make the particles grow and combine with each other to form a new material.

Electric furnace is widely used as heating device for sintering. In addition to pressureless sintering, there are hot pressing sintering and hot isostatic pressing sintering. Although continuous hot pressing sintering can increase the output, the cost of equipment and mould is too high. In addition, the length of products is limited due to the axial heating. Hot isostatic pressing sintering uses high temperature and high pressure gas as pressure transfer medium, which has the advantage of uniform heating in all directions, and is very suitable for the sintering of complex shaped products. Because of the uniform structure, the properties of the material are 30-50% higher than that of cold pressed sintering. It is 10-15% higher than common hot pressing sintering. 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 barrel and other products, are fired by hot isostatic pressing.

In addition, microwave sintering, arc plasma sintering and self propagating sintering are also being developed.

Finishing and packaging process

Some alumina ceramic materials need finishing after sintering. For example, products that can be used as artificial bone require high surface finish, such as mirror, to increase lubricity. Due to the high hardness of alumina ceramic materials, it is necessary to finish them with harder abrasive polishing materials. Such as SiC, B4C or diamond. Generally, the coarse to fine abrasive is grinded step by step and the final surface is polished. Generally, the grinding and polishing can be carried out by using alumina powder or diamond paste with a diameter of less than 1 μ M. In addition, laser processing and ultrasonic processing, grinding and polishing methods can also be used.

Strengthening process of alumina ceramics

In order to enhance the mechanical strength of alumina ceramics, a new strengthening process of alumina ceramics is introduced abroad. The process is novel and simple. The technology adopted is to coat a layer of silicon compound film on the surface of alumina ceramics by means of electron ray vacuum coating, sputtering vacuum coating or chemical vapor evaporation. The alumina ceramics are tempered by heating at 1200 ℃ ~ 1580 ℃.

The mechanical strength of the strengthened alumina ceramics can be greatly increased on the original basis, and the alumina ceramics with strength can be obtained.