Alumina is very abundant in the earth’s crust, with an average content of 15.34% in rocks, which is the second largest oxide in nature after SiO2. Therefore, alumina ceramics tube are widely used in the industrial field because of their high cost-effectiveness. This article briefly introduces the preparation process of alumina ceramic tubes.
The properties of ceramic materials are controlled by the mixture and are affected by the particle size and the porosity of the ceramic sintered body, which is also affected by the preparation method. In the ceramic production process, the key steps are firing and sintering, which are sometimes carried out simultaneously. During these two processes, the components of the particles will be redistributed in such a way that the free energy of the system is minimized, a large number of ions migrate, and the ions diffuse into each other to form new phases. At the same time, the internal particle surface area is reduced to a minimum and the particle size increases. Usually, the entire volume will shrink. The volume shrinkage rate must have repeatability, which can guide the preparation of a specific size of the embryo. It is also necessary to have uniform internal shrinkage in a given embryo, otherwise the embryo will deform. To this end, the density of the entire green body must vary very little (green body refers to the unsintered alumina ceramic body). The production process of ceramics is generally divided into five stages, namely, classification/purchase/storage of raw materials, prefabrication of powdered mixtures, molding, sintering, and processing.
Alumina ceramic raw materials
Classification of raw materials according to chemical composition is only one aspect. Particle size and degree of agglomeration are often very important, and it is difficult to accurately determine data consistent with raw material manufacturers. It is also more difficult to specify the “activity” index of the material, but it is also very important. Activity and particle size, crystal integrity, and particle composition are related. Many raw materials need to be pre-heat treated during processing, and changing the temperature and holding time has an impact on their activity. These raw material characteristics can be changed by adjusting certain parameters of the subsequent process. More detailed classification descriptions are required for expensive materials, such as establishing a comparison table between classification details and test costs and corrections to variables in the process.
Homogeneity of mixing
To reduce the sintering temperature of alumina ceramics, appropriate additives must be added to the powder before sintering. Therefore, the level of mixing is also an important factor affecting the sintered ceramic body. The purpose of mixing is to make the powder composition uniform. If the composition is unevenly distributed, the local composition will deviate from the overall ratio, resulting in less additives in some areas, making it difficult for alumina to sinter at low temperatures, while the melting point is low in areas with more additives, which is prone to liquid phase and rapid grain growth, ultimately leading to the uneven microstructure of the product and low density.