The technique of densifying the granular ceramic body and forming a solid material is called sintering. Sintering is to eliminate voids between particles in the body, to remove a small amount of gas and organic impurities, so that the particles grow and combine with each other to form a new substance. Electric heating is the most widely used heating device for firing. In addition to normal pressure sintering, that is, pressureless sintering, there are hot press sintering and hot isostatic sintering. Although continuous hot-press sintering increases production, the cost of equipment and molds is too high. In addition, due to axial heating, the length of the product is limited.
Hot isostatic pressure firing uses high temperature and high pressure gas as the pressure transmission medium, which has the advantages of uniform heating in all directions, and is very suitable for sintering of complex shaped products. Due to the uniform structure, the material performance is improved by 30-50% compared to cold-press sintering. It is 10-15% higher than general hot press sintering. Therefore, some high-value-added alumina ceramic products or special parts required by the defense military industry, such as ceramic bearings, reflectors, nuclear fuel and barrels, use hot isostatic pressing firing methods. In addition, microwave sintering, arc plasma sintering, and self-propagating sintering technology are also under development.
