Alumina ceramic is a kind of ceramic material with alumina (Al2O3) as the main body, which is used in thick film integrated circuit. Alumina ceramics have good conductivity, mechanical strength and high temperature resistance. It should be noted that ultrasonic cleaning is required. Alumina ceramic is a kind of widely used ceramic. Because of its superior performance, it has been used more and more widely in modern society, meeting the needs of daily use and special performance.
Forming method
      The forming methods of alumina ceramic products include dry pressing, grouting, extrusion, cold isostatic pressing, injection, casting, hot pressing and hot isostatic pressing. In recent years, many molding technologies have been developed at home and abroad, such as pressure filtration molding, direct solidification molding, gel casting, centrifugal grouting molding and solid free molding. Different products with different shapes, sizes, complex shapes and precision need different forming methods.
      1. Dry pressing
      The dry pressing technology of alumina ceramics is limited to the objects with simple shape, inner wall thickness of more than 1mm, and the ratio of length to diameter of less than 4:1. The forming methods are single axial or two-way. There are two types of press, hydraulic and mechanical, which can be semi-automatic or full-automatic forming. The upper pressure limit of the press is 200MPa, and the output can reach 15-50 pieces per minute.
Because the stroke pressure of hydraulic press is even, the height of pressing parts is different when the filling of powder is different. However, the applied pressure of mechanical press changes with the amount of powder filling, which is easy to cause the difference of size shrinkage after sintering and affect the product quality. Therefore, the uniform distribution of powder particles in the process of dry pressing is very important for mold filling. Whether the filling quantity is accurate or not has a great influence on the dimensional accuracy control of alumina ceramic parts. The free flow effect of the powder particles is more than 60 μ m and between 60 and 200 mesh, and the better pressure forming effect is obtained.
     2. Injection molding
     Injection molding is an earlier molding method for alumina ceramics. Due to the use of gypsum mold, low cost and easy to form large-scale, complex shape parts, the key to the injection molding is the preparation of alumina slurry. Usually, water is used as the flux medium, and then glue dissolving agent and binder are added. After full grinding, air is exhausted, and then poured into the gypsum mold. Because of the absorption of water by the capillary of gypsum mold, the slurry is solidified in the mold. During hollow grouting, when the adsorbed slurry on the formwork wall reaches the required thickness, the excess slurry shall be poured out. In order to reduce the shrinkage of green body, high concentration slurry should be  used as much as possible.
      In addition, organic additives should be added to the alumina ceramic slurry to form a double electric layer on the surface of the slurry particles so that the slurry can be stably suspended without precipitation. In addition, vinyl alcohol, methylcellulose, alginate amine and other binders, polypropylene amine, Arabic gum and other dispersing agents should be added to make the slurry suitable for grouting and molding.