There are many common insulating ceramics, including fine ceramics, alumina ceramics, mullite ceramics, modified silicon carbide ceramics, silicon nitride ceramics, aluminum nitride ceramics, lead borate glass ceramics, barium tin borate ceramics, beryllium oxide ceramics and so on. These ceramics have similar performance requirements, including the permittivity to meet the technical requirements for use, generally lower permittivity; The lowest possible dielectric loss; High volume resistivity and dielectric strength; Good dielectric temperature and frequency characteristics; Excellent thermal conductivity, mechanical strength, fracture toughness, chemical stability and thermal stability.
Therefore, insulating ceramics can be used in electronic equipment as a ceramic for installing, fixing, supporting, protecting, insulating, isolating and connecting various radio components and devices. In addition to ordinary insulating ceramics, high temperature ceramic insulation materials have alumina, it can be used as crucible, high temperature thermocouple casing, tools, molds, etc.; Silicon nitride, with good high temperature strength, low thermal expansion coefficient, high thermal conductivity, good thermal shock resistance, good electrical insulation, for mechanical sealing ring, thermocouple bushing, steam turbine blade. Still have is silicon carbide, its characteristic lies in high temperature strength, make nozzle, furnace tube, high temperature bearing, high temperature heat exchanger.
Grouting is insulating ceramic alumina ceramics using early forming method, because use gypsum mold, low cost and easy to forming large size and complex shape parts, injection molding is the key to the preparation of alumina slurry, usually with water as the solvent medium, add the glue and adhesive, fully exhaust after grinding, then pour it into the plaster mould. Because gypsum mold capillary adsorption of water, slurry solidification in the mold, hollow grouting, in the mold wall adsorption slurry thickness requirements, but also need to pour out the excess slurry. In order to reduce the shrinkage of the blank, high concentration slurry should be used as far as possible.
The electric furnace is widely used as the heating device for the firing of insulating ceramics. In addition to normal pressure sintering (non-pressure sintering), there are also hot pressure sintering and hot isostatic pressure sintering. Although continuous hot pressing increases production, the cost of equipment and die is too high. In addition, due to the axial heating, the length of products is limited.
High temperature and high pressure gas is used as the pressure transfer medium, which has the advantage of uniform heating in all directions. Due to the uniform structure, the material properties are improved by 30 ~ 50% compared with cold pressing sintering. Compared with the general hot pressing sintering increased by 10-15%. Therefore, some high value-added alumina ceramic products or special parts needed for national defense, such as ceramic bearings, mirrors, nuclear fuel and gun barrel products, the field by thermal isostatic firing method.