1.Overview of alumina insulating porcelain
The ceramic material with α-Al2O3 as the main crystalline phase, high mechanical strength, good thermal conductivity, high electrical strength and insulation resistance,low dielectric loss, stable electrical properties with temperature and frequency changes, also has other excellent properties. It is easy to manufacture, has a uniform and flat surface, and is low in price. It is widely used as an electrical insulating material.
Alumina ceramic is one of the largest electronic ceramic. Electric insulating porcelain occupies a certain proportion in electronic ceramics, while electronic ceramics occupies a large proportion in advanced ceramics.
2. The formula composition of alumina insulating porcelain
CaO, MgO, SiO2, transition metals and rare earth metal oxides are commonly used as additives in 95 ceramics. It can be in the microstructure of porcelain body usually contains 10% glass phase and subcrystalline phase. In CaO - Al2O3 - SiO2 In the phase diagram, the lowest eutectic phase temperature is 1495℃.
The advantages of MgO-Al2O3-SiO2 system are good acid resistance and fine grain in the structure, but the sintering temperature is a few tens of degrees higher than that of CaO- Al2O3-SiO2 system. The introduction of rare earth oxide Y2O3 and La2O3 combined with it can further reduce the sintering temperature.
CaO-MgO-Al2O3 -SiO2 system is characterized by low sintering temperature, fine grain, compact structure and strong resistance to acid and alkali corrosion. It is a preferable typical white porcelain system.
95 Porcelain can also be added with BaO. The BaO-Al2O3-SiO2 system is used to produce ceramics. According to its composition, excellent performance of mullite porcelain and corundum-mullite porcelain can be produced. BaO-Al2O3-SiO2 system has the characteristics of good surface finish of porcelain body, good acid and alkali corrosion resistance, and high volume resistivity. Transition metal oxides such as Cr2O3, MnO2, TiO2 are used as additives to produce colored 95 porcelain, which has the characteristics of low sintering temperature, high mechanical strength, wear resistance and metal sealing performance.
Add kaolin, bentonite and barium carbonate to 75 porcelain. As additives, calcite, talc and magnesite can be divided into two categories: one is the porcelain family with silica as the main additive, and the main crystal phase has a certain amount of mullite in addition to corundum. In the other category, a small amount of alkaline earth metal oxides such as CaO, MgO, BaO, etc. are added. Corundum is still the most crystalline phase in this type of porcelain, while mullite is rare.
3. Manufacturing process of alumina insulating porcelain
Alumina porcelain contains a relatively small amount of clay, the main component is alumina, can be processed according to the general production process, in the ball mill grinding ball, as well as in the production process to avoid iron and other impurities mixed. The ball grinding and grinding lining should be made of aluminum oxide porcelain or rigid jade porcelain, or rubber. The fineness of raw materials has great influence on sintering temperature and properties of products. The finer the particle size, the lower the sintering temperature and the higher the flexure strength.
Due to the poor plasticity of 95 porcelain and 75 porcelain blanks, various organic plasticizers must be added. According to the shape of the product and the nature of the ingredients, determine the molding method, such as dry pressing, grouting, hot die casting and isostatic pressing.
4. Application of alumina insulating porcelain
Alumina ceramics used for electrical insulation materials include corundum porcelain, high-alumina porcelain, 75 porcelain and colored alumina ceramics. Porcelain 95, Porcelain 96 and Porcelain 99 are more used in electric vacuum technology as a package of dense ceramic and metal sealing.
Electrical insulating ceramics are widely used in dielectric porcelains ceramics. Alumina ceramics are mainly used for substrates, housings, fixing, sealing or insulating parts in electronic components and circuits, such as insulators, resistor substrates, integrated circuit substrates, and packaging tubes.
Alumina ceramic insulated lamp holder