Alumina ceramics are currently classified into two types, high-purity and normal-type. High-purity alumina ceramics ceramic materials with a content of 99.9% or more of Al2O3 have a sintering temperature of 1650-1990°C and a transmission wavelength of 1-6 μm. They are generally made of a molten glass in place of a platinum crucible. Alkaline and corrosive alkali metals can be used as sodium lamps; it can be used as an integrated circuit substrate and high-frequency insulation material in the electronics industry. Ordinary type alumina ceramics are divided into 99 porcelains, 95 porcelains, 90 porcelains, 85 porcelains and so on according to the content of Al2O3. Sometimes the content of Al2O3 is 80% or 75%, which is also classified as ordinary alumina ceramics. Among them, 99 alumina ceramic materials are used to make high-temperature crucibles, refractory furnace tubes and special wear-resistant materials, such as ceramic bearings, ceramic seals, and water valve plates; 95 alumina ceramics are mainly used as corrosion-resistant and wear-resistant components; 85 porcelain As part of the talc is often incorporated, the electrical properties and mechanical strength are improved, and it can be sealed with molybdenum, tantalum, niobium, and other metals, and some are used as electrical vacuum devices.
Formula composition
CaO, MgO, SiO2, and transition metal and rare earth metal oxides are commonly used as additives in 95 porcelains. It can be calcined at a lower temperature, and generally has 10% (by volume) glass and secondary crystal phases in the microstructure. In the CaO-Al2O3_SiO2 phase diagram, the lower eutectic phase has a temperature of 1495°C. When the ratio of SiO2/CaO in the porcelain composition is less than 2.16, the minerals coexisting with corundum are anorthite and calcium hexaaluminate; and when SiO2/CaO is greater than 2.16, corundum will coexist with mullite and anorthite.
The advantage of MgO-Al2O3-SiO2 system is that it has good acid resistance and fine grains in the structure, but the sintering temperature is a few degrees higher than that of CaO-Al2O3-SiO2. The introduction of Y2O3 and La2O3 combined with it can further reduce the firing temperature.
The CaO-MgO-Al2O3-SiO2 system has the characteristics of low firing temperature, small grain size, compact structure, and strong resistance to acid and alkali corrosion.
95 porcelain can also be added BaO, BaO-Al2O-SiO2 series has a porcelain surface finish is good, good acid and alkali corrosion resistance, high volume resistivity advantages. With the addition of transition metal oxides such as Cr2O3, MnO2, and TiO2 as additives, colored 95 porcelain is produced, featuring low sintering temperature, high mechanical strength, good wear resistance, and good metal sealing properties.
In addition to kaolin, bentonite, BaCO3, calcite, talc, and magnesite as additives, 75 porcelains have two types, one is porphyrin with SiO2 as the main additive, and the main crystal phase has a fused silica. Quantitative mullite phase; the other added a small amount of CaO, MgO, BaO and other alkaline-earth metal oxides, the crystal phase in this porcelain is still more corundum, mullite love less.
Black alumina ceramics with excellent properties are produced by introducing transition elements Fe, Co, Ni, Cr, Mn, Ti, V, and the like. If a mixture of 3%-4% of the above transitional elements is added to the alumina ceramic, a black alumina ceramic can be fired.
Recipe example
Several 95 porcelain, 75 porcelain practical formula:
95 porcelain:
1# calcined Al2O393.5%, SiO21.28%, CaCO33.25%, 1# Suzhou soil 1.29%
2# calcined Al2O3%, talc 3%, 1# Suzhou 3%
3# Calcined Al2O34%, Calcined talc 4%
75 Porcelain:
1# calcined Al2O35%, 1# Suzhou soil 24%, bentonite 2%, BaCO34%, calcite 3%, talc 2%
2# calcined Al2O365%, 1# Suzhou earth 25%, BaCO3 4%, calcite 3%, talc 3%
3# calcined Al2O350%, 1# Suzhou soil 10%, bentonite 7%, BaCO35%, calcite 3%, talc 5%
4# calcined Al2O370%, 1# Suzhou soil 10%, bentonite 7%, BaCO35%, calcite 3%, talc 5%
