High temperature sintered oxide ceramics

The melting point of oxide ceramics is more than 2000 ℃, and the firing temperature is about 1800 ℃; the single-phase polycrystal structure, sometimes with a small amount of gas phase; the strength decreases with the increase of temperature, and keeps high strength under 1000 ℃, with little change of temperature; pure oxide ceramics will not be oxidized at any high temperature.

(1) aluminium oxide ceramics
The structure of alumina is o 2-arranged in dense hexagonal structure, and Al 3 + occupies the gap position.
According to the amount of impurities, alumina is red (such as Ruby) or blue (such as sapphire); in actual production, alumina ceramics can be divided into 75, 95 and 99 according to Al2O3 content.
Alumina with a melting point of 2050 ℃ has good oxidation resistance and is widely used in refractories;
Alumina refractory brick, high-pressure vessel, crucible, electric furnace tube, thermowell, etc. were obtained after high-purity Al2O3 powder was pressed and sintered at high temperature;
The hardness of microcrystalline corundum is very high (next to diamond), and its red hardness is up to 1200 ℃. It can be used as a tool with high requirements, such as cutting quenched steel tools, metal drawing dies, etc. High resistivity and low thermal conductivity are good electrical insulation materials and thermal insulation materials. It has high strength and heat-resistant strength (5 times that of ordinary ceramics), and is a good high-temperature fire-resistant structural material, such as can be used as spark plug of internal combustion engine, air compressor pump parts, etc.
Single crystal alumina can be used as sapphire laser;
Aluminum oxide tube blank is used as sodium vapor light bulb.

(2) beryllium oxide ceramics
Beryllium oxide ceramics have the characteristics of general ceramics, excellent thermal conductivity, high thermal stability, low strength, high thermal shock resistance, strong ability to dissipate high energy radiation and large thermal neutron damping coefficient.
Beryllium oxide ceramics are used to make crucibles, vacuum ceramics, atomic reactor ceramics, gas laser tubes, transistor fins, substrates and shells of integrated circuits, etc.

(3) zirconia ceramics
The melting point of zirconia ceramics is above 2700 ℃, and it is resistant to 2300 ℃, and the recommended temperature is 2000 ℃ ~ 2200 ℃; it can resist the erosion of molten metal, and can be used as smelting crucible and 1800 for platinum, germanium and other metals Zirconia can be used as an additive to improve the strength and toughness of ceramic materials. Zirconia toughened ceramics can replace metal manufacturing dies, wire drawing dies, pump impellers and auto parts such as cams, push rods and connecting rods.

(4) MgO / Ca ceramics
MgO / Ca ceramics are usually made by heating dolomite (magnesium or calcium carbonate) ore to remove CO2, which is characterized by resistance to various metal alkaline slag, so they are often used as refractory bricks for furnace lining. However, the disadvantage of this kind of ceramics is its poor thermal stability. MgO is volatile at high temperature, and Cao is easy to hydrate even in air.