Industrial ceramic materials
1. Calcium oxide ceramics (calcia ceramics)
Calcium oxide ceramics (calcia ceramics) refer to ceramics with calcium oxide as the main component.
Properties: Calcium oxide has a NaCl-type crystal structure with a density of 3.08~3.40g/cm and a melting point of 2570°C. It has thermodynamic stability and can be used at high temperatures (2000°C). It has little reaction with highly active metal melts and is affected by There is little pollution of oxygen or impurity elements. The product has good resistance to molten metal erosion and molten calcium phosphate. It can be formed by dry pressing or grouting.
Application:
1) It has excellent metal corrosion resistance and is an important container for smelting non-ferrous metals, such as high-purity platinum and uranium;
2) Calcium oxide brick stabilized with titanium dioxide can be used as the lining material of rotary kiln for molten phosphate ore;
3) In terms of thermodynamic stability, CaO exceeds SiO2, MgO, Al2O3, ZrO2, etc., and is the highest among oxides. This property shows that it can be used as a crucible for molten metals and alloys;
4) In the process of metal melting, CaO quality samplers and protective tubes can be used, which are mostly used in quality management or temperature control of active metal melts such as high-titanium alloys;
5) In addition to the above, the use of CaO ceramics in metallurgy is also suitable for thermal insulation jackets for arc melting or containers for balancing experimental corners.
Calcium oxide has two disadvantages:
① Easy to react with moisture or carbon dioxide in the air;
②It can react with oxides such as iron oxide at high temperature. This slagging effect is the reason why ceramics are easy to corrode and have low strength. These shortcomings also make it difficult for calcium oxide ceramics to be widely used. CaO is still in the primary stage as a ceramic. It has two sides, sometimes stable and sometimes unstable. In the future, through the advancement of raw materials, molding, firing and other technologies, it can better plan its use and make it really join the ranks of ceramics.
2. Zircon ceramics (zircon ceramics)
Zircon ceramics (zircon ceramics) refer to ceramics with zircon (ZrSiO4) as the main component.
Properties: ZrSiO4 ceramics have good thermal shock resistance, acid resistance and chemical stability, but poor alkali resistance. The thermal expansion coefficient and thermal conductivity of zircon ceramics are low, and its flexural strength can be maintained at 1200 ~ 1400 ℃ without decreasing, but its mechanical properties are poor, and the production process is similar to general special ceramics.
Application:
1) As an acid refractory material, zircon has been widely used in low-alkali aluminum borosilicate glass kilns for producing glass balls and glass fibers. Zircon ceramics have high dielectric properties and mechanical properties. Can be used as electrical insulators and spark plugs;
2) Mainly used for making high-strength high-temperature electric porcelain, porcelain boat, crucible, high-temperature kiln burner, lining of glass melting furnace, infrared radiation ceramics, etc.;
3) Can be made into thin-walled products-crucibles, thermocouple sleeves, nozzles, thick-walled products-mortars, etc.;
4) Research shows that zirconite has chemical stability, mechanical stability, thermal stability and radiation stability, and has good tolerance to actinides such as U, Pu, Am, Np, Nd, Pa, etc. It is solidified The ideal medium material for high-level radioactive waste (HLW) of steel;
At present, there is no report on the relationship between the production process of zircon ceramics and their mechanical properties. To a certain extent, it has hindered the further in-depth study of their properties, and the application of zircon ceramics has been restricted to a certain extent.
3. Lithium oxide ceramics
Lithium oxide ceramics (lithia ceramics) refer to ceramic products whose main components are Li2O, Al2O3, and SiO2. The main mineral raw materials containing Li2O in nature are spodumene, spodumene, lithium apatite, lepidolite and spodumene.
Properties: The main crystal phases of lithium oxide ceramic products are spodumene (Li2O·Al2O3·2SiO2) and spodumene (Li2O·Al2O3·4SiO2), which is characterized by low thermal expansion coefficient (-0.03× within the range of 100~1000℃) 10/℃~ 4.08×10/℃), good thermal shock resistance. Li2O is a kind of network exosome oxide, which has the effect of strengthening the glass network and can effectively improve the chemical stability of the glass.
Application: It can be used to make the lining brick of electric furnace (especially induction furnace), thermocouple protection tube, constant temperature parts, laboratory utensils, cooking utensils, etc. Li2O-A12O3-SiO2 (LAS) series materials are typical low-expansion ceramics, which can be used as thermal shock-resistant materials. Li2O can also be used as a ceramic bonding agent, and has potential use value in the glass industry.
4. Ceria ceramics
Ceria ceramics refers to ceramics with cerium oxide as the main component.
Performance: The product has a specific gravity of 7.73 and a melting point of 2600°C. It will become Ce2O3 in a reducing atmosphere and the melting point will be reduced from 2600°C to 1690°C. The resistivity at 700°C is 2 × 10 ohm·cm, and at 1200°C it is 20 ohm·cm. At present, the commonly used process technologies for industrial production of cerium oxide in my country are as follows:
1) Chemical oxidation method, including air oxidation method and potassium permanganate oxidation method;
2) Roasting oxidation method;
3) Extraction separation method.
Application:
1) Can be used as heating elements, crucibles for melting metals and semiconductors, thermocouple bushings, etc.;
2) Can be used as a sintering aid for silicon nitride ceramics, and can also modify aluminum titanate composite ceramics, and CeO2 is an ideal toughening stabilizer;
3) The rare earth trichromatic phosphor added with 99.99% CeO2 is a luminescent material for energy-saving lamps, which has high light efficiency, good color rendering and long life;
4) The high-cerium polishing powder made of CeO2 with a mass fraction of more than 99% has high hardness, small and uniform particle size, and crystals with angular corners, which is suitable for high-speed polishing of glass;
5) Using 98% CeO2 as the glass decolorizer and clarifier can improve the quality and performance of the glass and make the glass more practical;
6) Cerium oxide ceramics have poor thermal stability and strong sensitivity to atmosphere, which limits its use to a certain extent.
5. Thorium ceramics
Thorium ceramics (thoria ceramics) refer to ceramics with ThO2 as the main component.
Properties: Pure thorium oxide is cubic crystal, fluorite structure, thorium oxide ceramic products have a large thermal expansion coefficient, 9.2×10/℃ at 25~1000℃; thermal conductivity is small, 0.105 J/(cm at 100℃ ·S·℃), the thermal stability is poor, but the melting temperature is high, the high temperature conductivity is good, and it is radioactive. The molding method can be grouting (adding 10% aqueous solution of polyvinyl alcohol as a suspending agent) or compression molding (adding 20% of thorium tetrachloride as a binder).
Application: It is mainly used as a crucible for smelting osmium, pure rhodium and refined radium. It can also be used as a heating element for searchlight light sources, incandescent lamp gauze covers, or as nuclear fuel. It can also be used as a cathode for electron tubes and electrodes for arc melting.
6. Alumina ceramics
The ceramic is a ceramic with AL2O3 as the main component (AL2O3 mass fraction is divided into >45%). According to the main crystal phase in the porcelain blank, it can be divided into corundum porcelain, corundum-mullite porcelain and mullite porcelain, etc.; According to the mass fraction of AL2O3, it can be divided into 75 porcelain, 95 porcelain and 99 porcelain.
application:
Alumina porcelain has a high melting point, high hardness, high strength, and has good chemical resistance and dielectric properties. However, it has high brittleness, poor impact resistance and thermal shock resistance, and cannot withstand the drastic changes of the ambient temperature. It can be used to manufacture high temperature furnace tubes, linings, spark plugs for internal combustion engines, etc. It can also be used to manufacture high hardness cutting tools, and is also a good material for manufacturing thermocouple insulating sleeves.
7. Silicon carbide ceramic
The biggest characteristic of silicon nitride ceramics is high temperature strength, high thermal conductivity, high wear resistance, corrosion resistance, and creep resistance. It is often used as a high-temperature sintering material in the fields of defense, aerospace and other sciences, that is, it is used for High-temperature parts such as nozzles for making rocket tail nozzles, throats for pouring metal, thermocouple bushings, and furnace tubes.
application:
Due to its high thermal conductivity, it can also be used to manufacture gas turbine blades, high-temperature strength parts for bearings, materials used as high-temperature heat exchangers, and nuclear fuel encapsulation materials.