High Temperature Structural Ceramic
What Is High Temperature Structural Ceramic
High-temperature structural ceramics are ceramics that can withstand static or dynamic mechanical loads under high temperature conditions in certain devices, equipment, or structures. It has high melting point, high high temperature strength and small high temperature creep performance, as well as good thermal shock resistance, corrosion resistance, oxidation resistance and structural stability. High-temperature structural ceramics include high-temperature oxides and high-temperature non-oxides (or refractory compounds). Metals have been widely used as structural materials. However, since metals are susceptible to corrosion and are not resistant to oxidation at high temperatures, they are not suitable for use at high temperatures. The emergence of high-temperature structural materials has made up for the weakness of metal materials.
Among the materials, there is a class called structural materials, which are mainly made of various materials made of mechanical properties such as strength, hardness and toughness. The emergence of high-temperature structural materials has made up for the weakness of metal materials. This kind of material has the advantages of being able to withstand high temperature, not afraid of oxidation, acid and alkali corrosion resistance, high hardness, wear resistance, low density, etc. It is very suitable as a high temperature structural material.
The Classification Of High Temperature Structural Ceramic
Alumina Ceramic
Alumina ceramic (artificial corundum) is an extremely promising high temperature structural material. It has a high melting point and can be used as advanced refractory materials, such as crucibles, high-temperature furnace tubes, etc. Taking advantage of the high hardness of alumina, it is possible to manufacture corundum ball mills used in the laboratory to grind materials that are less hard than it. Using high-purity raw materials and using advanced technology, alumina ceramics can also be made transparent, which can be used to make lamps for high-pressure sodium lamps.
Silicon Nitride Ceramic
Silicon nitride ceramic is also an important structural material. It is a super-hard substance with low density, lubricity, and wear resistance. Except for hydrofluoric acid, it does not react with other inorganic acids and has corrosion resistance. Strong; can also resist oxidation at high temperature. And it can also resist the shock of cold and heat, it can be heated to more than 1000 degrees in the air, cooled sharply and then heated sharply, and it will not break. It is silicon nitride that has such good properties that people often use it to manufacture mechanical components such as bearings, turbine blades, mechanical seal rings, and permanent molds.
Boron Nitride Ceramic
Boron nitride ceramics, appearance and properties: lubricated, easy to absorb moisture. Boron nitride is a white, insoluble, high temperature resistant substance. Boron nitride ceramic can be obtained by co-melting B2O3 with NH4Cl, or by burning elemental boron in NH3. The boron nitride usually obtained is a graphite-type structure, commonly known as white graphite. The other is diamond type. Similar to the principle of converting graphite into diamond, graphite-type boron nitride can be converted into diamond-type boron nitride at high temperature (1800°C) and high pressure (800Mpa). The B-N bond length (156pm) in this boron nitride is similar to the C-C bond length (154pm) of diamond, and its density is similar to that of diamond. Its hardness is comparable to that of diamond, and its heat resistance is better than that of diamond. It is a new type of high temperature resistant superhard material for making drills, abrasives and cutting tools.
Boron Carbide Ceramic
Boron carbide material has the properties of light weight, high hardness, high wear resistance, high impact resistance, neutron absorption, etc. It has broad application prospects in high-tech industry, nuclear power technology, national defense and military industry and other fields. Important strategic boron carbide ceramic material with a wide range of uses. Specifically for:
1. Neutron absorption and radiation protection material
Element B has a neutron absorption cross-section of up to 600 barn, and is the main material of choice for deceleration elements in nuclear reactors—control rods or radiation protection components of nuclear reactors.
2. Composite armor materials
Utilizing its lightweight, super-hard and high-modulus properties, it is used as a lightweight body armor and bulletproof armor material. The bulletproof farmer made of boron carbide is more than 50% lighter than the same type of steel bulletproof vest. Boron carbide is also an important bulletproof armor material for land armored vehicles, armed helicopters and civil airliners.
Such as AH-64 Apache (AH-64 Apazhe), Super Cobra (Super Cobra), Super Puma (Super Puma), Black Hawk (Black Hawk) and other helicopters have just used boron carbide armor.
3. Semiconductor industry components and thermoelectric components
Boron carbide ceramics have semiconductor properties and good thermal conductivity, and can be used as high-temperature semiconductor components, as well as gas distribution disks, focus rings, microwave or infrared windows, DC plugs, etc. in the semiconductor industry. The combination of B4C and C can be used as a high temperature thermocouple element, the operating temperature is up to 2300 ℃, and it can also be used as an anti-radiation thermoelectric element.
4. Mechanical seal parts
The superhard properties and excellent wear resistance of boron carbide make it an important material for mechanical seals. Due to its relatively high cost, it is mainly used in some special mechanical sealing occasions.
5. Nozzle material
The ultra-high hardness and excellent wear resistance of boron carbide make it an important nozzle material. Boron carbide nozzles have the advantages of long life, relatively low cost, time saving and high efficiency. The life of boron carbide nozzles is dozens of times longer than that of alumina nozzles, and many times longer than that of WC and SiC nozzles.
The Field And Differentiation Methods
The general term for ceramic materials whose melting temperature is above the melting point of silicon oxide (1728 ° C) is called high-temperature structural ceramics. An important component of special ceramics, and sometimes as a component of high-temperature refractories.
According to the main chemical composition of the material, it can be divided into high temperature oxide ceramics (such as Al2O3, ZrO, MgO, CaO, ThO2, Cr2O3, SiO2, BeO, 3Al2O3 2SiO2, etc.), carbide ceramics, boride ceramics, nitride ceramics and silicides Ceramics etc. Usually has high temperature resistance, high strength, high hardness, good electrical properties, thermal properties and chemical stability. Oxide high-temperature ceramics are mostly sintered in an oxidizing atmosphere, vacuum and other states, and non-oxide high-temperature ceramics are often sintered by hot pressing or in a specific atmosphere (such as argon, nitrogen). There are also methods such as hot isostatic pressing and microwave sintering. For thin films, etc., it can also be prepared by methods such as vapor deposition. It can be used as a high-temperature structural material in many departments such as aerospace, atomic energy, electronic technology, machinery, chemical industry, metallurgy, etc. It is an indispensable high-temperature engineering material for modern science and technology.
Distinguishing Method From Low Temperature Ceramic
Listening to the sound can be easily distinguished, the high temperature has a good degree of porcelain, and the sound is crisp. But it still depends on the size of the water absorption rate, and the water absorption rate of high-temperature sintered ceramics is small. Water absorption test method:
- Measure with a special instrument (vacuum immersion in water).
- Boil in boiling water for 2 hours.
- Soak in water for 24 hours.
No matter which measurement method is used, the tile is first weighed to obtain m0, and after the experiment is weighed to obtain m1, the water absorption rate is (m1-m0)/m0; the data obtained by each measurement method is slightly different, but only two The tiles are measured by the same method, and the results are not comparable.