What does ceramic material include?What is the difference between its performance and application
Ceramic material is a kind of inorganic non-metallic material made of natural or synthetic compound through forming and high-temperature sintering, which has the advantages of high melting point, high hardness, high abrasion resistance, oxidation resistance, etc.
classification
Ordinary ceramic material
Using natural ingredients such as feldspar, quartz and clay sintering and become, is a typical silicate material, is the main constituent elements silicon, aluminum, oxygen, 90% of the total of the three elements of the earth's crust element, ordinary ceramic rich source, low cost and process maturity. This type of ceramic according to the performance characteristics and purposes: daily-use ceramics, building ceramics, electrical insulating ceramics, chemical ceramics, etc.
Special ceramic material
It is made of high purity synthetic raw materials and sintered by precise control process, generally having some special properties to meet various needs.Special ceramics have special mechanical, optical, acoustic, electrical, magnetic, thermal and other properties. This section mainly introduces special ceramics.
performance features mechanical properties
Ceramic materials have the best stiffness and the highest hardness among engineering materials, and the hardness is mostly above 1500HV. The compressive strength of ceramics is high, but the tensile strength is low, and the plasticity and toughness are poor.
Thermal performance
Ceramic materials have high melting point (mostly in above 2000 ℃), and has excellent chemical stability at high temperature;The thermal conductivity of ceramics is lower than that of metal materials, and ceramics are also good thermal insulation materials. At the same time, the linear expansion coefficient of ceramics is lower than that of metal, so ceramics have good dimensional stability when the temperature changes.
electrical
Most ceramics have good electrical insulation, so used to produce various kinds of voltage (1 kv ~ 110 kv) insulation device. Barium titanate (BaTiO3) ferroelectric ceramics with high dielectric constant, can be used in the production of capacitor, ferroelectric ceramics under the action of electric field, can also change shape, converts electrical energy into mechanical energy (with the characteristics of the piezoelectric material), can be used as an amplifier, phonograph records, ultrasonic apparatus, sonar, medical use spectrograph etc. A few ceramic also has the characteristics of the semiconductor, rectifier.
Chemical properties
Ceramic materials are not easy to oxidize at high temperature, and have good corrosion resistance to acid, alkali and salt.
Optical performance
Ceramic materials have unique optical properties, can be used as a solid state laser, optical fiber, optical storage, such as transparent ceramic can be used for high pressure sodium lamp tube, etc. The magnetic ceramics (ferrite, such as: MgFe2O4, CuFe2O4, Fe3O4) in the recording tape, record, transformer core and large computer memory element has a broad future.
Special ceramic materials
According to different purposes, special ceramic materials can be divided into structural ceramics, tool ceramics, functional ceramics.
1.Structural ceramics
Alumina ceramic main compositions for Al2O3, general content greater than 45% alumina ceramic has a variety of excellent performance. High temperature resistant, to 1600 ℃ commonly use for a long time, corrosion resistance, high strength, its strength is 2 ~ 3 times of ordinary ceramic, up to 5 ~ 6 times higher. Its disadvantage is that brittleness is big, can't accept the sudden environmental temperature change. USES is very wide, can be used as a crucible, engine spark plug, high-temperature refractory, thermowells, sealing ring, etc., can also be as a tool and die.
Silicon nitride ceramics is the main component Si3N4, this is a kind of high temperature and high strength, high hardness, wear resistance, corrosion resistance and can be self lubrication of high temperature ceramic, linear expansion coefficient of minimum in all kinds of ceramic, using temperature as high as 1400 ℃, with excellent corrosion resistance, except hydrofluoric acid, and other kinds of acid corrosion, and alkali resistance, all kinds of metal corrosion, and it has excellent electrical insulation and radiation resistance. Can be used for high temperature bearing, seal ring used in corrosive medium, thermowells, also used for metal cutting tools.
Silicon carbide is the main component SiC ceramic, this is a kind of high strength, high hardness, high temperature resistant ceramic, in 1200 ℃ ~ 1400 ℃ using can still maintain a high bending strength, is the highest high temperature strength of ceramics, silicon carbide ceramics also has good thermal conductivity, oxidation resistance, electrical conductivity and high impact toughness. Is good high temperature structural materials, can be used in the rocket the exhaust nozzle, thermowells, parts under the high temperature furnace tube and so on work;It can be used to produce heat exchange material at high temperature.Using its high hardness and wear resistance to make grinding wheel, abrasive, etc.
The structure and properties of hexagonal boron nitride are similar to that of graphite. Therefore, it is called "white stone ink" with low hardness. It can be machined with self-lubricity and can be made into self-lubricated high-temperature bearing and glass forming mold.
2.Ceramic tools
Carbide main ingredients for carbide and binder, carbide WC, TiC, TaC, NbC, VC, etc., adhesive mainly for cobalt (Co). Carbide compared with tool steel, high hardness (87 ~ 91 hra), good red hardness (excellent abrasion resistance around 1000 ℃), when used as a tool, cutting speed 4 ~ 7 times higher than that of high speed steel, 5 ~ 8 times higher life, its defect is too high hardness, brittle, are difficult to machining, so often as the blade and welding used on tool rod, hard alloy is mainly used for machining tool;Various dies, including drawing die, drawing die, cold heading die;Various drill bits are used for mining tools, geology and petroleum.
Natural diamond (diamond) is a precious decoration, while synthetic diamond is widely used in industry. Diamond is the hardest material in nature and has a very high elastic modulus.The thermal conductivity of diamond is the highest among the known materials.Diamond can be used as drill bit, cutter, grinding tool, drawing die and dressing tool.Diamond tool in ultra-precision machining, can be up to a mirror finish. But the poor thermal stability of the diamond tool, with the affinity of iron group elements, therefore, cannot be used for processing iron and nickel base alloy, and the main processing of non-ferrous metals and non-metallic, are widely used in ceramics, glass, stone, concrete, stone, agate and other processing.
Cubic boron nitride (CBN) has cubic crystal structure, and its hardness is second only to diamond, with better thermal and chemical stability than diamond
Other tool ceramics are alumina, zirconia, silicon nitride and other ceramics, but from the comprehensive performance and engineering applications are not as good as the above three tool ceramics.
3.Functional ceramics
Functional ceramics usually have special physical properties, involving many fields. The characteristics and applications of common functional ceramics are shown in the table.
Composition, properties and applications of functional ceramics in common use
Kinds of performance characteristics Main USES dielectric ceramic insulation Al2O3, Mg2SiO4 integrated substrate thermoelectricity PbTiO3, BaTiO3 thermistor piezoelectric PbTiO3, strong sexual BaTiO3 dielectric capacitor LiNbO3 oscillator optical ceramic fluorescence, luminance Al2O3CrNd permeability CaAs, CdTe infrared laser infrared window glass High transparency SiO2 optical fiber electric hair color effect WO3 display soft magnetic magnetic ceramicsZnFe2O, gamma-fe2o3 tape, various high frequency magnetic core hard magnetic SrO.Fe2O3 electro-acoustic devices, instruments and control devices of the magnetic core semiconductor ceramic photoelectric effect CdS, Ca2Sx solar cell impedance temperature change effect VO2, NiO temperature sensor thermionic emission effect LaB6, BaO hot cathode
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