Alumina ceramics as a kind of precision technical ceramics, its performance has a series of advantages. With the continuous development of science and technology, alumina ceramics have been widely used in chemical industry, machinery manufacturing, biomedicine and other fields, and gradually expand the scope of application with the improvement of performance, the study of alumina properties in many industries in the production activities have high practical significance.
1, alumina ceramic mechanical strength is high
The bending strength of alumina ceramic sintered products can reach 250MPa, and hot pressing products can reach 500MPa. The purer the alumina composition, the higher the strength. The strength can be maintained up to 900℃ at high temperatures, as shown in the figure below. Using the mechanical strength of alumina porcelain, it can be made into device porcelain and other mechanical components. The Mohs hardness of alumina ceramics can reach 9, coupled with excellent wear resistance, etc., so it is widely used in the manufacture of tools, ball valves, grinding wheels, ceramic nails, bearings, etc., among which alumina ceramic tools and industrial valves are the most widely used.
2, alumina ceramics high resistivity, good electrical insulation performance
Room temperature resistivity 1015Ω·cm, insulation strength 15kV/mm, using its insulation and strength, can be made into substrate, tube base, spark plug, circuit shell.
3, high hardness of alumina ceramics
Mohs hardness of 9, coupled with excellent wear resistance, so widely used in the manufacture of cutting tools, grinding wheels, abrasives, wire drawing dies, extrusion dies, bearings and so on. When aluminum oxide ceramic tool is used to process automobile engine and aircraft parts, high precision can be obtained at high cutting speed.
4, alumina ceramics high melting point, corrosion resistance
Melting point 2050℃, can better resist Be, Sr, Ni, Al, V, Ta, Mn, Fe, Co and other molten metal erosion. It also has high resistance to the erosion of NaOH, glass and slag. It does not interact with Si, P, Sb and Bi in an inert atmosphere. Therefore, it can be used as refractory materials, furnace tubes, glass wire-drawn crucible, hollow balls, fibers, thermocouple protective sleeves, etc.
5, alumina ceramic chemical stability is excellent
Many complex sulfides, phosphates, arsenides, chlorides, nitrides, bromides, iodides, oxides, and sulfuric, hydrochloric, nitric, and hydrofluoric acids do not interact with alumina. Therefore, alumina can be made into pure metal and single crystal growth crucible, human joints, artificial bones and so on.
6. Optical characteristics
It can be made into transparent materials (transparent alumina porcelain), which can be used to manufacture sodium vapor lamps, microwave fairing, infrared Windows, laser oscillating elements, etc.
7. Ionic conductivity
Used as solar cell material and battery material.
The main application of alumina ceramics
1. Mechanical aspects
Alumina ceramic tool because of its high hardness, high temperature mechanical properties, good wear resistance, good chemical stability, not easy to bond with metal and other characteristics, widely used in hard material cutting, high-speed steel cutting, ultra-high speed cutting and other difficult to process materials cutting. The best cutting speed of the alumina ceramic tool is higher than that of the general carbide tool, which can greatly improve the cutting efficiency of different materials.
① Pure alumina ceramic tool
Pure alumina ceramic tools refer to high-purity alumina ceramics containing only a small amount of other oxides, of which alumina purity is more than 99%. The fracture toughness of pure alumina ceramics can be improved by adding zirconia as a sintering agent. Effective control of original purity and grain size was realized in the preparation of ceramic cutting tools, and other components were added to form two-phase or solid solution in the matrix alumina composite ceramics and whisker reinforced ceramics. These technologies make up for the shortcomings of pure alumina ceramics, thereby improving its cutting performance and durability. Because of the high temperature performance and good wear resistance of pure alumina ceramic tools, but the characteristics of low bending strength and poor impact resistance, it is more and more replaced by various composite alumina ceramic tools.
② Composite alumina ceramic tool
In composite ceramics, there are several composite directions: alumina - carbide ceramic tools, alumina - carbide - cermet tools, alumina - nitride or boride ceramic tools. For example, alumina - carbide ceramic tool, adding a certain carbide in alumina (TiC, WC, TaC, NbC, Mo,C, Cr,C2, etc.) can improve its strength, wear resistance, impact resistance and high temperature performance, etc. Among the additives, TiC is the most widely used, compared with pure alumina ceramics. The bending strength of alumina-carbide composite ceramics is better than that of pure alumina ceramics at room temperature or high temperature. This composite tool is suitable for high speed rough, fine machining wear-resistant cast iron, hardened steel and high strength steel and other difficult materials.
③ Toughened alumina ceramic tool
Toughening alumina ceramic tool refers to the addition of toughening or strengthening materials in the alumina matrix. At present, the commonly used toughening methods are: Zr02 phase transition toughening, whisker toughening, second phase particle dispersion toughening and so on.
2. Industry
At present, there are many kinds of industrial valves, and the commonly used valves for alumina industry are plug valves, gate valves, globe valves, ball valves and so on.
Ball Valve: The main characteristics of the ball valve are its compact structure, reliable sealing, simple structure, convenient maintenance, sealing surface and spherical surface are often in a closed state, not easy to be washed away by the medium, easy to operate and maintain, suitable for water, solvents, acids and natural gas and other general working media, but also suitable for poor working conditions of the medium, such as oxygen, hydrogen peroxide, methane and ethylene, etc. It is widely used in various industries.
Plug valve: It is widely used in oilfield exploitation, transportation and refining equipment, but also widely used in petrochemical, chemical, gas, natural gas, liquefied petroleum gas, HVAC industry and general industry.
Gate valve, globe valve: It can be widely used in tap water, sewage, construction, petroleum, chemical, food, medicine, textile, electric power, shipbuilding, metallurgy, energy system and other body pipelines as a regulating and intercepting device used.
3. Electronics and electricity
In terms of electronics and power, there are various alumina ceramic baseboards, substrates, ceramic films, transparent ceramics and various alumina ceramic electrical insulating ceramics, electronic materials, magnetic materials, etc., among which alumina transparent ceramics and substrates are the most widely used.
4. Chemical industry
In chemical applications, alumina ceramics also have a wide range of uses, such as alumina ceramic chemical packing balls, inorganic microfiltration membranes, corrosion resistant coatings, etc., among which alumina ceramic membranes and coatings are the most studied and applied.
① Alumina ceramic membrane: the membrane is divided into organic polymer membrane and inorganic membrane, etc. Since the 1980s, the development and development of alumina ceramic membrane, especially porous alumina ceramic membrane, has been greatly improved, and occupies an important position in the membrane field. Alumina ceramic membrane has a large number of applications in purifying industrial water processing, seawater desalination, gas separation, catalytic reaction, etc., so ceramic inorganic membrane has been increasingly concerned by the scientific and industrial circles.
Aluminum oxide coating: titanium alloy material high temperature oxidation is serious, in order to improve its performance, can be coated with aluminum oxide coating on the surface of titanium alloy material, which can also improve the corrosion resistance and high temperature oxidation resistance of titanium alloy material.
5. Medical science
In medicine, alumina is more used in the manufacture of artificial bones, artificial joints, artificial teeth and so on. Alumina ceramics have excellent biocompatibility, bioinertness, physical and chemical stability, high hardness, high wear resistance, and are ideal materials for the preparation of artificial bones and joints. However, it has the same shortcomings as other ceramic materials, such as large brittleness, low fracture toughness, high machining technology difficulty, complex process, etc., so it needs further research and application.
6, building sanitary ceramics
In the aspect of building sanitary ceramics, alumina ceramic products can be found everywhere, such as alumina ceramic lining bricks, grinding media, sticks, ceramic protective tubes and alumina refractory materials. Among them, alumina ball milling medium is the most widely used. Alumina ball milling medium has the characteristics of suitable hardness, moderate density, wear resistance, corrosion resistance and low price, so most of the building sanitary ceramics raw materials are processed with alumina ball milling medium.
7. Other aspects
Alumina ceramics is currently one of the most studied and widely used materials in new materials, in addition to the above applications, it is also widely used in some other high-tech fields, such as aerospace, high temperature industrial furnaces, composite reinforcement and other fields.
① Aerospace
Alumina based fiber is widely used in aerospace, which has high strength, high temperature resistance, oxidation resistance, corrosion resistance and other properties. Alumina can be prepared into high temperature heat resistant fiber, used in space shuttle insulation tiles and flexible insulation materials. In addition, the use of alumina fibers can also be used to strengthen metal and ceramic matrix composite materials, a large number of supersonic jet nozzle and rocket engine gaskets.
② High temperature industrial furnace
In the field of high temperature industrial furnaces, alumina based short fiber materials are mainly used as thermal insulation refractory materials, because it has the advantages of low density, good heat insulation, and small heat capacity. These advantages can not only reduce the weight of high temperature furnace, but also make the temperature control of high temperature furnace more accurate, and thus more energy saving.
③ Composite enhancement
Alumina fiber reinforced metal matrix composites have good mechanical properties, high wear resistance, low expansion coefficient and high hardness, which is because of good infiltration and low interface reaction between alumina fiber and metal matrix. These materials have been used in the manufacture of automotive pistons and air compressor blades. The combination of alumina fiber and resin is good, so it can be prepared into alumina/resin composite material, which has the characteristics of high elasticity and high hardness, and can be applied to the manufacturing industry of sports equipment such as fishing rods, golf clubs, snowboards, tennis rackets.
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