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The application of alpha alumina in new alumina ceramics

Although there are many varieties of new ceramic materials, they can be roughly divided into three categories according to their functions and uses functional ceramics (also known as electronic ceramics), structural ceramics (also known as engineering ceramics), and biological ceramics. It can be divided into oxide ceramics, nitride ceramics, boride ceramics, carbide ceramics, and cermets according to the different raw materials used. Among them, alumina ceramics is a very important one, and its raw material is α-alumina powder of various specifications.

Alpha alumina has been widely used in the production of various new ceramic materials due to its high strength, high hardness, high temperature resistance, abrasion resistance, and a series of excellent properties. It is not only used as a powder raw material for advanced alumina ceramics such as integrated circuit substrates, artificial gems, cutting tools, artificial bones, etc., but also used as phosphor carriers, advanced refractory materials, and special abrasive materials. With the development of modern science and technology, the application fields of α-alumina are rapidly expanding, and the market demand is also increasing, and its prospects are very broad.

Application of αlpha-alumina in functional ceramics

Functional ceramics refer to advanced ceramics that use their electrical, magnetic, acoustic, optical, thermal, and other properties or their coupling effects to achieve a certain use function. They have insulation, dielectric, piezoelectric, pyroelectric, and semiconductor properties. , Ionic conductivity, superconductivity, and many other electrical properties, so it has a wide range of functions and a wide range of uses. At present, the large-scale practical applications are mainly insulating ceramics for integrated circuit substrates and packaging, automotive spark plug insulating ceramics, capacitor dielectric ceramics widely used in televisions and video recorders, piezoelectric ceramics for various purposes, and various sensors. Sensitive ceramics are also used in high-pressure sodium lamps, etc.

1. Spark plug insulating ceramic

Spark plug insulating ceramics is currently the single largest application of ceramics in engines. Because alumina has excellent electrical insulation, high mechanical strength, high voltage resistance and thermal shock resistance, alumina insulated spark plugs are widely used in the world. The requirement of alpha-alumina for spark plugs is ordinary low-sodium alpha aluminum monoxide powder, in which sodium oxide content is ≤0.05%, and the average particle size is 325 mesh.

2. Integrated circuit substrate and packaging materials

Ceramics used as substrate materials and packaging materials are superior to plastics in the following aspects: high insulation resistance, high chemical resistance, high sealing, can prevent moisture from passing through, have no reactivity, and will not pollute ultra-pure semiconductor silicon.

The properties of α-alumina required for integrated circuit substrates and packaging materials are thermal expansion coefficient 7.0×10-6/℃, thermal conductivity 20-30W/K·m (room temperature), dielectric constant 9-12 (IMHz), dielectric loss 3~10-4(IMHz), volume resistivity>1012-1014Ω·cm (room temperature).

With the high performance and high integration of integrated circuits, more stringent requirements are placed on substrates and packaging materials:

-As the heat generation of the chip increases, higher thermal conductivity is required.

-As arithmetic components increase in speed, a low dielectric constant is required.

-The coefficient of thermal expansion is required to be close to that of silicon. This puts higher requirements on α-alumina, that is, it develops towards high purity and fineness.

3. High pressure sodium luminous tube

Fine ceramics made of high-purity ultra-fine alumina as raw materials have the characteristics of high temperature resistance, corrosion resistance, good insulation, and high strength. It is an excellent optical ceramic material. It is a transparent polycrystal made of high-purity alumina with a small amount of magnesia, lanthanum oxide, or iridium oxide, and other additives, and is made by atmosphere sintering and hot pressing sintering. It can withstand the corrosion of high-temperature sodium vapor and can be used as a high-pressure sodium light-emitting lamp. , Its lighting efficiency is high.

Application of α-Alumina in Structural Ceramics

Application of α-Alumina in Bioceramics

As inorganic biomedical materials, bioceramic materials have no toxic and side effects compared with metal materials and polymer materials and have good biocompatibility and corrosion resistance with biological tissues. People have paid more and more attention to them. The research and clinical application of ceramic materials have developed from short-term replacement and filling to permanent and firm planting, from biologically inert materials to biologically active materials and multiphase composite materials.

In recent years, alumina porous ceramics have been used to make artificial skeletal joints, artificial knee joints, artificial femoral heads, other artificial bones, artificial tooth roots, and bones due to their chemical resistance, wear resistance, high temperature stability, and thermoelectric properties. Fixing screws and repairing cornea, etc. The method for controlling the pore size during the preparation of porous alumina ceramics is: mixing alumina particles of different particle sizes, foaming the particles, and spray drying the particles. The aluminum plate can also be anodized to produce oriented nano-scale microporous channel-type pores.

Compared with the above method, the sol-gel method can further improve the control of the pore size distribution, phase transition, purity, and microstructure of alumina porous ceramics. The process of preparing porous alumina ceramics by the sol-gel method is as follows: aluminum powder is hydrolyzed in aluminum chloride solution to obtain aluminum sol, and the pore-forming agent is directly mixed with the aluminum sol, and the product is formed and fired.

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