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 bioceramics. According to the different raw material components used, they can be divided into oxide ceramics, nitride ceramics, boride ceramics, carbide ceramics and metal ceramics. Among them, alumina ceramics are very important, and its raw material is α-alumina powder of various specifications.
α-alumina is widely used in the production of various new ceramic materials due to its high strength, high hardness, high temperature resistance, wear resistance and other excellent properties. It is not only a powder raw material for advanced alumina ceramics such as integrated circuit substrates, artificial gems, cutting tools, artificial bones, etc., but also can be used as a phosphor carrier, advanced refractory materials, special grinding materials, etc. With the development of modern science and technology, the application field of α-alumina is rapidly expanding, and the market demand is also increasing, and its prospects are very broad.
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 function. They have multiple electrical properties such as insulation, dielectric, piezoelectric, thermoelectric, semiconductor, ion conductivity and superconductivity, so they have many functions and extremely wide applications. At present, the main ones that have been put into practical use on a large scale are 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 with multiple uses and sensitive ceramics for various sensors. In addition, they are also used for high-pressure sodium lamp light-emitting tubes.
1. Spark plug insulating ceramicsSpark plug insulating ceramics are currently the only largest application of ceramics in engines. Because alumina has excellent electrical insulation, high mechanical strength, high pressure resistance and thermal shock resistance, alumina insulating spark plugs are widely used in the world. The requirements for α-alumina for spark plugs are ordinary low-sodium α-alumina micropowders, in which the sodium oxide content is ≤0.05% and the average particle size is 325 mesh.
2. Integrated circuit substrates and packaging materialsCeramics used as substrate materials and packaging materials are superior to plastics in the following aspects: high insulation resistance, high chemical corrosion resistance, high sealing, moisture penetration prevention, no reactivity, and no pollution to 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 put forward for substrates and packaging materials: As the heat generation of the chip increases, higher thermal conductivity is required.
With the high speed of the computing element, a low dielectric constant is required.
The thermal expansion coefficient is required to be close to silicon. This places higher requirements on α-alumina, that is, it develops in the direction of high purity and fineness.
3. High-pressure sodium light-emitting lampFine ceramics made of high-purity ultrafine alumina as raw materials have the characteristics of high temperature resistance, corrosion resistance, good insulation, high strength, etc., and are an excellent optical ceramic material. Transparent polycrystalline made of high-purity alumina with a small amount of magnesium oxide, iridium oxide or iridium oxide additives, and made by atmosphere sintering and hot pressing sintering, can withstand the corrosion of high-temperature sodium vapor and can be used as high-pressure sodium light-emitting lamps with high lighting efficiency.
As inorganic biomedical materials, bioceramic materials have no toxic side effects compared with metal materials and polymer materials, and have good biocompatibility and corrosion resistance with biological tissues. They have been increasingly valued by people. The research and clinical application of bioceramic materials have developed from short-term replacement and filling to permanent and firm implantation, and from biological inert materials to biologically active materials and multiphase composite materials.
In recent years, porous alumina ceramics have been used to make artificial skeletal joints, artificial knee joints, artificial femoral heads, other artificial bones, artificial tooth roots, bone fixation screws, and corneal repairs due to their chemical corrosion resistance, wear resistance, good high temperature stability, and thermoelectric properties. The method for controlling the pore size during the preparation of porous alumina ceramics is to mix alumina particles of different particle sizes, foam impregnate, and spray dry the particles. Aluminum plates can also be anodized to produce directional nano-scale microporous channel-type pores.
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