What are the classifications of ceramics?

Ordinary materials
Sintered from natural raw materials such as feldspar, clay, and quartz, it is a typical silicate material, mainly composed of silicon, aluminum, and oxygen, which account for 90% of the total crustal elements. Ordinary ceramics have abundant sources, low costs, and mature processes. This type of ceramic can be further divided into daily ceramics, architectural ceramics, electrical insulation ceramics, chemical ceramics, etc. based on its performance characteristics and uses.
Special materials
Made from high-purity artificially synthesized raw materials and formed and sintered using precision controlled processes, it generally has certain special properties to meet various needs. According to its main components, there are oxide ceramics, nitride ceramics, carbide ceramics, metal ceramics, etc; Special ceramics have special mechanical, optical, acoustic, electrical, magnetic, thermal and other properties.
Classification of special materials
According to different purposes, special ceramic materials can be divided into structural ceramics, tool ceramics, and functional ceramics.
Structural ceramics
The main component of alumina ceramics is Al2O3, with a general content greater than 45%. Alumina ceramics have various excellent properties. High temperature resistance, generally suitable for long-term use at 1600 ℃, corrosion resistance, high strength, and its strength is 2-3 times that of ordinary ceramics, up to 5-6 times higher. Its disadvantage is that it is brittle and cannot accept sudden changes in environmental temperature. It is widely used as a crucible, engine spark plug, high-temperature refractory material, thermocouple sleeve, sealing ring, etc. It can also be used as a cutting tool and mold.
The main component of silicon nitride ceramics is Si3N4, which is a high-temperature ceramic with high strength, high hardness, wear resistance, corrosion resistance, and self-lubricating properties. Its coefficient of linear expansion is the smallest among various ceramics, with a service temperature of up to 1400 ℃. It has excellent corrosion resistance. In addition to hydrofluoric acid, it can withstand corrosion from various acids, alkali, and metals, and has excellent electrical insulation and radiation resistance. Can be used as high-temperature bearings, sealing rings for use in corrosive media, thermowells, and also as metal cutting tools.
The main component of silicon carbide ceramics is SiC, which is a high strength, high hardness high temperature resistant ceramic. It can still maintain high Flexural strength when used at 1200 ℃~1400 ℃. It is the ceramics with the highest high temperature strength at present. Silicon carbide ceramics also have good thermal conductivity, oxidation resistance, conductivity and high impact toughness. It is a good high-temperature structural material that can be used for components such as rocket tail nozzle, thermocouple sleeve, furnace tube, etc. that work at high temperatures; By utilizing its thermal conductivity, heat exchanger materials can be made at high temperatures; Utilize its high hardness and wear resistance to produce grinding wheels, abrasives, etc.
The main component of hexagonal Boron nitride ceramics is BN, and the crystal structure is Hexagonal crystal family. Hexagonal Boron nitride is similar to graphite in structure and performance, so it is called "white graphite" with low hardness. It can be cut and processed with self-lubricating properties, and can be made into self-lubricating high-temperature bearings, glass forming molds, etc.
Tool ceramics
The main components of hard alloy are carbides and binders, with carbides mainly including WC, TiC, TaC, NbC, VC, etc. The binder mainly consists of cobalt (Co). Compared with Tool steel, cemented carbide has high hardness (up to 87~91HRA) and good thermal hardness (excellent wear resistance at about 1000 ℃). When used as a tool, its cutting speed is 4~7 times higher than that of high-speed steel, and its service life is 5~8 times longer. Its disadvantage is that its hardness is too high, its brittleness is very difficult to be machined. Because of this, it is often made into blades and welded on the cutter bar. Cemented carbide is mainly used for machining tools; Various molds, including drawing molds, drawing molds, and cold heading molds; Various drill bits are used in mining tools, geology, and petroleum exploration.
Natural diamond (diamond) is a precious decoration, while synthetic diamond is widely used in industry. Diamond is the hardest material in nature and also has a very high elastic modulus; Diamond has the highest thermal conductivity among known materials; Diamond has excellent insulation performance. Diamond can be used as drill bits, cutting tools, grinding tools, wire drawing dies, and trimming tools; Diamond tools perform ultra precision machining to achieve mirror finish. However, due to its poor thermal stability and strong affinity with iron group elements, diamond tools cannot be used to process iron and nickel based alloys, but mainly to process non-ferrous metals and nonmetals, which are widely used to process ceramics, glass, stones, concrete, gemstones, agates, etc.
Cubic Boron nitride (CBN) has cubic crystal structure, its hardness is high, second only to diamond, and its thermal stability and chemical stability are better than diamond. It can be used for cutting hardened steel, wear-resistant cast iron, Thermal spraying materials, nickel and other difficult to machine materials. Can be made into cutting tools, grinding tools, drawing dies, etc
Other tool ceramics include alumina, zirconia, silicon nitride, and other ceramics, but their comprehensive performance and engineering applications are not as good as the above three tool ceramics.