Ceramic materials are those inorganic non-metallic materials which are formed and sintered with natural or synthetic compounds under high temperature. They have the characteristics of a high melting point, high hardness, high wear resistance, oxidation resistance, etc. And they can be used as structural materials, tool material. Since the ceramic also has some special properties, it can also be used as functional materials.
Common ceramic material
It is sintered with natural raw materials such as feldspar, clay and quartz, and is typical silicate materials. The main elements of it are silicon, aluminum, oxygen, and these three elements account for 90% of total crustal element. The common ceramic sources’ are rich, cost of them is low, and the technology of them is mature. This kind of ceramic can be divided into daily-use ceramics, architectural ceramics, electrical insulation, ceramic, chemical and ceramics according to the performance of characteristics and uses.
Special ceramic material
It is sintered with high-purity synthetic material and precise control of the molding process. It generally has some special properties to suit various needs. According to its main component, it can be divided an oxide ceramics, nitride ceramics, carbide ceramics, cermets etc. These special ceramics have some special mechanical, optical, acoustic, electric, magnetic, thermal and other properties. This section focuses on special ceramics.
Mechanical properties
Ceramic materials are the engineering materials with the most preferable stiffness and the highest hardness. Its hardness is mostly above 1500HV. The compressive strength of this ceramic is high, but the tensile strength is low, ductility and toughness is poor.
Thermal Performance
Ceramic materials generally have a high melting point (mostly above 2000 ℃), and at high temperatures, they have excellent chemical stability; the thermal conductivity of ceramic is lower than metal materials, and the ceramic materials are also good thermal insulation. Meanwhile, the linear expansion coefficient of the ceramic is lower than the metal. With change of the temperature, the ceramic will have good dimensional stability.
Electrical properties
Most ceramics have good electrical insulating properties, so they are used as insulation device for the production of a large voltage (1kV ~ 110kV). The ferroelectric ceramics (Barium titanate BaTiO3) have a higher dielectric constant, and they can be used to produce capacitors. Under the action of an external electric field, the iron ceramics can change shapes, converting electrical energy into mechanical energy (with piezoelectric material properties). They can be used as amplifiers, record players, ultrasonic instrument, sonar, medical spectrograph, etc. Also a few ceramics have the characteristics of a semiconductor, and can be used for the rectifier.
Chemical properties
Ceramic materials are resistant to oxidation at high temperatures, and have good corrosion resistance towards the acid, alkali, and salt.
Optical Performance
The ceramic materials have unique optical properties, and can be used as solid-state laser materials, fiber materials, optical storage, etc. The transparent ceramic tube can be used as high pressure sodium lamp. The magnetic ceramic (eg. ferrites: MgFe2O4, CuFe2O4, Fe3O4) has a broad prospect in the applications of the recording tapes, records, transformer core, large computer memory devices.
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