Properties of ceramic silicon carbide
The high hardness of Silicon Carbide Ceramics is high, with a high melting point (23400), good wear resistance and resistance to corrosion, and also excellent chemical stability, thermal shock resistance. This makes it a popular choice in many fields, including energy, metallurgy and machinery, as well chemical, aeronautics, defense, and petroleum.
You can choose between black and green silicon carbide
Abrasive industries often divide silicon carbide in black carbonized leel and green silica according to its color. These are both hexagonal crystals that belong to a-SiC.
Black silicon carbide has a siC content of about 98.5%. Black silicon caride is made up of petroleum coke, quartz sand, high-quality silica, and petroleum coke as its main ingredients. The material is then melted at high temperatures by an electric furnace. It has hardness that is similar to diamond. Also, its mechanical strength is much higher than corundum. It is tougher than green silicon caride. This is why it is most commonly used in processing materials of low tensile strengths, like glass, ceramics, stone and cast iron.
SiC content in green silicon carbide is greater than 99 percent. It is made up of high-quality silicona and petroleum coke. You can add salt to make it more smeltable and then melt in a high temperature furnace. It can be used to machine hard alloys, alloys and optical lenses. You can also use it to create wear-resistant liner cylinders and fine-grained, high-speed tools from steel.
Ceramics made of silicon carbide
SiC's covalent bond is strong, which leads to a variety of exceptional properties in SiC ceramics. But it makes it difficult for SiC ceramics to sinter. It is difficult to sinter SiC ceramics because the covalent bond between SiC and SiC is too strong. The sintering temperature must be raised to compensate. It also increases costs and makes it less useful in the industry.
According to thermodynamics, densification can be driven by the loss of energy from the original powder during sintering. The SiC grain boundary's free energetic is high. This causes a decline in the powder's energy even if it becomes a solid solid interface. The driving force behind the sintering procedure is lessened the larger the difference in the free energy. The SiC powder can be more difficultly sintered than other ceramics. The common practice is to add sintering additive, reduce the powder size, and pressurize. This will change the free energy of the powder and encourage SiC to be densified.
According to kinetics, there are five main mass transfer mechanisms involved in the sintering of materials. These include evaporation and condensation, surface diffusion, viscous circulation, surface diffusion, grain border or lattice diffusion, as well as plastic deformation. Because SiC has a strong covalent link, it results in a slower solid-phase mass transport rate like surface diffusion and lattice distribution. However, gas phase mass Transfer requires high temperature to facilitate powder decomposition. SiC's decomposition temperature is approximately 2500°C so it is not possible to use gas phase mass transfer for ceramics density. To achieve viscous flow, existing sintering processes add a sintering help to either increase SiC's solid phase diffusion rate or create a liquid phase-assisted SiC.
SiC ceramics have a high purity and are capable of increasing the thermal conductivity. Sintering aids are needed to lower the sintering temperatures and increase the density. High thermal conductivity SiC ceramics can be sintered to resolve the contradiction. Priorities and challenges
The sintering temperatures of Al2O3 ceramics are low, they have low costs and excellent electrical insulation. These ceramics have been used extensively, however, they possess low thermal conductivity, making them ineffective for high-power circuits.
BeO ceramics possess good dielectric qualities and can be used in high-heat conducting fields as substrate materials. BeO is toxic and Europe, Japan and America have issued regulations to limit the development and sale of electronic products.
AlN ceramics offer excellent thermal insulation, low electrical insulation, and low dielectric constant. This makes them ideal for high power circuits. AlN ceramics' sintering temperatures are too high. Because of this, it is difficult to prepare and expensive. It has also not been used in large scale production. AlN can also be subject to the hydrolysis reaction and is not reliable in moist environments.
Low density SiC ceramics offer high mechanical strength and low oxidation resistance. They resist chemical corrosion and are well-developed in the area of electronic products. They can also meet future demands for small sizes, high reliability, high efficiency, and light weight of electronic devices.
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