Silicon carbide is a colorless crystal, commonly known as corundum. It is industrially produced by the reaction of quartz sand and excess coke at a high temperature of 2000-2500℃. It has a structure similar to diamond and a hardness close to diamond. It is a widely used industrial abrasive. If certain impurity elements are added to it, it will also become a semiconductor, which can be used as a high-temperature semiconductor for electric heating elements. It has good thermal and chemical stability, high mechanical strength and low thermal expansion coefficient, and is also widely used in high-temperature structural ceramic materials. Silicon carbide ceramic fibers with good mechanical properties can be obtained by high-temperature pyrolysis of silane containing organic groups.
Silicon nitride is a new type of ceramic material. It is an off-white solid. Like silicon carbide, it has high thermal and chemical stability. The friction coefficient is only 0.1-0.2, which is equivalent to a metal surface lubricated with oil. Its hardness is second only to diamond and cubic boron nitride. Its largest application area is also as a high-temperature structural ceramic material. A small amount of aluminum oxide is added to silicon nitride to make a new type of ceramic, whose trade name is sialon. Seron ceramics have been widely used in gas turbine blades, machine housings, engine parts, rocket tail nozzles, bearings and cutting tools.
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Silicon carbide, commonly known as corundum, is generally made by mixing silica and coke and then reacting with electricity. Silicon carbide is composed of SiC, and it appears green, black and yellow due to impurities. In industry, it is divided into two categories according to color: green silicon carbide and black silicon carbide, and their SiC content is ≥99% and 98.5% respectively. Silicon carbide is a covalent bond compound with strong interatomic bonding, high melting point, high hardness, high strength and low expansion, high thermal conductivity, high electrical conductivity, and strong chemical stability. Therefore, it is a good refractory raw material. However, in an oxidizing atmosphere, silicon carbide is easily oxidized, and oxidation can only be slowed down when a SiO2 protective film is formed.
The molecular formula of silicon nitride is Si3N4, and there are two types of crystal forms: α-type and β-type, both of which are hexagonal crystal systems. Silicon nitride is gray, with a Si3N4 content of 98.5% and free silicon of 1.5%. Its melting point is 1900℃ (sublimation decomposition), high strength, low thermal expansion, toughness, and strong corrosion resistance. Silicon nitride is made by nitriding silicon powder with nitrogen and then sintering it. It is mainly used in advanced refractory materials.
Although both silicon carbide and silicon nitride are third-generation compound semiconductors with high hardness, high wear resistance, high thermal conductivity, and high elastic modulus, there are some key differences between them:
Different chemical stability and chemical corrosion resistance
Silicon carbide has strong chemical corrosion resistance and can work in most acids and alkalis, but has poor high temperature resistance; silicon nitride is very stable in strong acids and alkalis, but has low hardness and poor wear resistance.
Different application scenarios
Silicon carbide is usually used to make tools such as drills and molds and refractory materials for high-temperature furnaces; silicon nitride is used to make parts for aircraft engines and gas turbines.
Different physical properties
Silicon carbide has a higher density and greater hardness, especially maintaining stability in high temperature environments; silicon nitride has a lower density and lower hardness, but has good wear resistance and corrosion resistance.
Different thermal conductivity and electrical conductivity
Silicon carbide has excellent thermal conductivity and good electrical conductivity, and can be used as a semiconductor material; silicon nitride has poor thermal conductivity, but has insulating properties, and is mainly used in insulation and electronic packaging.
Different colors
Silicon nitride is usually an off-white powder, while silicon carbide is black or gray-black.
These differences make silicon carbide and silicon nitride each have their own unique advantages and applicable fields in industrial applications.
