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Main Components and Applications of Atmospheric-Pressure Sintered Silicon Carbide
Release time:
2022-01-13
Atmospheric-pressure sintered silicon carbide It is a nonmetallic carbide formed by covalent bonding between silicon and carbon, with a hardness second only to that of diamond and boron carbide. Its chemical formula is SiC. It appears as colorless crystals, but when its surface is oxidized or contains impurities, it can exhibit blue or black hues. Silicon carbide with a diamond-like crystal structure is commonly referred to as carborundum. Carborundum has a hardness nearly equivalent to that of diamond, excellent thermal stability, and is stable in aqueous solutions of hydrofluoric and sulfuric acids as well as in concentrated sulfuric acid. However, it is unstable in mixed acids consisting of concentrated hydrochloric and nitric acids, or in phosphoric acid. In an atmosphere containing alkalis, it melts and decomposes. Silicon carbide is classified into synthetic silicon carbide and natural silicon carbide. Natural silicon carbide, known as moissanite, is primarily found in kimberlite and volcanic hornfels, though its occurrence is very rare and it holds little economic value for mining.
Industrial atmospheric-pressure sintered silicon carbide is a mixture of α-SiC and β-SiC, available in black and green colors. Pure silicon carbide is colorless by nature; when impurities are present, it appears black, green, blue, or yellow. It exhibits hexagonal and cubic crystal structures, with crystals shaped like plates or composite columns. It has a vitreous luster, a density ranging from 3.17 to 3.47 g/cm³, and a Mohs hardness of 9.2. Under microscopic examination, its compressive strength ranges from 30,380 to 33,320 MPa. Its melting point is 2050°C in air, where it begins to decompose, and 2600°C in a reducing atmosphere, where decomposition starts earlier. Its elastic modulus is between 466 and 480 MPa. The tensile strength is 171.5 MPa, and the compressive strength reaches 1029 MPa. Its linear thermal expansion coefficient is (5.0 × 10⁻⁶) per degree Celsius in the temperature range from 25°C to 1000°C. Its thermal conductivity at 20°C is 59 W/(m·K). Chemically, it is highly stable and remains uncorroded even when boiled in HCl, H₂SO₄, or HF.
Depending on the intended use, Atmospheric-pressure sintered silicon carbide It is divided into abrasive materials, refractory grades, deoxidizers, and silicon carbide for electrical applications. The SiC content of silicon carbide used as an abrasive material must be no less than 98%. Silicon carbide for refractory applications is categorized as follows: (1) High-grade black silicon carbide for refractories, whose SiC content is identical to that of silicon carbide used for grinding; (2) Secondary-grade black silicon carbide for refractories, with an SiC content exceeding 90%; (3) Low-grade black silicon carbide for refractories, with an SiC content of at least 83%. For deoxidizers, the SiC content of silicon carbide typically needs to be above 90%. However, in carbon industry graphitization furnaces, treated silicon carbide containing more than 45% SiC can also be used as a steelmaking deoxidizer. Deoxidizing silicon carbide is available in two forms: powdered and molded blocks. Powdered black silicon carbide deoxidizers generally have particle sizes ranging from 4 to 0.5 mm and from 0.5 to 0.1 mm. There are two main categories of silicon carbide used for electrical utilities: (1) Green silicon carbide for electric heating elements, which is essentially the same as green silicon carbide used for grinding; (2) Silicon carbide for surge arresters, which has particularly stringent electrical performance requirements and differs from black silicon carbide used for refractories and grinding.
Applications of Normal-Pressure Sintered Silicon Carbide
Atmospheric-pressure sintered silicon carbide The product boasts special features such as high-temperature resistance, wear resistance, thermal shock resistance, fire resistance, radiation resistance, excellent electrical conductivity, and superior thermal conductivity, making it widely used across various sectors of the national economy. In China, green silicon carbide is primarily used as an abrasive material. Black silicon carbide is employed in the manufacture of grinding stones and is commonly used for cutting and grinding materials with low tensile strength, such as glass, ceramics, stone, and refractory materials; it is also utilized for grinding cast iron parts and non-ferrous metal components. Grinding wheels made from green silicon carbide are mainly used for grinding cemented carbides, titanium alloys, and optical glasses, as well as for grinding cylinder liners and high-speed steel tools. Cubic silicon carbide abrasives are exclusively reserved for ultra-precision grinding of miniature bearings. By applying silicon carbide powder onto turbine impellers via electroplating, the wear resistance of these impellers can be significantly enhanced. Using mechanical pressure to apply cubic SiC No. 200 abrasive particles and W28 fine powder onto the cylinder walls of internal combustion engines can more than double the service life of the cylinders.
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