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Application of Pressureless Sintering of Silicon Carbide Ceramics

With the development of science and technology, especially the high development of energy and space technology, it is often required that materials must have superior properties such as high temperature resistance, corrosion resistance, and wear resistance before they can be used in relatively harsh working environments. Because special ceramic materials have excellent properties such as strong oxidation resistance, good wear resistance, high hardness, good thermal stability, high temperature strength, small thermal expansion coefficient, high thermal conductivity, thermal shock resistance and chemical corrosion resistance, it has become a cutting-edge ceramic material. It is an important part of science and is generally valued.

1.1 Main properties and applications of SiC ceramics
1.1.1 Main properties of SiC ceramics
Structure of silicon carbide
Silicon carbide is a man-made material. It was only after the artificial synthesis of silicon carbide that it was confirmed that silicon carbide occasionally exists in meteorites and on the crust. The molecular formula of silicon carbide is SiC, the molecular weight is 40.07, and the mass percent composition is 70.045 silicon and 29.955 carbon. , the theoretical density of silicon carbide is 3.16~3.2g/cm3.
SiC is a covalent compound dominated by covalent bonds. When carbon and silicon form a SiC crystal, its basic unit is a tetrahedron. All SiC is formed by stacking SiC tetrahedrons. The difference is that they are combined in parallel. There are 75 variants of SiC with diamond structure, such as 3C-SiC, 4H-SiC, 15R-SiC, etc., of which α-SiC and β-SiC are the most common. The crystal structure of β-SiC is cubic, and Si and C respectively form a face-centered cubic lattice; α-SiC has more than 100 polytypes such as 4H, 15R, and 6H, among which the 6H polytype is used in industrial applications. The most common one.
1.1.2 Main application fields of SiC ceramics
(1) Abrasive
Due to its superhard properties, it can be prepared into various grinding wheels, abrasive cloths, sandpapers and various abrasives, which are widely used in the machining industry. Industrial silicon carbide is mainly used for abrasives. Abrasives made of black silicon carbide are mostly used for cutting and grinding materials with low tensile strength, such as glass, ceramics, stones and refractories, as well as cast iron parts and non-ferrous metal materials. grinding. Grinding tools made of green silicon carbide are mostly used for grinding hard alloys, titanium alloys and optical glass, as well as for honing cylinders and fine grinding of high-speed steel tools. Cubic silicon carbide is specially used for ultra-fine grinding of miniature bearings. W3.5 cubic silicon carbide powder is used for ultra-fine grinding of bearings (material ZGCrl5), and the smoothness can be directly ground from 9 to more than 12. Therefore, among other abrasives of the same particle size, cubic silicon carbide has the highest processing efficiency.
(2) Refractory material
①High-grade refractory black silicon carbide. The chemical composition of this grade is exactly the same as that of black silicon carbide for abrasives. It is mainly used to manufacture high-grade silicon carbide products, such as recrystallized silicon carbide products, gas turbine components, nozzles, silicon nitride-bonded silicon carbide products, and blast furnace high temperature zone linings. materials, high-temperature kiln components, high-temperature kiln-mounted kiln supports, refractory saggers, etc.
②The secondary refractory black silicon carbide contains more than 90% silicon carbide. Mainly used to manufacture medium and high temperature resistant kiln components, such as muffle furnace lining materials. In addition to using the heat resistance and thermal conductivity of silicon carbide, these components also use its chemical stability in many occasions.
③ Black silicon carbide, a low-grade refractory material, whose silicon carbide content is required to be greater than 83%, is mainly used for the lining of tapping grooves, ladle, zinc smelting and sponge iron manufacturing.
(3) Deoxidizer
In steelmaking, ferrosilicon is usually used for deoxidation. In modern times, silicon carbide has been used instead of ferrosilicon as a deoxidizer. The quality of the steel produced is better and more economical. Because when silicon carbide is used for deoxidation, the slag is less and faster, which effectively reduces the content of some useful elements in the slag, and the steelmaking time is short and the composition is better controlled. The deoxidizer black silicon carbide is used in the steel of the United States and Japan Commonly used in industry. The materials suitable for deoxidizers produced by silicon carbide for abrasives or refractories in the furnace can all be sold and used in production without returning to the furnace. The comprehensive utilization rate of the product is high, and the economic effect of production is excellent.
(4) Electrical and electrician
Using the high thermal conductivity and good insulation of silicon carbide ceramics, it is used as a substrate and packaging material for large-scale integrated circuits. Silicon carbide heating element is a commonly used heating element. Because of its advantages of simple and convenient operation, long service life and wide range of use, it has become the most durable and inexpensive heating material. The operating temperature can reach 1600 ℃ . In addition, silicon carbide can also be used as the valve body of the arrester and the far infrared generator.
(5) Wear-resistant and high-temperature parts
Utilizing the high hardness, wear resistance, acid and alkali corrosion resistance of silicon carbide ceramics, it is used in the machinery industry and chemical industry to prepare a new generation of mechanical sealing materials, such as sliding bearings, corrosion-resistant pipes, valve plates and fans. blade. Especially as a mechanical sealing material, it has been recognized internationally as the fourth-generation basic material since metal, alumina, and cemented carbide. Its acid and alkali resistance is extremely excellent compared with other materials, and there is almost no one. Materials are comparable. Using the high thermal conductivity of silicon carbide ceramics, it can be used in high-temperature heat exchangers in metallurgical industrial furnaces, etc., and the operating temperature can reach 1300 ° C: Coating silicon carbide powder on the turbine impeller by electroplating method can greatly improve the impeller resistance. Grinding performance, extending its maintenance cycle. Pressing the cubic silicon carbide powder and W28 fine powder into the cylinder wall of the internal combustion engine with mechanical pressure can prolong the service life of the cylinder block by more than 1 times. Using a mixture of silicon carbide and borax to perform surface boronizing chemical heat treatment on the 45# steel harvester blade, the hardness of the boronized layer can reach the Kjeldahl microhardness of 1800~2000kg/mm2, thereby prolonging its service life several times. Support rollers made of silicon carbide have already been successfully used in rolling mills. They have better heat resistance and wear resistance than metal support rollers, and can improve the quality of rolled steel. Sand pumps and hydrocyclones made of silicon carbide materials have good wear resistance; wear parts such as cylinder liners made of silicon carbide materials can be widely used in petroleum and chemical industries. Silicon carbide can also be used as a high temperature thermomechanical material, and is the first choice for thermomechanical high temperature resistant components. Such as: the combustion chamber of the high temperature gas turbine, the stationary blade of the turbine, the high temperature nozzle, etc. Pistons and cylinder liners made of silicon carbide are used in diesel engines without lubricating oil and cooling, which can reduce friction by 30% to 50% and reduce noise significantly.
Selection of heat treatment equipment: The RVS silicon carbide pressureless sintering furnace provided by SIMUWU is an excellent product for handling the vacuum sintering process of silicon carbide. The product has the characteristics of good temperature uniformity, high temperature control accuracy, stable sintering, and fully automatic control. SIMUWU provides a professional team of engineers who can solve various problems encountered in the production process, reduce the cost of trial and error in production, and are committed to giving customers the most convenient and fast experience.