As advanced refractory materials, silicon nitride combined with silicon carbide refractory materials can be used at a normal temperature of about 1500℃ in various atmospheres, so Si3N4-SiC is widely used in sanitary ceramics, daily ceramics, electronic ceramics, architectural ceramics, abrasive tools and metallurgy industries, and has a broad market as kiln tools. 01 Iron and steel metallurgical industry The steel industry is the largest user of silicon nitride combined with silicon carbide refractory materials. With the large-scale development of blast furnaces and the development of special steel grades such as clean steel and low-carbon steel, iron and steel metallurgy has put forward higher requirements for refractory materials. In 1976, Point in the United States and Dunkerque in France in 1977 began to apply silicon nitride combined with silicon carbide refractory materials to the waist of blast furnaces. In my country, in 1985, Anshan Iron and Steel first applied silicon nitride combined with silicon carbide refractory materials to the lower part, waist and tuyere area of blast furnaces. Nippon Steel Corporation once studied the damage rate of different refractory materials used in the lower part of the blast furnace shaft. The results showed that compared with clay bricks, the damage rate of high-alumina bricks is 3/5, and the damage rate of Si3N4-SiC is 1/5. Silicon nitride combined with silicon carbide bricks have intact appearance after erosion by blast furnace slag, and the erosion is not obvious. They also have good resistance to molten iron corrosion. After 60 minutes of molten iron corrosion at 1425℃, the corrosion result is 0.
02 Nonferrous metallurgical industry
In the field of copper alloy smelting, magnesium crucibles have shortcomings such as poor thermal shock resistance and easy leakage of copper liquid. In the field of aluminum alloy smelting, cast steel, cast iron and graphite have been used for a long time. Metal crucibles will experience iron infiltration during contact with aluminum alloy melts, reducing metallurgical quality. Graphite crucibles are severely oxidized during use, which increases production costs. With the development of advanced nonferrous metallurgical technology, higher requirements are placed on the quality and performance of the refractory materials used.
Si3N4-SiC products do not wet non-ferrous metal melts and are significantly superior to oxide ceramics in performance. In addition, Si3N4-SiC materials have the advantages of high thermal conductivity, good thermal shock resistance, erosion resistance, and metal vapor erosion resistance. Therefore, they are widely used in smelting furnaces in non-ferrous smelting industries such as lead, zinc, aluminum, and copper. Its uses include the walls of the distillation tank and the condenser rotor of the vertical tank zinc distillation furnace, the working layers of the zinc distillation tower wall, condenser, and various channels, and the trays that determine the service life of the continuous distillation and refining equipment for zinc smelting; the side walls of the lead mist chamber of the lead-zinc closed drum furnace that withstands the erosion and chemical erosion of lead mist; the aluminum outlet of the aluminum smelting reverberatory furnace, the aluminum flow trough and its lining, the side walls of the aluminum electrolytic cell, etc.; the working layer of the furnace wall and the burner area of the refined copper melting vertical furnace and other vulnerable parts. The use of Si3N4-SiC significantly increases the life of non-ferrous smelting furnaces, reduces the consumption of refractory materials, and improves smelting efficiency.
It should be pointed out that Si3N4-SiC materials are currently widely used in the aluminum electrolysis industry. Silicon nitride combined with silicon carbide bricks as the lining of the side walls of aluminum electrolytic cells have made important contributions to extending the life of aluminum electrolytic cells and the development of large aluminum electrolytic cells, and have promoted the advancement of aluminum electrolytic cell technology and the development of the aluminum electrolytic industry. SiC does not react with aluminum liquid, and is significantly more resistant to electrolyte corrosion and air oxidation than traditional cathode carbon blocks. Its resistivity is also much higher than that of traditional cathode side wall lining materials. SiC has high thermal conductivity and can form a protective side solidification groove when used as the side wall material of the electrolytic cell. In addition, the application of silicon carbide materials can reduce the horizontal current of the cell, increase the heat dissipation of the side wall of the cell, reduce the cell temperature, and improve the current efficiency. The use of SiC refractory side walls can reduce the thickness of the side walls, help expand the tank chamber, and increase the output of aluminum.
03 Ceramics and grinding wheel industry
Since the firing temperature and load of sanitary ceramics are high, rollers made of general materials cannot meet the requirements of roller kiln firing of sanitary ceramics. Therefore, Si3N4-SiC or Sialon-SiC rollers are ideal choices. At present, more and more daily-use ceramics are fired with cold coal gas, natural gas, and liquefied petroleum gas. Si3N4-SiC kiln can significantly reduce the weight ratio of kiln to products, have a long service life, save energy consumption, and improve product quality and qualified rate.
The electronic ceramics industry has higher and higher requirements for the quality of kiln, requiring kiln to have high high-temperature strength, good thermal stability, long service life, and suitable price, which provides a broad application space for Si3N4-SiC materials.
In recent years, building ceramics have developed in the direction of high-end and large-scale development, requiring roller kiln transmission support rollers to be used at temperatures above 1250℃ and high-temperature flexural strength above 50MPa. Si3N4-SiC is an ideal choice. In addition, the burner sleeve of this material has a long service life and a moderate price, and has a good development prospect.
The grinding wheel has a high firing temperature, a long firing cycle, and a large kiln load. Therefore, the grinding wheel industry has high requirements for kiln tools, especially the shelf. Traditional grinding wheel manufacturers mostly use 50mm thick clay plates or clay combined with SiC plates, which not only occupy the furnace space, reduce production efficiency, but also have a short service life. If Si3N4-SiC or Sialon-SiC material shelves are used, not only the thickness can be reduced to about 25mm, but also the heat transfer rate can be improved, extending the life of the kiln.
04 Waste incinerator
The main purpose of applying waste incineration technology and equipment is to carry out harmless treatment of garbage at high temperature, and at the same time convert the energy contained in the garbage into steam, electricity or hot water for utilization, so as to incinerate the garbage at the lowest possible cost. The world's first solid waste incineration equipment was born in Europe during the second technological revolution. In 1870, the first waste incinerator was put into operation in Paddington. This year, some cities in my country have also begun to build waste incinerators to solve the dilemma of urban garbage siege.
The working temperature of the garbage incinerator generally does not exceed 1400℃, but the working environment is relatively complex, such as severe gas erosion, and the wear and impact of garbage on the furnace body during high-temperature movement. Therefore, the garbage incinerator requires refractory materials to have good high-temperature strength, wear resistance, acid and alkali corrosion resistance, thermal shock stability, resistance to CO, Cl2, SO2, HCl, alkali metal vapor erosion and other properties. At present, Si3N4-SiC materials have been widely used in garbage incinerators and have satisfactory performance.
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