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Silicon Nitride Material Properties And Si3N4 Ceramic Applications

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Update time : 2020-05-22 09:31:54

Silicon Nitride Material Properties:

Silicon nitride is a relevant structural ceramic material. Silicon nitride formula Si3N4, it is a super-hard substance, which has lubricating and wears resistance, and is an atomic crystal; it is resistant to oxidation at high temperatures. Si3N4 powder can resist the impact of cold and heat, heating in the air to more than 1000 ℃, rapid cooling and then fast heating, it will not break.

Silicon Nitride is precise because Si3N4 ceramics have such excellent characteristics that people often use it to manufacture bearings, gas turbine blades, mechanical seal rings, permanent molds, and other mechanical components. If Si3N4 ceramics that are resistant to high temperatures and difficult to transfer heat are used to manufacture the heating surface of engine components, not only can improve the quality of the diesel engine, save fuel, but also improve the thermal efficiency.

Silicon nitride has high strength, especially hot-pressed silicon nitride, which is one of the hardest substances in the world. Si3N4 powder is extremely resistant to high temperatures, and its strength can be maintained at a high temperature of 1200 °C without falling. It will not melt after being heated and will not decompose until 1900 °C. Silicon nitride has an amazing chemical resistance. It can withstand almost all inorganic acids and caustic soda solutions below 30%, as well as many organic acids. At the same time, it is a high-performance electrical insulation material.

Silicon Nitride Applications:

Silicon nitride, as a compound synthesized mainly by artificial conditions, was successfully developed by foreign scientists more than 150 years ago. The silicon nitride naturally present on the earth until the nineties of the 20th century. It was only in the meteorites that the age was discovered by humans.

As an important structural ceramic material, Si3N4 powder has superior performance to other metals and materials such as high-temperature resistance, corrosion resistance, wear resistance, high toughness, and high bending strength. It can be applied to traditional metal materials. It can't adapt to the extreme operating environment with high requirements, and its products such as parts can be used in mechanical engineering, ultra-fine grinding, high-performance machine cutting tools, metallurgy, and other fields.

I will briefly introduce several kinds of Si3N4 ceramic products (including but not limited to):

(1) Si3N4 ceramic bearings and bearing balls

As an important mechanical basic part, ceramic bearings are admired for their application in the field of new materials because of their superior performance in high-temperature resistance and high strength compared to metal bearings. With the increasing processing technology and process level, its manufacturing costs have fallen, and the product market price has become practical. The application of ceramic bearings has begun to march into various industries, and it is no longer limited to high, precise, sharp, and small applications.

The materials of ceramic bearings are mainly divided into silicon nitride and zirconia. Compared with zirconia, silicon nitride ceramics are suitable for higher speed, high load, and high-temperature environments. High-precision, high-precision rigid spindle precision ceramic bearings are manufactured using silicon nitride, and the highest manufacturing accuracy can reach P4 to UPgrade. Silicon nitride or silicon nitride-based ceramic composite materials are therefore recognized as the ideal material for manufacturing bearings and their parts. At present, silicon nitride ceramic bearings are mainly used in four aspects: ① high-speed bearings ② high-temperature bearings ③ vacuum bearings ④ corrosion bearings.

Silicon nitride ceramic balls are precision ceramic products sintered at high temperature in a non-oxidizing environment. They have the characteristics of acid and alkali resistance and corrosion resistance. Not only can they be used for a long time in seawater, but they also have excellent insulation and self-lubricating properties so that they can be used.

In a highly polluted environment without lubricating media. At 800 ℃, the strength and hardness of the silicon nitride ceramic ball are almost unchanged, the density is 3.20g / cm3, and the weight is nearly 1/3 of the bearing steel's weight and the centrifugal force during rotation is small. It can achieve high-speed operation. Therefore, silicon nitride ceramic balls can mainly become the first choice for ceramic bearings and hybrid ceramic bearings, and also play an important role in the field of ultra-fine grinding.

(2) Turbine rotor made of silicon nitride

Turbocharging is a technology that uses the exhaust gas generated by the operation of the internal combustion engine to drive the air compressor. The role is to increase the intake air of the engine, thereby increasing the power and torque of the engine. At the same time, it reduces fuel consumption, noise, and exhaust gas. Harmful molecules are of great significance. The key part of the turbocharger is the turbine rotor, which is mainly composed of rotor blades, turbine disks, turbine shafts, and other parts.

Silicon nitride-based ceramics have excellent properties such as lightweight, high strength, high heat resistance, impact resistance, and high fracture toughness, which are very suitable for the application requirements of high-quality rotors. Tests have shown that the rotor inertia of the turbine rotor made of silicon nitride can be reduced by 40%, and the boost response time is 30% faster, which significantly improves the acceleration at low speed. And the application of silicon nitride ceramics in turbochargers provides the possibility of lightweight technology for automotive turbochargers.

(3) Silicon nitride ceramic tools

In the global environment of decreasing metal mineral resources for the production of cemented carbide and rising prices, the development of new technologies has promoted the event of a variety of new materials with high strength, high hardness, corrosion resistance, wear-resistance, and high-temperature resistance, and ceramic tools Born. The first generation of ceramic cutters is alumina ceramic cutters, which began to be used in production in 1950. In 1968, the second generation composite alumina ceramic cutters were more excellent in strength and toughness than the first generation performance.

The third generation of international ceramic cutting tools-silicon nitride ceramic cutting tools appeared in the late 1970s and early 1980s. This type of device has higher toughness, impact resistance, high-temperature strength, and thermal shock resistance than the second-generation composite alumina tool. Silicon nitride tools are mainly suitable for roughing, high-speed cutting, and heavy cutting of cast iron and high-temperature alloys. Their excellent chemical stability and wear resistance can be cut and operated for a long time under high-speed conditions, which is better than ordinary carbide tools. The efficiency has increased more than three times on average.

(4) Aluminum metallurgy Si3N4 ceramic parts

Silicon nitride ceramics have the characteristics of anti-aluminum liquid corrosion so that it can be used to make temperature measurement thermocouple tube sleeves, aluminum smelting furnace lining, aluminum liquid bun lining in aluminum casting continuous rolling production line and aluminum smelting and melting operations, crucibles, cast aluminum molds, aluminum electrolytic cells, and other appliances.

The technology of thermocouple tube sleeve made of silicon nitride ceramics for aluminum liquid temperature measurement has begun to spread in China. This type of tube sleeve is more excellent in performance than the commonly used stainless steel and corundum ceramic tube sleeves. After all, stainless steel It is easy to be corroded by an aluminum liquid, and it will be damaged after 20 hours of continuous use, and corundum cannot withstand thermal shock. The silicon nitride ceramic sleeve with long-term stability in aluminum liquid and no cracking for more than 1200 intermittent temperature measurements can be described as a great weapon during the processing process.

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