In the early days of silicon nitride ceramics, they were mainly used in parts of certain equipment or products in industries such as machinery, metallurgy, chemical industry, aviation, semiconductors, and medicine, and they achieved good expected results. In recent years, with the development of manufacturing processes and testing and analysis technologies, the reliability of silicon nitride ceramic products has been continuously improved, so the application area is constantly expanding. The characteristics of silicon nitride are as follows:
1. Sintered silicon nitride has a low linear expansion coefficient, so it has good thermal shock resistance, second only to quartz and microcrystalline glass;
2. Silicon nitride has a small friction coefficient and self-lubricating properties. It has excellent wear resistance and becomes an excellent wear-resistant material;
3. Silicon nitride has high mechanical strength and low high-temperature creep;
4. It has excellent electrical insulation;
5. Silicon nitride has excellent chemical properties and can withstand corrosion from all inorganic acids and certain alkalis except hydrofluoric acid.
1. Application of silicon nitride in the metallurgical industry
-Application in aluminum, copper, zinc and other industries
In aluminum casting and rolling production lines and aluminum smelting and aluminum melting operations, silicon nitride ceramics can be used as temperature-measuring thermocouple sleeves, and can also be used as aluminum smelting furnace linings, crucibles, etc., and even pumps, pipes, valves, and aluminum casting molds for conveying aluminum liquid can all be made of silicon nitride.
-In steelmaking and rolling industries
The most important use of silicon nitride as a refractory material in the steelmaking industry is as a separation ring for horizontal continuous casting. In horizontal continuous casting, the separation ring divides the molten steel flow into the molten steel zone and the molten steel solidification zone, plays the role of separating the liquid-solid interface of the steel, and plays a great role in maintaining a stable starting point for the solidification of the molten steel and the quality of the ingot.
-Application in the ironmaking industry
In recent years, silicon nitride and sialon combined with silicon carbide products for blast furnaces have developed rapidly. In particular, 68% of large blast furnaces with a furnace diameter of 12 to 15m have adopted it. Experiments show that silicon nitride has good slag corrosion resistance and oxidation resistance.
2. Application of silicon nitride in the chemical industry
-Application in the metal heat treatment industry
The gear to be processed is made of silicon nitride ceramics, and heated from room temperature to 900℃ in an induction furnace in 45s, and then the gear is quenched with clean oil. This cycle is repeated, and the operation is 5,000 times a week. After continuous use for more than a year, the silicon nitride ceramic shaft has only slight wear. Silicon nitride ceramics are very suitable as workpiece fixtures and heating element hooks in vacuum heat treatment because they are resistant to high temperatures and have stable dimensions at high temperatures.
-Preparation of porous ceramics
Porous silicon nitride ceramics have the properties of both silicon nitride ceramics and porous materials. They have the advantages of high strength, good toughness, good creep resistance, good structural stability, rain erosion resistance, and excellent thermal shock resistance of silicon nitride ceramics, as well as the characteristics of porous materials such as low density, low dielectric constant, and low dielectric loss. Therefore, porous silicon nitride can be used in the aerospace field as a radome material used in harsh environments. Radar antenna covers made of silicon nitride ceramics can be used in high-speed aircraft at 6 to 7 Ma. They have high strength, good thermal shock resistance, and rain erosion resistance.
3. Application in the field of machinery
– Used for energy saving and emission reduction in automobile engines
The ceramic materials of automobiles are inorganic non-metallic materials with fine structures obtained by pre-treatment, crushing, grinding, mixing, forming, drying, sintering, and other special processes using high-purity ultra-fine oxides, nitrides, borides, and other raw materials. In particular, the tensile strength and bending strength are comparable to those of metals. The weight of silicon nitride ceramics is half that of iron, and the energy-saving effect is very significant. At the same time, it can also reduce environmental pollution and save metal materials such as steel. Silicon nitride ceramics have abundant raw materials and good processability. Various parts with precise dimensions can be produced at low cost, especially parts with complex shapes, and the yield rate is higher than other ceramic materials. Silicon nitride ceramics have good resistance to rapid temperature changes and high hardness. Its hardness is second only to materials such as diamond and boron nitride. When silicon nitride ceramic materials are used to manufacture engines, the fuel can be fully burned due to the increase in temperature, and the pollutant components in the exhaust gas are greatly reduced, which not only reduces energy consumption but also reduces environmental pollution.
-The silicon nitride all-ceramic engine under development will replace the metal engine of the same type.
4. Application in the aerospace field
In the new generation of Airbus engines mass-produced by General Electric in 2005, silicon nitride was mainly used as raw material. The high temperature is generated when the aircraft engine is running. Experts pointed out that the average use time of aircraft engines exceeds thousands of hours, and there is a problem of engine resistance to high temperatures, which thermal insulation ceramics must solve. At the same time, domestic aircraft fly tens of thousands of times a day. To reduce fuel consumption, the weight of the aircraft must be reduced. Ceramic engines help achieve this goal.