Silicon nitride was first synthesized in 1857 but was not further studied and developed until 50 years ago. Nowadays, silicon nitride has been widely used in aerospace, internal combustion engine manufacturing, grinding, and cutting fields, this paper introduces seven applications of silicon nitride, to help you better understand silicon nitride.
What is silicon nitride?
Silicon nitride (Si3N4) is composed of silicon and nitrogen. It took silicon powder as raw material and synthesized it with nitrogen at high temperatures.
Si3N4 can be used to produce ball bearings because of its lightweight and high stiffness. It has higher accuracy than metal bearings, produces less heat, high-temperature resistance, and corrosion resistance. The steam nozzle made of Si3N4 ceramics has the characteristics of wear resistance and heat resistance.
The properties of silicon nitride
| Properties | index |
| Chemical formula | Si3N4 |
| Molar mass | 140.283g.mol-1 |
| Density | 3.17g/cm3 |
| Melting point | 1,900℃ (decomposes) |
| Solubility | insoluble |
| Fracture strength | 3.1 – 6.2 MPa-m1/2 |
| Maximum temperature | 1000 – 1330℃ |
| Maximum thermal shock | 290 – 750 ℃ |
| Thermal expansion | 2.5 – 3.2µm/m-K |
| Refractive index | 2.016 |
The application of silicon nitride
1. Silicon nitride is used in aerospace industry
The most advanced technologies and the latest materials are concentrated in the field of aeronautical manufacturing. Silicon nitride is a kind of new material that is used in the turbine engine of the airplane.
Take the aircraft vortex jet engine for example, at temperatures below 650℃, compressor parts are mainly made of titanium alloy, aluminum alloy, and heat-resistant steel. When the temperature of the combustor is up to 1800-2000℃, after airflow cooling, the wall temperature of the combustion chamber is still above 900℃, the compressor parts are made of high-temperature alloy (nickel-base or cobalt-base alloy). In order to prevent the brush of the high temperature and thermal etching，it is usually to spray protecting coating. Nowadays, the strengthened dispersion alloy without coating can be used to produce a combustor that can withstand 1200℃.
Ceramic silicon nitride is heat resistant, and with high strength and stiffness at 1400 ℃(≥ 1200℃, the mechanical strength decline). The silicon nitride can be used in the component of the turbine, especially for the ceramic blade of small engines, turbine outer rings, air bearing. In addition, Silicon nitride ceramics have a low density, which is only 41% of that of steel bearings, which can effectively reduce the weight of aircraft engines, and reduce fuel consumption.
2. Silicon nitride is used in mechanical engineering
Silicon nitride ceramics have the properties such as low friction coefficient, self-lubrication, high strength, and a small coefficient of thermal expansion. So the silicon nitride ceramics can be made into bearing balls and mechanical seal rings.
Although the cost of silicon nitride is relatively high, its strength is large, used in bearing manufacturing, can withstand harsh working environments, and its working life is higher than that of ordinary bearings.
Traditional valve is made of metallic material，which is easy to corrosion. Some of the metallic valves that are used in the petroleum industry do not work because of chemical corrosion. Silicon nitride ceramics have excellent properties such as corrosion resistance, abrasive resistance, and high-temperature resistance, which can replace the traditional valve.
3. Silicon nitride is used in super fine grinding tools
Silicon nitride has high hardness, which is ranked only second to diamond and Cubic Boron Nitride. Because of its very low consumption, it reduces the wear of the grinding media and the pollution of the grinding material and is beneficial to obtain higher purity ultra-fine powder.
4. Silicon nitride is used for internal combustion engine
Nowadays, the heat resistant parts of automobile internal combustion engines are made of nickel-based heat resistant material, which can work on the condition of 1000℃. When it is made of ceramic material, the working temperature can up to 1300℃ and increase efficiency by 30%. Silicon nitride ceramics have high-temperature strength and thermal conductivity and can extend the working life of the engine.
At present, the internal combustion engine is mainly made of oxide base ceramics, and nitrogen base ceramics (silicon nitride). The most disadvantage of ceramics is brittleness, which lowers the reliability of the ceramic engine. If this problem is solved, it will provide a powerful impetus to the development of human society.
5. Silicon nitride is used for the glow plug of diesel engine
The glow plug offers thermal energy for diesel engines in bitterly cold conditions. So the diesel engine must have the properties that heat up rapidly and keep the condition of high temperature.
Silicon nitride ceramic glow plug heating up faster than metal glow plug. Silicon nitride working temperature (about 1200℃) is higher than metal glow plug working temperature (about 1000℃).
In addition, silicon nitride can be used in heating elements such as electric water heaters, air conditioner heaters, direct hot water faucets, thermostats, steam generators, and other households, industrial, and commercial electric water heaters industries.
6. Silicon nitride is used in metallurgical industry
Silicon nitride is widely used in the metallurgical industry because of its chemical stability and good mechanical property. Silicon nitride has outstanding thermal oxidation stability, which can withstand high temperatures (1400℃). The operating temperature in neutral or reducing condition is up to 1800℃. In addition, silicon nitride thermal expansion is small, and it can be used for rapid cooling and rapid heating conditions.
7. Silicon nitride is used for high performance cutting tools
High-speed cutting is an efficient workpiece process. Silicon nitride tools are used in various fields such as cutting cast iron and high-temperature alloys, its durability is several times that of the hard alloy cutter, increasing efficiency three times compared with hard alloy cutter.
Silicon nitride can help us realize using turning instead of grinding, improve the surface quality of the component, and the dry-type cutting come true, control the environmental pollution and reduce the production cost.
Silicon nitride ceramic cutting tools are very promising, and widely used in production, In Germany, about 70% of the castings are made by ceramic cutting tools. In Japan, the annual consumption of ceramic cutting tools accounts for about 8% of the total. Therefore, China’s silicon nitride ceramic tool development space is very large.
In addition to the fields mentioned above, silicon nitride is also used in the medical industry, electronic industry, etc. Silicon nitride has a very broad application prospect. With the progress of technology, silicon nitride will better serve human beings.