Silicon nitride ceramics
are advanced engineering ceramics with high strength, fracture toughness, hardness, wear resistance and good chemical and thermal stability. Silicon nitride is a polycrystalline composite material consisting of silicon nitride grains (single crystals) embedded in an amorphous or partially crystalline glass phase matrix. Their properties depend not only on the intrinsic properties of silicon nitride single crystals, but also on the size and morphology of the silicon nitride grains, as well as the volume fraction and chemical properties of the glassy phase at the silicon nitride grain boundaries. Si3N4 has excellent mechanical, thermal and physicochemical properties and can be used in traditional and highly innovative solutions. Si3N4's light weight, high flexural strength, good wear resistance, and ability to withstand the harshest environments make Si3N4 a reliable alternative to traditional materials such as stainless steel, tungsten carbide, oxide-based, and sometimes the only alternative to ceramics.
Silicon nitride ceramic structural parts
One of the main applications of sintered silicon nitride is in the automotive industry as a material for engine parts. These include, in diesel engines, glow plugs for faster starts; pre-chambers for lower emissions, faster starts and lower noise; and turbochargers for reduced engine lag and emissions. In spark-ignition engines, silicon nitride is used for rocker pads to reduce wear, turbocharger turbines to reduce inertia and reduce engine lag, and exhaust gas control valves to increase acceleration. As an example of production levels, it is estimated that more than 300,000 sintered silicon nitride turbochargers are produced annually.
Silicon nitride bearings are both full ceramic bearings and ceramic hybrid bearings. The ball is ceramic and the seat ring is steel. Compared with other ceramics, silicon nitride ceramics have good shock resistance. Therefore, ball bearings made of silicon nitride ceramics are used for high-performance bearings. A representative example is the use of silicon nitride bearings in the main engines of NASA's space shuttles. Since silicon nitride ball bearings are harder than metal, this reduces contact with the bearing track. Compared to traditional metal bearings, this results in 80% less friction, 3 to 10 times longer life, 80% faster speed, 60% lighter weight, ability to operate with insufficient lubrication, higher resistance Corrosive and higher operating temperatures. Silicon nitride balls are 79% lighter than tungsten carbide balls. Silicon nitride ball bearings are used in high-end automotive bearings, industrial bearings, wind turbines, motorsport, bicycles, roller skates and skateboards. Silicon nitride bearings are particularly useful in applications where corrosion or electrical or magnetic fields prohibit the use of metal, such as in tidal flow schemes, where seawater erosion is an issue, or in electric field detectors.
high temperature material
Silicon nitride has long been used in high temperature applications. In particular, it was identified as one of the few monolithic ceramic materials capable of withstanding the severe thermal shock and thermal gradients produced by hydrogen/oxygen rocket engines. To demonstrate this capability in a complex configuration, NASA scientists used advanced rapid prototyping techniques to fabricate a one-inch diameter single-piece combustor/nozzle (thrust) assembly. The thrusters were hot-fire tested with hydrogen/oxygen propellants and were subjected to five cycles, including a 5-minute cycle to a material temperature of 1320°C.
Silicon nitride has many orthopedic applications. The material is also an alternative to PEEK (polyetheretherketone) and titanium used in spinal fusion devices. Compared to PEEK and titanium, silicon nitride's hydrophilic, micro-textured surface helps improve the material's strength, durability, and reliability. Certain compositions of this material have antibacterial, antifungal or antiviral properties.
Metalworking and Cutting Tools
Bulk, monolithic silicon nitride is used as a material for cutting tools due to its hardness, thermal stability and wear resistance. Especially recommended for high speed machining of cast iron. Hot hardness, fracture toughness and thermal shock resistance mean that sintered silicon nitride can cut cast iron, hard steel and nickel-based alloys with surface speeds up to 25 times faster than traditional materials such as tungsten carbide. Cutting tools have a huge impact on manufacturing output. For example, face milling of grey cast iron with silicon nitride inserts doubles the cutting speed, increases tool life from one to six parts per edge, and reduces the average cost of inserts compared to conventional tungsten carbide tools Reduced by 50%.
Silicon nitride is commonly used as an insulator and chemical barrier in integrated circuit fabrication to electrically isolate different structures or as an etch mask in bulk micromachining. As a passivation layer for microchips, it is superior to silicon dioxide because it has a significantly better diffusion barrier to water molecules and sodium ions, two major sources of corrosion and instability in microelectronics. It also acts as a dielectric between polysilicon layers in analog chip capacitors.