Silicon Nitride (Si3N4)

What is Silicon Nitride Ceramic (Si3N4)?

Silicon nitride (Si3N4) is a special high-performance industrial ceramic material with high melting point, corrosion resistance, extremely high hardness and other characteristics. Silicon nitride ceramic has a Mohs hardness of 9~9.5 and a Vickers hardness of about 1550. It is usually used to make machined parts, such as bearings, blades, seals, flanges, blades, screws, nuts, etc.

Compared with alumina, the use temperature of silicon nitride will be lower, and mechanical fatigue will occur at 1450 degrees Celsius, so it is recommended that the use temperature of silicon nitride does not exceed 1200 degrees Celsius.

Silicon nitride ceramics are very wear-resistant and are particularly suitable for applications involving repeated mechanical motion, such as plungers, gears, bearings, etc. And it has very stable chemical properties. Except for hydrofluoric acid, it almost does not react with other inorganic acids. Therefore, it also has many applications in some chemical fields. It can be used as a container for chemical solvents, a pump body for chemical solvents, etc.

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Silicon Nitride (Si3N4)

Application

In severe cold environments, when the diesel engine is cooling, in order to ensure good starting performance, glow plugs are used to provide heat energy. The selection of the glow plug is very important, as it needs to meet the conditions of rapid heating and long-term high temperature resistance. Compared with traditional metal glow plugs, silicon nitride ceramic glow plugs heat up to 1000°C 2 seconds faster. Not only that, the operating temperature of silicon nitride glow plugs is about 1200°C, which is also higher than the 1000°C operating temperature of metal glow plugs.

Silicon nitride ceramic balls
In addition, silicon nitride ceramics are widely used in household, industrial and commercial electric heater industries due to their excellent high temperature resistance and thermal conductivity. It can be used as a heating element in direct heating and storage-type, energy-saving and rapid heating electric water heaters. Silicon nitride also plays an important role in liquid heating, electric heating, hot and cold water dispensers, air conditioning heaters, direct hot water taps, thermostats, steam generators and other equipment. Its use not only improves the heating efficiency of the equipment, but also enhances the stability and durability of the equipment in high temperature environments.

There are two crystal forms of silicon nitride (Si3N4): α-Si3N4 is in the form of granular crystals, while β-Si3N4 is in the form of long columnar or needle-shaped crystals. Although they all belong to the hexagonal crystal system, they are all three-dimensional spatial networks composed of [SiN4] tetrahedrons with shared vertex angles. It is particularly worth mentioning that the composition of α-Si3N4 contains six almost completely symmetrical [SiN4] tetrahedrons.

The linear expansion coefficient of silicon nitride ceramics is only 20% of that of 45-gauge steel, which means that ceramic bearings have smaller dimensional changes when temperature changes, and the resulting thermal preload is also lower. This characteristic enables silicon nitride ceramic bearings to effectively avoid fatigue and failure caused by excessive heat accumulation when used in environments with large temperature changes. In addition, silicon nitride is a covalent compound, and its atoms are tightly bound by strong covalent bonds, giving it the characteristics of high hardness and high melting point. This unique property allows silicon nitride ceramics to maintain excellent performance under high temperature and high pressure environments.

Silicon nitride ceramics are outstanding representatives of new high-temperature engineering ceramics and have attracted much attention for their high melting point, excellent high-temperature strength, excellent high-temperature creep properties, excellent thermal shock resistance, oxidation resistance and structural stability. This ceramic material exhibits strong corrosion resistance and can resist the erosion of almost all inorganic acids (except hydrofluoric acid) and caustic soda solutions below 30%, as well as a variety of organic acids.

Silicon Nitride Ball Custom size

Silicon nitride degassing rotor
However, in high-temperature environments, silicon nitride ceramics become thermodynamically unstable, and the surface will oxidize to form a silicon dioxide protective film. Although this protective film usually gives the base material excellent anti-oxidation properties, in practical applications, such as in thermal engines, the deposited molten salt may dissolve silicon dioxide, causing molten salt corrosion of silicon nitride ceramics, and ultimately causing the material to damage. In the electrolytic aluminum industry, cryolite as the electrolyte will also cause corrosion to the silicon nitride ceramics used as the lining material of the electrolytic cell. Therefore, how to improve the corrosion resistance of ceramics to molten salt has become a research focus in the field of fine ceramics in recent years. This article takes the research on molten salt corrosion of silicon nitride ceramics as an example to summarize recent research progress, aiming to explore how to enhance the corrosion resistance of silicon nitride ceramics to cope with various harsh environments and usage scenarios.