Silicon nitride (Si3N4) is a strong covalently bonded compound composed of silicon and nitrogen. It has been mass-produced as a ceramic material. As a typical covalently bonded ceramic material, the core difficulty in the development and application of silicon nitride ceramics is the sintering densification of the product. Therefore, it is necessary to add a certain amount of sintering aids and complete the densification process with the help of liquid phase sintering. By adding different sintering aids and adopting different sintering processes, silicon nitride ceramic materials with different comprehensive properties can be prepared. Due to its covalent bonding mode, silicon nitride has excellent wear resistance, corrosion resistance, high temperature resistance (bending strength can reach over 350MPa at 1200℃) and thermal shock resistance. At the same time, the unique interwoven microstructure of silicon nitride columnar crystals gives silicon nitride ceramics higher toughness.

Among various applications of silicon nitride ceramics, bearing balls are the most widely used, and their annual output accounts for three-tenths of the world's high-performance silicon nitride products.

Compared with traditional steel balls, silicon nitride ceramic bearing balls have the excellent properties of low density, high temperature resistance, self-lubrication and corrosion resistance. They are mainly used in machine tool precision bearings, automobile bearings, wind turbine insulation bearings, petrochemical corrosion-resistant and high-temperature resistant bearings and other fields. In addition, due to the insulation of silicon nitride shafts, they are very suitable for use in electric vehicles and other fields. With the development of high-end equipment manufacturing and new clean energy, especially the wind power industry, the use of insulating bearings and main shaft bearings for wind turbines has increased significantly, and the demand for silicon nitride ceramic bearing balls used in conjunction with them is strong.

According to incomplete statistics:

In 2019, the global consumption of silicon nitride bearing balls reached US$470 million,

In 2020, the global consumption of silicon nitride bearing balls reached US$510 million,

In 2021, the global consumption of silicon nitride bearing balls reached US$550 million, a year-on-year increase of 7.8%.

Future: With the continued growth of demand in new energy vehicles, wind power and other fields, the market space for silicon nitride ceramic bearings is expected to expand further.

Bearing balls are one of the main applications of silicon nitride ceramics and have many advantages over traditional steel balls.

Silicon nitride ceramics are mostly composed of atomic crystals, and the atoms are connected by covalent bonds. Compared with metal bonds, covalent bonds have higher bond energy, so ceramics have higher hardness, corrosion resistance, and stable chemical properties, but poor toughness. There is a cloud of free electrons near metal bonds, but atomic crystals do not have this phenomenon. Therefore, compared with metals, ceramics have stronger thermal insulation capabilities and are not conductive.

The hardness of silicon nitride ceramics is more than twice that of steel balls, but its thermal expansion coefficient is less than one-third of that of steel balls, and its operating temperature can reach 1000°C.

At present, the most widely used sintering processes for silicon nitride ceramic balls are hot isostatic pressing (HIP) and gas pressure sintering (GPS). The ceramic balls produced by the two processes have a wide range of applications in different use environments. Among them, HIP sintering can completely densify silicon nitride ceramic balls, greatly reduce defects, and greatly improve various mechanical properties; GPS sintering can prepare products with better performance and complex shapes at a lower cost, and realize mass production in industry.