Ceramic bearings: zirconia and silicon nitride bearing
There are many types of ceramic bearings available that offer numerous advantages over traditional bearing components. Two common ceramic materials used for bearing applications are silicon nitride (Si3N4) and zirconia (ZrO2).
Silicon nitride is a material with high hardness and relatively light weight. It exhibits excellent resistance to water, saltwater, and many acids and alkalis, performing well over a wide temperature range. As a
result, it finds widespread applications in industries such as aerospace, aviation, semiconductor manufacturing, wind energy, vacuum technology, and chemical industry. For instance, NASA initially used steel bearings for the turbine pumps inside space shuttles, but they proved inadequate when subjected to extreme loads and temperatures. Under such extreme operating conditions, NASA engineers upgraded the bearings to silicon nitride ones, which demonstrated clear advantages in vacuum environments. According to NASA's analysis report, Si3N4 bearings lasted 40% longer than steel bearings. Additionally, in the wind energy and chemical industry, silicon nitride bearings are favored due to their corrosion resistance and high-temperature performance.The extreme hardness of silicon nitride also means greater brittleness, so shock or impact loads should be minimized to avoid the risk of cracking.
Zirconium dioxide, commonly known as ZrO2, is a robust ceramic material used in the production of 
ceramic bearings. These bearings exhibit similar expansion properties to steel, but with a 30% lighter weight. This characteristic is advantageous in applications with higher temperatures, as it helps prevent issues with shaft and housing fits, where bearing expansion could lead to misalignment. Although commonly referred to as ZrO2 bearings, they are actually composed of ZrO2 stabilized with yttrium oxide. This stabilizing agent enhances the material's strength and fracture resistance at room temperature. Additionally, ZrO2 bearings are highly resistant to water, making them well-suited for marine applications where equipment is fully submerged or where traditional steel bearings cannot withstand the load or speed requirements.
| Item | Unit | Technical parameters | |
| Material | - | Zirconia | Silicon Nitride |
| Color | - | White | Black |
| Density | g/cm3 | 5.95-6.05 | ≥3.20 |
| Hardness(HV 0.5) | Mpa | 1300 | 1500 |
| Max.Working Temperature | ℃ | 850 | 1200 |
| Fracture Toughness (@R.T.) | Mpa.M1/2 | 7 | 6.2 |
| Compressive Strength (@R.T.) | Mpa | >720 | 2200 |
| Thermal Conductivity (@R.T.) | W/Mk | 2.2 | 15-20 |
| Coefficient Of Thermal Expansion (20-1000℃) | 10-6/℃ | 10.3 | 3.0-3.2 |
(Please note that this is a simplified performance table listing some common characteristics. In reality, bearing performance is influenced by multiple factors, including specific design requirements, operating conditions, and application environments. Therefore, when selecting suitable bearing materials, it is important to consider other factors and conduct detailed engineering evaluations.)
In general, the use of ceramic bearings offers several advantages, such as high hardness, lightweight, corrosion resistance, and high-temperature tolerance. These benefits make them an ideal choice for specific environments and applications. However, due to their inherent fragility and higher cost, proper design and operating conditions are crucial to ensure the reliability and performance of ceramic bearings.
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