Zirconia
Chemical Formula: ZrO2
Background
Zirconia (ZrO2) was developed in the 1960s and '70s and was used to produce the external tiles which created a thermal barrier on the space shuttle that allowed it to re-enter the earth's atmosphere.
Zirconia ZrO2 is a strong, tough, lightweight ceramic material ideal for structural applications such as rolling elements and races for bearing assemblies. Zirconia is used in both fully ceramic and hybrid ball bearings and offer the following advantages:
- Higher reliability at high speeds and loads
- Higher stiffness
- Reduced friction
- Electrical insulator
- Non-magnetic
- Can run with no lubrication
Zirconia is stable in oxidizing and mildly reducing atmospheres. It reacts with carbon, nitrogen and hydrogen at temperatures above 2200°C. It is inert to acids and bases at room temperature with the exception of HF and does not react with the refectory metals up to 1400°C.
Ceramics offer many advantages compared to traditional materials. Their hardness and stiffness combined with heat, corrosion resistance, light weight, LOX compatible and non magnetic characteristics offer designers the ability to drastically improve on all aspects of performance leading them to be used in the following applications:
High vacuum, medical, oil & gas, research, motorsport, semi conductor industry, nuclear, defence, aerospace and renewable energy.
Bearings
The wear resistance, low friction and high stiffness of zirconia improve the performance of high temperature unlubricated roller and ball bearings. zirconia bearings have shown increased bearing life, better speed capability and greater corrosion resistance compared to conventional higher-density steel and hard metal bearings. Silicon nitride can be used in bearings in two ways:
A) For rolling elements only this type is known as a ‘Hybrid Bearing’. Applications
include machine tool spindles, vacuum pumps and sterilisable and unlubricated dental drills.
B) For ‘Fully ceramic bearings’ this type of bearing has ceramic races and rolling
elements, the cage can be produced from ceramic material or alternatively PTFE,
PEEK or as a full compliment bearing. Applications for this type of bearing include
high vacuum, chemically corrosive environments and high temperature applications.
All ceramic bearings are used in applications where corrosion, electric or magnetic fields prohibit the use of metals. For example in tidal flow meters where seawater attack is a problem or electric field seekers.
Future Applications
There are continually growing numbers of applications where silicon nitride can be used to provide solutions to problems which were though of as impossible when using standard materials. Carter are able to offer small batch production of silicon nitride bearings and components with short lead times and competitive pricing allowing our customers to test and approve the products in their working environments without the need for costly large production runs.
| Composition | Unit | Zirconia |
|---|---|---|
| Density | g/cc (#/cu.in.) | 570 (0.21) |
| Flexural | MPa (psi x 10³) | 620 (90) |
| Water Absorption | % | 0 |
| Stiffness/Weight | GPa/g/cc | 35 |
| Compressive Strength | MPa (kpsi) | 1750 (254) |
| Colour | - | Ivory |
| Hardness | GPa (Kg/mm²) | 11.8 (1200) |
| Thermal Contduct | cal/cm³ cm/sec/c° | 0.06 |
| Fracture Toughness | MPa (m½ x 107) | 11 |
| Max Wk Temp | °C | 500 |
| Coefficient of Thermal Expansion | 10-6/°C | 10.1 |
| Thermal Shock Resistance | °C | 350 |
| Thermal Conductivity | W/m °K | 2.2 |
