Ceramics
Ceramics
A ceramic is an inorganic non-metallic solid made up of either metal or nonmetal compounds that have been shaped and then hardened by heating to high temperatures. In general, they are hard, corrosion-resistant and brittle.
Traditional ceramics are clay–based. Most likely earthenware, stoneware and porcelain. The composition of the clays used, type of additives and firing temperatures determine the nature of the end product.
Advanced ceramics are not generally clay-based. Instead, they are either based on oxides or non-oxides or combinations of the two:
- Typical oxides used are alumina (Al2O3).
- Non-oxides are often carbides, borides, nitrides and silicide, for example, boron carbide (B4C), silicon carbide (SiC) and molybdenum disilicate (MoSi2).
Production processes firstly involve thoroughly blending the very fine constituent material powders. After shaping them into a green body, this is high-temperature fired (1,600–1,800°C). This step is often carried out in an oxygen-free atmosphere.
The high temperature allows the tiny grains of the individual ceramic components to fuse together, forming a hard, tough, durable and corrosion-resistant product. This process is called sintering.
The common ceramic we find in the sealing industry includes:
- 95: meaning 95% aluminum oxide with the balance mainly silica.
- 5: meaning 99.5% aluminum oxide with no silica. A small amount of caesium is added to control the grain size and improve the firing characteristics.
Ceramic is a versatile seal face material that is generally inexpensive. It is a hard material & light to touch, with a white color. Ceramic offers excellent wear characteristics & chemical compatibility. Unlike other mechanical seal face materials though, it cannot handle thermal shocks. Ceramics retain heat when equipment is not operating, and general start-up procedures can easily crack this seal face material. Ceramic, like silicon carbide, will shatter/crack if contacted with force or dropped.
Classification of Ceramics are based on their:
- Oxides,
- Carbides,
- Nitrides,
- Sulfides,
- Fluorides
Technical properties of CERAMIC in 96% AL2O3 (low alumina):
| Properties | Unit of Measurement | Value |
| Alumina Content | % | ~96 |
| Density | g/cm3 | 3.6 – 3.7 |
| Hardness | HRA | 78 |
| Water Absorption | % | 8 |
| Flexure Strength @20 oC | MPa | 300 – 350 |
| Elastic strength @20 oC | GPa | 350 – 370 |
| Stiffness/weight @20 oC | Per sec | 80 |
| Compressive Strength @20 oC | GPa | 2.4 – 2.8 |
| Tensile Strength @25 oC | GPa | 0.24 – 0.26 |
| Fracture toughness K10 | MPa | 3.0 – 3.3 |
| Max. use Temp | oC | 1500 |
Technical properties of CERAMIC in 99.5% AL2O3 (high alumina):
| Properties | Unit of Measurement | Value |
| Alumina Content | % | ~99.5 |
| Density | g/cm3 | 3.8 |
| Hardness | HRA | 80 |
| Water Absorption | % | 5 |
| Flexure Strength @20 oC | MPa | 382 |
| Elastic strength @20 oC | GPa | 393 |
| Stiffness/weight @20 oC | Per sec | 92.1 |
| Compressive Strength @20 oC | GPa | 2.945 |
| Tensile Strength @25 oC | GPa | 0.2552 – 0.2667 |
| Fracture toughness K10 | MPa | 3.5 +- 0.05 |
| Max. use Temp | oC | 1600 |
