Alumina is the most mature of the engineering ceramics, offering excellent electrical insulation properties together with high hardness and good wear resistance but relatively low strength and fracture toughness.
During the prodcution, small amounts of silica (SiO2), magnesia (MgO) and zirconia (ZrO2) may be added to alumina ceramics. The applications vary with the purity of Alumina. 99% Alumina Ceramics are mostly used for high temperature crucibles, kiln furniture, special abrasion resistant parts, such as ceramic bearings, ceramic sealings or faucet discs; 95% Alumina Ceramics are usually applied for corrosion-resitant components or wear proof parts; 85% Alumina Ceramis can be metallized with metals like molybdenum, niobium, tantalum to use for electric vacuum devices.
Properties of Alumina Ceramics
Alumina has a high melting point, high hardness and high mechanical strength, although mechanical strength is reduced at temperatures above 1000° C. Due to the relatively large coefficient of thermal expansion, thermal shock resistance is reduced. Alumina is an electrically insulating material, with a high electrical resistivity, increasing with purity. Good chemical stability of alumina, leads to a high corrosion resistance. It is insoluble in water and only slightly soluble in strong acid and alkaline solution.
| Characteristics | Unit | 95 Al2O3 | 99 Al2O3 | ZrO2 | GPSi3N4 | BN | Glass Ceramic |
| Crystal Structure | - | hexagonal | hexagonal | tetragonal | hexagonal | hexagonal | - |
| Color | - | white | ivory | white | gray | white | white |
| Density | g/cm3 | 3.65 | 3.88 | 5.95 | 3.22 | 2.26 | 2.55 |
| Water Absorption | % | 0 | 0 | 0 | 0 | 0.0-1.0 | 0 |
| Young's Modulus | Gpa | 280 | 350 | 205 | 295 | 670 | 65 |
| Vickers Hardness | Gpa | 14 | 20 | 12 | 18-20 | - | - |
| Flexural Strength @R.T. | Mpa | 280 | 300 | 900 | 650 | 51 | 100 |
| Compressive Strength @R.T. | Mpa | 2000 | 2500 | 2200 | 2200 | 230 | 500 |
| Thermal Conductivity @R.T. | W/(m*k) | 18-25 | 30 | 2.2 | 25 | 20 | 1.7 |
| Thermal shock resistance | Δ(℃) | 220 | 180-200 | 280-350 | 450-650 | >1500 | 25-100 |
| Max. Working Temperature @R.T. | ℃ | 1500 | 1700 | 850 | 1200 | 960 | 800 |
| Volume Resistivity @R.T. | Ω*cm | >10^15 | >10^14 | >10^12 | >10^14 | 10^13 | 10^16 |
| Dielectric Constant (1 MHz @R.T. ) | - | 9.5 | 9.8 | 26 | 8.2 | 4.08 | 6.02 |
| Dielectric Strength | kV/mm | 16 | 22 | - | 16 | 375 | 40 |
Various Application of Alumina Ceramics
1. Seal rings
2. Medical prostheses
3. Laser tubes
4. Electronic substrates
5. Ballistic armour
6. Thermocouple tubes
7. Electrical insulators
8. Grinding media
9. Threadguides
10. Wear components
About UniPreTec
UniPreTec provides high-performance ceramic products in Alumina, Zirconia, Boron Nitride, Machinable Glass Ceramic, Silicon Nitride and further special materials. Along with these materials, we offer several machining from which to choose such as cutting, drilling, sawing, turning, grinding, polishing etc.. Furthermore, our technologies and equipments allow us to provide various and flexible forming processes, like dry pressing, isostatic pressing, extrusion, injection moulding and slip casting.
