| Al2O3 |
Characteristics of the colorless synthetic sapphire, i.e. corundum single crystal |
|
| Physical | crystal system | hexagonal |
| Properties | chemical formula | Al2O3 |
| purity | 99.99% | |
| cleavage | conchoidal | |
| specific gravity | 3.99 ÷ 3.98 | |
| dislocation density | 10 ÷ 10 /cm | |
| Thermal | melting point | 2050°C |
| Properties | softening point | 1800°C |
| specific heat at 25°C | 0.18cal/g | |
| thermal conductivity at 25°C | 0.1 cal/sec . cm . °C | |
| thermal expansion | ||
| face to c axis | 5.4 . 10/°C | |
| face = to c axis | 6.2 . 10/°C | |
| Mechanical | Hardness Mohs | 9 |
| Properties | Knoop scale face to c axis | 1800 |
| Knoop scale face = to c axis | 2200 | |
| modulus of elasticity | 4.4 x 10 kg/cm | |
| 1% Young E | ||
| modulus of rupture at 25°C | 4000 kg/cm | |
| compressive strength at 25°C | 21000 kg/cm | |
| ultimate tensile strength | 1900 kg/cm | |
| chemical resistance | unattacked by | |
| common acids | ||
| or NaOH | ||
| Chemical | acids and alkalis attack at 300°C | 0 |
| Properties | porosity | 0 |
| Electrical | dielectric constant (permittivity) | 7.5 at 10.5 |
| Properties | electrical resistance at 500°C | 10 ohm/cm |
| electrical resistance at 1000°C | 10 ohm/cm | |
| electrical resistance at 2000°C | 10 ohm/cm | |
