Technical data
PHYSICAL PROPERTIES
| Crystallographic structure | Rhombohedral single crystal; R3c |
| Density | 3.98x103 kg.m-3 (20 °C) |
| Hardness by Mohs | 9 |
| Hardness by Knoop | 1800 parallel to ,c' axis (0001) |
| 2200 perpendicular to ,c' axis | |
| Tensile strength | 2.1x109 N.m-2 (25 °C) |
| Compressive strength | 3.0x109 N.m-2 (25 °C) |
| Young's modulus of elasticity | 4.6x1011 N.m-2 (25 °C) |
| Modulus of rupture | 0.7x109 N.m-2 (25 °C) |
| Coefficient of friction | 0.15 - against steel |
THERMAL PROPERTIES
| Melting point | 2053 °C (3727 °F) |
| Thermal expansion | 6.6x10-6 °C-1 (20-50 °C) parallel to ,c' axis |
| 5.0x10-6 °C-1 (20-50 °C) perpendicular to ,c' axis | |
| Thermal conductivity | 42 W.m-1.K-1 |
| Specific heat | 0.75x103 J.kg-1.K-1 |
| Maximum operating temperature | 2000 °C (3632 °F) |
ELECTRICAL PROPERTIES
|
Resistivity |
1x1018 Ω.m (25 °C) |
| Dielectric constant | 11.5 parallel to ,c' axis |
| 9.3 perpendicular to ,c' axis (103 - 1010 Hz) | |
| Dieletric loss tangent | 3x10-5 parallel to ,c' axis |
| 8.6x10-5 perpendicular to ,c' axis | |
| Dielectric strenght | 48x106 V.m-1 (60 Hz) |
OPTICAL PROPERTIES
| Index of refraction | n0 = 1.768 (Sodium D-line) |
| ne = 1.760 | |
| Optical transmition | 0.18 - 6µm (Total transmition up to 87%) |
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