Sapphire and its properties
Sapphire (Al2O3) boasts superior optical, mechanical and chemical properties to other common optical glasses and crystals. With a hardness of 9 Mhos and chemical inertness Sapphire windows are utilized in high pressure systems and in applications where other materials suffer from scratching and chipping from abrasive, gritty and otherwise hazardous environments.
Sapphire’s wide transmission range allows it to be used in all visible applications and increasingly in NIR systems, particularly in optical defence applications such as imaging system covers and missile domes.
In addition to its mechanical durability Sapphire’s resistance to thermal shock and prolonged high temperature stability (>1500C) make it ideal for high pressure and temperature applications, from portholes in oil and gas systems to vacuum chambers and spectroscopy instruments.
Below are listed common Sapphire forms and component types offered by Roditi; choose one of the categories to find out more about our capabilities. In addition to the following forms, Roditi offer highly customised Sapphire components. Contact us directly to discuss your specifications and requirements.
Sapphire Properties
General
| Property | Value |
|---|---|
| Chemical Formula | Al2O3 |
| Crystal Structure | Hexagonal System ((hk o 1) |
| Unit Cell Dimension | a=4.758 Å,Å c=12.991 Å, c:a=2.730 |
Physical
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Density | 3.98 g/cc | 0.144 lb/in3 |
| Hardness | 1525 – 2000 Knoop, 9 mhos | |
| Melting Point | 2310 K (2040° C) | 3700° F |
Structural
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Tensile Strength | 275 MPa to 400 MPa | 40,000 to 58,000 psi |
| Tensile Strength at 20° | 400 MPa | 58,000 psi (design min.) |
| Tensile Strength at 500° C | 275 MPa | 40,000 psi (design min.) |
| Tensile Strength at 1000° C | 355 MPa | 52,000 psi (design min.) |
| Flexural Strength | 480 MPa to 895 MPa | 70,000 to 130,000 psi |
| Compression Strength | 2.0 GPa (ultimate) | 300,000 psi (ultimate) |
Modulus
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Young’s Modulus, E (Modulus of Elasticity) |
345 GPa | 50 x 106 psi |
| Bulk Modulus, k (Modulus of Compression) |
250 GPa | 36 x 106 psi |
| Shear Modulus, G (Modulus of Rigidity) |
145 GPa | 21 x 106 psi |
| MOR (Modulus of Rupture) |
350 MPa to 690 MPa | 50,000 to 100,000 psi |
| Poisson’s Ratio | Sapphire is anisotropic. It is orientation dependent. | |
Thermal
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Thermal Conductivity at at 0° C | 46.06 W/(m • K) | 319.4 BTU in/hr ft2 °F |
| Thermal Conductivity at at 100° C (60° orientation) |
25.12 W/(m • K) | 174.2 BTU in/hr ft2 °F |
| Thermal Conductivity at at 400° C | 12.56 W/(m • K) | 87.1 BTU in/hr ft2 °F |
| Specific Heat at 20° C | 0.187 cal/(g • °C) | 0.1827 BTU/lb °F |
| Heat Capacity at 20° C | 18.63 cal/ (mole • °C) | 18.6 BTU/lb mole °F |
| Heat Capacity at 1000° C | 29.86 cal/ (mole • °C) | 29.9 BTU/lb mole °F |
| Thermal Expansion Coefficient 20° to 50° C | 5.8 x 10-6/ °C | 3.2 x 10-6/ °F |
| Thermal Expansion Coefficient 20° to 500° C (60° orientation) |
7.7 x 10-6/ °C | 4.3 x 10-6/ °F |
Electrical
| Property | E l to C axis Dielectric Constant |
E l to C axis Loss Tangent |
E ll to C axis Dielectric Constant |
E ll to C axis Loss Tangent |
|---|---|---|---|---|
| 1 MHz | 9.39 | 0.0001 | 11.58 | 0.0001 |
| 3 GHz | 9.39 | <0.0001 | 11.58 | <0.0001 |
| 8.5 GHz | 9.39 | <0.00002 | 11.58 | <0.00002 |
| Volume Resistivity at 25 °C | 1014 ohm • cm | |||
Sapphire is, as stated above, an anisotropic crystal, and the values given above are average values. Please remember that this engineering data is representative only, and should not be considered absolute or warrantable.
To discuss Sapphire or any of Roditi’s other products, please contact us.
