Properties of sapphire
Monocrystalline sapphire
(synthetic sapphire or colorless artificial corundum)
has a unique combination of chemical and physical properties: high hardness and strength, optical transparency from ultraviolet to infrared, chemical resistance to aggressive environments, high melting point and thermal conductivity. Thanks to this, sapphire products are widely used in many industries: watch glasses, bearings, transparent reactors, protective covers and windows, plunger pairs.
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Basic information |
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Chemical formula |
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Al2O3 |
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Сlass |
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Trigonal |
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Type of crystal lattice |
Hexagonal | ||||
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The unit cell parameters |
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a=4.758 Å, c=12.991 Å |
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Physical and mechanical properties |
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Melting point |
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2050°C (2323°C) |
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Density |
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3.98 g/cm3 |
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Hardness |
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2000 (Knup), 9 (Mohs) |
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Thermal conductivity coefficient |
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7.2 W/(m.K) at 300 K |
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| Poisson 's of thermal expansion |
5.6x10-6/K (parallel to the axis) 5.0x10-6/K (perpendicular to the axis) |
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| Specific heat capacity |
419 j/(kg K) |
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| Dielectric constant |
(f=1 MHz) 11.5 (parallel to the axis) 9.4 (perpendicular to the axis) |
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| Young's modulus, E |
335 GPa |
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| Shear modulus, G |
148.1 GPa |
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| Volume information module, К |
240 GPa |
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| The elastic limit |
275MPa |
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| Poisson's coefficient |
0.25 |
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Chemical Properties |
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Solubility |
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98x10-6 g /100 g of water |
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Molecular weight |
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101.96 |
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Optical properties |
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Transmission range |
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0.17 – 5.5 microns |
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Refractive index |
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1.75449 (o), 1.74663 (e) (L=1.06 microns) |
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Absorption coefficient |
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0.3x10-3 cm-1 (L=2.4 microns) |
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