Sapphire Properties

SapphireSapphire is an anisotropic, rhombohedral crystalline form of aluminium oxide

As an anisotropic crystal, it will have some properties (such as hardness and thermal expansion) which vary significantly by orientation. Whilst this is unimportant for most applications it should still be considered when determining your requirements.

Saphire is also birefringent. For some optical applications, where this may be an important consideration, C-plane sapphire should be specified as birefringence is eliminated along the C-axis (sometimes called the "optical axis).

GENERAL
Chemical Formula
Al2O3
Crystal Stucture
Hexagonal System ((hk o 1)
Unit Cell Dimension
a=4.758 Å,Å c=12.991 Å, c:a=2.730
PHYSICAL
 
Metric
English (Imperial)
Density
3.98 g/cc
0.144 lb/in3
Hardness
1525 - 2000 Knoop,  9 mhos
3700° F
Melting Point
2310 K (2040° C)
STRUCTURAL
Tensile Strength
275 MPa to 400 MPa
40,000 to 58,000 psi
 
at 20°
400 MPa
58,000 psi (design min.)
 
at 500° C
275 MPa
40,000 psi (design min.)
 
at 1000° C
355 MPa
52,000 psi (design min.)
Flexural Stength
480 MPa to 895 MPa
70,000 to 130,000 psi
Compression Strength
2.0 GPa (ultimate)
300,000 psi (ultimate)
MODULUS
Young's Modulus, E
345 GPa
50 x 106 psi
(Modulus of Elasticity)
Bulk Modulus, k
250 GPa
36 x 106 psi
(Modulus of Compression)
Shear Modulus, G
145 GPa
21 x 106 psi
(Modulus of Rigidity)
MOR
350 MPa to 690 MPa
50,000 to 100,000 psi
(Modulus of Rupture)
Poisson's Ratio
Sapphire is anisotropic.  It is orientation dependent.
THERMAL
Thermal Conductivity
at 0° C
46.06 W/(m • K)
319.4 BTU in/hr ft2 °F
(60° orientation)
at 100° C
25.12 W/(m • K)
174.2 BTU in/hr ft2 °F
 
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
 
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
(60 degree orientation)
20° to 500°C
7.7 x 10-6/ °C
4.3 x 10-6/ °F
ELECTRICAL
Frequency
E l to C axis
E ll to C axis
 
DielectricConstant
Loss Tangent
DielectricConstant
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.