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Sapphire Properties

 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.

General information

Chemical formula

 

Al2O3

Crystal lattice

 

Hexagonal

The unit cell parameters

 

a=4.758 Å, c=12.991 Å

Physical properties

 

 

The metric system

English system

Density

 

3.98 g/sm³

0.144 lb/in3

Hardness

 

1525 - 2000 Knoop,  9 mhos

3700° F

Melting point

 

2310 K (2040° C)

 

Structural properties

Ultimate strength

 

275 MPa to 400 MPa

40,000 to 58,000 psi

 

20°C

400 MPa

58,000 psi (design min.)

 

500° C

275 MPa

40,000 psi (design min.)

 

1000° C

355 MPa

52,000 psi (design min.)

Ultimate bending strength

 

480 MPa to 895 MPa

70,000 to 130,000 psi

The limit of compressive strength

 

2.0 GPa

300,000 psi (ultimate)

Modulus

The Young's Modulus, E

 

345 GPa

50 x 106 psi

 

 

 

 

Modulus of bulk elasticity, k

 

250 GPa

36 x 106 psi

 

 

 

 

Shear modulus, G

 

145 GPa

21 x 106 psi

 

 

 

 

Thermal properties

Thermal Conductivity

0° C

46.06 W/(m • K)

319.4 BTU in/hr ft2 °F

(60° orientation)

100° C

25.12 W/(m • K)

174.2 BTU in/hr ft2 °F

 

400° C

12.56 W/(m • K)

87.1 BTU in/hr ft2 °F

Specific heat capacity at 20° C

 

0.187 cal/(g • °C)

0.1827 BTU/lb °F

Heat capacity

20° C

18.63 cal/ (mol • °C)

18.6 BTU/lb mole °F

 

1000° C

29.86 cal/ (mol • °C)

29.9 BTU/lb mole °F

Coefficient of thermal expansion

20° to 50° C

5.8 x 10-6/ °C

3.2 x 10-6/ °F

(orientation of 60 degrees)

20° to 500°C

7.7 x 10-6/ °C

4.3 x 10-6/ °F

Electrical properties

Frequency

 

E is perp. to the C axis

E // to the C axis

 

 

Dielectric constant

Tangent of loss

Dielectric constant

Tangent of loss

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

Volumetric resistivity at 25 °C

1014 Ом•sm