Characteristics of Colourless Synthetic Sapphire

 i.e. Corundum Single Crystal. AI2 O3

Physical properties

Crystal system

Hexagonal

Chemical formula

AI2 O3

Purity

99.99 %

Cleavage

Conchoidal

Specific gravity

3.99 3.98

Dislocation density

10⁵ 10⁴ /cm

Thermal properties

Melting point

2050C

Softening point

1800C

Specific heat at 25C

0.18 cal / g

Thermal conductivity at 25C

0.1cal / sec / cm /C

Thermal expansion

Face ^ to c axis.

5.4. 10⁻⁶ / C
Face = to c axis.

6.2. 10⁻⁶ / C

Mechanical properties

Hardness (Mohs)

9

Knoop scale face ^ to c axis

1800

Knoop scale face = to c axis

2200

Modulus of elasticity

4.4 w 10⁶kg/cm 1% young E

Modulus of rupture at 25C

4000 kg/cm

Compressive strength at 25C

21000 kg/cm

Ultimate tensile at 25C

1900 kg/cm

Chemical resistance

Inert to common acids or NaOH

Chemical properties

Acids & alkalis attack at 300C

0

Porosity

0

Electrical properties

Dielectric constant permittivity

7.5 at 10.5

Electrical resistance at 500C

10 ohm / cm

Electrical resistance at 1000C

10⁶ ohm / cm

Electrical resistance at 2000C

10 ohm / cm

Optical properties

Refractive index at 5893 nd

Face ^ to c axis.

1.769

Face = to c axis.

1.760

Chromatic dispersion

6563 - 4861 nf - nc

0.011

Transmission

Visible light

Excellent

Infrared (1mm thick specimen)

0.75 - 5 μ m

85 %

5.5 μ m

60 %

6 μ m

50 %

Standard quality

4000 - 3000

80 %

2800

60 %

2000

50 %

UV quality

4000 - 3000

80 %

2000

75 %

1800

65 %

1600

50 %

1470

30 %

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