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Properties

Typical characteristics of colourless corundum

Physical Properties

crystalline structure

rhomboedral hexagonal

composition AI2O3
purity 99.99%
cleavage cochidal
density 3.99- 3.98 g / cm3

 

Thermal Properties

melting point 3722°F

softening point

3272°F
specific heat at 77°F 0.18 cal/g. °F
thermal conductivity at 77°F 0.1 cal/sec. cm. °F

                 

Mechanical Properties

Fläche ⊥ zur C- Achse 5.4. 10-6/°C
Fläche = zur C- Achse 6.2. 10-6/°C
Härte Mohs 9
Knoop Fläche ⊥ zur C- Achse 1800
Knoop Fläche // zur C- Achse 2200
Elastizitätsmodul 4.4 x 106 kg/cm2 ± 1% Young E
Bruchmodul bei 25°C 4000 kg/cm2
Druckfestigkeit bei 25°C 21000 kg/cm2
Zugfestigkeit 1900 kg/cm2

 

Chemical properties

acid or alkaline attack at 570°C 0
porosity 0

 

Electrical properties

dielectric constant

10.5 electric field // C- axis at 77°F

  8.6 electric field ⊥ C- axis at 77°F
electrical resistivity at 932°C 1011 ohm/cm
electrical resistivity at 1832°C 106 ohm/cm
electrical resistivity at 3632°C 103 ohm/cm

 

 Optical properties

refractive index ND at 0.5893 um

1.760 face // C- axis at 77°C

 

1.760 face ⊥ C- axis at 77°C

transmission:
at 1mm thickness

 
- visible light excellent
- infrared 85%= 0.75- 5 µm
  70%= 5.5 µm
  50%= 6 µm
- ultraviolett 80%= 0.4- 0.3 µm 
  60%= 0.28 µm
  50%= 0.2 µm

 

 Transmission