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Synthetic ruby and sapphire are monocrystalline aluminium oxides. Sapphire more less is pure ( 99,99% Al2O3), ruby’s color comes from admixture with a little chromium oxide (CrO3). Both crystallines are hexagonal rhombohedral structured, hardness of both is ca. 2300 Vickers.


  • excellent transmission (diaphanous with wide spectrum – from UV to IR)
  • inert and very resistant against aggressive media
  • excellent heat conductivity (particularly at kryotemperatures
  • also excellent heat resistance and resistance against thermal shocks.
  • brilliant resistance against scratching and wear
  • good resistance against corrosion and abrasivity
  • extreme hardness (behind diamond the most hard technical material)
  • excellent electrical characteristics (high electrical resistance, high dielectric coefficient)

The combination from high E-modul, extreme hardness, brilliant optical characteristics and mechanical and chemical resistance offers phenomenal advantages compared against glass or ceramic!

Technical characteristics of sapphire:

chemical formula  Al 2O3
structure  hexagonal rhombohedral
molar weight  101,94
mass density, g/cm³ (20 °C)  3,98
Reflexionsverlust, % zwei Oberflächen bei 4 µm  12
dielectric coefficient at 102-108Hz at 298K
melting pointt, K  2300
heat conductivity, W/(m K) bei 300 K
thermal expansion, 1/K bei 293 K
 5,6 x 10 -6
 5,0 x 10-6
spec. thermal capacity, cal/(g K) at 298 K  0,18
band gap. eV  9,9
water solubility  Keine
Mohs hardness  9
Knoop hardness, kg/mm²  1370
elasticity modulus E, GPa  335
shear modulus G, GPa  148
compressive modulus K, GPa at 273 K  240
rupture modulusl, MPa  350…690
Poisson's Ratio  0,25