Sapphire (Al2O3)

Sapphire (Al2O3)


Sapphire (Al2O3)

Sapphire is a crystalline form of aluminum oxide (Al2O3) that is prized for its hardness, strength, and optical properties. It has a hexagonal crystal structure and is typically transparent or translucent with a wide range of colors, including blue, yellow, green, pink, and clear.

Sapphire is one of the hardest and most scratch-resistant materials known, second only to diamond. This makes it an ideal material for applications where durability is critical, such as watch crystals, lenses, and other optical components. Its hardness also makes it resistant to chemical corrosion and wear, making it an ideal material for use in harsh environments.

Sapphire is also known for its excellent optical properties. It has a high refractive index, meaning that it bends light more than other materials, making it useful in lenses and prisms. Sapphire also has a high transparency in the ultraviolet, visible, and infrared regions of the electromagnetic spectrum, making it useful in various applications such as infrared windows, sensors, and LEDs.

In addition to its optical and mechanical properties, sapphire is also an excellent electrical insulator, with a high dielectric strength and low electrical conductivity. This makes it useful in electronic applications such as insulators, substrates, and power electronics.

Sapphire is also used in various industrial applications such as bearings, nozzles, and cutting tools due to its exceptional hardness and resistance to wear.

Main properties of sapphire:

Chemical formula Al2O3
Crystal class Hexagonal system, rhomboidal class 3m
Lattice constants, A a=4.785, c=12.991
Density, g/cm3 3.98
Melting point, °K 2303
Hardness Knoop(daN/mm2): 1800 parallel to C-axis, 2200 perpendicular to C-axis, Mohs: 9
Optical transmission range, µm 0.17 - 5.5
Refractive index at 0.532 µm n0=1.7717, ne=1.76355
Water absorption nil
Young Modulus, Gpa 345
Shear Modulus, Gpa 145
Bulk Modulus, Gpa 240
Bending Modulus (Modulus of Rupture), Mpa 420 at 20°C, 280 at 500°C
Elastic Coefficient C11=496, C12=164, C13=115, C33=498, C44=148
Poisson ratio 0.25-0.30
Friction Coefficient 0.15 on steel, 0.10 on sapphire
Tensile strength, MPa 400 at 25°, 275 at 500°, 345 at 1000°
Flexural strength, daN/mm2 35 to 39
Compressive strength, GPa 2.0
Young’s modulus E, daN/mm2 3.6 x 104 to 4.4 x 104
Specific heat, J/(kg x K)
105 at 91°K, 761 at 291°K
Thermal coefficient of linear expansion, K-1,at 323K 6.66 x 10-6 parallel to optical axis, 5 x 10-6 perpendicular to optical axis
Thermal conductivity, W/(m x K) at 300K
23.1 parallel to optical axis, 25.2 perpendicular to optical axis
Resistivity, Ohm x cm 1016 (25°), 1011 (500°), 106 (1000°)
Dielectric constant 11.5 (103 - 109 Hz, 25°) parallel to C-axis, 9.3 (103 - 109 Hz, 25°) perpendicular to C-axis
Dielectric strength, V/cm 4 x 105
Loss tangent 1 x 10-4
  -in water
  -in HNO3,H2SO4, HCl, HF
  -in alcalis
  -in melts of metals  Mg, Al, Cr, Co, Ni, Na, K, Bi, Zn, Cs
insoluble to 300°C
insoluble to 800°C 
insoluble to 800-1000°C
g -radiation stability No change in transmission above 2.5 mm after exposure to 107 Rads. No visible coloration after exposure to 108 Rads/hr for 60 minutes at - 195°C
Proton radiation stability  No change in transmission below 0.3 µm after exposure to 1012 proton/cm2 total dose
Chemical resistance
Sapphire is highly inert and resistant to attack in most process environments including hydrofluoric acid and the fluorine plasma applications commonly found in semiconductor wafer processing (NF3, CF4)

Typical specifications:

Available orientations: C-axis [0001], R-axis [1-102], A-axis [11-20], M-axis [10-10], Random
Sapphire windows / blanks
Diameter / Width: 25.0 - 250.0 mm
Tolerance: Standard ± 2°, Special to ± 0.1°
Thickness: Minimum 0.15, maximum 120.0 mm
Surface finish: As cut, fine ground, lapped, polished s/d 80/50, 60/40, 40/20, 20/10, 10/5, according to the MIL-0-13830A
Ends / Edge quality: Fine ground, 80/50
"As-grown" sapphire tubes:
Dimensions Up to 50 mm inner diameter, 0,5 - 4,0 mm wall thickness, 300-600 mm tubes length
Orientation C-axis in the length of the tube
Polished sapphire tubes: Up to 50 mm inside diameter, 0,5 - 3,0 mm wall thickness, 80-350 mm tubes length
Ingots: Diameter/Width 5-220 mm, Thickness/Length 25 – 125 mm
Surface quality As-cut, Ends/Edge Quality Diamond cut

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