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Sapphire Properties

Properties of Sapphire

Chemical Properties:

  • Non-porous, unlike alumina ceramics
  • Unaffected by weathering
  • Unaffected by hydration
  • Virtually unaffected by any solvents or acids at room temperature. (Some etching by hot phosphoric acid and strong caustics at temperatures exceeding 600°C – 800°C)

Thermal Properties:

  • Melting Point: ~2053°C (3727°F)
  • Most properties useful to (maximum): ~1800°C (3272°F)
  • Conductivity: 40 W/M°K @ 298°K
  • Expansion @ 25°C: 4.5×10-6/K-1 and @ 1000°C: 9.0×10-6/K-1 (90° orientation)
  • Specific Heat Capacity: 750 J/K at 300°K
  • Viscosity @ 2053°C: 0.0584 Pa•s

Optical Properties:

  • Refractive Indices:
  • Ordinary Ray (No) (C-axis direction): 1.768
  • Extraordinary Ray (Ne) (perpendicular to C-axis direction): 1.760
  • Birefringence (Ne – No): 0.008
  • Temperature Coefficient of Refractive Index: 13×10-6/°C (@ 0.57 µm, 20°C)
  • Transmittance: >85% 0.3-4.0 µm (@ 0.1 mm thick) uncorrected
  • Emissivity @ 3,4,5 µm: 16%, 25%, 70% (@500°C)
  • Absorption @ 0.66 mm @ 1600°C: 0.1 – 0.2 cm-1

Sapphire IR Transmission

Guild UV Grade Sapphire

Guild UV Grade Sapphire

Mechanical Properties:

  • Hardness (9 Mohs std): 2000 kg/mm2, Knoop
  • Coefficient of friction: 0.14 (on steel)
  • Young’s Modulus: 400 GPa @ 20°C
  • Poisson’s Ratio: 0.29
  • Compressive Strength: 2.0 GPa
  • Creep @ 100 Mpa, 1600°C: 1.5×10-4/hr
  • Fracture Toughness: 2.0 MPa (m½)
  • Flexural Strength: 900 MPa
  • Bulk Modulus: 240 GPa
  • Shear Modulus: 175 GPa (Rigidity Modulus)
  • Tensile Strength: 300 to 400 MPa
  • Rupture Modulus: 65 – 100,000 psi

Electrical Properties:

  • Bulk Resistivity: 1016 ohm-cm @ 25°C, 1011 ohm-cm @ 500°C
  • Dielectric Strength:<. 48 kv/mm, (1.2kv/mil)
  • Dielectric Constant 25°C: 9.4 perpendicular to the c-axis, 11.6 parallel to the c-axis between 10Hz and 3×109 Hz
  • Loss Tangent 25°C: 3.0 – 8.6×10-5; between 10 Hz and 3×109 Hz
  • Magnetic Susceptibility: -0.21×10-6 to -0.25×10-6

Physical Properties:

  • Density: 3.98 g/cm3, (0.143 lbs./in3)
  • Hardness: Knoop microindenter: 1800 FACE perpendicular to c-axis, 2200 FACE parallel to c-axis
  • Young’s Modulus: 400 GPa @ 20°C
  • Tensile Strength: 300 to 400 MPa
  • Point Group; Symmetry: 3 2/m; [C,1A3, 3A2, 3P]
  • Lattice Dimensions: a = 4.748 Angstroms, c = 12.957 Angstroms
  • Sound Speed: ~10 km/s

NOTE: These sapphire properties may be dependent upon relative crystal orientation, form and surface quality