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Sapphire Machining and Grinding

Sapphire is diamond ground using the same general processes as any dense alumina oxide material. While it tends to chip easier than alumina, simple grinding procedure and technic can accommodate this characteristic. Due to the relatively high cost of sapphire care should be taken to remove a minimal amount of material to reach the final specified dimensions. Sapphire is quite unique both physically, chemically and electrical as you will observe below. San Jose Delta has over 40 years of grinding intricate closely tolerance features in sapphire. Contact us today.

Sapphire Material Properties Data

General Value
Chemical Formula: Al203 (aluminum oxide)
Names: Corundum, Sapphire, Alpha-alumina
Crystal System Trigonal
Class: Hexagonal-scalenohedral
Thermal Value
Melting Point 2053°C (3727°F)
Maximum Useful Temperature ≈2000°C
Specfic Heat 0.181 cal/gm °K (25°C)
0.300 cal/gm °K (1000°C)
Thermal Conductivity 0.4 watts/cm °K(25°C)
0.1 watts/cm °K (1000°C)
Thermal Expansion Coefficient (25-1000°C)
8.8 X 10-6; parallel to C-axis
7.9 X 10-6; perpendicular to C-axis
Physical/Mechanical Value
Density 3.97 gm/cm3 (o.143 lb/in3) (25°C)
Young's Modulus 435 GPa (63 X 106 psi) parallel to C-axis (25°C
386 GPa (56 X 106 psi) parallel to C-axis (1000°C)
Modulus of Rigidity (Shear Modulus) 175 GPa (26 X 106 psi)
Poisson's Ratio 0.27 - 0.30 orientatium dependent
Flexural Strength 1035 MPa (150 kpsi) parallel to C-axis (25°)
760 MPa (110 kpsi) perpendicular to C-axis (25°)
Compressive Strength ≈2 GPa (300kpsi) 25°C
Hardness 9 Moh's Scale
1900 Knoop parallel to C-axis
2200 Knoop perpendicular to C-axis
Optical Value
Uniaxial Negative Refractive Index Ordinary ray (C-axis) No = 1.768
Extraordinary ray Ne = 1.760
Birefringence: 0.008
Temperature Coefficient of Refractive Index 13 X 10-6° C-1 (Visible range)
Spectral Emittance 0.1 (1600°C)
Spectral Absorption Coefficient 0.1-0.2cm-1 (0.66μm, 1600°C)
Electrical Value
Volume Resistivity 1016 ohm-cm (25°C)
1011 ohm-cm (500°C)
106 ohm-cm (1000°C)
Dielectric Strength 480,000 volts/cm (1200 volts/mil)
Dielectric Constant 11.5 (103-109Hz, 25°C) parallel to C-axis
9.3 (103-109Hz, 25°C) perpendicular to C-axis
Loss Tangent 8.6 X 10-5 (@1010Hz, 25°C) parallel to C-axis
3.0 X 10-5 (@1010Hz, 25°C) perpendicular to C-axis
Magnetic Susceptibility -0.21 X 10-6 parallel to C-axis
-0.25 X 10-6 perpendicular to C-axis
Chemical Value
Weathering Resistance Unaffected by atmospheric exposure
Sea Water resistance Unaffected by marine exposure
Biological Resistance Unaffected by in-vivo exposure
Non-reactive with body fluids

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