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Optical Silicon (Si)

Optical silicon is a non-glass, inorganic optical material. It has the highest thermal conductivity among non-glass optical ceramics. In addition, it has a fairly low density and a fairly high melting temperature. The graph bars on the material properties cards below compare optical silicon to other non-glass optical ceramics (top) and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.

Mechanical Properties

Compressive (Crushing) Strength

120 MPa 17 x 103 psi

Elastic (Young's, Tensile) Modulus

150 GPa 21 x 106 psi

Flexural Strength

300 MPa 44 x 103 psi

Fracture Toughness

3.5 MPa-m1/2 3.2 x 103 psi-in1/2

Knoop Hardness


Poisson's Ratio


Shear Modulus

80 GPa 12 x 106 psi

Tensile Strength: Ultimate (UTS)

110 MPa 16 x 103 psi

Thermal Properties

Maximum Temperature: Mechanical

1350 °C 2460 °F

Melting Onset (Solidus)

1560 °C 2830 °F

Specific Heat Capacity

700 J/kg-K 0.17 BTU/lb-°F

Thermal Conductivity

150 W/m-K 88 BTU/h-ft-°F

Thermal Expansion

3.0 µm/m-K

Other Material Properties


2.3 g/cm3 150 lb/ft3

Dielectric Constant (Relative Permittivity) At 1 MHz


Light Transmission Range

1.2 to 15 µm

Refractive Index


Common Calculations

Stiffness to Weight: Axial

35 points

Stiffness to Weight: Bending

75 points

Strength to Weight: Axial

13 points

Strength to Weight: Bending

22 points

Thermal Diffusivity

93 mm2/s

Thermal Shock Resistance

18 points

Followup Questions

Further Reading

Handbook of Optical Materials, Marvin J. Weber, 2003

Handbook of Optical Constants of Solids, Edward D. Palik (editor), 1998