# 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).

## Mechanical Properties

Compressive (Crushing) Strength

120 *MPa* 17 *x 10 ^{3} psi*

Elastic (Young's, Tensile) Modulus

150 *GPa* 21 *x 10 ^{6} psi*

Flexural Strength

300 *MPa* 44 *x 10 ^{3} psi*

Fracture Toughness

3.5 *MPa-m ^{1/2}* 3190

*psi-in*

^{1/2}Knoop Hardness

1130

Poisson's Ratio

0.28

Shear Modulus

80 *GPa* 12 *x 10 ^{6} psi*

Tensile Strength: Ultimate (UTS)

110 *MPa* 16 *x 10 ^{3} psi*

## Thermal Properties

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

Density

2.3 *g/cm ^{3}* 150

*lb/ft*

^{3}Dielectric Constant (Relative Permittivity) At 1 MHz

12

Light Transmission Range

1.2 to 15 *µm*

Refractive Index

3.5

## 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 *m ^{2}/s*

Thermal Shock Resistance

18 *points*

## Followup Questions

## Further Reading

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

Handbook of Optical Materials, Marvin J. Weber, 2003