# Synthetic Sapphire

Synthetic sapphire is an oxide-based engineering ceramic. It has the highest tensile strength among oxide-based engineering ceramics. In addition, it has a very high thermal conductivity and a moderately high density.

The graph bars on the material properties cards below compare synthetic sapphire to other oxide-based engineering 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

2700 *MPa* 390 *x 10 ^{3} psi*

Elastic (Young's, Tensile) Modulus

450 *GPa* 65 *x 10 ^{6} psi*

Flexural Strength

1090 *MPa* 160 *x 10 ^{3} psi*

Fracture Toughness

1.9 *MPa-m ^{1/2}* 1.7

*x 10*

^{3}psi-in^{1/2}Knoop Hardness

1860

Poisson's Ratio

0.28

Shear Modulus

150 *GPa* 22 *x 10 ^{6} psi*

Tensile Strength: Ultimate (UTS)

2470 *MPa* 360 *x 10 ^{3} psi*

## Thermal Properties

Maximum Temperature: Mechanical

2000 *°C* 3630 *°F*

Melting Onset (Solidus)

2050 *°C* 3720 *°F*

Specific Heat Capacity

760 *J/kg-K* 0.18 *BTU/lb-°F*

Thermal Conductivity

30 *W/m-K* 17 *BTU/h-ft-°F*

Thermal Expansion

5.3 *µm/m-K*

## Electrical Properties

Dielectric Constant (Relative Permittivity) At 1 MHz

10

Dielectric Strength (Breakdown Potential)

9.9 *kV/mm* 0.39 *V/mil*

Electrical Resistivity Order of Magnitude

17 *10 ^{x} Ω-m*

## Otherwise Unclassified Properties

Density

4.0 *g/cm ^{3}* 250

*lb/ft*

^{3}Light Transmission Range

0.17 to 5.5 *µm*

Refractive Index

1.8

## Common Calculations

Stiffness to Weight: Axial

63 *points*

Stiffness to Weight: Bending

64 *points*

Strength to Weight: Axial

170 *points*

Strength to Weight: Bending

100 *points*

Thermal Diffusivity

9.9 *m ^{2}/s*

Thermal Shock Resistance

74 *points*

## Followup Questions

## Further Reading

Ceramics and Composites: Processing Methods, Narottam P. Bansal and Aldo R. Boccaccini (editors), 2012

Springer Handbook of Condensed Matter and Materials Data, W. Martienssen and H. Warlimont (editors), 2005

CRC Materials Science and Engineering Handbook, 4th ed., James F. Shackelford et al. (editors), 2015