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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 103 psi

Elastic (Young's, Tensile) Modulus

450 GPa 65 x 106 psi

Flexural Strength

1090 MPa 160 x 103 psi

Fracture Toughness

1.9 MPa-m1/2 1.7 x 103 psi-in1/2

Knoop Hardness

1860

Poisson's Ratio

0.28

Shear Modulus

150 GPa 22 x 106 psi

Tensile Strength: Ultimate (UTS)

2470 MPa 360 x 103 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 10x Ω-m

Otherwise Unclassified Properties

Density

4.0 g/cm3 250 lb/ft3

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 m2/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