Alumina (Aluminum Oxide, Al2O3)
Alumina is an oxide-based engineering ceramic. It can have a fairly high thermal conductivity and a moderately high heat capacity among oxide-based engineering ceramics.
The properties of alumina include six common variations. This page shows summary ranges across all of them. For more specific values, follow the links immediately below. The graph bars on the material properties cards further below compare alumina 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
1920 to 2750 MPa 280 to 400 x 103 psi
Elastic (Young's, Tensile) Modulus
220 to 370 GPa 32 to 54 x 106 psi
Flexural Strength
260 to 430 MPa 38 to 63 x 103 psi
Fracture Toughness
3.7 to 7.2 MPa-m1/2 3.3 to 6.5 x 103 psi-in1/2
Knoop Hardness
960 to 1660
Poisson's Ratio
0.22 to 0.24
Tensile Strength: Ultimate (UTS)
210 to 290 MPa 30 to 42 x 103 psi
Electrical Properties
Dielectric Constant (Relative Permittivity) At 1 Hz
8.0 to 9.0
Dielectric Constant (Relative Permittivity) At 1 MHz
7.8 to 11
Dielectric Strength (Breakdown Potential)
8.9 to 12 kV/mm 0.35 to 0.48 V/mil
Electrical Dissipation At 1 Hz
0.00031 to 0.0011
Electrical Dissipation At 1 MHz
0.00049 to 0.0013
Electrical Resistivity Order of Magnitude
6.2 to 14 10x Ω-m
Other Material Properties
Density
3.4 to 4.1 g/cm3 210 to 260 lb/ft3
Maximum Temperature: Mechanical
650 to 1730 °C 1200 to 3140 °F
Maximum Thermal Shock
200 to 300 °C 380 to 580 °F
Melting Onset (Solidus)
2040 °C 3700 °F
Specific Heat Capacity
870 to 940 J/kg-K 0.21 to 0.22 BTU/lb-°F
Thermal Conductivity
14 to 30 W/m-K 8.2 to 17 BTU/h-ft-°F
Thermal Expansion
6.7 to 8.2 µm/m-K
Common Calculations
Stiffness to Weight: Axial
35 to 53 points
Stiffness to Weight: Bending
57 to 62 points
Strength to Weight: Axial
14 to 23 points
Strength to Weight: Bending
19 to 28 points
Thermal Diffusivity
3.7 to 10 mm2/s
Thermal Shock Resistance
4.9 to 14 points
Followup Questions
Further Reading
ASTM D2442: Standard Specification for Alumina Ceramics for Electrical and Electronic Applications
Ceramic and Glass Materials: Structure, Properties and Processing, James F. Shackelford and Robert H. Doremus (editors), 2008
Ceramics and Composites: Processing Methods, Narottam P. Bansal and Aldo R. Boccaccini (editors), 2012
IEC 60672-3: Ceramic and glass-insulating materials - Part 3: Specifications for individual materials
Springer Handbook of Condensed Matter and Materials Data, W. Martienssen and H. Warlimont (editors), 2005