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Sintered Alumina ( Al₂O₃ )

Reference: NIST Structural Ceramics Database, SRD Database Number 30

Reference: "Evaluated Material Properties for a Sintered alpha-Al₂O₃," R. G. Munro, Journal of the American Ceramic Society, Vol. 80, pp. 1919-1928 (1997).

Other materials: Property Data Summaries

Material Summary:

Alumina ceramics are typically polycrystalline materials that are formed by sintering or hot pressing. Sintering is typically performed at about 1700 °C. A small amount of MgO may be added to control the grain size during sintering.

The data presented here were derived from reported values for high purity (99.5 % or higher) and nearly fully densified (98 % of the theoretical density, or higher) sintered alpha-alumina materials with a nominal grain size of 5 µm.

Property Summary:

Special Notes on Properties:
Data Status: Validated
Crystal System: Corundum, space group R3(bar)c, 2 formula units per unit cell, but
                most commonly referred to a larger hexagonal cell with 6 formula units.
Melting Point: 2050(4) °C
Nominal Grain Size: 5 µm
Creep Characteristics in Flexure in the range 100 MPa to 200 MPa, 1200 °C to 1800 °C:
   Activation energy: 325(25) kJ/mol
   Stress exponent: 1.08(5)
Tribology Characteristics (dry alumina on alumina):
   With increasing temperature, both friction and wear increase sharply at 200(5) °C to a nearly
   constant value; subsequently, both properties decrease roughly linearly over the range 600 °C to 900 °C,
   attaining high temperature values that are nearly the same as the low temperature values.
Property Table
Numbers in parentheses denote estimated combined standard uncertainties of the last given digit.
For example, 2050(4) is equivalent to 2050 +/- 4.
Property [unit]                       20 °C        500 °C       1000 °C      1200 °C      1400 °C      1500 °C
------------------------------------  ----------   ----------   ----------   ----------   ----------   ----------
Bulk Modulus [GPa]..................  257(50)      247          237          233          229          227
Compressive Strength [GPa]..........  3.0(5)       1.6          0.7          0.4          0.3          0.28
Creep Rate [10-9 s-1] at 150 MPa.....  0            0            4            280          6600         24600
Density [g/cm3].....................  3.984(2)     3.943        3.891        3.868        3.845        3.834
Elastic Modulus [GPa]...............  416(30)      390          364          354          343          338
Flexural Strength [MPa].............  380(50)      375          345          300          210          130
Fracture Toughness [MPa m1/2]........  3.5(5)       3.0          2.7          2.6          2.5          2.5
 for crack length of 300 µm
Friction Coefficient [] at 2 GPa....  0.40(5)      0.8          0.4
Hardness (Vickers, 1 kg) [GPa]......  15(2)        8.5          4.6          3.7          2.9          2.5
Lattice Parameter a(hexagonal) [Å]..  4.761(3)     4.777        4.797        4.806        4.815        4.820
Lattice parameter c(hexagonal) [Å]..  12.991(7)    13.040       13.102       13.129       13.156       13.169
Poisson's Ratio []..................  0.231(1)     0.237        0.244        0.247        0.250        0.252
Shear Modulus [GPa].................  169(1)       158          146          142          137          135
Sound Velocity, longitudinal [km/s].  11.00(30)    10.77        10.54        10.44        10.35        10.30
Sound Velocity, shear [km/s]........  6.51(20)     6.33         6.14         6.06         5.97         5.93
Specific Heat [J/kg·K]..............  755(15)      1165         1255         1285         1315         1330
Tensile Strength [MPa]..............  267(30)      267          243          140          22           13
Thermal Conductivity [W/m·K]........  33(2)        11.4         7.22         6.67         6.34         6.23
Thermal Diffusivity [cm2/s].........  0.111(20)    0.0251       0.0150       0.0136       0.0127       0.0124
Thermal Expansion from 0 °C [10-6K-1]  4.6(2)       7.1          8.1          8.3          8.5          8.6
Wear Coefficient (Log10) [] at 2 GPa  -6(1)       -4           -6            ...          ...          ...
Weibull Modulus []..................  11(4)        11           11           11           11           11
Weibull Characteristic Strength,[MPa] 395(25)      390          360          310          210          125