Alumina and Alumina Fibres - Properties and Applications - Supplier Data by Goodfellow

Background

Minerals containing Alumina represent some 15% of the earth’s crust. It is therefore an abundant material and virtually inexhaustable, unlike raw materials for many alloys developed for special applications.

Properties

The combination of high thermal conductivity, low thermal expansion and high compressive strength leads to good thermal shock resistance, so Alumina is suited to furnace use as crucibles, tubes and thermocouple sheaths.

High purity Alumina can be used up to 1700 °C and is gas tight up to 1300 °C. Few chemicals attack Alumina. It also shows good electrical insulation at high temperatures, good wear resistance and high hardness, making it suitable for components such as ball valves, piston pumps and deep drawing tools. Diamond tools are needed to machine or grind alumina.

Alumina Fibres

Remarkably, continuous filament yarns have been made from alumina with reasonable but not complete success and two, similar, versions are available from Goodfellow. They are both much less flexible than normal continuous filament yarns and are rather “hairy” i.e. have broken filaments - especially the FP version.

Applications

As mentioned above, alumina is used for applications including ball valves, piston pumps and deep drawing tools.

Typical Properties

The typical properties of alumina are tabulated below.

Table 1. Key properties of alumina

Chemical Resistance
Acids - concentrated Good
Acids - dilute Good
Alkalis Good
Halogens Good
Metals Good
Electrical Properties
Dielectric constant 9.0-10.1
Dielectric strength ( kV.mm-1 ) 10-35
Volume resistivity ( Ohm.cm ) >1014 @ 25 °C
Mechanical Properties
Compressive strength ( MPa ) 2200-2600
Hardness - Knoop ( kgf.mm-2 ) 2100
Hardness - Vickers ( kgf.mm-2 ) 1500-1650
Shear strength ( MPa ) 330
Tensile modulus ( GPa ) 300-400
Tensile strength ( MPa ) 260-300
Physical Properties
Apparent porosity ( % ) 0
Density ( g.cm-3 ) 3.9
Water absorption - saturation ( % ) 0
Thermal Properties
Coefficient of thermal expansion ( x10-6 K-1 ) 8.0 @ 20-1000 °C
Melting point ( °C ) 2100
Specific heat ( J.K-1.kg-1 ) 850-900 @ 25 °C
Thermal conductivity ( W.m-1.K-1 ) 26-35 @ 20 °C
Upper continuous use temperature ( °C ) 1700
Properties Alumina Fibre
Property Value
Coefficient of thermal expansion - Longitudinal x10-6 K-1 5.7
Density g.cm-3 3.9
Modulus GPa 380
Tenacity GPa 1.4

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