Chemical Formula

Al2O3
Topics Covered

Background

Different Types of Alumina

Properties of Alumina

Key Properties of Dynallox Alumina

Physical Properties

Mechanical Properties

Thermal Properties

Electrical Properties
Background

Alumina is the most mature of the engineering ceramics, offering excellent electrical insulation properties together with high hardness and good wear resistance but relatively low strength and fracture toughness.

Different Types of Alumina

Aluminas are generally white but are sometimes pink (88% alumina) or brown (96% Alumina). The colour is derived from either the sintering additives or impurities in the raw materials. Dynamic-Ceramic produces a range of alumina from 96% - 99.9% purity.
Properties of Alumina

Alumina has a high melting point, high hardness and high mechanical strength, although mechanical strength is reduced at temperatures above 1000°C. Due to the relatively large coefficient of thermal expansion, thermal shock resistance is reduced.

Alumina is an electrically insulating material, with a high electrical resistivity, increasing with purity.

Good chemical stability of alumina, leads to a high corrosion resistance. It is insoluble in water and only slightly soluble in strong acid and alkaline solution.
Key Properties of Dynallox Alumina
Physical Properties

Typical physical properties of Dynallox alumina from Dynamic Ceramic.




Units


Dynallox Z


Dynallox 94


Dynallox 95


Dynallox 96


Dynallox 99


Dynallox 100

Nom. Comp.





-


94% Al2O3


95% Al2O3


96% Al2O3


99.5% Al2O3


99.9% Al2O3

Density


g/cm3


4.6


3.69


3.67


3.67


3.89


3.92
Mechanical Properties

Typical mechanical properties of Dynallox alumina from Dynamic Ceramic.




Units


Dynallox Z


Dynallox 94


Dynallox 95


Dynallox 96


Dynallox 99


Dynallox 100

Flexural Str @ 20°C


MPa


900


330


330


360


330


350

Flexural Str @ 800°C


MPa


-


240


240


250


250


250

Comp Str


MPa


2500


2100


2100


2100


2100


2500

Mod of Elasticity


GPa


330


275


275


275


330


350

Hardness


R45N


85


78


80


81


83


84

Hardness


Hv0.3


1650


1500


1550


1590


1600


1700

Fracture Toughness (K1C)


MPa½


7.3


3.5


3.6


3.5


4.0


4.5
Thermal Properties

Typical thermal properties of Dynallox alumina from Dynamic Ceramic.




Units


Dynallox Z


Dynallox 94


Dynallox 95


Dynallox 96


Dynallox 99


Dynallox 100

Max. Use Temp.


°C


1500


1500


1450


1700


1800


1725

Therm Exp Co-Eff.


X10-6 /°C


8


8.1


8.3


7.8


8.4


8.5

Therm. Cond


W/m.K


17


19


22.5


25


29


28

Thermal Shock Resist


°C





200


200


200


200


220
Electrical Properties

Typical electrical properties of Dynallox alumina from Dynamic Ceramic.




Units


Dynallox Z


Dynallox 94


Dynallox 95


Dynallox 96


Dynallox 99


Dynallox 100

Resistivity 25°C


Ohm.cm


>1014


>1014


>1015


>1014


>1014


>1014

Resistivity 300°C


Ohm.cm


1013


9x1011


5x109


3.1x1011


1.6x1013




Resistivity 500°C


Ohm.cm


3x1013


2.5x109


4x107


4x109


2.1x1010


1012

Resistivity 700°C


Ohm.cm





5x109


2.5x106


1.0x108


4.4x108




Resistivity 1000°C


Ohm.cm





5x105





1x106





106