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Aluminium oxide – Al2O3

Aluminium oxide or alumina is the most commonly used technical ceramic. The material is available in various purities, depending on the specific application. The percentage of alumina typically lies between 92-99,7% Al2O3, the remaining percentage consists of SiO2, CaO, Na2O and Fe2O3.

 

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The reason for its favoured position is its price, technical properties and variety of production methods. The use of alumina can be very cost effective if its characteristics are used in the right way and by choosing the right production method.

Aluminium oxide

The most widely used material for ceramic insulators.

Key characteristics
  • Heat resistance
  • High wear resistance
  • Electrical insulation
  • High compressive strength
  • Relatively low cost
Applications
  • Electrical insulators
  • Crucibles
  • Plungers
  • Bearings
  • Nozzles
  • Vacuum parts
The first step is always powder preparation where the powder is mixed with a binder so that it can be formed. After powder preparation, the part is formed by pressing, casting or injection moulding. The green product can be machined for rough dimensions before being placed in the furnace. The first process in the furnace is called debinding, where the binder is burned out of the form to make the part ready for sintering. The part is then sintered at a high temperature to create the final form. After this stage, machining is only possible by grinding.
For small quantities, it may be worth investigating whether products can be machined out of standard products available in the market, e.g., products from tubes or substrates. For larger quantities and more complex products, the right forming process has to be selected to produce the parts in the most cost-effective way.
High-tech precision parts are usually made out of 99.7% alumina, because the price of the material has limited influence on the price of the end product and the requirements are high. For large products with less stringent demands (e.g., anti-wear applications), alumina with a percentage between 92%-96% is chosen. There are, of course, exceptions for cases where a certain percentage of alumina is beneficial to other processing steps.
In general, this is very similar to machining metals. Please note that machining ceramics is an expensive activity, so avoiding unnecessary machining has a direct influence on your pricing. If tolerances can be kept above ±0.1mm, they can be achieved by green machining injection moulded parts, which will make a big price difference.
The combination of the quantity and requirements will determine the most cost-effective production method. This requires a lot of experience and we can support you in this process. Do not hesitate to reach out to us.
In general, the ground alumina products have a surface roughness greater than Ra 1.6 µm. An Ra of 0.4 or 0.8 µm is in most cases possible, but will necessitate an additional machining step, adding to the costs.
Electrical properties
Mechanical properties
Thermal properties
Temperature application
Properties Density g/cm3 Porosity % Mechanical properties Hardness (Vickers) kg/mm2 Compressive strength N/mm2 Bending strength N/mm2 E-modulus kN/mm2 Weibull modulus m Fracture toughness K1c Mpam Coefficient of friction Thermal properties
(Max. use temperature) *in air ℃ *in inert atm. ℃ Thermal shock resistance Expansion coefficient *20C - 200C *20C - 600C *20C - 1000C Thermal conductivity at 20C W/mK Electrical properties (Resistivity) * at 20C ohm cm * at 400C ohm cm * at 1000C ohm cm
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