Aluminium Oxide – AL₂O₃

Alumina is one of the most versatile materials processed by Agate Products Ltd. We are able to supply it in a number of grades and carry a large inventory of `as-fired` parts in order to be in a position to give our customers a fast turnaround. Most commonly stocked grades are 99.5% in plate and disc form and 99.7% as rods or tubes.

We also carry stock of 96% Tape Cast substrates mainly of 1mm thickness. Parts with 99.8% purity can be supplied if required. All our precision Alumina Spheres are supplied in this high grade of material and range in size from Ø0.50mm to Ø19.00mm.  Larger spheres can be made on request.

Alumina is a polycrystalline material whose crystals are usually between eight and twelve microns in size, though material with crystals as small as four microns is available on request. It has numerous applications and is used in many different industries including the Semiconductor, Medical, Ultra High Vacuum, Electronic and Electrical fields.

Main Characteristics

  • High mechanical strength (over 400 MPa)
  • Good electrical insulation (up to 1×1015 Ohm/cm)
  • High compressive strength (up to 3000 MPa)
  • Very Hard (>16GPa)
  • High no load operating temperature (>1300°C)
  • Density (±3.8g/cm³)
  • Good corrosion and wear resistance
  • Thermally stable
  • Thermal conductivity up to 30W/mK

The values listed may vary slightly depending on the grade and type of alumina selected.

Most of the alumina that we machine is fully dense and can be susceptible to thermal shock. Porous material, better suited for conditions that involve thermal shock, is also available.


Discs, plates and rings can generally be supplied to any given thickness to meet our customer’s requirements, even sometimes ground to as thin as 0.10mm (depending on size).

We carry stock of tubes as small as 0.6mm OD x 0.4mm ID and can supply items as large as 500mm diameter as relatively thin rings or long tubes.

Many intricate shapes are produced using Cylindrical Grinding, Surface Grinding, Drilling and CNC machining techniques.

A general machining tolerance of +/- 0.10mm is easily achievable and, with extra care, tolerances as low as +/- 0.01mm are achievable depending on the size and shape of the component.

Most ground surfaces are within 0.5µm RA but both cylindrical and flat surfaces can be polished to within 0.02µm RA (grade of material depending).

Parts for subsequent metalising are clean fired to 1,300⁰C and supplied wrapped in acid free tissue using special handling equipment.

We are able to supply small batch quantities for R & D work as well as large volumes of Alumina parts for ongoing production requirements.

Typical Properties of 96% and 99.5% Alumina

Property Unit 96% 99.5%
Flexural Strength @ 20°C MPa 358 379
Compressive Strength @ 20°C MPa 2068 2600
Hardness GPa 11.5 14.1
Tensile Strength @ 25°C MPA 221 262
Fracture Toughness K(Ic) MPa mE0.5 4-5 4-5
Thermal Conductivity @ 20°C W/mK 24.7 30.0
Coefficient of Thermal Expansion 25-1000°C 1x10E-6/°C 8.2 8.2
Dielectric Strength ac-kV/mm 8.3 8.7
Volume resistivity @ 25°C ohm-cm >10E14 >10E14

Please contact Agate Products Ltd for values of grades not listed above.