What are ceramic magnets and how are they made?

What is a ceramic magnet?

Ceramic magnets (also known as ferrite magnets) were developed in the 1960’s as a low cost alternative to metallic magnets. They are composed of iron oxide and strontium carbonate. While their hard, brittle quality and low energy exclude them from some applications, ceramic magnets have won wide acceptance due to their corrosion and demagnetization resistance, and low price per pound. Ferrite represents more than 75 percent of world magnet consumption (by weight). It is the first choice for most types of DC motors, magnetic separators, magnetic resonance imaging and automotive sensors.

How are they made?

Ceramic magnets are manufactured using powder technology techniques. The primary raw material – ferrite – is made by using iron oxide and strontium carbonate. These materials are mixed together and then elevated in temperature to 1800-2000 degrees F. At this temperature they undergo a chemical conversion and the resulting material is ferrite.

The ferrite material is then reduced to a very small particle size by wet milling. The milled powder is then either dried (for dry pressed material) or injected into a die (in wet slurry form) in a large hydraulic press. The die is non-magnetic steel with carbide liners. The die cavities are the shape of the part to be pressed. 

The wet powder (slurry) is then compacted in the presence of a magnetic field. The water allows the flat ferrite particle to more easily align itself in the magnetic field. Most of the water is removed during the compaction process. The remaining water is evaporated during the initial stages of the sintering process. The sintering takes place at 2000 degrees F. approximately. After sintering the material is fully dense and ready for finish grinding to customer specifications. As the material is very hard and brittle, all of the grinding of ceramic magnets is done using diamond wheels.