Hard Ferrite Magnets
Hard ferrite magnets are manufactured from iron oxide and either barium carbonate or strontium carbonate. The raw materials are mixed in the correct proportions, granulated, and calcined (presintered). After going through several intermediate phases, a hexaferrite phase (BaFe12O19 or SrFe12O19) is achieved. The presintered granulate is ground to a powder. It can then be pressed wet or dry in a magnetic field (anisotropic) or in the absence of a magnetic field (isotropic) and sintered. Hard ferrites are ceramic materials, with the mechanical hardness and brittleness typical of ceramics. A typical way of processing them is by grinding with diamond discs.
History
Development: End of the 1940s
Use: Beginning of the 1950s
Production begins at MS-Schramberg
1963
Raw material availability
The essential components of hard ferrite magnets are iron oxide and either barium carbonate or strontium carbonate. Iron oxide and the alkali earth elements barium and strontium occur in nature in sufficient abundance. Iron oxide is also a by-product of industrial steel processing.
Raw material sources
Iron oxide and alkali earths: From nature by open pit mining, iron oxide industrially. Warm rolled steel sheet is pickled. The iron chloride from the pickling is then converted to iron oxide. The alkali earths are industrially converted to barium carbonate and strontium carbonate.
Type of material
Ceramic material
Manufacturing process
Pressing and sintering in oxidising atmosphere.
Application areas and particular properties
Hard ferrite magnets have these advantages:
- economical raw materials
- very good resistance against corrosion and chemicals
- easy to magnetise
