Hard Ferrite (ceramic) magnets, composed of barium or strontium, were developed in the early 1960's as an alternative to the more expensive metallic magnets. This class of magnet is very hard, brittle and possesses lower energy characteristics compared to other magnetic materials. However, it is very popular and widely used because of its excellent resistance to demagnetization, corrosion, and the advantageous pricing.
Sintering, or injection molding manufactures ferrite magnets. These magnets can be both anisotropic and isotropic. Anisotropic grades are oriented in the manufacturing direction and must be magnetized in the direction of orientation. Isotropic grades are not oriented and can be magnetized in any direction.
Ceramic magnets retain about 45% of their room-temperature magnetic specifications at 350 °F. Degradation with increasing temperature is nearly linear, and changes in magnetization are essentially reversible up to approximately 840 °F, at which temperature ceramic magnets become completely demagnetized. Ceramic magnets exposed to temperatures up to 1800 °F can be remagnetized for continued use. However, changes are irreversible above 1800 °F.
Ceramic 5 magnets are the most commonly used and must be magnetized in the direction of their orientation.
Ceramic 8 magnets are used for their excellent peak energy product and greater resistance to demagnetization than Ceramic 5 magnets. They also must be magnetized in the direction of their orientation. Ceramic 8 is an excellent choice wherever magnet length is at minimum or where the magnetic circuit is subject to severe demagnetizing field. See table below for grades and properties of Ceramic magnets.
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