Ferrite (ceramic) magnets
Hardferrite (ceramic) magnets consist of ca. 80% of iron oxide and 20% of barium (BaO•6Fe2O3) or strontium (SrO•6Fe2O3) oxide. These raw materials are available in big quantities, so magnets made of them are cost effective. Basic manufacture process is pressing, there are two processes - isotropic ferrite magnets are made applying "dry" process, while anisotropic ferrites are made by "wet" process.
Isotropic magnets have the same magnetic properties in all directions, can be magnetized easily in any direction, but the energy product is low. Anisotropic magnets are pressed in magnetic field and keep prefered magnetization direction. Remanence and energy product of anisotropic magnets is much higher than isotropic magnets.
Ferrite magnets are hard, brittle and sensitive to crack. Machining is possible by grinding with diamond tools or cutting by water jet.
Ferrite magnets are corrosion resistant in ambient environment, against weak acids, oils and solvents. Ferrites are not sensitive to external demagnetizing fields, magnetic properties remain constant in wide temperature range from -40°C to +250°C. Small cracks and stripping is normal for ferrite magnets and this wearing does not have any effect on magnetic properties, functionality and holding force.
Table of magnetic properties of ferrite magnets:
|Coercivity Hc (kA/m)||
Max. energy product
Max. working temp.
|Normal Hcb||Intrinsic Hci|
|izotrop||0.20 - 0.24||125 - 160||210 - 280||6.5 - 9.5||<= 250|
|Y30BH||0.38 - 0.39||223 - 235||231 - 245||27.0 - 30.0||<= 250|
|Y35||0.40 - 0.41||175 - 195||180 - 200||30.0 - 32.0||<= 250|
Other magnetic and mechanic parameters of ferrite magnets:
|Temp. coefficient of Br (%/°C)||Temp. coefficient of Hci (%/°C)||Magnetizing field (kA/m)||Curie temp. (°C)||Density (g/cm3)||Hardness (Hv)|
|- 0.2||+ 0.4||> 800||450||4.9||500|