Thermal Aging of NdFeB Compression Molded Magnets

Compression moulded rare earth magnets are used in many applications, and one of them is in electrical motors, which can operate at temperatures as high as 150 °C. In high temperatures, oxidation and phase transformations may affect magnetic properties. Another issue to be considered is polymer degradation. In this paper cylindrical samples of a commercial ready-to-press raw material (MQPB+, Molycorp-Magnequench) were pressed to densities close to 5.50 g/cm3. These samples were cured (low temperature heat treatment) and thermal aged at 200 °C for 72 hours, under dynamic air. Physical characteristics (weight, dimensions and densities) and magnetic properties were measured at room temperature in a TCH2020 hysteresigraph (Globalmag). Degradation of magnetic properties was observed, and oxidation seems to be the main reason.