Hydrogen Decrepitation and Spark Plasma Sintering to Produce Recycled SmCo5 Magnets With High Coercivity

The spark plasma sintering (SPS) technique is applied in combination with the hydrogen decrepitation process for the recycling of SmCo
₅
magnets. The SmCo
₅
magnets for recycling were first decrepitated by hydrogen gas at a pressure of 4 bar for 3 h to produce decrepitated powder. This powder was then used to prepare isotropic sintered magnets using the SPS technique by sintering at 800 °C-1000 °C for 1 min. Full densification of the SPS magnets was possible at a temperature of 1000 °C. The sample that was sintered at 900 °C showed the best internal coercivity (
_i
H
_c
) of higher than 1500 kA/m with a high remanence (
B
_r
) value of 0.47 T and energy product (
BH
_max
) of 43.4 kJ/m
³
. The properties of the SPS sample sintered at 900 °C are compared to the conventionally sintered (CVS) sample prepared by using fresh SmCo
₅
powder. The results show an improvement in the magnetic properties of the SPS sample in comparison to the CVS sample at room temperature, and the possibility to use the SPS sample at a high temperature of 180 °C, where the sample showed good magnetic properties of
_i
H
_c
of 1502 kA/m,
B
_r
of 0.44 T, and
BH
_max
of 36.4 kJ/m
³
. Microstructure and X-ray diffraction patterns of the SPS and the CVS samples show that they consist of a SmCo
₅
matrix with Sm
₂
Co
₇
and Sm oxides.