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

Abstract

Spark plasma sintering (SPS) technique is applied in combination with hydrogen decrepitation process for the recycling of SmCo5 magnets. The SmCo5 magnets for recycling were first decrepitated by hydrogen gas of a pressure of 4 bar for 3 hours to produce decrepitated powder. This powder was then used to prepare isotropic sintered magnets using the SPS technique, by sintering at 800-1000 oC for 1 minute. Full densification of the SPS-ed magnets was possible at a temperature of 1000 oC. The sample sintered at 900 oC showed the best internal coercivity (jHc) of higher than 1500 kA/m with high remanence (Br) value of 0.47 T and energy product (BH(max)) of 43.4 kJ/m3. The properties of the SPS-ed sample sintered at 900 oC were compared with conventionally sintered (CVS-ed) sample prepared by using fresh SmCo5 powder. The results showed the improvement of the magnetic properties of the SPS-ed sample in comparison to the CVS-ed sample at room temperature, and the possibility to use the SPS-ed sample at high temperature of 180 oC, where the sample showed good magnetic properties of jHc of 1502 kA/m, Br of 0.44 T and BH(max) of 36.4 kJ/m3. The microstructure and X-ray diffraction patterns of the SPS-ed and the CVS-ed samples were studied; where the samples showed to basically consist of SmCo5 matrix phase with Sm2Co7 and Sm-oxides.