Sustainable ferrite permanent magnet fabrication: Recycling steel scale into high-performance strontium hexaferrite magnet

In this study, the production of strontium hexaferrite permanent magnets from powders obtained by mechanochemical synthesis and subsequent annealing of SrCO3 and rolled steel scale was investigated. By this method, the steel scale was transformed into a technological product. To obtain the strontium hexaferrite powders, SrCO3 and steel scale prepared in the stoichiometric ratio were subjected to mechanochemical synthesis for 16 h, followed by annealing at 975 degrees C for 1 h. Afterward, a green compact product was obtained with a pressure of 200 MPa and sintered for 1, 2, and 3 h in the temperature range of 900-1100 degrees C. As the sintering temperature and time increase, the particles tend to grow. The relative density of SrFe12O19 permanent magnets was increased from 85 % to 95.5 % with increasing sintering temperature and time. TEM analysis revealed that the disordered seen at the contact points of the particles disappeared after 3 h of sintering at 1100 degrees C. According to XRD analysis, it was determined that the dominant phase in the structure is the SrFe12O19 ferrimagnetic phase, with a small amount of alpha-Fe2O3 phase. The SrFe12O19 crystal size increased from 72.7 nm to 103.44 nm with increasing sintering temperature and time. The highest coercivity value of the permanent magnets, whose magnetic properties were examined in the vibrating sample magnetometer, was determined as 5526.59 Oe, permanent magnetization 35.89 emu/g and saturation magnetization 69.09 emu/g after 1 h sintering at 1100 degrees C.