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

Abstract

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 °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 °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 °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 α-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 °C.