An Investigation Into Magnetic Properties, Sintering Shrinkage Characteristics, and Formability of Isotropic Barium Ferrite Permanent Magnets

In this study, traditional ceramic process was used to prepare isotropic barium-based ferrite permanent magnets. The lower grade iron oxide powder (Fe ₂ O ₃ ) manufactured by China Steel Corporation (CSC) was used as the main raw material to prepare calcined magnetic powders with different Fe ₂ O ₃ /BaCO ₃ mole ratios (5.3–5.65). It can be seen from the experimental results that the remanence ( $B_{\mathrm {r}}$ ) decreases with the increase of mole ratio, but the intrinsic coercivity ( $_{\mathrm {i}}H_{\mathrm {c}}$ ) shows the opposite trend. On the other hand, the sintering radial shrinkage rate (Sh-D) and sintering height shrinkage rate (Sh-H) both decrease as mole ratio increases, but the required molding pressure is higher. On condition of Fe ₂ O ₃ /BaCO ₃ mole ratio = 5.4, Fe ₂ O ₃ = 81.38 wt%, BaCO ₃ = 18.62 wt%, the magnetic properties of the final sintered magnet can reach: $B_{\mathrm {r}}$ > 2250 G, $_{\mathrm {b}}H_{\mathrm {c}}$ > 1950 Oe, $_{\mathrm {i}}H_{\mathrm {c}}$ > 3300 Oe, ( BH ) _max > 1.15 MGOe, which are obtained on the basis without expensive lanthanum and cobalt. In terms of the operability, the sintering shrinkage rate Sh-D < 15.1% and required molding pressure of magnetic powder < 2.5 ton/cm ² both meet the specifications of the permanent magnet industry. Above results successfully overcome high-cost technical bottlenecks in the past in order to achieve high characteristics and formability, and comprehensively improve magnetic properties, operability, and production efficiency. The low-cost isotropic barium-based ferrite permanent magnets with good magnetic properties and operability realized in this work have been practically used in high-efficiency small automobiles motors, such as electric rearview mirror motor.