Kenji Noguchi

High-performance alloyed In metal-bonded magnets produced from Zn/Sm2Fe17Nx powders

Alloyed In metal-bonded magnets with ρ=∼6.5 g cm−3 were molded from surface-coated fine powders, Zn/Sm2Fe17Nx (x=∼3), under conditions of 1.4 GPa, ∼460 K, and 1.4 MA m−1 by adding an appropriate amount of In metal powder. The resulting In–Zn alloy with an eutectic composition served as the metal binder and the lowered melting point was responsible for improving the effective alignment of the Sm2Fe17Nx particles along a direction of the applied magnetic field for the bonded magnets. The following high-performance magnetic characteristics were attained: (BH)max=∼151 kJ m−3, Br=∼0.96 T, and Hcj=∼0.72 MA m−1. In–Zn metal-bonded Sm2Fe17Nx magnets showed good thermal stability, good oxidation resistance, and high densification due to effective surface coating by the In–Zn eutectic alloy. The temperature dependence of reversible flux losses measured over temperatures from 273 to 393 K provided a thermal coefficient of α(Br)=−0.06 % K−1.

High-performance resin-bonded magnets produced from zinc metal-coated Sm2(Fe0.9Co0.1)17Nx fine powders

Fine powders of Sm2(Fe0.9Co0.1)17Nx (x=∼3) with particle sizes (d) around 1 μm as coated with zinc metal produced via the photodecomposition of diethylzinc [Zn(C2H5)2], which still provided high remanence (Br) and coercivity (Hcj) values of ∼1.43 T and ∼0.85 MAm−1, were molded to compression-type resin bonded Zn/Sm2(Fe0.9Co0.1)17Nx magnets with density values of ∼6.33 g cm−3. By optimizing the preparation conditions such as grinding, surface coating, and molding for them, the highest maximum energy product of (BH)max=186 kJm−3 for Hcj=0.73 MAm−1 was recorded among all kinds of the Sm–Fe–N based magnets reported to date. Furthermore, the excellent aging behavior of the bonded Zn/Sm2(Fe0.9Co0.1)17Nx magnets was observed after standing in air at ∼393 K and the thermal coefficient for permanent magnet was evaluated to be α(Br)=−0.04% K−1.

High-Performance Epoxy-Resin-Bonded Magnets Produced from the Sm2Fe17Nx Powders Coated by Copper and Zinc Metals

Fine powders of Sm2Fe17Nx coated with copper metal reduced from CuCl2 and/or zinc metal subsequently derived by photo-decomposition of diethylzinc [Zn(C2H5)2] were prepared, and their magnetic properties were characterized in addition to those of epoxy-resin-bonded magnets produced from the coated powders (Cu/Sm2Fe17Nx, Zn/Sm2Fe17Nx and Zn/Cu/Sm2Fe17Nx). The remanence (Br) and maximum energy product [(BH)max] of double metal-coated Zn/Cu/Sm2Fe17Nx powders were maintained at higher levels than those of single Zn metal-coated Sm2Fe17Nx ones (Zn/Sm2Fe17Nx) even after heat treatment at 673 K since the oxidation resistance and thermal stability were effectively improved by formation of the thick and uniform protection layer on the surface of Sm2Fe17Nx particles. Moreover, the epoxy-resin-bonded magnets produced from the Zn/Cu/Sm2Fe17Nx powders possessed good corrosion resistance in air at 393 K which it resulted in the smaller thermal irreversible flux loss than that of uncoated and single Zn metal-coated Sm2Fe17Nx powders in the temperature range of above 393 K.