Relation between oxidation microstructure and the maximum energy product loss of a Sm ₂Co ₁₇ magnet oxidized at 500 °c

The oxidation microstructure and maximum energy product (BH) _max loss of a Sm(Co _0.76, Fe _0.1, Cu _0.1, Zr _0.04) ₇ magnet oxidized at 500 °C were systematically investigated. Three different oxidation regions were formed in the oxidized magnet: a continuous external oxide scale, an internal reaction layer, and a diffusion zone. Both room-temperature and high-temperature (BH) _max losses exhibited the same parabolic increase with oxidation time. An oxygen diffusion model was proposed to simulate the dependence of (BH) _max loss on oxidation time. It is found that the external oxide scale has little effect on the (BH) _max loss, and both the internal reaction layer and diffusion zone result in the (BH) _max loss. Moreover, the diffusion zone leads to more (BH) _max loss than the internal reaction layer. The values of the oxidation rate constant k for internal reaction layer and oxygen diffusion coefficient D for diffusion zone were obtained, which are about 1.91×10 ^-10 cm ²/s and 6.54×10 ^-11 cm ²/s, respectively.