Influence of Residual Carbon on Magnetic Properties of Sintered Sm-Co Magnets

Abstract

The addition of organic binder in a small amount improves the compressibility and compactibility of Sm-Co magnet alloy powders. However, impurity carbon which comes from the binder is thought to lower magnetic properties of the sintered magnets. In this study, the relationships between the resid-ual carbon content and magnetic properties in SmCo₅ and Zr containing Sm₂ Co₁₇ magnets have been studied varying the amount of the binder. Effects of thermal debinding atmosphere on binder removal have been also investigated. When the green compacts were debound in vacuum atmosphere, the carbon content of the magnets increased with increase of the binder addition, which decreased coercivities of the magnets markedly. It was observed that carbon forms SmCoC₂ and ZrC carbides in SmCo₅ and Sm₂Co₁₇ magnets respectively. Thermal debinding treatment in hydrogen atmosphere was found to be very effective for removing the binder and reducing the carbon content in the mag-nets. In the binder addition ranges of the present study, the magnets produced through use of this debinding treatment have exhibited nearly the same magnetic properties as those of the magnets made from the powders without the binder.