Abstract
SmCo5 sintered magnets are vital for a wide variety of high-temperature applications, such as permanent magnet motors and actuators within the aerospace industry. They benefit these applications through their high coercivity values, usually > 2000 kA/m, their high Curie temperatures of ̴ 800 ˚C and their low thermal coefficients of remanence and coercivity.
However, these magnets use vast amounts of Sm and Co, both of which have been deemed ‘critical materials’ of which there is a short supply in the UK and EU. Volatile pricing and shipping lead times have directed research towards methods with which to recycle these materials. One process that could be used as a starting point for recycling SmCo5 magnets is hydrogen decrepitation (HD).
This process involves exposing SmCo5 magnets to hydrogen at room temperature which then allows the hydrogen to diffuse into the material at the Sm-rich grain boundary phase and into the hexagonal SmCo5 matrix phase. The differential volume expansion caused by the formation of the orthorhombic hydride phase within the matrix generates intergranular and transgranular cracking of the brittle material. The powder generated can then be degassed, milled, aligned, pressed and finally sintered/heat treated to form a recycled compact.
Multiple factors during the post HD processing of SmCo5 will influence both the final density and magnetic properties of the sintered material. This study primarily looks at the effects of different milling and pressing parameters on the recycled sintered magnets using only the HD material. Smaller particle sizes and narrower particle distributions tend to generate magnets with improved magnetic properties; in some cases exceeding the as-received material. Greater pressing forces led to marginal improvements in recycled magnet density and magnetic properties.
Further work in this area will explore the impact of Sm-rich milled additions on recycled magnet density and magnetic properties.
However, these magnets use vast amounts of Sm and Co, both of which have been deemed ‘critical materials’ of which there is a short supply in the UK and EU. Volatile pricing and shipping lead times have directed research towards methods with which to recycle these materials. One process that could be used as a starting point for recycling SmCo5 magnets is hydrogen decrepitation (HD).
This process involves exposing SmCo5 magnets to hydrogen at room temperature which then allows the hydrogen to diffuse into the material at the Sm-rich grain boundary phase and into the hexagonal SmCo5 matrix phase. The differential volume expansion caused by the formation of the orthorhombic hydride phase within the matrix generates intergranular and transgranular cracking of the brittle material. The powder generated can then be degassed, milled, aligned, pressed and finally sintered/heat treated to form a recycled compact.
Multiple factors during the post HD processing of SmCo5 will influence both the final density and magnetic properties of the sintered material. This study primarily looks at the effects of different milling and pressing parameters on the recycled sintered magnets using only the HD material. Smaller particle sizes and narrower particle distributions tend to generate magnets with improved magnetic properties; in some cases exceeding the as-received material. Greater pressing forces led to marginal improvements in recycled magnet density and magnetic properties.
Further work in this area will explore the impact of Sm-rich milled additions on recycled magnet density and magnetic properties.
| Original language | English |
|---|---|
| Publication status | Unpublished - 4 Sept 2023 |
| Event | 27th International Workshop on Rare Earth and Future Permanent Magnets and their Applications - University of Birmingham, Birmingham, United Kingdom Duration: 3 Sept 2023 → 7 Sept 2023 https://uobevents.eventsair.com/repm2023/ |
Conference
| Conference | 27th International Workshop on Rare Earth and Future Permanent Magnets and their Applications |
|---|---|
| Abbreviated title | REPM 2023 |
| Country/Territory | United Kingdom |
| City | Birmingham |
| Period | 3/09/23 → 7/09/23 |
| Internet address |