Method for classifying articles and method for fabricating a magnetocalorically active working component for magnetic heat exchange

1. A method for classifying articles comprising magnetocalorically active material according to magnetic transition temperature, comprising:

providing a source of articles to be classified, the source comprising articles comprising magnetocalorically active materials having differing magnetic transition temperatures, wherein the articles comprise one or more of a La(Fe 1-b Si b ) 13 -based phase, a Gd 5 (Si, Ge) 4 -based phase, a Mn (As, Sb)-based phase, a MnFe (P, As)-based phase, a Tb—Gd-based phase, a (La, Ca, Pr, Nd, Sr)MnO 3 -based phase, a Co—Mn—(Si, Ge)-based phase and a Pr 2 (Fe, Co) 17 -based phase;

sequentially applying a magnetic field at differing temperatures to the source, the magnetic field being sufficient to exert a magnetic force on the source that is greater than the inertia of a fraction of the articles causing the fraction of the articles to move and thereby produce an article fraction for each temperature at which a magnetic field is applied, wherein the sequentially applying a magnetic field at differing temperatures comprises placing the source in a thermally conductive container, and altering the temperature of the container to thereby alter the temperature of the source by thermal conduction, and

collecting the article fraction at each temperature at which a magnetic field is applied to provide a plurality of separate article fractions of differing magnetic transition temperature, thereby classifying the articles comprising magnetocalorically active material according to magnetic transition temperature.

2. The method according to claim 1 , wherein the sequential applying a magnetic field at differing temperatures to the source comprises:

setting the temperature of the source at a temperature T 1 corresponding to a first desired magnetic transition temperature T trans1 ,

applying a magnetic field to the source, causing a first article fraction within the source having a magnetic transition temperature of T trans1 ±3° C. to be magnetically attracted to the magnet and removed from the source, and

collecting the first article fraction.

3. The method according to claim 2 , wherein the sequentially applying a magnetic field at differing temperatures to the source further comprises:

altering the temperature of the source to a temperature T 2 corresponding to a second desired magnetic transition temperature T trans2 , wherein T trans2 ≠T trans1 ,

applying a magnetic field to the source, thereby causing a second article fraction within the source having a magnetic transition temperature of T trans2 ±3° C. to be magnetically attracted to the magnet and removed from the source, and

collecting the second article fraction.

4. The method according to claim 3 , wherein 0.5° C.≦|T 2 −T 1 |≦5° C.

5. A method for classifying articles comprising magnetocalorically active material according to magnetic transition temperature, comprising:

providing a source of articles to be classified, the source comprising articles comprising magnetocalorically active materials having differing magnetic transition temperatures, wherein the articles comprise one or more of a La(Fe 1-b Si b ) 13 -based phase, a Gd 5 (Si, Ge) 4 -based phase, a Mn (As, Sb)-based phase, a MnFe (P, As)-based phase, a Tb—Gd-based phase, a (La, Ca, Pr, Nd, Sr)MnO 3 -based phase, a Co—Mn—(Si, Ge)-based phase and a Pr 2 (Fe, Co) 17 -based phase;

sequentially applying a magnetic field at differing temperatures to the source, the magnetic field being sufficient to exert a magnetic force on the source that is greater than the inertia of a fraction of the articles causing the fraction of the articles to move and thereby produce an article fraction for each temperature at which a magnetic field is applied, wherein the sequentially applying a magnetic field at differing temperatures comprises subjecting the source to a temperature gradient, moving the source along the temperature gradient to thereby alter the temperature of the source by thermal conduction and removing an article fraction from the source at different temperatures along the temperature gradient.

6. The method according to claim 5 , wherein the moving the source along the temperature gradient comprises:

moving the source along the temperature gradient from a higher temperature to a lower temperature, or from a lower temperature to a higher temperature.

7. The method according to claim 5 , wherein the moving the source along the temperature gradient comprises:

placing the source on a band which carries the source through the temperature gradient.

8. The method according to claim 7 , wherein the moving of the source along the temperature gradient comprises vibration of the band.

9. The method according to claim 7 , wherein the moving of the source through the temperature gradient is continuous and wherein the applying a magnetic field comprises applying at intervals along the band, wherein the source has a different temperature at each interval.

10. The method according to claim 1 , wherein the source is supported on a surface and the magnetic field is applied perpendicularly to the surface.

11. The method according to claim 1 , wherein the source is supported on a surface and the magnetic field is applied parallel to the surface.

12. The method according to claim 11 , further comprising rotating the magnetic field about an axis perpendicular to the surface.

13. The method according to claim 5 , wherein the temperature gradient lies in the range of 10° C./m to 200° C./m.

14. The method according to claim 1 , wherein the sequentially applying a magnetic field comprises applying a current to an electromagnet or applying a magnetic field from a permanent magnet.

15. The method according to claim 14 , further comprising positioning a first magnet adjacent a first side of the source.

16. The method according to claim 15 , further comprising positioning a further magnet adjacent the opposing side of the source.

17. The method according to claim 1 , wherein the sequentially applying a magnetic field comprises applying a magnetic field of 0.003 T to 0.3 T or 0.01 T to 0.1 T.

18. The method according to claim 1 , wherein the sequential applying of a magnetic field comprises applying a magnetic field gradient to the source.

19. The method according to claim 18 , wherein the magnetic gradient is 0.5 T/m to 10 T/m.

20. The method according to claim 1 , wherein the magnetic field applied, B, is such that B≧J s /3, where J s is the saturation polarization.

21. The method according to claim 1 , wherein the articles have a maximum diameter of 2 mm.

22. The method according to claim 1 , wherein the articles are particles having a diameter within the range of 50 μm to 750 μm.

23. The method according to claim 1 , further comprising securing an article fraction on a removal surface.

24. A method of fabricating a magnetocalorically active working component for magnetic heat exchange, comprising:

classifying articles comprising magnetocalorically active material according to the method of claim 1 thereby producing a plurality of particle fractions having differing average magnetic transition temperatures, and

arranging the particle fractions in order of increasing or decreasing average magnetic transition temperature and producing a magnetocalorically active working component for magnetic heat exchange.

25. The method according to claim 24 , further comprising compacting a first particle fraction before arranging a further particle fraction on the first particle fraction.

26. The method according to claim 25 , further comprising compacting the further particle fraction.

27. The method according to claim 24 , further comprising:

heat treating and sintering the particle fractions after the particle fractions are arranged in order of increasing or decreasing magnetic transition temperature to produce a sintered magnetocalorically active working component for magnetic heat exchange.

28. The method according to claim 24 , further comprising mixing the particles of the particle fraction with adhesive before compaction.

29. The method according to claim 28 , further comprising curing the adhesive after compaction.

30. The method according to claim 28 , wherein the adhesive is cured at a temperature, T cure , of 0° C.<T cure <200° C.