METHOD FOR PRODUCING A RARE EARTH-BASED MAGNET

1 . A method for producing a rare earth-based magnet, comprising:

providing a precursor sintered R 2 Fe 14 B-type magnet,

applying particles comprising a rare earth element R′ to a first surface of the precursor sintered magnet,

applying particles of a further material to the first surface of the precursor sintered magnet and/or a further surface of the precursor sintered magnet,

heat treating the precursor sintered magnet at a temperature T and for a time t selected to allow diffusion of the rare earth element R′ into the precursor sintered magnet and producing a magnet, wherein the further material remains solid and particulate after the heat treating.

2 . The method according to claim 1 , further comprising

providing a plurality of precursor sintered R 2 Fe 14 B-type magnets,

applying the particles comprising the rare earth element R′ to the first surface of the precursor sintered magnets,

applying the particles of the further material to the first surface of the precursor sintered magnets and/or a further surface of the precursor sintered magnets,

arranging the plurality of precursor sintered magnets such that the particles of the rare earth element R′ and the particles of the further material are positioned between adjacent precursor sintered magnets,

heat treating the plurality of precursor sintered magnets at a temperature T and for a time t selected such that the rare earth element R′ diffuses into the precursor sintered magnets and such that after the heat treating adjacent magnets remain unbonded to one another.

3 . The method according to claim 2 , wherein

the plurality of precursor sintered magnets are arranged such that a surface of the precursor sintered magnets is in contact with the particles of the rare earth element R′ applied to an adjacent precursor sintered magnet.

4 . The method according to claim 2 , wherein

the plurality of precursor sintered magnets is arranged in a row such that particles of the rare earth element R′ and particles of the further material are positioned between adjacent precursor sintered magnets of the row,

heat treating the plurality of precursor sintered magnets whilst arranged in the row at a temperature T and for a time t selected such that the rare earth element R′ diffuses into the sintered precursor magnets and such that after the heat treating adjacent magnets of the row remain unbonded to one another.

5 . The method according to claim 4 , wherein

the particles of the rare earth element R′ and the particles of the further material are applied to the first surface and the plurality of precursor sintered magnets are arranged such that a surface of the precursor sintered magnets is in contact with the particles of the rare earth element R′ applied to an adjacent precursor sintered magnet of the row.

6 . The method according to claim 1 , further comprising

applying the particles comprising the rare earth element R′ to a second surface of at least one of the precursor sintered magnets, the second surface opposing the first surface, and

applying particles of the further material to the second surface of the at least one precursor sintered magnet.

7 . The method according to claim 6 , wherein the plurality of precursor sintered magnets is arranged in a row such that the outermost side surfaces of the endmost precursor sintered magnets of the row comprise particles of the rare earth element R′ and particles of the further material.

8 . The method according to claim 1 , wherein

the particles comprising the rare earth element R′ and the particles of the further material are applied to three or more surfaces of the at least one precursor sintered magnet.

9 . The method according to claim 1 , wherein

a substrate is provided, the particles of the further material and, optionally, the particles of the rare earth element R′ are placed on the substrate and the precursor sintered magnets are placed on the particles of the further material arranged on the substrate.

10 . The method according to claim 1 , wherein

the rare earth element R of the precursor sintered magnet is different from the rare earth element R′.

11 . The method according to claim 1 , wherein

the rare earth element R′ is Dy and/or Tb.

12 . The method according to claim 1 , wherein

the rare earth element R′ is applied in the form of a hydride or an alloy or a hydrogenated alloy.

13 . The method according to claim 1 , wherein

0.01 wt % to 2 wt % or 0.1 wt % to 0.6 wt % of the rare earth element R′ is applied to the first surface of the precursor sintered magnet.

14 . The method according to claim 1 , wherein

a volume ratio of the rare earth element R′ to the further material is between 20 to 1 and 1 to 10.

15 . The method according to claim 1 , wherein

the precursor sintered magnet has a coercive field strength of H c and the temperature T and the time t are selected such that after the heat treating the magnet has a coercive field strength of at least H c +1 kOe.

16 . The method according to claim 1 , wherein the temperature T lies within the range of 700° C. to 1100° C. and the time t lies within the range of 0.1 to 100 hours.

17 . The method according to claim 1 , wherein

the further material is an oxide.

18 . The method according to claim 17 , wherein

the further material is an oxide of a rare earth element R″ where R″ is different from R and R′.

19 . The method according to claim 17 , wherein

the further material is an oxide of the rare earth element R.

20 . The method according to claim 19 , wherein

the further material is Nd 2 O 3 .

21 . The method according to claim 1 , wherein

the first surface is an as sintered surface.

22 . The method according to claim 1 , wherein

the second surface is an as-sintered surface.

23 . The method according to claim 1 , wherein

the particles of the rare earth element R′ and the particles of the further material are intimately mixed with one another and applied to the first surface and optionally to one or more further surfaces of the precursor sintered magnets in the form of a single layer.

24 . The method according to claim 23 , wherein

the particles of the rare earth element R′ and the particles of the further material are mixed with at least one liquid or organic substance to form a suspension or a paste and the suspension or the paste is applied to the first surface and optionally to one or more further surfaces of the precursor sintered magnet.

25 . The method according to claim 23 , wherein

the particles of the rare earth element R′ are mixed with at least one liquid or organic substance to form a first suspension or a first paste and the particles of the further material are mixed with at least one liquid or organic substance to form a second suspension or a second paste and the first suspension or the first paste and the second suspension or the second paste are applied as separate layers to the first surface and optionally to one or more further surfaces of the precursor sintered magnet.

26 . The method according to claim 1 , wherein

before being heat treated at temperature T, a drying treatment is performed.

27 . The method according to claim 1 , wherein

one or more metals and/or one or more alloys and/or one or more metal hydrides and/or one or more hydrogenated alloys are applied to the first surface and optionally one or more further surfaces.

28 . The method according to claim 1 , wherein

Al, and/or Ni and/or copper or their alloys is applied to the first surface and optionally one or more further surfaces.

29 . The method according to claim 24 , wherein

one or more binders and/or one or more dispersants is added to form the paste.

30 . The method according to claim 24 , wherein

the paste comprises Nd 2 O 3 , fumed silica and 3-methoxy-1-butanol.

31 . The method according to claim 24 , wherein

the paste is applied by painting or screen printing or doctor-blading or gravity or dipping or roller application or spraying.

32 . The method according to claim 1 , wherein

after the heat treating, the magnets are separable from the adjacent magnets by applying a predetermined force between the adjacent magnets.

33 . The method according to claim 1 , wherein

after the heat treating the magnet comprises a content of the rare earth element R′ having a distribution that varies from the first surface in directions towards a centre of the magnet.

34 . The method according to claim 1 , wherein the rare earth element R′ content is highest at the first surface and decreases in directions towards the centre of the magnet.