Method of fabricating an article for magnetic heat exchanger

Abstract

A method of fabricating an article for magnetic heat exchange, is provided which comprises plastically deforming a composite body comprising a binder having a glass transition temperature TG and a powder comprising a magnetocalorically active phase or elements in amounts suitable to produce a magnetocalorically active phase such that at least one dimension of the composite body' changes in length by at least 10%.

Claims

1. A method of fabricating an article for magnetic heat exchange, comprising: plastically deforming a composite body comprising a binder having a glass transition temperature TG and a powder comprising a magnetocalorically active phase or elements in amounts suitable to produce a magnetocalorically active phase such that at least one dimension of the composite body changes in length by at least 10%, wherein the binder comprises a polypropylene carbonate, and the magnetocalorically active phase comprises La.sub.1-aR.sub.a(Fe.sub.1-x-yT.sub.yM.sub.x).sub.13H.sub.zC.sub.b wherein M is Si and, optionally, Al, T is one or more of the elements from the group consisting of Mn, Co, Ni, Ti, V and Cr and R is one or more of the elements from the group consisting of Ce, Nd, Y and Pr, wherein 0a0.5, 0.05x0.2, 0.003y0.2, 0z3 and 0b1.5.

2. The method according to claim 1, wherein the composite body is plastically deformed such that an elongated form is produced having a first dimension that is at least 1.5 times greater than a second dimension.

3. The method according to claim 1, wherein the composite body is plastically deformed such that an ellipsoid form is produced having a long axis that is at least 1.5 times greater than a shortest axis.

4. The method according to claim 1, wherein the plastically deforming the composite body comprises plastically deforming the composite body at a temperature T which is above the glass transition temperature TG of the binder.

5. The method according to claim 4, wherein T>TG+20K.

6. The method according to claim 1, wherein the plastically deforming the composite body comprises plastically deforming the composite body by rolling.

7. The method according to claim 6, wherein the rolling comprises passing the composite body between two rolls rotating in opposing directions.

8. The method according to claim 6, wherein the rolling comprises passing the composite body between two rolls rotating with differing speeds.

9. The method according to claim 1, wherein the plastically deforming the composite body comprises pressing a roller against a band, the surfaces of the roller and the band moving at substantially the same speed.

10. The method according to claim 1, wherein the plastically deforming the composite body comprises pressing a roller against a band, the surfaces of the roller and the band moving at differing speeds.

11. The method according to claim 1, wherein the composite body has a substantially cylindrical shape and the plastically deforming the composite body comprises treating the composite body in a spheronizer.

12. The method according to claim 1, wherein the plastically deforming the composite body comprises plastically deforming the composite body in an inert atmosphere.

13. The method according to claim 1, wherein the composite body comprises 0.1 weight percent to 10 weight percent binder.

14. The method according to claim 13, wherein the composite body comprises 0.5 weight percent to 4 weight percent binder.

15. The method according to claim 1, wherein the binder has a decomposition temperature of less than 300 C.

16. The method according to claim 15, wherein the binder has a decomposition temperature of less than 200 C.

17. The method according to claim 1, further comprising removing the binder from the composite body to form a green body, sintering the green body and producing an article for magnetic heat exchange.

18. The method according to claim 17, wherein the removing the binder is carried out at a temperature of less than 400 C.

19. The method according to claim 17, wherein the removing the binder is carried out in at least one of the group consisting of a noble gas, a hydrogen-containing atmosphere and a vacuum.

20. The method according to claim 17, wherein the removing the binder is carried out for 30 minutes to 20 hours.

21. The method according to claim 17, wherein at least 90% by weight of the binder is removed.

22. The method according to claim 21, wherein more than 95% by weight of the binder is removed.

23. The method according to claim 17, wherein the sintering is carried out at a temperature between 900 C. and 1200 C.

24. The method according to claim 23, wherein the sintering is carried out at a temperature between 1050 C. and 1150 C.

25. The method according to claim 17, wherein the sintering is carried out in a noble gas, a hydrogen containing atmosphere or a vacuum.

26. The method according to claim 17, wherein the green body for a total sintering time trot, wherein the green body is sintere in vacuum for 0.95t.sub.tot to 0.75t.sub.tot and subsequently in a noble gas or hydrogen-containing atmosphere for 0.05t.sub.tot to 0.25t.sub.tot.

27. The method according to claim 20, wherein the removing the binder is carried out for 2 hours to 6 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments and examples will now be described with reference to the drawings and tables.

(2) FIG. 1 illustrates a schematic diagram of a method of fabricating an article for magnetic heat exchange by plastically deforming a composite body.

(3) FIG. 2 illustrates a schematic diagram of plastically deforming an elongate composite body by rolling.

(4) FIG. 3 illustrates a schematic diagram of plastically deforming a substantially spherical composite body between a roller and a band.

(5) FIG. 4 illustrates a schematic diagram of plastically deforming a substantially spherical composite body between two rollers rotating in opposing directions.

(6) FIG. 5 illustrates a schematic diagram of a method of fabricating an article for magnetic heat exchange.

(7) FIGS. 6A-6C illustrate three differing debinding heat treatment profiles.

(8) FIGS. 7A and 7B illustrate graphs of carbon and oxygen uptake for samples after debinding a PVP binder.

(9) FIGS. 8A and 8B illustrate graphs of carbon and oxygen uptake for samples after debinding a PVB binder.

(10) FIGS. 9A and 9B illustrate graphs of carbon and oxygen uptake for samples after debinding a PPC binder.

(11) FIG. 10 illustrates a schematic diagram of apparatus for fluidized bed granulisation.

(12) FIGS. 11A-11C illustrate graphs of the adiabatic temperature change (MCE) of sintered samples fabricated using fluidized bed granulisation.

(13) FIGS. 12A-12C illustrate graphs of entropy change of sintered samples fabricated using fluidized bed granulisation.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(14) FIG. 1 illustrates a schematic diagram of a method 10 of fabricating an article for magnetic heat exchange by plastically deforming a composite body 11. The composite body 11 includes a powder 12 including a plurality of particles 13 and a binder 14. The binder 14 may bridge gaps between the particles 13. The binder 14 has a glass transition temperature TG such that the composite body 11 may be plastically deformed at temperatures above TG, for example at temperatures of around 20 to 30K higher than TG. The plastic deformation of the composite body 11 is schematic indicated with the arrows 15. After plastic deformation the composite body 11 has a different shape. For example, a composite body 11 having a spherical form may be plastically deformed to produce an ellipsoid 11 having three axes of differing length or an ellipsoid 11 having two axes of the same-length and a third axis which is longer or shorter than other two ones.

(15) Elongate forms including ellipsoid forms are useful for working components of a magnetic heat exchanger since they can be arranged such that the longer axis or dimension is substantially parallel to the direction of the flow of the coolant and the shortest axis is substantially perpendicular to the direction of flow of coolant. This arrangement reduces turbulence in the coolant flow and increases heat exchange between the working component and the heat transfer fluid.

(16) The composite body may be plastically deformed using different techniques. In some embodiments, the composite body is plastically deformed such that at least one dimension of the composite body changes in length by at least 10%. For example the length of a rod shaped composite body may increase by at least 10% or the diameter of the rod-shaped composite body may decrease by at least 10%.

(17) FIG. 2 illustrates a schematic diagram of plastically deforming an elongate composite body 20 by rolling. The composite body 20 includes a plurality of particles 21 of a powder embedded in a matrix 22 comprising a binder 23. The composite body 20 has a rod-like shape and may have a square, rectangular, circular or elliptical cross-section. The composite body 20 is passed between two rollers 24, 25 rotating in opposing directions, plastically deforming the composite body 20 such that the length of the composite body is increased from 11 to 12 and the thickness is decreased from t.sub.1 to t.sub.2.

(18) FIG. 3 illustrates a schematic diagram of plastically deforming a substantially spherical composite body 30 including a powder 31 and a binder 32 between a roller 33 and a band 34 which each have a surface 35, 36 which is moving at the same speed s. This arrangement may be used to produce an ellipsoid composite body with three axes of differing length. The shape produced may be thought of as similar to the shape of a convex lens.

(19) FIG. 4 illustrates a schematic diagram of plastically deforming a substantially spherical composite body 40 including a powder 41 and binder 42 between two rollers 43, 44, rotating in opposing directions as is indicated schematically by the arrows 45, 46. In the case these two speeds are different, the shape produced may be thought of as similar to the shape of a grain of rice.

(20) FIG. 5 illustrates a schematic diagram of a method of fabricating an article for magnetic heat exchange, in particular, an article which may be used as, or as part of, a working component of a magnetic heat exchanger.

(21) The composite body may be fabricated by mixing a binder 50 and a solvent 51 with a powder 52 comprising a magnetocalorically active phase with a NaZn.sub.13-type crystal structure. In some embodiments, the powder may comprise a composition suitable to form a magnetocalorically active phase after reactive sintering. The binder 50 may comprise a poly (alkylene carbonate), for example poly (ethylene carbonate), poly (propylene carbonate), poly (butylene carbonate) or poly (cyclohexene carbonate). The solvent 51 may comprise 2,2,4-Trimethylpentane, isopropanol, 3 Methoxy-1-butanol, propylacetate, dimethyl carbonate or methylethylketone. The magnetocalorically active phase may be La.sub.1-aR.sub.a(Fe.sub.1-x-yT.sub.yM.sub.x).sub.13H.sub.zC.sub.b, wherein M is Si and, optionally, Al, T is one or more of the elements from the group consisting of Mn, Co, Ni, Ti, V and Cr and R is one or more of the elements from the group consisting of Ce, Nd, Y and Pr, wherein 0a0.5, 0.05x0.2, 0.003y0.2, 0z3 and 0b1.5.

(22) In one embodiment, the binder 50 is poly (propylene carbonate) and the solvent 51 is methylethylketone. These compositions of the binder 50 and solvent 51 are found to be suitable for the La.sub.1-aR.sub.a(Fe.sub.1-x-yT.sub.yM.sub.x).sub.13H.sub.zC.sub.b phase, since they can be removed from powder including this phase leaving an acceptably low residual carbon and oxygen content.

(23) Around 0.1% weight percent to 10 weight percent, preferably 0.5 weight percent to 4 weight percent of binder 50 may be added to the powder 52.

(24) The mixture of the binder 50, solvent 51 and powder 52 including a magnetocalorically active phase with a NaZn.sub.13-type crystal structure may be further processed by removing some or substantially all of the solvent 51 as is indicated schematically with the arrow 53 to form a composite body 54. The composite body 54 may be termed a brown body which includes the powder 52 and the binder 50. The composite body 54 may be plastically deformed to change its shape as is schematically indicated with the arrow 55. The composite body 54 may be plastically deformed by rolling.

(25) In some embodiments, the composite body 54 may have the form of a granule which is substantially spherical. Granules may be formed by fluidized bed granulisation. In some embodiments, the composite body 54 may be mechanically formed by extruding the composite body 54 to form a rod, singulating the rod to form a plurality of composite bodies and rounding at least the edges of the plurality of composite bodies.

(26) The binder 50 may then be removed from the composite body 54, as is indicated schematically in FIG. 1 by the arrow 56, to produce a green body 57. The green body 57 may then be sintered, as is schematically indicated in FIG. 1 by arrows 58, to produce an article 59 for magnetic heat exchange.

(27) The binder 50 may be removed by heat treating the composite body 54 at a temperature of less than 400 C. in a noble gas atmosphere, a hydrogen containing atmosphere, under vacuum or a combination of these for a period of around 30 min to 20 hours, preferably 2 to 6 hours. Preferably, the conditions are selected such that at least 90% by weight or 95% by weight of the binder 50 is removed.

(28) The green body 57 may be sintered at a temperature between 900 C. and 1200 C. in a noble gas atmosphere, a hydrogen containing atmosphere or under vacuum or a combination of these, if the composite body 54 and green body 57 includes the magnetocalorically active phase. If the composite body 54 and the green body 57 include elements suitable for forming the magnetocalorically active phase, i.e. precursors which are magneto-calorically passive, the green body may be reactive sintered to form the magnetocalorically active phase from the elements or precursors.

(29) The binder and the treatment for its removal from the composite body may be selected so as to avoid detrimentally affecting the magnetocaloric properties of the working component.

(30) The suitability of different binders for La.sub.1-aR.sub.a(Fe.sub.1-x-yT.sub.yM.sub.x).sub.13H.sub.zC.sub.b is investigated. The binders polyvinylpyrrolidone (PVP), polyvinylbutyral (PVB) and polypropylene carbonate (PPC) are investigated. Samples are made using 0.1, 0.5, 1 and 2 weight percent binder (related to the powder), around 40 g of powder and 20 g of solvent. For PVP and PVB, isopropanol is used as a solvent and for PPC, methylethylketone (MEK) is used as the solvent. The mixtures were in each case mixed for 30 minutes in a turbula mixer and dried at 70 C. for 14 hours under vacuum.

(31) FIG. 6 illustrates three types of heat treatment for removing the binder or debinding. In heat treatment 1, the debinding was carried out under vacuum using a constant heating rate to the debinding temperature T.sub.debind which was held for four hours. The heating rate is variable between 2 C. per minute and 4 C. per minute. For the second debinding heat treatment, slower heating rates were used. In a first step, sample was heated at around 3 C. per minute to a first temperature T.sub.onset, then the heating rate was slowed to around 0.5 to 1 C. per minute from T.sub.onset to the debinding temperature T.sub.debind which was held for 4 hours. The second debinding treatment was also carried out in vacuum.

(32) The third debinding heat treatment uses the same heat treatment profile as the second debinding treatment. However, after reaching the temperature T.sub.onset, the vacuum is replaced by 1300 mbar argon.

(33) After the debinding treatment, the samples are sintered by heating from the debinding temperature to the sinter temperature in 7 hours under vacuum, held at the sintering temperature for 3 hours, the atmosphere changed to argon and the sample held at the sintering temperature for further 1 hour in argon. A further homogenisation heat treatment at 1050 C. for 4 hours in argon is used and the samples cooled quickly to room temperature using compressed air.

(34) FIG. 7 illustrates the carbon uptake and oxygen uptake measured for samples mixed with PVP after the three debinding heat treatments. Values obtained using thermogravimetric analysis (TGA) in nitrogen are included as a comparison. The debinding temperature T.sub.debind is 460 C. and T.sub.onset is 320 C. The debinding treatments carried out entirely under vacuum, that is debinding heat treatments 1 and 2, result in a lower level of increase in carbon than under nitrogen, as is indicated by TGA comparison values illustrated in FIG. 7. The debinding treatment 1 results in the lowest increase in the carbon contents. However, the debinding treatments carried out entirely under vacuum, that is debinding heat treatments 1 and 2, result in a higher level of increase in oxygen than under nitrogen, as is indicated by TGA comparison values illustrated in FIG. 7.

(35) FIG. 8 illustrates the carbon uptake and oxygen uptake measured from samples mixed with PVB after use of each of the three debinding treatments. The debinding temperature T.sub.debind is 400 C. and T.sub.onset is 200 C. The use of a PVB binder results in an increase in the carbon content of around 0.3 weight percent and an increase in the oxygen content of around 0.3 weight percent for a binder amount of 2 weight percent. The uptake of carbon and oxygen for PVB is lower compared to PVP. However, about 30% of the binder remains in the final sintered product which may affect the magnetocaloric properties of the material.

(36) FIG. 9 illustrates a graph of the carbon uptake and oxygen uptake as function of weight percent of PPC binder for samples given each of the three debinding heat treatments. The debinding temperature is 300 C. and T.sub.onset is 100 C. The carbon uptake in the samples after the debinding treatment is much lower than the TGA values for each of the three debinding heat treatments and it is also much lower compared to PVP and PVB. Also the oxygen uptake is lower than the TGA values for each of the three debinding heat treatments and it is also lower compared to PVP and PVB.

(37) The carbon uptake and oxygen uptake after the three debinding treatments are summarized in table 1.

(38) TABLE-US-00001 TABLE 1 PVP PVB PPC Density (mean 5.99 g/cm.sup.3 6.70 g/cm.sup.3 6.72 g/cm.sup.3 value) Preferred Vacuum Vacuum or Argon Vacuum or Argon debinding atmosphere Preferred Profile 1 Profile 2/Profile 3 Profile 1 debinding profile C.sub.x (0.25*PVP + (0.135*PVB + (0.0106*PPC + 0.06) wt. % 0.045) wt. % 0.0153) wt. % O.sub.x (0.12*PVP + (0.10*PVB + (0.0273*PPC + 0.138) wt. % 0.14) wt. % 0.0599) wt. % Compatibility Low Medium very high with LaFeSi

(39) In summary, PPC is a particular suitable binder for the La.sub.1-aR.sub.a (Fe.sub.1-x-yT.sub.yM.sub.x).sub.13H.sub.zC.sub.b phase since the increase in carbon and oxygen after the debinding treatment is lowest for the three binders investigated.

(40) As discussed above, the mixture of the powder, the binder and solvent may be mechanically formed before removal of solvent, for example by casting or screen printing, or after removal of some or substantially all of the solvent by methods such as extrusion or calendaring of the brown body. In some embodiments, spherical granulates or granules are useful for use in the working component of a magnetic heat exchanger. In some embodiments, the granules including particles of the powder and a binder are plastically deformed, before a subsequent debinding and sintering or reactive sintering treatments.

(41) In some embodiments, the spherical or substantially spherical granules may be made using fluidized bed granualisation. FIG. 10 illustrates apparatus for fluidized bed granualisation.

(42) In the fluidized bed granulisation method, powder including the magnetocalorically active phase or precursors thereof or elements in amounts suitable to produce a magnetocalorically active phase is caused to circulate by application of a gas and a fluid, such as a suitable solvent or a mixture of a suitable solvent and a suitable binder, is sprayed into the moving particles to create the granules. The binder may be added to form stable granules. As discussed above, PPC and methylethylketone is a combination of binder and solvent which is suitable for the La.sub.1-aR.sub.a (Fe.sub.1-x-yT.sub.yM.sub.x).sub.13H.sub.zC.sub.b phase. The gas temperature, pressure and speed may be adjusted to adjust the size of the granules formed.

(43) Conditions suitable for fabricating the granules using fluidized bed granulisation are summarized in table 2.

(44) TABLE-US-00002 TABLE 2 Parameter Value Starting material 200 g powder (<315 m) or granules (<400 m) Binder 2 wt. % PPC Suspension 60 wt. % LaFeSi, 40 wt. % MEK Gas flow 13 m.sup.3/h Temperature 45 C. Spraying rate 29 g/min Spraying pressure 1.5 bar Purging pressure 2 bar

(45) The nominal compositions of the powder in weight percentage summarized in table 3.

(46) TABLE-US-00003 TABLE 3 Charge SE Si La Co Mn C O N Fe MFP- 17.86 4.13 17.85 0.09 1.84 0.015 0.31 0.025 75.73 1384 MFP- 17.82 4.12 17.81 0.1 1.65 0.015 0.3 0.024 75.96 1385 MFP- 17.78 4.09 17.77 0.11 1.47 0.015 0.3 0.023 76.21 1386

(47) For each powder, three runs in the fluidized bed granulisation apparatus were performed. In run 1, the binder containing material is used as the starting material. In run 2, granules with a diameter of less than 400 m obtained from run 1 are mixed with fine powder from the filter and used as the starting powder. In run 3, granules with a diameter less than 400 m obtained from run 2 are mixed with fine powder from the filter and used as starting material.

(48) The results are summarised in table 4.

(49) TABLE-US-00004 TABLE 4 1384 1384 1384 1385 1385 1385 1386 1386 1386 Run 1 Run 2 Run 3 Run 1 Run 2 Run 3 Run 1 Run 2 Run 3 Sprayed material 761 g 487 g 405 g 911 g 515 g 679 g 757 g 653 g 468 g Starting material 230 g 200 g 200 g 80 g 200 g 200 g 200 g 200 g 200 g Fraction <400 m 113 g 62 g 72 g 17 g 7 g 33 g 95 g 97 g 24 g Fraction 400-630 m 210 g 298 g 133 g 71 g 34 g 23 g 133 g 242 g 90 g Fraction >630 m 82 g 8 g 31 g 372 g 210 g 243 g 248 g 88 g 1 g Yield ~41% ~53% ~39% ~46% ~35% ~34% ~49% ~50% ~17% Filter powder 585 g 318 g 369 g 530 g 462 g 580 g 480 g 425 g 551 g

(50) The granules fabricated by fluidized bed granulisation are subjected to a debinding heat treatment and then sintered to form an article comprising magnetocalorically active material for use in magnetic heat exchange. The magnetocaloric properties of the sintered samples are tested to determine if the use of a binder and solvent and the use of fluidized bed granulation affect the magnetocaloric properties.

(51) The granules are packed in iron foil and gettered before the debinding and sintering heat treatments. The debinding temperature is 300 C. and the sinter temperature is 1120 C. The granules are heated under vacuum in 1 hours to the debinding temperature and held that the debinding temperature 300 C. for 4 hours. Afterwards, the temperature is raised in 7 hours under vacuum to the sintering temperature, held for 3 hours at the sintering temperature under vacuum and additionally for one hour at the sintering temperature in argon. Afterwards the granule's are cooled to 1050 C. in 4 hours and held at 1050 C. for 4 hours under argon to homogonize the samples. The samples are then cooled quickly under compressed air to room temperature.

(52) The samples were found to have a carbon uptake of 0.04 weight percent to 0.06 weight percent and an oxygen uptake of 0.15% to 0.3 weight percent. These values correspond substantially to those obtained during the investigation of suitable binders.

(53) The sintered granules are hydrogenated by heating the granules in 2 hours under argon to 500 C. and held for one hour at 500 C. Afterwards, the atmosphere is changed to hydrogen and the samples cooled to room temperature in 8 hours and held under hydrogen for 24 hours. The granules are not found to disintegrate after the hydrogenation treatment.

(54) The magnetocaloric properties of the samples are investigated. FIG. 11 illustrates the diagrams of the adiabatic temperature change and FIG. 12 illustrates diagrams of the entropy change for the samples. The results are also summarized in table 5.

(55) The values of the adiabatic temperature change and entropy change for granules fabricated in the first run are comparable to those of the reference sample fabricated by powder metal metallurgical techniques without using a binder.

(56) TABLE-US-00005 TABLE 5 1384 1384 1384 1385 1385 1385 1386 1386 1386 @ 1.5T Run 1 Run 2 Run 3 Run 1 Run 2 Run 3 Run 1 Run 2 Run 3 (g/cm.sup.3) 6.81 6.59 6.92 6.91 6.8 6.45 6.94 6.99 7.07 Nominal T.sub.c 30 35 40 ( C.) T.sub.Peak ( C.) 34.9 35.4 34.2 38.5 36.4 36.6 44.4 44.9 40.8 T ( C.) 3.4 2.9 1.3 3.7 3.4 3.3 4.2 3.8 3.7 T Ref. 4.32 4.36 4.35 ( C.) S (J/KgK) 12.2 9.8 2.9 13 11 11.3 14.9 14.3 13.7 S Ref. 14.7 15.9 16.2 (J/KgK) T.sub.Peak ( C.) 35 35.4 33.9 37.8 36.6 36.5 42.9 43.3 40 -Fe (wt. %) 3.7 4.7 5.4 3.8 3.3 3.8 6.2 4.7 5.3

(57) In a further set of experiments, starting materials for fluid bed granulisation of 1.5 kg of powder having a composition of 2.54 weight percent neodymium, 4.24 weight percent silicon, 15.95 weight percent lanthanum, 0.15 weight % cobalt, 3.61 weight percent manganese, 73.25 weight percent iron, 0.013 weight percent carbon, 0.21 weight percent oxygen and 0.028 weight percent nitrogen, 1 kg methyl ethyl ketone and two weight percent poly (propylene carbonate) (PPC) binder are prepared. After fluid bed granulisation, 80% of the granules produced have a diameter between 1000 m and 1600 The granules can be considered as a composite body or brown body including a powder and a binder.

(58) Granules or spherical composite bodies having a diameter of 1.2 to 1.5 mm are plastically deformed by pressing between an aluminum block and an annealed copper plate by applying a force of around 10N to 50N. The plastically deformed spherical granules may have disc shape. The temperature of the aluminum block, granule and copper plate is adjusted in order to plastically deform the composite bodies at different temperatures.

(59) At a temperature of 23 C., the applied pressure caused the composite bodies to fracture. The temperature of 23 C. lies under the glass transition temperature of the poly (propylene carbonate) binder which is around 40 C. At a temperature of around 40 C., deformation of the composite bodies is observed. As the ratio of the diameter to the thickness of the resulting particles became greater than 1.5, cracks were formed which in some cases lead to fracture.

(60) At a temperature of around 45 C., the composite bodies can be deformed such that a ratio of diameter to thickness of around 2 can be produced without cracks appearing. At a temperature of 50 C., composite bodies having a diameter of around 2.25 mm and a thickness of 0.75 mm can be produced, which corresponds to a ratio of the long to the short direction around 3. At a temperature of 60 c., which is around 20K higher than the glass transition temperature of the binder, plastically deformed disc shaped composite bodies with a diameter of around 2.45 mm and a thickness of 0.6 mm can be produced without cracking from a spherical particle having a diameter of between 1.2 to 1.5 mm.

(61) This demonstrates that at temperatures above the glass transition temperature of the binder, for example 20K above the glass transition temperature of the binder, the composite bodies may be plastically deformed to an extent that after plastic deformation the composite body may have a first dimension d.sub.1 which is at least 1.5 times a second dimension d.sub.2, i.e. d.sub.1>1.5d.sub.2.

(62) In a further experiment, a similar powder to the previous experiment having a particle size of around 6 m is mixed with 2 to 8 weight percent of a poly (propylene carbonate) binder which was dissolved in methyl ethyl ketone. The solvent is removed by drying. The resulting composite body including the powder and binder was plastically deformed in a twin screw extruder including a gap between the screws of around 12 mm at a temperature of 100 C. to form cylinder shaped rods having a diameter of around 1 mm. The rods were rounded at a temperature of 130 C. for 5 minutes in a spheronizer. The rods having an initial length of several millimeters are formed into several shorter cylinder shaped portions. The movement in the spheronizer rounds the corners of the cylinder shaped portions to form ellipsoid particles having a diameter of around 1 mm and a length of between 1 to 4 mm. The plastic deformation may be performed under inert conditions, for example under argon or nitrogen. The extruder and the spheronizer may be placed in a glove box filled with argon to avoid oxidation of the powders at the elevated temperatures.

(63) The plastically deformed granules or composite bodies may be given a debinding and sintering treatment as discussed above resulting in essentially the same magnetocaloric properties as without the plastically deformation.