U.S. patent application number 12/989020 was filed with the patent office on 2011-03-17 for method for producing metal-based materials for magnetic cooling or heat pumps.
This patent application is currently assigned to Technology Foundation STW. Invention is credited to Ekkehard Brueck, Thanh Trung Nguyen.
Application Number | 20110061775 12/989020 |
Document ID | / |
Family ID | 40785565 |
Filed Date | 2011-03-17 |
United States Patent
Application |
20110061775 |
Kind Code |
A1 |
Brueck; Ekkehard ; et
al. |
March 17, 2011 |
METHOD FOR PRODUCING METAL-BASED MATERIALS FOR MAGNETIC COOLING OR
HEAT PUMPS
Abstract
The process for preparing metal-based materials for magnetic
cooling or heat pumps comprises the following steps: a) reacting
chemical elements and/or alloys in a stoichiometry which
corresponds to the metal-based material in the solid phase and/or
liquid phase, b) if appropriate converting the reaction product
from stage a) to a solid, c) sintering and/or heat treating the
solid from stage a) or b), d) quenching the sintered and/or heat
treated solid from stage c) at a cooling rate of at least 100
K/s.
Inventors: |
Brueck; Ekkehard; (Delft,
NL) ; Nguyen; Thanh Trung; (Delft, NL) |
Assignee: |
Technology Foundation STW
Utrecht
NL
University of Amsterdam
Amsterdam
NL
|
Family ID: |
40785565 |
Appl. No.: |
12/989020 |
Filed: |
April 27, 2009 |
PCT Filed: |
April 27, 2009 |
PCT NO: |
PCT/EP2009/055024 |
371 Date: |
October 21, 2010 |
Current U.S.
Class: |
148/559 ;
148/400 |
Current CPC
Class: |
H01F 1/015 20130101;
C22C 2200/04 20130101; C22C 2202/02 20130101; B22F 2998/10
20130101; C22C 1/0491 20130101; B22F 2998/10 20130101; B22F
2009/041 20130101; B22F 3/1028 20130101; B22F 3/1028 20130101; B22F
9/04 20130101; B22F 3/222 20130101 |
Class at
Publication: |
148/559 ;
148/400 |
International
Class: |
C21D 9/00 20060101
C21D009/00; C21D 1/00 20060101 C21D001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2008 |
EP |
08155259.8 |
Claims
1. A process for preparing a metal-comprising material, the process
comprising: a) reacting at least one chemical element and/or at
least one alloy in a stoichiometry which corresponds to the
metal-comprising material, in solid phase and/or liquid phase, to
yield a first reaction product; b) optionally., converting the
first reaction product from a) to a solid; c) sintering and/or heat
treating the first reaction product from a) or the solid from b),
to give a second solid; and d) quenching the second solid from c)
at a cooling rate in a range from 200 to 1300 K/s.
2. The process according to claim 1, wherein the reacting in a) is
effected by heating the at least one element and/or alloy together
in a closed vessel or in an extruder, or by solid phase reaction in
a ball mill.
3. The process according to claim 1, wherein the converting to a
solid in b) is effected by melt spinning or spray cooling.
4. The process according to claim 1, wherein, in c), first
sintering is effected at a temperature in a range from 800 to
1400.degree. C. and then heat treating at a temperature in a range
from 500 to 750.degree. C.
5. The process according to claim 1, wherein the metal-comprising
is at least one selected from the group consisting of (1) a
compound of formula (I)
(A.sub.yB.sub.y.sub.-.sub.1).sub.2+.delta.C.sub.wD.sub.xE.sub.z
(I), wherein A is Mn or Co, B is Fe, Cr, or Ni, C, D, E at least
two of C, D, E are different, have a non-vanishing concentration
and are selected from the group consisting of P, B, Se, Ge, Ga, Si,
Sn, N, As, and Sb, whereby at least one of C, D, and E is Ge or Si,
.delta. is a number in a range from -0.1 to 0.1, w, x, y, z are
numbers in a range from 0 to 1, whereby w+x+z=1; (2a) an La- and
Fe-based compound of formulae (II)
La(Fe.sub.xAl.sub.1-x).sub.13H.sub.y or
La(Fe.sub.xSi.sub.1-z).sub.13H.sub.y (II), wherein x is a number
from 0.7 to 0.95, and y is a number from 0 to 3; (2b) an La- and
Fe-based compound of formula III
La(Fe.sub.xAl.sub.yCo.sub.z).sub.13 or
La(Fe.sub.xSi.sub.yCo.sub.z).sub.13 (III), wherein x is a number
from 0.7 to 0.95, y is a number from 0.05 to 1-x, and z is a number
from 0.005 to 0.5; (2c) an La- and Fe-based compound of formula IV
LaMn.sub.xFe.sub.2-xGe (IV), wherein x is a number from 1.7 to
1.95; and (3) a Heusler alloy of MnTP composition, wherein T is a
transition metal and P is a p-doping metal with an electron count
per atom, e/a, in a range from 7 to 8.5.
6. The process according to claim 5, wherein the metal-comprising
material is at least one at least quaternary compound of formula
(I) which, as well as Mn, Fe, P, and optionally Sb, additionally
comprises Ge or Si or As, or Ge and As, or Si and As, or Ge, Si and
As.
7. The process according to claim 1, wherein a) is a solid phase
reaction of the at least one element and/or alloy in a ball mill,
to give a first material; b) is melt spinning the first material
obtained in a) to give a second solid; c) is heat treating the
second solid from b) at a temperature in a range from 430 to
1200.degree. C., for a period of from 10 seconds or 1 minute to 5
hours, to give a heat treated shaped body; and d) is quenching the
heat treated shaped body from c) at a cooling rate of from 200 to
1300 K/s.
8. (canceled)
9. A metalized material, obtained by a process as defined in claim
5, excluding As-comprising materials, with an average crystal size
in a range from 10 to 400 nm.
10. (canceled)
11. The process according to claim 2, wherein the converting to a
solid in b) is effected by melt spinning or spray cooling.
12. The process according to claim 2, wherein, in c), first
sintering is effected at a temperature in a range from 800 to
1400.degree. C. and then heat treating at a temperature in a range
from 500 to 750.degree. C.
13. The process according to claim 3, wherein, in c), first
sintering is effected at a temperature in a range from 800 to
1400.degree. C. and then heat treating at a temperature in a range
from 500 to 750.degree. C.
14. The process according to claim 11, wherein, in c), first
sintering is effected at a temperature in a range from 800 to
1400.degree. C. and then heat treating at a temperature in a range
from 500 to 750.degree. C.
Description
[0001] The present invention relates to processes for preparing
metal-based materials for magnetic cooling or heat pumps, to
materials of this type and to the use thereof. The materials
prepared in accordance with the invention are used in magnetic
cooling, in heat pumps or in air conditioning systems.
[0002] Materials of this type are known in principle and are
described, for example, in WO 2004/068512. Magnetic cooling
techniques are based on the magnetocaloric effect (MCE) and may
constitute an alternative to the known vapor circulation cooling
methods. In a material which exhibits a magnetocaloric effect, the
alignment of randomly aligned magnetic moments by an external
magnetic field leads to heating of the material. This heat can be
removed from the MCE material to the surrounding atmosphere by a
heat transfer. When the magnetic field is then switched off or
removed, the magnetic moments revert back to a random arrangement,
which leads to cooling of the material below ambient temperature.
This effect can be exploited for cooling purposes; see also Nature,
vol. 415, Jan. 10, 2002, pages 150 to 152. Typically, a heat
transfer medium such as water is used for heat removal from the
magnetocaloric material.
[0003] Customary materials are prepared by solid phase reaction of
the starting elements or starting alloys for the material in a ball
mill. and subsequent pressing, sintering and heat treatment under
inert gas atmosphere and subsequent gradual cooling to room
temperature. Such a process is described, for example, in J. Appl.
Phys. 99, 2006, 08Q107.
[0004] Processing by means of melt spinning is also possible. This
makes possible a more homogeneous element distribution, which leads
to an improved magnetocaloric effect; cf. Rare Metals, vol. 25,
October 2006, pages 544 to 549. In the process described there, the
starting elements are first induction-melted in an argon gas
atmosphere and then sprayed in the molten state through a nozzle
onto a rotating copper roller. There follow sintering at
1000.degree. C. and gradual cooling to room temperature.
[0005] The materials obtained by the known process frequently
exhibit high thermal hysteresis. For example, in compounds of the
Fe.sub.2P type which are substituted by germanium or silicon, large
values for thermal hysteresis in a wide range of 10 K or more are
observed. These materials are therefore not very suitable for
magnetocaloric cooling.
[0006] It is an object of the present invention to provide a
process for preparing metal-based materials for magnetic cooling,
which leads to a reduction in the thermal hysteresis. At the same
time, a large magnetocaloric effect (MCE) should be achieved.
[0007] The object is achieved in accordance with the invention by a
process for preparing metal-based materials for magnetic cooling or
heat pumps, comprising the following steps: [0008] a) reacting
chemical elements and/or alloys in a stoichiometry which
corresponds to the metal-based material in the solid phase and/or
liquid phase, [0009] b) if appropriate converting the reaction
product from stage a) to a solid, [0010] c) sintering and/or heat
treating the solid from stage a) or b), [0011] d) quenching the
sintered and/or heat treated solid from stage c) at a cooling rate
of at least 100 K/s.
[0012] It has been found in accordance with the invention that the
thermal hysteresis can be reduced significantly when the
metal-based materials, after sintering and/or heat treatment, are
not cooled gradually to ambient temperature but rather are quenched
with a high cooling rate. This cooling rate is at least 100 K/s.
The cooling rate is preferably from 100 to 10 000 K/s, more
preferably from 200 to 1300 K/s. Especially preferred cooling rates
are from 300 to 1000 K/s.
[0013] This quenching can be achieved by any suitable cooling
processes, for example by quenching the solid with water or aqueous
liquids, for example cooled water or ice/water mixtures. The solids
can, for example, be allowed to fall into ice-cooled water. It is
also possible to quench the solids with subcooled gases such as
liquid nitrogen. Further processes for quenching are known to those
skilled in the art. What is advantageous here is controlled and
rapid cooling.
[0014] Without being bound to a theory, the reduced hysteresis can
be attributed to smaller particle sizes for the quenched
compositions.
[0015] In the processes known to date, sintering and heat treatment
have in each case been followed by gradual cooling, which leads to
the formation of greater particle sizes and hence to an increase in
the thermal hysteresis.
[0016] The rest of the preparation of the metal-based materials is
less critical, provided that, in the last step, the sintered and/or
heat treated solid is quenched at the inventive cooling rate. The
process can be applied to the preparation of any suitable
metal-based materials for magnetic cooling. Typical materials for
magnetic cooling are multimetal mixtures which often comprise at
least three metallic elements and additionally, if appropriate,
nonmetallic elements. The expression "metal-based materials"
indicates that the predominant proportion of these materials is
formed from metals or metallic elements. Typically, the proportion
in the overall material is at least 50% by weight, preferably at
least 75% by weight, especially at least 80% by weight. Suitable
metal-based materials are explained in detail hereinafter.
[0017] In step (a) of the process according to the invention, the
elements and/or alloys which are present in the later metal-based
material are converted in a stoichiometry which corresponds to the
metal-based material in the solid or liquid phase.
[0018] Preference is given to performing the reaction in stage a)
by heating the elements and/or alloys together in a closed vessel
or in an extruder, or by solid phase reaction in a ball mill.
Particular preference is given to performing a solid phase
reaction, which is effected especially in a ball mill. Such a
reaction is known in principle; cf. the documents cited in the
introduction. Typically, powders of the individual elements or
powders of alloys of two or more of the individual elements which
are present in the later metal-based material are mixed in
pulverulent form in suitable proportions by weight. If necessary,
the mixture can additionally be ground in order to obtain a
microcrystalline powder mixture. This powder mixture is preferably
heated in a ball mill, which leads to further comminution and also
good mixing, and to a solid phase reaction in the powder
mixture.
[0019] Alternatively, the individual elements are mixed as a powder
in the selected stoichiometry and then melted.
[0020] The combined heating in a closed vessel allows the fixing of
volatile elements and control of the stoichiometry. Specifically in
the case of use of phosphorus, this would evaporate easily in an
open system.
[0021] The reaction is followed by sintering and/or heat treatment
of the solid, for which one or more intermediate steps can be
provided. For example, the solid obtained in stage a) can be
pressed before it is sintered and/or heat treated. This allows the
density of the material to be increased, such that a high density
of the magnetocaloric material is present in the later application.
This is advantageous especially because the volume within which the
magnetic field exists can be reduced, which may be associated with
considerable cost savings. Pressing is known per se and can be
carried out with or without pressing aids. It is possible to use
any suitable mold for this pressing. By virtue of the pressing, it
is already possible to obtain shaped bodies in the desired
three-dimensional structure. The pressing may be followed by the
sintering and/or heat treatment of stage c), followed by the
quenching of stage d).
[0022] Alternatively, it is possible to send the solid obtained
from the ball mill to a melt-spinning process. Melt-spinning
processes are known per se and are described, for example, in Rare
Metals, Vol. 25, October 2006, pages 544 to 549, and also in WO
2004/068512.
[0023] In these processes, the composition obtained in stage a) is
melted and sprayed onto a rotating cold metal roller. This spraying
can be achieved by means of elevated pressure upstream of the spray
nozzle or reduced pressure downstream of the spray nozzle.
Typically, a rotating copper drum or roller is used, which can
additionally be cooled if appropriate. The copper drum preferably
rotates at a surface speed of from 10 to 40 m/s, especially from 20
to 30 m/s. On the copper drum, the liquid composition is cooled at
a rate of preferably from 10.sup.2 to 10.sup.7 K/s, more preferably
at a rate of at least 10.sup.4 K/s, especially with a rate of from
0.5 to 2.times.10.sup.6 K/s.
[0024] The melt spinning, like the reaction in stage a) too, can be
performed under reduced pressure or under an inert gas
atmosphere.
[0025] The melt spinning achieves a high processing rate, since the
subsequent sintering and heat treatment can be shortened.
Specifically on the industrial scale, the production of the
metal-based materials thus becomes significantly more economically
viable. Spray-drying also leads to a high processing rate.
Particular preference is given to performing melt spinning.
[0026] Alternatively, in stage b), spray cooling can be carried
out, in which a melt of the composition from stage a) is sprayed
into a spray tower. The spray tower may, for example, additionally
be cooled. In spray towers, cooling rates in the range from
10.sup.3 to 10.sup.5 K/s, especially about 10.sup.4 K/s, are
frequently achieved.
[0027] The sintering and/or heat treatment of the solid is effected
in stage c) preferably first at a temperature in the range from 800
to 1400.degree. C. for sintering and then at a temperature in the
range from 500 to 750.degree. C. for heat treatment. These values
apply especially to shaped bodies, whereas lower sintering and heat
treatment temperatures can be employed for powders. For example,
the sintering can then be effected at a temperature in the range
from 500 to 800.degree. C. For shaped bodies/solids, the sintering
is more preferably effected at a temperature in the range from 1000
to 1300.degree. C., especially from 1100 to 1300.degree. C. The
heat treatment can then be effected, for example, at from 600 to
700.degree. C.
[0028] The sintering is performed preferably for a period of from 1
to 50 hours, more preferably from 2 to 20 hours, especially from 5
to 15 hours. The heat treatment is performed preferably for a
period in the range from 10 to 100 hours, more preferably from 10
to 60 hours, especially from 30 to 50 hours. The exact periods can
be adjusted to the practical requirements according to the
material.
[0029] In the case of use of the melt-spinning process, sintering
can frequently be dispensed with, and the heat treatment can be
shortened significantly, for example to periods of from 5 minutes
to 5 hours, preferably from 10 minutes to 1 hour. Compared to the
otherwise customary values of 10 hours for sintering and 50 hours
for heat treatment, this results in a major time advantage.
[0030] The sintering/heat treatment results in partial melting of
the particle boundaries, such that the material is compacted
further.
[0031] The melting and rapid cooling in stage b) thus allows the
duration of stage c) to be reduced considerably. This also allows
continuous production of the metal-based materials.
[0032] Particular preference is given in accordance with the
invention to the process sequence of [0033] a) solid phase reaction
of chemical elements and/or alloys in a stoichiometry which
corresponds to the metal-based material in a ball mill, [0034] b)
melt spinning the material obtained in stage a), [0035] c) heat
treating the solid from stage b) at a temperature in the range from
430 to 1200.degree. C., preferably from 800 to 1000.degree. C., for
a period of from 10 seconds or 1 minute to 5 hours, preferably from
30 minutes to 2 hours, [0036] d) quenching the heat treated shaped
body from stage c) at a cooling rate of from 200 to 1300 K/s.
[0037] The process according to the invention can be used for any
suitable metal-based materials.
[0038] The metal-based material is more preferably selected
from
[0039] (1) compounds of the general formula (I)
(A.sub.yB.sub.y-1).sub.2+.delta.C.sub.wD.sub.xE.sub.z (I)
where [0040] A is Mn or Co, [0041] B is Fe, Cr or Ni, [0042] C, D,
E at least two of C, D, E are different, have a non-vanishing
concentration and are selected from P, B, Se, Ge, Ga, Si, Sn, N, As
and Sb, where at least one of C, D and E is Ge or Si, [0043]
.delta. is a number in the range from -0.1 to 0.1, [0044] w, x, y,
z are numbers in the range from 0 to 1, where w+x+z=1;
[0045] (2) La- and Fe-based compounds of the general formulae (II)
and/or (III) and/or (IV)
Le(Fe.sub.xAl.sub.1-x).sub.13H.sub.y or
La(Fe.sub.xSi.sub.1-x).sub.13H.sub.y (II)
where [0046] x is a number from 0.7 to 0.95; [0047] y is a number
from 0 to 3, preferably from 0 to 2;
[0047] La(Fe.sub.xAl.sub.yCo.sub.z).sub.13 or
La(Fe.sub.xSi.sub.yCo.sub.z).sub.13 (III)
where [0048] x is a number from 0.7 to 0.95; [0049] y is a number
from 0.05 to 1-x; [0050] z is a number from 0.005 to 0.5;
[0050] LaMn.sub.xFe.sub.2-xGe (IV)
where [0051] x is a number from 1.7 to 1.95 and
[0052] (3) Heusler alloys of the MnTP type where T is a transition
metal and P is a p-doping metal with an electron count per atom e/a
in the range from 7 to 8.5.
[0053] Materials particularly suitable in accordance with the
invention are described, for example, in WO 2004/068512, Rare
Metals, Vol. 25, 2006, pages 544 to 549, J. Appl. Phys. 99, 08Q107
(2006), Nature, Vol. 415, Jan. 10, 2002, pages 150 to 152 and
Physica B 327 (2003), pages 431 to 437.
[0054] In the aforementioned compounds of the general formula (I),
C, D and E are preferably identical or different and are selected
from at least one of P, Ge, Si, Sn and Ga.
[0055] The metal-based material of the general formula (I) is
preferably selected from at least quaternary compounds which, as
well as Mn, Fe, P and if appropriate Sb, additionally comprise Ge
or Si or As or Ge and Si or Ge and As or Si and As or Ge, Si and
As.
[0056] Preferably at least 90% by weight, more preferably at least
95% by weight, of component A is Mn. Preferably at least 90% by
weight, more preferably at least 95% by weight, of B is Fe.
Preferably at least 90% by weight, more preferably at least 95% by
weight, of C is P. Preferably at least 90% by weight, more
preferably at least 95% by weight, of D is Ge. Preferably at least
90% by weight, more preferably at least 95% by weight, of E is
Si.
[0057] The material preferably has the general formula
MnFe(P.sub.wGe.sub.xSi.sub.z).
[0058] x is preferably a number in the range from 0.3 to 0.7, w is
less than or equal to 1-x and z corresponds to 1-x-w.
[0059] The material preferably has the crystalline hexagonal
Fe.sub.2P structure. Examples of suitable structures are
MnFeP.sub.0.45 to 0.7, Ge.sub.0.55 to 0.30 and MnFeP.sub.0.5 to
0.70, (Si/Ge).sub.0.5 to 0.30.
[0060] Suitable compounds are additionally
M.sub.n1+xFe.sub.1-xP.sub.1-yGe.sub.y with x in the range from -0.3
to 0.5, y in the range from 0.1 to 0.6. Likewise suitable are
compounds of the general formula
Mn.sub.1+xFe.sub.1-xP.sub.1-yGe.sub.y-zSb.sub.z with x in the range
from -0.3 to 0.5, y in the range from 0.1 to 0.6 and z less than y
and less than 0.2. Also suitable are compounds of the formula
Mn.sub.1+xFe.sub.1-xP.sub.1-yGe.sub.y-zSi.sub.z with x in the range
from 0.3 to 0.5, y in the range from 0.1 to 0.66, z less than or
equal to y and less than 0.6.
[0061] Preferred La- and Fe-based compounds of the general formulae
(II) and/or (III) and/or (IV) are
La(Fe.sub.0.90Si.sub.0.10).sub.13,
La(Fe.sub.0.89Si.sub.0.11).sub.13,
La(Fe.sub.0.880Si.sub.0.120).sub.13,
La(Fe.sub.0.877Si.sub.0.123).sub.13, LaFe.sub.11.8Si.sub.1.2,
La(Fe.sub.0.88Si.sub.0.12).sub.13H.sub.0.5,
La(Fe.sub.0.88Si.sub.0.12)13, La(Fe.sub.0.877Si.sub.0.123).sub.13,
LaFe.sub.11.57Si.sub.1.43H.sub.1.3,
La(Fe.sub.0.88Si.sub.0.12)H.sub.1.5,
LaFe.sub.11.2Co.sub.0.7Si.sub.1.1,
LaFe.sub.11.5Al.sub.1.5C.sub.0.1, LaFe.sub.11.5Al.sub.1.5C.sub.0.2,
LaFe.sub.11.5Al.sub.1.5C.sub.0.4,
LaFe.sub.11.5Al.sub.1.5Co.sub.0.5,
La(Fe.sub.0.94Co.sub.0.06).sub.11.83Al.sub.1.17,
La(Fe.sub.0.92Co.sub.0.08).sub.11.83Al.sub.1.17.
[0062] Suitable manganese-comprising compounds are MnFeGe,
MnFe.sub.0.9Co.sub.0.1Ge, MnFe.sub.0.8Co.sub.0.2Ge,
MnFe.sub.0.7Co.sub.0.3Ge, MnFe.sub.0.6Co.sub.0.4Ge,
MnFe.sub.0.5Co.sub.0.5Ge, MnFe.sub.0.4Co.sub.0.6Ge,
MnFe.sub.0.3Co.sub.0.7Ge, MnFe.sub.0.2Co.sub.0.8Ge,
MnFe.sub.0.15Co.sub.0.85Ge, MnFe.sub.0.1Co.sub.0.9Ge, MnCoGe,
Mn.sub.5Ge.sub.2.5Si.sub.0.5, Mn.sub.5Ge.sub.2Si,
Mn.sub.5Ge.sub.1.5Si.sub.1.5, Mn.sub.5GeSi.sub.2, Mn.sub.5Ge.sub.3,
Mn.sub.5Ge.sub.2.9Sb.sub.0.1, Mn.sub.5Ge.sub.2.8Sb.sub.0.2,
Mn.sub.5Ge.sub.2.7Sb.sub.0.3, LaMn.sub.1.9Fe.sub.0.1Ge,
LaMn.sub.1.85Fe.sub.0.15Ge, LaMn.sub.1.8Fe.sub.0.2Ge,
(Fe.sub.0.9Mn.sub.0.1).sub.3C, (Fe.sub.0.8Mn.sub.0.2).sub.3C,
(Fe.sub.0.7Mn.sub.0.3).sub.3C, Mn.sub.3GaC, MnAs, (Mn, Fe)As,
Mn.sub.1+.delta.As.sub.0.8Sb.sub.0.2, MnAs.sub.0.75Sb.sub.0.25,
Mn.sub.1.1As.sub.0.75Sb.sub.0.25,
Mn.sub.1.5As.sub.0.75Sb.sub.0.25.
[0063] Heusler alloys suitable in accordance with the invention
are, for example, Fe.sub.2MnSi.sub.0.5Ge.sub.0.5,
Ni.sub.52.9Mn.sub.22.4Ga.sub.24.7,
Ni.sub.50.9Mn.sub.24.7Ga.sub.24.4,
Ni.sub.55.2Mn.sub.18.6Ga.sub.26.2,
Ni.sub.51.6Mn.sub.24.7Ga.sub.23.8,
Ni.sub.52.7Mn.sub.23.9Ga.sub.23.4, CoMnSb,
CoNb.sub.0.2Mn.sub.0.8Sb, CoNb.sub.0.4Mn.sub.0.6SB,
CoNb.sub.0.6Mn.sub.0.4Sb, Ni.sub.50Mn.sub.35Sn.sub.15,
Ni.sub.50Mn.sub.37Sn.sub.13, MnFeP.sub.0.45As.sub.0.55,
MnFeP.sub.0.47As.sub.0.53,
Mn.sub.1.1Fe.sub.0.9P.sub.0.47As.sub.0.53,
MnFeP.sub.0.89-XSi.sub.XGe.sub.0.11, X=0.22, X=0.26, X=0.30,
X=0.33.
[0064] The invention also relates to a metal-based material for
magnetic cooling, which is obtainable by a process as described
above.
[0065] In addition, the invention relates to a metal-based material
for magnetic cooling as defined above with reference to the
composition, excluding As-comprising materials, with an average
crystal size in the range from 10 to 400 nm, more preferably from
20 to 200 nm, especially from 30 to 80 nm. The average crystal size
can be determined by X-ray diffraction. When the crystal size
becomes too small, the maximum magnetocaloric effect is reduced.
When the crystal size, in contrast, is too great, the hysteresis of
the system rises.
[0066] The inventive metal-based materials are preferably used in
magnetic cooling, as has been described above. A corresponding
refrigerator comprises, in addition to a magnet, preferably a
permanent magnet, metal-based materials as described above. The
cooling of computer chips and solar power generators is also
possible. Further fields of use are heat pumps and air conditioning
systems.
[0067] The metal-based materials prepared by the process according
to the invention may be in any desired solid form. They may also be
present in the form of flakes, ribbons, wire, powders, or else in
the form of shaped bodies. Shaped bodies such as monoliths or
honeycombs can be produced, for example, by a hot extrusion
process. It is possible, for example, for cell densities of from
400 to 1600 CPI or more to be present. Thin sheets obtainable by
rolling processes are also preferred in accordance with the
invention. Advantageous non-porous shaped bodies are those formed
from shaped thin material, for example tubes, plates, meshes, grids
or rods. Shaping by metal injection molding (MIM) processes is also
possible in accordance with the invention.
[0068] The invention is illustrated in detail by the examples which
follow.
EXAMPLES
Example 1
[0069] Evacuated quartz ampoules which comprised pressed samples of
MnFePGe were kept at 1100.degree. C. for 10 hours in order to
sinter the powder. This sintering was followed by heat treatment at
650.degree. C. for 60 hours in order to bring about homogenization.
Instead of slow cooling in the oven to room temperature, the
samples were, however, immediately quenched in water at room
temperature. The quenching in water caused a certain degree of
oxidation at the sample surfaces. The outer oxidized shell was
removed by etching with dilute acid. The XRD patterns showed that
all samples crystallized in a structure of the Fe.sub.2P type.
[0070] The following compositions were obtained:
[0071] Mn.sub.1.1Fe.sub.0.9P.sub.0.81Ge.sub.0.19;
Mn.sub.1.1Fe.sub.0.9P.sub.0.78Ge.sub.0.22,
Mn.sub.1.1Fe.sub.0.9P.sub.0.75Ge.sub.0.25 and
Mn.sub.1.2Fe.sub.0.8P.sub.0.81Ge.sub.0.19. The values observed for
the thermal hysteresis are 7 K, 5 K, 2 K and 3 K for these samples
in the given sequence. Compared to a slowly cooled sample, which
has a thermal hysteresis of more than 10 K, the thermal hysteresis
has been greatly reduced.
[0072] The thermal hysteresis was determined in a magnetic field of
0.5 tesla.
[0073] FIG. 1 shows the isothermal magnetization of
Mn.sub.1.1Fe.sub.0.9B.sub.0.78Ge.sub.0.22 close to the Curie
temperature with a rising magnetic field. Field-induced transition
behavior which leads to a large MCE is observed for magnetic fields
of up to 5 tesla.
[0074] The Curie temperature can be adjusted by varying the Mn/Fe
ratio and the Ge concentration, as can the value of the thermal
hysteresis.
[0075] The change in the magnetic entropy, calculated from the
direct current magnetization using the Maxwell relationship, for a
maximum field change of from 0 to 2 tesla, is 14 J/kgK, 20 J/kgK
and 12.7 J/kgK respectively for the first three samples.
[0076] The Curie temperature and the thermal hysteresis decrease
with increasing Mn/Fe ratio. As a result, the MnFePGe compounds
exhibit relatively large MCE values in a low field. The thermal
hysteresis of these materials is very low.
Example 2
Melt Spinning of MnFeP(GeSb)
[0077] The polycrystalline MnFeP(Ge, Sb) alloys were first produced
in a ball mill with high energy input and by solid phase reaction
methods, as described in WO 2004/068512 and J. Appl. Phys. 99, 08
Q107 (2006). The material pieces were then introduced into a quartz
tube with a nozzle. The chamber was evacuated to a vacuum of
10.sup.-2 mbar and then filled with high-purity argon gas. The
samples were melted by means of a high frequency and sprayed
through the nozzle owing to a pressure difference to a chamber
containing a rotating copper drum. The surface speed of the copper
wheel was adjustable, and cooling rates of about 10.sup.5 K/s were
achieved. Subsequently, the spun ribbons were heat treated at
900.degree. C. for one hour.
[0078] X-ray diffractometry reveals that all samples crystallize in
the hexagonal Fe.sub.2P structure pattern. In contrast to samples
not produced by the melt-spinning method, no smaller contaminant
phase of MnO was observed.
[0079] The resulting values for the Curie temperature, the
hysteresis and the entropy were determined for different peripheral
speeds in the melt-spinning. The results are listed in Tables 1 and
2 which follow. In each case, low hysteresis temperatures were
determined.
TABLE-US-00001 TABLE 1 V (m/s) T.sub.c (K) .DELTA.T.sub.hys (K)
-.DELTA.S(J/kgK) Ribbons
Mn.sub.1.2Fe.sub.0.8P.sub.0.73Ge.sub.0.25Sb.sub.0.02 30 269 4 12.1
Mn.sub.1.2Fe.sub.0.8P.sub.0.70Ge.sub.0.20Sb.sub.0.10 30 304 4.5
19.0 45 314 3 11.0 MnFeP.sub.0.70Ge.sub.0.20Sb.sub.0.10 20 306 8
17.2 30 340 3 9.5 MnFeP.sub.0.75Ge.sub.0.25 20 316 9 13.5 40 302 8
-- Mn.sub.1.1Fe.sub.0.9P.sub.0.78Ge.sub.0.22 20 302 5 -- 40 299 7
-- Mn.sub.1.1Fe.sub.0.9P.sub.0.75Ge.sub.0.25 30 283 9 11.2
Mn.sub.1.2Fe.sub.0.8P.sub.0.75Ge.sub.0.25 30 240 8 14.2
Mn.sub.1.1Fe.sub.0.9P.sub.0.73Ge.sub.0.27 30 262 5 10.1 Bulk
MnFeP.sub.0.75Ge.sub.0.25 327 3 11.0
Mn.sub.1.1Fe.sub.0.9P.sub.0.81Ge.sub.0.19 260 7 14.0
Mn.sub.1.1Fe.sub.0.9P.sub.0.78Ge.sub.0.22 296 5 20.0
Mn.sub.1.1Fe.sub.0.9P.sub.0.75Ge.sub.0.25 330 2 13.0
Mn.sub.1.2Fe.sub.0.8P.sub.0.81Ge.sub.0.19 220 3 7.7
Mn.sub.1.2Fe.sub.0.8P.sub.0.75Ge.sub.0.25 305 3 --
Mn.sub.1.2Fe.sub.0.8P.sub.0.73Ge.sub.0.27 313 5 --
Mn.sub.1.3Fe.sub.0.7P.sub.0.78Ge.sub.0.22 203 3 5.1
Mn.sub.1.3Fe.sub.0.7P.sub.0.75Ge.sub.0.25 264 1 --
TABLE-US-00002 TABLE 2 T.sub.c (K) .DELTA.T.sub.hys (K)
-.DELTA.S(J/kgK) Bulk MnFeP.sub.0.75Ge.sub.0.25 327 3 11.0
Mn.sub.1.16Fe.sub.0.84P.sub.0.75Ge.sub.0.25 330 5 22.5
Mn.sub.1.18Fe.sub.0.82P.sub.0.75Ge.sub.0.25 310 3 16.1
Mn.sub.1.20Fe.sub.0.80P.sub.0.75Ge.sub.0.25 302 1 12.0
Mn.sub.1.22Fe.sub.0.78P.sub.0.75Ge.sub.0.25 276 4 11.7
Mn.sub.1.26Fe.sub.0.74P.sub.0.75Ge.sub.0.25 270 1 8.5
Mn.sub.1.1Fe.sub.0.9P.sub.0.81Ge.sub.0.19 260 6 13.8
Mn.sub.1.1Fe.sub.0.9P.sub.0.78Ge.sub.0.22 296 4 20.0
Mn.sub.1.1Fe.sub.0.9P.sub.0.77Ge.sub.0.23 312 2 14.6
Mn.sub.1.1Fe.sub.0.9P.sub.0.75Ge.sub.0.25 329 2 13.0 Ribbons
Mn.sub.1.20Fe.sub.0.80P.sub.0.75Ge.sub.0.25 288 1 20.3
Mn.sub.1.22Fe.sub.0.78P.sub.0.75Ge.sub.0.25 274 2 15.3
Mn.sub.1.24Fe.sub.0.76P.sub.0.75Ge.sub.0.25 254 2 16.4
Mn.sub.1.26Fe.sub.0.74P.sub.0.75Ge.sub.0.25 250 4 14.4
Mn.sub.1.30Fe.sub.0.70P.sub.0.75Ge.sub.0.25 230 0 9.8
* * * * *