DE102009002640A1 - Magnetic alloy material and process for its production - Google Patents

Abstract

The invention relates to the field of materials science and material physics and relates to a magnetic alloy material which can be used, for example, as a magnetic cooling material (magnetocaloric material) for cooling purposes or for power generation purposes, and a method for its production.
The object of the present invention is to specify a magnetic alloy material which has improved mechanical properties with comparable magnetic and / or magnetocaloric properties compared to the materials of the prior art.
The object is achieved by a magnetic alloy material which exhibits a magnetocaloric effect and which has a foam-like structure with an open porosity of at least 1% and / or a closed porosity of at least 1%, or in which particles of the magnetic alloy material in a matrix material embedded with a higher ductility than the magnetic alloy material.

Description

The This invention relates to the field of materials science and material physics and relates to a magnetic alloy material, which, for example, as a magnetic cooling material (magnetocaloric Material) for cooling purposes or for power generation purposes can be used, and a method for its preparation.

The magnetic cooling by magnetic alloy materials opens up an environmentally friendly, energy and cost effective Alternative to conventional gas compression cooling. The Magnetic cooling is based on the magnetocaloric Effect (MCE = magnetocaloric effect), in which a temperature change As a result of the change in the magnetization of the material occurs. For applications are in particular materials with a great MCE interresant.

Magnetic materials with a crystal structure of NaZn ₁₃ type show a particularly large MCE, which is caused by a thermally and field-induced phase transition from the paramagnetic to the ferromagnetic state near the Curie temperature T _{c of} the material.

Magnetic alloy materials of the NaZn ₁₃ type crystal structure are known and could be used as magnetic cooling materials. The composition of such materials can be given by the formula R (T _1-a M _a ) ₁₃ H _d , where R is rare earth elements or a combination of rare earth elements, T is Fe or a combination of Fe and Co and M is Al, Si, Ga or Ge or combinations thereof. For a, 0.05 ≤ a ≤ 0.2 and for d, 0 ≤ d ≤ 3.0. Such materials have very good magnetocaloric properties at temperatures near the Curie temperature and are considered to be promising candidates for magnetic cooling [ C. Zimm et al., Int. J. Refrigeration 29, 1302 (2006) ].

As is known, such magnetic alloys are produced by means of an arc or high-frequency melting process and then, for example, for about 168 h at about 1050 ° C. under vacuum ( DE 103 38 467 A1 ) heat treated. It is also possible to melt the alloying elements at 1200 to 1800 ° C, then cool the alloy at a cooling rate of 10 ² to 10 ⁶ ° C / s (solidify rapidly) and then thermally treat the rapidly solidified alloy [ US 2006/0076084 A1 ; A. Van, K.-H. Müller, O. Gutfleisch, J. Appl. Phys. 97, 036102 (2005) ; XB Liu, Z. Altounian, GH Tu, J. Phys .: Condens. Matter 16, 8043 (2004) ].

Furthermore, a number of magnetic alloys, such. Gd ₅ Si ₂ Ge ₂ , MnAs, Mn ₁ -x Fe _x As, Ni ₂ MnSn and (Mn, Fe) ₂ (P, As) are known, some of which show a particularly large MCE, which is characterized by a thermal and / or field-induced magnetic phase transition near the Curie temperature T _c and / or near a structural phase transition [ VK Pecharsky and KA Gschneidner, Jr., Phys. Rev. Lett. 78, 4494 (1997) ; H. Wada and Y. Tanabe, Appl. Phys. Lett. 79, 3302 (2001) ; A. de Campos et al., Nature Materials 5, 802 (2006) ; T. Krenke et al., Nature Materials 4, 450 (2005) ; O. Tegus, E. Brüsk, KHJ Buschow, and FR de Boer, Nature 415, 150 (2002) ; DE 103 38 467 A1 . US 2007/0137732 A1 . US 2004/007944 A1 . US 7,186,303 B2 . US 2006/0231163 ; US Patent 7069729 ].

A significant disadvantage of these alloys is known to be the occurrence of volume changes due to isotropic or anisotropic expansion of the crystal lattice during the magnetic or structural phase transition, especially in the alloys which show a first-order phase transition [ A. Fujita et al., Phys. Rev B 65, 014410 (2001) ; H. Yabuta et al., J. Phys. Soc. Japan, 75, 113707 (2006) ]. These changes in volume can result in significantly reduced mechanical integrity and thus severely limiting conditions of use.

The The object of the present invention is to specify a magnetic Alloy material, which in comparable magnetic and / or magnetocaloric properties over the materials of the prior art has improved mechanical properties, and specifying an effective method of making the magnetic alloy material.

The The object is achieved by the invention specified in the claims solved. Advantageous embodiments are the subject of Dependent claims.

The magnetic alloy material according to the invention, which shows a magnetocaloric effect, has a foamy Structure with an open porosity of at least 1% and / or a closed porosity of at least 1%, or particles of magnetic alloy material in one Matrix material with a higher ductility than the magnetic alloy material embedded.

Advantageously,> 35% by volume of the magnetic alloy material has a NaZn ₁₃ -type crystal structure, more preferably at least 50% by volume, more preferably 80-90% by volume, of the magnetic alloy material having a NaZn ₁₃ type crystal structure on.

Also advantageously, the magnetic alloy material has a composition according to the formula: R _a Fe _100-axyz T _x M _y L _z With
R = La or a combination of La with Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and / or Y,
T = at least one element selected from the group Sc, Ti, V, Cr, Mn, Co, Ni, Cu and / or Zn,
M = Al, Si, P, Ga, Ge, In and / or Sn,
L = H, B, C and / or N,
5 ≤ a ≤ 11 and 0 ≤ x ≤ 12 and 2 ≤ y ≤ 20 and 0 ≤ z ≤ 18, (all in atomic%).

Farther Advantageously, to change the Curie temperature of the magnetic alloy material, the conditions 2 ≦ z ≦ 15 atomic% and / or 3 ≤ y ≤ 16 and / or 0.3 ≤ x ≤ 9 realized, with varying proportion z and / or y and / or x the Curie temperature changes between 170 K and 400 K.

And Also advantageously, the foam-like structure of the magnetic Alloy material has an open porosity of 2 to 50% and / or a closed porosity of 2 to 50%.

Advantageous it is also when particles of magnetic alloy material with a particle size of 10 nm to 1 mm in a matrix material are embedded.

Also it is advantageous if the matrix material with a higher Ductility as the magnetic alloy material of at least an element of Al, Ag, Au, Bi, C, Co, Cu, Fe, Ga, Ni, Pb, Pd, Pt, Sn, Ti, Zn or combinations and / or reaction products thereof, consists.

Farther It is advantageous if, in addition to the matrix material, a second material at least one element of Al, Ag, Au, Bi, C, Co, Cu, Fe, Ga, Ni, Nb, Pb, Pd, Pt, Sn, Ta, Ti, V, Zn, Zr or combinations and / or reaction products also with the matrix material thereof is.

And It is also advantageous if the matrix material is one at least 10% higher ductility than the magnetic alloy material having.

From It is also advantageous if the particles of the magnetic alloy material in the form of a ribbon, a wire, a plate, a foil or a Flake, a needle or in the form of powder particles.

at the process according to the invention for the preparation of a magnetic alloy material becomes the magnetic alloy material to a foam-like structure by means of foaming or compaction processed or particles of magnetic alloy material with a matrix material which has a higher ductility as the magnetic alloy material, mixed and then so far heated that the matrix material the matrix around the Particles of the magnetic alloy material forms.

advantageously, the compaction is carried out by hot or cold pressing.

Also Advantageously, the foaming is carried out, by placing on a foam-like structure a suspension with particles of the magnetic alloy material and dried is burned out, and then the foam-like structure or is pyrolyzed.

Farther Advantageously, particles of the magnetic alloy material become and the matrix material and into a shaped body processed and subsequently this shaped body to a temperature heated, in which the matrix material at least softens and the particles of magnetic alloy material substantially completely covered.

Also Advantageously, the application temperature by applying a Vacuum set.

With It is the first time the solution according to the invention possible to specify a magnetic alloy material its mechanical properties, in particular the strength (integrity), while retaining the good magnetic properties of the magnetocaloric effect, have been significantly improved.

This is inventively achieved in that the magnetic alloy material has a foam-like structure or particles of the magnetic alloy material in a matrix material are embedded, which has a higher ductility as the magnetic alloy material.

Under foam-like structure is intended in the context of this invention, a structure be understood that consists of webs that limit foam cells. These foam cells are open. The bridge material consists essentially from the magnetic alloy material and has an open and / or closed porosity on. Furthermore, the foam-like Structure but also essentially only magnetic alloy material exist with open and / or closed pores.

The Magnetic alloy material can be in the form of particles processed in a suspension to form a molding or be applied to a foam structure and after drying and a temperature increase to the magnetic alloy material are processed. The particles of the magnetic alloy material can take the form of a band, a wire, a plate, a foil or a flake, a needle or in Form of powder particles are present.

in the Case that the magnetic alloy material of the invention as a particle is embedded in a matrix material, can the particles also form a ribbon, a wire, a plate, a Foil or a flake, a needle or in the form of powder particles available. The particle size can be of some Nanometers to ~ 100 microns.

The Particles of the magnetic alloy material can then mixed with particles of the matrix material and to a shaped body are processed. Subsequently, the molded body of a temperature increase exposed, wherein at least one such temperature are reached must that the matrix material form a matrix around the particles of the magnetic Alloy material forms and the surface of the particles substantially completely covered as far as possible.

The Inventive magnetic alloy material shows a much higher mechanical strength, as the Volume changes of the magnetic alloy material much better by the phase transition, which at one Pore or the more ductile matrix material is collected can and therefore cracking and possibly even counteract the destruction of the molding and prevent them partially or completely.

The solution according to the invention shows, in particular, improved results in the predominant use of magnetic alloy materials whose crystal structure is of the NaZn ₁₃ type. These materials are known to have a large magnetocaloric effect and therefore can be used particularly advantageously.

Also It is advantageous if the inventive Solution used for magnetic alloy materials which is a composition according to the formula having the known elements, element combinations and proportions.

It is particularly advantageous if in particular H, B, C and / or N are present in the alloy material. These elements are known to be incorporated into interstitial sites and in particular affect the Curie temperature T _c , which is known to be important for magnetic alloy materials, and which determines the temperature of use by increasing the Curie temperature as the proportion of these elements, and in particular H, increases. Thus, an application temperature for the magnetic alloy material is adjustable within relatively wide limits.

Of the Effect of loading the magnetic alloy material with these Elements is the solution of the invention even more improved, since the resulting from the storage increased Brittleness of the magnetic alloy material as well collected by the foam-like structure or the matrix material become.

The Curie or application temperature adjustment may be, for example by applying a vacuum during the temperature increase done, which also in the compaction by means of hot pressing or Pressing at moderate temperatures is feasible. about the amount of temperature or time can be the application temperature be set.

With a specially selected coating method, such as the electrochemical coating or coating by electroless plating, hydrogen can be introduced interstitially into the crystal lattice at the same time or elements such. B. Co, Ni, Cu, substituted by diffusion processes Fe and thereby increase the Curie temperature T _c . The hydrogen can arise in a secondary reaction, such as. B. be released as a by-product of a cathodic electrode reaction or during the oxidation of the reducing agent. Thus, this effect is also in the solution according to the invention in almost unchanged manner, so that in addition to improved mechanical properties and improved primary properties, such as application temperature and size of the MCE can be achieved with the inventive solution.

The by compaction, z. By hot or cold pressing, or by foaming produced according to the invention magnetic alloy material has open and / or closed Pores on, with particularly advantageously also a regular Porosity can be adjusted. This is understood to mean according to the invention be that the pores are arranged in the material so that for example an effective flow through a (cooling) liquid can be achieved. A high specific surface the porous material is also effective Heat exchange very beneficial.

by virtue of has the porosity according to the invention the magnetic alloy material according to the invention a density between 50% and 99% of the theoretically achievable density of the magnetic alloy material.

in the If the use of the matrix material, this can also be another Contain material or the other material may be due to reactions of the matrix material or of another material. This additional material can also be on the surface attach the particles of the magnetic alloy material.

Very advantageous is the reduction of the magnetic or thermal Hysteresis, with the inventive magnetic Alloy material can be achieved. For applications the hysteresis should be minimized. By the porosity or the ductility of the second phase becomes the volume change or does not prevent expansion and reduces hysteresis.

The magnetic entropy change remains virtually unchanged, ie the relative cooling power remains high. The adiabatic temperature change ΔT _ad decreases slightly. However, a high reproducibility after significantly more work cycles in comparison to a solid material is advantageous.

following the invention is based on two embodiments explained in more detail.

example 1

From the elements La, Fe, and Si, a solid material having the composition LaFe _11.6 Si _{1.4 is} produced by induction melting and subsequent heat treatment at 1050 ° C. for 7 days. The resulting material consists of 97 wt .-% of the NaZn ₁₃ -type phase and 3 wt .-% of α-Fe.

Subsequently become 2 plates with dimensions of 8 mm × 4 mm × 1 mm from the solid material for the investigation of the magnetic properties cut.

The solid material with the composition LaFe _11.6 Si _1.4 shows at a magnetic field change of 2 Tesla a maximum entropy change ΔS _max of 162 kJ / m ³ K at 194 K. Here, the half width is 8 K and the relative cooling capacity is 1.5 MJ / m ³ . The entropy change and the relative cooling power remain unchanged after thermal cycling.

Nevertheless, a decrease of the adiabatic temperature change ΔT _{ad is} observed. In the first thermal cycle, the maximum adiabatic temperature change ΔT _ad ^max at a magnetic field change of 1.9 Tesla 7.3 K at 191 K when cooling from room temperature. When heating from 170 K to room temperature, the maximum adiabatic temperature change decreases with a magnetic field change from 1.9 Tesla to 5.2 K at 194 K. The thermal hysteresis is 3 K and magnetic hysteresis up to 0.7 T.

During the second and third thermal cycle, ΔT _ad ^max decreases to 6.7 K and 6.6 K when cooling from room temperature to 5 K and 4.9 K when heating 170 K to room temperature. The thermal hysteresis is 2.2 K and 2.1 K in the second and third thermal cycle.

The Reduction of the adiabatic temperature change and the thermal hysteresis is mostly on one attributed to microscopic cracking, the after repeated thermal or field change cycles for Loss of mechanical integrity can result.

According to the invention, a porous, foam-like material is produced from the pulverized solid material by hot pressing at a press temperature of 600-1423 K and pressing pressure of the order of magnitude of -10 ² -10 ³ MPa. The resulting material consists of 91% by weight of the NaZn ₁₃ -type phase and 9% by weight of α-Fe. Depending on the press operations, the density of the pressed material is 70 to 90% of the theoretical density of the material which consists of 91% by weight of LaFe _11.6 Si _1.4 and 9% by weight of α-Fe.

For the investigation of the magnetic properties become 2 plates from a cylindrical hot-pressed material cut with the dimensions of 8 mm × 4 mm × 1 mm.

The hot-pressed material with the composition LaFe _11.6 Si _1.4 shows a maximum entropy change ΔS _max of 110 kJ / m ³ K at 194 K with a magnetic field change of 2 Tesla. The half-width is 10.5 K and the relative cooling capacity is 1.3 MJ / m ³ . The entropy change and the relative cooling power remain unchanged after thermal cycling.

The adiabatic temperature change ΔT _{ad also} remains unchanged after the thermal and magnetic field alternating stress and is 4.3 K on cooling from room temperature and during heating of 170 K to room temperature with a magnetic field change of 1.9 Tesla. The thermal hysteresis is less than 1 K, ie significantly lower compared to the solid material. The magnetic field dependence of the adiabatic temperature change is nearly hysteresis-free (less than 0.05 T).

The mechanical integrity of the hot-pressed material remains after multiple thermal or field change cycles receive.

Example 2

From the elements La, Fe and Si, an alloy having the composition LaFe _11.6 Si _{1.4 is} produced by means of an arc melting process. The alloy is then rapidly solidified with the surface speed of the copper wheel of 30 m / s and then heat treated at 1050 ° C for 2 hours. J. Lyubina et al., J. Magn. Magn. Mater. 320, 2252 (2008) ]. The resulting material is in the form of a band having a thickness of 60 microns and consists of 90 wt .-% of the NaZn ₁₃ -type phase and 10 wt .-% of α-Fe.

From the pulverized rapidly solidified strips, a porous, foam-like material is produced by pressing at room temperature (cold pressing) and pressing pressure of 500 MPa. The dimensions of the pressed LaFe _11.6 Si _1.4 alloy are 11 mm diameter × 1 mm height and the density is 85% of the theoretical density of the material.

The cold-pressed LaFe _11.6 Si _1.4 alloy exhibits a maximum magnetic entropy change .DELTA.S _max of 145 kJ / m ³ at 193 K K and a change in magnetic field of 2 Tesla. The half width is 8.3 K and the relative cooling capacity is 1.5 MJ / m ³ . The adiabatic temperature change ΔT _ad remains unchanged after the thermal and magnetic field alternating stress and is 4.3 K at 193 K on cooling from room temperature and during heating of 170 K to room temperature with a magnetic field change of 1.9 Tesla. The thermal hysteresis is less than 0.5 K. The magnetic field dependence of the adiabatic temperature change is virtually hysteresis-free.

This cold-pressed LaFe _11.6 Si _1.4 alloy is hydrogenated at 400 ° C in 0.5 MPa hydrogen gas. The hydrogen concentration of z = 1.64 was measured by hot extraction. This corresponds to a composition of LaFe _11.6 Si _1.4 H _1.64 .

After the hydrogen loading of the cold-pressed material, the temperature at which the maximum of the entropy change or the adiabatic temperature change occurs shifts to 338 K. The adiabatic temperature change ΔT _ad remains unchanged after the thermal and magnetic field cycling and is 3.7 K on cooling Room temperature and when heating from 170 K to room temperature with a magnetic field change of 1.9 Tesla. The temperature and magnetic field dependence of the adiabatic temperature change are almost hysteresis-free.

Alternatively, the rapidly solidified and heat-treated ribbons are hydrogenated at 400 ° C in 0.5 MPa of hydrogen gas and then produced at a temperature of 650 K and a compacting pressure of 500 MPa. The adiabatic temperature change ΔT _ad remains unchanged after the thermal and magnetic field alternating stress and is 3.6 K at 335 K with a magnetic field change of 1.9 Tesla. The temperature and magnetic field dependence of the adiabatic temperature change are almost hysteresis-free.

The Pressing at a temperature of 650 K under vacuum can be done simultaneously used to set the Curie temperature or application temperature become. When pressing in vacuum of 1 Pa at 423 K shifts the temperature at which the maximum of the entropy change or adiabatic temperature change occurs, to 300 K.

The mechanical integrity of the hot or cold pressed material or at a temperature of 650 pressed material lags behind obtained multiple thermal or field change cycles.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 10338467 A1 [0005, 0006]
• US 2006/0076084 A1 [0005]
• US 2007/0137732 A1 [0006]
• US 2004/007944 A1 [0006]
• - US 7186303 B2 [0006]
• US 2006/0231163 [0006]
• US 7069729 [0006]

Cited non-patent literature

• C. Zimm et al., Int. J. Refrigeration 29, 1302 (2006) [0004]
• A. Van, K.-H. Müller, O. Gutfleisch, J. Appl. Phys. 97, 036102 (2005) [0005]
• XB Liu, Z. Altounian, GH Tu, J. Phys .: Condens. Matter 16, 8043 (2004) [0005]
• - VK Pecharsky and KA Gschneidner, Jr., Phys. Rev. Lett. 78, 4494 (1997) [0006]
• - H. Wada and Y. Tanabe, Appl. Phys. Lett. 79, 3302 (2001) [0006]
• A. de Campos et al., Nature Materials 5, 802 (2006) [0006]
• T.Krenke et al., Nature Materials 4, 450 (2005) [0006]
• - O. Tegus, E. Brüsk, KHJ Buschow, and FR de Boer, Nature 415, 150 (2002) [0006]
• A. Fujita et al., Phys. Rev B 65, 014410 (2001) [0007]
• H. Yabuta et al., J. Phys. Soc. Japan, 75, 113707 (2006) [0007]
• J. Lyubina et al., J. Magn. Magn. Mater. 320, 2252 (2008) [0055]

Claims (17)

Magnetic alloy material containing a magnetocaloric effect, and which is a foamy structure with an open porosity of at least 1% and / or having a closed porosity of at least 1%, or at the particle of the magnetic alloy material in a Matrix material with a higher ductility than the magnetic alloy material is embedded. Alloy material according to claim 1, in which ≥ 35 vol .-% of the magnetic alloy material having a crystal structure of NaZn ₁₃ type. The alloy material of claim 2, wherein at least 50% by volume of the magnetic alloy material has a NaZn ₁₃ type crystal structure. An alloy material according to claim 3, wherein 80-90% by volume of the magnetic alloy material has a NaZn ₁₃ type crystal structure. The alloy material of claim 1, wherein the magnetic alloy material has a composition according to the formula: R _a Fe _100-axyz T _x M _y L _z where R = La or a combination of La with Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and / or Y, T = at least one element selected from the group Sc, Ti , V, Cr, Mn, Co, Ni, Cu and / or Zn, M = Al, Si, P, Ga, Ge, In and / or Sn, L = H, B, C and / or N, 5 ≤ a ≤ 11 and 0 ≤ x ≤ 12 and 2 ≤ y ≤ 20 and 0 ≤ z ≤ 18, (all in atomic%) An alloy material according to claim 5, wherein the alteration the Curie temperature of the magnetic alloy material the conditions 2 ≦ z ≦ 15 at% and / or 3 ≦ y ≦ 16 and / or 0.3 ≤ x ≤ 9, where with varying proportion z and / or y and / or x the Curie temperature varies between 170 K and 400 K The alloy material of claim 1, wherein the foam-like Structure of the magnetic alloy material an open porosity from 2 to 50% and / or a closed porosity of 2 to 50%. The alloy material of claim 1, wherein particles of the magnetic alloy material having a particle size from 10 nm to 1 mm embedded in a matrix material. The alloy material of claim 1, wherein the matrix material with a higher ductility than the magnetic one Alloy material from at least one element of Al, Ag, Au, Bi, C, Co, Cu, Fe, Ga, Ni, Pb, Pd, Pt, Sn, Ti, Zn or combinations and / or Reaction products thereof. Alloy material according to claim 1, wherein besides the matrix material, a second material of at least one element of Al, Ag, Au, Bi, C, Co, Cu, Fe, Ga, Ni, Nb, Pb, Pd, Pt, Sn, Ta, Ti, V, Zn, Zr or combinations and / or reaction products also with the matrix material thereof. An alloy material according to claim 1, wherein said Matrix material has at least a 10% higher ductility as the magnetic alloy material. The alloy material of claim 1, wherein the Particles of the magnetic alloy material in the form of a band, a wire, a plate, a foil or a flake, a Needle or in the form of powder particles. Method for producing a magnetic alloy material, wherein the magnetic alloy material becomes a foam-like structure processed by foaming or compaction or particles of the magnetic alloy material with a matrix material, which a higher ductility than the magnetic alloy material has mixed, and then heated so far that the Matrix material the matrix around the particles of the magnetic alloy material formed. The method of claim 13, wherein the compaction performed by hot or cold pressing. The method of claim 13, wherein the foaming is done by putting on a foamy structure a suspension with particles of magnetic alloy material is applied and dried, and subsequently the foam-like structure is burned out or pyrolyzed. A method according to claim 13, wherein particles of the mixed magnetic alloy material and the matrix material and processed into a shaped article and subsequently heated this shaped body to a temperature in which the matrix material at least softens and the particles of the magnetic alloy material substantially complete covered. The method of claim 13, wherein the application temperature by applying a vacuum is set.