MAGNETOCALORIC REGENERATORS COMPRISING MATERIALS CONTAINING COBALT, MANGANESE AND BORON

Abstract

Described is a magnetocaloric regenerator comprising one or more materials containing cobalt, manganese and boron and optionally carbon.

Claims

1. A method for preparing a material, the method comprising: (a) providing a mixture of precursors comprising atoms of the elements cobalt, manganese, boron, and carbon, and (b) reacting the mixture provided in step (a) to obtain a solid reaction product, comprising (b-1) reacting the mixture provided in step (a) in the solid phase obtaining a solid reaction product, and/or (b-2) transferring the mixture provided in step (a) or the solid reaction product obtained in step (b-1) into the liquid phase and reacting it in the liquid phase obtaining a liquid reaction product, and transferring the liquid reaction product into the solid phase obtaining a solid reaction product, and (c) optionally shaping of the solid reaction product obtained in step (b) to obtain a shaped solid reaction product, and (d) heat treatment of the solid reaction product obtained in step (b-1) or (b-2) or of the shaped solid reaction product obtained in step (c) to obtain a heat treated product, and (e) cooling the heat treated product obtained in step (d) to obtain a cooled product, and (f) optionally shaping of the cooled product obtained in step (e).

2. The process according to claim 1, wherein said mixture of precursors comprises one or more substances selected from the group consisting of elemental cobalt, elemental manganese, elemental boron, elemental carbon, borides of cobalt, borides of manganese, carbides of manganese, and carbides of boron.

3. The process according to claim 1, wherein in step (b-2) transferring the mixture provided in step (a) or the solid reaction product obtained in step (b-1) into the liquid phase comprises arc-melting.

4. The process according to claim 1, wherein in step (b-2) transferring the mixture provided in step (a) into the liquid phase comprises arc-melting and transferring the obtained liquid reaction product into the solid phase comprises casting the obtained melt into an ingot, and step (b-2) optionally comprises up to 6 times remelting the obtained ingot and recasting the obtained melt into a recast ingot.

5. The process according to claim 1, wherein in step (d) the heat treatment comprises holding the solid reaction product obtained in step (b) or the shaped solid reaction product obtained in step (c) at a temperature in the range of from 1000 K to 1300 K, over a duration of from 10 to 180 hours, and in step (e) the heat treated product obtained in step (d) is cooled by quenching at a cooling rate of at least 10 K/s, or by furnace cooling.

6. A magnetocaloric regenerator comprising one or more materials having a composition according to general formula (A)
Co.sub.2-xMn.sub.xB.sub.1-yC.sub.y(A) wherein 0.5x1 and 0y0.5.

7. The magnetocaloric regenerator according to claim 6, wherein said materials having a composition according to general formula (A) are materials having a composition according to formula (II)
Co.sub.2-xMn.sub.xB(II) wherein 0.5x1.

8. The magnetocaloric regenerator according to claim 7, wherein one or more of said materials have a composition according to formula (II), wherein 0.65x0.85.

9. The magnetocaloric regenerator according to claim 6, wherein the magnetocaloric regenerator comprises a cascade comprising three or more different materials each having a composition according to general formula (A), wherein in said cascade said materials are arranged in succession by ascending or descending Curie temperature.

10. The magnetocaloric regenerator according to claim 9, wherein said materials having a composition according to general formula (A) have Curie temperatures in the range of from 160 K to 420 K.

11. The magnetocaloric regenerator according to claim 9, wherein in said cascade the temperature difference between two succeeding materials is in each case in the range of from 0.5 K to 6 K.

12. A device selected from the group consisting of refrigeration systems, climate control units, air conditioning devices, thermomagnetic power generators, heat exchangers, heat pumps, magnetic actuators, and magnetic switches. said device comprising a magnetocaloric regenerator according to claim 6.

13. A process for producing a magnetocaloric regenerator according to claim 6, wherein said process comprises preparing or providing one or more materials having a composition according to general formula (A)
Co.sub.2-xMn.sub.xB.sub.1-yC.sub.y(A) wherein 0.5x1 and 0y0.5.

14. The process according to claim 13, wherein a material having a composition according to formula (II) is prepared, formula (II)
Co.sub.2-xMn.sub.xB(II) wherein 0.5x1 wherein preparing said material comprises the steps of (a) providing a mixture of precursors comprising atoms of the elements cobalt, manganese and boron and (b) reacting the mixture provided in step (a) to obtain a solid reaction product, comprising (b-1) reacting the mixture provided in step (a) in the solid phase obtaining a solid reaction product and/or (b-2) transferring the mixture provided in step (a) or the solid reaction product obtained in step (b-1) into the liquid phase and reacting it in the liquid phase obtaining a liquid reaction product, and transferring the liquid reaction product into the solid phase obtaining a solid reaction product, and (c) optionally shaping of the solid reaction product obtained in step (b) to obtain a shaped solid reaction product, and (d) heat treatment of the solid reaction product obtained in step (b-1) or (b-2) or of the shaped solid reaction product obtained in step (c) to obtain a heat treated product, and (e) cooling the heat treated product obtained in step (d) to obtain a cooled product, and (f) optionally shaping of the cooled product obtained in step (e).

15. The process according to claim 14, wherein said mixture of precursors comprises one or more substances selected from the group consisting of elemental cobalt, elemental manganese, elemental boron, borides of cobalt, and borides of manganese.

16. The process according to claim 14, wherein in step (b-2) transferring the mixture provided in step (a) or the solid reaction product obtained in step (b-1) into the liquid phase comprises arc-melting.

17. The process according to claim 14, wherein in step (b-2) transferring the mixture provided in step (a) into the liquid phase comprises arc-melting and transferring the obtained liquid reaction product into the solid phase comprises casting the obtained melt into an ingot, and step (b-2) optionally comprises up to 6 times remelting the obtained ingot and recasting the obtained melt into a recast ingot.

18. The process according to claim 14, wherein in step (d) the heat treatment comprises holding the solid reaction product obtained in step (b) or the shaped solid reaction product obtained in step (c) at a temperature in the range of from 1000 K to 1300 K, over a duration of from 10 to 180 hours, and in step (e) the heat treated product obtained in step (d) is cooled by quenching at a cooling rate of at least 10 K/s, or by furnace cooling.

Description

EXAMPLES

Materials Having a Composition According to Formula (II)

[0204] For each material of formula (II) to be produced, in step (a) a mixture of precursors (total mass about 0.3 g) consisting of stoichiometric amounts of [0205] cobalt powder (99.5%, 325 mesh, purified by heating under H.sub.2 flow at 773 K for 5 hours), [0206] manganese powder (99.95%, 325 mesh), [0207] and crystalline boron powder (98%, 325 mesh) [0208] (all obtained from Alfa Aesar) was provided.

[0209] The powders were mixed mechanically inside glass vials and the obtained mixtures were compacted into pellets.

[0210] In step (b-2), the compacted mixtures of precursors provided in step (a) were transferred into the liquid phase by arc melting and the obtained liquid reaction products were transferred into the solid phase by casting the obtained melt into an ingot. Each ingot was turned over and remelted up to 6 times in order to increase homogeneity of the chemical composition and crystal structure of the as-cast samples.

[0211] The ingots obtained in step (b-2) were placed in silica tubes having 10 mm inner diameter, and the tubes were sealed under vacuum (<10.sup.2 mbar). In step (d) the sealed tubes containing the ingots were heated to 1273 K in 10 hours, held at this temperature for 96 hours, and in step (e) the tubes containing the samples were cooled to room temperature with the furnace turned off (furnace-cooling).

[0212] The preparation and handling of the samples were performed in an atmosphere of argon inside a glove-box (content of O.sub.2<1 ppm).

[0213] All synthesized samples were characterized by powder X-ray diffraction using a PANalytical X'Pert Pro diffractometer equipped with X'Celerator detector (MoK radiation, =0.71073 ). Phase identification was performed by means of WinXPOW and HighScore Plus software. Profile deconvolution, indexing and refinement of unit cell parameters were performed by WinCSD.

[0214] Magnetic measurements were performed on ground samples using a MPMS XL SQUID magnetometer (Quantum Design). Magnetization was measured in an applied magnetic field of 0.01 T in a field-cooled (FC) mode over a temperature range of from 3 K to 400 K. The Curie temperature was determined from these measurements.

[0215] To calculate the magnetocaloric effect (MCE), magnetization (M) as a function of temperature (T) curves were recorded in various magnetic fields (H) in the range of 0.1 T to 2 T using Quantum Design magnetometers SQUID MPMS-XL and VersaLab VSM. The measured M(T) curves were converted to M(H) curves by interpolation. The entropy change, S, was then derived indirectly using the Maxwell equation.

[00001]$S\left(T,H\right)={}_0^{H_{\max }}{\left(\frac{M}{T}\right)}_{H}dH$

[0216] Table 1 compiles crystallographic data and Curie temperatures of all prepared samples showing the unit cell parameters with estimated standard deviation (e.s.d.) values in parentheses.

TABLE-US-00001 TABLE 1 x (Mn) a [] c [] V [3] Tc [K] 0.50 not determined not determined not determined 386 0.55 5.0016(5) 4.1723(5) 104.37(3) 365 0.60 5.0033(6) 4.1783(6) 104.59(4) 349 0.65 5.0084(4) 4.1739(4) 104.70(3) 325 0.75 5.0127(3) 4.1730(3) 104.85(2) 288 0.80 5.0173(9) 4.170(1) 104.97(6) not determined 0.85 5.0187(6) 4.1692(5) 105.01(4) 228 0.90 5.0227(5) 4.1707(4) 105.22(3) 201 0.95 5.022(1) 4.1652(7) 105.06(6) 169 1.00 5.0256(8) 4.1678(6) 105.26(5) 162

[0217] FIG. 1 shows the powder X-ray diffraction (XRD) patterns of the materials listed in table 1. With increasing content of manganese the positions of diffraction lines observed in the X-ray pattern gradually changes. No additional reflections are observed.

[0218] FIG. 2 shows that the Curie temperature decreases continuously with increasing content of manganese.

[0219] FIG. 3 shows the specific magnetization (M) as a function of temperature (T) at a magnetic field strength of 0.01 T for the materials listed in table 1.

[0220] FIGS. 4A and 4B show the magnetic entropy change Sm at a field change of 0.5 T, 1 T, 1.5 T and 2 T for Co.sub.1.35Mn.sub.0.65B and Co.sub.1.25Mn.sub.0.75B, resp.

Comparison of Materials Having a Composition According to General Formula (A) With and Without Carbon

[0221] For each material to be produced (see table 3 below), in step (a) a mixture of precursors (total mass about 0.3 g) consisting of stoichiometric amounts of [0222] cobalt powder (99.5%, 325 mesh, purified by heating under H.sub.2 flow at 773 K for 5 hours), [0223] manganese powder (99.95%, 325 mesh), [0224] and crystalline boron powder (98%, 325 mesh) [0225] acetylene black [0226] was provided.

[0227] The powders were mixed mechanically inside glass vials and the obtained mixtures were compacted into pellets.

[0228] In step (b-2), the compacted mixtures of precursors provided in step (a) were transferred into the liquid phase by arc melting and the obtained liquid reaction products were transferred into the solid phase by casting the obtained melt into an ingot. Each ingot was turned over and remelted up to 6 times in order to increase homogeneity of the chemical composition and crystal structure of the as-cast samples.

[0229] The ingots obtained in step (b-2) were placed in silica tubes having 10 mm inner diameter, and the tubes were sealed under vacuum (<10.sup.2 mbar). In step (d) the sealed tubes containing the ingots were heated to 1273 K in 10 hours, held at this temperature for 168 hours, and in step (e) the tubes containing the samples were cooled to room temperature with the furnace turned off (furnace-cooling).

[0230] The preparation and handling of the samples were performed in an atmosphere of argon inside a glove-box (content of O.sub.2<1 ppm).

[0231] All synthesized samples were characterized by powder X-ray diffraction using a PANalytical X'Pert Pro diffractometer equipped with X'Celerator detector (CuK radiation, =1.54178 ). Phase identification, profile deconvolution, indexing and refinement of unit cell parameters were performed by WinCSD or Highscore Plus.

[0232] Magnetic measurements were performed on ground samples using a MPMS XL SQUID magnetometer (Quantum Design). Magnetization was measured in an applied magnetic field of 0.01 T in a field-cooled (FC) mode over a temperature range of from 3 K to 400 K. The Curie temperature (see table 3) was determined from these measurements.

[0233] FIG. 5 shows the powder X-ray diffraction (XRD) patterns of materials having a composition Co.sub.2-xMn.sub.xB.sub.0.5C.sub.0.5 with x=0.6; 0.7 and 0.75. For comparison, the powder X-ray diffraction (XRD) pattern of Co.sub.2B is displayed, too. As in FIG. 1, with increasing content of manganese the X-ray pattern gradually changes. The XRD patterns do not exhibit any features related to the presence of carbon. Without wishing to be bound by any theory, it is presently assumed that the presence of carbon virtually does not change the crystal structure. It is noted thatas known by the skilled personthe application of CuK radiation instead of MoK radiation (see above and FIG. 1) causes a shift in the diffraction angles to higher values, as can be recognized by comparison of FIG. 5 and FIG. 1. For instance the peak at about 2=22 in FIG. 1 is shifted to about 2=46 in FIG. 5.

[0234] Table 2 compiles crystallographic data of materials having a composition Co.sub.2-xMn.sub.xB.sub.0.5C.sub.0.5 with x=0.6; 0.7 and 0.75, showing the unit cell parameters with estimated standard deviation (e.s.d.) values in parentheses. In table 2 as well as in table 1, the e.s.d. values are in each case associated with the last digit. For example 4.2273(8) shall mean that the value could vary between 4.2265 and 4.2281.

TABLE-US-00002 TABLE 2 x (Mn) a [] c [] 0.60 5.07326(6) 4.2273(8) 0.7 5.069(1) 4.227(1) 0.75 5.0645(8) 4.228(1)

[0235] FIG. 6 shows the specific magnetization (M) as a function of temperature (T) at a magnetic field strength of 0.01 T for the materials listed in table 3. As in FIG. 3 it can be seen that the Curie temperature decreases continuously with increasing content of manganese.

TABLE-US-00003 TABLE 3 x y Tc/[K] 0.6 0 371.4 0.6 0.05 375.4 0.6 0.1 379.7 0.7 0.05 345.9 0.7 0.1 369.1 0.75 0 325.2 0.75 0.05 326.9

[0236] FIG. 7 shows the specific magnetization (M) as a function of temperature (T) at a magnetic field strength of 0.01 T of materials having a composition Co.sub.1.4Mn.sub.0.6B.sub.1-yC.sub.y with y=0, 0.05 and 0.1. It can be seen from FIG. 7 and table 3 that the Curie temperature slightly increases with the substitution of carbon for boron.

[0237] Comparison of the Curie temperatures of those materials in table 3 with y=0 with the Curie temperature of materials having the same manganese content x in table 1 shows that the increased annealing time in step (d) (96 hours for the materials in table 1 vs. 168 hours for the materials in table 3) results in an increase of the Curie temperature. Thus, the Curie temperature can be varied by means of changing the chemical composition as well as by means of changing the annealing time in step (d).

[0238] The invention also relates to the following embodiments: [0239] 1. A magnetocaloric regenerator comprising one or more materials having a composition according to formula (I)

Co.sub.2-xMn.sub.xB(I) [0240] wherein 0.5 x1. [0241] 2. The magnetocaloric regenerator according to embodiment 1, wherein one or more of said materials have a composition according to formula (II)

Co.sub.2-xMn.sub.xB(II) [0242] wherein 0.5<x<1 [0243] with the proviso that x is not one of 0.6, 0.7 and 0.8. [0244] 3. The magnetocaloric regenerator according to embodiment 1, wherein one or more of said materials have a composition according to formula (I)

Co.sub.2-xMn.sub.xB(I) [0245] wherein 0.65 x0.85. [0246] 4. The magnetocaloric regenerator according to any preceding embodiment, [0247] wherein the magnetocaloric regenerator comprises a cascade comprising three or more different materials each having a composition according to formula (I), [0248] preferably 5 to 100 different materials each having a composition according to formula (I), [0249] wherein in said cascade said materials are arranged in succession by ascending or descending Curie temperature. [0250] 5. The magnetocaloric regenerator according to embodiment 4, wherein said materials having a composition according to formula (I) have Curie temperatures in the range of from 160 K to 390 K, [0251] preferably of from 220 K to 330 K. [0252] 6. The magnetocaloric regenerator according to embodiment 4 or 5, wherein in said cascade the temperature difference between two succeeding materials having a composition according to formula (I) is in each case in the range of from 0.5 K to 6 K, preferably 0.5 to 4 K and even more preferably 0.5 to 2.5 K. [0253] 7. Use of a material having a composition according to the general formula (I)

Co.sub.2-xMn.sub.xB(I) [0254] wherein 0.5x1 [0255] in a magnetocaloric regenerator. [0256] 8. A device selected from the group consisting of [0257] refrigeration systems, climate control units, air conditioning devices, thermomagnetic power generators, heat exchangers, heat pumps, magnetic actuators and magnetic switches, [0258] said device comprising a magnetocaloric regenerator according to any of embodiments 1 to 6. [0259] 9. Use of a magnetocaloric regenerator according to any of embodiments 1 to 6 in a device selected from the group consisting of refrigeration systems, climate control units, air conditioning devices, thermomagnetic power generators, heat exchangers, heat pumps, magnetic actuators and magnetic switches. [0260] 10. A process for producing a magnetocaloric regenerator according to any of embodiments 1 to 6, [0261] wherein said process comprises preparing or providing one or more materials having a composition according to formula (I)

Co.sub.2-xMn.sub.xB(I) [0262] wherein 0.5x1. [0263] 11. The process according to embodiment 10, wherein preparing a material having a composition according to formula (I) comprises the steps of [0264] (a) providing a mixture of precursors comprising atoms of the elements cobalt, manganese and boron [0265] and [0266] (b) reacting the mixture provided in step (a) to obtain a solid reaction product, comprising [0267] (b-1) reacting the mixture provided in step (a) in the solid phase obtaining a solid reaction product [0268] and/or [0269] (b-2) transferring the mixture provided in step (a) or the solid reaction product obtained in step (b-1) into the liquid phase and reacting it in the liquid phase obtaining a liquid reaction product, and transferring the liquid reaction product into the solid phase obtaining a solid reaction product, [0270] and [0271] (c) optionally shaping of the solid reaction product obtained in step (b) to obtain a shaped solid reaction product, [0272] and [0273] (d) heat treatment of the solid reaction product obtained in step (b-1) or (b-2) or of the shaped solid reaction product obtained in step (c) to obtain a heat treated product, [0274] and [0275] (e) cooling the heat treated product obtained in step (d) to obtain a cooled product, [0276] and [0277] (f) optionally shaping of the cooled product obtained in step (e). [0278] 12. Process according to embodiment 11, wherein said mixture of precursors comprises one or more substances selected from the group consisting of elemental cobalt, elemental manganese, elemental boron, borides of cobalt, borides of manganese. [0279] 13. Process according to embodiment 11 or 12, wherein in step (b-2) transferring the mixture provided in step (a) or the solid reaction product obtained in step (b-1) into the liquid phase comprises arc-melting. [0280] 14. Process according to any of embodiments 11 to 13, wherein [0281] in step (b-2) transferring the mixture provided in step (a) into the liquid phase comprises arc-melting and transferring the obtained liquid reaction product into the solid phase comprises casting the obtained melt into an ingot, [0282] and step (b-2) optionally comprises up to 6 times remelting the obtained ingot and recasting the obtained melt into a recast ingot. [0283] 15. Process according to any of embodiments 11 to 14 wherein [0284] in step (d) the heat treatment comprises holding the solid reaction product obtained in step (b) or the shaped solid reaction product obtained in step (c) at a temperature in the range of from 1000 K to 1300 K, over a duration of from 10 to 170 hours, [0285] and in step (e) the heat treated product obtained in step (d) is cooled by quenching at a cooling rate of at least 10 K/s, or by furnace cooling.