MAGNETOCALORIC MATERIALS COMPRISING MANGANESE, IRON, SILICON, PHOSPHORUS AND CARBON

Abstract

Described are magnetocaloric materials comprising manganese, iron, phosphorus, silicon, carbon and optionally one or both of nitrogen and boron, and processes for producing said magnetocaloric materials.

Claims

1. A magnetocaloric material, which has a composition satisfying formula (I)
(Mn.sub.xFe.sub.1-x).sub.2+uP.sub.ySi.sub.vC.sub.zN.sub.rB.sub.w(I) wherein 0.1u0.1, 0.2x0.8, 0.3y0.75, 0.25v0.7, 0.001z0.15, 0r0.1, 0w0.1, y+v+w1.05, and y+v+w+r0.95.

2. The magnetocaloric material of claim 1, which exhibits a hexagonal crystalline structure of the Fe.sub.2P type with a crystal lattice having the space group P-62m, wherein carbon atoms occupy interstitial sites of said crystal lattice, boron atoms, if present, occupy crystal sites of said crystal lattice, and nitrogen atoms, if present occupy crystal sites and/or interstitial sites of said crystal lattice.

3. The magnetocaloric material of claim 2, wherein carbon atoms occupy interstitial sites selected from the group consisting of 6k and 6j sites.

4. The magnetocaloric-material of claim 1, wherein 0.05u0.05 0.3x0.7, 0.4y0.7 0.3v0.6 0.003z0.12, 0r0.07, 0w0.08 y+v+w1.02, and y+v+w+r0.98.

5. The magnetocaloric material of claim 1, wherein 0.1u0.1, 0.2x0.8, 0.3y0.75, 0.25v0.7, 0.001z0.15, and 0.95y+v1.05.

6. The magnetocaloric material of claim 5, which is selected from the group consisting of Mn.sub.1.25Fe.sub.0.7P.sub.0.5Si.sub.0.5C.sub.0.05, Mn.sub.1.25Fe.sub.0.7P.sub.0.5Si.sub.0.5C.sub.0.1, Mn.sub.1.25Fe.sub.0.7P.sub.0.5Si.sub.0.5C.sub.0.15, Mn.sub.1.25Fe.sub.0.7P.sub.0.5Si.sub.0.5N.sub.0.03C.sub.0.059 Mn.sub.1.25Fe.sub.0.7P.sub.0.5Si.sub.0.5N.sub.0.03C.sub.0.1, Mn.sub.1.25Fe.sub.0.7P.sub.0.5Si.sub.0.5N.sub.0.03C.sub.0.159 Mn.sub.1.25Fe.sub.0.7P.sub.0.6Si.sub.0.4C.sub.0.05, Mn.sub.1.25Fe.sub.0.7P.sub.0.6Si.sub.0.4C.sub.0.1, Mn.sub.1.25Fe.sub.0.7P.sub.0.6Si.sub.0.4C.sub.0.15, MnFe.sub.0.95P.sub.0.67Si.sub.0.33C.sub.0.01, MnFe.sub.0.95P.sub.0.67Si.sub.0.33C.sub.0.02, MnFe.sub.0.95P.sub.0.67Si.sub.0.33C.sub.0.03, MnFe.sub.0.95P.sub.0.67Si.sub.0.33C.sub.0.05, MnFe.sub.0.95P.sub.0.67Si.sub.0.33C.sub.0.1, MnFe.sub.0.95P.sub.0.575Si.sub.0.33B.sub.0.075C.sub.0.05N.sub.0.02, Mn.sub.1.18Fe.sub.0.73P.sub.0.48Si.sub.0.52C.sub.0.012, Mn.sub.1.19Fe.sub.0.73P.sub.0.48Si.sub.0.52C.sub.0.032, and Mn.sub.1.16Fe.sub.0.75P.sub.0.47Si.sub.0.53C.sub.0.06.

7. A process for preparing the magnetocaloric material of claim 1, said process comprising: (a) providing a mixture of precursors comprising atoms of the elements iron, manganese, phosphorous, silicon and optionally carbon (b) reacting the mixture provided in (a) to obtain a solid reaction product, wherein (b) comprises (b-1) reacting the mixture provided in (a) in the solid phase and obtaining a solid reaction product and/or (b-2) transferring the mixture provided in (a) or the solid reaction product obtained in (b-1) into the liquid phase, reacting it in the liquid phase, obtaining a liquid reaction product, transferring the liquid reaction product into the solid phase, and obtaining a solid reaction product, (c) optionally shaping of the solid reaction product obtained in (b) to obtain a shaped solid reaction product, (d) optionally exposing the solid reaction product obtained in (b) or the shaped solid reaction product obtained in (c) to an atmosphere comprising one or more hydrocarbons to obtain a carburized product, (e) heat treatment of the solid reaction product obtained in (b), the shaped solid reaction product obtained in (c) or the carburized product obtained in (d) to obtain a heat treated product, (f) cooling the heat treated product obtained in (e) to obtain a cooled product, and (g) optionally shaping of the cooled product obtained in (f), with the proviso that at least one of the following conditions is fulfilled: the mixture provided in (a) comprises atoms of the elements iron, manganese, phosphorous, silicon and carbon (d) is performed.

8. The process of claim 7, wherein said mixture of precursors comprises one or more substances selected from the group consisting of elemental manganese, elemental iron, elemental silicon, elemental phosphorus, an iron phosphide, a manganese phosphide, and optionally one or more of elemental carbon, an iron carbide, a manganese carbide, a carbonizable organic compound, elemental boron, an iron nitride, an iron boride, a manganese boride, ammonia gas and nitrogen gas.

9. The process of claim 7, wherein (b-1) comprises ball-milling so that a reaction product in the form of a powder is obtained.

10. The process of claim 7, wherein in (b-2) transferring the liquid reaction product into the solid phase is carried out by quenching, melt-spinning or atomization.

11. The process of claim 7, wherein the one or more hydrocarbons used in (d) are selected from the group consisting of methane, propane and acetylene.

12. The process of claim 7, wherein in (e) the heat treatment comprises sintering the solid reaction product obtained in (b), the shaped solid reaction product obtained in (c) or the carburized product obtained in (d).

13. The process of claim 7, wherein in (e) the heat treatment is carried out at a temperature in the range of from 900 to 1250 C.

14. (canceled)

15. A device, selected from the group consisting of a cooling system, a heat exchanger, a heat pump, a thermomagnetic generator and a thermomagnetic switch, wherein said device comprises at least one magnetocaloric material of claim 1.

Description

[0207] FIGS. 1A to 1D show the temperature dependence of the specific magnetization (magnetization per mass) recorded on cooling and heating (sweeping rate 2 k/min) in a magnetic field of 1 T for materials the materials according to tables 1-4.

[0208] FIG. 2 shows for all the materials of table 1 the magnetic entropy change Sm at a field change of 1 T

[0209] FIGS. 3A to 3D show the magnetic entropy change Sm at a field change of 0.5 T, 1 T, 1.5 T and 2 T for each of the individual materials of table 1.

[0210] 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 each material of table 4.

[0211] The parameters Curie temperature Tc, thermal hysteresis Thys and magnetic entropy change Sm (if measured) of the materials according to tables 1-4 are listed in tables 5-8 below:

TABLE-US-00005 TABLE 5 T.sub.C/[K] S.sub.m/[Jkg.sup.1K.sup.1] Mn.sub.1.25Fe.sub.0.7P.sub.0.5Si.sub.0.5C.sub.z cooling heating T.sub.hys/[K] 0.5 T 1.0 T 1.5 T 2.0 T z = 0.00 257.6 262.2 4.6 6.97 13.43 18.56 21.01 z = 0.05 276.7 277.2 0.5 5.88 9.79 11.65 13.02 z = 0.10 259.6 263.1 3.5 3.46 7.12 9.60 11.19 z = 0.15 269.9 271.2 1.3 3.05 5.61 7.53 9.21

TABLE-US-00006 TABLE 6 T.sub.c/[K] Mn.sub.1.25Fe.sub.0.7P.sub.0.5Si.sub.0.5N.sub.0.03C.sub.z cooling heating T.sub.hys/[K] z = 0.00 216.8 228.5 11.7 z = 0.05 239.7 247.1 7.4 z = 0.10 229.7 238.1 8.4 z = 0.15 229.8 239.2 9.4

TABLE-US-00007 TABLE 7 T.sub.c (K) Mn.sub.1.25Fe.sub.0.7P.sub.0.6Si.sub.0.4C.sub.z cooling heating T.sub.hys (K) z = 0.00 120.8 156.2 35.4 z = 0.05 128.5 154.2 21.0 z = 0.10 147.5 168.5 25.7 z = 0.15 130.8 159.1 28.3

TABLE-US-00008 TABLE 8 T.sub.C/[K] S.sub.m/[Jkg.sup.1K] MnFe.sub.0.95P.sub.0.595rSi.sub.0.33B.sub.0.075C.sub.0.05N.sub.r cooling heating T.sub.hys/[K] 0.5 T 1.0 T 1.5 T 2.0 T r = 0.00 274.9 276.3 1.4 2.1 4.0 5.4 6.6 r = 0.02 243.7 248.2 4.5 2.1 4.8 6.9 8.8

[0212] It is concluded from tables 5-8 that the presence of carbon, and optionally one or both boron and nitrogen allows to adjust the parameters Curie temperature Tc, thermal hysteresis Thys and magnetic entropy change Sm, relative to the corresponding parent material consisting of iron, manganese, phosphorus and silicon.

[0213] FIG. 5A shows for the melt-spun materials MnFe.sub.0.95P.sub.0.67Si.sub.0.33, MnFe.sub.0.95P.sub.0.67Si.sub.0.33C.sub.0.05 and MnFe.sub.0.95P.sub.0.67Si.sub.0.33C.sub.0.01 that the magnetic field strength needed to reach a specific magnetization of 154 Am.sup.2/kg decreases with increasing carbon content. FIG. 5B shows for the same materials that the specific magnetization achieved at a field strength of 0.2 T increases with increasing carbon content. Accordingly, magnetocaloric materials which comprise carbon in addition to manganese, iron, phosphorus and silicon reach the same specific magnetization at a lower magnetic field strength, compared to magnetocaloric materials which comprise manganese, iron, silicon, phosphorus and no carbon.