TWI459409B - Process for preparing metal-based materials for magnetic cooling or heat pumps - Google Patents

Description

Method for manufacturing a metal-based material for magnetic cooling or heat pump

The present invention relates to a method of manufacturing a metal-based material for magnetic cooling or heat pump, a material of this type and its use. The materials made in accordance with the present invention are used in magnetic cooling, heat pump or air conditioning systems.

Materials of this type are generally known and described, for example, in WO 2004/068512. The magnetic cooling technique is based on the Magnetic Card Effect (MCE) and can form an alternative to a known vapor cycle cooling method. In materials exhibiting a magnetic card effect, aligning the magnetic moments of random alignment by an external magnetic field causes the material to heat up. This heat can be removed from the MCE material to the surrounding atmosphere by thermal transfer. When the magnetic field is subsequently turned off or removed, the magnetic moments return to random alignment, which causes the material to cool below the ambient temperature. This effect can be used for cooling purposes; see also Nature, Vol. 415, January 10, 2002, pp. 150-152. Typically, a heat transfer medium such as water is used to remove heat from the magnetic card material.

A commonly used material is obtained by a method in which a starting element or a starting alloy of the material is subjected to a solid phase reaction in a ball mill, and then pressed, sintered and heat-treated in an inert atmosphere and then gradually cooled to room temperature. This method is described, for example, in J. Appl. Phys. 99, 2006, 08Q107.

It is also possible to process by means of melt spinning. This makes it possible to achieve a more uniform elemental distribution which results in an improved magnetic card effect; see Rare Metals, Vol. 25, October 2006, pages 544-549. In the method described therein, the starting element is first inductively melted in an argon atmosphere and then sprayed onto the rotating copper drum via a nozzle in a molten state. Then at Sintering at 1000 ° C and gradually cooling to room temperature.

Materials obtained by known methods typically exhibit high thermal hysteresis. For example, in the Fe ₂ P type compound substituted by ruthenium or osmium, a large thermal hysteresis value is observed in a wide range of 10 K or more. These materials are therefore not well suited for magnetic card cooling.

It is an object of the present invention to provide a method for producing a metal-based material for magnetic cooling which reduces thermal hysteresis. At the same time, a large magnetic card effect (MCE) should be achieved.

This object is achieved according to the invention by a method for the production of a metal-based material for magnetic cooling or heat pumping, the method comprising the steps of: a) bringing the chemical elements and/or alloys into a solid phase and/or a liquid phase Corresponding to the stoichiometric reaction of the metal-based material, b) converting the reaction product from stage a) to a solid, c) sintering and/or heat treating the solid from stage a) or b), d) The sintered and/or heat treated solid from stage c) is quenched at a cooling rate of at least 100 K/s.

It has been found in accordance with the present invention that thermal hysteresis can be significantly reduced when the metal-based materials are not gradually cooled to ambient temperature after sintering and/or heat treatment but are quenched at a high cooling rate. This cooling rate is at least 100 K/s. The cooling rate is preferably from 100 K/s to 10000 K/s, more preferably from 200 K/s to 1300 K/s. A particularly preferred cooling rate is from 300 K/s to 1000 K/s.

This quenching can be achieved by any suitable cooling method, such as by quenching the solids with water or an aqueous liquid (e.g., via cooling water or an ice/water mixture). Example In this case, the solid can be allowed to fall into the ice-cooled water. The solid may also be quenched by a supercooled gas such as liquid nitrogen. Other quenching methods are known to those skilled in the art. The preferred method herein is controlled and rapid cooling.

Without being bound by theory, the reduced hysteresis can be attributed to the smaller particle size of the quenched composition.

In the methods known hitherto, in each case sintering and heat treatment are gradually cooled, which leads to the formation of larger particle sizes and thus to an increase in thermal hysteresis.

The remaining steps of making a metal-based material are less critical, with the proviso that the sintered and/or heat treated solids in the final step are quenched at the cooling rate of the present invention. The method can be applied to the manufacture of any metal-based material suitable for magnetic cooling. A typical material for magnetic cooling is a multi-metal mixture which typically comprises at least three metal elements and, where appropriate, additionally comprises a non-metallic element. The expression "metal-based materials" indicates that the major proportions of such materials are formed by metals or metallic elements. Typically, the proportion of all materials is at least 50% by weight, preferably at least 75% by weight, especially at least 80% by weight. Suitable metal-based materials are described in detail below.

In step (a) of the process according to the invention, the elements and/or alloys present in the later metal-based material correspond to the stoichiometric conversion of the metal-based material in a solid or liquid phase.

Preferably, the reaction in stage a) is carried out by heating the elements and/or alloys together in a sealed vessel or in an extruder or by performing a solid phase reaction in a ball mill. It is especially preferred to carry out a solid phase reaction, which is especially in a ball mill. Row. This reaction is generally known; see the literature cited in the introduction. Usually, the powder of the individual elements present in the later metal-based material or the alloy powder of two or more of the individual elements is mixed in a powder form in a suitable weight ratio. If necessary, the mixture may be additionally ground to obtain a microcrystalline powder mixture. It is preferred to heat the powder mixture in a ball mill which results in further comminution and good mixing and results in a solid phase reaction of the powder mixture.

Alternatively, the individual elements are mixed in powder form in selected stoichiometry and subsequently melted.

Combined heating in a sealed container allows for the immobilization of volatile elements and control of stoichiometry. In particular, in the case of phosphorus, this element will easily evaporate in an open system.

The reaction is followed by a sintered and/or heat treated solid wherein one or more intermediate steps are provided. For example, the solid obtained in stage a) can be pressed before it is sintered and/or heat treated. This increases the density of the material so that there is a high density of magnetic card material in later applications. This is particularly advantageous because the volume of the magnetic field can be reduced, which may be associated with significant cost savings. The pressing itself is known and can be carried out with or without the presence of a press aid. It is possible to use any suitable mold for this pressing. By pressing, it is possible to obtain a shaped object having a desired three-dimensional structure. The pressing can be followed by sintering and/or heat treatment of stage c) followed by quenching of stage d).

Alternatively, it is possible to deliver the solids obtained from the ball mill to the melt spinning process. The melt spinning process itself is known and, for example, described in Rare Metals, Volume 25, October 2006, pages 544 to 549, and WO 2004/068512.

In such processes, the composition obtained in stage a) is melted and sprayed onto a rotating cold metal roll. This spray can be achieved by means of a high pressure upstream of the nozzle or a low pressure downstream of the nozzle. Usually, a rotating copper drum or reel is used, which can be additionally cooled as appropriate. The copper drum preferably rotates at a surface speed of from 10 m/s to 40 m/s, especially from 20 m/s to 30 m/s. On a copper drum, the liquid composition is at a rate of preferably from 10 ² K/s to 10 ⁷ K/s, more preferably at a rate of at least 10 ⁴ K/s, especially from 0.5 x 10 ⁶ K/s to 2 x 10 ⁶ The rate of K/s is cooled.

Also as in the reaction in stage a), melt spinning can be carried out under reduced pressure or in an inert atmosphere.

Melt spinning achieves a high processing rate because subsequent sintering and heat treatment can be shortened. In particular, on an industrial scale, the manufacture of metal-based materials is therefore economically significant. Spray drying also results in high processing rates. It is especially preferred to carry out melt spinning.

Alternatively, in stage b), spray cooling can be carried out in which the composition from stage a) is melted into the spray tower. The spray tower can, for example, be additionally cooled. In the spray tower, a cooling rate in the range from 10 ³ K/s to 10 ⁵ K/s, especially about 10 ⁴ K/s, is usually achieved.

The sintering and/or heat treatment of the solid is carried out in stage c), preferably by first sintering at a temperature in the range of from 800 ° C to 1400 ° C and then at a temperature in the range of from 500 ° C to 750 ° C. This value is especially suitable for shaped objects, while lower sintering and heat treatment temperatures can be used for powders. For example, sintering can then be carried out at temperatures in the range of from 500 °C to 800 °C. for In the case of a shaped object/solid, sintering is preferably carried out at a temperature in the range of from 1000 ° C to 1300 ° C, especially from 1100 ° C to 1300 ° C. The heat treatment can then be carried out, for example, at 600 ° C to 700 ° C.

Sintering is preferably carried out for a period of from 1 hour to 50 hours, more preferably from 2 hours to 20 hours, especially from 5 hours to 15 hours. The heat treatment is preferably carried out for a period of time ranging from 10 hours to 100 hours, more preferably from 10 hours to 60 hours, especially from 30 hours to 50 hours. The exact period can be adjusted according to the actual needs of the materials.

In the case of using the melt spinning method, sintering can usually be omitted, and the heat treatment can be remarkably shortened, for example, to 5 minutes to 5 hours, preferably 10 minutes to 1 hour. This gives a greater time advantage than the usual values of 10 hours of sintering and 50 hours of heat treatment.

The sintering/heat treatment causes partial melting of the particle boundaries, so that the material is further densified.

The melting and rapid cooling in stage b) thus significantly reduces the duration of stage c). This also allows the continuous manufacture of metal-based materials.

According to the invention, the following sequence of processes is particularly preferred: a) subjecting the chemical elements and/or alloys to a solid phase reaction in a ball mill corresponding to the stoichiometry of the metal-based material, b) in the melt spinning stage a) The material obtained, c) heat treating the solid from stage b) for a period of 10 seconds or 1 minute to 5 hours, preferably 30 minutes, at a temperature in the range of from 430 ° C to 1200 ° C, preferably from 800 ° C to 1000 ° C. Up to 2 hours, d) quenching from stage c) at a cooling rate of 200 K/s to 1300 K/s Heat treated shaped object.

The process of the invention can be used with any suitable metal based material.

Preferably, the metal-based material is selected from the group consisting of: (1) a compound of the formula (I) (A _y B _y-1 ) _2+δ C _w D _x E _z (I)

Wherein: A is Mn or Co, B is Fe, Cr or Ni, and C, D and at least two of EC, D and E are different, have a non-zero concentration and are selected from P, B, Se, Ge, Ga, Si, Sn, N, As, and Sb, wherein at least one of C, D, and E is Ge or Si, and δ is a value in the range of -0.1 to 0.1, and w, x, y, and z are 0 to 1. a value within the range, where w+x+z=1; (2) La and Fe-based compounds La(Fe _x Al _{1-x of} formula (II) and/or (III) and/or (IV) ₁₃ H _y or La(Fe _x Si _1-x ) ₁₃ H _y (II)

Wherein: x is a value from 0.7 to 0.95, y is a value from 0 to 3, preferably from 0 to 2; La(Fe _x Al _y Co _z ) ₁₃ or La(Fe _x Si _y Co _z ) ₁₃ (III)

Where: x is a value from 0.7 to 0.95, y is a value from 0.05 to 1-x, and z is a value from 0.005 to 0.5; LaMn _x Fe _2-x Ge (IV)

Where: x is a value from 1.7 to 1.95, and (3) a MnTP type of Heusler alloy, where T is a transition metal and P is the number of electrons per atom e/a in the range of 7 to 8.5 P-doped metal.

Particularly suitable materials 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. 99.08 Q107 (2006); Nature, 415 Vol. 1, 10, 2002, pp. 150-152; and Physica B 327 (2003), pp. 431-437.

In the compound of the above formula (I), C, D and E are preferably the same or different and are selected from at least one of P, Ge, Si, Sn and Ga.

The metal-based material of the formula (I) is preferably selected from at least a quaternary compound comprising not only Mn, Fe, P and, if appropriate, Sb, but additionally Ge or Si or As or Ge and Si or Ge and As or Si and As or Ge, Si and As.

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.

The material preferably has the general formula MnFe(P _w Ge _x Si _z ).

x is preferably a value in the range of 0.3 to 0.7, w is less than or equal to 1-x and z corresponds to 1-x-w.

The material preferably has a crystalline hexagonal Fe ₂ P structure. Examples of suitable structures are MnFeP _{0.45 to 0.7} , Ge _{0.55 to 0.30,} and MnFeP _{0.5 to 0.70} , and (Si/Ge) _{0.5 to 0.30} .

A suitable compound is additionally M _n1+x Fe _1-x P _1-y Ge _y , wherein x is in the range of -0.3 to 0.5 and y is in the range of 0.1 to 0.6. Also suitable are compounds of the formula Mn _1+x Fe _1-x P _1-y Ge _yz Sb _z wherein x is in the range from -0.3 to 0.5, y is in the range from 0.1 to 0.6, and z is less than y and Less than 0.2. Also suitable are compounds of the formula Mn _1+x Fe _1-x P _1-y Ge _yz Si _z wherein x is in the range of 0.3 to 0.5, y is in the range of 0.1 to 0.66, z is less than or equal to y and less than 0.6.

Preferred La and Fe-based compounds of the formula (II) and/or (III) and/or (IV) are La(Fe _0.90 Si _0.10 ) ₁₃ , La(Fe _0.89 Si _0.11 ) ₁₃ , La (Fe _0.880 Si _{0.120) 13, La (Fe 0.877} Si 0.123) 13, LaFe 11.8 Si 1.2, La (Fe 0.88 Si 0.12) 13 H 0.5, La (Fe 0.88 Si 0.12) 13 H 1.0, LaFe 11.7 Si 1.3 H 1.1, LaFe 11.57 Si _1.43 H _1.3 , La(Fe _0.88 Si _0.12 )H _1.5 , LaFe _11.2 Co _0.7 Si _1.1 , LaFe _11.5 Al _1.5 C _0.1 , LaFe _11.5 Al _1.5 C _0.2 , LaFe _11.5 Al _1.5 C _0.4 , LaFe _11.5 Al _1.5 Co _0.5 , La (Fe _0.94 Co _0.06 ) _11.83 Al _1.17 , La(Fe _0.9 2Co _0.08 ) _11.83 Al _1.17 .

Suitable manganese-containing compounds are MnFeGe, MnFe _0.9 Co _0.1 Ge, MnFe _0.8 Co _0.2 Ge, MnFe _0.7 Co _0.3 Ge, MnFe _0.6 Co _0.4 Ge, MnFe _0.5 Co _0.5 Ge, MnFe _0.4 Co _0.6 Ge, MnFe _0.3 Co _0.7 Ge, MnFe _0.2 Co _0.8 Ge, MnFe _0.15 Co _0.85 Ge, MnFe _0.1 Co _0.9 Ge, MnCoGe, Mn ₅ Ge _2.5 Si _0.5 , Mn ₅ Ge ₂ Si, Mn ₅ Ge _1.5 Si _1.5 , Mn ₅ GeSi ₂ , Mn ₅ Ge ₃ , Mn ₅ Ge _2.9 Sb _0.1 , Mn ₅ Ge _2.8 Sb _0.2 , Mn ₅ Ge _2.7 Sb _0.3 , LaMn _1.9 Fe _0.1 Ge, LaMn _1.85 Fe _0.15 Ge, LaMn _1.8 Fe _0.2 Ge, (Fe _0.9 Mn _0.1 ) ₃ C, (Fe _0.8 Mn _0.2 ) ₃ C, (Fe _0.7 Mn _0.3 ) ₃ C, Mn ₃ GaC, MnAs, (Mn, Fe) As, Mn _1+δ As _0.8 Sb _0.2 , MnAs _0.75 Sb _0.25 , Mn _1.1 As _0.75 Sb _0.25 , Mn _1.5 As _0.75 Sb _0.25 .

Suitable Haussler alloys according to the invention are, for example, Fe ₂ MnSi _0.5 Ge _0.5 , Ni _52.9 Mn _22.4 Ga _24.7 , Ni _50.9 Mn _24.7 Ga _24.4 , Ni _55.2 Mn _18.6 Ga _26.2 , Ni _51.6 Mn _24.7 Ga _23.8 , Ni _52.7 Mn _23.9 Ga _23.4 , CoMnSb, CoNb _0.2 Mn _0.8 Sb, CoNb _0.4 Mn _0.6 SB, CoNb _0.6 Mn _0.4 Sb, Ni ₅₀ Mn ₃₅ Sn ₁₅ , Ni ₅₀ Mn ₃₇ Sn ₁₃ , MnFeP _0.45 As _0.55 , MnFeP _0.47 A _0.53 , Mn _1.1 Fe _0.9 P _0.47 As _0.53 , MnFeP _0.89-x Si _x Ge _0.11 (x = 0.22, x = 0.26, x = 0.30, x = 0.33).

The present invention is also directed to a metal-based material for magnetic cooling which can be obtained by the method described above.

Further, the present invention relates to a metal-based material for magnetic cooling as defined above with reference to a composition not including an As-containing material, the composition having an average crystal size of from 10 nm to 400 nm, more preferably from 20 nm to It is in the range of 200 nm, especially 30 nm to 80 nm. The average crystal size can be determined by X-ray diffraction. When the crystal size becomes too small, the maximum magnetic card effect is lowered. Conversely, when the crystal size is too large, the hysteresis of the system increases.

As described above, the metal-based material of the present invention is preferably used in magnetic cooling. In addition to containing a magnet (preferably a permanent magnet), the corresponding freezer also contains a metal-based material as described above. Cooling of computer chips and solar generators is also possible. Other areas of use are heat pumps and air conditioning systems.

The metal-based material produced by the process of the invention can be in any desired solid form. It can also be in the form of flakes, strips, threads, powders or in the form of shaped objects. Shaped objects such as monoliths or honeycombs can be made, for example, by a hot extrusion process. For example, a cell density of 400 CPI to 1600 CPI or above 1600 CPI may be present. According to the invention, the preference is also The sheet obtained by the rolling method. Advantageous non-porous shaped objects are those formed from thin shaped materials such as tubes, plates, meshes, grids or rods. It is also possible according to the invention to carry out the shaping by means of a metal injection molding (MIM) process.

The invention is illustrated in detail by the following examples.

Instance Example 1

A vacuum quartz ampoule containing a pressed sample of MnFePGe was stored at 1100 ° C for 10 hours to sinter the powder. This sintering was followed by heat treatment at 650 ° C for 60 hours to produce homogenization. Instead of slowly cooling to room temperature in an oven, the sample was immediately quenched to room temperature in water. Quenching in water produces some degree of oxidation on the surface of the sample. The outer oxide shell is removed by dilute acid etching. The XRD pattern shows that all samples were crystallized in a Fe ₂ P type structure.

The following composition was obtained: Mn _1.1 Fe _0.9 P _0.81 Ge _0.19 ; Mn _1.1 Fe _0.9 P _0.78 Ge _0.22 ; Mn _1.1 Fe _0.9 P _0.75 Ge _0.25 ; and Mn _1.2 Fe _0.8 P _0.81 Ge _0.19 . For these samples in a given order, the observed values of thermal hysteresis were 7 K, 5 K, 2 K, and 3 K. This thermal hysteresis has been substantially reduced compared to slow cooled samples with thermal hysteresis greater than 10K.

The thermal hysteresis was measured in a magnetic field of 0.5 tesla.

Mn _1.1 Fe _0.9 B _0.78 Ge _0.22 close to the Curie temperature is magnetized isothermally with an elevated magnetic field. For a magnetic field of up to 5 Tesla, a field-induced transition behavior of a large MCE is observed.

The Curie temperature can be adjusted by changing the Mn/Fe ratio and the Ge concentration, and the thermal hysteresis value can also be adjusted in this way.

For the maximum magnetic field change of 0 to 2 Tesla, the change in magnetic entropy calculated from DC magnetization using Maxwell's relationship is 14 J/kgK, 20 J/ for the first three samples, respectively. kgK and 12.7 J/kgK.

The Curie temperature and thermal hysteresis decrease as the Mn/Fe ratio increases. Therefore, the MnFePGe compound exhibits a relatively large MCE value in a low magnetic field. The thermal hysteresis of these materials is extremely low.

Example 2 Melt spinning of MnFeP (GeSb)

Polycrystalline MnFeP (Ge, Sb) alloys are first produced in a ball mill with high energy input and by a solid phase reaction process as described in WO 2004/068512 and J. Appl. Phys. 99, 08 Q107 (2006). The sheet of material is then introduced into a quartz tube with a nozzle. The chamber was evacuated to a vacuum of 10 ^-2 mbar and then filled with high purity argon. The sample is melted by means of high frequency and is sprayed through the nozzle into the chamber containing the rotating copper drum due to the pressure difference. The surface speed of the copper wheel is adjustable and reaches a cooling rate of about 10 ⁵ K/s. Subsequently, the spun ribbon was heat treated at 900 ° C for 1 hour.

X-ray diffraction measurements revealed that all samples were crystallized in a hexagonal Fe ₂ P structure. No smaller contaminant phase of MnO was observed compared to the sample that was not produced by the melt spinning process.

The values obtained for Curie temperature, hysteresis and entropy were determined for different circumferential velocities in the melt spinning. The results are shown in Tables 1 and 2 below. In each case, a low hysteresis temperature was measured.

Claims (9)

A method of manufacturing a metal-based material for magnetic cooling or heat pump, comprising the steps of: a) causing a chemical element and/or an alloy to correspond to the metal-based material in a solid phase and/or a liquid phase; a stoichiometric reaction, b) converting the reaction product from stage a) to a solid, c) sintering and/or heat treating the solid from stage a) or b), d) at a cooling rate of at least 100 K/s Cooling the sintered and/or heat treated solid from stage c), wherein the metal-based material is selected from the group consisting of: (1) a compound of formula (I) (A _y B _1-y ) _2+δ C _w D _x E _z (I) wherein: A is Mn or Co, B is Fe, Cr or Ni, and C, D and at least two of EC, D and E are different, have a non-zero concentration and are selected from P , B, Se, Ge, Ga, Sn, N, As, and Sb, wherein at least one of C, D, and E is Ge, and δ is a value in the range of -0.1 to 0.1, w, x, y, z is a value in the range of 0 to 1, wherein w+x+z=1; (2) a compound La based on La and Fe of the formula (II) and/or (III) and/or (IV) _{Fe x Al 1-x) 13} H y or _{(Fe x Si 1-x)} 13 H y (II) wherein La: X is a number of from 0.7 to 0.95, y Numerical 0-3 _{of; La (Fe x Al y Co} z) 13 or the _{La (Fe x Si y Co z} ) 13 (III) wherein: X is a number from 0.7 to 0.95 of, y is the value 0.05 to 1-x, the z is a value of 0.005 to 0.5; LaMn _x Fe _2-x Ge (IV) wherein: X is a value of 1.7 to 1.95, and (3) a MnTP type Hausler alloy in which T is a transition metal and P is per atom A p-doped metal having an electron number e/a in the range of 7 to 8.5. The method of claim 1, wherein the quenching in stage d) is performed at a cooling rate in the range of from 200 K/s to 1300 K/s. The method of claim 1, wherein the reaction in stage a) is carried out by heating the elements and/or alloys in a sealed container or in an extruder or by solid phase reaction in a ball mill. . The method of any one of claims 1 to 3, wherein the conversion to solids in stage b) is carried out by melt spinning or spray cooling. The method of any one of claims 1 to 3, wherein in stage c), the sintering system is first carried out at a temperature in the range of 800 ° C to 1400 ° C, and then the heat treatment is in the range of 500 ° C to 750 ° C The temperature is carried out. The method of claim 1, wherein the metal-based material is selected from the group consisting of at least a quaternary compound of the formula (I), which comprises not only Mn, Fe, P, and Suitable Sb, and additionally includes Ge or As or Ge and As. A metal-based material for magnetic cooling or heat pump, which can be obtained by the method of any one of claims 1 to 3. A metal-based material for magnetic cooling or heat pump, obtainable by the method of claim 1, excluding the As-containing material and having an average crystal size in the range of 10 nm to 400 nm. Metal-based material of claim 7 for use in magnetic cooling, heat pump or air conditioning systems.