JP2006283074A - Magnetic alloy powder and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain homogeneous La(Fe-Si)<SB>13</SB>H<SB>x</SB>room temperature magnetic refrigeration alloy powder free frm α-Fe without solution heat treatment. <P>SOLUTION: A production method for magnetic alloy powder is characterized in that a mixture including Fe-Si-based alloy powder, lanthanum oxide, and alkaline earth metal is held at the temperature region of 950 to 1,200°C in an inert gaseous atmosphere or in a vacuum for 2 hours or more, then the obtained reaction product is subjected to hydrogenation reaction in hydrogen or in a partial hydrogen atmosphere at 200 or 350°C. The magnetic alloy having the maximum grain size of ≤500 μm and an amount of the alkaline earth metal of ≥0.005 to ≤0.2mass% is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic material used for magnetic refrigeration that does not use Freon gas, and relates to a magnetic alloy powder used in an efficient refrigeration system that realizes an environment-friendly refrigerator, air conditioner, and the like using the magnetocaloric effect, and a method for manufacturing the same. About.

  Currently, global environmental issues include the destruction of the ozone layer and global warming. It was pointed out that the cause of the ozone depletion was chlorofluorocarbon gas used in refrigerators such as air conditioners, and at the international conference in Montreal in 1992, specific chlorofluorocarbons were completely abolished in 1995. However, the so-called CFC substitute, which is approved for use as a substitute for specific CFCs, has a warming action that is several thousand to tens of thousands of carbon dioxide, and it is a target for reduction at the Kyoto Conference on Global Warming Prevention in 1997. became. In Europe, it has already been decided to completely eliminate the use of alternative CFCs in automobiles in the future. Under such circumstances, development of energy-saving and low environmental load refrigeration air-conditioning equipment has become an urgent task, and magnetic refrigeration technology that does not use chlorofluorocarbons has begun to attract attention. Magnetic refrigeration technology has been widely used to realize cryogenic temperatures, but at room temperature, the heat capacity due to lattice vibration of the work material is large, and the energy due to thermal disturbance of the magnetic system increases. It was difficult to put it into practical use.

As the room-temperature magnetic refrigeration material, a magnetic material that is inexpensive and exhibits a large magnetocaloric effect is required. Conventionally, Gd (gadolinium) having a magnetic transformation point (Curie temperature) near room temperature is known as a room temperature magnetic refrigeration material, but Gd is a rare and expensive metal among rare earth elements and is industrially practical. It is not a certain material. In recent years, magnetic materials exhibiting metamagnetic transition have attracted attention as room temperature magnetic refrigeration materials that replace Gd. Magnetic refrigeration magnetic materials exhibiting a metamagnetic transition are materials that undergo a magnetic transformation from paramagnetism to ferromagnetism by applying a magnetic field in the vicinity of the Curie point. It has the feature that it can be obtained.
As such magnetic _{materials, Gd 5 Si 2 Ge 2,} Mn (As 1-x Sb x) and _{MnFe (P 1-x As x} ), La (Fe-Si) such as 13 _{H x} is proposed . Among these room-temperature magnetic refrigeration work materials, considering raw material cost, environmental load, safety in the manufacturing process, etc., La (Fe—Si) ₁₃ H _x alloy is considered to be the most promising candidate substance as a practical material. It is done. With regard to this material, studies are mainly conducted at universities focusing on physical property research. (Non-Patent Documents 1 and 2) La (Fe—Si) ₁₃ H _x which is a room temperature magnetic refrigeration material causes hydrogen to enter solid solution in a La (Fe—Si) ₁₃ crystal lattice having a NaZn ₁₃ type crystal structure. As a result, the crystal lattice is expanded to raise the Curie temperature. As an industrial production method for this material, a single-phase La (Fe—Si) ₁₃ master alloy is prepared in advance, and hydrogen is dissolved between lattices by a gas-solid phase reaction to obtain a desired La (Fe—Si). It has been investigated to obtain ₁₃ H _x alloys. (Non Patent Literature 3)
However, since La and Fe do not have a solid solution region in the solid phase region, it is extremely difficult to obtain an industrially single La (Fe—Si) ₁₃ master alloy. (Non-Patent Document 4)

For example, in order to obtain a La (Fe—Si) ₁₃ master alloy, an ingot in which La, Fe, and Si alloy are cast by high frequency melting or arc melting at a high temperature of 1600 ° C. or more has a large amount of α-Fe as a primary crystal. Precipitates. Patent Document 1 discloses that the alloy ingot is subjected to uniform heat treatment in order to eliminate the α-Fe. In addition, a rapid solidification method such as a water atomizing method, a gas atomizing method, and a strip casting method as disclosed in Patent Document 2 is applied to suppress the precipitation of α-Fe.
Solid physics vol 37. (2002) 419. Metal vol 73. (2003) 849. Appl. Phys. Lett. 79 (2003) 653. Binary Phase Diagrams, ASM, Eds. TB Massalski (1986) JP 2003-96547 A (0036) JP 2004-100043 A (0034)

However, it is difficult to completely eliminate α-Fe in this alloy even after a long-time solution treatment. In addition, it is extremely difficult to obtain a single-phase La (Fe—Si) ₁₃ alloy in a rapidly cooled state even by using means such as a rapid solidification method. According to the rapid cooling method, the ferromagnetic α-Fe that is precipitated while being rapidly cooled (as cast) can be reduced in a short time compared to the casting method, but after rapid cooling, solution treatment at 1000 ° C or higher. Is necessary, and it is difficult to completely eliminate α-Fe. Since α-Fe remaining in the mother alloy is ferromagnetic, the magnetic field preferentially enters, so that there is a problem that the magnetocaloric characteristics are deteriorated even with a small amount.

As a result of intensive investigations on a method for producing a La (Fe—Si) ₁₃ H _x alloy having a NaZn ₁₃ type crystal structure used as a room temperature magnetic refrigeration material, the present inventors have adjusted the composition to 500 μm or less that has been adjusted to a desired composition in advance. A mixture obtained by mixing a predetermined amount of rare earth oxide (La ₂ O ₃ ) and metal Ca in Fe—Si alloy powder was held at 950 to 1200 ° C. in an inert gas atmosphere or in vacuum for 2 hours or more, and obtained. After the reaction product was subjected to a hydrogen storage reaction in a hydrogen atmosphere at 200 to 350 ° C. for 0.5 to 50 hours, the reaction product was decanted in water to convert CaO as a reaction byproduct into calcium hydroxide. It has been found that by dissolving and removing in water as (Ca (OH) ₂ ), a La (Fe—Si) ₁₃ H _x single-phase alloy powder with no α-Fe remaining can be obtained.

The manufacturing method of this alloy having a NaZn ₁₃ type crystal structure is obtained by melting and casting Fe and Si blended in a predetermined composition ratio by high frequency melting or arc melting, and pulverizing the obtained Fe-Si ingot to 500 μm or less, Alternatively, the molten metal melted at high frequency is sprayed with a high-pressure inert gas or water to directly obtain a powder of 500 μm or less. It is also possible to obtain a powder directly by spraying the molten metal on a rotating roll, or to obtain a powder by grinding a ribbon.

A predetermined rare earth oxide (La ₂ O ₃ ) and calcium for reducing the rare earth oxide are mixed into the obtained Fe—Si powder at least in a stoichiometric composition. By heating and maintaining this mixture at 950 to 1200 ° C. in an inert atmosphere such as argon, the rare earth oxide is reduced, and the reduced rare earth metal diffuses into the Fe—Si powder, resulting in a reaction product. As a result, a mixture of La (Fe—Si) ₁₃ alloy and CaO on the cake is obtained. This mixture is heat-treated in an atmospheric gas containing 1% or more of hydrogen in a temperature range of 200 to 350 ° C. for 0.5 to 50 hours, so that hydrogen is dissolved in the lattice of the La (Fe—Si) ₁₃ alloy. An obtained La (Fe—Si) ₁₃ Hx alloy is obtained. The reaction product after the hydrogenation treatment is poured into water and decantation is repeated for a predetermined time and number of times to discharge CaO into the water as calcium hydroxide, whereby a single-phase La (Fe—Si) ₁₃ alloy powder is obtained. It is possible to obtain. If the reaction temperature is 950 ° C. or lower, the diffusion rate of La into the Fe—Si alloy is slow, and the Fe—Si phase remains unreacted in the center of the powder. Sintering and decantation are not preferable because CaO discharge becomes difficult. When the reaction time is 2 hours or less, Fe—Si remains in the center of the powder.

On the other hand, if the particle size of the Fe—Si alloy is 500 μm or more, the reaction takes a long time, which is not appropriate. In addition, when the particle size is 10 μm or less, the powder after the hydrogenation treatment is active and has problems such as oxidation. Therefore, the Fe—Si raw material powder particle size is preferably 10 to 500 μm. Oxygen in the magnetic alloy powder exists as a rare-earth oxide or a non-magnetic oxide such as CaO. Therefore, if it is 0.15 mass% or more, the magnetic refrigeration performance is lowered, which is not preferable. As the reducing agent for the rare earth oxide, Mg or a mixture of Ca and Mg can be used instead of Ca. The powder from which CaO has been removed by decantation is dehydrated and dried in an inert atmosphere or in vacuum at 40 to 80 ° C., and the resulting powder is La (Fe · Si) ₁₃ single phase, such as a cast ingot. There is an advantage that a solution treatment for phase formation is not required. When the production method of the present invention is used, the amount of Ca in the powder is characterized by 0.005 mass% or more. However, if a large amount of Ca remains, the magnetic properties are deteriorated, so 0.2 mass% or less is preferable. A more preferable range is 0.01 mass% to 0.1 mass%.

Magnetic powder obtained by the present production method, composition _{formula, (La 1-x R x} ) a A b TM bal H c ( wherein, R is a rare earth element including Y, A is Si or Si and Al, At least one element selected from the group consisting of Ga, Ge and Sn, and TM is selected from the group consisting of Fe or Fe and Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn At least one element selected from the group consisting of 0 ≦ x ≦ 0.2, 5 ≦ a ≦ 10, 7 ≦ b ≦ 19%, 0 <c ≦ 2.5%, the balance TM and inevitable impurities) It becomes. A part of the rare earth metal La can be substituted with a lanthanoid element such as Ce, Pr, Nd, Dy, etc. If the substitution is 20% or more, a second phase other than the NaZn ₁₃ phase is precipitated, which is not preferable. Further, a part of Fe can be substituted with at least one element selected from the group consisting of Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn. Furthermore, a part of Si can be replaced with at least one element selected from the group consisting of Al, Ga, Ge, and Sn. When a part of Fe is replaced with another element (Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn), or a part of Si is replaced with another element (Al, Ga, Ge, Sn) In the case of substituting with, it is preferable to alloy with an Fe—Si alloy in advance so as to have a predetermined composition.

In the present invention, the material composition of the present invention has an important meaning in order to exhibit the magnetic refrigeration effect near room temperature. Formula: in _{(La 1-x R x)} a A b TM bal H c, a is the reaction product insufficient rare earth elements to form a La (Fe · _{Si) 13} is less than 5at% Ferromagnetic Fe-Si remains. On the other hand, if a exceeds 10 at%, the rare earth element becomes excessive and a rare earth-rich nonmagnetic phase or rare earth oxide is generated in the reaction product, so that the magnetocaloric effect after hydrogen storage is reduced. A preferable range of a is 6.5 to 8.5 atomic%. When b is less than 7.0 at%, the La (Fe · Si) ₁₃ phase becomes unstable and the Fe—Si phase remains, and when b exceeds 19 at%, the saturation magnetization is reduced and the magnetocaloric effect is reduced. There is a problem. A preferable range of b is 9 to 12 atomic%. In this alloy, part of La can be replaced with other lanthanoid elements including Y. Although c does not directly affect the magnetocaloric effect itself, when c increases, the crystal lattice expands and the magnetic transformation temperature rises. By controlling the hydrogen partial pressure, the reaction time, and the temperature, it is possible to control the amount of hydrogen dissolved in the alloy. When the reaction temperature is 350 ° C. or higher, the hydride is thermodynamically unstable and the hydrogenation reaction does not proceed. Moreover, at 200 degrees C or less, reaction rate is slow and hydrogenation reaction does not advance. As the hydrogen partial pressure is higher, the reaction proceeds in a shorter time. However, in order to obtain a uniform alloy powder having a target magnetic transformation temperature, it is preferable to select an appropriate hydrogen partial pressure and reaction time. Not only can the process be shortened by performing decantation in water after the hydrogenation reaction, but also CaO is partially reduced to Ca (OH) ₂ by heat treatment in a hydrogen atmosphere, so that Ca is discharged. There are also attendant advantages that make

  It is also possible to partially replace part of Fe with elements such as Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn. If these elements exceed 10 atomic% in the total alloy composition, the magnetic properties are deteriorated. It is also possible to replace a part of Si with an element such as Al, Ga, Ge, or Sn. The magnetic transformation temperature can be adjusted by the substitution amount.

According to the present invention, a single-phase La (Fe—Si) ₁₃ H _x- based alloy powder having a NaZn ₁₃ type crystal structure, which is a room temperature magnetic refrigeration material, can be directly produced without a solution treatment.

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.
Example 1
An Fe—Si alloy ingot having a composition of Fe 94.7 mass% —Si 5.3 mass% (Fe 90 atomic% —Si 10 atomic%) was melted by arc melting. This ingot was pulverized in advance to 500 μm or less with a disc-shaped pulverizer. Weigh 83.8 g of Fe-Si powder of 500 μm or less, 19.1 g of lanthanum oxide, and 18.1 g of metallic calcium (1.1 times the stoichiometry), and mix for 10 minutes with a V-type mixer. It was. The above mixture was placed in an iron tray, subjected to a reduction diffusion reaction at 1050 ° C. for 4 hours in an argon atmosphere, then cooled to 280 ° C., and the hydrogen atmosphere was changed from argon to argon + hydrogen mixed atmosphere. did. The hydrogen partial pressure during the hydrogenation reaction was changed from 10 to 90%, and the reaction time was changed from 1 to 10 hours. After the hydrogenation reaction, the obtained reaction product was cooled to 200 ° C. or lower, poured into about 2 L of water, allowed to stand for 1 hour, and then washed with water repeatedly. Washing with water was repeated, and when the pH of water became 8.5 or less, washing with water was stopped, and the powder obtained by dehydration was dried in vacuum at 80 ° C. for 2 hours.
Table 1 shows the results of measuring the hydrogen content and magnetic transformation temperature of the powder after drying. Further, an X-ray diffraction pattern of a typical powder is shown in FIG. It can be seen that the higher the hydrogen partial pressure, the higher the amount of hydrogen and the higher the magnetic transformation temperature. Further, FIG. 1 shows that this alloy powder is a NaZn ₁₃ type single phase.

(Comparative Examples 1 and 2)
The alloy composition was adjusted so as to be La _7.0 Si _11.0 Fe _bal (atomic%) by arc melting, and a La—Si—Fe based master alloy was prepared. Aiming at the disappearance of α-Fe generated in the production process of the mother alloy, the mother alloy was subjected to a uniform heat treatment at 1050 ° C. for 48 hours. FIG. 3 shows a structure observation photograph of the mother alloy, and FIG. 4 shows a structure observation photograph after the uniform heat treatment. Even after the heat treatment, the master alloy is not completely homogenized. When a magnetic refrigeration material is used, there is a concern that the magnetocaloric characteristics may be degraded by α-Fe. Moreover, the inhibitory effect of (alpha) -Fe by the super rapid example method (roll peripheral speed 15m / s) using the single roll made from Cu for the molten metal of the same alloy composition was confirmed. FIG. 5 shows a structure observation photograph of the ultrathin ribbon.

(Example 2)
An alloy having a composition of Fe 88.8 mass% -Si 11.2 mass% (Fe 80 atomic% -Si 20 atomic%) was melted by arc melting to obtain a powder of 500 μm or less in the same manner as in Example 1. 83 g of this Fe—Si powder, 19.9 g of lanthanum oxide and 18.1 g of metallic calcium (1.05 times the stoichiometry) were weighed and mixed in a V-type mixer in the same manner as in Example 1, and the pre-reaction mixture was mixed. Obtained. This mixture was subjected to a reduction diffusion reaction in an argon atmosphere at 1150 ° C. for 4 hours, and then a hydrogen occlusion reaction was performed by changing the reaction temperature from 200 to 300 ° C. for 2 hours at a hydrogen partial pressure of 50%. The obtained reaction product was cooled to 200 ° C. or lower in the same manner as in Example 1, washed with water and dried to obtain La—Fe—Si alloy powder. The hydrogen storage amount and Curie temperature of the dried powder were measured. The results are shown in Table 2.

  The magnetic powder according to the present invention can be applied to refrigeration and air conditioning equipment that does not use chlorofluorocarbon as a magnetic refrigeration material, and can be used in a highly efficient refrigeration system that realizes an environment-friendly refrigerator, air conditioner, and the like.

The XRD figure of the magnetic powder by this invention. The magnetization curve of the magnetic powder according to the present invention. An as-cast structure of an arc melting ingot. Structure after arc melting ingot of 1050 ° C. × 48 h. An as-cast structure of strip cast alloy.

Claims (8)

A mixture containing Fe—Si alloy powder, lanthanum oxide, and alkaline earth metal is maintained in an inert gas atmosphere or in a vacuum at a temperature range of 950 to 1200 ° C. for 2 hours or more, and then hydrogenated at 200 to 350 ° C. A method for producing a La—Si—Fe-based magnetic alloy powder, characterized in that a hydrogenation reaction is performed in a partial hydrogen atmosphere. A mixture of Fe-Si alloy powder, lanthanoid oxide containing 80% or more of lanthanum oxide (including Y oxide), and alkaline earth metal is held at 950 to 1200 ° C. for 2 hours or more, and then at 200 to 350 ° C. A method for producing a magnetic alloy powder, characterized by performing a hydrogenation reaction in hydrogen or in a partial hydrogen atmosphere. 3. The method for producing a magnetic alloy powder according to claim 1, wherein after the hydrogenation reaction, the reaction product is cooled to 200 ° C. or less, and the reaction product is washed with water and dried. The method for producing a magnetic alloy powder according to claim 1, wherein the alkaline earth metal is at least one of Ca and Mg. The method for producing a magnetic alloy powder according to any one of claims 1 to 4, wherein an atmosphere during the hydrogenation reaction is a hydrogen partial pressure of 1% or more. Selection composition _{formula, (La 1-x R x} ) a A b TM bal H c ( wherein, R is a rare earth element including Y, A is Si or Si and Al, Ga, Ge, from a group consisting of Sn TM is at least one element selected from the group consisting of Fe or Fe and Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Magnetic alloy powder of atomic percent, 0 ≦ x ≦ 0.2, 5 ≦ a ≦ 10, 7 ≦ b ≦ 19%, 0 <c ≦ 3.0%, balance TM and inevitable impurities) A magnetic alloy powder characterized by containing an alkaline earth metal content of 0.005 mass% to 0.2 mass%. The magnetic alloy powder according to claim 6, wherein the oxygen content is 0.15 mass% or less. The magnetic alloy powder according to claim 6 or 7, wherein the maximum particle size is 500 µm or less.