JP2006274345A - Magnetic alloy powder and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain homogeneous La (Fe-Si)<SB>13</SB>ordinary temperature magnetic refrigeration alloy powder free of α-Fe without solution heat treatment. <P>SOLUTION: Fe-Si system alloy powder and a mixture including lanthanum oxide and alkaline earth metal are held for ≥2 hours at 950 to 1,200°C in an inert gaseous atmosphere or in vacuum and is thereafter cooled down to ≤200°C and the reaction product resulted therefrom is washed and dried. The magnetic alloy which is ≤500 μm in maximum grain size, is paramagnetic at ordinary temperature (23°C), and is ≤5 Am<SP>2</SP>/kg in saturation magnetization 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)

In order to obtain a La (Fe—Si) ₁₃ master alloy, a large amount of α-Fe is precipitated as a primary crystal in 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 higher. ing. 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.

The present inventors have prepared a method for producing a La (Fe—Si) ₁₃ single phase mother alloy having a NaZn ₁₃ type crystal structure, which is a mother alloy of a La (Fe—Si) ₁₃ H _x alloy used as a room temperature magnetic refrigeration material. As a result of intensive studies, a mixture of a predetermined amount of rare earth oxide (La ₂ O ₃ ) and metal Ca mixed with Fe—Si alloy powder adjusted to a desired composition in advance in an inert gas atmosphere at 950 to 1200 ° C. Alternatively, after holding in vacuum for 2 hours or more, decant the obtained reaction product in water to dissolve and remove CaO as a reaction by-product as calcium hydroxide (Ca (OH) ₂ ) in water. Thus, it was found that La (Fe—Si) ₁₃ single-phase alloy powder without α-Fe remaining was 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 with the obtained Fe—Si-based 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 rare earth metal produced by the reduction reaction diffuses into the Fe—Si powder, resulting in a reaction. A mixture of La (Fe—Si) ₁₃ alloy and CaO on the cake is obtained as a product. By introducing this mixture into water and repeating decantation for a predetermined time and number of times, CaO is discharged into the water as calcium hydroxide, so that a single-phase La (Fe—Si) ₁₃ alloy powder can be obtained. is there. If the reaction temperature is less than 950 ° C., 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, which is not preferable, and if the reaction temperature exceeds 1200 ° C., the reaction product Sintered and decantation makes it difficult to discharge CaO, which is not preferable. If the reaction time is less than 2 hours, the rare earth metal does not diffuse sufficiently and Fe—Si remains in the center of the powder.

Further, if the particle size of the Fe—Si alloy is 500 μm or more, the reaction takes a long time, which is not suitable. 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. Ca is mainly used as the alkaline earth metal used as the reducing agent for the rare earth oxide. Instead of Ca, it is also possible to use Mg or a mixture of Ca and Mg. 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 no solution treatment is required for heat treatment. 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 ( wherein, R is a rare earth element including Y, A is Si or Si and Al, Ga, And at least one element selected from the group consisting of Ge and Sn, and TM is an element selected from the group consisting of Fe or Fe and Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn At least one of the following, and in atomic%, 0 ≦ x ≦ 0.2, 5 ≦ a ≦ 10, 7 ≦ b ≦ 19%, the balance TM and inevitable impurities). Further, the particle diameter is 500 μm or less, paramagnetism is exhibited at room temperature, and the value of magnetization measured by applying a 2T applied magnetic field is 5 A / m ² or less at maximum. 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, a ferromagnetic in the reaction product insufficient rare earth elements to form a La (Fe · _{Si) 13} is less than 5at% 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. Even if a part of La is replaced with a lanthanoid element containing 20 at% or less of Y, single-phase NaZn ₁₃ type (La _1-x R _x ) (Fe · Si) ₁₃ alloy powder (R includes Y and La Lanthanoid elements) can be obtained. If the substitution amount x of R exceeds 0.2, a heterogeneous phase having a different crystal structure is precipitated, so that the magnetocaloric effect is lowered. Preferably it is 10 at% or less.

  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 based alloy powder having a NaZn ₁₃ type crystal structure necessary for producing La (Fe—Si) ₁₃ H _x which is a room temperature magnetic refrigeration material can be obtained without solution treatment. It is possible to manufacture. According to the present invention, the obtained La—Fe—Si based alloy powder is reacted with a reaction gas containing hydrogen at 200 to 350 ° C. to obtain homogeneous La (Fe—Si) ₁₃ H _x normal temperature without α-Fe. Magnetic refrigeration alloy powder is obtained.

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 mixture was placed in an iron tray and heat-treated at 1050 ° C. for 4 hours in an argon atmosphere to cause a reduction diffusion reaction. After the heat treatment, the obtained reaction product was put 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. The alloy composition of the obtained La—FeSi alloy is La _6.9 Si _9.3 Fe _bal (residual oxygen content 0.12 mass%, Ca content 0.03 mass%). The X-ray diffraction pattern of the powder after drying is shown in FIG. From this diffractogram, it can be seen 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 to obtain a pre-reaction mixture. Got. The mixture was subjected to a reduction diffusion reaction in an argon atmosphere at 1150 ° C. for 4 hours, and the obtained reaction product was washed with water and dried in the same manner as in Example 1 to obtain a La—Fe—Si alloy powder. The alloy composition of the obtained La-FeSi alloy is La _6.86 Si _18.67 Fe _bal (residual oxygen content 0.12 mass%, Ca content 0.03 mass%). The powder after drying was measured for X-ray diffraction and room temperature saturation magnetization and Curie temperature. As a result of X-ray diffraction, it was found that this powder was a NaZn ₁₃ type single phase, was paramagnetic at room temperature, as shown in FIG. 2, and had a magnetization of 5 Am ² / kg or less.

(Example 3)
Fe-Si based alloy powder having a composition of Fe 94.7 mass% -Si 5.3 mass% (Fe 90 atomic% -Si 10 atomic%) was prepared by arc melting as in Example 1. In this alloy powder, the amount of lanthanum oxide was changed so that the composition ratio of La and Fe—Si in the final product was 1:11 to 14, and the amount of Ca of the reducing agent was changed to 1.1 of the stoichiometric composition. After adjusting the weight so as to be doubled, the mixed mixture was subjected to a reduction diffusion reaction in an argon atmosphere while changing the reaction temperature and time. The obtained reaction product was washed with water and dried in the same manner as in Example 1, and X-ray diffraction and magnetization measurement at room temperature were performed. The powder subjected to the reduction diffusion reaction under the conditions of a reaction temperature of 900 ° C. and a reaction time of 1 hour showed weak ferromagnetism, and a weak diffraction line of Fe was observed. It was also confirmed that the powder having a composition ratio of lanthanum and Fe—Si of 14 showed ferromagnetism. Table 1 shows the results.

  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 (7)

Holding the mixture containing the Fe—Si-based alloy powder, lanthanum oxide and alkaline earth metal in an inert gas atmosphere or in a vacuum at a temperature range of 950 to 1200 ° C. for 2 hours or more, then cooling to 200 ° C. or less, A method for producing a La—Si—Fe-based magnetic alloy powder, wherein the reaction product is washed with water and dried. A mixture of Fe—Si based alloy powder, lanthanoid oxide (including Y oxide) containing 80% or more of lanthanum oxide and alkaline earth metal in an inert gas atmosphere or in a vacuum at a temperature range of 950 to 1200 ° C. A method for producing a La—Si—Fe-based magnetic alloy powder, which is maintained for 2 hours or more, then cooled to 200 ° C. or less, and the reaction product is washed with water and dried. The composition formula of the magnetic _{alloy, (La 1-x R x} ) a A b TM bal ( wherein, R is a rare earth element including Y, A is a group consisting of Si or Si and Al, Ga, Ge, 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. The raw material is mixed so that the atomic percent is 0 ≦ x ≦ 0.2, 5 ≦ a ≦ 10, 7 ≦ b ≦ 19%, the balance TM and inevitable impurities). Or the manufacturing method of the magnetic alloy powder of 2. Composition _{formula, (La 1-x R x} ) a A b TM bal ( wherein, R is a rare earth element including Y, A is selected from Si or Si and Al, Ga, Ge, from a group consisting of Sn At least one element, and 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, and atomic% And 0 ≦ x ≦ 0.2, 5 ≦ a ≦ 10, 7 ≦ b ≦ 19%, the balance TM and inevitable impurities), and the amount of alkaline earth metal in the magnetic alloy powder is 0.005 mass. % To 0.2 mass% of magnetic alloy powder. The magnetic alloy powder according to claim 4, wherein the amount of oxygen in the magnetic alloy powder is 0.15 mass% or less. 6. The magnetic alloy powder according to claim 4, wherein the magnetic alloy powder is paramagnetic at room temperature (23 ° C.) and has a saturation magnetization of 5 Am ² / kg or less. The magnetic alloy powder according to claim 4, wherein the maximum particle size is 500 μm or less.