JP2006124783A - Magnetic grain and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide magnetic grains having magnetocaloric effect practical in the vicinity of room temperature, and also having excellent corrosion resistance, and to provide a method for producing the same. <P>SOLUTION: The magnetic grains are obtained by providing the surface of each alloy grain having a composition expressed by (La-Y)<SB>A</SB>M<SB>B</SB>Si<SB>C</SB>H<SB>D</SB>T<SB>bal</SB>(wherein, M is one or more kinds of elements selected from Ti, Zr and Hf; T includes Fe as an essential element, and, if required, also includes one or more kinds of elements selected from Co, Ni and Cr, and, 6.0≤A≤7.5 atomic%, 0≤B≤5.0 atomic%, 8.0≤C≤14.0 atomic% and 0≤D≤15.0 atomic% are satisfied) with a chemical conversion film with phosphoric acid. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic particle having a magnetocaloric effect capable of realizing a highly efficient refrigeration system that realizes an environmentally friendly refrigerator, an air conditioner, and the like, and a method for producing the same.

If chlorofluorocarbon gas used in refrigerators and air conditioners leaks into the atmosphere, it will cause ozone depletion, so legal regulations such as the chlorofluorocarbon recovery and destruction law have been implemented. It is difficult to recover without leaking. For this reason, it has been studied to realize a magnetic refrigeration cycle using the magnetocaloric effect of a magnetic material instead of using chlorofluorocarbon gas and alternative chlorofluorocarbon gas as a refrigerant. In recent years, as disclosed in Non-Patent Document 1, research on magnetic refrigeration materials that operate at room temperature has been conducted. Gd particles, Mn-As-Sb system, Gd ₅ Ge ₂ Si _{2 and the} like are known as materials that exhibit magnetocaloric effect near room temperature. In particular, the NaZn ₁₃ type disclosed in Patent Document 1 is known. A La (Fe _0.88 Si _0.12 ) ₁₃ H _1.0- based magnetic material having a crystal structure is considered to be highly practical because the Curie temperature is around room temperature and has a large magnetic entropy difference.
A.Fujita, S.Fujieda, K.Fukamichi, Y.Yamazaki and Y.Iijima, Material Transactions 43 (2002) 1202. JP 2003-96547 A ((0022) to (0024))

However, the La (Fe · Si) ₁₃ H _0- based magnetic material described in Patent Document 1 first produces a La—Fe—Si alloy by vacuum melting or the like, and then performs hydrogen storage treatment on the alloy. However, at present, the alloy composition and the production method for industrial production have not been established at all. Further, the present material needs to contain a relatively large amount of La in order to form a NaZn ₁₃ type crystal structure. Since La is a rare earth element that easily oxidizes, it is a material with low weather resistance and corrosion resistance. Since a fluid or gas is used as the heat exchange medium, and a magnetic material is used in the fluid, it is necessary to consider so as not to cause rust and deterioration of magnetic characteristics. Patent Document 1 describes replacing one or more elements selected from a group of transition metal elements such as Co, Ni, Mn, and Cr in order to improve corrosion resistance. Among them, Mn is not effective in improving the corrosion resistance, and when a large amount of the above elements are substituted, the magnetic properties change greatly, so that only a very small amount can be added, and the corrosion resistance is not sufficiently improved.

  General surface treatment methods for imparting corrosion resistance to materials that are easily oxidized include coating with a polymer compound such as a resin and forming a metal having corrosion resistance by plating, etc., but the magnetocaloric effect As the surface treatment film of the particles for exhibiting the above, it is not sufficient that the corrosion resistance is simply good, and it is necessary to be a film having excellent heat conductivity because it also acts to mediate heat. For this reason, since a polymer film generally has low thermal conductivity, it is not preferable as a coating film for magnetic particles as a subject of the present invention. Other dry coating methods include the CVD method, but the CVD method requires heating the substrate to 200 to 400 ° C., and is applicable to the coating of materials that are easily oxidized such as the magnetic particles of the present invention. Is difficult.

  Therefore, the problem to be solved by the present invention is to provide a magnetic particle capable of obtaining a magnetic particle having a practical magnetocaloric effect near room temperature and having excellent corrosion resistance, and a method for producing the same. is there.

As a result of various investigations in order to impart corrosion resistance to magnetic particles containing a large amount of easily oxidizable elements that form a NaZn ₁₃ type crystal structure, the present inventors have found that the magnetic properties of the magnetic particles are higher than the addition of elements that improve corrosion resistance. It is effective to apply a corrosion-resistant coating to the particles, and the surface treatment method for this kind of magnetic particles is not a general method such as wet coating (plating) or dry coating. I found out.
That magnetic particles of the present _{invention, (La · Y) A M} B Si C H D T bal ( although, M is Ti, Zr, one selected from Hf or more elements, T is the Fe essential One or two or more elements selected from Co, Ni, and Cr are included as necessary, and 6.0 ≦ A ≦ 7.5 atomic%, 0 ≦ B ≦ 5.0 atomic%, 8.0 ≦ C ≦ 14.0 atomic%, (0 ≦ D ≦ 15.0 atomic%) is characterized in that a chemical conversion film made of phosphoric acid is provided on the surface of a magnetic particle having a composition represented by:

  In addition, it is also within the equivalent scope of the present invention that the phosphoric acid-added liquid is passed through the pores of the porous magnetic alloy having a porous shape so that a phosphoric acid film is applied to the porous outer surface and the entire inner wall surface of the pore. .

As a specific manufacturing method, in a liquid containing phosphoric acid, (La · Y) _A M _B Si _C H _D T _bal (where M is one or more elements selected from Ti, Zr, and Hf) , T contains Fe as an essential element, and optionally contains one or more elements selected from Co, Ni, and Cr, 6.0 ≦ A ≦ 7.5 atomic%, 0 ≦ B ≦ 5.0 atomic%, 8.0 ≦ C ≦ 14.0 atomic%, 0 ≦ D ≦ 15.0 atomic%) is stirred in a dipped state to form a chemical conversion treatment film with phosphoric acid. Although normal water may be used as the liquid, it is preferable to use an organic solvent in order to prevent oxygen in the water from binding to the particles. Moreover, it is preferable that the addition amount of phosphoric acid is 0.05-1.0 g / 100cc with respect to an organic solvent. If it is less than 0.05 g / 100 cc, the chemical conversion film is not sufficiently formed, and satisfactory corrosion resistance cannot be obtained. On the other hand, if it exceeds 1.0 g / 100 cc, the magnetic properties of the magnetic particles are greatly lowered, which is not preferable. The film thickness of the chemical conversion treatment with phosphoric acid is about 5 to 50 nm. The temperature of the liquid to be stirred is preferably from room temperature to 80 ° C.

  After stirring the alloy particles in a liquid containing phosphoric acid, it is preferable to add a hydroxide to the liquid and stir again to carry out phosphoric acid neutralization treatment. The hydroxide is not particularly limited, but for example, an inorganic hydroxide soluble in an organic solvent (alcohol or the like) is preferable. Of the inorganic hydroxides, sodium hydroxide, potassium hydroxide or ammonium hydroxide is useful. In order to obtain good corrosion resistance, 0.005 to 0.2 g / 100 cc and preferably 0.01 to 0.1 g / 100 cc with respect to the liquid to be stirred. If the amount of hydroxide added is less than 0.005 parts by weight, it is difficult to improve the corrosion resistance, and if it exceeds 0.2 parts by weight, the effect of improving the corrosion resistance is saturated. In other words, since excess phosphoric acid inevitably remains, it is a neutralization treatment for removing this. It is preferable to add by measuring the amount of neutralization appropriately neutralized with respect to the concentration of the remaining phosphoric acid.

  After stirring the particles, it is preferable to perform a heat treatment at 50 ° C. or higher and 400 ° C. or lower in an inert gas or vacuum. By this heat treatment, the phosphoric acid compound existing outside the particles is stabilized, and corrosion resistance that can withstand even in a corrosive environment is imparted.

  When used in a cooling device or the like, since the present magnetic particles are incorporated in a porous bulk state, the particle size of the magnetic particles to be surface-treated is preferably 0.5 to 1500 μm. If the particle size is less than 0.5 μm, a porous magnetic particle combination with a large surface area cannot be obtained, and if the particle size exceeds 1500 μm, the magnetic particle combination cannot be formed.

In the magnetic particle of the present invention, the composition of each element is determined as follows in order to obtain the magnetocaloric effect. First, La is an essential element for forming the NaZn ₁₃ type structure which is the crystal structure of this compound. If the amount of La is less than A = 6.0 atomic%, α-Fe is excessively formed in the molten alloy, and even if homogenization is performed, it is impossible to eliminate α-Fe. In addition, when A = 7.5 atomic% is exceeded, not only the NaZn ₁₃ type crystal structure but also ThMn ₁₂ type, Th ₂ Zn ₁₇ type, and CaCu ₅ type crystal structures are formed, and the magnetocaloric effect is caused by causing a change in the magnetization curve. It is not preferable as a material. Preferably 6.5 ≦ A ≦ 7.3 atomic%. On the other hand, Si is an element essential for forming a NaZn ₁₃ type structure. When the amount of Si is less than C = 8.0 atomic%, it is difficult to sufficiently form a NaZn ₁₃ type crystal structure. On the other hand, when C = 14.0 atomic% is exceeded, the NaZn ₁₃ type crystal structure is hardly formed and Fe ₂ Si unnecessary for the magnetocaloric effect is formed. Preferably it is 9.0-13 atomic%. Al is an element that can replace Si, but it is desirable that there are few unavoidable impurities such as Al, but it is allowed as long as the magnetic refrigeration performance is not deteriorated. The amount of hydrogen D is an essential element for improving the Curie temperature. When D exceeds 15.0 atomic%, the crystal lattice expands excessively, resulting in the destruction of the NaZn ₁₃ type crystal structure. If the amount of hydrogen D is less than 3.5 atomic%, the Curie temperature becomes lower than room temperature, so it is preferable to set it to 3.5 atomic% or more. M is at least one of Ti, Zr, and Hf, and Zr is most preferable from the viewpoint of cost and effect. When the substitution amount for Fe is less than B = 0.01 atomic%, the above effect is small, and when B = 5.0 atomic% or more, an Fe—M phase is formed, which is not preferable. The balance is Fe, Co, Ni, and Cr. Co, Ni, and Cr are added in an amount of 0.01 to 30 atomic% with respect to Fe. If it is 0.01 atomic% or less, the effect of improving the corrosion resistance is small, and if the substitution amount exceeds 30 atomic%, the magnetic properties are deteriorated. And since Y is harder to oxidize than La metal, it is effective in improving corrosion resistance and is substituted in the range of 0.1 to 40 atomic% of La. If it is 0.01 atomic% or less, the effect of improving the corrosion resistance is small, and if the substitution amount exceeds 40 atomic%, it becomes difficult to form a NaZn ₁₃ type crystal structure.

  If an organic solvent is used, the magnetic particles can be shielded from the atmosphere and the effect of suppressing oxidation can be obtained. For example, alcohol such as ethanol, methanol or propyl alcohol, or ketone can be used.

  The phosphoric acid added to the liquid may be a phosphoric acid compound. Examples of applicable phosphoric acid compounds include orthophosphoric acid, monomethyl phosphoric acid, monoethyl phosphoric acid, 1-hydroxyethylidene 2-diphosphonic acid, phosphorous acid, hypophosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, lauryl phosphoric acid, Stearyl phosphate, 2-ethylhexyl phosphate, isodecyl phosphate, butyl phosphate, monoisopropyl phosphate, propyl phosphate, aminotrimethylene phosphonate, hydroxymethyl acrylate acid phosphate, hydroxymethyl methacrylate acid phosphate, (2-hydroxyethyl) acrylate Examples include, but are not limited to, acid phosphate and (2-hydroxyethyl) methacrylate acid phosphate.

According to the manufacturing method of the magnetic particles of the present invention, by coating the chemical conversion film with phosphoric acid to the magnetic particles, it exhibits a magnetocaloric effect at room temperature _{(La · Y) A M B} Si C H D T bal It becomes possible to form a corrosion-resistant film on the surface of the magnetic particle represented.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by these Examples.

Example 1
A vacuum melting furnace that weighs 99.9% or more of electrolytic iron, La metal, and ferrosilicon so that the final composition after dissolution is La _7.14 Si _10.2 Fe _bal (atomic%), and the total weight is 20 kg. And dissolved. After melting, the La-Fe-Si melt was poured onto a rotating copper roll via a tundish to produce La-Fe-Si alloy flakes. The obtained flakes were subjected to a hydrogen storage treatment using an atmospheric pressure furnace PHSG manufactured by Shimadzu Mectem. The hydrogen storage conditions were set to 300 ° C. × 5 h and the hydrogen pressure set to 5065 hPa. The alloy lump subjected to the hydrogen occlusion treatment was pulverized with a bantam mill in a nitrogen gas atmosphere in which the oxygen amount was controlled to 5 ppm by a jaw crusher or the like to obtain a powder having an average particle diameter of 180 μm. Next, using a classifier micron separator manufactured by Hosokawa Micron Corporation, particles having a particle size of 10 μm or less were removed to produce alloy particles having the above composition.
Next, the following (1) and (2) were prepared as surface treatment agents.
(1) A solution of 0.75 g of phosphoric acid dissolved in 100 cc IPA (phosphoric acid is an 85% strength by weight aqueous solution, manufactured by Kanto Chemical Co., Inc.)
(2) Solution of 0.2g NaOH dissolved in 100cc ethanol (pH = 12.0)
Next, a total of four beakers each containing 20 g of the above alloy particles in IPA 60 cc (one sample) were prepared. Next, each beaker was heated to 20, 40, 60, and 80 ° C., and then the beaker was stirred with a stirrer, and 40 cc of the solution (1) was divided into 4 times every 5 minutes for each beaker. Added and mixed over a minute. The amount of phosphoric acid added in this case corresponds to 0.3 g / beaker. The reason why the solution (1) is added is to coat the phosphate film as uniform as possible. Next, 50 cc of the supernatant of each beaker is discarded so that the surface of each alloy particle is coated with the phosphate coating as uniformly as possible. Next, 50 cc of the solution in (2) is added and stirred with a stirrer for 10 minutes, and then the supernatant is added. Abandoned. During these series of treatments, the IPA and alloy particles in each beaker were kept at 20, 40, 60 and 80 ° C., respectively. Next, it was dried at room temperature in an inert gas (nitrogen) stream. Next, it was heated at 220 ° C. for 1 hour while being evacuated with a rotary pump, and then cooled to room temperature to obtain magnetic particles according to the present invention.
A constant temperature and humidity test was performed in which the magnetic particles were placed in a constant temperature and humidity chamber maintained at 80 ° C. and a relative humidity (RH) of 90% for 13 hours, and then returned to the atmosphere at room temperature. The mass increase due to the participation of magnetic particles was measured. In addition, as a comparative example, magnetic particles not coated with anything were measured in the same manner.
As shown in Table 1, the increase in the mass of the phosphoric acid-coated magnetic particles before / after the constant temperature and humidity test was smaller than that of the comparative example, and it was found that good corrosion resistance was imparted by the surface treatment method of the present invention.

(Example 2)
Experiments were performed in the same manner as in Example 1 except that normal water was used instead of IPA used in Example 1. The temperature of water was 60 ° C., and the magnetic particles were stirred.
A constant temperature and humidity test was performed in which the magnetic particles were placed in a constant temperature and humidity chamber maintained at 80 ° C. and a relative humidity (RH) of 90% for 13 hours, and then returned to the atmosphere at room temperature. The mass increase due to the participation of magnetic particles was measured.
As shown in Table 1, the increase in mass of the phosphoric acid-coated magnetic particles before / after the constant temperature and humidity test is not as large as that of Example 1, but is sufficiently small, and good corrosion resistance is imparted by the surface treatment method of the present invention. I understood.

(Example 3)
In the same manner as in Example 1, phosphoric acid-coated magnetic particles dried at room temperature in a nitrogen stream were obtained. A constant temperature and humidity test was conducted in the same manner as in Example 1 except that this fine powder was not subjected to vacuum heat treatment, and the mass of the phosphoric acid-coated magnetic particles before and after the constant temperature and humidity test was measured. The measurement results are shown in Table 1.
As shown in Table 1, the increase in mass of the phosphoric acid-coated magnetic particles before and after the constant temperature and humidity test was sufficiently small, and it was found that good corrosion resistance was imparted by the surface treatment method of the present invention.

Example 4
In order to investigate the correlation between the addition amount of phosphoric acid and the corrosion resistance, the following examination was performed.
A vacuum melting furnace that weighs 99.9% or more of electrolytic iron, La metal, and ferrosilicon so that the final composition after dissolution is La _7.14 Si _10.2 Fe _bal (atomic%), and the total weight is 20 kg. And dissolved. After melting, the La-Fe-Si melt was poured onto a rotating copper roll via a tundish to produce La-Fe-Si alloy flakes. The obtained flakes were subjected to a hydrogen storage treatment using an atmospheric pressure furnace PHSG manufactured by Shimadzu Mectem. The hydrogen storage conditions were set to 300 ° C. × 5 h and the hydrogen pressure set to 5065 hPa. The alloy lump subjected to the hydrogen occlusion treatment was pulverized with a bantam mill in a nitrogen gas atmosphere in which the oxygen amount was controlled to 5 ppm by a jaw crusher or the like to obtain a powder having an average particle diameter of 180 μm. Next, using a classifier micron separator manufactured by Hosokawa Micron Corporation, particles having a particle size of 10 μm or less were removed to produce alloy particles having the above composition.
Next, the following solutions (3) and (4) in which the amount of phosphoric acid added to IPA was changed were prepared. The same solution (2) as in Example 1 was used.
(3) Solution in which 0.75 g of phosphoric acid is dissolved in 100 cc IPA (4) Solution in which 0.50 g of phosphoric acid is dissolved in 100 cc IPA (5) Solution in which 0.25 g of phosphoric acid is dissolved in 100 cc IPA
A total of two beakers prepared by immersing 20 g of alloy particles in IPA 60 cc (one sample) were prepared. Next, each beaker was heated to 60 ° C., and then the solution of (3) and (4) was added to each beaker by 40 cc over 20 minutes while stirring the inside of each beaker with a stirrer. The amount of phosphoric acid added thereby corresponds to 0.1 g, 0.2 g, and 0.3 g. Next, 40 cc of the supernatant of each beaker was discarded. Next, 10 cc of the solution (2) and 30 cc of IPA were added and stirred for 10 minutes with a stirrer, and then the supernatant was discarded. During this series of treatments, the stirring IPA was maintained at 60 ° C. Next, it was dried at room temperature in a nitrogen stream. Next, it was heated at 220 ° C. for 1 hour while being evacuated with a rotary pump, and then cooled to room temperature to obtain magnetic particles according to the present invention.
The magnetic particles were placed in a constant temperature and humidity chamber maintained at 80 ° C. and a relative humidity (RH) 90%, maintained for 13 hours, and then returned to the room temperature atmosphere. The mass increase due to the participation of magnetic particles was measured. Table 2 shows the results.

Claims (9)

(La · Y) _A M _B Si _C H _D T _bal (where M is one or more elements selected from Ti, Zr, and Hf, T includes Fe as an essential element, and Co, Ni, One or more elements selected from Cr are included as necessary, 6.0 ≦ A ≦ 7.5 atomic%, 0 ≦ B ≦ 5.0 atomic%, 8.0 ≦ C ≦ 14.0 atomic%, 0 ≦ D ≦ 15.0 atomic%) A magnetic particle comprising a chemical conversion film formed of phosphoric acid on the surface of an alloy particle having a composition represented by In a solution containing phosphoric acid, (La · Y) _A M _B Si _C H _D T _bal (where M is one or more elements selected from Ti, Zr and Hf, and T is essential for Fe) One or two or more elements selected from Co, Ni, and Cr are included as necessary, and 6.0 ≦ A ≦ 7.5 atomic%, 0 ≦ B ≦ 5.0 atomic%, 8.0 ≦ C ≦ 14.0 atomic%, A method for producing magnetic particles, characterized in that a chemical conversion treatment film with phosphoric acid is formed on a surface by immersing and stirring alloy particles having a composition represented by 0 ≦ D ≦ 15.0 atomic%). The method for producing magnetic particles according to claim 2, wherein the amount of phosphoric acid added is 0.05 to 1.0 g / 100 cc with respect to the amount of the liquid. 4. The method for producing magnetic particles according to claim 2, wherein the particles are stirred in the liquid containing phosphoric acid, and then neutralized by adding a hydroxide to the liquid. 5. The method for producing magnetic particles according to claim 4, wherein the amount of the hydroxide added is 0.005 to 0.2 g / 100 cc with respect to the amount of the liquid containing phosphoric acid. The method for producing magnetic particles according to claim 2, wherein the liquid is obtained by adding phosphoric acid to an organic solvent. The method for producing magnetic particles according to claim 4 or 6, wherein the hydroxide is added in a state where an inorganic hydroxide is dissolved in an organic solvent. The method for producing magnetic particles according to claim 2, wherein the particles are further subjected to heat treatment at 50 ° C. or more and 400 ° C. or less in an inert gas or vacuum after stirring. The method for producing magnetic particles according to any one of claims 2 to 8, wherein the magnetic particles have a particle size in a range of 0.5 to 1500 µm.