JP2010238761A - Permanent magnet and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a permanent magnet in which heat resistance and a magnetic characteristic can be effectively improved without increasing cost. <P>SOLUTION: An insulating film composed of at least one of fullerene or chemically modified fullerene is formed on a boundary surface of magnetic powder containing rare earth, molding or density growth is performed on the magnetic powder in a magnetic field to obtain a primary compact, sintering or plastic working is performed on the primary compact to obtain a secondary compact, and then heat treatment is performed on the secondary compact. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a permanent magnet made of a material in which an insulating coating is formed on the surface of a magnetic powder containing a rare earth-containing magnetic powder and a method for manufacturing the permanent magnet, and more particularly to an improvement in the technology for forming the insulating coating.

  Development of an electric vehicle using a motor as a driving source or a hybrid vehicle combining a motor and an engine has been progressing rapidly in recent years due to the influence of environmental problems. Magnets used in drive motors installed in this type of automobile tend to self-heat due to the generation of eddy currents, and there is a problem that the residual magnetic flux density is reduced in combination with external thermal effects. It was.

  Therefore, a high coercive element such as Dy (dysprosium) or Tb (terbium), which is a rare metal, is added to improve the heat resistance of the magnet itself (Patent Document 1), or inorganic at the interface of the material magnetic powder. By interposing an insulating material, measures are taken such as increasing the insulation between powders and reducing eddy current loss (Patent Documents 2 and 3). In addition, attempts have been made to divide the magnets and disperse the eddy current generation region to make it difficult to generate heat.

Japanese Patent Publication No. 7-105289 JP 2003-22905 A JP 2006-283042 A

  Addition of a high coercive element causes a decrease in residual magnetic flux density, and since it is a rare metal, stable supply is not guaranteed, and it is disadvantageous in terms of cost. In terms of cost, the measure of dividing the magnet is also disadvantageous because the steps of magnet division and magnet assembly increase. On the other hand, measures to improve the insulation by interposing an inorganic insulating material at the interface of the magnet powder may greatly reduce the magnetic properties because substances that are not related to the magnetic properties are mixed. Absent. Further, in the hot plastic working magnet, an insulator (particularly a metal oxide) is present at the powder interface, resulting in a decrease in workability, and a problem in that magnetic properties are further deteriorated. Furthermore, an RE (rare earth, such as Nd) rich phase is formed in the liquid phase between the powder interfaces, so that even if an insulator is present, the RE rich phase permeates between the insulators, so that the powders Will not be completely insulated.

  Accordingly, an object of the present invention is to provide a permanent magnet that can effectively improve heat resistance and magnetic properties without causing an increase in cost due to the use of rare metals or an increase in the number of processes, and a method for manufacturing the same.

  The permanent magnet of the present invention includes a rare earth-containing magnetic powder, and an insulating film made of at least one of fullerene or chemically modified fullerene is formed at the interface of the rare earth-containing magnetic powder.

  According to the permanent magnet of the present invention, since the insulating coating made of fullerene having high insulating properties or chemically modified fullerene is formed at the interface of the rare earth-containing magnetic powder as the material powder, high resistance is achieved and insulation is achieved. Therefore, the eddy current loss is reduced and the magnetic characteristics are improved. Further, it is not necessary to use a rare metal or divide the magnet, which is advantageous in manufacturing.

  The fullerene or chemically modified fullerene forming the insulating film is excellent in terms of heat resistance and lubricity. High heat resistance has the advantage that heat treatment at high temperatures is possible. Concerning lubricity, since it has excellent followability to plastic deformation and excellent moldability, it is possible to increase the density of a molded product produced by compression molding, and it is difficult to cause damage such as cracks in the insulating coating. . From these facts, the magnetic characteristics are improved.

  In the permanent magnet of the present invention, the insulating coating contains an inorganic compound formed by combining the chemically modified fullerene and a rare earth of a RE (rare earth) -rich phase generated on the surface of the rare earth-containing magnetic powder. Is a preferred form. This is because, when the chemically modified fullerene forming the insulating film is a mixed fullerene with a fluoride such as a fullerene fluoride, an inorganic compound formed by combining the fluoride and the rare earth of the rare earth-containing magnetic powder. In this form, a uniform insulating film is formed between the powder interfaces.

  Next, the method for producing a permanent magnet according to the present invention is a method for suitably producing the above-described permanent magnet according to the present invention, and comprises at least one of fullerene or chemically modified fullerene at the interface of the rare earth-containing magnetic powder. A step of forming an insulating film, a step of forming a rare earth-containing magnetic powder on which the insulating film has been formed in a magnetic field or densifying the powder, and obtaining a primary molded body; and sintering or plastic working the primary molded body And a step of obtaining a secondary molded body and a step of heat-treating the secondary molded body.

Further, as a method for producing the permanent magnet of the present invention, in the above production method, a step of heat-treating the rare earth-containing magnetic powder between the step of forming the first insulating film and the step of obtaining the next primary molded body is performed. Includes methods to add. That is, a step of forming an insulating film made of at least one of fullerene or chemically modified fullerene at the interface of the rare earth-containing magnetic powder;
A step of heat-treating the rare earth-containing magnetic powder on which the insulating film is formed, a step of forming the heat-treated powder in a magnetic field or densifying it, and obtaining a primary compact, and sintering the primary compact Or it is a manufacturing method characterized by including the process of obtaining a secondary molded object by plastic working, and the process of heat-processing the said secondary molded object.

  In each of the above production methods, the chemically modified fullerene is combined with the rare earth of the rare earth-containing magnetic powder to form an inorganic compound, whereby an insulating film can be formed with the inorganic compound. Magnetic characteristics can be greatly improved.

  Moreover, in the manufacturing method of this invention, it is preferable to perform in the formation process of the said insulating film using the solution which melt | dissolved at least 1 of the fullerene or the chemically modified fullerene in the nonpolar solvent or the polar solvent. . In this form, fullerene or chemically modified fullerene is solvated, so that the fullerene or chemically modified fullerene can be coated thinly and uniformly on the surface of the magnetic powder. For this reason, fullerene or chemically modified fullerene can be coated on the surface of the magnetic powder with as little usage as possible, and an increase in cost can be suppressed. Moreover, since it coats uniformly and reliably, a uniform insulating layer is formed.

  According to the present invention, an insulating coating composed of at least one of fullerene or chemically modified fullerene having excellent insulating properties, heat resistance and heat resistance is formed at the interface of the rare earth-containing magnetic powder as a material. Thus, there is an effect that it is possible to obtain a permanent magnet that can effectively improve the heat resistance and the magnetic characteristics without incurring manufacturing concerns.

It is a figure which shows typically the process of the manufacturing method of the permanent magnet which concerns on 1st Embodiment of this invention. It is a figure which shows typically the process of the manufacturing method of the permanent magnet which concerns on 2nd Embodiment of this invention. It is a graph which shows the measurement result of the electrical resistivity performed in the Example.

Embodiments according to the present invention will be described below with reference to the drawings.
[1] First Embodiment FIG. 1 shows a process of a method for manufacturing a permanent magnet according to a first embodiment. In this method, first, a magnetic powder 1 containing a rare earth metal shown in FIG. The composition of the magnetic powder 1 is not particularly limited, and examples thereof include RE (rare earth) -Fe-B, RE-Fe-N, and RE-Co. In addition, rare earth-containing magnetic powder made of a magnetic material whose magnetic properties are enhanced by refining crystal grains and making them anisotropic by HDDR treatment (decomposition by absorption of hydrogen and recombination by dehydrogenation) can also be used.

  Examples of the rare earth metal include, but are not limited to, Nd (neodymium) and Pr (praseodymium). The rare earth content is not particularly limited, but is preferably contained in the magnetic powder at a ratio of 27.0 to 32.0 wt%. This is because if the amount is less than 27.0 wt%, the powders are difficult to bond to each other, making it difficult to manufacture, and if it exceeds 32.0 wt%, the ratio of the main phase is reduced and the magnetic properties are lowered, which is not practical. It is.

  Next, as shown in FIG. 1B, the particulate material P made of fullerene is dissolved in a solvent S to solvate the particulate material P. In this case, instead of fullerene, chemically modified fullerene or a mixture of fullerene and chemically modified fullerene may be used.

The fullerenes _{include C 60, C 70, C 76} , C 78, C 82, C 84, C 90, C 94, C 96, single _{C 100} or more higher fullerenes or mixtures thereof alone, it is . Further, as the chemically modified fullerene, simple substances such as C ₆₀ -F _X (fluorinated fullerene), C ₆₀ -O _X (oxide fullerene), C ₆₀ -OH _X (fullerene hydroxide), or a mixture thereof can be mentioned. (X at the lower right of the element symbol is a coefficient). As the chemical modification fullerene, as will be described later, a compound that forms an inorganic compound by combining with a rare earth in the RE-rich phase when heated is used.

  Although the solvent S is not particularly limited, when fullerene is used as the particulate material P, a nonpolar solvent such as a benzene solvent in which fullerene is dissolved may be mentioned. In this case, after the particulate material P is dissolved in a nonpolar solvent, the nonpolar solvent may be mixed with a highly volatile polar solvent. Further, when chemically modified fullerene is used as the particulate material P, the chemically modified fullerene is dissolved in a polar solvent, and therefore the solvent S may be either nonpolar or polar. Furthermore, the mixing method of the particulate material P to the solvent S is not particularly limited, and various mixing methods such as a container rotating method, a mechanical stirring method, and a fluid stirring method can be applied.

  Next, as shown in FIG. 1 (C), the solvent S in which the particulate material P is dissolved to become a fullerene solvent is uniformly applied to the surface of the magnetic powder 1 and dried, so that the fullerene is removed from the magnetic powder 1. Stick to the surface. Thereby, the insulating coating 2 made of fullerene is formed on the surface of the magnetic powder 1. By using a fullerene solvent having a low viscosity, the insulating coating 2 is thinly and uniformly formed on the surface of the magnetic powder 1.

  Although the specific formation method of the insulating film 2 is not specifically limited, For example, ultrasonic irradiation, the air current spray method, barrel mixing, etc. are mentioned. The thickness of the insulating coating 2 is not particularly limited, but is preferably 0.7 nm to 10 μm. When the thickness of the insulating coating 2 is less than 0.7 nm, the insulating effect is reduced because the thickness is less than the diameter of the minimum fullerene molecule. On the other hand, when the film thickness of the insulating coating 2 is more than 10 μm, the magnetization is greatly reduced, so that the practicality is lost.

  Next, as shown in FIG. 1D, the magnetic powder 1 having the insulating coating 2 formed on the surface thereof is compressed to obtain a primary compact 31. In order to obtain the primary molded body 31, in this case, one of the following two methods is selected. One is molding in a magnetic field, and the other is densification in a normal environment that is not a magnetic field. In any case, a method of compressing and molding the magnetic powder 1 in the mold is employed, but there is a difference in molding pressure in addition to whether or not the molding is performed in a magnetic field. That is, the molding pressure in the molding in the magnetic field is, for example, about 30 to 300 MPa, while the densification is performed at, for example, about 50 to 100 MPa while heating to about 550 to 800 ° C.

  Next, as shown in FIG. 1 (E), regarding the primary molded body 31 obtained by molding in the magnetic field in the compression molding step, a secondary molded body 32 is obtained by sintering, and then heat treatment is performed. Permanent magnet. Sintering to obtain the secondary compact 32 is a process in which the primary compact 31 molded in a magnetic field is heated at, for example, 900 to 1200 ° C. for 60 minutes. Further, the densified primary molded body 31 is further subjected to plastic working to form a secondary molded body 32, and finally subjected to heat treatment as shown in FIG. 1 (F). In the plastic working to obtain the secondary molded body 32, the densified primary molded body 31 is set in a mold capable of obtaining a predetermined shape, and is deformed by applying a load. This plastic working may be performed while heating to about 550 to 800 ° C., for example.

  The heat treatment of the last secondary molded body 32 is performed at 600 to 900 ° C. for 10 to 150 minutes, for example. The atmosphere during the heat treatment is not particularly limited, and examples thereof include an inert atmosphere such as argon or nitrogen in a vacuum, and a reducing atmosphere such as hydrogen. The heat treatment temperature is not particularly limited, but 600 ° C. or higher is preferable because the chemically modified fullerene and the rare earth of the RE-rich layer are easily bonded to form an inorganic compound.

A permanent magnet molded into a predetermined shape is obtained by the above manufacturing method.
In the obtained permanent magnet, an insulating coating 2 made of fullerene or chemically modified fullerene having high insulation is formed at the interface of the magnetic powder 1. For this reason, the permanent magnet exhibits a high resistance value, improves insulation, reduces eddy current, and suppresses self-heating.

  The fullerene or chemically modified fullerene forming the insulating coating 2 is excellent in terms of heat resistance and lubricity. High heat resistance enables heat treatment at high temperatures, and thus a uniform insulating film can be obtained. In addition, because of high lubricity and high followability to plastic deformation and excellent moldability, when primary molding is performed in a magnetic field, friction at the powder interface during orientation is reduced, and high magnetic field orientation is obtained. Further, when the secondary forming is hot plastic working, high magnetic properties can be obtained because the hot plastic workability is not hindered by the lubrication effect at the interface as compared with the conventional solid insulator.

  Here, particularly when chemically modified fullerene is used as the particulate material P, the rare earth metal is extracted from the base material forming the main phase of the magnetic powder 1 on the surface of the magnetic powder 1 during the process having the influence of heating. A part of the molten metal is melted, and the rare earth-rich phase reacts with the chemically modified element of the chemically modified fullerene to bond to form an inorganic compound. This inorganic compound forms the insulating coating 2.

For example, when the magnetic powder 1 is Nd-Fe-B (neodymium-iron-boron) and the chemically modified fullerene forming the insulating coating 2 is C ₆₀ -F _X (fluorinated fullerene), rich phase melts on the surface of the magnetic powder 1, the Nd and a fluoride of C ₆₀ -F _X is bond by reacting an inorganic compound is produced. The inorganic compound produced in this way has a very high insulating property. Therefore, a high resistance can be achieved by forming the insulating coating 2 made of an inorganic compound.

  Note that the action of the rare earth-rich phase to dissolve on the surface of the magnetic powder 1 due to the heating effect is during sintering after sintering in a magnetic field, during molding by densification (when molding by heating), or even at high density. Occurs at the time of plastic working after forming by plasticizing (when plastic working by heating) or at the last heat treatment. Further, the chemical modification element for forming an inorganic compound by reacting with the rare earth-rich phase is not limited to fluorine, and may be an oxide, a hydroxide, or the like.

  Further, when the insulating coating 2 is formed on the surface of the magnetic powder 1, the particulate material P is made into a solvent to have a low viscosity, and this is applied to the surface of the magnetic powder 1. For this reason, fullerene or chemically modified fullerene can be thinly and uniformly coated on the surface of the magnetic powder 1. As a result, fullerene or chemically modified fullerene can be coated on the surface of the magnetic powder 1 with as little usage as possible, and an increase in cost can be suppressed. Moreover, since it coat | covers uniformly and reliably, high resistance is achieved. Thus, according to the method of forming the insulating coating 2 by solvent coating, there is an advantage that the manufacturing method becomes simple because resistance heating or vapor deposition using an electron beam is unnecessary.

  In terms of cost, there is a significant cost control effect in that magnetic properties can be improved without using rare metals such as Dy (dysprosium) and Tb (terbium) and without using a method of dividing the magnet. Is fulfilled.

[2] Second Embodiment FIG. 2 shows a process of a method for manufacturing a permanent magnet according to a second embodiment. This method heat-treats the magnetic powder 1 indicated by (C ′) between the step of forming the first insulating coating 2 and the step of obtaining the next primary molded body 31 in the manufacturing method of the first embodiment. A process has been added. The condition of the heat treatment performed in FIG. 2C ′ is, for example, a process of heating at 100 to 1000 ° C. for 10 to 150 minutes.

  Thus, the method of performing the heat treatment in the stage before obtaining the primary molded body 31 is advantageous when the insulating film is formed from the above-described inorganic compound to greatly improve the insulation. That is, in the method of the second embodiment, the insulating coating 2 is formed on the surface of the magnetic powder 1 by using chemically modified fullerene such as fullerene fluoride as the particulate material P in FIG. Thereafter, when the magnetic powder 1 having the insulating coating 2 formed thereon is heat-treated under the above conditions, the insulating coating 2 formed on the surface thereof is made of an inorganic compound. As described above, by performing the heat treatment at the stage of the magnetic powder 1, it is possible to reliably cover the entire surface of the magnetic powder 1 with the insulating coating 2 made of an inorganic compound. Therefore, the obtained permanent magnet exhibits high insulation.

Hereinafter, examples will be presented to demonstrate the effects of the present invention.
[Example 1]
_Fullerene: The _{C 60} was dissolved in 1,2,4-trimethylbenzene (solubility 17.9 mg / ml), to produce a fullerene solvent and mixing the solution with the highly volatile ethanol. Subsequently, the fullerene solvent and the magnetic powder composed of Nd—Fe—B were temporarily mixed in a beaker, and then subjected to ultrasonic irradiation under conditions of 40 kHz / 250 W / 60 minutes. The amount of fullerene added to the magnetic powder here was 1.3 vol.%.

  Next, the magnetic powder mixed with the fullerene solvent was dried while being irradiated with ultrasonic waves under a vacuum of 5 kPa or less under the condition of 40 kHz / 50 W / 60 minutes to form a fullerene film as an insulating coating on the surface of the magnetic powder. Next, using a mold having a predetermined shape, a pressure of 50 MPa was applied while heating to 700 ° C., and the magnetic powder on which the fullerene film was formed was densified to obtain a primary molded body.

  Next, the obtained primary molded body was subjected to hot plastic working at a pressure of 30 MPa while being heated to 750 ° C. to obtain a secondary molded body having a predetermined shape. Next, the obtained secondary compact was heated and sintered at 600 to 800 ° C. for 60 minutes to obtain a permanent magnet.

[Example 2]
A permanent magnet was obtained in the same manner as in Example 1 except that the amount of fullerene added to the magnetic powder was 2.2 vol.

[Example 3]
A permanent magnet was obtained in the same manner as in Example 1 except that the amount of fullerene added to the magnetic powder was 4.3 vol.

[Example 4]
A permanent magnet was obtained in the same manner as in Example 1 except that C ₆₀ -F (fluorinated fullerene) was used as the chemically modified fullerene instead of fullerene C ₆₀ in Example 1.

[Comparative Example 1]
A permanent magnet was obtained in the same manner as in Example 1 except that no additive such as fullerene was used.
[Comparative Example 2]
A permanent magnet was obtained in the same manner as in Example 1 except that B ₂ O ₃ was used instead of fullerene as an additive.
Table 1 shows the magnetic powder materials of Examples 1 to 4 and Comparative Examples 1 and 2 and the amount of additive for forming an insulating film on the surface of the magnetic powder.

  Next, the electrical resistivity of the permanent magnets of Examples 1 to 4 and Comparative Examples 1 and 2 was measured by the 4-terminal method. The measurement results are shown in Table 1 and represented by the graph of FIG. In addition, the numerical value of the electrical resistivity of Table 1 shows the ratio when the measured value of Comparative Example 1 is 1.

According to Table 1, it was found that in Examples 1 to 4 to which fullerene or chemically modified fullerene was added, the electrical resistivity was higher than that of Comparative Example 1 without the additive, and the insulation was improved. . In particular, the electrical resistivity of Example 4 was significantly increased to 8.24 times that of Comparative Example 1, and this was a significant improvement in insulation due to the formation of the insulating film made of the inorganic compound described above. It is estimated that On the other hand, in Comparative Example 2 using B ₂ O ₃ , the electrical resistivity is increased, but the amount added is several times as large as in Examples 1 to 4, and thus a significant decrease in magnetization occurs.

DESCRIPTION OF SYMBOLS 1 ... Magnetic powder 2 ... Insulating film 31 ... Primary molded object 32 ... Secondary molded object P ... Particulate material S ... Solvent

Claims (6)

  A permanent magnet comprising a rare earth-containing magnetic powder, and an insulating film made of at least one of fullerene or chemically modified fullerene formed on an interface of the rare earth-containing magnetic powder.   2. The permanent magnet according to claim 1, wherein the insulating coating contains an inorganic compound formed by combining the chemically modified fullerene and the rare earth of the rare earth-containing magnetic powder. Forming an insulating coating composed of at least one of fullerene or chemically modified fullerene at the interface of the rare earth-containing magnetic powder;
Forming a rare earth-containing magnetic powder with the insulating coating formed in a magnetic field or densifying to obtain a primary molded body;
A step of sintering or plastic working the primary molded body to obtain a secondary molded body;
Heat treating the secondary compact,
The manufacturing method of the permanent magnet characterized by comprising. Forming an insulating coating composed of at least one of fullerene or chemically modified fullerene at the interface of the rare earth-containing magnetic powder;
Heat treating the rare earth-containing magnetic powder on which the insulating film is formed;
Molding the heat-treated powder in a magnetic field or densifying to obtain a primary molded body;
A step of sintering or plastic working the primary molded body to obtain a secondary molded body;
Heat treating the secondary compact,
The manufacturing method of the permanent magnet characterized by comprising.   5. The method for producing a permanent magnet according to claim 3, wherein the chemically modified fullerene forms an inorganic compound by combining with the rare earth of the rare earth-containing magnetic powder.   6. The insulating film formation step is performed using a nonpolar solvent or a solution in which at least one of fullerene or chemically modified fullerene is dissolved in a polar solvent. Of manufacturing permanent magnets.

Images