JPH0435549B2 - - Google Patents

Description

[Detailed description of the invention]

This invention has fewer impurities that degrade the magnetic properties of Fe-B-R permanent magnets (R is at least one rare earth element including Y), especially Fe-B-Nd permanent magnets with excellent magnetic properties. The present invention relates to a method for producing a raw material alloy for rare earth magnets. Permanent magnetic materials are extremely important electrical and electronic materials used in a wide range of fields, from various household appliances to peripheral terminal equipment for large computers. The miniaturization of electrical and electronic equipment in recent years,
With the demand for higher efficiency, permanent magnet materials are required to have increasingly higher performance. Current typical permanent magnet materials are alnico, hard ferrite and rare earth cobalt magnets. As the cobalt raw material situation has become unstable in recent years, the demand for alnico magnets containing 20 to 30 wt% cobalt has decreased, and inexpensive hard ferrite, whose main component is iron oxide, has become the mainstream magnet material. Summer. On the other hand, rare earth cobalt magnets contain cobalt.
It is very expensive because it contains 50-60wt% Sm, which is not included in rare earth ores, but it has much higher magnetic properties than other magnets, so it is mainly small and has high added value. It came to be widely used in magnetic circuits. Therefore, the inventor first developed a new high-performance permanent magnet that does not necessarily contain expensive Sm or Co.
We proposed a Fe-BR-based permanent magnet (R is a rare earth element containing Y) (Japanese Patent Application No. 145072/1982). This Fe
-B-R magnet material has a composition (atomic %) of 8% or more
Consisting of 30% R, 2% to 28% B, and the balance Fe, it exhibits the magnetic properties of coercive force Hc≧1KOe, residual magnetic flux density Br>4KG, and the maximum energy product (BH) max is equal to or higher than that of hard ferrite. In a preferred composition range, (BH)max≧10MGOe, and the maximum value reaches 25MGOe or more. Also, as R, Nd,
In a preferred composition range centered on light rare earth metals such as Pr, (BH)max is 36MGOe or more. The above novel permanent magnet, for example in the case of a sintered magnet, is manufactured by the following steps. (1) As a starting material, electrolytic iron with a purity of 99.9%,
Feroboron alloy containing 19.4% B and the remainder consisting of Fe and impurities such as Al, Si, and C, purity 99.7%
Rare earth metals of more than 99.9 purity or even more
% of electrolytic Co was high-frequency melted, then cast into a water-cooled copper mold, (2) coarsely ground to 35 mesh through using a stamp mill, then finely ground (3 to 10 μm) using a ball mill for 3 hours, (3) magnetic field. (10KOe) Medium oriented and pressure molded (1.5t/
( ⁴ ) Sintering, 1000℃~1200℃, 1 hour in Ar, cooling after sintering, (5) Aging treatment, 500℃~700℃, 1 hour, in Ar ,
Cool after processing. The rare earth metals that are the starting materials for manufacturing the above-mentioned Fe-B-R system (R is at least one rare earth element including Y) permanent magnets have excellent properties when they are light rare earth metals such as Nd and Pr. is obtained, especially
Nd shows the best magnetic properties. However, Nd has only been used as an oxide in some parts of cathode ray tube glass and ceramic capacitors, and Nd metal has almost no use.
Regarding the smelting method, generally only the Ca reduction method and the electrolytic method are known, but it is not fully established. Generally, when manufacturing by electrolytic method, the melting point of Nd is as high as 1024℃, so the temperature of the molten metal and salt bath is adjusted.
It is necessary to raise the temperature to a high temperature of about 1200℃, which makes it inevitable that impurities from electrodes, furnace refractories, fluorides, chlorides, etc. are mixed in. Furthermore, molten Nd has a high viscosity, making it difficult to separate impurities. Various problems arose. This invention is based on the fact that the purity of the rare earth metal as the starting material in Fe-B-R permanent magnets (R is at least one rare earth element including Y) has a significant effect on the magnetic properties of the magnet alloy. In view of this, it is an object of the present invention to provide Fe-BR-based permanent magnets with few impurities through a highly pure intermediate raw material alloy for rare earth magnets. That is, this invention provides rare earth metal oxides,
In addition, when halides such as fluorides and chlorides are subjected to a reduction reaction using an electrolytic method, by adding and melting Fe and B, 3wt% to 20wt% of halides with a low melting point and low impurities such as oxygen can be obtained. Fe, 0.5wt
% to 10 wt% B, and the remainder is substantially a rare earth metal. It is generally known that Nd and Fe have a low melting point in a certain composition range. For example, 10wt% Fe
The melting point of the -Nd alloy is about 700°C, which is much lower than the 1050°C of Nd alone. However, although this Nd-Fe alloy has a slight improvement effect over Nd alone, it is still molten and has a high viscosity, making it difficult to separate impurities and containing a large amount of oxygen. To solve the above problem, Nd or Nd
It is necessary to lower the melting point of the alloy and the temperature of the electrolytic bath, and to make Nd or Nd alloy have oxidation resistance. The present inventors believe that Fe-B-R magnets contain B as an essential element, and that the addition of halides and oxides of B is a combination of mixed salts with lithium fluoride, barium fluoride, rare earth fluoride, etc. Focusing on the possibility of lowering the bath temperature, various studies were conducted and the above Fe-B
When producing magnet materials using the -R intermediate raw material alloy, Fe-B-R magnets exhibit lower impurity concentration and better magnetic properties than when Nd or Nd-Fe alloys are used using conventional methods. I found out that it can be obtained. Furthermore, accompanying this, the melting point of the electrolytic bath decreases during electrolysis, and Fe-B-Nd
It was found that separation from the alloy progressed easily and inclusions were reduced. A specific method for obtaining Fe-BR alloy by the electrolytic reduction method of the present invention is as follows. First, the oxide electrolysis method will be explained. Lithium fluoride and neodymium fluoride are used as the electrolytic bath. Since this mixed bath has a low melting point around 68 wt% NdF ₃ -LiF, a composition near this value is desirable.
Also, part of _NdF3 or LiF can be replaced with barium fluoride,
Substitution with magnesium fluoride, calcium fluoride, etc. has the effect of lowering the temperature of the mixed bath and increasing the electrolyte of Nd ₂ O ₃ . Nd ₂ O ₃ , which is the raw material for Nd, has a solubility of only about 2 wt% in the above mixed bath at, for example, 900°C, and in order to continue the electrolysis normally, it must be equivalent to the Nd powder deposited by electrolysis. Nd ₂ O ₃ must be constantly supplied in fixed amounts. A considerable amount of B ₂ O ₃ , which is the raw material for B, is melted at the above composition and temperature, but if the supply amount is increased, an alloy outside the above composition range will be produced, so the B content of the Fe-B-R intermediate raw material alloy The amount of supply can be adjusted depending on the aim. In the electrolytic reduction method according to the present invention, the electrolytic cell is preferably made of graphite, and the anode may be made of graphite so that it also serves as the electrolytic cell. Furthermore, although Mo or the like is generally used for the cathode, an iron rod or plate is used as the consumable electrode to avoid contamination with impurities. If one made of Fe is used, it can also serve as a source of Fe raw material for Fe-BR alloy. In addition, in the method of this invention, 900°C to 1000°C
When electrolyzed, the Nd and B deposited on the iron cathode react with iron to form a low-melting point Fe-B-Nd alloy, which is precipitated at the bottom of the electrolytic cell and can be produced continuously. An Fe-B-Nd alloy can also be obtained by mixing Fe oxide in the electrolytic bath, using fluoride or chloride as B, or using an electrode other than iron. Next, when electrolyzing rare earth chlorides, a mixed bath of NdCl ₃ , KCl, CaF ₂ , CaCl ₂ NaCl, etc. is used as the mixed bath. Nd is obtained by reducing NdCl ₃ , and for B, in addition to oxides, fluorides and chlorides are used. Other conditions are the same as in the case of the oxide electrolysis method described above. Note that these steps are preferably performed in an inert gas atmosphere. Above, we mainly explained Nd as R, but
The method of this invention is also effective for rare earth elements other than Nd, and it is also effective for rare earth elements other than Nd.
Of the heavy rare earth elements, Dy, Tb,
By substituting with Ho, Er, Gd, Yb, etc., the energy product and coercive force can be improved. However, these heavy rare earth elements, except for Yb,
Since both have high melting points of 1300°C or higher, oxygen and impurities tend to remain in the metal raw materials. Therefore, in such a case, it is possible to add halides and oxides of the heavy rare earth elements mentioned above to the electrolytic bath.
-Fe-B alloy etc. can be obtained. Next, the reason for limiting the composition of the raw material alloy for rare earth magnets according to the present invention will be explained. If the Fe content is less than 3wt% or more than 20wt%,
When the melting point of the alloy reaches 1000℃ or higher, NdF ₃ and LiF may be mixed into the resulting alloy, or the furnace material,
NdF ₃ , the impurity O ₂ in LiF dissolves with Nd and Nd
The purity of Nd decreases, deteriorating the magnetic properties of the magnet alloy made from it.
A range of 3wt% to 20wt% is preferred. B lowers the melting point of the Nd-Fe alloy and increases oxidation resistance, and halides and oxides of B have the effect of lowering the melting point of the electrolyte salt bath, so it is desirable to have a large amount, but if it exceeds 10 wt%, When adjusting the magnet composition to the above, as in the conventional method, Nd or Nd-
Fe alloy must be used together, and 0.5wt%
The above effects cannot be expected with less than 0.5wt.
% to 10wt%. The rare earth element R includes Y, light rare earths and heavy rare earths, and includes Nd, Pr, La, Ce,
Tb, Dy, Ho, Er, Eu, Sm, Gd, Tm, Yb,
Includes Lu. Furthermore, in the Fe-BR-based magnet alloy according to the present invention, by replacing up to 50 at% of Co with Fe, it is possible to raise the Curie point and reduce the temperature coefficient of Br without impairing the magnetic properties. In order to obtain an intermediate raw material alloy containing Co, R-Fe
-Co-B alloy or R-Co-B alloy can be obtained. Furthermore, the coercive force (iHc) can be increased by incorporating at least one of the following additive elements M into the Fe-BR-based magnet alloy. In addition, when two or more types are added, the content is set to be less than the maximum value of the additional element M. Ti 4.5% or less, Ni 4.5% or less, Bi 5% or less, V 9.5% or less, Nb 12.5% or less, Ta 10.5% or less, Cr 8.5% or less, Mo 9.5% or less, W 9.5% or less, Mn 3.5% or less, Al: 9.5% or less, Sb: 2.5% or less, Ge: 7% or less, Sn: 3.5% or less, Zr: 5.5% or less, Hf: 5.5% or less. These additional elements are added during the melting process for adjusting the composition of single metals or alloys. You may also
An oxide compound is mixed in an electrolytic salt bath, and R
-Fe-B-M can be obtained as an intermediate raw material alloy. Using the intermediate raw material alloy for rare earth magnets according to the present invention, the composition (atomic %) is 8% to 30%R, 2% to
A magnetically anisotropic magnet with a composition of 28% B and the balance Fe, which is made from an ingot melted in argon or vacuum, is crushed, formed in a magnetic field, sintered, and aged, and has a coercive force.
It exhibits magnetic properties such as Hc≧1KOe and residual magnetic flux density Br>4KG, and the maximum energy product (BH) max is equal to or higher than that of hard ferrite. In addition, the main component of R, that is, 50 atomic% or more
Magnetic anisotropic magnet alloys made of light rare earth metals such as Nd and Pr have a composition (atomic %) of 12% to 20% R, 4%
~24%B, balance Fe, (BH)max≧
It shows excellent magnetic properties of 10MGOe or more, and especially when the light rare earth metal is Nd, the maximum value of (BH)max reaches 36MGOe or more. Examples according to the present invention will be shown below to clarify its effects. Example 1 As an electrolytic bath, a mixed bath of LiF32wt%-68wt% _NdF3 was placed in a graphite container and heated to 900°C to 1000°C, and further, 91wt% _Nd2O3 was _added to this mixed bath.
and 9wt _{% B2O3} . A BN sintered body is used as a saucer on the bottom of the tank, an iron rod is held as a cathode so that its tip is always immersed in the bath, a graphite container is used as an anode, and the entire device is housed in a stainless steel container. The structure was configured so that electrolysis could be carried out in an Ar gas flow, and a current of about 20 A was applied for 10 hours to obtain 164 g of Fe--B--Nd intermediate raw material alloy. The composition of the obtained alloy is 16.8wt%Fe−3.0wt%
The amount of impurities contained in this Fe-B-Nd alloy is shown in Table 1. Next, using the above 16.8wt%Fe-3.0wt%B-Nd alloy and adjusting other raw materials, 14at%Nd-7at%
Melting was carried out in vacuum to obtain a composition of B-Fe. The obtained ingot was coarsely ground to 35 mesh through using a crushing stamp mill, and further ground to a fine powder with an average particle size of 3 μm using a ball mill. Then, after being oriented in a magnetic field (10 KOe), it was press-molded at 2 t/cm ² to obtain a molded body. The obtained molded body was heated at 1100°C for 1 hour at 20 Torr.
After sintering under sintering conditions in Ar and cooling after sintering,
Furthermore, aging treatment was performed in Ar at 600°C for 1 hour to obtain a magnetic alloy. For comparison, a comparison magnet alloy with the same composition was prepared under exactly the same manufacturing conditions except that commercially available Nd containing the impurities shown in Table 1 was used as the starting material Nd, and other magnetic alloys were prepared without supplying B. The magnetic properties of comparative magnet alloys produced under exactly the same conditions are measured and shown in Table 2, and the amounts of impurities in each of the above intermediate raw materials are shown in Table 1. It can be seen that the intermediate raw material alloy for magnet materials according to the present invention has a small amount of impurities, especially oxygen, and that by using this intermediate alloy, the influence of impurities contained in rare earth metals is reduced and the magnetic properties are improved. Example 2 As electrolytic bath, KCl 37.5wt%, NdCl ₃ 62.5wt%
Place the mixed bath in a graphite container and heat it to 950℃~1100℃.
heated to. _B2O3 is always about 0.5wt% in the electrolytic bath _.
121g of 19.1wt%Fe-1.3%
A wtB-Nd alloy was obtained. Measure the impurities in the obtained Fe-B-Nd alloy,
The results are shown in Table 1, and further, this alloy was made into a magnet material by the same manufacturing method as in Example 1, and the characteristics of the obtained magnet were measured and shown in Table 2. As is clear from the results, it can be seen that even with the chloride electrolysis of the present invention, a magnet containing few impurities and exhibiting excellent magnetic properties can be obtained.

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Claims (1)

[Claims] 1 Rare earth metal oxides or halides
3 wt% ~ by electrolytic reduction in the presence of Fe and B
A method for producing a raw material alloy for rare earth magnets, which comprises obtaining an Fe-B-R intermediate raw material alloy consisting of 20 wt% Fe, 0.5 wt% to 10 wt% B, and the remainder substantially rare earth metal.