JPS6338216A - Manufacture of corrosion-resistant rare-earth magnetic powder and magnetic unit made of the powder - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing a corrosion-resistant ferromagnetic powder of a magnet alloy containing rare earth-iron-boron, and a magnetic body produced by compression molding the same. .

[Prior art and its problems] Materials with permanent magnetic properties are widely used in electrical and electronic fields, such as motors, microphones, loudspeakers, measuring instruments, etc., or everyday items such as magnets. Currently, these include original ferrites, Al-Ni-Co magnet alloys or rare earth-boron containing magnet alloys. The first two types of magnets have relatively weak coercivity, while the disadvantages of the last type of magnetic alloy are that the rare earth samarium is difficult to obtain and the alloy is very expensive. Therefore, various efforts have been made to produce magnetic alloys with good magnetic properties, exhibiting high coercivity and high remanence, using raw materials that are not very expensive and are commercially available in sufficient quantities. . Then rare earth-iron-boron type alloys were discovered, where the rare earth mainly used is neodymium, which is relatively inexpensive. In this alloy, neodymium can be replaced with dysprosium, for example, and cobalt can be used in place of the residual iron, significantly increasing magnetic properties such as coercive force and increasing temperature resistance (one Curie point increase). I can do it.

In order to prevent the oxidation of rare earth metals that are easily oxidized, metallurgical melting is performed in vacuum or in an inert gas atmosphere.
It is known to make iron-boron alloys. The alloy thus obtained is solidified into alloy pieces or ingots!・Make it. In order to enhance its magnetic properties, it must be crushed.

This grinding can be done by placing the alloy pieces or ingots on pressure rolls and grinding or milling them, by spraying the alloy pieces or ingots to obtain powder particles (U.S. Pat. No. 4,585,473), or by grinding the alloy pieces or ingots into powdered particles (U.S. Pat. In order to obtain a unique structure, the solution spinning method (melt spanni
ng process ) (U.S. Pat. No. 4,490
゜No. 395). When the alloy particles are crushed to a particle size of 1 to 10 μm, they are extremely fine and therefore have extremely high oxidizing properties.

Upon absorption of oxygen, the rare earth metal component, such as neodymium, converts to its oxide, so that it is no longer able to form the Nd-Fe-B phase required to create the ferromagnetic properties of the alloy. At a certain oxygen concentration, the magnetic properties begin to deteriorate substantially, and when this oxygen concentration reaches a certain critical point, the alloy loses its magnetic properties altogether. Therefore, the alloy powder must be protected from atmospheric oxygen by operating in a protective atmosphere or organic solvent. To obtain an anisotropic or isotropic magnet, the powder is compressed into a magnetic material in a magnetic field.

This compression molded product is then sintered at temperatures above 1000°C in a vacuum or in an inert atmosphere to achieve oxidation resistance, and to make this sintered body into a high quality product. , must undergo a thermal post-treatment to sufficiently enhance its magnetic properties.

Even if this results in a high product cost, the stability of this sintered product is not always sufficient, since residual susceptibility to oxidation tends to remain. U.S. Patent No. 4,4
Powders produced by solution spinning and milling according to No. 9B, No. 395 are generally embedded in a synthetic resin 7 trix or result in a low energy isotropic magnet.

According to the disclosure of European Patent Application No. 0125752:
In order to obtain an isotropic magnet, the amorphous structure of the remaining component is crushed after the solution spinning method of the magnet alloy, and the powder is compression molded, and then this compression molded body is coated, and the surface of the powder particles is The pores are filled with synthetic resin. However, if there is a scratch on this coating, even if it is extremely small, the alloy particles inside the compression molded body are not coated and are exposed to the oxygen in the atmosphere, resulting in an unstable magnetic material. .

The first object of the present invention is to provide a corrosion-resistant ferromagnetic powder of a magnet alloy containing rare earth elements, iron, and boron, which is characterized by its excellent oxidation resistance, and which also has high coercivity, isotropy, or anisotropy. It is an object of the present invention to provide a manufacturing method capable of producing a magnet having a directional maximum energy.

91 The next object of the present invention is to produce a magnetic material exhibiting excellent permanent magnetic properties by compression molding the "-2 powder, preferably in a magnetic field."

[Means for Solving the Problems and Their Effects] The above two objects are achieved by the present invention as follows. That is, one piece or ingot of the alloy is crushed to produce alloy particles, the alloy particles are heat treated to enhance their magnetic properties, and the surface of the heat treated alloy particles is then protected with a corrosion-resistant material. It is covered with layers. The above alloy 1.
The heptads are preferably heat treated at a temperature in the range of 300°C to 1000°C. The anti-corrosion material is one type of ceramic material or one type of metal material, such as copper, preferably in the form of an aqueous solution, and is deposited on the surface of the -distributed particles by electrolysis.

The magnetic material of the present invention is a magnetic material formed by compression molding particles of a magnetic alloy containing rare earth element-iron-boron, and is composed of the above-mentioned magnetic alloy or a heavy base containing 25-45% of at least one type of rare earth element, 0.5-3% boron, the remainder of the magnetic alloy being iron or an additive of at least one other metal selected from the group consisting of cobalt, aluminum and niobium. It is a magnetic material in which the alloy particles are coated with a protective layer of corrosion-resistant material.

The starting alloy material contains - in the membrane at least one rare earth metal, e.g. neodymium, or 1.2 rare earth metals, e.g. neodymium and dysprosium, by weight;
-45% NATA alloy.

Adding certain other rare earth metals, certain properties of synthetic products,
For example, coercivity can be improved. 0.5-3% coulometric boron can be added to the starting alloy material to create the desired ferromagnetic phase in the alloy. The remaining component of the starting alloy material is iron, or iron and other components, such as cobalt,
It is a complex with aluminum, niobium and other metals.

By combining iron with such elements, it is possible to improve the temperature stability as well as the magnetic properties of the composite product.

The starting alloy material is made by metallurgical melting methods, in which case it is important to keep the oxygen content to a minimum to ensure an alloy powder with low oxygen content.

Good magnetic properties are only obtained when the starting alloy material is ground to a powder that is sufficiently clean and has a low oxygen content. In the present invention, this is accomplished by performing pulverization by spraying and/or milling. Two parameters decisively influence the magnetic properties of the product: particle size and oxygen content.

By spraying in an inert atmosphere, diameter 1
Spherical particles smaller than dragon size are obtained. The oxygen content of this spray alloy is less than 1%. This sprayed alloy is
If you sieve it with a sieve size of 3p or less, it will be 30 to 40IIIR.
F S S S (f'1shersubsieve
5izer ) value fragments are obtained. When such alloy powder is heat treated and coated by the method of the present invention,
An isotropic powder with high coercivity but low energy production is obtained.

Moving the atomized alloy droplets through a magnetic field during spraying and solidifying therein improves the magnetic properties of the sprayed alloy. Before heat treating this spray alloy, it was briefly milled in liquid in a ball mill with an agitator, resulting in an FSSS value of 301! Below IR, preferably 3-15p, a magnetically anisotropic material with low oxygen content is obtained. Compared to conventional solution spinning methods, which are subsequently milled, this milling method has the advantage that at least a portion of the milled particles are spherical and therefore coating is easily carried out. .

To illustrate the importance of the oxygen content in this alloy, Table 1 shows the oxygen content of the uncoated dry powder of the Nd-Fe-B alloy in weight percent. The powder was ground and held in air for 2 hours to determine the amount of oxygen uptake due to its particle size.

Table 1 Before crushing 0.04% oxygen 1 mm
Less than (after spraying) 0.08%〃63, z or less (FSSS35) 0.11% //FSSS 2o4
0.15% //FSSS 111IIR
0,18% //FSSS 7,07a++
0.28%〃FSSS 4,8p O,4
2%〃FSSS 3.27a+ 0.61
%. If an inert working environment is available, the desired particle size can be obtained by conventional grinding methods, ie two-stage milling.

The next important step in the method of the invention is the heat treatment of this powder. For this purpose, the powder is conveyed directly to a vacuum kiln in a solvent or inert gas atmosphere. 300 here
Heated to -1000°C in one or several stages. Such heat treatment increased the coercive force of the milled magnet alloy with FSSS value of 51 nR from 222.9 kA/m of the original material to 802 kA/m. That is, its properties essentially change for the better. In other words, high-quality magnetic powder can only be produced through two process steps.

However, within the scope of the present invention, it is possible to reverse this series of steps. That is, the sprayed alloy is first heat treated and then the heat treated powder is milled.

The corrosion resistance of the particles is obtained by completely coating the surface of the particles with a layer of corrosion-protecting ceramic or metallic material. Deposition of the metal layer on the surface of the particles is carried out, for example, by an electrolytic method of coating copper without electrodes, as described below.

For this purpose, an aqueous solution of copper sulfate, thorium hydroxide and sodium potassium tartrate is prepared, the alloy powder is mixed into it with stirring, and formaldehyde is then added. A layer of metallic copper is deposited on the surface of the powder particles.

What has been found along with this is that the alloy particles are not substantially corroded by this aqueous solution, and that the increase in the oxygen content m of the alloy powder due to this is negligible.

The amount of coating material required depends on the surface area of the powder particles and thus their particle size. For the particle sizes referred to herein, the amount is about 10 to 25% by weight of the particles.

This corrosion-resistant surface layer on each particle gives the powder the desired corrosion resistance.
1-Well, I guarantee the permanent magnets made from this.

This powder can be directly compression molded into an isotropic magnet, or placed in a magnetic field to create an anisotropic magnet. If the magnet is designed to be a particularly large object, it must be made of metal before compression molding.
It can be made by adding ceramic or synthetic resin powder to this coated magnet alloy.

[Example 1 By weight, 33.3% rare earth (98.7% of which is Nd)
, 1.3% B, 65.2% iron, and 0.04
A piece or ingot of the alloy containing 63% O is melt-smelted in an inert gas atmosphere, sprayed and then reduced to a grain size of 63. It was sieved to obtain fragments below M.

The pieces were heat treated at a temperature of 630° C. and then electrolytically coated with copper in a two-part process. For this purpose, sprayed and heat-treated alloy powder or 30 g of C.
uSO4 and 60% NaOH of 809 and 150
The mixture was mixed with an aqueous solution containing 10 g of KNa10i taric acid while being stirred. Next, 1 part by volume of 37% formaldehyde was added per 5 parts by volume of the above mixture.

The coated alloy was thoroughly cleaned after the metallic copper was deposited on the particles and the coated particles were sieved from the liquid. This alloy contained 13.2% copper and 0.17% oxygen.

Table ■ shows the coercive force values of intermediate products and final products.

Table ■ Powder iHc (kA/m) Untreated - 637#'' or less 175 After copper coating, before heat treatment 160 After heat treatment and coating 640 This powder was isotropic (BHmax = 42 kJ/cu
,m,).

Example 2 The sprayed magnetic alloy of Example 1 has an FSSS value of 5.
Attrition mill (aLLri L) until it reaches 61p
or) in cyclohexane. While still wet with solvent, the powder was transferred to a vacuum kiln and heat treated therein at 630°C. The coating was carried out in the same manner as in Example 1, and the coated powder contained 18.2% copper and 0.27% oxygen. Table ■ shows the values of coercive force in the same way as Table ■.

Table ■ Powder 1Hc (kA/m) Untreated = FSSS value 5.2 PA7L223 After copper coating, before heat treatment 204 After heat treatment and coating
802 This powder was anisotropic (BHmax=195
．． 8kJ/cu, m,).

Claims (23)

[Claims] (1) A method for producing a corrosion-resistant ferromagnetic powder of a magnetic alloy containing rare earths-iron-boron, the steps of which include: (a) crushing a piece or ingot of said alloy to produce alloy particles; (b) heat-treating said alloy particles to enhance their magnetic properties; and (c) then coating the surface of said heat-treated alloy particles with a protective layer of corrosion-resistant material. A method for manufacturing rare earth magnetic powder. (2) The method for producing a corrosion-resistant rare earth magnetic powder according to claim 1, wherein the alloy particles are heat-treated at a temperature in the range of 300°C to 1000°C. (3) The method for producing a corrosion-resistant rare earth magnetic powder according to claim 2, wherein the alloy particles are heat-treated at a temperature in the range of 500°C to 800°C. (4) The method for producing a corrosion-resistant rare earth magnetic powder according to claim 1, wherein the corrosion-resistant material is one type of metal material. (5) The method for producing a corrosion-resistant rare earth magnetic powder according to claim 4, wherein the metal material is copper. (6) The method for producing a corrosion-resistant rare earth magnetic powder according to claim 4, wherein the corrosion-resistant material is an aqueous solution and is deposited on the surface of the particles by electrolysis. (7) The method for producing a corrosion-resistant rare earth magnetic powder according to claim 1, wherein the corrosion-resistant material is a ceramic material. (8) The magnetic alloy contains, by weight, 25-45% of at least one rare earth element and 0.5-3% of boron.
A method for producing a corrosion-resistant rare earth magnetic powder according to claim 1. (9) The method for producing a corrosion-resistant rare earth magnetic powder according to claim 8, wherein the remaining component of the magnetic alloy is iron. (10) The remaining component of the magnetic alloy is iron containing an additive of at least one different metal selected from the group consisting of cobalt, aluminum and niobium. The method for producing the corrosion-resistant rare earth magnetic powder described above. (11) Corrosion-resistant as claimed in claim 1, wherein the grinding is carried out by a series of grinding steps consisting of spraying the alloy into an inert gas to obtain a powder and milling the powder. A method for manufacturing rare earth magnetic powder. (12) A method for producing a corrosion-resistant rare earth magnetic powder according to claim 11, wherein the powder is milled in a protective gas atmosphere. (13) A method for producing a corrosion-resistant rare earth magnetic powder according to claim 11, wherein the powder is milled in an organic liquid. (14) The method for producing a corrosion-resistant rare earth magnetic powder according to claim 11, wherein the powder is milled before the heat treatment of the particles. (15) The method for producing a corrosion-resistant rare earth magnetic powder according to claim 11, wherein the powder is milled after the heat treatment. (16) A method for producing a corrosion-resistant rare earth magnetic powder according to claim 11, wherein the alloy is placed in a magnetic field during spraying in order to impart magnetic orientation to the powder. (17) A method for producing a corrosion-resistant rare earth magnetic powder according to claim 1, wherein the alloy is ground until the particles have a size in the range of 1 to 30 μm. (18) A method for producing a corrosion-resistant rare earth magnetic powder according to claim 17, wherein the alloy is ground until the particles have a size in the range of 3 to 15 μm. (19) The method for producing a corrosion-resistant rare earth magnetic powder according to claim 1, wherein the alloy particles are heat-treated in a vacuum or an inert gas atmosphere. (20) A method for producing a corrosion-resistant rare earth magnetic powder according to claim 1, comprising the step of compression molding the particles into a magnetic material, preferably while placing the particles in a magnetic field. (21) In order to increase the solidity of the magnetic material, the particles are mixed with additives and compression molded together into a magnetic material, and the additives are composed of synthetic resin, metal powder, and ceramic powder.
A method for producing a corrosion-resistant rare earth magnetic powder according to claim 20, which is selected from the group consisting of: (22) A magnetic material whose substantial element is compression molded magnet alloy particles of a magnet alloy containing rare earths-iron-boron,
The magnetic alloy contains at least 25-45% by weight of at least 1
1. A magnetic body made from corrosion-resistant rare earth magnetic powder, comprising a variety of rare earths and 0.5-3% boron, the alloy particles being coated with a protective layer of corrosion-resistant material. (23) Claim 22, wherein the remaining component of the magnet alloy is iron containing an additive of at least one other metal selected from the group consisting of cobalt, aluminum, and niobium. A magnetic material made from the corrosion-resistant rare earth magnetic powder described in .