EP0255816A2 - Preparation process for corrosion resistant magnetic permanent powder used in magnet manufacturing; permanent magnets produced from permanent magnet powder and their manufacturing method - Google Patents

Preparation process for corrosion resistant magnetic permanent powder used in magnet manufacturing; permanent magnets produced from permanent magnet powder and their manufacturing method Download PDF

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Publication number
EP0255816A2
EP0255816A2 EP87890182A EP87890182A EP0255816A2 EP 0255816 A2 EP0255816 A2 EP 0255816A2 EP 87890182 A EP87890182 A EP 87890182A EP 87890182 A EP87890182 A EP 87890182A EP 0255816 A2 EP0255816 A2 EP 0255816A2
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Prior art keywords
powder
alloy
magnet
permanent
iron
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EP87890182A
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German (de)
French (fr)
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EP0255816A3 (en
Inventor
Herwig Dr. Winkler
Alexander Dr. Bouvier
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Treibacher Chemische Werke AG
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Treibacher Chemische Werke AG
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
    • H01F1/0578—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together bonded together
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0572—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes with a protective layer
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
    • H01F1/0576—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together pressed, e.g. hot working

Definitions

  • Permanent magnet materials are a basic material for many electrical and electronic applications such as motors, microphones, loudspeakers, measuring devices etc. or for daily needs, e.g. as simple holding magnets.
  • ferrites, alnico magnets or rare earth cobalt magnets are mainly used for these purposes.
  • the low magnetic performance is a disadvantage of the first two types, it is the low availability of the SE raw material samarium and the high price of the connection for the SE cobalt magnets.
  • Great efforts have therefore been made to find a new alloy that is characterized on the one hand by good magnetic properties such as high coercive force and high remanence, and on the other hand by cheaper raw materials that are available in larger quantities.
  • the SE-Fe-B alloy is produced by melt metallurgy under vacuum or inert gas in order to prevent oxygen uptake by the rare earth metals, which tend to oxidize.
  • the alloy is produced in pieces or in the form of ingots. To improve the magnetic properties, it must be crushed.
  • the comminution of the alloy takes place either by atomization into powder (US Pat. No. 4,585,473) or in the so-called "melt spinning" process (US Pat. No. 4,496,395), whereby amorphous structures are formed, by a pressure roller or by Bre and grinding the alloy. In this way, the alloy particles are brought to grain sizes between 1 and 10 microns. With this fineness, they are extremely sensitive to oxidation.
  • the absorption of oxygen primarily binds the rare earth metal, eg neodymium, in the form of an oxide and is therefore no longer available for the Nd-Fe-B phase, which is responsible for achieving the hard magnetic properties. From a certain oxygen concentration, this leads to a significant loss of quality and, at higher values, even to a complete loss of magnetic properties.
  • the powders must therefore be protected against atmospheric oxygen, processed further under an inert gas atmosphere or in organic solvents. This is usually done by pressing, possibly with the application of an external magnetic field, whereby anisotropic or isotropic magnets are obtained.
  • the compacts are then sintered and the sinterings are subjected to a thermal aftertreatment to improve the magnetic properties. It is only through the process of sintering that the magnet regains extensive resistance to oxidation. Complete resistance of the magnet can only be achieved by coating it.
  • the magnets produced according to these described processes must therefore be subjected to a sintering treatment under vacuum or an inert gas atmosphere, which must run at over 1000 ° C and only leads to high-quality products in connection with a subsequent heat treatment. This represents a costly process step.
  • the powders produced according to the "melt spinning" process with subsequent comminution are usually embedded in plastic, resulting in isotropic magnets with a low energy product (BHmax).
  • the aim of the present invention is therefore a process for the production of corrosion-resistant, hard magnetic powders from an alloy of the basic type SE-Fe-B for magnet production, the magnetic powders produced in this way being distinguished by excellent resistance to oxidation and without sintering to isotropic or anisotropic magnets with high Coercivity and maximum energy product can be processed.
  • This aim is achieved according to the invention by combining the following process steps, that the starting alloy present in pieces or in the form of ingots is crushed, the powder particles thus obtained are heat-treated to improve their magnetic properties, preferably in a temperature range of 300-1000 ° C., and then the The surface of the individual heat-treated powder particles is coated with a ceramic or metallic protective layer to prevent corrosion, the metallic coating preferably being carried out electrolytically from an aqueous solution.
  • the powders produced by the process according to the invention can then, if appropriate with the addition of a pressing aid, be processed by simple pressing, if appropriate with application of an external magnetic field, to permanent magnets with excellent properties.
  • the invention also relates to a magnet made of hard magnetic powder, which is characterized in that the powder particles consist of an alloy containing 25-45% by weight SE, 0.5-3% by weight B and iron or a combination of iron contains at least one other metal from the group cobalt, aluminum and niobium and are coated with a ceramic or metallic protective layer.
  • the invention also relates to a method for Production of such a magnet, which consists in that the coated powder is optionally pressed into magnets under the action of an external magnetic field, the pressing preferably taking place with the addition of a plastic, a metal or ceramic powder to improve the strength of the compact.
  • the addition of other rare earths can increase certain properties, such as the coercive field strength.
  • Another component of the alloy is boron, which is necessary to form the hard magnetic phase and is present in quantities of 0.5-3% by weight.
  • the remainder of the alloy is iron or a combination of iron with another element, e.g. Cobalt, aluminum, niobium or others. The combination of iron with these elements can lead to an improvement in temperature resistance and magnetic properties.
  • the starting alloy is produced by the molten metal-lurgic route, it being of the utmost importance that the oxygen content be kept as low as possible so that the prerequisite for the production of the lowest possible oxygen powder is given.
  • An improvement in the magnetic properties of an atomized powder can be achieved if the alloy droplets move through a magnetic field during the atomization process and solidify in it. If the atomized alloy is ground briefly before the heat treatment, for example in a stirred ball mill under liquid, to an FSSS value of ⁇ 30 ⁇ m, preferably 15-3 ⁇ m, a magnetically anisotropic material is obtained, which also has a low oxygen content. Compared to the powders produced by the known "melt spinning" process with subsequent grinding, this comminution method is advantageous since the particles are also partially spherical after grinding and can therefore be coated more easily. To explain the importance of oxygen, Table 1 shows the oxygen contents of dry powders of an NdFeB alloy, which were finely divided for two hours and stored in air to determine 02 uptake, depending on the grain size.
  • Another necessary step in the manufacturing process according to the invention is the heat treatment of the powders.
  • the powders are transferred directly into a vacuum oven under solvent or in an inert gas atmosphere and subjected to heat treatment between 300 ° and 1000 ° C in one or more stages.
  • a heat treatment of the powder for example, increased the coercive field strength of a ground alloy with an FSSS value of 5 ⁇ m from 222.9 kA / m in the original material to 802 kA / m, which represents a significant improvement.
  • the production of the magnetic powder in the manner described is the prerequisite for achieving good magnetic properties.
  • a prerequisite for the corrosion resistance of the powder is a complete coating of the individual powder particles with a metallic or ceramic material.
  • a metal is deposited, for example, by an electrolytic process, as in the case of electrodeless coating with copper, which is described below:
  • An aqueous solution of copper sulfate, sodium hydroxide solution and potassium sodium tartrate is prepared, the alloy is stirred in and formaldehyde is added. The copper is deposited metallically on the surface of the powder.
  • the proportion of coating material varies depending on the fineness of the powder and the surface associated with it. It is between 10 and 25% for the previously described grain sizes. Just By applying a corrosion-resistant layer to each individual powder particle, however, there is sufficient resistance to corrosion of the powder and the magnets.
  • a lumpy NdFeB alloy with the following composition 33.3% SE (in 100% SE 98.7% Nd) 1.3% B 65.2% Fe 0.04% O was melted under an inert gas atmosphere, then atomized and a fraction ⁇ 63 ⁇ m was sieved out. It was then heat-treated at 630 ° C and then coated with copper without electrodes. For this purpose, the atomized and heat-treated alloy was stirred into an aqueous solution which contained 30 g / l CuSo4, 80 g / l 60% NaOH and 150 g / l KNa tartrate. Then 1 part by volume of 37% formaldehyde was added to 5 parts by volume of this solution. After the Cu had been deposited and the coated alloy had been filtered, it was washed thoroughly. It contained 13.2% Cu and 0.17% oxygen. Table 2 shows the values for the coercive field strength for the individual intermediates and the end material.
  • Example 2 A lumpy NdFeB alloy with the same composition as in Example 1 was melted under an inert gas atmosphere, atomized and the atomized material was ground under cyclohexane to an FSSS value of 5.2 ⁇ m in an attritor. The powder was placed in a vacuum oven while wet with solvent and heat-treated at 630 ° C. The coating was again carried out according to Example 1 and the powder had a copper content of 18.2% and an oxygen content of 0.27% O. Table 3 again summarizes the coercive field strengths.

Abstract

A preparation process for corrosion-resistant, permanently magnetic powders consisting of an alloy of the basic type Se-Fe-B used in magnet manufacturing, the magnetic powders prepared in this way being characterised by excellent resistance to oxidation and being capable of being processed, without sintering, into isotropic or anisotropic magnets with high coercitivity field strengths and maximum energy product. This is achieved by the original alloy, provided in pieces or in the form of ingots, being crushed, the powder particles produced in this way being heat-treated to improve their magnetic characteristics, preferably in a temperature range from 300 - 1000 DEG C, and the surfaces of the individual heat-treated powder particles subsequently being coated with a ceramic or metallic protective layer, to prevent corrosion, the metallic coating preferably being applied by electrolytic means from an aqueous solution. The invention also relates to a magnet of permanently magnetic powder which is characterised by the powder particles consisting of an alloy containing 25-45% by weight of Se, 0.5-3% by weight of B and iron or a combination of iron with at least one other metal of the cobalt, aluminium and niobium group, and by being coated with a ceramic or metallic protective coating.

Description

Permanentmagnetwerkstoffe stellen in großem Umfang ein Grundma­terial für viele elektrische und elektronische Anwendungen wie Motoren, Mikrophone, Lautsprecher, Meßgeräte etc. oder für den täglichen Bedarf, z.B. als einfache Haftmagnete, dar. Derzeit werden für diese Zwecke vorwiegend Ferrite, Alnico-Magnete oder Seltenerd-Kobalt-Magnete eingesetzt. Während bei den ersten bei­den Typen die geringe magnetische Leistungsfähigkeit von Nach­teil ist, ist es bei den SE-Kobalt-Magneten die geringe Verfüg­barkeit des SE-Rohstoffes Samarium und der hohe Preis der Ver­bindung. Es wurden deshalb große Anstrengungen unternommen, eine neue Legierung zu finden, die sich einerseits durch gute magne­tische Eigenschaften wie hohe Koerzitivfeldstärke und hohe Remanenz, andererseits durch billigere und in größeren Mengen verfügbare Rohstoffe auszeichnet. Diese wurde in Form einer Le­gierung des Grundtypus SE-FeB gefunden, wobei als SE vorwiegend der billige Rohstoff Neodym eingesetzt wird. Allerdings können die Bestandteile des Grundtypus durch verschiedenste andere Ele­mente, Nd zum Beispiel durch Dysprosium oder Eisen zum Beispiel durch Kobalt ersetzt werden, um eine Verbesserung gewisser Eigen­schaften wie Koerzitivfeldstärke oder Temperaturverhalten (Er­höhung des Curiepunktes) zu erzielen.Permanent magnet materials are a basic material for many electrical and electronic applications such as motors, microphones, loudspeakers, measuring devices etc. or for daily needs, e.g. as simple holding magnets. Currently ferrites, alnico magnets or rare earth cobalt magnets are mainly used for these purposes. While the low magnetic performance is a disadvantage of the first two types, it is the low availability of the SE raw material samarium and the high price of the connection for the SE cobalt magnets. Great efforts have therefore been made to find a new alloy that is characterized on the one hand by good magnetic properties such as high coercive force and high remanence, and on the other hand by cheaper raw materials that are available in larger quantities. This was found in the form of an alloy of the basic type SE-FeB, whereby the cheap raw material neodymium is mainly used as SE. However, the constituents of the basic type can be replaced by various other elements, Nd, for example, by dysprosium or iron, for example by cobalt, in order to improve certain properties such as coercive force or temperature behavior (increase in the Curie point).

Es ist weiters bekannt, daß die SE-Fe-B-Legierung auf schmelzme­tallurgischem Wege unter Vakuum oder Inertgas hergestellt wird, um eine Sauerstoffaufnahme durch die stark zur Oxidation neigen­den Seltenerdmetalle zu verhindern. Die Legierung fällt bei die­ser Herstellungsart stückig oder in Form von Ingots an. Zur Ver­besserung der magnetischen Eigenschaften muß sie zerkleinert wer­den. Die Zerkleinerung der Legierung erfolgt entweder durch Ver­düsung zu Pulver (US-Patent 4,585,473) oder beim sogenannten "Melt-Spinning"-Verfahren (US-Patent 4,496,395), wobei amorphe Strukturen entstehen, durch eine Druckwalze oder aber durch Bre­ chen und Mahlen der Legierung. Auf diese Art und Weise werden die Legierungspartikel auf Korngrößen zwischen 1 und 10 µm gebracht. Bei dieser Feinheit sind sie aber extrem oxidationsempfindlich. Durch die Aufnahme von Sauerstoff wird vor allem das Seltenerd­metall, z.B. Neodym, in Form eines Oxides gebunden und steht somit nicht mehr für die - zur Erzielung der hartmagnetischen Eigen­schaften verantwortliche - Nd-Fe-B-Phase zur Verfügung. Ab einer gewissen Sauerstoffkonzentration führt dies bereits zu einem bedeutenden Qualitätsverlust und bei höheren Werten sogar zum vollständigen Verlust der magnetischen Eigenschaften. Die Pul­ver müssen daher gegen Luftsauerstoff geschützt, unter Inertgas­atmosphäre oder in organischen Lösungsmitteln weiterverarbeitet werden. Dies erfolgt meist über ein Verpressen, gegebenenfalls unter Anlegen eines äußeren Magnetfeldes, wodurch man aniso­trope oder isotrope Magnete erhält.It is also known that the SE-Fe-B alloy is produced by melt metallurgy under vacuum or inert gas in order to prevent oxygen uptake by the rare earth metals, which tend to oxidize. In this type of production, the alloy is produced in pieces or in the form of ingots. To improve the magnetic properties, it must be crushed. The comminution of the alloy takes place either by atomization into powder (US Pat. No. 4,585,473) or in the so-called "melt spinning" process (US Pat. No. 4,496,395), whereby amorphous structures are formed, by a pressure roller or by Bre and grinding the alloy. In this way, the alloy particles are brought to grain sizes between 1 and 10 microns. With this fineness, they are extremely sensitive to oxidation. The absorption of oxygen primarily binds the rare earth metal, eg neodymium, in the form of an oxide and is therefore no longer available for the Nd-Fe-B phase, which is responsible for achieving the hard magnetic properties. From a certain oxygen concentration, this leads to a significant loss of quality and, at higher values, even to a complete loss of magnetic properties. The powders must therefore be protected against atmospheric oxygen, processed further under an inert gas atmosphere or in organic solvents. This is usually done by pressing, possibly with the application of an external magnetic field, whereby anisotropic or isotropic magnets are obtained.

Die Preßlinge werden anschließend gesintert und zur Verbesserung der magnetischen Eigenschaften werden die Sinterlinge einer thermischen Nachbehandlung unterzogen. Erst durch den Vorgang des Sinterns erreicht der Magnet wieder eine weitgehende Wider­standsfähigkeit gegen Oxydiation. Eine vollständige Beständigkeit des Magneten ist aber nur durch eine Beschichtung desselben erreichbar.The compacts are then sintered and the sinterings are subjected to a thermal aftertreatment to improve the magnetic properties. It is only through the process of sintering that the magnet regains extensive resistance to oxidation. Complete resistance of the magnet can only be achieved by coating it.

Die nach diesen beschriebenen Verfahren hergestellten Magnete müssen also einer Sinterbehandlung unter Vakuum oder Inertgas­atmosphäre unterzogen werden, welche bei über 1000°C ablaufen muß und erst in Verbindung mit einer nachfolgenden Wärmebehandlung zu qualitativ hochwertigen Produkten führt. Dies stellt einen kostenaufwendigen Verfahrensschritt dar. Die nach dem "Melt-­Spinning"-Verfahren mit anschließender Zerkleinerung herge­stellten Pulver werden meist in Kunststoff eingebettet, wodurch isotrope Magnete mit geringem Energieprodukt (BHmax) entstehen.The magnets produced according to these described processes must therefore be subjected to a sintering treatment under vacuum or an inert gas atmosphere, which must run at over 1000 ° C and only leads to high-quality products in connection with a subsequent heat treatment. This represents a costly process step. The powders produced according to the "melt spinning" process with subsequent comminution are usually embedded in plastic, resulting in isotropic magnets with a low energy product (BHmax).

In der EU-Anm. 0 125 752 von General Motors ist ein Verfahren beschrieben, bei dem isotrope Magnete hergestellt werden, indem man die Legierung nach dem "Melt-Spinning"-Verfahren herstellt, zerkleinert, verpreßt und dann die Pulver solcherart beschichtet, daß die Poren zwischen den Partikeln mit Kunststoff ausgefüllt sind. Bei fehlerhafter Beschichtung an der Oberfläche ist aber nach diesem Verfahren ein Angriff des Sauerstoffs auf innen­liegende, unbeschichtete Teile des Magnetmaterials nicht zu ver­hindern, was wieder zu den schon oben beschriebenen Nachteilen führt.In the EU note General Motors 0 125 752 describes a process in which isotropic magnets are produced by producing the alloy according to the "melt spinning" process, crushed, pressed and then coated the powder such that the pores between the particles are filled with plastic. If the surface is defective, however, an attack of the oxygen on internal, uncoated parts of the magnetic material cannot be prevented by this method, which again leads to the disadvantages already described above.

Ziel der vorliegenden Erfindung ist daher ein Verfahren zur Her­stellung korrosionsbeständiger, hartmagnetischer Pulver aus einer Legierung des Grundtyps SE-Fe-B für die Magneterzeugung, wobei die so hergestellten Magnetpulver sich durch hervorra­gende Beständigkeit gegenüber Oxidation auszeichnen und ohne Sinterung zu isotropen oder anisotropen Magneten mit hoher Koer­zitivfeldstärke und maximalem Energieprodukt verarbeitet werden können. Dieses Ziel wird erfindungsgemäß erreicht durch die Kombination der folgenden Verfahrensschritte, daß die stückig oder in Form von Ingots vorliegende Ausgangslegierung zerkleinert wird, die so erhaltenen Pulverpartikel zur Verbesserung ihrer magnetischen Eigenschaften, vorzugsweise in einem Temperaturbereich von 300 - 1000°C, wärmebehandelt und anschließend die Oberfläche der einzelnen wärmebehandelten Pulverpartikel zur Verhinderung der Korrosion mit einer keramischen oder metallischen Schutz­schicht überzogen wird, wobei die metallische Beschichtung vor­zugsweise auf elektrolytischem Weg aus einer wässerigen Lösung erfolgt. Die nach dem erfindungsgemäßen Verfahren hergestellten Pulver können dann gegebenenfalls unter Zusatz eines Preßhilfs­mittels durch einfaches Verpressen, gegebenenfalls unter Anlegen eines äußeren Magnetfeldes, zu Permanentmagneten mit hervorragen­den Eigenschaften verarbeitet werden.The aim of the present invention is therefore a process for the production of corrosion-resistant, hard magnetic powders from an alloy of the basic type SE-Fe-B for magnet production, the magnetic powders produced in this way being distinguished by excellent resistance to oxidation and without sintering to isotropic or anisotropic magnets with high Coercivity and maximum energy product can be processed. This aim is achieved according to the invention by combining the following process steps, that the starting alloy present in pieces or in the form of ingots is crushed, the powder particles thus obtained are heat-treated to improve their magnetic properties, preferably in a temperature range of 300-1000 ° C., and then the The surface of the individual heat-treated powder particles is coated with a ceramic or metallic protective layer to prevent corrosion, the metallic coating preferably being carried out electrolytically from an aqueous solution. The powders produced by the process according to the invention can then, if appropriate with the addition of a pressing aid, be processed by simple pressing, if appropriate with application of an external magnetic field, to permanent magnets with excellent properties.

Die Erfindung betrifft auch einen Magneten aus hartmagnetischem Pulver, der dadurch gekennzeichnet ist, daß die Pulverpartikel aus einer Legierung bestehen, die 25-45 Gew.-% SE, 0,5 - 3 Gew.-% B und Eisen oder eine Kombination von Eisen mit mindestens einem anderen Metall der Gruppe Kobalt, Aluminium und Niob enthält und mit einer keramischen oder metallischen Schutzschicht überzogen sind. Die Erfindung betrifft ferner auch ein Verfahren zur Herstellung eines solchen Magneten, das darin besteht, daß das beschichtete Pulver gegebenenfalls unter Einwirkung eines äußeren Magnetfeldes zu Magneten verpreßt wird, wobei das Ver­pressen vorzugsweise unter Zumischung eines Kunststoffes, eines Metall- oder Keramikpulvers zur Verbesserung der Festigkeit des Preßlings erfolgt.The invention also relates to a magnet made of hard magnetic powder, which is characterized in that the powder particles consist of an alloy containing 25-45% by weight SE, 0.5-3% by weight B and iron or a combination of iron contains at least one other metal from the group cobalt, aluminum and niobium and are coated with a ceramic or metallic protective layer. The invention also relates to a method for Production of such a magnet, which consists in that the coated powder is optionally pressed into magnets under the action of an external magnetic field, the pressing preferably taking place with the addition of a plastic, a metal or ceramic powder to improve the strength of the compact.

Als Ausgangslegierung des Grundtyps SE-FE-B wird normalerweise eine Legierung mit einem Gehalt von 25 - 45 Gew.-% SE eingesetzt, wobei als SE = Seltene Erde entweder Neodym allein oder ein anderes Element aus der Gruppe der Seltenen Erden oder eine Kom­bination von zwei oder mehreren Seltenen Erden, zum Beispiel Neodym und Dysprosium, verwendet werden. Durch den Zusatz an­derer Seltener Erden können bestimmte Eigenschaften, wie zum Beispiel die Koerzitivfeldstärke, erhöht werden. Weiterer Be­standteil der Legierung ist Bor, welches zur Bildung der hart­magnetischen Phase notwendig ist und in Mengen von 0,5 - 3 Gew.-% vorliegt. Der restliche Anteil der Legierung ist Eisen oder eine Kombination von Eisen mit einem anderen Element, wie z.B. Kobalt, Aluminium, Niob oder andere. Die Kombination des Eisens mit die­sen Elementen kann zu einer Verbesserung der Temperaturbeständig­keit sowie der magnetischen Eigenschaften führen.An alloy with a content of 25-45% by weight SE is normally used as the basic alloy of the basic type SE-FE-B, whereby as SE = rare earth either neodymium alone or another element from the group of rare earths or a combination of two or more rare earths, for example neodymium and dysprosium, can be used. The addition of other rare earths can increase certain properties, such as the coercive field strength. Another component of the alloy is boron, which is necessary to form the hard magnetic phase and is present in quantities of 0.5-3% by weight. The remainder of the alloy is iron or a combination of iron with another element, e.g. Cobalt, aluminum, niobium or others. The combination of iron with these elements can lead to an improvement in temperature resistance and magnetic properties.

Die Herstellung der Ausgangslegierung erfolgt auf schmelzmetall­lurgischem Weg, wobei es von größter Wichtigkeit ist, daß der Sauerstoffgehalt möglichst gering gehalten wird, damit die Voraussetzung zur Herstellung möglichst sauerstoffarmer Pulver gegeben ist.The starting alloy is produced by the molten metal-lurgic route, it being of the utmost importance that the oxygen content be kept as low as possible so that the prerequisite for the production of the lowest possible oxygen powder is given.

Gute magnetische Eigenschaften sind aber nur erzielbar, wenn diese Ausgangslegierung zu Pulvern zerkleinert wird, wobei diese Pulver neben einer ausreichenden Feinheit einen geringen Sauer­stoffgehalt aufweisen müssen. Erfindungsgemäß wird dies durch eine Verdüsung und/oder Mahlung erreicht. Beide Parameter, Korn­größe und 02-Gehalt haben entscheidenden Einfluß auf die magne­tische Qualität.However, good magnetic properties can only be achieved if this starting alloy is ground into powders, these powders not only having a sufficient fineness but also having a low oxygen content. According to the invention, this is achieved by spraying and / or grinding. Both parameters, grain size and 02 content have a decisive influence on the magnetic quality.

Mit Hilfe der Verdüsung unter Inertgasatmosphäre erhält man sphärische Partikel mit einem Korndurchmesser < 1 mm. Der Sauer­stoffgehalt einer derartig verdüsten Legierung liegt unter 0,1%. Siebt man unter Schutzgas aus dieser verdüsten Legierung eine Fraktion < 63 µm aus, so weist diese einen FSSS-Wert (Fisher Subsieve Sizer) von 30 - 40 µm auf. Werden diese Pul­ver wärmebehandelt und beschichtet, so erhält man isotrope Pulver, die hohe Koerzitivfeldstärken, aber geringe Energiepro­dukte zeigen.With the help of atomization under an inert gas atmosphere, spherical particles with a grain diameter of <1 mm are obtained. The oxygen content of such an atomized alloy is less than 0.1%. If a fraction <63 µm is screened out from this atomized alloy under protective gas, this has an FSSS value (Fisher Subsieve Sizer) of 30 - 40 µm. If these powders are heat-treated and coated, isotropic powders are obtained which have high coercive field strengths but low energy products.

Eine Verbesserung der magnetischen Eigenschaften eines verdüsten Pulvers ist zu erzielen, wenn sich die Legierungströpfchen während des Verdüsungsvorganges durch ein magnetisches Feld be­wegen und in diesem erstarren. Wenn man die verdüste Legierung vor der Wärmebehandlung kurz, beispielsweise in einer Rührwerks­kugelmühle unter Flüssigkeit, auf einen FSSS-Wert <30 µm, vorzugs­weise 15 - 3 µm vermahlt, so erhält man ein magnetisch anisotro­pes Material, welches ebenfalls einen niedrigen Sauerstoffgehalt aufweist. Gegenüber den nach dem bekannten "Melt-Spinning"-Verfah­ren mit anschließender Mahlung hergestellten Pulvern ist diese Zerkleinerungsmethode vorteilhaft, da die Partikel auch nach der Mahlung teilweise in Kugelform vorliegen und somit leichter be­schichtet werden können. Zur Erläuterung der Bedeutung des Sauer­stoffes sind in Tabelle 1 Sauerstoffgehalte trockener Pulver einer NdFeB-Legierung, die zwei Stunden feinverteilt, zur Bestimmung der 02-Aufnahme in Luft gelagert wurden, in Abhängigkeit von der Korngröße dargestellt.An improvement in the magnetic properties of an atomized powder can be achieved if the alloy droplets move through a magnetic field during the atomization process and solidify in it. If the atomized alloy is ground briefly before the heat treatment, for example in a stirred ball mill under liquid, to an FSSS value of <30 μm, preferably 15-3 μm, a magnetically anisotropic material is obtained, which also has a low oxygen content. Compared to the powders produced by the known "melt spinning" process with subsequent grinding, this comminution method is advantageous since the particles are also partially spherical after grinding and can therefore be coated more easily. To explain the importance of oxygen, Table 1 shows the oxygen contents of dry powders of an NdFeB alloy, which were finely divided for two hours and stored in air to determine 02 uptake, depending on the grain size.

Tabelle 1 SAUERSTOFFGEHALTE EINER NdFeB-LEGIERUNG UNBESCHICHTET NACH 2 STUNDEN AN LUFT Table 1 OXYGEN CONTENT OF AN NdFeB ALLOY UNCOATED AFTER 2 HOURS OF AIR

Stückig 0,04 % O
< 1 mm (verdüst) 0,08 % O
<63 µm (FSSS 35 µm) 0,11 % O
FSSS 20 µm 0,15 % O
FSSS 11 µm 0,18 % O
FSSS 7,0 µm 0,28 % O
FSSS 4,8 µm 0,42 % O
FSSS 3,2 µm 0,61 % OPieces 0.04% O
<1 mm (atomized) 0.08% O
<63 µm (FSSS 35 µm) 0.11% O
FSSS 20 µm 0.15% O
FSSS 11 µm 0.18% O
FSSS 7.0 µm 0.28% O
FSSS 4.8 µm 0.42% O
FSSS 3.2 µm 0.61% O

Andererseits ist es bei Einhaltung inerter Bedingungen auch mög­lich, auf herkömmliche Weise, also durch zwei Mahlschritte, eine ausreichende Feinheit zu erzielen.On the other hand, if inert conditions are met, it is also possible to achieve sufficient fineness in a conventional manner, that is to say by two grinding steps.

Ein weiterer notwendiger Schritt im erfindungsgemäßen Herstel­lungsverfahren ist die Wärmebehandlung der Pulver. Dabei werden die Pulver unter Lösungsmittel oder in Inertgasatmosphäre direkt in einen Vakuumofen übergeführt und einer Wärmebehandlung zwi­schen 300° und 1000°C in ein oder mehreren Stufen unterzogen. Durch eine Wärmebehandlung des Pulvers konnte beispielsweise die Koerzitivfeldstärke bei einer vermahlenen Legierung mit einem FSSS-Wert von 5 µm von 222,9 kA/m im Originalmaterial auf 802 kA/m gesteigert werden, was eine bedeutende Verbesserung dar­stellt. Die Herstellung der Magnetpulver auf die beschriebene Weise ist die Voraussetzung für die Erzielung guter magnetischer Eigenschaften. Es ist aber laut dem erfindungsgemäßen Verfahren auch möglich, die beiden Schritte, Mahlung der verdüsten Pulver und Wärmebehandlung, in umgekehrter Reihenfolge durchzuführen. Die Voraussetzung für die Korrisionsbeständigkeit der Pulver ist eine vollständige Beschichtung der einzelnen Pulverpartikel mit einem metallischen oder keramischen Material. Die Abscheidung eines Metalls erfolgt beispielsweise auf elektrolytischem Weg wie bei der elektrodenlosen Beschichtung mit Kupfer, die im folgenden beschrieben wird:Another necessary step in the manufacturing process according to the invention is the heat treatment of the powders. The powders are transferred directly into a vacuum oven under solvent or in an inert gas atmosphere and subjected to heat treatment between 300 ° and 1000 ° C in one or more stages. A heat treatment of the powder, for example, increased the coercive field strength of a ground alloy with an FSSS value of 5 µm from 222.9 kA / m in the original material to 802 kA / m, which represents a significant improvement. The production of the magnetic powder in the manner described is the prerequisite for achieving good magnetic properties. However, according to the method according to the invention, it is also possible to carry out the two steps, grinding the atomized powder and heat treatment, in the reverse order. A prerequisite for the corrosion resistance of the powder is a complete coating of the individual powder particles with a metallic or ceramic material. A metal is deposited, for example, by an electrolytic process, as in the case of electrodeless coating with copper, which is described below:

Dabei wird eine wäßrige Lösung aus Kupfersulfat, Natronlauge und Kalium-Natrium-Tartrat hergestellt, die Legierung eingerührt und Formaldehyd zugefügt. Das Kupfer wird metallisch auf der Ober­fläche der Pulver abgeschieden.An aqueous solution of copper sulfate, sodium hydroxide solution and potassium sodium tartrate is prepared, the alloy is stirred in and formaldehyde is added. The copper is deposited metallically on the surface of the powder.

Überraschenderweise wurde dabei festgestellt, daß trotz des Vor­handenseins einer wäßrigen Lösung praktisch keine Korrosion der Teilchen festzustellen war und der Sauerstoffgehalt des Pul­vers nur geringfügig anstieg.Surprisingly, it was found that, despite the presence of an aqueous solution, there was practically no corrosion of the particles and the oxygen content of the powder increased only slightly.

Je nach Feinheit des Pulvers und der damit verbundenen Oberfläche ist der Anteil an Beschichtungsmaterial verschieden. Er liegt bei den vorher beschriebenen Korngrößen zwischen 10 und 25 %. Nur durch das Aufbringen einer korrosionsfesten Schicht auf jedes einzelne Pulverpartikel ist aber eine ausreichende Beständigkeit gegen Korrosion der Pulver und der Magnete gegeben.The proportion of coating material varies depending on the fineness of the powder and the surface associated with it. It is between 10 and 25% for the previously described grain sizes. Just By applying a corrosion-resistant layer to each individual powder particle, however, there is sufficient resistance to corrosion of the powder and the magnets.

Diese Pulver können direkt zu isotropen oder durch Anlegen eines magnetischen Feldes zu anisotropen Magneten verpreßt werden. Reicht für gewisse Anwendungen die Festigkeit nicht aus, so kann diese durch Zugabe eines Metall-, Keramik- oder Kunststoffpulvers zum beschichteten Magnetpulver verbessert werden. Die Erfindung soll abschließend durch zwei Beispiele erläutert werden.These powders can be pressed directly into isotropic magnets or into anisotropic magnets by applying a magnetic field. If the strength is not sufficient for certain applications, it can be improved by adding a metal, ceramic or plastic powder to the coated magnetic powder. In conclusion, the invention will be explained by two examples.

Beispiel 1:Example 1:

Eine stückige NdFeB-Legierung folgender Zusammensetzung
33,3 % SE (in 100% SE 98,7% Nd)
1,3 % B
65,2 % Fe
0,04% O
wurde unter Inertgasatmosphäre aufgeschmolzen, anschließend ver­düst und eine Fraktion < 63 µm ausgesiebt. Danach wurde sie bei­630°C wärmebehandelt und daraufhin elektrodenlos mit Kupfer be­schichtet. Die verdüste und wärmebehandelte Legierung wurde zu diesem Zweck in eine wäßrige Lösung eingerührt, die 30 g/l CuSo₄, 80 g/l 60% NaOH und 150 g/l KNa-Tartrat enthielt. An­schließend wurde auf 5 Volumsteile dieser Lösung 1 Volumsteil 37% Formaldehyd zugegeben. Nach Abscheidung des Cu und nach Filtratrion der beschichteten Legierung wurde diese gründlich gewaschen. Sie enthielt 13,2 % Cu und 0,17 % Sauerstoff. In Tabelle 2 sind die Werte für die Koerzitivfeldstärke bei den einzelnen Zwischenprodukten und dem Endmaterial dargestellt.

Figure imgb0001
A lumpy NdFeB alloy with the following composition
33.3% SE (in 100% SE 98.7% Nd)
1.3% B
65.2% Fe
0.04% O
was melted under an inert gas atmosphere, then atomized and a fraction <63 μm was sieved out. It was then heat-treated at 630 ° C and then coated with copper without electrodes. For this purpose, the atomized and heat-treated alloy was stirred into an aqueous solution which contained 30 g / l CuSo₄, 80 g / l 60% NaOH and 150 g / l KNa tartrate. Then 1 part by volume of 37% formaldehyde was added to 5 parts by volume of this solution. After the Cu had been deposited and the coated alloy had been filtered, it was washed thoroughly. It contained 13.2% Cu and 0.17% oxygen. Table 2 shows the values for the coercive field strength for the individual intermediates and the end material.
Figure imgb0001

Beispiel 2Example 2

Eine stückige NdFeB-Legierung mit gleicher Zusammensetzung wie in Beispiel 1 angeführt wurde unter Inertgasatmosphäre aufge­schmolzen, verdüst und das verdüste Material unter Cyclohexan auf einen FSSS-Wert von 5,2 µm in einem Attritor vermahlen. Das Pulver wurde lösungsmittelfeucht in einen Vakuumofen eingetragen und bei 630°C wärmebehandelt. Die Beschichtung erfolgte wiederum gemäß Beispiel 1 und das Pulver wies einen Kupfergehalt von 18,2 % und einen Sauerstoffgehalt von 0,27% O auf. In Tabelle 3 sind wiederum die Koerzitivfeldstärken zusammengefaßt.

Figure imgb0002
A lumpy NdFeB alloy with the same composition as in Example 1 was melted under an inert gas atmosphere, atomized and the atomized material was ground under cyclohexane to an FSSS value of 5.2 μm in an attritor. The powder was placed in a vacuum oven while wet with solvent and heat-treated at 630 ° C. The coating was again carried out according to Example 1 and the powder had a copper content of 18.2% and an oxygen content of 0.27% O. Table 3 again summarizes the coercive field strengths.
Figure imgb0002

Die auf diese Art hergestellten Pulver zeigten anisotropes Ver­halten (BHmax = 195,8 kJ/m³.The powders produced in this way showed anisotropic behavior (BHmax = 195.8 kJ / m³.

Claims (11)

1. Verfahren zur Herstellung korrosionsbeständiger, hartmagneti­scher Pulver aus einer Legierung des Grundtyps SE-Fe-B für die Magneterzeugung, gekennzeichnet durch die Kom­bination der folgenden Verfahrensschritte, daß die stückig oder in Form von Ingots vorliegende Ausgangslegierung zer­kleinert wird, die so erhaltenen Pulverartikel zur Verbes­serung ihrer magnetischen Eigenschaften, vorzugsweise in einem Temperaturbereich von 300 - 1000°C, wärmebehandelt und anschließend die Oberfläche der einzelnen wärmebehandelten Pulverpartikel zur Verhinderung der Korrosion mit einer ke­ramischen oder metallischen Schutzschicht überzogen wird, wobei die metallische Beschichtung vorzugsweise auf elek­trolytischem Weg aus einer wässerigen Lösung erfolgt.1. A process for the production of corrosion-resistant, hard magnetic powder from an alloy of the basic type SE-Fe-B for magnet production, characterized by the combination of the following process steps, that the starting alloy present in pieces or in the form of ingots is crushed, the powder articles thus obtained for improvement their magnetic properties, preferably in a temperature range of 300 - 1000 ° C, heat-treated and then the surface of the individual heat-treated powder particles is coated with a ceramic or metallic protective layer to prevent corrosion, the metallic coating preferably being carried out electrolytically from an aqueous solution . 2. Verfahren nach Anspruch 1, dadurch gekennzeich­net, daß eine Legierung eingesetzt wird, die aus 25-45 Gew.-% SE (SE ist eines oder die Summe mehrerer Elemente der Gruppe der Seltenen Erden), 0,5-3 Gew.-% B und aus Fe oder einer Kombination von Eisen mit anderen Metallen, z.B. Ko­balt, Aluminium und/oder Niob, besteht.2. The method according to claim 1, characterized in that an alloy is used which consists of 25-45 wt .-% SE (SE is one or the sum of several elements of the Group of rare earths), 0.5-3 wt .-% B and of Fe or a combination of iron with other metals, for example cobalt, aluminum and / or niobium. 3. Verfahren anch Anspruch 1 oder 2, dadurch gekenn­zeichnet, daß die Zerkleinerung mittels einer Kombi­nation mehrerer Zerkleinerungsverfahren, vorzugsweise be­stehend aus einer Inertgasverdüsung der Ausgangslegierung und einer Mahlung des verdüsten Pulvers, vorzugsweise unter Schutzgas und/oder einer organischen Flüssigkeit erfolgt, wobei die Mahlung des verdüsten Pulvers vor oder nach der Wärmebehandlung vorgenommen werden kann.3. The method according to claim 1 or 2, characterized in that the comminution by means of a combination of several comminution processes, preferably consisting of an inert gas atomization of the starting alloy and a grinding of the atomized powder, preferably under protective gas and / or an organic liquid, the grinding of the atomize powder can be made before or after the heat treatment. 4. Verfahren nach Anspruch 3, dadurch gekennzeich­net, daß die Partikel bereits während er Verdüsung durch Anlegen eines äußeren magnetischen Feldes ausgerichtet werden.4. The method according to claim 3, characterized in that the particles are already aligned during the atomization by applying an external magnetic field. 5. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß die Legierung zerkleinert wird, bis die Korngrößen der erhaltenen Partikel im Bereich von 1-30 µm, vorzugsweise von 3-15 µm liegen.5. The method according to any one of claims 1 to 4, characterized in that the alloy is crushed until the grain sizes of the particles obtained are in the range of 1-30 microns, preferably 3-15 microns. 6. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß die Pulverpartikel unter Vakuum oder Inertgasatmosphäre wärmebehandelt werden.6. The method according to any one of claims 1 to 5, characterized in that the powder particles are heat-treated under vacuum or an inert gas atmosphere. 7. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß die Wärmebehandlung im Temperaturbereich zwischen 300 und 1000°C, vorzugsweise zwi­schen 500 und 800°C, erfolgt.7. The method according to any one of claims 1 to 6, characterized in that the heat treatment in the temperature range between 300 and 1000 ° C, preferably between 500 and 800 ° C takes place. 8. Verfahren nach Anspruch 1, dadurch gekenn­zeichnet, daß als Beschichtungsmaterial Kupfer ver­wendet wird.8. The method according to claim 1, characterized in that copper is used as the coating material. 9. Magnet aus hartmagnetischem Pulver, dadurch ge­kennzeichnet, daß die Pulverpartikel aus einer Legierung bestehen, die 25-45 Gew.-% SE, 0,5 - 3 Gew.-% B und Eisen oder eine Kombination von Eisen mit mindestens einem anderen Metall der Gruppe Kobalt, Aluminium und Niob enthält und mit einer keramischen oder metallischen Schutz­schicht überzogen sind.9. magnet made of hard magnetic powder, characterized in that the powder particles from a Alloy consisting of 25-45 wt .-% SE, 0.5 - 3 wt .-% B and iron or a combination of iron with at least one other metal from the group cobalt, aluminum and niobium and with a ceramic or metallic protective layer are covered. 10. Verfahren zur Herstellung eines Magneten nach Anspruch 9, dadurch gekennzeichnet, daß das be­schichtete Pulver gegebenenfalls unter Einwirkung eines äußeren Magnetfelds zu Magneten verpreßt wird.10. A method for producing a magnet according to claim 9, characterized in that the coated powder is optionally compressed under the action of an external magnetic field to form magnets. 11. Verfahren nach Anspruch 10, dadurch gekenn­zeichnet, daß das Verpressen unter Zumischung eines Kunststoffes, eines Metall- oder Keramikpulvers zur Verbes­erung der Festigkeit des Preßlings erfolgt.11. The method according to claim 10, characterized in that the pressing with admixture of a plastic, a metal or ceramic powder is carried out to improve the strength of the compact.
EP87890182A 1986-08-04 1987-07-31 Preparation process for corrosion resistant magnetic permanent powder used in magnet manufacturing; permanent magnets produced from permanent magnet powder and their manufacturing method Withdrawn EP0255816A3 (en)

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Cited By (21)

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Publication number Priority date Publication date Assignee Title
US4959273A (en) * 1988-09-20 1990-09-25 Sumitomo Special Metals Co., Ltd. Corrosion-resistant permanent magnet and method for preparing the same
EP0361308A1 (en) * 1988-09-20 1990-04-04 Sumitomo Special Metals Co., Ltd. Corrosion-resistant permanent magnet and method for preparing the same
EP0392077A2 (en) * 1989-04-14 1990-10-17 Hitachi Metals, Ltd. Magnetically anisotropic hot-worked magnets and composition and method for their production
EP0392077A3 (en) * 1989-04-14 1991-06-26 Hitachi Metals, Ltd. Magnetically anisotropic hot-worked magnets and composition and method for their production
US4990876A (en) * 1989-09-15 1991-02-05 Eastman Kodak Company Magnetic brush, inner core therefor, and method for making such core
US5464670A (en) * 1990-04-13 1995-11-07 Seiko Epson Corporation Resin bound magnet and its production process
EP0452580A1 (en) * 1990-04-19 1991-10-23 Seiko Epson Corporation A resin bound magnet and its production process
EP0504397A1 (en) * 1990-10-09 1992-09-23 Iowa State University Research Foundation, Inc. Method of making permanent magnets
EP0504397A4 (en) * 1990-10-09 1993-01-27 Iowa State University Research Foundation, Inc. Method of making permanent magnets
US6399146B1 (en) 1998-02-26 2002-06-04 The University Of Birmingham Method of applying a corrosion-resistant coating
WO1999043862A1 (en) * 1998-02-26 1999-09-02 The University Of Birmingham Method of applying a corrosion-resistant coating
GB2351741A (en) * 1998-02-26 2001-01-10 Univ Birmingham Method of applying a corrosion-resistant coating
EP1022929A2 (en) * 1999-01-23 2000-07-26 Harman Audio Electronic Systems GmbH Loudspeaker with a jacketed magnetic core
EP1022929A3 (en) * 1999-01-23 2007-06-13 Harman Becker Automotive Systems GmbH Loudspeaker with a jacketed magnetic core
EP1211700A2 (en) * 2000-11-30 2002-06-05 Tokin Corporation Magnetic core including magnet for magnetic bias and inductor component using the same
EP1211700A3 (en) * 2000-11-30 2003-10-15 NEC TOKIN Corporation Magnetic core including magnet for magnetic bias and inductor component using the same
KR100924037B1 (en) * 2000-11-30 2009-10-27 엔이씨 도낀 가부시끼가이샤 Magnetic core including magnet for magnetic bias and inductor component using the same
DE102013004985A1 (en) 2012-11-14 2014-05-15 Volkswagen Aktiengesellschaft Method for producing a permanent magnet and permanent magnet
WO2014075890A1 (en) * 2012-11-14 2014-05-22 Volkswagen Aktiengesellschaft Method for producing a permanent magnet and permanent magnet
US10312019B2 (en) 2012-11-14 2019-06-04 Volkswagen Aktiengesellschaft Method for producing a permanent magnet and permanent magnet
DE102013213494A1 (en) 2013-07-10 2015-01-29 Volkswagen Aktiengesellschaft Method for producing a permanent magnet and permanent magnet and electric machine with such a permanent magnet

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AT386554B (en) 1988-09-12
ATA209386A (en) 1988-02-15
EP0255816A3 (en) 1988-12-21
JPS6338216A (en) 1988-02-18

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