EP0063730A2 - Process for stabilising pyrophoric acicular ferromagnetic metal particles essentially consisting of iron - Google Patents
Process for stabilising pyrophoric acicular ferromagnetic metal particles essentially consisting of iron Download PDFInfo
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- EP0063730A2 EP0063730A2 EP82103010A EP82103010A EP0063730A2 EP 0063730 A2 EP0063730 A2 EP 0063730A2 EP 82103010 A EP82103010 A EP 82103010A EP 82103010 A EP82103010 A EP 82103010A EP 0063730 A2 EP0063730 A2 EP 0063730A2
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
- C23C8/12—Oxidising using elemental oxygen or ozone
- C23C8/14—Oxidising of ferrous surfaces
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/14—Treatment of metallic powder
- B22F1/145—Chemical treatment, e.g. passivation or decarburisation
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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
- H01F1/06—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 in the form of particles, e.g. powder
- H01F1/061—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 in the form of particles, e.g. powder with a protective layer
Definitions
- the invention relates to a method for stabilizing pyrophoric, needle-shaped metal particles consisting essentially of iron by reaction with oxygen-containing gases at elevated temperature.
- acicular ferromagnetic metal particles with single-region behavior as a magnetizable material for the production of magnetic recording media.
- the high coercive field strengths and high values for the remanent magnetization that can be achieved with such materials prompted the search early on for ways to produce these substances in a simple manner.
- a disadvantage of these materials, which have excellent magnetic properties, is their pyrophoric character.
- the cause of the pyrophoric behavior is the extremely fine grain size of the metal powder with particle sizes of 50 to 2,000 A and the resulting large free surface.
- lattice disorders are also discussed as the cause (cf. Hollemann-Wiberg, Textbook of inorganic chemistry, 1964, page 398).
- the pyrophoric acicular ferromagnetic particles consisting essentially of iron can be stabilized in accordance with the task by reaction with oxygen-containing gases if, in a first stage, at a temperature between 25 and 45 ° C. up to 1/3 of those in the final state Passivation layer formed and then in a second stage at a temperature between 50 and 70 ° C until the formation of the entire passivation layer, the pyrophoric metal particles are treated with an oxygen-containing inert gas, with the proviso that the respective temperature range is set by the oxygen content of the inert gas stream.
- the finely divided, pyrophoric, ferromagnetic and acicular metal particles which consist essentially of iron, are exposed to an oxygen-containing inert gas stream, generally an air / nitrogen stream, in a known manner.
- an oxygen-containing inert gas stream generally an air / nitrogen stream
- the temperature during the stabilization process of the pyrophoric metal particles is adjusted by regulating the oxygen content of the gas stream.
- the difference in the reaction temperatures between the first and the second stage is 15 to 20 ° C. during stabilization.
- Needle-shaped ferromagnetic metal powders are used as starting materials, which consist essentially of iron, but possibly also cobalt and / or L. can contain ickel.
- the pyrophoric metal powder is expediently prepared in a manner known per se by reducing the associated powdery metal oxides by the action of a gaseous reducing agent, preferably hydrogen or a gas containing hydrogen, at temperatures up to 500 ° C., preferably between 250 and 400 ° C.
- the method according to the invention permits effective stabilization of the finely divided ferromagnetic metal particles consisting essentially of iron.
- the two-stage process encloses the finely divided metal particles in a particularly uniform and uniformly oxidic shell, a result that cannot be achieved, for example, by a so-called re-passivation of already passivated material at a higher temperature.
- Stabilized metal particles of this type are therefore outstandingly suitable for the production of magnetic recording media, since they can be processed without special precautionary measures and, above all, can be incorporated excellently into the layer-forming organic binder.
- This particularly good stability when dispersing the stabilized metal particles obtained by the process according to the invention results in magnetic recording layers with a markedly higher remanent magnetization.
- the material produced according to the method according to the invention generally also has a narrower switching field strength distribution, i.e. has a narrower particle size distribution with regard to the remagnetization.
- 392 parts of an iron powder stabilized in this way are mixed with 105 parts of a 20% solution of a polyphenoxy resin with a molecular weight of 30,000 in a mixture of equal parts of tetrahydrofuran and dioxane, 392 parts of a 12.5% solution of a thermoplastic polyester urethane from adipic acid, 1.
- the dispersion is then filtered and applied in a known manner to a 6 / um thick polyethylene terephthalate film in such a thickness that after the alignment of the needle-shaped particles by passing them past a magnetic field and then drying and calendering, a magnetic layer with a layer thickness of 7.1 / um remains.
- the magnetic properties of this layer were determined with a vibration magnetometer at a measuring field of 160 kA / m.
- the coercive field strength Hc [kA / m], the remanent magnetization M [mT], the ratio of remanent magnetization to saturation magnetization M r / M m and the directivity factor RF, ie the ratio of the remanent magnetization in the layer along to across the magnetic, are determined Preferred direction.
- the measured values are given in Table 1.
- Example 1 The procedure is as described in Example 1, but the stabilization process is only carried out at a product temperature of 40 ° C. The drop in reaction temperature occurred after 3.5 hours. The processing of the stabilized iron powder into the magnetic layer was also carried out as indicated in Example 1. The magnetic properties are given in Table 1.
- Example 1 an unstabilized iron powder as used in Example 1 is processed into a magnetic layer in the manner specified there.
- the magnetic properties are given in Table 1.
- a according to Comparative Experiment 1 at a product temperature of 40 0 C stabilized iron powder is then repassivated at 60 ° C. To set this temperature during the post-passivation, however, it is necessary to supply the necessary heat from the outside because of the insufficient heat of reaction. During the post-passivation, the proportion of air in the nitrogen fluidizing gas is 34 percent by volume. After 8 hours, the iron powder is cooled, discharged from the fluidized bed furnace and processed into a magnetic layer as described in Example 1. The magnetic properties are given in Table 1.
- a pyrophoric needle-shaped ferromagnetic iron powder prepared as described in Example 4 of US Pat. No. 4,155,748, is stabilized in the same way as described in Example 1. However, the temperature of 40 ° C is maintained for one hour in the first stage. The stabilized iron powder is further processed into the magnetic layer as described in Example 1. The magnetic properties are given in Table 2.
- Example 2 The procedure is as described in Example 2, but the stabilization process is carried out only at one temperature (40 ° C.). The drop in the reaction temperature occurred after 5.5 hours. Further processing takes place in accordance with Example 2.
- the magnetic values are given in Table 2.
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- Mechanical Engineering (AREA)
- Power Engineering (AREA)
- Materials Engineering (AREA)
- General Chemical & Material Sciences (AREA)
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- Organic Chemistry (AREA)
- Hard Magnetic Materials (AREA)
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Abstract
Die Erfindung betrifft ein Verfahren zur Stabilisierung von pyrophoren, im wesentlichen aus Eisen bestehenden nadelförmigen Metallteilchen durch Reaktion mit sauerstoffhaltigen Gasen in zwei Stufen, wobei in der ersten Stufe bei einer Temperatur zwischen 25 und 45 °C bis zu ¹/3 der im Endzustand vorliegenden Passivierungsschicht und in einer daran anschließenden zweiten Stufe bei einer Temperatur zwischen 50 und 70 °C der restliche Teil der Passivierungsschicht gebildet wird.The invention relates to a method for stabilizing pyrophoric, essentially iron-shaped metal particles by reaction with oxygen-containing gases in two stages, in the first stage at a temperature between 25 and 45 ° C up to ½ of the passivation layer present in the final state and in a subsequent second stage the remaining part of the passivation layer is formed at a temperature between 50 and 70 ° C.
Description
Die Erfindung betrifft ein Verfahren zur Stabilisierung von pyrophoren, im wesentlichen aus Eisen bestehenden nadelförmigen Metallteilchen durch Reaktion mit sauerstoffhaltigen Gasen bei erhöhter Temperatur.The invention relates to a method for stabilizing pyrophoric, needle-shaped metal particles consisting essentially of iron by reaction with oxygen-containing gases at elevated temperature.
Die Verwendung von nadelförmigen ferromagnetischen Metallteilchen mit Einbereichsverhalten als magnetisierbares Material für die Herstellung von magnetischen Aufzeichnungsträgern ist bekannt. Die mit solchen Materialien erreichbaren hohen Koerzitivfeldstärken und'hohen Werte für die remanente Magnetisierung waren schon frühzeitig der Anlaß dafür, nach Wegen zu suchen, diese Stoffe auf einfache Weise herzustellen. Ein Nachteil dieser in ihren magnetischen Eigenschaften hervorragenden Materialien liegt in ihrem pyrophoren Charakter. Als Ursache für das pyrophore Verhalten wird einerseits die überaus- große Feinkörnigkeit der Metallpulver mit Teilchengrößen von 50 bis 2.000 A und die sich daraus ergebende große freie Oberfläche angesehen. Andererseits werden auch Gitterstörungen als Ursache diskutiert (vgl. Hollemann-Wiberg, Lehrbuch der anorganischen Chemie, 1964, Seite 398). Es ist zwar möglich, den pyrophoren Charakter der Metallpulver durch Wärmebehandlung zu beseitigen. Bei der Wärmebehandlung tritt aber bei diesen feinteiligen Metallpulvern, besonders bei solchen aus nadelförmigen Teilchen, durch Versinterungsprozesse eine beträchtliche Erhöhung der Teilchendicke bzw. der Verlust der Nadelform ein. Da jedoch die Koerzitivfeldstärke bei ferromagnetischen Metallpulvern an die Nadelform gebunden ist und ein Maximum bei Teilchendicken zwischen 100 und 500 Å erreicht, muß zum Erzielen guter magnetischer Eigenschaften die Teilchengröße in diesem Bereich erhalten bleiben, so daß eine reine Wärmebehandlung zur Beseitigung des pyrophoren Charakters von Metallpulver ungeeignet ist.The use of acicular ferromagnetic metal particles with single-region behavior as a magnetizable material for the production of magnetic recording media is known. The high coercive field strengths and high values for the remanent magnetization that can be achieved with such materials prompted the search early on for ways to produce these substances in a simple manner. A disadvantage of these materials, which have excellent magnetic properties, is their pyrophoric character. On the one hand, the cause of the pyrophoric behavior is the extremely fine grain size of the metal powder with particle sizes of 50 to 2,000 A and the resulting large free surface. On the other hand, lattice disorders are also discussed as the cause (cf. Hollemann-Wiberg, Textbook of inorganic chemistry, 1964, page 398). It is possible to remove the pyrophoric character of the metal powder by heat treatment. During heat treatment, however, these fine-particle metal powders, especially those made of needle-shaped particles, cause a considerable increase in the particle thickness or loss of needle shape due to sintering processes. However, since the coercive field strength in ferromagnetic metal powders is bound to the needle shape and reaches a maximum with particle thicknesses between 100 and 500 Å, this must be achieved good magnetic properties keep the particle size in this range, so that a pure heat treatment to remove the pyrophoric character of metal powder is unsuitable.
Es ist nun bekannt, pyrophore Metallpulver in der Weise zu stabilisieren, daß man die Metallteilchen durch kontrol- ; lierte Oxidation mit einer Oxidschicht umhüllt. Dies kann bei einer Temperatur zwischen 20 und 50°C durch überleiten von Inertgas geschehen, das zunächst wenig Sauerstoff enthält und dessen Sauerstoff-Konzentration im Laufe der Reaktion langsam gesteigert wird (DE-OS 20 28 536). In ähnlicher Weise wird auch gemäß den,in den DE-OSen 22 12 934 und 23 61 539 offenbarten Verfahren vorgegangen. Diese Verfahren haben jedoch den Nachteil, daß wegen der hohen Reaktionsenthalpie bei der Bildung der Eisenoxidhülle einerseits die Reaktionstemperatur möglichst tief und andererseits auch der Sauerstoffgehalt des Gases sehr niedrig sein muß, damit durch entsprechende Wärmetransportvorgänge, beispielsweise durch den Gasstrom im Reaktionsraum, die entstehende Reaktionswärme abgeführt werden kann. Dadurch sind entsprechend vorgenommene Stabilisierungsprozesse meist sehr zeitaufwendig. Auch sind die oxidischen Schutzschichten u.U. nicht einheitlich genug, so daß bei der späteren Verarbeitung dieser Metallpulver zu Magnetschichten für magnetische Aufzeichnungsträger beim mechanischen Beanspruchen der Teilchen während des Dispergierens in einem organischen Bindemittel nicht stabilisierte Oberflächenbereiche entstehen. Zwar lassen sich bei höheren Temperaturen knapp unterhalb der Selbstentzündlichkeitstemperatur kürzere Stabilisierungszeiten erreichen, jedoch ist dann die Kontrolle des Reaktionsablaufs äußerst kritisch und die Ergebnisse sind nur schwer reproduzierbar. Auch das in der DE-OS 25 24 520 offenbarte Verfahren, bei dem unter Einhaltung einer durch den Gasstrom geregelten, bei 40°C liegenden Reaktionstemperatur zur Verkürzung der Reaktionszeit die Reaktion mit dem sauerstoffhaltigen Gas unter erhöhtem Druck durchgeführt wird, kann nicht voll befriedigen, da es bei dem erreichbaren Ergebnis zu aufwendig ist.It is now known to stabilize pyrophoric metal powder in such a way that the metal particles can be controlled; Oxidation coated with an oxide layer. This can be done at a temperature between 20 and 50 ° C by passing inert gas which initially contains little oxygen and whose oxygen concentration is slowly increased in the course of the reaction (DE-OS 20 28 536). A similar procedure is followed in accordance with the methods disclosed in DE-OSes 22 12 934 and 23 61 539. However, these processes have the disadvantage that because of the high reaction enthalpy in the formation of the iron oxide shell, on the one hand the reaction temperature must be as low as possible and on the other hand the oxygen content of the gas must be very low so that the heat of reaction generated is dissipated by appropriate heat transport processes, for example by the gas stream in the reaction space can be. As a result, stabilization processes carried out accordingly are usually very time-consuming. Also, the oxidic protective layers may not be uniform enough, so that when these metal powders are subsequently processed into magnetic layers for magnetic recording media, surface areas which are not stabilized when the particles are mechanically stressed during dispersion in an organic binder. Although shorter stabilization times can be achieved at higher temperatures just below the self-igniting temperature, the control of the course of the reaction is extremely critical and the results are difficult to reproduce. The method disclosed in DE-OS 25 24 520, in which, in compliance with a regulated by the gas flow, at 40 ° C reaction temperature to shorten the reaction time, the reaction with the oxygen-containing gas is carried out under elevated pressure, can not be completely satisfactory, since it is too expensive to achieve the result.
Aufgabe der Erfindung war es daher, ein Verfahren zur Stabilisierung pyrophorer, im wesentlichen aus Eisen bestehender nadelförmiger ferromagnetischer Metallteilchen bereitzustellen, das unter Vermeidung der vorgenannten Nachteile . stabiliserte Metallteilchen liefert, welche insbesonders bei ihrer Verwendung als magnetische Materialien für magnetische Aufzeichnungsträger durch eine verbesserte Einarbeitbarkeit in das schichtbildende organische Bindemittel, eine erhöhte Koerzitivfeldstärke und eine höhere remanente Magnetisierung ergeben.It was therefore an object of the invention to provide a method for stabilizing pyrophoric, needle-shaped ferromagnetic metal particles consisting essentially of iron, while avoiding the aforementioned disadvantages. supplies stabilized metal particles which, in particular when used as magnetic materials for magnetic recording media, result in improved incorporation into the layer-forming organic binder, an increased coercive force and a higher remanent magnetization.
Es wurde nun überraschend gefunden, daß sich die pyrophoren im wesentlichen aus Eisen bestehenden nadelförmigen ferromagnetischen Teilchen durch Reaktion mit sauerstoffhaltigen Gasen aufgabengemäß stabilisieren lassen, wenn in einer ersten Stufe bei einer Temperatur zwischen 25 und 45°C bis zu 1/3 der im Endzustand vorliegenden Passivierungsschicht gebildet und daran anschließend in einer zweiten Stufe bei einer Temperatur zwischen 50 und 70°C bis zur Ausbildung der gesamten Passivierungsschicht die pyrophoren Metallteilchen mit einem sauerstoffhaltigen Inertgas behandelt werden, mit der Maßgabe, daß der jeweilige Temperaturbereich durch den Sauerstoffgehalt des Inertgasstromes eingestellt wird.It has now surprisingly been found that the pyrophoric acicular ferromagnetic particles consisting essentially of iron can be stabilized in accordance with the task by reaction with oxygen-containing gases if, in a first stage, at a temperature between 25 and 45 ° C. up to 1/3 of those in the final state Passivation layer formed and then in a second stage at a temperature between 50 and 70 ° C until the formation of the entire passivation layer, the pyrophoric metal particles are treated with an oxygen-containing inert gas, with the proviso that the respective temperature range is set by the oxygen content of the inert gas stream.
Dies läßt sich insbesondere dann erreichen, werüi`die pyrophoren Metallteilchen in einer ersten Stufe 0,5 bis 2 Stunden bei einer Temperatur zwischen 25 und 45°C und daran anschließend in einer zweiten Stufe während 2 bis 20, insbe- ''sondere 4 bis 10 Stunden bei einer Temperatur zwischen 50 und 700C'mit einem sauerstoffhaltigen Inertgas behandelt werden, mit der Maßgabe, daß der jeweilige Temperaturbereich durch den Sauerstoffgehalt des Inertgasstromes eingestellt wird.This can be achieved in particular if the pyrophoric metal particles in a first stage for 0.5 to 2 hours at a temperature between 25 and 45 ° C. and then in a second stage for 2 to 20, in particular '' In particular 4 to 10 hours at a temperature between 50 and 70 0 C 'are treated with an oxygen-containing inert gas, with the proviso that the respective temperature range is set by the oxygen content of the inert gas stream.
Zur Durchführung des erfindungsgemäßen Verfahrens werden die in bekannter Weise hergestellten feinteiligen pyrophoren ferromagnetischen und nadelförmigen, im wesentlichen aus Eisen bestehenden Metallteilchen einem sauerstoffhaltigen Inertgasstrom, im allgemeinen einem Luft/Stickstoffstrom ausgesetzt. Dies kann dadurch geschehen, daß in einem Drehrohrofen der Gasstrom über das Material geleitet wird oder daß das Verfahren in hierfür bekannten Wirbelschichtöfen mit einem Luft/Inertgasgemisch als Wirbelgas durchgeführt wird. Dabei wird die Temperatur während des Stabilisierungsprozesses der pyrophoren Metallteilchen durch die Regelung des Sauerstoffgehalts des Gasstromes eingestellt.To carry out the process according to the invention, the finely divided, pyrophoric, ferromagnetic and acicular metal particles, which consist essentially of iron, are exposed to an oxygen-containing inert gas stream, generally an air / nitrogen stream, in a known manner. This can be done by passing the gas stream over the material in a rotary tube furnace or by carrying out the process in fluidized bed furnaces known for this purpose with an air / inert gas mixture as fluidizing gas. The temperature during the stabilization process of the pyrophoric metal particles is adjusted by regulating the oxygen content of the gas stream.
Für das erfindungsgemäße Verfahren ist es wesentlich, daß die beiden Stufen des Stabilisierungsprozesses unmittelbar hintereinander durchgeführt werden. Das Ende der Stabilisierung der Metallteilchen läßt sich dann am Abfall der Reaktionstemperatur bei sonst gleichbleibenden Verfahrensbedingungen erkennen.It is essential for the method according to the invention that the two stages of the stabilization process are carried out directly one after the other. The end of the stabilization of the metal particles can then be recognized by the drop in the reaction temperature under otherwise constant process conditions.
Im Rahmen des erfindungsgemäßen Verfahrens hat es sich außerdem als besonders vorteilhaft herausgestellt, wenn bei der Stabilisierung der Unterschied der Reaktionstemperaturen zwischen der ersten und der zweiten Stufe 15 bis 20oC beträgt.In the context of the method according to the invention, it has also proven to be particularly advantageous if the difference in the reaction temperatures between the first and the second stage is 15 to 20 ° C. during stabilization.
Als Ausgangsmaterialien werden nadelförmige ferromagnetische Metallpulver eingesetzt, die im wesentlichen aus Eisen bestehen, gegebenenfalls aber auch Kobalt und/oder L ickel enthalten können. Die Herstellung der pyrophoren ' Metallpulver erfolgt zweckmäßig in an sich bekannter Weise durch Reduktion der zugehörigen pulverförmigen Metalloxide durch Einwirkung eines gasförmigen Reduktionsmittels, bevorzugt Wasserstoff oder ein Wasserstoff enthaltendes Gas, bei Temperaturen bis 500 C, vorzugsweise zwischen 250 und 400°C.Needle-shaped ferromagnetic metal powders are used as starting materials, which consist essentially of iron, but possibly also cobalt and / or L. can contain ickel. The pyrophoric metal powder is expediently prepared in a manner known per se by reducing the associated powdery metal oxides by the action of a gaseous reducing agent, preferably hydrogen or a gas containing hydrogen, at temperatures up to 500 ° C., preferably between 250 and 400 ° C.
Das erfindungsgemäße Verfahren erlaubt eine wirkungsvolle Stabilisierung der feinteiligen ferromagnetischen im wesentlichen aus Eisen bestehenden Metallteilchen. Durch das Zwei-Stufen-Verfahren werden die feinteiligen Metallteilchen von einer besonders einheitlichen und gleichmäßign oxidischen Hülle umschlossen, ein Ergebnis, das sich beispielsweise durch eine sogenannte Nachpassivierung von bereits passiviertem Material bei einer höheren Temperatur nicht erreichen läßt.The method according to the invention permits effective stabilization of the finely divided ferromagnetic metal particles consisting essentially of iron. The two-stage process encloses the finely divided metal particles in a particularly uniform and uniformly oxidic shell, a result that cannot be achieved, for example, by a so-called re-passivation of already passivated material at a higher temperature.
Solche stabilisierten Metallteilchen eignen sich damit in hervorragender Weise zur Herstellung von magnetischen Aufzeichnungsträgern, da sie sich ohne besondere Vorsichtsmaßnahmen verarbeiten und vor allem ausgezeichnet in das schichtbildende organische Bindemittel einarbeiten lassen. Diese besonders gute Stabilität beim Dispergieren der nach dem erfindungsgemäßen Verfahren erhaltenen stabilisierten Metallteilchen ergibt magnetische Aufzeichnungsschichten mit einer merklich höheren remanenten Magnetisierung. Weiter ist hervorzuheben, daß neben einer erhöhten Koerzitivfeldstärke in der Magnetschicht das gemäß dem erfindungsgemäßen Verfahren hergestellte Material im allgemeinen auch eine engere Schaltfeldstärkenverteilung, d.h. eine hinsichtlich der Ummagnetisierung engere Teilchengrößenverteilung aufweist.Stabilized metal particles of this type are therefore outstandingly suitable for the production of magnetic recording media, since they can be processed without special precautionary measures and, above all, can be incorporated excellently into the layer-forming organic binder. This particularly good stability when dispersing the stabilized metal particles obtained by the process according to the invention results in magnetic recording layers with a markedly higher remanent magnetization. It should also be emphasized that in addition to an increased coercive field strength in the magnetic layer, the material produced according to the method according to the invention generally also has a narrower switching field strength distribution, i.e. has a narrower particle size distribution with regard to the remagnetization.
Die Vorteile der erfindungsgemäß hergestellten Metallteilchen wird anhand der Beispiele gegenüber den Vergleichsversuchen nach dem Stand der Technik aufgezeigt.The advantages of the metal particles produced according to the invention are shown on the basis of the examples compared to the comparative tests according to the prior art.
4000 Teile eines pyrophoren nadelförmigen ferromagnetischen Eisenpulvers, hergestellt nach den Angaben in Beispiel 1 der US-PS 4 155 748, werden in einem Wirbelschichtofen mit einem Stickstoffstrom von 10 Nm2/h fluidisiert. Dem Stickstoffstrom wird dann anschließend Luft in einer solchen Menge zudosiert, daß die Produkttemperatur, hervorgerufen durch den exothermen Oxidationsvorgang, sich auf 400C einstellt. Nach 30 Minuten wird der Luftanteil am Wirbelgas derart angehoben, daß die Produkttemperatur nunmehr 60°C beträgt. Nach weiteren 1,5 Stunden beginnt die Temperatur abzufallen. Jetzt wird der Stickstoffanteil des Wirbelgases durch Luft ersetzt und nach dem Abkühlen des stabilisierten Materials aus dem Wirbelofen ausgetragen.4000 parts of a pyrophoric acicular ferromagnetic iron powder, produced according to the information in Example 1 of US Pat. No. 4,155,748, are fluidized in a fluidized bed furnace with a nitrogen flow of 10 Nm 2 / h. Air is then metered into the nitrogen stream in such an amount that the product temperature, brought about by the exothermic oxidation process, is adjusted to 40 ° C. After 30 minutes, the air portion of the fluidizing gas is raised in such a way that the product temperature is now 60 ° C. After a further 1.5 hours, the temperature begins to drop. Now the nitrogen content of the fluidizing gas is replaced by air and discharged from the fluidizing furnace after the stabilized material has cooled.
392 Teile eines so stabilisierten Eisenpulvers werden mit 105 Teilen einer 20%igen Lösung eines Polyphenoxyharzes mit einem Molekulargewicht von 30 000 in einem Gemisch aus gleichen Teilen Tetrahydrofuran und Dioxan, 392 Teilen einer 12,5%igen Lösung eines thermoplastischen Polyesterurethans aus Adipinsäure, 1,4-Butandiol und 4,4'-Diisocyanatodiphenylmethan in einem Gemisch aus gleichen Teilen Tetrahydrofuran und Dioxan, 47,7 Teilen eines handelsüblichen anionenaktiven Netzmittels auf Basis Phosphorsäureester und 973 Teilen des genannten Lösungsmittelgemisches gemischt und 8 Stunden lang in einer Schüttelkugelmühle mit Hilfe von Stahlkugeln mit einem Durchmesser von 2 mm dispergiert. Danach wird mit 212 Teilen der oben erwähnten 12,5%igen Lösung eines thermoplastischen Polyesterurethans aus Adipinsäure, 1,4-Butandiol und 4,4'-Diisocyanatodiphe- nylmethan in einem Gemisch aus gleichen Teilen Tetrahydrofuran und Dioxan, 56,7 Teilen der oben genannten Phenoxy- . harzlösung und 1,12 Teilen eines handelsüblichen Silikonöls versetzt und eine weitere Stunde dispergiert. Danach wird die Dispersion filtriert und in bekannter Weise auf eine 6 /um dicke Polyäthylenterephthalatfolie in einer solchen Stärke aufgetragen, daß nach dem Ausrichten der nadelförmigen Teilchen durch Vorbeiführen an einem Magnetfeld und anschließendem Trocknen und Kalandrieren eine Magnetschicht mit einer Schichtdicke von 7,1 /um verbleibt.392 parts of an iron powder stabilized in this way are mixed with 105 parts of a 20% solution of a polyphenoxy resin with a molecular weight of 30,000 in a mixture of equal parts of tetrahydrofuran and dioxane, 392 parts of a 12.5% solution of a thermoplastic polyester urethane from adipic acid, 1. 4-butanediol and 4,4'-diisocyanatodiphenylmethane in a mixture of equal parts of tetrahydrofuran and dioxane, 47.7 parts of a commercially available anionic surfactant based on phosphoric acid ester and 973 parts of the solvent mixture mentioned and mixed for 8 hours in a shaker ball mill using steel balls dispersed with a diameter of 2 mm. Thereafter, 212 parts of the 12.5% solution of a thermoplastic polyester urethane from adipic acid, 1,4-butanediol and 4,4'-diisocyanatodiphe- nylmethane in a mixture of equal parts of tetrahydrofuran and dioxane, 56.7 parts of the above phenoxy. resin solution and 1.12 parts of a commercially available silicone oil and dispersed for a further hour. The dispersion is then filtered and applied in a known manner to a 6 / um thick polyethylene terephthalate film in such a thickness that after the alignment of the needle-shaped particles by passing them past a magnetic field and then drying and calendering, a magnetic layer with a layer thickness of 7.1 / um remains.
Die magnetischen Eigenschaften dieser Schicht wurden mit einem Schwingmagnetometer bei einem Meßfeld von 160 kA/m bestimmt. Bestimmt wird die Koerzitivfeldstärke Hc [kA/m], die remanente Magnetisierung M [mT], das Verhältnis von remanenter Magnetisierung zu Sättigungsmagnetisierung Mr/Mm und der Richtfaktor RF, d.h. das Verhältnis der remanenten Magnetisierung in der Schicht längs zu quer der magnetischen Vorzugsrichtung. Die gemessenen Werte sind in Tabelle 1 angegeben.The magnetic properties of this layer were determined with a vibration magnetometer at a measuring field of 160 kA / m. The coercive field strength Hc [kA / m], the remanent magnetization M [mT], the ratio of remanent magnetization to saturation magnetization M r / M m and the directivity factor RF, ie the ratio of the remanent magnetization in the layer along to across the magnetic, are determined Preferred direction. The measured values are given in Table 1.
Es wird wie in Beispiel 1 beschrieben verfahren, jedoch wird der Stabilisierungsprozeß nur bei einer Produkttemperatur von 40°C durchgeführt. Der Abfall der Reaktionstemperatur trat nach 3,5 Stunden ein. Die Verarbeitung des stabilisierten Eisenpulvers zur Magnetschicht wurde ebenfalls wie in Beispiel 1 angegeben durchgeführt. Die magnetischen Eigenschaften sind in Tabelle 1 angegeben.The procedure is as described in Example 1, but the stabilization process is only carried out at a product temperature of 40 ° C. The drop in reaction temperature occurred after 3.5 hours. The processing of the stabilized iron powder into the magnetic layer was also carried out as indicated in Example 1. The magnetic properties are given in Table 1.
Es wird wie in Vergleichsversuch 1 angegeben verfahren, jedoch wird die Stabilisierung bei einer Produkttemperatur von 60°C während 2 Stunden durchgeführt. Die magnetischen Eigenschaften sind in Tabelle 1 angegeben.The procedure is as in Comparative Experiment 1, but the stabilization is carried out at a product temperature of 60 ° C for 2 hours. The magnetic properties are given in Table 1.
Unter geeigneten Vorsichtsmaßnahmen wird ein wie in Beispiel 1 eingesetztes unstabilisiertes Eisenpulver in der dort angegebenen Weise zu einer Magnetschicht verarbeitet. Die magnetischen Eigenschaften sind in Tabelle 1 angegeben.With suitable precautionary measures, an unstabilized iron powder as used in Example 1 is processed into a magnetic layer in the manner specified there. The magnetic properties are given in Table 1.
Ein gemäß Vergleichsversuch 1 bei einer Produkttemperatur von 400C stabilisiertes Eisenpulver wird anschließend bei 60°C nachpassiviert. Zur Einstellung dieser Temperatur bei der Nachpassivierung ist es aber wegen der nicht mehr ausreichenden Reaktionswärme erforderlich, die nötige Wärme von außen zuzuführen. Bei der Nachpassivierung beträgt der Luftanteil am Stickstoffwirbelgas 34 Volumenprozent. Nach 8 Stunden wird das Eisenpulver abgekühlt, aus dem Wirbelschichtofen ausgetragen und wie in Beispiel 1 beschrieben zu einer Magnetschicht verarbeitet. Die magnetischen Eigenschaften sind in Tabelle 1 angegeben.
Ein pyrophores nadelförmiges ferromagnetisches Eisenpulver, hergestellt nach den Angaben in Beispiel 4 der US-PS 4 155 748, wird in gleicher Weise wie in Beispiel 1 beschrieben stabilisiert. Jedoch wird in der ersten Stufe die Temperatur von 40°C eine Stunde lang aufrechterhalten. Die Weiterverarbeitung des stabilisierten Eisenpulvers zur Magnetschicht erfolgt ebenfalls wie in Beispiel 1 beschrieben. Die magnetischen Eigenschaften sind in Tabelle 2 angegeben.A pyrophoric needle-shaped ferromagnetic iron powder, prepared as described in Example 4 of US Pat. No. 4,155,748, is stabilized in the same way as described in Example 1. However, the temperature of 40 ° C is maintained for one hour in the first stage. The stabilized iron powder is further processed into the magnetic layer as described in Example 1. The magnetic properties are given in Table 2.
Es wird wie in Beispiel 2 beschrieben verfahren, jedoch wird der Stabilisierungsprozeß nur bei einer Temperatur (40°C) durchgeführt. Der Abfall der Reaktionstemperatur trat nach 5,5 Stunden ein. Die Weiterverarbeitung erfolgt entsprechend Beispiel 2. Die magnetischen Werte sind in Tabelle 2 angegeben.
Claims (3)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19813116489 DE3116489A1 (en) | 1981-04-25 | 1981-04-25 | METHOD FOR STABILIZING PYROPHORES, SUBSTANTIALLY IRON, FERROMAGNETIC, NEEDLE-SHAPED METAL PARTICLES |
| DE3116489 | 1981-04-25 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0063730A2 true EP0063730A2 (en) | 1982-11-03 |
| EP0063730A3 EP0063730A3 (en) | 1983-04-13 |
Family
ID=6130824
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP82103010A Withdrawn EP0063730A3 (en) | 1981-04-25 | 1982-04-08 | Process for stabilising pyrophoric acicular ferromagnetic metal particles essentially consisting of iron |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4420330A (en) |
| EP (1) | EP0063730A3 (en) |
| JP (1) | JPS57181301A (en) |
| DE (1) | DE3116489A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4631090A (en) * | 1984-06-20 | 1986-12-23 | Bayer Aktiengesellschaft | Preparation and use of iron magnetic pigments |
| EP0305069A2 (en) * | 1987-08-24 | 1989-03-01 | Chisso Corporation | A process for producing a ferromagnetic metal powder having an oxidized coating |
| EP0512309A1 (en) * | 1991-05-10 | 1992-11-11 | BASF Magnetics GmbH | Process for stabilizing acicular ferromagnetic metal particles, essentially consisting of iron |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59110701A (en) * | 1982-12-16 | 1984-06-26 | Mitsui Toatsu Chem Inc | Stabilization of reduced iron powder for magnetic recording |
| DE3330767A1 (en) * | 1983-08-26 | 1985-03-14 | Bayer Ag, 5090 Leverkusen | HANDLING STABLES IN THE ESSENTIAL EXAMPLE OF IRON MAGNETIC PIGMENTS, METHOD FOR THEIR PRODUCTION AND THEIR USE |
| JPS63199801A (en) * | 1987-02-12 | 1988-08-18 | Chisso Corp | Stabilization treatment device for ferromagnetic metal powder |
| JP2739600B2 (en) * | 1989-10-03 | 1998-04-15 | 富士写真フイルム株式会社 | Method of processing ferromagnetic metal powder and method of manufacturing magnetic recording medium |
| DE4294047T1 (en) * | 1991-11-22 | 1996-09-26 | Ampex Media Corp | Storage of metal particles |
| US5849817A (en) * | 1994-03-24 | 1998-12-15 | Silberline Limited | Metal pigments |
| GB2288411B (en) * | 1994-03-24 | 1998-04-15 | Silberline Ltd | Metal pigments |
| JP2001305733A (en) * | 2000-04-18 | 2001-11-02 | Sumitomo Chem Co Ltd | Method for preserving photosensitive composition |
| CN100463863C (en) * | 2006-11-24 | 2009-02-25 | 金川集团有限公司 | Method for preventing self-combustion of ultrafine carbonyl iron powder |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2046957A1 (en) * | 1969-06-20 | 1971-03-12 | Philips Nv | |
| FR2090199A1 (en) * | 1970-05-22 | 1972-01-14 | Ampex | |
| NL7018910A (en) * | 1970-12-29 | 1972-07-03 | Passivating ferromagnetic powder - by treating cooled moving powder with limited amount of oxygen at controlled temp and gradually | |
| DE2524520A1 (en) * | 1975-06-03 | 1976-12-16 | Philips Patentverwaltung | Stabilising pyrophoric iron powder - produced by reaction with gases contg. oxygen under press. |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3520676A (en) * | 1968-05-28 | 1970-07-14 | Eastman Kodak Co | Stabilization of pyrophoric metal powder |
| US3767477A (en) * | 1971-12-27 | 1973-10-23 | Eastman Kodak Co | Method for producing oxide coated iron powder of controlled resistance for electrostatic copying systems |
| DE2212934A1 (en) * | 1972-03-17 | 1973-09-20 | Philips Nv | Iron powder prodn for magnetic recording - by redn of needle-like crystals of iron oxide or its hydrate in presence of |
| US3926617A (en) * | 1973-02-21 | 1975-12-16 | Midrex Corp | Passivation of metallized pellets in bulk |
| US3967986A (en) * | 1975-01-27 | 1976-07-06 | U.S. Philips Corporation | Method of preparing ferromagnetic material |
| DE2646348C2 (en) * | 1976-10-14 | 1986-08-28 | Basf Ag, 6700 Ludwigshafen | Process for the production of acicular, ferromagnetic metal particles consisting essentially of iron and their use for the production of magnetic recording media |
| US4207092A (en) * | 1977-03-03 | 1980-06-10 | E. I. Du Pont De Nemours And Company | Acicular α-iron particles, their preparation and recording media employing same |
| US4251592A (en) * | 1979-04-03 | 1981-02-17 | Toda Kogyo Corp. | Stabilization treatment of acicular ferromagnetic iron or iron-alloy particles against the oxidation thereof |
-
1981
- 1981-04-25 DE DE19813116489 patent/DE3116489A1/en not_active Withdrawn
-
1982
- 1982-04-08 EP EP82103010A patent/EP0063730A3/en not_active Withdrawn
- 1982-04-16 US US06/368,984 patent/US4420330A/en not_active Expired - Fee Related
- 1982-04-19 JP JP57064086A patent/JPS57181301A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2046957A1 (en) * | 1969-06-20 | 1971-03-12 | Philips Nv | |
| FR2090199A1 (en) * | 1970-05-22 | 1972-01-14 | Ampex | |
| NL7018910A (en) * | 1970-12-29 | 1972-07-03 | Passivating ferromagnetic powder - by treating cooled moving powder with limited amount of oxygen at controlled temp and gradually | |
| DE2524520A1 (en) * | 1975-06-03 | 1976-12-16 | Philips Patentverwaltung | Stabilising pyrophoric iron powder - produced by reaction with gases contg. oxygen under press. |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4631090A (en) * | 1984-06-20 | 1986-12-23 | Bayer Aktiengesellschaft | Preparation and use of iron magnetic pigments |
| EP0305069A2 (en) * | 1987-08-24 | 1989-03-01 | Chisso Corporation | A process for producing a ferromagnetic metal powder having an oxidized coating |
| EP0305069A3 (en) * | 1987-08-24 | 1990-07-11 | Chisso Corporation | A process for producing a ferromagnetic metal powder having an oxidized coating |
| EP0512309A1 (en) * | 1991-05-10 | 1992-11-11 | BASF Magnetics GmbH | Process for stabilizing acicular ferromagnetic metal particles, essentially consisting of iron |
Also Published As
| Publication number | Publication date |
|---|---|
| US4420330A (en) | 1983-12-13 |
| EP0063730A3 (en) | 1983-04-13 |
| JPS57181301A (en) | 1982-11-08 |
| DE3116489A1 (en) | 1982-11-11 |
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