Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-01-16
2003-05-13
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S403000, C428S407000, C264S611000, C264S612000, C264S613000
Reexamination Certificate
active
06562458
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of providing a thin electrically insulating surface layer on iron powder particles which are to be used for soft magnetic applications. The invention also relates to the powder per se as well as a method concerning compacting and heat treating such powders. Specifically the powders according to the invention are suitable for the preparation of soft magnetic materials for high frequency applications.
BACKGROUND OF THE INVENTION
Iron-based particles have long been used as a base material in the manufacture of structural components by powder metallurgical methods. Magnetic core components have also been manufactured by such powder metallurgical methods, but the iron-based particles used in these methods are generally coated with a circumferential layer of insulating material.
The research in the powder metallurgical manufacture of magnetic core components using coated iron-based powders has been directed to the development of iron powder compositions that enhance certain physical and magnetic properties without detrimentally affecting other properties. Desired properties include a high permeability through an extended frequency range, high pressed strength, low core losses and suitability for compression moulding techniques.
Different types of insulating coatings which are used for particles of iron are disclosed in the literature.
Thus the German patent application 1291028 discloses a method for providing electrical coatings by mixing an iron powder with water including chromic acid and phosphoric acid at an elevated temperature, washing and drying the powder. The iron powder should have a particle size less than 10 &mgr;m. The publication does not disclose any magnetic properties for materials prepared by using the iron powder.
Another publication within this field is DE 2 825 235, which discloses an iron powder consisting of particles which are coated with an oxide layer. The particle size is between 0.05 and 0.15 mm and the particles have an oxide coating which, calculated on the particle weight, included 0.3 to 0.8% by weight of oxygen. The oxide coating can be obtained by heating in air or by chemical oxidation, but no process parameters and no analysis of the coated particles are disclosed. From the examples it can be calculated that the permeabilities obtained are in the range of 30 to 35.
The European patent application 434 669 concerns a magnetic powder wherein an electrically insulating coating separates the magnetic powder particles. The particles have an average particle size of 10-300 &mgr;m, and the insulating material which covers each of the particles of the magnetic powder comprises a continuous insulating film having a thickness of 10 &mgr;m or less and this film comprises a metal alkoxide or a decomposition product thereof.
WO 95/29490 discloses iron powder particles having an insulating layer which is obtained by using an aqueous solution of phosphoric acid and WO 97/30810 discloses extremely thin insulating layers obtained with phosphoric acid in organic solvents.
The DE patent 3 439 397 discloses iron particles which are electrically insulated by a phosphate coating. This coating could be for example magnesium or zinc phosphate and preferably the coating is an iron phosphate coating. The insulating phosphate coating should be between 0.1 and 1.5% of the weight of the iron particles. The preparation of the iron phosphate coating which involves mixing the iron particles with a solution of 89% of phosphoric acid in acetone is disclosed in Example 1. The particles are then compacted and subsequently heated in an oxidising atmosphere. Before the compacting step the phosphate insulated iron particles are optionally mixed with a resin, preferably an epoxy resin. In order to obtain low hysteresis losses heating temperatures above 500° C. and below 800° C. are recommended. Furthermore this heat treatment should preferably be carried out stepwise with alternating reduced and normal or increased pressures and with stepwise increased temperatures for different periods of times. The advantages of this known process are experimentally disclosed for a heat treatment wherein the final step is carried out at a temperature of at least 600° C. Table IV of this patent discloses that the insulating phosphate layers are effective for comparatively low frequencies i.e. frequencies below 1 kHz.
EP 810 615 concerns powder particles enveloped by a insulating phosphate layer. According to this patent the insulating layer is obtained by using a specific phosphating solution, which comprises a solvent and phosphate salts and a rust inhibitor, which is an organic compound containing nitrogen and/or sulphur which has lone pair electrons suppressing the formation of iron oxide and surfactant. This powder is useful for the preparation of soft magnetic materials for high frequency applications.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a new iron based powder, the particles of which are provided with a thin insulating layer.
A second object is to provide a new powder which is specifically suitable for the preparation of soft magnetic materials intended for applications at high frequencies.
A third object is to provide a powder having a high permeability through an extended frequency range and which is resistant to high temperatures.
A forth object is to provide a powder which can be compacted to high densities.
A fifth object is to provide an insulation layer which can be obtained by an environmentally acceptable, energy and time saving process, which does not require the use of organic solvents, toxic metals or special organic additives.
SUMMARY OF THE INVENTION
The new powder is based on the discovery that an effective insulating layer or coating fulfilling the objects above can be obtained if the insulating layer includes a limited amount of magnesium. Such a layer may be obtained by treating an iron base powder with an acid in solvent, preferably water, including magnesium.
The invention also concerns a method of making a component having improved, soft magnetic properties especially at high frequencies, by compacting or die-pressing a powder composition of this insulated iron powder optionally in combination with a thermosetting or thermoplastic resin and subsequently subjecting the compacted composition to heat treatment at a temperature preferably not more than 750° C.
REFERENCES:
patent: 5160447 (1992-11-01), Ishikawa et al.
patent: 1 291 028 (1969-03-01), None
patent: 34 39 397 (1984-10-01), None
patent: 0 205 786 (1986-04-01), None
patent: 0 810 615 (1997-12-01), None
patent: 06260319 (1994-09-01), None
patent: 29490 (1995-11-01), None
patent: 03622 (1999-01-01), None
Elgelid Cecilia
Larsson Lars-Åke
Larsson-Westberg Anne
Burns Doane Swecker & Mathis L.L.P.
Hëganäs AB
Resan Stevan A.
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