WO2025093444A1 - Composition de poudre ferromagnétique et son procédé de production - Google Patents

Composition de poudre ferromagnétique et son procédé de production Download PDF

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WO2025093444A1
WO2025093444A1 PCT/EP2024/080274 EP2024080274W WO2025093444A1 WO 2025093444 A1 WO2025093444 A1 WO 2025093444A1 EP 2024080274 W EP2024080274 W EP 2024080274W WO 2025093444 A1 WO2025093444 A1 WO 2025093444A1
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coating
ferromagnetic powder
mol
powder composition
dopant
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Björn SKÅRMAN
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Hoganas AB
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Hoganas AB
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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
    • H01F1/12—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 soft-magnetic materials
    • H01F1/14—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 soft-magnetic materials metals or alloys
    • H01F1/20—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder
    • H01F1/22—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together
    • H01F1/24—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together the particles being insulated
    • 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
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
    • 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
    • B22F1/16—Metallic particles coated with a non-metal
    • 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
    • H01F1/12—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 soft-magnetic materials
    • H01F1/33—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 soft-magnetic materials mixtures of metallic and non-metallic particles; metallic particles having oxide skin
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F3/00—Cores, Yokes, or armatures
    • H01F3/08—Cores, Yokes, or armatures made from powder
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0206—Manufacturing of magnetic cores by mechanical means
    • H01F41/0246—Manufacturing of magnetic circuits by moulding or by pressing powder
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C2202/00—Physical properties
    • C22C2202/02—Magnetic
    • 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
    • H01F1/12—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 soft-magnetic materials
    • H01F1/14—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 soft-magnetic materials metals or alloys
    • H01F1/20—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder
    • H01F1/22—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together
    • H01F1/24—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together the particles being insulated
    • H01F1/26—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together the particles being insulated by macromolecular organic substances

Definitions

  • Ferromagnetic powders include soft magnetic composite (SMC) powders which comprise soft magnetic core particles, usually iron-based, with an electrically insulating coating on each particle. Such powders may be used to obtain soft magnetic components or parts, such as by compacting the powders into the desired shape. These components or parts, also known as soft magnetic composites, may be used as an alternative to laminated steel components in electric motors, generators, electromagnets in a wide range of applications.
  • SMC soft magnetic composite
  • the magnetic permeability p of a material is an indication of its ability to become magnetized or its ability to carry a magnetic flux.
  • Maximum permeability (p ma x) is defined as the highest value of B/H, i.e., the ratio of the magnetizing force B or field intensity to the induced magnetic flux H.
  • the hysteresis loss which constitutes the majority of the total core losses in most motor applications, is brought about by the necessary expenditure of energy to overcome the retained magnetic forces within the part made from the soft magnetic core particles and is influenced by the retentivity, or remanence B R , and the coercivity H c .
  • the retained magnetic forces within the component may be minimized by increasing the quality and purity of the soft magnetic core particles and, in particular, by heat treating the component so as to cause a release of stress caused by the compaction shear forces within the component.
  • Energy losses are further caused by Eddy current loss (AC-loss) which is caused by the induction of electric currents in the part due to the changing flux caused by alternating current (AC) conditions.
  • the Eddy current loss is minimized by the electrically isolating coating on each particle which thereby isolates the soft magnetic core particles from each other. Accordingly, the resistivity R of the coating becomes an important parameter for defining the characteristics and useability of the soft magnetic core particles.
  • the level of electrical resistivity R that is required to minimize the AC losses in a part made from soft magnetic core particles is dependent on the size distribution of the soft magnetic core particles, the size of the part, or the cross-sectional area of the magnetic flux, and the frequency of the alternating magnetic field in which the part is to be used.
  • EP 2 252 419 B1 generally discloses a ferromagnetic powder composition comprising soft magnetic iron-based core particles, wherein the surface of the core particles is provided with a first inorganic insulating layer and at least one metal-organic layer, located outside the first layer.
  • US 10,741 ,316 generally discloses a ferromagnetic powder composition including soft magnetic iron-based core particles, wherein the surface of the core particles is coated with at least one phosphorus-based inorganic insulating layer and then at least partially covered with metal-organic compound(s).
  • EP 3 411 169 B1 generally discloses a powder mixture comprising phosphorous coated iron alloy particles and phosphorous coated iron particles.
  • WO 2020/252551 generally concerns a particulate material comprising ferromagnetic particles covered by at least one oxide layer consisting of nanoparticles and at least one glassy layer covering the oxide layer.
  • BE 44486 generally concerns a method of constructing magnetic cores by mixing particles of a magnetic material covered by an insulator with a particle separating material.
  • First and second objects of the technology proposed herein concern the provision of ferromagnetic powder compositions and mixtures comprising soft magnetic core particles having improved electrical, magnetic and/or structural properties.
  • a third object of the technology proposed herein concerns the provision of a method of producing the ferromagnetic powder compositions and mixtures.
  • a fourth object of the technology proposed herein concerns the provision of a method of manufacturing an object from the ferromagnetic powder compositions or mixtures.
  • Fifth and sixth objects of the technology proposed herein concern an object comprising a compacted ferromagnetic powder composition or mixture as well as an object manufactured from the ferromagnetic powder composition or mixture.
  • a ferromagnetic powder composition comprising:
  • a first coating at least partially covering and being in direct contact with the surface of the core particles comprising: a. a silicate of the general formula (K 2 O)a(SiO 2 )P, wherein a is moles of K 2 O, P is moles of SiO 2 , and the p/a molar ratio is in the interval from 0.5 to 4.1 , i. wherein the silicate is present in an amount of 0.02 to 1 .0 wt% calculated based on the total weight of the ferromagnetic powder composition, b. optionally, particles of a compound comprising bismuth and oxygen having a D 5 O measured according to ISO 13320-1 in the interval of 0.1 to 10 pm, and, c. a dopant dissolved as an oxo- or hydroxy-anion in the silicate (a), and a method of producing a ferromagnetic powder composition comprising the steps of:
  • a silicate of the general formula (K 2 O)a(SiO 2 )P wherein a is moles of K 2 O, P is moles of SiO 2 , and the p/a molar ratio is in the interval from 0.5 to 4.1 , i. wherein the silicate is present in an amount of 0.02 to 1 .0 wt% calculated based on the total weight of the ferromagnetic powder composition, b. optionally, particles of a compound comprising bismuth and oxygen having a D 5 O measured according to ISO 13320-1 in the interval of 0.1 to 10 pm, c.
  • nanoparticles having a D 5 o measured according to ISO 13320-1 of 10-200 nm, or alternatively having a specific surface area (SSA) of 6- 120 m 2 /g as determined according to ISO 9277:2022.
  • a ferromagnetic powder composition comprising:
  • the further ferromagnetic powder composition comprises soft magnetic ironbased core particles that are different from the soft magnetic iron-based core particles of the ferromagnetic powder composition, and wherein preferably the soft magnetic iron-based core particles of the further ferromagnetic powder composition comprise or consist of an iron alloy having a higher electrical resistivity and/or hardness than the soft magnetic iron-based core particles of the ferromagnetic powder composition.
  • At least one of the above-mentioned objects or at least one of the further objects which will become evident from the below description, are according to a fourth aspect of the technology proposed herein achieved by a method of manufacturing an object from the ferromagnetic powder composition according the first aspect of the technology proposed herein or the ferromagnetic powder mixture according to the second aspect of the technology proposed herein, comprising the steps of:
  • At least one of the above-mentioned objects or at least one of the further objects which will become evident from the below description, are according to corresponding fifth and sixth aspects of the technology proposed herein achieved by an object comprising a compacted ferromagnetic powder composition according to the first aspect of the technology proposed herein or a compacted ferromagnetic powder mixture according to the second aspect of the technology proposed herein, and an object obtained by the method according to the fourth aspect of the technology proposed herein.
  • Figs. 1 shows a schematical cross-sectional illustration of a single particle of a ferromagnetic powder composition according to an embodiment of the first aspect of the technology proposed herein showing a soft magnetic ironbased core particle with a first coating comprising a silicate, nanoparticles, particles of a compound comprising bismuth and oxygen and a dopant, as well as a second coating comprising at least one metal-organic compound.
  • a first coating at least partially covering and being in direct contact with the surface of the core particles comprising: a. a silicate of the general formula (K 2 O)a(SiO 2 )P, wherein a is moles of K 2 O, P is moles of SiO 2 , and the p/a molar ratio is in the interval from 0.5 to 4.1 , i. wherein the silicate is present in an amount of 0.02 to 1 .0 wt% calculated based on the total weight of the ferromagnetic powder composition, b. optionally, particles of a compound comprising bismuth and oxygen having a D 5 O measured according to ISO 13320-1 in the interval of 0.1 to 10 pm, and, c. a dopant dissolved as an oxo- or hydroxy-anion in the silicate (a); and a method of producing a ferromagnetic powder composition comprising the steps of:
  • a silicate of the general formula (K 2 O)a(SiO 2 )P wherein a is moles of K 2 O, P is moles of SiO 2 , and the p/a molar ratio is in the interval from 0.5 to 4.1 , ii. wherein the silicate is present in an amount of 0.02 to 1 .0 wt% calculated based on the total weight of the ferromagnetic powder composition, b. optionally, particles of a compound comprising bismuth and oxygen having a D 5 O measured according to ISO 13320-1 in the interval of 0.1 to 10 pm, c.
  • nanoparticles having a D 5 o measured according to ISO 13320-1 of 10-200 nm, or alternatively having a specific surface area (SSA) of 6- 120 m 2 /g as determined according to ISO 9277:2022.
  • SSA specific surface area
  • the inclusion of the dopant in the first coating provides improved ageing properties and higher resistivity for a given coercivity level and coating density/thickness level to parts manufactured from the ferromagnetic powder composition. Specifically, these parts can be heat-treated at higher temperatures while at the same time maintaining acceptable electrical resistivity properties.
  • the inclusion of the dopant in the first coating provides better thermal stability, and/or specific electrical resistivity for a given coercivity level and coating density/thickness level, to the glassy coating that is formed from the first coating, and any second coating applied on top thereof, when the ferromagnetic powder composition has been compacted into a part and heat treated. This enables heat treatment at higher temperatures.
  • the heat treatment at higher temperatures provides for more fully or completely releasing the stresses induced in the part when the part is manufactured from the ferromagnetic powder composition, and thus allows the part to obtain a lower coercivity.
  • the improved thermal stability may alternatively be viewed as the obtaining or maintaining of an improved coverage of the glassy coating formed from first coating and any second coating on top thereof, and thus obtaining or maintaining a higher electrical resistivity of the soft magnetic iron-based core particles and hence a lower coercivity.
  • parts manufactured from the ferromagnetic powder composition suffer less deterioration in properties, especially resistivity and core losses, when subjected to ageing due to the environment of the part such as elevated temperatures, e.g., 30-250°C, or corrosive gases or fluids.
  • the silicate, the particles of a compound comprising bismuth and oxygen, when present, and the dopant are all provided in the same first coating.
  • the particles of a compound comprising bismuth and oxygen, when present, are dispersed in the silicate.
  • the dopant is dissolved in the silicate.
  • the dopant is distributed as oxo- or hydroxy-anions in the silicate (a).
  • the oxo- or hydroxy anion of the dopant is provided, e.g. distributed, in the silicate (a).
  • the first coating comprises the dopant as oxo- or hydroxy-anions distributed in the silicate.
  • the dopant is dissolved in the silicate regardless of the state of the coating because the oxo- or hydroxy anion interacts with the silicate both in the first aqueous solution and in the first coating.
  • the first coating, and any second coating applied on top thereof react to form a glassy coating formed from the silicate and dopant with the particles of the compound comprising bismuth and oxygen, when present, dispersed therein.
  • the ferromagnetic powder composition comprises a plurality of soft magnetic iron-based core particles.
  • the soft magnetic iron-based core particles comprise or consist of iron or an alloy of iron comprising at least 90% iron, preferably at least 99% iron, more preferably at least 99.5% iron.
  • the alloy of iron may be alloyed iron Fe-Si having up to 7% by weight, preferably up to 3% by weight of silicon, or another alloy of iron selected from the groups Fe-AI, Fe-Si-AI, Fe-Ni, Fe-Co, Fe-Ni-Co, or combinations or mixtures of such alloys.
  • the soft magnetic iron-based core particles may comprise mixtures of particles such as mixtures of iron particles and iron alloy particles or a mixture of particles made from two or more iron alloys.
  • the soft magnetic iron-based core particles are made of essentially pure iron, i.e., iron with inevitable impurities.
  • at least 80 wt%, more preferably at least 90 wt%, of all of the core particles have a diameter in the range 20- 1000 pm, measured according to ISO 4497.
  • low to medium frequency applications such as electric motors, generators, and converters
  • at least 80 wt%, more preferably at least 90 wt% such as at least 99 wt%, based on the total weight of the core particles, of the core particles are in the range 45-150 pm (100 mesh corresponding to a D 5 o of approximately 95-100 pm), as measured according to ISO 4497.
  • at least 80 wt%, more preferably at least 90 wt% such as at least 99 wt%, based on the total weight of the core particles, of the core particles are in the range 75-380 pm (40 mesh corresponding to a D 5 o of approximately 180-210 pm), as measured according to ISO 4497.
  • the soft magnetic iron-based core particles may be spherical or irregular shaped, irregular shaped particles being preferred.
  • the AD apparent density
  • the soft magnetic iron-based core particles may be spherical or irregular shaped, irregular shaped particles being preferred.
  • the AD apparent density
  • the AD may be between 2.8 and 4.0 g/cm 3 , preferably between 3.1 and 3.7 g/cm 3 .
  • the soft magnetic iron-based core particles may be water atomized, gas atomized or a sponge iron powder. Generally, water atomized soft magnetic iron-based core particles are irregular shaped.
  • the first coating is at least partially covering and is in direct contact with the surface of the core particles.
  • the first coating covers all of the surface of at least 50 wt%, such as at least 75 wt% of the core particles in the ferromagnetic powder composition. More preferably, the first coating covers all of the surface of at least 90 wt%, such as at least 95 wt%, such as at least 99 wt% of the core particles in the ferromagnetic powder composition.
  • the first coating preferably covers at least 50%, such as at least 75%, more preferably at least 90%, such as at least 95%, such as at least 99% of the total surface area of the core particles.
  • the first coating, and the second coating when present has an average thickness in the range of 20-100 nm.
  • the typical total thickness of the first and the second coatings combined is about 20-200 nm with a permeability of about 400-600.
  • the coating thickness may be estimated from the permeability where a maximum relative magnetic permeability of about 3000 correspond to zero thickness and a maximum relative magnetic permeability of about 700 corresponds to a thickness of about 30 nm for 40 mesh core particles.
  • the silicate of the general formula (K 2 O)a(SiO2)p is a potassium silicate or alternatively named K-silicate, K-waterglass, potassium waterglass or simply herein silicate.
  • the p/a molar ratio (i.e., the molar ratio of SiC>2 to K2O) is in the interval from 0.5 to 4.1 .
  • the molar ratio p/a is in the interval of 2.0 to 3.75, more preferably the molar ratio p/a is in the interval of 2.5 to 3.5.
  • the molar ratio p/a may thus alternatively be in the interval of 2.0 to 4.1 .
  • the silicate is present in the amount 0.02 to 1 .0 wt%, more preferably 0.05-0.5 wt% calculated based on the total weight of the ferromagnetic powder composition.
  • the silicate is present in the amount 0.05-0.2 wt% calculated based on the total weight of the ferromagnetic powder composition when at least 80 wt%, based on the total weight of the core particles, of the core particles are 75 pm or more, and 0.1 -0.5 wt% calculated based on the total weight of the ferromagnetic powder composition when at least 80 wt%, based on the total weight of the core particles, of the core particles are below 75 pm.
  • the first coating may be applied as shown using an aqueous solution and it has been found that when the soft magnetic iron-based core particles are contacted with such a solution, substantially all of the silicate and all of the other components, such as the particles of a compound comprising bismuth and oxygen, when present, and nanoparticles, when present, end up in the first coating. Accordingly, contents and ratios between components in the aqueous solution and the soft magnetic iron-based core particles carry over to the contents and ratios between components in the first coating and the soft magnetic ironbased core particles.
  • the particles of a compound comprising bismuth and oxygen are optional, but it is preferred that they are included, i.e., comprised, in the first coating as they further improve the properties of the glassy coating formed from the silicate and dopant during heat treatment.
  • the particles of a compound comprising bismuth and oxygen when present, are dispersed in the first coating, e.g., dispersed in the silicate.
  • the particles of a compound comprising bismuth and oxygen react with the silicate and are included in the formed glassy coating.
  • the particles of a compound comprising bismuth and oxygen preferably comprise oxides and hydroxides of bismuth.
  • the D 5 o measured according to ISO 13320-1 is in the interval of 0.5 to 2 pm.
  • Example 8 shows that these ranges of content of the particles of the compound comprising bismuth and oxygen give good results.
  • the content of the particles of the compound comprising bismuth is preferably at least 0.15 wt%, such as 0.15-0.30 wt%.
  • the compound comprising bismuth and oxygen may be selected from the group consisting of bismuth(lll) oxide (Bi20s) and bismuth(lll) hydroxide (Bi(OH)3), wherein the compound comprising bismuth and oxygen preferably is Bi(OH) 3 .
  • the presence of Bi 2 O3 or Bi(OH) 3 particles increase resistivity. Further, as shown in Example 9, the resistivity is increased more for Bi(OH) 3 particles than for Bi 2 O 3 particles.
  • the D 5 O measured according to ISO 13320-1 is defined in ISO 13320-1 as the median particle diameter used on a volumetric basis, i.e., 50% by volume of the particles is smaller than this diameter and 50% is larger.
  • references herein to ISO-standards are equivalent to references to SS-ISO standards where SS merely indicates that the concerned ISO standard has been adopted as a Swedish standard.
  • the D 5 O measured according to ISO 13320-1 can be determined using e.g., a Mastersizer 3000 from Malvern instruments.
  • the dopant is dissolved as an oxo- or hydroxy anion in the silicate (a).
  • the oxo- or hydroxo-anion may be a mono- or poly-anion, preferably a mono-anion to maximize distribution in the silicate.
  • the use of a mono-anion may also decrease the risk of an increase of the melting temperature of the glassy coating formed from the first coating, and any second coating applied on top thereof, during the heat treatment. Specifically, it is contemplated that an increase in melting temperature could be caused by the presence of the longer poly-anions competing with the polysilicate ions in the glassy coating. Such an increase in melting temperature could make it more difficult to obtain a good distribution of the glassy coating.
  • the dopant being dissolved as an oxo-or hydroxy-anion encompasses that the dopant is an oxo- or hydroxy-anion dopant.
  • the term dopant encompasses both compounds that form an oxo-or hydroxy-anion when dissolved in the silicate or an aqueous solution of the silicate, as well as the oxo-or hydroxy-anions themselves.
  • the dopant may be a compound that forms oxo-or hydroxy-anions when dissolved in an alkaline aqueous solution.
  • the content of dopant may be from 0.5-30 mol%, preferably 1-30 mol%, more preferably 1 -25 mol% based on the molar content of K (Potassium) in the first coating.
  • the contacting of the soft magnetic iron-based core particles with the first aqueous solution may be performed by mixing, e.g., in a mixer.
  • the result of contacting the soft magnetic iron-based core particles with the first aqueous solution is that the first coating is formed on the magnetic iron-based core particles so as to at least partially cover the magnetic iron-based core particles.
  • the method according to the third aspect of the technology proposed herein produces soft magnetic iron-based core particles coated with the first coating, i.e., the ferromagnetic powder composition according to the first aspect of the technology proposed herein.
  • the soft magnetic ironbased core particles coated with the first coating and optionally also coated with the second coating as described below may alternatively be referred to as coated core particles or coated soft magnetic iron-based core particles.
  • the first coating further comprises nanoparticles having a D 5 o measured according to ISO 13320-1 of 10-200 nm, or alternatively having a specific surface area (SSA) of 6-120 m 2 /g as determined according to ISO 9277:2022.
  • SSA specific surface area
  • inclusion of the nanoparticles further improves resistivity of the glassy coating formed form the first coating and any second coating applied on top thereof. Inclusion of nanoparticles further work well together with the dopant.
  • the nanoparticles when present, are dispersed in the first coating, e.g., dispersed in the silicate. During and after heat treatment, the nanoparticles become embedded in the formed glassy coating.
  • the nanoparticles have a D 5 o measured according to ISO 13320-1 of 10-200 nm.
  • the D 5 O measured according to ISO 13320-1 is defined in ISO 13320-1 as the median particle diameter used on a volumetric basis, i.e., 50% by volume of the particles is smaller than this diameter and 50% is larger.
  • references herein to ISO-standards are equivalent to references to SS-ISO standards where SS merely indicates that the concerned ISO standard has been adopted as a Swedish standard.
  • the D 5 O measured according to ISO 13320-1 can be determined using e.g., a Mastersizer 3000 from Malvern instruments.
  • An alternative parameter for determining the size of the nanoparticles is the specific surface area (SSA) [m 2 /g], i.e., the surface area of the particles per g of particles.
  • a D 5 o measured according to ISO 13320-1 of 10-200 nm may be equivalently replaced by a specific surface area (SSA) in the range of 6-120 m 2 /g.
  • SSA specific surface area
  • the SSA for the nanoparticles is preferably determined using the BET-method, which is a method for determination of the specific surface area of solids by gas adsorption.
  • the SSA for the nanoparticles is preferably determined according to ISO 9277:2022. Accordingly, a D 5 o measured according to ISO 13320-1 of 10-200 nm may be equivalently replaced by a specific surface area (SSA) of 6-120 m 2 /g as determined according to ISO 9277:2022.
  • SSA specific surface area
  • the specific surface area (SSA) of the nanoparticles is 10-50, more preferably 10-30, most preferably 15-30 m 2 /g.
  • One example is 18 m 2 /g. As above, these ranges are preferably determined according to ISO 9277:2022.
  • the specific surface area may be measured using a Micromeritics TriStar 3000 gas adsorption instrument which calculates the BET surface area.
  • an average diameter for the nanoparticles may be calculated from the specific surface area if the particles are assumed to be spherical.
  • the equation for calculating the average particle diameter in nanometres is 6000/(BET surface area in m2 /g) x (density in g/cm3).
  • the specific surface areas of 120, 6, 50, 10, and 18 m2/g respectively yield the average diameters of 10, 200, 24, 120, and 67 nm respectively.
  • the nanoparticles have a D 5 o measured according to ISO 13320-1 of 10 -100 nm. Most preferably the nanoparticles have a D 5 o measured according to ISO 13320-1 of 20-100 nm.
  • the former interval corresponds to a SSA of 12-120 m 2 /g
  • the latter interval corresponds to a SSA of 12-60 m 2 /g.
  • the D 5 o measured according to ISO 13320-1 is preferably between 10 and 100, where 90 wt% of the particles shall have maximum diameters between 1 and 500 nm.
  • nanoparticles generally have a D 5 o of 10 nm, and this size of nanoparticles have been shown to provide the best results.
  • the nanoparticles may have diameters of 1 -200 nm, preferably 1 -50 nm, more preferably 5-50 nm, such as 30-50 nm or such as 5-20 nm such as 10 nm.
  • the nanoparticles are preferably selected from the group consisting of Y2O3 nanoparticles, Zr ⁇ 2 nanoparticles, ZnO nanoparticles, Mg(OH) 2 nanoparticles, MgO nanoparticles, CaCOs nanoparticles, AI2O3 nanoparticles, SiC>2 nanoparticles, and TiC>2 nanoparticles, and more preferably the nanoparticles comprise or consist of Y2O3 nanoparticles.
  • the nanoparticles may comprise a mixture of nanoparticles, such as a mixture of two or more of the listed nanoparticles. Presently, preferred is however that only one type of nanoparticles, e.g., preferably Y2O3 nanoparticles, is present in the first coating.
  • Example 8 shows that Y2O3 nanoparticles, also known as yttria nanoparticles and yttrium oxide nanoparticles, provides the currently considered best magnetic and electric properties.
  • the first coating comprises:
  • - 1 -20 mol% preferably 5-20 mol%, more preferably 10-20 mol% ZnO nanoparticles based on the content of K in the first coating, or - 1 -30 mol%, preferably 10-30 mol%, more preferably 15-25 mol% such as 20 mol% MgO nanoparticles based on the content of K in the first coating, or
  • Example 8 shows that these contents of the various nanoparticles give good results. As above, different nanoparticles according to these ranges may be combined in the first coating.
  • the nanoparticles comprise or consist of Y2O3 nanoparticles and the content of nanoparticles in the first coating is 10-20 mol% based on the molar content of K (Potassium) in the first coating.
  • Y2O3 nanoparticles provides the currently considered best magnetic and electric properties.
  • 20 mol% Y2O3 particles when included in a first coating comprising 0.1 wt% potassium silicate with a p/a molar ratio of 3.4 on 5 kg of soft magnetic iron-based core particles corresponds to 0.94 g Y2O3 particles, i.e., 0.0188 wt% based on the weight of the ferromagnetic powder composition.
  • the dopant comprises at least one element from group 5, such as V (Vanadium) or Nb (Niobium), or comprises at least one element from group 6, such as Cr (Chromium), W (Tungsten), or Mo (Molybdenum), or comprises Al (Aluminium) or P (Phosphorus).
  • group 5 such as V (Vanadium) or Nb (Niobium)
  • element from group 6 such as Cr (Chromium), W (Tungsten), or Mo (Molybdenum
  • Al Al (Aluminium) or P (Phosphorus).
  • Preferred elements of group 5 include V (Vanadium), Nb (Niobium), and Ta (Tantalum).
  • Preferred elements of group 6 include Cr (Chromium), Mo (Molybdenum), and W (tungsten).
  • Exemplary dopants include V (Vanadium), Nb (Niobium), Ta (Tantalum), Cr (Chromium), Mo (Molybdenum), W (tungsten), and P (phosphorous).
  • W tungsten
  • the group 5 and 6 elements are known to form oxo- or hydroxo-anions in alkaline water solutions.
  • Al Al
  • Phosphorus in the form of a phosphate e.g., KHPO4, H3 O4, (NH 4 ) 3 PO 4 can also be used.
  • Nb and Tantal can form oxo- and/or hydroxo-anions analogously to W, Mo and W.
  • Preferred dopants are those that are easily dissolved and stable in the silicate solution.
  • Toxic dopants such as ions including Cr(VI), are less preferred.
  • the dopant is preferably provided to the first coating by dissolving a suitable compound comprising the dopant, such as for example an oxide, in the first aqueous solution that the soft magnetic iron-based core particles is contacted with. This typically leads to the provision of ions of the dopant in the first aqueous solution.
  • Preferred elements for the dopant include Al, Nb, V, Mo, Cr. More preferred elements include Al and Nb.
  • V vanadium
  • V2O5 vanadium(V) oxide
  • the Vanadium will form predominantly (VC ) 3- ions (pH>12). This will lead to the provision of VO4 3 - ions in the first aqueous solution.
  • the vanadium tends to form polyvanadate ions coordinating more than four oxo- or hydroxo groups, such as (V n’, analogue to polyphosphate chains.
  • the size of the vanadate ions may vary dependent on the concentration of potassium and the pH of the silicate solution.
  • the dopant ion shall preferably not exist as polyanions in the silicate prior to heat treatment in order to maximize the atomic distribution of dopants in the final glassy coating, which may theoretically increase the specific electrical resistivity of the bismuthsilicate glass.
  • Mo molybdenum
  • Mo molybdenum
  • M0O3 molybdenum(VI) oxide
  • M0O4 2 molybdate ions
  • W tungsten
  • tungsten is preferably provided to the first coating by dissolving Tungsten(VI) oxide, WO3 in the first aqueous solution that the soft magnetic iron-based core particles is contacted with. This will lead to the provision of tungstate ions (WO4 2 ), analogue with the vanadate ions, in the first aqueous solution.
  • Al, Aluminium is preferably provided to the first coating by dissolving Aluminium(lll) hydroxide, AI(OH) 3 in the first aqueous solution that the soft magnetic iron-based core particles is contacted with. This will lead to the provision of AI(OH)4 _ ions in the first aqueous solution.
  • the dopant comprises V and the content of dopant in the first coating is 1-30 mol%, preferably 5-20 mol%, more preferably 5-15 mol%, based on the molar content of K (Potassium) in the first coating,
  • the dopant comprises Nb and the content of dopant in the first coating is 1 -30 mol%, preferably 5-20 mol%, more preferably 5-15 mol%, based on the molar content of K in the first coating,
  • the dopant comprises Cr and the content of dopant in the first coating is 1 -30 mol%, preferably 5-20 mol%, more preferably 5-15 mol%, based on the molar content of K in the first coating,
  • the dopant comprises Mo and the content of dopant in the first coating is 1 -30 mol%, preferably 5-20 mol%, more preferably 5-15 mol%, based on the molar content of K in the first coating,
  • the dopant comprises W and the content of dopant in the first coating is 1-30 mol%, preferably 5-20 mol%, more preferably 5-15 mol%, based on the molar content of K in the first coating,
  • the dopant comprises Al and the content of dopant in the first coating is 0.5-5 mol%, preferably 1 -3 mol%, more preferably 1 .71-2.58 mol% based on the molar content of K in the first coating, and/or,
  • the dopant comprises P and the content of dopant in the first coating is 1-30 mol%, preferably 5-20 mol%, more preferably 5-15 mol%, based on the molar content of K in the first coating.
  • the dopant comprises V and the content of dopant in the first coating is 1-30 mol%, preferably 5-20 mol%, more preferably 10-15 mol%, based on the molar content of K in the first coating.
  • the dopant comprises Al and the content of dopant in the first coating is 0.5- 5 mol%, preferably 1 -3 mol%, more preferably 1.5-2.7 mol% such as 1.71 -2.58 mol%, based on the molar content of potassium K in the first coating.
  • an Al dopant to the first coating at a concentration in this range allows higher heat treatment temperatures yielding lower coercivity while maintaining good resistivity.
  • the effect is less than for V, but Al has less environmental effect and presents a lesser health risk.
  • the ferromagnetic powder composition further comprises:
  • R2 may include one or more of the following functional groups: amine, diamine, amide, imide, epoxy, hydroxyl, ethylene oxide, ureido, urethane, isocyanato, acrylate, glyceryl acrylate, benzyl-amino, vinyl-benzyl-amino.
  • the R2 group may alter between any of the mentioned functional R2-groups and a hydrophobic alkyl group with repeatable units.
  • the monomer of the metal-organic compound may thus be selected from 3-aminopropyl-trimethoxysilane, 3- aminopropyl-triethoxysilane, 3-aminopropyl-methyl-diethoxysilane, N-aminoethyl-3- aminopropyl/ethyl/methyl-alkoxy-silane such as N-aminoethyl-3-aminopropyl- trimethoxysilane and N-aminoethyl-3-aminopropyl-methyl-dimethoxysilane, 1 ,7- bis(triethoxysilyl)-4-azaheptan, triamino-functional propyl-trimethoxysilane, 3-ureidopropyl- triethoxysilane, 3-isocyanatopropyl-triethoxysilane, tris(3-trimethoxysilylpropyl)- isocyanurate, 0-(propargyloxy
  • the metal-organic compound is an oligomer.
  • An oligomer of the metalorganic compound may be selected from alkoxy-terminated alkyl-alkoxy-oligomers of silanes, titanates, aluminates, or zirconates.
  • the oligomer of the metal-organic compound may thus be selected from methoxy, ethoxy or acetoxy-terminated amino-silsesquioxanes, amino-siloxanes, oligomeric 3-aminopropyl-methoxy-silane, 3-aminopropyl/propyl-alkoxy- silanes, N-aminoethyl-3-aminopropyl-alkoxy-silanes, or N-aminoethyl-3- aminopropyl/methyl-alkoxy-silanes or mixtures thereof.
  • Suitable metal-organic compounds in particular include Dynasylan® 1 146 and Dynasylan® SIVO 203 from Evonik Industries AG, or XIAMETERTM OFS-6020 Silane from Dow Chemical Company.
  • Water-borne amino- or multifunctional silane systems are also comprised by the metalorganic compound, such as the corresponding Dynasylan® HYDROSIL products supplied by Evonik industries AG.
  • the hydrolysable alkoxy-groups have almost fully been replaced with hydroxyl groups, i.e., as per Formula (II), while the functionality is similar, e.g., hydrophobic alkyl-groups in combination with amino- or diamino-alkyl-groups.
  • Examples include the Dynasylan® HYDROSIL 2627, 2776, and 1151 silane systems.
  • Examples of such compounds can be 1 ,3-Bis(3-aminopropyl)disiloxane-1 ,1 ,3,3-tetrol or (3-aminopropyl)( ⁇ [(propyl)dihydroxysilyl]oxy ⁇ )silanediol. It is further contemplated that a part, or all, of the particles of a compound comprising bismuth and oxygen and having a D 5 o measured according to ISO 13320-1 in the interval of 0.1 to 10 pm, which are optionally comprised by the first coating, may be provided in the second coating also or instead.
  • Example 8 shows that a variety of metal organic compounds in the second coating can be used successfully in the ferromagnetic powder composition.
  • the at least one metal-organic compound has the general formula (I).
  • the at least one metal-organic compound has the general formula (II).
  • the ferromagnetic powder composition preferably further comprises:
  • a lubricant preferably a particulate lubricant.
  • a lubricant in the ferromagnetic powder composition improves compaction and leads to an increased density and strength of an object manufactured from the ferromagnetic powder composition.
  • the lubricant may be selected from the group consisting of primary and secondary fatty acid amides, trans-amides (bisamides) or fatty acid amides or alcohols.
  • the lubricating moiety of the lubricant may be a saturated or unsaturated chain containing between 12-22 carbon atoms.
  • the lubricant may preferably be selected from stearamide, behenyl alcohol, erucamide, stearylerucamide, erucyl- stearamide, behenyl alcohol, erucyl alcohol, ethylene-bisstearamide (i.e., EBS or amide wax).
  • the lubricant is an amide wax.
  • Preferably is also a mixture of stearamide or behenyl alcohol and an amide wax.
  • One example is 0.1 wt% stearamide combined with 0.3 wt% amide wax.
  • the lubricant may be present in an amount of 0.05-0.80 wt%, preferably 0.20-0.40 wt% of the ferromagnetic powder composition. If a very low amount of lubricant is added in the composition (0.05 to 0.20 wt%), the compaction and ejection can be facilitated by using die wall lubrication (DWL). The low amount of internal lubricant will improve compact density, permeability and mechanical strength.
  • DWL die wall lubrication
  • the second aspect of the technology proposed herein concerns a ferromagnetic powder composition
  • a ferromagnetic powder composition comprising:
  • the further ferromagnetic powder composition comprises soft magnetic ironbased core particles that are different from the soft magnetic iron-based core particles of the ferromagnetic powder composition, and wherein preferably the soft magnetic iron-based core particles of the further ferromagnetic powder composition comprise or consist of an iron alloy having a higher electrical resistivity and/or hardness than the soft magnetic iron-based core particles of the ferromagnetic powder composition.
  • the soft magnetic iron-based core particles of the further ferromagnetic powder composition comprise or consist of an iron alloy having a higher electrical resistivity than the soft magnetic iron-based core particles of ferromagnetic powder composition, then the ferromagnetic powder mixture will have an even lower core loss at higher frequencies.
  • the soft magnetic iron-based core particles of the further ferromagnetic powder composition are typically also harder and may thus provide further improvements in properties.
  • the soft magnetic iron-based core particles of the further ferromagnetic powder composition preferably comprise or consist of an iron alloy selected from the group consisting of FeSi, FeAl, FeSiAl, FeNi, FeCo, and FeNiCo, or combinations or mixtures of such alloys.
  • FeSi typically 3-6.8 wt% Si
  • FeSiAl also known as Sendust; typically 9 wt% Si and 6 wt% Al, or alternatively 3.5wt% Si and 3wt% Al.
  • the content of the further ferromagnetic powder composition may be up to 60 wt% such as 30-60 wt%, but is typically from 10-50 wt%, such as from 20-40 wt%, such as 20-30 wt%, based on the weight of the ferromagnetic powder mixture with the ferromagnetic powder composition according to the first aspect of the technology proposed herein making up the remainder.
  • the content of the further ferromagnetic powder composition is preferably low or non-existent so as to not decrease density, magnetic induction and permeability.
  • the content of the further ferromagnetic powder composition may instead be increased up to 90 wt%.
  • the soft magnetic iron-based core particles of the ferromagnetic powder composition preferably comprises or consists of essentially pure iron, i.e., iron with inevitable impurities.
  • the further ferromagnetic powder composition further comprises a coating or surface treatment on the soft magnetic iron-based core particles therein.
  • the coating or surface treatment preferably comprises the first, and optionally also the second, coating as described above.
  • the soft magnetic iron-based core particles of the further ferromagnetic powder composition may be coated or treated with another coating, such as by being treated with phosphoric acid diluted in acetone.
  • the soft magnetic iron-based core particles or the further ferromagnetic powder composition preferably have the same particle sizes as the soft magnetic iron-based core particles of the ferromagnetic powder composition according to the first aspect of the technology proposed herein as described further above.
  • the method according to the third aspect of the technology proposed herein may further comprise one or more of the steps of:
  • Step (iii) is preferably performed after step (ii).
  • Step (iii) may be performed by heating the soft magnetic iron-based core particles while stirring.
  • Step (iv) is preferably performed after step (ii) or (iii), and before step (v).
  • Step (v) is preferably performed after step (iii) and step (iv).
  • the fourth aspect of the technology proposed herein relates to a method of manufacturing an object from the ferromagnetic powder composition according the first aspect of the technology proposed herein or the ferromagnetic powder mixture according to the second aspect of the technology proposed herein, comprising the steps of:
  • the compaction may be cold die compaction, warm die compaction, or high-velocity compaction, preferably a controlled die temperature compaction (50-120°C) with an unheated powder is used. During the compaction, the coated soft magnetic iron-based core particles are pressed together and deformed so as to adhere to each other and form the compacted part.
  • a controlled die temperature compaction 50-120°C
  • the particles of the compound comprising bismuth and oxygen together with the nanoparticles and the silicate in the first coating and the amino and/or alkyl groups of the metal-organic compound of the second coating form an evenly distributed bismuth-silicate glass on the surface of the soft magnetic iron-based core particles which provides the desired electrical resistivity between the individual particles of the compacted and heat treated ferromagnetic powder composition in the finished object. Additionally, the heat treatment relieves the stress formed during the compaction.
  • the heat treatment process may be in vacuum, non-reducing, inert or in weakly oxidizing atmospheres, e.g., 0.01 to 3 wt% oxygen in nitrogen.
  • an essentially pure nitrogen atmosphere is used as a non-reducing atmosphere.
  • 0-22 wt% oxygen preferably 0.5-2 wt% oxygen.
  • Higher temperature, above 680-700 °C, may require lower oxygen levels such as 500-3000 ppm (0.05-0.3 wt%).
  • the oxygen levels may be higher during the initial heating, e.g., delubrication.
  • the heat treatment is performed in an inert atmosphere and thereafter exposed quickly in an oxidizing atmosphere, such as 0.5-22 wt% oxygen/nitrogen mixtures or in steam/nitrogen mixtures, to build a superficial crust of higher strength and/or corrosion resistance.
  • the temperature may in one embodiment be up to 800°C.
  • Heat treating the compacted part at a temperature in the range 300-800 °C means that the temperature compacted part is exposed to a temperature in the range 300-800 °C. This is typically done for a time period sufficient to cause the compacted part to be heated to a temperature in the range 300-800 °C, such as for example 20-120 minutes.
  • the heat treating is performed in three phases: a delubrication stage at about 300-400°C during which the compacted part is heated up towards the curing stage, a curing stage at about 350-450°C (first temperature and time) in which the first coating is cured so as to cause the formation of the electrically insulating glassy coating (the silicate and any present silane is being polymerised to form the silicate glass) from the first, and second coating, when present, and a relaxation stage at 600-700°C (second temperature and time) in which the glassy coating flows out to cover the core particles and the stresses from the compaction was released.
  • the temperature in the range of 300-800 °C given for step (ii) above corresponds to this last (second) temperature.
  • the first and second time period may typically be 0-60 minutes each, such as 1-60 minutes.
  • the compacted part is further preferably heat treated at a temperature below the glass crystallisation temperature of the first coating. This is because crystallisation of the silicate in the coating layer may decrease the resistivity and mechanical strength of the silicate and the first coating. Further, crystallisation of the silicate in the first coating may cause cracks in the glassy coating formed by the first coating and the second coating during the heat treatment.
  • the heat treatment may comprise a delubrication stage, wherein the temperature during said delubrication stage may be between 400 and 500°C, such as 420-480°C, such as 430-470°C.
  • the atmosphere in the delubrication stage may be an inert atmosphere, such as an N 2 (g.) atmosphere.
  • step (ii) comprises heat treating the compacted part at a (second) temperature of at least 650°C, more preferably at least 670°C to substantially or fully eliminate the stress in the compacted part.
  • the temperature where maximum elimination of stress in the compacted part occurs is called the maximum relaxation temperature.
  • step (ii) accordingly comprises heat treating the compacted part at a (second) temperature of 670-700 °C, preferably 680-700 °C.
  • a thicker first coating i.e., a higher wt% of the silicate, such as 0.25 wt%, is used as such thicker coating provide acceptable remaining resistivity while having the potential to provide even better ageing properties.
  • ferromagnetic powder mixture comprising harder or alloyed particles which benefit from being treat at these higher second temperatures as that allows a higher degree of relaxation of the comparative less degree of plastic deformation during the compaction.
  • finer powders e.g., 200-300 mesh, may advantageously be coated with the thicker first coating as the resulting lower permeability is generally acceptable for the type of passive components in which these finer powders are typically used.
  • the inclusion of the dopant allows these high heat treatment step temperatures with corresponding low coercivity while maintaining acceptable resistivity and thus acceptable core loss.
  • the heat treatment may further comprise an initial preoxidation step in ambient air at between 200 and 250°C for 1-30 h, such as 2-18 h. This improves electrical resistivity.
  • the heat treating step (ii) may comprise the preoxidation step followed by delubrication at 400-500 °C in inert atmosphere (e.g. nitrogen), followed by curing and stress relaxation treatment at between 600 and 700 °C in between 5000 and 15000 ppm oxygen.
  • inert atmosphere e.g. nitrogen
  • curing and stress relaxation treatment at between 600 and 700 °C in between 5000 and 15000 ppm oxygen.
  • the object may alternatively be referred to as a part or a component.
  • the object may be selected from the group consisting of a soft magnetic component of a sensor, inductor, converter, transformer, electric motor, and a generator.
  • various ferromagnetic powder compositions comprising soft magnetic iron-based core particles according to the first aspect of the technology proposed herein were produced by coating the soft magnetic iron-based core particles with various first and second coatings as per various embodiments of the method according to the third aspect of the technology proposed herein.
  • the ferromagnetic powder compositions were then used to produce test parts or test objects which were compacted and heat treated according to various embodiments of the method according to the fourth aspect of the technology proposed herein.
  • the finished test parts were finally investigated for relevant properties such as resistivity Res and permeability p-max.
  • test parts used in the examples were produced in the following steps:
  • Step 1 Soft magnetic iron-based core particles were mixed (10 min) with an aqueous solution of a silicate of the general formula (K 2 O)a(SiO2)P (potassium silicate K12, Sibelco Nordic AB, p/a molar ratio of about 3.35, solids content 35 wt%) at a concentration (based on dry matter content) of about 0.11 wt% (0.165 wt% and 0.275 wt% also tested) to form the first coating on the core particles.
  • nanoparticles were included in the first coating, then these were Y2O3 particles (nominally 10 nm) at 20 mol% based on the content of K, unless otherwise specified.
  • the aqueous solution further contained one or more additional compounds or additives of interest as specified for each sample.
  • the core particles After the initial mixing, the core particles where dried while being stirred at 60°C for 1 h, followed by further drying without stirring at 120°C.
  • Step 2 The mixture from step 1 was mixed with a silane (oligomeric diaminofunctional silane Dynasylan® 1146 from Evonik Industries AG, 2.0 g and 1 g H2O (corresponding to 2 g silane per kg of core particles coated with the first coating) unless otherwise specified for 5 min so as to form the second coating, and the resulting mixture was dried at 50°C for 2 h to produce a finished ferromagnetic powder composition comprising coated soft magnetic iron-based core particles.
  • silane oligomeric diaminofunctional silane Dynasylan® 1146 from Evonik Industries AG
  • Step 3 A lubricant (0.4 wt% amide wax unless otherwise specified) was added to the ferromagnetic powder composition in order to facilitate producing the test part, and the ferromagnetic powder composition was then shaped and compacted (800 MPa with a die temperature of 100°C) into test parts which were heat treated as detailed for each sample to release stress from the compaction to form the finished test parts.
  • the soft magnetic iron-based core particles were a water atomized annealed iron powder having dimensions according to 100 mesh and an apparent density of 3.32 g/cm 3 unless otherwise stated.
  • the heat treatment was performed in three stages in a pre-heated furnace.
  • the three stages comprised a delubrication stage at about 300-400°C during which the compacted part was heated up towards the curing stage, a curing stage at about 350-450°C (first time and temperature given for each sample) in which the first and second coatings were cured so as to cause the formation of an electrically insulating silicate glass from the first and second coatings, and a relaxation stage at 600-700°C (second time and temperature given for each sample) in which the stress from the compaction was released and improved coverage of the glassy coating was obtained.
  • the oxygen partial pressure during the heat treatment was 15000 ppm (1 .5 wt% oxygen in nitrogen) unless otherwise specified.
  • Total core loss* (at 1 T/1 kHz) - total core loss for a test part obtained for a given induction and frequency [W/kg], Tor the measurement of magnetic properties, the square toroids were wound with 100 drive and 100 sense turns of resin coated copper wire (diameter 0.63 mm) and measured using a Brockhaus MPG 200D. References: IEC 60404-4 (DC measurements) and IEC 60404-6 (AC-measurements).
  • Example 1 Initial experiments with and without nanoparticles and dopant
  • Example 1 tested the effects of adding a dopant to a first coating containing a silicate and particles of a compound comprising Bismuth and oxygen. For further exploration, also nanoparticles were added to the first coating.
  • Table 1 illustrates the problems encountered when heat treating at higher temperatures. Whereas the sample part had a resistivity of 2158 p m when heat treated at up to 650°C, heat treating at the higher temperature of 670°C resulted in an about 86 times lower resistivity of 25 p m. Such a low resistivity is unacceptable for almost all applications.
  • Table 1 B With dopant
  • Table 1 D With dopant and nanoparticles The results in Table 1 D indicate that the nanoparticles and dopant together provide high resistivity at both the lower and the higher heat treatment temperature. Moreover, the results indicate that the dopant provides for retaining a higher proportion of the resistivity when using the higher temperature. As an example, the resistivity at the 670°C heat treatment for the addition of 10 mol% V dopant, i.e., 9345 p m, is about 5.3 times larger than for sample 1 -3 at the same temperature.
  • Tables 1 E shows results obtained for a higher concentration of silicate, i.e., a thicker first coating.
  • the results show, similar to table 1 D, that the addition of the dopant provides for retaining a higher proportion of the low temperature treatment resistivity also when using the even higher temperature of 680°.
  • Example 2 The addition of a V dopant in the first coatings ensures an acceptable electrical resistivity also after heat treating at elevated temperatures.
  • Example 2 further tested the effects of adding a V dopant (in the form of V2O5) to the aqueous solution of the silicate in step 1 when producing the coated soft magnetic ironbased core particles in step 2. All samples further contained, in the first coating, Y2O3 nanoparticles (nominally 10 nm) at 20 mol% (based on the molar weight of K) and bismuth hydroxide (Bi(OH 3 )) at a concentration of 0.12 wt%.
  • a V dopant in the form of V2O5
  • All samples further contained, in the first coating, Y2O3 nanoparticles (nominally 10 nm) at 20 mol% (based on the molar weight of K) and bismuth hydroxide (Bi(OH 3 )) at a concentration of 0.12 wt%.
  • the progressively higher maximum temperature in the heat treatment step provided progressively lower coercivity for the samples.
  • These latter samples however, and in contrast to the reference 1 B sample, maintained an acceptable resistivity even at the highest maximum temperature of 700°C.
  • the results show that the electrical resistivity increased with increasing content of dopant for each heat treatment.
  • Adding the V dopant, preferably at least 5 mol%, more preferably 10 mol% or even more preferably 15 mol%, to the solution used to obtain the first coating thus provides that parts manufactured from the ferromagnetic powder compositions can be heat treated at higher maximum temperatures, e.g. 680 and 700 °C so as to obtain coercivity values in the range of 132 to 134 while maintaining electrical resistivity values in the range of 1889 to 6214.
  • the successively lower coercivity values obtained for higher amounts of V points towards less stress being introduced in the coated soft magnetic iron-based core particles.
  • one possible mechanism is that the addition of the V2O5 compound to the solution used to obtain the first coating, and the subsequent surmised inclusion of VO - ions in the first coating, provides a more thermally stable first coating which is less susceptible to the formation of cracks during the heat treatment.
  • the improved thermal stability may have different reasons.
  • the dopant may i) enhance the specific electrical resistivity of the bismuth silicate glass. Higher specific resistivity of the glass would allow the use of a higher relaxation temperature that would decrease the viscosity of the formed glass that could facilitate an improved coverage of the particle surfaces.
  • the effect of dopant may also ii) decrease the glass forming temperature, and/or ill) decrease the viscosity of the glass that may in turn facilitate the distribution and particle coverage of the glass, and/or iv) cause less change in volume during the heat treatment or cooling protocol, which thereby may cause less formation of cracks. Cracks would expose the soft magnetic iron-based core particles to oxidation that would cause a relative enhancement of coercivity during the heat treatment but also as a result of ageing during usage in an application involving elevated temperatures.
  • the distribution of the first coating is further facilitated by the nanoparticles, which inter alia acts are believed to prevent the formation of cracks during the drying of the first coating.
  • both the Mo (M0O3) dopant and the Al (AI(OH) 3 ) dopant provides a higher resistivity than the reference at the heat treatment at 450/700°C.
  • These dopants thus, similarly to V, allows heat treatment at higher temperatures to reach lower coercivity values while retaining acceptable resistivity values.
  • W provides a similar, albeit lower, resistivity compared to the reference at 450/680°C but retains more of if its initial resistivity (6% vs 5% for the reference). It should also be noted that at the two highest temperatures all samples with dopants had a higher remaining resistivity percentage than the reference.
  • the dopants are effective also with different amounts of nanoparticles.
  • Example 5 Effects of thermal ageing Further experiments were made to determine the effect of thermal ageing on the properties of the test parts. As detailed by table 5A below, test parts manufactured from the powder produced with the 420/640°C, 450/680°C, and 450/700°C heat treatments were further held at 260°C for 5 days. Table 5A: Effects of thermal ageing
  • samples comprising the V dopant provided better ageing properties with higher resistivity values.
  • the samples that did not include a dopant had higher FeOx/Fe-ratio than the samples that included a dopant. Consequently, a low ratio facilitates an improved ageing resistance of the heattreated component thanks to an improved coverage of the glassy coating. This applied to all the tested dopants.
  • Aluminium e.g., from AI(OH) 3
  • further experiments were made to evaluate effects of dopant and increased amount of silicate in the first coating.
  • a silicate solution having a higher p/a ratio (3.82) was used to compensate for the decrease in p/a ratio when the AI(OH) 3 was dissolved with the help of extra KOH.
  • the Al dopant provided better resistivity than the reference at the higher temperature and higher silicate concentration. At the lower silicate concentration, the Al dopant provided lower but comparable resistivity to the reference.
  • Example 8 Variations of non-dopant constituents Further experiments were made to evaluate variations in the other components of the first coating in the absence of the dopant. Heat treatment was 450/650°C (30/30min). The results are shown in table 9 below:
  • the non-dopant constituents of the ferromagnetic powder composition can be varied widely.
  • Example 9 Schematic cross-sectional illustration of the particles of the ferromagnetic powder composition
  • Fig. 1 shows a highly schematical cross-sectional illustration of a single particle 10 of a ferromagnetic powder composition according to an embodiment of the first aspect of the technology proposed herein.
  • the particle 10 comprises a soft magnetic iron-based core particle 11 covered by a first coating 12 comprising a silicate.
  • a second coating 13 is also shown and comprises a metal-organic compound. Particles of a compound comprising bismuth and oxygen and having approximate diameters of about 1 pm, one of which is designated the reference numeral 14, are shown dispersed within the first coating 12. Additionally, nanoparticles having an approximate diameter of about 10-200 nm, one of which is designated the reference numeral 15, are also shown dispersed within the first coating 12. Finally, as designated by the reference numeral 16, a dopant is schematically shown dissolved in the silicate of the first coating 11 .
  • Fig. 1 shows the particle prior to heat treatment, i.e., prior to the ferromagnetic powder being compacted and heat treated to manufacture an object as per the method according to the fourth aspect of the technology proposed herein.
  • the particles of the compound comprising bismuth and oxygen 14 together with the nanoparticles 15 and the silicate with its dissolved dopant 16 in the first coating 12 and the amino and/or alkyl groups of the metal-organic compound of the second coating 13 are believed to form an evenly distributed glassy coating (bismuth-silicate glass) which provides electrical resistivity and improved mechanical strength between the individual particles of the compacted and heat treated ferromagnetic powder composition.
  • Fig. 1 shows the particles of the compound comprising bismuth and oxygen 14 being present in the first coating 12, it is contemplated that the particles of the compound comprising bismuth and oxygen 14 may additionally be dispersed within the second coating 13 or divided between the first and second coatings.
  • Fig. 1 shows the first coating 12 and the second coating 13 completely covering the soft magnetic iron-based core particle 11 , one or both of these coatings may alternatively cover the soft magnetic iron-based core particle 11 only partially.
  • Example 10 Addition of alloyed soft-magnetic powder to the ferromagnetic powder composition
  • Table 9 Addition of alloyed soft-magnetic powder
  • the reference sample (9-1 ) shows excellent density and mechanical strength, however, the coercivity and DC-loss is higher compared to the alloyed mixtures.
  • Sample 9-2 mixed with 30% FeSi-powder, can reduce the coercivity slightly. However, due to the decreased density (and permeability pmax), the DC-loss remains similar as the reference.
  • the sample 9-4 incl. 50% phosphate-coated FeSi-powder and a relatively thicker silicate coating on the essentially pure iron powder (0.165wt%), shows improved total core loss and DC-loss as compared to the reference sample.
  • Example 11 Increased mechanical strength
  • the ferromagnetic powder composition was as generally described above with 0.11 wt% silicate.
  • the lubricant was amide wax (EBS).
  • the standard treatment (Ref.) is performed in a fixed atmosphere where the internal lubricant is carefully removed (ca 400°C, 20min), directly followed by the curing and stress relaxation treatment (615°C, 20min).
  • the fixed atmosphere is normally between 0.5-1 .5% oxygen (5000-15000 ppm) in nitrogen.
  • the TRS is increased (A).
  • the resistivity is improved (C, E-l).
  • the TRS is further improved without increasing the coercivity (D vs. E).
  • Sample F and H provide the highest TRS.
  • a ferromagnetic powder composition comprising:
  • a first coating at least partially covering and being in direct contact with the surface of the core particles comprising: a. a silicate of the general formula (K 2 O)a(SiO 2 )P, wherein a is moles of K 2 O, P is moles of SiO 2 , and the p/a molar ratio is in the interval from 0.5 to 4.1 , i. wherein the silicate is present in an amount of 0.02 to 1 .0 wt% calculated based on the total weight of the ferromagnetic powder composition, b. optionally, particles of a compound comprising bismuth and oxygen having a D 5 O measured according to ISO 13320-1 in the interval of 0.1 to 10 pm, and, c. a dopant dissolved as an oxo- or hydroxy-anion in the silicate (a).
  • a silicate of the general formula (K 2 O)a(SiO 2 )P wherein a is moles of K 2 O, P is moles of SiO 2 ,
  • the ferromagnetic powder composition according to claim 1 wherein the first coating further comprises nanoparticles having a D 5 o measured according to ISO 13320-1 of I Q- 200 nm, or alternatively having a specific surface area (SSA) of 6-120 m 2 /g as determined according to ISO 9277:2022.
  • SSA specific surface area
  • nanoparticles are selected from the group consisting of Y 2 O3 nanoparticles, ZrO 2 nanoparticles, ZnO nanoparticles, Mg(OH) 2 nanoparticles, MgO nanoparticles, CaCOs nanoparticles, AI 2 Os nanoparticles, SiO 2 nanoparticles, and TiO 2 nanoparticles, and wherein the nanoparticles preferably comprise or consist of Y 2 O3 nanoparticles.
  • nanoparticles comprise or consist of Y 2 Os nanoparticles and wherein the content of nanoparticles in the first coating is 10-20 mol% based on the molar content of K (Potassium) in the first coating.

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  • Power Engineering (AREA)
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  • Manufacturing & Machinery (AREA)
  • Powder Metallurgy (AREA)
  • Soft Magnetic Materials (AREA)

Abstract

L'invention concerne une composition de poudre ferromagnétique comprenant (i) des particules de noyau à base de fer magnétique doux, et (ii) un premier revêtement, recouvrant au moins partiellement et étant en contact direct avec la surface des particules de noyau, comprenant a) un silicate de formule générale (K2O)α(SiO2)β, dans laquelle α est le nombre de moles de K2O, β est le nombre de moles de SiO2, et le rapport molaire β/α est dans l'intervalle de 0,5 à 4,1, dans laquelle le silicate est présent en une quantité de 0,02 à 1,0% en poids calculée sur la base du poids total de la composition de poudre ferromagnétique, b) éventuellement, des particules d'un composé comprenant du bismuth et de l'oxygène ayant un D50 dans l'intervalle de 0,1 à 10 µm mesuré selon la norme ISO 13320-1, et, c) un dopant dissous en tant qu'oxo- ou hydroxy-anion dans le silicate (a). Un second revêtement peut être fourni. L'invention concerne également des procédés de production de la composition et de fabrication d'un objet ainsi que des objets comprenant la composition.
PCT/EP2024/080274 2023-10-30 2024-10-25 Composition de poudre ferromagnétique et son procédé de production Pending WO2025093444A1 (fr)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE440486A (fr) * 1941-02-06 1941-03-31
US20140319406A1 (en) * 2011-08-31 2014-10-30 Kabushiki Kaisha Toshiba Magnetic material, method for producing magnetic material, and inductor element
EP2252419B1 (fr) 2008-03-20 2017-06-21 Höganäs Ab (publ) Composition de poudre ferromagnétique, et procédé de production correspondant
US10741316B2 (en) 2010-02-18 2020-08-11 Höganäs Ab (Publ) Ferromagnetic powder composition and method for its production
WO2020252551A1 (fr) 2019-06-19 2020-12-24 Universidade Federal De Santa Catarina Matériau particulaire pour l'obtention d'un composite magnétique doux et procédé de production de matériau particulaire pour l'obtention d'un composite magnétique doux
EP3411169B1 (fr) 2016-02-01 2021-01-20 Höganäs Ab (publ) Composition de poudre a base de fer

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE440486A (fr) * 1941-02-06 1941-03-31
EP2252419B1 (fr) 2008-03-20 2017-06-21 Höganäs Ab (publ) Composition de poudre ferromagnétique, et procédé de production correspondant
US10741316B2 (en) 2010-02-18 2020-08-11 Höganäs Ab (Publ) Ferromagnetic powder composition and method for its production
US20140319406A1 (en) * 2011-08-31 2014-10-30 Kabushiki Kaisha Toshiba Magnetic material, method for producing magnetic material, and inductor element
EP3411169B1 (fr) 2016-02-01 2021-01-20 Höganäs Ab (publ) Composition de poudre a base de fer
WO2020252551A1 (fr) 2019-06-19 2020-12-24 Universidade Federal De Santa Catarina Matériau particulaire pour l'obtention d'un composite magnétique doux et procédé de production de matériau particulaire pour l'obtention d'un composite magnétique doux

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