Classifications

• • 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
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/12—Both compacting and sintering
• • 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
• • 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
  • H01F1/14—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
• • 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
• • 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
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • 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

Definitions

• the present invention relates to the technical field of the coating of metal particles, in particular metal iron, with a ferrite layer, in particular of the NiZn type. More particularly, the present invention relates to the technical field of coating processes of iron metal particles with a NiZn type ferrite layer and such particles. The present invention also relates to the technical field of processes for manufacturing articles sintered from ferromagnetic material particles coated with a NiZn type ferrite coating and such articles.
• the soft magnetic materials are used in applications such as inductors, stators, rotors for electromagnetic motors, actuators, sensors and transformer cores. These soft magnetic materials are generally iron-based and are used because of their magnetic properties and electrical insulation.
• one solution is to reduce the thickness of the soft magnetic materials.
• layers of soft magnetic material are stacked alternately with insulating layers.
• the eddy currents are reduced in a direction perpendicular to the surface of the layers.
• the article obtained does not have sufficiently high electrical resistivities. Indeed, the highest electrical resistivities that could actually be measured on the commercially available particles and in particular the reference particles in this technical field only reach 800 ⁇ / m. Moreover, the coatings used have no magnetic property, which affects the performance of the article produced with such particles. In addition, the losses by hysteresis are high when the frequency of the electric currents used exceeds a value of the order of kHz, for example the losses are about 1400 W / kg for 1T at 2kHz for reference particles obtained in the trade.
• Ferrite (masculine term), ceramic material based on iron III and iron II (Fe 3 0 4 ), is a magnetic material with high electrical resistivity (up to 10 5 ⁇ / m) compared to other metallic magnetic materials, which has led to its use as a magnetic core for high-frequency and high-speed applications.
• Ferrite has also been used in the manufacture of iron particles coated with ferrite, in particular of the NiZn type, as described in US 2004/0238796.
• the authors of this paper started from carbonyl iron-based spherical fine particles which they coated with ferrite by immersing them in a solution comprising salts of iron (II) chloride, nickel (II) chloride and chloride of zinc (II) and whose oxidative properties have been suppressed by adding nitrogen gas.
• the reaction was carried out under ultrasound.
• An oxidant NaN0 2 was used to oxidize ferrous (Fe 2+ ) ions to ferric ions (Fe 3+ ).
• the pH of the solution was monitored throughout the reaction with NH 4 OH to keep it at 6.
• the temperature was maintained at 80 ° C by heat bath.
• the present inventors have attempted to reproduce the teaching of this document and in particular to manufacture iron particles coated with ferrite NiZn.
• the particles obtained were unfortunately not homogeneously coated; which led to disappointing results in terms of electrical resistivity.
• the structure of the ferrite material NiZn was not preserved or was not completely crystallized.
• one of the objectives of the present invention is to overcome at least one of the above disadvantages in order to ultimately obtain an electrically insulating article with interesting magnetic properties.
• the present invention proposes a process for coating particles of ferromagnetic material with a NiZn type ferrite layer, the process comprising:
• the ferrite precursors may be an iron precursor, a nickel precursor and a zinc precursor.
• the precursors are chlorides of iron, nickel and zinc.
• the coating can be carried out with at least one of the following conditions:
• the method may further include forming an intermediate layer of silica on the surface of the particles prior to coating.
• the formation of the silica intermediate layer can be carried out by deposition of silica on the surface of the particles.
• the present invention also provides double-coated ferromagnetic material particles consisting of a core of a ferromagnetic material surrounded by an intermediate silica layer on which a NiZn-type ferrite layer is disposed.
• the present invention further provides a method of manufacturing a sintered article comprising:
• the present invention also provides a sintered article in one of the following ways:
• a material comprising particles of ferromagnetic material surrounded by a ferrite coating of NiZn type comprising less than 10% by weight of FeZnO;
• a material comprising particles of a double-coated ferromagnetic material consisting of a core of a ferromagnetic material surrounded by an intermediate layer of silica on which is disposed a NiZn-type ferrite layer.
• FIG. 2 schematically illustrates particles made of a ferromagnetic material, in particular the examples given above, coated with a ferrite layer of the NiZn type, and obtainable by means of a particular implementation of the method according to the invention; ;
• FIG. 3 is a photograph showing particles of the type of those of FIG. 2;
• FIG. 4 schematically illustrates double-coated ferromagnetic material particles consisting of a core made of a ferromagnetic material surrounded by an intermediate layer of silica on which the NiZn-type ferrite layer is disposed; and obtainable by another particular implementation of the method according to the invention.
• FIG. 5 is a photograph of the structure of a sintered object from the powder of particles of ferromagnetic material obtained from the process of the invention; and - Figure 6 is a schematic illustration of the picture of Figure 5.
• ferromagnetic materials are ferromagnetic metals and ferromagnetic alloys.
• Ferromagnetic metals include iron metal, cobalt metal and nickel metal; metal iron being the most preferred among ferromagnetic metals.
• iron-containing alloys such as iron-silicon alloys (Fe 1-x Si x , 0 ⁇ x ⁇ 3.2), iron-nickel (Fe 2+, 1> ⁇ > 0, 3) and iron-cobalt (Fe x Co x 25 ⁇ x ⁇ 50), the manganese-containing alloys such as MnSb and MnAs, etc.
• Preferred ferromagnetic materials are iron metal and iron alloys. In the case where the ferromagnetic material is iron metal, it is preferably in the allotropic form of iron.
• ferrite denotes neither iron allotropy, nor an alloy of iron (allotropy a) and carbon (which is otherwise a feminine term). Ferrite has a very high electrical resistivity characteristic compared to other magnetic metal materials and has been widely used as a magnetic core for high frequency and high speed applications.
• Such a method comprises:
• the particles of ferromagnetic material by contacting the activated ferromagnetic material particles with ferrite precursors, at a temperature of between 20 ° C. and 65 ° C., preferably between 40 ° C. and 60 ° C., more preferably between 52.5 ° C and 57.5 ° C, still more preferably at about 55 ° C; and in an oxidizing environment, the pH being controlled to a value of between 5 and 7, advantageously between 6 and 7; and
• the pH is controlled by means of a pH corrector during the entire duration of the coating reaction, that is to say when the activated ferromagnetic material particles are brought into contact with the ferrite precursors.
• activation is meant herein the formation of hydroxy group on the surface of the particles of ferromagnetic material due to the interaction between the acid and the ferromagnetic material of the particles.
• the acids that can be used are hydrochloric acid, nitric acid, citric acid, or their mixture.
• the preferred acid is hydrochloric acid.
• a preferred mixture is a mixture of hydrochloric acid and nitric acid, especially at a ratio HCl: HNO 3 of 3: 1.
• the acid is used at a concentration suitable for activation of the particle to take place.
• concentrations for hydrochloric acid, mention may be made of concentrations of 0.02 mol / L or 0.2 mol / L, preferably 0.02 mol / L; for nitric acid, 0.02 mol /; for citric acid, 1 mol / L or 2 mol / L.
• the usable acid concentrations are those presented in the following table:
• Acid or mixture Total acid concentration to acid (mol / L) HC1 0.001-1
• the duration of the activation step generally depends on the concentrations of the acids used and is advantageously between 30 s and 30 min. In particular, it is preferably at least 12.5 min, preferably less than 30 min, still preferably between 12.5 and 17.5 min, more preferably about 15 min, especially at a concentration of 0.2 mol / l for hydrochloric acid and nitric acid or 1 mol / L for citric acid.
• the activation step would be futile because the surface state of the particles would be identical to the surface of the particles that have not been activated. Beyond 30 min, the results would not be substantially improved compared to the induced cost.
• the particles are preferably rinsed to remove all traces of acid and then dried.
• the coating step is performed by contacting the particles of activated ferromagnetic material with ferrite precursors.
• Ferrite precursors are chemical species that by a chemical reaction between them form ferrite on the surface of particles. They are advantageously an iron precursor II, a nickel precursor II and a zinc precursor IL For each element iron, nickel and zinc respectively, at least one precursor of iron, nickel and zinc respectively, but more than one precursor may be used . The number of precursors is furthermore not necessarily identical for each of the elements iron, nickel and zinc.
• the ferrite precursors may be iron (II), nickel (II) and Zn (II) salts, such as halides or nitrides.
• the iron, nickel and zinc halides are, for example, for iron, iron (II) fluoride, iron (II) chloride, iron (II) bromide, iron iodide (II), the iron (II) astature or a mixture of these; for nickel, nickel (II) fluoride, nickel (II) chloride, nickel (II) bromide, nickel (II) iodide, nickel (II) astature or a mixture of those -this ; and for zinc, zinc fluoride (II), zinc (II) chloride, zinc (II) bromide, zinc (II) iodide, zinc (II) astature or a mixture of them.
• the ferrite precursors are iron (II), nickel (II) and zinc (II)
• the ferrite precursors are advantageously in solution, preferably in aqueous solution.
• the iron precursor is in a concentration which makes it possible to have an Fe 2+ ion concentration of between 1 and 0.05 mol / l, preferably between 0.5 and 0.1 mol / l, more preferably between 0.4 and 0. 2 mol / L, for example about 0.25 mol / L.
• the nickel precursor is in a concentration making it possible to have an Fe 2+ : Ni 2+ ion ratio of between 1: 1 and 15: 1, preferably between 2: 1 and 10: 1, more preferably between 3: 1 and 5: 1, for example 4: 1.
• the zinc precursor is in a concentration making it possible to have an Fe 2+ : Zn 2+ ion ratio of between 1: 1 and 15: 1, preferably between 2: 1 and 10: 1, more preferably between 3: 1 and 5: 1, for example 4: 1.
• the placing in contact is preferably carried out in two stages, firstly the solution of the ferromagnetic material particles in solution and then the introduction of the ferrite precursors into the solution containing the particles of ferromagnetic material in order to prevent the ferrite precursors. react with each other and rush.
• the contacting can nevertheless be carried out in two stages, firstly with the solution of the ferrite precursors in solution and then the introduction of the ferromagnetic material particles into the solution containing the ferrite precursors.
• the placing in contact can be carried out in a single step with the concomitant solution of the ferrite precursors and the particles of ferromagnetic material.
• the contacting time advantageously lasts 30 minutes to 5 hours, preferably 45 minutes to 2 hours, more preferably 1 hour to 1.5 hours, for example about 80 minutes.
• the pH corrector is a composition comprising one or more chemical species whose addition to a solution causes a change in pH.
• the pH corrector is advantageously a base.
• Basic examples are hydroxides such as potassium hydroxide (KOH) and sodium hydroxide (NaOH).
• the pH corrector is added during the coating reaction to maintain the pH at a desired level.
• the pH corrector can be added continuously or discontinuously at regular time intervals.
• the addition of pH corrector in a continuous manner is preferred because it makes it possible to avoid raising the pH favoring the growth of the ferrite precipitates.
• the amount of base added which is preferably KOH, can be adjusted so that the ratio n Fe : n base minute is between 50 and 250, preferably between 100 and 200, more preferably between 120 and 250. and 175, eg about 150, e np being the initial amount of Fe 2+ ion in the mixture and n t, ase the average amount of base added per minute.
• the oxidizing environment is advantageously obtained by adding an oxidant during the coating reaction.
• the oxidant are nitrites such as sodium nitrite (NaN0 2 ), nitrates such as NaN0 3 , peroxides such as hydrogen peroxide (H 2 O 2 ) or ambient air.
• the oxidant is added during the coating reaction to control the oxidation of Fe 2+ ions to Fe 3+ at a desired rate, for example continuously or discontinuously at regular time intervals.
• the pH corrector is added continuously, respectively discontinuous at regular time intervals
• the oxidant is added continuously, respectively discontinuous at regular time intervals.
• the amount of oxidant added which is preferably NaN0 2
• the amount of oxidant added may be adjusted so that the ratio nF e : n 0 xydant minute is between 200 and 350, preferably between 225 and 325, more preferably between 250 and 300, eg about 280, n Fe being the initial amount of Fe 2+ ion in the mixture and n oxy ant of the average amount of base added per minute.
• a preferred combination of a pH corrector and an oxidant is a mixture of KOH and NaN0 2 added during the coating reaction at the ratios indicated above.
• the process advantageously comprises rinsing the coated ferrite particles and drying them to obtain a powder.
• the method may also include forming an intermediate layer of silica on the surface of the ferromagnetic material particles prior to coating, for example by sol-gel (for example using tetraethyl orthosilicate (TEOS) in basic solution).
• TEOS tetraethyl orthosilicate
• the silica layer has the advantage of limiting, or even preventing, the diffusion of the ferrite inside the ferromagnetic material particles during the subsequent sintering step by creating a barrier protecting the particles of ferromagnetic material. This protection is obtained even at high sintering temperature, for example at 900 ° C.
• This step of forming an intermediate layer of silica is advantageously carried out after the activation of the ferromagnetic particles and on rinsed particles in order to remove any physisorbed elements.
• the process advantageously comprises rinsing the particles coated with silica and drying them before contacting with the ferrite precursor.
• the particles 1 obtainable by this process are particularly particles made of a ferromagnetic material 11, in particular the examples given above, coated with a ferrite layer 13 of the NiZn type (see FIGS. 2 and 3).
• the particles made of ferromagnetic material 11 preferably have a mean diameter of between ⁇ and 500 ⁇ . In the case where the particles 11 are not spherical, this mean diameter is the diameter of a sphere whose volume would be equal to the average volume of the particles.
• the ferrite layer 13 is preferably the thinnest possible, especially with a thickness less than 5 ⁇ , or even less than 4 ⁇ , or about 3 ⁇ .
• This ferrite layer 13 is advantageously continuous over substantially the entire surface of the particle, Le. on more than 75% of the surface of the particle, preferably more than 80, more preferably more than 90% or even more than 99%.
• these particles 1 are also double-coated ferromagnetic material particles consisting of a core 11 made of a ferromagnetic material surrounded by an intermediate layer of silica 12 on which the ferrite layer is placed. 13 NiZn type whose characteristics are the same as those of the NiZn type ferrite layer mentioned above (see Figure 4).
• the core 11 preferably has a mean diameter of between ⁇ and 500 ⁇ . In the case where the particles are not spherical, this mean diameter is the diameter of a sphere whose volume would be equal to the average volume of the cores.
• the intermediate layer of silica 12, for its part, is preferably the thinnest possible, in particular with a thickness of less than 250 nm, more preferably less than 200 nm, or even less than 150 nm, or even approximately 100 nm.
• This silica intermediate layer 12 is advantageously continuous over substantially the entire surface of the particle. on more than 75% of the surface of the particle, preferably more than 80%, still more preferably more than 90% or even more than 99%.
• the ferrite layer 13 is advantageously continuous over substantially the entire surface of the silica intermediate layer, Le. on more than 75% of the surface of the particle, preferably more than 80%, still more preferably more than 90% or even more than 99%.
• These ferromagnetic material particles coated with NiZn type ferrite, with or without an intermediate layer of silica can be used for the production of sintered articles.
• the particles are shaped by compression according to known rules of the art in order to obtain a preform having the desired shape of the article and then the preform is sintered.
• the sintering is advantageously carried out at a temperature of between 450 and 1000 ° C., preferably between 475 and 950 ° C., and preferably between 500 ° C. and 900 ° C., for example 500 ° C., 650 ° C. or 900 ° C.
• the sintering may be carried out under ambient atmosphere, but advantageously under a protective atmosphere, or inert, for example under nitrogen.
• the present invention also relates to a sintered article made of a material comprising particles of ferromagnetic material surrounded by a ferrite coating of NiZn type comprising less than 10% by weight of iron-zinc oxide (FeZnO), preferably between 2 and 9 %, preferably less than 5%, alternatively less than 1% or even 0%. These percentages being expressed relative to the total mass of the sintered article.
• This sintered article is advantageously obtained from the above manufacturing method using ferromagnetic material particles defined above. The structure of such an object is illustrated in FIGS. 5 and 6. In these figures, the particles made of ferromagnetic material 11 (even before coating) and the sintered ferrite 13 'originating from the ferrite coating 13 are still visible. Thus, unlike what happens with the coated particles of the prior art described in the preamble, the structure of ferromagnetic material particles surrounded by ferrite is retained.
• the present invention also relates to a sintered article made of a material comprising particles of a double-coated ferromagnetic material consisting of a core made of a ferromagnetic material surrounded by an intermediate silica layer on which a NiZn-type ferrite layer is placed.
• the sintered article preferably comprises less than 10% by weight of iron-zinc oxide (FeZnO), preferably between 2 and 9%, preferentially less than 5%, alternatively less than 1% or even 0%. These percentages being expressed relative to the total mass of the sintered article.
• the amount of silica is preferably less than 1% by weight, preferably between 0.8 and 0.1%, between 0.5 and 0.2%, about 0.3%. These percentages being expressed relative to the total mass of the sintered article.
• This sintered article is advantageously obtained from the above manufacturing method using particles of ferromagnetic material with double coating defined above.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Power Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Compounds Of Iron (AREA)
• Hard Magnetic Materials (AREA)
• Soft Magnetic Materials (AREA)

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• 2015
  • 2015-03-04 FR FR1551816A patent/FR3033271B1/fr not_active Expired - Fee Related
• 2016
  • 2016-03-03 EP EP16713538.3A patent/EP3265257A1/de not_active Withdrawn
  • 2016-03-03 WO PCT/FR2016/050497 patent/WO2016139431A1/fr active Application Filing

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