Soft ferromagnetic composite material, method for producing same and use thereof

Abstract

In particular, the invention relates to a composition for forming an electrically insulating coating on the surface of a substrate. The invention also relates to a method for preparing the composition and to the uses thereof, in particular for preparing a ferromagnetic composite material (SMC).

Description

[0001] DESCRIPTION

[0002] TITLE: SOFT FERROMAGNETIC COMPOSITE MATERIAL, ITS PREPARATION PROCESS AND ITS USE

[0003] Technical field of the invention

[0004] The invention relates to the field of ferromagnetic materials, in particular, soft ferromagnetic composite materials, or Soft Magnetic Composites (SMC) in English, which reduce eddy current losses in magnetic components, thus improving their magnetic properties.

[0005] In particular, the invention relates to a composition for forming an electrically insulating coating on the surface of a substrate. The invention also relates to a process for preparing said composition and its uses, notably for preparing a ferromagnetic composite material (SMC).

[0006] Technical background

[0007] It is well known that eddy currents are responsible for some of the losses (known as eddy current losses) in the magnetic circuits of AC machines and transformers. This is why magnetic circuits are made of laminated steel sheets to limit these currents and the resulting Joule heating losses, thereby improving the overall efficiency of transformers.

[0008] Traditionally, eddy current losses are reduced by confining them within the smallest possible structures. Rolled steel sheets fulfill this role by confining eddy currents within 2D (planar) structures in the microstructure.

[0009] Soft magnetic composites (SMCs) consist of a magnetic phase surrounded, at the microscopic level, by a dielectric phase. This design reduces eddy current losses (and therefore total losses) in magnetic components. The properties of SMCs are largely dependent on the nature of the phases and their distribution, which is why there is a wide variety of SMCs that meet diverse requirements in terms of magnetic, electrical, and mechanical properties for magnetic components.

[0010] The goal of sintered soft ferromagnetic composites (SMCs) is to confine these currents to the grain scale. Trade-offs are necessary to balance the magnetic, mechanical, and electrical performance of the SMCs.

[0011] Numerous publications exist showing:

[0012] - different development pathways for SMCs,

[0013] - the use of coatings of different types on ferromagnetic powders,

[0014] - SMC material characterizations.

[0015] Among the various approaches, several studies mention the use of tetraethylorthosilicate or TEOS (liquid) as a silica precursor, or the use of Fe2U3 or FesCM. Most often, the materials are manufactured by a flash sintering or SPS (Spark Plasma Sintering) process, after obtaining the composite powder.

[0016] However, many references describe cold or hot compaction while attempting to avoid degrading the insulating phase, which may be a phosphate or, in some cases, an organic insulator. Notable examples include the work of Wu et al. and Liu et al., who use TEOS as a silica precursor, but via a complex FCVD (Fluidized Bed Chemical Vapor Deposition) process.

[0017] There is therefore a need for a soft ferromagnetic composite material (SMC) in which the integrity of the insulating layer surrounding the magnetic phase is preserved during the various stages of its implementation (sintering, annealing, etc.), thus reducing eddy current losses.

[0018] In particular, there is a need for a ferromagnetic composite material as described above that is compatible with use at high temperatures, for example above 450°C. In addition, there is a need for a ferromagnetic composite material as described above whose manufacture is industrially attractive from the point of view of cost and ease of implementation.

[0019] Summary of the invention

[0020] The present invention is specifically designed to meet these needs by providing a composition for forming an electrically insulating coating on the surface of a substrate, comprising:

[0021] (a) of a silicon-based preceramic polymer precursor;

[0022] (b) of a compound comprising an iron oxide selected from FesCM and Fe2O3, or a mixture thereof;

[0023] (c) of a ferromagnetic metal selected from iron, cobalt, nickel and their alloys selected from iron-nickel, iron-silicon, iron-aluminium, iron-cobalt alloys, soft ferrites selected from manganese-zinc, nickel-zinc.

[0024] Polymer-derived ceramics (PDCs) are a class of materials obtained from the pyrolysis of a precursor polymer, called a preceramic polymer, with a silicon-based backbone. The success of these materials lies in the possibility of shaping them using techniques employed for polymers and obtaining ceramic properties after pyrolysis. The families of ceramics obtained are those based on silicon, such as silicon carbide (SiC), silicon nitride (SiSn4), and a wide range of glasses such as silicon carbonitrides (Si). x N4C y , silicon oxycarbons (SiO x C y ) and silicon oxynitrides (SiO x N y ), silicon-boron carbonitrides (SiBCN) and their composites. The electrical properties of these PDCs make them compatible as insulating phases in SMCs.

[0025] The composition of the invention makes it possible to obtain an insulating phase between the grains, which resists temperature once implemented.

[0026] The hardness of the materials (HV) comprising a composition according to the invention is greater than 225HV, a value never before achieved. The use of the pre-ceramic polymer makes it possible to maintain the integrity of the insulating layer surrounding the magnetic phase during the different stages for the implementation (sintering, annealing etc.) of the soft ferromagnetic composite material (SMC), thus reducing eddy current losses.

[0027] Another object of the invention is a method for preparing a composition according to the invention, characterized in that – by wet method – it comprises the following steps:

[0028] A1) the silicon-based preceramic polymer precursor (a), the compound comprising an iron oxide (b) and the ferromagnetic metal (c) and optionally the silica precursor and the coupling agent are mixed, B1) the mixture obtained in step A1) is dissolved or suspended in an anhydrous solvent selected from anhydrous ethanol, methyl ethyl ketone (MEK), xylene.

[0029] C1) The solvent is evaporated at a temperature between 40 and 60 °C, under vacuum, and

[0030] D1) we retrieve the composition;

[0031] Or

[0032] - by dry method, it includes the following steps:

[0033] A2) the silicon-based preceramic polymer precursor (a), the compound comprising an iron oxide (b) and the ferromagnetic metal (c) and optionally the silica precursor and the coupling agent are mixed in a three-dimensional mixer or mill, and

[0034] B2) we retrieve the composition.

[0035] Around the magnetic phase there is a deposit of the preceramic polymer, which is not yet silica because it has not been heat-treated. It is still the polymer that forms a coating around the grains of the magnetic powder.

[0036] The resulting composition is then shaped to produce a soft ferromagnetic composite material (SMC).

[0037] Another object of the invention relates to a soft ferromagnetic composite material (SMC) comprising:

[0038] (p) a silicon-based dielectric ceramic; (b) a ferromagnetic metal selected from iron, cobalt, nickel and their alloys selected from iron-nickel, iron-silicon, iron-aluminum, iron-cobalt alloys, soft ferrites selected from manganese-zinc, nickel-zinc; (c) a compound comprising an iron oxide selected from FesCM and Fe2Os, or a mixture thereof.

[0039] The soft ferromagnetic composite material (SMC) is prepared by a process comprising the following steps:

[0040] (i) preparation of a composition according to the invention by the process described above;

[0041] (ii) sintering the composition obtained in step (i), by a process of

[0042] - Flash sintering or SPS (Spark Plasma Sintering) (as shown in Figure 3) with

[0043] o a heating speed of 20 to 200K / min, preferably 50 to 100K / min, with a break in slope at 20K / min before the high-temperature plateau,

[0044] o a mechanical pressure of 10 to 80 MPa, preferably 50 to 75 MPa, applied from the start of the heating cycle, o a pressure increase and decrease over 30 seconds, with a pressure decrease 1 minute before the end of the high-temperature plateau,

[0045] at a temperature between 1000°C and 1150°C, and

[0046] o a high-temperature holding time between 0 and 60 minutes; - conventional sintering, or

[0047] - hot pressing with the same parameters as for SPS; and (iii) relaxation annealing (as shown in Figure 4) with

[0048] - a heating speed of 3K / min under H2,

[0049] - a plateau at 1150°C under H2 and 2 to 6 hours of temperature maintenance, - a descent at 3K / min under Ar.

[0050] This forms another object of the invention.

[0051] The electrical insulating coating formed on the surface of the grains of ferromagnetic compounds can have a thickness of between 0.5 and 1 pm.

[0052] The invention further relates to the use of a soft ferromagnetic composite material (SMC) as defined above, or obtained by a process as defined above, for the manufacture of inductors, transformers, and electromagnets.

[0053] Brief description of the figures

[0054] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the attached drawings in which:

[0055] [Fig. 1] represents an image obtained by Zeiss NVision 40 scanning electron microscopy in backscattered electron mode of the mixture of components in powder state (before densification) of the composition according to the invention.

[0056] These images show a composition with an insulating coating at the grain boundaries. Three different shades of gray are visible in the image:

[0057] Light grey: the largest grains correspond to Fe-3Si. Small grains of this colour can also be seen in the darkest grey phase.

[0058] Dark gray: SiÛ2

[0059] Intermediate grey: Fe3Û4

[0060] [Fig. 2] represents an image obtained by Zeiss NVision 40 scanning electron microscopy in backscattered electron mode of the microstructure of the soft ferromagnetic composite material according to the invention obtained after flash sintering or SPS, carried out in an FCT model HP-D5 or FCT model HP-D25 sintering furnace, on parts of diameter 20 or 30 mm indifferently at a temperature of 1050°C, at a pressure of 70 MPa, for 30 minutes, and annealed for 2 hours at a temperature of 1150°C in a hydrogen furnace, of the Elnik brand.

[0061] [Fig. 3] represents the SPS sintering cycles. The temperature and pressure cycles used can be seen. A vacuum is created before the start of the cycle.

[0062] [Fig. 4] represents the conditions for carrying out the relaxation annealing step of the composite material, which reduces stresses in the material and improves its magnetic and mechanical properties. The thermal cycle and the atmospheres applied during annealing can be seen.

[0063] [Fig. 5] represents the magnetic properties of the composite material according to the invention with:

[0064] - the sample numbers are on the x-axis;

[0065] - the frequency is represented by a color scale; and

[0066] - on the ordinate, the mass losses for each sample.

[0067] The numerical value at the top of each bar is also the ordinate (mass losses).

[0068] [Fig. 6] shows the values ​​of hysteresis and eddy current losses. These are the mass losses in W / kg as a function of the magnetic field strength in T (B(T) or induction). The frequency scale represents the frequency at which the losses are measured.

[0069] Extrapolations are made from a total loss model. The model coefficients allow us to extrapolate the loss values ​​(by hysteresis and by eddy currents) to other pairs of values ​​(f, B) not measurable by our instruments.

[0070] < < >< < > < < < > <

[0071]

[0072] Loss values ​​are measured (in some cases only, before and after annealing).

[0073] The best experimentally measured loss value is 2W / kg for a sample prepared as follows:

[0074] The composition is a mixture of 87% by weight of Fe-3Si + 13% by weight of a mixture of 50% by volume of Silres MK (polysilsesquioxane) + 50% by volume of FesCM powder, prepared by wet method,

[0075] Sintering 1050°C / 30 minutes / 70 MPa / Vacuum

[0076] Annealing 1150°C - 2h (Ar and H2 atmosphere, see annealing diagram of [Fig.

[0077] 4]) in an Elnik brand oven. These conditions correspond respectively to the temperature of the bearing, the bearing time, the mechanical pressure and the atmosphere in the sintering chamber (the vacuum is an air vacuum of approximately 1 Pa).

[0078] The cycle is the one shown in [Fig. 3],

[0079] [Fig. 7] represents the mechanical properties of the soft ferromagnetic composite material according to the invention. The abscissa represents Vickers hardness, and the ordinate represents total mass losses in W / kg.

[0080] [Fig. 8] represents the Vickers hardness of the samples prepared (on the x-axis are the references of the measured samples, similarly I have a table which summarizes the preparation conditions of each sample).

[0081] [Fig. 9] represents the microstructure of a SiCN - FesCM composite pyrolyzed at 600°C and 1100°C prepared by Saha et al. (“Polymer-derived SiCN composites with magnetic properties”, J. Mater. Res., vol. 18, no. 11, p. 2549-2551, Nov. 2003, doi: 10.1557 / JMR.2003.0356).

[0082] Detailed description of the invention

[0083] The present invention relates to a composition for forming an electrically insulating coating on the surface of a substrate, comprising:

[0084] (a) of a silicon-based preceramic polymer precursor;

[0085] (b) of a compound comprising an iron oxide selected from FesCM and Fe2O3, or a mixture thereof;

[0086] (c) of a ferromagnetic metal selected from iron, cobalt, nickel and their alloys selected from iron-nickel, iron-silicon, iron-aluminum, iron-cobalt alloys, soft ferrites selected from manganese-zinc, nickel-zinc. In one embodiment, the substrate is Fe-3 Si (Fe-3 wt% Si).

[0087] Silicon-based preceramic polymer precursor (a)

[0088] The silicon-based preceramic polymer precursor (a) is a molecular precursor that undergoes heat treatment, typically at a temperature between 150 and 300°C, to produce a preceramic polymer after polymerization. This polymer can then be partially or completely converted into an amorphous or crystalline ceramic during a second heat treatment or a second thermal plateau at a higher temperature, generally between 450 and 1300°C.

[0089] The precursor of silicon-based preceramic polymer is notably a monomer or a pre-polymer, that is to say an oligomer capable of undergoing further polymerization.

[0090] The preceramic polymer precursor can notably be applied to the surface of a powder, to lead, after heat treatment, to a polymer-derived ceramic coating or PDC for Polymer Derived Ceramic in English.

[0091] Preferably, the silicon-based preceramic polymer precursor is chosen from among polysiloxane, polysilazane, polycarbosilazane, polycarbosilane, polyborosiloxane, polyborosilane, and polyborosilazane precursors. After pyrolysis, these preceramic polymers will lead, respectively, to silicon oxycarbide (SiCO3), silicon nitride (SiSn4), silicon carbonitride (SiNC), and silicon carbide (SiC).

[0092] Preferably, the preceramic polymer precursor is a polysiloxane, polycarbosilane, or polysilazane precursor. Examples include:

[0093] Polycarbolisane: SMP 10 marketed by Starfire System; Polysiloxane: Silres H44 or Silres MK marketed by Wacker;

[0094] Polysilazane: Durazane 1500 or Durazane 1800 marketed by the company Merck.

[0095] The silicon-based preceramic polymer precursor (a) is advantageously in powder form, in particular with a particle size such that 50% of the particles of the compound have a diameter of less than 50 pm, preferably less than 10 pm, in particular between 1 and 10 pm, i.e. a Dso diameter of between 1 and 10 pm.

[0096] Within the framework of the invention, the measurement of the particle size distribution is carried out using a laser particle size analyzer.

[0097] The compound comprising an iron oxide (b) Compound (b) comprises an iron oxide selected from FesCM and Fe2Os, or a mixture thereof. It ensures continuity of magnetic flux in the electrically insulating phase and increases the effective magnetic cross-section of the composite.

[0098] Preferably, compound (b) is FesCM.

[0099] According to one embodiment, compound (b) comprises from 1 to 10% by weight, preferably from 1.5 to 8% by weight of an iron oxide as defined above, relative to the total weight of the composition.

[0100] The compound comprising an iron oxide (b) is advantageously in powder form, in particular with a particle size such that 50% of the particles of the compound have a diameter less than 50 nm, preferably less than 10 nm, in particular between 1 and 10 nm, i.e. a diameter Dso between 1 and 10 nm.

[0101] Ferromagnetic metal (c)

[0102] The presence of the ferromagnetic metal (c) gives a strong magnetizing capacity to the composition and the composite.

[0103] As stated above, the ferromagnetic metal (c) is chosen from iron, cobalt, nickel and their alloys chosen from iron-nickel, iron-silicon, iron-aluminum, iron-cobalt alloys, soft ferrites chosen from manganese-zinc, nickel-zinc.

[0104] Preferably, compound (c) is Fe-3 Si % by weight of Si.

[0105] The ferromagnetic metal (c) is advantageously in powder form, in particular with a particle size such that 90% of the particles of the compound have a diameter less than 100 pm, in particular between 1 and 100 pm, i.e. a diameter Dgo between 1 and 100 pm.

[0106] Proportion of constituents (a), (b) and (c) of the composition

[0107] According to one embodiment, the silicon-based preceramic polymer precursor (a) represents 1 to 20% by weight, preferably 4 to 16% by weight, relative to the total weight of the composition.

[0108] According to one embodiment, compound (b) represents strictly greater than 0 (0<) to 50% by weight, preferably from 0.1 to 50% by weight, more preferably from 10 to 50% by weight, relative to the weight of the silicon-based preceramic polymer precursor (a). According to one embodiment, compound (b) represents from 0.5 to 10% by weight, preferably from 1.5 to 7.5% by weight, relative to the total weight of the composition.

[0109] According to one embodiment, the ferromagnetic metal (c) represents 80 to 99% by weight, preferably 92 to 98% by weight, relative to the total weight of the composition.

[0110] Table 1 shows some examples of compositions according to the invention. Table 1

[0111]

[0112] In one embodiment, the composition of the invention further comprises,

[0113] - a silica precursor selected from tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), and / or

[0114] - a coupling agent chosen from polyethylene glycol (PEG), polyvinyl alcohol (PVA).

[0115] The silica precursor is mainly used as a crosslinking agent in silicon-based polymers and as a precursor to silicon dioxide.

[0116] The coupling agent can be used to improve adhesion and compatibility between the different components of the composition.

[0117] According to one embodiment, the composition comprises from 1 to 30% by weight, preferably from 5 to 10% by weight of silica precursor relative to the total weight of the composition. According to one embodiment, the composition comprises from 1 to 30% by weight, preferably from 1 to 10% by weight of coupling agent relative to the weight of the ferromagnetic metal.

[0118] Method for preparing the composition according to the invention

[0119] The invention also relates to a method for preparing a composition according to the invention comprising the following steps:

[0120] - via the wet method, it includes the following steps:

[0121] A1) the silicon-based preceramic polymer precursor (a), the compound comprising an iron oxide (b) and the ferromagnetic metal (c) and optionally the silica precursor and the coupling agent are mixed, B1) the mixture obtained in step A1) is dissolved or suspended in an anhydrous solvent selected from anhydrous ethanol, methyl ethyl ketone (MEK), lexylene.

[0122] C1) The solvent is evaporated at a temperature between 40 and 60 °C, under vacuum, and

[0123] D1) we retrieve the composition;

[0124] Or

[0125] - by dry method, it includes the following steps:

[0126] A2) the silicon-based preceramic polymer precursor (a), the compound comprising an iron oxide (b) and the ferromagnetic metal (c) and optionally the silica precursor and the coupling agent are mixed in a three-dimensional mixer or mill, and

[0127] B2) we retrieve the composition.

[0128] More specifically, the process for preparing a composition according to the invention comprises the following steps:

[0129] - by wet method comprising the following steps:

[0130] A1-1) The silica precursor and the coupling agent are dissolved in an anhydrous solvent chosen from anhydrous ethanol, methyl ethyl ketone (MEK), xylene,

[0131] with mechanical agitation (e.g., a paddle mixer) to form Mixture 1,

[0132] A1-2) the silicon-based preceramic polymer (a) is dissolved in the same anhydrous solvent to form Mixture 2, B1) the ferromagnetic powder is added to Mixture 1 and stirred for a given time (15 minutes to 2 hours at room temperature (20°C),

[0133] C1) Mixture 2 is added to Mixture 1,

[0134] D1) The compound containing an iron oxide (b) is added and stirring is continued for 1 to 24 hours

[0135] E1) The solvent is evaporated at a temperature between 40 and 80 °C, under vacuum.

[0136] F1) we retrieve the composition;

[0137] Or

[0138] - by dry method comprising the following steps:

[0139] A2) the silicon-based preceramic polymer precursor (a), the compound comprising an iron oxide (b) and the ferromagnetic metal (c) and optionally the silica precursor and the coupling agent are mixed in a three-dimensional mixer or mill,

[0140] B2) we retrieve the composition.

[0141] At this stage, the composition is a homogeneous mixture if the different components are in powder form. If the preceramic precursor (a) is in liquid form, the composition is in the form of a paste.

[0142] In the wet process, if no silica precursor or coupling agent is used, in step B1) the ferromagnetic powder (c) is put into Mixture 2.

[0143] In one embodiment, the composition according to the invention or obtained by the process as described above, is in powder form having a particle size such that 50% of the particles of the compound have a diameter (D50) between 15 and 45 pm.

[0144] According to one embodiment, in the composition

[0145] (a) the silicon-based preceramic polymer precursor as described above;

[0146] (b) the compound comprising an iron oxide as described above;

[0147] (c) the ferromagnetic metal as described above,

[0148] are dispersed, notably in solution or suspension, in an organic solvent. The organic solvent is, in particular, a solvent capable of dissolving the preceramic precursor (a). The compound (b) and the metal (c) are generally suspended in the solvent. This can be chosen from anhydrous ethanol, Diestone®, or methyl ethyl ketone (MEK).

[0149] Soft ferromactite composite material (SMC)

[0150] Another object of the invention is a soft ferromagnetic composite material (SMC) comprising:

[0151] (π) a silicon-based ceramic;

[0152] (b) a ferromagnetic metal selected from iron, cobalt, nickel and their alloys selected from iron-nickel, iron-silicon, iron-aluminium, iron-cobalt alloys, soft ferrites selected from manganese-zinc, nickel-zinc; (c) a compound comprising an iron oxide selected from FesCM and Fe2O3 or a mixture thereof.

[0153] The constituents (b) and (c) are as defined previously.

[0154] As mentioned previously, the ceramic families (p) can be silicon carbide (SiC), silicon nitride (SiSn4), and a wide range of glasses such as silicon carbonitrides (Si) x N4C y , silicon oxycarbons (SiO x C y ) and silicon oxynitrides (SiO x N y ), silicon-boron carbonitrides (SiBCN) and their composites.

[0155] According to one embodiment, the ceramic (p) is a silicon nitride (SiSiS), a silicon carbonitride (SiCN), a silicon oxycarbide (SiCO) or a silicon carbide (SiC).

[0156] Method for preparing soft ferromactite composite material (SMC) according to the invention

[0157] The soft ferromagnetic composite (SMC) material according to the invention can be prepared by a process comprising the following steps:

[0158] (i) preparation of a composition according to the invention by the process described above;

[0159] (ii) sintering the composition obtained in step (i), by a process of

[0160] - flash sintering or SPS (Spark Plasma Sintering), - conventional sintering, or

[0161] - hot pressing; and

[0162] (iii) relaxation annealing. According to one embodiment, sintering (ii) is flash sintering or SPS sintering. According to one embodiment, the conditions used for flash sintering or SPS sintering are:

[0163] Pressure: from 5 to 75 MPa,

[0164] Temperature from 1000 to 1150°C,

[0165] Maintenance time: from 0 to 120 minutes,

[0166] Heating speed: from 25 to 100°C.

[0167] The stress-relief annealing step (iii) aims to minimize residual stresses in the structure and reduce the risk of dimensional changes during subsequent manufacturing operations or the material's final use. It is carried out by heating, holding, and slow cooling. The temperature is chosen according to the material.

[0168] The originality of this process lies in the use of an organic precursor (a), which is a silicon-based preceramic polymer precursor, for the insulating layer. This precursor is a ceramisable polymer, which transforms into an amorphous ceramic during the successive processing steps (sintering).

[0169] The use of silicon-based preceramic polymer precursor (a) has the following advantages over known prior art precursors.

[0170] It allows for a cold shaping step

[0171] - by coating the powders (with or without solvent),

[0172] - by powder-to-powder mixing in the case of solid precursors available in powder form (Silres MK, commercial product based on polysilsesquioxane).

[0173] The silicon-based preceramic polymer precursor (a) is converted into a ceramic in a subsequent processing step. The conversion can be carried out in one step or in two steps (crosslinking, then pyrolysis). Crosslinking can be performed:

[0174] - on the ferromagnetic powder functionalized by a heat treatment at 200 or 250°C;

[0175] - on the SMC composite after cold pressing, or during hot pressing (temperatures 200 - 250°C). The ferromagnetic powder is Fe-x Si (with x between 2 and 10% by weight) or FeCo.

[0176] Pyrolysis is carried out on the SMC composite after pressing (with or without crosslinking) or during pressing in a single-step process (SPS sintering for example).

[0177] This involves in-situ pyrolysis during the sintering stage (whether it be SPS sintering, conventional sintering, or hot pressing).

[0178] The use of a precursor (a) makes it possible to consolidate the SMC by sintering while preserving the integrity of the insulating layer around the ferromagnetic grains. The resulting materials (SMC) are compatible with high-temperature applications, i.e., temperatures above 450°C, which is not the case with conventional organic insulating layers (phosphates, for example).

[0179] The method for depositing the insulating layer on the ferromagnetic powder used is inexpensive compared to some CVD or FCVD (fluidized bed CVD) deposition methods.

[0180] The organic precursors (a) used are available in a wide variety, allowing adaptation to the processing conditions (sintering temperature) of ferromagnetic powders (sintering temperatures can vary depending on the Si content in Fe-xSi (with x between 2 and 10 wt%), FeCo, FeCoV, FeAISi, FeCrSi). Furthermore, chemical modifications of the precursors (a) can enable the grafting of heteroatoms and the incorporation of electrically insulating but magnetically conductive phases into the insulating layer of SMC composites.

[0181] Example by Saha et al. Saha et al.

[0182] Saha et al. (J. Mater. Res., vol. 18, no. 11, pp. 2549-2551, Nov. 2003, doi:

[0183] 10.1557 / JMR.2003.0356) prepared SiCN-Fe composites from a liquid precursor (Ceraset®, polysilazane) into which they incorporated different contents of α-FesCM ferrite particles. After crosslinking (400°C / N2), then hot compression (400°C / N2 in a graphite mold) and finally pyrolysis for 9 h under N2 between 600°C and 1100°C, they obtained composites resistant to oxidation up to 500°C with an inexpensive method and a FesCM filler content of 70% by volume. The magnetic properties and microstructure of the composites are presented in [Fig. 9], The invention also relates to the use of a soft ferromagnetic composite material (SMC) as defined above, or obtained by a process as defined above, for the manufacture of inductance, transformer, and electromagnet.

[0184] EXAMPLES

[0185] Two examples of implementation are given below.

[0186] Example 1:

[0187] A material and its manufacturing process comprising:

[0188] The mixture

[0189] A ferromagnetic powder (Fe-3 wt% Si, or Fe-x wt% Si with x = [0, 12]), or FesoCoso or Fe49Co49V2, and FeAISi, FeCrSi, Powder used:

[0190] Atomized Fe powder with x% by weight of Si. Particle size 10-45 µm, grades used for additive manufacturing. Several references used from Carpenter and Ducal.

[0191] Atomized Fe-CoV powder, particle size 10-45pm.

[0192] Sandvik Osprey grade:

[0193]

[0194] <

[0195] <

[0196] <

[0197] <

[0198]

[0199] GSrade DUCAL (a chemical variation of the Co rate compared to the desired theoretical rate of 50% by weight is noted).

[0200]

[0201] These two powders were custom-made by the suppliers for the needs of the invention; they are not commercially available, off-the-shelf products.

[0202] A ceramisable polymer precursor from the polysiloxane, polycarbosilane, polysilazane family. 4-16% by weight relative to the total weight of the composition.

[0203] Polysiloxanes: Wacker Silres MK resin, or Silres H44 Polycarbosilanes: Starfire system: SMP-10

[0204] Polysilazanes: Merck Durazane 1500 or Durazane 1800

[0205] An oxide powder (Fe2O3, FesCM, Sigma aldrich) (0 to 50% by weight relative to the weight of ceramic precursor) -> From 10 to 50% by weight relative to the total weight of PDC (Polymer derived ceramic).

[0206] A silica precursor (TEOS - sigma aldrich) - (optional) - rate: 5-10 wt.%

[0207] A coupling agent such as PEG or PVA - (optional) - rate: 10 wt.% Powder preparation method

[0208] Dry mixing (gentle grinding (100 rpm, 15 min) in a planetary mixer or three-dimensional mixer of the constituents.

[0209] Mixing with an anhydrous solvent (e.g., anhydrous ethanol) followed by evaporation of the solvent using a rotary evaporator (60°C max). Part manufacturing method

[0210] - Spark plasma sintering (using an FCT HPD-5 or 25 machine). Note that any other machine model may be suitable (SUGA, Fuji, Dr Fritsch, etc.).

[0211] - [1050°C / 50MPa / 10'] (ideally) for Fe-xSi. The conditions can be extended to T=[1000 - 1150°C], P= [5-80MPa], t = [0-1200 min];

[0212] - [750°C / 50MPa / 10'] (ideally) for FeCo and FeCoV. The conditions can be extended to T=[750-970°C], P= [5-75MPa], t = [0-120 min]

[0213] - Conventional sintering;

[0214] - Stress relief annealing (Kiln used: Elnik MIM 3000)

[0215] - 1150 - 2 to 6 hours, H2 then Ar, heating and cooling @3K / min - Properties of the materials produced:

[0216] - Total losses in W / kg.

Claims

1. CLAIMS 1. Composition for forming an electrically insulating coating on the surface of a substrate, comprising: (a) of a silicon-based preceramic polymer precursor; (b) of a compound comprising an iron oxide selected from Fe3O4 and Fe2Os, or a mixture thereof; (c) of a ferromagnetic metal selected from iron, cobalt, nickel and their alloys selected from iron-nickel, iron-silicon, iron-aluminium, iron-cobalt alloys, soft ferrites selected from manganese-zinc, nickel-zinc.

2. Composition according to claim 1, characterized in that the silicon-based preceramic polymer precursor is selected from polysiloxane, polysilazane, polycarbosilazane, polycarbosilane, polyborosiloxane, polyborosilane and polyborosilazane precursors.

3. Composition according to claim 1 or 2, characterized in that the substrate is Fe-3 Si (Fe-3% by weight of Si).

4. Composition according to any one of claims 1 to 3, characterized in that it further comprises, - a silica precursor selected from tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), and / or - a coupling agent chosen from polyethylene glycol (PEG), polyvinyl alcohol (PVA).

5. Composition according to any one of claims 1 to 4, characterized in that the silicon-based preceramic polymer precursor (a) represents 1 to 20% by weight, preferably 4 to 16% by weight, relative to the total weight of the composition.

6. Composition according to any one of claims 1 to 5, characterized in that it comprises an amount of compound (b) strictly greater than 0 (0 <) to 50% by weight, preferably 0.1 to 50% by weight, more preferably 10 to 50% by weight, relative to the weight of the silicon-based preceramic polymer precursor (a).

7. Composition according to any one of claims 1 to 6, characterized in that the ferromagnetic metal (c) represents from 80 to 99% by weight, preferably from 92 to 98% by weight, relative to the total weight of the composition.

8. Composition according to claim 4, characterized in that the composition comprises from 1 to 30% by weight, preferably from 5 to 10% by weight of silica precursor, relative to the total weight of the composition.

9. Composition according to any one of claims 4 or 8, characterized in that the composition comprises from 1 to 30% by weight, preferably from 1 to 10% by weight of coupling agent relative to the weight of the ferromagnetic metal.

10. A method for preparing a composition according to any one of claims 1 to 9, characterized in that - by wet method comprising the following steps: A1) the silicon-based preceramic polymer precursor (a), the compound comprising an iron oxide (b) and the ferromagnetic metal (c) and optionally the silica precursor and the coupling agent are mixed, B1) the mixture obtained in step A1) is put into solution or suspension in an anhydrous solvent chosen from anhydrous ethanol, methyl ethyl ketone (MEK), lexylene. C1) The solvent is evaporated at a temperature between 40 and 60 °C, under vacuum, and D1) we retrieve the composition; or- by dry method comprising the following steps: A2) the silicon-based preceramic polymer precursor (a), the compound comprising an iron oxide (b) and the ferromagnetic metal (c) and optionally the silica precursor and the coupling agent are mixed in a three-dimensional mixer or mill, and B2) we retrieve the composition.

11. Composition according to any one of claims 1 to 9, or obtained by the process of claim 11, characterized in that it is in powder form having a particle size distribution such that 50% of the particles of the compound have a diameter (Dso) between 15 and 45 pm.

12. Soft ferromagnetic composite material (SMC) comprising: (p) a silicon-based ceramic; (b) a ferromagnetic metal selected from iron, cobalt, nickel and their alloys selected from iron-nickel, iron-silicon, iron-aluminium, iron-cobalt alloys, soft ferrites selected from manganese-zinc, nickel-zinc; (c) a compound comprising an iron oxide selected from FesCM and Fe2O3, or a mixture thereof.

13. Material according to claim 12, characterized in that the ceramic (p) is a silicon nitride (SisN4), a silicon carbonitride (SiCN), a silicon oxycarbide (SiCO) or a silicon carbide (SiC).

14. A method for preparing a material according to claim 12 or 13, characterized in that it comprises the following steps: (i) preparation of a composition according to the invention by a process according to claim 10; (ii) Sintering of the composition obtained in step (i), by a process of - flash sintering or SPS (Spark Plasma Sintering), - conventional sintering, or - hot pressing; and (iii) relaxation annealing.

15. Use of a soft ferromagnetic composite material (SMC) according to any one of claims 12 or 13, or obtained by a process as defined in claim 14, for the manufacture of inductance, transformer, and electromagnet.

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