DE102018125270A1 - Process for producing a ceramic material with a locally adjustable permeability gradient, its use in a coating process and its use - Google Patents

Abstract

The invention relates to a method for producing a ceramic material with a locally adjustable permeability gradient, its application in a coating method, material processing method and its use. The object of providing a material which is suitable for conducting and isolating magnetic fields and can be used in magnetic coupling elements is achieved by a method for producing a ceramic material with a locally adjustable permeability gradient, the method comprising the following steps: of a ceramic material by heating a starting material composition to a temperature below the melting temperature of the starting material composition, cooling the generated ceramic material to room temperature after a defined cooling rate to set a vortex density in the produced ceramic material, and subsequent local temperature treatment to heat the ceramic Material over its ferroelectric order temperature and for setting the local permeability gradient.

Description

The invention relates to a method for producing a ceramic material with a locally adjustable permeability gradient, its application in a coating method and its use.

So far, the ferro- or ferrimagnetic materials have been of particular importance due to their high permeability for conducting magnetic fields and as a magnetic insulator. 1a shows the schematic representation of a conductor for DC and AC magnetic fields in ferro- or ferrimagnetic layers 1 on a substrate 2nd . A disadvantage, however, is the finite magnetization hysteresis of ferromagnetic or ferrimagnetic materials, which determines part of the losses of magnetic field conductors made of a ferromagnetic or ferrimagnetic material, especially when conducting AC magnetic fields.

If an area is to contain few magnetic field lines and poorly conduct magnetic fields, then this area must have a lower permeability than the adjacent areas (middle area in 3b , 5b ). If, on the other hand, an area is to contain many magnetic field lines and conduct magnetic fields well, then this area must have a greater permeability than the adjacent areas (middle area in 3a , 5a ).

Magnetic reversal losses occur in the ferromagnetic or ferrimagnetic materials, these being made up of eddy current losses and hysteresis losses. Eddy current is a current that is induced in an extended electrical conductor in a magnetic field that changes over time, or in a moving conductor in a magnetic field that is constant over time and therefore spatially inhomogeneous. This displaces the current from the center of the conductor at high frequencies and large cross sections (skin effect). The skin effect mainly occurs at high signal frequencies. It causes only the outside of the conductor to contribute to the current flow. The skin effect is based on the shielding effect of electrically conductive materials against electromagnetic fields. The skin effect can be largely prevented by using high-frequency braid. In the case of HF strands, a conductor is replaced by the parallel connection of individual conductors which are electrically insulated from one another and interwoven.

Every transformer hums more or less audibly during operation. The reason for this is magnetostriction. With magnetostriction, the core of the transformer is forced into tiny changes in length. Magnetostriction is a material property and is ΔV / V ₀ = -3, 252 · 10 ^-4 in ceramic materials with charged domain walls ( T. Chatterji et al., J. Phys .: Condens. Matter 24 (2012) 336003), ΔV / V ₀ = -0, 26 · 10 ^-4 in amorphous Fe ₃₅ Co ₃₅ Si ₁₁ B ₁₉ (SA1) and ΔV / V ₀ = -1.20 · 10 ^-4 in Fe-Si 0.3 .

Hysteresis losses result from the work that has to be done, for example to re-magnetize a coil core of a transformer in the rhythm of the frequency. The lower the specific resistance of the transformer core, the higher the losses. The specific resistance is a material property and is in ceramic materials with charged domain walls p = 73 to 141 Ωm (specific resistance of an RLC sample), p = 10 to 100 Ωm in amorphous SA1 and p = 10 to 100 Ωm in Fe-Si 0.3.

The power losses of an EI 800/800/400 three-phase transformer for 500 kVA operated under full load with different core materials as a magnetic conductor (operation under full load) are made up of copper losses and iron losses. Table 1 shows the power dissipation of a three-phase transformer operated at full load for 500kVA with different core materials. Tab. 1: material Copper losses / W Iron losses / W Induction / T Efficiency /% Fe-Si 0.35 1602 2696 1.5 99.06 Fe-Si 0.30 1599 2442 1.5 99.12 amorphous SA1 2916 174 1.2 99.33

The iron loss when remagnetizing is $$W=\pi J_p^{\mathrm{2nd}}{\mu }^{\text{'}\text{'}}/\left({\mu }^{\text{'}\mathrm{2nd}}+{\mu }^{\text{'}\text{'}\mathrm{2nd}}\right).$$

wobei δ der Verlustwinkel ist. Magnetisches Eisen hat typische Verlustfaktoren im Bereich von d = 0,08 ... 0,60 (Tab. 3, page 8, Determination of electromagnetic properties of steel for prediction of stray losses in power transformers). Der Verlustfaktor d der keramischen Materialien mit geladenen Domänenwänden, welche einen RLC-Parallel-Schwingkreis bilden, wird aus dem Gütefaktor Q eines RLC-Parallel-Schwingkreises $$Q=R\surd \left(C/L\right)$$

wie folgt bestimmt: d = 1/Q und liegt im Bereich von d = 0,36 ... 1,38. Die Resonanzfrequenz f₀ $$f_0=\left(1/2\pi \right)\sqrt{1/\left(LC\right)}$$

beträgt f₀ = 64 MHz ... 107 MHz, wobei der Hochfrequenzbereich (HF) zwischen 30 kHz ... 300 MHz definiert ist.The loss factor d (Tab.2.9 in Magnetic Materials and their characterization, p. 25) $$d=tan\delta =\mu \text{'}\text{'}/\mu \text{'}$$

where δ is the loss angle. Magnetic iron has typical loss factors in the range of d = 0.08 ... 0.60 (Tab. 3, page 8, Determination of electromagnetic properties of steel for prediction of stray losses in power transformers). The loss factor d The ceramic materials with charged domain walls, which form an RLC parallel resonant circuit, become the quality factor Q an RLC parallel resonant circuit $$Q=R\surd \left(\mathrm{C.}/L\right)$$

determined as follows: d = 1 / Q and is in the range of d = 0.36 ... 1.38. The resonance frequency f ₀ $$f_0=\left(1/\mathrm{2nd}\pi \right)\sqrt{1/\left(L\mathrm{C.}\right)}$$

is f ₀ = 64 MHz ... 107 MHz, the high frequency range (HF) being defined between 30 kHz ... 300 MHz.

The eddy current losses (skin effect) in ferro- or ferrimagnetic materials increase quadratically with frequency and inversely proportional to the resistivity of the ferro- or ferrimagnetic material and become significant above about 10 kHz. Since the inductive reactance above the resonance frequency f _{0 is} greater than the capacitive reactance, it is advantageous to conduct alternating magnetic fields above the resonance frequency f ₀ in the ceramic material with charged domains.

In metallically conductive ferromagnetic or ferrimagnetic materials, the skin depth means that the penetration depth of alternating magnetic fields is only a few micrometers (1 ... 10 Qm) at 100 MHz and several micrometers (70 ... 707 Qm) at 50 Hz. Due to the skin effect, ferromagnetic and ferrimagnetic materials cannot be used in the HF range. The skin effect determines the thickness of the slats in which coil carriers are typically formed by transformers.

The resonance frequencies of the ceramic materials with charged domain walls are f ₀ = 64 MHz ... 107 MHz and are outside the hearing range (16 ... 20,000 Hz). Even if the ceramic material vibrates mechanically, this will not be noticeable through annoying noise (humming). Since the ceramic materials with charged domain walls have no magnetization hysteresis and a specific resistance comparable to amorphous SA1 and Fe-Si 0.3, hysteresis losses in this material are negligible.

In order to keep the effects of the skin effect as small as possible, cables with the largest possible surface area are used in high-frequency technology, for example in the form of thin-walled hose pipes, strands or tapes. The low losses of waveguides are partly due to the fact that a large part of the inner surface is not significantly involved in the current flow. Furthermore, the surfaces of high-frequency or ultra-high-frequency lines are often coated with precious metals such as silver or gold, in order to reduce the specific resistance of the outer surface of the wire, which conducts most of the current by far. In the case of gold in particular, the fact that this metal does not oxidize in air is used, so that the surface maintains long-term stable conductivity. Because gold itself has a lower electrical conductivity than copper, but a much better one than copper oxide. Care is also taken to ensure that the conductor surface is very smooth, since rough surfaces represent a longer path for the current and thus greater resistance. Ferromagnetic conductor materials are also particularly disadvantageous since the depth of penetration is greatly reduced. For this reason, they are also often coated with metal.

Iron alloys and ferromagnetic steels are of the greatest economic importance. So-called dynamo sheets are mainly used for transformers (operating frequency 50 Hz or 60 Hz) DIN EN 10107 , which consists of iron-silicon alloys. Nickel-iron alloys are also used for signal transmitters. The maximum flux density for iron is 1.5 to 2 Tesla depending on the specification. The core is built up from a stack of individual sheets, between which are electrically insulating Intermediate layers are located, the sheet metal surface being parallel to the direction of the magnetic flux and thus perpendicular to the induced electric field. This reduces eddy current losses. The higher the frequency, the thinner the sheets must be chosen. Damage to the insulation of the individual laminated cores can lead to considerable local heating of the bundle in the case of large transformers. Above frequencies in the kilohertz range, the eddy current losses in iron cores would be too great even with very thin sheets. Cores made of amorphous or nanocrystalline strips or ferrite cores are used. Ferrites have a high permeability, but only a low electrical conductivity. To manufacture ferrite cores, the mostly powdered starting material is placed in a mold and sintered (pressed) under pressure. This results in more design options than with the laminated core, in particular with regard to the adaptation to the coil former. The maximum flux density for ferrites is around 400 mT. The limit to the use of ferrite material lies in the manufacturability in the pressing and sintering process. Cores for larger transformers are partially composed of ferrite blocks. Due to their natural band thickness of typically 0.02 mm, the amorphous and nanocrystalline cores allow use at higher frequencies and have very low losses. Typical core shapes for these bands are toroidal cores or, more rarely, cutting band cores.

The materials known and used so far are not sufficient to overcome the disadvantages described above. It is therefore an object of the present invention to provide a material with which these disadvantages can be significantly reduced and which is suitable for conducting and isolating magnetic fields and can be used in magnetic coupling elements.

• - Erzeugen eines keramischen Materials mittels Erhitzen einer Ausgangsmaterialkomposition bis zu einer Temperatur unterhalb der Schmelztemperatur der Ausgangsmaterialkomposition,
• - Abkühlen des erzeugten keramischen Materials auf Raumtemperatur nach einer definierten Abkühlrate zur Einstellung einer Vortex-Dichte in dem erzeugten keramischen Material, und
• - nachfolgende lokale Temperaturbehandlung zum Erhitzen des keramischen Materials über dessen ferroelektrische Ordnungstemperatur und zum Einstellen des lokalen Permeabilitätsgradienten.

The object is achieved by a method for producing a ceramic material with a locally adjustable permeability gradient, the method comprising the following steps:

• Producing a ceramic material by heating a starting material composition to a temperature below the melting temperature of the starting material composition,
• Cooling the ceramic material produced to room temperature after a defined cooling rate to set a vortex density in the ceramic material produced, and
• - Subsequent local temperature treatment for heating the ceramic material above its ferroelectric order temperature and for setting the local permeability gradient.

The advantage of ceramic materials with charged domain walls is that they depend on the chemical composition, for example Y _1.00 Mn _1.00 O3, Y _0.95 Mn _1.05 O ₃ , Y _1.00 Mn _0.99 O ₃ + 1at. % Ti and Y _0.94 Mn _1.05 O ₃ + 1at. % Ti in table too 2 B at the same time have very large permeabilities and no magnetization hysteresis. Therefore, magnetic fields can be conducted in ceramic materials with charged domain walls without the losses caused by the magnetization hysteresis in ferrimagnetic and ferromagnetic materials. The permeability gradient of the ceramic material determines the location-dependent density of the magnetic field lines in the ceramic material with charged domain walls.

mit ε_r =11, 8 ... 73,8 und µ_r = 56000 ... 171000 und mit p = 75 ... 141 Ωm mehrere hundert Mikrometer (380 ... 540 µm). Die keramischen Materialien mit Domänenwänden können daher hervorragend im HF-Bereich eingesetzt werden. Keramische Materialien mit geladenen Domänenwänden können für die Hochfrequenztechnik zur Herstellung von Leitungen mit kleineren Oberflächen eingesetzt werden, beispielsweise zur Beschichtung von Drähten verwendet werden. Läuft die Magnetisierungsrichtung ringförmig um den Draht, wird ein solcher Draht mit einem in Längsrichtung verlaufenden Magnetfeld belegt, ändert sich der magnetische Fluss in dem keramischen Material und führt bei hohen Frequenzen durch die Beeinflussung des Skin-Effektes zu einer Änderung der Induktivität des beschichteten Drahtes. Beschichtete Drähte in der Nähe stromdurchflossener Leiter können auch zur Messung des Magnetfeldes stromdurchflossener Leiter verwendet werden.In addition, the skin effect in ceramic materials with domain walls is reduced and the penetration depth of the alternating magnetic fields approaches the value asymptotically at high frequencies $$\mathrm{2nd}p\sqrt{\left(\epsilon /\mu \right)}$$

with ε _r = 11, 8 ... 73.8 and µ _r = 56000 ... 171000 and with p = 75 ... 141 Ωm several hundred micrometers (380 ... 540 µm). The ceramic materials with domain walls can therefore be used excellently in the HF range. Ceramic materials with charged domain walls can be used for high-frequency technology for the production of lines with smaller surfaces, for example for the coating of wires. If the direction of magnetization runs in a ring around the wire, if such a wire is coated with a longitudinal magnetic field, the magnetic flux in the ceramic material changes and, at high frequencies, changes in the inductance of the coated wire by influencing the skin effect. Coated wires near current-carrying conductors can also be used to measure the magnetic field of current-carrying conductors.

The starting material composition for producing the ceramic material can be, for example, an oxide powder or a metal powder with subsequent oxidation. The weighed oxide is first ground and then dried. A pre-sintering process is used to bring the powder into a certain phase or to a certain grain size. In a further grinding process, the lump is partially clumped Grind the oxide mixture dry to a fine-grained powder. The powder is then finally dried and pressed together in a press mold and then sintered.

The ceramic material is now produced.

The cooling of the starting material composition to room temperature after a defined cooling rate serves to set a vortex density in the ceramic material produced. The ceramic material has the property of forming vortex states when it passes through a heating and / or cooling process. A vortex state can be understood as an intersection between charged domain walls within a material. The ceramic materials with charged domain walls form vortex states in the center of six different ferroelectric domain walls (DW), two charged DWs (head-to-head), two charged DWs (tail-to-tail) and two neutral DWs (head -to-tail). A vortex state is topologically protected, ie it cannot be transformed into the basic state by continuous transformation. The ferroelectric order temperature T _{c of} the hexagonal rare earth manganates RMnO depends on the rare earth element in RMnO. No ferroelectric order with ferroelectric domain walls and charged vortex states forms above a temperature of T _c . For example, the ferroelectric order temperature for HoMnO ₃ T _c = 875 K, for LuMnO ₃ T _c = 573 K and for YMnO ₃ T _c = 930 K. When the ceramic material is heated above the ferroelectric order temperature, the ferroelectric order is not pronounced. The vortex density during the subsequent cooling of the ceramic material depends on the cooling rate at the time of the cooling process, at which the cooling temperature is equal to the ferroelectric order temperature. Below the ferroelectric order temperature, the density of the vortices depends on the cooling rate. The vortex density therefore depends on the cooling rate when passing through the ferroelectric order temperature.

In a preferred embodiment of the method according to the invention, the local temperature treatment is carried out by means of short-term heat treatment - RTA - rapid temperature annealing in the ms range or by means of short-term tempering with flash lamps - FLA - flash light annealing in the μs to ms range or by means of pulsed laser radiation - PLA - pulsed laser annealing in the ns to µs range (Subsecond Annealing of Advanced Materials Annealing by Lasers, Flash Lamps and Swift Heavy Ions, Springer Series in Material Science, 2014). RTA is suitable for the thermal treatment of bulk materials with dimensions up to decimeters to centimeters, materials with rough surfaces and planar materials; FLA is suitable for the thermal treatment of materials with dimensions up to centimeters to micrometers with rough surfaces and of planar materials; and PLA is suitable for the thermal treatment of planar materials with dimensions of up to micrometers to nanometers. This subsequent short-term temperature treatment using RTA, FLA and / or PLA leads. This subsequent short-term temperature treatment using RTA, FLA and / or PLA leads to the setting of the final permeability gradient, which is required in the respective application.

Another advantageous embodiment of the method according to the invention is that the ceramic material can be produced as a bulk material. By pressing the powdery starting material composition, setting a vortex density according to a defined cooling rate in the ceramic material produced, and locally treating the ceramic material via its ferroelectric order temperature to set the local permeability gradient, a bulk material with a local can be produced in a very simple manner adjustable permeability gradients. A volume material is understood to mean the ceramic material in its spatial extension in the x, y and z directions.

The object of the present invention is also achieved by a method for the global coating of a surface with a ceramic material, the ceramic material being initially produced as already described. Furthermore, the ceramic material is deposited on the surface to be coated, the ceramic material being cooled to a room temperature after the deposition after a defined cooling rate to set a vortex density in the ceramic material. This is followed by a local temperature treatment for heating the ceramic material above its ferroelectric order temperature, so that a final local permeability gradient is established in the coating on the surface. The coating should have a thickness of less than the skin thickness.

A surface in the sense of the present invention is understood to mean any surface that is suitable for coating with the ceramic material. This can be, for example, the surface of an object or body of any shape or a planar surface or a film or a any substrate. This list is in no way to be interpreted as restrictive. The global coating therefore describes a coating of a surface in its entirety and is not to be understood as being spatially limited. Otherwise, prior to coating the surface, the surface must be provided with an adhesion promoter so that the ceramic material reliably bonds to the surface.

In a preferred embodiment of the coating method according to the invention, the ceramic material is deposited on the surface by means of pulsed laser plasma deposition from a ceramic target which has the ceramic material. For example, the ceramic material with charged domain walls can be deposited from a ceramic target by means of pulsed laser plasma deposition on a planar carrier material in thin film form.

It is particularly advantageous if the method for producing the ceramic material with a locally adjustable permeability gradient is used as a ferrite core in a transformer.

It is also advantageous if the ceramic material with a locally adjustable permeability gradient is used with the coating method according to the invention as a coating material for electrical conductors and / or wires.

It is also advantageous if the method for producing the ceramic material with a locally adjustable permeability gradient is used for producing electrical conductors.

The invention will be explained in more detail below using exemplary embodiments.

Figure list

• 1 Schematic representation a) of a ferromagnetic or ferrimagnetic layer of thickness d and b) a ceramic material with charged domain walls of thickness d on a substrate;
• 2nd Ceramic material according to the invention with charged domain walls a) with a low density of the charged domain walls; b) with a high density of the charged domain walls;
• 3rd Ceramic material according to the invention with charged domain walls a) with a high density of the charged domain walls in the center on the substrate and b) with a high density of the charged domain walls in the edge regions on the substrate;
• 4th Ceramic material according to the invention with charged domain walls a) with a low density of the charged domain walls and the thickness d on a ceramic material with a high density of the charged domain walls and b) with a high density of the charged domain walls and the thickness d on a ceramic material with a low density of the charged domain walls;
• 5 Ceramic material of the thickness according to the invention d a) with charged domain walls with a high density of the loaded domain walls and with loaded domain walls with a particularly high density of the loaded domain walls in the middle on a ceramic material with a low density of the charged domain walls and b) with charged domain walls with a high density of the charged domain walls Domain walls and with loaded domain walls with a particularly high density of the loaded domain walls at the edge on a ceramic material with a low density of the loaded domain walls;
• 6 Use for coating cables as a) a layer system made of ceramic materials i the thickness di and the permeability µ _i and b) as a layer system made of ceramic materials i the thickness di and the permeability µ _i and from dielectric materials j the thick d _j and permittivity ε _j ;
• 7 a ) Use for producing a transformer core from a b) spiral winding of a tape consisting of ceramic materials i the thickness di and the permeability µ _i which c) takes on different values on the tape, and d ) which on an insulator layer ( 7 ) are applied; and e) use for producing a transformer core from a radially symmetrical coating with ceramic materials i the thickness di and the permeability µ _i and with dielectric materials j the thick d _j and permittivity ε _j .

The ceramic material with charged domain walls can, for example, be deposited from a ceramic target by means of pulsed laser plasma deposition on a planar carrier material in thin film form. The manufacturing process of eg ceramic manganate thin films charged domain walls comprises the following process steps: First, a ceramic target, e.g. made of yttrium oxide, manganese oxide and titanium oxide with different proportions by weight (Y ₁ Mn ₁ O ₃ , Y _0.95 Mn _1.05 O ₃ , Y ₁ Mn _0.99 Ti _0.01 O ₃ , Y _0.94 Mn _1.05 Ti _0.01 O ₃ ). The oxides are weighed for this. The weighed oxides are then ground, for example in a grinding bowl using agate balls with diameters of 10 mm and 5 mm in a mill at 450 revolutions / minute, 8 hours in the dry state and 16 hours in the wet state, with the starting material composition being mixed with ethanol. After grinding, the oxide mixture is placed in a beaker, where the viscous oxide mixture is constantly stirred using a spatula and dried on a hot plate at approx. 60 ° C until the ethanol has evaporated and the oxide mixture is again in powder form. The powder is then presintered at 1000 ° C for 5 hours in air and cooled to room temperature: The dried powder is poured into an aluminum ceramic boat and presintered in the tube furnace in air under the conditions specified above. This serves to achieve a certain phase or grain size of the material. By re-grinding the partially clumped oxide mixture, the clusters and larger agglomerates are processed again after the sintering process in a grinding bowl at 450 revolutions per minute for about 3 hours to give fine-grained powder. This is followed by a drying process of the oxide mixture at 120 ° C for 1 day: For drying, the powder is poured into a beaker and finally dried in the drying oven under the above conditions. The entire liquid must have escaped so that the target does not tear when sintered. The powder of the oxide mixture is pressed in a press mold with a diameter of 32 mm in a press with a pressure of 2 ton = 39 bar in a time of approx. 20 min. After removing the compact and sintering at 1350 ° C for 10 hours in air, with a slow cooling from approximately 3 ° C / min to room temperature, a ceramic material with charged domain walls is obtained. If the starting material composition is cooled to room temperature after a defined cooling rate, a defined vortex density can be set in the ceramic material produced. The cooling rate can be, for example, 1 K / min to 20 K / min. It is also possible to reduce the cooling rate on the one hand by a low counter heating from 1K / min to 10 K / min and on the other hand to work with a high oxygen partial pressure of 0.1 to 0.3 mbar to increase the cooling rate.

In a subsequent local temperature treatment step, the ceramic material is heated above its ferroelectric order temperature, this step being necessary to set the local permeability gradient. This step takes place outside the pulsed laser plasma deposition chamber. Whether the short-term temperature treatment is carried out using Rapid Thermal Annealing (RTA), Flash Lamp Annealing (FLA) or Pulsed Laser Annealing (PLA) depends on the thickness i of the ceramic material i from, in which the temperature during the thermal treatment should be greater than the ferroelectric order temperature T _c and from how long the temperature during the thermal treatment should be greater than the ferroelectric order temperature.

2nd shows the results of the modeling of the impedance set by means of temperature treatment on various ceramic materials and the determination of the permittivity ε _r for ceramic materials with conductive domain walls of low density ( 2a ) and permittivity ε _r and permeability µ _r for ceramic materials with high density conductive domain walls ( 2 B ). 2 B shows an RCL sample with good conduction of the magnetic field, whereas 2a shows an RC sample with good shielding of the magnetic field. 2a shows the ceramic material according to the invention with charged domain walls with a low density 3D that in the RC modeling of the on the ceramic material with front electrode 15 and with back electrode 14 measured impedance the capacitive component C. and the resistance component R dominates. The values of resistance R , the capacity C. and permittivity ε _r were made from the impedance data of the ceramic material of the thickness d modeled in an RC parallel resonant circuit. 2 B shows the ceramic material according to the invention with charged domain walls of high density 3E that in the RLC modeling the on the ceramic material with front electrode 15 and with back electrode 14 measured impedance the capacitive component C. , the proportion of resistance R and the inductive part L dominates. The values of resistance R , the capacity C. , the permittivity ε _r and permeability µ _r were made from the impedance data of the ceramic material of the thickness d modeled in an RLC parallel resonant circuit.

In 3a is the permeability gradient µ _r in a ceramic material on a substrate 2nd with loaded domain walls 4th low density 3A on the edge and with loaded high density domain walls 3B shown schematically in the center. In 3b is the permeability gradient µ _r in a ceramic material on a substrate 2nd with loaded high density domain walls 3B on the edge and with loaded low density domain walls 3A shown schematically in the center.

In 4a is a ceramic material with charged low density domain walls 3A on a ceramic material with charged high density domain walls 3B shown schematically. In 4b is a ceramic material with loaded high density domain walls 3B on a ceramic material with charged domain walls of low density 3A shown schematically.

In 5a is the permeability gradient µ _r in a ceramic material with charged high density domain walls 3B on the edge and with loaded domain walls of particularly high density 3C in the center on a ceramic material with charged domain walls of low density 3A shown schematically. In 5b is the permeability gradient µ _r in a ceramic material with charged domain walls of particularly high density 3C on the edge and with loaded high density domain walls 3B in the center on a ceramic material with charged domain walls of low density 3A shown schematically.

The 6 shows how the ceramic materials are used for magnetic field shielding. Magnetic shielding materials have a high permeability µ _r and are robust against mechanical stress during processing and have a disappearing magnetostriction. A standard solution for magnetic field shielding are MUMETALL tapes with a thickness of 0.05 mm or 0.10 mm and a width of 155 mm with typical permeabilities of µ _r = 8000. Other standard solutions are shielding foils from VITROVAC 6025x, which have a thickness of 30 µm and a width of 50 mm. Both tapes are also supplied with a self-adhesive film from the vacuum melt. According to the invention, in order to achieve high shielding factors, several ( N ) Thin layers i, which by their permeability µ _i , their thickness di and their conductivity σ _i are used. The shielding factor of the total of N thin-film layers scales non-linearly with the permeabilities µ _{i of} the N thin-film layers i. Due to the partially disjoint material properties with regard to the permeability µ _i and the conductivity σ _i (µ (c _u ) = 1 - 6.4 · 10 ^-6 , σ _(Cu) = 58 · 10 ⁶ S / m and µ _(Al) = 1 + 2.2 · 10 ^-5 , σ _(Al) = 37 · 10 ⁶ S / m), thin layers with high conductivity and thin layers with high permeability are combined in standard applications. Al and Cu are not suitable for this. To solve the problem and to further improve the shielding of magnetic fields, for example on cables 6 , ie conductors, the use of a coating consisting of several (N) thin-film layers i is proposed, the permeability of the thin layer i = 1, which is in direct contact or only through an insulator layer from the cable 6 is separated, has the smallest permeability µ _i and the smallest conductivity σ _i . The thin layer i with the greatest conductivity determines the distance from the surface of the cable 6 the external magnetic field H _{ext is} effectively derived. Gradual changes in the flux density of the magnetic field lines within the N thin-film layers are possible, so that the temporal change in the flux density B _i in the thin-film i is reduced. Using electrical insulation between adjacent thin film layers i and i + 1 the voltage U _{Ii-Ii + 1} can be derived. Without this electrical insulation, so-called eddy currents would change the external magnetic field. An embodiment for dissipating an external magnetic field H _ext is in 6a shown. The skin thickness of the thin layer i depends on the frequency of change f of the external magnetic field, δ _Skin = (1 / σ · π · µ ₀ · f) ^1/2 . 6b shows how insulator layers j are inserted between the thin layer layers to prevent the eddy currents. At high frequencies, an interlayer voltage U _{Ii-Ii + 1} = 2π · w · d · f · dB / dt can develop. The induced eddy currents heat the material. That is why the insulator layers are inserted. In order to keep the formation U _{Ii-Ii + 1} as low as possible, the product µ _i · d _{i is} kept constant according to the invention.

7 shows the use of ceramic materials for the production of transformer cores for better conduction of the magnetic flux Φ . There is no leakage current in an ideal inductor. So-called magnetic leakage flux lines are a possible cause of leakage currents. According to the invention, the formation of leakage flow lines is prevented by the proposed manufacture of the transformer core. In a real transformer there are power losses P _Fe in the core material and copper losses Pcu in the turns of the primary and secondary circuits. These losses reduce the efficiency of the transformer and cause the temperature of the transformer to rise compared to the environment.

Reference list

1

ferro- or ferrimagnetic layer

2nd

Substrate

3rd

ceramic layer with charged domain walls

3A

ceramic material with loaded low density domain walls

3B

ceramic material with loaded high density domain walls

3C

ceramic material with charged domain walls of particularly high density

3D

ceramic material with charged domain walls of such a low density that in the RC-modeling the impedance measured on the ceramic material with front-side electrode and with rear-side electrode is the capacitive component C. and the resistance component R dominates

3E

ceramic material with charged domain walls of such a high density that in the RLC modeling the impedance measured on the ceramic material with the front-side electrode and with the rear-side electrode is the capacitive component C. , the proportion of resistance R and the inductive part L dominates

4th

loaded domain walls

6

electric wire

7

ceramic thin film i the thickness di and the magnetic permeability µ _i with loaded domain walls

8th

Insulator layer j the thick d _j and electrical permittivity ε _i

9

Transformer core

9A

Transformer core consisting of a spirally wound ceramic thin layer

9B

Transformer core consisting of alternatingly arranged ceramic thin layers i on insulator layers j

10th

Primary circuit of the transformer with N1 Windings and primary current I1

11

Secondary circuit of the transformer with N2 Turns and secondary current 12th

12th

Load resistance R2 in the secondary circuit of the transformer

13

transformer

14

Rear electrode

15

Front electrode

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Non-patent literature cited

• T. Chatterji et al., J. Phys .: Condens. Matter 24 (2012) [0005]
• DIN EN 10107 [0014]

Claims (9)

A method for producing a ceramic material (3, 3A, 3B, 3C, 3D, 3E) with a locally adjustable permeability gradient, the method comprising the following steps: Producing a ceramic material by heating a starting material composition to a temperature below the melting temperature of the starting material composition, Cooling the ceramic material produced to room temperature after a defined cooling rate to set a vortex density in the ceramic material produced, and - Subsequent local temperature treatment for heating the ceramic material above its ferroelectric order temperature and for setting the local permeability gradient. Procedure according to Claim 1 , characterized in that the starting material composition is an oxide powder and / or a metal powder. Procedure according to Claim 1 , characterized in that the local temperature treatment is carried out by means of a short-term heat treatment - RTA in the ms range or by means of short-term tempering with flash lamps - FLA in the µs to ms range or by means of pulsed laser radiation - PLA in the ns to µs range. Procedure according to Claim 1 , characterized in that the ceramic material is produced as a bulk material. Process for global coating of a surface with the ceramic material (3) Claim 1 , wherein the ceramic material is deposited on the surface, the ceramic material is cooled to room temperature after a defined cooling rate to set a vortex density in the ceramic material, and subsequently a local temperature treatment for heating the ceramic material takes place above its ferroelectric order temperature, so that there is a local permeability gradient in the coating of the surface. Process for global coating of a surface Claim 5 , characterized in that the ceramic material is deposited on the surface by means of pulsed laser plasma deposition from a ceramic target which has the ceramic material. Use of the ceramic material with a locally adjustable permeability gradient according to one of the preceding claims as a ferrite core (9, 9A, 9B) in a transformer (13). Use of the ceramic material with a locally adjustable permeability gradient according to one of the preceding claims as a coating material for electrical conductors and / or wires. Use of the ceramic material with a locally adjustable permeability gradient according to one of the preceding claims for the production of electrical conductors.

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