JP-7855766-B2 - MnZn ferrite

Inventors

• 石原 真由
• 中村 由紀子
• 吉田 裕史
• 菊地 孝宏

Assignees

• ＪＦＥケミカル株式会社

Dates

Publication Date

20260508

Application Date

20250610

Priority Date

20201216

Claims (7)

1. A MnZn-based ferrite consisting of a basic component and a minor component, The above basic components are: Iron: 52.50–54.00 mol% in Fe₂O₃ equivalent . Zinc: 15.00 to 21.00 mol% in terms of ZnO and manganese: the remainder. As the above minor components, Si:50-150 ppm by mass in terms of SiO₂ Ca: 250-1100 ppm by mass in CaCO3 equivalent. MnZn-based ferrite with Nb:50 to 500 ppm by mass (calculated as Nb₂O₅ ) and Li:more than 200 ppm and less than or equal to 600 ppm by mass (calculated as Li₂CO₃ ) .
2. A MnZn-based ferrite consisting of a basic component and a minor component, The above basic components are: Iron: 52.50–54.00 mol% in Fe₂O₃ equivalent . Zinc: 15.00 to 21.00 mol% in terms of ZnO and manganese: the remainder. As the above minor components, Si:50-150 ppm by mass in terms of SiO₂ Ca: 250-1100 ppm by mass in CaCO3 equivalent. MnZn-based ferrite with a V: V₂O₅ equivalent concentration of 100-700 ppm by mass and a Li: Li₂CO₃ equivalent concentration of over 200 ppm by mass and 600 ppm or less by mass.
3. A MnZn-based ferrite consisting of a basic component and a minor component, The above basic components are: Iron: 52.50–54.00 mol% in Fe₂O₃ equivalent . Zinc: 15.00 to 21.00 mol% in terms of ZnO and manganese: the remainder. As the above minor components, Si:50-150 ppm by mass in terms of SiO₂ Ca: 250-1100 ppm by mass in CaCO3 equivalent. Nb: 50-500 ppm by mass (calculated as Nb₂O₅ ) MnZn-based ferrite with a V: V₂O₅ equivalent concentration of 100-700 ppm by mass and a Li: Li₂CO₃ equivalent concentration of over 200 ppm by mass and 600 ppm or less by mass.
4. The MnZn ferrite according to any one of claims 1 to 3, wherein the value of ΔB [mT] obtained by the following equation (1) is 250 mT or more at 100°C. ΔB = B m - Br ... (1) (where B m is the saturation magnetic flux density [mT] and Br is the remanent magnetic flux density [mT])
5. The MnZn ferrite according to any one of claims 1 to 4, wherein the maximum value of the normalized impedance Z norm [Ω・ mm⁻¹ ] obtained by the following equations (2) and (3) in the frequency range of 500 kHz to 3 MHz is 40 Ω・ mm⁻¹ or more. Z norm = Z・c 1 / N 2 ... (2) c 1 = l e / A e ... (3) (where Z is impedance [Ω], c 1 is core constant [ mm⁻¹ ], l e is magnetic path length [mm], A e is cross-sectional area [ mm² ], and N is number of turns of the coil [-])
6. A MnZn-based ferrite according to any one of claims 1 to 5, wherein the μi' (real part of the initial permeability μi) at 10 kHz and 23°C is 4000 or more, and the μi' (real part of the initial permeability μi) at 500 kHz and 23°C is 4500 or more.
7. MnZn ferrite according to any one of claims 1 to 6 , wherein the sintering density is 4.97 g/cm³ or more.

Description

This invention relates to MnZn ferrite, which is widely used in noise suppression components such as switching power supplies, and more specifically to a high-permeability MnZn ferrite for noise filters with improved magnetic saturation and high-frequency characteristics of its magnetic material. MnZn ferrite, a representative soft magnetic material, is widely used in power transformers and noise suppression components in switching power supplies. In particular, MnZn ferrite used as a noise suppression component requires high magnetic permeability and is utilized as a common-mode choke in all kinds of electronic devices, such as air conditioners, televisions, and personal computers, playing a role in removing unwanted electrical components (noise). In recent years, with the increasing electrification of vehicles, demand for MnZn ferrites has been growing in the automotive electronics field. In automotive applications, particularly around the engine compartment, ambient temperatures range widely from -40°C to 150°C. Therefore, a common-mode choke that exhibits stable characteristics across this entire temperature range is required. Currently available MnZn ferrites, even those with high permeability, have a saturation magnetic flux density of approximately 440 mT at room temperature and 250 mT at 100°C. Furthermore, the difference between the saturation magnetic flux density Bm and the residual magnetic flux density Br at 100°C, ΔB, is at most about 190 mT, meaning that losses increase significantly at high temperatures. Consequently, noise filter components using such MnZn ferrites generate heat in their operating environment. Therefore, when used as a noise filter, the value of ΔB needs to be high enough to ensure stable operation even at high temperatures, taking into account its effect on pulse noise emitted by inverters, compressors, etc. For example, it needs to be 250 mT or higher at 100°C. Furthermore, in order to function as a common-mode choke for noise filtering, a normalized impedance that is sufficiently larger than the noise at the frequency of the noise to be removed is required. In recent years, power semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) have begun to be introduced as in-vehicle semiconductors for electric vehicles. However, these power semiconductors generate significant noise in the high-frequency band above 1 MHz. Therefore, when used with such power semiconductors, a common-mode choke with a high normalized impedance that can remove high-frequency noise is necessary. While MnZn ferrites are inexpensive compared to amorphous metals and are therefore easy to introduce as noise filters, their high Fe²⁺ content makes electron transfer between Fe³⁺ and Fe²⁺ more likely, resulting in a low resistivity on the order of 0.1 Ω·m. With such low resistivity, as the operating frequency band increases, losses due to eddy currents within the ferrite increase sharply, leading to a decrease in initial permeability. Consequently, the inductance decreases, simultaneously causing a decrease in the maximum value of the normalized impedance and a shift to a lower frequency at which the maximum value occurs. Therefore, in order to obtain a high normalized impedance on the MHz order, it is necessary to use NiZn-based ferrite, which has a relatively high resistivity of 10⁵ Ω·m or more among ferrites, or to increase the resistivity by reducing the amount of Fe²⁺ in MnZn-based ferrite. However, NiZn ferrites have a low initial permeability of only a few hundred at low frequencies, making them unsuitable for common-mode chokes. On the other hand, MnZn ferrites have the problem that reducing the Fe²⁺ content of the ferrite decreases the magnetic moment and thus the saturation magnetic flux density. Another method to increase resistivity is to add a small amount of metal oxide. This is because metal oxides other than the main component do not exhibit conductivity and segregate at grain boundaries within the crystal structure. Therefore, the grain boundary resistance increases, and the resistivity of the ferrite itself increases. However, when adding a small amount of metal oxide to increase resistivity in order to improve the normalized impedance and ΔB at high frequencies, there is a problem that the initial permeability at low frequencies around 10 kHz generally decreases. In this specification, the normalized impedance refers to the measured impedance normalized by the dimensions and the number of turns in the coil. Here, Patent Documents 1 and 2 show that the addition of Nb₂O₅ and V₂O₅ reduces the residual magnetic flux density and improves ΔB. Furthermore, Patent Documents 3 and 4 disclose MnZn-based ferrites containing Nb, V, and Li that are effective in improving high-frequency normalized impedance and ΔB. Japanese Unexamined Patent Publication No. 6-140231Japanese Patent Application Publication No. 6-283320Japanese Patent Publication No. 2014-080344Japanese Patent Publication