JPH05343220A - Manufacture of sintered compact of soft ferrite for high frequency - Google Patents

Abstract

PURPOSE:To obtain homogenous raw material powder for ferrite by mixing constituents to be mainly contained in the crystal grains, out of trace constituents, with a chloride solution by specified ratios in the form of chlorides, or mixing impalpable powder after oxidizing roasting before heat treatment for growing it to specified size. CONSTITUTION:Concerning to a manufacturing method for sintered compacts of ferrite whose main constituents are iron oxide, a manganese oxide, and a zinc oxide, a solution wherein major constituents to constitute the ferrite are contained by specified ratios in the form of a solution of chlorides is sprayed in a spray roasting furnace, and mixed oxide powder is obtained by thermal decomposition. Then with this powder, trace elements to be mainly contained in the crystal grains of the sintered compacts of ferrite are mixed in the form of oxides needed. After that, heat treatment is performed at 400-1,100 deg.C, and required amounts of trace elements to be to exist in the crystal grain boundary are added in the form of oxides. After that, raw material powder for soft ferrite obtained by mixing and grinding is formed into grains, molded, and burned. Consequently, it becomes possible to obtain sintered compacts of soft ferrite with less power loss at a high-frequency region and with high saturation magnetic flux density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an Mn-Zn ferrite having high power and low power loss characteristics for use in magnetic core materials such as power transformers and having a high sintering density.

[0002]

2. Description of the Related Art Conventionally, a power transformer used for a switching power supply or the like has been required to be downsized, and therefore the operating frequency is expanding to a high frequency region of about 100 KHz to about 500 KHz. In response to this trend toward higher frequencies, 5
When used in a high frequency region of about 00 KHz, the power loss of the power transformer becomes a size that cannot be ignored. Various solutions have been proposed to solve this problem. It is well known that the eddy current loss, which is a particular problem in the high frequency region of the power loss, is proportional to the crystal grain size of the sintered body and the square of the operating frequency, and inversely proportional to the electrical resistivity of the sintered body. (Basics of Magnetic Engineering II, Keizo Ota, Kyoritsu Shuppan).

In order to reduce the power loss in the high frequency region, (a) increase the electrical resistivity of the sintered body,
(B) It is focused on reducing the crystal grain size of the sintered body as much as possible. With regard to (a), it is well known to preferentially precipitate a component that increases electric resistance at the crystal grain boundaries to achieve the purpose. For example, it is well known that a trace amount of additives such as SiO ₂ and CaO is concentrated at the crystal grain boundaries and contributes to the prevention of eddy current loss due to the grain boundary resistance (Electronic Material Series Ferrite Hiraga et al. Maruzen, P39-48). .. It is also well known that even with a small amount of additive, TiO ₂ , SnO _2, etc. are mainly concentrated in the crystal grains to increase the intragranular resistance, prevent eddy current loss, and consequently reduce power loss. (W
ith ferrite TDK, Nikkan Kogyo Shimbun, P
82, 83) Furthermore, due to the magnetic characteristics of CoO,
It is well known that the addition of a trace amount of particles enters the crystal grains and affects the temperature characteristics of the soft ferrite core.

In recent years, as the above-mentioned operating frequency becomes higher, consideration has also been given to (b). For example, as shown in Japanese Patent Application No. 1-2224265, a sub-component that promotes sintering is added to lower the sintering temperature to increase the sintered density and suppress the growth of sintered grains, and thus a fine sintered crystal Secure particle size,
A method for producing Mn-Zn ferrite with less power loss is proposed. However, even the above ferrites are not sufficient to reduce power loss. To pursue power loss, suppress the growth of the sintered crystal grain size, use a large amount of additives, and lower the firing temperature, which affects the soundness of the crystal and reduces the saturation magnetic flux density and residual magnetic flux. This caused an increase in density. There is a demand for a low-loss ferrite that can be applied in a wide frequency range of 100 KHz to 500 KHz and that has good evaluation when mounted on a transformer.

[0005]

Conventionally, as a raw material of Mn-Zn ferrite, Fe ₂ O ₃ , Mn ₃ O ₄ , ZnO and the like have been used as a main component source, and auxiliary component sources such as SiO ₂ and CaO (these particles are used). The diameter is from several microns to several hundreds of microns), and these are mixed and pulverized to 900 ℃ ~ 1100 ℃
The one that was calcined at about the same temperature was used. After that, it is ground for a long time by a ball mill or the like to obtain a calcined powder as a raw material of a sintered body having a predetermined particle size, but such work causes deterioration of the particle size distribution, mixing of impurities, etc., and power loss. As a method for producing a soft ferrite raw material for eliminating these drawbacks, in a method for obtaining a mixed oxide powder by spray roasting a chloride solution of a main metal component constituting soft ferrite, in order to reduce the deviation of zinc A method for producing a mixed oxide ferrite raw material powder has been developed, which is characterized by rapidly cooling to a certain temperature or less within a predetermined time after roasting.

However, the mixed oxide ferrite raw material powder obtained by these methods was too fine, and it was not sufficient to control the obtained ferrite sintered body to a required characteristic of about 100 KHz which is usually used. Trace additives such as SiO ₂ and CaO of the soft ferrite sintered body are concentrated in the crystal grain boundaries and contribute to the prevention of eddy current loss due to grain boundary resistance. For example, the Auger analysis result of the soft ferrite sintered body containing SiO ₂ and CaO shows the strength ratio of SiO ₂ and Ca in the grains.
O strength is less than 1%. Further, V and Nb also show similar characteristics. As described above, the so-called grain boundary forming element is relatively easily concentrated in the crystal grain boundaries. Even with a trace amount of additive, TiO ₂ , Sn
It is well known that O ₂ mainly enters the crystal grains to increase the intragranular resistance and prevent the eddy current loss. For example, when Auger analysis of a soft ferrite sintered body produced by a conventional method containing Ti is carried out, Ti is found in the grain boundaries at the strength ratio.
The O ₂ strength is 10 to 20%, which is less likely to enter the intended place than the grain boundary forming element.

[0007]

[Means for Solving the Problems] Regarding the elements that affect the soft ferrite properties by entering the inside of the crystal grains, a predetermined amount is added in advance with a chloride solution, and pyrolysis is performed in a roasting furnace to improve the composition. It is possible to obtain a uniform mixed oxide ferrite raw material powder. The obtained powder is 0.05-0.1μ
At about m, the fine powder is appropriately heat-treated to grow the powder particle size, and the particle size is set to a value that can be processed by a normal powder molding process. Before this heat treatment process, the trace elements that enter the crystal grains are mixed in the form of oxides without mixing in the chloride state, and the trace elements that enter the crystal grains are mixed in the form of oxide, which is then heated to a suitable powder. The body particle size may be grown.

As described above, the present invention provides a raw material powder containing the components in the soft ferrite crystal homogeneously and having a finer and more uniform particle size than the conventional raw material powder for a soft ferrite sintered body. This raw material powder is 5-10μ in a normal sintering process.
It has a grain size of m and a sintered density of 4.95 g / cm ^2.
It is possible to easily produce a soft ferrite sintered body that exceeds the above. That is, it is an object of the present invention to provide a method for manufacturing a soft ferrite sintered body which has a small power loss in a high frequency region, has a good saturation magnetic flux density due to the soundness of its crystal, and has a so-called good mounting result.

The present invention will be described in detail below. Fe ₂ O which is the main component of these soft ferrite sintered bodies
_3, MnO, ZnO content is desirably 31 mol% ≦ MnO ≦ 44 mol% 5 mol% ≦ ZnO ≦ 14 mol% 51 mol% ≦ Fe ₂ O ₃ ≦ 55 mol%. The subcomponents are selected from 100 ppm ≤ TiO ₂ ≤ 5000 ppm 100 ppm ≤ SnO ₂ ≤ 5000 ppm 100 ppm ≤ ZrO ₂ ≤ 2000 ppm 80 ppm ≤ SiO ₂ ≤ 400 ppm 200 ppm ≤ CaO ≤ 800 ppm.

[0010]

【Example】

Example 1 First, a 40% solution of a ternary mixture containing iron chloride, zinc chloride, and manganese chloride was produced, and then, in a roasting furnace in which the furnace temperature was controlled at 800 to 900 ° C., with a two-fluid spray nozzle, for example, 150
It is sprayed with a droplet diameter of about μm, and oxidized and roasted. In order to obtain the target three-component composition, the composition of the components composing the ferrite such as Fe, Mn, and Zn in the three-component mixed 40% chloride solution is adjusted in advance to a predetermined composition after oxidation roasting. ,
A mixed oxide ferrite raw material powder was produced. S of this powder
The average particle diameter by EM observation was 0.06 μm. To this fine powder, TiO ₂ or the like, which mainly defines the soft ferrite characteristics by entering into the crystal grains, is added, and then the powder is heat-treated at 800 ° C. for 5 minutes. After that, grain boundary forming elements SiO ₂ and CaO were added and mixed and lightly pulverized to obtain a raw material powder of a soft ferrite sintered body. The particle size of the raw material powder observed by SEM is 0.5 μm
It was about.

FIG. 1 shows the particle size (specific surface area in this case) of the conventional raw material powder and the raw material powder of the present invention with respect to the grinding energy.
Indicate. The raw material powder of the present invention becomes fine particles very easily,
It is possible to obtain a powder having a uniform particle size distribution without impurities. Next, these powders are granulated to form an outer shape of 30 mm,
It was molded into a toroidal core having an inner diameter of 18 mm and a height of 5 mm. Sintering temperature of 1150 to 1300 ° C., 4
The firing was performed for a time in a nitrogen atmosphere containing 0.3 to 5% oxygen. The crystal grain size of the ferrite sintered body obtained by using the ferrite raw material powder according to the present invention is 6 μm in average grain size and 10 μm to 20 μm of the conventional crystal grain size obtained by such a usual treatment.
Fine particles compared to m. By using the raw material powder of the present invention having good reactivity, it is possible to easily obtain a fine sintered body having fine particles and high sintering density.

Example 2 As in Example 1, a 40% ternary mixed solution containing iron chloride, zinc chloride, and manganese chloride in a predetermined ratio is prepared. Further, titanium chloride is dissolved in alcohol or the like and added in the required amount to the above mixed solution, and then pyrolyzed in a roasting furnace in the same manner as in Example 1 to produce a mixed oxide ferrite raw material powder that also uniformly contains Ti. did. Next, this mixed ferrite powder was heat-treated in the atmosphere at 700 ° C. for 2 hours to grow the particle size of the powder. After that, SiO ₂ and CaO as sub-component
Was added and lightly treated with a mixing and disintegrating device. The particle size of the powder at this time was also 0.5 μm. Next, these powders were granulated, molded in the same manner as in Example 1, and fired. The crystal grain size of the obtained sintered body was similar to that in Example 1.

The conventional method and Examples 1 and 2 were adjusted as follows. The components are one of three methods. Conventional method: Mixing main components such as Fe, Mn, Zn, and Ti in the state of oxides and adjusting by a normal method Example 1; Adjusting with Fe, Mn, Zn chloride solution and performing oxidation roasting, Ti is added to the above roasted powder in an oxide state, and other subcomponents are added in an oxide state after heat treatment. Example 2; Fe, Mn, Zn, Ti Chloride solution is used to adjust the oxidation roasting. Conducted, other subcomponents are added in the oxide state after heat treatment

FIG. 2 shows the temperature dependence of the power loss value at 100 KHz and 200 mT. Fe ₂
Example 1 and Example 2 are compared with the loss value of the conventional method in which O ₃ , Mn ₃ O ₄ , ZnO and other necessary raw material powders are mixed and treated. Example 2 showed more than 10% improvement over Example 1. In addition to the characteristics shown in FIG. 2, the difference between the conventional method and the embodiment widens as the applied frequency is increased, which is a characteristic obtained from the characteristics of the sintered crystal according to the present invention. Furthermore, the saturation magnetic flux density (B ₁₀ ) of the core is 548 mT and the residual magnetic flux density is 10
It shows excellent characteristics of 0 mT. The core is not limited to this, and has the following outstanding features. When implemented as a power supply, it is often subject to load fluctuations in the so-called first quadrant rather than the sine wave.

FIG. 3 shows the result when a rectangular wave simulating the so-called first quadrant is used as the evaluation load. In this case, the ferrite core of the present invention exhibits excellent characteristics in all frequency regions measured. Here, the power loss evaluation measurement is replaced by the calorific value of the core. Incidentally, the results obtained by molding the ferrite raw material powder according to the present invention into a transformer core and evaluating the transformer core are shown below. The evaluation was carried out by incorporating it in a so-called partial resonance power supply circuit.

FIG. 4 shows the evaluation result as a rise in core surface temperature. When the power loss is small, the temperature rise of the core is small, but it can be seen that the core according to the present invention is superior as in the result of the power loss obtained in FIG. in this way,
By applying the present invention, from about 100 KHz to 5
A soft ferrite sintered body for a power source, which can be used with the same core in a frequency region up to about 00 KHz, was obtained.

[0017]

As described above, the composition of the constituents of the present invention is more uniform than the conventional method, less impurities are mixed, the average particle size is small, the particle size distribution is good, and the powder reactivity is high. It is possible to easily obtain a raw material powder (so-called calcined powder) of a good soft ferrite sintered body. Further, by using the raw material powder of the soft ferrite sintered body according to the present invention, it is possible to extremely easily control the crystal grain size of the sintered body to 5 to 10 μm, and therefore, it is excellent in the frequency range from 100 KHz to 500 KHz. It is possible to manufacture cores for high frequency power supplies that exhibit excellent power loss characteristics. Thus, the present invention is 100 KH
It is an object of the present invention to provide a magnetic core of a power transformer for a switching power supply and a method for producing a raw material powder thereof, which are compatible with z to about 500 KHz.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a particle size (specific surface area) of raw material powder and crushing energy,

FIG. 2 is a diagram showing power loss (100 KHz-200 mT) of a soft ferrite core according to the present invention,

FIG. 3 is a diagram showing a power loss comparison (the present invention and a conventional method) when a rectangular wave is applied as a load.

FIG. 4 is a view showing a power supply mounting evaluation result (core surface temperature rise measurement).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kaoru Ito 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Kanagawa Prefecture, Advanced Technology Research Laboratories (72) Inventor, Kazuma Sasaki 1618, Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Address Nippon Steel Co., Ltd. Advanced Technology Research Laboratory (72) Inventor Shinya Nariki 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Nippon Steel Co., Ltd. Advanced Technology Research Laboratory

Claims (2)

[Claims] 1. A method for producing a ferrite sintered body containing iron oxide, manganese oxide and zinc oxide as main components, wherein a liquid obtained by mixing main components constituting ferrite in a chloride solution at a predetermined ratio is spray roasted. After mixing in the required amount of trace elements present in the crystal grains of the ferrite sintered body in the form of oxide, in a mixed oxide powder obtained by spraying in a baking furnace and thermally decomposing, at 400 ° C or higher and 1100 ° C or lower. Characterized by adding the required amount of trace elements present in the crystal grain boundaries of the ferrite sintered body in the form of oxides after heat treatment, and then granulating, shaping and firing the soft ferrite raw material powder obtained by mixing and crushing And a method for manufacturing a high-frequency soft ferrite sintered body. 2. A method for producing a ferrite sintered body containing iron oxide, manganese oxide and zinc oxide as main components, wherein main components constituting ferrite are mixed in a chloride solution at a predetermined ratio and are mainly ferrite-fired. A mixed oxide powder obtained by pyrolyzing a liquid obtained by mixing a trace amount of trace elements existing in the crystal grains of the aggregate in the form of chloride in a spray roasting furnace to obtain a mixed oxide powder at 400 ° C or more and 1100 ° C or less. After the heat treatment, the necessary amount of trace elements existing in the crystal grain boundaries of the ferrite sintered body is added in the form of oxide, and then the soft ferrite raw material powder obtained by mixing and crushing is granulated, shaped and fired. A method for producing a characteristic high-frequency soft ferrite sintered body.