JPH06260321A - Sintered ferrite with fine crystalline grains and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture low-cost extrafine grain sintered material by using extrafine powder having specific mean primary grain size to be obtained by spray roasting method as raw material powder, and sintering it under normal pressure at a specific temperature controlled in a sintering atmosphere. CONSTITUTION:The sintered ferrite with fine crystalline grains comprises, as main ingredient composition, 50-55mol% of Fe2O3, 30-45mol% of MnO and 5-20mol% of ZnO; and a fine amount of additive elements 80-1000ppm of SiO2 and 200-6000ppm of CaO. Sintered Kn-Zn ferrite comprises, as trace impurities, 20ppm or less of P, 50ppm or less or Cr, sintering density of 4.7g/cm<3> or more, and a mean crystalline grain size of 2mum or less. Thus, a soft ferrite core having excellent power loss in a MHz range can be manufactured with low cost, and a high frequency transformer can be reduced in size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferrite sintered body used for a power transformer or the like.

[0002]

2. Description of the Related Art In recent years, power transformers used for switching power supplies and the like have been required to be smaller and lighter. Therefore, the driving frequency has been expanded from the conventional 100 kHz to the high frequency region of 500 kHz or more, and in the future. Is considered to be applied in the MHz region. However, the eddy current loss, which is a particular problem in the high frequency region of the power loss, is proportional to the square of the driving frequency, and therefore the power loss increases as the frequency increases, and the amount of heat generated cannot be ignored.

In order to solve such a problem, it is effective to reduce the grain size of the sintered body. For example, in JP-A-1-224265, the power loss is improved by setting the average crystal grain size of the sintered body to 5 μm or less. Further, there is also an example in which a fine powder manufactured by a hydrothermal synthesis method is used as a raw material and is sintered by a HIP method to form a fine sintered body having a crystal grain size of 2 μm to improve power loss in a high frequency region. Reported (Nikkei Materials & Technology, January 1993 issue, p. 24).

However, as disclosed in JP-A-1-224265, the particle size is 0.8 to 1.0 μm.
It is difficult to manufacture a sintered body having a grain size of 2 μm or less by a conventional method in which the calcined powder of 1 is used as a raw material and is fired at a temperature of 1150 to 1250 ° C. In order to produce a sintered body having an extremely fine grain size, it was necessary to use fine powder produced by the hydrothermal synthesis method as a raw material and perform sintering by HIP or hot pressing as described above. However, when the powder is produced by the hydrothermal synthesis method or when the sintering is performed by using HIP or hot press, the production cost becomes very high and there is a problem in mass production.

[0005]

DISCLOSURE OF THE INVENTION The present invention is capable of producing ultrafine particles of 2 μm or less by ordinary pressureless sintering without using the conventional hydrothermal synthesis method such as powder production or equipment such as HIP and hot pressing. The purpose is to inexpensively obtain a sintered body having a crystal grain size.

[0006]

In order to solve the above problems, particularly in the present invention, the firing conditions of the raw material calcined powder and the molded body were examined. As a result, ultrafine powder having an average primary particle size of 0.1 μm or less obtained by the spray roasting method was used as the raw material powder, and the firing atmosphere was controlled for this 1.
The inventors have found that the desired ultrafine grained sintered body can be obtained at a very low cost by performing atmospheric pressure sintering at 100 ° C. or less, and have completed the present invention.

That is, the present invention is as follows. (1) Main component composition is Fe ₂ O ₃ 50 to 55 mol%, MnO
It is in the range of 30 to 45 mol% and ZnO is 5 to 20 mol%, and SiO _{2 is} 80 to 1000 p as a minor addition element.
pm, CaO of 200 to 6000 ppm is contained, the amount of P as a trace impurity is 20 ppm or less, and the amount of Cr is 50.
ppm or less and a sintered density of 4.7 g / cm ³ or more,
Average crystal grain size is 2μm or less, minimum power loss is 1MH
M of 300 kW / m ³ or less under the condition of z-50 mT
n-Zn ferrite sintered body.

(2) In the method for producing a Mn-Zn based ferrite sintered body according to (1), Fe, Mn, and Zn are mixed in the form of a chloride solution, and the mixture is spray-baked to obtain an average primary Using Mn-Zn-based soft ferrite raw material powder having a particle size of 0.1 μm or less, this was directly granulated and molded, and the temperature was raised to 400 ° C. in the firing step in the atmosphere to remove the binder, and thereafter, The atmosphere in the temperature rising process is performed under a nitrogen atmosphere with an oxygen partial pressure of 100 ppm or less, and
A method for producing an Mn—Zn-based ferrite sintered body, which comprises sintering under normal pressure at a temperature of 100 ° C. or lower.

[0009]

According to the above invention, a sintered body having an extremely fine crystal grain size of 2 μm or less can be easily produced, and a ferrite core with greatly reduced eddy current loss in the MHz region can be produced. . In the present invention, the main component composition is Fe ₂ O ₃ 50
~ 55 mol%, MnO30-45 mol%, ZnO5-2
The reason for defining the range of 0 mol% is that the power loss deteriorates in the composition other than this range.

The purpose of adding SiO ₂ and CaO as the trace elements is to increase the resistance of the grain boundaries and further reduce the eddy current loss. Here, the addition amount of SiO ₂ is 80
The amount of SiO ₂ is less than 80 ppm, and the effect of improving the characteristics is small.
Grain growth is promoted when the amount exceeds 000 ppm,
This is because a sintered body having a target grain size cannot be obtained, and power loss also deteriorates. On the other hand, CaO is a component effective in increasing the resistance of the grain boundary in the coexistence with SiO ₂ , but the range was limited to 200 to 6000 ppm because
This is because if the amount is less than 200 ppm, the effect of improving the characteristics is small, and if it is more than 6000 ppm, the power loss is deteriorated. The amount of P and Cr is 20p each
The reason why the amount is less than or equal to pm and less than or equal to 50 ppm is that if the amount of impurities is larger than this, the power loss is significantly deteriorated.

In the second aspect, the average primary particle diameter of the raw material powder is set to 0.1 μm or less, because when powder having a larger particle diameter is used as the raw material, the sinterability is deteriorated and the sintered density is This is because the particle size becomes lower and the crystal grain size of the finally obtained sintered body becomes larger. Even if a wet method such as a hydrothermal synthesis method is used as a method for producing the raw material powder instead of the spray roasting method, an equivalent fine raw material powder can be obtained, but the production cost is much higher than that of the spray roasting method. There is a problem of becoming expensive. There is also a method of producing fine powder by excessively pulverizing the calcined powder obtained by the usual solid-phase method, but the particle size distribution is widened, and the characteristics are deteriorated due to contamination by pulverization. . Further, due to the non-uniformity of the composition, grain growth easily occurs, and it becomes difficult to obtain the fine grain sintered body of the present invention.

The reason why a fine-grained sintered body can be easily obtained by using a spray roasting powder as a raw material in the present invention is as follows. In the conventional raw material calcined powder, primary particles have a particle shape that is bonded by sintering, but such hard agglomerates are not removed even after molding, resulting in poor moldability or relatively large fine particles between particles. Since the pores are generated and the number of pores is increased after firing, the firing density becomes low. In addition, grain growth in the bonded portion occurs preferentially during firing, and the crystal grain size in that portion increases, resulting in an uneven microstructure.

On the other hand, in the spray-roasted powder of the present invention, since each primary particle exists independently, the moldability is good and the sintering also occurs uniformly. Further, in order to obtain a sintered body of such fine crystal grains, the initial sintering behavior is important, and the uniformity of the powder composition has an influence. Compared with the usual method, the spray roasted powder has an extremely uniform microchemical composition, so that the grain growth occurs uniformly without causing local grain growth, and the crystal grain size of the finally obtained core is It has an extremely fine and uniform structure. Further, by subjecting the solution to be sprayed to high purification treatment, it is possible to obtain high-purity raw material powder, and a core with high characteristics can be obtained.

The spray roasting powder used in the present invention can be obtained by roasting a mixture of Fe, Mn and Zn in the form of a chloride solution, and the solution at the time of roasting must always contain three components. Is essential, for example, when a method such as producing only one component or two components by spray roasting and then mixing the remaining components is used, the composition is non-uniform and The characteristics are deteriorated due to the incompleteness of the reaction.

There are some reports on the production of ferrite cores using spray roasted powder, but Japanese Patent Application No. 4-1
As disclosed in "Production Method of High Frequency Soft Ferrite Sintered Body" of No. 50656 or "Composite Soft Magnetic Core and Its Production Method" of Japanese Patent Laid-Open No. 4-213805, the fine powder after roasting is 400 to 1100 ° C or 80
It is usual to carry out molding after heat treatment at a temperature of 0 ° C. or higher to increase the particle size. Therefore, it can be said that direct granulation and molding of the fine powder is one of the features of the present invention.

When obtaining the sintered body, the firing temperature is 1100 ° C.
The reason for the following is that when firing at a temperature higher than this, grain growth occurs violently and the crystal grain size becomes larger than 2 μm. Further, the atmosphere at the time of temperature rise is a nitrogen atmosphere having an oxygen partial pressure of 100 ppm or less. When the oxygen partial pressure is higher than 100 ppm, a dense sintered body cannot be obtained or α-Fe ₂ O ₃ is produced. However, this is because a single ferrite phase may not be obtained.

[0017]

The present invention will be described below with reference to specific examples of the present invention.
Will be explained. Fe by spray roasting ₂O₃ 71 wt%, M
Produce powder with composition of nO 22wt% and ZnO 7wt%
And SiO₂ 200ppm, CaO 800ppm
Ferrai with an average particle size of approximately 400Å by adding and mixing the composition
The raw material powder was manufactured. The content of P and Cr in the raw material powder is
It is 15 ppm and 35 ppm. As a binder
After adding PVA to 1.0% and granulating, the outer diameter is 29 mm,
It was formed into a ring shape having an inner diameter of 18 mm and a height of 7 mm. this
The molded body is fired for 4 hours under the firing conditions described in claim 2.
It was

In this way, the firing density is 4.8 g / cm.
A dense sintered body of ³ or more was obtained. Crystal grain size of the fired core and 1
Table 1 shows the values of power loss at MHz-50 mT and 100 ° C. In Comparative Examples 1 and 2 in the table, the firing temperature was 1
The results for the fired cores obtained at 200 ° C. and 1300 ° C. are shown, and Comparative Example 3 adjusts the purity of the sprayed solution, and the P and Cr contents are 40 ppm and 85 p, respectively.
This is the characteristic of the core in pm. As is clear from Table 1, the fired core of the present invention has very excellent power loss at high frequencies.

[0019]

[Table 1]

[0020]

As described above, according to the present invention, high frequency,
In particular, a soft ferrite core excellent in power loss in the MHz region can be manufactured at low cost, which is extremely effective for downsizing a high frequency transformer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumihiko Hasegawa 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Inside Advanced Technology Research Laboratories, Nippon Steel Corporation (72) Inventor Yoshitaka Yamana 2-6 Otemachi, Chiyoda-ku, Tokyo -3 Inside Nippon Steel Corporation

Claims (2)

[Claims] 1. Main component of Fe ₂ O _{3 is} 50 to 55 mol%, M
nO30~45 mol%, in the range of ZnO5~20 mol%, SiO ₂ 80 to 1000 as further trace additive element
ppm, CaO of 200 to 6000 ppm is contained, the amount of P as a trace impurity is 20 ppm or less, and the amount of Cr is 5
0 ppm or less and a sintered density of 4.7 g / cm ³ or more,
Average crystal grain size is 2μm or less, minimum power loss is 1MH
M of 300 kW / m ³ or less under the condition of z-50 mT
n-Zn ferrite sintered body. 2. The average primary particle obtained by mixing Fe, Mn and Zn in the form of a chloride solution and spray-baking the mixture in the method for producing a Mn—Zn ferrite sintered body according to claim 1. Using Mn-Zn-based soft ferrite raw material powder having a diameter of 0.1 μm or less, this was directly granulated and molded, and the temperature was raised to 400 ° C. in the firing process in the air to remove the binder, and thereafter the ascending process was performed. The atmosphere in the temperature process was performed under a nitrogen atmosphere with an oxygen partial pressure of 100 ppm or less,
A method for producing an Mn—Zn-based ferrite sintered body, which comprises performing atmospheric pressure sintering at a temperature of 00 ° C. or less.