JP2000235912A - Mn-Zn ferrite core and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the machining workability and improve breakdown toughness by continuing the temp. rise in air from room temp. to a specified temp. or higher. SOLUTION: The temp. rise in air is continued from room temp. to 1000 deg.C or more. A material powder is made by using a powder containing manganese monoxide 35 mol%, zinc oxide 12 mol% and ferric oxide, the rest, with calcium oxide 0.05 wt.%, silicon dioxide 0.02 wt.% and diniobium pentaoxide 0.05 wt.% as sub-components. A granulating powder for molding is in a mean grain size of 150 μm and pressed at a forming pressure to form a molding of 60×20×20 mm3 and a density of 2.9 g/cm3. A basic sintering condition is such that in an air atmosphere having an oxygen partial pressure of 21% from room temp. to 1200 deg.C, it is heated at a temp. rise rate of 350 deg.C/h and held at this temp. for 30 min, the oxygen partial pressure is changed to 3%, it is heated at a temp. rise rate of 350 deg.C/h up to 1350 deg.C, held for 2 hrs. and cooled at a rate of 350 deg.C/h, providing a nitrogen atmosphere used at 1200 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Mn-Zn ferrite core used for various electronic components such as a transformer and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a method for producing an Mn-Zn ferrite core which is an oxide magnetic material, a powder after calcining is formed, and a shrinkage reaction in a sintering step is performed to produce a product. At this time, controlling the oxygen partial pressure is indispensable for spinel formation and valence control of iron ions. At a temperature of about 800 to 1200 ° C., which is the initial stage of sintering,
A reducing atmosphere is suitable as a driving force for reducing hematite, and the atmosphere switching temperature is generally set within the above range. This atmosphere requires that the oxygen partial pressure be controlled to a few percent.

[0003] However, the heating rate in all sections is 350 ° C / h.
In the case where the degree is set to be small, it is difficult to obtain a sintered body having good machinability, such as a high-density sintered body or an insufficient degree of grain boundary formation, because densification is promoted.

[0004]

In recent years, there has been an increasing need for miniaturization of electronic components, and easiness of processing is indispensable, and furthermore, there is a demand for improvement in durability when carried. For that purpose, it is necessary to improve the mechanical strength of the material. In particular, a material having high fracture toughness is required.

[0005] However, the above-described conventional technique has the following disadvantages. That is, there is a problem that the machinability is deteriorated due to the increase in density, or cracks are generated due to insufficient formation of grain boundaries.

Therefore, the present invention has good mechanical workability,
It is another object of the present invention to provide a Mn-Zn ferrite core having high fracture toughness and a method for producing the same.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a Mn-Zn ferrite core, wherein the sintering conditions are as follows.
This is a method for producing a Mn-Zn-based ferrite core in which the temperature in air is continuously increased from room temperature to 1000 ° C or higher.

The present invention also relates to a method for producing a Mn-Zn ferrite core, wherein the Mn-Zn is maintained at an arbitrary temperature of 1000 ° C. or higher and lower than the sintering temperature for 10 minutes to 3 hours.
This is a method for producing a ferrite core.

[0009] The present invention also relates to a method for producing a Mn-Zn ferrite core, wherein the atmosphere after completion of the holding is made to have an oxygen partial pressure of 5% or less.

[0010] The present invention also provides a fracture toughness KIC of 1.4M.
N / m ^1.5 or more, sintering density 4.75 to 4.92 g / c
m ³ is a Mn-Zn ferrite core with a.

[0011] The Mn-Zn ferrite core of the present invention comprises:
It is a porous material having a porosity of 6.0% after sintering, so that it is excellent in machinability such as cutting and grinding, and also has a feature that it is difficult to chip due to its high toughness. By holding at the initial stage of sintering at relatively low temperature, or by controlling the oxygen partial pressure,
The surface diffusion of the particles was promoted, and the formation of the grain boundaries was able to be remarkable. As a result, the effect of suppressing the fine cracks by the grain boundaries worked, and the material was resistant to cracking and chipping.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 35 mol% of manganese monoxide (MnO) and 12 mol% of zinc oxide (Zn) as main components
O) and the remaining ferric oxide (Fe ₂ O ₃ ), 0.05% by weight of calcium oxide (CaO)
A raw material powder was prepared using a powder containing wt% silicon dioxide (SiO ₂ ) and 0.05 wt% diniobium pentoxide (Nb ₂ O ₅ ).

The granulated powder used in the molding has an average particle size of 15
The molded body was pressed at a molding pressure of 0 μm and a molding pressure of 60 × 20 × 20 mm ^{3 and} a molded body density of 2.9 g / cm ³ .

The basic sintering conditions are as follows: an atmosphere from room temperature to 1200 ° C. is an air atmosphere with an oxygen partial pressure of 21%, and a temperature rising rate of 3%.
After heating at 50 ° C./h and holding at the same temperature for 30 minutes, the temperature was raised to 1350 ° C. at an oxygen partial pressure of 3% at a rate of 350 ° C./h.
h, hold for 2 hours, then cool at 350 ° C / h,
However, in order to control the amount of Fe ^{2+, a} nitrogen atmosphere was used at 1200 ° C.

For the purpose of comparison, evaluation was made by changing the holding temperature, the holding time, and the timing of switching the atmosphere. The evaluation sample was mirror-finished, and the fracture toughness was measured by the IF method of obtaining KIc from the crack length due to the introduction of a Vickers indenter and Vickers hardness. The results are shown in Table 1.

[0016]

[Table 1]

The preferred holding temperature is 1000 ° C.
As described above, the holding time is preferably in the range of 30 minutes to 3 hours.
It can be seen that was obtained.

Tables 2 and 3 show the results obtained by using a Kistler dynamometer for the grinding resistance when grinding with a surface grinder and a comparison of the amount of chipping.

[0019]

[Table 2]

[0020]

[Table 3]

The comparison of the amount of chipping is the result of measuring one surface of the same size for mirror observation for chipping observation, and subjecting a surface perpendicular to the surface to rotary polishing.

As described above, the superiority of the product of the present invention could be confirmed, as compared with the conventional product, having lower resistance and less tendency to chip.

[0023]

As described above, according to the present invention, a core having excellent mechanical strength can be easily produced, and its industrial value is very large.

Claims (4)

[Claims] 1. A method for producing a Mn—Zn ferrite core, wherein the sintering condition is such that a temperature rise in the air is continued from room temperature to 1000 ° C. or more.
A method for producing an n-type ferrite core. 2. A method for producing a Mn—Zn ferrite core, wherein the core is held at an arbitrary temperature of 1000 ° C. or higher and lower than a sintering temperature for 10 minutes to 3 hours.
A method for producing the Mn-Zn-based ferrite core described in the above. 3. The method for producing a Mn—Zn ferrite core according to claim 2, wherein in the method for producing a Mn—Zn ferrite core, the atmosphere after completion of the holding is set to an oxygen partial pressure of 5% or less. 4. A Mn—Zn ferrite core having a fracture toughness KIC of at least 1.4 MN / m ^1.5 and a sintering density of 4.75 to 4.92 g / cm ³ .