JP2003068517A - Mn-Zn FERRITE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide Mn-Zn ferrite which is small in dependency on frequency from a low frequency domain around 1 kHz to a high frequency domain of 300 kHz and besides can get high initial permeability extending for these frequency domain. SOLUTION: This Mn-Zn ferrite has such composition that it contains MnO by 20-30 mol% and ZnO by 18-25 mol% and the rest is Fe2 O3 , and out of impurities mixed in that ferrite, the quantities of mixing of Na, B, and P are suppressed to 10 ppm or under for Na, 5 ppm or under for B, and 15 ppm or under for P by mass ppm.

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 having a high initial magnetic permeability, which is mounted on a switching power supply, a noise filter, a choke coil or the like.

[0002]

2. Description of the Related Art Mn-Zn soft ferrites are used in switching power supplies, noise filters, choke coils and the like. Above all, since the ferrite core used for the noise filter is required to have a large impedance against noise current in the frequency band where noise is desired to be removed, it is desired that the high initial permeability (μ _i ) can be maintained up to a higher frequency band. However, Mn-Zn ferrite can increase the initial permeability compared to Ni-Zn ferrite, but as the initial permeability increases, magnetic relaxation and resonance phenomena occur in the low frequency range, so the initial permeability is Falls sharply.

The frequency characteristic of the initial magnetic permeability is such that Fe ₂ O ₃ , ZnO, which constitutes spinel which is a crystal matrix,
It has been clarified that the composition ratio of MnO and the minor components existing near the crystal grain boundaries have a great influence, and from this viewpoint, various examples of improving the frequency characteristic of initial permeability have been reported. For example, in Japanese Patent Publication No. 51-49079,
By adding an appropriate amount of Bi ₂ O ₃ or CaO to Mn-Zn ferrite, a high initial magnetic permeability of about 8000 to 9000 at 100 kHz is obtained. Further, JP-A-7-21535 and JP-A-7-21
In the 1536 publication, by adding an appropriate amount of CaO, Bi ₂ O ₃ , and SiO ₂ , the initial permeability is 5000 or more at a frequency of 100 kHz,
We have proposed Mn-Zn ferrites of 4000 or more at a frequency of 500 kHz. Furthermore, in JP 2001-85217, P is 0.00
03-0.003% by weight, with an average crystal grain size of more than 50 μm 200
We have proposed a Mn-Zn ferrite with an initial permeability of 15,000 or more at 10 kHz or 100 kHz by making it below μm.

However, in the case of Japanese Patent Publication No. 51-49079, the characteristic improvement is limited to a relatively low frequency region up to around 100 kHz, and there is little improvement effect around 500 kHz, which is becoming more and more important in practical use. Further, in the cases of JP-A-7-211535 and JP-A-7-211536, the characteristic improving effect can be seen up to a high frequency region of about 500 kHz, but the initial permeability at 500 kHz is limited to about 5500 at the maximum. Further, JP 2001-
In the case of 85217, although the initial permeability up to 100 kHz is extremely high, the rate of change with respect to frequency fluctuation is extremely large, so the initial permeability decreases by about 50% only when the frequency changes from 10 kHz to 100 kHz. Therefore, in the frequency region of 300 kHz or higher, the initial magnetic permeability is extremely reduced, and it cannot be put to practical use in applications such as noise filters.

By the way, in order to improve such an initial magnetic permeability, if a device for increasing the initial magnetic permeability in a low frequency region of about 1 kHz to 100 kHz is adopted, the initial magnetic permeability is inevitably lowered in a high frequency region of 300 kHz to 1 MHz. Is inevitable, and it is difficult to maintain a high initial permeability even in the high frequency range. Also, in order to secure a high initial permeability even at 100 kHz or higher, the initial permeability in the low frequency range of 10 kHz or lower must be extremely high.
In this case, the frequency change becomes extremely large. In this way, when the initial magnetic permeability fluctuates greatly according to the fluctuation of the frequency and the variation becomes large, it becomes difficult to design the noise filter and the like. Therefore, there has been a demand for the development of a ferrite core having a high initial magnetic permeability with a small change in the initial magnetic permeability even in a high frequency region of about 300 kHz or more.

[0006]

SUMMARY OF THE INVENTION The present invention has been developed in view of the above-mentioned circumstances, and it has been developed from a low frequency region of about 1 kHz.
The frequency dependence up to a high frequency region of about 300 kHz is small,
Moreover, it is an object of the present invention to propose an Mn-Zn system ferrite that can obtain a high initial permeability over these frequency regions.

[0007]

That is, the present invention is based on Mn
O: 20 to 30 mol% and ZnO: 18 to 25 mol%,
The balance is Mn-Zn type ferrite having a composition of Fe ₂ O ₃ , and the amounts of Na, B and P mixed in the ferrite are respectively mass ppm of Na: 10 ppm or less, B: 5 ppm or less. And P: Mn characterized by being suppressed to 15 ppm or less
-Zn type ferrite.

Further, the present invention contains MnO: 20 to 30 mol% and ZnO: 18 to 25 mol%, and the balance is Fe ₂ O ₃ as a basic component. Calcium (calculated as CaO): 50-1000 ppm, silicon dioxide (Si
O ₂ conversion: 50 to 200 ppm and bismuth oxide (Bi ₂ O ₃
Conversion), indium oxide (In ₂ O ₃ conversion), tantalum oxide (Ta ₂ O ₅ conversion), niobium oxide (Nb ₂ O ₅ conversion), titanium oxide (TiO ₂ conversion), tin oxide (SnO ₂ conversion) and oxidation A total of at least one selected from molybdenum (converted to MoO ₃ ): a Mn-Zn ferrite having a composition containing one or more selected from 3000 ppm or less,
Mn-Zn characterized in that the amounts of Na, B, and P mixed in the ferrite are suppressed to Na: 10 ppm or less, B: 5 ppm or less, and P: 15 ppm or less in mass ppm, respectively.
It is a system ferrite.

The basic components MnO, ZnO, Fe ₂ O ₃
Content is mol based on the total amount of MnO, ZnO and Fe ₂ O _3.
%, Na, B, P, CaO, SiO ₂ , Bi ₂ O ₃ , In ₂ O ₃ , Ta
The content of ₂ O ₅ , Nb ₂ O ₅ , TiO ₂ , SnO ₂ , and MoO ₃ is mass ppm in the Mn—Zn ferrite.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION First, the reason why the basic component composition is limited to the above range in the present invention will be explained. It is known that the magnetic anisotropy constant and magnetostriction constant that have a significant effect on the initial magnetic permeability depend on the composition ratio of Fe ₂ O ₃ , MnO, and ZnO. These Fe ₂ O ₃ and MnO are selected from the viewpoints of the initial magnetic permeability and the peaks (secondary peaks) and Curie points due to small magnetic anisotropy and magnetostriction near room temperature. Therefore, the composition range of ZnO is limited. Furthermore, the operating temperature of noise filters is usually from room temperature.
Since it is about 120 ° C, it is required that the initial magnetic permeability is high and the temperature coefficient is positive in this temperature range.

From the above viewpoints, the composition range of Fe ₂ O ₃ , MnO and ZnO is limited as follows. MnO: 20~30 mol% ZnO: 18~25 mol% Fe 2 O 3: rest Here, the MnO exceeds 20 mol% or less than 30 mol%, also ZnO is more than less than 18 mol% or 25 mol%, of the spinel chemistry The initial permeability is significantly reduced due to the change in composition. Therefore, the content of MnO and ZnO is limited to the above range. As the MnO or ZnO raw material, not only an oxide but also a compound such as a carbonate which can be changed into this form by firing can be used.

The Mn-Zn ferrite of the present invention has the above-mentioned composition as a basic composition, but in addition, calcium oxide, silicon dioxide, bismuth oxide, indium oxide, tantalum oxide, niobium oxide, titanium oxide, tin oxide and At least one selected from molybdenum oxide can be appropriately contained. Such Mn-Zn _{ferrite, Fe 2 O 3 -ZnO-MnO} -CaO-SiO 2, Fe 2 O 3 -ZnO-
_{MnO-CaO-Bi 2 O 3} , Fe 2 O 3 -ZnO-MnO-CaO-In 2 O 3
_{, Fe 2 O 3 -ZnO-MnO} -CaO-TiO 2, Fe 2 O 3 -ZnO-Mn
_{O-CaO-SiO 2 -Ta 2} O 5 and _{Fe 2 O 3 -ZnO-MnO-} Ca
Examples thereof include O—SiO ₂ —Nb ₂ O ₅ —Bi ₂ O _{3 and the} like, but the present invention is not limited to these examples.

Among the above-mentioned additive components, CaO and SiO ₂ segregate at the grain boundaries to contribute to the reduction of loss of Mn-Zn ferrite, and Bi ₂ O ₃ and In ₂ O ₃ are low melting point compounds. By promoting crystal growth, it contributes to high magnetic permeability.
In addition, TiO ₂ and SnO ₂ contribute to lower loss by increasing the resistance inside the crystal, and Ta ₂ O ₅ and Nb ₂ O ₅ contribute to lowering the loss by increasing resistance at the grain boundaries. Furthermore, MoO ₃ contributes to uniform grain growth. From the above viewpoint, the content of calcium oxide is
50-1000 ppm in terms of CaO, the content of silicon dioxide is Si
It was set to 50 to 200 ppm in terms of O ₂ . In addition, bismuth oxide, indium oxide, tantalum oxide, niobium oxide, titanium oxide,
The contents of tin oxide and molybdenum oxide are
_{Bi 2 O 3, In 2 O} 3, Ta 2 O 5, Nb 2 O 5, was limited to a total of 3000ppm in TiO _2, SnO ₂ and MoO ₃ conversion. All the above ppm are mass ppm.

As described above, Fe ₂ O ₃ , ZnO, Mn
Of course, it is important to determine the composition of the basic component of O and the amount of the additional component, but it is difficult to effectively suppress the fluctuation of the initial magnetic permeability in the desired frequency band by only this. Therefore, as a result of intensive studies on this point, the present inventors have found that among the impurities that are inevitably mixed during the production of the ferrite core, particularly, the inclusion of sodium (Na), boron (B), and phosphorus (P). It has been newly found that the intended purpose can be advantageously achieved by suppressing the amount as much as possible.

Of the trace elements in the Mn-Zn ferrite,
Regarding the influence of sodium, it is described, for example, in the document “Ferrite” (Hiraga et al., Maruzen, 1986), “suppressing the action of compounds that significantly promote grain growth” on page 47.
Further, as an effect of boron on the Mn-Zn ferrite, for example, in page 92 of the same document "Ferrite", since the crystal structure is made non-uniform to inhibit the development of high magnetic permeability,
It must be below pm ". However, the effect of Mn-Zn ferrite on the frequency dependence of the initial permeability is not mentioned at all. Further, according to the document "Ferrite", sodium suppresses the effect of boron, but there is no mention of the effect of the initial magnetic permeability on the frequency dependence and its variation when both are present at the same time. Furthermore, phosphorus is not described at all in the above literature.

Regarding phosphorus, for example, "J. PHYS.
IV France 7 (1997) Colloque Cl-128 ", shows the relationship between iron loss and phosphorus content in low-loss Mn-Zn ferrites for power supplies.The frequency dependence of the initial permeability of Mn-Zn ferrites in particular. Nothing is said about the effect of phosphorus on the.

Further, Japanese Patent Laid-Open No. 2000-277318 discloses a technique for limiting the amounts of boron and phosphorus in Mn-Zn ferrite. This technique is intended to obtain high initial permeability over a wide temperature range. However, the objective is completely different from the present invention which aims at reducing the frequency dependence of the initial magnetic permeability. Further, in this publication, there is no mention of sodium.

With respect to these points, the inventor has conducted various studies, and as a result, (1) sodium, boron and phosphorus were
-Once mixed in the Zn-based ferrite manufacturing process,
It is very difficult to remove it in the middle of the process such as the firing process,
Therefore, the amount of sodium, the amount of boron, and the amount of phosphorus in the raw material (for example, in iron oxide) must be specified, and the amount contained in the final ferrite must be specified.
In the frequency region of 300 kHz, in order to suppress structural nonuniformity such as abnormal grain generation and variation in grain size distribution of crystal grains, and to achieve high magnetic permeability stably without fluctuation, regarding the mixing amount of these elements in ferrite, By mass ppm, it was newly clarified that it is necessary to suppress sodium: 10 ppm or less, boron: 5 ppm or less, and phosphorus: 15 ppm or less, and the present invention has been completed.

As described above, in order to manufacture a ferrite core containing a small amount of impurity elements such as sodium, boron and phosphorus, the manufacturing process is taken into consideration, and the mixing of these impurities in the raw material is suppressed. For example, for iron oxide, iron oxide obtained by spray roasting after removing impurities using a co-precipitation method or the like from a hydrochloric acid pickling waste liquid (iron chloride aqueous solution) for steel plates Fits in an advantageous way.

The minor components mixed in the Mn-Zn type ferrite include Al, Cr, Ni, Co and Mg in addition to Na, B, P and the like. If it is too large, disadvantages such as abnormal grain growth and deterioration of magnetic properties will occur, so it is desirable to reduce these trace components to a total of 1000 ppm or less.

Next, a preferred method for producing the Mn-Zn ferrite according to the present invention will be described. In general, Mn-Zn-based ferrite is prepared by mixing each powder raw material including raw iron oxide so as to have a predetermined final composition and calcining, and then mixing the additive components in the obtained calcined ferrite powder and pulverizing the mixture. After that, it is manufactured by granulating, compression molding, and then firing.
In such a production method, in the present invention, the temperature is raised at a rate of at least 400 ° C./h or more in a non-oxidizing atmosphere until the temperature reaches 1100 ° C. during the firing process until the firing holding temperature is reached. In doing so, adjust the oxygen concentration in the firing atmosphere.
It is preferable to bake at 10 vol% or less. here,
Grain size consisting of a single spinel crystal phase means that the temperature is raised from 1100 ° C during the firing to the firing holding temperature at a rate of at least 400 ° C / h and the firing atmosphere is a non-oxidizing atmosphere. This is because a large and uniform sintered body is formed, the specific resistance is increased by the subsequent firing while maintaining the temperature in a controlled oxygen atmosphere, and the decrease in the initial permeability in the high frequency region due to the occurrence of eddy current loss is suppressed. The non-oxidizing atmosphere may be industrially used nitrogen or carbon dioxide, or a vacuum that can be produced by a normal rotary pump or the like. Of course, a rare gas such as Ar or He can be used although it is expensive.

[0022]

[Example] The content of each element in the ferrite is fluorescent X
After mixing the raw materials so as to have various basic compositions as shown in Table 1, using a sample in which the content of each element is clear in advance and using iron oxide containing various ranges of sodium, boron, and phosphorus It was calcined at 950 ° C for 3 hours. Then, calcium oxide, silicon dioxide, bismuth oxide, indium oxide, tantalum oxide, niobium oxide, titanium oxide, tin oxide, molybdenum oxide, etc. are appropriately added to this basic component, and after crushing with a ball mill for 8 hours, ring-shaped Molded into a core, then heated in air at a heating rate of 250 ° C / h, and the temperature was raised from 1100 ° C to a nitrogen atmosphere at a heating rate of 500 ° C / h.
Temperature, and after reaching a holding temperature of 1340 ° C, firing was performed for 2 to 5 hours with the oxygen concentration controlled to 10 vol% or less, so that Na, B, and P in the core as shown in Table 2 were obtained. Ferrite cores containing various types of were prepared. The ferrite cores thus obtained have a frequency of 1kHz and 300kHz (25kHz
The initial permeability μ _i at (° C.) was measured. In Table 2, the initial permeability μ _i is the permeability in vacuum μ for easy comparison.
_{The value} is divided by ₀ and expressed as μ _i / μ ₀ (specific initial permeability). The obtained results are also shown in Table 2. In Table 2, Nos. 1 to 15 are inventive examples, and Nos. 16 to 32 are comparative examples.

[0023]

[Table 1]

[0024]

[Table 2]

As is clear from Table 2, in each of the invention examples obtained according to the present invention, the change in initial permeability at frequency: 300 kHz was within 10% with respect to the initial permeability at frequency: 1 kHz. It can be seen that the frequency dependence of the initial permeability is extremely small.

[0026]

Thus, according to the present invention, the initial magnetic permeability μ
The frequency dependence of _i is small, and it is possible to obtain Mn-Zn ferrite with excellent initial permeability from the low frequency region of 1 kHz to the high frequency region of 300 kHz, and especially when applied to noise filters in the high frequency region. Play a great effect.

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Claims (2)

[Claims] 1. A Mn--Zn type ferrite containing MnO: 20 to 30 mol% and ZnO: 18 to 25 mol% and the balance being Fe ₂ O ₃ and Na mixed in the ferrite. , B and P
The Mn-Zn ferrites are characterized in that the content of each of these is suppressed to Na: 10 ppm or less, B: 5 ppm or less and P: 15 ppm or less in mass ppm, respectively. 2. MnO: 20 to 30 mol% and ZnO: 18 to 25 mol%, the balance being Fe ₂ O ₃ as a basic component, and calcium oxide (calculated as CaO) in mass ppm in this basic component. ):
50 to 1000 ppm, silicon dioxide (SiO ₂ conversion): 50 to 200 ppm, bismuth oxide (Bi ₂ O ₃ conversion), indium oxide (In ₂ O ₃
Tantalum oxide (Ta ₂ O ₅ equivalent), niobium oxide (Nb
₂ O ₅ conversion, titanium oxide (TiO ₂ conversion), tin oxide (SnO ₂ conversion)
(Combination) and molybdenum oxide (in terms of MoO ₃ ) at least one in total: Mn-Zn-based ferrite having a composition containing one or two or more selected from 3000 ppm or less. Na and B mixed in
An Mn-Zn-based ferrite characterized in that the content of P and P is suppressed to 10 ppm or less for Na, 5 ppm or less for B, and 15 ppm or less for P, respectively in mass ppm.