JPH08169756A - Low loss manganese-zinc ferrite core and its production - Google Patents

Abstract

PURPOSE: To provide an Mn-Zn ferrite core capable of considerably reducing loss at about 100kHz frequency applied to a switching power source at present by adopting a specified compsn. CONSTITUTION: This Mn-Zn ferrite core consists essentially of 25-40mol% MnO, 6-25mol% ZnO and the balance Fe2 O3 and further contains 0.002-0.040wt.% SiO2 and 0.02-0.20wt.% CaO as secondary components. The secondary components are segregated on crystal boundaries and the half-width of the concn. distribution is <=10nm. Powdery starting materials are prepd. so as to give the primary and secondary compsns. and they are mixed, calcined, pulverized, compacted and fired to obtain the objective Mn-Zn ferrite core.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for magnetic cores such as transformers for switching power supplies and has a low power loss, Mn-.
The present invention relates to Zn-based ferrite.

[0002]

2. Description of the Related Art Oxide magnetic materials are generically called ferrites. Among them, hard magnetic materials such as Ba ferrite and Sr ferrite, and Mn-Zn ferrite and Ni-Z.
It is divided into soft magnetic materials such as n-ferrite. A soft magnetic material is a material that is sufficiently magnetized even with a very small magnetic field, and is used for power supplies, communication equipment, measurement control equipment, magnetic recording,
It is used in a wide range of computers. Properties required for these soft magnetic materials include low coercive force, high magnetic permeability, high saturation magnetic flux density, and low loss.

In addition to oxide ferrite, soft magnetic materials include metal-based materials. Metal-based soft magnetic materials have a high saturation magnetic flux density, so they are more advantageous than oxide-based ones, but on the other hand, they have low electrical resistance, and when used at high frequencies, magnetic loss due to eddy currents is large. turn into. In particular, in recent years, there has been a demand for downsizing and high density of electronic devices, and the operating frequency has been increasing. In the frequency band of about 100 kHz used for switching power supplies, etc., the resistance of conventional metal-based materials is low. Therefore, the heat generation became large, and its use was almost impossible.

Therefore, it has been mainstream to use Mn-Zn type ferrite as a magnetic material of a power transformer in a high frequency range. However, since this material also has a low electrical efficiency value of several Ω · cm, it has been desired to further reduce the eddy current by further increasing the electric resistance to reduce the magnetic loss as a whole and suppress the heat generation amount. . In order to solve this problem, for example, Japanese Patent Publication No. 36-2283 and Japanese Patent Laid-Open No. 60
In JP-A-12302 and JP-A-5-226138, a small amount of an oxide such as SiO ₂ or CaO is added as a sub-component to Mn-Zn-based ferrite to segregate at the grain boundaries to improve the resistance at the grain boundaries. The total resistivity is several hundred Ω · c
It is higher than m.

[0005]

However, it is not always possible to obtain a low-loss material as it is by simply adding an oxide as a subcomponent, and magnetic loss can be reduced by increasing only the electric resistance value. Do not mean. The present invention is applied to a switching power supply at 100 k.
An object of the present invention is to provide a low-loss Mn-Zn-based ferrite core capable of significantly reducing loss at a frequency of about Hz and a method for manufacturing the same.

[0006]

The present invention SUMMARY OF THE INVENTION may, MnO as main components: 25~40mol% ZnO: 6~25mol% and Fe ₂ O _3: wherein the remaining portion, SiO ₂ as subcomponent: 0.002 to 0. It is characterized in that it contains 040 wt% CaO: 0.02 to 0.20 wt%, and these subcomponent elements segregate at the grain boundaries, and the width thereof is 10 nm or less as the half-value width of the concentration distribution. It is a low-loss Mn-Zn ferrite core.

In addition to the above components, Nb ₂ O ₅ : 0.001 to 0.04% by weight Ta ₂ O ₅ : 0.001 to 0.4% by weight ZrO ₂ : 0.001 to 0.05% by weight V ₂ O _5: 0.001~0.03 should preferably contain at least one selected from weight%.

[0008] Such low loss Mn-Zn ferrite core, MnO as main components: 25~40mol% ZnO: 6~25mol% and Fe ₂ O _3: wherein the remaining portion, SiO ₂ as subcomponent: 0.002 0.040 wt% CaO: 0.02 to 0.20 wt% The raw material powder is adjusted so as to be mixed, calcined, crushed, molded, and then baked. . In this case, 110 in the cooling process after firing
When the oxygen partial pressure at 0 to 800 ° C. is 1.0% or less and the cooling rate is 0.5 to 2 ° C./hour, preferable results can be obtained.

Furthermore, MnO as main components: 25~40mol% ZnO: 6~25mol% and Fe ₂ O _3: wherein the remaining portion, SiO ₂ as subcomponent: 0.002 to 0.040 wt% CaO: 0.02 containing 0.20 wt%, further Nb ₂ O ₅ as an auxiliary component: 0.001 to 0.04 wt% Ta ₂ O _5: 0.001 to 0.4 wt% ZrO _2: .001 to 0 0.05% by weight V ₂ O ₅ : low loss Mn-Z containing at least one selected from 0.001 to 0.03% by weight
When manufacturing n-ferrite core, one of the cooling process after firing
A method for producing a low-loss Mn-Zn ferrite core, wherein the oxygen partial pressure at 100 to 950 ° C is 1.0% or less and the cooling rate is 0.5 to 2 ° C / hour.

Next, according to the present invention, the main components are MnO: 25 to 40 mol% ZnO: 6 to 25 mol% and Fe ₂ O ₃ : the balance is an auxiliary component SiO ₂ : 0.002 to 0.040 wt% CaO: 0. In producing a low-loss Mn-Zn ferrite core composed of 0.02 to 0.20% by weight, the oxygen partial pressure at 1100 to 950 ° C in the cooling process after firing was set to 1.0% or less, and the atmosphere was kept under this atmosphere for 20 minutes. ~ 5
A method for producing a low-loss Mn-Zn ferrite core characterized by holding for a time is provided.

Furthermore, MnO as main components: 25~40mol% ZnO: 6~25mol% and Fe ₂ O _3: wherein the remaining portion, SiO ₂ as subcomponent: 0.002 to 0.040 wt% CaO: 0.02 containing 0.20 wt%, further Nb ₂ O ₅ as an auxiliary component: 0.001 to 0.04 wt% Ta ₂ O _5: 0.001 to 0.4 wt% ZrO _2: .001 to 0 0.05% by weight V ₂ O ₅ : low loss Mn-Z containing at least one selected from 0.001 to 0.03% by weight
In producing the n-ferrite core, the oxygen partial pressure at 1100 to 950 ° C. in the cooling process after firing is set to 1.0% or less, and the n-ferrite core is kept in this atmosphere for 20 minutes to 5 hours. A method of manufacturing a core is provided.

The inventor has found that MnO: 25-40 mol%,
ZnO: 6-25 mol% and Fe ₂ O₃ : The rest is basic
Included as a component and silica (SiO₂ ),
Lucia (CaO) is SiO₂ : 0.002-
0.040% by weight, CaO: 0.02 to 0.20% by weight
Distribution of the added subcomponent elements in the sintered body containing
As a result of investigating the relationship between magnetic loss and
When segregated to high concentration in the vicinity, the loss is the lowest and wide.
When distributed over the range, the loss becomes large
I found that. Furthermore, as an accessory component, Nb₂ O_Five 
(0.001-0.04% by weight), Ta₂ O_Five (0.0
01-0.4% by weight), ZrO₂ (0.001-0.0
5% by weight), V₂ O_Five (0.001-0.03% by weight)
A sintered body containing at least one selected from
Also investigated the relationship between the distribution of the added subcomponent element and the magnetic loss.
As a result, these elements were segregated to a high concentration near the grain boundaries.
Has the lowest loss and is distributed over a wide range
If it is, the loss is found to be large.

As a result of further investigation with higher accuracy, it was revealed that the loss at the grain boundary segregation greatly decreased when the width of the grain boundary segregation was 10 nm as the half-value width of the concentration distribution.

[0014]

As described above, the magnetic characteristics required for the soft magnetic ferrite are high saturation magnetic flux density, high Curie temperature, and low loss.
Saturation magnetic flux density and Curie temperature are the basic components MnO:
It is almost determined by the ratio of ZnO: Fe ₂ O ₃ . In the region where the amount of ZnO is small, the saturation magnetic flux density increases as the amount of ZnO increases, but at the same time, the Curie temperature also decreases.
The temperature at which the magnetic loss is minimized is also largely determined by the basic component ratio.

When the temperature at which the magnetic loss is the minimum is near room temperature, the magnetic core itself generates heat due to the magnetic loss when used as a power transformer, and the temperature rises to increase the loss, and accordingly the heat generation further increases. , There is a risk that this will be repeated and cause thermal runaway. Therefore, the composition of the basic components must be determined so that the temperature coefficient of loss near room temperature is negative, and the temperature is minimized at 80 to 100 ° C in consideration of the temperature of other electronic components when incorporated in a transformer.
As described above, from the viewpoint of optimizing the saturation magnetic flux density, the Curie temperature, and the minimum loss temperature, the basic component is M
nO: 25-40 mol%, ZnO: 6-25 mol%
And the balance is Fe ₂ O ₃ .

The small amount of the auxiliary component additive is effective mainly for promoting / suppressing the growth of crystal grains during firing, forming grain boundaries, etc., and the microstructure of the sintered body changes depending on the amount of the additive, and the magnetic permeability. , Coercive force and eventually the absolute value of magnetic loss are affected. SiO ₂ forms a grain boundary together with CaO and contributes to increasing the resistance of the grain boundary. However, if the added amount is small, its contribution is small, and if it is contained excessively, abnormal grain growth is caused during sintering and the loss is greatly increased. If CaO is added in a small amount, its contribution is small, and if it is too large, the loss is increased. Therefore, the addition amounts of SiO ₂ and CaO are SiO ₂ : 0.002-0.040% by weight, C
aO: 0.02 to 0.20% by weight.

Nb₂ O_Five , Ta₂ O_Five , ZrO₂ , V₂ 
O_Five Is SiO₂ Loss when added with CaO and CaO
Is an element that contributes to the reduction of
Nb₂ O_Five : Less than 0.001% by weight, Ta₂ O_Five :
Less than 0.001% by weight, ZrO ₂ : 0.001% by weight
Man, V₂ O_Five : Addition amount is less than 0.001% by weight
If the amount is small, the effect does not appear, while Nb₂ O_Five :
Over 0.04% by weight, Ta₂O_Five : More than 0.04% by weight, Z
rO₂ : Over 0.05% by weight, V₂ O_Five : 0.03% by weight
On the other hand, if the addition amount exceeds a certain concentration range, such as over, loss will occur on the contrary.
Will increase. Therefore, Nb₂ O_Five : 0.001 to 0.04 wt% Ta₂ O_Five : 0.001-0.4 wt% ZrO₂ : 0.001 to 0.05% by weight V₂ O_Five : Limited to 0.001 to 0.03% by weight.

The inventors made samples with different firing conditions for selected basic composition and additive composition, and examined their fine structures. As a result, the magnetic loss was large due to the degree of segregation of the additive elements at the grain boundaries. Although they found different things, these results are considered as follows. First, by increasing the degree of segregation of crystal grain boundaries, the insulating property between crystal grains is increased to increase the specific resistance, and as a result, the effect of reducing eddy current loss can be obtained. For this purpose, it is important to make the grain boundary layer as thick as possible and to increase the concentration of the accessory component element at the crystal grain boundary in order to form an insulating layer at the crystal grain boundary and increase the insulation resistance. . Next, the effect that elements that do not form a solid solution in spinel are extruded to the grain boundaries, that is, strain in the crystal lattice is reduced by not remaining in the crystal grains, and hysteresis loss is also reduced by facilitating the movement of domain walls. There is.

Subcomponent elements Si and C in the present invention
a, Nb, Ta, V, and Zr are all elements that do not form a solid solution with spinel. Therefore, when any one of these elements remains in the crystal grains, it strains the crystal lattice, so that it is required that all subcomponent elements are segregated at the grain boundaries at a high concentration. It That is, when not only simply forming the grain boundary insulating layer to increase the insulation resistance but also considering the strain of the crystal and the like, the thickness of the crystal grain boundary, that is, the width of the segregation of the additive element is taken into consideration when the total loss is considered. Setting the thickness to 10 nm or less greatly contributes to loss reduction. Here, what is more important is that all the added subcomponent elements are segregated within a range of a half value width of 10 nm or less. The width of segregation referred to in the present invention refers to the half-value width of the concentration of the additive element in the line analysis that extends between the crystal grains at right angles to the grain boundaries, that is, the distance connecting the points having the half value of the peak value of the distribution curve. .

Further, an element that does not form a solid solution in the spinel is extruded to the crystal grain boundary and does not remain in the crystal grain, so that crystal strain is reduced and high magnetic permeability is realized. Therefore, the effect of the present invention can be applied not only to low loss but also to high magnetic permeability material. In order to segregate the additive element in the highest possible concentration and in a narrow region, it is important to select raw materials and firing conditions. Use iron oxide, manganese oxide, or zinc oxide, which is the basic component as the starting material, or a compound that is not limited to these and that can be converted to the oxide of the basic component by firing, and whose impurity concentration is as low as possible It is essential. Even if the impurities are of the same kind as the additive element intentionally added, there is no exception. If the starting material contains a large amount of impurities, these often remain in the crystal grains even after calcination and firing, achieving the ideal microstructure described above. Can not do it.

On the other hand, under the firing conditions, it is important to control the oxidation degree of the sintered body by strictly adjusting the temperature control and the oxygen partial pressure control during the cooling process. In the firing step, crystal grains grow and grain boundaries are formed with it, but during the cooling process, oxidation or reduction reaction near the crystal grain boundaries, that is, absorption of oxygen into the crystal grains or release from the crystal grain boundaries occurs. At this time, it is considered that the movement of these additional elements occurs with the inflow and outflow of oxygen, and the grain boundary segregation of the additional elements can be sharpened by selecting an appropriate oxidizing atmosphere.

As a specific firing method, the temperature is maintained at 1100 to 950 ° C. in the cooling process after firing for 20 minutes to 5 hours in an atmosphere having an oxygen partial pressure of 1.0% or less. It is considered that the addition element can be concentrated to the grain boundary by keeping it at a constant temperature. The longer the holding time, the higher the degree of thickening. The effect equivalent to the case of holding at a constant temperature is to perform cooling at a cooling rate of 0.5 to 2 ° C./hour in a certain temperature range of 1100 to 800 ° C. during the cooling process.

From the results of the experiments under different cooling conditions, the tendency of the subcomponent element in the present invention to concentrate at the grain boundaries is 1100 ° C. or lower, and the diffusion occurs promptly at 800 ° C. or higher. Since it is considered that there is some, it is possible to increase the degree of segregation of grain boundaries by slowing the cooling rate partially or entirely at 0.5 to 2 ° C./hour in this temperature range.

[0024]

【Example】

[Example 1] Fe ₂ O ₃ : 53.5mo as the final composition
1%, MnO: 34.5 mol%, ZnO: 12.0 m
After blending the raw materials of the basic components to be ol%, wet mixing was performed for 12 hours using a ball mill, and then dried. When selecting the raw material, the impurity concentration is SiO ₂ : 20 p
Those below pm were selected. 9 this mixed powder in the atmosphere
Calcination was performed at 50 ° C. for 3 hours. For this calcined powder, S
iO _2: 0.0025 weight%, CaO: 0.1% by weight,
Nb ₂ O ₅ : SiO ₂ to be 0.025 wt%,
CaO and Nb ₂ O ₅ were added, and the mixture was again wet mixed and ground using a ball mill and dried. After adding 5% by weight of polyvinyl alcohol and 10% by weight of an aqueous solution to this powder, 3
Granulate by passing through a 0 mesh sieve. This granulated powder was molded into a ring having an outer diameter of 36 mm, an inner diameter of 24 m, and a height of 12 mm, and 1
Baking was performed at 300 ° C. for 3 hours. In the cooling process after firing, the oxygen partial pressure in the atmosphere was switched to 0.01 to 1.2% at any temperature of 900 to 1150 ° C., and the conditions were maintained for 10 minutes to 5 hours, and then the furnace was used. A cooled sample was prepared. The sintered body sample thus obtained was wound (5 windings on the primary side and 5 windings on the secondary side), and the power loss was measured by an AC BH tracer under the condition of a maximum magnetic flux density of 200 mT at a frequency of 100 kHz. It was measured at 90 ° C. Further, an observation sample by ion milling was prepared from each sample cut out from a sintered body in a thin plate shape. The element distribution was investigated using EDX of a field emission transmission electron microscope. Table 1 shows the full width at half maximum and the power loss value of each sample. In addition, in each of FIGS. 1, No. 3, No. 5 shows the concentration distribution of each subcomponent element in the crystal grain boundary of No. 5.

As is clear from the results shown in Table 1, 1100 to 1010 of the cooling process after firing according to the method of the present invention.
At 950 ° C., the Mn—Zn-based soft ferrite retained in an atmosphere with an oxygen partial pressure of 1.0% or less for 20 minutes to 5 hours has a half-value width of the concentration distribution of each subcomponent element of 10 nm or less and a high value at the grain boundary. It is segregated to the concentration and the power loss is greatly improved.

Example 2 A ring-shaped compact having an outer diameter of 36 mm, an inner diameter of 24 m, and a height of 12 mm produced in the same manner as in Example 1 was placed in a mixed gas of nitrogen and air with controlled oxygen partial pressure.
It was baked at 300 ° C. for 3 hours. In the cooling process after firing, the cooling rate at 1100 to 900 ° C to 1000 to 800 ° C is 0.5, 1.0, 2.0 to 5.0 ° C.
/ Hour and cooled thereafter. The oxygen concentration in the atmosphere after the above temperature range was 0.01% or less. The power loss and the half-value width of the concentration distribution of each sub-component element of the sintered body sample thus obtained were measured in the same manner as in Example 1, and Table 2
It was shown to.

From these results, the oxygen partial pressure is 1.0% or less and the cooling rate is 0.5 to 2 ° C. at 1100 to 800 ° C. in the cooling process after firing according to the present invention.
The Mn-Zn-based soft ferrite set to / hour segregates to a high concentration at the grain boundary when the half-value width of the concentration distribution of each sub-component element is 10 nm or less, and the power loss is greatly improved. Example 3 Example 1 Fe ₂ O as the final composition was prepared in the same manner as _{3: 53.5mol%,} MnO: 34.5
As shown in Table 3, various additive elements were added to the calcined powder of the basic component of which mol% and ZnO: 12.0 mol%,
Similar to Example 1, outer diameter 36 mm, inner diameter 24 m, height 12
mm ring-shaped compact was prepared, and the mixture was fired in a nitrogen / air mixed gas whose oxygen partial pressure was controlled at 1300 ° C. for 3 hours.
At 1100 ° C., the oxygen partial pressure in the atmosphere was switched to 1.0% or less, and the cooling rate from 1100 to 900 ° C. was 1.
The temperature was set to 0 ° C./hour, and then the furnace was cooled. The power loss and the half value of the concentration distribution of each sub-component element of the thus obtained sintered body sample were measured in the same manner as in Example 1 and shown in Table 3.

From the results shown in Table 3, Mn-Z having the composition of the present invention was obtained.
When the n-type soft ferrite is cooled under the cooling conditions of the present invention, the half-value width of the concentration distribution of each sub-component element is 10 n.
When it is less than m, it segregates to a high concentration in the grain boundary, and the power loss is greatly improved. [Example 4] A ring-shaped molded product having the same components and shapes as those of the ring-shaped molded product used in Example 3 was prepared and fired in a nitrogen / air mixed gas whose oxygen partial pressure was controlled at 1300 ° C for 3 hours. Then, the oxygen partial pressure in the atmosphere was switched to 0.01% at 1000 ° C., and the condition was maintained for 2 hours.
Then, a furnace-cooled sample was prepared. The power loss and the half-value width of the concentration distribution of each sub-component element of the thus obtained sintered body sample were measured in the same manner as in Example 1 and shown in Table 4.

From these results, the Mn-Zn system soft ferrite having the composition according to the present invention was cooled under the cooling conditions according to the present invention, and the half-width of the concentration distribution of each sub-component element was 10 nm or less and the grain boundary was reduced. Segregated to a high concentration and the power loss was greatly improved.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

According to the present invention, by increasing the grain boundary segregation of the sub-component element, Mn-Zn suitable for a magnetic core of a switching power supply transformer and having a much smaller power loss than conventional materials. A system ferrite can be provided.

[Brief description of drawings]

FIG. 1 is a graph showing a concentration distribution of a sub-component element at a grain boundary.

FIG. 2 is a graph showing a concentration distribution of a sub-component element at a grain boundary.

FIG. 3 is a graph showing a concentration distribution of a sub-component element at a grain boundary.

Claims (7)

[Claims] 1. A MnO as main components: 25~40mol% ZnO: 6~25mol% and Fe ₂ O _3: wherein the remaining portion, SiO ₂ as subcomponent: 0.002 to 0.040 wt% CaO: 0.02 A low-loss Mn-Zn ferrite core containing 0.1 to 0.20% by weight of these sub-component elements segregated at grain boundaries and having a half-value width of the concentration distribution of 10 nm or less. 2. As a subcomponent, Nb ₂ O ₅ : 0.001 to 0.04% by weight Ta ₂ O ₅ : 0.001 to 0.4% by weight ZrO ₂ : 0.001 to 0.05% by weight V The low loss Mn-Zn ferrite core according to claim 1, containing at least one selected from ₂ O ₅ : 0.001 to 0.03% by weight. 3. A low loss M characterized in that raw material powders are adjusted so as to be the main component and subcomponents according to claim 1, mixed, calcined, crushed, molded, and then fired.
Manufacturing method of n-Zn ferrite core. 4. MnO as main components: 25~40mol% ZnO: 6~25mol% Fe 2 O 3: SiO the balance subcomponent _2: 0.002 to 0.040 wt% CaO: 0.02 to 0.20 In producing a low-loss Mn-Zn ferrite core composed of 10% by weight, the oxygen partial pressure at 1100 to 800 ° C in the cooling process after firing was 1.0% or less, and the cooling rate was 0.5 to 2
And a low loss Mn-Zn ferrite core manufacturing method. 5. MnO as main components: 25~40mol% ZnO: 6~25mol% and Fe ₂ O _3: wherein the remaining portion, SiO ₂ as subcomponent: 0.002 to 0.040 wt% CaO: 0.02 containing 0.20 wt%, further Nb ₂ O ₅ as an auxiliary component: 0.001 to 0.04 wt% Ta ₂ O _5: 0.001 to 0.4 wt% ZrO _2: .001 to 0 0.05% by weight V ₂ O ₅ : low loss Mn-Z containing at least one selected from 0.001 to 0.03% by weight
When manufacturing n-ferrite core, one of the cooling process after firing
A method for producing a low-loss Mn-Zn ferrite core, wherein the oxygen partial pressure at 100 to 800 ° C is 1.0% or less and the cooling rate is 0.5 to 2 ° C / hour. 6. MnO as main components: 25~40mol% ZnO: 6~25mol% and Fe ₂ O _3: SiO the balance subcomponent _2: 0.002 to 0.040 wt% CaO: 0.02-0. In producing a low-loss Mn-Zn ferrite core composed of 20% by weight, the oxygen partial pressure at 1100 to 950 ° C in the cooling process after firing was set to 1.0% or less, and the atmosphere was kept under this atmosphere for 20 minutes to 5 minutes.
A method for producing a low-loss Mn-Zn ferrite core, which is characterized by holding for a time. 7. MnO as main components: 25~40mol% ZnO: 6~25mol% and Fe ₂ O _3: wherein the remaining portion, SiO ₂ as subcomponent: 0.002 to 0.040 wt% CaO: 0.02 containing 0.20 wt%, further Nb ₂ O ₅ as an auxiliary component: 0.001 to 0.04 wt% Ta ₂ O _5: 0.001 to 0.4 wt% ZrO _2: .001 to 0 0.05% by weight V ₂ O ₅ : low loss Mn-Z containing at least one selected from 0.001 to 0.03% by weight
In producing the n-ferrite core, the oxygen partial pressure at 1100 to 950 ° C. in the cooling process after firing is set to 1.0% or less, and the n-ferrite core is kept in this atmosphere for 20 minutes to 5 hours. Core manufacturing method.