JP2009012999A - Mn-Zn-Co ferrite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Mn-Zn-Co-based ferrite characterized in that the absolute value of iron loss and the temperature change of the absolute value of iron loss are small, and the absolute value of amplitude relative magnetic permeability is high and the temperature change of the absolute value of amplitude relative magnetic permeability is small, in a wide temperature zone of 25-140°C. <P>SOLUTION: In the Mn-Zn-Co-based ferrite having a basic component composition comprising, by mol, 52.0-53.0% Fe<SB>2</SB>O<SB>3</SB>, 0.15-0.5% CoO, 11.5-12.5% ZnO and the balance being MnO and inevitable impurities, the Mn-Zn-Co-based ferrite is characterized by containing, as an additive component, BeO in an amount of 10-100 mass ppm to the Mn-Zn-Co-based ferrite. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a Mn—Zn—Co based ferrite with low iron loss, and particularly suitable for use in a magnetic core such as a transformer for switching power supply, which exhibits low energy loss and high permeability in a wide temperature range. It relates to Co-based ferrite.

  Oxide magnetic materials are generally referred to as “ferrites”, but the ferrites are broadly classified into hard magnetic materials such as Ba ferrite and Sr ferrite, Mn—Zn ferrite, and Ni—Zn ferrite. There are soft magnetic materials such as ferrite. Among these, the soft magnetic material is a material that is sufficiently magnetized even with a small magnetic field, and is therefore used in a wide range of fields such as power supplies, communication devices, measurement control devices, magnetic recording, and computers. The properties required for this soft magnetic material include a low coercive force, a high magnetic permeability, a high saturation magnetic flux density, and a low iron loss.

  In addition to the oxide ferrite, the soft magnetic material includes metal. However, metal-based soft magnetic materials have a feature that the saturation magnetic flux density is higher than that of oxide-based materials, but they have low electrical resistance. There is a problem that the iron loss becomes large. Therefore, in recent years when the frequency of use has been increased due to demands for downsizing and increasing the density of electronic devices, for example, a switching power supply used in a high frequency band of about 100 kHz uses a metallic magnetic material. It is almost impossible.

  From such a background, Mn—Zn based ferrite having a small iron loss (less heat generation) has been mainly used as a magnetic core material of a power transformer used in a high frequency range. However, since this material has a low electrical resistivity of about 0.01 to 0.05 Ω · m, by further increasing the electrical resistance and reducing eddy current loss, the overall iron loss is reduced and heat is generated. Development of a magnetic material with a reduced amount has been desired.

For this problem, for example, in Patent Document 1, a small amount of an oxide such as SiO ₂ or CaO is added to the Mn—Zn-based ferrite as a subcomponent, and segregates at the grain boundary to increase the grain boundary resistance. A technique for suppressing heat generation by setting the overall resistivity to several Ω · m or more is disclosed.

  In addition, when ferrite is used in power transformers, it is necessary to consider the temperature (operating temperature) when using a device that incorporates ferrite and the temperature rise caused by heat generation due to the iron loss of the ferrite itself. It is. For example, when the temperature at which the iron loss of ferrite is at a minimum is near room temperature, the core temperature increases due to heat generation, so that the iron loss increases and the heat generation further increases, and this is repeated to accelerate the temperature increase. This is because there is a risk of causing a so-called thermal runaway.

  The operating temperature of the transformer is conventionally around 50 to 70 ° C. However, in order to avoid the risk of the thermal runaway, in the current ferrite, the temperature at which the iron loss is minimized is about 100 ° C, and the iron near room temperature is used. The material design is such that the iron loss decreases as the temperature rises with a negative temperature coefficient of loss. However, even with a material having a minimum iron loss temperature of about 100 ° C., if the temperature rises to 100 ° C. or higher, the iron loss increases and there is a high risk of thermal runaway.

  Furthermore, recently, in order to cope with the downsizing of electronic devices, the loading density of electronic components has been increased, and the temperature rise due to heat generation tends to be larger. For this reason, recent electronic components that are used in a high temperature range of 120 to 140 ° C. exceeding 100 ° C., which has not been assumed so far, have come to appear. However, the operating temperature at the time of design is still around 100 ° C., and the demand for low iron loss in this temperature range remains unchanged. Therefore, the iron loss of ferrite needs to be small in a wide temperature range, particularly in a high temperature range of about 100 to 140 ° C.

  In addition, among the switching power supplies that use ferrite cores, in the circuit type power supply called the forward type, the power used to excite the transformer primary coil is not transmitted to the secondary side, so it is invalid. It becomes electric power, and it becomes a factor of electric power efficiency fall. In order to reduce the excitation power, it is effective to increase the inductance of the transformer coil, and it is necessary to increase the magnetic permeability of the core. Therefore, the ferrite used in this application has low iron loss over a wide temperature range, and at the same time, the magnetic permeability during operation of the transformer, that is, the initial magnetic permeability for a minute signal, the amplitude under a large excitation of about 200 mT. It is desired that the relative permeability is high.

Meanwhile, as one of the factors governing the core loss of ferrite, and magnetic anisotropy constant K _1. The iron loss changes with the temperature change of the magnetic anisotropy constant K ₁ and becomes minimum at a temperature at which K ₁ = 0. Therefore, to reduce the temperature change of the ferrite core loss, it is necessary to reduce the temperature dependence of the magnetic anisotropy constant K ₁ (the core loss temperature coefficient).

The magnetic anisotropy constant K ₁ is almost determined by the type of elements constituting the spinel compound that is the main phase of ferrite. In the case of Mn—Zn-based ferrite, the temperature dependence can be reduced by introducing Co ions, and the absolute value of the iron loss temperature coefficient can be reduced (for example, see Non-Patent Documents 1 and 2). It is possible to obtain a ferrite material having a small iron loss in the vicinity of 100 ° C. and a relatively small iron loss in the temperature range before and after that. However, adding Co causes another problem that the iron loss minimum temperature decreases, or the iron loss temperature coefficient and the minimum temperature fluctuate greatly due to slight fluctuations in the firing temperature and oxygen concentration in the firing atmosphere. Has occurred.

For example, Patent Document 2 discloses that a Mn—Zn—Co-based ferrite containing Fe ₂ O ₃ , ZnO, and MnO as main components and containing CoO in an amount of 0.01 mol% or more and less than 0.5 mol% has a wider temperature than that in the past. Since K ₁ = 0 in the range, it is disclosed that high magnetic permeability and low loss can be realized in a wide temperature range. However, in the technique of Patent Document 2, as shown in FIG. 1 of the same document, since the minimum temperature of the core loss shifts to the low temperature side, the loss at the high operating temperature as described above is large. Therefore, the risk of acceleration of temperature rise has not been resolved.

In Patent Document 3, Fe ₂ O ₃ , ZnO, and MnO are the main components, and CaO, Ta ₂ O ₅ , and SiO ₂ are further added in addition to 1000 to 4000 ppm of CoO. In the above frequency region, a Mn—Zn-based ferrite with a small power loss can be obtained in a wider temperature range than the conventional one, and if this amount of CoO is added, the temperature curve of the power loss is on the low temperature side. It is described that it does not shift too much. However, this technique also has a problem that depending on the main component composition, the temperature coefficient of loss and the minimum temperature greatly vary due to slight fluctuations in the firing temperature and the oxygen concentration in the atmosphere.

As a technique for improving these problems, Patent Document 4 discloses a ferrite material having a low power loss and a small temperature change of the power loss. Further, this document discloses a ferrite material having a small power loss temperature change in a temperature range of 40 ° C., which is 60 ° C. to 20 ° C. lower than the temperature at which the power loss is minimized. Patent Document 5 discloses a technique that not only obtains a small power loss by adding CoO and Nb ₂ O ₅ but also flattens the power loss to minimize the power loss in a wide temperature range.

Patent Document 6 discloses that in a magnetic ferrite material mainly composed of iron oxide, zinc oxide, and manganese oxide, ZnO: 7.0 to 9.0 mol%, MnO: 36.8 to 39.2 mol%, and remaining oxidation. It has a main component composition of iron and contains Co ₃ O ₄ as a subcomponent in the range of 2500 to 4500 ppm, and the minimum value of power loss in the temperature range of 20 to 100 ° C. is 300 kW / m ³ or less and the temperature range Discloses a magnetic ferrite material in which the difference between the maximum value and the minimum value of power loss is 150 kW / m ³ or less. In the same document, the minimum value of power loss in the temperature range of 20 to 100 ° C. is 350 kW / m ³ or less, and the difference between the maximum value and the minimum value of power loss in the temperature range is 50 kW / m ³ or less. Ferrite materials are also disclosed.

Furthermore, in Patent Document 7, Fe ₂ O ₃ : 53.2 to 54.5 mol% as a main component, ZnO: 7.5 to 11.5 mol%, and Mn—Zn-based ferrite containing the balance MnO, Co Mn—Zn system containing ₃ O ₄ : 2000 to 4500 ppm, SiO ₂ : 60 to 140 ppm, CaO: 300 to 700 ppm, and further containing Nb ₂ O ₅ : 100 to 350 ppm and / or ZrO ₂ : 50 to 450 ppm It has been disclosed that ferrite can realize reduction of power loss and reduction of loss in a wide temperature range.
Japanese Patent Publication No. 36-002283 Japanese Patent Publication No. 04-033755 Japanese Patent Laid-Open No. 06-290925 Japanese Patent Laid-Open No. 08-191011 JP 09-134815 A JP 2001-080952 A JP 2002-231520 A JP 2006-213532 A “The Ffect of Cobalt Substitutations on Some Properties of Manganese Zinc Ferrites”, A.M. D. Giles and F.M. F. Westendorp: J.M. Phys. D: Appl. Phys. , 9 (1976) 2117 “Low-loss Power Ferrites for frequencies up to 500 kHz”, T.W. G. W. Stijintjes and J.M. J. et al. Roelofsma; Adv. Cer. 16 (1986) 493

However, the power loss of the ferrite described in Patent Document 4 and Patent Document 5 is not sufficiently low, and it cannot be said that the temperature change of the power loss is sufficiently flattened. Moreover, in these documents, as a transformer material for a power source, a low power loss is shown in a wider temperature range, particularly a high temperature range of about 140 ° C., the temperature change is reduced, and the amplitude relative permeability is increased. There is no disclosure about what to do. Moreover, although the ferrite described in Patent Document 6 has low power loss, the minimum value of power loss is about 300 kW / m ³ , and it does not fully meet the demand for low loss. Moreover, this document does not disclose low loss and high magnetic permeability in a high temperature range up to 140 ° C. Also in the technique of Patent Document 7, as shown in Tables 1 and 2 of the same document, a low-loss ferrite of 250 kW / m ³ or less (100 kHz, 200 mT) is obtained at 100 ° C. However, it is not disclosed that a low loss of 350 kW / m ³ or less and a high amplitude relative permeability μa of 6500 or more are obtained in a wide temperature range from a low temperature of 25 ° C. to a high temperature of 140 ° C.

  The present invention has been made in view of the situation as described above, and its purpose is in a wide temperature range of 25 to 140 ° C., particularly in a high temperature range of 140 ° C., and the absolute value of the iron loss and its temperature change. Is to provide a Mn—Zn—Co based ferrite having a small absolute value of amplitude relative permeability and a small temperature change.

The inventor narrowed down the composition of Fe ₂ O ₃ , ZnO and MnO to an appropriate range in the previous application (Patent Document 8), and the effect of CoO differs depending on the composition of the basic component, so the optimum according to the composition By selecting the amount of CoO, it is possible to obtain a ferrite with low loss, high relative permeability and small temperature change up to a high temperature range, and further limit the amount of chlorine in the raw iron oxide to a certain value or less. It has been disclosed that the effect is further improved by reducing the amount of chlorine in the final sintered body after firing to a predetermined value or less.

The inventor further investigated the influence of the contents of Fe ₂ O ₃ , ZnO, and CoO, which are basic components, on the temperature characteristics of the iron loss and the magnetic permeability in order to solve the above-described problems of the prior art. Further, intensive studies were conducted on the effects of various metal oxides contained as additive components on the core loss and amplitude relative permeability of the final core and their temperature dependence. As a result, the composition of Fe ₂ O ₃ , ZnO and MnO is narrowed down to an appropriate range, and by selecting the optimal amount of CoO according to that range, the temperature changes to a high temperature range with extremely low loss and high relative permeability. The present inventors have found that a ferrite having a small particle size can be obtained, and that the effect can be further enhanced by adding BeO as an additive component within a predetermined range, thereby completing the present invention.

That is, the present invention includes Fe ₂ O ₃ : 52.0 to 53.0 mol%, CoO: 0.15 to 0.5 mol%, ZnO: 11.5 to 12.5 mol%, and the balance from MnO and inevitable impurities. In the Mn—Zn—Co-based ferrite having the basic component composition, BeO: 10 to 100 massppm, SiO ₂ : 50 to 500 massppm, CaO: 200 to 2000 massppm, ZrO ₂ : 100 to 1500 massppm and Ta ₂ O ₅ : A Mn—Zn—Co based ferrite characterized by containing 50 to 1000 mass ppm.

The Mn—Zn—Co ferrite of the present invention has a minimum iron loss temperature measured at a maximum magnetic flux density of 200 mT and a frequency of 100 kHz in a temperature range of 80 to 120 ° C., and an iron loss at 100 ° C. of 250 kW / m ³ or less, 25 The iron loss maximum value in a temperature range of ˜140 ° C. is 350 kW / m ³ or less.

The Mn—Zn—Co ferrite of the present invention has an amplitude relative permeability μa measured in a temperature range of a maximum magnetic flux density of 200 mT, a frequency of 100 kHz, and 25 to 140 ° C. of 6500 or more, and the following formula:
Coefficient of variation (%) = (standard deviation of μa value in the temperature range of 25 to 140 ° C.) / (Average value of μa value in the temperature range of 25 to 140 ° C.) × 100
The variation coefficient of μa defined by the above is characterized by being 1.5% or less.

  According to the present invention, it is possible to provide a Mn—Zn—Co based ferrite having a low iron loss and a high amplitude relative permeability in a wide temperature range of 25 to 140 ° C. Therefore, the ferrite of the present invention is suitable for use in a transformer core material such as a switching power supply.

From the viewpoint of optimizing the saturation magnetic flux density, the Curie temperature, the minimum temperature of the iron loss, and the temperature characteristics, the Mn—Zn—Co ferrite of the present invention has a main component composition of Fe ₂ O ₃ : 52.0 to 53.53. It consists of 0 mol%, CoO: 0.15 to 0.5 mol%, ZnO: 11.5 to 12.5 mol%, and the balance MnO. The reason for limiting to the above range will be specifically described below.

Fe ₂ O _3: 52.0~53.0mol%
Fe ₂ O ₃ needs to be 52.0 mol% or more in order to make the iron loss minimum temperature 80 ° C. or more in relation to CoO. However, if it exceeds 53.0 mol%, the iron loss near room temperature increases, so the upper limit is made 53.0 mol%. Preferably, it is the range of 52.3-52.7 mol%.

ZnO: l1.5-12.5 mol%
As described above, the magnetic properties required for soft magnetic ferrite include high saturation magnetic flux density, high Curie temperature, low iron loss, and high magnetic permeability. Among these, the saturation magnetic flux density and the Curie temperature are substantially determined by the ratio of the basic components MnO, ZnO, and 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 the Curie temperature also decreases accordingly. If the amount of ZnO is less than 11.5 mol%, the effect of suppressing the temperature change of the magnetic permeability due to CoO is small, resulting in a high iron loss value and no improvement in the amplitude relative magnetic permeability. Further, as described above, the temperature at which the iron loss is minimized is almost determined by the ratio of the basic components. If the amount of ZnO is too large, the change in the iron loss minimum temperature due to the fluctuation of the CoO amount becomes very sensitive. The minimum temperature changes greatly with a slight increase in CoO content. In particular, when the amount of ZnO is more than 12.5 mol%, the minimum iron loss temperature may change by about 25 ° C. even if the amount of CoO is about 0.1 mol%. Therefore, in order to set the iron loss minimum temperature to 80 to 120 ° C., the ZnO amount needs to be in the range of 11.5 to 12.5 mol%.

CoO: 0.15-0.5 mol%
CoO also has a function of reducing the temperature coefficient of permeability. However, when it exceeds 0.5 mol% and excessively contained, the temperature coefficient of iron loss becomes positive at room temperature or higher, or thermal runaway occurs. This is not desirable because the change with time increases. On the other hand, when the amount of CoO is less than 0.15 mol%, the effect of suppressing the temperature change of the permeability is small. Therefore, the content of CoO is in the range of 0.15 to 0.5 mol%.

The ferrite according to the present invention is Mn—Zn—Co—Fe ₂ O ₃ quaternary ferrite, and the remaining basic component other than the above Fe ₂ O ₃ , CoO, and ZnO is MnO. The balance other than the basic components is an unavoidable impurity except for additive components described later.

BeO: 10-100 massppm
In the Mn—Zn—Co based ferrite of the present invention, it is most important to control the composition range of Fe ₂ O ₃ , ZnO, MnO and CoO, which are basic components, to the above appropriate range. However, in the ferrite of the present invention, in order to stably realize a small iron loss and a large amplitude relative permeability at the same time, it is necessary to further contain an appropriate amount of BeO as an additive component. The mechanism by which the addition of BeO affects the magnetic properties of the final sintered body is not clear. However, since BeO is an oxide having a high specific resistance and a low relative dielectric constant and dielectric loss, the final sintering is performed. This is considered to have a favorable effect on the body characteristics, particularly the iron loss and amplitude relative permeability on the high temperature side of 100 ° C. or higher. The above effect of BeO does not appear when the amount added to the entire ferrite is less than 10 massppm, while when it exceeds 100 massppm, abnormal grain growth occurs on the contrary and the iron loss is greatly increased. Therefore, in this invention, it adds in the range of BeO: 10-100massppm.

In addition to the above essential components, the following additive components can be added to the ferrite of the present invention. That is, Fe ₂ O ₃ , ZnO, MnO and CoO, which are basic components of the ferrite of the present invention, form a spinel structure, and in addition to this, SiO ₂ , CaO, Ta ₂ O ₅ , ZrO that does not form spinel. By adding an appropriate amount of additive components such as ₂ , Nb ₂ O ₅ and V ₂ O ₅ , a high-performance Mn—Zn—Co-based ferrite with less iron loss can be obtained. In particular, the combined addition of SiO ₂ , CaO, Ta ₂ O ₅ and ZrO ₂ is effective.

SiO ₂ forms a grain boundary high resistance phase together with CaO to increase the resistance of the grain boundary and contribute to the reduction of iron loss. However, if the amount added is less than 50 massppm, the effect is small. On the other hand, if it exceeds 500 massppm, abnormal grain growth occurs during sintering, which causes a significant increase in iron loss. When CaO coexists with SiO ₂ , it contributes to lowering the iron loss by increasing the grain boundary resistance. However, if the amount added to the entire ferrite is less than 200 massppm, the effect is small, whereas if it exceeds 2000 massppm, Conversely, iron loss increases. Therefore, it is preferable to add the addition amount of SiO ₂ and CaO to the whole ferrite in the ranges of SiO ₂ : 50 to 500 massppm and CaO: 200 to 2000 massppm, respectively.

Ta ₂ O ₅ has the effect of increasing the specific resistance in the presence of SiO ₂ and CaO. However, if the amount of addition to the whole ferrite is less than 50 massppm, the addition effect is poor, whereas if it exceeds 1000 massppm, iron is conversely This increases the loss. Therefore, Ta ₂ O ₅ is preferably added in the range of 50 to 1000 massppm. Further, ZrO ₂ contributes effectively to the reduction of iron loss at high frequencies by increasing the resistance of grain boundaries in the coexistence of SiO ₂ , CaO, Ta ₂ O ₅ as well as Ta ₂ O _5. If the added amount relative to the whole is less than 100 massppm, the effect is poor. On the other hand, if it exceeds 1500 massppm, the effect of increasing the specific resistance is reduced and the iron loss increases. Accordingly, ZrO ₂ is preferably added in the range of 100～1500Massppm.

After mixing the ferrite raw materials so as to have various Fe ₂ O ₃ , ZnO, and CoO compositions shown in Tables 1 and 2 and the balance being MnO, calcination was performed at 930 ° C. for 3 hours. As shown in Tables 1 and 2 to the calcined powder, various amounts of BeO, SiO ₂ , CaO, Ta ₂ O ₅ and ZrO ₂ were added as additive components, and pulverized for 10 hours with a ball mill. It was molded into a ring-shaped core having a diameter of 31 mm, an inner diameter of 19 mm, and a height of 7 mm. Thereafter, the molded core was fired at 1330 ° C. for 3 hours in a nitrogen / air mixed gas controlled to have a partial pressure of oxygen of 1 to 5 vol% to obtain a sintered body sample. In addition, the temperature increase rate from 500 degreeC to 1300 degreeC at the time of baking was 650 degreeC / hr.

25 ° C when the ring-shaped sample obtained as described above is subjected to winding of 5 turns on the primary side and 5 turns on the secondary side, and is excited to a magnetic flux density of 200 mT at a frequency of 100 kHz using an AC BH loop tracer. The iron loss and the amplitude specific permeability μa in the temperature range of ˜140 ° C. were measured.
Further, from the average value and the standard deviation of the amplitude relative permeability μa, the following formula:
Coefficient of variation (%) = (standard deviation of μa value in the temperature range of 25 to 140 ° C.) / (Average value of μa value in the temperature range of 25 to 140 ° C.) × 100
Was used to obtain the coefficient of variation.
Further, based on the measurement results, the temperature at which the iron loss is minimized, the iron loss value at 100 ° C., the iron loss maximum value in the temperature range of 25 to 140 ° C., the minimum value of the amplitude relative permeability, and the coefficient of variation are calculated. Asked.

The results of the above measurements are shown together in Tables 1 and 2. Here, the sample Nos. 1 to 24 are invention examples of the present invention, sample Nos. 25 to 48 are comparative examples of the present invention. As can be seen from Tables 1 and 2, in the examples of the present invention, the basic composition of Fe ₂ O ₃ , ZnO, MnO, and CoO and the composition of additive components of SiO ₂ , CaO, Ta ₂ O ₅ , and ZrO ₂ were appropriately selected. Furthermore, since BeO is added in an amount of 10 to 100 massppm, the iron loss minimum temperature measured at a maximum magnetic flux density of 200 mT and a frequency of 100 kHz is in the range of 80 to 120 ° C., and the iron loss at 100 ° C. The maximum value of iron loss in the temperature range of 250 kW / m ³ or less and 25 to 140 ° C. is 350 kW / m ³ or less, the amplitude relative permeability in the temperature range of 25 to 140 ° C. is 6500 or more, and the coefficient of variation is 1. It can be seen that a Mn—Zn—Co-based ferrite having a low loss, high magnetic permeability, and little temperature change is obtained in a wide temperature range. On the other hand, in the comparative example outside the scope of the present invention, any one or more of the above characteristics is inferior to the invention example.

  Since the ferrite of the present invention has an excellent characteristic of high magnetic permeability in a wide temperature range, it can be suitably used for a noise filter core.

Claims (3)

Fe ₂ O ₃ : 52.0 to 53.0 mol%, CoO: 0.15 to 0.5 mol%, ZnO: 11.5 to 12.5 mol%, the balance having a basic component composition consisting of MnO and inevitable impurities In the Mn—Zn—Co ferrite, BeO: 10 to 100 massppm, SiO ₂ : 50 to 500 massppm, CaO: 200 to 2000 massppm, ZrO ₂ : 100 to 1500 massppm, and Ta ₂ O ₅ : 50 with respect to the ferrite. A Mn—Zn—Co based ferrite containing ˜1000 mass ppm. The iron loss minimum temperature measured at a maximum magnetic flux density of 200 mT and a frequency of 100 kHz is in the temperature range of 80 to 120 ° C., and the iron loss at 100 ° C. is 250 kW / m ³ or less, and the iron loss maximum value in the temperature range of 25 to 140 ° C. is 2. The Mn—Zn—Co based ferrite according to claim 1, which is 350 kW / m ³ or less. The amplitude relative permeability μa measured in the temperature range of maximum magnetic flux density 200 mT, frequency 100 kHz, 25-140 ° C. is 6500 or more, and the variation coefficient of μa defined by the following formula is 1.5% or less. The Mn—Zn—Co based ferrite according to claim 1, wherein:
Coefficient of variation (%) = (standard deviation of μa value in the temperature range of 25 to 140 ° C.) / (Average value of μa value in the temperature range of 25 to 140 ° C.) × 100