JPH06267726A - Low loss manganese-zinc ferrite and manufacture thereof - Google Patents

Abstract

PURPOSE:To realize manganese-zinc ferrite in which not only an eddy current loss but also hysteresis loss are remarkably reduced by containing iron, manganese and zinc as main ingredients and incorporating no specific large grains. CONSTITUTION:The low loss manganese-zinc ferrite comprises, iron, manganese and zinc as main ingredients in such a manner that Fe2O3 is 50-60mol%, MnO is 20-40mol%, ZnO is 8-15mol%, SiO2 is 0.01-0.2mol% and CaO is 0.08-0.4 mol%. Large grains each having a grain size of 50mum or more are not contained at 1% or more of an area ratio to a sectional area of a ferrite core in the core. In the case of baking, an atmospheric oxygen concentration in the step of raising a temperature of 300-1000 deg.C is set to 100ppm or less. Further, the atmospheric oxygen concentration up to arrival to a highest arrival temperature from 1000 deg.C and the atmospheric oxygen concentration at the time of cooling are set to a range specified by a formula (P: oxygen concentration, T: temperature and a: constant).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low core loss ferrite containing iron, manganese and zinc as main components and a method for producing the same.

[0002]

2. Description of the Related Art Manganese zinc ferrite is widely used as a transformer core of a power supply section of electronic products. Since these transformers are driven at a frequency on the order of kHz, if manganese zinc ferrite with relatively low specific resistance is used as it is, eddy current loss increases as the frequency becomes higher, and as a result, magnetic core loss increases. There was a problem of causing fever. In order to solve this, as disclosed in Japanese Patent Publication No. 36-2283, the manganese-zinc ferrite was added with SiO ₂ and CaO, which have the function of forming a layer with high resistance at the crystal grain boundaries. .

However, in recent years, electronic products have been downsized, and the power supply section thereof has also been required to be downsized. As a result, the drive frequency of the transformer is shifted to a higher frequency.
The addition of ₂ and CaO was not sufficient to suppress the eddy current loss, and manganese-zinc ferrite of this system could not be used at a frequency of about 100 kHz or higher.

Therefore, for example, as disclosed in JP-A-58-15037, for the purpose of further suppressing the eddy current loss, a component for increasing the specific resistance of the entire crystal grain by forming a solid solution in the crystal lattice and a hysteresis loss. In addition to SiO ₂ and CaO, a component that promotes densification has been added for the purpose of lowering it. Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 4-149027, a method of controlling the oxygen concentration in the atmosphere during the main firing to reduce the magnetic core loss by refining the crystal grains while densifying the sintered body. Was also done.

[0005]

In the above prior art, the core loss at high frequencies was reduced by adding SiO ₂ and CaO or other components to manganese zinc ferrite. Further, the oxygen concentration in the atmosphere during the main firing is controlled so that the sintered body is densified and the crystal grains are made finer to reduce the magnetic core loss, particularly the eddy current loss. The present invention, by strictly controlling the atmospheric oxygen concentration at the time of temperature rise from the temperature raising process, suppresses the generation of coarse particles in the manganese zinc ferrite, and seeks to homogenize the oxygen content distribution in the core, It is intended to provide a manganese zinc ferrite in which not only eddy current loss but also hysteresis loss is remarkably reduced and a method for producing the same.

[0006]

The present invention is a low loss manganese zinc ferrite characterized by containing iron, manganese and zinc as main components and not containing coarse particles of 50 μm or more, and a method for producing the same.

The present invention will be described in detail below. When producing low-loss manganese zinc ferrite by the conventional technique, SiO ₂ and Ca, which are the constituents of the grain boundary,
It is necessary to add O or other components, but if an addition amount that maximizes the low loss characteristics is selected for these additives, coarse particles will be generated if an extremely small change occurs in the addition amount. There was a phenomenon. Further, even when low-loss manganese zinc ferrite was produced by controlling atmospheric oxygen during firing, a phenomenon in which grain growth remarkably progressed and coarse grains were generated was often observed depending on the method of atmosphere control. The coarse particles are expected to deteriorate the magnetic properties, especially the core loss. Before discussing the relationship between coarse grains and magnetic core loss, magnetic core loss will be described.

The magnetic core loss is generally a hysteresis loss Ph.
And the eddy current loss Pe (for example, edited by Kazu Yamada; “calculation method of magnetic circuit for R & D”, published by Trikeps 1987). <Magnetic core loss> = Ph + Pe = phf + pef ² However, ph: hysteresis loss coefficient, pe: eddy current loss coefficient, f; frequency That is, the hysteresis loss is proportional to the frequency, and the eddy current loss is proportional to the square of the frequency. That is, it is effective to reduce the eddy current loss in order to reduce the magnetic core loss at high frequencies, but in order to reduce the magnetic core loss in the frequency region of 100 kHz level, which is the object of the present invention, It is effective to reduce not only eddy current loss but also hysteresis loss.

Therefore, the present inventors investigated the relationship between the generation ratio of coarse particles in the cross section of the manganese zinc ferrite core manufactured by the conventional method and the magnetic core loss. As shown in FIG. 1, the magnetic core loss tended to worsen as the generation ratio of coarse particles increased. Especially, the occurrence rate is about 1
%, There was a tendency to worsen rapidly. At this time,
It was confirmed that both eddy current loss and hysteresis loss increased. According to the investigation by the present inventors, it was found that the generation of the coarse particles can be suppressed by strictly controlling the atmospheric oxygen concentration at the time of heating in the main firing.

In the prior art, as a measure for making the oxygen amount distribution in the ferrite core uniform, there is a control of the atmospheric oxygen concentration according to the temperature in the soaking process and the cooling process in the main firing. However, when reaching the soaking process, the ferrite core has already reached 85% or more of the theoretical density, and there are almost no open pores in the core. According to Haneda et al., The diffusion rate of oxygen in manganese zinc ferrite is D = 6.70 × 10 ⁻⁴ exp ((−330 kJ / mol) / RT) m ² / s (> 135
0 ℃) D = 3.94 × 10 ^-10 exp ((−137 kJ / mol) / RT) m ² / s (1100
-1350 ° C) D = 7.82 × 10 ⁴ exp ((-507 kJ / mol) / RT) m ² / s (1100
C) All are O ₂ ; 5.3 × 10 ³ Pa (in 5.2%)

For example, when manganese-zinc ferrite is fired at a soaking temperature of 1300 ° C., even if it is held for 4 hours, 20 μ
Oxygen diffuses only about m. Further, it is said that the diffusion coefficient at the crystal grain boundary is 3 to 4 orders of magnitude higher than that inside the crystal grain. Therefore, even if it is considered that oxygen diffuses along the grain boundaries, oxygen diffuses in the ferrite core at most about 2 mm. That is, strictly speaking, in the manganese zinc ferrite produced by the conventional method, the oxygen amount in the core varies, and by reducing this, it becomes possible to reduce the magnetic core loss, particularly the hysteresis loss.

For this reason, in the manganese zinc ferrite of the present invention, the ratio of coarse particles to the core cross-sectional area is 1%.
Defined to be less than or equal to%. Further, in order to obtain this manganese-zinc ferrite, it is necessary to control the atmospheric oxygen concentration in the main firing. This control method is set to conditions that can suppress the generation of coarse particles and at the same time reduce the distribution of the amount of oxygen in the ferrite core to reduce the hysteresis loss.

The means for obtaining the manganese zinc ferrite of the present invention will be described in detail below. In the manganese-zinc ferrite of the present invention, iron, manganese, zinc as the main components and SiO ₂ and CaO as additives have soft magnetism and may have the same composition range as the material used as the high magnetic permeability material. ₂ O ₃ 50-60 mol%, MnO 20-40
mol%, ZnO 8-15 mol%, SiO ₂ 0.01
˜0.2 mol%, CaO 0.08˜0.4 mol%. If the composition of iron, manganese, and zinc as the main components is outside this range, the magnetic permeability is low, it is not practical as a soft magnetic material, and if the added amount of SiO ₂ and CaO is outside this range, the effect of increasing the specific resistance is small. is there.

The composition of the three main components described above is preferably Fe ₂ O ₃ 52 to 55 mol% and MnO.
34-37 mol% and ZnO 9-13 mol% are effective for obtaining manganese zinc ferrite with reduced core loss. Further, preferably, TiO ₂ having the effect of forming a solid solution in the crystal lattice to increase the specific resistance of the entire crystal grain
It is possible to obtain a manganese-zinc ferrite in which the magnetic core loss is further reduced by adding additives such as the above.

Next, the manufacturing method will be described. In order to obtain a manganese-zinc ferrite molded body from a mixture of the above components, generally, a process of mixing-pre-baking-milling-granulating-molding is performed, but these are carried out under usual manufacturing conditions of manganese zinc ferrite. The molded body is then subjected to main firing, but in order to obtain a low-loss manganese zinc ferrite containing no coarse particles in the sintered body of the present invention, the present inventors pay attention to this main firing condition, The method described below was used.

Normally, the soaking temperature is set to 1280 to 1350 ° C. in the firing of manganese zinc ferrite. Furthermore, in order to achieve densification, the atmospheric oxygen concentration is 1% in the temperature range of 600 to 700 ° C. or higher during the temperature rising process in which the sintering reaction starts.
Below is a method to reduce it. The purpose of this is to introduce oxygen ion vacancies into the ferrite by lowering the atmospheric oxygen concentration and promote the movement of oxygen ions that control the sintering reaction.

As a result of detailed investigation of the sintering reaction, the present inventors have found that the oxygen content in ferrite changes depending on the atmospheric oxygen concentration in the temperature range of 300 ° C. or higher. Therefore, by setting the atmospheric oxygen concentration to 100 ppm in the temperature range of 300 ° C. or higher, oxygen ion vacancies were introduced into the ferrite to promote the sintering reaction. 100
The sintering rate remarkably increases in the temperature range of 0 ° C. or higher. Therefore, if the atmospheric oxygen concentration is kept at 100 ppm or less in the temperature range of 1000 ° C. or higher, coarse particles are likely to occur. Therefore, the atmospheric oxygen concentration is set to 100p.
The temperature range of pm was set to 300 to 1000 ° C.

In order to suppress the sintering rate in the temperature range of 1000 ° C. or higher, it is effective to raise the atmospheric oxygen concentration and reduce the amount of oxygen ion vacancies in the ferrite. At the same time, it can be expected that the distribution of oxygen content in the sintered body becomes uniform by increasing the atmospheric oxygen concentration while changing with temperature. As a result, it is possible to reduce the hysteresis loss. The atmospheric oxygen concentration condition is expressed by the following equation. log P = a-20000 / (T + 273) 13.6 ≦ a ≦ 14.3 P ≦ 8 where P: oxygen concentration, T: temperature, a: constant

Here, a is a constant selected from the range of 13.6 ≦ a ≦ 14.3, and the atmospheric oxygen concentration at the time of temperature rise in the temperature range of 1000 ° C. or higher is obtained by substituting a and temperature T in the above equation. It is defined by P obtained by a is 1
The reason for the range of 3.6 ≦ a ≦ 14.3 is a <13.
When it is 6, the sintering rate becomes too fast and coarse particles are likely to occur. Further, if a> 14.3, the ferrite is excessively oxidized and non-magnetic α-Fe ₂ O ₃ is likely to precipitate. The temperature rising rate in the above temperature rising process is selected from the range of 50 to 300 ° C./h as in the usual case.

The soaking temperature in the firing process is 1200 to
It was set to 1300 ° C. This is because firing at a temperature of 1300 ° C. or higher increases the crystal grain size as a whole and increases eddy current loss. Moreover, if the firing is performed in a temperature range of 1200 ° C. or less, the densification does not proceed sufficiently and the hysteresis loss increases. Furthermore, if the soaking temperature is preferably 1200 to 1250 ° C., it becomes possible to further reduce the eddy current loss.

Regarding the cooling conditions after soaking, the cooling rate is selected from the range of 50 to 250 ° C./h as in the usual case. At this time, the oxygen concentration in the atmosphere is non-magnetic α-F.
It is necessary to select conditions under which e ₂ O ₃ and FeO do not precipitate, and conditions under which the distribution of oxygen content in the ferrite core becomes uniform. In order to satisfy this condition, the atmospheric oxygen concentration defined by the following equation is set as in the temperature raising process. log P = a−20000 / (T + 273) 13.6 ≦ a ≦ 14.3 P ≦ 8 where P is oxygen concentration, T is temperature, and a is a constant. It is desirable to make it the same as the value.

[0022]

EXAMPLES Table 1 shows the chemical composition of the manganese zinc ferrite used. A system in which only SiO ₂ and CaO are added as trace additives, and in addition to these, TiO ₂ and V
_The system to which ₂ O ₅ was added was selected. Table 2 shows the firing conditions.
As a comparative example, the test was carried out for a case where the oxygen concentration at the time of temperature rise was fixed at 100 ppm and 21%. Table 3 shows the characteristics of the samples obtained under the respective manufacturing conditions.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

According to the present invention, it is possible to reduce the hysteresis loss by devising the firing conditions to suppress the generation of coarse particles and to make the oxygen content in the ferrite core uniform. It was Furthermore, it is possible to reduce eddy current loss by selecting an appropriate temperature, and it is possible to provide manganese zinc ferrite with significantly reduced magnetic core loss.

[Brief description of drawings]

FIG. 1 is a chart showing a relationship between a core loss and a generation rate of coarse particles.

Claims (3)

[Claims] 1. A raw material containing iron, manganese, and zinc as main components.
Fe composition range₂ O ₃50-60 mol%, MnO20
~ 40mol%, ZnO8 ~ 15mol%, SiO
₂0.01-0.2 mol%, CaO 0.08-0.4
mol%, coarse particles with a particle size of 50 μm or more in the ferrite core
Large grains do not contain more than 1% in area ratio with respect to core cross section
A low-loss manganese zinc ferrite characterized in that 2. A low-loss manganese zinc which is characterized by setting an atmospheric oxygen concentration to 100 ppm or less in a temperature rising process from 300 ° C. to 1000 ° C. or less when firing a molded body of ferrite calcined powder containing a binder. Ferrite manufacturing method. 3. Low loss manganese zinc characterized in that, in the main calcination, the atmospheric oxygen concentration from 1000 ° C. to the maximum reached temperature and the atmospheric oxygen concentration during cooling are within the ranges defined by the following formulas. Ferrite manufacturing method. log P = a-20000 / (T + 273) 13.6 ≦ a ≦ 14.3 P ≦ 8 where P: oxygen concentration, T: temperature, a: constant