JPH04322410A - Manufacture of low power loss manganese-zinc ferrite - Google Patents

Abstract

PURPOSE:To provide a low power loss Mn-Zn ferrite which ensures high reliabil ity even under high frequency and high loading condition by offering, during the manufacturing process, a practical adjusting method for determining the final magnetic characteristic of Mn-Zn ferrite in which TiO2 is added as a sub-element. CONSTITUTION:In the Mn-Zn ferrite including TiO2 of ppm wt. to 20000ppm wt. as the one of sub-elements and a method of manufacturing the same, a degree of oxidation of baked material is adjusted to increase so that the amount of bivalent Fe ion becomes almost equal to that at the time of adding no TiO2 (deviation of + or -10% or less while it becomes 100% when TiO2 is not added). Moreover, quantitative variation of oxidation degree to be controlled and variation of baking oxygen concentration to be changed depending on such quantitative variation are also restricted.

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 having low power loss characteristics required for transformer core materials such as switching power supplies, and a method for manufacturing the same.

0002

[Prior Art] In Mn-Zn ferrite having low power loss characteristics, the main composition is Fe2O3 50-56
mol%, MnO30-40 mol%, ZnO5-
20 mol% of various additives such as CaO, SiO2, etc. are used as sub-compositions.

However, in recent years, with the miniaturization and higher frequency of power supplies, there is a demand for transformer core materials with even lower power loss characteristics than before, and conventional Mn-Zn ferrite materials cannot be used under such conditions. However, there are major problems in such devices, such as unusability due to increased power loss or decreased reliability due to heat generation.

Conventionally, in order to cope with this problem, TiO2 was added as a subcomponent to Mn-Zn ferrite (Japanese Patent Laid-Open No. 61-108109, Japanese Patent Laid-open No. 58-3).
No. 6974) is disclosed. However, as ferrite oxides are easily oxidized, they are easily affected by the stoichiometric oxidation degree and the firing atmosphere, so even after the component system has been decided, the firing conditions etc. The effort required to determine the manufacturing conditions through trial and error was essential.

In other words, the effectiveness of using TiO2 as a subcomponent has been well known, but this control method focuses on the non-stoichiometric oxidation degree of ferrite oxide when adding TiO2 in mol%. has not been disclosed until now.

[0006]

[Problems to be Solved by the Invention] In order to solve the above problems, the present invention has developed a method of manufacturing Mn-
It provides a specific adjustment method during firing to determine the final magnetic properties of Zn ferrite, instead of the conventional trial-and-error approach, and provides highly reliable Mn-Zn ferrite even under high frequency and high loads. The present invention provides a method for manufacturing the same.

[0007]

[Means for Solving the Problems] The present inventors have discovered that TiO2
as one of the subcomponents 500 ppm by weight ~2000
We focused on the possibility that an optimal range exists for the oxidation degree and ion distribution of the fired body in Mn-Zn ferrite containing 0 ppm by weight, and conducted various studies.

As a result, in the TiO2-added Mn-Zn ferrite, the oxidation of the fired body is made such that the amount of divalent iron ions is almost the same as that of the TiO2-free case, which has the same composition ratio of other elements except Ti. The inventors discovered that the best results can be obtained by increasing the degree of adjustment, and have completed the present invention.

[0009] The term "almost the same amount" as used herein means that the amount of TiO2-free Mn-Zn ferrite has a Ti
TiO2-added MnZ with the same composition ratio of other elements except
It refers to a range in which the amount of divalent iron ions is 0.9 to 1.1 times that of n-ferrite.

[0010] Mn doped with Ti having a relatively high valence
-When manufacturing Zn ferrite, if the manufacturing conditions are the same as for TiO2-free Mn-Zn ferrite, which has the same composition ratio of elements except Ti2, that is, the degree of oxidation is not taken into account,
Due to the charge balance in the ferrite, the amount of divalent iron ions increases by the amount of Ti introduced, and the magnetic properties deteriorate significantly.

In order to control the amount of divalent iron ions in the oxide within the above range, it is necessary to adjust the degree of oxidation of the fired product, and the degree of oxidation Δγ to be increased is determined by the following relational expression: It was found that the range indicated by is optimal. Δγ=ε·η Here, Δγ is the amount of change in oxidation degree, ε is the coefficient, and η is the amount of TiO2 added. In the chemical formula, η is expressed as a composition ratio when the amount of oxygen is 4. coefficient ε
ranges from 0.9 to 1.5.

[0012] If the amount of TiO2 added directly leads to an increase in divalent iron ions, then ε=0.75.
It should be. If ε is 0.9 or less, the increment in the degree of oxidation will be insufficient, and if ε is 1.5 or more, it will be excessive, and both of these will significantly deteriorate the power loss characteristics. The above-mentioned absolute value γ of the degree of oxidation is defined by the deviation from the stoichiometry of oxygen ions.

As a specific method for controlling the above-mentioned increase in oxidation degree Δγ, the present invention is characterized by controlling the oxygen concentration so as to correspond to the following equation. log10Po2 = -K(1/T)+f(γ) where Po2: oxygen concentration during firing (atm), T: firing temperature (K).

For example, when the firing temperature is the same, γ is changed from γ to γ'
If you want to change by Δγ to =γ+Δγ, the required oxygen concentration Po2' is given by the ratio to the current oxygen concentration Po2, log10(Po2'/Po2)=f(γ')-f
(γ). The formula f(γ) can be expressed as follows. f(γ)=(aγ2 +bγ+c)+δ where a=-4
200, b=160, c=7.1, and δ indicates the tolerance, and when |δ|<0.3, a practically excellent control result can be obtained. Further, when changing the temperature, a term related to temperature is required, and the coefficient K in that case is 14,500.

[0015]

According to the present invention, in Mn--Zn ferrite containing TiO2 as one of the subcomponents, it is possible to achieve an optimum balance of ions in the oxide, and even if the composition changes, the optimum adjustment method can be immediately determined. As a result, it has become possible to produce a ferrite that exhibits excellent power loss characteristics.

[0016]

[Example] Fe2 O3 52.7 mol%, M
nO35.6 mol%, ZnO 11.7 mol
% of the main ferrite component, CaO as a subcomponent
440 ppm of TiO2 and 90 ppm of SiO2 were added, and the amount of divalent iron ions in the fired body was varied under various TiO2 addition conditions as shown in Table 1.
Power loss was measured at 0 kHz and 100°C.

As shown in Sample 1, the amount of divalent iron ions without the addition of TiO2 was 1.3% by weight as measured by titration. When TiO2 of Samples 2 to 13 was added, the power loss was divided into two types: those that increased and were improved, and those that actually worsened. Among them, the amount of divalent iron ions is almost the same as when no additives are added (±10% with no additives as 100%).
It was confirmed that sample numbers 3, 4, 7, 8, and 11 with the following deviations showed a significant improvement in power loss value of 20% or more compared to that without additives.

Next, the same main components as above and CaO, S
In addition to iO2 addition, 1900 ppm TiO2
The optimum value of the amount of change Δγ in the degree of oxidation γ when added will be described. When the amount of oxygen in the chemical formula is 4, the composition ratio η is C
Assuming that the amount of aO and SiO2 added is sufficiently small,
It is given by the following formula. η=3d/(2a+b+c+d) a, b, c, d are Fe2 O3, MnO, respectively
Addition of ZnO, TiO2 mol%. For TiO2 1900ppm, η=0.00
It will be 55.

FIG. 1 shows the power loss values of the ferrite core at 200 mT, 100 kHz, and 100° C. when α is varied when Δγ=α·η. Excellent power characteristics are ensured in the range of 0.9<α<1.5, centered around α=1.2.

In other words, the amount of change in oxidation degree Δγ is 6.6×1
5.0×10-3 to 8.3× centered around 0-3
The range is 10-3. The ferrite core γ before TiO2 addition is 5×10−3, and Δγ is 6.6×10−3.
When aiming at 3, γ after increasing the oxidation degree is 11.6×1
The result will be 0-3. The amount of change in oxygen concentration corresponding to this is calculated below.

First, at a firing temperature of 1250°C, initial γ=5×1
The oxygen concentration corresponding to 0-3 is

[0022]

[Math 1]

Substituting into [0023], K=14500, a=-42
00, b=160 and c=7.1, then Po2 =10-1.726 =1.88%. On the other hand, when γ is increased to 11.6 x 10-3, Po2 = 10-1.13 = 7.40%
becomes.

[0024] That is, the oxygen concentration during firing at 1250°C is increased from 1.88% to 7.40%. This △γ is 6.6×10-3 and Po2 = 7.40
The power loss values of the ferrite core fired at % correspond to those for a=1.2 in FIG.

[0025]

[Effects of the Invention] The present invention enables the most effective control of the degree of oxidation of the Mn-Zn ferrite core when TiO2 is added as a subcomponent, compared to the conventional method in which only additives are added. As a result, significant improvements and stabilization of the power loss characteristics of ferrite have been achieved.

[Brief explanation of drawings]

FIG. 1 is a chart of power loss and oxidation degree change.

Claims (2)

[Claims] Claim 1: TiO2 as one of the subcomponents, 5
MnZn containing 00 to 20,000 ppm by weight and the amount of divalent iron ions is TiO-free and the other composition ratios are the same.
MnZn ferrite characterized in that the degree of oxidation is adjusted to be 0.9 to 1.1 times as much as ferrite. 2. The method for producing MnZn ferrite according to claim 1, wherein the oxidation degree of the MnZn ferrite is adjusted by the following method. △γ=ε・η Here, △γ: Change in degree of oxidation η: Addition amount of TiO2 (composition ratio when oxygen amount is 4 in the chemical formula) α: Coefficient 0.9<ε<1.5 Degree of oxidation γ is defined by the following chemical formula. A1+αB2+βO4+γ A: Metal cation, spinel structure tetrahedral position B: Metal cation, spinel structure octahedral position O: Oxygen anion α, β, γ: Deviation of ion composition ratio from stoichiometric value [
3. According to claim 2, the oxygen concentration in the firing atmosphere during firing of the ferrite core is controlled so as to correspond to the following relational expression with respect to Δγ calculated from the formula Δγ=ε·η. A method for manufacturing Mn-Zn ferrite. log10Po2 = -K (1/T) + f (γ) However, Po2: Calcining oxygen concentration (atm) T: Calcining temperature (K) f (γ): Functional expression of γ K: Temperature coefficient In the above, K = 14500 f (γ) = (aγ2 + bγ + c) + δa, b, c: coefficient a = -4200 b = 160 c = 7.1 δ: tolerance coefficient | δ | <0.3