JPH04149026A - Low-loss mn-zn ferrite - Google Patents

Abstract

PURPOSE:To decrease loss in high frequency region by incorporating an essential component comprising Fe2O3, MnO and ZnO and other components of Si, Ca, Nb, Ta and Ti, each by specified amt. CONSTITUTION:The source material of the essential component comprising (i) Fe2O3 by 51.5-54.5mol%, (ii) MnO by 33-40mol% and (iii) ZnO by 6-13mol% is mixed and calcined to obtain a calcined powder. To this powder, (iv) SiO2 by 0.008-0.035wt.%, (v) CaCO3 by 0.02-0.20wt.% calculated as CaO, (vi) Nb2O5 by 0.005-0.05wt.%, (vii) Ta2O5 by 0.005-0.5wt.% and (viii) TiO2 by 0.005-0.65wt.% are compounded, pulverized and mixed to obtain a pulverized powder. Then, a binder (e.g. PVA) is added to this pulverized powder, granulated, molded and calcined to obtain the ferrite of this purpose containing the essential components (i)-(iii) and Si, Ca, Nb, Ta and Ti.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a low-loss Mn-Zn ferrite suitable for use in transformers for switching power supplies and the like.

(Prior Art) Mn-Zn ferrite is used as a transformer material for various communication devices, consumer devices, and the like. Such Mn-
Various properties are required of Zn-based ferrite, such as high saturation magnetic flux density, high magnetic permeability, high resistance, and low iron loss, but especially for transformers for switching power supplies, such as the one targeted by this invention. It is particularly important to have low loss under high frequency and high magnetic fields.

For this reason, attempts have been made to improve Mn--Zn ferrite by adding various trace components.

For example, in JP-A-58-15037, by adding Nb2O5, and in JP-A-60-132302, Nb, O5°Cab, V30SI ZrO2, Al2
Due to the addition of O3, Snug, CuO, etc., 100kHz is now becoming the standard switching frequency.
We are trying to improve the loss at 100kHz, 2
Iron loss value at 00mT is 350 to 40/CC
This level has been achieved.

By the way, recently, in order to further downsize power supplies, there is a tendency to use higher frequencies (500kHz to IM)Iz), and the development of Mn-Zn ferrites that meet this purpose is also progressing. It's still not enough.

For example, commercially available low-loss ferrite for power supplies has a power of 500kHz.
z, 100 mT, it is about 1000 mW/cc at most, which is not sufficient as a high frequency power source material.

(Problems to be Solved by the Invention) As described above, the present invention is compatible with low-loss high frequencies that can improve the iron loss value at 100 kHz, which is currently becoming the standard switching power frequency, and furthermore, the iron loss value at high frequencies of 500 kHz or higher. The purpose is to propose Mn-Zn-based ferrite.

(Means for Solving the Problems) That is, the present invention provides FezOz: 51.5 to 54.5 mol%, Mn
O: 33-40 mol% and ZnO: 6-13
mol% as the basic component, and this basic component contains Si, Ca, N
b.

Ta and Ti are each 5iOz in terms of the following oxides.
: 0.008~0.035 t%, CaO:
0.02-0.20 wt%, Nb2O5: 0.0
05-0.05 wt%, Ta2O5: 0.005
~0.05 wt% and TiO□: 0.005~0
．． Low loss Mn-Z containing in the range of 65 wt%
It is an n-type ferrite.

(Function) First, in this invention, the reason why the blending ratio of the basic components is limited to the above range will be explained.

Fetch: 51.5-54.5 mol%, Mn
O: 33-40 mol%, ZnO: 6-13 m
ol% The operating temperature of a switching power supply transformer is usually 60~
70°C, therefore, it is desirable that the power loss is low in this temperature range, and that the iron loss has a negative temperature dependence from room temperature to a temperature range of about 60 to 80°C, which exceeds the operating temperature. As a result of examining the blending ratios of Fe2O3, MnO and ZnO from this point of view, the above range was obtained.

Note that Fe, 03 raw materials include not only Fe2O3 but also
FeO, Fe5g4, and also compounds that can be converted into Fe, 03 by calcination, such as iron compounds such as iron hydroxide, iron oxalate, iron oxyhydroxide, iron sulfate, and iron nitrate, can be used. In addition, as a MnO raw material,
Not only MnO but also Mn0z, Mn30a+ MnzO
Furthermore, it is possible to use compounds that can be converted into MnO by calcination, such as manganese carbonate and manganese oxalate. Furthermore, as a ZnO raw material, ZnO
In addition to ZnO, it is also possible to use compounds that can be converted into ZnO by firing, such as zinc carbonate and zinc oxalate.

In this invention, Si, CaN are included in the above basic components.
b, Ta, and Ti oxides are each contained in predetermined amounts, and these contents are determined in terms of oxides as described below.

5jOz: 0.008-0.035 wt%5i0
2 increases the specific resistance of grain boundaries by coexisting with CaO and effectively contributes to reducing eddy current loss, but the content of 0.008
If it is less than wt%, the effect of addition is poor; on the other hand, 0.0
If it exceeds 35 svt%, abnormal grain growth tends to occur during firing and the properties become unstable, so 0.008 to 0.035
The range was limited to wt%.

CaO: 0.02 to 0.20 wt% CaO is a useful component that effectively increases grain boundary resistance in coexistence with SiO□ and thereby brings about low iron loss, but when the content is less than 0.02 wt% If it is too small, the effect of improving grain boundary resistance will be poor, and if it exceeds 0.20 wt%, the loss will increase, so the content was determined to be in the range of 0.02 to 0.20 wt%.

Nb2O5: 0.005 to 0.05 wt% niobium oxide (mainly Nb2O5) effectively contributes to reducing loss in the high frequency region. Although the reason why the loss is improved by adding niobium oxide has not yet been clearly elucidated,
It has the function of altering the high-resistance grain boundary phase formed by the combined inclusion of iO□ and CaO, increasing the specific resistance, and mitigating the negative magnetic effects caused by the presence of foreign phases at the grain boundaries. It is thought that this is because of this. However, if the content is less than 0.005 wt%, the effect is poor, while if the content exceeds 0.05 wt%, abnormal grain growth is likely to occur during sintering.
It was limited to a range of 0.05 wt%.

Ta2O5: 0.005 to 0.05imt% Tantalum oxide (mainly Ta2es) effectively contributes to increasing resistivity in coexistence with SiO2 and CaO, but when the content is 0.
．． If it is less than 0.005 wt%, the effect is poor; on the other hand, if it is less than 0.0
If it exceeds 5 wt%, the loss will conversely increase.

Ti0z: 0.005 to 0.65 wt% Titanium oxide (Ti0z as a seed) promotes re-oxidation of grain boundaries during the cooling process during ferrite core firing and has the effect of increasing grain boundary resistance, but 0.005 wt% If it is less than 0.65vt%, the effect will be small, while if it exceeds 0.65vt%, it will cause an increase in loss.

As mentioned above, increasing resistivity is very effective in reducing loss in the high frequency region of 100 kHz or higher, but in this invention, in the presence of Sin, CaO, niobium oxide (mainly Nb20ff), Tantalum oxide (mainly Ta205) and titanium oxide (mainly Ti(h)
The above objective is achieved by containing and uniformly dispersing it in the grain boundaries.

In order to manufacture the ferrite according to the present invention, each component powder raw material is carefully examined, mixed homogeneously to a predetermined composition, and then subjected to calcination treatment, pulverization treatment, molding treatment, and sintering treatment according to conventional methods. All you have to do is apply

(Example) Fezes: 52. Omol%, MnO: 38.
8 mol% and ZnO: After mixing raw materials with a basic composition of 9.2 mol%, the mixture was heated at 900°C in the atmosphere.
Calcining was performed for 13 hours. To this calcined powder, SiO□, Ca0 (using CaCOs) + N in various proportions
b, o, TaJs and Tag were added and blended, and simultaneously ground and mixed using a wet ball mill.

Next, polyvinyl alcohol (PVA) was added to the pulverized powder as a binder, and after granulation, it was formed into a ring shape, and then heated at 1300°C5 in a nitrogen atmosphere with controlled oxygen concentration.
Firing was performed for 3 hours.

The composition range of the sintered core thus obtained and the 500k
Table 1 shows the measurement results of iron loss values at Hz and 100+++T.
Shown below.

Note that since the iron loss value exhibited the minimum value in the range of 60 to 90°C, the iron loss value in Table 1 showed the minimum value in this temperature range. In the table, N011 to Nα16 are invention examples, while Nα17
- No. 26 are comparative examples whose composition range deviates from the appropriate range of the present invention.

Sample 5iot CaONb2O5T
a205 TiO2 iron loss value number (wtX)
(wtX) (wtX) (wtX) (-tχ)
(mW/cc) o, oos O,012 0,033 0,012 0,013 0,030 0,018 0,013 0,014 0,021 0,011 0,015 0,013 0,014 0,013 0,012 0,120 0,107 0,045 0,025 0,128 0,193 0,125 0,126 0,125 0,124 0,113 0,115 0,125 0,131 0,128 0, 127 0,033 0,032 0,028 0,031 0,032 0,031 0,006 0,017 0,032 0,047 0,033 0,034 0,031 0,033 0,031 0,030 0 ,022 0,024 0,026 0,025 0,028 0,026 0,033 0,030 0,031 0,029 0,006 0,04B 0.033 0.008 0.008 o,oos 0.253 0.262 0.257 0.046 0.046 0.044 0.215 0.231 0.227 0.222 0.1B5 0.177 0.009 Q, 047 0.214 0.605 o, oos O, 041 0,016 o, ois O,017 0,019 0,019 0,016 0,020 0,022 0,095 0,125 0,010 0,234 0,135 0,140 0,125 0,128 0 ,175 0,168 0,035 0,035 0,035 0,034 0,003 0,068 0,041 0,039 0,015 0,018 0,012 0,011 0,018 0,016 0,035 0,033 0,002 0,059 0,042 0,041 0,100 0,105 0,114 0,120 0,256 0,248 0,2B3 0.244 0.001 0.753 500kHz.

100i+T (Effects of the Invention) Thus, according to the present invention, Mn-Zn, which has much lower loss in the high frequency range than conventional materials, can be used as the core of a power transformer with a high switching power frequency.
Soft ferrite can be obtained.

Claims (1)

[Claims] 1. Fe_2O_3: 51.5 to 54.5 mol%,
The basic components are MnO: 33-40 mol% and ZnO: 6-13 mol%, and these basic components include Si, Ca, Nb,
Ta and Ti are converted into the following oxides: SiO_2: 0.008 to 0.035 wt%, CaO:
0.02-0.20wt%, Nb_2O_5:0.005-0.05wt%, Ta_
2O_5: 0.005-0.05wt% and TiO_
2: Low loss Mn-Zn ferrite containing in the range of 0.005 to 0.65 wt%.