Mn-Zn system ferrite

Details Mn-Zn system ferrite Mn-Zn system ferrite

1998-11-13

2001-04-17

Koslow, C. Melissa (Department: 1755)

Compositions

Magnetic

Iron-oxygen compound containing

C252S062630

Reexamination Certificate

active

06217789

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a Mn—Zn system Ferrite having a high magnetic permeability with its excellent temperature characteristics.
BACKGROUND ART
The Mn—Zn system ferrite is used as a magnetic core for transformers and noise filters since it has the high magnetic permeability.
A pulse transformer used in S/T point interface of ISDN is sometimes installed in the open air when used for public telephones and digital service units (DSU). Therefore, the pulse transformer is required to have temperature compensation in the range from low to high temperature.
However, in case of the conventional Mn—Zn system ferrite, the initial magnetic permeability remarkably decreases in the low temperature range (−20 to 20° C.). For this reason, in order to maintain the inductance at the low temperature range, it was necessary to increase a number of winding or to use a ferrite which is higher than necessary in the initial magnetic permeability at a normal temperature so that the initial magnetic permeability increases at the low temperature range. Hence, such a ferrite was not efficient at all.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a Mn—Zn system ferrite which maintains the high initial magnetic permeability in the wide range of temperature of −20 to 100° C.
This object is achieved by the present invention which is defined below as (1) to (8).
(1) A Mn—Zn system ferrite containing main components comprising manganese oxide, zinc oxide and iron oxide, and subordinate components comprising bismuth oxide and molybdenum oxide,
said Mn—Zn system ferrite comprising 22.0 to 25.0 mol % of a manganese oxide component calculated as MnO, 22.0 to 25.0 mol % of a zinc oxide calcuated as ZnO component and the remainder calculated as Fe
2
O
3
respectively in main components, and
said Mn—Zn system ferrite having been sintered after adding thereto 50 to 400 ppm of a bismuth oxide component calculated as Bi
2
O
3
and 50 to 400 ppm of a molybdenum oxide component calculated as MoO
3
as subordinate component source materials.
(2) The Mn—Zn system ferrite of the above (1), wherein the initial magnetic permeability at 10 KHz is 8,500 or more at −20 to 20° C. and 10,000 or more at 20 to 100° C.
(3) The Mn—Zn system ferrite of the above (1), comprising the ratio of Fe
2
O
3
52.5 to 53.8 mol % and the ratio of ZnO 22.5 to 24.5 mol % in main components.
(4) The Mn—Zn system ferrite of the above (3), wherein the initial magnetic permeability at 10 KHz is 9,000 or more at −20 to 20° C. and 11,000 or more at 20 to 100° C.
(5) The Mn—Zn system ferrite of the above (1), comprising the ratio of Fe
2
O
3
53.0 to 53.3 mol % and the ratio of ZnO 23.3 to 23.9 mol % in main components.
(6) The Mn—Zn system ferrite of the above (5), wherein the initial magnetic permeability at 10 KHz is 9,500 or more at −20 to 20° C. and 11,500 or more at 20 to 100° C.
(7) The Mn—Zn system ferrite as claimed in claim
1
, comprising the ratio of Fe
2
O
3
52.6 to 53.8 mol % and the ratio of MnO 22.9 to 20.5 mol %.
(8) The Mn—Zn system ferrite as claimed in claim
7
, wherein the initial magnetic permeability at 10 KHz is 12,000 or more at −20 to 100° C.
Function and Effect
According to the present invention, the bismuth oxide and the molybdenum oxide are contained in the Mn—Zn system ferrite and the contents of manganese oxide, zinc oxide and iron oxide as main components is within a given amount. Thus, a high initial magnetic permeability could be obtained within the range from low to high temperatures. That is why the Mn—Zn system ferrite according to the present invention is preferred, for example, for the pulse transformer used for S/T point interface of ISDN.
Now, it is to be noted that Japanese Patent Application Kokai No. 204025/1995 describes the technology wherein the high initial magnetic permeability can be obtained at the normal temperature by containing bismuth oxide and molybdenum oxide into the Mn—Zn system ferrite. However, there is no mention made of improvement of the initial magnetic permeability at the low temperature range of about −20 to 20° C. Besides, main components as described in the embodiments of said Patent are out of the scope of the present invention.
More, Japanese Patent Application Kokai No. 263447/1995 describes the Mn—Zn system ferrite, wherein &mgr;i is 8,000 or more in the range of −20 to 100° C. and the ratio of variation thereof is within 70%. However, there is no description about one having the same performance, that is to say, as that of the Mn—Zn system ferrite of the present invention, wherein the initial magnetic permeability at 10 KHz is 8,500 or more at −20 to 20° C. and 10,000 or more at 20 to 100° C. Moreover, in the sample 25 as described in Table 2 of said publication, the initial magnetic permeability at 100 KHz is 8,500 or more at −20 to 20° C. and 10,000 or more at 20 to 100° C. However, 100 KHz is close to a critical frequency of the Mn—Zn system ferrite and the initial magnetic permeability only shows a high value since the resonance is generated in this vicinity. Hence, the initial magnetic permeability at 10 KHz becomes less than that according to the Mn—Zn system ferrite of the present invention. Moreover, there is no description about that, wherein the initial magnetic permeability at 10 KHz is 12,000 or more at −20 to 100° C.


REFERENCES:
patent: 5498361 (1996-03-01), Matsukawa et al.
patent: 5779930 (1998-07-01), Inoue
patent: 5846448 (1998-12-01), Yasuhara et al.
patent: 6-263447 (1994-09-01), None
patent: 9-165220 (1997-06-01), None

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