Method of producing Ni-Cu-Zn ferrite material

Details Method of producing Ni-Cu-Zn ferrite material Method of producing Ni-Cu-Zn ferrite material

1999-09-29

2001-02-13

Koslow, C. Melissa (Department: 1755)

Compositions

Magnetic

Iron-oxygen compound containing

C252S062620

Reexamination Certificate

active

06187218

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a ferrite material, in particular a Ni—Cu—Zn ferrite material which is suitable for use as a chip inductor.
2. Description of the Related Art
An inductor element has been used as a noise filter in an electric circuit of an electronic device. In order to achieve a compact size and effect a high density attachment, there has been suggested and put into practical use a chip inductor involving only a small amount of a magnetic flux leakage, occupying only a small area, and having a structure in which the inner conductor is disposed within a ferrite ceramic (core).
Such chip inductors, for example, may be obtained by simultaneously calcining a plurality of ferrite material layers and electrically conductive material layers formed between the ferrite layers. In general, there has been used a Ni—Cu—Zn ferrite material as the ferrite material for forming the chip inductors, and, as an electrically conductive material, there has been used a Ag material which has a high electric conductivity.
When Ag is used as an electrically conductive material and the above chip inductor is obtained by means of a simultaneous calcining treatment, the melting point of Ag is 950° C. under the oxygen equilibrium conditions in the atmosphere. If it is heated to a temperature of 900° C. or higher, a plastic deformation of Ag will begin as the time of heating progresses, thereby causing it to penetrate and disperse throughout the ferrite. Because of this, there will occur some problems which can include the cross sectional area of the internal conductor will decrease, the direct current resistance value will increase, and the consumption electric power will thus increase. Moreover, if it is heated to a high temperature which is higher than 950° C., a part of the internal conductor will be disconnected, losing the predetermined function as an inductor. For this reason, it is required that the calcining treatment should be conducted at a temperature of 950° C. or lower, preferably 900° C. or lower, in order to obtain a chip inductor using Ag as an internal conductor.
However, it is necessary to calcine a Ni—Cu—Zn ferrite material which was used as a core material (ferrite ceramic) of a chip inductor at a temperature of 1000° C. or higher so as to obtain a dense calcined body. If the calcining treatment is conducted at a temperature lower than such a value, it is impossible to obtain a sufficient calcining density, hence causing a problem in that the initial magnetic permeability becomes low and pores are adversely created in the calcined body.
Further, in order to effectively remove a noise component having a low frequency of 30 MHz or lower, it is required that, as a characteristic of a noise filter for use in an electric circuit, the cross point frequency at the intersection of an R component frequency curve and the X component frequency curve should be controlled to a value of 10 MHz or lower. For this reason, it is required that the initial magnetic permeability of the Ni—Cu—Zn ferrite material, which is used as a core material of a chip inductor, be maintained at a value of 800 or higher for this purpose.
Furthermore, in order to inhibit a wave form distortion in a frequency component, it is required that, as a characteristic of a noise filter for use in an electric circuit, the cross point frequency at an intersection of an R component frequency curve and an X component frequency curve should be controlled at a value of 5 MHz or lower. For this reason, it is required that the initial magnetic permeability of the Ni—Cu—Zn ferrite material, which is for use as a core material of a chip inductor, be maintained at a value of 1200 or higher.
SUMMARY OF THE INVENTION
The present invention can solve the aforementioned problems associated with the conventional art and provides a method of producing a Ni—Cu—Zn ferrite material can be calcined at a temperature of 900 degrees or lower so as to obtain a high density, and has an initial magnetic permeability of 800 or higher or an initial magnetic permeability of 1200 or higher.
The method of producing a Ni—Cu—Zn ferrite material comprises the steps of: preparing a mixture of an iron compound powder having a specific surface area of about 8.5 m
2
/g or more, a nickel compound powder, copper compound powder and a zinc compound powder, the mixture having a specific surface area of about 8.0 m
2
/g or more; pre-calcining the mixture such that the pre-calcined mixture has a surface area of about 5.0 m
2
/g or more and a spinel crystal synthesizability within a range of about 80.5% to 98%; and milling the pre-calcined mixture to obtain a powder of a Ni—Cu—Zn ferrite material having a specific surface area of about 6.0 m
2
/g or more.
To achieve larger initial magnetic permeability, the nickel compound powder and the zinc compound powder have a specific surface area of about 8.0 m
2
/g or more, respectively, the mixture has the specific surface area of about 10.0 m
2
/g or more, the pre-calcining is performed such that the pre-calcined mixture has a surface area of about 6.0 m
2
/g or more and the spinel crystal synthesizability within a range of about 90% to 95% and the powder of a Ni—Cu—Zn ferrite material has the specific surface area of about 8.0 m
2
/g or more.
According to the present invention, it is possible to conduct a dense calcining treatment at a temperature of 900° C. or lower, and thus one can obtain Ni—Cu—Zn ferrite material having an initial magnetic permeability of 800 or higher or an initial magnetic permeability of 1200 or higher.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
According to the method of producing a Ni—Cu—Zn ferrite material of the present invention, a mixture of an iron compound, a nickel compound powder, copper compound powder and a zinc compound powder is first prepared. The mixture has a specific surface area of about 8.0 m
2
/g or more, and the iron compound has a specific surface area of about 8.5 m
2
/g or more.
The mixture is then pre-calcined. The pre-calcining process is performed such the obtained pre-calcined mixture has a surface area of about 5.0 m
2
/g or more and a spinel crystal synthesizability of the obtained pre-calcined mixture within a range of about 80.5% to 98%.
Thereafter, the pre-calcined mixture is milled to obtain a powder of a Ni—Cu—Zn ferrite material having a specific surface area of about 6.0 m
2
/g or more. Note that the spinel crystal synthesizability referred in this specification is defined as a value calculated by the following equation using a peak intensity (I
Fe101
) of (104) surface of Fe
2
O
3
and a peak intensity (I
sp311
) of (311) surface of the spinel crystal, both of which are measured during X-ray diffraction on the powder material:
Spinel crystal synthesizability (%)=I
sp311
/(I
Fe104
+I
sp311
)×100.
The iron compound used present invention is preferably &agr; Fe
2
O
3
, and more preferably &agr; Fe
2
O
3
synthesized in a wet method. In addition, the thus obtained Ni—Cu—Zn ferrite material preferably consists of about 48.0 mol % to 49.8 mol % of Fe
2
O
3
, about 20.0 mol % to 34.0 mol % of ZnO, about 6.0 mol % to 20.0 mol % of CuO, with the remainder being NiO.
When the specific surface area of the powder of the Ni—Cu—Zn ferrite material after milling is smaller than about 6.0 m
2
/g, a reactivity of the powder will be low, thus making it impossible to effect a sufficient calcining treatment at a temperature of 900° C. or lower and the calcining density will be low, making it impossible to obtain an initial magnetic permeability of 800 or higher. For this reason, it is preferred that the specific surface area of the powder material after disintegration is about 6.0 m
2
/g or larger.
If the specific surface area of the pre-calcined mixture is smaller than about 5.0 m
2
/g, the particle of the pre-calcined mixture is undergrown. It may be necessary to extend the milling time or to employ a milling machine of a medium stirring type so to obtain a specific surface

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