JP5445733B2 - Ferrite composition - Google Patents

Description

  The present invention relates to a ferrite composition, and more particularly to a ferrite composition suitable for use in a biomedical electrode.

  Generally, as an electrode for measuring an electric signal, a metal electrode is often used because it needs to have high electric conductivity.

  On the other hand, special purpose electrodes such as biomedical electrodes used to detect electrical signals generated by bioelectric phenomena such as electrocardiogram signals, myoelectric signals, and electroencephalograms react in consideration of effects on the human body. An active metal electrode cannot be used.

  In such an application, an electrode made of a material that is chemically stable, does not harm the human body, and has low electrical resistance is required.

  As such a living body electrode, for example, Patent Document 1 discloses an electrode material made of ferrite in which ferric oxide and nickel oxide have a specific composition range.

According to this electrode material, it is described that electric resistance is low. However, when it is actually used, sufficient mechanical strength is required, but it has been unclear whether or not the electrode described in Patent Document 1 can satisfy such a requirement.
JP 49-43876 A

  The present invention has been made in view of such a situation, is composed of an element safe for the human body, has a low electrical resistance, and can suppress the chipping of the sintered body, and uses the same. An object of the present invention is to provide a living body electrode.

The present inventors have made intensive studies in order to achieve the above object, the presence in the over-over - the Fe ²⁺ in the spinel structure of the ferrite composition in a specific range, to lower the electrical resistance, yet The present inventors have found that chipping (chipping) of the sintered body can be improved and have completed the present invention.

That is, the ferrite composition of the present invention is
Fe ₂ O ₃ : 60 to 90 mol% and MO (wherein M is at least one selected from Ni, Mg, Cu and Zn): 10 to 40 mol%, and a ferrite composition having a spinel structure There,
When the ratio of Fe ²⁺ ions present in the spinel structure is converted as the amount of FeO, the following formula is satisfied.
b ≧ 0.630 × a-30.7 Formula where a: Fe ₂ O ₃ (mol%) and b: FeO amount (% by weight).

The amount of FeO is not the content of FeO present in the ferrite composition, but the amount of Fe ²⁺ present in the spinel structure of the ferrite composition is converted as the amount of FeO.

In the present invention, in the above ferrite composition and a secure element in the human body, so as to satisfy the above expression, the presence in the spinel structure in Fe ²⁺ by excessive over - a ratio, low electrical resistance Furthermore, since excessive sintering can be suppressed, chipping of the sintered body can be effectively suppressed.

  Preferably, the ratio of NiO to the entire MO is 50% or more in terms of mole. By doing in this way, the crack which generate | occur | produces on the sintered compact surface can be effectively suppressed in addition to the above-mentioned effect. As a result, a sintered body having a good appearance can be obtained, and the surface resistance of the sintered body can be stabilized, so that the quality is improved.

  According to the present invention, a biological electrode having any one of the above ferrite compositions as an electrode is provided.

In the ferrite composition of the present invention, the amount of Fe ²⁺ is converted to the amount of FeO and is in the above range. Such ferrite compositions, excessive over - such Fe ²⁺ is present in the spinel structure. In addition, since Fe ²⁺ and Fe ³⁺ are mixed in the spinel structure, the conduction electrons can be easily transferred and the electrical resistance can be reduced by exchanging the conduction electrons between these ions. . Furthermore, the larger the proportion of Fe ^2+, the more the hardening of the sintered body due to oversintering can be suppressed. As a result, chipping (chipping) of the sintered body is reduced, and it becomes easy to process the sintered body into a desired shape.

  Furthermore, the crack which generate | occur | produces on the sintered compact surface can be suppressed by making the ratio of NiO with respect to the whole MO into said range. As a result, a sintered body having a good appearance can be obtained, and the surface resistance of the sintered body can be stabilized, leading to quality improvement.

  The ferrite composition of the present invention is composed of elements that are safe for the human body, and has both low electrical resistance and chipping resistance. Therefore, it is an electrode for detecting bioelectric signals such as electrocardiogram signals and myoelectric signals. Can be suitably used. Moreover, since the surface resistance of the sintered body is stable, the quality is improved. According to the biomedical electrode of the present invention, it is possible to prevent debris lacking the sintered body from adhering to the human body and damage to the human body due to the chipped surface.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
FIG. 1 is a graph showing the relationship between the amount of Fe ₂ O ₃ and the measured amount of FeO in Examples and Comparative Examples of the present invention,
FIG. 2 is a graph showing the relationship between the amount of Fe ₂ O ₃ and the electrical resistance in Examples and Comparative Examples of the present invention,
FIG. 3 is a graph showing the relationship between the amount of Fe ₂ O ₃ and the rate of change in chipping weight in Examples and Comparative Examples of the present invention,
FIG. 4 is an X-ray diffraction chart for an embodiment of the present invention.

Ferrite composition The ferrite composition of the present invention includes Fe ₂ O ₃ and MO (wherein M is at least one selected from Ni, Mg, Cu and Zn) and has a spinel structure. .

Fe ₂ O ₃ is 60 to 90 mol%, preferably is contained in a proportion of 70 to 80 mol%. In the present invention, the amount of Fe ₂ O ₃ is a (mol%). That is, 60 ≦ a ≦ 90.

  The balance is substantially composed of MO (where M is at least one selected from Ni, Mg, Cu and Zn), and preferably the ratio of NiO to the entire MO is 50% in terms of mole. Or more, more preferably 70% or more, and particularly preferably 75% or more. For example, when MO is contained in the ferrite composition at 40 mol%, it is preferable that NiO is contained in the ferrite composition at 20 mol% or more.

When the content of Fe ₂ O ₃ is too small (the content of MO is too large), the generation of Fe ²⁺ described later is reduced, resulting in an increase in electrical resistance and sintering due to excessive sintering. There is a tendency that the chip of the body increases and the processability is poor.

On the other hand, if the Fe ₂ O ₃ content is too high (the MO content is too low), the spinel structure becomes unstable, and a high-resistance impurity phase is generated. Tends to cause chipping, so that the workability tends to be poor.

  Moreover, the crack which generate | occur | produces on the sintered compact surface can be effectively suppressed because the ratio of NiO with respect to the whole MO satisfies said range. As a result, the surface resistance of the sintered body can be stabilized, and the quality is improved.

  This is considered to be because the ion radius of Ni ions is the closest to the ion radius of Fe ions among the metal elements selected as M in MO. That is, when NiO is contained in the ferrite composition of the present invention, the degree of thermal expansion in the spinel structure is considered to be the slowest, and it is strong against disturbance of the fine structure of the crystal. Therefore, it is considered that cracks due to the difference in thermal expansion can be suppressed during firing.

The ferrite composition of the present invention may contain inevitable impurity elements in addition to the above components. Specifically, _MnO, etc. SiO 2, CaO and the like.

The present invention is characterized in that a specific amount of Fe ²⁺ is present in the sintered body of the above ferrite composition. That is, when the amount of Fe ₂ O ₃ converted to a (mol%) and Fe ²⁺ converted to FeO is b (wt%), the following formula is satisfied.
b ≧ 0.630 × a-30.7 Formula

Incidentally, the above formula, although a relationship between the FeO content and the amount of Fe ₂ O _3, which for convenience of measurement, only quantifies the abundance of Fe ²⁺ as FeO amount, It does not mean that FeO is present in the ferrite composition of the present invention. Rather, it has been confirmed by the present inventors that FeO is not present in the ferrite composition of the present invention, and Fe ²⁺ is present in the spinel structure.

The ferrite composition of the present invention is expressed as Fe ³⁺ ₂ O ₃ ^{.M 2+} O (M = Ni ²⁺ , Mg ²⁺ , Cu ²⁺ , Zn ²⁺ ) and has a spinel structure, but Fe ₂ O ₃ and The MO is not a 1: 1 composition but an Fe-rich composition. Therefore, a part of Fe ³⁺ is reduced and exists as Fe ²⁺ .

The amount of Fe ²⁺ is determined stoichiometrically from the contents of Fe ₂ O ₃ and MO . In the present invention, by satisfying the above formula, many Fe ²⁺ is present in the spinel structure.

Therefore, in the spinel structure, conduction electrons are easily exchanged between the mixed Fe ²⁺ and Fe ^3+, and the conduction electrons are easily moved. As a result, the electrical resistance can be lowered.

Specifically, according to the ferrite composition of the present embodiment, the electric resistance is preferably 1.0 × 10 ⁻¹ Ω · cm or less, more preferably 1.0 × 10 ⁻² Ω · cm or less. Can do.

Further, the presence of Fe ²⁺ in the spinel structure can suppress brittleness even if the sintered body becomes too hard due to excessive sintering.

The presence of excess Fe ²⁺ causes a valence imbalance in the ferrite composition, which is considered to be compensated for by defects in oxygen ions in the spinel structure and the arrangement of excess cations. .

From the above, when the Fe ²⁺ content satisfies the above formula, the electrical resistance of the ferrite composition of the present invention can be lowered, and a ferrite composition having excellent chipping resistance can be obtained. Furthermore, the crack of the sintered compact which generate | occur | produces at the time of baking can be suppressed by making the ratio of NiO in the whole MO into said range. Such a ferrite composition can be particularly suitably used as a biological electrode.

In addition, the amount of Fe ²⁺ can be controlled by firing conditions as will be described later, and in the present invention, the amount of Fe ²⁺ is measured by being converted to the amount of FeO by valence analysis. Specifically, it can be measured by a potassium dichromate redox titration method.

Method for Producing Ferrite Composition Hereinafter, the method for producing the ferrite composition of the present embodiment will be specifically described.

First, as a starting material, Fe ₂ O ₃ , NiO, MgO, CuO, ZnO, or a material that becomes these oxides after firing is prepared. Next, the prepared raw materials are weighed and mixed so as to be in the above composition range after firing to obtain a raw material mixture. Examples of the mixing method include wet mixing using a ball mill. It is preferable to use a starting material having an average particle size of 0.1 to 3 μm.

  At this time, inevitable impurities may be contained, but it is preferably 3% by mass or less with respect to 100% by mass of the ferrite composition.

  Next, the raw material mixture is calcined to obtain a calcined material. Calcining causes thermal decomposition of raw materials, homogenization of ingredients, formation of ferrite, disappearance of ultrafine powder due to sintering and grain growth to an appropriate particle size, and converts the raw material mixture into a form suitable for the subsequent process. Done for. Such calcination is preferably performed at a temperature of 800 to 1100 ° C. for about 1 to 3 hours. The calcination may be performed in the atmosphere (air) or may be performed in an atmosphere having a higher oxygen partial pressure than in the atmosphere.

  Next, the calcined material is pulverized to obtain a pulverized material. The pulverization is performed in order to produce a powder having appropriate sinterability by destroying the aggregation of the calcined material. In this embodiment, wet pulverization is performed using a ball mill. The wet pulverization is performed until the average particle size of the calcined material is preferably about 0.5 to 2 μm.

  Next, the pulverized material is granulated (granular) to obtain a granulated product. The granulation is performed in order to convert the pulverized material into aggregated particles having an appropriate size and convert it into a form suitable for molding. Examples of such a granulation method include a pressure granulation method and a spray drying method. The spray drying method is a method in which a commonly used binder such as polyvinyl alcohol is added to the pulverized material, and then atomized in a spray dryer and dried.

  Next, the granulated product is molded into a predetermined shape to obtain a molded body. Examples of the molding of the granulated product include dry molding, wet molding, and extrusion molding. The dry molding method is a molding method in which a granulated product is filled in a mold and compressed and pressed (pressed). The shape of the molded body is not particularly limited, and may be appropriately determined according to the application.

  Next, the compact is fired to obtain a sintered body (the ferrite composition of the present embodiment). This firing is performed in order to obtain a dense sintered body by causing sintering in which the powder adheres at a temperature below the melting point between the powder particles of the molded body containing many voids.

In the present embodiment, the main calcination is preferably performed at a temperature of 1350 ° C. or higher, more preferably 1400 ° C. or higher, and in an atmosphere with an oxygen concentration of preferably 1 ppm or less, more preferably 0.1 ppm or less. preferable. That is, it becomes easy to produce | generate Fe2 ⁺ which satisfies the above-mentioned formula in the spinel structure of a sintered compact by having both a calcination temperature and oxygen concentration in said range. The upper limit of the firing temperature is 1500 ° C.

  As other firing conditions, the holding time at the firing temperature is usually about 2 to 5 hours. Further, the rate of temperature rise is preferably 100 to 200 ° C./hour, and the cooling rate is preferably 100 to 300 ° C./hour.

  The ferrite composition thus obtained is processed into a predetermined shape according to the use, and is preferably used as a bioelectrode electrode element. Then, a lead terminal, a protective cover, etc. are attached, Preferably it uses for a biomedical electrode.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to the embodiment mentioned above at all, and can be variously modified within the range which does not deviate from the summary of this invention.

  In the above-described embodiment, it has been described that the ferrite composition according to the present invention is suitably used for a biomedical electrode. However, the ferrite composition according to the present invention is not limited to a biomedical electrode, for example, a plating electrode. Etc.

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

Example 1
First, Fe ₂ O ₃ and NiO were prepared as starting materials. Next, each prepared starting material powder was weighed so as to have the composition shown in Table 1, and then wet mixed by a ball mill for 5 hours to obtain a raw material mixture. Next, the obtained raw material mixture was calcined in air at 900 ° C. for 2 hours to obtain a calcined material, and then wet pulverized with a ball mill for 20 hours to obtain a pulverized material. Next, after drying the pulverized material, 1.0% by weight of polyvinyl alcohol as a binder was added to 100% by weight of the pulverized material, and granulated to obtain a granulated product, which was added at a pressure of 100 kPa. A compact was obtained by pressure molding. Next, each of these molded bodies was fired at the temperature and atmosphere shown in Table 1 for 2 hours to obtain a sintered body. In addition, the nitrogen atmosphere in Table 1 indicates an atmosphere in which nitrogen is 99.999% (oxygen concentration is 1 ppm or less).

Subsequently, about the obtained sintered compact, the amount of FeO (Fe2 ⁺ amount) was measured by the valence analysis method shown below.

  Each sample of 0.1 g was thermally decomposed with oxalic acid and phosphoric acid in a nitrogen gas stream, and after cooling, sodium diphenylaminesulfonate was added as an indicator, and oxidation-reduction titration was performed with a potassium dichromate standard solution. Quantitative analysis was performed. The results are shown in Table 1 and FIG.

From Table 1 and FIG. 1, it can be confirmed that the amount of FeO, that is, the amount of Fe ²⁺ increases as the firing temperature increases or the reducibility of the firing atmosphere increases. In FIG. 1, sample numbers 1-5 are located above the formula of the present invention and are within the scope of the present invention. Therefore, it can be seen that by firing in a nitrogen atmosphere (N ₂ : 99.999%), the amount of FeO to be measured is increased and the range of the present invention is satisfied.

On the other hand, sample numbers 6 to 13 are located below the formula of the present invention, and it can be confirmed that they are outside the scope of the present invention. In FIG. 1, indicated points in a white square, a sample was calcined at described in Patent Document 1 a firing condition _{(1350 ℃ -2% O 2)} ( Sample No. 6-8).

Further, the obtained sintered body was evaluated for the characteristics of electric resistance and chipping weight change rate. About electrical resistance, In-Ga was apply | coated to both surfaces of the sintered compact, and it measured by the two-terminal method using the electrical resistance meter. The electric resistance was set to 1.0 × 10 ⁻¹ Ω · cm or less. The results are shown in Table 2 and FIG.

  The chip weight change rate was determined by measuring the decrease in the weight of the sintered body after the sintered body was put into a ball mill and rotated for 3 minutes. The chip weight change rate was 0.3% or less. The results are shown in Table 2 and FIG. As the chip weight change rate is smaller, the chip of the sintered body can be reduced.

  Furthermore, X-ray diffraction was performed on the obtained sintered body. X-ray diffraction uses Cu-Kα rays as an X-ray source. The measurement conditions are a voltage of 50 kV and a current of 30 mA, a range of 2θ = 20 ° to 80 °, a step width of 0.02 °, and a counting time of 0. It was 5 seconds.

From Table 2 and FIG. 2, it can be confirmed that the Fe ₂ O ₃ content is within the range of the present invention and the sample fired at 1350 ° C. or higher in a nitrogen atmosphere can have a low electrical resistivity. From Table 1 and FIG. 1, this is considered to be because the amount of Fe ²⁺ generated in the sintered body is within the scope of the present invention, and Fe ²⁺ contributes to electrical conduction.

On the other hand, for the sample fired under the condition of 1350 ° C.−2% O ₂ , the Fe ²⁺ amount is not within the scope of the present invention, so that the electrical resistivity cannot be reduced, that is, the sample described in Patent Document 1 Then, it can confirm that the effect of this invention is not acquired.

Moreover, from Table 2 and FIG. 3, the Fe ₂ O ₃ content is within the range of the present invention, and the sample that is fired at 1350 ° C. or higher in the nitrogen atmosphere has the Fe ²⁺ content within the range of the present invention. Therefore, it can be confirmed that the chipping weight change rate can be lowered.
On the other hand, for the sample fired under the condition of 1350 ° C.-2% O ₂ , the amount of Fe ²⁺ is not within the scope of the present invention. It can be confirmed that the effect of the present invention cannot be obtained with the sample.

FIG. 4 shows an X-ray diffraction chart of Sample 5. As a result of identifying the obtained X-ray peak, it can be confirmed that only the X-ray peak of (Ni, Fe) Fe ₂ O ₄ having a spinel structure is observed. Moreover, it turns out that the obtained X-ray peak does not correspond with the X-ray peak of FeO. That is, it can be confirmed that Fe ²⁺ does not exist as FeO. Since the FeO phase is a high resistance phase, the effect of the present invention cannot be achieved when the FeO phase is present.

Example 2
A sintered body was produced in the same manner as in Example 1 except that NiO of the ferrite composition of Example 1 was changed to MgO, CuO, and ZnO. In addition to the same characteristic evaluation as in Example 1, the sintered body was The presence or absence of surface cracks was evaluated. The results are shown in Table 3.

  The method for evaluating cracks on the surface of the sintered body is not particularly limited, and examples include visual inspection using an optical microscope and automatic inspection using an appearance determination device. In this example, 1000 samples were inspected using an optical microscope, and it was examined whether or not cracks having a length of about several mm were generated on the surface of the sintered body. Table 3 shows the number of cracks observed in 1000 samples.

From Table 3, it can be confirmed that even when NiO is changed to MgO, CuO, ZnO, the amount of Fe ²⁺ is within the range of the present invention, and as a result, good characteristics are exhibited. Moreover, when MO is NiO, it can be confirmed that there is no sample in which cracks are observed on the surface of the sintered body.

Example 3
Example 1 except that the content of Fe ₂ O ₃ in the ferrite composition was 60 mol%, the content of MO was 40 mol%, and each oxide constituting the MO had the composition shown in Table 4. A sintered body was produced in the same manner as described above, and the same characteristic evaluation as in Example 2 was performed. The results are shown in Table 4.

  From Table 4, it can be seen that the higher the ratio of NiO with respect to the entire MO, the fewer samples with cracks on the sintered body surface. In particular, when the NiO ratio is 75% or more, it can be confirmed that there is no sample in which cracks are observed on the surface of the sintered body.

Example 4
Example 1 except that the content of Fe ₂ O ₃ in the ferrite composition was 90 mol%, the content of MO was 10 mol%, and each oxide constituting the MO had the composition shown in Table 5. A sintered body was produced in the same manner as described above, and the same characteristic evaluation as in Example 2 was performed. The results are shown in Table 5.

  From Table 5, it can be confirmed that even when the MO content in the ferrite composition is small, the same tendency as in Example 3 is observed.

FIG. 1 is a graph showing the relationship between the amount of Fe ₂ O ₃ and the measured amount of FeO in Examples and Comparative Examples of the present invention. FIG. 2 is a graph showing the relationship between the amount of Fe ₂ O ₃ and the electrical resistance in Examples and Comparative Examples of the present invention. FIG. 3 is a graph showing the relationship between the amount of Fe ₂ O ₃ and the chipping weight change rate in the examples and comparative examples of the present invention. FIG. 4 is an X-ray diffraction chart for an embodiment of the present invention.

Claims (3)

Fe ₂ O ₃ : 60 to 90 mol% and MO (wherein M is at least one selected from Ni, Mg, Cu and Zn): 10 to 40 mol%, and a ferrite composition having a spinel structure There,
A ferrite composition characterized by satisfying the following formula when the proportion of Fe ²⁺ present in the spinel structure is converted as the amount of FeO.
b ≧ 0.630 × a-30.7 Formula where a: Fe ₂ O ₃ (mol%) and b: FeO amount (% by weight).   The ferrite composition according to claim 1, wherein the ratio of NiO to the entire MO is 50% or more in terms of mole.   A biological electrode having the ferrite composition according to claim 1 as an electrode.

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