JPH09306717A - Manufacture of magnetic oxide powder and sintered soft ferrite material, and sintered ni-zn ferrite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of magnetic oxide powder for soft ferrite which may be fired at a low temperature and in which crystalline grains may be grown large. SOLUTION: Slurry is formed by suspending and dispersing magnetic oxide powder having a specific surface area of not smaller than 10m<2> /g into a solution in which a metal salt compound containing at least one metal element of Bi, Mg, Pb, Ca and V is dissolved. This slurry is atomized into a decomposition furnace set at a temperature not higher that 500 deg.C so that the slurry is thermally decomposed. Thus, a compound which promotes surface diffusion and volume diffusion of magnetic oxide when sintering the magnetic oxide powder at a predetermined sintering temperature is attached to the surface of the magnetic oxide powder.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a magnetic oxide powder for soft ferrite which can be used in a relatively weak magnetic field and has a high initial magnetic permeability suitable for high frequency applications, and a method for producing the same. The present invention relates to a method for manufacturing a soft ferrite sintered body used and a Ni-Zn ferrite sintered body.

[0002]

2. Description of the Related Art Conventionally, as a method for producing magnetic oxide powder (ferrite powder) for soft ferrite, iron, nickel, which are the main constituent metal elements constituting ferrite,
800 to 100 after mixing powder compounds such as individual oxides such as manganese and zinc or carbonates at a predetermined composition ratio
A dry method for obtaining magnetic oxide powder by calcination at a high temperature of 0 ° C. and pulverization, and spray pyrolysis of a solution in which a water-soluble compound of a metal element constituting ferrite is dissolved to obtain magnetic oxide powder. Wet methods are mainly used.

However, since 1) the conventional dry method employs a method of mixing and dispersing powders of oxides or carbonate compounds of metal element ions constituting ferrite, there is a limit in that they are uniformly mixed. However, when a ferrite is formed by using this magnetic oxide, there are problems such as variations in the electromagnetic characteristics of the ferrite. Further, in the 2) dry method, the magnetic oxide obtained after the calcination step has a particle size of 100 μm or more, and in order to obtain excellent magnetic permeability, it is necessary to grind to a particle size of 1 μm or less. It must be crushed using a crusher with a large shearing energy, impurities are mixed by the wear of the inner wall of the crusher and the compression grinding section, and the magnetic properties of the manufactured ferrite are deteriorated by the mixed impurities. There is a problem.

Further, 3) the surface activity of the obtained magnetic oxide powder is low because the magnetic oxide powder obtained by pre-baking at a high temperature of 800 to 1000 ° C. has a low surface activity. However, there is a big problem that the firing temperature must be raised by a lower amount, and a method of adding a sintering aid has been proposed as a method of lowering the firing temperature. There is a problem that the magnetic characteristics are deteriorated by the addition.

On the other hand, a wet method has been proposed in order to solve the above-mentioned problems of the dry method. In this method, a magnetic substance oxide powder having a particle size of 1 μm or less having a high surface activity is produced. Therefore, it has a feature that it is suitable for low temperature sintering, and since the constituent metal elements are uniformly dispersed, there is no problem such as variations in the electromagnetic characteristics of ferrite.

[0006]

However, the specific surface area of the magnetic oxide powder obtained by this method is 60 to 20 m.
² / g, which is very large, and when converted to particle size 0.01-
0.05 μm, which is 1/10 of the powder obtained by the conventional dry method.
The particle size is extremely fine as 00 to 1/200, and the specific surface area is too large, so that a molded body having a high molding density cannot be obtained unless the binder is increased in the step of manufacturing the granulated powder for molding.
In this way, by forming with a large amount of binder, densification during main firing is hindered, it is difficult to obtain a dense sintered body, and the advantage of using fine powder with high surface activity can be fully utilized. I can't. Also, at a predetermined firing temperature,
Even when the desired dense sintered body is obtained, the number of contact points between the fine powder particles is decreasing,
There was a problem that smooth mass transport did not occur and the grain size (crystal grain size) of the sintered body was 1/6 to 1/5 of the target crystal grain size, which was too small to increase the magnetic permeability. .

A first object of the present invention is to provide a method for producing a magnetic oxide powder for soft ferrite, which can be fired at a low temperature and can grow large crystal grains during firing. .

A second object of the present invention is to provide a soft ferrite sintered body having a large magnetic permeability.

[0009]

The present invention provides a magnetic oxide powder which can be burned at a low temperature of 1 μm or less by a wet method, but at least one selected from the group consisting of Bi, Mg, Pb, Ca and V. It has been completed by discovering that when a metal oxide of a kind is supported, the surface diffusion and the volume diffusion of the magnetic oxide powder can be promoted at the time of sintering, and the particle diameter showing a large magnetic permeability can be grown. , Mg, Pb, C
In a solution in which at least one metal salt compound selected from the group consisting of a and V is dissolved, the specific surface area is 10 m ² /
A magnetic oxide powder is produced by spraying a slurry obtained by suspending and dispersing magnetic oxide powder (g or more) into a decomposition furnace set at a temperature of 500 ° C. or lower and thermally decomposing it. Characterize. According to the invention, Bi, Mg,
It is possible to produce a magnetic oxide powder having a specific surface area of 10 m ² / g or more, which carries one metal oxide of Pb, Ca and V. Here, it is preferable that the above-mentioned metal oxide does not affect the electromagnetic characteristics of the ferrite after sintering and is selected so as to melt at the sintering temperature of the magnetic oxide powder. Lead salt compound is selected.

In the present invention, an organic compound and an inorganic compound or a mixture thereof can be used as the metal salt compound. When an organic compound is used, the general formula _{(C n H 2n + 1 COO} ) m Me , or (C _n H _2n-1 CO
O) _{m An} organometallic salt compound represented by Me (in the formula, Me is Bi, Mg, Pb, Ca or V; n is 5 to 19; m is a valence number of Me) or a carvone having a cyclo ring. It is preferable to use acid salts. Such an organometallic compound has a surface activating effect and has a property of forming a micelle structure on the surface of the magnetic oxide powder, and this function is very effective in improving the dispersibility of the magnetic oxide powder. It is advantageous. Therefore, it becomes possible to obtain a slurry in which the added metal ions are uniformly adsorbed on the surface of each of the particles of the magnetic oxide powder that are well dispersed. Therefore, by using the magnetic powder obtained by thermal decomposition, the subsequent sintering reaction can proceed smoothly. Examples of the metal salt compound include, but are not limited to, caprate, caprylate, laurate, stearate, palmitate, naphthenate, and abietic acid salt. On the other hand, when an inorganic compound is used as the metal salt compound, the inorganic metal salt compound represented by the general formula MeX _m (wherein Me is at least one metal ion of Bi, Mg, Pb, Ca and V). , X is CH ₃ COO ⁻ , C
L ⁻ , NO ₃ ⁻ , SO ₄ ⁻² , HCOO ⁻ , (COO) ₂ ^−2, and HCO ₃ ⁻ ) are preferably used.), for example, lead acetate, calcium acetate, Examples thereof include bismuth nitrate, magnesium chloride and bismuth acetate. By using such an inorganic metal salt compound, when the magnetic oxide powder slurry is dried in the drying zone, the inorganic metal salt compound is uniformly dried on the surface of each particle of the magnetic oxide powder. Adhere to. Therefore, a uniform oxide layer of added metal ions is formed on the surface of the magnetic oxide powder after thermal decomposition, and this oxide acts as a sintering aid, and the magnetic oxide at the time of sintering is formed. It is effective in smoothly promoting the sintering reaction of the powder. The mixing ratio of the metal salt compound to the magnetic oxide is 0.05 of the magnetic oxide.
˜0.5 wt% is preferred. This is because if the content is 0.05 wt% or less, a predetermined grain size growth cannot be expected during sintering, and the grain size growth effect does not increase even if the upper limit is exceeded.

The slurry composed of the magnetic oxide and the metal salt compound is subjected to spray pyrolysis at a furnace temperature of 500 ° C. or lower. 5
This is because if the temperature exceeds 00 ° C, the surface energy of the magnetic oxide powder tends to decrease. On the other hand, in order to thermally decompose the metal salt compound, it is necessary to make the temperature above the thermal decomposition temperature of each metal salt. For example, in the case of lead stearate, the temperature needs to be 400 ° C. or higher.

Since the magnetic oxide powder produced by the method of the present invention has a specific surface area of 10 m ² / g or more,
The surface energy, which is the driving force of sintering, is large, and low temperature (7
Since it can be sintered even if fired at 00 ° C. or lower), and at least one metal oxide of Bi, Mg, Pb, Ca and V is supported on the surface of the magnetic oxide. The crystal grains can be grown large during firing. In this case, when an Ag electrode that can be fired in the air is used as the internal electrode, it can be fired at a temperature of 900 ° C. or lower, which is lower than the melting point of Ag.

Therefore, the Ni-Zn ferrite sintered body according to the present invention is sintered so that the sintered density is 5.2 or more and the average crystal grain size of the sintered body is 1 μm or more, and the magnetic permeability is 600. The above can be done.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a method for producing a magnetic oxide powder according to this embodiment will be described with reference to FIG. In the manufacturing method, in step S1, the raw materials forming the magnetic oxide are weighed and separated so as to have a predetermined ratio, and dissolved in water or an organic solvent to prepare a precursor solution. In step S2, the precursor solution prepared in step S1 is pyrolyzed by spraying in a mist into the furnace for thermal decomposition set to a predetermined temperature to have a specific surface area of 10 m.
A magnetic oxide powder of ² / g or more is prepared.

In step S3, the magnetic oxide powder prepared in step S2 is mixed and dispersed in a solution in which an organic metal salt compound or an inorganic metal salt compound is dissolved to prepare a suspension slurry.

In step S4, the slurry prepared in step S3 is pyrolyzed by spraying it in a mist into a furnace for thermal decomposition set to a predetermined temperature of 500 ° C. or 500 ° C. or lower, A compound that facilitates the movement of particles during mass transport by surface diffusion and volume diffusion is attached to the surface of the magnetic oxide powder. In this step S4, the temperature of the furnace for thermal decomposition is preferably set to a predetermined temperature of 500 ° C. or lower and 400 ° C. or higher. Since the compound used for coating undergoes thermal decomposition at a temperature of 400 ° C. or higher and 500 ° C. or lower to become an oxide, it is not necessary to perform heat treatment at a temperature higher than this. In particular, vanadium oxide has the property of changing variously between VO and V ₂ O ₅ depending on the temperature, so it has a low melting point, and the temperature should be as low as possible in order to maintain the most stable form. Is advantageous. Further, since lead oxide also has a property of volatilizing in the form of an oxide, in order to prevent volatilization, the heat treatment temperature is lowered to maintain a form with high reaction activity.
It is most effective to carry out the thermal decomposition at 00 ° C to 500 ° C. The magnetic oxide powder of the present embodiment is manufactured through the above steps.

In the present embodiment, the magnetic oxide powder may be further calcined at a temperature of 500 ° C. or 500 ° C. or lower. That is, since the time during which the slurry is sprayed and exposed to thermal decomposition is a short time of 1 second or less, it is expected that the thermal decomposition rate of the coating compound is low. In this case, calcination is further performed at a temperature of 500 ° C. or lower to increase the thermal decomposition rate and improve the oxidization, so that the subsequent sintering reaction of the obtained magnetic material powder proceeds more smoothly. be able to.

The magnetic oxide powder produced by the method for producing magnetic oxide powder according to the present embodiment described above has a compound that promotes sintering attached to the surface of the magnetic oxide powder. , Particles can be easily moved during mass transport by surface diffusion and volume diffusion during firing,
Densification and grain growth can be promoted.

The magnetic oxide powder to which the Bi or Pb compound is attached, which can be produced by using the production method of this embodiment, produces a liquid phase even when fired at a temperature of 900 ° C. or lower. In addition, mass transfer through the liquid phase can be easily performed during firing, and densification and grain growth can be further promoted.

[0020]

Next, an embodiment according to the present invention will be described. <Example 1> In Example 1, first, a Ni-Zn ferrite with a constituent element ratio of Fe: Ni: Zn = 0.67: 0.
Iron (II) nitrate, nickel nitrate, and zinc nitrate were accurately weighed and separated so as to be 15: 0.18 (atomic molar ratio), and the concentration of Ni—Zn ferrite was 0.25 mol /
A precursor solution was prepared by dissolving the product in 5 L (liter) of pure water so that the amount became liter. This precursor solution was atomized and blown into a vertical pyrolysis furnace prepared at 750 ° C. for thermal decomposition to obtain a Ni—Zn ferrite oxide powder.

100 g of the obtained Ni-Zn ferrite magnetic oxide and 0.15 w in terms of lead oxide were added to the powder.
Lead stearate weighed to t% and an organic solvent consisting of 600 cc of toluene and 300 g of partially stabilized zirconia (PSZ) having a diameter of 5 mm are put in a polyethylene pot and mixed and dispersed for 16 hours. The resulting suspension slurry was atomized and sprayed into a vertical pyrolysis furnace prepared at 500 ° C. for pyrolysis to obtain a magnetic oxide powder having lead oxide supported and fixed on the surface.

A vinyl acetate binder is added to the magnetic oxide powder.
Granulated powder for molding is prepared by adding it to the powder so as to be 12 wt% in terms of solid content, and molded into a molded body of 10 × 20 × 5 (mm) using this granulated powder. did. Further, the molded body was fired at 850 ° C. for 4 hours to prepare a sintered body, and the firing density, grain size and magnetic permeability of the sintered body were measured. Here, the grain size was measured by observing the fracture surface of the sintered body by SEM.

Example 2 In Example 2, in step S3 of FIG. 1, lead nitrate was used in place of lead stearate, and pure water was used in place of toluene as a solvent to carry and fix lead oxide. Sintered bodies were prepared and evaluated in the same manner as in Example 1 except that the oxide powder was prepared.

<Comparative Example 1> In the same manner as in Example 1, Ni
-Zn ferrite oxide powder is obtained, and a vinyl acetate-based binder is added to this ferrite oxide powder without supporting and fixing lead oxide on the surface of the ferrite oxide powder, and granulated powder for molding After manufacturing, the molded product was fired and sintered to prepare a sintered body for evaluation.

Comparative Example 2 Nickel oxide, iron (III) oxide and zinc oxide were accurately weighed out so as to have the same composition as in Example 1, mixed and dispersed, and then calcined at 850 ° C. for 4 hours. Then, Ni-Zn ferrite magnetic oxide powder was obtained. A vinyl acetate binder was added to the obtained oxide powder in an amount of 6 wt% based on the solid content of the powder to prepare a granulated powder for molding. An evaluation sample was prepared and evaluated in the same manner as in Example 1. The measurement results are shown in Table 1. That is, the evaluation sample of Comparative Example 2 was prepared using the Ni—Zn ferrite oxide powder prepared according to the dry method of the conventional example.

[0026]

[Table 1]

<Evaluation> As can be seen from the results shown in Table 1, in Examples 1 and 2, powder having high surface activity was used, and the surface of the oxide powder was oxidized at a melting point almost equal to the firing temperature. This is an example in which a lead layer is formed, and the grain size is large and the magnetic permeability reaches a high value. On the other hand, Comparative Example 1 is an oxide powder having high surface activity, and the sintered body density is the same as that of Example 1 and Example 2, but the grain size and the magnetic permeability are those of Example 1 and Example 2. It is smaller than Example 2 and is about 1/2. In addition, in Comparative Example 2, the state is almost in the state where sintering is not caused, and the magnetic permeability is 1/6 or less of the target value.

As can be seen from these results, it is clear that the powder of the conventional dry method (Comparative Example 2) does not sinter at the main firing temperature of 900 ° C. or lower, which is the magnetic oxide powder. The cause is that the surface activity of the body is too low. In addition, even if the oxide powder has high surface activity, it is 900 in the case of the powder not subjected to the surface treatment as in Comparative Example 1.
It can be seen that the grain size cannot be increased although it can be sintered at ℃. From the above results,
It can be seen that forming an oxide layer having a melting point approximately the same as the main firing temperature is very effective in growing the grain size of the sintered body.

[0029]

As is clear from the above description, according to the present invention, it is possible to provide an ultrafine magnetic oxide powder having a high surface activity and a large specific surface area. On the other hand, the metal oxide supported on the surface of the magnetic oxide powder can promote the surface diffusion and the volume diffusion of the magnetic oxide at the time of firing, so that the grains can be largely grown. Therefore, by using the magnetic oxide powder according to the present invention, it is possible to provide a Ni—Zn ferrite sintered body having a large initial magnetic permeability by low temperature firing.

[Brief description of drawings]

FIG. 1 is a process drawing showing a method for producing a magnetic oxide powder according to an embodiment of the present invention.

Claims (6)

[Claims] 1. A magnetic oxide powder having a specific surface area of 10 m ² / g or more is suspended in a solution in which at least one metal salt compound selected from the group consisting of Bi, Mg, Pb, Ca and V is dissolved. A method for producing a magnetic oxide powder, which comprises spraying a slurry, which is turbidly dispersed, into a decomposition furnace set at a temperature of 500 ° C. or lower in a mist state to thermally decompose. 2. The metal salt compound is represented by the general formula (C _n H
_{2n + 1} COO) _m Me or (C _n H _2n-1 COO) _m Me
An organometallic salt compound represented by the formula (wherein Me is Bi, M
g, Pb, Ca or V; n is 5 to 19; m is a valence of Me) or a carboxylic acid salt having a cyclo ring. 3. The metal salt compound has a general formula of MeX _m.
Inorganic metal salt compound represented by the formula (wherein Me is Bi, M
At least one metal ion of g, Pb, Ca and V, X is CH ₃ COO ⁻ , Cl ⁻ , NO ₃ ⁻ , SO ₄ ⁻² , H
COO ⁻ , (COO) ₂ ⁻² and HCO ₃ ⁻ are an anion selected from the group, and m is a valence number of Me). 4. A method for producing a soft ferrite sintered body, which comprises molding the magnetic oxide powder obtained in any one of claims 1 to 3 into a predetermined shape and firing it. 5. The firing temperature is 900 ° C. or lower.
A method for producing the soft ferrite sintered body described. 6. A specific surface area of 1 supporting at least one metal oxide selected from Bi, Mg, Pb, Ca and V.
A sintered body of a magnetic oxide powder of 0 m ² / g or more, having a sintered density of 5.2 g / cm ³ or more, an average crystal grain size of 1 μm or more, and a magnetic permeability of 600 or more. A Ni-Zn ferrite sintered body characterized by the above.