JP2002145620A - Iron oxide and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide α-Fe2O3 transformable into a ferrite for compact magnetic element that can obtain high sintered density even when being sintered at a low temperature and has good initial permeability and its production method, and to provide Fe3O4 that is the raw material of the α-Fe2O3 and its production method. SOLUTION: An aqueous iron chloride solution and an aqueous alkali solution are mixed at a specified Fe3+ concentration so that the concentrations of the aqueous iron chloride solution and the aqueous alkali solution are controlled within specified ranges. The mixture is neutralized. The obtained aqueous iron hydroxide solution is heated and oxidized to produce Fe3O4 having the specific surface area of 10 to 40 m2/g and the chlorine content of 100 to 3,000 ppm, and is further heated and oxidized to produce α-Fe2O3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to Fe ₃ O ₄ , α-F
The present invention relates to e ₂ O ₃ and a method for producing the same, particularly to α-Fe ₂ O ₃ which can lower the calcination temperature and the raw material F
The present invention relates to e ₃ O ₄ and a method for producing them.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller and lighter, multilayer chip inductors and power type planar inductors have been proposed as noise filters in the field of magnetic devices, and some of them have been put to practical use. The multilayer chip inductor is manufactured by laminating and firing a magnetic part (core layer) formed by printing a ferrite paste or a doctor blade method and a conductor part (internal electrode) formed by a printing method (Japanese Patent Application Laid-Open No. Hei 4 (1994)). -180610). Multilayer chip inductors are advantageous for miniaturization and have an outer iron structure, so they have low leakage magnetic flux and are suitable for high-density mounting.

On the other hand, a planar inductor is manufactured by printing a ferrite paste on a silicon substrate, baking it to form a magnetic material portion, and then forming a planar coil thereon by photolithography and plating. 11-2623
No. 9). Planar inductors are also excellent in thinning and high-density mounting.

The magnetic material of these devices is NiZn.
, NiZnCu or other ferrite is used. Raw materials for these ferrites are usually α-F
mixing e ₂ O ₃ and nickel oxide, zinc oxide, and metal oxides such as copper oxide, calcined, the ferrite powder obtained by pulverizing mixed with a solvent, that a paste (ferrite paste) is used As described above, the ferrite paste is fired to form a magnetic portion.

If the firing temperature of small magnetic elements such as multilayer chip inductors and planar inductors is as high as about 1000 ° C., the silver alloy of the conductive material reacts with the ferrite to deteriorate the ferrite characteristics and short-circuit the electrodes. Therefore, it is necessary to fire at a low temperature lower than the melting point of the silver alloy. However, in the case of firing at a low temperature of 900 ° C. or less, the sintered density of ferrite does not become sufficiently high, and magnetic properties such as magnetic permeability become insufficient. Therefore, in order to further improve the performance of the small magnetic element, there is a demand for a ferrite which can obtain a high sintered density even when fired at a low temperature of 900 ° C. or lower and has excellent magnetic properties such as initial magnetic permeability.

As a method for lowering the firing temperature, a method using calcined and finely ground ferrite powder at a lower temperature than usual is known. However, simply lowering the calcining temperature is insufficient for spinel formation during calcining, and 900%.
The sintering density does not increase even if it is fired at a temperature of not more than ℃.

Therefore, as a method of enhancing spinel formation even when calcined at a low temperature, a chlorine compound and / or a metal oxide such as nickel oxide, zinc oxide and copper oxide are mixed in a powder mixture.
Alternatively, a method of calcining by adding a sulfuric acid compound has been proposed (JP-A-11-144934). Also, on page 246 of the outline of the 2000 Spring Meeting of the Powder and Powder Metallurgy Association, the calcination temperature was lowered by adding chlorine ions to the ferrite raw material powder, and a high sintering density was obtained even at low temperature. It is reported that it can be obtained.

All of these methods are based on α-Fe ₂ O ₃
In this method, a chlorine compound is added to a powder mixture of a metal oxide such as nickel oxide, zinc oxide, and copper oxide. However, if a component capable of lowering the calcination temperature is previously contained in an iron source such as α-Fe ₂ O _3, a step of adding a chlorine compound, a sulfuric acid compound, or the like is unnecessary, which is industrially advantageous. Become.

Α-Fe which is a main raw material of ferrite powder
_There are many methods for producing ₂ O ₃ , for example, a method of spray roasting and producing an aqueous solution of iron chloride obtained in a pickling process of steel (dry method), and a method of neutralizing an aqueous solution of iron chloride or an aqueous solution of iron sulfate with alkali. , Iron hydroxide, which is oxidized and
There is a method of obtaining ₃ O ₄ (wet method) and further oxidizing.

[0010] α-Fe ₂ O ₃ obtained by the dry method may be capable of reducing the calcination temperature due to the residual chlorine content, but has a small specific surface area of 10 m ² / g or less due to restrictions of the roasting furnace. It is difficult to obtain particles, and there are many aggregated particles. For this reason, when obtaining a ferrite powder, it is necessary to grind in advance before mixing with another metal oxide in order to obtain a uniform mixture. However, since contamination such as iron is mixed during pulverization, there is a problem that characteristics are likely to be degraded, which is not suitable for small magnetic elements.

On the other hand, Fe ₃ O ₄ obtained by a wet method is fine particles having a specific surface area of 10 m ² / g or more, has a sharp particle size distribution, and is excellent in dispersibility. Dimensions and shape of the Fe ₃ O ₄ and further oxidizing the obtained α-Fe ₂ O ₃ is Fe ₃
It is almost the same as O ₄ and is suitable as a raw material for ferrite powder for small magnetic elements. However, alkali added at the time of neutralization remains in Fe ₃ O ₄ , which may affect magnetic properties. Therefore, it must be sufficiently washed and removed.

In the wet method, sodium chloride or the like is used during neutralization.
Since chlorine-containing substances are generated, the calcining temperature can be lowered.
Sodium chloride is almost completely eliminated by the above-mentioned washing process.
The effect of lowering the calcining temperature is too early
I can't wait. However, Fe produced by a wet method_ThreeO_FourYako
Α-Fe obtained by oxidizing_TwoO_ThreePowder properties of small magnet
Since it is most suitable for ferrite powder raw materials for devices,
_ThreeO_FourAnd α-Fe_TwoO _ThreeIf you can use
Very effective as a raw material for ferrite powder for type magnetic elements
It is.

[0013]

SUMMARY OF THE INVENTION Therefore, in the wet method,
Α-
Fe_TwoO_ThreeAnd Fe_ThreeO_FourInclusion of chlorine in
investigated. As a result, iron chloride used as a raw material for the wet method
Ferrous ion (Fe²⁺) And ferric iron (Fe³⁺)
Is a specific ratio, and when mixing at the time of neutralization
The ratio between the concentration of the aqueous solution of iron fossil and the concentration of the alkaline solution
Chlorine that cannot be easily removed even if washed
And found that it could be controlled arbitrarily.
It is a thing. An object of the present invention is to provide Fe_ThreeO_Four, Α-F
e_TwoO_ThreeLow temperature calcination is possible by controlling the chlorine content
Α-Fe as a raw material for efficient ferrite powder_TwoO_Three,
α-Fe _TwoO_ThreeFe that is most suitable as a raw material for_ThreeO_FourAnd this
These manufacturing methods are provided.

[0014]

The first invention is Fe ₃ O ₄ produced by a wet method, and has a specific surface area of 10-4.
0 m ² / g, a Fe ₃ O _4, wherein the chlorine content is 100ppm or 3000ppm or less.

In the second invention, an aqueous solution of iron chloride and an aqueous solution of an alkali are mixed and neutralized.
_In the method for producing ₃ O ₄ , the ferric ion concentration (mol) in the aqueous iron chloride solution is adjusted to 2 to 30% with respect to the total iron ion concentration (mol) of ferrous ion and ferric ion. And the concentrations of the aqueous iron chloride solution and the aqueous alkali solution are set so that 0.8 ≦ total iron ion concentration (mol / l) / A ≦ 1
2 where A = (hydroxyl equivalent (mol) required for neutralization of Fe ²⁺ and Fe ³⁺ ) × R / (amount of alkaline aqueous solution (l)) (where R is the iron chloride aqueous solution and shows the equivalent ratio of alkaline aqueous solution, a method of producing Fe ₃ O _4, characterized in that neutralization is adjusted to a 0.90 ≦ R ≦ 1.5).

A third aspect of the present invention is the above-described Fe ₃ of the first aspect.
Α-Fe ₂ O ₃ characterized by having a specific surface area obtained by oxidizing O ₄ of 10 to 40 m ² / g and a chlorine content of 100 ppm or more and 3000 ppm or less.

A fourth invention is a method for producing α-Fe ₂ O ₃ , wherein the Fe ₃ O ₄ produced by the production method of the second invention is heated and oxidized.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Fe ₃ O ₄ of the present invention is obtained by neutralizing an aqueous solution of iron chloride containing ferrous chloride and ferric chloride with an aqueous alkali solution, and heating and oxidizing the resulting aqueous solution ( Iron oxide having a specific surface area of 10 to 40 m ² / g and a chlorine content of 100 ppm or more and 3000 ppm or less produced by a wet method).

Fe ₃ O ₄ produced by the wet method has a small particle size and a sharp particle size distribution, so that it has excellent dispersibility and α
-Fe ₂ O ₃ grain growth during heating oxidation to the is suppressed, excellent in grindability as ferrite powder. When the specific surface area is less than 10 m ² / g, the particle size is large, and it becomes difficult to perform calcination at a low temperature for a short time. On the other hand, if the specific surface area exceeds 40 m ² / g, the particles tend to aggregate, have poor dispersibility, and tend to grow during thermal oxidation. Preferred specific surface area is 15 to 30
m ² / g. The specific surface area can be controlled by, for example, the amount of ferric ions in the aqueous iron chloride solution.

The Fe ₃ O ₄ of the present invention has a chlorine content of 100.
ppm or more and 3000 ppm or less. Since the chlorine content is relatively large, the effect of reducing the calcination temperature of ferrite formation is great, and the sintered density of ferrite is high even at low temperatures. If the chlorine content is less than 100 ppm, the effect of reducing the calcination temperature for ferrite formation is not recognized. On the other hand, if it exceeds 3000 ppm, although the calcination temperature decreases, the sintered density does not increase at the time of sintering, and desired electromagnetic characteristics cannot be obtained.
The chlorine content can be controlled by, for example, the concentration ratio between the aqueous solution of iron chloride and the aqueous solution of the alkali during neutralization, as described later. Preferred chlorine content is 300 ppm or more and 1600 pp
m, more preferably 500 to 1200 ppm.

[0021] Fe ₃ O ₄ of the present invention is not may be used as it is but ferrite raw materials, Fe ₃ O ₄ is Fe
^Since the ratio of ²⁺ to Fe ³⁺ , that is, the ratio of iron to oxygen is not always constant, it is difficult to put it into practical use as a ferrite raw material. Therefore, usually, this is further heated and oxidized to obtain α. -fe ₂ O ₃ it is used as a starting ferrite. The present invention relates to two types of iron oxides, Fe ₃ O ₄ and α-Fe ₂ O ₃ .

Next, a method for producing Fe ₃ O ₄ will be described. The Fe ₃ O ₄ of the second invention is produced by a method of heating and oxidizing an aqueous iron hydroxide solution obtained by neutralizing an aqueous iron chloride solution containing ferrous chloride and ferric chloride with an aqueous alkaline solution. You. Hitherto, Fe ₃ O ₄ for toner has been manufactured by heating and oxidizing an aqueous iron hydroxide solution obtained by neutralizing an aqueous ferrous chloride solution with an aqueous alkaline solution.
e ₃ O ₄ has a sharp particle size distribution but a specific surface area of 1
Since the particle size is as small as less than 0 m ² / g, the particle size is slightly smaller than Fe ₃ O ₄ produced by the spray roasting method, and is not a particle size that solves the above-mentioned problem. Further, since the chlorine content is easily removed in a washing step such as washing with water, the chlorine content is as low as less than 100 ppm, and the effect of lowering the calcining temperature for ferrite formation is not sufficient. Therefore, it is not suitable for small magnetic elements.

In the production of Fe ₃ O ₄ of the present invention, an aqueous solution sharing ferrous chloride and ferric chloride is used as an iron source. Iron chloride is used to incorporate the chlorine constituting it into Fe ₃ O ₄ . The aqueous ferric chloride solution containing ferrous chloride and ferric chloride has a ferric ion (Fe ³⁺ ) concentration (mol
/ l) are ferrous ions (Fe ²⁺ ) and ferric ions (Fe
It is important to adjust the total iron ion concentration (total Fe amount) (mol / l) of ( ³⁺ ) to 2 to 30% for use. By adding ferric chloride and regulating the content to the above range, the particle size of the generated Fe ₃ O ₄ can be controlled to be small, the specific surface area is 10 to 40 m ² / g, and the particle size distribution is Fe ₃ O ₄ that is sharp and excellent in dispersibility can be obtained. In addition, the content of chlorine is also appropriate.

The amount of ferric ion added is 2% in the above concentration ratio.
If it is less than 1, the target small particle size Fe ₃ O ₄ cannot be obtained, and particles having a specific surface area of less than 10 m ² / g can be obtained. Further, the content of chlorine is small and does not contribute to the reduction of the calcining temperature of the ferrite powder. Conversely, if the amount of addition exceeds 30% in the above concentration ratio, Fe ₃ O ₄ having a specific surface area of more than 40 m ² / g is obtained, and the dispersibility becomes poor due to magnetic cohesion. Sintering tends to proceed, and the crushability of the calcined product also deteriorates. The preferred ferric ion content is 5 to 20% in the above concentration ratio.

In order to obtain Fe ₃ O ₄ of the present invention, it is also important to neutralize the aqueous solution of iron chloride by adjusting the concentrations of the aqueous solution of alkali and the aqueous solution of alkali in the following relationship. 0.8 ≦ total iron ion concentration (mol / l) / A ≦ 12 [1] where A = (amount of hydroxyl group required for neutralization of Fe ²⁺ and Fe ³⁺ (mol)) × R / (alkali Amount of aqueous solution (l)) (where R indicates an equivalent ratio of an aqueous solution of iron chloride to an aqueous solution of an alkali, and 0.90 ≦ R ≦ 1.5)

Equation [1] shows the ratio of the concentration of the aqueous solution of iron chloride to the concentration of the aqueous solution of the alkali when mixing during neutralization. For example, 1 liter of iron chloride aqueous solution (concentration: 10 mol / l)
And 9 l of aqueous sodium hydroxide solution (concentration 2.2 mol / l)
When a small amount of a high-concentration iron chloride aqueous solution and a large amount of a low-concentration alkaline aqueous solution are mixed, as in the case of mixing and neutralizing, the value of the formula [1] becomes large.

The present inventor has found that, in this case, the amount of chlorine contained in Fe ₃ O ₄ varies depending on the concentration conditions of the aqueous solution of iron chloride and the concentration of the aqueous alkali solution. 1], it was confirmed that the chlorine content contained contributed to a decrease in the calcination temperature of α-Fe ₂ O ₃ .

The concentration ratio in the formula [1] is 0.8 or more and 12 or less. Within this range, the amount of chlorine contained in Fe ₃ O ₄ that is effective in lowering the calcination temperature becomes an appropriate amount.
If the concentration ratio is less than 0.8, the concentration of the aqueous solution of iron chloride is too low compared to the concentration of the aqueous alkaline solution, and the amount of chlorine necessary for lowering the calcination temperature is not contained in Fe ₃ O ₄ ,
The calcination temperature cannot be lowered. Conversely, when the concentration ratio is 1
If it exceeds 2, the concentration of the aqueous solution of iron chloride may exceed the solubility of ferrous chloride, which is not practical. When the concentration of iron chloride after neutralization is very low, it is possible that the concentration exceeds 12, but excessive chlorine content is taken into Fe ₃ O ₄ , which conversely inhibits sintering. become. When the concentration ratio of the formula [1] is 1.0 to 12, the amount of the incorporation is an appropriate amount, and 1.5 to 10 is more preferable.

The amount of alkali required for neutralization of Fe ²⁺ and Fe ³⁺ must be a concentration converted to hydroxyl groups (OH ⁻ ). For example, in the case of a 1 mol / l sodium carbonate aqueous solution, it is converted to a carbonate ion (CO ₃ ²⁻ ), which is 2 mol / l in terms of a hydroxyl group concentration. R represents the equivalent ratio between the aqueous solution of iron chloride salt and the aqueous solution of alkali. R <1 when the aqueous solution of iron chloride is excessive, and R> 1 when the aqueous solution of alkali is excessive. When 0.90 ≦ R ≦ 1.5, Fe ₃ O ₄ having a particle size suitable as a ferrite raw material is obtained.

When the equivalent ratio R is less than 0.90, the amount of hydroxyl groups becomes insufficient and the pH becomes low, so that the number of generated nuclei decreases, and the surplus Fe ³⁺ is referred to as green last. Since it is consumed for the production of the intermediate product, the obtained particle size becomes large, and it is difficult to obtain a suitable particle size. Equivalent ratio R is 1.5
If it exceeds, the amount of unreacted alkali is large and the reaction rate is low, which is not preferable in terms of cost. In addition, the grain size is likely to be too large due to easy grain growth.

As the alkali raw material of the present invention, alkali hydroxides such as sodium hydroxide and potassium hydroxide, alkali carbonates such as sodium carbonate, ammonia and the like can be used.

Some ferrous ions in the aqueous solution of iron chloride react with ferric chloride according to the reaction of the following formula [2] to form Fe ₃
O ₄ is produced. The remaining ferrous ions are neutralized to ferrous hydroxide. When an oxygen-containing gas is passed while maintaining the obtained aqueous solution at 50 to 100 ° C., the generated Fe ₃
The grains grow with O ₄ as a nucleus. The oxygen-containing gas is usually air. If the oxidation temperature is lower than 50 ° C., a needle-like hydrated oxide is generated, which is not preferable. On the other hand, when the temperature exceeds 100 ° C., the equipment becomes large-scale and is not suitable for industrialization. Fe ²⁺ + Fe ³⁺ + 8OH ⁻ → Fe ₃ O ₄ + 4H ₂ O [2]

The α-Fe ₂ O ₃ of the third invention is produced by heating oxidation of Fe ₃ O ₄ of the first invention, Fe ₃ O
Specific surface area and chlorine content substantially the same as ₄ . That is, the specific surface area is 10 to 40 m ² / g, and the chlorine content is 100 ppm or more and 3000 ppm or less. Preferred specific surface area is 15 to 30 m ² / g, preferred chlorine content is 300 to
1600 ppm, more preferably 500-1200 ppm.
ppm.

The method for producing α-Fe ₂ O _{3 according to} the fourth invention can be easily carried out by heating and oxidizing the Fe ₃ O ₄ produced by the second production method. The heating temperature depends on the purity, but is preferably 300 ° C. or higher. Heating temperature is 300
If the temperature is lower than ℃, γ-Fe ₂ O ₃ is generated. γ-Fe ₂
O ₃ can also be a ferrite raw material, but is easily magnetically aggregated, which is not preferable from the viewpoint of dispersibility. Fe ₃ since the heating temperature of O ₄ is between the particles of too high iron oxide grain growth by melting, difficult to obtain a particle size of small α-Fe ₂ O ₃ for the purpose, α-Fe ₂ O ₃ in Tends to have a low chlorine content. The preferred heating temperature is 450-600 ° C.

The α-Fe ₂ O ₃ of the present invention is obtained by heating and oxidizing Fe ₃ O ₄ produced by a wet method, so that the chlorine content is 1%.
It has a particle size of 100 to 3000 ppm, a specific surface area of 10 to 40 m ² / g, a small particle size, a sharp particle size distribution, and excellent dispersibility. Therefore, when ferrite is manufactured using this, calcining at a low temperature is possible, and as a result, a high sintered density can be obtained even when the obtained ferrite powder is fired at a low temperature of 900 ° C. It is possible.

The α-Fe ₂ O ₃ thus obtained is mixed with nickel oxide, zinc oxide, cupric oxide, manganese oxide and the like, and calcined to obtain a ferrite powder. For example, a ferrite powder is formed into a paste by mixing a binder, then a magnetic material layer is formed by a printing method, a doctor blade method, or the like, and after firing, a laminated chip inductor or a planar inductor can be obtained. Also, a ferrite core can be obtained by adding a binder such as polyvinyl alcohol (PVA) or a trace amount of an additional element to the ferrite powder, granulating and molding, and then firing.

[0037]

(Example 1) Stainless steel cylindrical container (capacity 1)
To 5 l), 7 l of an aqueous sodium hydroxide solution having a concentration of 1.37 mol / l was added, and a nitrogen gas was passed to create a nitrogen atmosphere. An aqueous solution of ferrous chloride and an aqueous solution of ferric chloride are ^combined with Fe ³⁺ /
(Fe ²⁺ + Fe ³⁺ ) = 9% were mixed to prepare 3 L of an aqueous solution having a concentration of iron chloride of 1.5 mol / L. The aqueous iron salt solution was added to the aqueous sodium hydroxide solution in the cylindrical container with stirring. The equivalent ratio R of 10 l of the mixed solution is 1.02
And the value of (total iron ion concentration (mol / l)) / A was 1.095.

The temperature of the solution was raised to 85 ° C. in a nitrogen atmosphere, and after the temperature was stabilized, air was passed through the solution at a flow rate of 3 l / min to perform oxidation to produce Fe ₃ O ₄ particles. After the completion of the oxidation, precipitation and desalination were sufficiently repeated using ion-exchanged water, suction-filtered, dried at 70 ° C. in the air, and pulverized to obtain Fe ₃ O ₄ powder. This is heated and oxidized at 480 ° C. for 1 hour to obtain α-F
e ₂ O ₃ was obtained. The specific surface areas of the Fe ₃ O ₄ powder and the α-Fe ₂ O ₃ powder were measured by the BET method. The chlorine content and the sodium content were determined by ICP.

Using a ball mill, α-Fe ₂ O ₃ and nickel oxide, zinc oxide and cupric oxide were used to obtain α-Fe ₂ O ₃ :
NiO: ZnO: CuO = 49: 11: 30: 10 (molar ratio) and mixed and dried. The mixed powder was calcined at a temperature of 600 ° C. or higher for 2 hours to obtain a NiZnCu-based ferrite. The spinelization rate of the obtained ferrite powder was determined by XRD.
The lowest temperature at which the spinel conversion rate becomes 90% or more, which was determined by (X-ray diffraction), was 725 ° C., which was the calcinable temperature.

The calcined ferrite powder was further wet-pulverized by a ball mill until the specific surface area became 12 ± 1 m ² / g. The obtained powder was dried, mixed with a PVA solution, granulated, and then pressed into a toroidal shape. The formed body was fired at 850 to 900 ° C. to obtain a sintered body (ferrite). The sintering density was calculated from the weight and dimensions of the sintered body. The initial magnetic permeability was measured for the core fired at 900 ° C. using an LCR meter. Table 1 shows manufacturing conditions and evaluation results.
It was shown to.

(Comparative Example 1) Using the high-purity α-Fe ₂ O ₃ produced from the ferrous chloride of Example 1 by the spray roasting method, the ferrite powder production and ferrite production conditions in Example 1 were as follows: A sample was manufactured in the same manner as in Example 1 except that the conditions shown in Table 1 were changed. Table 1 shows manufacturing conditions and evaluation results.
It was shown to.

(Comparative Examples 2 and 3) In Example 1, instead of the aqueous solution of ferric chloride containing ferrous chloride and ferric chloride, it was prepared from industrial reagents of ferrous sulfate and ferric sulfate. Except that an aqueous solution of iron sulfate is used, F
e ₃ O ₄ was produced, α-Fe ₂ O ₃ was produced, and further, ferrite powder and ferrite were produced. Table 1 shows the manufacturing conditions and the evaluation results.

From the comparison between Example 1 and Comparative Examples 1 to ₃ , the ferrite powder from α-Fe ₂ O _{3 according} to the present invention is different from the ferrite powder from α-Fe ₂ O ₃ by the spray roasting method.
It can be seen that the calcining temperature can be lowered, and that even when firing at a low temperature of 900 ° C. or less, ferrite having a high sintered density and a high initial permeability can be produced.

(Examples 2 to 6, Comparative Examples 4 to 6) Example 1
The samples were manufactured in the same manner as in Example 1 except that the conditions for producing Fe ₃ O ₄ , α-Fe ₂ O ₃ , ferrite powder and ferrite were changed to the conditions shown in Table 2. Table 2 shows the manufacturing conditions and evaluation results.

From the comparison between Examples 2 to 6 and Comparative Examples 4 to 6,
The ferrite powder from α-Fe ₂ O _{3 of the} present invention is 900
It can be seen that ferrite having a high sintering density and a high initial permeability can be produced even when firing at a low temperature of not more than ℃.
In the case of Comparative Example 5, it was impossible to prepare an aqueous solution of iron salt because the concentration of the aqueous solution of iron salt exceeded the solubility of ferrous chloride.

Examples 7 to 11 and Comparative Examples 7 to 8 In the same manner as in Example 1, except that the mixing ratio of the aqueous ferrous chloride solution and the aqueous ferric chloride solution was changed, Fe ₃ O _{4 was used.} Was manufactured. Except that the heating temperature of Fe ₃ O ₄ was changed to 600 ° C. and the heating time of 1 hour was changed to 30 minutes, α
-Fe ₂ O ₃ was produced, and ferrite powder and ferrite were produced in the same manner as in Example 1. Table 3 shows the manufacturing conditions and evaluation results
It was shown to.

Comparison between Examples 7 to 11 and Comparative Examples 7 to 8
Et al. Of the present invention³⁺/ (Fe²⁺+ Fe ³⁺) = 2-30%
Fe that satisfies_ThreeO_FourFerrite powder from
High sintering density and high initial permeability even when fired at low temperatures below ℃
It can be seen that the production of ferrite exhibiting a ratio is possible.

(Examples 12 to 17, Comparative Examples 9 to 10)
In Example 1, except that the equivalent ratio R at the time of neutralization was changed,
As in the first embodiment, _ThreeO_FourWas manufactured. Fe_ThreeO_FourAddition
Except for changing the heat temperature to 550 ° C.,
-Fe_TwoO_ThreeAnd ferrite powder was produced in the same manner as in Example 1.
Powder and ferrite were manufactured. Table 4 shows manufacturing conditions and evaluation results.
It was shown to.

From the comparison between Examples 12 to 17 and Comparative Examples 9 to 11, the ferrite powder from Fe ₃ O ₄ of the present invention when the equivalent ratio R during neutralization was 0.9 to 1.5 was as follows: It can be seen that even when firing at a low temperature of 900 ° C. or less, ferrite having high sintering density and high initial permeability can be produced. When R is less than 0.9, the effect of lowering the calcining temperature is not recognized because the particle size is large and the chlorine content is small. Conversely, if R exceeds 1.5, the oxidation reaction at the time of producing Fe ₃ O ₄ becomes slow, and particles grow and the particle size increases, which is not preferable.

[0050]

Effects of the Invention α-Fe ₂ O ₃ of the present invention, since obtained by heating oxidation of Fe ₃ O ₄ prepared by a wet process, a small particle size, particle size distribution is sharp, yet excellent dispersibility ing. When producing a ferrite powder from this α-Fe ₂ O ₃ , the calcination temperature can be lowered, and even when the ferrite powder is fired at a low temperature of 900 ° C. or less, the sintered density is high,
Ferrite suitable as a magnetic material for a small magnetic element having excellent initial permeability can be obtained.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G002 AA03 AA04 AB04 AE03 5E041 AB11 AB19 CA01 HB09 HB15 HB17 NN02 NN06 NN17

Claims (4)

[Claims] 1. Fe ₃ O ₄ produced by a wet method, having a specific surface area of 10 to 40 m ² / g and a chlorine content of 100 pp.
Fe ₃ or less and 3000 ppm or less
O ₄ . 2. A method for producing Fe ₃ O ₄ by mixing and neutralizing an aqueous solution of iron chloride and an aqueous alkali solution and oxidizing the resulting neutralized solution, wherein the concentration of ferric ion in the aqueous solution of iron chloride is mol) is adjusted to 2 to 30% with respect to the total iron ion concentration (mol) of ferrous ions and ferric ions, and the concentrations of the aqueous iron chloride solution and the alkaline aqueous solution are set to 0.8 ≦ total iron Ion concentration (mol / l) / A ≦ 1
2 where A = (hydroxyl equivalent (mol) required for neutralization of Fe ²⁺ and Fe ³⁺ ) × R / (amount of alkaline aqueous solution (l)) (where R is the iron chloride aqueous solution and The method of producing Fe ₃ O ₄ , wherein the neutralization is performed by adjusting the equivalent ratio of the aqueous alkali solution to 0.90 ≦ R ≦ 1.5). 3. The Fe according to claim 1,_ThreeO_FourOxidize
Specific surface area is 10-40m^Two/ g, chlorine content 100ppm
At least 3000 ppm or less.
_TwoO _Three. 4. A method according to claim 2, wherein
Α-Fe ₂ characterized by heating and oxidizing ₃ O ₄
Method for producing O ₃ .