JPH0145725B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing ferromagnetic metal powder, and more particularly to a method for producing ferromagnetic iron powder for use as a high-density recording medium from ferric hydroxide. Magnetic iron oxide powder has conventionally been generally used as a magnetic recording or magnetic storage material for magnetic tapes, magnetic disks, magnetic drums, etc., but in recent years, as the demand for higher density and higher output magnetic recording has increased, iron oxide powder has been used. Acicular iron powder is expected to have better coercive force and magnetic moment than powder. This acicular iron powder generally uses acicular goethite (α-FeOOH) as a starting material, which is dehydrated to form acicular α-Fe ₂ O ₃ and then fired at a high temperature (300 to 500°C). However, reduction with hydrogen or other gaseous reducing agents has been carried out. but,
In this case, because the goethite undergoes a dehydration process by heating, it is inevitable that a large number of micropores will be created and the goethite will become a mere shell. Although it is possible to obtain particles with little evidence of dehydration holes by special operations, it is difficult to maintain the original acicular shape. Goethite is a unique acicular aggregate, forming so-called tactoid particles, and its particle morphology tends to change during heat treatment, and the acicular iron particles obtained from it have the following drawbacks. Due to the sintering that occurs during the heat treatment process, it contains a large amount of branched particles and coagulation between the particles is observed. Holes (dehydration holes) remain in the acicular iron particles. Wide particle size distribution. The needle-like shape has almost completely collapsed. The above drawbacks result in poor dispersion of the acicular iron particles in the paint and a decrease in magnetic properties (coercive force, saturation magnetization, squareness ratio, etc.). The present inventors have discovered that the α
-Fe ₂ O ₃ is produced by high-temperature dehydration of goethite (α-FeOOH) at 300℃, so many vacancies (dehydration pores) and branches occur in the α-Fe ₂ O ₃ crystal particles. However, it was found that this was the cause of interparticle sintering during the reduction process. Therefore, the present inventors first heated an aqueous suspension of ferric hydroxide together with a crystallization control agent dissolved therein to produce a new α-Fe ₂ O ₃ without vacancies. developed a method to do so. (U.S. Pat. No. 4,202,871) The present invention provides needles that can be obtained by further reducing pore-free needle-like α-Fe ₂ O ₃ produced under the above-mentioned specific conditions in a reducing gas flow. The present invention provides a novel method for producing iron powder. That is, the present invention provides an aqueous suspension of ferric hydroxide,
Acicular ferric oxide is produced by heating in an alkaline environment in the presence of a crystallization control agent that has a coordinating ability for iron to produce acicular α-ferric oxide, which is then heated and reduced with a reducing gas. The gist is a method for producing magnetic iron powder. The ferric hydroxide used in the present invention may be produced by any method, but generally, for example, an aqueous solution of a ferric salt such as ferric chloride, ferric sulfate, or ferric nitrate. An alkali such as sodium hydroxide, potassium hydroxide, or ammonia is added to the mixture to obtain ferric hydroxide as an amorphous precipitate. Such methods are already well known. Depending on the reaction conditions, the resulting precipitate may still contain the constituent anions of the ferric salt as its constituent atoms; however, such a precipitate may also be used as ferric hydroxide in the present invention. Can be done. As will be explained later, the aqueous suspension of ferric hydroxide used only needs to be stirred in the presence of a crystallization control agent and preferably seed crystals, as long as it is not difficult to stir. , the concentration of ferric hydroxide is 1.5 mol/or less in terms of iron, preferably 0.1 to 1
It is assumed to be mole/. The crystallization control agent used in the present invention has a coordinating ability to iron, and due to this coordinating ability, α-
It is selected from water-soluble organic compounds or inorganic compounds that control the growth direction and speed of ferric oxide crystals to produce needle-like crystals. Such an organic compound has at least one coordinating group in its molecule containing an atom capable of coordinating iron, such as an oxygen, nitrogen and/or sulfur atom. Specific examples of such coordination ability include -OH, -COOH, -O-, >C=O, -SO ₃ H,
_-PO3H2 , _{-NH2 ,} =N-OH, ->N, -SH, -S
-, >C=S, _-CS2H , -COSH, -OCN, etc. can be mentioned. Preferably, in the present invention, the crystallization control agent has two or more of the above-mentioned coordination groups of the same type or different types in the molecule. Specific examples of crystallization control agents preferably used in the present invention include polycarboxylic acids such as succinic acid, maleic acid, and nitrilotriacetic acid, particularly di- and tricarboxylic acids, citric acid, tartaric acid, glycolic acid, malic acid, and α-methylmalic acid. , hydroxycarboxylic acids such as α-hydroxyglutaric acid, dihydroxyglutaric acid, and salicylic acid, aminocarboxylic acids such as lysine and glycine, polyamines such as ethylenediamine, hydroxylamine, aminotri(methylenephosphonic acid), and ethylenediaminotetra(methylenephosphonic acid). , organic phosphonic acids such as ethylene-1,1'-diphosphonic acid and 1-hydroxyethylene-1,1'-diethylenephosphonic acid, thiocarboxylic acids such as cysteine and mercaptoacetic acid, polyhydric alcohols such as mannitol and pentaerythritol, and acetylacetone. , ethyl acetoacetate, etc.
-dicarbonyl compounds, aromatic sulfonic acids such as sulfophenyliminodiacetic acid, and the like. Further, these water-soluble salts and esters can also be used as crystallization control agents as long as they have coordination ability to iron. Examples include sodium citrate, sodium tartrate, sodium 1-hydroxypropyl-1,1'-diphosphonate, triethyl citrate, dimethyl hydroxysuccinate, ethyl mercaptoacetate, and the like. Further, in the present invention, phosphates can also be used as crystallization control agents. Specific examples include sodium phosphate, potassium phosphate, ammonium phosphate, and the like. In the present invention, various compounds can be used as crystallization control agents as described above, but particularly preferred crystallization control agents are the aliphatic hydroxycarboxylic acids and the following organic phosphonic acids, and their salts and esters. be. That is, the general formula (However, n represents an integer of 2 to 6, m is O or 1
Indicates an integer between ~5. ) Organic phosphonic acid, its salt or its ester, general formula (However, X and Y represent hydrogen, a hydroxyl group, an amino group, an alkyl group, or an aryl group, and q represents an integer of 1 to 6.) An organic phosphonic acid, its salt, or its ester, and the general formula (However, R represents hydrogen or an alkyl group.) An organic phosphonic acid, a salt thereof, or an ester thereof. Specific examples of the organic phosphonic acid represented by the above formula (1) include aminotri(methylenephosphonic acid),
Ethylene diaminotetra (methylene phosphonic acid),
Examples include diethylenetriaminopenta (methylenephosphonic acid), triethylenetetraaminohexa (methylenephosphonic acid), tetraethylenepentaaminohepta (methylenephosphonic acid), pentaethylenehexaaminoocta (methylenephosphonic acid), and the like. In the organic phosphonic acid represented by the above formula (), the alkyl group has 1 to 6 carbon atoms.
is preferable, and the aryl group preferably has 6 to 14 carbon atoms. Specific examples of such are methylene diphosphonic acid,
Ethylene-1,1'-diphosphonic acid, ethylene-
1,2-diphosphonic acid, propylene-1,1'-diphosphonic acid, propylene-1,3-diphosphonic acid, hexamethylene-1,6-diphosphonic acid,
2,6-dihydroxypentamethylene-2,4-
Diphosphonic acid, 2,5-dihydroxyhexamethylene-2,5-diphosphonic acid, 2,3-dihydroxybutylene-2,3-diphosphonic acid, 1-hydroxybenzyl-1,1'-diphosphonic acid, 1-aminoethylene- Examples include 1,1'-diphosphonic acid. In the above formula (), the alkyl group preferably has 1 to 5 carbon atoms, and specific examples of such organic phosphonic acids include hydroxymethylene diphosphonic acid,
1-hydroxyethylene-1,1'-diphosphonic acid, 1-hydroxypropylene-1,1'-diphosphonic acid, 1-hydroxybutylene-1,1'-diphosphonic acid, 1-hydroxyhexamethylene-1,
Examples include 1'-diphosphonic acid. The amount of crystallization control agent used is α in the hydrothermal reaction.
- There is no particular restriction as long as the amount is sufficient to control the growth direction and speed of ferric oxide crystals, but usually 1×
The amount is 10 ^-5 to 3 mol, preferably 1 x 10 ^-4 to 1 x 10 ^-1 mol. In general, when the amount of the crystallization control agent used is too small, it is difficult to obtain α-iron oxide with excellent needle-like properties, while when it is too large, the reaction takes a long time, which is not preferable. Heating an aqueous suspension of ferric hydroxide under alkaline conditions in the presence of a crystallization control agent as described above yields acicular α-Fe ₂ O ₃ with virtually no vacancies;
During this hydrothermal reaction, α-
By further coexisting Fe ₂ O ₃ seed crystals, acicular α-Fe ₂ O ₃ with a narrower particle size distribution can be obtained.
Therefore, by reducing this, an iron powder with further improved magnetic properties can be obtained. The shape of the particles of this seed crystal α-Fe ₂ O ₃ is not particularly limited and may be arbitrary, such as acicular, spherical, cubic, etc., but the average diameter of the shortest axis is required to be 0.4μ or less. , preferably 0.2μ or less. When the average diameter of the shortest axis of the seed crystal iron ferrite exceeds 0.4μ, the resulting acicular α-iron oxide has a small acicular ratio defined as the ratio of the long axis to the short axis. And/or the average particle diameter is too large, making it difficult to obtain excellent magnetic properties from iron powder made from such acicular α-iron oxide. Seed crystal α
- The lower limit of the shortest axis average diameter of iron oxide is not particularly limited, but is usually about 100 Å. α-Iron oxide having the shortest axis average diameter within such a range can be obtained as a commercial product or by a known production method. In addition, the amount of seed crystal used is preferably 0.1 mol% to 25 mol% in terms of iron based on the raw material ferric hydroxide.
It is 0.5-15 mol%. When this usage amount is less than 0.1 mol%, the obtained acicular α-iron oxide particles are too large, while when it is more than 25 mol%, the obtained acicular α-iron oxide has a small acicular ratio; and/or the particles are too small, in neither case giving an iron powder with good magnetic properties. In the present invention, crystallization control agent (and seed crystal)
It is sufficient that they are present during the heat treatment of the ferric hydroxide aqueous suspension, and the order of their addition is arbitrary.
Therefore, for example, when precipitating ferric hydroxide from an aqueous ferric salt solution, a crystallization control agent and/or seed crystals may be added in advance to the aqueous ferric salt solution. At this time, the crystallization control agent coordinates with the iron atoms in the ferric hydroxide and is included in the precipitate, so it is necessary to newly add it during the heat treatment of the ferric hydroxide suspension. do not. However, seed crystals and a crystal control agent are usually added to the aqueous suspension of ferric hydroxide. The heating reaction is carried out at a pH of 7 or more, preferably in the range of 8 to 12.5. The alkali used is not particularly limited, but is usually sodium hydroxide, potassium hydroxide, ammonia, etc., and is added to the aqueous suspension of ferric hydroxide before or after adding the crystallization control agent and seed crystals. In the present invention, the reaction temperature is generally 100°C or higher. In the reaction at temperatures lower than 100℃, the formation of cross-shaped or T-shaped branched particles and α-FeOOH particles was observed, and α-Fe ₂ O ₃ with excellent acicular properties was observed.
difficult to obtain. By performing the reaction at a high temperature of 100°C or higher, the formation of branched particles and α-FeOOH is eliminated, but the upper limit of the reaction temperature is a temperature that does not cause thermal decomposition of the crystallization control agent used. Although pressure may be applied during the reaction, it is usually not necessary to apply pressure intentionally, and the reaction mixture may simply be heated and stirred in a closed container. In this case, the reaction temperature is usually about 100 to 250°C, preferably about 130 to 200°C. The reaction time is not particularly limited, but is usually several tens of minutes to several hours. In this way, acicular α-iron oxide is obtained, and its shape and dimensions are determined by the heating temperature during the above reaction, the type and amount of the crystallization control agent, the size and amount of the seed crystal, etc. It is also possible to control it within a desired range. The acicular α-Fe ₂ O ₃ obtained as described above has properties optimal for reduction treatment. That is, there are no pores or branches that would cause sintering, and since the crystallization control agent is adsorbed, there is no risk of sintering or deformation during the reduction process. For reduction, the acicular α-Fe ₂ O ₃ is treated, for example, at 300 to 500° C. in a hydrogen stream to obtain the desired acicular iron powder. When a magnetic tape is manufactured using the iron powder thus obtained, the following tape properties are greatly improved. That is, since the iron powder has no holes or branches, the saturation magnetization is high and the coercive force (HC) is greatly improved. Since there is no sintering between particles, significant improvements in coercive force (HC), squareness ratio, and orientation ratio are achieved. Example 1 To the ferric chloride aqueous solution (16.7 gFe/) of 3,
Add 10% caustic soda aqueous solution to adjust the pH to 7.5, and heat the resulting ferric hydroxide suspension to 60°C. Thereafter, the suspension is filtered, and the red precipitate is washed with water and then dispersed in water from step 1. 1.6 g of aminotrimethylenephosphonic acid was added to the suspension of 1 thus obtained, and a 5% aqueous solution of caustic soda was added to adjust the pH to 11.2. This suspension was heated at 150°C for 90 minutes with stirring in an autoclave, then cooled, filtered,
Wash with water and dry to obtain 71 g of red-orange precipitate. This powder was identified as α-Fe ₂ O ₃ by X-ray diffraction, and was found to have an average major axis diameter of 0.6 μm and an average minor axis diameter by electric microscope.
It turned out to be acicular particles of 0.08 μm. Fill a reduction furnace with 300g of the above powder, heat it to 370℃, introduce H ₂ gas at a rate of 5 minutes per minute, reduce it for 4 hours, cool it, and use a mixture of N ₂ gas and a small amount of air. The iron powder was sent and post-processed to obtain iron powder. Electron micrographs revealed crystals with excellent branching and needle-like properties not found in sintered crystals. Table 1 shows the results of measuring the powder magnetic properties and tape magnetic properties of this iron powder.

[Table] (Measurement of tape magnetic properties) 300 parts of ferromagnetic metal powder, 80 parts of cellulose acetate butyrate EAB-381, 3 parts of lecithin, 2 parts of fluorine oil, 500 parts of butyl acetate (30 g)
The mixture was uniformly dispersed and mixed using a paint conditioner, then coated on a polyester film, oriented in a magnetic field, and dried to produce a magnetic tape with a coating thickness of 5.4 μm, and its magnetic properties were measured. Example 2 Into the ferric chloride aqueous solution (21.2 gFe/) of 2,
Add 10% caustic soda aqueous solution to adjust the pH to 7.0, and heat the resulting ferric hydroxide suspension to 60°C. Thereafter, the suspension was filtered and the reddish-brown precipitate was washed with water and then dispersed in water from step 1. In the suspension of 1 thus obtained,
A mixture of phosphonic acids with an acid value of 1205 mgKOH/g (diethylenetriaminepentermethylenephosphonic acid,
Add 3g of triethylenetetraminehexamethylenephosphonic acid, tetraethylenepentaminehexamethylenephosphonic acid, and adjust the pH to 11.0 by adding 5% aqueous sodium hydroxide solution. This suspension was heated to 160°C for 90°C while stirring in an autoclave.
Heat for a minute, then cool, filter, wash and dry.
63 g of α-Fe ₂ O ₃ particle powder was obtained. By electron microscopy, the average major axis diameter was 0.4 μm, and the average minor axis diameter was 0.08 μm.
It turned out to be acicular particles of m. The above powder was reduced in the same manner as in Example 1 to obtain acicular iron powder. The magnetic properties of this powder and tape are shown in Table 1. Example 3 To the ferric nitrate aqueous solution (12.5 gFe/) of 2,
Add 5% caustic soda aqueous solution to adjust the pH to 6.5, filter the resulting ferric hydroxide suspension, wash the reddish brown precipitate with water, and add 0.2 g of d-tartaric acid (2 molecules of crystal water).
and 0.75 g of sodium citrate (2 molecules of crystallized water) are dispersed in the aqueous solution of 1. Adjust the pH to 11.3 with aqueous caustic soda solution and heat at 170°C for 90 minutes without stirring in an autoclave. Thereafter, it was washed, filtered, washed with water, and dried to obtain α-Fe ₂ O ₃ particle powder. The average major axis diameter was determined by electron microscopy.
It was found that the particles were acicular particles with an average minor axis diameter of 0.5 μm and an average minor axis diameter of 0.08 μm. The above powder was reduced in the same manner as in Example 1 to obtain acicular iron powder. The magnetic properties of this powder and tape are shown in Table 1. Example 4 In a 1.5 ferric sulfate aqueous solution (13.8 gFe/),
Blow in ammonia gas at a flow rate of 0.8/min,
While stirring, when the pH reaches 8, the blowing of ammonia gas is stopped and ferric hydroxide is precipitated. Separately, this precipitate was washed with water, and water was added to the resulting cake to form a suspension of pulp i and ferric hydroxide.
get. This suspension has an average long axis of 0.1 μm and an average short axis of 0.02 μm.
Add 1.5 g of rod-shaped crystals of α-Fe ₂ O ₃ of m as seed crystals, add 116 ml of sodium citrate aqueous solution (0.1 mol/) as a crystallization control agent, and add caustic soda aqueous solution with stirring to adjust the pH to 11.9. Prepare to. This suspension was then transferred into an autoclave and
Heat with stirring at a temperature of 120°C for 2 hours. The resulting red-orange precipitate was filtered, washed with water, and dried to obtain α-
_{Fe2O3 powder} was obtained. Electron microscopic observation revealed that they were needle-shaped particles with an average major axis of 0.3 μm and an average minor axis of 0.04 μm. The above powder was reduced in the same manner as in Example 1 to obtain acicular iron powder. The magnetic properties of this powder and tape are shown in Table 1. Comparative example 1 Goethite powder 70 with a major axis of 0.6 μm and a minor axis of 0.08 μm
g (synthesized according to conventional methods) in air.
Acicular ferric oxide was obtained by heating and dehydrating at .degree. C., and this was reduced in the same manner as in Example 1 to obtain iron powder. The powder magnetic properties and tape magnetic properties of this were measured and the results are shown in Table 1.

Claims (1)

[Claims] 1. An aqueous suspension of ferric hydroxide is heated under alkaline conditions in the presence of a crystallization control agent that has coordination ability for iron to form acicular α-ferric oxide. , a method for producing acicular ferromagnetic iron powder, which is characterized by heating and reducing it with a reducing gas. 2. Crystallization control agent has coordination ability for iron.
OH, -COOH, -O-, >C=O, _-SO3H , -
PO ₃ H ₂ , -NH ₂ , =N-OH, ->N, -SH, -S
2. The method for producing a ferromagnetic iron powder according to claim 1, wherein the ferromagnetic iron powder has at least one group selected from -, >C=S, _-CS2H , -COSH, and -OCN. 3. The crystallization control agent is selected from polycarboxylic acids, hydroxycarboxylic acids, aminocarboxylic acids, polyamines, organic phosphonic acids, thiocarboxylic acids, polyhydric alcohols, β-dicarbonyl compounds, aromatic sulfonic acids, salts thereof, and esters thereof. 2. A method for producing ferromagnetic iron powder according to claim 1, characterized in that: 4. The method for producing ferromagnetic iron powder according to claim 1, wherein the crystallization control agent is a phosphate. 5 a hydroxycarboxylic acid in which the crystallization control agent is selected from citric acid, tartaric acid, malic acid, α-hydroxyglutaric acid and dihydroxyglutaric acid;
The method for producing ferromagnetic iron powder according to claim 1, wherein the ferromagnetic iron powder is a salt thereof or an ester thereof. 6 Crystallization control agent has general formula (However, n represents an integer of 2 to 6, m is 0 or 1
Indicates an integer between ~5. 2. The method for producing ferromagnetic iron powder according to claim 1, wherein the ferromagnetic iron powder is an organic phosphonic acid represented by the following formula, a salt thereof, or an ester thereof. 7 Crystallization control agent has general formula (However, X and Y represent hydrogen, a hydroxyl group, an amino group, an alkyl group, or an aryl group, and q represents an integer of 1 to 6.) Characterized by being an organic sulfonic acid, a salt thereof, or an ester thereof. A method for producing ferromagnetic iron powder according to claim 1. 8 Crystallization control agent has general formula (However, R represents hydrogen or an alkyl group.) The method for producing ferromagnetic iron powder according to claim 1, characterized in that it is an organic phosphonic acid, a salt thereof, or an ester thereof. 9. Any one of claims 1 to 8, characterized in that a crystallization control agent is allowed to coexist with ferric hydroxide in an amount of 1 x 10 ^-5 to 3 mol per gram atom of iron. A method for producing the described ferromagnetic iron powder. 10 An aqueous suspension of ferric hydroxide is mixed with one or more crystallization control agents selected from water-soluble compounds having a coordinating ability for iron, and ferric hydroxide in terms of iron atoms. In the presence of 0.1 mol % to 25 mol % of α-ferric oxide seed crystals with an average particle diameter of 0.4 μ or less on the shortest axis, heat in alkaline to form acicular α-ferric oxide. A method for producing ferromagnetic iron powder characterized by heating reduction with a reducing gas. 11 Crystallization control agent has coordinating ability to iron -OH, -COOH, -O-, >C=O, -SO ₃ H, -
PO ₃ H ₂ , -NH ₂ , =N-OH, ->N, -SH, -S
11. The method for producing ferromagnetic iron powder according to claim 10, wherein the ferromagnetic iron powder has at least one group selected from -, >C=S, _-CS2H , -COSH, and -OCN. 12 The crystallization control agent is polycarboxylic acid, hydroxycarboxylic acid, aminocarboxylic acid, polyamine,
Ferromagnetic iron powder according to claim 10, characterized in that it is selected from organic phosphonic acids, thiocarboxylic acids, polyhydric alcohols, β-dicarbonyl compounds, aromatic sulfonic acids, salts thereof, and esters thereof. manufacturing method. 13. The method for producing ferromagnetic iron powder according to claim 10, wherein the crystallization control agent is a phosphate. 14 A hydroxycarboxylic acid in which the crystallization control agent is selected from citric acid, tartaric acid, malic acid, α-hydroxyglutaric acid and dihydroxyglutaric acid,
11. The method for producing ferromagnetic iron powder according to claim 10, wherein the ferromagnetic iron powder is a salt thereof or an ester thereof. 15 Crystallization control agent has general formula (However, n represents an integer of 2 to 6, m is 0 or 1
Indicates an integer between ~5. 11. The method for producing a ferromagnetic iron powder according to claim 10, wherein the ferromagnetic iron powder is an organic phosphonic acid represented by: ), a salt thereof, or an ester thereof. 16 Crystallization control agent has general formula (However, X and Y represent hydrogen, a hydroxyl group, an amino group, an alkyl group, or an aryl group, and q represents an integer of 1 to 6.) Characterized by being an organic phosphonic acid, a salt thereof, or an ester thereof. A method for producing ferromagnetic iron powder according to claim 10. 17 Crystallization control agent has general formula (However, R represents hydrogen or an alkyl group.) Claim 10 is an organic phosphonic acid, a salt thereof, or an ester thereof.
2. Method for producing ferromagnetic iron powder as described in . 18 Claim 10, characterized in that the crystallization control agent is allowed to coexist with ferric hydroxide in an amount of 1 x 10 ^-5 to 3 mol per gram of iron atom.
18. A method for producing ferromagnetic iron powder according to any one of items 1 to 17.