JPS63183111A - Production of fine ferromagnetic metal particles - Google Patents

Abstract

PURPOSE:To produce fine ferromagnetic metal particles having superior magnetic characteristics and dispersibility in paint by adding an Ni salt, etc., to a suspension of alpha-iron oxyhydroxide particles, aging the suspension to form metallic compd. layers on the surfaces of the particles and carrying out baking and reduction. CONSTITUTION:A suspension of fine alpha-iron oxyhjydroxide particles in an aq. org. acid soln. is prepd. and adjusted to <=4.0 pH. An aq. Ni salt soln. is added to the suspension and this suspension is adjusted to 9.0-11.0 pH with ammonia and aged at >=70 deg.C to deposit an Ni compd. on the surfaces of the particles. While the suspension is kept at >=7.0 pH as required, an aq. silicic acid soln. is added to stick a silicon compd. on the Ni compd. An Al compd., a ferrous salt and an aq. alkali soln. are then added and brought into an oxidation reaction to form surface layers of alpha-iron oxyhydroxide contg. Al. The resulting slurry is filtered and the separated particles are dried, baked by heating and reduced. Thus, the sintering of the particles is prevented and fine ferromagnetic metal particles having superior dispersibility in paint are obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention involves adding a nickel salt or the like to an aqueous suspension of α-iron oxyhydroxide fine particles, attaching a metal compound to the α-iron oxyhydroxide fine particles, and reducing the The present invention relates to a method for producing acicular ferromagnetic metal fine particles.

[Conventional technology]

Acicular iron oxide particles have traditionally been used as fine particles for magnetic recording media, but with the development of high-performance audio cassette tapes and compact video tapes, higher recording density and higher performance are required. Became. For this reason, magnetic properties, especially high coercive force (Hc), high magnetic flux density (saturation magnetization (σS) in powder magnetic properties, saturation magnetic flux density (Bm) in tape magnetic properties, and squareness ratio (
Ferromagnetic metal fine particles having a high Br/Bm) are attracting attention. As a solution to this problem, fine particles mainly composed of iron oxide or α-iron oxyhydroxide can be used to
The most widely known are ferromagnetic metal iron fine particles obtained by thermal reduction in a reducing gas stream such as ferromagnetic iron particles. Furthermore, in order to cope with higher density and higher performance recording, it is necessary to make the ferromagnetic metal fine particles even finer. However, the finer the particles are, the more likely the particles are to sinter when heated and reduced, and the problem arises that the dispersibility of the paint becomes extremely poor at the stage of forming the magnetic fine particles into a paint.

Regarding the prevention of sintering of particles, which is the first problem mentioned above, Japanese Patent No. 1268089 (Japanese Patent Publication No. 59-47
This problem was solved by the method proposed in No. 004). This patent describes a method for producing acicular fine metal particles by adding a metal salt to an aqueous suspension of α-iron oxyhydroxide, attaching a metal compound to the α-iron oxyhydroxide particles, and post-reducing the particles. An organic acid is added to the aqueous suspension of α-iron oxyhydroxide to adjust the pH of the slurry to 4.0 or less, then a metal salt is added, and then ammonia is added to adjust the pH of the slurry to 9.0 to 11.0. After aging at 70°C or above, add a silicic acid aqueous solution, further add ammonia if necessary, separate this slurry by filtration or other methods, and dry it to obtain dry α-iron oxyhydroxide. discloses a method to reduce

However, regarding the paint dispersibility of the second fish, high dispersion,
In addition to the ever-increasing demand for higher filling, the method of the above-mentioned patent is no longer sufficient to meet the demands.

Many proposals have been made to solve these problems, but at the same time it has excellent magnetic properties, especially high coercive force, high saturation magnetization, prevents sintering due to fine particles, and has excellent paint dispersibility. A satisfactory manufacturing method has not yet been found.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for producing nine ferromagnetic metal fine particles that have excellent magnetic properties, particularly high coercive force and high saturation magnetization, prevent particles from sintering together, and have excellent paint dispersibility. .

[Means for Solving the Problems] The present invention involves adding an aqueous solution of a nickel salt to a suspension of an organic acid aqueous solution of α-iron oxyhydroxide fine particles, the slurry having a DH of 4.0 or less, Ammonia is added to adjust the pH of the slurry to 9.0 to 11.0, and it is aged at 70°C or higher to firmly adhere the nickel compound to the surface of the α-iron oxyhydroxide fine particles. Add ammonia to the slurry. While keeping the pH at 7.0 or higher, add an aqueous solution of silicic acid to the α-
After adhering a silicon compound to the surface of the iron oxyhydroxide fine particles, an aqueous solution of an aluminum compound, a ferrous salt, and an alkali is further added to the slurry to carry out an oxidation reaction. An α-iron oxyhydroxide layer containing aluminum (hereinafter referred to as "Al-doped α-iron oxyhydroxide layer") is formed on the surface layer of the deposited α-iron oxyhydroxide fine particles, and this slurry is filtered. In this method, ferromagnetic metal fine particles are produced by fractionating, washing with water, and drying to obtain dry α-iron oxyhydroxide, which is then heated and fired, and then reduced.

To explain this in detail, first, a suspension of α-iron oxyhydroxide fine particles in an aqueous organic acid solution is prepared. For this purpose α
- An organic acid may be added to an aqueous suspension of iron oxyhydroxide fine particles, or α-iron oxyhydroxide fine particles may be added to an organic acid aqueous solution.

The pH of this slurry is preferably 4.0 or less.

Preferably it is 3.5 to 2.0. In this state, an aqueous solution of an inorganic salt or an organic acid salt of nickel is added.

Thereafter, ammonia is added to adjust the pH of the slurry to 9.0 or more, preferably in the range of 9.5 to 11.0, and nickel hydroxide is precipitated on the surface of the α-iron oxyhydroxide fine particles. Next, the mixture is heated or boiled and aged to firmly adhere the nickel compound to the surface of the α-iron oxyhydroxide fine particles. At this time, the slurry temperature should be 70°C or higher, the higher the better. Preferably the temperature is 90°C or higher. Also, the aging time is 30 minutes ~
2 hours, preferably 1 to 2 hours. Next, the slurry is cooled or maintained at a temperature of 70° C. or higher, preferably 90° C. or higher, and ammonia is added as needed to maintain the pH of the slurry at 7.0 or higher, and an aqueous silicic acid solution is gradually added. Next, the slurry is cooled, and an aqueous solution of an aluminum compound, a ferrous salt, and an alkali are added to carry out an oxidation reaction, which causes the surface layer of the α-iron oxyhydroxide particles to be coated with a nickel compound and then a silicon compound. A kll-doped iron oxyhydroxide layer is formed. This slurry is separated by a method such as filtration, washed with water, and dried to obtain dry α-iron oxyhydroxide fine particles, which are heated and calcined and then reduced with a reducing gas such as H, etc.

The α-iron oxyhydroxide fine particles used as a starting material in the present invention are acicular α-iron oxyhydroxide fine particles (including powder and wet cake) or α-iron oxyhydroxide containing cobalt, manganese, nickel, zinc, and chromium. , needle-like fine particles doped with metals such as copper and silicon, or these with zinc,
Refers to materials coated with compounds such as chromium and copper.

The organic acid used in the present invention can be any of acetic acid, formic acid, citric acid, oxalic acid, etc., but acetic acid is most preferred from the viewpoint of dispersion ability.

As the aqueous solution of nickel salt used in the present invention, an aqueous solution of an inorganic salt such as nickel sulfate, nickel nitrate, or nickel chloride, or an aqueous solution of an organic acid salt such as nickel acetate or nickel oxalate can be used. An aqueous solution of is particularly preferred. The amount of the nickel salt used is 1 to 1 nickel atom per 100 parts by weight of iron atoms of α-iron oxyhydroxide.
30 parts by weight is preferred. If the amount of nickel is less than 1 part by weight, there is no effect, and if it exceeds 30 parts by weight, the effect is saturated.

In the present invention, ammonia may be added by any method such as addition as aqueous ammonia or blowing ammonia gas, as long as it is added so that the pH of the slurry becomes 9.0 to 11.0. Instead of ammonia, a substance such as urea which is thermally decomposed by heating in an aqueous solution state to produce ammonia may be used. This case is also included in the present invention.

As the silicic acid aqueous solution used in the present invention, various silicic acid aqueous solutions such as ortho-silicic acid and meta-silicic acid, silica sol, silica sol stabilized with ammonia, silica sol modified with aluminum, etc. can be used. The amount of silicon used in these aqueous solutions or sol is 100 iron atoms of α-iron oxyhydroxide.
It is preferably 0.5 to 7 parts by weight, preferably 0.7 to 5 parts by weight, based on silicon atoms.

If it is less than 0.5 parts by weight, there will be no sintering prevention effect, and if it exceeds 7 parts by weight, reduction will be suppressed, making it impossible to obtain desired magnetic properties, especially high saturation magnetization. When adding the silicic acid aqueous solution, the pH of the slurry is 7.0 or more, preferably 8.0 to 11.
．． 0 is good. If this cord is removed, the deposited nickel will easily dissolve. In addition, the silicic acid aqueous solution may be added while maintaining the temperature at which the nickel compound was added and aged, but if the slurry is cooled once and added at the time of cooling, the slurry is heated to a temperature of 70°C or higher, preferably 90°C or higher, and then aged. It is better. The aging time is preferably 30 minutes to 2 hours, preferably 1 hour.
More than an hour is better.

The aqueous solution of aluminum compounds used in the present invention includes aluminum sulfate, aluminum chloride, aluminum nitrate,
Aqueous solutions of inorganic salts such as aluminum phosphate and aluminate, aqueous solutions of organic salts such as aluminum acetate and aluminum lactate, and alumina sol can be used. The amount of these aluminum compounds added is FA relative to the amount of ferrous salt added.
A'/Fe (■ It is best to set it to 3 to 35% by weight. If it exceeds 355% by weight, the aluminum compound will not be completely absorbed into the surface layer of the α-iron oxyhydroxide fine particles, and the formed particles will be Problems such as difficulty in reduction occur, which is undesirable.Also, if it is less than 3% by weight, the addition effect of the aluminum compound is not obtained.On the other hand, the amount of the aluminum compound added is It is preferable that the amount of AA/FeJ be 0.5 to 2.5% by weight based on the total amount of iron in the ferrous salt added during the formation of the doped iron oxyhydroxide layer.

If the amount is less than 0.5% by weight, the improvement in dispersibility of the reduced ferromagnetic metal fine particles when forming into a paint will be insufficient. Moreover, if it exceeds 2.5 weight f%, reduction in the subsequent process will be suppressed, making it impossible to obtain desired magnetic properties, particularly high saturation magnetization.

The amount of the ferrous salt (for example, ferrous sulfate) used in the present invention is 1 as rFe (Ill/α-FeoOHj) with respect to α-iron oxyhydroxide of the α-iron oxyhydroxide fine particles.
~20 weight ratio weight-. If it exceeds 200% by weight, α-iron oxyhydroxide produced by air oxidation takes in the aluminum compound and grows on the surface of the α-iron oxyhydroxide fine particles coated with metal compounds and silicon compounds. Since the reaction is carried out, fine particles or branched particles are formed, and the particle size becomes uneven, which is not preferable. If the amount is less than 1% by weight, the α-iron oxyhydroxide produced by air oxidation will not completely absorb the aluminum compound, and the nickel compound and silicon compound will be deposited on the surface layer of the α-iron oxyhydroxide fine particles. The aluminum compound precipitates alone, which is undesirable because it causes uneven adhesion of the aluminum compound on the surface of the α-iron oxyhydroxide fine particles and between the particles.

The alkaline aqueous solution used in the present invention is NaOH.

An aqueous solution of a basic substance such as NH, NatCOs, etc. can be used. Alternatively, ammonia gas may be blown.

The amount of the alkaline aqueous solution added should be at least the chemical equivalent of the added ferrous salt and aluminum compound ([(added base f) ≧
(Amount of added ferrous salt) + (added aluminum compound i) J
) in the area where α-iron oxyhydroxide fine particles are generated.

The slower the addition rate of the aluminum compound aqueous solution and the ferrous salt aqueous solution, the more preferable it is. The aluminum compound and ferrous salt may be added as a mixed solution as long as precipitation does not occur, or the aluminum compound may be added after adding the ferrous salt, but in these cases, fine particles may be formed. It is preferable to add the aqueous solution of the ferrous salt after adding the aqueous solution of the aluminum compound, since this makes the process easier. Thereafter, an oxidation reaction is carried out by blowing in a gas containing oxygen such as air or adding an oxidizing agent.

Through the above operations, the outermost layer of the α-iron oxyhydroxide fine particles coated with the nickel compound and then the silicon compound is coated with Al.
A doped iron oxyhydroxide layer is formed.

This slurry is separated by a method such as filtration, washed with water, and dried to obtain dry α-oxyhydroxide fine particles (coated with Ni-8i-FeAl). This drying temperature is 100-180℃
is preferred.

The dried α-iron oxyhydroxide fine particles are heated and fired and then reduced to become ferromagnetic metal fine particles. The heating and firing is usually carried out at 450 to 850°C in an atmosphere of non-reducing gas such as argon, nitrogen, or air, and the reduction is usually carried out at 400 to 600°C in a hydrogen stream.

[Action/Effect]

According to the present invention, a nickel compound and then a silicon compound are sequentially deposited on the surface of α-iron oxyhydroxide fine particles, and an All-doped iron oxyhydroxide layer is formed on the outside thereof.

The use of nickel salts is effective in controlling coercive force, improving corrosion resistance, and lowering reduction temperature. Silicon compounds exhibit the greatest effect in preventing sintering (this is because the coercive force and squareness ratio of the magnetic metal fine particles are large, and the coercive force, residual magnetic flux density, and squareness ratio in the tape magnetic properties are large; F, D
This appears in the fact that it becomes smaller. ). Forming an All-doped iron oxyhydroxide layer on the outermost layer means that Altos is uniformly applied to the surface of each ferromagnetic metal fine particle after reduction.
(This is because the squareness ratio in tape magnetic properties is large, and S, F.

This appears in the fact that D becomes smaller. ). This is AI.

This is thought to be because the surface of the ferromagnetic metal fine particles was modified by No. 03.

Note that, unlike the present invention, it is possible to introduce an aluminum compound into the outermost layer of α-iron oxyhydroxide fine particles by a deposition method, but the biggest drawback of the deposition method is that α-iron oxyhydroxide This causes uneven adhesion of the aluminum compound on the surface of the fine particles as well as between the fine particles.

In addition, in the process of forming an All-doped iron oxyhydroxide layer on the outermost layer of the α-iron oxyhydroxide fine particles in the present invention, free nickel compounds not attached to the α-iron oxyhydroxide fine particles in the slurry are removed. and the silicon compound is Al
Since it is incorporated into the l-doped iron oxyhydroxide layer and increases adhesion strength and adhesion efficiency, it is also effective for the adhesion of large amounts of nickel compounds or silicon compounds. In addition, microparticles of α-iron oxyhydroxide are also incorporated at the same time, and the particle size of the α-iron oxyhydroxide microparticles becomes uniform and the particle size distribution becomes sharp (
This is manifested in the fact that the coercive force of the magnetic metal particles increases, and that the coercive force in the magnetic properties of the tape increases and S, F, and D become smaller. ).

Therefore, by forming an All-doped iron oxyhydroxide layer on the outermost layer of α-iron oxyhydroxide fine particles, the particles have a sharp particle size distribution and excellent magnetic properties, especially high coercive force and high saturation magnetization. Ferromagnetic metal fine particles having excellent initial dispersibility and capable of being highly dispersed can be obtained.

〔Example〕

Examples are shown below. In the following Examples and Comparative Examples, "related" refers to "related by weight" unless otherwise specified.

Example 1 0.34 in 6 mol/1 NaOH aqueous solution 12.64'
Mo 1/1 FeSO4 aqueous solution 381 was added and maintained at 40° C. with an air flow rate of 20 Al/M to synthesize α-iron oxyhydroxide, which was filtered and washed with water to obtain a wet cake.

This wet cake of α-iron oxyhydroxide (10
0011) was put into pure water 20 to 9 to obtain an aqueous suspension of α-iron oxyhydroxide. Add to this acetic acid (purity 99.5
401R1 was added to adjust the pH to 3.2 (20°C). After stirring for 30 minutes, pre-prepared nickel acetate ((CH3COO)).

Ni・4H,O; Nickel content 22.9) 294.
An aqueous solution of nickel acetate in which 9 was dissolved in 2.71 parts of water was gradually added. After stirring for another 30 minutes, 2001d of aqueous ammonia solution of Section 28 was added to adjust the pH of the slurry to 9.6 (20°
I made it C). After that, stirring was continued for 30 minutes, and the temperature was increased to 9.
The temperature was raised to 0°C and aged for 60 minutes. Add 28% to the slurry again.
Aqueous ammonia solution was added to maintain pn at 9.0 or higher.

While maintaining this slurry at the above-mentioned aging temperature, an aqueous ortho-silicic acid solution (Si concentration 1%) 1930.9 was gradually added thereto, stirred for 60 minutes, and then cooled to 25°C. 5 mol/1 NaOH15001 Lt was added to this slurry. After stirring for 30 minutes, 560 m of 0.5 mol/l aluminum sulfate aqueous solution was added, followed by 0.5 mol, 4! 3570 (1) of ferrous sulfate aqueous solution was added. After stirring for 15 minutes, air was blown at a flow rate of Q,'ll/rnix to 25°C.
The Ni-Si deposition-AJ
A suspension of α-iron oxyhydroxide fine particles in which a doped α-iron oxyhydroxide layer was formed was obtained.

This suspension was filtered, washed with water, and dried overnight at 130 to 135°C to obtain treated dry α-iron oxyhydroxide fine particles as shown in Table 1.

The dried α-iron oxyhydroxide fine particles 500.9 were first
The α-Fe, O, particles were heated and fired in an atmosphere at 600°C for 30 minutes to obtain α-Fe, O, fine particles with a tough particle shape, and then reduced at the temperature shown in Table 1 for H2 flow rate of 301/NR residence time of 6 hours to obtain needle-like particles. ferromagnetic metal fine particles were obtained. The magnetic property value is the first
Shown in the table.

Example 2 Ferromagnetic metal fine particles were obtained in the same manner as in Example 1, except that sodium aluminate was used instead of aluminum sulfate, and their magnetic properties were measured.

The results are shown in Table 1.

Example 3 The first experiment was carried out by changing the amounts of ferrous sulfate and aluminum sulfate.
The ratio of the amounts of ferrous sulfate to the starting α-iron oxyhydroxide shown in the table (expressed in weight percent of Fe(I[)/Fe00H).

) and the ratio of the added amounts of aluminum sulfate and ferrous sulfate (
Expressed in weight percent of Al/Fe(n). ) Ferromagnetic metal fine particles were obtained in the same manner as in Example 1, and their magnetic properties were measured.

The results are shown in Table 1.

Example 4 AAl/F shown in Table 1 was prepared by using sodium aluminate for aluminum sulfate and changing the amount added.
Ferromagnetic metal fine particles were obtained in the same manner as in Example 1, except that the weight ratio was set to e(n), and their magnetic properties were measured. The results are shown in Table 1.

Example 5.6 Al/
Ferromagnetic metal fine particles were obtained in the same manner as in Example 1 except that the weight ratio of Fe (II) was changed, and the magnetic properties thereof were measured. The results are shown in Table 1.

Comparative Example 1 By changing the amounts of ferrous sulfate and aluminum sulfate, the ratio of the amounts of ferrous sulfate and starting α-iron oxyhydroxide fine particles and the weight ratio of AAl/Fe (Ill) shown in Table 1 were adjusted. Ferromagnetic metal fine particles were obtained in the same manner as in Example 1 except that
Its magnetic properties were measured.

The results are shown in Table 1.

Comparative Example 2 Al/
Ferromagnetic metal fine particles were obtained in the same manner as in Example 1 except that the weight ratio of Fe (If) was changed, and the magnetic properties thereof were measured. The results are shown in Table 1.

Comparative Example 3 The same wet cake of α-iron oxyhydroxide (1000!1 on dry basis) as in Example 1 was added to 20% pure water and 9O.
- An aqueous suspension of iron oxyhydroxide was obtained and treated in the same manner as in Example 1 to deposit a Ni compound and a Si compound.

This suspension was separated, dried overnight at 130-135°C,
Ni-Si coated α-iron oxyhydroxide containing no AI compound as shown in Table 1 was obtained. This dried α-iron oxyhydroxide was heated, fired, and reduced in the same manner as in Example 1 to obtain acicular ferromagnetic metal fine particles, and their magnetic properties were measured. The results are shown in Table 1.

Comparative Example 4 Ferromagnetic metal fine particles were obtained in the same manner as in Example 1, except that 480 d of a 0.5 mol/l aluminum sulfate aqueous solution was deposited by the same deposition method as the Ni compound and Si compound instead of the surface doping method. The magnetic properties were measured. The results are shown in Table 1.

Procedural amendment (voluntary) May 6, 1986

Claims (7)

[Claims] (1) Add an aqueous solution of nickel salt to a suspension of α-iron oxyhydroxide fine particles in an organic acid aqueous solution with a pH of 4.0 or less, and then add ammonia to adjust the pH of the slurry. 9.0 to 11.0, and after aging at 70°C or higher, add ammonia as necessary to keep the pH of the slurry at 7.0 or higher, add an aqueous solution of silicic acid, and attach a nickel compound. -A silicon compound is attached to the surface of iron oxyhydroxide fine particles, and then an aluminum compound,
By adding an aqueous solution of ferrous salt and alkali and performing an oxidation reaction, an α-iron oxyhydroxide layer containing aluminum is formed on the surface layer of α-iron oxyhydroxide fine particles coated with a nickel compound and then a silicon compound. (hereinafter referred to as "Al-doped α-iron oxyhydroxide layer"), this slurry is separated by a method such as filtration, washed with water and dried to obtain dry α-iron oxyhydroxide, which is heated and calcined. , a method for producing ferromagnetic metal fine particles characterized by reduction. (2) The aqueous solution of silicic acid is at least one of aqueous solutions of various silicic acids such as ortho-silicic acid and meta-silicic acid, aqueous silica sol, aqueous silica sol stabilized with ammonia, and aqueous silica sol modified with aluminum. The method according to item (1), characterized in that: (3) The aqueous solution of the aluminum compound is at least an aqueous solution of an inorganic salt of aluminum such as aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum phosphate, or an aluminate, an aqueous solution of an organic acid of aluminum such as aluminum acetate or aluminum lactate, or an alumina sol. Paragraph (1) or (2) characterized in that it is one type of
The method described in section. (4) Item (1) characterized in that the amount of the silicic acid aqueous solution added is 0.5 to 7 parts by weight based on silicon atoms based on 100 parts by weight of iron atoms of the α-iron oxyhydroxide. ,
The method described in (2) or (3). (5) In forming the Al-doped α-iron oxyhydroxide layer, the amount of aluminum compound added is in the range of 3 to 35% by weight of “Al/Fe(II)” based on the amount of ferrous salt added. The method according to any one of items (1) to (4), characterized in that: (6) In forming the Al-doped α-iron oxyhydroxide layer, the amount of the aluminum compound to be added is adjusted to the raw material α-iron oxyhydroxide and the ferrous iron added at the time of forming the Al-doped α-iron oxyhydroxide layer. For the total amount of iron in salt, “Al/F
5. The method according to any one of items (1) to (5), characterized in that the amount of carbon dioxide is 0.5 to 2.5% by weight. (7) Paragraph (1) characterized in that the amount of the ferrous salt added is 1 to 20% by weight of "Fe(II)/α-FeOOH" based on the α-iron oxyhydroxide. A method according to any of paragraph (6).