JP2958370B2 - Method for producing composite ferrite magnetic powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a novel composite ferrite magnetic powder. More specifically, the present invention has a coercive force of 200 to 2000 Oe, which is suitable for use in a magnetic recording medium for high-density recording, has an improved saturation magnetization as compared with the conventional one, and has a temperature of coercive force. Small change, low electric resistance of powder, and particle size of 50
The present invention relates to a method for producing a composite ferrite magnetic powder having a thickness of not more than 5 nm and a tabular ratio of not less than 5. In recent years, with the demand for higher density of magnetic recording, development of a perpendicular magnetic recording system using a magnetoplumbite type ferrite magnetic powder as a magnetic recording medium has been promoted, and applications such as a DAT tape, an 8 mm tape, and a Hi-Vision tape have been made. It is considered.
The magnetoplumbite ferrite magnetic powder used in the perpendicular magnetic recording system is a fine particle having an appropriate coercive force (200 to 2000 Oe), a high saturation magnetization, a small temperature change of the coercive force, and a low electric resistance. What is small and has good orientation is desired.

[0002]

2. Description of the Related Art Conventionally, various methods for producing magnetoplumbite-type ferrite magnetic powder, such as a coprecipitation method, a glass crystallization method, and a hydrothermal synthesis method, are known. For the conversion method, see JP-B-60-155
No. 75, the hydrothermal synthesis method, for example, JP-A-59-175
No. 707, Japanese Patent Publication No. 60-12973, Japanese Patent Publication No. 60-15576, Japanese Patent Application Laid-Open No. 60-137002, and the like. However, the magnetoplumbite-type ferrite magnetic powder obtained by any of the above methods has a saturation magnetization of 6%.
There are drawbacks such as a low value of 0 emu / g or less and a large change in coercive force with temperature. In particular, the particle size required for high density
It was difficult to obtain fine particles having a uniform particle shape at 50 nm or less and excellent magnetic properties. On the other hand, magnetoplumbite-type ferrite magnetic powder is the same as conventional Co-γ-Fe
_Since the electric resistance of the powder is larger than that of ₂ O ₃ , a large amount of a conductive substance must be added when forming a coating medium.
Therefore, there is a problem that the electromagnetic conversion characteristics deteriorate. As a method for solving these problems, JP-A-62-139122, JP-A-62-139124, and JP-A-62-265122
JP-A-63-144118 and JP-A-63-144119 propose to coat the surface of ferrite magnetic powder with spinel-type ferrite. Ferrite magnetic powder obtained by this, although the above-mentioned various properties are actually improved, since a large amount of spinel-type ferrite is coated on the surface of the ferrite magnetic powder, the orientation of the particles becomes poor,
The squareness ratio when formed into a coating film becomes small, and
There is a problem that the axis of easy magnetization deviates from the C axis.

[0003]

An object of the present invention is to solve the above problems,
The coercive force is 200-2000 Oe, the saturation magnetization is high,
The temperature change of coercive force is small, the electric resistance of powder is small,
Another object of the present invention is to provide a method for producing a composite ferrite magnetic powder having a particle diameter of 50 nm or less and a plate-like ratio of 5 or more and excellent in orientation.

[0004]

[Means for Solving the Problems] The present invention provides a compound represented by the following general formula:
_{AO · n (Fe 12-xy} Sb x M y O 18-z) ( however, A is indicated Ba, Sr, one or more elements selected from Ca and Pb, M is Co, Ni, Zn, Cu , Mg, Mn, Fe (II), Si,
Represents one or more elements selected from Ti, Zr, Sn, Ta, Nb, Mo, V and W, n = 1.2 to 3.0, x = 0.01 to 0.6, y = 0.1 to 4.
0, 0 <z <2. ) Is suspended in water, and a reducing agent, Co, Ni, Zn, M
One or more metal ions selected from g, Mn and Cu and Fe ²⁺
And an aqueous alkali solution is added, and the resulting mixed suspension is subjected to a heat treatment at 50 to 200 ° C. in a non-oxidizing atmosphere, followed by washing and filtration, and then 100 to 500 in a non-oxidizing atmosphere. A ferrite fine particle surface represented by the above general formula characterized by heat treatment at
(M′O) · Fe ₂ O ₃ (where M ′ is one or more metal elements selected from Co, Ni, Zn, Cu, Mg, Mn and Fe (II), and 0 <
a ≦ 1. The present invention relates to a method for producing a composite ferrite magnetic powder having a spinel ferrite layer represented by the formula (1).

In the composite ferrite magnetic powder of the present invention,
The ferrite fine particles serving as nuclei are represented by the general formula AOn (Fe
Represented by _{12-xy Sb x M y O} 18-z). A in the general formula represents one or more elements selected from Ba, Sr, Ca and Pb, and M represents Co, Ni, Zn, Cu, Mg, Mn, Fe (II), Si, Ti, Zr, Sn, T
a, Nb, Mo, represents one or more elements selected from V and W,
n = 1.2-3.0, preferably 1.4-2.5, x = 0.01-
0.6, preferably 0.1 to 0.4, and y = 0.1 to 4.0. Z is z when the average valence of M is m.
= (3-m) y / 2, where 0 <z <
2, preferably 0.2 <z <1.5. In the present invention, the saturation magnetization is improved as compared with the conventional magnetoplumbite ferrite by substituting a part of Fe with M as shown in the above general formula and setting n in the range of 1.2 to 3.0. As a result, a ferrite magnetic powder having a small change in coercive force with temperature can be obtained. Further, by substituting a part of Fe with Sb, the particle diameter of the ferrite magnetic powder can be 50 nm or less and the plate ratio can be 5 or more.

[0006] Such ferrite fine particles are produced by the following method. A constituting ferrite fine particles,
The solution containing Fe, Sb, and M and the alkali hydroxide are mixed so that the concentration of the alkali hydroxide in the mixed solution becomes 3 M or more to form a precipitate, and the slurry containing the precipitate is mixed with one solution.
After hydrothermal treatment at 20 to 300 ° C., the slurry containing the precipitate is washed, and the slurry contains one or more metal ions selected from Co, Ni, Zn, Mg, Mn and Cu, and Fe ²⁺ . An aqueous solution and an aqueous alkali solution were added, and the resulting mixed suspension was heated at 50 to 200 ° C.
By baking at 00 to 950 ° C., the ferrite fine particles are obtained. As the compound of A, nitrates, chlorides, hydroxides and the like are used. The use amount of A is desirably set so that the concentration of A is in the range of 0.03 to 0.50 M in order to obtain particles having good crystallinity.

As the Fe compound, nitrates, chlorides and the like are used. The amount of Fe used is 8 for 1 gram atom.
~ 12 gram atoms are preferred. If the amount of Fe is too small,
The amount of ferrite magnetic powder generated is small, and the crystallinity also deteriorates. If the amount of Fe is too large, hematite is produced as a by-product,
In addition, the particles of the ferrite magnetic powder become large, and the magnetic properties become poor. Chloride or the like is used as the Sb compound. As the compound of M, chloride, nitrate, ammonium salt and the like are used. As the alkali hydroxide, sodium hydroxide, potassium hydroxide or the like is used. The amount of the alkali hydroxide used must be such that the alkali hydroxide concentration in the solution after mixing the alkali hydroxide is 3 M or more, and is preferably in the range of 4 to 8 M. If the amount of the alkali hydroxide is too small, the particles become large, the particle size distribution becomes wide, and hematite is generated. It is not economical to use an excessive amount of alkali hydroxide. A, Fe, Sb
The method of mixing the solution containing Al and M with the alkali hydroxide is not particularly limited. For example, A, Fe, Sb and M
There is a method of adding an aqueous solution of an alkali hydroxide to a solution containing

Next, the slurry containing the obtained precipitate is subjected to a hydrothermal treatment, whereby fine crystals are formed and precipitated.
The temperature of the hydrothermal treatment is 120 to 300 ° C. If the temperature is too low, the formation of crystals is not sufficient, and if the temperature is too high, the particle size of the finally obtained ferrite powder is undesirably large. The hydrothermal treatment time is usually about 0.5 to 20 hours, and an autoclave is usually employed for the hydrothermal treatment. Next, the precipitate of fine crystals generated by the hydrothermal treatment is washed with water to remove free alkali, and then the slurry is coated with one or more metal ions selected from Co, Ni, Zn, Mg, Mn and Cu. And an aqueous solution containing Fe ²⁺ and an alkaline aqueous solution are added, and the resulting mixed suspension is heated at 50 to 200 ° C. As compounds of Co, Ni, Zn, Mg, Mn and Cu, those soluble in water such as nitrates, chlorides and sulfates are used, and as compounds of Fe, ferrous sulfate and ferric chloride are used. One iron is commonly used. Next, the obtained precipitate is washed with water and then fired to obtain ferrite fine particles.

In the firing, it is preferable to mix a flux with the precipitate obtained in advance. As the flux, at least one of sodium chloride, barium chloride, potassium chloride, strontium chloride and sodium fluoride is used. The amount of the flux used is preferably 10 to 180% by weight, particularly preferably 30 to 120% by weight, based on the precipitate (dry matter basis). If the amount of the flux is too small, sintering of the particles occurs,
If it is too much, there is no advantage from doing so and it is not economical. The method of mixing the precipitate and the flux is not particularly limited.For example, after adding a flux to the slurry of the precipitate and wet-mixing, the slurry may be dried, or after drying the precipitate,
A flux may be added and dry-mixed. Firing temperature is 700 ~
The temperature is 950 ° C, preferably 800 to 930 ° C. If the temperature is too low, crystallization does not proceed and the saturation magnetization decreases. If the temperature is too high, the particles become large and sintering occurs, which is not preferable. The firing time is suitably about 10 minutes to 30 hours.

The composite ferrite magnetic powder of the present invention is characterized in that the surface of the ferrite fine particles has a general formula a (M'O) .Fe ₂ O ₃ (where M 'is Co, Ni, Zn, Cu, Mg, Mn and Fe A spinel ferrite layer represented by (II) is one or more metal elements and 0 <a ≦ 1.) The composite ferrite magnetic powder of the present invention is obtained by suspending the ferrite fine particles in water, and adding thereto a reducing agent, one or more metal ions selected from Co, Ni, Zn, Mg, Mn and Cu, and Fe ²⁺ . After adding the aqueous solution and the alkaline aqueous solution containing, and heating the resulting mixed suspension at 50 to 200 ° C. in a non-oxidizing atmosphere,
Wash, filter, then 100-5 in non-oxidizing atmosphere
It is obtained by heat treatment at 00 ° C.

To form the spinel ferrite layer, first, ferrite fine particles are sufficiently dispersed in water to prepare a suspension solution, a reducing agent is added thereto in a non-oxidizing atmosphere, and An aqueous solution is added, and then an aqueous alkali solution is added to cause the hydroxide to adhere to the surface of the fine particles. Alternatively, the order of adding the aqueous solution of metal ions and the aqueous alkali solution may be reversed. The molar ratio of one or more metal ions selected from Co, Ni, Zn, Mg, Mn and Cu to Fe ²⁺ is preferably from 1: 2 to 20, particularly preferably from 1: 3 to 12. As the reducing agent, aldehydes, hydroquinone, hydrazine,
An organic reducing agent such as formic acid or an inorganic reducing agent such as H ₂ or CO is used. Next, the obtained mixed suspension is heated at 50 to 200 ° C. in a non-oxidizing atmosphere.

By the heat treatment, a spinel ferrite layer is formed on the surface of the fine particles. Heat treatment is 50-200 ° C
In particular, by performing at a low temperature of 50 to 120 ° C., the orientation of the obtained particles in the coating film is improved,
The squareness ratio is improved. Insufficient heat treatment reduces the amount of spinel ferrite produced, while excessive heat treatment does not improve the properties. The proportion of the spinel ferrite layer is 5 to 30% by weight, preferably 10 to 20% by weight, based on the ferrite fine particles. If it is less than this range, the saturation magnetization is high, the temperature change of the coercive force is small, and the electric resistance of the powder is not small, and if it is more than this range, the orientation of the particles becomes poor, Perpendicular magnetic anisotropy deteriorates.

In the present invention, the spinel ferrite layer may partially contain an oxide of a metal element constituting the spinel ferrite. Next, the obtained powder is placed in a non-oxidizing atmosphere at 100 to 500 ° C., preferably 1 to 500 ° C.
Heat treatment at 50 to 400 ° C. The non-oxidizing atmosphere is preferably an inert gas such as nitrogen or helium, or a vacuum. In the present invention, by using the ferrite fine particles represented by the above general formula, a spinel ferrite layer is formed on the surface of the ferrite fine particles with three-dimensional regularity. As a result, a composite ferrite magnetic powder having a high saturation magnetization, a small change in coercive force with temperature, a small electric resistance, and an excellent orientation can be obtained. In addition, it is possible to prevent the deterioration of various characteristics over time.

[0014]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. Example 1 2.519 mol of ferric chloride, 0.061 mol of antimony trichloride, 0.061 mol of cobalt chloride, 0.061 mol of nickel chloride, 0.123 mol of titanium tetrachloride and 0.123 mol of zinc chloride were added to 1800 ml of deionized water.
Separately, 0.368 mol of barium hydroxide and 36 mol of caustic soda were dissolved in 2000 ml of deionized water, and the two solutions were mixed to form a precipitate. The resulting slurry containing the precipitate was placed in an autoclave and subjected to a hydrothermal treatment at 140 ° C. for 6 hours. Then, the obtained precipitate was sufficiently washed with water, and then, in the slurry, 0.061 mol of cobalt chloride and 0.1 ml of zinc chloride in 200 ml of water.
After a solution in which 22 mol and 0.549 mol of ferrous chloride were dissolved was added and mixed well, a solution in which 1.7 mol of sodium hydroxide was dissolved in 300 ml of water was added, and the mixture was aged at 80 ° C. Next, the obtained precipitate is sufficiently washed with water, filtered and dried, and a mixture of NaCl and BaCl ₂ .2H ₂ O at a weight ratio of 1: 1 as a flux is added to the precipitate in an amount of 100% by weight. % And mixed. The mixture was calcined at 860 ° C. for 2 hours under a nitrogen atmosphere. The obtained fired product was sufficiently washed with water, filtered and dried to obtain a ferrite magnetic powder.

As a result of composition analysis, the obtained ferrite magnetic powder was found to be BaO.1.6 (Fe _10.0 Sb _0.2 Co _0.4 Ni _0.2 Zn _0.8 Ti _0.4 O _17.5 ). The ferrite magnetic powder had a particle size of 0.046 μm, a plate ratio of 6.8, a coercive force of 540 Oe, a saturation magnetization of 64.4 emu / g, and a temperature change of coercive force of 0.2 Oe / ° C. The electric resistance of the powder compact was 1.2 × 10 ⁷ Ω · cm. 100 g of this ferrite magnetic powder was suspended in 1000 ml of water, and 0.0189 mol of hydrazine was added thereto.
After adding a solution obtained by dissolving 0.027 mol of cobalt chloride and 0.162 mol of ferrous chloride in 00 ml and mixing well,
A solution prepared by dissolving 1.7 mol in 300 ml of water was added, and the mixture was aged in a nitrogen atmosphere at 120 ° C. to form a spinel ferrite layer at 15% by weight on the surface of the ferrite fine particles. Next, the obtained slurry was washed and filtered, and the powder was dried at 400 ° C. for 1 hour in a nitrogen atmosphere.
Heat treated for hours. The properties of the obtained composite ferrite magnetic powder were as follows: coercive force 760 Oe Saturation magnetization 68.4 emu / g Temperature change of coercive force -0.7 Oe / ° C Electric resistance of the powder compact was 1.4 × 10 ⁴ Ω · cm.

Example 2 2.639 mol of ferric chloride, 0.061 mol of antimony trichloride, 0.061 mol of cobalt chloride, 0.061 mol of nickel chloride, 0.061 mol of titanium tetrachloride and 0.061 mol of zinc chloride were added to 1800 ml of deionized water.
Separately, 0.368 mol of barium hydroxide and 36 mol of caustic soda were dissolved in 2000 ml of deionized water, and both solutions were mixed to form a precipitate. The resulting slurry containing the precipitate was placed in an autoclave and subjected to a hydrothermal treatment at 140 ° C. for 6 hours. Next, the obtained precipitate was sufficiently washed with water, and then, in the slurry, 0.061 mol of cobalt chloride, 200 ml of water and zinc chloride were added.
After a solution in which 0.123 mol of ferrous chloride and 0.552 mol of ferrous chloride were dissolved was added and mixed well, a solution in which 1.7 mol of sodium hydroxide was dissolved in 300 ml of water was added, and the mixture was aged at 80 ° C. Next, the obtained precipitate is sufficiently washed with water, filtered and dried, and a mixture of NaCl and BaCl ₂ .2H ₂ O at a weight ratio of 1: 1 as a flux is added to the precipitate in an amount of 100% by weight. % And mixed. The mixture was calcined at 870 ° C. for 2 hours under a nitrogen atmosphere. The obtained fired product was sufficiently washed with water, filtered and dried to obtain a ferrite magnetic powder.

As a result of composition analysis, the obtained ferrite magnetic powder was BaO.2.0 (Fe _10.4 Sb _0.2 Co _0.4 Ni _0.2 Zn _0.6 Ti _0.2 O _17.5 ). The characteristics of the ferrite magnetic powder are as follows: particle diameter 0.045 μm plate ratio 6.9 coercive force 530 Oe saturation magnetization 63.3 emu / g temperature change of coercive force 0.3 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω · cm. Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of the ferrite fine particles in the same manner as in Example 1. The properties of the obtained composite ferrite magnetic powder were as follows: the coercive force was 770 Oe, the saturation magnetization was 68.1 emu / g, and the temperature change of the coercive force was -0.6 Oe / ° C. The electric resistance of the powder compact was 1.1 × 10 ⁴ Ω · cm.

Comparative Example 1 3.129 mol of ferric nitrate, 0.123 mol of cobalt nitrate, 0.061 mol of nickel nitrate, 0.123 mol of titanium tetrachloride and 0.24 mol of zinc nitrate
5 mol was dissolved in 1800 ml of deionized water, and separately, 0.460 mol of barium hydroxide and 37 mol of caustic soda were added to 2000 m of deionized water.
and mixed both solutions to form a precipitate. The slurry containing the obtained precipitate was placed in an autoclave, and 14
Hydrothermal treatment was performed at 0 ° C. for 6 hours. Next, the obtained precipitate is sufficiently washed with water, filtered, dried, and then used as a flux.
A mixture having a weight ratio of 1: 1 between NaCl and BaCl ₂ .2H ₂ O was added to 100% by weight of the precipitate and mixed. The mixture was calcined at 860 ° C. for 2 hours under a nitrogen atmosphere. The obtained fired product was sufficiently washed with water, filtered and dried to obtain a ferrite magnetic powder.

As a result of composition analysis, the obtained ferrite magnetic powder was found to be BaO · 0.99 (Fe _10.2 Co _0.4 Ni _0.2 Zn _0.8 Ti _0.4 O _17.5 ). The characteristics of the ferrite magnetic powder are as follows: particle size 0.061 μm plate ratio 7.7 coercive force 560 Oe saturation magnetization 60.2 emu / g temperature change of coercive force 2.3 Oe / ° C Electric resistance of powder compact 1.8 × 10 ⁷ Ω · cm. Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1 except that no reducing agent was added. The characteristics of the obtained composite ferrite magnetic powder were as follows: coercive force 650 Oe Saturation magnetization 62.3 emu / g Temperature change of coercive force 1.6 Oe / ° C Electric resistance of the powder compact was 5.6 × 10 ⁶ Ω · cm.

Comparative Example 2 3.252 mol of ferric nitrate, 0.123 mol of cobalt nitrate, 0.061 mol of nickel nitrate, 0.061 mol of titanium tetrachloride and 0.18 mol of zinc nitrate
4 mol are dissolved in 1800 ml of deionized water, and separately 0.460 mol of barium hydroxide and 37 mol of caustic soda are added to 200 ml of deionized water.
0 ml and both solutions were mixed to form a precipitate.
Put the slurry containing the obtained precipitate in an autoclave,
Hydrothermal treatment was performed at 140 ° C. for 6 hours. Next, the obtained precipitate is sufficiently washed with water, filtered and dried, and a mixture of NaCl and BaCl ₂ .2H ₂ O at a weight ratio of 1: 1 as a flux is added to the precipitate in an amount of 100% by weight. % And mixed. The mixture was calcined at 870 ° C. for 2 hours under a nitrogen atmosphere. The obtained fired product was sufficiently washed with water, filtered and dried to obtain a ferrite magnetic powder.

As a result of composition analysis, the obtained ferrite magnetic powder was found to be BaO · 1.0 (Fe _10.6 Co _0.4 Ni _0.2 Zn _0.6 Ti _0.2 O _17.5 ). The characteristics of the obtained ferrite magnetic powder are as follows: particle diameter 0.066 μm plate ratio 7.8 coercive force 540 Oe saturation magnetization 60.1 emu / g temperature change of coercive force 2.4 Oe / ° C Electric resistance of powder compact 1.9 × 10 ⁷ Ω · cm 2. Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1 except that no reducing agent was added. The characteristics of the obtained composite ferrite magnetic powder were as follows: coercive force 660 Oe Saturation magnetization 61.8 emu / g Temperature change of coercive force 1.7 Oe / ° C Electric resistance of the powder compact was 6.9 × 10 ⁶ Ω · cm.

[0022]

The composite ferrite magnetic powder obtained by the present invention has a significantly improved saturation magnetization as compared with the conventional one, a small change in coercive force with temperature, a small electric resistance of the powder, and Since the particle diameter is 50 nm or less and the plate ratio is 5 or more, it is suitably used as a magnetic recording material for high-density recording.

Claims (2)

(57) [Claims] [Claim 1] The general formula AOn · (Fe _12-xy Sb _x M
_y O _18-z ) (where A represents one or more elements selected from Ba, Sr, Ca and Pb, and M represents Co, Ni, Zn, Cu, Mg, Mn, Fe (II), Si ,
Represents one or more elements selected from Ti, Zr, Sn, Ta, Nb, Mo, V and W, n = 1.2 to 3.0, x = 0.01 to 0.6, y = 0.1 to 4.
0, 0 <z <2. ) Is suspended in water, and a reducing agent, Co, Ni, Zn, M
One or more metal ions selected from g, Mn and Cu and Fe ²⁺
And an aqueous alkali solution is added, and the resulting mixed suspension is subjected to a heat treatment at 50 to 200 ° C. in a non-oxidizing atmosphere, followed by washing and filtration, and then 100 to 500 in a non-oxidizing atmosphere. A ferrite fine particle surface represented by the above general formula characterized by heat treatment at
(M′O) · Fe ₂ O ₃ (where M ′ is one or more metal elements selected from Co, Ni, Zn, Cu, Mg, Mn and Fe (II), and 0 <
a ≦ 1. A method for producing a composite ferrite magnetic powder in which a spinel ferrite layer represented by () is formed. 2. The method for producing a composite ferrite magnetic powder according to claim 1, wherein the particle diameter of the ferrite magnetic powder is 50 nm or less and the plate ratio is 5 or more.