JPH0647467B2 - Barium ferrite magnetic powder and method for producing the same - Google Patents

Description

The present invention relates to a hexagonal plate-shaped magnetoplumbite-type barium ferrite magnetic powder and a method for producing the same.

More specifically, the present invention is suitable for use in a magnetic recording medium for high density recording, has a specific surface area of 20 to 70 m ² / g, a coercive force of 200 to 1500 Oe, and a saturation magnetization of a conventional hydrothermal synthesis method. The present invention relates to a magnetoplumbite-type barium ferrite magnetic powder which is dramatically improved as compared with the magnetic powder obtained by the above method and a method for producing the same.

In recent years, along with the demand for higher density of magnetic recording, development of a perpendicular magnetic recording system using barium ferrite magnetic powder as a magnetic recording medium has been advanced.

The barium ferrite magnetic powder used in the perpendicular magnetic recording system has an appropriate coercive force (200 to 1500 Oe).
), The saturation magnetization is as high as possible, the magnetic properties of each particle are uniform, the particles are small and uniform, and there is no aggregation or sintering of particles, and there is a demand for good dispersibility.

In particular, barium ferrite magnetic powder has a low saturation magnetization as compared with other magnetic powders for recording media, and therefore fine particles having a saturation magnetization as high as possible are desired.

(Prior Art) Conventionally, as a method for producing barium ferrite magnetic powder,
For example, various methods such as a coprecipitation method, a glass crystallization method and a hydrothermal synthesis method are known.
-15574, the hydrothermal synthesis method is described in, for example, JP-A-5959.
-175707, JP60-12973, JP60-155
No. 76, JP-A-60-137002, etc.

Said portion of Co conventional methods Fe atoms neither barium ferrite magnetic powder produced is represented by the following formula Ba O · n Fe ₂ O ₃ at, Ti, Ni, Mn, Cu , Zn, In, Ge, A metal element such as Nb or Zr, or a combination thereof is used, and the substitution is performed so that the total valence of the substitution atoms becomes equal to that of the Fe atom to be substituted.

Further, in Japanese Patent Laid-Open No. 61-236104, Fe atoms are Al and C.
It is disclosed that the saturation magnetization is improved by substituting one or more atoms selected from d and Zn.

(Problems to be Solved by the Invention) The barium ferrite magnetic powder obtained by the hydrothermal synthesis method generally has less aggregation of particles and relatively good dispersibility,
Although they were fine particles, only those having a saturation magnetization of about 55 emu / g or lower were obtained. This is because when the surface area of the barium ferrite magnetic powder is 20 m ² / g or more, especially when it is 50 m ² / g in the case of ultrafine magnetic powder, the non-magnetic layer part on the particle surface cannot be ignored, and for coercive force adjustment. It is thought to be due to various metallic elements added.

The barium ferrite magnetic powder described in JP-A-61-236104 is obtained by a glass crystallization method, and the specification of the publication specifically describes the effect of Zn alone. Moreover, there is no description about the crystal structure, particle size, specific surface area, coercive force and control of coercive force of barium ferrite magnetic powder.

(Object of the Invention) The object of the present invention is to solve the above problems in the hydrothermal synthesis method, to have a high saturation magnetization, and to have a specific surface area of 20 as fine particles.
A barium ferrite magnetic powder having a coercive force of about 70 m ² / g and a coercive force of 200 to 1500 Oe and suitable for use in a magnetic recording medium for high density recording, and a method for producing the same.

(Means for Solving the Problems) As a result of earnest studies, the present inventors have found that when a part of Fe atoms in barium ferrite magnetic powder is replaced by Zn atoms alone, almost no effect is obtained. It has been found that the saturation magnetization is significantly improved by substituting a specific combination of -Zn.

That is, according to the present invention, the general formula Ba O.n (Fe _12-xy Co _x Zn _y O _{18- (x + y) / 2} ) (where n = 0.8 to 1.0 and x = 0.1 ~ 1.5,
It is a numerical value of y = 0.1 to 1.5. ) Related to hexagonal plate magnetoplumbite type barium ferrite magnetic powder and a method for producing the same.

In the present invention, as a starting material, 1 to 12 gram atoms of barium and 1 to 12 gram atoms of iron, 12 to xy gram atoms of iron, x gram atoms of cobalt and y to zinc are used.
Using the compounds of the respective elements in the proportion of gram atom, the starting materials are dissolved in water, and alkali hydroxide is added to the solution so that the concentration of the alkali hydroxide in the solution after mixing is 3 mol / or more, and precipitation is performed. A precipitate is formed, and the slurry containing the precipitate is hydrothermally treated at 130 to 300 ° C., a flux is mixed with the formed precipitate, and the mixture is calcined at 700 to 950 ° C.
The hexagonal plate-shaped magnetoplumbite-type barium ferrite magnetic powder is obtained by washing the obtained fired product.

In the present invention, first, starting materials barium, iron,
Dissolve the cobalt and zinc compounds in water,
Alkali hydroxide is added to this to form a precipitate.

As the barium compound, barium nitrate, barium chloride, barium hydroxide or the like is used. The amount of barium used is preferably such that the barium concentration is in the range of 0.03 to 0.50 mol / mol in order to obtain particles having a good hexagonal plate shape.

As the iron compound, ferric nitrate, ferric chloride or the like is used. The amount of iron used is 1 to 1 g atom of barium.
It is 12 grams atom. When the amount of iron is too small, the amount of magnetoplumbite-type barium ferrite produced is small and the shape is not hexagonal. Further, if the amount of iron is too large, hematite is by-produced, and the barium ferrite particles become large, resulting in poor magnetic properties.

As the cobalt compound, its chloride, nitrate or the like is used. It is preferable that the amount of cobalt used be x gram atom (x = 0.1 to 1.5) with respect to 12-xy gram atom of iron, and the magnetic property, The coercive force can be controlled.

As the zinc compound, zinc chloride, zinc nitrate or the like is used. The amount of zinc used is y gram atom (y = 0.1 to 1.5, preferably 0.
5 to 1.0) is preferable. Co −
By substituting a part of Fe atoms with a specific combination of Zn, the saturation magnetization of the obtained barium ferrite magnetic powder is dramatically improved.

As the alkali hydroxide, sodium hydroxide, potassium hydroxide or the like is used. The amount of alkali hydroxide used should be such that the alkali hydroxide concentration in the solution after mixing the alkali hydroxide is 3 mol / or more, and is 4 to 8 mol /
Is preferred. If the amount of alkali hydroxide is too small, the particles become large, the particle size distribution becomes broad, and hematite is formed. Also, it is not economical to increase the amount of alkali hydroxide excessively.

The method of mixing the starting material aqueous solution with the alkali hydroxide is not particularly limited, and for example, there is a method of directly adding the alkaline hydroxide to the starting material aqueous solution or adding the aqueous solution of the alkali hydroxide. . Alternatively, there is a method in which a barium compound is added to the aqueous solution side of alkali hydroxide and this is mixed with an aqueous solution containing iron.

Further, a water-soluble compound such as Si and Ca, for example, silicic acid, sodium silicate, calcium nitrate, calcium chloride and the like can be added to the starting material aqueous solution or the alkali hydroxide aqueous solution in advance. These additives are preferable in controlling the particle shape.

Next, by hydrothermally treating the slurry containing the precipitate,
Fine crystals of barium ferrite are formed and precipitated. The temperature of hydrothermal treatment is 130 to 300 ° C., preferably 140 to
280 ° C. If the temperature is too low, the formation of crystals will not be sufficient, and if the temperature is too high, the particle size of the barium ferrite powder finally obtained will be large, such being undesirable.
The hydrothermal treatment time is usually about 0.5 to 20 hours, and an autoclave is usually adopted for the hydrothermal treatment.

Next, the precipitate of fine crystals produced by the hydrothermal treatment is washed with water to remove free alkali components, and then the resulting precipitate is mixed with a flux. As the flux, at least one of sodium chloride, potassium chloride, barium chloride, strontium chloride and sodium fluoride is used. The amount of flux used is based on the precipitate (dry matter basis)
10 to 180% by weight, preferably 30 to 120% by weight are suitable. If the amount of the flux is too small, the particles will sinter, and if the amount is too large, there will be no advantage due to the large amount and it is not economical. The method of mixing the precipitate and the flux is not particularly limited, and for example, the flux may be added to the slurry of the precipitate and wet-mixed, and then the slurry may be dried, or the precipitate may be dried and then the flux is added. You may dry-mix.

Then, the obtained mixture is fired to completely crystallize the barium ferrite. Firing temperature is 7
The temperature is from 00 to 950 ° C, preferably from 800 to 930 ° C.
If the temperature is too low, crystallization does not proceed and the saturation magnetization becomes low. On the other hand, if the temperature is too high, particles become large and sintering occurs, which is not preferable. A firing time of about 10 minutes to 30 hours is suitable. The firing atmosphere is not particularly limited, but an air atmosphere is generally convenient.

After washing the obtained baked product, by overdrying,
Barium ferrite magnetic powder is obtained. The washing may be performed by any method as long as impurities such as flux and excess barium in the fired product can be sufficiently removed. As the cleaning liquid, water, an inorganic acid such as nitric acid or hydrochloric acid, an organic acid such as acetic acid or propionic acid, or the like can be used.

(Examples) Hereinafter, the present invention will be described with reference to Examples.

Example 1 Deionized water 9.8, ferric nitrate _{[Fe (NO 3) 3 ·} 9
H ₂ O] 23.1 mol, cobalt nitrate [Co (NO ₃ ) ₂ ·
6H ₂ O] 1.78 mol and zinc nitrate [Zn (NO ₃ ) ₂
・ 6H ₂ O] 1.78 mol was dissolved and separately deionized water 1
3.5, barium hydroxide _{[Ba (OH) 2 · 8H} 2 O]
3.33 mol and caustic soda (NaOH) 263.
1 mol was dissolved and both solutions were mixed to form a precipitate.

The slurry containing the obtained precipitate was placed in an autoclave,
Hydrothermal treatment was performed at 200 ° C. for 5 hours. Then sufficiently washed with water and the resulting precipitate, over, dried, Na Cl and Ba Cl ₂ · 2H _{2 O} weight ratio of to as a flux is 1: 1
100% by weight of the mixture was added to the precipitate and mixed. The mixture was calcined under an air atmosphere at 860 ° C. for 2 hours. The obtained fired product was thoroughly washed with water, dried and dried to obtain barium ferrite magnetic powder.

The obtained barium ferrite magnetic powder was BaO.0.98 (Fe _10.4 Co _0.8 Zn _17.2 ) as a result of X-ray powder diffraction spectrum and composition analysis, and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

Example 2 In Example 1, ferric nitrate 23.6 was used as a starting material.
4 moles, cobalt nitrate 1.82 moles, zinc nitrate 1.82
Mol, barium hydroxide 2.73 mol and caustic soda 263.6 mol were used and barium ferrite magnetic powder was obtained in the same manner as in Example 1 except that the hydrothermal treatment was performed at 260 ° C. for 3 hours.

The obtained barium ferrite magnetic powder was BaO.0.99 (Fe _10.4 Co _0.8 Zn _0.8 O _17.2 ) as a result of X-ray powder diffraction spectrum and composition analysis, and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

Example 3 In Example 1, as a starting material, ferric nitrate 24.0 was used.
0 mol, cobalt nitrate 1.33 mol, zinc nitrate 1.33
Barium ferrite magnetic powder was obtained in the same manner as in Example 1 except that mol, barium hydroxide 2.73 mol and caustic soda 263.6 mol were used.

The obtained barium ferrite magnetic powder was BaO.0.98 (Fe _10.8 Co _0.6 Zn _0.6 O _17.4 ) as a result of X-ray powder diffraction spectrum and composition analysis, and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

Example 1 In Example 1, ferric nitrate 22.6 was used as a starting material.
7 mol, cobalt nitrate 2.00 mol, zinc nitrate 2.00
Barium ferrite magnetic powder was obtained in the same manner as in Example 1, except that mol, barium hydroxide 3.33 mol and caustic soda 262.7 mol were used.

As a result of X-ray powder diffraction spectrum and composition analysis, the obtained barium ferrite magnetic powder was Ba 2 O.0.98 (Fe _10.2 Co _0.9 Zn _0.9 O _17.1 ) and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

Example 5 In Example 1, as a starting material, ferric nitrate 23.3
3 mol, cobalt nitrate 1.56 mol, zinc nitrate 1.78
Barium ferrite magnetic powder was obtained in the same manner as in Example 1 except that mol, barium hydroxide 3.33 mol and caustic soda 263.3 mol were used.

The obtained barium ferrite magnetic powder was BaO.0.98 (Fe _10.5 Co _0.7 Zn _0.8 O _17.25 ) as a result of X-ray powder diffraction spectrum and composition analysis, and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

Example 6 In Example 1, as a starting material, ferric nitrate 22.8 was used.
9 mol, cobalt nitrate 2.00 mol, zinc nitrate 1.78
Barium ferrite magnetic powder was obtained in the same manner as in Example 1, except that mols, barium hydroxide 3.33 mols, and caustic soda 262.9 mols were used.

The obtained barium ferrite magnetic powder was Ba 2 O.0.98 (Fe _10.3 Co _0.9 Zn _0.8 O _17.15 ) as a result of X-ray powder diffraction spectrum and composition analysis, and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

Example 7 In Example 1, as a starting material, ferric nitrate 23.3
3 mol, cobalt nitrate 1.78 mol, zinc nitrate 1.56
Mol barium hydroxide 3.33 mol and caustic soda 263.3 mol were used, and the barium ferrite magnetic powder was obtained in the same manner as in Example 1 except that the hydrothermal treatment was performed at 140 ° C. for 10 hours.

The obtained barium ferrite magnetic powder was Ba 2 O.0.98 (Fe _10.5 Co _0.8 Zn _0.7 O _17.25 ) as a result of X-ray powder diffraction spectrum and composition analysis, and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

Example 8 In Example 1, as a starting material, ferric nitrate 22.8 was used.
9 mol, cobalt nitrate 1.78 mol, zinc nitrate 2.00
Barium ferrite magnetic powder was obtained in the same manner as in Example 1, except that mols, barium hydroxide 3.33 mols, and caustic soda 262.9 mols were used.

The obtained barium ferrite magnetic powder was BaO.0.98 (Fe _10.3 Co _0.8 Zn _0.9 O _17.15 ) as a result of X-ray powder diffraction spectrum and composition analysis, and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

Comparative Example 1 In Example 1, ferric nitrate 23.1 as a starting material
0 mol, cobalt nitrate 1.78 mol, titanium tetrachloride (T
i Cl ₄₎ 1.78 mol, but using barium hydroxide 3.33 mol and sodium hydroxide 266.7 moles, to give a barium ferrite magnetic powder in the same manner as in Example 1.

The obtained barium ferrite magnetic powder was BaO.0.98 (Fe _10.4 Co _0.8 Ti _0.8 O ₁₈ ) as a result of X-ray powder diffraction spectrum and composition analysis, and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

Comparative Example 2 In Example 1, as a starting material, ferric nitrate 24.0 was used.
0 mol, 1.33 mol of cobalt nitrate, titanium tetrachloride 1.
Barium ferrite magnetic powder was obtained in the same manner as in Example 1 except that 33 mol, 3.33 mol of barium hydroxide and 266.7 mol of caustic soda were used.

The obtained barium ferrite magnetic powder was BaO.0.98 (Fe _10.8 Co _0.6 Ti _0.6 O ₁₈ ) as a result of X-ray powder diffraction spectrum and composition analysis, and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

Comparative Example 3 In Example 1, as a starting material, ferric nitrate 22.6 was used.
7 mol, cobalt nitrate 2.00 mol, titanium tetrachloride 2.
Barium ferrite magnetic powder was obtained in the same manner as in Example 1 except that 00 mol, 3.33 mol of barium hydroxide and 266.7 mol of caustic soda were used.

The obtained barium ferrite magnetic powder was BaO.0.98 (Fe _10.2 Co _0.9 Ti _0.9 O ₁₈ ) as a result of X-ray powder diffraction spectrum and composition analysis, and was a magnetoplumbite type.

Table 1 shows the results of observing the shape of the barium ferrite magnetic powder with a transmission electron microscope (TEM) and the magnetic characteristics with a vibrating sample magnetometer.

According to the present invention (Effect of the Invention), the general formula _{Ba O · n (Fe 12-} xy Co x Zn y O 18- (x + y) / 2) ( however, n = 0.8 to 1.0, x = 0.1-1.5,
It is a numerical value of y = 0.1 to 1.5. The hexagonal plate-shaped magnetoplumbite type barium ferrite magnetic powder represented by) is obtained. As shown in the above general formula, this barium ferrite magnetic powder has the general formula B produced by the conventional hydrothermal synthesis method.
a part of Fe atoms represented by _{a O · nFe 2 O 3 Co} , Ti,
Substitution using a simple metal such as Ni, Mn, Cu, Zn, In, Ge, Nb, Zr, or a combination thereof so that the sum of the valences of the substituted atoms becomes equal to that of the Fe atom to be substituted. The composition is different from that of the barium ferrite magnetic powder. Furthermore, the magnetoplumbite-type barium ferrite magnetic powder obtained in the present invention has an average particle diameter of 100 nm.
Hereinafter, the powder has a sharp particle size distribution and a standard deviation of 30 nm or less. Further, by substituting a part of Fe atoms with a specific combination of Co-Zn, when the specific surface area by the BET method is about 30 m ² / g, the saturation magnetization is 65 emu / g or more and about 50 m ² / g. In addition, the saturation magnetization is 60 emu / g or more, which is dramatically improved as compared with that obtained by the conventional hydrothermal synthesis method. The plate ratio of the barium ferrite magnetic powder is in the range of 2-15. Further, the coercive force can be freely controlled by changing the amount of cobalt added.

Claims (2)

[Claims] 1. A general formula Ba O.n (Fe _12-xy Co _x Zn _y O _{18- (x + y) / 2} ) (where n = 0.8 to 1.0, x = 0.1 1.5,
It is a numerical value of y = 0.1 to 1.5. ) Hexagonal plate-shaped magnetoplumbite type barium ferrite magnetic powder represented by. 2. As a starting material, 1 to 12 gram atoms of iron to 1 gram atom of barium, x gram atoms of cobalt and y gram atoms of zinc to iron 12-xy gram atoms, respectively. The starting material is dissolved in water, and alkali hydroxide is added to this so that the concentration of alkali hydroxide in the solution after mixing is 3 mol / or more to form a precipitate, 13 slurries containing sediment
After hydrothermal treatment at 0 to 300 ° C., a flux is mixed with the produced precipitate, the mixture is calcined at 700 to 950 ° C., and the obtained calcined product is washed. (Fe _12-xy Co _x Zn _y O _{18- (x + y) / 2} ) (where n = 0.8 to 1.0, x = 0.1 to 1.5,
It is a numerical value of y = 0.1 to 1.5. ) A method for producing a hexagonal plate-shaped magnetoplumbite-type barium ferrite magnetic powder represented by.