JPH0649579B2 - Method for producing barium ferrite magnetic powder - Google Patents

Description

The present invention relates to a method for producing hexagonal magnetoplumbite-type barium ferrite magnetic powder.

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, a fine powder and a sharp particle size distribution. In addition, the present invention relates to a method for producing magnetoplumbite type barium ferrite magnetic powder in which coercive force changes little with temperature.

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 particle size distribution is sharp, and the change in coercive force with temperature is small.

(Prior art and its problems) 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.

However, the barium ferrite magnetic powder obtained by the conventional method has a problem that the coercive force changes greatly with temperature.

On the other hand, JP-A-60-122726, JP-A-61-174118, JP-A-61-219720, JP-A-61-295236, JP-A-62-51026, etc. Sn as a substitution element
A barium ferrite magnetic powder added with is disclosed. Although the change in coercive force with temperature was small, the particle size distribution could not be sharpened.

(Object of the Invention) The object of the present invention is to solve the above-mentioned problems, and is suitable for use in a magnetic recording medium for high-density recording, which is fine particles, has a sharp particle size distribution, and has a small change in coercive force with temperature. Another object of the present invention is to provide a method for producing hexagonal magnetoplumbite-type barium ferrite magnetic powder.

(Means for Solving Problems) General formula Ba O · n (Fe _12-xy M _x Sn _y O _{18 + α} ) (where M is Co, Ni, Zn, Cu, Ti, Zr, Nb, V, Mo represents one or more elements selected from W, and n = 0.9 to 1.
2, x and y are not 0, but x + y = 0.01 to 2.5,
The numerical value is −2 ≦ α ≦ 0. In producing the hexagonal magnetoplumbite type barium ferrite magnetic powder represented by the formula (1), one or more fine powders selected from iron hydroxide, hydrous iron oxide and iron oxide, and Ba, Sn and M are used as starting materials. Using the compound of 1), an alkali hydroxide is added to an aqueous solution containing the starting material so that the concentration of the alkali hydroxide in the solution after mixing is 1 mol / or more, and a precipitate is formed,
After aging the slurry containing the precipitate at 50 to 80 ° C., the resulting precipitate is mixed with a flux, and the mixture is mixed at 500 to 950.
The present invention relates to a method for producing a hexagonal magnetoplumbite-type barium ferrite magnetic powder, which comprises firing at 0 ° C. and washing the obtained fired product.

In the present invention, first, one or more fine powders selected from iron hydroxide, hydrous iron oxide and iron oxide as a starting material, and B
The compounds a, Sn and M are dissolved or suspended in water and / or alcohol, and alkali hydroxide is added thereto to form a precipitate.

As the iron raw material, one or more fine powders selected from iron hydroxide, hydrous iron oxide and iron oxide are used. Particularly, fine particles having a specific surface area of 50 m ² / g or more are preferable. The amount of iron used is preferably a concentration of 1 to 10% by weight. Concentration is 1% by weight
When the amount is less, the amount of magnetoplumbite-type barium ferrite produced is small and the crystallinity is poor. On the other hand, if it is more than 10% by weight, the particles of barium ferrite will become large and the magnetic properties will deteriorate, which is not preferable.

The compounds of Ba include barium nitrate, barium chloride,
Barium hydroxide or the like is used. The amount of Ba used is preferably in the range of 0.03 to 0.50 mol / mol in order to obtain hexagonal crystal grains having good crystallinity.

As the Sn compound, tin chloride, tin nitrate, sodium stannate, or the like is used.

Examples of the compound of M include Co, Ni, Zn, Cu, Ti, Zr, Nb,
One or more compounds selected from chlorides of V, Mo and W, nitrates, ammonium salts, alkoxides and the like are used.

The amount of substitutional elements added is such that Sn is x gram atom, M is y gram atom, and x + y = 0.1 to 2.5 with respect to iron 12-xy gram atom. If the added amount is out of the above range, the coercive force is too high and the axis of easy magnetization deviates from the C axis, which is not preferable.

In addition, it is not always necessary to compensate the valence as long as the hexagonal crystal structure is maintained.

As the alkali hydroxide, sodium hydroxide, potassium hydroxide or the like is used. The amount of the alkali hydroxide used is such that the alkali hydroxide concentration in the solution after mixing the alkali hydroxide is 1 mol / or more, and 3 to 8 mol /
Is preferred. If the amount of alkali hydroxide is too small, the particles become large and the particle size distribution becomes broad. 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. .

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

Then, the slurry containing the precipitate is aged at 50 to 80 ° C., whereby fine crystals of barium ferrite are produced and precipitated. The aging time is preferably 1 hour or longer, particularly preferably 10 hours or longer. If the temperature is too low or the time is too short, the formation of crystals is not sufficient, and if the temperature is too high, the average particle size of the obtained magnetic powder becomes large and the particle size distribution becomes broad. Therefore, the recording medium using such magnetic powder is not preferable because the noise level becomes high and the recording density becomes low.

Then, the precipitate of fine crystals produced by the aging treatment is washed with water to remove free alkali components or neutralized with hydrochloric acid, 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 the flux used is appropriately 10 to 180% by weight, preferably 30 to 120% by weight, based on the deposit (dry matter basis). 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 increasing the amount, which 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.
Alternatively, the precipitate may be dried, and then the flux may be added and dry-mixed. Then, the obtained mixture is fired to completely crystallize the barium ferrite. The firing temperature is preferably 500 to 950 ° C. Especially 550-7
A two-stage firing method at 00 ° C and 800 to 930 ° C is preferable. 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. Firing time is 10 minutes to 30
Time is appropriate. 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 it can sufficiently remove impurities such as flux and excess barium in the fired product. 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 Example 1 Water 1000ml cobalt nitrate _{[Co (NO 3) 2 ·} 6H 2
O] 22.4 g, zinc nitrate _{[Zn (NO 3) 2 ·} 6H 2 O]
5.7 g, tin chloride [Sn Cl _4] 30.0g and nickel nitrate _{[Ni (NO 3) 2 ·} 6H 2 O] was dissolved 22.4 g, this specific surface area 150 meters ² / g iron hydroxide [Fe
(OH) ₃ ] 214g was added and stirred vigorously. Separately water 10
Barium hydroxide [Ba (OH) ₂ .8H ₂ O] to 00 ml
40 g, caustic soda (NaOH) 480 g are dissolved,
Both solutions were mixed to form a precipitate.

The slurry containing this precipitate was aged at 80 ° C. for 20 hours.
Then, the obtained precipitate was thoroughly washed with water, dried and dried with Na Cl and Ba Cl ₂ .2H ₂ O as fluxing agents.
The mixture having a weight ratio of 1: 1 was added to 100% by weight of the precipitate and mixed. 650 this mixture under air atmosphere
After firing at ℃ for 2 hours, it was further fired at 870 ℃ for 1 hour. The obtained product was thoroughly washed with water, dried and dried to obtain barium ferrite magnetic powder.

The obtained barium ferrite magnetic powder was analyzed by X-ray powder diffraction spectrum and composition analysis, and was found to be BaO.1.02 (Fe _10.4 Co _0.4 Ni _0.4 Zn _0.2 Sn _0.6 O
_17.8 ) and was a magneto-plybite type.

Table 2 shows the results of measuring the magnetic properties of the barium ferrite magnetic powder with a vibrating sample magnetometer and observing the particle shape with a transmission electron microscope. The temperature change of the holding power was measured at 20 ° C to 100 ° C.

Examples 2 to 6 According to Example 1, barium ferrite magnetic powders having the compositions shown in Table 1 were obtained.

Table 2 shows the results of measuring the magnetic properties and observing the particle shape of the obtained barium ferrite magnetic powder in the same manner as in Example 1.

Comparative Example 1 Barium ferrite magnetic powder was obtained in the same manner as in Example 1 except that aging was not performed in Example 1.

Table 2 shows the results of measuring the magnetic properties and observing the particle shape of the barium ferrite magnetic powder in the same manner as in Example 1.

Comparative Example 2 Barium ferrite magnetic powder was obtained in the same manner as in Example 1, except that hydrothermal treatment was performed at 200 ° C. for 3 hours instead of performing aging in Example 1.

Table 2 shows the results of measuring the magnetic properties and observing the particle shape of the barium ferrite magnetic powder in the same manner as in Example 1.

Claims (1)

[Claims] 1. A general formula Ba O.n (Fe _12-xy M _x Sn _y O
_{18 + α} ) (where M is Co, Ni, Zn, Cu, Ti, Zr, Nb,
Indicates one or more elements selected from V, Mo, W, and n =
0.9 to 1.2, x and y are not 0, and x + y = 0.0
The numerical values are 1 to 2.5 and −2 ≦ α ≦ 0. In producing the hexagonal magnetoplumbite-type barium ferrite magnetic powder represented by), as a starting material, one or more fine powders selected from iron hydroxide, hydrous iron oxide and iron oxide,
Using compounds of Ba, Sn and M, an alkali hydroxide is added to an aqueous solution containing the starting materials so that the concentration of the alkali hydroxide in the solution after mixing is 1 mol / or more to form a precipitate. The slurry containing the precipitate was aged at 50 to 80 ° C., and then the resulting precipitate was mixed with a flux, and the mixture was mixed with 5
A method for producing a hexagonal magnetoplumbite-type barium ferrite magnetic powder, which comprises firing at 00 to 950 ° C. and washing the obtained fired product.