JP2883962B2 - Method for producing acicular goethite particle powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing acicular goethite particles used as a starting material when producing magnetic particles for magnetic recording. An object is to obtain acicular goethite particles which are uniform, do not contain dendritic particles, have a large axial ratio (major axis diameter / minor axis diameter), and have high crystallinity.

[Conventional technology]

In recent years, as the size and weight of magnetic recording / reproducing devices have been reduced, the need for higher performance for recording media such as magnetic tapes and magnetic disks has been increasing.

That is, high recording density, high sensitivity characteristics, high output characteristics, and the like are required.

The characteristics of the magnetic material particles required to satisfy the above requirements for the magnetic recording medium are to have high coercive force and excellent dispersibility.

That is, in order to increase the sensitivity and the output of the magnetic recording medium, it is necessary that the magnetic particle powder has a coercive force as high as possible. Technology and Technology for Highly Dispersing Magnetic Powder "
(1982), p. 310, “Improvement of magnetic tape performance was due to high sensitivity and high output.
_The emphasis was on increasing the coercive force of the ₂ O ₃ particles. Is clear from the description.

In addition, for the high recording density of magnetic recording media, the conditions for high-density recording on coated tapes on page 312 of “Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Particles,” On the other hand, high output characteristics can be maintained with low noise, but for this purpose, both the coercive force Hc and the residual magnetization Br must be large and the thickness of the coating film must be thinner. " As described above, it is necessary that the magnetic recording medium has a high coercive force and a large residual magnetization Br. In order for a magnetic recording medium to have a high coercive force, it is required that the magnetic particles used have as high a coercive force as possible.

As is well known, the magnitude of the coercive force of the magnetic particle powder depends on one of shape anisotropy, crystal anisotropy, strain anisotropy, and exchange anisotropy, or their interaction.

The residual magnetic flux density Br of the magnetic recording medium depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property. In order to improve these characteristics, disperse in the vehicle. It is required that the magnetic particles have a uniform particle size, do not contain dendritic particles, and have a large axial ratio (major axis diameter / minor axis diameter).

At present, acicular magnetite particle powder used as magnetic particle powder for magnetic recording, or acicular maghemite particle powder, utilizing anisotropy derived from its shape,
That is, a relatively high coercive force is obtained by increasing the axial ratio (major axis diameter / minor axis diameter).

These known acicular magnetite particle powders, or acicular maghemite particle powders, goethite particles as a starting material or hematite particles obtained by heating and dehydrating the goethite particles, 300 to 400 ° C. in a reducing gas such as hydrogen. To give magnetite particles, or this is then
It is obtained by oxidizing at 0 to 300 ° C to form maghemite particles.

As described above, magnetic particle powders having a uniform particle size, no mixture of dendritic particles, and a high axial ratio (major axis diameter / minor axis diameter) are currently the most demanded, In order to obtain magnetic particle powders having various characteristics, the starting material, goethite particle powder, has a uniform particle size,
Dendritic particles are not mixed, and the axial ratio (major axis diameter / minor axis diameter)
Needs to be large.

Further, the shape and distribution of the goethite particles as the starting material or the hematite particles obtained by heating and dehydrating the goethite particles are effectively retained and inherited in a heat treatment step such as a subsequent reduction step without impairing as much as possible. In addition, the degree of crystallinity is increased, and in order to obtain a magnetic particle powder having a high coercive force due to the substantially high density, the degree of crystallinity of the goethite particles or hematite particles as the starting material can be increased. Only high density is strongly required.

This fact is based on the fact that, in order to improve the coercive force of acicular maghemite particles, it is necessary to retain and inherit acicular crystals of acicular goethite particles and to improve the product maghemite. It is necessary to increase the degree of crystallinity of the particles. ”,“ ‥‥ To obtain high-density needle-like magnetic iron oxide particles, ‥‥ prior to heat reduction ‥‥ It is important to obtain substantially high-density acicular hematite particles. ”And“ The physical change of single-particle growth prior to the heat-reduction process by the conventional method is sufficiently generated. ‥
‥ Speaking of the produced particles, there is no adverse effect on the particle morphology such as sintering and deformation between the particles and the particles. ".

Conventionally, as a method for producing goethite particle powder as a starting material, a suspension containing ferrous hydroxide obtained by adding an equivalent amount or more of an aqueous alkali hydroxide solution to an aqueous ferrous salt solution at pH 11 or higher is used. A method of producing needle-like goethite particles by performing an oxidation reaction by passing an oxygen-containing gas at a temperature of not more than ℃, and reacting an aqueous ferrous salt solution with an aqueous alkali carbonate solution or an aqueous alkali carbonate / alkali hydroxide solution. A method is known in which a suspension containing FeCO ₃ or a Fe-containing precipitate obtained as described above is subjected to an oxidation reaction by passing an oxygen-containing gas into the suspension, thereby producing spindle-shaped goethite particles.

Furthermore, the axial ratio of the spindle-shaped goethite particle powder produced by the above-described method (Japanese Patent Application Laid-Open Nos.
-21819, JP-A-61-174119, JP-A-63-2
No. 02137, JP-A-1-115827, JP-A-2-514
The method described in Japanese Patent Publication No. 29 is known.

[Problems to be solved by the invention]

Particle size is uniform, dendritic particles are not mixed,
Magnetic particle powders having a large axial ratio (major axis diameter / short axis diameter) and a high degree of crystallinity are currently the most demanded, but produce goethite particle powder as a starting material. According to the above-described method, needle-like goethite particles having a large axial ratio (major axis diameter / short axis diameter), especially 10 or more, are formed. For example, it is hard to say that the particles have a uniform particle size.

According to the method described above, spindle-shaped particles having a uniform particle size and containing no dendritic particles are produced, while the axial ratio (major axis diameter / minor axis diameter) is at most 7%. And it is difficult to produce particles having a large axial ratio (major axis diameter / minor axis diameter). In particular, this phenomenon tends to become more pronounced as the major axis diameter of the produced particles decreases. .

In the case of the above method, the particle size is uniform,
Dendritic particles are not mixed, and the axial ratio (major axis diameter / minor axis diameter)
Is large, but the degree of crystallinity is small as shown in a comparative example described later, and it is difficult to say that the density is high.

Therefore, the present invention provides a uniform particle size, dendritic particles are not mixed, the axial ratio (major axis diameter / minor axis diameter) is large,
Moreover, it is a technical problem to obtain goethite particles having high crystallinity.

[Means for solving the problem]

The technical problem can be achieved by the present invention as described below.

That is, the present invention generates goethite particles by passing an oxygen-containing gas into a suspension containing ferrous hydroxide having a pH of 11 or more obtained by reacting an aqueous ferrous salt solution and an alkaline aqueous solution. In this case, the axial ratio (major axis diameter / minor axis) as a seed crystal in any solution of the ferrous salt aqueous solution, the alkaline aqueous solution, and the suspension containing ferrous hydroxide before aerating the oxygen-containing gas. Spindle-shaped goethite particles having a diameter of 6 to 7 are present, and Si / Fe
Needle-like goethite particles having an axial ratio (major axis diameter / minor axis diameter) of 10 to 12 by adding 0.2 to 5.0 atomic% of a Si compound in terms of conversion and then growing the seed crystal by passing an oxygen-containing gas therethrough. Is a method for producing acicular goethite particle powder.

Next, conditions for implementing the method of the present invention will be described.

As the aqueous ferrous salt solution in the present invention, an aqueous ferrous sulfate solution, an aqueous ferrous chloride solution, or the like can be used.

Sodium hydroxide, potassium hydroxide and the like can be used as the alkaline aqueous solution in the present invention.

The spindle-shaped goethite particles used in the present invention can be obtained by the following method.

That is, the spindle-shaped goethite particles are FeCO obtained by reacting an aqueous ferrous salt solution with an aqueous alkali carbonate solution.
It can be obtained by oxidizing by passing an oxygen-containing gas through an aqueous solution containing ₃ . In this case, the axial ratio (major axis diameter / minor axis diameter) of the obtained spindle-shaped goethite particles is at most
It is about 6: 1 to 7: 1.

The abundance of the spindle-shaped goethite particles is 30 to 70% by weight based on the resulting acicular goethite particles.

When the content is less than 30% by weight, new nuclei of goethite particles are generated to generate dendritic particles, and the distribution of the generated goethite particles is deteriorated.

If the content exceeds 70% by weight, the growth reaction of spindle-shaped goethite particles as seed crystals does not sufficiently occur, and needle-like goethite particles having a large axial ratio (major axis diameter / minor axis diameter) cannot be obtained. .

The existence time of the spindle-shaped goethite particle powder may be any time before the start of the goethite growth reaction, and the suspension containing ferrous hydroxide solution before passing the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas. It may be present in any of the suspensions. Alternatively, a growth reaction may be performed by directly using a reaction mother liquor in which spindle-shaped goethite particle powder is generated, and adding an aqueous ferrous salt solution and an alkaline aqueous solution to the reaction mother liquor.

The pH during the growth reaction in the present invention is 11 or more.

When the pH is less than 11, the spindle-shaped goethite particles grow only in a similar shape, and the axial ratio (major axis diameter / minor axis diameter) is large, and needle-like goethite particles having high crystallinity can be obtained. Absent.

Water glass, sodium silicate, potassium silicate, colloidal silica and the like can be used as the Si compound in the present invention.

The addition amount of the Si compound is 0.2 to 5.0 in terms of Si / Fe with respect to the total iron.
Atomic%.

When the content is less than 0.2 atomic%, it is difficult to obtain acicular goethite particles having a high axial ratio (major axis diameter / minor axis diameter) and high crystallinity.

If the content exceeds 5.0 atomic%, the saturation magnetization value of the acicular magnetic particle powder obtained using the acicular goethite particles produced as a starting material is undesirably reduced.

The addition time of the Si compound may be any time before the growth reaction of the goethite particles starts, and may be any of a ferrous salt aqueous solution, an alkaline aqueous solution, and a suspension containing ferrous hydroxide before aeration with an oxygen-containing gas. May be present.

[Action]

First, the most important point in the present invention is to aerate an oxygen-containing gas into a suspension containing ferrous hydroxide having a pH of 11 or more obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution. In producing goethite particles, the axial ratio (length) of any one of the aqueous ferrous salt solution, the alkaline aqueous solution, and the suspension containing ferrous hydroxide before passing the oxygen-containing gas as a seed crystal. After the presence of goethite particles having a spindle shape with a shaft diameter / short axis diameter of 6 to 7 and addition of a 0.2 to 5.0 atomic% Si compound in terms of Si / Fe with respect to all iron, an oxygen-containing gas is added. When the seed crystal is grown by aeration, the grain size is uniform, dendritic particles are not mixed, the axial ratio (major axis diameter / minor axis diameter) is large, and the crystallinity is high. The axial ratio (major axis diameter / minor axis diameter), which is the density, is 10
This is the fact that ~ 12 acicular goethite particles are obtained.

Regarding this fact, the present inventor added the Si compound in the growth reaction of the present invention when the Si compound was not added in the growth reaction of the spindle-shaped goethite particle powder in the present invention, as shown in a comparative example described later. Only in the spindle-shaped goethite particle powder, which is a seed crystal without seeding
In any case where Si is contained, since the acicular goethite particle powder intended for the present invention cannot be obtained,
This is considered to be due to a synergistic effect between the growth reaction of spindle-shaped goethite particle powder having a spindle ratio (major axis diameter / short axis diameter) of 6 to 7 as a seed crystal and a Si compound.

Regarding the reason why acicular goethite particles having high crystallinity are obtained, the present inventor has shown a spindle shape having a large axial ratio (major axis diameter / minor axis diameter) obtained by the above-mentioned method. As shown in the electron micrograph (FIG. 8) of Comparative Example 4 below, goethite particles are spindle-shaped particles having a structure in which a large number of elongated primary particles are aggregated into a bundle, and the primary particles are oriented in the minor axis direction. While growing only in the long axis direction without growing, acicular goethite particles according to the present invention,
As shown in the electron micrographs of Examples 1 and 5 (FIGS. 4 and 5), it is considered that the primary particles of the spindle-shaped particles grow not only in the long axis direction but also in the short axis direction. ing.

Now, a description will be given of a part of many experimental examples conducted by the inventor as described below.

FIG. 1 shows the relationship between the BET specific surface area of the goethite particle powder and the bulk density.

FIG. 2 shows the relationship between the volume of the goethite particle powder and the crystallite size.

In FIGS. 1 and 2, the circles indicate goethite particles in the form of spindles having a large axial ratio (major axis diameter / minor axis diameter) obtained by the method described above, and the Δ marks indicate acicular goethite particles according to the present invention. It is a powder.

As shown in FIG. 1, the acicular goethite particle powder according to the present invention has a larger bulk density and a higher crystallinity for the same BET specific surface area than the spindle-shaped goethite particle powder obtained by the above method. Is high density.

Further, as shown in FIG. 2, the acicular goethite particle powder according to the present invention has the same volume as the spindle-shaped goethite particle powder obtained by the above-mentioned method, with respect to the same volume.
It can be seen that the crystallite size is large and the crystallinity is high.

Incidentally, as a method for producing goethite particles by growing spindle-shaped goethite particles as seed crystals, there are methods described in JP-A-61-72628 and JP-A-61-111925, In either case, the needle is a strip-shaped or rice-grained particle having an axial ratio (major axis diameter / minor axis diameter) of at most about 9 and a needle having a large axial ratio (major axis diameter / minor axis diameter) in the present invention. It is different from particle-shaped particles.

Further, a method of adding a Si compound in the method described above assuming that a Si compound is added in the reaction for forming goethite particles (Japanese Patent Publication No. 55-8461, Japanese Patent Publication No. 55-32652).
Japanese Patent Application Laid-Open No. 63-13941, Japanese Patent Publication No. 63-13941), and in any of these methods, the axial ratio (length) is increased with an increase in the amount of the Si compound added. The ratio (shaft diameter / short axis diameter) tends to be small, and the operation and effect are completely different from those of the Si compound of the present invention in which the axis ratio (long axis diameter / short axis diameter) is increased.

〔Example〕

Next, the present invention will be described with reference to Examples and Comparative Examples.

In addition, the major axis diameter and the axial ratio (major axis diameter / minor axis diameter) of the particles in the above experimental examples, the following examples, and comparative examples are all shown by the average value of the numerical values measured from the electron micrographs. The specific surface area was measured by the BET method, and the bulk density was measured by the method described in JIS K 5101.

The volume of the goethite particles was determined by calculation from the measured values of the long axis and the short axis, considering the shape of the particles as a rectangular parallelepiped.

The crystallite size is a value obtained by expressing the size of a crystal particle measured by the X-plug diffraction method by the diameter of the crystal particle in a direction perpendicular to the (010) crystal plane.
The value was calculated from the line profile of the diffraction plug on the surface using the following Scherrer equation.

Here, β = half value width of the true diffraction peak obtained by subtracting the mechanical width by the apparatus K = Scherrer constant (0.9) λ = wavelength of characteristic X-ray θ = diffraction angle Example 1 Sulfuric acid containing 0.50 mol / Fe ²⁺ The aqueous iron solution 25 was previously prepared in a 3.2-N NaOH aqueous solution 25 prepared in the reactor.
In addition, ferrous hydroxide particles were produced at pH 13.1 and a temperature of 40 ° C.

Spindle-shaped goethite particles having a major axis of 0.15 μm and an axial ratio (major axis diameter / minor axis diameter) of 6: 1 as shown in the electron micrograph (× 30000) of the aqueous solution containing ferrous hydroxide particles. 1113g
(Corresponds to 50% by weight based on the generated acicular goethite.)
And No.3 water glass (SiO ₂ 28.55% by weight) 26.3g (Si / Fe =
(Atomic ratio of 0.5 atomic%) was added, and the mixture was stirred and mixed. Then, at a temperature of 40 ° C., air at 150 rpm was passed for 2.0 hours to perform a growth reaction of the spindle-shaped goethite.

The end point of the oxidation reaction was determined by extracting a part of the reaction solution, adjusting the acidity to hydrochloric acid, and then using a red blood salt solution to determine the presence or absence of a Fe ²⁺ blue color reaction.

The produced particles were washed with water, separated, dried and pulverized by a conventional method. The obtained needle-like goethite particle powder has a major axis of 0.25 μm and an axial ratio (major axis diameter / minor axis diameter) of 11: 1 as shown in the electron micrograph (× 100,000) shown in FIG. No particles were mixed at all, and the particle size was uniform.

The specific surface area is 53.5 m ² / g, the bulk density is 0.57 g / cm ² ,
The particle volume was 1.3 × 10 ⁻⁴ μm ³ and the crystallite size was 225 °.

Examples 2 to 5, Comparative Examples 1 to 2 Types, abundance and timing of spindle-shaped goethite particles, concentration of ferrous salt aqueous solution, concentration of sodium hydroxide aqueous solution, presence or absence of Si compound, addition amount and addition A goethite growth reaction was performed in the same manner as in Example 1 except that the timing and the temperature in the goethite growth reaction were variously changed.

Table 1 shows the main production conditions at this time, and Table 2 shows the characteristics of the resulting goethite particles.

In addition, as a seed crystal in Comparative Example 2, Si
Spindle-shaped goethite particles containing 0.2 atomic% of Si in terms of / Fe were used.

Acicular goethite particle powder obtained in Examples 2 to 5,
As a result of observation with an electron microscope, no dendritic particles were present in any of the samples, and the particles were uniform in particle size.

FIG. 5 shows an electron micrograph (× 100,000) of the goethite particle powder obtained in Example 5.

The goethite particles obtained in Comparative Examples 1 and 2 were both strip-shaped as a result of observation with an electron microscope. Electron micrograph of the goethite particles obtained in Comparative Example 1 (× 30000)
Is shown in FIG.

Comparative Example 3 (corresponding to the method described above.) A ferrous sulfate aqueous solution 25 containing 0.60 mol / Fe ²⁺ was previously prepared in a 5.2-N NaOH aqueous solution 25 prepared in a reactor.
In addition, ferrous hydroxide particles were produced at pH 13.3 and a temperature of 45 ° C.

Air was passed through the aqueous solution containing the ferrous hydroxide particles at a temperature of 55 ° C. at 150 min / min for 12 hours to perform a goethite generation reaction.

The end point of the oxidation reaction was determined by extracting a part of the reaction solution, adjusting the acidity to hydrochloric acid, and then using a red blood salt solution to determine the presence or absence of a Fe ²⁺ blue color reaction.

The produced particles were washed with water, separated, dried and pulverized by a conventional method.

The obtained needle-like goethite particle powder had a major axis of 0.7 μm as is clear from the electron micrograph (× 20000) shown in FIG.
m, the axis ratio (major axis diameter / minor axis diameter) was 10: 1, and dendritic particles were mixed, and the particle size was uneven.

Comparative Example 4 (The above corresponds to the method described in JP-A-63-202137.) In a reaction vessel maintained in a non-oxidizing atmosphere by flowing N ₂ gas at a rate of 3.4 cm per second. 1.32 mol / Na ₂ C
O ₃ aqueous solution 580 and 13.5 mol / NaOH aqueous solution 20.0 (Na ₂
CO ₃ to correspond to 17.6%. ) (Na ₂ CO ₃ and NaO
The total amount of H corresponds to 1.5 equivalents to Fe. ), And then added an aqueous solution of ferrous 400 sulfuric acid containing Fe ²⁺ 1.5 mol /, mixed (Fe ²⁺ concentration corresponds to 0.6 mol /.), And the precipitate containing ferrous at temperature 45 ° C. Generated.

A suspension comprising a precipitate containing the ferrous, while continuing blowing N ₂ gas at a rate per second 3.4cm, temperature 45
After holding at 50 ° C. for 50 minutes, 4.5 cm / sec air per second at a temperature of 47 ° C. was introduced into the suspension comprising the ferrous precipitate.
It was aerated for 5.5 hours to produce tan precipitated particles. The pH during air ventilation was 8.5 to 10.0.

The yellow-brown precipitate particles are separated, washed with water, dried,
Crushed.

The obtained tan particle powder was goethite as a result of X-ray diffraction. As is clear from the electron micrograph (× 120,000) shown in FIG. 8, the average value of the major axis diameter was 0.29 μm and the axial ratio (major axis) It consisted of spindle-shaped particles (diameter / short axis diameter) of 12.0, had uniform particle size, and did not contain dendritic particles.

The specific surface area is 86.9 m ² / g, the bulk density is 0.53 g / cm ² ,
The particle volume was 1.5 × 10 ⁻⁴ μm ³ and the crystallite size was 182 °.

[Effects of the Invention] According to the method for producing acicular goethite particle powder according to the present invention, as shown in the preceding examples, the particle size is uniform, dendritic particles are not mixed, and the axial ratio ( Acicular goethite particles having a large (major axis diameter / short axis diameter) and high crystallinity can be obtained.

The acicular goethite particle powder obtained in this manner is used as a starting material, and the acicular magnetite particle powder obtained by heat reduction and the acicular maghemite particle powder obtained by further oxidation have uniform particle sizes. Since it is a magnetic particle powder that does not contain dendritic particles, has a large axial ratio (major axis diameter / minor axis diameter), and has a high density of crystallinity, it is the most demanded high recording capacity at present. It is suitable as a magnetic particle powder for high density, high sensitivity and high output.

[Brief description of the drawings]

FIG. 1 shows the relationship between the BET specific surface area of the goethite particle powder and the bulk density. FIG. 2 shows the relationship between the volume of the goethite particle powder and the crystallite size. 3 and 4 are electron micrographs showing the particle structures of the goethite particles of the seed crystal and the produced goethite particles used in Example 1, respectively. 5 to 8 are electron micrographs showing the particle structures of the goethite particles obtained in Example 5, Comparative Example 1, Comparative Example 3, and Comparative Example 4, respectively.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-101717 (JP, A) JP-A-61-111925 (JP, A) JP-A-61-72628 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) C01G 49/00-49/68

Claims (1)

(57) [Claims] 1. A method for producing goethite particles by passing an oxygen-containing gas into a suspension containing ferrous hydroxide having a pH of 11 or more obtained by reacting an aqueous ferrous salt solution with an alkaline aqueous solution. Axial ratio (major axis diameter / minor axis diameter) as a seed crystal in any solution of the ferrous salt aqueous solution, the alkaline aqueous solution, and the suspension containing ferrous hydroxide before aeration with an oxygen-containing gas. ) Presents 6 to 7 spindle-shaped goethite particles and has a total iron content of 0.2 / Si / Fe equivalent.
After adding an Si compound of about 5.0 atomic%, an oxygen-containing gas is passed through to grow the seed crystal to generate needle-like goethite particles having an axial ratio (major axis diameter / short axis diameter) of 10 to 12. A method for producing acicular goethite particle powder, comprising: