JPH03223120A - Production of needlelike crystal goethite particle powder - Google Patents

Abstract

PURPOSE:To obtain particle powder having a uniform particle size and relatively high axial ratio without any dendritic particles mixed therein by aerating a reaction solution of a ferrous salt containing a specific colloid with an oxygen-containing gas, then adding an aqueous solution of an alkali carbonate thereto and further aerating the resultant solution with the oxygen-containing gas. CONSTITUTION:An aqueous solution of a ferrous salt and an aqueous solution of an alkali hydroxide or alkali carbonate in a smaller amount than equivalent to Fe<2+> in the aqueous solution of the ferrous salt are reacted to provide a reaction solution of a ferrous hydroxide colloid or ferrous salt containing iron-containing precipitate colloid. The resultant solution is then aerated with an oxygen-containing gas to oxidize the aforementioned ferrous hydroxide colloid or iron-containing precipitate colloid and form needlelike crystal goethite nuclear particles. An aqueous solution in a larger amount than equivalent to the Fe<2+> in the above-mentioned solution is added to the reaction solution of the ferrous salt containing the aforementioned needlelike crystal goethite nuclear particles and the obtained solution is then aerated with the oxygen- containing gas to carry out growth reaction of the above-mentioned needlelike crystal goethite nuclear particles and afford the objective particle powder.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is suitable as a starting material for producing magnetic material particle powder for magnetic recording.The particle size is uniform and dendritic particles are not mixed. Moreover, the present invention relates to a method for producing acicular goethite particles having a large axial ratio (major axis diameter/minor axis diameter), particularly 20 or more.

[Prior Art] In recent years, as magnetic recording and reproducing equipment has become smaller and lighter, there has been an increasing need for recording media such as magnetic tapes and magnetic disks to have higher performance.

That is, high recording density, high sensitivity characteristics, high output characteristics, etc. are required.

In order to satisfy the above-mentioned requirements for magnetic recording media, the characteristics required for magnetic material particles are high coercive force and excellent dispersibility.

In other words, in order to increase the sensitivity and output of magnetic recording media, it is necessary for magnetic particles to have as high a coercive force as possible. Development and high dispersion technology of magnetic powder J (
1982) No. 310, ``The aim of improving magnetic tape performance was to increase sensitivity and output, so we decided to increase the coercive force of acicular γ-Fe, O, particles...'' This is clear from the statement "The emphasis was on

In addition, in order to achieve high recording density in magnetic recording media, the conditions for high-density recording in coated tapes, as described in the aforementioned "Development of Magnetic Materials and Highly Dispersed Magnetic Powder Technology" on page 312, are as follows: On the other hand, it is possible to maintain high output characteristics with low noise, but for this purpose, it is necessary that both the coercive force He and the residual magnetization Br be large, and that the thickness of the coating film be thinner.

'', it is necessary for the magnetic recording medium to have a high coercive force and a large residual magnetization Br, and for this purpose, the magnetic particles must have a high coercive force, have good dispersibility in the vehicle, and have a good coating film. Excellent orientation and filling properties are required.

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

The magnetic iron oxide particles or metal magnetic particles whose main component is iron, such as acicular magnetite particles and acicular maghemite particles, which are currently used as magnetic particles for magnetic recording, originate from their shape. A relatively high coercive force is obtained by making use of the anisotropy, that is, by increasing the axial ratio (major axis diameter/minor axis diameter).

These known magnetic particles are produced by reducing goethite particles as a starting material at 300 to 400°C in a reducing gas such as hydrogen to produce magnetite particles or iron-based metal particles, or , in the air 2
It is obtained by oxidizing it at 00 to 300°C to form maghemite particles.

The residual magnetization Br of a magnetic recording medium depends on the dispersibility of the magnetic particles in the vehicle, the orientation and filling properties in the coating film, and in order to improve these properties, it is necessary to disperse them in the vehicle. It is required that the magnetic particles have uniform particle size, do not contain dendritic particles, and have as large an axial ratio (major axis diameter/minor axis diameter) as possible.

As mentioned above, magnetic particle powders with uniform particle size, no dendritic particles mixed in, and a large axial ratio (major axis diameter/minor axis diameter) are currently in greatest demand. In order to obtain magnetic particles with such characteristics, the particle size of the starting material, goethite particles, must be uniform, dendritic particles are not mixed, and the axial ratio (major axis diameter / It is necessary that the short axis diameter) be large.

Conventionally, the method for producing goethite particles, which is a starting material, is as follows: (1) Adding an equivalent or more aqueous alkali hydroxide solution to an aqueous ferrous salt solution to obtain a suspension containing a ferrous hydroxide colloid of 9811 or more. A method of producing acicular goethite particles by conducting an oxidation reaction by passing an oxygen-containing gas through the air at a temperature of 80°C or lower (Japanese Patent Publication No. 39-5610), A method of producing spindle-shaped goethite particles by performing an oxidation reaction by passing an oxygen-containing gas through a suspension containing FeCO5 obtained by the reaction (Japanese Patent Application Laid-Open No. 50-8099
No. 9) and ■ A ferrous salt aqueous solution containing a ferrous hydroxide colloid obtained by adding an equivalent amount or less of an alkali hydroxide aqueous solution or an alkali carbonate aqueous solution to a ferrous salt aqueous solution is aerated with an oxygen-containing gas. Acicular goethite core particles are generated by performing an oxidation reaction, and then Fe in the ferrous salt aqueous solution is added to the ferrous aqueous solution containing the acicular goethite core particles.
``A method of growing the acicular goethite core particles by adding an aqueous alkali hydroxide solution in an amount equivalent to or more than the amount and then aerating an oxygen-containing gas (Japanese Patent Publication No. 59-48766, Japanese Patent Application Laid-open No. 5912893, ° Japanese Patent Publication No. 59-12894
No. 1, JP-A-59-128295, JP-A-Sho 60
-21818) etc. are known.

[Problem to be solved by the invention]

Magnetic particle powder with uniform particle size, no dendritic particles mixed in, and a large axial ratio (major axis diameter/minor axis diameter) is
Currently, the most demanded method is to produce goethite particles as a starting material using the method (2) above, especially when the axial ratio (major axis diameter/minor axis diameter) is large.
Although the above-mentioned acicular goethite particles are produced, dendritic particles are mixed therein, and in terms of particle size, it is difficult to say that the particles have a uniform particle size. Note that "acicular" refers to a shape in which the ridge lines in the long axis direction are substantially parallel.

In the case of method (2) above, spindle-shaped particles with uniform particle size and no dendritic particles are produced, but on the other hand, the axial ratio (major axis diameter/minor axis diameter) is about 7 at most, and it has the disadvantage that it is difficult to produce particles with a large axial ratio (major axis diameter/minor axis diameter), and this phenomenon is said to become especially pronounced as the major axis diameter of the produced particles becomes smaller. There is a tendency. Various methods have been attempted to increase the axial ratio (major axis diameter/minor axis diameter) of spindle-shaped goethite particles, but the ratio is only 17 to 1 at most.
It is about 8, which is still not enough. In addition, since the particle shape is spindle-shaped with the tip of the image tapered in the long axis direction,
Sintering occurs during thermal reduction, and the particle shape tends to collapse, making it difficult to obtain magnetic particle powder with a large axial ratio (major axis diameter/minor axis diameter).

The above-mentioned method (■) is based on the characteristics of the acicular goethite particles obtained by the above-mentioned methods (2) and (2), such as particle size, axial ratio (major axis diameter/minor axis diameter), presence or absence of dendritic particles, etc. However, goethite particles with sufficiently satisfactory properties have not yet been obtained.

Therefore, the technical problem of the present invention is to obtain acicular goethite particles having a uniform particle size, no dendritic particles mixed therein, and a large axial ratio (major axis diameter/minor axis diameter). That is.

[Means for Solving the Problems] The above technical problems can be achieved by the present invention as follows.

That is, the present invention provides a ferrous hydroxide colloid or oxidizing the ferrous hydroxide colloid or the iron-containing precipitate colloid to produce acicular goethite core particles by passing an oxygen-containing gas through the ferrous salt reaction solution containing the iron-containing precipitate colloid; Next, an aqueous alkali carbonate solution in an amount equal to or more than Fe'' in the ferrous salt reaction solution is added to the ferrous salt reaction solution containing the cough needle-like goethite core particles, and then an oxygen-containing gas is aerated. , a method for producing acicular goethite particle powder, which comprises performing a growth reaction of the acicular goethite core particles.

(Function) First, the most important point in the present invention is that the ferrous salt aqueous solution is obtained by reacting an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution in an amount less than the equivalent amount of Fe in the aqueous ferrous salt solution. The ferrous hydroxide colloid or iron-containing precipitate colloid is oxidized to form needles by passing an oxygen-containing gas through the ferrous salt reaction solution containing the ferrous hydroxide colloid or iron-containing precipitate colloid. After producing crystalline goethite core particles, and then adding to the ferrous salt reaction solution containing the acicular crystalline goethite core particles an aqueous alkali carbonate solution in an amount equal to or more than the amount of Fe in the ferrous salt reaction solution. When the growth reaction of the acicular goethite core particles is carried out by aeration of oxygen-containing gas, the particle size is uniform and dendritic particles are not mixed, and the axial ratio (major axis diameter) is uniform. This is the fact that goethite particles having a large acicular crystal structure (/minor axis diameter) of 20 or more can be obtained.

In either case, if an alkali hydroxide aqueous solution is used instead of an alkali carbonate aqueous solution in the growth reaction of goethite core particles, or if an equivalent or more amount of alkali hydroxide aqueous solution or alkali carbonate aqueous solution is used in the goethite core particle production reaction, As shown in the comparative example, the objective of the present invention is to obtain acicular goethite particles having uniform particle size, no dendritic particles mixed therein, and a large axial ratio (major axis diameter/minor axis diameter). cannot be obtained.

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

Examples of the ferrous salt aqueous solution used in the present invention include a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution.

Examples of the alkali hydroxide aqueous solution used in the reaction for producing acicular goethite core particles of the present invention include sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, etc.; Ammonium etc. can be used.

The amount of alkali hydroxide aqueous solution or alkali carbonate aqueous solution used is less than the equivalent amount to Fe''° in the ferrous salt aqueous solution. If the amount is more than the equivalent amount, the particle size will be asymmetric and dendritic particles will be mixed. In addition, granular magnetite particles are obtained.

In the present invention, the amount of the acicular goethite core particles present is preferably in the range of 25 to 90+++olχ based on the generated goethite particles. If it is less than 25 so 11, spindle-shaped goethite particles will be mixed in the acicular goethite particles. If it exceeds 90 so Iχ, the ratio of iron carbonate to the acicular goethite core particles decreases, so the reaction becomes non-uniform and the particle size of the resulting goethite particles becomes asymmetric.

As the aqueous alkali carbonate solution used in the growth reaction of the acicular goethite core particles of the present invention, the same aqueous alkali carbonate solution used in the reaction for producing the acicular goethite core particles can be used.

The amount of the alkaline carbonate aqueous solution used is at least equivalent to the amount of Fe'' in the remaining ferrous salt aqueous solution. If the amount is less than the equivalent, the particle size of the resulting goethite particles will be asymmetric, and the spherical magnetite particles will be It's going to be mixed.

The oxidation means in the present invention is carried out by passing an oxygen-containing gas (for example, air) into the liquid, and may be accompanied by stirring by mechanical operation or the like if necessary.

The reaction temperature in the present invention may be generally 80° C. or lower at which goethite particles are generated. If the temperature exceeds 80°C, granular magnetite particles will be mixed in the acicular goethite particles.

In addition, in the present invention, it is possible to carry out the production reaction of goethite core particles and the growth reaction of the goethite core particles using the same reaction tower, and even when separate reaction towers are used, it is an object of the present invention. Goethite particles are obtained.

Furthermore, in the present invention, in order to improve various properties of magnetic particles, it is possible to add different elements other than Fe, such as CO1Ni, Zn, AI, and P, which are usually added during the production of goethite particles. In this case, the same effects as those of the present invention can be obtained.

〔Example〕

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

In addition, the major axis diameter of the particles in the following examples and comparative examples,
The axial ratio (major axis diameter/minor axis diameter) was expressed as an average value of values measured from electron micrographs.

Example I Ferrous sulfate aqueous solution containing 1.5 mol/l of Fe"° 12
．． 81 and 0.44-N Na0)l aqueous solution 30.1!
(corresponds to 0.35 equivalent to Fe"° in the ferrous sulfate aqueous solution), pH 6.7, temperature 38 °C
An aqueous ferrous sulfate solution containing Fe(O)l)z was produced.

Goethite core particles were generated by passing air through the ferrous sulfate aqueous solution containing Fe (OH) z at a temperature of 40°C for 3.0 hours at a rate of 1301/min. A part of the reaction solution was taken out, filtered, washed with water, and dried according to a conventional method, and an electron micrograph (X30000) of the obtained particles is shown in FIG. 1.

Ferrous sulfate aqueous solution containing the above goethite core particles (the amount of goethite core particles is 35s
This corresponds to +olχ. ), 5.4-N NazCO4
Aqueous solution? , Of (Fe in the residual ferrous sulfate aqueous solution)
This corresponds to 1.5 equivalents. ), pH 9.4,
130 per minute at a temperature of 42°C! Goethite particle powder was produced by passing air through the solution for 4 hours.

The produced goethite particles were filtered, washed with water, and dried by a conventional method.

As shown in the electron micrograph (x 30,000) in Fig. 2, the obtained goethite particles have a uniform particle size, do not contain dendritic particles, and have a long axis of 0.33 #.
They were acicular crystal particles with a diameter of 1 m and an axial ratio (major axis diameter/minor axis diameter) of 25.

Examples 2 to 8 Type, Fe concentration and usage amount of ferrous salt aqueous solution, type, concentration and usage amount of alkaline aqueous solution, type and amount of different elements, reaction temperature, and goethite core particles in the production of goethite core particles Goethite particles were obtained in the same manner as in Example 1, except that the type, concentration, and amount of the alkaline aqueous solution used, the type and amount of the different element, and the reaction temperature during the growth were varied.

The main manufacturing conditions and characteristics of the goethite particles are shown in Tables 1 and 2.

The acicular goethite particles obtained in Examples 2 to 8 were
As a result of electron microscopic observation, the particle size was uniform in all cases, and dendritic particles were not mixed.

Comparative Example 1 5.4-N Na2CO3 aqueous solution7. 5 instead of OR.
4-N NaOH aqueous solution 7! Goethite particles were obtained in the same manner as in Example 1, except for using 1.5 equivalents of Fe'' in the residual ferrous sulfate aqueous solution.

As shown in the electron micrograph (x 30,000) of FIG. 3, the obtained goethite particles had asymmetric particle sizes and contained dendritic particles.

Comparative Example 2 0.4-N NaOH aqueous solution 3021 was replaced with 0.4-N NaOH aqueous solution 3021.
4-N Na2CO3 aqueous solution 30.2f (corresponds to 0.35 equivalent to Pe"° in the ferrous sulfate aqueous solution.

) and a 5.4-N NaOH aqueous solution 7.0 in place of the 5.4-N NaZCO3 aqueous solution 7.01.
f (1.5 for Fe in the residual ferrous sulfate aqueous solution)
corresponds to equivalent amount. ) Goethite particles were obtained in the same manner as in Example 1, except that Goethite particles were used.

As shown in the electron micrograph (X 30000) of FIG. 4, the obtained goethite particles had asymmetric particle sizes and contained dendritic particles.

Comparative Example 3 Ferrous sulfate aqueous solution containing 1.0mol/It of Fe” 7.52 and 1.3-N Na2CO3 aqueous solution 24.21
(corresponding to 2.1 equivalents to Fe"° in the ferrous sulfate aqueous solution) to generate FeCO at a pH of 9.9 and a temperature of 42°C. Goethite particles having a spindle shape were produced by blowing air at 100 l/min for 5 hours at a temperature of 45°C.

F is added to the aqueous solution containing the spindle-shaped goethite particles.
Ferrous sulfate aqueous solution containing 1.8 mol/12
3p, and 13-N NaOH aqueous solution 10! (This corresponds to 4.4 equivalents of Fe in the added ferrous sulfate aqueous solution.) and stirred and mixed (the spindle-shaped goethite particles correspond to 33 molχ based on the generated goethite particles). After that, a goethite growth reaction was carried out by aerating air at a rate of 150!/min for 3 hours at a temperature of 50°C.

The generated goethite particles are filtered, washed with water, and
Dry.

As shown in the electron micrograph (x 30,000) in Figure 5, the obtained goethite particles have a uniform particle size and no dendritic particles, but the axial ratio (major axis diameter/minor axis diameter) The particles were small and had a rectangular shape.

Comparative Example 4 Ferrous sulfate aqueous solution 12.i containing 1.3 mol/ffi of Fe" and 2.4-N NaOH aqueous solution 30.21 (corresponding to 2.2 equivalents to Fe" in the ferrous sulfate aqueous solution) ) at p old 3.2 and temperature 40°C.
e (01() t was generated.The above Fe(OH)
130 per minute when an aqueous solution containing i is heated to +145°C!
of air was aerated for 15 hours to produce needle-shaped goethite particles. The produced goethite particles were filtered and washed with water by a conventional method.

27.5 aqueous solution containing 586 g of the above acicular goethite particles
2, ferrous sulfate aqueous solution 12°51 containing Fe" 1.0 sol/j! and 3.8-N NazCO3 aqueous solution 10
2 (1 for Fe"" in the added ferrous sulfate aqueous solution
．． This corresponds to 5 equivalents.

After stirring and mixing (the acicular goethite particles correspond to 35 molχ with respect to the generated goethite particles), at a temperature of 42°C, +30% per minute! ! The goethite growth reaction was performed by aerating air for 4 hours.

The generated goethite particles are filtered, washed with water, and
Dry.

The obtained goethite particles had asymmetric particle sizes, contained dendritic particles, and had a small axial ratio (major axis diameter/minor axis diameter) of 10.

Comparative Example 5 Ferrous sulfate aqueous solution 1 containing 1.5 mol/l of Fe”
ON and 2,]-N NaOH aqueous solution 33! (corresponding to 2.3 equivalents of Fe in the ferrous sulfate aqueous solution), and at a pH of 3 and a temperature of 38°C, Fe(OH) was mixed.
2 colloid generation). 13 Il/min of air was passed through the suspension containing the Fe (OB) z colloid at a temperature of 42° C. for 15 hours to generate acicular goethite particles. The resulting goethite particles were washed, washed with water, and dried in a conventional manner.

As shown in the electron micrograph (x 30,000) of FIG. 6, the obtained goethite particles had asymmetric particle sizes and contained dendritic particles.

Comparative Example 6 Ferrous sulfate aqueous solution 1 containing Fe”°1.5 mol/j!
0Il and a 1.8-N @BzCOs aqueous solution 331 (corresponding to 2.0 equivalents to "Fe" in the ferrous sulfate aqueous solution) were mixed to form pecOs at pH 9.8 and temperature 45 °C. I did it.

Goethite particles were generated by passing air through the aqueous solution containing FeC0z at a rate of +00 ffi per minute for 5 hours at a temperature of 50°C. The resulting goethite particles were washed, washed with water, and dried in a conventional manner.

The obtained goethite particles have a spindle shape, as shown in the electron micrograph (x 30000) of FIG.
The axial ratio (major axis diameter/minor axis diameter) was 7, which was a small axial ratio.

〔Effect of the invention〕

According to the method for producing acicular goethite particles according to the present invention, as shown in the previous example, the particle size is uniform and dendritic particles are not mixed, and the axial ratio (major axis diameter /minor axis diameter) can be obtained.

The magnetic particles obtained by thermal reduction or further oxidation using the acicular goethite particles according to the present invention as a starting material also have uniform particle size and do not contain dendritic particles, and Since they are acicular crystal particles with a large axial ratio (major axis diameter/minor axis diameter), they are suitable as magnetic particles for high recording density, high sensitivity, and high output.

[Brief explanation of drawings]

1 to 7 are electron micrographs (x 30,000) showing the particle structure of goethite particles. FIG. 1 shows the acicular goethite core particle powder obtained in Example 1, and FIGS. 2 to 7 show Example 1 and Comparative Example 1, respectively.
3 to 3, goethite particles obtained in Comparative Example 5 and Comparative Example 6.

Claims (1)

[Claims] (1) Ferrous salt aqueous solution and Fe^2 in the ferrous salt aqueous solution
Oxygen-containing gas is passed through a ferrous salt reaction solution containing a ferrous hydroxide colloid or an iron-containing precipitate colloid obtained by reacting an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution in an amount less than the equivalent amount to ^+. The ferrous hydroxide colloid or the iron-containing precipitate colloid is oxidized to produce acicular goethite core particles, and then the ferrous salt reaction solution containing the acicular goethite core particles is added to the ferrous salt reaction solution containing the acicular goethite core particles. The growth reaction of the acicular goethite core particles is carried out by adding an aqueous alkali carbonate solution in an amount equal to or more than an equivalent amount to Fe^2^+ in the ferrous salt reaction solution and then aerating oxygen-containing gas. A method for producing acicular goethite particles.