JPS6350326A - Production of hematite - Google Patents

Abstract

PURPOSE:To produce hematite which is free from voids in a particle and has high density and is free from branching and excellent in magnetic characteristics by heat-treating the aq. suspension of ferric hydroxide under the presence of tetravalent metallic compd. in an alkaline pH region. CONSTITUTION:0.001-0.1mol tetravalent metallic compd. (i.e. SnCl4) for 1g atom Fe and 0.001-0.1mol phosphorus compd. (i.e. orthophosphoric acid) and/or oxycarboxylic acid compd. (i.e. citric acid) for 1g atom Fe in accordance with necessity are added to aq. suspension contg. 0.01-100g/l (as Fe) ferric hydroxide obtained by adding alkali (i.e. NaOH) to ferric salt (i.e. FeCl3) aq. soln., and alkali is added to regulate pH to >=8. Then after heating this suspension at 80-300 deg.C, acicular hematite is obtained by separation and recovery.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention produces magnetic powder for magnetic recording materials that has no pores in the particles, has substantially high density, has no branches, and has excellent magnetic properties. This invention relates to a method for obtaining hematite, which is a suitable raw material for the production of hematite, by a wet method.

[Technical background of the invention]

In recent years, magnetic recording media such as magnetic tapes, magnetic disks of magnetic cards, and magnetic drums have been required to have higher density recording and higher output. It is desired that magnetic powders used in magnetic fields have even higher performance.

By the way, needle-shaped magnetic iron oxide powder has traditionally been most commonly used as magnetic powder;
Normally, needle-shaped iron oxyhydroxide (e.g. α-FeOOH) is dehydrated by heating at 300 to 700'C to form hematite (α-FeOOH).
Fe, O,), then heat-reduced at 300 to 500°C to form magnetite (F e , O-), and then further oxidized as necessary to form magnetite (γ-Fe=O-).
s).

However, a large number of pores (dehydration pores) in the hematite crystal particles generated in the heat dehydration process of iron oxyhydroxide remain in the target magnetite and γ-Fe 2 (') s, and the vacancies are Spontaneous magnetization is partially disturbed in the periphery, which tends to have a negative effect on magnetic properties, and when attempting to densify the inside of the particles by processing the dehydration process at high temperatures, interparticle sintering and particle shape streaks may occur. Since the magnetic anisotropy of the target material, the dispersibility into the magnetic recording medium, and the filling property are likely to be significantly impaired, various proposals have been made in the past to resolve the above problems. For example, a method is known in which hematite is directly produced by a wet method by heating an alkaline aqueous suspension of ferric hydroxide. However, in hematite obtained by this method, and furthermore, in magnetite and magnetic iron oxide powders such as magnetite that use this as a starting material, although the formation of pores is suppressed to some extent, the shape property is easily impaired, and the result,
The desired magnetic iron oxide powder has not yet reached the point where it fully satisfies the requirements for high-density recording and high output, and there is a strong desire for improvement.

[Purpose of the invention]

The present invention has been made in order to solve the above problems, and is a raw material for producing magnetic powder for magnetic recording media, which has substantially no pores, excellent acicularity, and narrow particle size distribution. An object of the present invention is to provide a method for producing hematite suitable for use as a hematite.

[Structure of the invention]

The present invention has been carried out by the present inventors for some time using a wet method to produce hematite. As a result of conducting various studies on the above-mentioned problems in the method, we found that ferric hydroxide aqueous The present invention was completed based on the finding that hematite having substantially no pores and excellent in shape can be produced by heating a suspension. That is, the first aspect of the present invention is a method for producing hematite, which is characterized in that an aqueous suspension of ferric hydroxide is heat-treated in an alkaline pH range in the presence of a tetravalent metal compound, The second aspect of the present invention is characterized in that an alkaline aqueous suspension of ferric hydroxide is heat-treated in the presence of a tetravalent metal compound and a phosphorus compound or (and) an oxycarboxylic acid compound. This is a method for producing hematite.

In the present invention, the ferric hydroxide used can be produced by various methods, but is usually an aqueous solution of a ferric salt such as ferric chloride, ferric sulfate, or ferric nitrate. It is obtained by precipitating ferric hydroxide by adding an alkali such as sodium hydroxide, potassium hydroxide, ammonia, or sodium carbonate to ferric hydroxide. The aqueous suspension using the ferric hydroxide has an Fe concentration of usually 0.01 to 100 g/Q, preferably 1 to 30 g/ρ.

If the Fe concentration is lower than the above range, it is not economically advantageous, and if it is higher than the above range, the viscosity becomes high and it is difficult to uniformly stir the reaction system.

In the present invention, the tetravalent metal compounds used include Sn4+, Si41, Ge4, Ti, Zr
4f% V'', a metal compound such as Nb4f, for example 5nCd, , 5iCQ4, Na25nO=
, Ti(j!, , Zr0Cρ2, voso, , Ge
Examples include CQ, 4, etc. The amount of the tetravalent metal compound added is 0.001 to 0.1 mol, preferably 0.003 to 0.1 mol, per 1 gram atom of iron atom of ferric hydroxide.
It is 0.08 mol. If the amount of the tetravalent metal compound added is less than the above range, it will be difficult to obtain highly acicular hematite, and if it is more than the above range, the hematite formation reaction will take a long time and the obtained hematite will be difficult to obtain. The shape of the particles tends to become granular, which is not preferable.

In the present invention, when a tetravalent metal compound is present and a phosphorus compound or (and) an oxycarboxylic acid compound is also present, the shape of the acicular hematite obtained becomes more preferable. Various phosphorus compounds can be used to coexist, such as orthophosphoric acid, birophosphoric acid, metaphosphoric acid, hypophosphoric acid, polyphosphoric acid, etc.
Examples of the oxycarboxylic acid compounds coexisting include citric acid, tartaric acid, lactic acid, malic acid, salicylic acid, mandelic acid, and salts thereof. be able to.

The amount of the phosphorus compound or (and) oxycarboxylic acid compound added is preferably 0.001 to 0.1 mol as P per 1 gram atom of iron atom of ferric hydroxide, preferably o, oos. -0.03 mol, and in the case of oxycarboxylic acid compounds, it is 0.001-0.1 mol, preferably 0.005-0.03 mol. When the phosphorus compound or (and) oxycarboxylic acid is coexisting, the amount of the tetravalent metal compound added is from o.oos to 0.0.
1 mol is suitable, preferably 0.003 to 0.06 mol.

The above-mentioned tetravalent metal compounds, phosphorus compounds, and oxycarboxylic acid compounds can be added at various stages before the hematization reaction occurs. It may be added to the heated suspension of ferric hydroxide in the presence or absence of the compound or before addition of the alkali compound, or it may be added during the production of the raw material ferric hydroxide. It can also be done by

In the present invention, the heating reaction of the ferric hydroxide suspension is carried out in an alkaline region where the pH of the suspension is 8 or more, preferably 9 to 13;
If the pH is lower, it is difficult to obtain acicular hematite crystals, and if the pH of the suspension is significantly high, it is not only economically advantageous but also undesirable because dacite tends to be produced as a by-product. The reaction is suitably carried out in a closed or open reaction vessel under normal pressure or increased pressure, usually at a temperature of 80 to 300°C, preferably 130 to 250°C.

The hematite crystals of the present invention can be obtained by separating and recovering the reaction product obtained by the heating reaction treatment from the treatment system by a conventional method. Therefore, the acicular hematite of the present invention can be used as a raw material to obtain a magnetic powder for magnetic recording by a conventional method.
When heated and reduced at °C, magnetite retaining the acicular form of hematite can be obtained, and this is further heated at 200 to 400 °C.
If oxidized at a temperature of , maghemite which retains the acicular form of hematite F can be obtained. Mainly, the above-mentioned magnetite and maghemite can be converted into a bertolide compound if necessary, and furthermore, in order to impart high coercive force characteristics, a modification treatment using a cobalt compound can also be performed. Further, a metal iron magnetic powder can be obtained by applying a reducing agent such as hydrogen gas. In either case, it is possible to obtain a magnetic powder that is highly acicular, has substantially no pores or branches, has high density, and is suitable for use in high-density magnetic recording media.

[Embodiments of the invention]

The present invention will be further explained below with reference to Examples and Comparative Examples.

Example 1 Add sodium hydroxide aqueous solution (19.7% concentration) to 1.5ρ of ferric nitrate aqueous solution (iron concentration 20 g/ff) with stirring, and neutralize until the pi-t of the liquid becomes 7. Ferric hydroxide was precipitated.

This precipitate was separated by filtration and washed with water, and the resulting wet cake was repulped by adding water to obtain 1.5Q of an aqueous suspension of ferric hydroxide. (Iron concentration 20g/ρ) To the obtained suspension, 12.2- orthophosphoric acid aqueous solution (P concentration 1.35%) and stannic chloride aqueous solution (Sn+r concentration 5.7%) were added 22.211IQ.
and the pH was adjusted to 11 with an aqueous sodium hydroxide solution (19.7% concentration).Then, this suspension was heated in a stainless steel autoclave (volume 3ρ) and heated to 150°C with stirring for 2 hours. Allowed time to react. The resulting red-orange precipitate was filtered, washed with water, and dried to obtain 42 g of red powder.

As shown in Table 1 below, this was a hematite (α-Fe20.) crystal fine powder with good acicularity and uniform particle size. (Sample A) Example 2 In Example 1, instead of adding orthophosphoric acid, a sodium citrate aqueous solution (0.25 mol/Q concentration) 10.
7+6121- was added and treated in the same manner as in the same example to obtain acicular hematite of the present invention. (Sample B) Example 3 In Example 1, stannic chloride and
In addition to the addition of 8.5 mff (concentration 1.35%), an additional sodium citrate aqueous solution (0.25 mol/ρ concentration) 3
．． Acicular hematite of the present invention was obtained by processing in the same manner as in the same example except that 2a+ff was added. (Sample C) Example 4 The present invention was prepared in the same manner as in Example 1 except that orthophosphoric acid was not added and the amount of the stannic chloride aqueous solution was 44.4 mρ. Acicular hematite was obtained.

(Sample D) Comparative Example 1 A sample was treated in the same manner as in Example 1, except that orthophosphoric acid added to stannic chloride was not added.

(Sample E) Comparative Example 2 A sample was treated in the same manner as in Example 1 except that stannic chloride was not added. (Sample F) Comparative Example 3 The same treatment as in Example 2 was performed except that stannic chloride was not added. (Sample G) Comparative Example 4 A sample was treated in the same manner as in Example 1, except that the pH of the aqueous suspension of ferric hydroxide was adjusted to 6.

(Sample H) Table 1 shows the results of measuring the characteristics of each sample obtained in each of the Examples and Comparative Examples described above.

Table 1 In Table 1, I-2 is the average long sleeve diameter (X, μ) based on the results of observing 500 particles using an electron microscope.

L/W: Specific surface area between the average long sleeve diameter and the average short axis diameter (Wμ) based on the results of observing 500 particles with an electron microscope:) Measured by the 3ET method Particle shape: Observed with an electron microscope Crystal system: Identification by X-ray diffraction method (reference) As an example of the hematite powder, sample A of Example 1 was hydrogen-reduced at 380°C in a rotary heating furnace, and further heated at 300°C.
When heated and oxidized in air, maghemite magnetic iron oxide powder with good magnetic properties was obtained.

As is clear from Table 1 and the illustrative results of electron micrographs, the hematite particles obtained by the method of the present invention are acicular particles with a well-developed shape and are substantially empty. It can be seen that no holes or branches were observed, making it an excellent raw material for producing magnetic powder for high-density magnetic recording media.

〔Effect of the invention〕

As detailed above, according to the method of the present invention, it is possible to substantially avoid pores, particle branching, particle entanglement, etc. due to changes in particle morphology during the heat treatment step during hematite formation, which is an industrially advantageous method. It is possible to provide a production method, and the magnetic powder produced using the hematite as a raw material can be made into high-density particles with excellent magnetic properties that inherit the high acicularity of hematite. This is extremely useful in achieving high-density recording in magnetic recording media.

[Brief explanation of drawings]

Figure 1 is an electron micrograph (30,000x magnification) showing an example of the crystal structure of hematite (Example 1) obtained by the method of the present invention, and Figure 2 is a comparative example (example 1) in which the method of the present invention is not used.
It is an electron micrograph (30,000 times) showing an example of the crystal structure of hematite obtained in comparative example 2). Patent applicant: Ishihara Sangyo Co., Ltd. Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1) A method for producing hematite, which comprises heat-treating an aqueous suspension of ferric hydroxide in the presence of a tetravalent metal compound in an alkaline pH range. 2) Hematite production characterized by heat-treating an aqueous suspension of ferric hydroxide in an alkaline pH region in the presence of a tetravalent metal compound and a phosphorus compound or (and) an oxycarboxylic acid compound. Production method.