JPS59174532A - Manufacture of iron oxide hydrate - Google Patents

Abstract

PURPOSE:To obtain iron oxide hydrate suitable for use as a starting material for needlelike magnetic powder of iron oxide or metallic iron for a magnetic recording medium by forming nuclei of iron oxide hydrate crystals in an acidic state, adding an alkali, and growing the crystals. CONSTITUTION:A suspension contg. Fe(OH)3 prepd. by reacting a ferric salt such as Fe2(SO4)3 or FeCl3 with an aqueous soln. of an alkli such as NaOH is aged to manufacture iron oxide hydrate as a starting material for magnetic powder. At this time, nuclei of iron oxide hydrate crystals are formed by aging at 1-6 pH and 20-100 deg.C for 5-240min, the alkali is further added, and the crystals are grown at 10-13.5pH. Relatively coarse particles of iron oxide hydrate are obtd. when the nuclei forming stage is carried out at a lower temp. for a shorter time, and the alkali is added before many nuclei are formed. Relatively fine particles of iron oxide hydrate are obtd. when the nuclei forming stage is carried out at a higher temp. for a longer time and the alkali is added after many nuclei are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing hydrated iron oxide suitable as a starting material for producing acicular iron oxide magnetic powder or acicular metal iron magnetic powder for magnetic recording media. More specifically, the present invention relates to a method for producing acicular hydrated iron oxide with no branching and a narrow particle size distribution by freely controlling the length of the major axis.

In general, the particle shape of iron oxide magnetic powder or metal iron magnetic powder is based on the starting material hydrated iron oxide (a -FeOO
The shape of the hydrated iron oxide used as a raw material is extremely important, since the shape of the hydrated iron oxide (H-β-FeOOH or r-FeOOH) greatly depends on the shape.

Conventionally, hydrated iron oxide has been produced by treating ferrous salt with an alkaline aqueous solution and an oxygen-containing gas to produce hydrated iron oxide. Although it is possible to obtain products with an excellent ratio of the axis to short axis, and it is relatively easy to control the size of the hydrated iron oxide particles, on the other hand, branching is likely to occur and the particle size distribution range is wide. On the other hand, a method for obtaining hydrated iron oxide by aging a suspension containing ferric hydroxide obtained by reacting a ferric salt with an alkaline aqueous solution has been proposed; Although iron oxide is unbranched, it is difficult to control the size of hydrated iron oxide particles, making it difficult to obtain particularly fine particles, and the particle size distribution range eliminates the drawbacks.
It is an object of the present invention to provide a method for producing fine hydrated iron oxide having a narrow particle size distribution range and easily controlling the particle size.

In order to achieve the object of the present invention, the present inventor changed the conditions for producing hydrated iron oxide from iron salt and the crystal growth conditions. 2
In a method for producing hydrated iron oxide, which is a starting material for magnetic powder, by aging an iron-containing suspension, the pH is 1 to 1.
6. After reacting at a temperature of 20 to 100°C for 5 to 240 minutes to generate nuclei of hydrated iron oxide crystals, an alkali is further added to P.
A method for producing hydrated iron oxide characterized by growing crystals as H10-13.5.

According to the method of the present invention for producing hydrated iron oxide, crystal nuclei of the produced hydrated iron oxide are easily generated on the acidic side, but since the crystal growth is very slow, the number of crystal nuclei generated increases as time passes. However, the growth of individual nuclei is hardly observed. Furthermore, when the temperature at which the nuclei grow is changed, the number of nuclei increases as the temperature increases. 5-7240 on the acidic side
After generating crystal nuclei, add alkali to raise the pH to 10.
In the above manner, no new crystal nuclei were generated, and it was observed that the existing crystal nuclei were uniformly grown.

As is clear from the above, when attempting to obtain relatively large particles of hydrated iron oxide, the temperature during the crystal nucleation stage should be lowered and the time should be shortened, and the alkali should be added while the number of nuclei generated is small. In addition, it is sufficient to grow crystal nuclei, and if you are trying to obtain relatively small particles of hydrated iron oxide, increase the number of nuclei generated by setting the temperature during the crystal nucleus generation stage to a high temperature and increasing the time. Then add alkali to grow crystal nuclei.

At the stage of crystal nucleation of hydrated iron oxide, at pH below 1, hydrated iron oxide is formed and dissolved faster.

In addition, if the pH exceeds 6, ferric hydroxide becomes stable, making it difficult to produce hydrated iron oxide, and in either case, sufficient crystal nuclei cannot be obtained, so the pH condition is 1-6, preferably 2.5-6.
It is 4.0. In addition, if the temperature at this stage of crystal nucleation is less than 20°C, the rate of nucleation is slow and nucleation is insufficient, so even when the temperature is made alkaline, new nuclei will be generated and abnormal growth will occur, resulting in abnormally large crystals. It is not desirable to mix them together.

In addition, uniform crystal nuclei can be obtained even at temperatures exceeding 100°C, but at this time the crystal nuclei are formed extremely quickly, so the number of crystal nuclei is large relative to the total tK of iron. If the diameter is 0.1μ or less, it is too small to be suitable as a starting material for magnetic powder.

At the crystal growth stage, if the pH is less than 10, hydroxide #2
Because iron oxide is relatively stable, the growth of hydrated iron oxide is slow, and even if it does grow, it has poor crystallinity. Moreover, when the pH exceeds 13.5, granular α·Fet03 is produced, which is not suitable as a starting material for magnetic powder. Therefore, the pH condition is 10-16.5, preferably 11-16. The temperature conditions in this case are not particularly limited and may be the same as the temperature at the crystal nucleation stage; however, raising the temperature is industrially advantageous because the growth rate is faster and the time required to complete ripening is shortened.

The ferric salts used in the present invention include ferric sulfate,
Examples include ferric chloride and ferric nitrate. Alternatively, ferrous sulfate may be oxidized using a suitable oxidizing agent such as hydrogen peroxide. As the alkali, an aqueous caustic alkali solution such as sodium hydroxide or potassium hydroxide is usually used, but an aqueous solution of sodium carbonate, sodium bicarbonate, ammonium carbonate, etc. may also be used.

The present invention will be described below based on Examples and Comparative Examples.

Example 1 A sodium hydroxide aqueous solution was added to a 500-mL ferric sulfate aqueous solution of 0.50 m, oL/1 to adjust the pH to 2.9, and then the liquid volume was 1 t, the temperature was 801°C, and the reaction time was 30°C.
°min (Test A1) 1 hour (Test 2) 2 hours (Testing shop 6)
After changing the time to 4 hours (Test A4) and stirring for each hour, a sodium hydroxide solution was further added to adjust the pH to 12.3, and the growth was performed for 4 hours, and Tests 41 to 4 were conducted respectively.
Got OOH. Table 1 shows these test conditions and the average grain size (long axis) of the crystals obtained by observing the obtained hydrated iron oxide (α-Fe OOH) with an electron microscope. Further test A
Reference photo A1 is the 30,000x electron micrograph of Test 2. Reference photo A2 is the 63,000x electron micrograph of Test A4.
It was shown as

As shown in Table 1 and the reference photos, the average crystal grain size of hydrated iron oxide is 0.1 to 0.5μ, and the average grain size can be controlled by changing the crystal nucleation time. Hydrous iron oxide was obtained without any droplets and with a narrow particle size distribution range as shown in FIG.

Example 2 0.5 mo1/l ferrous sulfate aqueous solution 500-65
After oxidizing by adding 17.5% hydrogen peroxide solution, hydroxide is added) Add IJum aqueous solution to adjust the pH to 6.5, bring the liquid volume to 16, and stir at 60°C for 2 hours to remove sodium hydroxide. Add an aqueous solution to bring the pH to 12.41C, raise the temperature to 80°C, strain, and continue stirring for 4 hours. The obtained hydrated iron oxide (α
-Fe OOH) has an average particle size of 0.25 as shown in Table 1.
μ, the particle size distribution was narrow.

Example 6 A sodium hydroxide aqueous solution was added to a 0.5 mol/l ferric chloride aqueous solution to adjust the pH to 3.1, the liquid volume was brought to 1 t, and then the temperature was raised to 90°C and stirred for 30 minutes. After adding an aqueous sodium hydroxide solution to adjust the pH to 11.8, stirring was continued for 4 hours. Obtained hydrated iron oxide (β-Fe00H)
As shown in Table 1, the average particle size was 0.65μ and the particle size distribution was narrow.

Comparative Example 1゜The reaction was carried out under exactly the same conditions as in Example 1, except that the pH 2.9 at the time of crystal formation of the test plate 3 was changed to PH 7.0, and the crystals were aged. I couldn't.

Comparative Example 2 A sodium hydroxide aqueous solution was added to 500 m/l of a 0.5 mot/l ferric sulfate aqueous solution to adjust the pH to 12.3, and the liquid volume was adjusted to 1 t, and the mixture was stirred at a temperature of 80°C for 5 hours to obtain hydrated iron oxide α. -FeOOH was obtained, but the distribution of crystal long axes was 1 to 3μ, and if the ripening time was too long, the crystallinity was poor.

Comparative Example 3 0.5 mol/l ferrous sulfate aqueous solution 500 dK3
After oxidizing by adding 17.5% of 5% hydrogen oxide solution, add sodium hydroxide aqueous solution to adjust the pH to 12.5, and make liquid 1.
After stirring at 20° C. for 24 hours, the temperature was raised to 80° C. and stirring was continued for 8 hours. The obtained hydrated iron oxide (α-
As shown in Table 1, the average particle size of FeOOH) was 0.8 μm, and the particle size distribution was wider than that of Example '1 of the method of the present invention, as shown in FIG.

In addition to the differences in the above examples, the experimental conditions of the comparative example and the average particle diameter (long axis) of the obtained hydrated iron oxide (α-Fe00H) are shown in Table 1. Figure 1 shows the particle size distribution of the hydrated iron oxide.

As mentioned above, the hydrated iron oxide according to the present invention is suitable as a raw material for producing acicular iron oxide magnetic powder or acicular metal iron magnetic powder for magnetic recording media.

FIG. 3 is a distribution diagram of the particle size (length of major axis) of hydrated iron oxide produced in each of the above.

Agent Patent Attorney Mitsuro Kimura 1st cause ()) 1. Indication of the case Patent application 1982-45326 2. Name of the invention Process for producing hydrated iron oxide 3. Relationship with the case of the person making the case O Applicant 8” (618) Mitsui Kinzoku Mining Co., Ltd. (name) 4. Agent 7. Contents of Ura IF 1. The title of the invention “method for producing hydrated iron oxide”. Correct it as j.

Claims (1)

[Claims] 1. Hydrous iron oxide, which is a starting material for magnetic powder, is produced by aging a suspension containing ferric hydroxide obtained by reacting a ferric salt with an aqueous alkaline solution. In the method for producing Pt (1 to 6, at a temperature of 20 to 100°C, 5 to 240
1. A method for producing hydrated iron oxide, which comprises reacting to generate a nucleus of hydrated iron oxide crystals, and then adding an alkali to grow crystals at PHIO~16.5. 2. The method for producing hydrated iron oxide according to claim 1, wherein the ferric salt is ferric sulfate, ferric chloride, or ferric nitrate. 6. Hydrous iron oxide is α-FeOOH, β-FeOOH-
or r-Fe00H, the method for producing hydrated iron oxide according to claim 1. 4. Claims 1 and 2, wherein the ferric salt is a ferrous salt oxidized with an oxidizing agent such as hydrogen peroxide.
The method for producing hydrated iron oxide described in