JPH0259431A - Production of iron oxyhydroxide - Google Patents

Abstract

PURPOSE:To suppress branching and to improve particle size distribution by allowing ferrous ion to coexist in an iron oxyhydroxide suspension obtd. by feeding O2-contg. gas into a ferrous hydroxide suspension and by aging the iron oxyhydroxide suspension at a specified temp. in a nonoxidizing atmosphere. CONSTITUTION:An alkali such as NaOH is allowed to act on an aq. soln. of a ferrous salt such as FeSO4 and O2-contg. gas is fed into the resulting ferrous hydroxide suspension to obtain an iron oxyhydroxide suspension. Ferrous ion is allowed to coexist in the iron oxyhydroxide suspension, this suspension is aged at a temp. which is above the synthesis temp. of iron oxyhydroxide by at least 3 deg.C in a nonoxidizing atmosphere and the iron oxyhydroxide is dehydrated by heating.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing iron oxyhydroxide, which is a raw material for metal magnetic powder used in magnetic recording media, as fine particles with less branching and a good particle size distribution. .

[Background of the invention and conventional technology]

Generally, magnetic recording media are manufactured by coating a magnetic paint on a support, but when preparing this magnetic paint, the dispersibility and filling properties of the magnetic powder in the paint are factors that greatly control the performance of the magnetic recording medium. The magnetic properties of magnetic recording media, especially B r / B m (squareness ratio), 5FD (
Coercive force distribution) and Br (residual magnetic flux density) are considered to determine the superiority or inferiority (Bm is the maximum magnetic flux density). When using metal magnetic powder whose main component is α-Fe as the magnetic powder. The dispersibility and filling properties are determined by the shape and particle size distribution of iron oxyhydroxide, which is the raw material for producing this metal magnetic powder. and.

The shape and particle size distribution of this iron oxyhydroxide are greatly influenced by the synthesis conditions of iron oxyhydroxide.

Traditionally, iron oxyhydroxide was synthesized using an aqueous solution of ferrous salts such as ferrous sulfate and ferrous chloride.

Adding an alkaline solution such as ammonium hydroxide, sodium hydroxide, potassium hydroxide or sodium carbonate to produce ferrous hydroxide through a neutralization reaction;
A method of synthesizing iron oxyhydroxide by blowing an oxygen-containing gas into the suspension is generally known and is the most common method.

After the obtained iron oxyhydroxide is heated and dehydrated,
The metal magnetic powder is heated and reduced in an atmosphere of a reducing gas such as H, gas, etc., and a metal magnetic powder corresponding to the shape and particle size distribution of iron oxyhydroxide is produced.

[Problem that the invention seeks to solve]

If the iron oxyhydroxide produced by the above method contains divided particles called twins or grain crystals, the dispersibility and filling properties of the metal magnetic powder produced using these as raw materials may be affected. As a result, Br/8
It is not possible to obtain a magnetic recording medium with excellent m, SFD and Br. The present invention aims to solve this problem.

[Means for solving problems]

The present invention provides a method for synthesizing iron oxyhydroxide by supplying an oxygen-containing gas to a ferrous hydroxide suspension obtained by reacting an alkali to a ferrous salt aqueous solution, during or after the synthesis. In addition to coexisting ferrous iron in a suspension of iron oxyhydroxide, the temperature is at least 3°C higher than the synthesis temperature of iron oxyhydroxide.
The present invention provides a method for producing iron oxyhydroxide, which comprises a step of ripening in a non-oxidizing atmosphere at a higher temperature.

In other words, the present inventors have found that when a suspension of iron oxyhydroxide is aged at a very high temperature in the coexistence of ferrous iron and in a non-oxidizing atmosphere, there are fewer divided particles such as twins or dendrites. It was discovered that iron oxyhydroxide powder with a good particle size distribution could be obtained. It is convenient to insert this aging step in the middle of the synthesis reaction for synthesizing iron oxyhydroxide crystals, but it may be provided separately after the synthesis reaction is completed. In the case of insertion, unreacted ferrous iron is present in the reaction medium in addition to the partially produced iron oxyhydroxide.

A method may be adopted in which the supply of oxidizing gas is stopped during the synthesis reaction to stop crystal growth, and the reaction solution itself is maintained at a higher temperature in a non-oxidizing atmosphere. In this case, it is necessary to maintain the temperature higher than the temperature of the first synthesis reaction, specifically at least 3°C higher, and to maintain a non-oxidizing atmosphere, an inert gas such as N8 gas must be supplied to the liquid. Alternatively, the rest of the synthesis reaction can be continued after completing this aging step. Furthermore, when iron oxyhydroxide containing particles that have already been synthesized and has been refined is aged according to the present invention, such particles can be reduced.

The reason why such an effect was obtained is not necessarily clear, but it can be considered as follows. In other words, the generation of particles with many branches and poor particle size distribution is due to the generation of crystal nuclei and crystal growth proceeding in parallel.1. Fine crystal nuclei are generated or attached to the surface of the crystal during the synthesis process, and these are caused by branching. However, it is presumed that when ripening according to the present invention is performed, fine particles (crystal nuclei) on the surface of the crystal are redissolved and the cause of branching is removed.

The iron oxyhydroxide that has gone through the aging process in this way is 1
Iron oxyhydroxide was heated and dehydrated according to a well-known process, and Hz
Metal magnetic powder may be obtained by heating reduction in a reducing gas atmosphere such as, etc., and a magnetic recording medium using a magnetic paint of this magnetic powder has good results as shown in the following examples.
Bm, S F D and Br are shown.

[Example 1] 2.5 mol of ferrous sulfate and 10 mol of sodium hydroxide
51 with water to form a suspension containing ferrous hydroxide, air was blown at 200 cc/min at 35°C, and when 80% of the total ferrous in the raw material was oxidized, the air The blowing was interrupted and the mixture was aged at 40°C for 60 minutes in a N gas atmosphere, then cooled to 35°C, and air was blown at 200 cc/min again to produce iron oxyhydroxide with a specific surface area (BET value) of 44 m''/g. Obtained.

[Example 2] The example was repeated except that the synthesis temperature was 50'C and the aging temperature was 60'C, and iron oxyhydroxide with a BET value of 42 m''/g was obtained.

[Example 3] Example 1 was repeated except that the synthesis temperature was 50°C and the aging temperature was 90°C to obtain iron oxyhydroxide with a BET value of 39 m''/'g.

[Example 4] BET value 45 m''/g produced at a synthesis temperature of 45°C
Add 100g of iron oxyhydroxide and 10g of ferrous sulfate to 55g of pure water.
1 and aged at 80° C. for 3 hours in a Nz gas cloud atmosphere to obtain iron oxyhydroxide with a BET value of 40 m”/g.

[Comparative Example 1] Iron oxyhydroxide with a BET value of 45 m''/g was obtained under the same conditions as in Example 1 except that the synthesis temperature was 45"C and no aging was performed.

[Comparative Example 2] Iron oxyhydroxide with a BET value of 43 m''/g was obtained under the same conditions as in Example 1 except that the synthesis temperature was 50°C and P formation was not performed.

The iron oxyhydroxide obtained in the above-mentioned Examples and Comparative Examples was heated and dehydrated, then reduced at 450°C for 10 hours in an IHz atmosphere, cooled to room temperature, and then reduced to 5% in N2 gas containing 1% 02. A slow oxidation treatment was performed for a period of time to obtain ferromagnetic powder No. 1.

Table 1 shows the magnetic properties of each of the obtained ferromagnetic powders. In addition, each powder was made into a magnetic paint using a known method under the same conditions, and this was applied onto a polyester film under the same conditions, magnetically oriented under the same conditions, and cut into a predetermined size to produce a magnetic tape. The magnetic properties of each magnetic tape are also listed in Table 1.

As seen in the results in Table 1, the magnetic tape made of magnetic powder made from iron oxyhydroxide that was aged according to the present invention had a higher Br/B+ than that of the comparative example that was not aged.
s, S F D and Br are all good. It also has a high filling rate and is highly dispersible and highly packed.

Claims (1)

[Claims] When synthesizing iron oxyhydroxide by supplying an oxygen-containing gas to a ferrous hydroxide suspension obtained by reacting an alkali to a ferrous salt aqueous solution, oxyhydroxide is added during or after this synthesis. An oxywater comprising a step of coexisting ferrous iron in a suspension of iron oxide and aging in a non-oxidizing atmosphere at a temperature at least 3°C higher than the synthesis temperature of iron oxyhydroxide. Method for producing iron oxide.