DE2706315A1 - Acicular, alpha gesite prodn. - used in alpha iron oxide prepn. for magnetic recording powder - Google Patents

Abstract

Method comprises oxidising ferrous oxide with minute air or oxygen bubbles, 3 mm dia, in an aq alkali soln. As alpha-iron oxide of uniform dia. is obtd. property of magnetic recording tape can be increased.

Description

Process for the production of needle-shaped fine partial

Chen of α-goethite The invention relates to a method of production of acicular fine α-goethite particles of uniform particle size, which for the production of 7 iron oxide powder (which is used for magnetic recording and is required in the electronics industry) or a-iron oxide, which is suitable as Starting material for the production of various types of ferrites, i.e. oxide ceramics Materials, is suitable.

In the field of magnetic recording using 7-iron oxide powder, it is necessary to determine the magnetic field orientation characteristics, the transition characteristic and the noise characteristic (noise ratio, i.e.

the ratio of the strength of the noise to that of the recording signal) in particular the powder used as a recording medium in magnetic tapes to enhance.

One method is useful for improving these properties known, in which for the most uniform possible particle size of the 7 iron oxide powder Taken care of will. On the other hand, y-iron oxide is produced, adding a-goethite (FeOOH) to a dehydration and reduction reaction at about Subjected to 3500C in a hydrogen stream and thereby converted into magnetite (Fe304) which further oxidizes at about 2500C in the air and thereby turns into γ-iron oxide is converted. For the production of γ-iron oxide with a uniform particle size it is therefore necessary for a uniform particle size distribution of the as Starting material used to provide a-Goethite.

For the production of «goethite in the form of fine powders with uniform Particle size, various methods have been investigated, but a useful one Process has not yet been developed for this purpose.

The invention accordingly has the object of providing a method for Production of uniformly sized acicular fine particles of # -goethite, that for the production of fine γ-iron oxide powder for magnetic recording is suitable and required in the electronics industry, as well as for manufacture of # -iron oxide, a raw material for the manufacture of various types of ferrites or oxide-ceramic materials.

In the case of in-depth research with the aim of finding a method of manufacture of fine particles of a-goethite, which for the most part are uniform, to develop, it has now been found that this problem can be achieved if in the manufacture of a-goethite by oxidation of iron (II) hydroxide contained in an aqueous alkali solution with air or oxygen fine air or oxygen bubbles, for the most part are uniform, are formed, where- by an almost constant Number of oxygen molecules evenly with each particle in the reaction system contained iron (11) hydroxide is converted and evenly large needle-shaped fine particles of <x -goethite are formed.

The subject of the invention on which this finding is based is as far as the production of acicular fine particles of # -goethite according to a The method, which is characterized in that iron (II) hydroxide in a aqueous alkali solution with fine air or oxygen bubbles that for the most part have a uniform diameter, oxidized.

For the production of iron (II) hydroxide by the process according to In accordance with the invention, an alkali is added to an aqueous solution of an iron salt and this adjusted the pH of the solution to 10 to 13, whereby iron <II) hydroxide is formed.

Preferably at this point the oxidation of the formed Prevent iron (II) hydroxide from coming into direct contact with the atmosphere. Further is preferably the amount of iron (II) hydroxide contained in the aqueous alkali solution set to 0.1 to 0.2 mobile.

As the alkali for the preparation of the alkali aqueous solution, is preferred Sodium, potassium or ammonium are used. Examples of suitable iron salts are Iron (II) sulfate, iron (II) chloride, iron (II) nitrate and mixtures of these salts to call. The alkali aqueous solution to be subjected to oxidation preferably has a temperature of 500C or less and preferably does not contain any ferric hydroxide, To oxidize the iron (II) hydroxide contained in the solution, the air or the oxygen preference 5 wise in the form of bubbles that are 90% or more a uniform diameter of 3 mm or less, preferably 1 mm or less, blown into the alkali aqueous solution. These fine bubbles which for the most part have a uniform diameter, can be according to different Procedures are formed. For example, bubbles can be used for the procedure according to of the invention by the method described in U.S. Patent No. 3,802,674 easily formed (see Example 1 below).

With the aid of the method according to the invention, needle-shaped fine Particles of a-goethite with a ratio of the length of the major axis to that the smaller axis of about 10: 1 can be produced in a simple manner. as well can a-goethite with different particle sizes by changing the oxidation temperature of the iron (II) hydroxide contained in the aqueous alkali solution, the size of the Air or oxygen bubbles etc. can be produced.

The method according to the invention is illustrated by the following examples further explained.

Example 1 A solution of 112.2 9 iron (II) sulfate (Fe2S04.7H # O) in 2 l of distilled water was added to a 5 l vessel. On the surface of the Solution was poured liquid paraffin in such an amount that a paraffin layer a thickness of about 2 cm. While the ferrous sulfate solution is careful was stirred so that the layer of liquid paraffin was not disturbed a solution of 40 g of sodium hydroxide in 1.5 1 of distilled water gradually the Iron (II) sulfate solution added, whereby iron (II) hydroxide was precipitated.

A device for forming bubbles of uniform diameter was then immersed in the vessel and the device shown in Figure 1 for oxidation formed by iron (II) hydroxide.

Fig.1 shows a vessel 1 contained in an aqueous alkali solution precipitated ferrous hydroxide particles 2 and one on the surface of the aqueous Alkali solution 3 floating layer 4 of liquid paraffin. Into the aqueous alkali solution Fig. 3 is a forming apparatus 5 described in said U.S. Patent No. 3,802,674 used by bubbles of uniform diameter. This device consists of the rods 7, a mounting plate 6, which is above the liquid surface the rods 7 rests, an electric motor 8 mounted on the mounting plate 6, an inverted cylindrical body 10, the bottom of which at the lower end of a rotating Shaft 9 is attached, which is directly connected to the electric motor 8, and one Tube 11, which is used to supply air or oxygen and its end inside of the inverted cylindrical body 10 with a closed bottom.

While the temperature of the liquid in the vessel is kept at 500C and the electric motor was running at 4000 rpm, air was used to carry out the oxidation about 1 hour at an amount of 0.9 1 / minute in the inverted cylindrical body with a closed bottom (outer diameter 40 mm, height 60 mm). Here it was found that about 95% of the total bubbles have a diameter of about 0.5 mm.

The liquid had a pH of 12.4 and before the reaction after the reaction a pH of 13.0.

The obtained fine particles of # -goethite were distilled six times with Water at 500C Decant washed, filtered and taken under dried under reduced pressure at 500C. An electron microscope picture of the in Fine particles of α-goethite produced in this way are shown in FIG. Like these Figure shows, almost all of the fine particles of # -goethite are needle-shaped, and too an extremely small part are assemblies from existing pairs Particles, splinters and / or parallel adhesions under the extremely fine a-goethite particles ascertain. The length of the major axis is in the range from 0.2 to 0.4 / µm, and the ratio of the length of the major axis to the length of the minor axis is about 10: 1.

Then there was 10 g of the fine powder thus prepared of a-goethite 2 hours of dehydration and reduction reaction in flowing Nitrogen containing 5 vol. X hydrogen, subjected at 3300C. The received Material was oxidized in air at 2500C for 1.5 hours, whereby powdery y-iron oxide, the magnetic properties of which were then measured became. The measurements showed a coercive force (HC) of 450 Oersted, a saturation magnetization (s) of 67.0 electromagnetic units / g and a square ratio (R) (squareness ratio) of 0.55.

Example 2 In the manner described in Example 1 was in a Vessel an aqueous alkali solution by mixing ferrous sulfate with sodium hydroxide produced in the same proportions and a floating layer is liquid Paraffins applied.

The same device for producing fine bubbles with uniform Diameter as in Example 1 was immersed in the vessel. While the temperature the liquid was kept at 300C and the electric motor with 5000 R.p.m., air was made to carry out oxidation in an amount of 1.5 hours 0.4 1 / minute introduced. It was found to produce about 98X of all Bubbles were approximately 0.3 mm in diameter.

The liquid had a pH of 12.3 and before the reaction after the reaction a pH of 12.8.

The formed fine particles of # -goethite were distilled six times with Washed water at 300C by decanting, filtered and under reduced pressure dried at SOOC. The electron micrograph of the fine thus produced Particle is shown in Fig.3. As the illustration shows, the fine particles of a-goethite had almost the same shape as the particles prepared according to Example 1, however its major axis has a length of 0.1 to 0.15 mm.

Then, 10 g of the dried fine powder of α-goethite was applied treated in the manner described in Example 1 to obtain # iron oxide powder whose magnetic properties were measured. The measurements gave a Coercive force (HC) of 455 Oersted, a saturation magnetization (6s) of 70.0 electromagnetic units Ig and a squareness ratio of 0.55.

Claims (9)

Claims process for the production of needle-shaped fine Particles of a-goethite, characterized in that iron (II) hydroxide, the is contained in an aqueous alkali solution with fine air or oxygen bubbles, which for the most part have a uniform diameter, is oxidized. 2) Method according to claim 1, characterized in that iron (II) hydroxide used, which has been prepared by adding an alkali to an aqueous solution of an iron salt without bringing the solution into contact with the atmosphere, and thereby iron (II) hydroxide at a pH of the resulting solution of 10 to 13 forms. 3) Method according to claim 1 or 2, characterized in that one with a concentration of ferrous hydroxide in the aqueous alkali solution of 0.1 to 0.2 mol / l alkali solution works. 4) Process according to claim 1 to 3, characterized in that one the oxidation is carried out with fine air or oxygen bubbles reaching 90X or more a uniform diameter of 3 mm or less, preferably 1 mm or have less. 5) Process according to claim 1 to 4, characterized in that one Forms fine air or oxygen bubbles by putting air or oxygen in an inverted cylindrical body with a closed bottom that extends into the watery Alkali solution dips and moves around its vertical axis at high speed rotates, introduces. 6) Process according to claim 1 to 5, characterized in that one keeping the alkali aqueous solution at a temperature of 50 ° C or less. 7) Method according to claim 1 to 6, characterized in that one used as alkali in the aqueous alkali solution sodium, potassium or ammonium. 8) Process according to claim 1 to 7, characterized in that one an aqueous alkali solution that does not contain ferric hydroxide is used. 9) Process according to claim 1 to 8, characterized in that one as iron salt iron (II) sulfate, iron (1I) chloride, iron (II) nitrate or a mixture these iron salts are used.