JPS60161343A - Preparation of hexagonal ferrite magnetic powder - Google Patents

Abstract

PURPOSE:To prepare hexagonal ferrite magnetic powder having small particle size and superior magnetic characteristics by treating hydrothermally the coprecipitate obtd. by adding alkali to aq. soln. contg. Ba salt, etc. and Fe salt, then heat-treating the coprecipitate in a flux. CONSTITUTION:Aq. soln. of alkali is added to aq. soln. contg. Fe salt and at least one kind among Ba salt, Sr salt, and Pb salt. Thus obtd. coprecipitate is treated hydrothermally in an autoclave at ca. 200-350 deg.C for 1-6hr to grow fine particles of hexagonal ferrite. The particles are then heat-treated in a flux such as NaCl, etc. at >= melting point of the flux. By this process, sintering between particles is inhibited by the interposition of the flux and crystallizing property of particles is improved. As the result, preferred hexagonal ferrite suitable to a magneticrecording medium for high density recording having extremely small particle size, high saturation magnetization, and superior in dispersibility and orientation, is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for producing hexagonal ferrite magnetic powder suitable for use in magnetic recording media suitable for high-density recording.

[Background technology]

Orthogonal ferrite magnetic powder is conventionally obtained by adding an alkaline aqueous solution to 1 g of water containing one of Ba salt, Sr salt, and PB salt and iron salt. The coprecipitate was subjected to hydrothermal treatment using an autoclave (T, Takada, M, Kiya
ma XProcXICF, Conf, P 69
(1971)] is produced in the form of a plate with an axis of easy magnetization perpendicular to the plate surface. The magnetic layer is oriented so that its plane is parallel to the plane of the magnetic layer to utilize the residual magnetization component in the perpendicular direction, and it is attracting attention as a method suitable for high-density recording.

However, hexagonal ferrite magnetic powder obtained by these conventional methods has the disadvantage that when the particle size is reduced to make it suitable for high-density recording, the amount of saturation magnetization decreases. 0, 3μ suitable for
If the size is smaller than 1, a sufficiently large amount of saturation/phasing cannot be obtained, and if the particle size is less than 0.1 μm, the amount of saturation magnetization will drop significantly. Therefore, in order to improve this and reduce the high saturation magnetic flux, the coprecipitate obtained by the above hydrothermal treatment was washed with water, dried, and then heat treated in air at 450 to 1100'C (Kojima Hiroshi, Choji Miyayo, Powder Metallurgy 1st Association, 1971 Spring Conference Lecture Summary Collection P118 (197
2)) However, when such force LIQ treatment is performed, although the saturation magnetization increases, the particle size is extremely small, and since these fine particles come into contact with each other at high temperatures, sintering between particles occurs. However, there are problems in that dispersibility and orientation deteriorate, and a hexagonal ferrite magnetic powder that is fully satisfactory for use in magnetic recording media suitable for heavy density recording has not yet been obtained.

[Purpose of the invention]

The present invention eliminates such drawbacks and provides a hexagonal ferrite 1 suitable for use in high-density recording magnetic recording media, which has small particle size, large saturation magnetization, and excellent dispersibility and orientation.
- It was made for the purpose of obtaining magnetic powder.

[Summary of the invention]

This invention involves adding an alkaline aqueous solution to an aqueous solution of a metal salt containing one or more metal salts selected from Ba salts, Sr salts, and Pb salts, and an iron salt; A step of hydrothermally treating the precipitate to produce hexagonal ferrite particles, and a step of heat-treating the hexagonal ferrite particles obtained in this step in a flux at a temperature higher than the melting point of the flux. It is characterized by containing,
First, fine hexagonal ferrite particles with an extremely small particle size are produced using a hydrothermal treatment method, and then they are melted at a high temperature and placed in a flux that does not form a solid solution with the hexagonal ferrite particles at the melting point of the flux. By heat-treating at a temperature above, sintering between particles is effectively suppressed and crystallinity is improved, resulting in extremely small particle size, high saturation magnetization, and high density with excellent dispersibility and orientation. A hexagonal ferrite magnetic powder suitable for use in recording magnetic recording media was obtained.

In this invention, when hexagonal ferrite particles are generated,
An alkaline aqueous solution is added to a metal salt water/8 solution containing one or more metal salts selected from Ba salt, Sr salt, and Pb salt and an iron salt, and by addition of this alkaline aqueous solution, fl
By hydrothermal treatment of the coprecipitate, B
As the a salt, Sr salt, pb salt, and iron salt, chlorides, sulfates, nitrates, carbonates, etc. of these metals are preferably used.

At this time, if appropriate amounts of metal ions such as Co, Ti, Zn, and Mn are added together with these, the coercive force can be controlled arbitrarily, the particle size can be reduced, and hexagonal ferrite particles with a sharp particle size distribution can be obtained. Therefore, these C
Chlorides, sulfates, nitrates of o, Ti, Zn, Mn, etc.
Carbonate may also be added at the same time if necessary.

Caustic soda is usually used as the alkali.
The preferred amount is more than the molar equivalent of the metal salt to be added,
It is preferable that the excess alkali concentration is 0.1 mol/12 or more, and in particular, the excess alkali concentration is 2 mol/7! in order to make the particle size of the obtained hexagonal ferrite particles extremely small. It is preferable to do the following.

The hydrothermal treatment is carried out using an autoclave, and the heat treatment in the Ohmy crepe is carried out at 200 to 350 °C in order to extremely reduce the particle size of the hexagonal ferrite particles.
This is done by heating at a temperature of 1 to 6 hours.

The extremely fine hexagonal ferrite particles produced in this way are then heat-treated in a flux at a temperature higher than the melting point of the flux. Since the hexagonal ferrite particles do not come into contact with each other due to the presence of a flux, sintering between the particles does not occur even if the hexagonal ferrite particles are non-dense and small particles. The heat treatment inside improves the crystallinity of the hexagonal ferrite particles without sintering between the particles, resulting in hexagonal ferrite particles with extremely small particle size, high saturation magnetization, and excellent dispersibility and orientation. A crystalline ferrite magnetic powder is obtained.

The flux used here has a temperature of 500 to 1000°C.
It is preferable to use a material that melts at a temperature of 100° C. and does not form a solid solution with the hexagonal ferrite particles at all. If the melting temperature is lower than this, the heat treatment of the hexagonal ferrite particles will be insufficient, and the crystallinity of the hexagonal ferrite particles will deteriorate. It is not possible to sufficiently improve the saturation magnetization and increase the saturation magnetization sufficiently, and on the other hand, the crystal growth of hexagonal ferrite particles in the flux becomes noticeable and the particles become coarse, so it is preferable. do not have. Further, it is not preferable to use a substance that forms even a small solid solution with the hexagonal crystal fiber (hexagonal crystal fiber) particles because the saturation magnetization cannot be sufficiently improved. As such a fluxing agent, for example, Na
, and Li sulfates, chlorides, bromides, iodides, etc. are used as preferred, especially NaCl and K
Since Cl dissolves well in water, it is easy to remove these fluxes by washing with water after heat treatment, and it does not remain as an impurity in the powder particles, so it is preferably used.

It is preferable that the heat treatment using the flux be carried out at a temperature within the range of 800 to 850°C for 1 to 4 hours; if the treatment temperature is too low or the treatment time is too short, the heat treatment will be insufficient.
If the crystallinity of the hexagonal ferrite particles cannot be sufficiently improved to sufficiently increase the saturation magnetization, and the processing temperature is too high or the processing time is not long, the flux will adhere to the particle surface. There is a risk that the amount of saturation magnetization may be reduced instead.

As described above, in the present invention, first, fine hexagonal ferrite particles with extremely small particle sizes are produced by a hydrothermal treatment method, and then these are melted at one temperature, and the hexagonal ferrite particles and all ( Because the heat treatment is carried out in a flux that does not form a solid solution at a temperature above the melting point of the flux, the crystallinity of the hexagonal ferrite particles is improved without sintering between particles, and the particle size is extremely small and the amount of saturation magnetization is low. A hexagonal ferrite magnetic powder which is large in size and has excellent dispersibility and orientation and is suitable for use in high-density recording magnetic recording media can be obtained.

〔Example〕

Next, embodiments of the invention will be described.

Example I <Production of 13a fluorite particles> 1 mol of ferric chloride, 1/8 mol of barium chloride, and 1/20 mol of cobal chloride I-17! The mixed solution dissolved in water was added to the caustic soda aqueous solution of 1a in which 5 mol of caustic soda was dissolved and stirred. Next, this one suspension! After aging for 1 day, put the sediment in an autoclave and
The 13a fluorite particles were removed by a heating reaction at 80°C for 4 hours.

<Heat treatment of Ba ferrite particles in a flux> After thoroughly washing the Ba ferrite particles obtained by the above method with water until the pH becomes 8 or less, suspend the Ba ferrite particles so that the total volume containing the Ba ferrite particles is 1β. Add the liquid to this suspension.
00g of NaCp was added and stirred to dissolve.

Next, put this Ba ferrite (Ba ferrite) particle suspension in which NaCl has been dissolved into a large-area hat, and dry it in a dryer.
'C to evaporate the water.

The Ba ferrite particles thus obtained and NaCf
The mixture of f was placed in a rutsuho, heated at 830°C for 2 hours, and then cooled to room temperature. Next, NaC (
1 was dissolved and removed, and only Ba ferrite particles were taken out to obtain Ba ferrite magnetic powder. The particle size of the obtained Ba ferrite magnetic powder was 0.10μ.

Example 2 In the production of Ba ferrite particles in Example 1,
Ba ferrite particles were synthesized in the same manner as in Example 1, except that cobalt chloride was omitted and the amount of barium chloride used was changed from 1/8 mol to 1/6 mol, and heat treatment was performed in a flux to form Ba ferrite. A magnetic powder was obtained. The particle size of the obtained Ba ferrite magnetic powder was 0.15μ.

Example 3 Ba ferrite particles were produced in the same manner as in Example 1, except that the same amount of KCI was used instead of NaC6 in the heat treatment in a flux of Ba ferrite particles in Example 1, and the heat treatment in a flux was performed. Ba ferrite magnetic powder was obtained. The particle size of the obtained Ba ferrite magnetic powder was 0.08
It was μ.

Regarding the Ba ferrite magnetic powder obtained in each example,
Coercive force, saturation magnetization, and square shape were measured before and after heat treatment in a flux.

The table below shows the results.

〔Effect of the invention〕

As is clear from Table 2, after heat treatment in a flux,
The coercive force, saturation magnetization, and square shape are significantly increased. Therefore, according to the manufacturing method of the present invention, a hexagonal ferrite with large coercive force and saturation magnetization, and excellent dispersibility and orientation. It can be seen that magnetic powder can be obtained.

In addition, the increase in saturation magnetization was particularly remarkable.Furthermore, when the shape of the Ba ferrite particles was observed before and after heat treatment in a flux using an electron microscope, the shape of the particles was hexagonal plate-like, and no interparticle sintering was observed. No changes in shape were observed. Therefore, it can be seen that according to the manufacturing method of the present invention, sintering between particles is effectively suppressed, and as a result, a particularly high saturation magnetization amount of +t'li is obtained. Furthermore, as a result of X-ray diffraction, the diffraction line of the particles before heat treatment in the flux was 13
The diffraction lines were only due to the A ferrite particles, but the diffraction lines were broad, while the diffraction lines due to the Ba ferrite particles were sharp in the case of the particles heat-treated in a flux. Therefore, depending on the manufacturing method of this invention,
It is thought that the crystallinity of the Ba ferrite magnetic powder was improved and the saturation magnetization was significantly improved.

Claims (1)

[Claims] 1. Add 8 liquids of alkaline water to 18 liquids of metal salt water containing at least one cup of Ba salt, Sr salt, Pb salt, and 2 metal salts and iron salts. The coprecipitate thus obtained is hydrothermally treated to produce hexagonal ferrite particles] and the hexagonal ferrite particles obtained in this step are added to a flux in a flux. 1. A method for producing a hexagonal ferrite powder, the method comprising the step of heat treatment at a temperature higher than the melting point of the hexagonal ferrite powder.