JPS5921366B2 - Method for producing acicular Fe-Co alloy magnetic particle powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing acicular Fe(O) alloy magnetic particles.

More specifically, it is a substantially high-density particle powder that retains acicular crystals and particle size, does not contain dendritic particles, and has an increased degree of crystallinity on the particle surface and inside the particle. Due to this, it has magnetic properties such as large saturation magnetic flux density σs and high coercive force Hc, and powder properties as a magnetic material for magnetic recording with high dispersibility, high orientation, and high packing property. It is an object of the present invention to provide a new technical means that can easily produce a particularly suitable acicular Fe--CO alloy magnetic particle powder.

In recent years, as magnetic recording and reproducing equipment has become smaller and lighter, there has been an increasing need for higher performance recording media such as magnetic tapes and magnetic disks.

That is, high recording density, high sensitivity characteristics, high output characteristics, and especially improvement in frequency characteristics are required. The characteristics of a magnetic material suitable for satisfying the above-mentioned requirements for a magnetic recording medium are that it has a large saturation magnetic flux density and a high coercive force. By the way, the magnetic materials conventionally used in magnetic recording media are magnetic powders such as magnetite, maghemite, and chromium dioxide, and these magnetic powders have a saturation magnetic flux density σS7O~85emu/9 and a coercive force Hc25O~
5000e.

In particular, the σs of the oxide magnetic particles is at most 85 emu.
/9, and generally σS7O to 80 emu/9, which is the main reason for limiting the reproduction output and recording density. Furthermore, CO-magnetite and CO-maghemite magnetic powders containing CO are also used, but these magnetic particle powders have a coercive force Hc of 400 to 400.
It has the characteristic of being as high as 8000e, but on the other hand, the saturation magnetic flux density σs is as low as 60 to 70 emu/9. Recently, there has been active development of magnetic particles with characteristics suitable for high output and high density recording, that is, magnetic particles with higher saturation magnetic flux density and higher coercive force. , acicular crystal goethite particles obtained by reacting a ferrous salt solution with an alkali and air oxidation (usually referred to as wet reaction), acicular crystal hematite particles obtained by heating and dehydrating the acicular crystal goethite particles, or Acicular goethite particles containing various metals other than Fe are used as a starting material, and the starting material is immersed in a reducing gas.
It is an acicular crystal metal iron magnetic particle powder or an acicular crystal alloy magnetic particle powder obtained by reduction at a relatively low temperature of about 50° C. for a long time.

The coercive force Hc of the acicular metal iron magnetic particles or the acicular alloy magnetic particles can be expressed by the following relational expression.

Hc-K・(Nb-Na)・Ms In this relational expression, K is related to the degree of crystallinity of the particles, (Nb-Na) is related to the shape (acicularity) of the particles, and Ms is related to the chemical composition of the particles. It is a term.

As is clear from this relational expression, in order to improve the coercive force of the acicular metal iron magnetic particles or the acicular alloy magnetic particles, it is necessary to reduce the acicular crystals of the acicular goethite particles as the starting material. It is necessary to increase the degree of crystallinity of the product acicular metal iron magnetic particles or acicular alloy magnetic particles.

Conventionally, in producing acicular crystal metal iron magnetic particles or acicular crystal alloy magnetic particles, a large amount of reducing gas is used at the lowest possible temperature that allows the reduction reaction to occur at about 350°C, as described above. The reason why the heat reduction treatment is carried out over a long period of time using is because the primary consideration was how to retain and inherit the acicular crystals of the acicular goethite particles. This is described, for example, in Japanese Patent Publication No. 49-7313 as follows.

Acicular metal iron magnetic particle powders are also known to be made by reducing pulverized hydroxide oxides with hydrogen or other gas-generating reducing agents.

In order to carry out the reduction at a rate that can be practically used, it is necessary to carry out the reduction at a temperature of 350°C or higher. However, the resulting metal particles are fused together, which is not desirable as a magnetic recording material. On the other hand, when the reduction is carried out at a temperature of 350° C. or lower, this is preferable because the metal particles produced do not fuse together, but the reduction time becomes longer, which is actually undesirable. ”. However, although it is possible to retain and inherit the acicular crystals of particles relatively well by employing heat reduction treatment at low temperatures, the produced acicular metal iron magnetic particles or acicular alloy magnetic particles are The degree of crystallinity is small, and therefore the coercive force Hc is also small. The higher the temperature at which acicular goethite particles, acicular hematite particles, or acicular goethite particles containing various metals other than Fe are heated and reduced in a reducing gas, the higher the degree of crystallinity. It is known that acicular crystal metal iron magnetic particles or acicular crystal alloy magnetic particle powders having a large saturation magnetic flux density can be obtained. However, when the temperature of heating and reduction increases, the deformation of the acicular crystal grains of this metal iron magnetic particle powder or alloy magnetic particle powder and the sintering between particles and particles become significant, resulting in the resulting metal iron magnetic particle powder or alloy magnetic particle powder The coercive force of the magnetic particles will be extremely reduced.

On the other hand, the output characteristics and sensitivity characteristics of magnetic recording media such as magnetic tapes and magnetic disks depend on the residual magnetic flux density Br.
It depends on the orientation and filling properties in the coating film. and,
In order to improve the dispersibility in the vehicle, the orientation and filling properties in the coating film, the magnetic particles dispersed in the vehicle must have excellent acicular crystals and have uniform particle size.
Further, it is required that dendritic particles are not mixed therein.

In order to obtain magnetic particles with such characteristics, the starting material, acicular goethite particles, must have excellent acicular crystals, uniform particle size, and a mixture of dendritic particles. It is necessary that there be no. As mentioned above, in the manufacturing process of acicular crystal metal iron magnetic particles powder or acicular crystal alloy magnetic particle powder, the starting material must first have excellent acicular crystals, have uniform particle size, and It is necessary to generate acicular goethite particles without dendritic particles or acicular goethite particles containing various metals other than Fe, and how to control the acicular crystals and particle size. The major issue is whether to make substantially high-density acicular crystal metal iron magnetic particles or acicular crystal alloy magnetic particles with an increased degree of crystallinity through thermal reduction while retaining and inheriting the above properties. .

The present inventor has been involved in the production and development of acicular crystal goethite particles for many years, and in the course of his research, he discovered that the particles have acicular crystals and are uniform in particle size.
We have also already developed a method to obtain acicular goethite particles that do not contain dendritic particles.

For example, as described below.

That is, it has acicular crystals, has uniform particle size, and
Acicular goethite particles without dendritic particles are
When obtaining a mixed aqueous solution containing Fe(0H)2 and CO(0H)2 of PHL2 or more (however, the amount of CO(0H)2 mixed is 0.1 to 7.0 at% in terms of CO relative to Fe). All metal atoms (Fe(!:.CO
) to give an amount of 0.1 to 1.1 atomic% calculated as S1 (however, the amount of CO(0H)2 mixed and the amount of water-soluble silicate added are based on the amount of CO converted to Fe). and 5 times the amount of Si equivalent to all metal atoms (Fe and CO) (total of 8 atoms? or less), then the alkaline aqueous solution is reacted with a ferrous salt aqueous solution and a water-soluble CO salt aqueous solution to form fine particles. P containing symmetrical Fe(0H)2 and CO(0H)2
It can be obtained by obtaining a mixed aqueous solution of Hl2 or more and then oxidizing it.

This method will be explained as follows.

Conventionally, the most typical known method for producing CO-containing acicular goethite particles in the alkaline region of PHL2 or higher by reacting an aqueous ferrous salt solution with an alkali and air oxidation is For the Fe ion of
A solution with a PHL of 2 or more obtained by adding an equivalent amount or more of alkali to an aqueous solution containing 10 atomic % or less of CO ions was heated at 50°C.
CO-containing acicular goethite particles are obtained by carrying out an oxidation reaction at the following temperature. The CO-containing acicular goethite particles obtained by this method generally have asymmetric particle sizes and contain dendritic particles.

Generally, CO-containing acicular goethite particles are produced through two steps: generation of CO-containing acicular goethite core particles and growth of the CO-containing acicular goethite core particles.

The CO-containing acicular goethite core particles are formed by combining dissolved oxygen with a floc consisting of Fe(0H)2 and CO(0H)2 obtained by reacting an aqueous ferrous salt solution containing CO with an alkali. It is produced by a reaction, but because the contact reaction with dissolved oxygen is partial and nonuniform, the generation of CO-containing acicular goethite core particles and the growth of the CO-containing acicular goethite core particles occur simultaneously. Moreover, since many new nuclei are generated until the production reaction of CO-containing acicular goethite is completed, the obtained CO-containing acicular goethite particles have asymmetric particle sizes and also contain dendritic particles. It is thought that it will become a thing. The generation of dendritic particles is thought to be caused by the generation mechanism of core particles, but the details are unknown. In the above conventional technology, Fe(0H)2 and CO(
A water-soluble silicate is added in advance to the alkaline aqueous solution used to obtain a mixed aqueous solution of PIll2 or more containing 0H)2 and all metal atoms (Fe and CO2) in the mixed aqueous solution.
) is 0.1 to 1.1 atoms in terms of Si? (However, the amount of CO(0H)2 mixed and the amount of water-soluble silicate added are based on the amount of CO equivalent to Fe and the total metal atoms
The total amount of 5 times the amount of Si equivalent to Fe (5C0) is 8
atom? below), Fe(0H)2 and CO(0
H) 2 can be made homogeneous, and furthermore, the water-soluble silicate is composed of Fe(0H)2 and CO(0H)
The production of CO-containing acicular goethite core particles and the CO-containing acicular goethite core are due to the effect of suppressing the oxidation reaction when producing CO-containing t-shaped goethite particles from an aqueous solution containing 2. Since the particles can be grown in stages, it is possible to obtain CO-containing acicular goethite particles that have uniform particle size and do not contain dendritic particles.

Figure 1 shows the reaction between the amount of water-soluble silicate added to an alkaline aqueous solution and the formation of CO-containing acicular goethite particles under conditions where the reaction solution concentration, reaction temperature, and air aeration amount are constant. It is a time relationship diagram.

In the figure, curves A, B, and C each have a reaction solution concentration of 0.3 m
This is the case of 01/1, 0.4m01/1, and 0.7m01/l. As shown in Figure 1, the reaction solution concentration, the reaction solution PH
Even though the reaction temperature and air aeration rate are constant, the formation reaction time of CO-containing acicular goethite particles is significantly shortened as the amount of water-soluble silicate added increases. 0H)2 and CO(0H)2, and Fe(0H)2 particles and CO(0H)2 particles that make up the floc of Fe(0H)2 and CO(0H)2, and dissolved oxygen. This is thought to be because the contact reaction was carried out very efficiently.

This indicates that as the amount of water-soluble silicate added increases, the flocs consisting of Fe(0H)2 and CO(0H)2 become sufficiently fine and homogenized, and at the same time Fe(0H)2
and 4 Fe(
This is considered to indicate that the 0H)2 particles and CO(0H)2 particles themselves are also refined and homogenized.

Figure 2 shows the relationship between the amount of water-soluble silicate added to an alkaline aqueous solution and the specific surface area of CO-containing acicular goethite particles produced under exactly the same reaction conditions as in Figure 1. It is something that

In the figure, curves A, B, and C each have a reaction solution concentration of 0.3 m
This is the case of 011/1, 0.4m01/2, and 0.7m02/l.

Generally, when the concentration of the reaction solution is kept constant, the specific surface area of the particles tends to increase as the reaction time for producing CO-containing acicular goethite particles becomes shorter.

However, in the above method, as shown in the figure,
The reason why the specific surface area of the CO-containing acicular goethite particles remains almost constant despite the shortening of the production reaction time is because the water-soluble silicate has Fe(0H)2 and C
It has the effect of suppressing the oxidation reaction when producing CO-containing acicular goethite particles by oxidizing an aqueous solution containing This is thought to be because the growth of CO-containing acicular goethite core particles occurs in stages.

Examples of the ferrous salt aqueous solution used in the above method include a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution.

As CO, water-soluble CO salts such as cobalt sulfate and cobalt chloride can be used.

As water-soluble silicates, sodium and potassium silicates can be used.

The water-soluble CO salt aqueous solution and the water-soluble silicate are Fe(
The amount of CO(0H)2 mixed with respect to 0H)2 is 0.1 to 7.0 at% in terms of CO with respect to Fe, and the amount of water-soluble silicate added is in terms of Si with respect to all metal atoms (Fe and CO). So 0.
1 to 1.1 at%, provided that the mixed amount of CO(0H)2 and the added amount of water-soluble silicate are 5 times the CO equivalent amount for Fe and the Si equivalent amount for all metal atoms (Fe.15CO). They may be mixed and added so that the total amount is 8 atomic % or less.

The amount of CO(0H)2 mixed is 0.1 atom in terms of CO compared to Fe? If it is below, the contribution of CO to the coercive force and saturation magnetic flux density is insufficient and it is impossible to obtain acicular Fe--CO alloy magnetic particles having high coercive force and high saturation magnetic flux density.

If it is 7.0 atoms or more in terms of CO compared to Fe,
Granular magnetite particles are mixed in.

The amount of water-soluble silicate added is all metal atoms (Fe and CO)
If it is 0.1 atomic % or less in terms of Sl, the particle size will be asymmetric and there will be a large amount of dendritic particles mixed in.
If it is 1.1 atomic % or more, granular magnetite particles will be mixed in.

The amount of CO(0H)2 mixed and the amount of water-soluble silicate added is 8 atoms, which is the sum of the CO equivalent amount for Fe and 5 times the Si equivalent amount for all metal atoms (Fe and CO)? If it is more than that, granular magnetite particles will be mixed in. This will be explained with reference to FIG.

In FIG. 3, the shaded area is the region where CO-containing acicular goethite particles used in the present invention are generated, and the triangular area surrounded by points A, b, and c with straight line A as one side is the area where the CO A mixture of acicular goethite and granular magnetite particles is produced.

That is, acicular goethite particles are defined by straight line A indicating that the sum of the mixed amount of CO(0H)2 and the added amount of water-soluble silicate is 8 atomic % based on Fe, respectively, in terms of CO and Si. There is a distinction between the region where magnetite particles are produced and the region where granular magnetite particles are produced. Considering the particle size and axial ratio of the obtained CO-containing acicular goethite particles, the amount of CO(0H)2 mixed with Fe(0H)2 is 0.5 to 7.0 at% in terms of CO to Fe, The amount of water-soluble silicate added is 0.3 to 0.0% in terms of Si relative to all metal atoms (Fe and CO).
7 atomic%, however, the amount of CO(0H)2 mixed and the amount of water-soluble silicate added is 8 as the sum of the CO equivalent amount for Fe and 5 times the Si equivalent amount for all metal atoms (Fe(5C0)). It is preferable that the amount is less than atomic.The CO-containing acicular goethite particles obtained by the above method naturally contain a trace amount of Si in the particles.Next, how to obtain the above Acicular crystals of CO-containing acicular goethite particles, which have acicular crystals obtained by the method detailed in 2003, have uniform particle size, and are not mixed with dendritic particles and are contaminated with a trace amount of Si. The problem is whether to thermally reduce the magnetic particles while maintaining the crystallinity and particle size to obtain substantially high-density acicular Fe--CO alloy magnetic particles with an increased degree of crystallinity.

As mentioned above, even if the acicular crystals and particle size of the particles can be maintained relatively well by employing a thermal reduction treatment at low temperatures, the acicular crystal Fe-CO alloy magnetic particles produced have a low crystallinity. The degree of The higher the heating reduction temperature, the higher the degree of crystallinity, but on the other hand, the deformation of the acicular crystal grains of the Fe-CO alloy magnetic particles and the sintering of the particles and their mutual particles become significant, resulting in a decrease in coercive force. becomes extremely low. In particular, the shape of the particles is easily affected by the heating temperature, and especially when the atmosphere is reducing, the particle growth is significant, and a single particle grows to a size exceeding that of the skeletal particle.
The outer shape of the skeleton particles gradually disappears, causing deformation of the particle shape and sintering of the particles and each other. As a result, the coercive force decreases. The present inventor has determined that the particle size of the CO-containing acicular goethite particles used in the present invention is uniform and that the particles are contaminated with a trace amount of Si without any dendritic particles, by heating and dehydrating them at around 300°C. Using the obtained CO-containing acicular hematite particles contaminated with Si as a starting material, the starting material is heated and reduced in a reducing gas to obtain acicular Fe.
The deformation of the particle shape and the sintering phenomenon between the particles and each other in the case of -CO alloy particles were studied in detail. That is,
Figure 4 shows CO-containing acicular goethite particles (2.0 atoms in terms of CO compared to Fe) that are uniform in particle size and are contaminated with a trace amount of Si without any dendritic particles. %, S relative to all metal atoms (Fe and CO)
Acicular crystals with an average major axis length of 0.70 μm and a specific surface area of 120 m/9, consisting of a group of fine hematite single particles obtained by heating and dehydrating 0.6 atomic % (calculated as i) The skeleton particles are reduced by heating at 400°C in a hydrogen stream to produce acicular Fe.
degree of reduction X (FeOxl, 1.5〉X〉
0) and the specific surface area.

As can be seen from Figure 4, the specific surface area of the generated particles rapidly decreases as thermal reduction progresses, which is due to the rapid occurrence of deformation of the particle shape and sintering of the particles and their mutual particles. It shows.

This phenomenon will be explained in detail below.

In general, acicular hematite particles obtained from acicular goethite particles contaminated with S1 have many pores generated by dehydration on the particle surface and inside the particles, and these pores are On the other hand, it is known that when the heating temperature exceeds 800°C, sintering progresses and the acicular crystal grains collapse.

This is described in Japanese Unexamined Patent Publication No. 48-83100 as follows.

Acicular goethite particles that are contaminated with a small amount of Si can be heated to 800°C without sintering of the needles during dehydration treatment or subsequent tempering (high-temperature heating treatment of acicular hematite particles). It is possible to use temperatures up to

"Acicular hematite particles, which have been generally used as a starting material, are produced by heating acicular goethite particles at 300°C.
These are acicular crystal skeleton particles obtained by heating and dehydrating at a temperature in the vicinity, and retain the outer shape of acicular crystal goethite particles, and these skeleton particles are composed of agglomerated particles in which a large number of single particles are connected.

In this case, the reason why the acicular goethite particles are heated and dehydrated at a relatively low temperature of around 300° C. is because the primary consideration is how to retain and inherit the acicular crystals of the acicular goethite particles. However, acicular hematite particles obtained by heating at a relatively low temperature around 300°C retain and inherit acicular crystals, but on the other hand, the growth of single particles is not sufficient, and therefore The degree of crystallinity of the particles is small. In particular, when acicular goethite particles contaminated with a small amount of Si are heated and dehydrated at a low temperature around 300°C by a conventional method, the crystallinity decreases due to the well-known particle growth inhibiting effect of Si. The degree becomes even smaller.

Therefore, acicular hematite particles contaminated with a small amount of Si have many pores on the particle surface and inside the particle, and only particles with a large specific surface area can be obtained.

In FIG. 5, the average major axis length is 0.75 μm and the specific surface area is 40.0Tr1/f! The particle size used in the present invention is uniform, and CO-containing acicular goethite particles (2.0 at. , 0.6 at% in terms of Si based on all metal atoms (Fe and CO))
This figure shows the relationship between the dehydration rate and the specific surface area of particles produced under conditions of different dehydration rates in the process of heating and dehydrating CO-containing acicular hematite particles contaminated with S1.

In the figure, curves A, B, and C are for dehydration rates of 7.2 mol/min, 2.0 mol/min, and 0.25 mol/min, respectively. As is clear from FIG. 5, the specific surface area of CO-containing acicular hematite particles contaminated with a small amount of Sl obtained by changing the dehydration rate differs; the slower the dehydration rate, the smaller the specific surface area of Si. CO contaminated with
Although it is possible to obtain a powder containing acicular hematite particles,
It is 50-807 TI/9th place at most.

In this way, when CO-containing acicular hematite particles that are contaminated with a trace amount of Si and have insufficient particle growth and therefore have a small degree of crystallinity are thermally reduced in a reducing gas, thermal reduction occurs. Because the growth of a single particle during the process, that is, the physical change, is rapid, uniform growth of a single particle is difficult to occur. It is thought that sintering between particles occurs and the particle shape becomes easily distorted.

In addition, during the thermal reduction process, rapid volumetric contraction from the oxide to the metal occurs, making the particle shape more likely to collapse.

Furthermore, since the atmosphere in the heat treatment in the thermal reduction process is reducing, a chemical change called a reduction reaction occurs at the same time as a physical change such as growth of a single particle.

Therefore, in order to obtain acicular crystalline Fe-CO alloy magnetic particles, it is necessary to simultaneously control physical and chemical changes, which requires a very long time for thermal reduction treatment, and , large amounts of reducing gas were also required. The fact that the heat reduction treatment requires a long time causes deformation of the particle shape of the generated particles and further progresses sintering of the particles and the particles themselves. As mentioned above, the reason for the deformation of particle shape and sintering between particles and particles during the thermal reduction process is that the uniform particle growth of single particles occurs because the particle growth of single particles is rapid. It is difficult to imagine that a rapid volume contraction occurs from the oxide to the metal, and that the physical change of single particle growth and the chemical change of reduction reaction occur simultaneously.

Therefore, in view of the above phenomenon, the inventors of the present invention have proposed that, prior to the thermal reduction process, under a non-reducing atmosphere where the physical change of particle growth of a single particle and the chemical change of reduction reaction do not occur at the same time. Heat and sinter to produce a single particle,
In addition, if the starting material is used as a starting material that has a substantially high density with an increased degree of crystallinity and retains acicular crystals by uniform particle growth, it will not be chemically oxidized during the thermal reduction process. We thought that it would be possible to prevent particle deformation and sintering between particles and particles during the thermal reduction process by mainly performing the change.

The present inventor then heats and calcinates the CO-containing acicular hematite particles contaminated with a trace amount of Si used in the present invention in a non-reducing gas to achieve sufficient and uniform particle growth of a single particle. As a result of various studies in order to obtain starting material hematite particles that have a substantially high density with an increased degree of crystallinity and retain and inherit acicular crystals, the present invention was arrived at. be.

That is, the present invention provides a mixed aqueous solution containing Fe(0H)2 and CO(0H)2 with a PHL2 or higher (however, CO(0H)2
The mixing amount of Fe is 0.1 to 7.0 atomic% in terms of CO.
), a water-soluble silicate is added in advance to the alkaline aqueous solution used to obtain 0.1 to 1.1 atomic % in terms of Sl based on the total metal atoms (Fe and CO) in the mixed aqueous solution.
(However, the amount of CO(0H)2 mixed and the amount of water-soluble silicate added are
Si equivalent amount and total metal atoms ((Fe.l5CO))
8 atomic % or less in total with 5 times the equivalent amount), then the alkaline aqueous solution is reacted with a ferrous salt aqueous solution and a water-soluble CO salt aqueous solution to form fine and homogeneous Fe(0H)2 and CO.
(0H)2 is obtained, and then oxidized to produce CO-containing acicular goethite particles, and the produced CO-containing acicular goethite particles are washed door to door, washed with water, and dried. The average major axis length obtained by heating and dehydration is 0.3 to 2.0 μm, and BET
CO-containing acicular hematite particles having a specific surface area of 50 to 300 I/9 by the method and maintaining the long axis length and axial ratio of CO-containing acicular goethite particles are heated with heated steam and a non-reducing gas. Water vapor partial pressure -6 in an atmosphere consisting of
-PS+Pl (Ps is water vapor partial pressure, Pi is non-reducing gas partial pressure) 30~
Needles with an average major axis length of 0.1 to 1.5 μm and a specific surface area of 10 to 30 I/9 by the BET method by heating and firing at a temperature of 350 to 700°C. After forming substantially high-density CO-containing acicular hematite particles inheriting the crystal structure, the CO-containing acicular hematite particles are reduced by heating in a reducing gas in a temperature range of 350 to 600°C. This is a method for producing acicular Fe-CO alloy magnetic particles by obtaining acicular Fe-CO alloy magnetic particles.

The structure and effects of the present invention will be explained as follows.

First, various findings on which the present invention is based will be described.

Acicular crystal goethite particles, which are generally contaminated with a trace amount of Si, are heated and dehydrated at around 300°C.The needle-shaped hematite particles, which are contaminated with a trace amount of Si, retain and inherit needle-shaped crystals as described above. However, on the other hand, the growth of single grains is not sufficient, and therefore the degree of crystallinity is very small.

Even with such acicular hematite particles having a small degree of crystallinity and containing a trace amount of Si, single particle growth can be achieved by further heating and firing such as tempering, and therefore, The degree of crystallinity can also be increased. As mentioned above, the higher the temperature at which acicular hematite particles contaminated with a small amount of Si are fired in a non-reducing gas, the more effectively single particles can be grown. , it is possible to form acicular hematite particles with an increased degree of crystallinity, but at temperatures above 800°C, single particles grow beyond the size of the skeleton particles, causing deformation of the acicular crystal particles and particles and It is known to cause sintering between particles.

Furthermore, the starting material, which is contaminated with a small amount of Si, is heated and calcined at a temperature as high as possible within a temperature range of 800°C or lower that can retain and inherit the needle-shaped crystals, thereby increasing the grain growth of single grains. A method is known for obtaining acicular hematite particles having an increased degree of crystallinity and containing a trace amount of Si.

For example, Japanese Patent Application Laid-Open No. 52-95097 describes the following.

By heating and sintering α-FeOOH or α-Fe2O3 particles adsorbed or mixed with Sl under appropriate heat treatment conditions, ``while suppressing mutual sintering between particles and maintaining acicularity, Dehydration and pore-sealing properties are promoted, and acicular hematite particles with high crystal integrity can be obtained.

According to the description in the examples, "appropriate heat treatment conditions" in this method mean that acicular goethite particles contaminated with a trace amount of Si are heated in a non-reducing atmosphere such as argon or air for 70 minutes.
It is heated and fired at a temperature of 0 to 800°C.

That is, if acicular hematite particles contaminated with a small amount of Si are heated and calcined to grow single particles and thereby increase the degree of crystallinity, a temperature of 700°C or higher is required. However, at temperatures below 700° C., the grain growth suppressing effect of Si actually inhibits the grain growth of single grains, and only a very small degree of crystallinity can be obtained.

In this way, heating and firing at a high temperature of 700°C or higher requires highly accurate equipment and advanced technology, and it is not suitable for industrial use.
I can't say it's economical.

Therefore, in view of the above-mentioned facts, the present inventor has determined that the CO containing a trace amount of Si used in the present invention can be used in the present invention at a temperature as low as 700°C or lower in a non-reducing atmosphere.
CO-containing acicular hematite particles contaminated with a trace amount of Si, the degree of crystallinity of which has been increased by heating and firing the acicular hematite particles to achieve sufficient and uniform particle growth of a single particle. Further consideration was given to this. As a result, a trace amount of Si used in the present invention
The average major axis length obtained by heating and dehydrating CO-containing acicular goethite particles contaminated with
CO-containing acicular hematite particles having the same long-axis length and axial ratio as CO-containing acicular goethite particles were heated under an atmosphere consisting of heated steam and non-reducing gas at a water vapor partial pressure ←( Ps is water vapor partial pressure, Pi is non-reducing gas partial pressure) By heating and firing at a temperature range of 350 to 700°C, the average major axis length is 0.1 to 1.
5 μm, and the specific surface area by BET method is 10~
In the case of CO-containing acicular hematite particles having a size of 30w1/9, the CO-containing acicular hematite particles have a substantially high density with an increased degree of crystallinity and retain and inherit acicular crystals. We obtained the knowledge that it is possible to obtain

This will be explained in more detail as follows.

The process in which CO-containing acicular goethite particles contaminated with a small amount of Si undergo heating dehydration to become CO-containing acicular hematite particles consists of generation of a single particle of hematite and growth of the single particle. If this dehydration reaction occurs rapidly, uniform particle growth of a single particle of produced CO-containing hematite becomes difficult to occur. Therefore, rapid grain growth of a single grain causes sintering of the grains and between grains, resulting in deformation of the grain shape of the skeleton grain, making it difficult to retain and inherit the acicular crystals. Therefore, the present inventor developed CO-containing acicular hematite particles that have substantially high density with an increased degree of crystallinity and are contaminated with a trace amount of Si that retains and inherits acicular crystals. In order to obtain this, it was considered necessary to separately control the timing of the generation of the nucleus of a single hematite particle and the timing of the growth of the nucleus of the single particle.

That is, at the beginning of the generation of the nucleus of a single particle of hematite,
It is necessary to control nuclear growth.

Strictly speaking, the time when the nucleus of a single hematite particle is generated is when the dehydration rate of CO-containing acicular goethite particles reaches 100%, but on an industrial scale, the reaction is stopped at this point. It is impossible, and it is extremely difficult to judge. However, according to the ordinary method for obtaining acicular hematite particles, as described in the above-mentioned Japanese Patent Publication No. 15759/1983, hematite skeleton particles that retain and inherit acicular crystals have a large specific surface area, In other words, it consists of a single group of fine, uniform hematite particles. The inventor conducted a detailed study on this phenomenon, and as explained in detail in the explanation of FIG. 5 above, the dehydration rate and the trace amount of S used in the present invention! The relationship between the specific surface area of CO-containing hematite skeleton particles contaminated with CO was confirmed through experiments, and as a result,
Controlling the dehydration rate and the specific surface area of the produced CO-containing hematite skeleton particles contaminated with a trace amount of Si (BE removal)
This makes it possible to determine the timing of the generation of the nucleus of a single hematite particle from the value of .

In addition, the heating temperature for the dehydration reaction of goethite particles is approximately 250°C.
Although it is known that dehydration occurs in the above conditions, the rate of dehydration generally increases as the heating temperature increases, but it also changes depending on the heating rate, atmospheric pressure, etc. Next, the acicular crystal skeleton particles, which are made up of numerous nuclei of fine single particles of CO-containing hematite that are contaminated with a trace amount of Si used in the present invention, are heated and calcined to retain the acicular crystals of the skeleton particles. In order to achieve sufficient growth of a large number of nuclei in a single particle while maintaining the size of the particle, it is necessary to control the growth of the single particle within a range that does not exceed the size of the skeletal particle.

Therefore, the present inventor proposed that 70%
Acicular crystalline skeleton particles consisting of many nuclei of fine CO-containing single hematite particles that are contaminated with a trace amount of Si are heated and fired at a temperature as low as possible below 0°C to obtain a sufficient number of single particles and We investigated the possibility of producing acicular crystal grains with an increased degree of crystallinity by achieving uniform grain growth.

As a result, acicular crystal-shaped skeleton grains with uniform particle size consisting of numerous nuclei of fine single hematite particles containing CO and containing a trace amount of Si were heated in an atmosphere consisting of heated steam and non-reducing gas. In the case of PS+P1, when heating and firing in the range of pressure-b 30 to 100%, sufficient and uniform particle growth of CO-containing hematite single particles contaminated with a trace amount of Si occurs at a temperature of 700°C or less. The inventors have found that it is possible to obtain CO-containing acicular hematite particles containing substantially high-density Si with an increased degree of crystallinity.

The following is an explanation of some of the many experimental examples conducted by the present inventor. Figure 6 shows the relationship between the specific surface area of fired particles obtained by heating and firing the CO-containing acicular hematite particles contaminated with a trace amount of Si used in the present invention under different heating and firing atmospheres and the heating and firing temperature. It is a diagram. That is, the average major axis length is 0.85 μm
1 Si with a specific surface area of 1.60 TI/g has all metal atoms (Fe
and CO) 0.6 atoms? Contaminated, CO conversion table shows Fe
vs. 2.0 atoms? Acicular crystal skeleton particle powder 3009 consisting of many nuclei of single hematite particles is put into a retort container with one end open in volume 31, and heated to 300 to 800°C under different heating and firing atmospheres while driving and rotating.
This figure shows the relationship between the specific surface area of CO-containing acicular hematite particles contaminated with Si obtained by heating and firing at each temperature for 90 minutes and the heating and firing temperature. In the figure, curve A uses air, curve B uses N2 gas as non-reducing gas Ps, and water vapor partial pressure is 7.

When the ratio is 75%, curve C shows N2 as a non-reducing gas.
This is the case when gas is used and the water vapor partial pressure is 95%.
As can be seen from the figure, the partial pressure of water vapor in the heating firing atmosphere -b
- is 75% or 95%, CO-containing acicular hematite particles having a specific surface area of 30rr1/9 or less and containing a trace amount of Si can be obtained at a heating and firing temperature of 700Ps+Pi°C or less.

That is, a substantially dense trace amount of Si with an increased degree of crystallinity due to sufficient and uniform grain growth of a single grain.
This makes it possible to obtain CO-containing acicular hematite particles contaminated with CO. From this, it can be seen that the partial pressure of water vapor in the heating and firing atmosphere is
It is thought that this worked very effectively for the growth of single particles of O-containing acicular hematite particles. By the way, as a conventional technology for particle growth of hematite particles, in which acicular hematite particles are heated and fired at a temperature of 500°C to 600°C or higher in a non-reducing gas, for example, Japanese Patent Publication No. 39-20939 discloses , Special Public Service 1976-11
733, Japanese Patent Publication No. 50-30037, Japanese Patent Publication No. 52-28120, and U.S. Patent No. 405232
There is a method described in No. 6.

However, none of these takes into account the partial pressure of water vapor in the heating and firing atmosphere. Further, methods for causing particle growth of acicular hematite particles using water vapor include, for example, methods (1) and (2) described in Powder Metallurgy Association 1960 Fall Lecture Abstracts 2-1. There is.

In method (1), acicular goethite particles are placed in water vapor (N
In this method, needle-shaped hematite particles are obtained by heating the mixture at 350° C. for 30 minutes (passing two gases through water maintained at temperatures of 25° C., 50° C., 70° C., and 90° C.) for 30 minutes. This method does not concern the preparation of acicular hematite particles, but rather the generation of acicular hematite particles.Moreover, this method does not involve the production of acicular hematite particles from acicular goethite particles. In this case, the timing of the generation of the nucleus of a single particle and the timing of the growth of the nucleus of the single particle occur at the same time, making it difficult to uniformly grow many nuclei of a single particle, making it difficult to control it. Therefore, it is difficult to maintain and inherit needle-like crystals. The method (2) is to heat acicular hematite particles obtained by heating acicular goethite particles in air at 350°C for 30 minutes using an autoclave in a state where water vapor pressure is high, The effect of changes in water vapor pressure corresponding to changes in heating temperature in a closed container on the growth of acicular hematite particles was observed.

To elaborate on this method, 150
This is a method of heating acicular hematite particles at a temperature of ~350°C, and as is clear from the well-known water phase diagram, it is a method of heating acicular hematite particles in the presence of water and steam. [heat treatment method], and therefore does not include a step of controlling the timing of the generation of nuclei of hematite single particles, making it difficult to retain and inherit needle-like crystals.

Further, the same document states that in this method, when acicular goethite particles are used as the object to be treated, the produced hematite particles become granular particles. This phenomenon occurs during the generation of hematite particles from acicular goethite particles under high temperature and high pressure in an autoclave. It is thought that the hematite produced becomes granular particles as a result of particle growth exceeding the size of the acicular crystal skeleton particles.

Next, in the thermal reduction process in the conventional method, when hydrogen is used as the reducing gas, iron oxide particles and hydrogen gas react to generate water vapor.

In this way, the reducing atmosphere containing water vapor has a significant effect on the particle growth of single particles, and therefore, single particles are caused to grow excessively, causing sintering and deformation of the particles and each other. It is becoming. Therefore, conventional efforts have been made to minimize the amount of water vapor generated by the reaction between iron oxide particles and hydrogen gas. For example, there are examples in which carbon monoxide, which does not generate water vapor, is used as the reducing gas. That is, Japanese Patent Publication No. 39-5009 describes the following. [It has been found that the partial pressure of water vapor is extremely important in order to prevent jitter between needle particles, and that the partial pressure and flow rate of hydrogen in the reducing atmosphere are important.
"It is desirable to keep the water vapor partial pressure low." Therefore, "
When hydrogen is used, it is necessary to increase its flow rate in order to lower the water vapor partial pressure. ``It was observed that when the partial pressure of water vapor in the reducing atmosphere exceeds 0.05 atm (partial pressure of water vapor 5%) for one hour or more, significant agglomeration of particles tends to occur.''
``To prevent mutual agglomeration of particles due to water vapor partial pressure, it is best to use carbon monoxide gas as the reducing gas.

This is because carbon dioxide gas produced by the reaction between carbon monoxide and iron oxide has no effect on coagulating particles. Next, various conditions for carrying out the method of the present invention will be described.

C contaminated with a trace amount of Si used in the present invention
S obtained by heating and dehydrating O-containing acicular goethite particles
The CO-containing acicular hematite particles contaminated with i have an average major axis length of 0.3 to 2.0 μm, a specific surface area of 50 to 3
00i/9, which maintains and inherits the long axis length and axial ratio of the CO-containing acicular goethite particles.

Particles having an average major axis length of 0.3 μm or less and 2.0 μm or more are not preferred as raw materials for magnetic powder for magnetic recording. Normally, it is difficult to obtain CO-containing acicular hematite particles having a specific surface area of 50 m1/9 or less and containing a trace amount of Si.

This is because dehydration must be carried out at a slow rate in order to retain the needle-like crystals of the skeleton particles, which results in a long dehydration process, which is not industrially preferable. On the other hand, under extreme dehydration conditions, it is possible to obtain CO-containing hematite particles with a specific surface area of 50 i/fl or less that are contaminated with Si, but they no longer retain the particle shape of needle-like crystals. do not have. It is possible to carry out the method of the present invention even if the specific surface area is 300 m1/9 or more, but even if the dehydration rate is accelerated, the specific surface area of the CO-containing acicular hematite particles contaminated with Si is It is about 300 i/g at most.

CO-contaminated CO containing Si-contaminated acicular goethite particles that maintain the long axis length and axial ratio of CO-containing acicular goethite particles.
The contained acicular hematite particles are skeleton particles consisting of many nuclei of fine single hematite particles, and this is done in consideration of the retention and inheritance of the acicular crystals. In the present invention, when the water vapor partial pressure Vτ Also, control is difficult because the management range is narrow.

In order to stably and effectively obtain CO-containing acicular hematite particles with a specific surface area of 307rI/9 or less and contaminated with a small amount of Si, the water vapor partial pressure of 1L〒Ps+Pi is 50 to 100%. It is preferable that there be.

The steam partial pressure can be controlled by controlling the flow rate of heating steam using a steam flow meter. Air, nitrogen gas, etc. can be used as the non-reducing gas in the present invention. The heating and firing temperature in the present invention is 350°C
If it is below, it takes a long time to obtain CO-containing acicular hematite particles having a specific surface area of 30Tr1/9 or less and containing a trace amount of Si, which is not effective.

If the temperature is 7(1)°C or higher, highly accurate equipment and advanced technology are required, which is not industrially or economically viable.

When economic efficiency is considered in terms of the material of the industrial material and the structure of the equipment, a temperature range of 450 to 650° C. is preferable. The average long axis length of the CO-containing acicular hematite particles contaminated with a trace amount of Si obtained by heating and firing in the present invention is 0.1 to 1.5 μm, and the specific surface area is 10 ~
It is 30i/9. Considering the acicularity and high density of hematite particles, the average major axis length is preferably 0.1 to 1.5 μm. If the specific surface area is less than 10Tr1/9, the shape of the acicular crystal particles is distorted, and the Fe-CO alloy magnetic particles obtained using such particles are also not suitable for magnetic recording because the acicular crystals are defective. Not preferred as a magnetic material.

If the specific surface area is 30/9 or more, it is difficult to say that the growth of a single particle of the CO-containing acicular hematite particles contaminated with Sl is sufficient, and therefore the degree of crystallinity is I can't say it's elevated. In the present invention, when the temperature for heating reduction in a reducing gas is 350° C. or lower, the reduction reaction progresses slowly and takes a long time.

If the temperature is 600° C. or higher, the reduction reaction will rapidly proceed, resulting in deformation of the acicular crystal particles and sintering of the particles and the particles themselves. Moreover, heating and reducing in a reducing gas at a high temperature of 600° C. or higher requires highly accurate equipment and advanced technology, and cannot be said to be industrially economical. When considering the speed of the reduction reaction, the shape of the particles, the sintering between the particles, and the industrial materials and equipment structure, the temperature is preferably 450° C. or higher and 550° C. or lower. next,
The effects of the present invention will be described.

According to the present invention as described above, the acicular crystals and particle size of the starting material particles are maintained and inherited, and there are no dendritic particles mixed in, and there are sufficient and uniform particles of a single particle. It is possible to obtain substantially high-density acicular Fe--CO alloy magnetic particle powder in which the degree of crystallinity on the particle surface and inside the particle is increased due to the growth.

The thus obtained acicular Fe-CO alloy magnetic particle powder has magnetic properties such as high saturation magnetic flux density σs and high coercive force Hc, and powder properties such as high dispersibility and high orientation. Since it has high filling properties, it is suitable as a magnetic particle powder for high output, high sensitivity, and high recording density, which are currently most required.

In addition, the above-mentioned acicular Fe-CO alloy magnetic particles have superior oxidation stability compared to acicular metal iron particles, and are less susceptible to oxidation in the air. It has the following.

In addition, when producing magnetic paint, the above-mentioned acicular crystal Fe-CO
When alloy magnetic particles are used, the dispersibility in the vehicle is good, and the orientation and filling properties in the coating film are excellent, making it possible to obtain a magnetic recording medium with favorable electromagnetic conversion characteristics. . Furthermore, by carrying out the method of the present invention, it is possible to sufficiently cause the physical change of particle growth of a single particle prior to the thermal reduction process by the conventional method, so that the chemical change called reduction reaction occurs during the thermal reduction process. Because it only needs to be carried out mainly in There is no adverse effect on particle morphology.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

In addition, the specific surface area in the practical examples, experimental examples, and comparative examples was determined by the BET method, and the amount of Sl was determined by JIS Gl2l2.
The amount of CO was measured by fluorescent X-ray analysis using the Si analysis method.

<Production of CO-containing acicular goethite particles> Example 1
~7 Comparative Example 1; In advance, 55.21 ferrous sulfate 1.52 m01/l aqueous solution obtained by mixing cobalt sulfate so as to contain CO2O atomic % with respect to 1e Leri 1 Fe was reacted to the fruit b. Sodium silicate (No. 3) (SlO228
．． 6.43-N obtained by adding 55 wt%) 229
(7) In addition to 64.81% of the NaOH aqueous solution, a mixed aqueous solution containing Fe(0H)2 and CO(0H)2 was obtained at PHL3 and a temperature of 50°C.

The above mixed aqueous solution containing Fe(0H)2 and CO(0H)2 was fed with 14.5 liters of air at a rate of 1501/min at a temperature of 50°C.
After aeration for a period of time, CO-containing acicular goethite particles contaminated with Si were produced.

The end point of the oxidation reaction was determined by taking out a portion of the reaction solution and adjusting the acidity with hydrochloric acid, and then using a red blood salt solution to determine the presence or absence of a blue coloring reaction of Fe2+. The generated particles are washed with water and
Separated, dried, and crushed.

As a result of electron microscopic observation, the obtained CO-containing acicular goethite particles contaminated with Si have an average major axis length of 0.80.
It had an axial ratio (major axis: short axis) of 18:1, a uniform particle size, and no dendritic particles. Also,
The CO content was 1.96 at% with respect to Fe, the Si content was 0.54 at% with respect to all metal atoms (Fe and CO), and the specific surface area was 40.2 Tr1/g.

Examples 2 to 7 Types of ferrous aqueous solutions, types of water-soluble CO salts, amount of water-soluble CO salts mixed, concentration and usage amount of CO-containing ferrous salt aqueous solutions, concentration and usage amount of NaOH aqueous solutions,
CO-containing acicular goethite particles contaminated with Sl were produced in the same manner as in Example 1, except that the amount of water-soluble silicate added was varied.

Table 1 shows the main manufacturing conditions and characteristics at this time. Actual example 2
The Si-contaminated CO-containing acicular goethite particles obtained in Steps 7 to 7 were all found to have uniform particle sizes as a result of electron microscopic observation, and were free of dendritic particles.

Comparative Example 1 A ferrous sulfate 1.21 m01/l aqueous solution 401 obtained by mixing cobalt sulfate so as to contain CO2O atomic % with respect to Fe was prepared in advance in a reactor.
In addition to 5-N(7) NaOH aqueous solution 801, PHL3,
A mixed aqueous solution containing Cn(0H)2 and Fe(0H)2 was obtained at a temperature of 50°C.

Air was passed through the mixed aqueous solution containing Fe(0H)2 and CO(0H)2 at a rate of 1201/min for 12 hours at a temperature of 50°C to produce CO-containing acicular goethite particles. The end point of the oxidation reaction was determined by taking out a portion of the reaction solution, acidifying it with hydrochloric acid, and then using a red blood salt solution to determine the presence or absence of a blue coloring reaction of Fe2+.

The resulting particles were washed with water, separated, dried, and pulverized by a conventional method.

As a result of electron microscopic observation, the obtained CO-containing acicular goethite particles had an average long axis length of 0.85 μm, a uniaxial ratio (long axis: short axis) of 12:1, and asymmetric particle sizes, and Many aggregated particles were mixed. Also, the specific surface area is 38.1
It was d/9. Production of raw material CO-containing acicular hematite particles> Examples 8 to 14 Comparative Example 2, Example 8 5000 g of CO-containing acicular goethite particles contaminated with Si obtained in Practical Example 1 was blown into air. The mixture was heated and dehydrated at 300° C. (dehydration rate: 0.5 mol/min) to obtain CO-containing acicular hematite particle powder contaminated with Si.

The obtained CO-containing acicular hematite particles contaminated with Si had an average long axis length of 0.80 μm and a uniaxial ratio (long axis:
It is a needle-like crystal skeleton particle consisting of a group of fine hematite single particles that maintains the long axis length and axial ratio of CO-containing needle-like goethite particles with a ratio of 18:1 (minor axis), and has a specific surface area of 1.
It was 28m2/9. Examples 9 to 14, Comparative Example 2 CO-containing acicular hematite particles were prepared in the same manner as in Practical Example 8, except that the type of CO-containing acicular goethite particles, heating dehydration rate, and heating temperature were varied. I got it.

Table 2 shows the main manufacturing conditions and various properties of the obtained CO-containing acicular hematite particle powder. Preparation of CO-containing acicular hematite particles> Examples 15-30 Comparative Examples 3-
6; Practical Example 15 The Ti-containing CO-containing acicular crystals obtained in Practical Example 10 were charged with ÷ tight particle powder 5009 into a retort container with a volume of 71 that was open at one end, and while being driven and rotated, it was mixed with air. Steam is vented into the retort, and the partial pressure of water vapor inside the retort (−
+) was maintained at 85% and baked at a temperature of \370°C for 220 minutes.

The obtained CO-containing acicular hematite particles contaminated with Si had an average long axis length of 0.75 μm and a uniaxial ratio (long axis:
short axis) 18:1, and the specific surface area is 28.2 m2/
It was l.

Examples 16 to 30, Comparative Examples 4 to 5 CO-containing needles were prepared in the same manner as in Example 15, except that the type of raw material, the type of non-reducing gas, the partial pressure of water vapor, the calcination temperature, and the calcination time were variously changed. Crystalline hematite particle powder was obtained.

Table 3 shows the main manufacturing conditions and various properties of the obtained CO-containing acicular hematite particle powder. Comparative example 3 Temperature: 30℃, temperature: 80010 without blowing water vapor
S1 was carried out in exactly the same manner as in Example 17 except that air of
A CO-containing hematite particle powder contaminated with CO was obtained.

Table 3 shows the characteristics of the obtained CO-containing hematite particles contaminated with Si. Comparative Example 6 C obtained in Comparative Example 1
CO-containing acicular hematite particles were obtained in exactly the same manner as in Example 17, except that the O-containing acicular goethite particles were used as they were.

The obtained CO-containing acicular hematite particles had an average major axis length of 1.5 μm and an axial ratio (major axis: minor axis) of 3:1, resulting in deformation of the particle shape and sintering of the particles and each other. The specific surface area was 10.5w1/9. Production of acicular crystal Fe-CO alloy magnetic particle powder> Practical examples 31 to 49 Comparative examples 7 to 13; Example 31 CO-containing acicular hematite particle powder contaminated with Si obtained in Example 17 320f1 was placed in a retort container with a volume of 71 that was open at one end, and while rotating for one drive, H2
Gas was aerated at a rate of 2.21 per minute and the mixture was reduced at a reduction temperature of 350°C to obtain acicular Fe-CO alloy magnetic particle powder.

The acicular Fe-CO alloy magnetic particle powder obtained by reduction is first stabilized by immersing it in toluene and evaporating it to prevent rapid oxidation when taken out into the air. provided.

As a result of electron microscopic observation, the thus obtained acicular crystal Fe-CO alloy magnetic particle powder retains and inherits acicular crystals, has an average long axis length of 0.60 μm, and an axial ratio (long axis: short axis). )13:
1, the particle size was uniform, and aggregated particles and dendritic particles were not mixed. In addition, the coercive force Hc is 16150e1
The saturation magnetic flux density CIVs was 164 emu/9.

Practical Examples 32 to 49, Comparative Examples 8 to 12 Fe-CO alloy particles were obtained in the same manner as Practical Example 31, except that the type of CO-containing acicular hematite particles and the reduction temperature were varied. Ta.

Tables 4 and 5 show various properties of the obtained Fe-CO alloy particles. In addition, as a result of electron microscope observation, Examples 32 to 4
All of the Fe-CO alloy particles obtained in Comparative Examples 8 to 12 retained and inherited acicular crystals, had uniform particle sizes, and did not contain dendritic particles. All of the obtained Fe--CO alloy particles had deformation of the particles and sintering between the particles and the particles.

Comparative Example 7 Acicular crystal Fe--CO alloy particles were obtained in exactly the same manner as in Example 31, except that the CO-containing acicular goethite particles obtained in Comparative Example 1 were used as they were.

As a result of electron microscopy observation, the obtained Fe-CO alloy particles had particle deformation and sintering between particles and particles, and had an average long axis length of 1.80 μm and a uniaxial ratio (long axis : short axis) was 3:1. Also, the coercive force Hc is 3650
e, the saturation magnetic flux density CVs was 130 emu/g.
Comparative Example 13 The CO-containing acicular hematite particle powder 3509 obtained in Example 8 was placed in a 71-volume retort container with one end open, and while rotating for one drive, hydrogen gas and water vapor were passed through at 2.21/min. , while maintaining the water vapor partial pressure in the retort (lower + back arch, where Pr is the hydrogen gas partial pressure) at 450°C.
The mixture was heated and reduced to obtain Fe--CO alloy particle powder.

As a result of electron microscope observation, the obtained Fe-CO alloy particles were found to have deformed particles and sintered between particles and particles, and had an average long axis length of 185 μm and a uniaxial long axis:
short axis) was 3:1. The coercive force Hc was 3500, and the saturation magnetic flux density Cys was 138 emu/9.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of water-soluble silicate added to an aqueous alkaline solution and the reaction time for producing CO-containing acicular goethite particles. In the figure, curves A, B, and C each have a reaction solution concentration of 0.3 m
01/1, 0.4m01/! , 0.7m01/2. Figure 2 shows the amount of water-soluble silicate added to the alkaline aqueous solution and the CO produced under the same reaction conditions as in Figure 1.
This figure shows the relationship between the specific surface area of the acicular goethite particles contained therein. In the figure, curves A, B, and C each have a reaction solution concentration of 0.3 m
This is the case of 02/1, 0.4m01/1, and 0.7m01/l. FIG. 3 shows the formation region of the CO-containing acicular goethite particles used in the present invention in relation to the amount of Si added (atomic %) and the amount of CO mixed (atomic %).
The shaded area is the production area of the CO-containing acicular goethite particles used in the present invention, and the triangular area surrounded by points A, b, and c with straight line A as one side is the area where the CO-containing acicular goethite particles are generated. This is a region where a mixture of magnetite and granular magnetite particles is produced. Figure 4 shows CO-containing acicular goethite particles contaminated with Si (2.0 atomic % in terms of CO with respect to Fe, 0.6 atomic % in terms of S1 with respect to all metal atoms (Fe and CO)). Needle-like crystal grain powder with a specific surface area of 120 m/9 consisting of fine hematite single particles obtained by heating and dehydration is heated and reduced at 400°C in a hydrogen stream to obtain needle-like Fe-CO alloy magnetic particle powder. FIG. 2 is a diagram showing the relationship between the degree of reduction and the specific surface area of particles produced by thermal reduction in the thermal reduction process. Figure 5 shows CO-containing acicular goethite particles contaminated with Si (2.0 atomic % in terms of CO with respect to Fe, 0.6 atomic % in terms of S1 with respect to total metal atoms (Fe. (5C0)). This is a diagram showing the relationship between the dehydration rate and the specific surface area of particles produced under conditions of different dehydration rates in the process of heating and dehydrating to form acicular hematite particles. The speeds are 7.2 mol/min, 2.0 mol/min, and 0.25 mol/min. Figure 6 shows CO-containing acicular hematite particles with Si encrustation under different heating and firing atmospheres. Powder (2.0 atomic% in terms of CO based on Fe, total metal atoms (Fe(5C0)
FIG. 2 is a diagram showing the relationship between the specific surface area of fired particles obtained by heating and firing 0.6 atomic % (calculated as Sl) and heating and firing temperature. In the figure, A is air, B is N2 gas as a non-reducing gas, and water vapor partial pressure VF is 75%, C is N2 gas is non-reducing gas, and water vapor content is 75%. Pressure F fortune 〒? {95% of the time.

Claims (1)

[Claims] 1 pH containing Fe(OH)_2 and Co(OH)_2
12 or more (however, the mixed amount of Co(OH)_2 is 0.1 to 7.0 atomic % in terms of Co based on Fe). All metal atoms (Fe
and Co) in an amount of 0.1 to 1.1 atomic % in terms of Si (however, the amount of Co(OH)_2 mixed and the amount of water-soluble silicate added are based on the Co 5 of Si equivalent amount and total metal atoms (Fe and Co)
8 atomic % or less in total), then the alkaline aqueous solution is reacted with a ferrous salt aqueous solution and a water-soluble Co salt aqueous solution to form fine and uniform Fe(OH)_2 and Co(OH).
_2 to obtain a mixed aqueous solution with a pH of 12 or higher, and then oxidized to produce Co-containing acicular goethite particles,
Next, the produced Co-containing acicular goethite particles were filtered, washed with water, dried, and then heated and dehydrated to obtain an average major axis length of 0.3 to 2.0 μm, and a specific surface area determined by the BET method. Co-containing acicular hematite particles having a diameter of 50 to 300 m^2/g and maintaining the long axis length and axial ratio of Co-containing acicular goethite particles are placed in an atmosphere consisting of heated steam and non-reducing gas. Below the water vapor partial pressure Ps/
Ps+Pi (Ps is water vapor partial pressure, Pi is non-reducing gas partial pressure) 30-100%, by heating and firing at a temperature of 350-700°C, the average major axis length is 0.1-1.5.
μm, and the specific surface area by BET method is 10 to 30
After forming substantially high-density Co-containing acicular hematite particles inheriting acicular crystals of m^2/g, the Co-containing acicular hematite particles were heated at 350°C to 600°C in a reducing gas.
Acicular crystal Fe-
Acicular crystal Fe- characterized by obtaining Co alloy magnetic particles
A method for producing Co alloy magnetic particle powder. 2 The amount of Co(OH)_2 mixed with Fe(OH)_2 is 0.5 to 7.0 at% in terms of Co, and the amount of water-soluble silicate added is based on the total metal atoms (Fe and Co). 0.3 to 0.7 atomic% in terms of Si, however, Co(OH
)_2 mixing amount and the addition amount of water-soluble silicate are the Co equivalent amount with respect to Fe and the S with respect to all metal atoms (Fe and Co).
The method for producing acicular Fe-Co alloy magnetic particles according to claim 1, wherein the total amount including 5 times the i equivalent amount is 8 atomic % or less. 3 Steam partial pressure Ps/Ps+Pi (Ps is steam partial pressure,
3. The method for producing acicular Fe--Co alloy magnetic particle powder according to claim 1 or 2, wherein Pi is a non-reducing gas partial pressure) of 50 to 100%. 4. The method for producing acicular Fe-Co alloy magnetic particles according to any one of claims 1 to 3, wherein the heating and firing temperature is in the range of 450 to 650°C. 5. The method for producing acicular Fe-Co alloy magnetic particles according to any one of claims 1 to 4, wherein the heating reduction temperature in the reducing gas is in the temperature range of 450 to 550°C.