JPS5921364B2 - Method for producing acicular Fe-Zn alloy magnetic particle powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing acicular Fe--Zn 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. Because of this, it has magnetic properties such as a large saturation magnetic flux density σs and a high coercive force Hc, and powder properties such as high dispersibility, high orientation, and high packing properties for magnetic recording. It is an object of the present invention to provide a new technical means that can easily produce acicular Fe-Zn alloy magnetic particle powder that is particularly suitable as a material.

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.
000e.

In particular, the σs of the oxide magnetic particles is at most 85 emu.
/9, and generally σS7O to 80 emu/g, 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 a 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 with 3
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 crystal metal magnetic particle powder or the acicular crystal alloy magnetic particle powder can be expressed by the following relational expression.

Hc-K・(Nb-Na)・Ms In this relational expression, K is the degree of crystallinity of the particles, (Nb-Na) is the shape (acicularity) of the particles, and Ms is the chemical composition of the particles. This is a related 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. ”0 However, although it is possible to retain and inherit the acicular crystals of the particles relatively well by employing heat reduction treatment at low temperatures, the acicular metal iron magnetic particles or acicular alloy magnetic particles produced has a small degree of crystallinity and therefore has a small coercive force Hc. 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 also known that acicular metal iron magnetic particles or acicular alloy magnetic particles 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. In order to improve the dispersibility in the vehicle, the orientation and filling properties in the coating film, it is necessary that the magnetic particles dispersed in the vehicle have excellent acicular crystals and have uniform particle size. , it is also required that dendritic particles are not mixed.

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. A major issue is whether to thermally reduce the particles while retaining them to obtain substantially high-density acicular metal iron magnetic particles or acicular alloy magnetic particles with an increased degree of crystallinity.

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 excellent acicular crystals and are uniform in particle size. In addition, we have already developed a method to obtain acicular goethite particles that do not contain dendritic particles.

For example, as described below.

That is, it has excellent acicular crystals and uniform particle size,
In addition, acicular goethite particles without dendritic particles are mixed with Fe(0H)2Zn(0H)2 in a mixed aqueous solution of PH11 or more (however, Zn(0H)2 has Z
A water-soluble silicate is added in advance to the alkaline aqueous solution used to obtain Fe
(However, the total amount of Zn(0H)2 mixed and the amount of water-soluble silicate added is 2.5 at. P of
It can be obtained by obtaining a mixed aqueous solution of Hll or more, and then oxidizing the mixed aqueous solution by passing an oxygen-containing gas through the mixed aqueous solution.

This method will be explained as follows.

Conventionally, acicular goethite particles obtained in the alkaline region of PHll or higher by reacting an aqueous ferrous salt solution with an alkali and air oxidation generally have asymmetric particle sizes and a mixture of dendritic particles. This is because the Fe(0H)2 flocs, which are the precursors of acicular goethite particles, are asymmetric, and at the same time, the Fe(0H)2 particles themselves that make up the Fe(0H)2 flocs are asymmetric. Furthermore, when producing acicular goethite particles from an aqueous solution containing Fe(0H)2, the generation of acicular goethite core particles and the growth of the acicular goethite core particles occur simultaneously; This is due to the fact that many new nuclei are generated until the production reaction is completed. In the above conventional technology, F obtained by reacting a ferrous salt aqueous solution with an alkali
A water-soluble silicate is added in advance to an aqueous alkaline solution used to obtain an aqueous solution containing e(0H)2 with a pH of PH11 or higher, in an amount of 0.1 to 1.7 atomic % based on Fe in terms of Si, and then When the alkaline aqueous solution and the ferrous salt aqueous solution are reacted, the Fe(0H)2 flocs are made into fine and uniform flocs when Fe(0H)2 is produced, and at the same time, the Fe(0H)2 flocs are The FeFe(0H)2 particles constituting the FeFe(0H)2 particles themselves can be made into sufficiently fine and uniform particles, and furthermore, the water-soluble silicate is Fe(0H)2.
0H) Stages the generation of acicular goethite core particles and the growth of the acicular goethite core particles due to the effect of suppressing the oxidation reaction when generating acicular goethite particles from an aqueous solution containing 2. Since the process can be carried out in a uniform manner, it is possible to obtain acicular goethite particles with uniform particle size and without dendritic particles mixed therein.

However, in this method, as shown in Figure 1,
Axial ratio (major axis/minor axis) of acicular goethite particles is 10:1
However, as the amount of water-soluble silicate added increases, particles with uniform particle size and no dendritic particles are easily obtained. This causes a decrease in the particle axial ratio (major axis/minor axis).

Figure 1 shows the relationship between the axial ratio of Zn-containing acicular goethite particles obtained under constant conditions except for the amount of water-soluble silicate added and the amount of water-soluble silicate added. .

Therefore, as a result of repeated studies to improve the axial ratio of acicular goethite particles that have uniform particle size and do not contain dendritic particles, the inventors found that Fe(0H)2 and Zn(
A mixed aqueous solution of PHll or higher with Zn(0H)2 (however, Zn(
0H)2 is 0.1 to 2.3 atoms in terms of Zn with respect to Fe01)) Water-soluble silicate is added in advance to the alkaline aqueous solution used to obtain 0 in terms of Si with respect to Fe.
．． Addition of 1 to 1.7 at% (however, the total amount of Zn(0H)2 mixed and the amount of water-soluble silicate added is
2.5 atomic % or less each calculated as Zn and S1), and then the alkaline aqueous solution is reacted with a ferrous salt aqueous solution and a water-soluble Zn salt aqueous solution to form fine and homogeneous Fe(0H)2 and Zn(0H)2. ) 2 is obtained and then oxidized by passing an oxygen-containing gas through the mixed aqueous solution, it has excellent acicular crystals, uniform particle size, and no dendrites. It has been found that it is possible to obtain acicular goethite particle powder containing no acicular crystal particles.

The acicular goethite particles obtained by the above method naturally contain trace amounts of Zn and Si in the particles, and the acicular goethite particles obtained by heating and reducing the acicular goethite particles The metal magnetic particle powder is acicular crystal Fe-Zn
In Figures 2 and 3, the amount of water-soluble silicate added to form the alloy magnetic particles is 0.5 in terms of Si relative to Fe.
FIG. 2 is a diagram showing the relationship between the Zn mixing amount and the axial ratio (major axis/minor axis) and long axis of acicular goethite particles when the amount is kept constant at atomic %.

Zn used in the above method includes water-soluble Zn salts such as zinc sulfate, zinc chloride, and zinc sulfate. The water-soluble Zn salt may be mixed in advance into an aqueous ferrous salt solution or into an aqueous solution containing Fe(0H)2; in either case, the same effect can be obtained. Obtainable.

As water-soluble silicates, sodium and potassium silicates are used.

The amount of Zn(0H)2 mixed and the amount of water-soluble silicate added are 0.1 to 2.3 atomic % based on Fe, calculated as Zn, and Fe
0.1 to 1.7 atomic% in terms of Si, however, Zn(
The sum of the mixed amount of 0H)2 and the added amount of water-soluble silicate may be set to 2.5 atomic % or less in terms of Zn and Si, respectively, based on Fe.

The amount of water-soluble silicate added is 0.0% compared to Fe in terms of Si.
If it is 1 atomic % or less, the particle size is uniform and the effect of obtaining particles without dendritic particles mixed therein is insufficient, and if it is 1.7 atomic % or more, magnetite particles are mixed.

The mixing amount of Zn(0H)2 is 0.1 in terms of Zn with respect to Fe.
If it is less than atomic %, the effect of improving the axial ratio of the particles is not sufficient, and if it is 2.3 atomic % or more, magnetite particles will be mixed.

When the sum of the mixed amount of Zn(0H)2 and the added amount of water-soluble silicate is 2.5 atomic % or more in terms of Zn and Si, respectively, based on Fe, granular magnetite particles will be mixed.

This will be explained with reference to FIG. In FIG. 4, the shaded area is the region where the Zn-containing acicular goethite particles used in the present invention are generated, and the area A, b with straight line A as one side is
, c is a region where the Zn-containing acicular goethite and granular magnetite particles are mixed and produced.

That is, the sum of the mixed amount of Zn(0H)2 and the added amount of water-soluble silicate is 2.0% in terms of Zn and Si, respectively, with respect to Fe.
A straight line A indicating 5 atomic % distinguishes the region where Zn-containing acicular goethite particles are produced and the region where granular magnetite particles are produced.

Next, we will discuss how to obtain a trace amount of Zn and Sl-containing acicular crystals, which have excellent acicular crystals, are uniform in particle size, and do not contain dendritic particles. The problem is whether to thermally reduce the goethite particles while maintaining their acicular crystals and particle size to obtain substantially high-density acicular Fe--Zn alloy magnetic particles with an increased degree of crystallinity.

As mentioned above, even if the acicular crystals and grain size of the particles can be maintained relatively well by employing the thermal reduction treatment at low temperatures, the acicular crystal Fe-Zn alloy magnetic particles produced have poor 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--Zn alloy magnetic particles and the sintering of the grains and the particles among themselves become significant, and the coercive force is extremely reduced. 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. Its coercive force decreases. The present inventor has determined that the particle size used in the present invention is uniform and that a trace amount of Zn and Si-containing acicular goethite particles containing no dendritic particles are used in the present invention.
Deformation of particle shape when acicular hematite particles obtained by heating and dehydration at around ℃ are used as a starting material, and the starting material is heated and reduced in a reducing gas to obtain acicular Fe-Zn alloy particles. The sintering phenomenon between particles and particles was studied in detail. That is, FIG. 5 shows the needle-like crystals used in the present invention, in which the particle size is uniform, and the Zn content is 1.41 atomic % and the Si content is 0.6 atomic %, with no dendritic particles mixed. Acicular crystal particles with an average major axis length of 0.85 μm and a specific surface area of 160 m2/9, which are made up of fine hematite single particles obtained by heating and dehydrating goethite particles, were heated at 400'C in a hydrogen stream. The acicular crystals Fe-
This figure shows the relationship between the degree of reduction X (FeOx, 1.5>x>O) and the specific surface area of particles produced by thermal reduction during the thermal reduction process to form Zn alloy magnetic particles.

As can be seen from Figure 5, 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.

Generally, acicular hematite particles obtained from acicular goethite particles containing Sl have many pores generated by dehydration on the particle surface and inside the particles, and these pores become smaller as the heating temperature increases. However, 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 containing a trace amount of Si can be heated up to 800℃ without sintering of the needles during dehydration treatment or subsequent tempering (high-temperature heating treatment of acicular hematite particles). Temperature can be used.

"Acicular hematite particles, which have been commonly used as a starting material, are obtained by heating and dehydrating acicular goethite particles at a temperature of around 300°C. They are crystalline shell particles, and these shell particles are composed of aggregated 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, single particle growth is not sufficient, and therefore the particles are It has a low degree of crystallinity.
In particular, when acicular goethite particles containing a small amount of Sl are heated and dehydrated at a low temperature around 300°C by a conventional method, the degree of crystallinity decreases due to the particle growth inhibiting effect of S1, as is well known. It becomes even smaller.

Therefore, acicular hematite particles containing a trace 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. 6, the average major axis length is 0.85 μm, and the specific surface area is 36.5 m1/f! The particle size used in the present invention is uniform, and the Zn content is 1.41 at.
This graph shows the relationship between the dehydration rate and the specific surface area of particles produced under different conditions of dehydration rate in the process of heating and dehydrating acicular goethite particles with a concentration of 6 at % to produce acicular hematite particles. be. 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 Figure 6, a trace amount of S can be obtained by changing the dehydration rate.
The specific surface area of the i and Zn-containing acicular hematite particles differs, and the slower the dehydration rate, the smaller the specific surface area of the acicular hematite particles can be obtained.
~80m 179th place.

In this way, when a trace amount of Si and Zn-containing acicular hematite particles with insufficient particle growth and a low degree of crystallinity are thermally reduced in a reducing gas, single crystals in the thermal reduction process Because the growth of particles, that is, the physical change, is rapid, uniform growth of single particles is difficult to occur. It is thought that sintering occurs, making the particle shape more likely to collapse.

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 called single particle growth.

Therefore, in order to obtain excellent acicular crystal Fe-Zn alloy magnetic particles, it is necessary to control both physical and chemical changes at the same time, and therefore, the heat reduction treatment requires a very long time. It also required a large amount of reducing gas. 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 an oxide to a metal, and that a physical change such as growth of a single particle and a chemical change such as a 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 (both particles and between particles) during the thermal reduction process by mainly performing the change.

Then, the present inventors succeeded in heating and calcining the minute amounts of Si and Zn-containing acicular hematite particles used in the present invention in a non-reducing gas to achieve sufficient and uniform particle growth of single particles. The present invention was achieved as a result of various studies aimed at obtaining starting material hematite particles that have a substantially high density with an increased degree of crystallinity and retain and inherit needle-like crystals.

That is, the present invention provides a mixed aqueous solution of Fe(0H)2 and Zn(0H)2 with a pH higher than PHll (however, Zn(0H)2 is
Add water-soluble silicate in advance to the alkaline aqueous solution used to obtain 0.1 to 2.3 atom % of Fe (calculated as Zn).
(However, the sum of the mixed amount of Zn(0H)2 and the added amount of water-soluble silicate is 2.5 atomic % or less in terms of Zn and Si, respectively, based on Fe), and then the alkaline aqueous solution and the water-soluble silicate are added. A monoferric salt aqueous solution and a water-soluble Zn salt aqueous solution are reacted to obtain a mixed aqueous solution of fine and homogeneous Fe(0H)2 and Zn(0H)2 with a pH of 1 or more, and then oxygen-containing is added to the mixed aqueous solution. Zn-containing acicular goethite particles are produced by passing gas through oxidation, and then the produced Z
The average major axis length obtained by separating the n-containing goethite particles, washing with water, drying, and then heating and dehydrating the particles is 0.3 to 2.5.
μm, and the specific surface area by BET method is 50 to 3
Zn-containing acicular hematite particles, which have a size of 00 m2/9 and maintain the long axis length and axial ratio of acicular goethite particles, were placed at a water vapor partial pressure of +7 ( Fs is water vapor partial pressure, Pi is non-reducing gas partial pressure) 30-100 (!), temperature 350-700
By heating and firing in the range of ℃, the average major axis length is 0.
．． After forming substantially high-density acicular hematite particles inheriting acicular crystals having a diameter of 1 to 2.0 μm and a specific surface area of 10 to 30 m 1/9 by the BET method, This is a method for producing acicular Fe-Zn alloy magnetic particles, which comprises obtaining acicular Fe-Zn alloy magnetic particles by heating and reducing hematite particles in a reducing gas in a temperature range of 350 to 600°C.

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.

Generally, acicular goethite particles containing a trace amount of Si are
The acicular hematite particles containing a small amount of Sl obtained by heating and dehydration at around 00°C retain and inherit acicular crystals as described above, but on the other hand, the particle growth of single particles is not sufficient. Therefore, the degree of crystallinity is very small.

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

Furthermore, the acicular crystals of the starting material containing a trace amount of Si are heated and calcined at a temperature as high as possible within a temperature range of 800°C or less to maintain and inherit the needle-like crystals of the starting material, in order to grow single grains and thereby improve crystallinity. A trace amount of S with an increased degree of
A method for obtaining acicular hematite particles containing i is known. 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 containing a trace amount of S1 are heated to 700 to 8
It is heated and fired at a temperature of 00°C.

That is, if acicular hematite particles containing a small amount of Si are heated and fired to grow single particles and thereby increase the degree of crystallinity, a temperature of 700° C. or higher is required. At temperatures below 700° C., the grain growth suppressing effect of S1 actually inhibits the grain growth of single grains, and only a very small degree of crystallinity can be obtained.

As described above, heating and firing at a high temperature of 7000C or higher requires highly accurate equipment and advanced technology, and cannot be said to be industrial or economical. Therefore, in view of the above-mentioned facts, the present inventor heated and calcined the trace amount of Zn and Si-containing acicular hematite particles used in the present invention at a temperature as low as 700° C. or lower in a non-reducing atmosphere. Trace amounts of Zn and Si with increased degree of crystallinity by achieving sufficient and uniform grain growth of single grains
Further studies were conducted to obtain needle-like hematite particles. As a result, the average major axis length obtained by heating and dehydrating the trace amounts of Zn and Si-containing acicular goethite particles used in the present invention was 0.3 to 2.5 μm,
And, the specific surface area by BET method is 50 to 300 m2/9
The acicular hematite particles, which retain the long axis length and axial ratio of the acicular goethite particles, are heated under an atmosphere consisting of heated steam and non-reducing gas to reduce the water vapor partial pressure - Σ
- (Ps is water vapor Ps + Pi partial pressure, Pl 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 0.1-2.0
μm, and the specific surface area by BET method is 10 to 3
In the case of acicular hematite particles having a ratio of 0 m2/1, it is possible to obtain acicular hematite particles that have a substantially high density with an increased degree of crystallinity and retain and inherit acicular crystals. I learned that it can be done.

This will be explained in more detail as follows.

The process in which acicular goethite particles containing a small amount of Zn and Si become acicular hematite particles by heating and dehydration consists of the generation of a single particle of hematite and the growth of this single particle, and this dehydration reaction If this occurs rapidly, uniform particle growth of a single particle of the produced 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 discovered that Zn has a substantially high density with an increased degree of crystallinity, and retains and inherits acicular crystals.
In order to obtain Si-containing acicular hematite particles, we considered that it is 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 the acicular goethite particles reaches 100%, but on an industrial scale, it is impossible to stop the reaction at this point. It is impossible and very 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 present inventor conducted a detailed study on this phenomenon, and as explained in detail in the explanation of FIG. As a result, by controlling the dehydration rate and from the value of the specific surface area (AET method) of the produced hematite skeleton particles containing trace amounts of Zn and Si, the timing of the generation of nuclei of hematite single particles can be determined. This made it possible to do what was possible.

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 used in the present invention, which are made up of numerous nuclei of fine hematite single particles containing trace amounts of Zn and Si, are heated and fired to retain and inherit the needle crystals of the skeleton particles. In order to achieve sufficient growth of a large number of nuclei in a single 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 numerous nuclei of fine hematite single particles containing trace amounts of Zn and 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.

j As a result, acicular crystal skeleton particles with uniform particle size consisting of numerous nuclei of fine hematite single particles containing trace amounts of Zn and Si are heated in an atmosphere consisting of water vapor and non-reducing gas to reduce the water vapor partial pressure. -1ゝIn the case of heating and firing in the range of -30 to 100% Ps+Pi, sufficient and uniform particle growth of hematite single particles containing trace amounts of Zn and Si should be achieved at a temperature of 700°C or less. can be done, therefore,
It was discovered that it is possible to obtain substantially dense acicular hematite particles with an increased degree of crystallinity.
The following is an explanation of some of the many experimental examples conducted by the present inventor.

FIG. 7 shows the fired acicular hematite particles obtained by heating and firing the acicular hematite particles with a Zn content of 1.41 at% and a Si content of 0.6 at% used in the present invention under different heating and firing atmospheres. FIG. 2 is a diagram showing the relationship between the specific surface area of particles and heating and firing temperature. That is, acicular crystalline particle powder 3009 consisting of numerous nuclei of fine hematite single particles containing trace amounts of Zn and Si and having an average major axis length of 0.85 μm and a specific surface area of 160 m7g was placed in a retort container with a volume of 31 and one end open. The relationship between the specific surface area and the heating and firing temperature of the acicular hematite particles obtained by heating and firing at each temperature of 300 to 800°C for 90 minutes under different heating and firing atmospheres while driving and rotating. This is what is shown. In the figure, curve A uses air, curve B uses N2 gas as non-reducing gas Ps, and water vapor partial pressure . is 2Ps+Pi75
%, curve C is the case where N2Ps gas is used as the non-reducing gas and the water vapor partial pressure is 95%, Ps+Pi.

As can be seen from the figure, the partial pressure of water vapor in the heating firing atmosphere f
Fortune telling? is 75% or 95%, a trace amount of Zn and S with a specific surface area of 30 my9 or less at a firing temperature of 700°C or less
1-containing acicular hematite particle powder can be obtained.

That is, a trace amount of substantially dense Zn with an increased degree of crystallinity due to sufficient and uniform grain growth of a single grain.
And Si-containing acicular hematite particle powder can be obtained. From this, it is considered that the water vapor partial pressure in the heating and firing atmosphere worked very effectively for the growth of single particles of acicular hematite particles containing trace amounts of Zn and SI. By the way, conventionally, as a technique related to 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,
No. 20939, Japanese Patent Publication No. 11733/1973, Japanese Patent Publication No. 30037/1986, Japanese Patent Publication No. 52-281
There are methods described in Japanese Patent No. 20 and US Pat. No. 4,052,326.

However, none of these takes into account the partial pressure of water vapor in the heating and firing atmosphere. In addition, examples of methods for stimulating particle growth of acicular hematite particles using water vapor include (1) and (2) described in 2-1 of the 1960 Autumn Lecture Abstracts of the Powder Metallurgy Association. There is a method.

In method (1), acicular goethite particles are placed in water vapor (N
In this method, acicular hematite particles are obtained by heating the acicular hematite particles for 35 minutes at a temperature of 25°C, 50°C, 70°C, and 90°C.

This method is not related to the preparation of acicular hematite particles, but is concerned with the production of acicular hematite particles, and moreover, when using this method, acicular hematite particles are produced from acicular goethite particles. When generating,
Since 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, uniform growth of many nuclei of the single particle is difficult to occur, and it is difficult to control it. Difficult to retain and inherit needle-like crystals. Method (2) involves heating needle-like goethite particles in air at 350°C for 30 minutes, then heating the obtained needle-like hematite particles in an autoclave at high water vapor pressure. The effect of changes in water vapor pressure corresponding to changes in heating temperature in a container on acicular hematite particles and particle growth 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 so-called "hydrothermal treatment" in which acicular hematite particles are treated in the presence of water and steam. This method does not include the step of controlling the timing of the generation of the nucleus of a single hematite particle, making it difficult to maintain and inherit needle-like crystals.

Furthermore, 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, and the timing of the generation of the nucleus of a single hematite particle and the timing of the growth of a single particle nucleus occur at the same time and rapidly. Therefore, it is difficult to maintain and inherit the needle-like crystals, and as a result of particle growth exceeding the size of the needle-like crystal skeleton particles, the produced hematite is thought to become granular particles.Next, in the thermal reduction process in the conventional method, teeth,
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. ``We found that water vapor partial pressure is extremely important to prevent jitter between needle particles, and that hydrogen partial pressure and flow rate in the reducing atmosphere are also 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 has been observed that when the water vapor partial pressure in the reducing atmosphere exceeds 0.05 atm (water vapor partial pressure 501) for more than one hour, significant particle aggregation tends to occur." Therefore, in order to prevent particles from coagulating with each other, it is recommended to use carbon monoxide gas as a reducing gas.This is because carbon dioxide gas, which is produced by the reaction between carbon monoxide and iron oxide, has no effect on coagulating particles. be."
Next, various conditions for carrying out the method of the present invention will be described.

The acicular hematite particles obtained by heating and dehydrating acicular goethite particles containing trace amounts of Zn and Sl used in the present invention have an average major axis length of 0.3 to 2.5 μm.
The specific surface area is 50 to 300 m2, and the long axis length and axial ratio of the acicular goethite particles are maintained and inherited.

Particles having an average major axis length of 0.3 μm or less and 2.5 μm or more are not preferred as raw materials for magnetic powder for magnetic recording. Normally, it is difficult to obtain trace amounts of Zn and Si-containing hematite particles having a specific surface area of 50 m7g or less.

This is because dehydration must be performed 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, the specific surface area is 50m7f! Although the following hematite particles can be obtained, it can no longer be said that they retain and inherit the particle shape of acicular crystals. Specific surface area is 300m2/9
Although it is possible to carry out the method of the present invention even under the above conditions, even if the dehydration rate is increased, the specific surface area of the hematite particles obtained is at most 300 m2.

The acicular hematite particles that maintain the long axis length and axial ratio of the acicular goethite particles are shell particles consisting of many nuclei of fine hematite single particles, and this is done in consideration of the preservation and inheritance of the acicular crystals. This is what I did. In the present invention, when the water vapor partial pressure v is 30% or less, the specific surface area is 30 m
In order to obtain acicular hematite particles containing trace amounts of Zn and Sl of 2/9 or less, a high temperature is required, and control is difficult because the control range is narrow.

In order to stably and effectively obtain small amounts of Zn and Si-containing acicular hematite particles with a specific surface area of 30 m1 or less, the water vapor partial pressure -E1- must be 50 to 100 (Ff) Ps+Pi is preferred.

The steam partial pressure can be controlled by controlling the flow rate of heating steam using a steam flow meter.
j As the non-reducing gas in the present invention, air, nitrogen gas, etc. can be used. When the heating and firing temperature in the present invention is 350°C or less,
It takes a long time to obtain acicular hematite particles containing a small amount of Zn and Si with a specific surface area of 30 m2/9 or less, which is not effective.

If the temperature is 700° 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 materials and the structure of the equipment, a temperature range of 450°C to 650°C is preferable.

Trace amounts of Zn and S obtained by heating and firing in the present invention
The average major axis length of the i-containing acicular hematite particles is 0.
1 to 2,0 μm, and the specific surface area is 10 to 30 m
It is 2/9.

Considering the acicularity and high density of hematite particles, the average major axis length is preferably 0.1 to 2.0 ttm.
Particles with a specific surface area of 10m79 or less are acicular crystal particles whose particle shape is distorted, and Fe-Z obtained using the particles
N-alloy magnetic particles are also not preferred as magnetic materials for magnetic recording because they have poor acicular crystals. Specific surface area is 30m2/
f! If this is the case, it cannot be said that the growth of a single particle of the acicular hematite particles is sufficient, and therefore it cannot be said that the degree of crystallinity has been increased. 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.

Further, if the temperature is 600° C. or higher, the reduction reaction rapidly progresses, causing deformation of the acicular crystal particles and sintering of the particles and each other. Moreover, 600℃ in reducing gas
Reduction by heating at such high temperatures requires highly accurate equipment and advanced technology, and cannot be said to be industrial or 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 the dendritic particles are not mixed, and the sufficient and uniformity of single particles is obtained. It is possible to obtain substantially high-density acicular Fe--Zn alloy magnetic particle powder in which the degree of crystallinity on the particle surface and inside the particle is increased due to particle growth.

The thus obtained acicular Fe-Zn alloy magnetic particles have 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 crystal Fe-Zn alloy magnetic particle powder has superior oxidation stability compared to acicular crystal metal iron particle powder, and is characterized by being less susceptible to oxidation in the air. It has the following.

In addition, when producing magnetic paint, the above-mentioned acicular crystal Fe-Z
When n-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. be. 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 heating reduction process by the conventional method, so that the chemical change called reduction reaction occurs during the heating 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 Examples, Experimental Examples, and Comparative Examples was determined by the BET method, and the amount of Si was determined by JIS Gl2l2.
The amount of Zn was measured by fluorescent X-ray analysis using the S1 analysis method.

<Production method of acicular goethite particle powder> Examples 1 to 9
Comparative Example 1: Example 1 1.73 m01/l of ferrous sulfate obtained by adding zinc sulfate to contain 1.50 atomic % in terms of Zn based on Fe
5 obtained by adding 22 g of sodium silicate (No. 3) (SiO2 28.55 wt%) to the aqueous solution 361 in advance so that it contains 0.5 atomic % in terms of Si with respect to Fe prepared in a reaction vessel. .65-N(:f) NaOH aqueous solution 541 plus PHL3.

Fe(0H)2 and Zn(0H) at Ol temperature 500C
) 2 was obtained. Air was passed through the aqueous solution containing Fe(0H)2 and Zn(0H)2 at a rate of 150 l/min for 18.5 hours at a temperature of 50°C to produce Zn-containing acicular goethite particles.

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 colored reaction of Fe2+. The resulting particles were washed with water, filtered, dried, and pulverized using conventional methods. As a result of electron microscopic observation, the obtained acicular goethite particles containing Zn and Si have an average long axis length of 1.0 μm, a uniaxial ratio (long axis: short axis) of 30:1, and a uniform particle size. The dendritic particles were not mixed. Further, it contained 1.43 atom % of Zn based on Fe, and the specific surface area was 35 m2/9.

Examples 2 to 9 Example 1 except that the type of ferrous salt aqueous solution, the type of water-soluble Zn salt, the amount and timing of addition of water-soluble Zn salt, and the amount of water-soluble silicate added were varied. Acicular goethite particles containing Zn and Sl were produced in exactly the same manner as above.

Table 1 shows the main manufacturing conditions and characteristics at this time. Example 2
As a result of electron microscopic observation, the acicular goethite particles containing Zn and Si obtained in steps 9 to 9 had excellent axial ratios, uniform particle sizes, and no dendritic particles. It was hot. Comparative Example 1 A ferrous sulfate solution 601 containing Fe2+0.55m0I was added to a 2.65N (7
) In addition to NaOH aqueous solution 4011, an aqueous solution containing Fe(0H)2 was obtained at a pH of 2.8 and a temperature of 50°C.

Acicular goethite particles were produced by blowing air at 120 l/min into the aqueous solution containing Fe(0H) 2 at a temperature of 50° C. for 12 hours. At the end point of the oxidation reaction, a part of the reaction solution is extracted, adjusted to acidic with hydrochloric acid, and then treated with Fe using red blood salt solution.
Judgment was made based on the presence or absence of a 2+ blue color reaction.

The resulting particles were washed with water, filtered, dried, and pulverized using conventional methods.

As a result of electron microscopic observation, the obtained acicular goethite particles had an average long axis length of 0.8 μm and a uniaxial ratio (long axis: short axis) of 8.
:1, the particle size was asymmetric, and many aggregated particles were present. Further, the specific surface area was 35.5i/9. Production of raw material acicular hematite particle powder> Example 1
0 to 18 Comparative Example 2; Example 10 5000 g of acicular goethite particles containing Zn and Si obtained in Example 1 were heated and dehydrated at 350°C in air (dehydration rate 2.2 mol/min). Acicular hematite particles were obtained.

The obtained acicular hematite particles containing Zn and S1 have an average long axis length of 1.0 μm and a uniaxial ratio (long axis: short axis).
It was an acicular crystal skeleton particle consisting of a group of fine hematite single particles that inherited the long axis length and axial ratio of acicular goethite particles at a ratio of 30:1, and the specific surface area was 173 I/9. . Examples 11 to 18, Comparative Example 2 Acicular hematite particles were obtained in exactly the same manner as in Example 10, except that the type of acicular goethite particles, the heating dehydration rate, and the heating temperature were varied.

Table 2 shows the main manufacturing conditions and various properties of the obtained acicular hematite particles. Preparation of acicular hematite particles> Examples 19 to 36 Comparative Examples 3 to 6; Example 19 The acicular hematite particles 5009 containing Zn and Si obtained in Example 10 were opened at one end of the volume 71. The retort is placed in a molded retort container, and air and steam are vented into the retort while being driven and rotated, and the partial pressure of water vapor inside the retort (?
) at 85% and Ps + Pi at a temperature of 370°C.
It was heated and baked for 00 minutes.

The obtained acicular hematite particles containing Zn and Sl have an average long axis length of 0.85 μm, a uniaxial ratio (long axis: short axis) of 25:1, and a specific surface area of 28.2 i/ It was hot at g. Examples 20 to 36, Comparative Examples 4 to 5 Acicular hematite was produced in exactly the same manner as in Example 19, except that the type of raw material, the type of non-reducing gas, the water vapor partial pressure, the calcination temperature, and the calcination time were variously changed. Particle C powder was obtained.

Table 3 shows the main manufacturing conditions and various properties of the obtained acicular hematite particles. Comparative Example 3 Zn was produced in the same manner as in Example 21, except that air at a temperature of 30°C and a humidity of 80% was used without blowing in water vapor.
Acicular hematite particles containing S1 and S1 were obtained.

Table 3 shows various properties of the obtained acicular hematite particles containing Zn and Sl. Comparative Example 65 Acicular hematite particles were obtained in exactly the same manner as in Example 21, except that the acicular goethite particles obtained in Comparative Example 1 were used as they were.

The obtained acicular hematite particles have an average major axis length of 1
．． A 30 μm uniaxial ratio (long axis: short axis) of 3:1 caused deformation of the particle shape and sintering of the particles and each other, and the specific surface area was 10/9. Production of needle-shaped Fe-Zn alloy or metal iron magnetic particle powder> Examples 37 to 57, Comparative Examples 7 to 13; Example 37 Example 1
Acicular hematite particle powder containing Zn and Sl obtained in step 9 320f! is put into a retort container with a volume of 71 and one end open, and while driving and rotating, H2 gas is supplied at a rate of 2.
The mixture was aerated at a rate of 21% and reduced at a reduction temperature of 430°C to obtain acicular Fe-Zn alloy magnetic particle powder.

The acicular Fe-Zn 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-Zn alloy magnetic particle powder retains and inherits acicular crystals, with an average major axis length of 0.80 μm and a uniaxial ratio (major axis: short axis). 20:
It was 1. Further, the coercive force He was 18050e1, and the saturation magnetic flux density σs was 168 emu/9. Example 38~
57, Comparative Examples 8 to 12 Fe-Zn alloy magnetic particles or metal iron particles were obtained in exactly the same manner as in Example 37, except that the type of acicular hematite particles and the reduction temperature were varied.

Tables 4 and 5 show various properties of the obtained Fe-Zn alloy magnetic particles or metal iron particles. As a result of electron microscopic observation, all of the Fe-Zn alloy particles obtained in Examples 38 to 57 retained and inherited acicular crystals, had uniform particle size, and did not contain dendritic particles. However, the Fe-Zn alloy particle powder obtained in Comparative Examples 8 to 12,
In both cases, the metal iron particles caused deformation of the particles and sintering between the particles and each other.

Comparative Example 7 Acicular crystal metal iron particles were obtained in exactly the same manner as in Example 37, except that the acicular goethite particles obtained in Comparative Example 1 were used as they were.

As a result of electron microscopic observation, the obtained metallic iron particle powder was found to have caused deformation of the particles and sintering between the particles and each other, and had an average long axis length of 1.35 μm and a uniaxial ratio (long axis: short axis). axis) was 3:1. Also, the coercive force Hc is 3650e1, and the saturation magnetic flux density σs is 138emu/f! It was hot. Comparative example
13 Acicular hematite particles obtained in Example 10 350
9 into a retort container with one end open at the required volume 71, and while rotating it for 5 minutes while aerating hydrogen gas 2.21/min and water vapor, the water vapor Ps partial pressure in the retort (?where Pr is the hydrogen gas partial pressure ) was thermally reduced at 450° C. while maintaining 40Ps+Pr% to obtain metallic iron powder.

As a result of electron microscopy observation of the obtained metallic iron particle powder, it was found that the particles were deformed and sintered between the particles.
Average major axis length 1.80 μm 1 axis ratio (major axis: short axis) 3:1
It was hot. Further, the coercive force Hc was 3900, and the saturation magnetic flux density σS was 142 emu/9.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the axial ratio of Zn-containing acicular goethite particles obtained under constant conditions except for the amount of water-soluble silicate added. Figures 2 and 3 show the amount of Zn mixed and the axial ratio of Zn-containing acicular goethite particles when the amount of water-soluble silicate added is constant at 0.5 atomic % in terms of Si with respect to Fe. (long axis/short axis) and a relationship diagram of the long axis. FIG. 4 shows the Si of Zn-containing acicular goethite particles used in the present invention.
It shows the formation region in the relationship between the addition amount (atomic %) and the Zn mixing amount (atomic %). The shaded area in the figure is the formation region of the Zn-containing acicular goethite particles used in the present invention, and the straight line A triangular portion surrounded by points A, b, and c with A as one side is a region where the Zn-containing acicular goethite and granular magnetite particles are mixed and produced. Figure 5 shows a particle with a specific surface area of 160 atomic % consisting of a group of fine hematite single particles obtained by heating and dehydrating acicular goethite particles with a Zn content of 1.41 atomic % and a Si content of 0.6 atomic %. A/9 needle-like crystal grain powder was added to the hydrogen stream for 40 minutes.
1 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 of heating and reducing with C to obtain acicular Fe--Zn alloy particles. Figure 6 shows that the Zn content is 1.4.
Dehydration rate of particles produced under conditions of different dehydration rates in the process of heating and dehydrating acicular goethite particles with a Si content of 1 atomic % and a Si content of 0.6 atomic % to obtain acicular hematite particles. FIG. 2 is a diagram showing the relationship between 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. Figure 7 shows that the Zn content was 1 under different heating and firing atmospheres.
．． FIG. 2 is a diagram showing the relationship between the specific surface area and heating and firing temperature of fired particles obtained by heating and firing acicular hematite particles having a Si content of 41 at% and a Si content of 0.6 at%. In the figure, A is air, B is N2 gas as a non-reducing gas, and water vapor partial pressure? When Ps+Pi is 75%, C uses N2 gas as a non-reducing gas, and water Ps vapor partial pressure - - 1 =
is 950! ).

Claims (1)

[Claims] 1 pH 11 of Fe(OH)_2 and Zn(OH)_2
A water-soluble silicate was added in advance to the alkaline aqueous solution used to obtain the above mixed aqueous solution (Zn(OH)_2 is 0.1 to 2.3 at% in terms of Zn relative to Fe). It is added so that it is 0.1 to 1.7 at% in terms of Fe (however, the sum of the mixed amount of Zn(OH)_2 and the added amount of water-soluble silicate is equivalent to Fe, respectively in terms of Zn and Si). 2.5 atomic % or less), and then the alkaline aqueous solution is reacted with a ferrous salt aqueous solution and a water-soluble Zn salt aqueous solution to form fine and homogeneous Fe(OH)_2 and Zn(O
H)_2 A mixed aqueous solution with a pH of 11 or more is obtained, and then an oxygen-containing gas is passed through the mixed aqueous solution to oxidize it to produce Zn-containing acicular goethite particles, and then the generated Zn-containing goethite particles The average major axis length obtained by filtering, washing with water, drying, and dehydrating by heating is 0.
．． Zn-containing acicular hematite particles having a size of 3 to 2.5 μm and a specific surface area of 50 to 300 m^2/g by the BET method, maintaining the long axis length and axial ratio of acicular goethite particles. , in an atmosphere consisting of heated steam and non-reducing gas, the steam partial pressure Ps/Ps+Pi (Ps
is water vapor partial pressure, Pi is non-reducing gas partial pressure) 30 to 100
%, by heating and firing at a temperature in the range of 350 to 700°C, it becomes acicular with an average major axis length of 0.1 to 2.0 μm and a specific surface area of 10 to 30 m^2/g by BET method. After forming substantially high-density acicular hematite particles inheriting the acicular crystal structure, the acicular hematite particles are heated and reduced in a reducing gas at a temperature range of 350 to 600°C to obtain acicular crystal Fe. - A method for producing acicular Fe-Zn alloy magnetic particles, characterized by obtaining Zn alloy magnetic particles. 2 The amount of Zn(OH)_2 mixed with respect to Fe(OH)_2 is 1.0 to 2.0 at% in terms of Zn with respect to Fe, and the amount of water-soluble silicate added is 0.0% in terms of Si with respect to Fe. 3
~0.7 atomic%, however, the sum of the mixed amount of Zn(OH)_2 and the added amount of water-soluble silicate is
The method for producing acicular Fe-Zn alloy magnetic particle powder according to claim 1, wherein the content is 2.5 atomic % or less in terms of n and Si. 3 Steam partial pressure Ps/Ps+Pi (Ps is steam partial pressure,
3. The method for producing acicular Fe-Zn 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-Zn alloy magnetic particle powder 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-Zn alloy magnetic particle powder 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.