JPH026805B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a magnetic material for magnetic recording such as audio and video, and in particular, has acicular crystals that are optimal as a magnetic material for video, has uniform particle size, does not contain dendritic particles, and has As a result, the bulk density is large, the particles have a large specific surface area, and the degree of crystallinity on the particle surface and inside the particle is increased, resulting in substantially high density, high coercive force Hc, and large saturation magnetization σ _s and coated with a P compound and a Si compound that have excellent oxidation stability, or if necessary coated with a P compound and a Si compound and Ni and/or Al.
The present invention relates to a method for producing acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with a compound. When producing a magnetic recording medium, Si, Cr, Ni and Mg coated with the P compound and Si compound obtained by the present invention, or coated with the P compound and Si compound and Ni and/or Al compound as necessary, are used. When using the acicular iron alloy magnetic particle powder containing acicular crystals, the particle size is uniform, dendritic particles are not mixed, and as a result, the bulk density is large, and It is a fine particle with a large specific surface area, a substantially high density with an increased degree of crystallinity on the particle surface and inside the particle, and also has a high coercive force.
Due to its high Hc and large saturation magnetization _σs , as well as its excellent oxidation stability, the magnetic particles have extremely excellent dispersibility in the vehicle, orientation and filling properties in the coating film. Therefore, it is possible to obtain an excellent magnetic recording medium that has a low noise level generated during recording and reproduction of magnetic tape and can obtain high output characteristics. In recent years, magnetic recording and reproducing equipment for video and audio has become increasingly compact and lightweight.
The popularity of VTRs (recorders) has been remarkable, and VTRs are being actively developed with the aim of recording for longer periods of time and being smaller and lighter.On the other hand, efforts are being made to improve the performance and density of magnetic tape, which is a magnetic recording medium. Demand is increasing. In other words, magnetic recording media are required to have high image quality, high output characteristics, especially improved frequency characteristics, and lower noise levels. filling property,
It is necessary to improve the smoothness of the tape surface, and there is an increasing demand for an improvement in the S/N ratio. These characteristics of magnetic recording media are closely related to the magnetic materials used in magnetic recording media.
For example, Nikkei Electronics (1976) May 3
In the document "Recent Advances in Magnetic Tapes for Video and Audio" published on pages 82 to 105 of the Japanese issue, "Video Tape" described on pages 83 to 84.
The main characteristics of recorder image quality that change depending on the tape are the S/N ratio, chroma noise, and video frequency characteristics. ...These quantities representing image quality are determined by the electromagnetic conversion characteristics of the tape and head system, and the electromagnetic conversion characteristics have a correlation with the physical characteristics of the tape. Furthermore, the physical properties of the tape are largely determined by the magnetic material. It is clear from the statement, etc. As described above, the various characteristics of magnetic recording media, such as high image quality, are closely related to the magnetic materials used, and there is a strong desire to improve the characteristics of magnetic materials. The relationship between the various characteristics of the magnetic recording medium and the characteristics of the magnetic material used will now be detailed as follows. In order to obtain high image quality as a magnetic recording medium for video, it is clear from the Nikkei Electronics article mentioned above that the video S/N ratio, chroma,
Improvements in noise and video frequency characteristics are required. In order to improve the video S/N ratio, it is necessary to make the magnetic particles finer, improve their dispersibility in the vehicle, improve orientation and filling properties in the coating film, and improve the surface of the magnetic recording medium. It is important to improve the smoothness of the surface. This fact is based on the above-mentioned Nikkei Electronics, page 85, ``The physical quantities of the tape that are related to the SN ratio (CN ratio) of the luminance signal are the average number of particles per unit volume, their dispersion state (dispersibility), and the surface If the surface properties and dispersibility are constant, the signal-to-noise ratio will improve in proportion to the square root of the average number of particles, so the smaller the particle volume and the higher the degree of filling, the more advantageous a magnetic powder can be. It is clear from the description. That is, as one method for improving the video S/N, it is important to reduce the noise level caused by the magnetic recording medium, and for this purpose, as is clear from the above description, it is necessary to reduce the noise level caused by the magnetic material used. It is known that a method of reducing the particle size of acicular magnetic particles is effective. The value of the specific surface area of the magnetic particles is often used as a general method of expressing the particle size of the magnetic particles, but the noise level caused by the magnetic recording medium tends to decrease as the specific surface area of the magnetic particles increases. This is also generally known. This phenomenon can be seen, for example, in the Technical Research Report of the Institute of Electronics and Communication Engineers.
This is shown in "Fig 3" on page 27, 23-9 of MR81-11. "Fig. 3" is a diagram showing the relationship between the specific surface area of particles and the noise level in Co-coated acicular maghemite particle powder, and the noise level decreases linearly as the specific surface area of the particles increases. This relationship also applies to the acicular iron magnetic particles and the acicular iron alloy magnetic particles. In order to improve the dispersibility of the magnetic particles in the vehicle, the orientation and filling properties in the coating film, it is necessary that the magnetic particles dispersed in the vehicle have acicular crystals and have a uniform particle size. It is required that dendritic particles are not mixed therein, and as a result, the bulk density is high. Next, in order to improve chroma noise, it is important to improve the surface properties of magnetic recording media, and for this purpose, magnetic particle powder with good dispersibility and orientation is recommended. It is required to have acicular crystals, uniform particle size, no dendritic particles, and, as a result, a high bulk density. This fact is based on the above-mentioned Nikkei Electronics, p. 85, ``Chroma noise is caused by relatively long-period roughness on the tape surface, and is closely related to coating technology. It is clear from the statement, "It is easier to improve the surface properties." Furthermore, in order to improve the video frequency characteristics, it is necessary that the magnetic recording medium has a high coercive force Hc and a high saturation residual magnetic flux density Br. In order to increase the coercive force Hc of the magnetic recording medium, it is required that the coercive force Hc of the magnetic particles be as high as possible. The saturated residual magnetic flux density Br depends on the saturation magnetization σ _s of the magnetic particles as large as possible, the dispersibility of the magnetic particles in the vehicle, the orientation and filling properties in the coating film. This fact is based on Nikkei Electronics No. 84~
On page 85, "The maximum output is the saturation residual magnetic flux density of the tape.
Determined by Br and Hc and effective spacing. If Br is large, more magnetic flux will enter the reproducing head and the output will increase. ……. Increasing Hc reduces self-demagnetization and increases output. ……. Tape Br
In order to increase the saturation magnetization Is (σ _s ) that the magnetic material has in a perfect state (for example, a single crystal state)
First of all, it is basic that it is large. ……. Even if the material is the same, Br changes depending on the degree of filling, which indicates the proportion of magnetic powder. In addition, the squareness ratio (residual magnetization amount/
Since it is proportional to the saturation magnetization (amount of saturation magnetization), it is required that this is large. ……. In order to increase the squareness ratio, it is advantageous to use magnetic powder that has uniform particle sizes, a high acicularity ratio, and excellent magnetic field orientation. ...”
It is clear from the descriptions such as. As detailed above, improvements in high image quality and high output characteristics, especially frequency characteristics, of magnetic recording media, and
In order to meet the demands for higher performance such as lower noise levels, the characteristics of the magnetic particles used are that they have acicular crystals, uniform particle size, and do not contain dendritic particles. In addition, it is necessary to have a large specific surface area, a high coercive force Hc, and a large saturation magnetization σ _s . By the way, magnetic materials conventionally used in magnetic recording media include magnetite, maghemite,
Magnetic powder such as chromium dioxide, these magnetic powders have a saturation magnetization σ _s 70 to 85 emu/g and a coercive force Hc250.
~500 Oe. In particular, the σ _s of the above oxide magnetic particles is the maximum
It is about 85emu/g, and generally σ _s 70~80emu/
g is the main reason for limiting the reproduction output and recording density. Furthermore, Co-magnetite and Co containing Co
-Maghemite magnetic powder is also used, but these magnetic particles have a high coercive force Hc of 400 to 800 Oe, but on the other hand, they have a low saturation magnetization _σs of 60 to 80 emu/g. be. Recently, there has been active development of magnetic particles with characteristics suitable for high-output and high-density recording, that is, magnetic particles with large saturation magnetization σ _s and high coercive force. Particle powders are generally acicular crystals obtained by heating and reducing acicular crystal hydrated iron oxide particles, acicular crystal iron oxide particles, or particles containing a different metal other than iron in a reducing gas at about 350°C. It is a crystalline iron magnetic particle powder or an acicular crystalline iron alloy magnetic particle powder. These acicular iron magnetic particles or acicular iron alloy magnetic particles have significantly higher saturation magnetization σ _s than conventionally used magnetic iron oxide particles and Co-containing magnetic iron oxide particles, and magnetic force
It is characterized by high Hc, and when coated as a magnetic recording medium, it has a large residual magnetic flux density Br.
Since it has a high coercive force Hc and high density recording and high output characteristics, it has attracted attention and has been put into practical use in recent years. In the method for producing the acicular crystal iron magnetic particles or the acicular crystal iron alloy magnetic particles, the higher the heating reduction temperature in the reducing gas, the higher the saturation magnetization of the acicular crystal magnetic particles or needles. It is known that crystalline iron alloy magnetic particles can be obtained. On the other hand, the higher the heating reduction temperature in a reducing gas, the higher the saturation magnetization of acicular iron magnetic particles or acicular iron alloy magnetic particles can be obtained. ,
The deformation of the acicular crystal grains of the acicular ferromagnetic particles or the acicular ferromagnetic particles and the sintering between the particles and the particles become significant, and the resulting acicular ferromagnetic particles or acicular ferromagnetic particles become The coercive force of the crystalline iron alloy magnetic particles will be extremely reduced. That is, the coercive force of the acicular iron magnetic particles or the acicular iron alloy magnetic particles largely depends on the shape anisotropy. Acicularity is one of the important properties. In addition, the magnetic particles used for magnetic recording media are very fine particles of 1 μm or less, and the method described above produces fine acicular iron magnetic particles or acicular iron alloy magnetic particles. However, since the surface activity of the particles is extremely high, when they are taken out into the air after reduction, they rapidly react with oxygen in the air, causing heat generation and ignition, making them extremely unstable. At the same time, the above-mentioned oxidation reaction causes the particles to become oxides, resulting in a significant drop in magnetic properties, making it impossible to obtain the desired magnetic particles with high coercive force and high saturation magnetization. As mentioned above, acicular iron magnetic particles or acicular iron alloy magnetic particles having a high coercive force Hc and a large saturation magnetization _σs have acicular crystals, uniform particle size, and dendritic particles. In order to obtain magnetic particle powder with such characteristics, it is necessary that the starting material acicular crystal α-
It is necessary that the FeOOH particles have a uniform particle size and do not contain dendritic particles, and then how to maintain and inherit this particle morphology, especially needle-like crystals, by heating and reducing them to produce needle-like crystals. The ferromagnetic particles or the acicular iron alloy magnetic particles are made into ferromagnetic particles, or the acicular ferromagnetic particles or the acicular iron alloy magnetic particles after heat reduction are taken out into the air and then oxidized to saturation magnetization. A major issue is how to prevent a decrease in σ _s . First, the production of acicular α-FeOOH particle powder, which is a starting material, will be described. Conventionally, acicular crystal α-
The most typical known method for producing FeOOH particles is to add an equivalent or more alkaline solution to a ferrous salt aqueous solution to obtain an aqueous solution containing Fe(OH) ₂ at a pH of 11 or higher and a temperature of 80°C or lower. Acicular α-FeOOH particles are obtained by performing an oxidation reaction. Acicular crystals α- obtained by this method
FeOOH particles have a needle-like shape with a length of about 0.5 to 1.5 μm, but they also contain dendritic particles, and in terms of particle size, they cannot be said to have a uniform particle size. hard. The reason for the formation of acicular α-FeOOH particles with asymmetric particle sizes and a mixture of dendritic particles will be discussed below. Generally, the generation of acicular α-FeOOH particles involves the generation of acicular α-FeOOH nuclei and the acicular α-FeOOH particles.
It consists of two stages of FeOOH nucleus growth. Acicular α-FeOOH nuclei are generated by the reaction between dissolved oxygen and Fe(OH) ₂ obtained by reacting a ferrous salt aqueous solution with an alkali, but the contact reaction with dissolved oxygen is partially , and because it is non-uniform, the acicular crystal α-
The generation of FeOOH nuclei and the growth of the acicular α-FeOOH nuclei occur simultaneously, and many new nuclei are generated until the α-FeOOH production reaction is completed, so that the resulting acicular α-FeOOH The particles are asymmetric in particle size and contain a mixture of dendritic particles. In addition, the reaction iron (Fe ²⁺ ) concentration in the reaction aqueous solution in the above method is usually about 0.2 mol/,
Moreover, it takes a long time to generate acicular α-FeOOH particles. That is, according to the above method, even at a low reaction iron concentration of about 0.2 mol/min, the particle size is asymmetric and acicular α-
FeOOH particles were easily generated. Next, how to reduce the shape of the acicular α-FeOOH particles by heating while retaining and inheriting the acicular crystals to form acicular ferromagnetic particles or acicular iron alloy magnetic particles. The question is whether to do so. The causes of deformation of the acicular crystal particles and sintering of the particles and their mutual particles during the thermal reduction process will be explained below. Generally, acicular α-FeOOH particles are obtained by heating and dehydrating acicular α-FeOOH particles at a temperature around ₃₀₀ ℃ _.
The particles retain and inherit acicular crystals, but on the other hand, there are many pores generated on the particle surface and inside the particles due to dehydration, and the growth of single particles is not sufficient. , the degree of crystallinity is very small. When thermal reduction is performed using such acicular α-Fe ₂ O ₃ particles, uniform particle growth of a single particle is difficult to occur because the physical change is rapid. Therefore, it is considered that sintering of the particles and the particles among themselves occurs in the portion where the particle growth of a single particle occurs rapidly, and the particle shape becomes easily distorted. Furthermore, in the thermal reduction process, rapid volumetric contraction from the oxide to the metal occurs, making the particle shape more likely to collapse. Therefore, in order to prevent particle shape deformation and sintering between particles and particles during the thermal reduction process, acicular crystals α-
By achieving sufficient and uniform particle growth of single Fe ₂ O ₃ particles, the degree of crystallinity is increased, resulting in substantially high density and acicular α-
It is necessary to use acicular α-Fe ₂ O ₃ particles that retain and inherit the acicular crystals of FeOOH particles. A method for obtaining substantially high-density acicular α-Fe ₂ O ₃ particles with an increased degree of crystallinity is to heat-treat acicular α-FeOOH particles in a non-reducing atmosphere. Are known. In general, the higher the heat treatment temperature in a non-reducing atmosphere, the more effectively the acicular α-Fe ₂ O ₃ particles obtained by heating and dehydrating acicular α-FeOOH particles become single particles. It is possible to measure the particle growth of
Therefore, the degree of crystallinity can also be increased, but
On the other hand, it is known that when the heat treatment temperature exceeds 650°C, sintering progresses and the acicular crystal grains collapse. Therefore, acicular α-Fe ₂ O ₃ particles are obtained which have an increased degree of crystallinity, have a substantially high density, and retain and inherit the acicular structure of the acicular α-FeOOH particles. A known method for this purpose is to coat the surface of acicular α-FeOOH particles with an organic or inorganic compound that has an anti-sintering effect prior to heat treatment in a non-reducing atmosphere. . The present inventor has been involved in the production and development of acicular crystal magnetic particles for many years, and in the course of his research, he discovered acicular crystals coated with a Si compound that has a sintering prevention effect. We have already developed a method to produce α-FeOOH particles. For example, as described below. That is, the acicular α-FeOOH particles coated with the P compound and the Si compound are obtained by separating the acicular α-FeOOH particles produced by a wet reaction between a ferrous salt aqueous solution and an alkaline aqueous solution from the mother liquor. Suspended in water, 0.1 to 2 wt% (calculated as PO ₃ ) of phosphate is added to the acicular α-FeOOH particles while the pH value of the suspension is 8 or higher, and then 0.1 to 7.0 wt% of phosphate is added to the acicular α-FeOOH particles. wt%
It can be obtained by adding a water-soluble silicate (in terms of SiO ₂ ) and then adjusting the PH value to 3-7. The above method will be explained as follows. Generally, acicular α-FeOOH particles form a group of particles that are quite tightly entangled and bonded together during the crystal growth process in the reaction mother liquor during wet reaction. If the particles of acicular α-FeOOH particles are coated with an anti-sintering agent, further sintering will be prevented, and the entanglement and bonding that occurred during the crystal growth process in the reaction mother liquid will be prevented. Since they remain as they are, the intertwined and bonded needle crystals α-
The acicular iron alloy magnetic particles obtained by heat-treating FeOOH particles in a non-reducing atmosphere and then thermally reducing the particles also become entangled and bonded together. Such particles are characterized by their dispersibility in the vehicle,
It cannot be said that the orientation and filling properties in the coating film are sufficient. Therefore, before coating the acicular α-FeOOH particles with a Si compound, it is necessary to disentangle the entanglements and bonds generated during the crystal growth process in the reaction mother liquor. After separating the acicular α-FeOOH particles from the mother liquor, suspend them in water and add 0.1 to 2 wt% to the acicular α-FeOOH particles when the pH value of the suspension is 8 or higher.
By adding phosphate (calculated as _PO3 ),
It is possible to disentangle the entanglements and bonds of acicular α-FeOOH particles. Acicular α-FeOOH particles are acicular α-
After FeOOH particles are produced, they may be filtered from the reaction mother liquor and washed with water using a conventional method. The concentration of the suspension is preferably 20 wt% or less based on water. If it exceeds 20 wt%, the viscosity of the suspension will be too high and the effect of disentangling entanglements caused by the addition of phosphate will be insufficient. The amount of phosphate added is determined by the amount of acicular crystals α-
0.1-2wt% in terms of PO ₃ based on FeOOH particles
If so, disentangle the particles,
Particles can be uniformly dispersed. The added phosphate is adsorbed on the surface of the needle-like α-FeOOH particles, and almost all of it is absorbed into the formed needle-like α-FeOOH particles.
Contained in FeOOH particles. If the amount added is less than 0.1 wt%, the effect of addition is not sufficient. On the other hand, if the amount added exceeds 2 wt%, the particles can be dispersed, but since the particles are uniformly and strongly dispersed in the liquid, it is difficult to separate them by filtration from the liquid, which is not appropriate. Examples of the phosphate to be added include sodium metaphosphate and sodium pyrophosphate. The pH value of the suspension to which phosphate is added must be 8 or higher. If the PH value is less than 8, it is necessary to add more than 2wt% of phosphate to disperse the particles, and as mentioned above, if more than 2wt% of phosphate is added, , which is not preferable because it causes harmful effects during filtration and separation. Next, regarding the Si compound film formed on the surface of the acicular α-FeOOH particles, the formation of the Si compound film must be done by disentangling the acicular α-FeOOH particles using a phosphate. must be done after It is desirable that the pH value of the suspension is 8 or higher when the water-soluble silicate is added. If water-soluble silicate is added when the pH value of the suspension is less than 8, it will precipitate as solid SiO ₂ at the same time it is added, and it will form on the particle surface. It cannot be efficiently formed as a thin film. Therefore, water-soluble silicate is added when the pH value of the suspension is 8 or more, and after being mixed uniformly into the suspension, the pH value is adjusted to the range where SiO ₂ precipitates, that is, the pH value is When adjusted to 3 to 7, SiO ₂ precipitates on the surface of the particles to form a film. The amount of water-soluble silicate to be added is 0.1 to 7.0wt in terms of SiO ₂ based on the acicular α-FeOOH particles.
%. The added water-soluble silicate is acicular crystal α-
It is precipitated and adsorbed on the FeOOH particle surface, and almost the entire amount is contained in the produced acicular α-FeOOH particles. If the amount is less than 0.1wt%, the effect of addition will not be noticeable, and if it exceeds 7.0wt%, acicular iron alloy magnetic particles with excellent acicular crystals can be obtained, but the purity may be low. This decrease leads to a decrease in saturation magnetic flux density, which is undesirable. Note that examples of the water-soluble silicate to be added include sodium silicate and potassium silicate. Next, acicular crystal α containing Si, Cr, Ni and Mg
-The conditions for forming a film on FeOOH particles with a compound and a Si compound and then filtering and separating the particles from the suspension will be described. When using ordinary filtering means, if the particles are uniformly and strongly dispersed in the liquid, this may cause leakage of the filter cloth, clogging of the filter cloth, and other factors that may deteriorate the filtration efficiency. In order to increase the filtration efficiency, it is necessary that the particles dispersed by the addition of the phosphate described above are appropriately aggregated. When the amount of phosphate added is within the range of 0.1 to 2 wt%, if the pH value of the suspension is adjusted to 3 to 7, the viscosity of the suspension will increase, particles will aggregate, and filtration will be difficult. can be easily done. Furthermore, even if the PH value of the suspension is set to less than 3, it is possible to aggregate the acicular α-FeOOH particles, adsorb phosphate, and even form the SiO ₂ film mentioned above, but due to equipment limitations. This is not desirable as it may cause problems and quality problems (dissolution, etc.). In addition, in order to adjust the pH to 3-7, use acetic acid, sulfuric acid,
Phosphoric acid etc. can be used. Acicular α-FeOOH coated with P compound and Si compound obtained as explained above
The acicular α-Fe ₂ O ₃ particles obtained by heat-treating the particles in a non-reducing atmosphere have a substantially high density with an increased degree of crystallinity, and are free from particle entanglement. It retains and inherited excellent needle-like crystals with no interlocking or bonding. The temperature range of the heat treatment in a non-reducing atmosphere is preferably 500 to 900°C. When the heat treatment temperature in a non-reducing atmosphere is less than 500℃, the degree of crystallinity of the acicular α- _Fe2O3 particles coated with P and _Si compounds is increased. It is hard to say that it is a dense particle, 900℃
If it exceeds this, deformation of the acicular crystal grains and sintering of the grains and the grains will occur. In addition, it requires highly accurate equipment and advanced technology, and is not industrially or economically viable. Another problem is how to prevent the saturation magnetization σ _s from decreasing due to oxidation after the acicular iron magnetic particles or the acicular iron alloy magnetic particles are taken out into the air after thermal reduction. The present inventor has been involved in the production and development of acicular crystal magnetic particles for many years, and in the course of his research, he has developed acicular crystal iron magnetic particles or needles with excellent oxidation stability. A method for obtaining crystalline iron alloy magnetic particles has already been developed. In other words, the acicular iron magnetic particles or the acicular iron alloy magnetic particles with excellent oxidation stability are obtained by heating and reducing the acicular iron magnetic particles or the acicular iron alloy magnetic particles. In a mixed gas atmosphere of hydrogen and water vapor, at a temperature range of 150 to 700℃, the water vapor partial pressure (PH ₂ O / PH ₂ ) in the atmosphere is maintained at 10% or more and less than 100% to form ₄ layers of Fe ₃ O on the particle surface. form, then
It can be obtained by converting the surface of the above-mentioned ₄ Fe ₃ O layers into a ₃ -layer Fe ₂ O layer by applying an oxygen-containing gas at a temperature of 100° C. or lower. (Special Publication No. 58-5241,
Special Publication No. 58-52522). First, in the above method, the surface of metal particles is
The conditions for obtaining Fe ₂ O ₄ will be explained. The most important conditions for this are the processing atmosphere and processing temperature. First, regarding the atmosphere, the atmosphere must be a mixed gas atmosphere of hydrogen gas and water vapor. If there is no hydrogen gas, which is a reducing gas, in the atmosphere, no matter how you control other conditions,
No formation of Fe ₃ O ₄ was observed. Further, the water vapor partial pressure (PH ₂ O/PH ₂ ) in the atmosphere must be 10% or more and less than 100%. If it is less than 10% or more than 100%, it is difficult to generate Fe ₃ O ₄ . Furthermore, from an industrial standpoint, it is 50 to 90%.
A water vapor partial pressure of . Next, regarding the temperature, it must be in the temperature range of 150 to 700°C. At temperatures below 150°C, the production of Fe ₃ O ₄ is extremely slow and it takes a long time to produce the necessary amount of Fe ₃ O ₄ , which is not industrially practical. On the other hand, if it exceeds 700°C, the shape of the obtained metal particles will be distorted and the coercive force and squareness ratio will decrease, which is not preferable. Note that from an industrial standpoint, a temperature range of 150 to 550°C is preferable. Next, the conditions when the surface of the Fe ₃ O ₄ layer formed on the surface of the metal particles is further made of Fe ₂ O ₃ will be explained. After forming Fe ₃ O ₄ on the surface of metal particles,
Even when converting the surface of Fe ₃ O ₄ to Fe ₂ O ₃ , it is necessary to first turn the mixed gas atmosphere of hydrogen gas and water vapor into an inert gas atmosphere, cool it to a predetermined temperature, and then ventilate the oxidizing gas. It is. In order to make the surface of the Fe ₃ O ₄ layer Fe ₂ O ₃ , an oxidizing gas may be applied at a temperature of 100° C. or lower. At temperatures above 100℃, the oxidation reaction progresses rapidly, making it difficult to convert only the surface portion of Fe ₃ O ₄ to Fe ₂ O ₃ , and oxidizing all of the Fe ₃ O ₄ layers and even the internal metal parts. This is not preferable because there is a possibility that the problem will progress. Even if the temperature is below 100°C, the oxidation reaction tends to proceed excessively at temperatures above 50°C, so it is desirable to control the supply of the oxidizing gas. For example, a method of aerating a mixed gas of an oxidizing gas (air, etc.) and an inert gas (nitrogen, etc.), a method of intermittently aerating an oxidizing gas, etc. can be used. As mentioned above, after forming Fe ₃ O ₄ and Fe ₂ O ₃ layers on the particle surface of the acicular iron magnetic particles or the acicular iron alloy magnetic particles, they are immersed in an organic solvent and taken out by a conventional method. Good too. For example, toluene, acetone, benzene, methyl ethyl ketone,
The above-mentioned metal particles are cooled to around room temperature in an organic solvent such as methyl isobutyl ketone, xylene, or cyclohexanone in a state that minimizes contact with air (for example, in an inert gas atmosphere such as nitrogen).
The method of immersion is sufficient. In view of the above, the present inventor has developed a material that has acicular crystals, uniform particle size, no dendritic particles, large specific surface area, and low crystallinity on the particle surface and inside the particle. Various studies were conducted in order to obtain acicular iron alloy magnetic particles with substantially higher density, high coercive force Hc, large saturation magnetization σ _s , and excellent oxidation stability. I've been piling it up. Then, the present inventors discovered Fe(OH) ₂ obtained by reacting a ferrous salt aqueous solution with an alkali aqueous solution.
When generating acicular α-FeOOH particles by passing an oxygen-containing gas through a suspension containing PH11 or above to oxidize, A water-soluble silicate is added in an amount of 0.1 to 1.7 atomic % based on Fe in terms of Si in any of the suspensions, and the ferrous salt aqueous solution, the alkali aqueous solution, and the oxygen-containing gas are added. A water-soluble chromium salt is added to Fe in terms of Cr in either the suspension before the oxidation reaction is carried out by aerating the gas, or the reaction solution in which the oxidation reaction is carried out by aeration of the oxygen-containing gas. at 0.1
~5.0 atom% water-soluble nickel salt to Fe vs. Ni
Acicular α-FeOOH particles containing Si, Cr, Ni, and Mg can be formed by adding 0.1 to 7.0 atom% in terms of Mg and water-soluble magnesium salt to Fe in an amount of 0.1 to 15.0 atom% in terms of Mg. to generate the Si,
Acicular α-FeOOH particles containing Cr, Ni and Mg are coated with a P compound and a Si compound, and then heat treated in a non-reducing atmosphere to form densified Si, Cr, Ni and Si, Cr, Ni, and Mg coated with a P compound and a Si compound obtained by forming Mg-containing acicular α-Fe ₂ O ₃ particles and then heating and reducing the particles in a reducing gas. on the particle surface of acicular iron alloy magnetic particles containing
When Fe ₃ O ₄ and Fe ₂ O ₃ layers are formed, they have acicular crystals, uniform particle size, no dendritic particles, no entanglement of particles, etc. ,
It has a large specific surface area, a substantially high density with an increased degree of crystallinity on the particle surface and inside the particle, has a high coercive force Hc and a large saturation magnetization _σs , and has excellent oxidation stability. The present invention was completed by discovering that acicular iron alloy magnetic particles for magnetic recording can be obtained. That is, the present invention provides a PH containing Fe(OH) ₂ obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution.
In producing acicular α-FeOOH particles by passing an oxygen-containing gas through the suspension of 11 or more for oxidation, A water-soluble silicate is added in an amount of 0.1 to 1.7 atomic % based on Fe in terms of Si, and the ferrous salt aqueous solution, the alkaline aqueous solution,
Adding a water-soluble chromium salt to Fe in either the suspension before an oxidation reaction is carried out by passing an oxygen-containing gas through it, or the reaction solution before an oxidation reaction is carried out by passing an oxygen-containing gas through the solution. 0.1 to 5.0 at% in terms of Cr, water-soluble nickel salt in terms of Ni to Fe.
0.1-7.0 at%, and water-soluble magnesium salt
By adding 0.1 to 15.0 atomic % in terms of Mg to Fe, acicular α-FeOOH particles containing Si, Cr, Ni and Mg are generated, and the Si, Cr, Ni and Mg are contained. Acicular α-FeOOH particles are suspended in water, and Si,
0.1 to 2 wt% (calculated as PO ₃ ) of phosphate is added to acicular α-FeOOH particles containing Cr, Ni, and Mg to form a dispersion, and then Si, Cr,
By adding 0.1 to 7.0 wt% (calculated as SiO ₂ ) of water-soluble silicate to acicular α-FeOOH particles containing Ni and Mg, Si, Cr coated with P and Si compounds can be produced. Acicular α-FeOOH particles containing Ni and Mg are obtained, and the particles are coated with densified P and Si compounds by heat treatment in a non-reducing atmosphere at a temperature range of 500 to 900°C. Acicular crystal α containing Si, Cr, Ni and Mg
- Si, Cr, which is coated with P compounds and Si compounds by heating and reducing it in a reducing gas after forming Fe ₂ O ₃ particles.
Acicular iron alloy magnetic particles containing Ni and Mg are obtained, or if necessary, Si, Cr,
By adding 0.1 to 7.0 wt% (calculated as _SiO2 ) of water-soluble silicate to acicular α-FeOOH particles containing Ni and Mg, Si, Cr coated with P and Si compounds can be produced. Acicular α-FeOOH particles containing Ni and Mg are obtained, and the particles are coated with densified P and Si compounds by heat treatment in a non-reducing atmosphere at a temperature range of 500 to 900°C. Acicular crystal α containing Si, Cr, Ni and Mg
- Acicular iron containing Si, Cr, Ni, and Mg that is formed into Fe ₂ O ₃ particles and then heated and reduced in a reducing gas and coated with P and Si compounds and Ni and/or Al compounds. In forming alloy magnetic particles, the dispersion contains 0.5 to 10.0 of Fe in terms of Ni and/or Al.
Adding atomic % of Ni and/or Al compounds, or
Alternatively, the acicular α-Fe ₂ O ₃ particles containing Si, Cr, Ni and Mg coated with the densified P compound and Si compound after the above heat treatment are suspended in water. P compounds and Si compounds and Ni
Si, Cr, Ni coated with and/or Al compound
and obtain acicular iron alloy magnetic particles containing Mg,
Si, Cr, coated with the P compound and Si compound,
Acicular iron alloy magnetic particles containing Ni and Mg, or the above P compound and Si compound and Ni and/or
Either acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with an Al compound are heated to 150 to 700 in a mixed gas atmosphere of hydrogen and water vapor.
Temperature range of °C, partial pressure of water vapor in the atmosphere (PH ₂ O/
PH ₂ ) is maintained at 10% or more and less than 100% to form a Fe ₃ O ₄ layer on the particle surface, and then the Fe ₃ O ₄ is treated with an oxygen-containing gas at a temperature of 100° C. or less.
This is a method for producing acicular iron alloy magnetic particles for magnetic recording, which comprises forming the surface of the layer into a _three- layer Fe ₂ O layer. Next, the technical background that led to the completion of the present invention and the structure of the present invention will be described. As mentioned above, the acicular α-FeOOH particles produced by the conventional method in the alkaline region of pH 11 or higher have asymmetric particle sizes and contain dendritic particles. The present inventor has been developing needle-shaped α-FeOOH for many years.
We are involved in the production and development of particle powders, and in the process, we produce acicular α- crystals with uniform particle size and no dendritic particles.
We have already established a technology that allows us to obtain FeOOH particles. That is, acicular α-FeOOH particles with uniform particle size and no dendritic particles were obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution.
In a method of generating acicular α-FeOOH particles by passing an oxygen-containing gas through a suspension containing Fe(OH) ₂ for oxidation, the oxidation reaction is carried out by passing the alkaline aqueous solution and the oxygen-containing gas through the suspension. It can be obtained by adding water-soluble silicate in an amount of 0.1 to 1.7 at.
8461, Special Publication No. 55-32652). Conventionally, acicular α-FeOOH particles obtained in the alkaline region with a pH of 11 or higher generally have asymmetric particle sizes and contain dendritic particles;
The Fe(OH) ₂ floc, which is the precursor of FeOOH particles, is asymmetric, and at the same time, the Fe(OH) ₂ particles themselves that make up the Fe(OH) ₂ floc are asymmetric. Generation of acicular α-FeOOH core particles from an aqueous solution containing Fe(OH) ₂ and the acicular α-
This is due to the fact that the growth of FeOOH core particles occurs simultaneously, and new nuclei are generated in multiple layers until the acicular α-FeOOH production reaction is completed. As mentioned above, acicular α-FeOOH particles are produced by passing an oxygen-containing gas through a suspension containing Fe(OH) ₂ obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution to oxidize it. In producing the aqueous alkaline solution and oxygen-containing gas, water-soluble silicate is added to any of the suspensions before the oxidation reaction is carried out by passing the aqueous alkali solution and oxygen-containing gas through the aqueous alkali solution and the oxygen-containing gas.
When added to 1.7 at%, Fe
(OH) ₂ flocs can be made into sufficiently fine and uniform flocs, and the Fe(OH) ₂ particles themselves that make up the Fe(OH) ₂ flocs can be made into sufficiently fine and uniform particles. Furthermore, water-soluble silicates form needle-shaped α-FeOOH from aqueous solutions containing Fe(OH) _2.
Due to the effect of suppressing the oxidation reaction during particle generation, generation of acicular α-FeOOH core particles and growth of the acicular α-FeOOH core particles can be performed in stages. Therefore, the particle size is uniform, and the acicular α-
FeOOH particles can be obtained. The water-soluble silicates used in the above method include sodium and potassium silicates. The amount of water-soluble silicate added to the alkaline aqueous solution is 0.1 to 1.7 atomic % based on Fe in terms of Si. Almost all of the added water-soluble silicate is contained in the produced acicular α-FeOOH particles. If the amount of water-soluble silicate added is less than 0.1 atomic % based on Fe in terms of Si, the effect of obtaining acicular grains with uniform grain size and no dendritic grains will not be sufficient; If it exceeds atomic percent, granular magnetite particles will be mixed in. The above-mentioned acicular α-FeOOH particles with uniform particle size and no dendritic particles are coated with a P compound and a Si compound, and then heated in a non-reducing atmosphere. The acicular iron alloy magnetic particle powder obtained by using densified acicular α-Fe ₂ O ₃ particles as a starting material and heating and reducing the starting material also has uniform particle size and has dendritic particles. are not mixed, and as a result,
It has a large bulk density and has good dispersibility when made into paint.
In addition, it has high filling properties in the coating film and has a low residual magnetic flux density.
Although it is characterized by a large Br, the specific surface area is about 20 m ² /g at most. Therefore, as a result of various studies on methods for improving the specific surface area of Si-containing acicular iron alloy magnetic particles with uniform particle size and no dendritic particles, the inventors have found that the particle size is uniform. It is symmetrical,
To generate acicular α-FeOOH particles containing Si without dendritic particles, Fe(OH) is prepared before the oxidation reaction is carried out by passing through a ferrous salt aqueous solution, an alkaline aqueous solution, and an oxygen-containing gas. ₂ A water-soluble chromium salt is added to either the suspension or the reaction solution in which an oxidation reaction is carried out by passing oxygen-containing gas through the suspension, and the resulting acicular crystals containing Si and Cr α-
We have found that when FeOOH particles are thermally reduced, the specific surface area of Si-containing acicular iron alloy magnetic particles can be improved. This phenomenon will be explained as follows by extracting some of the many experimental examples conducted by the present inventor. Figure 1 shows the amount of water-soluble chromium salt added, the acicular iron alloy magnetic particle powder containing Si and Cr coated with a P compound and a Si compound, and the needle containing Cr coated with a P compound and a Si compound. FIG. 3 is a relationship diagram of the specific surface area of crystalline iron alloy magnetic particles. That is, 300% of an aqueous ferrous sulfate solution containing 1.2 mol of Fe ²⁺ was mixed with sodium silicate prepared in advance in a reactor at a concentration of 0 to 1.0 atomic % based on Fe in terms of Si.
Add chromium sulfate to a NaOH aqueous solution 400 obtained by adding 0 to 5.0 atomic % of Fe in terms of Cr, and
In step 13.8, a suspension containing Fe(OH) ₂ was obtained, and an oxidation reaction was carried out by passing 1000 air per minute into the suspension at a temperature of 45°C to form acicular crystals α containing Si and Cr. - producing FeOOH particles, coating the particles with P compounds and Si compounds, and then
Si and Si coated with densified P and Si compounds by heat treatment at 770℃ in air.
Acicular crystals containing Si and Cr coated with a P compound and a Si compound obtained by converting the particles into acicular α-Fe ₂ O ₃ containing Cr and then heating and reducing the particles at 450°C for 5.0 hours. A crystalline iron alloy magnetic particle powder and an acicular crystalline iron alloy magnetic particle powder containing Cr were stably extracted into the air by forming Fe ₃ O ₄ and Fe ₂ O ₃ layers on the particle surface of the particles. This figure shows the relationship between the specific surface area and the amount of chromium sulfate added. In the figure, curve a is for the case without Si addition, curves b and c
are the case where the amount of Si added is 0.35 atomic % and 1.0 atomic %, respectively. As shown in curves b and c, when Si and Cr are added together, the specific surface area of the resulting acicular iron alloy magnetic particles containing Si and Cr can be significantly improved; , the specific surface area tends to increase as the amount of chromium sulfate added increases. Since this phenomenon appears more markedly than when Cr is added alone, as shown by curve a in FIG. 1, the present inventor believes that it is due to the synergistic effect of Si and Cr. As mentioned above, the acicular iron alloy magnetic particle powder containing Si and Cr coated with a P compound and a Si compound has a uniform particle size, does not contain dendritic particles, and has a large specific surface area. However, on the other hand, there was a tendency for the coercive force to decrease as the amount of Cr added increased. Therefore, the present inventors have proposed a method for improving the coercive force of acicular iron alloy magnetic particles containing Si and Cr coated with a P compound and a Si compound.
As a result of various studies, we found that when producing acicular α-FeOOH particles containing Si and Cr, Fe(OH ) ₂ A water-soluble nickel salt is added to either the suspension or the reaction solution in which an oxidation reaction is carried out by passing an oxygen-containing gas through the resulting acicular needle containing Si, Cr, and Ni. When crystalline α-FeOOH particles are coated with a P compound and a Si compound and then thermally reduced, the coercive force of the acicular crystalline iron alloy magnetic particle powder containing Si and Cr can be reduced while maintaining a large specific surface area. We found that it is possible to improve the situation. This phenomenon will be explained as follows by extracting some of the many experimental examples conducted by the present inventor. FIG. 2 is a diagram showing the relationship between the amount of water-soluble nickel salt added and the coercive force of acicular iron alloy magnetic particles containing Si, Cr, and Ni coated with a P compound and a Si compound. That is, 300% of an aqueous ferrous sulfate solution containing 1.2 mol of Fe ²⁺ was mixed with sodium silicate, prepared in advance, in a reactor at 0.35 atomic % relative to Fe in terms of Si, and chromium sulfate in an amount equivalent to Cr relative to Fe. A suspension containing Fe(OH) ₂ was obtained at pH 14.0 by adding 0.5 at% nickel sulfate to an aqueous NaOH solution 400 obtained by adding 0 to 7.0 at% nickel based on Fe. ,
Si, Cr was produced by aerating 1000 ml of air per minute through the suspension at a temperature of 45°C to carry out an oxidation reaction.
and Ni-containing acicular α-FeOOH particles, which were coated with a P compound and a Si compound obtained in the same manner as in Figure 1 using the particles as starting materials.
This figure shows the relationship between the coercive force of acicular iron alloy magnetic particles containing Si, Cr, and Ni and the amount of nickel sulfate added. As shown in FIG. 2, as the amount of nickel sulfate added increases, the coercive force of the acicular iron alloy magnetic particles containing Si, Cr, and Ni tends to increase. This phenomenon of increasing coercive force while maintaining a large specific surface area cannot be achieved by removing Si, Cr, or Ni;
The present inventor believes that this is due to the synergistic effect of Si, Cr, and Ni. Furthermore, as a result of repeated studies on methods for improving the specific surface area and coercive force of acicular iron alloy magnetic particles containing Si, Cr, and Ni, the present inventors found that
In the production of acicular α-FeOOH particles containing Si, Cr, and Ni, Fe(OH) ₂ suspension is mixed with a ferrous salt aqueous solution, an alkaline aqueous solution, and an oxygen-containing gas before being subjected to an oxidation reaction. A water-soluble magnesium salt is added to either of the reaction solutions in which an oxidation reaction is carried out by passing oxygen-containing gas through the resulting acicular crystals α- containing Si, Cr, Ni, and Mg.
It has been found that when FeOOH particles are thermally reduced, the specific surface area and coercive force of acicular iron alloy magnetic particles containing Si, Cr, and Ni can be further improved. This phenomenon will be explained as follows by extracting some of the many experimental examples conducted by the present inventor. Figures 3 and 4 show the coercive force and specific surface area of acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with P and Si compounds and the amount of water-soluble magnesium salt added, respectively. It is a relationship diagram. That is, 300% of an aqueous ferrous sulfate solution containing 1.2 mol of Fe ²⁺ was mixed with sodium silicate, prepared in advance, in a reactor at 0.35 atomic % relative to Fe in terms of Si, and chromium sulfate in an amount equivalent to Cr relative to Fe. 0.50 atomic%, nickel sulfate 3.0 atomic% based on Ni in terms of Ni, magnesium sulfate 0 to 15.0 atomic% based on Fe in terms of Mg.
NaOH aqueous solution obtained by adding 400
In addition, a suspension containing Fe(OH) ₂ was obtained at pH 14.0, and an oxidation reaction was carried out by passing air through the suspension at a rate of 1000 °C per minute at a temperature of 50 °C.
Acicular crystal α- containing Si, Cr, Ni and Mg
FeOOH particles were generated, and P compound and Si obtained in the same manner as in Figure 1 using the particles as starting materials.
This figure shows the relationship between the coercive force and specific surface area of acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with a compound and the amount of magnesium sulfate added. As shown in Figures 3 and 4, as the amount of magnesium sulfate added increases, the coercive force of the acicular iron alloy magnetic particles containing Si, Cr and Ni coated with P and Si compounds changes. Both specific surface areas can be further improved. Since the phenomenon of further improving the coercive force and specific surface area cannot be obtained by removing any of Si, Cr, Ni, and Mg, the present inventors
We believe that this is due to the synergistic effect of Si, Cr, Ni, and Mg. Furthermore, as a result of repeated studies on a method for further improving the specific surface area of acicular iron alloy magnetic particle powder containing Si, Cr, Ni, and Mg coated with a P compound and a Si compound, the present inventor found that P Acicular α-FeOOH particles containing Si, Cr, Ni, and Mg coated with a compound and a Si compound, or acicular α-Fe ₂ O ₃ particles obtained by heating and dehydrating the same, or the above-mentioned acicular α-FeOOH particles. A suspension containing either densified acicular α-Fe ₂ O ₃ particles obtained by heating crystal α-FeOOH particles in a non-reducing atmosphere is prepared, and the suspension is By adding and mixing 0.5 to 10.0 atomic % of Ni and/or Al compounds in terms of Ni and Al to Fe in the liquid, Si coated with P compound and Si compound and Ni and/or Ai compound can be formed. ,Cr,
Acicular α-FeOOH particles containing Ni and Mg or Acicular α- containing Si, Cr, Ni and Mg
Fe ₂ O ₃ particles or densified Si, Cr, Ni and
After forming acicular α-Fe ₂ O ₃ particles containing Mg,
When heated and reduced in a reducing gas, the specific surface area of the acicular iron alloy magnetic particles containing Si, Cr, Ni and Mg coated with a P compound and a Si compound can be further improved. I obtained this knowledge. This phenomenon will be explained as follows by extracting some of the many experimental examples conducted by the present inventor. Figure 5: Coated with Ni and/or Al compounds
FIG. 2 is a diagram showing the relationship between Mg content and specific surface area of acicular iron alloy magnetic particle powder containing Si, Cr, Ni, and Mg. That is, the P compound and Si obtained in FIGS. 3 and 4
2000 g of acicular α-FeOOH particles containing Si, Cr, Ni, and Mg coated with a compound were suspended in 60 g of water, and then nickel sulfate and/or aluminum sulfate were added and mixed to the suspension. After, filtration,
Figure 3 shows acicular α-FeOOH particles containing Si, Cr, Ni, and Mg coated with P and Si compounds and Al and/or Ni compounds obtained by drying.
and acicular iron alloy magnetic particles containing Si, Cr, Ni and Mg coated with P and Si compounds and Ni and/or Al compounds obtained by reduction under the same conditions as in Figure 4. This figure shows the relationship between Mg content and specific surface area. In the figure, curve a shows 2.0 atomic% of Ni equivalent to Fe.
For acicular iron alloy magnetic particle powder containing Si, Cr, Ni and Mg coated with Ni compound, curve b
In the case of acicular iron alloy magnetic particle powder containing Si, Cr, Ni, and Mg coated with an Al compound of 4.0 atomic % in terms of Al based on Fe, curve c is 2.0 atomic % in terms of Ni based on Fe. and 2.0 atomic% in terms of Al with respect to Fe.
Si, Cr, Ni coated with Al and Ni compounds
Curve d is for the acicular iron alloy magnetic particle powder containing Si, Cr, Ni, and Mg without Ni and/or Al compound treatment. . As shown in Figure 5, when coated with Ni and/or Al compounds, acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with P and Si compounds. The specific surface area can be further improved. This phenomenon is caused by acicular crystals α-
If Ni and/or Al compounds are added during the FeOOH particle formation reaction, or if Mg-free acicular α-FeOOH particles are coated with Ni and/or Al compounds, acicular iron Since the effect of increasing the specific surface area of the alloy magnetic particles is not so great, the present inventor believes that this is due to the synergistic effect of Mg and the Ni and/or Al compounds. P compound and Si compound obtained by the above method, or if necessary, P compound and Si compound
Si, Cr, Ni coated with Ni and/or Al compounds
Acicular iron alloy magnetic particles containing Mg and Mg have very high saturation magnetization, but when taken out in an organic solvent by a conventional method, they do not have sufficient oxidation stability and are susceptible to oxidation by air, etc. As a result, the saturation magnetization decreases rapidly. In particular, this phenomenon increases as the particle size decreases and the specific surface area increases. Therefore, the present inventor developed a needle-like structure containing Si, Cr, Ni, and Mg coated with a P compound and a Si compound having large saturation magnetization, or, if necessary, a P compound and a Si compound and a Ni and/or Al compound. After repeated studies on the oxidation stability of crystalline iron alloy magnetic particles, we were able to improve the oxidation stability by forming Fe ₃ O ₄ and Fe ₂ O ₃ layers on the particle surface. Figure 6 coated with P compound and Si compound
The rate of decrease in saturation magnetization σ _s over time when acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg are taken out into the air is calculated under conditions of a temperature of 50°C and a relative humidity of 80%. The value obtained by dividing the difference (Δσ _s ) before and after the change by the saturation magnetization before the change is expressed as a percentage. In FIG. 6, curve a shows the curve b when Fe ₃ O ₄ and Fe ₂ O ₃ layers are formed on the particle surface of the acicular iron alloy magnetic particles, which are then immersed in an organic solvent and then taken out into the air. Curve c is the case where Fe ₃ O ₄ and Fe ₂ O ₃ layers are formed on the particle surface and then taken out into the air, and curve c is the case where the particle is directly immersed in an organic solvent and then taken out into the air. As is clear from FIG. 6, Fe ₃ O ₄ and
When _three layers of Fe ₂ O are formed, a product with extremely excellent oxidation stability can be obtained. Next, various conditions for implementing the present invention will be described. As the water-soluble chromium salt used in the present invention, chromium sulfate and chromium chloride can be used. Regarding the timing of addition of the water-soluble chromium salt, in the present invention, it is necessary to make chromium present during the formation reaction of acicular α-FeOOH particles.
It may be added either to a suspension containing (OH) ₂ or to a reaction solution in which acicular α-FeOOH particles are being formed after the start of aeration of oxygen-containing gas. Furthermore, even if water-soluble chromium salt is added at a stage when the formation of acicular α-FeOOH particles has been completely completed, chromium will not enter the particles, so the effect of chromium addition in the present invention cannot be obtained. . The amount of water-soluble chromium salt added in the present invention is
It is 0.1 to 5.0 atomic % in terms of Cr relative to Fe. Almost all of the added water-soluble chromium salt is formed into needle-shaped α- crystals.
Contained in FeOOH particles. If the amount of water-soluble chromium salt added is less than 0.1 atomic % based on Fe in terms of Cr, the effect of increasing the specific surface area of the obtained acicular iron alloy magnetic particles cannot be obtained. Even if it exceeds 5.0 at %, the effect of increasing the specific surface area of the obtained acicular iron alloy magnetic particles can be obtained, but the coercive force and saturation magnetization decrease, which is not preferable. As the water-soluble nickel salt used in the present invention, nickel sulfate, nickel chloride, nickel nitrate, etc. can be used. Regarding the timing of addition of the water-soluble nickel salt, in the present invention, it is necessary to make nickel present during the formation reaction of acicular α-FeOOH particles, and for this purpose, it is necessary to add the water-soluble nickel salt to the ferrous salt aqueous solution or the alkaline aqueous solution. , into a suspension containing Fe(OH) ₂ , or into a reaction solution in which acicular α-FeOOH particles are being formed after the start of aeration of oxygen-containing gas. Furthermore, even if water-soluble nickel salt is added at a stage when the formation of acicular α-FeOOH particles has been completely completed, the effect of nickel addition in the present invention cannot be obtained because nickel does not enter the particles. . The amount of water-soluble nickel salt added in the present invention is
It is 0.1 to 7.0 atomic % based on Ni in terms of Ni. Almost all of the added water-soluble nickel salt is formed into needle-shaped crystals α.
-Contained in FeOOH particles. If the amount of water-soluble nickel salt added is less than 0.1 atomic % based on Fe in terms of Ni, the effect of increasing the coercive force of the obtained acicular iron alloy magnetic particles cannot be obtained. If the content exceeds 7.0 atomic %, the object of the present invention can be achieved, but this is not preferable because foreign matter other than needle crystals will be mixed during the production of α-FeOOH particles. As the water-soluble magnesium salt used in the present invention, magnesium sulfate and magnesium chloride can be used. Regarding the timing of addition of the water-soluble magnesium salt, in the present invention, it is necessary to have magnesium present during the formation reaction of acicular α-FeOOH particles, and for this purpose, it is necessary to add the water-soluble magnesium salt to the ferrous salt aqueous solution or the alkaline aqueous solution. , in a suspension containing Fe(OH) ₂ , or
After the start of aeration of the oxygen-containing gas, acicular α-FeOOH particles may be added to any part of the reaction solution that is being generated. Furthermore, even if water-soluble magnesium salt is added at a stage when the formation of acicular α-FeOOH particles has been completely completed, the effect of magnesium addition in the present invention cannot be obtained because magnesium does not enter the particles. . The amount of water-soluble magnesium salt added in the present invention is 0.1 to 15.0 atomic % based on Fe in terms of Ni.
Almost all of the added water-soluble magnesium salt is contained in the produced acicular α-FeOOH particles. Addition amount of water-soluble magnesium salt relative to Fe
If it is less than 0.1 atomic % in terms of Mg, the effect of further increasing the specific surface area and coercive force of the obtained acicular iron alloy magnetic particles cannot be obtained. Although the object of the present invention can be achieved even if the content exceeds 15.0 atomic %, it is not preferable because the saturation magnetization decreases. As the nickel compound used in the present invention, nickel sulfate, nickel chloride, nickel nitrate, etc. can be used, and as the aluminum compound, aluminum sulfate, aluminum chloride, sodium aluminate, etc. can be used. The coating particles used in the coating treatment with Ni and/or Al compounds include Si, Cr, Ni and Mg-containing acicular crystals α generated in the reaction mother liquor.
- FeOOH particles, Si, Cr, Ni and Mg-containing acicular crystals α after being filtered from the reaction mother liquor, washed with water, and dried -
FeOOH particles, Si, Cr, Ni and Mg containing acicular α
-Which of Fe ₂ O ₃ particles and acicular α-Fe ₂ O ₃ particles obtained by high-temperature heat treatment of Si, Cr, Ni, and Mg-containing acicular α-FeOOH particles? can also be used, and the same effect can be obtained in either case. It is necessary that the Ni and/or Al compound be uniformly coated on the particle surface.
Preferably, the compound is deposited as a hydroxide of Ni and/or Al using an alkali. The amount of Ni and/or Al compound added is
It is 0.5 to 10.0 atomic % in terms of Ni and/or Al. If it is less than 0.5 atomic %, the object of the present invention cannot be fully achieved. If it exceeds 10.0 at%, Si, Cr, Ni and
Acicular iron alloy magnetic particles containing Mg are undesirable because their saturation magnetization is significantly reduced due to a decrease in purity. Examples of alkalis used in coating with Ni and/or Al compounds include sodium hydroxide and potassium hydroxide. The Ni and/or Al compound and the alkali may be added in any order, or may be added at the same time. The present invention configured as described above has the following effects. That is, according to the present invention, the particles have acicular crystals, have a uniform particle size, do not contain dendritic particles, have a large bulk density, have a large specific surface area, and have a high degree of crystallinity on the particle surface and inside the particle. is substantially high-density, has a high coercive force Hc and a large saturation magnetization _σs , and is coated with a P compound and a Si compound with excellent oxidation stability, or if necessary Acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with P and Si compounds and Ni and/or Al compounds can be obtained, which provides the high image quality that is currently most required. It can be used as magnetic particle powder for image quality, high output, high sensitivity, and high recording density. Furthermore, in the production of magnetic paint, it contains Si, Cr, Ni, and Mg coated with the above-mentioned P compound and Si compound, or optionally coated with P compound and Si compound and Ni and/or Al compound. When using acicular iron alloy magnetic particles, the noise level is low and the dispersibility in the vehicle is low.
It is possible to obtain a preferred magnetic recording medium with extremely excellent orientation and filling properties in the coating film. Next, the present invention will be explained with reference to Examples and Comparative Examples. In addition, the specific surface area of the particles in the previous experimental examples, the following examples, and comparative examples was measured by the BET method, and the particle axis ratio (long axis: short axis) and long axis were measured using an electron microscope. It is shown as the average value of the numerical values measured from the photographs. Moreover, the bulk density was measured according to JIS K5101-1978 "Pigment test method". P content, Si content, Cr content, Ni content, Mg content and
The amount of Al was determined by performing fluorescence X-ray analysis using a "fluorescence X-ray analyzer model 3063M" (manufactured by Rigaku Denki Kogyo) in accordance with the "General Rules for Fluorescence X-ray Analysis" of JIS K0119-1979. It was measured. The magnetic property values are the results measured under an external magnetic field of 10 KOe using a sample vibrating magnetometer. In addition, oxidation stability is measured at a temperature of 50°C and a relative humidity of 80%.
It is expressed as a decrease rate (%) of saturation magnetization after being left in an atmosphere for 2 days. <Production of needle-shaped α-FeOOH particle powder> Examples 1 to 5, Comparative Example 1; Example 1 Ferrous sulfate aqueous solution containing 1.2 mol/Fe ²⁺ 300
Sodium silicate (No. 3) (SiO ₂ 28.55wt%) 379g was prepared in advance in a reactor to contain 0.50 at% in terms of Si, and 0.50 at% in terms of Cr was added to Fe. Contains 644g of chromium sulfate,
In addition to 400 g of a 5.46-N NaOH aqueous solution obtained by adding 2,884 g of nickel sulfate to contain 3.0 atomic % of Fe in terms of Ni, and 4473 g of magnesium sulfate to contain 5.0 atomic % of Fe in terms of Mg, PH
13.8, a reaction was carried out to produce a Fe(OH) ₂ suspension containing Si, Cr, Ni and Mg at a temperature of 45°C. The Fe(OH) ₂ suspension containing Si, Cr, Ni and Mg was bubbled with air at a rate of 1000/min for 5.1 hours at a temperature of 50°C to produce acicular α-FeOOH containing Si, Cr, Ni and Mg. generated particles. The end point of the oxidation reaction was determined by extracting a portion of the reaction solution and 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 Fe ²⁺ . The generated particles are separated by filtration, washed with water, dried, and
Shattered. The obtained acicular α-FeOOH particles containing Si, Cr, Ni and Mg were found to be α-FeOOH particles as a result of X-ray diffraction.
A diffraction pattern similar to the crystal structure of FeOOH particles was obtained. In addition, as a result of fluorescent X-ray analysis, Si was compared to Fe.
0.504 atomic%, Cr to Fe 0.498 atomic%, Ni
3.03 at% to Fe, 4.98 at% Mg to Fe
It contained. Therefore, Si, Cr, Ni and Mg have acicular crystal α-
It is thought that it is dissolved in FeOOH particles. This acicular crystal α- containing Si, Cr, Ni and Mg
As a result of electron microscopic observation, the FeOOH particles had an average long axis of 0.55 μm and an axial ratio (long axis:short axis) of 33:1. Examples 2 to 5 The type and concentration of ferrous salt aqueous solution, the concentration of NaOH aqueous solution, and the type, amount, and timing of addition of water-soluble silicate, water-soluble chromium salt, water-soluble nickel salt, and water-soluble magnesium salt. Acicular α-FeOOH particles containing Si, Cr, Ni, and Mg were produced in the same manner as in Example 1 except that various changes were made. The main manufacturing conditions at this time are shown in Table 1, and the characteristics are shown in Table 2. Comparative Example 1 Acicular α-FeOOH particle powder was produced in the same manner as in Example 1, except that sodium silicate, chromium sulfate, nickel sulfate, and magnesium sulfate were not added and the concentration of the NaOH aqueous solution was varied. The main manufacturing conditions at this time are shown in Table 1, and the characteristics are shown in Table 2. As a result of electron microscopic observation, the obtained acicular α-FeOOH particles had an average long axis of 0.45 μm and an axial ratio (long axis: short axis) of 9:1, and the particle size was asymmetric.
It contained a mixture of dendritic particles. <Highly densified P compound and Si compound or P
Example 6 Obtained in Example 1 Example 6 to ₁₃ , Comparative Example ₂ ; Example 6 Obtained in Example 1 Filtered and washed Si, Cr,
6,600 g of paste of acicular α-FeOOH particles containing Ni and Mg (equivalent to approximately 2,000 g of acicular α-FeOOH particles containing Si, Cr, Ni, and Mg).
was suspended in 100% water. of the suspension at this time
The pH value was 10.0. Next, 500 ml of an aqueous solution containing 16 g of sodium hexametaphosphate (Si, Cr, Ni and
For acicular α-FeOOH particles containing Mg,
Equivalent to 0.56wt% as _PO3 . ) and add 30
Stir for 1 minute. Next, 260 g of sodium silicate (No. 3 water glass) (as SiO ₂ for acicular α-FeOOH particles containing Si, Cr, Ni, and Mg) was added to the above suspension.
This corresponds to 3.7wt%. ) and stirred for 30 minutes, 10% acetic acid was added so that the pH value of the suspension was 6.0, and Si, Cr,
Needle crystal α- FeOOH particles containing Ni and Mg are filtered and dried, and needle-like α- FeOOH particles containing Si, Cr, Ni and Mg are coated with P compound and Si compound.
FeOOH particle powder was obtained. Si coated with the above P compound and Si compound,
1,500 g of acicular α-FeOOH particles containing Cr, Ni, and Mg were heat-treated in air at 780°C to coat them with highly dense P and Si compounds.
Acicular α-Fe ₂ O ₃ containing Si, Cr, Ni and Mg
A particulate powder was obtained. Table 3 shows the powder characteristics of the obtained acicular α-Fe ₂ O ₃ particle powder. Examples 7 and 8, Comparative Example 2 The type of particles to be treated, the pH of the suspension, the amount of P compound added, the amount of Si compound added and adjustment of PH, the heat treatment temperature and the type of non-reducing atmosphere were varied. Si, Cr, Ni and
Acicular α-Fe ₂ O ₃ particle powder containing Mg was obtained.
Table 3 shows the main manufacturing conditions at this time. Example 9 Si, Cr, filtered and washed with water obtained in Example 5
9.6 kg of paste of acicular α-FeOOH particles containing Ni and Mg (equivalent to approximately 3000 g of acicular α-FeOOH particles containing Si, Cr, Ni, and Mg).
was suspended in 100% water. of the suspension at this time
The pH value was 9.5. Next, 600 ml of an aqueous solution containing 30 g of sodium hexametaphosphate (Si, Cr, Ni and
PO ₃ for Mg-containing acicular α-FeOOH particles
This corresponds to 0.70wt%. ) and stirred for 30 minutes. Next, nickel sulfate ( _NiSO4 .
6H ₂ O) 266g (corresponding to 3.0 atomic% of Ni in terms of Fe) and aluminum sulfate (Al ₂
(SO ₄ ) ₃ 18H ₂ O) 337 g (corresponding to 1.5 atomic % of Fe in terms of Al) was added, and while stirring, 2-
1.5 liters of N aqueous NaOH was added. continuation,
Add sodium silicate (No. 3 water glass) to the above suspension.
435g (acicular crystal α containing Si, Cr, Ni and Mg
-Equivalent to 4.1wt% as SiO ₂ with respect to FeOOH particles. ) and stirred for 30 minutes, the pH of the suspension
After adding 10% acetic acid so that the value is 7.0,
Acicular α-FeOOH particles containing Si, Cr, Ni, and Mg are filtered and dried using a press filter to form Si, Cr, Ni, and Mg coated with P compounds, Si compounds, Ni compounds, and Al compounds. Acicular α-FeOOH particles containing α-FeOOH were obtained. The above P compound, Si compound, Ni compound and Al
2000 g of acicular α-FeOOH particles containing Si, Cr, Ni, and Mg coated with a compound were placed in the air.
Highly densified acicular crystal α- heated at 650℃
Fe ₂ O ₃ particle powder was obtained. The obtained needle crystal α-
Table 3 shows the powder properties of Fe ₂ O ₃ particle powder. Examples 10, 11 Type of particles to be treated, pH of suspension, amount of P compound added, type and amount of Ni and/or Al compound,
Coated with P compound and Si compound and Ni compound and/or Al compound was carried out in the same manner as in Example 9 except that the amount of Si compound added and the pH adjustment were varied.
Acicular crystal α- containing Si, Cr, Ni and Mg
FeOOH particle powder was obtained. The above P compound, Si compound, Ni compound and/or
or Si, Cr, Ni and Mg coated with Al compounds
P and Si compounds are densified by heat-treating the acicular α-FeOOH particle powder at the heat treatment temperature and atmosphere shown in Table 3.
Si coated with Ni compound and/or Al compound,
Acicular α-Fe ₂ O ₃ particle powder containing Cr, Ni and Mg was obtained. Table 3 shows the main manufacturing conditions and characteristics at this time. Example 12 Paste of acicular α-FeOOH particles containing Si, Cr, Ni and Mg obtained in Example 2, 6.3Kg
(Acicular crystal α- containing Si, Cr, Ni and Mg
This corresponds to approximately 2000g of FeOOH particles. ) was suspended in 60% water. The pH value of the suspension at this time was 9.6. Next, 300 ml of an aqueous solution containing 12 g of sodium hexametaphosphate (Si, Cr, Ni
It corresponds to 0.42 wt% as PO ₃ with respect to the acicular α-FeOOH particles containing Mg and Mg. ) by adding
Stir for 30 minutes, then add 60 g of sodium silicate (No. 3 water glass) (Si, Cr, Ni and Mg) to the above suspension.
This corresponds to 0.86 wt% as SiO ₂ in the acicular α-FeOOH particles containing . ) and stirred for 30 minutes, 10% acetic acid was added so that the pH value of the suspension was 5.5, and then Si,
Acicular α-FeOOH particles containing Cr, Ni and Mg are filtered and dried to produce acicular α- FeOOH particles containing Si, Cr, Ni and Mg coated with P and Si compounds.
FeOOH particle powder was obtained. Si coated with the above P compound and Si compound,
1500g of acicular α-FeOOH particles containing Cr, Ni and Mg were coated with densified P and Si compounds by heat treatment at 600℃ in air.
Acicular α-Fe ₂ O ₃ containing Si, Cr, Ni and Mg
A particulate powder was obtained. 1000 g of acicular α-Fe ₂ O ₃ particle powder containing Si, Cr, Ni and Mg coated with the densified P compound and Si compound was suspended in 30 g of water. Next, 33.4 g of sodium aluminate (NaAlO ₂ ) (6.5 atomic % in terms of Al relative to Fe) was added to the above suspension.
Applies to. ) and stirred for 30 minutes, then 10% acetic acid was added so that the pH value of the suspension was 8.0, and acicular crystals containing Si, Cr, Ni and Mg were filtered using a press filter. Filter out Fe ₂ O ₃ particles,
After drying, acicular α-Fe ₂ O ₃ particle powder containing Si, Cr, Ni, and Mg coated with a P compound, a Si compound, and an Al compound was obtained. Table 3 shows the main manufacturing conditions and characteristics at this time. Example 13 Type of particles to be treated, pH of suspension, amount of P compound added, type and amount of Ni and/or Al compound,
P and Si compounds and Ni were densified in the same manner as in Example 12, except that the amount of Si compound added, PH adjustment, heat treatment temperature and atmosphere were varied.
Si, Cr, Ni coated with compounds and Al compounds
Acicular crystal α-Fe ₂ O ₃ particle powder containing Mg and Mg was obtained. Table 3 shows the main manufacturing conditions and characteristics at this time. Comparative Example 2 Without coating with Ni and Al compounds,
Acicular α-Fe ₂ O ₃ particle powder coated with a P compound and a Si compound was obtained in the same manner as in Example 6 by varying the type of particles to be treated, the pH of the suspension, and the heat treatment temperature. Ta. Table 3 shows the main manufacturing conditions and characteristics at this time. <Production of acicular iron or iron alloy magnetic particles> Examples 14 to 21, Comparative Example 3; Example 14 Si, Cr, Ni, and Mg coated with the P compound and Si compound obtained in Example 6 Acicular crystal α containing
- Pour 120g of Fe ₂ O ₃ particle powder into a rotating retort container, and supply H ₂ gas at a rate of 50 per minute while rotating the container.
Aerated at a rate of , and reduced at a reduction temperature of 420℃,
Si, Cr, Ni coated with P and Si compounds
and Mg-containing acicular iron alloy magnetic particles. Next, the temperature was set to 150°C, hydrogen gas was aerated with water vapor (partial pressure of water vapor 80%), and the temperature was maintained for 60 minutes. Next, after cooling to room temperature while passing nitrogen gas through the chamber, air was vented at a rate of 1/min while nitrogen gas was vented at 2/min, and when the temperature exceeded 40°C due to heat generation due to oxidation, air ventilation was stopped. An operation was performed in which only nitrogen gas was vented for 45 minutes. After the above operation is completed, the acicular iron alloy magnetic particles are immersed in toluene to form Si, Cr, and P compounds coated with P and Si compounds with an oxide film formed on the surface.
Acicular iron alloy magnetic particles containing Ni and Mg were obtained. Table 4 shows various properties of the obtained acicular iron alloy magnetic particles. Examples 15 to 21 Types of starting materials, reduction temperature, temperature in oxidation treatment in hydrogen and steam atmosphere, steam partial pressure, treatment time, temperature in oxidation treatment in oxygen-containing gas, aeration amount, treatment time, and organic A P compound and a Si compound with an oxide film formed on the surface were prepared in the same manner as in Example 14, or a P compound and a Si compound and a Ni and Acicular iron alloy magnetic particles coated with /Al compound were obtained. Table 4 shows the main manufacturing conditions and various characteristics at this time. Comparative Example 3 The same procedure as in Example 14 was carried out except that the acicular α-Fe ₂ O ₃ particle powder coated with the densified P compound and Si compound obtained in Comparative Example 2 was brought to a reduction temperature of 460°C. The powder was reduced to obtain acicular iron magnetic particles coated with a P compound and a Si compound. The acicular iron magnetic particles coated with the P compound and the Si compound obtained by reduction are once heated to prevent rapid oxidation when taken out into the air.
A stable oxide film was formed on the particle surface by immersing it in a toluene solution and evaporating it. Table 4 shows various properties of the acicular iron magnetic particles coated with the P compound and the Si compound.

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【table】 [Brief explanation of drawings]

Figure 1 shows the amount of water-soluble chromium salt added, the acicular iron alloy magnetic particle powder containing Si and Cr coated with a P compound and a Si compound, and the needle containing Cr coated with a P compound and a Si compound. FIG. 3 is a relationship diagram of the specific surface area of crystalline iron alloy magnetic particles. FIG. 2 is a diagram showing the relationship between the amount of water-soluble nickel salt added and the coercive force of acicular iron alloy magnetic particles containing Si, Cr, and Ni coated with a P compound and a Si compound. Figures 3 and 4 show the amount of water-soluble magnesium salt added and the amount coated with P compound and Si compound, respectively.
FIG. 2 is a diagram showing the relationship between coercive force and specific surface area of acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg.
Figure 5 shows P compounds and Si compounds and Al and/or
FIG. 2 is a diagram showing the relationship between Mg content and specific surface area of acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with a Ni compound. Figure 6 shows the change in saturation magnetization σ _s over time when acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with P and Si compounds were taken out into the air. It is something.

Claims (1)

[Scope of Claims] 1. A suspension containing Fe(OH) ₂ obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution and having a pH of 11 or above is oxidized by passing an oxygen-containing gas through it to form a acicular shape. In producing crystalline α-FeOOH particles, a water-soluble silicate is added to Fe to Si in any of the suspensions before the alkali aqueous solution and oxygen-containing gas are passed through to perform the oxidation reaction. In conversion,
0.1 to 1.7 atomic % is added, and the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas are aerated to perform the oxidation reaction. In any of the reaction solutions in which the reaction is being carried out, a water-soluble chromium salt is added to Fe in an amount of 0.1 to 5.0 at% in terms of Cr, a water-soluble nickel salt is added to Fe in an amount of 0.1 to 7.0 atom% in terms of Ni,
By adding water-soluble magnesium salt to Fe in an amount of 0.1 to 15.0 at.
Acicular α-FeOOH particles containing Cr, Ni, and Mg are generated, and the acicular α-FeOOH particles containing Si, Cr, Ni, and Mg are suspended in water, and the pH of the suspension is 0.1 to 2wt for acicular α-FeOOH particles containing Si, Cr, Ni and Mg with a value of 8 or more
% (calculated as _PO3 ) to form a dispersion, and then 0.1 to 7.0 wt% to the acicular α-FeOOH particles containing Si, Cr, Ni, and Mg to the dispersion.
coated with P compounds and Si compounds by adding water-soluble silicates (in terms of _SiO2 )
Acicular crystal α- containing Si, Cr, Ni and Mg
Obtain FeOOH particles and place the particles in a non-reducing atmosphere.
Acicular crystal α- containing Si, Cr, Ni and Mg coated with P compound and Si compound densified by heat treatment in the temperature range of 500-900℃
After forming Fe ₂ O ₃ particles, heat reduction is performed in a reducing gas to form Si, Cr,
Acicular iron alloy magnetic particles containing Ni and Mg are obtained, and the particles are heated in a mixed gas atmosphere of hydrogen and water vapor at a temperature range of 150 to 700°C, and at a water vapor partial pressure (PH ₂ O / PH ₂ ) in the atmosphere. is kept at 10% or more and less than 100% to form ₄ layers of Fe ₃ O on the particle surface, and then
A method for producing acicular iron alloy magnetic particles for magnetic recording, characterized in that the surface of the Fe ₃ O ₄ layer is made into a Fe ₂ O ₃ layer by applying an oxygen-containing gas at a temperature of 100° C. or lower. 2 Acicular α-FeOOH particles are produced by passing an oxygen-containing gas through a suspension containing Fe(OH) ₂ and having a pH of 11 or higher obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution to oxidize it. To generate the water-soluble silicate, add 0.1 of the water-soluble silicate to Fe in terms of Si in any of the suspensions before the aqueous alkaline solution and oxygen-containing gas are passed through to perform the oxidation reaction.
~1.7 atomic % is added, and the suspension and oxygen-containing gas before the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas are aerated to perform the oxidation reaction, and the oxidation reaction is carried out by aerating the suspension and the oxygen-containing gas. In any of the reaction solutions in which the reaction is carried out, a water-soluble chromium salt is added to Fe in an amount of 0.1 to 5.0 atom % in terms of Cr, a water-soluble nickel salt is added as Fe in an amount of 0.1 to 7.0 atom % in terms of Ni, and Water-soluble magnesium salt as Mg equivalent to Fe
By adding 0.1 to 15.0 atomic%, Si,
Acicular α-FeOOH particles containing Cr, Ni, and Mg are generated, and the acicular α-FeOOH particles containing Si, Cr, Ni, and Mg are suspended in water, and the pH of the suspension is 0.1 to 2wt for acicular α-FeOOH particles containing Si, Cr, Ni and Mg with a value of 8 or more
% (calculated as _PO3 ) to form a dispersion, and then 0.1 to 7.0 wt% to the acicular α-FeOOH particles containing Si, Cr, Ni, and Mg to the dispersion.
coated with P compounds and Si compounds by adding water-soluble silicates (in terms of _SiO2 )
Acicular crystal α- containing Si, Cr, Ni and Mg
Obtain FeOOH particles and place the particles in a non-reducing atmosphere.
Acicular crystal α- containing Si, Cr, Ni and Mg coated with P compound and Si compound densified by heat treatment in the temperature range of 500-900℃
Acicular iron alloy containing Si, Cr, Ni, and Mg, which is formed into Fe ₂ O ₃ particles and then heated and reduced in a reducing gas and coated with a P compound, a Si compound, and a Ni and/or Al compound. When forming magnetic particles, the dispersion liquid contains 0.5 to 10.0 of Fe in terms of Ni and/or Al.
Adding atomic % of Ni and/or Al compounds, or
Alternatively, the acicular α-Fe ₂ O ₃ particles containing Si, Cr, Ni and Mg coated with the densified P compound and Si compound after the above heat treatment are suspended in water. P compounds and Si compounds and Ni
Acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with an Al compound are obtained, and the particles are exposed to a temperature range of 150 to 700°C in a mixed gas atmosphere of hydrogen and water vapor. The water vapor partial pressure (PH ₂ O / PH ₂ ) inside is maintained at 10% or more and less than 100% to form ₄ Fe ₃ O layers on the particle surface, and then oxygen-containing gas is applied at a temperature of 100°C or less. A method for producing an acicular iron alloy magnetic particle powder for magnetic recording, characterized in that the surface of the Fe ₃ O ₄ layer is made into a Fe ₂ O ₃ layer.