JPS6239202B2 - - 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 particles have a large bulk density, are fine particles, have a large specific surface area, have a high degree of crystallinity on the particle surface and inside the particle, and are substantially dense, with a high coercive force Hc and a large saturation magnetization σs. Si coated with a P compound and a Si compound that have excellent oxidation stability,
The present invention relates to a method for producing acicular iron alloy magnetic particles containing Cr and Ni. For the production of magnetic recording media, Si, Cr coated with P compounds and Si compounds obtained according to the present invention
When acicular iron alloy magnetic particles containing Ni and Ni are used, they have acicular crystals, uniform particle size, and no dendritic particles, resulting in a large bulk density. , and are fine particles with a large specific surface area, substantially high density with an increased degree of crystallinity on the particle surface and inside the particle, and have a high coercive force Hc and a large saturation magnetization σs, and,
Due to its excellent oxidation stability, the dispersibility of the magnetic particles in the vehicle, orientation and filling properties in the coating film are extremely excellent, and the noise level generated during recording and reproduction of magnetic tape is low. , and an excellent magnetic recording medium with high output characteristics can be obtained. In recent years, magnetic recording and reproducing devices for video and audio have become increasingly compact and lightweight. VTRs are being actively developed with the aim of reducing their weight, and on the other hand, demands for higher performance and higher density recording of magnetic tape, which is a magnetic recording medium, are 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 Video and Audio Magnetic Tapes,'' published on pages 82 to 105 of the Japanese issue, ``The image quality of video tape recorders is The main characteristics that change are the S/N ratio, chroma noise, and video frequency characteristics. ...These quantities that represent image quality are determined by the electromagnetic conversion characteristics of the tape and head system, and the electromagnetic conversion It is clear from the statement, "The characteristics have a correlation with the physical properties of the tape. Furthermore, the physical properties of the tape are largely determined by the magnetic material." 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 their 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 aforementioned Nikkei Electronics, p. 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 SN 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 is the magnetic powder. 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 recording medium. 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, page 85, which states, ``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 is determined by the saturation magnetization σs of the magnetic particles as large as possible, and depends on 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. ……. of tape
To increase Br, the saturation magnetization Is that the magnetic material has in a perfect state (for example, in a single crystal state)
First of all, it is basic that (σs) is large. ……
…. Even if the material is the same, Br changes depending on the degree of filling, which indicates the proportion of magnetic powder. Furthermore, since it is proportional to the squareness ratio (amount of residual magnetization/amount of saturation magnetization), this is required to be 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 statements 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 magnetic particles used must have acicular crystals, uniform particle size, and no dendritic particles. In addition, it is necessary to have a large specific surface area, a high coercive force Hc, and a large saturation magnetization σs. 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 σs70~85emu/g and a coercive force.
It has a Hc of 250 to 500 Oe. In particular, the σs of the oxide magnetic particles is the maximum
It is about 85emu/g, and generally σs70~
80 emu/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, their saturation magnetization σs is low at 60 to 80 emu/g. . 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 σs and high coercive force. The powder is generally acicular crystals obtained by heating and reducing acicular crystal hydrated iron oxide particles, acicular iron oxide particles, or particles containing a different metal other than iron in a reducing gas at about 350°C. It is iron magnetic particle powder or acicular iron alloy magnetic particle powder. These acicular iron magnetic particles or acicular iron alloy magnetic particles have significantly larger saturation magnetization σs than conventionally used magnetic iron oxide particles and Co-containing magnetic iron oxide particles, and have a coercive force.
It is characterized by high Hc, and when coated as a magnetic recording medium, it has a large residual magnetic flux density Br.
Because it has a high coercive force Hc, it can achieve high density recording and high output characteristics, so it has attracted attention and has been put into practical use in recent years. In the method for producing the acicular ferromagnetic particles or acicular ferroalloy magnetic particles, the higher the temperature of heating and reduction in the reducing gas, the higher the saturation magnetization of the acicular ferromagnetic particles or the acicular ferromagnetic particles. It is known that acicular iron alloy magnetic particle powders 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 grains of the acicular ferromagnetic particles or the acicular ferromagnetic particles and the sintering between particles and particles become significant, resulting in the acicular ferromagnetic particles or acicular iron alloy magnetic particles. 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 above-mentioned method produces such 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 described above, the acicular iron magnetic particles or the 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 prepared, or the acicular ferromagnetic particles or the acicular iron alloy magnetic particles after thermal reduction are taken out into the air and then saturated by oxidation. A major issue is how to prevent a decrease in magnetization σs. 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 there are dendritic particles mixed in, and in terms of particle size, it cannot be said that the particles 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. Further, 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 needle-like α-Fe ₂ O ₃ particles that retain and inherit the needle-like 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 break down. 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. Suspend in water, add 0.1 to 2 wt% (calculated as PO ₃ ) of phosphate to the acicular α-FeOOH particles while the suspension has a pH value of 8 or higher, and then add 0.1 to 7.0 wt % of phosphate to the acicular α-FeOOH particles. %
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. remains as it is, so the intertwined and bonded needle crystals α-
After the FeOOH particles are heat-treated in a non-reducing atmosphere, the acicular iron alloy magnetic particles obtained by thermal reduction become entangled and bonded together. It cannot be said that such particles have sufficient dispersibility in a vehicle, orientation in a coating film, and filling properties. 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 in a state where the pH value of the suspension is 8 or higher.
By adding phosphate (in terms of PO ₃ ), it is possible to loosen the entanglements and bonds of the 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 is more than 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, when the amount added is 2 wt% or more, 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 8 or less, it is necessary to add 2wt% or more of phosphate to disperse the particles, and as mentioned above, adding phosphate of 2wt% or more may cause adverse effects in filtration separation. This is not desirable because it causes Next, regarding the Si compound film formed on the particle 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 When adding the water-soluble silicate, the pH value of the suspension is preferably 8 or higher. If water-soluble silicate is added when the pH value of the suspension is 8 or less, 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 uniformly mixing into the suspension, the pH value is adjusted to the range where SiO ₂ precipitates, that is, the pH value is 3. When adjusted 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 is more than 7.0wt%, it is possible to obtain acicular iron alloy magnetic particles with excellent acicular crystals, but the purity is low. As a result, the saturation magnetic flux density decreases, 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 and Ni
The conditions for forming a film on FeOOH particles with a P compound and a Si compound and then separating the particles from the suspension by filtration will be described. When using ordinary filtration 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%, adjusting the PH value of the suspension to 3 to 7 will increase the viscosity of the suspension, causing particle aggregation and making it difficult to separate by filtration. It can be done easily. Furthermore, even if the pH value of the suspension is set to 3 or less, agglomeration of acicular α-FeOOH particles and adsorption of phosphates, as well as the formation of the SiO ₂ film described above, are possible, but due to the equipment 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 500℃ or less, the degree of crystallinity of the acicular α-Fe ₂ O ₃ particles coated with P and Si compounds is increased. It is hard to say that it is a dense particle, and the temperature is 900℃.
If this is the case, deformation of the acicular crystal grains and sintering of the grains and the grains may occur. Also,
Industrial, requiring highly accurate equipment and advanced technology,
It's not economical. A further problem is how to prevent the saturation magnetization σs from decreasing due to oxidation after the acicular iron magnetic particles or the acicular iron alloy magnetic particles after thermal reduction are taken out into the air. 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. Temperature range of 150 to 700°C in a mixed gas atmosphere of hydrogen and water vapor, partial pressure of water vapor in the atmosphere (PH ₂ O / PH ₂ ) 10% or more 100%
By keeping _the Fe ₃ O ₄ layer at _a temperature _of less _than Obtainable. (Tokuko Showa 58-
5241, Special Publication No. 58-52522). First, in the above method, the surface of metal particles is
The conditions for obtaining Fe ₃ 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. In addition, the water vapor partial pressure (PH ₂ O/PH ₂ ) in the atmosphere is 10% or more and 100%.
Must be less than If it is less than 10% or 100%, it is difficult to generate Fe ₃ O ₄ . Note that from an industrial standpoint, a water vapor partial pressure of 50 to 90% is preferable. 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 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°C, 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).
You can use the method of immersion. 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 an increased degree of oxidation stability, substantially high density, high coercive force Hc, large saturation magnetization σs, and excellent oxidation stability. I've been piling it up. Then, the present inventors discovered Fe obtained by reacting a ferrous salt aqueous solution and an alkaline aqueous solution.
Acicular crystal α-FeOOH is produced by oxidizing a suspension containing (OH) ₂ with a pH of 11 or higher by passing oxygen-containing gas through it.
In producing the particles, water-soluble silicate is added to the aqueous alkali solution and the suspension 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, at a concentration of 0.1 to 0.1 to Si in terms of Fe. 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.The suspension and the oxygen-containing gas are aerated to perform the oxidation reaction. A water-soluble chromium salt is added in an amount of 0.1 to 5.0 atomic % based on Fe in terms of Cr, and a water-soluble nickel salt is added in an amount of 0.1 to 7.0 atomic % based on Fe in terms of Ni to any of the reaction solutions being carried out. Acicular crystal α-FeOOH containing Si, Cr and Ni
The acicular α-FeOOH particles containing Si, Cr and Ni are coated with a P compound and a Si compound, and then heated in a non-reducing atmosphere to obtain densified P. P compound and Si obtained by forming acicular α-Fe ₂ O ₃ particles containing Si, Cr and Ni coated with a compound and a Si compound, and then reducing the particles by heating in a reducing gas. Fe ₃ O ₄ and
When _three layers of Fe ₂ O are formed, it has acicular crystals,
Substantially high density with uniform particle size, no intermingling of dendritic particles, no intertwining of particles, large specific surface area, and increased degree of crystallinity on the particle surface and inside the particle. The inventors have completed the present invention by discovering that it is possible to obtain acicular iron alloy magnetic particles for magnetic recording which have a high coercive force Hc and a large saturation magnetization σs and have excellent oxidation stability. be. 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 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, 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 in Cr conversion
Si,
Acicular α-FeOOH particles containing Cr and Ni are generated, and acicular α-FeOOH particles containing Si, Cr and Ni are generated.
FeOOH particles are suspended in water, and when the pH value of the suspension is 8 or higher, 0.1 to 2 wt% (in terms of PO ₃ ) is added to the acicular α-FeOOH particles containing Si, Cr, and Ni. Add phosphate to form a dispersion, then
Acicular crystal α- containing Si, Cr and Ni in the dispersion
0.1 to 7.0wt% to FeOOH particles (converted to SiO ₂ )
Acicular α-FeOOH particles containing Si, Cr and Ni coated with P and Si compounds are obtained by adding water-soluble silicate of Acicular α-Fe ₂ O ₃ particles containing Si, Cr, and Ni coated with densified P and Si compounds are formed by heat treatment in the temperature range of ℃, and then heated in a reducing gas. Si coated with P compound and Si compound by heating reduction with
Acicular iron alloy magnetic particles containing Cr and Ni are obtained, and the particles are placed in a mixed gas atmosphere of hydrogen and water vapor at a temperature range of 150 to 700°C and subjected to water vapor partial pressure (P H ₂ O / P H ₂ ) is maintained at 10% or more and less than 100% to form ₄ Fe ₃ O layers on the particle surface, and then the surface of the ₄ Fe ₃ O layers is converted to Fe by applying 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 by forming a ₂ O ₃ 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 particulate powder, 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. Water-soluble silicate is added to any of the above suspensions before
It can be obtained by adding 0.1 to 1.7 at. 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 caused by the simultaneous growth of FeOOH core particles and the generation of new nuclei over and over again until the 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
The (OH) ₂ flocs are made into sufficiently fine and uniform flocs, and the Fe(OH) ₂ flocs are also formed.
The Fe(OH) ₂ particles themselves can be made into sufficiently fine and uniform particles, and furthermore, water-soluble silicate
Needle-shaped α-FeOOH from aqueous solution 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 is more than atomic %, 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 high 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, acicular iron alloy magnetic particle powder containing Si and Cr coated with P compound and Si compound, and Cr coated with P compound powder and Si compound. FIG. 2 is a relationship diagram of the specific surface area of acicular iron alloy magnetic particles. That is, 300% of an aqueous ferrous sulfate solution containing 1.2 mol of Fe ²⁺ was added, sodium silicate prepared in advance in a reactor was mixed with 0 to 1.0 atomic % of Si in terms of Fe, and chromium sulfate was mixed with Cr in terms of Fe. In addition to the NaOH aqueous solution 400 obtained by adding 0 to 5.0 atom% in terms of Fe(OH)2, a suspension containing Fe(OH) ₂ at pH 13.8 was obtained, and the suspension was heated at a rate of 1000 NaOH per minute at a temperature of 45°C. Acicular α-FeOOH particles containing Si and Cr are produced by aeration of air and an oxidation reaction, and the particles are coated with a P compound and a Si compound, and then heated in air at 700°C. After forming acicular α-Fe ₂ O ₃ particles containing Si and Cr coated with densified P and Si compounds by heating and reducing the particles at 450°C for 5.0 hours, The obtained acicular iron alloy magnetic particles containing Si and Cr coated with the P compound and Si compound and the acicular iron alloy magnetic particles containing Cr were coated with Fe ₃ O ₄ on the particle surface of the particles. This figure shows the relationship between the specific surface area and the amount of chromium sulfate added when stably taken out into the air by forming a Fe ₂ O ₃ layer. In the figure, curve a is for the case without Si addition, curves b and c
The Si addition amount is 0.35 at% and 1.0 at%, respectively.
This is the case. 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 particles containing Si and Cr have uniform particle size, do not contain dendritic particles, and have a large specific surface area. There was a tendency for the coercive force to decrease as the amount added increased. Therefore, as a result of various studies on methods for improving the coercive force of acicular iron alloy magnetic particles containing Si and Cr, the inventors found that Si and Cr
In the production of acicular α-FeOOH particles containing Fe
A water-soluble nickel salt is added to either the (OH) ₂ suspension or the reaction solution in which an oxidation reaction is carried out by passing an oxygen-containing gas through the solution, and the resulting mixture contains Si, Cr, and Ni. We obtained the knowledge that when acicular α-FeOOH particles are thermally reduced, the coercive force of acicular iron alloy magnetic particles containing Si and Cr can be improved while maintaining a large specific surface area. Ta. 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,
Acicular α-FeOOH particles containing Cr and Ni are produced, and the particles containing Si, Cr and Ni are coated with a P compound and a Si compound obtained in the same manner as in Figure 1 using the particles as a starting material. This figure shows the relationship between the coercive force of the acicular iron alloy magnetic particles 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. The phenomenon of improving coercive force while maintaining such 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. The acicular iron alloy magnetic particles containing Si, Cr and Ni coated with a P compound and a Si compound obtained by the above method have extremely high saturation magnetization. If it is taken out at a later date, its oxidation stability is insufficient, and it is oxidized by air etc., resulting in a rapid decrease in saturation magnetization. In particular, this phenomenon increases as the particle size decreases and the specific surface area increases. Therefore, the present inventors developed a method for using Si, Cr, and Ni coated with P and Si compounds that have large saturation magnetization.
We have repeatedly investigated the oxidation stability of acicular iron alloy magnetic particles containing Fe 3 O 4 and Fe ₃ O ₄ on the particle surface.
The oxidation stability could be improved by the method of forming _three Fe ₂ O layers. Figure 3: Coated with P compound and Si compound
It shows the change over time in the saturation magnetization σs when acicular iron alloy magnetic particles containing Si, Cr, and Ni are taken out into the air, and the horizontal axis is the number of days;
The vertical axis represents the rate of decrease in saturation magnetization at a temperature of 50°C and relative humidity.
The value obtained by dividing the difference (Δσs) before and after the saturation magnetization changes by the saturation magnetization before the change under the 80% condition is expressed as a percentage. In FIG. 3, curve a shows the curve a when Fe ₃ O ₄ and Fe ₂ O ₃ layers are formed on the particle surface of acicular iron alloy magnetic particles, which are then immersed in an organic solvent and then taken out into the air. Curve b is the case when Fe ₃ O ₄ and Fe ₂ O ₃ layers are formed on the particle surface and then taken out into the air. Curve c is the case when the particles are directly immersed in an organic solvent and then taken out into the air. . As is clear from FIG. 3, Fe ₃ O ₄ and Fe ₂ O ₃ are present on the particle surface of the acicular iron alloy magnetic particle powder containing Si, Cr, and Ni coated with a P compound and a Si compound.
When a layer is formed, a product with 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, and for this purpose, it is necessary to add chromium in the ferrous salt aqueous solution or in the alkaline aqueous solution. ,
It may be added either to a suspension containing Fe(OH) ₂ or to a reaction solution in which acicular α-FeOOH particles are being generated 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 the water-soluble chromium salt added is 0.1 atomic % or less in terms of Cr based on Fe, the effect of increasing the specific surface area of the obtained acicular iron alloy magnetic particles cannot be obtained. If the content is 5.0 atomic % or more, 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. Although it is possible to achieve the object of the present invention when the content is 7.0 atomic % or more, it is not preferable because foreign substances other than needle crystals are mixed during the production of α-FeOOH particles. 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. It has a substantially high density, high coercive force Hc, large saturation magnetization σs, and excellent oxidation stability.
It is possible to obtain acicular iron alloy magnetic particles containing Si, Cr, and Ni coated with compounds and Si compounds, which are currently most required for high image quality, high output, high sensitivity, and high recording density. It can be used as magnetic particle powder. Furthermore, when manufacturing a magnetic paint, the acicular iron alloy magnetic particle powder containing Si, Cr, and Ni coated with the above-mentioned P compound and Si compound is used, the noise level is low, and the vehicle It is possible to obtain a preferred magnetic recording medium with excellent dispersibility in the film, orientation in the coating film, and filling property. 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 above experimental examples and the following examples and comparative examples was measured by the BET method, and the axial ratio of the particles (long axis: short axis),
The long axes are all shown as average values of numerical values measured from electron micrographs. Moreover, the bulk density was measured according to JIS K 5101-1978 "Pigment test method". The amounts of P, Si, Cr, and Ni in the particles were measured using a Fluorescent X-ray Analyzer Model 3063M (manufactured by Rigaku Denki Kogyo) in accordance with JIS K 0119-1979, "General Rules for Fluorescent X-ray Analysis." It was measured by performing fluorescence X-ray analysis according to the above. The values of magnetic properties are determined using a sample vibrating magnetometer.
These are the results measured under an external magnetic field of 10 KOe. 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-like α-FeOOH particles> 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%) 152g was prepared in advance in a reactor to contain 0.20 at% in terms of Si, and 0.50 at% in terms of Cr was added to Fe. Contains 644g of chromium sulfate,
5.45-N obtained by adding 2884g of nickel sulfate to contain 3.0 at% of Ni in terms of Fe.
In addition to NaOH aqueous solution 400, a reaction was performed to produce a Fe(OH) ₂ suspension containing Si, Cr, and Ni at pH 14.0 and temperature 45°C. Into the Fe(OH) ₂ suspension containing Si, Cr and Ni,
Acicular crystal α- containing Si, Cr and Ni was produced by aerating 1000 air per minute for 6.3 hours at a temperature of 50℃.
FeOOH particles were produced. 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 crystal α- containing Si, Cr and Ni
As a result of X-ray diffraction, FeOOH particles were found to be α-FeOOH
A diffraction pattern identical to the crystal structure of the particles was obtained. In addition, as a result of fluorescent X-ray analysis, Si was compared to Fe.
0.204 atomic%, Cr to Fe 0.496 atomic%, Ni
The content was 3.02 atomic % based on Fe. Therefore, it is considered that Si, Cr and Ni are dissolved in solid solution in the acicular α-FeOOH particles. This acicular crystal α- containing Si, Cr and Ni
As a result of electron microscopic observation, the FeOOH particles had an average long axis of 0.50 μm and an axial ratio (long axis: short axis) of 28:1. Examples 2 to 5 The type and concentration of the ferrous salt aqueous solution, the concentration of the NaOH aqueous solution, and the type, amount, and time of addition of the water-soluble silicate, water-soluble chromium salt, and water-soluble nickel salt were varied. is the same as in Example 1.
Acicular α-FeOOH particles containing Si, Cr and Ni were produced. 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 was produced in the same manner as in Example 1, except that sodium silicate, chromium sulfate, and nickel sulfate were not added, and the concentration of the NaOH aqueous solution was changed.
A particulate powder was produced. 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. <Production of acicular α-Fe ₂ O ₃ particle powder coated with densified P compound and Si compound> Examples 6 to 13, Comparative Example 2; Example 6 The filter obtained in Example 1 Separately, 6000 g of water-washed paste of acicular α-FeOOH particles containing Si, Cr, and Ni (acicular α-FeOOH particles containing Si, Cr, and Ni)
This corresponds to approximately 2000g of FeOOH particles. ) was suspended in 100% water. The pH value of the suspension at this time was 9.7. Next, 500 ml of an aqueous solution containing 16 g of sodium hexametaphosphate (as PO ₃ for acicular α-FeOOH particles containing Si, Cr and Ni) was added to the above suspension.
This corresponds to 0.56wt%. ) was added and stirred for 30 minutes. Next, 296 g of sodium silicate (No. 3 water glass) (corresponding to 4.2 wt% as SiO ₂ based on the acicular α-FeOOH particles containing Si, Cr, and Ni) was added to the above suspension. After stirring for a minute, 10% acetic acid was added so that the pH value of the suspension was 6.0, and the acicular α-FeOOH particles containing Si, Cr and Ni were filtered out using a press filter and dried. Si, Cr and Ni coated with P and Si compounds
Acicular α-FeOOH particles containing α-FeOOH were obtained. Si, Cr coated with the above P compound and Si compound
Acicular crystal α-FeOOH particle powder containing and Ni
1500g was heat treated in air at 780℃ to produce Si, Cr coated with densified P compound and Si compound.
Acicular crystal α-Fe ₂ O ₃ particle powder containing Ni and Ni was obtained. Table 3 shows the powder characteristics of the obtained acicular α-Fe ₂ O ₃ particle powder. Examples 7 to 13, 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. Acicular crystal α-Fe ₂ O ₃ particle powder and acicular crystal α- containing Si, Cr and Ni coated with densified P compound and Si compound in the same manner as in Example 6 except that
Fe ₂ O ₃ particle powder was obtained. Table 3 shows the main manufacturing conditions at this time. <Manufacture of acicular iron or iron alloy magnetic particles> Examples 14 to 21, Comparative Example 3; Example 14 Contains Si, Cr and Ni coated with the P compound and Si compound obtained in Example 6 Acicular crystal α-
_{P compound and} coated with Si compound
Acicular iron alloy magnetic particles containing Si, Cr and Ni were prepared. Next, the temperature was set to 150°C, hydrogen gas was aerated with water vapor (partial pressure of water vapor 85%), and the temperature was maintained for 30 minutes. Next, after cooling to room temperature while blowing nitrogen gas, blow air at a rate of 0.5/min while blowing nitrogen gas at 2.0/min, and when the temperature exceeds 40°C due to heat generation due to oxidation, turn off the air ventilation. The operation was performed for 60 minutes by stopping and only nitrogen gas was vented. After the above operation was completed, the acicular iron alloy magnetic particles were immersed in toluene to coat the surface with a P compound and a Si compound with an oxide film formed on the surface.
Acicular iron alloy magnetic particles containing Si, Cr and Ni 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 solvent Acicular crystal iron alloy magnetic particle powder coated with a P compound and a Si compound with an oxide film formed on the surface in the same manner as in Example 14, except that whether or not it was taken out into the interior and the type of organic solvent was varied. I got it. 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 alloy magnetic particles coated with a P compound and a Si compound. The acicular iron alloy magnetic particle powder coated with the P compound and Si compound obtained by reduction is once immersed in a toluene solution to prevent rapid oxidation when taken out into the air. By steaming this, a stable oxidized coating was applied to the particle surface. 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 the drawing]

Figure 1 shows the amount of water-soluble chromium salt added, acicular iron alloy magnetic particle powder containing Si and Cr coated with P compound and Si compound, and Cr coated with P compound and Si compound. FIG. 2 is a relationship diagram of the specific surface area of acicular iron alloy magnetic particles. Figure 2 shows
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.
Figure 3 shows Si coated with P compound and Si compound,
This figure shows the change over time in the saturation magnetization σs when acicular iron alloy magnetic particles containing Cr and Ni are taken out into the air.

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. 0.1 in conversion
~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. A water-soluble chromium salt is added in an amount of 0.1 to 5.0 atomic % based on Fe in terms of Cr, and a water-soluble nickel salt is added in an amount of 0.1 to 7.0 atomic % based on Fe in terms of Ni to any of the reaction solutions in which the reaction is carried out. By keeping it for a long time, acicular α-FeOOH particles containing Si, Cr and Ni are generated, and the Si, Cr
and Ni-containing acicular α-FeOOH particles are suspended in water, and when the pH value of the suspension is 8 or higher, Si,
0.1 to 2 wt% (calculated as PO ₃ ) of phosphate is added to acicular α-FeOO particles containing Cr and Ni to form a dispersion, and then Si, Cr and
0.1 to acicular α-FeOOH particles containing Ni
By adding 7.0 wt% (calculated as SiO ₂ ) of water-soluble silicate, acicular α-
Obtain FeOOH particles and place the particles in a non-reducing atmosphere.
Acicular α-Fe ₂ O ₃ particles containing Si, Cr and Ni coated with densified P and Si compounds by heat treatment in the temperature range of 500 to 900°C are then reduced. Acicular iron alloy magnetic particles containing Si, Cr and Ni coated with a P compound and a Si compound are obtained by thermal reduction in a neutral gas, and the particles are heated in a mixed gas atmosphere of hydrogen and water vapor to 700℃
temperature range, water vapor partial pressure in the atmosphere (P H ₂ O/
P H 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 surface of the Fe ₃ O ₄ layer is treated with an oxygen-containing gas at a temperature of 100° C. or less. of
A method for producing acicular iron alloy magnetic particles for magnetic recording, characterized by having _three layers of Fe ₂ O.