JPS61196502A - Magnetic material and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable to reduce the quantity of iron oxide and carbon by-produced when the fine grains of iron carbide are manufactured by a method wherein magnetic material, to be used for a magnetic recording medium consisting of ferromagnetic fine grains containing needle-like iron carbide, is formed. CONSTITUTION:Needle-like metal fine grains having iron for magnetic recording as the main component is manufactured, and a carbonic reaction is advanced by introducing carbon monoxide gas or the mixed gas or carbon monoxide gas and inert gas containing no hydrogen in the carbonization reaction process to be performed subsequently. Besides, when a compound is reduction-reacted using reducing gas having hydrogen as the main component after said carbonization reaction is finished, the generation of ion oxide and carbon can be reduced, thereby enabling to obtain ferromagnetic fine grains containing iron carbon.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a magnetic material and a method for manufacturing the same.

The material can be suitably used as a magnetic material in a magnetic recording medium suitable for high-density recording mainly for audio and video.

BACKGROUND OF THE INVENTION Magnetic powders useful for magnetic tapes and magnetic recording media used to be mainly composed of γ-iron oxide. In recent years, there has been a demand for high-density recording media for VTRs and high-end audio, and metallic iron, cobalt, or nickel, which is obtained by a gas-phase catalytic reduction reaction of iron oxyhydroxide or iron oxide-based powder using a reducing gas, has become desirable. Magnetic powders with high coercive force, mainly consisting of alloys of steel and iron, have come to be used. Because the coercive force of metal magnetic fine particles has strong shape anisotropy,
Although it depends on the particle size, acicularity, etc., suitable coercive force is required for tape recording in consideration of the capabilities of the reproducing head and erasing head. Magnetic recording media are for audio,
Regardless of whether it is for video use, high output and low noise are required over a wide recording frequency band. That is, the shape of magnetic powder tends to become finer. In addition, it is desired to further improve the affinity and dispersibility with paint resins, as well as the orientation and filling properties of coating films, and research has been carried out to improve binder resins and various additives, as well as paint dispersion and media processing technology. has been done (for example,
Okabe Akashi, “Advances in magnetic tape,” Journal of the Japanese Society of Applied Magnetics,
7(3), 185 (1983), ).

Therefore, increasing the Hc value as much as possible within the permissible range of magnetic powder and making it finer are extremely rate-limiting elemental technologies for realizing high-density recording.

In the case of acicular metal powder particles containing iron as the main component, although there is room for large variations depending on the manufacturing method,
Broadly speaking, the above-mentioned Hc-value is almost determined by the values of the major axis diameter (: L) and minor axis diameter (=D) or their axial ratio (: L / D), for example, L / D: 10 In the case of acicular fine particle systems with a diameter of around 1 μm or more, L: around 1μ and Hc-value: 500 to 7.
About 000e, L: around 0.5μ, Hc-value: 100
0 to 12000e, or 140 at around 20.1μ
A value of about 0 to 16,000e is normally achieved.

Conventionally, the techniques for reducing the particle size while maintaining the shape of magnetic powder and having an appropriate holding force are (1) extremely low axial ratio (design method) (2) a large amount of Ni-component. Further, (3) a method for producing semimetallic alloyed particles based on the introduction of Si, B, P, C, N, etc. is also known.

In (1), by reducing the shape anisotropy,
The principle is to suppress the ferromagnetic expression mechanism, and (2)
In this case, it is a method that actively utilizes the fact that the magnetic anisotropy decreases due to the magnetic dilution caused by the lattice substitution of the body-centered cubic crystal (:bcc) formed by the Fe component due to Ni. However, when processed into a tape medium, sufficient orientation cannot be achieved, and the residual magnetic flux density (:Br) and maximum magnetic flux density (:
Bm): There is a drawback that the Br/Bm value, that is, the squareness ratio thereof is greatly reduced.

In (3), the starting material is various iron oxyhydroxides, and even if a compound containing B, Si, and P is surface-modified, the oxides can be stopped by a gas phase catalytic reaction mainly using hydrogen gas. Therefore, their introduction is impossible. A gas phase catalytic reaction using expensive borane gas, silane gas, and phosphine gas will be performed. Only the remaining N and C are inexpensive and can be introduced into iron by gas phase catalytic reaction, but since ammonia is used as a nitriding agent to introduce N, special manufacturing equipment is required. It was necessary to take measures against corrosion, which was impractical when considering industrial production.

Problems to be Solved by the Invention Regarding acicular magnetic powder as a magnetic material for high-density magnetic recording media mainly intended for audio and video, its particle size and magnetic properties, particularly its coercive force Hc-value. The design technology that independently controls the magnetic powder is one of the ultimate elemental technologies related to magnetic powder. This can be positioned as one of the most awaited industrial technologies for densification.

The present inventors have already proposed a method for producing iron carbide fine particles by a gas phase catalytic reaction of reduced iron with a carbonizing gas. However, in this technique, it was necessary to complete the reduction of iron oxyhydroxide as much as possible in the step before the carbonization reaction.

If the reduction is not completed, the production of iron oxide and carbon occurs as a side reaction during the carbonization reaction due to the unreduced iron oxyhydroxide in the carbonization process, resulting in a high efficiency (coercive force cannot be lowered) while maintaining a high σS. There was a case.

Furthermore, fear of incomplete reduction increases the reduction temperature or lengthens the reduction time (this causes sintering between fine metal particles, which causes deterioration of tape properties (Br78m), etc., which is extremely undesirable.

The main purpose of the present invention is to minimize the amount of iron oxide and carbon produced as by-products in the production of fine iron carbide particles.

Basic Idea In order to solve the above-mentioned problems, the present inventors conducted various studies, and while continuing to research the improvement of its properties, the inventors discovered that reducing gas was used together with carbonizing gas in the carbonization process. It has been discovered that iron carbide, which is suitable as a magnetic material and which generates small amounts of iron oxide and carbon, can be produced by also entraining iron carbide. This method is efficient (as the carbonization reaction progresses, the coercive force (Hc) can be lowered to about 8000e depending on the degree of carbonization, and it is also possible to maintain a high saturation magnetization (σS). In other words, it is possible to maintain a high saturation magnetization (σS). We have discovered a revolutionary technology that can dramatically reduce noise while minimizing the drop in the output of the electromagnetic conversion characteristics of the media tape, even if the particles are controlled to drop to an appropriate Hc. .

That is, the gist of the present invention is to manufacture acicular metal powder particles for magnetic recording with iron as a main component as a first step, and then to carbonize and reduce the metal powder particles as a second step. It consists of providing.

DISCLOSURE OF THE INVENTION Acicular metal powder fine particles containing iron as a main component for magnetic recording can be produced basically by a well-known method. For example, α-iron oxyhydroxide with a specific surface area of 20 to 150 =/gr, or A1, Ti, Cr, Mn%Co
In order to avoid sintering, maintain shape, control coercive force, improve corrosion resistance, etc., B, AI, etc. , S
i, P% Ti, Zn, Cr, Mn, Co, Ni, Cu
.

Surface-modified α coated with at least one element selected from elements such as Zr, Sn, Pb, C3, Ba, etc.
- Grind iron oxyhydroxide to 300 to 800 granules as necessary.
After calcining at ℃ to form surface-modified α-iron oxide, it is subjected to a gas phase catalytic reduction reaction at a temperature of about 300 to 500 ℃ using a reducing gas mainly composed of hydrogen gas to form body-centered cubic iron oxide crystallographically. It is possible to produce α-Fe powder that forms a crystal system (:bcc).

The completion of the reduction reaction is usually determined by setting the hydrogen flow temperature and time, or by analyzing the water concentration of the exhaust gas from the reactor system, for example, by measuring the dew point.

After stopping the reduction, a portion was extracted under a nitrogen gas atmosphere and the magnetic properties were measured, and the saturation magnetization (σS) was 150 to 200 e.
mu / gr, which is the value of the degree, saturation magnetization of pure iron (
σs ) 217. Oemu/gr indicates a lower value [Chemical Handbook Revised 3rd Edition Basic Edition [p, 511]
.

In the next carbonization reaction step, when carbon monoxide gas that does not contain hydrogen or a mixed gas of carbon monoxide gas and inert gas is introduced to advance the carbonization reaction, iron-carbonization occurs depending on the degree of carbonization. A compound with a complex composition based on iron monoxide and carbon is obtained. A compound with this composition was subjected to powder X-ray diffraction measurement, and when identified from the diffraction angle of the crystalline diffraction peak group, iron carbide was found to be a so-called cementite species (Fe5C, ASTM-
23-1113) was detected, and magnetite species (Fe3O4, ASTM-19-629) were detected as iron oxide. α-Fe phase is simultaneously detected only when the degree of carbonization is low.

Further, after the carbonization reaction is completed, if the compound having the composition is subjected to a reduction reaction with a reducing gas mainly composed of hydrogen, it is possible to reduce the production of iron oxide and carbon, thereby reducing the iron carbide-containing ferromagnetic fine particles of the present invention. is obtained.

Alternatively, in the carbonization reaction step, a mixed gas of carbon monoxide gas and hydrogen gas is introduced, or a mixed gas of carbon monoxide gas, hydrogen gas, and an inert gas is introduced to simultaneously carry out the carbonization and reduction reactions. By allowing the process to proceed, it becomes possible to suppress the production of iron oxide and carbon, and the iron carbide-containing ferromagnetic fine particles of the present invention can be obtained.

The temperature of the carbonization reaction is 200 to 700°C, preferably 30°C.
A temperature of 0 to 500°C is suitable. If the reaction temperature is lower than 200° C., carbonization will not substantially proceed and the object of the present invention will not be met. If the temperature exceeds 700°C, although the carbonization reaction itself will proceed, the acicular fine particles will be severely sintered, making the powder unsuitable as a magnetic powder for magnetic recording. Further, the appropriate time for the carbonization reaction is about 5 to 600 m1n. If it is less than this, the carbonization reaction cannot be controlled with good reproducibility, and if it exceeds this, it is economically unsuitable.

The supply amount and speed of the reaction gas are determined by the gas hourly space velocity (:G
H8V) is 0.1 to 100. Preferably 10
~30 NA'-totaA? gas/gr-Fe/
The range of Hr is appropriate. If it is less than this range, the carbonization reaction will proceed but at a slow rate, which is not practical, and if it exceeds this range, the pressure drop in the reaction system will increase, which is not preferable as a reaction operation.

The mixing ratio of carbon monoxide gas and hydrogen gas must be selected appropriately depending on contact conditions such as contact temperature, contact time, and flow velocity (gas space velocity), and raw material conditions such as the axial ratio of reduced iron powder and particle size. However, the ratio (CO:H2) is 200:1~
It is desirable that it be between 1 and 200. If the amount of carbon monoxide is large, carbon and iron oxide will be produced, and if the amount is small, the carbonization reaction will take a long time. Although it is possible to use helium gas, argon gas, or carbon dioxide gas as the inert gas to be accompanied with the mixed gas, nitrogen gas is most preferable because it is relatively inexpensive. The volume ratio of the mixed gas (CO:
The ratio of N, ) is suitably 1:1 to 1:500, and the main purpose is to control the reaction rate of the carbonization reaction. If the reaction rate of the carbonization reaction is too fast, free carbon will be produced,
Moreover, if it is too slow, it is not economical, so this composition range is appropriate.

When the obtained composition is expressed as FeCxOy, the value of 1 is o, o5 to 0.5 and the value of y is 0.01 to 1.0.
It is appropriate that the value be within the range of .

When the X-value is less than 0.05, the desired ferromagnetic properties, especially the Hc-value, decreases to less than 2000e. In addition, when the X-value exceeds 0.5, the Hc-value decreases greatly, but the saturation magnetization: σS, which is one of the factors that regulates the residual magnetic flux density: Br-value when processed into a magnetic medium.
- The value is extremely reduced, making it unsuitable as a magnetic material powder for magnetic recording media.

As for the value of y, even if y≦1.0, the wustite species (F
ed) was not observed and magnetite species were confirmed, it is desirable to have a value as small as possible, but the above range can be said to be practical.

When the particle shape of the carbonized powder is observed under an electron microscope with a magnification of 30,000 to 90,000 times, it appears to be exactly the same as the particle shape of the fine powder particles formed in the previous reaction, that is, the reduced metal powder containing iron as the main component. That is, its shape has an acicular outer shape that closely follows the shape of the iron oxyhydroxide fine particles used as the primary raw material, and it has a spherical ultrafine particle (about 100 to 300X).
(referred to as crystallites, microcrystals, crystallinotes, grains, etc.) are aggregated to form each needle-shaped carbonized powder skeleton particle. Incidentally, there is hardly any damage, destruction, or interparticle bonding, that is, sintering.

In this way, acicular iron oxyhydroxide fine particles are used as the primary raw material, and through a gas phase catalytic reduction reaction, acicular reduced iron powder is produced.
Carbonized powder can be produced by gas phase catalytic carbonization reaction. As mentioned above, the gas-phase catalytic carbonization reaction in the second stage can use the same reactor system that carries out the gas-phase catalytic reduction reaction in the first stage, and since carbon monoxide is used as the carbonizing agent, the reaction equipment can be easily used. Problems such as corrosion do not occur, which is extremely convenient.

The magnetic properties of the acicular iron carbide powder have a He value of 50.
00e or more, and a σS-value of 90 emu/gr or more is appropriate. If the temperature is below this value, the desired high-output, high-density magnetic recording cannot be achieved. This magnetic property is determined by
Furthermore, it is possible to control the characteristics of the reduced iron powder used as the secondary raw material, especially the conditions of the subsequent carbonization reaction.

Function The function of the present invention will be explained by comparing it with that of the prior art and clarifying its position.

Iron carbide itself is a well-known chemical species, and the material obtained by carbonizing α-Fe with carbon monoxide gas is also known (
For example: H. A. Bahr et al.
noxyd-Spaltung an Eiseno
xyd und Eisenj.

Berichte, 66, 1238 (1933))
. Although there are many well-known facts about its carbonization mechanism, most of its uses have so far been for the so-called carburizing treatment for designing the phase structure of steel plates and improving their mechanical hardness.

Little is known about synthesizing iron carbide as fine particles and utilizing its ferromagnetic properties as magnetic material powder for magnetic recording media, and there are only a few US patents: USP-3,572,
993 (Mar, 1971: D, B, Rog
ers ) K can only be seen. According to the patent specification, an iron carbonyl compound (=especially Fe(CO)) is thermally decomposed in a range of 280 to 340°C in an atmosphere of hydrogen and carbon monoxide gas to form a fine particle type χ-phase. This material is used as a magnetic powder.The χ-phase is a species called □gg iron carbide, and is expressed as Fe2C.According to the description of the patent specification, its particle shape is They are spherical ultrafine particles of 0.005 to 0.1μ, and their magnetic properties are H
The c-value is said to be about 200 to 10,000e, and the σS-value is about 85 to 100 emu/gr. There are almost no known examples of using bulk iron carbide as a magnetic material in the field of magnetic recording. However, this is also only briefly seen in JP-A-53-26218. In the Japanese Patent Laid-Open Publication No. 2003-120033, an iron-based alloy containing 0.5 to 5.0% carbon is melted, and the melt is rapidly cooled by centrifugation to form a ribbon-shaped sample with a thickness of about 3 μm. Next, the rapidly cooled sample is heated to 800° C. at a heating rate of 100° C./H, and then cooled to room temperature at the same rate. It has been shown that this heat treatment increases the saturation magnetization of the ribbon-shaped sample.

As a method for synthesizing iron carbide fine particles, there is a method of thermal decomposition of iron-cyanide compounds under a non-oxidizing atmosphere (Japanese Patent Application Laid-Open No. 1989-1999-1).
22,000), a method by evaporation of iron metal in a low-pressure active gas (Japanese Patent Laid-Open No. 52-84179), a method by gas spraying of a melt (Japanese Patent Laid-Open No. 54-29305), etc. are known.

In the method of the present invention, acicular iron oxyhydroxide fine particles are prepared, and are converted into acicular ferromagnetic reduced iron powder through a modification treatment with a shape-retaining component, calcination, and reduction process, followed by a carbonization process. Then, through the reduction step, the molecular species is Fe5
It is characterized by having acicular ferromagnetic iron carbide fine particles of C.

In the method of US Pat. No. 3,572,993, ferromagnetic spherical ultrafine particles are formed by thermal decomposition of an iron carbonyl compound in a reducing atmosphere, and the molecular species thereof are Fe and C. Therefore, the present invention can be said to be a completely different system from the patented technology system. In the method of the present invention, one of the key points is the use of specific acicular fine particles, which cannot be omitted due to the characteristics of the magnetic medium.

The technique described in JP-A-53-26218 is a manufacturing recipe for improving the ferromagnetic properties of iron carbide, and is completely different from the present invention in terms of purpose and effect.

Furthermore, JP-A-50-22000.52-84179.5
No. 4-29305 and the like are methods for producing spherical particles, and it can be said that the technical idea is different from the present invention.

As seen above, the method of the present invention is completely different from conventional related technology systems, and provides a novel magnetic material powder that has never been seen before in the field of magnetic recording technology. I understand that it is something.

The effect of acicular ferromagnetic fine particles whose molecular species is expressed as Fe5C is that the particle size that exhibits the same He value can be designed to be sufficiently small when compared with α-Fe powder fine particles. This is something that can be done. Moreover, even if more than the stoichiometric amount of carbon is contained, as long as the present invention is applicable, Fe5C will be formed as a molecular species, so unlike the case of Fe2C mentioned above, the saturation magnetization will be large. There is no decline, which is extremely convenient.

As a result, when media processing is performed, it is possible to create a system in which the magnetic properties are almost unchanged even though finer particles are used as the material powder. As a direct result of this, the magnetic recording characteristics are strongly controlled by the particle size of the magnetic powder, that is, the electromagnetic conversion characteristics at high frequencies (:
Sensitivity/output) and noise will be significantly improved.

In particular, for acicular iron carbide fine particles with a major axis diameter of about 20.1μ, if it is α-Fe powder, the Hc-value is 150.
00e, which can be used as so-called 8i video powder, has an Hc-value of around 8000e, making it optimal as a so-called high band type magnetic powder in current home video systems.

EXAMPLES Hereinafter, the method and effects of the present invention will be described in detail with reference to Examples and Comparative Examples. The reduction reaction and carbonization reaction were mainly carried out using a thermogravimetric measuring device TG-30 manufactured by Shimadzu Corporation.

[Examples 1 to 3] In this example, the raw material adhered powder of so-called 8 m/m video iron powder was reduced at a predetermined temperature, and then a carbonization reaction was performed with a mixed gas of carbon monoxide gas and hydrogen gas. 1 is an example illustrating an overview of the method of the present invention and its effects for a case.

Production of reduced iron powder> P, Si and Ni as a coprecipitated component were
- Weight ratio of components: P/Fe = 0.5/10
0, Si/Fe=4, 2/100 and N i /
Fe=8. Acicular iron oxyhydroxide fine particles containing only O/100 were synthesized.

The shape of the fine particles has a specific surface area (: SA) of 105.2 m'/gr calculated from the adsorption characteristics of nitrogen gas, and a major axis diameter (: L
) and the minor axis diameter (:D), that is, the axial ratio (:L/D) is 1
It was 5.

Next, after passing through a drying and pulverizing process, calcining (temperature = 725
℃), and sample 360~ was subjected to a gas phase catalytic reduction reaction using hydrogen gas at 100 mVmin (gas hourly space velocity = 24N eH2/, gr -F'e/Hr,
) to obtain reduced iron powder. When the magnetic properties of the reduced iron powder were measured in a nitrogen gas atmosphere using a vibrating magnetic property measuring device manufactured by Toei Kogyo Co., Ltd.: Model VSM-III, H
c = 14000e, σs = 148 emu
/gr, R2 was 0.495.

Carbonization reaction> Next, a gas phase catalytic carbonization reaction (gas hourly space velocity = 2
0 Nm'-mix gas/kgr-Fe/Hr+)
to obtain iron carbide powder.

Results> Table 1 shows the carbon and iron analysis of the product, and the specific surface area and magnetic properties obtained by the nitrogen gas method.

[Examples 6 to 7] Reduced iron powder was produced under the same conditions as in Example 1. The carbonization reaction was carried out using carbon monoxide gas and nitrogen gas composition without hydrogen gas under the conditions listed in Table 1, and the results are shown in Table 1.
Shown in 1.

[Example 4] A carbonization reaction was carried out under the same conditions as in Example 6, and the obtained product was further subjected to a gas phase reduction reaction using hydrogen gas. The results are shown in Table-1.

[Example 5] This example is for metal position audio applications.
This is an example showing an overview of the method of the present invention and its effects regarding acicular ferromagnetic fine particles containing iron carbide as a main component.

Production of iron carbide powder> 30 grams of the same surface-modified powder as in Example 1 was charged into a steel pipe reactor equipped with a preheater for the raw material gas for reaction and whose temperature could be controlled from the outside, and the results were as shown in Table 1. Reduction reaction and
It was subjected to a carbonization reaction. The results are shown in Table-1. Next, after thoroughly immersing the fine particles in toluene, the fine particle slurry was transferred onto an enamel vat to a thickness of about 1 cIrL, and subjected to toluene scattering treatment in the atmosphere. When the solvent odor disappeared, the magnetic powder was collected and made into air-dried iron carbide powder.

<Evaluation of air-dried iron carbide powder into paint, coating, and tape properties>
10 grams of the air-dried iron carbide powder was collected and put into a pot with an internal volume of 550 ml together with the following materials, and mixed and dispersed for 5 hours using a paint shaker manufactured by Red Devil Co., Ltd., USA. As a distributed medium, α of 211iIφ
- using alumina beads.

・UCC salt vinyl acetate poly-q-VAGH: t, o
gr・Polyurethane NL-2448 manufactured by Mitsui Toatsu Chemical Co., Ltd.: 1. Ogr ・Phosphate ester manufactured by Oiri Kagakusha AP-13: 0.2
gr・α-Alumina AKP-30 manufactured by Sumima Kagaku Co., Ltd.:
0.2 gr/solvent Toluene: 14 gr, ME
K: 14 gr The dispersion media was then separated to obtain a seven-magnetic paint, which was coated onto a 12μ thick polyester film (Nilmirror 12B-LIO) made by Toshi Co., Ltd. using an applicator with a precision coater equipped with magnetic tape. . Thereafter, the coating surface was smoothed by calender roll treatment, and heat treatment was applied at 50° C. for 2 days to complete the polyurethane curing reaction. The sheet was cut to 3.81 inches to produce a magnetic tape of the current cassette specification size.

The magnetic properties of the magnetic tape are measured using the measuring device described above.
After evaluation, HC:11950eSBr=2630 GaussSB
r/Bm=0.746, indicating sufficient characteristic values.

Evaluation of audio characteristics> Tape tester manufactured by Nippon Columbia: DENON-031
Measurement and evaluation of audio characteristics using IEC Standard Type-IV tape as standard, using IEC standard head (equipped with IEC specified standard head) and according to the measurement method described in Japan Magnetic Tape Standard: MT S-0101 ('72). I did it.

Low frequency sensitivity (: 333 Hz sensitivity) is +0.3 dB, high frequency sensitivity (: 20 kHz sensitivity) is +2.4 dB, maximum output (: 3% MOL) is +5.8 dB, saturated output (::
10kHz.

SQL) was +0.7 dB, and AC bias noise (Nac) after audibility correction was -58.6 dB.

This characteristic shows sufficient high-frequency sensitivity and saturation output, and provides uniquely low noise.

[Comparative Example-1] This comparative example is an example of a ferromagnetic metal powder containing iron as a main component for metal position audio applications.

Production of reduced iron powder> By the method described in JP-A-57-106527 and JP-A-57-96504, P, Si, and a Ni-component as a coprecipitated component were mixed in a weight ratio of P/Fe = 0.5/100, S i/
Fe=2.2/100 and Ni/Fe=7.0/1
Acicular iron oxyhydroxide fine particles containing as much as 0.00 were synthesized.

The shape of the fine particles has a specific surface area (SA) of 39.8 m7g r, calculated from the adsorption characteristics of nitrogen gas, and a range of 6 to 9
The axial ratio (: L/D > of the major axis diameter (: L) and the minor axis diameter (=D) calculated from a transmission electron microscope image at a magnification of 10,000 times was 12.

Next, after passing through a drying and pulverizing process, calcination (temperature = 650
℃), and using the same apparatus as in Example 5, 50g of the sample was subjected to gas phase catalytic reduction reaction with hydrogen gas (gas space velocity = 2ONn/-H2/kgr-) under the conditions listed in Table 1.
Fe/'Hr, ) in row 1. -Reduced iron powder.

The results are shown in Table-1. Next, after thoroughly immersing the fine particles in toluene, the fine particle slurry was transferred onto an enamel vat to a thickness of about 1'm, and subjected to toluene scattering treatment in the atmosphere. When the magnetic powder became non-existent, the magnetic powder was collected and made into air-dried iron carbide powder.

<Evaluation of coating/coating and tape properties of air-dried iron powder> 10 gr of the air-dried iron powder was collected, a coating was prepared in the same manner as in Example-5, and coating/film smoothing and heat treatment were performed. - Cutting was done to make the magnetic tape the size of the current cassette specification.

The magnetic properties of the magnetic tape are measured using the measuring device described above.
As a result of evaluation, Hc=11560e, Br=2570Gauss,
The characteristic value was Br/Bm=0.754.

Evaluation of audio characteristics> In the same manner as in Example-5, IEC standard Type-IV
We measured and evaluated audio characteristics using tape as a standard.

Low frequency sensitivity (:333Hz sensitivity) is +0.5dB, high frequency sensitivity (:20kHz sensitivity) is +3.8dB, maximum output (:
3%MOL) is +5.2dB, saturated output (:10kHz
z.

SQL) was +0.8 dB, and AC bias noise (Nac) after audibility correction was -55.4 dB.

Actions/Effects and Industrial Applicability The actions/effects of the present invention can be summarized as follows from the results of Examples and Comparative Examples.

That is, in the case of acicular ferromagnetic fine particles as a magnetic recording material suitable for high-density magnetic recording, the fine particles are mainly iron-based fine particles containing a predetermined amount of carbon, and the acicular ferromagnetic fine particles are coated with modified acicular ferromagnetic particles. Ferromagnetic reduced iron is made from iron hydroxide fine particles through a gas phase catalytic reduction reaction using a reducing gas, and then through a gas phase catalytic carbonization reaction using a mixed gas of (al carbon monoxide gas and hydrogen gas), or ( ) After the gas-phase catalytic carbonization reaction using a carbonizing gas, the ferromagnetic iron carbide-containing iron fine particles are obtained by subjecting them to a further reduction reaction using a reducing gas. While exhibiting acicular properties well inheriting the shape of iron hydroxide, (2) magnetic property values, especially coercive force Hc-value, can be controlled over a wide range according to the degree of carbonization, and (3) magnetic powder (4) Because the particles are fine and have appropriate magnetic properties (coercive force, magnetization, etc.), high frequency electromagnetic conversion properties (sensitivity, output) and noise are significantly improved. It was found that the manufacturing equipment for ferromagnetic metal powder using iron oxyhydroxide as a raw material can be used as is.

As described above, the substance of the present invention is a magnetic material with remarkable characteristics for use in audio and video applications, and provides a method for producing the same.

Claims (8)

[Claims] (1) A magnetic material for magnetic recording media consisting of ferromagnetic fine particles containing acicular iron carbide. (2) The value of x in iron carbide composition FeCxOy is 0.
The magnetic material according to claim 1, wherein the magnetic material has a value of 0.05 to 0.5 and a value of y of 0.01 to 1.0. (3) The magnetic material according to claim 1, wherein the fine particles have a long axis diameter of 1 μm or less, a short axis diameter of 0.1 μm or less, and an axial ratio of 10 to 30. (4) Magnetic property values are 500 Oe or more as coercive force and 90 emu/gr as saturation magnetization. An iron carbide-containing magnetic material characterized by exhibiting the above characteristics. (5) Acicular iron oxyhydroxide fine particles that have been modified with a shape-retaining component are made into ferromagnetic reduced iron powder by a gas phase catalytic reduction reaction using a reducing gas, and (a) are then treated with a carbonizing gas and a reducing gas. or (b) ferromagnetic iron carbide is first made into ferromagnetic iron carbide by a vapor phase catalytic carbonization reaction using a carbonizing gas or a mixed gas of a carbonizing gas and a reducing gas. A method for producing acicular iron carbide-containing ferromagnetic fine particles for magnetic recording, which comprises converting the ferromagnetic iron carbide into iron carbide and then subjecting the ferromagnetic iron carbide to a gas phase catalytic reduction reaction using a reducing gas. (6) The manufacturing method according to claim 5, wherein the reducing gas is a gas mainly composed of hydrogen, and the gas phase catalytic reduction reaction is carried out at 300 to 500°C. (7) The carbonizing gas is a gas mainly composed of carbon monoxide, and the reducing gas is a gas mainly composed of hydrogen, and the ratio of carbon monoxide and hydrogen is between 1:200 and 200:1. Supplied as a mixed gas with the composition (CO:H_2 volume ratio),
The manufacturing method according to claim 5, wherein the gas phase catalytic carbonization reaction is carried out at 200 to 700°C. (8) The manufacturing method according to claim 5, wherein a gas phase catalytic carbonization reaction is carried out by diluting a mixed gas of a carbonizing gas and a reducing gas with an inert gas.