JPH05163512A - Method and device for producing magnetic metal powder - Google Patents

Abstract

PURPOSE:To stably and highly reproducibly produce a magnetic metal powder having >=700 Oe coercive force and >=130 emu/g saturation magnetization and suitable for high-density recording by reducing the vapor of a metal halide. CONSTITUTION:The vapor of a metal halide 5 contg. at least one kind among Fe, Co and Ni is reduced in a reaction furnace 1 by a reducing gas to produce the magnetic metal powder. In this case, a reaction part 19 kept at >=900 deg.C, a part 20 for cooling the gas contg. the magnetic metal powder from the reaction part 19 to 500-750 deg.C and a soaking part 21 for keeping the gas contg. the magnetic metal powder from the cooling part 20 at 500-750 deg.C are provided in the reaction furnace 1, and a solenoid coil 13 for impressing a magnetic field on the soaking part 21 is furnished. The magnetic metal powder generated in the reaction part 19 is soaked at the soaking part 21 while impressing a magnetic field, and a magnetic metal powder excellent in magnetic characteristics is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for producing a magnetic metal powder having a high coercive force and a high saturation magnetization used in, for example, a high density magnetic recording medium.

[0002]

2. Description of the Related Art Recently, in recent years,
The demand for higher recording density of magnetic recording media is increasing, and it is expected to increase more and more in the future.
The areal recording density can be improved both by shortening the recording wavelength to improve the linear recording density and by narrowing the width of the recording track to improve the track density. As is well known, in order to perform short wavelength recording, a medium having a high coercive force sufficient to overcome a demagnetizing field is required, and for narrow track recording, a sufficient signal output can be obtained even from a narrow track width. Thus, a medium with high remanence is needed. That is, in order to achieve a higher recording density in the future, in the case of a coating type magnetic recording medium, both the coercive force and the saturation magnetization of the raw metal magnetic powder are required to be large.

At present, almost all practical magnetic metal powders for magnetic recording media are produced by dehydrating and reducing acicular goethite (FeOOH) formed by a wet method. The metal magnetic powder produced in this way has a coercive force of 1
000 to 1600 Oe, saturation magnetization 120 to 130 emu /
It is about g, which is not yet a sufficient value.

Although it is possible to produce a metal magnetic powder having a larger coercive force by this method, in that case, it is usually necessary to make the particles small and increase the acicular ratio.
The magnetic metal powder is stabilized by forming a thin oxide film on the surface to prevent ignition, and when the particles are small, the volume ratio of the oxide film is large and the saturation magnetization is reduced. In order to increase the saturation magnetization, it is desirable to use an Fe-Co alloy, but it is not easy to make needle-like goethite in such a composition. After all, it is difficult to simultaneously achieve a high coercive force of 1700 Oe or more and a high saturation magnetization of 130 emu / g or more by a method of dehydrating / reducing acicular goethite formed by a wet method.

On the other hand, conventionally, a metal halide powder containing at least one of Fe, Co, and Ni is vapor-phase reduced with a reducing gas to produce a metal magnetic powder that can be used in a high-density magnetic recording medium. Has been tried.

For example, Japanese Examined Patent Publication No. 61-60123 discloses a method of quenching the vapor of a metal halide vapor and a reducing gas with a flow velocity difference and placing the reaction part in a magnetic field. Further, JP-A-63-31263 discloses a method of promoting a reaction by mixing a small amount of active gas with a reducing gas, and JP-A-1-36706 discloses a method of carrying out the reaction under reduced pressure. As such, a number of improved techniques are known for this method.

According to this method, an alloy powder having a composition ratio corresponding to the mixing ratio can be prepared by mixing two or more kinds of metal halide vapors at an appropriate ratio. Is easy to make.

However, even with this technique, the coercive force of the magnetic powder obtained is usually up to about 1600 to 1650 Oe, as shown in the examples of these publications.
It has not been possible to easily obtain a magnetic powder having a high coercive force of 00 Oe or more, and further exceeding 2000 Oe. That is, in this technique, knowledge of a method for controlling the coercive force is not sufficient, so that it is difficult to obtain a metal magnetic powder having a high coercive force. Therefore, the metal magnetic powder using this method has not been put to practical use for high density magnetic recording media.

The present invention has been made in view of the above circumstances, and is achieved by the vapor phase reduction of a metal halide vapor.
High coercive force of 1700 Oe or more suitable for high recording density and 1
An object of the present invention is to provide a manufacturing method and a manufacturing apparatus capable of stably manufacturing a metal magnetic powder having a high saturation magnetization of 30 emu / g or more with good reproducibility.

[0010]

Means and Actions for Solving the Problems The present inventors have
As a result of various studies to produce metal magnetic powder having both high coercive force and high saturation magnetization by the vapor phase reduction reaction of metal halide vapor, the specific temperature was controlled while controlling the thermal history of the reduced metal magnetic powder. It has been found that this is achieved by applying a magnetic field at. That is, a metal magnetic powder having both high coercive force and high saturation magnetization can be obtained by holding the reduced metal magnetic powder at a temperature within a specific range below the Curie point while applying a magnetic field for an extremely short time. Was found. The present invention was made based on such knowledge.

That is, the method for producing a metal magnetic powder according to the present invention is a method for producing a metal magnetic powder by vapor-phase reducing a vapor of a metal halide containing at least one of Fe, Co and Ni with a reducing gas. In addition, the metal magnetic powder after the gas phase reduction is applied at a temperature of 500 ° C. or higher and 750 ° C. in a state where a magnetic field is applied
It is characterized in that the temperature in the following range is maintained for 0.005 seconds or more. In this case, the gas phase reduction reaction preferably proceeds at a temperature of 900 ° C. or higher. This makes it possible to easily and stably produce metal magnetic powder having a coercive force of 1700 Oe or more.

Further, in the apparatus for producing metal magnetic powder according to the present invention, vapor of a metal halide containing at least one of Fe, Co and Ni is vapor-phase reduced with a reducing gas in a reaction furnace to produce metal magnetic powder. In the manufacturing apparatus, the reaction furnace includes a heat retaining unit that holds the metal powder after the reaction at 500 ° C. or more and 750 ° C. or less, and further includes a magnetic field applying unit that applies a magnetic field to the heat retaining unit. Characterize. In this case, this reaction furnace is designed to keep the reaction part maintained at 900 ° C. or higher and the outflow gas containing the magnetic metal powder from the reaction part at 500 ° C.
It is preferable to include a cooling unit that cools to 750 ° C. or lower and a heat retention unit that holds the outflow gas containing the metal magnetic powder from the cooling unit at a temperature of 500 ° C. to 750 ° C. Hereinafter, the present invention will be described in detail.

In the present invention, the metal halide vapor obtained by reacting the metal halide vapor diluted with the inert gas with the reducing gas is obtained. At this time, when the metal halide vapor is mixed with the reducing gas at the nozzle tip in the reaction furnace, nucleation and growth follow the reduction reaction. Here, in order to sufficiently bring about the reduction reaction, it depends on the composition of the metal halide vapor, but at least 900 ° C. or higher, preferably 1 or more.
000 ° C or higher is required. If each gas before mixing is preheated to a sufficiently high temperature, it is possible to configure the outer periphery of the reaction part with a water cooling wall to allow the reaction while cooling as shown in JP-B-61-60123. If such a method is adopted, there is a possibility that the reaction rate may be lowered and the magnetic properties may be deteriorated by being cooled too much before the reduction reaction sufficiently occurs. For this reason, the reactor is provided with a reaction section maintained at 900 ° C or higher,
Therefore, it is desirable to cause a gas phase reduction reaction.

At this time, in order to suppress grain growth, addition of a trace amount of active gas to the reducing gas or reaction under reduced pressure as shown in JP-A-63-313603 and JP-A-1-36706. May be done.

After this reaction, the metal magnetic powder was heated at a temperature in the range of 500 ° C. to 750 ° C. for 0.005 seconds or more,
Keeps heat while applying a magnetic field. By this treatment, the magnetic characteristics of the metal magnetic powder can be improved as described later. In this heat-retaining process, a heat-retaining part is provided in the reaction furnace, and a magnetic field applying means for applying a magnetic field is further provided in the heat-retaining part. Should be supplied.

In order to carry out such a treatment in a preferable state, a cooling unit is provided in the reaction furnace, and the gas in which the magnetic metal powder flowing out from the reaction unit is suspended is cooled to 500 ° C. or higher and 750 ° C. or lower, It is preferable to supply the cooled magnetic metal powder to the heat retaining portion. This facilitates heat retention at a temperature of 500 ° C. or higher and 750 ° C. or lower in the heat retaining section.

The reason why the holding temperature in the heat retaining portion must be 750 ° C. or lower is that the magnetic metal powder needs to be magnetized at a temperature lower than its Curie temperature. The Curie temperature of Fe or Fe-Co alloy having a large saturation magnetization is usually 750 to 850 though it depends on the composition.
The temperature is about ℃, and the metal magnetic powder in the gas becomes magnetized by cooling to 750 ℃ or less. Magnetic individual spherical particles (metal magnetic powder particles produced by the reduction reaction are spherical due to surface tension) attract each other with Brownian motion and collide to form a chain.

A magnetic field is applied to the metal magnetic powder during the heat treatment, for the purpose of straightening the chain and improving the magnetic characteristics. If the spherical magnets attract each other and are connected in a chain, the shape will not necessarily be straight, and normally a chain with a wavy, curved chain will be generated. Upon application, the chain extends straight along the direction of the magnetic field lines to form a straight chain. In order to cause this action, it is necessary that the temperature at that position is equal to or lower than the Curie temperature as described above. In addition,
The applied magnetic field in this case has a sufficient effect at 100 Oe or more, but it is preferably 300 Oe if possible.

The reason why the holding temperature in the heat-retaining section is required to be 500 ° C. or higher is to fuse the individual spherical particles in the linear chain. When the temperature is low, the individual spherical particles forming the linear chain simply attract and stick to each other due to the magnetic force, and are easily broken during handling in the subsequent steps to form a long linear chain. The chain is broken. In order to prevent this, the temperature is maintained at 500 ° C. or higher to promote fusion between adjacent particles forming the chain and prevent the chain from being cut thereafter.

The reason why the holding time in the heat retaining part is set to 0.005 seconds or more is that the chain formation is not sufficiently performed in less than 0.005 seconds. The holding time is more preferably 0.01 seconds or more. The retention time is 0.5
The holding time is preferably 0.5 seconds or less because the effect of chain formation and fusion is saturated even if it exceeds the second, and the apparatus is only unnecessarily enlarged.

As is well known, as means for increasing the coercive force of the metal magnetic powder, the particle size is reduced to about 300 angstroms or less to form single domain particles, and the shape is elongated to enhance the shape anisotropy effect. Is. In the conventional production technology of metal magnetic powder by vapor-phase reduction of metal halides, the technology for controlling the particle diameter was almost established, but the effects of temperature and magnetic field in forming chains have not always been elucidated, The entire reactor was simply cooled and a magnetic field was applied to the entire reactor. Therefore, when the gas amount was changed and the temperature distribution in the reaction furnace was changed, it was not always possible to stably obtain powder having the same characteristics. In addition, it is practically impossible to form a long straight chain, and the spherical particles that form the chain are fused to each other and are not separated thereafter. Therefore, it was not possible to stably produce a metal magnetic powder having a high coercive force of 1700 Oe or more.

The present invention elucidates the effects of temperature and magnetic field on the magnetic properties in the production of metal magnetic powder by vapor phase reduction of metal halides, and controls the properties of the chain by setting the conditions as described above. This is to enable the stable production of metal magnetic powder having a high coercive force of 1700 Oe or more with good reproducibility.

Regarding the saturation magnetization, the metal magnetic powder produced by the vapor phase reduction method of metal halides tends to be essentially higher than the one obtained by dehydrating and reducing acicular goethite. This is due to dehydration in the vapor phase reduction method of metal halides.
This is because there are no pores at the time of reduction and the crystal integrity is high. Further, in the vapor phase reduction method of this metal halide, it is easy to obtain a Fe—Co alloy composition having a high saturation magnetization. Therefore, according to the present invention, which is based on the vapor phase reduction method of metal halides, it is possible to easily obtain the required high saturation magnetization of 130 emu / g or more.

As described above, according to the present invention, a high coercive force of 1700 Oe or more and 130 emu suitable for high density recording are obtained.
It has become possible to obtain a high-performance metal magnetic powder having a high saturation magnetization of not less than / g at the same time.

[0025]

Embodiments of the present invention will be described in detail below. FIG. 1 is a schematic block diagram showing an example of an apparatus used for carrying out the method of the present invention.

In FIG. 1, reference numeral 1 is a reactor. The reaction furnace 1 has a reaction part 1 in order from the bottom to the top.
9, a cooling unit 20, a heat retaining unit 21, and a cooling unit 22. A raw material gas supply pipe 2 is attached to the reactor 1 from below.
Is inserted, and two raw material evaporators 3 are connected to the raw material gas supply pipe 2. A carrier gas supply pipe 4 is connected to the raw material evaporator 3. Raw material evaporator 3
The metal halide 5 is accommodated therein, and is heated and melted by the heater 6, and the metal halide vapor generated from the metal halide vapor is a carrier gas supplied from the supply pipe 4 and does not contain preheated N ₂ , Ar or the like. Diluted with active gas,
The carrier gas carries the reaction gas into the reaction section 19 of the reaction furnace 1.

A hydrogen gas supply pipe 7 is attached to the bottom of the reaction furnace 1, and preheated hydrogen gas as a reducing gas is supplied to the reaction furnace 1 from there. The hydrogen gas supplied from the hydrogen gas supply pipe 7 to the reaction furnace 1 is the raw gas supply pipe 2
The metal halide vapor from the above is mixed in the reaction part 19 to cause a reduction reaction. A heater 8 is provided around the reaction section 19. The heater 8 heats the reaction part to 900 ° C. or higher.

The magnetic metal powder generated as a result of the reduction reaction in the reaction section 19 is diluted with the carrier gas and then cooled in the cooling section 2.
It reaches 0, and is cooled by the water cooling jacket 9 to a range of 500 ° C. or higher and 750 ° C. or lower. Reference numerals 10 and 11 are a supply pipe and a discharge pipe of cooling water to the water cooling jacket 9.

The gas in which the magnetic metal powder is suspended is cooled by the cooling unit 20.
After being cooled by, the heat retention unit 21 is reached. In the heat retaining section 21, the metal magnetic powder is held at a temperature of 500 ° C. or higher and 750 ° C. or lower for 0.005 seconds or longer. Also, the heat retention unit 2
A solenoid coil 13 is arranged around 1
By supplying electric current to the
A magnetic field in the range up to Oe is applied.

Reference numeral 12 indicates the temperature of the heat retaining portion 500.
It is a heat insulating material for keeping the temperature between ℃ and 750 ℃. When a large amount of heat is dissipated, the heat insulating material 12 may be replaced with a heater for heat compensation.

The gas in which the magnetic metal powder has passed through the heat retaining portion 21 is suspended and reaches the powder collector 18 through the exhaust pipe 17.
The magnetic powder is separated by the powder collector 18. At this time, in order to avoid heat damage to the powder collector and to prevent the magnetic metal powder from being fused or sintered in the powder collector, the gas in which the magnetic metal powder is suspended should be Second stage cooling unit 22
In, the water cooling jacket 14 cools it down to about 200 ° C. or lower. Reference numerals 15 and 16 are a supply pipe and a discharge pipe of cooling water to the water cooling jack.

In FIG. 1, the raw material gas and the hydrogen gas are 9
If it is preheated to a temperature sufficiently higher than 00 ° C., the heater 8 is omitted as shown in Japanese Patent Publication No. 61-60123, and the water cooling jacket 9 is extended to a position where the heater 8 is located to cool the reaction part. While reacting, you may make it react. However, even in this case, the heat retaining portion 21 is necessarily required.

Solenoid coil 1 as magnetic field generating means
Although 3 is arranged only at the position corresponding to the heat retaining portion 21 in FIG. 1, the coil length may be extended to cover other portions such as the cooling portions 20 and 22 and the reaction portion 19 as well. I do not care. However, as is clear from the role of the magnetic field described above, no special effect can be expected even if the cover range is widened, and the facility cost is unnecessarily increased. Is enough.

Next, as the reaction furnace of FIG. 1, a tube diameter of 53.5 mm
Gas flow rate, metal halide vapor partial pressure,
The results of actually producing the magnetic metal powder by varying the heat retaining portion passage time and the heat retaining portion temperature will be described. Here, the temperature of the heat retaining portion was changed by adjusting the temperature of the reaction portion heater 8 and adjusting the thickness of the heat insulating material of the heat retaining portion or by attaching heat to the heat retaining portion heater. In addition, the heat retention section transit time was changed by changing the gas amount and the heat retention section length. The magnitude of the magnetic field applied to the heat retaining part was 500 Oe. Further, the composition of the magnetic metal powder was 0 to 40% Co, 100 to 60% Fe, or an Fe-Co alloy.

Table 1 shows the conditions in that case and the magnetic properties of the obtained metal magnetic powder. In Table 1, Examples 1 to 8 are within the scope of the present invention, and Comparative Examples 1 to 4 are outside the scope of the present invention.

[0036]

[Table 1]

As is clear from Table 1, even if the amount of gas and the vapor partial pressure of the metal chloride are changed, the temperature of the heat retaining part is 500 ° C.
It was confirmed that a high coercive force magnetic metal powder having a coercive force of 1700 Oe or more could be stably obtained by keeping the temperature in the range of 750 ° C. and the heat retention section passage time of 0.005 seconds or more. Furthermore, it was confirmed that a particularly high coercive force was obtained when the heat retention section transit time was 0.01 seconds or more. Regarding the saturation magnetization, it was confirmed that the metal magnetic powder produced by this process stably exhibits a high saturation magnetization of about 140 to 160 emu / g. On the other hand, outside the range of the conditions of the present invention, the coercive force was lower than 1700 Oe and was insufficient.

[0038]

According to the present invention, the coercive force of 1700 Oe suitable as a high density magnetic recording material is obtained by vapor-phase reducing a vapor of a metal halide containing at least one of Fe, Co and Ni with a reducing gas. Above, saturation magnetization 130 emu / g
Provided is a method and an apparatus for producing metal magnetic powder, which can stably produce the above metal magnetic powder.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an apparatus used for carrying out the method of the present invention.

[Explanation of symbols]

1 ... Reactor, 2 ... Raw material gas supply pipe, 7 ... Hydrogen gas supply pipe, 13 ... Solenoid coil (magnetic field generating means),
19 ... Reaction part, 20, 22 ... Cooling part, 21 ... Heat retaining part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiichi Okuyama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (4)

[Claims] 1. A method of producing a metal magnetic powder by vapor-phase reducing a vapor of a metal halide containing at least one of Fe, Co and Ni with a reducing gas, the metal magnetic powder after the vapor-phase reduction. At a temperature of 500 ° C or higher with a magnetic field applied
A method for producing a metal magnetic powder, which is characterized by holding at a temperature in the range of 0 ° C. or less for 0.005 seconds or more. 2. A method for producing a magnetic metal powder by vapor-phase reducing a vapor of a metal halide containing at least one of Fe, Co and Ni with a reducing gas, the vapor phase being at a temperature of 900 ° C. or higher. A reduction reaction is caused to occur, and then the reduced metal magnetic powder is cooled to a temperature in the range of 500 ° C. to 750 ° C., and the magnetic powder is heated to 500 ° C. to 7 ° C. under a magnetic field.
A method for producing a magnetic metal powder, which is characterized by holding at a temperature in the range of 50 ° C. or less for 0.005 seconds or more. 3. An apparatus for producing metal magnetic powder by vapor-phase reducing a vapor of a metal halide containing at least one of Fe, Co and Ni with a reducing gas in a reaction furnace, wherein the reaction furnace is a reactor. After finishing the metal powder, 500 ℃ or more 7
An apparatus for producing metal magnetic powder, comprising: a heat-retaining section for holding at 50 ° C. or lower, and further having a magnetic field applying means for applying a magnetic field to the heat-retaining section. 4. An apparatus for producing metal magnetic powder by vapor-phase reducing a vapor of a metal halide containing at least one of Fe, Co and Ni with a reducing gas in a reaction furnace, wherein the reaction furnace comprises: The reaction part maintained at 900 ° C or higher and the outflow gas containing the magnetic metal powder from the reaction part are heated to 500 ° C.
A cooling unit that cools the temperature to 750 ° C. or lower and a heat retaining unit that holds the outflow gas containing the magnetic metal powder from the cooling unit at a temperature of 500 ° C. to 750 ° C. are provided, and a magnetic field is applied to the heat retaining unit. An apparatus for producing metal magnetic powder, further comprising magnetic field applying means.