JP2000272909A - Production of iron nitride and iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a single phase Fe2N powder, Fe3N powder, Fe4N powder and Fe powder by firing iron oxalate obtained by a precipitation reaction of ferrous chloride with ammonium oxalate in a liquid phase, in ammonia atmosphere at a specific temperature. SOLUTION: Ferrous chloride and ammonium oxalate are subjected to a precipitation reaction in a solution, preferably aqueous solution for 1-3 hr to provide iron oxalate powder. The obtained iron oxalate is fired in an ammonia atmosphere at 425-475 deg.C for >=30 min to provide,a single phase Fe2N powder. The iron oxalate is fired in the ammonia atmosphere at 475-525 deg.C for <=1.5 hr to provide a single phase Fe3N powder. Further, the iron oxalate is fired in the ammonia atmosphere at 525-575 deg.C for <=1 hr to provide Fe4N powder. When the iron oxalate is fired at >=700 deg.C, Fe powder can be obtained. The obtained iron nitride powders have each <=1 nm primary particle diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to iron nitride and a method for producing iron. More specifically, Fe ₂ N, Fe ₃ N, F
The present invention relates to a method for producing e ₄ N, Fe powder.

[0002]

2. Description of the Related Art Iron nitride bulk materials have been synthesized in the past, and various materials such as magnetic recording and magnetic fluid have been studied for practical use. Fe ₁₆ N ₂ , Fe ₄
Four of N, Fe ₃ N and Fe ₂ N are known. Among them, Fe ₁₆ N ₂ and Fe ₄ N are ferromagnetic substances and have practically excellent magnetic properties, so that many research results such as synthesis and evaluation have been reported. However, Fe ₃ N and Fe ₂
N is structurally unstable and therefore difficult to produce, and there are few reports.

Conventionally, these iron nitrides have been produced by a reaction between iron powder and nitrogen or ammonia in a reducing atmosphere, but in these reactions, Fe ₂ N, Fe ₃ N,
Only a mixture of Fe ₄ N crystal phases was obtained, and it was very difficult to separate each crystal phase from the product in a single phase.

[0004] There is also a method of producing iron nitride by vapor deposition, but only a film-like product can be obtained by this method, and a powdery product cannot be obtained.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a single-phase iron nitride powder in view of the above-mentioned conventional problems.

[0006]

That is, according to the method for producing iron nitride of the present invention, iron oxalate is reduced to 425 in an ammonia atmosphere.
° C or more and less than 475 ° C, preferably 440 ° C or more and 460 ° C
It is characterized in that it is calcined below to obtain Fe ₂ N powder.

Further, iron oxalate is heated to 475 ° C. or more and less than 525 ° C., preferably 490 ° C. or more in an ammonia atmosphere.
It is characterized by firing at 10 ° C. or lower to obtain Fe ₃ N powder.

In an ammonia atmosphere, iron oxalate is heated to 525 ° C. or higher and lower than 575 ° C., preferably 540 ° C. or higher.
It is characterized in that Fe ₄ N powder is obtained by firing at 60 ° C. or lower.

Further, in the method for producing iron of the present invention, iron oxalate is calcined at a temperature of 700 ° C. or more in an ammonia atmosphere, and
It is characterized by obtaining a powder.

In the above-mentioned production method, it is preferable that iron oxalate as a starting material is obtained by a precipitation reaction of ferrous chloride and ammonium oxalate in a liquid phase.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The present invention is characterized in that iron oxalate is fired in an ammonia atmosphere to obtain iron nitride and iron powder.

In order to nitride iron oxalate, it is necessary to perform thermal decomposition in an atmosphere-controlled system. Therefore, the atmosphere is controlled by continuously flowing a certain amount of gas in the system. In addition to the thermal decomposition, an NH ₃ atmosphere is used as the firing atmosphere, which has a reducing property to oxygen and enables desorption of oxygen and intrusion of nitrogen.

In the conventional method of nitriding iron powder, the reaction proceeds in the order of Fe → Fe ₄ N → Fe ₃ N → Fe ₂ N, but in the method of the present invention, Fe ₂ N → Fe ₃ N → Fe ₄ N
→ The reaction proceeds in the order of Fe. This is because iron nitride is an interstitial alloy in which nitrogen penetrates into the crystal lattice of iron metal. When nitriding iron powder, nitrogen gradually penetrates and changes from nitrogen deficiency to nitrogen-excess iron nitride. However, in the case of the method of the present invention, the presence of Fe ₃ O _{4 in} the intermediate first produces nitrogen-rich iron nitride. The process of changing to nitrogen deficiency is because if the flow rate of NH ₃ is constant, the nitrogen concentration decreases due to the expansion of the NH ₃ gas in the system as the firing temperature increases, and the amount of nitrogen intrusion decreases. Conceivable.

In the present invention, the temperature of iron oxalate is 300 ° C.
Decompose in the vicinity to produce Fe ₃ O ₄ and FeO,
At 0 ° C., Fe ₃ O ₄ and Fe ₂ N are formed. Further, when the sintering temperature is increased to 450 ° C., iron oxalate is completely reduced, and Fe _{2, which} allows nitrogen to penetrate as much as iron nitride, is used.
N single phases are formed. At 500 ° C., Fe ₃ N is 5
In 50 ° C. Fe ₄ 4 respectively, produced in substantially single-phase state. When the firing temperature exceeds 600 ° C., Fe ₄ N and Fe are generated, and when the firing temperature is 700 ° C. or more, only the Fe phase is formed.

Therefore, the sintering temperature for obtaining the Fe ₂ N powder is 425 ° C. or more and less than 475 ° C., preferably 440 ° C.
460 ° C. or lower and calcination temperature for obtaining Fe ₃ N powder is 475 ° C. or higher and lower than 525 ° C., preferably 49 ° C. or lower.
0 ° C. or higher and 510 ° C. or lower, and the firing temperature for obtaining Fe ₄ N powder is 525 ° C. or higher and lower than 575 ° C., preferably 540 ° C. or higher and 560 ° C. or lower, and the firing temperature for obtaining Fe powder is 700 ° C. That is all.

The firing time, that is, the time for maintaining the above firing temperature, is not particularly limited in order to obtain Fe ₂ N powder, but if it is too short, Fe ₃ O ₄ remains as a heterogeneous phase, so that it is 30 minutes. It is preferable to make the above.

There is no particular limitation for obtaining Fe ₃ N powder, but if it is too long, nitrogen in Fe ₃ N is desorbed and F ₃ N
It becomes mixed phase of the e ₄ N, and since there is a tendency that generation rate of Fe ₄ N is increased in accordance with the retention time becomes longer, 1.5
It is preferable to set the time to not more than the time.

There is no particular limitation for obtaining Fe ₄ N powder, but if it is too long, a mixed phase state of Fe ₄ N and Fe will occur, so it is preferable that the time be 1 hour or less.

As the starting material, iron oxalate powder,
Although it is possible to use those produced by a known method, in order to obtain good quality iron nitride without causing morphology during the thermal decomposition process, it is necessary to use fine particles and those in which each particle is uniform. preferable.

As a method for obtaining such iron oxalate powder, there is a method in which a liquid phase of ferrous chloride and ammonium oxalate is used.
Preferably, a precipitation reaction in an aqueous solution is preferable. At this time, the precipitation time is preferably 1 hour to 3 hours in order to attain fine particles and uniformity of the particles. If the settling time is less than 1 hour, the particle growth is not yet complete, and there is a tendency for the rectangular particles to have a mixture of two particles, that is, particles having slightly corners and finished rectangular particles. If the precipitation time exceeds 3 hours, the particle size tends to increase.

According to the present invention, it is possible to obtain an iron nitride fine powder having a primary particle size of 1 μm or less.

[0023]

The present invention will be described in more detail with reference to the following examples. In addition, the evaluation method in an Example is as follows.

(1) Identification of Crystal Phase X-ray diffractometer (XRD, RAD-B, RA manufactured by Rigaku Corporation)
Using DC), the area of the main peak of each phase was calculated from the peak intensity and the half width, and was defined as the production rate α.

(2) Measurement of Magnetic Properties A vibrating sample magnetometer (VSM, manufactured by Tamagawa Seisakusho) was used.

(3) Observation of particle morphology Scanning electron microscope (SEM, Hitachi S2400, S41
00) was used.

(4) Chemical composition analysis An energy dispersive X-ray fluorescence analyzer (EDS, keve)
x company).

(Example 1) <Production of iron oxalate powder>
Ammonium oxalate monohydrate (NH ₄ ) ₂ C ₂ O ₄ H ₂ O
(99% or more manufactured by Kojundo Chemical Laboratory) and ferrous chloride (Fe
Cl ₂ ) (99.9% or more, manufactured by Kojundo Chemical Laboratory).

In order to cause ammonium oxalate monohydrate and ferrous chloride to undergo precipitation reactions at concentrations of 0.11 mol / l and 0.1 mol / l, respectively, they were produced by the following procedure.

(1) Ammonium oxalate monohydrate
91 g is weighed, put into a 250 ml volumetric flask, and made up with 250 ml of pure water.

(2) The solution is put into a Kapha flask, and 250 ml of pure water for ferrous chloride is further added.

(3) A stirrer is set in the Kapha flask and stirred. The stirring speed was 300 rpm / min.

(4) Ferrous chloride is added to the flask in an amount of 1 to 2
Charge over a minute.

(5) The solution is stirred for 2 hours to precipitate the particles in order to suppress aggregation of the precipitated particles. The stirring speed is 300 rpm
m / min.

(6) After stirring, the precipitate solution is subjected to suction filtration using a filter paper of A4, 110 size to separate the solution from the precipitate product.

(7) The precipitated product adhering to the filter paper is washed out into a flask made of ethanol.

(8) A small amount of water and ethanol are separated and removed from the precipitated product by a reduced-pressure evaporator.

(9) After the removal, the obtained precipitate product is recovered and is dried for 1 hour in a dryer at 80 ° C. in order to completely evaporate the water.
Dry above. As a result, uniform particles having a particle size of 2 μm were obtained.

(10) In order to prevent moisture absorption, the obtained powder is stored in a vacuum desiccator.

<Thermal Decomposition of Iron Oxalate Powder> Using the apparatus shown in FIG. 1, the iron oxalate powder was fired in a system under an NH ₃ atmosphere according to the following procedure.

(1) An alumina boat is charged with 0.5 g of iron oxalate, and this is put into a quartz reaction tube.

(2) First, in order to remove air in the system, N
_The gas is replaced with ₂ gases, and then NH ₃ gas is flowed at 200 ml / min to drive out N ₂ gas.

(3) The sintering conditions are as follows: a heating rate of 10 K / mi.
The temperature was raised to 300 to 700 ° C. with n, and the holding time was set to 1 hour.

(4) After the calcination was completed, the reaction tube was quenched with water to terminate the reaction.

FIG. 2 shows the relationship between the firing temperature and the production rate of each phase.

As shown in FIG. 2, iron oxalate is at 300 ° C.
Decompose in the vicinity to produce Fe ₃ O ₄ and FeO,
At 0 ° C., Fe ₃ O ₄ and Fe ₂ N are formed.

Further, when the firing temperature is raised to 450 ° C., iron oxalate is completely reduced, and a Fe ₂ N single phase is formed as iron nitride, into which nitrogen can enter as much as possible. Also, 50
At 0 ° C., Fe ₃ N, and at 550 ° C., Fe ₄ N,
Produced almost in a single phase.

When the firing temperature exceeds 600 ° C.,
₄ generates N and Fe, the Fe phase only at 700 ° C. or higher.

FIG. 3 shows the firing temperature dependence of the saturation magnetization value of a sample prepared by thermally decomposing iron oxalate. Magnetic measurement of a sample manufactured at 400 ° C. or lower was impossible because the sample was unstable (burned) in the atmosphere.

As shown in FIG. 3, the saturation magnetization at 450 ° C. was 0 emu / g, indicating that Fe ₂ N has no magnetism. Above 450 ° C., the magnetization increased sharply to 70
At 0 ° C., it almost coincides with the magnetization value of Fe. 500 ° C, 55
At 0 ° C., Fe ₃ N and Fe ₄ N are generated, and the magnetization value is also in agreement with the literature value.

Observation of the obtained iron nitride powder by SEM showed that sintering progressed with an increase in the firing temperature, and that the primary particles had rounded corners. The size of the primary particles was 1 μm or less, which was suitable as a coating medium.

Example 2 The firing temperature was 450 ° C. and 500 ° C.
° C and 550 ° C, and iron nitride was produced in the same manner as in Example 1 except that the holding time was changed to 0.5 to 4 hours.

FIG. 4 shows the firing time dependence of the product phase obtained by pyrolyzing iron oxalate powder at 450 ° C. In this case, a single phase of Fe ₂ N is generated regardless of the retention time. From this, the conditions of this example (200 ml / min.
It can be seen that the flow rate of H ₃ gas and the firing temperature of 450 ° C.) are suitable conditions for synthesizing Fe ₂ N. However, if the holding time is as short as 1 hour or less, the reproducibility of the obtained sample is low and the synthesis tends to be difficult. In a short time of 1 h or less, the generation rate of a complete single phase depends on the amount of the sample and the state of dispersion of the NH ₃ gas, but Fe ₃ O ₄ remains as a different phase.

When the saturation magnetization values of these samples were measured, the magnetization values were 0 emu / g at all holding times, indicating that a single phase of Fe ₂ N was formed.

FIG. 5 shows the firing time dependency of the product phase obtained by pyrolyzing iron oxalate powder at 500 ° C. Up to the retention time of 1 h, Fe ₃ N remains in a single phase and does not change, but if the retention time is longer than that, nitrogen in Fe ₃ N is desorbed and Fe ₄ N
It becomes a mixed phase with N. Further, the generation rate of Fe ₄ N tends to increase as the retention time becomes longer.

This is because, in the case of the present invention, nitrogen is initially generated via Fe ₃ O ₄ as an intermediate, and at 450 ° C. there is nitrogen enough to generate Fe ₂ N, but at 500 ° C., Fe ₃ N is generated. This is because the nitrogen cannot be kept in an equilibrium state at a NH ₃ gas flow rate of 200 ml / min, and the nitrogen evaporates with the extension of the retention time.
In other words, in this temperature range, the process is divided into an iron oxalate → Fe ₃ N oxygen reduction process, a nitrogen intrusion process, and a Fe ₃ N → Fe ₄ N heat treatment nitrogen evaporation process.

When the saturation magnetization values of these samples were measured, when the holding time was 1 hour or longer, a mixed phase of Fe ₄ N and Fe ₃ N was formed.

FIG. 6 shows the firing time dependence of the formed phase of the sample obtained by pyrolyzing iron oxalate powder at 550 ° C. According to this figure, the holding time is 1 h. In the following, a single phase of Fe ₄ N is obtained according to the same reaction result as the calcination at 500 ° C.
However, the equilibrium state shifts from Fe ₄ N to Fe with the extension of the retention time. That is, a mixed phase state of Fe ₄ N and Fe is obtained.

When the saturation magnetization values of these samples were measured, the retention time was 1 h. Has a magnetization value of 183 emu / g, which is almost the same as the literature value, because it is a single phase of Fe ₄ N. On the other hand, the holding time is 1 h. By doing the above, F
A mixed phase of e ₄ N phase and Fe phase was obtained, and a magnetization value proportional to the generation ratio shown in FIG. 6 was obtained.

[0060]

As described above, according to the present invention, single-phase Fe ₂ N, Fe ₃ N, Fe ₄ N, and Fe powder can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a manufacturing apparatus in an embodiment.

FIG. 2 is a graph showing a relationship between a firing temperature and a production rate.

FIG. 3 is a graph showing a relationship between a firing temperature and a saturation magnetization value.

FIG. 4 is a graph showing a relationship between a retention time at a firing temperature of 450 ° C. and a generation rate.

FIG. 5 is a graph showing a relationship between a holding time at a firing temperature of 500 ° C. and a generation rate.

FIG. 6 is a graph showing a relationship between a retention time at a firing temperature of 550 ° C. and a production rate.

Continued on the front page (72) Inventor Minoru Fujita 4-14-12 Koishikawa, Bunkyo-ku, Tokyo Kyodo Printing Co., Ltd. F-term (reference) 4K017 AA03 AA04 BA09 BB06 DA02 EH20 FA01 FB03 FB05

Claims (6)

[Claims] 1. The method according to claim 1, wherein iron oxalate is added in an ammonia atmosphere.
A method for producing iron nitride, comprising sintering at 5 ° C. or more and less than 475 ° C. to obtain Fe ₂ N powder. 2. The method according to claim 2, wherein iron oxalate is added in an ammonia atmosphere.
A method for producing iron nitride, characterized in that Fe ₃ N powder is obtained by firing at 5 ° C. or more and less than 525 ° C. 3. The method according to claim 3, wherein iron oxalate is added in an ammonia atmosphere.
A method for producing iron nitride, comprising sintering at 5 ° C. or more and less than 575 ° C. to obtain Fe ₄ N powder. 4. The iron nitride according to claim 1, wherein the iron oxalate is obtained by a precipitation reaction between ferrous chloride and ammonium oxalate in a liquid phase. Production method. 5. An iron oxalate in an ammonia atmosphere at 70
A method for producing iron, which comprises sintering at 0 ° C. or higher to obtain Fe powder. 6. The method for producing iron according to claim 5, wherein the iron oxalate is obtained by a precipitation reaction between ferrous chloride and ammonium oxalate in a liquid phase.