Preparation method of high-purity Fe4N powder

Abstract

The invention discloses a preparation method of high-purity Fe4N powder, which comprises the following steps: selecting high-purity iron powder with a proper particle size, adding a proper amount of ceramic powder with special particle size distribution into the iron powder, then adding a binder and a release agent, and pressing into a solid block with a certain size; carrying out high-temperature treatment on the block, so that the binder and the release agent in the block are completely volatilized to form a porous block material; the porous block material is subjected to hydrogen reduction treatment at a certain temperature, and the surface activity of powder inside the porous block material is improved; ammonia-hydrogen mixed gas is introduced for nitridation at a certain temperature; and the powder blocks are ground, and high-purity Fe4N powder is finally obtained through a magnetic separation method. The purity of the Fe4N powder obtained through the method ranges from 90.0% to 99.9%.

Description

Technical Field

[0001] The present invention relates to a method for preparing high-purity Fe4N powder, belonging to the technical field of magnetic materials. Background Art

[0002] As a new type of metallic soft magnetic material, Fe4N has gradually demonstrated unique performance advantages in the soft magnetic field in recent years. Compared with traditional metallic soft magnetic materials such as silicon steel and ferrite, Fe4N exhibits excellent comprehensive magnetic properties of high saturation magnetic flux density (Bs), low coercivity (Hc), and low loss. Compared with traditional ferrite soft magnetic materials, the saturation magnetic flux density of Fe4N can reach more than 1.6 T, significantly higher than 0.4 - 0.5 T of ferrite, which makes it more competitive in miniaturized and high-frequency scenarios. At the same time, Fe4N has a relatively high resistivity, which can effectively reduce eddy current loss in high-frequency applications and is suitable for inductors and transformers at the MHz level, meeting the requirements of high efficiency and high power density in fields such as photovoltaic inverters and new energy vehicle electric drive systems.

[0003] However, it should be noted that due to the extremely narrow phase formation region of the Fe4N phase in the iron-nitrogen series alloy, it is difficult to obtain high-purity Fe4N materials with a purity of more than 80% by conventional nitriding processes. Currently, the reported high-purity Fe4N materials are limited to micron- or even sub-micron-sized powders prepared in the laboratory or thin film materials prepared by special methods, and it is difficult to achieve large-scale production or application. Therefore, how to stably and efficiently produce high-purity Fe4N powder has become an urgent problem to be solved. Summary of the Invention

[0004] Based on the problems existing in the above-mentioned prior art, the present invention aims to provide a method for stably and efficiently preparing high-purity Fe4N powder. The Fe4N powder prepared by this method has a micron-sized particle size and a relatively high purity, which can reach 90.0 - 99.9%.

[0005] To achieve the purpose, the present invention adopts the following technical solutions:

[0006] A method for preparing high-purity Fe4N powder, comprising the following steps:

[0007] (1) Controlling the particle size of high-purity iron powder (purity ≥ 99.9%) by air classification to obtain iron powder raw materials with a particle size range of D50 = 2 - 35 μm.

[0008] (2) Add ceramic powder to the iron powder raw material. The addition amount of the ceramic powder is 10-60% of the mass of the iron powder to obtain a mixed powder. Among them: the ceramic powder is at least one of alumina, zirconia, magnesia, yttria, silicon carbide, silicon nitride, boron nitride, molybdenum disilicide or mullite; the D50 of the particle size distribution of the ceramic powder is D50 of the particle size distribution of the iron powder raw material + (2-5) μm.

[0009] (3) Add a binder accounting for 2-15% of the mass of the mixed powder and a release agent accounting for 0.3-2% of the mass of the mixed powder to the mixed powder and mix them evenly. Subsequently, press them into a cubic block at a pressure of 200-800 MPa. Any side length of the cubic block is 1-20 mm.

[0010] (4) Heat-treat the cubic block in an inert gas protection furnace at 200-600 °C for 1-5 h to fully decompose the binder and release agent in the block and obtain a porous material with a large number of pores.

[0011] (5) Place the porous material in a tubular furnace and introduce hydrogen for reduction treatment. The reduction treatment temperature is 400-850 °C, and the treatment time is 2-8 h.

[0012] (6) After the reduction treatment is completed, without taking out the porous material, directly replace the gas introduced into the furnace with an ammonia-hydrogen mixed gas (the volume ratio of ammonia to hydrogen in the mixed gas is 1-10:1), and perform nitridation treatment on the material. The nitridation treatment temperature is 500-750 °C, and the treatment time is 4-10 h.

[0013] (7) After nitridation is completed, take out the porous material from the tubular furnace, crush it with a mortar, and separate the ceramic powder in it by magnetic separation to obtain high-purity Fe4N powder with a purity of 90.0-99.9%.

[0014] The beneficial effects of the present invention are as follows:

[0015] In the present invention, ceramic powder, binder and release agent are added to high-purity iron powder and pressed into a block material. Subsequently, a porous material with a large number of pores is obtained through high-temperature treatment, which increases the effective contact area between the iron powder and the nitriding atmosphere in the subsequent nitriding treatment, greatly improves the nitriding efficiency of the iron powder, and can stably obtain Fe4N loose powder with a particle size of several microns or even dozens of microns, far exceeding the particle size of nano-scale or sub-micron-scale Fe4N powder that can only be prepared by conventional processes; before the nitriding treatment of the material, hydrogen is used for sufficient reduction to reduce the content of impurities such as iron oxide in the block material, further improving the purity of the Fe4N powder in the finished product, making it reach a purity of 90.0-99.9%; at the same time, the addition of ceramic powder avoids the phenomenon that iron powder particles are connected to each other and combine during the subsequent nitriding process to form serious powder caking. Brief Description of the Drawings

[0016] Figure 1 It is the XRD pattern of the high-purity Fe4N powder obtained after nitriding treatment. Detailed Embodiments

[0017] To describe the present invention more clearly, the technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] Embodiment 1

[0019] The preparation method of the high-purity Fe4N powder in this embodiment includes the following steps:

[0020] (1) Control the particle size of high-purity iron powder (purity 99.9%) by air classification to obtain iron powder raw materials with a particle size D50 = 3μm.

[0021] (2) Add ceramic powder with D50 = 5μm to the iron powder raw materials to obtain a mixed powder. Among them, the addition amount of the ceramic powder is 15% of the mass of the iron powder raw materials, and the ceramic powder is composed of alumina powder and boron nitride powder mixed in a mass ratio of 1:1.

[0022] (3) Add 13.5% of the mass of the mixed powder of silicone resin powder as a binder and 2% of the mass of the mixed powder of zinc stearate as a release agent to the mixed powder and mix them evenly. Subsequently, press them into a cube block with a length of 20mm, a width of 20mm, and a height of 1mm under a pressure of 350MPa.

[0023] (4) Heat-treat the cube block in a nitrogen protection furnace at 300°C for 3h to fully decompose the binder and release agent in the block and obtain a porous material with a large number of pores.

[0024] (5) Put the porous material into a tube furnace and introduce hydrogen for reduction treatment. The reduction treatment temperature is 600°C and the treatment time is 6h.

[0025] (6) After the reduction treatment is completed, without taking out the porous material, directly replace the gas introduced into the furnace with an ammonia-hydrogen mixed gas with a volume ratio of ammonia to hydrogen of 1:1, and perform nitriding treatment on the material. The nitriding treatment temperature is 500°C and the treatment time is 10h.

[0026] (7) After the nitridation is completed, the porous material is taken out of the tube furnace, crushed using a mortar, and the ceramic powder therein is separated by magnetic separation, that is, high-purity Fe4N powder is obtained. After testing, the purity of the Fe4N powder obtained in this example is 99.8%, and the powder particle size D50 = 3 μm.

[0027] Example 2

[0028] The preparation method of high-purity Fe4N powder in this example includes the following steps:

[0029] (1) The particle size of high-purity iron powder (purity 99.9%) is controlled by air classification to obtain iron powder raw materials with a particle size D50 = 35 μm.

[0030] (2) Ceramic powder with D50 = 40 μm is added to the iron powder to obtain a mixed powder. Among them, the addition amount of the ceramic powder is 50% of the mass of the iron powder raw materials, and the ceramic powder is composed of silicon oxide powder and mullite powder mixed in a mass ratio of 3:1.

[0031] (3) 3% of the mass of the mixed powder of organosilicon resin powder is added to the mixed powder as a binder and 0.5% of the mass of the mixed powder of zinc stearate is added as a release agent and mixed evenly. Subsequently, it is pressed into a cube block with a length of 10 mm, a width of 10 mm, and a height of 10 mm under a pressure of 800 MPa.

[0032] (4) The cube block is heat-treated in a nitrogen protection furnace at 600 °C for 1 h to fully decompose the binder and release agent in the block, obtaining a porous material with a large number of pores.

[0033] (5) The porous material is placed in a tube furnace, and hydrogen is introduced for reduction treatment. The reduction treatment temperature is 850 °C, and the treatment time is 8 h.

[0034] (6) After the reduction treatment is completed, without taking out the porous material, the gas introduced into the furnace is directly replaced with an ammonia-hydrogen mixed gas with a volume ratio of ammonia to hydrogen of 5:1, and the material is nitrided. The nitridation treatment temperature is 600 °C, and the treatment time is 8 h.

[0035] (7) After the nitridation is completed, the porous material is taken out of the tube furnace, crushed using a mortar, and the ceramic powder therein is separated by magnetic separation, that is, high-purity Fe4N powder is obtained. After testing, the purity of the Fe4N powder obtained in this example is 91.6%, and the powder particle size D50 = 35 μm.

[0036] Example 3

[0037] The preparation method of high-purity Fe4N powder in this example includes the following steps:

[0038] (1) The particle size of high-purity iron powder (purity 99.9%) is controlled by air classification to obtain an iron powder raw material with a particle size D50 = 20 μm.

[0039] (2) Ceramic powder with D50 = 22 μm is added to the iron powder raw material to obtain a mixed powder. Among them, the addition amount of the ceramic powder is 35% of the mass of the iron powder raw material, and the ceramic powder is composed of molybdenum disilicide powder and silicon nitride powder mixed in a mass ratio of 2:1.

[0040] (3) 8% of the mass of the mixed powder of organosilicon resin powder is added to the mixed powder as a binder and 1% of the mass of the mixed powder of zinc stearate is added as a release agent and mixed evenly. Subsequently, it is pressed into a cube block with a length of 5 mm, a width of 5 mm, and a height of 10 mm under a pressure of 600 MPa.

[0041] (4) The cube block is heat-treated in a nitrogen protection furnace at 400 °C for 5 h to fully decompose the binder and release agent in the block, obtaining a porous material with a large number of pores.

[0042] (5) The porous material is placed in a tube furnace, and hydrogen is introduced for reduction treatment. The reduction treatment temperature is 400 °C, and the treatment time is 4 h.

[0043] (6) After the reduction treatment is completed, without taking out the porous material, the gas introduced into the furnace is directly replaced with an ammonia-hydrogen mixed gas with a volume ratio of ammonia to hydrogen of 3:1, and the material is nitrided. The nitriding treatment temperature is 750 °C, and the treatment time is 4 h.

[0044] (7) After nitriding is completed, the porous material is taken out of the tube furnace, crushed with a mortar, and the ceramic powder in it is separated by magnetic separation to obtain high-purity Fe4N powder. After testing, the purity of the Fe4N powder obtained in this example is 94.5%, and the powder particle size D50 = 20 μm.

[0045] The method of the present invention obtains a porous material with a large number of pores by mixing iron powder, ceramic powder, binder and release agent, pressing them into a block and performing high-temperature treatment. Such materials are extremely easy to be nitrided in subsequent processing, thereby obtaining Fe4N powder with extremely high purity. As Figure 1 shown, by controlling various parameters in the nitriding process, the present invention can nitride micron-scale iron powder into high-purity Fe4N powder with a purity of 99.8%.

Claims

1. A method for preparing high-purity Fe4N powder, characterized in that: The steps include: (1) controlling the particle size of high-purity iron powder by airflow classification to obtain iron powder raw material; (2) adding ceramic powder to the iron powder raw material, wherein the amount of ceramic powder added is 10 to 60% of the mass of the iron powder to obtain a mixed powder; (3) adding a binder accounting for 2 to 15% of the mass of the mixed powder and a release agent accounting for 0.3 to 2% of the mass of the mixed powder to the mixed powder and mixing them thoroughly, and then pressing them into cubic blocks at a pressure of 200 to 800 MPa; (4) heat treating the cubic block material in an inert gas protection furnace at 200 to 600° C. for 1 to 5 hours to fully decompose the binder and the release agent in the block material to obtain a porous material containing a large number of pores; (5) placing the porous material into a tubular furnace and introducing hydrogen for reduction treatment at a temperature of 400 to 850° C. for a treatment time of 2 to 8 hours; (6) After the reduction treatment is completed, the gas introduced into the furnace is directly replaced with an ammonia-hydrogen mixed gas to perform nitriding treatment on the material. The nitriding treatment temperature is 500-750°C and the treatment time is 4-10 hours; (7) After nitridation is completed, the porous material is taken out from the tube furnace, crushed with a mortar, and the ceramic powder therein is separated by a magnetic separation method to obtain high-purity Fe4N powder.

2. The preparation method according to claim 1, characterized in that: In step (1), the particle size range of the iron powder raw material obtained after particle size control is D50=2 to 35 μm.

3. The preparation method according to claim 1, characterized in that: In step (2), the D50 of the particle size distribution of the ceramic powder is the D50 of the particle size distribution of the iron powder raw material + 2 to 5 μm.

4. The preparation method according to claim 1, characterized in that: In step (2), the ceramic powder is at least one of aluminum oxide, zirconium oxide, magnesium oxide, yttrium oxide, silicon carbide, silicon nitride, boron nitride, molybdenum disilicide or mullite.

5. The preparation method according to claim 1, characterized in that: In step (3), the length of any side of the cubic block is 1 to 20 mm.

6. The preparation method according to claim 1, characterized in that: In step (6), the volume ratio of ammonia to hydrogen in the ammonia-hydrogen mixed gas is 1 to 10:

1.

7. The preparation method according to claim 1, characterized in that: In step (7), the purity of the obtained Fe4N powder is 90.0-99.9%.

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