A preparation process for micron-sized single-phase Fe4N powder

Abstract

The application relates to a preparation process of micron-level single-phase Fe4N powder and belongs to the field of magnetic materials. The operation steps are as follows: (1) hydrogen reduction pretreatment is carried out on iron powder to obtain reduced iron powder; (2) the reduced iron powder is added into ethanol, ultrasonic dispersion is carried out, and drying is carried out to obtain pretreated iron powder; (3) a reaction bed is formed in a tube furnace, reaction gas is introduced for nitriding reaction, the reaction gas is a mixed gas of ammonia, water vapor and hydrogen, and the single-phase iron four nitrogen powder is obtained through furnace cooling. The application realizes the preparation of single-phase iron four nitrogen material with a large size in the micron level, the overall preparation method has a simple and efficient process flow, and the cost is relatively low.

Description

Technical Field

[0001] This invention belongs to the field of magnetic materials, specifically relating to a preparation process for micron-sized single-phase Fe4N powder. Background Technology

[0002] Fe4N belongs to the Fe-N alloy system and is a metallic magnetic material with excellent magnetic properties, mechanical properties, microwave absorption performance, and high thermal stability. It shows promising application prospects in consumer electronics, motors, electromagnetic shielding, and military industries. Currently, Fe-N alloys are mainly prepared through nitriding processes, including gas nitriding, high-pressure nitriding, plasma nitriding, laser nitriding, and magnetron sputtering. Fe-N alloys include various phase structures (Fe2N, Fe3N, Fe4N, Fe...). 16 Different phase structures (such as N2) correspond to different nitrogen (N) element contents, resulting in a very narrow composition range. If a certain preparation process causes a specific concentration distribution of N element along the thickness of the sample, it is difficult to fabricate a single-phase Fe-N alloy with a particular phase structure. Therefore, for Fe4N alloys, most currently disclosed preparation techniques can only achieve a relatively uniform N element concentration distribution within a very small size range, such as the submicron scale, thus enabling the preparation of single-phase Fe4N phase structures. For example, some literature reports the use of molecular beam epitaxy, magnetron sputtering, and pulsed laser deposition to prepare single-phase Fe4N films with thicknesses in the nanometer and submicron scales. However, the small size in the nanometer and submicron scales leads to very weak magnetic signals in the relevant Fe4N samples, significantly increasing the difficulty of preparing related powder metallurgy products, thus greatly limiting the application of the excellent magnetic properties of Fe4N materials. To prepare single-phase Fe4N materials in the micrometer scale and larger size ranges, researchers have tried many methods. These include methods combining high-energy ball milling with high-pressure nitriding at 20 atmospheres, plasma nitriding, and laser nitriding. Unfortunately, for samples with dimensions at the micrometer scale and above, most processing methods can only obtain composite materials in which the Fe4N phase coexists with one or more other phases such as Fe2N, Fe3N, and Fe, making it difficult to fabricate large-sized single-phase Fe4N materials. However, the presence of other Fe-N alloy phases can affect the realization of the superior properties of Fe4N materials. Currently, only a very few publications report the use of a mixed atmosphere of ammonia and hydrogen to heat-treat iron powder to obtain micrometer-sized single-phase Fe4N materials, but this requires strict control of the ammonia and hydrogen ratio, and different researchers often cannot replicate the preparation of micrometer-sized single-phase Fe4N materials under similar experimental conditions. Clearly, how to achieve stable preparation of larger single-phase Fe4N materials at the sub-micrometer scale and above is a current challenge in Fe-N material research and urgently needs to be addressed. Summary of the Invention

[0003] This invention proposes a preparation process for micron-sized single-phase Fe4N powder to solve the problem of how to prepare large-size single-phase Fe4N materials at the submicron level or above in current Fe-N material research.

[0004] The present invention solves the practical technical problem by adopting the following technical solution:

[0005] Step S1: Place iron powder with a particle size within a certain range into a tube furnace, heat treat it at a certain temperature for a certain time under an ammonia atmosphere, and then cool it with the furnace to obtain preliminary nitriding iron powder.

[0006] Step S2: Add the pre-nitrided iron powder to ethanol, disperse it in an ultrasonic machine, and finally dry it to obtain pretreated iron powder.

[0007] Step S3: After sieving the pretreated iron powder, place it in a tube furnace that rotates continuously at a certain speed to form a reaction bed. At a certain reaction temperature, introduce reaction gas into the reaction bed for nitriding. According to the different particle sizes of the iron powder participating in the reaction, set different reaction gas flow rates and different nitriding reaction times. After the reaction is completed, cool with the furnace to obtain single-phase Fe4N powder.

[0008] As a preferred embodiment, in step S1, the particle size of the iron powder ranges from 1 to 30 μm.

[0009] As a preferred embodiment, in step S1, the temperature and time of the heat treatment under the ammonia atmosphere are 300-400℃ and 2-4h, respectively.

[0010] As a preferred embodiment, in step S2, the ultrasonic time is 45 minutes, the drying temperature is 60-80℃, and the drying time is 4-6 hours.

[0011] As a preferred embodiment, in step S3, the sieve mesh size is 80 mesh and the rotation speed of the tube furnace is 25 r / min.

[0012] As a preferred embodiment, in step S3, the reaction temperature is 400-750℃ and the nitriding reaction time is 4-72h.

[0013] As a preferred embodiment, in step S3, the reaction gas is a mixture of ammonia, water vapor, and hydrogen.

[0014] As a preferred embodiment, in step S3, the flow rate ratio of ammonia, water vapor, and hydrogen in the reaction gas is (1-3):(1-2):(1-2).

[0015] As a preferred embodiment, in step S3, the water vapor flow rate in the reaction gas is reduced to 0 after half of the reaction time has elapsed.

[0016] Compared with existing technologies, the present invention has the following advantages:

[0017] (1) The preparation method of the present invention pre-treats iron powder with ammonia gas to form a certain nitrogen concentration distribution in the near-surface region of the powder, which helps to improve the nitriding surface activity of the powder and promote the uniformity of nitrogen diffusion in subsequent secondary nitriding.

[0018] (2) The present invention breaks up the uneven agglomeration between some iron powders by means of ultrasound, so that the powder is dispersed as evenly as possible, reducing large-sized agglomerates and ensuring the uniformity of subsequent reactions.

[0019] (3) In the preparation method of the present invention, the tube furnace rotates continuously and at a constant speed throughout the reaction process, which avoids the powder pressed at the bottom layer during the static reaction from not being able to fully contact the reaction gas, and ensures that all powders can be uniformly contacted with the reaction gas during the reaction process. This solves the problem of insufficient reaction and the occurrence of multiple phase structures caused by the concentration gradient of nitrogen element in the sample thickness direction in the traditional nitriding technology.

[0020] (4) In the preparation method of the present invention, a mixed gas of ammonia, water vapor, and hydrogen is used for the nitriding reaction. Ammonia provides the nitrogen source, water vapor oxidizes the iron powder, and hydrogen reduces the iron powder. The advantages of this reaction mechanism are: on the one hand, the combined effect of oxidation and reduction by water vapor and hydrogen helps to appropriately loosen the dense structure of the iron powder, opening the diffusion path of nitrogen into the iron powder at the microscopic level, thereby helping to improve the penetration and diffusion efficiency of nitrogen into the iron powder. This measure, together with the preliminary nitriding treatment, avoids the formation of too large a concentration gradient of nitrogen in the diffusion path; on the other hand, the fresh iron powder that has undergone continuous oxidation and reduction reactions will always maintain high activity during the reaction process, thus helping to significantly improve the efficiency of the nitriding reaction. Obviously, this invention addresses the problem of large concentration gradient distribution of nitrogen in the diffusion path, which is difficult to solve in the traditional nitriding process for large-size iron powder, resulting in the formation of multiple Fe-N phase structures in the diffusion path. By using a triple combination reaction of oxidation, reduction, and nitriding, the diffusion efficiency of nitrogen is improved, effectively avoiding the problem of uneven nitrogen distribution in the diffusion path of large-size processes in traditional nitriding processes, thus helping to achieve the preparation of micron-sized single-phase Fe4N powder.

[0021] (5) In the preparation method of this invention, for iron powders with different particle sizes, the reactivity and micro-loosening degree of the iron powder can be flexibly controlled by simply adjusting the initial nitriding temperature and time, as well as the flow rate ratio of the mixed gas of ammonia, water vapor, and hydrogen during high-temperature nitriding and the reaction time. This achieves uniform diffusion of nitrogen into the iron powder and high-efficiency nitriding reaction, thereby enabling the preparation of large-sized single-phase Fe4N materials at the micrometer level. The overall preparation method has a simple and efficient process flow, low cost, and a wide range of flow rate ratios for the three gases (ammonia, water vapor, and hydrogen), which is also convenient for control in mass production. Attached Figure Description

[0022] Figure 1 The image shows the X-ray diffraction pattern of the single-phase Fe4N powder prepared in Example 1 of this invention.

[0023] Figure 2 This is a scanning electron microscope image of the single-phase Fe4N powder prepared in Example 1 of the present invention.

[0024] Figure 3 The image shows the X-ray diffraction pattern of the single-phase Fe4N powder prepared in Example 2 of this invention.

[0025] Figure 4 This is a scanning electron microscope image of the single-phase Fe4N powder prepared in Example 2 of the present invention.

[0026] Figure 5 The image shows the X-ray diffraction pattern of the single-phase Fe4N powder prepared in Example 3 of this invention.

[0027] Figure 6 This is a scanning electron microscope image of the single-phase Fe4N powder prepared in Example 3 of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Example 1:

[0030] Step S1: Place iron powder with a median particle size of 3 μm in a tube furnace and heat treat it at 400°C for 2 hours under an ammonia atmosphere. Then cool it with the furnace to obtain preliminary nitriding iron powder.

[0031] Step S2: Take 100g of the pre-nitrided iron powder and add it to ethanol. Disperse it in an ultrasonic machine for 45min and finally dry it at 60℃ for 4h to obtain pretreated iron powder.

[0032] Step S3: After passing the pretreated iron powder through an 80-mesh sieve, place it in a tube furnace with a rotation speed of 25 r / min to form a reaction bed. At 400°C, a mixture of ammonia, water vapor, and hydrogen is introduced into the reaction bed at a flow rate ratio of 1:1:2 and reacted for 8 hours. Then, the water vapor flow rate is reduced to 0 and the reaction continues for another 8 hours. After that, the furnace is cooled to obtain single-phase Fe4N powder.

[0033] The X-ray diffraction pattern and scanning electron microscope image of the single-phase Fe4N powder prepared in this embodiment are as follows: Figure 1 and Figure 2 As shown, the obtained powder has a single-phase Fe4N structure with a particle size on the micrometer scale.

[0034] The magnetic properties of the single-phase Fe4N powder prepared in this embodiment, as measured by a vibrating sample magnetometer, are shown in Table 1. At 25℃, the coercivity Hc = 15.22 Oe and the saturation magnetization Ms = 180.32 emu / g, exhibiting strong anti-saturation ability and high saturation magnetization.

[0035] Table 1 compares the coercivity and saturation magnetization of the single-phase Fe4N powders prepared in Examples 1-3 of this invention.

[0036]

[0037] Example 2:

[0038] Step S1: Place iron powder with a median particle size of 15 μm in a tube furnace and heat treat it at 350°C for 2.5 h in an ammonia atmosphere, then cool it with the furnace to obtain preliminary nitriding iron powder.

[0039] Step S2: Take 80g of the pre-nitrided iron powder and add it to ethanol. Disperse it in an ultrasonic machine for 45min and finally dry it at 70℃ for 4.5h to obtain pretreated iron powder.

[0040] Step S3: After passing the pretreated iron powder through an 80-mesh sieve, place it in a tube furnace with a rotation speed of 25 r / min to form a reaction bed. At 500°C, a mixture of ammonia, water vapor, and hydrogen is introduced into the reaction bed at a flow rate ratio of 2:1.5:1.5 and reacted for 25 h. Then, the water vapor flow rate is reduced to 0 and the reaction continues for another 25 h. After that, the furnace is cooled to obtain single-phase Fe4N powder.

[0041] The X-ray diffraction pattern and scanning electron microscope image of the single-phase Fe4N powder prepared in this embodiment are as follows: Figure 3 and Figure 4 As shown, the obtained powder has a single-phase Fe4N structure with a particle size on the micrometer scale.

[0042] The magnetic properties of the single-phase Fe4N powder prepared in this embodiment, as measured by a vibrating sample magnetometer, are shown in Table 1. At 25℃, the coercivity Hc = 12.45 Oe and the saturation magnetization Ms = 187.26 emu / g, exhibiting strong anti-saturation ability and high saturation magnetization.

[0043] Example 3:

[0044] Step S1: Place iron powder with a median particle size of 30 μm in a tube furnace and heat treat it at 300°C for 4 hours under an ammonia atmosphere. Then cool it with the furnace to obtain preliminary nitriding iron powder.

[0045] Step S2: Take 60g of the pre-nitrided iron powder and add it to ethanol. Disperse it in an ultrasonic machine for 45min and finally dry it at 80℃ for 6h to obtain pretreated iron powder.

[0046] Step S3: After passing the pretreated iron powder through an 80-mesh sieve, place it in a tube furnace with a rotation speed of 25 r / min to form a reaction bed. At 750°C, a mixture of ammonia, water vapor, and hydrogen is introduced into the reaction bed at a flow rate ratio of 3:2:1 and reacted for 36 h. Then, the water vapor flow rate is reduced to 0 and the reaction continues for another 36 h. Afterward, the furnace is cooled to obtain single-phase Fe4N powder.

[0047] The X-ray diffraction pattern and scanning electron microscope image of the single-phase Fe4N powder prepared in this embodiment are as follows: Figure 5 and Figure 6 As shown, the obtained powder has a single-phase Fe4N structure with a particle size on the micrometer scale.

[0048] The magnetic properties of the single-phase Fe4N powder prepared in this embodiment, as measured by a vibrating sample magnetometer, are shown in Table 1. At 25°C, the coercivity Hc = 10.56 Oe and the saturation magnetization Ms = 195.43 emu / g, exhibiting strong anti-saturation ability and high saturation magnetization.

[0049] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

Claims

1. A process for the production of a micrometric single-phase Fe4N powder, characterized in that, The method comprises the following steps: S1, iron powder with a certain particle size range is placed in a tube furnace, and is heat treated at a certain temperature for a certain time under ammonia atmosphere, and then is cooled with the furnace to obtain preliminary nitriding iron powder; S2, the preliminary nitriding iron powder is added into ethanol, and is dispersed in an ultrasonic machine, and finally is dried to obtain pretreated iron powder; S3, the pretreated iron powder is sieved and is placed in a tube furnace rotating at a certain speed to form a reaction bed, and a reaction gas is introduced into the reaction bed to perform nitriding at a certain reaction temperature, different reaction gas flow rate ratios and different nitriding reaction times are set according to different particle sizes of the iron powder participating in the reaction, and the reaction is completed, and then the reaction bed is cooled with the furnace to obtain single-phase Fe4N powder.

2. The process for preparing a micrometer-scale single-phase Fe4N powder according to claim 1, characterized by, The particle size of the iron powder ranges from 1 to 30 μm.

3. The process for preparing a micrometer-scale single-phase Fe4N powder according to claim 1, characterized by, The temperature and time of the heat treatment under ammonia atmosphere are 300-400 ℃ and 2-4 h respectively.

4. The process for preparing a micrometer-scale single-phase Fe4N powder according to claim 1, characterized by, The ultrasonic time is 45 min, the drying temperature is 60-80 ℃, and the drying time is 4-6 h.

5. The process for preparing a micrometer-scale single-phase Fe4N powder according to claim 1, characterized by, The mesh number of the sieve is 80 meshes, and the rotating speed of the tube furnace is 25 r / min.

6. The process for preparing a micrometer-scale single-phase Fe4N powder according to claim 1, characterized by, The reaction temperature is 400-750 ℃, and the nitriding reaction time is 4-72 h.

7. The process for preparing a micrometer-scale single-phase Fe4N powder according to claim 1, characterized by, The reaction gas is a mixture of ammonia, water vapor and hydrogen.

8. The process for preparing a micrometer-scale single-phase Fe4N powder according to claim 1, characterized by, The flow rate ratio of ammonia, water vapor and hydrogen in the reaction gas is (1-3) : (1-2) : (1-2).

9. The process for preparing a micrometer-scale single-phase Fe4N powder according to claim 1, characterized by, The flow rate ratio of water vapor in the reaction gas is lowered to 0 when the reaction time reaches half.

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