Method for modifying surface of carbonyl iron powder through high-temperature inert treatment

Abstract

The invention relates to the technical field of wave-absorbing materials, and provides a modification method for high-temperature inert treatment of the surface of carbonyl iron powder. The modification method comprises the following steps: carrying out ball milling treatment on carbonyl iron powder, absolute ethyl alcohol and zirconium oxide balls to obtain ball-milled carbonyl iron powder; adopting absolute ethyl alcohol to separate the ball-milled carbonyl iron powder and zirconium oxide balls, centrifuging or standing, drying, and screening to obtain loose carbonyl iron powder; the obtained carbonyl iron powder is placed in a high-temperature tube furnace, then CO is introduced before the high-temperature tube furnace is heated to 600 DEG C, N2 is introduced after the high-temperature tube furnace is heated to 600 DEG C, heat preservation is carried out for 1-2 h, cooling is carried out, carbonyl iron powder with an iron nitrogen compound FexN generated on the surface is obtained, screening treatment is carried out, and the corrosion-resistant wave-absorbing material is obtained. The carbonyl iron powder obtained through the modification method is the carbonyl iron powder with an iron nitrogen compound FexN film generated on the surface, a coating layer and carbonyl iron are tightly combined, good corrosion resistance, oxidation resistance and adjustable wave absorbing performance are achieved, and the service life of a carbonyl iron powder absorbent is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave absorbing materials, and particularly relates to a modification method for treating the surface of carbonyl iron powder at high temperature and in an inert atmosphere. Background Art

[0002] With the rapid development of electronic information technology and communication technology, the widespread application of electronic devices has caused electromagnetic pollution problems. This not only interferes with the normal operation of devices but also poses risks to human health and the ecological system. At the same time, the demand for stealth materials in the military field continues to rise, and the research and development of high-performance microwave absorbing materials have become an important topic.

[0003] Microwave absorbing materials are mainly divided into dielectric loss type and magnetic loss type according to the loss type. Dielectric loss type microwave absorbing materials include carbon fiber, conductive polymers, graphite, etc.; magnetic loss type microwave absorbing materials cover carbonyl iron powder, ferrite, metal ultrafine powder, etc. Among them, carbonyl iron powder is the most widely used absorber. In China, the preparation process of carbonyl iron powder is mature, and it has electromagnetic property advantages such as high saturation magnetization intensity, high Curie temperature, and good magnetic permeability dispersion characteristics. However, with the increasingly complex application scenarios of microwave absorbing materials, the disadvantages of the active chemical properties of carbonyl iron gradually emerge. In corrosive environments such as high temperature and high humidity, carbonyl iron powder is easily eroded, resulting in changes in chemical composition and electromagnetic properties, and further leading to a decline in microwave absorbing performance, which limits its long-term use effect. Therefore, improving the corrosion resistance of carbonyl iron powder has become an urgent technical problem to be solved.

[0004] Currently, the chemical coating method is a commonly used means to improve the corrosion resistance and oxidation resistance of carbonyl iron powder, including sol-gel method, emulsion polymerization method, graft polymerization method, in-situ polymerization method, etc. These methods can form an inorganic layer (such as silica, graphene) or an organic layer (polyaniline, polypyrrole, organosilane) on the surface of carbonyl iron powder. Although it can enhance the corrosion resistance of the material, there are disadvantages in chemical coating modification, and there is often a problem of poor bonding between the coating layer and carbonyl iron.

[0005] In view of this, this invention is specifically proposed. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned disadvantages of the prior art and provide a modification method for treating the surface of carbonyl iron powder at high temperature and in an inert atmosphere, which solves the problem of poor bonding between the coating layer and carbonyl iron and improves the corrosion resistance and oxidation resistance of carbonyl iron powder.

[0007] The purpose of the present invention is solved by the following technical solutions:

[0008] The present invention provides a modification method for treating the surface of carbonyl iron powder at high temperature and in an inert atmosphere, including the following steps:

[0009] S1. Add carbonyl iron powder, absolute ethanol, and zirconia balls into a ball mill tank according to a mass ratio of 1:(0.6 - 1):(2 - 3), and conduct ball milling treatment to obtain ball-milled carbonyl iron powder.

[0010] S2. Use absolute ethanol to separate the ball-milled carbonyl iron powder and zirconia balls in S1. After centrifugation or standing, conduct drying treatment, and then obtain loosened carbonyl iron powder through filtration and screening, and spread it in a crucible.

[0011] S3. First, place the crucible with carbonyl iron powder in S2 into a high-temperature tube furnace. Subsequently, introduce a mixed gas of CO and N2 into the high-temperature tube furnace, and keep the N2 valve closed before the temperature of the high-temperature tube furnace rises to 600°C.

[0012] S4. After the high-temperature tube furnace heats up to 600°C, introduce N2 and adjust the flow ratio of CO and N2 to (8 - 10):1, keep the temperature for 1 h - 2 h, and obtain carbonyl iron powder with iron nitride compound Fe x N formed on the surface after cooling.

[0013] S5. Conduct screening treatment on the carbonyl iron powder with iron nitride compound Fe x N formed on the surface to obtain a corrosion-resistant wave-absorbing material.

[0014] Furthermore, in S1, the stirring speed of the ball milling treatment is 150 r / min - 180 r / min, and the time is 4 h - 6 h.

[0015] Furthermore, the ball-milled carbonyl iron powder in S1 is flaky carbonyl iron powder.

[0016] Furthermore, in S2, the temperature of the drying treatment is 50°C - 80°C, and the time is 3 h - 6 h; a sieve mesh with a size of ≥100 meshes is used for the filtration and screening treatment.

[0017] Furthermore, the thickness of the carbonyl iron powder spread in the crucible in S2 is ≤15 mm.

[0018] Furthermore, in S3, the molar ratio of CO to N2 in the mixed gas of CO and N2 is (8 - 10):1.

[0019] Furthermore, in S3, first evacuate the internal pressure of the high-temperature tube furnace to ≤0.1 bar, then introduce CO into the high-temperature tube furnace and circulate CO three times to displace the miscellaneous gas. Subsequently, continuously introduce CO into the high-temperature tube furnace, and set the flow rate to 80 sccm - 160 sccm.

[0020] Furthermore, in S4, the heating rate of the high-temperature tube furnace when heating up to 600°C is 5°C / min - 10°C / min; the flow rate of the introduced N2 is set to 8 sccm - 20 sccm.

[0021] Furthermore, the carbonyl iron powder described in S4 decomposes into Fe and CO under high-temperature conditions, and the introduced CO can inhibit the decomposition reaction of the carbonyl iron powder.

[0022] Furthermore, the sieving process described in S5 uses a sieve mesh with 200 to 400 meshes.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. By controlling parameters such as temperature, time, and protective atmosphere during high-temperature treatment, the present invention can well inhibit a series of adverse changes of carbonyl iron powder at high temperature, and at the same time, in-situ self-generated iron nitride Fe x N is formed on its surface to improve the corrosion resistance and oxidation resistance of the carbonyl iron powder. The high-temperature treatment temperature is selected as 600 °C, which is the critical temperature value for the reaction of N2 and carbonyl iron, and at the same time, it can avoid the occurrence of over-sintering; by freely controlling the high-temperature treatment time to be 1 h to 2 h, the thickness of the Fe x N layer can be controlled, and then the electromagnetic properties and corrosion resistance and oxidation resistance of the carbonyl iron powder can be balanced and regulated; the high-temperature atmosphere selects CO as the main component, which can not only greatly inhibit the forward occurrence of the decomposition reaction of the carbonyl iron powder, but also reduce the oxide impurities formed on its surface during the preparation, transportation, and storage of the carbonyl iron powder due to its strong reducibility, thereby improving the electromagnetic properties of the carbonyl iron powder. And N2, as the secondary component of the high-temperature atmosphere, is mainly responsible for reacting with Fe to produce the inert iron nitride film Fe x N. Moreover, the molar masses and densities of CO and N2 are almost the same. Mixing them as the high-temperature atmosphere can be used without being restricted by the specifications of the high-temperature vacuum furnace, and can avoid obvious physical stratification phenomena between different atmospheres when the capacity of the high-temperature vacuum furnace is too large and the atmosphere flow rate is relatively low, thus ensuring the uniformity of the effect of high-temperature surface inert treatment of carbonyl iron powder.

[0025] 2. The Fe x N film formed on the surface of the carbonyl iron powder of the present invention can not only meet the purpose of improving the corrosion resistance and oxidation resistance of carbonyl iron by conventional chemical coating, and the main component element Fe of the film comes from the carbonyl iron powder itself. The in-situ self-generated Fe x N film on the carbonyl iron matrix has a higher bonding strength with the carbonyl iron matrix compared with conventional chemical coating, so as to avoid stress imbalance between the matrix and the film caused by harsh environments such as mechanical shock and thermal shock, and thus can better avoid the risk of the film peeling off from the matrix, further extending the service life of the carbonyl iron powder absorbent.

[0026] 3. The present invention can make the wave absorption performance of carbonyl iron powder have a certain degree of adjustability. Generally, after ball milling, the carbonyl iron powder will increase its magnetic loss ability due to the increase in its aspect ratio. When used as an absorber under the same conditions, the absorption band will shift towards the low frequency. For the carbonyl iron powder after high-temperature surface inert treatment, since an inert Fe x N layer is added on its surface, the eddy current effect on the surface of the carbonyl iron powder is inhibited to a certain extent, and the absorption peak will shift towards the high frequency. In actual production, the wave absorption performance of the carbonyl iron powder can be adjusted by finely tuning the process parameters of high-temperature surface treatment and ball milling, such as ball milling time, high-temperature treatment time, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings here are incorporated into the specification and form a part of this specification, and are used together with the specification to explain the principle of the present invention.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 is a flow chart of the modification method for the surface of carbonyl iron powder by high-temperature and inert treatment of the present invention;

[0030] Figure 2 is a SEM scanning electron micrograph of the spherical carbonyl iron powder provided by the present invention;

[0031] Figure 3 is a SEM scanning electron micrograph of the flaky carbonyl iron powder after ball milling without high-temperature surface inert treatment provided by the present invention;

[0032] Figure 4 is a SEM scanning electron micrograph of the flaky carbonyl iron powder after ball milling and high-temperature surface inert treatment provided by the present invention;

[0033] Figure 5 is a comparison diagram of the magnetic permeability of the flaky carbonyl iron powder and the spherical carbonyl iron powder after high-temperature surface inert treatment provided by the present invention;

[0034] Figure 6 is a comparison diagram of the reflectivity of the flaky carbonyl iron powder and the spherical carbonyl iron powder after high-temperature surface inert treatment provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] Here, exemplary embodiments will be described in detail, and examples thereof are shown in the accompanying drawings. When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. On the contrary, they are merely examples consistent with some aspects of the present invention detailed in the appended claims.

[0036] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0037] The present invention provides a method for modifying the surface of carbonyl iron powder by high-temperature and inert treatment. Refer to Figure 1-6 As shown, it includes the following steps:

[0038] S1. Pre-ball milling of carbonyl iron powder.

[0039] Select common commercially available ordinary spherical carbonyl iron powder formed by gas atomization.

[0040] Specifically: Add carbonyl iron powder, absolute ethanol, and zirconia balls to the ball mill tank according to a mass ratio of 1:(0.6 - 1):(2 - 3), set the stirring speed of the ball mill to 150 r / min - 180 r / min, and perform stirring ball milling treatment for 4 h - 6 h. During the ball milling process, the collision between the zirconia balls and the carbonyl iron powder causes the microstructure of the carbonyl iron powder to change, promoting the formation of flakiness on its surface. Through this process, carbonyl iron powder with a certain degree of flakiness is finally obtained. The increase in the aspect ratio of the carbonyl iron powder is beneficial to enhancing its magnetic loss ability in electromagnetic wave absorption materials.

[0041] S2. Drying and loosening treatment of carbonyl iron powder.

[0042] Specifically: First, use absolute ethanol to separate the ball-milled carbonyl iron powder and zirconia balls in S1 to obtain a suspension of carbonyl iron powder and ethanol; after centrifugation or standing treatment, when the carbonyl iron powder has settled, initially separate the absolute ethanol and the carbonyl iron powder; then place the separated carbonyl iron powder in a blast drying oven, set the temperature to 50°C - 80°C, and continuously blast dry for 3 h - 6 h until the carbonyl iron powder is in a sufficiently dry state; subsequently, filter and screen the dried carbonyl iron powder through a sieve with a mesh size of ≥100 meshes; finally, evenly spread the sieved and loose carbonyl iron powder in a high-temperature crucible, and keep the average thickness of the laid carbonyl iron powder ≤15 mm.

[0043] S3. Preparation of the atmosphere in the high-temperature tube furnace.

[0044] Specifically: First, place the crucible with carbonyl iron powder in S2 in a high-temperature tube furnace, and avoid multiple or strong vibrations during the process. Select CO and N2 as the high-temperature atmosphere. Among them, the molar ratio of CO to N2 is (8 - 10):1. At the same time, connect the two gases to the high-temperature tube furnace and keep the N2 valve open before the temperature rises to 600°C. Before introducing gas into the high-temperature tube furnace, ensure that the high-temperature tube furnace has good airtightness. Use an air pump to pump the high-temperature tube furnace to near vacuum inside. After the internal pressure of the high-temperature tube furnace reaches ≤0.1 bar, introduce CO into the high-temperature tube furnace. After the internal pressure is the same as the atmospheric pressure, continue to pump to vacuum and then introduce CO. Repeat this process three times to discharge O2 and other miscellaneous gases inside the high-temperature tube furnace to prevent other chemical reactions of carbonyl iron powder under high-temperature conditions. Finally, continuously introduce CO into the high-temperature tube furnace, and set the flow rate to 80 sccm - 160 sccm.

[0045] S4. High-temperature inert treatment of the surface of carbonyl iron powder.

[0046] Specifically: First, set the heating and cooling rate of the high-temperature tube furnace to 5°C / min - 10°C / min. After the high-temperature tube furnace heats up to 600°C, open the N2 valve, set the flow rate to 8 sccm - 20 sccm, and ensure that the flow rate ratio of CO to N2 is (8 - 10):1. Keep the temperature for 1 h - 2 h, and then cool down to room temperature to obtain carbonyl iron powder with iron nitride Fe x N formed on the surface.

[0047] At high temperature, carbonyl iron powder will decompose into Fe and CO. Since the main component of the introduced atmosphere is CO, the forward decomposition reaction of carbonyl iron powder is inhibited. A small amount of Fe produced after the decomposition of carbonyl iron powder undergoes an in-situ self-generation reaction with N2 on the surface of carbonyl iron powder to form iron nitride Fe x N. At the same time, CO can reduce a small amount of oxides formed on the surface of carbonyl iron powder during the preliminary preparation process at high temperature, improving the purity of carbonyl iron powder.

[0048] S5. Obtain a corrosion-resistant wave-absorbing material.

[0049] Specifically: After taking out the carbonyl iron powder with iron nitride Fe x N formed on the surface in S4, perform sieving treatment with 200 - 400 meshes. Since some compacted carbonyl iron powder may sinter during the high-temperature treatment process, the carbonyl iron powder under the sieve is taken as the qualified corrosion-resistant wave-absorbing material.

[0050] To verify the beneficial effects brought by the modification method of the present invention, it is further illustrated through the following examples.

[0051] Example 1

[0052] This embodiment provides a method for modifying the surface of carbonyl iron powder at high temperature under inert conditions, including the following steps:

[0053] S1. Pre-ball milling of carbonyl iron powder.

[0054] First, weigh 1000 g of carbonyl iron powder, 600 g of absolute ethanol, and 2500 g of zirconia balls, add them to a 2 L ball milling tank, set the stirring speed of the ball mill to 160 r / min, and perform stirring ball milling for 5 h. During the ball milling process, the collision between the zirconia balls and the carbonyl iron powder causes changes in the microstructure of the carbonyl iron powder, obtaining carbonyl iron powder with a certain degree of flakiness.

[0055] S2. Drying and loosening treatment of carbonyl iron powder.

[0056] First, use absolute ethanol to separate the ball-milled carbonyl iron powder and zirconia balls in S1 to obtain a suspension of carbonyl iron powder and ethanol; after centrifugation or standing treatment, when the carbonyl iron powder has settled, perform preliminary separation of the absolute ethanol and the carbonyl iron powder; then place the separated carbonyl iron powder in a blast drying oven, set the temperature to 60 °C, and continuously blast dry for 4 h; subsequently, filter and screen the dried carbonyl iron powder through a sieve with a mesh size of ≥100 meshes; finally, evenly spread the sieved and loose carbonyl iron powder in a high-temperature crucible, and keep the average thickness of the laid carbonyl iron powder ≤15 mm.

[0057] S3. Preparation of the atmosphere in the high-temperature tube furnace.

[0058] First, place the crucible with carbonyl iron powder in S2 into the high-temperature tube furnace, select CO and N2 as the high-temperature atmosphere, where the molar ratio of CO and N2 is 8:1, and connect the two gases to the high-temperature tube furnace at the same time. Keep the N2 valve open before the temperature rises to 600 °C. Before introducing the gas into the high-temperature tube furnace, ensure that the high-temperature tube furnace has good sealing. Use an air pump to pump the high-temperature tube furnace to near vacuum inside. After the internal pressure of the high-temperature tube furnace reaches ≤0.1 bar, introduce CO into the high-temperature tube furnace. After its internal pressure is the same as the atmospheric pressure, continue to pump to vacuum and then introduce CO. Repeat this three times to exhaust the O2 and other miscellaneous gases inside the high-temperature tube furnace to prevent other chemical reactions of the carbonyl iron powder under high-temperature conditions. Finally, continuously introduce CO into the high-temperature tube furnace, and set the flow rate to 80 sccm.

[0059] S4. High-temperature inert treatment of the surface of carbonyl iron powder.

[0060] Specifically: First, set the heating and cooling rate of the high-temperature tube furnace to 10 °C / min. After the high-temperature tube furnace is heated to 600 °C, open the N2 valve, set the flow rate to 8 sccm, keep the temperature for 1 h, and then cool down to room temperature to obtain iron nitride Fe formed on the surfacex Carbonyl iron powder of N inert film.

[0061] S5. Obtain corrosion-resistant wave-absorbing materials.

[0062] After taking out the carbonyl iron powder with iron nitride Fe x N in S4, perform sieving treatment through a 400-mesh sieve, and take the carbonyl iron powder under the sieve as qualified corrosion-resistant wave-absorbing materials.

[0063] Example 2

[0064] This example provides a modification method for treating the surface of carbonyl iron powder at high temperature and in an inert atmosphere, including the following steps:

[0065] S1. Pre-ball milling of carbonyl iron powder.

[0066] First, weigh 8000 g, 6000 g, and 16000 g of carbonyl iron powder, anhydrous ethanol, and zirconia balls respectively, add them to a ball mill tank with a volume of 20 L, set the stirring speed of the ball mill to 180 r / min, and perform stirring ball milling for 4 h. During the ball milling process, the collision between the zirconia balls and the carbonyl iron powder causes the microstructure of the carbonyl iron powder to change, obtaining carbonyl iron powder with a certain degree of flakiness.

[0067] S2. Drying and loosening treatment of carbonyl iron powder.

[0068] First, use anhydrous ethanol to separate the ball-milled carbonyl iron powder from the zirconia balls in S1 to obtain a suspension of carbonyl iron powder and ethanol; after centrifugation or static treatment, when the carbonyl iron powder has settled, perform preliminary separation of the anhydrous ethanol and the carbonyl iron powder; then place the separated carbonyl iron powder in a blast drying oven, set the temperature to 80 °C, and continuously blow dry for 3 h; subsequently, filter and screen the dried carbonyl iron powder through a sieve with a mesh size of ≥100; finally, evenly spread the sieved and loose carbonyl iron powder in a high-temperature crucible, and keep the average thickness of the laid carbonyl iron powder ≤15 mm.

[0069] S3. Preparation of the atmosphere in the high-temperature tube furnace.

[0070] First, place the crucible containing carbonyl iron powder in S2 into a high-temperature tubular furnace. Select CO and N2 as the high-temperature atmosphere. Among them, the molar ratio of CO to N2 is 9:1. At the same time, connect the two gases to the high-temperature tubular furnace. Keep the N2 valve open before the temperature rises to 600°C. Before introducing the gas into the high-temperature tubular furnace, ensure that the high-temperature tubular furnace has good airtightness. Pump the high-temperature tubular furnace with an air pump until the inside is close to vacuum. After the internal pressure of the high-temperature tubular furnace reaches ≤0.1 bar, introduce CO into the high-temperature tubular furnace. Wait until the internal pressure is the same as the atmospheric pressure, then pump it to vacuum again and introduce CO. Repeat this cycle three times to discharge the O2 and other miscellaneous gases inside the high-temperature tubular furnace to prevent other chemical reactions of carbonyl iron powder under high-temperature conditions. Finally, continuously introduce CO into the high-temperature tubular furnace, and set the flow rate to 153 sccm.

[0071] S4. High-temperature inert treatment of the surface of carbonyl iron powder.

[0072] Specifically: First, set the heating and cooling rate of the high-temperature tubular furnace to 8°C / min. After the high-temperature tubular furnace heats up to 600°C, open the N2 valve, set the flow rate to 17 sccm, keep it warm for 2 h, and then cool it down to room temperature to obtain carbonyl iron powder with an iron nitride Fe x N inert film on the surface.

[0073] S5. Obtain a corrosion-resistant wave-absorbing material.

[0074] After taking out the carbonyl iron powder with iron nitride Fe x N generated on the surface in S4, perform sieving treatment with a 200-mesh sieve, and take the carbonyl iron powder under the sieve as the qualified corrosion-resistant wave-absorbing material.

[0075] Example 3

[0076] This example provides a modification method for high-temperature and inert treatment of the surface of carbonyl iron powder, including the following steps:

[0077] S1. Pre-ball milling of carbonyl iron powder.

[0078] First, weigh 1000 g, 1000 g, and 3000 g of carbonyl iron powder, anhydrous ethanol, and zirconia balls respectively, add them to a ball mill tank with a volume of 2 L, set the stirring speed of the ball mill to 150 r / min, and perform stirring ball milling treatment for 6 h. During the ball milling process, the collision between the zirconia balls and the carbonyl iron powder causes the microstructure of the carbonyl iron powder to change, obtaining carbonyl iron powder with a certain degree of flakiness.

[0079] S2. Drying and loosening treatment of carbonyl iron powder.

[0080] First, anhydrous ethanol is used to separate the milled carbonyl iron powder and zirconia balls in S1 to obtain a suspension of carbonyl iron powder and ethanol. After centrifugation or standing treatment, when the carbonyl iron powder has settled completely, the anhydrous ethanol and the carbonyl iron powder are preliminarily separated. Then, the separated carbonyl iron powder is placed in a blast drying oven, the temperature is set at 50 °C, and it is dried by continuous blowing for 6 h. Subsequently, the dried carbonyl iron powder is filtered and screened through a sieve with a mesh size of ≥100 meshes. Finally, the loose carbonyl iron powder after screening is evenly spread in a high-temperature crucible, and the average thickness of the laid carbonyl iron powder is ≤15 mm.

[0081] S3. Preparation of the atmosphere in the high-temperature tube furnace.

[0082] First, the crucible containing carbonyl iron powder in S2 is placed in the high-temperature tube furnace. CO and N2 are selected as the high-temperature atmosphere. Among them, the molar ratio of CO and N2 is 10:1. At the same time, the two gases are connected to the high-temperature tube furnace, and the N2 valve is kept before the temperature rises to 600 °C. Before introducing the gas into the high-temperature tube furnace, it is necessary to ensure that the high-temperature tube furnace has good airtightness. The high-temperature tube furnace is pumped to near vacuum with an air pump. After the internal pressure of the high-temperature tube furnace reaches ≤0.1 bar, CO is introduced into the high-temperature tube furnace. After the internal pressure is the same as the atmospheric pressure, it is pumped to vacuum again and then CO is introduced. This cycle is repeated three times to discharge the O2 and other miscellaneous gases inside the high-temperature tube furnace to prevent other chemical reactions of the carbonyl iron powder under high-temperature conditions. Finally, CO is continuously introduced into the high-temperature tube furnace, and the flow rate is set at 160 sccm.

[0083] S4. High-temperature inert treatment of the surface of carbonyl iron powder.

[0084] Specifically: First, the heating and cooling rate of the high-temperature tube furnace is set at 5 °C / min. After the high-temperature tube furnace is heated to 600 °C, the N2 valve is opened, the flow rate is set at 20 sccm, and it is kept warm for 1.5 h, and then cooled to room temperature to obtain carbonyl iron powder with an iron nitride Fe x N inert film on the surface.

[0085] S5. Obtaining a corrosion-resistant wave-absorbing material.

[0086] After taking out the carbonyl iron powder with iron nitride Fe x N formed on the surface in S4, it is sieved through a 300-mesh sieve, and the carbonyl iron powder under the sieve is taken as the qualified corrosion-resistant wave-absorbing material.

[0087] The corrosion-resistant wave-absorbing materials obtained in Examples 1-3 of the present invention not only form an Fe x N film on the surface of the carbonyl iron powder, which not only improves the corrosion resistance and oxidation resistance of carbonyl iron, but also, compared with conventional chemical coating, Fe xThe N film has a higher bonding strength with the carbonyl iron matrix; moreover, the electromagnetic wave absorption performance of the corrosion-resistant electromagnetic wave absorption material obtained in the present invention has certain adjustability. Due to the increase in the aspect ratio of the carbonyl iron powder after ball milling, its magnetic loss ability will increase. When used as an absorber under the same conditions, the absorption band will shift to the low frequency. And for the carbonyl iron powder after high-temperature surface passivation treatment, since an inert Fe x N layer is added on its surface, the eddy current effect on the surface of the carbonyl iron powder is inhibited to a certain extent, and the absorption peak will shift to the high frequency. In actual production, the electromagnetic wave absorption performance of the carbonyl iron powder can be adjusted by fine-tuning the process parameters of high-temperature surface treatment and ball milling, such as the ball milling time, high-temperature treatment time, etc.

[0088] The above are only specific embodiments of the present invention, which enable those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0089] It should be understood that the present invention is not limited to the above-described content and can be modified and changed without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A method for modifying the surface of carbonyl iron powder by high-temperature and inert treatment, characterized in that It includes the following steps: S1. Add carbonyl iron powder, absolute ethanol, and zirconia balls into a ball mill tank according to a mass ratio of 1:(0.6 - 1):(2 - 3), and conduct ball milling treatment to obtain the ball-milled carbonyl iron powder; S2. Use absolute ethanol to separate the ball-milled carbonyl iron powder from the zirconia balls in S1, conduct drying treatment after centrifugation or standing, and then obtain the loosened carbonyl iron powder through filtration and screening, and spread it in a crucible; S3. First, place the crucible with carbonyl iron powder in S2 into a high-temperature tube furnace, then introduce a mixed gas of CO and N2 into the high-temperature tube furnace, and keep the N2 valve closed before the temperature of the high-temperature tube furnace rises to 600 °C; S4. After the high-temperature tube furnace is heated to 600 °C, N2 is introduced and the flow ratio of CO to N2 is adjusted to (8-10):1, and it is kept warm for 1 h to 2 h. After cooling, carbonyl iron powder with iron nitride Fe x N is obtained; S5. Sieving the carbonyl iron powder with a surface-generated iron nitride Fe x N to obtain a corrosion-resistant wave-absorbing material.

2. The surface modification method for carbonyl iron powder treated at high temperature and in an inert atmosphere according to claim 1, wherein The stirring speed of the ball milling treatment in S1 is 150 r / min - 180 r / min, and the time is 4 h - 6 h.

3. The surface modification method of carbonyl iron powder treated at high temperature and inert described in claim 1, characterized in that, The ball-milled carbonyl iron powder in S1 is flaky carbonyl iron powder.

4. The surface modification method for carbonyl iron powder by high-temperature and inert treatment according to claim 1, characterized in that, The temperature of the drying treatment in S2 is 50 °C - 80 °C, and the time is 3 h - 6 h; a sieve mesh with a size of ≥100 meshes is used for the filtration and screening treatment.

5. The modified method for the surface of carbonyl iron powder by high-temperature and inert treatment according to claim 1, characterized in that The thickness of the carbonyl iron powder laid in the crucible in S2 is ≤15 mm.

6. The modified method for the surface of carbonyl iron powder by high-temperature and inert treatment according to claim 1, characterized in that, In the mixed gas of CO and N2 in S3, the molar ratio of CO to N2 is (8 - 10):

1.

7. The surface modification method of carbonyl iron powder by high-temperature and inert treatment according to claim 1, characterized in that, In S3, first evacuate the internal pressure of the high-temperature tube furnace to ≤0.1 bar, then introduce CO into the high-temperature tube furnace to circulate CO three times to displace the miscellaneous gas, and then continuously introduce CO into the high-temperature tube furnace, and set the flow rate to 80 sccm - 160 sccm.

8. The surface modification method of carbonyl iron powder treated at high temperature and inertness according to claim 1, characterized in that, In S4, the heating rate of the high-temperature tube furnace rising to 600 °C is 5 °C / min - 10 °C / min; the flow rate of the introduced N2 is set to 8 sccm - 20 sccm.

9. The surface modification method of carbonyl iron powder treated at high temperature and inert according to claim 1, characterized in that In S4, the carbonyl iron powder decomposes into Fe and CO under high-temperature conditions, and the introduced CO can inhibit the decomposition reaction of the carbonyl iron powder.

10. The surface modification method of carbonyl iron powder by high-temperature and inert treatment according to claim 1, characterized in that, In S5, a sieve mesh with a size of 200 - 400 meshes is used for the sieving treatment.

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