Modified carbonyl iron powder, its preparation method and use

Abstract

The application provides modified carbonyl iron powder and a preparation method thereof, and belongs to the technical field of electromagnetic wave absorbing materials. The surface of the iron powder is roughened by surface activation of the carbonyl iron powder, so that the specified metal particles can be reduced on the surface of the iron powder during electroless plating, and the reduction reaction is accelerated during electroless plating. A metal plating layer is formed on the surface of the iron powder by electroless plating, so that the electromagnetic performance of the carbonyl iron powder is improved. The surface metal plating layer and the bottom carbonyl iron powder are diffused by vacuum heat treatment, so that an alloy diffusion layer is formed, the performance of the iron powder is improved, and the continuity of the surface magnetism of the iron powder is ensured. A dense oxide film is formed on the surface of the alloyed carbonyl iron powder by controlling oxidation, so that the corrosion resistance of the carbonyl iron powder is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials, and in particular to a modified carbonyl iron powder, its preparation method, and its application. Background Technology

[0002] Electromagnetic absorbing materials are a class of materials that can absorb or significantly reduce the electromagnetic wave energy received on their surface, thereby reducing electromagnetic interference. Electromagnetic absorbing materials mainly rely on absorbers to attenuate and reduce electromagnetic waves, with carbonyl iron powder being the most commonly used absorber. However, with the advancement of modern military countermeasures technology, the high conductivity, high complex permittivity, poor impedance matching characteristics, and poor resistance to oxidation and acids / alkalis of carbonyl iron powder have severely limited its use.

[0003] Currently, researchers mainly modify carbonyl iron powder by coating it to form a core-shell structure. Common methods include: 1) Physical methods, which achieve the core-shell structure through surface adsorption, such as atomic layer deposition and mechanical ball milling; 2) Chemical methods, which obtain the core-shell structure through chemical reactions between surface additives and particles, including electroless plating, vapor deposition, sol-gel, and precipitation. However, for the above modification methods, if a single metal coating is used, the severe skin effect of carbonyl iron powder cannot be improved because most magnetic metals are weaker than carbonyl iron powder and have strong conductivity. The impedance matching performance is poor, and the improvement in electromagnetic properties is not significant. Furthermore, the surface activity of chemically coated metals is relatively high, making them prone to oxidation. On the other hand, if a non-metallic oxide coating is used, although it can improve the dielectric parameters of carbonyl iron powder, the non-metallic oxide does not bond tightly with the iron particle surface, resulting in a significant interface layer, which cannot improve the characteristic of iron powder being susceptible to acid and alkali corrosion.

[0004] Therefore, how to improve the dielectric properties, acid and alkali corrosion resistance, and impedance matching properties of carbonyl iron powder has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a modified carbonyl iron powder, its preparation method and application. The preparation method provided by this invention can improve the dielectric properties, acid and alkali corrosion resistance, impedance matching and other properties of carbonyl iron powder.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing modified carbonyl iron powder, comprising the following steps:

[0008] (1) Surface activation of carbonyl iron powder to obtain pretreated carbonyl iron powder;

[0009] (2) The pretreated carbonyl iron powder obtained in step (1) is subjected to chemical plating to obtain composite carbonyl iron powder;

[0010] (3) The composite carbonyl iron powder obtained in step (2) is subjected to vacuum heat treatment and controlled oxidation in sequence to obtain modified carbonyl iron powder.

[0011] Preferably, the surface activation in step (1) includes etching carbonyl iron powder in an etching solution.

[0012] Preferably, the pH value of the etching solution is 1 to 3.

[0013] Preferably, the plating metal in step (2) includes one or more of Ni, Co, Cu, Sn, In, Ag, Au, Pt, Rh, Pd, Ir, W, Mo and Zn.

[0014] Preferably, the vacuum heat treatment in step (3) includes a low-temperature heat treatment and a high-temperature heat treatment performed sequentially.

[0015] Preferably, the temperature of the low-temperature heat treatment is 500℃~650℃; and the time of the low-temperature heat treatment is 2~6h.

[0016] Preferably, the temperature of the high-temperature heat treatment is 800℃~950℃; the time of the high-temperature heat treatment is 4~8h.

[0017] Preferably, in step (3), the partial pressure of oxygen during oxidation is controlled to be 0.3% to 8%.

[0018] The present invention also provides modified carbonyl iron powder prepared by the preparation method described above, comprising carbonyl iron powder, a transition alloy layer and a metal coating on the surface of the transition alloy layer.

[0019] The present invention also provides the application of the modified carbonyl iron powder described in the above technical solution in microwave absorbing materials.

[0020] This invention provides a method for preparing modified carbonyl iron powder, comprising the following steps: surface activation of carbonyl iron powder to obtain pretreated carbonyl iron powder; electroless plating of the pretreated carbonyl iron powder to obtain composite carbonyl iron powder; and sequential vacuum heat treatment and controlled oxidation of the composite carbonyl iron powder to obtain modified carbonyl iron powder. This invention, by surface activation of carbonyl iron powder, roughens the surface of the iron powder, facilitating the reduction of specified metal particles on the iron powder surface during electroless plating. Furthermore, the surface-activated iron powder exhibits a certain degree of catalytic reaction effect during electroless plating, accelerating the reduction reaction. This invention also improves the electromagnetic properties of carbonyl iron powder by forming a metal coating on the iron powder surface through electroless plating. Vacuum heat treatment allows the surface metal coating to diffuse with the underlying carbonyl iron powder, forming an alloy diffusion layer, which improves the iron powder properties while ensuring the continuity of the iron powder's magnetic properties. Finally, controlled oxidation forms a dense oxide film on the alloyed carbonyl iron powder surface, significantly enhancing the corrosion resistance of the carbonyl iron powder. The results of the examples show that the modified carbonyl iron powder 1.5mm sample prepared by the preparation method provided by the present invention has a higher R value. L It has a maximum voltage of -45dB and a bandwidth of 8.2 to 12.4 GHz; and it also has excellent corrosion resistance. Detailed Implementation

[0021] This invention provides a method for preparing modified carbonyl iron powder, comprising the following steps:

[0022] (1) Surface activation of carbonyl iron powder to obtain pretreated carbonyl iron powder;

[0023] (2) The pretreated carbonyl iron powder obtained in step (1) is subjected to chemical plating to obtain composite carbonyl iron powder;

[0024] (3) The composite carbonyl iron powder obtained in step (2) is subjected to vacuum heat treatment and controlled oxidation in sequence to obtain modified carbonyl iron powder.

[0025] This invention involves surface activation of carbonyl iron powder to obtain pretreated carbonyl iron powder. In this invention, the surface activation roughens the iron powder surface, promoting the reduction of metal particles on the iron powder surface during electroless plating; furthermore, the etched iron powder exhibits a certain degree of catalytic reaction effect during electroless plating, accelerating the reduction reaction.

[0026] The present invention does not impose any special limitations on the size and source of the carbonyl iron powder; commercially available products known to those skilled in the art can be used.

[0027] In this invention, the surface activation preferably includes etching carbonyl iron powder in an etching solution. In this invention, the etching solution preferably comprises an aqueous solution of one or more of citric acid, hydrochloric acid, sulfuric acid, oxalic acid, malic acid, and tartaric acid; the concentration of the acid in the etching solution is preferably 0.1–1 mol / L, more preferably 0.5–1 mol / L. In this invention, when the etching solution is of the above type, it is more conducive to the surface activation of carbonyl iron powder.

[0028] In this invention, the pH value of the etching solution is preferably 1-3, more preferably 2-3; the etching time is preferably 2-8 min, more preferably 4-6 min. When the pH value of the etching solution and the etching time are within the above ranges, iron powder can be etched rapidly, thus fully activating the surface of the iron powder.

[0029] In this invention, the etching solution preferably further includes a surfactant. In this invention, when the carbonyl iron powder has poor wettability with water, adding a surfactant to the etching solution can promote the dispersion of the carbonyl iron powder in water and promote the etching of the carbonyl iron powder by the etching solution. In this invention, the surfactant preferably includes one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and Gemini surfactant; the amount of surfactant added is preferably 0.1% to 0.3% of the mass of the etching solution, more preferably 0.2% to 0.3%.

[0030] After surface activation, the powder obtained after surface activation is preferably filtered and washed sequentially to obtain pretreated carbonyl iron powder. In this invention, the filtration and washing can remove the etching solution from the surface of the pretreated carbonyl iron powder, preventing it from affecting subsequent electroless plating. This invention does not have specific limitations on the filtration and washing methods; methods well-known to those skilled in the art can be used. In this invention, water is preferably used as the washing reagent.

[0031] After obtaining the pretreated carbonyl iron powder, the present invention performs chemical plating on the pretreated carbonyl iron powder to obtain composite carbonyl iron powder.

[0032] In this invention, the electroless plating metal preferably includes one or more of Ni, Co, Cu, Sn, In, Ag, Au, Pt, Rh, Pd, Ir, W, Mo, and Zn, and more preferably includes one or more of Co, Ni, Pt, Cu, Sn, and Ag. In this invention, when the plating metal is of the above type, the electromagnetic properties of carbonyl iron powder can be improved.

[0033] This invention does not impose any particular limitation on the electroless plating solution; any plating solution well-known to those skilled in the art can be used, as long as it can form the aforementioned metal coating on the surface of carbonyl iron powder. In this invention, the electroless plating solution preferably includes metal salts, complexing agents, pH adjusters, wetting agents, buffers, and reducing agents.

[0034] In this invention, the metal salt preferably includes one or more of the following metal salts: Ni, Co, Cu, Sn, In, Ag, Au, Pt, Rh, Pd, Ir, W, Mo, and Zn; more preferably, it includes one or more of the following metal salts: Co, Ni, Pt, Cu, Sn, and Ag. In this invention, the cobalt salt preferably includes cobalt sulfate or cobalt sulfamate; the concentration of the cobalt salt in the plating solution is preferably 30–60 g / L, more preferably 40–50 g / L. The nickel salt in the plating solution preferably includes nickel sulfate, nickel chloride, or nickel sulfamate; the concentration of the nickel salt in the plating solution is preferably 30–60 g / L, more preferably 40–50 g / L. The platinum salt preferably includes dinitrodiamine platinum or platinum chloride; the concentration of the platinum salt in the plating solution is preferably 5–10 g / L. More preferably, the concentration is 6-8 g / L; the copper salt preferably includes copper sulfate or copper chloride; the concentration of the copper salt in the plating solution is preferably 5-20 g / L, more preferably 10-15 g / L; the tin salt preferably includes stannous chloride; the concentration of the tin salt in the plating solution is preferably 80-120 g / L, more preferably 100-110 g / L; the silver salt preferably includes silver nitrate; the concentration of the silver salt in the plating solution is preferably 10-20 g / L, more preferably 15-20 g / L. In this invention, when the type and concentration of the metal salt are within the above ranges, a metal coating of uniform thickness can be formed on the carbonyl metal surface.

[0035] In this invention, the complexing agent preferably includes one or more of citrate, tartrate, pyrophosphate, EDTA, and malate. The amount of the complexing agent is not particularly limited in this invention and can be adjusted according to experimental needs. In this invention, the amount of citrate is preferably close to the amount of the metal salt; the amount of tartrate is preferably 1.5 to 2 times that of the metal salt; and the amount of pyrophosphate is preferably 1.5 to 2 times that of the metal salt.

[0036] In this invention, the pH adjuster is preferably ammonia. Ammonia is a strong ligand that can complex with metal ions, thereby resulting in a smoother deposition rate during electroless plating. This invention does not impose a specific limit on the amount of pH adjuster used; it can be adjusted according to the required pH of the plating solution. In this invention, when the plating layer is cobalt, the amount of pH adjuster added is preferably sufficient to adjust the pH of the plating solution to 6-8.

[0037] In this invention, the reducing agent preferably includes sodium phosphite or aminoborane. In this invention, the introduction of an appropriate amount of phosphorus (P) into the sodium phosphite series reducing agent can improve the magnetic coercivity of iron powder to a certain extent, and the aminoborane series reducing agent is green, environmentally friendly, and non-toxic.

[0038] In this invention, the amount of sodium phosphite added is preferably 20-40 g / L, more preferably 30-35 g / L; the amount of aminoborane added is preferably 3-6 g / L, more preferably 4-5 g / L. When the amounts of sodium phosphite and aminoborane added are within the above ranges, the metal ions can be fully reduced to elemental metals.

[0039] The present invention does not impose any special limitations on the type and amount of the wetting agent; it can be selected as needed.

[0040] This invention does not impose any special limitations on the type and amount of the buffer; it can be selected as needed. In this invention, the buffer includes ammonium chloride.

[0041] In this invention, the thickness of the coating obtained by electroless plating is preferably 1–5 μm, more preferably 1–3 μm. In this invention, a coating thickness within the above range can sufficiently improve the electromagnetic properties of the modified carbonyl iron powder. This invention adjusts the coating thickness by controlling the temperature and time of the electroless plating. In this invention, the electroless plating temperature is preferably 40℃–80℃, more preferably 60℃±5℃; the electroless plating time is preferably 10 min–60 min, more preferably 15 min–30 min. In this invention, when the temperature and time of the electroless plating are within the above ranges, the coating thickness can reach the required thickness to sufficiently improve the electromagnetic properties of the modified carbonyl iron powder.

[0042] After obtaining the composite carbonyl iron powder, the present invention sequentially subjectes the composite carbonyl iron powder to vacuum heat treatment and controlled oxidation to obtain modified carbonyl iron powder.

[0043] In this invention, the vacuum heat treatment preferably includes a low-temperature heat treatment and a high-temperature heat treatment performed sequentially.

[0044] In this invention, the preferred temperature for the low-temperature heat treatment is 500℃ to 650℃, more preferably 550℃ to 600℃; the preferred duration of the low-temperature heat treatment is 2 to 6 hours, more preferably 4 hours. In this invention, the metal coating on the surface of the composite carbonyl iron powder is an amorphous metallic phase. Low-temperature heat treatment allows this amorphous metallic phase to transform into crystals and grow, resulting in a denser coating of metal on the iron powder surface. When the temperature of the low-temperature heat treatment is within the above range, mutual diffusion between the deposited metal and the underlying metal can be avoided, while allowing the deposited metal to transform into metallographic crystals and grow.

[0045] After low-temperature heat treatment, the product of the low-temperature heat treatment is preferably directly heated to the temperature of high-temperature heat treatment. In this invention, the temperature of the high-temperature heat treatment is preferably 800℃~950℃, more preferably 850℃~900℃; the time of the high-temperature heat treatment is preferably 4~8h, more preferably 6h. In this invention, performing high-temperature heat treatment directly after low-temperature heat treatment allows iron and the surface-coated metal to diffuse into each other. When the temperature of the high-temperature heat treatment is within the above range, the deposited metal and the underlying iron can diffuse into each other to form a transition alloy layer. By controlling the diffusion temperature and time within the above range, the depth of diffusion of the surface metal and iron powder can be controlled to meet the required requirements.

[0046] In this invention, the oxygen partial pressure for controlled oxidation is preferably 0.3% to 8%, more preferably 0.3% to 8%, and even more preferably 6% to 8%. When the oxygen partial pressure for controlled oxidation is within the above range, a dense oxide film can be formed on the surface of the alloyed carbonyl iron powder, improving the corrosion resistance of the carbonyl iron powder; and it can prevent the formation of non-magnetic Fe2O3 or FeO, preferentially forming magnetic Fe3O4; and when coating the surface with metal or forming alloys, it can preferentially form magnetic spinel structures such as NiFe2O4 or CoFe2O4.

[0047] This invention does not specifically limit the operation method of controlled oxidation, as long as the above-mentioned oxygen partial pressure range can be achieved. In this invention, the controlled oxidation preferably includes: spreading the powder obtained from the vacuum heat treatment evenly on a ceramic plate; then placing the ceramic plate containing the powder in a vacuum device, and slowly introducing oxygen and argon gas into the vacuum device after mixing them in a certain proportion. In this invention, the temperature of the controlled oxidation is preferably 550–750°C, more preferably 650±50°C; the time of the controlled oxidation is preferably 4–10 hours, more preferably 6–8 hours.

[0048] This invention does not impose any particular limitation on the vacuum device; any device well-known to those skilled in the art capable of achieving a vacuum may be used. In this invention, the vacuum device preferably includes a vacuum furnace or an atmosphere furnace.

[0049] Preferably, before slowly introducing the mixture of oxygen and argon into the vacuum device, the pressure inside the vacuum device is evacuated to ≤10. -3 Pa. In this invention, the pressure inside the vacuum device is evacuated to ≤10 Pa. -3 Pa ensures that the air inside the furnace is completely removed, facilitating subsequent control of the partial pressure of oxygen and argon.

[0050] The present invention does not have any particular limitations on the devices used to introduce oxygen and argon into the vacuum device; any gas mixing system well known to those skilled in the art can be used.

[0051] This invention, through surface activation of carbonyl iron powder, roughens the surface of the iron powder, facilitating the reduction of specified metal particles on the iron powder surface during electroless plating. Furthermore, the surface-activated iron powder exhibits a certain degree of catalytic reaction during electroless plating, accelerating the reduction reaction. This invention also improves the electromagnetic properties of carbonyl iron powder by forming a metallic coating on the iron powder surface through electroless plating. Vacuum heat treatment allows the surface metallic coating to diffuse with the underlying carbonyl iron powder, forming an alloy diffusion layer that improves the iron powder's properties while maintaining the continuity of its magnetic properties. Finally, controlled oxidation forms a dense oxide film on the alloyed carbonyl iron powder surface, enhancing its corrosion resistance.

[0052] This invention also provides modified carbonyl iron powder prepared by the preparation method described above, comprising carbonyl iron powder, a transition alloy layer coating the surface of the carbonyl iron powder, a metal coating coating the surface of the transition alloy layer, and an oxide film coating the surface of the metal coating. The modified carbonyl iron powder provided by this invention has a transition alloy layer between the metal coating and the carbonyl iron powder. The metal coating tightly coats the carbonyl iron powder, preventing loose bonding between the metal coating and the carbonyl iron powder, thereby giving the modified carbonyl iron powder excellent dielectric properties, acid and alkali resistance, and impedance matching.

[0053] The present invention also provides the application of the modified carbonyl iron powder described in the above technical solution in microwave absorbing materials.

[0054] The present invention does not impose any particular limitation on the application method of the modified carbonyl iron powder in microwave absorbing materials; any application method known to those skilled in the art can be used.

[0055] The modified carbonyl iron powder provided by this invention has excellent dielectric properties, acid and alkali resistance, and impedance matching, and can therefore be used in microwave absorbing materials.

[0056] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0057] Example 1

[0058] A method for preparing modified carbonyl iron powder, comprising the following steps:

[0059] (1) Carbonyl iron powder was surface activated in a 0.1 mol / L hydrochloric acid dilute solution with pH 1 for 3 min. After washing, pretreated carbonyl iron powder was obtained.

[0060] (2) The pretreated carbonyl iron powder obtained in step (1) is subjected to chemical plating to obtain composite carbonyl iron powder;

[0061] The electroless plating process involved a coating thickness of 3 μm, a plating temperature of 65℃, and a plating time of 30 min. The coating metal was Co. The electroless plating solution formulation was as follows: CoSO4 as the metal salt, with a concentration of 30 g / L; sodium tartrate as the complexing agent, with a concentration of 80 g / L; sodium citrate as the complexing agent, with a concentration of 10 g / L; ammonium chloride as the buffer; ammonia as the pH adjuster, with a volume of 60 mL and a concentration of 1 mol / L; and DMAB as the reducing agent, with a concentration of 3 g / L. The pH value of the electroless plating solution was approximately 8.5.

[0062] (3) The composite carbonyl iron powder obtained in step (2) is subjected to vacuum heat treatment and controlled oxidation in sequence to obtain modified carbonyl iron powder;

[0063] The vacuum heat treatment includes a low-temperature heat treatment and a high-temperature heat treatment performed sequentially. The low-temperature heat treatment is performed at a temperature of 600℃ for 2 hours, and the high-temperature heat treatment is performed at a temperature of 900℃ for 2 hours.

[0064] The oxidation control step involves: spreading the powder obtained from the vacuum heat treatment evenly on a ceramic plate; then placing the ceramic plate containing the powder in a vacuum device and evacuating the pressure inside the vacuum device to ≤10. -3 Pa, oxygen and argon are mixed in a certain ratio, with the oxygen partial pressure controlled at 0.5%, and slowly introduced into a vacuum device to control oxidation. The oxidation temperature is controlled at 680℃ and the time is controlled at 6h.

[0065] Example 2

[0066] A method for preparing modified carbonyl iron powder, comprising the following steps:

[0067] (1) Carbonyl iron powder was surface activated in a dilute hydrochloric acid solution with pH 1 for 3 min, and then washed to obtain pretreated carbonyl iron powder.

[0068] (2) The pretreated carbonyl iron powder obtained in step (1) is subjected to chemical plating to obtain composite carbonyl iron powder; wherein, the coating thickness of the chemical plating is 5 μm, the temperature of the chemical plating is 65℃, and the time is 40 min; the coating metal is Ni, and the formulation of the chemical plating solution is as follows: the metal salt is NiSO4: the concentration of the metal salt in the plating solution is 30 g / L, the complexing agent is sodium citrate: the concentration of the complexing agent in the plating solution is 30 g / L, the buffer is ammonium chloride 20 g / L, the pH adjuster is ammonia water, the amount of ammonia water is 10 mL, the concentration is 10 mol / L, the reducing agent is DMAB: the concentration of DMAB in the plating solution is 3 g / L, and the pH value of the chemical plating solution is 5.5;

[0069] (3) The composite carbonyl iron powder obtained in step (2) is subjected to vacuum heat treatment and controlled oxidation in sequence to obtain modified carbonyl iron powder;

[0070] This includes sequential low-temperature heat treatment and high-temperature heat treatment, wherein the low-temperature heat treatment is performed at a temperature of 550℃ for 2 hours, and the high-temperature heat treatment is performed at a temperature of 870℃ for 4 hours.

[0071] The oxidation control step involves: spreading the powder obtained from the vacuum heat treatment evenly on a ceramic plate; then placing the ceramic plate containing the powder in a vacuum device and evacuating the pressure inside the vacuum device to ≤10. -3 Pa, oxygen and argon are mixed in a certain ratio, with the oxygen partial pressure controlled at 0.5%, and slowly introduced into a vacuum device to control oxidation. The oxidation temperature is controlled at 680℃ and the time is controlled at 6h.

[0072] Example 3

[0073] A method for preparing modified carbonyl iron powder, comprising the following steps:

[0074] (1) Carbonyl iron powder was surface activated in a dilute hydrochloric acid solution with pH 1 for 3 min, and then washed to obtain pretreated carbonyl iron powder.

[0075] (2) The pretreated carbonyl iron powder obtained in step (1) is subjected to chemical plating to obtain composite carbonyl iron powder; wherein, the coating thickness of the chemical plating is 3μm, the temperature of the chemical plating is 65℃, and the time is 30min; the coating metal is Co, and the formulation of the chemical plating solution is as follows: the metal salt is CoSO4: the concentration of the metal salt in the plating solution is 30g / L, the complexing agent is sodium tartrate: the concentration of the complexing agent in the plating solution is 80g / L, the complexing agent is sodium citrate: the concentration of the complexing agent in the plating solution is 10g / L, the buffer is ammonium chloride 20g / L, the pH adjuster is ammonia water, the amount of ammonia water is 50mL, the reducing agent is sodium hypophosphite: the concentration of sodium hypophosphite in the plating solution is 30g / L, and the pH value of the chemical plating solution is 7.5;

[0076] (3) The composite carbonyl iron powder obtained in step (2) is subjected to vacuum heat treatment and controlled oxidation in sequence to obtain modified carbonyl iron powder;

[0077] The vacuum heat treatment includes a low-temperature heat treatment and a high-temperature heat treatment performed sequentially. The low-temperature heat treatment is performed at a temperature of 600℃ for 2 hours, and the high-temperature heat treatment is performed at a temperature of 900℃ for 2 hours.

[0078] The oxidation control step involves: spreading the powder obtained from the vacuum heat treatment evenly on a ceramic plate; then placing the ceramic plate containing the powder in a vacuum device and evacuating the pressure inside the vacuum device to ≤10. -3 Pa, oxygen and argon are mixed in a certain ratio, with the oxygen partial pressure controlled at 0.5%, and slowly introduced into a vacuum device to control oxidation. The oxidation temperature is controlled at 700℃ and the time is 4 hours.

[0079] Example 4

[0080] A method for preparing modified carbonyl iron powder, comprising the following steps:

[0081] (1) Carbonyl iron powder was surface activated in a dilute hydrochloric acid solution with pH 1 for 3 min, and then washed to obtain pretreated carbonyl iron powder.

[0082] (2) The pretreated carbonyl iron powder obtained in step (1) is subjected to chemical plating to obtain composite carbonyl iron powder; wherein, the coating thickness of the chemical plating is 3μm, the temperature of the chemical plating is 65℃, and the time is 30min; the coating metal is Ni, and the formulation of the chemical plating solution is as follows: the metal salt is NiSO4: the concentration of the metal salt in the plating solution is 30g / L, the complexing agent is sodium citrate: the concentration of the complexing agent in the plating solution is 30g / L, the buffer is ammonium chloride 20g, the pH adjuster is ammonia water, the amount of ammonia water is 10mL, the reducing agent is DMAB: the concentration of DMAB in the plating solution is 3g / L, and the pH value of the chemical plating solution is 5.5;

[0083] (3) The composite carbonyl iron powder obtained in step (2) is subjected to vacuum heat treatment and controlled oxidation in sequence to obtain modified carbonyl iron powder;

[0084] The vacuum heat treatment includes a low-temperature heat treatment and a high-temperature heat treatment performed sequentially. The low-temperature heat treatment is performed at a temperature of 600℃ for 2 hours, and the high-temperature heat treatment is performed at a temperature of 950℃ for 2 hours.

[0085] The oxidation control step involves: spreading the powder obtained from the vacuum heat treatment evenly on a ceramic plate; then placing the ceramic plate containing the powder in a vacuum device and evacuating the pressure inside the vacuum device to ≤10. -3Pa, oxygen and argon are mixed in a certain ratio, with the oxygen partial pressure controlled at 0.3%, and slowly introduced into a vacuum device to control oxidation. The oxidation temperature is controlled at 650℃ and the time is controlled at 10h.

[0086] Example 5

[0087] A method for preparing modified carbonyl iron powder, comprising the following steps:

[0088] (1) Carbonyl iron powder was surface activated in a dilute hydrochloric acid solution with pH 1 for 3 min, and then washed to obtain pretreated carbonyl iron powder.

[0089] (2) The pretreated carbonyl iron powder obtained in step (1) is subjected to chemical plating to obtain composite carbonyl iron powder; wherein, the coating thickness of the chemical plating is 5 μm, the temperature of the chemical plating is 65℃, and the time is 40 min; the coating metal is a Co and Ni composite, and the formulation of the chemical plating solution is as follows: the metal salts are CoSO4 and NiSO4: the concentrations of the metal salts in the plating solution are 30 g / L and 30 g / L, respectively; the complexing agent is sodium tartrate: the concentration of the complexing agent in the plating solution is 80 g / L; the complexing agent is sodium citrate: the concentration of the complexing agent in the plating solution is 10 g / L; the buffer is ammonium chloride 20 g / L; the pH adjuster is ammonia water, the amount of ammonia water is 30 ml; the reducing agent is DMAB: the concentration of DMAB in the plating solution is 3 g / L; and the pH value of the chemical plating solution is 8.0.

[0090] (3) The composite carbonyl iron powder obtained in step (2) is subjected to vacuum heat treatment and controlled oxidation in sequence to obtain modified carbonyl iron powder;

[0091] The vacuum heat treatment includes a low-temperature heat treatment and a high-temperature heat treatment performed sequentially. The low-temperature heat treatment is performed at a temperature of 500°C for 2 hours, and the high-temperature heat treatment is performed at a temperature of 870°C for 4 hours.

[0092] The oxidation control step is as follows: the powder obtained by vacuum heat treatment is spread evenly on a ceramic plate; then the ceramic plate containing the powder is placed in a vacuum device, the pressure in the vacuum device is evacuated to ≤10-3Pa, oxygen and argon are introduced into the vacuum device at a certain ratio to control the oxygen partial pressure to 0.3%, and the oxidation is controlled at a temperature of 650℃ for 10h.

[0093] Test Example 1

[0094] The modified carbonyl iron powder prepared in Example 1 was pressed into a coaxial ring. The room-temperature dielectric and magnetic properties of the sample were tested using a vector network analysis instrument, and then the microwave absorption performance of the sample was derived. The microwave absorption performance R of the 0.4 mm thick powder sample was tested. L <-5dB, with a bandwidth of 3.2GHz.

[0095] Test Example 2

[0096] The modified carbonyl iron powder prepared in Example 2 was pressed into a coaxial ring. The room-temperature dielectric and magnetic properties of the sample were tested using a vector network analysis instrument, and then the microwave absorption properties of the sample were derived. Tests showed that in the X-band (8.2–12.4 GHz), a 1.2 mm sample exhibited [insert value here, likely related to R]. L The maximum value is -31dB, and the bandwidth is 8.2 to 12.4GHz.

[0097] Test Example 3

[0098] The modified carbonyl iron powder prepared in Example 3 was pressed into a coaxial ring. The room-temperature dielectric and magnetic properties of the sample were tested using a vector network analysis instrument, and then the microwave absorption properties of the sample were derived. The test showed that the sample contained 3% P, and the measured R value of a 1.5mm sample was [missing information]. L The maximum value is -45dB, and the bandwidth is 8.2 to 12.4GHz.

[0099] Test Example 4

[0100] The modified carbonyl iron powder prepared in Example 4 was pressed into a coaxial ring. The room-temperature dielectric and magnetic properties of the sample were tested using a vector network analysis instrument, and then the microwave absorption properties of the sample were derived. The test results showed that, compared with carbonyl iron powder oxidized at 300℃ for 50 hours, the carbonyl iron powder was completely oxidized to Fe2O3, turning red and completely losing its magnetism; the prepared sample remained blackish-blue and retained its magnetic properties.

[0101] Test Example 5

[0102] The modified carbonyl iron powder prepared in Example 5 was pressed into a coaxial ring. The room-temperature dielectric and magnetic properties of the sample were tested using a vector network analysis instrument, and then the microwave absorption properties of the sample were derived. The test results showed that the sample surface contained approximately 23 wt% Co and Ni.

[0103] As can be seen from the above test examples, this invention can provide carbonyl iron powder modified with one or more elements selected from Ni, Co, Cu, Sn, In, Ag, Au, Pt, Rh, Pd, Ir, W, Mo, Zn, and Si. Furthermore, based on the reaction of Fe with other elements, high-performance binary or ternary phases can be obtained. By controlling the oxygen partial pressure, a suitable, dense, and highly bonded surface oxide film can be obtained, greatly improving the corrosion resistance of carbonyl iron powder while stabilizing its electromagnetic properties, enabling its use in microwave absorbing materials.

[0104] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1.A method for preparing modified carbonyl iron powder, comprising the following steps: (1) surface activation of carbonyl iron powder to obtain pretreated carbonyl iron powder; (2) electroless plating of the pretreated carbonyl iron powder obtained in step (1) to obtain composite carbonyl iron powder; (3) vacuum heat treatment and controlled oxidation of the composite carbonyl iron powder obtained in step (2) in sequence to obtain modified carbonyl iron powder; wherein the surface activation in step (1) comprises etching of the carbonyl iron powder in an etching solution; the vacuum heat treatment in step (3) comprises low-temperature heat treatment and high-temperature heat treatment in sequence; the temperature of the low-temperature heat treatment is 500-650℃; the time of the low-temperature heat treatment is 2-6h; the temperature of the high-temperature heat treatment is 800-950℃; the time of the high-temperature heat treatment is 4-8h; the oxygen partial pressure of the controlled oxidation in step (3) is 0.3%-8%; the temperature of the controlled oxidation is 550-750℃; the time of the controlled oxidation is 4-10h; the plating metal in the electroless plating in step (2) comprises one or more of Ni, Co, Cu, Sn, In, Ag, Au, Pt, Rh, Pd, Ir, W, Mo and Zn. The pH value of the etching solution is 1-3. 3.Modified carbonyl iron powder prepared by the method of any one of claims 1-2, comprising carbonyl iron powder, a transition alloy layer wrapped around the surface of the carbonyl iron powder, a metal plating layer wrapped around the surface of the transition alloy layer, and an oxide film wrapped around the surface of the metal plating layer. 4.Use of the modified carbonyl iron powder of claim 3 in wave-absorbing materials. ​ ​ ​ ​ 2. The method of producing modified carbonyl iron powder according to claim 1, characterized by, ​ ​ ​