A composite magnetic powder and its preparation method

Abstract

This application belongs to the field of materials technology, and particularly relates to a composite magnetic powder, a preparation method thereof, and an application thereof. The composite magnetic powder includes modified magnetic micron particles and modified magnetic nano particles. The modified magnetic micron particles are magnetic micron particles modified by a first surfactant, and the magnetic nano particles are magnetic nano particles modified by a second surfactant. The first surfactant includes a double hydrophilic end surfactant, and the second surfactant includes one or more of a long-chain fatty acid, a silane coupling agent, and a polymer. The beneficial effects of this application include: The composite magnetic powder of this application has both the high saturation magnetization intensity of the magnetic micron particles and can withstand higher pressures; at the same time, it contains the low porosity of the magnetic nano particles, which can reduce the leakage of the sealing medium.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials, and particularly relates to a composite magnetic powder, a preparation method thereof, and an application thereof. Background Art

[0002] Magnetic powder sealing is a key technology widely used in fields such as mechanical sealing and hydraulic sealing, and has multiple advantages such as strict sealing performance, high temperature and high pressure resistance, low maintenance components, and high reliability. The existing magnetic powder sealing materials mainly use nano-scale Fe3O4 magnetic powder, which has good sealing performance, but pure nano-scale magnetic powder is prone to agglomeration under high-pressure conditions, affecting its pressure resistance performance. While micron-scale magnetic powder has better pressure resistance performance, its sealing performance is relatively poor and it is easy to leak.

[0003] The prior art discloses a preparation method of radiation-resistant magnetic particles, which can achieve effective sealing during the magnetic powder sealing process. However, since the prepared magnetic particles are all nano-scale, they are prone to agglomeration during the sealing process, affecting their pressure resistance performance. The prior art also discloses a preparation and synthesis method of micron-scale magnetic particles. It has been proved that although micron-scale magnetic particles have better pressure resistance performance, their sealing performance is relatively poor and it is easy to leak. To solve the above problems, it is of great practical significance to study a composite material containing both micron-scale and nano-scale Fe3O4 magnetic powder to balance the sealing performance and pressure resistance. Summary of the Invention

[0004] The present application provides a composite magnetic powder and a preparation method thereof, aiming to solve the problem that the existing magnetic powder cannot simultaneously have good sealing performance and pressure resistance.

[0005] In a first aspect of the present application, a composite magnetic powder is provided, including modified magnetic micron particles and modified magnetic nano particles. The modified magnetic micron particles are magnetic micron particles modified by a first surfactant, and the magnetic nano particles are magnetic nano particles modified by a second surfactant;

[0006] The first surfactant includes a double hydrophilic end surfactant, and the second surfactant includes one or more of long-chain fatty acids, silane coupling agents, and polymers.

[0007] The composite magnetic powder of the present application has both the high saturation magnetization intensity of magnetic micron particles, which can withstand higher pressures; and at the same time contains the low porosity of magnetic nano particles, which can reduce the leakage of the sealing medium.

[0008] According to some embodiments of the composite magnetic powder of the present application, the magnetic micron particles and the magnetic nano particles are each independently selected from one or more of Fe3O4, γ-Fe2O3, and ferrite magnetic particles.

[0009] According to some embodiments of the composite magnetic powder of the present application, the particle size of the magnetic micron particles is 10 - 20 μm.

[0010] According to some embodiments of the composite magnetic powder of the present application, the particle size of the magnetic nano particles is 1 - 10 nm.

[0011] According to some embodiments of the composite magnetic powder of the present application, the mass ratio of the modified magnetic micron particles to the modified magnetic nano particles is 1:9 - 9:1.

[0012] According to some embodiments of the composite magnetic powder of the present application, the first surfactant includes one or more of glutamic acid, lysine, cysteine, sebacic acid, adipic acid, carboxyl - PEG - amine, mercapto - PEG - carboxyl, and dimercaptopropionic acid.

[0013] According to some embodiments of the composite magnetic powder of the present application, the molar ratio of the magnetic micron particles to the first surfactant in the modified magnetic micron particles is 1:(0.1 - 2).

[0014] According to some embodiments of the composite magnetic powder of the present application, the molar ratio of the magnetic nano particles to the second surfactant in the modified magnetic nano particles is 1:(0.1 - 2).

[0015] According to some embodiments of the composite magnetic powder of the present application, the chemical formula of the ferrite - type magnetic particles is MFe2O4, where M includes one or more of Mn, Co, Ni, Cu, Cd, Pb, Sn, Ca, Sr, Ba, and Mg.

[0016] According to some embodiments of the composite magnetic powder of the present application, the long - chain fatty acid includes one or more of oleic acid, stearic acid, and palmitic acid.

[0017] According to some embodiments of the composite magnetic powder of the present application, the silane coupling agent includes one or more of tetraethoxysilane, methacryloxypropyltriethoxysilane, and octadecyltrimethoxysilane.

[0018] According to some embodiments of the composite magnetic powder of the present application, the polymer includes one or more of polyethylene glycol, polyvinylpyrrolidone, and perfluoropolyether carboxylic acid.

[0019] According to some embodiments of the composite magnetic powder of the present application, the mass ratio of the modified magnetic micron particles to the modified magnetic nano particles is 3:7.

[0020] According to some embodiments of the composite magnetic powder of the present application, the particle size of the composite magnetic powder is 1 - 10 μm.

[0021] In a second aspect of the present application, there is provided a method for preparing the composite magnetic powder described in the first aspect of the present application, comprising the following steps:

[0022] (1) Prepare modified magnetic micron particles;

[0023] (2) Prepare modified magnetic nano particles;

[0024] (3) Mix the modified magnetic micron particles, the modified magnetic nano particles and a crosslinking agent to obtain the composite magnetic powder.

[0025] In some embodiments of the method for preparing the composite magnetic powder according to the present application, in step (1), the method for preparing the modified magnetic micron particles comprises the following steps: Mix magnetic micron particles, a first surfactant and a first solvent for a first time to obtain the modified magnetic micron particles.

[0026] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the method for preparing the modified magnetic micron particles further comprises subjecting the first mixed product to magnetic sedimentation washing treatment in sequence.

[0027] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the content of the first surfactant in each liter of the first solvent is 0.01 - 1 mol.

[0028] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the first solvent comprises ethanol and / or deionized water.

[0029] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the temperature of the first mixing is 20 - 80 °C, the time of the first mixing is 1 - 180 min, and the rotation speed of the first mixing is 100 - 400 r / min.

[0030] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the washing comprises washing successively with ethanol and deionized water.

[0031] In some embodiments of the method for preparing the composite magnetic powder according to the present application, in step (2), the method for preparing the modified magnetic nano particles comprises the following steps: Mix magnetic nano particles, a second surfactant and a second solvent for a second time to obtain the modified magnetic nano particles.

[0032] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the method for preparing the modified magnetic nano particles further comprises subjecting the second mixed product to magnetic sedimentation washing treatment in sequence.

[0033] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the content of the second surfactant in each liter of the second solvent is 0.01 - 1 mol.

[0034] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the second solvent includes ethanol and / or deionized water.

[0035] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the temperature of the second mixing is 20 - 100 °C, the time of the second mixing is 1 - 180 min, and the rotation speed of the second mixing is 100 - 400 r / min.

[0036] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the washing includes washing successively with ethanol and deionized water.

[0037] In some embodiments of the method for preparing the composite magnetic powder according to the present application, in step (3), the mixing is carried out in a third solvent, and the third solvent includes deionized water.

[0038] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the crosslinking agent includes one or more of glutaraldehyde, epichlorohydrin, hexamethylene diisocyanate, and γ-aminopropyltriethoxysilane.

[0039] In some embodiments of the method for preparing the composite magnetic powder according to the present application, the mass ratio of the addition amount of the crosslinking agent to the total amount of the modified magnetic microparticles and the modified magnetic nanoparticles is 1:(0.3 - 1).

[0040] In some embodiments of the method for preparing the composite magnetic powder according to the present application, in step (3), the temperature of the mixing is 20 - 100 °C, the time of the mixing is 30 - 240 min, and the rotation speed of the mixing is 100 - 200 r / min. Detailed Embodiments

[0041] The embodiments of the present invention will be described in detail below, and examples of the embodiments are shown below. The embodiments described below are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0042] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0043] An embodiment of the present application provides a composite magnetic powder, which includes modified magnetic micron particles and modified magnetic nano particles. The modified magnetic micron particles are magnetic micron particles modified by a first surfactant, and the magnetic nano particles are magnetic nano particles modified by a second surfactant; the first surfactant includes a double hydrophilic end surfactant, and the second surfactant includes one or more of long-chain fatty acids, silane coupling agents, and polymers.

[0044] The composite magnetic powder of the present application has both the high saturation magnetization intensity of the magnetic micron particles and can withstand higher pressures; at the same time, it contains the low porosity of the magnetic nano particles and can reduce the leakage of the sealing medium.

[0045] In some embodiments of the present application, the magnetic micron particles and the magnetic nano particles are each independently selected from one or more of Fe3O4, γ-Fe2O3, and ferrite magnetic particles. These particles have strong chemical stability, are resistant to high and low temperatures, and have a relatively high saturation magnetization intensity.

[0046] In some embodiments of the present application, the chemical formula of the ferrite magnetic particles is MFe2O4, where M includes one or more of Mn, Co, Ni, Cu, Cd, Pb, Sn, Ca, Sr, Ba, and Mg.

[0047] In some embodiments of the present application, the particle size of the magnetic micron particles is 10 - 20 μm;

[0048] In some embodiments of the present application, the particle size of the magnetic nano particles is 1 - 10 nm.

[0049] In some embodiments of the present application, the mass ratio of the modified magnetic micro-particles to the modified magnetic nano-particles is 1:9 - 9:1; for example, 1:9, 1:6, 1:5, 1:3, 1:1, 2:1, 3:1, 6:1, 9:1, etc. Due to the high saturation magnetization intensity of the magnetic micro-particles, they can withstand higher pressures; the magnetic nano-particles have low porosity, reducing the leakage of the sealing medium; the pressure resistance and leakage resistance properties can be regulated by adjusting the mass ratio of the magnetic nano-particles to the magnetic micro-particles.

[0050] In some embodiments of the present application, the mass ratio of the modified magnetic micro-particles to the modified magnetic nano-particles is 3:7.

[0051] In some embodiments of the present application, the first surfactant includes one or more of glutamic acid, lysine, cysteine, sebacic acid, adipic acid, carboxyl-PEG-amine, mercapto-PEG-carboxyl, and dimercaptopropionic acid. The surfactant selected in the present application is a double hydrophilic-end surfactant, and the end chains are hydrophilic groups such as amino, carboxyl, and mercapto, which can combine with Fe3O4 through hydrogen bonds or chemical bonds.

[0052] In some embodiments of the present application, the molar ratio of the magnetic micro-particles to the first surfactant in the modified magnetic micro-particles is 1:(0.1 - 2), for example, 1:0.1, 1:0.5, 1:1, 1:1.2, 1:1.6, 1:2, etc. If the proportion of the surfactant is too low, it will cause the magnetic micro-particles not to be completely coated by the surfactant and be easily oxidized; if the proportion of the surfactant is too high, it will cause overcoating, resulting in a decrease in the saturation magnetization intensity and agglomeration.

[0053] In some embodiments of the present application, the second surfactant includes one or more of long-chain fatty acids, silane coupling agents, and polymers. The second surfactant selected in the present application can effectively prevent the magnetic nano-particles from agglomerating. One end is a hydrophilic end that can bind to the magnetic particles, and the other end is a hydrophobic end that prevents the particles from being oxidized and improves stability.

[0054] In some embodiments of the present application, the long-chain fatty acids include one or more of oleic acid, stearic acid, and palmitic acid.

[0055] In some embodiments of the present application, the silane coupling agents include one or more of tetraethoxysilane (TEOS), methacryloxypropyltriethoxysilane (KH570), and octadecyltrimethoxysilane (OTMOS).

[0056] In some embodiments of the present application, the polymers include one or more of polyethylene glycol, polyvinylpyrrolidone, and perfluoropolyether carboxylic acid.

[0057] In some embodiments of the present application, the molar ratio of the magnetic nanoparticles to the second surfactant in the modified magnetic nanoparticles is 1:(0.1 - 2), such as 1:0.1, 1:0.5, 1:1, 1:1.2, 1:1.6, 1:2, etc. If the proportion of the second surfactant is too low, the magnetic nanoparticles will not be completely coated by the second surfactant and are easily oxidized; if the proportion of the second surfactant is too high, overcoating will occur, reducing the saturation magnetization intensity and causing agglomeration.

[0058] In some embodiments of the present application, the particle size of the composite magnetic powder is 1 - 10 μm.

[0059] The embodiments of the present application further provide a preparation method of the composite magnetic powder described in the first aspect of the present application, including the following steps:

[0060] (1) Prepare modified magnetic micron particles;

[0061] (2) Prepare modified magnetic nanoparticles;

[0062] (3) Mix the modified magnetic micron particles, the modified magnetic nanoparticles and a crosslinking agent to obtain the composite magnetic powder. Introducing a crosslinking agent in the preparation process of the composite magnetic powder described in the present application can better improve the stability and high and low temperature resistance characteristics of the magnetic micron particles and the nanoparticles. At the same time, the crosslinking agent can combine with the surfactant to form a three-dimensional network structure, enhancing the pressure resistance and wear resistance in the magnetic powder sealing.

[0063] In some embodiments of the present application, in step (1), the preparation method of the modified magnetic micron particles includes the following steps: First, mix magnetic micron particles, a first surfactant and a first solvent to obtain the modified magnetic micron particles.

[0064] In some embodiments of the present application, the content of the first surfactant in each liter of the first solvent is 0.01 - 1 mol, such as 0.01 mol, 0.05 mol, 0.08 mol, 0.5 mol, 0.6 mol, 0.8 mol, 1 mol, etc.

[0065] In some embodiments of the present application, the first solvent includes ethanol and / or deionized water.

[0066] In some embodiments of the present application, the temperature of the first mixing is 20 - 80 °C, such as 20 °C, 30 °C, 50 °C, 80 °C, etc., the time of the first mixing is 1 - 180 min, such as 1 min, 10 min, 50 min, 78 min, 86 min, 95 min, 110 min, 125 min, 130 min, 160 min, 180 min, etc., and the rotation speed of the first mixing is 100 - 400 r / min, such as 100 r / min, 120 r / min, 150 r / min, 180 r / min, 200 r / min, 260 r / min, 290 r / min, 320 r / min, 400 r / min, etc. If the mixing temperature is too low, the reaction rate will be too slow, the formed magnetic particles will be unstable, and the coating magnetization intensity will not be ideal; if the temperature is too high, the generated Fe3O4 will be directly oxidized to Fe2O3.

[0067] In some embodiments of the present application, the method for preparing the modified magnetic micron particles further includes sequentially filtering and washing the first mixing product; preferably, the washing includes sequentially washing with ethanol and deionized water; repeatedly washing until the pH of the washing liquid is 7, and then performing vacuum drying.

[0068] In some embodiments of the present application, the method for preparing the magnetic micron particles includes the following steps: According to the molar ratio of Fe 2+ and Fe 3+ being 0.5 - 0.75:1, dissolve FeCl3•6H2O and FeCl2•4H2O in deionized water, add a crystal form control agent such as sodium citrate or PVP, and add it according to the molar ratio of Fe 3+ : crystal form control agent = 1:0.2 - 1. At the same time, add NaOH to adjust the pH of the solution to 10 - 12; control the reaction temperature at 25 - 100 °C, the stirring speed at 200 r / min - 500 r / min, and the reaction time under these conditions at 10 min - 120 min to form Fe(OH)3 precipitate. Move the obtained Fe(OH)3 precipitate to an autoclave and perform hydrothermal reaction at 150 - 200 °C for 5 - 8 h, naturally cool to room temperature, repeatedly wash with deionized water until the pH of the washing liquid is 7, and perform vacuum drying to obtain micron-sized magnetic micron particles.

[0069] In some embodiments of the present application, in step (2), the method for preparing the modified magnetic nanoparticles includes the following steps: Perform a second mixing of the magnetic nanoparticles, the second surfactant, and the second solvent to obtain the modified magnetic nanoparticles.

[0070] In some embodiments of the present application, the content of the second surfactant in each liter of the second solvent is 0.01 - 1 mol; for example, 0.01 mol, 0.05 mol, 0.1 mol, 0.2 mol, 0.3 mol, 0.5 mol, 0.8 mol, 1 mol, etc.

[0071] In some embodiments of the present application, the second solvent includes ethanol and / or deionized water.

[0072] In some embodiments of the present application, the temperature of the second mixing is 20 - 100 °C, such as 20 °C, 30 °C, 50 °C, 80 °C, 100 °C, etc., the time of the second mixing is 1 - 180 min, such as 1 min, 10 min, 50 min, 78 min, 86 min, 95 min, 110 min, 125 min, 130 min, 160 min, 180 min, etc., and the rotation speed of the second mixing is 100 - 400 r / min; for example, 100 r / min, 120 r / min, 150 r / min, 180 r / min, 200 r / min, 260 r / min, 290 r / min, 320 r / min, 400 r / min, etc. If the mixing temperature is too low, it will cause uneven coating and the formed coating layer will be thinner; if the mixing temperature is too high, it may cause thermal decomposition of the coating material and oxidation of the magnetic particles.

[0073] In some embodiments of the present application, the preparation method of the modified magnetic nanoparticles further includes sequentially filtering and washing the second mixing product; preferably, the washing includes sequentially washing with ethanol and deionized water. Wash repeatedly until the pH of the wash liquor is 7, and then perform vacuum drying.

[0074] In some embodiments of the present application, magnetic nanoparticles are prepared by the co - precipitation method. The specific steps include: according to the molar ratio of Fe 2+ 、Fe 3+ 、OH - being (0.5 - 0.75):1:(4 - 4.5), dissolving FeCl3•6H2O and FeCl2•4H2O in deionized water and stirring evenly to obtain a mixed iron salt solution, adding ammonia water to the mixed iron salt solution; and controlling the reaction temperature to be 25 - 100 °C, the stirring speed to be 200 - 500 r / min, reacting for 1 - 60 min under these conditions, repeatedly washing the obtained product with deionized water until the pH of the wash liquor = 7, and performing vacuum drying to obtain magnetic nanoparticles.

[0075] In some embodiments of the present application, the crosslinking agent includes glutaraldehyde, epichlorohydrin, hexamethylene diisocyanate, γ-aminopropyltriethoxysilane (APTES). The crosslinking agent glutaraldehyde in the present application has aldehyde groups at both ends of the chain, which can react with amino groups to form imines and react with carboxylic acids to form esters for crosslinking. At the same time, epichlorohydrin contains epoxy groups and hexamethylene diisocyanate contains isocyanate groups -NCO, which can react with amino groups and carboxyl groups for crosslinking.

[0076] In some embodiments of the present application, the mass ratio of the addition amount of the crosslinking agent to the total mass of the modified magnetic microparticles and the modified magnetic nanoparticles is 1:(0.3 - 1), such as 1:0.3, 1:0.5, 1:0.7, 1:0.9, 1:1, etc.

[0077] In some embodiments of the present application, in step (3), the mixing is carried out in a third solvent, and the third solvent includes deionized water.

[0078] In some embodiments of the present application, in step (3), the temperature of the mixing is 20 - 100 °C, such as 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 50 °C, 60 °C, 80 °C, 100 °C, etc., the time of the mixing is 30 - 240 min, such as 30 min, 80 min, 100 min, 120 min, 160 min, 180 min, 240 min, etc., and the rotation speed of the mixing is 100 - 200 r / min, such as 100 r / min, 110 r / min, 120 r / min, 150 r / min, 160 r / min, 180 r / min, 200 r / min, etc. If the mixing temperature is too low, the crosslinking is slow; if the mixing temperature is too high, it may cause the surfactant to fail.

[0079] The technical solution of the present application will be further described below in combination with specific implementation cases.

[0080] Example 1

[0081] A method for preparing a composite magnetic powder includes the following steps:

[0082] Weigh 11 g of FeCl₃•6H₂O and 9.7 g of FeCl₂•4H₂O and dissolve them in 400 ml of deionized water. Add 5 g of sodium citrate, and slowly drip 2 mol / l NaOH solution until the pH of the solution reaches 10. Stir and react at a speed of 400 r / min under the condition of 80 °C for 1 h. It can be observed that the solution turns into a black suspension, indicating that iron ions have started to form precipitates. Transfer the suspension generated from the above reaction to a high-pressure reactor and seal it. Carry out hydrothermal reaction at 180 °C and 1 MPa for 12 hours. After naturally cooling to room temperature, take out the reaction product. Place the prepared solution on a permanent magnet to separate the solvent and magnetic particles, and repeatedly wash it five times with deionized water until the pH of the washing solution is 7. Vacuum dry to obtain micron-sized magnetic micron particles.

[0083] Redisperse 11 g of Fe₃O₄ magnetic micron particles with a particle size of 10 μm into 400 ml of deionized water, add 1 g of glutamic acid surfactant, stir evenly to form a suspension. Heat the above suspension in a water bath to 60 °C and keep it warm for 60 min under the condition of a stirring speed of 400 r / min. After the reaction is completed, let the reaction solution cool naturally until it reaches room temperature. Magnetically separate the black solid, and repeatedly wash it with ethanol and deionized water in turn until the pH of the washing solution is 7. Vacuum dry to obtain modified Fe₃O₄ micron-sized magnetic micron particles.

[0084] Weigh 25.6 g of FeCl₃•6H₂O and 22.6 g of FeCl₂•4H₂O, dissolve them in 400 mL of deionized water, slowly drip 100 ml of 2 mol / l NaOH solution, and stir at 400 r / min and 40 °C for 1 h. It can be observed that the mixed solution quickly changes from yellow to black. After the reaction is completed, magnetically separate the magnetic particles, and repeatedly wash them five times with deionized water until the pH of the washing solution is 7. Vacuum dry to obtain Fe₃O₄ nanoscale magnetic nanoparticles.

[0085] Redisperse 27 g of Fe₃O₄ magnetic nanoparticles with a particle size of 10 nm into 400 ml of deionized water, add 1 g of oleic acid surfactant, stir evenly to form a suspension. Heat the above suspension in a water bath to 80 °C and keep it warm for 60 min under the condition of a stirring speed of 400 r / min. After the reaction is completed, let the reaction solution cool naturally until it reaches room temperature. Magnetically separate the black solid, and repeatedly wash it with ethanol and deionized water in turn until the pH of the washing solution is 7 to obtain a solution of modified Fe₃O₄ magnetic nanoparticles.

[0086] Dissolve 12 g of modified Fe3O4 magnetic micro-particles and 28 g of modified Fe3O4 magnetic nano-particles in deionized water. At the same time, add 2 ml of 25% glutaraldehyde solution as a cross-linking agent, and stir at a speed of 200 r / min at 40 °C for 2 h. After the reaction is completed, magnetically separate the magnetic particles, and wash them repeatedly with deionized water until the pH of the washing solution is 7. Vacuum dry to obtain composite magnetic powder with a particle size of 10 μm and stable nano-micro structure.

[0087] Example 2

[0088] A method for preparing composite magnetic powder, comprising the following steps:

[0089] Weigh 11 g of FeCl3•6H2O and dissolve it in 400 ml of deionized water. Add 5 g of sodium citrate, and slowly drop 2 mol / l NaOH solution until the pH of the solution is 10. Stir and react at a speed of 400 r / min at 80 °C for 1 h. It can be observed that the solution becomes a black suspension, indicating that iron ions have started to form precipitates. Transfer the above-mentioned reaction-generated suspension to a high-pressure reactor and seal it. Carry out hydrothermal reaction at 180 °C and 1 MPa for 12 hours. After naturally cooling to room temperature, take out the reaction product. Place the prepared solution on a permanent magnet to separate the solvent and magnetic particles, and wash it repeatedly with deionized water five times until the pH of the washing solution is 7. Vacuum dry to obtain micron-sized magnetic micro-particles.

[0090] Redisperse 3 g of γ-Fe2O3 magnetic micro-particles with a particle size of 10 μm into 400 ml of deionized water, and add 1 g of glutamic acid surfactant. Stir evenly to form a suspension. Heat the above suspension in a water bath to 60 °C, and keep it at a constant temperature for 60 min under the condition of a stirring speed of 400 r / min. After the reaction is completed, let the reaction solution cool naturally until it cools to room temperature. Magnetically separate the black solid, and wash it repeatedly with ethanol and deionized water until the pH of the washing solution is 7. Vacuum dry to obtain modified γ-Fe2O3 micron-sized magnetic micro-particles.

[0091] Weigh 25.6 g of FeCl3•6H2O and dissolve it in 400 mL of deionized water. Slowly drop 2 mol / l NaOH solution until the pH of the solution is 10. Stir at 400 r / min and 40 °C for 1 h. After the reaction is completed, magnetically separate the magnetic particles, and wash them repeatedly with deionized water five times until the pH of the washing solution is 7. Vacuum dry to obtain γ-Fe2O3 nano-sized magnetic nano-particles.

[0092] Disperse 7 g of γ-Fe2O3 magnetic nanoparticles with a particle size of 10 nm into 400 ml of deionized water again, add 1 g of oleic acid surfactant, stir evenly to form a suspension. Heat the above suspension in a water bath to 80 °C, and keep it warm for 60 min under the condition of a stirring speed of 400 r / min. After the reaction is completed, let the reaction solution cool naturally until it cools to room temperature. Magnetically separate the black solid, and repeatedly wash it with ethanol and deionized water in turn until the pH of the washing solution is 7 to obtain a solution of modified γ-Fe2O3 magnetic nanoparticles.

[0093] Dissolve 4 g of modified γ-Fe2O3 magnetic micro-particles and 8 g of modified γ-Fe2O3 magnetic nanoparticles in deionized water, and at the same time add 2 ml of 25% glutaraldehyde solution as a cross-linking agent. Stir at a speed of 200 r / min at 40 °C for 2 h. After the reaction is completed, magnetically separate the magnetic particles, and repeatedly wash them with deionized water until the pH of the washing solution is 7, and vacuum dry to obtain stable nano-micro composite magnetic powder with a particle size of 10 μm.

[0094] Example 3

[0095] A preparation method of composite magnetic powder, comprising the following steps:

[0096] Weigh 8 g of CoCl2•6H2O and 11 g of FeCl3·6H2O, dissolve them in 400 ml of deionized water, add 5 g of sodium citrate, slowly drop 2 mol / l NaOH solution until the pH of the solution is 10, and stir and react at a rotation speed of 400 r / min at 80 °C for 1 h. It can be observed that the solution becomes a black suspension, indicating that iron ions have started to form a precipitate. Transfer the above-mentioned suspension generated by the reaction to a high-pressure reaction kettle and seal it. Carry out hydrothermal reaction at 180 °C and 1 MPa for 12 hours. After naturally cooling to room temperature, take out the reaction product, place the prepared solution on a permanent magnet to separate the solvent and magnetic particles, and repeatedly wash it with deionized water five times until the pH of the washing solution is 7, and vacuum dry to obtain micron-sized magnetic micro-particles.

[0097] Disperse 4.8 g of CoFe2O4 magnetic micro-particles with a particle size of 10 μm into 400 ml of deionized water again, add 1 g of glutamic acid surfactant, stir evenly to form a suspension. Heat the above suspension in a water bath to 60 °C, and keep it warm for 60 min under the condition of a stirring speed of 400 r / min. After the reaction is completed, let the reaction solution cool naturally until it cools to room temperature. Magnetically separate the black solid, and repeatedly wash it with ethanol and deionized water in turn until the pH of the washing solution is 7, and vacuum dry to obtain modified CoFe2O4 micron-sized magnetic micro-particles.

[0098] Weigh 18.7 g of CoCl2•6H2O and 25.6 g of FeCl3·6H2O and dissolve them in 400 mL of deionized water. Slowly add 2 mol / l NaOH solution dropwise until the pH of the solution reaches 10. Stir at 400 r / min and 40 °C for 1 h. After the reaction is completed, magnetically separate the magnetic particles, and wash them repeatedly with deionized water five times until the pH of the washing solution is 7. Then, vacuum dry to obtain CoFe2O4 nanoscale magnetic nanoparticles.

[0099] Redisperse 11.2 g of CoFe2O4 magnetic nanoparticles with a particle size of 10 nm into 400 ml of deionized water, add 1 g of oleic acid surfactant, stir evenly to form a suspension. Heat the above suspension in a water bath to 80 °C and keep it warm for 60 min under the condition of a stirring speed of 400 r / min. After the reaction is completed, let the reaction solution cool naturally until it reaches room temperature. Magnetically separate the black solid, and wash it repeatedly with ethanol and deionized water until the pH of the washing solution is 7 to obtain a solution of modified CoFe2O4 magnetic nanoparticles.

[0100] Dissolve 5.8 g of modified CoFe2O4 magnetic micro-particles and 5.8 g of modified CoFe2O4 magnetic nanoparticles in deionized water, and simultaneously add 2 ml of 25% glutaraldehyde solution as a cross-linking agent. Stir at 200 r / min at 40 °C for 2 h. After the reaction is completed, magnetically separate the magnetic particles, and wash them repeatedly with deionized water until the pH of the washing solution is 7. Then, vacuum dry to obtain composite magnetic powder with a particle size of 10 μm of stable nano-micro-nano.

[0101] Example 4

[0102] The difference between Example 4 and Example 1 is only that: in the composite magnetic powder described in Example 4, lysine is used to modify the magnetic micro-particles.

[0103] Example 5

[0104] The difference between Example 5 and Example 1 is only that: in the composite magnetic powder described in Example 5, adipic acid is used to modify the magnetic micro-particles.

[0105] Example 6

[0106] The difference between Example 6 and Example 1 is only that: in the composite magnetic powder described in Example 6, 3-mercaptopropionic acid is used to modify the magnetic micro-particles.

[0107] Example 7

[0108] The difference between Example 7 and Example 1 is only that: in the composite magnetic powder described in Example 7, the mass ratio of the modified Fe3O4 magnetic micro-particles to the modified Fe3O4 magnetic nanoparticles is 2:8.

[0109] Example 8

[0110] The difference between Example 8 and Example 1 is only that: in the composite magnetic powder described in Example 8, the mass ratio of the modified Fe3O4 magnetic micron particles to the modified Fe3O4 magnetic nano particles is 1:9.

[0111] Example 9

[0112] The difference between Example 9 and Example 1 is only that: in the composite magnetic powder described in Example 9, the mass ratio of the modified Fe3O4 magnetic micron particles to the modified Fe3O4 magnetic nano particles is 1:1.

[0113] Example 10

[0114] The difference between Example 10 and Example 1 is only that: in the composite magnetic powder described in Example 10, the mass ratio of the modified Fe3O4 magnetic micron particles to the modified Fe3O4 magnetic nano particles is 7:3.

[0115] Comparative Example 1

[0116] The difference between Comparative Example 1 and Example 1 is only that: in the composite magnetic powder described in Comparative Example 1, the magnetic micron particles are modified with a second surfactant, and the magnetic nano particles are modified with a first surfactant.

[0117] Comparative Example 2

[0118] The difference between Comparative Example 2 and Example 1 is only that: in the composite magnetic powder described in Comparative Example 2, the magnetic nano particles are modified with a first surfactant.

[0119] Comparative Example 3

[0120] The difference between Comparative Example 3 and Example 1 is only that: in the composite magnetic powder described in Comparative Example 3, the magnetic micron particles are modified with a second surfactant.

[0121] Performance study of the composite magnetic powders described in Examples 1-11 and Comparative Examples 1-3 of the present application:

[0122] Test method: The composite magnetic powders described in Examples 1-9 and Comparative Examples 1-3 of the present application are modeled and simulated by COMSOL Multiphysics to obtain the permeability of different magnetic particles, which is used to describe the ease of fluid passing through a porous medium under a certain driving force and reflect its leakage resistance; the saturation magnetization intensity of each magnetic powder is analyzed by a vibrating sample magnetometer (VSM) to reflect its pressure resistance; the oxidation days are judged by visually observing whether the color of the magnetic powder changes to compare the stability of the magnetic particles.

[0123] The test results are shown in Table 1:

[0124] Table 1

[0125]

[0126] It can be seen from Table 1 that:

[0127] Through the analysis of Examples 1-3, it can be found that when using Fe3O4, γ-Fe2O3, and CoFe2O4 to prepare micro-nano composite magnetic powder respectively, their particle permeability and stability show relatively similar performances, and the differences are not significant. However, in terms of the key index of saturation magnetization intensity, there is a size relationship of Fe3O4 > γ-Fe2O3 > CoFe2O4 among the three. This result indicates from the side that the micro-nano composite magnetic powder prepared based on Fe3O4 performs better in terms of pressure resistance and can withstand greater pressure while maintaining a better performance state.

[0128] Through the analysis of Example 1 and Examples 4-6, it can be found that the influence of different first surfactants on the saturation magnetization intensity is relatively small. In terms of permeability, it shows a rule of increasing in the order of glutamic acid, lysine, adipic acid, and dimercaptopropionic acid. In terms of stability, from the perspective of the oxidation days, glutamic acid performs the best, and lysine, adipic acid, and dimercaptopropionic acid weaken in turn. It is speculated that this may be due to the decreasing bonding stability of the aldehyde group in glutaraldehyde cross-linking agent with amino group, carboxyl group, and mercapto group in turn.

[0129] Through the analysis of Example 1 and Examples 7-10, it can be known that the saturation magnetization intensity of the composite magnetic powder shows a trend of increasing with the increase of the mass ratio of magnetic micron particles to magnetic nano particles. However, when the mass ratio of the two reaches 3:7, even if the proportion of magnetic micron particles is further increased, the growth rate of the saturation magnetization intensity of the composite magnetic powder is extremely limited, almost negligible, and approximately does not increase. On the other hand, the change rule of the permeability of the composite magnetic powder is that it increases correspondingly with the decrease of the mass ratio of magnetic micron particles and magnetic nano particles. But when the mass ratio is 3:7, if the proportion of magnetic nano particles is continuously increased, the decrease degree of the permeability of the composite magnetic powder is extremely small, and it can be basically considered that there is no obvious decrease. The above experimental results can show that when the mass ratio of magnetic micron particles and magnetic nano particles is exactly 3:7, the composite magnetic powder exhibits the strongest pressure resistance, and at the same time its permeability reaches the minimum state.

[0130] Analysis of Example 1 and Comparative Example 1 shows that when the second surfactant is used to modify magnetic micron particles and the first surfactant is used to modify magnetic nano particles respectively, the saturation magnetization intensity of the finally obtained composite magnetic powder is not significantly affected. However, the leakage rate of Comparative Example 1 is significantly higher than that of Example 1, and there is also a large gap in its stability compared with Example 1, far lower than the stability level of Example 1.

[0131] Further comparison of Example 1 and Comparative Example 2 shows that when the first surfactant is used to modify magnetic nano particles, the saturation magnetization intensity of Comparative Example 2 is significantly lower than that of Example 1, while its leakage rate is higher than that of Example 1, and its stability is far inferior to that of Example 1. Through analysis and speculation, this may be due to the simultaneous introduction of a surfactant with two hydrophilic ends, resulting in overcoating of the magnetic particles, thereby reducing the saturation magnetization intensity and causing particle agglomeration problems, ultimately having a negative impact on its performance.

[0132] Analysis of Example 1 and Comparative Example 3 shows that after using the second surfactant to modify magnetic micron particles, the obtained saturation magnetization intensity and leakage rate are similar to those of Example 1, but the stability is significantly lower than that of Example 1. Through in-depth analysis, it is considered that this may be because the coating process is incomplete and the effect of the cross-linking agent is not good, resulting in a decrease in the stability of the particles and unable to reach the stability level of Example 1.

[0133] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the protection scope of the present invention.

Claims

1. A composite magnetic powder, characterized in that, It includes modified magnetic micron particles and modified magnetic nano particles. The modified magnetic micron particles are magnetic micron particles modified by a first surfactant, and the magnetic nano particles are magnetic nano particles modified by a second surfactant; The first surfactant is glutamic acid, and the second surfactant includes one or more of long-chain fatty acids, silane coupling agents, and polymers; The mass ratio of the modified magnetic micron particles to the modified magnetic nano particles is 3:

7.

2. The composite magnetic powder according to claim 1, wherein The magnetic micron particles and the magnetic nano particles are each independently selected from one or more of Fe3O4, γ-Fe2O3, and ferrite magnetic particles; and / or, the particle size of the magnetic micron particles is 10-20 μm; and / or, the particle size of the magnetic nano particles is 1-10 nm.

3. The composite magnetic powder according to claim 2, wherein The molar ratio of the magnetic micron particles to the first surfactant in the modified magnetic micron particles is 1:(0.1-2); and / or, the molar ratio of the magnetic nano particles to the second surfactant in the modified magnetic nano particles is 1:(0.1-2).

4. The composite magnetic powder according to claim 3, wherein The chemical formula of the ferrite magnetic particles is MFe2O4, where M includes one or more of Mn, Co, Ni, Cu, Cd, Pb, Sn, Ca, Sr, Ba, and Mg; and / or, the long-chain fatty acids include one or more of oleic acid, stearic acid, and palmitic acid; and / or, the silane coupling agents include one or more of tetraethoxysilane, methacryloxypropyltriethoxysilane, and octadecyltrimethoxysilane; and / or, the polymers include one or more of polyethylene glycol, polyvinylpyrrolidone, and perfluoropolyether carboxylic acid; and / or, the particle size of the composite magnetic powder is 1-10 μm.

5. The preparation method of the composite magnetic powder according to any one of claims 1-4, characterized in that, It includes the following steps: (1) Prepare modified magnetic micron particles; (2) Prepare modified magnetic nano particles; (3) Mix the modified magnetic micron particles, the modified magnetic nano particles, and a crosslinking agent to obtain the composite magnetic powder.

6. The preparation method of the composite magnetic powder according to claim 5, characterized in that, In step (1), the preparation method of the modified magnetic micron particles includes the following steps: First mix the magnetic micron particles, the first surfactant, and a first solvent to obtain the modified magnetic micron particles; and / or, the preparation method of the modified magnetic micron particles further includes performing magnetic sedimentation washing treatment on the first mixed product in sequence.

7. The preparation method of the composite magnetic powder according to claim 6, wherein The content of the first surfactant in each liter of the first solvent is 0.01-1 mol; and / or, the first solvent includes ethanol and / or deionized water; and / or, the temperature of the first mixing is 20-80 °C, the time of the first mixing is 1-180 min, and the rotation speed of the first mixing is 100-400 r / min; and / or, the washing includes washing successively with ethanol and deionized water.

8. The preparation method of the composite magnetic powder according to claim 5, characterized in that, In step (2), the preparation method of the modified magnetic nano particles includes the following steps: Second mix the magnetic nano particles, the second surfactant, and a second solvent to obtain the modified magnetic nano particles; and / or, the preparation method of the modified magnetic nano particles further includes performing magnetic sedimentation washing treatment on the second mixed product in sequence.

9. The preparation method of the composite magnetic powder according to claim 8, characterized in that, The content of the second surfactant in the second solvent per liter is 0.01 - 1 mol; and / or, the second solvent includes ethanol and / or deionized water; and / or, the temperature of the second mixing is 20 - 100 °C, the time of the second mixing is 1 - 180 min, and the rotation speed of the second mixing is 100 - 400 r / min; and / or, the washing includes washing successively with ethanol and deionized water.

10. The preparation method of the composite magnetic powder according to claim 5, characterized in that, In step (3), the mixing is carried out in a third solvent, and the third solvent includes deionized water; and / or, the crosslinking agent includes one or more of glutaraldehyde, epichlorohydrin, hexamethylene diisocyanate, and γ-aminopropyltriethoxysilane; and / or, the mass ratio of the addition amount of the crosslinking agent to the total amount of the modified magnetic microparticles and the modified magnetic nanoparticles is 1:(0.3 - 1); and / or, in step (3), the temperature of the mixing is 20 - 100 °C, the time of the mixing is 30 - 240 min, and the rotation speed of the mixing is 100 - 200 r / min.

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