A nanomagnetic particle, its preparation method, and a magnetic liquid

Abstract

This invention relates to the field of magnetic materials technology, specifically to a type of magnetic nanoparticle, its preparation method, and a magnetic liquid. The magnetic nanoparticle comprises an iron-cobalt alloy, wherein the cobalt-iron molar ratio of the iron-cobalt alloy is 2-5, and the saturation magnetization of the magnetic nanoparticle is ≥200 emu / g. This invention directly obtains iron-cobalt alloy magnetic nanoparticles with high saturation magnetization by synthesizing an iron-cobalt layered double hydroxide precursor and then reducing it with hydrogen. The nanoparticles are then surface-modified and dispersed in a suitable carrier liquid to obtain a magnetic liquid with high saturation magnetization.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, specifically to a nanomagnetic particle, its preparation method, and a magnetic liquid. Background Technology

[0002] Magnetic fluids are a novel type of smart material with wide applications in many high-tech fields such as aerospace, electronics, machinery and chemical engineering, energy and metallurgy, instrumentation, and biomedicine. Typically, magnetic fluids are colloidal liquids composed of highly dispersed nanoscale magnetic particles in a carrier liquid (usually an organic solvent or water). The interaction between the carrier liquid and the nanoscale magnetic particles gives the magnetic fluid both the fluidity of a liquid and the magnetic properties of a solid.

[0003] Saturation magnetization (Ms) is one of the important indicators for evaluating the performance of magnetic fluids. It is mainly determined by the properties of the magnetic particles that make up the magnetic fluid and the volume fraction of these particles in the fluid. Currently, commonly used magnetic fluids are classified into ferrite-type magnetic fluids, metallic-type magnetic fluids, and iron nitride-type magnetic fluids. Ferrite-type magnetic fluids are the most widely used due to their good stability. For example, in Chinese patent CN109065319A, Fe3O4 particles with a saturation magnetization of 84 emu / g were prepared by an oxidative co-precipitation method and used to prepare fluorinated ether-based magnetic fluids. In Chinese patent CN107799262B, Mn3O4 particles with a saturation magnetization of 54 emu / g were prepared by a two-step precipitation method. 0.8 Zn 0.2 Fe₂O₄ magnetic particles are used, but when applied to prepare magnetic liquids, the saturation magnetization is only 3-14 emu / g, which is unsatisfactory. Ferrite-based magnetic liquids also have low saturation magnetization, generally between 200-300 G, with a maximum of only 600 G, thus limiting their application range. Iron nitride-based magnetic liquids developed in recent years possess high Ms, but also suffer from poor chemical stability, complex preparation processes, and difficulty in detecting magnetic particles. Metal-based magnetic liquids also have high Ms, but similarly exhibit poor chemical stability. Therefore, there is an urgent need to develop a magnetic liquid with both high saturation magnetization and high stability. Summary of the Invention

[0004] This invention is based on the inventor's discovery and understanding of the following facts and problems: FeCo alloy is a soft magnetic metal material widely used in magnetic recording, sensors and magnetic liquid preparation. At present, FeCo alloy is mainly prepared by metal smelting and chemical reduction. However, both of these methods have problems such as complex metal precursor sources leading to uneven distribution of metal atoms in the alloy particles, which affects the saturation magnetization. In addition, the preparation process is complex, energy consumption is high, and there are environmental hazards.

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a high-saturation-magnetization nanoparticle, its preparation method, and a high-saturation-magnetization nanoparticle magnetic liquid. High-saturation-magnetization iron-cobalt layered double hydroxide precursors are directly obtained by hydrogen reduction. The nanoparticles are then surface-modified and dispersed in a suitable carrier liquid to obtain a magnetic liquid with high saturation-magnetization.

[0006] A high saturation magnetization nanoparticle according to an embodiment of the present invention comprises an iron-cobalt alloy, wherein the cobalt-iron molar ratio of the iron-cobalt alloy is 2-5:1, and the saturation magnetization of the nanoparticle is ≥200 emu / g.

[0007] The advantages and technical effects of the high saturation magnetization nanoparticles in this invention are as follows: using alloyed iron and cobalt metals as the magnetic source of the nanoparticles, the nanoparticles have high saturation magnetization, providing a material basis for the subsequent preparation of magnetic liquids with good magnetic separation performance.

[0008] In some embodiments of the present invention, the particle size of the nanomagnetic particles is 20-150 nm.

[0009] A method for preparing the above-mentioned nanomagnetic particles according to an embodiment of the present invention includes the following steps:

[0010] a. Add a precipitant to a mixed solution of iron and cobalt ions to obtain a suspension, perform hydrothermal treatment, collect the precipitate, and obtain iron-cobalt hydrotalcite;

[0011] b. The iron-cobalt hydrotalcite is reduced under a hydrogen atmosphere to obtain the nano-magnetic particles.

[0012] The advantages and technical effects of the above-mentioned method for preparing nanomagnetic particles in this invention are as follows: 1. Using iron-cobalt hydrotalcite as a precursor, iron-cobalt alloy nanomagnetic particles are directly obtained through hydrogen reduction. Since the metal ion composition of the hydrotalcite layers is adjustable, precise ratios and uniform dispersion of iron and cobalt ions can be achieved. The metal source ratio in the reduced iron-cobalt alloy nanomagnetic particles is precise and the dispersion is uniform, avoiding lattice defects caused by metal source diversification or uneven dispersion, thereby improving the magnetic properties of the nanomagnetic particles; 2. Granular iron-cobalt hydrotalcite is prepared by co-precipitation, and then... 1. After hydrogen reduction, nanoscale powder of iron-cobalt alloy can be directly obtained without high-intensity grinding, thus avoiding the destruction of the lattice structure of nanomagnetic particles caused by high-intensity grinding; 2. During the preparation of iron-cobalt hydrotalcite, hydrothermal treatment of the obtained suspension can make the hydrotalcite grains fully developed, small in size, and uniformly distributed, with less particle agglomeration, and can obtain suitable stoichiometry and crystal form; 3. The preparation method of the nanomagnetic particles of the present invention is simple and efficient, and the prepared products have excellent magnetic properties and stability. At the same time, the equipment requirements are low, and it is easy to realize applications in various fields.

[0013] In some embodiments of the present invention, in step a, the molar ratio of cobalt to iron in the iron-cobalt mixed solution is 2-5:1;

[0014] And / or, the precipitant is selected from at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, and ammonia water;

[0015] And / or, the precipitant is added dropwise, with the endpoint being a solution pH of 9-10.

[0016] In some embodiments of the present invention, in step a, the temperature for hydrothermal treatment of the suspension is 100-120°C, and the treatment time is 8-16 hours.

[0017] And / or, step a further includes filtering, washing and drying the precipitate.

[0018] In some embodiments of the present invention, in step b, the reduction reaction temperature is 327-627°C and the reduction reaction time is 1-6 hours.

[0019] This invention also provides a method for preparing modified magnetic nanoparticles, comprising: reacting the above-mentioned magnetic nanoparticles with a surfactant treated with ammonia water to obtain the modified magnetic nanoparticles.

[0020] The advantages and technical effects of the modified magnetic nanoparticle preparation method of this invention are as follows: by using a surfactant treated with ammonia water to modify the magnetic nanoparticles, the nanoparticles can be well coated by the surfactant, which improves the dispersibility and compatibility of the magnetic nanoparticles in the magnetic liquid and prevents the particles from agglomerating or settling.

[0021] In some embodiments of the present invention, the molar ratio of the surfactant to the nanomagnetic particles is (0.1-1.0):1;

[0022] And / or, the surfactant is selected from silane coupling agents or fatty acids with a carbon chain length ≥16, wherein the silane coupling agent is selected from at least one of methacryloxypropyltriethoxysilane (KH570), dodecyltrioxysilane (DTEOS), or octadecyltrioxysilane (OTMOS); and the fatty acid with a carbon chain length ≥16 is selected from at least one of oleic acid, stearic acid, or palmitic acid;

[0023] And / or, the modification reaction temperature is 20-100℃, the modification reaction time is 1-60min, and the stirring speed of the modification reaction is 200-400r / min;

[0024] And / or, the method for preparing the surfactant after ammonia treatment includes adding ammonia to the surfactant, wherein the mass ratio of the surfactant to ammonia is 1:(1-2), and the concentration of ammonia is 5-30%;

[0025] And / or, the preparation method further includes filtering, washing and drying the modified magnetic nanoparticles.

[0026] A magnetic liquid with high saturation magnetization according to an embodiment of the present invention includes the above-mentioned modified nanomagnetic particles and a base carrier liquid.

[0027] The advantages and technical effects of the high saturation magnetization magnetic liquid in this invention are as follows: 1. Using iron-cobalt alloy nanomagnetic particles obtained by hydrogen reduction of iron-cobalt layered double hydroxide precursors, the metal ion composition of the layered double hydroxide plates can be adjusted, achieving precise ratio and uniform dispersion of iron and cobalt ions. The metal source ratio in the reduced iron-cobalt alloy nanomagnetic particles is precise and the dispersion is uniform, avoiding lattice defects caused by metal source diversification or uneven dispersion, thereby improving the magnetic properties of the gold nanomagnetic particles; 2. The granular iron-cobalt layered double hydroxide prepared by the co-precipitation method can be directly reduced with hydrogen to obtain iron-cobalt alloy nanoparticles, without the need for high strength 1. **Grinding:** This process avoids damage to the lattice structure of the nanomagnetic particles caused by high-intensity grinding, thus improving the magnetic separation performance of the magnetic liquid. 2. **Modification of the nanomagnetic particles with a surfactant treated with ammonia water:** The nanoparticles are well coated with the surfactant, improving their dispersibility and compatibility in the magnetic liquid, preventing particle aggregation or sedimentation, and enhancing the dispersibility and stability of the magnetic solution. 3. **The high saturation magnetization magnetic liquid of this invention has a simple and efficient preparation method, producing products with excellent magnetic properties and stability. It also has low equipment requirements and is easily applicable in various fields.

[0028] In some embodiments of the present invention, the modified magnetic nanoparticles have a particle size of 20-150 nm;

[0029] And / or, the carrier fluid is selected from at least one of kerosene, mineral oil, vegetable oil, engine oil, esters or water. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0031] A high saturation magnetization nanoparticle according to an embodiment of the present invention comprises an iron-cobalt alloy, wherein the cobalt-iron molar ratio of the iron-cobalt alloy is 2-5:1, and the saturation magnetization of the nanoparticle is ≥200 emu / g.

[0032] The high saturation magnetization nanoparticles of this invention use alloyed iron and cobalt metals as the magnetic source for the nanoparticles, giving them high saturation magnetization and providing a material basis for the subsequent preparation of magnetic liquids with good magnetic separation performance.

[0033] In some embodiments of the present invention, the particle size of the nanomagnetic particles is 20-150 nm. The nanomagnetic particles of the embodiments of the present invention have a small particle size and uniform particle size dispersion, making them suitable for preparing magnetic liquids.

[0034] A method for preparing the above-mentioned nanomagnetic particles according to an embodiment of the present invention includes the following steps:

[0035] a. Add a precipitant to a mixed solution of iron and cobalt ions to obtain a suspension, perform hydrothermal treatment, collect the precipitate, and obtain iron-cobalt hydrotalcite;

[0036] b. The iron-cobalt hydrotalcite is reduced under a hydrogen atmosphere to obtain the nano-magnetic particles.

[0037] The method for preparing nanomagnetic particles according to embodiments of the present invention uses iron-cobalt hydrotalcite as a precursor, and directly obtains iron-cobalt alloy nanomagnetic particles through hydrogen reduction. Since the metal ion composition of the hydrotalcite layers is adjustable, the precise ratio and uniform dispersion of iron and cobalt ions can be achieved. The metal source ratio in the iron-cobalt alloy nanomagnetic particles obtained after reduction is precise and the dispersion is uniform, avoiding lattice defects caused by metal source diversification or uneven dispersion, thereby improving the magnetic properties of the nanomagnetic particles. Granular iron-cobalt hydrotalcite is prepared by co-precipitation method, and after hydrogen reduction, nanoscale powder of iron-cobalt alloy can be directly obtained without grinding, avoiding the destruction of the lattice structure of nanomagnetic particles caused by grinding. During the preparation of iron-cobalt hydrotalcite, the obtained suspension is subjected to hydrothermal treatment, which can make the hydrotalcite grains fully developed, small in size, and uniformly distributed, with less particle agglomeration, and can obtain suitable stoichiometry and crystal form. 4. The method for preparing nanomagnetic particles of the present invention is simple and efficient, and the prepared products have excellent magnetic properties and stability. At the same time, the equipment requirements are low, and it is easy to realize applications in various fields.

[0038] Hydrotalcite, also known as layered bimetallic hydroxide, has the general formula: [M 2+ 1-x M 3+ x (OH)2] x+ (A n- ) x / n ·yH2O, where M 2+ and M 3+ Corresponding to the divalent and trivalent metal cations on the plate, A n- M represents inorganic or organic anions, and x is the molar ratio of cations, typically between 0.20 ≤ x ≤ 0.33. In the preparation method of the nanomagnetic particles of this invention, M... 2+ It is a divalent cobalt ion, M 3+ It is a ferric ion, A n- It is a hydroxide ion.

[0039] In some embodiments of the present invention, in step a, the molar ratio of cobalt to iron in the iron-cobalt mixed solution is 2-5:1;

[0040] Preferably, the precipitant is selected from at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, and ammonia water;

[0041] Preferably, the precipitant is added dropwise, with the endpoint being a solution pH of 9-10, which can achieve complete precipitation of iron and cobalt ions.

[0042] In some embodiments of the present invention, in step a, the temperature of the hydrothermal treatment of the suspension is 100-120°C and the treatment time is 8-16h. In the embodiments of the present invention, the temperature and time of the hydrothermal treatment are preferred, which can further obtain hydrotalcite with more complete crystal development, smaller particle size, uniform distribution and less particle agglomeration.

[0043] Preferably, step a further includes filtering, washing, and drying the precipitate;

[0044] Preferably, the precipitate is washed until the pH of the washing solution is ≤7.2.

[0045] In some embodiments of the present invention, in step b, the reduction reaction temperature is 327-627°C, and the reduction reaction time is 1-6 hours. If the reaction temperature is too low, the ionic metal in the hydrotalcite cannot be fully reduced to the alloy state, which will reduce the saturation magnetization of the nanomagnetic particles; if the reaction temperature is too high, the hydrotalcite material will sinter into spheres, the particle size will increase, and nanoscale magnetic particles cannot be obtained.

[0046] A method for preparing modified magnetic nanoparticles according to an embodiment of the present invention includes: reacting the aforementioned magnetic nanoparticles with a surfactant treated with ammonia water to obtain the modified magnetic nanoparticles. In this method, the surfactant is converted to an ammonium salt form after ammonia treatment, which allows for better dissolution in water and easier chemical adsorption onto the surface of the magnetic particles. This enables the surfactant to effectively adsorb onto the surface of the magnetic particles. By using a surfactant treated with ammonia water to modify the magnetic nanoparticles, the nanoparticles can be well coated with the surfactant, improving the dispersibility and compatibility of the magnetic nanoparticles in the magnetic liquid and preventing particle aggregation or sedimentation.

[0047] In some embodiments of the present invention, the molar ratio of the surfactant to the nanomagnetic particles is (0.1-1.0):1;

[0048] Preferably, the surfactant is selected from silane coupling agents or fatty acids with a carbon chain length ≥16, wherein the silane coupling agent is selected from at least one of methacryloxypropyltriethoxysilane (KH570), dodecyltrioxysilane (DTEOS) or octadecyltrioxysilane (OTMOS), and the fatty acid with a carbon chain length ≥16 is selected from at least one of oleic acid, stearic acid or palmitic acid, preferably oleic acid;

[0049] Preferably, the modification reaction temperature is 20-100℃, the modification reaction time is 1-60min, and the stirring speed of the modification reaction is 200-400r / min;

[0050] Preferably, the method for preparing the surfactant after ammonia treatment includes adding ammonia to the surfactant, wherein the mass ratio of the surfactant to ammonia is 1:(1-2), and the concentration of ammonia is 5-30%.

[0051] Preferably, the preparation method further includes filtering, washing, and drying the modified magnetic nanoparticles;

[0052] Preferably, the washing and drying method includes: washing repeatedly with deionized water until the conductivity of the washing solution σ≤30μs / cm, then washing with acetone 2-4 times to remove residual water, and finally vacuum drying to remove acetone; the washing and drying method can ensure that the surface of the modified nanomagnetic particles is pure and free of impurities.

[0053] A magnetic liquid with high saturation magnetization according to an embodiment of the present invention includes the above-mentioned modified nanomagnetic particles and a base carrier liquid.

[0054] The high saturation magnetization magnetic liquid of this invention comprises: 1. Iron-cobalt alloy nanoparticles obtained by reducing an iron-cobalt layered double hydroxide (LDH) precursor with hydrogen. Because the metal ion composition of the LDH layers is adjustable, precise ratios and uniform dispersion of iron and cobalt ions can be achieved. The reduced iron-cobalt alloy nanoparticles have precise metal source ratios and uniform dispersion, avoiding lattice defects caused by diverse or uneven metal sources, thereby improving the magnetic properties of the gold nanoparticles; 2. Granular iron-cobalt LDH prepared by a co-precipitation method can be directly reduced with hydrogen to obtain iron-cobalt alloy nanoparticles without grinding. 1. It avoids the destruction of the crystal structure of nano-magnetic particles caused by grinding, thus improving the magnetic separation performance of the magnetic liquid; 2. The nano-magnetic particles are modified by surfactants after ammonia treatment, which can effectively coat the nano-magnetic particles, improving their dispersibility and compatibility in the magnetic liquid, preventing particle aggregation or sedimentation, and enhancing the dispersibility and stability of the magnetic solution; 3. The magnetic liquid with high saturation magnetization intensity of the present invention has a simple and efficient preparation method, and the prepared product has excellent magnetic properties and stability. At the same time, it has low equipment requirements and is easy to apply in various fields.

[0055] In some embodiments of the present invention, the modified magnetic nanoparticles have a particle size of 20-150 nm;

[0056] Preferably, the carrier liquid is selected from at least one of kerosene, mineral oil, vegetable oil, engine oil, esters or water, preferably esters, and more preferably dioctyl phthalate.

[0057] The present invention will now be described in detail with reference to specific embodiments.

[0058] Example 1

[0059] Preparation of Co2Fe1 alloy nanomagnetic particles

[0060] (1) Weigh 11g of FeCl3·6H2O and 19g of CoCl2·6H2O, dissolve them in 513mL of deionized water, control the stirring speed at 400r / min, stir for 1.5h, then adjust the pH of the mixed salt solution to 9-10 with NaOH solution, and continue stirring for 0.5h. Then transfer it to a hydrothermal reactor and heat it to 120℃ for 12h. Then, filter, wash and dry the mixture to obtain the precursor hydrotalcite powder.

[0061] (2) The obtained precursor hydrotalcite powder was placed in a quartz tube, pure hydrogen was introduced, and the mixture was heated to 873K and kept for 3 hours. After cooling to room temperature, the atmosphere was switched to nitrogen and kept for 1 hour to obtain Co2Fe1 alloy nanomagnetic particles.

[0062] Preparation of magnetic fluids

[0063] (1) Disperse the obtained magnetic particles into an appropriate amount of deionized water, weigh 3.5g oleic acid, 4g water, and 3.5g concentrated ammonia (mass concentration 28%), stir evenly to obtain oleic acid amine, add it to the deionized water and stir evenly to form a suspension, heat the suspension to 80℃ in a water bath, control the stirring speed to 400r / min, maintain for 60min, wait for it to cool to room temperature, magnetically separate the solid, wash with water until pH=7, wash three times with acetone, and vacuum dry at 60℃ for 12h to obtain modified Co2Fe1 alloy nanomagnetic particles.

[0064] (2) The modified Co2Fe1 alloy nanomagnetic nanoparticles were ground in a mortar and pestle to disperse the soft agglomerates that may exist after drying. Then, they were dispersed in dioctyl phthalate and sonicated for 2.5 hours to form a stable magnetic liquid with high saturation magnetization.

[0065] Example 2

[0066] Preparation of Co3Fe1 alloy magnetic fluid

[0067] (1) Weigh 11g of FeCl3·6H2O and 28g of CoCl2·6H2O, dissolve them in 513mL of deionized water, control the stirring speed at 400r / min, stir for 1.5h, then adjust the pH of the mixed salt solution to 9-10 with NaOH solution, and continue stirring for 0.5h. Then transfer it to a hydrothermal reactor and heat it to 120℃ for 12h. Then, filter, wash and dry the mixture to obtain the precursor hydrotalcite powder.

[0068] (2) The obtained precursor hydrotalcite powder was placed in a quartz tube, pure hydrogen was introduced, and the mixture was heated to 873K and kept for 3 hours. After cooling to room temperature, the atmosphere was switched to nitrogen and kept for 1 hour to obtain Co3Fe1 alloy nanomagnetic particles.

[0069] Preparation of magnetic fluids

[0070] (1) Disperse the obtained magnetic particles into an appropriate amount of deionized water, weigh 4g of oleic acid, 4g of water, and 4g of concentrated ammonia (mass concentration 28%), stir evenly to obtain the preferred acetic acid, add it to the deionized water and stir evenly to form a suspension, heat the suspension to 80℃ in a water bath, control the stirring speed to 400r / min, maintain for 60min, wait for it to cool to room temperature, magnetically separate the solid, wash with water until pH=7, wash three times with acetone, and vacuum dry at 60℃ for 12h to obtain modified Co3Fe1 alloy nanomagnetic particles.

[0071] (2) The obtained modified Co3Fe1 alloy magnetic nanoparticles were ground in a mortar and pestle to disperse any soft agglomerates that might exist after drying. Then, they were dispersed in dioctyl phthalate and sonicated for 2.5 hours to form a stable magnetic liquid with high saturation magnetization.

[0072] Example 3

[0073] Preparation of Co4Fe1 alloy magnetic fluid

[0074] (1) Weigh 5.5g of FeCl3·6H2O and 19g of CoCl2·6H2O, dissolve them in 513mL of deionized water, control the stirring speed at 400r / min, stir for 1.5h, then adjust the pH of the mixed salt solution to 9-10 with NaOH solution, and continue stirring for 0.5h. Then transfer it to a hydrothermal reactor and heat it to 120℃ for 12h. Then, filter, wash and dry the mixture to obtain the precursor hydrotalcite powder.

[0075] (2) The obtained precursor hydrotalcite powder was placed in a quartz tube, pure hydrogen was introduced, and the mixture was heated to 873K and kept for 3 hours. After cooling to room temperature, the atmosphere was switched to nitrogen and kept for 1 hour to obtain Co4Fe1 alloy nanomagnetic particles.

[0076] Preparation of magnetic fluids

[0077] (1) Disperse the obtained magnetic particles into an appropriate amount of deionized water, weigh 3g of oleic acid, 4g of water, and 3g of concentrated ammonia (mass concentration 28%), stir evenly to obtain oleic acid amine, add it to the deionized water and stir evenly to form a suspension, heat the suspension to 80℃ in a water bath, control the stirring speed to 400r / min, maintain for 60min, wait for it to cool to room temperature, magnetically separate the solid, wash with water until pH=7, wash three times with acetone, and vacuum dry at 60℃ for 12h to obtain modified Co4Fe1 alloy nanomagnetic particles.

[0078] (2) The obtained modified Co4Fe1 alloy nanomagnetic nanoparticles were ground in a mortar and pestle to disperse the soft agglomerated particles that may exist after drying. Then, they were dispersed in dioctyl phthalate and sonicated for 2.5 hours to form a stable magnetic liquid with high saturation magnetization.

[0079] Comparative Example 1

[0080] The preparation method is the same as in Example 1, except that iron-cobalt alloy magnetic nanoparticles are prepared by chemical reduction. The preparation method of iron-cobalt alloy magnetic nanoparticles is as follows: Weigh 11g of FeCl3·6H2O and 19g of CoCl2·6H2O, dissolve them in 513mL of deionized water, stir evenly to obtain a cobalt-iron mixed solution, add it to a constant pressure dropping funnel, add a slightly excess of hydrazine hydrate to a 1000mL round-bottom flask, and then add an appropriate amount of dispersant PVP. At 80°C, the mixed salt is added dropwise to the flask at a rate of 1 drop / second while stirring vigorously. A black precipitate is immediately observed to form. After the mixed solution has been added, continue stirring for 30 minutes, age for one hour, then filter, wash 3-4 times each with distilled water and anhydrous ethanol, and dry in a vacuum drying oven at a temperature controlled within 50-100°C to obtain the product.

[0081] Comparative Example 2

[0082] The preparation method is the same as in Example 1, except that the iron-cobalt hydrotalcite is prepared by reaction at room temperature instead of hydrothermal treatment.

[0083] Comparative Example 3

[0084] The preparation method is the same as in Example 1, except that step (1) is omitted in the preparation of the magnetic liquid and the nano-magnetic particles are not modified.

[0085] In the magnetic liquid prepared in Comparative Example 3, the magnetic particles quickly separated and precipitated from the base liquid, making it impossible to obtain a stable magnetic liquid.

[0086] The nanomagnetic particles and magnetic liquids prepared in the above examples and comparative examples were tested. The test results are shown in Table 1.

[0087] Table 1

[0088]

[0089] As can be seen from the above embodiments and Comparative Example 1, the nanomagnetic particles and magnetic liquid prepared in the embodiments of the present invention have high saturation magnetization. As can be seen from Comparative Example 2, hydrothermal treatment of the suspension during the preparation of iron-cobalt hydrotalcite effectively improved the saturation magnetization of the nanomagnetic particles and magnetic liquid. As can be seen from Comparative Example 3, modification treatment of the nanomagnetic particles allows them to be well coated with surfactants, improving their dispersibility and compatibility in the magnetic liquid and effectively preventing particle aggregation or sedimentation.

[0090] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0091] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0092] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A magnetic liquid with high saturation magnetization, characterized in that, The product includes modified magnetic nanoparticles and a carrier liquid, wherein the carrier liquid is dioctyl phthalate. The modified magnetic nanoparticles are prepared by reacting the magnetic nanoparticles with a surfactant treated with ammonia water to obtain the modified magnetic nanoparticles, followed by filtration, washing, and drying. The method for preparing the nanomagnetic particles includes the following steps: a. Add a precipitant to a mixed solution of iron and cobalt ions by dropwise addition. The endpoint of the addition is when the pH of the solution is 9-10. A suspension is obtained and subjected to hydrothermal treatment at a temperature of 120°C for 12 hours. The precipitate is collected to obtain iron-cobalt hydrotalcite. b. The iron-cobalt hydrotalcite is reduced under a hydrogen atmosphere to obtain the nanomagnetic particles. The nanomagnetic particles include an iron-cobalt alloy with a cobalt-iron molar ratio of 2-5:

1. The saturation magnetization of the nanomagnetic particles is ≥200 emu / g. The method for preparing the surfactant after ammonia treatment is to add ammonia to the surfactant.

2. The magnetic fluid according to claim 1, characterized in that, The particle size of the nanomagnetic particles is 20-150 nm.

3. The magnetic fluid according to claim 1, characterized in that, In step a, the molar ratio of cobalt to iron in the iron-cobalt mixed solution is 2-5:1; And / or, the precipitant is selected from at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, and ammonia water.

4. The magnetic fluid according to claim 1, characterized in that, Step a further includes filtering, washing, and drying the precipitate.

5. The magnetic fluid according to claim 1, characterized in that, In step b, the reduction reaction temperature is 327-627℃, the reduction reaction time is 1-6h; and / or, after the reaction is completed, the temperature is lowered to 20-30℃ and kept at that temperature for 1-3h under nitrogen protection.

6. The magnetic fluid according to claim 1, characterized in that, The molar ratio of the surfactant to the nanomagnetic particles is (0.1-1.0):1; And / or, the surfactant is selected from silane coupling agents or fatty acids with a carbon chain length ≥16, wherein the silane coupling agent is selected from at least one of methacryloxypropyltriethoxysilane, dodecyltrioxysilane or octadecyltrioxysilane; and the fatty acid with a carbon chain length ≥16 is selected from at least one of oleic acid, stearic acid or palmitic acid. And / or, the modification reaction temperature is 20-100℃, the modification reaction time is 1-60min, and the stirring speed of the modification reaction is 200-400r / min; And / or, the mass ratio of the surfactant to ammonia is 1:(1-2), and the concentration of the ammonia is 5-30%.

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