Double-dispersion magnetorheological fluid and preparation method thereof

Abstract

The invention relates to the technical field of magnetorheological fluids, and discloses a double-dispersion magnetorheological fluid and a preparation method thereof.The double-dispersion magnetorheological fluid comprises a dispersion phase and a dispersion medium, and the dispersion phase is evenly dispersed in the dispersion medium; the dispersion phase is formed by compounding FeCo alloy nanoparticles and NiXFe1-XFe2O4 micron particles, and the dispersion medium is a mixed base solution formed by mixing dimethyl silicone oil and poly-alpha olefin synthetic oil. According to the magnetorheological fluid, collaborative innovation is achieved in the three aspects of materials, structures and systems, comprehensive improvement of sedimentation stability, magnetic saturation strength, yield stress and redispersibility is synchronously achieved, meanwhile, the zero-field viscosity is reduced, and the magnetorheological fluid with excellent comprehensive performance is obtained. The prepared magnetorheological fluid can stand for a long time without hard block deposition, is fast in magnetic response and high in working stability, can better adapt to the actual working condition of the magnetorheological damper, and has outstanding application value.

Description

Technical Field

[0001] This invention relates to the field of magnetorheological fluid technology, specifically to a bidisperse magnetorheological fluid and its preparation method. Background Technology

[0002] Magnetorheological fluids are a class of intelligent soft materials with rapid magnetic field response characteristics. They can achieve continuous and reversible changes in rheological properties under the action of an external magnetic field, and have important application value in vibration control, precision machining, and automotive engineering. As related equipment continues to develop towards high performance and long service life, the stability, response speed, and service reliability of magnetorheological fluids also need to be improved in tandem. Traditional material systems and preparation processes are no longer sufficient to meet the higher standards of use.

[0003] Most conventional magnetorheological fluids currently use carbonyl iron powder micron-sized particles as the main magnetic dispersion phase, dispersed in silicone oil or synthetic hydrocarbon base fluids through mechanical stirring or high-shear emulsification. To reduce particle agglomeration, thixotropic agents such as spherical silica and organobentonite are typically added during production, while surfactants such as stearic acid and lauric acid are used for physical adsorption treatment of the particles, thereby improving the compatibility between the particles and the base fluid. This preparation method is relatively cumbersome, and the process parameters are difficult to control, making it difficult to ensure production efficiency while improving material performance, which is not conducive to the large-scale production and cost control of magnetorheological fluids.

[0004] Traditional magnetorheological fluids generally suffer from insufficient sedimentation stability in practical applications. These systems primarily rely on increasing the viscosity of the base fluid and adding surfactants to delay particle settling, but they do not fundamentally address the problem of excessive density differences between magnetic particles and the base fluid. The surfactants used are mostly physically adsorbed, resulting in weak adhesion to the particle surface. Under prolonged static conditions or repeated shearing, they are prone to desorption. Once they lose their effectiveness, the particles settle rapidly and form dense, hard clumps that are difficult to disperse.

[0005] To prevent particle aggregation and agglomeration, traditional magnetorheological fluids rely on thixotropic agents to provide physical support, such as fumed silica. The three-dimensional network structure formed by the thixotropic agent prevents particles from contacting each other. However, this physical support structure is unstable and will gradually collapse under the continuous action of gravity. The constraint effect on the particles will continuously weaken, and after the particles lose their effective barrier, they will still agglomerate and eventually harden and deposit, affecting the normal use and redispersibility of the magnetorheological fluid.

[0006] Traditional magnetorheological fluids typically employ magnetic particles of a single size, presenting an inherent challenge in balancing particle size selection. Increasing particle size enhances magnetic properties but significantly slows down the magnetic field response, while decreasing particle size accelerates the response rate but reduces saturation magnetization. In practical applications, a compromise particle size must be chosen, failing to simultaneously satisfy the requirements of high magnetic properties and fast response. Under dynamic operating conditions, magnetic response hysteresis persists, leading to sluggish operation of related devices and impacting control accuracy and overall performance. Summary of the Invention

[0007] The purpose of this invention is to provide a bidisperse magnetorheological fluid to solve at least one problem existing in the prior art, such as the easy sedimentation and poor stability of magnetorheological fluids.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A bidispersive magnetorheology includes a dispersed phase and a dispersion medium, wherein the dispersed phase is uniformly dispersed in the dispersion medium; the dispersed phase consists of FeCo alloy nanoparticles and Ni. X Fe1- X The composition consists of Fe2O4 micron-sized particles; the dispersion medium is a mixed base liquid formed by mixing dimethyl silicone oil and polyalphaolefin synthetic oil.

[0009] Preferably, the FeCo alloy nanoparticles have a particle size of 8 nm, and Ni X Fe1- X The particle size of Fe2O4 micron particles ranges from 35μm to 60μm.

[0010] Preferably, FeCo alloy nanoparticles and Ni X Fe1- X The mass ratio of Fe2O4 micron particles is 1:4.

[0011] Preferably, the volume ratio or mass ratio of dimethyl silicone oil to polyalphaolefin synthetic oil is 1:1.

[0012] Preferably, the surface of the FeCo alloy nanoparticles is modified by coating with oleic acid.

[0013] Preferably, benzotriazole and polyether-modified siloxane are also added to the dispersion medium.

[0014] Preferably, the amount of benzotriazole added is 1.0 wt% of the total mass of the dispersion medium, and the amount of polyether-modified siloxane added is 0.5 wt% of the total mass of the dispersion medium.

[0015] Another objective of this invention is to provide a method for preparing a bidisperse magnetorheological fluid, thereby improving the stability of the magnetorheological fluid.

[0016] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a bidisperse magnetorheological fluid includes the following steps: FeCo alloy nanoparticles were prepared using an electric arc device and then coated with oleic acid to obtain surface-modified FeCo alloy nanoparticles. Ni was prepared by ultrasonic atomization pyrolysis. X Fe1- X Fe2O4 micron-sized particles; Dimethyl silicone oil is mixed with polyalphaolefin synthetic oil to obtain a mixed base liquid; FeCo alloy nanoparticles with Ni X Fe1- X After premixing Fe2O4 micron-sized particles, they are added to the mixed base liquid and dispersed evenly to obtain a bidispersed magnetorheological fluid.

[0017] Preferably, the preparation process of FeCo alloy nanoparticles is as follows: The iron-cobalt alloy target was placed in the arc plasma device, and argon gas was introduced after the vacuum was drawn. The electric arc is ignited and maintained at a high temperature, causing the target material to evaporate and form metal vapor. The vapor is then rapidly cooled, nucleated, and clustered in an inert atmosphere to obtain FeCo alloy nanoparticles.

[0018] Preferably, Ni X Fe1- X The preparation process of Fe2O4 micron-sized particles is as follows: Iron and nickel salts were dissolved in water to prepare a precursor solution; The prepared precursor solution was ultrasonically atomized into micron-sized droplets, which were then introduced into a 900℃ high-temperature zone for dehydration, reduction, and crystallization to obtain hollow spherical Ni. X Fe1- X Fe2O4 micron-sized particles.

[0019] The present invention has the following beneficial effects: 1. This invention uses FeCo alloy nanoparticles prepared by an electric arc device to replace traditional carbonyl iron powder. Combined with a mixed base liquid, it significantly reduces the density difference between magnetic particles and base liquid, effectively weakens the particle sedimentation driving force, and greatly improves the sedimentation stability of the magnetorheological fluid. At the same time, the density of magnetic particles is reduced and the magnetic saturation intensity is increased. Under the premise of ensuring high magnetization response capability, it achieves low sedimentation and high stability long-term service performance. 2. By chemically coating FeCo alloy nanoparticles with oleic acid, a dual protection mechanism of chemical anchoring and steric hindrance is constructed, which can significantly inhibit particle agglomeration and hard deposition, and significantly improve the redispersibility of magnetorheological fluid. The organic lubricating layer formed on the particle surface can reduce the frictional resistance between particles, resulting in lower viscosity and better fluidity of the magnetorheological fluid under zero field conditions, thus balancing smooth operation and convenient maintenance. 3. This invention constructs FeCo alloy nanoparticles and Ni X Fe1- X A dual-dispersion system of Fe2O4 micron-sized particles forms a composite chain structure with micron-sized particles as the framework and nanoparticles as the filler under the action of a magnetic field. The nanoparticles can effectively bridge the micron-sized particles, significantly improving the magnetic flux strength and structural toughness. This dual-dispersion system can achieve dynamic self-healing of the magnetic flux structure, greatly increase the yield stress of the magnetorheological fluid, and maintain a fast magnetic field response speed, meeting the high damping and high reliability requirements of vibration dampers. 4. Overall, this invention achieves synergistic innovation in materials, structure, and system, simultaneously improving sedimentation stability, magnetic saturation strength, yield stress, and redispersibility, while reducing zero-field viscosity, resulting in a magnetorheological fluid with excellent comprehensive performance. The prepared magnetorheological fluid can be left to stand for a long time without hardening deposits, exhibits fast magnetic response, and strong operational stability, making it better suited to the actual working conditions of magnetorheological vibration dampers and possessing outstanding application value. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention discloses a bidispersed magnetorheological fluid for use in magnetorheological vibration dampers. The magnetorheological fluid comprises a dispersed phase and a dispersion medium, wherein the dispersed phase is uniformly dispersed in the dispersion medium. The dispersed phase consists of FeCo alloy nanoparticles (FeCoNPs, with a particle size of 8 nm) and Ni... X Fe1- X Composed of Fe2O4 micron-sized particles (35μm~60μm in diameter); FeCo alloy nanoparticles and Ni X Fe1- X The mass ratio of Fe2O4 micron particles was 1:4. The dispersion medium was a mixed base liquid formed by mixing dimethyl silicone oil and polyalphaolefin synthetic oil at a mass ratio of 1:1. The surface of the FeCo alloy nanoparticles was modified with oleic acid coating, and the total mass fraction of the dispersed phase in the magnetorheological fluid was 20%–30%. The dispersion medium also contained 1.0 wt% benzotriazole and 0.5 wt% polyether-modified siloxane.

[0022] This invention also provides a method for preparing a bidisperse magnetorheological fluid, comprising the following steps: 1. The preparation method of FeCo alloy nanoparticles is as follows: Place an iron-cobalt alloy target (ratio 50-65:35-50) in the arc plasma device. The target should be 50-100 mm in diameter and 5-10 mm thick. Mount the target on a water-cooled copper cathode at the top of the arc plasma device to ensure that it does not overheat and melt under the high-temperature arc impact, thus maintaining a stable discharge gap. Close the vacuum chamber and start the vacuum system to evacuate the chamber to a high vacuum (5 × 10⁻⁶). -4 To remove air and prevent metal oxidation, high-purity argon (purity >99.999%) is introduced into the vacuum chamber as the working gas to maintain the chamber pressure (0.5-5 kPa). Argon, as an inert protective gas, will not chemically react with metals such as iron and cobalt under high-temperature arc conditions. Simultaneously, as the medium for generating and maintaining plasma, its pressure directly affects the diffusion and cooling rate of metal vapor, thus influencing the final particle size. The arc triggering device is activated, applying a high-frequency, high-voltage pulse (5-10 kV) between the cathode (target) and anode (water-cooled copper crucible) to break down the argon and ignite the arc. Afterward, the system switches to a low-voltage, high-current DC mode (voltage 20-40V, current 100-300A), generating a stable and continuous high-temperature arc plasma between the target and the crucible. The high-temperature arc instantly heats the target surface to over 100°C, causing the evaporated Fe... 0 Co 0 Metal atoms have extremely high thermal motion speeds and will undergo inelastic collisions with low-speed, low-temperature argon atoms, resulting in energy redistribution and the formation of supersaturated vapor. When metal atoms in the supersaturated vapor collide, cool, and nucleate, they form small clusters. Eventually, these small clusters collide with each other to form atomic clusters. As a large number of unnucleated individual metal atoms continuously collide and attach to the already formed atomic clusters (crystal nuclei), FeCo alloy nanoparticles are formed. The generated FeCo alloy nanoparticles fall into a water-cooled copper crucible. FeCo alloy nanoparticles were added to a 0.1 mol / L oleic acid-ethanol solution, and the ultrasonic treatment system was turned on. The frequency was set to 40 kHz, the power to 300 W, and the treatment time to 30 minutes. The cavitation effect and microjets generated by the ultrasound produced strong impact force and local high temperature and pressure, which effectively destroyed the adsorption energy barrier and soft agglomeration on the particle surface, and promoted the full exposure of the fresh particle surface. Oleic acid molecules chemically bonded or strongly physically adsorbed with the metal atoms on the surface of FeCo alloy nanoparticles through their carboxyl heads, while their long alkyl carbon chains extended into the solvent to form a dense protective layer. This protective layer effectively prevented the particles from approaching each other and agglomerating through the steric hindrance effect, and endowed the particles with oleophilicity, thereby obtaining surface-modified FeCo alloy nanoparticles.

[0023] 2.Ni X Fe1- XThe preparation method of Fe2O4 micron-sized particles is as follows: Ferrous chloride tetrahydrate (0.994 g), nickel chloride hexahydrate (1.18 g), and deionized water (80 mL) were added to a vector cup. The vector cup was placed in a magnetic stirrer and stirred at 300-500 rpm for 1 hour to obtain a solution containing Fe. 2+ / Fe 3+ and Ni 2+ Precursor solution; The prepared precursor solution is injected into the reservoir of the ultrasonic nebulizer. The tube furnace is powered on, and the heating program is set: first, the temperature is increased from room temperature to 200°C at a rate of 5°C / min (to quickly pass through the low-temperature zone and avoid slow evaporation of droplets leading to component segregation), and then increased to the target temperature of 900°C at a rate of 10°C / min. After the tube furnace temperature stabilizes at 900°C, the ultrasonic nebulizer is powered on, the argon flow rate is adjusted, and the micron-sized droplets (approximately 1-5 μm in diameter) generated by atomization are loaded into the high-temperature reaction zone of the tube furnace. After the droplets enter the high-temperature reaction zone with the carrier gas (high-purity nitrogen), the water molecules in the nitrogen are rapidly vaporized and removed by heating, causing the metal ions dissolved in the water to accumulate and precipitate; in the reducing atmosphere (made of high-purity nitrogen carrier gas... ) and reducing gas hydrogen ( A mixture of gases, consisting of hydrogen and Fe. Hydrogen provides electrons to the metal ions, thus reducing Fe... 2+ / Fe 3+ and Ni 2+ Reduced to neutral Fe 0 Ni 0 Atoms. Fe produced by reduction. 0 Ni 0 At high temperatures, atoms migrate, collide, and bond together via metallic bonds, gradually agglomerating and growing to form Ni. X Fe1- X Fe2O4 alloy hollow spherical particles; after the reaction is complete, turn off the atomization and ultrasonic power supply, and collect the obtained nickel-based Ni. X Fe1- X Fe2O4 alloy powder.

[0024] 3. The preparation method of the mixed base solution is as follows: Add dimethyl silicone oil and polyalphaolefin synthetic oil to a beaker at a volume (or mass) ratio of 1:1. Place the beaker on a magnetic stirrer and stir at 300-500 rpm for 30 minutes to ensure that the two are fully miscible and form a uniform and transparent mixed base liquid. After stirring, let the beaker stand at room temperature for 20-30 minutes to allow the air bubbles introduced during stirring to escape naturally, thus obtaining the base liquid. Add benzotriazole (1.0 wt% of the base liquid mass) and polyether-modified siloxane (0.5 wt% of the base liquid mass) to the base liquid, place a stir bar, and stir for 30 minutes at room temperature to obtain a mixed base liquid.

[0025] 4. Surface-modified FeCo alloy nanoparticles and Ni X Fe1- X Fe2O4 micron particles were premixed at a mass ratio of 1:4 and then added to the composite base liquid. The entire mixture was placed on a magnetic stirrer and stirred continuously at a speed of 300-500 rpm for several hours to finally obtain a uniform, stable, and non-visible agglomerate-free bidisperse magnetorheological liquid. The resulting product exhibited good fluidity under zero magnetic field and could rapidly form chain or columnar structures when an external magnetic field was applied, showing a significant magnetorheological effect.

[0026] Iron-cobalt alloy nanoparticles prepared by an arc plasma device replaced traditional carbonyl iron powder micron particles (78.5 μm in diameter) as the magnetic dispersed phase. The particle size was reduced from micron (78.5 μm) to nano (8 nm), the specific surface area increased dramatically, the density difference between the particles and the base liquid (silicone oil, density about 0.96 g / cm³) was significantly weakened, and the sedimentation driving force was greatly reduced.

[0027] The magnetic particle density decreased from 7.20 g / cm³ to 5.75 g / cm³, a reduction of approximately 1.45 g / cm³; the magnetic saturation strength increased from 130 emu / g to 145 emu / g, an increase of 15 emu / g (approximately 11.5%); the yield stress increased from 52 kPa to 58.3 kPa, an increase of 6.3 kPa (approximately 12%); the sedimentation stability increased from 60.1% to 82.6%, an increase of 22.5 percentage points (approximately 37.4%); the zero-field viscosity decreased from 1.25 Pas to 0.87 Pas, a reduction of 0.38 Pas; the redispersibility increased from 1.3% to 1.5%, an increase of 0.2 percentage points; data for the nanoparticle-only system: the yield stress increased from ≤60 kPa to over 80 kPa; no hard deposits were formed after 6 months of settling; the magnetic response time was <3 ms.

[0028] The present invention will be further described in detail below through specific embodiments and in conjunction with data.

[0029] Example 1 The dispersed phase consists of FeCo alloy nanoparticles (FeCoNPs, with a particle size of 8 nm) and Ni X Fe1- X Fe2O4 micron-sized particles (Ni) X Fe1- X Fe2O4 (particle size 35μm~50μm) is composed of composite materials; Preparation of FeCo alloy nanoparticles: FeCo alloy target material (Fe:Co atomic ratio 50:50) was used as cathode in an arc plasma device. Evaporation and condensation were carried out under argon pressure of 1 kPa and discharge current of 200 A to collect FeCo alloy nanoparticles with an average particle size of about 8 nm. The obtained FeCo alloy nanoparticles were added to a 0.1 mol / L oleic acid ethanol solution and treated with ultrasound at 40 kHz and 300 W for 30 minutes. After centrifugation, washing, and vacuum drying, oleic acid-coated surface-modified FeCo alloy nanoparticles were obtained. Ni X Fe1- X Preparation of Fe2O4 micron-sized particles: 0.994 g FeCl2·4H2O and 1.18 g NiCl2·6H2O were weighed and dissolved in 80 mL of deionized water, and magnetically stirred for 1 hour to prepare a precursor solution. The solution was atomized into micron-sized droplets at a rate of 10 mL / min using ultrasonic atomization pyrolysis and fed into the high-temperature reaction zone of a 900℃ tube furnace. High-purity nitrogen was used as the carrier gas. After collecting the powder, it was placed in an annealing furnace and held at 350℃ under an argon atmosphere for 1 hour to obtain NiCl2·6H2O particles with an average particle size of 35–50 μm. X Fe1- X Fe2O4 micron-sized particles; Preparation of the mixed base liquid: Mix dimethyl silicone oil and polyalphaolefin synthetic oil at a mass ratio of 1:1, stir for 30 minutes and let stand to remove bubbles, add 1.0 wt% benzotriazole and 0.5 wt% polyether modified siloxane, and continue stirring for 30 minutes to obtain the mixed base liquid; Take the above oleic acid-coated surface-modified FeCo alloy nanoparticles and Ni X Fe1- X Fe2O4 micron particles were mixed at a mass ratio of 1:4 (total particle mass fraction 25%) and a gradient addition method was used: first, a small amount of mixed base liquid was added and ground into a paste, then the remaining mixed base liquid was added in batches and stirred to disperse evenly to obtain a bidispersed magnetorheological fluid.

[0030] Performance results: Excellent settling stability, with no hard lumps deposited after 6 months of standing; shear stress of 50 kPa under 0.5T magnetic field, with response time <3ms; performance retention rate >95% after 48h of high temperature at 100℃; moderate zero-field viscosity (0.87 Pa·s), with no significant decay in magnetorheological properties after 20 cycles of testing.

[0031] Example 2 FeCo alloy nanoparticles were treated with oleic acid ethanol solution under ultrasonication at 40 kHz and 300 W for 10 minutes. Other raw materials, proportions and preparation steps were the same as in Example 1.

[0032] Performance results: The FeCo particles were not fully coated on the surface and had slightly poor dispersibility. The sedimentation rate was 10% after standing for 7 days. The shear stress under a 0.5T magnetic field was 45kPa and the response time was 4ms.

[0033] Example 3 Ni X Fe1- X The Fe2O4 micron particles were annealed at 300°C in an annealing furnace. Other raw materials, proportions, and preparation steps were the same as in Example 1.

[0034] Performance results: The low annealing temperature resulted in trace amounts of oxides on the particle surface, which slightly reduced the magnetic properties. The shear stress under a 0.5T magnetic field was 42kPa. The sedimentation stability was comparable to that of Example 1, but the shear stress dropped to 38kPa after 5 cycles.

[0035] Comparative Example 1 Magnetorheological fluid uses only Ni X Fe1- X Fe2O4 micron-sized particles (particle size 35μm~50μm) were used as the dispersed phase, without the addition of FeCo alloy nanoparticles. The total particle mass fraction was 25%. Other raw materials, proportions and preparation steps were the same as in Example 1.

[0036] Performance results: poor settling stability, with a settling rate of 40% after 7 days of standing, and obvious clear liquid in the upper layer; shear stress under a 0.5T magnetic field is 38kPa, response time is 6ms, and zero-field viscosity is slightly low (0.6Pa·s).

[0037] Comparative Example 2 FeCo alloy nanoparticles are used directly in the preparation of magnetorheological fluids without being coated with oleic acid ethanol solution. Other raw materials, proportions and preparation steps are the same as in Example 1.

[0038] Performance results: FeCo particles were severely agglomerated, the magnetorheological fluid showed obvious stratification, and it completely settled after standing for 24 hours; the shear stress under a 0.5T magnetic field was only 20kPa, which is of no practical value.

[0039] Comparative Example 3 FeCo alloy nanoparticles and Ni X Fe1- X When mixing Fe2O4 micron particles, all of them are added at once and mechanical stirring is used only. Gradient addition and ultrasonic-assisted dispersion are not used. Other raw materials, proportions and preparation steps are the same as in Example 1.

[0040] Performance results: The dispersion is uneven, with micron-sized agglomerates present. The sedimentation rate after 7 days of standing is 25%. The shear stress under a 0.5T magnetic field is 30kPa, and the response time is 40ms.

[0041] Comparative Example 4 The dispersion medium used only was dimethyl silicone oil, without the addition of polyalphaolefin synthetic oil. Other raw materials, proportions and preparation steps were the same as in Example 1.

[0042] Performance results: The dispersion medium has poor compatibility with the additives and insufficient stability at high temperatures. After being placed at 100℃ for 24 hours, the shear stress decreased by 30%, and the zero-field viscosity increased to 1.5 Pas.

[0043] Comparative Example 5 Ni X Fe1- X The annealing temperature of the Fe2O4 micron particles was 600℃, and the other raw materials, proportions and preparation steps were the same as in Example 1.

[0044] Performance results: Ni X Fe1- X Fe2O4 particles undergo sintering and growth, with the average particle size increasing to 50-65 μm. The magnetic properties decrease, and the shear stress under a 0.5T magnetic field is 3 kPa. Although the sedimentation stability is slightly improved (settling rate of 8% after 7 days), the response time is prolonged to 45 ms.

[0045] Comparative Example 6 The total mass fraction of magnetic particles in the magnetorheological fluid is 5%, and the other raw materials, proportions and preparation steps are the same as in Example 1.

[0046] Performance results: The magnetorheological effect is weak, the shear stress under a 0.5T magnetic field is only 10kPa, and the zero-field viscosity is 0.3Pa·s, which basically does not have practical performance.

[0047] Comparative Example 7 When preparing the mixed base solution, benzotriazole and polyether-modified siloxane were not added. Other raw materials, proportions and preparation steps were the same as in Example 1.

[0048] Performance results: The particles are easily corroded, and after standing for 7 days, the shear stress decreased by 50%, and obvious precipitation occurred, indicating poor system stability.

[0049] Comparative Example 8 Surface-modified FeCo alloy nanoparticles and Ni X Fe1- X The mass ratio of Fe2O4 micron particles was adjusted to 1:1, and the total particle mass fraction was 25%. Other raw materials, proportions, and preparation steps were the same as in Example 1.

[0050] Performance results: Excessive nanoparticles lead to thickening of the base liquid, increasing the zero-field viscosity to 2.0 Pa·s. The shear stress under a 0.5T magnetic field is 40 kPa, the response time is 30 ms, and the sedimentation stability is good (6% sedimentation rate after 7 days). However, the high zero-field viscosity affects its use.

[0051] The experimental results of Examples 1 to 3 and Comparative Examples 1 to 8 are shown in the table below: As can be seen from the table above, Example 1 is the optimal example.

[0052] As can be seen from Example 1 and Comparative Example 1, the bidisperse magnetorheological fluid of the present invention has significant advantages over the traditional monodisperse system in terms of sedimentation stability, magnetorheological effect, and response speed. Example 1 showed a sedimentation rate of <5% after 7 days of standing, far superior to the 40% of Comparative Example 1; the shear stress under a 0.5T magnetic field reached 50kPa, an increase of approximately 30% compared to the 38kPa of Comparative Example 1; and the response time was <20ms, indicating a faster dynamic response. These improvements stem from the interaction between nano-FeCo alloy nanoparticles and Ni... X Fe1- X The synergistic effect of Fe2O4 particles allows nanoparticles to effectively suppress the sedimentation of micron-sized particles through Brownian motion, while the bimodal gradation structure also improves the particle packing density and the strength of the chain structure under a magnetic field.

[0053] Comparative Example 2 shows that coating with oleic acid-ethanol solution is a necessary condition for the stable dispersion of FeCo alloy nanoparticles. Uncoated FeCo alloy nanoparticles have high surface energy and are prone to aggregation, leading to severe instability in the magnetorheological fluid system. Oleic acid-ethanol solution forms a dense organic protective layer by chemically bonding with the particle surface through carboxyl groups. This layer inhibits aggregation and enhances the oleophilicity of the particles through steric hindrance, ensuring the uniformity and stability of the system.

[0054] Comparing Example 1 and Comparative Example 3, it is evident that ultrasonic-assisted gradient wetting is key to achieving uniform particle dispersion. Single-pass feeding and simple stirring are insufficient to break up soft particle agglomerates, easily leading to uneven dispersion, residual agglomerates, and a significant decrease in magnetorheological properties. Ultrasonic cavitation and gradient wetting allow for thorough wetting of the particle surface and interaction with the base liquid and additives, forming a stable and uniform dispersion system.

[0055] Comparing Example 1, Example 3 and Comparative Example 5, it can be seen that Ni X Fe1- X There is an optimal annealing temperature range of 300–400℃ for Fe2O4 micron-sized particles. If the temperature is too low (300℃), the oxide on the particle surface will not be fully reduced, and the magnetic properties will decrease slightly. If the temperature is too high (600℃), the particles will sinter and grow, resulting in a decrease in magnetic properties and a significant increase in response time. Annealing at 350℃ can fully reduce the oxide and improve the crystal structure while avoiding particle sintering, thus ensuring excellent magnetic properties.

[0056] As can be seen from the comparison between Example 1 and Comparative Example 6, the concentration of magnetic particles needs to be controlled within a reasonable range. When the concentration is too low (5wt%), the magnetorheological effect is weak and has no practical value; only when the particle mass fraction reaches the threshold of 2-30% can a sufficiently strong magnetic field response chain structure be formed.

[0057] Comparing Example 1 and Comparative Example 8, it is evident that the ratio of nanoparticles to microparticles significantly affects the system's performance. An excessively high nanoparticle ratio (1:1) causes a substantial increase in zero-field viscosity to 2.0 Pa·s, affecting flowability; an excessively low ratio results in insufficient sedimentation suppression. The 1:4 mass ratio in Example 1 achieves the optimal balance between sedimentation stability, magnetorheological properties, and zero-field viscosity.

[0058] Comparative Examples 4 and 7 demonstrate that the mixed base fluid and additives are indispensable for the stability of the system. A single base fluid exhibits poor high-temperature stability, and without additives, particles are easily corroded, leading to a significant decrease in overall performance. The corrosion-inhibiting effect of benzotriazole and the steric hindrance effect of polyether-modified siloxane, working synergistically with the mixed base fluid of polyalphaolefin synthetic oil and dimethyl silicone oil, jointly ensure the long-term stability and high-temperature reliability of the magnetorheological fluid.

[0060] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A bidisperse magnetorheological fluid, comprising a dispersed phase and a dispersion medium, wherein the dispersed phase is uniformly dispersed in the dispersion medium; characterized in that, The dispersed phase consists of FeCo alloy nanoparticles and Ni X Fe1- X The composition consists of Fe2O4 micron-sized particles; the dispersion medium is a mixed base liquid formed by mixing dimethyl silicone oil and polyalphaolefin synthetic oil.

2. The bidisperse magnetorheological fluid according to claim 1, characterized in that, The FeCo alloy nanoparticles have a particle size of 8 nm, and Ni X Fe1- X The particle size of Fe2O4 micron particles ranges from 35μm to 60μm.

3. The bidisperse magnetorheological fluid according to claim 1, characterized in that, FeCo alloy nanoparticles and Ni X Fe1- X The mass ratio of Fe2O4 micron particles is 1:

4.

4. The bidisperse magnetorheological fluid according to claim 1, characterized in that, The volume ratio or mass ratio of dimethyl silicone oil to polyalphaolefin synthetic oil is 1:

1.

5. The bidisperse magnetorheological fluid according to claim 1, characterized in that, The surface of FeCo alloy nanoparticles is modified by coating with oleic acid.

6. The bidisperse magnetorheological fluid according to any one of claims 1 to 5, characterized in that, The dispersion medium also contains benzotriazole and polyether-modified siloxane.

7. The bidisperse magnetorheological fluid according to claim 6, characterized in that, The amount of benzotriazole added is 1.0 wt% of the total mass of the dispersion medium, and the amount of polyether-modified siloxane added is 0.5 wt% of the total mass of the dispersion medium.

8. A method for preparing a bidisperse magnetorheological fluid, characterized in that, Includes the following steps: FeCo alloy nanoparticles were prepared using an electric arc device and then coated with oleic acid to obtain surface-modified FeCo alloy nanoparticles. Ni was prepared by ultrasonic atomization pyrolysis. X Fe1- X Fe2O4 micron-sized particles; Dimethyl silicone oil is mixed with polyalphaolefin synthetic oil to obtain a mixed base liquid; FeCo alloy nanoparticles with Ni X Fe1- X After premixing Fe2O4 micron-sized particles, they are added to the mixed base liquid and dispersed evenly to obtain a bidispersed magnetorheological fluid.

9. The method for preparing the bidisperse magnetorheological fluid according to claim 8, characterized in that, The preparation process of FeCo alloy nanoparticles is as follows: The iron-cobalt alloy target was placed in the arc plasma device, and argon gas was introduced after the vacuum was drawn. The electric arc is ignited and maintained at a high temperature, causing the target material to evaporate and form metal vapor. The vapor is then rapidly cooled, nucleated, and clustered in an inert atmosphere to obtain FeCo alloy nanoparticles.

10. The method for preparing the bidisperse magnetorheological fluid according to claim 8 or 9, characterized in that, Ni X Fe1- X The preparation process of Fe2O4 micron-sized particles is as follows: Iron and nickel salts were dissolved in water to prepare a precursor solution; The prepared precursor solution was ultrasonically atomized into micron-sized droplets, which were then introduced into a 900℃ high-temperature zone for dehydration, reduction, and crystallization to obtain hollow spherical Ni. X Fe1- X Fe2O4 micron-sized particles.

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