Single Crystal Magnetic Powder, Its Magnetorheological Fluid and Method

Abstract

The present invention relates to single crystal magnetic powder, its magnetorheological fluid and method. Specifically, the present invention provides a magnetorheological fluid containing single crystal magnetic powder, comprising: single crystal magnetic powder; and a fluid used as a carrier liquid, wherein the single crystal magnetic powder is dispersedly distributed in the fluid. Compared with traditional magnetorheological fluids, the magnetorheological fluid containing single crystal magnetic powder prepared according to the present invention has huge irreplaceable advantages, for example, high specific saturation magnetization intensity, can obtain higher working shear stress under the same magnetic field intensity, faster response, not easy to settle, low viscosity, low wear rate of components, long service life, high reliability, faster response and other performance advantages.

Description

Technical Field

[0001] The present invention relates to the field of magnetorheological fluids. Specifically, the present invention relates to single-crystalline (monocrystalline) magnetic powder and magnetorheological fluids prepared therefrom. The present invention also relates to a method for preparing magnetorheological fluids containing single-crystalline magnetic powder. Background Art

[0002] Magnetorheological fluid is a liquid whose viscosity changes with the application of a magnetic field. It is a stable suspension system composed of soft magnetic particles with high magnetic permeability and low remanence, uniformly dispersed in a non-magnetic carrier liquid through the action of a surfactant. The working principle of magnetorheological fluid is as follows: under the action of an externally applied magnetic field, each particle is polarized into a magnetic dipole, and the dipoles attract each other to form a chain-like structure between the two magnetic pole plates, which bridges across the pole plates like a bridge, hindering the normal flow of the fluid and giving it the characteristics of a quasi-solid. When the externally applied magnetic field is removed, the fluid returns to its original state, that is, the magnetorheological fluid undergoes a rapid and reversible conversion between the liquid state and the solid state. The degree of solidification has a stable and reversible relationship with the current intensity, that is, by controlling the current intensity, the shear yield strength of the solidified magnetorheological fluid can be precisely controlled.

[0003] For many years, there have been many researchers on magnetorheological fluids, and currently, they have been gradually applied to various devices to control damping forces, such as shock absorbers, vibration absorbers, artificial limbs, and elastic seats. The rheology of magnetorheological fluid under the action of a magnetic field is instantaneous, reversible, and the shear yield strength after rheology has a stable corresponding relationship with the magnetic field strength, making it very easy to achieve intelligent control. Therefore, magnetorheological fluid is an intelligent material with wide applications and excellent performance, and the application fields of magnetorheological fluid are expanding rapidly.

[0004] An essential defect of existing magnetorheological fluids is that, whether it is the magnetorheological fluid products sold in the existing market or the single-crystalline magnetorheological fluid products previously invented by the applicant, the magnetic powder in the fluid is of the polycrystalline type. A polycrystal is a whole crystal composed of a large number of grains, and a single space lattice pattern cannot penetrate the entire crystal, having the basic characteristic of magnetic crystal isotropy. Compared with the magnetically anisotropic magnetic particles, the polycrystalline magnetic powder with magnetic crystal isotropy in the existing magnetorheological fluids has a slower response speed to the magnetic field and a lower magnetic saturation. This defect of the existing technology enables the present invention to provide significant improvements over the existing technology in this regard.

[0005] Another defect of existing magnetorheological fluids is that the shear yield strength of the existing products on the market is not very satisfactory, requiring a larger working current and possibly more than two excitation coils, which makes the control of the equipment more complex and the cost higher.

[0006] Traditional magnetorheological fluids use polycrystalline magnetic powders, which have a low specific magnetic saturation intensity, low magnetic force under a magnetic field, and low shear force of the magnetorheological fluid. To increase the working shear force of the magnetorheological fluid, the particle size of the magnetic particles in the traditional magnetorheological fluid is greater than 0.1 μm, preferably greater than 1 μm (see US Patent US6203717B1, etc.). This brings another prominent problem, that is, the magnetic particles are prone to sedimentation in the magnetorheological fluid.

[0007] One of the reasons for the tendency of particles to settle is that the density of the oil (0.7 - 0.95 g / cm3) is very different from the density of the metal particles (the density of iron particles is about 7.86 g / cm3). The second reason is that the magnetizable particle size in the traditional magnetorheological fluid is relatively large (its preferred particle size is greater than 1 μm, that is, 1000 nanometers, such as US Patent US6203717B1, etc.). For example, most of the magnetic powder particle sizes in the prior art are about 2 - 5 microns (see the attached drawings), and the shapes are spherical, quasi-spherical, and chain-spherical. The terminal velocity of free settlement of fine solid particles in a fluid medium is proportional to the square of their particle size. Particles with too large a particle size settle faster and are more prone to sedimentation, resulting in non-uniform distribution of particles and interfering with the activity of the magnetorheological fluid. Some early magnetorheological fluids (see US Patents 2575360, 2661825, 2886151, US6203717B1, etc.) mainly consist of iron powder and low-viscosity oil. These magnetorheological fluids are all prone to sedimentation, and the sedimentation rate increases with the increase in temperature. Therefore, various thickeners and suspending agents usually need to be added. Due to the large addition of these anti-sedimentation components, the viscosity of the magnetorheological fluid has been greatly increased. However, this also increases the flow resistance (viscosity) of the material in the non-magnetic field state.

[0008] The sedimentation of magnetic particles directly leads to a short service life and low reliability of the magnetorheological fluid, and ultimately results in the failure of the magnetorheological fluid.

[0009] The initial viscosity of the magnetorheological fluid is large and the flow resistance is large, which directly leads to poor performance of some equipment in the non-magnetic field state, such as moving parts or devices.

[0010] Another prominent technical problem existing in the existing magnetorheological fluids is the wear problem. The magnetic particles in the magnetorheological fluid will cause wear on the surface of the moving parts in contact with them. The larger the particle size of the magnetized particles, the more serious the abrasive wear.

[0011] Another defect of the existing magnetorheological fluids is that there are deficiencies and room for improvement in the performance consistency and product performance degradation time of the magnetorheological fluid products on the market.

[0012] Based on the above and other considerations, there is a need in the art to further improve the magnetorheological fluid, its preparation method and equipment to overcome the defects in the prior art. Summary of the Invention

[0013] To address the issues of magnetic crystal isotropy in existing magnetic powders, the tendency of larger magnetic particles in some existing magnetorheological fluid products to easily settle, resulting in poor performance and lifespan, and the excessive initial viscosity of some existing magnetorheological fluid products, the present inventors have proposed and implemented the use of single-crystal magnetic powder in the preparation of magnetorheological fluids. This makes it possible to provide industrially produced magnetorheological fluids containing single-crystal magnetic powders, addressing the aforementioned inherent drawbacks of polycrystalline magnetic powders and other drawbacks of the existing technology. The present invention also discloses an apparatus and method for preparing magnetorheological fluids containing single-crystal magnetic powders.

[0014] Single crystal magnetic powder has a high specific magnetic saturation intensity and can generate higher magnetic force than traditional polycrystalline magnetic powder under the same magnetic field, allowing magnetorheological fluid to obtain greater shear force.

[0015] The basic principle of single-crystal magnetic powder in magnetorheological fluid is that the magnetic powder contained therein is a single-crystal particle, that is, there is only one lattice type within a single magnetic powder. A single crystal is a crystal with the same atomic arrangement and consistent lattice phase. The basic structural feature of a single crystal is that the entire crystal is composed of either a single grain or a plurality of grains with the same lattice and consistent crystal orientation. Therefore, the entire lattice of a single crystal is continuous, that is, a spatial lattice pattern can be used to run through the entire single crystal, regardless of whether the single crystal is composed of one or multiple grains. Single-crystal magnetic powder makes it possible to achieve magnetocrystalline anisotropy, thereby solving the above-mentioned existing technologies and other deficiencies.

[0016] In single crystals of magnetic materials, the anisotropy of atomic arrangement leads to magnetic anisotropy. The magnetization curves measured when a single crystal is magnetized along different crystal axes, as well as the ease with which it is magnetized to magnetic saturation, differ from one another. In other words, a single crystal is easily magnetized along certain crystal axes, but not along others. This phenomenon is called magnetocrystalline anisotropy. For body-centered cubic (bcc) crystals, for example, the easy magnetization axis is the

[100] axis, and the difficult magnetization axis is the

[111] axis.

[0017] According to an example of the present invention, the prepared single-crystal anisotropic magnetic powder is a body-centered cubic single crystal, and each magnetic powder or most of the magnetic powder in the magnetorheological fluid base liquid is a body-centered cubic single crystal. In the magnetorheological fluid base liquid, each single-crystal magnetic powder is in a freely dispersed state. Under an external magnetic field, the single-crystal magnetic powder quickly rotates around the easy magnetization axis (

[100] axis) and arranges itself in a natural direction, that is, it presents the maximum magnetic saturation direction of the material, presents a magnetic saturation magnetization intensity in this direction, and makes the material have a very high magnetic saturation intensity. For example, the magnetic saturation intensity of the single-crystal magnetic powder used in an example of the present invention can be as high as 245emu / g. The shear force of the magnetorheological fluid prepared using the single-crystal magnetic powder under the same magnetic field is much higher than that of the traditional polycrystalline magnetic powder magnetorheological fluid.

[0018] Throughout this patent application, those skilled in the art should understand that "particle size" is intended to represent and characterize the size of particles. Unless otherwise specified, if the particles have a substantially spherical microscopic shape, "particle size" refers to their "particle diameter". Unless otherwise specified, if the particles have a non-spherical microscopic shape, "particle size" refers to the "equivalent particle diameter".

[0019] Compared with traditional magnetorheological fluids, the magnetorheological fluid material containing single-crystal magnetic powder prepared by the present invention has the following advantages:

[0020] a. Higher specific magnetic saturation intensity (as Figure 7 shown)

[0021] b. Under the same working shear strength requirement, we can use finer powder, and the finer the powder, the less likely it is to settle (as Figure 8 shown)

[0022] The terminal velocity of free settlement of fine solid particles in a fluid medium is proportional to the square of their particle size. In order to reduce the remanent magnetism, the particle size of traditional magnetic response particles may need to reach more than 1 μm. The particle size of the material of the present invention is much smaller than that of the magnetic powder of traditional magnetorheological fluids, and it is not easy to settle, solving the problem that the magnetic response particles in traditional magnetorheological fluids are easy to settle. The state where the magnetic particles in the magnetorheological fluid of the present invention are not easy to settle is preferably that at least 50%, preferably at least 60%, more preferably at least 80%, and most preferably at least 90% of the magnetic particles do not settle during a period of standing in the magnetorheological fluid for more than 3 days, preferably more than 1 week, more preferably more than 1 month, most preferably more than 2 months or even longer at room temperature (25 °C).

[0023] c. Facilitate the miniaturization and lightweight of devices

[0024] The magnetorheological fluid prepared from single-crystal magnetic powder can obtain a higher working shear force than traditional polycrystalline magnetic powder of the same particle size under the same working magnetic field, enabling the excitation components of the device to be miniaturized and lightweight.

[0025] d. Reduce the wear rate on components

[0026] Obviously, the scratching, cutting, and wear effects of finer single-crystal magnetic powder particles on components are smaller than those of coarser magnetic powder.

[0027] e. The single-crystal magnetic powder has a higher specific magnetic saturation intensity, requires a lower proportion of magnetic powder to achieve the same required shear force, and the initial viscosity can be adjusted lower as needed, with a larger adjustment range. Because the single-crystal magnetic powder can be finer and the sedimentation speed is low, there is no need to add a large amount of high-viscosity anti-settling components in the carrier liquid, and the initial viscosity can also be reduced (as Figure 10 shown).

[0028] f. Good thermal stability

[0029] The magnetorheological fluid material containing single-crystal magnetic powder prepared according to the present invention has good thermal stability. (See Figure 9 as shown)

[0030] According to an embodiment of the present invention, a single-crystal magnetorheological fluid and a preparation method thereof are disclosed. The single-crystal magnetorheological fluid is prepared by mixing and stirring single-crystal magnetic powder with a carrier liquid, additives, etc. The single-crystal magnetorheological fluid prepared by this method can achieve the following technical advantages: obtaining a greater working yield strength, a faster magnetic response speed; a smaller single-crystal particle size, and the sedimentation resistance is greatly increased (compared with the magnetorheological fluid of the prior art); the miniaturization and lightweight of the device can be achieved.

[0031] According to an embodiment of the present invention, a single-crystal magnetic powder for a magnetorheological fluid is disclosed, which is composed of magnetizable magnetic particles with a separated single-crystal structure, and the average particle size of the magnetic particles is in the range of about 0.1-8 microns; wherein, each of the magnetic particles is basically composed of a single crystal grain, or basically composed of multiple crystal grains with the same crystal lattice and the same crystal orientation.

[0032] According to an embodiment of the present invention, the material of the magnetizable magnetic particles is selected from pure iron, iron-aluminum alloy, iron-silicon alloy, iron-cobalt alloy, iron-nickel alloy, iron-vanadium alloy, iron-molybdenum alloy, iron-chromium alloy, iron-tungsten alloy, iron-manganese alloy, iron-platinum alloy, iron-copper alloy, nickel, cobalt, SmCo, NdFeB, stainless steel, silicon steel, and combinations of the above materials.

[0033] According to an embodiment of the present invention, the single crystal of the single-crystal magnetic powder has one of the following crystal lattices: hexagonal lattice, cubic lattice, rhombohedral lattice, and body-centered cubic lattice.

[0034] According to an embodiment of the present invention, the single-crystal magnetic powder is a single-particle crystal and has the characteristic of magnetocrystalline anisotropy.

[0035] According to an embodiment of the present invention, a magnetorheological fluid containing single-crystal magnetic powder is provided, which includes: the single-crystal magnetic powder as described above; and a fluid used as a carrier liquid, wherein the single-crystal magnetic powder is diffusely distributed in the fluid.

[0036] According to an embodiment of the present invention, the average particle size of the magnetic particles is between about 0.1-8 microns, preferably between about 0.8-3 microns, more preferably between about 0.8-1.5 microns, wherein the number of magnetic particles with an average particle size between about 0.8-1.5 microns preferably accounts for more than 50% of the total magnetic particles.

[0037] According to an embodiment of the present invention, the fluid is an organic liquid, such as α-olefin, naphthene, saturated alkane, or a combination thereof.

[0038] According to an embodiment of the present invention, the fluid further comprises an additive selected from the group consisting of surfactants, dispersants, anti-settling agents, organic thixotropic agents, thickeners, antioxidants, lubricants, viscosity regulators, flame retardants, organic clay rheology additives, sulfur-containing compounds, and combinations of these additives.

[0039] According to an embodiment of the present invention, the volume of the magnetic particles accounts for more than 0.5% of the total volume of the magnetorheological fluid, preferably 1-70%, more preferably 10-30%.

[0040] According to an embodiment of the present invention, the microscopic shape of the magnetic particles is selected from the group consisting of substantially spherical, substantially cylindrical, substantially ellipsoidal, substantially prismatic, substantially cuboid, substantially truncated pyramid, stepped substantially cuboid or prismatic, or any combination thereof.

[0041] According to an embodiment of the present invention, the magnetic particles in the magnetorheological fluid containing single crystal magnetic powder do not substantially settle or stratify during at least 1 week, preferably at least 2 weeks, more preferably at least 1 month of standing at room temperature.

[0042] According to an embodiment of the present invention, the microscopic shape of the magnetic particles presents a specific geometric shape according to its single crystal structure and main growth crystal orientation.

[0043] According to an embodiment of the present invention, during 1 month of standing at room temperature of the magnetic particles in the magnetorheological fluid containing single crystal magnetic powder, at least 50% by volume, preferably at least 60% by volume, more preferably at least 80% by volume, most preferably at least 90% by volume of the single crystal magnetic powder does not substantially settle.

[0044] According to an embodiment of the present invention, a method for preparing a magnetorheological fluid containing single crystal magnetic powder is provided, comprising: providing a precursor in oxide form for preparing the single crystal magnetic powder, the precursor containing iron element, and at least one element selected from the group consisting of aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese, platinum, copper, boron, and samarium; chemically reducing and recrystallizing the precursor in a reducing atmosphere to obtain the single crystal magnetic powder; adding the raw material of the single crystal magnetic powder, an additive, and a part of the carrier liquid to a primary mixer, mixing and dispersing to obtain a primary slurry; further screening and separating the primary slurry to obtain a slurry containing the desired single crystal magnetic powder, the screening and separation including at least one of gravity separation, centrifugal separation, and magnetic separation; selectively adding the carrier liquid and the additive to the slurry containing the desired single crystal magnetic powder in a stirrer and stirring to obtain a magnetorheological fluid containing single crystal magnetic powder.

[0045] According to an embodiment of the present invention, the additive comprises at least one of an antioxidant, an anti-precipitant and a dispersant.

[0046] According to the present invention, the use of the magnetorheological fluid containing single-crystal magnetic powder in shock absorption and / or buffering in load-bearing applications is disclosed, and the load-bearing applications include at least one of transportation vehicles, construction machinery, processing machinery, medical equipment, bridges and drilling platforms. Applicable transportation vehicles include various light and heavy cars, trucks, lorries, ships and civil aircraft. Construction machinery includes various mining vehicles, lifting equipment, excavators, drilling machinery, and the like.

[0047] The magnetorheological fluid of the present invention can be applied to (but not limited to) devices and components such as dampers, buffers, shock absorbers, vibration absorbers, artificial limbs and elastic seats, brakes, for example, automotive buffers, automotive shock absorbers, shock absorbers for precision machining equipment such as machine tools, shock absorbers for high-speed trains, and the like.

[0048] Compared with traditional magnetorheological fluids, the magnetorheological fluid containing single-crystal magnetic powder of the present invention has great irreplaceable advantages, for example, higher shear yield strength, not easy to settle, low viscosity, low wear rate of components, long service life, high reliability, quick and crisp response, excellent thermal stability and other performance advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] By reading this specification in conjunction with the following drawings, the features, objects and advantages of the present invention will become more apparent, in the drawings:

[0050] Figure 1 Schematically shows an apparatus for preparing a single-crystal magnetorheological fluid according to an embodiment of the present invention.

[0051] Figure 2 Schematically shown in a plan view Figure 1 The shown apparatus for preparing a single-crystal magnetorheological fluid.

[0052] Figure 3 Is a scanning electron microscope (SEM) photograph of single-crystal magnetic powder particles magnified 10,000 times according to an embodiment of the present invention.

[0053] Figure 4A Is a scanning electron microscope (SEM) photograph of single-crystal magnetic powder particles magnified 10,000 times according to an embodiment of the present invention.

[0054] Figure 4B Is a scanning electron microscope (SEM) photograph of commercially available magnetic powder particles magnified 10,000 times as a comparative example.

[0055] Figure 5It is a comparison chart of the hysteresis loop detection of the single-crystal magnetic powder of an embodiment of the present invention, the nano-magnetic powder invented by the applicant before, and the conventional magnetic powder available on the market, showing the comparison of the hysteresis loop detection of the magnetic powder.

[0056] Figure 6 It is a comparison chart of the hysteresis loop detection of the single-crystal magnetic powder of an embodiment of the present invention and the magnetic powder available on the market.

[0057] Figure 7 It is a comparison of the shear force detection of the single-crystal magnetic powder of an embodiment of the present invention and the magnetic powder available on the market at the same ratio.

[0058] Figure 8 It shows that the single-crystal magnetorheological fluid of an embodiment of the present invention can reach the shear force of the conventional magnetorheological fluid at 72% magnetic powder concentration at 50% single-crystal magnetic powder concentration. As shown in the figure, the shear strength of the single-crystal magnetorheological fluid at 50% magnetic powder concentration can reach that of the conventional magnetorheological fluid at 72% magnetic powder concentration.

[0059] Figure 9 It shows the thermal stability of the single-crystal magnetorheological fluid of an embodiment of the present invention.

[0060] Figure 10 It shows the comparison of the shear force detection of the single-crystal magnetic powder of an embodiment of the present invention and the conventional polycrystalline magnetic powder under the same particle size, the same concentration, and the same magnetic field.

[0061] Figure 11 It shows the comparison of the sedimentation ratio of the single-crystal magnetorheological fluid of an embodiment of the present invention and the conventional magnetorheological fluid after standing still. Detailed implementation manners

[0062] In the following descriptions of the drawings and the detailed implementation manners, the details of one or more embodiments of the present invention will be elaborated. From these descriptions, the drawings, and the claims, other features, purposes, and advantages of the present invention can be clearly understood.

[0063] The following will describe several specific embodiments of the present invention in more detail.

[0064] Before further describing the embodiments of the present invention, the inventor of the present invention wants to explain several terms of the present invention as follows.

[0065] The term "anisotropy" refers to the fact that all or part of the chemical, physical, etc. properties of a substance change with the change of direction, showing different properties in different directions. Anisotropy is a common property in materials and media. The term "magnetic anisotropy" refers to the phenomenon that the magnetism of a substance changes with direction, mainly manifested in that the magnetic susceptibility of a weak magnet and the magnetization curve of a ferromagnetic body change with the magnetization direction. The magnetic anisotropy of ferromagnetic bodies is particularly prominent and is one of the basic magnetisms of ferromagnetic bodies, indicating that the free energy density is different when the saturation (or spontaneous) magnetization is in different crystal directions. Typical magnetic anisotropy comes from the anisotropy of magnetic crystals.

[0066] In the context of the present invention, compared with isotropic magnetic powder, "magnetic anisotropy" enables magnetic particles to combine into chains more quickly with stronger binding force and torsional resistance after the application of a magnetic field, respond more quickly to the applied magnetic field, and return to the previous original state more quickly after removing the applied magnetic field.

[0067] Different magnetic crystal structures of magnetic powder particles will have a significant impact on the properties of magnetic powder particles after the application of an external magnetic field, such as responsiveness, rapid chain-forming performance, and torsional resistance. Compared with isotropic magnetic crystal structures, magnetic powder particles with anisotropic magnetic crystal structures can provide more excellent properties in terms of, for example, responsiveness, rapid chain-forming performance, and torsional strength. For example, anisotropic magnetic crystal structures, such as hexagonal crystal systems, some cubic crystal systems, rhombohedral crystals, etc., can provide significantly improved properties after the application of an external magnetic field, and are therefore preferred.

[0068] The inventors of the present invention unexpectedly found that although the body-centered cubic (bcc) crystal structure can be regarded as generally isotropic, its bcc lattice structure has an easy magnetization axis. Therefore, single-crystal magnetic powder with a bcc lattice structure is easily magnetized along the easy magnetization axis, and can thus be regarded as magnetically anisotropic in terms of magnetization, can exhibit magnetic anisotropy, and thus possess various advantages of anisotropic magnetorheological fluids. Therefore, in the context of the present invention, magnetic materials (magnetic particles) having a body-centered cubic (bcc) single-crystal structure are preferred.

[0069] Selection of magnetic powder (magnetic particle) materials

[0070] Any known solid with a high magnetic saturation intensity can be used in the present invention, specifically including paramagnetic and ferromagnetic elements and compounds. For example, examples of suitable magnetizable particles include iron, iron alloys (alloying elements include aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese, and / or copper), iron oxides (including Fe2O3 and Fe3O4), iron nitride, iron carbide, iron carbonyl, nickel, cobalt, chromium dioxide, stainless steel, and silicon steel. For example, examples of suitable particles include pure iron powder, reduced iron powder, and mixtures of iron oxide powder and pure iron powder. Preferred magnetic response particles are pure iron and iron-cobalt alloys.

[0071] Selection of Carrier Fluid

[0072] The carrier fluid constitutes the continuous phase of the magnetorheological fluid. Non-volatile, non-polar organic oils can all be used as carrier fluid components. Examples of suitable carrier fluids include silicone oil, hydraulic oil, engine oil, gearbox oil, α-olefins, etc. The carrier fluid also contains additives, such as, for example, organoclay, organothixotropic agent, anti-settling agent, metal soap, and other additives, etc., which are described in detail below.

[0073] 1. Organoclay, Organothixotropic Agent

[0074] Adding organoclay and organothixotropic agent can control the viscosity and sagging property of the magnetorheological fluid and delay the settlement of magnetizable particles. Examples of selectable organoclays include tallow bentonite, 2-methyl-2-hydrogenated tallow bentonite ammonium salt, 2-methyl-2-hydrogenated nontronite ammonium salt. Optional organothixotropic agents can be Advitrol 100 rheological additive, Thixatrol ST, Rheox 1 rheological additive, etc.

[0075] 2. Anti-settling Agent

[0076] Adding an anti-settling agent to prevent the settlement of nano-magnetizable particles. Optional anti-settling agents include M-P-A 2000X, M-P-A 60X anti-settling agent, or Y-25, Y-40, YPA-100 anti-settling agent, etc.

[0077] 3. Thickening Agent

[0078] The thickening agent can include metal soap, aluminum stearate, aluminum (iso)octanoate, and calcium linoleate in paste form, which together with the solvent produce a gel structure to improve the suspension property of the magnetorheological fluid.

[0079] 4. Other Additives

[0080] According to the use of the magnetorheological fluid, other additives can also be added, including antioxidants, lubricants, etc.

[0081] In the present invention, the magnetic particles in the magnetorheological fluid are in a state of not easily settling. In this regard, the term "not easily settling" should be understood as that not only during the intermittent period between the working states of the magnetorheological fluid, but also in the natural static state of the magnetorheological fluid, such as the natural static state at about 25 °C room temperature, no obvious settlement that will substantially affect the electromagnetic characteristics or normal operating performance of the magnetorheological fluid occurs in the magnetic particles in the magnetorheological fluid.

[0082] More precisely, if at least 50%, preferably at least 60%, more preferably at least 80%, and most preferably at least 90% of the magnetic particles in the magnetorheological fluid do not settle during the period when the magnetorheological fluid is naturally static at room temperature for more than 3 days, preferably more than 1 week, more preferably more than 1 month, most preferably more than 2 months or even longer, it can be regarded as achieving the state of "not easily settling" as referred to in the present invention.

[0083] The single-crystal magnetic powder and its preparation process of the present invention will be further described below with reference to the accompanying drawings and in combination with a specific embodiment.

[0084] Preparation of metal or alloy oxides

[0085] Purchase iron-cobalt alloy powder with a particle size less than 100 mesh (for example, iron: cobalt = 2:1), and calcine the iron-cobalt alloy powder at a high temperature (about 600 - 1000 °C) in an oxidizing atmosphere to obtain an iron oxide-cobalt oxide mixture. The ratio of iron / cobalt in the iron-cobalt alloy powder can be any ratio according to the required properties of the single-crystal magnetic powder of the final product, such as 1:1, 7:3, 3:7, 2:8, etc. And, a certain proportion of other elements can also be added to the iron-cobalt alloy powder according to the required properties of the single-crystal magnetic powder of the final product, such as Mn, Ni, Cr, etc. It is obvious to those skilled in the art that the composition of the alloy powder can be other ferromagnetic alloy powders containing two or more metal components.

[0086] Ball milling and screening

[0087] Feed the obtained iron oxide-cobalt oxide mixture into a commercially available ball mill, such as a ball mill of the JQM series, ball mill for 24 - 48 hours, with a ball-to-material ratio of 1:1, a ball mill filling coefficient of 50%, and a rotational speed of 70% of the critical speed. After obtaining the crushed material, perform a preliminary screening through 60 - 100 mesh to obtain the iron oxide-cobalt oxide mixture as the precursor.

[0088] Chemical reduction and crystallization

[0089] According to a preferred example, a reducing atmosphere containing 20 - 100% hydrogen plus 80 - 0% nitrogen can be selected. Load the above-mentioned precursor into a commercially available industrial chemical reduction reactor. Among them, the loading amount is 5 Kg; the gas flow rate of the reducing atmosphere is 1.5 - 5 L / min; the reaction time is 30 - 80 H; the temperature setting is 520 - 720 °C; then, cool to room temperature in the reducing atmosphere to obtain single-crystal iron-cobalt alloy powder. Those skilled in the art can understand that according to differences in composition, required properties, grain size, etc., the above-mentioned various parameters can be adjusted and changed. <on

[0090] Single crystal magnetic powder testing: The single crystal magnetic powder of the present invention is scanned and tested using various conventional testing equipment, such as a scanning electron microscope, a specific saturation magnetization measuring instrument, a shear force testing device, and so on.

[0091] Figure 3 is a scanning electron microscope (SEM) photograph of single crystal magnetic powder particles prepared according to an embodiment of the present invention, magnified 10,000 times, showing the morphology of the single crystal magnetic powder particles at this magnification; Figure 4A is a scanning electron microscope (SEM) photograph of single crystal magnetic powder particles in another size range according to an embodiment of the present invention, magnified 10,000 times, showing the morphology of the single crystal magnetic powder particles at this magnification; Figure 4B is a scanning electron microscope (SEM) photograph of commercially available magnetic powder particles, which is a comparative example compared with the present invention, magnified 10,000 times. Figure 3 - 4A shows the different sizes and morphologies of the single crystal magnetic powder particles prepared according to the present invention. It can be seen that the overall size distribution of the single crystal magnetic powder is uniform, the morphology is regular and controllable, and the particle size is much smaller than that of the Figure 4B existing polycrystalline magnetic powder particles as a comparative example. As described above, this is obviously beneficial to the basic anti-settling performance of the magnetorheological fluid, and the consistency and reliability of the product are more controllable and easier to achieve.

[0092] Figure 5 is a comparison chart of the hysteresis loop detection of the single crystal magnetic powder of an embodiment of the present invention, the nano magnetic powder previously invented by the applicant, and the commercially available traditional magnetic powder. Figure 6 is a comparison chart of the hysteresis loop detection of the single crystal magnetic powder of an embodiment of the present invention and the commercially available magnetic powder. According to Figure 5 - 6 it can be seen that the performance index parameters of the single crystal magnetic powder of the present invention in terms of magnetic saturation intensity, remanence, and coercive force far exceed those of the magnetic powder in traditional magnetorheological fluids.

[0093] Preparation of magnetorheological fluid from single - crystal magnetic powder

[0094] See Figure 1 and Figure 2 where Figure 1 is a schematic perspective view of a mixing-separation device for mixing and separating the single crystal magnetic powder and the carrier liquid according to an embodiment of the present invention, Figure 2 is Figure 1 a schematic plan view of an embodiment of the mixing-separation device shown in

[0095] As shown in Figure 1 - 2As shown, an embodiment of the preparation device of the magnetorheological fluid containing single-crystal magnetic powder according to the present invention includes a primary mixer 1, a sedimentation separator 2, a magnetic separator 3, a pump 5, and a stirrer 4. Among them, the sedimentation separator 2 is preferably located downstream of the primary mixer 1 and is connected to the primary mixer 1 through a pipeline 6. The magnetic separator 3 is preferably located downstream of the sedimentation separator 2 and is also connected to the sedimentation separator 2 through a pipeline. Among them, the magnetic separator 3 and the sedimentation separator 2 are preferably each provided with an outlet to the primary mixer 1, so that the unqualified residual liquid can be selectively returned to the primary mixer 1 through a pump 7 for reprocessing.

[0096] The stirrer 4 is preferably located downstream of the magnetic separator 3 and is also connected to the magnetic separator 3 through a pipeline, and is used to receive the fluid containing the required single-crystal magnetic powder particles from the magnetic separator 3.

[0097] In the primary mixer 1, the above-mentioned single-crystal iron-cobalt alloy powder is initially stirred and mixed with the carrier liquid of the selected magnetorheological fluid to disperse the single-crystal iron-cobalt alloy powder. The carrier liquid can adopt, for example, α-olefin as the grinding medium. In this primary mixing process, a surfactant can be added, which can also be used as a dispersant to prevent the single-crystal magnetic powder from agglomerating and welding. For example, in this regard, the following examples can be referred to.

[0098] According to Example 1, 30 g / l of single-crystal magnetic powder is provided, the carrier liquid is 28.05 g / l of α-olefin, 1.2 g / l of anti-wear agent, 0.3 g / l of dispersant, and 0.45 g / l of antioxidant. The carrier liquid and various additives are stirred at a low speed of 300 r / min for 10 min, and then the single-crystal magnetic powder is added, and stirred at 1200 r / min for 20 min to prepare a slurry of the primary mixture of the single-crystal magnetorheological fluid with a magnetic powder ratio of about 72%.

[0099] According to Example 2, 30 g / l of single-crystal magnetic powder is provided, the carrier liquid is 28.05 g / l of α-olefin, 1.2 g / l of anti-wear agent, 0.3 g / l of dispersant, and 0.45 g / l of antioxidant. First, the carrier liquid and various additives are stirred at a low speed of 300 r / min for 10 min, then the single-crystal magnetic powder is added, and stirred at 1200 r / min for 20 min to prepare a slurry of the primary mixture of the single-crystal magnetorheological fluid with a magnetic powder ratio of about 50%.

[0100] Precipitation separation process

[0101] The slurry after primary mixing is transported into the precipitation separator 2, such as a self-made gravity separator or a centrifugal separator (e.g., model LW50*1100). Using gravity or centrifugal force, single crystal magnetic powder particles with particle sizes meeting the requirements (e.g., a particle size range of approximately 0.1 - 8 microns, which may vary according to the specific type of single crystal magnetic powder, process requirements, and application requirements) are separated out, and the fine particles meeting the requirements are sent to the magnetic separator 3. As an example, single crystal magnetic particles with particle sizes not meeting the requirements or still agglomerated can be selectively recycled by the pump 5 back to the primary mixer 1, and thus can be used for re-dispersion and screening again, such as another standard screening, avoiding waste of single crystal materials.

[0102] According to a preferred embodiment, the slurry in the gravity separator or centrifugal separator can be heated to a certain temperature, such as heated to 35 - 50 degrees Celsius to promote separation.

[0103] Magnetic separation process

[0104] According to an alternative embodiment, as an alternative or additional process to the gravity sedimentation separation or centrifugal separation process, through the magnetic separator 3, by applying an exciting current to the magnetic powder particles to generate electromagnetic suction, a slurry of single crystal magnetic powder particles with a higher concentration meeting the predetermined requirements can be separated out and sent to the mixer 4 for the next stirring process. According to this example, the concentration of single crystal magnetic powder in the separated slurry can be controlled by controlling the magnitude of the exciting current.

[0105] Stirring process

[0106] The slurry containing single crystal magnetic powder particles separated from the magnetic separator 3 is characterized by the density value to represent the content of magnetic particles, supplemented with a carrier liquid (such as α-olefin), an anti-settling agent (e.g., M-P-A2000X, NL Chemicals Company), a lubricant (e.g., silicone oil), and an optional defoaming agent, and stirred by the mixer 4 (model DX-L500) for about 1 hour to obtain a magnetic rheological fluid containing single crystal magnetic powder meeting the requirements.

[0107] Sedimentation test

[0108] Test (1)

[0109] The magnetic rheological fluid containing single crystal magnetic powder is naturally static at room temperature to test its sedimentation performance. The test shows that almost no sedimentation stratification is observed after 2 weeks of natural static in the magnetic rheological fluid containing single crystal magnetic powder of the present invention. After 4 weeks of natural static, no sedimentation stratification is observed. After 8 weeks of natural static, no sedimentation stratification is observed either. At least 50%, and even more than 90% of the magnetic particles in the magnetic rheological fluid containing single crystal magnetic powder do not settle during this period.

[0110] Test (2)

[0111] The TZC-4 particle analyzer produced by Shanghai Fangrui Instrument Co., Ltd. was used to test the magnetorheological fluid containing single-crystal magnetic powder of the present invention in a constant-temperature oven at a set temperature of 70 °C at room temperature. The sedimentation height was set to 3 cm and the time was set to 180 hours. The ratio of the height of the stratified clear liquid to the total height (Ratio) was used to represent the sedimentation degree of the two magnetorheological fluids. Figure 11 It shows the comparison of the sedimentation ratio (Ratio) of the single-crystal magnetorheological fluid and the traditional magnetorheological fluid after standing in an embodiment of the present invention. This figure shows that the single-crystal magnetorheological fluid of the present invention is significantly superior to the traditional magnetorheological fluid in terms of anti-sedimentation performance.

[0112] Shear strength test

[0113] The magnetorheological fluids prepared from the single-crystal magnetic powder of the present invention and the traditional magnetic powder available on the market were respectively subjected to shear force detection in an applied magnetic field. The Anton Paar detection equipment MRC301 magnetorheological rheological property detector was used, and the detection parameters were a speed of 10-1, a detection current of 0-3.6 A, a magnetic field of 0-1 T, and 50 sampling points were taken.

[0114] Figure 7 It is a comparison of the shear force tests of the magnetorheological fluids prepared from the single-crystal magnetic powder of an embodiment of the present invention and the traditional magnetic powder available on the market at the same ratio. It can be seen that when the magnetic powder concentration is the same (72%) and the same excitation current is applied, the shear strength of the magnetorheological fluid prepared from the single-crystal magnetic powder of the present invention is much better than that of the magnetorheological fluid prepared from the traditional magnetic powder.

[0115] Figure 8 It shows that the single-crystal magnetorheological fluid of an embodiment of the present invention can reach the shear force of the traditional magnetorheological fluid at a 72% magnetic powder concentration at a 50% single-crystal magnetic powder concentration.

[0116] Figure 9 It shows the shear strength parameters of the single-crystal magnetorheological fluid of an embodiment of the present invention and the traditional magnetorheological fluid as a comparative example tested at 25 °C and 75 °C respectively. Obviously, in terms of shear strength, the thermal stability of the single-crystal magnetorheological fluid of the present invention is also better than that of the traditional magnetorheological fluid.

[0117] Figure 10 It shows the comparison of the shear forces measured in an applied magnetic field of the magnetorheological fluids with the same concentration prepared from the 2-micron-sized single-crystal magnetic powder and the 2-micron-sized traditional polycrystalline magnetic powder in an embodiment of the present invention. The figure shows that in this case, the shear strength indexes of the different single-crystal magnetorheological fluids of the present invention always exceed those of the traditional magnetorheological fluids.

[0118] In the foregoing, embodiments of the single-crystal structure magnetic powder of the present invention, the magnetorheological fluid prepared therefrom, and its methods and apparatuses have been described in detail in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above are merely illustrative examples and descriptions of some specific embodiments, and do not have any limitation on the scope of the present invention, especially the scope of the claims. The scope of the present invention is only defined by the appended claims.

Claims

1. A magnetorheological fluid containing single-crystal magnetic powder, comprising: Single crystal magnetic powder, composed of magnetizable magnetic particles with a separated single crystal structure, the average particle size of the magnetic particles being in the range of 0.1 - 8 microns; wherein, Each of the magnetic particles is composed of a single crystal grain or multiple crystal grains with the same crystal lattice and consistent crystal orientation, whereby the magnetic particles have magnetocrystalline anisotropy; and A fluid serving as a carrier liquid, wherein the single-crystal magnetic powder is dispersed in the fluid; Wherein the single crystal of the single-crystal magnetic powder has one of the following crystal lattices: cubic lattice, rhombohedral lattice, and body-centered cubic lattice; Wherein the material of the magnetizable magnetic particles is selected from iron-aluminum alloy, iron-silicon alloy, iron-cobalt alloy, iron-nickel alloy, iron-vanadium alloy, iron-molybdenum alloy, iron-chromium alloy, iron-tungsten alloy, iron-manganese alloy, iron-platinum alloy, iron-copper alloy, SmCo, NdFeB, stainless steel, silicon steel, and combinations of the above materials; and Wherein the volume of the magnetic particles accounts for 1-70% of the total volume of the magnetorheological fluid.

2. The magnetorheological fluid according to claim 1, wherein The average particle size of the magnetic particles is between 0.8 and 3 microns, wherein the number of magnetic particles with an average particle size between 0.8 and 1.5 microns accounts for more than 50% of the total number of magnetic particles.

3. The magnetorheological fluid according to claim 1, characterized in that, The fluid is an organic liquid.

4. The magnetorheological fluid according to claim 1, characterized in that, The single crystal of the single-crystal magnetic powder has a body-centered cubic lattice.

5. The magnetorheological fluid according to any one of claims 1-4, characterized in that, The magnetorheological fluid containing single-crystal magnetic powder does not undergo sedimentation and stratification during at least 2 weeks of standing at room temperature.

6. Use of the magnetorheological fluid containing single-crystal magnetic powder according to any one of claims 1-5 in shock absorption and / or buffering in load-bearing application scenarios, wherein the load-bearing application scenarios include at least one of transportation vehicles, construction machinery, processing machinery, medical equipment, bridges, and drilling platforms.

7. A method for preparing the magnetorheological fluid containing single-crystal magnetic powder according to any one of claims 1-5, comprising: Providing a precursor in oxide form for preparing the single-crystal magnetic powder, the precursor containing iron element and at least one element selected from the group consisting of aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese, platinum, copper, boron, and samarium; Chemically reducing and recrystallizing the precursor in a reducing atmosphere to obtain the single-crystal magnetic powder; Adding the single-crystal magnetic powder, additives, and a part of the carrier liquid to a primary mixer, and performing mixing and dispersion to obtain a primary slurry; Further screening and separating the primary slurry to obtain a slurry containing the desired single-crystal magnetic powder, wherein the screening and separation include at least one of gravity separation, centrifugal separation, and magnetic separation; Selectively adding the carrier liquid and additives to the slurry containing the desired single-crystal magnetic powder in a blender and stirring to obtain a magnetorheological fluid containing single-crystal magnetic powder; Wherein each of the magnetic particles of the prepared single-crystal magnetic powder is composed of a single crystal grain or multiple crystal grains with the same crystal lattice and consistent crystal orientation, whereby the magnetic particles have magnetocrystalline anisotropy.

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