Nano magneto-rheological fluid and preparation method and device thereof

Abstract

A nano magneto-rheological fluid, comprising nano-scale magnetizable magnetic particles, wherein an average particle size or a minimum size in one dimension is less than 100 nanometers; and fluids used as carrier liquids, wherein the magnetic particles are dispersively distributed in the fluids. An apparatus for making the nanometric magnetorheological fluid including a ball mill, a settling separator located downstream of the ball mill for receiving the primary magnetic particles, a magnetic separator located downstream of and connected to the settling separator for receiving the upper layer of fluid containing fine magnetic particles, and an agitator for mixing the desired secondary magnetic particles with a carrier liquid and an additive. A method for making the nano magneto-rheological fluid wherein the nano magneto-rheological fluid has performance advantages such as no remanent magnetization, non-settlement, low viscosity, low abrasive rate for components, long service life, high reliability and fast and clear response.

Claims

1. A nanometric magnetorheological fluid, comprising: nanometric magnetizable magnetic particles, wherein the magnetic particles are magnetically anisotropic magnetic particles and have an average particle size or a minimum unidimensional size of less than 99 nanometers; and a fluid for use as a carrier liquid, wherein the magnetic particles are dispersedly distributed in the fluid in a state that is not prone to settle; wherein the materials of the magnetic particles are selected from the group consisting of: iron, iron alloy, iron-cobalt alloy, iron-platinum alloy, iron oxide, iron nitride, iron carbide, carbonyl iron, nickel, cobalt, chromium dioxide, FePt, SmCo, NdFeB, stainless steel, silicon steel, and the combinations thereof; and wherein the magnetic particles are shape-anisotropic, and/or magnetocrystalline-anisotropic, and/or stress-induced magnetically anisotropic.

2. The nanometric magnetorheological fluid according to claim 1, wherein the magnetic particles have an average particle size or a minimum unidimensional size between 0.1 and 80 nanometers, wherein the number of magnetic particles with a particle size or minimum unidimensional size smaller than 90 nm is 50% or more of the total magnetic particles.

3. The nanometric magnetorheological fluid according to claim 2, wherein the number of magnetic particles having a particle size or minimum unidimensional size between 0.1 and 80 nanometers accounts for 60% or more of the total magnetic particles.

4. The nanometric magnetorheological fluid according to claim 1, wherein the fluid is an organic liquid.

5. The nanometric magnetorheological fluid according to claim 1, wherein the fluid further comprises additives selected from the group consisting of: a surfactant, a dispersant, an anti-settling agent, an organic thixotropic agent, a thickening agent, an anti-oxidant, lubricants, viscosity modifiers, flame retardants, organic clay-type rheological additives, sulfur compounds, and combinations thereof.

6. The nanometric magnetorheological fluid according to claim 1, wherein the volume of the magnetic particles accounts for one of the following: 0.8-5% of the total volume of the nanometric magnetorheological fluid; and 10% to 70% of the total volume of the nanometric magnetorheological fluid.

7. The nanometric magnetorheological fluid according to claim 1, wherein the magnetic particles have a non-spherical shape, wherein the non-spherical shape is selected from the group consisting of a flake, a strip, a needle, a rod, a cylindrical shape, and any combination thereof.

8. The nanometric magnetorheological fluid according to claim 1, wherein the magnetic particles do not settle or stratify when the nanometric magnetorheological fluid rests at room temperature for a period of at least 2 weeks.

9. The nanometric magnetorheological fluid according to claim 7, wherein the magnetic particles are flake-shaped, strip-shaped or needle-shaped magnetic particles, and the number of the flake-shaped or strip-shaped or needle-shaped magnetic particles accounts for 50% or more of the total number of the magnetic particles in the nanometric magnetorheological fluid.

10. The nanometric magnetorheological fluid according to claim 1, wherein the minimum unidimensional size of the magnetic particles is between 0.05D.sub.SP-1 D.sub.SP, with the single-domain critical size of the magnetic particles being excluded therefrom.

11. The nanometric magnetorheological fluid according to claim 10, wherein the magnetic particles are in the form of a flake, a strip, a needle, a rod or a cylindrical shape, with a maximum unidimensional size between 2 D.sub.SD and 100 D.sub.SD.

12. The nanometric magnetorheological fluid according to claim 1, wherein at least 50% of the magnetic particles in the nanometric magnetorheological fluid do not settle or stratify when the nanometric magnetorheological fluid rests at room temperature for a period of at least 2 weeks.

13. A nanometric magnetorheological fluid, comprising: flake-shaped nanometric magnetic particles, wherein the flake-shaped magnetic particles have a thickness of less than 100 nanometers; and a fluid for use as a carrier liquid, wherein the magnetic particles are dispersed in the fluid.

14. The nanometric magnetorheological fluid according to claim 13, wherein the flake-shaped magnetic particles are magnetocrystalline-anisotropic and/or stress-induced magnetically anisotropic.

15. The nanometric magnetorheological fluid according to claim 13, wherein the maximum unidimensional size of the flake-shaped magnetic particles is between greater than 1 D.sub.SD and 100 D.sub.SD.

16. The nanometric magnetorheological fluid according to claim 13, wherein at least 50% of the flake-shaped magnetic particles in the nanometric magnetorheological fluid do not settle or stratify when the nanometric magnetorheological fluid rests at room temperature for a period of at least 2 weeks.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features, objects and advantages of the present disclosure will become more apparent from the following description taken in conjunction with the accompanying drawings in which:

(2) FIG. 1 is a graphical illustration of the relationship between the coercivity and the particle size of magnetic particles;

(3) FIG. 2 is a graphical illustration of the single-domain critical size (D.sub.SD) and superparamagnetic critical size (D.sub.SP) of some ferromagnetic materials;

(4) FIG. 3 is a schematic perspective view of an apparatus for fabricating a nanometric magnetorheological fluid according to one aspect of the present disclosure; and

(5) FIG. 4 is a schematic view of the embodiment of the apparatus for fabricating a nanometric magnetorheological fluid as shown in FIG. 3.

DESCRIPTION OF THE ENABLING EMBODIMENT

(6) In the following description of the drawings and the detailed description, details of one or more embodiments of the disclosure will be set forth. Other features, objects, and advantages of the present disclosure will become apparent from the description, drawings, and claims.

(7) Several particular embodiments of the present disclosure will be described in more detail as below.

(8) Before further describing the embodiments of the present disclosure, the inventors would like to explain several terms in the present disclosure as follows.

(9) In the present disclosure, the term anisotropy or anisotropic has meanings in several aspects.

(10) Firstly, the term anisotropy or anisotropic may refer to the anisotropy in the shape of magnetic nanoparticles in a magnetorheological fluid, which can enable the magnetic nanoparticles to be quickly combined into a chain with a strong binding force and torsional force once magnetic field being applied thereto, the response to the applied magnetic field is fast and distinct, and the previous original state can be quickly restored once the magnetic field is removed. In contrast, for example, existing magnetic particles in the magnetorheological fluid are not only large in size, for example up to about 1 micron, but also their magnetic particles generally exhibit spherical or substantially spherical shape, making a slow response to the applied magnetic field.

(11) Since the size of the magnetic particles in the magnetorheological fluid is in the order of nanometric range, the anisotropic shape of the magnetic nanoparticles belongs to microscopic shape, and needs to be sufficiently enlarged, for example, under SEM or TEM to clearly show. For example, but not limited to, the anisotropic shape of the magnetic nanoparticles is preferably non-spherical in shape, including but not limited to flakes, strips, rods, columns, prisms, cylinders, and the like. The inventor of the present disclosure has surprisingly found through experiment that, the preferred flake or strip or needle-like magnetic nanoparticles facilitate the rapid formation of the particle-chain after the magnetic field is applied, such that the magnetorheological fluid has excellent torsional resistance, in particular, elongated flake or strip or needle-like magnetic nanoparticles are preferred.

(12) Secondly, the term anisotropy or anisotropic may refer to the anisotropy in the magnetocrystalline structure of the magnetic nanoparticles in the magnetorheological fluid. The inventor of the present disclosure has surprisingly found that, the different magnetocrystalline structures of the magnetic nanoparticles has significant effect on the properties of the magnetic nanoparticles after the magnetic field is applied, such as responsiveness, rapid formation of the particle-chain properties and torsional resistance. The magnetic nanoparticles with anisotropic magnetocrystalline structure may provide more superior performance in terms of responsiveness and fast formation properties of the particle-chain, torsional strength, and the like, as compared with the isotropic magnetocrystalline structure. For example, in this respect, the crystalline structure of the face-centered cubic (fcc) and body-centered cubic (bcc) structure is considered to be an isotropic magnetocrystalline structure, and thus is not preferred. By contrast, an anisotropic magnetocrystalline structure, such as a hexagonal crystallographic system, part of cubic crystallographic system, rhombohedral crystal system, etc., can provide remarkably improved properties after application of a magnetic field, and is therefore preferred.

(13) It will be understood by those ordinary skilled in the art that, the term superparamagnetism or superparamagnetic means that, the remanence and coercivity of the magnetic particles are substantially zero with no remanence phenomenon occurring.

(14) The conventional magnetorheological fluid fabrication technique cannot make the particle size or the minimum unidimensional size of the magnetic particles smaller than the superparamagnetic critical size (D.sub.SP). In order to reduce the remanence, the preferred particle size of the conventional magnetic particles is 1 m or more (as disclosed in U.S. Pat. No. 6,203,717 B1), bringing about the problem of easy settlement, high viscosity and wear on parts and other problems.

(15) The apparatus of the present disclosure combines the settlement separation with the high-energy ball mill, utilizes the relationship between the particle settling rate and the particle size to automatically separate the particles that meet the requirements, and automatically return the coarse particles that do not meet the requirements back to the ball mill for further ball milling, to produce the novel magnetorheological fluid, i.e., nanometric magnetorheological fluid. The particle size of the magnetically responsive particles in this fluid may be smaller than that of the superparamagnetic conversion particle size D.sub.SP (obtainable by adjusting the settling conditions), thus showing superparamagnetic properties, with no remanence, anti-settlement, low initial viscosity and low wear rate of the components.

(16) Selection of Superparamagnetic Magnetically Responsive Nanoparticle Material

(17) Any known solid having high magnetic saturation strength can be used in the present disclosure, especially including paramagnetic, superparamagnetic and ferromagnetic elements and compounds. Examples of suitable magnetizable particles include iron and iron alloys (alloying elements including aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese, and/or copper), iron oxides (including Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4), iron nitride, iron carbide, carbonyl iron, nickel, cobalt, chromium dioxide, stainless steel and silicon steel. For example, examples of suitable particles include pure iron powder, reduced iron powder, a mixture of iron oxide powder and pure iron powder. The preferred magnetically responsive particles are pure iron and iron-cobalt alloys.

(18) Selection of Particle Size of Superparamagnetic Magnetically Responsive Nanoparticles

(19) The magnetically responsive particles of the present disclosure have a particle size in the order of nanoscale, preferably with a particle size or a minimum unidimensional size which is smaller than the superparamagnetic critical size (D.sub.SP) of the selected material, preferably, the average particle size or the minimum unidimensional size is in the range of 0.1 D.sub.SP-1 D.sub.SP, more preferably between 0.1 D.sub.SP and 0.9 D.sub.SP. Preferably, the number of magnetic particles having a particle size between 0.1 D.sub.SP and 0.9 D.sub.SP is at least 50%, preferably at least 70% or at least 80%, more preferably 90% or more, of the total number of magnetic particles.

(20) Preferably, if the magnetically responsive particles are non-spherical in shape, such as flake-like, strip-like, needle-like, rod-like or cylindrical shape, the minimum unidimensional size may range between 0.1 D.sub.SP-1 D.sub.SP, more preferably between 0.1 D.sub.SP and 0.9 D.sub.SP, with the single-domain critical size D.sub.SD being excluded therefrom.

(21) Preferably, if the magnetically responsive particles are non-spherical in shape, such as flake-like, strip-like, needle-like, rod-like or cylindrical shape, the maximum unidimensional size may range between greater than 1 D.sub.SD and 100 D.sub.SD, more preferably between 2 D.sub.SD-100 D.sub.SD, most preferably between 5 D.sub.SD-50 D.sub.SD.

(22) Fabrication Method of Magnetically Responsive Nanoparticles

(23) The fabrication method of nanometric magnetically responsive particulate material may include, but not limited to, co-precipitation method, chemical synthesis method with polyol solution, chemical reduction method, aqueous solution reduction method, polyol reduction method, sol-gel method, hydro-thermal method, ball milling method, and so on.

(24) Carrier Liquid

(25) The carrier liquid constitutes a continuous phase of the magnetorheological fluid. Non-volatile, non-polar organic oils may be used as the carrier composition, and suitable carrier liquid examples include silicone oil, hydraulic oil, engine oil, gearbox oil, -olefin, and the like. The carrier liquid may also contain additives, such as organic clays, organic thixotropic agents, anti-settling agents, metal soaps and other additives, and so on, as described below.

(26) [1] Organic Clay, Organic Thixotropic Agent

(27) Addition of organic clay or organic thixotropic agent may control the viscosity and sagging of the magnetorheological fluid, and delay the settling of the magnetizable particles. Examples of optional organoclays include tallow bentonite, 2-methyl-2-hydrogenated tallow bentonite ammonium salts, and 2-methyl-2-hydrogenated tallow saladstone salts. The optional organic thixotropic agents may be Advitrol 100 rheological additives, and Thixatrol ST, Rheox 1 rheological additives.

(28) [2] Anti-Settling Agent

(29) Addition of anti-settling agent can prevent the settlement of magnetizable nanoparticles, the optional anti-settling agent includes M-P-A 2000X, M-P-A 60X anti-settling agent, or Y-25, Y-40 and YPA-100 anti-settling agents.

(30) [3] Metal Soap

(31) Additional thickeners include metal soaps, including aluminum stearate, Ethylhexanoic acid aluminum salt and slurry calcium linoleate, which together with the solvent can produce a gel structure that improves the suspension property of the magnetorheological fluid.

(32) [4] Other Additives

(33) Depending on the applications of magnetorheological fluids, other additives may be added, including dispersants, surfactants, antioxidants, lubricants, and the like.

(34) In the present disclosure, the magnetic particles in the magnetorheological fluid are hardly to settle, and in this respect, the term hardly to settle should be understood as: not only during the interval of the operating state of the magnetorheological fluid, but also in the natural resting state of the magnetorheological fluid, for example, in the natural resting state at room temperature of about 25 C., there is no obvious or substantive settlement of the magnetic particles in the magnetorheological fluid which will affect the electromagnetic characteristics or normal operating performance of the magnetorheological fluid.

(35) 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, in the natural resting state at room temperature, the settlement or stratification will not occur in the fluid after passing a period of 1 week or more, preferably 2 weeks or more, more preferably 1 month or more, and most preferably 2 months or more or longer, it is considered that the hardly to settle state as referred to in the present application is achieved.

(36) The fabrication of the nanometric magnetorheological fluid of the present disclosure is further described below in connection with particular embodiments.

(37) The disclosure will now be further described with reference to the accompanying drawings and particular embodiments.

(38) Referring to FIGS. 3 and 4, wherein FIG. 3 is a schematic perspective view of an apparatus for fabricating a nanometric magnetorheological fluid according to an aspect of the present disclosure, and FIG. 4 is a schematic view of the embodiment of the apparatus for fabricating a nanometric magnetorheological fluid as shown in FIG. 3. An embodiment of the apparatus for fabricating a nanometric magnetorheological fluid according to the present disclosure comprises a stirring ball mill 1, a settling separator 2, a magnetic separator 3, a pump 5, an agitator 4, wherein the settling separator 2 is preferably located downstream of the stirring ball mill 1 and is connected to the stirring ball mill 1 via a pipe line 6, the magnetic separator 3 is preferably located downstream of the settling separator 2 and is also connected to the settling separator 2 by means of a pipe line. Preferably, the magnetic separator 3 and the settling separator 2 are respectively provided with an outlet in connection with the stirring ball mill 1, so that the undesired residual liquid therein is selectively returned back to the stirring ball mill 1 by the pump 7 for re-processing.

(39) The agitator 4 is preferably located downstream of the magnetic separator 3, and is also connected to the magnetic separator 3 by means of a pipe line, for receiving the fluid containing the desired magnetic nanoparticles from the magnetic separator 3.

(40) (1) Grinding Process

(41) The iron and cobalt salts are dissolved together in water, for example, by a polyol solution chemical synthesis method, to obtain an iron-cobalt mixed salt solution, a precipitant containing but not limited to oxalic acid, oxalate or carbonate is utilized, wherein ions of the precipitant react with Co and Fe ions to form precipitates of iron-cobalt compound salt, which will be subject to liquid-solid separation, drying, calcination, reduction and other processes, so as to obtain iron-cobalt alloy powder.

(42) An iron-cobalt alloy (1:2) powder such as obtained via the above process, a grinding medium, a surfactant such as Tween 80, an antifoaming agent such as n-butanol, combined at a ratio (weight ratio: 70:29:0.9:0.1, n-butanol may be appropriately added thereto according to the amount of the foam) are put into a ball mill (an exemplary type of stirring ball mill 1 is JQM-500), and are ball milled therein at a ball-stock ratio of 10:1. This type of stirring ball mill 1 has a high rotational speed with a large milling force, thus the milling efficiency is also high.

(43) Preferably, the milled slurry is recycled by means of a circulating pump to increase the utilization of the magnetic powder raw material.

(44) -olefin may be used as the grinding medium. According to a non-limiting example, a surfactant may be added, which may also be used as a dispersant to prevent the magnetic powder from agglomerating and bonding together. The use of defoaming agent is intended to eliminate the bubbles as generated by the addition of surfactant.

(45) (2) Settling Separation Process

(46) The ball milled slurry is then delivered to the settlement separator 2, such as a self-made gravity separator or centrifugal separator (Model LW50*1100), which utilizes gravitational or centrifugal forces to separate out the desired magnetic nanoparticles which meet the requirements (e.g., a particle size range of less than 50 nanometers, which size or size range may vary according to the particular type of magnetic powder, process requirements and application requirements), and then the desired magnetic nanoparticles are sent to the magnetic separator 3. However, those coarse magnetic particles whose size does not meet the requirements (e.g., particle size of more than 50 nm) are pumped back to the mixing ball mill 1, for further grinding.

(47) According to a preferred embodiment, the ball mill slurry in the gravity separator or centrifugal separator can be heated to a temperature, for example, to a temperature of 25-50 degrees Celsius, to facilitate centrifugal separation.

(48) (3) Magnetic Separation Process

(49) According to a preferred embodiment, in addition to gravity-settling separation or centrifugal separation, a self-control apparatus can be used to generate electromagnetic energy by applying an exciting current to the magnetic nanoparticles, to further concentrate and separate out the superparamagnetic magnetic nanoparticles from the ball milling medium. The separated magnetic nanoparticles (containing part of the milling medium) may preferably be sent to the agitator 4 for the next agitating process. Wherein the ball milling medium with magnetic nanoparticles being separated out, may be passed through the pump 5 and sent back to the stirring ball mill 1 via the pipe line 7. According to a preferred embodiment of the present disclosure, the concentration of the separated magnetic particles can be controlled, by controlling the exciting current.

(50) (4) Agitating Process

(51) The content of the magnetic particles is characterized by the density value of the slurry containing the magnetic nanoparticles which is separated from the magnetic separator 3, and the -olefin is added to the slurry, together with anti-settling agent (e.g., MP-A2000X, NL Chemical Co.) and lubricant (such as silicone oil), then the composition is stirred for about 1 hour via an agitator 4 (such as model DX-L500) to obtain the desired nanometric magnetorheological fluid.

(52) Settlement Test

(53) Test (a)

(54) The nanometric magnetorheological fluid obtained after the above-mentioned agitating process (4) was placed for natural resting at room temperature, to test its settling performance. The result shows that, there is almost no settlement-induced stratification in the nanometric magnetorheological fluid after 2 weeks of natural resting. After 4 weeks of natural resting, no settlement-induced stratification was observed. After 8 weeks of natural resting, no settlement-induced stratification was observed. At least 50%, or even more than 90% of the magnetic particles in the nanometric magnetorheological fluid do not settle during the period.

(55) Test (b)

(56) The nanometric magnetorheological fluid obtained after the above-mentioned agitating process (4) was tested at room temperature, using a TZC-4 Type Particle Size Measuring Instrument manufactured by Shanghai Fangrui Instrument Co., Ltd., wherein the settling height was set to 2 cm, and the natural resting time was set to 96 hours. No occurrence of particles stratification or settlement was observed in this test.

(57) Embodiments of the nanometric magnetorheological fluid, the method and the apparatus of the present disclosure have been described in detail with reference to the accompanying drawings. It should be understood by those skilled in the art, however, that the foregoing is merely illustrative of and describing some particular embodiments, without departing from the scope of the invention, particularly the scope of the claims. The scope of the invention is defined only by the appended claims.