Magnetorheological fluid based on aluminum oxide coated carbonyl iron powder

Abstract

The invention discloses magnetorheological fluid based on aluminum oxide coated carbonyl iron powder. The magnetorheological fluid comprises the following raw material components in percentage by volume: 35%-45% of aluminum oxide coated carbonyl iron powder, 0.001%-0.5% of nano diamond powder, 0.001%-1.5% of a dispersing agent, 0.5%-1% of a wetting agent, 0.1%-3% of a pH regulator and the balance of deionized water. The dispersing agent and the wetting agent serve as additives, the stability of the fluid can be improved within the range, the viscosity of the liquid can be improved through the excessive additive, the zero-field viscosity of the magnetorheological polishing liquid is sharply increased, the transmission difficulty is increased, and even the liquid cannot be circulated. In addition, the excessive additive can inhibit hydration of the surface of the optical glass and water and significantly reduce the strength formed by magnetic linkage so as to reduce the shear yield stress, which is not beneficial to the process of processing optical elements.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetorheological polishing materials, and particularly relates to a magnetorheological fluid based on alumina-coated carbonyl iron powder. Background Art

[0002] With the continuous development of fields such as space optics, inertial confinement fusion, lithography technology, and lasers, the requirements for the surface quality and accuracy of their optical components are getting higher and higher. As a mature and effective processing method, magnetorheological polishing technology has the advantages of non-wearing of the polishing tool, precise computer control, small subsurface damage, high processing accuracy, etc., which can further improve the quality of processed products, so it has broad development and application prospects.

[0003] As the polishing tool carrier of magnetorheological polishing technology, the magnetorheological polishing fluid has an important impact on the processing quality and efficiency of components. Good surface roughness can bring advantages such as reducing energy loss and improving image contrast. However, since the density of ferromagnetic particles in the magnetorheological fluid is much greater than that of non-magnetic fluids, the settlement of magnetic particles will be inevitable; and during the use of the magnetorheological polishing fluid, various problems such as water evaporation, oxidation and deterioration, and particle adhesion and aggregation will occur, reducing the rheological properties of the magnetorheological polishing fluid. The large agglomerated particles will cause uneven particle sizes of iron powder in the liquid, which is not only unfavorable for the normal operation of the circulation system, but also reduces the surface quality of the processed components, affecting the processing cost and efficiency. Therefore, how to maintain a good dispersion state of particles in the magnetorheological polishing fluid is crucial.

[0004] Settling stability, zero-field viscosity, and shear yield stress are three important performance indicators for preparing magnetorheological fluids with excellent performance. An excellent magnetorheological polishing fluid should have the characteristics of low zero-field viscosity, strong anti-settling property, good secondary redispersibility, high shear yield stress, and environmentally friendly components. The main difficulty in obtaining a high-performance magnetorheological fluid lies in how to better improve the anti-settling property and dispersibility of the magnetorheological fluid under the target requirements of viscosity and shear stress. Therefore, there is an urgent need for a magnetorheological polishing fluid with good anti-settling property and dispersibility and excellent performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a magnetorheological fluid based on alumina-coated carbonyl iron powder with good anti-settling property and dispersibility and excellent performance.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions: A magnetorheological fluid based on alumina-coated carbonyl iron powder, the raw materials include the following components by volume fraction: alumina-coated carbonyl iron powder: 35%-45%, nano-diamond powder: 0.001%-0.5%, dispersant: 0.001%-1.5%, wetting agent: 0.5%-1%, pH regulator: 0.1%-3%, deionized water: the balance.

[0007] As a further improvement to the above technical solution: The dispersant is diammonium hydrogen citrate, the wetting agent is glycerol, and the pH regulator is sodium hydroxide.

[0008] The volume percentage of the alumina-coated carbonyl iron powder is 38%-42%.

[0009] The volume percentage of the diammonium hydrogen citrate is 1%-1.5%.

[0010] The volume percentage of the diammonium hydrogen citrate is 0.5%-1%.

[0011] The alumina-coated carbonyl iron powder includes carbonyl iron powder particles and an alumina coating layer coated on the surface of the carbonyl iron powder particles. The average particle size of the carbonyl iron powder particles is 1-5 μm, and the thickness of the alumina coating layer is 15-20 nm.

[0012] The alumina coating layer is an ALD-deposited alumina coating layer.

[0013] The average particle size of the nano-diamond powder is 70-120 nm. In the present invention, if the average particle size is greater than this range, although the material removal efficiency is high, it is easy to leave deeper and larger scratches on the surface of the workpiece, resulting in an increase in surface roughness, and the movement under the action of the magnetic field is relatively less flexible, and local aggregation or uneven distribution is likely to occur. If the average particle size is less than this range, the particles are too small, and the material removal efficiency will be greatly reduced, and even the processing task cannot be completed. Moreover, the van der Waals force and other effects between the too-small abrasive grains are enhanced, and agglomeration is likely to occur. The agglomerated large particles will cause uneven polishing effects.

[0014] The pH value of the magnetorheological fluid is 9-12. Within this range, on the one hand, it can provide a benign environment suitable for the additives used in the present invention to exert their activity and improve the liquid performance, such as dispersibility. On the other hand, this pH value helps to slow down the oxidation process and improve the service life. However, an overly alkaline or overly acidic environment may cause corrosion to the workpiece. Finally, it helps to maintain the stability of the magnetorheological effect of the liquid, such as yield stress, viscosity, etc.

[0015] The volume percentage of the nano-diamond powder is 0.001%-0.005%.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The raw materials of the present invention include the following components by volume fraction: alumina-coated carbonyl iron powder: 35-45%, nano-diamond powder: 0.0001-0.5%, dispersant: 0.001-1.5%, wetting agent: 0.5-1%, pH regulator: 0.1-3%, deionized water: the balance. The dispersant and the wetting agent are used as additives, and within this range, they can improve the stability of the fluid. Excessive additives will increase the viscosity of the liquid, causing the zero-field viscosity of the magnetorheological polishing liquid to rise sharply, increasing the difficulty of transmission, and even causing the liquid to be unable to circulate. In addition, excessive additives will inhibit the hydration of the optical glass surface and water and significantly reduce the strength of the magnetic chain formation, thereby reducing the shear yield stress, which is not conducive to the process of processing optical components. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the double-layer structure of the alumina-coated carbonyl iron powder of the present invention.

[0018] Figure 2 It is a schematic diagram of the test results of the shear force and shear rate of the magnetorheological fluid in Example 1.

[0019] Figure 3 It is a comparison of the argon ion polishing cross-section scanning electron microscope results of the alumina-coated carbonyl iron powder in Example 1 and the carbonyl iron powder in Comparative Example 2.

[0020] Figure 4 It is a comparison of the hydrophilicity test results of the alumina-coated carbonyl iron powder in Example 1 and the carbonyl iron powder in Comparative Example 2.

[0021] Figure 5 It is a comparison of the energy dispersive spectroscopy test results of the alumina-coated carbonyl iron powder in Example 1 and the carbonyl iron powder in Comparative Example 2.

[0022] Figure 6 It is the preparation process of the magnetorheological fluid.

[0023] Figure 7 It is a comparison of the polishing results of the magnetorheological fluid without polishing (left), Comparative Example 2 (middle), and Example 1 (right) on a fused silica flat plate.

[0024] Figure 8 It is the polishing result of the magnetorheological fluid in Comparative Example 1 on a fused silica flat plate. Detailed Embodiments

[0025] The present invention will be further described in detail below. Unless otherwise specified, the instruments or materials used in the present invention are commercially available.

[0026] Example 1 (Alumina Coating Example) A magnetorheological polishing fluid based on alumina-coated carbonyl iron powder, with a pH of 10. By volume fraction, the components include: alumina-coated carbonyl iron powder: 38%, nano-diamond: 0.005%, diammonium hydrogen citrate: 1%, glycerol: 0.5%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.12% in this example), deionized water: the balance.

[0027] The applicant found that: on the one hand, excessive additives in the magnetorheological polishing fluid will increase the viscosity of the liquid, causing a sharp rise in the zero-field viscosity of the magnetorheological liquid, increasing the difficulty of transmission, unstable flow rate and other problems, and even leading to the inability of the liquid to circulate. On the other hand, it will inhibit the hydration of the optical glass surface with water and significantly reduce the strength of magnetic chain formation, reducing the shear yield stress, making it difficult to ensure the stable progress of the material removal process. At the same time, during the magnetorheological polishing process, the magnetorheological fluid is in full contact with air, absorbs carbon dioxide in the air, and thus oxidizes the carbonyl iron powder, making the magnetorheological fluid extremely unstable.

[0028] The alumina coating is an ALD-deposited alumina coating. The ALD (Atomic Layer Deposition, ALD) technology is used to deposit an atomic-level alumina coating on the surface of carbonyl iron powder, forming a dense oxide film. On the one hand, it can slow down the chemical reaction of air components with carbonyl iron powder; on the other hand, it enhances the surface strength of the particles and reduces the adhesion and agglomeration caused by strong collisions between particles. The ALD technology alternately introduces gas-phase precursors and reactants into the reaction vessel, and a chemical reaction occurs on the substrate material to form a thin film. This technology has the advantages of uniform coating and controllable film thickness, solving the technical problems of the rough surface of composite particles in the existing coating technology, the sharp increase in internal friction between particles leading to an increase in viscosity, and the uncontrollability of coating uniformity and shape. When the coating layer is too thick, the shear yield strength of the magnetorheological liquid is significantly reduced, and the shear stress required for polishing cannot be achieved, and the rough surface will inhibit the realization of an ultra-smooth surface.

[0029] Comparative Example 1 (SiO2 coating example) A magnetorheological polishing fluid based on silica-coated carbonyl iron powder, with a pH of 10. By volume fraction, the components include: SiO2 carbonyl iron powder: 38%, nano-diamond: 0.005%, diammonium hydrogen citrate: 1%, glycerol: 0.5%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.12% in this example), deionized water: the balance.

[0030] Comparative Example 2 (uncoated example) A kind of magnetorheological polishing fluid without coating of carbonyl iron powder, with a pH of 10. By volume fraction, the components include: uncoated carbonyl iron powder: 38%, nano-diamond: 0.005%, diammonium hydrogen citrate: 1%, glycerol: 0.5%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.12% in this example), deionized water: the balance.

[0031] Example 2 (aluminum oxide coating example) A kind of magnetorheological polishing fluid based on aluminum oxide-coated carbonyl iron powder, with a pH of 10. By volume fraction, the components include: aluminum oxide-coated carbonyl iron powder: 42%, nano-diamond: 0.005%, diammonium hydrogen citrate: 1%, glycerol: 0.5%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.12% in this example), deionized water: the balance.

[0032] Comparative Example 3 (aluminum oxide coating example) A kind of magnetorheological polishing fluid based on aluminum oxide-coated carbonyl iron powder, with a pH of 10. By volume fraction, the components include: aluminum oxide-coated carbonyl iron powder: 30%, nano-diamond: 0.005%, diammonium hydrogen citrate: 1.5%, glycerol: 0.5%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.15% in this example), deionized water: the balance.

[0033] Example 3 (aluminum oxide coating example) A kind of magnetorheological polishing fluid based on aluminum oxide-coated carbonyl iron powder, with a pH of 10. By volume fraction, the components include: aluminum oxide-coated carbonyl iron powder: 38%, nano-diamond: 0.005%, diammonium hydrogen citrate: 0.5%, glycerol: 1%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.1% in this example), deionized water: the balance.

[0034] Comparative Example 4 (aluminum oxide coating example) A kind of magnetorheological polishing fluid based on aluminum oxide-coated carbonyl iron powder, with a pH of 10. By volume fraction, the components include: aluminum oxide-coated carbonyl iron powder: 30%, nano-diamond: 0.005%, diammonium hydrogen citrate: 1%, glycerol: 1%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.12% in this example), deionized water: the balance.

[0035] Comparative Example 5 (aluminum oxide coating example) A magnetorheological polishing fluid based on alumina-coated carbonyl iron powder, with a pH of 10. By volume fraction, the components include: alumina-coated carbonyl iron powder: 34%, nano-diamond: 0.005%, diammonium hydrogen citrate: 1.5%, glycerol: 1%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.17% in this example), deionized water: the balance.

[0036] Comparative Example 6 (alumina coating example) A magnetorheological polishing fluid based on alumina-coated carbonyl iron powder, with a pH of 10. By volume fraction, the components include: alumina-coated carbonyl iron powder: 30%, nano-diamond: 0.005%, diammonium hydrogen citrate: 0.5%, glycerol: 1.5%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.1% in this example), deionized water: the balance.

[0037] Comparative Example 7 (alumina coating example) A magnetorheological polishing fluid based on alumina-coated carbonyl iron powder, with a pH of 10. By volume fraction, the components include: alumina-coated carbonyl iron powder: 34%, nano-diamond: 0.005%, diammonium hydrogen citrate: 1%, glycerol: 1.5%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.15% in this example), deionized water: the balance.

[0038] Comparative Example 8 (alumina coating example) A magnetorheological polishing fluid based on alumina-coated carbonyl iron powder, with a pH of 10. By volume fraction, the components include: alumina-coated carbonyl iron powder: 42%, nano-diamond: 0.005%, diammonium hydrogen citrate: 1.5%, glycerol: 1.5%, sodium hydroxide: 0.1% - 3% (specifically based on the pH of the solution, 0.17% in this example), deionized water: the balance.

[0039] Table 1 Volume percentages of glycerol, diammonium hydrogen citrate, and alumina-coated carbonyl iron powder in each example

[0040] Table 2 Experimental results of key indicators for each example and comparative example

[0041] As can be seen from Table 2, for magnetorheological processing, if the viscosity value of the magnetorheological fluid is around 0.5 - 1.5 Pa·s and the shear yield strength value is between 5000 - 15000 Pa, the processing can be better completed. However, the Zeta potential of Comparative Examples 5 - 8 is relatively low, and the agglomeration and sedimentation performance of the magnetorheological fluid is poor. The viscosity value of Comparative Example 4 is relatively low, and the shear yield strength of Comparative Example 3 is poor, resulting in these comparative examples not being able to complete magnetorheological processing well.

[0042] Dispersion: The better the dispersion, the less the agglomeration phenomenon of the components. In the present invention, the influence of the alumina atomic layer coating on the dispersion of the liquid system is explained from the classical colloid stability theory, the DLVO theory. When the surface of the carbonyl iron powder particles is coated with alumina, the surface chemical properties of the particles are changed. The alumina surface has more surface hydroxyl groups (–OH), which helps to generate ionizable surface groups in an alkaline aqueous solution as shown in Equation (1), thus enhancing the formation of the electrical double layer (EDL) structure, as Figure 1 shown:

[0043] The electrical double layer structure can be described by the Debye-Hückel approximation and the Gouy-Chapman model. The surface of the particles will carry a certain net charge in an aqueous solution, and a corresponding electrical double layer structure will be formed in the solution. The charge forms an inner layer (Stern layer) and a diffuse layer. This structure can be represented by the Debye length ( ) to represent the spatial scale of the charge distribution in the diffuse layer.

[0044]

[0045]

[0046] In Equations (2) and (3): The potential at a distance from the particle surface; is the potential of the particle surface; is the reciprocal of the electrical double layer thickness, describing the potential decay rate; is the electronic charge amount; is the Avogadro constant; is the ionic strength in the solution; is the vacuum permittivity; is the relative permittivity of the medium; is the Boltzmann constant; is the absolute temperature. The alumina coating layer increases the surface charge of the particles due to the surface hydroxyl groups and surface chemical properties, improves the surface potential, increases the electrostatic repulsion force between the particles when approaching each other, increases the thickness of the electrical double layer, that is, a thicker ion layer is formed outside the atomic layer, reduces agglomeration, and improves dispersion. Moreover, the electrical double layer structure is enhanced, so that even after the system is subjected to shear, stirring or mild accelerated sedimentation, the particles can still be evenly redistributed in the liquid phase through a mild redispersion operation (such as the stirring action of the magnetorheological polishing cycle system). Therefore, the magnetorheological polishing fluid of the present invention has good "secondary dispersibility".

[0047] Anti-settling property: Due to the existence of the double electric layer structure, the particles of alumina-coated carbonyl iron powder are relatively dispersed, which inhibits the agglomeration effect and is not easy to form large and dense clusters, reducing the sedimentation rate. The particles settle relatively slowly only under the action of gravity, enabling the magnetorheological polishing fluid to maintain a relatively uniform suspension state after long-term static settlement. The sedimentation rate can be expressed by the Stokes formula as shown in Equation (4):

[0048] In Equation (4): is the particle movement speed (m·s -1 ), is the density of a single particle,[[]] is the density of the carrier liquid,[[]] is the kinematic viscosity of the carrier liquid,[[]] is the acceleration due to gravity,[[]] is the diameter of a single particle,[[]] is the volume content percentage of the particles. Due to the presence of alumina coating on the surface of carbonyl iron powder, the overall density of the composite particles is reduced, the density difference from the carrier liquid is narrowed, and appropriately reducing the diameter of the carbonyl iron powder used effectively reduces the sedimentation rate of the particles.[[]]

[0049] Shear yield strength: During the operation of the magnetorheological fluid, due to the existence of the gradient magnetic field, a row of chain-like structures is formed along the direction of the magnetic induction line. The shear yield strength in the magnetorheological polishing process is the resistance of these chain-like structures to the shear force. The shear yield strength is analyzed by analyzing the single-chain structure. Equation (5) is a widely used formula model for describing the shear yield strength:[[]]

[0050] In the formula is the volume fraction of magnetic particles in the magnetorheological fluid;[[]] is the radius of the magnetic particles;[[]] is the magnetic susceptibility of the magnetic particles;[[]] is the magnetic flux density;[[]] is the permeability of free space;[[]] is the distance between two particles;[[]] is the shear rate parameter.[[]]

[0051] When the mass fraction is the same, for the coated CIP, due to the existence of atomic layers, the radius and the average gap length between particles slightly increase, resulting in a slight decrease in the shear yield stress. A large number of experiments and experiences show that although a larger shear yield strength can effectively improve the polishing efficiency, a smaller shear yield strength can obtain a higher surface roughness. As long as the shear force provided by the magnetorheological polishing fluid is sufficient to resist the resistance generated by material removal, material removal can occur.[[]]

[0052] Figure 2 For the rheological property test results in Example 1, the four curves represent the relationship between the shear rate and the shear force of the magnetorheological fluid in Example 1 under different magnetic field strengths. When the shear force is greater than the material yield stress, material removal can occur, indicating that the magnetorheological fluid in this example can provide sufficient shear yield stress to ensure a certain material removal efficiency.

[0053] Zero-field viscosity: It should be noted that the particles in the magnetorheological polishing fluid usually need to reach a certain volume fraction to obtain sufficient dynamic yield strength and sedimentation stability. This often requires sacrificing a certain degree of zero-field viscosity to meet the shear force requirements while maximizing the dynamic yield strength and sedimentation stability. If only reducing the diameter of the carbonyl iron powder in the magnetorheological polishing fluid or adding additives to reduce the sedimentation rate, the viscosity of the magnetorheological liquid will increase significantly. However, the carbonyl iron powder coated with alumina has a strong double-layer structure, strong surface chemical stability and a smooth surface morphology, enabling the particles to be suspended relatively independently and uniformly in the base liquid, reducing the internal friction, and to a certain extent reducing the increasing trend of viscosity.

[0054] In the present invention, an argon ion polishing cross-section scanning electron microscope is used to observe the coating effect of the carbonyl iron powder particles. The scanning electron microscope images of the uncoated carbonyl iron powder particles in Comparative Example 2 are as Figure 3 (a), Figure 3 as shown in (b), where Figure 3 (a) has a magnification of 15,000 times, Figure 3 (b) has a magnification of 40,000 times. The scanning electron microscope images of the coated carbonyl iron powder particles in Example 1 are as Figure 3 (c), Figure 3 as shown in (d), Figure 3 (c) has a magnification of 1,000 times, Figure 3 (d) has a magnification of 70,000 times. It can be seen from Figure 3 that for the cross-section, morphology and distribution of Example 1 and Comparative Example 2, the alumina coating layer on the surface of the alumina-coated particles shows good uniformity, presenting a good spherical structure. The good spherical surface structure can reduce the uncontrollable damage to the polished surface during the processing. Compared with the uncoated example, the double-layer structure on the surface of the alumina-coated carbonyl iron powder can indeed improve the dispersibility of the particle components in the magnetorheological polishing fluid. The particle components have high dispersion characteristics, reducing the adhesion and aggregation phenomena between the particles.

[0055] The hydrophilicity tests were respectively carried out on the carbonyl iron powder particles of Example 1 and Comparative Example 2. The test solvent was deionized water. The contact angles of the two groups of particles at different times were measured respectively. The contact angle of the liquid on the surface of the solid material is an important parameter to measure the wetting performance of the liquid on the material surface. The test solvent was deionized water. The contact angles of the two groups of particles at different times were measured respectively. The smaller the contact angle, the stronger the hydrophilicity of the material, which can improve the anti-settling stability and dispersion to a certain extent. The results are as Figure 4 shown Figure 4 (a), Figure 4 (b) are for Example 1, Figure 4 (c), Figure 4 (d) are for Comparative Example 2, indicating that the hydrophilicity of the carbonyl iron powder particles coated with alumina has been improved to a certain extent and is higher than that of the carbonyl iron powder without alumina coating. Therefore, when the particles with an atomic layer of alumina coating are dispersed in the liquid at the same mass fraction, the liquid will have a higher viscosity, which helps to improve the dispersion and sedimentation stability of the overall solution.

[0056] Element distribution maps can be obtained using energy-dispersive spectroscopy (EDS) images to analyze the content of different elements in the sample. Figure 5 The energy-dispersive spectroscopy diagrams of the samples of Example 1 and Comparative Example 2 are shown as follows. Figure 5 (a) is for Comparative Example 2, Figure 5 (b) is for Example 1. It can be seen from the figure the elemental composition of the coating layer in the sample of Example 1.

[0057] The difference in the magnetic properties between the carbonyl iron powder of Comparative Example 2 and Example 1 is small, meeting the requirements of the magnetorheological polishing fluid for magnetic properties, as shown in Table 3.

[0058] Table 3 Comparison table of magnetic properties of carbonyl iron powder between Comparative Example 2 and Example 1

[0059] When the content of the magnetic-sensitive particles in the magnetorheological polishing fluid is too low (such as <25%), the shear force provided by the cluster structure in the magnetic field is not sufficient to resist the resistance generated by material removal, and the material removal efficiency drops sharply, resulting in low efficiency and not meeting the actual processing requirements; when the content is too high (such as >65%), the distance between the particles will be very close and they will contact each other, forming agglomeration or network structures between the particles. This dense structure formed at a high concentration makes the suspension exhibit solid-like behavior, restricting the flow of the carrier liquid, and the viscosity increases rapidly, and it may even not flow normally in the circulation system of the machine tool.

[0060] Take three portions of the magnetorheological polishing fluids prepared in Example 1, Comparative Example 1, and Comparative Example 2 respectively, with each portion being 5 ml for making small samples. Add 200 ml of deionized water for dilution, and then use an electromagnetic stirrer to fully stir the diluted liquid. Then adjust the pH value back to around 10, and measure the average absolute value of the Zeta potential for the three small samples respectively. The test results are shown in Table 4 below.

[0061] Table 4 Test Results of Zeta Potential Meter

[0062] As Figure 6 shown, the magnetorheological fluid of this example includes the following preparation steps: S1. Mix a dispersant (diammonium hydrogen citrate), a wetting agent (glycerol), other additives (sodium hydroxide), and deionized water; S2. Continuously stir magnetically at a constant speed of 200 - 500 r / min for 1 - 5 min; S3. Add iron powder and nano - diamond; S4. Continuously stir by rolling at a constant speed of 30 - 100 r / min for 3 - 5 h.

[0063] Use a magnetorheological polishing machine to conduct a uniform scanning experiment on a fused silica flat element. The processing parameters are shown in Table 5: Table 5 Processing Parameters

[0064] The surface roughness is measured using a white - light interferometer Zygo newview 9000. Select a 20 - magnification lens, and the analysis area is 0.43×0.43 to obtain the surface roughness data, as Figure 7 shown. Figure 7 (a) and (b) are respectively one - dimensional profile schematic diagrams of the surface roughness and surface characteristics of the element before polishing; Figure 7 (c) and (d) are respectively a schematic diagram of the roughness of the element processed with the magnetorheological polishing fluid of Comparative Example 2 and a one - dimensional profile schematic diagram of the surface characteristics; Figure 7 (e) and (f) are respectively a schematic diagram of the roughness of the element processed with the magnetorheological polishing fluid of Example 1 and a one - dimensional profile schematic diagram of the surface characteristics.

[0065] Figure 8 (a), Figure 8 (b) are respectively a schematic diagram of the roughness of the element processed with the magnetorheological polishing fluid of Comparative Example 1 and a one - dimensional profile schematic diagram of the surface characteristics. From Figure 8 and Figure 7It can be seen that the surface quality of the component polished by the magnetorheological polishing fluid in Example 1 is better than that polished by the magnetorheological polishing fluids in Comparative Example 2 and Comparative Example 1. The Ra value reaches 0.204 nm, meeting the standard of an ultra-smooth surface (<0.3 nm), improving the polishing performance of the magnetorheological polishing fluid to a certain extent and enhancing the surface quality of the component.

[0066] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the above-disclosed technical content, or modify it into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A magnetorheological fluid based on alumina-coated carbonyl iron powder, characterized in that: The raw materials include the following components by volume fraction: Aluminum oxide-coated carbonyl iron powder: 35%-45%, Nanodiamond powder: 0.001%-0.5%, Dispersant: 0.001%-1.5%, Wetting agent: 0.5%-1%, pH regulator: 0.1%-3%, Deionized water: the balance.

2. The magnetorheological fluid based on alumina-coated carbonyl iron powder according to claim 1, characterized in that: The dispersant is diammonium hydrogen citrate, the wetting agent is glycerol, and the pH regulator is sodium hydroxide.

3. The magnetorheological fluid based on alumina-coated carbonyl iron powder according to claim 2, wherein: The volume percentage of the aluminum oxide-coated carbonyl iron powder is 38%-42%.

4. The magnetorheological fluid based on alumina-coated carbonyl iron powder according to claim 2, characterized in that: The volume percentage of the diammonium hydrogen citrate is 1%-1.5%.

5. The magnetorheological fluid based on alumina-coated carbonyl iron powder according to claim 2, characterized in that: The volume percentage of the diammonium hydrogen citrate is 0.5%-1%.

6. The magnetorheological fluid based on alumina-coated carbonyl iron powder according to any one of claims 1 to 5, characterized in that: The aluminum oxide-coated carbonyl iron powder includes carbonyl iron powder particles and an aluminum oxide coating layer coated on the surface of the carbonyl iron powder particles. The average particle size of the carbonyl iron powder particles is 1-5 μm, and the thickness of the aluminum oxide coating layer is 15-20 nm.

7. The magnetorheological fluid based on alumina-coated carbonyl iron powder according to claim 6, wherein: The aluminum oxide coating layer is an ALD-deposited aluminum oxide coating layer.

8. The magnetorheological fluid based on alumina-coated carbonyl iron powder according to any one of claims 1 to 5, characterized in that: The average particle size of the nanodiamond powder is 70-120 nm.

9. The magnetorheological fluid based on alumina-coated carbonyl iron powder according to any one of claims 1 to 5, characterized in that: The pH value of the magnetorheological fluid is 9-12.

10. The magnetorheological fluid based on alumina-coated carbonyl iron powder according to any one of claims 1 to 5, characterized in that: The volume percentage of the nanodiamond powder is 0.001%-0.005%.

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