Magnetorheological polishing fluid based on alumina-coated carbonyl iron powder

Abstract

This invention discloses a magnetorheological polishing slurry based on alumina-coated carbonyl iron powder. The raw materials, by volume fraction, include the following components: 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 adjuster: 0.1%-3%, and deionized water: balance. The dispersant and wetting agent, as additives, can improve the stability of the fluid within this range. Excessive additives will increase the viscosity of the liquid, causing a sharp increase in the zero-field viscosity of the magnetorheological polishing slurry, making transport more difficult and even preventing liquid circulation. Furthermore, excessive additives will inhibit the hydration of the optical glass surface with water and significantly reduce the strength of magnetic flux formation, thus reducing the shear yield stress, which is detrimental to the processing of optical components.

Description

Technical Field

[0001] This invention relates to the field of magnetorheological polishing materials, and in particular to a magnetorheological polishing slurry based on alumina-coated carbonyl iron powder. Background Technology

[0002] With the continuous development of fields such as space optics, inertial nuclear fusion, photolithography, and lasers, the requirements for the surface quality and precision of optical components are becoming increasingly stringent. Magnetorheological polishing technology, as a mature and effective processing method, offers advantages such as non-wearing polishing tools, precise computer control, minimal subsurface damage, and high processing accuracy. It can further improve the quality of processed products, thus possessing broad development and application prospects.

[0003] Magnetorheological polishing slurry, as the polishing tool carrier in magnetorheological polishing technology, plays a crucial role in the processing quality and efficiency of components. Good surface roughness can bring advantages such as reduced energy loss and improved image contrast. However, because the density of ferromagnetic particles in magnetorheological polishing slurries is much greater than that of non-magnetic liquids, the sedimentation of magnetic particles is inevitable. Furthermore, during use, magnetorheological polishing slurries can experience various problems such as water evaporation, oxidation and deterioration, and particle agglomeration, reducing their rheological properties. Agglomerated large particles lead to uneven iron powder particle size in the liquid, which not only hinders the normal operation of the circulation system but also reduces the surface quality of the processed components, affecting processing costs and efficiency. Therefore, maintaining a good dispersion of particles in the magnetorheological polishing slurry is crucial.

[0004] Sedimentation stability, zero-field viscosity, and shear yield stress are three important performance indicators for preparing high-performance magnetorheological polishing fluids. A high-performance magnetorheological polishing fluid should possess characteristics such as low zero-field viscosity, strong anti-sedimentation properties, good secondary redispersibility, high shear yield stress, and environmentally friendly composition. The main challenge in obtaining high-performance magnetorheological polishing fluids lies in how to better improve their anti-sedimentation and dispersibility while meeting the target requirements for viscosity and shear stress. Therefore, there is an urgent need for a magnetorheological polishing fluid with good anti-sedimentation and dispersibility and superior performance. Summary of the Invention

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

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder comprises 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 adjuster: 0.1%-3%, and deionized water: balance.

[0008] As a further improvement to the above technical solution:

[0009] The dispersant is diammonium citrate, the wetting agent is glycerol, and the pH adjuster is sodium hydroxide.

[0010] The volume percentage of the alumina-coated carbonyl iron powder is 38%-42%.

[0011] The volume percentage of the diammonium citrate is 1%-1.5%.

[0012] The volume percentage of the diammonium citrate is 0.5%-1%.

[0013] The alumina-coated carbonyl iron powder includes carbonyl iron powder particles and an alumina coating layer 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.

[0014] The alumina coating is an ALD-deposited alumina coating.

[0015] The average particle size of the nanodiamond powder is 70-120 nm. In this invention, if the average particle size is larger than this range, although the material removal efficiency is high, it is easy to leave deeper and larger scratches on the workpiece surface, resulting in increased surface roughness. Furthermore, the movement under the influence of a magnetic field is relatively less flexible, easily leading to localized aggregation or uneven distribution. If the average particle size is smaller than this range, the particles are too small, and the material removal efficiency will be significantly reduced, even making it impossible to complete the processing task. Moreover, the van der Waals forces between excessively small abrasive particles are enhanced, easily causing agglomeration. Agglomerated large particles lead to uneven polishing results.

[0016] The pH value of the magnetorheological polishing fluid is 9-12. Within this range, on the one hand, it provides a favorable environment for the additives used in this invention to exert their activity, improving liquid properties such as dispersibility; on the other hand, this pH value helps to slow down the oxidation process and extend service life. However, excessively alkaline or acidic environments may corrode the workpiece. Finally, it helps to maintain the stability of the liquid's magnetorheological effect, such as yield stress and viscosity.

[0017] The volume percentage of the nanodiamond powder is 0.001%-0.005%.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The raw materials of this invention comprise 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 adjuster: 0.1-3%, and deionized water: balance. The dispersant and wetting agent, as additives, can improve the stability of the fluid within this range. Excessive additives will increase the viscosity of the liquid, causing a sharp increase in the zero-field viscosity of the magnetorheological polishing liquid, making transport more difficult, and even preventing liquid circulation. Furthermore, excessive additives will inhibit the hydration of the optical glass surface with water and significantly reduce the strength of magnetic flux formation, thus reducing the shear yield stress, which is detrimental to the processing of optical components. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the double-layer structure of alumina-coated carbonyl iron powder according to the present invention.

[0021] Figure 2 This is a schematic diagram showing the detection results of shear force and shear rate of the magnetorheological polishing fluid in Example 1.

[0022] Figure 3 The results of argon ion polishing cross-section scanning electron microscopy of carbonyl iron powder in Example 1 (alumina-coated carbonyl iron powder) and Comparative Example 2 (carbonyl iron powder) are compared. Figure 3 (a) Figure 3 (b) is a scanning electron microscope image of the uncoated carbonyl iron powder particles in Comparative Example 2. Figure 3 (a) The magnification is 15,000 times. Figure 3 (b) Magnification is 40,000 times. Figure 3 (c) Figure 3 (d) is a scanning electron microscope image of carbonyl iron powder particles coated in Example 1. Figure 3 (c) Magnification is 1000x. Figure 3 (d) The magnification is 70,000 times.

[0023] Figure 4 This is a comparison of the hydrophilicity test results of alumina-coated carbonyl iron powder in Example 1 and carbonyl iron powder in Comparative Example 2. Figure 4 (a) Figure 4 (b) shows the hydrophilicity test results of Example 1. Figure 4 (c) Figure 4 (d) shows the hydrophilicity test results of Comparative Example 2.

[0024] Figure 5 This is a comparison of the energy dispersive spectroscopy test results of alumina-coated carbonyl iron powder in Example 1 and carbonyl iron powder in Comparative Example 2. Figure 5(a) shows the energy dispersive spectroscopy test results of Comparative Example 2. Figure 5 (b) shows the energy dispersive spectroscopy test results of Example 1.

[0025] Figure 6 This describes the preparation process of magnetorheological polishing slurry.

[0026] Figure 7 The polishing results of the unpolished (left), Comparative Example 2 (middle), and Magnetorheological polishing slurry of Example 1 (right) on a fused silica plate are compared. Figure 7 (a) and (b) are schematic diagrams of one-dimensional cross-sections of the surface roughness and surface features of the component before polishing; Figure 7 (c) and (d) are schematic diagrams of the roughness of the component after processing with magnetorheological polishing fluid in Comparative Example 2 and one-dimensional cross-sectional schematic diagrams of the surface features, respectively. Figure 7 (e) and (f) are schematic diagrams of the roughness of the component after processing with magnetorheological polishing fluid in Example 1 and one-dimensional cross-sectional schematic diagrams of the surface features.

[0027] Figure 8 The polishing results of the magnetorheological polishing slurry on the fused silica plate are shown in Comparative Example 1. Figure 8 (a) is a schematic diagram of the surface roughness of the component after processing with magnetorheological polishing fluid in Comparative Example 1. Figure 8 (b) is a one-dimensional cross-sectional schematic diagram of the surface features of the component after processing with magnetorheological polishing fluid in Comparative Example 1. Detailed Implementation

[0028] 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.

[0029] Example 1 (Alumina Coating Example)

[0030] A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder, with a pH of 10, comprises the following components by volume fraction: alumina-coated carbonyl iron powder: 38%, nano diamond: 0.005%, diammonium citrate: 1%, glycerol: 0.5%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.12% in this example), and deionized water: balance.

[0031] The applicant discovered that excessive additives in the magnetorheological polishing slurry can, on the one hand, increase the viscosity of the liquid, causing a sharp rise in the zero-field viscosity, which increases transport difficulty, leads to unstable flow rates, and may even prevent liquid circulation. On the other hand, it inhibits the hydration of the optical glass surface with water and significantly reduces the strength of magnetic flux formation, decreasing shear yield stress and making it difficult to ensure the stable progress of the material removal process. Simultaneously, during the magnetorheological polishing process, the slurry comes into full contact with air, absorbing carbon dioxide and oxidizing carbonyl iron powder, making the slurry extremely unstable.

[0032] The alumina coating is deposited using ALD (Atomic Layer Deposition) technology. An atomic-level alumina coating is deposited on the surface of carbonyl iron powder, forming a dense oxide film. This process slows down the chemical reaction of air components with the carbonyl iron powder and enhances the surface strength of the particles, reducing adhesion and agglomeration caused by strong collisions. ALD technology involves alternately introducing gaseous precursors and reactants into a reaction vessel, where a chemical reaction occurs on the substrate material to form a thin film. This technology offers advantages such as uniform coating and controllable film thickness. It solves the problems of existing coating technologies, such as rough particle surfaces, rapidly increasing internal friction between particles leading to increased viscosity, and uncontrollable coating uniformity and shape. Furthermore, when the coating layer is too thick, the shear yield strength of the magnetorheological polishing fluid is significantly reduced, making it impossible to achieve the shear stress required for polishing. Additionally, the rough surface inhibits the achievement of ultra-smooth surfaces.

[0033] Comparative Example 1 (SiO2 Coating Example)

[0034] A magnetorheological polishing slurry based on silica-coated carbonyl iron powder, with a pH of 10, comprises the following components by volume fraction: SiO2 carbonyl iron powder: 38%, nano diamond: 0.005%, diammonium hydrogen citrate: 1%, glycerol: 0.5%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.12% in this example), and deionized water: balance.

[0035] Comparative Example 2 (Uncovered Example)

[0036] A magnetorheological polishing slurry for uncoated carbonyl iron powder, with a pH of 10, comprises, by volume fraction: uncoated carbonyl iron powder: 38%, nano diamond: 0.005%, diammonium citrate: 1%, glycerol: 0.5%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.12% in this example), and deionized water: balance.

[0037] Example 2 (Alumina Coating Example)

[0038] A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder, with a pH of 10, comprises the following components by volume fraction: alumina-coated carbonyl iron powder: 42%, nano diamond: 0.005%, diammonium citrate: 1%, glycerol: 0.5%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.12% in this example), and deionized water: balance.

[0039] Comparative Example 3 (Alumina Coating Example)

[0040] A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder, with a pH of 10, comprises, by volume fraction: alumina-coated carbonyl iron powder: 30%, nano diamond: 0.005%, diammonium hydrogen citrate: 1.5%, glycerol: 0.5%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.15% in this example), and deionized water: balance.

[0041] Example 3 (Alumina Coating Example)

[0042] A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder, with a pH of 10, comprises the following components by volume fraction: alumina-coated carbonyl iron powder: 38%, nano diamond: 0.005%, diammonium citrate: 0.5%, glycerol: 1%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.1% in this example), and deionized water: balance.

[0043] Comparative Example 4 (Alumina Coating Example)

[0044] A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder, with a pH of 10, comprises the following components by volume fraction: alumina-coated carbonyl iron powder: 30%, nano diamond: 0.005%, diammonium citrate: 1%, glycerol: 1%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.12% in this example), and deionized water: balance.

[0045] Comparative Example 5 (Alumina Coating Example)

[0046] A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder, with a pH of 10, comprises the following components by volume fraction: alumina-coated carbonyl iron powder: 34%, nano diamond: 0.005%, diammonium citrate: 1.5%, glycerol: 1%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.17% in this example), and deionized water: balance.

[0047] Comparative Example 6 (Alumina Coating Example)

[0048] A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder, with a pH of 10, comprises the following components by volume fraction: alumina-coated carbonyl iron powder: 30%, nano diamond: 0.005%, diammonium citrate: 0.5%, glycerol: 1.5%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.1% in this example), and deionized water: balance.

[0049] Comparative Example 7 (Alumina Coating Example)

[0050] A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder, with a pH of 10, comprises the following components by volume fraction: alumina-coated carbonyl iron powder: 34%, nano diamond: 0.005%, diammonium citrate: 1%, glycerol: 1.5%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.15% in this example), and deionized water: balance.

[0051] Comparative Example 8 (Alumina Coating Example)

[0052] A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder, with a pH of 10, comprises the following components by volume fraction: alumina-coated carbonyl iron powder: 42%, nano diamond: 0.005%, diammonium citrate: 1.5%, glycerol: 1.5%, sodium hydroxide: 0.1%-3% (depending on the pH of the solution, 0.17% in this example), and deionized water: balance.

[0053] Table 1 shows the volume percentages of glycerol, diammonium hydrogen citrate, and alumina-coated carbonyl iron powder in each example.

[0054]

[0055] Table 2. Experimental results of key indicators for each embodiment and comparative example.

[0056]

[0057] As shown in Table 2, for magnetorheological processing, if the viscosity of the magnetorheological polishing slurry is around 0.5~1.5 Pa·s and the shear yield strength is between 5000~15000 Pa, the processing can be completed well. However, the Zeta potential of Comparative Examples 5-8 is low, and the agglomeration and sedimentation performance of the magnetorheological polishing slurry is poor. Furthermore, the viscosity of Comparative Example 4 is low, and the shear yield strength of Comparative Example 3 is poor, which means that these comparative examples cannot complete magnetorheological processing well.

[0058] Dispersibility: Better dispersibility indicates less aggregation of components. This invention explains the effect of alumina atomic layer coating on the dispersibility of liquid systems based on the classic DLVO theory of colloidal stability. When carbonyl iron powder particles are coated with alumina, the surface chemical properties of the particles are changed. The alumina surface has more surface hydroxyl groups (–OH), which help to generate ionizable surface groups in alkaline aqueous solutions, as shown in formula (1), thereby enhancing the formation of the electrical double layer (EDL) structure, as shown in formula (1). Figure 1 As shown:

[0059]

[0060] The electric double layer structure can be described using the Debye-Hückel approximation and the Gouy-Chapman model. The particle surface carries a net charge in aqueous solution, resulting in a corresponding electric double layer structure. The charge forms the stern layer and the diffuse layer. This structure can be described by the Debye length (…). ) represents the spatial scale of charge distribution in the diffusion layer.

[0061]

[0062]

[0063] In equations (2) and (3): Distance from particle surface Potential at the location; The potential of the particle surface; The value is the reciprocal of the thickness of the electric double layer, describing the rate of potential decay. It represents the electron charge. It is Avogadro's constant; The ionic strength in the solution; It is the vacuum permittivity; The relative permittivity of the medium; Boltzmann's constant; The absolute temperature is 100°C. The alumina coating increases the surface charge of the particles due to the surface hydroxyl groups and surface chemical properties, thereby increasing the surface potential. This leads to greater electrostatic repulsion between particles when they approach each other, and a thicker double layer, forming a thicker ionic layer outside the atomic layer. This reduces agglomeration and improves dispersibility. Furthermore, the enhanced double layer structure allows the particles to be redistributed uniformly in the liquid phase even after shearing, stirring, or mild accelerated sedimentation, through mild redispersion operations (such as the stirring action of a magnetorheological polishing circulation system). Therefore, the magnetorheological polishing fluid of this invention has excellent "secondary dispersibility".

[0064] Anti-settling property: Due to the presence of the double electric layer structure, the carbonyl iron powder coated with alumina has a relatively dispersed particle distribution, which inhibits agglomeration and makes it difficult to form large and dense clusters, thus reducing the settling velocity. The particles settle relatively slowly under the action of gravity alone, which allows the magnetorheological polishing slurry to maintain a relatively uniform suspension state even after a long period of standing. The settling velocity can be expressed by the Stokes formula as shown in equation (4):

[0065]

[0066] In equation (4): The velocity of the particles (m·s) -1 ), The density of a single particle. The density of the carrier fluid, The kinematic viscosity of the carrier fluid. It is the acceleration due to gravity. The diameter of a single particle. This represents the volume percentage of the particles. Due to the alumina coating on the surface of the carbonyl iron powder, the overall density of the composite particles is reduced, the density difference between the composite particles and the carrier liquid is narrowed, and the diameter of the carbonyl iron powder used is appropriately reduced, all of which effectively reduce the settling velocity of the particles.

[0067] Shear yield strength: During the operation of magnetorheological polishing fluid, due to the presence of a gradient magnetic field, parallel chain-like structures are formed along the magnetic field lines. The shear yield strength of the magnetorheological polishing process is the resistance of these chain-like structures to shear force. The shear yield strength is analyzed by analyzing the single-chain structure. Formula (5) is a widely used formula model describing the shear yield strength:

[0068]

[0069] In the formula The volume fraction of magnetic particles in the magnetorheological polishing slurry; The radius of the magnetic particle; denoted as the magnetic susceptibility of the magnetic particle; Magnetic flux density; The vacuum permeability; It is the distance between two particles; This is the shear rate parameter.

[0070] When the mass fraction is the same, the radius of the atomic layer and the average interparticle length of the coated CIP vary. A slight increase in shear yield strength results in a slight decrease in shear yield stress. Extensive experiments and experience show that while a higher shear yield strength can effectively improve polishing efficiency, a lower shear yield strength can achieve a higher surface roughness. Material removal can be achieved as long as the shear force provided by the magnetorheological polishing slurry is sufficient to overcome the resistance generated by material removal.

[0071] Figure 2 The four curves represent the relationship between the shear rate and shear force of the magnetorheological polishing 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 polishing fluid in this example can provide sufficient shear yield stress to ensure a certain material removal efficiency.

[0072] Zero-field viscosity: It is worth noting that particles in magnetorheological polishing slurries typically 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 shear force requirements while maximizing dynamic yield strength and sedimentation stability. Simply reducing the diameter of carbonyl iron powder in the magnetorheological polishing slurry or adding additives to reduce sedimentation velocity would lead to a significant increase in the viscosity of the slurry. However, alumina-coated carbonyl iron powder possesses a strong double-layer structure, strong surface chemical stability, and a smooth, rounded surface morphology, allowing the particles to be suspended relatively independently and uniformly in the base liquid, reducing internal friction and mitigating the tendency for viscosity to increase to some extent.

[0073] This invention uses argon ion polishing cross-section scanning electron microscopy to observe the coating effect of carbonyl iron powder particles. Comparative Example 2 shows the scanning electron microscopy image of uncoated carbonyl iron powder particles as follows. Figure 3 (a) Figure 3 As shown in (b), where Figure 3 (a) The magnification is 15,000 times. Figure 3 (b) Scanning electron microscope image of carbonyl iron powder particles from Example 1, magnified at 40,000x. Figure 3 (c) Figure 3 (d) Figure 3 (c) Magnification is 1000x. Figure 3 (d) The magnification is 70,000 times, from Figure 3 As can be seen from the cross-sections, morphology, and distribution of Example 1 and Comparative Example 2, the alumina coating layer on the surface of the alumina-coated particles exhibits good uniformity and a good spherical structure. This good spherical surface structure can reduce uncontrollable damage to the polished surface during processing. Compared to the uncoated example, the double electric layer structure on the surface of the alumina-coated carbonyl iron powder does indeed improve the dispersibility of the particle components in the magnetorheological polishing slurry. The particle components have high dispersion characteristics, reducing particle adhesion and aggregation.

[0074] Hydrophilicity tests were conducted on carbonyl iron powder particles from Example 1 and Comparative Example 2, using deionized water as the test solvent. The contact angles of the two groups of particles were measured at different times. The contact angle of a liquid on a solid material surface is an important parameter for evaluating the wettability of the liquid on the material surface. A smaller contact angle indicates stronger hydrophilicity of the material, which can improve anti-settling stability and dispersion to a certain extent. The results are as follows... Figure 4 As shown, Figure 4 (a) Figure 4 (b) is Example 1. Figure 4 (c) Figure 4 (d) is Comparative Example 2, showing that the hydrophilicity of carbonyl iron powder particles coated with alumina is improved to a certain extent and is higher than that of carbonyl iron powder without alumina coating. Therefore, when particles with an alumina atomic layer on their surface are dispersed in a liquid at the same mass fraction, the liquid will have a higher viscosity, which helps to improve the overall solution dispersibility and sedimentation stability.

[0075] Energy-dispersive X-ray spectroscopy (EDS) images can be used to obtain elemental distribution maps and analyze the content of different elements in a sample. Figure 5 The following are the energy dispersive spectra of the samples from Example 1 and Comparative Example 2. Figure 5 (a) is Comparative Example 2. Figure 5 (b) is Example 1. The elemental composition of the coating layer of the sample in Example 1 can be seen from the figure.

[0076] The magnetic properties of the carbonyl iron powder in Comparative Example 2 and Example 1 are similar, meeting the requirements of magnetorheological polishing slurry for magnetic properties, as shown in Table 3.

[0077] Table 3 Comparison of magnetic properties of carbonyl iron powder between Comparative Example 2 and Example 1

[0078]

[0079] When the content of magnetic sensitive particles in the magnetorheological polishing slurry is too low (e.g., <25%), the shear force provided by the cluster structure in the magnetic field is insufficient to resist the resistance generated by material removal, resulting in a sharp drop in material removal efficiency and low efficiency, which does not meet the actual processing requirements. When the content is too high (e.g., >65%), the distance between the particles will be very close, and they will come into contact with each other, forming agglomerates or network structures. This dense structure formed by high concentration makes the suspension exhibit solid-like behavior, restricting the flow of the carrier liquid, and the viscosity will increase rapidly, even making it impossible to flow normally in the machine tool's circulation system.

[0080] Take three portions of each of the magnetorheological polishing fluids prepared in Example 1, Comparative Example 1, and Comparative Example 2, and make a small sample of 5 ml each. Add 200 ml of deionized water to dilute the sample, and then use an electromagnetic stirrer to stir the diluted liquid thoroughly. Adjust the pH value back to about 10. Test the mean absolute value of the zeta potential of the three small samples. The test results are shown in Table 4 below.

[0081] Table 4. Zeta Potentiometer Test Results

[0082]

[0083] like Figure 6 As shown, the magnetorheological polishing slurry in this embodiment includes the following preparation steps:

[0084] S1. Mix the dispersant (diammonium hydrogen citrate), wetting agent (glycerol), other additives (sodium hydroxide), and deionized water;

[0085] S2. Continuous magnetic stirring at a constant speed of 200-500 r / min for 1-5 min;

[0086] S3, Add iron powder and nano diamond;

[0087] S4. Constant speed 30-100r / min, stirring time 3-5h, continuous rolling.

[0088] A uniform scanning experiment was conducted on the fused silica flat plate element using a magnetorheological polishing machine. The processing parameters are shown in Table 5.

[0089] Table 5 Processing Parameters

[0090]

[0091] Surface roughness was measured using a Zygo Newview 9000 white light interferometer with a 20x lens and an analysis area of ​​0.43 × 0.43. The surface roughness data were obtained as follows: Figure 7 As shown. Figure 7 (a) and (b) are schematic diagrams of one-dimensional cross-sections of the surface roughness and surface features of the component before polishing; Figure 7 (c) and (d) are schematic diagrams of the roughness of the component after processing with magnetorheological polishing fluid in Comparative Example 2 and one-dimensional cross-sectional schematic diagrams of the surface features, respectively. Figure 7 (e) and (f) are schematic diagrams of the roughness of the component after processing with magnetorheological polishing fluid in Example 1 and one-dimensional cross-sectional schematic diagrams of the surface features.

[0092] Figure 8 (a) Figure 8 (b) shows a schematic diagram of the component roughness and a one-dimensional cross-sectional schematic diagram of the surface features after processing with the magnetorheological polishing slurry in Comparative Example 1, respectively. Figure 8 and Figure 7 As can be seen, the surface quality of the component polished by the magnetorheological polishing slurry in Example 1 is better than that of the components polished by the magnetorheological polishing slurry in Comparative Example 2 and Comparative Example 1. The Ra value reaches 0.204nm, which meets the standard of ultra-smooth surface (<0.3nm). This improves the polishing performance of the magnetorheological polishing slurry to a certain extent and improves the surface quality of the component.

[0093] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, should fall within the protection scope of the present invention.

Claims

1. A magnetorheological polishing slurry based on alumina-coated carbonyl iron powder, characterized in that: The raw materials, by volume fraction, include the following components: Alumina-coated carbonyl iron powder: 38%-42%, Nano diamond powder: 0.001%-0.005%, Dispersant: 0.5%-1%, Wetting agent: 0.5%-1%, pH adjuster: 0.1%-3%, Deionized water: Balance; The dispersant is diammonium citrate, the wetting agent is glycerol, and the pH adjuster is sodium hydroxide.

2. The magnetorheological polishing slurry based on alumina-coated carbonyl iron powder according to claim 1, characterized in that: The alumina-coated carbonyl iron powder includes carbonyl iron powder particles and an alumina coating layer 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.

3. The magnetorheological polishing slurry based on alumina-coated carbonyl iron powder according to claim 2, characterized in that: The alumina coating is an ALD-deposited alumina coating.

4. The magnetorheological polishing slurry based on alumina-coated carbonyl iron powder according to claim 1, characterized in that: The average particle size of the nanodiamond powder is 70-120 nm.

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

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