Magnetorheological polishing fluid and method of making same

Abstract

The application provides a magneto-rheological polishing liquid and a preparation method thereof. The magneto-rheological polishing liquid comprises magnetic powder and abrasive. The ratio of the volume average particle size of the magnetic powder to the volume average particle size of the abrasive is 1:(0.4-0.8). The volume average particle size of the magnetic powder is 2.5-4.0 mu m. The volume average particle size of the abrasive is 1.0-3.2 mu m. The abrasive comprises 10%-25% of diamond in terms of mass ratio and 75%-90% of cerium oxide in terms of mass ratio. When the magnetic powder and the abrasive meet the above requirements, a complete and stable magnetic chain structure can be formed under the action of a magnetic field, sufficient and stable shear stress can be provided, polishing unevenness can be avoided, the stability of material removal efficiency can be ensured, the abrasive can efficiently act on the surface of a workpiece, the removal efficiency can be improved, scratches can be reduced, and a high-smooth workpiece surface machining effect can be achieved.

Description

Technical Field

[0001] This application relates to the field of polishing technology, and more specifically, to a magnetorheological polishing slurry and its preparation method. Background Technology

[0002] Magnetorheological polishing, as an advanced ultra-precision machining technology for optical components, utilizes the transient solid-liquid phase transition of the magnetorheological polishing slurry in a high-intensity gradient magnetic field. By controlling the shear yield stress and local morphology of the slurry through an external magnetic field, a flexible polishing film adapted to the contour of the workpiece surface is formed, thereby achieving deterministic, high-precision, and quantitative shaping and polishing of optical components. This technology can simultaneously ensure surface finish with sub-nanometer roughness, minimal sub-surface damage to the workpiece, and high processing efficiency.

[0003] The performance of magnetorheological polishing slurries directly determines the processing effect: to improve workpiece polishing efficiency, the magnetorheological polishing slurry needs to have high stiffness in the processing area to generate strong shear force, thereby achieving high material removal efficiency; to ensure workpiece surface quality, it is required that no scratches or other defects are generated during processing to obtain a smooth surface with low roughness. However, in actual processing, increasing the stiffness of the magnetorheological polishing slurry to improve material removal efficiency can easily exacerbate surface scratches, leading to increased surface roughness and decreased processing quality. Existing technologies mostly improve magnetorheological polishing slurries from the perspective of a single component or a single performance aspect, making it difficult to effectively balance high material removal efficiency and high surface finish, thus restricting the further application of magnetorheological polishing technology in ultra-precision optical processing. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in the related art.

[0005] In a first aspect, this application proposes a magnetorheological polishing slurry. According to an embodiment of this application, the magnetorheological polishing slurry comprises magnetic powder and abrasive; the ratio of the volume average particle size of the magnetic powder to the volume average particle size of the abrasive is 1:(0.4~0.8); wherein the volume average particle size of the magnetic powder is 2.5~4.0 μm; the volume average particle size of the abrasive is 1.0~3.2 μm; the abrasive comprises 10%~25% diamond by mass and 75%~90% cerium oxide by mass. The particle size distribution of the magnetic powder and abrasive is derived from an optimal physical matching principle based on the geometric relationship of the contact model between the magnetic powder and the abrasive during magnetorheological polishing. When the magnetic powder and abrasive meet the above ratio requirements, the magnetic powder in the polishing slurry can form a complete and stable magnetic flux structure under the action of the magnetic field. This can provide a sufficiently high and stable shear stress for the polishing process, effectively avoiding uneven polishing caused by abrasive embedding in the magnetic flux and ensuring the stability of material removal efficiency. At the same time, it can also enable the polishing abrasive to be efficiently transferred to the surface of the polishing ribbon and have sufficient physical and chemical interaction with the glass surface. While improving the material removal efficiency, it can effectively avoid scratches and achieve a highly smooth workpiece surface processing effect.

[0006] According to embodiments of this application, the magnetorheological polishing slurry may also have the following additional technical features: According to an embodiment of this application, the magnetic powder accounts for 75% to 85% of the total mass of the polishing slurry.

[0007] According to an embodiment of this application, the mass percentage of the abrasive is 2% to 6% based on the total mass of the polishing slurry.

[0008] According to an embodiment of this application, the magnetic powder is selected from carbonyl iron powder.

[0009] According to embodiments of this application, the magnetorheological polishing slurry further includes at least one of a base carrier, a dispersant, an antioxidant, a thixotropic agent, and a pH adjuster.

[0010] According to an embodiment of this application, the magnetorheological polishing slurry comprises, by mass percentage: 75%–85% of the magnetic powder, 2%–6% of the abrasive, 10%–20% of the carrier liquid, 0.1%–1.0% of the dispersant, 0.05%–0.3% of the antioxidant, 0.1%–0.5% of the thixotropic agent, and 0.05%–0.2% of the pH adjuster.

[0011] According to an embodiment of this application, the carrier liquid is deionized water.

[0012] According to embodiments of this application, the dispersant includes at least one of anionic dispersants and nonionic dispersants.

[0013] According to embodiments of this application, the antioxidant includes at least one of sodium benzoate, sodium nitrite, and benzotriazole.

[0014] According to embodiments of this application, the thixotropic agent includes at least one of nano-silica, diatomaceous earth, organobentonite, xanthan gum, and sodium alginate.

[0015] According to embodiments of this application, the pH adjuster includes at least one of triethanolamine, potassium hydroxide, sodium hydroxide, sodium carbonate, and disodium hydrogen phosphate.

[0016] In a second aspect of this application, a method for preparing the magnetorheological polishing slurry described in the first aspect is proposed. According to an embodiment of this application, the method includes: mixing a mixture with abrasive particles to obtain a first mixture; and adding magnetic powder to the first mixture to obtain the magnetorheological polishing slurry. Thus, the magnetorheological polishing slurry prepared by the method of this application allows the magnetic powder to form a more complete and stable magnetic flux structure under the action of a magnetic field. This provides high and stable shear stress for the polishing process and promotes efficient transfer of abrasive particles to the surface of the polishing ribbon, enabling them to fully interact physically and chemically with the glass. This achieves both high material removal efficiency and a sub-nanometer ultra-smooth polished surface, balancing polishing efficiency and workpiece surface quality, overcoming the industry technical bottleneck of traditional magnetorheological polishing slurries that struggle to achieve both simultaneously.

[0017] According to an embodiment of this application, the mixture is prepared by the following method: a base carrier liquid and a pH adjuster are mixed in a second manner to obtain a second mixture; a dispersant, an antioxidant, and a thixotropic agent are added to the second mixture, and a third mixing is performed to obtain the mixture.

[0018] According to an embodiment of this application, the pH value of the mixture is 8.0 to 9.5.

[0019] According to an embodiment of this application, the abrasive is prepared by mixing diamond and cerium oxide.

[0020] In a third aspect, this application proposes the application of the magnetorheological polishing slurry described in the first aspect or prepared using the method described in the second aspect in glass polishing. Therefore, when using the magnetorheological polishing slurry of this application for glass polishing, the magnetic powder can form a stable magnetic flux structure under a magnetic field. This ensures the stability of material removal efficiency during polishing and promotes the efficient transfer of polishing abrasive to the surface of the polishing ribbon, allowing for sufficient physicochemical interaction with the glass surface. Ultimately, this improves material removal efficiency while effectively preventing scratches on the workpiece surface, achieving a sub-nanometer level highly smooth glass surface.

[0021] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0022] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the contact model of polishing abrasive (blue) and magnetic powder (red) according to an embodiment of this application; Figure 2 This is an experimental flowchart of the preparation of magnetorheological polishing fluid according to an embodiment of this application. Detailed Implementation

[0023] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0024] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0025] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this application.

[0026] In this application, the terms "comprising" or "including" are open-ended expressions, meaning they include the content specified in this application but do not exclude other aspects.

[0027] This application is based on the inventor's following discoveries: Magnetorheological polishing is a precision machining process that uses a magnetic field to precisely control the behavior of abrasive particles. Its core consists of a rotating polishing wheel, a stationary workpiece, and a magnetorheological fluid strip between them. The entire process can be divided into three key stages: Initial stage: When the magnetic field is turned off, the magnetorheological polishing slurry exhibits Newtonian fluid characteristics on the polishing wheel, with the magnetic powder randomly dispersed and the abrasive particles suspended in a disordered manner.

[0028] Magnetic field activation stage: A significant transformation occurs after the application of a magnetic field. Magnetic powder rapidly (5-20 ms) aligns into a chain-like structure along the magnetic field lines, forming a "flexible polishing mold" framework. This transformation causes the apparent viscosity of the fluid to surge hundreds of times and generates shear stress of 8-20 kPa. Simultaneously, abrasive particles are "squeezed" onto the polishing mold surface by the magnetic chains of the magnetic powder and precisely fixed within the chain structure, forming a regular array of micro-cutting edges.

[0029] Dynamic polishing stage: In the contact area, the abrasive exerts a dual effect: mechanically, the particles physically cut at a certain depth of penetration; chemically, the combined action of the abrasive and the carrier fluid promotes surface hydrolysis and softening. A shear flow field continuously removes debris, while the circulation system constantly renews the MR fluid band, maintaining stable polishing performance. The entire process achieves sub-nanometer surface accuracy and deterministic material removal by real-time adjustment of the magnetic field strength and workpiece motion parameters.

[0030] Through analysis of the dynamic process of magnetorheological polishing, the inventors discovered that magnetorheological polishing is a complex process involving multi-phase coupling of magnetic field, fluid, abrasive, and workpiece. The interfacial interaction between magnetic powder and abrasive particles, and the physicochemical interaction between abrasive particles and the glass workpiece surface, directly determine the final material removal efficiency and workpiece surface finish, making them core factors affecting polishing performance. However, existing technologies lack a scientific basis for matching the particle size of magnetic powder and abrasive, easily leading to problems such as insufficient stability of the magnetic flux structure, low abrasive transfer efficiency, and easy scratching during polishing, making it difficult to simultaneously achieve high removal efficiency and ultra-smooth surfaces. Based on this research pain point, the inventors conducted a systematic study on the particle size matching relationship between magnetic powder and abrasive particles, discovering an optimal physical matching law between their particle sizes. By adjusting the particle size ratio of magnetic powder and abrasive particles, the forming stability of the magnetic flux structure and the surface interaction efficiency of the abrasive can be effectively optimized, achieving synergistic effects between magnetic powder, abrasive, and workpiece during polishing, ultimately achieving a polishing effect that combines high material removal efficiency with a sub-nanometer ultra-smooth surface.

[0031] In view of this, in the first aspect of this application, a magnetorheological polishing slurry is proposed. According to an embodiment of this application, the magnetorheological polishing slurry comprises magnetic powder and abrasive; the ratio of the volume average particle size of the magnetic powder to the volume average particle size of the abrasive is 1:(0.4~0.8). For example, it can be 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, etc., or it can be any range of the above values.

[0032] In the magnetorheological polishing slurry system, magnetic powder is the core component with a relatively high mass proportion, while abrasive serves as the polishing medium with a relatively low mass proportion. Under actual polishing conditions, without an applied magnetic field, the magnetorheological polishing slurry exhibits low-viscosity Newtonian fluid characteristics in the equipment's storage tank, circulation pipeline, and polishing wheel. The magnetic powder and abrasive particles in the system are randomly dispersed and suspended in a disordered state. However, when an external magnetic field is applied, the magnetic powder will instantly align along the magnetic field lines to form a regular magnetic chain structure, providing basic support for the polishing process.

[0033] The matching degree between the abrasive particle size and the magnetic powder particle size directly affects the stability of the magnetic flux structure and the final polishing effect. If the abrasive particle size is too small, it is very easy to embed into the magnetic flux structure, which will not only destroy the integrity and stability of the magnetic flux, but also lead to insufficient proportion of abrasive components that can play a role on the surface of the polishing mold, and even cause direct grinding between the magnetic powder and the workpiece. Ultimately, this results in poor material removal efficiency and stability, and the workpiece surface is prone to scratches and high roughness. If the abrasive particle size is too large, although the problem of abrasive embedding into the magnetic flux will not occur, when large-diameter abrasive comes into contact with the workpiece surface, it is easy to form deep scratches. Even if the material removal rate is high, it will lead to a significant decrease in the surface processing quality of the workpiece.

[0034] To address this problem, the inventors developed a contact model between magnetic powder and abrasive. Figure 1 Based on geometric relationships, theoretical derivation revealed that the critical matching size of the abrasive particle size is approximately 0.4 times the magnetic powder particle size. Considering that the magnetic flux structure is not ideally arranged during actual polishing, and that the actual particle size of the powder has a certain deviation, the inventors further determined the optimal matching principle between the magnetic powder and abrasive particle sizes—the abrasive particle size should be 0.4 to 0.8 times the magnetic powder particle size, i.e., the ratio of the volume average particle size of the magnetic powder to the volume average particle size of the abrasive is 1:(0.4~0.8). Under this optimal powder particle size combination, the magnetic powder can form a complete and stable magnetic flux structure, providing sufficient and stable shear stress for the polishing process, effectively avoiding uneven polishing caused by abrasive embedding in the force chain, providing stable support for efficient polishing, and thus improving material removal efficiency. Simultaneously, the abrasive can be efficiently transferred to the polishing ribbon surface, fully interacting with the workpiece surface through physicochemical processes, achieving a sub-nanometer ultra-smooth surface while ensuring high removal efficiency.

[0035] In some embodiments of this application, the volume average particle size of the magnetic powder is 2.5~4.0 μm. For example, it can be 2.5 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.0 μm, etc., or can be any range of the above values. In some embodiments, the morphology of the magnetic powder is uniform spherical, with a magnetization ≥200 emu / g and a coercivity ≤20 Oe. Thus, the magnetic powder can rapidly form a stable magnetic flux structure under the action of a magnetic field, providing sufficient magnetostrictive shear stress, thereby serving as a skeleton support layer for the polishing mold.

[0036] It should be noted that the volume average particle size of the abrasive only needs to meet the matching principle of being 0.4 to 0.8 times the volume average particle size of the magnetic powder. It can be flexibly adjusted according to the process requirements of the actual application scenario, and this application does not impose a unique limitation on it. For example, the volume average particle size of the abrasive can be selected in the range of 1.0 to 3.2 μm, specifically 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, etc., or any range formed by any two of the above values ​​can be selected.

[0037] It should be noted that the "volume average particle size" mentioned in this invention refers to the D50 particle size measured by laser particle size analysis, which is the particle size value corresponding to the cumulative distribution percentage of particle volume distribution in the sample reaching 50%.

[0038] In some embodiments of this application, the abrasive includes diamond and cerium oxide. The diamond content, based on the total mass of the abrasive, is 10% to 25% by mass. For example, it can be 10%, 12%, 15%, 17%, 20%, 22%, 25%, or any range of the above values. The cerium oxide content, based on the total mass of the abrasive, is 75% to 90% by mass. For example, it can be 75%, 78%, 80%, 82%, 85%, 88%, 90%, or any range of the above values.

[0039] During the polishing process, the abrasive is pushed out through the gaps in the magnetic flux and fixed on the surface of the magnetic flux, making full contact with the workpiece surface and undergoing a series of physicochemical reactions. Diamond and cerium oxide play their respective roles based on their physicochemical properties, and through precise ratio design, the two achieve synergistic effects. The specific mechanism of action is as follows: Diamond is a superhard abrasive with a Mohs hardness of 10. Its particles have an acute-angled polyhedral morphology. Under the rigid support of a magnetic flux, it can create localized high stress with the minute protrusions on the workpiece surface, thereby achieving rapid material peeling. Based on this, this application controls the mass ratio of diamond in the composite abrasive to 10%–25%. This ratio ensures sufficient cutting point density, guaranteeing efficient mechanical cutting, while avoiding deep scratches on the workpiece surface or disruption of the continuity of the softened layer formed by cerium oxide due to excessive hard particles.

[0040] Cerium oxide has a highly chemically active surface. When it comes into contact with a glass (SiO2) surface, the oxygen vacancies in its crystal lattice can capture oxygen atoms in SiO2, forming strong Si-O-Ce bonds, which weakens the surface structure of the quartz glass. Simultaneously, Ce bonds also form. 3+ / Ce 4+ Redox cycles further promote the breaking of Si–O–Si bonds on the glass surface, thereby forming a surface softening layer. Therefore, this application sets the mass ratio of cerium oxide in the composite abrasive to a high proportion of 75%~90%, which can ensure that the abrasive and the continuously exposed fresh surface of the glass workpiece react fully during the polishing process, maintain a stable softening layer thickness, effectively reduce the cutting resistance of diamond, and reduce microcracks and subsurface damage generated during the cutting process.

[0041] In summary, diamond, with its high mechanical cutting force, can significantly increase the amount of material removed per unit time; cerium oxide weakens the glass surface structure through chemical action, reducing surface damage caused by cutting and achieving sub-nanometer surface roughness. The two work together stably in a micro-cutting array formed by magnetic flux fixation, ultimately achieving dual stability in material removal efficiency and workpiece surface quality during long-term polishing.

[0042] It should be noted that, in addition to the physical compounding of diamond and cerium oxide, the abrasive of this application can also preferably be a diamond@CeO2 core-shell composite abrasive material as a polishing abrasive. In this case, diamond is the core and CeO2 is the shell. Relying on the spatial composite characteristics of the core-shell structure, the mechanical cutting action of diamond and the chemical softening action of cerium oxide can achieve a closer and more efficient synergy, thereby further improving the polishing performance.

[0043] In some embodiments of this application, the mass percentage of magnetic powder is 75% to 85% based on the total mass of the polishing slurry. For example, it can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, etc., or any range of the above values. Therefore, by ensuring the mass percentage of magnetic powder is within the above range, sufficient powder material is provided to allow the magnetic powder to rapidly align under a magnetic field, forming a dense and regular magnetic chain, thus creating a robust framework for the "flexible polishing mold."

[0044] In some embodiments of this application, the mass percentage of abrasive is 2% to 6% based on the total mass of the polishing slurry. For example, it can be 2%, 3%, 4%, 5%, 6%, or any range of the above values. Therefore, by ensuring the mass percentage of abrasive is within the above range, both polishing efficiency and surface quality protection can be achieved. On the one hand, this ensures that after the abrasive is pushed out through the magnetic flux gap, it can form an effective micro-cutting array on the surface of the polishing ribbon, achieving efficient physicochemical polishing. On the other hand, it avoids particle agglomeration and damage to the magnetic flux structure caused by excessive abrasive, while also preventing scratches on the workpiece surface caused by excessive hard abrasive.

[0045] In some embodiments of this application, the magnetic powder is selected from carbonyl iron powder. Therefore, when an external magnetic field is applied, the carbonyl iron powder can rapidly align along the magnetic field lines within 5-20 ms, quickly forming a regular and dense magnetic chain structure, providing a stable framework support for the "flexible polishing mold".

[0046] In some embodiments of this application, the magnetorheological polishing slurry further includes at least one of a base carrier, a dispersant, an antioxidant, a thixotropic agent, and a pH adjuster. This can further improve the polishing quality.

[0047] In some embodiments of this application, the magnetorheological polishing slurry comprises, by mass percentage: 75%–85% magnetic powder, 2%–6% abrasive, 10%–20% carrier fluid, 0.1%–1.0% dispersant, 0.05%–0.3% antioxidant, 0.1%–0.5% thixotropic agent, and 0.05%–0.2% pH adjuster.

[0048] For example, the mass percentage of magnetic powder can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, etc., or can be any range of the above values. Thus, by making the mass percentage of magnetic powder within the above range, the magnetic powder can be rapidly arranged under a magnetic field to form a dense and regular magnetic chain, providing sufficient powder base to form a robust framework for the "flexible polishing mold".

[0049] For example, the mass percentage of the abrasive can be 2%, 3%, 4%, 5%, 6%, or any range of the above values. Therefore, by ensuring the mass percentage of the abrasive is within the above range, both the polishing efficiency and surface quality protection of the abrasive can be achieved. On the one hand, this ensures that after the abrasive is pushed out through the magnetic flux gap, it can form an effective micro-cutting array on the surface of the polishing ribbon, achieving efficient physicochemical polishing. On the other hand, it avoids particle agglomeration and damage to the magnetic flux structure caused by excessive abrasive, while also preventing scratches on the workpiece surface caused by excessive hard abrasive.

[0050] For example, the mass percentage of the carrier fluid can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., or can be any range of the above values. Therefore, by ensuring the mass percentage of the carrier fluid is within the above range, a suitable fluid base can be provided for the polishing slurry, ensuring that the polishing slurry exhibits low-viscosity Newtonian fluid characteristics in the absence of a magnetic field, allowing the magnetic powder and abrasive to achieve uniform dispersion and disordered suspension.

[0051] In some embodiments of this application, deionized water with a conductivity ≥18 MΩ is used as the carrier fluid. cm is not only inexpensive and environmentally friendly, but also provides good cooling and lubrication for the polishing process, while effectively promoting the hydrolysis reaction on the glass surface and helping to improve polishing efficiency.

[0052] For example, the mass percentage of the dispersant can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc., or can be any range of the above values. Therefore, by ensuring the mass percentage of the dispersant is within the above range, it can be fully adsorbed onto the surface of the magnetic powder or abrasive particles, reducing inter-particle agglomeration and achieving uniform powder dispersion.

[0053] In some embodiments of this application, the dispersant includes at least one of anionic and nonionic dispersants. In some embodiments, the anionic dispersant includes sodium polyacrylate, sodium hexametaphosphate, sodium polyphosphate, sodium citrate, etc., and the nonionic dispersant includes polyethylene glycol, polyether-modified polysiloxane, polyvinylpyrrolidone, ethoxylated alkylphenol, etc. This improves the dispersibility of magnetic particles and abrasives in water-based polishing fluids, preventing agglomeration and sedimentation.

[0054] For example, the mass percentage of the antioxidant can be 0.05%, 0.07%, 0.10%, 0.12%, 0.15%, 0.17%, 0.20%, 0.22%, 0.25%, 0.27%, 0.30%, etc., or can be any range of the above values. Therefore, by keeping the mass percentage of the antioxidant within the above range, the oxidation reaction of the magnetic powder in the water-based system can be effectively suppressed, preventing the degradation of the magnetic properties of the magnetic powder and the formation of flocculent precipitates in the polishing slurry.

[0055] In some embodiments of this application, the antioxidant includes at least one of sodium benzoate, sodium nitrite, and benzotriazole. This inhibits the oxidation reaction of the magnetic powder in the carrier liquid.

[0056] For example, the mass percentage of the thixotropic agent can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any range of the above values. Therefore, by keeping the mass percentage of the thixotropic agent within the above range, a reversible three-dimensional hydrogen bond network can be formed in the carrier liquid, effectively reducing the powder settling rate and improving the storage and recycling stability of the polishing slurry.

[0057] In some embodiments of this application, the thixotropic agent includes at least one of nano-silica, diatomaceous earth, organobentonite, xanthan gum, and sodium alginate. This allows for the formation of a reversible three-dimensional hydrogen bond network after sufficient dispersion and activation in the carrier liquid, thereby reducing the settling rate of the magnetorheological polishing slurry.

[0058] For example, the mass percentage of the pH adjuster can be 0.05%, 0.07%, 0.10%, 0.12%, 0.15%, 0.17%, 0.20%, etc., or can be any range of the above values. Therefore, by keeping the mass percentage of the pH adjuster within the above range, the polishing slurry system can be stabilized in the weakly alkaline range of 8.0–9.5 at room temperature, ensuring the chemical activity of cerium oxide while further slowing down the oxidation of the magnetic powder.

[0059] In some embodiments of this application, the pH adjuster includes at least one of triethanolamine, potassium hydroxide, sodium hydroxide, sodium carbonate, and disodium hydrogen phosphate. This stabilizes the pH of the polishing solution at 8.0–9.5, ensuring both the chemical reactivity of cerium oxide and slowing down the oxidation of the magnetic particles.

[0060] It is understood that the above description of the selection of materials for the base carrier, dispersant, antioxidant, thixotropic agent and pH adjuster is only exemplary. In actual application, it is necessary to determine the specific materials based on the actual application situation. No single limit is set here.

[0061] In a second aspect of this application, a method for preparing the magnetorheological polishing slurry described in the first aspect is proposed. According to embodiments of this application, such as... Figure 2 As shown, the method includes: S100: The mixture is first mixed with the abrasive particles to obtain the first mixture.

[0062] In some embodiments of this application, the mixture is prepared by the following method: a base carrier liquid and a pH adjuster are mixed in a second mixture to obtain a second mixture; a dispersant, an antioxidant, and a thixotropic agent are added to the second mixture, and a third mixture is performed to obtain the mixture.

[0063] In some embodiments of this application, deionized water with a conductivity ≥18 MΩ is used as the carrier fluid. cm is not only inexpensive and environmentally friendly, but also provides good cooling and lubrication for the polishing process, while effectively promoting the hydrolysis reaction on the glass surface and helping to improve polishing efficiency.

[0064] In some embodiments of this application, the pH adjuster includes at least one of triethanolamine, potassium hydroxide, sodium hydroxide, sodium carbonate, and disodium hydrogen phosphate. This stabilizes the pH of the polishing solution at 8.0–9.5, ensuring both the chemical reactivity of cerium oxide and slowing down the oxidation of the magnetic particles.

[0065] In some embodiments of this application, the pH value of the mixture is 8.0 to 9.5. For example, it can be 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, etc., or it can be any range of the above values.

[0066] In some embodiments of this application, the temperature of the second mixing is 35~45°C. For example, it can be 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, etc.

[0067] In some embodiments of this application, the dispersant includes at least one of anionic and nonionic dispersants. In some embodiments, the anionic dispersant includes sodium polyacrylate, sodium hexametaphosphate, sodium polyphosphate, sodium citrate, etc., and the nonionic dispersant includes polyethylene glycol, polyether-modified polysiloxane, polyvinylpyrrolidone, ethoxylated alkylphenol, etc. This improves the dispersibility of magnetic particles and abrasives in water-based polishing fluids, preventing agglomeration and sedimentation.

[0068] In some embodiments of this application, the antioxidant includes at least one of sodium benzoate, sodium nitrite, and benzotriazole. This inhibits the oxidation reaction of the magnetic powder in the carrier liquid.

[0069] In some embodiments of this application, the thixotropic agent includes at least one of nano-silica, diatomaceous earth, organobentonite, xanthan gum, and sodium alginate. This allows for the formation of a reversible three-dimensional hydrogen bond network after sufficient dispersion and activation in the carrier liquid, thereby reducing the settling rate of the magnetorheological polishing slurry.

[0070] In some embodiments of this application, the abrasive grains are prepared by mixing diamond and cerium oxide to obtain the abrasive.

[0071] In some embodiments of this application, the mass ratio of diamond to cerium oxide is (10~25):(75~90). For example, it can be 10:90, 12:88, 15:85, 17:83, 20:80, 22:78, 25:75, etc.

[0072] S200: Magnetic powder is added to the first mixture to obtain the magnetorheological polishing slurry.

[0073] In some embodiments of this application, the ratio of the volume average particle size of the magnetic powder to the volume average particle size of the abrasive is 1:(0.4~0.8). For example, it can be 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, or any range of the above values. Therefore, when the particle sizes of the magnetic powder and the abrasive meet the above ratio requirements, the magnetic powder in the polishing slurry can form a complete and stable magnetic flux structure under the action of the magnetic field. This provides sufficiently high and stable shear stress for the polishing process, effectively avoiding uneven polishing caused by the abrasive embedding into the magnetic flux, and ensuring the stability of material removal efficiency. Simultaneously, it allows the polishing abrasive to be efficiently transferred to the surface of the polishing ribbon, undergoing sufficient physicochemical interaction with the glass surface. This improves material removal efficiency while effectively preventing scratches and achieving a highly smooth workpiece surface finish.

[0074] In some embodiments of this application, the volume average particle size of the magnetic powder is 2.5~4.0 μm. For example, it can be 2.5 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.0 μm, etc., or can be any range of the above values. In some embodiments, the morphology of the magnetic powder is uniform spherical, with a magnetization ≥200 emu / g and a coercivity ≤20 Oe. Thus, the magnetic powder can rapidly form a stable magnetic flux structure under the action of a magnetic field, providing sufficient magnetostrictive shear stress, thereby serving as a skeleton support layer for the polishing mold.

[0075] In some embodiments of this application, the volume average particle size of the abrasive is 1.0~3.2 μm. For example, it can be a specific value such as 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, etc., or a range consisting of any two of the above values ​​can be selected.

[0076] In a third aspect, this application proposes the application of the magnetorheological polishing slurry of the first aspect or the magnetorheological polishing slurry prepared by the method of the second aspect in glass polishing. Therefore, when using the magnetorheological polishing slurry of this application for glass polishing, the magnetic powder can form a stable magnetic flux structure under a magnetic field. This ensures the stability of material removal efficiency during polishing and promotes the efficient transfer of polishing abrasive to the surface of the polishing ribbon, allowing for sufficient physicochemical interaction with the glass surface. Ultimately, while improving material removal efficiency, it effectively avoids scratches on the workpiece surface, achieving a sub-nanometer level highly smooth glass surface.

[0077] It should be noted that the term "glass" in this application is not particularly limited and can refer to various glass substrates, including but not limited to optical glass, quartz glass, borosilicate glass, silicate glass, phosphate glass, fluoride glass, etc. It can also be applied to various glass substrates and optical components for optical elements, such as wafer-level glass, optical substrates, lenses, windows, etc.

[0078] The following will explain the solution of this application with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0079] Example 1 This embodiment provides a water-based magnetorheological polishing slurry for high-efficiency polishing of optical glass. Its composition by mass percentage is as follows: 80% carbonyl iron powder (volume average particle size of 3μm), 4% polishing abrasive (a blend of diamond and cerium oxide), and a base carrier liquid (deionized water with a conductivity ≥18MΩ). The polishing abrasive comprises 14.5% diamond (C) and 0.8% sodium hexametaphosphate (CeO2) as dispersant, 0.2% sodium benzoate (CeO2) as antioxidant, 0.3% nano-silica (CeO2) as thixotropic agent, and 0.2% sodium carbonate (CeO2) as pH adjuster. The polishing abrasive contains 20% diamond (C) by mass and 80% cerium oxide (CeO2) by mass, and the volume average particle size of the polishing abrasive (diamond and cerium oxide) is 1.2 μm.

[0080] The magnetorheological polishing slurry in this embodiment is prepared by the following method, the specific steps of which include: 1. Preparation of aqueous carrier liquid: Take the prescribed amount of deionized water and place it in a flask. Keep the system temperature constant at 40℃. Add the prescribed amount of pH adjuster sodium carbonate to adjust the pH of the system to 8.0~9.5. Then, control the stirring speed at 500~800 rpm and add the prescribed amounts of dispersant sodium hexametaphosphate, thixotropic agent nano silica, and antioxidant sodium benzoate to the system in sequence. Continue stirring for 60 min to obtain a uniform aqueous carrier liquid.

[0081] 2. Preparation of abrasive-aqueous carrier liquid mixture system: Diamond abrasive and cerium oxide abrasive that meet the particle size matching requirements are strictly screened, weighed according to the above mass ratio and added to a mixer, and centrifuged for 20 minutes until the two are evenly mixed to obtain a composite polishing abrasive; the composite polishing abrasive is mixed with the aqueous carrier liquid obtained in step 1, transferred to a sealed cylindrical bottle, and placed on a shaker at a speed of 70 rpm for 60 minutes to obtain the abrasive-aqueous carrier liquid mixture system.

[0082] 3. Preparation of magnetorheological polishing slurry: Strictly screen carbonyl iron powder that meets the particle size requirements, add it to the sealed cylindrical bottle of the abrasive-water-based carrier liquid mixture obtained in step 2 according to the formula mass ratio, keep the shaking speed at 70 rpm, and continue to shake for 120 min to obtain the magnetorheological polishing slurry.

[0083] Example 2 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that the volume average particle size of the carbonyl iron powder was 3.0 μm and the volume average particle size of the polishing abrasive was 1.8 μm.

[0084] Example 3 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that the volume average particle size of the carbonyl iron powder was 3.0 μm and the volume average particle size of the polishing abrasive was 2.4 μm.

[0085] Example 4 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that the volume average particle size of the carbonyl iron powder was 2.5 μm and the volume average particle size of the polishing abrasive was 1.0 μm.

[0086] Example 5 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that the volume average particle size of the carbonyl iron powder was 4.0 μm and the volume average particle size of the polishing abrasive was 3.2 μm.

[0087] Example 6 The magnetorheological polishing slurry was prepared according to the method of Example 3, except that the mass ratio of diamond in the polishing abrasive was 10% and the mass ratio of cerium oxide was 90%.

[0088] Example 7 The magnetorheological polishing slurry was prepared according to the method of Example 3, except that the mass percentage of diamond in the polishing abrasive was 25% and the mass percentage of cerium oxide was 75%.

[0089] Example 8 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that its composition by mass percentage is as follows: 75% carbonyl iron powder (volume average particle size of 3 μm), 6% polishing abrasive (a composite of diamond and cerium oxide), and base carrier liquid (deionized water with conductivity ≥18 MΩ). The composition of the product is as follows: 17.5% (cm), 0.8% (dispersant sodium hexametaphosphate), 0.2% (antioxidant sodium benzoate), 0.3% (thixotropic agent nano silica), and 0.2% (pH adjuster sodium carbonate).

[0090] Example 9 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that its composition by mass percentage is as follows: 85% carbonyl iron powder (volume average particle size of 3 μm), 2% polishing abrasive (a mixture of diamond and cerium oxide), and base carrier liquid (deionized water with conductivity ≥18 MΩ). The composition of the following components is as follows: 11.5% (cm), 0.8% (dispersant sodium hexametaphosphate), 0.2% (antioxidant sodium benzoate), 0.3% (thixotropic agent nano silica), and 0.2% (pH adjuster sodium carbonate).

[0091] Example 10 The magnetorheological polishing slurry was prepared according to the method of Example 1, with the difference being that its composition by mass percentage is as follows: 77% carbonyl iron powder (volume average particle size of 3 μm), 2.7% polishing abrasive (a blend of diamond and cerium oxide), and base fluid (deionized water with conductivity ≥18 MΩ). The ingredients are: 20% (cm), 0.1% sodium hexametaphosphate (dispersant), 0.05% sodium benzoate (antioxidant), 0.1% nano silica (thixotropic agent), and 0.05% sodium carbonate (pH adjuster).

[0092] Example 11 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that its composition by mass percentage is as follows: 84% carbonyl iron powder (volume average particle size of 3 μm), 4% polishing abrasive (a mixture of diamond and cerium oxide), and base carrier liquid (deionized water with conductivity ≥18 MΩ). The ingredients are: 10% (cm), 1.0% (dispersant sodium hexametaphosphate), 0.3% (antioxidant sodium benzoate), 0.5% (thixotropic agent nano silica), and 0.2% (pH adjuster sodium carbonate).

[0093] Comparative Example 1 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that the volume average particle size of the carbonyl iron powder was 3.0 μm and the volume average particle size of the polishing abrasive was 1.0 μm.

[0094] Comparative Example 2 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that the volume average particle size of the carbonyl iron powder was 3.0 μm and the volume average particle size of the polishing abrasive was 2.6 μm.

[0095] Comparative Example 3 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that the volume average particle size of the carbonyl iron powder was 2.0 μm and the volume average particle size of the polishing abrasive was 1.2 μm.

[0096] Comparative Example 4 The magnetorheological polishing slurry was prepared according to the method of Example 1, except that the volume average particle size of the carbonyl iron powder was 4.5 μm and the volume average particle size of the polishing abrasive was 2.7 μm.

[0097] Comparative Example 5 The magnetorheological polishing slurry was prepared according to the method of Example 3, except that the mass percentage of diamond in the polishing abrasive was 5% and the mass percentage of cerium oxide was 95%.

[0098] Comparative Example 6 The magnetorheological polishing slurry was prepared according to the method of Example 3, except that the mass ratio of diamond in the polishing abrasive was 30% and the mass ratio of cerium oxide was 70%.

[0099] Comparative Example 7 The magnetorheological polishing fluid was prepared according to the method in Example 3, except that only diamond was used as the polishing abrasive.

[0100] Comparative Example 8 The magnetorheological polishing slurry was prepared according to the method of Example 3, except that only cerium oxide was used as the polishing abrasive.

[0101] The specific differences between Examples 1-11 and Comparative Examples 1-8 are shown in Table 1.

[0102] Table 1

[0103] Workpiece to be processed: Quartz glass with a diameter of 50mm and an initial Ra of 1200nm.

[0104] Polishing parameters: polishing wheel speed 200 rpm, pressure depth 0.4 mm.

[0105] Test method: 1. Material removal rate (MRR, μm / min): Method: Before polishing, the initial mass of the workpiece was measured using an electronic balance. After polishing, the residual polishing solution on the workpiece surface was thoroughly cleaned, and the final mass was measured after drying. The mass difference was calculated. And based on the workpiece radius r and material density The material removal rate (MRR) is calculated based on the polishing time t.

[0106]

[0107] 2. Surface roughness (Ra, nm): Method: After polishing, the workpiece is cleaned and dried, and placed on a shockproof platform. Five measurement areas (1mm × 1mm each) are randomly selected on the workpiece surface. A white light interferometer is used to acquire surface profile data and calculate the arithmetic mean roughness Ra.

[0108] The specific test results are shown in Table 2. When the removal efficiency meets the requirement of 2.8-4.0 μm / min, it indicates that the polishing slurry can provide efficient and stable material removal capability for the optical glass polishing process. When the surface roughness is less than 1 nm, it indicates that the polishing slurry can achieve sub-nanometer level ultra-smooth surface processing effect of optical glass, effectively avoiding the generation of scratches, microcracks, sub-surface damage and other problems during the polishing process, so that the surface of optical glass can meet the processing quality requirements of high-precision optical components.

[0109] Table 2

[0110] Comparing Examples 1-5 with Comparative Examples 1-4, it can be seen that when the volume average particle size ratio of carbonyl iron powder to polishing abrasive is controlled at 1:(0.4-0.8), and the particle size of carbonyl iron powder is 2.5-4.0 μm, and the particle size of abrasive is 1.0-3.2 μm, the polishing slurry can achieve a high material removal efficiency of 2.8-4.0 μm / min, while making the surface roughness of the polished workpiece less than 1 nm, achieving excellent dual effects of efficiency and surface quality. Conversely, in Comparative Example 1, the particle size ratio of magnetic powder to abrasive was 1:0.33 (<1:0.4). The abrasive easily embedded itself in the magnetic flux structure, disrupting its stability. This not only failed to effectively remove the initial morphology of the workpiece but also resulted in a material removal rate as low as 0.5 μm / min and a surface roughness as high as 500 nm. In Comparative Example 2, the particle size ratio of magnetic powder to abrasive reached 1:0.87 (>1:0.8), easily causing scratches on the workpiece during polishing, and the surface roughness increased sharply to 300 nm, both failing to meet the requirements for polishing. Furthermore, the particle size of the carbonyl iron powder directly affects the material removal efficiency of the polishing slurry and the surface roughness of the workpiece. In Comparative Example 3, when the magnetic powder particle size is smaller than 2.5 μm (e.g., 2.0 μm) as specified in this invention, the strength of the magnetic flux structure formed under the magnetic field is insufficient, the material removal rate is only 0.8 μm / min, and the surface roughness of the workpiece is relatively high. In Comparative Example 4, when the magnetic powder particle size is larger than 4.0 μm (e.g., 4.5 μm) as specified in this invention, the strength of the magnetic flux structure is relatively high. Although the material removal rate can reach 3.6 μm / min, it is easy to cause scratches on the workpiece surface, resulting in a significant increase in roughness.

[0111] Comparing Examples 3, 6-7 and Comparative Examples 5-8 reveals that the mass ratio of diamond to cerium oxide in the polishing abrasive has a certain impact on the final performance of the polishing slurry. When the diamond content is too low (e.g., 5%), the mechanical cutting ability of the abrasive is insufficient, the material removal rate is only 1.8 μm / min, and the polishing efficiency decreases to some extent. When the diamond content is too high (e.g., 30%), the hard particles easily scratch the workpiece, and the surface roughness increases to 100 nm. When using diamond alone (100%), although the material removal rate can reach 4.5 μm / min, the surface roughness reaches 600 nm, resulting in poor surface quality. When using cerium oxide alone (100%), although the surface roughness can be as low as 50 nm, the material removal rate is extremely low (0.7 μm / min) due to chemical softening alone, which cannot meet the requirements for high-efficiency polishing.

[0112] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A magnetorheological polishing slurry, characterized in that, Includes magnetic powder and abrasive; The ratio of the volume average particle size of the magnetic powder to the volume average particle size of the abrasive is 1:(0.4~0.8); wherein, The volume average particle size of the magnetic powder is 2.5~4.0 μm; The abrasive has a volume average particle size of 1.0~3.2 μm; The abrasive comprises 10% to 25% diamond and 75% to 90% cerium oxide by mass.

2. The magnetorheological polishing slurry according to claim 1, characterized in that, Based on the total mass of the polishing slurry, the magnetic powder accounts for 75% to 85% of the mass. And / or, based on the total mass of the polishing slurry, the mass percentage of the abrasive is 2% to 6%.

3. The magnetorheological polishing slurry according to claim 2, characterized in that, The magnetic powder is selected from carbonyl iron powder.

4. The magnetorheological polishing slurry according to any one of claims 1 to 3, characterized in that, The magnetorheological polishing fluid further includes at least one of a base fluid, a dispersant, an antioxidant, a thixotropic agent, and a pH adjuster.

5. The magnetorheological polishing slurry according to claim 4, characterized in that, The magnetorheological polishing slurry comprises, by mass percentage: 75%–85% of the magnetic powder, 2%–6% of the abrasive, 10%–20% of the carrier liquid, 0.1%–1.0% of the dispersant, 0.05%–0.3% of the antioxidant, 0.1%–0.5% of the thixotropic agent, and 0.05%–0.2% of the pH adjuster.

6. The magnetorheological polishing slurry according to claim 5, characterized in that, The carrier liquid is deionized water; And / or, the dispersant includes at least one of anionic dispersants and nonionic dispersants; And / or, the antioxidant includes at least one of sodium benzoate, sodium nitrite, and benzotriazole; And / or, the thixotropic agent comprises at least one of nano-silica, diatomaceous earth, organobentonite, xanthan gum, and sodium alginate; And / or, the pH adjuster includes at least one of triethanolamine, potassium hydroxide, sodium hydroxide, sodium carbonate, and disodium hydrogen phosphate.

7. A method for preparing the magnetorheological polishing slurry according to any one of claims 1 to 6, characterized in that, include: The mixture is first mixed with the abrasive particles to obtain the first mixture; Magnetic powder is added to the first mixture to obtain the magnetorheological polishing slurry.

8. The method according to claim 7, characterized in that, The mixture is prepared by the following method: The carrier liquid and the pH adjuster are mixed a second time to obtain a second mixture. A dispersant, an antioxidant, and a thixotropic agent are added to the second mixture, and a third mixing is performed to obtain the mixture.

9. The method according to claim 8, characterized in that, The pH value of the mixture is 8.0~9.5; And / or, the abrasive is prepared by mixing diamond and cerium oxide.

10. The application of the magnetorheological polishing slurry according to any one of claims 1 to 6 or the magnetorheological polishing slurry prepared by the method according to any one of claims 7 to 9 in glass polishing.

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