A nano-PMMA core coated with SiO 2 / CeO 2 Preparation method of double-shell abrasive

Abstract

This invention discloses a method for coating SiO with nano-PMMA as the core. 2 / CeO 2 A method for preparing double-shell abrasives relates to the field of composite abrasive technology. The method includes the following steps: First, a soap-free emulsion polymerization method using a boiling system is employed, with methyl methacrylate as the monomer and 3-(methacryloyloxy)propyltrimethoxysilane as the coupling agent. The polymerization reaction is initiated with 2,2'-azobisisobutylamidine dihydrochloride to prepare PMMA microspheres with controllable particle size and good monodispersity. Then, using tetraethyl silicate as the raw material, a strawberry-shaped PMMA / SiO2 microsphere is prepared using the sol-gel method. 2 Composite microspheres; finally, nano-CeO was prepared by homogeneous precipitation using soluble cerium salt as raw material and hexamethylenetetramine as precipitant. 2 Uniformly coated double-shell PMMA / SiO 2 / CeO 2 Composite abrasive; this abrasive has a flexible core and a large number of surface active sites, which can achieve lower surface roughness and higher material removal rate in ultra-precision surface polishing.

Description

A method for preparing a nano-PMMA core-coated SiO2 / CeO2 double-shell abrasive. Technical Field

[0001] This invention relates to the field of composite abrasive technology, and in particular to a method for preparing a nano-PMMA core-coated SiO2 / CeO2 double-shell abrasive. Background Technology

[0002] In today's industrial manufacturing sector, the surface quality requirements for high-end precision components such as optical elements are becoming increasingly stringent. Taking polished KDP crystals as an example, as large-sized optical components, KDP crystals are relatively brittle and have low hardness, requiring a surface roughness at the sub-nanometer level. Chemical mechanical polishing (CMP), a unique technology used in surface processing, achieves surface planarization through the synergistic effect of chemical etching and mechanical friction, and is currently one of the mainstream technologies for obtaining ultra-smooth surfaces.

[0003] In chemical mechanical polishing (CMP), the selection of abrasive type plays a crucial role. Traditional single inorganic polishing abrasives often fail to achieve satisfactory results in actual polishing processes. Cerium-based rare earth polishing powder has the advantages of high polishing efficiency, easy cleaning after polishing, and relatively low environmental pollution. However, its dispersibility is poor, and it is prone to agglomeration, which can adversely affect the polishing quality. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a double-shell abrasive with nano-PMMA as the core and coated with SiO2 / CeO2. The method uses nano-PMMA as the core and sequentially coats the outside of PMMA microspheres with SiO2 and CeO2 shells to obtain a double-shell abrasive. This abrasive, while ensuring polishing efficiency, further reduces surface roughness, thereby meeting the requirements for polishing quality of high-end precision components.

[0005] The technical solution adopted in this invention is as follows:

[0006] This invention provides a method for preparing a nano-PMMA core-coated SiO2 / CeO2 double-shell abrasive, comprising the following steps:

[0007] Step 1: Prepare PMMA microspheres using soap-free emulsion polymerization: Wash methyl methacrylate with sodium hydroxide solution, add the washed methyl methacrylate to deionized water, and then add 3-(methacryloyloxy)propyltrimethoxysilane to prepare mixed solution A. Disperse mixed solution A by ultrasonication and heat it to boiling in a constant temperature oil bath. Add 2,2'-azobisisobutylamidine dihydrochloride aqueous solution under stirring to react. After the reaction is completed, cool to obtain a uniformly dispersed PMMA microsphere emulsion.

[0008] Step 2: Preparation of PMMA / SiO2 nanocomposite microspheres by sol-gel method: The PMMA microsphere emulsion obtained in Step 1 was added to anhydrous ethanol and ultrasonically dispersed. Ammonia was added to adjust the pH value to 8-10 to obtain solution B. A tetraethyl orthosilicate anhydrous ethanol solution C with a concentration of 40-200 g / L was prepared. Solution C was then added dropwise to solution B under continuous stirring, and the reaction was carried out by heating in a constant temperature water bath. The final product was centrifuged and washed repeatedly with deionized water and anhydrous ethanol, then dried and ground to obtain core-shell structured silica-coated polymethyl methacrylate nanocomposite microspheres.

[0009] Step 3: Preparation of PMMA / SiO2 / CeO2 composite abrasive by uniform precipitation method: The silica-coated polymethyl methacrylate nanocomposite microspheres prepared in Step 2 were added to deionized water and ultrasonically dispersed to obtain solution D; soluble cerium salt was added to solution D, and then hexamethylenetetramine was added to obtain solution E. The reaction was carried out under constant temperature water bath heating and continuous stirring; the final product was centrifuged and washed repeatedly with deionized water and anhydrous ethanol, then dried, and ground to obtain PMMA / SiO2 / CeO2 nanocomposite abrasive with a double shell structure.

[0010] Furthermore, in step 1, the concentration of the sodium hydroxide solution is 10%.

[0011] Further, in step 1, the ratio of methyl methacrylate to deionized water is 10–30 g: 100–150 ml; the ratio of 3-(methacryloyloxy)propyltrimethoxysilane to methyl methacrylate is 1–4 g: 10–30 g; 20 ml of 2,2'-azobisisobutylamidine dihydrochloride aqueous solution with a concentration of 50–200 g / L is added, and after reacting for 1.5–3 h, the mixture is cooled to obtain a uniformly dispersed PMMA microsphere emulsion.

[0012] Furthermore, in step 2, 10-60 ml of the PMMA microsphere emulsion prepared in step 1 is added to 50-100 ml of anhydrous ethanol and ultrasonically dispersed; 25 ml of solution C is added dropwise to solution B under continuous stirring; the constant temperature water bath is heated at 30-60℃, and the reaction time is 4-7 h.

[0013] Further, in step 3, 0.5–4 g of PMMA / SiO2 composite microspheres are added to 100–250 ml of deionized water and ultrasonically dispersed to obtain solution D; 1–5 g of soluble cerium salt is added to solution D, and then 2–10 g of hexamethylenetetramine is added to obtain solution E; the solution is heated in a constant temperature water bath at 60–85 °C and reacted for 2–4 h under continuous stirring.

[0014] Furthermore, in step 3, the soluble cerium salt is any one or a combination of cerium nitrate, cerium sulfate, and cerium chloride.

[0015] The beneficial effects of this invention are as follows: This invention discloses a method for preparing a double-shell abrasive with nano-PMMA as the core and coated with SiO2 / CeO2. The method includes the following steps: First, a soap-free emulsion polymerization method is used in a boiling system, with methyl methacrylate as the monomer and 3-(methacryloyloxy)propyltrimethoxysilane as the coupling agent. The polymerization reaction is initiated by 2,2'-azobisisobutylamidine dihydrochloride to prepare PMMA microspheres with controllable particle size and good monodispersity. Then, using tetraethyl silicate as the raw material, strawberry-shaped PMMA / SiO2 composite microspheres are prepared by sol-gel method. Finally, using soluble cerium salt as the raw material and hexamethylenetetramine as the precipitant, a uniform precipitation method is used to prepare a double-shell PMMA / SiO2 / CeO2 composite abrasive with nano-CeO2 particles uniformly coated.

[0016] The PMMA / SiO2 / CeO2 composite abrasive prepared by this invention exhibits excellent flexibility, chemical stability, and wear resistance. The PMMA core is malleable, with SiO2 and CeO2 layers covering it respectively. This core-shell structure effectively buffers external frictional forces. Silicon atoms in the SiO2 layer and oxygen atoms in the CeO2 layer form a stable interface structure through covalent bonds. During polishing, the CeO2 layer forms a lubricating film on the surface of the polished crystal, allowing for both mechanical and intermolecular interactions between the CeO2 layer and the crystal surface. This reduces direct friction between the PMMA / SiO2 / CeO2 composite abrasive and the crystal surface, thereby lowering the crystal surface roughness. Attached Figure Description

[0017] Figure 1 is a SEM image of the PMMA microspheres prepared in Example 1 of the present invention.

[0018] Figure 2 shows the infrared spectra of the PMMA microspheres, PMMA / SiO2 composite microspheres, and PMMA / SiO2 / CeO2 composite abrasives prepared in Example 1 of the present invention.

[0019] Figure 3 shows the XRD patterns of the PMMA / SiO2 composite microspheres and PMMA / SiO2 / CeO2 composite abrasives prepared in Example 1 of this invention.

[0020] Figure 4 is a TEM image of PMMA / SiO2 composite microspheres prepared by the present invention without MPS and with 2g of MPS.

[0021] Figure 5 is a SEM image of PMMA / SiO2 composite microspheres prepared under three different amounts of tetraethyl orthosilicate (TEOS) according to the present invention.

[0022] Figure 6 is a TEM image of the PMMA / SiO2 / CeO2 composite abrasive prepared under different amounts of cerium nitrate according to the present invention.

[0023] Figure 7 shows the AFM images of the PMMA / SiO2 / CeO2 composite abrasive prepared in Example 1 of this invention and the PMMA / CeO2 composite abrasive prepared in Comparative Experiment 1 after polishing a KDP crystal. Detailed Implementation

[0024] The technical solution of the present invention will be described in detail below through specific embodiments, but the content of the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0025] Example 1

[0026] A method for preparing a nano-PMMA-core coated SiO2 / CeO2 double-shell abrasive includes the following steps:

[0027] (1) Preparation of polymethyl methacrylate microspheres:

[0028] Measure 20g of methyl methacrylate and wash it with 10% sodium hydroxide. Add the washed methyl methacrylate to 120ml of deionized water and then add 2g of 3-(methacryloyloxy)propyltrimethoxysilane to prepare mixed solution A. Disperse mixed solution A by ultrasonication and heat it to boiling in a constant temperature oil bath. After 5min, add 20ml of 100g / L aqueous solution of 2,2'-azobisisobutylamidine dihydrochloride under stirring. After reacting for 2h, cool to obtain a uniformly dispersed PMMA microsphere emulsion.

[0029] (2) Preparation of PMMA / SiO2 composite microspheres:

[0030] Take 30 ml of the PMMA microsphere emulsion prepared in step 1 and add it to 80 ml of anhydrous ethanol for ultrasonic dispersion. Adjust the pH to 9 with ammonia to obtain solution B. Prepare a 120 g / L tetraethyl silicate anhydrous ethanol solution C, and then add 25 ml of solution C dropwise to solution B with continuous stirring. Heat in a constant temperature water bath at 35°C for 5 hours. Separate the final product using a centrifuge, wash repeatedly with deionized water and anhydrous ethanol, dry in a drying oven, and grind to obtain core-shell structured silica-coated polymethyl methacrylate nanocomposite microspheres.

[0031] (3) Preparation of PMMA / SiO2 / CeO2 composite abrasive:

[0032] 2g of PMMA / SiO2 composite microspheres were ultrasonically dispersed in 200ml of deionized water to obtain solution D. 3g of soluble cerium salt was added to solution D, followed by 6g of hexamethylenetetramine to obtain solution E. The mixture was heated in a constant-temperature water bath at 75℃ with continuous stirring for 3 hours. The final product was separated by centrifugation, repeatedly washed with deionized water and anhydrous ethanol, dried in a drying oven, and then ground to obtain a double-shell structured PMMA / SiO2 / CeO2 nanocomposite abrasive.

[0033] Figure 1 shows a SEM image of the PMMA microspheres prepared in Example 1 of this invention. As can be seen from the figure, the PMMA microspheres prepared in this embodiment exhibit good spherical shape, without aggregation or adhesion. The PMMA microspheres show good monodispersity, and the average particle size of the PMMA microspheres is approximately 295 nm.

[0034] Figure 2 shows the infrared spectra of the PMMA microspheres, PMMA / SiO2 composite microspheres, and PMMA / SiO2 / CeO2 composite abrasives prepared in Example 1 of this invention. As can be seen from the figure, the FTIR curve of the PMMA microspheres prepared in this embodiment of the invention is at 1730.84 cm⁻¹. -1 The strong absorption peak at 2994.9 cm⁻¹ belongs to the stretching vibration peak of C=O. -1 and 2951cm -1 The characteristic peaks at 1246.7 cm⁻¹ and 1150.4 cm⁻¹ are the stretching vibration peaks of -CH₃ and -CH₂-, respectively, while the characteristic peaks at 1246.7 cm⁻¹ and 1150.4 cm⁻¹ are the stretching vibration peaks of COC. Furthermore, a stretching vibration peak of C=C in MPS also appears at 1637.4 cm⁻¹. For the FTIR curve of PMMA / SiO₂ composite microspheres, the peak intensity increases near 1149.52 cm⁻¹, which is caused by the characteristic peak of Si-O-Si stretching vibration; symmetric and asymmetric stretching vibration peaks of Si-O bonds appear at 808.5 cm⁻¹ and 1093.9 cm⁻¹, respectively, indicating that a SiO₂ layer has grown on the surface of the PMMA microspheres. The PMMA / SiO₂ / CeO₂ composite abrasive exhibits a significant increase in intensity at 1026.4 cm⁻¹. -1 The characteristic peak at 699.3 cm⁻¹ is a characteristic peak of Ce-O. -1 The characteristic peak at this point is the asymmetric stretching vibration peak of Ce-O-Ce metal oxide in the crystal lattice, which further indicates that CeO2 grains are deposited on the surface of the abrasive.

[0035] Figure 3 shows the XRD patterns of the PMMA / SiO2 composite microspheres and PMMA / SiO2 / CeO2 composite abrasives prepared in Example 1 of this invention. As can be seen from the figure, the PMMA / SiO2 composite microspheres prepared in Example 1 of this invention have a broad, diffuse peak at 2θ = 13°, which is the strong amorphous diffraction peak of PMMA. A very broad "bun peak" can be seen near 2θ = 27°, which is caused by the overlap of the weak amorphous peak of PMMA and the amorphous diffraction peak of SiO2. The PMMA / SiO2 / CeO2 composite abrasive exhibits diffraction peaks at 2θ = 28.5°, 33.1°, 47.4° and 56.3°, 59.0°, 69.4°, the positions and relative intensities of which are consistent with the CeO2 standard card (JCPDS 34-0394). A weak SiO2 amorphous diffraction peak appears near 2θ = 21°, indicating that the CeO2 grain layer has completely covered the SiO2 particle layer, forming a PMMA / SiO2 / CeO2 double-layer core-shell structure.

[0036] Example 2

[0037] A method for preparing a nano-PMMA-core coated SiO2 / CeO2 double-shell abrasive includes the following steps:

[0038] (1) Preparation of polymethyl methacrylate microspheres:

[0039] Measure 10g of methyl methacrylate and wash it with 10% sodium hydroxide. Add the washed methyl methacrylate to 100ml of deionized water and then add 1g of 3-(methacryloyloxy)propyltrimethoxysilane to prepare mixed solution A. Disperse mixed solution A by ultrasonication and heat it to boiling in a constant temperature oil bath. After 5min, add 20ml of 50g / L aqueous solution of 2,2'-azobisisobutylamidine dihydrochloride under stirring. After reacting for 1.5h, cool to obtain a uniformly dispersed PMMA microsphere emulsion.

[0040] (2) Preparation of PMMA / SiO2 composite microspheres:

[0041] Take 10 ml of the PMMA microsphere emulsion prepared in step 1 and add it to 50 ml of anhydrous ethanol for ultrasonic dispersion. Adjust the pH to 8 with ammonia to obtain solution B. Prepare a 40 g / L tetraethyl silicate anhydrous ethanol solution C, and then add 25 ml of solution C dropwise to solution B with continuous stirring. Heat in a constant temperature water bath at 30°C for 4 hours. Separate the final product using a centrifuge, wash repeatedly with deionized water and anhydrous ethanol, dry in a drying oven, and grind to obtain core-shell structured silica-coated polymethyl methacrylate nanocomposite microspheres.

[0042] (3) Preparation of PMMA / SiO2 / CeO2 composite abrasive:

[0043] 0.5 g of PMMA / SiO2 composite microspheres were ultrasonically dispersed in 100 ml of deionized water to obtain solution D. 1 g of soluble cerium salt was added to solution D, followed by 2 g of hexamethylenetetramine to obtain solution E. The mixture was heated in a constant-temperature water bath at 60 °C with continuous stirring for 2 hours. The final product was separated by centrifugation, repeatedly washed with deionized water and anhydrous ethanol, dried in a drying oven, and then ground to obtain a double-shell structured PMMA / SiO2 / CeO2 nanocomposite abrasive.

[0044] Example 3

[0045] A method for preparing a nano-PMMA-core coated SiO2 / CeO2 double-shell abrasive includes the following steps:

[0046] (1) Preparation of polymethyl methacrylate microspheres:

[0047] Measure 30g of methyl methacrylate and wash it with 10% sodium hydroxide. Add the washed methyl methacrylate to 150ml of deionized water and then add 4g of 3-(methacryloyloxy)propyltrimethoxysilane to prepare mixed solution A. Disperse mixed solution A by ultrasonication and heat it to boiling in a constant temperature oil bath. After 5min, add 20ml of 200g / L 2,2'-azobisisobutylamidine dihydrochloride aqueous solution under stirring. After reacting for 3h, cool to obtain a uniformly dispersed PMMA microsphere emulsion.

[0048] (2) Preparation of PMMA / SiO2 composite microspheres:

[0049] Take 60 ml of the PMMA microsphere emulsion obtained in step 1 and add it to 100 ml of anhydrous ethanol for ultrasonic dispersion. Adjust the pH to 10 with ammonia to obtain solution B. Prepare a 200 g / L tetraethyl silicate anhydrous ethanol solution C, and then add 25 ml of solution C dropwise to solution B with continuous stirring. Heat in a constant temperature water bath at 60°C for 7 hours. Separate the final product using a centrifuge, wash repeatedly with deionized water and anhydrous ethanol, dry in a drying oven, and grind to obtain core-shell structured silica-coated polymethyl methacrylate nanocomposite microspheres.

[0050] (3) Preparation of PMMA / SiO2 / CeO2 composite abrasive:

[0051] 4g of PMMA / SiO2 composite microspheres were ultrasonically dispersed in 250ml of deionized water to obtain solution D. 5g of soluble cerium salt was added to solution D, followed by 10g of hexamethylenetetramine to obtain solution E. The mixture was heated in a constant-temperature water bath at 85℃ with continuous stirring for 4 hours. The final product was separated by centrifugation, repeatedly washed with deionized water and anhydrous ethanol, dried in a drying oven, and then ground to obtain a double-shell structured PMMA / SiO2 / CeO2 nanocomposite abrasive.

[0052] SEM analysis showed that the PMMA microspheres prepared by the method of the present invention have a particle size of 250-300 nm, the PMMA / SiO2 composite microspheres have a particle size of 260-330 nm, and the PMMA / SiO2 / CeO2 nanocomposite abrasive has a particle size of 280-365 nm.

[0053] Comparative Experiment 1

[0054] A method for preparing a nano-PMMA core-coated CeO2 shell abrasive includes the following steps:

[0055] (1) Preparation of polymethyl methacrylate microspheres:

[0056] Measure 20g of methyl methacrylate and wash it with 10% sodium hydroxide. Add the washed methyl methacrylate to 120ml of deionized water and then add 2g of 3-(methacryloyloxy)propyltrimethoxysilane to prepare mixed solution A. Disperse mixed solution A by ultrasonication and heat it to boiling in a constant temperature oil bath. After 5min, add 20ml of 100g / L aqueous solution of 2,2'-azobisisobutylamidine dihydrochloride under stirring. After reacting for 2h, cool to obtain a uniformly dispersed PMMA microsphere emulsion.

[0057] (2) Preparation of PMMA / CeO2 composite abrasive:

[0058] 20 ml of the PMMA microsphere emulsion prepared in step 1 was added to 200 ml of deionized water and ultrasonically dispersed to obtain solution D. 3 g of soluble cerium salt was added to solution D, followed by 6 g of hexamethylenetetramine to obtain solution E. The mixture was heated in a constant temperature water bath at 75°C and reacted for 3 hours with continuous stirring. The final product was separated by centrifugation, repeatedly washed with deionized water and anhydrous ethanol, dried in a drying oven, and then ground to obtain a double-shell structured PMMA / CeO2 nanocomposite abrasive.

[0059] Comparative Experiment 2

[0060] Based on Example 1, only the amount of 3-(methacryloyloxy)propyltrimethoxysilane (MPS) in step (1) was changed to study its effect on the abrasive of the present invention. Specifically, the amounts of MPS were 0g, 1g, 1.5g, 2g, 3g, and 4g, respectively. This experiment yielded a series of PMMA microspheres with different particle sizes, as shown in Table 1 below.

[0061] Table 1. Statistical table of the effect of different dosages of 3-(methacryloyloxy)propyltrimethoxysilane (MPS) on the particle size of PMMA microspheres.

[0062]

[0063] As shown in Table 1, the PMMA particle size decreased significantly after the addition of MPS. With increasing MPS dosage, the PMMA microsphere particle size continued to increase. When the MPS dosage reached 2g, the PMMA microsphere particle size stabilized at approximately 295nm.

[0064] Figure 4 shows TEM images of PMMA / SiO2 composite microspheres prepared by the present invention with and without the addition of 2g of MPS.

[0065] As shown in Figure 4(a), without the addition of MPS, the PMMA microspheres were not coated with a SiO2 layer. After the addition of MPS, SiO2 particles coated the surface of the PMMA microspheres and grew into a strawberry shape (as shown in Figure 4(b)). This is because there is a weak interaction between SiO2 and PMMA, and mechanical stirring easily disrupts this interaction. After the addition of MPS, the lipophilic alkyl group at one end can react with the hydroxyl groups on the PMMA surface, achieving anchoring, significantly improving the dispersibility of the PMMA microspheres, and promoting the uniform coating of SiO2 on the surface of the PMMA microspheres.

[0066] Comparative Experiment 3

[0067] Based on Example 1, only the concentration of the tetraethyl silicate ethanol solution in step (2) was changed to study its effect on the material of the present invention. Specifically, the concentrations of the tetraethyl silicate ethanol solution were 40, 120, and 200 g / L; this experiment yielded a series of PMMA / SiO2 composite microspheres with different SiO2 layer thicknesses.

[0068] Figure 5 shows SEM images of PMMA / SiO2 composite microspheres prepared under three different tetraethyl orthosilicate (TES) concentrations according to the present invention. As can be seen from the figures, when the TES concentration is 40 g / L, the number of SiO2 particles generated is relatively small, failing to form a complete coating layer on the surface of the PMMA microspheres (Figure 5(a)). When the TES concentration is 120 g / L, the number of SiO2 particles generated increases significantly, forming a complete SiO2 coating layer on the surface of the PMMA microspheres (Figure 5(b)). When the TES concentration is increased to 200 g / L, the SiO2 layer becomes thicker, and a large number of secondary nucleated SiO2 particles are generated (Figure 5(c)).

[0069] Comparative Experiment 4

[0070] Based on Example 1, only the amount of cerium nitrate in step (3) was changed to study its effect on the material of the present invention. Specifically, the amount of cerium nitrate was 1g and 6g, respectively. This experiment yielded different CeO2 layer thicknesses and formed PMMA / SiO2 / CeO2 composite abrasives.

[0071] Figure 6 shows TEM images of the PMMA / SiO2 / CeO2 composite abrasives prepared under different amounts of cerium nitrate according to the present invention. As can be seen from Figure 6, when the amount of cerium nitrate is 1g, Ce... 3+ The number of nuclei is relatively small, and they cannot completely cover the surface of the PMMA / SiO2 composite microspheres (as shown in Figure 6(a)). When the amount of cerium nitrate is 6g, Ce... 3+ The number of nuclei increased significantly, and they were electrostatically adsorbed onto the surface of PMMA / SiO2 composite microspheres, eventually forming a complete CeO2 layer (as shown in Figure 6(b)).

[0072] Comparative Experiment 5

[0073] The polishing performance of the PMMA / SiO2 / CeO2 composite abrasive prepared in Example 1 and the PMMA / CeO2 composite abrasive prepared in Comparative Experiment 1 was compared. The specific methods are as follows:

[0074] The composite abrasives obtained in Examples 1 and 4 were prepared into a 1w% polishing slurry using anhydrous ethanol and ultrasonically dispersed for 10 minutes.

[0075] (2) Apply a polishing pressure of 21.43 kPa, set the polishing disc speed to 150 r / min and the polishing slurry flow rate to 100 ml / min, and polish the KDP crystal surface for 10 min each time.

[0076] (3) The surface smoothness of the polished crystal was examined using an atomic force microscope (AFM). The mass loss of the crystal after polishing was recorded. The polishing was repeated 4 times, and the average mass loss of the crystal over the 4 times was calculated to derive the removal rate of KDP crystal material.

[0077] Polishing with the composite abrasive prepared in Example 1 resulted in a surface roughness Ra of 0.46 nm for the KDP crystal within the same range (as shown in Figure 7(b)), with a material removal rate of 187 nm / min. Polishing with the composite abrasive prepared in Comparative Experiment 1 resulted in a surface roughness Ra of 0.55 nm for the KDP crystal within a 5 μm × 5 μm range (as shown in Figure 7(a)), with a material removal rate of 148 nm / min. Comparative analysis shows that the nano-PMMA core-coated SiO2 / CeO2 double-shell abrasive prepared in this invention achieves higher polishing efficiency while maintaining surface smoothness.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a nano-PMMA-core coated SiO2 / CeO2 double-shell abrasive, characterized in that, The process includes the following steps: Step 1: Preparation of PMMA microspheres using soap-free emulsion polymerization: Methyl methacrylate is washed with sodium hydroxide solution, and the washed methyl methacrylate is added to deionized water. Then, 3-(methacryloyloxy)propyltrimethoxysilane is added to prepare mixed solution A. Mixed solution A is ultrasonically dispersed and heated to boiling in a constant temperature oil bath. Under stirring conditions, an aqueous solution of 2,2'-azobisisobutylamidine dihydrochloride is added for reaction. After the reaction is completed, the mixture is cooled to obtain a uniformly dispersed PMMA microsphere emulsion. In Step 1, the ratio of methyl methacrylate to deionized water is 10~30g:100~150ml; the ratio of 3-(methacryloyloxy)propyltrimethoxysilane to methyl methacrylate is 1~4g:10~30g; 20ml of an aqueous solution of 2,2'-azobisisobutylamidine dihydrochloride with a concentration of 50~200g / L is added, and the reaction is carried out for 1.5~3 minutes. After h, cooling yields a uniformly dispersed PMMA microsphere emulsion; Step 2: Preparation of PMMA / SiO2 nanocomposite microspheres by sol-gel method: The PMMA microsphere emulsion obtained in Step 1 is added to anhydrous ethanol and ultrasonically dispersed. Ammonia is added to adjust the pH to 8-10 to obtain solution B; a 40-200 g / L tetraethyl silicate anhydrous ethanol solution C is prepared, and solution C is added dropwise to solution B under continuous stirring. The reaction is carried out using a constant temperature water bath; the final product is centrifuged and washed repeatedly with deionized water and anhydrous ethanol, then dried and ground to obtain core-shell structured silica-coated polymethyl methacrylate nanocomposite microspheres; In Step 2, 10-60 ml of the PMMA microsphere emulsion obtained in Step 1 is added to 50-100 ml of anhydrous ethanol and ultrasonically dispersed; 25 ml of solution C is added dropwise to solution B under continuous stirring; the constant temperature water bath heating temperature is 30-60 °C. The reaction time was 4-7 h. Step 3: Preparation of PMMA / SiO2 / CeO2 composite abrasive by uniform precipitation method: The silica-coated polymethyl methacrylate nanocomposite microspheres prepared in step 2 were added to deionized water and ultrasonically dispersed to obtain solution D; cerium nitrate was added to solution D, and then hexamethylenetetramine was added to obtain solution E. The reaction was carried out under constant temperature water bath heating and continuous stirring. The final product was centrifuged and washed repeatedly with deionized water and anhydrous ethanol, then dried and ground to obtain PMMA / SiO2 / CeO2 nanocomposite abrasive with a double shell structure. In step 3, 0.5-4 g of PMMA / SiO2 composite microspheres were added to 100-250 ml of deionized water and ultrasonically dispersed to obtain solution D; 1-5 g of cerium nitrate was added to solution D, and then 2-10 g of hexamethylenetetramine was added to obtain solution E; the reaction was carried out under constant temperature water bath heating at a temperature of 60-85 ℃ and continuous stirring for 2-4 h.

2. The method for preparing nano-PMMA as a core-coated SiO2 / CeO2 double-shell abrasive according to claim 1, characterized in that, In step 1, the concentration of the sodium hydroxide solution is 10%.

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