Preparation method of sodium-free green cerium dioxide polishing powder

Abstract

The invention discloses a sodium-free green cerium dioxide polishing powder preparation method, which comprises: 1, adding tannic acid to a soluble cerium salt solution to obtain a mixed solution, and dropwise adding an ammonium carbonate solution to the mixed solution to obtain a precursor suspension; step 2, carrying out hydrothermal reaction on the precursor suspension, centrifuging and washing to obtain precursor powder; and 3, calcining the precursor powder to obtain the sodium-free cerium dioxide polishing powder. According to the preparation method, soluble cerium salt, ammonium carbonate and tannic acid are adopted as raw materials, nucleation and growth of Ce < 3 + > are regulated and controlled through tannic acid in the preparation process, particle aggregation is inhibited, and the sodium-free cerium dioxide polishing powder which is uniform in particle size and high in dispersity is prepared after hydrothermal reaction and calcination. The polishing powder is suitable for the fields of optical lenses, semiconductors and the like.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and green manufacturing technology, and in particular relates to a method for preparing sodium-free green cerium dioxide polishing powder. Background Technology

[0002] In existing technologies, the preparation of CeO2 polishing powder commonly uses NaOH as a precipitant, precipitating and crystallizing cerium ions to form CeO2 through liquid-phase precipitation or hydrothermal methods. However, NaOH is highly corrosive, posing not only operational safety hazards during use but also generating large amounts of high-sodium-containing wastewater with high treatment costs, making it difficult to meet the requirements of green manufacturing and sustainable development. Furthermore, residual Na in the product... + Ions are difficult to remove completely and can easily cause surface corrosion or residual contamination of high-end substrates such as semiconductor silicon wafers and optical glass during precision polishing, which seriously affects device performance and yield.

[0003] To improve particle dispersibility, existing processes often add synthetic polymers such as polyvinylpyrrolidone (PVP) as dispersants. However, PVP is difficult to biodegrade, increasing the environmental burden and easily forming carbon residues during calcination, affecting the purity and surface activity of CeO2. Simultaneously, due to the lack of effective control over nucleation and growth processes, the resulting CeO2 particles are prone to agglomeration and have a wide particle size distribution, leading to poor polishing slurry stability and uneven polishing rates, making it difficult to meet the stringent requirements of high-end CMP (chemical mechanical polishing) for ultra-smooth, scratch-free surfaces.

[0004] Although some studies have attempted to replace NaOH with weak bases such as ammonia and urea, or to use organic acids such as citric acid to control particle size, problems such as insufficient alkalinity, incomplete precipitation, and poor particle size control still exist, failing to meet the requirements of both green synthesis and the preparation of high-performance polishing powder. Currently, there is a lack of a green CeO2 preparation process that can completely avoid the use of strong bases and synthetic polymers, while achieving high dispersion, no sodium residue, and suitability for high-end polishing. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing sodium-free green cerium dioxide polishing powder. This preparation method uses soluble cerium salt, ammonium carbonate, and tannic acid as raw materials, and regulates the Ce content during the preparation process using tannic acid. 3+ By inhibiting the nucleation and growth of cerium dioxide particles and suppressing particle aggregation, a sodium-free cerium dioxide polishing powder with uniform particle size was prepared through hydrothermal reaction and calcination, thus solving the problem that cerium dioxide polishing powder could not simultaneously achieve green synthesis and high performance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing sodium-free green cerium dioxide polishing powder, characterized in that the preparation method includes the following steps: Step 1: Add tannic acid to a soluble cerium salt solution to obtain a mixed solution, and then add ammonium carbonate solution dropwise to the mixed solution to obtain a precursor suspension; Step 2: The precursor suspension obtained in Step 1 is subjected to a hydrothermal reaction, and after centrifugation and washing, the precursor powder is obtained. Step 3: Calcining the precursor powder obtained in Step 2 to obtain sodium-free cerium dioxide polishing powder.

[0007] This invention utilizes ammonium carbonate as a green alkali source, completely replacing the strong alkali NaOH used in traditional preparation. In a hydrothermal reaction, it reacts with soluble cerium salts to generate a suspension of basic cerium carbonate precursors. Furthermore, it introduces tannic acid, a natural polyphenol, as a stabilizer and reducing agent to regulate the Ce content. 3+ The nucleation and growth process reduces the nucleation rate and makes the growth more uniform, laying the foundation for the formation of uniform particles in the subsequent hydrothermal process: (1) Multiple phenolic hydroxyl groups and carboxyl groups in tannic acid molecules react with Ce 3+ Formation of soluble complexes, delaying the release of free Ce 3+ (1) The concentration increases rapidly, avoiding explosive nucleation; (2) It has steric hindrance, and tannic acid molecules are adsorbed on the surface of the primary crystal nucleus, inhibiting the rapid growth and aggregation of particles; (3) The phenolic hydroxyl groups of tannic acid molecules are partially oxidized by oxygen to quinone structure, and at the same time, electrons are transferred to Ce. 4+ , restored to Ce 3+ It can regulate the redox environment, affect the precursor composition, and enhance the chemical activity of CeO2 chemical mechanical polishing.

[0008] During the hydrothermal reaction, the basic cerium carbonate precursor gradually dehydrates and oxidizes, transforming into primary CeO2 nanocrystals (approximately 10 nm to 20 nm in diameter). Due to the partial carbonization or decomposition of tannic acid at high temperatures, some functional groups remain adsorbed on the CeO2 surface. The moderate steric hindrance effect of tannic acid allows the nanocrystals to aggregate controllably under van der Waals forces or electrostatic interactions, rather than being completely dispersed or severely agglomerated. Simultaneously, the primary particles self-assemble into spherical secondary particles (approximately 300 nm to 500 nm in diameter) through non-random, low-energy orientation aggregation. This structure possesses internal porosity and surface roughness, unlike the dense, solid spheres directly generated by the NaOH method. Furthermore, through CO3... 2- It can induce the formation of layered or flower-like basic carbonate precursors, and its inherent anisotropy is inherited by CeO2 during hydrothermal conversion, eventually forming clustered spherical particles.

[0009] The method for preparing sodium-free green cerium dioxide polishing powder described above is characterized in that the soluble cerium salt in step one is one of cerium nitrate hexahydrate, cerium acetate, and cerium citrate.

[0010] The above-mentioned method for preparing sodium-free green cerium dioxide polishing powder is characterized in that the Ce in the mixed solution described in step one is... 3+ The concentration is 0.05 mol / L to 0.2 mol / L, and the ammonium carbonate reacts with Ce. 3+ The molar ratio is 2:1 to 4:1.

[0011] This invention controls Ce 3+ Concentration, avoid Ce 3+ Too low a concentration leads to slow nucleation rate and low yield, avoiding Ce 3+ Excessive concentration can lead to explosive nucleation, wide particle size distribution, and severe aggregation; by controlling the concentration of ammonium carbonate and Ce... 3+ The molar ratio should be adjusted to avoid incomplete precipitation due to an excessively low molar ratio, resulting in residual Ce in the solution. 3+ The yield decreased, so it's important to avoid an excessively high molar ratio that could lead to an excess of NH4+. 4+ and CO3 2- The process of heating up can cause particles to burst or structures to collapse.

[0012] The method for preparing sodium-free green cerium dioxide polishing powder described above is characterized in that the amount of tannic acid added in step one is 0.5% to 2.0% of the theoretical yield of sodium-free cerium dioxide polishing powder in step four.

[0013] This invention directly affects the dispersibility, morphology, purity, and polishing performance of CeO2 polishing powder by controlling the amount of tannic acid added. If the amount added is too low, the stability is insufficient, and it cannot be effectively adsorbed onto CeO2. 3+ Or on the surface of nascent crystal nuclei, leading to uncontrolled nucleation and easily causing uneven morphology and particle agglomeration; excessive addition: over-complexation of Ce. 3+ This could lead to an excessively slow reaction rate or even incomplete precipitation, and increase the risk of carbon residue.

[0014] The method for preparing sodium-free green cerium dioxide polishing powder described above is characterized in that the pH of the precursor suspension in step one is 7.5~8.5.

[0015] The method for preparing sodium-free green cerium dioxide polishing powder described above is characterized in that the temperature of the hydrothermal reaction in step two is 140℃~180℃, and the time of the hydrothermal reaction is 6h~24h.

[0016] The method for preparing the above-mentioned sodium-free green cerium dioxide polishing powder is characterized by calcining at 400℃~800℃ for 1h~4h in an air atmosphere.

[0017] Because the precursor generated by the ammonium carbonate system, Ce(OH)CO3 / Ce2(OH)6CO3, begins to dehydrate and decarbonize at 350℃~400℃ to form CeO2; if the temperature is below 400℃, the precursor is not completely converted into CeO2, and impurity phases are likely to appear; at the same time, by controlling the calcination temperature to not exceed 800℃, excessive grain growth is prevented.

[0018] The method for preparing sodium-free green cerium dioxide polishing powder described above is characterized in that the heating rate is 3℃ / min~5℃ / min.

[0019] The method for preparing sodium-free green cerium dioxide polishing powder described above is characterized in that the precursor powder is preheated before calcination, and the preheating temperature is below 300°C.

[0020] The method for preparing sodium-free green cerium dioxide polishing powder described above is characterized in that the precursor powder is dried before calcination in step three.

[0021] Compared with the prior art, the present invention has the following advantages: 1. This invention uses NaOH as a green alkali source to completely replace the strong alkali NaOH used in traditional preparation, achieving the preparation of a green precursor without strong alkali or sodium residue. At the same time, the introduction of tannic acid synergistically disperses the particles in the precursor suspension, thereby improving the dispersibility of sodium-free cerium dioxide polishing powder. Furthermore, the introduction of tannic acid can regulate the redox environment and enhance the chemical activity of CeO2 chemical mechanical polishing.

[0022] 2. The preparation method of the present invention does not use NaOH and synthetic polymer dispersants. All additives can be completely decomposed or volatilized during calcination, which effectively reduces the residue of impurities and obtains high-purity products. It is suitable for electronic-grade polishing of semiconductor silicon wafers and high-end CMP polishing of sapphire, optical glass and other materials.

[0023] 3. The preparation method of the present invention can produce clustered spherical particles by means of the synergistic effect of ammonium carbonate and tannic acid. Compared with traditional dense spherical particles, it significantly improves the surface roughness and specific surface area, thereby enhancing the mechanical force and chemical reactivity in the CMP process.

[0024] 4. The preparation method of the present invention has the advantages of being green and environmentally friendly, having a simple process, and being capable of large-scale production.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 The image shows the XRD pattern of the sodium-free cerium dioxide polishing powder in Example 1 of this invention.

[0027] Figure 2 This is a SEM image of the sodium-free cerium dioxide polishing powder in Example 1 of the present invention.

[0028] Figure 3 This is the EDS diagram of the sodium-free cerium dioxide polishing powder in Example 1 of the present invention.

[0029] Figure 4 The image shows the AFM image of K9 glass after polishing with the polishing slurry prepared by the sodium-free cerium dioxide polishing powder in Example 1 of this invention.

[0030] Figure 5 This is a SEM image of the rare earth polishing powder in Comparative Example 1 of the present invention.

[0031] Figure 6 This is a SEM image of the rare earth polishing powder in Comparative Example 2 of the present invention. Detailed Implementation

[0032] Example 1 The preparation method of this embodiment includes the following steps: Step 1: Add 5.208g of Ce(NO3)3·6H2O to 60mL of deionized water, then add 0.021g of tannic acid. Stir at 500rpm for 30min until fully dissolved to obtain a mixed solution. Dissolve 3.460g of (NH4)2CO3 in 60mL of deionized water. Stir at 500rpm for 30min until fully dissolved to obtain an ammonium carbonate solution. Slowly add the ammonium carbonate solution dropwise to the mixed solution, controlling the pH to 7.5~8.5, to obtain a precursor suspension. Step 2: Transfer the precursor suspension obtained in Step 1 to a 200mL reactor and perform a hydrothermal reaction at 160℃ for 12h. After alternating centrifugation and washing 5 times with deionized water and anhydrous ethanol as media, cerium oxide precursor powder is obtained. The washing is ultrasonic cleaning for 10min, and the centrifugation speed is 1000rpm for 3min. Step 3: Dry the cerium oxide precursor powder obtained in Step 2 at 60°C, then transfer it to a muffle furnace and heat it to 300°C at a rate of 3°C / min and hold for 1 hour. Then heat it to 600°C at a rate of 3°C / min and hold for 2 hours to obtain sodium-free cerium dioxide polishing powder.

[0033] In this embodiment, Ce(NO3)3·6H2O can also be replaced with cerium acetate or cerium citrate.

[0034] XRD analysis was performed on the sodium-free cerium dioxide polishing powder obtained in this embodiment, and the results are as follows: Figure 1As shown, the phase of this sodium-free cerium dioxide polishing powder is CeO2, consistent with the results of standard card PDF#34-0394; SEM analysis of this sodium-free cerium dioxide polishing powder, as shown... Figure 2 As shown, the sodium-free cerium dioxide polishing powder has a uniform particle size of approximately 400 nm and a clustered, spherical morphology without agglomeration. EDS analysis of the sodium-free cerium dioxide polishing powder revealed the following: Figure 3 As shown, only characteristic peaks of Ce and O were detected in the spectrum, with no impurity elements such as Na, Cl, and N detected. Semi-quantitative elemental analysis showed that the atomic ratio of Ce to O was close to 1:2, consistent with the stoichiometric ratio of CeO2. Surface scan results indicated that Ce and O were uniformly distributed, with no sodium-rich regions. In summary, the sodium-free cerium dioxide polishing powder prepared in this embodiment exhibits high purity and no sodium ion residue, thanks to the green synergistic system of ammonium carbonate and tannic acid, avoiding the use of NaOH in traditional processes.

[0035] A 3% (w / w) polishing slurry was prepared using the sodium-free cerium dioxide polishing powder prepared in this embodiment, and CMP performance tests were performed on K9 glass. The measured material removal rate (MRR) reached 543 nm / min, indicating that the sodium-free cerium dioxide polishing powder has excellent material removal capabilities. The surface roughness (Ra) of the polished glass was as low as 0.45 nm. Figure 4 As shown, the surface is smooth and flat, without scratches or fogging, approaching atomic-level smoothness. In summary, the sodium-free cerium dioxide polishing powder prepared in this embodiment not only has a high polishing rate, but also enables ultra-precision surface processing, meeting the stringent surface quality requirements of high-end fields such as optical lenses and semiconductors.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is that tannic acid was not added in step one.

[0037] The rare earth polishing powder obtained in this comparative example was analyzed by SEM, such as... Figure 5 As shown, the rare earth polishing powder particles are severely agglomerated, and the polishing solution prepared with a mass concentration of 3% has poor stability compared with Example 1; this indicates that the addition of tannic acid can effectively disperse the sodium-free cerium dioxide polishing powder and improve the stability of the polishing solution.

[0038] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: In step one, 5.208 g of Ce(NO3)3·6H2O was added to 120 mL of deionized water, and 2.604 g of polyvinylpyrrolidone (PVP) was added. The mixture was stirred at 500 rpm for 30 min until fully dissolved. Then, 20 μL of 1 mol / L NaOH solution was added, and a white flocculent precipitate was generated. The mixture was stirred at 500 rpm for 30 min until the precipitate disappeared, resulting in a precursor suspension.

[0039] The rare earth polishing powder obtained in this comparative example was analyzed by SEM, such as... Figure 6 As shown, the rare earth polishing powder has poor particle size uniformity, but its morphology is a smooth sphere with no agglomeration. Trace element analysis of the rare earth polishing powder was performed by ICP, and the results are shown in Table 1.

[0040] Table 1 ICP Test Results

[0041] As shown in Table 1, Na in rare earth polishing powder + The mass content is 0.06%, indicating that Na + Residues are unavoidable due to Na + It is easily adsorbed on the surface of CeO2 or enters lattice defects, and even after multiple water washes, it is difficult to reduce it to below 1 ppm. A 3% (w / w) polishing slurry was prepared using the rare earth polishing powder prepared in this comparative example and its CMP performance was tested on K9 glass. The measured surface removal rate (MRR) was 384 nm / min, significantly lower than that in Example 1. The lower MRR is mainly attributed to: firstly, although the CeO2 prepared by the NaOH method is smooth and spherical without obvious agglomeration, the particle size distribution is uneven, resulting in uneven polishing; secondly, ICP analysis showed that Na... + With a residue level as high as 0.06%, it may not only cause alkaline corrosion on the glass surface, but also affect the dispersion stability of particles in the polishing slurry and reduce the concentration of effective active components. In contrast, this invention uses the synergistic regulation of ammonium carbonate and tannic acid to prepare CeO2 powder with uniform particle size, good dispersibility, and no sodium residue. It has both high chemical activity and excellent mechanical action ability, thus exhibiting better overall polishing performance and having a significant advantage in improving polishing efficiency.

[0042] Example 2 The difference between this embodiment and Embodiment 1 is that: in step one, 2.604g of Ce(NO3)3·6H2O is added to 60mL of deionized water, and then 0.010g of tannic acid is added and fully dissolved and mixed; 1.730g of (NH4)2CO3 is dissolved in 60mL of deionized water and fully dissolved.

[0043] Upon inspection, the sodium-free cerium dioxide polishing powder obtained in this embodiment has uniform particle size and a clustered, spherical morphology without agglomeration. A polishing slurry with a mass concentration of 3% was prepared and subjected to CMP performance testing on K9 glass, and the measured MRR was 540 nm / min.

[0044] Example 3 The difference between this embodiment and Example 1 is that in step one, 10.422g of Ce(NO3)3·6H2O is added to 60mL of deionized water, and then 0.062g of tannic acid is added and fully dissolved and mixed; 6.920g of (NH4)2CO3 is dissolved in 60mL of deionized water and fully dissolved.

[0045] Upon inspection, the sodium-free cerium dioxide polishing powder of this embodiment has uniform particle size and a clustered, spherical morphology without agglomeration. A polishing slurry with a mass concentration of 3% was prepared and subjected to CMP performance testing on K9 glass, and the measured MRR was 545 nm / min.

[0046] Example 4 The preparation method of this embodiment includes the following steps: Step 1: Add 5.208g of Ce(NO3)3·6H2O to 60mL of deionized water, then add 0.021g of tannic acid. Stir at 500rpm for 30min until fully dissolved to obtain a mixed solution. Dissolve 2.307g of (NH4)2CO3 in 60mL of deionized water. Stir at 500rpm for 30min until fully dissolved to obtain an ammonium carbonate solution. Slowly add the ammonium carbonate solution dropwise to the mixed solution, controlling the pH to 7.5~8.5, to obtain a precursor suspension. Step 2: Transfer the precursor suspension obtained in Step 1 to a 200mL reactor and perform a hydrothermal reaction at 140℃ for 24h. After alternating centrifugation and washing with deionized water and anhydrous ethanol as media 6 times, cerium oxide precursor powder is obtained. The washing is ultrasonic cleaning for 10min, and the centrifugation speed is 1000rpm for 3min. Step 3: Dry the cerium oxide precursor powder obtained in Step 2 at 60°C, then transfer it to a muffle furnace and heat it to 300°C at a rate of 4°C / min and hold for 1 hour. Then heat it to 400°C at a rate of 4°C / min and hold for 4 hours to obtain sodium-free cerium dioxide polishing powder.

[0047] Upon inspection, the sodium-free cerium dioxide polishing powder of this embodiment has uniform particle size and a clustered, spherical morphology without agglomeration. A polishing slurry with a mass concentration of 3% was prepared and subjected to CMP performance testing on K9 glass, and the measured MRR was 493 nm / min.

[0048] Example 5 The preparation method of this embodiment includes the following steps: Step 1: Add 5.208g of Ce(NO3)3·6H2O to 60mL of deionized water, then add 0.021g of tannic acid. Stir at 500rpm for 30min until fully dissolved to obtain a mixed solution. Dissolve 4.613g of (NH4)2CO3 in 60mL of deionized water. Stir at 500rpm for 30min until fully dissolved to obtain an ammonium carbonate solution. Slowly add the ammonium carbonate solution dropwise to the mixed solution, controlling the pH to 7.5~8.5, to obtain a precursor suspension. Step 2: Transfer the precursor suspension obtained in Step 1 to a 200mL reactor and perform a hydrothermal reaction at 180℃ for 6 hours. After alternating centrifugation and washing with deionized water and anhydrous ethanol as media 5 times, cerium oxide precursor powder is obtained. The washing is ultrasonic cleaning for 10 minutes, and the centrifugation speed is 1000rpm for 3 minutes. Step 3: Dry the cerium oxide precursor powder obtained in Step 2 at 60°C, then transfer it to a muffle furnace and heat it to 300°C at a rate of 5°C / min and hold for 1 hour. Then heat it to 800°C at a rate of 5°C / min and hold for 1 hour to obtain sodium-free cerium dioxide polishing powder.

[0049] Upon inspection, the sodium-free cerium dioxide polishing powder of this embodiment has uniform particle size and a clustered, spherical morphology without agglomeration. A polishing slurry with a mass concentration of 3% was prepared and subjected to CMP performance testing on K9 glass, and the measured MRR was 560 nm / min.

[0050] Example 6 The difference between this embodiment and embodiment 5 is that in step one, Ce(NO3)3·6H2O is replaced with cerium acetate.

[0051] Upon inspection, the sodium-free cerium dioxide polishing powder of this embodiment has uniform particle size and a clustered, spherical morphology without agglomeration. A polishing slurry with a mass concentration of 3% was prepared and subjected to CMP performance testing on K9 glass, and the measured MRR was 554 nm / min.

[0052] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing sodium-free green cerium dioxide polishing powder, characterized in that, The preparation method includes the following steps: Step 1: Add tannic acid to a soluble cerium salt solution to obtain a mixed solution, and then add ammonium carbonate solution dropwise to the mixed solution to obtain a precursor suspension; Step 2: The precursor suspension obtained in Step 1 is subjected to a hydrothermal reaction, and after centrifugation and washing, the precursor powder is obtained. Step 3: Calcining the precursor powder obtained in Step 2 to obtain sodium-free cerium dioxide polishing powder.

2. The method for preparing a sodium-free green cerium dioxide polishing powder according to claim 1, characterized in that, The soluble cerium salt mentioned in step one is one of cerium nitrate hexahydrate, cerium acetate, and cerium citrate.

3. The method for preparing a sodium-free green cerium dioxide polishing powder according to claim 1, characterized in that, Ce in the mixed solution described in step one 3+ The concentration is 0.05 mol / L to 0.2 mol / L, and the ammonium carbonate reacts with Ce. 3+ The molar ratio is 2:1 to 4:

1.

4. The method for preparing a sodium-free green cerium dioxide polishing powder according to claim 1, characterized in that, The amount of tannic acid added in step one is 0.5% to 2.0% of the theoretical yield of the sodium-free cerium dioxide polishing powder in step four.

5. The method for preparing a sodium-free green cerium dioxide polishing powder according to claim 1, characterized in that, The pH of the precursor suspension mentioned in step one is 7.5~8.

5.

6. The method for preparing a sodium-free green cerium dioxide polishing powder according to claim 1, characterized in that, The hydrothermal reaction in step two is carried out at a temperature of 140℃ to 180℃ for 6 hours to 24 hours.

7. The method for preparing a sodium-free green cerium dioxide polishing powder according to claim 1, characterized in that, The calcination method described in step three is as follows: calcining at 400℃~800℃ for 1h~4h in an air atmosphere.

8. The method for preparing a sodium-free green cerium dioxide polishing powder according to claim 7, characterized in that, The heating rate is 3℃ / min to 5℃ / min.

9. The method for preparing a sodium-free green cerium dioxide polishing powder according to claim 7, characterized in that, The precursor powder is preheated before calcination, and the preheating temperature is below 300°C.

10. The method for preparing a sodium-free green cerium dioxide polishing powder according to claim 1, characterized in that, The precursor powder is dried before calcination, as described in step three.

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