A method for preparing zinc phosphate with a sheet-like structure

Abstract

This invention belongs to the field of materials preparation and discloses a method for preparing plate-like zinc phosphate, comprising the following steps: (1) adding an inducing agent to a phosphoric acid solution; (2) adding the mixed solution from step (1) to a zinc oxide slurry, stirring the mixture at 60-90°C, and filtering and drying the reaction product after the reaction to obtain plate-like zinc phosphate. This invention directly controls the growth morphology of plate-like crystals through an aqueous synthesis reaction, eliminating the need for ultrafine grinding, reducing process flow and equipment investment, lowering energy consumption per unit product, and meeting the requirements of green manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation, and particularly relates to a method for preparing sheet-like zinc phosphate. Background Technology

[0002] Ordinary zinc phosphate is an inorganic anti-rust pigment with a brick-shaped granular polymeric structure and a typical particle size range of 3-60 micrometers. It is used in inks, coatings, and pigments for corrosion protection of metal substrates. Through particle accumulation and filling, a coating of a certain thickness is formed. Within this coating, zinc phosphate particles ionize to release phosphate ions, which then undergo a complexation reaction with ions (such as iron ions) on the surface of the oxidized metal substrate, forming a dense chemical protective film (phosphating film). This inhibits substrate corrosion and protects the metal substrate.

[0003] In coating practice, the pigment particle size needs to be less than 25μm to ensure that the coating thickness is controlled within 20-40μm to balance cost and performance, and to avoid excessive coating thickness leading to increased raw material consumption and higher costs. To meet this particle size requirement, existing technologies generally use ultrafine grinding (mechanical grinding method) to reduce the size of ordinary zinc phosphate particles. Although this method can reduce particle size, it has the following serious problems: (1) High process complexity and increased energy consumption: Ultrafine grinding requires additional grinding processes (such as ball milling or air jet milling), which not only increases the production process, but also significantly increases the energy consumption per unit product, leading to increased production costs; (2) Particle quality defects: The grinding process leads to poor particle uniformity and wide particle size distribution, and destroys the integrity of the particles, producing particles with surface defects and sharp edges, which further reduces the purity of the product; (3) Decreased coating performance: When irregularly shaped particles accumulate in the coating, the porosity between particles increases, affecting the density of the coating. The pores become permeation channels, making it easy for moisture and harmful gases to penetrate and reach the surface of the metal substrate, resulting in a reduction in the protective function of the coating and accelerating the corrosion of the substrate; (4) Functional limitations: The existing brick-type particle structure relies on chemical ionization protection (phosphate ion complexation) and lacks a physical barrier mechanism, which limits its application in high-performance coating.

[0004] In summary, the current process of achieving small particle size for zinc phosphate through ultrafine grinding is inefficient and harmful, and cannot simultaneously ensure particle integrity, uniformity, and coating density, ultimately resulting in insufficient corrosion resistance and high costs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above and to provide a method for preparing zinc phosphate with a sheet-like structure.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A method for preparing sheet-like zinc phosphate includes the following steps: (1) Add an inducing agent to the phosphoric acid solution; (2) Add the mixed solution from step (1) to the zinc oxide slurry, stir the reaction at 60-90℃, and after the reaction is completed, filter and dry the reaction product to obtain zinc phosphate with a sheet structure.

[0008] In the above-described method for preparing sheet-like zinc phosphate, preferably, the inducing agent comprises a water-soluble polymer.

[0009] In the above-described method for preparing sheet-like zinc phosphate, preferably, the amount of the inducing agent added is 0.5%-5% of the mass of zinc oxide in the zinc oxide slurry. More preferably, the amount of the inducing agent added is 2%-5% of the mass of zinc oxide in the zinc oxide slurry.

[0010] In the above-mentioned method for preparing sheet-like zinc phosphate, preferably, the water-soluble polymer includes one or more of polyvinyl alcohol (PVA), polydimethylsiloxane (PDMS), polyethylene oxide (PEO), polyethylene glycol (PEG), or emulsifier OP-10.

[0011] In the above-mentioned method for preparing sheet-like zinc phosphate, preferably, the water-soluble polymer is polyvinyl alcohol and polyethylene glycol, and the mass ratio of polyvinyl alcohol to polyethylene glycol is 1:1-6; or, the water-soluble polymer is a mixture of polyvinyl alcohol and emulsifier OP-10.

[0012] In the above-mentioned method for preparing sheet-like zinc phosphate, preferably, in step (1), the mass concentration of the phosphoric acid solution is 10%-20%.

[0013] In the above-mentioned method for preparing zinc phosphate with a sheet-like structure, preferably, in step (2), the stirring speed is 500-800 r / min and the reaction temperature is 60-70℃.

[0014] In the preferred method for preparing the above-mentioned sheet-like zinc phosphate, in step (2), when the pH of the reaction system decreases to 5.0-4.5, the addition of the mixed solution from step (1) is stopped, and the mixture is kept warm and aged for 0.5-2 hours.

[0015] In the above-mentioned method for preparing sheet-like zinc phosphate, preferably, the sheet-like zinc phosphate is composed of zinc phosphate crystals with a length and width planar dimensions of 2-10 μm and a thickness of 200-500 nm.

[0016] In the above-mentioned method for preparing sheet-like zinc phosphate, preferably, the drying temperature is 180-220℃ and the drying time is 3-5 hours.

[0017] The inventors of this application, while researching how to improve the particle size of zinc phosphate, accidentally discovered that introducing water-soluble polymers (such as polyvinyl alcohol, polydimethylsiloxane, polyethylene oxide, and polyethylene glycol) during the preparation of zinc phosphate could yield a flake-like zinc phosphate. Based on this, the applicants continued their research and found that this flake-like zinc phosphate not only ionizes more easily and exerts chemical anti-corrosion effects, but more importantly, it is oriented and stacked in the coating (fish scale effect), forming a dense labyrinthine physical barrier that extends the penetration path of corrosive media (water vapor, acidic media, or gases) by 3–5 times, which can significantly improve the physical shielding performance of the coating.

[0018] The applicant hypothesizes the mechanism of this invention as follows: In the crystallization process of inorganic salts, uniform microcrystalline nuclei are first formed in a supersaturated solution. Ions in the solution diffuse to the surface of the nuclei and deposit, causing crystal growth. The growth rate of the crystal is related to the ion diffusion rate and the surface reaction rate. Changing the adsorption rate of ions on a specific surface of the nucleus can affect the growth direction of the crystal. Therefore, this invention introduces an inducing agent into the solution, which can promote the uniform dispersion of ions in the solution, making the formation of zinc phosphate nuclei more uniform; enhance the surface activity of the nuclei, and affect the adsorption capacity of a specific surface of the nucleus. Principle: The molecular chains of polymers contain a large number of -OH hydroxyl groups or -O ether bonds, which have strong polarity and adsorption capacity. Through hydrogen bonding or electrostatic interaction, they can combine with the surface of the zinc phosphate nucleus in the early stage of nucleus formation, adsorbing onto the high surface energy crystal face of zinc ions, reducing the surface energy of that crystal face, inhibiting the growth rate of that crystal face, and thus the growth rate of other crystal faces will be relatively faster, thereby forming a plate-like or layered crystal structure.

[0019] Due to zinc phosphate (Zn3(PO4)2 2H₂O has specific crystal structures (brick-shaped, columnar, granular, etc.). Different crystal facets expose different types and arrangements of atoms, leading to differences in polarity and surface energy among the facets. The highly polar crystal facets expose metal cations (Zn₂). 2+ ) or anion (PO4) 3- With more active sites, (-OH) or (-O) are typical polar groups with electrophilic or nucleophilic properties. These groups readily undergo hydrogen bonding or coordination with ions (such as zinc ions or phosphate ions) exposed on the highly polar crystal facets of zinc phosphate crystal nuclei, thereby selectively adsorbing onto specific crystal faces, reducing the surface energy of the adsorbed crystal facets, and creating steric hindrance to the continued aggregation of ions, thus inhibiting the growth rate of high surface energy crystal faces, leading to preferential and faster growth of other crystal faces.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention directly controls the growth morphology of plate-like crystals through aqueous synthesis reaction, eliminating the ultrafine grinding process, reducing process flow and equipment investment, reducing energy consumption per unit product, and meeting the requirements of green manufacturing.

[0021] (2) The preparation method of the present invention does not involve mechanical external force, which avoids impurity contamination and particle surface defects caused by crushing, maintains the natural integrity and purity of the product particles, and the particle size distribution is uniform, the surface is smooth and the morphology and structure are complete.

[0022] (3) The sheet-like zinc phosphate prepared by the present invention is not only easier to ionize and exert chemical anti-corrosion effect, but more importantly, it is oriented and stacked in the coating (fish scale effect) to form a dense labyrinth-like physical barrier, which extends the penetration path of corrosive media (water vapor, acidic media or gas) by 5-10 times and significantly improves the physical shielding performance of the coating. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 , Figure 2 This is a SEM image of the sheet-like zinc phosphate prepared in Example 1 of this invention.

[0025] Figures 3-4 This is a SEM image of the sheet-like zinc phosphate prepared in Example 2 of the present invention.

[0026] Figure 5 This is a SEM image of the sheet-like zinc phosphate prepared in Example 3 of this invention.

[0027] Figure 6 , Figure 7 This is a SEM image of zinc phosphate prepared in Comparative Example 1 of this invention.

[0028] Figure 8 , Figure 9 and Figure 10 This is a SEM image of zinc phosphate prepared in Comparative Example 2 of this invention. Detailed Implementation

[0029] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0031] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0032] Example 1: A method for preparing the sheet-like zinc phosphate structure of the present invention comprises the following specific steps: (1) Dilute 230g (2M) 85% phosphoric acid in 1000mL of deionized water, stir well, and prepare a phosphoric acid solution.

[0033] (2) PVA and PEG were dissolved in 35 mL of warm water at a ratio of 1:5 to prepare an inducing agent solution, wherein the total mass of PVA and PEG was 7.35 g; then the inducing agent solution was slowly added dropwise to the phosphoric acid solution under stirring to obtain a mixed solution.

[0034] (3) Add 244.8g of zinc oxide with a mass content of 99.7% (3M) to 1300mL of deionized water and stir and disperse it at a speed of 600r / min to make zinc oxide slurry.

[0035] (4) Add the mixed solution obtained in step (2) to the zinc oxide slurry in step (3), stir at 70°C (600 r / min) and react. When the pH of the reaction system drops to 4.6, it is determined to be the reaction endpoint. Stop adding the mixed solution in step (1) and continue to keep warm and age for 1 hour.

[0036] (5) The product obtained in step (4) is filtered, the filter cake is washed with deionized water, and then dried at 200°C for 4 hours to obtain zinc phosphate with a sheet-like structure.

[0037] The SEM image of the sheet-like zinc phosphate prepared in Example 1 is shown below. Figure 1 , Figure 2 As shown, Figure 1 The SEM images show the major and minor dimensions of zinc phosphate, that is, the long and wide planar morphology of this plate-like crystal, and the data on the scale mark the major and minor planar dimensions. Figure 2 This is another dimension of morphology under SEM electron microscopy – thickness. The scale data marks the crystal thickness dimensions.

[0038] The physicochemical properties of the sheet-like zinc phosphate prepared in this embodiment are shown in Table 1.

[0039] Table 1 Physicochemical properties of zinc phosphate with lamellar structure

[0040] Example 2: The difference between this embodiment and embodiment 1 is that step (2) is different. In this embodiment, step (2) is to add PVA and PEG to 50mL of warm water in a ratio of 1:3 to prepare an inducing agent solution, wherein the total mass of PVA and PEG is 9.8g; then the inducing agent solution is slowly added dropwise to the phosphoric acid solution under stirring to obtain a mixed solution; other processes and parameters are consistent with those in embodiment 1.

[0041] The SEM image of the sheet-like zinc phosphate prepared in this embodiment is shown below. Figure 3 , 4 As shown.

[0042] The physicochemical properties of the sheet-like zinc phosphate prepared in this embodiment are shown in Table 2.

[0043] Table 2 Physicochemical properties of zinc phosphate with plate-like structure

[0044] Example 3: The difference between this embodiment and embodiment 1 is that the inducing agent in step (2) is different. In this embodiment, PVA+OP-10 is used as the inducing agent. In step (2) of this embodiment, 5g of PVA and OP-10 are taken and mixed and diluted in 50ml of warm water in a 1:1 ratio. After cooling to room temperature, the mixture is slowly added to the zinc oxide slurry. Other conditions remain unchanged, and other processes and parameters are consistent with those in embodiment 1. The obtained zinc phosphate sample has a sheet-like structure.

[0045] The SEM image of the sheet-like zinc phosphate prepared in this embodiment is shown below. Figure 5 As shown.

[0046] The physicochemical properties of the sheet-like zinc phosphate prepared in this embodiment are shown in Table 3.

[0047] Table 3 Physicochemical properties of zinc phosphate with lamellar structure

[0048] Comparative Example 1: This comparative example uses zinc phosphate sample synthesized directly added dropwise to zinc oxide slurry without an inducing agent. The difference between this preparation method and Example 1 is that step (2) in Example 1 is omitted. The specific process steps are as follows: (1) Dilute 230g (2M) 85% phosphoric acid in 1000mL of deionized water, stir well, and prepare a phosphoric acid solution.

[0049] (2) Add 244.8g of zinc oxide with a mass content of 99.7% (3M) to 1300mL of deionized water and stir and disperse it at a speed of 600r / min to make zinc oxide slurry.

[0050] (3) Add the phosphoric acid solution from step (1) to the zinc oxide slurry from step (2), stir at 70°C (600 r / min), and when the pH of the reaction system drops to 4.6, the reaction is considered to be at its endpoint. Stop adding the mixed solution from step (1) and continue to keep warm for 1 hour.

[0051] (4) The product obtained in step (3) is filtered, the filter cake is washed with deionized water, and then dried at 200°C for 4 hours to obtain zinc phosphate with a sheet-like structure.

[0052] The SEM image of the zinc phosphate prepared in this comparative example is shown below. Figure 6 , Figure 7 As shown, the SEM image in Figure 6 displays the overall size of zinc phosphate, with the scale bar indicating the particle size. Figure 7 shows the morphological characteristics of the particles under an SEM microscope, revealing them as irregular and non-uniform particles of varying sizes, with the scale bar indicating the crystal size.

[0053] The zinc phosphate samples prepared in this comparative example have large differences in particle size, wide particle size distribution, and are irregular particles. Their physicochemical properties are shown in Table 4.

[0054] Table 4 Physicochemical properties of zinc phosphate

[0055] Comparative Example 2: This comparative example involves adding the synthesized zinc phosphate sample directly to the phosphoric acid solution using zinc oxide slurry without an inducing agent. The specific steps are as follows: (1) Dilute 230g (2M) 85% phosphoric acid in 1000mL of deionized water, stir well, and prepare a phosphoric acid solution.

[0056] (2) Add 244.8g of zinc oxide with a mass content of 99.7% (3M) to 1300mL of deionized water and stir and disperse it at a speed of 600r / min to make zinc oxide slurry.

[0057] (3) Slowly add the zinc oxide slurry from step (2) to the phosphoric acid solution from step (1), stir at 70°C (600 r / min), and when the pH of the reaction system drops to 4.6, the reaction is considered to be at its endpoint. Stop adding zinc oxide slurry and continue to keep warm for 1 hour.

[0058] (4) The product obtained in step (3) is filtered, the filter cake is washed with deionized water, and then dried at 200°C for 4 hours to obtain zinc phosphate with a sheet-like structure.

[0059] The SEM image of the zinc phosphate prepared in this comparative example is shown below. Figure 8 , Figure 9 , Figure 10 As shown, images 8 and 10 are SEM images displaying the overall size of zinc phosphate, with the scale bar indicating the particle size. Image 9 shows the morphological characteristics of the particles under an SEM microscope, revealing them as irregular and non-uniform particles of varying sizes, with the scale bar indicating the crystal size.

[0060] The zinc phosphate samples prepared in this comparative example have large differences in particle size, wide particle size distribution, and are irregular particles. Their physicochemical properties are shown in Table 5.

[0061] Table 5 Physicochemical properties of zinc phosphate

Claims

1. A method for preparing zinc phosphate with a sheet-like structure, characterized in that, Includes the following steps: (1) Add an inducing agent to the phosphoric acid solution; (2) Add the mixed solution from step (1) to the zinc oxide slurry, stir the reaction at 60-90℃, and after the reaction is completed, filter and dry the reaction product to obtain zinc phosphate with a sheet structure.

2. The method for preparing sheet-like zinc phosphate as described in claim 1, characterized in that, The inducing agent includes a water-soluble polymer.

3. The method for preparing sheet-like zinc phosphate as described in claim 2, characterized in that, The water-soluble polymer includes one or more of polyvinyl alcohol (PVA), polydimethylsiloxane (PDMS), polyethylene oxide (PEO), polyethylene glycol (PEG), and emulsifier OP-10.

4. The method for preparing sheet-like zinc phosphate as described in claim 2, characterized in that, The water-soluble polymer is polyvinyl alcohol and polyethylene glycol, wherein the mass ratio of polyvinyl alcohol to polyethylene glycol is 1:1-6; or, the water-soluble polymer is a mixture of polyvinyl alcohol and emulsifier OP-10.

5. The method for preparing the sheet-like zinc phosphate as described in claim 1, characterized in that, In step (1), the mass concentration of the phosphoric acid solution is 10%-20%.

6. The method for preparing the sheet-like zinc phosphate as described in claim 1, characterized in that, The amount of the inducing agent added is 0.5%-5% of the mass of zinc oxide in the zinc oxide slurry.

7. The method for preparing sheet-like zinc phosphate as described in claim 1, characterized in that, In step (2), the stirring speed is 500-800 r / min and the reaction temperature is 60-70℃.

8. The method for preparing sheet-like zinc phosphate as described in claim 1, characterized in that, In step (2), when the pH of the reaction system drops to 5.0-4.5, stop adding the mixed solution from step (1) and continue to keep it warm for aging for 0.5-2 hours.

9. The method for preparing the sheet-like zinc phosphate as described in claim 1, characterized in that, The sheet-like zinc phosphate is composed of zinc phosphate crystals with a length and width planar dimensions of 2-10 μm and a thickness of 200-500 nm.

10. The method for preparing the sheet-like zinc phosphate as described in claim 1, characterized in that, The drying temperature is 180-220℃, and the drying time is 3-5 hours.

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