Stainless steel passivation solution and preparation method thereof

Abstract

The invention belongs to the technical field of stainless steel surface treatment, and particularly relates to a stainless steel passivation solution and a preparation method thereof. The water-based cutting fluid is prepared from the following raw materials: cerium salt, copper sulfate, citric acid, sodium dihydrogen phosphate, ammonium molybdate, sodium tungstate, aminated-silane modified SiO2 nanoparticles, polyethylene glycol, L-ascorbic acid, polyaspartic acid, an anti-settling agent, a surfactant and the balance of deionized water. According to the invention, a three-dimensional network skeleton is constructed by using aminated-epoxy group silane modified SiO2 nanoparticles, so that the problem of weak interface bonding force of a traditional passivation layer is solved; according to the formula, the proportion of biodegradable components such as citric acid and polyaspartic acid is extremely high, cerate adopts a low-toxicity rare earth compound, molybdenum / tungsten elements are fixed in a stable oxide form, the dosage of EDTA is remarkably reduced through a compounding technology, residual ions are adsorbed in combination with a three-dimensional network, and the balance of environment friendliness and long-acting corrosion resistance is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel surface treatment, and particularly relates to a stainless steel passivation solution and a preparation method thereof. Background Art

[0002] Stainless steel has become a core material in the fields of aerospace, biomedicine, food processing and chemical equipment due to its excellent corrosion resistance, mechanical strength and surface finish. However, its corrosion resistance essentially depends on the nano-scale chromium oxide (Cr2O3) passivation film naturally formed on the surface. During mechanical processing (such as cutting, welding, polishing) or service, this passivation film is easily damaged and causes multiple risks: the residual free iron (Fe) and carbon (C) particles form a micro-battery effect, inducing local electrochemical corrosion; high temperature processing leads to chromium carbide (Cr X C) precipitation, resulting in chromium-poor areas and weakening the continuity of the passivation film; while pollutants such as grease and oxides attached to the surface will accelerate the chloride ion (Cl ⁻ ) penetration, aggravating pitting and stress corrosion cracking (SCC). Although traditional physical rust prevention technologies (such as coating rust-proof oil and spray painting) can block corrosive media in the short term, they have defects such as volatile organic compound (VOCs) pollution, easy peeling of the film layer and affecting the conductivity of the material. Therefore, chemical passivation treatment uses acidic media (such as nitric acid and citric acid) to dissolve surface pollutants and activate the matrix, and promotes the selective oxidation of chromium with the help of oxidants (molybdates and persulfates), and forms a dense Cr2O3 / Fe3O4 composite oxide film in situ on the metal surface. At the same time, silica sol or rare earth salts (such as Ce 3+ ) Close the micropores and block the corrosive media (O2, H2O, Cl ⁻ ) diffusion path, thereby achieving long-term corrosion protection, zero substrate size loss and food-grade cleanliness requirements. However, traditional passivation solutions represented by the nitric acid-hydrofluoric acid (HNO3-HF) system still have significant technical bottlenecks. For example, the severe toxicity of hydrofluoric acid and the NOx gas volatilized by nitric acid will endanger operational safety, and the cost of treating fluorine-containing wastewater is relatively high; in addition, it is easy to cause over-corrosion to materials such as duplex steel, resulting in increased surface roughness, and the passivation film's resistance to marine environment corrosion is also extremely poor. Therefore, based on the above problems, it is extremely necessary to develop a safe, environmentally friendly, and corrosion-resistant stainless steel passivation solution. Summary of the invention

[0003] In view of the defects of the prior art, the present invention aims to provide a stainless steel passivation solution and a preparation method thereof. The present invention adopts amination-epoxy group silane to modify SiO2 nanoparticles to construct a three-dimensional network skeleton, and the surface amino groups thereof react with Ce in cerium salt. 3+The coordination-anchored metal active sites form passivation nuclei. Meanwhile, the epoxy groups form covalent bonds with the substrate hydroxyl groups through ring-opening reactions, solving the problem of weak interfacial binding force of traditional passivation layers. Then, a hydrogen bond cross-linking network is constructed with sodium carboxymethylcellulose to strengthen the adhesion. The amino-functionalized SiO2 network combines physical and chemical dual-mode adsorption of iron ions, and cooperates with polyaspartic acid to achieve efficient capture of metal ions, solving the contradiction between heavy metal leakage and environmental protection of traditional passivation solutions. In the formula of the present invention, biodegradable components such as citric acid and polyaspartic acid account for a very high proportion. Moreover, the cerium salt uses a low-toxic rare earth compound, and the molybdenum / tungsten elements are fixed in the form of stable oxides. The dosage of EDTA is significantly reduced through compounding technology, and the residual ions are adsorbed by the three-dimensional network, achieving a balance between environmental friendliness and long-term anti-corrosion performance.

[0004] The technical effects described in the present invention are achieved through the following technical solutions: A stainless steel passivation solution, the composition of which includes the following raw materials by mass percentage: 0.2-0.5% cerium salt, 0.1-0.3% copper sulfate, 2-3% citric acid, 0.4-0.6% sodium dihydrogen phosphate, 0.3-0.6% ammonium molybdate, 0.2-0.5% sodium tungstate, 1.2-2% amino-functionalized silane-modified SiO2 nanoparticles, 0.5-1% polyethylene glycol, 0.8-1.5% L-ascorbic acid, 0.8-1.2% polyaspartic acid, 1.2-1.5% anti-settling agent, and 0.1-0.3% surfactant, with the balance being deionized water.

[0005] Preferably, the cerium salt is any one of cerium nitrate, cerium sulfate, and cerium chloride. Further, preferably, it is cerium nitrate; Preferably, the anti-settling agent is sodium carboxymethylcellulose; Preferably, the surfactant is disodium ethylenediaminetetraacetate; Preferably, the specific preparation steps of the amino-functionalized silane-modified SiO2 nanoparticles are as follows: S1: Add SiO2 nanoparticles to absolute ethanol, ultrasonically disperse them evenly, centrifuge, filter, and vacuum dry at 120°C for 2-3 h to obtain activated SiO2; S2: Add the activated SiO2 prepared in step S1 to a 95 wt% ethanol solution, ultrasonically disperse it evenly, and then slowly dropwise add γ-aminopropyltriethoxysilane at a rate of 0.5-1 mL / min. Adjust the pH to 4.8-5.5 with glacial acetic acid, heat to 60-65°C and react for 3-4 h, centrifuge, filter, wash repeatedly 3 times with 75 wt% ethanol, and vacuum dry at 60°C for 6-12 h to obtain amino-functionalized SiO2; S3: Add the amino-functionalized SiO₂ prepared in step S2 into a 90 wt% ethanol solution, ultrasonically disperse it evenly, add triethylamine, and then slowly dropwise add γ-glycidoxypropyltrimethoxysilane at a rate of 0.1 - 0.2 mL / min. Stir and react at 45 - 50 °C for 5 - 6 h, centrifuge, and repeatedly wash with acetone and ethanol three times. Dry in vacuum at 40 °C for 12 - 16 h to obtain amino-functionalized-silane modified SiO₂ nanoparticles; Preferably, in step S1, the dosage ratio of the SiO₂ nanoparticles to anhydrous ethanol is 1 g:50 mL; Preferably, in step S2, the dosage ratio of the activated SiO₂, ethanol solution, and γ-aminopropyltriethoxysilane is 1 g:200 mL:0.3 - 0.5 mL; Preferably, in step S3, the dosage ratio of the amino-functionalized SiO₂, ethanol solution, and γ-glycidoxypropyltrimethoxysilane is 1 g:100 - 150 mL:0.8 - 1 mL; the addition of triethylamine is 2 - 4% of the volume of the added γ-glycidoxypropyltrimethoxysilane; Preferably, on the other hand, the present invention provides a preparation step of a stainless steel passivation solution, and the specific preparation steps are as follows: S101: Add citric acid, sodium dihydrogen phosphate, and an anti-settling agent into deionized water with 50% of the total water amount, heat to 50 - 60 °C, stir until completely dissolved, and then successively add copper sulfate, ammonium molybdate, and sodium tungstate. Keep the stirring speed at 200 - 300 rpm until a homogeneous and transparent solution is formed to obtain a mixed solution; S102: Slowly add the amino-functionalized-silane modified SiO₂ nanoparticles into the mixed solution prepared in step S101, perform ultrasonic treatment, add a cerium salt, heat to 55 - 60 °C, and stir at 300 - 500 rpm for 1 - 2 h to obtain an activated solution; S103: Cool the activated solution prepared in step S102 to 40 - 45 °C, add L-ascorbic acid, stir at 200 - 300 rpm for 2 - 3 h, and then successively add polyaspartic acid and a surfactant. Adjust the pH to 3.5 - 4.5 with dilute sulfuric acid and ammonia water, and stir at 300 - 500 rpm for 1 - 2 h to obtain a complexing system; S104: Add polyethylene glycol into the complexing system prepared in step S103, heat to 45 - 55 °C and stir for 30 - 50 min, add the remaining deionized water, and perform ultrasonic degassing treatment to obtain a passivation solution; Preferably, in step S102, the ultrasonic treatment parameters are 30 - 40 kHz, 100 - 120 W, and the time is 20 - 30 min; Preferably, in step S104, the ultrasonic degassing treatment parameters are 40 kHz, 100 - 150 W, and the time is 15 - 20 min.

[0006] The beneficial effects of the present invention are as follows: The present invention uses aminated - epoxy group silane - modified silica (SiO2) nanoparticles to construct a three - dimensional network skeleton. The amino groups on its surface coordinate with Ce in the cerium salt, and preferentially anchor on the metal active sites to form a passivation core. The epoxy groups at the end of the silane form covalent bonds with the hydroxyl groups on the metal substrate surface through ring - opening reactions, significantly enhancing the chemical binding force between the nanoparticles and the matrix. Citric acid, as a biodegradable complexing agent, its carboxyl groups form soluble complexes with copper ions (Cu 3+ ), iron ions (Fe 2+ ), and cooperate with the carboxylic acid groups of polyaspartic acid to accelerate the spreading of the passivation film. At the same time, the dendritic molecular chains of polyaspartic acid can selectively chelate free Fe 3+ , cooperate to chelate metal ions and inhibit the precipitation of Fe(OH)3, and inhibit rust deposition. Ammonium molybdate and sodium tungstate are reduced by L - ascorbic acid to form a molybdenum - tungsten composite oxide film. Among them, L - ascorbic acid has both reducibility and environmental friendliness, and can reduce Fe 3+ to Fe 3+ which is easy to complex. It cooperates with the strong chelating ability of disodium ethylenediaminetetraacetate (EDTA) to remove iron ions in the system and block the chain corrosion reaction initiated by iron ions. 2+

[0007] In the formula used in the present invention, sodium carboxymethyl cellulose, as a natural polysaccharide derivative, its hydroxyl groups form a hydrogen - bond cross - linked network with the epoxy groups on the surface of silica. While enhancing the adhesion of the passivation film, it disperses iron oxide particles through the steric hindrance of the molecular chain to avoid local corrosion. The water - soluble ether chains of polyethylene glycol and the carboxylic acid groups of disodium ethylenediaminetetraacetate form a hydrophobic - hydrophilic dynamic protection layer through molecular self - assembly. Among them, disodium ethylenediaminetetraacetate can not only stabilize heavy metal ions and reduce environmental release, but also form stable chelates with free Fe 2+ / Fe 3+ to improve the recycling efficiency of the passivation solution; the three - dimensional network of aminated silica captures iron ions through the dual actions of physical adsorption and amino coordination, and cooperates with the chelating function of polyaspartic acid to form a hierarchical iron - ion scavenging mechanism.

[0008] ​In the formulation used in the passivation solution of the present invention, citric acid, polyaspartic acid, sodium carboxymethyl cellulose, and L-ascorbic acid are all biodegradable components. The cerium salt is selected as a low-toxic rare earth compound, and the molybdenum / tungstate is fixed in the passivation film in the form of a stable oxide, significantly reducing the risk of heavy metal ion leakage. Although disodium ethylenediaminetetraacetate has strong chelating properties, its dosage is effectively reduced by compounding with polyaspartic acid and sodium carboxymethyl cellulose, and residual metal ions are adsorbed by combining with the silica network, achieving a balance between environmental friendliness and efficient removal of iron ions. In summary, the final system constructed by the synergistic action of multiple substances in the present invention achieves the unity of green environmental protection and long-term anti-corrosion through biodegradable components, stabilization of heavy metals, and multi-stage chelation-adsorption synergy of iron ions. Brief Description of the Drawings

[0009] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only those of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0010] Figure 1 It is a graph of the adhesion test results of the passivation solutions prepared in Example 2 of the present invention and Comparative Examples 1-4; Figure 2 It is a SEM scanning electron micrograph of the passivation solution prepared in Example 2 of the present invention after salt spray corrosion resistance test; Figure 3 It is an FTIR infrared spectrum of the amino-functionalized-epoxy-functionalized SiO2 nanoparticles prepared in Example 2 of the present invention. Detailed Description of the Embodiments

[0011] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. It should be noted that unless otherwise specified, the raw materials involved in the present invention are purchased through conventional commercial channels.

[0012] Example 1: A stainless steel passivation solution, the composition of which includes the following raw materials by mass percentage: 0.2% cerium salt, 0.1% copper sulfate, 2% citric acid, 0.4% sodium dihydrogen phosphate, 0.3% ammonium molybdate, 0.2% sodium tungstate, 1.2% amino-functionalized-silane-modified SiO2 nanoparticles, 0.5% polyethylene glycol, 0.8% L-ascorbic acid, 0.8% polyaspartic acid, 1.2% anti-settling agent, 0.1% surfactant, and the balance is deionized water.

[0013] The specific preparation steps of the aminated-silane modified SiO2 nanoparticles are as follows: S1: Add 1 g of SiO2 nanoparticles into 50 mL of anhydrous ethanol, disperse them evenly by ultrasonic treatment, centrifuge, filter, and vacuum dry at 120 °C for 2 h to obtain activated SiO2; S2: Add 1 g of the activated SiO2 prepared in step S1 into 200 mL of 95 wt% ethanol solution, disperse them evenly by ultrasonic treatment, then slowly drop 0.3 mL of γ-aminopropyltriethoxysilane at a rate of 0.5 mL / min, adjust the pH to 5.5 with glacial acetic acid, heat to 60 °C and react for 3 h, centrifuge, filter, wash repeatedly with 75 wt% ethanol for 3 times, and vacuum dry at 60 °C for 6 h to obtain aminated SiO2; S3: Add 1 g of the aminated SiO2 prepared in step S2 into 100 mL of 90 wt% ethanol solution, disperse them evenly by ultrasonic treatment, add 0.016 mL of triethylamine, then slowly drop 0.8 mL of γ-glycidoxypropyltrimethoxysilane at a rate of 0.1 mL / min, stir and react at 45 °C for 5 h, centrifuge, wash repeatedly with acetone and ethanol for 3 times, and vacuum dry at 40 °C for 12 h to obtain aminated-silane modified SiO2 nanoparticles; The specific preparation steps of the stainless steel passivation solution are as follows: S101: Add citric acid, sodium dihydrogen phosphate, and sodium carboxymethylcellulose into deionized water with 50% of the total water volume, heat to 50 °C, stir until completely dissolved, and then add copper sulfate, ammonium molybdate, and sodium tungstate in sequence, keep the stirring speed at 200 rpm until a homogeneous and transparent solution is formed to obtain a mixed solution; S102: Slowly add the aminated-silane modified SiO2 nanoparticles into the mixed solution prepared in step S101, the ultrasonic treatment parameters are 30 kHz, 100 W, and the time is 20 min, add cerium sulfate, heat to 55 °C, and stir at 300 rpm for 1 h to obtain an activated solution; S103: Cool the activated solution prepared in step S102 to 40 °C, add L-ascorbic acid, stir at 200 rpm for 2 h, then add sodium dihydrogen phosphate, polyaspartic acid, and disodium ethylenediaminetetraacetate in sequence, adjust the pH to 3.5 with dilute sulfuric acid and ammonia water, and stir at 300 rpm for 1 h to obtain a complexing system; S104: Add polyethylene glycol into the complexing system prepared in step S103, heat to 45 °C and stir for 30 min, add the remaining deionized water, and the ultrasonic degassing treatment parameters are 40 kHz, 100 W, and the time is 15 min to obtain a passivation solution.

[0014] Example 2: A stainless steel passivation solution, the composition of which includes the following raw materials by mass percentage: 0.5% cerium salt, 0.3% copper sulfate, 3% citric acid, 0.6% sodium dihydrogen phosphate, 0.6% ammonium molybdate, 0.5% sodium tungstate, 2% amino-silane modified SiO2 nanoparticles, 1% polyethylene glycol, 1.5% L-ascorbic acid, 1.2% polyaspartic acid, 1.5% anti-settling agent and 0.2% surfactant, with the balance being deionized water.

[0015] The specific preparation steps of the amino-silane modified SiO2 nanoparticles are as follows: S1: Add 1 g of SiO2 nanoparticles to 50 mL of absolute ethanol, ultrasonically disperse them evenly, centrifuge, filter, and vacuum dry at 120 °C for 3 h to obtain activated SiO2; S2: Add 1 g of the activated SiO2 prepared in step S1 to 200 mL of 95 wt% ethanol solution, ultrasonically disperse them evenly, then slowly dropwise add 0.5 mL of γ-aminopropyltriethoxysilane at a rate of 1 mL / min, adjust the pH to 5.2 with glacial acetic acid, heat to 65 °C and react for 3.5 h, centrifuge, filter, wash repeatedly 3 times with 75 wt% ethanol, and vacuum dry at 60 °C for 12 h to obtain amino-functionalized SiO2; S3: Add 1 g of the amino-functionalized SiO2 prepared in step S2 to 150 mL of 90 wt% ethanol solution, ultrasonically disperse them evenly, add 0.04 mL of triethylamine, then slowly dropwise add 1 mL of γ-glycidoxypropyltrimethoxysilane at a rate of 0.15 mL / min, stir and react at 50 °C for 5.5 h, centrifuge, wash repeatedly 3 times with acetone and ethanol, and vacuum dry at 40 °C for 16 h to obtain amino-silane modified SiO2 nanoparticles; The specific preparation steps of the stainless steel passivation solution are as follows: S101: Add citric acid, sodium dihydrogen phosphate and sodium carboxymethylcellulose to deionized water with 50% of the total water volume, heat to 60 °C, stir until completely dissolved, then sequentially add copper sulfate, ammonium molybdate and sodium tungstate, and maintain the stirring speed at 300 rpm until a homogeneous and transparent solution is formed to obtain a mixed solution; S102: Slowly add the amino-silane modified SiO2 nanoparticles to the mixed solution prepared in step S101, the ultrasonic treatment parameters are 40 kHz, 120 W, and the time is 25 min, add cerium nitrate, heat to 60 °C, and stir at 500 rpm for 1.5 h to obtain an activated solution; S103: Cool the activated solution prepared in step S102 to 45 °C, add L-ascorbic acid, stir at 300 rpm for 2.5 h, then sequentially add polyaspartic acid and disodium ethylenediaminetetraacetate, adjust the pH to 4 with dilute sulfuric acid and ammonia water, and stir at 500 rpm for 1.5 h to obtain a complex system; S104: Add polyethylene glycol to the complexing system prepared in step S103, heat to 55 °C, stir for 40 min, add the remaining deionized water, and perform ultrasonic degassing treatment with parameters of 40 kHz, 150 W, and a time of 18 min to obtain a passivation solution.

[0016] Example 3: A stainless steel passivation solution, the composition of which includes the following raw materials by mass percentage: 0.4% cerium salt, 0.2% copper sulfate, 2.5% citric acid, 0.5% sodium dihydrogen phosphate, 0.5% ammonium molybdate, 0.4% sodium tungstate, 1.6% amino-silane modified SiO2 nanoparticles, 0.8% polyethylene glycol, 1.3% L-ascorbic acid, 1% polyaspartic acid, 1.4% anti-settling agent, 0.3% surfactant, and the balance is deionized water.

[0017] The specific preparation steps of the amino-silane modified SiO2 nanoparticles are as follows: S1: Add 1 g of SiO2 nanoparticles to 50 mL of absolute ethanol, ultrasonically disperse evenly, centrifuge, filter, and vacuum dry at 120 °C for 2.5 h to obtain activated SiO2; S2: Add 1 g of the activated SiO2 prepared in step S1 to 200 mL of a 95 wt% ethanol solution, ultrasonically disperse evenly, then slowly dropwise add 0.4 mL of γ-aminopropyltriethoxysilane at a rate of 0.8 mL / min, adjust the pH to 4.8 with glacial acetic acid, heat to 62 °C and react for 4 h, centrifuge, filter, wash repeatedly 3 times with 75 wt% ethanol, and vacuum dry at 60 °C for 10 h to obtain amino-functionalized SiO2; S3: Add 1 g of the amino-functionalized SiO2 prepared in step S2 to 130 mL of a 90 wt% ethanol solution, ultrasonically disperse evenly, add 0.035 mL of triethylamine, then slowly dropwise add 0.9 mL of γ-glycidoxypropyltrimethoxysilane at a rate of 0.2 mL / min, stir and react at 48 °C for 6 h, centrifuge, wash repeatedly 3 times with acetone and ethanol, and vacuum dry at 40 °C for 15 h to obtain amino-silane modified SiO2 nanoparticles; The specific preparation steps of the stainless steel passivation solution are as follows: S101: Add citric acid, sodium dihydrogen phosphate, and sodium carboxymethylcellulose to deionized water with 50% of the total water volume, heat to 55 °C, stir until completely dissolved, then sequentially add copper sulfate, ammonium molybdate, and sodium tungstate, and maintain a stirring speed of 250 rpm until a homogeneous and transparent solution is formed to obtain a mixed solution; S102: Slowly add the aminated-silane modified SiO2 nanoparticles into the mixed solution prepared in step S101. The ultrasonic treatment parameters are 35 kHz, 110 W, and the time is 30 min. Add cerium chloride, heat to 58 °C, and stir at 400 rpm for 2 h to obtain an activation solution; S103: Cool the activation solution prepared in step S102 to 42 °C, add L-ascorbic acid, stir at 260 rpm for 3 h, then sequentially add polyaspartic acid and disodium ethylenediaminetetraacetate, and adjust the pH to 4.5 with dilute sulfuric acid and ammonia water, and stir at 400 rpm for 2 h to obtain a complexation system; S104: Add polyethylene glycol to the complexation system prepared in step S103, heat to 50 °C and stir for 50 min, add the remaining deionized water, and the ultrasonic degassing treatment parameters are 40 kHz, 140 W, and the time is 20 min to obtain a passivation solution.

[0018] Comparative Example 1: The operation of Comparative Example 1 is basically the same as that of Example 2, except that in Comparative Example 1, unmodified SiO2 nanoparticles are used to replace the aminated-silane modified SiO2 nanoparticles.

[0019] Comparative Example 2: The operation of Comparative Example 2 is basically the same as that of Example 2, except that in Comparative Example 2, the cerium salt is removed.

[0020] Comparative Example 3: The operation of Comparative Example 3 is basically the same as that of Example 2, except that in Comparative Example 3, L-ascorbic acid is removed.

[0021] Comparative Example 4: The operation of Comparative Example 4 is basically the same as that of Example 2, except that in Comparative Example 4, polyaspartic acid is removed.

[0022] Performance test: Adhesion test: Passivate the 304 stainless steel samples with the passivation solutions prepared in Example 2 and Comparative Examples 1-4 by conventional technical means, and then use a universal material testing machine to gradually apply a tensile force at a constant rate (10 mm / min) to test the adhesion (N / mm 2 ) when the coating starts to peel off, and the results are as Figure 1 shown.

[0023] From Figure 1It can be seen from the results that the passivation solution prepared by the present invention has excellent adhesion, can effectively adhere to stainless steel for long-term use; from the results of Comparative Example 1 and Example 2, it can be seen that without the SiO2 network and relying only on physical adsorption, the epoxy covalent bond and amino coordination are missing, and the adhesion significantly decreases; from the results of Comparative Example 2 and Example 2, it can be seen that the cerium salt forms a passivation nucleus through amino coordination and selectively anchors at the metal active sites, enhancing the local binding strength. When the cerium salt is missing, the SiO2 network and the substrate are combined only through hydrogen bonds and van der Waals forces, and the adhesion is significantly affected; from the results of Comparative Example 3 and Example 2, it can be seen that the absence of L-ascorbic acid results in partial Fe 3+ not being effectively reduced, and the deposition of Fe(OH)3 destroys the continuity of the passivation film, and local stress concentration causes interfacial peeling, resulting in a certain degree of influence on the adhesion; from the results of Comparative Example 4 and Example 2, it can be seen that the absence of polyaspartic acid and the increase in the proportion of EDTA may lead to the loosening of the chelating network, and the hydrogen bond cross-linking between the SiO2 network and the substrate is also affected to a certain extent, thereby affecting the adhesion.

[0024] Contact angle test: The passivation solution prepared in Examples 1 to 3 above was used to passivate 304 stainless steel samples by conventional technical means, and then the contact angle test was continued. All samples were tested under the conditions of room temperature and 50% humidity. Each test used 5 μL of water droplets, and the test results are shown in Table 1.

[0025] Table 1. Contact angle test results of passivation solution-treated stainless steel

[0026] It can be seen from the results in Table 1 that the passivation solution prepared by the present invention has excellent hydrophobicity after passivation treatment, can effectively support the feasibility of the hydrophobic-hydrophilic dynamic protection layer in the passivation solution design, and can inhibit electrochemical corrosion by reducing the penetration of water molecules.

[0027] Corrosion resistance test: The passivation solutions prepared in Example 2 and Comparative Examples 1 to 4 were used to passivate 304 stainless steel samples by conventional technical means, and then salt spray tests were carried out using 5% NaCl solution at 50 °C for 300 h. The appearance changes were recorded at 36 h, 96 h, 168 h and 300 h respectively, and the results are shown in Table 2; the passivation solutions prepared in Example 2 and Comparative Examples 1 to 3 were used to passivate 304 stainless steel samples by conventional technical means and immersed in 6% FeCl3 solution at a temperature of 50 °C for 24 h. The pitting density (number / cm 2 ) was recorded at 4 h, 12 h and 24 h respectively, and the results were recorded as the average value. The results are shown in Table 3.

[0028] Table 2. Salt spray corrosion resistance test results of passivation solution-treated stainless steel

[0029] Table 3. Test results of pitting corrosion resistance of stainless steel treated with passivation solution

[0030] It can be seen from the results of Table 2 and Table 3 that the passivation solution prepared by the present invention has excellent corrosion resistance, and the multi-layer network structure can effectively block the penetration of chloride ions to achieve long-term use; from the results of Comparative Example 1 and Example 2, it can be seen that the lack of a three-dimensional network leads to accelerated penetration of chloride ions, and the corrosion resistance decreases significantly, but the cerium salt and the chelating agent (EDTA + polyaspartic acid) still effectively delay the appearance of red rust; from the results of Comparative Example 2 and Example 2, it can be seen that the lack of cerium ions prevents the formation of passivation cores, and the metal active sites lose selective protection, which leads to local pitting in weak places. It germinates preferentially and expands rapidly; from the results of Comparative Example 3 and Example 2, it can be seen that the lack of L-ascorbic acid leads to the lack of Mo-W film, which in turn leads to an increase in the chloride ion penetration path, an accelerated corrosion rate, and the deposition of Fe(OH)3 destroys the continuity of the film, resulting in an expansion of the white rust area in the salt spray test; from the results of Comparative Example 4 and Example 2, it can be seen that the lack of polyaspartic acid leads to an incomplete chelating network, the excessive proportion of EDTA affects the density of the film layer, and the chloride ions quickly penetrate into the loose area of ​​the film layer, which leads to the diffusion of white rust; and from the results of Comparative Example 3, it can be seen that Spectrum test: The stainless steel passivation film of Example 2 after the salt spray corrosion resistance test was subjected to SEM scanning spectrum test. The test results are as follows: Figure 2 As shown; the spectrum of the amino-epoxysilane-modified SiO2 nanoparticles prepared in Example 2 was measured by FTIR spectrometer, and the results were as follows Figure 3 shown.

[0031] Depend on Figure 2 The results show that the passivation solution prepared by the present invention, after passivation treatment of stainless steel, still maintains good protection effect and corrosion resistance after experiencing 240 hours of salt spray corrosion, and no obvious accumulation of corrosion products, nor obvious depressions or pits are observed on the surface.

[0032] Depend on Figure 3 The results show that in the spectrum between 3200 and 3500 cm -1 There is an obvious broad absorption valley near , which overlaps with the stretching vibration of O–H and N–H (amino group); 800–1200 cm -1 A typical Si–O–Si vibration peak can be seen in the region, and it is between 2800 and 3000 cm -1 The obvious shoulder peaks showed that the alkyl chains were successfully introduced on the surface.

[0033] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A stainless steel passivation solution, characterized in that, Its composition includes the following raw materials by mass percentage: 0.2 - 0.5% cerium salt, 0.1 - 0.3% copper sulfate, 2 - 3% citric acid, 0.4 - 0.6% sodium dihydrogen phosphate, 0.3 - 0.6% ammonium molybdate, 0.2 - 0.5% sodium tungstate, 1.2 - 2% amino-silane modified SiO2 nanoparticles, 0.5 - 1% polyethylene glycol, 0.8 - 1.5% L-ascorbic acid, 0.8 - 1.2% polyaspartic acid, 1.2 - 1.5% anti-settling agent and 0.1 - 0.3% surfactant, with the balance being deionized water.

2. A stainless steel passivation solution according to claim 1, characterized in that, The cerium salt is any one of cerium nitrate, cerium sulfate and cerium chloride.

3. A stainless steel passivation solution according to claim 2, characterized in that, The surfactant is disodium ethylenediaminetetraacetate.

4. A stainless steel passivation solution according to claim 3, characterized in that, The specific preparation steps of the amino-silane modified SiO2 nanoparticles are as follows: S1: Add SiO2 nanoparticles into anhydrous ethanol, ultrasonically disperse them evenly, centrifuge, filter, and vacuum dry to obtain activated SiO2. S2: Add the activated SiO2 prepared in step S1 into an ethanol solution, ultrasonically disperse it evenly, then slowly dropwise add γ-aminopropyltriethoxysilane, adjust the pH with glacial acetic acid, heat and react, centrifuge, filter, wash repeatedly with ethanol, and vacuum dry to obtain amino-functionalized SiO2. S3: Add the amino-functionalized SiO2 prepared in step S2 into an ethanol solution, ultrasonically disperse it evenly, add triethylamine, then slowly dropwise add γ-glycidoxypropyltrimethoxysilane, stir and react, centrifuge, wash repeatedly with acetone and ethanol, and vacuum dry to obtain amino-silane modified SiO2 nanoparticles.

5. A stainless steel passivation solution according to claim 4, characterized in that, In step S2, the dosage ratio of the activated SiO2, ethanol solution and γ-aminopropyltriethoxysilane is 1 g:200 mL:0.3 - 0.5 mL.

6. A stainless steel passivation solution according to claim 5, characterized in that, In step S3, the dosage ratio of the amino-functionalized SiO2, ethanol solution and γ-glycidoxypropyltrimethoxysilane is 1 g:100 - 150 mL:0.8 - 1 mL; the addition amount of triethylamine is 2 - 4% of the volume of the added γ-glycidoxypropyltrimethoxysilane.

7. A preparation method of the stainless steel passivation solution according to any one of claims 1-6, characterized in that, The specific preparation steps are as follows: S101: Add citric acid, sodium dihydrogen phosphate and anti-settling agent into deionized water, heat and stir until completely dissolved, then sequentially add copper sulfate, ammonium molybdate and sodium tungstate, and maintain the stirring speed until a homogeneous and transparent solution is formed to obtain a mixed solution. S102: Slowly add the amino-silane modified SiO2 nanoparticles into the mixed solution prepared in step S101, ultrasonically treat, add cerium salt, heat and stir to obtain an activated solution. S103: Cool down the activated solution prepared in step S102, add L-ascorbic acid, stir, then sequentially add polyaspartic acid and surfactant, adjust the pH with dilute sulfuric acid and ammonia water, and stir to obtain a complex system. S104: Add polyethylene glycol into the complex system prepared in step S103, heat and stir, supplement the remaining deionized water, and perform ultrasonic degassing treatment to obtain a passivation solution.

8. A method for preparing the stainless steel passivation solution according to claim 7, characterized in that, In step S102, the ultrasonic treatment parameters are 30 - 40 kHz, 100 - 120 W, and the time is 20 - 30 min.

9. A method for preparing the stainless steel passivation solution according to claim 8, characterized in that, In step S104, the ultrasonic degassing treatment parameters are 40 kHz, 100 - 150 W, and the time is 15 - 20 min.

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