Low-temperature curing self-repairing phosphate anticorrosive coating, and preparation method and application thereof

Abstract

The application discloses a low-temperature curing self-repairing phosphate anticorrosive coating and a preparation method and application thereof, and belongs to the technical field of functional coating. The coating is prepared through three steps of passivation of a curing agent and filler, preparation of aluminum dihydrogen phosphate adhesive, and coating compounding. Through passivation of the curing agent, the activity of the curing agent can be effectively controlled, the compactness of the coating can be improved, the curing temperature of the phosphate coating is reduced from 110-250 DEG C to 80 DEG C, and the corrosion resistance of the coating is improved. Meanwhile, self-repairing microcapsules are added, after the coating is scratched, the repair components released by the microcapsules, the slow-release active components of the passivated curing agent and the corrosion / phosphate deposition products cooperatively block the defects, and the barrier property of the coating is recovered. The prepared coating has the advantages of low-temperature curing, strong adhesion, compact coating, good corrosion resistance and certain self-repairing protection capacity, is suitable for anticorrosive application in the fields of large ships, ocean engineering and steel structure, and has a good practical application prospect.

Description

Technical Field

[0001] This invention relates to the field of functional coatings technology, specifically to a low-temperature curing self-healing phosphate anti-corrosion coating and its preparation method. Background Technology

[0002] Metal corrosion is a progressive destructive process that occurs to materials under the influence of environmental media, causing not only huge economic losses but also potential safety hazards. To effectively slow down metal corrosion, the use of anti-corrosion coatings is an economical and efficient method. These coatings form an isolation layer on the metal surface, blocking contact with corrosive media. However, traditional organic self-healing anti-corrosion coatings are mostly based on epoxy resins, polyurethanes, etc. While they possess certain anti-corrosion and self-healing properties, they suffer from problems such as easy aging, poor high-temperature resistance, environmental pollution, and limited repair life, making it difficult to meet the long-term protection requirements of complex environments such as high temperatures and marine environments.

[0003] In contrast, the low-temperature curing of self-healing phosphate inorganic anti-corrosion coatings exhibits significant advantages. This coating, based on aluminum dihydrogen phosphate, forms a dense inorganic ceramic structure through low-temperature baking curing (typically below 200°C). This not only avoids the risk of thermal damage to the metal substrate caused by high-temperature processing but also possesses excellent chemical stability. Simultaneously, the introduction of self-healing functional components into the coating allows it to release repair substances after localized damage such as scratches or abrasions, filling and sealing the defective areas, preventing further penetration of corrosive media, and thus restoring the barrier and protective performance of the damaged areas. Although organic polymer encapsulation technology is widely used, its poor compatibility with inorganic phosphate systems and insufficient shell thermal stability have become bottlenecks restricting performance improvement. In stark contrast, inorganic encapsulation technologies (such as silica encapsulation), with their perfect chemical compatibility with the substrate, excellent thermal stability, and mechanical strength, can achieve better protection and precise release of active components, fundamentally overcoming the inherent defects of organic encapsulation and providing an ideal solution for preparing high-performance, long-life inorganic anti-corrosion coatings. Chen, Z.; Kuckling, D.; Tiemann, M. Porous Aluminum Oxide and MagnesiumOxide Films Using Organic Hydrogels as Structure Matrices. Nanomaterials2018, 84.).

[0004] However, some traditional phosphate anticorrosive coatings often require high curing temperatures to ensure coating performance. 1. In 2009, Ishizaki, T. described that conventional phosphate-based coatings usually require specific methods to promote their curing at high temperatures. The requirement for high-temperature curing leads to high energy consumption and complex equipment, which severely limits its application in small-scale and field scenarios. The raw materials rely on expensive special additives / modifiers, resulting in high overall costs and hindering large-scale popularization. (Ishizaki, T.; Shigematsu, I.; Saito, N. Anticorrosive Magnesium Phosphate Coating on AZ31 Magnesium Alloy. Surface and Coatings Technology 2009, 203 (16), 2288–2291). 2. In 2012, Yaskova introduced phosphate powder coatings that can achieve relatively low-temperature curing at 150°C and have advantages such as reduced energy consumption. (Jašková, Veronika Kalendová, Andréa. Anticorrosive coatings containing modified phosphates. Progress in Organic Coatings 2012, 75, 328-344), but their curing temperature remains relatively high. A 2023 paper by Yang Ning also found that while some coatings have innovations in energy saving, their curing temperatures are still relatively high (ZY, QM, HW, Yadi.A, MZ, XY, Ning. Effect of zinc oxide on corrosion resistance of magnesium ammonium phosphate cement-based coating. Construction and Building Materials 2023, 398). Traditional phosphate coatings rely on high-temperature curing (>150℃), resulting in high energy consumption, complex equipment, and expensive raw materials, severely limiting their application.

[0005] Furthermore, existing self-healing anti-corrosion coatings mainly include externally assisted and self-healing types. Externally assisted types mostly rely on microcapsules filled with corrosion inhibitors (SN Lang, QX Zhou, Synthesis and characterization of poly(urea-formaldehyde) microcapsules containing linseed oil for self-healing coating development, Prog. Org. Coat. 105 (2017) 99–110.) or fibers (XH Ji, WHJi, S. Pourhashem, et al., Novel superhydrophobic core-shell fibers / epoxycoatings with self-healing anti-corrosion properties in both acidic and alkaline environments, React. Funct. Polym. 187 (2023), 105574.) to release corrosion inhibitors. However, they have poor compatibility with the coating, easily reduce the mechanical properties of the coating, and their self-healing ability has a limited lifespan. Self-healing types usually require external stimuli such as temperature, light, or pH, and are mostly based on organic coatings. Therefore, developing inorganic coatings with low-temperature curing self-healing properties is of great significance. Existing research on the self-healing properties of phosphate anticorrosive coatings often requires high curing temperatures and is limited. 1. A 2023 paper by Wang Jianyu utilized a fluorinated silane coupling agent to modify alumina, achieving hydrophobicity restoration and self-healing of the coating through the thermally driven migration of perfluorinated chains in FAS-Al2O3 (JL Yao, CP Yang, CFZhu, BQ Hou, Preparation Process of Epoxy Resin Microcapsules for Self-healing Coatings, Progress in Organic Coatings 132 (2019) 440–444), but its curing temperature was high.2. The research paper published by Wang Jianyu in 2024, although self-repair was achieved in the phosphate system by adding UF@PFDTES microcapsules (Wang, JY; Wu, MP; Huang, JQ; Wang, YY; Miao, XJ; Chen, YW; Bian, D.; Zhao, YW In-situ polymerized microcapsule as multifunctional filler for phosphate ceramic anticorrosion coating. ACS Appl. Mater. Interfaces 2024, 16, 26768). (26786), but its curing temperature is high. Summary of the Invention

[0006] In view of this, the present invention provides a low-temperature curing self-healing phosphate anti-corrosion coating and its preparation method. The low-temperature curing self-healing phosphate anti-corrosion coating combines low-temperature curing, dense protection, and barrier recovery capabilities after scratches. By passivating the curing agent and filler, the curing reaction of the coating is effectively controlled, and the density of the structure and corrosion resistance are improved. By compounding with self-healing microcapsules, the coating can still maintain good protective recovery capabilities after localized damage. This effectively solves the defects of existing phosphate anti-corrosion coatings, such as high curing temperature, poor application adaptability, and insufficient protection after damage, and has good practical value and application prospects.

[0007] To achieve the above objectives, this application first provides a method for preparing a low-temperature curing self-healing phosphate anti-corrosion coating, specifically including the following steps:

[0008] S1, passivation of curing agent and filler The curing agent and filler were passivated by using an aqueous solution of chromium trioxide, followed by washing, drying, and grinding to obtain passivated curing agent and filler.

[0009] S2, Preparation of aluminum dihydrogen phosphate binder base material Aluminum hydroxide solution was placed in a three-necked flask, heated and stirred, and phosphoric acid solution was gradually added. The temperature was further increased and the reaction was stirred until the solution was completely transparent, thus obtaining aluminum dihydrogen phosphate binder.

[0010] S3, Coating Compound Aluminum dihydrogen phosphate binder is mixed with deionized water and stirred until homogeneous. Passivated filler is added and stirred until a mixed solution is obtained. Passivated curing agent is mixed with deionized water to obtain a dispersion. The dispersion and mixed solution are mixed and stirred until homogeneous. Self-healing microcapsules are added and stirred until the low-temperature curing self-healing phosphate anticorrosive coating is obtained.

[0011] The concentration of the chromium trioxide aqueous solution in step S1 is 50 g / L to 150 g / L, preferably 100 g / L; The passivation treatment of the curing agent is specifically as follows: after mixing the curing agent, chromium trioxide aqueous solution and deionized water, ultrasonic treatment is performed for 0.5 h; wherein the molar ratio of chromium trioxide to curing agent is 1:17~18; preferably 1:17.37; and the volume ratio of chromium trioxide aqueous solution to deionized water is 5:6.

[0012] The passivation treatment of the filler is as follows: the filler and chromium trioxide aqueous solution are mixed and ultrasonically treated for 0.5 h; wherein the molar ratio of chromium trioxide to filler is 1:6~10.

[0013] The washing water used in step S1 is deionized water; the drying temperature is 120°C.

[0014] The curing agent in step S1 is magnesium oxide whiskers; the filler is one or more of aluminum hydroxide, silicon dioxide, aluminum powder, aluminum oxide, glass flakes, and iron oxide.

[0015] Preferably, the filler in step S1 is aluminum hydroxide and silicon dioxide. When the filler is aluminum hydroxide and silicon dioxide, the concentration of the chromium trioxide aqueous solution during the passivation treatment is 50 g / L to 150 g / L, preferably 100 g / L; the molar ratio of chromium trioxide to aluminum hydroxide is 1:6 to 7, preferably 1:6.5; the molar ratio of chromium trioxide to silicon dioxide is 1:9 to 10, preferably 1:9.98. Preferably, the concentration of the aluminum hydroxide solution in step S2 is 600 g / L to 650 g / L, more preferably 636.11 g / L; the heating and stirring temperature is 80 to 90°C, more preferably 90°C. The phosphoric acid has a mass fraction of 85 wt%, and the molar ratio of aluminum hydroxide to phosphoric acid is 1:2~3, preferably 1:2.555; the further heating and stirring reaction is carried out at a temperature of 98~120℃, preferably 98℃, for a time of 2 hours.

[0016] The self-healing microcapsules mentioned in step S3 are one or more of UF@E-51 microcapsules, PUA@E-51 microcapsules, and UF@n-octadecane, preferably UF@E-51 microcapsules (produced by Wuhan Taichu Nanotechnology Co., Ltd.).

[0017] In step S3, the passivated filler is passivated aluminum hydroxide and passivated silicon dioxide; the mass ratio of the aluminum dihydrogen phosphate adhesive, passivated aluminum hydroxide, passivated silicon dioxide, passivated curing agent, and self-healing microcapsules is 36~38:12~14:8~10:1.5~2.5:0.9~1.2; the mass ratio of aluminum dihydrogen phosphate adhesive to deionized water in the mixed solution is 36~38g:9~11mL; and the mass ratio of the dispersion to deionized water is 1.5~2.5g:7~9mL.

[0018] Its beneficial effects are as follows: the addition of passivated aluminum hydroxide and passivated silica can fill the gaps and pores in the coating, improving the density and mechanical strength of the coating; at the same time, the dense inorganic filler structure is also conducive to the stable dispersion of microcapsules in the coating, thereby further enhancing the corrosion resistance and scratch protection and recovery ability of the coating.

[0019] The present invention also provides a low-temperature curing self-healing phosphate anti-corrosion coating prepared by the method described above.

[0020] The significant advantages of this invention are as follows: By passivating aluminum hydroxide, silicon dioxide, and whisker-shaped magnesium oxide and adding self-healing microcapsules, it achieves four major breakthroughs: 1. Low-temperature curing: Curing can be completed at 80℃ (nearly 50% lower than the 150℃ scheme of Jašková et al. in 2012), requiring only simple heating equipment; 2. Enhanced anti-corrosion performance: The passivation process significantly reduces the temperature while improving the density and corrosion resistance of the coating, outperforming traditional high-temperature curing systems; 3. Significant cost advantages: Using inexpensive industrial raw materials (no need for nanomaterials / modifiers), combined with energy savings and equipment savings from low-temperature construction, reduces overall costs; 4. This technological breakthrough enables the coating to be widely used in outdoor and small-scale applications, promoting the large-scale popularization of phosphate anti-corrosion coatings. The coating formed by the low-temperature curing self-healing phosphate anti-corrosion coating of this invention exhibits significant advantages.

[0021] Regarding corrosion resistance, through scientific and reasonable raw material ratios and process optimization, the coating of this invention forms a dense protective film structure. Compared with some phosphate coatings that require high-temperature curing, tests have shown that the corrosion resistance of the coating of this invention is no less impressive.

[0022] The present invention also provides the application of the above-mentioned low-temperature curing self-healing phosphate anti-corrosion coating. The low-temperature curing self-healing phosphate anti-corrosion coating is evenly brushed onto the treated steel plate, placed in a ventilated place at room temperature for 1 hour, and then placed in an oven at 60℃~110℃ for 2 hours~12 hours to bake completely, thus obtaining a low-temperature curing anti-corrosion coating.

[0023] Its beneficial effects are as follows: During actual service, coatings inevitably suffer scratches due to transportation, assembly, wear, or impact. Traditional phosphate anti-corrosion coatings mainly rely on initial shielding; once locally damaged, corrosive media can quickly reach the metal substrate along the scratch, leading to pitting, crevice corrosion, or corrosion propagation. Therefore, emphasizing only low-temperature curing and initial anti-corrosion performance is insufficient to fully meet the requirements of long-life service. This invention combines the intrinsic self-sealing effect induced by passivated MgO with the release and repair effect of self-healing microcapsules, enabling the coating to actively restore its local barrier capacity after damage, thereby enhancing the functional appeal and engineering application value of the invention.

[0024] In summary, this invention provides a low-temperature curing self-healing phosphate anti-corrosion coating, its preparation method, and its application. Compared with the prior art, this invention has the following significant advantages: (1) Passivating magnesium oxide whiskers with an aqueous solution of chromium trioxide to form a dense passivation film on the surface can effectively delay the degradation of magnesium oxide. 2+ The release of [something] reduces the curing speed. This method not only enables anti-corrosion coatings to cure efficiently at low temperatures, but also significantly extends the workable time of the coating, avoiding the construction difficulties caused by the excessively rapid reaction of traditional curing systems.

[0025] (2) Passivation treatment of fillers with chromium trioxide further optimizes the microstructure of the coating. The passivated fillers are more uniformly dispersed in the coating system, reducing agglomeration and making the cured coating more compact, which significantly improves the corrosion resistance of the coating.

[0026] (3) By compounding an appropriate amount of self-healing microcapsules into the passivated MgO phosphate coating system, the coating can have better barrier and recovery capabilities after being damaged by scratches or other local damage. The repair components released by the microcapsules can work synergistically with the slow-release active components of passivated MgO and corrosion / phosphate deposition products to seal the defect area, thereby enhancing the long-term anti-corrosion and self-healing protective effect of the coating.

[0027] The synergistic effect of these three aspects enables the low-temperature curing self-healing phosphate inorganic anti-corrosion coating of the present invention to have the characteristics of low-temperature curing, good construction adaptability, dense coating, excellent corrosion resistance and strong barrier recovery ability after scratches, and has important industrial application value. Attached Figure Description

[0028] 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 will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1 For scanning electron microscopy (SEM): (a) magnesium oxide whiskers, (b) magnesium oxide whiskers after passivation.

[0030] Figure 2 For scanning electron microscopy (SEM): (a) the treated Q235 carbon steel substrate, (b) the coating of Example 2, (c) the coating of Example 4, and (d) the coating of Example 1.

[0031] Figure 3 Electrochemical tests: (a) Potential polarization curve, (b) Nyquist plot, (c) Bode plot, (d) Bode phase angle plot, (e) Low-frequency impedance modulus of the coating |Z|f=0.01.

[0032] Figure 4 The thermogravimetric curve is 80℃. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1 S1, passivation of curing agent and filler Weigh out 3.5g of curing agent magnesium whisker, 5 mL of chromium trioxide aqueous solution (100g / L), and 6 mL of deionized water, mix them, and ultrasonically disperse them for 0.5 h to ensure sufficient passivation. Then wash them three times with deionized water, dry them in an oven at 120℃, and grind them to obtain passivated curing agent magnesium whisker. Images of magnesium whisker before and after passivation are shown below. Figure 1 As shown.

[0035] Weigh 13g of aluminum hydroxide filler and 25 mL of chromium trioxide aqueous solution (100g / L), mix them, and ultrasonically disperse them for 0.5 h to ensure sufficient passivation. Then wash them three times with deionized water, dry them in an oven at 120℃, and grind them to obtain passivated aluminum hydroxide filler.

[0036] Weigh 9g of silica filler and 15mL (100g / L) of chromium trioxide aqueous solution, mix them, and ultrasonically disperse them for 0.5h to ensure sufficient passivation. Then wash them three times with deionized water, dry them in an oven at 120℃, and grind them to obtain passivated silica filler.

[0037] S2, Preparation of aluminum dihydrogen phosphate binder base material Mix 18.32 g of aluminum hydroxide with 28.8 mL of water, heat the mixture in an oil bath to 90 °C and stir. Gradually add 69.19 g of 85 wt% phosphoric acid, then heat the oil bath to 98 °C and stir for 2 h until the solution is completely transparent to obtain aluminum dihydrogen phosphate adhesive.

[0038] S3, Coating Compound 37 g of the prepared aluminum dihydrogen phosphate adhesive was added to 10 mL of deionized water and stirred until homogeneous. Then, 13 g of passivated aluminum hydroxide and 9 g of passivated silicon dioxide were added, and the mixture was stirred for 5 min to obtain a homogeneous solution. Then, 2 g of passivated magnesium whisker was dispersed in 8 mL of deionized water to obtain a dispersion. The dispersion was added to the mixed solution and stirred for 15 min. Finally, 0.915 g of UF@E-51 self-healing microcapsules were added and stirred for 90 min to obtain a low-temperature curing self-healing phosphate anti-corrosion coating.

[0039] Example 2 The only difference from Example 1 is that unpassivated whisker magnesium oxide is used as the curing agent, and unpassivated aluminum hydroxide and silicon dioxide are used as fillers.

[0040] Example 3 The coating preparation is the same as in Example 1, except that no self-healing microcapsules were added.

[0041] Example 4 The only difference from Example 1 is that the magnesium oxide whiskers are passivated, the filler is not passivated, and no self-healing microcapsules are added.

[0042] Example 5 The only difference from Example 1 is that the 5 mL (100 g / L) chromium trioxide aqueous solution used for passivating magnesium oxide whiskers is replaced with 2 mL (100 g / L) chromium trioxide aqueous solution, the filler is not passivated, and self-healing microcapsules are not added.

[0043] Example 6 The only difference from Example 1 is that the 5 mL (100 g / L) chromium trioxide aqueous solution used for passivating magnesium oxide whiskers is replaced with 8 mL (100 g / L) chromium trioxide aqueous solution, the filler is not passivated, and self-healing microcapsules are not added.

[0044] Comparative Example 1 The literature reports on high-temperature curing anticorrosion coatings (Chen, Z.; Guo, X.; Zhang, L.; Lu, G.; Liu, M.; Liu, S. Anticorrosion Mechanism of Al-Modified Phosphate Ceramic Coating in the High-Temperature Marine Atmosphere. Surface and Coatings Technology 2022, 128572). Comparative Example 2 Self-healing anti-corrosion coatings reported in the literature (JL Yao, CP Yang, CF Zhu, BQ Hou, Preparation Process of Epoxy Resin Microcapsules for Self-healing Coatings, Progress in Organic Coatings 132 (2019) 440–444). Comparative Example 3 Literature reports on self-healing anticorrosion coatings (Wang, JY; Wu, MP; Huang, JQ; Wang, YY; Miao, XJ; Chen, YW; Bian, D.; Zhao, YW: In-situ polymerized microcapsule as multifunctional filler for phosphate ceramic anticorrosion coating. ACS Appl. Mater. Interfaces 2024, 16, 26768). 26786) Performance testing To comprehensively evaluate the performance of the anti-corrosion coatings prepared in Examples 1-4 and Comparative Examples 1-3, the coatings were applied to a Q235 carbon steel substrate. Specifically, the prepared low-temperature curing self-healing phosphate anti-corrosion coating was uniformly brushed onto a steel plate that had been polished with a metallographic sample polisher, soaked in anhydrous ethanol for 15 minutes, and dried in an oven at 60°C for 10 minutes. The coating was then cured to obtain a low-temperature curing anti-corrosion coating. The coating morphology is shown in [Figure 1]. Figure 2 .

[0045] A series of professional instruments were used for precise testing. Adhesion testing was performed using an Airipu QFH-A cross-cut adhesion tester, strictly following the GB / T 9286-1998 standard. Coating hardness was measured using a Ruiwen Instruments RW-5101s electric pencil surface hardness tester, operated according to the GB / T 6739-2022 standard, to obtain accurate data on coating hardness. Contact angle measurement was performed using a HARKE-SPCAX1 contact angle tester, manufactured by HARKE Instruments Testing Plant. This instrument accurately measures the contact angle of the coating, thereby evaluating the hydrophobic properties of the coating surface. Self-healing efficiency testing was conducted using a CHI 760E electrochemical workstation manufactured by Shanghai Chenhua Instruments Co., Ltd. This instrument accurately obtains precise EIS (0.01Hz) data, allowing for the calculation of self-healing efficiency.

[0046] Table 1. Adhesion, coating hardness, contact angle, curing temperature, self-healing efficiency, and coating surface test results for Examples 1 and Comparative Examples 1-2

[0047] Note: Self-healing efficiency Eself-healing = [(|Z| f =0.01 Hz 48h |Z| f =0.01 Hz ,6h) / |Z| f =0.01 Hz ,6h] × 100%.

[0048] According to Table 1 and Figure 2 Data analysis shows that the low-temperature curing self-healing phosphate anti-corrosion coating (Example 1) exhibits a significant advantage in curing time extension compared to Example 2. This improvement is mainly due to the introduction of the chromium trioxide aqueous solution passivation method, which not only enhances the coating's adhesion and increases the contact angle but also significantly improves its anti-corrosion performance and surface smoothness. Although self-healing microcapsules were added in Example 2, the curing reaction was too fast because neither the curing agent nor the filler underwent passivation treatment, resulting in multiple cracks on the coating surface and low self-healing efficiency. The chromium trioxide aqueous solution can form a passivation film on the surface of magnesium oxide whiskers, delaying the curing of Mg. 2+ The release of the filler, and the passivation treatment significantly increases the density to improve the anti-corrosion effect and the barrier recovery ability after scratches.

[0049] Compared to Example 4, the low-temperature curing self-healing phosphate anti-corrosion coating (Example 1) shows improvements in both surface condition and barrier recovery capability after scratches. This improvement is primarily due to the passivation treatment of the filler by the chromium trioxide aqueous solution, which allows for more uniform dispersion of the filler in the coating system, reducing internal defects and improving coating density. Simultaneously, the addition of self-healing microcapsules releases repair components after coating damage, filling and sealing the scratched area, thereby further enhancing the coating's protective and recovery capabilities.

[0050] Compared to Example 5, the low-temperature curing self-healing phosphate anti-corrosion coating (Example 1) shows a significant improvement in coating density. This improvement stems from two main factors: firstly, the appropriate amount of chromium trioxide solution allows for the formation of a complete passivation layer on the surface of the magnesium oxide whiskers, effectively slowing down the release rate of magnesium ions and mitigating the internal porosity problem caused by excessive curing reaction, thus effectively improving the coating's hardness and hydrophobic shielding ability; secondly, the combination of passivation-modified filler and self-healing microcapsules allows the filler to fill the internal gaps and pores of the coating, while the microcapsules endow the coating with self-healing ability to scratches, further enhancing the overall anti-corrosion protection effect.

[0051] Compared to Example 6, the low-temperature curing self-healing phosphate anti-corrosion coating (Example 1) exhibits a significant advantage in coating integrity. This improvement is attributed to two main factors: firstly, controlling the amount of chromium trioxide added prevents the formation of an excessively thick passivation film that would result in numerous microcracks, thus significantly enhancing the coating's interfacial bonding strength and long-term anti-corrosion barrier capability; secondly, the combination of passivation-modified fillers and self-healing microcapsules optimizes the coating's microscopic dense structure, while the microcapsules enable active sealing and repair of damaged areas, greatly improving the coating's long-term protective performance.

[0052] Compared with Comparative Example 1, the low-temperature curing self-healing phosphate anti-corrosion coating (Example 1) shows outstanding performance in reducing the curing temperature, which makes the application process simpler. Comprehensive test results show that the low-temperature curing anti-corrosion coating of this invention has a low curing temperature (baking at 80°C for 2 hours). Furthermore, the coating exhibits excellent performance in terms of adhesion, hardness, and self-healing ability, making it an ideal choice for various anti-corrosion applications.

[0053] Compared with Comparative Example 2, the low-temperature curing self-healing phosphate anticorrosive coating (Example 1) mainly relies on FAS-Al2O3 to achieve thermally driven hydrophobic recovery self-healing, focusing on the restoration of surface hydrophobicity. In contrast, the present invention achieves self-healing through the synergistic effect of passivated MgO, passivated filler and microcapsules and has a lower curing temperature (baking at 80°C for 2 hours).

[0054] Compared with Comparative Example 3, the low-temperature curing self-healing phosphate anti-corrosion coating (Example 1) is different. Comparative Example 3 mainly achieves self-healing through UF@PFDTES microcapsules. Although the self-healing efficiency is high, the curing process still requires multi-stage heating treatment. In contrast, the present invention has a lower curing temperature (baking at 80°C for 2 hours) and a simpler process.

[0055] Electrochemical testing To evaluate the protective performance of the coating in corrosive media, a three-electrode system was used for electrochemical testing. A Q235 carbon steel sample coated with the anti-corrosion solution was used as the working electrode, a platinum sheet as the counter electrode, and mercury-mercury oxide as the reference electrode. The corrosive medium was a 3.5 wt% NaCl aqueous solution. Before testing, the coated sample was immersed in the NaCl solution, and open-circuit potential stability tests were performed at different immersion times. Subsequently, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PVP) tests were performed sequentially. The frequency range of the EIS tests was 10 Hz. 5 Hz~10 -2 The AC disturbance voltage is 10 mV. The potentiodynamic polarization test is performed with the open circuit potential as the center to compare the corrosion current density and corrosion potential changes of the coating under different immersion times.

[0056] See results Figure 3 Figure 3(a) shows the potentiodynamic polarization curves of the complete coating under different immersion times. As the immersion time increases, the overall corrosion potential of the coating does not shift significantly negatively, and the corrosion current changes little, indicating that the corrosive medium does not quickly penetrate to the surface of the Q235 carbon steel substrate, and the coating can still effectively protect the metal substrate.

[0057] Figure 3(b) shows the Nyquist curves of the complete coating at different immersion times. A larger Nyquist curve radius generally indicates a higher charge transfer resistance in the coating system, making the corrosion reaction more difficult. As can be seen from the figure, the coating maintains a large impedance arc during immersion, indicating good barrier properties. With increasing immersion time, the impedance response did not show a significant decrease, indicating good immersion stability of the coating in NaCl solution.

[0058] Figure 3(c) shows the Bode impedance modulus of the complete coating. Low-frequency impedance modulus is typically used to evaluate the coating's ability to shield against corrosive media; a higher low-frequency impedance value indicates better barrier performance. As shown in the figure, the coating maintains a high low-frequency impedance modulus even after different immersion times, indicating a relatively dense coating structure that effectively prevents the diffusion of moisture, oxygen, and chloride ions into the metal substrate.

[0059] Figure 3(d) shows the Bode phase angle diagram of the complete coating. The phase angle can reflect the capacitance characteristics and interfacial stability of the coating. The coating still maintains a significant phase angle response during immersion, indicating that the coating has not suffered serious failure in the corrosive medium. The phase angle changes with immersion time, indicating that there may be moisture penetration and interfacial reaction processes inside the coating, but overall it still exhibits good shielding effect and corrosion resistance stability.

[0060] Figure 3(e) shows the low-frequency impedance modulus variation curves of coatings with different self-healing microcapsule contents at different immersion times after scratching. During the test, artificial scratches were prepared on the surface of the cured coating, and the scratched coating was immersed in 3.5 wt% NaCl solution. Electrochemical impedance spectroscopy was performed at 6 h, 12 h, 24 h, and 48 h, respectively. The low-frequency impedance modulus |Z|f=0.01Hz at 0.01Hz was extracted to evaluate the recovery of the barrier performance of the scratched area. The results showed that the low-frequency impedance modulus of the coating without microcapsules recovered to some extent during immersion, indicating that the passivated MgO and phosphate system itself has a certain self-sealing effect. After adding self-healing microcapsules, the overall low-frequency impedance modulus of the coating improved. Among them, the 1.5 wt% microcapsule coating maintained a high impedance after immersion for 24 h and 48 h, indicating that the repair component released by an appropriate amount of microcapsules can effectively fill scratch defects and synergistically seal the defect area with the slow-release active component of passivated MgO and corrosion / phosphate deposition products, thereby improving the barrier recovery ability after scratching. If the microcapsule content is too low, the repair component is insufficient; if the content is too high, it may affect the coating density. Therefore, 1.5 wt% is the optimal addition amount.

[0061] Thermogravimetric Curing Curve Test at 80℃ To evaluate the effect of different curing agents on the low-temperature curing behavior of phosphate coatings, four control groups were set up, referring to the parameters of Example 1: passivated whisker magnesium oxide, unpassivated whisker magnesium oxide, ordinary magnesium oxide, and no curing agent. Except for the type of curing agent or whether a curing agent was added, the other formulations and preparation processes remained consistent. Specifically, aluminum dihydrogen phosphate adhesive was used as the base material, and aluminum hydroxide, silica filler, and deionized water were added to form a coating slurry. Then, the corresponding curing agent was added and stirred evenly. A certain amount of uncured coating sample was placed in the sample crucible of a thermogravimetric analyzer, and the change in sample mass over time was recorded under a constant temperature of 80℃ to obtain the 80℃ thermogravimetric isothermal curing curve.

[0062] Depend on Figure 4It can be seen that the system without curing agent has a lower weight loss, indicating that the simple aluminum dihydrogen phosphate base and filler system is difficult to form a fully cured structure at 80℃. The ordinary magnesium oxide and unpassivated whisker magnesium oxide systems have a faster weight loss in the early stage, indicating that their curing reaction is more concentrated, which easily causes rapid water loss and rapid curing of the coating. In contrast, the passivated whisker magnesium oxide system has a more gradual weight loss process at 80℃ and eventually tends to stabilize, indicating that the chromium trioxide passivation treatment reduces the instantaneous reactivity of whisker magnesium oxide, making the curing process more controllable, which is conducive to reducing internal stress and coating cracking caused by rapid curing, thereby promoting the formation of a dense and uniform low-temperature curing coating.

[0063] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a low-temperature curing self-healing phosphate anticorrosive coating, characterized in that, Specifically, the steps include the following: S1, passivation of curing agent and filler The curing agent and filler were passivated by using an aqueous solution of chromium trioxide, followed by washing, drying, and grinding to obtain passivated curing agent and filler; S2, Preparation of aluminum dihydrogen phosphate binder base material Aluminum hydroxide solution was placed in a three-necked flask, heated and stirred, and phosphoric acid solution was gradually added. The temperature was further increased and the reaction was stirred until the solution was completely transparent, thus obtaining aluminum dihydrogen phosphate binder. S3, Coating Compound Aluminum dihydrogen phosphate binder is mixed with deionized water and stirred until homogeneous. Passivated filler is added and stirred until a mixed solution is obtained. Passivated curing agent is mixed with deionized water to obtain a dispersion. The dispersion and mixed solution are mixed and stirred until homogeneous. Self-healing microcapsules are added and stirred until the low-temperature curing self-healing phosphate anticorrosive coating is obtained.

2. The preparation method according to claim 1, characterized in that, The concentration of the chromium trioxide aqueous solution in step S1 is 50 g / L to 150 g / L; The passivation treatment of the curing agent is as follows: after mixing the curing agent, chromium trioxide aqueous solution and deionized water, ultrasonic treatment is performed for 0.5 hours; wherein the molar ratio of chromium trioxide to curing agent is 1:17~18; and the volume ratio of chromium trioxide aqueous solution to deionized water is 5:

6. The passivation treatment of the filler is as follows: the filler and chromium trioxide aqueous solution are mixed and ultrasonically treated for 0.5 h; wherein the molar ratio of chromium trioxide to filler is 1:6~10.

3. The preparation method according to claim 1, characterized in that, The washing water used in step S1 is deionized water; the drying temperature is 120°C.

4. The preparation method according to claim 1, characterized in that, The curing agent in step S1 is magnesium oxide whiskers; the filler is one or more of aluminum hydroxide, silicon dioxide, aluminum powder, aluminum oxide, glass flakes, and iron oxide.

5. The preparation method according to claim 4, characterized in that, The filler in step S1 is aluminum hydroxide and silicon dioxide.

6. The preparation method according to claim 1, characterized in that, In step S2, the concentration of the aluminum hydroxide solution is 600 g / L to 650 g / L; the heating and stirring temperature is 80 to 90 °C; the mass fraction of the phosphoric acid solution is 85 wt%, and the molar ratio of aluminum hydroxide to phosphoric acid is 1:2 to 3; the temperature for further heating and stirring is 98 to 120 °C, and the time is 2 hours.

7. The preparation method according to claim 1, characterized in that, The self-healing microcapsules mentioned in step S3 are one or more of UF@E-51 microcapsules, PUA@E-51 microcapsules, and UF@n-octadecane.

8. The preparation method according to claim 1, characterized in that, The passivation filler mentioned in step S3 is passivated aluminum hydroxide and passivated silicon dioxide; The mass ratio of the aluminum dihydrogen phosphate adhesive, passivated aluminum hydroxide, passivated silicon dioxide, passivated curing agent, and self-healing microcapsules is 36~38:12~14:8~10:1.5~2.5:0.9~1.

2. The mass ratio of aluminum dihydrogen phosphate adhesive to deionized water in the mixed solution is 36~38g:9~11mL. The mass-to-volume ratio of the dispersion to deionized water is 1.5~2.5g:7~9mL.

9. A low-temperature curing self-healing phosphate anti-corrosion coating prepared by the method according to any one of claims 1 to 8.

10. The application of a low-temperature curing self-healing phosphate anti-corrosion coating prepared by the method according to any one of claims 1 to 8, or the low-temperature curing self-healing phosphate anti-corrosion coating according to claim 9, characterized in that, Apply the low-temperature curing self-healing phosphate anti-corrosion coating evenly to the treated steel plate, place it in a ventilated area at room temperature for 1 hour, and then place it in an oven at 60℃~110℃ for 2 to 12 hours to fully cure, thus obtaining a low-temperature curing anti-corrosion coating.

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