MOF glass / epoxy resin anti-corrosion composite coating and preparation method thereof

Abstract

The invention relates to the technical field of material science and engineering, and discloses an MOF glass / epoxy resin anti-corrosion composite coating and a preparation method thereof.The material is prepared from an epoxy resin matrix and an amorphous metal organic framework glass functional filler with the surface subjected to chemical anchoring treatment; the preparation method comprises the following steps: firstly, converting crystalline MOF powder into amorphous MOF glass through heat treatment, and carrying out surface chemical anchoring on the amorphous MOF glass to enhance the interface bonding force so as to prepare a functional filler; and mixing the functional filler with epoxy resin, and constructing a gradient structure coating with filler concentration decreasing from bottom to top on the surface of a base material through a layer-by-layer coating process. Grain boundary defects are eliminated through filler amorphization, a physical barrier is strengthened through an interface anchoring technology, stress distribution is optimized in combination with gradient structure design, excellent physical barrier is achieved, and then the high-performance anti-corrosion coating with high adhesive force and long-term durability is obtained.

Description

Technical Field

[0001] This invention relates to the fields of materials science and engineering technology, specifically to a MOF glass / epoxy resin anti-corrosion composite coating and its preparation method. Background Technology

[0002] Anti-corrosion coatings are protective thin layers applied to the surface of materials to isolate them from corrosive environments. Their core function is to prevent or delay the corrosion process of metal substrates. Introducing functional fillers into polymer matrices to prepare composite coatings is a key technological approach to improve protective performance. Among these, epoxy resins are widely used due to their excellent adhesion and chemical stability. In recent years, metal-organic frameworks (MOFs), as a new type of porous crystalline material, have shown great potential as reinforcing fillers in anti-corrosion coatings due to their regular pore structure and large specific surface area.

[0003] In the prior art, a common method to improve the anti-corrosion performance of epoxy coatings is to directly use micron or nano-sized crystalline metal-organic framework powder as a functional filler and physically blend it into epoxy resin. This method aims to utilize the physical barrier formed by the metal-organic framework particles themselves to extend the penetration path of corrosive media.

[0004] However, the aforementioned existing technologies face problems stemming from the inherent properties of materials and structural design when achieving the goal of long-term and efficient protection. First, the inherent grain boundary defects of crystalline fillers become rapid penetration shortcuts for corrosive media. This not only fails to effectively prolong the corrosion path but also forms localized corrosion enrichment zones within the coating, undermining the integrity of the coating's physical barrier from the inside, resulting in a protective effect far below theoretical expectations. Second, the poor interfacial compatibility between crystalline fillers and the organic epoxy resin matrix leads to low interfacial bonding. Weak interfaces are prone to microscopic debonding under the action of water molecule penetration or internal and external stress, forming new defect sources. These defects are interconnected with the grain boundary channels of the fillers, forming a penetration network that runs through the coating, greatly accelerating the failure process of the coating from decreased adhesion and blistering to eventual peeling. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a MOF glass / epoxy resin anti-corrosion composite coating and its preparation method, aiming to solve the problems of coating physical barrier failure and poor long-term adhesion caused by the inherent defects of crystalline fillers and poor interfacial compatibility.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a first aspect of a MOF glass / epoxy resin anti-corrosion composite coating, which adopts the following technical solution: A MOF glass / epoxy resin anti-corrosion composite coating is made from raw materials comprising the following parts by weight: epoxy resin: 100 parts; curing agent: 25-35 parts; functional filler: 7-28 parts; wherein the raw materials are mixed, coated and cured to form the coating, and during the coating process, the functional filler is applied in a gradient structure with decreasing concentration from the bottom layer close to the substrate to the top layer away from the substrate.

[0007] By adopting the above technical solutions, the core innovation of this invention lies in the composite modification of functional fillers, the gradient distribution structure of fillers, and the interfacial synergistic effect between fillers and the matrix.

[0008] The functional filler of this invention is a composite functional body prepared through specific steps. First, crystalline MOF powder is transformed into amorphous MOF glass through heat treatment. This process eliminates the regular grain boundaries of crystalline MOF, which are weak points for the penetration of corrosive media. At the same time, the disordered surface of the amorphous state provides more active sites and improves compatibility with the polymer matrix.

[0009] Next, a silane coupling agent was used to chemically anchor the surface of the amorphous MOF glass. The silane coupling agent acts as a molecular bridge between the inorganic filler and the organic matrix; one end forms a MO-Si chemical bond with the MOF glass surface, while the other end forms a covalent bond with the epoxy resin or curing agent during curing. This chemical bonding constructs a robust interfacial transition layer, improving the interfacial adhesion between the inorganic filler and the organic matrix, and ensuring the long-term adhesion and barrier properties of the coating in humid and hot environments.

[0010] This invention utilizes a specific coating process to construct a gradient structure where the concentration of functional fillers decreases from bottom to top. The bottom layer, closer to the metal substrate, has a high concentration of filler, whose main function is to form a high-density physical barrier layer. The top layer, farther from the substrate, has a low concentration of filler, whose main function is to maintain the excellent mechanical properties (such as toughness) and weather resistance of the epoxy resin matrix itself, preventing the coating from becoming brittle due to excessive filler in the top layer. This gradient structure achieves optimized distribution of functions along the thickness direction and avoids the stress concentration and interlayer delamination risks caused by abrupt changes in physical properties between traditional multilayer coatings.

[0011] Regarding system synergy, this invention uses epoxy resin and polyetheramine curing agent as the film-forming matrix. The chemically anchored functional filler is no longer an isolated particle, but participates in the curing network of the epoxy resin as an active crosslinking node. This strong interfacial interaction allows stress to be effectively transferred from the matrix to the filler, while the presence of the filler further improves the crosslinking density and compactness of the polymer network.

[0012] Preferably, the functional filler is amorphous MOF glass, and the surface of the amorphous MOF glass is chemically anchored by a silane coupling agent.

[0013] Preferably, the functional filler is prepared by the following steps: (a) Reacting metal salts and organic ligands in a solvent to synthesize MOF crystalline powder; (b) The MOF crystalline powder is heat-treated under an inert atmosphere to transform it into the amorphous MOF glass powder; (c) The amorphous MOF glass powder is chemically anchored on the surface using the silane coupling agent.

[0014] Preferably, the epoxy resin is a bisphenol A diglycidyl ether type epoxy resin; the curing agent is a polyetheramine curing agent; the organic ligand of the MOF crystal powder is selected from at least one of imidazole, benzimidazole and 5-chlorobenzimidazole; and the silane coupling agent is selected from one of γ-aminopropyltriethoxysilane, γ-glycidyl etheroxypropyltrimethoxysilane and γ-methacryloyloxypropyltrimethoxysilane.

[0015] A second aspect of this invention provides a method for preparing a MOF glass / epoxy resin anti-corrosion composite coating, employing the following technical solution: A method for preparing a MOF glass / epoxy resin anti-corrosion composite coating includes the following steps: (a) Mix epoxy resin, curing agent and functional filler to prepare at least two slurries with different concentrations of functional filler, including at least a high-concentration slurry and a low-concentration slurry; (b) Apply the high-concentration slurry to the surface of the substrate, and then apply the low-concentration slurry on top of the high-concentration slurry to construct a gradient structure; (c) Curing treatment of the applied coating.

[0016] By adopting the above technical solution, the innovation of the method of the present invention lies in the controllable preparation of gradient composite coatings through precise control of slurry concentration, selectable gradient construction process and optimized curing regime.

[0017] Step (a) is a prerequisite for achieving the gradient structure. The functional filler concentration (wt%) here refers to the percentage of the mass of the functional filler relative to the total mass of the slurry (i.e., the sum of the filler, epoxy resin, and curing agent).

[0018] Preferably, the concentration of functional filler in the high-concentration slurry is 10-30 wt%. This range balances barrier performance and workability. If the concentration is below 10 wt%, the underlying physical barrier is insufficient. If it is above 30 wt%, the slurry viscosity increases sharply, resulting in poor fluidity and difficulty in forming a uniform coating.

[0019] Preferably, the concentration of functional filler in the low-concentration slurry is 1-5 wt%. This range balances mechanical properties and gradient transition. If the concentration is higher than 5 wt%, the surface toughness of the coating decreases and it becomes brittle. If it is lower than 1 wt%, the functional difference from the high-concentration layer is too large.

[0020] Step (b) is the core process for achieving the gradient structure. The coating method can specifically employ either discontinuous gradient construction or continuous gradient construction. For discontinuous gradient construction, the coating method is selected from multi-layer spraying or layer-by-layer spin coating. This method forms a stepped gradient by applying multiple layers of slurry with different concentrations. When using the layer-by-layer spin coating method, it is preferable to pre-dry each layer at 40°C for 5 minutes after spin coating to ensure the stability of the interlayer interfaces.

[0021] The continuous gradient coating method is a dual-channel spraying method. This method controls the flow ratio of high-concentration slurry and low-concentration slurry through a program, so that they are mixed at the nozzle and sprayed out. The flow ratio is continuously changed during the spraying process. This method can produce a gradient coating with continuously changing concentration. There is no physical interface inside, so the integrity is stronger and internal stress concentration can be avoided to the greatest extent.

[0022] Step (c) is the process of transforming the liquid slurry into a solid coating. This invention provides two optimized curing pathways to adapt to different working conditions: the first is high-temperature short-time curing, which involves heating and curing at 60-100°C for 2-3 hours. This pathway provides sufficient activation energy for the ring-opening addition reaction between the epoxy groups and amine groups through heating, thereby accelerating the reaction rate and making it suitable for scenarios requiring rapid preparation.

[0023] The second method is long-term room temperature curing, which involves curing at 20-30°C for 24 hours. This method relies on the high reactivity of polyetheramine curing agents at room temperature and is suitable for large components, heat-sensitive substrates, or construction sites without heating facilities. 24 hours is the necessary curing time to ensure that the polymer chains diffuse sufficiently at room temperature and form a stable three-dimensional network structure.

[0024] This invention provides a MOF glass / epoxy resin anti-corrosion composite coating and its preparation method. It has the following beneficial effects: 1. This invention transforms crystalline MOF powder into amorphous MOF glass as a filler, eliminating the inherent grain boundary defects of crystalline materials and avoiding the problem of rapid penetration of corrosive media along grain boundaries, thereby improving the physical barrier ability of the filler itself. At the same time, a chemical bond is formed between the filler surface and the epoxy resin matrix through a silane coupling agent, forming a stable interface transition layer, which helps to inhibit the decrease in adhesion and corrosion propagation of the coating due to interface failure in humid and hot environments, and helps to enhance the overall barrier performance and durability of the coating.

[0025] 2. This invention forms a gradient structure in which the concentration of functional fillers decreases from the substrate to the surface through a preparation method. The high-concentration filler layer close to the substrate ensures excellent physical barrier properties, while the low-concentration filler layer far from the substrate retains the excellent mechanical toughness and weather resistance of the epoxy resin matrix. This integrated gradient design not only achieves the optimized configuration of different functions within a single coating, but also avoids the risk of stress concentration and peeling caused by abrupt changes in interlayer interface properties in traditional multi-coating systems, thereby improving the overall protective performance and service life of the coating. Attached Figure Description

[0026] Figure 1 The Fourier transform infrared spectra of the MOF crystal and amorphous MOF glass powder prepared in the embodiments of the present invention are shown below. Figure 2 The X-ray diffraction patterns of the MOF crystal and amorphous MOF glass powder prepared in the embodiments of the present invention are shown below. Figure 3 These are scanning electron microscope (SEM) images of some of the raw material powders used in the embodiments of the present invention; Figure 4 Cross-sectional SEM images of a pure epoxy resin coating and a composite coating prepared according to embodiments of the present invention; Figure 5 Comparison of the macroscopic corrosion morphology of the surface of the pure epoxy resin coating and the composite coating prepared in the embodiments of the present invention after salt spray test. Detailed Implementation

[0027] The technical solutions in 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.

[0028] Please see the appendix Figure 1 - Appendix Figure 5 : The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0029] MOF precursor materials include: Zinc nitrate hexahydrate (CAS No.: 10196-18-6), imidazole (CAS No.: 288-32-4), benzimidazole (CAS No.: 51-17-2) and 5-chlorobenzimidazole (CAS No.: 4887-88-1).

[0030] The epoxy resin (EP) is a bisphenol A diglycidyl ether type epoxy resin with an epoxy equivalent (EEW) of 180–200 g / eq and an average molecular weight (Mn) of 350–400 g / mol.

[0031] The curing agent is polyetheramine D230 (CAS No.: 9046-10-0), with a chemical structure of poly(propylene glycol) di(2-aminopropyl) ether and an average molecular weight of approximately 230 g / mol.

[0032] Silane coupling agents include: γ-aminopropyltriethoxysilane (KH-550, CAS No.: 919-30-2), γ-glycidyl etheroxypropyltrimethoxysilane (KH-560, CAS No.: 2530-83-8), and γ-methacryloyloxypropyltrimethoxysilane (KH-570, CAS No.: 2530-85-0).

[0033] The base material is Q235 carbon steel sheet, and its chemical composition conforms to the Chinese national standard GB / T700-2006.

[0034] The functional fillers, including crystalline MOF powder, amorphous MOF glass, and surface chemically anchored MOF glass, are all self-made products of this invention and not commercially available products.

[0035] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing functional filler A (agZIF-4-Si), the product of which is used in subsequent examples, including the following steps: (1) Weigh 3.0 g of imidazole and dissolve it in 100 mL of N,N-dimethylformamide (DMF) solvent; add 4.37 g of zinc nitrate hexahydrate and 0.5 g of NaOH (dissolved in 5 mL of water). Stir the mixture magnetically at 70 °C for 12 hours. After the reaction is complete, centrifuge to separate the precipitate, wash it with DMF and anhydrous ethanol, and then vacuum dry it at 60 °C for 12 hours to obtain ZIF-4 crystal powder.

[0036] (2) Place the ZIF-4 powder obtained in step (1) in a tube furnace and introduce nitrogen gas. Heat to 350°C at a heating rate of 10°C / min and hold at that temperature for 20 minutes. Stop heating and cool to room temperature with the furnace. Grind to obtain agZIF-4 glass powder.

[0037] (3) Prepare a mixed solution of 950 mL anhydrous ethanol and 50 mL deionized water, and adjust the pH to 4.5 with acetic acid. Add 5 g of KH-560 coupling agent (1.0 wt% of the filler mass) and stir for 30 minutes to hydrolyze it. Add 500 g of agZIF-4 powder obtained in step (2), heat to 70 °C and reflux for 4 hours. Centrifuge, wash with anhydrous ethanol, and vacuum dry at 70 °C for 12 hours to obtain agZIF-4-Si powder, i.e., functional filler A.

[0038] Preparation Example 2: This preparation example provides a method for preparing functional filler B (agZIF-62-Si), the product of which is used in subsequent examples, including the following steps: (1) Weigh 1.5g imidazole and 5.16g benzimidazole and dissolve them in 150mL LMF solvent. Add 6.51g zinc nitrate hexahydrate and 0.8g NaOH (dissolved in 8mL water). Stir the mixture magnetically at 65℃ for 10 hours. After centrifugation, washing and drying, ZIF-62 crystal powder is obtained.

[0039] (2) Place the ZIF-62 powder obtained in step (1) in a tube furnace and introduce nitrogen gas. Heat to 400°C at a heating rate of 5°C / min and hold at that temperature for 10 minutes. Stop heating and cool to room temperature with the furnace. Grind to obtain agZIF-62 glass powder.

[0040] (3) Prepare a mixed solution of 900 mL anhydrous ethanol and 100 mL deionized water, and adjust the pH to 5.0. Add 15 g of KH-550 coupling agent (3.0 wt% of the filler mass) and stir for 60 minutes to hydrolyze it. Add 500 g of agZIF-62 powder obtained in step (2), heat to 60 °C and reflux for 6 hours. After centrifugation, washing and drying, agZIF-62-Si powder is obtained, which is functional filler B.

[0041] Preparation Example 3: This preparation example provides a method for preparing functional filler C (agZIF-76-Si), the product of which is used in subsequent examples, including the following steps: (1) Weigh 1.5g imidazole and 3.36g 5-chlorobenzimidazole and dissolve them in 150mL LMF solvent. Add 4.37g zinc nitrate hexahydrate and 0.5g NaOH (dissolved in 5mL water). Stir the mixture magnetically at 75℃ for 12 hours. After centrifugation, washing, and drying, ZIF-76 crystal powder is obtained.

[0042] (2) Place the ZIF-76 powder obtained in step (1) in a tube furnace and introduce argon gas. Heat to 300°C at a heating rate of 15°C / min and hold at that temperature for 30 minutes. Stop heating and cool to room temperature with the furnace. Grind to obtain agZIF-76 glass powder.

[0043] (3) Prepare a mixed solution of 950 mL anhydrous ethanol and 50 mL deionized water, and adjust the pH to 4.0. Add 25 g of KH-570 coupling agent (5.0 wt% of the filler mass) and stir for 30 minutes to hydrolyze it. Add 500 g of agZIF-76 powder obtained in step (2), heat to 75 °C and reflux for 3 hours. After centrifugation, washing and drying, agZIF-76-Si powder is obtained, which is the functional filler C.

[0044] Examples 1-5: Example 1: This example provides a MOF glass / epoxy resin anti-corrosion composite coating and its preparation method, including the following steps: (1) Weigh each component according to the following mass values ​​and prepare gradient slurries respectively: a. High-concentration underlayer slurry: Weigh epoxy resin E-51 (27.69g), curing agent D230 (8.31g) and functional filler A (4.0g) prepared in Preparation Example 1.

[0045] b. Low-concentration top dressing: Weigh epoxy resin E-51 (42.0 g), curing agent D230 (12.6 g) and functional filler A (1.0 g) prepared in Preparation Example 1.

[0046] (2) Place the two groups of slurry a and b in a high-speed shear mixer and disperse them evenly to obtain a high-concentration bottom layer slurry (filler concentration 10.0wt%) and a low-concentration top layer slurry (filler concentration 1.8wt%).

[0047] (3) A double-layer spraying method is adopted. The high-concentration bottom layer slurry is sprayed onto the surface of the pretreated Q235 carbon steel sheet, and allowed to stand for 10 minutes to level. Then, the low-concentration top layer slurry is sprayed. The total dry film thickness is controlled to be 80 μm.

[0048] (4) Place the sprayed sample in an oven and heat it at 60°C for 2 hours to cure it. Then cool it to room temperature with the oven.

[0049] Example 2: This example provides a MOF glass / epoxy resin anti-corrosion composite coating and its preparation method, including the following steps: (1) Weigh each component according to the following mass values ​​and prepare gradient slurries respectively: a. High-concentration underlayer slurry: Weigh epoxy resin E-51 (23.08g), curing agent D230 (6.92g) and functional filler B (10.0g) prepared in Preparation Example 2.

[0050] b. Medium-concentration intermediate layer slurry: Weigh epoxy resin E-51 (23.08g), curing agent D230 (6.92g) and functional filler B (4.0g) prepared in Preparation Example 2.

[0051] c. Low-concentration top dressing: Weigh epoxy resin E-51 (19.23g), curing agent D230 (5.77g) and functional filler B (1.0g) prepared in Preparation Example 2.

[0052] (2) Place the three groups of slurry a, b and c in a high-speed shear mixer and disperse them evenly to obtain high, medium and low concentration slurries (filler concentrations of 25.0wt%, 11.8wt% and 3.8wt% respectively).

[0053] (3) Using a layer-by-layer spin coating method, high, medium and low concentration slurries are sequentially spin-coated onto the surface of the pretreated Q235 carbon steel sheet. After each layer is spin-coated, it is pre-dried at 40°C for 5 minutes. The total dry film thickness is controlled to be 75 μm.

[0054] (4) Place the spin-coated sample in an oven and heat it at 80°C for 1 hour. Then heat it to 100°C for 1 hour and cool it to room temperature in the oven.

[0055] Example 3: This example provides a MOF glass / epoxy resin anti-corrosion composite coating and its preparation method, including the following steps: (1) Weigh each component according to the following mass values ​​and prepare gradient slurries respectively: a. High-concentration slurry: Weigh epoxy resin E-51 (53.85g), curing agent D230 (16.15g) and functional filler C (30.0g) prepared in Preparation Example 3.

[0056] b. Low-concentration slurry: Weigh epoxy resin E-51 (73.08g), curing agent D230 (21.92g) and functional filler C (5.0g) prepared in Preparation Example 3.

[0057] (2) Place the two groups of slurry a and b in a high-speed shear mixer and disperse them evenly to obtain a high-concentration slurry (filler concentration 30.0wt%) and a low-concentration slurry (filler concentration 5.0wt%).

[0058] (3) A dual-channel spraying method is adopted, in which high and low concentration slurries are placed in a dual-channel spray gun. The flow ratio of the two channels is controlled by a program during the spraying process, so that the filler concentration of the coating changes continuously from the substrate (high concentration) to the surface (low concentration). The total dry film thickness is controlled to be 90 μm.

[0059] (4) Place the sprayed sample in an oven and heat it at 100°C for 3 hours to cure it. Then cool it to room temperature with the oven.

[0060] Example 4: This example provides a MOF glass / epoxy resin anti-corrosion composite coating and its preparation method, including the following steps: (1) Weigh each component according to the following mass values ​​and prepare gradient slurries respectively: a. High-concentration base slurry: Weigh epoxy resin E-51 (30.77g), curing agent D230 (9.23g) and functional filler A (8.0g) prepared in Preparation Example 1.

[0061] b. Low-concentration top dressing: Weigh epoxy resin E-51 (38.46g), curing agent D230 (11.54g) and functional filler A (2.0g) prepared in Preparation Example 1.

[0062] (2) Place the two groups of slurry a and b in a high-speed shear mixer and disperse them evenly to obtain a high-concentration bottom layer slurry (filler concentration 16.7wt%) and a low-concentration top layer slurry (filler concentration 3.8wt%).

[0063] (3) A double-layer spraying method is adopted. The high-concentration bottom layer slurry is sprayed onto the surface of the pretreated Q235 carbon steel sheet, and allowed to stand for 10 minutes to level. Then, the low-concentration top layer slurry is sprayed. The total dry film thickness is controlled to be 85μm.

[0064] (4) Place the sprayed sample in an environment with room temperature of 25°C and relative humidity of 60% for 24 hours to cure it.

[0065] Example 5: This example provides a MOF glass / epoxy resin anti-corrosion composite coating and its preparation method, including the following steps: (1) Weigh each component according to the following mass values ​​and prepare gradient slurries respectively: a. High-concentration slurry: Weigh epoxy resin E-51 (61.54g), curing agent D230 (18.46g) and functional filler C (20.0g) prepared in Preparation Example 3.

[0066] b. Low-concentration slurry: Weigh epoxy resin E-51 (75.38g), curing agent D230 (22.62g) and functional filler C (2.0g) prepared in Preparation Example 3.

[0067] (2) Place the two groups of slurry a and b in a high-speed shear mixer and disperse them evenly to obtain a high-concentration slurry (filler concentration 20.0wt%) and a low-concentration slurry (filler concentration 2.0wt%).

[0068] (3) The same dual-channel spraying method as in Example 3 was used to continuously change the filler concentration in the coating. The total dry film thickness was controlled to be 80 μm.

[0069] (4) Place the sprayed sample in an oven and heat it at 80°C for 2 hours to cure it. Then cool it to room temperature with the oven.

[0070] Comparative Examples 1-4: Comparative Example 1: Compared with Example 2, the difference is that a gradient structure is not used. Instead, the total amount of functional filler B is mixed with epoxy matrix at one time to prepare a uniform coating with a filler concentration of 15.0 wt%. All other aspects are the same.

[0071] Comparative Example 2: Compared with Example 1, the difference is that when preparing functional filler A, crystalline ZIF-4 powder was used instead of amorphous agZIF-4 glass powder, and all other aspects were the same.

[0072] Comparative Example 3: Compared with Example 1, the difference is that the preparation process of functional filler A does not include a surface chemical anchoring step, but all other steps are the same.

[0073] Comparative Example 4: Compared with Example 3, the difference is that zinc phosphate of equal mass is used to replace the functional filler C of the present invention, and all other aspects are the same.

[0074] Test Example 1-3: Test Example 1: Electrochemical Impedance Spectroscopy The experimental steps are as follows: Take coating samples prepared according to the methods of the examples and comparative examples, with 3 parallel samples in each group.

[0075] The coated sample was used as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum sheet as the auxiliary electrode, forming a three-electrode testing system. The electrolyte was a 3.5 wt% NaCl solution, and the exposed area of ​​the working electrode was controlled to be 1.0 cm². 2 .

[0076] The test was conducted using a CHI660E electrochemical workstation, with a 20mV AC perturbation signal applied at open circuit potential, and a scan frequency range of 10. 2 Hz to 10 -2 Hz.

[0077] Measurements were taken after the samples were soaked for 1 day, 7 days, 15 days, and 30 days, and the results were recorded. -2 The impedance modulus value at the Hz frequency was calculated, and the average value of three parallel samples in each group was taken as the final result.

[0078] The experimental results are shown in Table 1.

[0079] Table 1. Low-frequency impedance modulus (Ω·cm²) of each sample under different soaking times Test results show that the low-frequency impedance modulus of the sample in Example 1 was higher than that of all comparative samples throughout the 30-day test period, indicating that it has better protection performance.

[0080] Compared with Comparative Example 1, the latter, which has a uniform structure, had its impedance value decrease by about two orders of magnitude after immersion for 7 days. The gradient structure of Example 1, which combines a bottom layer with a high filler content with a top layer with a low filler content, effectively delayed the penetration of corrosive media.

[0081] Comparing Example 1 and Comparative Example 2, Comparative Example 2, which uses crystalline ZIF-4 filler, has an initial impedance value that is two orders of magnitude lower than that of Example 1. This is because the amorphous MOF glass filler, due to its long-range disordered structure, avoids grain boundary defects that serve as permeation pathways in crystalline materials.

[0082] Compared with Comparative Example 1 and Comparative Example 3, the coating of Comparative Example 3, which did not undergo surface chemical anchoring, had its impedance reduced to 10 after immersion for 15 days. 5 Ω·cm 2 The magnitude indicates that the covalent bond between the filler and the matrix is ​​crucial for maintaining interfacial stability and effectively prevents the rapid expansion of water molecules at the interface after intrusion.

[0083] Comprehensive data indicate that the combination of gradient structure, filler amorphization, and interfacial chemical anchoring is the reason for the long-lasting protective performance of the coating.

[0084] Test Example 2: Neutral Salt Spray Test The experimental steps are as follows: Take coating samples prepared according to the methods of the examples and comparative examples, with 3 parallel samples in each group.

[0085] According to GB / T10125-2012 standard, the samples were placed in a neutral salt spray test chamber for accelerated aging test.

[0086] The test conditions were set as follows: sodium chloride solution concentration of 50 g / L (5 wt%), solution pH of 6.5-7.2, test chamber temperature of (35±2)℃, and spraying method of continuous spraying.

[0087] The surface condition of the samples was observed and recorded every 240 hours, including the time when rust spots appeared. The total test duration was 1200 hours. After the test, the corrosion area of ​​the samples was evaluated according to GB / T1771-2007. The average value of three parallel samples in each group was taken as the final result.

[0088] The experimental results are shown in Table 2.

[0089] Table 2. Corrosion records of each sample in neutral salt spray test Test results showed that the sample in Example 1 maintained an intact coating surface without rust spots after 1200 hours of neutral salt spray testing. In contrast, all comparative samples showed varying degrees of corrosion during the testing period.

[0090] The uniform coating of Comparative Example 1 showed corrosion after 750 hours, indicating that the gradient structure design of the present invention, by optimizing the distribution of filler in the coating, can more effectively hinder the erosion of corrosive media, thereby providing a longer protection period.

[0091] Comparative Example 2, which used crystalline fillers, showed rust spots much earlier (490 hours) than Example 1. This confirms that the amorphous structure of the MOF glass eliminates grain boundary defects, improves the compactness of the filler itself, and thus enhances the overall barrier capability of the coating.

[0092] Comparative Example 3 exhibited the worst salt spray resistance among all coating samples, showing rust spots after 220 hours and reaching a corrosion area of ​​35% by the end of the test. This directly demonstrates that without the strong interfacial bonding provided by surface chemical anchoring, the coating will prematurely fail at the interface in humid environments, leading to a rapid decline in protective capabilities.

[0093] The macroscopic corrosion results of the salt spray test are consistent with the electrochemical data of Test Example 1, which once again proves that the present invention achieves long-term effective protection of the substrate through the synergy of multiple mechanisms.

[0094] Test Example 3: Coating Adhesion Test The experimental steps are as follows: Take coating samples prepared according to the methods of the examples and comparative examples, with 3 parallel samples in each group.

[0095] According to GB / T5210-2006 standard, the adhesion between the coating and the substrate was tested using the pull-off method. A test spindle with a diameter of 20 mm was bonded to the surface of each sample.

[0096] After the adhesive has fully cured, use a portable pull-off adhesion tester to apply tensile force in a direction perpendicular to the coating surface until the coating separates from the substrate or reaches the upper limit of the instrument's range.

[0097] Record the tensile strength value that caused the coating to separate and observe the type of interface where failure occurred. Take the average value of three parallel samples in each group as the final result.

[0098] The experimental results are shown in Table 3.

[0099] Table 3 Adhesion test results of coatings for each sample Test results show that the adhesion of the sample in Example 1 is 7.8 MPa, which is significantly higher than that of Comparative Example 1 and Comparative Example 3.

[0100] The key difference between Example 1 and Comparative Example 3 lies in whether surface chemical anchoring was performed. The adhesion of Example 1 is more than three times that of Comparative Example 3. In the tensile test, the failure in Comparative Example 3 occurred at the interface between the filler and the epoxy matrix, which is considered interfacial failure. This indicates that the filler and the matrix only have a weak physical bond. In contrast, the failure in Example 1 occurred inside the coating, which is considered cohesive failure, indicating that its interfacial bond strength exceeds the strength of the coating itself. This is because the silane coupling agent on the surface of the functional filler forms stable covalent bonds with the epoxy matrix, constructing a strong interfacial bond layer.

[0101] The adhesion of Comparative Example 1 (6.5 MPa) was also lower than that of Example 1, and its failure mode was a mixed mode of coating cohesive failure and interfacial failure. This may be because the high filler content in the homogeneous structure increased the internal stress of the coating, resulting in a decrease in overall bonding performance.

[0102] Adhesion is crucial in determining the long-term protective performance of a coating. Excellent adhesion effectively prevents the lateral spread of corrosive media at the coating-substrate interface, thereby inhibiting the spread of localized corrosion. These test results explain, from a mechanical property perspective, why Example 1 exhibited superior corrosion resistance in Test Examples 1 and 2.

Claims

1. A MOF glass / epoxy resin anti-corrosion composite coating, characterized in that, Made from raw materials comprising the following parts by weight: Epoxy resin: 100 parts; Hardener: 25-35 parts; Functional filler: 7-28 parts; The raw materials are mixed, coated and cured to form the coating, and in the coating step, the functional filler is applied in a gradient structure with decreasing concentration from the bottom layer near the substrate to the top layer away from the substrate.

2. The MOF glass / epoxy resin anti-corrosion composite coating according to claim 1, characterized in that, The functional filler is an amorphous MOF glass, and the surface of the amorphous MOF glass is chemically anchored by a silane coupling agent.

3. The MOF glass / epoxy resin anti-corrosion composite coating according to claim 1, characterized in that, The functional filler is prepared by the following steps: (a) Reacting metal salts and organic ligands in a solvent to synthesize MOF crystalline powder; (b) The MOF crystal powder is heat-treated under an inert atmosphere to transform it into amorphous MOF glass powder; (c) The amorphous MOF glass powder is chemically anchored on the surface using a silane coupling agent.

4. The MOF glass / epoxy resin anti-corrosion composite coating according to claim 3, characterized in that, The epoxy resin is a bisphenol A diglycidyl ether type epoxy resin. The curing agent is a polyetheramine curing agent; The organic ligand of the MOF crystal powder is selected from at least one of imidazole, benzimidazole and 5-chlorobenzimidazole; The silane coupling agent is selected from one of γ-aminopropyltriethoxysilane, γ-glycidyl etheroxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

5. A method for preparing the MOF glass / epoxy resin anti-corrosion composite coating according to any one of claims 1-4, characterized in that, Includes the following steps: (a) Mix epoxy resin, curing agent and functional filler to prepare at least two slurries with different concentrations of functional filler, including at least a high-concentration slurry and a low-concentration slurry; (b) Apply the high-concentration slurry to the surface of the substrate, and then apply the low-concentration slurry on top of the high-concentration slurry to construct a gradient structure; (c) Curing treatment of the applied coating.

6. The method for preparing a MOF glass / epoxy resin anti-corrosion composite coating according to claim 5, characterized in that, In step (a), the concentration of functional filler in the high-concentration slurry is 10-30 wt%, and the concentration of functional filler in the low-concentration slurry is 1-5 wt%.

7. The method for preparing a MOF glass / epoxy resin anti-corrosion composite coating according to claim 5, characterized in that, The coating method in step (b) is selected from: multi-layer spraying method and layer-by-layer spin coating method.

8. The method for preparing a MOF glass / epoxy resin anti-corrosion composite coating according to claim 7, characterized in that, When using the layer-by-layer spin coating method, each layer is pre-dried at 40°C for 5 minutes after spin coating.

9. The method for preparing a MOF glass / epoxy resin anti-corrosion composite coating according to claim 5, characterized in that, The coating method in step (b) is a dual-channel spraying method. The flow ratio of high-concentration slurry and low-concentration slurry is controlled by the program to form a gradient structure with continuously changing concentration of functional filler.

10. The method for preparing a MOF glass / epoxy resin anti-corrosion composite coating according to claim 5, characterized in that, The curing process described in step (c) specifically includes: Heating at 60-100℃ for 2-3 hours to cure; Curing time is 24 hours at room temperature (20-30℃).

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