An in-situ preparation method of a layered double hydroxide-silane composite film for preventing corrosion of steel

Abstract

This invention provides an in-situ preparation method for a layered bimetallic hydroxide-silane composite film to prevent steel corrosion, relating to the field of steel surface anti-corrosion treatment technology. The in-situ preparation method of the layered bimetallic hydroxide-silane composite film to prevent steel corrosion provided by this invention includes the following steps: mixing a divalent metal salt, a trivalent metal salt, an alkali source, silane, and water to obtain a mixed solution; placing steel in the mixed solution and performing a hydrothermal reaction to grow a layered bimetallic hydroxide-silane composite film in situ on the steel surface. This invention uses a one-step method to grow a layered bimetallic hydroxide-silane composite film in situ on the steel surface, exhibiting excellent corrosion resistance, delaying steel corrosion, and using a green and environmentally friendly preparation method.

Description

Technical Field

[0001] This invention relates to the field of steel surface anti-corrosion treatment technology, specifically to an in-situ preparation method of a layered bimetallic hydroxide-silane composite film for preventing steel corrosion. Background Technology

[0002] Steel, as a high-strength and low-cost material, has been widely used in various industries. However, steel corrosion has caused significant maintenance costs and a range of environmental problems. Currently, steel surface coating is considered an ideal anti-corrosion solution. Applying a coating to the steel surface provides a protective barrier against corrosion, preventing the steel from contacting corrosive media. There are many methods for applying coatings, among which in-situ coating growth on the steel surface offers the advantage of strong adhesion.

[0003] Layered bimetallic hydroxide (LDH) is a substance with a structure similar to brucite. The chemical composition of LDH has the following general formula: [M 2+ 1-x M 3+ (OH)2] x+ (A n- ) x / n ·mH2O, where M 2+ and M 3+ These are divalent and trivalent metal cations located on the main plate, respectively, while x is M. 3+ / (M 2+ +M 3+ The molar ratio of ) is given by , where m is the number of water molecules in the interlayer. Furthermore, the adsorption capacity of LDH for anions increases with increasing anion charge and decreasing anion particle size. The following is the order of LDH's anion absorption strength: CO3 2- >SO4 2- >HPO4 - >OH - >F - >Cl - >Br - >NO3 - .

[0004] Silanization is a surface treatment process that utilizes the unique molecular structure of organosilicon to treat the substrate material. Compared to traditional metal surface treatments, silanization offers numerous advantages, including being environmentally friendly, energy-efficient, and cost-effective. Silanization can improve the adhesion between organic materials and metals while providing good corrosion protection for metals. Furthermore, silanes can be introduced into the inner and outer surfaces and edges of clay sheets.

[0005] Because LDH has a good chemical bond with the steel substrate and can be grown in situ and thinly on the metal surface, it is a promising material in the field of metal corrosion protection. LDH can be grown in situ on the steel substrate using a hydrothermal method. However, LDH grown on the steel surface has a micron-porous structure, and considering that the surface of the LDH phase has abundant hydrophilic hydroxyl groups, which facilitates water permeation but is not conducive to corrosion protection, it is further modified with silane to become a superhydrophobic structure. However, most current methods involve first growing LDH in situ and then performing surface hydrophobic modification, which is a cumbersome process. Summary of the Invention

[0006] The purpose of this invention is to provide an in-situ preparation method for a layered bimetallic hydroxide-silane composite film that prevents steel corrosion. This invention uses a one-step method to grow a layered bimetallic hydroxide-silane composite film in situ on the surface of steel, which has excellent corrosion resistance, can delay the rusting of steel, and the preparation method is green and environmentally friendly.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides an in-situ preparation method for a layered bimetallic hydroxide-silane composite film to prevent steel corrosion, comprising the following steps:

[0009] A mixed solution is obtained by mixing a divalent metal salt, a trivalent metal salt, an alkaline source, silane, and water.

[0010] The steel is placed in the mixed solution and subjected to a hydrothermal reaction, resulting in the in-situ growth of a layered bimetallic hydroxide-silane composite film on the surface of the steel.

[0011] Preferably, the divalent metal salt includes one or more of magnesium nitrate and cobalt nitrate.

[0012] Preferably, the molar ratio of the divalent metal salt to the trivalent metal salt is 2 to 3:1.

[0013] Preferably, the trivalent metal salt includes one or more of aluminum nitrate and ferric nitrate.

[0014] Preferably, the alkali source is urea.

[0015] Preferably, the silane includes one or more of n-octyltriethoxysilane and aminopropyltriethoxysilane.

[0016] Preferably, the steel is further pretreated before being placed in the mixed solution;

[0017] The pretreatment includes sanding with sandpaper and acid washing in sequence.

[0018] Preferably, the temperature of the hydrothermal reaction is 90–140°C; and the time of the hydrothermal reaction is 10–48 h.

[0019] Preferably, the hydrothermal reaction further includes: sequentially washing and drying the obtained specimen to obtain a layered bimetallic hydroxide-silane composite membrane.

[0020] Preferably, the hydroxyl groups of the layered bimetallic hydroxide in the layered bimetallic hydroxide-silane composite membrane are chemically bonded to the hydrolyzed silane.

[0021] This invention provides an in-situ preparation method for a layered bimetallic hydroxide-silane composite film to prevent steel corrosion. The preparation method of this invention is simple. LDH can form chemical bonds on the steel surface, and silane and LDH can form a chemical bond, becoming a firmly bonded whole. The presence of silane changes LDH from hydrophilic to hydrophobic. In addition, it can also chemically bond with other substances through the hydroxyl groups of silane, forming a strong physical barrier effect, which greatly delays the corrosion of steel. The results of the examples show that this invention can grow a layered bimetallic hydroxide-silane composite film on the steel surface in one step in situ, which has the advantages of simple preparation method and can greatly improve the corrosion resistance of steel.

[0022] This invention provides an in-situ grown layered bimetallic hydroxide-silane composite film (LDH / Si) on steel surfaces, exhibiting excellent stability. Furthermore, due to the large specific surface area of ​​LDH, numerous hydroxyl functional groups between the LDH layers form chemical bonds with the hydrolyzed silane, effectively blocking water and corrosive ions. The method involves only solution preparation and reaction, simplifying the operation and eliminating the need for extensive pretreatment of the steel. The materials used are environmentally friendly. This invention's in-situ growth of LDH / Si on steel surfaces demonstrates excellent corrosion resistance, strong rust-retarding effect, and a green and environmentally friendly preparation process. Attached Figure Description

[0023] Figure 1 XRD patterns of blank steel sheet, steel sheet with LDH attached in Comparative Example 2, and steel sheet with LDH / Si attached in Example 1;

[0024] Figure 2 FTIR peak diagrams of LDH prepared in Comparative Example 2 and LDH / Si prepared in Example 1;

[0025] Figure 3 SEM / EDS images of the steel sheet with LDH attached in Comparative Example 2 and the steel sheet with LDH / Si attached in Example 1;

[0026] Figure 4 The surface element distribution diagram of LDH / Si prepared in Example 1;

[0027] Figure 5 Morphology of steel sheets coated with LDH / Si (a) prepared by the one-step method in Example 1, LDH / Si (b) prepared by the two-step method in Comparative Example 1, and pure LDH (c) prepared in Comparative Example 2, respectively, in 3.5 wt.% NaCl solution over time.

[0028] Figure 6 Nquist plot of LDH / Si prepared in Example 1 in 3.5 wt.% NaCl solution;

[0029] Figure 7 for Figure 6 Enlarged version of the front arc;

[0030] Figure 8 Bode-impedance diagram of LDH / Si prepared in Example 1 in 3.5 wt.% NaCl solution;

[0031] Figure 9 Bode phase angle diagram of the LDH / Si steel sheet prepared in Example 1 in 3.5 wt.% NaCl solution;

[0032] Figure 10 The Nquist plot shows the change of LDH / Si in 3.5 wt.% NaCl solution over time after scratching.

[0033] Figure 11 The elemental surface scan of the scratched LDH / Si was performed after immersion in 3.5 wt.% NaCl solution for 4 days.

[0034] Figure 12 Elemental surface scan of the scratched area of ​​the LDH / Si blank sample after scratching;

[0035] Figure 13 The surface morphology of the steel sheet with LDH / Si(a) prepared by the one-step method in Example 1 after immersion in 3.5 wt.% NaCl solution for 60 days. Detailed Implementation

[0036] This invention provides an in-situ preparation method for a layered bimetallic hydroxide-silane composite film to prevent steel corrosion, comprising the following steps:

[0037] A mixed solution is obtained by mixing a divalent metal salt, a trivalent metal salt, an alkaline source, silane, and water.

[0038] The steel is placed in the mixed solution and subjected to a hydrothermal reaction, resulting in the in-situ growth of a layered bimetallic hydroxide-silane composite film on the surface of the steel.

[0039] This invention involves mixing a divalent metal salt, a trivalent metal salt, an alkaline source, silane, and water to obtain a mixed solution. In this invention, the divalent metal salt preferably includes one or more of magnesium nitrate and cobalt nitrate, more preferably magnesium nitrate nonahydrate. In this invention, the trivalent metal salt preferably includes one or more of aluminum nitrate and ferric nitrate, more preferably aluminum nitrate hexahydrate. In this invention, the alkaline source is preferably urea.

[0040] In this invention, the mixing of the divalent metal salt, trivalent metal salt, alkali source, silane, and water preferably comprises: mixing the divalent metal salt, trivalent metal salt, alkali source, and water to obtain a salt solution; and mixing the salt solution with silane to obtain a mixed solution. In this invention, the concentration of the divalent metal salt in the salt solution is preferably 0.025–0.1 mol / L, more preferably 0.0575 mol / L. In this invention, the molar ratio of the divalent metal salt to the trivalent metal salt is preferably 2–3:1, more preferably 2.3–2.5:1. In this invention, the concentration of the alkali source in the salt solution is preferably 0.3–1 mol / L, more preferably 0.375 mol / L.

[0041] In this invention, the silane preferably includes one or more of n-octyltriethoxysilane and aminopropyltriethoxysilane. In this invention, the volume ratio of the salt solution to the silane is preferably 10:0.5 to 1.5, more preferably 10:1.

[0042] In this invention, the water is preferably deionized water.

[0043] After obtaining the mixed solution, the present invention places steel in the mixed solution and performs a hydrothermal reaction, thereby growing a layered bimetallic hydroxide-silane composite film in situ on the surface of the steel. In the present invention, the steel is preferably a steel sheet.

[0044] In this invention, the steel is preferably pretreated before being placed in the mixed solution; the pretreatment preferably includes sequential sanding and pickling. In this invention, the sanding preferably includes sequential sanding with 240#, 500#, 1000#, and 2000# sandpaper, followed by removing surface impurities using alcohol via ultrasonic vibration. In this invention, the pickling solution is preferably 5wt% dilute nitric acid; the pickling time is preferably 15 seconds. This invention pretreatment of the steel not only removes impurities but also, through surface pickling, promotes the growth of the layered bimetallic hydroxide-silane composite film.

[0045] In this invention, the steel is preferably placed vertically in the mixed solution, which enables the layered bimetallic hydroxide-silane composite film to grow more uniformly on the steel surface.

[0046] In this invention, the temperature of the hydrothermal reaction is preferably 90–140°C, more preferably 100–120°C; the time of the hydrothermal reaction is preferably 10–48 h, more preferably 12–24 h. In this invention, the hydrothermal reaction is preferably carried out in a reaction vessel lined with polytetrafluoroethylene.

[0047] In this invention, the hydrothermal reaction preferably further includes: sequentially washing and drying the obtained sample with water to obtain a layered bimetallic hydroxide-silane composite film. In this invention, the water washing is preferably deionized water washing. In this invention, the drying temperature is preferably 45°C; the drying time is preferably 3 hours.

[0048] In the early stage of the hydrothermal reaction, the silane hydrolysis is insufficient, resulting in in-situ growth of LDH on the steel surface. Subsequently, the hydroxyl groups from the silane hydrolysis connect with the hydroxyl groups of the LDH layer, thereby forming a connection between silane and LDH.

[0049] In this invention, the hydroxyl groups of the layered bimetallic hydroxide-silane composite film are chemically bonded to the hydrolyzed silane. Preferably, the hydroxyl groups of the layered bimetallic hydroxide and the hydrolyzed silane are chemically bonded through the hydroxyl groups.

[0050] In this invention, the thickness of the layered bimetallic hydroxide-silane composite film is preferably 20-30 μm, more preferably 20-25 μm.

[0051] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0052] Example 1

[0053] Magnesium nitrate nonahydrate, aluminum nitrate hexahydrate, and urea were dissolved in 32 mL of deionized water and poured into a polytetrafluoroethylene container to obtain a salt solution. 3.2 mL of n-octyltriethoxysilane was added to the salt solution to obtain a mixed solution. The concentrations of magnesium nitrate nonahydrate, aluminum nitrate hexahydrate, and urea in the salt solution were 0.0575 mol / L, 0.025 mol / L, and 0.375 mol / L, respectively.

[0054] After cleaning the steel sheet with 240#, 500#, 1000# and 2000# sandpaper, the surface impurities were removed by ultrasonic vibration with alcohol. Then, the steel sheet was acid-washed with 5wt% dilute nitric acid for 15 seconds. The pretreated steel sheet was then vertically placed into a polytetrafluoroethylene (PTFE) liner, and the mixed solution was poured in. The PTFE liner was placed in a reaction vessel and subjected to a hydrothermal reaction at 120°C for 24 hours. After cooling to room temperature, the reacted steel sheet was removed, rinsed four times with deionized water, and dried in a drying oven at 45°C for 3 hours to obtain a steel sheet with LDH / Si coating. The thickness of LDH / Si was 20-25 μm.

[0055] Comparative Example 1

[0056] Magnesium nitrate nonahydrate, aluminum nitrate hexahydrate, and urea were dissolved in 35 mL of deionized water to obtain a mixed solution; the concentration of magnesium nitrate nonahydrate in the mixed solution was 0.0575 mol / L, the concentration of aluminum nitrate hexahydrate was 0.025 mol / L, and the concentration of urea was 0.375 mol / L.

[0057] After the steel sheet was cleaned by sequentially polishing with 240#, 500#, 1000# and 2000# sandpaper, the surface impurities were removed by ultrasonic vibration with alcohol. Then, it was acid-washed with 5wt% dilute nitric acid for 15 seconds. The pretreated steel sheet was then vertically placed into a polytetrafluoroethylene (PTFE) liner, and the mixed solution was poured in. The PTFE liner was placed in a reaction vessel and subjected to a hydrothermal reaction at 120°C for 24 hours. After cooling, the steel sheet with the LDH film attached was removed.

[0058] Dissolve 3.2 mL of n-octyltriethoxysilane in 32 mL of deionized water and let stand at room temperature for 12 h to obtain a hydrolyzed TTOS solution.

[0059] The steel sheet with the attached LDH film was placed in the hydrolyzed TTOS solution and reacted at 60°C for 3 hours. The reacted steel sheet was washed four times with deionized water and dried at 60°C for 3 hours to obtain a steel sheet with two-step LDH / Si attachment.

[0060] Comparative Example 2

[0061] The preparation method is basically the same as that in Example 1, except that no silane is added, and a steel sheet with LDH is obtained.

[0062] Test case

[0063] (1) X-ray diffractometer (XRD, Germany Bruker D8 Advance, CuKα) was used to characterize the crystal structure and material composition of different samples. The scanning time was set to 0.1s, the scanning step size was 0.02, the scanning range 2θ was 5° to 70°, and the radiation voltage and current were 40kV and 40mA, respectively. Figure 1 XRD patterns of a blank steel sheet, a steel sheet with LDH attached (Comparative Example 2), and a steel sheet with LDH / Si attached (Example 1). Figure 1 As can be seen, the peak value of XRD did not change, which indicates that the addition of silane did not affect the in-situ growth of LDH on the steel sheet.

[0064] (2) The material composition of LDH / Si was further determined using an attenuated total reflectance Fourier transform infrared spectrometer (FTIR, Spectrum 100), with a scanning range of 4000–400 cm⁻¹. -1 . Figure 2 FTIR peak patterns of LDH prepared in Comparative Example 2 and LDH / Si prepared in Example 1. (The text repeats itself here.) Figure 2 FTIR analysis revealed that LDH / Si had an additional 2925 cm⁻¹. -1 2850cm -1 950cm -1 1060cm -1 1110cm -1 Several peaks, representing -CH3, -CH2, Si-OH, Si-O-Si, and Si-OC respectively, indicate the successful recombination of silane and LDH.

[0065] (3) The morphology of the LDH film on the steel sheet and the size of the LDH sheet were observed using a field emission environmental scanning electron microscope (SEM, Quanta TM 250 FEG equipped with an EDS detector). Figure 3 SEM / EDS images of the steel sheet with LDH attached in Comparative Example 2 and the steel sheet with LDH / Si attached in Example 1. Figure 4 The image shows the surface element distribution of the LDH / Si prepared in Example 1. Figure 3 SEM images show that the morphology of LDH / Si exhibits some electrostatic interference, while pure LDH is clearer. This is because LDH / Si itself has a certain degree of non-conductivity, indicating that silane is composited on LDH. Simultaneously, EDS spot scanning and... Figure 4 A surface scan revealed that silane was uniformly distributed on the surface of the LDH sample.

[0066] (4) Figure 5Morphology images of steel sheets coated with LDH / Si (a) prepared by the one-step method in Example 1, LDH / Si (b) prepared by the two-step method in Comparative Example 1, and pure LDH (c) prepared in Comparative Example 2, respectively, in 3.5 wt.% NaCl solution over time.

[0067] pass Figure 5 It can be seen that after soaking in a 3.5 wt.% NaCl solution for 30 days, the one-step LDH / Si still showed no signs of corrosion. However, the two-step LDH / Si and LDH steel sheets were severely corroded. EIS was performed on the LDH / Si prepared in Example 1 after 30 days of soaking (see...). Figure 6 , Figure 7 , Figure 8 The results showed that LDH / Si still exhibited strong corrosion resistance after immersion for 30 days, and good corrosion resistance even after immersion for 60 days (e.g., Figure 13 (As shown). It was also found that LDH / Si possesses a certain degree of self-healing ability; on day 30, its high-frequency capacitive arc was larger than that on day 1 after immersion in 3.5 wt.% NaCl solution.

[0068] Figure 9 Bode phase angle diagram of the LDH / Si steel sheet prepared in Example 1 in 3.5 wt.% NaCl solution, by Figure 9 It can be seen that the phase angle of LDH / Si in the low-frequency region is approximately -50°, indicating that the thin film is equivalent to an isolation layer with high resistance. It is generally believed that materials with high low-frequency impedance amplitude have better corrosion resistance, and a phase angle of (10°) at high frequencies... 4 -10 5 The increase in Hz indicates a certain improvement in its corrosion resistance.

[0069] (5) In order to further explore the self-healing ability, scratches of about 60 to 100 μm were made on the LDH / Si prepared in Example 1, and electrochemical impedance measurements were performed at different times. Figure 10 The Nquist plot shows the change in impedance of LDH / Si after scratching in 3.5 wt.% NaCl solution over time. It was found that the impedance increased to some extent after 18 h, reached its maximum at 36 h, and then decreased to a stable value. SEM observation of LDH / Si after four days of soaking compared to the blank group (…). Figure 12 Without soaking in 3.5 wt.% NaCl solution), a one-step LDH / Si method was found. Figure 11 The presence of a high concentration of Si and C at the scratches indicates that the LDH / Si prepared by the one-step method has self-healing capabilities.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for in-situ preparation of a layered bimetallic hydroxide-silane composite film to prevent steel corrosion, comprising the following steps: A salt solution is obtained by mixing a divalent metal salt, a trivalent metal salt, an alkaline source, and water. The salt solution and silane are mixed to obtain a mixed solution; The steel is placed in the mixed solution and subjected to a hydrothermal reaction, and a layered bimetallic hydroxide-silane composite film is grown in situ on the surface of the steel. The concentration of the divalent metal salt in the salt solution is 0.025~0.1 mol / L, the molar ratio of the divalent metal salt to the trivalent metal salt is 2~3:1, and the concentration of the alkaline source in the salt solution is 0.3~1 mol / L. The volume ratio of the salt solution to silane is 10:0.5~1.5; Before being placed in the mixed solution, the steel material undergoes a pretreatment process; the pretreatment includes sequential sanding and pickling; the pickling solution used is 5wt% dilute nitric acid, and the pickling time is 15s; the steel material is a steel sheet. In the layered bimetallic hydroxide-silane composite membrane, the hydroxyl groups of the layered bimetallic hydroxide are chemically bonded to the hydrolyzed silane.

2. The in-situ preparation method according to claim 1, characterized in that, The divalent metal salts include one or more of magnesium nitrate and cobalt nitrate.

3. The in-situ preparation method according to claim 1, characterized in that, The trivalent metal salts include one or more of aluminum nitrate and ferric nitrate.

4. The in-situ preparation method according to claim 1, characterized in that, The alkaline source is urea.

5. The in-situ preparation method according to claim 1, characterized in that, The silane includes one or more of n-octyltriethoxysilane and aminopropyltriethoxysilane.

6. The in-situ preparation method according to claim 1, characterized in that, The hydrothermal reaction temperature is 90~140℃; the hydrothermal reaction time is 10~48h.

7. The in-situ preparation method according to claim 1, characterized in that, The hydrothermal reaction process further includes: sequentially washing and drying the obtained specimens with water to obtain a layered bimetallic hydroxide-silane composite membrane.

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