A zif-8-based magnesium alloy super-hydrophobic corrosion-resistant coating and a preparation method thereof

Abstract

The application provides a ZIF-8-based magnesium alloy super-hydrophobic corrosion-resistant coating and a preparation method thereof, and belongs to the technical field of functional materials. In the application, ZIF-8 in a metal organic framework is used as a skeleton, zinc nitrate hexahydrate is used as a metal zinc source, and 2-methyl imidazole is used as an organic ligand; under normal temperature reaction, a structure-stable precursor ZIF-8 is self-grown; ZIF-8@SiO2 particles with multi-level roughness are formed by loading nano-scale SiO2 on the surface of the ZIF-8; long-chain stearic acid is introduced on the ZIF-8@SiO2 to improve the hydrophobicity; finally, the multi-layer assembled ZIF-8@SiO2 / STA is embedded into a polyvinyl butyral uniform mixed solution, and a composite coating is obtained by flow casting on the surface of a magnesium alloy. The preparation process of the application is simple, and high-temperature and high-pressure reactions and complex equipment are not needed; the obtained composite coating has a super-hydrophobic surface, greatly improves the corrosion resistance of the magnesium alloy, and has good market competitiveness.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, specifically relating to a ZIF-8 based magnesium alloy superhydrophobic and corrosion-resistant coating and its preparation method. Background Technology

[0002] Magnesium (Mg) and its alloys are important engineering materials due to their light weight, high specific stiffness, and good mechanical properties. Magnesium alloys are also hailed as the most promising next-generation alloy materials. Furthermore, magnesium alloys possess high thermal conductivity, low thermal expansion, high damping capacity, excellent electromagnetic shielding, and machinability; therefore, they are widely used in many fields such as the automotive industry, aerospace, and biomedicine. However, magnesium alloys have a low standard electrode potential, high chemical reactivity, and a loose, porous surface oxide film, making them susceptible to corrosion in humid environments or corrosive media containing chlorides. This severely limits their practical applications.

[0003] While traditional surface treatment techniques can protect magnesium alloys from corrosion to some extent, the poor adhesion between the coating and the metal substrate prevents long-term corrosion protection and can also burden the environment. Surface coating technology is one of the most effective methods to improve material surface properties. Inspired by superhydrophobic phenomena in nature, low surface energy materials are used to modify metal-organic frameworks (MOFs) and incorporate them into polymer binders. Various film-forming methods are then used to form a hydrophobic protective coating on the magnesium alloy surface, thereby improving its corrosion resistance. ZIF-8 is widely used in anti-corrosion coatings due to its excellent structural properties. However, ZIF-8 exhibits poor stability and dispersibility in aqueous solutions, and most low surface energy materials used to modify ZIF-8 contain environmentally harmful fluorine-containing segments. Both of these factors hinder the development of green, long-lasting, hydrophobic, and corrosion-resistant coatings for magnesium alloys. Therefore, how to perform green modification of ZIF-8 to improve its structural stability and the long-lasting corrosion resistance of the coating is extremely important for the development of anti-corrosion coatings for magnesium alloy surfaces. Summary of the Invention

[0004] In view of the content mentioned in the background art, the purpose of this invention is to provide a ZIF-8 based magnesium alloy superhydrophobic and corrosion-resistant coating and its preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for preparing a ZIF-8 based magnesium alloy superhydrophobic and corrosion-resistant coating, comprising the following steps:

[0007] Step 1: Dissolve zinc nitrate hexahydrate and 2-methylimidazole separately in methanol. Add the methanol solution of 2-methylimidazole to the methanol solution of zinc nitrate hexahydrate and stir evenly. Let stand for separation, then centrifuge to separate the precipitate, wash and dry to obtain ZIF-8 particles.

[0008] Step 2: Dissolve the obtained ZIF-8 particles and hexadecyltrimethylammonium bromide in anhydrous ethanol, sonicate, add tetraethyl orthosilicate and stir continuously, then centrifuge to separate the precipitate, wash and dry to obtain ZIF-8@SiO2 particles.

[0009] Step 3: Add the obtained ZIF-8@SiO2 particles and long-chain stearic acid (STA) to anhydrous ethanol, stir and ultrasonically disperse to obtain ZIF-8@SiO2 / STA solution;

[0010] Step 4: Dissolve polyvinyl butyral (PVB) in anhydrous ethanol, then add the resulting solution to the ZIF-8@SiO2 / STA solution in Step 3, and sonicate to obtain the ZIF-8@SiO2 / STA / PVB solution.

[0011] Step 5: Drop the obtained ZIF-8@SiO2 / STA / PVB solution onto the cleaned magnesium alloy surface and dry it to form a film to obtain a ZIF-8-based magnesium alloy superhydrophobic and corrosion-resistant coating (PSZS).

[0012] Furthermore, in step 1, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:(6-8).

[0013] Furthermore, the standing time mentioned in step 1 is to stand in the dark at 25±5℃ for 12-24 hours.

[0014] Furthermore, the washing process described in step 1 uses methanol and is repeated 3-5 times.

[0015] Furthermore, in step 2, the molar ratio of ZIF-8 particles, hexadecyltrimethylammonium bromide, and tetraethyl orthosilicate is 1:(0.7-1):(1-3).

[0016] Furthermore, in step 2, the pH value needs to be adjusted to 9-11 with ammonia before ultrasound.

[0017] Furthermore, the washing in step 2 uses a mixture of anhydrous ethanol and deionized water in a volume ratio of (1-1.5):1, and the washing is repeated 3-5 times.

[0018] Furthermore, the centrifugation speed in both steps 1 and 2 is 6000-8000 rpm.

[0019] Furthermore, in step 3, the mass ratio of ZIF-8@SiO2 particles to STA is 1:(8-15).

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] This invention utilizes nano-SiO2 to coat ZIF-8 to improve its stability in aqueous solutions; it employs environmentally friendly long-chain stearic acid to modify the ZIF-8@SiO2 nanoparticles, avoiding the use of environmentally burdensome fluorine-containing materials; the prepared ZIF-8@SiO2 / STA / PVB composite coating exhibits excellent corrosion resistance in salt solutions, while also possessing good superhydrophobicity. The preparation process of this PSZS composite coating is simple, requiring no high-temperature, high-pressure reactions or complex equipment, making it suitable for industrial production. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation of the PSZS composite coating in Example 1 of the present invention.

[0023] Figure 2 The image shows the FT-IR images of the ZIF-8, ZIF-8@SiO2 and PSZS composite coatings prepared in Example 1 of this invention.

[0024] Figure 3 The image shows the XRD pattern of the ZIF-8, ZIF-8@SiO2 and PSZS composite coatings prepared in Example 1 of this invention.

[0025] Figure 4 In the image: a, b, and c are SEM images of ZIF-8 prepared in Example 1; d, e, and f are SEM images of ZIF-8@SiO2 prepared in Example 1; g, h, and i are SEM images of PSZS composite coating prepared in Example 1.

[0026] Figure 5 a is a contact angle diagram of the PSZS composite coating prepared in Example 1; Figure 5 b is the contact angle wear resistance curve of the PSZS composite coating prepared in Example 1.

[0027] Figure 6 The polarization curves of the PSZS composite coating and AZ31B magnesium alloy prepared in Example 1 in 3.5wt% NaCl solution are shown.

[0028] Figure 7 The image shows the Nyquist plot of the PSZS composite coating and AZ31B magnesium alloy prepared in Example 1 in a 3.5 wt% NaCl solution.

[0029] Figure 8 The Nyquist plot shows the PSZS composite coating prepared in Example 1 after immersion in 3.5 wt% NaCl solution for different times. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] Example 1

[0033] 1. Zinc nitrate hexahydrate (1g) and 2-methylimidazole (2.2g) were added to 50mL of methanol solution (concentration > 99.5%), respectively. The mixture was magnetically stirred at 25℃ and 300rpm until completely dissolved, resulting in solution A and solution B. Solution B was added to solution A and stirred until homogeneous. The mixture was then allowed to stand at 25℃ in the dark for 12h to obtain a layered solution C. Solution C was separated by high-speed centrifugation at 6000rpm. The precipitate was washed three times with methanol (concentration > 99.5%) and dried at 50℃ for 12h to obtain product ZIF-8 particles.

[0034] 2. Disperse ZIF-8 (0.16g) and hexadecyltrimethylammonium bromide (0.2g) in anhydrous ethanol and stir magnetically at 25℃ and 300rpm until completely dissolved to obtain solution D. Adjust the pH of solution D to 11 with ammonia water and then sonicate for 5min to obtain solution E. Then add 1mmol of tetraethyl orthosilicate to solution E and stir continuously to obtain solution F. Centrifuge solution F at 6000rpm and wash the precipitate three times with anhydrous ethanol / deionized water (volume ratio 1:1). After drying at 50℃ for 12h, obtain ZIF-8@SiO2 particles.

[0035] 3. Add 0.01g ZIF-8@SiO2 and 0.1g STA to 2mL of anhydrous ethanol, stir and sonicate for 30min to obtain ZIF-8@SiO2 / STA solution.

[0036] 4. Add 8g of PVB to 92mL of anhydrous ethanol and stir at 55℃ until completely dissolved to obtain an 8% solution G. Then take 2mL of solution G and add it to ZIF-8@SiO2 / STA solution, and sonicate for 30min to obtain ZIF-8@SiO2 / STA / PVB solution.

[0037] 5. Polish the magnesium alloy surface with 1200-grit sandpaper, and ultrasonically clean it with acetone and anhydrous ethanol. After drying, a clean magnesium alloy without surface oxide film and oil stains is obtained. The ZIF-8@SiO2 / STA / PVB solution is drop-coated onto the clean magnesium alloy surface and dried at 50°C to form a film, thus obtaining a ZIF-8-based magnesium alloy superhydrophobic and corrosion-resistant PSZS composite coating.

[0038] A schematic diagram of the PSZS composite coating preparation process is shown below. Figure 1 As shown.

[0039] The materials prepared in Example 1 were characterized and tested. The infrared spectra of the ZIF-8, ZIF-8@SiO2 and PSZS composite coatings are as follows: Figure 2 As shown in the image. It can be seen that 2927cm -1 The absorption peak at 1557 cm⁻¹ is attributed to the vibration of the CH absorption band on the imidazole ring. -1 The absorption peak at 1458 cm⁻¹ is attributed to the C=N vibration on the imidazole ring. -1 and 1419cm -1 The peak at 1307-925 cm⁻¹ is attributed to the tensile vibration of the entire ring. -1 The peaks are attributed to the vibration of the imidazole ring, and are located at 756 cm⁻¹. -1 and 690cm -1 Zn-O and Zn-N absorption peaks were observed in ZIF-8; in addition, Si-O-Si peaks of SiO2 were also observed in ZIF-8@SiO2, and CH vibrations of PVB and C=O vibrations of STA were observed in PSZS; it can be seen that ZIF-8@SiO2 and STA were successfully introduced into the PSZS composite coating.

[0040] The XRD patterns of the ZIF-8, ZIF-8@SiO2 and PSZS composite coatings prepared in Example 1 are as follows: Figure 3 As shown. For ZIF-8 particles, 7.07°, 10.1°, 12.4°, 14.4°, 16.2°, 17.7°, 21.8°, 24.2°, and 26.4° correspond to the (011), (002), (112), (022), (013), (222), (114), (233), and (134) crystal planes. The ZIF-8@SiO2 and PSZS composite coatings also exhibit the same peaks at the corresponding positions.

[0041] The SEM images of the ZIF-8, ZIF-8@SiO2 and PSZS composite coatings prepared in Example 1 are as follows: Figure 4 As shown. Figure 4 a, b, and c show the SEM images of ZIF-8, which clearly show the typical rhombic dodecahedral structure of ZIF-8. Figure 4Images d, e, and f show SEM images of ZIF-8@SiO2, showing that SiO2 completely coats the ZIF-8 surface. Figure 4 g, h, and i show the SEM images of the PSZS composite coating. It can be seen that there are some nano-sized particles on the coating surface. This is the result of the STA-coated ZIF-8@SiO2 particles being dispersed in PVB, which increases the roughness of the coating surface and thus improves the hydrophobicity of the coating surface.

[0042] The contact angle and abrasion resistance of the PSZS composite coating prepared in Example 1 are tested as follows: Figure 5 As shown. Figure 5 Figure a shows the contact angle between the PSZS composite coating and water. Water droplets appear spherical on the surface of the PSZS composite coating, indicating that the PSZS composite coating has excellent hydrophobic properties. Figure 5 The contact angle measurement at the upper right corner shows that the contact angle between the PSZS composite coating and water is 153°, indicating that the PSZS composite coating has superhydrophobicity. Figure 5 b shows that the PSZS composite coating still exhibits superhydrophobicity at a certain friction distance, indicating that the prepared PSZS composite coating has excellent wear resistance.

[0043] The polarization curves of the PSZS composite coating and AZ31B magnesium alloy prepared in Example 1 in 3.5wt% NaCl solution are as follows: Figure 6 As shown in Table 1, the corrosion potentials of AZ31B magnesium alloy and the PSZS composite coating are -1.527V and -1.18V, respectively, indicating that the prepared PSZS composite coating can effectively improve the corrosion resistance of magnesium alloy; moreover, the corrosion current density of the PSZS composite coating is 1.28 × 10⁻⁶. -11 A / cm 2 This is far less than the corrosion current density of magnesium alloy, which is 1.14 × 10⁻⁶. -4 A / cm 2 This also shows that the PSZS composite coating can very effectively slow down the corrosion rate of magnesium alloys; calculations show that the corrosion protection rate of the PSZS composite coating on magnesium alloys is close to 100%.

[0044] Table 1

[0045] Sample <![CDATA[β a ]]> <![CDATA[β c ]]> <![CDATA[E corr (V / (SCE))]]> <![CDATA[i corr (A·cm -2 )]]> η Bare Mg 0.06 0.20 -1.527 <![CDATA[1.14×10 -4 ]]> PSZS coating 0.08 0.07 -1.18 <![CDATA[1.28×10 -11 ]]> 99.99％

[0046] The electrochemical impedance spectroscopy (Nyquist plot) of AZ31B magnesium alloy and the PSZS composite coating prepared in Example 1 in 3.5 wt% NaCl solution is shown below. Figure 7 As shown in a and b. From Figure 7As shown in Figure a, all impedance diagrams reveal that the AZ31B magnesium alloy substrate exhibits a relatively complete small-diameter semicircular arc, while the PSZS composite coating displays an incomplete large-diameter capacitive arc. This demonstrates that the PSZS composite coating can prevent corrosive media from penetrating the coating and entering the interface between the substrate and the coating, thereby effectively avoiding corrosion.

[0047] The Nyquist plot of the PSZS composite coating prepared in Example 1 in 3.5 wt% NaCl solution is shown below. Figure 8 As shown in a and b. Figure 8 a is the Nyquist electrochemical impedance spectroscopy plot after 12 hours of immersion. Figure 8 b is the Nyquist plot of electrochemical impedance spectroscopy 15 days after immersion. It can be seen that as the immersion time increases, the diameter of the capacitance arc of the PSZS composite coating gradually shortens, indicating that the corrosion resistance decreases with the increase of immersion time. However, for the AZ31B magnesium alloy substrate, the diameter of the capacitance ring of the PSZS coating after 15 days of immersion is much larger than that of the AZ31B magnesium alloy substrate, proving that the prepared PSZS composite coating has very good long-term corrosion resistance.

[0048] Example 2

[0049] 1. Zinc nitrate hexahydrate (0.8 g) and 2-methylimidazole (1.6 g) were added to 30 mL of methanol solution (concentration > 99.5%), respectively. The mixture was magnetically stirred at 25 °C and 400 rpm until completely dissolved, resulting in solution A and solution B. Solution B was added to solution A and stirred until homogeneous. The mixture was then allowed to stand at 25 °C in the dark for 18 h to obtain a layered solution C. Solution C was separated by high-speed centrifugation at 7000 rpm. The precipitate was washed three times with methanol (concentration > 99.5%) and dried at 55 °C for 18 h to obtain ZIF-8 particles.

[0050] 2. ZIF-8 (0.13g) and hexadecyltrimethylammonium bromide (0.18g) were dispersed in anhydrous ethanol and magnetically stirred at 25°C and 400 rpm until completely dissolved to obtain solution D. The pH of solution D was adjusted to 11 with ammonia water and then sonicated for 8 min to obtain solution E. Then, 0.8 mmol of tetraethyl orthosilicate was added to solution E and stirred continuously to obtain solution F. Solution F was separated by high-speed centrifugation at 7000 rpm, and the precipitate was washed three times with anhydrous ethanol / deionized water (volume ratio 1.2:1). After drying at 55°C for 18 h, ZIF-8@SiO2 particles were obtained.

[0051] 3. Add 0.005g ZIF-8@SiO2 and 0.08g STA to 2mL of anhydrous ethanol, stir and sonicate for 30min to obtain ZIF-8@SiO2 / STA solution.

[0052] 4. Add 2g of PVB to 23mL of anhydrous ethanol and stir at 60℃ until completely dissolved to obtain an 8% solution G. Then take 2mL of solution G and add it to ZIF-8@SiO2 / STA solution, and sonicate for 30min to obtain ZIF-8@SiO2 / STA / PVB solution.

[0053] 5. Grind the magnesium alloy surface with 1200-grit sandpaper, and ultrasonically wash it with acetone and anhydrous ethanol. After drying, a clean magnesium alloy without surface oxide film and oil stains is obtained. The ZIF-8@SiO2 / STA / PVB solution is drop-coated onto the clean magnesium alloy surface and dried at 55°C to form a film, thus obtaining a ZIF-8-based magnesium alloy superhydrophobic and corrosion-resistant PSZS composite coating.

[0054] Example 3

[0055] 1. Zinc nitrate hexahydrate (1.2 g) and 2-methylimidazole (2.4 g) were added to 60 mL of methanol solution (concentration > 99.5%), respectively. The mixture was magnetically stirred at 25 °C and 500 rpm until completely dissolved, resulting in solution A and solution B. Solution B was added to solution A and stirred until homogeneous. The mixture was then allowed to stand at 25 °C in the dark for 24 h to obtain a layered solution C. Solution C was separated by high-speed centrifugation at 8000 rpm. The precipitate was washed three times with methanol (concentration > 99.5%) and dried at 60 °C for 24 h to obtain product ZIF-8 particles.

[0056] 2. Disperse ZIF-8 (0.16 g) and hexadecyltrimethylammonium bromide (0.2 g) in anhydrous ethanol and stir magnetically at 25 °C and 500 rpm until completely dissolved to obtain solution D. Adjust the pH of solution D to 11 with ammonia water and then sonicate for 10 min to obtain solution E. Then add 1.2 mmol of tetraethyl orthosilicate to solution E and stir continuously to obtain solution F. Centrifuge solution F at 8000 rpm and wash the precipitate three times with anhydrous ethanol / deionized water (volume ratio 1.5:1). After drying at 60 °C for 24 h, obtain ZIF-8@SiO2 particles.

[0057] 3. Add 0.015g ZIF-8@SiO2 and 0.2g STA to 2mL of anhydrous ethanol, stir and sonicate for 30min to obtain ZIF-8@SiO2 / STA solution.

[0058] 4. Add 1g PVB to 12mL of anhydrous ethanol and stir at 65℃ until completely dissolved to obtain an 8% solution G. Then take 2mL of solution G and add it to ZIF-8@SiO2 / STA solution, and sonicate for 30min to obtain ZIF-8@SiO2 / STA / PVB solution.

[0059] 5. Polish the magnesium alloy surface with 1200-grit sandpaper, and ultrasonically wash it with acetone and anhydrous ethanol. After drying, a clean magnesium alloy without surface oxide film and oil stains is obtained. The ZIF-8@SiO2 / STA / PVB solution is drop-coated onto the clean magnesium alloy surface and dried at 60°C to form a film, thus obtaining a ZIF-8-based magnesium alloy superhydrophobic and corrosion-resistant PSZS composite coating.

[0060] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they are not intended to limit the present invention. It should be noted that various changes and modifications can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the concept and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a ZIF-8 based magnesium alloy superhydrophobic and corrosion-resistant coating, characterized in that, Includes the following steps: Step 1: Dissolve zinc nitrate hexahydrate and 2-methylimidazole separately in methanol. Add the methanol solution of 2-methylimidazole to the methanol solution of zinc nitrate hexahydrate and stir evenly. Let stand for separation, then centrifuge to separate the precipitate, wash and dry to obtain ZIF-8 particles. Step 2: Dissolve the obtained ZIF-8 particles and hexadecyltrimethylammonium bromide in anhydrous ethanol, sonicate, add tetraethyl orthosilicate and stir continuously, then centrifuge to separate the precipitate, wash and dry to obtain ZIF-8@SiO2 particles. The molar ratio of ZIF-8 particles, hexadecyltrimethylammonium bromide and tetraethyl orthosilicate is 1:(0.7-1):(1-3); Step 3: Add the obtained ZIF-8@SiO2 particles and long-chain stearic acid to anhydrous ethanol, stir and ultrasonically disperse to obtain ZIF-8@SiO2 / STA solution; The mass ratio of ZIF-8@SiO2 particles to long-chain stearic acid is 1:(8-15). Step 4: Dissolve polyvinyl butyral in anhydrous ethanol, then add the resulting solution to the ZIF-8@SiO2 / STA solution in Step 3, and sonicate to obtain the ZIF-8@SiO2 / STA / PVB solution. Step 5: Drop the obtained ZIF-8@SiO2 / STA / PVB solution onto the cleaned magnesium alloy surface and dry it to form a film to obtain a ZIF-8-based magnesium alloy superhydrophobic and corrosion-resistant coating.

2. The method for preparing the ZIF-8 based magnesium alloy superhydrophobic and corrosion-resistant coating according to claim 1, characterized in that, In step 1, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:(6-8).

3. The method for preparing the ZIF-8 based magnesium alloy superhydrophobic and corrosion-resistant coating according to claim 1, characterized in that, The step 1 step involves allowing the food to stand in the dark at 25±5℃ for 12-24 hours.

4. The method for preparing the ZIF-8 based magnesium alloy superhydrophobic and corrosion-resistant coating according to claim 1, characterized in that, The washing process described in step 1 uses methanol and is repeated 3-5 times.

5. The method for preparing the ZIF-8 based magnesium alloy superhydrophobic and corrosion-resistant coating according to claim 1, characterized in that, Step 2: Before ultrasound, the pH value needs to be adjusted to 9-11 with ammonia.

6. The method for preparing the ZIF-8 based magnesium alloy superhydrophobic and corrosion-resistant coating according to claim 1, characterized in that, The washing process in step 2 uses a mixture of anhydrous ethanol and deionized water in a volume ratio of (1-1.5):1, and is repeated 3-5 times.

7. The method for preparing the ZIF-8 based magnesium alloy superhydrophobic and corrosion-resistant coating according to claim 1, characterized in that, The centrifugation speed in both steps 1 and 2 is 6000-8000 rpm.

Images