Intelligent super-hydrophobic composite coating with hydrophilic-hydrophobic conversion property on surface of magnesium alloy and preparation method of intelligent super-hydrophobic composite coating

Abstract

The invention discloses a preparation method of an intelligent super-hydrophobic composite coating with hydrophilic-hydrophobic conversion performance on the surface of a magnesium alloy. The preparation method comprises the following steps: dissolving a zinc nitrate hexahydrate solution with ethanol and water; graphite serves as an anode, magnesium alloy serves as a cathode, and a ZnO layer is obtained through electro-deposition; the method comprises the following steps: dissolving a zinc nitrate hexahydrate solution and a 2-methylimidazole solution by using ethanol and water, taking a magnesium alloy as an anode, taking a ZnO-loaded magnesium alloy as a cathode, and carrying out electrodeposition on the cathode to obtain a ZIF-8 layer; and washing and drying to obtain the ZnO / ZIF-8 intelligent super-hydrophobic composite coating and the magnesium alloy with the ZnO / ZIF-8 intelligent super-hydrophobic composite coating on the surface. The ZnO / ZIF-8 composite coating prepared through the method has good binding force with a magnesium alloy base material, can be evenly distributed on the surface of magnesium alloy, can achieve super-hydrophobicity without modification of low-surface-energy substances and has the hydrophilic-hydrophobic conversion performance. And good corrosion resistance is also achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of corrosion-resistant super-hydrophobic coatings for metal materials, and in particular to an intelligent super-hydrophobic composite coating with affinity-repellency conversion performance prepared on the surface of a magnesium alloy and a preparation method thereof. Background Art

[0002] As the lightest structural metal in practical applications, magnesium (Mg) alloy is widely used in aerospace, biomedicine, new energy vehicles and other fields due to its low density, high specific strength and excellent electrical and thermal conductivity. And the demand for magnesium alloys is increasing year by year. Although magnesium alloys have many excellent properties, their chemical properties are active. The standard electrode potential of Mg is -2.37V, indicating that magnesium alloys have a strong tendency to corrode. Galvanic corrosion and localized corrosion are common corrosion modes in magnesium alloys. All these factors limit the wide application of magnesium alloys in humid, salt, acid and oxidizing environments. In response to this phenomenon, researchers have developed many processing technologies, and superhydrophobic coatings are popular because of their many excellent properties. Smart coatings with affinity-repellent conversion properties show switchable wettability, mainly between high (or super) hydrophobicity and super hydrophilicity. Due to its many potential applications, such as self-cleaning materials, microfluidics, adjustable optical lenses, drug delivery carriers and sensors, they have been actively studied. At present, weak bonding strength is a fatal disadvantage of superhydrophobic coatings in practical applications. Traditionally, the preparation of super-hydrophobic coatings requires modification with low surface energy materials (fluorides or silicides), and these toxic materials have a negative impact on the environment. Therefore, the development of an intelligent super-hydrophobic coating that does not require modification with low surface energy materials and has affinity-repellent conversion properties is a long-term exploration in materials science. The introduction of ZnO as a transition layer and the use of its rough surface structure are beneficial to improving the adhesion of the super-hydrophobic coating. This application aims to prepare an intelligent super-hydrophobic coating with strong adhesion and affinity-repellent conversion properties on the surface of magnesium alloys, effectively inhibit the rapid degradation of magnesium alloys, and extend the service life of magnesium alloys.

[0003] Prior patent CN113604851B discloses a super hydrophobic coating on the surface of a magnesium alloy without the need for modification of a low surface energy substance and a preparation method thereof, wherein a micro arc oxidation film is formed on the surface of the magnesium alloy by micro arc oxidation treatment, and then a ZnO@ZIF-8 coating is formed on the surface of the magnesium alloy by a reactor, which is evenly distributed on the surface of the magnesium alloy and has super hydrophobicity and good corrosion resistance. However, the ZnO@ZIF-8 coating formed on the surface of the magnesium alloy only has super hydrophobicity, but does not have affinity conversion performance, and cannot meet the requirements of an intelligent super hydrophobic coating.

[0004] Compared with the ZnO and ZIF-8 coatings prepared by a reactor, the microscopic morphology formed by the ZnO / ZIF-8 coating prepared by the electrodeposition method of the present invention enables the coating to have a hydrophobic conversion effect, and also enables the ZnO / ZIF-8 coating to have super-hydrophobic properties; and the preparation process of the present invention is simpler, the cost is lower, the electrochemical impedance value of the prepared coating is larger, and the corrosion resistance is better. Summary of the invention

[0005] The object of the present invention is to provide an intelligent super-hydrophobic composite coating with affinity-repellency conversion performance on the surface of a magnesium alloy and a preparation method thereof, so as to effectively inhibit the rapid degradation of the magnesium alloy and prolong the service life of the magnesium alloy.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] <First aspect>

[0008] The present invention provides a method for preparing an intelligent super-hydrophobic composite coating having affinity-repellency conversion performance on a magnesium alloy surface, comprising the following steps:

[0009] S1. Electrodeposition of ZnO layer: dissolve zinc nitrate hexahydrate by ultrasonication in a mixed solution of ethanol and water to prepare a 0.33-0.35 mol / L zinc nitrate hexahydrate solution A; use graphite as an anode and a magnesium alloy as a cathode (put in an electrolytic cell) to perform cathode electrodeposition to obtain a magnesium alloy loaded with ZnO;

[0010] S2. Using a mixed solution of ethanol and water, respectively, the zinc nitrate hexahydrate and 2-methylimidazole are ultrasonically dissolved to prepare a 0.18-0.19 mol / L zinc nitrate hexahydrate solution B and a 0.74-0.75 mol / L 2-methylimidazole solution, and the 2-methylimidazole solution is added to the zinc nitrate hexahydrate solution B; using the magnesium alloy as the anode and the ZnO-loaded magnesium alloy obtained in step S1 as the cathode, (putting it in an electrolytic cell) cathode electrodeposition is performed; after rinsing, drying (in an oven) is performed to obtain a ZnO / ZIF-8 intelligent super-hydrophobic composite coating and a magnesium alloy having a ZnO / ZIF-8 intelligent super-hydrophobic composite coating on the surface.

[0011] As an embodiment of the present invention, the volume ratio of ethanol to water in step S1 is 9: 1. If the volume ratio of ethanol to water is not 9: 1, the deposited ZnO film will be uneven and discontinuous, so that the anchor points of the ZnO layer when depositing ZIF-8 will be reduced, thereby affecting the performance of the entire composite film.

[0012] As an embodiment of the present invention, the volume ratio of ethanol and water in step S2 is 1:9; a composite film layer with super-hydrophobic properties can be prepared only when the volume ratio of ethanol to water is 1:9, and when the volume ratio of ethanol to water is not 1:9, the prepared film layer cannot have a super-hydrophobic effect.

[0013] As an embodiment of the present invention, the magnesium alloy is pre-treated; the pre-treatment includes: grinding and polishing the magnesium alloy substrate to remove surface stains and oxides; degreasing in a degreasing liquid and then ultrasonically treating with ethanol and deionized water respectively and then drying.

[0014] Furthermore, the magnesium alloy substrate is AZ91D magnesium alloy, which is cut into carriers with specifications of 30×30×2 mm before grinding and polishing, and AZ91D is grinded and polished with #180, #600, #1000, and #1500 metallographic sandpaper in sequence, and the residue is rinsed with a large amount of deionized water after grinding and polishing.

[0015] Further, the composition of the degreasing liquid includes: 20-50 g / L NaOH, 10-30 g / L Na2CO3, 10-30 g / L Na3PO4;

[0016] And / or, the degreasing treatment is performed at a temperature of 60-80°C and for a time of 1-2 min.

[0017] As an embodiment of the present invention, in step S1, the ultrasonic dissolution is followed by standing for 10 to 30 minutes.

[0018] As an embodiment of the present invention, in step S1, the cathode electrodeposition is carried out under the condition of a DC power supply constant voltage of 5 to 5.5 V;

[0019] And / or, the cathode electrodeposition is performed at a temperature of 20-30° C. and for a time of 10-20 min.

[0020] Preferably, the temperature of the cathode electrodeposition is 25°C.

[0021] As an embodiment of the present invention, in step S1, after the cathode electrodeposition is completed, the step further includes rinsing with ethanol for 3 to 5 times and then drying at 45 to 55°C (oven).

[0022] Preferably, the drying temperature is 50°C.

[0023] As an embodiment of the present invention, in step S2, the cathode electrodeposition is carried out under a DC power supply at a constant current of 0.02 to 0.03 A;

[0024] And / or, the cathode electrodeposition is performed at a temperature of 20-30° C. and for a time of 15-20 min.

[0025] Preferably, the cathode electrodeposition temperature is 25°C.

[0026] As an embodiment of the present invention, in step S2, the rinsing is rinsing with distilled water, and the number of rinsing is 3 to 5 times;

[0027] And / or, the drying temperature is 45-55° C. and the drying time is 10-12 h.

[0028] Preferably, the drying temperature is 50°C.

[0029] As an embodiment of the present invention, the sodium hydroxide, sodium carbonate, sodium phosphate, zinc nitrate hexahydrate, 2-methylimidazole and ethanol are all of chemical purity or above.

[0030] <Second Aspect>

[0031] The present invention provides an intelligent super-hydrophobic composite coating with affinity-dissipation conversion performance on the surface of a magnesium alloy, which is prepared by any of the methods described above.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1) The ZnO / ZIF-8 composite coating prepared by the present invention has good bonding strength with the magnesium alloy substrate and can be evenly distributed on the surface of the magnesium alloy;

[0034] 2) It can achieve super hydrophobicity and have affinity-repellency conversion performance without the need for modification of low surface energy materials;

[0035] 3) The electrochemical performance test showed that the composite coating also has good corrosion resistance;

[0036] 4) The ZnO / ZIF-8 composite coating was prepared on the surface of the magnesium alloy by electrodeposition instead of a reactor. The steps were simplified, the preparation process was simple, and the electrochemical impedance of the smart super-hydrophobic film layer achieved significant improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0038] Figure 1 SEM images and water contact angle test diagrams of magnesium alloy (a, d), ZnO (b, e) and ZnO / ZIF-8 composite coating (c, f) in Example 1;

[0039] Figure 2The XRD spectrum of the phase characterization of the ZnO / ZIF-8 composite coating prepared in Example 1;

[0040] Figure 3 This is a test diagram of affinity conversion of the ZnO / ZIF-8 composite coating prepared in Example 1;

[0041] Figure 4 The potentiodynamic polarization curves of the magnesium alloy, ZnO and ZnO / ZIF-8 composite coating in 3.5 wt.% NaCl solution of Example 1 are shown;

[0042] Figure 5 This is the electrochemical impedance spectroscopy of the magnesium alloy, ZnO and ZnO / ZIF-8 composite coating in 3.5 wt.% NaCl solution of Example 1. DETAILED DESCRIPTION

[0043] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0044] Example 1

[0045] (1) Magnesium alloy pretreatment

[0046] In order to remove stains and oxides on the surface of magnesium alloy, #180, #600, #1000 and #1500 metallographic sandpaper were used to grind and polish it in turn. After that, the residue was rinsed with a large amount of deionized water; degreasing treatment was carried out at 65 °C for 1 min (degreasing liquid composition: 20 g / L NaOH, 30 g / L Na2CO3, 20 g / L Na3PO4); finally, ethanol and water were used for ultrasonic treatment for 10 min respectively, and then dried for use.

[0047] (2) Preparation of intelligent super-hydrophobic composite coating

[0048] ① Electrodeposition of ZnO layer: Weigh 1.99 g zinc nitrate hexahydrate, add 18 mL ethanol and 2 mL water for ultrasonic dissolution. After dissolution, let the solution stand for 10 minutes. Then use graphite as the anode and the pretreated magnesium alloy as the cathode in the electrolytic cell for cathode electrodeposition. Electrodeposition was performed for 10 minutes at room temperature of 25 °C and a constant voltage of 5 V under a DC power supply. After the electrodeposition was completed, rinse with ethanol 3 times and dry in an oven at 50 °C.

[0049] ② Electrodeposition of ZIF-8 layer: First, dissolve 0.558 g of zinc nitrate hexahydrate in 9 mL of water and 1 mL of ethanol, then dissolve 0.616 g of 2-methylimidazole in 9 mL of water and 1 mL of ethanol, and then pour the dissolved 2-methylimidazole solution into the zinc nitrate hexahydrate solution. The anode is a magnesium alloy treated with #180 sandpaper, and the cathode is a magnesium alloy loaded with ZnO obtained in ①, which is placed in an electrolytic cell for cathode electrodeposition. At room temperature of 25 ℃, a constant current of 0.026 A under a DC power supply, the electrodeposition was performed for 15 min. After the electrodeposition, rinse with distilled water 3 times and dry in a 50 ℃ oven for 10 h. Thus, a ZnO / ZIF-8 intelligent superhydrophobic composite coating is obtained.

[0050] The above-mentioned sodium hydroxide, sodium carbonate, sodium phosphate, zinc nitrate hexahydrate, 2-methylimidazole and ethanol are all of chemical purity or above.

[0051] Comparative Example 1

[0052] The film layer after the electrodeposition in step (2) ② of Example 1 was dried at 25° C. for 10 h. The other treatment methods were the same as those of Example 1. The film layer was hydrophilic with a water contact angle of 63.78° and did not have hydrophilic-repellent conversion performance.

[0053] Comparative Example 2

[0054] A super-hydrophobic coating was prepared on the surface of a magnesium alloy according to the method disclosed in the embodiment of the prior patent CN113604851B.

[0055] The results show that the corrosion potential of the ZnO / ZIF-8 coating on the magnesium alloy surface is -1.479 V and the corrosion current density is 5.611*10 -9 A.cm -2 .

[0056] The paper Jiang Shiquan, Li Weidong, Liu Jinyu, et al. ZnO@ZIF-8 core-shellstructure nanorods superhydrophobic coating on magnesium alloy with corrosion resistance and self-cleaning[J]. Journal of Magnesium and Alloys, 2023, 11(9): 3287-3301. The MAO / ZIF-8 coating was prepared on the surface of magnesium alloy by the method in the prior patent, and the electrochemical impedance spectroscopy test was carried out. The results showed that the electrochemical impedance of the ZnO@ZIF-8 coating was 1.414×10 6Ω·cm 2 .

[0057] Test Case

[0058] The magnesium alloy, ZnO and ZnO / ZIF-8 composite coating in Example 1 were subjected to SEM images and water contact angle tests respectively; the ZnO / ZIF-8 composite coating was subjected to XRD characterization, affinity conversion test, corrosion resistance test and electrochemical impedance test. The test results are shown in FIG. Figure 1-Figure 5 shown.

[0059] 1. Figure 1 SEM images and water contact angle test diagrams of magnesium alloy (a, d), ZnO (b, e) and ZnO / ZIF-8 composite coating (c, f) in Example 1; Figure 2 This is the XRD spectrum for phase characterization of the ZnO / ZIF-8 composite coating prepared in Example 1.

[0060] The results showed that the ZnO / ZIF-8 composite coating on the surface of the magnesium alloy was obtained by SEM ( Figure 1 c) and XRD characterization ( Figure 2 ) showed that the coating had good bonding with the magnesium alloy substrate and could be evenly distributed on the surface of the magnesium alloy, mainly consisting of ZnO and ZIF-8. The water contact angle was tested using a water drop static contact angle tester, and the water contact angle was 153.31°, indicating super hydrophobicity without modification by low surface energy materials.

[0061] 2. Closeness conversion test:

[0062] The prepared ZnO / ZIF-8 composite coating becomes hydrophilic after being immersed in distilled water for 2 h, and becomes superhydrophobic after being dried at 50 °C for 2 h. Figure 3 After three cycles of hydrophobic conversion, it can still maintain good hydrophobicity.

[0063] 3. Corrosion resistance test:

[0064] The corrosion resistance of the prepared ZnO / ZIF-8 composite coating was characterized by using a CHI760 electrochemical workstation in a three-electrode system (calomel electrode as reference electrode, platinum electrode as auxiliary electrode, magnesium alloy surface coating as working electrode), and 3.5 wt.% sodium chloride solution as electrolyte. Potentiodynamic polarization curves and electrochemical impedance spectroscopy were used to study the corrosion resistance of the magnesium alloy surface coating. After the open circuit potential was stabilized, the voltage window was open circuit potential ±300 mV, and the potentiodynamic polarization test was performed at a scan rate of 10 mV / s.

[0065] like Figure 4The test results show that the corrosion potential of the ZnO / ZIF-8 composite coating on the surface of the magnesium alloy is -0.751 V, and the corrosion current density is 3.540×10 -9 A.cm -2 The corrosion potential of ZnO coating is -1.502 V, and the corrosion current density is 1.100×10 -3 A.cm -2 The corrosion potential of AZ91D magnesium alloy substrate is -1.486 V, and the corrosion current density is 3.565×10 -5 A.cm -2 The corrosion potential of the ZnO / ZIF-8 superhydrophobic coating shifted significantly (0.735 V more positive than the corrosion potential of the magnesium alloy substrate), and the corrosion current density was reduced by six and four orders of magnitude compared with that of the ZnO and magnesium alloy substrates, respectively, significantly improving the corrosion resistance of the magnesium alloy.

[0066] By comparing the test results of the embodiment with the test results of comparative example 2, it is found that the corrosion current density of the coating of embodiment 1 is lower than that of comparative example 2, and the corrosion potential is also significantly more positive than that of comparative example 2. Therefore, the magnesium alloy surface coating prepared by the method of the present invention has better corrosion resistance.

[0067] 4. Electrochemical impedance performance test:

[0068] The prepared ZnO / ZIF-8 composite coating was subjected to electrochemical impedance spectroscopy at an open circuit voltage in the frequency range of 10 5 ~10 -2 Hz, such as Figure 5 The electrochemical impedance of the ZnO / ZIF-8 composite coating shown is four orders of magnitude higher than that of the magnesium alloy substrate. The corrosion resistance of the ZnO / ZIF-8 intelligent superhydrophobic composite coating with affinity-repellency conversion performance on the magnesium alloy surface is significantly improved.

[0069] The electrochemical impedance of the ZnO / ZIF-8 coating prepared in Example 1 reached 4.398×10 7 Ω·cm 2 , much higher than 1.414×10 in Comparative Example 2 6 Ω·cm 2 Therefore, the magnesium alloy surface coating prepared by the method of the present application has better electrochemical impedance performance.

[0070] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing an intelligent super-hydrophobic composite coating having affinity-repellency conversion performance on a magnesium alloy surface, comprising the following steps: S1. Electrodeposition of ZnO layer: dissolving zinc nitrate hexahydrate by ultrasonication in a mixed solution of ethanol and water to prepare a 0.33-0.35 mol / L zinc nitrate hexahydrate solution A; using graphite as an anode and a magnesium alloy as a cathode, cathode electrodeposition is performed to obtain a magnesium alloy loaded with ZnO; S2, using a mixed solution of ethanol and water to ultrasonically dissolve zinc nitrate hexahydrate and 2-methylimidazole respectively, to prepare 0.18-0.19 mol / L zinc nitrate hexahydrate solution B and 0.74-0.75 mol / L 2-methylimidazole solution, and adding the 2-methylimidazole solution to the zinc nitrate hexahydrate solution B; Using the magnesium alloy as an anode and the ZnO-loaded magnesium alloy obtained in step S1 as a cathode, cathode electrodeposition is performed; After rinsing and drying, a ZnO / ZIF-8 intelligent super-hydrophobic composite coating and a magnesium alloy having the ZnO / ZIF-8 intelligent super-hydrophobic composite coating on the surface are obtained.

2. The preparation method according to claim 1, characterized in that: The volume ratio of ethanol to water in step S1 is 9:1; And / or, the volume ratio of ethanol to water in step S2 is 1:

9.

3. The preparation method according to claim 1, characterized in that: The magnesium alloy is pre-treated; the pre-treatment includes: grinding and polishing the magnesium alloy substrate to remove stains and oxides on its surface; degreasing in a degreasing liquid, ultrasonically treating with ethanol and deionized water respectively, and then drying.

4. The preparation method according to claim 3, characterized in that: The degreasing liquid comprises: 20-50 g / L NaOH, 10-30 g / L Na2CO3, 10-30 g / L Na3PO4; And / or, the degreasing treatment is performed at a temperature of 60-80°C and for a time of 1-2 min.

5. The preparation method according to claim 1, characterized in that: In step S1, the cathode electrodeposition is performed under the condition of a DC power supply constant voltage of 5-5.5 V; And / or, the cathode electrodeposition is performed at a temperature of 20-30° C. and for a time of 10-20 min.

6. The preparation method according to claim 1, characterized in that: In step S1, after the cathode electrodeposition is completed, the step further includes rinsing with ethanol for 3 to 5 times and then drying at 45 to 55°C.

7. The preparation method according to claim 1, characterized in that: In step S2, the cathode electrodeposition is performed under a DC power supply at a constant current of 0.02-0.03 A; And / or, the cathode electrodeposition is performed at a temperature of 20-30° C. and for a time of 15-20 min.

8. The preparation method according to claim 1, characterized in that: In step S2, the rinsing is rinsing with distilled water, and the number of rinsing is 3 to 5 times; And / or, the drying temperature is 45-55° C. and the drying time is 10-12 h.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The NaOH, Na2CO3, Na3PO4, zinc nitrate hexahydrate, 2-methylimidazole and ethanol are of chemical purity or above.

10. An intelligent super-hydrophobic composite coating with affinity-dissipation conversion performance on the surface of a magnesium alloy, prepared by the method according to any one of claims 1 to 9.

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