阅读说明：本技术 一种用于碳钢表面的疏水性密胺树脂纳米土/聚乙烯防腐复合涂层及其制备方法与应用 (Hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating for carbon steel surface and preparation method and application thereof ) 是由 廖伯凯 曾巧 康磊 郭兴蓬 于 2021-07-22 设计创作，主要内容包括：本发明属于金属表面防腐蚀技术领域,公开了一种用于碳钢表面的疏水性密胺树脂纳米土/聚乙烯防腐复合涂层及其制备方法与应用,本方法首先利用硫酸镍沉积液,在Q235碳钢表面电沉积制备层状双氢氧化物(LDH),再将Q235碳钢依次浸泡于密胺树脂纳米土交联溶液和聚乙烯溶液,形成LDH-密胺树脂纳米土-聚乙烯涂层。所得涂层能有效地防止碳钢中腐蚀,电化学阻抗测试的低频阻抗模值|Z|-(0.01Hz)达到10～(9)ohm·cm～(2),相对空白Q235碳钢增加了6个数量级。同时,纳米级LDH-密胺树脂纳米土-聚乙烯涂层较空白Q235碳钢腐蚀电流密度下降了21.4μA·cm～(-2),自腐蚀电位升高了181.64mV。(The invention belongs to the technical field of metal surface corrosion prevention, and discloses a hydrophobic melamine resin nano soil/polyethylene corrosion prevention composite coating for a carbon steel surface, and a preparation method and application thereof. The obtained coating can effectively prevent corrosion in carbon steel, and can be used for electrochemical impedance testLow frequency impedance module value | Z $ 0.01Hz Up to 10 9 ohm·cm 2 Compared with blank Q235 carbon steel, the number of the carbon steel is increased by 6 orders of magnitude. Meanwhile, compared with the blank Q235 carbon steel corrosion current density of the nano-scale LDH-melamine resin nano-soil-polyethylene coating, the nano-scale LDH-melamine resin nano-soil-polyethylene coating is reduced by 21.4 muA cm ‑2 The self-etching potential was increased by 181.64 mV.)

1. A preparation method of a hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating for a carbon steel surface is characterized by comprising the following steps:

(1) performing electrodeposition on the surface of Q235 carbon steel in a nickel sulfate solution to form an LDH layer;

(2) mixing and dispersing the nano soil and water, and prefabricating a nano soil solution; mixing melamine, formaldehyde and water, adjusting the pH value of the system to be alkaline, heating for reaction, mixing with the nano soil solution, and continuing the heat preservation reaction to obtain a melamine resin crosslinked nano soil solution; then putting the Q235 carbon steel with the LDH layer formed in the step (1) into a melamine resin cross-linked nano soil solution for soaking and aging, and forming an LDH-melamine resin nano soil coating on the surface of the Q235 carbon steel;

(3) and (3) soaking the Q235 carbon steel with the LDH-melamine resin nano soil coating formed in the step (2) in a polyethylene solution to form a hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating on the surface of the Q235 carbon steel.

2. The method of claim 1, wherein: the mass volume ratio of the melamine to the formaldehyde to the water in the step (2) is 0.60-0.65 g to 0.80-0.85 g to 20-25 mL.

3. The method of claim 1, wherein: the mass ratio of the nano soil to the water in the step (2) is 2-4 g: 6-15 g.

4. The method of claim 1, wherein: the concentration of the nickel sulfate solution in the step (1) is 3-7 mmol.L^-1(ii) a The particle size of the nano soil in the step (2) is 500-1000 nm.

5. The method of claim 1, wherein: the electrodeposition in the step (1) is carried out by three-electrode constant potential deposition, wherein the constant potential in the three-electrode constant potential deposition is-0.45 to-0.55V; the electrodeposition time is 0.5-1.5 h.

6. The method of claim 1, wherein: the heating reaction temperature in the step (2) is 75-85 ℃, and the heating reaction time is 30-50 min; and (3) keeping the temperature for reaction for 15-25 min in the step (2).

7. The method of claim 1, wherein: and (3) aging at the temperature of 135-145 ℃ for 1-3 h.

8. The method of claim 1, wherein: the mass concentration of the polyethylene solution in the step (3) is 2-5%.

9. A hydrophobic melamine resin nano soil/polyethylene anticorrosion composite coating for the surface of carbon steel, which is prepared by the method of any one of claims 1 to 8.

10. The use of the hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating for the carbon steel surface according to claim 9 in the preparation of anticorrosive materials.

Technical Field

The invention belongs to the technical field of metal surface corrosion prevention, and particularly relates to a method for preparing a hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating on a carbon steel substrate and application thereof.

Background

The Q235 carbon steel is low-cost medium-low strength steel and is generally applied to the industries of petroleum, chemical engineering, engineering and the like, however, the Q235 carbon steel is very easy to induce corrosion in neutral, acidic and high-chlorine environments, and the service life of the Q235 carbon steel is greatly shortened.

At present, coating protection is an effective anti-corrosion measure, but the traditional coating has poor water resistance, and corrosive media easily enter a metal matrix through pores on the surface of the coating; the traditional coating has the defect of weak bonding with a metal substrate, and the coating is easy to peel off, so that the substrate is directly exposed to air or a corrosive environment, and the corrosion can rapidly spread.

Chinese patent application No. 202110039570.1 discloses 'a waterborne epoxy resin for an anticorrosive coating, application and a preparation method thereof', the method realizes the self-emulsifying function of the epoxy resin by introducing a strong hydrophilic polyethylene glycol branched chain on the molecular chain of the epoxy resin, no additional alcohol-soluble solvent or other high-boiling organic solvents are needed to be used in the preparation process, and the waterborne epoxy resin can be mixed with a waterborne ammonia curing agent to be cured into a film for corrosion prevention. Chinese patent number 'a hydrophobic fluorinated epoxy acrylic resin anticorrosive coating and a preparation method thereof', the method comprises the following raw materials: the preparation method comprises the steps of modifying graphene, dodecafluoroheptyl methacrylate, glycidyl methacrylate, 50-76 parts of epoxy resin, an initiator, an emulsifier and a curing agent by using alkenyl silver oxide to prepare the hydrophobic fluorinated epoxy acrylic resin anticorrosive coating, wherein the generated nano silver oxide is uniformly attached to the graphene with huge specific surface area and lamellar structure, and the fluorinated epoxy acrylic resin coating is endowed with excellent performances of preventing biological corrosion, chemical corrosion and electrochemical corrosion. The coating preparation method disclosed in the above patent is not strong in bonding between the coating and the metal substrate, and is liable to cause defects or peeling of the coating, which is not favorable for popularization and application. The invention enhances the combination between the coating and the matrix through the chemical bonding effect, and simultaneously, the hydrophobic property of the surface of the coating is increased, so that the coating has excellent anti-corrosion performance.

Disclosure of Invention

The invention aims to provide a preparation method of a hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating for the surface of carbon steel, which is simple to operate, has simple and easily-obtained raw materials, and enhances the anticorrosive capacity of a matrix while forming the hydrophobic coating on the surface of the carbon steel.

The invention further aims to provide the hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating for the carbon steel surface, which is prepared by the method.

The invention also aims to provide the application of the hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating in carbon steel.

In order to achieve the purpose, the scheme of the invention is as follows:

a preparation method of a hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating for a carbon steel surface comprises the following steps:

(1) performing electrodeposition on the surface of Q235 carbon steel in a nickel sulfate solution to form an LDH layer;

(2) mixing and dispersing the nano soil and water, and prefabricating a nano soil solution; mixing melamine, formaldehyde and water, adjusting the pH value of the system to be alkaline, heating for reaction, mixing with the nano soil solution, and continuing the heat preservation reaction to obtain a melamine resin crosslinked nano soil solution; then putting the Q235 carbon steel with the LDH layer formed in the step (1) into a melamine resin cross-linked nano soil solution for soaking and aging, and forming an LDH-melamine resin nano soil coating on the surface of the Q235 carbon steel;

(3) and (3) soaking the Q235 carbon steel with the LDH-melamine resin nano soil coating formed in the step (2) in a polyethylene solution to form a hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating on the surface of the Q235 carbon steel.

Before the reaction, the Q235 carbon steel in the step (1) is preferably subjected to surface polishing on the Q235 carbon steel by sequentially adopting 180#, 400#, 800# and 1200# sandpaper to remove surface oxides, then is subjected to ultrasonic cleaning by respectively using acetone and absolute ethyl alcohol to remove surface impurities and oil stains, and is taken out and dried by cold air;

the concentration of the nickel sulfate solution in the step (1) is 3-7 mmol.L^-1Preferably 4 mmol. multidot.L^-1；

The electrodeposition in the step (1) is preferably carried out by three-electrode constant potential deposition, more preferably, the constant potential in the three-electrode constant potential deposition is-0.45 to-0.55V, and is preferably-0.5V; the electrodeposition time is 0.5-1.5 h, preferably 1 h;

the particle size of the nano soil in the step (2) is 500-1000 nm.

The mass ratio of the nano soil to the water in the step (2) is 2-4: 6-15 g, preferably 2-4 g: 9-11 g, and more preferably 3g:10 g;

the mass volume ratio of the melamine to the formaldehyde (37 wt%) to the water in the step (2) is 0.60-0.65 g: 0.80-0.85 g: 20-25 mL, preferably 0.63g:0.81g:24 mL;

the alkalinity in the step (2) means that the pH value is 8-11, and preferably 8-9.

The temperature of the heating reaction in the step (2) is 75-85 ℃, and preferably 80 ℃; the heating reaction time is 30-50 min, preferably 40 min;

the time of the heat preservation reaction in the step (2) is 15-25 min, preferably 20 min;

the temperature in the aging process in the step (2) is 135-145 ℃, and preferably 140 ℃; the aging time is 1-3 h, preferably 2 h.

The mass concentration of the polyethylene solution in the step (3) is 2-5%, preferably 3%.

The hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating for the carbon steel surface is prepared by the method. The thickness of the LDH-melamine resin nano soil-polyethylene coating is 30-50 mu m.

The hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating for the carbon steel surface is applied to preparation of anticorrosive materials.

The mechanism of the invention is as follows: carbon steel is used as a matrix, so that chemical substances required by LDH growth can be provided, and the LDH can directly participate in the LDH generation reaction. Due to the action of chemical bond force, the LDH membrane is firmly combined with the matrix and is not easy to fall off; meanwhile, the LDH membrane can also increase the roughness of the matrix surface. After the nano soil is crosslinked with the melamine resin, the nano soil is uniformly distributed on the surface of the base material, and meanwhile, the nano soil crosslinked with the melamine resin has a plurality of surface gaps, so that space and active sites are provided for the penetration of polyethylene. The melamine resin on the surface and the polyethylene form van der Waals force action, and the adhesion of the polyethylene and the surface is enhanced. Thus, the polyethylene coating is used as a final supplement to improve the corrosion protection function of the coating.

Compared with the prior art, the invention has the beneficial effects that:

(1) the hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating prepared by the invention enhances the combination between the coating and a metal matrix, and can effectively reduce the loss caused by damage or peeling of the coating.

(2) The hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating prepared by the invention reduces the penetration of water molecules, and simultaneously, the nano soil particles and the LDH lamellar structure prolong the diffusion path of corrosive media and enhance the anticorrosive performance of the coating.

(3) The hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating prepared by the invention is low in cost and wide in source, and is beneficial to solving the problems of white pollution, industrial raw material waste and the like.

(4) The hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating prepared by the invention has the characteristics of hydrophobicity, corrosion resistance and the like, and has practical value and wide application prospect.

(5) The hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating prepared by the invention can play a role in metal corrosion prevention in acidic, alkaline, high-salt and neutral environments.

Drawings

FIG. 1 is an SEM image of the electrodeposition of LDH film on the surface of carbon steel of comparative example 1;

FIG. 2 is a photograph of the static contact angle of LDH-melamine resin nano soil-polyethylene coating formed on the surface of carbon steel in example 1, the contact angle is 95.5 °;

FIG. 3 is an electrochemical impedance spectrum of example 1 and comparative examples 1 to 3, with a being an impedance vs. frequency plot; b is a phase angle-frequency diagram;

FIG. 4 is a polarization curve of example 1, comparative example 3 and bare carbon steel;

FIG. 5 is an electrochemical impedance spectrum of comparative example 4 and bare carbon steel, wherein a is a Nyquist diagram, and b and c are Bode diagrams;

fig. 6 is a polarization curve of comparative example 4 and bare carbon steel.

Detailed Description

The method for forming a hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating for a carbon steel surface according to the present invention will be described in further detail with reference to the following examples and accompanying drawings, but the embodiments of the present invention are not limited thereto. The formaldehyde concentration used in the examples was 37% by weight.

Example 1

The preparation method of the hydrophobic melamine resin nano soil/polyethylene anticorrosive composite coating on the surface of Q235 carbon steel comprises the following specific steps:

(1) sequentially grinding the surface of Q235 carbon steel by 180#, 400#, 800# and 1200# sandpaper to remove surface oxides, then respectively ultrasonically cleaning the surface of the Q235 carbon steel for 10min by acetone and absolute ethyl alcohol to remove surface impurities and oil stains, taking out the surface of the Q235 carbon steel and drying the Q235 carbon steel by cold air;

(2)4mmol·L^-1depositing for 1h in a nickel sulfate solution by using a three-electrode-0.5V constant potential, and depositing on the surface of Q235 carbon steel to form an LDH layer;

(3) prefabricating 3g of nano soil with the particle size of 500-1000 nm and 10g of deionized water into a nano soil solution under ultrasonic vibration, mixing 0.63g of melamine, 0.81g of formaldehyde and 24mL of water, adjusting the pH value to 8, carrying out water bath reaction at 80 ℃ for 40min, mixing the mixture with the nano soil solution, reacting at the same temperature for a period of time, cooling to form a melamine resin cross-linked nano soil solution, then putting the Q235 carbon steel forming the LDH membrane in the step (1) into the melamine resin cross-linked nano soil solution, soaking and drying for multiple times, and aging for 2 hours at 140 ℃ to form an LDH-melamine resin nano soil coating;

(4) preparing a molten polyethylene solution, soaking the Q235 carbon steel forming the LDH-melamine resin nano soil coating in the step (2) in a 3% polyethylene solution, and naturally cooling to form the LDH-melamine resin nano soil-polyethylene coating.

The coating thickness was 47 μm, the contact angle of a water drop was 95.5 °, and the contact angle of a water drop on the surface of untreated Q235 carbon steel was 43.2 °.

Example 2

Different from the embodiment 1, the electro-deposition time of the step (2) is 2h, and the concentration of the nickel sulfate solution is 3 mmol.L^-1. The thickness of the formed LDH-melamine resin nano soil-polyethylene coating is 45 mu m, and the contact angle of a water drop on the surface of the coating is 94.2 degrees.

Example 3

Different from the embodiment 1, the mass ratio of the nano-soil to the deionized water in the step (3) is 2g to 10g, and the mass volume ratio of the melamine to the formaldehyde to the water is 0.6g to 0.8g to 25 mL. The thickness of the coating of the formed LDH-melamine resin nano soil-polyethylene coating is 40 mu m, and the contact angle of a water drop on the surface of the coating is 91.6 degrees.

Example 4

Different from the embodiment 1, the mass ratio of the nano-soil to the deionized water in the step (3) is 4g:10g, and the mass volume ratio of the melamine to the formaldehyde to the water is 0.65g:0.85g:25 mL. The thickness of the formed LDH-melamine resin nano soil-polyethylene coating is 44 mu m, and the contact angle of a water drop on the surface of the formed LDH-melamine resin nano soil-polyethylene coating is 90.9 degrees.

Example 5

Different from the embodiment 1, the mass volume ratio of the melamine, the formaldehyde and the water in the step (3) is 0.65g:0.85g:20mL, the aging temperature is 135 ℃, and the aging time is 1 h. The thickness of the coating of the formed LDH-melamine resin nano soil-polyethylene coating is 45 mu m, and the contact angle of a water drop on the surface of the coating is 85.2 degrees.

Comparative example 1

Sequentially adopting 180#, 400#, 800# and 1200# sandpaper to polish the surface of Q235 carbon steel so as to remove surface oxides, then respectively carrying out ultrasonic cleaning on the surface for 10min by using acetone and absolute ethyl alcohol so as to remove surface impurities and oil stains, taking out and drying by cold air. At 4 mmol. multidot.L^-1Depositing at constant potential of-0.5V for 1h in the nickel sulfate solution, and depositing on the surface of Q235 carbon steel to form an LDH layer.

Comparative example 2

Sequentially adopting 180#, 400#, 800# and 1200# sandpaper to polish the surface of Q235 carbon steel so as to remove surface oxides, then respectively carrying out ultrasonic cleaning on the surface for 10min by using acetone and absolute ethyl alcohol so as to remove surface impurities and oil stains, taking out and drying by cold air. At 4 mmol. multidot.L^-1Depositing at constant potential of-0.5V for 1.5h in the nickel sulfate solution, and depositing on the surface of Q235 carbon steel to form an LDH layer.

Comparative example 3

Sequentially adopting 180#, 400#, 800# and 1200# sandpaper to polish the surface of Q235 carbon steel so as to remove surface oxides, then respectively carrying out ultrasonic cleaning on the surface for 10min by using acetone and absolute ethyl alcohol so as to remove surface impurities and oil stains, taking out and drying by cold air. At 4 mmol. multidot.L^-1Depositing at constant potential of-0.5V for 1h in the nickel sulfate solution, and depositing on the surface of Q235 carbon steel to form an LDH layer.

Mixing 0.63g of melamine, 0.81g of formaldehyde and 24mL of water, adjusting the pH value to 8, carrying out water bath reaction at 80 ℃ for 40min to form a melamine resin solution, putting Q235 carbon steel forming an LDH membrane into the melamine resin solution, soaking and drying for multiple times, and aging at 140 ℃ for 2h to form an LDH-melamine resin coating; preparing a 3% polyethylene solution, soaking the Q235 carbon steel forming the LDH-melamine resin coating in the polyethylene solution, and naturally cooling to form the LDH-melamine resin-polyethylene coating.

Comparative example 4

This comparative example is different from example 1, step (2), in that nickel sulfate was replaced with nickel nitrate.

Comparative example 5

This comparative example differs from example 2 in that the steel of Q235 carbon steel was replaced with 304 steel.

The results show that no deposited film could be formed on 304 steel.

Effects of the embodiment

(1) Electrochemical impedance testing

Q235 carbon steel prepared in the comparative example and the example is soaked in 3.5 wt% NaCl solution, and a three-electrode system is adopted, wherein a reference electrode is a saturated calomel electrode, and a counter electrode is a platinum black electrode. Electrochemical impedance measurements were performed using a Princeton electrochemical workstation at a frequency range of 10⁴-10^-210 points per doubling. ResultsAs shown in table 1:

TABLE 1 electrochemical impedance test results

(2) Polarization curve testing

Q235 carbon steel prepared in the comparative example and the example is soaked in 3.5 wt% NaCl solution, and a three-electrode system is adopted, wherein a reference electrode is a saturated calomel electrode, and a counter electrode is a platinum black electrode. The polarization curve was measured using a Princeton electrochemical workstation at a potential ranging from-0.2V to 0.2V (vs OCP). The scan rate was 0.5mV/s, and the results are shown in Table 2:

TABLE 2 polarization curve test results

	Example 1	Example 2	Example 3
				Icorr(A cm-2)	6.3×10-9	5.9×10-9	1.2×10-9
	Example 4	Example 5	Comparative example 3
				Icorr(A cm-2)	4.6×10-9	9.8×10-9	1.1×10-7

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.