Study on Preparation and Performance of Graphene Waterborne Anticorrosive Coatings

Tan Weimin1, Luo Xinliang1, Gai Xinlu2, Yu Fei1

1.
CNOOC Changzhou Coating Chemical Research Institute Co.
, Ltd.
;

2.
China Huayin Weapon Test Center

introduction

Metal materials are damaged by the surrounding medium, which is called metal corrosion.

It has been found that when pure graphene is applied in a large area, countless defects will be formed on the boundary of the graphene domain, thereby forming a galvanic couple between the cathode graphene and the anode substrate, resulting in accelerated local corrosion.

Therefore, this article focuses on the preparation and performance of graphene water-based anticorrosive coatings.

Experimental part

(1) Preparation of paint

➤Preparation of curing agent components: add polyamine, solvent, dispersant, bentonite, iron-titanium powder, and zinc powder to the tank in sequence, then put it into the automatic clamping oscillating oil mixer, shake and mix for 1 hour, and filter it.

➤Epoxy emulsion component preparation: add epoxy resin emulsion, graphene, sodium nitrite solution, deionized water in the dispersion tank, and then disperse and stir for 30 min at 1000 r/min under a high-speed disperser, and filter Then the epoxy emulsion components can be obtained.

(2) Preparation of anti-corrosion coating

Mix the curing agent component and the epoxy component according to a specific mass ratio, dilute with water and stir evenly, make a sample according to HG/T 5573-2019 "Graphene Zinc Powder Coating", and conduct subsequent coating performance tests.

(3) Testing and characterization

The drying time refers to GB/T 1728-1979 "Coating and Putty Film Drying Time Determination Method", the solid content refers to GB/T 1725-2007 "The determination of the non-volatile content of paints, varnishes and plastics", the viscosity test refers to GB/ T 9751-88 "Determination of Viscosity of Coatings at High Shear Rates", storage stability refers to GB/T 67853.

Results and discussion

(1) The effect of dispersant dosage on the viscosity and storage stability of curing agent components

The 64# rotor was selected, the viscosity of the curing agent components with different dispersant dosages was measured at 12 r/min and 20 r/min, and the storage stability was observed after 30 d storage in an oven at 50 ℃.

Table 1 The viscosity of the curing agent component changes with the amount of dispersant

From the data in Table 1, it can be seen that as the amount of dispersant increases, the viscosity of the dispersed curing agent becomes smaller; in order to investigate the thixotropy of the coating, it is found at different speeds.

(2) The effect of thixotropic agent on the viscosity of curing agent components

The thixotropic agent can make the coating thixotropic.

Table 2 The effect of thixotropic agent dosage on curing agent components

It can be seen from the data in the table that with the increase of 881B organic soil, the viscosity of the curing agent component shows an upward trend, and its thixotropy becomes obvious.
However, in the actual production process, when the viscosity is too large, it cannot be filtered.
Therefore, after investigating the storage stability, it is found that when the thixotropic agent dosage is 1.
7%, there is no sedimentation after storage in an oven at 50 ℃ for 30 days, and the production It is easy to discharge at times.

(3) The influence of the ratio of active hydrogen to epoxy-based substance on coating performance

➤Flexibility

According to the different ratios of active hydrogen and epoxy-based substances, paint the board, and then conduct the flexibility test.
The test results are shown in Figure 1.

Figure 1 The influence of the ratio of active hydrogen to epoxy-based substance on the flexibility of the coating

As shown in Figure 1, as the ratio of active hydrogen to epoxy-based substances increases, the flexibility of the coating gradually decreases.
This may be because with the increase of the curing dose, the epoxy resin cures faster, and the formed coating has high hardness and high brittleness.
When the coating is subjected to a bending test, it is prone to reticulation cracks, so the flexibility is poor.
Consider active hydrogen and The amount ratio of epoxy-based substances is 0.
8.

➤Pencil hardness

According to different ratios of active hydrogen and epoxy-based substances, the paint board was prepared, and then the pencil hardness test was performed.
The test results are shown in Figure 2.

Figure 2 The influence of the ratio of active hydrogen to epoxy-based substance on the flexibility of the coating

As shown in Figure 2, as the ratio of active hydrogen to epoxy-based substances increases, the hardness of the coating increases.
This may be because the more curing agent is added, the faster the epoxy resin cures, the denser the coating formed, and the higher the hardness of the coating.
Therefore, it is determined that the ratio of active hydrogen to epoxy-based substances is 0.
8~ Between 1.
0.

➤Neutral salt spray resistance

As shown in Figure 3, from left to right, the ratio of active hydrogen to epoxy-based substances is 0.
6, 0.
8, 1.
0, 1.
2, 1.
4.
When the ratio of active hydrogen to epoxy-based substances is less than 0.
8, the curing agent The amount of addition is small, the curing reaction rate is slow, and the curing is incomplete, the formed coating has poor sealing, and the coating surface has rust and blistering; when the ratio of active hydrogen to epoxy-based substances is greater than 1.
0, the curing agent Too much addition results in a faster curing reaction and poor anchoring and bonding ability between the coating and the substrate.
At the same time, the residual amine curing agent is highly hydrophilic, and moisture easily penetrates into the coating, resulting in salt spray resistance of the coating.
Performance is poor.
Therefore, the salt spray test results show that when the ratio of active hydrogen to epoxy is 0.
8-1.
0, the coating has better corrosion resistance.

Figure 3 Neutral salt spray resistance results of different curing ratios

(4) The influence of different types of graphene on coating performance

On the basis of the previous research work of this research group, the dosage of graphene was selected to be 0.
3% of the dry film mass, and the effect of different types of graphene on the coating performance was studied, and the results were verified theoretically by electrochemistry.
Sex.

➤The influence of different types of graphene on the resistance to neutral salt spray

Table 3 Neutral salt spray resistance results of different graphene types

Judging from the neutral salt spray resistance results tested in the table, the graphene powder has the worst resistance to neutral salt spray, the graphene slurry has the best neutral salt spray resistance, and the graphene oxide slurry has the best resistance to neutral salt spray.
The result is between the two.
This may be because the graphene powder is difficult to disperse evenly when dispersed in the coating, and the defects in the coating are relatively large, and it does not have a good anti-corrosion effect; There are a large number of hydrophilic groups, which leads to a decrease in the corrosion resistance of the coating; when the graphene slurry (solution exfoliation method) is used, because the graphene has been pre-dispersed in the early stage, it can be well dispersed in the coating, and the graphite The alkene does not have a large number of hydrophilic groups, so it exhibits its excellent anti-corrosion performance.

➤Electrochemical test

Table 4 Corrosion measurement results

On the whole, the highest open circuit potential is sample GEZ-2 (107 mV), and the open circuit potential of other samples is closer to -520 mV to -528 mV.
It shows that a protective film is formed on the surface of sample GEZ-2, while the other samples will corrode and dissolve.
The potential value of sample GEZ-2 is the largest.
In terms of corrosion current, the corrosion current of sample GEZ-2 is the smallest.

Judging from the above electrochemical test results, it is basically consistent with the neutral salt spray resistance result, and the graphene slurry (solution exfoliation method) shows the best performance.
This may be because when the graphene powder is dispersed in the coating, it is difficult to disperse uniformly, and the defects in the coating are large, and it does not have a good anti-corrosion effect; when using graphene oxide, the graphene oxide contains A large number of hydrophilic groups cause the corrosion resistance of the coating to decrease; when graphene slurry (solution exfoliation method) is used, because the graphene has been pre-dispersed in the early stage, it can be well dispersed in the coating, and the graphene It does not have a large number of hydrophilic groups, so it exhibits its excellent anti-corrosion performance.
Therefore, the formulation uses graphene slurry.

Conclusion

Through this research, the following conclusions can be drawn:

❶ When the amount of dispersant in the curing agent component is determined to be 0.
6% and the amount of thixotropic agent is 1.
7%, the production process of the coating curing agent component is simple, and the coating has excellent storage stability;

❷ When the ratio of active hydrogen to epoxy-based substance is 0.
8~1.
0, the coating shows better physical and mechanical properties and neutral salt spray resistance;

❸ Graphene powder, graphene slurry (solution exfoliation method), and graphene oxide are added to the water-based epoxy zinc-rich coating, and the coating is subjected to neutral salt spray resistance and electrochemical tests.
The results show that the graphene The slurry (solution stripping method) shows the most excellent anti-corrosion performance among the coatings, and the electrochemical test is consistent with the neutral salt spray resistance test, indicating that the electrochemical test can guide the development of anti-corrosion coatings more efficiently.