Application and performance study of graphene in anti-corrosion coatings

0 Introduction

From the discovery of graphene in 2004 to 2010, the research on nano-two-dimensional graphene has made great progress
.
Graphene peeled from graphite is a two-dimensional crystal, in addition to the σ bond between the carbon atoms to form a hexagonal ring layer structure, the vertical layer forms a multi-atom connected π bond, similar to the benzene six-membered ring bond is very stable, so that graphene has high chemical stability, excellent mechanical strength, good physical shielding performance and large specific surface area and other advantages, so that its application to coatings can play a long-term anti-corrosion effect, further improve the protective role
of the coating.

Epoxy anti-corrosion coatings in industrial paints are mainly composed of epoxy resin, additives, functional pigment fillers and solvents, etc.
, and epoxy curing agent B components are composed of coating online coatingol.
com
.
Epoxy resin anti-corrosion coatings have good mechanical properties, adhesion, impact and flexibility can meet standard requirements, and excellent chemical properties of solvents, acids, alkalis and water, so epoxy resins are widely
used in anti-corrosion coatings.
At present, graphene coatings are mainly formed on the substrate to form graphene deposition film to achieve shielding and rust prevention, the research on the anti-corrosion mechanism of graphene is still not comprehensive enough, graphene in the coating mainly has dispersion problems and graphene conductivity problems, so graphene coatings need further research
.
Based on this, this study uses modified functional graphene to directly disperse in the coating to form a stable dispersion, to avoid the difficulty of graphene dispersion and deposition, and add it to epoxy resin to prepare modified coatings with different graphene content, and systematically study the salt water resistance, salt spray resistance and electrochemical properties
of graphene modified coatings.

1 Experimental part

1.
1 Preparation of graphene-modified epoxy zinc-rich coatings

1.
1.
1 Preparation method

(1) A component: take xylene and n-butanol mixed diluent and add functional graphene dispersion and stirring (800 r/min) for 10 min to fully mix until completely dispersed, add the resin to the dispersion tank, stir and disperse (800 r/min) for 10 min to completely dissolve, add additives, stir for 15 min Add zinc powder and anti-rust filler, disperse at high speed (1200 r/min) for 30 min, add the rest of the filler (800 r/min) to disperse for 15 min, Filter the packaging after passing the
inspection.
Component B: The curing agent is divided
in proportion.
The reference recipes are shown
in Table 1.

Table 1 Graphene epoxy zinc-rich primer reference formula table

(2) The components of paint A and B (direct packaging of finished products) are mixed according to the mass ratio of 10:1 and diluted to the construction viscosity
.

1.
1.
2 Coating plates

Performance test board is divided into basic physical property test and salt spray performance test, of which the physical property test sample with 50×120mm tinplate plate, sample thickness 0.
2-0.
3 mm, polishing according to the standard provisions before spraying, according to GB/T 9271-2008 "Color paint and varnish standard test board" for polishing degree inspection and alcohol cleaning
。 Then, according to GB/T 1727-2021 "General Preparation Method of Paint Film", the sample coating was prepared, and the thickness of the dry film of the coating was determined at (23±3)μm for curing; The salt spray performance test sample uses low carbon steel sandblasting steel plate, the size specification is 70mm×150mm thickness 1mm thickness, the surface sandblasting roughness is 40-70μm, according to the standard surface treatment grade according to GB/T 8923.
1-2011 "steel surface treatment before coating" specified in the spray cleaning grade reached Sa2.
5 grade, the dry film thickness (90±10) μm was determined, and the performance test
was carried out after preparing the sample for 10 days.

2 Results and discussion

2.
1 Basic performance test of graphene epoxy zinc-rich primer

According to the test standard: GB/T 28699-2012 "General Technical Conditions for Protective Coating of Steel Structures", its basic properties are tested, and the test results are shown
in Table 2.

Table 2 Properties of graphene epoxy zinc-rich primer

It can be seen from Table 2 that the addition of graphene does not affect the impact resistance and adhesion of the paint film, and the salt spray resistance of the paint film has significantly improved the standard, because the graphene is uniformly dispersed in the coating to form a good shielding effect, effectively isolating the entry
of corrosive media.

It can be seen from the scanning electron microscope photos A and B in Figure 1 that due to the high content of zinc powder, the traditional zinc-rich primer has a large number of pinholes in the paint film coated on the surface of the steel plate, and the shielding effect on the corrosive medium is poor, mainly relying on the cathodic protection of the sacrificial anode to play the anti-corrosion effect; After adding graphene to the coating, due to the uniform dispersion of graphene, the pores in the paint film are filled, which has a good promoting effect on the shielding effect of the paint film, and forms a stable structure to reduce coating defects
.

Figure 1 Scanning electron microscopy of epoxy zinc-rich primer (a) and graphene modified epoxy zinc-rich (b).

2.
2 Salt water resistance test of paint film

On the surface of Q235 steel plate coated with a paint film thickness of about 30 μm, the test piece after the coating surface is dried is sealed and soaked in salt water with a mass concentration of 3.
5%, and the paint film is regularly observed and recorded at different times
.
It can be seen from Figure 2 that the brine soaked for 1500h, the paint film does not appear blistering and cracking, and the surface of the test piece is not corroded by salt water, indicating that the graphene modified epoxy anti-corrosion coating has a strong salt water resistance, which can effectively prevent the penetration of salt water and play a good anti-corrosion effect
.

Fig.
2 Surface corrosion of graphene-modified epoxy anticorrosive coating soaked in salt water for 720h, 1008h and 1500h

2.
3 Effect of graphene addition on corrosion rate

Functional graphene can effectively shield the corrosion medium to slow down the transformation caused by corrosion, ensure the corrosion resistance and long-term durability of the paint film, and calculate the corrosion rate after 800h of the neutral salt spray test of the paint film by weight gain method, and the effect of the amount of graphene added on the paint film is shown in Figure 3
。 When the amount of graphene is added at 0.
5%, the corrosion rate of the paint film is significantly reduced, and when the amount of addition is less, the shielding effect is poor, and the stable structure cannot be completely dispersed, and the corrosion rate of zinc powder consumption will increase; When the amount of addition is large, due to the agglomeration of graphene, the shielding defect of the paint film will appear and the corrosion rate will increase significantly, so it can play a good role
when the addition amount is 0.
5%.

Fig.
3 Effect of graphene addition on corrosion rate of paint film

2.
4 Electrochemical performance test

The Tafel test was performed on the paint film under different graphene addition amounts, and the corrosion current and corrosion potential were compared, and the results were shown in Figure 4
.

Fig.
4 Tafel curves of different graphene additions

It can be seen from Figure 4 that when the amount of graphene added is 0.
5%, the corrosion resistance of the paint film is the strongest, and the corrosion potential is significantly negative when the addition amount is too high or too low, the corrosion current increases, and the corrosion resistance is weakened, it can be seen that the corrosion resistance of the paint film is the best when the graphene addition amount is 0.
5%, which is the best addition amount
.

2.
5 Film adhesion test

Bond strength is a very important mechanical property of a coating, because once the coating is detached from the substrate, other protection mechanisms will fail
.
Figure 5 shows the comparison of surface morphology and bond strength after drawing experiments with and without graphene coating
.

Fig.
5 Comparison chart of graphene (a) without addition and 5% graphene (b) and adhesion value (c).

It can be seen from Figure 5 that there are no cracks around the aluminum ingots with and without epoxy coating, the bonding strength of 10.
9 MPa without epoxy zinc-rich coating, and the bonding strength of 5% graphene modified coating is 11.
7 MPa, both higher than 10 MPa, indicating that the adhesion performance of the coating and the matrix is excellent, and the addition of graphene further improves the bonding strength of the paint film, improves the corrosion resistance, and meets the technical requirements
of adhesion with the metal matrix greater than 5 MPa.

2.
6 Performance comparison with commercially available products

Due to the development of the long-term anti-corrosion coating market, the application of graphene in coating technology is gradually extensive, but the product quality is mixed
.
In this experiment, the performance of commercially available graphene coating products was compared with this product, and the apparent appearance of the sample paint film after 2000 hours of salt spray resistance was compared as shown in
Figure 6.
Among them, the unmarked part of this product does not appear blistering and corrosion phenomenon, the paint film is good, and the unidirectional expansion of trace corrosion corrosion in the marking part does not exceed 2mm; The integrity of the unmarked part of the commercial product is good, but the blistering phenomenon appears in the paint film part, and the corrosive expansion of the marked part is obvious, indicating that this product has better corrosion resistance than the commercial product and has a long-term protection effect
.
Table 3 shows the comparison of physical and chemical properties, and the results show that the adhesion, salt water and salt spray resistance of this product are better than those of commercially available products
.

Figure 6 Comparison chart of salt spray resistance 2000h between this experimental product (a) and commercial product (b).

Table 3 Performance comparison between this product and commercially available products

3 Conclusion

The graphene epoxy anti-corrosion primer in this study can be directly dispersed in the epoxy paint system, which has good corrosion resistance, can reach 5000h long-term anti-corrosion, and the addition of 0.
5% graphene can significantly enhance the corrosion stability of the coating, but the improvement effect of 1% graphene decreases, which is mainly related to its agglomeration behavior in the coating; The addition of graphene does not affect the adhesion of the paint film, and further improves the adhesion of the paint film.
The preparation of graphene anti-corrosion coatings meets the standard requirements
.
In this study, the graphene epoxy anti-corrosion primer was compared with the commercially available graphene coating, and the salt spray resistance, adhesion and salt water resistance of this product were better than those of commercially available products.
Due to the guidance of national policies on the development of new materials, the research and application of graphene in the field of anti-corrosion have been promoted, but the research is still insufficient, the storage stability of this product still needs to be improved, and the research on long-term anti-corrosion mechanism still needs to be further carried out
.

References (omitted)

Authors| Zhou Zhongwei, Zhang Jianxiong, Jin Shaobo, et al

(Jinyu Micro (Cangzhou) Chemical Co.
, Ltd.
, Cangzhou, Hebei 061108)