Study on the Corrosion Resistance of Graphene Oxide-Based Epoxy Zinc-Rich Coatings

Abstract

In order to improve the corrosion resistance of zinc-rich epoxy coatings and reduce the amount of zinc used, first, graphene oxide (GO) was modified by sulfonated multiwall carbon nanotubes (SMWCNTs) to obtain the modified graphene oxide (SM-GO). The samples were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Raman spectroscopy. Then, four kinds of coatings were prepared, namely pure zinc-rich coating (0-ZRC), graphene oxide-based zinc-rich coating (GO-ZRC), sulfonated multiwall carbon nanotube-based zinc-rich coating (SM-ZRC) and SM-GO-based zinc-rich coating (SG-ZRC). The corrosion resistance of the above coatings was studied by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), a salt spray test, 3D confocal microscope, and electron scanning electron microscope (SEM). The results indicate that GO is successfully non-covalently modified by SMWCNTs, of which the interlayer spacing increases and dispersion is improved. The order of the corrosion resistance is GO-ZRC > SG-ZRC > SM-ZRC > 0-ZRC. The addition of GO, SMWCNTs, and SM-GO increases the shielding effect and increases the electrical connection between Zn particles and metal substrates, which improves the corrosion resistance. However, SMWCNTs and SM-GO also strengthen the galvanic corrosion, which decreases the corrosion resistance to some extent.

Keywords: corrosion resistance; epoxy zinc-rich coating; graphene oxide; multiwall carbon nanotubes; sulfonated.

Figure 1

Schematic illustration of the preparation of GO and SM-GO.

Figure 2

FT−IR characterization of SM−GO, SMWCNTs, GO.

Figure 3

XRD characterization of GO, SMWCNTs and SM-GO samples.

Figure 4

Raman characterization of GO, SMWCNTs and SM−GO samples.

Figure 5

OCP for the different coating samples with immersion time.

Figure 6

Visual observations of the different coating samples after 0, 15, 30, 50 and 70 d exposure to salt spray; results after peeling of coating after 70 d salt spray.

Figure 7

Macroscopic morphology (left) and microscopic 3D morphology (right) of the metal substrate of (a) 0-ZRC, (b) GO-ZRC, (c) SM-ZRC, (d) SG-ZRC.

Figure 8

SEM of the 0-ZRC (a), GO-ZRC(b), SM-ZRC(c) and SG-ZRC(d) samples.

Figure 9

SEM of the 0-ZRC, GO-ZRC, SM-ZRC and SG-ZRC samples after 0, 15, 30, 50 and 70 days exposure to salt spray.

Figure 10

Nyquist and Bode diagrams of the (a1,a2) 0−ZRC, (b1,b2) SM− ZRC, (c1,c2) GO−ZRC and (d1,d2) SG−ZRC samples after 15, 30,50 and 70 days immersion in 3.5 wt.% NaCl solution.

Figure 11

Coating structures and equivalent circuits of (a) 0-ZRC; (b) SM-ZRC; (c) GO-ZRC; (d) SG-ZRC.

Figure 12

The values of impedance at 10 mHz obtained from Bode diagrams after 15, 30 50, and 70 days immersion in 3.5 wt.% NaCl solution.

Figure 13

Pure zinc-rich coating (a) cathodic protection stage; (b) shielding stage; (c) failure stage; zinc-rich coating containing nanoparticles (d) initial shielding stage; (e) cathodic protection stage; (f) shielding stage; (g) failure stage.

Figure 14

Galvanic corrosion of (a) SM−GO and zinc particles; (b) SM−GO and metal substrate.