Tuning F-doped degree of rGO: Restraining corrosion-promotion activity of EP/rGO nanocomposite coating

doi:10.1016/j.jmst.2019.09.043

Abstract

Abstract:

Given that graphene features high electrical conductivity, it is a kind of material with corrosion-promotion activity. This study aimed to inhibit the corrosion-promotion activity of graphene in coatings. Here, we report an exciting application of epoxy matrix (EP)/F-doped reduced graphene oxide (rGO) coatings for the long-term corrosion protection of steel. The synthesized F-doped rGO (FG) did not reduce the utilization of rGO by a wide margin and possessed distinctive electrically insulating nature. The electrical conductivity of rGO was approximately 1500 S/m, whereas those of FG-1, FG-2 and FG-3 were 1.17, 5.217 × 10^-2 and 3.643 × 10^-11 S/m, respectively. FG and rGO were then dispersed into epoxy coatings. The chemical structures of rGO and FG were investigated by transmission electron microscopy (TEM), scanning probe microscopy (SPM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). EP/FG coatings exhibited outstanding corrosion protection in comparison with blank EP and EP/rGO coatings mainly because the corrosion-promotion effect of rGO was eliminated. The anticorrosion ability of EP/FG coatings was improved with increased F-doped degree of FG. In addition, electrochemical impendance spectroscopy (EIS) results indicated that the R_c values of EP/FG-2 and EP/FG-3 were four orders of magnitude higher than those of EP/rGO in diluent NaCl solution (3.5 wt.%) after immersion for 90 days.

Key words: Graphene, F-doped rGO, Electrically insulating nanofillers, Long-term anticorrosion

Lu Shen, Yong Li, Wenjie Zhao, Kui Wang, Xiaojing Ci, Yangmin Wu, Gang Liu, Chao Liu, Zhiwen Fang. Tuning F-doped degree of rGO: Restraining corrosion-promotion activity of EP/rGO nanocomposite coating[J]. J. Mater. Sci. Technol., 2020, 44: 121-132.

Figures/Tables 15

Fig. 1. Preparation of few-layer FG nanosheets.

Fig. 2. TEM images and corresponding SAED of (a) rGO, (b) FG-1, (c) FG-2, (d) FG-3. AFM images of (e) rGO, (f) FG-1, (g) FG-2, (h) FG-3.

Table 1 Chemical composition of rGO, FG-1, FG-2 and FG-3.

Sample names	Chemical composition (wt.%)
	C	F	O
rGO	88.84	-	11.16
FG-1	77.91	12.56	9.52
FG-2	62.11	33.98	3.91
FG-3	52.67	43.36	3.97

Fig. 3. Full spectrum of (a) rGO, (b) FG-1, (c) FG-2, (d) FG-3. High-resolution XPS spectra of (e) rGO, (f) FG-1, (g) FG-2, (h) FG-3.

Fig. 4. (a) FTIR spectra of rGO, FG-1, FG-2 and FG-3. (b) XRD spectra of rGO, FG-1, FG-2 and FG-3.

Fig. 5. SEM images for fracture surfaces of (a) blank EP, (b) EP/rGO, (c) EP/FG-1, (d) EP/FG-2 and (e) EP/FG-3.

Fig. 6. Trend of OCP values of five kinds of coatings in period of immersion in diluent NaCl solution.

Fig. 7. EIS results of the steels coated with different coatings. (a1-c1) bland EP, (a2-c2) EP/rGO, (a3-c3) EP/FG-1, (a4-c4) EP/FG-2 and (a5-c5) EP/FG-3.

Fig. 8. (a) Equivalent electric circuits models (Model I, Model II and Model III) of coatings. (b) Cc results as a function of immersion time of the five coatings. (c) The coating resistance Rc as a function of the immersion of the five coatings.

Fig. 9. Optical images of salt spray tests steel substrates coated by blank EP, EP/rGO, EP/FG-1, EP/FG-2 and EP/FG-3 coatings after 48, 114, 240 and 336 h (Test length of the artificial scribes was 2 cm).

Table 2 Results of salt spray tests.

Samples	Blistering state (336 h)	Corrosion behavior at scribes
Blank EP	Lots of blisters	Obvious rusting after 114 h
EP/rGO	Lots of blisters	Obvious rusting after 114 h
EP/FG-1	Some blisters	Obvious rusting after 240 h
EP/FG-2	Without blisters	Obvious rusting after 240 h
EP/FG-3	Without blisters	Obvious rusting after 240 h

Fig. 10. SVET results of current density for blank EP (a), EP/rGO (b), EP/FG-1 (c), EP/FG-2 (d) and EP/FG-3 (e) immersed in diluent NaCl solution.

Fig. 11. Micrographs of coating-exfoliated steel surfaces after 90 days immersion in 3.5 wt.% NaCl solution: (a1) blank EP, (b1) EP/rGO, (c1) EP/FG-1, (d1) EP/FG-2 and (e1) EP/FG-3. SEM images of coating-exfoliated steel surfaces coated by blank EP (a2), EP/rGO (b2), EP/FG-1 (c2), EP/FG-2 (d2) and EP/FG-3 (e2). (a3-e3) EDS results corresponded to areas selected in (a2-e2).

Fig. 12. Raman results of rusting layers formed on steel substrate coated by the five kinds of coatings.

Fig. 13. Schematic of corrosion protection mechanism of EP coating (a), composite coatings enhanced via rGO or FG (b); (c) Coating was exaggerated to clearly show the electron transfer in EP/rGO coating; (d) Coating was exaggerated to clearly show the electron transfer in EP/FG coatings.

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