Preparation and Anticorrosion Properties of Silane Grafted Nano-silica/Epoxy Composite Coating†

doi:10.7503/cjcu20170821

Abstract

Abstract:

2-(3,4-Epoxycyclohexyl) ethyltriethoxysilane(ETEO) was synthesized by a highly effective hydrosilylation reaction using 1,2-epoxy-4-vinylcyclohexane and triethoxysilane as substrates and Karstedt catalyst as the catalyst. Different methods were employed to characterize the coatings. The surface of nano-silica was treated with ETEO in order to obtain a new silane grafted on nano-silica(ETEO-SiO₂). The structure of ETEO was characterized by means of ¹H nuclear magnetic resonance spectrometer and Fourier transform infrared spectroscopy. The X-ray photoelectron spectroscopy showed that ETEO was successfully grafted on nano-silica. In addition, the morphology of the coating cross section and dispersion of ETEO-SiO₂ were investigated by field emission scanning electron microscopy. The wettability of the coating surface was analyzed by the contact angle measurement. The electrochemical impedance spectroscopy(EIS) and salt spray test of the composite coatings revealed that the corrosion resistance of coatings with ETEO-SiO₂ nanoparticles was signiﬁcantly improved as compared with that of the epoxy(EP) and SiO₂/EP coatings. Corrosion resistance achieved the highest value when ETEO-SiO₂ content reached 4%(mass fraction). It can be indicated that the SiO₂ nano-particles grafted by ETEO enhanced its compatibility effectively in the organic matrix so that ETEO-SiO₂ could distribute in the epoxy resin evenly. What’s more, the ETEO-SiO₂ increased the shielding effect of the coating and filled the coating defects, which can reduce the corrosive diffusion channels and inhibit the progress of the corrosion reaction.

Key words: Composite coating, Silane grafted nano-silica, Epoxy resin, Surface treatment, Anticorrosion property

CLC Number:

O633.13

TrendMD:

WANG Yingnan, DAI Xueyan, XU Tianlu, QU Lijie, ZHANG Chunling. Preparation and Anticorrosion Properties of Silane Grafted Nano-silica/Epoxy Composite Coating^†[J]. Chem. J. Chinese Universities, 2018, 39(7): 1564.

Figures/Tables 13

Scheme 1 Schematic reaction of VCHO and triethoxysilane

Scheme 2 Schematic illustration of the surface treatment of nano SiO2

Fig.1 FTIR(A) and 1H NMR(B) spectra of triethoxysilane(a), VCHO(b) and ETEO(c)

Fig.2 XPS full spectrum(A) and C1s(B), O1s(C), Si2p(D) spectra of ETEO-SiO2

Fig.3 SEM images of coating cross section of EP(A), SiO2/EP(B) and 1%—5%ETEO-SiO2/EP coatings(C—G)

Fig.4 Typical Si mapping micrographs of the 4%ETEO-SiO2/EP coating^ (A) Digital image; (B) Si mapping.

Fig.5 Water contact angle(CA) values of EP(A), SiO2/EP(B) and 1%—5%ETEO-SiO2/EP(C—G) coatings^(A) CA=62.6°; (B) CA=42.7°; (C) CA=65.6°; (D) CA=67.2°; (E) CA=70.4°; (F) CA=83.7°; (G) CA=76.1°.

Fig.6 Bode diagrams of the EP, SiO2/EP and 1%—5%ETEO-SiO2/EP samples immersed in 3.5%NaCl solution for 10 h(A, B), 100 h(C, D), 500 h(E, F) and 1500 h(G, H)^ (A, C, E, G) Frequency vs. |Z|; (B, D, F, H) frequency vs. phase angle.

Fig.7 Nyquist diagrams of the EP, SiO2/EP and 1%—5%ETEO-SiO2/EP samples immersed in 3.5% NaCl solution for 10 h(A), 100 h(B), 500 h(C) and 1500 h(D—F)

Fig.8 Equivalent circuit models used to perform EIS data

Table 1 Electrochemical parameters from the equivalent electrical circuits

Time/h	EP		SiO₂/EP		4%ETEO-SiO₂/EP
Time/h	R_c/(Ω∙cm²)	CPE/(F∙cm^-2)	R_c/(Ω∙cm²)	CPE/(F∙cm^-2)	R_c/(Ω∙cm²)	CPE/(F∙cm^-2)
10	6.395×10⁹	4.873×10^-10	7.686×10⁹	2.594×10^-10	1.863×10¹¹	3.534×10^-12
100	1.806×10⁹	1.058×10^-10	2.805×10⁹	8.362×10^-9	9.163×10¹⁰	8.658×10^-11
500	6.385×10⁸	3.246×10^-9	1.472×10⁹	6.424×10^-9	6.694×10¹⁰	3.547×10^-11
1500	6.806×10⁶	9.832×10^-7	9.235×10⁶	1.207×10^-7	2.845×10¹⁰	3.644×10^-10

Fig.9 Photographs of EP(A), SiO2/EP(B) and 1%—5% ETEO-SiO2/EP coatings(C—G) after salt spray test for 400 h

Fig.10 Corrosive protection mechanism graph of the SiO2/EP(A) and 4%ETEO-SiO2/EP(B) coatings

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