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. 2024 Feb 26;17(5):1075.
doi: 10.3390/ma17051075.

Improving the Corrosion Performance of Organically Coated Steel Using a Sol-Gel Overcoat

Evan Watkins  1 , Chris M Griffiths  1 , Calvin A J Richards  1 , Sarah-Jane Potts  1 , Chris Batchelor  1 , Peter Barker  2 , Justin Searle  1 , Eifion Jewell  1
Affiliations

Improving the Corrosion Performance of Organically Coated Steel Using a Sol-Gel Overcoat

Evan Watkins et al. Materials (Basel). .

Abstract

Organically coated steels are widely used in applications in which they are subjected to the natural environment and therefore require excellent corrosion resistance. Organic clearcoats are typically employed as a barrier that improves the overall corrosion resistance; however, they are typically derived from fossil fuel-based feedstock. A more sustainable alternative could be possible using sol-gel coatings. The application of a simple tetraethoxysilane (TEOS)-based sol-gel was applied to polyurethane-coated steels using a spray coater. The concentration of TEOS was altered to produce coatings containing either 2.5% or 10%. The 10% TEOS resulted in dense, homogeneous coatings that offered a significant improvement in corrosion resistance compared to an uncoated substrate. Whereas the 2.5% TEOS coatings were inhomogeneous and porous, which indicated a limitation of concentration required to produce a uniform coating. The successful demonstration of using a simple TEOS-based coating to improve the corrosion resistance of organically coated steel highlights the potential for further investigation into the use of sol-gels for these applications.

Keywords: barrier; coatings; coil coating; corrosion; sol–gel.

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Conflict of interest statement

Author Peter Barker was employed by Tata Steel UK, Shotton Works. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Schematic of sample preparation for use in the FTIR closed-loop flow reactor.
Figure 2
Figure 2
Schematic of the FTIR closed-loop flow reactor [38].
Figure 3
Figure 3
Calibration plot showing the FTIR signal response with varying concentration of injected CO2.
Figure 4
Figure 4
FEG SEM cross-sectional images produced by ion beam milling. Images taken at 10,000× magnification (scale bar = 2 μm). The images show the sol–gel surface, cross-section of the sol–gel coating and cross-section of the PU substrate; 2.5% Si yield (A–C) and 10% Si yield (X–Z).
Figure 5
Figure 5
White light interferometer maps of a bare PU-coated steel surface (control) and sol–gel-coated PU substrates; 2.5% Si yield (A–C) and 10% Si yield (X–Z).
Figure 6
Figure 6
Optical images of a PU sample and sol–gel-coated PU samples after 1000 h salt spray exposure (5% NaCl); 2.5% Si yield (A–C) and 10% Si yield (X–Z).
Figure 7
Figure 7
The edge and scribe creep area (mm2) observed on sol–gel-coated PU samples after 1000 h salt spray exposure (5% NaCl).
Figure 8
Figure 8
The time-dependent change in FTIR peak between 2200 and 2500 cm−1 for a PVB-coated glass sample containing 40 wt% TiO2.
Figure 9
Figure 9
(a) The time-dependent change in CO2 recorded for UV-irradiated sol–gel-sprayed PVB-coated glass samples using a closed-loop FTIR flat panel reactor. (b) Peak CO2 measured for each sample over the 300 min flat panel reactor experiment.
Figure 10
Figure 10
Contact angle images showing a droplet of (left) 2.5% Si solution and (right) 10% Si solution on a polyurethane coating. The CA measurements were calculated to be 13° and 9°, respectively.
Figure 11
Figure 11
FTIR spectra of 2.5% and 10% TEOS coatings.
Figure 12
Figure 12
Schematic of the cathodic disbondment mechanism responsible for the coating failure observed in Figure 9 with (a) polyurethane-coated HDG steel sample and (b) a sol–gel-sprayed polyurethane-coated HDG steel sample.
Figure 13
Figure 13
The peak CO2 concentration for varying sol–gel thicknesses. Data points are labelled with the corresponding sample I.D.
See this image and copyright information in PMC

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