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Review
. 2018 Jan 26;11(2):197.
doi: 10.3390/ma11020197.

Functionalizable Sol-Gel Silica Coatings for Corrosion Mitigation

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Free PMC article
Review

Functionalizable Sol-Gel Silica Coatings for Corrosion Mitigation

Jolanta Gąsiorek et al. Materials (Basel). .
Free PMC article

Abstract

Corrosion is constantly a major problem of the world economy in the field of metal products, metal processing and other areas that utilise metals. Previously used compounds utilizing hexavalent chromium were amongst the most effective materials for corrosion protection but regulations have been recently introduced that forbid their use. Consequently, there is a huge drive by engineers, technologists and scientists from different disciplines focused on searching a new, more effective and environmentally-friendly means of corrosion protection. One novel group of materials with the potential to solve metal protection problems are sol-gel thin films, which are increasingly interesting as mitigation corrosion barriers. These environmentally-friendly and easy-to-obtain coatings have the promise to be an effective alternative to hexavalent chromium compounds using for anti-corrosion industrial coatings. In this review the authors present a range of different solutions for slow down the corrosion processes of metallic substrates by using the oxides and doped oxides obtained by the sol-gel method. Examples of techniques used to the sol-gel coating examinations, in terms of anti-corrosion protection, are also presented.

Keywords: corrosion inhibitors; layers; sol-gel.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Historical publication data concerning sol-gel matrices for alloys substrates.
Figure 2
Figure 2
Schematic layout of the respective layers in a coating.
Figure 3
Figure 3
Schematic of the spin-coating technique: (a) application of the coating material on the substrate; (b) spreading of the coating material over the substrate via rapid rotation or spinning of the substrate; (c) resultant thin-film deposition across the substrate.
Figure 4
Figure 4
Schematic of the dip-coating technique: (a) appropriate presentation of the substrate for the dip-coating procedure; (b) immersion of the substrate (optional holding period of the submerged substrate within the coating solution); (c) ascent of the substrate from the coating solution; (d) fully coated substrate removed from the coating solution.
Figure 5
Figure 5
Images taken by a metallographic microscope for steel substrates with phosphate chemical coating: (a) after 2 min and (b) after 10 min deposition (magnification: ×10).
Figure 6
Figure 6
AFM images of poly(ethylene terephthalate) before (a) and after (b) SiO2/TiO2 4-layered coating deposition.
Figure 7
Figure 7
(a) Scanning Electron Microscopy (SEM) micrograph of a transparent silica coating on stainless steel (magnification 1000×), (b,c) EDX analysis shows the presence and uniform distribution of silicon on the substrate surface.
Figure 8
Figure 8
SEM micrographs of silica coatings with different morphologies. (a) SiO2 coating on the surface of stainless steel: Note the surface appears smooth at low magnification, while a good distribution of visible particles of silica is observable at high magnification. (b) SiO2 coating on the surface of a titanium alloy substrate after an expansion test: Note it is difficult to see at low magnification, while at high magnification there are visible silica particles. In addition, an interesting property of this coating is its flexibility. (c) A cracked SiO2 coating on steel. (d) SiO2 coating with bubbles on the surface of the steel.
Figure 9
Figure 9
TEM images of: (a) uncoated carbon fibre, (b) carbon fibre with silica coating.
Figure 10
Figure 10
Raman spectra of 316L steel before (black spectrum) and after (red spectrum) SiO2 coating deposition.
Figure 11
Figure 11
High-resolution spectra of Si2p line in SiO2/TiO2 hybrid coating.

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