Ureasilicate Hybrid Coatings for Corrosion Protection of Galvanized Steel in Chloride-Contaminated Simulated Concrete Pore Solution

Abstract

Organic-inorganic hybrid (OIH) sol-gel coatings based on ureasilicates (U(X)) have promising properties for use as eco-friendly coatings on hot dip galvanized steel (HDGS) and may be considered potential substitutes for pre-treatment systems containing Cr(VI). These OIH coatings reduce corrosion activity during the initial stages of contact of the HDGS samples with highly alkaline environments (cementitious media) and allow the mitigation of harmful effects of an initial excessive reaction between cement pastes and the zinc layer. However, the behavior of HDGS coated with U(X) in the presence of chloride ions has never been reported. In this paper, the performance of HDGS coated with five different U(X) coatings was assessed by electrochemical measurements in chloride-contaminated simulated concrete pore solution (SCPS). U(X) sol-gel coatings were produced and deposited on HDGS by a dip coating method. The coatings performance was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization curves measurements, macrocell current density and polarization resistance in contact with chloride-contaminated SCPS. The SEM/EDS analyses of the coatings before and after the tests were also performed. The results showed that the HDGS samples coated with the OIH coatings exhibited enhanced corrosion resistance to chloride ions when compared to uncoated galvanized steel. Corrosion of the reinforcing steel is one of the most important causes of degradation in reinforced concrete structures (RCS).1 The presence of chloride, carbonation of the concrete or the low quality of the concrete cover causes serious damage to RCS. The entrance of chloride ions through the concrete from marine environments or deicing salts can cause rupture of the passive layer, allowing the steel surface to act as a coupled anodic and cathodic reaction cell in which corrosion processes take place.1-3 Therefore, the presence of chlorides in concrete can seriously shorten the service life of RCS. 3,4The expanded volume of corrosion products deposited in the interface between the concrete and the steel imposes expansive stresses, leading to delamination, cracking or spalling and eventually to the collapse of the RCS. 1 Several methods to improve the corrosion resistance of RCS have been proposed. 1,[5][6][7] In the last few years, the use of hot-dip galvanized steel (HDGS) has been recognized as an effective measure to increase the service life of RCS. [8][9][10][11] The galvanized coating (zinc layer) acts as a physical barrier, hindering the contact of aggressive agents with the steel substrate and the zinc acts as a sacrificial anode protecting the steel against corrosion. In addition, the formed zinc corrosion products have a smaller volume than those produced from iron, thus reducing the corrosion-induced delamination, cracking or spalling of the concrete.8 Additionally, the galvanized steel reinforcement can withstand exposure to chloride ion concentrations several times higher than the chloride level that causes corrosion in ste...

Hybrid Sol–gel Coatings for Corrosion Mitigation: A Critical Review

“…This allows one to obtain materials with distinctive properties when compared to the separated components. Therefore, OIH sol-gel materials show a huge potential for applications in a wide range of fields as diverse as optical [13], electronics [14], surface treatments [15], construction [16][17][18][19], textile [20], energy [21] and health [22], among others. The development of OIH materials, being a multidisciplinary field, involves materials engineering, chemistry, biology, physics, medicine, etc.…”

Hybrid Coatings Enriched with Tetraethoxysilane for Corrosion Mitigation of Hot-Dip Galvanized Steel in Chloride Contaminated Simulated Concrete Pore Solutions

“…Therefore, these materials mitigate the corrosion reaction rate on the metal surface of HDGS in chloride contaminated SCPS [36]. U(X) hybrids are prepared from 3-isocyanate propyltriethoxysilane (ICPTES) and di-amino functionalized polyether (hereafter referred generically as Jeffamine ® ) [27,33,34,35].…”

“…Ureasilicate (U(X)) coatings were proven to behave as a physical barrier in highly alkaline environments (pH > 12.5) [ 32 , 33 , 34 , 35 ] and to be effective in hindering the chloride ion diffusion to the substrate. Therefore, these materials mitigate the corrosion reaction rate on the metal surface of HDGS in chloride contaminated SCPS [ 36 ]. U(X) hybrids are prepared from 3-isocyanate propyltriethoxysilane (ICPTES) and di-amino functionalized polyether (hereafter referred generically as Jeffamine ® ) [ 27 , 33 , 34 , 35 ].…”

Corrosion Protection Systems and Fatigue Corrosion in Offshore Wind Structures: Current Status and Future Perspectives

“…In the last decades, EIS has been widely used for coatings characterization [119,120,[193][194][195][196][197][198][199][200][201][202]. EIS is a transient technique where a sinusoidal signal (potential) is applied with low amplitude, to not disturb the equilibrium conditions of the system.…”

“…The sample dimensions and sensibility (>0.1% mass) are limited. As a representative example, Figure 9a shows a SEM image of a sample of HDGS uncoated (1) and coated (2) with a hybrid sol-gel coating [118,199,200]. The EDS analysis is also shown (Figure 9b,c) and is clearly observed the presence of Carbon (C), Silicium (Si) and Oxygen (O) in the coated area which cannot be found on the surface of uncoated substrate and only zinc was detected.…”