Failure mechanisms for organic coatings subjected to 0.1M sulfuric acid

Abstract

The ability of a fluoropolymer and an epoxy coating to protect steel against corrosion in 0.1 M H2S04 at 60 °C was evaluated by four techniques: (1) cathodic delamination, (2) tensile adhesion, (3) rate of blister formation, and (4) gas analysis of blisters. The data obtained show that acid diffuses through the coating to react with the steel surface to oxidize (corrode) it and to form hydrogen gas by the reduction of the hydrogen ion in the acid. If the generation of hydrogen occurs faster than its removal by diffusion through the coating or into the steel, a blister will form. If the rate of hydrogen formation is less than Its removal rate, there can be almost complete disbonding of the coating with no visible blisters.

Failure of multi-layer graphene coatings in acidic media

“…The formation of hydrogen bubbles at the interface between coating and substrate in aggressive acid environment is a known phenomenon in corrosion science. 20,21 Also, it is worth reminding that, though under different conditions, the evolution of hydrogen bubbles at the interface between graphene and metal substrate during the cathodic reaction is a method largely used for graphene transfer. 22 To investigate whether the hydrogen bubbles are being generated both at the surface of the MLG lm and underneath, we applied a xed negative potential (À0.6 V vs. Ag/AgCl) to the coated nickel sample in 0.5 M HCl solution for only a short period of time (3 min).…”

In Situ Confocal Laser Scanning Microscopy of AA2024-T3 Corrosion Metrology

“…Blister formation can occur as a consequence of underpaint corrosion by anodic undercutting, 4,29,40,41 corrosion product wedging, 30 cathodic delamination, 2,3,29,30 or by chemically induced loss of adhesion, 42,43 as well as osmotic effects. 28,44,45 In the mechanisms that involve underpaint corrosion processes, generally galvanic coupling between heterogeneous sites such as IMC and the matrix is involved.…”

“…Large-scale coating delamination in acids has been reported in literature but for much lower pH. 43 It was related to hydrogen evolution destroying the bonds between metal surface and coating. The apparent diffusion coefficient of sulfate at pH 3.5 is smaller than that of chloride at pH 3.0 by a factor of 5, and the ion-diffusion coefficients increase with decreasing pH.…”

Cerium conversion coating and sol-gel coating for corrosion protection of the WE43 Mg alloy

“…Even though no accordance exists about the mechanism behind the H 2 evolution process [73,79], it is clear that it involves H 2 O either by means of a chemical [75,80] or electrochemical [73] reaction. The protective efficiency of polymeric coatings dramati-cally relies on their adhesion to the metallic surface; it has been reported that if the rate of hydrogen generation at the coating-metal interface is faster than its removal by diffusion through the coating, a blister will form [81]; therefore, the increased amount of hydrogen gas generated upon anodic polarization of the samples (NDE effect) during the potentiodynamic experiments may develop blisters underneath the hybrid coating leading to their early failure when compared, for instance, with the CeP coating. On the other hand, considering the effect of immersion time on the breakdown potential, it is likely that with increased immersion time, the coatings will be more soaked with water molecules which will be more readily available for the NDE mechanism, thus decreasing the breakdown potential.…”