06-24-2018, 08:41 AM
Rob if I understand this correctly the change in the patina signifies the corrosion itself will eventually develop a temporary barrier similar to weathering steel, however eventually that itself will eventually corrode:
Corrosion behavior of hot-dip galvanized steel in simulated acid rain environment
Abstract
Corrosion behavior and failure mechanism of hot-dip galvanized steel (HDG) were investigated in an indoor simulated acid rain environment. The surfacial and cross-sectional morphologies of corroded HDG were observed by SEM; the elemental composition of the corrosion product was analyzed by EDX; the phase constituent of corrosion products was characterized by XRD; the corrosion rates of HDG were tested by mass-loss method. The results showed that the corrosion rate firstly decreases sharply, and declines slowly, and then rises slightly with time; corrosive media locally attack the galvanized layer generating pitts and corrosion products (ZnO ZnCl2 xH2O), then the later accumulated on the HDG surface. It follows that the corrosion products may act as a barrier, soon after it totally covers the surface of the HDG plate, to inhibit the penetration of corrosive media in the simulated acid environment. Initially corrosion rate decreases rapidly because the corrosion reactions proceed and corrosion products occur. The corrosion products become so dense that the corrosion rate further slows. Finally corrosive media penetrates galvanized layer, and corrodes the substrate, the corrosion rate becomes larger slightly. Throughout the process, the HDG layer provides certain protection to itself and the substrate.
Corrosion behavior of hot-dip galvanized steel in simulated acid rain environment.
Available from: https://www.researchgate.net/publication...nvironment [accessed Jun 24 2018].
Corrosion behavior of hot-dip galvanized steel in simulated acid rain environment
Abstract
Corrosion behavior and failure mechanism of hot-dip galvanized steel (HDG) were investigated in an indoor simulated acid rain environment. The surfacial and cross-sectional morphologies of corroded HDG were observed by SEM; the elemental composition of the corrosion product was analyzed by EDX; the phase constituent of corrosion products was characterized by XRD; the corrosion rates of HDG were tested by mass-loss method. The results showed that the corrosion rate firstly decreases sharply, and declines slowly, and then rises slightly with time; corrosive media locally attack the galvanized layer generating pitts and corrosion products (ZnO ZnCl2 xH2O), then the later accumulated on the HDG surface. It follows that the corrosion products may act as a barrier, soon after it totally covers the surface of the HDG plate, to inhibit the penetration of corrosive media in the simulated acid environment. Initially corrosion rate decreases rapidly because the corrosion reactions proceed and corrosion products occur. The corrosion products become so dense that the corrosion rate further slows. Finally corrosive media penetrates galvanized layer, and corrodes the substrate, the corrosion rate becomes larger slightly. Throughout the process, the HDG layer provides certain protection to itself and the substrate.
Corrosion behavior of hot-dip galvanized steel in simulated acid rain environment.
Available from: https://www.researchgate.net/publication...nvironment [accessed Jun 24 2018].