“…In this case, only small crystalline deposits were observed (see images given at 100 nm z-scale, Fig. 2 ), corresponding to the zinc oxide and hydroxide species expected to form in the alkaline environment at the cathode 18 . Figure 2 Peak force tapping mode AFM images of steel coupled to zinc during immersion in 3.5 wt % NaCl in the presence of a saturated solution (<50 ppm) SAPP inhibitor (left) and in the absence of added inhibitor, displayed using both a 3 µm and 100 nm z scale.…”
Polyphosphate corrosion inhibitors are increasingly marketed as chromate replacements for coil coated steel. The mechanisms underpinning corrosion prevention by these species is, however, not fully understood; corrosion inhibition is ordinarily assessed using electrochemical techniques, followed by ex-situ surface analysis. As a result, the formation of a clear film over cathodic sites is known to contribute to corrosion prevention, but little is known about its formation. Here, we apply advanced microscopy techniques (in-situ fluid cell AFM, SEM-EDX, and AFM-IR nano-chemical analysis) to examine early cathodic film formation by strontium aluminium polyphosphate (SAPP) in detail. For a model cut edge system, it is found that cathodic inhibition dominates during the first 24 hours of immersion, and surprisingly, that strontium carbonate impurities play a significant role. Rapidly precipitated zinc carbonate provides protection almost immediately after immersion, before the film structure evolves to include (poly)phosphate species. This suggests that the purposeful inclusion of carbonates may provide a new, environmentally sound approach to enhancing inhibitor efficacy.
“…In this case, only small crystalline deposits were observed (see images given at 100 nm z-scale, Fig. 2 ), corresponding to the zinc oxide and hydroxide species expected to form in the alkaline environment at the cathode 18 . Figure 2 Peak force tapping mode AFM images of steel coupled to zinc during immersion in 3.5 wt % NaCl in the presence of a saturated solution (<50 ppm) SAPP inhibitor (left) and in the absence of added inhibitor, displayed using both a 3 µm and 100 nm z scale.…”
Polyphosphate corrosion inhibitors are increasingly marketed as chromate replacements for coil coated steel. The mechanisms underpinning corrosion prevention by these species is, however, not fully understood; corrosion inhibition is ordinarily assessed using electrochemical techniques, followed by ex-situ surface analysis. As a result, the formation of a clear film over cathodic sites is known to contribute to corrosion prevention, but little is known about its formation. Here, we apply advanced microscopy techniques (in-situ fluid cell AFM, SEM-EDX, and AFM-IR nano-chemical analysis) to examine early cathodic film formation by strontium aluminium polyphosphate (SAPP) in detail. For a model cut edge system, it is found that cathodic inhibition dominates during the first 24 hours of immersion, and surprisingly, that strontium carbonate impurities play a significant role. Rapidly precipitated zinc carbonate provides protection almost immediately after immersion, before the film structure evolves to include (poly)phosphate species. This suggests that the purposeful inclusion of carbonates may provide a new, environmentally sound approach to enhancing inhibitor efficacy.
“…Manhabosco et al reported the difference of Zn corrosion products deposited on low-angle cross section of Zn coated steel. 23) Hydrozincite are deposited on the coating/steel interface and simonkolleite are deposited on the outer Zn coating region. Okada et al reported pH change with Fe/Zn interface by numerical analysis.…”
Section: Changes In Zn Corrosion Products With Deposition Positionmentioning
In this study, hydrogen permeation current from scratch formed on Zn coated steel during 1 000 h wet and dry cyclic corrosion test was investigated. The scratch was fabricated by focused pulsed Nd: YAG laser irradiation. The obtained hydrogen permeation current has peaks during wetting, and the peak currents decrease with time. Formation of Zn corrosion products prevent hydrogen entry. After the test, there are Zn oxide (ZnO) on the substrate steel, hydrozincite (Zn 5 (OH) 6 (CO 3 ) 2 ) around the scratch boundary and simonkolleite (Zn 5 (OH) 8 Cl 2 ) on Zn coated region. It is suggested that pH change with distance from the formed scratch is the reason for the composition of Zn corrosion products change with location.
“…Ni et al [44] studied the typical polarity reversal of Cu-304SS galvanic couple (GC) in solution containing Cl − with different pH values by electrochemical test and SVET test. Manhabosco et al [45] employed the microcapillary cell (MEC) and SVET and low-angle cross sections to elucidate the role of each coating region on the protection of the cut-edge corrosion of galvanized steels.…”
The influence of pH and metallographic structure on the corrosion behavior of copper-drawn steel is studied with the simulated system. The effect of pH on the corrosion behavior of copper-drawn steel has been investigated using open-circuit potential, potentiodynamic polarization, galvanic current measurement, scanning electron microscopy and scanning vibrating electrode technique techniques. The steel is corroded as anode, while the corrosion of copper plate is protected as cathode. All the results revealed that pH and metallographic structure had a significant influence on the corrosion behavior of copper-drawn steel. With the decrease in pH value from 6 to 2.4, the corrosion rate of copper-drawn steel galvanic couple (Cu-Fe GC) obviously increased in the simulated solution of acidic red soil. The electric field formed by the Cu-Fe GC changes the direction of ion migration between the copper and drawn steel electrodes, which impacts the composition and microstructure of corrosion products formed on the electrode surface.
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