In this research, the Pistia stratiotes leaf (PSL) extract was evaluated as a green corrosion inhibitor for the corrosion of mild steel in 1 M HCl using electrochemical measurements and surface characterization. Electrochemical impedance spectroscopy (EIS) spectra showed that the inhibitory activity of the phytochemical compounds enhanced with increasing concentration up to 400 ppm, which was reflected in the increase in the charge transfer resistance and double-layer capacitance. Regarding the effect of immersion time, EIS results indicated that the persistence of the PSL extract was between 4 h and 8 h of exposure time. From polarization curve (PCC) results, the best performance of the corrosion inhibitor was achieved at 400 ppm with an inhibition efficiency of 93.7%. The PSL extract acted as a mixed-type corrosion inhibitor. The adsorption of the phytomolecules on the metal surface obeyed the Langmuir isotherm through a mixed mechanism (physical and chemical interactions) dominated by physisorption. Scanning electron microscopy (SEM) examinations and energy-dispersive X-ray spectroscopy (EDS) elemental analysis of the corroded samples confirmed the anticorrosive protection of the PSL extract. Chemical characterization of the PSL extract by GC-MS revealed the presence of phytol, steroids, and aromatic and long-chain unsaturated fatty acid esters, in order of abundance. Chemical quantum calculations by DFT allowed for determining that the phthalic acid, di(2-propylpentyl) ester compound has the most significant potential to act as the main active component in corrosion inhibition activity.

In the last years, electrochemical noise (EN) has demonstrate that is capable of detect the initiation of cracks during the slow strain rate tests (SSRT). In this research, EN has been used as a tool to detect stress corrosion cracking (SCC) in low carbon steel (X52) exposed to a synthetic soil solution called NS4 at room temperature with pH of 5, 8 and 10. The electrochemical potential and current noise were measured simultaneously during SSRT. Relation between EN and SCC process was analyzed. EN readings of current consisted of transients with high intensity and frequency during all SSRT tests. EN readings of potential at the maximum strength (UTS) and before fracture, increase intensity and amplitude of the transients, attributed to beginning of cracking. Localized index (LI) values indicate a mix corrosion type (general and localized corrosion) during SSRT tests. According to SCC index obtained from mechanical properties, it is clear that X52 steel has low SCC susceptibility. Scanning electron microscopy (SEM) observations were carried out in the fracture surface and longitudinal sections. The specimens tested in NS4 solution with pH 5 were the most likely to present SCC, additionally in this condition a brittle fracture with transgranular appearance was observed.