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The inhibitory action of Red onion seeds and peels extracts (ROSE & ROPE) was testing and comparing on the corrosion of steel in 0.75 M H 3 PO 4 using chemical measurements (hydrogen evolution, HE and mass loss, ML) and SEM technique. The effect of temperature on the corrosion of steel in 0.75 M H 3 PO 4 without and with certain concentration of each extract was studied in the temperature range of 303-333 K. Generally, the inhibition efficiency (i.e. surface coverage) increases with extracts concentration and fits the Langmuir adsorption isotherm. The results of HE, ML and SEM showed that ROSE has a capability to protect steel surface in 0.75 M H 3 PO 4 more than ROPE. Good agreement between HE and ML measurements was obtained. Temperature coefficients without and with each extract revealed somewhat chemisorptive and physiosorptive behavior of ROSE and ROPE, respectively. Good correlation between the major effective constituents of each extract and the inhibition mechanism was obtained.

Corrosion behavior of Al 7075, Al 2024, and Al 6061 in the Red Sea water was studied using weight loss (WL) measurements and potentiodynamic polarization (PDP) technique. The corrosion patterns and corrosion products formed on Al alloys were characterized using optical photography (OP), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The results showed that WL data were consistent with bimodal model rather than the power law function and the corrosion rates exhibit a continuous decrease with exposure time. The increasing order of the Red Sea corrosivity on the studied Al alloys can be given as follows: Al 6061 < Al 2024 < Al 7075. The results of temperature effect revealed that an increase in temperature resulted in an increase in both anodic and cathodic current density and a decrease in corrosion potential. Al 7075 was less influenced by temperature than the other alloys. Pitting corrosion was the predominant corrosion pattern detected on all Al alloy surfaces after prolonged immersion in the Red Sea water. The appearance of S peak in EDS spectra of Al 7075 after corrosion gives an indication of the contribution of bacteria in the corrosion process.