The corrosion inhibition properties of the acidic extract of Eucalyptus globulus (EG) was investigated for mild steel (MS) using the weight loss method and open circuit potential (OCP) measurement. Corrosion inhibition of MS in 0.1M HCl was studied in the absence and presence of various concentrations of the acidic extract of EG barks. The results showed an increase in corrosion inhibition with increasing concentration of the extract. The inhibition efficiency of 100% EG extract was approximately 98.0% after 24 hours immersion in the acidic solution. FTIR spectrum showed the presence of compounds containing oxygen and nitrogen functional groups responsible for forming barrier layers onto MS surface. Open circuit potential (OCP) measurements showed that the EG extract acts as a mixed type inhibitor.

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The effect of cations on the corrosion of galvanized steel (GS) is scarcely reported. In this study, a wet–dry cyclic test was conducted to study NH4 +, Na+, and Mg2+ cation effect on the corrosion behavior of GS available in Nepal. Fourteen wet–dry cycles (18 h wet and 6 h dry) were performed by exposing samples at 298 K with a relative humidity of 90% in a wet cycle and 50% in a dry cycle for 14 days. The cations strongly affect the corrosion rate of the GS sample estimated by weight loss and potentiodynamic polarization. The potentiodynamic polarization curves showed the inhibition of cathodic and anodic reactions by Mg2+ ion, while the NH4 + ion only changed the cathodic reaction. Mg2+ ion was found to shift the corrosion potential to noble values compared with NH4 + and Na+ ions. A compact and thin corrosion products layer was developed in Mg2+ salt solution in contrast to a thick and porous corrosion products layer in NH4 + and Na+ salt solutions. Red rust due to corrosion of underlying steel appeared in the presence of NH4 + and Na+ salt solutions. Finally, the weight loss data revealed that the corrosivity of cations for GS decreased in the order Na+ > NH4 + > Mg2+.

Elettaria cardamom (Alaichi) is a spice available in Nepal, from the bark of which alkaloid can be extracted to use as a corrosion inhibitor. The corrosion inhibition of methanolic extract of Elettaria cardamom (EC) for mild steel (MS) in 1M H2SO4 was studied using the weight loss method. The effect of time of immersion and concentration of EC extract on corrosion inhibition was investigated. The result showed that the corrosion inhibition efficiency increased with an increase in the time of immersion and concentration of the EC extract. The maximum inhibition efficiency of 1000 ppm EC extract was 93.36% for 3 hours of immersion in 1M H2SO4 solution. FTIR spectroscopic analysis showed the presence of functional groups containing oxygen and nitrogen in the extract, which is responsible for the adsorption of the extract onto mild steel and reduces the corrosion rate.