Corrosion inhibition of carbon steel in hydrochloric acid solution by self-formation of a Malpighia glabra leaf extract-based organic film

A forming organic film applied onto a metallic surface to resist electrochemical corrosion is demonstrated as a potentially new low-cost, low toxicity solution. In this work, the inhibitory effect of Malpighia glabra leaf extract (MGLE) on the corrosion of mild steel in 0.01, 0.10, and 1.00 M hydrochloric acid (HCl) media and the changes in its inhibitory efficiency were investigated. The analyses indicate that the inhibition performance increases up to 94.87% with an increase in MGLE concentration in the range of 0-2500 ppm when MGLE is added to 0.1 M HCl solution. However, it slightly decreased with MGLE concentrations greater than 3000 ppm owing to a reduction in the mobility and activity of the MGLE species under the investigated conditions. Notably, the in-hibition occurs at a higher level (97.07%) when the steel is immersed in a more aggressive solution (1 M HCl). The results also show good inhibition effectiveness as a mixed corrosion inhibitor with more anodic predomi-nation in a less acidic environment (0.01 M HCl). Furthermore, the surface analysis results show that the un-inhibited steel surface is severely corroded, while less corrosion is observed on the inhibited surfaces covered by a protective film. The corrosion mitigation of carbon steel could be attributed to the bonding of the MGLE species on the surface to form a protective layer with densely packed organic compounds involving the MGLE species. Therefore, this work could deliver a new inhibitor with high resistance to steel corrosion in an acidic medium through controlled corrosive electrolytes.

Automated summary

This study demonstrates the potential of an organic film applied on a metallic surface as a low-cost, low-toxicity solution for electrochemical corrosion resistance. The inhibitory effect of Malpighia glabra leaf extract (MGLE) on mild steel corrosion in hydrochloric acid (HCl) media was investigated. The results showed that MGLE had a good inhibitory effect on steel corrosion, especially in more aggressive solutions. Surface analysis revealed the formation of a protective film on the inhibited steel surfaces, reducing corrosion.