Detailed experimental investigation of the highly active corrosion inhibitive green molecules based on zinc cations/Nepeta Pogonosperma extract and toward the corrosion mitigation of mild steel in the saline solution

Abstract

This work has been focused on the synergistic corrosion retardation performance (CRP) of the Nepeta pogonosperma leaves from the Lamiaceae family, which is locally called Larzeh (LA), and zinc cations (Zn2+) over the mild steel plates (MSPs) in the 3.5 wt% sodium chloride (NaCl) solution (3.5%-SCS). Different concentrations of the LA extract and Zn2+ were dissolved in the saline solutions to prepare the solution systems. The electrochemical evaluation of MSPs submerged in the solution systems was performed using EIS and PP tests. Among various ratios of LA:Zn, the 300:700 ppm LA:Zn solution illustrated the highest CRP (119.3 kΩ cm2) and efficiency (93.7%) after 12 h and was selected as the optimal solution, while the CRP values of the blank, 700:300, and 500:500 ppm LA:Zn were 1.59, 57.1, and 38.4 kΩ cm2, respectively. In the presence of 700:300, 500:500, and 300:700 ppm LA:Zn, Icorr decreased from 3.78 μA cm−2 for the blank solution to 0.372, 0.345, and 0.236 μA cm−2, respectively. WCA results proved that a more hydrophobic layer (≈55°) was formed on the MSP with 300:700 ppm LA:Zn compared to those with 700:300 (≈33°) and 500:500 (≈24°) ppm LA:Zn. The surface characterization of MSPs submerged in 300:700 ppm LA:Zn solution was carried out using FT-IR, Raman, and GIXRD analyses. Surface characterization results proved the construction of a thicker multilayer zinc-centered organic inhibitive layer by the 300:700 ppm LA:Zn extract over the MSP surface compared to other MSPs with maximum amounts of O (7.85 wt%), C (6.55 wt%), N (1.78 wt%), and Zn (20.57 wt%) elements.