Green corrosion inhibitor for mild steel extracted from soybean leaves

Abstract

The use of green-soluble inhibitors in the corrosive medium as alternatives to traditionalinhibitors has increased due to the toxicity of the commonly used substances. These novelsubstances are selected owing to their low cost, ease of application as well as maintenance,and low environmental risk. This work aims to evaluate ethanolic-water extracts from postharvestsoybean (Glycine max) by-products as corrosion inhibitors for mild steel in anaggressive medium of sodium chloride. Soybean extracts were obtained by percolation at acontrolled flow rate and temperature. To evaluate the anticorrosive efficiency, polarizationcurves of AISI 1030 steel were carried out at 1 and 7 days of immersion with different concentrationsof the soybean extract. Weight loss measurements were carried out alongsidepotentiodynamic measurements. The steel samples were analyzed by scanning electronmicroscopy. The soybean extracts obtained reduced the corrosion rate of the steel, showingan efficiency of 30% at day 1. The inhibition efficiency increased up to 80% after 7 days ofincubation with 2000 ppm of the extract. A Langmuir adsorption model was fitted to weightloss measurements. Kads and DGads obtained from the model were characteristic of physisorption.The corrosion potential was shifted toward more negative values, classifying theethanolic-water soybean extract as a cathodic inhibitor. The steel surface for the samplesincubated with 2000 ppm of soybean extract was greatly improved showing significantlyfewer agglomeration of corrosion products. Soybean leaves are a promising by-product usefulto produce ethanolic-water extracts to be used as green corrosion inhibitors.