Avaliação de aminoácidos como inibidores de corrosão para aço carbono AISI 1018 submetidos a meio contendo NaCl com e sem saturação de CO2

Abstract

Corrosion represents one of the most significant challenges faced by industries, leading to considerable financial losses. Various compounds are used to prevent, reduce, or even halt corrosion in different materials affected by these effects. Thus, sectors such as oil and gas employ chemical compounds known as corrosion inhibitors. However, some substances, despite having inhibitory effects, may pose environmental and human health risks. In this context, natural, non-aggressive, and ecologically sustainable compounds, such as amino acids, aqueous extracts, and ionic liquids, are being investigated as alternatives to conventional corrosion inhibitors. Amino acids have been demonstrated to be corrosion inhibitors for a variety of materials, such as carbon steel, stainless steel, and metal alloys, in different corrosive environments. This study proposes an analysis of five amino acids — histidine, methionine, cysteine, serine, and phenylalanine — as potential corrosion inhibitors. These amino acids were investigated with varying inhibitor concentrations (250, 500, and 1000 ppm), medium temperature (25, 40, and 60°C), and the use of a surfactant to evaluate the synergism, based on whether or not inhibition efficiency increased, and the evaluation of the medium with carbon dioxide (CO2) saturation. To assess the effectiveness of these compounds as corrosion inhibitors, gravimetric and electrochemical techniques, such as potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS), were employed. UV-VIS measurements were performed to analyze the compounds in solution. A molecular modeling study complemented the analysis of the amino acids. The characterization of the amino acids was carried out using techniques such as Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). For surface analysis, images were collected using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results indicated an efficiency order of the amino acids: histidine > cysteine > phenylalanine > serine > methionine, which was confirmed by theoretical calculations. In the tests performed, the amino acids histidine, cysteine, and phenylalanine respectively showed efficiencies of 91%, 90%, and 88%, standing out as the most promising results. The amino acids showed the best inhibition response at a temperature of 25°C to 3.5 wt% NaCl.