Evaluation of surfactant nonylphenol polyethoxylated 9.5 as a corrosion inhibitor of SAE1020 steel in saline medium

Due to its relatively low cost and good chemical stability, nonylphenol polyethoxylated with an ethoxylation degree of 9.5 (NPE95) is produced on a large scale and widely used in the industry as an emulsifier, detergent, and solubilizer. Despite its extensive applicability, there is a gap in the literature regarding its corrosion inhibition properties. This study evaluated the surfactant NPE95 as a corrosion inhibitor for SAE1020 steel in 3% NaCl aqueous solution at concentrations of 5 ppm, 10 ppm, and 25 ppm. Measurements of mass loss and visual and microscopic verification of the corrosion products on the metal surface were performed using photographic records obtained with an Olympus® SZ61 optical stereoscope and an Olympus® BX51M microscope. In addition to these techniques, electrochemical impedance spectroscopy (EIS) was conducted using an AUTOLAB PGSTAT 204 potentiostat/galvanostat to better confirm the surfactant's inhibitory potential. The impedance results with the inhibitor in the corrosive medium show two capacitive arcs. The first capacitive arc is attributed to the adsorbed film on carbon steel, while the second, at low frequencies, indicates a charge transfer process at the metal/electrolyte interface, or corrosion process. The ΔGads values obtained from the Langmuir and El-Awady models were –21.987 kJ.mol-1 and –10.061 kJ.mol-1, respectively, indicating spontaneous physisorption processes. Data on total mass loss showed that the lowest mass loss occurred in the sample exposed to the highest surfactant concentration (25 ppm), demonstrating a reduction of approximately 17% in the corrosion rate in the saline medium.