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

Abstract

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. In this work, the surfactant NPE95 was evaluated as a corrosion inhibitor for SAE1020 steel in 3% NaCl aqueous solution, at concentrations of 5, 10 and 25 ppm. Measurements of mass loss and visual and microscopic verification of the corrosion products on the metal surface were performed through photographic records using an Olympus ® SZ61 optical stereoscope and an Olympus ® BX51M microscope. In addition to the previously mentioned techniques, electrochemical impedance spectroscopy (EIS) was obtained using an AUTOLAB PGSTAT 204 potentiostat/galvanostat to better confirm the surfactant's inhibitory potential. The impedance results using an inhibitor in the corrosive medium show two capacitive arcs. The first capacitive arc can be attributed to the adsorbed film on carbon steel. The second, at low frequencies, indicates a charge transfer process in the metal/electrolyte interface, or corrosion process. The Δ Gads values obtained by Langmuir and El-Awady models were respectively -21.987 kJ.mol -1 and -10.061 kJ.mol -1 , indicating spontaneous physisorption processes. Data on total mass loss shows that the lowest mass loss occurred in the sample exposed to the highest surfactant concentration (25 ppm), showing a reduction of approximately 17% in the corrosion rate in the saline medium.