coatings Article Anti-Corrosion Behavior of Olmesartan for Soft-Cast Steel in 1 mol dm -3 HCl B. M. Praveen 1 , A. Alhadhrami 2 , B. M. Prasanna 3, * , Narayana Hebbar 4 and Radhakrishna Prabhu 5   Citation: Praveen, B.M.; Alhadhrami, A.; Prasanna, B.M.; Hebbar, N.; Prabhu, R. Anti-Corrosion Behavior of Olmesartan for Soft-Cast Steel in 1 mol dm −3 HCl. Coatings 2021, 11, 965. https://doi.org/10.3390/ coatings11080965 Academic Editor: Tao-Hsing Chen Received: 10 July 2021 Accepted: 10 August 2021 Published: 13 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Chemistry, College of Engineering & Technology, Srinivas University, Mukka, Mangalore 574146, India; researchdirector@srinivasuniversity.edu.in 2 Department of Chemistry, College of Science, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia; a.babtin@tu.edu.sa 3 Department of Chemistry, Jain Institute Technology, Davanagere 577003, India 4 Department of Chemistry, Sri Darmasthala Manjunatheshwara College (Autonomous), Ujire 574240, India; dr.nahebbar@sdmcujire.in 5 School of Engineering, Robert Gordon University, Aberdeen AB10 1FR, UK; r.prabhu@rgu.ac.uk * Correspondence: drbmprasanna@jitd.in Abstract: This study discusses the effects of temperature on corrosion inhibition for soft-cast steel by the pharmaceutically active drug olmesartan in 1 mol dm −3 HCl. The sufficient number of electron-rich elements and non-bonding π electrons in its structure favored a good capability for coating onto the electron-deficient steel surfaces. Theoretical and electrochemical measurements were carried out at the temperature region of 303 K to 333 K. Therefore, the experiment suggests that the inhibition efficiency of olmesartan increases with its increasing concentrations due to the adsorption. Additionally, even at a higher temperature of 333 K, the inhibitor molecules attain their stability towards corrosion resistance of steel surfaces. The adsorption of inhibitors on steel surfaces is spontaneously found to include the mixture of physisorption and chemisorption, and it obeys Temkin’s adsorption isotherm model. Theoretical and computational considerations were made using quantum chemical parameters and molecular dynamics simulations, which confirmed that the olmesartan has a suitable corrosion inhibitive capability intended for soft-cast steel in 1 mol dm −3 HCl. Additionally, scanning electron microscopic measurement was used to obtain a visual idea of the inhibitive action of the inhibitor attained by forming an adsorbed protective layer onto the steel surfaces. The minute concentration of olmesartan of about 10–50 ppm shows high inhibition efficiency of ~80%, even at elevated temperatures. Keywords: soft-cast steel; electrochemical; SEM; adsorption; molecular dynamic simulation 1. Introduction Soft cast steel is one of the most important iron alloys with a lower carbon content (i.e., carbon content less than 0.15%). These have industrial, automobile, and construction appli- cations because of their superior thermal and mechanical stability. Hence, soft-cast steel is cast off for many practices viz., acid pickling, descaling, oil well acidifying, petroleum refineries, etc. [1,2]. Under these conditions, steel surface exposure with aggressive media leads to corrosion. Hence, various methods are to be adopted, such as anodization, cathodic protection, coatings, and corrosion inhibitors, for metal protection by corrosion. Among those different practices of protecting the metal, the use of corrosion inhibitors is the most appropriate, experimentally acceptable, and cost-effective technique [3]. Corrosion inhibitors are organic heterocyclic compounds that contain electron-rich N, S, O, and non-bonding π electrons present in the heterocyclic ring system of its structure. Through these, the inhibitor molecules are coated onto the electron-deficient metal sur- faces [4]. Similarly, various physio-chemical properties of an inhibitor play an important role in determining adsorption capability onto steel surfaces [5]. Coatings 2021, 11, 965. https://doi.org/10.3390/coatings11080965 https://www.mdpi.com/journal/coatings