Thienylpicolinamidine derivatives as new dissolution inhibitors for carbon steels in HCl medium: experimental and theoretical studies

Abstract

Abstract One of the main ways that metallic materials lose their useful qualities is through dissolution; hence corrosion management is crucial for protecting the metal. In this paper, new thienylpicolinamidine derivatives, namely; 5-[5-(3,4,5-trimethoxyphenyl)thiophen-2-yl]picolinamidine hydrochloride salt (MA-1517), 5-[5-(4-methoxyphenyl)thiophen-2-yl]picolinamidine hydrochloride salt (MA-1543), and 5-[5-(3-chloro-4-methoxyphenyl)thiophen-2-yl]picolinamidine hydrochloride salt (MA-1516), were utilized as corrosion inhibitors for C-steel in 1.0 mol L−1 HCl. Their corrosion inhibiting impact can be demonstrated by experimental methods as chemical approaches (mass reduction) and electrochemical techniques (electrochemical impedance examination, EIS, and Tafel polarization). These methods gave inhibition efficiencies (IE%) of 97.41 %, 93.84 % and 91 % for MA-1517, MA-1543 and MA-1516, respectively at 323 K and concentration 17 × 10−6 mol. L−1. The rise in IE% with rising inhibitor concentration and temperature illustrate that the adsorption of these studied compounds is chemisorption, declared via the Langmuir isotherm. Thermodynamic and kinetic parameters are computed and discussed. Polarization research exhibits that these thienylpicolinamidines act as mixed type inhibitors. The outer part morphology of C-steel surfaces and the adsorption of these compounds on C-steel outer part can be checked by atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX). The mechanism of inhibition can be backed by quantum chemical examination and Monte Carlo model. A theoretical estimate proves that the use of cationic derivatives of pyridine is good impediments versus corroding of C-steel in HCl medium.