Protection of mild steel in h2so4 solution with 3-((3-(2-hydroxyphenyl)-5-thioxo-1,2,4-triazol-4-yl)imino)indolin-2-one

Abstract

The use of a natural or synthesized corrosion inhibitor is an important method for the protection of surfaces of metals and alloys from corrosion. The inhibitor molecules adsorbed on a metal surface block the contact between the corrosive solution and the metal surface. In this work, a new indoline derivative, namely, 3-((3-(2-hydroxyphenyl)-5-thioxo-1,2,4-triazol-4-yl)imino)-indolin-2-one (HTTI), was synthesized by condensation of equimolar quantities of 2,3-dioxoindoline and 4-amino-5-thioxo-3-(2-hydroxyphenyl)-1,2,4-triazole in methanol. The molecular structure of HTTI was characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopies along with micro-elemental analysis that was utilized to determine the elemental concentrations of carbon, hydrogen and nitrogen atoms in the synthesized compound. The corrosion inhibition efficiency of HTTI was investigated for mild steel in 0.5 M sulfuric acid solution by using the weight loss method to determine the concentration, time and temperature effects. The new synthesized inhibitor shows a high inhibition activity of 93.4% at 500 ppm. The results indicate that HTTI slows down the corrosion reaction in the corrosive environment and the inhibitor efficiency increases with increasing inhibitor concentration and decreases with an increase in time and temperature. Moreover, the inhibition efficiency increases with immersion time till 10 hours and decreases after 24 hours. The adsorption of the new synthesized corrosion inhibitor on mild steel surface obeys the Langmuir adsorption isotherm.