Effect of protonation on the inhibition efficiency of thiourea and its derivatives as corrosion inhibitors

Abstract

PurposeThioureas (TUs) have been studied extensively, but their inhibition mechanism is not fully understood. Experimental results and theoretical calculations were used to investigate the effect of TU and its derivatives on the corrosion reaction of mild steel in 1 M H2SO4 at 40°C. An attempt was made to correlate some molecular parameters of these compounds with their corrosion inhibitor efficiency.Design/methodology/approachThe influence of the additives' N‐substituted derivatives of TU such as methylthiourea (MTU), phenylthiourea (PHTU), thiosemicarbazide (TSC) and thiocarbazide (TC) on the dissolution process of the specimen in sulphuric acid was monitored chemically by hydrogen evolution measurements.FindingsThe results show that inhibitor efficiency increased with increase in inhibitor concentration. The protonation process appeared to be the effective parameter with lowering of the inhibition efficiency. Alkyl N‐substituted TU with the least protonation and with the maximum adsorption was a better inhibitor than TU and aryl N‐substituted TU. The thiocarbazide molecule showed less efficiency with the highest protonation due to high charge density on the sulphur atom as well as lengthening and weakening of the C‐ S bond than the thiosemicarbazide.Originality/valueThe paper provides useful information relative to the corrosion inhibition efficiency of N‐substituted TU. It presents the experimental results and theoretical calculations that were used to investigate the effect of derivatives TU on their inhibition efficiency.

Corrosion Inhibition Effects of Some New Synthesized N-Aroyl-N\ -Aryl thiourea Derivatives for Carbon Steel in Sulfuric Acid Media

“…Furthermore, the compounds containing both N and S can provide excellent inhibition, compared with compounds containing only N or S [10]. There are many investigations about thiourea and various thiourea derivatives as good inhibitors of the corrosion of iron or steel in HCl [11][12][13], H2SO4 [14][15][16], HNO3 [17], HClO4 [18], H3PO4 [19]. Such compounds can adsorb on the surface of the metal, blocking the active centers on the surface and thus reduces the corrosion rate [20].…”