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

Abstract

Purpose

Thioureas (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/approach

The 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.

Findings

The 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/value

The 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.

Citation

Mahgoub, F.M. (2008), "Effect of protonation on the inhibition efficiency of thiourea and its derivatives as corrosion inhibitors", Anti-Corrosion Methods and Materials, Vol. 55 No. 6, pp. 324-328. https://doi.org/10.1108/00035590810913114