Kinetics and mechanism of corrosion of mild steel in new types of ionic liquids

It has been established that the corrosion of mild steel in Ethaline and Reline (choline chloride based deep eutectic solvents with the ethylene glycol and urea respectively) occurs with oxygen depolarization. The rate of corrosion is significantly affected by the contact time of solvents with air and temperature. These two factors determine the physicochemical properties and play a decisive role in the rate of diffusion of the depolarizer, and hence the corrosion rate. It is shown that both solvents are hygroscopic (for 160 h of contact with air in Ethaline 15 vol% of water is detected, in Reline about 7 vol%). It is noted that the rate of corrosion of mild steel in Ethaline is noticeably higher than in Reline. However, when operating temperatures of solvents becomes ≈70 ÷ 80 °C the corrosion rates in Ethaline and Reline is very close to each other, which is primarily due to the convergence of the viscosity parameters. SEM studies of the surface of the steel samples showed that in Ethaline and Reline solvents corrosion occurs with the formation of pitting and elements of subsurface corrosion. The mechanism of corrosion is established and the essential role of chloride anions in the formation of intermediate corrosion products is shown.