Aldehyde–Aminotriazole Condensation Products as Novel Corrosion Inhibitors for Mild Steel in Hydrochloric Acid

The significance of this study arises from the urgent need to develop new corrosion inhibitors for the oil and gas industry. These inhibitors should be synthesized from readily available raw materials and be capable of providing effective protection for steel structures against corrosion when exposed to technological hydrochloric acid solutions over a wide temperature range (20-100 °C). The search for such environmentally acceptable and cost-efficient inhibitors is crucial for improving the durability and operational safety of oilfield equipment under aggressive acidic conditions. A new high-temperature corrosion inhibitor for steel in hydrochloric acid solutions has therefore been developed. The inhibitor, designated CATA, is the product of chemical condensation between cinnamaldehyde and 3-amino-1,2,4-triazole. Its protective action is based on the formation of an organic layer up to 12 nm thick, strongly bound to the steel surface. The results suggest with high probability that this protective film consists of polymeric products formed through chemical transformation of CATA on the corroding metal surface. It was shown that the addition of CATA significantly suppresses the electrode processes of steel, affecting both cathodic and anodic partial reactions as well as the kinetics of hydrogen permeation. Adsorption of CATA on steel is satisfactorily described by the Temkin isotherm. The free energy of adsorption (-Δ<i>G_ads</i>) was determined to be 54 kJ mol^-1, which is characteristic of chemisorption. This unique inhibition mechanism enables effective corrosion protection of steel in HCl solutions over a wide temperature range (20-100 °C). Under the most aggressive experimental conditions (2 M HCl, 100 °C), the addition of 10 mM CATA achieved an inhibition efficiency of 99.6%, with a corrosion rate of 3.3 g m^-2 h^-1, which represents an outstanding result. Furthermore, for spring steels, even in hot HCl solutions (20-60 °C), CATA strongly suppresses hydrogen uptake and allows complete preservation of their ductility.