Evaluation of 2,5,7-Triphenyl-1,2,4-triazolo[1,5-a] pyrimidine as an Efficient Corrosion Inhibitor for Stainless Steel in 1.0 M Hydrochloric Acid

Abstract

Corrosion inhibition of 316 L stainless steel in 1.0 M hydrochloric acid by 2,5,7-triphenyl-1,2,4-triazolo[1,5-a]pyrimidine (TPTP) was evaluated using weight-loss measurements, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarisation (PDP). The effect of inhibitor concentration was examined over the reported test range, and adsorption behaviour and thermodynamic parameters were assessed to elucidate the inhibition process. Weight-loss measurements showed a progressive decrease in corrosion rate as TPTP concentration increased, with inhibition efficiency reaching 94.0% at 500 ppm and 303 K. Surface coverage increased with concentration, consistent with progressively greater adsorption of TPTP molecules on the stainless-steel surface. The tabulated EIS results showed that charge-transfer resistance increased from 32 to 535 Ω cm², while double-layer capacitance decreased from 162 to 33 μF cm⁻² between the uninhibited solution and 500 ppm TPTP. The tabulated PDP results showed a reduction in corrosion current density from 126.4 to 7.6 μA cm⁻², accompanied by a 19 mV shift in corrosion potential, supporting mixed-type inhibition. The adsorption data were described by the Langmuir adsorption isotherm, while the reported Gibbs free-energy values indicated spontaneous adsorption with contributions from physical and chemical interactions. Overall, the reported gravimetric and electrochemical data indicate that TPTP reduces stainless-steel corrosion through adsorption and formation of a protective interfacial layer under the investigated conditions.