Effect of some thiophene derivatives on the electrochemical behavior of AISI 316 austenitic stainless steel in acidic solutions containing chloride ions: II. Effect of temperature and surface studies

The temperature coefficient of 2-thiophene carboxylic hydrazide (TCH) at austenitic stainless steel of type 316 (AISI 316) was determined in an acid medium in the temperature range 20–40 °C. The corrosion rate increases with temperature with an inhibition efficiency that ranges between 89 and 99%. The inhibitor forms a surface layer at the metal substrate. Evidence of the formation of the surface layer was confirmed from surface reflectance infrared spectroscopy measurements. The elemental composition of the surface as indicated from energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy (XPS) proved that the application of the inhibitor increases the concentration of Cr at the surface of the specimen. The adsorption model for this inhibitor follows a Langmuir isotherm and the heat of adsorption indicates a chemical bond formation. The latter was confirmed from the XPS data that indicated the possible formation of a chemical bond between the sulfur atom of the inhibitor molecule and the metal substrate. Scanning electron microscopy was used to study the surface morphology before and after exposure to the inhibitor.