International audienceEssential oil of aerial parts of Salvia aucheri Boiss. var. mesatlantica was obtained by hydrodistillation and analyzed by GC and GC/MS. The oil was predominated by camphor (49.59%). The inhibitory effect of this essential oil was estimated on the corrosion of steel in 0.5M H2SO4 using electrochemical polarisation and weight loss measurements. The corrosion rate of steel is decreased in the presence of natural oil. The inhibition efficiency was found to increase with oil content to attain 86.12% at 2g/L. Polarisation curves revealed that this oil of Salvia aucheri mesatlantica act as mixed type inhibitor with a strong predominance of anodic character. The temperature effect on the corrosion behaviour of steel in 0.5M H2SO4 without and with the inhibitor at 2g/L was studied in the temperature range from 303and 343 K, the associated activation energy have been determined. The adsorption of oil on the steel surface was found to obey Langmuir's adsorption isotherm

The corrosion inhibition properties of three spiro-isoxazoline derivatives, namely 3,4-diphenyl-1,7-dioxa-2-azaspiro[4.4]non-2-en-6-one (DDA), 3-phenyl-4-(p-tolyl)-1,7-dioxa-2-azaspiro[4.4]non-2-en-6-one (PDA) and 4-(4-methoxyphenyl)-3-phenyl-1,7-dioxa-2-azaspiro[4.4]non-2-en-6-one (MDA) on carbon steel in 1.0 mol/L HCl acid medium were experimentally and computationally investigated. The experimental results showed that the inhibitory efficiency reached remarkable values of 76.26, 80.31, and 82.91%, respectively, for DDA, PDA and MDA at a maximum concentration of 10⁻³ mol/L. The potentiodynamic polarization curves (PPCs) showed that investigated compounds had a mixed type character, controlling both anodic and cathodic corrosion reactions. In addition, electrochemical impedance spectroscopy (EIS) indicated that the addition of increasing concentration of tested compounds to HCl solutions led to a significant increase in the polarization resistance of the carbon steel, which was accompanied with a simultaneous decrease in the double layer capacitance. On the other hand, the morphological study of the metal surface by scanning electron microscope (SEM) and energy dispersive X-ray (EDX) confirmed the effective protection of the carbon steel by the inhibitors against corrosion through the formation of a protective film on its surface. The adsorption characteristics of investigated compounds on carbon steel were assessed at microscopic level using Density Functional Based Tight Binding (DFTB) simulation, which revealed the formation of covalent bonds between inhibitors’ atoms and Fe atoms. Furthermore, additional insights into the compounds’ reactivity and adsorption configurations on steel surface were obtained from global reactivity descriptors and Monte Carlo simulation. The present work’s outcomes are interesting for further design and performance evaluation of effective organic corrosion inhibitors for acid environments.