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Statistical modeling of the corrosion inhibition process by twenty-one pyridazine derivatives for mild steel in acidic medium was investigated by the quantitative structure property relationship (QSPR) approach. This modeling was established by the correlation between the corrosion inhibition efficiency ( IE % ) and a number of the electronic and structural properties of these inhibitors such as: the E HOMO (highest occupied molecular orbital energy), the E LUMO (lowest unoccupied molecular orbital energy), the energy gap ( E L-H ), the dipole moment ( μ ), the hardness ( η ), the softness ( σ ), the absolute electronegativity (χ), the ionization potential ( IP ), the electron affinity ( EA ), the fraction of electrons transferred ( ΔN ), the electrophilicity index ω the molecular volume ( V m ), the logarithm of the partition coefficient ( Log P ), and the molecular mass ( M ), in addition to the inhibitor concentration ( C i ). The structure electronic properties was calculated by the use of the density functional theory method (DFT), at B3LYP/6-31G (d, p) level of theory and the analysis of dimensionality and redundancy as well as the test of collinearity between descriptors are carried out using principal component analysis (PCA). Whereas, the correlation between EI % and molecular structure is performed through the development of tree mathematical models, based-QSPR approaches: the partial least squares regression (PLS), the principal component regression (PCR) and the artificial neural networks (ANN). Indeed, the statistical quantitative results revealed that PCR and ANN were the most relevant and predictive models in comparison with the PLS model. This pertinence was demonstrated by using leave one-out cross-validation as an efficient method for testing the internal stability and predictive capability of said models with a high cross-validated determination coefficient R 2 cv = 0.92 and predicted determination coefficient R 2 pred = 0.92 and R 2 pred = 0.90 for PCR and ANN respectively; in addition to an extrapolation test set as an external validation with a significant external coefficient of determination: R 2 test = 0.94 and R 2 test = 0.92 , for the two correspondingly models.

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The Mentha Piperita essential oil (MPEO) rich in anthraquinone,1-(p-fluorophen) as major compound (42.8 %) has been investigated as corrosion inhibitor for mild steel in 1 M HCl. weight loss, polarization curves (Tafel, Stern & Geary as well as Stern methods) and electrochemical impedance spectroscopy measurements were used to evaluate the inhibition performance of MPEO. The results obtained from different techniques were in best accord. The inhibiting efficiency, reaching circa 87 % at 0.7 g L-1 of MPEO, was found to increase with rise of inhibitor concentration, whereas the increase of temperature was in favour of its slow decrease. The adsorption data fitted well to Langmuir isotherm model and involved both physisorption. Scanning electron microscopic results testified the formation of a protective film onto the mild steel in the presence of MPEO.

Thymus Sahraouian essential oil (TSEO), as a new corrosion eco-friendly inhibitor, has been used to protect mild steel in 1 M HCl. Weight loss, three potentiodynamic polarization methods (Tafel, Stern and Stern-Geary), and electrochemical impedance spectroscopy measurements were undertaken to evaluate corrosion inhibition by TSEO. TSEO acted as an efficient corrosion inhibitor for mild steel in 1 M HCl, and its inhibition efficiency increased with a concentration of 77.82 % at 2 g L -1 . The polarization curves revealed that TSEO acted as a mixed type inhibitor, with predominant anodic action. The EIS studies were fitted to a suitable equivalent circuit model, at 293 K, only reflecting a one-time constant characteristic of a charge transfer process. Besides, the higher is the temperature the lowest is the inhibiting efficiency. The kinetic parameters were in favour of an electrostatic character of TSEO components adsorption onto the mild steel surface, and adsorption followed the Langmuir isotherm model. Micrographic scanning electron microscopy and energy dispersive X-ray spectroscopy analyses confirmed the formation of a protective adsorbed film upon the mild steel surface.