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The corrosion behavior of Al in 1 M HCl solution with and without thiophene derivatives is studied utilizing altered chemical and electrochemical methods. Thiophene derivatives have been prepared and characterized by infrared (IR), proton nuclear magnetic resonance (1H NMR) and mass spectral studies. The corrosion data were obtained using weight reduction and electrochemical techniques. The outcome data revealed that the efficiency rises with improving the dose of thiophene derivatives in aggressive solution, while it lowered with the rise of temperature. The adsorption of the studied thiophene derivatives on the surface of Al follows Langmuir isotherm. The thermodynamic parameters such as adsorption constant Kads and free energy of adsorption ( $$\Delta G_{{{\text{ads}}}}^{^\circ }$$ ) are calculated and discussed. Polarization curves indicated that the thiophene derivatives are mixed-kind inhibitors. The quantum calculation such as EHOMO, ELUMO and ΔE were obtained and related to the experimental data. The biological effect of these derivatives also discussed.

Expired Famotidine was tested as a corrosion protection for α-brass in 1 M HCl using modified methods: weight loss (WL), Tafel polarization (TP), AC impedance spectra (EIS) and electrochemical frequency modulation (EFM). The polarization resistance (Rp) data increased with increasing famotidine dose. The inhibition efficiency (IE) improved with raising famotidine concentration. The maximum IE of 90% has been achieved at 300 ppm. On the other hand, the efficiency lowered with temperature increased. The outcome data obtained revealed that famotidine performed excellently as a corrosion inhibitor for α‑brass in this medium at dissimilar temperatures. The surface of α-brass was tested utilizing scanning electron microscope (SEM), energy dispersion spectroscopy X-ray spectra (EDX), Fourier transform infrared spectroscopy (FT–IR), and atomic force microscopy (AFM analysis).

The influence of corrosion inhibition of some thiazole derivatives, namely: 2-(3,5-dimethyl-4-(p-tolyldiazenyl)-1H-pyrazole-1-yl)thiazol-5(4H)-one, 2-(3,5-dimethyl-4(phenyldiazenyl)-1H-pyrazole-1-yl)thiazol-5(4H)-one, and 2-(4-((4-chlorophenyl)diazenyl)-3,5-dimethyl-1H-pyrazole-1-yl)thiazol-5(4H)-one on Zn in 1.0 M HCl solution was studied by utilizing electrochemical and non-electrochemical tests. The obtained data without and with these derivatives were utilized to measure the protection efficiency (η %) which rises with the rise in the concentration of these derivatives. The phenomenon of physical adsorption was proposed and inhibitors adsorption was established to adapt Langmuir adsorption isotherm. Polarization data clearly indicated that these derivatives behaved as mixed inhibitors.

Novel anionic 4-tert-Octylphenol Ethoxylated Phosphate Dipotassium salt (ethoxylated with 5 moles of ethylene oxide) surfactant was prepared and designated as OP-5-EO-K2PO, was characterized for its structure using spectroscopic measurements, in addition, its surface properties were investigated. The results indicated that OP-5-EO-K2PO exhibits excellent surface activity. Evaluation of the prepared surfactant as a corrosion inhibitor was carried out. The inhibition effect of OP-5-EO-K2PO surfactant, on the corrosion of C-steel in 0.5 M HCl was studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. It was found that the novel anionic surfactant acts as effective inhibitor and its inhibition efficiency was significantly increased with increasing concentration. Polarization curves revealed that the novel prepared anionic surfactant represents mixed-type inhibitors. Adsorption of the investigated surfactant led to a reduction in the double layer capacitance and an increase in the charge transfer resistance.