Influence of two novel corrosion inhibitors of bis(chromeno[4,3-c]pyrazol-4-oxo-2-yl)phosphineoxide (CPO) and bis(4-formyl-3-phenyl-1H-pyrazol-1-yl)phosphineoxide (FPO) on the localized corrosion protection of 304 stainless steel (304 SS) in a 1.0 M HCl solution was investigated at different concentrations (10-13-10-5 M) and at different temperatures (298-343 K). Weight loss and electrochemical measurements indicated that the pyrazole derivatives are efficient inhibitors for corrosion of 304 SS, and the inhibition efficiency was increased with inhibitor concentrations up to 73.18 and 98.50 % for CPO and FPO, respectively. Langmuir adsorption isotherm was found to be the more fitted model for the adsorption process description with mixed adsorption mechanisms. UV-visible and XRD measurements showed the formation of a protective film formed by corrosion inhibitors. The scanning electron microscope (SEM) images, energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and static contact angle measurement corroborated the protection provided by CPO and FPO inhibitors on the surface of 304 SS immersed in a 1.0 M HCl solution. FPO exhibits antibacterial activity, and CPO has antifungal activity. The relationships between the corrosion protection performance of the pyrazole derivatives, their structural properties, and the adsorption type were determined by density functional theory (DFT), natural bond orbital (NBO), and molecular dynamics (MD), which confirmed that FPO has a higher corrosion protection efficiency than CPO. The theoretical parameters were in good agreement with the experimental results.
