Experimental/computational assessments of steel in HCl medium containing aminocarbonitrile-incorporated polyhydroxy-functionalized pyrido[2,3-d]pyrimidine as a green corrosion inhibitor

This research deals with insights into the inhibitory effects of a new synthetic bio/green corrosion inhibitor based on aminocarbonitrile-incorporated polyhydroxy-functionalized pyrido[2,3-d]pyrimidine derivative (PPAC) on steel substrate exposed to 1 M HCl cleaning electrolyte. The electrochemical examinations resulted in mixed corrosion inhibition activity having a paramount cathodic hindrance with ca. 91% reduction in corrosion current density (icorr) and also 92.5% inhibition efficiency (η%) achievement after 6 h steel exposing to 0.5 mM PPAC/HCl solution. A new-route, in-situ multi-step image processing method was successfully created to extract the adsorbed hydrogen bubbles on the electrolyte/steel interface by developing a mathematical exponentiated model. The model based on image-based shape descriptors precisely reproduced the electrochemical data with errors of less than 13%. A low corrosion rate upon PPAC adsorption led to a considerable diminution of bubbles number, T, while their surface area, SA, increased remarkably. The variations of experimental icorr data against (T)-2.09(SA)0.65 and also |Z|10mHz values against (T)-0.3(SA)-0.24 showed the best correlative results (R2 ~ 0.99). Theoretical atomic/electronic simulations relying on DFT, classical MD, and MC proved PPAC planar orientation via the donor-acceptor adsorptive mechanism of its functional groups with the greatest protonation power of CN and C=O in the pyrimidine-fused aminocarbonitrile moiety for strong spontaneous physical/chemical bondings with Fe.