Synergistic inhibition effect of Mikania micrantha extract with KI on steel corrosion in H2SO4 solution

Corrosion inhibition of mild steel by Praecitrullus fistulosus (tinda fruit and peel) extracts

Metal corrosion has recently emerged as a growing concern, impacting both local and industrial operations and disrupting conventional production methods. The utilization of green inhibitors to mitigate the metal degradation has garnered extensive attention from researchers and industrial professionals due to their prominent advantages: high efficiency, cost-effectiveness, and eco-friendliness. A novel ecofriendly inhibitor was prepared from Praecitrullus fistulosus (tinda fruit and peel) for mild steel (MS) corrosion in 1 M HCl. The presence of phenol, 3,5-bis (1,1-dimethyl ethyl)-, 9-octadecenoic acid, methyl ester, hexadecanoic acid 15-methyl-, methyl ester, 9, 12-octadecadienoic acid, methyl ester, 9, 12, 15-octadecatrienoic acid, methyl ester, (Z,Z,Z-), ascorbic acid, and phytol were identified as major constituent through LC/MS analysis of tinda extracts. The existence of these compounds was further confirmed through FTIR analysis, which shows the presence of various functional groups, such as -OH, CO, C-O-C, CC, and aromatic rings in the tinda extracts. Electrochemical and gravimetric analyses were used to investigate the inhibitory effect of tinda extracts. Outcomes of Tafel analysis revealed that both tinda extracts significantly reduced the corrosion current as compared to blank and achieved 83.73 % and 87.59 % inhibition efficiencies at 200 mg L-1 of tinda peel extract (TPE) and tinda fruit extract (TFE), respectively. The change in corrosion potential (Ecorr) was within an ±85 mV range compared to that of the uninhibited system, indicating that both tinda extracts demonstrated a mixed-type inhibition behavior. During adsorption studies, the best fit was obtained for the Langmuir adsorption model. The obtained values of standard Gibbs free energy (ΔG°ads) for TPE and TFE lie between -20 and - 40 kJ mol-1 but close to -20 kJ mol-1, which reveals preferential physical adsorption of the extracts on the metal surface. Thermodynamic parameters, including activation energy, enthalpy, and entropy, were computed across the temperature range of 303 to 323 K, suggesting that corrosion occurs spontaneously by the endothermic process. FESEM analysis depicted that inhibited systems exhibited smooth and crack-free surfaces as compared to blank system. AFM images demonstrated that surface roughness was significantly reduced for the inhibited system. In EDX analysis, the weight percentage of Cl was reduced in the presence of tinda extracts as compared to blank, and in XRD analysis, iron chloride (FeCl2) peak did not appear in the presence of inhibitor but it was in the uninhibited system. All surface-related findings signify that tinda extracts are adsorbed on the MS surface and form a protective layer that separates the metal from the corrosive solution.

Synergistic effect of KI on the corrosion inhibition of a poly(diallylammonium chloride)-based cyclocopolymer containing bis-cationic motifs for mild steel corrosion in 20% formic acid

This study entails the syntheses of a homopolymer, poly(diallylammonium chloride) (3), and copolymers (8a-c) containing hydrophilic/hydrophobic pendants and their role in mitigating mild steel in aggressive 20% formic acid, a type of corrosion that is not frequently discussed in the literature. The synthesized homopolymer and copolymers were characterized by FTIR, NMR, viscometry, and TGA. Inhibitor 8b was found to be the most potent, with 81.8% inhibition efficiency (IE) registered via the potentiodynamic polarization method for 100 ppm of inhibitor concentration at 30 °C. Inhibitor 8b, mixed with 2 mmol KI, showed more than 90% IE for a meager 1 ppm inhibitor concentration. For a synergism of 50 ppm inhibitor and 2 mmol KI, the IE reached a high value of 99.1%. The synergism was so good that it helped the inhibitor retain ∼100% of its original IE even after a 24 h weight loss study at 60 °C. The adsorption isotherm study showed that 8b followed the Langmuir adsorption isotherm and adsorbed via chemisorption. A very high value (2.48 × 105 L mol-1) of the equilibrium adsorption constant (Kads) indicated strong adsorption. XPS and SEM surface studies provided evidence of the inhibitor found on the metal surface. Some toxicological parameters, such as LC50, bioaccumulation factor, and developmental toxicity, have been measured computationally. A brief mechanistic insight into how the inhibitors functioned has been offered along with the DFT study.