N¹,N¹-diallyl-N⁶,N⁶,N⁶-tripropylhexane-1,6-diaminium chloride (NDTHDC) and its polymer poly(N¹,N¹-diallyl-N⁶,N⁶,N⁶-tripropylhexane-1,6-diaminium chloride) (poly-NDTHDC) were synthesized and tested against API X60 carbon steel corrosion in 15 wt % HCl solution. Weight loss, electrochemical, and surface analysis techniques were used. Results show that poly-NDTHDC is better than NDTHDC. Moreover, 1000 mg/L NDTHDC protected the studied surface by 79.1% at 25 °C, while 100 mg/L poly-NDTHDC afforded 86.1% protection. Inhibition efficiency increases with temperature (up to 60 °C) but depreciates thereafter. NDTHDC and poly-NDTHDC perform better under the hydrodynamic condition than the static condition. TGA and FTIR results reveal that poly-NDTHDC is chemically and thermally stable.

The corrosion inhibition effect of red apple (Malus domestica) fruit extract for mild steel in hydrochloric acid was investigated by gravimetric and electrochemical methods at 30–60°C. Inhibition efficiency increased with the increase in concentration and temperature. Polarization curves indicate that the extract functions as mixed-type inhibitor. The adsorption of the extract onto mild steel surface followed Langmuir adsorption isotherm model. Chemisorption mechanism is proposed based on the trend of inhibition efficiency with temperature. Quantum chemical calculations and molecular dynamics simulations have been used to provide insights into the mechanism of interaction of the major extract components with mild steel.