Musa paradisiaca extract as a corrosion inhibitor of steel. Role of KI as a synergistic additive

The synergistic effect of KI addition to the system Musa paradisiaca shell (ECMP-KI extract) with ethanol/water on SAE 1010 carbon steel in 1 M HCl solution was studied.Musa paradisiaca (ECMP extract), was obtained by Soxhlet extraction with ethanol/water and characterized by gas chromatography (GC-MS).The following main components were found: C18H36O (octadecane), C16H32O2 (palmitic acid) and C6H6O (phenol).The weight loss (WL) shows a maximum efficiency of 91% with ECMP extract and 93% with ECMP-KI extract.Electrochemical impedance (EIS) and potentiodynamic polarization (PDP) tests were performed at three immersion times: t1: 1 h, t2: 24 h, and t3: 48 h.The obtained efficiencies by EIS with ECMP extract were in the range 75-93% and 80-94% for the system ECMP-KI.The addition of KI showed a slight increase in efficiency, but higher than under WL evaluation.Respecting PDP technique, it was possible to identify ECMP extract as a mixed type inhibitor for the three immersion times, obtaining efficiencies of 76-91% with ECMP extract and 78-93% for ECMP-KI extract.Data obtained from the EIS and PDP electrochemical techniques were fitted to Langmuir, Temkin and Freundlich adsorption isotherm models.It was observed that the Langmuir model showed the best fit for the ECMP extract and for ECMP-KI extract.Only a slight effect of KI as a synergistic additive was observed, possibly because the extract shows high inhibitory efficiency, and the surface was already saturated with the adsorbed natural inhibitor.