Enhancing pitting corrosion inhibition of AISI 304 stainless steel using a green frankincense-modified ferric chloride solution

To inhibit pitting corrosion of AISI 304 stainless steel (SS), the effect of different percentages of frankincense addition to a 0.5 M ferric chloride solution was explored in this work for the first time. The samples were investigated for pitting corrosion susceptibility via electrochemical noise (EN) tests, where the current and potential noises were recorded for 10000 seconds, and potentiodynamic polarization. The frequency domain of EN data was analyzed using power spectral density (PSD). Frankincense addition to the ferric chloride solution effectively reduced the pitting corrosion of AISI 304 SS. The pitting inhibition was concluded from the high fluctuations in current noises over the test period, its decreasing amplitude, the greater positive potential, the lower current values, and the lower spectral noise and noise resistances with increasing frankincense additions. Optical microscope images supported pitting inhibition with frankincense addition, where pits decreased in number per mm² and size. A significant decrease in the pit size and pits mm⁻² was observed with the 10 wt.% frankincense addition. It was attributed to the adsorption of the inhibitor on the stainless steel surface, inhibiting the adsorption of chloride ions. Additionally, frankincense addition reduced the corrosion current and increased the corrosion potential positively.