Eupatorium adenophorum Spreng leaves extract/potassium iodide as a highly sustainable inhibitor for the corrosion protection of steel in citric acid solution

Abstract

Plants extract inhibitor has the standout merits of low-cost, eco-friendly and rich natural raw resources. The synergism between Eupatorium adenophorum Spreng leaves extract (EASLE) and KI for the corrosion of cold rolled steel (CRS) in citric acid (H3C6H5O7) solution was tested in detail by weight loss and electrochemical techniques. The micro-morphology of CRS surface was fully characterized by both scanning electron microscope (SEM) and atomic force microscope (AFM). Fourier transform infrared spectrometer (FTIR) and high performance liquid chromatography (HPLC) were employed to deeply analyze the main bio-active components in EASLE. The results show that either EASLE or KI can moderately inhibits the corrosion of CRS, and their maximum inhibition efficiency values are below 75%. As EASLE is combined with KI, their mixture has a better inhibition of over 90%. There is a synergism between EASLE and KI, and the corresponding synergism parameters are all higher than unity with a highest value of 3.5 for 400 mg L-1 EASLE/ 100 mg L-1 KI at 60 °C. The adsorption of EASLE, KI or EASLE/KI mixture follows Langmuir isotherm, and the adsorption is strengthened for the synergistic mixture. EASLE mainly retards the anodic reaction, while EASLE/KI mixture drastically inhibits both cathodic and anodic reactions simultaneously with a low corrosion current densities of 17.8 µA cm−2. Nyquist graph appears a depressed capacitive loop at high frequencies followed by an inductive loop at low frequencies. EASLE/KI mixture has larger charge transfer resistance (Rt) comparing with either EASLE or KI. Rt values for 500 mg L-1 EASLE, 100 mg L-1 KI and 500 mg L-1 EASLE/100 mg L-1 KI mixture are 464.9, 382.9 and 1068 Ω cm2, respectively. SEM and AFM micro-images clearly confirm that the corrosion extent as well as surface roughness of CRS surface were sharply dropped after adding EASLE/KI mixture. The main bio-active components in EASLE are phenylpropanoids like chlorogenic acid, caffeic acid and ferulic acid.