Corrosion inhibition properties of spinach extract on Q235 steel in a hydrochloric acid medium

The use of environmentally friendly corrosion inhibitors (CIs) is an effective way to overcome the environmental problems caused by existing CIs that contain nitrogen or phosphorus components. Plant extracts, as a type of environmentally friendly CI, have attracted considerable attention. In this work, the corrosion inhibition properties of spinach extract (AESPE) on Q235 steel were studied in a hydrochloric acid medium. First, AESPE was extracted from spinach by an ethanol-acetone reflux method and its main structural and stability parameters in hydrochloric acid medium were determined by infrared spectroscopy (FTIR) and ultraviolet spectroscopy (UV–vis). Second, the corrosion inhibition properties of AESPE on Q235 steel in a 0.5 M hydrochloric acid solution were studied by weight loss (WTL), dynamic potential polarisation (PDP), linear polarisation (LPR), electrochemical impedance spectroscopy (EIS) and quantum chemical calculation methods. The results showed that AESPE could significantly slow the corrosion rate (Vcorr) of Q235 steel in 0.5 M hydrochloric acid medium, which was via a mixed corrosion inhibition mechanism at the cathode and anode. As the AESPE concentration increased, the cathode and anode currents decreased and the active corrosion sites were blocked; thus, the Vcorr decreased and the corrosion inhibition efficiency (E (%)) increased. Under the conditions of 303 K and 300 mg⋅L–1 AESPE, the E (%) of AESPE for Q235 steel was>90%. As the system temperature increased, the E% of AESPE for Q235 steel decreased but the extent of this decrease was small. This work shows that AESPE is an environmentally friendly CI with a good corrosion inhibition effect.