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The harmful effects of most synthetic corrosion inhibitors on the environment are the motivation for the study of environmentally friendly extracts. The main components of silkworm sand extract (SSE) were studied by infrared spectroscopy (FTIR) and ultraviolet visible spectroscopy (UV-vis). The scale inhibition effect of SSE as scale inhibitor in calcium chloride solution was studied by means of electrical conductivity, static scale inhibition and scanning electron microscopy (SEM). Electrochemical impedance (EIS) and potentiodynamic polarization curve (PDP) were used to study its corrosion inhibition performance in simulated cooling water. The results showed that chlorophyll was the main component of SSE. When the concentration of SSE was more than 30 mg/L, the scale inhibition efficiency of calcium carbonate and calcium sulfate was both more than 90%. SSE could inhibit the supersaturation of calcium carbonate, prolong the nucleation time, and change the crystal shape of calcium scale. SSE had a good corrosion inhibition effect on Q235 steel in salt solution, and its corrosion inhibition mechanism was that SSE formed a protective film on the surface of Q235 steel. SSE could play a dual role of scale inhibition and corrosion inhibition, which was a potential new, environmentally safe corrosion and scale inhibitor for cooling water system.

In order to adapt to the rapid development of green plant extract corrosion inhibitors, spinach extract (SPE) was selected as a corrosion inhibitor for Q235 steel in citric acid (CA) environment. SPE was extracted using a simple ethanol reflux method, and its main components, as well as their stability in CA, were confirmed through Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). The corrosion inhibition performance of SPE on Q235 steel in 0.5 mol/L CA solution was investigated using various methods including weight loss, dynamic potential polarization (PDP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and contact angle measurements. Effects of temperature on the activation parameters (Ea, were studied by calculation. Results showed that chlorophyll was the main component of SPE, which exhibited good stability in a 0.5 mol/L CA solution. Furthermore, SPE significantly reduced the corrosion rate of Q235 steel in the 0.5 mol/L CA medium, acting as a mixed corrosion inhibitor for both cathodic and anodic reactions. With the increase of SPE concentration, both cathodic and anodic currents were reduced, active corrosion sites were blocked, the corrosion rate was decreased, and the corrosion inhibition efficiency was enhanced. The corrosion inhibition efficiency of Q235 steel obtained by weight loss method, PDP, LPR and EIS was more than 80% with 2.134 g/L of SPE concentration at 303 K. With the increase of system temperature, the corrosion inhibition efficiency of SPE on Q235 steel decreased, but the change was smaller. Compared to the blank system, the activation energy (Ea) of the system significantly increased after the addition of SPE. The effective components of SPE adsorped to the surface of Q235 steel in accordance with the Langmuir isotherm, predominantly through physical adsorption, and were characterized as monolayer adsorption. SPE exhibited good corrosion inhibition performance for Q235 steel in a 0.5 mol/L CA solution system, which was a green corrosion inhibitor with good application prospects in the pickling field. It could provide certain guidance for the development of plant extract-based corrosion inhibitors.