Inhibition Properties of Silkworm Sand Extract as an Eco-friendly Corrosion Inhibitor
In order to expand the scope of green corrosion inhibitors,the corrosion inhibition performance of silkworm sand extract (SSE) on Q235 steel in hydrochloric acid medium was studied. First,SSE was extracted from silkworm sand by ethanol-acetone reflux method. The main structure and stability of SSE in hydrochloric acid medium were determined by infrared spectroscopy (FTIR) and ultraviolet spectroscopy (UV-vis). Secondly,the corrosion inhibition properties to Q235 steel were studied in 0.5 mol/L hydrochloric acid solution with SSE by weight loss method,dynamic potential polarization (PDP),electrochemical impedance spectroscopy (EIS),X-ray photoelectron spectroscopy (XPS),scanning electron microscope (SEM),energy dispersive spectroscopy (EDS),atomic force microscopy (AFM) and contact angle. The effects of temperature on dynamic performance parameter (activation energy (Ea),activation entropy (ΔS0a) and activation enthalpy (ΔH0a)) and adsorption property parameters (adsorption enthalpy (ΔH0ads,adsorption entropy (ΔS0ads) and adsorption free energy (ΔG0ads) were studied by fitting calculations. The results showed that SSE delayed the corrosion of Q235 steel and protected the test piece,belonging to the mixed green corrosion inhibitor by inhibiting the reaction of anode reaction in the hydrochloric acid system. With the increase of SSE concentration,the corrosion current density was reduced from 11.78 mA/cm2 to 1.32 mA/cm2,and the active corrosion sites were blocked,the corrosion rate decreased and the corrosion inhibition efficiency increased. Under the condition of 293 K and SSE of 0.252 g/L,the corrosion inhibition efficiency of SSE to Q235 steel was 94.84％ by weight loss method. The higher the temperature of the working system was,the lower the ability of SSE to inhibit the corrosion of the steel sheet was,and the higher the corrosion rate was,but it also had good corrosion inhibition performance. Compared with the blank system,the dynamic activation parameter (activation energy) Ea of the system with SSE was significantly improved. In the range of 293-333 K,SSE adsorption on carbon steel surface followed the Langmuir adsorption isotherm. The mean value of Gibbs adsorption free energy (ΔG0ads) was-25.20 kJ/mol,indicating that SSE was a physical and chemical mixed adsorption on carbon steel surface and was spontaneous. By means of surface analysis,the corrosion inhibition performance of SSE to Q235 steel surface was proved to reduce the corrosion of steel. XPS and EDS confirmed that the main components of SSE (such as chlorophyll) containing a lot of—OH,—CHO and other functional groups with corrosion inhibition properties,could form a adsorption film on the surface of carbon steel through electrostatic attraction,and the lone pair electrons could combine with the unoccuated d orbital of Fe to form a coordination bond,thus forming a chemisorbed film on the surface of carbon steel. SEM,contact angle and AFM micrographs showed that the damage of carbon steel was obviously reduced after SSE was added,and the surface was covered with a protective layer. This work shows that SSE is an environment-friendly corrosion inhibitor with good corrosion inhibition performance in the field of pickling,which can provide stronger scientific and technological support and broader application prospects for the comprehensive utilization of silkworm sand.
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