Corrosion Inhibition Of Potassium Sorbate On Q235 Steel In NaCl Solution And Its Synergistic Effect

Potassium sorbate,also known as 2,4-hexadienoic acid potassium salt,is commonly used as a kind of preservative in the food industry.It is environmentally friendly,non-toxic and edible.Therefore,potassium sorbate can be used as the best choice for green environmentally friendly inhibitor.This work uses potassium sorbate as the research object,Q235 steel as the test metal.The inhibition behavior of potassium sorbate on Q235 steel in 0.5 mol/L NaCl solution and its synergistic effect with Zn²⁺ have been studied by weight-loss method,potentiodynamic polarization test,linear polarization test,electrochemical impedance spectroscopy?EIS?,scanning electron microscope?SEM?,X-ray photoelectroscopy?XPS?and UV-visible absorption spectrum?UV-Vis?and the corrosion inhibition synergism was discussed.The main research conclusions are as follows:1.Potassium sorbate has some inhibition efficiencies for Q235 steel in 0.5 mol/L NaCl solution and the inhibition efficiency increases with the increase of potassium sorbate concentration.The maximum corrosion inhibition efficiency value is only 38.37%.When the potassium sorbate is combined with Zn²⁺,the corrosion inhibition performance is greatly improved.When 60 mg/L Zn²⁺ was added to 0.16 mol/L potassium sorbate solution,the corrosion inhibition efficiency is as high as 91.03% indicating that a synergistic effect exists between potassium sorbate and Zn²⁺.2.Potassium sorbate and its compound with Zn²⁺ are both anode-type corrosion inhibitors.But the compound of potassium sorbate and Zn²⁺ can simultaneously inhibit the cathodic and anodic corrosion reactions of the Q235 steel electrode and the Tafel slope indicates that chloride ion has great inhibition on the anodic reaction controling with potassium sorbate.EIS test shows that potassium sorbate can form an adsorption film on the surface of the electrode and control the charge transfer process at the electric double layer.When potassium sorbate is combined with Zn²⁺,the charge transfer resistance Rct and modulus |Z| value increase further and the electric double layer capacitance Cdl value decreases indicating that the compound of potassium sorbate and Zn²⁺ can form a more compact and dense protective layer on the electrode surface.Linear polarization test shows that after adding Zn²⁺ to the potassium sorbate solution,the polarization resistance Rp value increases significantly indicating that Zn²⁺ helps to enhance the corrosion inhibition of potassium sorbate on Q235 steel.3.The adsorption of potassium sorbate and its compound with Zn²⁺ on the surface of Q235 steel conforms to the Freundlich adsorption isotherm.After adding Zn²⁺ to the potassium sorbate solution,the equilibrium constant of adsorption process Kads increases and the Gibbs free energy ?G°ads decreases indicating that Zn²⁺ enhances the adsorption action of potassium sorbate on the surface of Q235 steel.In addition,the adsorption of potassium sorbate and its compound on the surface of Q235 steel belongs to spontaneous physisorption.4.When potassium sorbate is used alone,the surface of Q235 steel sample is corroded and covered with blue-black corrosion product layer.The sample surface mainly forms a potassium sorbate adsorption film and oxide/hydroxide layer of iron.When potassium sorbate is combined with Zn²⁺,the surface of Q235 steel sample is bright,smooth and without any corrosion product layer.The protective film is mainly consisted of potassium sorbate adsorption film,oxide/hydroxide layer of iron and Zn?OH?2 precipitation film.5.In NaCl solution,potassium sorbate and calcium gluconate also have a certain corrosion inhibition synergistic effect,while there is an antagonistic effect between potassium sorbate and Mg²⁺.