Corrosion Inhibition Of Carbon Steel In Hydrochloric Acid Solution By Algae Extract

Iron and steel as the most widely used metal materials were applied to many fields,such as modern industry,agriculture,national defense,and construction and so on.The economic losses of steel corrosion were very huge.Corrosion inhibitors was one of the effective methods on the corrosion of steel materials in corrosive media.In recent years,the inhibitors from plant extracts have become a research foucs,but the study of algae extracts was rare.Therefore,it was of great theoretical and practical value to study the corrosion inhibition effects of algae extracts.Kelp,wakame and ulva lactuca were common in Dalian and were selected as research objects.The algae extract corrosion inhibitor was obtained by pressing,stirring,suction filtration,and drying with water as the solvent.The corrosion inhibition effects of extract on the carbon steel(Q235)in hydrochloric acid solution were investigated by weight loss method,electrochemical method(open circuit potential,potentiodynamic polarization curve,electrochemical impedance spectroscopy)and surface tests(SEM,EDAX spectroscopy,X-ray diffraction,infrared spectroscopy).The three algae extracts were effective on the corrosion inhibition of carbon steel in hydrochloric acid solution.The adsorption process of the extract on the surface of carbon steel in hydrochloric acid solution obeyed the Langmuir adsorption isotherm.In the test range of 20-60?,2-10 h,and 1.0-3.5 mol/L hydrochloric acid solution,the corrosion rate of carbon steel were decreased to invariable with increasing the extract concentration and increased with increasing the time,the temperature,and the concentration of hydrochloric acid.The corrosion rates of carbon in HCl solution with three kinds of extracts for 2 h at60?were 4.25 g/m~2·h,4.31 g/m~2·h,7.65 g/m~2·h,respectively.The corrosion inhibition efficiency of kelp extract,wakame,and ulva lactuca were 98.08%,98.05%,96.54%,respectively.The kelp extract was the best on the same condition.In the hydrochloric acid solution with extracts the open circuit potential of the carbon steel moved to positive,the corrosin potential changed slightly,the corrosion current density decreased and the the Tafels slope of the anode and cathode increased.So the three extracts were mixed inhibitors.In the hydrochloric acid solution with extracts,the charge transfer resistance increased,the low frequency impedance|Z|increased and the peak phase angle increased.The corrosion process of the carbon steel in hydrochloric acid was inhibited and of corrosion resistance the carbon steel was increased.The surface test results showed that the corrosion inhibition effects of algae extract on carbon steel in HCl solution was obviously.Polishing traces were still visible.No trace of local corrosion was observed.The surface of carbon steel was composed of Fe,C,and O elements.Infrared spectroscopy analysis showed that the algal extracts contained functional groups containing N and O.The extract adsorped on the carbon steel by forming coordination bond between lone pair electrons of N and O atoms and the empty d orbital of Fe.The adsorption film of the extract improved the electrochemical performance of the carbon steel and inhibited the corrosion.