Study On The Preparation And Corrosion Inhibition Performance Of Two Plant Extracts

In this paper,two kinds of plant extracts were made from pine needles and soybean meal to investigate the corrosion resistance of Q235 steel in lmol/L HC1 before and after adding extracts.The extracts were prepared by soaking method and soxhlet extraction method.The best preparation method and preparation conditions were compared.The results were as follows:pine needles extract was prepared by soaking method under the following conditions:45?,3 h,soybean meal extract was prepared by soaking method under the conditions of 45? and 5 h.Then,FTIR and GC-MS were used to analyze the composition of the extract.Inhibition effect was investigated by the weight loss method,potentiodynamic polarization curves,electrochemical impedance spectroscopy,quantum chemical study and scanning electron microscope.The results showed that the extract of pine needle contained volatile oil,sterols,flavonoids and other substances,including N-H,C-H,C=C,C=O and other absorption peaks.Soybean meal extract contains protein,amino acids,carboxylic acids and other substances,including N-H,O-H,C=O and other absorption peaks.In addition,several substances with high content were selected as the main corrosion inhibitors in pine needles and soybean meal extracts such as arginine,shikimic acid,caryophyllene,glutamic acid,aspartic acid,and daidzein.The weight loss measurements showed that the corrosion inhibition efficiency of pine needles extract increased with the increase of concentration.The inflection point occurred in 0.8g/L.The corrosion inhibition efficiency decreased with the increase of temperature.The corrosion inhibition efficiency of soybean meal extract increased with the increase of concentration,with the inflection in 0.6g/L,The weight loss experiment showed that the inhibition efficiency of pine needle extract increased with the increase of concentration,and the inflection point appeared at 0.8g/L,and the inhibition efficiency decreased with the increase of temperature.The inhibition efficiency of soybean meal extract increased with the increase of concentration,and the inflection point appeared at 0.6g/L.The corrosion inhibition efficiency increased first and then decreased with the increase of temperature.The corrosion inhibition efficiency was the highest at 40?.The potentiodynamic polarisation curves and electrochemical impedance spectroscopy showed that the corrosion current was significantly reduced,the charge transfer resistance was increased,and the electric double layer capacitance constant was reduced,with adding pine needles or soybean meal extract.The corrosion rate was reduced and the steel sheet was effectively protected.Scanning electron microscopy showed that after adding two extracts,the surface of steel sheet was smooth,the grinding scratches were visible,and the corrosion degree was obviously slowed down.Thermodynamic analysis shows that the adsorption of pine needles extract on the surface of steel sheet is physical adsorption,and the adsorption of soybean meal extract includes both physical adsorption and chemical adsorption.Both of the two ectracts are in accordance with Langmuir adsorption isothermal type.The corrosion inhibition mechanism is that the adsorption of pine needles extract is the physical adsorption of electrostatic adsorption,intermolecular force,etc.,and the adsorption of soybean meal extract is the comprehensive result of intermolecular force and the formation of coordination bond between N,O atom and Fe's empty D orbit.In order to study the corrosion inhibition performance of extracts,quantum chemistry studies on arginine,shikimic acid,caryophyllene,glutamic acid,aspartic acid,and daidzein were carried out.Results from the HOMO and LUMO orbital diagrams of each molecule,it can be seen that the electronegativity of N and O in the molecule is great.They can give full play to the role of functional groups to bond with metals,and then cover all the active parts of the metal surface.The alkyl chains contained in the groups can form films on the metal surface by adsorption.To further investigate the corrosion inhibition efficiency of the two extracts at 70?,the surfactants CTAB and OP-10 were added to the extract for compounding.The compounding results showed that the corrosion inhibition efficiency was improved after compounding.0.8g/L PMNE+0.2g/LCTAB,corrosion inhibition efficiency is 95.31%;0.8g/L PMNE+O.1g/L OP-10,corrosion inhibition efficiency is 89.21%;0.6g/LSME+0.1 g/LCTAB,corrosion inhibition efficiency is 97.12%;0.6g/LSME+0.2g/LOP-10,the corrosion inhibition efficiency was 88.11%.