Studies On The Corrosion Inhibitor Of Carbon Steel In Sulfamic Acid

When the carbon steel is pickling in sulfamic acid,suitable inhibitor needs to be added to inhibit the corrosion of carbon steel caused by the media,However,the corrosion inhibitors in sulfamic acid is rarely reported when the temperature is above 60?.In this paper,the corrosion mechanism of Q235 steel by sulfamic acid was studied at different temperatures and different sulfamic acid concentrations.At the same time,cinnamaldehyde and methylamine were used to synthesize corrosion inhibitor N-cinnamylidene methylamine schiff base(NCMA).The inhibitory performance and adsorption mechanism of NCMA for corrosion of Q235 steel in sulfamic acid at different temperatures were studied by weight loss,Electrochemistry method,Scanning Electron Microscopy(SEM),Atomic Force Microscopy(AFM),X-ray photoelectron(XPS)and quantum chemical calculations.The experimental results show that the corrosion rate of Q235 steel in sulfamic acid is increasing with the rise of temperature.And the increase of corrosion active sites on the surface of carbon steel is the main reason for the increase of corrosion rate when the concentration of sulfamic acid increases.The corrosion product film on the surface of Q235 steel is thin at different temperatures,and raising the temperature will make the S element to be reduced to form FeS.The corrosion inhibitor NCMA has excellent inhibition performance on Q235 steel at 70-90?.NCMA is a mixed-type corrosion inhibitor,it can overcome the influence of sulfamic acid hydrolysis.The NCMA molecules inhibit corrosion by adsorbing active spots on the surface of Q235 steel,the adsorption process is spontaneous and conforms to the Langmuir adsorption rule.The adsorption process of NCMA is physical and chemical adsorption at 30-50?,while it manifests as chemical adsorption at 70-90?.The adsorption is an endothermic and entropy increasing process,the elevated temperature is favorable for the chemical adsorption of the inhibitor molecules.The results of quantum chemical calculations show that the inhibitor NCMA is adsorbed on the surface of carbon steel by N atom.The results of XPS show that the adsorption film can effectively inhibit the formation of FeS.At the same time,it is found that the corrosion inhibitor NCMA has obvious synergistic effect with thiourea,the corrosion inhibition rate is more than 91% at 30-90? with less dosage of compound inhibitor,Compound corrosion inhibitor is also a mixed-type corrosion inhibitor,which can adsorb and significantly reduce the active spots on the surface of carbon steel.Small thiourea molecules can fill the gap of the NCMA adsorption film to make it denser and the corrosion inhibition effect enhanced.