Preparation And Action Mechanism Of Mannich Base As Corrosion Inhibitor On Carbon Steel In Seawater

Mannich base can inhibit the corrosion of carbon steel and it is a typicaladsorptive corrosion inhibitorin in acidic medium.Using the good adsorbability ofMannich base on carbon steel surface,this paper develops a new kind of Mannch baseas corrosion inhibitor for carbon steel which is used in non-acidic medium.This paperstudy on the behavior of corrosion inhibition of Mannch base on carbon steel and thesynergistic mechanism of Mannich base and other corrosion inhibitor.Then this paperestablished mechanism model of corrosion inhibition effect.The further research onthe exploration and development of Mannich base as corrosion inhibitor used inseawater circulating cooling system have been provided theoretical reference.The main research results could be summarized as follows:（1）This paper has designed and synthesized three water soluble Mannich baseMNX-H、 MNX-B and MNX-D respectively including hydroxyl、 phenyl、 anddual-phenyl group.Furthermore,using mass、infrared spectrum and¹HNMR test showthat the molecular weight of three Mannich base are131.1、177.1and324.2.IR resultsshow that all the three Mannich base appeared significantly characteristic peak ofcarbonyl between1750cm^-1and1680cm^-1. The results of1HNMR test could alsoshow corresponding to molecular structure.（2）By the electrochemical test,the results show that single dose of Mannich baseis a kind of anodic mixed inhibitor according to carbon steel corrosion in distilledwater and seawater.When the three Mannich base have lower concentrations（about5mg/L）,all of them presented relatively better effect of inhibition,but the effects ofinhibition are very finite. Because MNX-B containing phenyl,it could form adsorptionof π bond and have little steric hindrance,MNX-B has relatively better effect ofinhibition than MNX-H and MNX-D.（3）By researching effect of inhibition of combined inhibitor on20^#steel inseawater,the results show that Mannich base/surfactants complex inhibitor could notincrease surface adsorption coverage of Mannich base on carbon steel and thecollaborative effect is not good.Adding Mannich base could not change and make upoxide film structure of anodic inhibitor,they can not showed significantly collabo-rative synergism. Adding mixed corrosion inhibitor thiourea can change cathodicprocess of carbon steel corrosion and decrease current density of corrosion.Mannich base/thiourea complex inhibitor significantly inhibit cathodic and anodic process ofcorrosion,the inhibition rate could reach60%.Mannich base and CeCl₃which belongsto deposit type of cathodic one can produce significantly collaborative synergism.When Mannich base compounded with thiourea,Ce could occur chelating adsorptioneffct with Fe of the surface of carbon steel and MNX-B may show strong comple-xation with Ce precipitated on cathodic area of steel surface,they generate chelatingproduction with cyclic structure and adsorb on the surface of carbon steel and showcharacteristics of anodic mixed inhibitor. The impedance arc of Mannich base/CeCl₃complex inhibitor increased largely and it is25times higher than the one of singledose of MNX-B, the inhibition rate could reach more than90%.