Study Of Adsorption Behavior And Electrochemical Methods For Corrosion Inhibitors In Acidic Solutions

Electrochemical methods, which can conveniently and rapidly provide abundant interface information of inhibition system, are useful tools for corrosion inhibitors research. In acid solutions, the dynamic process of inhibitors adsorbing on electrode demands rapid measurements to provide information of interface changes as well as not to disturb the adsorption state. The coulostatic method having advantages of rapid measurement and weak perturbation enables determination of instantaneous parameters for interface reaction, so it is suitable for investigating corrosion inhibitor behavior and mechanism in acidic mediums.In this thesis, the advantages and disadvantages of potentiodynamic polarization curve, electrochemical impedance spectroscope (EIS) and coulostatic method for studying corrosion inhibitors in acidic mediums were compared. And then the effect of three popular acid corrosion inhibitors such as thiourea, dodecylamine and propargyl alcohol on the corrosion inhibition behaviors of Q235 steel in acidic solutions were investigated by these techniques. The anodic desorption behavior and extreme value phenomenon of concentration were surveyed thoroughly as well. The main conclusions as follows:Potentiodynamic polarization curve can classify inhibition mechanisms and deduce corrosion current from cathodic Tafel lines extrapolation. However, its intensive polarization causes anodic desorption of inhibitors. Although EIS can provide abundant information of adsorption process, the corrosion velocity can not be obtained directly. Moreover, the experiment duration is too long to measure rapidly. In coulostatic measurements, polarization resistance is always close to charge transfer resistance and Tafel slopes can be obtained instantaneously. Therefore, this method can obtain more accurate instantaneous corrosion rate and facilitate the rapid procedure for the evaluation of corrosion inhibitors simultaneously.The electrochemical results of Q235 steel clearly showed that, dodecylamine restrain corrosion mainly by geometric blocking effect; Thiourea decreased the cathodic current effectively and propargyl alcohol suppressed the anodic reaction instead.Inhibition behaviors of PA at different concentrations were investigated as well. The results showed that there existed an extreme value phenomenon of concentration after immersion 4 hours. However, this phenomenon was not significant after immersion 24 hours, which indicated some changes of the adsorption layer of the inhibitor. This may be attributable to the adsorption density of PA molecules increasing with time.