The Study On The Effect Of Calcareous Sediments On Cathodic Reaction Obtained Under The Condition Of Different Cathodic Protection

Nowadays cathodic protection technology has been widely applied to protect marine engineering facilities from corrosion.During the application of cathodic protection in marine environment,the surface of the metal was covered with calcium deposition layer generated which can protect the steel.But whether calcium deposition layer adsorbed on the surface of the metal has effect on hydrogen evolution potential.If it indeed do,it will make the hydrogen evolution potential negative shift,hinder hydrogen evolution reaction occurs,or make the hydrogen evolution potential a positive move to promote hydrogen evolution reaction? Therefore,It is significance for the study on the impact of calcium deposits on hydrogen evolution potential.Potentiostatic polarization method,potentiodynamic polarization,electrochemical impedance spectroscopy and Devanathan-Stachurshi test method were used to study the impact of calcium deposits on hydrogen evolution potential in this paper.VHX-2000 microscope,SEM were also used to get morphology of calcareous sediments.The result obtained provided a theoretical basis for the actual cathodic protection of marine engineering.The cathodic polarization curves of 16 Mn steel covered with calcareous sediments with various state parameters were got by using potentiodynamic polarization experiments.Combined with electrochemical impedance spectroscopy and Devanathan-Stachurshi test method,the potential of 16 Mn steel in each state for hydrogen evolution can be confirmed.The results showed that in static seawater,as the cathodic polarization potential negative shift within-0.90 V ~-1.05 V interval range,the potential for hydrogen evolution negative moved to-1.17 V,compared to initial potential for hydrogen evolution about-0.9V.But the potential for hydrogen evolution positive moved to-0.97 V when the applied cathodic protection potential was-1.10 V.In simulated dynamic marine environment,with the flow rate increased,the hydrogen evolution potential negative shifted constantly.And at the same flow rate,the hydrogen evolution potential of 16 Mn steel protected for 3d was negative than that without protected.For example,the hydrogen evolution potential of the steel at 0 rpm turned from-0.94 V to-0.96V;The hydrogen evolution potential of the steel at 1500 rpm turned from-1.035 V to-1.09V;In summary,calcareous sediments obtained have effects on hydrogen evolution potential.Combined with the hydrogen permeation current density curve and the morphology of calcium deposition layer,one mechanism was summarized that calcium deposition layer film can hinder the diffusion of hydrogen from the metal surface to the solution.The hydrogen continued to gather in the surface of 16 Mn steel and become more and more due to the obstruction of calcium deposits.According to the hydrogen evolution reaction: H2 O + e = OH-+ H(1)and H + H = H2(2),the increasing concentration of hydrogen,in turn,inhibit the reaction(2)and the reaction(2),in turn,inhibit the reaction(1).So more negative cathodic polarized potential should be applied to keep the hydrogen evolution reaction.Of course,an IR drop was produced because of calcareous sediments,which made the active potential of hydrogen evolution reaction shifting negative.