Electrochemical Performance Of Sacrificial Anodes Under Special Marine Conditions

Sacrificial anodes are widely used for corrosion protection of engineering equipment in marine environments.In some special marine conditions(e.g.low temperature seawater(below 4℃),high temperature seawater(50℃～70℃),cyclic immersion,low salinity seawater(salinity below 15))electrochemical performance of sacrificial anodes are greatly degraded and the protection of engineering equipment does not reach the desired effect.Firstly,the electrochemical performance of aluminum anodes(AZI anode,Al-Zn-In-Cd anode,Al-Zn-InMg-Ti anode,AZMG anode)was comparatively studied.The activation/failure mechanism was explored by combining microscopic characterization methods and electrochemical testing techniques in the special marine conditions.Finally,new sacrificial anodes that suitable for the special conditions were developed.The main conclusions are as follows:(1)In 0℃ seawater,the closed circuit potential of Al-Zn-In-Mg-Ti anode ranged from-1.048 V to-1.105 V,the current efficiency was 92.1%,the corrosion morphology was even,and the products automatically fell off,which was the most suitable for 0℃ seawater.In 50℃seawater,the products of four anodes did not automatically fall off,so the four anodes were not suitable for 50℃ seawater.In cyclic immersion condition,the closed circuit potential of AZI,Al-Zn-In-Mg-Ti and AZMG anodes ranged from-0.957 V to-1.104 V,the current efficiency ranged from 88.9%to 91.0%,the products automatically fell off.The corrosion morphology of AZI and Al-Zn-In-Mg-Ti anodes was relatively even and AZMG anode was even.Therefore,all of them could be used in cyclic immersion condition.In low salinity seawater,the current efficiency of Al-Zn-In-Mg-Ti and AZMG anodes was 91.7%and 92.4%,respectively.The corrosion morphology was even,the products automatically fell off,and the closed circuit potential ranged from-0.922 V to-1.076 V.Thus,both could not completely provide ideal protection for marine structures.The failure mechanism of anodes in 0℃ and low salinity seawater was mainly because the redeposition of active elements became difficult.The failure mechanism of anodes in 50℃ seawater was mainly because the adhesion of corrosion products on the surface,which hindered the dissolution of anodes.The failure mechanism of anodes in cyclic immersion condition was mainly because crusting on the surface,which hindered the reactivation process.Six aluminum and six zinc anodes were developed by regulating the ratios of Al,Zn,In,Mg,Ti,Ga,Mn,Sn,X or Y alloying elements.The performance studied of six aluminum anodes in 0℃,20℃ and 30℃ seawater found that when the anode components were Al-5%Zn-0.025%In-0.064%Ti-0.008%Ga-0.2%Mn-0.06%Sn and Al-5%Zn-0.035%In-1.2%Mg-0.048%Ti 0.016%Ga-0.04%Mn anodes,the closed circuit potential ranged from-1.069 V to-1.120 V,the current efficiency ranged from 87.3%to 90.9%,the corrosion morphology was even,and the products automatically fell off.The interaction between alloying elements and the electrochemical performance of aluminum anodes were better.The performance studied of six zinc anodes in 50℃ seawater found that the closed circuit potential of Zn-0.2%Al-0.05%Mg0.4%Y anode ranged from-1.001 V to-1.012 V,the actual capacity was 796 A·h·kg-1,the current efficiency was 96.6%,the corrosion morphology was even,and the products automatically fell off.The comprehensive performance was better than other domestic manufacturers.