Study On The Electrochemical Properties Of Fe-based Sacrificial Anode For Anti-corrosion Of Stainless Steel

Metal corrosion of industrial equipments seriously disrupts the regular working of these equipments, especially those working in corrosive environment like ocean. Stainless steels with high oxidation and corrosion resistance have been developed as reliable materials to build equipments in corrosive environment. However, corrosion-causing damages still happen in harsh conditions. Fe-based sacrificial anodes which have appropriate driving potential versus stainless steel and thus a high current efficiency, are promising materials used in anti-corrosion for stainless steel. In this thesis, polarization performance of 20 CrMn, 20 CrMo, 20 CrMnTi and 40 CrMo sacrificial anodes were evaluated by cyclic voltammetry curve, polarization curve and constant current polarization. The dissolving mechanism of sacrificial anodes was investigated by observing the dissolving process of sacrificial anodes. Cathodic protecting performances of sacrificial anodes on 310 S and F166 stainless steel were studied by constant current test and self-charge test.The result of open-circuit potential test showed that 20 CrMnTi sacrificial anode had a stable open-circuit potential. The cyclic voltammetry curve and anodic polarization curve demonstrated that 20 CrMnTi had the lowest current density when four anodes were at same working potential. The result of constant current polarization test proved that 20 CrMnTi had the most negative working potential and the highest polarization resistance. 20 CrMnTi sacrificial anode have the lowest polarization, and thus the best theoretical sacrificial anode performance.By observing the morphology of sacrificial anodes at different experimental time in constant current test, we concluded that the dissolving O2- in the solution reacted with anodes at Cr-rich area at first, producing circular corrosion products CrxFe1-xOOH. With corrosion went on, corrosion products became regional, and then became a uniform and compact corrosion product layer. After that, a part of corrosion products fell off anodes, exposing new area of anodes in the solution, the corrosion process was then accelerated. Corrosion products were eventually became separated and block-shaped on the surface of anodes.In cathodic protection of 310 S stainless steel, the working current of four anodes kept high, which proved that Fe-based sacrificial anodes had no passivation during the working process. The results of constant current test and self-discharge test demonstrated that, 20 CrMnTi has the most stable working potential, the most uniform and compact corrosion products layer, and the highest current efficiency(> 90%). 20 CrMnTi demonstrated the best sacrificial anode property among these four materials. 310 S stainless steel protected by sacrificial anodes showed less corrosion pits and oxidation products on the surface, compared with the 310 S sample under no protection. Due to the low driving potential between the anodes and F166 stainless steel(< 300mV), Fe-based sacrificial anodes showed no obvious protecting effect on F166 stainless steel.