Effect of rare earth element (erbium) on anti fouling sacrificial anode

The objective of introducing Erbium into the Al 5Zn-0.5Cu alloy model, as a potential candidate for an anti-fouling sacrificial anode, is to improve its protective efficacy. The corrosion behavior was characterized by cyclic potentiodynamic polarization, and the open circuit potential (OCP) of coupled steel was monitored to see the protection ability of anode. Addition of erbium to the alloy results in the formation of precipitates at grain boundaries, hence exerting a nucleating effect and contributing to the smoothening of the Secondary Dendrite Arm Spacing (SDAS). The introduction of erbium at a concentration of 0.3%wt successfully decreases the size of the secondary dendrite arm spacing (SDAS) to 53μm. However, the subsequent addition of 0.5%wt erbium leads to a modest increase in the SDAS. The grain refinement of the Al-Zn-Cu-Er based alloy sacrificial anode candidate improves the degradation rate of anode, accompanied by a more homogeneous corrosion attack pattern, as evidenced by the existence of smaller loops observed during cyclic potentiodynamic polarisation testing. The addition of Erbium leads to a reduction in the corrosion potential (Ecorr) when compared to the Al-Zn-Cu model alloy. Such a decrease makes the corrosion potential close to that of the Al-Zn alloy, with values ranging from -1200 mVsce to -1250 mVsce. The potential coupling with steel showed a potential around -780mV which exhibited a more favorable trend as promising anti fouling sacrifical anode.