Study Of Low Driving Voltage Sacrifice Anode Performance

Lower negative potential of traditional sacrificial anode led to excessivesusceptibility to hydrogen embrittlement of high-strength steel. To solve this problem,six kinds of Al-Zn-Ga-Si quaternary alloy sacrificial anodes were designed andfabricated in this paper. The electrochemical properties of the anodes were evaluatedusing constant current method. The microstructure of the anode was observed byscanning electron microscopy (SEM) and optical microscopy. The effects of Zn, Si,seawater temperature and hydrostatic pressure on the electrochemical performances oflow driving voltage sacrificial anode were analyzed. The main conclusions were asfollows:The anode of Al-0.3wt%Zn-0.10wt%Ga-0.8wt%Si exhibited goodelectrochemical performance. The working potential range was-0.765V～-0.789V,and the current efficiency was higher than80%. Moreover, the actual capacity washigher than2400A·h/kg. Besides, the anode was dissolved uniformly and the productcould be removed easily, indicating that this was an excellent low driving voltageanode.The trace element Zn was dissolved in aluminum phase to formed α-Al solidsolution. With an increase of Zn in the Al solid solution, the open circuit potential andworking potential of the anode shifted negative. The anode current efficiency anddissolution morphology did not change significantly.The trace element Si was dissolved in the Al phase and the grain size of Al wasrefined. The open circuit potential and working potential of the anode shiftedpositively. The dissolution of anode in the solution became uniform gradually, and thedistribution of the anode and cathode on the surface were also becoming equably.With increasing of hydrostatic pressure, the open circuit potential and workingpotential of the anode went up. The dissolution of anode became uneven and thecurrent efficiency decreased a little. The reasons may be as follows: firstly, theactivities of the element Zn, Ga and Al atoms were suppressed due to the dual roles ofhigh pressure and low temperature of the seawater. Meanwhile, the migration andoxidation of Al atoms were hindered, the activity of the anode decreased; Secondly, itwas difficult for the corrosion product of the reaction to move out from the pit, which deposited in the pit, hindering the migration of molecular or ions. Thus, the surfacemorphology of the dissolving anode deteriorated.As the temperature increased, the open circuit potential and working potential ofthe anode moved up. The dissolution of anode became uneven, but the currentefficiency changed little. The oxidation film resistance (Rf) and the charge transferresistor (Rt) of the anode surface increased. Moreover, the process of activationdissolution of anode was stopped. The electrochemical performance deteriorated dueto the decreased activity of trace elements Zn, Ga and other types of ions at lowtemperature.