Study On Electrochemical Performance Of Al-alloy Sacrificial Anode In Simulated Deep-sea Environment

21st century is the century of ocean，marine resources are mostly distributing inthe bottom of deep seawater， from hundreds of meters to several kilometers.Exploration and exploitation of these resources need to manufacture and use newinstruments and equipments. So we select sacrificial anode of which the installation iseasy and the maintenance is simple as the method to protect equipments. Deep-seaenvironment has some characteristics such as high pressure, low temperature, lowdissolved oxygen, etc. which have some merits, for example, a certain influence onthe electrochemical performance of sacrificial anode. Al alloy anode which has a highdriving potential, high theoretical capacity, abundant resources, low cost, has beenwidely usedBase on the above studies, temperature, medium mobility and dissolved oxygen(DO) were taken as variables and effects of these factors on the electrochemicalperformance of Al-Zn-In-Cd sacrificial anode in simulated deep-sea water wasdiscussed in this paper. The composition of Al sacrificial anode materials wereoptimized and determined through orthogonal test, and the electrochemicalperformance of the materials were investigated in deep-sea water. Galvanostaticpolarization and cyclic voltammetry (CV) were carried out for the studies of theelectrochemical performance, electron micro probe-analysis (EMPA) observations ofdissolution mechanism were carried out for the anodes, to lay the foundation for thefurther development of deep-sea anode.The electrochemical performance of Al-Zn-In-Cd sacrifical anodes in deep seawater has been investigated under different conditions: different temperatures，different flowing states and different concentration of dissolved oxygen.The resultsshowed that effects of temperature on the performance of Al-Zn-In-Cd sacrificialanode were significant, either open potential or current efficiency; Al-Zn-In-Cdsacrificial anodes has a higher current efficiency in flowing seawater but surfacedissolution was poorer. The corrosion rate of Al-Zn-In-Cd Sacrificial Anodes decreased in low concentration of DO, surface dissolution of which was uniform, andthe corrosion product fell off, thus this anode had slightly more excellentperformance.Electrochemical performance of nine kinds of sacrificial anodes was investigatedat low temperature. The results showed that the open circuit potential, workingpotential and the electrochemical capacity all meet or exceeded the national standard,especially the current efficiency were more than85%. Current efficiency anddissolution morphology were taken as objective function, by range analysis andvariance analysis, the composition of Al-Zn-In sacrificial anode was optimizedthorough orthogonal test and the Al-4.8Zn-0.020In（Si:0.08, Fe:0.06-0.10）sacrificial anode(Al-3) material was determined. Electrochemical behavior of Al-3anode was excellent at low temperature.In addition, other researches were carried at the same time, at low temperatureAl-1and Al-2sacrificial anode showed good performance; the current efficiency ofAl-Zn-In-Si(I) was high, but the dissolution morphology was poor and the low levelof impurity in iron increased the requirement of materials and costs. Thus Al-1, Al-2,Al-3anodes were selected as the objective for deep seawater. Three kinds ofaluminum anode showed good electrochemical performance in deep-sea conditions,and as the temperature decreased, open potential and working potential showed apositive shift, the current efficiency gradually increased, the dissolution morphologyof different temperature were uniform(except for the localized corrosion of Al-3anode at low temperature). The results of CV showed that Al-Zn-In-Cd sacrificialanode could be well activated at any temperature, and the current could meet thepractical requirements. Results of EMPA showed that at low temperature In elementwhich played an important role in the current efficiency of anode was distributeduniformly in the aluminum matrix; Local enrichment of Si element prevented theformation of amalgam between active element and aluminum matrix and had animpact of the anode active dissolution, thus increased the possibility of localizedcorrosion of the anode.