| Sacrificial anode has many exceptional merits, and has widely applied in offshore structure. However, the protective current density needed at the early stage of cathode protection is about3-5times than the average current density in the whole protection period. Thefore, it is significant to develop a new economical and environment-friendly composite sacrificial anode of aluminum alloy which satisfy both the requirement of the anode life and the need of the initial polarization current condition.The open circuit potential, the working potential, dissolved morphology, current efficiency, polarization degree, activation-dissolution behavior of sacrifical anodes were measured using constant current testing, speeded-up constant current test, electrochemical impedance (EIS) etc. in artificial seawater. The microstructure of sacrificial anodes was analyzed by metallography(OM), scanning electron microscopy (SEM) and X-ray energy dispersive analysis (EDX) and the distribution form, size and the phase composition in anodes were determined. The influence of the impurity elements to the current efficiency was discussed.The testing results of Al-Zn-In-Mg-Ti sacrificial anodes indicated that Al-6Zn-0.02In-1.5Mg-0.05Ti could significantly be used as the internal part of the composite sacrificial anode. The open potential of it was-1.116V, the working potential of it were-1.116V--1.088V and the current efficiency of it was91.48%. The influence of the extent factors to the current efficiency was In>Ti>Zn>Mg. The microcosmic construction of manufactured Al-Zn-In-Mg-Ti sacrificial anode was uniform. The reason of the uniform microcosmic construction was related to the refinement function of Ti element.The testing results of Al-Zn-In-Ga-Sn-Bi and Al-Mg-Ga-Sn sacrificial anodes indicated that the active performance of Al-4Zn-0.025In-0.22Ga-0.05Sn-0.04Bi with the theamal treatment which at460℃, furnace cooling6hours was got to the best condition. The open potential of it approach to-1.40V, but the working potential of it was too positive to be the high active anode; The open potential of Al-0.6Mg-0.075Ga-0.1Sn was-1.350V, but the working potential of it were-1.183V～-0.806V, it was also too positive to be the qualified high active anode.The testing results of Al-Mg-Ga-Sn-In sacrificial anodes indicated that Al-0.6Mg-0.05Ga-0.1Sn-0.025In anode which elements was found according to the single factor experiment could significantly be used as the external part of the composite sacrificial anode. The open potential of it was-1.509V, the working potential of it were-1.423V～-1.395V, and the current efficiency of it was45%. The advantages of the manufactured Al-Mg-Ga-Sn-In sacrificial anode were high active, low cost and easy process.The testing results of composite sacrificial anodes indicated that three periods of composite sacrificial anode were presenced in cathodic protection. The first period was high acitive anode protecting the steel construction, the second period was high active anode protecting the steel construction and the high efficiency anode, the last period was the high efficiency anode protecting the steel constroction. In practical engineering applications, the practical condition of the seawater should be investigated to acknowledge the initial protection time to adjust the thickness of the external sacrificial anode.The result of theorical design calculation indicated that applying composite sacrificial anode to protect steel construction could economize39.3%cost, compared to applying common sacrificial anode. The application of composite sacrificial anode had significantly economic value. |
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