Electrochemical Properties Of Aluminum-based And Zinc-based Sacrificed Anodes Under Hot Seawater Environment

There exists serious corrosion in the place of outlet of heat exchange equipment in circulation and cooling system, in which seawater temperature is rather high. And so it is a special significance that the problem of the equipment attacked is solved under high temperature seawater. The sacrificed anodes protection is a kind of effective methods widely used for prevention marine structures from corrosion. However, several kinds of sacrificed anodes in common use are of many difficulties such as increased potential, decreased efficiency, intercrystalline corrosion and so on. This task is proposed on the basis of above background, which aims to develop aluminum-based and zinc-based sacrificed anode materials of high efficiency used for high temperature environment.According to precursor's research, we determined 14 kinds of sacrificed anode composition to melt. A kind of material was chosen respectively from aluminum-based and zinc-based anodes for solution treatment tests. The electrochemical property tests were undertaken; the national standards are references for selecting anode composition. Meantime, these effects of alloy elements and solution treatment on potential, current efficiency, surface dissolution and intercrystalline erosion were studied.Experimental results show that Al-6.55Zn-0.023In-0.17Si-0.028Sn, Al-5.8Zn-0.074In-0.092Bi-0.028Ti, Zn-0.0006Al-0.3Cd, Zn-0.43Al-0.5Cd at 60°C and Al-6.53Zn-0.024In-0.19Si, Al-5.43Zn-0.024In-0.05Sn, Zn-0.05Cd at 70°C have good electrochemical behavior, and can be used for hot seawater environment as anode materials to develop further.Comparison on anodes both Al-Zn-In-Si and Al-Zn-In-Si-Sn, the addition of Sn is found that can decrease or remove intercrystalline corrosion at low temperature. At high temperature, however, it causes current efficiency lower, potential little stable and bad uniform dissolution of anode surface beyond greater electronegative potential provided.According to the studying result, the addition of alloy elements such as aluminum or magnesium has disadvantageous effect on the properties of zinc alloy anodes at high temperatures. After further analyzing effects of Al on intercrystalline corrosion of Zn-Al-Cd, we draw two conclusions that aluminum atoms activated in the area of grain boundary are essential to result in intercrystalline corrosion; moreover, separating-hydrogen reaction catalyses and aggravates it.Based on observing influence of solution treatment on properties of zinc-based and aluminum-based sacrificed anodes at high temperatures, it has been found that solution treatment can improve electrochemical behaviors of Al-Zn-In-Si-Sn anode. As to Zn-Al-Cd after solution treatment, however, solution treatment causes its behaviors worse.The experimental results exhibit that great current density helps in improving catholic-protection behavior of aluminum anodes on the basis of the self-discharge experiment for Al-2.98Zn-0.02In-l.24Mg compared to the constant current density experiment for it. In addition, the self-discharge experiments confirmed the fact that Al-6.55Zn-0.023In-0.17Si-0.028Sn and Al-5.8Zn-0.074In-0.092Bi-0.028Ti perform satisfactorily at high temperature.