Abstract

Our research has two directions: 1) experimental determination of the relationships between chemistry, microstructure and corrosion behavior and 2) computational design of new alloys based on the experimentally established relationships. A variety of aluminum based sacrificial anode chemistries (binary, ternary and quaternary alloys) were prepared using high purity materials at the Kroehling Advanced Materials Foundry at Virginia Tech and their electrochemical performance characterized using laboratory tests. As a result of this study, numerous, new anode chemistries that meet the current performance requirements for low voltage, aluminum, sacrificial anodes specified by MIL-DTL-24779C(SH) 20131 have been developed using a novel "three element" approach. The new chemistries are composed of a base metal element (Al), one or more active elements (Bi, Ga, In, Zn) and a voltage control element (Cu, Ge, Si). This research expands the understanding of the effects of alloy chemistry, heat treatment and microstructure on sacrificial anode performance.

Sacrificial anodes have been used on ships and marine structures for quite some time but these materials must be developed by trial and error since there is no materials theory that can be used for computational materials design. Typically, Zn, Mg or Al-Zn-In alloy anodes have been used, however, the electronegativity of these alloys can promote stress corrosion cracking (SCC) or hydrogen embrittlement (HE) of high strength steels.2 Pautasso determined that reducing the potential of the system to a range between -0.730 VSCE and -0.850 VSCE significantly reduced the amount of hydrogen liberated by the cathodic reaction thereby reducing the likelihood of SCC and/or HE. As a result of their work, an Al-0.1 wt% Ga anode was developed and large-scale experiments conducted by the U.S Navy confirmed that this low-voltage Al-Ga anode was a suitable option for cathodic protection of high strength steels. 3 Our research has developed a new, novel approach to developing aluminum, sacrificial anode chemistries.

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