51315-5702-A Novel Approach for the Development of Low-Voltage Aluminum Sacrificial Anodes

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Product Number: 51315-5702-SG

ISBN: 5702 2015 CP

Author: Alan Druschitz

Publication Date: 2015

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New anode chemistries that meet the current performance requirements for low voltage aluminum sacrificial anodes [MIL-DTL-24779C(SH) 2013] 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 an electronegativity control element. This research combines a more complete understanding of the effects of alloy chemistry heat treatment and microstructure on sacrificial anode performance which has led to the development of new anode chemistries with tailored 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 [Pautasso et al 1998]. 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 [Lemieux et al 2002]. In 2011 QuesTek began the development of a new alloy Alurium LV8TM using a physics-based computationally-enabled materials design; this new alloy is currently undergoing sea wall testing.Our effort had 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 and ternary alloys) were prepared using high purity materials at the Kroehling Advanced Materials Foundry and their electrochemical performance characterized using laboratory tests. Our research revealed that certain elements significantly affect the electronegativity which has allowed the development of new low voltage aluminum sacrificial anode chemistries.