The Use of Zinc to Control Aluminum Corrosion in Aqueous Glycol Solutions

Aluminum and its alloys are highly susceptible to pitting corrosion in aqueous glycol solutions, especially when chloride and heavy metal ions (Cu⁺² and Fe⁺³) are present. One approach to controlling such corrosion is the use of scavengers to remove the deleterious species from solution, and in this work the role of zinc as an effective heavy metal ion scavenger has been confirmed. In addition, it was discovered that zinc powder in suspension is capable of stopping aluminum pitting corrosion in aqueous glycol solutions containing chloride ions. Zinc is not expected to act as a chloride ion getter. However, it has been established that zinc also gives a protective effect through a cathodic protection mechanism produced by the zinc powder contacting the aluminum surface and concomitantly lowering the open circuit potential of the aluminum sample to below its critical pitting potential. A similar cathodic effect is expected also, of course, in the case of heavy metal ion contamination when simultaneous gettering action also occurs. Finally, it was found that the combined use of zinc powder and conventional corrosion inhibitors compatible with aqueous glycol solutions is 100% effective in stopping all aluminum corrosion problems at temperatures up to 130 C, even in solutions initially containing both chloride and heavy metal ions.