ALUMINUM CORROSION IN UNINHIBITED ETHYLENE GLYCOL-WATER SOLUTIONS

The corrosion characteristics of some selected types of aluminum in uninhibited ethylene glycol/water solutions have been studied under conditions relevant to the operation of aluminum solar heat collector systems. Measurements of linear polarization resistance and maximum pit depth were used to assess the extent of corrosion activity. Pure aluminum (99.9%) as well as 1100 (commercially pure aluminum) and 3000 (~1% Mn) series alloys were studied in aqueous solutions of 35 v/o (volume percent) reagent grade ethylene glycol. This investigation covered the temperature range from ~25° to 100°C. The corrosion behavior of these aluminum compositions were determined under various hydrodynamic conditions and in the presence of dissolved oxygen, common water contaminants, and ethylene glycol thermal decomposition products. It was found that the corrosion resistance of all four types of aluminum compositions in pure uninhibited ethylene glycol solutions is marginally acceptable. The maximum corrosion current density measured was 0.5 μiA/cm2 at 100°C. Localized pitting attack occurred even in the pure ethylene glycol/ water system, however, the probable pitting penetration depth in 20 years was estimated at under 10 mils which would be too shallow to cause perforation failure. The corrosion rate was slightly temperature dependent; activation energies were found to be less than 5 kcal/mole.The corrosion process was not significantly affected by the hydrodynamic conditions, the presence of dissolved oxygen, or by ethylene glycol decomposition products.In the presence of common water contaminants, however, such as Cl-, CU+2, and Fe+3, the corrosion resistance of aluminum and aluminum alloys decreased significantly. Severe pitting corrosion was observed in the presence of chloride and/or copper ions. Ferric ions produced significant acceleration of the uniform corrosion rate to up to several tens of mils per year, but pitting was less severe. These baseline corrosion data suggest that light gauge aluminum solar panels would not survive for a reasonable service period in uninhibited ethylene glycol-water systems without some method of corrosion control. © 1979, The Electrochemical Society, Inc. All rights reserved.