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The corrosion characteristics of some selected types of aluminum in uninhibitedethylene glycol/water solutions have been studied under conditionsrelevant to the operation of aluminum solar heat collector systems. Measurementsof linear polarization resistance and maximum pit depth were used toassess the extent of corrosion activity. Pure aluminum (99.9%) as well as1100 (commercially pure aluminum) and 3000 (~1% Mn) series alloys werestudied in aqueous solutions of 35 v/o (volume percent) reagent grade ethyleneglycol. This investigation covered the temperature range from ~25° to100°C. The corrosion behavior of these aluminum compositions were determinedunder various hydrodynamic conditions and in the presence of dissolvedoxygen, common water contaminants, and ethylene glycol thermaldecomposition products.It was found that the corrosion resistance of all four types of aluminumcompositions in pure uninhibited ethylene glycol solutions is marginally acceptable.The maximum corrosion current density measured was 0.5 µA/cm2at 100°C. Localized pitting attack occurred even in the pure ethylene glycol/watersystem, however, the probable pitting penetration depth in 20 years wasestimated at under 10 mils which would be too shallow to cause perforationfailure. The corrosion rate was slightly temperature dependent; activationenergies were found to be less than 5 kcal/mole.The corrosion process was not significantly affected by the hydrodynamicconditions, the presence of dissolved oxygen, or by ethylene glycol decompositionproducts.In the presence of common water contaminants, however, such as Cl–, Cu+2,and Fe+3, the corrosion resistance of aluminum and aluminum alloys decreasedsignificantly. Severe pitting corrosion was observed in the presenceof chloride and/or copper ions. Ferric ions produced significant accelerationof the uniform corrosion rate to up to several tens of mils per year, but pittingwas less severe. These baseline corrosion data suggest that light gaugealuminum solar panels would not survive for a reasonable service period inuninhibited ethylene glycol-water systems without some method of corrosioncontrol.