Comparison of Surface Coatings Formed from Carboxylic Acid-Based and Conventional Coolants in a Field-Test Study

Field-test samples cut from radiator tubes in two 1990 Chevy Luminas (3.1L engine) after 100,000 miles were analyzed to determine corrosion layer differences. One car used a carboxylic acid-based inhibitor technology (C1). The other car used a conventional coolant (C2). X-ray photoelectron spectroscopy (XPS) analysis of the two samples was performed.

Results indicate a significant difference between the two samples. The C1 sample had a thin (<60Å) organic coating bound to the aluminum alloy surface, while the C2 sample had a much thicker (>1000 Å) silicate-rich layer. This resulted in the C2 sample exhibiting “surface charging” behavior. These results relate directly to the metal/insulator (conductor/insulator) characteristics of the two samples, and imply that the heat transfer of the protective coating provided by the carboxylate technology (C1) is significantly better than that of traditional inhibitor technology (C2). A mechanism for the corrosion inhibition of the carboxylate system is discussed, and is supported by scanning electron microscopy (SEM) results.