SYMPOSIA PAPER Published: 01 January 1999

Composition of Incipient Passivating Layers on Heat-Rejecting Aluminum in Carboxylate- and Silicate-Inhibited Coolants: Correlation with ASTM D 4340 Weight Losses


X-ray photoelectron spectroscopy identified compositional differences between passivating layers initially formed in carboxylated coolants, in silicated coolants, and in a mixture thereof on well-controlled 319 aluminum surfaces under heat-rejecting conditions. The layer formed in silicated coolant was primarily silica, while that in carboxylated coolant was primarily hydrated alumina. Competition between inhibitor packages when carboxylated coolant was contaminated from the start with low levels of silicated coolant produced films which were not simply patchwise mixtures of the pure-coolant film types.

The surface analytical results aid the interpretation of subtle differences in weight losses under the ASTM Standard Test Method for Corrosion of Cast Aluminum Alloys in Engine Coolants Under Heat-Rejecting Conditions (D 4340) in carboxylated versus silicated coolants that became more pronounced when testing was carried out at a vehicle-like 50% coolant concentration. Results from time-resolved D 4340 measurements and from a two-step cleaning procedure further contribute towards proper evaluation of D 4340 weight losses in the different coolant types.

Author Information

Wagner, FT
General Motors R&D Center, Warren, MI
Moylan, TE
General Motors R&D Center, Warren, MI
Simko, SJ
General Motors R&D Center, Warren, MI
Militello, MC
General Motors R&D Center, Warren, MI
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Developed by Committee: D15
Pages: 23–42
DOI: 10.1520/STP38237S
ISBN-EB: 978-0-8031-5566-4
ISBN-13: 978-0-8031-2610-7