Figures 16–18 represent the post-exposure appearance of coupons of cartridge brass, phosphor bronze,
and galvanized steel, respectively, resulting from the expanded testing. These images indicate the degree
of discoloration and film formation associated with each exposure (other materials indicated far less, or
even no, discoloration and film formation). As indicated by the planned interval test results,31 particularly
for the copper-based alloys, these corrosion films form quickly upon exposure to fuel at elevated
temperature and tend to be adherent to and protective of the substrate.
X-ray photoelectron spectroscopy (XPS) was performed on representative coupon surfaces following
testing (to compare with results from unexposed coupons) to assess the corrosion film thickness and
composition as a function of ethanol content in the exposure environment. The corrosion film
composition and thickness were not found to be substantially functions of the percent of ethanol in the
fuel blends (~ 10, 17, 20, and 25%). In other words, the XPS results for a given material were
indistinguishable and independent of ethanol concentration. Representative XPS results, shown in Fig. 19,
were measured for cartridge brass exposed to CE25a. The plot reveals the composition of the corrosion
product film as a function of depth from the surface (the film is incrementally sputtered from the surface,
and the identity of released materials is distinguished by relative energy). As stated, the sputter profiles
for cartridge brass exposed to CE10a, CE17a, and CE20a were indistinct from that shown in Fig. 19 for
exposure to CE25a.