DECOMPOSITION OF PERFLUORO-1-METHOXY-2-ETHOXY ETHANE ON IRON SURFACESCHEMICALLY-MODIFIED WITH OXYGEN

Polymeric perfluoroalkylethers are being considered for use as lubrica nts in high temperature applications, but have been observed to cataly tically decompose in the presence of metals. X-ray photoelectron spect roscopy (XPS) and temperature programmed desorption (TPD) were used to explore the decomposition of a model perfluorinated ether, perfluoro- 1-methoxy-2-ethoxy ethane, CF3OCF2CF2OCF2CF3 on oxidized polycrystalli ne iron surfaces and polycrystalline iron surfaces, modified with an o verlayer of chemisorbed oxygen. Low temperature adsorption of the perf luorinated ether on both surfaces was molecular. Chemisorption of an o xygen overlayer lowered the reactivity of the surface to adsorption an d decomposition of the perfluorinated ether, by blocking active sites on the metal surface. Incomplete coverage of the iron surface with che misorbed oxygen results in a reaction, which resembles the defluorinat ion reaction observed on the clean iron surface. Perfluoro-1-methoxy-2 -ethoxy ethane reacts on the oxidized iron surface via a different pat hway from that seen on the clean iron surface. A reaction mechanism is proposed which involves Lewis acid assisted cleavage of the carbon-ox ygen bond, with preferential attack at the methoxy carbon.