Polymeric perfluoroalkylethers are being considered for use as lubricants in high temperature applications, but have been observed to catalytically decompose in the presence of metals. X-ray photoelectron spectroscopy (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 polycrystalline iron surfaces and polycrystalline iron surfaces, modified with an overlayer of chemisorbed oxygen. Low temperature adsorption of the perfluorinated ether on both surfaces was molecular. Chemisorption of an oxygen overlayer lowered the reactivity of the surface to adsorption and decomposition of the perfluorinated ether, by blocking active sites on the metal surface. Incomplete coverage of the iron surface with chemisorbed oxygen results in a reaction, which resembles the defluorination reaction observed on the clean iron surface. Perfluoro-1-methoxy-2-ethoxy ethane reacts on the oxidized iron surface via a different pathway from that seen on the clean iron surface. A reaction mechanism is proposed which involves Lewis acid assisted cleavage of the carbon-oxygen bond, with preferential attack at the methoxy carbon.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Condensed Matter Physics
- Surfaces and Interfaces