Degree Type

Dissertation

Date of Award

1989

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Patricia A. Thiel

Abstract

The interaction of oxygenated fluorocarbons with Ru(001) is investigated by thermal desorption spectroscopy in an effort to model how technologically important lubricants interact with metal surfaces. The data are compared with those of analogous oxygenated hydrocarbons. In the limit of low exposure, fluorinated molecules bond between 8 and 18 kJ/mol more weakly to Ru(001) than analogous hydrocarbons in cases where the interaction arises from oxygen lone pair electron donation to the surface. This weakening is attributed to inductive withdrawal of electron density at the oxygen by the fluorine atoms. Fluorinated molecules which can accept backbonding from the surface, on the other hand, bond up to 20 kJ/mol more strongly than the related hydrocarbons;Adsorbed oxygenated fluorocarbons are more stable toward decomposition than the hydrogenated compounds. The stability of the fluorocarbons is attributed to the weak adsorption bond, the strength of the C-F bond or the adsorption geometry. The first two facts suggest the molecules may not remain on the surface up to the temperatures required to activate the C-F bond. Alternatively, the fluorinated molecules, by virtue of the bulky fluorinated alkyl groups, may not approach the surface closely enough to undergo decomposition;The adsorption bonds of oligomeric ethers do not increase in multiples of the monoether-surface bond. For a fluorinated diether, the adsorption bond is approximately equal to that of the monoether. In this case the data suggest the diether bonds to the surface in a similar fashion as the monoether (i.e., primarily through one ether linkage). For the hydrogenated ethers, the adsorption bond increases up to 35% on the addition of an ether linkage. This increase is attributed to adsorption primarily through only one oxygen-metal bond or through several weaker-than-expected oxygen-metal bonds. The oxygen-metal interaction may be weakened by increased electron density at the surface. Such an increase is expected from an oxygen-metal bond in close proximity;Fundamental research on the interaction of oxygenated fluorocarbons with metal surfaces, such as that described here, can potentially improve the related industrially important lubricants.

DOI

https://doi.org/10.31274/rtd-180813-9075

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Mary Margaret Walczak

Language

en

Proquest ID

AAI8920194

File Format

application/pdf

File Size

215 pages

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