Effects of Perfluoropolyalkyl Ethers and Perfluorinated Acids on Crack Growth in Soda-Lime Glass

The growth of cone cracks in soda-lime glass during static loading with a spherical indenter shows that crack growth is accelerated by perfluorinated acids, probably by a stress corrosion mechanism involving reaction between the acids and strained Si-O bonds in the crack-tip region. The strained bonds are not reactive toward perfluoropolyalkyl ether (PFPE) oils under static conditions. In hybrid silicon nitride-steel contacts, acidic products of the degradation of PFPE oils by Lewis acid sites on the steel surfaces may be transported through the crack to the crack-wake region and attack the strained Si-O bonds. These results suggest that PFPE oils may not be the best choice for lubrication of silicon nitride-steel hybrid bearing systems.