Corrosion properties of chemically modified metal surfaces

The application of ultrathin plasma polymers and molecular adhesion promoters like thiols (RSH) are very promising methods to increase the stability of composite coatings on steel substrates. While the plasma polymers are deposited on the oxidised iron surface the thiols are adsorbed on bare iron under potential control. The investigation of the delamination of ultrathin plasma polymers (d < 10 nm) led to a detailed insight into the electrochemical and correlated chemical reactions at the metal-polymer interface in the delaminated area. The process of delamination was measured in situ by means of the scanning Kelvinprobe and the polymer/metal interface was studied by photoelectronspectroscopy with complementary local resolution. It turned out that the highly reactive intermediates of the oxygen reduction process give rise to the oxidative degradation of the polymer layer next to the oxidic substrate. Alternatively layers of dekanethiol were adsorbed on bare iron in a two phase arrangement at negative potentials. The structure of this adsorbate is compared to that of a self assembly film on gold and the potential dependence of thiol adsorption is investigated on gold by means of STM in detail. (C) 1997 Elsevier Science Ltd.