In order to develop new composite materials between reactive metals and polymers, it is proposed to place organic monomers at the metal/polymer phase boundary, which can be coupled by covalent/idc bonds to reactive centres of tbe metal substrate and later by covalent bonds to the polymer itself. As a Arst step, the model system iron/+ decanethiol (ndecylmercaptan, C,,H,,SH) has been investigated by AES and XPS. It is shown that the mercaptan binds to metallic clean iron surfaces through the sulphur atom, probably by cleavage of the S-H bond. The S 2p3,, peak has a binding energy of 162.4 f 0.2 eV. Anodic polarization and ageing in the laboratory atmosphere do not oxidize these chemisorbed molecules; the oxidation reactions of the substrate are suppressed too. After cyclovoltammetry (-1.0 V , , < U < + 0.6 VSH& better oriented chemisorbed molecules are packed more densely on top of the surface.

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half a monolayer (e' =0.5), corresponding to a c(2 x 2) structure (Fig. 4a) (Fig. 5a)

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Adsorption I Katalyse I ReaktionskinetikUsing a solid electrolyte cell inside an UHV-system the surface composition of oxides and metals can be studied at high temperatures 700 to 1OOO"C and well defined oxygen activities in the range po, = lo-'' to bar. AES-measurements on wustite have shown that at temperatures >8OO"C the composition of the surface shows the same change with the varied oxygen activity as would be expected for the bulk. At temperatures below 800 "C the change of surface oxygen content is larger than the change of bulk oxygen which indicates the presence of adsorbed oxygen. An adsorption isotherm obtained at 720°C shows that the degree of coverage 0 = 0.07 is approached near the

Presence of H2S in a carburizing atmosphere causes S‐adsorption which retards carbon transfer and deposition and can suppress metal dusting of iron and steels. In the latter process cementite Fe3C is an intermediate, graphite deposition would initiate its decomposition but graphite nucleation is prevented by adsorbed sulfur. Thus continued Fe3C growth can be observed in the presence of H2S. Thermogravimetric studies in CO‐H2‐H2O‐H2S mixtures have been conducted at 500°C at various carbon activities aC and H2S/H2‐ratios. With increasing aC higher H2S/H2‐ratios are needed to suppress metal dusting, with increasing H2S/H2‐ratio the kinetics of Fe3C growth change from diffusion controlled parabolic kinetics to linear carbon transfer controlled kinetics. At very high aC≥1000 besides Fe3C also the Hägg carbide Fe5C2 was observed as an outer layer on the cementite.

Layers of the oxides FeO, Fe30,, Fe203, Cr203 and M,03 were prepared by evaporation of the corresponding metal layers onto a preoxidized Si substrate and oxidation at elevated temperature. The oxidation was conducted under thermodynamically well-dehed conditions so that the pure oxide phases noted were obtained. The oxide layer thickness was calculated from the thickness of the initial metal film, which was determined by chemical analysis and from the frequency change of a quartz crystal upon evaporaton. Auger electron spectroscopy depth profiles of the oxide layers were measured during Ar+ sputtering, and the sputter time necessary to reach the interface oxide/substrate was determined. The determination of this sputter time was not very exact, because the transition from oxide to substrate in the profile was rather gradual, owing to the r o u g h and crystalline chracter of the oxide layers that causes inhomogeneous sputtering. However, from the sputter time, oxide thickness and ion beam current, the sputter rates were obtained for the oxides noted (in nm PA-' cm-2 min-I) and were compared to the sputter rate of amorphous Ta20,, which is generally wed as the sputter reference standard. Considerable differences were found. The results will lead to more reliable determinations of oxide scale thicknesses by sputtering.

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