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We describe the first experimental study of the molecular structure of the self-assembled monolayer of CH&H*)&H formed on the Ag(ll1) surface. Using both low-energy He diffraction and grazing incidence X-ray diffraction, we show that the monolayer formed on Ag is both incommensurate and rotated with respect to the Ag lattice, with a lattice spacing which is very similar to n-alkane chains in bulk hydrocarbon crystals. Lastly, by comparing the results of the X-ray and He diffraction experiments on the same sample, we observe that the outermost surface of the monolayer is less ordered than the interior.

In high‐temperature solid oxide fuel cells where natural gas is used as a fuel, high‐carbon‐activity environments can be encountered in the anode compartment. Under these conditions, nickel could corrode by a process known as metal dusting. In the present study, metal dusting corrosion of pure nickel is simulated in high‐carbon‐activity environments at temperatures between 350 and 1050°C. The focus of this research is to understand reaction mechanisms by characterizing interfacial processes at the nanometer level. Nickel corrodes by a combination of carbon diffusion and precipitation in the bulk metal and atom migration through surface carbon deposits. The nature of the carbon deposit is important in the overall corrosion process. At lower temperatures closer to about 350°C, nickel forms a carbide. Ni3C , which is rather stable and does not decompose. © 2000 The Electrochemical Society. All rights reserved.

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Metal dusting is a severe form of corrosive degradation that Fe, Co, and Ni base high-temperature alloys undergo when subjected to environments supersaturated with carbon (a c Ͼ 1). This corrosion process leads to the break-up of bulk metal into metal powder. The present study focuses on the fundamental understanding of the corrosion of Fe in carbon-supersaturated environments over the temperature range 350-1050°C. Building on earlier research, the role of deposited carbon in triggering corrosion is further clarified. The corrosion rate peaks at ϳ575°C with a sharp decrease in rate on either side of the maximum. High-resolution electron microscopy reveals, in addition to metal particles, a mixture of graphitic carbon, amorphous carbon, and filamentous carbon in the corrosion product. While the presence of a surface layer of Fe 3 C is characteristic of corrosion up to 850°C, such a layer is absent at the higher temperatures. The focus of this research is to understand reaction mechanisms by characterizing interfacial processes at the nano level.Metal dusting involves the disintegration of bulk metals and alloys into metal particles at high temperatures in environments that are supersaturated with carbon. It is generally believed that the phenomenon is most widespread in the temperature range 400-700°C. Hochman 1-3 did early research on metal dusting. Since then Grabke and co-workers 4-10 have carried out some detailed studies on the subject. Pippel et al. 11 and Chun et al. 12,13 have looked into the micromechanistic aspects of metal dusting by transmission electron microscopy ͑TEM͒. In most of this work carbon monoxide has been used as the main carbon-providing molecule. Metal dusting in the presence of methane and at higher temperatures has been addressed by Forseth and Kofstad. 14 It appears that CO is the most potent metal dusting molecule and the presence of hydrogen in carbon monoxide tends to accelerate metal dusting corrosion. When considering metal dusting corrosion in CO or CH 4 -containing environments, the following reactions can lead to the transfer of carbon to the metal surface CO ϩ H 2 ϭ C ϩ H 2 O ͓1͔2CO ϭ C ϩ CO 2 ͓2͔CH 4 ϭ C ϩ 2H 2 ͓3͔

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