Carbon sticking coefficient

Very recently, considerable effort has been devoted to the simulation of the oscillatory behavior which has been observed experimentally in various surface reactions. So far, the most studied reaction is the catalytic oxidation of carbon monoxide, where it is well known that oscillations are coupled to reversible reconstructions of the surface via structure-sensitive sticking coefficients of the reactants. A careful evaluation of the simulation results is necessary in order to ensure that oscillations remain in the thermodynamic limit. The roles of surface diffusion of the reactants versus direct adsorption from the gas phase, at the onset of selforganization and synchronized behavior, is a topic which merits further investigation. 

This effect can be explained by a desorption of N2 from the surface, the sticking coefficient of this element being smaller than that of carbon, while,... 

The calculation of Rero, and therefore also of reg, contains quite some uncertainties. Knowledge about the local plasma parameters, erosion yields and sticking coefficients is required [39]. A possible mix of different erosion mechanisms and a surface layer composition with different materials adds some complexity to the problem. However, the extreme case of erosion mentioned above with a layer of 4.5 m eroded per year is unrealistic, since it is only valid for Rep = 0 or Rero = oo. Instead, experiments indicate that Rero does not deviate very much from unity. Indeed, with values typical for carbon, namely S = 0.75, Yr = 0.015, Yj = 0.02-0.5, c = 0.01-0.03, we obtain Rero in the range of Rero = 0.7-2.7. 

The evaluation of the cavity deposition for the three different regimes of chemical erosion has resulted in the finding, that apart from the emission of volatile hydrocarbons at elevated temperature and physical sputtering of carbon atoms at high energies, predominantly species with sticking coefficients around 0.02 are produced. A summary of results is given in Table 9.1. 

Recent studies of the activation of methane on nickel have given evidence that the activation barrier for methane is caused by the energy required to deform the methane molecule in order to bring the carbon atom sufficiently close to the surface to form a Ni-C bond ( splash and haaner chemistry"). A translational activation barrier 1 to be expected from the effective medium theory which predicts no effect of electronic promoters on the activation of the syimetric methane molecule. This is supported by the observation that potassium has no effect on the sticking coefficient of methane on a Hi(111) surface. 

In an high-vacuum chamber, the partial pressure of carbon monoxide is zz 10 Pa (25 °C). By assuming a sticking coefficient of 0.5, calculate the time needed to form an monolayer of adsorbed CO. The number of adsorption sites is lO ... 

The precoverage of the surface of elemental metals by contaminants like oxygen, sulphur, carbon (SO2, CO) degrades their H adsorption, absorption and desorption properties drastically. The contamination can interfere in different steps in the sorption process The contaminating species themselves are chemisorbed, induce reconstruction and alter the electronic properties and the phonon spectra of the substrate surface. Thus sticking coefficient, chemisorption energy, vibrational properties and surface mobility of H2 and H are affected and dissociation and recombination are often made impossible. 

Zhou Y-G, Rees NV, Compton RG (2011) Electrode-nanoparticle collisions the measurement of the sticking coefficient of silver nanoparticles on a glassy carbon electrode. Chem Phys Lett 514 291-293... 

Differences in the frictional properties of most plastics can be explained in terms of the ratio of shear strenghth to hardness. Shooter and Tabor observed that the coefficients of friction for polytetrafluoroethylene are 2—3 times lower than anticipated by this calculation. It is believed that this discrepancy is caused by the inherently low cohesive forces between adjacent polymer chains and is responsible for the absence of stick-slip. The large fluorine atoms effectively screen the large carbon-fluorine dipole, reducing molecular cohesion so that the shear force at the interface is low. The shear strength of the bulk material is higher because of interlocking molecular chains. 

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