Oxide-free carbon surfaces

Consider, for example, a carbon surface burning in a concentration of oxygen in the free stream specified by pmox. The burning is at a steady mass rate. Then the concentration of oxygen at the surface is some value mos. If the surface oxidation rate follows first-order kinetics, as Frank-Kamenetskii [21] assumed,... 

If the surface oxidation inferred from the inequality of the component peaks of the 0ls levels is attributable to surface carbonyl features then this should also be manifest in the carbon Is levels. It should, however, be emphasized that since the escape depth depth dependence for photoemitted electrons in the energy range considered is such that the mean free path increases with increasing kinetic energy then any surface feature will be relatively more prominent for the more tightly bound 0ls levels than for the Cl5 levels. A detailed examination of the spectra... 

The surface chemical composition of InP as a function of thermal cleaning temperature was studied by Cheng, et al. (19), also using AES. They used an arsenic molecular beam and temperature of about 500 C to clean a freshly oxide passivated InP. The surface oxides are replaced by arsenic oxides which then vaporize at these temperatures. An atomically flat and carbon contamination free surface was obtained, as monitored in situ with AES and RHEED OJ). 

Vinogradov has pointed out that with the appearance of the biosphere somewhere on the verge of 3-10 yr ago, there was a major upheaval in the evolution of the Earth. Oxidizing processes were abruptly accelerated, a nitrogen atmosphere arose in which carbon dioxide predominated over methane, and free carbon was oxidized to CO2. After the carbon was oxidized or at the same time as that process, there began oxidation of divalent iron (at — 10 ), which led to subsequent wholesale deposition of the sediments of the Precambrian BIF. Free carbon in equilibrium with the atmosphere appeared only after complete oxidation of ferrous iron compounds in the hydrosphere and on the land surface. 

As is seen from the data in Table 4, upon treatment of the carbon surface with hydrogen, the value of its free surface energy sharply decreases. This agrees with the notion that such a treatment results in a decrease in the surface concentration of oxidized carbon atoms that form hydrogen-bonded complexes with water molecules. Besides, a sharp decrease in the concentration of water in the adsorbent micropores is also observed. This effect can be explained by lower accessibility of micropores for water molecules caused by deteriorating hydrophilic properties of the adsorbent surface. When a carbon surface is treated with hydrogen peroxide, we observe an increase in the bound water concentration at the expense of the creation of new oxidized sites that would form hydrogen-bonded complexes with water molecules. 

A summary is made of the general classes of phenomena which can influence the reactivity of functional groups at heterogeneous interfaces, and potential pitfalls are pointed out in the reliance upon molecular analogy. Experimental results are reviewed pertaining to the thermodynamic and kinetic encounter frequencies of reagents on crosslinked polystyrenes and the chemisorption of olefins on oxide-free surfaces of elemental carbon. 

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