Oxide films linear rate constant

Ru" (0)(N40)]"+ oxidizes a variety of organic substrates such as alcohols, alkenes, THE, and saturated hydrocarbons. " In all cases [Ru (0)(N40)] " is reduced to [Ru (N40)(0H2)] ". The C— H deuterium isotope effects for the oxidation of cyclohexane, tetrahydrofuran, 2-propanol, and benzyl alcohol are 5.3, 6.0, 5.3, and 5.9 respectively, indicating the importance of C— H cleavage in the transitions state. For the oxidation of alcohols, a linear correlation is observed between log(rate constant) and the ionization potential of the alcohols. [Ru (0)(N40)] is also able to function as an electrocatalyst for the oxidation of alcohols. Using rotating disk voltammetry, the rate constant for the oxidation of benzyl alcohol by [Ru (0)(N40)] is found to be The Ru electrocatalyst remains active when immobilized inside Nafion films. 

In both of these equations, x is the film thickness, t is the time of the oxidation, and k and are experimentally determined constants. The constant fep is called the parabolic rate constant. A linear rate is usually found when the film is porous or cracked. The parabolic equation is found when the film forms a coherent, impenetrable layer. As the rate of film growth, dx/dt, diminishes with time for the parabolic rate law, this equation is associated with protective kinetics. The parabolic rate law arises when the reaction is controlled by diffusion. The species with the lowest diffusion coefficient plays the most important role in this case. 

The oxidation rate of (OOOl)C is 5-10 times higher than of (OOOl)Si in the temperature range 1000-1300°C in dry and wet hydrogen flow at 15 liters per minute (Fig. 5). The oxidation rate of other facets, for instance, (1120), has an intermediate value compared with 0001 facets. The oxidation process of the (0001)C facet is limited by diffusion of the reaction components through the growing oxide film. Hence the oxidation rate of this facet does not depend on the crystal surface treatment, type and level of doping, or polytype structure. The constants of the linear-parabolic equation for (0001)C oxidation are shown in Table 4. 

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