Graphite surface boundary layer controlled

Usually processes (1) and (5) are diffusion processes, and if these are rate controlling it may be expected that the temperature dependence of the reaction rate varies proportionally to T 4 where T is the absolute temperature. Surface reactions have activation energies of the order of 30 kcal. whereas diffusion processes have much smaller activation energies (53). Since the reaction produces only small quantities of reaction products the boundary layer of reaction products is small and will not limit the access of the reacting gas to the outer surface. These considerations make it likely that processes of the types (2), (3), or (4) are the slow steps in the oxidation of graphite. 

The non-diamond carbon phase in polycrystalline diamond films (often referred to as graphite, although this conclusion is far from accurate [23]) is first and foremost the disordered carbon in the intercrystallite boundaries. Their exposure to the film surface can be visualized by using a high-resolution SEM techniques [24] the intercrystallite boundaries thickness comes to a few nanometers. In addition to the intercrystallite boundaries, various defects in the diamond crystal lattice contribute to the non-diamond carbon phase, not to mention a thin (a few nanometers in thickness) amorphous carbon layer on top of diamond. This layer would form during the latest, poorly controlled stage of the diamond deposition process, when the gas phase activation has ceased. The non-diamond layer affects the diamond surface conduc-... 

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