Mound growth particulates

Figure 12. Initial development of particulates between the mound growths. Methane exposure 406 torr h at 800°C.

The Development of Mound Growths. The mound carbon encapsulates the metal and prevents it from taking part in the reaction until particulate growth has caused substantial break-up of the bulk metal. Similar types of deposit have been reported in the Ni/C2H2 reaction at 990°C and Fe/CIfy system at 1100°C(19). A reduction in reactivity caused by encapsulation was reported for the Fe/CjHg deposition reaction(20)... 

Particulate and Filamentary Growth. It is implicit in the mechanism proposed above for carbon mound growth, that the crystalline particulates are nucleated at active sites within the metal. The evidence that further growth causes the particles to be ejected through laminar carbon overlayer is given in Figure 13c. 

The results of this in-situ SEM work suggest that solution-precipitation processes have some part in the development of four of the morphological types discussed, i.e. continuous laminar carbon films, mound growths, and two types of particulate material Although a small amount of filamentary carbon was observed, it does not appear to be a major characteristic of the Fe-CH4 reaction. 

The deposits formed on transition metals from hydrocarbons or carbon monoxide exhibit a variety of morphologies including graphitic laminar films, mound (monticular) growths, columnar, particulate, and numerous filamentary types of carbon, (1-4). The... 

Particulate Development Crystalline Particles. Particulate material is first detected in areas between the carbon mounds after lateral growth of the mounds has ceased, Figure 9b. Two types of particulate eventually develop, viz... 

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