Q2. What is the driving force for filament growth?
The driving force for filament growth is a gradient in the carbon content of nonstoichiometric carbides, decreasing in the direction to the metal-carbon interface.
Q3. What is the reason why the fast decarburization of iron films was observed at 569?
They attributed the observed fast decarburization after carburization at 569 K to the presence of the less stable E-carbide, whereas the 8- or x-carbides precipitating above 573 K exhibited a drastically decreased rate of decarburization owing to their higher stability.
Q4. What is the effect of the carburizing of nickel catalysts?
It was concluded that carburizing of nickel catalysts with methane at temperatures up to 573 K results in the formation of a surface carbide only.
Q5. At what temperature did the trigonal prismatic carbide decompose?
Also cementite was formed, but this carbide proved to be stable against decomposition and even against hydrogenation at temperatures where extensive filament growth was observed.
Q6. What is the main reason for the transport of carbon through the metal?
The transport of carbon atoms through the metal (carbide) particle may be explained by assuming the carbon content of the substoichiometric carbide to be highest at the metal-gas interface, and lowest at the metal-carbon interface, leading to transport in the direction of the metal-carbon interface.
Q7. What is the temperature dependence of nickel?
The temperature dependencecan be appreciated by realizing that the number of metal particles involved in fragmentation increases with rising temperature, due to the increase of the nucleation rate.
Q8. What is the reason why the authors observed no formation of FeS04?
As under their experimental conditions also no formation of FeS04 was observed, the authors conclude that all magnetization changes observed can be attributed to the formation and decomposition of carbides.
Q9. What is the reason for the increase in magnetization at temperatures above 573 K?
Turning to their TMA experiments, it should be noted that an increase in magnetization at temperatures above 573 K might also be ascribed to decomposition of theparamagnetic FeO.
Q10. What is the role of a carbide intermediate in filament growth?
whereas the involvement of 0-Fe3C can be definitively ruled out.(iv) Carbon filaments grow by a continuous decomposition of a metastable carbide intermediate.
Q11. What was the temperature at which the catalyst was kept prior to the magnetic measurements?
They adsorbed a great variety of hydrocarbons a 196 K, and performed saturation magnetization measurements varying the “holding temperature,” i.e., the temperature at which the catalyst was kept prior to the magnetic measurements.
Q12. What is the definition of induction period?
Induction periods can thus be interpreted as the time needed for both the formation of a carbide phase of high carbon content and the incubation time (40) associated with the decomposition of this phase.