THE EFFECT OF COPPER ON THE STRUCTURAL CHARACTERISTICS OF CARBON FILAMENTS PRODUCED FROM IRON-CATALYZED DECOMPOSITION OF ETHYLENE

Carbon filaments were produced by the decomposition of ethylene over u nsupported iron-copper powders in the presence of varying amounts of h ydrogen at temperatures ranging from 500 degrees C to 800 degrees C. T he structure and properties of the carbon filaments were found to be d ependent on a number of parameters including the composition of the ca talyst, the temperature and the percent of hydrogen in the reactant ga s mixture. Temperature programmed oxidation in CO2 of demineralized sa mples of carbon filaments indicated that the most stable structures we re those produced from a bimetallic catalyst containing a large fracti on of iron. The addition of hydrogen to the system also caused changes in the structure of the carbon filaments and this aspect was manifest ed by variations in the graphitic nature of the material. High resolut ion transmission electron microscopy examination indicated the presenc e of two distinct morphologies: one in which the filaments appeared to have smooth surfaces and where the graphite platelets were preferenti ally oriented at an angle with respect to the fiber axis; and a second type consisting of a tubular structure in which the graphite platelet s were aligned in a direction parallel to the axis of the fiber. Surfa ce areas of the carbon filaments, as determined by nitrogen adsorption at -196 degrees C, were also found to be dependent on the catalyst co mposition, the reaction temperature and the fraction of hydrogen in th e feed gas.