FURTHER-STUDIES OF THE FORMATION OF FILAMENTOUS CARBON FROM THE INTERACTION OF SUPPORTED IRON PARTICLES WITH ACETYLENE

gamma -iron to exhibits a higher intrinsic activity than alpha -iron for this reaction when the metal was supported on graphite. In both systems, catalytic action decreased at temperatures in excess of 700 degree C. Major changes were observed in the catalytic behavior of the metal particles when they were supported on silica. The rate of formation of carbon filaments from the alpha -iron/silica system showed a uniform increase up to 900 degree C. Mossbauer spectroscopy analysis revealed that alpha -iron was the only metallic phase present, even though experiments were conducted through a temperature region where the transformation of alpha -iron to gamma -iron can occur, suggesting that silica stabilizes the alpha -form of iron. In contrast, the catalytic activity displayed by gamma -iron particles supported on silica was reduced over that found for the graphite supported system. The results are discussed in terms of factors controlling the growth characteristics of filamentous carbon.