1.Fe/Co Alloys for the Catalytic Chemical Vapor Deposition Synthesis of Single-and Double-Walled Carbon Nanotubes(CNTs).2.The CNT-Fe/Co-MgAl_2O_4 System

摘要

A detailed ~(57)Fe Mossbauer study of the Mg_(0.8)Fe_(0.2-y)Co_yAl_2O_4(y = 0,0.05,0.1,0.15,0.2)solid solutions and of the CNT-Fe/Co-MgAl_2O_4 nanocomposite powders prepared by reduction in H_2-CH_4 has allowed characterization of the different iron phases involved in the catalytic process of carbon nanotube(CNT)formation and to correlate these results with the carbon and CNT contents.The oxide precursors consist of defective spinels of general formulas(Mg_(1-x-y)Fe_(x-3alpha)~(2+)Fe_(2alpha)~(3+)square_(alpha)Co_y~(2+)Al_2~(3+))O_4~(2-).The metallic phase in the CNT-Fe/Co-MgAl_2O_4 nanocomposite powders is mostly in the form of the ferromagnetic a-Fe/Co alloy with the desired composition.For high iron initial proportions,the additional formation of Fe_3C and gamma-Fe-C is observed while for high cobalt initial proportions,the additional formation of a gamma-Fe/Co-C phase is favored.The higher yield of CNTs is observed for postreaction alpha-Fe_(0.50)Co_(0.50)catalytic particles,which form no carbide and have a narrow size distribution.Alloying is beneficial for this system with respect to the formation of CNTs.