Role of Unstable Chemical Species (Non-graphitic Carbon and Flowing NH_3 Gas) on the Equilibrium Point of the Reaction Product (Carbide, Carbo-nitride or Nitride)

摘要

Elementary carbon in solid state might exist in variety of allotropic forms including graphite, diamond and amorphous carbon. Among them, graphite is in the stable form with chemical carbon activity a(C) = 1 whereas diamond is in meta-stable state and amorphous carbon is in un-stable state with a(C) higher than 1. Experimental evidences showed that carbide and carbo-nitride being in equilibrium with carbon possessing a(C) higher than 1 was with higher C content than the corresponding ones in equilibrium with graphite. In case of gaseous ammonia NH_3, higher nitrogen activity a(N) and higher hydrogen activity a(H) than the ones corresponding to the equilibrium partial pressure levels, p(N_2) and p(H_2), might be gained by suppressing its dissociation to a level away from the equilibrium state for the given temperature T by flowing. Thus, under flowing NH_3 gas, nitride or carbo-nitride with N content higher than that in equilibrium with N_2 gas at p(N_2) anticipated from the dissociation equilibrium at the given T might be obtained. Chronological development of this line of work started by Prof. Masahiro Katsura in early seventies at Osaka University is reviewed in this paper as I was one of collaborators involved in this very exciting research work from the early stage of its development.