Dampfdruckmessungen und Protonenresonanzuntersuchung an Hydriden der intermetallischen Phasen Ti2(Ni, Co) und Ti2(Ni, Fe)

Abstract

NMR and hydrogen equilibrium pressure measurements were performed on hydrides of the intermetallic compounds Ti2(Ni, Co) and Ti2(Ni, Fe). The following values of enthalpy ΔH and entropy ΔS for the formation of the hydrides of the intermetallic phases Ti2Co and Ti2Ni were found: ΔH(Ti2CoH y )=−47.6 kJ/mol H2, ΔH(Ti2NiH y )=−53.7 kJ/mol H2; ΔS(Ti2CoH y )=−119.8 J/(K·mol H2), ΔS(Ti2NiH y )=−127.5 J/(K·mol H2). By substitution of Ni or Co by Fe, the values of ΔH and ΔS of the corresponding quaternary hydrides become less negative. An interpretation of the experimental results is tried by the model ofShaltiel and coworkers. Proton diffusion was investigated in a series of the intermetallic hydrides Ti2(Ni, Co)H x and Ti2(Ni, Fe)H x . The diffusion rate is lowered by increased Ni/Fe substitution. Substitution of Ni by Co scarcely effects the “hopping process”. The activation energies were found to be smaller for the Ti2Ni-hydrides compared with the Ti2Co-hydrides.