Production of Low-Cost TiNbFe Alloys from the Elemental Powders of NbFe Pre-Alloy and Their Hydrogenation Features

Abstract

TiNb-based alloys with prevailing β-phase and BCC crystal structure are currently being investigated as hydrogen storage materials due to their relatively high absorption capacities that can be reached at moderate temperatures. In this paper, low cost TiNbFe alloys were prepared by arc melting starting from the elemental powders of the pre-alloy Nb_68.1Fe_30.4 with the addition of pure Ti following the proportion of Nb_68.1Fe_30.4 + X wt% Ti (X = 23, 33, 41, 47). The crystal structure including the phase’s evolution and absorption kinetics at 30°C were evaluated in detail as a function of Ti addition. XRD results in combination with SEM observations showed the presence of β-phase (Nb-rich) with a BCC type-structure in all compositions beyond that TiFe, NbFe and α (Ti-rich) phases. After a simple activation step, the samples containing 41 and 47 wt% of Ti showed very fast absorption kinetics at 30°C but with different hydrogen storage capacities of 1.95 and 1.37 wt% of H₂, respectively. Upon hydrogenation, the β-BCC phase is partially converted into FCC hydride TiH_1.9−X beyond that TiFeH_X and NbH_X hydrides. These hydrides resulted in different steps of decomposition as indicated by the DSC curves. The current study confirmed the significance of TiNbFe alloys for hydrogen storage applications at low temperatures.

Fig. 4 Absorption kinetics curves at 30°C under 20 bar of hydrogen pressure for the samples of Nb_68.1Fe_30.4 with 41 wt% and 47 wt% of Ti.