Activation of Ti-Fe-Cr alloys containing identical AB2 fractions

Activation of Ti-Fe-Cr alloys containing identical AB2 fractions
조영환서진유심재혁이영수홍지현무함마드 파이살이상인김하영김한진정지윤김도향
Hydrogen storage; TiFe alloy; Laves phase; Activation
Issue Date
Journal of alloys and compounds
VOL 864, 158876
TiFe-based alloys are solid-state hydrogen storage materials operated at room temperature (RT). The current study presents a systematic approach for solving the activation issue (difficulty in the first hydrogenation), one of the major obstacles to the practical application of TiFe alloys, via the use of a secondary AB2 phase. Based on the Ti?Fe?Cr ternary phase diagram, Ti?Fe?Cr alloys containing 80 at% Ti(Fe,Cr) (AB phase) and 20 at% Ti(Fe,Cr)2 (AB2 phase) were designed; the Cr concentrations in the AB and AB2 phase were systematically varied while maintaining fixed phase fractions. Activation at RT was achieved when the overall Cr concentration was higher than 9.7 at%. Analysis of the activation characteristics of the individual phases revealed that the AB2 phase readily absorbed hydrogen, thereby initiating activation of AB + AB2 alloys. Notably, higher Cr concentrations enable the AB phase to absorb hydrogen at RT during the activation process, although the kinetics are much slower than that of the co-existing AB2 phase. The equilibrium hydrogen pressures from the pressure-composition isotherms decrease as the Cr concentration increases, indicating that Cr stabilizes hydrides. Increased hydride stability may also promote the kinetics of the initial hydride formation in both the AB and AB2 phases. An optimal composition for Ti?Fe?Cr alloys can be designed given the conditions of easy activation at RT and maximum reversible capacity within an operating pressure range.
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