Analysis of Structure and P-c-T Curves for Hydrogen in TiZrNi-based Quasicrystals

Abstract

It is known that Ti-based quasicrystals absorb a significant amount of hydrogen because of their structural and chemical characteristics. In fact, the density of hydrogen in quasicrystals made with Ti, Zr and Ni is higher than that of it in a liquid state. The practical application of hydrogenated quasicrystals can be evaluated by measuring an equilibrium vapor pressure at constant temperature, called a P-c-T (Pressure-composition-Temperature) curve. However, the equilibrium vapor pressures of hydrogen in TiZrNi quasicrystals are too low (less than 1 Torr) for hydrogen storage materials. To overcome this barrier, I replaced Zr by Pd to the limit maintaining the quasicrystal structure (Ti53Zr27-xNi20Pdx, where 0 ≤ x ≤ 8) and investigated the thermodynamic properties of hydrogenated samples. The results of X-ray diffraction data (XRD) revealed that rapidly quenched Ti53Zr27-xNi20Pdx metallic ribbons contain pure quasicrystal phase to the maximum value of x=8. After hydrogenation, the quasi-lattice constants increased from 5.12 to 5.34Å, for x=0 and 8, respectively. A combined analysis of XRD data and selected area diffraction patterns of TEM demonstrated that the quasicrystal phase maintained after hydrogenation. The equilibrium vapor pressures measured at H/M (hydrogen to host metal atom ratio) values of 0.5 significantly increased from 0.41 to 3.41 Torr for x=0 and x=8, respectively, suggesting that Pd played a role to increase the vapor pressure of hydrogen. In addition, the potential application of TiZrNi quasicrytals was evaluated by measuring an electrochemical method. I hydrogenated the Ti53Zr27-xNi20Pdx and Ti53-xZr27-xNi20Vx quasicrystals by electrochemical method, and found that the method can store hydrogen without a phase transition in 24 hours at room temperature. This method provides higher number of H/M values and does not require Pd coating which is necessity for the gas phase loading technique.