TiZrNi 준결정체와 중기공성 실리카 물질의 수소 흡방출에 따른 구조와 물리적 특성

Abstract

The TiZrNi alloys were prepared by using three different techniques, an arc-melting, a rapid quenching, and a suction casting method. Ti53Zr27Ni20 alloy, produced by rapid quenching, showed a pure quasicrystal structure, and its coherence lengths increased after hydrogen absorption from 180 to 260 Å, which demonstrates that quasi-crystallinity was improved by hydrogen absorption. The hydrogen desorption temperature for Ti53Zr27Ni20 quasicrystals was 200~450 C. For the Ti53-XZr27Ni20PdX alloys, the quasicrystal structure was maintained as increasing the value of X from 0 to 10 at. %. For the Ti53-YZr27Ni20VY, 12 at. % of Y was the maximum V concentration to maintain the quasicrystal structure. As the Pd and V concentrations increased up to 10 and 12 at. %, respectively, the quasi-lattice constant decreased from 5.12 to 5.09 and 5.08 Å, respectively. The decrement in the quasi-lattice constant was caused by the smaller atomic radii of Pd (1.37 Å) and V (1.34 Å) compared to Ti (1.47 Å). By measuring the pressure–composition–temperature (P–c–T) curves from quasicrystal samples of Ti53Zr27Ni20, Ti45Zr27Ni20Pd8, and Ti45Zr27Ni20V8 alloys at 300 C, the maximum H/M values were found to be 1.33, 1.06, and 1.12, respectively. The equilibrium vapor pressures for Pd added samples were higher than that of V added samples. Measurements of the M-H curves for Ti53Zr27Ni20 quasicrystals and hydrogen-absorbed Ti53Zr27Ni20 quasicrystals with H/M=0.99 show that the magnetization value was 0.383 emu/g at 10000 Gauss, and the value was decreased to 0.242 emu/g after hydrogen absorption. This decrement in magnetization was caused by volume expansion of samples after hydrogen absorption. For the (Ti53Zr27Ni20)100-ZAgZ quasicrystals, the coherence lengths of the samples increased from 100 to 153 Å as the Z of Ag concentration increased from 0 to 4 at. %. The specific resistance value for Z=0 was 292 μΩ∙cm, and decreased to 275 μΩ∙cm as increasing the Ag concentration to 4 at. %. The cause of the decrease in resistance was confirmed by measuring the Hall effect. The product of carrier concentration and Hall mobility increased from 1.63  1019 to 3.87  1019 /cmVs as the Ag concentration increased from 0 to 4 at. %. For the hydrogenated Ti53Zr27Ni20 quasicrystals, the electrical resistance values decreased from 1.70 to 1.11 Ω as increasing H/M value from 0 to 1.33. The maximum H/M value of the Ti53Zr27Ni20 quasicrystal was estimated to be 1.79 under hydrogen pressure of 6813 Torr at room temperature. This H/M value corresponds to 2.93 wt. %. The hydrogen capacity increased to 4.10 wt. % (H/M=2.52) as the initial hydrogen pressure increased to 5.07 GPa by using a diamond anvil cell. The Ti53Zr27Ni20 quasicrystal shows no structural changes at the maximum of 5.07 GPa. Ti and Pd doped SBA-15 samples were prepared using a direct synthesis method. By analyzing the XRD patterns and TEM morphologies, the hexagonal-array structure degenerated with increasing Ti doping concentration. The structure of Pd doped SBA-15 was maintained with increasing Pd concentration up to 5.0 of PdCl2/TEOS. The surface area of SBA-15 was estimated by measuring the nitrogen adsorption curve at 77.3 K and the value was 620 m2/g. The number of absorbed hydrogen for the SBA-15 at 77.3 K was estimated to be 0.49 wt. %, and the value increased to 0.99 wt. % as increasing the PdCl2/TEOS ratio from 0 to 0.5.