Investigation of Formation, Stability, Structure and Hydrogen Storage Properties of Ti-Quasicrystals and Related Crystalline Phases

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9705202 Kelton The atomic structures of titanium-based quasicrystals and related phases, the formability of the quasicrystal and crystal approximants, the role of impurities in phase formation, and the nature of the phase transitions connecting the quasicrystal and the crystal approximants, are as yet poorly understood. Pursuing successes under the past grant period, these points are explored in titanium and zirconium-based quasicrystals and related crystal phases. Subjects include: (1) the investigation of the role of interstitial impurities on icosahedral phase formation; (2) the hydrogenation characteristics of quasicrystals, related crystalline and amorphous phases, and the hydrogen/quasicrystal phase diagram and pressure/composition isotherms; (3) X-ray and neutron diffraction to determine the atomic decoration of stable crystal approximants in TiZrTM alloys; (4) investigations of the sequence of phase formation in TiCrSiO, TiZrNi, and TiZrFe alloys; and (5) the nature of the phase transitions between the stable icosahedral-phase and the rational approximant phases in TiZrNi alloys. Several collaborations are underway, including studies of phase formation aided by drop-tube experiments in collaboration with Cambridge University, UK; the stabilizing role of impurities by magnetic susceptibility measurements in collaboration with scientists at Washington University; neutron scattering studies of hydrogenated (and deuterated) quasicrystals in collaboration with Missouri University Research Reactor (MURR), and Saclay, France; NMR studies of samples with Knox College, IL. The elastic neutron scattering and NMR studies lead to a better understanding of the distribution, symmetry and chemistry of the hydrogen containing sites in the TiZrNi quasicrystals. These data will be used to refine quasicrystal models constructed from determined structures for the crystal approximant phases. Inelastic neutron and NMR studies allow estimates to be made to hydrogen diffusion rates in the quasicrystal. %%% This research provides fundamental knowledge related to the potential for quasicrystal alloys to function as hydrogen storage materials. ***