An Electrical Resistivity Study on Hydrogen Absorption and Structural Change in Glassy Alloys

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Titanium and zirconium-based alloy glasses absord a large quantity of hydrogen and show P-C-T characteristics varying considerably according to the species and compositions of the alloying elements. The objective of the present research is to study the absorption-desorption behavior of hydrogen in Zr-Ni and Zr-Pd alloy glasses by electrical resistivity measurements as well as to clarify the crystallizing process in the hydrogenated glasses. A computer-controlled apparatus for the resistivity measuredments has been constructed. This enables us to hydrogenate a ribbon sample in a gas phase of 5MPa between 300K and 500K, and measure the resistivity in situ between 10K and 1000K. Resistivity changes during hydriding at 423K and 493K and subsequent dehydriding at higher temperatures have been measured for Zr_<67>Ni_<33> and Zr_<50>Ni_<50> alloy glasses. Both samples showed characteristic variations of the resistivity against the hydrogen content. Upon heating above 500K, Zr_<67>Ni_<33>H_x decomposed into ZrH_2 and Zr-Ni compounds, whereas Zr_<50>Ni_<50>H_x crystallized to ZrNi compound by releasing hydrogen prior to the crystallization. This behavior was confirmed by X-ray diffraction analysis.In addition to the above work, soft X-ray and photoemission studies have been carried out for Ti and Zr-based glassy alloys containing Fe, Ni and Pd. The results showed that hydrogen atoms preferentially combine with Zr or Ti atoms in these glasses to form chemical bonding. This effect is important to characterize the thermal stability of hydrogen in the metallic glasses.