Thermal stability of crystalline and amorphous Zr 2PdH x

Abstract

The thermal stabilities and crystallization behavior of the metallic glasses have been extensively investigated. Furthermore, there has recently been considerable interest in the thermal stabilities of various crystalline ternary metal hydrides. Although the formation and properties of amorphous metal hydrides have become active research topics, relatively few studies have compared the thermal stabilities of crystalline and amorphous ternary hydrides. The most thorough investigations to date have involved the Ti-Cu hydrides where the glassy ternary hydrides decompose into TiH /SUB x/ -Cu metal mixtures at temperatures about 150 K lower than the corresponding decomposition for similar crystalline hydrides. Furthermore, differential thermal analysis indicates the crystallization/decomposition is exothermic for the amorphous a-TiCuH /SUB x/ but the decomposition of crystalline c-TiCuH /SUB x/ is strongly endothermic. Although the greatly enhanced hydrogen mobility in a-TiCuH /SUB 1.3/ relative to c-TiCuH /SUB 0.9/ may be responsible for the lower decomposition temperature for the amorphous hydride, the reasons for the distinctly different thermal character are unclear. Since both crystalline c-Zr/sub 2/Pd intermetallic and the glassy alloy a-Zr/sub 2/Pd readily form ternary hydride phases, the Zr/sub 2/PdH /SUB x/ system is an excellent candidate for comparisons between crystalline and amorphous hydride phases. Differential scanning calorimetry (DSC) andmore » powder x-ray diffraction (XRD) have been used to study the phase transitions and decompositions of the a-Zr/sub 2/Pd alloy, a-Zr/sub 2/PdH /SUB 2.9/, and several crystalline C-Zr/sub 2/ PDH /SUB x/ compositions.« less