## Electronic Theses and Dissertations

1989

Doctoral Thesis

Ph.D.

#### Department

Mechanical, Automotive, and Materials Engineering

#### Keywords

Engineering, Materials Science.

#### Rights

info:eu-repo/semantics/openAccess

Zr(Fe$\sb{\rm x}$Cr$\sb{\rm 1-x}$)$\sb2$ (x = 0.5-0.8) alloys are promising hydride forming materials with various applications. Pressure-composition isotherms for Zr(Fe$\sb{\rm x}$Cr$\sb{\rm 1-x}$)$\sb2$-hydrogen systems are determined over temperature range 283.2 to 352.2 K in a accurate Sieverts'-type apparatus developed for this investigation. Pronounced hysteresis and sloping plateaus are observed. The degree of hysteresis decreases with increasing temperature, increases with Fe substitution for Cr and increases when determined with small aliquots. Hysteresis and sloping plateaus are reduced during the first few cycles of hydriding and dehydriding and they increase after the sample is exposed to air. The hysteresis factors, $1\over2$RTlnP$\sb{\rm f}$/P$\sb{\rm d}$, range from 217 J/mol H for x = 0.5 at 343.2 K to 1169 J/mol H for x = 0.8 at 283.2 K. The plateau slopes, d(lnP)/(H/M), are about 0.9 for hydride formation and range from 0.5 to 1.1 for hydride decomposition. Hysteresis and sloping plateaus have important effects on the application of hydride forming materials. A comprehensive and critical literature review reveals the complexity of hysteresis and sloping plateaus in metal-hydrogen systems and the existing theoretical models seem not to be adequate to explain the experimentally observed behavior. A model is proposed to identify the nature and origin(s) of hysteresis and sloping plateaus in metal-hydrogen systems, and the effects of temperature, composition, aliquot size, cycling, annealing and particle size are explained. In general, both elastic and plastic accommodation energies in both hydride formation and decomposition contribute to hysteresis and affect plateau slopes. For soft materials with ideal plastic behavior the elastic energy after plastic relaxation is small and the plastic energy is the major cause of hysteresis. For highly strain-hardening materials and brittle materials (most intermetallic compounds including Zr(Fe$\sb{\rm x}$Cr$\sb{\rm 1-x}$)$\sb2$), the elastic component dominates the total accommodation energy and hysteresis is primarily a consequence of the elastic strain energy. Source: Dissertation Abstracts International, Volume: 50-08, Section: B, page: 3648. Thesis (Ph.D.)--University of Windsor (Canada), 1989.