Kinetics of hydrogen absorption in the intermetallic Zr(Al_0.2Fe_0.8)₂

The hydriding kinetics of Zr(Al_0.2Fe_0.8)₂ was studied at four different temperatures between 238 K and room temperature (298 K) and at an approximately constant pressure of 10 atm H₂. This compound is characterized by the largest hydrogen capacity in the Zr(Al_ξFe_1-ξ)₂ intermetallic system, which exhibits an interesting and anomalous hydriding behaviour. The experiments were carried out with thin intermetallic pieces of definite thickness in order to facilitate the data interpretation. Special precautions were taken during the slicing of the brittle compounds. Visual and metallographic examinations of partly hydrogenated compounds imply a contracting envelope type of hydrogenation. A simple mathematical analysis of the time-dependent hydrogen absorption curves yields the interface velocity μ of the advancing hydride. The derived values are approximately in the range 10^-3-5 × 10^-3 mm s^-1 for the investigated temperatures and pressure. An activation energy of about 0.14 eV (H atom)^-1 (27 kJ (mol H₂)^-1) was estimated for the hydrogenation process.