Heat of absorption of hydrogen in the α and β phases of zirconium

The differential heat of absorption of hydrogen in zirconium has been measured by means of isoperibol calorimetry in the range of hydrogen concentration 0-0.5 H/Zr at temperatures 873-1123 K. In the α phase the differential heat decreases with increasing hydrogen concentration except for an increase at very small concentrations but, in contrast, increases in the α+β and β phases, varying between 0.35 and 0.90 eV. Changes in the differential heat due to changes in elastic constants, lattice parameters and Fermi energy accompanying the absorption of hydrogen have been calculated and compared with the experimental result. The change in Fermi energy is a major contribution to the change in the differential heat. (author)