THERMODYNAMIC PROPERTIES OF THE ZR0.8TI0.2(MNXCR1-X)FE-H2 SYSTEM

The effects of the substitution of chromium by manganese in Zr0.8Ti0.2(Mn(x)Cr1-x)Fe Laves phase alloys on the pressure-composition-isotherm P-C-T) relations, especially on the plateau slopes and hysteresis, were systematically investigated by P-C-T measurements. There is no dependence of the hydrogen storage capacity on composition as manganese is substituted for chromium. Increasing manganese substitution increases the extent of hysteresis but decreases the degree of the plateau slopes as well as the hydride stability. This is caused by the more sensitive change in the equilibrium pressures for hydride formation than for hydride decomposition in the two-phase region as the alloy composition x varies. It is suggested from the above results that the compositional dependence of the P-C-T relations of the Zr0.8Ti0.2(Mn(x)Cr1-x)Fe-H-2 system originates from the difference in nature of the hysteresis behavior between ZrMn2-type and ZrCr2-type Laves phase alloy systems, since the hysteresis energies show a drastic change around x = 0.5. The difference in hysteresis nature is probably related to the difference in mechanical properties of the alloy itself, i.e. between ZrCr2-type and ZrMn2-type Laves phases.