Thermodynamic Analysis of AB2 Hydrides: ZrCr1-xTixNiMo0.3 Alloys

Abstract

A thermodynamic analysis was performed on the role of titanium substitution in ZrCr1-xTixNiMo0.3 (Ti; x = 0.3, 0.5, 0.7) AB2 type alloys. The hysteresis in hydride/deshydruration processes was calculated from electrochemical isotherms as a dimensionless parameter related to yield strengths and hydrogen partial molar volumes. Zr0.7Ti0.3Cr0.7Mo0.3Ni samples exhibited large hysteresis, i.e. 1.6, but the lowest hydrogen molar volume (2.19 cm3 mol−1) and the greater yield strength (10.0 × 106 N cm−2). Thus, the amount of titanium has to be carefully dosed to avoid large fractures and low hydrogen dosages. The multiphase formation was explained by Pm-3m and Im-3m space groups, the first one describing TiNi phase and the second one CrMo phase segregation. A brief evaluation of the thermodynamic works and non-compensated heats was also conducted. On one hand, the largest maximum and real work were obtained from Zr0.7Ti0.3Cr0.7Mo0.3Ni, between 700 and 800 J g−1, although TiNi dissipates the lowest irreversible heat, −1 J, for attaining only half of the ideal and real works, between ca. 370 and 400 J g−1. In summary, the presence of low amounts of titanium as those in Zr0.7Ti0.3Cr0.7Mo0.3Ni alloys balance well the electrochemical hydruration process with the mechanical and thermodynamic stability.