Thermodynamic Analysis of AB₂ Hydrides: ZrCr_1-xTi_xNiMo_0.3 Alloys

Abstract

A thermodynamic analysis was performed on the role of titanium substitution in ZrCr 1-x Ti x NiMo 0.3 (Ti; x = 0.3, 0.5, 0.7) AB 2 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. Zr 0.7 Ti 0.3 Cr 0.7 Mo 0.3 Ni samples exhibited large hysteresis, i.e. 1.6, but the lowest hydrogen molar volume (2.19 cm 3 mol −1 ) and the greater yield strength (10.0 × 10 6 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 Zr 0.7 Ti 0.3 Cr 0.7 Mo 0.3 Ni, 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 Zr 0.7 Ti 0.3 Cr 0.7 Mo 0.3 Ni alloys balance well the electrochemical hydruration process with the mechanical and thermodynamic stability.

Study on Hydrogen Storage Properties, Anti-Oxide Ability and Rate Limiting Step of ZrCr-Based Alloy after Introducing Cobalt as Additive

“…We directly carried out the first hydrogen absorption process under mild experimental conditions. Table 2 shows the conditions needed before the first hydrogenation of different Zr-Cr alloys in previous studies [8,10,14,[16][17][18][19]26,30,[32][33][34]. The high temperature (573∼850 K) and prior hydrogen exposure (∼3 MPa) were needed to activate the Zr-Cr alloys in most previous studies.…”

“…Thus, one way to apply this alloy in practical applications is to make its first hydrogenation process possible under mild conditions. The other way is to reduce the stability of its hydrides [7][8][9][10].…”

“…In order to further improve the hydrogen storage properties and reduce the stability of hydrides, various elements including Mn, Fe, Co, Ni, Cu, Si, Ge have been introduced to ZrCr 2 alloy [8][9][10][11][12][13][14][15]. In the earliest days, Drasner et al [16] conducted in-depth research on Zr-Cr system hydrogen storage alloys.…”