Thermodynamics and Kinetics Analysis of Hydrogen Absorption by Zr0.8Ti0.2Co Alloy

The ZrCo-based alloy is considered one of the most promising materials for hydrogen isotope storage in the conceptual design of a fusion reactor. However, there are few systematic studies on the thermodynamic and kinetic models of hydrogen absorption in the new Zr0.8Ti0.2Co alloy. The aim of this study is to computationally derive the general mathematical equations for the thermodynamics and kinetics of hydrogen absorption by Zr0.8Ti0.2Co. In order to obtain the thermodynamic and kinetic data quickly, a constant-flow hydrogen absorption test was used in this study. The thermodynamic performance test revealed that the Zr0.8Ti0.2Co hydrogen absorption transition process was switched from ZrCo to ZrCoHx (metastable phase) and then to ZrCoH3 with an enthalpy of hydrogenation (& UDelta;H) of 66.59 kJ & BULL;mol(-1) H-2, which was obviously lower than that of the ZrCo-based alloy due to the metastable phase.A mathematical model of the hydrogen absorption coupled with the kinetic equations was established by kinetic process analysis. The hydrogen absorption process was divided into two stages, and the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model could fit the two stages of the Zr0.8Ti0.2Co hydrogen absorption well. In the first stage, the JMAK index was n(1) = 1.04, activation energy Ea(1) = 7594.6 J/mol, and rate coefficient of reaction k(01) = 1.958E-4 s(-1). While in the second stage, it was n(2) = 1.39, Ea(2) = 5221 J/mol, and k(02) = 9.938E-5 s(-1). Based on the range of n values, it can be inferred that both the nucleation and growth mechanisms or the diffusion mechanism were expressed as the rate-limiting steps. Combined with the simulation software, metal hydride bed performance could be better investigated and the structural design could be guided by the obtained mathematical equation of Zr0.8Ti0.2Co hydriding.

Automated summary

The aim of this study is to derive mathematical equations for the thermodynamics and kinetics of hydrogen absorption by Zr0.8Ti0.2Co. The results showed that the hydrogen absorption process can be divided into two stages, and the JMAK model fits well for both stages. The obtained mathematical equations can be used to investigate the performance and guide the design of metal hydride beds.