Hydriding of titanium: Recent trends and perspectives in advanced characterization and multiscale modeling

Low-Pressure Deuterium Storage on Palladium-Coated Titanium Nanofilms: A Versatile Model System for Tritium-Based Betavoltaic Battery Applications

“…Note that the diffusion coefficient of H in Ti-hydrides at room temperature (ca., 4 × 10 –12 cm 2 s –1 ) is about two orders of magnitude lower than that of the metallic Ti matrix. Furthermore, H transport in the Ti matrix is strongly affected by irreversible trapping phenomena originating from lattice imperfections and crystal defects such as dislocations, precipitates, and grain boundaries . These irreversible trapping sites facilitate the nucleation and growth of Ti-hydride phases.…”

“…Former studies on dehydrogenation of titanium hydrides (TiH x ) − reported that for x = 2, a face-centered tetragonal (FCT) ε-hydride (c/a < 1) was observed which transformed into the most stable face-centered cubic (FCC) δ-hydride phase within 1.5 < x < 1.99. Decrease in hydrogen content (1.0 < x < 1.5) led to the formation of a mixture of (FCC) δ-hydride and an FCT β-hydride (c/a >1) phases.…”

“…However, such high-temperature pretreatment and hydrogen isotope storage protocols can also trigger the formation of surface and/or bulk Ti oxides as a result of the reaction between the oxophilic Ti metal and oxygen-containing background gases such as O 2 , H 2 O, etc . Presence of surface/bulk titanium oxide (TiO x ) phases can increase the activation energy required for the diffusion and transport of hydrogen isotopes toward the bulk and suppress the ultimate hydrogen isotope storage capacity of the Ti-containing phases. For example, diffusion coefficients of hydrogen in metallic Ti polymorphs were reported to be 10 5 –10 15 times greater than that in titania (i.e., TiO 2 /TiO x ) polymorphs .…”

“…Presence of surface/bulk titanium oxide (TiO x ) phases can increase the activation energy required for the diffusion and transport of hydrogen isotopes toward the bulk and suppress the ultimate hydrogen isotope storage capacity of the Ti-containing phases. For example, diffusion coefficients of hydrogen in metallic Ti polymorphs were reported to be 10 5 –10 15 times greater than that in titania (i.e., TiO 2 /TiO x ) polymorphs . Thus, it is essential to minimize the exposure of pristine Ti films to air or other reactive gases.…”

Hydrogen in disordered titania: connecting local chemistry, structure, and stoichiometry through accelerated exploration

“…The oxide layer is likely polycrystalline, 7 with a number of unique and complex atomic environments existing between the oxide surface and the underlying metal, including grain boundaries, nano/microscale defects such as voids and cracks, and the interface region between the oxide and metal/alloy. [8][9][10][11][12][13] There is speculation that thermodynamic driving forces exist that result in larger hydrogen concentration in the grain boundaries, which themselves are likely disordered and resemble amorphous phases. 14 These then become channels for mass transport to the metallic material underneath.…”