Effect of h-BN Additive on Hydrogen Sorption by Ti under Mechanical Treatment in H₂/He Flow

Abstract

The effect of h-BN additive on hydrogen sorption by Ti under mechanical treatment in H2/He flow and on the thermal stability of Ti-hydride produced during milling were studied using kinetic, structural, microscopic, and spectroscopic techniques and theoretical first-principles calculations. The results obtained were compared with the corresponding properties of pure Ti and Ti with graphite additive. Like graphite, hexagonal BN was found to be an effective additive to improve the hydrogen sorption capacity of Ti. New types of occupation sites available for hydrogen, very similar to those detected for Ti/C, were observed. These sites are characterized by a low H2 desorption temperature: 630−670 K instead of ∼1000 K.

Boron Enhanced Synthesis of Ti-hydride Nanoparticles by Milling Ti/B in Hydrogen Flow

“…Figure. (2(b)) is a close-up, dark spots are nano-sized Ti or Ti hydride particles in a boron matrix, 2(c) is a HREM micrograph, where an ellipsoidal TiH 2-x particle about 4 x 8 nm in size is encircled, and the arrow points to a crystalline flake-like boron particle, 2(d) is a HREM micrograph, where the lattice fringes stem from TiH 2-x particles. A similar powder architecture was observed earlier for Ti/graphite and Ti/h-BN as-milled powders [13,27]. Figure. (3(a)) shows kinetics of H 2 uptake under mechanical treatment and during post-milling period for 25 and 36 min of treatment.…”

“…The large concentration of different surface defects generated during crushing of the Ti particles promotes H 2 dissociative chemisorption. However, the durability of these active sites is not evident: fresh Ti surface may be easily covered by Ti-hydride that locks the active sites, as was observed for pure Ti powder [27]. The prolonged post-milling sorption suggests that long-living active sites are localized not on Ti surface, but in positions, where no continuous titanium hydride layer can be formed, whereas hydrogen diffusion into the bulk goes rapidly.…”

“…The prolonged post-milling sorption suggests that long-living active sites are localized not on Ti surface, but in positions, where no continuous titanium hydride layer can be formed, whereas hydrogen diffusion into the bulk goes rapidly. According to [27], it might be Ti/TiO 2 interfaces or grain boundaries: compare hydrogen diffusion coefficients in Ti at 303 K for grain boundary diffusion equal to 9.1 x 10 -9 m 2 /s [30] with that in bulk Ti and TiH 2 equal to 2.6 x 10 -14 m 2 /s [30] and 3.8 x 10 -15 m 2 /s [31] , respectively. Ti-hydride nucleation goes preferably along the cracks and nearby structural defects because of the interaction of H atoms with bulk stress centers.…”

Nuclear Magnetic Resonance Study of Ball-Milled TiH2 with C, B, and BN Additives

“…In other words, the XES results indicate that B atoms do not penetrate into the TiH 2 lattice in this system. However, N atoms can occupy interstitial sites in Ti or TiH 2 lattices forming N−Ti bonds in the ball-milled Ti/BN in H 2 /He flow. This is also supported by the results of ab initio calculations of chemical bonding .…”

Hydrogen-sorption and thermodynamic characteristics of mechanically grinded TiH1.9 as studied using thermal desorption spectroscopy

“…It should be mentioned that there are a number of investigations, where different techniques were employed to explore effects of ball milling and a nanocrystalline state of TiH 2 , both pure and with different additives, upon some properties of the hydride (e.g., hydrogen mobility, thermal stability, sorption behavior, etc. [18][19][20][21][22][23]), however, to the best of our knowledge, the influence of the grinding of titanium dihydride on its thermodynamic characteristics has not been studied yet.…”