Comparison of hydrogen absorption properties of Ti mechanically milled with hexagonal boron nitride (h-BN) and with graphite

We compared the structural and hydrogen absorption properties of Ti mechanically milled with hexagonal boron nitride (h-BN) with those obtained when Ti was milled with graphite. With increasing milling time, the N and C atoms originating from h-BN and graphite dissolved into the interstitial sites of Ti, leading to the formation of the interstitial solid solutions, TiN and TiC, respectively. An investigation with X-ray photoelectron spectroscopy (XPS) suggested the existence of an interaction between Ti and N or C atoms due to their interstitial dissolution on the Ti surface. Milling with h-BN improved the kinetics of the hydrogen absorption of Ti as well as milling with graphite although the former required a longer milling time for full activation. The improvement in the kinetics can probably be attributed to the interstitial dissolution of N or C atoms on the Ti surface, which may provide the pathways for hydrogen penetration into Ti bulk. We revealed that the existence of the interstitial atoms on the Ti surface is an important factor in relation to the improvement in the hydrogen absorption kinetics of Ti.