T.I. Khomenko

Mechanism and kinetics of mechanically induced transformation of titanium and titanium hydride: Effect of reaction medium on microstructure, morphology and hydrogen-uptake properties

The stimulating effect of graphite addition on hydrogen sorption/desorption properties of titanium activated under ball milling and titanium hydride activated or prepared under ball milling is studied using X-ray diffraction, scanning and transmission electron microscopy, and temperature-programmed reaction/desorption techniques. The formation of microporous carbon matrix containing randomly distributed titanium or titanium hydride fragments of several nm in size is found to be the major effect of graphite addition. This kind of morphology allows the hydrogen transport to titanium or from titanium hydride surfaces without hindrances and improves titanium-hydrogen interaction through modifying the titanium surface and subsurface layers by interstitial C atoms.

Ti/C and Ti/B Nanocomposites: Comparison of Sorption-Desorption Properties

Hydrogen sorption-desorption properties of Ti/B and Ti/C nanocomposites prepared under ball-milling of the corresponding powders in H2 flow were studied using kinetic, microscopic and spectroscopic techniques. Amorphous boron was found to be more effective in spurring Ti – H2 interaction than carbon because of the following properties: (1) significant fragmentation of Ti powder by preventing agglomeration of the particles; (2) unhindered hydrogen access to the surface of Ti nanoparticles through the boron matrix; (3) appearance of new occupation sites available for H atoms, which are characterized by low H2 desorption temperature. The dynamics of the formation of these sites and the H2 distribution between different occupation sites in dependence on phase composition and morphology were studied for the Ti/B system.

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

Morphological, structural and chemical evolution in Ti/B/H2 system is studied in detail as a function of mechanical treatment. Ti/B powder continuously changes both in composition and morphology during ball-milling in H2 flow: The powder composition varies from Ti/B to TiH2-x/B causing a change in mechanical properties. The role of boron additive also changes from preventing the Ti nanoparticles from sticking together in the early stages to a matrix material participating in Ti - B interface reactions in the intermediate and final stages of the process. Boron atoms participating in the formation of nanoscopic holes give rise to new H states in the hydride by changing the local atomic state of Ti atoms. The dynamics of the formation of these sites and the redistribution of hydrogen between dif- ferent types of occupation sites in dependence of phase composition and milling time of the powders are also studied.