Formation of Ti Hydride Ultrafine Particles and Transformation between TiH2 and Ti

Abstract
TiH2 ultrafine particles are formed by the H2 gas evaporation technique. The typical habit of the particles shows a dodecahedron. Through the habit, the growth is considered to be resulting from a martensitic transformation from a bcc structure to a CaF2 structure due to the hydrogen absorption. The desorption of H2 from the TiH2 particles by heat treatment in a vacuum brings about the formation of hcp Ti particles, while the absorption of H2 gas of Ti particles due to heat treatment in a H2 atmosphere leads to the formation of TiH2 particles with CaF2 structure, in both cases always accompanied by twin planes.