Hydriding reactions in ball-milled titanium

The diffusion of hydrogen into titanium during ball milling has been investigated. A system is described that enables the milling to be done under approximately constant hydrogen pressure and allows for the continuous measurement of the quantity of hydrogen absorbed. Under appropriate milling conditions, samples may be saturated with hydrogen after milling for about 20 min. X-ray diffraction studies show that samples milled to saturation exhibit the titanium hydride structure with no evidence of residual Ti metal, and have a grain size of about 8 nm. Studies of the influence of milling conditions show that the ball-to-sample weight ratio and the number of balls are both important factors in determining the time to reach saturation. These results suggest the importance of local heating effects on the hydrogen absorption rate. (C) 1999 Elsevier Science S.A. All rights reserved.