EFFECTS OF THERMAL CYCLING ON THE PHYSICAL-PROPERTIES OF VH(X)

A thousand thermal cycles of vanadium hydride across the beta-gamma mi xed phase region decreased the reversible hydrogen storage capacity an d increased the absorption/desorption pressure hysteresis ratio. Therm al cycling also produced a large increase in hydride surface area. Nev ertheless, X-ray diffraction and transmission electron microscopy show ed the measured crystalline size to be larger after the 1000 cycles th an for activated materials. These results were not anticipated from th e behaviour exhibited by other metal hydrides.