Hydrogen absorbing properties and structures of Ti–Cr–Mo alloys

Ti–Cr–Mo alloys show different hydrogenation properties to Ti–Cr–V and Ti–Mn–V hydrogen absorbing alloys with b.c.c. structure. Ti–Cr–Mo alloys have a smaller solid solution range (<0.5 wt.%) than Ti–Cr–V (<1.3 wt.%). In order to understand this difference, crystal structure and hydrogenation behaviors were investigated by X-ray diffraction and pressure–composition isotherms (P–C–T) measurements. Most of the alloys investigated were single bcc phase. The relation of the plateau pressure vs. lattice volume of Ti–Cr–Mo alloys was opposite to Ti–Cr–V and many of conventional intermetallic alloys. The new parameter, the radius of tetrahedral hydrogen site, is introduced. This new parameter gives a linear relationship with the plateau pressure for both Ti–Cr–Mo and Ti–Cr–V alloys. Hydrogen capacity of Ti–Cr–Mo and Ti–Cr–V are the same in a hydrogen to metal ratio basis. Slight addition of V to Ti–Cr–Mo alloys leads to dramatic increase of solid solution range.