Solvus behavior of the vanadium-hydrogen and deuterium systems

Abstract

The solvus data for V-H and V-D exhibit an extended region of linearity when plotted as ln Z a against T −1 where Z a = [ a (β−a) ] where a is the H(D)-to-V, atom ratio, at the solvus composition and β is the number of available interstices per metal atom. This behavior contrasts with the Ta-H system which exhibits considerable curvature in the solvus plot over the same temperature range. It is shown that the linearity results from the opposing influences of nonideality and the variation of the solvus enthalpy and entropy with temperature; the latter is due to the occupation of octahedral and tetrahedral interstices in the hydride and dilute phases, respectively. In contrast to the Ta-H(D) system, there is a solvus isotope effect in the V-H and V-D systems and this is explained in terms of the occupation of different interstices in the two coexisting phases.