The phase diagram and superabundant vacancy formation in Fe-H alloys under high hydrogen pressures

In situ XRD measurements at high temperatures and high hydrogen pressures were performed on Fe-H alloys, and in combination with all available data a p(H-2)-T diagram was constructed up to p(H-2) = 10 GPa and T = 1500degreesC. A drastic reduction of the melting point with dissolution of hydrogen, down to 800 degreesC at 3 GPa, was observed. In the f.c.c. phase, a gradual lattice contraction due, to superabundant vacancy formation was found to take place over several hours. The lattice parameter at 784 degreesC, 4.7 GPa decreased by 6%, which implies that a vacancy concentration as high as 19 at.% was attained. (C) 2002 Elsevier Science B.V. All rights reserved.