CRYSTALLITE SIZE EFFECTS IN THE PALLADIUM-HYDROGEN SYSTEM - SIMULTANEOUS SORPTION AND X-RAY STUDY

The effect of crystallite size on hydrogen sorption by palladium blacks has been studied by simultaneous sorption and X-ray measurements. With decreasing crystallite size the hysteresis loop shrinks, but does not vanish. The lattice parameters of the α- and β-phases are independent of crystallite size; the enthalpies and entropies of sorption are nearly so. Two additional phases with lattice parameters between those of the α- and β-phases are detected. The apparent decrease, followed by an increase, in the fraction of the system in the α-phase before the α → β-transition commences is postulated to result from the formation initially of a disordered arrangement of H-atoms, which passes over into an ordered a-phase and then transforms to the β-phase. © by Akademische Verlagsgesellschaft