Kinetics and Mechanism of Hydrogen Sorption in Yttrium- Silicon D88- Structure Phases, Part II (Model for Predicting the Kinetics of Hydrogen Reactivity with Y5Si2Ge)

Abstract

Due to the limitations of the J-M-A approach as used by Goudy et.al (1) and
developed by Hassen et.al (part I of this research (7)), an analysis of fraction reacted
against reduced time has been introduced and the shape of the experimental curves
were compared to the theoretically predicted shapes for various rate controlling
mechanisms. From this pictorial analysis three steps appear to be dominant in
different temperature and pressure ranges; (i) nucleation of α-phase in a β-phase
matrix or for absorption the reverse, (ii) bulk growth of α or β-phase which is the β to
α phase change on desorption or α to β on absorption, ( i i i ) hydrogen diffusion in the
bulk with some hydrogen becoming trapped at less labile sites.
This approach has given an independent confirmation of the processes
involved in hydrogenation of the D88 structure special ceramic materials that has
been inferred in several earlier papers ^(1-6) .