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 (1) and developed by Hassen (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, (iii) 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) .