The kinetics of hydride formation and decomposition described by semi-empirical models generally does not involve particle and grain-size dependence. Involving grain size distribution, a multiparticle reaction function has been introduced for a nanocrystalline powder agglomerate and has been applied for surface controlled, contracting volume and Johnson-Mehl-Avrami (JMA) type of sorption processes. Taking into account the microstructural parameters describing the grain size distribution of nanocrystalline MgH2 powders obtained after repeated hydriding/dehydriding cycles, the type of reaction and the corresponding reaction constants were determined after each full cycle. The multiparticle reaction functions of the three different sorption processes follow the classical functions only if the grain size distribution is very sharp, however, a strong deviation takes place when the distribution is wider, i.e., the microstructure is less homogeneous.
ASJC Scopus subject areas
- Physics and Astronomy(all)