Studies Pertaining to Hydrogen Car Development. Part A. The Kinetics and Mechanism of Magnesium Alloy-Hydride Formation and Dissociation.

摘要

The reaction between high-pressure hydrogen and Mg-10Al to form MgH2in the range of 400to 450degrees C was found to be a diffusion-controlled process. Initially hydrogen dissolved rapidly into the metal particles,and MgH2generally nucleated homogeneously as spherical particles. Growth of the particles was controlled by hydrogen diffusion in the metal and the kinetics followed the Johnson-Mehl relationship. The particles were readily hydrided to 7 w/o hydrogen and were found to exhibit very little fragmentation. Dehydriding followed the same rate law and was found to be complete in 90minutes at 300degrees C,these conditions being favorable for the use of this hydride in vehicles combusting hydrogen. The reaction involving Mg-25Ni resulted in two hydrides, MgH2and Mg2NiH4,the former being more stable and forming first.