(1. State Key Laboratory of Advanced Special Steels, Shanghai University (2. Institute of Genomic Material, Shanghai University
Keywords:
-
CLC:
PACS:
-
DOI:
10.7502/j.issn.1674-3962.2016.01.07
DocumentCode:
Abstract:
Rare earth (RE) elements have been added into Mg-based hydrogen storage alloys to form Mg-based RE-Mg hydrogen storage alloys due to their active properties. These alloys have attracted extensive attention owning to their good hydrogen storage performance. However, because of the lack of the guidance by phase diagrams in the RE-Mg system, the material design is aimlessly and would fall into a “cooking” exploration. For the study of hydriding and dehydriding kinetics, the current experimental measurement mainly repeated on determining the relationship between reaction fraction and time at isothermal condition. Few research focused on the effect of temperature, pressure, particle size… on the reaction rate, much less the particle size distribution, heating rate and other factors. This work investigates the Mg-Ni-RE(La,Nd,Ce,Y)-H quarternary system based on the thermodynamic and kinetic calculations. The calculation based on thermodynamic database reveals the thermodynamic stability of hydrogen storage alloys and hydrides. The Pressure-Composition-Temperature (PCT) curves are predicted through CALPHAD method. The thermodynamic calculation and experimental results of in situ X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) indicate the thermodynamic mechanism of hydriding and dehydriding. Meanwhile, the isothermal and non-isothermal hydriding/dehydriding kinetics are investigated and the reacted fraction is expressed as a function of temperature, pressure, particle size, particle morphology etc. This method not only simplifies the calculation, but also makes the physical quantities easy to discuss theoretically. A new concept “characteristic time” is introduced, which will act an important role in the research of hydrogen storage materials.