Cryorolling of magnesium alloys aiming hydrogen storage applications

Abstract

Hydrogen storage is an important issue of applied research, to make possible the use of H2 as a cleaner and renewable energy carrier. The major recent advances in this field refer to developing solid hydrogen tanks using metal hydrides, in particular from MgH2. The main advantages of this material for hydrogen applications are its high volumetric energy density and the low cost of starting metal. On the other hand, the processing of MgH2 by high-energy ball milling for the manufacture of tanks is expensive and produces very fine powders, which exhibits low resistance to contamination by air. Thus, the search for alternative ways to produce Mg alloys for hydrogen storage purposes is relevant. In this project, commercial magnesium alloys such as AZ91 and AM60B will be processed by cryorolling, in order to acquire fast H-sorption kinetics at temperatures about 300°C. High microstructural refinement combined to low specific surface area are aimed, allowing to handle the material in not inert atmosphere. Cryorolling will be evaluated in terms of the processing, the obtained morphology and H-sorption properties. The cryorolling technique will be combined with a short stage of high-energy ball milling (HEBM) and the results will be compared with each other and with the literature. The structural characterization will be performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermal stability of the structure will be evaluated using differential scanning calorimetry (DSC), and the hydrogen storage properties will be measured by a Sievert apparatus. From the resulting data, the structures and properties of nanocrystalline Mg alloys and processing routes necessary to obtain them will be correlated.