Anna Lisa Fiorini

Desorption behaviour in nanostructured MgH2-Co

The influence of the Co addition and synthesis route on desorption properties of MgH2 were investigated. Ball milling of MgH2-Co blends was performed under Ar using different milling intensities and different weight ratios. Microstructural and morphological characterization, performed by XRD and SEM, show a huge correlation with thermal stability and hydrogen desorption properties investigated by DSC. A complex desorption behaviour is correlated with the dispersion of the catalytic particles that appears to play a main role in desorption performances. The optimum catalyst concentration was found to be around 10 wt.%, while the optimum value of the ball to powder ratio was 10:1.

Microstructure and Hydrogen Desorption in Nanostructured MgH2-Fe

Mg-based nanostructured hydrides have been synthesized by ball milling using two alternative approaches. The first is based on the reactive milling of Mg powders in H2 atmosphere, while the second on the milling of commercial MgH2 powders under inert atmosphere. In both cases 10 wt.% of Fe was added to the powder mixture, with the aim of introducing a catalyst agent. The microstructural characterization was carried out by X-ray diffraction, and both scanning and transmission electron microscopy. Hydrogen desorption behavior was evaluated by differential scanning calorimetry. Almost full hydrogenation of pure Mg powders can be achieved by reactive milling. Catalyst addition strongly accelerates the hydride formation. Both reactive milling of Mg powder and inert gas milling of MgH2 induce a nanosized microstructure with similar H-desorption behavior. The role played by Fe becomes particularly evident in H-desorption. In fact, a temperature decrease of about 100°C was found in samples having the same crystallite size and similar powder morphology.

Atomic ordering in CuZnAl shape memory alloys investigated via x-ray absorption and diffraction

We investigate the structure of the austenite phase in CuZnAl shape memory alloys by a combined x-ray absorption and diffraction analysis. Ab initio simulations of the near Zn-edge x-ray absorption coefficient allow us to directly discard the hypothesis of a DO3 superstructure. At the same time, we give evidence of the existence of an ordered structure (B2-like) different from the L21 one recently proposed by neutron diffraction. However, some partial L21 ordering is present at room temperature. This superstructure develops and recovers order when increasing the temperature above 400K.

Reaction with Hydrogen of Micro and Nano Composites Based on Mg

Hydrogen, being a regenerative and environmentally harmless fuel, can play a crucial role in the energetic scenario of the near future. In recent years several systems for solid-state hydrogen storage have been investigated, among which a few metals and metal alloys show the most promising properties. Mg and Mg-based micro and nanocomposites are widely studied for this application owing to the high gravimetric storage capacity, even if a proper microstructure, mainly at the material surface, has to be setup in order to overtake kinetic constraints often related to the high surface reactivity. In this paper, we present our approach to this problem and report the main findings. We have examined the influence on hydrogenation/dehydrogenation characteristics of different modifications of the bulk and surface microstructure of MgH2 powders processed by ball milling, which appears to be one the most useful methods for preparing powders suitable for hydrogen storage.

Hydrogen Desorption from MgH2 Based Nano-Micro Composites

The microstructure and hydrogen sorption behaviour of MgH2 based nano-hydrides with different additives prepared by ball milling and inert gas condensation has been investigated by XRD, Differential Scanning Calorimetry and Mechanical Spectroscopy. Preliminary results on materials with similar composition and different nanostructures show that suitable mechanical processing and additive additions induce in the nanostructured composites tailored channels for improved ab/de-sorption kinetics at reduced temperatures.