Daniel Rodrigo Leiva

Mg alloy for hydrogen storage processed by SPD

Abstract Mg-based nanocomposites are promising candidates for hydrogen storage applications exhibiting fast H-sorption kinetics at reasonably low temperatures when processed by high-energy ball milling techniques. However, since compaction of the highly reactive nanometric powder is desirable before application, the search for other effective processing routes for the preparation of Mg-based nanocomposites is relevant. In this work, we have used a combination of equal channel angular pressing, cold rolling and high-energy ball milling in the processing of the commercial AZ31 extruded alloy to evaluate its use as a hydrogen storage material. Severe plastic deformation carried out at different temperatures, combined with further mechanical processing resulted in a controlled texture and signifiant grain refinement, which are desirable microstructural characteristics for hydrogen storage applications.

Severe Plastic Deformation of Mg-Fe Powders to Produce Bulk Hydrides

We describe in the present work the production of bulk Mg hydrides by hydrogenation treatment of samples processed by severe plastic deformation. The compact bulk samples of Mg-Fe have been obtained by high pressure torsion. The ternary complex Mg2FeH6 and the binary MgH2hydrides have been synthesized by hydrogenation treatment at 350°C, at 3 MPa during 24 h. The average grain refinement after HPT was modest as estimated by XRD. A comparison between the XRD patterns of the powders and of the HPT samples showed the formation, as expected, of a preferred orientation in the latter. The XRD of the hydride HPT samples (H-HPT) showed the presence of Mg, Fe, MgH2 and Mg2FeH6. The first de-hydrating reaction of the alloys (after H-HPT) was studied by differential scanning calorimetry (DSC). These results showed a reduction in the hydrogen dessorption temperature in comparison with commercial MgH2, indicating thermodynamic destabilization of the hydrides as a result of the high density of dislocations in the H-HPT samples.

Patents in nanotechnology: an analysis using macro-indicators and forecasting curves

In this study, we evaluated future trends of worldwide patenting in nanotechnology and its domains using logistic growth curves while the patent activity from the main countries, technological domains and subdomains were assessed in four different contexts: worldwide, patents filed in the United States Patent and Trademark Office (USPTO), and patents applications in the triadic (TRIAD) and in the tetradic (TETRAD) countries. The indicators were developed based on a set of records recovered from the Derwent Innovation Index database. Nanotechnology has recently emerged as a new research field, with logistic trend behaviors generating interesting discussions since they suggest that technological development in nanotechnology and its domains has reached an initial maturation stage. Future scenarios were compiled due to the difficult to establish upper limits to forecasting curves. Although China’s share of patents is small in some cases, it was the only country to constantly increase the number of patents from a worldwide perspective. In contrast, the USA and the EU were the most active in the USPTO, TRIAD and TETRAD cases, followed by Japan and Korea. The technological subdomains of main interest from countries/region changed according to the perspective adopted, even though there was a clear bias towards semiconductors, surface treatments, electrical components, macromolecular chemistry, materials–metallurgy, pharmacy–cosmetics and analysis–measurement–control subdomains. We conclude that monitoring nanotechnology advances should be constantly reviewed in order to confirm the evidence observed and forecasted.

High-Yield Direct Synthesis of Mg2FeH6 from the Elements by Reactive Milling

Magnesium complex hydrides as Mg2FeH6 are interesting phases for hydrogen storage in the solid state, mainly due to its high gravimetric and volumetric densities of H2. However, the synthesis of this hydride is not trivial because the intermetallic phase Mg2Fe does not exist and Mg and Fe are virtually immiscible under equilibrium conditions. In this study, we have systematically studied the influence of the most important processing parameters in reactive milling under hydrogen (RM) for Mg2FeH6 synthesis: milling time, ball-to-powder weight ratio (BPR), hydrogen pressure and type of mill. Low cost 2Mg-Fe mixtures were used as raw materials. An important control of the Mg2FeH6 direct synthesis by RM was attained. In optimized combinations of the processing parameters, very high proportions of the complex hydride could be obtained.

Hydrogen Activation Behavior of Commercial Magnesium Processed by Different Severe Plastic Deformation Routes

Severe plastic deformation (SPD) techniques are being considered as low cost processing routes for Mg alloys, aiming hydrogen storage applications. The main objective is to develop air-resistant materials, with lower specific surface area in comparison with ball-milled powders, but with still attractive H-sorption kinetics associated to the microstructural refinement. In this study, the effects of different SPD processing routes (high-pressure torsion, extensive cold rolling and cold forging) in the hydrogen activation behavior of Mg was evaluated. The results show that both microstructural and textural aspects should be controlled during SPD processing to obtain Mg alloys with good H-sorption properties and enhanced activation kinetics.

Nanostructured MgH2 obtained by cold rolling combined with short-time high-energy ball milling

was processed by short time high-energy ball milling (BM) and cold rolling (CR). A new alternative processing route (CR + BM) using the combination of CR followed by short time BM step was also applied. The effects on the final morphology, crystalline structure and H-sorption properties were evaluated. The CR + BM processing (compared to BM and CR process) resulted in an inhomogeneous particle size distribution and the biggest crystallite size of MgH

Mechanochemistry and H-sorption properties of Mg2FeH6-based nanocomposites

Abstract Mg2FeH6 is a promising material for hydrogen storage applications, since it presents the highest known volumetric capacity of 150 kg m−3 of H2 and its metallic constituents are inexpensive. The major drawbacks for its application are the difficulties associated with its synthesis and also its high thermal stability. In this paper, Mg2FeH6-based nanocomposites were prepared from the elements via reactive milling. A high-yield of the complex hydride synthesis was obtained after a systematic processing study, and the best conditions were successfully extended to the mechanochemical synthesis of Mg2CoH5. The influence of different additives such as transition metals, transition metal fluorides and graphite on the H-sorption behavior of the Mg2FeH6-based nanocomposites was evaluated. Mixtures rich in both MgH2 and Mg2FeH6 hydrides present lower temperature ranges of hydrogen release than those which are rich in only one of these hydrides. The MgH2–Mg2FeH6-based nanocomposite presents ultra-fast H-sorption kinetics at 300°C with partial reversible formation of Mg2FeH6.

Materials Selection for Sustainable Executive Aircraft Interiors

This study proposes a methodological guide to explore and select materials for executive aircraft interiors, contributing toward a perspective of materials requirements, indicators and strategies to design more environmentally sustainable products. This was motivated by the signs from the aviation industry to reduce its environmental impact and the permanent need to push for cost efficiency. The guide includes a schedule framework of materials requirements for sustainable design, and also aeronautical materials and marketing requirements. It was prepared by mapping sustainability demands for materials selection during product development, supported by a case study. Patented eco-friendly materials solutions for the case study involving the aircraft furniture structural panels were described and analyzed, considering the materials requirements of the aeronautical project. Composites of bio-polymers reinforced with natural fibers, preferably with solid cores, seem to be the most promising solutions to substitute the current panels.

Exploring several different routes to produce Mg- based nanomaterials for Hydrogen storage

Severe mechanical processing routes based on high-energy ball milling (HEBM) or severe plastic deformation (SPD) can be used to produce Mg nanomaterials for hydrogen storage applications. In the last few years, we have been exploring in our research group different SPD processing routes in Mg systems to achieve good activation (first hydrogenation) and fast H-absorption/desorption kinetics, combined with enhanced air resistance. In this paper, we compare SPD techniques applied to Mg with HEBM applied to MgH2. Both advanced – melt spinning (MS), high-pressure torsion (HPT) – and more conventional – cold rolling (CR), cold forging (CF)- techniques are evaluated as means of production of bulk samples with very refined microstructures and controlled textures. In the best SPD processing conditions, attractive H-absorption/desorption kinetic properties are obtained, which are comparable to the ones of MgH2 milled powders, even if the needed temperatures are higher – 350°C compared to 300°C.CR and CF stand out as the processes with higher potential for industrial application, considering the level of the attained hydrogen storage properties, its simplicity and low cost.

Hydrogen Sorption Properties of the Complex Hydride Mg2FeH6 Consolidated by HPT

In the present work, we have processed 2Mg-Fe mixtures by reactive milling (RM) under hydrogen atmosphere to synthesize Mg2FeH6 phase in the powder form which were then systematically processed by High Pressure Torsion (HPT) to produce bulk samples. The bulk samples were characterized in terms of microstructural and structural analyses and of hydrogen desorption properties. The hydrogen sorption properties after HPT processing was evaluated in comparison with the Mg2FeH6 powder obtained by RM and with commercial MgH2. HPT processing of Mg2FeH6 can produce bulks with a high density of defects that drastically lower the activation barrier for hydrogen desorption. Therefore, the bulk nanocrystalline Mg2FeH6 samples show endothermic hydrogen decomposition peak at a temperature around 320°C. In addition, when compared with the Mg2FeH6 and MgH2 powders, the Mg2FeH6 HPT disks showed the same results presented by the Mg2FeH6 powders and certainly decreases the onset transition temperature by as much as 160°C when compared with the MgH2 powders.