Tomaz Toshimi Ishikawa

Synthesis of MgH2 and Mg2FeH6 by reactive milling of Mg-based mixtures containing fluorine and iron

A good method to store hydrogen is in it atomic form in crystalline structure of metals at low pressure. Thanks to magnesium’s high hydrogen storage capacity, its low weight and its high natural abundance, it is an attractive material to develop hydrogen solid state storage. The production of Mg-based nanocomposites can enhance the kinetics of H-sorption of magnesium and the temperature of release of hydrogen. Transition metals as iron, which have important catalytic activity in hydrogen reactions with Mg, and the surface protective compound MgF2, are interesting additions for magnesium mixtures for hydrogen storage. In this work, Mg-based nanocomposites containing Fe and MgF2 were produced by reactive milling under hydrogen using the addition of FeF3, or directly MgF2 and Fe. The efficiency of centrifugal and planetary mill in MgH2 synthesis was compared. The phase evolution during different milling times (from 1 to 96 h) using the planetary was investigated. The different H-desorption behavior of selected milled mixtures was studied and associated with the different present phases in each case.

Mechanical and Reactive Milling of a TiCrV BCC Solid Solution

Nowadays, many efforts have been concentrated in research and development of hydrogen absorbing materials due to a possible application as electrode for rechargeable batteries, on board hydrogen storage systems, getters, catalysts, etc. Novel technologies for materials processing have been used to generate new alloys with metastable structures, such as amorphous and/or nanocrystalline alloys. In this context, mechanical milling or mechanical alloying is a very attractive way to produce this alloys, specially when carried out under hydrogen atmosphere (reactive milling). In this work, we have studied the structural evolution of a TiCrV bcc solid solution during mechanical and reactive milling. The process parameters analyzed were: milling atmosphere (argon and hydrogen), milling time and gas pressure into the vials (in the case of reactive milling). Structural evolution was investigated by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). Hydrogen contents of the reactive milled alloys were determined using a Leco analyzer. Differential scanning calorimetry (DSC) was used to determine the hydrogen desorption temperature and the stability of the alloys.

Chemistry and tensile properties of a recycled AA7050 via spray forming and ECAP/E

The aim of this work is to evaluate the conjugation of advanced processing techniques, such as spray forming, extrusion and ECAP as a processing route for reuse of machining chips generated during aircrafts manufacturing parts from AA7050-T7451 raw material plates supplied according to AMS 4050H1. In this way, the sprayforming process was used for remelting, and billet production, followed by extrusion and ECAP. At the end of the process, an artificial aging according to AMS 2772E 2 was conducted. An assessment of chemical composition, microstructure, and mechanical properties evolution throughout the process were performed. The results have showed that this proposed route may be used as a potential technological route for secondary aluminum source. For extrusion route for overaged condition, 144 MPa yield strength and 14% of elongation was attained. Beside this, at this stage of work, was verified that the hot extrusion process is more effective for reduction of porosity and microstructure development than ECAP, but on the other hand this one has reduced porosity dispersion significantly for the extrusion parameters adopted. The adopted homogenization schedule, followed by artificial aging after has resulted in excessive grain growth.

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.

Magnesium-Nickel alloy for hydrogen storage produced by melt spinning followed by cold rolling

Severe plastic deformation routes (SPD) have been shown to be attractive for short time preparation of magnesium alloys for hydrogen storage, generating refined microstructures and interesting hydrogen storage properties when compared to the same materials processed by high-energy ball milling (HEBM), but with the benefit of higher air resistance. In this study, we present results of a new processing route for Mg alloys for hydrogen storage: rapid solidification followed by cold work. A Mg

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.

Reactive Milling of Magnesium under Hydrogen Using Transition Metals and their Fluorides as Additives

Magnesium is light, abundant and it can store up to 7.6 wt. % of hydrogen forming MgH2 and accordingly it is a promising material for hydrogen storage. Processing of Mg-based mixtures by high-energy ball milling (HEBM) can produce materials with high level H-sorption properties. In the present report, we display and compare the effects of different nanocrystalline additives (MgF2, Fe, NbH0,89, FeF3, VF3) on the formation of MgH2 by reactive milling. The H-desorption behavior of the as-prepared nanocomposites is also evaluated. A combined catalytic effect is observed due to the synergic action of MgF2 and Fe (or NbH0,89) on the hydrogenation rate during processing. The transition metal fluorides promote as well the MgH2 synthesis. By using more energy-intensive milling conditions and adequate additives in given proportions (e.g. 5 mol. % FeF3), is shown to be very effective for a full and fast synthesis (4 h) of MgH2 by reactive milling.

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.

Two Routes to Process the Mg-5at.%Nb Nanocomposite

In this work, we report the processing of MgH2 + 5at.% Nb nanocomposite by two different routes. In the first one, MgH2 and Nb powders were milled under argon for 20h, using a shaker mill. In the second route, Mg chips and Nb powders were milled under hydrogen atmosphere for 48h, using a centrifugal mill. The phase transformations and microstructural changes were studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Significant differences in the morphology and phase formation were observed between the two processing routes. The nanocomposite obtained under hydrogen atmosphere showed a slight improvement in the hydrogen desorption properties as compared with the nanocomposite obtained under inert atmosphere. Moreover, we have observed that the addition of Nb improves the kinetics of Mg hydriding.