Synchrotron radiographic studies of ultrasonic melt processing of metal matrix nano composites

Fast synchrotron radiography was used to investigate ultrasonic cavitation bubble formation and their dynamics during liquid metal processing of Al-Cu metal matrix nano composites (MMNC) in comparison with conventional alloys. The experimental observations showed enhanced cavitation potential in MMNC melts, due to the presence of Al2O3 nano particles which believed to be acting as heterogeneous nuclei for bubble formation. Quantitative image analysis demonstrates that the addition of nano particles increases melt agitation partially, while introducing higher flow velocity variations across the melt. This suggests that the presence of nano particles may substantially alter propensity for ultrasonic treatment effects during solidification processing of MMNCs.the ExoMet Project, which is co-funded by the European Commission in the 7th Framework Programme (contract FP7-NMP3-LA-2012-280421), by the European Space Agency and by the individual partner organisations. UK EPSRC grants (EP/I02249X/1, EP/K00588X/1, EP/K005804) and the Research Complex at Harwell

Enhanced Hydrogen Generation Properties of MgH2-Based Hydrides by Breaking the Magnesium Hydroxide Passivation Layer

Due to its relatively low cost, high hydrogen yield, and environmentally friendly hydrolysis byproducts, magnesium hydride (MgH2) appears to be an attractive candidate for hydrogen generation. However, the hydrolysis reaction of MgH2 is rapidly inhibited by the formation of a magnesium hydroxide passivation layer. To improve the hydrolysis properties of MgH2-based hydrides we investigated three different approaches: ball milling, synthesis of MgH2-based composites, and tuning of the solution composition. We demonstrate that the formation of a composite system, such as the MgH2/LaH3 composite, through ball milling and in situ synthesis, can improve the hydrolysis properties of MgH2 in pure water. Furthermore, the addition of Ni to the MgH2/LaH3 composite resulted in the synthesis of LaH3/MgH2/Ni composites. The LaH3/MgH2/Ni composites exhibited a higher hydrolysis rate—120 mL/(g·min) of H2 in the first 5 min—than the MgH2/LaH3 composite— 95 mL/(g·min)—without the formation of the magnesium hydroxide passivation layer. Moreover, the yield rate was controlled by manipulation of the particle size via ball milling. The hydrolysis of MgH2 was also improved by optimizing the solution. The MgH2 produced 1711.2 mL/g of H2 in 10 min at 298 K in the 27.1% ammonium chloride solution, and the hydrolytic conversion rate reached the value of 99.5%

A Recycling Hydrogen Supply System of NaBH4 Based on a Facile Regeneration Process: A Review

NaBH4 hydrolysis can generate pure hydrogen on demand at room temperature, but suffers from the difficult regeneration for practical application. In this work, we overview the state-of-the-art progress on the regeneration of NaBH4 from anhydrous or hydrated NaBO2 that is a byproduct of NaBH4 hydrolysis. The anhydrous NaBO2 can be regenerated effectively by MgH2, whereas the production of MgH2 from Mg requires high temperature to overcome the sluggish hydrogenation kinetics. Compared to that of anhydrous NaBO2, using the direct hydrolysis byproduct of hydrated NaBO2 as the starting material for regeneration exhibits significant advantages, i.e., omission of the high-temperature drying process to produce anhydrous NaBO2 and the water included can react with chemicals like Mg or Mg2Si to provide hydrogen. It is worth emphasizing that NaBH4 could be regenerated by an energy efficient method and a large-scale regeneration system may become possible in the near future

Thermodynamic Tuning of Mg-Based Hydrogen Storage Alloys: A Review

Mg-based hydrides are one of the most promising hydrogen storage materials because of their relatively high storage capacity, abundance, and low cost. However, slow kinetics and stable thermodynamics hinder their practical application. In contrast to the substantial progress in the enhancement of the hydrogenation/dehydrogenation kinetics, thermodynamic tuning is still a great challenge for Mg-based alloys. At present, the main strategies to alter the thermodynamics of Mg/MgH2 are alloying, nanostructuring, and changing the reaction pathway. Using these approaches, thermodynamic tuning has been achieved to some extent, but it is still far from that required for practical application. In this article, we summarize the advantages and disadvantages of these strategies. Based on the current progress, finding reversible systems with high hydrogen capacity and effectively tailored reaction enthalpy offers a promising route for tuning the thermodynamics of Mg-based hydrogen storage alloys

A Recycling Hydrogen Supply System of NaBH4 Based on a Facile Regeneration Process: A Review

NaBH4 hydrolysis can generate pure hydrogen on demand at room temperature, but suffers from the difficult regeneration for practical application. In this work, we overview the state-of-the-art progress on the regeneration of NaBH4 from anhydrous or hydrated NaBO2 that is a byproduct of NaBH4 hydrolysis. The anhydrous NaBO2 can be regenerated effectively by MgH2, whereas the production of MgH2 from Mg requires high temperature to overcome the sluggish hydrogenation kinetics. Compared to that of anhydrous NaBO2, using the direct hydrolysis byproduct of hydrated NaBO2 as the starting material for regeneration exhibits significant advantages, i.e., omission of the high-temperature drying process to produce anhydrous NaBO2 and the water included can react with chemicals like Mg or Mg2Si to provide hydrogen. It is worth emphasizing that NaBH4 could be regenerated by an energy efficient method and a large-scale regeneration system may become possible in the near future

Improvement in the Electrochemical Lithium Storage Performance of MgH2

Magnesium hydride (MgH2) exhibits great potential for hydrogen and lithium storage. In this work, MgH2-based composites with expanded graphite (EG) and TiO2 were prepared by a plasma-assisted milling process to improve the electrochemical performance of MgH2. The resulting MgH2–TiO2–EG composites showed a remarkable increase in the initial discharge capacity and cycling capacity compared with a pure MgH2 electrode and MgH2–EG composite electrodes with different preparation processes. A stable discharge capacity of 305.5 mAh·g−1 could be achieved after 100 cycles for the 20 h-milled MgH2–TiO2–EG-20 h composite electrode and the reversibility of the conversion reaction of MgH2 could be greatly enhanced. This improvement in cyclic performance is attributed mainly to the composite microstructure by the specific plasma-assisted milling process, and the additives TiO2 and graphite that could effectively ease the volume change during the de-/lithiation process as well as inhibit the particle agglomeration

Sn buffered by shape memory effect of NiTi alloys as high-performance anodes for lithium ion batteries

By applying the shape memory effect of the NiTi alloys to buffer the Sn anodes, we demonstrate a simple approach to overcome a long-standing challenge of Sn anode in the applications of Li-ion batteries - the capacity decay. By supporting the Sn anodes with NiTi shape memory alloys, the large volume change of Sn anodes due to lithiation and delithiation can be effectively accommodated, based on the stress-induced martensitic transformation and superelastic recovery of the NiTi matrix respectively, which leads to a decrease in the internal stress and closing of cracks in Sn anodes. Accordingly, stable cycleability (630 mA h g(-1) after 100 cycles at 0.7C) and excellent high-rate capabilities (478 mA h g(-1) at 6.7C) were attained with the NiTi/Sn/NiTi film electrode. These shape memory alloys can also combine with other high-capacity metallic anodes, such as Si, Sb, Al, and improve their cycle performance. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Molecular chemisorption: a new conceptual paradigm for hydrogen storage

Developing efficient hydrogen storage materials and the corresponding methods is the key to successfully realizing the “hydrogen economy”. The ideal hydrogen storage materials should be capable of reversibly ab-/desorbing hydrogen under mild temperatures with high hydrogen capacities. To achieve this target, the ideal enthalpy of adsorption is determined to be 15-50 kJ/mol for hydrogen storage. However, the current mainstream methods, including molecular physisorption and atomic chemisorption, possess either too high or too low enthalpy of hydrogen adsorption, which are not suitable for practical application. To this end, hydrogen storage via molecular chemisorption is perceived to regulate the adsorption enthalpy with intermediate binding energy between the molecular physisorption and atomic chemisorption, enabling the revisable hydrogen ad-/desorption possible under ambient temperatures. In this review, we will elaborate the molecular chemisorption as a new conceptual paradigm and materials design to advance future solid-state hydrogen storage