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Liu J.,Guizhou Normal University | Li Q.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing
Journal of Rare Earths | Year: 2013

The structure and hydriding/dehydriding behaviors of La2Mg 17-10 wt.%Ni composite prepared by mechanical milling were investigated. Compared with the un-milled sample, the as-milled alloys were ready to be activated and the kinetics of hydrogen absorption was relatively fast even at environmental temperature. The composite milled for 10 h absorbed 3.16 wt.% hydrogen within 100 s at 290 K. The kinetic mechanisms of hydriding/dehydriding reactions were analyzed by using a new model. The results showed that hydrogenation processes for all composites were controlled by hydrogen diffusion and the minimum activation energy was 15.3 kJ/mol H 2 for the composite milled for 10 h. Mechanical milling changed the dehydriding reaction rate-controlling step from surface penetration to diffusion and reduced the activation energy from 204.6 to 87.4 kJ/mol H2. The optimum milled duration was 5 h for desorption in our trials. © 2013 The Chinese Society of Rare Earths. Source


Li-Hui Z.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing | Qing-Wei H.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing
Ceramics International | Year: 2011

It is of great importance to control the morphology of α-Al 2O3 plate-like powders since α-Al2O 3 platelets with different shapes are needed in various applications. This paper was focused on how to control the morphology of α-Al 2O3 platelets by molten salt synthesis. Results show that the morphology of α-Al2O3 platelets is affected by the heating temperature, heating time, the molten salts species, the weight ratio of salt to powders, additives and the addition of nano-sized seeds. Especially, it is very effective to control the morphology of α-Al 2O3 platelets by adjusting the addition of additives such as Na3PO4·12H2O and TiOSO4. α-Al2O3 flakes with irregular shape are obtained by the addition of Na3PO4·12H2O, while thick α-Al2O3 particles with hexagonal shape are obtained by the addition of TiOSO4. The combination addition of Na3PO4·12H2O and TiOSO4 makes it possible to obtain thin α-Al2O3 platelets with discal shape. A small amount of nano-sized seeds addition also has a strong effect on the size of α-Al2O3 platelets. However, if the seeds are added too much, the overlapping and abnormal crystal growth of α-Al2O3 platelets occur, and the size distribution becomes nonuniform. The effect mechanism of additives and seeds on the morphology of α-Al2O3 platelets was also discussed in this paper. © 2010 Elsevier Ltd and Techna Group S.r.l. Source


Zou X.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing | Lu X.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing | Li C.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing | Zhou Z.,University of Oxford
Electrochimica Acta | Year: 2010

The titanium silicide intermetallics have been directly prepared from the mixture of titanium oxide (TiO2) and silicon oxide (SiO2) powder by using the solid-oxygen-ion-conducting membrane (SOM) electrolysis process. The electrochemical process was carried out in a molten flux CaCl2 at 950 °C with a potential of 3.5-4.0 V. The effects of the stoichiometry of the initial mixture on the electrolysis characteristics and the final product compositions were investigated. It has been found that the molar ratio of TiO2:SiO2 dominates the composition of final products. A single-phase silicide Ti5Si3 intermetallic was obtained when the TiO2:SiO2 molar ratio is 5:3; the TiSi was identified as the dominant phase with a minor amount of TiSi2 at TiO2:SiO2 molar ratio 1:1; three silicide phases, Ti5Si4, Ti5Si3 and TiSi, were found coexisting in the final product produced from TiO2-SiO2 mixture of molar ratio 5:4; the product of electrolysis consisted of the compound Ti5Si3 and the pure metal Ti as TiO2:SiO2 molar ratio equals to 3:1; and two silicide phases, TiSi and TiSi2, are formed as TiO2:SiO2 molar ratio equals to 1:2. The preliminary experimental results suggest that the electro-deoxidization process is fast and the current efficiency reached 75%. © 2010 Elsevier Ltd. Source


Wu Y.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing | Shen T.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing | Lu X.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing
Chemical Physics Letters | Year: 2013

A structural evolution during solidification and melting processes of nanoparticle Fe9577 was investigated from MD simulations. A perfect lamellar structure, consisting alternately of fcc and hcp layers, was obtained from solidification process. A structural heredity of early embryo is proposed to explain the structural preference of solidification. Defects were found inside the solid core and play the same role as surface premelting on melting. hcp was found more stable than fcc in high temperature. The difference between melting and solidification points can be deduced coming fully from the overcoming of thermodynamic energy barrier, instead of kinetic delay of structural relaxation. © 2013 Elsevier B.V. All rights reserved. Source


Pan Y.-B.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing | Wu Y.-F.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing | Li Q.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing
International Journal of Hydrogen Energy | Year: 2011

Chou model was used to analyze the influences of LaNi5 content, preparation method, temperature and initial hydrogen pressure on the hydriding kinetics of Mg-LaNi5 composites. Higher LaNi5 content could improve hydriding kinetics of Mg but not change hydrogen diffusion as the rate-controlling step, which was validated by characteristic reaction time tc. The rate-controlling step was hydrogen diffusion in the hydriding reaction of Mg-30 wt.% LaNi5 prepared by microwave sintering (MS) and hydriding combustion synthesis (HCS), and surface penetration was the rate-controlling step of sample prepared by mechanical milling (MM). Rising temperature and initial hydrogen pressure could accelerate the absorption rate. The rate-controlling step of Mg-30 wt.% LaNi5 remained hydrogen diffusion at temperatures ranging from 302 to 573 K, while that of Mg-50 wt.% LaNi5 changed from surface penetration to hydrogen diffusion with increasing initial hydrogen pressure ranging from 0.2 to 1.5 MPa. Apparent activation energies of absorption for Mg-30 wt.% LaNi5 prepared by MS and MM were respectively 25.2 and 28.0 kJ/mol H2 calculated by Chou model. Kinetic curves fitted and predicted by Chou model using temperature and hydrogen pressure were well exhibited. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source

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