Papers by Author: Ke Zhang

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Authors: Guo De Li, Jing Bian, Zhong Qiu Cao, Ke Zhang, Ya Jun Fu
Abstract: The two Cu60Ni20Cr20 alloys with the different grain size were prepared by conventional casting (CA) and mechanical alloying (MA) through hot pressing. Effect of the grain size on electrochemical corrosion behavior of the two Cu60Ni20Cr20 alloys was also studied in solutions containing chloride ions. Results show that the free corrosion potentials of the two alloys move toward to negative values, corrosion current densities increase and therefore corrosion rates become faster with the increment of chloride ion concentrations. CACu60Ni20Cr20 alloy and MACu60Ni20Cr20 alloy have passive phenomena in 0.05mol/L Na2SO4 neutral solution, but passive phenomena become weak or disappear when the chloride ions are added. Corrosion rates of the nanocrystalline MACu60Ni20Cr20 alloy become slower than those of the coarse grained CACu60Ni20Cr20 alloy in solutions containing the same chloride ion concentrations because MACu60Ni20Cr20 alloy is able to produce large concentrations of grain boundaries and passive elements is able to diffuse quickly to form the protective film.
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Authors: Yan Wang, Shi Wei Wu, Hao Yu, Na Na Gong, Zhong Qiu Cao, Ke Zhang
Abstract: We report on the preparation and hydrogen desorption/absorption kinetics of nanocrystalline magnesium hydride (MgH2) added commercial TiO2 by high-energy ball milling. The phase and composition of the as-milled powders are characterized by X-ray diffraction (XRD). The results show that the milled sample contained MgH2 phase, small amount of Mg and various phases of TiO2 such as tetragonal and orthorhombic structure. The effect of the milling time (10, 20 and 30 h) on the hydrogen desorption property of MgH2 has been investigated and found that the milling time of 20 h has excellent dehydrogenation properties, which can release 3.3 wt% H2 within 60 min at 300 oC, which indicates that the kinetics of hydrogen desorption of MgH2-TiO2 composite has been greatly enhanced compared to the pure MgH2. Moreover, hydrogen absorption kinetics of the sample milled 20 h has been studied and the hydrogen content is 0.7, 0.8 and 1.2 wt% H2 at 250, 280 and 300 oC within 60 min, respectively.
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Authors: Zhong Qiu Cao, Ting Wang, Ke Zhang, Hui Zhang
Abstract: Microstructural characteristics and electrochemical properties of Mg40Al60 hydrogen storage alloy prepared by mechanical alloying (MA) method were studied by XRD, discharge capacities, polarization curves and electrochemical impedance spectroscopies(EIS). The intensities of XRD peaks become weak and XRD peaks have a broadening with the increment of ball milling time due to fine grain size and increased internal stress. The discharge capacities of the alloy increase before the alloyed powders were milled for 10h, but they decrease after the alloyed powders were milled for 10h with the increment of ball milling time. The discharge capacities are highest when the alloyed powders were milled for 10h. There are passive phenomena in polarization curves. The corrosion current densities increase with time at the beginning of ball milling and then decrease. The electrochemical impedance spectroscopies(EIS) are composed of a single capacitive loop and the electrode reaction is controlled by charge transfer at alloy/electrolyte interface.
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Authors: Ke Zhang, Xiao Yu Zhao, Shu Li Liu, Zhong Qiu Cao, Hui Zhang
Abstract: Mg(NH2)2 was synthesized by first high energy milling MgH2 powder in a 99.995% NH3 atmosphere and then heat treating at 300oC, and hydrogen storage properties of prepared Mg(NH2)2+2.2LiH (molar ratio) had been studied in the temperature range of 150-240oC. It was found that mechanical milling of Mg (NH2)2 and LiH with molar ratio 1:2.2 followed by heat treatment under static hydrogen pressure and dehydrogenating at 208.5oC yields the desired reversible hydrogen storage phase: Li2Mg(NH)2. Desorption kinetics reveal a rapid reaction for the system and the maximum hydrogen capacity can reach 4.6 wt. % at 208.5oC. The system starts to dehydrogenate at 150oC and the Arrhenius activation energy Ea of desorption reaction can be determined to be 25.8 kJ/mol H2 based on the data of kinetics. Additionally, the desorption reaction enthalpy (H) and entropy (S) are calculated to be 42.8 kJ/mol H2 and 149.2 J. K-1/ mol H2 respectively from PCI measurements.
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