Papers by Author: Zhong Qiu Cao

Abstract: Recently, Magnesium hydride MgH₂ is one of the attractive hydrogen storage materials because it reaches a high hydrogen capacity. However, the reaction kinetics is too slow and needs high temperature for progressing hydrogen absorption and desorption reactions, which hinders the process of practical applications and it is necessary to improve the hydrogen storage propesties. In this paper, most used or under research methods (Doping with metal and compound) of improving on the hydrogen storage of magnesium hydride are reviewed, in particular to elements substitution, addition of transition metal oxides or fluorine and so on. The advantages and disadvantages of vaious methods of improving on the hydrogen storage of magnesium hydride are compared. The trend of the methods of improving is also introduced.

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.

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.

Abstract: Electrochemical corrosion behavior of Cu-20Fe-12Cr alloys prepared by powder metallurgy (PM) and mechanical alloy (MA) with the different grain size was studied in solutions containing chloride ions. The free corrosion potentials move toward negative values and corrosion rates become faster with the increase of chloride ion concentrations for two alloys. Electrochemical impedance spectroscopy (EIS) plots of PMCu-20Fe-12Cr alloy are composed of a capacitive loop and a diffusion tail. Corrosion processes are controlled by diffusion. EIS plots of MACu-20Fe-12Cr alloy in Na2SO4 or 0.02mol.L^-1NaCl solution are unable to have characteristics of Warburg impedance. Corrosion processes are controlled by electrochemical reactions. After chloride ion concentrations increase up to 0.05mol.L^-1, their EIS plots are composed of double capacitive loops with a straight line induced Warburg resistance between two capacitive loops. The above EIS plots imply the existence of pitting corrosion. The corrosion rates of MACu-20Fe-12Cr alloy become faster than those of PMCu-20Fe-12Cr alloy because the reduction in the grain size of MACu-20Fe-12Cr alloy produces large concentrations of grain boundaries.