Wang Zhongmin

Effect of Temperature on Structure and Electrode Properties of LaNi3.8Co0.6Mn0.3M0.3 Hydrogen Storage Alloys

Abstract A series of experiments have been performed to investigate the temperature effects on the structure and the electrochemical properties of LaNi3.8Co0.6Mn0.3M0.3 (M=Ni, Al, Cu) hydrogen storage alloys at different temperatures of 238, 273, 303 and 323 K. Samples A, B and C were used to represent LaNi4.1Co0.6Mn0.3 (Ni substituted alloy), LaNi3.8Co0.6Mn0.3Al0.3 (Al substituted alloy) and LaNi3.8Co0.6Mn0.3Cu0.3 (Cu substituted alloy), respectively. The structures and the electrochemical properties of A, B and C hydrogen storage alloys were investigated by XRD and simulated battery test, respectively. The results reveal that all of the alloys are composed of the homogeneous LaNi5 phase with a CaCu5-type hexagonal structure. The low-temperature properties of the Cu substituted alloy are improved, and the high-temperature discharge capacity of the Al substituted alloy is enhanced. Electrochemical impedance spectroscopy (EIS) analysis shows that the improvement of high-temperature discharge capacity of alloy electrode B is attributed to the formation of dense oxide film to protect the active material from corrosion, which is not favorable to charge-transfer reaction at the interface of electrode-electrolyte. The deterioration in the high-rate dischargeability (HRD) of alloy electrodes B and C are attributed to the degradation of electrochemical kinetics, including both charge-transfer reactions on the electrode surface and hydrogen diffusion in the bulk. Furthermore, the good low-temperature performance of alloy electrode C is due to the improvement of charge-transfer reaction.

Mechanical Properties of Nb-Ti-Ni Alloy Membranes for Hydrogen Permeation

Abstract The microstructure and the mechanical property of Nb-Ti-Ni alloy membranes for hydrogen permeation were investigated. XRD and SEM were employed to characterize the structures of Nb-Ti-Ni alloys, and the bending property of the alloy membranes was measured by three-point bending tests. The results indicate that the as-prepared alloy is mainly composed of two phases, i.e. the primary bcc-Nb(Ni, Ti) solid solution phase, and [bcc-Nb(Ni, Ti)+β2-NiTi] eutectic phase. The former acts as functional cell for hydrogen permeation and the later is structural cell to keep the stability of alloy membrane. Mechanical properties of Nb-Ti-Ni alloy membranes have been improved to a certain degree by magnetic heat-treatment (MHT) along the three directions (0°, 45° and 90°). An obvious improvement has been made in the case of N7 sample by MHT at both of 0° and 45°, and in the case of N5 sample by MHT at 90° angle. MHT can lead to the change of grain sizes and grain orientations. In the case of MHT at 0° angle, a tiny bar-like region (consisting of eutectic phase) is formed and spreads along the direction of membrane surface, while some oral-like (or spot-like) region is regularly arranged on the surface, and the region extends vertically to the surface in the case of MHT at 90° angle. It is suggested that suitable MHT is beneficial to the improvement of the bending property of Nb-Ti-Ni alloy membranes.

Phase Transformation and Magnetic Properties of NdxFe60.5-xPt39.5 (x = 0, 0.5, 1.0, 1.5) Alloys

Abstract The effect of Nd addition on the structure, phase transformation and magnetic properties of FePt based alloys was investigated. The results indicated that the transition temperature from ordered FCT to disordered FCC phase decreased with increasing Nd concentration, but for alloys quenched rapidly from the γ phase region into ice-water, it increased with increasing Nd. The Nd element not only effectively reduced the grain size of the ordered phase but also decreased the degree of the ordered phase and refined the grains of the FCC matrix phase. The remanence ratio and coercivity of the FePt based alloy as a function of the Nd content had maximum values, respectively.