Papers by Author: Hai Jun Yu

Abstract: In this experiment, electroless plating method was used to obtain the hollow nickel fibres. Polyacrylonitrile fibres with the diameter about 10μm and 3mm length were chosen as the templates of electroless-plating through screening and optimizing various fibres. Low temperature alkaline solution with the sodium hypophosphite as the reducer was adopted and the optimal parameters were determined. Polyacrylonitrile composite fibres with a dense nickel coating about 5~7 μm thickness were obtained. The plated fibres were then sintered in the air to remove the organic templates. It had been found that the sintering temperature had great influences on the formation of the hollow fibres. The Polyacrylonitrile fibres could not be removed completely at low temperature (300°C), and when the temperature increased to 400°C, no organic fibres could be observed from SEM and the hollow nickel oxide fibres with dense wall were obtained. However, when the sintering temperature further increased to 500°C, great changes had been found, the hollow fibres with brittle porous wall were obtained. A dense and uniform hollow nickel fibres with nickel content higher than 90% were finally obtained after the hydrogen reduction treatment at the temperature of 750°C for 2 hours.

Abstract: In this paper, the influences of different binders (Hydroxypropyl Methyl Cellulose (HPMC), Carboxymethyl Cellulose Sodium (CMC), Polytetrafluoroethylene (PTFE) and Styrene- butadiene Rubber (SBR)) on high-rate discharge performances at low temperature for the negative electrode of Ni/MH battery have been studied by orthogonal experimental design. Electrochemical measurements have been conducted to investigate the capacity, charge-discharge performance, cyclic voltammetry and electrochemical impedance characteristics. The surface morphology and chemical compositions have been investigated by SEM and EDS. Based on the range analysis, the primary and secondary influence factors as well as the optimization results were obtained. From the CV characteristic curves, the oxidization peaks and reduction peaks are not clearly shown, which indicates that the redox reaction does not occur clearly after binders added. The EIS experiments show that the deterioration of the voltage characteristic of the battery is due to drying out of the separator that increases the ohmic resistance (Rs ), and the decay of the discharge capacity is due to the passivity surface that increases the charge-transfer resistance (Rt) of the battery.

Abstract: SiGe alloy composite material including TiN nanoparticle were prepared. The TiN nanoparticles as the inert scattering center were fabricated by Nitrogen plasma-metal reaction. The sintered samples were characterized by electrical resistivity and seebeck coefficient measurement. Adding nanophase inclusion into the SiGe alloy matrix, the Seebeck coefficient increased, the electrical conductivity decreased and the electrical power factor only slightly reduced.

Abstract: P-type Bi0.5Sb1.5Te3 thermoelectric materials have been prepared by ultrarapid quenching method with various cooling rates. The microstructures of sample are very different from those prepared by normal cooling. The ultrarapid quenched material was obtained in the shape of foils, the thickness of which were found to vary in the range of 6-20 μm, which corresponds to a cooling rate of about 106 K/S. X-ray diffraction evidenced a microcrystalline structure of the expected composition with a (0015) plane. Increasing the cooling rate, the Seebeck coefficient increase, the electrical conductivity decrease and the power factor rise up to 4.4×10-3 Wm-1K-2 .The highest ZT value of 1.22 was achivedachieved for the materials with the copper roller roration speed 40 m/s in room temperarure.