Materials Science Forum Vols. 486-487

Abstract: In an effort to synthesize homogenized single phase d-CoSb3, this study considers the mechanical alloying (MA) of elemental Co and Sb powders using a nominal stoichiometric composition followed by hot pressing. Single phase, undoped CoSb3 skutterudites were successfully produced by vacuum hot pressing using MA powders without subsequent annealing. Phase transformations during mechanical alloying, powder annealing, and hot pressing were systematically investigated using XRD and SEM. Thermoelectric properties were measured and compared with the results of similar studies. Temperature dependences were also evaluated, and their correlations to phase transformation were examined.

Abstract: P-type Bi0.5Sb1.5Te3 compounds doped with 3wt.% Te were fabricated by spark plasma sintering after mixing large powders(PL) and small powders(PS). We could obtained the highest figure of merit(Zc) of 2.89×10-3/K in sintered compound mixed to PL:PS=80:20. This resulted from the increase of orientation by large powders(PS) and the reduce of pores by small powders. The figure of merit(Zc) of the sintered compound using only small powders(PS) showed lower value of 2.67×10-3/K compared with that of sintered compound mixed to PL:PS=80:20 due to the increase of electrical resistivity.

Abstract: A 49.8 at.%Ti-50.2 at.%Ni shape memory alloy was applied to a current collector of positive electrode for lithium/sulfur (Li/S) battery. Flexible austenitic phase having pseudoelasticity dominated in the Ti-Ni current collector at room temperature. In the discharge curve, two plateau regions due to the lithium polysulfide (Li2Sn) and the lithium sulfide (Li2S) were obviously observed. The initial discharge capacity was 1068 mAh/g for Li/S cell with the Al current collector, and that of the cell with the Ti-Ni current collector reached 1140 mAh/g. A little bit of declined cycle performance was associated with decreased sulfur utilization owing to a reaction with dissolved Ti and Ni elements. Compared with the Al current collector used commercially, the Ti-Ni alloy with pseudoelasticity was more suitable to apply for the current collector of Li/S battery.

Abstract: Thermoelectric properties of the spark plasma sintered n-type Bi2Te2.7Se0.3 compounds were characterized with the sintering temperature, time and hydrogen reduction process. The Seebeck coefficient, electrical resistivity and thermal conductivity were dependent on hydrogen reduction process as well as sintering temperature. The Seebeck coefficient and electrical resistivity decreased and thermal conductivity increased with reduction treatment and sintering temperature. The results suggest that the carrier density varies with the dissolved oxygen and Te vacancies generated during the pulverization process. The highest figure of merit of 3.11×10-3/K was obtained for the compounds spark plasma sintered at 460°C for 16min by using the reduced powders.

Abstract: Iron disulfide (FeS2) is attractive as a positive electrode material in lithium batteries because of its low material cost, environmental non-toxicity, and high specific energy density. Furthermore, natural pyrite is a secondary product of the mining extraction of coal. For such reasons, natural and synthetic pyrites have been proposed as active cathode materials in primary lithium batteries. We investigated the effect of temperature and current density on the electrochemical properties of lithium-FeS2 batteries. The specific discharge capacity of Li/FeS2 cells varied from 700 to 900mAh/g based on FeS2.

Abstract: Ni/YSZ composites for a cathode that can be used in high temperature electrolysis were prepared by ball milling of Ni and YSZ powder. Ball milling was performed in a dry process and in ethanol. The microstructure and electrical conductivity of the composites were examined by XRD, SEM, TEM and a 4-point probe. XRD patterns for both the dry and wet ball-milled powders showed that the composites were composed of crystalline Ni and YSZ particles. The patterns did not change with increases in the milling time up to 48 h. Dry-milling slightly increased the average particle size compared to starting Ni particles, but little change in theparticle size was observed with the increase in milling time. On the other hand, the wet-milling reduced the average size and the increasing milling time induced a further decrease in the particle size. After cold-pressing and annealing at 900 oC for 2 h, the dry-milled powder exhibited high stability against Ni sintering so that the particle size changed little, but the particle size increased in the wet-milled powder. The electrical conductivity increased after sintering at 900 oC. Particles from the dry and wet process became denser and contacted closer after sintering, providing better electron migration paths.

Abstract: Emissive carbon coating was prepared using a carbon black powder and a phenolic resin binder suspension. Interior of an alumina tube with an emissivity of 0.75 was coated with the emissive coating and its energy saving performance was investigated using a vacuumed alumina tube up to 1000°C. The vacuumed cavity temperature of the carbon-coated alumina tube embedded in an electrically heated furnace was always higher than that of the uncoated one for the same surface temperature of the tube. The cavity temperature difference between the carbon-coated and uncoated tube increased with the surface temperature of the alumina tube. At the surface temperature of 1000 °C, the cavity temperature difference reached about 20°C. Heating the carbon-coated alumina to raise the cavity temperature from an ambient temperature to 1000°C at a constant heating rate of 5°C/min yielded an energy consumption of 559 Wh, while the uncoated one resulted in energy consumption of 595 Wh. As the holding time to maintain the cavity temperature of 1000°C was extended to 120 min, the energy-saving increased from 6% to 11%.