Woosuck Shin

High performance p-type thermoelectric oxide based on NiO

Thermoelectric (TE) properties of NiO substituted by Na and Li were investigated at high temperature region. The Na-substituted NiO showed relatively low conductivity and high thermopower, compared to the Li-doped NiO. To increase the conductivity, additional Li doping on the Na0.05Ni0.95O was carried out, resulting in the increase in the power factor as high as 3.3×10−4 W/K2 m at 1260 K. Because of its rater high thermal conductivity, the ZT value of the Li-doped Na0.05Ni0.95O was similar level to that of the Li-doped NiO, but its temperature dependence was improved.

Electronic structure of NaCo2O4

Abstract Molecular orbital calculations for NaCo 2 O 4 have been carried out using the discrete-variational-Xα cluster method. NaCo 2 O 4 is the best oxide ever known for the thermoelectric power generation. To understand the transport properties of the NaCo 2 O 4 , the electronic states of Co ion was discussed, which plays an essential role in its transport property. The physical properties such as low spin state, p-type metallic conduction, and large effective mass of NaCo 2 O 4 were discussed using the calculated results of the cluster model in this study.

High temperature thermoelectric properties of Sr1−xLaxPbO3

Abstract The high temperature thermoelectric properties of 310–1160 K in air for the polycrystalline of Sr 1− x La x PbO 3 ( x =0–0.025) were investigated. The samples were prepared from the powder mixture of SrCO 3 , La 2 O 3 and PbO, and the changes with the La contents of the thermoelectric properties, conductivity and thermopower, of Sr 1− x La x PbO 3 showed that La acts as a dopant. Considering the temperature dependence of the thermoelectric properties of this oxide, the conduction mechanism for high temperature region could not be explained by broad band model adopted for low temperature region, but was similar to small polaron hopping and metallic. The electrical conducting mechanism at higher temperature region was discussed as reviewing from that of lower temperature.

Decomposition of (Bi, Pb)-2223 phase during sinter forging

Abstract Sinter forging is one of the pressure sintering methods, in which the side surface of a sample is free during uniaxial pressing at high temperatures. Such a condition caused unique phenomena in the decomposition of (Bi,Pb)-2223 phase. Bi 1.84 Pb 0.34 Sr 2.03 Ca 1.9 Cu 3.06 O y bulk superconductors were sinter-forged at the temperature range of 840–870°C and under the pressure of 9.8 MPa in air for 20 h. The (Bi,Pb)-2223 phase decomposed to (Sr,Ca) 2 CuO 3 phase and a liquid phase at high temperatures, followed by the extrusion of the liquid phase from the inner part to the outer part of samples due to the uniaxial pressure. Therefore, the decomposition of the (Bi,Pb)-2223 phase in the sinter forging was slow compared with that in the normal sintering or the hot pressing. The critical current increased with increasing sinter forging temperature. It was worth-noting that the sample sinter-forged at 870°C had the highest J c in spite of the highest content of (Sr,Ca) 2 CuO 3 phase. The high-temperature heat treatment was effective for the improvement of grain coupling. A better way in sinter forging is discussed for increasing J c .

6.3.4 Noble Metal Added Tin Oxide VOC Sensors as Nonanal Detection for Exhaled Breath Air Monitoring

We have investigated the VOCs-sensing properties of Pt, Pd, Au-loaded SnO2 thick film for exhaled breath air. It has been reported that breaths of lung cancer patients include long methylene chain-aldehydes, such as nonanal. The Pt, Pd, Au-loading for SnO2 type gas sensors is advantage for detect to low concentration VOCs. The Pt,Pd,Au/SnO2 element shows higher response to nonanal than a non-loaded SnO2 element. The combustion of nonanal molecules on the surface of SnO2 grains is assisted by added noble metals. A nonanal-sensing property of the The Pt,Pd,Au/SnO2 depend on an annealing temperature. We installed the sensor element to a prototype of breath monitor with gas-chromatograph system, and analyzed mixed gas including three long methylene chain-aldehyde gases.

P2.9.16 Deactivation mechanism of alumina supported Pt and Pd catalysts for gas sensor by hexamethyldisiloxane (HMDSO)

The deactivation mechanism of Pt/γ-alumina and Pd/γ-alumina catalysts for gas sensor by hexamethyldisiloxane (HMDSO) exposure has been investigated. The chemical state and local structure of Pd in the catalysts has been characterized under the reduction and oxidation after HMDSO exposure by in situ X-ray absorption fine structure (XAFS) measurement. The Pd/γ-alumina catalyst after HMDSO exposure hardly changed the chemical state of Pd even under the O2/N2 atmosphere though it oxidized easily under the O2/N2 atmosphere at the temperature of 300oC.