High-Performance Ceramics III

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Authors: Jing Liu, Jing Feng Li
Abstract: Bi2Te3-based alloys are currently best-known, technological thermoelectric materials near room temperature. In this paper, Bi2Te3 and nano-SiC dispersed Bi2Te3 were prepared by mechanical alloying followed by spark plasma sintering (SPS). Raw powders of Bi, Te and SiC were mixed and mechanically alloyed in an argon atmosphere using a planetary ball mill. The SPS temperature was 623K, and the holding time was 5 minutes. The samples were characterized by X-ray Diffraction (XRD) and Scanning electron Microscope (SEM). The thermoelectric properties: i.e. Seebeck coefficient, electrical resistivity and thermal conductivity were measured at temperatures from room temperature to 573K, followed by the evaluation of figure of merit. The results revealed that the SiC dispersion in the Bi2Te3 matrix increased Seebeck coefficient. Although the electrical resistivity was increased somewhat, the thermal conductivity was reduced by the SiC dispersion, indicating that promising thermoelectric materials with enhanced mechanical properties may be obtained in the nano-SiC dispersed Bi2Te3 composites with optimal compositions.
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Authors: Guan Jun Qiao, Y.W. Shi, Ji Qiang Gao, Hong Jie Wang, Jian Feng Yang, Zhi Hao Jin
Abstract: The effects of free silicon on thermoelectric properties of reaction-bounded silicon carbide (RB-SiC) were studied. RB-SiC ceramic consists of some free silicon after reaction sintering. Some RB-SiC samples were reheated at high temperature in vacuum to adjust silicon content. The results showed that free silicon affects thermoelectric properties remarkably, especially for the thermoelectric power. A surprising phenomenon was found in SiC/Si composite consisting ~20wt% free-Si, i.e., thermoelectric power, figure of merit Z and ZT are all sharply increased above 400oC. The peak value (4.2X10-4) of ZT appears in original SiC/Si composite at about 500oC, which is increased more than 1000 times than that at room temperature.
401
Authors: Min Zhou, Li Dong Chen, Chu De Feng, Xiang Yang Huang
Abstract: Pd-doped TiCo1-xPdxSb (0 £ x £ 0.08) half-Heusler compounds were synthesized by a solid-state reaction method and their electrical transport properties in the temperature range of 300-900 K were investigated. Single phase TiCo1-xPdxSb was obtained in the range of 0 £ x £ 0.08. The lattice parameters increased with Pd content. Doping of Pd on the Co site resulted in a great increase of electrical conductivity without significant decrease of Seebeck coefficient. A large power factor of 26 µW/K2 cm was observed for TiCo0.92Pd0.08Sb compound at 300 K.
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Authors: Gui Ying Xu, Xiao Feng Wu, Li Li Zhang, Chang Chun Ge
Abstract: SixGe1-x (x = 0.75 for n-type and 0.7 for p-type) is a typical thermoelectric material used at higher temperature as thermoelectric generator. Its property is dependent on the composition. SixGe1-x containing different amount of fullerite added as hollow quantum dot were fabricated by hot-pressing method. The relations among thermoelectric property, the amount of fullerite and the microstructure were investigated by normal measurement and analytical method.
409
Authors: Bin Zhu
Abstract: Our developments on ceramic composite conductors have experienced about 15 years from the oxyacid-salts oxide proton-based conductors, non-oxide containment salts, the ceria-based composite electrolytes, hybrid proton and oxygen ion conductors and nano-composites. A special emphasis is paid to new functional nano-composites based on hybrid proton and oxygen ion conductors that have demonstrated advanced properties and fuel cell applications, e.g., excellent ionic conductivity of 0.01 to 1 Scm-1 and performances of 200 - 1000 mWcm-2 for temperatures achieved for fuel cells between 400 and 700°C. Some proton and oxygen ion conducting mechanisms in the materials are reviewed and discussed. The hybrid ion conduction and dual electrode reactions and processes create a new generation fuel cell system.
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Authors: Franck Tancret, Donald M. Schleich
Abstract: One of the most promising technologies for future applications of solide oxide fuel cells (SOFC)is the so-called “anode-supported” configuration: a dense yttria-stabilised zirconia (YSZ) ceramic electrolyte is deposited as a thin film over a porous Ni / YSZ cermet substrate anode, followed by a porous ceramic cathode such as La1-xSrxMnO3 (LSM). In this paper, a short review is made of the current technologies available to achieve this particular architecture, and to optimise the service behaviour. Then, alternative materials and fabrication technologies, as well as their possible impact on performance, are proposed and investigated.
419
Authors: Xiang Rong Liu, Bin Zhu, Jin Rui Xu, Jun Cai Sun, Z.Q. Mao
Abstract: In this work ion conductivity and FC application were studied for the new type composite material based on SDC (samarium doped ceria) and Li2SO4. Significant conductivity enhancement was achieved, e.g. 10-2 – 0.4 Scm-1 for the SDC-Li2SO4 compared to 10-4 -10-2 Scm-1 for the SDC between 400 and 650°C. Some ion conductivity mechanisms were proposed correspondingly. Using the SDC-Li2SO4 composite materials as the electrolytes, we achieved high performances, 200-540 mWcm-2, for intermediate temperature (450-650°C) solid oxide FC (ITSOFC) applications. Sulfates, typically Li2SO4, have an excellent chemical stability in sulfur containing atmosphere. The sulfate-ceria (SDC-Li2SO4) composite materials can thus meet the demands to develop the sulfur tolerant and H2S FC technologies, which was also demonstrated successfully with significant importance for both fundamental and applied research.
425
Authors: Xing Shi, Yue Zhang
Abstract: A new type of amperometric oxygen sensor was developed by an approach of co-pressing and co-sintering YSZ solid electrolyte. A dense LSM+YSZ composite electrode which was used as both cathode and diffusion barrier. Pre-sintered composite and YSZ powders were dry-pressed together to form a sheet with dual-layer of LSM+YSZ/YSZ. The sheet was then sintered at 1450°C. The anode was made of Pt paste, which was printed on to the other side of YSZ. The experiment results showed that the oxygen sensor exhibited a quite low operating temperature. At 400°C, the limiting current appeared in the voltage from 0.7 to 1.2V and the limiting current was a good linear relationship with the oxygen concentration up to 10 %. The sensor has some excellent features such as a rapid response, no reference gas, simple configuration and low cost. Taken together with the chemical stability of the diffusion barrier, the sensor is suitable for the control of air-to-fuel ratio in lean-burn internal combustion engines.
431
Authors: Wei Tao Bao, Yin Zhu Jiang, Guang Yan Zhu, Jian Feng Gao, Guang Yao Meng
Abstract: Dense YSZ thin film with a thickness from 2 to 15 µm on porous Ni-YSZ anode support was fabricated by a novel powder coating process. The performance of the cell with a composite of Sm0.8Sr0.2CoO3- YSZ (40 wt.%) as cathode was examined over a temperature range from 550 to 800 °C, using H2 -3% H2O as fuel and air as oxidant. The maximum power density of the cells was over 300 mW/cm2 at 800 °C. The open circuit voltage of the cells reached 1.1 V at 750 °C, illustrating the full dense of the YSZ electrolyte. The anode-electrolyte interfacial resistances were negligible in comparison with that of cathode-electrolyte, indicating the good coherency of the YSZ electrolyte to the anode support. These results demonstrate the reliability of this novel process for thin electrolyte SOFCs.
435
Authors: Da Ming Chen, Xiao Guang Liu, Jian Feng Tong, Bao Wei Li
Abstract: A new technique for the fabrication of yttria stabilized zirconia (YSZ) substrates using aqueous gel-casting has been developed. This technique has been used to fabricate planar thin-substrate YSZ fuel cells. A thin-substrate YSZ electrolyte with high density and low porosity was prepared by this method with 57vol% solid content slurry. The character of the technique was discussed based on the influence of dispersant and pH value on slurry. After sintering, the YSZ electrolyte thickness is between 100 and 200µm, and the electrolyte area is 100 × 100 mm2. The research shows that aqueous gel-casting allows fabricate thin YSZ substrate with high density and homogenous structure. The method is suitable for preparing thin-substrate electrolyte of yttria stabilized zirconia.
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