Ion beam processing of oriented CuO films deposited on (100) YSZ by laser ablation

A systematic study of Ar ion implantation in cupric oxide films has been reported. Oriented CuO films were deposited by pulsed excimer laser ablation technique on (1 0 0) YSZ substrates. X-ray diffraction (XRD) spectra showed the highly oriented nature of the deposited CuO films. The films were subjected to ion bombardment for studies of damage formation, Implantations were carried out using 100 keV Arf over a dose range between 5 x 10(12) and 5 x 10(15) ions/cm(2). The as-deposited and ion beam processed samples were characterized by XRD technique and resistance versus temperature (R-T) measurements. The activation energies for electrical conduction were found from In [R] versus 1/T curves. Defects play an important role in the conduction mechanism in the implanted samples. The conductivity of the film increases, and the corresponding activation energy decreases with respect to the dose value.

Double-ceramic-layer thermal barrier coatings of La2Zr2O7/YSZ deposited by electron beam-physical vapor deposition

Double-ceramic-layer(DCL) thermal barrier coatings (TBCs) of La2Zr2O7 (LZ) and yttria stabilized zirconia (YSZ) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, surface and cross-sectional morphologies and cyclic oxidation behavior of the DCL coating were studied. Both the X-ray diffraction (XRD) and thermogravimetric-differential thermal analysis (TG-DTA) prove that LZ and YSZ have good chemical applicability to form a DCL coating. The thermal cycling test at 1373 K in an air furnace indicates the DCL coating has a much longer lifetime than the single layer LZ coating. and even longer than that of the single layer YSZ coating. The failure of the DCL coating is a result of both the bond coat oxidation and the thermal strain between bond coat and ceramic layer generated by the thermal expansion mismatch.

注浆法制备YSZ固体电解质及其性能研究

以多孔石膏模具为成型载体，以8mol%钇稳定氧化锆(YSZ)粉体为原料，采用注浆法制备出具一定体积和形状的全稳定YSZ固体电解质。对注浆成型工艺中制备素坯的各个环节的主要影响因素(粘结剂种类及用量的选择、固相含量、球磨时间等)与浆料稳定性、流动性及素坯密度之间进行优化实验，确定了制备悬浮稳定、流动性好的浆料的实验参数。 将利用上述浆料于多孔石膏模中成型后的素坯进行等静压操作，进一步提高其致密度，为制备致密化高的电解质材料奠定了条件。结果表明：注浆成型后的素坯在进一步等静压处理后相对密度可达53%左右，可以说注浆成型法是一种成型具一定体积素坯的简单可行的方法。 继而将成型后的素坯于不同的烧结条件下进行常压烧结，并对烧结后YSZ固体电解质的致密化程度、微观形貌(SEM)及导电性能进行测量和表征，借助于交流阻抗谱测量其导电性，采用氧浓差电池法测定其离子迁移数(能斯特响应)。通过对烧结体的性能分析，建立其致密程度、导电性与烧结条件之间的关系，并以此为依据来优化烧结工艺。 结果表明：样品的致密度随烧结温度和烧结时间的增加而提高，电导率随着致密度的提高而不断增加，其中在1550℃烧结3h的电解质制品500℃时的阻抗测试结果表明其离子导电率已超过投入实际使用的最小限定值；结合样品的微观形貌分析，在较高的烧结温度下晶粒增长显著，平均粒径可以达到微米级，而低温下增长不显著。 立足于砖层模型和多晶电解质晶界空间电荷层导电特性，对不同粒径的YSZ多晶固体电解质材料的晶界电导进行分析，结果表明随平均粒径的减小，YSZ多晶固体电解质材料晶界空间电荷层电势减小，而其中氧空位浓度增加，因此可以说，对高纯物质而言，晶粒的减小有助于提高其整体电导性。因而就优化烧结工艺而言，要制备高性能YSZ固体电解质可以以达到高致密度、抑制晶粒显著生长为原则来进行探讨。

Redox cycling of Ni-YSZ anode investigated by TPR technique

Effect of redox cycling on a Ni-YSZ anode prepared from 50 wt.% NiO and 50 wt.% YSZ was investigated by using temperature-programmed reduction (TPR), XRD and SEM techniques. XRD results showed that NiO was formed during re-oxidation. Both the XRD and TPR results depicted that the conversion of nickel to NiO depended on the re-oxidation temperature. The oxidation of Ni to NiO occurred quickly in the initial several minutes and then reached a quasi equilibrium. The TPR profiles tracing the redox cycling showed that it brought continuous changes in the NiO micro-structure at 800 degrees C, whereas at 600 degrees C it had only little effects on the reduction of NiO. Re-oxidation resulted in the formation of spongy aggregates of NiO crystallites. Redox cycling at 800 degrees C led to a continuous decrease in the primary crystallite size of NiO and a high dispersion of the Ni particles. A continuous expansion of the slice sample was observed in both of the oxidized and reduced states during the redox cycling at 800 degrees C, whereas this process did not occur during the redox cycling at 600 degrees C. (c) 2005 Elsevier B.V All rights reserved.

The role of Na surface species on oxygen charge transfer in the Pt/YSZ system

The role of sodium surface species in the modification of a platinum (Pt) catalyst film supported on 8 mol% yttria-stabilised-zirconia (YSZ) was investigated under a flow of 20 kPa oxygen at 400 °C. Cyclic and linear sweep voltammetry were used to investigate the kinetics of the oxygen charge transfer reaction. The Pt/YSZ systems of both ‘clean’ and variable-coverage sodium-modified catalyst surfaces were also characterised using SEM, XPS and work function measurements using the Kelvin probe technique.

Samples with sodium coverage from 0.5 to 100% were used. It was found that sodium addition modifies the binding energy of oxygen onto the catalyst surface. Cyclic voltammetry experiments showed that higher overpotentials were required for oxygen reduction with increasing sodium coverage. In addition, sodium was found to modify oxygen storage and/or adsorption and diffusion increasing current densities at higher cathodic overpotential. Ex situ XPS measurements showed the presence of sodium hydroxide, carbonate and/or oxide species on the catalyst surface, while the Kelvin probe technique showed a decrease of approximately 250 meV in the work function of samples with more than 50% sodium coverage (compared to a nominally ‘clean’ sample).

Co-tape casting fabrication, field assistant sintering and evaluation of a coke resistant La0.2Sr0.7TiO3-Ni/YSZ functional gradient anode supported solid oxide fuel cell

The ability to directly utilize hydrocarbons and other renewable liquid fuels is one of the most important issues affecting the large scale deployment of solid oxide fuel cells (SOFCs). Herein we designed La_0.2Sr_0.7TiO₃-Ni/YSZ functional gradient anode (FGA) supported SOFCs, prepared with a co-tape casting method and sintered using the field assisted sintering technique (FAST). Through SEM observations, it was confirmed that the FGA structure was achieved and well maintained after the FAST process. Distortion and delamination which usually results after conventional sintering was successfully avoided. The La_0.2Sr_0.7TiO₃-Ni/YSZ FGA supported SOFCs showed a maximum power density of 600mWcm^-2 at 750°C, and was stable for 70h in CH₄. No carbon deposition was detected using Raman spectroscopy. These results confirm the potential coke resistance of La_0.2Sr_0.7TiO₃-Ni/YSZ FGA supported SOFCs.

The role of low coverage sodium surface species on electrochemical promotion in a Pt/YSZ system

The effect of sodium-modification on the catalyst and electrocatalytic properties of a platinum catalyst supported on a YSZ solid electrolyte was studied. Increasing the sodium coverage on the catalyst surface appears to block some of the three-phase boundary (tpb) sites and reduces the rate of the charge transfer reaction. The promotion of the platinum surface reaction (ethylene oxidation) seems to a first approximation to be a function of the rate of oxygen supply or removal to or from the surface irrespective of whether this is contaminated by sodium or not (samples with sodium contamination require a higher overpotential to achieve the same current density as a clean sample because of poisoning in the tpb). At high negative polarisations (oxygen removed from the surface) the sodium contaminated samples show a significant increase in rate, possibly due to the decomposition of e.g. sodium hydroxides and carbonates. © 2012 Elsevier B.V.