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The aim of this work was to present the methodology for reliably determining the elastic moduli of partially sintered porous SOFC cathode films by appropriate nanoindentation experiments and analysis. The 3D microstructures of the porous crack-free perovskite LSCF films, which were prepared by sintering at 900-1200°C, were reconstructed based on dual-beam FIB/SEM tomography, followed by FEM to compute the elastic moduli. Detailed analysis of the nanoindentation results was also made to estimate the film-only elastic modulus for each film. The experiments showed that reliable measurements of the true film properties were obtained by data extrapolation provided that indentation depth was 0.1-0.2 of the film thickness. Effects from surface roughness and substrates responsible for the data deviation were taken into account. It was found that the elastic modulus increased from 32-122GPa as the sintering temperature raised from 900-1200°C and the porosity decreased from 47-15%. Further insights were gained into the porosity evolution, plastic deformation and substrate effect in the indented films with the aid of FIB/SEM. Excellent agreement was found when comparing the elastic moduli derived from nanoindentation and FEM, implying the present method could be an effective tool for investigating the way in which the mechanical properties of porous ceramic films is influenced by their microstructures. [ABSTRACT FROM AUTHOR]

The degradation of SOFC electrodes is often determined by their microstructure changes. It is desirable that the microstructure evolution of electrodes in service can be simulated in 3-D for real materials so that the changes in their electrochemical performance can be predicted. This involves changes in important parameters such as: electronic and ionic conductivities: TPB (triple phase boundary) density and connectivity; and tortuosity of condensed phases and porosity. In this contribution a new cellular automaton (CA) approach to simulating complex microstructure evolution is presented, which is based on free energy reduction by using an interface imbalanced interaction model. The approach is validated first in 2-D examples to reproduce wetting between two solids and grain boundary grooving, which shows the new approach is fully consistent with classical theories. The approach is then applied to simulation of the evolution of a real 3 dimensional microstructure of a Ni-YSZ cermet fuel cell anode. The modeling results show that the microstructure evolution is sensitive to the wettability of Ni on YSZ and that a good wettability is helpful in maintaining a slower coarsening rate and smaller reduction of electrode performance. [ABSTRACT FROM AUTHOR]

Gregory Melleuish, The Packaging of Australia: Politics and Culture Wars (Sydney: University of New South Wales Press, 1998), 143 pp., $25, ISBN 0 86840 584 1. This book is ambitious [...]

The transfer of chromium from metallic components into the cathode of a solid oxide fuel cell (SOFC) can severely degrade its performance and is known as 'chromium poisoning'. In this study we investigate the relationship between the amount of chromium introduced into La0.6Sr0.4Co0.2Fe0.8O3-δ, LSCF (6428), cathodes and their electrochemical performance, and clarify further the poisoning mechanism. LSCF cathodes were screen printed onto Ce0.9Gd0.1O1.95 electrolyte pellets and infiltrated with Cr(NO3)3 solutions to different Cr levels up to 2 wt%. Electrochemical impedance spectroscopy at 500--800°C showed that even very low levels of Cr give a significant increase in cathode polarization resistance, which increases with Cr concentration. The impedance response was analyzed using the model of Adler, Lane and Steele to extract oxygen self-diffusion (DO) and surface exchange (kO) parameters for the LSCF. The results show that Cr reduces both DO and kO, the latter being the more affected. However, the activation energies for polarization resistance, DO and kO are not significantly affected by Cr content. This indicates that the Cr poisoning mechanism involves the de-activation of sites for oxygen exchange on the LSCF surface and that the cathode's residual activity is by means of remaining active sites. [ABSTRACT FROM AUTHOR]

3YSZ green layers approximately 10 lm thick were screen printed onto 3YSZ substrates up to 300 lm in thickness. The stress induced by constrained sintering of the film (between 11501 and 1350°C) was measured by monitoring the bending displacement of vertical strips of bilayers using a long-distance microscope. In order to deduce the stress it was first necessary to measure the creep properties of the substrates by monitoring the bending of horizontal beams under gravity. The creep strain rate of the 3YSZ substrates was linearly dependent on applied stress at the low stresses and strains involved in the present work. The creep viscosity appeared to increase with strain (time), which might be due to changes in grain-boundary composition, and had higher activation energy at temperatures above approximately 1250°C. The magnitudes of the creep viscosities are in reasonable agreement with other creep data in the literature for 3YSZ. The in-plane stress induced during constrained sintering of the 3YSZ films had a maximum value of approximately 3 MPa at 1200°C. This behavior is consistent with literature results reported for constrained sintering of bulk alumina. The stress induced by the constraint is of a similar order to the estimated sintering potential. [ABSTRACT FROM AUTHOR]

Abstract: The oxygen tracer diffusion coefficient (D⁎) has been measured for 9 mol% scandia 2 mol% yttria co-doped zirconia solid solution, (Y2O3)2(Sc2O3)9(ZrO2)89, using isotopic exchange and line scanning by Secondary Ion Mass Spectrometry, as a function of temperature. The values of the tracer diffusion coefficient are in the range of 10−8–10−7 cm2 s−1 and the Arrhenius activation energy was calculated to be 0.9 eV; both valid in the temperature range of 600–900 °C. Electrical conductivity measurements were carried out using 2-probe and 4-probe AC impedance spectroscopy, and a 4-point DC method at various temperatures. There is a good agreement between the measured tracer diffusion coefficients (D⁎, Ea=0.9 eV) and the diffusion coefficients calculated from the DC total conductivity data (D σ , Ea=1.0 eV), the latter calculated using the Nernst–Einstein relationship. [Copyright &y& Elsevier]

The mechanical properties of magnesia–spinel composite ceramics, which are candidate materials for supporting solid oxide fuel cells, have been measured as a function of porosity (up to 30%) and temperature (up to 900°C). The theory for the ring-on-ring test has been re-examined to resolve an inconsistency in the literature. The Young's modulus shows an exponential dependence on porosity that is in agreement with the expectation of minimum solid area models. Fracture toughness, fracture energy, and flexural strength are all approximately proportional to Young's modulus. The mechanical properties are not greatly dependent on temperature, but there is a detectable increase in fracture toughness with temperature, which could be due to some limited plasticity. [ABSTRACT FROM AUTHOR]

Abstract: The bulk defect structure in Cr2−x Ti x O3 (x =0.05, 0.20 and 0.30) has been studied by X-ray absorption spectroscopy measurements at the Cr and Ti K-edges. The results show that the Ti is predominantly present in the IV oxidation state and resides on the normal Cr host lattice site. The dopant is charge compensated by Cr3+ vacancies and there is evidence for the formation of defect clusters; however, the detailed structure of these clusters could not be deduced. [Copyright &y& Elsevier]

Abstract: The defects in Cr2−x Ti x O3 (x =0, 0.2 and 0.3) were studied by a combination of X-ray diffraction, density and electrical conductivity measurements supported by atomistic simulation. The results are consistent with the Ti being dissolved as Ti4+ compensated by Cr vacancies which associate to form complex defects of lower energy. Ti doping gives n-type semiconductivity due to a small concentration of Ti3+ in equilibrium with the complexes. [Copyright &y& Elsevier]

The article evaluates the use of a computer model to predict the transport in composite cementitious barriers. The model includes the processes of advection, diffusion, and adsorption. The barrier used in the site trials had two layers of concrete with a layer of clay between them. Site trials have shown that the model provides a useful estimate but revealed some unexplained data.

Focuses on wet erosive wear of alumina with magnesium silicate additions. Effects of additive quantity, mean alumina grain size and residual stresses; Significance of residual stresses in magnesium silicate-densified alumina on microfracture of grain boundaries; Identification of the main material removal mechanism.

Examines the 1826 issues of the penal history of New South Wales (N.S.W.) and the place of convicts in local society. Arguments of `Sydney Gazette' and `Sydney Monitor'; Colonial government's right to take cash from convicts; Relationship between the Britain state and its N.S.W. colony; Problem in administration caused by dual status of convicts abroad.