Moderate additions of monoclinic SrAl 2 O 4 to perovskite-type SrFe͑Al͒O 3−␦ mixed conductors improve the sinterability and thermomechanical properties, including the thermal shock resistance, Vickers hardness, and fracture toughness, and decrease thermal expansion. The iron solubility in SrAl 2 O 4 , a mixed ionic and n-type electronic conductor with insulating properties, is lower than 5%. The total conductivity of SrAl 2 O 4 ceramics in air varies in the range 10 −7 -10 −5 S/cm at 973-1223 K. The transport properties and phase stability of dual-phase ͑SrFe͒ 1−x ͑SrAl 2 ͒ x O z ͑x = 0.3-0.7͒ composite membranes, where the partial dissolution of strontium aluminate in the ferrite phase leads to formation of A-site-deficient Sr 1−y Fe 1−2y Al 2y O 3−␦ ͑y Ϸ 0.08-0.12͒, are determined by the perovskite component. The total conductivity and Seebeck coefficient oxygen partial pressure dependencies exhibit general trends typical for SrFeO 3 -based solid solutions. Although the conductivity and oxygen permeability of ͑SrFe͒ 1−x ͑SrAl 2 ͒ x O z composites decrease with increasing x, the permeation fluxes through ͑SrFe͒ 0.7 ͑SrAl 2 ͒ 0.3 O z ceramics are comparable to those through single-phase SrFe 0.7 Al 0.3 O 3−␦ . Under high p O 2 gradients such as air/͑H 2 -H 2 O͒, the oxygen transport is limited by surfacerelated processes, enabling stable operation of ͑SrFe͒ 0.7 ͑SrAl 2 ͒ 0.3 O z membranes. This composition was selected for fabrication of tubular membranes by the cold isostatic pressing. Surface modification of ͑SrFe͒ 0.7 ͑SrAl 2 ͒ 0.3 O z in order to enhance the exchange kinetics was found inappropriate from a stability point of view.
stantial (Fig. 4b), especially for small Monte Carlo models. Nonetheless, the scatter diminished steadily upon increasing number of spheres, and the estimates obtained with 1000 spheres were already rather uniform. But strikingly, the ensemble minimum estimates obtained with a given, small number of spheres were practically stationary, and they delivered surprisingly accurate predictions for the results obtained with Monte Carlo models with 1000 spheres. We also conducted studies at four other sphere volume concentrations between 0.2 and 0.5, and saw the same picture, namely that the ensemble minimum estimates obtained with Monte Carlo models with a few dozen spheres delivered remarkably accurate estimates for the results obtained with 1000 spheres. These results indicate that small computer models with a few dozen spheres are already large enough to accommodate the local microstructural configurations that control the onset of catastrophic damage propagation.Technologically, by loading inclusions with a high dielectric permittivity into a polymer, one obtains a composite material with an increased effective permittivity. However, because of the local electric field magnifications, this improvement is accompanied by a parallel decrease in the effective voltage breakdown field. Table 1 presents results obtained for the random composite studied in this work, and one can see that the unwanted decrease in the effective voltage breakdown field is considerably more pronounced than the targeted increase in the effective dielectric constants. One could expect that the regular microstructure composites should exhibit a less pronounced decrease in the voltage breakdown of the composite. Results presented in Table 1 confirm this premise, but nonetheless they also indicate that the unwanted decrease in the voltage breakdown field of the composite is still stronger than the increase seen in the effective dielectric constants.To conclude, our results suggest that in random microstructure composites, the voltage breakdown is a strongly localized phenomenon and that it is feasible to employ remarkably small computer models to extract reliable estimates for the voltage breakdown field characteristic of large, laboratory samples.Ceramic foams are lightweight materials with a cellular structure. Due to the combination of properties resulting from the ceramic material and the cellular structure, these foams have a high potential for many applications. To have access to all these applications, the shaping techniques that are used to produce these ceramic foam structures must result in sufficient mechanical strength and in a well-controlled macroand microstructure. As the obtained structure is strongly related to the manufacturing route, the ceramic-processing group of Vito focuses on the development of new ceramic foam synthesis routes aiming at materials with improved properties.Three different manufacturing ways are tested: a reaction bonded-modified (RB) polyurethane replica technique, gel casting, and a method of hollow building ...
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