Correlation between structural and electrical properties in highly porous (Y,Sr)(Ti,Nb)O3−δ SOFC anodes

In order to find a relationship between structural and electrical properties, niobium and yttrium doped SrTiO₃ ceramics were prepared via solid-state reaction. The samples were sintered in hydrogen and air conditions. The samples were also fabricated with a pore-former to obtain highly porous specimens. The electrical properties of Nb-doped SrTiO₃ samples and yttrium and niobium co-doped SrTiO₃ were compared. The comparable electrical properties were observed and discussed according to previous literature reports. It was noticed that the synthesis in a reducing hydrogen atmosphere can increase the solubility of dopants. Moreover, the samples sintered in air presented lower conductivity level and worse structural properties than the samples sintered in hydrogen. The explanation of obtained results was also suggested and discussed.     

High temperature monoclinic-to-tetragonal phase transition in magnesium doped lanthanum ortho-niobate

Magnesium doped lanthanum ortho-niobate (La_0.98Mg_0.02NbO₄) was prepared by the molten salt synthesis method. X-ray diffraction and dilatometry methods were used to study high temperature behavior of the ceramic material. Special attention was paid to the phase transition between the monoclinic and tetragonal phases. The values of spontaneous strain on the basis of unit cell parameter, obtained by Rietveld refinement, have been calculated as well as Landau order parameter. The thermal expansion coefficient (TEC) of La_0.98Mg_0.02NbO₄ was determined to be 12×10^?6 1/K and 8×10^?6 1/K below and above 500 °C, respectively.     

Evaluation of 316 L porous stainless steel for SOFC support

Solid oxide fuel cells (SOFCs) supported on porous steel substrates are recently gaining much attention, because fabrication cost of SOFC might be significantly reduced. In this paper high temperature properties of porous stainless steel 316 L for application in SOFCs are evaluated. The 316 L was investigated using thermogravimetric analysis, XRD analysis and electrical measurements of scales formed on steel surface. The YSZ ceramic electrolyte was deposited on the 316 L and interaction of formed interlayer was evaluated. The results show that the 316 L is applicable only for SOFCs operated below 500 °C.     

Counseling: Theoretical & philosophical issues.

In this article the author discusses three main topics that focus on theoretical and philosophical issues. First he discusses "how philosophical considerations are relevant to our division," then he discusses "major theoretical orientations and question," and finally he discusses "future differences with regard to philosophical/theoretical constructions." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of porous 430L stainless steel for SOFC operation at intermediate temperatures

In this paper a 430L porous stainless steel is evaluated for possible SOFC applications. Recently, there are extensive studies related to dense stainless steels for fuel cell purposes, but only very few publications deal with porous stainless steel. In this report porous substrates, which are prepared by die-pressing and sintering in hydrogen of commercially available 430L stainless steel powders, are investigated. Prepared samples are characterized by scanning electron microscopy, X-ray diffractometry and cyclic thermogravimetry in air and humidified hydrogen at 400 °C and 800 °C. The electrical properties of steel and oxide scale measured in air are investigated as well. The results show that at high temperatures porous steel in comparison to dense steel behaves differently. It was found that porous 430L has reduced oxidation resistance both in air and in humidified hydrogen. This is connected to its high surface area and grain boundaries, which after sintering are prone to oxidation. Formed oxide scale is mainly composed of iron oxide after the oxidation in air and chromium oxide after the oxidation in humidified hydrogen. In case of dense substrates only chromium oxide scale usually occurs. Iron oxide is also a cause of relatively high area-specific resistance, which reaches the literature limit of 100 mΩ cm² when oxidizing in air only after about 70 h at 800 °C.     

Counseling psychology in Veterans Affairs medical centers: Perceptions of chiefs of psychology.

Counseling psychology (CP) has attempted to define itself in ways that accurately reflect the specialty, that do not limit its practitioners from working in their domains of competence, and that set it apart from clinical psychology. S. Cleveland (1980) considered the success of this self-definition in a survey on the perception of counseling psychologists by chiefs of psychology services in the Veterans Administration medical centers (VAMCs). He suggested that counseling psychologists were "defecting" to clinical positions in the VAMCs and that some negative bias existed toward CP by some VAMC chiefs. This survey attempts to determine whether the chiefs' attitudes have shifted as CP redefines itself. Results were similar to those found by Cleveland: Negative bias exists but has decreased. In addition, counseling psychologists in the VAMCs have found a variety of positions, expanding their role beyond previous narrow definitions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrical and structural properties of Nb-doped SrTiO<Subscript>3</Subscript> ceramics

Niobium-doped strontium titanate synthesized via conventional solid-state reaction has been studied. Influence of niobium content on the lattice parameters and electrical conductivity has been reported. Various reduction conditions have been investigated. For samples reduced in hydrogen at 1400°C, a transition from thermally activated to metallic behavior has been observed. Maximum electrical conductivity (ca. 55 Scm⁻¹ at 650°C) has been observed for the SrTi_0.98Nb_0.02O_3-δ sample. The relation of electrical conductivity with the porosity of the samples has been shown.     

Conductivity improvement of Ce0.8Gd0：2O1.9 solid electrolyte

Solid oxide fuel cells based on doped ceria electrolytes offer operating temperatures of 600 °C. During recent years much attention was aimed at successful powder preparation with high sinter activity and high conductivity. The properties of ceria electrolyte are very sensitive to impurities introduced during powder and electrolyte fabrication. One of the most successful and commercially available processes for the production of clean powders is based on the addition of several percent metallic cations that will react with impurities and segregate into the triple points of grain boundaries. In this work the results obtained from doping of CGO20 by 2% Ca and prepared by different routes were presented. The way of introducing Ca seemed to play an important role.     

Endogenous Shared Punishment Model in Threshold Public Goods Games

Computational Economics - Population growth and greater human well-being imply increased use of scarce resources, which makes innovative proposals for fair redistribution policies necessary. The...