Search

Dense and phase-pure ferroelectric ceramics of 75 mol.% Bi0.5K0.5TiO3– 25 mol.% BiFeO3are prepared by the conventional solid state reaction method. Their crystal structure is analyzed and discussed. The dielectric and piezoelectric properties of the ceramics are investigated at various temperatures. The ceramics exhibit relaxor-like dielectric properties and high electric field-induced strain (equivalent to 250-300 pm/V at 25-75°C), not previously reported for this composition, making it a promising lead-free alternative for actuator applications. [ABSTRACT FROM AUTHOR]

A thorough analysis of the thermal conductivity of virgin and spent porous Si3 N4-bonded SiC sidewall materials in the Hall- Héroult electrolysis cell is reported. The thermal conductivity, measured by the laser flash method, was observed to vary significantly among the virgin materials and also within a single block of the same material. A significant reduction of the thermal conductivity in both the bottom and top part of the spent blocks was observed, which could be correlated with significant changes in the microstructure in both regions due to chemical degradation. The thermal conductivity was correlated with the phase composition, apparent porosity, and microstructure related parameters like grain-boundary resistance, pore-shape, and pore-orientation factor. Analytical models were used to analyze the influence of these factors on the thermal conductivity of the Si3 N4-bonded SiC porous composites. Two different explanations for the significant reduction in the thermal conductivity in the bottom and the top parts of the spent block were proposed, and both were related to the microstructure evolution caused by the chemical degradation. [ABSTRACT FROM AUTHOR]

Abstract: The chemical and physical compatibility of SrCeO3 is investigated with respect to LaMO3 (M=Mn, Fe, Co) and La2− x Sr x NiO4 (x=0, 0.8), via the reaction of fine-grained powder compacts and solid-state diffusion couples. Compositions were chosen so as to give predictive insight into possible candidate materials for all-oxide electrochemical devices. Results show the primary reaction in these systems to be the dissolution of SrO from SrCeO3 into the LaMO3/La2− x Sr x NiO4, and corresponding formation of La-doped CeO2. Reaction kinetics are observed to be relatively fast, with element profiles suggesting the diffusion of Sr2+ in ceria to be surprisingly rapid. It is demonstrated that perovskite starting materials represent poor candidates for use with SrCeO3, reacting completely to form Ruddlesden-Popper/K2NiF4 type oxides. Reaction with La2NiO4 is less pronounced, and formation of secondary phases suppressed for the composition La1.2Sr0.8NiO4. It is thus concluded that Ruddlesden-Popper type oxides represent good candidate materials for use with a SrCeO3-based electrolytes when doped with appropriate levels of Sr. [Copyright &y& Elsevier]

Abstract: The pairing of proton conducting electrolytes with chemically compatible electrode materials is key to their use in electrochemical devices. The reactivity of BaZrO3 with respect to the well known ceramic oxides LaMnO3, LaFeO3, LaCoO3 and La2NiO4 has been investigated with a view to the development of chemically inert cathode materials. Annealing of powder mixtures of the candidate electrode and BaZrO3 showed only formation of small quantities of La2Zr2O7 as a secondary phase. The low level of reaction and good chemical compatibility were further evidenced by diffusion couples of electrode | electrolyte. Only minor inter-diffusion of Ba and La was observed. However, the materials show considerable mismatch in thermal expansivity, resulting in detachment of the electrode from the electrolyte on cooling. These results have predictive relevance across a wider range of systems, and indicate that co-existence can be achieved with careful balancing of chemical activity via chemical substitution. [Copyright &y& Elsevier]

Abstract In this paper the validity of the Operationalized Psychodynamic Diagnosis System is discussed. The discussion for each OPD axis is guided by the common scientific criteria like content-,criterion-,and construct validity. Reliability studies on OPD are summarized as an introduction to the validity issue. The studies show good to satisfying scores for interrater agreement for the research context. The results derived from the validity studies support the validity of the OPD system. There are also hints for improvements of multiple categories or items within each axis. For clinical routine OPD should become even more practice oriented. Therefore the OPD task force intends to construct a shorter version which will base on the results discussed in this article. [ABSTRACT FROM AUTHOR]

Stable and metastable phase equilibria in the binary system GeSe2-Se have been investigated by means of optical and electron microscopy, electron probe microanalysis (EPMA), x-ray diffraction (XRD), thermal analysis, and adiabatic calorimetry. A revised equilibrium phase diagram is presented. A not previously observed λ-type phase transition was observed near ∼420 K (147 °C) for GeSe2. The intermediate phase, φ, which earlier had been considered as metastable, is shown to be stable through extensive annealing experiments and by adiabatic calorimetry. The φ phase, with composition near Ge3Se7, melts incongruently at 658±5 K (385±5 °C) to GeSe2 and a liquid with 85±2 at.% Se. The liquidus of GeSe2 and φ was determined by EPMA of annealed-and-quenched samples. Both a stable (φ-Se-liquid) and a metastable (GeSe2-Se-liquid) eutectic point were observed. The stable one was observed at 480±2 K (207±2 °C) and 92.5±1.0 at.% Se, whereas the temperature of the metastable eutectic (GeSe2-Se-liquid) was observed to be ∼10 K lower. Metastable phase equilibria, obtained on thermal evolution of glasses with different compositions, are described and discussed. [ABSTRACT FROM AUTHOR]

Stability regions of θ-methods for the linear delay differential test equations where τ is a positive constant, are presented. In the case that p and q are real constant coefficients, necessary and sufficient conditions on the stepsize for the stability of a θ-method are obtained. Furthermore, when p and q are complex coefficients, sufficient conditions for the stability of the θ-methods are also given. [ABSTRACT FROM AUTHOR]

Presents a phase diagram of the system KF-AIF[sub 3]. Investigation of the system via differential thermal analysis, X-ray diffractometry and visual observation; Preparation of the samples by solution synthesis; Cell parameters of the compounds.

Describes the formation of glasses in the system Li3N-Ca3N2-P3N5 by the rapid quenching of fused mixtures of the nitrides at high pressures. Improvements in physical properties; Prevention of thermal decomposition; Description.

Abstract: The influence of the chemistry of the precursor solution on the deposition of thick oxide coatings by air blast spray pyrolysis is reported. Coatings of four different oxide materials were deposited using aqueous lanthanum–zirconyl, yttrium–zirconyl, aluminum, and aluminum–magnesium nitrate based precursor solutions. The most suitable deposition temperature interval was determined for each selected precursor solution system and correlated to thermogravimetric analyses of the as-deposited green coatings. The quality of the green coatings was further characterized in terms of microstructure, porosity, and crack-freeness by electron microscopy. The effect of the concentration of the precursor solution on the deposition temperature interval and the microstructure of the green coatings was explained in relation to the precursor salt saturation limit. A trend was established based on the results obtained for the four systems, and guidelines for successful deposition of thick coatings by spray pyrolysis are proposed. [Copyright &y& Elsevier]

Abstract: Compressive creep tests have been performed on perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3− δ ceramics. The activation energy, stress exponent and inverse grain size exponent of the steady-state creep rates are evaluated at p(O2)=0.21∙105 Pa and 0.01∙105 Pa in the stress, temperature and grain size ranges 5–20MPa, 1078–1208K and 2.5–17.4µm, respectively. The results indicate that the creep rate of Ba0.5Sr0.5Co0.8Fe0.2O3− δ is controlled by diffusion of cations via both the oxide lattice (bulk diffusion) and along grain boundaries. The creep rate of Ba0.5Sr0.5Co0.8Fe0.2O3− δ increases profoundly by more than one order of magnitude at 1153–1178K, which is tentatively linked with the onset of the hexagonal-to-cubic phase transition in this compound. [Copyright &y& Elsevier]

Abstract: The chemical and physical compatibility of the proton conducting electrolyte material LaNbO4 with the potential partner materials LaMO3 (Mo) and La2NiO4 is investigated via the reaction of fine-grained powders and solid-state diffusion couples. Results show generally good chemical compatibility for LaNbO4 with perovskite type compositions, particularly the LaFeO3 and LaMnO3 systems. In contrast, Ruddlesden–Popper type phases are predicted to be poor candidates for use with LaNbO4. Investigation of the La2O3–NiO–Nb2O5 and La2O3–CoO–Nb2O5 phase diagrams finds two new perovskite-related materials of stoichiometry LaNb1/3M2/3O3 (Mand indicates coexistence of LaNbO4 with the binary oxides NiO and CoO. Additionally, reduction of a LaNbO4–NiO composite confirms coexistence of LaNbO4 with Ni, and so it is concluded that doped-LaMO3|LaNbO4|Ni-LaNbO4 type electrochemical cells may be manufactured via a direct co-firing route without the formation of secondary phases at inter-phase boundaries. [Copyright &y& Elsevier]

The fracture strength, fracture toughness and apparent Young’s modulus of LaFeO3 ceramics in the temperature region 25–800 °C are reported. The fracture strength of the material was observed to increase from 202 ± 18 MPa at room temperature to 235 ± 38 MPa at 800 °C. The room temperature fracture toughness was 2.5 ± 0.1 MPa m1/2. The fracture toughness decreased to 2.1 ± 0.1 MPa m1/2 at 600 °C, followed by an increase to 3.1 ± 0.3 MPa m1/2 at 800 °C. The temperature dependence of the fracture toughness correlates well with the crystallographic strain, |(a-c)|/(a+c), and ferroelastic toughening of LaFeO3 materials is inferred. Non-elastic stress–strain behaviour of the LaFeO3 materials due to ferroelasticity was confirmed by cyclic compression experiments, and residual strain was observed in the material after unloading. [Copyright &y& Elsevier]

Magnetic separation is a well-developed area and many devices have been invented. In the future, industrial stage will only be achieved by the magnetic separators which present some economical advantages. Thus, we should design magnetic separators which are capable to perform many tasks at the same time, and/or to improve the relation accuracy vs expenditures. The area of magnetic classification within magnetic separation bears on the former case. In this paper the practical and theoretical definitions of differential magnetic classification are presented, and their distinction from selectivity stands out. The attempts to reach some sort of magnetic classification are reviewed, and the first optimised magnetic separator and classifier is briefly described. To achieve a fully optimised magnetic classification within magnetic separation on a device, some steps must be followed. Four of them – which were applied successfully to the development of the first optimised magnetic separator and classifier – are analysed in detail. Economical and practical advantages of using magnetic classification within magnetic separation on the same device applying only one step are described, as well as some potential industrial applications. [Copyright &y& Elsevier]