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A study is conducted on mono-, di-, tri and tetranuclear gold complexes with the dpmp ligand and with the gold centers in the oxidation states I, III, and mixed I-III. Results show that gold(I) derivatives luminescence while gold(III) and mixed gold(I)-gold(III) complexes do not. The crystal structures of (Au4(mu-dpmp)2Cl2)(CF3SO3)2 and (Au(C6F5)3(dpmp)) are also determined via X-ray diffraction.

Anionic heterobinuclear complexes (NBu4)({C6F5}3Pt{mu-X}Pt{C6F5}3)(X = Cl, OH) are formed by the reaction of (NBu4)(Pt{C6F5}3X) (X = Cl,I) and Pb(ClO4)2.3H2O in CH2Cl2 or by the substitution of the Cl group by OH group. The stability of the compound is due to the Pt-Pb donor-acceptor interactions between the platinate(II) moieties and Pb2+. Single crystal X-ray diffraction is used for determining the structure of the heterobinuclear complexes.

Fracture features, residual stresses, and zirconia transformation are studied in indentation strength specimens of alumina-Y2O3-stabilized zirconia (3% mol of Y2O3, 3YTZP) ceramics in order to analyze the extension of the indentation damage in the bulk of the specimens. Two compositions, 5 vol% 3YTZP (A5) and 40 vol% 3YTZP (A40), have been prepared by stacking tape-casted tapes and sintering. After indentation with loads ranging from 50 to 300 N, samples were fractured in four-point bending and the fracture surfaces were characterized by scanning electron microscopy. Raman and piezospectroscopic techniques were used to determine the monoclinic zirconia fraction and the residual stresses through the fracture surfaces. In the A5 composition, the indentation damage morphology was clearly half-penny, whereas the A40 composition presented Palmqvist crack formation. Zirconia transformation was only observed in the plastically deformed zones underneath the imprints whereas there were significant residual compressive stresses outside the plastic zones due to the indentation damage. The intensity of this residual compressive field was dependent on the level of zirconia transformation due to indentation damage because zirconia transformation induced tensile stress fields superimposed on the compressive stresses. [ABSTRACT FROM AUTHOR]

The deformation and fracture mechanisms in tension were studied in single-crystal Er2O3-doped ZrO2 monofilaments processed by the laser-heated floating zone method. Tensile tests were carried out between 25° and 1400°C at different loading rates and the dominant deformation and fracture mechanisms were determined from the shape of the stress–strain curves, the morphology of the fracture surfaces, and the evidence provided by monofilaments deformed at high temperature and broken at ambient temperature. The tensile strength presented a minimum at 600°–800°C and it was controlled by the slow growth of a crack from the surface. This mechanism was also dominant in some monofilaments tested at 1000°C and above, while others showed extensive plastic deformation before fracture at these temperatures. The strength of plastically deformed monofilaments was significantly higher than those which failed by slow crack growth due to the marked strain hardening capacity of this material. [ABSTRACT FROM AUTHOR]

A method for the preparation of Cr-doped Y2Sn2O7 powders based on the pyrolysis of aerosols generated from aqueous salt solutions of the corresponding metal cations Is reported. These powders yielded Cr-doped pyrochlore red-shade pigments on calcination in the absence of fluxes at lower temperature (900°-1100°C) than that Involved in the traditional ceramic method (1400°C). This process resulted in pigment particles with spherical shape and broad size distribution (<10 μm) not requiring milling. The oxidation state of the Cr ions dissolved in the pyrochlore lattice has also been analyzed by using XPS and ESR spectroscopies and at magnetic susceptibility measurements finding that the color observed for this material is due to Cr(IV) ions, most probably occupying the distorted octahedral position of Sn(IV). [ABSTRACT FROM AUTHOR]

The effect of Y2O3 content on the flexure strength of meltgrown Al2O3-ZrO2 eutectics was studied in a temperature range of 25°–1427°C. The processing conditions were carefully controlled to obtain a constant microstructure independent of Y2O3 content. The rod microstructure was made up of alternating bands of fine and coarse dispersions of irregular ZrO2 platelets oriented along the growth axis and embedded in the continuous A12O3 matrix. The highest flexure strength at ambient temperature was found in the material with 3 moi % Y2O3 in relation to ZrO2 (Y2O3). Higher Y2O3 content did not substantially modify the mechanical response; however, materials with 0.5 mol % presented a significant degradation in the flexure strength because of the presence of large defects. They were nucleated at the Al2O3-ZrO2 interface during the martensitic transformation of ZrO2 on cooling and propagated into the Al2O3 matrix driven by the tensile residual stresses generated by the transformation. The material with 3 mol% Y2O3 retained 80% of the flexure strength at 1427°C, whereas the mechanical properties of the eutectic with 0.5 mol% Y2O3 dropped rapidly with temperature as a result of extensive microcracking. [ABSTRACT FROM AUTHOR]

Studies residual thermoelastic stresses in monoclinic zirconia and tetragonal zirconia fibrous eutectics. Possible piezospectroscopic probes; Use of the dependence of the Raman spectra, relative to strain; Measurement of the luminescence of the R-lines and Raman spectra.

The flexure strength of tetragonal ZrO2(Er2O3) single-crystal monofilaments manufactured by the laser-heated floating zone method was measured as a function of the environment (air vs. water) and temperature (from 25 to 800ºC) at loading rates spanning three orders of magnitude to ascertain their susceptibility to the environmental conditions. These mechanical tests were completed with parallel tests on fully-annealed monofilaments (to relieve the thermal residual stresses induced during growth) and by detailed analysis of the fracture surfaces using scanning electron microscopy and micro-Raman spectroscopy. While environmental susceptibility of ZrO2(Y2O3) in previous investigations was always associated with the destabilization of the tetragonal phase, monoclinic phase was not detected on the fracture surfaces of the ZrO2(Er2O3) monofilaments and it was concluded that slow crack growth in this material at high temperature or immersed in water was due to stress-corrosion cracking.Partiendo de fibras monocristalinas de ZrO2(Er2O3) tetragonal fabricadas por un procedimiento de fusión zonal con láser (LHFZ), se efectuaron ensayos de flexión en los que se medía la resistencia mecánica en función de la temperatura (25 a 800 ºC) y el medio (aire o agua). Los ensayos fueron realizados a distintas velocidades con objeto de establecer la susceptibilidad a las condiciones ambientales. La susceptibilidad ambiental de la ZrO2(Y2O3) se había asociado siempre a la desestabilización de la fase tetragonal, pero el análisis de las superficies de fractura mediante microscopía electrónica de barrido y espectroscopia Raman confocal muestran una ausencia completa de fase monoclínica en las superficies de fractura de las fibras. Esta ausencia, junto con los ensayos complementarios sobre fibras sometidas a tratamientos de recocido para eliminar las tensiones residuales provenientes del procesado, indican que el crecimiento subcrítico de grieta se debe a un mecanismo de corrosión bajo tensión.

Abstract: Nanofibrillar Al2O3–Y3Al5O12–ZrO2 eutectic rods were manufactured by directional solidification from the melt at high growth rates in an inert atmosphere using the laser-heated floating zone method. Under conditions of cooperative growth, the ternary eutectic presented a homogeneous microstructure, formed by bundles of single-crystal c-oriented Al2O3 and Y3Al5O12 (YAG) whiskers of ≈100nm in width with smaller Y2O3-doped ZrO2 (YSZ) whiskers between them. Owing to the anisotropic fibrillar microstructure, Al2O3–YAG–YSZ ternary eutectics present high strength and toughness at ambient temperature while they exhibit superplastic behavior at 1600K and above. Careful examination of the deformed samples by transmission electron microscopy did not show any evidence of dislocation activity and superplastic deformation was attributed to mass-transport by diffusion within the nanometric domains. This combination of high strength and toughness at ambient temperature together with the ability to support large deformations without failure above 1600K is unique and shows a large potential to develop new structural materials for very high temperature structural applications. [Copyright &y& Elsevier]

Abstract: Rods of CeO2 and gadolinium-doped CeO2 (GDC)–CoO eutectics were prepared by directional solidification using a laser heated floating zone (LFZ) technique. The microstructure has been studied as a function of the growth rate from V =10 to 750mm/h. Regular eutectic microstructures are obtained except for the highest growth rate. The interspacing follows the λ 2 V = C law with C =4.1(3)×10−17 and 2.6(3)×10−17 m3/s for CeO2–CoO and GDC–CoO eutectics, respectively. A cross-over between fibrous and lamellar eutectic microstructures was observed depending on the growth rate. The crystallography of the eutectics was studied by Electron Backscatter Diffraction (EBSD). The growth directions [110]GDC ∼//[110]CoO, and the interfacial planes (200)GDC//(111)CoO, were identified. Solubility of Co in the ceria matrix was determined by Energy Dispersive X-ray (EDX) Spectroscopy after Co was leached out from the matrix. Co solubility in ceria at 1650°C was found to be less than 1mol%. [Copyright &y& Elsevier]

Abstract: Cermets composed of submicron size alternating lamellae of CeO2, or 10% Gadolinia doped Ceria (GDC), and porous-metallic Cobalt have been prepared from eutectic oxide mixtures. A fine eutectic structure was obtained by fast directional solidification of the cobalt oxide–ceria oxide eutectic composite using the Laser Floating Zone (LFZ) technique. The resulting microstructure, with an interphase spacing down to 0.5 μm, was obtained for solidification rates of 750 mm/h. Textured cermets were obtained by subsequent reduction under H2 containing atmosphere of the eutectic oxide composite. The reduction kinetics was studied in the 550–750 °C temperature range and effective diffusion coefficients were obtained. The reduction process does not correspond to a typical thermally activated process. The cermets are composed of ceria lamellae of about 200 nm thickness alternated with porous-metallic cobalt lamellae of ≤400 nm. The lamellar microstructure of the cermets favours oxygen ion mobility through ceria and its size can be controlled by solidification rate of the eutectic precursor. These materials are proposed as SOFC anodes. [ABSTRACT FROM AUTHOR]