E. Urones-Garrote

Notch Impact Behavior of Oxide Dispersion Strengthened (ODS) Fe20Cr5Al alloy

In this article, tensile tests as well as LS and LT notched Charpy impact tests were performed at the temperature range between 77 K (−196 °C) and 473 K (200 °C) on an oxide-dispersion-strengthened (ODS) Fe20Cr6Al0.5Y2O3 hot-rolled tube. The absorbed energy values in the range of high temperatures of LS notched specimens are considerably higher than those of LT notched specimens; however, such values tend to converge as temperature increases. Ductile fracture on the normal planes to RD with delaminations parallel to the tube surface was observed in the temperature range between room temperature (RT) and 473 K (200 °C). Delaminations of crack divider type were observed in LT specimens, whereas delaminations of crack arrester type were observed in LS specimens. The yttria particles in the grain boundaries and the transverse plastic anisotropy are the possible reasons why the delaminations were parallel to the tube surface.

Structured diffuse scattering, local crystal chemistry and metal ion ordering in the (1 - x )MgS • x 3Yb 2 S 3 , 0≤ x ≤~0.45, 'defect' NaCl system

Rare earth sulfide solid solutions of ‘defect’ NaCl average structure type exhibit excellent colour characteristics and thus represent good prospects for use in the paints and plastics industry. As the colour characteristics of such systems are closely related to the local distribution of rare earth ions, it is important to know as much as possible about the latter. In this contribution, the reciprocal space shape of a highly structured, diffuse intensity distribution observed in a (1 −x)MgS · xYb2/3S, x = 0.30, sample is used to show that the smallest polyhedral building blocks of the average NaCl structure type should each have, as far as possible, the same composition as the overall macroscopic composition. Local crystal chemical considerations suggest that both the Yb3+ ions and the vacancies □ would prefer to be opposite Mg2+ ions.

Chlorination and solvothermal treatment of Zr(C5H5)2Cl2: a synthetic combination to produce nanometric tetragonal ZrO2.

A novel synthetic strategy based on the combination of the chlorination of an organometallic precursor followed by solvothermal treatment is found to be successful in the synthesis of tetragonal nano-ZrO(2) or nano-ZrO(2), embedded in an amorphous carbon matrix, depending on the solvent employed in the solvothermal step. The chemical and structural features (chemical composition, size and surface defects) of the intermediate and final materials have been determined experimentally mainly by high resolution transmission electron microscopy, electron energy loss spectroscopy, and Z-contrast images. These local techniques reveal that the nanoparticles consist of tetragonal ZrO(2) with an average size of 1.7 ± 0.4 and 6.2 ± 0.9 nm for the embedded in carbon and the free nano-ZrO(2), respectively.

Crystal Structures at Atomic Resolution of the Perovskite-Related GdBaMnFeO5 and Its Oxidized GdBaMnFeO6

Perovskite-related GdBaMnFeO5 and the corresponding oxidized phase GdBaMnFeO6, with long-range layered-type ordering of the Ba and Gd atoms have been synthesized. Oxidation retains the cation ordering but drives a modulation of the crystal structure associated with the incorporation of the oxygen atoms between the Gd layers. Oxidation of GdBaMnFeO5 increases the oxidation state of Mn from 2+ to 4+, while the oxidation state of Fe remains 3+. Determination of the crystal structure of both GdBaMnFeO5 and GdBaMnFeO6 is carried out at atomic resolution by means of a combination of advanced transmission electron microscopy techniques. Crystal structure refinements from synchrotron X-ray diffraction data support the structural models proposed from the TEM data. The oxidation states of the Mn and Fe atoms are evaluated by means of EELS and Mössbauer spectroscopy, which also reveals the different magnetic behavior of these oxides.

Solid solutions Ln10S14+xO1−x (Ln:Ce, Nd) as possible pigments

Abstract The microstructure (via SEM, TEM), and color parameters of the solid solution (Ce 1− y Nd y ) 10 S 14+ x O 1− x (0≤ y ≤0.70) (0≤ x ≤1) were investigated. The samples structure corresponds to the Pr 10 S 14 O type. The scanning electron micrographs (SEM) show small particle size (around 100 nm). The samples have been characterized by transmission electron microscopy (TEM) and associated techniques. The observed variation in the powder X-ray diffraction refined unit cell parameters is due to the variable oxygen content.

Crystal structure and compositional effects on the electrical and electrochemical properties of GdBaCo2−xMnxO5+δ (0 ≤ x ≤ 2) oxides for use as air electrodes in solid oxide fuel cells

The effects of the substitution of Co with Mn in the crystal structure, oxygen content, thermal stability and expansion and electrical properties of GdBaCo2−xMnxO5+δ (0 ≤ x ≤ 2) oxides are reported. Composites of GdBaCo2−xMnxO5+δ–Ce0.9Gd0.1O2−δ (70 : 30 wt%) are used as cathode materials and their electrochemical behaviour is presented. Layered-type ordering of Ba and Gd cations in the perovskite structure occurs in the whole system when the materials are prepared in argon but only for compositions in the range corresponding to x < 1.4 when the materials are prepared in air. The oxygen content increases with increasing the Mn content, causing thermal stability to improve and thermal expansion to decrease. However, lowering of the dc conductivity and an increase of electrode polarization resistances are observed by Mn substitution for Co. Cation ordering of the Gd and Ba atoms seems to affect the electrochemical properties of the materials.

Influence of the synthesis conditions on the crystal structure and properties of GdBaCo2−xFexO5+δ oxides as air-electrodes for intermediate temperature solid oxide fuel cells

The influence of the synthesis conditions on the crystal structure and properties of the oxides of the system GdBaCo2−xFexO5+δ is reported in this article. The materials are prepared by a ceramic method either in air or in an argon atmosphere. Crystal structure characterization is carried out by a combination of powder X-ray diffraction (PXRD) with advanced methods of high resolution transmission electron microscopy (HRTEM), scanning-transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). Thermal expansion coefficients of the oxides decrease with increasing substitution of Co by Fe. Impedance spectroscopy analysis of symmetrical cells using these materials as electrodes reveals area-specific polarization resistance (ASR) values low enough for the use of the oxides as air electrodes in intermediate temperature solid oxide fuel cells (IT-SOFCs).

The non-steady state growth of pearlite outside the Hultgren extrapolation

The goal of this paper is to analyse the effect of adding Al on the non-steady pearlite growth occurring in a Fe–C–Mn system. The results are discussed in terms of the partitioning of elements across the austenite/ferrite and austenite/cementite interfaces, and the modification of the pearlite driving force related to the change in carbon activity in austenite.

Ordered and Disordered Carbon Structures Detected by TEM in Carbide-derived Carbons Produced from TiC

Nowadays, the selective etching of metal carbides by chlorine gas is one well established method to prepare highly porous and nanostructurated carbon materials with potential applications for hydrogen storage and supercapacitors The obtained products usually named as carbide-derived carbons (CDC) present high purity, high surface area and homogeneous pore size distribution and most of times present a graphitic structure; however, in some cases, disordered carbon nanostructures coexist among the ordered ones [1]. In this study, we report the synthesis and characterisation of CDC materials obtained from TiC at 900 oC. Powder precursor, purity of 99% Aldrich, was heated at 50 °C/min in a tubular furnace during 2 h, in a continuous flow of a mixture containing high purity chlorine gas (25 mL/min) and hydrogen (2.5 mL/min) according the next possible scheme:

Structural complexity in AA′MM′ O 6 Perovskites. A Transmission Electron Microscopy Study

We have prepared five perovskite compounds which have two different A-site cations and examined the ordering of the A-site lattice through powder X-ray diffraction, TEM, HRTEM, HAADF-STEM, STEM-EELS. NaLaTi 2 O 6 and NaLaZr 2 O 6 show no indication of cation ordering by XRD but TEM analysis reveals that the A-site cations are ordered into layers in nanometer domains which have perpendicular orientations of the layers. NaLaMgTeO 6 has larger domains which can be detected by XRD. XRD has revealed that both NaLaMgWO 6 and KLaMnWO 6 have nearly complete long range layered ordering of the A-site cations. TEM microscopy has further shown that a compositional modulation exists in both compounds. NaLaMgWO 6 organizes into alternating stripes ˜24A wide that are compositionally distinct from each other. KLaMnWO 6 shows similar behaviour except with a chessboard pattern.