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See detailDense La0.9Sr0.1Ga0.8Mg0.2O2.85 electrolyte for IT-SOFC's: Sintering study and electrochemical characterization
Traina, Karl ULg; Henrist, Catherine ULg; Vertruyen, Bénédicte ULg et al

in Journal of Alloys & Compounds (2011), 509(5), 1493-1500

This paper presents the sintering behaviour of a La0.9Sr0.1Ga0.8Mg0.2O2.85 coral-like microstructure powder. This is prepared by a successive freeze-drying and self-ignition process followed by ... [more ▼]

This paper presents the sintering behaviour of a La0.9Sr0.1Ga0.8Mg0.2O2.85 coral-like microstructure powder. This is prepared by a successive freeze-drying and self-ignition process followed by calcination at 1200 ◦C during 1 h. This synthesis method gives great uniformity of the powder and allows shaping into compacts without requiring a grinding step. The grain size distribution (between 0.5 and 4 m) favours a good sintering behaviour: open porosity disappear at 1400 ◦C and relative densities over 99% can be achieved after 6 h at 1450 ◦C. The same powder can also be sintered into a thin disc of ∼100 mthickness. The characterization of the dense material by impedance spectroscopy shows that the activation energies below and above 600 ◦C are 1.0 eV and 0.7 eV, respectively. The conductivity at 800 ◦C is ∼0.11 S cm−1. Special attention is devoted to the temperature range between 200 ◦C and 400 ◦C, where the intragrain and intergrain contributions can be distinguished. The analysis of the parameters describing the intragrain constant phase element in the equivalent circuit suggests that, above 325 ◦C, the system evolves from a distribution of relaxation time to only one relaxation time. The analysis of the data by the complexes permittivity show that ionic oxide conduction mechanism would occur in two steps. In the first, an oxygen vacancy would be released and, in the second, the migration of the ionic oxide would take place in the material. [less ▲]

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See detailImage analysis of pearlite spheroidization based on the morphological characterization of cementite particles
Nutal, Nicolas; Gommes, Cédric ULg; Blacher, Silvia ULg et al

in Image Analysis and Stereology (2010), 29

Pearlite spheroidization is a metallurgical process in steels by which cementite lamellaer decompose into spheroids, a process accompanied by a decrease of the Vickers hardness of the samples. In thi ... [more ▼]

Pearlite spheroidization is a metallurgical process in steels by which cementite lamellaer decompose into spheroids, a process accompanied by a decrease of the Vickers hardness of the samples. In thi study, different methods are compared for measuring cementite particles length and width from scanning electron micrographs. Based on a test-image, a so-called ribbon-like method is proposed for measuring particles length and width, and for discriminating lamellae from spheroids. Differently heat-treated samples are prepared and characterized. The results of analysis are used to rationalize the evolution of the microstructure of the samples. Compared to teh calssical DeHoff shape factor, it is shown that new insight into the spheroidization process is gained by analysing the lamellar length and widh distributions. [less ▲]

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See detailSynthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 by successive freeze-drying and self-ignition of a hydroxypropylmethyl cellulose solution
Traina, Karl ULg; Steil, M. C.; Pirard, Jean-Paul ULg et al

in Journal of the European Ceramic Society (2007), 27(12), 3469-3474

The present paper reports the synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 perovskite powders by a method combining freeze-drying and self-ignition of an aqueous solution of metallic nitrates containing ... [more ▼]

The present paper reports the synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 perovskite powders by a method combining freeze-drying and self-ignition of an aqueous solution of metallic nitrates containing hydroxypropylmethyl cellulose. The precursor powder obtained after self-ignition was submitted to various thermal treatments and the resulting powders were characterized by X-ray diffraction, electron microscopy, nitrogen adsorption-desorption isotherm analysis, mercury porosimetry and laser granulometry. It turns out that this synthesis method yields single-phase powders with good homogeneity and sinterability properties. The precursor powder treated at 1200 degrees C presents a coral-like structure which collapses under application of low uniaxial pressure, resulting in a narrow grain size distribution suitable for sintering (98.8% relative density for a pellet sintered at 1400 degrees C during 1 h). The fact that no milling step is necessary is an additional advantage of this method, which shows promising prospects for the synthesis of other multicationic oxides. (c) 2007 Elsevier Ltd. All rights reserved. [less ▲]

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See detailLiMn2-xTixO4 spinel-type compounds (x <= 1): Structural, electrical and magnetic properties
Krins, Natasha ULg; Hatert, Frédéric ULg; Traina, Karl ULg et al

in Solid State Ionics (2006), 177(11-12), 1033-1040

LiMn2-xTixO4 compounds with 0.5 =<x =< 1 were prepared by solid state reaction and Pechini technique. Powder X-ray diffraction showed that all samples crystallize with the spinel crystal structure (S.G ... [more ▼]

LiMn2-xTixO4 compounds with 0.5 =<x =< 1 were prepared by solid state reaction and Pechini technique. Powder X-ray diffraction showed that all samples crystallize with the spinel crystal structure (S.G. Fd3m). The cubic unit-cell parameter increases with the Ti content. The influence of the Ti content and cationic distribution on the magnetic properties of the compounds was studied by measuring the temperature and magnetic field dependences of the magnetization: substitution by non-magnetic d(0) Ti4+ ions appeared to weaken the magnetic interactions between the manganese ions. The electrical properties of LiMnTiO4 were studied by AC impedance spectroscopy and DC polarisation measurements, which revealed the electronic character of the conduction process. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailA Microstructural Study of Doped-LaGaO3 (La0.9Sr0.1Ga0.8Mg0.2O2.85) Produced by an Autocombustion from a Gel-like Precursor
Traina, Karl ULg; Pirard, Jean-Paul; Rulmont, André ULg et al

in Bossel, Ulf (Ed.) Sixth European Solid Oxide Fuel Cell Forum - Proceedings (2004, June)

Polycrystalline dense samples of lanthanum gallate doped with strontium and magnesium (La0.9Sr0.1Ga0.8Mg0.2O2.85 or LSGM) was prepared using a novel gel precursor synthesis method. This consists in ... [more ▼]

Polycrystalline dense samples of lanthanum gallate doped with strontium and magnesium (La0.9Sr0.1Ga0.8Mg0.2O2.85 or LSGM) was prepared using a novel gel precursor synthesis method. This consists in preparing a LSGM precursor from a freeze-dried Agar-Agar gel. After the freeze-drying step, the dry residue is put in an oven at 120°C where autocombustion occurred. The as-produced powders are then calcined. Investigations are made to follow both structural and microstructural evolutions from the dry residue to the end product. The effect of the temperature evolution was examined by thermogravimetric analysis, X-ray diffraction, environmental scanning electron microscopy, and specific surface area analysis. Dilatometric curves and density measurements have been also performed on the sintered products. Advantages of this method are the ability to control size distribution and to obtain high density materials without any milling step thus avoiding any contamination coming from the grinding medium. [less ▲]

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See detailProcessing and Characterization of Electrolytes Based on Doped Lanthanum Gallates for IT-SOFCs.
Traina, Karl ULg; Cloots, Rudi ULg

in Bossel, Ulf (Ed.) Sixth European Solid Oxide Fuel Cell Forum - Proceedings (2004, June)

Nowadays a huge interest exists towards the SOFC’s coming out on the large-scale market because of the variety of their advantageous applications. Clean conversion of chemical energy to electricity, co ... [more ▼]

Nowadays a huge interest exists towards the SOFC’s coming out on the large-scale market because of the variety of their advantageous applications. Clean conversion of chemical energy to electricity, co-generation of electricity and chemicals, low levels of noise and vibration, flexibility regarding the fuels used, high efhciency are evidences of this statement. One of the problems that still exist in this field concerns the effective and cost reasonable operation of SOFCs. In this context the lowering of the operation temperatures could be one of the solutions to this important issue. Because of their excellent oxide—ion conductivity and stability over a broad range of oxygen partial pressure, the appropriate doped lanthanum gallates are promising alternative electrolytes for intermediate temperature SOFCs (lT-SOFCs). The aim of this work is to present the experimental results, obtained in a close collaboration between the two Universities. The objects could be briefly outlined, as follows: to process planar electrolytes with different thicknesses, based on doped LaGaO3 via traditional ceramic techniques; to study the influence of the dopants type and their amount on the properties of electrolyte materials synthesized; to investigate the phase formation and phase composition in correlation with the phase diagrams, as well as the microstructure and elements distribution. A special emphasis was placed upon the electrochemical characterization in broad temperature range, using impedance spectroscopy. The results obtained have been discussed in details and conclusions have been drawn by common efforts of the two working groups. [less ▲]

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See detailStudy of the morphology of copper hydroxynitrate nanoplatelets obtained by controlled double jet precipitation and urea hydrolysis
Henrist, Catherine ULg; Traina, Karl ULg; Hubert, Cédric ULg et al

in Journal of Crystal Growth (2003), 254(1-2), 176-187

A copper hydroxynitrate of stoichiometry Cu-2(OH)(3)NO3, analogous to the layered double hydroxide family, was synthesized by the so-called controlled double jet precipitation technique, and by hydrolysis ... [more ▼]

A copper hydroxynitrate of stoichiometry Cu-2(OH)(3)NO3, analogous to the layered double hydroxide family, was synthesized by the so-called controlled double jet precipitation technique, and by hydrolysis of urea in the presence of copper nitrate. Special attention has been focused on the size, morphology and agglomeration tendency of the particles. The aim of this work is to define the optimum precipitation conditions in terms of quality and dispersability of the recovered product. Such platelet-like particles Can be used as anisotropic fillers in nanocomposite materials. Several reaction parameters such as flow and concentration of the reactant solutions, design of the reactor and addition of a growth modifier were studied. (C) 2003 Elsevier -Science B.V. All rights reserved. [less ▲]

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