References of "Cloots, Rudi"
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See detailColloidal stability of aqueous suspensions of barium zirconate
Boschini, Frédéric ULg; Rulmont, André ULg; Cloots, Rudi ULg et al

in Journal of the European Ceramic Society (2005), 25(13), 3195-3201

In this article, the colloidal behaviour of aqueous suspensions of barium zirconate is investigated. The variation of zeta-potential as a consequence of changing the pH and the concentration of an anionic ... [more ▼]

In this article, the colloidal behaviour of aqueous suspensions of barium zirconate is investigated. The variation of zeta-potential as a consequence of changing the pH and the concentration of an anionic polyelectrolyte is studied, the isoelectric point occurring at pH 5.3. The IEP shifts down on calcining the powder and also when anionic polyelectrolytes are added. Rheological studies have been made on suspensions prepared to a solids loading of 27 vol.% (72 wt.%). Optimum dispersing conditions are reached for suspensions prepared at basic pH with 1.5 wt.% tetramethylammonium hydroxide (TMAH) and a concentration of ammonium polymethacrylate (PMAA) of 1.6 wt.%. Comparison with similar suspensions prepared with NaOH instead PMAA demonstrated that TMAH gives an extra contribution to stability, probably related to the adsorption of N+(Me)(4) groups. The suspensions were slip cast, and green densities higher than 60% of theoretical were obtained. (c) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailVivianite formation and distribution in Lake Baikal sediments
Fagel, Nathalie ULg; Alleman, L. Y.; Granina, L. et al

in Global and Planetary Change (2005), 46(1-4), 315-336

In an effort to better understand vivianite formation processes, four Lake Baikal sediment cores spanning two to four interglacial stages in the northern, central and southern basins and under various ... [more ▼]

In an effort to better understand vivianite formation processes, four Lake Baikal sediment cores spanning two to four interglacial stages in the northern, central and southern basins and under various biogeochemical environments are scrutinized. The vivianite-rich layers were detected by anomalous P-enrichments in bulk geochemistry and visually by observations on X-radiographs. The millimetric concretions of vivianite were isolated by sieving and analysed by X-ray diffraction, scanning electron microscope (SEM), microprobe, infrared spectroscopy, inductively coupled plasma atomic emission spectrometry and mass spectrometry (ICP-AES, ICP-MS). All the vivianites display similar morphological, mineralogical and geochemical signature, suggesting a common diagenetic origin. Their geochemical signature is sensitive to secondary alteration where vivianite concretions are gradually transformed from the rim to the center into an amorphous santabarbaraite phase with a decreasing Mn content. We analysed the spatial and temporal distribution of the concretions in order to determine the primary parameters controlling the vivianite formation, e.g., lithology, sedimentation rates, and porewater chemistry. We conclude that vivianite formation in Lake Baikal is mainly controlled by porewater chemistry and sedimentation rates, and it is not a proxy for lacustrine paleoproductivity. Vivianite accumulation is not restricted to areas of slow sedimentation rates (e.g., Academician and Continent ridges). At the site of relatively fast sedimentation rate, i.e., the Posolsky Bank near the Selenga Delta, vivianite production may be more or less related to the Selenga River inputs. It could be also indirectly related to the past intensive methane escapes from the sediments. While reflecting an early diagenetic signal, the source of P and Fe porewater for vivianites genesis is still unclear. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailLow-field magnetoresistance in La0.7Ca0.3MnO3 manganite compounds prepared by the spray drying technique
Vertruyen, Bénédicte ULg; Rulmont, André ULg; Cloots, Rudi ULg et al

in Journal of Materials Science (2005), 40(1), 117-122

Calcium-substituted lanthanum manganite compounds were synthesized by the spray drying technique. This method - whose main advantages are versatility, high reproducibility and scalability - yields small ... [more ▼]

Calcium-substituted lanthanum manganite compounds were synthesized by the spray drying technique. This method - whose main advantages are versatility, high reproducibility and scalability - yields small grain materials of high homogeneity and displaying low-field magnetoresistance effects. We report about the physical and chemical characterizations of these samples in order to investigate the potential interest of spray drying for the production of materials for low-field magnetoresistance applications. We have studied the dependence of the low-field magnetoresistance on the temperature and duration of the thermal treatment applied to the pelletized powders. The issue of the shape anisotropy (demagnetisation effects) influence on the magnetoresistance properties has also been dealt with. (C) 2005 Springer Science + Business Media, Inc. [less ▲]

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See detailSound-producing apparatus of the snake-blenny Ophidion barbatum
Fontenelle, Nicolas; Henrist, Catherine ULg; Cloots, Rudi ULg et al

Poster (2005)

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See detailFrom RE-211 to RE-123. How to control the final microstructure of superconducting single-domains
Cloots, Rudi ULg; Koutzarova, T.; Mathieu, J.-P. et al

in Superconductor Science and Technology (2005), 18(3), 9-23

This paper reviews the usual techniques for producing YBCO-type single-domains and the microstructure of the as-obtained samples. The problems of seed dissolution and parasite nucleations are discussed in ... [more ▼]

This paper reviews the usual techniques for producing YBCO-type single-domains and the microstructure of the as-obtained samples. The problems of seed dissolution and parasite nucleations are discussed in detail. The formation of microstructural defects, such as pores and cracks, is examined. An important part of this review is devoted to the study of the influence of RE-211 particles (RE2BaCuO5 where RE denotes Y, Yb, Nd, Sm, Dy, Gd, Eu or a mixture of them. Generally Nd4Ba2Cu 2O10 is preferred to Nd2BaCuO5) for the microstructure and properties of RE-Ba-Cu-O single-domains. Pushing/trapping theory is described in order to explain the spatial distribution of RE-211 particles in the RE-123 ((RE)Ba2Cu3O7-δ) monoliths. The formation of RE-211-free regions is discussed. Different ways to limit the RE-211 coarsening are reviewed. Microstructural defects in the RE-123 matrix caused by the RE-211 particles are presented. It is also shown that RE-211 particles play a significant role in the mechanical properties of single-domain samples. We finish this review by discussing the infiltration and growth process as a good technique to control the microstructure. © 2005 IOP Publishing Ltd. [less ▲]

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See detailSurface modification of as-synthesized lamellar mesostructured silica obtained by liquid crystal templating
Henrist, Catherine ULg; Vogels, C.; Rulmont, André ULg et al

in New Journal of Chemistry (2005), 29(8), 1017-1021

We report a study of lamellar silica phase silylation, starting from as-synthesized silica, without the usual heat treatment step. Characterizations of the modified silica include X-ray diffraction ... [more ▼]

We report a study of lamellar silica phase silylation, starting from as-synthesized silica, without the usual heat treatment step. Characterizations of the modified silica include X-ray diffraction, thermal analysis, electron microscopy and solid state NMR. Special attention is given to the possibility of keeping the lamellar organisation along with the elimination of the organic template. [less ▲]

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See detailSilver paint as a soldering agent for DyBaCuO single-domain welding
Mathieu, Jean-Philippe; Fagnard, Jean-François ULg; Laurent, Philippe ULg et al

in Superconductor Science and Technology (2005), 18(4), 508-512

Silver paint has been tested as a soldering agent for DyBaCuO 4 single-domain welding. Junctions have been manufactured on Dy-Ba-Cu-O single domains cut either along planes parallel to the c-axis IT or ... [more ▼]

Silver paint has been tested as a soldering agent for DyBaCuO 4 single-domain welding. Junctions have been manufactured on Dy-Ba-Cu-O single domains cut either along planes parallel to the c-axis IT or along the ab-planes. Microstructural and superconducting characterizations of the samples have been performed. For both types of junctions, the microstructure in the joined area is very clean: no secondary phase or Ag particle segregation has been observed. Electrical and magnetic measurements for all configurations of interest are reported (rho(T) curves, and Hall probe mapping). The narrow resistive superconducting transition reported for all configurations shows that the artificial junction does not affect significantly the measured superconducting properties of the material. [less ▲]

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See detailMagneto-transport characterization of Dy123 monodomain superconductors
Pekala, Marek; Mucha, Jan ULg; Vanderbemden, Philippe ULg et al

in Applied Physics A : Materials Science & Processing (2005), 81(5), 1001-1007

We consider textured materials of the DyBa2Cu3O7 type seeded with a Nd123 seed as initiator. They are grown with an excess 20% Dy211 phase on a Dy2O3 substrate. We report chemical characterization ... [more ▼]

We consider textured materials of the DyBa2Cu3O7 type seeded with a Nd123 seed as initiator. They are grown with an excess 20% Dy211 phase on a Dy2O3 substrate. We report chemical characterization, electrical resistivity, thermoelectric power and thermal conductivity over a broad temperature range as a function of an applied magnetic field up to 6 T. We show that specific features appear in the magneto-thermal transport properties, different in these materials from those found in single crystals and polycrystalline samples. We propose that two vortex regimes can be distinguished in the mixed phase, due to the intrinsic microstructure. We calculate the viscosity, entropy and figure of merit of the samples. [less ▲]

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See detailInvestigation of DyBa2CU3O7-d superconducting domains grown by the infiltration technique starting with small size Dy-211 particles
Mathieu, Jean-Philippe; Koutzarova, T.; Rulmont, André ULg et al

in Superconductor Science and Technology (2005), 18(2 Sp. Iss. SI), 136-141

An infiltration and growth process is here used as an alternative to the classical top-seeded melt-textured growth process for the production of Dy-123 single-domains with finely dispersed small size Dy ... [more ▼]

An infiltration and growth process is here used as an alternative to the classical top-seeded melt-textured growth process for the production of Dy-123 single-domains with finely dispersed small size Dy-211 particles. The starting materials are the 211-particles and a barium and copper rich liquid phase precursor. The infiltration and growth process allows for controlling both the spatial and size distribution of the 211-particles in the final superconducting 123-single-domain. The main parameters (set-ups, maximum processing temperature with respect to the peritectic temperature, nature of reactant, porosity of the 211-preform) of the infiltration and growth process are discussed. Moreover, different processes of chimie douce are shown in order to produce Dy-211 particles with controlled shape and size, particles that can be used as precursors for the infiltration and growth process. [less ▲]

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See detailStudy by Hall probe mapping of the trapped flux modification produced by local heating in YBCOHTS bulks for different surface/volume ratios
Laurent, Philippe ULg; Mathieu, Jean-Philippe; Mattivi, Brice et al

in Superconductor Science and Technology (2005), 18(8), 1047-1053

The aim of this report is to compare the trapped field distribution under a local heating created at the sample edge for different sample morphologies. Hall probe mappings of the magnetic induction ... [more ▼]

The aim of this report is to compare the trapped field distribution under a local heating created at the sample edge for different sample morphologies. Hall probe mappings of the magnetic induction trapped in YBCO bulk samples maintained out of thermal equilibrium were performed on YBCO bulk single domains, YBCO single domains with regularly spaced hole arrays, and YBCO superconducting foams. The capability of heat draining was quantified by two criteria: the average induction (B) decay and the size of the thermally affected zone caused by a local heating of the sample. Among the three investigated sample shapes, the drilled single domain displays a trapped induction which is weakly affected by the local heating while displaying a high trapped field. Finally, a simple numerical modelling of the heat flux spreading into a drilled sample is used to suggest some design rules about the hole configuration and their size. [less ▲]

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See detailUnusual thermoelectric behavior of packed crystalline granular metals
Ausloos, Marcel ULg; Pekala, Marek; Latuch, J. et al

in Journal of Applied Physics (2004), 96(12), 7338-7345

Loosely packed granular materials are intensively studied nowadays. Electrical and thermal transport properties should reflect the granular structure, as well as intrinsic properties. We have compacted ... [more ▼]

Loosely packed granular materials are intensively studied nowadays. Electrical and thermal transport properties should reflect the granular structure, as well as intrinsic properties. We have compacted crystalline CaAl-based metallic grains and studied the electrical resistivity and the thermoelectric power as a function of temperature (T) from 15 to 300 K. Both properties show three regimes as a function of temperature. It should be pointed out: (i) The electrical resistivity continuously decreases between 15 and 235 K, (ii) with various dependencies, e.g., similar ~ T(-3/4) at low T, while (iii) the thermoelectric power (TEP) is positive, (iv) shows a bump near 60 K, and (v) presents a rather unusual square root of temperature dependence at low temperature. It is argued that these three regimes indicate a competition between geometric and thermal processes-for which a theory seems to be missing in the case of TEP. The microchemical analysis results are also reported, indicating a complex microstructure inherent to the phase diagram peritectic intricacies of this binary alloy. (C) 2004 American Institute of Physics. [less ▲]

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See detailAnisotropic behaviour in the magnetic field dependence of the low temperature electrical resistance of calcium-doped lanthanum manganate thin films grown by RF magnetron sputtering
Vertruyen, Bénédicte ULg; Dusoulier, Laurent; Fagnard, Jean-François ULg et al

in Journal of Magnetism and Magnetic Materials (2004), 280(2-3), 264-272

We report about the magnetoresistive properties of calcium-doped lanthanum manganate thin films grown by RF magnetron sputtering on single crystalline LaAiO(3) and MgO substrates. Two orientations of the ... [more ▼]

We report about the magnetoresistive properties of calcium-doped lanthanum manganate thin films grown by RF magnetron sputtering on single crystalline LaAiO(3) and MgO substrates. Two orientations of the magnetic field with respect to the electrical current have been studied: (i) magnetic field in the plane of the film and parallel to the electrical current, and (ii) magnetic field perpendicular to the plane of the film. The film grown on LaAlO3 is characterised by an unusual magneto resistive behaviour when the magnetic field is applied perpendicular to the film plane: the appearance of two bumps in the field dependence of the resistance is shown to be related to the occurrence of anisotropic magneto resistive effects in manganate films. (C) 2004 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 detailEffects of silicon addition on the electrical and magnetic properties of copper-doped (La,Ca)MnO3 compounds
Vertruyen, Bénédicte ULg; Rulmont, André ULg; Cloots, Rudi ULg et al

in Journal of Magnetism and Magnetic Materials (2004), 268(3), 364-373

In this paper we report about the electrical properties of La0.7Ca0.3MnO3 compounds substituted by copper on the manganese site and/or deliberately contaminated by SiO2 in the reactant mixture. Several ... [more ▼]

In this paper we report about the electrical properties of La0.7Ca0.3MnO3 compounds substituted by copper on the manganese site and/or deliberately contaminated by SiO2 in the reactant mixture. Several phenomena have been observed and discussed. SiO2 addition leads to the formation of an apatite-like secondary phase that affects the electrical conduction through the percolation of the charge carriers. On the other hand, depending on the relative amounts of copper and silicon, the temperature dependence of the electrical resistivity can be noticeably modified: our results enable us to compare the effects of crystallographic vacancies on the A and B sites of the perovskite with the influence of the copper ions substituted on the manganese site. The most original result occurs for the compounds with a small ratio Si/Cu, which display double-peaked resistivity vs. temperature curves. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

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See detailSuperconducting properties of magnetically textured Dy doped Bi-2212 nickel tapes
Fagnard, Jean-François ULg; Rahier, Sébastien ULg; Fonder, Nicole et al

in Andreone, A. (Ed.) Applied Superconductivity 2003 (Proceedings of the 6th European Conference on Applied Superconductivity) (2004)

This communication aims at reporting the superconducting properties of Dy-doped Bi-2212/NiO/Ni tapes prepared by a dip-coating process from an inorganic gel. The Bi-2212 is recrystallized at 965°C in ... [more ▼]

This communication aims at reporting the superconducting properties of Dy-doped Bi-2212/NiO/Ni tapes prepared by a dip-coating process from an inorganic gel. The Bi-2212 is recrystallized at 965°C in presence of an external 1.2 T magnetic induction. The precursor gel, the temperature and the thermal treatment duration are optimized regarding the microstructure The resulting tape samples are characterized by electrical resistance and I-V curves. The presence of secondary phases, such as Bi-2201, is reduced after a 750°C annealing but Ni diffusion limits the critical current density of the as-obtained tapes. The magnetic critical current density measured on textured Dy-doped Bi-2212 monoliths, obtained with the same type of texturation process, but showing no Ni contamination, is found to be about 30 times larger than the critical current density of the tapes. [less ▲]

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See detailThe contribution of 211 particles to the mechanical reinforcement mechanism of 123 superconducting single domains
Mathieu, Jean-Philippe; Cano, I. G.; Koutzarova, T. et al

in Superconductor Science and Technology (2004), 17(1), 169-174

Hardness and fracture toughness of Dy-123 single domains were studied by Vickers in micro-indentation. A significant anisotropy of the mechanical properties was observed. Hardness tests give higher values ... [more ▼]

Hardness and fracture toughness of Dy-123 single domains were studied by Vickers in micro-indentation. A significant anisotropy of the mechanical properties was observed. Hardness tests give higher values when performed in (001) planes rather than in planes parallel to the c-axis. Moreover, the cracks pattern around the indentation follows preferential orientation in planes parallel to the c-axis whereas a classical 'four-cracks' pattern is observed in the (001) planes. It has been possible to show the crucial role played by the 211 particles in the deviating mechanism of cracks and the relevance of the high homogeneity of 211-particle distribution in the material. [less ▲]

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See detailPreparation of nanosized barium zirconate powder by precipitation in aqueous solution
Boschini, Frédéric ULg; Guillaume, Bernard ULg; Rulmont, André ULg et al

in Key Engineering Materials [=KEM] (2004), 264-268(Part 1-3), 2335-2338

Several ways were explored to synthesize barium zirconate by soft chemistry methods in aqueous solution. In the first method the synthesis of barium zirconate was initiated by urea decomposition, through ... [more ▼]

Several ways were explored to synthesize barium zirconate by soft chemistry methods in aqueous solution. In the first method the synthesis of barium zirconate was initiated by urea decomposition, through an homogeneous precipitation of barium and zirconium salts followed by a "low temperature" thermal treatment. The kinetic of the reaction and the optimum urea/cation ratio have been determined by means of X-ray diffraction and Inductive Coupled Plasma analyses. It has been demonstrated that an amorphous zirconium hydrated oxide starts to precipitate followed by the precipitation of barium carbonate[1]. A calcination at 1200degreesC during 2 hours gives rise to the formation of a pure barium zirconate phase. In the other methods, barium zirconate was synthesized, in one step without any thermal treatments, by precipitation in highly basic aqueous solutions containing barium and zirconium salts. The effect of the hydroxide concentration was discussed in relation to the barium zirconate phase formation, the particles size and the particles size distribution. For each powder, microstructural characterisations have been performed on sintered bodies in order to evaluate the influence of the thermal treatment on the final density. Dilatometric measurements have been also performed in order to quantify the densification process. Important informations were obtained by these techniques, as for example the existence of an internal porosity which severely limits the final density of the material, even if sintering was performed at high temperature. Thus a careful control of the heating profile seems to be necessary in order to produce dense materials. [less ▲]

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See detailac magnetic behavior of large-grain magnetoresistive La0.78Ca0.22Mn0.90Ox materials
Vanderbemden, Philippe ULg; Vertruyen, Bénédicte ULg; Rulmont, André ULg et al

in Physical Review. B (2003), 68(22), 224418

We report a detailed set of ac magnetic measurements carried out on bulk large grain La-Ca-Mn-O samples extracted from a floating zone method-grown rod. Three samples with La0.78Ca0.22Mn0.90Ox ... [more ▼]

We report a detailed set of ac magnetic measurements carried out on bulk large grain La-Ca-Mn-O samples extracted from a floating zone method-grown rod. Three samples with La0.78Ca0.22Mn0.90Ox stoichiometry but differing in their microstructure were investigated by electrical resistivity and ac susceptibility measurements: (i) a single grain sample, (ii) a sample containing two grains, and (iii) a polycrystalline sample. We show that the superimposition of dc magnetic fields during ac magnetic susceptibility measurements is an efficient way for characterizing the magnetic transition of samples with different microstructures. Whereas both single grain and polycrystalline samples display a single susceptibility peak, an additional kink structure is observed in the case of the double grain sample. The temperature dependence of the ac susceptibility measured with superimposed dc magnetic fields is analyzed in the framework of second-order phase transition ideas. The relations between the critical exponents (beta+gamma ~ 1.5, delta ~ 2.5) are found to be close to those of the mean-field model for all samples. This is attributed to the disordering caused by unoccupied Mn sites. ©2003 The American Physical Society. [less ▲]

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See detailStructural evolution of lamellar surfactant-silica hybrids upon calcination
Henrist, Catherine ULg; Cano, I. G.; Rodriguez, M. A. et al

in Composites Science and Technology (2003), 63(8), 1127-1131

A lamellar mesostructured silica was subjected to a progressive heat treatment in order to study its structural evolution and the characteristics of the resulting calcined powder. By combining ... [more ▼]

A lamellar mesostructured silica was subjected to a progressive heat treatment in order to study its structural evolution and the characteristics of the resulting calcined powder. By combining informations from several physical methods, i.e. TG-DTA, XRD, TEM and nitrogen adsorption, it has been possible to evidence the formation of very small particles of silica at a temperature around 450 degreesC, exhibiting a very high value of aspect ratio, consequently to the template loss by combustion. By increasing the temperature above 530 degreesC, the dehydroxylation promotes a decrease in the surface area, followed by the sintering process at higher temperature, which nearly annihilate the surface area of the particles. (C) 2003 Elsevier Science Ltd. All rights reserved. [less ▲]

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