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See detailAC vs. DC electrophoretic deposition of hydroxyapatite on titanium
Ozhukil Kollath, Vinayaraj ULg; Chen, Qiang; Closset, Raphaël ULg et al

in Journal of the European Ceramic Society (2013), 33(13-14), 27152721

In this study, electrophoretic deposition (EPD) of hydroxyapatite (HA) powder on titanium plate was performed using butanol as solvent under direct current (DC) and alternating current (AC) fields. The ... [more ▼]

In this study, electrophoretic deposition (EPD) of hydroxyapatite (HA) powder on titanium plate was performed using butanol as solvent under direct current (DC) and alternating current (AC) fields. The zeta potential of the suspensions was measured to define their stability and the charge on the particles. Coating thickness was varied by adjusting the voltage and time of deposition. Surface morphology and cross section thickness were studied using scanning electron microscopy and image analysis software. Surface crack density was calculated from the micrographs. The results showed that the samples of similar thickness have higher grain density when coated using AC as compared to DC EPD. This facile but novel test proves the capability of AC-EPD to attain denser and uniform HA coatings from non-aqueous medium. [less ▲]

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See detailExperimental investigation of passive/active oxidation behavior of SiC based ceramic thermal protection materials exposed to high enthalpy plasma
Sakraker, Isil ULg; Asma, Cem Ozan

in Journal of the European Ceramic Society (2013), 33(2), 351-359

The passive/active oxidation behavior of a CVD-SiC coated C/C-SiC thermal protection material of the hypersonic SpaceLiner vehicle is investigated experimentally. For the safety of spacecraft and its ... [more ▼]

The passive/active oxidation behavior of a CVD-SiC coated C/C-SiC thermal protection material of the hypersonic SpaceLiner vehicle is investigated experimentally. For the safety of spacecraft and its passengers, it is important to know whether the thermal protection system will experience passive/active oxidation during the vehicle’s entry into Earth’s atmosphere. Active oxidation can promote material loss whereas passive oxidation forms a protective film. The high enthalpy flight conditions of SpaceLiner vehicle are duplicated in VKI Plasmatron, where the samples are exposed to high enthalpy plasma and the surface temperatures increase up to 2800 K at various total pressure (2–20 kPa) conditions. Surface temperature profiles, visual characteristics, mass changes, emissivity, spectrometer and SEM/EDX data are examined to identify the oxidation transition border of the tested material. A temperature jump is observed in all active oxidation regimes. The experimental results are found to be in good agreement with correlations from the literature. [less ▲]

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See detailYBa2Cu3O7−x dispersion in iodine acetone for electrophoretic deposition: Surface charging mechanism in a halogenated organic media
Dusoulier, Laurent; Cloots, Rudi ULg; Vertruyen, Bénédicte ULg et al

in Journal of the European Ceramic Society (2011), 31

Electrophoretic deposition (EPD) performance strongly depends on the particles surface chemistry and the ability to manipulate surface–liquid interfaces. In this study an extensive investigation of YBCO ... [more ▼]

Electrophoretic deposition (EPD) performance strongly depends on the particles surface chemistry and the ability to manipulate surface–liquid interfaces. In this study an extensive investigation of YBCO suspension in dry acetone, acetone–water mixtures and acetone–iodine is reported. Chemical instability of YBCO particles determines their colloidal behaviour. Charging mechanism of particles has therefore had to be deeply investigated for complete dispersion understanding. In order to determine the conditions of the YBCO suspension stability, measurements of pH, conductivity, zeta-potential, settling tests, modelling of the particle networks and electrophoretic deposition were done. The influence of the water and iodine concentration, and their role as stabilizers was evaluated. Based on experimental results, pair particle potentials were calculated and then different charging mechanisms of YBCO surfaces in acetone were proposed. [less ▲]

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See detailMullite coatings on ceramic substrates: Stabilisation of Al2O3-SiO2 suspensions for spray drying of composite granules suitable for reactive plasma spraying
Schrijnemakers, Audrey ULg; Andre, Sophie; Lumay, Geoffroy ULg et al

in Journal of the European Ceramic Society (2009), 29(11), 2169-2175

The present work deals with the preparation of stable alumina + silica suspensions with high solid loading for the production of spray-dried composite powders. These composite powders are to be used for ... [more ▼]

The present work deals with the preparation of stable alumina + silica suspensions with high solid loading for the production of spray-dried composite powders. These composite powders are to be used for reactive plasma spraying whereby the formation of mullite and the coating on a ceramic substrate are achieved in a single step process. Electrostatic stabilisation of alumina and silica suspensions has been studied as a function of pH. Silica suspensions are most stable at basic pH whereas alumina suspensions are stable at acidic pH. The addition of ammonium polymethacrylate (APMA) makes it possible to stabilise alumina and prepare a stable 50 wt% alumina + silica suspension at pH 10. The optimum amounts of dispersant and binder have been determined by zeta potential, viscosity and sedimentation measurements. Spray drying of the suspension yields composite powders whose morphology, size distribution and flowability have been characterized before realizing reactive plasma spraying tests. (C) 2009 Elsevier Ltd. All fights reserved. [less ▲]

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See detailRapid synthesis of submicron crystalline barium zirconate BaZrO3 by precipitation in aqueous basic solution below 100 degrees C
Boschini, Frédéric ULg; Rulmont, André ULg; Cloots, Rudi ULg et al

in Journal of the European Ceramic Society (2009), 29(8), 1457-1462

Pure crystalline BaZrO3 powders can be produced by precipitation in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH- concentration ([NaOH] = 20 mol/l ... [more ▼]

Pure crystalline BaZrO3 powders can be produced by precipitation in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH- concentration ([NaOH] = 20 mol/l), it is possible to obtain the well-crystallized stoichiometric perovskite phase at relatively low temperature (similar to 80 degrees C), after a short reaction time (15 min) and without requiring any precaution to avoid the presence of CO2. This synthesis method yields spherical particles, whose size can be controlled by changing the concentration of the Ba + Zr solution. No calcination treatment is necessary since the precipitate is crystalline. Suitable choice of the synthesis parameters ([NaOH] = 20 mol/l, [Ba + Zr] = 1 mol/l, reaction time= 15 min) yields a sub-micron precipitate with excellent densification behaviour. Corrosion tests in BaO-CuO melt show that similar to 98% dense BaZrO3 obtained by sintering at 1650 degrees C for 13 h could be used for crucibles in the synthesis of YBa2Cu3O7 superconducting single crystals. (C) 2008 Elsevier Ltd. All rights reserved. [less ▲]

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See detailElectrical transport and magnetic properties of Mn3O4-La0.7Ca0.3MnO3 ceramic composites prepared by a one-step spray-drying technique
Vertruyen, Bénédicte ULg; Fagnard, Jean-François ULg; Vanderbemden, Philippe ULg et al

in Journal of the European Ceramic Society (2007), 27(13-15), 3923-3926

La0.7Ca0.3MnO3/Mn3O4 composites can be synthesized in one step by thermal treatment of a spray-dried precursor, instead of mixing pre-synthesized powders. Another advantage of this composite system is ... [more ▼]

La0.7Ca0.3MnO3/Mn3O4 composites can be synthesized in one step by thermal treatment of a spray-dried precursor, instead of mixing pre-synthesized powders. Another advantage of this composite system is that a long sintering step can be used without leading to significant modification of the manganite composition. The percolation threshold is reached at ~ 20 vol% of manganite phase. The 77 K low field magnetoresistance is enhanced to ~ 11 % at 0.15 T when the composition is close to the percolation threshold. (c) 2007 Elsevier Ltd. All rights reserved. [less ▲]

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See detailSynthesis and characterization of inorganic, lamellar nanofillers with high aspect ratio
Henrist, Catherine ULg; Rulmont, André ULg; Cloots, Rudi ULg

in Journal of the European Ceramic Society (2007), 27(2-3), 1023-1027

Mesostructured silica phases with lamellar structure were prepared by the liquid crystal templating (LCT) technique, from double chain alkylammonium surfactant and sodium silicate or ... [more ▼]

Mesostructured silica phases with lamellar structure were prepared by the liquid crystal templating (LCT) technique, from double chain alkylammonium surfactant and sodium silicate or tetraethylorthosilicate (TEOS) silica precursors. The structural characterization of these phases is presented and compared. Surface modification of the silica layers, together with elimination of the organic template, is considered. Finally, a representative model of the microstructural organization is proposed. (c) 2006 Elsevier Ltd. All rights reserved. [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 detailInfluence of the shaping effect on hardness homogeneity by Vickers indentation analysis
Guillaume, Bernard ULg; Boschini, Frédéric ULg; Rulmont, André ULg et al

in Journal of the European Ceramic Society (2006), 26(15), 3191-3196

In this study, indentation technique (Vickers indentation) has been unconventionally used to evaluate the homogeneity of barium zirconate ceramic samples which have been shaped through different routes ... [more ▼]

In this study, indentation technique (Vickers indentation) has been unconventionally used to evaluate the homogeneity of barium zirconate ceramic samples which have been shaped through different routes. Statistical tools have been used to estimate the con-elation which can be established between heterogeneities within the samples and their shaping ways. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailSlip casting of barium zirconate aqueous concentrated suspensions
Boschini, Frédéric ULg; Guillaume, Bernard ULg; Rulmont, André ULg et al

in Journal of the European Ceramic Society (2006), 26(9), 1591-1598

The rheological behaviour of aqueous suspensions of barium zirconate was studied focusing on the effect of the Volume fraction of particles, leading to the determination of the maximum packing fraction ... [more ▼]

The rheological behaviour of aqueous suspensions of barium zirconate was studied focusing on the effect of the Volume fraction of particles, leading to the determination of the maximum packing fraction. Optimised suspensions dispersed with both polymethacrylic acid and tetramethylammonium hydroxide were slip cast on plaster Moulds to produce discs and crucibles, leading to relative green densities greater than 62% of theoretical ones. Densification was studied at temperatures ranging from 1450 to 1700 degrees C by static and dynamic sintering experiments. Scanning electron microscopy studies demonstrate that slip cast parts are dense and very homogeneous, without any significant processing-related defects or abnormal grain growth. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detail(Micro)-structural comparison between geopolymers, alkali-activated slag cement and Portland cement
Lecomte, I.; Henrist, Catherine ULg; Duyckaerts, Monique ULg et al

in Journal of the European Ceramic Society (2006), 26(16), 3789-3797

Concurrently to research conducted on ordinary Portland cement (PC), new types of binders were developed during the last decades. These are formed by alkali-activation of metakaolin or ground-granulated ... [more ▼]

Concurrently to research conducted on ordinary Portland cement (PC), new types of binders were developed during the last decades. These are formed by alkali-activation of metakaolin or ground-granulated blast furnace slag (GGBFS) and are named, respectively, geopolymers (GP) or alkali-activated slag (AAS). Four different cementitious materials were synthesised: PC, AAS, GP, and a mix GP-AAS and fully compared about their compositions and (micro)-structures. X-ray diffraction has revealed the presence of semi-crystalline C-S-H gel binding phase in PC while AAS, GP and GP-AAS are nearly amorphous. Progressive structural changes have been observed between the different samples by means of infrared spectroscopy, Si-29 and At-27 magic-angle-spinning nuclear magnetic resonance spectroscopy: there is a polymerisation extent of the (alumino)-silicate framework from PC [SiQ(1) and SiQ(2) units] to AAS [SiQ(2) and SiQ(2)(1Al) units] and finally to GP [SiQ(4)(2Al) and SiQ(4)(3Al) units]. Scanning electron microscopy has shown that GP is a homogeneous matrix while the other materials are composites containing GGBFS grains surrounded by a binding matrix. Energy dispersive X-ray EDX analyses (line scans) have shown the absence of formation of any specific phase at the matrix-grains interfaces. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

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See detailOptimization of BaZrO3 sintering by control of the initial powder size distribution; a factorial design statistical analysis
Guillaume, Bernard ULg; Boschini, Frédéric ULg; Garcia-Cano, I. et al

in Journal of the European Ceramic Society (2005), 25(16), 3593-3604

A factorial design statistical analysis has been conducted in order to obtain the optimum conditions in the solid state sintering process of barium zirconate bulk materials, optimum with respect to ... [more ▼]

A factorial design statistical analysis has been conducted in order to obtain the optimum conditions in the solid state sintering process of barium zirconate bulk materials, optimum with respect to density, closed and open porosities. The optimized heat treatment permits to sinter a 99% dense barium zirconate sample at 1650 degrees C during only 2 h. When the temperature is higher than 1650 degrees C or when the heating time is longer than 2 h, a decrease in density is observed. (c) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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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 detailPreparation of nanosized barium zirconate powder by thermal decomposition of urea in an aqueous solution containing barium and zirconium, and by calcination of the precipitate
Boschini, Frédéric ULg; Robertz, B.; Rulmont, André ULg et al

in Journal of the European Ceramic Society (2003), 23(16), 3035-3042

The synthesis of barium zirconate was initiated by urea induced homogeneous precipitation followed by a "low temperature" thermal treatment. The kinetic of the reaction and the optimum urea/cation ratio ... [more ▼]

The synthesis of barium zirconate was initiated by urea induced homogeneous precipitation 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. A calcination at 1200 degreesC during 2 h gives rise to the formation of a pure barium zirconate phase. Microstructural characterisations have been performed in order to evaluate the sintering behaviour. Dilatometric measurements, coupled with scanning electron microscopy analyses clearly indicate that barium carbonate decomposition process leads to the formation of internal porosity which severely limits the density of the material, even if a sintering was performed at 1500 degreesC. A careful control of the heating profile seems to be necessary in order to produce dense materials. (C) 2003 Elsevier Ltd. All rights reserved. [less ▲]

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