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See detailFlow abilities of powders and granular materials evidenced from dynamical tap density measurement
Traina, Karl; Cloots, Rudi ULg; Bontempi, Sébastien ULg et al

in Powder Technology (2013), 235

This paper offers an overview of the flow properties of granular systems, including voids, granular porosity and random packing characteristics. For the purposes of the study, the notion of additional ... [more ▼]

This paper offers an overview of the flow properties of granular systems, including voids, granular porosity and random packing characteristics. For the purposes of the study, the notion of additional porous volume is intro-duced. This volume is defined as the additional air volume added to the optimal granular packing. It represents the difference between the volume of the bulk powder bed and that of the same powder but when ideally packed. It appears as the volume of additional air (or voids) trapped/stored between the grains when the powder passes from a dynamical state to a static state (during the filling of a container or the formation of a powder heap, for example). Therefore, if the powder bed traps air, it is then able to restore air partially or completely or not at all, depending on the intergranular cohesion level. This mechanism of the storing and releasing of air can be analysed from the measurement of compressibility curves. If the powder is non-cohesive or free flowing, it traps a small amount of air in its static state. Conversely, if the powder is cohesive, it traps more air. These data can be related to the flow properties of granular materials. Indeed, the compressibility curves obtained for gran-ular materials provide information such as additional porosity, a kinetic parameter which characterizes the com-pressibility dynamics, a granular relaxation index which predicts how far a powder is from its optimal packing state and an index which gauges the de-areation speed of the powder. Measurement of such properties provides a better understanding of the nature of granular materials. Measurements of dynamical compressibility were car-ried out on five granular materials (two different lactose powders, hydrated lime Ca(OH)2, yttrium stabilized zir-conia balls and polystyrene balls). The overall results are presented using a radar graph. The use of this tool and its advantages are discussed in relation to the measurement and characterization of powder flow properties. [less ▲]

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See detailYBCO SUPERCONDUCTING THICK FILMS: ELECTROPHORETIC DEPOSITION (EPD) ON NON-PLANAR SILVER SUBSTRATES
Namburi, Devendra Kumar ULg; Closset, Raphaël ULg; Fagnard, Jean-François ULg et al

Scientific conference (2013, January 30)

A new formulation of a stable YBa2Cu3O7-δ (YBCO) suspension is proposed in which butanol is preferred to the commonly-used acetone as the suspension medium. Appropriate surfactant has been used to develop ... [more ▼]

A new formulation of a stable YBa2Cu3O7-δ (YBCO) suspension is proposed in which butanol is preferred to the commonly-used acetone as the suspension medium. Appropriate surfactant has been used to develop the superficial charge on the YBCO particles in order to promote migration during the process of electrophoresis. YBCO thick films were deposited on silver tubes and half-tubes by electrophoretic deposition (EPD). The EPD parameters (deposition voltage, deposition time, number of layers etc.) were optimized with respect to the microstructural properties of the YBCO layers after an intermediate heat treatment at 920°C. An essential criterion is the minimization of macrocracks after the 920°C heat treatment, since it was found to favour good superconducting properties after the final heat treatment. This final heat treatment involves (i) partial melting above the peritectic temperature, (ii) peritectic recombination at lower temperature and (iii) reoxygenation at 500°C. Finally, the superconducting properties of the best films are discussed. A uniformly coated 55μm-thick YBCO film on a curved Ag substrate showed excellent superconducting properties with the onset of critical temperature at 92.2 K and an associated sharp resistive transition with transition width < 1 K. [less ▲]

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See detailMorphological and opto-electrical properties of solution deposited Platinum counter electrode for low cost dye sensitized solar cells
Thalluri, Venkata Visveswara Gopala Kris ULg; Décultot, Marc ULg; Henrist, Catherine ULg et al

in Physical Chemistry Chemical Physics [=PCCP] (2013), 15

Although Platinum (Pt) is a rare and very expensive material, Pt counter electrodes are still very commonly used for reaching high efficiencies in dye-sensitized solar cells (DSCs). The use of alternative ... [more ▼]

Although Platinum (Pt) is a rare and very expensive material, Pt counter electrodes are still very commonly used for reaching high efficiencies in dye-sensitized solar cells (DSCs). The use of alternative cheaper catalyst materials did not yet yield to equivalent efficiencies. In this work, we tried to understand how to reduce the amount of deposited Pt-material and simultaneously to deliver higher DSC performances. We systematically compared the properties of Pt-counter electrodes prepared by simple solution deposition methods such as spray-coating, dip-coating, brushing with reference to the Pt-electrodes prepared by sputtering onto fluorine doped-tin oxides (FTOs). The morphological and structural characterizations of the deposited Pt-layers were performed by atomic force microscopy (AFM) and scanning electron microscope (SEM). The composition of Pt-material was quantified by using SEM electron dispersive x-ray (EDX) mapping measurements are further compared with optical transmission measurements. Also contact angle and sheet resistance measurements were performed. By taking Pt-layers composition, morphology and structural factors into account 9.16% efficient N3 dye based DSCs were assembled. The DSCs were subjected to various opto-electrical characterization techniques like current-voltage (I-V), external quantum efficiency (EQE), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and transient photo voltage (TPV) measurements. The obtained experimental data suggest that the Pt counter electrodes prepared by solution deposition methods can also reach to high DSC device performances with a consumption of very less amount of Pt material compared with sputtered Pt-layers. This process also proves that higher DSC performances are not limited to the usage of sputtered Pt-layer as counter electrode. [less ▲]

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See detailMullite plasma spraying for in situ repair of cracks in mullite refractories: Simultaneous optimization of porosity and thickness by statistical design of experiments
Schrijnemakers, Audrey ULg; Francq, B. G.; Cloots, Rudi ULg et al

in Journal of Thermal Spray Technology (2013), 22(7), 1133-1139

We report a laboratory-scale study about the suitability of the plasma spraying process for "in situ" repair of cracks in mullite refractories of industrial furnaces. The "design of experiments" approach ... [more ▼]

We report a laboratory-scale study about the suitability of the plasma spraying process for "in situ" repair of cracks in mullite refractories of industrial furnaces. The "design of experiments" approach is used to investigate how the coating porosity and thickness are influenced by six experimental parameters. Arc current, secondary gas (H 2) flow rate, and stand-off distance are the most significant parameters for both responses. Several interaction terms also affect significantly the thickness response. The validity of the model equations is discussed both from a statistical point of view and regarding the physical credibility of the main model terms. Additional experiments confirm that the measured properties lie into the prediction intervals provided by the model. Using a set of parameters optimized for minimal porosity and high thickness (relevant for the crack repair application), coatings with 6% porosity and 1070 μm thickness can be prepared reproducibly. © 2013 ASM International. [less ▲]

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See detailDifferences in the structural and magnetic properties of nanosized barium hexaferrite powders prepared by single and double microemulsion techniques
Koutzarova, T.; Kolev, S.; Ghelev, Ch et al

in Journal of Alloys & Compounds (2013), 579

Barium hexaferrite powders of nanometer particle size synthesized via two variants of the microemulsion technique, namely, single microemulsion and double microemulsion, were studied. The influence was ... [more ▼]

Barium hexaferrite powders of nanometer particle size synthesized via two variants of the microemulsion technique, namely, single microemulsion and double microemulsion, were studied. The influence was explored of the type of microemulsion technique on the microstructure and on the magnetic properties of the barium hexaferrite powders. The average particle size of the barium hexaferrite powders was in the range from 110 nm to 442 nm depending on the method and conditions of synthesis. The particles with size below 150 nm had irregular shapes between spherical and platehexagonal; the bigger ones had an almost perfect hexagonal shape. The powders obtained by single microemulsion had better magnetic characteristics (saturation magnetization of 65.12 emu/g and coercivity field of 3.6 × 105 A/m) than those obtained by double microemulsion. © 2013 Elsevier B.V. All rights reserved. [less ▲]

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See detailEffect of freeze-drying and self-ignition process on the microstructural and electrochemical properties of Li4Ti5O12
Jamin, Claire ULg; Traina, Karl; Eskenazi, David ULg et al

in Materials Research Bulletin (2013), 48

Crystalline Li4Ti5O12 is synthesized by a method involving the freeze-drying and self-ignition of a gel prepared from titanium isopropoxide, lithium nitrate and hydroxypropylmethylcellulose (HPMC). This ... [more ▼]

Crystalline Li4Ti5O12 is synthesized by a method involving the freeze-drying and self-ignition of a gel prepared from titanium isopropoxide, lithium nitrate and hydroxypropylmethylcellulose (HPMC). This synthesis route yields crystalline Li4Ti5O12 particles after calcination at 800°C for 2 h. In an alternative route, addition of ammonium nitrate shifts the self-ignition mode from wave-like propagation to simultaneous. Powders with different microstructures are thereby obtained. Electrochemical characterization shows that the best results for Li+ intercalation/desintercalation are obtained for the powder prepared without ammonium nitrate addition. These results highlight the necessity for a control of the self-ignition mode to obtain adequate properties. [less ▲]

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See detailCascade of granular flows for characterizing segregation
Lumay, Geoffroy ULg; Boschini, Frédéric ULg; Cloots, Rudi ULg et al

in Powder Technology (2013)

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See detailLithium transition metal (Ti, Nb, V) oxide mesoporous thin films: contrasting results when attempting direct synthesis by evaporation-induced self assembly
Caes, Sébastien ULg; Malherbe, Cédric ULg; Krins, Natacha ULg et al

in Microporous & Mesoporous Materials (2013), 172

This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution ... [more ▼]

This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution. Experimental conditions involve a hydrolysis molar ratio H2O/TM ~10 (TM = Ti,Nb,V) and the common Pluronic structuring agent P123 (EO20-PO70-EO20). Systematic formation of lithium-containing oxides as first-crystallizing phases points to a significant intermixture of lithium and transition metal ions in the inorganic network. In the case of Ti-based and Nb-based oxide films, addition of lithium to the precursor solution is compatible with the formation of amorphous mesoporous films at 350°C. On the contrary, addition of lithium has a detrimental effect on the notoriously difficult formation of vanadium-based mesostructured films: even when replacing half of the vanadium by niobium as a stabilizer, formation of mesostructured films has not been possible in the investigated range of experimental conditions. [less ▲]

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See detailThe influence of a grain boundary on the thermal transport properties of bulk, melt-processed Y-Ba-Cu-O
Marchal, C.; Fagnard, Jean-François ULg; Shi, Y. H. et al

in Superconductor Science and Technology (2013), 26

We report the dependence of thermal conductivity, thermoelectric power and electrical resistivity on temperature for a bulk, large grain melt-processed Y-Ba-Cu-O (YBCO) high temperature superconductor ... [more ▼]

We report the dependence of thermal conductivity, thermoelectric power and electrical resistivity on temperature for a bulk, large grain melt-processed Y-Ba-Cu-O (YBCO) high temperature superconductor (HTS) containing two grains separated by a well-defined grain boundary. Transport measurements at temperatures between 10 and 300 K were carried out both within one single grain (intra-granular properties) and across the grain boundary (inter-granular properties). The influence of an applied external magnetic field of up to 8 T on the measured sample properties was also investigated. The presence of the grain boundary is found to affect strongly the electrical resistivity of the melt-processed bulk sample, but has almost no effect on its thermoelectric power and thermal conductivity, within experimental error. The results of this study provide direct evidence that the heat flow in multi-granular melt-processed YBCO bulk samples should be virtually unaffected by the presence of grain boundaries in the material. © 2013 IOP Publishing Ltd. [less ▲]

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See detailYBa2Cu3O7-x thick films on silver tubes for magnetic shielding applications
Namburi, Devendra Kumar ULg; Closset, Raphaël ULg; Fagnard, Jean-François ULg et al

Scientific conference (2012, December 07)

YBa2Cu3O7-x (YBCO) thick films are investigated for magnetic shielding applications at low frequencies (< 1 kHz). This requires deposition of YBCO on curved substrates such as tubes, half-tubes or even ... [more ▼]

YBa2Cu3O7-x (YBCO) thick films are investigated for magnetic shielding applications at low frequencies (< 1 kHz). This requires deposition of YBCO on curved substrates such as tubes, half-tubes or even more complex shapes. Electrophoretic Deposition (EPD) is an efficient method to achieve this goal: positively-charged YBCO particles suspended in a non aqueous medium drift towards the substrate, used as negative electrode for the application of the electric field. A crucial point is then to optimize the heat treatment of the as-deposited layers in order to achieve suitable superconducting properties. In the present work, we have developed a new suspension formulation in butanol, using a suitable surfactant to stabilize the suspension of YBCO powder (grain size < 2 µm). The EPD parameters (deposition voltage, deposition time, number of layers,...) have been selected to provide uniform layers of YBCO on silver substrates of various shapes. In the proposed communication, we shall discuss in detail the optimization of the heat treatments to achieve densification, peritectic recombination and oxygenation of the YBCO thick films deposited on silver. Scanning electron microscopy coupled with energy dispersive analysis was extensively used to characterize the (i) density / porosity, (ii) presence of macro-cracks, (iii) thickness uniformity, (iv) secondary phase content. We shall then present the characterization of the superconducting properties of the best films. Typically, a uniformly coated 55μm-thick YBCO film on a curved Ag substrate shows a magnetic Tc onset at 92.2 K and sharp resistive transition (< 1K). [less ▲]

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See detailMeasuring the flowing properties of powders and grains
Lumay, Geoffroy ULg; Boschini, Frédéric ULg; traina, Karl et al

in Powder Technology (2012), 224

A granular material is a complex system which exhibits non-trivial transitions between the static, the quasi-static and the dynamical states. Indeed, an assembly of grains can behave like a solid or a ... [more ▼]

A granular material is a complex system which exhibits non-trivial transitions between the static, the quasi-static and the dynamical states. Indeed, an assembly of grains can behave like a solid or a fluid according to the applied stress. In between solid and fluid granular states, very slow dynamics are observed. When a complete macroscopic characterization of a powder is needed, all these granular states have to be precisely analyzed. In this paper, we show how three measurement techniques can be used to measure the physical properties of a powder. The measurements are based on classical tests modified to meet the recent fundamental researches on granular materials. The static properties of the powder are analyzed through the shape of a heap. The quasi-static behavior is studied with the analysis of the compaction dynamics. Finally, the dynamical regime is monitored through the flow in a rotating drum. In order to illustrate how these measurements can be used in practical cases, analyses are performed with three types of granular materials: silicon carbide abrasives, flours and rice. These selected materials allow to show the influence of the different parameters (grain size, grain size distribution, grain shape) on the macroscopic properties of the assembly. Moreover, these studies show the pertinence of the parameters obtained with the proposed techniques for the rheological characterization of powders and grains. [less ▲]

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See detailREVIEW: CONCERNS OF FORCE SPECTROSCOPY USING ATOMIC FORCE MICROSCOPY
Ozhukil Kollath, Vinayaraj ULg; Vinck, Evi; Karl, Traina et al

Report (2012)

Atomic force microscopy (AFM) and its various applications helped many industries for characterisation of materials. One of such field is the biomaterial research where biocompatibility of implant ... [more ▼]

Atomic force microscopy (AFM) and its various applications helped many industries for characterisation of materials. One of such field is the biomaterial research where biocompatibility of implant materials is the main question. Force spectroscopy, one of the AFM technique helps to find the interaction between individual molecules in a non-destructive manner and hence helps to find the biocompatibility. Through this report, we try to review the principles and major concerns of force spectroscopy method of AFM. [less ▲]

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See detailMaterial Aspects of Bone Tissue Engineering
Ozhukil Kollath, Vinayaraj ULg; Cloots, Rudi ULg

Diverse speeche and writing (2012)

Bone tissue engineering is a highly studied topic in material science in the recent decades. Basic principles of chemistry and biology along with advanced material science techniques should be used in ... [more ▼]

Bone tissue engineering is a highly studied topic in material science in the recent decades. Basic principles of chemistry and biology along with advanced material science techniques should be used in order to elucidate the parameters which may influence the bone tissue growth on artificial implants. Progress has been made to an advanced level but still there is room for improvements. Especially in case of large bone defects, finding a ‘universal’ replacement implant is difficult. Patient specific data have to be taken in to account to get a good osteointegration. Metal and ceramic implants are commonly tested in case of large bone defects, but a good mimic of natural bone is hard due to various reasons. However fine tuning these materials and combination of these materials are finding good results. Addition of polymer materials in such implants is a recent effective attempt. Different combinations of these materials along with functionalisation using bioactive molecules make the bone tissue engineering nearly perfect. This presentation will discuss about the recent trends in the materials used in bone tissue engineering. [less ▲]

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See detailTiO2 templated multilayer films used as high efficiency photoelectrode in liquid or solid DSSCs
Dewalque, Jennifer ULg; Cloots, Rudi ULg; Mathis, François ULg et al

Conference (2012, April 10)

Mesoporous anatase thin films are very promising materials to act as electrode in dye-sensitized solar cells. Randomly oriented nanocrystalline TiO2 particles are usually used to prepare photoelectrodes ... [more ▼]

Mesoporous anatase thin films are very promising materials to act as electrode in dye-sensitized solar cells. Randomly oriented nanocrystalline TiO2 particles are usually used to prepare photoelectrodes with a thickness of 10-15 µm. Templated-assisted dip-coating techniques are used to obtain thin films with ordered porosity. However, monolayer films prepared by dip-coating from a solution suffer from a low quantity of active material with a limited surface area, leading to poor photovoltaic performances. Therefore a multilayer deposition process is needed to increase the film thickness along with surface area. Multilayer dip-coating procedures have already been reported but are usually characterized by a lack of linearity in the evolution of parameters (roughness, surface area, PV performances) as the number of layer increases. In this study, we investigate a dip-coating-based multilayer deposition technique delaying these limitations. First, the influence of the template on the film organization and porosity is studied in terms of long-range order, percentage of porosity, pore size, surface area and pores connectivity. Different techniques such as transmission electron microscopy (TEM), atmospheric poroellipsometry (AEP) and UV-visible absorption spectroscopy (UV-vis.) have been used to describe the microstructural features of the films. The film exhibiting the highest dye loading was selected and its thickness gradually increased up to 4 µm. Finally, the photovoltaic performances of the thick films (1 to 4 µm) have been evaluated in combination with the N719 dye and a liquid electrolyte and show excellent efficiency (6.1%) when compared to values reported in the literature. Such mesostructured films were compared in terms of photovoltaic performance with TiO2 nanoparticles films, generally used in DSSC. Films were further evaluated by Rutherford Backscattering Spectrometry (RBS) as high performance photoelectrode in solid-state DSSCs, in combination with Z907 dye and Spiro-OMeTAD as solid electrolyte. [less ▲]

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See detailRutherford backscattering analysis of porous thin TiO2 films
Mayer, Matej; von Toussaint, Udo; Dewalque, Jennifer ULg et al

in Nuclear Instruments & Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms (2012), 273

The additional energy spread due to sample porosity was implemented in the SIMNRA simulation code, version 6.60 and higher. Deviations of the path length and energy loss distributions from the ones ... [more ▼]

The additional energy spread due to sample porosity was implemented in the SIMNRA simulation code, version 6.60 and higher. Deviations of the path length and energy loss distributions from the ones expected from a Poisson distribution of the number of traversed pores are taken into account. These deviations are due to the interaction of pores at higher pore concentrations by overlap or blocking. The skewnesses of the energy distributions are approximated by two-piece normal distributions with identical first three moments. Propagation of porosity-induced energy spread in thick layers is taken into account. Calculated results are compared to experimental data obtained with thin TiO2 mesoporous films measured by Rutherford backscattering (RBS),transmission electron microscopy (TEM), and atmospheric poroellipsometry. [less ▲]

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See detailMagnetic properties of nanosized MgFe2O4 powders prepared by auto-combustion
Ghelev, Ch; Koutzarova, T.; Kolev, S. et al

in Journal of Physics: Conference Series (2012), 356(1), 012048

Targets were prepared to be used for magnetron sputtering and laser ablation and their microstructural and magnetic properties were investigated. The base material was nanosized MgFe2O4 powder produced by ... [more ▼]

Targets were prepared to be used for magnetron sputtering and laser ablation and their microstructural and magnetic properties were investigated. The base material was nanosized MgFe2O4 powder produced by citrate auto-combustion synthesis. The auto-combusted powders were annealed at temperatures in the range 600 - 1000°C in air to study the effect of temperature on thofe formation MgFe2O4. The saturation magnetization Ms was 24.30 emu/g at room temperature. © Published under licence by IOP Publishing Ltd. [less ▲]

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