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International audience; Grinding is one of the main unit operation in industrial processes handling powders. The particle size reduction that takes place during grinding tests, usually results in a significant change in the flow behavior of the ground powder. Up to now, a model predicting the evolution of powder flowability with grinding time, according to the operating conditions is still missing. In this paper, a methodology combining a grinding kinetic model and a flowability model involving the population-dependent granular Bond number is developed. The methodology has been applied to an alumina powder, ground in a batch ball mill. The flow function coefficient of the ground samples is measured after various grinding times in a powder shear tester. The comparison between model predictions and experimental data shows that this method allows an accurate prediction of the powder flow behavior over the first sixteen minutes of grinding.

This study aims at characterizing the rheological properties of uranium oxide powders for nuclear fuel pellets manufacturing. The flowability of these powders must be compatible with a reproducible filling of press molds. The particle size distribution is known to have an impact on the rheological properties and fine particles (

International audience; The flow properties of alumina powder mixtures have been investigated using shear tests on a powder rheometer. The evolution of the flow index, ffc, as a function of the powder mixture composition show that all the points form a single curve whatever the pre-shear consolidation stress value adopted, the mixing conditions and the preconditioning of the powder bed (relative humidity) before the tests. It has been also shown that the flow properties of the mixtures are controlled by the competition between the inter-particle interaction forces (Van der Waals and capillary contributions) and gravity via the Bond number.

International audience; The standard methodology employed for estimating homogeneity of powder mixtures relies on the concept of scale of scrutiny. This parameter defines the relevant scale at which a homogeneous distribution of a given compound is critical regarding the final application of the blend. However, such a scale is not always known in advance. In this paper, a process involving two ceramic powders, co-ground and pressed into pellets is investigated in terms of homogeneity at various scales, from macroscopic to microstructural. According to the scale considered, different methodologies are employed. In particular, a reverse method is developed providing homogeneity indexes that are characterizing the microstructural state, without knowing the scale of scrutiny in advance. The results show that the homogeneity is improved by the co-grinding process as compared to simple drum-mixing experiments, even at a macroscopic scale. This method also shows that the microstructural homogeneity increases according to the grinding time during the first 16 minutes of grinding. The evolution of the microstructural homogeneity according to the grinding time is also investigated.

An N-type Ti 0.5 Zr 0.5 NiSn 0.994 Sb 0.006 powder, synthesized by levitation melting, has been mixed with 1.5 wt% of HfO 2 particles and sintered by spark plasma sintering (grain size around 10 μm). Three kinds of nanocrystalline particles have been identified in the sintered microstructure. They are thought to promote scattering of lattice vibrations, leading to a 25% increase of the dimensionless-thermoelectric figure of merit (ZT, around 1.0 at 500 °C) in comparison to the standard Zr 0.25 Hf 0.25 Ti 0.5 NiSn 0.994 Sb 0.006 composition. In the same time, the replacement of Hf by HfO 2 leads to a significant decrease (in the range 25–60%) of the cost per kilogram of raw material.

An N-type Zr 0.25 Hf 0.25 Ti 0.5 NiSn 0.994 Sb 0.006 powder, directly prepared by levitation melting from the raw elements, has been sintered by spark plasma sintering at different temperatures. SEM and TEM observations enabled to detect two sorts of nano-sized precipitates mostly dispersed in the bulk of individual grains constituting the sintered polycrystal (grain size around 3–4 μm, depending on the sintering temperature). These precipitates are thought to scatter lattice vibrations, leading to a dimensionless-thermoelectrical figure of merit (ZT) around 0.91 at 500 °C for the sample sintered at 1140 °C.

Our aim in the EU funded JERICO project was to develop a flexible and scalable imaging platform that could be used in thewidest possible set of ecological situations. Depending on research objectives, both image acquisition and analysis procedures may indeed differ. Up to now the attempts for automating image analysis procedures have consisted of the development of pieces of software specifically designed for a given objective. This led to the conception of a new software: AVIExplore. Its general architecture and its three constitutive modules: AVIExplore — Mobile, AVIExplore — Fixed and AVIExplore — ScriptEdit are presented. AVIExplore provides a unique environment for video analysis. Its main features include: (1) image selection tools allowing for the division of videos in homogeneous sections, (2) automatic extraction of targeted information, (3) solutions for long-term time-series as well as large spatial scale image acquisition, (4) real time acquisition and in some cases real time analysis, and (5) a large range of customized image-analysis possibilities through a script editor. The flexibility of use of AVIExplore is illustrated and validated by three case studies: (1) coral identification and mapping, (2) identification and quantification of different types of behaviors in a mud shrimp, and (3) quantification of filtering activity in a passive suspension-feeder. The accuracy of the software ismeasured comparingwith visual assessment. It is: 90.2%, 82.7%, and 98.3% for the three case studies, respectively. Some of the advantages and current limitations of the software as well as some of its foreseen advancements are then briefly discussed.

An antimony doped magnesium–silicon–tin alloyed powder, prepared by gas-phase atomization from a melt made of the raw elements, has been sintered by spark plasma sintering to manufacture 60 mm diameter pellets of the Mg2Si0.5875Sn0.4Sb0.0125 material. TEM observations enabled to detect nanometer-sized inclusions (averaged diameter of 7 and 10 nm, depending on the sort, 5.1 × 10−3 inclusions/nm2) dispersed in the bulk of individual grains constituting the as-sintered polycrystal (grain size around 7 μm). These inclusions (most are enriched in Sn and impoverished in Mg/Si in comparison to the surrounding matrix) are thought to scatter lattice vibrations, leading to a dimensionless-thermoelectrical figure of merit (ZT) around 1.4 at 510 °C. It has also been scrupulously verified that the thermoelectrical properties are robust from one area of a given pellet to another one and from one as-sintered pellet to another one.

International audience; In this work, we produce bulk nanostructured Mg2Si0.4Sn0.6 thermoelectric materials made of nanograins with sizes below 200 nm and containing a fine distribution of Sn-rich nanoparticles. These materials are obtained by the mechanical alloying followed by spark plasma sintering. The microstructure and transport properties, and their evolutions upon aging, are investigated. A model is developed to capture the different contributions to the phonon scattering processes arising from the nano/microstructural parameters. The calculations show quantitative agreement with the temperature and the temporal dependence of the lattice thermal conductivity of the nanostructured Mg2Si0.4Sn0.6 alloy. This work provides a general analytic approach for identifying the individual contributions of the microstructural parameters on the thermal conductivity which is a very important property controlling the performance of thermoelectric materials.

Usual multi-class classification techniques often rely on the availability of all relevant features. In practice, however, this requirement restricts the type of features that can be considered. Features whose value depends on some partial, intermediate classification results, can convey precious information but their nature hinders their use. A typical example is the identification of objects in a scene, where the distance from some yet unclassified object to some other that would already be identified earlier in the process. This paper proposes a generic method that solves classification problems involving such features in an incremental way. It proceeds by decomposing the multi-class problem into a sequence of simpler binary problems. Once a binary classifier gives an object its class tag, all features depending on this object are computed and appended to the list of known features. Experiments with both synthetic and real data, comprised of tomographic images, show that the proposed method is effective.

A polycrystalline higher manganese silicide (HMS) material has been sintered from an aluminium-enriched gas-phase atomized powder using spark plasma sintering (SPS). After tailoring the SPS parameters, the polycrystal is almost fully dense, mainly constituted by the Mn15Si26 HMS phase and the average grain size is around 10 μm. Transmission electron microscopy investigations coupled to energy dispersive X-ray spectroscopy (EDS) measurements show that: (i) alumina is segregated at grain boundaries and multiple points; (ii) a small amount of residual silicon is homogeneously distributed in the sintered microstructure; (iii) intragranular nanometre-sized inclusions (averaged diameter around 20 nm, concentration of 8.9 × 10−4 inclusions/nm2) are observed in most of the individual grains constituting the polycrystal. Some are crystalline and made of metallic MnSi, some are residual holes/gas bubbles entrapped into the sintered microstructure during the manufacturing step; (iv) each individual grain contains around 1 at.% of aluminium that is dispersed in the Mn15Si26 elemental lattice and then acts possibly as a dopant. Thermoelectrical properties of the sintered material have been investigated in the 20–700 °C temperature range and compared to the literature. The material exhibits the desired P-type conduction, the Seebeck coefficient has a high value for all the temperature range and in the same time the thermal conductivity is especially low. It is postulated that aluminium doping and the presence of nanometre-sized inclusions in the sintered microstructure are responsible for the dimensionless figure of merit (ZT) around 0.7 measured at 500 °C. Such a value, obtained on a sample manufactured with a very simple process, is the best one ever reported for this kind of material.

Tailoring the amount of nanometer-sized nodules made of amorphous silica, resulting from natural oxidation during the processing steps, in an N-type sintered polycrystalline Si92Ge08 material is shown as an effective way to reduce the thermal conductivity without affecting significantly the thermoelectric power factor.

An N-type Mg2Si0.3875Sn0.6Sb0.0125 powder, directly prepared by mechanical alloying from the raw elements, has been sintered by spark plasma sintering. TEM observations enabled to detect nano-sized inclusions (diameter around 13 nm, 1.9 × 109 inclusions/mm2) dispersed in the bulk of individual grains constituting the sintered polycrystal (grain size around 450 nm). These inclusions (enriched in Sn and impoverished in Mg) are thought to scatter lattice vibrations, leading to a dimensionless-thermoelectrical figure of merit (ZT) around 0.85 at 500 °C.

Transmission electron microscopy observations and thermoelectrical property measurements (electrical conductivity, Seebeck coefficient and thermal conductivity) at room temperature have been completed on two fully dense polycrystalline p-type bismuth–tellurium–antimony alloy samples. It is shown that the presence of antimony oxide-based nanosized inclusions (controlled as to volume fraction and size distribution), homogeneously dispersed in the surrounding matrix leads to a dimensionless figure of merit ( ZT ) of ∼1.3 at room temperature. For comparison, when such inclusions are missing the ZT value is only 0.6.

New relationships between grain size and relative density have been established for the case of solid-state sintering of ceramic powders. These new expressions have been used to fit experimental points, obtained during solid-state sintering of a pure submicronic α-alumina powder shaped by slip casting. In contrast to what was established in the past, it is shown that densification is controlled by grain boundary diffusion and grain growth is controlled by the grain boundaries. The quality of the green state (homogeneity of the pore size and homogeneity of the spatial distribution of pores) is used to explain the difference between the results reported here and previous results, where diffusion at the surface of the pores was claimed to control grain growth.

The microstructure of TZ3Y zirconia samples sintered by spark plasma sintering was investigated using transmission electron microscopy. The results of these observations were used to confirm the mechanisms involved in the control of densification. For the second time, the ionic conductivity of some samples obtained by SPS was investigated as a function of temperature. The results were compared with the best results found in the literature and discussed.

The Berre Lagoon receives freshwater from three rivers and a hydroelectric plant. The latter has become the main tributary since the beginning of its functioning in 1966. In a recent juridical context of the plant's discharge restriction, this study focussed on rivers’ implication in the lagoon's eutrophication, with a strategy particularly adapted to floods. Rivers carry an annual mean load of 27,100 tons of suspended matter (SM) into the lagoon, 275 tons N–NO 3 , 36 tons P–PO 4 , 680 tons total N and 130 tons total P. Depending on the river, floods are responsible for up to 99% of SM annual input, 33% nitrate, 53% phosphate, 44% total nitrogen, and 72% total phosphorus. Respecting the quotas given, the power plant remains the main tributary of the lagoon: at least doubling the annual natural discharge of SM and nutrients. Nevertheless, global discharges are lower than those measured 20 to 30 years ago were due to the restrictions applied to the power plant, to dryer conditions and better treatment of sewage waters along the catchment basin.

The Berre lagoon (Provence, France), one of the largest Mediterranean brackish lagoons (155 km 2 ), was occupied, at the turn of the 20th century, by extensive Zostera meadows (Zostera marina and probably Zostera noltii; perhaps over 6000 ha). Subsequently, the lagoon was disturbed by urban and industrial pollution and, from 1966, by the diversion of the Durance River. This resulted in a 10e49-fold and 8e31-fold increase of the freshwater and silt inputs, respectively. By means of digital analysis of aerial photographs for the years 1944, 1992, 1998 and 2004, coupled with ground truth for the last three dates, we mapped the Zostera meadows. The replacement of Z. marina by Z. noltii, the latter species being already dominant in the 1970s, was completed in 1990. In parallel to this substitution, the Zostera beds underwent a dramatic decline. Their depth limit, which was (6e9) m in the early 20th century, withdrew to 3.5, 3, 1 and less than 1 m by 1944, the 1970s, 1992 and 1998, respectively. Since 1998, Zostera must be considered as functionally extinct. The total surface area of Zostera meadows was of the order of 1.5 ha in 2004. In an attempt to alleviate disturbance, the input of freshwater and silt from the Durance River was significantly reduced from the early 1980s and 1990s respectively. Similarly, from the 1970s to the 1990s, urban and domestic pollution was drastically reduced. Despite these steps, Zostera meadows continued to shrink to near extinction. The lagoon has shifted from a system dominated by seagrass beds to a system with bare silt bottoms, which now occupy most of the lagoon. The reasons could be, in addition to continuing nutrient inputs, the resuspension of silt, no longer trapped under the seagrass canopy, during wind episodes, which are frequent in the area, and/or the release of nutrients from the bare silt habitat, which would constitute an indication of a possible hysteresis of the system. However, since 2000, the establishment of the mussel Mytilus galloprovincialis, a drop in turbidity and a slight, inconspicuous progression of Z. noltii could be the harbinger of a reverse shift of the system. 2007 Elsevier Ltd. All rights reserved.

Sintering in air was performed on pure slip cast α-alumina and yttria samples. The “grain size/relative density” trajectory, called “sintering path”, has been established for both materials. With simple considerations, it is shown that it is possible to determine the mechanisms controlling grain growth and densification from the “sintering path” of alumina and yttria. Previous results, obtained when investigating sintering of pure or doped alumina, are re-analyzed using the formalism that has been developed.

Sintering in air was performed on pure, MgO-doped or TiO2-doped slip cast α-alumina samples. The “relative density/grain size” trajectory, called the “sintering path”, was established for each composition. Fully dense samples were obtained by an additional hot isostatic pressing step on the pure and doped materials. After grinding and polishing, the optical properties were measured on flat windows (thickness around 1 mm) in the visible, near-infrared and mid-infrared ranges.

Spark plasma sintering (SPS) of a commercially available granulated zirconia powder has been investigated. The “relative density/grain size” trajectory, or “sintering path”, has been established for a constant heating rate (50 °C/min) and a constant applied pressure (100 MPa). In addition, an attempt has been made to identify the mechanism(s) that could be invoked for the control of densification during the SPS experiments.

International audience; Silicon nitride processed by gas pressure sintering contains a very small amount of glassy phase and consequently exhibits a strong resistance to deformation until 1450 degreesC. Above this temperature, both relaxation kinetics and creep rate rapidly increase. To explain such a behaviour, the formation of a liquid phase by dissolution of YSiAlON phases was proposed. The present paper shows that mechanical spectroscopy argues for the existence of such a liquid phase at high temperature. The mechanical loss is very low in the as-sintered material. Nevertheless, the internal friction peak generally observed in silicon nitride, and attributed to the glass transition in the glassy pockets, is also observed in the gas pressure sintered silicon nitride. Moreover, the peak is much higher in annealed and "quenched" specimens and it increases with annealing time. These results show that the annealed and "quenched" material contains much more glassy phase and so argues for the dissolution of crystalline phases at high temperature. (C) 2002 Elsevier Science Ltd. All rights reserved.

The improvement in high temperature mechanical properties of silicon nitride ceramics has been explored by fabrication of a β′-Si 3 N 4 α-YSiAlON ceramic densified, without additives and without HIP treatment, by sintering of a mixture of α-Si3N4 and α- YSiAlON powders under a nitrogen pressure of 5 MPa. The high temperature creep behaviour was investigated in the ranges 100–400 MPa and 1280–1400 ° C by compressive tests. The creep performances were very impressive. The activation energy (Q = 770 kJ/mol) and the stress exponent (n = 1) are consistent with a deformation mechanism resulting from grain boundary sliding accommodated by volume diffusion. Microstructure was not affected by the deformation conditions, in particular no cavity formation was observed after creep at 1400 °C and 300 MPa. This behaviour is related to the probable absence of a thick boundary film which may result from crystallization during cooling of small glass pockets and from internal stresses caused by the volume change of crystallizing pockets.

Silicon nitride materials have been studied by mechanical spectroscopy in parallel with creep tests and TEM. A mechanical loss relaxation peak was observed (∼ 1270 K, 1 Hz). The associated activation energy and limit relaxation rate (> 1000 kJ/mol and > 1045 s1) are unusually high, indicating a transformation of the material, i.e. “glass transition” of the amorphous grain boundary phase. The evolution of the spectra during thermal cycling could be associated with the crystallization respectively reamorphization of this phase. Effectively, TEM observations carried out at different stages of thermal treatment were found in direct correlation with the spectra. As the anelastic phenomena appear at temperatures below the ones at which plasticity begins at a macroscopical range, the analysis of the mechanical loss spectra could provide valuable information concerning the mechanisms of microplasticity in silicon nitride. In fact, a good qualitative agreement is found between creep and anelastic behaviour of these materials.

Alumina-zirconia ceramics reinforced with SiC whiskers have been superplastically deformed during compressive creep tests up to true strains near 90%. Deformation resulted mainly from diffusion mechanisms. The influence of whisker orientation relative to stress axis has been studied. It appeared that the angle between the whisker direction and the stress axis is not adequate to characterize the resultant creep rate. It is the direction of the matter flow relative to the whisker axis which seemed to be the preponderant criterion. Observations of porosity in highly strained specimens are in agreement with superplasticity models involving pores as a second phase.