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Nous avons étudié, par microscopie électronique à transmission, la structure tridimensionnelle des particules métalliques de catalyseurs Pd/Al2O3. Un modèle de cuboctaèdre tronqué est proposé pour des particules de taille de l'ordre de 30 nm. Pour des particules de taille inférieure (~ 5 nm) l'observation des profils et des orientations cristallographiques vis-à-vis du support sont compatibles avec un modèle cuboctaédrique. Transmission electron microscopy has been used to study the three dimensional structure of metal particles in Pd/Al2O3 catalysts. A model in the form of a truncated cuboctahedron is proposed for particles of size about 30 nm. For smaller (~ 5 nm) particles observations of profiles and crystallographic orientations with respect to the support are compatible with a cuboctahedron model.

Les techniques de visualisation des supports et des particules métalliques en microscopie conventionnelle à haute résolution sont précisées. On discute l'apport des principales méthodes de microanalyse en microscopie à balayage (STEM), c'est-à-dire analyse par émission X, microdiffraction et spectroscopie de pertes d'énergie, aussi bien que de la combinaison électronique des images. On examine les améliorations techniques qui sont à attendre à moyen terme. Available imaging techniques for supports and small metal particles in conventional electron microscopy are presented. The advantages of the methods of microanalysis in the scanning transmission electron microscope (STEM) are discussed. These include X-ray emission analysis, microdiffraction and electron energy loss spectroscopy as well as the electronic mixing of images. Improvements to be expected in these techniques in the near future are considered.

Cet article présente les différentes techniques de débitmétrie polyphasique non intrusive décrites dans la littérature du domaine public. Ces techniques sont considérées du point de vue de leur application dans le cadre de la production pétrolière sous-marine (mélange eau/huile/gaz). A partir d'une analyse des différentes méthodes physiques qui peuvent être utilisées, des perspectives d'avenir sont proposées. Several operations in the oil reservoir exploitation industry call for flowmeters capable of delivering information on the quantity and rate of flow of the different phases (gas, oil, water, solids . . . ) present in a pipeline. Amongst these are the estimation of remaining reserves and of well performance, control of production units such as multiphase pumping systems and fiscal monitoring in the case of pipeline networking. Existing methods, based on phase separation, require separate test lines and thus tend to be cumbersome, give only intermittent values of flow parameters and need to be calibrated due to the intrusive nature of the measurements. These drawbacks are seen to be all the more critical in subsea production where the ideal flowmeter would be compact, require little maintenance and supply precise real time data for network and multiphase pump control. In recent years flow measurement in two or more phase systems has received increasing attention both in laboratory studies and for applications in a variety of industries (for example : nuclear power production and food processing as well as of course oil production). We review here the many methods considered for non-intrusive flow metering with two or more components from the point of view of an industrial (in particular subsea oil production) application. The situation is rendered delicate, in particular for density measurement, by the uncontrolled nature of the flow which may occur in any of several regimes with differing spatial distributions of the components. Parameters permitting the various phases to be discriminated are identified in order to evaluate the various techniques. The latter are classified in two major families of interaction for which a range of frequencies are explored : mechanical interactions from ultrasound to simple pressure and noisemeasurement and electromagnetic interactions from the use of gamma rays to the measurement of static electrical properties. Consideration is also given to two techniques of special interest falling outside this classification : the use of neutron bombardment and that of nuclear magnetic resonance (NMR). Most of the techniques considered give only partial responses to the question of measuring the quantites and velocities of each of the three major components : oil water and gas. Some, such as visible light or infrared spectroscopy, are eliminated entirely due to the local nature of the measurements in the system considered. Methods such as acoustic or pressure measurement, providing a rapid and simple means of detecting major events such as the passage of slugs and gas pockets and of measuring their velocity in favorable cases, may be incorporated into the final system. Little information is however furnished as to the flow rates of individual components. Four types of measurement have been selected as presenting particular advantages in all or part of the range of parameters for which information is required. Neutron based methods, particularly when coupled to induced gamma ray spectroscopy, promise to provide useful information on water/oil ratios and on salinity although the development of practical sources is as yet only in its earliest stage. NMR is potentially capable of providing independant measurements of both the quantity and velocity of the two liquid phases although the size of such a flowmeter would be prohibitive in the application envisaged. A restricted application (both in terms of size and in the number of measured parameters) may however be advantageous in combination with other techniques. Two regions of the electromagnetic spectrum are identified as of particular interest. The first is the hard X-ray to gamma ray region where the use of two energies would allow evaluation of three phases : oil water and gas. Velocity measurement is however intrinsically difficult and, for industrial applications, detector technology still has to be improved. In the microwave region (including high frequency capacitance and resistivity measurements) most of the necessary parameters appear to be attainable by combining absorption and reflection measurements with the easy tunability of sources. Although this technology is already used in a wide variety of applications from food processing to traffic control, the range of conditions for which it will be applicable in multiphase oil production is not yet clear. A successful industrial flowmeter may imply a combination of several of these techniques incorporating intelligent use of more classical measurements such as temperature and pressure for auto calibration. Further work on evaluating the range of attainable measurements in a compact, reliable and economic system is likely to further stimulate the development of subsea multiphase production systems.

The effect of wetting on the structure and localisation of cobalt species on various supports (Al2O3, SiO2, TiO2, HZSM-5 zeolite) was studied using X-ray diffraction, Fourier transform infrared spectroscopy with CO as a molecular probe, X-ray photoelectron spectroscopy and extended X-ray absorption fine structure analysis. Aqueous impregnation to incipient wetness of reduced and passivated cobalt catalysts results, even in the absence of any promoter, in a considerable decrease in the concentration of Co crystalline phases and modifies the surface sites. The decrease in the concentration of Co3O4 crystallites was especially pronounced on silica supported catalysts prepared via impregnation of cobalt and on a mixture of Co3O4 and HZSM-5 zeolite. Saturation with water of the passivated Co/SiO2 sample results in an amorphous solid with a local structure close to that of Co2SiO4. For Co/Al2O3 and Co/TiO2 catalysts, the effect of wetting on the concentration of Co3O4 crystalline phase was considerably smaller.

Ten micrometers resolution 3D representations of different media, were obtained with a laboratory computer microtomograph developed from an electron microprobe column. From the original electron microprobe, only minor modifications have been required, indeed several of the utilities of the microprobe have been used to ensure high resolution radiography (2 micrometers). The impact of the electron beam focused onto a thin film is used to form a pointX-ray source and the radiographic image of the sample is acquired on a CCD camera. A specimen rotation mechanism allows multiple radiograph acquisition and reconstruction of the X-ray attenuation 3D cartography. Since X-ray attenuation is directly related to density and atomic number, the microscanner provides 3D cartographs of the different phases present in the sample. System performances have been evaluated on various samples, mainly rocks and composites. Comparison with scanning electron micrographs was used when possible to validate the reconstructions. Results are mostly qualitative but already show the potential of the technique in describing 3D connectivity and topology of pore networks or 3D orientation of fibres in composites.

Introduction: Most individual preventive therapies potentially narrow or widen health disparities depending on the difference in community effectiveness across socioeconomic position (SEP). The equity tipping point (defined as the point at which health disparities become larger) can be calculated by varying components of community effectiveness such as baseline risk of disease, intervention coverage and/or intervention efficacy across SEP., Methods: We used a simple modelling approach to estimate the community effectiveness of diabetes prevention across SEP in Canada under different scenarios of intervention coverage., Results: Five-year baseline diabetes risk differed between the lowest and highest income groups by 1.76%. Assuming complete coverage across all income groups, the difference was reduced to 0.90% (144 000 cases prevented) with lifestyle interventions and 1.24% (88 100 cases prevented) with pharmacotherapy. The equity tipping point was estimated to be a coverage difference of 30% for preventive interventions (100% and 70% coverage among the highest and lowest income earners, respectively)., Conclusion: Disparities in diabetes risk could be measurably reduced if existing interventions were equally adopted across SEP. However, disparities in coverage could lead to increased inequity in risk. Simple modelling approaches can be used to examine the community effectiveness of individual preventive interventions and their potential to reduce (or increase) disparities. The equity tipping point can be used as a critical threshold for disparities analyses.