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排序方式: 共有643条查询结果,搜索用时 15 毫秒
71.
72.
Marlin Magallanes-Perdomo Sylvain Meille Jean-Marc Chenal Elodie Pacard Jérôme Chevalier 《Journal of the European Ceramic Society》2012,32(11):2765-2775
A discussion of the effects of Bioglass® powder crystallisation on the in vitro bioactivity in simulated body fluid (SBF) is presented.Starting from Bioglass® powder, different glass–ceramics were obtained by thermal treatments between 580 °C and 800 °C, with variable crystallisation content (from 10 to 92 wt%). All samples (glass and glass–ceramics) showed apatite formation at their surface when immersed in SBF. In case of the glass and the samples with lowest crystallinity, the first step of apatite formation involved a homogenous dissolution followed by an amorphous calcium phosphate (CaP) layer precipitation. For the samples with a high crystallisation content, heterogeneous dissolution occurred. For the first time, the Stevels number of the amorphous phase is used to explain the possible dissolution of the crystalline phase present in materials with a similar chemical composition of the Bioglass®. All samples presented at 21 days of immersion in SBF B-type hydroxycarbonate apatite crystals. 相似文献
73.
FePO Catalysts for the Selective Oxidative Dehydrogenation of Isobutyric Acid into Methacrylic Acid 总被引:1,自引:0,他引:1
Jean-Marc M. Millet 《Catalysis Reviews》1998,40(1):1-38
This review presents the iron phosphorus oxides used as catalysts for isobutyric acid oxidative dehydrogenation. Research on this catalytic system has been developed in the last decade and many publications have been devoted to this reaction, as it can be a step in a new process of production of methyl methacrylate. We emphasize particularly the nature of the active phase, the active centers, and the role of water and promoters. The mechanistic aspects of the reaction, which corresponds to an extension of the Mars and van Krevelen mechanism with a special role of water partial pressure, are discussed. 相似文献
74.
Jean-François Barthélémy Martin L.E. Guiton Jean-Marc Daniel 《International Journal of Rock Mechanics and Mining Sciences》2009,46(3):590-603
This paper aims at building a method to estimate the probability law governing the 3D fracture density of a fractured rock conditioned to the number of traces observed on a borehole image when the spatial distribution of fracture centers is assumed to follow a Poisson process. A closed-form expression of this law, allowing to calculate its mean value as well as a confidence interval, is derived in both cases of a lineic well (scanline) and a cylindrical well. The latter is better adapted to the situation of fracture size of the same order of magnitude as the well radius, which enables the presence of partial traces. In particular, the method takes into account the bias in the density estimate due to the fact that a fracture may cut the well along two distinct traces according to the considered fracture size. Monte Carlo simulations finally show a good agreement with the theoretical results of mean density and confidence interval. 相似文献
75.
76.
Carbon supports (glassy carbon and Vulcan XC72 powder) were modified by electrochemical and spontaneous grafting of phenylsulfonic acid (PSA) or trifluoromethylphenyl (TFMP) groups via diazonium ion reduction. The effectiveness of the grafting was confirmed electrochemically, by XPS measurements and elemental analyses. The hydrophobic or hydrophilic character of carbon surfaces was evidenced by measuring the contact angles of drops of different liquids (water, ethylene glycol and glycerol) in heptane. The surface energy was calculated and it was found, for example, that spontaneous grafting of a glassy carbon surface by PSA groups led to an increase by a factor 20 of the surface energy compared with an unmodified glassy carbon surface. The study of the grafting of such groups on XC72 carbon powder indicated that a very low grafting ratio (in wt%) led to a significant change in the macroscopic properties of the powder. Thermogravimetric analysis coupled with mass spectroscopy measurements (TGA-MS) showed that these grafted layers were thermally stable even in the presence of dispersed platinum nanoparticles. It was shown by cyclic voltammetry that the carbon substrate modification did not affect the electrochemical behavior of platinum catalyst, since the same active surface area was determined on Pt-XC72, Pt-PSA-XC72 and Pt-TFMP-XC72 catalysts. 相似文献
77.
Jean-Marc Haudin Aurélien Carin Michel Vincent Nicolas Amouroux Gaëlle Bellet Fabrice Montezin 《International Journal of Material Forming》2010,3(4):225-231
In polyamide 12 (PA12) tube extrusion, calibration is the key step of the process that affects the subsequent mechanical properties. In previous work it has been shown that according to the calibration conditions, a very oriented skin layer may be created, which has been correlated to an important decrease of elongation at break. In this paper, we present new results showing a good correlation between molecular orientation and fracture toughness, as evaluated by the EWF (Essential Work of Fracture) approach. They concern notched specimens and confirm the results obtained in classical tensile testing. The specific essential work of fracture is very sensitive to the orientation generated in the skin region by appropriate processing conditions: it decreases from the external to the inner regions of the tube, and increases with skin orientation. 相似文献
78.
Francois Carmona Serge Flandrois Laurent Antunes Jean-Marc Heintz 《Journal of Low Temperature Physics》1999,117(3-4):783-787
We report the results of the study of the resistive transition and the screening effect on similar random composites made of a silver matrix containing sintered superconducting grains of bismuth phase with two different stoichiometries. We show that most of the observed behaviors are compatible with a phenomenological approach in which the intergrain junctions behave as weak links whose the state depends strongly on temperature and field. We find that these links a much weaker in one of the series of samples. 相似文献
79.
Semiclosed-Cell Mullite Foams: Preparation and Macro- and Micromechanical Characterization 总被引:2,自引:0,他引:2
Jean-Marc Tulliani Laura Montanaro Trevor J. Bell Michael V. Swain 《Journal of the American Ceramic Society》1999,82(4):961-968
The preparation and characterization of the properties of mullite ceramic foams suitable for diesel exhaust filtration systems are described. Two foams of different cell sizes, 32 and 61 ppi (pores per inch), were prepared from slurries by the replication process with polyurethane sponges as the templates. The microstructure and the dependence of the porosity and the mechanical properties on the preparation and resulting foam cell size and normalized density are discussed. In addition the micro- and macromechanical properties have been characterized using instrumented indentation techniques; with sharp (Berkovich) and small spherical-tipped indenters the hardness and modulus of the dense strut materials have been measured. The macroproperties have been measured with a large sapphire indenter, ∼5 mm radius using a load partial-unloading technique. The latter enables the modulus and the contact pressure versus penetration to be measured. These values are compared with traditional bulk measurements for crushing strength and elastic modulus. The results are discussed in terms of available theoretical treatments of the indentation of brittle porous materials. 相似文献
80.
Micro-scale truss optimization using genetic algorithm 总被引:1,自引:1,他引:0
María Belén Prendes-Gero Jean-Marc Drouet 《Structural and Multidisciplinary Optimization》2011,43(5):647-656
This paper describes the development of a genetic algorithm that is capable of optimizing the mass of micro-scale trusses.
Belonging to the group of periodic cellular materials, micro-scale trusses are characterized by the creation of a base cell
with a pattern that is repeated in space until a global structure is obtained. Investigation in this field has generally been
focused on the design of base cells and their resistance once the final structure is obtained. In this project we have attempted
to optimize each individual cell and in particular its elements according to the loads and boundary conditions applied to
the global structure. With this objective, we defined a dichotomic search algorithm that establishes a set of cross-sectional
areas suitable for the micro-scale truss, formulated the penalty coefficient for the over-sized elements, and studied the
clones and rebirth process in order to avoid stagnation of the genetic algorithm. The cell elements used in this project were
equal to or less than to 1 mm long, with a cross-sectional area in the order of 10 − 9 m2. 相似文献