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排序方式: 共有1536条查询结果,搜索用时 15 毫秒
51.
Mikko Hongisto Sonya Ghanavati Arnaud Lemiere Gregory Hauss Shashank Boraiah Louis Cornet Angeline Poulon-Quintin Dominique Pagnoux Dominique Bernard Jonathan Massera Laeticia Petit Veronique Jubera Sylvain Danto 《Journal of the American Ceramic Society》2023,106(11):6527-6540
Here, we report on core–clad bioactive borosilicate fibers, that we have prepared both with round and rectangular cross-section profile. The exposed approach, which relies on the stacking and drawing of glass slabs, demonstrates our ability to develop bioactive-based glass fibers with tailored cross-section profiles. Tens-of-meters-long fibers were successfully drawn, although suffering from elevated losses in the case of the rectangular ones. The response of the fibers in simulated body fluid was studied for both geometries. We found that a round cladding can act as protective layer, tempering effects of the corrosion. We also noticed that rectangular fibers are more prone to degradation, the enhanced corrosion beginning from their sharp corners as they accumulated residual tensile stress during drawing. To the best of our knowledge, this is the first report on the effect of residual tensile stresses from surface tension deformations applied to the corrosion of rectangular fibers. As geometry plays a critical role on the biodegradation behavior of the fiberglass, we believe the enclosed results could lead to the design of fiber devices with tailored cross-section profile in order to tune their rate of degradation on solely based geometrical effects. 相似文献
52.
53.
Laurent Boilet Michel Descamps Emmanuelle Rguiti Arnaud Tricoteaux Jianxi Lu Fabrice Petit Véronique Lardot Francis Cambier Anne Leriche 《Ceramics International》2013,39(1):283-288
Stoichiometric β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA) powders were synthesized by chemical precipitation of aqueous solutions of diammonium phosphate and calcium nitrate. After a calcination treatment and a milling step, the powders were shaped by slip casting. The sintering temperature effect on the relative density and the average grain size was investigated. By natural sintering at 1200 and 1120 °C, densities of 98% and 99% were obtained for HA and TCP, respectively. After determination of minimum temperatures to obtain only closed porosity and a pre-sintering at these temperatures, hot isostatic pressing (HIP) treatment was carried out. Transparent or translucent samples were obtained, indicating a relative density very close to the theoretical value (>99.9%). Mechanical properties (three-point bending strength, fracture toughness, Young's modulus and Vickers hardness) were measured on both materials with similar grain size (~ 1 μm). Bending strengths of 181 and 105 MPa were measured for TCP and HA, respectively. 相似文献
54.
This paper investigates the way modelling mixing phenomena occur in unsteady stirring conditions in agitated vessels. In particular, a new model of torus reactor including a well-mixed zone and a transport zone is proposed. The originality of the arrangement of ideal reactors developed here lies in the time-dependent location of the boundaries between the two zones. This concept is applied to model the positive influence of unsteady stirring conditions on homogenization process: the model avoids a mass balance discontinuity when the transition from steady to unsteady stirring conditions is performed.To ascertain the reliability of the model proposed, experimental runs with highly viscous fluids have been carried out in an agitated tank. The impeller used was a non-standard helical ribbon impeller, fitted with an anchor at the bottom. The degree of homogeneity in the tank was observed using a conductivity method after a tracer injection.It is shown that for a given agitated fluid and mixing system, model parameters are easy to estimate and that modelling results are in close agreement with experimental ones. Moreover, it would appear that this model allows the easy derivation of a control law, which is a great advantage when optimizing the dynamics of a mixing process. 相似文献
55.
Johan Petit Philippe DethareAlessandra Sergent Robert MarinoMarie-Hélène Ritti Stéphane LandaisJean-Luc Lunel Sandrine Trombert 《Journal of the European Ceramic Society》2011,31(11):1957-1963
In this paper we present our results on the sintering of α alumina ceramics by hot isostatic pressing. It describes a simple method for obtaining precise relative density values on our almost 100% dense samples. Then, transparency results are discussed with respect to grain size and residual porosity measurements, comparing them to scattering calculations. Our results are not far from the best reported transmission values: almost 60% for a 1 mm thick sample. The other 40% diffuse light comes from the birefringence of alumina for the most part. However, they are transparent enough to see detailed structures at several kilometers through them. 相似文献
56.
A. M. Podurets V. A. Raevskii V. G. Khanzhin A. I. Lebedev O. N. Aprelkov V. V. Igonin I. N. Kondrokhina A. N. Balandina M. I. Tkachenko J. Petit M. A. Zocher 《Combustion, Explosion, and Shock Waves》2011,47(5):606-614
The structure of copper formed after high-rate loading up to pressures of 20–80 GPa with a strain rate of 105–109 sec?1 is considered. In situations with pressures above 20 GPa and strain rates above 106 sec?1, the deformation twins are grouped into packets, which are seen in an optical microscope as parallel bands of localized strains inside individual grains. The number of bands in the structure increases with increasing grain size and strain rate, with decreasing sample temperature, and with increasing period of sample loading. The characteristic time of formation of twin bands in copper is estimated as 0.3 µsec. 相似文献
57.
NOx sorption and reduction capacities of 12-tungstophosphoric acid hexahydrate (H3PW12O40·6H2O, HPW) were measured under representative alternating conditions of lean and rich exhaust-type gas mixture. Under lean conditions, the sorption of NOx is large and is equivalent to 37 mg of NOx/gHPW. Although a part of these NOx remains unreduced, HPW is able to reduce some of the NOx to produce N2 by a reaction between the sorbed NO2 and hydrocarbon (HC), but this process is slow. The addition of 1% Pt affects strongly the chemical behaviour occurring during the course of a rich operation. The NO desorption observed at the beginning of the rich phase is strongly accelerated. The direct correlation between NO2 consumption and CO2 production shows that the principal pathway is the reaction CO+NO2→CO2+NO. In a mixture of reducing gas (CO, HC, H2), the competition is strongly in favour of CO though in its absence the reaction observed was the hydrogenation of propene to propane. 相似文献
58.
Charlotte Porteneuve Hlne Zanni Christian Vernet Knut O. Kjellsen Jean-Pierre Korb Dominique Petit 《Cement and Concrete Research》2001,31(12)
In the present study, we show that high-resolution 29Si and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) can be a powerful tool for analyzing actual concrete mixes. The influence of the amount of silica fume and of the type of cement in high-performance concrete (HPC), as well as the influence of the type of silica fume and of the granular packing in ultrahigh-performance concrete (UHPC) were investigated. Significant effects on the amount and shape of C-S-H, on the incorporation of aluminum in the C-S-H structure, and on the distribution of aluminum-containing hydrates were observed. Nuclear magnetic relaxation of protons was also performed and it showed the fractal feature of the pore size distribution in UHPC and the higher amount of larger pores in HPC. The microstructure of the surface of these same formulations leached by mineral water for up to 1 year exhibits slight modifications. 相似文献
59.
M. Parvary S. H. Jazayeri A. Taeb C. Petit A. Kiennemann 《Catalysis communications》2001,2(11-12):357-362
Mixed LaNixAl1−xO3perovskite oxides have been prepared by a sol–gel related method and characterized by X-ray diffraction (XRD), specific surface area measurements and scanning electron microscopy (SEM) coupled to an energy dispersive X-ray spectrometer (EDS) shows the possibility to obtain a solid solution of LaNixAl1−xO3 (0.1x0.9) with propionic acid as solvent. These systems are highly efficient catalysts for syngas production in dry reforming of methane. 相似文献
60.
Natanaël Basile Maurice Gonon Fabrice Petit Francis Cambier 《Journal of the European Ceramic Society》2012,32(12):3303-3311
The research work reported in this paper is an investigation of the behavior of barium titanate powders under selective laser irradiation. Our goal is to determine suitable conditions to sinter the powders and form dense layers usable in some electronic components. On that purpose, compacts of micro/nano BaTiO3 powder mixes are used for a parametric investigation of the laser scans parameters (power, speed, etc.) with a Nd-YVO4 laser (23 W). The microstructures obtained after laser treatments are evaluated by XRD, SEM and EDS and compared to a reference specimen manufactured in a conventional way. From this work it can be concluded that a high laser beam power is required to obtain a consolidation of the powder grains and the use of a high scan speed avoids the melting. The scanning speed also influences the final crystallographic state of BaTiO3. Optimal parameters were founded in order to form a dense and homogeneous tetragonal BaTiO3 surface. 相似文献