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41.
Jean-Pierre Guin Tanguy Rouxel Jean-Christophe Sanglebuf Isabelle Melscoët Jacques Lucas 《Journal of the American Ceramic Society》2002,85(6):1545-1552
Ge–Se chalcogenide glasses are characterized by relatively low hardness (0.39–2.35 GPa) and low fracture toughness (0.1–0.28 MPa·m1/2 ). Actually, the hardness of chalcogen-rich glasses is low enough so that the brittleness parameter, B = H / K c , is lower than that of silicate glasses. Whereas hardness and Young's modulus increase with increasing germanium contents, fracture toughness follows a trend similar to that of the density and exhibits a maximum for the Ge20 Se80 composition, which corresponds to the rigidity percolation threshold. Optical microscopy and atomic force microscopy observations suggest that the indentation deformation proceeds by a localized shear deformation phenomenon. Glasses in the chalcogen-rich region behave viscoelastically at room temperature. As a consequence, an increase of the loading time results in a decrease of hardness and toughness. 相似文献
42.
Jean-Pierre Montheard Bernard Boinon Ahmed Belfkira Abderahim Sadel Quang-Tho Pham 《Polymer Bulletin》1992,28(6):615-620
Summary Vinylidene cyanide has been copolymerized in solution by radical reaction with equal initial mole fraction of para substituted acetoxystyrenes. The copolymers have been characterized by means of DSC, TGA and GPC. These products are stable up to 220° and have no visible glass transition temperature. The microstructure of these new copolymers has been studied by 13CNMR; they have an alternating structure and monomers units are arranged in head-to-tail placements. 相似文献
43.
Daniel Sirugue Odile Bonnard Jean-Luc Le Quere Jean-Pierre Farine Rémy Brossut 《Journal of chemical ecology》1992,18(12):2261-2276
InNauphoeta cinerea, male calling behavior is associated with sex pheromone release by the sternal glands. The male pheromone that attracts females from a distance is a mixture of 2-methylthiazolidine and 4-ethylguaiacol. It is active at very low concentrations, 0.05 and 0.01 ng, respectively. Two other compounds, 3-hydroxy-2-butanone and 2-methyl-2thiazoline, act at close range, keeping the female in the vicinity of the male. The function of the volatile pheromone and those of previously described contact pheromones are discussed in regard to their possible involvement in the establishment of male dominant-subordinate relationships. 相似文献
44.
Olivier Renoult Jean-Pierre Boilot Frédéric Chaput Renée Papiernik Liliane G. Hubert-Pfalzgraf Martine Lejeune 《Journal of the American Ceramic Society》1992,75(12):3337-3340
The sol–gel method has been developed for the preparation of pure Ba(Mg1/3 Ta2/3 )O3 ceramics. This involves the reaction of the heterometallic alkoxide Ta2 Mg(OEt)12 with hydrated barium hydroxide Ba(OH)2 ·8H2 O. Complete crystallization of the sol–gel-derived powder is achieved at 600°C, leading to a cubic perovskite type phase. After sintering at 1400°C (2–5 h), a trigonal cell arises from Mg–Ta ordering (the degree of order is greater than 0.9), and about 98.5% of the theoretical density is obtained. Preliminary microwave dielectric measurements show that the dielectric constant and the unloaded Q u of the ceramics are 24.2 and 6750, respectively, at 7.7 GHz. 相似文献
45.
Dendrimers constitute an increasingly important field of research in chemistry for more than 15 years. After pioneering works concerning synthesis, the interest in dendrimers is now mainly driven by their properties and applications. This Account will emphasize the properties of a special class of dendrimers, that is, phosphorus-containing dendritic macromolecules, as tools for the elaboration of nanomaterials. Indeed, these dendrimers can be considered themselves as materials, or they can be used as an intrinsic constituent of a material or as a modifier of the surface of a material. In this latter case, a fundamental work about surfaces covalently modified by dendrimers recently opened the way to the elaboration of DNA chips. 相似文献
46.
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
47.
Amélia H. U. Torres Jean-Pierre Habas 《Polymer-Plastics Technology and Engineering》2013,52(15):1594-1599
The effects caused upon the physicochemical behavior of high-density polyethylene pipes by exposure to a diesel lubricant were investigated, as a function of time and temperature, by thermogravimetric and gravimetric analysis and by FT-IR. The gravimetric data were satisfactorily described using Fick's law. The fitting of the experimental points showed that diesel, which can be regarded as a model fluid to analyze the effects caused by aromatic unities present in oil derivatives, has a high diffusion rate into HDPE. The FT-IR results showed that no main structural modifications have occurred after exposure, besides solubilization of low molecular weight units. From the analysis performed, physical aging was identified as the aging process occurring when the HDPE pipes came in contact with diesel lubricant. 相似文献
48.
Nasreddine Kébir Albert Laguerre Claude Bunel Jean-Pierre Couvercelle 《Polymer》2005,46(18):6869-6877
New telechelic cis-1,4-polyisoprene oligomers bearing an hydroxyl group at the end of the polyisoprene backbone and possessing controlled molecular weights were used as soft segments in the elaboration of polyurethane elastomers. Besides, the well defined hydroxytelechelic cis-1,4-polyisoprene (HTPI) structure obtained through a controlled methodology, was chemically modified leading to hydrogenated and epoxidized oligomers based polyurethanes. The influence of the structural changes of these precursors on the polyurethanes properties have been studied. Thus, mechanical parameters as well as glass transition and mechanical transition temperature measurements indicated an increase in PUs hardness when the length of soft segment decreases and when the degree of epoxidized and hydrogenated isoprenic moieties increases. Moreover, based on thermogravimetric analysis (TGA), a linear relationship was established between the weight loss in the urethane stage degradation and the amount of hard segments in the PUs. Otherwise, the hydrogenated soft segments were found more thermally stable than the epoxidized and the non modified ones. By comparison with similar investigations developed from commercial oligodienes (PBHT R20 LM® and EPOL®), this study mainly showed that the PUs based on hydrogenated hydroxytelechelic cis-1,4-polyisoprenes were more thermally stable and softer than the EPOL® based analogues. 相似文献
49.
A concept of reactive compatibilizer‐tracer for studying reactive polymer blending processes 下载免费PDF全文
Wei‐Yun Ji Lian‐Fang Feng Cai‐Liang Zhang Sandrine Hoppe Guo‐Hua Hu Dominique Dumas 《American Institute of Chemical Engineers》2016,62(2):359-366
A concept called reactive compatibilizer‐tracer is proposed. The latter bears reactive groups capable of reacting with its counterpart on forming a copolymer for in situ compatibilization, and fluorescent labels allowing determining very small amounts of the in situ formed compatibilizer and formation of micelles when it occurs. Owing to this concept, it is shown that a reactive compatibilizer may be very efficient at the beginning of a reactive blending process and may suddenly become completely inefficient, resulting in an abrupt and drastic increase in size of the dispersed phase domains. © 2015 American Institute of Chemical Engineers AIChE J, 62: 359–366, 2016 相似文献
50.
Conditions for theoretical inactivation of Cryptosporidium by ozone could be achieved at full-scale facilities if their design is appropriate. To perform this task correctly the chemical engineer's approach for process design must be applied. This paper discusses the basic equations the estimation of the disinfection efficiency of different ozone reacting systems. Available kinetic data have been integrated in a global model accounting for the hydrodynamics and mass transfer performances of the ozonation reactor. Thus the proposed method allows one to predict Cryptosporidium inactivation level in a given ozonation system. However, if a specified disinfection goal is to be achieved for Cryptosporidium with the developed model it is also possible to choose and optimize the design of the ozone reactor. 相似文献