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排序方式: 共有517条查询结果,搜索用时 15 毫秒
101.
Karim Hentour Viviane Turq Alicia Weibel Florence Ansart Jean-Michel Sobrino Julien Garcia Pierre-François Cardey Christophe Laurent 《Journal of the European Ceramic Society》2019,39(4):1304-1315
Carbon-alumina coatings on stainless steel were prepared by a sol-gel route. The dispersion of the commercial graphite flakes by an ultrasonic bath, an ultrasonic probe and a high-shear mixer, produce thinner flakes, few-layered-graphene and bi-layer-graphene (BLG), respectively. The coatings were examined by optical and electron microscopy, interferential rugosimetry, optical profilometry and Raman spectroscopy. The friction coefficient against a steel ball is decreased by a factor of 5–7 and the wear volume is reduced by a factor of 6–38 compared to a pure alumina coating. The best results correspond to the sample prepared using the high-shear mixer. Delamination of the graphite flakes into BLG during the friction test provides the system with debris suitable for tribofilm building up and lubrication but it is better to already have carbon dispersed as BLG in the coating before the test, notably because the carbon surface area available is much higher. 相似文献
102.
103.
The doping of lanthanum oxide with strontium maintains the good selectivity of the oxidative methane coupling for the catalysts prepared or calcined at high temperature (> 800 °C) by preserving the platelet shape of oxide particles. 相似文献
104.
Jérémie Pourchez Sandrine Parisse Gwendoline Sarry Sophie Perinel-Ragey Jean-Michel Vergnon Anthony Clotagatide 《Aerosol science and technology》2018,52(4):359-369
The new high-power Electronic Nicotine Delivery System (ENDS) can generate aerosols with higher nicotine concentrations than older ENDS. Aerosol particle sizes affect deposition patterns and then plasma nicotine levels in vapers. Consequently, understanding the factors influencing particle size distribution of high-power ENDS is relevant to assess their performance in terms of nicotine delivery. The particle size distribution and the aerosol output (aerosol mass) were measured using cascade impactors. The effects of the refill liquid composition (80% PG/20% VG vs. 80% VG/20% PG; PG refers to propylene glycol and VG to vegetable glycerin) and the power level of the battery (from 7 W to 22 W) were investigated. The aerosol output increases significantly with the power level following a logarithmic law. The PG/VG ratio also has an impact on the aerosol output. The higher the VG content in the refill liquid, the higher is the aerosol output. Besides, particle size distribution is positively related to the power level, following linear correlations between the mass median aerodynamic diameter (MMAD) and the power level in the range of 7–22 W. A moderate impact of the PG/VG ratio on size distribution is equally observed. Changes in the power level allow the transition between a dominant mode with MMAD from 613 nm to 949 nm. We demonstrated that the power level can strongly change the aerodynamic properties of high-power ENDS, especially at high voltage. Associated with the aerosol nicotine level assessment, MMAD could be determined as a means for comparing ENDS devices and nicotine delivery.
Copyright © 2018 American Association for Aerosol Research 相似文献
105.
Alkylation of isobutane with ethylene was investigated over a -Al2O3-Cl catalyst at temperatures below 380 K. Ethylene was fully converted over a period of 5–20 h, then conversion steadily decreased. The only products were alkanes, mainly C6 and C8. The composition of the alkylate varied with the isobutane/ethylene ratio and with time-on-stream. Among the C6, 2,3-dimethylbutane became predominant (>95%) after a few hours. The composition of octanes appeared less selective. The kinetic distributions of isomers are interpreted by a new mechanism based on cyclopropane-carbonium ions. Upon catalyst ageing, alkane isomerization decays faster than alkylation, oligomerization being least affected. 相似文献
106.
Electrocatalysis for the direct alcohol fuel cell 总被引:1,自引:0,他引:1
Fabrice Vigier Séverine Rousseau Christophe Coutanceau Jean-Michel Leger Claude Lamy 《Topics in Catalysis》2006,40(1-4):111-121
The basic principles of a direct alcohol fuel cell are first presented. Low temperature fuel cells (working between ambient
temperature and 80–120 °C) need improved catalysts to reach performance levels sufficient for practical applications, particularly
for the electric vehicle and for portable electronic devices. This is the case of proton exchange membrane fuel cells (PEMFC)
and of direct alcohol fuel cells (DAFC) for which the kinetics of the electrochemical reactions involved (oxidation of reformate
hydrogen containing some traces of carbon monoxide, oxidation of alcohols, reduction of oxygen) is rather slow. Basic understanding
of electrocatalysis is then examined, showing how to increase the reaction rate both by the nature and the structure of the
catalytic electrode and by the electrode potential. Finally the most used Pt-based electrocatalysts to activate the electrode
reactions occurring in a direct ethanol fuel cell (DEFC) are discussed on the basis of electrochemical, spectro-electrochemical
and fuel cell experiments. 相似文献
107.
108.
Olga Klinkova Joël RechSylvain Drapier Jean-Michel Bergheau 《Tribology International》2011,44(12):2050-2058
Carbon fiber reinforced polymers (CFRP) are increasingly employed within the aerospace industry, particularly within the aircraft sector. However, machining of fiber reinforced composites can be quite complex, first due to the inherent heterogeneity resulting from the reinforcements/matrix assembly and second due to the presence of high modulus/high strength fibers. Therefore, a lot of Finite Element models have been developed in order to understand their material removal mechanisms. Among the scientific issues faced by these works, the identification of friction coefficients between CFRP and cutting tool materials remains a strategic field of research. This paper aims at characterizing the friction properties between composite and cutting tool materials. More precisely, the paper focuses on the context of a randomly structured CFRP, called HEXTOOL™, machined with a carbide tool under dry conditions. The specific tribological conditions during machining of such heterogeneous materials are discussed in the paper, especially the configuration of the tribosystem (‘opened tribosystem’). The great lack of friction coefficient is mainly due to the absence of relevant tribometers simulating the tribological conditions occurring in cutting. This paper presents the development of a new tribometer designed to simulate conditions corresponding to machining of randomly structured CFRP materials. It provides quantitative values of friction coefficient and heat partition coefficient depending on sliding velocities. This work has revealed that friction coefficients are very low in dry regime compared to those obtained in metal cutting. Moreover, experimental results confirm that friction coefficient decreases from 0.25 to 0.1 when sliding velocity increases. Finally this works establishes that a TiN layer deposited on carbide tools is not able to modify friction properties. 相似文献
109.
110.
Ligno-cellulosic biomass from different sources presents very variable compositions. Consequently, there is a wide variation in the nature and quantities of gaseous products obtained after thermal treatment of biomasses.The objective of this work is to establish a link between the composition of a biomass and its pyrolysis gas yields and composition. Experimental flash pyrolysis of several biomasses at a temperature of 950 °C and a gas residence time of about 2 s was carried out. An attempt was then made to predict gas yields of any biomass according to its composition. We show that an additivity law does not allow the gas yields of a biomass to be correlated with its fractions of cellulose, hemicellulose and lignin. Several potential explanations are then offered and quantitatively demonstrated: it is shown that interactions occur between compounds and that mineral matter influences the pyrolysis process. 相似文献