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排序方式: 共有78条查询结果,搜索用时 15 毫秒
1.
Conducting carbon/polymer composites as a catalyst support for proton exchange membrane fuel cells 下载免费PDF全文
Carbon/poly(3,4‐ethylene dioxythiophene) (C/PEDOT) composites are synthesized by in situ chemical oxidative polymerization of EDOT monomer on carbon black in order to decrease carbon corrosion that occurred in carbon‐supported catalysts used in proton exchange membrane fuel cell. The effects of different dopants including polystyrene sulfonic acid, p‐toluenesulfonic acid and camphorsulfonic acid with the addition of ethylene glycol or dimethyl sulfoxide on the properties of the composites are investigated. The synthesized composites are characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, surface area analysis and scanning electron microscope. Electrical conductivity is determined by using the four‐point probe technique. Electrochemical oxidation characteristics of the synthesized C/PEDOT composites are investigated by cyclic voltammetry by applying 1.2 V for 24 h. The composite prepared at 25 °C with p‐toluenesulfonic acid and ethylene glycol shows the best carbon corrosion resistance. Platinum‐supported catalyst by using this composite was prepared using microwave irradiation technique, and it was seen that the prepared catalyst did not significantly lose its hydrogen oxidation and oxygen reduction reaction activities after electrochemical oxidation. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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There are a lot of technologically interesting characteristics of glass–ceramics, which are hard, wear resistant, oxidation and corrosion resistant ceramic materials. In the present study, the production of the basalt-based glass–ceramic coating by atmospheric plasma spray technique and their structural characterization were reported. Basalt-based glass coating was performed on AISI 1040 steel substrate which was pre-coated with Ni–5 wt% Al by using plasma spray gun. Basalt coatings of the glass form were crystallized at 800, 900 and 1000 °C for 1–4 h in orders to transform to the glass–ceramic structure. The presence of augite [(CaFeMg)SiO3], diopside [Ca(Mg0.15Fe0.85)(SiO3)2] and aluminian diopside [Ca(Mg,Al)(Si,Al)2O6] crystalline phases formed in the basalt-based glass–ceramic coating layer was detected by X-ray diffraction analysis. Optical microscopy with micrometer was used for metallographic examinations. Differential scanning calorimeter was used for determining the crystallization temperature of glass form basalt-based coatings. Microhardness measurements were carried out on the basalt-based glass–ceramic coating layer with Vickers indenter. The hardness of coating layers is changing between 1009 and 1295 HV0.05 depending on crystallization temperature and process times. It was found that, the higher the crystallization temperature, the more the crystalline phases were resulted. In addition, the lower the crystallization temperature and the longer the treatment time, the harder the coating layer became. 相似文献
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Sule Bayrak Fusun Ozer Markus B. Blatz 《Journal of Adhesion Science and Technology》2013,27(6):581-590
To investigate the effect of fluoride varnish with added casein phosphopeptide-amorphous calcium phosphate on the shear bond strength (SBS) of two adhesive systems to enamel. Specimens obtained from permanent teeth were randomly distributed among four groups for enamel pretreatment [Control (no treatment, CNT), Duraphat varnish (DV), Clinpro White varnish (CWV), MI Varnish (MIV)], and each group was further divided into two subgroups according to adhesive [Etch&rinse (Adper Single Bond, ASB), self-etch (Clearfil SE Bond, CSE)]. Specimens were stored in distilled water at 37 °C for 24 h. Cylindrical composite specimens (2.3 mm in diameter, 3.0 mm in height) were then bonded to the enamel surfaces. SBS tests were performed and data were analyzed with two-way ANOVA and Tukey’s tests. For both CSE and ASB, SBS values of the CNT groups were significantly higher than those of all the enamel pretreatment groups (p < 0.05). Among the enamel pretreatment groups, SBS values with both adhesive systems were lowest in the MIV groups, followed by CWV and DV groups. In conclusion, pretreatment of enamel surfaces with fluoride-containing varnishes reduced bonding performance of adhesive systems to enamel. MIV appeared to cause greater enamel surface alterations and precipitation, which interfered with adhesive bonding mechanisms. 相似文献
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Hüseyin Topallar Yüksel Bayrak Mehmet Işcan 《Journal of the American Oil Chemists' Society》1997,74(10):1323-1327
Unhydrogenated and hydrogenated sunflowerseed oils were exposed to the autoxidation process by sunlight under atmospheric
conditions. Experiments were carried out in equal-sized glass, PET (polyethylene terephthalate) polymer, and metal (covered
by tin) containers. The reaction time was 30 d, and the reaction course was observed by determining weight changes and peroxide
values (PV) of the oil samples at the same time within 2-d intervals. The logarithm of the PV was plotted against time, and
straight lines were obtained from the 4th or 6th d. The autoxidation reaction constants were obtained for each oil in each
container. When comparing the reaction constants, the unhydrogenated oils autoxidize easily, and the autoxidation reaction
occurs faster in sunlight in glass than in the PET polymer container and much faster than in the darkness of the metal container. 相似文献
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Because of the global warming impact of hydro fluorocarbons, the uses of natural refrigerants in automotive and HVAC industries have received worldwide attention. CO2 is the most promising refrigerant in these industries, especially the transcritical CO2 refrigeration cycle. The objective of this work is to identify the main factors that affect two‐stage compression transcritical CO2 system efficiency. A second law of thermodynamic analysis on the entire two‐stage CO2 cycle is conducted so that the exergy destruction of each system component can be deduced and ranked, allowing future efforts to focus on improving the components that have the highest potential for advancement. The inter‐stage pressure is used as a variable parameter in the analysis study. The second law efficiency, coefficient of cooling performance and total exergy destruction of the system variations with the inter‐stage pressure are presented graphically. It was concluded that there is an optimum inter‐stage pressure that maximizes both first law and second law efficiencies. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Arzu Özbey Mehrdad Karimzadehkhouei Özgecan Bayrak Ali Koşar 《Microfluidics and nanofluidics》2018,22(6):62
Inertial microfluidics has become one of the emerging topics due to potential applications such as particle separation, particle enrichment, rapid detection and diagnosis of circulating tumor cells. To realize its integration to such applications, underlying physics should be well understood. This study focuses on particle dynamics in curvilinear channels with different curvature angles (280°, 230°, and 180°) and different channel heights (90, 75, and 60 µm) where the advantages of hydrodynamic forces were exploited. We presented the cruciality of the three-dimensional particle position with respect to inertial lift forces and Dean drag force by examining the focusing behavior of 20 µm (large), 15 µm (medium) and 10 µm (small) fluorescent polystyrene microparticles for a wide range of flow rates (400–2700 µL/min) and corresponding channel Reynolds numbers. Migration of the particles in lateral direction and their equilibrium positions were investigated in detail. In addition, in the light of our findings, we described two different regions: transition region, where the inner wall becomes the outer wall and vice versa, and the outlet region. The maximum distance between the tight particle stream of 20 and 15 µm particles was obtained in the 90 high channel with curvature angle of 280° at Reynolds number of 144 in the transition region (intersection of the turns), which was the optimum condition/configuration for focusing. 相似文献
9.
Ayşenur Öztürk Berker Fıçıcılar İnci Eroğlu Ayşe Bayrakçeken Yurtcan 《International Journal of Hydrogen Energy》2017,42(33):21226-21249
Microporous layers (MPLs) were prepared with different hydrophobic polymers to establish water management in polymer electrolyte membrane (PEM) fuel cells. Besides conventionally used polymers polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene (FEP), two different molecular weights (MW) of polydimethylsiloxane (PDMS) polymer were used as hydrophobic materials in MPL. Membrane electrode assemblies (MEAs) having MPLs with low MW PDMS polymer exhibited the best fuel cell performance compared to the PTFE and FEP based ones. Thus it is concluded that PDMS polymer has a great potential to be used as hydrophobic material for MPL to reduce flooding phenomena in PEM fuel cell. 相似文献
10.
Blends of Cold Pressed Black Cumin Oil and Sunflower Oil with Improved Stability: A Study Based on Changes in the Levels of Volatiles,Tocopherols and Thymoquinone during Accelerated Oxidation Conditions 下载免费PDF全文