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141.
This work constitutes detailed EIS (Electrochemical Impedance Spectroscopy) measurements on a PBI-based HT-PEM unit cell. By means of EIS the fuel cell is characterized in several modes of operation by varying the current density, temperature and the stoichiometry of the reactant gases. Using Equivalent Circuit (EC) modeling key parameters, such as the membrane resistance, charge transfer resistance and gas transfer resistance are identified, however the physical interpretation of the parameters derived from EC’s are doubtful as discussed in this paper. The EC model proposed, which is a modified Randles circuit, provides a reasonably good fit at all the conditions tested. The measurements reveal that the cell temperature is an important parameter, which influences the cell performance significantly, especially the charge transfer resistance proved to be very temperature dependent. The transport of oxygen to the Oxygen Reduction Reaction (ORR) likewise has a substantial effect on the impedance spectra, results showed that the gas transfer resistance has an exponential-like dependency on the air stoichiometry. Based on the present results and results found in recent publications it is still not clear what exactly causes the distinctive low frequency loop occurring at oxygen starvation. Contrary to the oxygen transport, the transport of hydrogen to the Hydrogen Oxidation Reaction (HOR), in the stoichiometry range investigated in this study, shows no measurable change in the impedance data. Generally, this work is expected to provide a basis for future development of impedance-based fuel cell diagnostic systems for HT-PEM fuel cell. 相似文献
142.
Some organic inhibitors of steel corrosion in saturated calcium hydroxide solutions containing 0.1 M chlorides were investigated to elucidate their interactions with the steel surface. The compounds studied were dicyclohexylammonium nitrite (DCHAMN), dicyclohexylamine (DCHA), sodium -glycerophosphate (GPH) and 5-hexyl-benzotriazole (C6BTA). Sodium nitrite (SN) was also studied as a reference. The techniques applied were electrochemical impedance spectroscopy (EIS), polarization curves, cyclic voltammetry (CV) and Fourier transform infrared (FTIR) spectroscopy. FTIR spectra showed that DCHAMN, DCHA, GPH and C6BTA interact with the steel surface by chemisorption and some information about the mechanism also emerged. From DCHAMN solution, DCHA chemisorption is induced by slow salt hydrolysis. CV tests show that, among chemisorbed substances, only GPH avoids chloride penetration on cycling, most likely due to a quick chemisorption, while DCHAMN can only enlarge the passive potential range. Addition of SN also prevents chloride attack on cycling. Twenty days of immersion in inhibited solutions revealed that, besides SN, GPH and DCHAMN also form an impervious surface film on steel, which blocks any localized corrosion attack, whereas in the case of DCHA and C6BTA solutions, pitting corrosion is slowed down, but not avoided. DCHAMN exhibits the highest inhibiting efficiency at long immersion times, as a result of a synergetic inhibitive action which develops between nitrite and chemisorbed DCHA. 相似文献
143.
144.
王媛 《北京建筑工程学院学报》2002,18(4):80-85
本文从高层管理信息系统的概念入手,重点对E(高层管理者)、I(高层管理者的信息需求)、S(提供信息的计算机系统)三大部分中的E进行系统研究,对高层管理者的角色,职能,工作进行分析,以供管理者参考. 相似文献
145.
The corrosion inhibition effect of the following organic additives: 2‐butin‐1,4‐diol (BD), N,N′‐dimethylthiourea (DMTU), N,N′‐diethylthiourea (DETU) and N,N′‐diisopropylthiourea (DITU), in steel pickling baths (sulphuric acid solutions) was studied by means of weight loss and electrochemical measurements like open circuit potential (OCP), polarization curves and impedance spectroscopy (EIS). A significant decrease in the corrosion rate was observed in presence of the investigated compounds depending on the nature and the concentration of the additives. The weight loss experiments show an inhibitory efficiency that reaches values beyond 98 %. The protective effect increases with the enlargement of the lateral chain size in the case of the thioureas. The electrochemical experiments show also a protective effect of the organic additives against corrosion. Their adsorptive behaviour is found to follow the Langmuir model. 相似文献
146.
The selectivity of metal oxide gas sensors (MOG) can be improved significantly by forming composites with solid ionic conductor additives. First investigations were done using model composites of SnO2/Natrium Super Ionic Conductor (NASICON) with the result of a huge sensitivity enhancement to substances ending with R–OH, R–HO or R–COOH groups and a reduction of sensitivity to other gas components. This selectivity of the new composite to those functional groups could be confirmed by catalytic conversion measurements with FTIR-spectroscopy at three gas components, respectively. The specific conductivity of the NASICON containing composites is significantly lower than that of pure SnO2. Advanced studies show that the activation energy of the bulk-conductivity increases by approximately 30% in the presence of NASICON. In spite of high volume parts of NASICON (20%), no polarization effects were found (a complete Ohmic current–voltage behavior) and mainly the resistive part of the electrical impedance is influenced. 相似文献
147.
M irghasem Hosseini Habib Ashassi-Sorkhabi Heshmat Allah Yaghobkhani Ghiasvand 《中国稀土学报(英文版)》2007,25(5):537-543
A A cerium-based chemical conversion process was studied. First, zinc coating obtained from a free-cyanide alkaline bath, with derivative of imidazol with new brightener, was investigated, zinc-plated steel specimens were treated with a solution of 50 mmol· L^-1 Ce(NO3 )3 The corrosion behavior of bare and treated mild galvanized steel was evaluated during exposure to 0.5 mol · L^-1 NaCl for different immersion time, using Tafel polarization curves and electrochemical impedance spectroscopy (EIS) measurements. The surface morphology of the coating was studied using scanning electron microscopy (SEM). The composition and chemical percent of the coating were examined by X-ray dispersion energy (EDAX). The results of these measurements showed that the newly developed cerium-based conversion coating process was a promising candidate for replacing the conventional chromate treatments used at present for galvanized steel. 相似文献
148.
《Materials and Manufacturing Processes》2007,22(3):328-332
It has been reported that the mechanical properties and corrosion resistance of metallic alloys depend strongly on the solidification microstructural arrangement. The correlation of corrosion behavior and mechanical properties with microstructure parameters can be very useful for planning solidification conditions in order to achieve desired final properties. The aim of the present work is to investigate the influence of dendritic microstructural parameters of an Al-9 wt.% Si alloy on mechanical properties and corrosion resistance. The experimental results establish correlations between secondary dendrite arm spacings (λ2) and ultimate tensile strength (σu), yield strength (σy), corrosion potential (ECorr), and corrosion rate (iCorr). 相似文献
149.
应用刷涂-热氧化法,在不同热氧化温度(分别为400℃、440℃、470℃)下制备Ru、Ir、Ti三元金属氧化物电极。通过电化学性能、强化寿命以及电极形貌分析得出:440℃热氧化温度下制备的Ru0.15Ir0.15Ti0.7/Ti电极析氯电位低、催化活性强、强化寿命长;且该温度下的反应电阻也最小。 相似文献
150.