1,721,018 research outputs found
Application of the Differential Impedance Analysis (DIA) on the Microbiologically Induced Corrosion (MIC) of Bronze
No full textIn this work, the behavior of a binary Cu-Sn (12wt% Sn) alloy has been studied in presence and absence of bacteria in aqueous solution simulating stagnant fresh water. The corrosion processes have been investigated using the Electrochemical Impedance spectroscopy (EIS) technique. The application of the Differential Impedance Analysis (DIA) allowed identifying three processes attributed to the electrical double layer, electrical properties of the passive film and mass transfer processes at the metal/solution interface. Based on DIA structural analysis, equivalent circuit model was proposed and used for better parametric identification of the impedance data. The formation of a biofilm strongly influenced the passive layer behavior, promoting localized corrosion. Post-experiment characterization performed by Scanning electron microscopy (SEM) supported the electrochemical characterization
Interaction between differently coated commercial stainless steels and contacting layer (LSCF) aged in air at 800°C
No full textInteraction between crofer 22 APU current collector and LSCF cathode contacting layer under cell operation
No full textIn this work the oxidation of Crofer 22 APU and its interaction with La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) applied as contacting layer have been investigated in air at 750°C under a current load of 0.5 Acm-2 with the aim to reproduce as close as possible the interconnect interface in real operating conditions. The effects of such interaction and of the pre-oxidation treatment have been studied by means of ASR measurement and post-experiment characterizations. The behavior of such samples has been compared with the results on a working Crofer 22 APU bipolar plate tested as cathode current collector of an anode-supported cell reproducing the stack cathode compartment conditions
Structural vs. electrochemical investigation of niobium oxide layers anodically grown in a Ca and P containing electrolyte
No full textThe growth of anodic oxide on niobium has been investigated as a function of the applied potential in a solution containing P and Ca-EDTA complexes. Anodizing below and above the breakdown potential has been explored via morphological (AFM and SEM) and compositional (XPS and EDX) analysis. Below the breakdown potential, thin (few hundreds of nanometers) and uniform oxide layers are formed, with negligible inclusions of electrolyte ions. Conversely, above the breakdown potential, in the so-called ASD regime, thicker and microporous oxide layers are observed, with a significant enrichment of the matrix with Ca and P. At potentials around 250 V the structure evolves towards a highly inhomogeneous and porous layer with the presence of some fractures, potentially affecting the oxide passivation properties. The corrosion resistance properties of the oxide layers have been investigated by electrochemical methods (OCP, anodic polarization and EIS). Data indicate that the corrosion resistance, initially increasing with the anodizing potential, weakens at potentials around 250 V. A potential of about 200 V represents, therefore, a good tradeoff between morphological and compositional properties and resistance to corrosion, which are important issues in view of osteoconductive properties for orthopaedic implant applications. (C) 2020 Elsevier B.V. All rights reserved
Characterization of Glass-Ceramic Sealant for Solid Oxide Fuel Cells at Operating Conditions by Electrochemical Impedance Spectroscopy
No full textA commercially available glass-ceramic composition is applied on a ferritic stainless steel (FSS) substrate reproducing a type of interface present in solid oxide fuel cells (SOFCs) stacks. Electrochemical impedance spectroscopy (EIS) is used to study the electrical response of the assembly in the temperature range of 380–780 °C and during aging for 250 h at 780 °C. Post-experiment analyses, performed by means of X-ray diffraction (XRD), and along cross-sections by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis, highlight the microstructural changes promoted by aging conditions over time. In particular, progressive crystallization of the glass-ceramic, high temperature corrosion of the substrate and diffusion of Fe and Cr ions from the FSS substrate into the sealant influence the electrical response of the system under investigation. The electrical measurements show an increase in conductivity to 5 × 10−6 S∙cm−1, more than one order of magnitude below the maximum recommended value
K44M ferritic stainless steel as possible interconnect material for SOFC stack operating at 600 °C: Characterization of the oxidation behaviour at early working stages
No full textA commercial ferritic stainless steel (FSS) known as K44M (Type 444, according to ASTM A240, DIN 1.4521 according to NF EN 10088-2) was aged in static air in two differing thick-nesses (i.e. 1.5 and 0.4 mm) at a thermal cycle corresponding to the curing phase of anexperimental glass used as sealing in solid oxide fuel cell (SOFC) stacks, and to an ageingprocess in air of 200 h at 600C.The characterization performed on the aged samples after the complete treatment andat each step of the thermal cycle allowed to investigate the scale formed depending on thetemperature and to the thickness of the sample
Behavior of commercial ferritic stainless steel during the starting process of intermediate temperature SOFC stacks
No full textAging of materials at inlet and outlet fuel manifolds in a SOFC stack
No full textAnalyses performed on a stack operated for more than 4000h at 750°C at high fuel utilization (80%) revealed significant differences in aging behaviour of stack components when comparing fuel inlet and fuel outlet areas. Two samples were cut from the fuel inlet and outlet manifolds of the operated SOFC stack. The glass-ceramic sealing material and the interconnect alloy were exposed to a dual atmosphere (external air and internal fuel stream). The fuel composition was dry H2/N2 (60:40 vol. %) at the inlet and H2O/H2/N2 (48:12:40 vol. %) at the outlet. The stack was operated in co-flow configuration, with a large excess of air. It was found that the interfaces between the seal and the alloy were significantly affected by the difference in fuel composition. The sealant exposed to the outgoing air was significantly polluted by chromium generated in the stack and transported by the air stream. These investigations therefore reveal that the long-term evolution of the sealing and of the metallic support depends on the local conditions in the stack, as well as on additional interactions with other degradation phenomena
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