The processing of sintered ceramics is often conditioned by the debinding step. The binders may determine some defects in the final product directly, by causing some gas evolution even at an advanced ...state of densification, due to incomplete decomposition at low temperature, or indirectly, by offering poor adhesion between particles, so that ‘green’ compacts may be easily damaged. The present investigation is aimed at exploring a novel concept for sintered glass-ceramics, based on the adoption of a silicone polymer as reacting binder, providing an abundant ceramic residue after firing. A glass belonging to the CaO-MgO-Al2O3-SiO2 system, already studied as a sealant in solid oxide fuel cell (SOFC) planar stack design, was reproduced in form of ‘silica-defective’ variants, featuring a SiO2 content, in the overall formulation, reduced up to 15 wt%. The overall silica content was recovered by mixing powders of the new glasses with the silicone: upon firing in air, the interaction between glass powders and polymer-derived silica led to glass-ceramics with the same phase assemblage than that formed by the reference glass and with a CTE of 9.5 × 10−6 K-1. The new approach has been successfully applied to the manufacturing of glass-ceramic seals as joining materials for solid oxide cells.
► We investigate whether banks’ risk management structure affects their crisis-performance. ► We use a sample of up to 372 US banks and focus on the credit crisis of 2007/2008. ► Banks with a CRO, ...who directly reports to the board of directors, perform better. ► Standard corporate governance mechanisms do not improve banks’ crisis performance.
The recent financial crisis has raised several questions with respect to the corporate governance of financial institutions. This paper investigates whether risk management-related corporate governance mechanisms, such as for example the presence of a chief risk officer (CRO) in a bank’s executive board and whether the CRO reports to the CEO or directly to the board of directors, are associated with a better bank performance during the financial crisis of 2007/2008. We measure bank performance by buy-and-hold returns and ROE and we control for standard corporate governance variables such as CEO ownership, board size, and board independence. Most importantly, our results indicate that banks, in which the CRO directly reports to the board of directors and not to the CEO (or other corporate entities), exhibit significantly higher (i.e., less negative) stock returns and ROE during the crisis. In contrast, standard corporate governance variables are mostly insignificantly or even negatively related to the banks’ performance during the crisis.
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•Electrophoretic deposition technique to produce protective coatings for SOC interconnects.•EPD co-deposition approach is a new and an interesting route.•EPD is effective as a ...versatile deposition method for SOCs protective coating.
The application of ceramic protective coatings to the metallic interconnects in solid oxide cells (SOCs) is a viable and effective method to limit interconnect degradation issues. This featured letter provides a critical overview of the main outcomes of current research on the use of the electrophoretic deposition (EPD) technique to produce protective coatings for SOC metallic interconnects, specifically focusing on different approaches to stabilise spinel-based suspensions, as well as the possible sintering procedures. The protective properties of EPD coatings are reviewed and discussed in terms of oxidation kinetics and area specific resistance evaluation.
A summary and update of the research on the design, process, and testing of glass and glass‐ceramic to metal seals for solid oxide cells (SOC) conducted during the last 13 years at the Politecnico di ...Torino, Italy, within our research group and with several international collaborations, is presented and discussed. Glass and glass‐ceramic‐based materials play a key role in SOC performance and durability as well as in the sealing and joining of metallic interconnects. The sinter‐crystallization method is a powerful technique that is used to obtain dense and reliable glass‐ceramics capable of providing hermetic joining and seals. The issues, learned from our experience, that have an impact on the lifetime behavior of glass and glass‐ceramic to metal seals are briefly reviewed in terms of challenges and working conditions. The mechanical characterization of glass‐to‐metal seal materials has a crucial impact on the overall performance, as the metal–glass interface plays a key role on the final joining strength and reliability. Several glass compositions are presented along with results on their characterization and behavior as joining materials for metallic interconnects, with a focus on their potential use as SOC seals.
Novel Glass-Ceramic Composition as Sealant for SOFCs Smeacetto, Federico; De Miranda, Auristela; Chrysanthou, Andreas ...
Journal of the American Ceramic Society,
December 2014, Volume:
97, Issue:
12
Journal Article
Peer reviewed
Open access
This work deals with the design, the characterization, and testing of a novel glass‐ceramic to be used as sealant for planar solid oxide fuel cells and its compatibility with Mn1.5Co1.5O4‐coated ...Crofer22APU. Thermal, sintering, and crystallization behavior and thermo mechanical properties of the sealant are reviewed and discussed, indicating therefore that these compositions can be deposited at 850°C and provide an excellent compatibility with both the Mn1.5Co1.5O4‐coated Crofer22APU and the anode‐supported electrolyte. In particular, Mn1.5Co1.5O4‐coated Crofer22APU/sealant/anode‐supported‐electrolyte joined samples have been submitted to thermal tests (in air atmosphere) from RT to 800°C (SOFC operating temperature) up to 500 h. No interactions, cracks formation, or failure were observed at the Mn1.5Co1.5O4‐coated Crofer22APU/sealant interface and between the glass‐ceramic and the anode‐supported‐electrolyte after 500 h of thermal tests in air atmosphere.
The crystallization behaviour of a glass-ceramic suitable as SOFCs sealant has been investigated using differential thermal analysis (DTA). Glass powders of two different particle sizes (< 38µm and ...38–75µm) have been considered. The exothermic peak in DTA thermographs has been associated with the crystallization of the diopside phase, as revealed by X-ray diffraction analysis (XRD). Avrami exponents (n) have been calculated for both particle sizes using the Ozawa equation, while Matusita and Sakka equation has been used to calculate the activation energy for the crystallization (Ec). The values found for n are 2.6 (< 38µm) and 2.1 (38–75µm). The obtained values for Ec are 403kJ/mol and 262kJ/mol for the finest and the coarsest glass powders, respectively. As a comparison, the activation energies for the viscous flow (Eη) have been also evaluated: 349kJ/mol for powders sized<38µm and 265kJ/mol for those sized 38–75µm.
•The crystallization behaviour of a glass-ceramic sealant has been investigated by DTA.•The activation energy for the crystallization and Avrami parameter have been calculated.•Glass powder size affected the crystallization mechanism and the activation energy for crystallization.
The performance of the generalized belief propagation algorithm to compute the noiseless capacity and mutual information rates of finite-size two-dimensional and three-dimensional run-length limited ...constraints is investigated. In both cases, the problem is reduced to estimating the partition function of graphical models with cycles. The partition function is then estimated using the region-based free energy approximation technique. For each constraint, a method is proposed to choose the basic regions and to construct the region graph which provides the graphical framework to run the generalized belief propagation algorithm. Simulation results for the noiseless capacity of different constraints as a function of the size of the channel are reported. In the cases that tight lower and upper bounds on the Shannon capacity exist, convergence to the Shannon capacity is discussed. For noisy constrained channels, simulation results are reported for mutual information rates as a function of signal-to-noise ratio.
Ceramic coatings for metallic interconnects play a key role in limiting corrosion and chromium evaporation in solid oxide cells. This study presents the upscaling of the electrophoretic deposition ...(EPD) technique to process Mn-Co spinels on real-dimension Crofer 22 APU interconnects and the test in a SOFC stack. Area specific resistance of long-term test conducted for 5000 h at 850 °C demonstrated that two-steps sintering has a significant influence on the coating performance; an area specific resistance degradation rate of 0.5 mΩ cm2 kh−1 is recorded. Stack test, operated in fuel cell mode at 850 °C for 3000 h under application of 227 mA/cm², including 5 thermal cycles, demonstrated the effectiveness of the electrophoretically deposited Mn-Co spinel in limiting the oxide scale growth on the Crofer 22 APU. An advanced post mortem investigation showed the effectiveness of the EPD ceramic coating, even when considering different and complex surfaces of the Crofer 22 APU.
We report a systematic microstructural and electrical characterization of iron doped Mn–Co spinel coatings processed by electrophoretic co-deposition of Mn1.5Co1.5O4 and Fe2O3 powders on Crofer 22 ...APU and AISI 441 steel substrates. Iron addition to Mn–Co spinel coating leads to a reduction of the area specific resistance on both substrates, after 3200 h at 750 °C. The Fe doped Mn–Co coating both leads to a thinner oxide scale and reduces the sub scale oxidation for the Crofer 22 APU substrate. Fe doped Mn–Co on AISI 441 shows both a thicker oxide scale and low area specific resistance values, likely due to a doping effect of the oxide scale by minor alloying elements. The different mechanisms by which iron doping of Mn–Co spinels can influence elemental interdiffusion at the steel-oxide scale-coating interfaces and relative contributions to the overall area specific resistance are evaluated by means of advanced electron microscopy. The promising results are further confirmed in a cell test, where the Fe doped MnCo coated interconnect does not induce any degradation of the oxygen electrode, proving its efficiency.
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•Electrophoretic co-deposition of MnCo spinel and Fe2O3.•Fe addition to MnCo spinel coating leads to a reduction of the ASR.•Fe doped Mn–Co coating leads to a thinner oxide scale for the Crofer 22APU.•Different interfacial phenomena for coated Crofer 22APU and AISI 441.
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