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Since reliable long term operation of SOFC and SOEC devices depends critically on the mechanical behavior of the sealant material, the current work focuses on the characterization of the shear strength by a torsion test of two different glass-ceramic sealants that are used to join Crofer22APU substrates in an application relevant configuration. The two glass-ceramic sealants differ in terms of characteristic temperatures and crystalline phases with possible impications on the joining behavior. Statistically identical shear stress values were measured at room temperature for joined hourglasses of different size with both sealants, thus confirming a size independence of the measured strength values. Experimental post-test examination results confirm that the interfaces play a strong role regarding the measured shear strength and provide important insights with respect to integration of metallic and glass-ceramic components in SOFC/SOEC stacks. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on the microstructure and properties of two glass–ceramics based on SiO2–Al2O3–MgO (SAMg) and SiO2–Al2O3–Y2O3 (SAY), which have been designed to be used as pressure-less low activation joining materials for SiC/SiC and SiC based components for nuclear applications. Glass–ceramic pellets (SAY and SAMg) were irradiated for approximately 1year in the reactor core of the LVR-15 research reactor at Nuclear Research Institute Rez, Czech Republic, at about 50°C, 6.92×1024 n/m2 (E >1MeV, about 1dpa in steel); SiC/SiC composites joined by SAY were irradiated about 1year at High Flux Reactor (HFR), Petten, The Netherlands, 550°C, 9–11×1024 n/m2 (E >1MeV, about 1.4–1.8dpa in C), 600°C, 16–22×1024 n/m2 (E >1MeV, about 2.6–3.3dpa in C) and 820°C 31–32×1024 n/m2(E >1MeV, about 5dpa in C). Optical microscopy with image analysis and scanning electron microscopy (SEM) with X-ray microanalysis (EDS) were used to investigate the glass–ceramics morphology and composition, showing a remarkable similarity before and after neutron irradiation for both glass–ceramics. Comparison of bending strength for irradiated and non-irradiated SAY joined SiC/SiC indicate that the mechanical strength is unaffected by irradiation at these conditions. [Copyright &y& Elsevier]

Abstract: This paper reports on the preliminary results of a project involving Politecnico di Torino (Italy), ORNL (USA) and Kyoto University (Japan) on low activation joining materials, techniques and mechanical testing for SiC-based materials. Results on glass ceramic joined SiC will be presented. A new torsion test based on miniaturized hour-glass shaped specimens is proposed here to be used as pure shear strength test method for joined samples to be submitted to neutron irradiation. Preliminary results on hour-glass shaped joined specimens have been obtained by this method. [Copyright &y& Elsevier]

Abstract: A simple and low cost method based on slurry coating was used to produce silicon carbide, titanium carbide and glass-ceramic coatings on low density carbon/carbon composites in order to improve their erosion resistance. Microstructural analyses were performed for substrate and coatings by optical microscopy, and scanning and transmission electron microscopy. As-received and coated composites were submitted to erosion tests using a sandblasting machine according to ASTM G76-95. The best results were obtained with a silica–alumina–yttria based glass-ceramic coating. [Copyright &y& Elsevier]

This study focuses on the design, characterization and testing of a new glass-ceramic sealant for Na-based batteries. The thermo-mechanical properties as well as the sintering behaviour of the new sealant have been characterized by thermal analyses and x-rays diffraction studies. The exothermic peak in the differential thermal analysis plots has been assigned to the crystallization of a calcium sodium aluminum silicate (anorthite sodian), as confirmed by the X-ray diffraction data. The activation energy for the crystallization was found to be 482.3 kJ/mol. The compatibility at the interface between the glass-ceramic sealant and beta- and alpha-alumina is examined before and after corrosion test with molten Na. Tests of this novel silica-based glass-ceramic sealant with Na at 300 °C for 250 h in a real battery operating conditions showed no reactions with Na or evidence of corrosion, as demonstrated by SEM post mortem examinations after cell disassembly. [ABSTRACT FROM AUTHOR]

CaO–Al 2 O 3 (CA) and SiO 2 –Al 2 O 3 –Y 2 O 3 (SAY) glass-ceramics are promising candidates for SiC/SiC indirect joints. In view of their use in locations where high radiation level is expected (i.e. fusion plants) it is important to investigate how radiation-induced damage can modify the material microstructure. To this aim, pellets of both types were irradiated with 5.5 MeV 4 He + ions at an average temperature of 75 °C up to a fluence of almost 2.3·10 18 cm −2 . This produces a displacement defect density that increases with depth and reaches a value of about 40 displacements per atom in the ion implantation region, where the He-gas reaches a concentration of several thousands of atomic parts per million. X-ray diffractometry and scanning electron microscopy showed no change in the microstructure and in the morphology of the pellet surface. Moreover, a transmission electron microscopy investigation on cross-section lamellas revealed the occurrence of structural defects and agglomerates of He-bubbles in the implantation region for the CA sample and a more homogeneous He-bubble distribution in the SAY pellet, even outside the implantation layer. In addition, no amorphization was found in both samples, even in correspondence to the He implantation zone. The radiation damage induced only occasional micro-cracks, mainly located at grain boundaries (CA) or within the grains (SAY). [ABSTRACT FROM AUTHOR]

Abstract: The development of sealants for solid oxide fuel cells (SOFCs) is a significant challenge as they must meet very restrictive requirements; they must withstand the severe environment of the SOFC (i.e., be resistant to oxidative and reducing gas environments) and be thermo-chemically and thermo-mechanically compatible with the materials to which they are in contact with. This work discusses the design and the operation of two SOFC short stacks (based on planar anode-supported cells) along with the performance of a glass ceramic sealant inside the stack. In particular, a joined Crofer22APU frame/glass-ceramic sealant/anode-supported-cell (ASC) was tested in two SOFC short stack configurations (referred to as “m1stack” and “m2stack” tests, respectively), in order to study the stability and the effectiveness of the glass-ceramic (boron and barium-free silica-based) sealant used in the experiment. The difference between the two stacks was the presence of a Mn1.5Co1.5O4 protective coating on the Crofer22APU frame prevent Cr poisoning of the cathode used in the m2stack. A full cell open circuit voltage was achieved during the experiments, indicating therefore that the glass ceramic sealant employed provided effective gas separation. The time-evolution of the cell voltage was investigated to evaluate eventual degradation caused by chromium poisoning at the cathode. The m2stack was operated at ∼0.3 A cm−2 and an FU (Fuel Utilisation) of 25% and no voltage degradation was observed for the duration of the galvanostatic experiment (350 h). Microstructural post-mortem analysis after the experiments (m1stack and m2stack) in the short stack configuration highlighted the excellent compatibility of the glass-ceramic sealant with Crofer22APU and YSZ, respectively, as well as the effectiveness of Mn1.5Co1.5O4 coating on Crofer22APU to prevent Cr poisoning of the cathode. [Copyright &y& Elsevier]

Abstract: Thermal cycling and thermal ageing tests were performed on Crofer22APU/glass-ceramic/Anode-Supported-Electrolyte (ASE) joined samples in air at the SOFC operating temperature of 800 °C. The Crofer22APU had been polished and preoxidised at 900 °C for 2 h. The diffusion behaviour at the two interfaces was examined and revealed slight diffusion of chromium and manganese from Crofer22APU into the glass-ceramic. No interactions, failure or crack formation were observed at the Crofer22APU/glass-ceramic interface and between the glass-ceramic and YSZ. [Copyright &y& Elsevier]

Abstract: This paper aims to investigate the performance and testing of joined Crofer22APU/glass-ceramic sealant/anode-supported solid oxide fuel cell (SOFC) in dual atmosphere in order to study the stability and effectiveness of the sealant. The sealant was able to prevent corrosion effects of the Crofer22APU after thermal treatments in SOFC relevant conditions at 800°C for 460h; an effective gas stream separation between the anode and cathode side was also obtained, as indicated by a very high measured open circuit potential, close to the theoretical one. Chromium poisoning was found to degrade the fuel cell performance, whereas the sealant was chemically and physically stable, as shown by post-mortem analysis. [Copyright &y& Elsevier]

Abstract: This work describes the design of three new glass and glass ceramic compositions to join the ceramic electrolyte (YSZ wafer) to the metallic interconnect (Crofer22APU) in planar SOFC stacks. The designed sealants are low-sodium, barium free and boron-oxide free silica-based glasses. The sealing process was optimized for the most promising composition and joined Crofer22APU/glass–ceramic sealant/YSZ samples were morphologically characterized and tested for 300h in humidified hydrogen atmosphere at the fuel cell operating temperature of 800°C. The study showed that the use of the glass–ceramic was successful in joining the YSZ ceramic electrolyte to the Crofer22APU metallic interconnect and in preventing severe corrosion effects at the Crofer22APU/glass–ceramic interface after static treatments in humidified hydrogen at 800°C for 300h. [Copyright &y& Elsevier]

Abstract: This work describes the performance and testing of a glass-ceramic sealant used to join the ceramic electrolyte (anode-supported-electrolyte (ASE)) to the metallic interconnect (Crofer22APU) in planar SOFC stacks. The designed glass-ceramic sealant is a barium and boron free silica-based glass, which crystallizes by means of the heat-treatment after being deposited on substrates by the slurry technique. Joined ASE/glass-ceramic seal/Crofer22APU samples were tested for 500h in H2–3H2O atmosphere at the fuel cell operating temperature of 800°C. Moreover, the joined ASE/glass-ceramic seal/Crofer22APU samples were submitted to three thermal cycles each of 120h duration, in order to evaluate the thermomechanical stability of the sealant. The microstructures and elemental distribution at Crofer22APU/glass-ceramic and ASE/glass-ceramic interfaces were investigated. SEM micrograph observations of joined samples that underwent cyclic thermal tests and exposure for 500h in H2–3H2O atmosphere showed that the adhesion between the glass-ceramic and Crofer22APU at either interface was very good and no microstructural changes were detected at the interfacial boundaries. The study showed that the use of the glass-ceramic was successful in preventing strong adverse corrosion effects at the Crofer22APU/glass-ceramic sealant interface. [Copyright &y& Elsevier]