Shear Strength Tests of a Glass-Ceramic Sealant for Solid Oxide Fuel Cells Applications

Different approaches are used for the integration of ceramic components in solid oxide fuel cells stacks, where dissimilar materials (ceramics and metals) have to be joined and coupled for a reliable long term operation. This work focuses on the mechanical characterisation of a glass ceramic sealant used for the joining of Crofer22APU metallic interconnect samples as well as the interaction with a preoxidised Crofer22APU. Crofer22APU–glass ceramic sealant joined samples are tested by two different mechanical tests. Hourglass samples with different geometries were tested using an in-house developed torsion test machine at room temperature. In addition, their mechanical strength was also evaluated according to the ISO 13124 standard. The comparison of the two different testing methods, with particular focus on the shear strength of the joined samples, are reviewed and discussed

Design, production and characterization of glass-ceramic based sealants for solid oxide fuel cells applications

Planar solid oxide fuel cells (SOFCs) are capable of achieving higher power density than tubular SOFC, but hermetic seals are required to prevent mixing of the fuel and oxidant, It is still a challenge to develop sealing materials that retain desirable physical properties, are chemically compatible with other fuel cell components at high temperature (e.g. 800 °C) in a wide range of oxygen partial pressure, and remain operational over thousands of hours. In most planar SOFCs stacks designs, the interconnect is sealed to the cell components. The seal between the metal interconnect and the ceramic SOFCs components presents a challenge. Design, development and implementation of reliable sealants may contribute to the destiny of SOFC electrical power-generation technology. Glass–ceramics, which can be prepared by controlled sintering and crystallization of glasses, possess superior mechanical properties and higher viscosity at the SOFC operating temperature than glasses. The application of a protective coating on the alloy surface has been proven as a practical and effective method to reduce corrosion rates and/or inhibit Cr volatilization and thus cathode poisoning. Though some coatings can be highly effective in reducing corrosion rates and reducing area specific resistance of metallic interconnects, their properties for blocking chromium diffusion are limited and need more research on advanced materials and new processing methods. Furthermore, in the complex contest of the SOFC stack, the interconnect/sealant interface plays a key role in the stack reliability, efficiency and durability that depends also on the gas tightness provided by seals during SOFC operation for thousands of hours. It is desirable that reactions between the sealant and the coating or the metallic interconnect are limited during SOFC relevant operating conditions, otherwise spallation and detachments at the interfaces can occur and determine leakage and SOFC degradation. Finally, different approaches are used in this work for the integration (i. e. joining) of ceramic and metallic components in solid oxide fuel cells (SOFCs) stacks, where dissimilar materials have to be joined and sealed for a reliable long-term operation. In particular, the thermo-mechanical compatibility of sealants with other stack components critically influence the reliability and the robustness of SOFCs devices

Crystallization behaviour of glass-ceramic sealant for solid oxide fuel cells

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 (< 38 µm and 38–75 µm) 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 (< 38 µm) and 2.1 (38–75 µm). The obtained values for Ec are 403 kJ/mol and 262 kJ/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: 349 kJ/mol for powders sized<38 µm and 265 kJ/mol for those sized 38–75 µm

Can Clinical Pathways be Developed to Offer Assistance in Child Care Cases?

Clinical and care pathways are increasingly being used to help with decision-making in various areas of health and social care. The value of these pathways is that they provide a standard approach to offering care, help maintain quality of delivery, and control cost. This paper reports on the first step in developing a pathway which may assist in the very difficult process of deciding the level of contact to birth parents of children after their removal from their care. The use of such a pathway in this area is fraught with difficulty, but if successful may help practitioners achieve the arrangements that are in the best interests of the child