Flexural Strength and Viscosity of Glass Ceramic Sealants for Solid Oxide Fuel Cell Stacks

Malzbender, Jürgen; Zhao, Yilin

doi:10.1002/fuce.201100116

Cited by 33 publications

(6 citation statements)

References 16 publications

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“…The mean apparent shear strengths in Table 2 span a wide range (from 7.3 to 83 MPa). Malzbender and Zhao 28 tested glass‐ceramic butt joints between ferritic steel adherends in 4‐point flexure. Their arrangement applies opening mode tensile stress to the joint rather than the shear applied in the 4‐point loading of the present study.…”

Section: Resultsmentioning

confidence: 99%

Measurement of Mechanical Strength of Glass‐to‐Metal Joints

Selçuk

Atkinson

2015

Fuel Cells

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Three different test geometries were used to apply shear loading to fracture glass-to-metal joints typical of seals intended for use in planar solid oxide fuel cells: asymmetric compression; symmetric compression; and four-point asymmetric bending.The measured apparent shear strengths were found to differ by an order of magnitude depending on the test configuration employed. In particular, the apparent shear strength measured in the asymmetric compression test was very low. Conversely, the highest apparent shear strengths were measured using the symmetric compression test and the four-point asymmetric bend test gave an intermediate result. It is shown by finite element modelling that these differences are caused by differences in the normal stresses transverse to the joint. The locus of failure was always along the glass/metal interface in all test geometries.It is concluded that mechanical test procedures used to characterise glass-ceramic seals in SOFC stacks need to be selected and interpreted with great care. Keywords:Solid oxide fuel cell, seal, testing, glass, strength 2 IntroductionInterfaces between metals and brittle materials, such as ceramic or glass, are encountered in a wide variety of situations in which their mechanical properties are important. These include composites, coatings, and structural joints. Joints in the form of a layer between two metal surfaces are used as electrically insulating, gas-tight high temperature seals in solid oxide fuel cells [1]. The seal materials are often of glass, glass-ceramic or glass and ceramic [2,3,4,5,6,7,8,9,10]. Since these composite joints have a brittle adhesive layer, the mechanical properties of the joints are crucial for the reliability of the fuel cell stack and suitable test methods are required to assess their mechanical performance [11,12,13,14]. Such a test method should reflect, as closely as possible, the stress state expected in the actual application.The stresses experienced by these joints are the summation of residual stresses and applied operational stresses. The residual stresses arise mainly from differences in thermal expansion between the adhesive material and the adherends being joined when the operating (or testing) temperature is different from the effective temperature at which the seal was fabricated in a stress-free state. For a glass adhesive the effective fabrication temperature is approximately its glass transition temperature, since above this temperature the glass is sufficiently fluid to allow stresses to be relaxed. In planar fuel cell concepts the residual stresses are predominantly in-plane biaxial stresses and they are concentrated in the material having the smallest thickness, which is usually the adhesive layer. The residual stresses are in-plane biaxial in the bulk of the seal at distances greater than a few times the seal thickness from the seal edges. However, closer to the seal edges the free surfaces at the edges convert the residual stresses into shear stresses of similar magnitude to the bulk biaxial str...

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Section: Resultsmentioning

confidence: 99%

Measurement of Mechanical Strength of Glass‐to‐Metal Joints

Selçuk

Atkinson

2015

Fuel Cells

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“…The SOFC stacks can be fabricated using various geometries of individual cells, such as flat-plate, planar and (micro-)tubular (Mahato et al , 2015; Singhal, 2000; Stambouli and Traversa, 2002). Sealants are reported to be one the most failure-susceptible components (Han et al , 2020; Kuhn et al , 2009, 2010; Lin et al , 2007, 2018; Malzbender and Zhao, 2012; Smeacetto et al , 2011; Wang et al , 2017; Yan et al , 2017; Yokokawa et al , 2017; Zhang et al , 2018b, 2019), which show catastrophic effects even with relatively small microstructural changes of the material (Ahmed and Foger, 2017). The effects of sealant design is discussed in Ref.…”

Section: Solid Oxide Fuel Cellmentioning

confidence: 99%

Reliability analysis for a multi-stack solid oxide fuel cell system subject to operation condition-dependent degradation

Colombo

Schütz

Хартон

2020

JQME

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PurposeA reliability analysis of a solid oxide fuel cell (SOFC) system is presented for applications with strict constant power supply requirements, such as data centers. The purpose is to demonstrate the effect when moving from a module-level to a system-level in terms of reliability, also considering effects during start-up and degradation.Design/methodology/approachIn-house experimental data on a system-level are used to capture the behavior during start-up and normal operation, including drifts of the operation point due to degradation. The system is assumed to allow replacement of stacks during operation, but a minimum number of stacks in operation is needed to avoid complete shutdown. Experimental data are used in conjunction with a physics-based performance model to construct the failure probability function. A dynamic program then solves the optimization problem in terms of time and replacement requirements to minimize the total negative deviation from a given target reliability.FindingsResults show that multi-stack SOFC systems face challenges which are only revealed on a system- and not on a module-level. The main finding is that the reliability of multi-stack SOFC systems is not sufficient to serve as sole power source for critical applications such as data center.Practical implicationsThe principal methodology may be applicable to other modular systems which include multiple critical components (of the same kind). These systems comprise other electrochemical systems such as further fuel cell types.Originality/valueThe novelty of this work is the combination of mathematical modeling to solve a real-world problem, rather than assuming idealized input which lead to more benign system conditions. Furthermore, the necessity to use a mathematical model, which captures sufficient physics of the SOFC system as well as stochasticity elements of its environment, is of critical importance. Some simplifications are, however, necessary because the use of a detailed model directly in the dynamic program would have led to a combinatorial explosion of the numerical solution space.

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“…Some researchers polish the edges of the samples for strength testing, which reduces the variation from sample to sample, see e.g. 48 . Nevertheless, such measurements will not be representative for the strength variations in a typical stack, as making a sample that replicates the geometry and flaws of the SOC stack is very difficult.…”

Section: Introductionmentioning

confidence: 99%