Glass-Ceramic Seal for SOFC Stack Reducing Thermal Stress
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Solution Overview
Problem
Current solid oxide fuel cell (SOFC) sealing technologies face challenges in achieving high power densities due to seal-induced stresses, requiring materials that are both hermetic and thermally stable, while also being mechanically robust and electrically insulating, with glass-ceramic materials being promising but needing to balance viscosity and crystallization temperatures.
Innovation Solution
A glass-ceramic seal comprising a Sanbornite (BaO•2SiO2) and Hexacelsian (BaO•Al2O3•2SiO2) crystal phase with a residual glass phase, matched to the thermal expansion coefficient of the substrate, and a molar ratio of SiO2:BaO between 1:1 and 4:1, allowing for a thin, fully dense, and hermetic seal without boron, which reduces volatility and bubbling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If relatively thick seals (0.5 mm to 2 mm) are employed to fulfill hermeticity, full density, and mechanical strength requirements, then sealing reliability is improved, but seal-induced stresses on the stack increase
Solution Approach 1:
The patent changes the material parameters of the seal by using a specifically formulated glass-ceramic composition with controlled crystallization. The seal thickness is reduced from 0.5-2 mm to 20-100 μm through optimized material properties including crystal phase composition (sanbornite and hexacelsian phases) and glass transition temperature (Tg) between 600-800°C, which allows thin seals to achieve adequate mechanical strength and hermeticity
Solution Approach 2:
The patent employs a composite glass-ceramic material consisting of multiple crystal phases (sanbornite BaO•2SiO2 and hexacelsian BaO•Al2O3•2SiO2) embedded in a glass matrix. This composite structure provides both the hermeticity and mechanical strength needed for reliable sealing while enabling reduced thickness, thereby reducing seal-induced stresses on the stack
2Manufacturing precision
If the parent glass is made fluid enough to wet cell components and sinter efficiently, then sintering quality is improved, but material flow out increases
Solution Approach 1:
The patent optimizes the glass composition parameters to achieve a glass transition temperature (Tg) between 600-800°C and controls the crystallization behavior to occur slightly above the optimal sintering temperature. This parameter optimization allows the glass to be sufficiently fluid during sintering to wet components and eliminate porosity, while the controlled crystallization prevents excessive flow
Solution Approach 2:
The patent utilizes phase transition control by designing the glass-ceramic to crystallize slightly above the optimal sintering temperature. The phase transition from glassy state to crystalline state (forming sanbornite and hexacelsian phases) occurs after sintering is complete, ensuring the material maintains structural integrity and prevents flow-out while achieving full density during sintering
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables a thin, fully dense, and hermetic seal for SOFC stacks with a coefficient of thermal expansion matching the substrate, reducing seal-induced stresses and maintaining stability at high temperatures, and eliminating boron-related volatility issues.
Implementation Method 1
by controlling the crystallization of glasses (i.e., the nature, shape, and volume fraction of crystals)
Implementation Method 2
ready application to the surfaces to be sealed as glass-frit powder dispersed in a paste, or as a tape-cast sheet that subsequently is subjected to thermal treatments of sintering and crystallization
Implementation Method 3
the CTE of the material can be tuned to match the CTEs of the cell components
Data Source
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AI summary
A solid oxide ceramic includes a substrate defining a surface, the substrate including at least one material selected from the group consisting of yttria-stabilized zirconia (YSZ), lanthanum strontium titanate (LST), lanthanum strontium manganite (LSM), and nickel oxide -YSZ composite. The solid oxide ceramic further includes a seal coating at least a portion of the surface, the seal including a Sanbornite (BaO·2SiO2) crystal phase, a Hexacelsian (BaO·Al2O3·2SiO2) crystal phase, and a residual glass phase, wherein the seal has a coefficient of thermal expansion equal to or less than that of the substrate at said surface. The glass composition can have a difference between a glass crystallization temperature and a glass transition temperature in a range of between about 200 °C and about 400 °C at a heating rate of about 20 °C/min.