Glass Solder Composition for SOFC High-Temperature Joining
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Solution Overview
Problem
Current glass solder compositions for SOFCs fail to meet the high-temperature requirements and chemical stability needed for long-term operation, particularly when used with chromium materials, and often result in thermomechanical strains and unwanted crystal phases that can lead to cracking and deformations.
Innovation Solution
A glass solder composition with specific mol% ranges of SiO2, Al2O3, B2O3, BaO, CaO, and R2O3, excluding ZrO2, which forms a partially crystalline structure with a thermal coefficient of expansion suitable for high-temperature applications, ensuring mechanical stability and chemical compatibility, and avoiding undesirable crystal phases like cristobalite.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If glass solder composition uses conventional amorphous glass, then joining temperature can be reached with low viscosity, but thermal coefficient of expansion is too low (4·10−6 K−1) causing thermomechanical strains
Solution Approach 1:
The patent changes the chemical composition parameters of the glass solder by incorporating specific oxide ratios (SiO2: 48-62 mol%, B2O3: 4-12 mol%, BaO: 12-30 mol%, CaO: 2.5-15 mol%, Al2O3: 0.5-6 mol%) to transform the thermal expansion properties while maintaining low viscosity at joining temperatures
Solution Approach 2:
The patent creates a composite glass-ceramic material that combines amorphous glass phases with crystalline phases (barium disilicate BaSi2O5, barium calcium silicate BaxCaySi2O5, and lanthanum borosilicates) to achieve both low viscosity at high temperature and appropriate thermal expansion coefficient
2Reliability
If glass solder contains critical components like alkali oxides, heavy metal oxides, or critical rare earth oxides, then certain properties are improved, but long-term stability, reactivity, and electrical insulating capability are negatively affected
Solution Approach 1:
The patent extracts and eliminates harmful components (critical rare earth oxides, heavy metal oxides, and excessive alkali oxides) from the glass solder composition, retaining only non-critical oxides (BaO, CaO, B2O3, SiO2, Al2O3) that provide the necessary functional properties without compromising long-term stability
Solution Approach 2:
The patent changes the chemical composition parameters by setting specific ranges for each oxide component, optimizing the balance between joining reliability and long-term stability under operating conditions
3Stability of the object's composition
If glass solder forms unwanted crystal phases like cristobalite, then thermal coefficient of expansion increases, but cracking and deformations occur
Solution Approach 1:
The patent applies local quality by having different phases serve different functions: the amorphous glass phase provides low viscosity for bonding, while the crystalline phases (30-70 wt%) provide mechanical stability and appropriate thermal expansion
Solution Approach 2:
The patent changes the chemical composition parameters to control crystallization behavior, specifying SiO2 content (48-62 mol%) and Al2O3 content (0.5-6 mol%) to promote formation of desirable crystal phases while suppressing cristobalite formation
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 composition achieves a thermal coefficient of expansion within the required range, providing mechanical stability and chemical stability, enabling long-term use at temperatures up to 1000°C without significant thermomechanical strains, and forming desired crystal phases like BaSi2O5 and lanthanum silicates, ensuring reliable SOFC operation.
Implementation Method 1
The crystallization of solid phases in the glass melt already begins at the start of the joining process. The object of the crystalline phase is, on the one hand, to raise the thermal coefficient of expansion (TCE) of the completely amorphous glass
Implementation Method 2
When the joining temperature is reached, the glass phase must have a sufficiently low viscosity (−6 Pas) to ensure a good bonding to the metallic and ceramic joining partners. During the joining process, the gas phase portion must be sufficiently large (>40% by volume) to allow a sufficient flow of the glass
Data Source
AI summary
A composition is for the manufacture of glass solders for high-temperature applications up to temperatures of approximately 1000° C., which composition, having no ZrO2, has SiO2 at a proportion in the range from 48 mol-% to 62 mol %, Al2O3 at a proportion in the range from 0.5 mol % to 6 mol %, B2O3 at a proportion in the range 4 mol % to 12 mol %, BaO at a proportion in the range 12 mol % to 30 mol %, and either CaO at a proportion in the range from 2.5 mol % to 15 mol %, or an R2O3 at a proportion in the range 0.5 mol % to 20 mol % where the R2O3 is selected from La2O3, Y2O3, Sc2O3, and from a further oxide of a chemical element from the series of lanthanoids, wherein the SiO2:BaO ratio is in the range from 1.9 to 4.