Glass Joining Material Thermal Expansion and Flowability
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Solution Overview
Problem
Existing glass-based joining materials for high-temperature applications, such as fuel cells, face challenges in achieving reliable joints due to difficulties in processing and compatibility with chromium-containing alloys, leading to issues like expansion mismatches and reduced cycle stability.
Innovation Solution
A glass-based joining material with a linear coefficient of thermal expansion between 7×10^-6 and 11×10^-6 K^-1, composed of >30% SiO2, 0.5-15% B2O3, optional Al2O3, 5-30% BaO, 5-40% CaO, and up to 20% MgO, which ensures improved flowability and stability, preventing undesirable crystal phase formation and enhancing compatibility with chromium alloys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If glass-based joining materials with high BaO content are used to achieve high-temperature stability, then reliability at high temperatures is improved, but manufacturing difficulty increases and compatibility with chromium alloys deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters by limiting BaO to 5-30% (down from up to 40% in prior art) and introducing CaO (5-40%) and MgO (up to 20%) to replace excessive barium oxide. This parameter adjustment reduces manufacturing difficulty and improves compatibility with chromium-containing alloys while maintaining high-temperature stability through the synergistic effect of multiple alkaline earth metal oxides
Solution Approach 2:
The patent creates a composite glass composition combining SiO2 (>30%), B2O3 (0.5-15%), Al2O3 (optional), and multiple alkaline earth metal oxides (BaO, CaO, MgO). This composite material approach distributes the functional requirements across different components: SiO2 provides structural stability, B2O3 enhances flowability, and the combination of alkaline earth oxides delivers both high-temperature resistance and chromium alloy compatibility, eliminating the need for excessive single-component reliance
2Temperature
If glass-based joining materials with high melting temperature are used to ensure high-temperature operation stability, then operating temperature range is improved, but soldering temperature must be significantly higher than operating temperature
Solution Approach 1:
The patent adjusts the melting temperature parameter by optimizing the glass composition with controlled BaO (5-30%), CaO (5-40%), and B2O3 (0.5-15%) content. This composition tuning reduces the melting temperature compared to high-BaO glasses, allowing the soldering temperature to be closer to the operating temperature range (above 800°C), thereby reducing energy consumption during the joining process while maintaining high-temperature operational stability
3Stability of the object's composition
If glass-based joining materials with high viscosity at operating temperature are used to prevent material extrusion, then joint stability is improved, but flowability during soldering process deteriorates
Solution Approach 1:
The patent optimizes the viscosity parameter by controlling the content of B2O3 (0.5-15%) and alkaline earth metal oxides. B2O3 acts as a flux that enhances flowability during the soldering process by reducing viscosity at elevated temperatures. Simultaneously, the balanced composition of SiO2 (>30%) and alkaline earth oxides ensures that viscosity increases sufficiently at operating temperatures to prevent material extrusion, achieving both good flowability during joining and stability during operation
Solution Approach 2:
The patent exploits the temperature-dependent periodic behavior of glass viscosity. During the soldering process at high temperatures, the glass exhibits low viscosity for good flowability and wetting. As the joint cools to operating temperature, the viscosity periodically increases to provide structural stability and prevent extrusion. This temperature-induced periodic viscosity change allows the same material to satisfy both contradictory requirements at different stages
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 material provides improved flowability and stability, enabling reliable and durable joints at high temperatures, particularly above 800°C, with controlled crystallization and reduced thermal stress, suitable for applications in fuel cells and other high-temperature environments.
Implementation Method 1
glass powder, which is melted during the soldering process
Implementation Method 2
glass-based joining materials that are suitable for high-temperature applications must usually have a soldering temperature or hemispherical temperature that is significantly higher than the later operating temperature and/or they must crystallize sufficiently
Implementation Method 3
their composition is often chosen so that the thermal expansion coefficient roughly corresponds to that of the components to be joined
Data Source
AI summary
Amorphous and/or at least semi-crystalline glass-based joining material, particularly suitable for high-temperature applications, such as in fuel cells and/or sensors. In addition to SiO₂ and B₂O₃ as glass formers, the joining material also contains BaO and CaO and exhibits a linear coefficient of thermal expansion of at least 7.0 × 10⁻⁶ K⁻¹ in the temperature range of 20°C to 300°C, with a limited Al₂O₃ content. It can be used, in particular, for joining ferritic stainless steels and/or chromium-containing alloys and/or ceramics such as stabilized zirconium oxide and/or aluminum oxide.