Active Brazing Ni Rings to Alpha-Alumina Collars
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Solution Overview
Problem
The existing metallization and thermal compression bonding (TCB) processes for bonding nickel (Ni) rings to alpha-alumina collars in sodium-based thermal batteries are difficult, time-consuming, expensive, and not scalable, while active brazing methods face challenges in achieving sufficient bond strength due to corrosion resistance and thermal expansion mismatches.
Innovation Solution
The use of active brazing with a braze alloy composition that includes nickel and an active metal element, such as titanium, to form a strong bond between Ni rings and alpha-alumina collars, reducing the number of processing steps and costs, and minimizing residual stresses from thermal expansion mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metallization and thermal compression bonding (TCB) processes are used to bond Ni rings to alpha-alumina collars, then bond strength is achieved, but the process becomes difficult, time-consuming, expensive, and not scalable
Solution Approach 1:
The invention changes the bonding parameters by using active brazing instead of metallization and TCB. This involves using a braze alloy composition with specific chemical composition (containing 40-70 wt% Ni, 5-20 wt% Cr, 5-20 wt% Mn, and 5-30 wt% glass) and bonding at lower temperatures (900-1100°C) for shorter times, transforming the process from a multi-step, high-temperature, long-duration process to a single-step, lower-temperature, short-duration process that is more scalable and efficient
Solution Approach 2:
The invention extracts and eliminates the metallization step from the bonding process. Instead of requiring a separate metallization layer (Mo-Mn paste application, drying, firing) followed by TCB, the active brazing alloy is applied directly to bond the Ni ring to the alumina collar, simplifying the process while maintaining bond strength
2Productivity
If active brazing is used to bond Ni rings to alpha-alumina collars, then manufacturing time and cost are reduced, but bond strength is insufficient due to corrosion resistance and thermal expansion mismatches
Solution Approach 1:
The invention uses a composite braze alloy material that combines multiple elements (Ni, Cr, Mn, glass) to achieve both strong bonding and corrosion resistance. The composite structure includes metallic phases (Ni-Cr-Mn intermetallics) for strength and a glass phase for wetting and corrosion protection, creating a multi-phase composite that addresses both thermal expansion mismatch and corrosion issues while providing sufficient bond strength
Solution Approach 2:
The invention applies local quality by creating a braze alloy with spatially differentiated functions: the Cr and Mn elements locally form protective oxide layers and intermetallic compounds at the metal-ceramic interface to prevent corrosion, while the glass phase locally provides wetting and fills gaps at the bonding interface, and the Ni matrix provides overall structural strength and thermal expansion compatibility
3Reliability
If 100% Mo paste is used for metallization of alumina in NaMx cells, then compatibility with cell chemistry is achieved, but the metallization process becomes more difficult and the process window is narrowed
Solution Approach 1:
The invention extracts and eliminates the Mo metallization layer entirely from the bonding process. Instead of applying Mo paste, drying, firing, and then performing TCB, the active brazing alloy is applied directly to bond the Ni ring to the alumina collar in a single step, removing the difficult metallization process while maintaining chemistry compatibility through the use of Cr and Mn in the braze alloy that are compatible with NaMx cell chemistry
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
Active brazing achieves bond strengths comparable to metallization and TCB processes, is cost-effective, and reduces manufacturing time, while providing reliable and high-performance metal-ceramic joints with minimal residual stresses.
Implementation Method 1
active brazing with a braze alloy composition that includes nickel and an active metal element, such as titanium, to form a strong bond between Ni rings and alpha-alumina collars
Implementation Method 2
The braze alloy composition includes nickel and an active metal element, such as titanium
Implementation Method 3
minimizing residual stresses from thermal expansion mismatches
Data Source
AI summary
The present application provides for metal rings and ceramic collars for active brazing in sodium-based thermal batteries. The metal rings may be outer and inner Ni rings configured for sealing to an alpha-alumina collar via active brazing for use in NaMx cells. The inner and outer Ni metal rings may be sealed to differing portions of the alpha-alumina collar. The portions of the outer and inner Ni rings active brazed to the alpha-alumina collar may define a tapered thickness that reduces internal stresses at the active brazed joints resulting from differing coefficients of thermal expansion between the Ni metal rings and the alpha-alumina collar. The portions of the outer and inner Ni rings and alpha-alumina collar sealed by active brazing, and thereby the active braze joints themselves, may be oriented to control or dictate the stresses on the joints during use.