Cryogenic Hermetic Seal Assembly for Precompressed Martensitic Metal
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Solution Overview
Problem
Hermetic sealing of martensitic metals like lithium using brazing or welding to sapphire windows is problematic due to potential deformity and chemical reactions, making it difficult to achieve a commercially viable and integrity-preserving seal for cryogenic applications.
Innovation Solution
A hermetically sealed assembly using sapphire windows with a gasket or metallic sealing member, including a bellows element, to accommodate the expansion and contraction of martensitic metals, secured by fasteners or brazing, ensuring a hermetic seal and positive pressure contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If brazing or welding is used to hermetically seal sapphire windows, then hermetic sealing is achieved, but seal deformity and loss of integrity occur
Solution Approach 1:
A metallic seal acts as an intermediary component between the sapphire windows and the brazing/welding process. The metallic seal is brazed to the sapphire windows, while the martensitic metal is contained within the metallic seal structure, preventing direct exposure to high-temperature welding/brazing processes that would cause deformity and chemical reactions.
Solution Approach 2:
The sealing system is divided into separate functional components: sapphire windows for optical transparency, metallic seals for structural integrity and hermetic sealing, and bellows elements for pressure accommodation. This segmentation allows each component to be optimized for its specific function without compromising others.
2Power
If precompression is applied to martensitic metal, then negative pressure energy transfer is enabled, but rupture of the martensitic metal occurs
Solution Approach 1:
The bellows element is designed with specific geometric parameters (convolutions, thickness, material properties) that allow it to flex and accommodate pressure changes. This enables the system to apply precompression to the martensitic metal while the bellows expands/contracts to prevent rupture during cryogenic cycling.
Solution Approach 2:
The bellows element provides a cushioning mechanism that absorbs and distributes mechanical stress before it reaches the martensitic metal. This pre-cushioning effect prevents sudden pressure spikes from causing rupture while maintaining the necessary precompression for negative pressure energy transfer.
3Reliability
If KOVAR or molybdenum seals are brazed to sapphire windows, then hermetic sealing is achieved, but chemical reactions with martensitic metal occur
Solution Approach 1:
The metallic seal serves as a protective intermediary between the brazing materials (KOVAR, molybdenum) and the martensitic metal. The brazing process occurs between the metallic seal and sapphire window, while the martensitic metal remains isolated within the sealed chamber, preventing direct chemical interaction.
Solution Approach 2:
The harmful chemical interaction is extracted from the system by separating the brazing process from the martensitic metal. The brazing is performed only on the metallic seal and sapphire window interface, removing the martensitic metal from the zone where chemical reactions could occur.
4Manufacturing precision
If annealing is performed on assembled seals containing martensitic metal, then seal deformity is reduced, but chemical reaction with sapphire occurs
Solution Approach 1:
The metallic seal acts as a protective barrier during annealing, preventing direct contact between the martensitic metal and sapphire window. The annealing process can be performed on the entire assembly without causing harmful chemical reactions, as the metallic seal isolates the martensitic metal from the sapphire surface.
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 provides a hermetic seal that maintains positive pressure contact with martensitic metals, preventing rupture and leakage during cryogenic temperature changes, ensuring precise precompression without deformity or chemical reactions.
Implementation Method 1
a bellows element interposed between the first and second metallic seals. The bellows element can be a metallic ring having a substantially one or more U-shaped cross section(s)
Implementation Method 2
a plurality of fasteners, which can comprise positive pressure components, to secure the gasket and the first and second sapphire windows
Implementation Method 3
metals such as molybdenum, or alloys such as KOVAR, which are necessary to match the coefficient of thermal expansion of the sapphire windows can be brazed to each sapphire window
Data Source
AI summary
Disclosed is a hermetically sealed assembly for precompression of a martinsetic metal for use in negative pressure energy transfer systems, and method of making same. The assembly comprising a martinsteic metal disposed between and in contact with flanged sapphire windows, the flanges defining an open area therebetween to accommodate expansion and contraction of the martinsetic metal. Hermetic sealing means include a bellows element, which can comprise a convoluted cross section, at the periphery of the assembly to enable operation over temperature ranges from ambient to cryogenic without loss of integrity or leakage.