Multi-Layer Seal for Ceramic Oxygen Generators
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Solution Overview
Problem
Conventional brazing techniques for ceramic-to-ceramic or ceramic-to-metal components, particularly in ceramic oxygen generators, face challenges in establishing reliable seals without causing detrimental interfacial reactions that lead to premature failure due to uncontrolled migration and chemical reactions of active metals with ceramic surfaces.
Innovation Solution
A multi-layer seal arrangement is introduced, comprising a braze alloy and a dissolution barrier, with specific layers of different compositions and thicknesses, along with controlled processing conditions, to manage chemical reactions and diffusion, ensuring a gas-tight, thermally, chemically, and mechanically compatible seal that resists degradation and promotes solid-state bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single active-metal brazing alloy is used to join ceramic components, then wetting and bonding between components is promoted, but detrimental interfacial reactions occur causing pitting and stress concentrations in the ceramic electrolyte
Solution Approach 1:
The single brazing alloy is segmented into multiple functional layers: a reactive active-metal layer (Ti, Zr, or Hf) for interfacial bonding, a base metal layer (Ag, Au, or Pd) for structural integrity, and an oxidation-resistant outer layer. This segmentation allows each layer to perform its specific function while preventing harmful reactions from propagating through the entire brazing joint.
Solution Approach 2:
The base metal layer (Ag, Au, or Pd) acts as an intermediary between the active-metal layer and the ceramic components. It mediates the bonding process by providing a diffusion barrier that prevents excessive interfacial reactions while maintaining good wetting and bonding properties. The intermediary layer controls the chemical interactions between the reactive active metal and the ceramic electrolyte.
2Reliability
If the braze alloy is sufficiently fluid at brazing temperature to provide good wetting, then bonding strength is improved, but uncontrolled flow causes electrical shorting to the electrodes
Solution Approach 1:
The brazing alloy exhibits different properties at different locations: the active-metal layer provides high reactivity and fluidity at the ceramic interface for excellent wetting and bonding, while the base metal layer provides lower fluidity and higher viscosity in the bulk to control flow and prevent electrical shorting. This local differentiation of material properties resolves the contradiction between wetting capability and flow control.
3Object-affected harmful factors
If a dissolution barrier is added to prevent interfacial reactions, then ceramic degradation is reduced, but the complexity of the seal arrangement increases
Solution Approach 1:
The dissolution barrier function is merged with the base metal layer of the brazing alloy. The Ag, Au, or Pd layer simultaneously serves as the structural base metal and as the diffusion barrier that prevents interfacial reactions. This merging eliminates the need for a separate dissolution barrier layer, reducing overall structural complexity while maintaining protection against ceramic degradation.
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 multi-layer seal arrangement achieves high bond strengths with minimal ceramic degradation, controlling braze alloy flow, and maintaining electrical contact, thereby extending the service life and reliability of ceramic oxygen generators and other electrochemical devices.
Implementation Method 1
a dissolution barrier which is sandwiched between layers of Ti on one side and Ti/Au/Ti on the other. The composition and quantity (thickness) of each layer is tailored to control the chemical reactions and diffusion of species at each of the layer interfaces
Implementation Method 2
Conventional techniques for joining ceramic-to-ceramic or ceramic-to-metal components involve such practices as active-metal brazing
Implementation Method 3
The base metal provides the bulk of the braze structure, which is usually ductile, while the active metal promotes interfacial wetting and bonding between the components during the brazing process
Implementation Method 4
One method of this invention establishes the seal between the ceramic component and the other selected component, which may be ceramic or metal for example, by brazing at a temperature in the range from 1050° C. to 1060° C.
Data Source
AI summary
A multi-layer seal arrangement includes a dissolution barrier between a braze alloy and a ceramic component. The inventive seal is useful for joining a ceramic component to another ceramic component or a metal component, for example. In one example, the braze comprises a gold alloy and the dissolution barrier comprises a layer of alumina on the order of 2-3 microns thick. A titanium wetting layer is provided between the alumina layer and the alloy. A metallization layer provided between the dissolution barrier and the ceramic component in one example comprises a layer of gold between two thin layers of titanium. In one particular example, a platinum mesh is included with the gold of the braze alloy to control braze flow during the brazing operation.