SOFC Interconnect Protective Layer Sintering for Chromium Diffusion Control

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Solution Overview

Problem

The existing manufacturing methods for solid oxide fuel cell stacks face challenges in forming protective layers on interconnects that are effective in reducing chromium diffusion and ensuring dimensional stability at high temperatures, particularly in inert atmospheres.

Innovation Solution

A method involving coating interconnects with metal oxide powder, sintering them in an inert atmosphere to partially reduce the protective layer, and subsequently oxidizing them to densify and oxidize the layer, using a combination of easily reducible metals like copper, nickel, and cobalt oxides with harder-to-reduce metals like manganese and iron oxides.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional sintering methods are used in air atmosphere, then the protective layer forms, but chromium diffusion occurs and dimensional stability is compromised

Engineering Contradiction:

Improveprotective layer effectivenessVSAvoidchromium diffusion

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent applies inert atmosphere sintering by conducting the sintering process in a nitrogen or argon atmosphere instead of air. This prevents chromium diffusion and unwanted oxidation during sintering, while the protective layer is subsequently formed through controlled oxidation in air or oxygen atmosphere after sintering is complete. The inert atmosphere eliminates harmful chromium vaporization and diffusion that occur in conventional air sintering.

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

2Object-generated harmful factors

If the protective layer is fully reduced in inert atmosphere, then chromium diffusion is prevented, but the layer becomes too porous and loses protective function

Engineering Contradiction:

Improvechromium diffusion reductionVSAvoidprotective layer integrity

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The patent employs a two-stage atmospheric process: first, sintering in inert atmosphere to partially reduce the metal oxide powder and prevent chromium diffusion; second, controlled oxidation in air or oxygen atmosphere to densify and form the protective chromium oxide layer. This periodic alternation between reducing and oxidizing atmospheres ensures both chromium diffusion prevention and protective layer integrity.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent changes the atmospheric parameters (oxygen partial pressure) in sequence: starting with low oxygen partial pressure in inert atmosphere during sintering to prevent chromium diffusion, then transitioning to high oxygen partial pressure in air or oxygen atmosphere after sintering to form and densify the protective oxide layer. This parameter change approach resolves the contradiction between reduction and oxidation requirements.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If metal oxide powder is coated on interconnects, then protective layer formation is enabled, but processing complexity increases

Engineering Contradiction:

Improveprotective layer formationVSAvoidmanufacturing process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines multiple functions into the sintering process itself: the inert atmosphere sintering simultaneously densifies the interconnect substrate, partially reduces the metal oxide powder coating, and prevents chromium diffusion. The subsequent oxidation step then forms the protective layer. This merging of densification, reduction, and protection functions into a coordinated two-step process reduces overall manufacturing complexity compared to separate sequential operations.

Inventive Principle:

Principle #5Merging (Combining)

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

This approach results in a densified protective layer that effectively reduces chromium diffusion and enhances the structural integrity of the interconnects, maintaining dimensional stability and reducing processing costs compared to conventional methods.

Implementation Method 1

sintering the coated interconnect in an inert atmosphere to at least partially reduce the protective layer

Methodology Applied

Scientific EffectSintering: Sintering

Implementation Method 2

oxidizing the sintered interconnect in an oxidizing atmosphere to oxidize and densify the protective layer

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 3

oxidize and densify the protective layer

Methodology Applied

Scientific EffectDensification:

Implementation Method 4

a densified protective layer that effectively reduces chromium diffusion

Methodology Applied

Scientific EffectDiffusion barrier: Diffusion Barrier

Data Source

PatentUS20240347739A1Inert atmosphere sintering of electrochemical cell stack interconnects

Publication Date: 2024.10.17 BLOOM ENERGY CORP

AI summary

A method of forming a protective layer on an interconnect for an electrochemical cell stack includes coating at least one side of the interconnect with a metal oxide powder to form a protective layer, sintering the coated interconnect in an inert atmosphere to at least partially reduce the protective layer, and oxidizing the sintered interconnect in an oxidizing atmosphere to oxidize and densify the protective layer.