Ferritic Steel for SOFC Interconnectors with Cu-W Spinel Oxide
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Solution Overview
Problem
Solid oxide fuel cells face challenges with the oxidation resistance of metallic materials, particularly the evaporation of Cr from the Cr oxide layer, which degrades the performance of ceramic parts and interfaces, and existing metallic materials do not adequately meet the demands for improved durability and electrical conductivity.
Innovation Solution
A steel composition with controlled amounts of C, Si, Al, Mn, Cr, Ni, La, Zr, W, and Cu is developed, minimizing impurity elements and optimizing alloying elements to reduce Cr evaporation and enhance oxidation resistance, while maintaining good electrical conductivity and thermal expansion compatibility with ceramic parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metallic materials are used for fuel cell parts to reduce cost and improve workability, then manufacturing cost and ease of manufacture are improved, but oxidation resistance is insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters of the steel, including limiting C to 0.03% max, Si to 0.05% max, Al to 0.05% max, Mn to 0.10-0.35%, Cr to 18.0-26.0%, and adding specific amounts of W (0.10-3.0%), Cu (0.20-4.0%), and REM (0.01-0.50%). This compositional parameter optimization enables metallic materials to achieve both good workability and excellent oxidation resistance at 700-900°C
Solution Approach 2:
The patent creates a composite oxide layer structure on the steel surface consisting of an inner Cr2O3 layer and an outer spinel-type oxide layer containing Mn, Cr, and Cu. This composite oxide structure provides superior oxidation resistance while maintaining the underlying metallic material's workability and electrical conductivity properties
2Reliability
If Cr is added to improve oxidation resistance, then oxidation resistance is improved, but Cr evaporates from the oxide layer and degrades ceramic part performance
Solution Approach 1:
The patent introduces W (tungsten) and Cu (copper) as intermediary elements that form a spinel-type oxide layer (Mn-Cr-Cu spinel) on the outer surface. This spinel layer acts as a protective barrier that reduces Cr evaporation while maintaining oxidation resistance. The spinel structure incorporates Cr in a stable crystalline form, preventing its volatilization and subsequent degradation of ceramic components
Solution Approach 2:
The patent optimizes the Cr content parameter to 18.0-26.0% and combines it with specific amounts of W (0.10-3.0%) and Cu (0.20-4.0%). This parameter combination creates a stable oxide layer composition that minimizes Cr evaporation. The presence of W and Cu in the oxide layer alters the thermodynamic stability of Cr oxide, reducing its vapor pressure and evaporation rate
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 steel exhibits significantly improved oxidation resistance, reduced Cr evaporation, and sustained electrical conductivity, leading to enhanced durability and performance in solid oxide fuel cell components like separators and interconnectors.
Implementation Method 1
a problem has been revealed that Cr evaporates from a Cr oxide layer on the metallic material
Implementation Method 2
W is effective for suppressing outward diffusion of Cr
Implementation Method 3
reducing amount of Mn, which forms a spinel-type oxide layer together with Cr at the top surface of the ferritic stainless steels
Data Source
Figure 1~2
Figure 3
AI summary
Disclosed is steel for a solid oxide fuel cell, which has excellent oxidation resistance, reduces Cr evaporation, has good electrical conductivity and has a thermal expansion coefficient similar to that of a ceramic component such as an electrolyte or an electrode. Specifically disclosed is steel for solid oxide fuel cells, which has excellent oxidation resistance and contains, in mass%, 0.1% or less of C, 0.2% or less ofAl, 0.2% or less of Si, 0.4% or less of Mn, 16.0-28.0% of Cr, 1.5% or less ofNi, 1.0% or less of REM and/or Zr in total, 1.0-3.0% of W, and more than 0.2% but 4.0% or less of Cu, with the balance made up of Fe and unavoidable impurities.