Oxidation behavior and area specific resistance of La, Cu and B alloyed Fe-22Cr ferritic steels for solid oxide fuel cell interconnects

On the High-Temperature Oxidation and Area Specific Resistance of New Commercial Ferritic Stainless Steels

“…In addition, EDS elemental maps show that Cu as well segregates, as small nodules, at the TGO/FSS interface (Steel A, Figure 10d) and within the alloy at the grain boundaries where Laves phases are also present (Steel B, Figure 11c,e). According to [13,34] the largest concentration of this element at the TGO/FSS interface (Steel A, Figure 10d), enhance the oxidation resistance since the segregated Cu acts as a diffusion barrier for both the anions and cations.…”

“…For more than a decade, ICs have been mainly made of ferritic stainless steels (FSSs). In fact, after the successful reduction of SOFC operation temperature in the range 650 • C to 850 • C, this class of materials was selected among others (e.g., chromium-based alloys and Ni-Cr based alloys) to replace LaCrO 3 -based interconnects since it exhibits adequate application characteristics: a thermal expansion coefficient (TEC) similar to the other ceramic parts of the fuel cell (11.5-14.0 × 10 −6 /K from RT to 800 • C), good thermal and electrical conductivity, good manufacturability and mechanical properties, easy fabricability, affordable cost and, in the case of chromia-former steels containing over 16 wt.% Cr, the formation of a comparatively conductive and protective Cr 2 O 3 scale in presence of an oxidizing atmosphere [13][14][15].…”

“…Under IT-SOFC operating conditions and for a planned service of thousands of hours ( 40,000), FSSs interconnects show, however, some limitations: an inadequate oxidation resistance which determines a drop in metallic interconnect (MIC) stability and electrical conductivity; the formation and migration of volatile Cr(VI) species (e.g., CrO 3 and Cr(OH) 2 O 2 ) from ICs into the cathode where they form, after reduction at the three-phase boundary (TPB), Cr 2 O 3 [13,[16][17][18][19]. Cr poisoning, whose mechanism and kinetics have been extensively studied [20][21][22][23], represents one of the main disadvantages to the use of chromia-forming MIC since this phenomenon causes a drastic reduction of cell performances.…”

Initial stage oxidation corrosion of commercial ferritic stainless steels with different Cr contents at 650 °C for solid oxide fuel cells

“…After 40,000 h oxidation at 850 °C, Cu appeared in the surface spinel layer and formed (Mn, Cr, Cu) 3 O 4 phase, which impeded Cr volatilization effectively [ 26 ]. Swaminathan et al [ 27 ] found that the best oxidation resistance was achieved by doping 1.57 wt.% Cu into an FSS with 22 wt.% Cr. Due to the weaker oxygen affinity of Cu than Cr, after 2000 h oxidation at 800 °C, the metallic Cu in FSS was precipitated below Cr 2 O 3 .…”

Characterization of Metallic Interconnects Extracted from Solid Oxide Fuel Cell Stacks Operated up to 20,000 h in Real Life Conditions: The Air Side

“…The physical and chemical properties of the MIC are modulated in order to obtain good and reliable performances of the entire SOFC at high temperatures [8]. These components are typically made of ferritic stainless steels (FSSs) that have a suitable oxidation resistance, a coefficient of thermal expansion (CTE) matching with the one of the other components of the fuel cells (11.5-14.0 × 10 −6 K −1 from room temperature to 800 • C), good thermal and electrical conductivity, good manufacturability, suitable mechanical properties, easy fabricability, and affordable costs [6,7,[9][10][11]. In particular, CROFER22APU, CROFER22H and AISI441 are grades commonly used as MICs for these applications [12][13][14][15][16][17].…”