In-Situ Observation of Co-Ce Coated Metallic Interconnect Oxidation Combined with High-Resolution Post Exposure Analysis

Abstract

Oxidation of Sanergy SSHT steel with Ce-Co coating, used as interconnect material, was observed in-situ in a modified environmental scanning electron microscope (ESEM) at nominal temperature between 800°C and 900°C under 33Pa of oxygen, for different durations (up to 60h). After these in-situ observations, lamellas of the observed target areas were prepared using a focused ion beam (FIB). This allowed the evaluation in the cross section of the final composition of the oxidation layers of the steel by scanning transmission electron microscopy (STEM) and energy dispersive x-ray analysis (EDX), of the same zone observed directly on the surface by ESEM. Results show the diffusion of manganese and iron towards the cobalt coating. Underneath, chromia scale forms. Under the applied conditions, the very thin cerium layer does not prevent the diffusion of other elements from the steel. Niobium (with silicium) and titanium form oxidized precipitates in the steel just below the chromia scale.

Experimental Investigation of the Initial Stage of the Oxidation Mechanism of Co Coating for Solid Oxide Fuel Cell Interconnects at 650 °C

“…After 3000 h of oxidation, the Cr 2 O 3 layer thickened and the inner Cr 2 MnO 4 spinel layer was dissolved, while the surface layer of (Co, Fe, Mn) 3 O 4 remained stable. Poitel et al [33] confirmed the diffusion behavior of Fe and Mn from the metal substrate to the Co coating at high temperature via an in situ observation with a modified environmental scanning electron microscope (ESEM). Karlsson et al [34,35] characterized the microstructure variations of 800 nm-thick Ce-Co/Mn coatings with time using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS).…”

Method to Measure Area Specific Resistance and Chromium Migration Simultaneously from Solid Oxide Fuel Cell Interconnect Materials

“… and Poitel et al. show that the oxidation of the metallic Co layer is a fast process compared to the measurement times. Froitzheim have demonstrated that oxidation of a similar 640 nm metallic Co layer in 850 °C takes place in less than 30 s.…”

“…The Co coating reacts with manganese diffusing from the bulk steel and forms a (Mn,Co) 3 O 4 spinel, whereas the cerium layer further aids to hinder chromia formation [31]. Studies by Froitzheim et al [32] and Poitel et al [33] show that the oxidation of the metallic Co layer is a fast process compared to the measurement times. Froitzheim have demonstrated that oxidation of a similar 640 nm metallic Co layer in 850°C takes place in less than 30 s.…”

Revealing the Kinetics of Non-Metallic Inclusion Reactions in Steel Using In-Situ High Temperature Environmental Scanning Electron Microscopy

“…In recent years, the use of HT-ESEM has become increasingly popular due to its ability to provide in-situ imaging and analysis in controlled atmospheres and elevated temperatures [9]. While HT-ESEM has been used to investigate topics such as the morphology and structural transformation of Al-Si coated boron steel [10] and the oxidation of Co-Ce coated interconnect steel [11], and recently, observing the bainite formation in a medium carbon steel [12], it has yet to be extensively utilized in NMI research within the steel industry. During hot rolling of steel, the phase composition of NMIs determines their tendency for elongation and fragmentation [13].…”