Raman spectroscopic studies of Polymer Derived Ceramics in the form of protective coatings for SOFCs’ interconnects2021.04.16 16:16 - Katarzyna Kuźniar
Nowadays, with an exponentially increasing amount of people over the world along witha rising demand for the energy, an emphasis is put on the development of the low-emission energy production technologies such as Solid Oxide Fuel Cells (SOFCs). However, despite high electrical efficiency, easiness in manufacturing and low costs of their production, the problem of high-temperature corrosion of SOFCs’ interconnects casts a shadow on such a promising idea .
Among abundant solutions, the application of protective coatings on the ferritic steels seems to be the most interesting one . Thus, in this work, Polymer Derived Ceramics (PDCs) in the form of SiAlOC glasses’ coatings were proposed as a very innovative protection measure. Due to the duality of carbon form (Si-C covalent strong bonds and so called “free carbon phase”), the necessary balance between high thermomechanical stability and electrical conductivity is provided, respectively. Moreover, sol-gel method gives an opportunity to form PDCs in numerous shapes i.e. layers .
It is crucial to report that vibrational spectroscopy, including especially Raman spectroscopy is the powerful tool when investigating material’s structure, but at the same time very underestimated while determining high-temperature corrosion phenomena and mechanisms of diffusive processes, particularly for the ferritic steels.
The main aim of this study was to present the possibilities of Raman spectroscopy as a method of the evaluation of corrosion rate of Crofer 22APU ferritic steel used for SOFCs’ interconnects in two systems: uncoated and coated with layers based on SiAlOC glasses.
The corrosion resistance of the protective layers was investigated using thermogravimetric analysis within isothermal (500 h) and cyclic (500 1h-cycles) conditions at 800°C in the laboratory air. The application of Raman spectroscopy allowed for the determination of:
a) bulk material’s (gel and glasses) structure used as reference for coatings – point measurements,
b) structure of coating along with coating/steel interface (MnCr2O4 spinel) – linear depth profiles,
c) distribution of oxidation products on the surface and across the multi-layered scale - imaging.
The Raman studies supported with additional structural (XRD, FTIR) and microstructural (SEM+EPMA) investigation, revealed the outbreak improvement in the oxidation resistance of the steel due to the application of SiAlOC glasses coatings.