Paul E. Gannon

Evaluation of SOFC Interconnects Made of Ferritic Steels with Nano-Structured Oxi-Ceramic Protective Coatings Deposited by the LAFAD Process

When Solid Oxide Fuel Cells (SOFCs) are operated in the temperature range from 750 to 800°C, it becomes possible to use inexpensive ferritic steels as interconnects (ICs). Due to the demanding SOFC-IC operating environment, protective coatings are gaining attention as a way to increase long-term stability. In this study, the large area filtered arc deposition (LAFAD) process was used to deposit nano-structured coatings from the (Co,Mn)TiCrAlY(O,N) system. Both nano-laminated as well as nano-composite coating architectures were studied and compared. Coatings were deposited on ferritic steel with the aid of an ultra-thin, adhesion-promoting bond-coat, and were subsequently annealed in air for various time intervals. Surface oxidation was investigated using RBS, SEM, and EDS analyses. Cr-volatilization was evaluated using a modified transpiration apparatus and Area Specific Resistance (ASR) was studied as a function of time using a four-point technique. Significant improvement in oxidation resistance, Cr volatility, and ASR were observed in the coated samples. In addition, a set of sample IC plates were subjected to LAFAD coatings and tested in a SOFC stack. Transport mechanisms for various oxidizing species and coating diffusion barrier properties are discussed, as are the trades-offs between ionic diffusion and electronic conductivity.

The Surface Films and Their Possible Roles in Mg Corrosion

The poor corrosion performance of Mg alloys stems from the non-protectiveness of their surface films. It is important to understand how the corrosion resistance of surface films is affected by their composition and microstructure. This paper reports on the Mg surface film microstructure and its dependence on polarization potential, the differences of the film from the anodized coatings formed at high anodic potentials, the influence of passivating elements on the passivity and corrosivity of single phase Mg alloys, and the possibility of forming a sacrificial anode coating to protect Mg from corrosion attack.