Formulation and Process of Powder Coating for Solid Oxide Fuel Cell Interconnects
Solid oxide fuel cell (SOFC) interconnects, which are made of chromia-forming ferritic stainless steels, are used to connect individual SOFCs in series to increase the overall cell voltage output. They are usually exposed to high operating temperature (around 800oC) and both oxidative and reductive atmosphere. Mn1.5Co1.5O4 (MCO) spinel is used for SOFC interconnect coating to decrease the oxidation rate and the chromium migration, and to increase the SOFC lifetime. The current preferred coating method is air-plasma spray (APS) which has transfer efficiency of only around 40%, and is relatively expansive. The objective of this project is to develop powder coating technology as an alternative in SOFC interconnect coating, given its environmental friendliness, recyclability and cost-effectiveness. However, the key problems of powder coating techniques are how to make MCO powder well dispersed in polymer matrix (also known as coating binder, i.e. the resin and corresponding curing agent) and to form uniform film after binder burn off. Four techniques of mixing and dispersing MCO powder were investigated in this project. Slurry powder coating showed a big tendency to form a good film, a further optimization is needed. Both thermally compacted and cold pressed powder coatings showed poor quality and severe defects of non-uniformity. The formed film by extruded powder coating exhibited excellent adhesion, moderate hardness and high gloss. This technique is the best of four and is used for SOFC interconnect testing. For SOFC interconnects by extruded powder coating, thickness of the coating observed by cross-section analysis was fairly uniform, which is a key advantage of this technique. But a significant change in coating morphology was observed after thermal treatment, mainly due to the high dosage of binder used in the formulation. Extruded powder coating is promising but needs to be further optimized for SOFC application.
powder coating, slurry, SOFC interconnect, MCO, formulation, electrostatic spray, polyester/TGIC, epoxy
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