Formulation of Spinel based Inkjet Inks for Protective Layer Coatings in SOFC Interconnects

In this study, inkjet printing technology was adopted for the application of protective layer coatings on metallic Solid Oxide Fuel Cell (SOFC) interconnects. The study highlights the potential of the inkjet printing process to fabricate aqueous-based protective layer coatings over ferritic stainless steels, a novel, very flexible and low-cost approach to coating. The work presented focusses on the formulation of aqueous-based spinel particulate inks for the inkjet
printing process using an electro-magnetic inkjet printer. An ink formulation route based on a two-stage ball milling technique was developed to produce a printable ink composition with Manganese Cobalt Oxide (MnCo2O4, MCO) and Manganese Cobalt Ferrite (MnCo1.8Fe0.2O4, MCF) as the coating materials. The stability of the ink suspensions, and particle size distribution were studied and characterised using zeta and a particle size analysis, respectively.
The flow properties of the inks were analysed using a conventional rheometer at shear rates 1 to 1000 s-1 and Piezo Axial Vibrator rheometer at higher shear rates (10-6 s-1). Finally, the printability of the inks was assessed theoretically based on the Ohnesorge number, Z. The formulated MCO and MCF inks with ~ 25 wt.% solid loading exhibited Z values of 4.17 and 6.77, satisfying the printability criteria of the inkjet inks. The printability of the inks was
demonstrated by printing them on stainless-steel substrates. The printed layers were free of any visible defects after heat-treatment. The demonstrated ink formulation procedure provides a guide for inkjet inks development with respect to inkjet printer requirements. Furthermore, the outlined methodology can be employed to fabricate protective and other coatings for any kind
of metallic components such as bipolar plates and heat-exchangers.