Solid oxide fuel cells are a developing technology where advanced ceramics play a crucial role. Within the fuel cell the most common electrolyte material is yttria-stabilised zirconia (YSZ). The use of nano particles may provide lower sintering temperatures enabling the possibility of co-sintering the electrolyte with the anode layer. One route for deposition is screen-printing, which is scalable and cost-effective. In this research an aqueous screen-printing route was adopted, which adds the benefits of reduced health and safety risks with reduced costs. The aims of the work were to produce aqueous zirconia inks suitable for screen-printing and to understand the factors involved in ink formulation. The overall objective of the project was to produce a dense impermeable zirconia layer by screen-printing.
Sub-micron (~100 nm) and nano (20 nm) primary particles were used to prepare suspensions and inks. The suspensions were optimised for dispersion with the addition of a dispersant (Darvan C or TAC) by zeta potential and rheological methods. The addition of a binder (Rheolate 216) to the suspensions was used to create a 60 wt% screen-printing paste. The inks were characterised by rotational and/or oscillatory rheometry techniques and printed layers were characterised by optical microscopy where cracking was not observed.
The input parameters for ink formulation have been investigated. The binder concentration increased the structural properties of the ink and above 5 wt% produced level prints. The dispersant structure was shown to influence the rheological characteristics of the ink. This was linked to the interaction of binder and dispersant.
This thesis has shown that it was possible to formulate an aqueous sub-micron zirconia ink that levels after printing and does not crack during drying. Defects in the form of pinholes still remained. Excessively high drying rates were obtained from the aqueous ink making it difficult to process over long time periods and this was overcome through the use of co-solvents at a cost of print quality. Surfactants have been shown to improve the printed layer, but a fully optimised ink has not been found.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.