Advances in YSZ Coatings Prepared by Sol-Gel Route. Applications to Fuel Cells or Thermal Barrier Coatings

Abstract

The objective of this research is to develop a novel process for SOFC electrolytes and fully ceramic TBC to prepare yttria stabilized zirconia (YSZ) by both a sol-gel derived route and a dip-coating method. The research focuses on the development of a process compatible with industrial requirements in terms of cost and easiness to processing. The microstructure of dipcoated thick films is studied by varying the characteristics of an organic YSZ suspension (concentration, rheology) used as coating bath. The suspension was obtained by addition of a polymeric matrix in a stable suspension of YSZ powders dispersed in an azeotropic MEK-EtOH mixture. The obtained films are continuous, homogeneous and films thicknesses vary between 1 to 100 µm. Different microstructures are obtained depending on the synthesis parameters of the slurry composition. The microstructure of the films is found to depend on the YSZ precursor powders content and the polymeric sol /dispersant solution (EtOH-MEK) ratio. Finally, the dip-coated suspensions are used to prepare dense or porous layers according to the applications. The coating microstructure is engineered to decrease sintering ability, to be gas-tight for fuel cells electrolytes or to enhance thermal shock resistance for Thermal Barrier applications.

The sol–gel route: A versatile process for up-scaling the fabrication of gas-tight thin electrolyte layers

“…The composite alkoxide sol (b) promotes a brick-mortar [20] effect during the sintering step of the coating. Indeed, in situ crystallization of YSZ particles from the alkoxide sol improves the coating density [12]. Finally, the polymeric matrix (c) is used as a binder.…”

“…This process, in which chemicals are often expensive, is not suitable for upscaling the production of electrolyte layers. That is the reason why, mixed sol-gel/suspension procedures are considered for preparing, in a single step, thick coatings for either SOFCs [11][12][13] or, more recently, thermal barrier applications [14,15]. In this study, the mixed sol-gel/suspension strategy has been adapted in order to produce gas-tight electrolytes at laboratory scale but with a view towards up-scaling.…”