Thermal Spray Multilayer Ceramic Structures with Potential for Solid Oxide Cell Applications

The objective of this paper is to manufacture free-standing solid oxide cells (SOCs) through the atmospheric plasma spray process (APS), without the aid of a metallic support nor the need for a post-process heating treatment. A five-layered cell was fabricated. Fused and crushed yttria-stabilized zirconia (YSZ) powder in the 5–22 μm particle size range was used in order to achieve a dense electrolyte layer, yet still permitting satisfactory ionic diffusivity. Nickel oxide (NiO) powder that was obtained by in-house flame spray (FS) oxidation of pure nickel (Ni) powder was mixed and sprayed with the original Ni-YSZ feedstock, so as to increase the porosity content in the supporting electrode. Two transition layers were sprayed, the first between the support electrode and the electrolyte (25% (Ni/NiO)–75% YSZ) and the second at the electrolyte and the end electrode interface (50% YSZ–50% lanthanum strontium manganite (LSM)). The purpose of intercalation of these transition layers was to facilitate the ionic motion and also to eliminate thermal expansion mismatches. All the as-sprayed layers were separately tested by an in-house developed acetone permeability comparative test (APCT). Electrodes with adequate porosity (25–30%) were obtained. Concerning electrolytes, relatively thick (150–200 µm) layers derived from fused and crushed YSZ were found to be impermeable to acetone, while thinner YSZ counterparts of less than 100 µm showed a low degree of permeability, which was attributed mostly to existent microcracks and insufficient interparticle cohesion, rather than to interconnected porosity.