Suspension plasma sprayed YSZ coatings were deposited at lab-scale and production-scale facilities to investigate the effect of process equipment on coating properties. The target application for these coatings is SOFC electrolytes, so dense microstructures with low permeabilities were desired. Both facilities had the same torch but different suspension feeding systems, torch robots and substrate holders. These differences meant that the lab facility had higher torch-substrate relative speeds compared to the production facility. When using porous stainless steel substrates with relatively smooth surfaces, permeabilities and microstructures were comparable for coatings from both facilities, and no segmentation cracks were observed. Coating permeability could be further reduced by increasing substrate temperatures during deposition or reducing suspension feed rates. On rougher substrates representative of SOFC cathodes, production facility coatings had higher permeabilities and more segmentation cracks compared to lab coatings. The increased cracking may be due to larger heat impulses with each torch pass at the production facility caused by its lower torch-substrate relative speed. This work highlights some of the challenges associated with scaling up the spray process from the lab to production.

The performance of solid oxide fuel cell cathodes can be improved by increasing the number of electrochemical reaction sites. This is often done by controlling microstructures and using composite materials that consist of an ionic conductor and a mixed ionic and electronic conductor. LSCF (La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 -δ) and SSC (Sm 0.5 Sr 0.5 CoO 3 ) cathodes were manufactured by axial-injection atmospheric plasma spraying (APS), and composite cathodes were fabricated by mixing SDC (Ce 0.8 Sm 0.2 O 1.9 ) into the feedstock powders. The plasma power was varied by changing the proportion of nitrogen in the plasma gas. The microstructures of cathodes produced with different plasma powers were characterized by scanning electron microscopy and gas permeation measurements. The deposition efficiencies of these cathodes were calculated based on the mass of the sprayed cathode. Particle surface temperatures were measured in-flight to enhance understanding of the relationship between spray parameters, microstructure, and deposition efficiency.

Nickel – yttria stabilized zirconia coatings and nickel – samaria doped ceria coatings were fabricated by solution precursor plasma spraying using the Northwest Mettech Axial III plasma torch. Three sets of plasma spray parameters were used resulting in comparatively low, intermediate, and high plasma powers of 63 kW, 102 kW, and 152 kW, respectively. The high and low power conditions resulted in powdery type coatings with poor adhesion to the substrate and between particles. The intermediate power conditions resulted in harder coatings with improved adhesion and electrical conductivity.

Samaria-doped ceria (SDC) has become a promising material for the fabrication of intermediate-temperature, metal-supported solid oxide fuel cells (SOFCs). While typical SOFC materials, such as yttria-stabilized zirconia (YSZ), require high temperatures (> 700°C) to exhibit suitable ionic conductivity for high cell performance, SDC displays similar ionic conductivities at lower temperatures (600°C – 650°C). The atmospheric plasma spray (APS) process is a promising technique for manufacturing metal-supported SOFCs. In this study, the in-flight characteristics, such as particle velocity and surface temperature, of spray-dried SDC agglomerates were analyzed at various plasma spray conditions using the DPV-2000 in-flight particle sensor manufactured by Tecnar Automation. Coatings of SDC were applied on stainless steel substrates using a range of spray conditions, and their resulting microstructures and deposition efficiencies were analyzed. It was found that particle temperature could be related to the specific plasma energy, and that coating porosity was related closely to the measured average particle temperature.

A substrate surface thermocouple was developed for thermal spraying. The substrate used for the study is a porous 430 stainless steel disk, though the thermocouple concept can be applied with other materials. Type N thermocouple wires are cemented in holes through the substrate, and then a copper coating is deposited across the surface to electrically connect the wire tips to complete the thermocouple circuit. The copper also promotes temperature equalization between the wire tips and the surrounding substrate surface to increase accuracy. Using finite element analysis (FEA), it was determined that the optimum thickness of the copper layer is 38 µm. With this thickness, the thermocouple should be able to measure peak-to-peak surface temperature swings due to a passing plasma jet within +/-3% when the copper thickness is uniform and all physical properties of the coating and substrate system are well-known. However, a number of assumptions were used for the FEA, so a detailed uncertainty analysis was performed. This analysis found that the expected accuracy window of the thermocouple is +19%/-10% as implemented for measuring surface temperature swings. For measuring average temperatures, the thermocouple is very accurate, because large heat fluxes into the substrate occur only when the plasma torch is directly in front of the substrate. Experimental measurements of surface temperatures with the optimized thermocouple are presented.

Atmospheric plasma spraying is attractive for manufacturing solid oxide fuel cells (SOFCs) because it allows functional layers to be built rapidly with controlled microstructures. The technique allows SOFCs that operate at low temperatures (500 to 700 °C) to be fabricated by spraying directly onto metallic supports. However, standard cathode materials used in SOFCs have high polarization resistance at low temperatures, necessitating alternative materials. In this study, coatings of lanthanum strontium cobalt ferrite (LSCF) were fabricated on steel substrates using axial-injection atmospheric plasma spraying. Coating thickness and microstructure were evaluated and X-ray diffraction (XRD) analysis was performed to detect material decomposition and the formation of undesired phases in the plasma. The results define the envelope of plasma spray parameters for depositing LSCF coatings and the conditions in which composite cathode coatings can be produced.

An axial injection suspension plasma spray system has been used to produce layers of fully stabilized yttria-stabilized zirconia (YSZ) that could be used as solid oxide fuel cell (SOFC) electrolytes. Suspension plasma spraying is a promising technique for the rapid production of coatings with fine microstructures and controlled porosity without requiring a post-deposition heat treatment. This new manufacturing technique to produce SOFC active layers requires the build up of a number of different plasma sprayed SOFC functional layers (cathode, electrolyte and anode) sequentially on top of each other. To understand the influence of the substrate and previously-deposited coating layers on subsequent coating layer properties, YSZ layers were deposited on top of plasma sprayed composite lanthanum strontium manganite (LSM)/YSZ cathode layers that were first deposited on porous ferritic stainless steel substrates. Three layer half cells consisting of the porous steel substrate, composite cathode, and suspension plasma sprayed electrolyte layer were then characterized. A systematic study was performed in order to investigate the effect of parameters such as substrate and cathode layer roughness, substrate surface pore size, and cathode microstructure and thickness on electrolyte deposition efficiency, cathode and electrolyte permeability, and layer microstructure.

Suspension plasma spraying is a promising modification to traditional plasma spray techniques that may allow plasma sprayed layers with finer microstructures and better porosity control to be produced. The fine microstructures and controlled porosity of these layers, combined with plasma spraying’s ability to produce layers rapidly without requiring a post-deposition heat treatment, makes this an interesting new manufacturing method to produce solid oxide fuel cell (SOFC) active layers. This study uses an axial injection suspension plasma spray system to produce thin, high-density layers of fully stabilized yttria-stabilized zirconia (YSZ) for use as an SOFC electrolyte. Three different aqueous feedstock suspensions with varying solid contents were sprayed, which resulted in coatings with splat thicknesses of approximately 0.5 µm and some intersplat porosity. Total coating thickness increased as the suspension solid content was increased, but suspension flow rates and deposition efficiencies decreased.

Atmospheric plasma spraying has emerged as a cost-effective alternative to traditional sintering processes for solid oxide fuel cell (SOFC) manufacturing. However, the use of plasma spraying for SOFCs presents unique challenges, mainly due to the high porosity required for the electrodes and fully dense coatings required for the electrolytes. By using optimized spray conditions combined with appropriate feedstocks, SOFC electrolytes and electrodes with required composition and microstructure could be deposited with an axial plasma spray system. In this paper, the challenges for manufacturing SOFC anodes, electrolytes, and cathodes are addressed. The effects of plasma parameters and different feedstocks on coating microstructure are discussed, and examples of optimized coating microstructures are given.

Yttria stabilized zirconia (YSZ) is the most commonly used electrolyte material for solid oxide fuel cells (SOFCs), due to its pure ionic conductivity and chemical stability. Standard electrolyte fabrication techniques for planar fuel cells involve wet ceramic techniques such as tape-casting or screen printing, which require sintering at temperatures above 1300°C. Plasma spraying (PS) may provide a more rapid and cost efficient method of producing SOFCs without requiring high temperature post-deposition heat treatments. However, it is difficult to produce plasma sprayed layers that are both thin (<20µm) and completely dense. It is of utmost importance to have a dense electrolyte to prevent the mixing of cathode and anode reactant gases. This study investigates the use of spin coated sol gel derived YSZ precursor solutions to fill the pores present in plasma sprayed YSZ layers.

A porous composite cathode containing (La 0.8 Sr 0.2 ) 0.98 MnO 3 (LSM) and yttria stabilized zirconia (YSZ) for use in a solid oxide fuel cell has been produced by air plasma spraying. Deposition was carried out using axial powder injection for increased deposition efficiency and composition control. A plasma composed of argon and nitrogen was used to decrease processing costs and avoid decomposition of the cathode material during deposition. Preliminary investigations focused on determining the range of plasma conditions under which each of the materials could be successfully deposited separately. A set of conditions was thereby determined that were suitable for the deposition of a composite cathode from pre-mixed LSM and YSZ powders. Graphite pore former was added to the powder mixture in order to achieve sufficient porosity in the final coating. A tape cast YSZ electrolyte was used as the substrate for the deposition of the cathode and also as the mechanical support layer in the finished cell. Following deposition of the cathode, an anode was produced by traditional wet ceramic processing techniques. Plasma sprayed cathode was characterized by SEM, EDX, and XRD, and the electrochemical performance of the full fuel cell was evaluated.