Michael Marr

Permeability and Microstructure of Suspension Plasma-Sprayed YSZ Electrolytes for SOFCs on Various Substrates

Yttria-stabilized zirconia electrolyte coatings for solid oxide fuel cells were deposited by suspension plasma spraying using a range of spray conditions and a variety of substrates, including finely structured porous stainless steel disks and cathode layers on stainless steel supports. Electrolyte permeability values and trends were found to be highly dependent on which substrate was used. The most gas-tight electrolyte coatings were those deposited directly on the porous metal disks. With this substrate, permeability was reduced by increasing the torch power and reducing the stand-off distance to produce dense coating microstructures. On the substrates with cathodes, electrolyte permeability was reduced by increasing the stand-off distance, which reduced the formation of segmentation cracks and regions of aligned and concentrated porosity. The formation mechanisms of the various permeability-related coating features are discussed and strategies for reducing permeability are presented. The dependences of electrolyte deposition efficiency and surface roughness on process conditions and substrate properties are also presented.

The Influence of Process Equipment on the Properties of Suspension Plasma Sprayed Yttria-Stabilized Zirconia Coatings

Suspension plasma-sprayed YSZ coatings were deposited at lab-scale and production-type facilities to investigate the effect of process equipment on coating properties. The target application for these coatings is solid oxide fuel cell (SOFC) electrolytes; hence, dense microstructures with low permeability values were preferred. Both facilities had the same torch but different suspension feeding systems, torch robots, and substrate holders. The lab-scale facility had higher torch-substrate relative speeds compared with the production-type facility. On porous stainless steel substrates, permeabilities and microstructures were comparable for coatings from both facilities, and no segmentation cracks were observed. Coating permeability was further reduced by increasing substrate temperatures during deposition or reducing suspension feed rates. On SOFC cathode substrates, coatings made in the production-type facility had higher permeabilities and more segmentation cracks compared with coatings made in the lab-scale facility. Increased cracking in coatings from the production-type facility was likely caused mainly by its lower torch-substrate relative speed.

An Investigation of Metal and Ceramic Thermal Barrier Coatings in a Spark-Ignition Engine

An investigation of metal and ceramic thermal barrier coatings in a spark-ignition engine Michael Anderson Marr Master of Applied Science Graduate Department of Mechanical and Industrial Engineering University of Toronto 2009 Surface temperature and heat flux measurements were made in a single cylinder SI engine piston when uncoated and with two different surface coatings: a metal TBC and YSZ. A new thermocouple was developed to accurately measure surface temperatures. The engine was operated in a standard full load mode and a knock promoting mode featuring heated intake air and advanced spark timing. Cylinder pressures were measured to quantify knock. It was found that average heat flux into the piston substrate was 33 % higher with the metal TBC and unchanged with the YSZ relative to the uncoated surface. The increase with the metal TBC was attributed to its surface roughness. However, the metal TBC and YSZ reduced peak heat flux by 69 and 77 %, respectively. Both the metal TBC and YSZ reduced knock compared to the uncoated surface. After testing, the metal TBC was undamaged and the YSZ was slightly chipped.

Preliminary Testing of Metal-Based Thermal Barrier Coating in a Spark-Ignition Engine

A novel metal-based thermal barrier coating was tested in a spark-ignition engine. The coating was applied to the surface of aluminum plugs and exposed to in-cylinder conditions through ports in the cylinder wall. Temperatures were measured directly behind the coating and within the plug 3 and 11 mm from the surface. In-cylinder pressures were measured and analyzed to identify and quantify knock. Test results suggest the coating does not significantly reduce overall heat transfer, but it does reduce the magnitude of temperature fluctuations at the substrate surface. It was found that heat transfer can be reduced by reducing the surface roughness of the coating. The presence of the coating did not promote knock.