Preparation of Ultra-Low Thermal Conductivity Coatings Via Suspension Plasma Spray Using a Defect Clustering Approach

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The objective of this research award is to investigate a novel processing method to produce ultra-low conductivity thermal barrier coatings that would overcome the deficiencies of current yttria-stabilized zirconia coatings. Thermal barrier coatings are used in gas turbine engines to thermally protect the superalloy blades in the combustion area, affording hotter, more efficient operating temperatures. Our approach for preparing next generation thermal barrier coatings couples for the first time two newly developed techniques: suspension plasma spray and defect clustering. In suspension plasma spray, nanosized powders are dispersed in ethanol to form a colloidal suspension; the suspension is then sprayed into a hot plasma plume to evaporate the solvent and melt the powder. The second technique, defect clustering, involves doping yttria-stabilized zirconia with paired rare-earth ions (such as ytterbium and neodymium) to create immobile clusters in the plasma-sprayed coating. The presence of these clusters in a thermal barrier coating scatters phonons, reducing coating thermal conductivity by over one-half compared to current yttria-stabilized zirconia-only coatings. If successful, the results of this research will allow gas turbine engines to be operated at higher, more fuel efficient temperatures, saving fuel and reducing energy usage. New coating designs emerging from this research have the potential to influence key industries that are concerned with finding the least expensive method to transport people and goods and produce energy. In terms of educational impact, the primary investigator for this grant is heavily involved in mentoring at the graduate, undergraduate, and high school levels through prior NSF support. This grant would continue these efforts for all three groups of students by providing research opportunities.