In‐Flight Alloying of Nanocrystalline Yttria‐Stabilized Zirconia Using Suspension Spray to Produce Ultra‐Low Thermal Conductivity Thermal Barriers
Abstract:Previous researchers have shown that it is possible to combine rare‐earth oxides with the standard thermal barrier coating material (4.5 mol% Y2O3–ZrO2 or YSZ) to form ultra‐low thermal conductivity coatings using a standard powder manufacturing route. A similar approach to making low thermal conductivity coatings by adding rare‐earth oxides is discussed presently, but a different manufacturing route was used. This route involved dissolving hydrated ytterbium and neodymium nitrates into a suspension of 80 nm diameter 4.5 mol% YSZ powder and ethanol. Suspension plasma spray was then used to create coatings in which the YSZ powders were alloyed with rare‐earth elements while the plasma transported the melted powders to the substrate. Mass spectrometry measurements showed a YSZ coating composition, in mol%, of ZrO2–4.4 Y2O3–1.4 Nd2O3–1.3 Yb2O3. The amount of Yb3+ and Nd3+ ions in the final coating was ∼50% of that added to the starting suspension. Wide‐angle X‐ray diffraction revealed a cubic ZrO2 phase, consistent with the incorporation of more stabilizer into the zirconia crystal structure. The total porosity in the coatings was ∼35–36%, with a bulk density of 3.94 g/cm3. Small‐angle X‐ray scattering measured an apparent void specific surface area of ∼2.68 m2/cm3 for the alloyed coating and ∼3.19 m2/cm3 for the baseline coating. Thermal conductivity (k th) of the alloyed coating was ∼0.8 W/m/K at 800°C, as compared with ∼1.5 W/m/K at 800°C for the YSZ‐only baseline coating. After 50 h at 1200°C, k th increased to ∼1.1 W/m/K at 800°C for the alloyed samples, with an associated decrease in the apparent void specific surface area to ∼1.55 m2/cm3.
Document Type: Research Article
Affiliations: 1: School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907 2: Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6064 3: Ames Laboratory, Iowa State University, Ames, Iowa 50011-3020 4: Argonne National Laboratory, Argonne, Illinois 60439
Publication date: 2011-11-01