Effect of gas pressure on thermal conductivity of zirconia thermal barrier coatings

Abstract The thermal diffusivity of thermal barrier coatings (zirconia stabilized with 7–8 wt% yttria) deposited by air plasma spraying has been measured by the laser flash method. Free-standing samples (0.5–0.6-mm thick) polished on both sides were coated with graphite. Deduced values of thermal conductivity (e.g., 1.5 W m −1 K −1 at 200 °C in 1 atm. of nitrogen) are in the range measured in other studies for this type of thermal barrier coating. The % increase in thermal conductivity in 1 atm. of gas compared to its value in vacuum was found to be about 10% in nitrogen at 500 °C, close to a calculated value of 7% using a model in the literature. A simple extension of the model to higher temperatures and gas pressures predicts a significant rise, so that by 10 atm. of gas pressure the % increase would be 30% (with little sensitivity to temperature).