In this study, lanthanum (LZ) and gadolinium zirconate (GZ) powders were prepared by spray drying and deposited on graphite substrates by air plasma spraying. Free-standing 1-1.5 mm thick LZ and GZ coating samples were obtained by mechanical delamination and subjected to long-term annealing in air at 1250 °C. Significant changes occurred during heat treating in the form of microstructure evolution, crystal structure ordering, and phase transitions as observed via SEM, XRF, and XRD analysis. These changes affected a number of coating properties, including hardness, porosity, fracture toughness, and thermal conductivity. In the first 20 h, thermal conductivity increased in gadolinium zirconate from 0.5 to 1.0 W/m·K and in lanthanum zirconate from 0.5 to 1.5 W/m·K.

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