Characteristics of thermal properties of Gd₂Zr₂O ₇ - ZrO₂XY₂O₃ powder mixtures intended for deposition of gradient layers of TBC type

This article presents a study and results concerning the characteristics of selected thermal properties of the powders intended for deposition of gradient structure layers of the TBC type. The study included evaluation of the thermal diffusivity and specific heat of the powders in the initial state, and also calorimetric analysis of powder mixtures. Thermal diffusivity tests were performed with the laser-flash method. The temperature range of the tests was 25°C-1400°C. Specific heat and calorimetric analyses were performed with the heat flux method within a similar temperature range. The Gd ₂Zr₂O₇ powders obtained by spray drying method and standard ZrO₂ × 8Y₂O₃ powder were analysed. The thermal diffusivity analysis and calorimetric analysis were performed for the samples obtained by pressing the Gd₂Zr ₂O₇ - ZrO₂ × 8Y₂O₃ powder mixture of equal weight fractions. Specific heat measurements were taken for pure powders. The calorimetric analysis performed showed that no significant thermal effects were observed in both pure powders and their mixture within the temperature range of 800°C-1400°C. A small endothermic effect (approx.-7J/g) was observed for gadolinium powder within the temperature range of 350°C-615°C. Specific heat measurements revealed that gadolinium powder was characterized by stable values of that parameter within the whole temperature range like zirconium powder. The analyses performed showed that the powders were characterized by small mutual reactivity, and gadolinium powder showed a definitely lower thermal diffusivity, which is advantageous as regards obtaining TBC layers with a gradient structure on the basis of those two powders.