Characterization of thermal properties of micro-sized ceramic powders for APS deposition of ceramic layers

The paper presents test results concerning characteristics of the selected thermal properties of ceramic powders based on rare earth zirconates with a pyrochlore structure of RE₂Zr₂O₇ type, intended for thermal spraying of TBCs. Gadolinium, lanthanum, samarium and neodymium based powders were tested. The scope of the tests encompassed thermal diffusivity analysis of the powders in a compressed pellets form within temperature range 25-1500°C, and also tests of specific heat and thermal expansion coefficient within similar temperature range. Standard powder of 8YSZ type on the basis of zirconium oxide modified with yttrium oxide was used as a reference material. Specific heat measurements of the powders showed that the highest values within the entire test temperature range were obtained for the standard YSZ type powder. In the case of new type of powders, the results obtained are very similar and only slightly lower in comparison with YSZ powder. The lowest values were obtained for the samarium based powder (temperature range corresponding to operating temperature). Character of the curves obtained do not show course of strong reactions connected with phase changes. Dilatometric tests of materials made it possible to determine thermal expansion coefficient. Mean coefficient values are included within the range from 5.5 × 10⁶mm/°C to 10.0 × 10⁶mm/°C. The highest mean value of thermal expansion coefficient was obtained for Nd ₂Zr₂O₇ powder and the lowest one for La ₂Zr₂O₇ powder. The lowest thermal diffusivity value at room temperature was shown by Nd₂Zr₂O₇ powder, and the highest one by 8YSZ powder (0.215 mm²/s).