| Characteristics of Zirconate-based Oxides for Thermal Barrier Coatings (TBCs) |
| Seongwon KIM |
| Korea Institute of Ceramic Engineering and Technology |
|
Keywords: Thermal Barrier Coatings (TBCs), Rare-earth Zirconate, Pyrochlore/Fluorite, Thermal Conductivity
Over the past decades, studies of thermal barrier coatings (TBCs) have been conducted to increase the operating temperature of gas turbines for power generation and aircraft. One of the most widely used materials for TBC application is yttria-stabilized zirconia (YSZ), which has low thermal conductivity and a high thermal expansion coefficient. Among candidates for future TBCs, fluorite and pyrochlore oxides are two prevailing materials. Both have analogous cubic structures with a space group of Fm3(-)m for the former and Fd3(-)m for the latter. The general formula of the fluorite and pyrochlore oxides is AO2 and A2B2O7, respectively. The low thermal conductivities of rare earth oxides with these structures are attributed to the phonon scattering by point defects in the crystallographic structures.
In this study, we characterized the phase structures and thermal conductivities of rare-earth zirconates. Several compositions from La2(Zr1-xCex)2O7 or (La1-yGdy)2Zr2O7 are fabricated using solid-state reaction for this study using La2O3(High Purity Chemicals , 99.9% , 11レm), Gd2O3(High Purity Chemicals , 99.9% , 11レm), CeO2(High Purity Chemicals , 99.9% , 5レm), and ZrO2(Aldrich , 99% , 5レm) oxide powders. The samples were prepared by the solid-state reaction. For heat-treated samples, apparent densities were measured by using the Archimedes Principle. Crystallographic phase of heat-treated samples were identified by X-ray diffractometer with Cu Kメ radiation(0.1506nm). The specific heat capacities (Cp) and thermal diffusivities (ル) of the sintered samples were measured by laser flash analysis as a function of the temperature up to 1000”. The thermal conductivity (ナ) can be calculated by Eq. (1) with the apparent density (ヱ), heat capacity (Cp), and thermal diffusivity (ル)(1).
Figure 1 shows the XRD patterns of sintered (La1-xGdx)2Zr2O7 samples. Among these XRD patterns, the existence of (331) and (511) peaks of superlattice confirms the presence of pyrochlore phases in this (La1-xGdx)2Zr2O7 system. The LZ to GZ composition turns out to have a pyrochlore phase through the whole composition range.
References:
[1] D.R. Clarke and C.G. Levi, Annu. Rev. Mater. Res.,33 (2003) 383.
[2] C.G. Levi, Curr. Op. in Sol. Sta. & Mater. Sci., 8 (2004) 77.
[3] M.R. Winter and D.R. Clarke, J. Am. Ceram. Soc., 90 (2007) 553.
[4] P.K. Schelling, S.R. Plillpot, and R.W. Grimes, Philos. Mag. Lett., 84 (2004) 127.
[5] J. Wu, X. Wei, N.P. Padture, P.G. Klemens, M. Gell, E. Garcia, P. Miranzo, and M.I. Osendi, , J. Am. Ceram. Soc., 85 (2002) 3331. |
| Acknowledgements : This research was supported by a grant from the Fundamental R&D Program for Strategic Core Technology of Materials funded by the Ministry of Trade, Industry and Energy and by a grant from the Basic and Strategic R&D Program funded by the Korea Institute of Ceramic Engineering and Technology, Republic of Korea. |
|
