As we know, the thermal conductivity is of great importance for thermal insulation function, which can operate above the service temperature of the Ni-based or Co-based superalloys. The specific heat capacities of YSZ, GZ and GEZ materials are calculated by Neumann-Kopprule at different temperature. The thermal conductivity of YSZ, GZ and GEZ is calculated by the formula: λ = ρ × α ×Cp. As shown in Fig. 1, the value of YSZ, GZ and GEZ bulk ceramics has been measured under same condition. The value is the average of three measurement data. Firstly, the value of YSZ and GZ ceramic material quickly decreases with temperature increasing to 600 ◦C. Then, the value of YSZ and GZ ceramic material gently increase when the temperature increase from 600 ◦C to 1200 ◦C. The thermal conductivity of YSZ ceramic material is 2.03 W/mK at 1000 ◦C and 2.09 W/mK at 1200 ◦C. The thermal conductivity of GZ ceramic material is 1.16 W/mK at 1000 ◦C and 1.20 W/mK at 1200 ◦C. The reason of the increase of thermal diffusivity and thermal conductivity might be attributed to the increased radiation at high temperature. For GEZ ceramic material, the value of thermal diffusivity and thermal conductivity continuously decreases with temperature increasing to 1000 ◦C. Only a little increase of thermal diffusivity and thermal conductivity occurs at 1200 ◦C. The thermal conductivity of GEZ ceramic material is 0.95 W/mK at 1000 ◦C and 1.02 W/mK at 1200 ◦C. At 1000 ◦C–1200 ◦C, the thermal conductivity of GEZ is nearly 50 % lower than that of YSZ, andfurther nearly 10 % lower than that of GZ.
Fig. 1. (a) Thermal diffusivity and (b) Thermal conductivity of YSZ, GZ and GEZ ceramic materials.
As we know, thermal conductivity is mainly related to phonon-phonon and phonon-defect scattering. Strong phonon scat-tering leads to short phonon mean free path, and further lower thermal conductivity. The structural disorder of defect fluorite structure lattice enhances the phonon scattering. Based on XRD data, the ordering degree of GEZ decreases with the addition of the Er content. Thus, the reduced ordering degree of defect fluorite structure would lead to a low thermal conductivity of GEZ. On the other hand, the point defect, such as substitution atom or vacancy, has a significant effect on the reduction of thermal conductivity. The GEZ could be regarded as the solid solution of Er3+substitution for Gd3+site of Gd2Zr2O7. Due to the difference of atomic mass and ionic radius between Gd3+and Er3+, massive point defect is introduced in Gd2Zr2O7 material. Thus, the introduction of Er3+in Gd2Zr2O7 material would lead to the relatively high efficiency of phonon-phonon and phonon-defect scattering. These are two main reasons for the low thermal conductivity of GEZ ceramic material, which is relevant to the TBCs application.
本文由桑尧热喷涂网收集整理。本站文章未经允许不得转载；如欲转载请注明出处，北京桑尧科技开发有限公司网址：http://www.sunspraying.com/
|
